5 \
La
a
ia

A

Pea NUAL OF PALAONTOLOGY

\ SOMX eS

|
ANUAL OF Palo loLoGy

HOnRVhaee USE OF SLTODEN LS

With A GENERAL INTRODUCTION ON THE
PRUNCEEIEES Ob “PALAONTLOLOGY

BY

HENRY ALLEYNE NICHOLSON

Wis IWhSex, INC. Shy SINS:

REGIUS PROFESSOR OF NATURAL HISTORY IN THE
UNIVERSITY OF ABERDEEN

AND

RCE VND EY DPMhKER

BAG Ee GuSea nC

THIRD £DITION
REWRITTEN AND GREATLY ENLARGED

IN TWO MOLUNMES

VOEAE

Wher iraAM BLACKWOOD AND SONS
EDINBURGH AND LONDON
MDCCCLXXXIX

All Rights reserved

(SONA |
MAY 1.4 1955

Noa

A Je

Pee PA BE.

THERE is, perhaps, no branch of Biology which in recent years has
advanced so rapidly, and, on the whole, so surely and in so many
directions, as has Palzeontology. In the earlier periods of its devel-
opment, a tendency has, indeed, been sometimes shown by investi-
gators concerned exclusively with existing forms of life to depreciate
the position of Paleontology as a Science, and to contest its claims
to recognition as a separate department of Zoology and Botany ; nor
can it be said that this tendency has yet altogether died out. Even
now, it is sometimes considered that Paleontology, on the ground
of its relation to the chronological history of the earth, should be
regarded as a branch of Geology, rather than of Biology ; while on
the ground of its being necessarily concerned almost wholly with
the skeletal structures of animals and plants, its conclusions have
been discredited, and the adéquacy of its methods of investigation
has been questioned.

No one, however, who has made himself thoroughly acquainted
with the progress of this branch of investigation during the last
decade, can doubt that Paleontology has amply vindicated its claim
to be regarded as a special department of Biology, as entirely sci-
entific in its character and methods, and in all respects as worthy
of separate and special study as is, for example, the department of
Embryology.

So numerous and so extensive have been the advances made by
Palzontology of late years, that the Authors have found it necessary
not only to largely increase the bulk of the present, as compared
with the last, edition of this work ; but also to entirely recast and
rewrite it, while the illustrations to the text have been nearly

vi PREFACE.

doubled in number. The present edition may therefore be con-
sidered as, to all intents and purposes, an entirely new work. The
Authors also trust that this edition will be found to have gained
much from the fact that the Invertebrates and Vertebrates have
been dealt with by different writers.

With regard to the general plan of the work, the Authors need
only say that the Invertebrate and Vertebrate animals have been
treated of as fully as considerations of space would permit; while
the fossil plants have been dealt with in a comparatively summary
fashion. This course has been followed primarily on the ground
that Palsozoology is of much greater importance to the general
student than is Palzeobotany ; but it has been also dictated by the
consideration that the latter subject is one of great complexity, and
is at the same time one upon which neither of the Authors has any
claim to speak with authority. It did not seem advisable, however,
to entirely omit the subject of Paleobotany; and an attempt has
accordingly been made to give such a general summary of the pres-
ent condition of our knowledge of this department as may be found
useful to those studying Palezeontology as a whole.

In dealing with the vast mass of facts constituting the modern
science of Palzeontology, much has been, necessarily, omitted ; while
the Authors can scarcely hope that errors have been altogether
avoided. Moreover, in its present condition of rapid growth and
development, Palzeontology presents many questions—sometimes
affecting points of fundamental importance—upon which the opinions
of different investigators are widely divergent. It is, therefore, in-
evitable that there should be many questions dealt with in the pres-
ent work in regard to which the opinions expressed by the Authors
differ from those held by other workers in the same field. The
Authors can only hope that on such controverted points they have
not expressed themselves too dogmatically ; and that, while the
limits and scope of the work would not admit of any detailed dis-
cussion of divergent views, the existence of such has nevertheless
been generally indicated. It may be added that where a definite
position has been taken up upon a controverted question, this has
been, in general, the result of original investigation on the part of
the writer. Theoretical questions, again, have been for the most
part avoided, partly because of their unsuitability for discussion
in a work intended for students, and partly also from want of

PREFACE. Vil

space. Finally, the minute structure of the skeleton in different
groups of animals, and particularly in the lower types, has been
treated of as fully as the limits of the work have allowed.

Owing to the circumstance that a large portion of the first volume
of this work has been in type for a considerable time, the Authors
regret that they have not been able to avail themselves fully, or at
all, of some recent publications, of both a general and a special
nature, such, for example, as Neumayr’s ‘Die Stamme des Thier-
reichs,’ and the newly published volume of Barrande’s monumental
work dealing with the Cystideans. In an Appendix to the second
volume attention is, however, directed to certain points of importance
which have emerged during the passage of this work through the
press. Such errors as have been recognised will be found in a list
of Corrigenda at the end of the Table of Contents to each volume.

To many of their fellow-workers the Authors have to express their
obligation for direct or indirect assistance in their task. To no
one is this more largely due than to Professor Karl von Zittel, to
whose masterly ‘ Handbuch der Palezontologie’ they have been on
many occasions indebted for guidance in questions of doubt or diffi-
culty. The very special gratitude of the Authors is due to Dr P.
Herbert Carpenter for the most valuable assistance in the prepara-
tion of the chapters dealing with the Echinoderms, as also to Mr
A. Smith Woodward and Dr R. H. Traquair for much information
concerning fossil Fishes. They have likewise to express their best
thanks to Dr George J. Hinde, Dr H. B. Brady, Dr Henry Wood-
ward, Professor T. Rupert Jones, Mr A. H. Foord, Mr John Young,
and others of their fellow-workers, from whom they have received
much friendly help. Finally, the Authors have to express their
gratitude to those who have assisted them by allowing them the use
of illustrations. Amongst those to whom thanks are due on. this
score are M. Louis Dollo, Professors H. F. Osborne and W. B.
Scott, Professor A. Gaudry, Professor E. D. Cope, Professor O. C.
Marsh, Professor E. Koken, Dr Anton Fritsch, Dr Henry Wood-
ward, the Director of British Museum (Natural History), the
present and late Directors of the Geological Survey of India, and
the Director of the Geological Survey of Canada.

SOVEEN TS (OF THE FIRST VOLUME:

PART [—GENERAL INTRODUCTION.

CHARTERS I

PAGE
Definition of Palzeontology—Paleozoology and Palzobotany—Def-

nition of the term “ fossil”—Processes of fossilisation—Defini-
tion of Rock—Classification of rocks, . 3 : : é 3-10

GHAPTER Il.

Characters of the Sedimentary rocks — Mode of formation of the
Sedimentary rocks—General use of the term “ formation ”—Chief
divisions of the Aqueous rocks—Mechanically-formed rocks—
Chemically-formed rocks—Rock-salt—Gypsum—Phosphate of
lime—The mode of origin of the Calcareous rocks generally
Organic origin of many limestones — Chief varieties of the
organic limestones—Secondary crystallisation in limestones—
Fibro-crystalline structure in limestones—Summary of the chief
groups of organisms concerned in the formation of limestones—
Sorby’s researches on aragonite and calcite—Chemical compo-
sition of the skeleton of calcareous organisms—Preservation of
calcareous organisms in limestones—Lithological characters of
different limestones—Magnesian limestones—Oolitic structure
of limestones—Superinduced crystallisation in hmestones—Met-
amorphic limestones— Siliceous organic deposits — Beds of
Sponge spicules—Flint and chert—Deposits of silicates—Car-
bonaceous deposits, : : : : : ‘ ; a aei35

CHAPLTER LI.

Different ages of the Aqueous rocks as determined by stratigra-
phical and paleontological evidence—General chronological suc-
cession of the Aqueous rocks—Definition of names of rock-
groups—General classification of the Post-Archzean fossiliferous

x CONTENTS.

deposits—The value and nature of paleontological evidence in
stratigraphical geology—Relative value of different groups of
organisms as tests of the age of strata—Contemporaneity and
homotaxis—General sequence of phenomena at the close of
each geological period—Migrations—Differences between the
organic remains of known contemporaneous deposits—Geologi-
cal continuity—Stratigraphical breaks and their general causes

—Life-zones—The doctrine of “colonies,” .. . ; . 36-62

CHAP DER lv;

Causes of the imperfection of the palzcontological record—Causes
of the absence of certain animals as fossils — Unrepresented
time—Geological breaks—Sequence of phenomena indicated by
unconformity—Thinning-out of beds—Deep-sea deposits, and
their supposed absence from the stratified series—Disappear-

ance of fossils, : é ‘ : 4 ; : : : _ 63-76

CHAP T ERs ov:

Conclusions to be drawn from fossils—Age of rocks—Mode of origin
of any fossiliferous bed—Fluviatile, lacustrine, and marine de-
posits—Conclusions as to climate—Existence of climatic zones

in past time, - ; : ; ‘ ‘ ; : : . zen

CHAP HE Vil:

Relations of Paleontology to Geology—Relations of Palzeontology
to Zoology and Botany—Methods of palzeontological investiga-
tion—Correlation of organs—Classification of the Animal King-
dom—Primary morphological types—Impossibility of a linear
classification—The term “species” in Palzeontology—Tabular

view of the divisions of the Animal Kingdom, . : . 82-95

GHAPRTER Wik

The evolution of organic types in time—FEarlier theories on the sub-
ject—The primordial types of lfe—The introduction of new
species—The abrupt appearance of new species—The relative
persistence of species in time—The relative range of morpho-
logical types in space—The extinction of morphological types
—The evolution of morphological types from pre-existing forms
—Comprehensive types—Generalised character of many fossil
animals—Embryonal types—General paleontological evidence
in favour of the evolution of species from pre-existing species—
General progression of organic types—The absence of closely-
graduated transitional forms between allied morphological

IBAOESS oc : j : ‘ ‘ , , ; ‘ . 96-105

CONTENTS. xi

PART [II1—PALAOZOOLOGY.
INVERTEBRATA.

CHAPTER OVI:

Zoological characters and chief divisions of the Protozoa—The pale-
ontological history of the Protozoa—The general characters of
the Foraminifera—Variations in the structure of the test in the
Foraminifera—The form of the Foraminiferal test and its varia-
tions—Distribution of the Foraminifera in space—Distribution
of the Foraminifera in time—Classification of the Foraminifera
—The general characters and distribution in time of the fami-
lies of the Foraminifera—Appendix on Eozoén Canadense, 109-143

CHARTER LX.

The general zoological characters of the Radiolaria—The skeleton
of the Radiolarians and its chief variations as regards chemical
composition and form—Classification of the Radiolarians—Dis-
tribution of the Radiolarians in space— Distribution of the
Radiolarians in time—Literature of the Protozoa, : . 144-150

CHAP LER: 2X.

General zoological characters of the Porifera— Canal-system of
Sponges—General structure of the skeleton and its Variations in
Sponges—Distribution of Sponges in space—Different modes in
which the skeleton of Sponges may be preserved in the fossil
condition—General geological distribution of Sponges, . 151-159

CHAPTER Xa.

Classification of Sponges—Class Plethospongiz—Order Myxospon-
gize—Ceratospongiz—Characters and geological distribution of
the Monactinellidee—Tetractinellidaee—Lithistidee—Hexactinel-
lidaa—Groups and geological distribution of Hexactinellids—
Octactinellidae—Heteractinellidz—Class Calcispongize—Homo-
coela — Heteroccela — Syconidz — Leuconidz — Pharetrones—
Ewerature,:- < : ‘ : : : ; : . 160-182

CHAPTER XL.

Groups of doubtful affinities—Archzocyathine—Archeocyathus—
Ethmophyllum — Pasceolus — Cyclocrinus — Nidulites—Litera-
ture, : : : : ; : ; ; : ; . 183-189

Xi CONTENTS.

CHAPTER xXaihle

General characters and divisions of the Ccelenterata—General dis-
tribution of Ccelenterates in time—General characters of the
Hydrozoa— Distribution of the Hydrozoa in time—The Hydroid
Zoophytes — Corynida—H ydractinia— Parkeria — Mitchf&deania
—Solenopora — Thecaphora — Dendrograptus — Dictyonema—
Oldhamia— Trachymedusee—The Lucernarians—Acraspedote
Jelly-fishes—Eophyton, . : ‘ , F _ ‘ . 190-209

CHAPAR Rav.

General characters of the Graptolitoidea—Development—Morphol-
ogy of a simple Graptolite—Reproduction of Graptolites—Lead-
ing types of structure among the Graptolites—Corynoides—Mon-
ograptidae— Leptograptidae—Dichograptide— Dicranograptidz
—Diplograptidee—Lasiograptidee—Retiolitida—Phyllograptidze
—Distribution of the families of Graptolites in time—Zoological
relationships of the Graptolites, . , ‘ : : » 210-222

CEAP TR Ove

General characters of the Hydrocorallines—Structure of Millepora—
Geological distribution of the Milleporoids—General characters
of the Stylasteridee—Structure of Allopora—Distribution of the
Stylasteridze in time—The Syringosphzridae—General charac-
ters of the Stromatoporoids—Structure of the skeleton—Chief
types of the Stromatoporoids—Actinostroma—Labechia—Beat-
ricea — Stromatopora—Amphiphora and _ Idiostroma—“ Cauno-
pora ”—Zoological relationships of the Stromatoporoids—Gene-
ral distribution of the Stromatoporoids in time—Literature of
the Hydrozoa, ; ; , ‘ : : ; : . 223-239

CEVAUe (hin ovale

General characters of the Actinozoa—Structure of the soft parts of a
simple Actinozo6n— Development of the mesenteries— The
nature of the skeleton in the Actinozoa—Spicular skeleton—
Sclerobasic corals—The structure of a simple sclerodermic coral-
lum—Structure of septa—Development of the corallum—Rela-
tions of the polype to the corallum—Composite corals—Chief
methods of multiplication in corals—Classification of the Actino-
zoa— Distribution of the Actinozoa in space-—Distribution of the
Actinozoa in time, . : : : ; : : ; . 240-260

CONTENTS. Xili

CHAPTER aval:

General characters of the Zoantharia—Classification of Zoantharia—
Distribution of Zoantharians in time—Characters and divisions
of the Madreporaria—Characters and geological distribution of
the Madreporaria Aporosa—The Turbinolida—Oculinide—
Pocilloporide—Astreidee—H olocystis—Stauria—Acervularia—
Columnaria—Moseleya, ‘ , é : ‘ ; . 261-275

CLAP TE RSeVII

General characters of the Madreporaria Rugosa—Structure of the
corallum of the Rugosa—Kunth’s law of the development of the
septa—Classification of the Rugosa—Cyathophylloid Rugosa—
Cyathophyllidee— Heliophyllidee— Clisiophyllidze—Zaphrentoid
Rugosa — Zaphrentidee — Hadrophyllidee — Palzeocyclidee —
Streptelasmidze— Fed cle cae Rugosa— Cysti-
phyllidee—Calceolide, . : : : ; : . 276-302

@HAPARERS Xx

General characters of the Madreporaria Fungida—Plesiofungidea—
Fungidze— Lophoseridze— Anabacidze— Plesioporitidaze— Gene-
ral characters and geological distribution of the Madreporaria
Perforata — Eupsammidz— Madreporide— Poritidze — Favosi-
tidae—Syringoporideae—Thecide, . : : : ; 303-323

CHALE RIO

General characters of the Alcyonaria—Divisions of the Aleyonaria—
Distribution in time—Pseudaxonia—Tubiporidee—Gorgonidze—
Pennatulidze— Helioporidee— Heliolitida — Halysitidze—Tetra-
diidze—Cheetetidae—Auloporide—Literature of Actinozoa, 324-345

CHAPATE RS Sexi:

The general characters of the Monticuliporoids—Zoological affinities
of the Monticuliporoids—Geological distribution—Monticulipor-
idee—Fistuliporide, ; ; ; ; : ; ; . 346-360

CHAPTER SOM.

The general characters of the Echinodermata—The digestive, am-
bulacral, and reproductive systems of Echinoderms— Minute
structure of the skeleton of the Echinoderms—Bolboporites—
Classification of Echinoderms—Distribution of Echinoderms in
time, : q : ; : : ; : : ; . 361-365

XIV CONTENTS.

CHAPTER] XXII

General characters of the Echinoidea—Structure of the test and its
appendages—Classification of the Echinoids—Distribution of
the Echinoids in time—Characters and distribution of the Pale-
chinoids— Cystocidaridze— Bothriocidaridas—Perischoechinidze
—Characters and distribution of the Euechinoids — Regular
Euechinoids — Cidaridae— Salenidze— Echinothuridee—Glypho-
stomata—Irregular Euechinoids—Conoclypeidze—Clypeastridz
Echinoconidee—Cassidulidee—Holasteride—Spatangide, 366-390

CHAPTER XXIV.

General characters of the Asteroidea—Integumentary skeleton of the
Star-fishes—Ambulacral system and skeleton—Distribution of
Asteroids in space and time—Classification—The Encrinas-
teriz and their chief types—The Asterize veree—General char-
acters of the Ophiuroidea—Integumentary skeleton of Ophi-
uroids—Ambulacral system—Reproductive system—Distribu-
tion of Ophiuroids in space and time—The Euryalida—The
Ophiurida— The Protophiurida— General characters of the
Holothuroidea—Remains of fossil Holothurians, ; . 391-407

CEA Re Oar

General characters of the Pelmatozoa—General characters of the
Crinoidea—Structure of Antedon—Development of Antedon—
General morphology of the Stalked Crinoids—Classification of
the Crinoids—Distribution of the Crinoids in space and in time—
Characters of the Palzeocrinoidea—Actinocrinidee—Barrandeo-
crinidee—Platycrinidze— Rhodocrinidze— Calyptocrinidz— Ich-
thyocrinidaz—Crotalocrinidze—Haplocrinidaa—Symbathocrinidz
—Cupressocrinidze— Gasterocomida — Hybocrinidz — Hetero-
crinida—Anomalocrinide—Belemnocrinidze—Cyathocrinidzee—
Poteriocrinida—Astylocrinidaee—Catillocrinidze—Calceocrinidz
—Characters of the Neocrinoidea— Encrinide—Eugeniacrinide
—Holopide — Hyocrinidze — Plicatocrinidaze — Apiocrinide—
Bourgueticrinidze—Pentacrinidze—Marsupitide—Comatulidae—
Saccocomide, : j : ; ; 5 ; ; . 408-446

CH APRER POCA:

General characters of the Cystoidea—Morphology of Cystoids—Dis-
tribution of the Cystideans in time—Classification of Cystideans
—Suborders and principal genera of the Cystideans—General

CONTENTS.

characters of the Blastoidea—Morphology of the Blastoids—
Distribution of the Blastoids in time—Classification of the
Blastoids—Table of the families and genera of Blastoids—

XV

Literature of Echinoderms, . A é : : : - 447-467

CHAPTER -XXVII.

General characters of the Annulosa—Supposed remains of fossil
Entozoa—Characters of the Anarthropoda—Gephyrea—Myzos-
tomida—Characters and distribution in time of the Annelida—
The Tubicolous Annelides—The Errant Annelides—Trails and

eracks, : é d : : : : : : . 468-490

CHAPTER XXVIII.

General characters of the Arthropoda—Distribution of the Arthro-
poda in time—General characters of the Crustacea— Morphology
of the Crustacea—Classification of the Crustacea—Distribution
of the Crustacea in time—General characters of the Cirripedia—
Divisions of the Cirripedia—The Balanidz-—Verrucidze— Lepa-

didze> . : : 3 : : . 491-502

CE APA RY XOX

General characters of the Entomostraca—The Lophyropoda—Gen-
eral characters of the Ostracoda—Types of Ostracodes—General
characters of the Copepoda—The Branchiopoda—General char-
acters of the Cladocera — Characters and chief types of the
Phyllopoda—Characters and types of the Phyllocarida—Gen-
eral characters of the Trilobita—Systematic position and dis-
tribution in time of the Trilobites—Families of the Trilobites—
The Merostomata—General characters of the Xiphosura—Types
of the Xiphosura— Hemiaspidze— Limulidze—General charac-
ters of the Eurypterida—Systematic position and distribution of

Eurypterids—Types of the Eurypterida, . ' : » 503-555

CHAP PER XXX:

General characters of the Malacostraca — Hedriophthalmata—
Amphipoda—Isopoda—Thoracostraca—Cumacea— Schizopoda
—Stomatopoda— Decapoda— Macrura —Anomura—Brachyura

—Literature of Crustacea, . : : ; . 556-571

CHAPTER XXXI.

General characters of the Arachnida—Distribution of the Arachnida
in space and time — Acarida — Anthracomarti — Adelarthroso-

Xvi CONTENTS.

mata—Pedipalpi—Araneida—General characters of the Myri-
opoda—Distribution of Myriopods in space and time—Proto-
syngnatha — Chilopoda — Archipolypoda— Diplopoda— Litera-
ture of Arachnida and Myriopoda, : : : : . 572-586

‘CHAPTER XXXII.

General characters of the Insecta—Distribution of the Insecta in
time—Apterous Insects — Palzeodictyoptera— Rhynchota—Or-
thoptera—Neuroptera—A phaniptera— Diptera — Lepidoptera—
Hymenoptera—Strepsiptera—Coleoptera, . : ; . 587-602

CVA ERS oO:

General characters of the Molluscoidea—General characters of the
Polyzoa—Structure of the skeleton in the Polyzoa—Classifica-
tion of the Polyzoa—Distribution of the Polyzoa in time—Gen-
eral characters of the Cyclostomatous Polyzoa—Distribution of
Cyclostomata in time—Characters and distribution of the chief
groups of Cyclostomata—General characters of the Cheilosto-
matous Polyzoa—Characters and geological distribution of the
chief families of Cheilostomata, . ; ; : . 603-639

CH APA ae DOOON:

General characters of the Brachiopoda—Distribution of the Brachi-
opoda in space and in time—Characters of the Inarticulata—
Characters and geological distribution of the Families of Inarti-
culated Brachiopods—Characters of the Articulata—Characters
and geological distribution of the Articulated Brachiopods—
Piteratuke, eae : ‘ ; ; ; : : : . 640-679

CHEAP ROW.

General characters of the Mollusca—Classification of the Mollusca
—Distribution of the Mollusca in space and in time — Gen-
eral characters of the Lamellibranchiata—Structure of the shell
of Lamellibranchiates—Distribution of Lamellibranchs in space
—Classification of the Lamellibranchs—Distribution of the La-
mellibranchs in time, . , : : 3 : : . 680-693

OEVANIE IMEI LOO,

Divisions of the Lamellibranchiata—Ostreacea—Pectinacea—M yti-
lacea—Arcacea—Submytilacea—Erycinacea —Cardiacea—Cha-
macea— Conchacea—Myacea —Adesmacea—Lucinacea—Telli-
nacea—Anatinacea, 3 ; : : : é : . 694-752

CONTENTS. XVil

CHAPTER XXXVI:

General characters of the Gastropoda—Shell of the Gastropods—
Odontophore and respiratory organs of Gastropods—Classifica-
tion of Gastropods—Distribution of Gastropods in space—Dis-

tribution of Gastropods in time, . 5 ; : : . 753-759

CHAPTER XXXVIII.

Branchiogastropoda—Characters of the Prosobranchiata— Patel-
lidee— Fissurellidze— Capulidaze—Velutinidze— Pleurotomariidez
—Bellerophontide — Haliotidee — Euomphalidz— Solariidae —
Trochidz — Turbinidze — Xenophoridee — Neritidze — Neritop-
sidee— Helicinidee— Naticidee—Paludinidze—Rissoidze—Littori-
nidae — Scalariidee — Ianthinide — Turritellidae — Vermetidee—
Czecidze — Pyramidellidze — Pseudomelanidz — Melaniidae —
Cyclostomidae—A ciculidze— Subulitidze — Nerineidze— Cerithi-
idze — Aporrhaidze — Strombidz — Cyprzeidee — Cassididze—
Doliidze — Ficulide — Tritoniidee — Buccinidze— Columbellidz
—Purpuridze— Fusidze— Muricidze—Volutidze — Harpide—Oli-

vidaee—Cancellariida—Conidz—Pleurotomidz—Terebridez, 760-799

CHAPTER XXXIX.

Characters of the Opisthobranchiata—Acteeonidee—Bullide—Aply-
siadze—Pleurobranchidee—Characters and distribution in time
of the Heteropoda— Firolidze—Atlantidee— Characters of the
Pteropoda — Limacinidee—Cavoliniida—Cymbuliide—Hyolith-
idee — Conulariidee— Tentaculitidae—Characters of the Pulmo-
gastropoda—Characters of the Stylommatophora—Testacellidz
—Limacidae—Helicide—Characters of the Basommatophora—

Auriculidee—Limnzidze—Siphonariide—Gadiniide, . . 800-815

CHAPTER XL.

Characters of the Polyplacophora—Characters and distribution of
the Chitonidze—Structure of the shell of Chiton—The Palz-
ozoic Chitons—Characters and distribution of the Scaphopoda

—Dentalium—Entalis—Siphonodentalium—Cadulus, . 816-820

CHAPTER XL

Characters of the Cephalopoda—Classification of the Cephalopoda

—Distribution in space—Distribution in time, . : . 821-825

XVili CONTENTS.

CHAP iii aon:

General characters of the Tetrabranchiata—Divisions of the Tetra-
branchiata — Characters of the Nautiloidea — Orthoceratidae—
Endoceratidze— Actinoceratidze— Gomphoceratidz — Ascocera-
tidee — Poterioceratidze — Cyrtoceratidze — Lituitidae — Trocho-
ceratidze—Nautilidee—Bactritidee—Prosiphonate Nautiloids, 826-847

CHAPAE Ree iit:

General characters of the Ammonoidea—Structure of the shell in
the Ammonoidea—The Aptychus—Zoological affinities of the
Ammonoidea— Distribution of the Ammonoidea in time—Clym-
eniidee — Goniatitidz — Arcestidze — Tropitidze — Ceratitidae—
Cladiscitidee — Pinacoceratidze— Phylloceratidze— Lytoceratidz
—Ptychitidee— Amaltheidze— A‘ goceratidze— Harpoceratidae—
Haploceratide—Stephanoceratide, . : . 848-870

CEA ol ve

General characters of the Dibranchiate Cephalopods—Skeleton of
the Dibranchiates—Classification—Distribution in time—Gen-
eral characters of the Decapoda—Phragmophora—Spirulide—
Belemnitidze — Belemnoteuthidz— Sepiophora— Chondrophora
—Characters and distribution in time of the Octopoda—Litera-
ture of Mollusca, . : : : ; : 3 . 871-885

CORRKIGENDA TO) PAR Tai:

Page 397 and page 398, for “ Phanerogonia” and “ Cryptogonta” read
“ Phanerozonia” and “ Cryptozonia.”
1 451, line 23 from top, for “ Sporadiporous ” vead “* Sporadipodous.”

| A ead (paar

fave INTRODUCTION

BY

Hy ALLEYNE NICHOLSON

eee ON Ol O Gy.

Colaba bly Ron oll,

INDPRODSCLLON:
DEFINITION OF PALZONTOLOGY.

PALZONTOLOGY (Gr. Aadaios, ancient ; ota, beings ; Zogos, discourse)
is the science which treats of the living beings, whether animal or
vegetable, which have inhabited this globe at past periods in its
history. It is the ancient life-history of the earth, and if its record
could ever be completed, it would furnish us with an account of the
structure, habits, and distribution of all the animals and plants which
have at any time flourished upon the land-surfaces of the globe or
inhabited its waters. From causes, however, which will be subse-
quently discussed, the paleontological record is most imperfect, and
our knowledge is interrupted by gaps which not only bear a large
proportion to our solid information, but which in many cases are of
such a nature that we can never hope to have them filled up.

As Zoology, then, treats of the animals now inhabiting the earth,
and as Botany treats of the now existing plants, Paleontology may
be defined as the Zoology and Botany of the past, and may be
subdivided into the two subjects of Palzeozoology and Palzobotany.
The study of fossil animals and plants is, however, based upon the
knowledge of living animals and plants, and for this reason Palzeo-
zoology and Palzobotany are inseparably connected with Neozoology
and Neobotany. ‘The materials, again, which fall to be studied by
the paleontologist, are drawn entirely from the proper province of
the geologist. Fossils are derived from rocks. It will therefore be
necessary to trespass to some extent upon the peculiar domain of
the geologist, and to obtain some knowledge of the origin, com-

4 INTRODUCTION.

position, and mode of occurrence of the rocks from which Pale-
ontology obtains its materials. Lastly, Paleontology, apart from
its Own importance as an independent branch of Zoology, is em-
ployed by the geologist to assist him in his determination of the
chronological succession of the materials which compose the crust
of the earth. Palzeontology, therefore, in one of its aspects, is a
branch of geological science, and requires separate study in its
relation to historical Geology.

DEFINITION OF FOSSILS.

All the natural objects which come to be studied by the palzeon-
tologist are termed “fossils” (Lat. fossws, dug up). In most cases,
fossils, or, as they are often termed, “ petrifactions,” are actual por-
tions of animal or vegetable organisms, such as the shells of Molluscs,
the skeletons of Corals, the bones of Vertebrate animals, the wood,
bark, or leaves of plants, &c.; and these may be preserved very
much in their original condition, or may have been very much
altered by changes subsequent to their burial. Strictly speaking,
however, by the term “fossil” is understood ‘‘any body, or the
traces of the existence of any body, whether animal or vegetable, which
has been buried in the earth by natural causes” (Lyell). We shall
find, therefore, that we must include under the head of fossils ob-
jects which at no time themselves formed parts of any animal or
vegetable, but which, nevertheless, point to the former existence of
such organisms, and enable us to reason as to their nature. Under
this head come such fossils as the moulds or “casts” of shells and
the footprints or markings left by various animals upon sand or mud.

In the great majority of cases fossils are the remains of animals or
plants which are now ex/émct—that is to say, which no longer are in
existence, but have entirely disappeared from the earth’s surface.
In some cases, however, fossils are the remains of vecent animals—
that is, of animals which are still found in a living condition upon
the globe. The term ‘‘ sub-fossil,” sometimes applied to these, has
been more appropriately applied in another sense, and is best dis-
carded in this connection. In any case, the fact that a given speci-
men belongs to an extinct species of animal or plant, or that it is
referable to some existing form, does not enter in any way whatever
into the determination of the question as to whether or not it is
truly a fossi7. If such a specimen is found in those portions of the
earth’s crust which we can show by other evidence to have been
formed prior to the establishment of the existing terrestrial order,
then it is a fossil; while any remains, even though belonging to the
same animal, which are found in deposits which have been formed
during the historical period, would be, strictly speaking, referred to

FOSSILISATION. 5

the domain of the neozoologist or the neobotanist, and would not
rightly be termed “fossils.” It must be admitted, however, that in
approaching the ‘‘ Recent” period of the earth’s history, it becomes
a matter of difficulty—in some cases an impossibility—to draw any
precise line between fossil and recent specimens.

The terms “fauna” and “ flora” are employed in Palzontology
much as they are by the student of recent forms, to mean the entire
assemblage of the animals or of the plants respectively belonging to
a particular region or a particular time. Thus we may speak of the
“fauna” of the Carboniferous Period, or the “ flora” of the Tertiary
Epoch, or the fauna of the Chalk, or of any other set of beds.

FOSSILISATION.

The term “ fossilisation” may be applied in a general sense to all
the processes through which an organic body passes in order to be-
come a fossil. Here we need only consider the three leading forms
in which fossils present themselves. In the first instance, the fossil
is to all intents and purposes an actual organic remain, being itself a
fragment of an animal or plant. Thus we may meet with fossil
bones, shells, or wood, which may have undergone certain changes,
such as would be produced by pressure, by the deprivation of or-
ganic matter originally present, or by more or less complete infiltra-
tion with mineral matter, but which, nevertheless, are practically the
real bodies they represent. As a matter of course, it is in the more
modern formations that we find fossils least changed from their
primitive condition, but almost all formations contain some fossils in
which the original structure is more or less completely retained.

In the second place, we very frequently meet with fossils in the
state of ‘“‘casts” or moulds of the original organic body. What
occurs in this case will be readily understood, if we imagine any
common bivalve shell, as an Oyster, or Mussel, or Cockle, embedded
in clay or mud. If the clay were sufficiently soft and fluid, the first
thing would be that it would gain access to the interior of the shell
and would completely fill up the space between the valves. The
pressure, also, of the surrounding matter would ensure that the clay
would everywhere adhere closely to the exterior of the shell. If
now we suppose the clay to be in any way hardened so as to be
converted into stone, and if we were to break up the stone, we
should obviously have the following state of parts. The clay which
filled the shell would form an accurate cast or mould of the zxéerior
of the shell, and the clay outside would give us an exact impression
or cast of the exterior of the shell (fig. 1). We should have, then,
two casts, an interior and an exterior, and the two would be very
different from one another, since the inside of a shell is very unlike the

6 : INTRODUCTION.

outside. In the case, in fact, of many Molluscan shells, the interior
cast is so unlike the exterior or unlike the shell itself, that it may be
difficult to determine the true origin of the former.

It only remains to add that there is sometimes a further compli-
cation. If the rock be very porous and permeable by water, it may
happen that the original shell is en-
tirely dissolved away, leaving the in-
terior cast or “‘mould” loose, like
the kernel of a nut, within the case
formed by the exterior cast. Or it
may happen that subsequent to the
attainment of this state of things, the
space thus left vacant between the

2 interior and exterior cast—the space,

Fig. 1.—T77igonta longa, showing casts that iS, formerly occupied by the shell

Oe eae and interior of the shell. itself — may be filled up by some

foreign mineral deposited there by

the infiltration of water. In this last case the splitting open of the

rock would reveal an interior cast, an exterior cast, and finally a

body which would have the exact form of the original shell, but

which would really be of much later origin and would not exhibit
under the microscope the minute structure of shell.

In the third class of cases we have fossils which present with the
greatest accuracy the external form, and sometimes even the internal
minute structure, of the original organic body, but which, neverthe-
less, are not themselves truly organic, but have been formed by a
“replacement” of the particles of the primitive organism by some
mineral substance. The most beautiful example of this is afforded
by fossil wood which has been ‘“silicified” or converted into flint.
In this case we have a piece of fossil wood, which presents the
rings of growth and fibrous structure of wood, and under the micro-
scope exhibits even the minutest vessels which characterise ligneous
tissue. The whole, however, instead of being composed of the
original carbonaceous matter of the wood, is now converted into
pure flint. The only explanation which can be given of this by no
means very rare phenomenon, is that the wood must have undergone
a slow process of decay in water holding silica or flint in solution.
As each particle of the wood was removed by decay, its place was
taken by a particle of flint deposited from the surrounding water,
till ultimately the entire wood was silicified. The replacing sub-
stance is by no means necessarily flint, but may be iron-pyrites,
oxide of iron, sulphur, malachite, magnesite, talc, &c. ; and it is not
uncommon to find many other fossils besides wood preserved in
this way, such as shells, corals, or sponges.

The replacement of -the original substance of a fossil by some

FOSSILISATION. 7

foreign body is thus a matter of common occurrence, but it is by no
means always easy to determine whether or not such replacement
has taken place. By far the commonest mode of replacement is
that whereby an originally calcareous skeleton is replaced by silica.
This process of “ silicification ”—of the replacement of “me by szlica
—is not only an extremely common one, but it is also a readily
intelligible one; since carbonate of lime is an easily and flint a
hardly soluble substance. It is thus easy to understand that origin-
ally calcareous fossils, such as the shells of Mollusca, or the skeletons
of Corals, should have in many cases suffered this change, long after
their burial in the rock, their carbonate of lime being dissolved
away, particle by particle, and replaced by precipitated silica, as
they were subjected to percolation by heated or alkaline waters
holding silica in solution.

In a large number of cases of silicification, the minute structure of the
fossil which has been subjected to this change is found to have been
more or less injuriously affected, and may be altogether destroyed, even
though the form of the fossil be perfectly preserved. This is the rule
where the silicification has been secondary, and has taken place at some
period long posterior to the original entombment of the fossil in the
enveloping rock ; whereas if the original fossilisation has been effected
by infiltration with silica in the first instance, then the minute structure
is usually perfectly preserved. In secondary silicification, as seen in
corals and shells, the carbonate of lime of the original fossil is gradually
more or less completely replaced by silica, the process beginning on the
exterior and gradually extending inwards. In the first stage of the pro-
cess, the outer layer of the fossil very commonly becomes more or less
largely converted into, or covered by, small circular deposits of silica,
having the form of a central boss surrounded by one or more concentric
rings (“orbicular silica” or “ Beekite markings”). If the process goes
on, the whole of the fossil may ultimately become converted into flint.
Secondarily silicified fossils, though ill adapted for microscopic exam-
ination, are often of great beauty, as they commonly “ weather out” from
the more readily soluble limestone in which they are embedded, and
can thus be obtained in absolute entirety.

When we meet with fossils, such as those alluded to above, which
we £now to have been originally calcareous, but which we now find,
unchanged in form, although converted into flint, then we cannot
doubt that we have to deal with cases of “‘silicification,” and that the
primitive skeleton of lime has in these cases been slowly, and more
or less perfectly, replaced by silica. We cannot, however, speak in
such a positive manner as to fossils which we now find to be com-
posed of flint, but as to the original constitution of which we cannot
be certain. We find, namely, some fossils which are of uncertain
affinities, and which sometimes occur in a siliceous and sometimes
in a calcareous state. If we are not positive as to the zoological
position of these fossils, or if they belong to a group of animals in

8 . INTRODUCTION.

which we find the living forms to possess sometimes a calcareous
and at others a siliceous skeleton, then it is obviously a matter of
extreme difficulty to determine whether the extinct forms were really
composed of lime or of flint. In such cases, we must be guided
principally by the condition of preservation of the fossils which
occur associated with such obscure forms in the same beds; the
fact that the associated remains are converted into flint pointing to
the probability that the problematical forms were originally calcare-
ous, and wice versa. In the case, also, of all fossils which present
themselves sometimes in a siliceous and sometimes in a calcareous
form, there is always the presumption that the skeleton was originally
composed of /ime, this presumption being based upon the fact that
the conversion of the calcareous skeletons of animals into silica by
a process of replacement is an unquestionable, an extremely common,
and a readily intelligible occurrence.

Until recently, indeed, naturalists never allowed themselves to
contemplate the alternative possibility of an originally szzceous
skeleton being replaced by “me, but we have now unequivocal
evidence that this anomalous mode of replacement is of not very
uncommon occurrence. The researches of Zittel, Hinde, and
Sollas have, in fact, proved that the colloid silica of the siliceous
skeletons of the Flinty Sponges is comparatively unstable, and that
under certain circumstances it can be readily dissolved in water.
Hence these Sponges are commonly found in the fossil condition
with the silica of the original skeleton more or less extensively
replaced by carbonate of lime, or by oxide or sulphide of iron.
When the replacing agent is lime, it is found not only that the
microscopic structure of the original skeleton has been completely
lost ; but that the lime is always in the crysta//ine condition, consist-
ing of unoriented crystals of calcite. This latter fact affords conclu-
sive proof that the skeleton was not primitively calcareous, but that
the lime is of secondary origin and has replaced some other material

In any case we must carefully distinguish between replacement,
whether by flint or any other mineral, and 7zz/t/tration, the latter
being merely the process whereby the cavities and natural vacuities
of a fossil are liable to become filled by some mineral substance,
subsequent to its entombment in sediment. When such a fossil as
a shell or a coral, for example, becomes buried in the sandy, cal-
careous, or argillaceous mud at the bottom of the sea, the surround-
ing sediment often does not penetrate into the deeper parts of the
fossil, and there are thus left in its interior certain empty spaces,
into which the surrounding water makes its way by percolation.
Any mineral substances, such as carbonate of lime or silica, which
may be contained in solution in the water, are then liable to undergo
precipitation, and to be deposited in a solid form within the fossil.

CLASSIFICATION OF ROCKS. 9

All the natural cavities of a fossil, even down to the minutest micro-
scopic pores or tubes, may in this way become filled with some such
infiltrated material, the two commonest agents in this process being
lime and flint. If the skeleton of the fossil be a calcareous one,
while the infiltrating material has been some less soluble substance,
such as silica or some silicate, then the skeleton may be artificially
or naturally dissolved away, leaving a cas¢ of the internal cavities of
the fossil formed of the infiltrated matter. ‘Thus the minute shells
of Foraminifera are often infiltrated with the silicate glauconite, and
exquisitely perfect casts of their interior cavities are subsequently
formed by dissolution of the shell itself. In this way, as we shall
see hereafter, deposits of greensand have been sometimes produced.

DEFINITION OF ROCK.

The crust of the earth consists of various different materials, pro-
duced at different successive periods, occupying certain definite
spaces, and not confusedly mixed together, but, on the contrary,
exhibiting a definite and discoverable order of arrangement. All
these materials, however different in appearance, texture, or mineral
composition, are called ‘‘rocks” by the geologist. The term “ rock,”
then, is to be understood as applying to a// the materials which
compose the crust of the earth. In the language of geology, the
finest mud, the loosest sand, and the most incoherent gravel, are
just as much vocks as are the hardest and most compact granites or
limestones.

CLASSIFICATION OF ROCKS.

For the purposes of the paleontologist all the rocks which enter
into the composition of the solid exterior of the earth may be
divided into two great classes: 1. The Igneous Rocks, which are
formed within the body of the earth itself, and owe their struc-
ture and origin to the action of heat; and 2. the Aqueous or
Sedimentary Rocks, which are formed at the surface of the earth,
and owe their structure, at any rate in part, to the mechanical
action of water. The Igneous Rocks are principally formed below
the surface of the earth, are as a general rule destitute of organic
remains or fossils, and are mostly in the form of wzstratified masses.
The Aqueous and Sedimentary Rocks are formed at the surface by
the disintegration and reconstruction of previously existing rocks, or
by the vital chemistry of animals or plants, are mostly fossiliferous,
and are stratified—1i.e., are arranged in distinct layers or “strata.”
The Aqueous Rocks, as containing fossils, are the only rocks with
which it is essential for the paleontologist to be acquainted, and we
shall very briefly consider their leading physical characters, their

IO INTRODUCTION.

chief varieties, their mode of origin, and their historical succession.
It should be borne in mind, however, that there are cases in which
strictly volcanic deposits may come to contain the remains of animals
and plants. Thus, animals and plants may be enveloped and en-
tombed in showers of volcanic ashes falling upon land, and deposits
of subaerial volcanic ash may thus become fossiliferous. Moreover,
it is very common for volcanic ashes to fall in vast quantities into
the sea or into a lake, when they become subjected to the action of
water, and may envelop the animals living at the bottom. Hence
it is by no means unusual to meet in the crust of the earth with
more or less extensive deposits of volcanic ashes, which though
igneous in origin are secondarily aqueous, being not only stratified
but also containing the remains of aquatic animals.

1k

@Ebaee Eke ae

THE FOSSTLIFEROGS ROGEKES.

THE Sedimentary or Fossiliferous Rocks form the greater portion of
that part of the earth’s crust which is open to our examination, and
are distinguished by the fact that they are regularly “stratified,” or
arranged in distinct and definite layers or “strata.” These layers
may consist of a single material, as in a block of sandstone, or they
may consist of different materials. When examined on a large scale,
they are always found to consist of alternations of layers of different
mineral composition. We may examine any given area, and find in
it nothing but one kind of rock—sandstone, perhaps, or limestone.
In all cases, however, if we extend our examination sufficiently far,
we shall ultimately come upon different rocks; and, as a general
rule, the thickness of any particular set of beds is comparatively
small, so that different kinds of rock alternate with one another in
comparatively small spaces.

As regards the origin of the Sedimentary Rocks, they are for the
most part “derivative,” being derived from the wear and tear of
pre-existent rock. Sometimes, however, they owe their origin to
chemical or vital action, when they would more properly be spoken
of simply as Aqueous Rocks. As to their mode of deposition, we
are enabled to infer that the materials which compose them have
formerly been spread out by the action of water, from what we see
going on every day at the mouths of our great rivers, and on a
smaller scale wherever there is running water. Every stream, where
it runs into a lake or into the sea, carries with it a burden of mud,
sand, and rounded pebbles, derived from the waste of the rocks
which form its bed and banks. When these materials cease to be
impelled by the force of the moving water they sink to the bottom,
the heaviest pebbles, of course, sinking first, the smaller pebbles
and sand next, and the finest mud last. Ultimately, therefore, as
might have been inferred upon theoretical grounds, and as is proved
by practical experience, every lake becomes a receptacle for a series

12 INTRODUCTION.

of stratified rocks produced by the streams flowing into it. These
deposits may vary in different parts of the lake, according as one
stream brought down one kind of material and another stream con-
tributed another material; but in all cases the materials will bear
ample evidence that they were produced, sorted, and deposited by
running water. The finer beds of clay or sand will all be arranged in
thicker or thinner layers or laminz; and if there are any beds of
pebbles these will all be rounded or smooth, just like the water-worn
pebbles of any brook-course. In all probability, also, we should
find in some of the beds the remains of fresh-water shells, plants,
or other organisms which inhabited the lake at the time these beds
were being deposited.

In the same way large rivers—such as the Ganges or Mississippi
—deposit at their mouths much of the material which they bring
down, forming in this way their “deltas.” Whenever such a delta
is cut through, either by:man or by some channel of the river alter-
ing its course, we find that it is composed of a succession of hori-
zontal layers or strata of sand or mud, varying in mineral composition,
in structure, or in grain, according to the nature of the materials
brought down by the river at different periods. Such deltas, also,
will contain the remains of animals which inhabit the river, with
fragments of the plants which grew on its banks, or bones of the
animals which lived in its basin.

Lastly, the sea itself—airrespective of the materials delivered into
it by rivers—is constantly preparing fresh stratified deposits by its
own action. Upon every coast-line the sea is constantly eating
back into the land and reducing its component rocks to form the
shingle and sand which we see upon every shore. The materials
thus produced are not, however, lost, but are ultimately deposited
elsewhere in the form of new stratified accumulations, in which are
buried the remains of animals inhabiting the sea at the time.

Whenever, then, we find anywhere in the interior of the land any
series of beds having these characters—composed, that is, of distinct
layers, the particles of which, both large and small, show distinct
traces of the wearing action of water—whenever and wherever we
find such rocks, we are justified in assuming that they have been
deposited by water in the manner above mentioned. Either they
were laid down in some former lake by the combined action of the
streams which flowed into it; or they were deposited in some por-
tion of the course of an ancient river; or they were laid down at
the bottom of the ocean. In the first two cases, any fossils which
the beds might contain would be the remains of fresh-water or ter-
restrial organisms. In the last case, the majority, at any rate, of the
fossils would be the remains of marine animals. _

The term ‘ formation” is often employed by geologists in a loose

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 13

general sense to signify “‘ any group of rocks which have some char-
acter in common, whether of origin, age, or composition” (Lyell) ;
so that we may speak of stratified and unstratified formations, aqueous
or igneous formations, fresh-water or marine formations, and so on.

CHIEF DIVISIONS OF THE AQUEOUS ROCKS.

The Aqueous Rocks may be divided into two great sections, the
Mechanically-formed and the Chemically-formed, including under
the last head all rocks which owe their origin to vital action, as well
as those produced by ordinary chemical agencies. It must not be
forgotten, however, that such a division, though convenient in prac-
tice, is largely artificial. Thus many organically-formed rocks are to
a large extent the product of mechanical action, since, though con-
sisting of the skeletons of organisms, their component materials have
been mechanically broken down and transported by water. More-
over, no sharp line of demarcation can be drawn between the above
two groups of rocks, innumerable transitions existing between rocks
which are purely mechanical in origin and those which are the direct
result of vital action.

A. MECHANICALLY-FORMED Rocxks.—These are all those Aqueous
Rocks of which we can obtain proofs that their particles have been
mechanically transported to their present site. Thus, if we examine
a piece of conglomerate or pudding-stone, we find it to be composed
of a number of rounded pebbles embedded in an enveloping paste
or matrix. The pebbles are worn and rounded, and thus show that
they have been subjected to much mechanical attrition, whilst they
have been mechanically transported for a greater or less distance
from the rock of which they originally formed part. In the case of
an ordinary sandstone, the component grains of sand are equally the
result of mechanical attrition, and have been equally transported
from a distance. In the case of still finer rocks, such as shale, the
particles have been so much water-worn that their source cannot be
recognised, though a microscopical examination would reveal that
their edges were all worn and rounded. It follows from this that
the mechanically-formed Aqueous Rocks are such as can be proved
to have been derived from the abrasion of other pre-existent rock :
hence they are often spoken of as ‘‘ Derivative Rocks.” Every bed,
therefore, of any mechanically-formed rock, is the equivalent of a
corresponding amount of destruction of some older rock.

The mechanically-formed Rocks may be divided into the two
groups of the Arenaceous or Siliceous Rocks, and the Argillaceous
or Aluminous Rocks. In the Arenaceous group are those Aqueous
Rocks which are mainly composed of smaller or larger grains of flint
or silica. The chief varieties are the various kinds of sand and

14 INTRODUCTION.

sandstone, grits, and most conglomerates and breccias. In the
Argillaceous group are those Aqueous Rocks which contain a cer-
tain amount of clay or hydrated silicate of alumina. Under this -
head come clays, shales, marls, clay-slate, and most flags or flag-
stones. In nature there exists, it need hardly be said, no rigid line
which separates the Arenaceous from the Argillaceous rocks. ‘The
two groups are connected together by endless transitional forms, and
.we must regard all the mechanically-formed rocks as variable mix-
tures of different ingredients, their precise character depending on
the predominance of some one constituent.

B. CHEMICALLY-FORMED Rocxks.—lIn this section are comprised
all those Aqueous Rocks which have been formed by chemical
agencies. Since, however, many of these chemical agencies are
exerted through the medium of living beings, whether animals or
plants, we get into this section a number of what may be called
‘“‘ organically-formed ” rocks. ‘The most important of the Chemi-
cally-formed Rocks are the so-called Calcareous Rocks, comprising
all those which contain a large proportion of carbonate of lime, or
are wholly made up of this substance; but there are other rocks,
of different composition, formed by chemical or organic agency,
which may be briefly noticed.

As an example of a rock the origin of which is purely chemical,
we may take vock-salt or sodium chloride, extensive deposits of which
occur in formations of all ages, from the Silurian upwards. Whatever
may have been the precise mode in which these deposits were
formed, it is quite certain that the salt existed, to begin with, in
solution in water, and that its assumption of the solid form was the
result simply of precipitation. Hence, rock-salt is invariably com-
posed of larger or smaller crystals of sodium chloride, though not
uncommonly rendered impure by intermixture with sand or clay.

Another rock which may be regarded as a direct product of
chemical action, apart from the operation of living beings, is gypsum
or calcium sulphate. ‘This substance, apart from other modes of
occurrence, is not uncommonly found interstratified with the ordinary
sedimentary rocks, in the form of more or less irregular beds; and
in these cases it has a certain paleeontological importance, as occa-
sionally yielding well-preserved fossils. In general appearance,
gypsum, when occurring in mass, is usually a whitish, yellowish,
or reddish granular rock, which can be easily shown by the micro-
scope to be composed of crystals of calcium sulphate. Very com-
monly, indeed, the rock is as coarsely crystallised as loaf-sugar, or
more so, and the microscope is not needed for the recognition of its
true structure. With regard to its mode of origin, there is no reason
to doubt that deposits of gypsum are formed by the direct precipita-
tion of calcium sulphate from solution in water, without the inter-

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 15

vention of living beings ; though it is possible that in some cases the
chemical changes which have resulted in the production of masses
of gypsum may have been secondary, and may have acted at some
period posterior to the original deposition of the rocks associated
with these.

Another lime-salt which owes to chemical action its present form,
and its present relations to the rocks with which it is associated, is
phosphate of time. Calcium phosphate occurs in the form of larger
or smaller crystals (apatite) in many crystalline rocks, whether these
be metamorphic or igneous in origin. It also sometimes occurs in
considerable beds (phosphorite) in formations of various ages ; and
it occurs abundantly in the form of nodules in some parts of the
Secondary and Tertiary deposits. It likewise may occur dissem-
inated through the ordinary stratified rocks in such a condition as
not to be capable of detection save by chemical analysis, as has
been shown by Dr Hicks in the case of the Cambrian rocks of
Wales. When it is found in the crystalline or in the massive con-
dition, there is no reason to doubt that calcium phosphate is the
product of direct chemical action. Even in these cases, however, it
is quite possible that it may have been sometimes derived in the
first place from the skeletons or excrements of animals. Phosphate
of lime forms the larger proportion of the earthy matter of the bones
in Vertebrate animals, and also occurs in less amount in the skeletons
of certain of the Invertebrates (e.g., Zingula and Discina, among the
Brachiopods ; Conularia and FHyolithes, among the Pteropods ; and
the Crustacea in general). Phosphate of lime is thus, perhaps even
more distinctively than carbonate of lime, an organic compound.
When calcium phosphate occurs minutely disseminated through a
rock, it is tolerably certain that it has been derived from animals
and plants. It is also almost certain that the phosphate of lime in
the so-called ‘‘ coprolites” of the Cambridge Greensand, as in other
similar phosphatic nodules, is organic in origin. Some of these
nodules consist of organisms, such as Sponges, infiltrated with phos-
phate of lime, but most of them would seem to have been formed by a
process of segregation similar to that which has given rise to nodules
of clay-ironstone or of carbonate of lime in beds of shale. The
name of ‘ coprolites” given to these phosphatic nodules is founded
upon a misconception, as they are not actually the fossilised excre-
ments of animals. In various formations, however, there are found
genuine “‘ coprolites ”—z.e., the petrified excreta of Fishes, Reptiles,
or Mammals,—and these are largely composed of phosphate of lime.

By far the largest and most important group of the chemically-
formed rocks is that of the Calcareous Rocks, comprising all those
rocks in which carbonate of lime is the predominating ingredient,
and which are therefore spoken of by the general name of “mestones.

16 INTRODUCTION.

In all cases, the carbonate of lime which exists in a limestone has
previously existed in solution in water, either in the water of a spring,
river, or lake, or in that of the ocean itself. Owing, in fact, to the
ready solubility of calcium carbonate in water holding in solution
a certain proportion of carbon dioxide, a larger or smaller quantity
of this mineral is invariably found dissolved in all natural waters,
whether fresh or salt, since these waters are always to some extent
charged with this solvent gas. There are two principal methods by
which the carbonate of lime held in solution in water may again
assume the solid form. One of these methods consists in the chem-
ical precipitation of the carbonate of lime from the water. This
takes place whenever the carbonic acid in the water becomes so far
reduced in quantity that it is no longer able to retain in solution all
the lime that had been previously dissolved ; or whenever the water
undergoes partial or complete evaporation ; or, again, when water
which had been enabled by a high temperature to take up an excess
of lime, is subjected to cooling. Various well-known calcareous
deposits, such as the “ stalactites” and ‘‘ stalagmites” of limestone
caves, and the “calcareous tufa” and “travertine” of springs, are
produced in this way by the direct precipitation of carbonate of lime
from solution. All limestones deposited in this chemical way directly
from saturated solutions are necessarily composed of larger or smaller
crystals of carbonate of lime, and the microscope will show that their
structure is more or less clearly crystalline. ‘They may contain the
remains of animals or plants, as is not uncommon in the spongy
calcareous tufa deposited by “ petrifying springs”; but as such
remains are usually only excrusted by the precipitated lime, and are
not infiltrated, they generally become dissolved out in the course of
time, leaving cavities which mark their former presence. Calcareous
deposits formed by direct precipitation occasionally occur on a large
scale, and thus become geologically important, but the ordinary
limestones are formed in a different way, and are of much greater
palzeontological interest.

By far the most general method in which the dissolved carbonate
of lime in water may be converted into the solid form is by the vital
chemistry of animals and plants. Very many animals, and a con-
siderable number of plants, have the power of abstracting from the
water the carbonate of lime which it holds in solution, and of build-
ing up in this way a calcareous skeleton. Hence, while the waters
which percolate through the earth’s crust are constantly taking up
fresh carbonate of lime, this is being as constantly removed from the
waters of rivers, lakes, and the sea, and again converted into the solid
form, by the agency of living beings. It is owing to the fact that
animal life is much more abundant in the sea than in rivers and
lakes, that sea-water contains a proportionately smaller proportion of

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 4

dissolved lime than fresh waters, in spite of the circumstance that
rivers are constantly pouring into the sea vast quantities of this
substance.

Considering the constant production of carbonate of lime by vari-
ous animals and plants, it is not surprising to find on investigation
that many limestones are more or less extensively composed of the
skeletons of living beings. Most limestones are therefore, more or
less clearly, oxganic rocks. There are, however, two methods—not
always very clearly separated from one another—in which an organic
limestone may be formed. In one set of cases, the limestone is the
result of the accumulation of the calcareous skeletons of animals in
the place where these organisms actually lived and grew. This is
seen occasionally where a limestone has been formed by the growth
of innumerable generations of sedentary Molluscs, such, for example,
as Oysters. Some Crinoidal limestones have also been formed by
the accumulation of Crinoids in place; and many of the more
modern coral-limestones are similarly the result of the growth of
the lime-producing polypes in the locality where we now find the
rock. In another and more extensive set of cases, the limestone has
been formed by the gradual accumulation of the skeletons of animals
or plants which lived in some place more or less widely removed
from that occupied by the limestone itself. Thus, extensive calcare-
ous deposits may be formed at the bottom of the deep sea by the
slow accumulation of the calcareous skeletons of animals which live
at the surface of the ocean, and the shells of which fall to the bottom
on the death of the animal which produced them. This is seen
in certain Foraminiferal limestones and in Pteropodal limestones,
though in all such cases the rock is in part made up of the skeletons
of animals which actually lived at the bottom of the sea. In other
cases, the calcareous skeletons of animals are thrown up in great
banks by the action of the sea in the neighbourhood of land. This
is the case, for example, with the great accumulations of shell-sand
on many parts of our shores, or with the still more extensive deposits
of coral-sand in warm seas. In such cases, the limestone is so far
organic that it is formed mainly out of the skeletons of lime-secreting
animals or plants, but it is also so far mechanical that the actual
formation of the limestone has been due to the breaking up and
wearing down of these skeletons by the movements of the waves
of the sea.

If this wearing-down action has been sufficiently long-continued
and sufficiently complete, we may not be able to recognise in the
limestone many, or indeed any, actual fragments of shells or other
animal structures ; but the rock may appear under the microscope as
a fine-grained calcareous mud, made up of minute, mostly non-crys-
talline granules of carbonate of lime (fig. 2, 4). This is the case, for

VOL. I. B

18 INTRODUCTION. ~

example, with some limestones of quite recent date, and with the so-
called “ lithographic ” limestones of various geological periods from
the Ordovician onwards. Similar fine-grained calcareous muds may
likewise be formed by the slow digestion and consequent disintegra-
tion of the calcareous skeletons of animals and plants, which takes
place when such skeletons are long exposed to the action of sea-
water. In other cases, again, a calcareous mud of the kind here
spoken of may be produced by the wearing down of previously exist-

ss

‘
=

enya t

¥g7 ers
erie
Vee: x
2, ayer QE
Fa Ap RES

fj

1
xi
OR aSee

ti

Fig. 2.—a, Thin section of lithographic limestone, Jurassic, Solenhofen, greatly magnified.
The rock is a fine-grained calcareous mud, for the most part non-crystalline. B, Thin section
of an arenaceous limestone from the Middle Permian of Westmorland. ‘The rock is largely
mechanical in origin, angular fragments of quartz being cemented together by a crystalline
dolomitic matrix. (Original.)

ing limestones. More commonly the abrasive action of the sea has
not been sufficiently prolonged or severe to reduce the calcareous
fragments to the form of mere calcareous grains, in which the organic
structure is no longer perceptible. Hence the great majority of
limestones, when examined microscopically, are found to consist of
more or less complete skeletons, or portions of the skeletons, of dif-
ferent kinds of hme-producing animals or plants, cemented together
by a general crystalline or granular matrix. The general mode of
origin of such limestones is rendered sufficiently clear by an investi-
gation of calcareous deposits now in process of formation. Such a
limestone to begin with exists in the form of an accumulation of
entire or fragmentary calcareous skeletons, of all shapes and sizes,
loosely heaped together, and more or less extensively separated by
vacant spaces. In the process of consolidation, the irregular lacunze
between the component fragments of the mass may become infil-
trated with fine calcareous mud, produced by the disintegration and
wearing down of the superficial portions of the mass; and the result-
ing rock will then have the structure of a granular matrix enclosing
innumerable entire or fragmentary organisms. An excellent example
of such a rock is to be obtained in the White Chalk (fig. 3), which
consists of innumerable organic fragments, mostly referable to the

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 19

Foraminifera, cemented together by a fine calcareous mud, and
which was probably formed in water of considerable depth. In the
more ordinary limestones—most of which have been formed close to
a shore-line—the original accumulation of partially broken-up cal-
careous skeletons is subjected to the percolation through its mass of
water holding carbonic acid in solution. As the result of this, par-
tial solution of the mass takes place, and the dissolved carbonate of
lime is ultimately deposited in the form of calcite, the rock thus

SSS FEE
SY Care ER
ENS @)s028

ASE

Fig. 3.—Thin section of White Chalk, from Fig. 4.—Thin section of Carboniferous lime-
Sussex, enlarged about fifty times. The ma- stone, from Shap, enlarged about fifteen times.
trix is a calcareous mud, and the contained The matrix is crystalline, and the included
organisms are mostly entire or broken Fora- organisms are Foraminifera, calcareous Alge,
minifera. (Original.) joints of Crinoids, &c. (Original.)

assuming the character of a congeries of organic fragments bound
together by a general matrix of crystalline carbonate of lime (fig. 4).
Even accumulations of sand may be in this way subjected to the per-
colation of acidulated water holding lime in solution, and may thus
be converted into arenaceous limestones, in which angular quartz-
grains are united by a matrix of crystalline carbonate of lime (fig. 2, B).
The microscope shows us that very many of the limestones com-
posing the crust of the earth, of all geological ages except the most
ancient, have been formed in the general method above described.
Limestones of essentially similar structure are also now in process of
formation on a large scale. This is specially seen in the warm seas
of the coral-region, where the broken down coral-sand commonly
becomes converted in time into a hard, crystalline or semi-crystalline
limestone ; and we may occasionally see the same process at work,
on a smaller scale, in the shell-sand of our own shores.

It follows from the above, that the formation of the crystalline matrix
of an ordinary limestone is always secondary to the accumulation of the

20 INTRODU CRONE

organic fragments which compose the mass of the rock. In some cases
the matrix has been deposited in the first instance in a crystalline form,
and is the result of the percolation through the mass of water charged
with carbonate of lime in solution. In other instances, the matrix has,
to begin with, been composed of a fine calcareous mud, which has later
undergone crystallisation, as the result of secondary chemical and me-
chanical changes. Sometimes this superinduced crystallisation may be
the result of pressure; in other cases it may be caused by the per-
colation through the rock of heated or carbonated water ; while in many
instances it is connected with the process of dolomitisation.

In this process of superinduced crystallisation, the organic fragments
contained in the rock usually show themselves more stable than does the
matrix. Hence the matrix may become more or less highly crystalline,
while the included organic fragments remain more or less distinct and
unaffected. It often happens, however, as specially insisted upon by Dr
Sorby, that the fragments of calcareous organisms have crystallised along
with the surrounding matrix, in such a manner as to have more or less
extensively lost not only their organic structure but also their external
outline. There are various degrees in which this superinduced crystal-
lisation, and consequent obliteration, of the included organic fragments
in a limestone takes place. It is noticeable, however, that the agencies
which give rise to this condition are not necessarily of any great intensity,
since complete crystallisation and obliteration of the included organic
remains may occur in modern calcareous deposits (¢.g., some coral-lime-

i

AG
—\

7

Fig. 5.—a, Section of Ordovician limestone, from Keisley, Westmorland, in which the crystal-
lisation of the matrix has extended to the included fragments of Crinoids, as shown by the con-
tinuation of the cleavage-planes from one to the other. Enlarged about five times. 8, Fibro-
crystalline structure developed in the same limestone, considerably enlarged. (Original.)

stones). An interesting example of this phenomenon is commonly seen
in Crinoidal limestones, in which the entire rock may be so crystallised
that the cleavage-planes of the calcite run continuously through both the
matrix and the included fragments of Crinoids, the latter nevertheless
preserving their outlines (Fig. 5, A.)

In many of the older limestones, portions of the rock often exhibit a
peculiar fibro-crystalline structure, being composed of feather-like col-
umns of crystalline carbonate of lime, placed side by side and intersected
by a double cleavage. Sections of such fibro-crystalline masses (Fig.
5, B), examined microscopically, commonly show, therefore, a character-
istic pinnate or “herring-bone” structure, due to the crossing of the two
sets of cleavage-planes. This remarkable structure is obviously the

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 21

result of secondary changes affecting the limestone. It is of frequent
occurrence in the calcareous material which occupies the interior of
fossils, such as the shells of Mollusca or the crusts of Trilobites, in which
case the columns radiate from the surface of attachment. In other cases,
it occupies irregular winding spaces in the rock, when it exhibits a con-
centrically banded structure, indicating its formation in successive layers,
while the constituent fibres radiate inwards in all directions from the
bounding surfaces of the mass. Under ordinary conditions, this peculiar
fibro-crystalline structure can only be regarded as purely inorganic. In
some instances, however, an apparently identical structure is produced
by the partial crystallisation of organic remains, such as the calcareous
skeletons of Stromatoporoids or Corals. It would appear that the so-
called Stromatactzs of Monsieur E. Dupont, which plays a very important
part in the formation of some of the Devonian limestones of Belgium,
is really of the nature of the above-mentioned fibro-crystalline masses,
being partly of inorganic origin, and probably in part the result of sec-
ondary change in suitable fossils, such as Stromatoporoids.

Any of the great groups of Invertebrates in which a calcareous
skeleton is produced may take a more or less prominent part in the
formation of a limestone; and the principal facts connected with
this subject will be dealt with in greater detail in treating of each
group of animals separately. It may be well, however, to indicate
here, in the briefest manner, the chief groups of organisms, whether
animal or vegetable, which may be considered as pre-eminently
makers of limestones. As regards animals, a very important place
must be assigned to the /oram-
inifera, a group of the Profozoa in
which a calcareous shell is com-
monly developed. So far as the
older Paleozoic limestones (Or-
dovician, Silurian, and Devonian)
are concerned, it is noteworthy
that in very few instances, so far as
yet known, do the tests of Foram-
inifera constitute a prominent con-
stituent of the rock. In all the
later formations, however, begin-
ning with the Carboniferous, we ; :

: : . Fig. 6.—Section of Carboniterous lime-
meet with limestones which are stone from Spergen Hill, Indiana, U.S.,
more or less highly charged with towing numerous lasgesiaed Poraorinyre
the calcareous tests of these min- nified. (Original.)
ute organisms, sometimes in such
numbers that the rock becomes what may be properly called a
‘“‘Foraminiferal limestone” (fig. 6). Of this nature are the “ Sac-
cammina limestone” of the North of England, the “ Endothyra
limestone” of North America, and the ‘ Fusulina limestone” of
Russia, all of which are of Carboniferous age. Of the Foram-

Z2 INTRODUCTION.

iniferal limestones of the Mesozoic period the most interesting and
important is the White Chalk, the characters of which will be con-
sidered more fully later on. Lastly, in the Tertiary period there
are various well-known Foraminiferal limestones, of which the most
important and most widely distributed is the great calcareous
deposit known as the ‘‘ Nummulitic limestone.”

Among Ccelenterate animals, the principal lime-makers are the
true Corals (AZadreporaria). Many of the limestones which enter
into the composition of the crust of the earth, dating from the
Ordovician period onwards, are more or less extensively composed
of the skeletons of Corals. ‘Though the Corals commonly occur in
such a manner in the rock as to show clearly that they grew on the
spot where the limestone was formed, it is questionable if any of the
Paleozoic limestones can be properly said to be actual “ coral-
reefs,” though some of the Devonian limestones of North America
and Belgium may possibly be truly of this nature. In the Secondary
and Tertiary periods, however, we meet with coralline limestones
which may be considered as essentially similar in structure and mode
of formation to the ‘‘coral-reefs” of the warm seas of the present
epoch. The Corals, however, are not the only Ccelenterate ani-
mals which play an important part in the formation of limestones,
for it is now known that certain of the ydrozoa are likewise capable
of giving rise to extensive calcareous deposits by the accumulation
of their skeletons. Thus, certain of the Silurian and Devonian
limestones are largely composed of the calcareous skeletons of the
extinct AZydvozoa which constitute the group of the “‘ Stromatopo-
roids.” Other Palzeozoic limestones are extensively made up of the
remains of organisms like Solenopora and Mitcheldeania, which are
possibly referable to the Aydrozoa. At the present day, the only
ffydrozoon which is conspicuously concerned in the formation of
limestone is the Hydrocoralline genus J//efora, which plays an
important part in the construction of many of the existing “ coral-
RSENS,”

Of the Echinodermata there is only one order—viz., that of the
Sea-lilies or Cvznoids—which demands special mention in the pres-
ent connection. At the present day, the Crinoids constitute a but
feeble remnant of a once powerful and widely distributed group, and
they are not known to exist anywhere in numbers sufficient to render
them noteworthy as lime-makers. Among the older rocks of the
earth’s crust, however, and more particularly in deposits of Ordovi-
cian, Silurian, Devonian, and Carboniferous age, are found great
beds of limestone, essentially composed of the broken stems and
detached plates of Crinoids (fig. 7). Such limestones are known to
geologists as ‘‘Crinoidal limestones” and “ Encrinital marbles,”
and they are usually composed of more or less broken and rolled

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 23

fragments of Crinoids, showing that the materials of which they are
composed had been subjected to the action of the sea before being
consolidated into rock. In other
cases, especially among some of
the Crinoidal limestones of the Me-
sozoic period, the Crinoids seem to
have grown on the spot where the
limestone was deposited. Very
generally, the Crinoidal fragments
are sufficiently large and well pre-
served to be readily recognised,
even with the unassisted eye ; but
even when they have been greatly
abraded and worn down, their pres-
ence can usually be detected with-
out difficulty by an examination of
thin sections by means of the mi- = yess aN BES:
croscope. By this method it is, at Fig. 7.—Section of Crinoidal limestone,
any rate, almost always possible to from the Devonian (Hamilton Formation)

: z of Canada, enlarged ten times. The matrix
determine whether or not a given in which the Crinoidal fragments are en-

fragment is Echinodermal, since (Onicinal) Rasa sue caereets. ey)
the minute structure of the skele-
ton in the animals of this group is highly characteristic.

None of the members of the great series of the Annulose Animals
can be said to play a very important part in the formation of lime-
stones. Apart from the occasional presence in limestones of the
calcareous cases of the Tubicolous Annelides, almost the only
Annulose animals which ever contribute to lime-making are the
Crustacea. In some cases, however, the calcareous crusts of certain
groups of Crustaceans (particularly the Trilobites and the Ostra-
codes) constitute a noteworthy element in the composition of lime-
stones.

On the other hand, the two existing groups of the Molluscoids—
viz., the Polyzoa and the Arachiopoda, have both been extensively
concerned in lime-making. In many of the Paleozoic limestones, the
remains of /olyzoa constitute a conspicuous feature, though they
cannot be said to form the bulk of the rock. In some of the
Secondary and Tertiary limestones, however, the rock is really made
up to a predominating extent of the calcareous skeletons of Poly-
zoa. Well-known examples of such so-called “ Coralline limestones ”
are found in the Upper White Chalk of the continent of Europe,
and in the “Coralline Crag” (Pliocene) of Suffolk and Norfolk.
The Brachiopods, again, exerted their greatest activity as lime-
makers during the Paleozoic period, many of the limestones of the
Ordovician, Silurian, Devonian, and Carboniferous periods being

24 INTRODUCTION.

largely made up of the entire or fragmentary shells of animals
belonging to this group.

Still more important are the true Molluscs, the shells of which
have commonly been accumulated to form beds of limestone in all
the great periods from the Ordovician onwards. Some of these
‘* shell-limestones” are composed of the exuvize of sedentary Mol-
luscs, such as Oysters, and have therefore been formed in place.
Excellent examples of such limestones are afforded by portions of
the ‘‘ Muschelkalk” of the Trias of Germany, and the massive
*“ Hippurite limestone” of southern Europe. In other cases, the
limestone is made up principally of the broken fragments of Mol-
luscan shells which have been subjected to the transporting and
abrading action of the sea; and the rock has therefore been formed
in a manner similar to that in which the ‘“shell-sand” of modern
shores has been produced. In still other cases, again, the limestone
has been formed by the slow accumulation on the sea-bottom of the
shells of ‘‘ pelagic” Molluscs, which live at or-near the surface of
the sea, and the skeletons of which fall to the bottom on the death
of their owners. Of this nature are the ‘‘ Pteropodal ooze” of the
present period and the “ Pteropodal limestones” associated with

Ee \
=

Fig. 8.—Section of a Pteropodal limestone, Fig. 9.—Section of a Tertiary limestone
made up of the shells of Styliola fissurelia, (‘‘ Leitha-kalk”’), from Nussdorf, near Vienna,
Hall, from the Devonian (Genesee Slates), composed almost entirely of fragments of
Canandaigua, United States. Enlarged Nullipores cemented together by a crystalline
twenty times. (Original.) matrix. Enlarged three times. (Original.)

uplifted coral-reefs. Similar “‘ Pteropodal limestones ” are known to
occur even in deposits as old as the Devonian (fig. 8), but they are
of rare occurrence and are usually of small thickness. Lastly, it
is to be noticed that limestones may be formed as well by fresh-

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 25

water Molluscs as by those which inhabit the sea. The recent
“‘shell-marls”” are examples of deposits of this nature, and various
Tertiary and Secondary limestones are more or less extensively
charged with the shells of fresh-water Gastropods and Bivalves.

Finally, it is to be noted that animals are not the exclusive agents
concerned in the building up of limestones. Certain of the calcare-
ous Algze—such as the ‘“ Corallines,” the ‘‘ Nullipores,” and the
singular family of the Dactyloporide—are capable, singly or in com-
bination with other organisms, of forming accumulations of lime,
sometimes upon a most extensive scale. The two latter groups, in
particular, have given rise to vast masses of limestone. Examples
of the Dactyloporide occur even in the Paleozoic limestones, but
the most famous and most extensive deposit formed by 4/ege of this
group is the well-known “ Gyroporella-limestone” of the Bavarian
and Tyrolese Alps, the age of which is Triassic. Limestones formed
more or less largely of ‘‘ Nullipores” (Lzthothamnion) occur to some
extent in the Secondary rocks, and are extensively developed in the
Tertiary series. The most famous of these is the ‘“ Nulliporen-
kalk” or ‘“‘ Leitha-kalk” of the Vienna basin (fig. 9), which attains
a considerable thickness, and extends from Austria, through the
Balkans, to Asia Minor and Persia.

In connection with the subject of the constitution of the ordinary or-
ganic limestones, the researches of Dr Sorby on the precise chemical
composition of calcareous organisms demand a brief notice. The car-
bonate of lime in calcareous organisms exists sometimes in the condition
of avagonite, sometimes in that of calcite. The chief differences between
these two allotropic conditions of calcium carbonate are: (1) that calcite
is optically uniaxial, whereas aragonite is biaxial; (2) that calcite has a
specific gravity of about 2.72, whereas the density of aragonite is 2.93;
and (3) that aragonite is harder than calcite, as shown by the fact that
the former will scratch a crystal of Iceland spar along the line of the
short diagonal of one of the crystalline facets, whereas the latter will not
do so. In the second place, the composition of the skeleton of calcareous
organisms varies in different groups, some having a skeleton wholly of
calcite and others wholly of aragonite, while in some cases the skeleton
is composed in part of calcite and in part of aragonite. The following
table shows the principal variations in this respect, as determined by the
researches of Sorby :—

1. Foramintfera.—The test of the calcareous Foraminifera appears to
be in general composed of calcite, though a certain amount of aragonite
seems to be sometimes present. [In the porcellanous /oramunzfera the
test is very probably wholly composed of aragonite. ]

2. Madreporaria.—The true Corals have the skeleton composed,
mainly or wholly, of aragonite.

3. Alcyonaria.—The skeleton of the Alcyonarian Corals is mainly of
calcite, but with indications of the presence of a small amount of aragon-
ite or phosphate of lime.

4. Echinodermata.—The skeleton is always composed essentially of
calcite.

26 INTRODUCTION.

5. Annelida.—The skeleton seems to be always composed of calcite.

6. Crustacea.—The shell of the Crustaceans is mainly composed of
calcite, with a variable intermixture of phosphate of lime.

7. Polyzoa.—The skeleton of the calcareous Polyzoa consists of a vari-
able intermixture of calcite and aragonite, the two inseparably blended
together.

8. Brachiopoda.—The shell appears to be always composed of calcite
[sometimes with a considerable proportion of phosphate of lime].

9. Lamellibranchiata.—The shell of the Bivalve Molluscs is often com-
posed wholly of aragonite, but in other cases (e¢.g., Oysters and Scallops)
itis wholly of calcite, while in others (¢.g., in Mussels, Pzzua, &c.) the
shell has an outer layer of calcite and an inner layer of aragonite.

10. Gastropoda.—Most Univalve Molluscs have the shell wholly com-
posed of aragonite, but some (such as Patella, Fusus, Littorina, and
Purpura) possess an outer layer of calcite and an inner layer of
aragonite.

11. Cephalopoda.—The shells of Cephalopods appear to be mainly
composed of aragonite.

The above-mentioned variations in the chemical composition of the skele-
ton of calcareous organisms have been shown by Sorby to be associated
with important differences as to the condition of preservation of these
skeletons as fossils. It has been shown, namely, that aragonite is rela-
tively much less s¢aédde than calcite. Calcite has no tendency, under any
natural circumstances, to pass into the condition of aragonite ; aragonite
very readily passes into the condition of calcite. Hence in the processes
connected with fossilisation, calcareous skeletons composed of aragonite
are much more liable to undergo alteration, replacement, or even dissolu-
tion, than are those composed of the more stable calcite. It is for this
reason that the shells of Gastropods and Lamellibranchs—which are
commonly composed entirely of aragonite—are so often found as fossils
in the condition of mere “casts,” the original shell having been wholly
removed by solution, or having been replaced by a pseudomorph com-
posed of irregularly placed (unoriented) crystals of calcite. For the
same reason, in cases where the shell consists in part of aragonite and
in part of calcite, it is common for the aragonite layer to have been re-
moved, while the calcite layer has been preserved.

Before leaving the subject of limestones, it may be advisable to
notice briefly the more important differences as regards chemical
constitution or minute structure which give rise to special types of
limestone, and which not infrequently have a paleontological signifi-
cance. ‘The differences here specially alluded to may be considered
under the following heads :—

(1.) Lithological Nature-—Many of the differences which dis-
tinguish particular varieties of limestone concern simply the mineral
nature of the rock, and are of no special importance from a palzon-
tological point of view. ‘Thus, many limestones are more or less
extensively made up of angular quartz-grains embedded in a matrix
of crystalline calcite (fig. 2, B), the rock becoming an avenaceous lime-
stone. There are innumerable links, in fact, between what may be
called a “‘ calcareous sandstone” and a true “ limestone” containing

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 27

a small number of scattered grains of quartz. In other cases more
or less silicate of alumina is present, and the rock becomes an azgi/-
Zaceous limestone, passing, in extreme cases, into a ‘calcareous
shale.” In other cases, again, the limestone may be more or less
highly charged with minute particles of carbon, or may be more or
less impregnated with certain hydrocarbons, the rock becoming a
carbonaceous limestone or a bituminous limestone, as the case may be.
The term ‘‘marble” is one of no very precise signification, any
limestone which is sufficiently hard and compact to take a high
polish being usually spoken of under this name. ‘“‘ Chalk,” again,
from a purely lithological point of view, is a soft pulverulent lime-
stone, but it is occasionally quite hard and compact; and its truly
essential characters depend upon its organic structure, which will be
more fully considered later on.

(2.) Chemical Constitution—The most important variation in
limestones, from a chemical point of view, is established by the
presence in the rock of more or less carbonate of magnesia. The
presence of a certain amount of magnesia in a limestone is a very
common phenomenon, and often only admits of detection by means
of chemical analysis. Limestones which contain a variable and
comparatively small amount of carbonate of magnesia are spoken of
as “magnesian limestones,” and they often differ little or not at all
from ordinary limestones in either appearance or structure. Where
there is a notable proportion of carbonate of magnesia present, the
limestone often assumes a brownish or yellowish colour, with a
sandy aspect, while it shows a marked tendency to undergo
secondary crystallisation. This is shown in some cases by the
development of a concretionary structure in the rock, the so-called
“concretions” being truly the result of an imperfect form of crystal-
lisation. Thin sections, also, of such magnesian limestones invari-
ably show that the rock has undergone more or less extensive re-
crystallisation, subsequent to consolidation; and the organic fragments
originally present in the rock have been thereby more or less largely
obscured, or, it may be, completely obliterated. Owing, further, to
the comparative insolubility in water of carbonate of magnesia as
compared with carbonate of lime, the larger calcareous organisms
(such as the shells of Molluscs) in the more highly magnesian lime-
stones have been commonly dissolved out of the rock, and are now
only represented by casts and moulds. Where the carbonate of
magnesia is present in a limestone in such quantity as to form with
the carbonate of lime a true double carbonate, the rock is what is
strictly called a “‘ dolomite.” The true dolomites, when examined
microscopically, are always found to be more or less intensely crys-
talline. In some cases the recrystallisation to which the rock has
been subjected subsequent to its original formation has not been

28 INTRODUCTION.

sufficient to absolutely destroy any organic remains present in the
rock. Thus, in the dolomites of the Guelph formation (Silurian) of
Canada, the presence of fossils can commonly be recognised in thin
sections, though these have always undergone more or less secondary
change, and have usually been replaced by calcite or by peroxide of
iron, or are represented simply by vacant spaces in the rock. On
the other hand, in many dolomites (fig. 10) secondary crystallisation
has been as complete as in statuary marble, and any organic remains
which may have existed in the rock to begin with have been totally
obliterated.

With regard to the origin of magnesian limestones, it is sufficient
here to say that those in which magnesia is present in comparatively
small quantity probably owe their peculiarities to the conditions
under which they were originally deposited ; and there are even true
dolomites in which there is ground for thinking that the rock was

KWL RT Gi a
OX ESS 7) Ex
. SSS ; XQ E
| di Ty \ LIK RAR re

\ ba

ZN ie \ [
Ad 3 S : Ss

Fig. 10.—Thin section of dolomite, from Fig. 11.—Section of oolitic limestone, Car-
Sweden, enlarged ten times. The rock is boniferous, Kershope Foot, enlarged thirty
an aggregate of comparatively large crystals, times. Some of the spheroids have no defin-
which exhibit the characteristic cleavage- ite boundaries, and consist simply of diffuse
lines of carbonate of lime. (Original.) radiating crystallisations. (Original.)

magnesian from the first. In other cases, again, it cannot be
doubted that the rock was originally a normal limestone, and that
‘“dolomitisation ” was the result of secondary changes affecting the
rock subsequent to its original formation.

(3.) Minute Structure.—The most important of the ordinary struc-
tural peculiarities of limestones is what is known as the “ ooftc”
structure. ‘The subject of the oolitic structure of calcareous rocks is
one of great complexity, and the morphological differences which
exist between different oolites are very numerous and highly remark-

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 29

able. It will not, therefore, be possible here to do more than glance
at some of the more salient peculiarities presented by oolitic lime-
stones. Ifa thin slice of any ordinary oolitic limestone be examined
under the microscope, it will be found to exhibit more or less
numerous rounded or oval grains, of variable size, embedded in a
matrix of crystalline calcite (fig. 11). Each oolitic grain, or spheroid,
ordinarily exhibits a more or less obvious structure out of concen-
trically superimposed layers, each layer being composed of minute
crystals of calcite arranged in a radiating manner, with their long
axes perpendicular to the surface. Very commonly there may be
detected in the centre of the grain a larger or smaller foreign body,
such as a grain of quartz or a fragment of some calcareous organism,
which has served as a nucleus round which the spheroid has been
built up. In other cases, no traces of a foreign nucleus can be re-
cognised. According to the view usually entertained, oolitic grains
of the type just described have been produced by ‘the original
deposition of calcite round nuclei gently drifted along by currents of
the ordinary temperature, which caught up more or less of the sur-
rounding mechanical impurities” (Sorby). According to this view,
therefore, the rock was primitively a loosely compacted aggregate of
oolitic grains, along with entire or fragmentary calcareous organisms,
and solidification was a secondary process, due to the percola-
tion through the mass of water charged with carbonate of lime
in solution, and the consequent precipitation of crystalline calcite
in all the vacant spaces between the grains. This view, doubtless,
affords an adequate explanation of the formation of the ordinary
oolitic limestones. There are, however, cases in which it would
rather seem that the formation of the oolitic grains has been due to
secondary crystallisation in an originally normal limestone. Thus,
in certain limestones some of the oolitic grains have no definite
boundaries, but consist simply of diffuse radiate crystallisations,
which may or may not have a central nucleus for their starting-point
(fig. 11). The structure just alluded to must, however, be carefully
distinguished from cases in which the oolitic grains have undergone
recrystallisation at some period posterior to their original formation.
In this latter case, the grains preserve their outlines, but the primitive
radiate and concentric structure is more or less completely destroyed,
and the spheroids consist simply of irregularly placed crystals of
comparatively large size.

In all the fossiliferous formations, from the Ordovician onwards,
oolitic limestones are of common occurrence; but they vary con-
siderably in their more minute characters. In one of the commonest
varieties of oolitic limestones the grains assume a greatly elongated
form, when the name of “spheroids” is hardly applicable to them.
Such elongated grains have been sometimes regarded as owing their

30 INTRODUCTION.

shape to pressure, but it does not appear that this is an adequate
explanation, and their mode of origin is still obscure.

(4.) Superinduced Structure-—There are probably no limestones,
including even those now actually in process of formation, which are
absolutely free from superinduced structural peculiarities of one kind
or another. In a general way, these superinduced peculiarities
depend upon a more or less extensive recrystallisation of portions
of the rock, it being sometimes the matrix of the limestone which is
thus affected, sometimes the included fragments, and sometimes
both. In many cases, the secondary crystallisation of a limestone
may be the result of slow chemical or physical changes, connected
in the main with the percolation through the rock of water holding
carbonic acid or other ingredients in solution. As regards the
organic fragments present in most limestones, these gradual changes
are doubtless much facilitated by the readiness with which aragonite
passes into the condition of calcite. As a general rule, however,
these slow alterations do not affect the structure of the limestone so
profoundly but that the original constitution of the rock is easily
recognisable by suitable methods of examination. In many cases,
on the other hand, and especially among the older limestones of the
earth’s crust, the rock has undergone changes of a much deeper and
more far-reaching character than those above alluded to. The most
prominent of these changes consists in a more or less complete
crystallisation of the rock, leading to a more or less complete oblit-
eration of any fossils which it may have contained. The general
causes which contribute to bring about this thorough crystallisation
of limestones are heat and pressure, singly or together, combined
with the action of percolating water, which is rendered chemically
potent by having certain substances dissolved in it.

That the application of a powerful heat to limestone will cause its
crystallisation is sufficiently exemplified by the well-known pheno-
mena observable in a limestone when intersected by an intrusive
igneous rock. ‘Thus, limestone in the immediate neighbourhood of
a trap-dyke or a mass of granite is found to have been converted
into a crystalline marble, in which, as a rule, no traces of organic
structure can be detected under the microscope. When developed
upon a larger scale, crystalline limestones are usually found in regions
which can be shown to have been subjected to powerful earth-move-
ments, one result of which must have been the application to the
rocks of the region of intense pressure. Usually greater or less
elevation of temperature has co-operated with the pressure in pro-
ducing alterations in the structure of the rocks affected by these
movements. Speaking generally, therefore, we may regard the
‘“‘regional” crystallisation of limestones as due to the application of
great pressure to deeply buried masses of these rocks, raised to a

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. Si

moderately high temperature and impregnated with water holding
more or less powerful chemical agents in solution.

The initial stages of the changes above alluded to can be well
observed in many of the older limestones, where the rock has been
subjected to sufficient pressure to produce crushing and cleavage,
but where crystallisation has been imperfectly or not at all induced.
Some of such limestones show plain signs of intense pressure in the
distortion and partial destruction of their contained organic frag-
ments, as seen in microscopic sections, at the same time that the
mass of the rock has remained free from crystallisation. In other
cases, as in some of the Devonian limestones of Devonshire, not
only are the organic remains in the rock more or less distorted by
pressure, but they have usually undergone recrystallisation, though
this has not been sufficiently intense to render them unrecognisable.
The complete development of the changes here in question is seen
in statuary marble and in the ‘‘ metamorphic” limestones generally,
where a microscopic examination of the rock shows it to be a mere
ageregate of variously-sized crystals of carbonate of lime (or, in the
case of dolomites, of the double carbonate of lime and magnesia),
all traces of organic structure being entirely obliterated (fig. 10). In
some instances (as, for example, in the case of the white statuary
marble of Carrara) it can be shown that such a purely crystalline
limestone was, to begin with, a quite normal limestone, which was in
part caught up in the folds of a mountain-chain, and thus subjected
locally to enormous pressure. In other cases, we have evidence that
a whole region has been subjected to powerful earth-movements, the
pressure evolved in which has been so intense and so widely diffused
that no part of the original limestone has preserved its primary
organic structure. In such cases-—as, for example, in the crystal-
line limestones of the Highlands—adventitious minerals, such as
serpentine, are commonly developed in the rock, showing that active
chemical changes have accompanied the mechanical pressure to which
the rock has been subjected. We must not, however, lose sight of
the possibility that the ‘‘metamorphic” limestones of the Archzean
period (such as the Laurentian limestones of Canada) may owe their
crystalline character and their mineral peculiarities, not to alteration
subsequent to deposition, but to the conditions under which they
were originally formed. It is also to be remembered that in some
cases we meet with beds of granular and crystalline limestone inter-
calated in a series of more or less completely normal limestones,
without there being any obvious reason for the difference. In such
cases, it is probable that the entire series of deposits has been sub-
jected to pressure, and that, owing to slight peculiarities in mineral
or chemical constitution, certain bands have undergone crystallisa-
tion, while others have escaped with nothing more than a certain

1132 INTRODUCTION.

degree of induration. Indeed, even in a single hand-specimen, it is
not unusual to find that some portions of the rock have undergone
complete secondary crystallisation, while others are comparatively
unchanged.

Stliceous Organic Rocks.—We have seen that the calcareous or
lime-containing rocks are the most important group of organic de-
posits, while the sz/ceous or flint-containing rocks may be regarded
as the most important, most typical, and most generally distributed
of the mechanically formed deposits. We have, however, now briefly
to consider certain deposits which are more or less completely formed
of flint, but which nevertheless are essentially organic in their origin.

Silica is probably invariably held in solution in small quantity in
natural waters, whether these be fresh or salt. Small as is the quan-
tity of silica dissolved by rivers or by the sea, there is sufficient of
it to supply material for the flinty skeletons of innumerable organ-
isms, both animal and vegetable; and the accumulation of such
skeletons may, under favourable conditions, give rise to very con-
siderable deposits of siliceous matter. The two principal groups of
animals which secrete a siliceous skeleton, and may thus produce
deposits of silica, are certain forms of the Sponges and the minute
organisms known as the /olycysttna. In a very large number of
Sponges, the skeleton consists of variously shaped needles or “ spi-
cules” of flint, sometimes detached and entirely separate, at other
times more or less closely united with one another. The accumu-
lation of these spicules at the bottom of the sea may give rise to
extensive siliceous deposits, such as have been described by Dr
Hinde as occurring in the Lower and Upper Greensand of Britain.
In some cases the skeletal structures of Sponges which have been
accumulated to form deposits such as those above alluded to, have
undergone comparatively little change, and their presence can be
readily recognised. In other cases, however, these siliceous struc-
tures have undergone much alteration, and their existence cannot be
demonstrated without difficulty. It is known, namely, that there is
a marked difference as regards relative solubility in water between
ordinary crystalline gwar¢z, on the one hand, and the peculiar form
of silica which occurs in the skeletons of animals and plants, on the
other hand. Quartz is relatively a very stable substance, and it is
only in highly heated waters, containing in solution such ingredients
as the alkaline carbonates (as, for example, in the waters of certain
hot springs), that quartz is ever found to be dissolved in large quan-
tity. On the other hand, the silica which forms the skeleton of flint-
secreting animals and plants exists under a peculiar modification
—as “amorphous” or “colloidal” silica—which is comparatively
unstable, and, under suitable conditions, freely soluble in water.
Hence, siliceous deposits formed by the accumulation of the flinty

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 33

skeletons of animals and plants are very liable to be affected by
secondary changes, chiefly due to the percolation of water through-
out their mass. As the main result of these changes, the siliceous
skeletons become more or less extensively dissolved, the percolating
water becoming thus charged with a larger or smaller amount of
silica in solution. This dissolved silica is ultimately redeposited in
the solid form, having, however, now lost its organic structure. By
this partial solution of the skeletons of siliceous organisms, and the
subsequent precipitation of the dissolved silica thus obtained, we
may explain the common presence of nodules or beds of “ flint” or
“chert” in many of the great geological formations. This subject
will, however, be treated of in greater detail in connection with the
paleontological history of the Sponges.

The Polycystina are minute organisms belonging to the Pro/ozoa,
and nearly related to the Foraminifera, from which they differ,
among other characters, by the fact that they secrete a ‘‘ test” or
skeleton of flint instead of one composed of lime. The Polycystina
have a wide distribution in our present seas, and their skeletons are
very generally recognisable, in greater or less numbers, in the deep-
sea muds of the great oceans, being easily recognised by their
exquisite shape, their glassy transparency, the general presence of
longer or shorter spines, and the sieve-like perforations in their walls.
In many places, in fact, especially in the colder portions of the great
oceans, or at very great depths, the “‘ Globigerina ooze” disappears,
and its place is taken by a “ Radiolarian ooze” composed almost
wholly of the shells of Polycystina. Similar deposits, made up of
the flinty skeletons of these Radiolarians, have been formed at pre-
vious periods of the earth’s history, and now form part of the earth’s
crust. ‘The two most famous of these deposits occur in Barbados
and in the Nicobar Islands, the former being well known to workers
with the microscope as the “ Barbados earth” (fig. 12).

In addition to flint-producing animals, we have also the great
group of fresh-water and marine microscopic plants known as
Diatoms, which likewise secrete a siliceous skeleton, often of great
beauty. The skeletons of Diatoms are found abundantly at the
present day in lake-deposits, guano, the silt of estuaries, and in the
mud which covers many parts of the sea-bottom; they have been
detected in strata of great age; and in spite of their microscopic
dimensions, they have not uncommonly accumulated to form de-
posits of great thickness, and of considerable superficial extent.
Thus the celebrated deposit of ‘tripoli” (‘‘ Polir-schiefer”) of
Bohemia, largely worked as polishing-powder, is composed wholly,
or almost wholly, of the flinty cases of Diatoms, of which it is cal-
culated that no less than forty-one thousand millions go to make up
a single cubic inch of stone. Another celebrated deposit is the so-

VOL. I. (C:

34 INTRODUCTION.

called “ Infusorial earth” of Richmond in Virginia (fig. 13), where
there is a stratum, in places thirty feet thick, composed almost
entirely of the microscopic shells of Diatoms.

In addition to deposits formed of flint itself, there are other
siliceous deposits formed by certain s¢/cates, and also of organic

Fig. 12.— Shells of Polycystina from Fig. 13.—Cases of Diatoms in the Rich-
‘‘ Barbados earth”; greatly magnified. mond “ Infusorial earth”; highly magni-
(Original.) fied. (Original.)

origin. It has been shown, namely—by observations carried out
in our present seas—that the shells of /oraminifera are liable to
become completely infiltrated by silicates (such as “ glauconite,” or
silicate of iron and potash). Should the actual calcareous shell
become dissolved away subsequent to this infiltration—as is also
liable to occur—then, in place of the shells of the Foraminifera, we
get a corresponding number of green sandy grains of glauconite, each
grain being the cas¢ of a single shell. It has thus been shown by Dr
W. B. Carpenter that the green sand found covering the sea-bottom
in certain localities (as found by the Challenger expedition along the
line of the Agulhas current) is really organic, and: is composed of
casts of the shells of Horaminifera. Long before these observations
had been made, it had been shown by Professor Ehrenberg that the
green sands of various geological formations are often composed in
part of the internal casts of the shells of Hovaminifera ; and we have
thus another and a very interesting example how rock-deposits of
considerable extent and of geological importance can be built up by
the operation of the minutest living beings.

Carbonaceous Deposits —It only remains in connection with the
general subject of the organically formed rocks to shortly consider
the rock-deposits in which carbon is found to be present in greater
or less quantity. In the great majority of cases where rocks are
found to contain carbon or carbonaceous matter, it can be stated
with certainty that this substance is of organic origin, though it is

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 35

not necessarily derived from vegetables. Carbon derived from the
decomposition of animal bodies is not uncommon ; though it never
occurs in such quantity from this source as it may do when it is
derived from plants. Thus, many limestones are more or less highly
bituminous ; the celebrated siliceous flags or so-called ‘‘ bituminous
schists” of Caithness are impregnated with oily matter apparently
derived from the decomposition of the numerous fishes embedded in
them ; Silurian shales containing Graptolites, but destitute of plants,
are not uncommonly “anthracitic,” and contain a small percentage
of carbon derived from the decay of these zoophytes ; whilst the
petroleum so largely worked in North America has not improbably
an animal origin. That the fatty compounds present in animal
bodies should more or less extensively impregnate fossiliferous rock-
masses, is only what might be expected; but the great bulk of the
carbon which exists stored up in the earth’s crust is derived from
plants ; and the form in which it principally presents itself is that of
coal. We shall have to speak again, and at greater length, of coal,
and it is sufficient to say here that all the true coals, anthracites, and
lignites, are of organic origin, and consist principally of the remains
of plants in a more or less altered condition. The bituminous shales
which are found so commonly associated with beds of coal, also derive
their carbon primarily from plants; and the same is certainly, or
probably, the case with similar shales which are known to occur in
formations younger than the Carboniferous. Lastly, carbon may
occur as a conspicuous constituent of rock-masses in the form of
graphite or black-lead. In this form it occurs in the shape of detached
scales, or of veins or strings, or sometimes of regular layers ; and
there can be little doubt that in some instances it has an organic
origin, though this is not capable of direct proof. When present,
at any rate, in quantity, and in the form of layers associated with
stratified rocks, as is sometimes the case in the Laurentian formation,
there seems to be considerable probability in the hypothesis which
would regard it as primarily of organic origin and as of the nature of
an altered coal.

36

Cita Bel Bay oer

SUCCESSION OF FORMATIONS—CONTEMPORANEITY
OF STRATA—GEOLOGICAL CONTINUITY.

DIFFERENT AGES OF THE AQUEOUS ROCKS.

THE two principal tests by which the age of any particular bed, or
group of beds, may be determined, are superposition and organic
remains—a third test being sometimes afforded by mineral char-
acters. The first and most obvious test of the age of any aqueous
rock is its relative position to other rocks. Any bed or set of beds
of sedimentary origin is obviously and necessarily older than all the
strata which surmount it, and younger than all those upon which it
rests. It is to be remembered, however, that superposition can at
best give us but the vedative age of a bed as compared with other
beds of the same region. It cannot give us the adsolute age of any
bed ; and if we are ignorant of the age of any of the beds with which
we may be dealing, we have to appeal to other tests to learn more
than the mere order of succession in the particular region under
examination. Moreover, deposits formed in isolated basins, and
not in an area of continuous sedimentation, have necessarily no
stratigraphical relations to deposits laid down in other areas, and
their age can only be determined by palzontological tests. This
difficulty, as pointed out by Professor C. A. White, is enhanced
when such isolated sediments have been produced within inland
SJresh waters ; since such sediments, from their mode of formation,
can have no place in any observed order of superposition of marine
deposits, and would, in addition, necessarily contain wholly different
fossils as compared with beds laid down in the sea.

The second, and in the long-run more valuable, test of the age
of the different sedimentary beds, is that afforded by their organic
remains. Still, this test is also by no means universally applicable,
nor in all cases absolutely conclusive. Many aqueous rocks are
unfossiliferous through a thickness of hundreds, or even thousands,

DIFFERENT AGES OF THE AQUEOUS ROCKS. 37

of feet of little altered sediments ; and even amongst beds which do
contain fossils, we often meet with strata of a few feet or yards in
thickness, which are wholly destitute of any traces of life. Many
fossils, again, range vertically through many groups of strata, and in
some cases even through several formations. Such fossils, there-
fore, if occurring by themselves, or considered apart from other
associated organisms, are not conclusive as to the age of any par-
ticular set of beds. As the result, however, of combined palzeonto-
logical and geological researches, it is now possible for us to divide
the entire series of stratified deposits in any given region into a
number of definite rock-groups or formations, each of which is
characterised by possessing an assemblage of organic remains which
do not occur in association in any other formation. Such an
assemblage of fossils, characteristic of any given formation, repre-
sents the Ze of the particular period in which the formation was
deposited. It follows from this, that whenever we can get a group
or collection of fossils from any particular bed or set of beds, there
is rarely any difficulty in determining, as regards the particular region
under examination, the precise geological horizon of the beds in
which the fossils occur.

With certain limitations, however, we may go much further than
this. Not only are the great formations characterised by special and
characteristic assemblages of animals and plants; but, in a general
way, each subdivision of each formation has its own peculiar fossils,
by which it may be recognised by a skilled worker in paleontology.
Whenever, for instance, we meet in Britain with the fossils known as
Graptolites, we may be sure that we are dealing with Cambrian,
Ordovician, or Silurian rocks. We may, however, go much further
than this. If the Graptolites belong to certain genera, we may be
sure that we are dealing with Ordovician rocks. Furthermore, if
certain special forms are present, we may be even able to say to
what exact part or subdivision of the Ordovician series they belong.

All these conclusions, however, would have to be accompanied
by a tacit but well-understood reservation. No Graptolites have
ever been found in Britain out of rocks known upon other grounds
to belong to one or other of the three formations above mentioned ;
but there is no reason why they might not at any time be found in
younger deposits. In the same way, the species and genera which
we now regard as characteristic of the Ordovician, might at any
time be found to have survived into the Silurian period. We
should never forget, therefore, in determining the age of a rock by
palzeontological evidence only, that we are always reasoning upon
generalisations which are the result of experience alone, and which
may at any time be overthrown by fresh discoveries.

There is, moreover, another important principle to take into

38 INTRODUCTION.

account in considering the value of fossils as tests of the age of
strata. Within a given area of such dimensions that we may sup-
pose it to have formed a single life-province, we shall undoubtedly
find that there is a recognisable succession of life-forms, so that
particular groups of rocks may be safely assigned, on the strength
of their contained fossils, to fixed places in the geological series, and
a definite chronological succession of the strata may thus be estab-
lished for the region examined. When we come, however, to com-
pare together the successive life-forms of widely remote areas, which
must be supposed to have always belonged to different life-provinces,
we cannot expect to find anything like a fvecise identity. We
shall probably be able to establish a general correspondence or
analogy, sufficient to establish a general parallelism of the successive
groups of strata in the two regions compared ; but it can only be in
exceptional circumstances that the fauna of a particular series of beds
in one region can possibly be largely identical with that of a coeval
series in a widely distant region. ‘This principle is sufficiently estab-
lished by the simple consideration that the assemblages of animals
now existing simultaneously in different regions are so unlike each
other that we can by their means divide the earth’s surface into a
number of definitely bounded ‘zoological provinces,” and that there
is every reason to suppose that similar life-provinces have existed in
all the great geological periods of which the paleontological history
has been preserved. If, on the other hand, we were to find that
the rocks deposited in any particular period of the earth’s history con-
tained absolutely identical fossils in all parts of the world, we should
be forced to conclude that during that period there were no “‘ zoologi-
cal provinces” developed, but that the entire terrestrial surface con-
stituted a single vast life-province inhabited by the same kinds of
animals and plants. Nothing that we have of actual evidence, de-
rived either from the past or the present, would, however, support
such a supposition ; but this point will be more clearly brought out
in dealing with the “‘contemporaneity ” of strata in different regions.

GENERAL CHRONOLOGICAL SUCCESSION OF THE
STRATIFIED ROCKS.

As the result of observations made upon the superposition of
rocks in different regions, from their mineral characters, and from
their included fossils, geologists have been able to divide the series
of the stratified rocks into a number of different divisions or “ rock-
systems,” each characterised, in any given region, by a general
uniformity of mineral composition and by a special and peculiar
assemblage of life-forms, and each representing a “period” in the
earth’s history. In every country in the world that has been geo-

CHRONOLOGICAL SUCCESSION OF STRATIFIED ROCKS. 39

logically investigated, such a chronological succession of the stratified
rocks has been established, but the order of succession is not neces-
sarily identical even in regions geographically close together. On
the contrary, as above pointed out, a comparison of the succession of
the stratified deposits in two regions widely remote from one another
in space will show that, though a general parallelism will exist, the
corresponding rock-groups in the two regions will not contain
absolutely identical fossils, and that certain rock-groups which are
present in one region are absent in the other. In no one region,
therefore, do we meet with an absolutely complete and continuous
succession of stratified rock-groups, nor could such ever have been
laid down except in a region which had been continuously beneath
the sea and constantly the seat of sedimentation since the beginning
of geological time. At all times of which we have geological rec-
ord, the earth’s surface has, however, consisted partly of dry land
and partly of sea, and the terrestrial and marine areas have simply
undergone displacement and have been changed in position from
time to time. During each successive epoch, therefore, certain areas
have been the seat of sedimentation, while others have been dry land ;
but the dry land of one period may become the sea of the next, and
vice versa, and sedimentation is thus transferred in the course of ages
from one place to another. Hence when we meet with a stratified
deposit in one region (A) which has no representative in an adjoin-
ing region (B), we know that one or other of two things has occurred.
In the first place, B may have been dry land while A was beneath
the ocean. In that case, the missing deposit was never laid down in
B at all. Or, in the second place, both of the areas may have been
under the sea simultaneously, and the deposit in question may have
been originally laid down in both; but A may have remained con-
tinuously under water, while B may have been elevated to form dry
land, undergoing in process of elevation sufficient denudation to
destroy the deposit in question.

By a comparison of many different areas, geologists have been en-
abled to frame a general order of succession of the stratified rocks,
which, though based originally upon the facts observed in Europe, is
nevertheless, zz z¢s main outlines, applicable to other and widely
distant regions. ‘This general succession is diagrammatically shown
in the annexed ideal section of the crust of the earth. The most
ancient of all the stratified rocks are more or less intensely crystalline
in character, and no undoubted fossils have hitherto been detected
in them. They are grouped together under the general name of the
Archean rocks, and comprise several rock-systems, of which the best
established is the Laurentian series of North America and of Europe.
All the rock-groups above the Archzan are more or less richly
fossiliferous, and are divided into three main “ groups,” each com-

40 INTRODUCTION.

IDEAL SECTION OF THE CRUST OF THE EARTH.
: IMGs 2g

Quaternary and Recent.

6) ;
= Pliocene.
Oo
N
© °
Z Miocene.
=<
4
Eocene.
Cretaceous.
O
—
fe)
N
3
3 Oolitic or Jurassic.
=
Triassic.
Permian.
2o 8 O40 F006 7002509000
oO Sa Se SO SO SS 05 Co ee
oar Rae Carboniferous.
|
S)
_—
S
© Devonian, or Old Red Sandstone.
=
a
Ax
Ordovician and Silurian.
VOL LSP Led LEELA ppd,
LLC ST LILI EAT gh Cambrian.
Huronian.
Z,
=<
:
g Laurentian.
<ac!

prising several smaller divisions or ‘“‘ systems.” The oldest group
comprises the Cambrian, Ordovician, Silurian, Devonian, Carbonif-
erous, and Permian “systems,” which are spoken of as the Przmary

CHRONOLOGICAL SUCCESSION OF STRATIFIED ROCKS. 4I

or Paleozoic rocks (Gr. palaios, ancient ; z0e, life), because of the
wide divergence of their animals and plants from any now existing
upon the globe. The Triassic, Jurassic, and Cretaceous systems are
grouped together as the Secondary or Mesozoic formations (Gr. mesos,
intermediate ; zoe, life), because their organic remains are interme-
diate between those of the Paleozoic period, and those of more
modern strata. ‘The Eocene, Miocene, Pliocene, and Pleistocene
rocks are grouped together under the head of Zertiary or Kainozoic
rocks (Gr. kaznos, new ; z0e, life), because the fossil animals and
plants which they contain approximate in character to those now
existing upon the globe.

According to the recommendations of the International Geological
Congress, the following names should be employed for the larger and
smaller divisions of the stratified rocks and the time-divisions to which
these correspond, the terms being arranged in order of their compre-
hensiveness.

Divisions of sedimentary Corresponding chrono-
Jormations (“ terranes”). logical terms.
Group. Era.
System. Period.
Series (or Section). Epoch.
Stage (or Beds). Age.

The term “ formation,” very commonly employed by British geologists,
is perhaps best retained as a loose general term to indicate any set of
beds, large or small, which have some common characteristic, either as
to mineral nature or fossil contents, or as to the mode in which the de-
posit has been formed. If used in a definzte sense, it should be employed
with reference to the mode of formation or the lithological nature of the
rocks ; so that we may suitably speak of the “ Chalk Formation,” or
the “Coal Formation,” or of a “marine formation,” or a “lacustrine
formation.”

The following table exhibits the great geological “systems,” as
developed in Europe, in chronological order, beginning with the
youngest, the more important and typical British representatives of
each being likewise mentioned :—

GENERAL CLASSIFICATION OF POST-ARCHZAN FOSSILIFEROUS
DEPOSITS.

I. RECENT FORMATIONS.—Deposits now in process of formation
in seas, rivers, and lakes, and on land, such as the sands and
muds of shallow seas, modern calcareous deposits like shell-
beds, coral- reefs, &c., deep-sea muds, shell-marls, river-
gravels, peat-mosses, &c.

2. QUATERNARY OR PLEISTOCENE FORMATIONS.—Post-glacial,
Glacial, and Pre-glacial deposits, in which the Molluscs be-
long to existing species, but some of the Mammals are refer-
able to extinct forms. Often grouped with the preceding
under the general name of the “ Post-tertiary deposits.”

ROUP.

~
I

TARY aC

KAINOZOIC OR TER-

TS
N

KAINOZOIC OR TER-
TIARY GROUP.

MESOZOIC OR SECONDARY GROUP.

PALOZOIC GROUP.

IO.

Il.

12.

13s
14.

INTRODUCTION.

. PLIOCENE SYSTEM.—(British representatives, the Norwich

Crag, and the Red and White Crags of Suffolk.)

. MIOCENE SySTEM.—(The Upper Miocene or “ Falunian”

series and the Middle Miocene or “ Mayencian” series are
wanting or doubtfully represented in Britain. The Lower
Miocene series is often grouped with the Upper Eocene
series aS a Separate system, under the name of O/zgocene,
represented in Britain by the Hempstead, Bembridge,
Osborne, and Headon beds.)

. EOCENE SYSTEM.—(British representatives, the Barton Clay,

Bagshot and Bracklesham beds, London Clay, Thanet
Sands, &c.)

. CRETACEOUS SYSTEM.—(British representatives, the Chalk,

the Upper Greensand, the Gault, the Lower Greensand, and
the Wealden Clays and Hastings Sand. The Lower Green-
sand and Wealden series are commonly grouped together
as the “ Neocomian” series.)

. JURASSIC SYSTEM. —(British representatives, the Purbeck

beds, Portland beds, Kimeridge Clay, Coral Rag, Oxford
Clay, Cornbrash and Forest Marble, Great Oolite, Stones-
field Slate, Fuller’s Earth, Inferior Oolite, and Lias.)

TRIASSIC SYSTEM.—(The uppermost Triassic or “ Rheetic”
beds are feebly represented in Britain by the Penarth beds
and White Lias, and the “ Keuper” and “ Bunter Sand-
stein” of the continent of Europe have corresponding
British representatives. The great marine division of the
““Muschelkalk,” which is largely represented in the Trias
of Germany, is not developed in Britain.)

. DYAS OR PERMIAN SYSTEM.—(The deposits included under

this name are more extensively developed in the European
area than they are known to be in any other region, and it
is doubtful if they can be regarded as a distinct “system.”
The chief British representatives of the Permian rocks are
the Marl-slate and Magnesian Limestone, or “ Zechstein,”
and the Penrith Sandstones or “ Rothtodthegendes.”)

CARBONIFEROUS SYSTEM.—(British representatives, the Coal-
measures, the Millstone Grit series; the Yoredale series,
the Scar-limestone series, and the Tuedian or Cement-
limestone series.)

DEVONIAN SYSTEM. —(The Devonian rocks of Devonshire
are marine, and contain representatives of the Lower, Mid-
dle, and Upper Devonian of the continent of Europe. The
Old Red Sandstone of Scotland and of South-Western Eng-
land and Wales was perhaps deposited in inland waters.)

SILURIAN SYSTEM. — (British representatives, the Ludlow
series, Wenlock series, and May Hill series.)

ORDOVICIAN SYSTEM.—(British representatives, the Bala
series, the Llandeilo series, and the Arenig series.)

CAMBRIAN SYSTEM.—(British representatives, the Tremadoc
series, the Lingula Flag series, the Menevian series, and the
Harlech series. )

EVIDENCE IN STRATIGRAPHICAL GEOLOGY. 43

PALZONTOLOGICAL EVIDENCE IN STRATIGRAPHICAL GEOLOGY.

As regards the division of the entire series of stratified deposits
into the above enumerated primary “systems,” the value of palzeon-
tological evidence has never been disputed. In any given country,
it would be possible, undoubtedly, to determine the order and rela-
tive succession of the great formations, to some extent at any rate,
by a mere appeal to the mineral character and order of superposition
of the rocks themselves ; but it is perfectly clear that this method of
procedure would necessarily break down totally the moment we came
to try and determine which were the corresponding formations in
some far-distant region. By the stratigraphical evidence alone we
could determine the relative position and age, for example, of the
Silurian, Devonian, and Carboniferous systems in Britain; but it
would be an entire impossibility to identify these same systems,
say in North America, except by means of the fossils which they
contain. So far, then, as this goes, no question has ever been
raised as to the value and powers of Paleontology ; but when we
come to consider the minor rock-groups included in these systems,
we find much difference of opinion as to the extent to which the
evidence of the fossils is available in determining stratigraphical hori-
zons. Part of this difference of opinion is due to imperfect acquaint-
ance on the part of stratigraphical geologists with the methods of
paleontological inquiry, and needs no discussion here; but part is
well founded, and either arises from actual defects in the modes of
research employed by paleontologists, or is due to the fact that the
conditions under which different systems, or different portions of the
same system, have been deposited have not been identical, and that
conclusions which might be well founded in one case might be found
to break down in another apparently similar case. To both of these
points a brief consideration may be given.

As regards imperfections in the methods of paleontological re-
search, by far the most important arises from the fact that too
- much weight has been attached by observers, especially in the earlier
periods of the science, to the age of the rocks in which any given
fossil occurred. So long as the opinion was current that fossils occur-
ring in different formations were necessarily different, it followed of
necessity that the smallest and most trivial varietal, or even indi-
vidual, peculiarities of form or structure were considered as sufficient
to establish specific distinction. At present, however, palzeontolo-
gists are tolerably agreed that the mere fact of a difference of physi-
cal position, and consequently of age, ought not to be taken into
account in considering the true affinities and systematic position of
a fossil. At the same time it is, for many reasons, most important
that paleontologists should have a general personal acquaintance

A4 INTRODUCTION.

with the rocks in which occur any fossils that they may have to
examine and describe; and many errors have arisen from the
neglect of this sound rule.

Again, it is now clearly recognised that in any comparison between
two sets of beds by means of their fossils, with a view of ascertain-
ing their relative age, it is essential to take into account ‘the condt-
tions under which the deposits in question were formed. ‘Thus, two
marine deposits, both accumulated in shallow water, can be fairly
and fully compared with one another, but they can only be imperfectly
compared with a deposit formed in a deep sea, and they cannot
be compared at all with deposits which have been formed in inland
fresh waters or on land. Hence we find that paleontologists have
differed, and still differ, widely with regard to the relative value as
tests of the age of strata, to be assigned to different c/asses of fossils.
In certain cases—some of which will be more fully referred to sub-
sequently—a different age would be assigned to a group of beds on
the strength of its vegetable remains to that which would be deduced
from a study of the animal fossils of the same or of associated beds.
Or, the marine Invertebrate fossils in some cases may point to one
age for the beds, while the remains of Vertebrates indicate another.
Such cases must be dealt with on the following general principle :—

Deposits containing numerous land-plants or the bones of terres-
trial Vertebrates are mostly estuarine, lacustrine, or fluviatile in
origin, though in some cases they have been formed on land. On
the other hand, deposits containing marine Invertebrates have been
laid down in the sea itself, for the most part at moderate depths.
There is, however, absolutely no reason for thinking that the succes-
sion of life as regards the land-plants and land-animals of any given
region has been in any way parallel with the evolution of the marine
animals of the seas of the same region. The evolution of the ter-
restrial organisms may have been much more rapid or much slower
than that of the marine forms. Hence, it is quite possible that the
land-plants and land-animals which are regarded as characteristic of
a particular geological period, may be found coexisting with marine
animals which are considered to characterise a different geological
period. If, however, we take the stratified formations as a whole,
we find that it is in the main by means of their marine faunz that
their relative age has been determined, the reason of this being the
obvious one that the great majority of stratified deposits have been
laid down in the sea, and the record of the succession of terrestrial
organisms in time is a very incomplete one. The general chrono-
logical standard, as based upon paleontological evidence, is, there-
fore, founded mainly on the results afforded by the marine Inverte-
brates. In those cases, therefore, in which the marine deposits of a
given series of beds would indicate through their Invertebrate fossils

EVIDENCE IN STRATIGRAPHICAL GEOLOGY. 45

a particular stage in chronological succession, while the fresh-water or
terrestrial deposits of the same series through their vegetable remains
would indicate another, it is to the former that we should give the
precedence as determining the age of the entire series. Such cases
are sometimes spoken of as instances of ‘‘ homotaxis,” but this is not
strictly so. In the particular cases here in question, two sets of beds,
which may have been formed contemporaneously, are found to con-
tain fossils of apparently different geological ages, in consequence of
the fact that the beds have been formed under different conditions, the
one containing the remains of land-plants, and the other the remains
of marine Invertebrates. The apparent difference of age is due to
the fact that the evolution of the land-flora in the particular region
where the beds are found has not been parallel with that of the
marine fauna of the same region. On the other hand, ‘“ homo-
taxial” deposits, properly so called, are deposits which have been
formed during the same geological period, and have been laid down
under similar conditions, thus coming to contain similar classes of
fossils, but which have been formed in regions very far apart. The
similarity, or identity, of the fossils in the two sets of beds proves
them to belong to the same general period ; but their geographical
remoteness is a proof that they were formed at different stages of
this period, and that they were not precisely identical. Together
with the similarity of certain types of life in ‘‘homotaxial” beds,
there is found a dissimilarity as regards other types, this being a
consequence of the fact that the two sets of beds have been formed
in widely distant areas, and therefore in distinct zoological provinces.
In other words, the dissimilarity in the fossils in ‘‘ homotaxial” beds,
in the strict sense of the term, is dependent on the distance in space
of the beds, and is not due to difference of origin.

An excellent concrete example of the above general principle is afforded
by the so-called “ Dakota Beds” of North America. These are largely
developed in the basin of the Upper Missouri, are mainly of brackish-
water or fresh-water origin, and contain a series of plant-remains the
general aspect of which is clearly Tertiary. If judged, therefore, by
purely palzobotanical evidence, the “ Dakota Beds” would be assigned
to the Eocene system. The ‘“ Dakota Beds” are, however, overlain by
some thousands of feet of stratigraphically younger deposits charged
with marine fossils of Cretaceous type. Judged, therefore, by a palzo-
zoological standard, the “ Dakota Beds” must be assigned to the Cre-
taceous period. The explanation of this discrepancy in the age of the
beds as deduced from the plants and animals respectively is apparently
twofold. On the one hand, the “ Dakota Beds” are mainly of fresh-
water origin, whereas the strata by which they are surmounted were laid
down in the sea. On the other hand, we must suppose that the Tertiary
flora had been introduced into the American area at a time when the
seas of the same area were still tenanted by the characteristic animals of
the Cretaceous period, and that the latter were not replaced by the ani-
mals distinctive of the Tertiary period until long after the land-vegeta-

46 INTRODUCTION.

tion had assumed the Kainozoic facies. That the “ Dakota Beds” are
truly of Cretaceous age is further shown by the fact that part of the series
iS marine in origin, and that in it are met with the remains of such
characteristic Cretaceous types of Invertebrates as Ammonites and
Belemnites.

A somewhat more complicated case is that of the so-called “ Laramie
Beds,” or “ Lignitic Series,” of North America. ‘These constitute a series
of beds, of some thousands of feet in thickness, which repose upon strata
with marine fossils of unquestionable Cretaceous type, and are unconform-
ably surmounted by strata containing equally unquestionable marine
Tertiary (Eocene) fossils. The “ Laramie Beds” are admittedly of purely
inland origin, and were probably laid down in a vast brackish-water lake.
The Invertebrate fossils which they contain consist almost wholly of
brackish-water, fresh-water, and terrestrial Molluscs, and the characters
of these are such that they do not afford a decisive test of the age of the
series. The remaining fossils are mostly those of land-plants or of ter-
restrial Vertebrates, and the evidence as to age yielded by these respec-
tively 1s discrepant, the vegetable remains being of distinctly Tertiary type,
while the Vertebrates belong to the characteristic Mesozoic group of the
Dinosaurian Reptiles. When we consider, however, that the evidence
afforded by the “‘ Dakota Beds” and the strata overlying these renders
it certain that the Tertiary vegetation had been introduced into America
at a time when the marine Invertebrates of the Cretaceous period still
existed in full force, we cannot attach much value to the plant-remains
of the “‘ Laramie Group” as indicating a reference of these strata to the
Tertiary period. Adding to this consideration the presence of such.
characteristic Cretaceous Vertebrates as the Dinosaurs, and the further
fact that the Laramie beds are surmounted wzconformably by beds of
unequivocal Eocene age, it seems difficult to resist the conclusion that
these disputed strata are either truly of Cretaceous age, or that they
form a transitional group between the Cretaceous and the Tertiary
systems.

A good example in the European area of the contradictory evidence
sometimes yielded by different classes of fossils as tests of age is afforded
by the “ Pikermi Beds” of Attica. These beds contain an abundance of
the remains of terrestrial Mammals, which have generally been regarded
as of a distinctively Miocene type; and on the strength of this the
‘“‘Pikermi Beds” have been referred to the Upper Miocene period. The
mammaliferous clays of Pikermi repose, however, upon strata containing
marine Molluscs of unquestionable Pliocene type. The explanation of
this appears to be, that the terrestrial Mammals of the Miocene period
had persisted unchanged in the south-east of Europe, while the Miocene
Mollusca of the Mediterranean had been replaced by the later Pliocene
forms. Since it is by the marine Invertebrates that the age of strata can
be most uniformly and most reliably judged, we are thus bound to refer
the “ Pikermi Beds” to the Phocene period.

CONTEMPORANEITY AND HOMOTAXIS.

The discovery of the use of fossils as tests of the age of the sedi-
mentary rocks, and the recognition of the fact that by their means
a chronological succession of the stratified deposits of any particular
region could be established, constituted great advances in geological

CONTEMPORANEITY AND HOMOTAXIS. 47

science, as also in Paleontology itself, but they led at first to erron-
eous generalisations. When it had been clearly established that
particular groups of strata in Europe were characterised by particular
assemblages of animals and plants, it was, not unnaturally, concluded
that similar or identical assemblages of organisms would be found to
characterise corresponding groups of strata all over the world. This
led to the idea that the successive faunze and florze observable in the
area first examined had been wzzversally distributed over the whole
globe ; from which followed the old catastrophistic view that the
close of each geological period had been signalised by a more or less
complete extinction of the animals and plants then in existence, and
that a new fauna and flora had been introduced at the commence-
ment of each succeeding period.

It is, however, now universally admitted that in nature the chron-
ological succession of the rocks, as determined by fossil remains, is
local and not universal—in the sense that the precise order of phen-
omena must necessarily have differed in different regions. That this
must be so is proved by the existence at the present day of ‘ zoolog-
ical provinces” ; by the fact that dry land and sea must always have
existed since the beginning of Palzeozoic time at any rate, and that
sedimentation can, therefore, never have been universal ; and by the
certainty that the sedimentary deposits now in process of formation,
and therefore necessarily coeval, contain the remains of dissimilar
groups of animals and plants.

In view of these considerations, it is necessary to consider what
precise significance is to be attached to the term “‘ contemporaneous ”
as applied to different groups of strata. When groups of beds in
different parts of the earth’s surface, however widely separated from
one another, contain the same fossils, or rather an assemblage of
fossils in which many identical or closely allied species occur, they
are generally said to be ‘‘ contemporaneous ”—that is to say, they
are ordinarily supposed to belong to the same geological period, and
to have been formed at the same time in the history of the earth.
They would therefore be ordinarily regarded as ‘‘ geological equiva-
lents,” and would be classed as Silurian, Devonian, Carboniferous,
and so on. ‘The use of the term “‘ contemporaneous” in the above
comprehensive sense cannot, however, be accepted without serious
qualification. Within the limits of a single geographical area of
moderate size, beds containing identical, or nearly identical, fossils,
may doubtless be safely regarded as strictly “‘ contemporaneous,” since
there is no reason why such should not have been deposited within
one ocean, and during a single geological period. When, on the
other hand, we find precisely identical or even representative species
of fossils in beds which are very widely removed from one another
geographically, there is a presumption that such beds are zo? exactly

48 INTRODUCTION.

contemporaneous, but that they succeeded each other in point of
time, though not necessarily by any very long interval geologically
speaking. The general ground for this presumption is the readily
intelligible one that such beds, if sufficiently far apart, must have
been deposited in different oceans, but that we cannot suppose that
any given species could have been developed to begin with in more
than one ocean. When, therefore, we find identical species in strata
in two widely remote areas, we are forced to conclude that these
species must have appeared sooner in one area than in the other,
and that the one set of strata must be later than the other, if by no
more than the time required for the migration of these species from
their original area to the other.

Most of the facts bearing upon this question may be elicited by a
consideration of such a well-known and widely extended group of
deposits as the marine division of the Carboniferous system, of which
the chief member is the Carboniferous Limestone. This group of
deposits is more or less extensively developed in regions as remote
from one another as Europe, Central Asia, China, Japan, Australia,
South America, and North America; and it is characterised by an
assemblage of distinctive fossils, among which certain species of
Brachiopods are specially noteworthy. Not only are the Carboniferous
Brachiopods in these widely distant areas referable to the same genera
(Producta, Athyris, Streptorhynchus, &c.), but identical species are in
some cases found to range over the greater part of the vast area
occupied by these deposits.‘ Now, if we believe that the Lower
Carboniferous rocks in all these widely distant regions were “‘ con-
temporaneous,” in the sense that they were deposited at precisely
the same time, we should be compelled to admit the existence during
Carboniferous time of an ocean embracing all these points, and, in
spite of its enormous extent, so uniform in temperature, depth, and
the other conditions of marine life, that organisms either the same,
or very nearly the same, inhabited it from end to end. We can,
however, point to no such uniformity of conditions and consequent
uniformity of life over any such vast area at the present day; and we
have, therefore, no right to assume that this is the true explanation
of the facts. Moreover, all that we know of the geographical distri-
bution of recent organisms would prove that these identical species
cannot have been produced simultaneously in all the areas where
their remains are now found, but that they must have been dispersed

1 Among the commoner and more characteristic types of Brachiopods found in
the Lower Carboniferous rocks of Europe, Producta semireticulata, P. longispina,
P. aculeata, P. costata, and Streptorhynchus crenistria occur, along with other
European forms, in the Carboniferous rocks of China (Kayser). All these species,
with the exception of P. costata, have been identified in the Carboniferous deposits
of Australia and India; and all of them occur, with various other European
types, in the Lower Carboniferous rocks of North America.

CONTEMPORANEITY AND HOMOTAXIS. 49

from one or other of these areas, or from some point still unknown ;
and this dispersal must necessarily have consumed a long period of
time. Any other view would lead us almost inevitably to the now
abandoned theory that each period in geological history was char-
acterised by a special group of organisms spreading over the whole
globe, and that there took place at the close of each period a general
destruction of all existing forms of life, and a fresh creation of the
new forms characteristic of the next period.

In our inability, then, to accept this view, we must seek for some
other explanation of the observed facts. The most probable view,
and the one which is supported most strongly both by what we see
at the present day and by what we learn from numerous examples in
past time, is this: The Carboniferous Limestone—to take this mem-
ber of the Lower Carboniferous deposits in particular — was not
deposited all over the world in one given period, by one sea, or at
exactly the same time; so that it cannot be said to be strictly ‘‘ con-
temporaneous ” wherever it is found. ‘This would imply a uniformity
of conditions over vast distances, such as exists nowhere at the present
day, and such as we have no right to assume ever existed. On the
contrary, the deposition of the Carboniferous Limestone must have
first taken place in one comparatively limited area—say in Europe—-
where fitting conditions were present both for the animals which
characterise it, and for the formation of beds of its peculiar mineral
and physical characters. How wide this area may have been, signifies
very little. It may have been as large as the area now covered by
the Pacific, or larger, and yet it could not include all those localities
in which strata of Lower Carboniferous age with identical or repre-
sentative fossils are already known to exist. Under any circum-
stances, some dispersion of the species of the original Carboniferous
area must have been going on by the ordinary processes of migration
from the commencement of the Carboniferous period, but this dis-
persion must have been greatly accelerated towards the close of the
period of the deposition of the Carboniferous Limestone. At this
time the conditions present in the original area must be supposed to:
have become unsuitable for the further existence in that area of the
assemblage of animals which had been its inhabitants, or, at any
rate, for a great many of them. The change from suitable to unsuit-
able conditions must, it is hardly necessary to say, have been an
_extremely slow and gradual one, and would doubtless be connected
with the progressive shallowing of the sea, the diversion of old cur-
rents of heated water, or the incoming of new currents of cold water,
or other physical changes tending to alter the climatic conditions of
the area. What, then, would be the effect of such a change of con-
ditions as we have supposed, upon the animals inhabiting the area ?'
—Some of them would, doubtless, be sufficiently hardy and accom-

VOL. I. D

50 | INTRODUCTION.

modating to bear up under the new state of things ; and these would
persist into the ensuing period, without any perceptible change, it
might be, or more probably in the form of varieties or species allied
to the old ones. In this case, therefore, we should get a certain
number of species which would pass from the Carboniferous Lime-
stone up into the Yoredale series, the Millstone Grit, or the Coal-
measures ; or, if we did not find any species exactly the same in all
these groups, we should still find in the later groups some forms
which would be varieties of those of the older, or which would be
allied or representative species.

There would, in the second place, be a certain number of
species which would be utterly unable to withstand the altered con-
ditions of the area; and these would gradually die out and become
wholly extinct. We should thus get a certain number of fossils
which would be either exclusively confined to the Carboniferous
Limestone in general, or which, perhaps, might not be found out of
the Carboniferous Limestone of a single region, or even of a single
particular locality.

Lastly, some species would yield so far to the altered conditions
of the area that they would “migrate,” and seek elsewhere a more
congenial home. ‘This term is apt to convey false impressions ; and
it will be well here to consider what is meant by the ‘‘ migration” of
species or groups of animals. It is quite obvious that only animals
like birds, mammals, insects, &c., which enjoy when grown up the
power of active locomotion, can actually ‘‘ migrate” in person, sup-
posing they find themselves placed under unfavourable conditions.
There are many animals, however, such as most Molluscs, Corals,
Polyzoans, &c., which have, when adult, either no power of chang-
ing their place, or at best a very limited one. Still in these cases
even, though the zza:vzdual has no means of removing his quarters
to some more favoured spot, there may be a “migration” of the
species from an unsuitable to a suitable locality. This is effected
through the medium of the young, which have the power of choosing
where they will settle, and are endowed with vigorous powers of
locomotion. If, for example, a bed of oysters should become placed
under conditions unsuitable for the development of these Molluscs,
it is clear that the old oysters cannot change their location. The
young oysters, however, swim about freely; and these will move
away from the original bed till they find a place which will suit them.
By a repetition of this process there may be in course of time a
removal or “migration” of a species to almost any distance, irre-
spective of the fact that the adult is permanently rooted.

To return, then, to the case which we have been considering :
When the conditions of life in the seas of the Carboniferous Lime-
stone became unfavourable for the further existence of their fauna,

CONTEMPORANEITY AND HOMOTAXIS. 51

some species would migrate to a more congenial area. In this way
a greater or less number of the species characteristic of the Carbon-
iferous Limestone would ultimately be transferred to some other area.
Here they would mingle with the forms already inhabiting that area,
perhaps more or less completely supplanting these, or perhaps merely
succeeding in maintaining a more or less precarious existence. In
either case, their remains would be preserved in the sedimentary
deposits of the new area. When, ages afterwards, we come to
examine the crust of the earth geologically, we should find these
identical and characteristic species of fossils in the rocks of the two
areas, and we should say—‘‘these rocks are contemporaneous.” It
is clear, however, that we should be wrong in so saying. ‘The rocks
in question would belong to the same geological period, but they
would belong to different stages of the same period, and they would
not be strictly contemporaneous. For deposits of this nature, be-
lieved to hold this relation to each other, the term of “‘ homotaxial ”
has been proposed, in place of the term “‘ contemporaneous.”

What has just been said about the Carboniferous rocks would
apply with equal justice to all the great formations, and to many of
the smaller rock-groups all over the world. The Ordovician and
Silurian rocks of Europe, North America, South America, Australia,
&c., contain very similar fossils, and are undoubtedly “ homotaxial.”
Nothing, however, that we see at the present day can justify us in
believing that these widely separated deposits are strictly ‘‘ contem-
poraneous,” in the sense that they were deposited at exactly the same
period of time. We should have to believe, if this conclusion is to
be justified, that in Ordovician and Silurian times the ocean spread
over a much larger area of the earth’s surface than it does now, and
that its temperature and depth were unnaturally uniform’ and there
are, perhaps, some who would accept this view. What has been
said about the Ordovician and Silurian rocks as a whole, applies
with still greater force to certain of the minor subdivisions of the
same, which contain many of the same specific forms in parts of
the globe very widely removed from one another. It is the very
identity of the fossils, however, which proves that the beds in ques-
tion, from their geographical position, cannot have been deposited
at exactly the same time, though they doubtless belong to the same
period, and may even be said to be related to one another, so far
as their identical fossils are concerned, by lineal descent. Similar
remarks might be made about the Devonian, Permian, Triassic, Ju-
rassic, Cretaceous, and other formations; but it is not necessary
further to multiply examples.

If we consider the present state of things upon the globe, we
shall be further convinced of the justice of these views, which were
first prominently brought forward in Britain by Professor Huxley.

52 INTRODUCTION.

If we could suddenly remove the sea from the earth, we should find
at various points of the earth’s surface deposits of different kinds,
now concealed from us by the ocean, or only partially known by
dredgings or soundings. ‘Thus we should find vast accumulations
of calcareous matter, in the form of coral-rock and coral-reef, where
now rolls the Pacific Ocean. In high northern and low southern
latitudes we should find great deposits of sand and mud, with
angular blocks of stone, the whole derived from the ice-clad regions
of the poles. Over vast areas, again, in. the deep. Atlantic, we
should find an impalpable chalky mud, or “ooze.” All these dif-
ferent deposits are obviously and necessarily ‘‘ contemporaneous,”
not only in the geological acceptation of the word, but in its most
literal sense. In spite of this fact they would not contain the same
fossils ; and, indeed, they would be characterised by organic remains
which would be wholly different in each case. The coral-reefs of
the Pacific would be essentially characterised by the abundance of
the remains of reef-building corals, though they would also present
other tropical forms of life, especially Brachiopods and Echinoderms.
The glacial mud of the Polar regions would contain the remains of
Arctic Molluscs, along with such other animals as delight in severe
cold. Lastly, the ooze of the deep Atlantic would contain innumer-
able Foraminifera, along with siliceous Sponges and Crinoids. We
learn, therefore, from this, that contemporaneous deposits not only
do not necessarily contain the same fossils, but that, if widely sep-
arated geographically, they may be characterised by wholly dissimilar
assemblages of organisms.

It may happen, again, as pointed out by Sir Charles Lyell, that
deposits belonging to different geographical and zoological provinces
may, as regards space, be nearly approximated, and, as regards time,
may be actually contemporaneous, and yet may not contain any fos-
sils in common, or only a very few. If, for example, any sudden
upheaval were to lay bare what is now the floor of the Red Sea, to-
gether with that of the Mediterranean, we should find the two areas
to contain deposits actually synchronous as regards the time of their
deposition, and very near to one another in point of distance, and
yet containing, upon the whole, entirely distinct groups of organic
remains. We learn, therefore, from this, that owing to the exist-
ence of geographical barriers, it is possible for contemporaneous
deposits to be found in close contiguity, in a single region, and yet
to contain very different fossils.

Again, it has been abundantly proved that even within the limits
of a single ocean deposits are now in process of formation which,
though strictly contemporaneous in point of time, nevertheless differ
from one another altogether both in mineral characters and in their
included organic remains. Thus, the mechanical deposits formed

CONTEMPORANEITY AND HOMOTAXIS. 53

on the borders of an ocean, in the neighbourhood of land, differ
wholly in mineral character from the peculiar “muds” formed in
the profound depths of the same ocean ; an equal difference existing
as to the character of the animals buried in each. We thus learn
that marine deposits may be strictly contemporaneous, and may be
placed near to one another in point of distance, and yet may be
wholly unlike both lithologically and zoologically. Lastly, synchron-
ous deposits necessarily contain wholly different fossils, if one has
been deposited by fresh water and the other has been laid down in
the sea. ‘The fresh-water deposits of one period are obviously con-
temporaneous with the marine formations of the same period, and
they may not be far removed from one another in point of distance,
but they must contain altogether different organic remains. ‘The
former will contain remains of the fresh-water and terrestrial animals
of the period, and of these only ; whilst the latter will principally, if
not exclusively, be characterised by the remains of marine forms of
life. In this way, there is reason to believe, may be explained the
differences between the fossils of the Old Red Sandstone and of the
Devonian rocks, strictly so called. Both are believed to have been
deposited in the same geological period, and to be truly “ contem-
poraneous”; but they do not contain the same fossils. This may
be readily explained, however, if we suppose the former to represent
the fresh-water deposits of the Devonian period, or to have been laid
down in an inland sea, whilst the latter is the true marine formation
of the same period.

In the strictest sense, then, of the term, deposits may be spoken
of as “‘homotaxial” when they contain identical or closely allied
fossils, but have nevertheless not been laid down at precisely the
same time. If such deposits are widely separated from one another
in space, then the possession of identical fossils is a direct argu-
ment in favour of a want of absolute contemporaneity—suppos-
ing that the deposits compared have been formed under similar
conditions, in which case alone a complete comparison is possible.
Thus, the Lower Carboniferous rocks of Britain, Russia, China,
and North America are all marine in origin; and the fact that
they contain identical species of Brachiopods is thus an argument
in favour of the view that they were not formed at freczse/y the
same time, since they are so widely apart that they cannot be re-
garded as having been simultaneously laid down within the limits of
a single ocean. Nevertheless, the deposits in question were laid
down in the same geological period, and are therefore “ geological
equivalents.” The doctrine of “ homotaxis,” therefore, if rightly
limited and defined, in no way diminishes the value of fossils as indi-
cative of the age of the formations in which they occur. If we
give the term “ contemporaneous” a purely geological sense, and

54 INTRODUCTION.

endeavour to forget its literal signification as applying to events
which have occurred at precisely the same moment of time, then it is
just as good an epithet for the different deposits belonging to a given
geological formation as is the term “ homotaxial.” All the de-
posits which possess Carboniferous fossils, at whatever point of the
earth’s surface they may be situated, belong to the Carboniferous
period, and are therefore geologically contemporaneous. All that is
really implied by the doctrine of “ homotaxis,” rightly regarded, is
that we cannot say that any great formation in any one country is
the precise equivalent of the same formation in any country very
widely removed in point of distance, in the sense that its deposition
began and ended at exactly the same times; and therefore we can-
not parallel the subdivisions of such formations with anything
approaching to absolute precision. Regarded as a whole, however,
the Carboniferous formation of America is the geological equivalent
of the Carboniferous formation of Europe, and both belong to what
geologists understand as the ‘‘ Carboniferous period.” As the same
is true of all the great formations, in all parts of the world, it is clear
that the principal advantage of the use of such a term as “ homo-
taxis” is simply that we thereby avoid the employment of a word
which common usage would wrongly interpret ; and it is quite cer-
tain that we cannot abolish the idea of geological ‘‘ contemporaneity,”
as demonstrated by the presence of identical or representative species
of fossils; nor can we refuse to admit that formations containing
such fossils, however far removed from one another in point of dis-
tance, must have been laid down within the limits of the same great
“‘ period” in the history of our earth.

In the case of the Lower Carboniferous deposits above alluded to, not
only are the fossils generally similar to one another in all the widely sep-
arated regions in which these strata have been recognised, but certain
characteristic speczes seem to have an almost universal distribution. The
enormous range of certain specific types remains a most noteworthy fact,
_ whatever explanation may be given of it. As a general rule, however,
deposits in different geographical areas, which occupy a corresponding
position in the series of the stratified rocks, and are therefore geo-
logically speaking “contemporaneous,” contain but few or no actually
identical sfectes. The faunee of such deposits, on the contrary, are usu-
ally composed of allied or representative forms, the same groups of ani-
mals being the ones prevalent in and characteristic of the deposits, but the
species being different. Thus, there can be no doubt that the Devonian
deposits of North America and Western Europe are geological equiv-
alents, since they occupy in each region the interval between the highest
Silurian and the lowest Carboniferous sediments. The fauna of the
Devonian rocks of North America, also, presents a close general resem-
blance to that of the Devonian of Devonshire, Belgium, and Germany.
In both cases there is a predominance of certain special groups of ani-
mals, amongst which the great Hydrozoal group of the Stromatoporoids
may be particularly singled out. The Stromatoporoids of the American

GEOLOGICAL CONTINUITY. 55

Devonian represent those of the European Devonian, and certain peculiar
generic types (such as /dzostroma) are common to both regions ; but
there is, nevertheless, a marked difference as regards the forms most
prevalent in each. Thus, the European Devonian is specially character-
ised by the prevalence of species of Actznxostroma and Stromatopora,
while the most characteristic types of the American Devonian belong to
the genus C/athrodictyon, a genus which in Europe attains its maximum
in the Silurian period. Again, only few sfeczes of Stromatoporoids are
common to the two regions in question. Precisely similar facts could be
brought forward with regard to the Corals, Brachiopods, &c., of the De-
vonian formation in these areas ; and the general law which these facts
illustrate would seem to be one of very wide application.

In other cases, while the general fauna of two geologically equivalent
deposits in widely remote areas is broadly similar, special organic types
may occur in one or other area which indicate a later or an earlier age
than that pointed to by the general assemblage of fossils. A marked
example of this is found in the occurrence of such characteristic Second-
ary types of Cephalopods as Ammonites and Ceratites in certain strata
in North-western India, the general fossils of which are of unequivocal
Carboniferous type (Waagen). In this case, special organic types which
are in general characteristic of a later age, are associated with a general
fauna distinctive of an earlier period. An instance of the opposite of this
—z.é., of the occurrence of a special organic form of an earlier period in
association with a general fauna of a later type—is found in the occur-
rence of Ammonites in California in strata containing abundant fossils
characteristic of the Eocene Tertiary.

GEOLOGICAL CONTINUITY.

We are now in a position very briefly to discuss the question of
what may be called “geological continuity.” It has already been
stated that the entire series of Fossiliferous or Sedimentary rocks
may be naturally divided into a certain number of definite rock-
groups or ‘‘formations,” each of which is characterised by the
possession of a peculiar and characteristic assemblage of fossils,
constituting, or rather representing, the “life” of the “period” in
which the formation was deposited. The older geologists held, what
probably every one would be tempted to think at first, that the close
of each formation was characterised by a general destruction of the
forms of life of the period, and that the commencement of each new
formation was accompanied by the creation of a number of new
animals and plants, destined to figure as the characteristic fossils of
the same. This theory, however, not only invokes forces and pro-
cesses which it can in no way account for, but overlooks the fact
that most of the great formations are separated by lapses of time,
unrepresented perhaps by any deposition of rock, or represented
only in some particular area, and yet, perhaps, as great as, or
greater than, the whole time occupied in the production of the
formation itself.

Upon any theory of evolution, however, it must be held that

56 INTRODUCTION.

there was no such sudden destruction of life at the close of each
great geological epoch, and no such creation of fresh forms at the
commencement of the next period. On the contrary, it is certain
that there is a geological “continuity,” such as we see in other
departments of nature, and that the lines which we draw between
the great formations merely mark periods of time in which no rocks
were laid down, or the rocks deposited in which are at present
unknown to us.

What are we to believe occurred at the close of any great geo-
logical period—say, the Cretaceous period? If we reject the view
that the close of the period was marked by a sudden and universal
extinction and destruction of the characteristic Cretaceous forms of
life, there is only one other view which we can take. Confining our
attention solely to those seas of the period of which alone we know
enough for safe reasoning, we know that the close of the Cretaceous
period in Europe was accompanied, or rather caused, by an upheaval
of the Cretaceous area, and an obliteration of the Cretaceous sea.
This upheaval was, of course, effected with extreme slowness, or, at
any rate, not suddenly, and it must have completely changed the
life-conditions or “environment” of the animals which swarmed in
the Cretaceous seas. Some of these would doubtless be unable to
accommodate themselves to their altered surroundings, and would
simply die out. Others, we may presume, would migrate to some
more favourable area, and some of these might accomplish their
migration without undergoing any change. Most of the forms which
migrated, in the process of migration, and by reason of coming into
contact with strange neighbours and untried conditions, would,
however, probably undergo more or less modification. Ultimately,
therefore, many characteristic Cretaceous forms might be transferred
to some sea far distant from their original home. Not only so, but
some of the transferred species might have suffered so much modifi-
cation that they would no longer be regarded as specifically identical
with the original Cretaceous forms, but would be looked upon simply
as allied or ‘“‘representative” species, though really the lineal de-
scendants of the animals of the Chalk.

It is perfectly clear that the process of rock-deposition which was
going on in Europe towards the close of the Cretaceous period was
not, and could not be, abolished by the elevation of the European
area, and the obliteration of the Cretaceous sea, but was simply
transferred to some other area. In this particular case, we do not
happen to know where the new area of deposition may have been.
It is quite certain, however, that in whatever area the Cretaceous
animals took refuge, there rocks must have been deposited in course
of time, as they are in all seas, though it does not in the least follow
that the rocks of this new era should have the smallest likeness in

GEOLOGICAL CONTINUITY. 57

mineral composition to the Cretaceous sediments. If we should at
any time discover these rocks, it may pretty safely be predicted what
we should find in them in the way of fossils. We should find,
namely, some Cretaceous species, probably unchanged ; with these
there would be forms allied to the Cretaceous species, but differing
from them to a greater or less extent ; in addition, there would be a
certain proportion of forms of life wholly unknown in the Cretaceous
rocks ; and lastly, there would be a conspicuous absence of certain
characteristic species of the Chalk period. In other words, such
deposits as we have been speaking of would contain an assemblage
of fossils more or less intermediate in character between those of
the true Cretaceous period and those of the lowest Tertiary beds
(Eocene), which rest upon the Chalk; or they would present an
intermixture of Cretaceous with Eocene types. In point of fact,
we have fragments of such intermediate deposits (in the Maestricht
beds of Holland, the Pisolitic Limestone of France, the Faxoe Lime-
stone of Denmark, and the Thanet Sands of Britain), and we find
in them traces of such an intermixture. Moreover, when we come
to examine the boundary-line between the Cretaceous and Tertiary
in other regions, we do actually meet with strata which have been
deposited during the period marking in Europe the interval between
the White Chalk and the lowest Tertiary deposits, and which con-
tain, therefore, an intermixture of Cretaceous and Eocene types of
life. The most celebrated of these transitional formations, so far
as known, is the ‘ Laramie Group” of North America, the precise
position of which in relation to the strata above and below has been
a matter of much controversy.

We may pause here to consider how it is that we may never hope
to find a complete series of deposits linking on one great formation
to another, as, for example, the Chalk to the Eocene rocks. In the
first place, only a limited portion of the earth has as yet been
properly examined, and we have therefore no right to expect that
we have as yet hit upon the area, or areas, to which the process of
rock-forming was transferred at the close of the Cretaceous period
proper in Europe. We have, however, the full right to expect that
we shall ultimately find formations which will have to be intercalated
in point of time between the White Chalk and the Eocene ; and, as
before said, examples of such are already known to us. In the
second place, we have every reason to suppose that many of these
intermediate deposits have been destroyed at some period subse-
quent to their formation by what is technically called ‘ denudation,”
or, in other words, by the action of rain, rivers, ice, and the sea.
In the third place, many of the missing deposits may have been
concealed since their formation by the deposition upon them of
other newer rocks; or they may be situated in areas which are at

58 INTRODUCTION.

present covered by the ocean. Lastly, we must not forget that
there may have been times in which great changes in life were
actively progressing in areas in which there might be little or no
contemporaneous deposition of rock, so that the extreme terms of
a series might be preserved to us whilst all the intermediate links
might have escaped record.

From these and similar causes, it is certain that we shall rarely
be able to point to a complete series of deposits linking one great
geological period, such as the Cretaceous, to another, such as the
Eocene. Still, we may well have a strong conviction that such
deposits must exist, or must have existed, as memorials of, at any
rate, part of the time which elapsed between the close of the one
formation and the commencement of the next. Upon any theory
of “evolution,” at any rate, it is certain that there can be no total
break in the great series of the stratified deposits, but that there
must have been a complete continuity of life, and a more or less
complete continuity of deposition, from the Cambrian period to the
present day. ‘There was, and could have been no such continuity
in any one given area ; but the chain could never have been snapped
at one point and taken up at a wholly different one. It remains
certain, however, that we can never dispense with the division of
the stratified series into definite rock-groups and life-periods. We
can never hope to discover all the lost links of the geological chain,
and the great geological systems will always be separated from one
another by more or less evident physical or paleeontological breaks,
or by both combined. The utmost we can at present do is to
arrive at the conviction that the lines of demarcation between the
great formations only mark gaps in our knowledge, and that there
can in nature be no /zatus in the long series of fossiliferous deposits.

LIFE - ZONES.

While each geological rock-system is characterised by a general
assemblage of distinctive types of animals and plants, the minor sub-
divisions of each system are likewise distinguished by the prevalence
of particular forms of life. There are, no doubt, cases in which an
extensive series of successive strata may appear to be characterised
throughout by essentially the same organic types, there being appar-
ently no restriction of special fossils to special horizons in the series.
In so far as such cases have any real existence, they may be ex-
plained as instances in which a great series of sediments has been ac-
cumulated with such rapidity that there has been no time for marked
biological changes, resulting in the dying out of old species and the
introduction of new forms. In many cases, however, the apparent
diffusion of the same kinds of fossils from the base to the summit of

LIFE-ZONES. 59

a series of beds perhaps two or three thousand feet in thickness, is
due simply to the fact that the organic remains met with in the for-
mation have not been sufficiently investigated, and that the exact
horizon at which each occurs in the series has not been accurately
determined. The determination of the horizons of particular life-
forms is a work of time, and demands both great stratigraphical
knowledge and also a wide and accurate acquaintance with the char-
acters of the fossils themselves—two requirements rarely fulfilled in
the same individual.

In a considerable number of cases, however, it has now been
shown that the fossils of a given formation may be divided into
two principal groups. In the one group is comprised a series of
common forms of life which may be regarded as characterising
the formation as a whole. In the other group are included cer-
tain special fossils confined to particular parts of the formation,
and characteristic of certain definite orvzzons or zones within the
limits of the formation. All the great formations are to some extent
capable of being broken up into minor rock-groups, characterised by
special life-forms. Some of the differences in the kinds of fossils
found in different parts of the same formation must, of course, be
simply set down to the fact that different kinds of sediment imply
changed conditions in the sea, and hence changes in the marine
fauna. If, for example, part of a formation consisted of limestone
and part of sandstone, we should expect, beforehand, to find that
each of these rock-groups would have some fossils not found in the
other, since the two would have been formed under different condi-
tions. Apart, however, from differences arising from causes of this
nature, we meet with cases in which a formation, even if essentially
homogeneous in its mineral nature, can be divided into zones, each
of which is characterised by the possession of special groups of fos-
sils. Organisms belonging to any class of animals may serve in this
way as test-forms (‘“‘ Leit-fossilien ”) for special horizons in a series of
stratified formations, but there are particular groups of fossils which
have been found to be pre-eminently available for this purpose.
Among the older rocks of the earth’s crust, the forms which have
proved specially valuable for the determination of particular ‘‘ zones ”
are the Graptolites, the Trilobites, and the Brachiopods, while the
Cephalopods have been found to afford the most satisfactory tests in
the case of the Secondary rocks. A well-known instance of this
subdivision of a system of strata by means of special types of fossils
is that afforded by the Ordovician and Silurian rocks of Europe, in
which palzontologists, following Professor Lapworth, have recognised
numerous well-marked “ life-zones,” characterised for the most part
by the possession of particular types of Graptolites, though in some
cases the distinctive fossils belong to other groups. Another well-

60 INTRODUCTION.

known example of the same phenomenon is afforded by the Jurassic
deposits. These have been shown to contain a number of well-
marked zones, each of which 1s characterised by the possession of
some special fossils, and particularly by some special Ammonite.
These zones are extremely constant, in any particular region, and
they enable the observer to effect a division of the formation into
special horizons, which have no stratigraphical existence, and are
not separated by any physical break, but are of the utmost paleeonto-
logical importance, and can be rendered readily available in working
out the stratigraphy of any given area.

Certain life-zones appear to have nothing more than a local devel-
opment and importance, but in other cases they have proved to be
astonishingly constant even over very large areas. Perhaps the most
remarkable known instance of the extension of particular life-forms
over a vast area is that afforded by the Arenig rocks (a subdivision
of the Ordovician system), which have been recognised as occurring
in Europe, in Canada, and in Australia, and contain in all these
widely remote areas the same peculiar types of Graptolites.

The principal difficulty that we have to confront in dealing with
these ‘‘ zones,” is to produce any plausible explanation accounting
for the destruction of the special life-forms of the one zone and the
appearance of those of the next zone. For the most part, these
zones are of very limited vertical extent, and they succeed each other
in such a manner as totally to preclude the idea that the dying out
of the old forms can have been in any way caused by a physical
disturbance of the area. Perhaps the most probable view to adopt
in the meanwhile is, that the formations in which distinct and limited
life-zones can be recognised were deposited with extreme slowness ;
whereas those which show an essentially compact and homogeneous
fauna from base to summit were deposited with comparative rapidity.
Upon this view, a formation like the Lias is one formed by a process
of very slow and intermittent sedimentation, the life-zones being
separated by intervals, during which sedimentation must have been
at a stand-still, but which were long enough to allow of more or less
considerable biological changes, some forms dying out, or becoming
modified, while other new ones came in. Upon this view, further, a
formation like the Lias, though of comparatively small vertical extent,
may represent as long a period of time as the whole of such a great
formation as the Lower Carboniferous, which appears to have been
formed under conditions of comparatively rapid sedimentation.

““ COLONIES.”

It only remains in this connection to consider very briefly the
doctrine of “colonies,” laid down by M. Barrande, the eminent

“ COLONIES.” 61

Bohemian paleontologist. It has been laid down as a law that when
once a species disappears it never again makes its appearance in the
- geological record. This is almost certainly true, so long as we
remember that it can only apply to cases in which a species has
entirely and totally disappeared from the earth, and that it is often
very difficult, or altogether impossible, to obtain evidence as to the
exact time at which a given species has thus become actually extinct.
There are plenty of cases in which a species seemingly disappears in
a particular set of rocks, to reappear in some higher and later set of
rocks in the same region, whilst its remains are wanting in all the
intermediate deposits of the area. It also often occurs that a species,
having disappeared in one region, is found in deposits of a later age
in another area. The above-mentioned law, therefore, can obviously
only hold good of cases in which a species has definitely and finally
become extinct ; and this implies an amount of knowledge on our
part which we seldom or never possess. M. Barrande, however, has
endeavoured to prove that there are other cases in which groups of
species peculiar to one set of beds may appear in a temporary and
sporadic manner in a much earlier set of beds, the two deposits thus
characterised being separated by beds containing fossils peculiar to the
earlier and older series. Thus, the Ordovician and Silurian rocks of
Bohemia are characterised by very distinct assemblages of fossils.
According to M. Barrande, however, the Ordovician rocks contain in
places a group of fossils characteristic of the Silurian series. The
beds containing this “‘ colony ” of Silurian forms are succeeded by
strata filled with Ordovician fossils ; and it is only after several
alternations of this kind that the Silurian fauna comes in definitely
and generally. These temporary appearances of a later fauna in the
midst of an older fauna are termed by M. Barrande “ colonies,” and
he explains their occurrence as follows: If we suppose the seas of
the Bohemian area to have been peopled with Ordovician animals at
a time when other portions of Europe were covered by a sea con-
taining Silurian animals, and suppose the former area to have been
shut off from the latter by a land-barrier, we can readily understand
how ‘‘ colonies” might be produced. If, from any cause, a channel
of communication were opened between the Bohemian area and the
general area of Northern Europe, an immigration of species would
take place from the latter into the former area. ‘The Silurian species
of the latter area would thus be imported, in greater or less numbers,
into the midst of the general Ordovician fauna of Bohemia, and
would be preserved in the Ordovician rocks. If, however, the
channel of communication were speedily closed, so that the new-
comers could not be constantly reinforced by fresh immigrants, the
* colonial ” species would die out, and the general Ordovician fauna
would again reign supreme. A reopening of the channel of com-

62 INTRODUCTION.

munication would allow of a fresh immigration and the formation of
a fresh “colony,” and the process might be indefinitely repeated.
Finally, however, we must suppose that the Bohemian area was per-
manently thrown open to immigration from the general European
area, when the Silurian fauna of the latter would succeed in perma-
nently and completely displacing the old Ordovician fauna of the
former region. ‘The phenomenon, therefore, of ‘‘ colonies ” may be
defined as ‘‘ the coexistence of two general faunas, which, considered
in their entirety, are nevertheless distinct ;” and it is to be regarded
as merely a case of migration under certain peculiar and exceptional
circumstances.

Not only have the phenomena described by M. Barrande in con-
nection with his “‘ colonies” never been recognised with any certainty
in any region outside Bohemia; but there are strong grounds for
believing that the actual facts in this area will not bear the interpre-
tation which has been placed upon them by this distinguished pale-
ontologist. Thus, Mr J. E. Marr, after a careful examination of
the facts on the spot, was led to the conclusion that the so-called
‘colonies ” have no real existence, but are the result of disturbances
of the strata, being due, in reality, to the repeated ‘‘ faulting down ”
of a band of the Silurian rocks among the underlying Ordovician
deposits. This explanation seems to account adequately for the
observed phenomena, and relieves us of the necessity of accepting a
theory which can with difficulty be reconciled with the ascertained
laws of the distribution of animals in past time.

63

Cia Tb Reeve

mea PERE ECTION OF THE PALZONTOLOGICAL
RECORD,

As has been already pointed out, the series of the stratified forma-
tions is an imperfect one, and is likely ever to remain so. The
causes of this ‘‘imperfection of the geological record,” as it has been
termed by Darwin, are various; but it is chiefly to be ascribed to
our as yet incomplete knowledge of the geology of vast areas of the
earth’s surface, to denudation, and to the fact that many of the
missing groups are buried beneath other deposits, whilst more than
half of the superficies of the globe is hidden from us by the waters
of the sea. ‘The imperfection of the geological record necessarily
implies an equal imperfection of the ‘ palzeontological record” ; but,
in truth, the record of life is far more imperfect than the mere phys-
ical series of deposits. As we are here chiefly concerned with the
biological aspect of the question, we may advantageously consider
some of the main causes of the numerous breaks and gaps in the
paleontological record at some length.

I. CAUSES OF THE ABSENCE OF CERTAIN ANIMALS IN FOSSIL-
IFEROUS DeEposits.—In the first place, even if the series of the
stratified deposits had been preserved to us in its entirety, and we
could point to the sedimentary accumulations belonging to every
period of the earth’s history, there would still be enormous deficien-
cies in the palzontological record, owing to the differences in the
facility with which different animals may be preserved as fossils.
This subject is sufficiently important to render it advisable to con-
sider each of the primary groups of the animal kingdom separately
from this point of view :

a. Protozoa.—As regards the sub-kingdom of the Protozoa, the
Gregarines are destitute of hard parts, and have therefore left no
traces of their past existence. The great majority of the Infusorian
Animalcules are similarly destitute of hard parts, and are also un-
represented as fossils ; though a few forms (e.g., Peridinium) possess

64 INTRODUCTION.

an integumentary covering which under favourable circumstances is
capable of preservation, and remains of these are believed to occur
in some of the later sediments. Of the Rhizopods, the Wonera and
the most of the Amabea have no hard structures, and are unknown
as fossils, but a few of the latter possess a ‘‘ test” which might pos-
sibly be preserved in the fossil condition. On the other hand,
skeletal structures of lime or flint are almost always developed in the
great Rhizopodous orders of the Foraminifera and Radiolaria,; and
these groups, therefore, have left abundant traces of their existence
in past time.

b. Portfera.—A few of the Sponges (JZyxospongie) are completely
destitute of hard parts, and have therefore no palzontological
history. The greater number of the Porvijfera, however, possess a
calcareous or siliceous skeleton, which is more or less capable of
fossilisation, and the record of such types is therefore a long and
comparatively full one.

c. Celenterata.—Amongst the Coelenterate animals, the Fresh-water
Polypes (ydra), the Oceanic Hydrozoa, the Jelly-fishes (AZeduside),
the Sea-blubbers (Lucernarida), the Sea-anemones (Actinide), and
the Crenophora are destitute of hard parts which could be preserved
as fossils. The Jelly-fishes and Sea-blubbers, however, supply us
with an instance of how a completely soft-bodied creature may leave
traces of its past existence ; for impressions left by the stranded car-
casses of these animals have been detected in certain fine-grained
rocks (e.g., the Lithographic Slates of Solenhofen). On the other
hand, the coralligenous Zoophytes or “Corals” (comprising the
Madreporaria and most of the A/cyonaria) possess hard parts cap-
able of preservation, and there are therefore few classes of organisms
which are more fully represented in past time than the true Corals.
As regards the Hydrozoa, most of the Hydroid Zoophytes have a
horny skeleton, and do not become readily fossilised, though the
large extinct group of the Graffolites is generally regarded as allied
to the recent Sertularians. In a few of the AWydractinide, and in
the whole group of the Hydrocorallines, a calcareous skeleton is
present, and various fossil forms of these are known. In the great
extinct group of the S¢vomatoporoids, now usually referred to the
Ffydrozoa, the skeleton was also of a calcareous nature.

a. Echinodermata.—Since the integument of the Echinoderms is
liable to undergo more or less extensive calcification, this great divi-
sion of animals is represented more or less completely in past time
by all its sections. In the group, however, of the Sea-cucumbers
(Holothuroidea), the ealcareous structures so characteristic of other
Echinoderms are reduced to their minimum ; and accordingly, the
evidence of the past existence of these animals is of a very limited
description.

IMPERFECTION OF PALAZONTOLOGICAL RECORD. 65

e. Annulosa.—The lowest division of the Annu/osa (viz., that of the
Scolecida) comprises animals almost without exception destitute of
hard parts, and mostly living parasitically in the interior of other
animals. With the exception, therefore, of some excessively prob-
lematical fossils which have been supposed to indicate the past exist-
ence of Ribbon-worms (/Vemerteans), the palzeontological history of
the Scolecida is a total blank. Most of the true Worms (Azxarthro-
poda) possess few or no structures by which we could expect to get
direct evidence of their past existence. The Polychzetous Annelides
have, however, left ample traces of their former presence either by
their horny jaws or by means of their investing tubes. There are
also numerous fossils of the nature of burrows or “ tracks” upon the
mud or sand of ancient sea-bottoms, which have been regarded, with
more or less probability, as having been produced by Annelides.

In the case of the higher Axnulosa (Arthropoda), another law
steps in to regulate their comparative abundance as fossils. Most,
in fact almost all, fossiliferous formations have been deposited in
water ; and of necessity, therefore, most fossils are the remains of
animals whose habits are naturally aquatic. As most deposits, fur-
ther, are not only aqueous, but are also marine, most fossils are those
of sea-animals. It follows, therefore, that the remains of air-breath-
ing animals, whether these be terrestrial or aerial, can only be pre-
served in an accidental manner, so to speak—except the animal
inhabit water (as the Cetaceans do), or except in the rare instances
in which old land-surfaces have been buried up by sediment, and
thus partially kept for our inspection. In accordance with this law,
the most important and abundant fossil Annulose animals are Crus-
taceans ; since these not only have a resisting shell or ‘‘ exoskeleton,”
but are also generally aquatic in their habits. The air-breathing
classes of the JZyriopoda (Centipedes and Millepedes), the Avach-
mida (Spiders and Scorpions), and the /msecfa or true Insects, on the
other hand, have been much less commonly and completely pre-
served, though many of them are perfectly capable of being fossil-
ised. Almost all such remains, moreover, as we have of these three
great classes, are the remains of isolated individuals, which may have
been accidentally drowned ; or else they occur in hollow trees, or in
fragments of ancient soils, or in vegetable accumulations such as
coal and peat. There is, however, a considerable number of aquatic
insects (but almost exclusively in fresh water), and there are many
insects the larvee of which inhabit water, whether this be fresh or salt ;
so that instances of these occurring as fossils are not very infrequent.

J. Molluscoidea.—W ith regard to the Molluscoids, the great majority
of the Polyzoa and all of the Brachiopoda possess skeletal structures
of a horny or calcareous nature, which are capable of preservation in
the fossil condition. Both these classes of animals, therefore, possess

VOL: I: E

66 INTRODUCTION.

a long and tolerably complete palzeontological record. In the case
of the Polyzoa, however, the group of the fresh-water forms is not at
present known to have any fossil representatives.

g. Mollusca.—This sub-kingdom requires little notice, since the
greater number of its members possess hard structures readily cap-
able of preservation in the fossil condition. Hence, all the great
existing groups of Molluscs are more or less extensively represented
in past time. The oceanic Pteropods, however, perhaps owing to
their pelagic habit of life, or possibly as the result of their having
fragile and easily destructible shells, have left a more incomplete
record of their past existence than is the case with the other
classes of Molluscs. Amongst the Gastropoda, again, the Sea-
slugs and their allies (Vudibranchiata) possess no shell, and are
unknown to the paleontologist ; whilst the shell of the Land-slugs is
extremely minute, and has only rarely been recognised as fossil.
Lastly, the air-breathing terrestrial Molluscs, from their habits, rarely
occur as fossils; whilst those which inhabit rivers, ponds, and lakes
are less largely represented than marine forms, owing to the prepon
derance of salt-water deposits over those of fresh water.

h. Tunicata.—The Tunicates, so far as living forms are concerned,
are almost always destitute of skeletal structures, or possess only
microscopic spicules of carbonate of lime. Only the most limited
traces of the past existence of these animals have as yet been cer-
tainly detected ; but it is quite probable that further investigations
will considerably extend our knowledge on this point.

2. Vertebrata.—-The majority of Vertebrate animals possess a bony
skeleton, so that their preservation in a fossil state—so far as this
point is concerned—is attended with no difficulty. Some of the
fishes, however (such as the Lancelet, the Hag-fishes, and the Lam-
preys), have no scales, and either possess no ‘‘endoskeleton” or
have one which is wholly or almost wholly unossified. The only
evidence, therefore, which could be obtained of the past existence
of such fishes would be afforded by their teeth ; but these are want-
ing in the Lancelet, and are small and horny in the Lampreys: so
that we need not wonder that these fishes are unknown as fossils.
The higher groups of the fishes, however, taking everything into
consideration, may be said to be abundantly represented in a fossil
condition by their scales, bones, teeth, and defensive spines.

The Amphibians are tolerably well represented by their bones and
teeth, and, as regards one extinct order, by integumentary plates as
well. They have also left many traces of their existence in the form
of footprints. Most living Amphibians, however, frequent fresh
waters, or spend a great part of their time upon the land; and
hence their remains would not be likely to be preserved in marine
deposits.

IMPERFECTION OF PALZXONTOLOGICAL RECORD. 67

The abundance of Reptiles as fossils naturally varies much, accor-
ding to the habits of the different orders. Of the living orders, the
Chelonians (Tortoises and Turtles) are by no means rare; since
many of them are habitual denizens of fresh water or of the sea,
whilst all are provided with a well-developed skeleton. The exist-
ing Sguamata (Lizards and Snakes) and the Ahynchocephatia live
chiefly upon the land, and do not therefore abound as fossils; but
some extinct types of the former (the Mosasauroids) were marine in
their habits, and have consequently been pretty fully preserved.
The Cyrocodifia, again, are so essentially aquatic in their habits,
that their comparative frequency in aqueous deposits is no matter of
wonder, especially if we recollect that many of the extinct members
of this order frequented the sea itself. Of the extinct orders of Rep-
tiles, the great /chthyosaurs and the Plestosaurs and their allies were
marine in their habits, and their remains occur in what may fairly
be called profusion. The Flying Reptiles, or Prerodactyles, would
not seem to have any better chance of being preserved than Birds,
if as good, yet their remains occur by no means very rarely in certain
formations. The terrestrial Dinosaurs and Anomodonts, again, come
very much under the laws which regulate the preservation of Mam-
mals as fossils ; and their remains are chiefly, but not exclusively,
to be found in fluviatile or estuarine deposits.

As regards Birds, their powers of flight, as pointed out by Sir
Charles Lyell, would save them from many destructive agencies, and
the lightness of their bones would favour the long floating of the
body in water, and thus increase the chances of its being devoured
by predaceous animals. In accordance with these considerations,
the most abundant remains of Birds belong to species which fre-
quent the sea-shore, lakes, estuaries, or rivers, or which delight in
marshy situations ; though in certain regions the principal fossil rep-
resentatives of the class Aves are large wingless forms, of terrestrial
habit, and with their bones largely filled with marrow instead of air.

Lastly, as regards Mammals, the record is far from being a full
one, and from obvious causes. The great majority of Mammals
live on land, and therefore are not likely to be buried in aqueous,
and especially in marine, accumulations. That this cause is the
chief one which has operated against the frequent preservation of
Mammalian remains is shown by the fact that when we exhume an
old land-surface, the remains of Mammals may be found in tolerable
plenty. The strictly aquatic Mammals—such as Whales, Dolphins,
and the like—are, of course, much more likely to have been pre-
served as fossils than the strictly terrestrial forms ; but their want of
integumentary hard structures places them at a disadvantage in this
respect as compared with fishes. In a general way, we may conclude
that the preservation of the terrestrial Mammals as fossils is due to

68 INTRODUCTION.

the occurrence of individuals being killed whilst swimming a river
or some other piece of water, or being mired in a bog, or to
the bones of those that had died on land being washed into some
stream, and thence into a lake or into the sea, by floods; but there
are other cases for which a different explanation must be sought.
The most abundant remains of Mammals have been found in de-
posits which have been laid down in lakes.

II. UNREPRESENTED Time.—In the second place, we have seen
that the geological record is very imperfect, and this of necessity
causes vast gaps in our palzontological knowledge. In this con-
nection we may briefly consider the evidence which we possess as
to the immensity of the “‘ unrepresented time” between some of the
great formations, and no better example can be chosen than that
of the Cretaceous and Eocene rocks, as developed in Europe. In
considering such a case, the evidence may be divided into two
heads, the one palzeontological, the other purely physical, and each
may be looked at separately.

The Chalk, as is well known, constitutes in Britain the topmost
member of the Cretaceous formation, and is the highest deposit
there known as appertaining to the great Secondary or Mesozoic
series. It is directly overlaid in various places by strata of Eocene
age, which form the base of the great Tertiary or Kainozoic series
of rocks. The question, then, before us is this, What evidence have
we as to the lapse of time represented in Britain merely by the
dividing-line between the highest beds of the Chalk and the lowest
beds of the Eocene?

Taking the palzontological evidence first, it is found that not a
single specific type out of the vast number of known Cretaceous
fossils has hitherto been recognised with certainty as occurring in
the immediately overlying Eocene beds. ‘These latter, on the con-
trary, are replete with organic remains wholly distinct from those of
the Cretaceous beds. It may be said, therefore, that the very ex-
tensive assemblage of animals which lived in the later Cretaceous
seas of Britain had entirely passed away and become a thing of the
past, before a single grain of the Eocene rocks had been deposited.
Now it is of course open to us to believe that the animals of the
Chalk sea were suddenly extinguished by some natural agencies
unknown to us, and that the animals of the Eocene sea had
been in as sudden and as obscure a manner introduced en masse
into the same waters. This theory, however, calls upon the stage
forces of which we know nothing, and is contradicted by the whole
tenor of the operations which we see going on around us at the
present day. It is preferable, therefore, to believe that no such
violent processes of destruction and repeopling took place, but that
the marked break in the life of the two periods indicates an enor-

IMPERFECTION OF PALAZZSONTOLOGICAL RECORD. 69

mous lapse of time. The Cretaceous animals, in consequence of
the elevation of the British area at the close of the Cretaceous
period, must have mostly migrated, some doubtless perishing, and
others probably becoming modified in the process. When the
British area became once more submerged beneath the sea, and be-
came again a fitting home for marine life, an immigration into it
would set in from neighbouring seas. By this time, however, the
Cretaceous animals must have mostly died out, or must have be-
come greatly changed in their characters; and the new immigrants
would be forms characteristic of the Lower Eocene. How long the
processes here described may have taken, it is utterly impossible to
say, even approximately. Judging, however, from what we can ob-
serve at the present day, the paleontological break between the
Chalk and the Eocene indicates a perfectly incalculable lapse of
time ; for all species change or die out slowly, marine species es-
pecially so; and we have here the disappearance of a large fauna
almost in its entirety, and its replacement by another wholly
distinct.

In the second place, to come to the physical evidence, the Eocene
strata in Britain are seen to rest upon an eroded and denuded sur-
face of Chalk, filling up “pipes” and winding hollows which de-
scend far below the general surface of the latter. Not only so, but
the base of the Eocene rocks is commonly composed of a bed of
rolled and rounded flints, derived from the Chalk, affording incon-
testable proof that the Chalk had been greatly worn down and re-
moved by denudation before the Eocene beds were deposited upon
its surface. In short, the Eocene rocks repose ‘‘ unconformably ”
upon the Chalk, and this, as is well known, indicates the following
series of phenomena: Firstly, the Chalk was deposited in horizontal
layers at the bottom of the Cretaceous sea. Secondly, at some
wholly indefinite time after its deposition, after it had become more
or less consolidated, the Chalk must have been raised by a gradual
process of elevation above the level of the sea, during which it
would inevitably suffer vast denudation. Thirdly, after another
wholly indefinite period, the Chalk was again submerged beneath
the sea, in which process it would be subjected to still further denu-
dation, and an approximately level surface would be formed upon it.
Fourthly, strata of Eocene age were deposited upon the denuded
surface of the Chalk, filling up all the hollows and inequalities of its
eroded surface (fig. 15).

In the unconformability, then, between the Chalk and the Eocene
rocks, we have unequivocal evidence—uirrespective of anything that
we learn from Paleontology—that the break between the two for-
mations was one of enormous length. In Britain the interval of
time thus indicated is not represented by any deposits; and in

70 INTRODUCTION.

Europe generally there are but fragmentary traces of such. We
may be quite sure, however, that during the time represented in
Britain by the mere line of unconformability between the Chalk
and the Eocene, there were somewhere deposited considerable accu-
mulations of sediment.

It is not probable that we shall ever discover any very consider-
able portion of these, considering the large extent of the terrestrial
surface which is covered by the ocean. In New Zealand, however,

Fig. 15.—Section showing strata of Tertiary age (@), resting upon a worn and denuded surface
of White Chalk (4), the stratification of which is marked by lines of flints.

and still more notably in North America, extensive deposits are
already known, which were laid down subsequent to the formation
of the White Chalk and prior to the deposition of the Eocene Ter-
tiary, and which serve, therefore, to partially bridge over the great
hiatus which separates these formations in Europe. ‘These tran-
sitional formations are charged, as might have been anticipated,
with the remains of animals which in part resemble Cretaceous
types and in part are characteristic Eocene forms.

The break between the Cretaceous and lowest Tertiary de-
posits is one of the most extensive and universal of which we have
at present any knowledge. Almost equally extensive and wide-
spread is the break which separates the Paleeozoic from the Meso-
zoic group of deposits. ‘Throughout the whole stratified series,
however, we meet at intervals with physical and paleontological
breaks of greater or less magnitude. Sometimes a paleontological
break occurs unaccompanied by marked physical disturbance or
discordance of the strata; but usually a gap in the succession of
life-forms is associated with clear physical evidence of elevation and
subsequent denudation.

It may be pointed out that the unconformities above alluded to
must be distinguished from the common cases in which strata of
one age are /oca//y superimposed in an unconformable manner upon

IMPERFECTION OF PALZONTOLOGICAL RECORD. 7%

beds much older than themselves., ‘These local unconformities are
exceedingly common in regions which have undergone much dis-
turbance, and they merely indicate that the region has been sub-
jected to a local elevation, resulting in a temporary cessation of
sedimentation in that particular area. In such cases, an examina-
tion of neighbouring areas, which remained submerged, and in
which, therefore, sedimentation was uninterrupted, will show the
missing deposits which were laid down during the period represented
in the first area by a local unconformity. ‘The instances above
alluded to, though really only differing from the local unconformi-
ties just alluded to in nothing more than in being the result of a very
widespread elevation, are distinguished by an important point. In
the case of a mere local unconformity, we know what formation is
wanting, and we can intercalate it from foreign areas, and can thus
complete the series. In the general unconformities, such as that
between the Paleozoic and Mesozoic groups of sediments, we are
not at present acquainted with the deposits which were laid down
during the interval represented by the physical discordance of the
strata, and the series of rock-formations thus remains a broken
one.

From the above facts, then, we learn that one of the chief causes of
the imperfection of the palzontological record is to be found in the
vast spaces of time which separate most of the great ‘‘ systems,” and
which, so far as we yet know, are not represented by any formation
of rock. In process of time we shall doubtless succeed in finding
deposits to account for more or less of this ‘‘ unrepresented time,”
but much will ever remain for which we cannot hope to find the
representative sediments. It only remains to add that we have
ample evidence within the limits of each formation, and wholly
irrespective of any want of conformity, of such lengthened pauses
in the work of deposition as to have allowed of great zoological
changes in the interim, and to have thus caused irremediable blanks
in the paleontological record. The work of rock-deposition is at
best an intermittent process; the changes in a fauna, if slowly
effected, are continuous. ‘Thus there are scores of instances in
which the fauna of a given bed, perhaps but a few inches in thick-
ness, differs altogether from that of the beds immediately above and
below, and is characterised by species peculiar to itself. In such
cases we can only suppose, that though no physical break can be
detected, the deposition of sediment was interrupted by pauses of
incalculable length, during which no additional material was added
to the sea-bottom, whilst time was allowed for the dying out of old
species and the coming in of new. ‘The incessant repetition of such
intervals of unrepresented time throughout the whole stratified
series 1s convincing proof that the palzontological record is, and

Uf os INTRODUCTION.

ever must be, a mere excerpt from the biological annals of the
globe.

III. THrnninc out oF Breps.—Another cause by which the
continuity of the paleontological record is affected is what is tech-
nically called the “thinning out” of beds. Owing to the mode in
which sedimentary rocks are produced, it is certain that there must
be for every bed a point whence the largest amount of sediment
was derived, and in the neighbourhood of which the bed will there-
fore be thickest. Thus, if we take a series of beds, such as sand-
stones and conglomerates, which are the product of littoral action,
and are deposited in shallow water near a coast-line, it will be found
that these gradually decrease in thickness, or “thin out,” as we pass
away from the coast in the direction of deep water. On approach-
ing deep water, however, we might find that, though the sandstones
were rapidly dying out, the thickness of the entire series might still
be preserved, owing to the commencement now of some deep-water
deposit, such as limestone. The beds of limestone would at first
be very thin, but in proceeding still in the direction of deeper water,
we should find that they would gradually expand till they reached a
point of maximum thickness, on the other side of which they would

=

Fig. 16.—Diagram to show the “‘ thinning out” of beds. a, Sandstones and

Conglomerates ; 4, Limestones.

gradually thin out. Each individual bed, therefore, in any group
of stratified rocks, may be regarded as an unequal mass, thickest in
the centre, and gradually tapering off or “thinning out” in all direc-
tions towards the circumference (fig. 16).

In-a general way this holds good, not only for any particular bed,
but for any particular aggregation or group of beds which we may
choose to take. In the case, namely, of every group of beds, there
must have been a particular point whither sediment was most abun-
dantly conveyed, or where the other conditions of accumulation were
especially favourable. At this point, therefore, the beds are thickest,
and from this they thin out in all directions. It need scarcely be
pointed out, indeed, that some such state of things is unavoidable in
the case of every bed or group of beds, since no sea is boundless,
and the sedimentary deposits of every ocean must come to an end
somewhere.

An excellent example of the phenomena above described may be

IMPERFECTION OF PALZONTOLOGICAL RECORD. 73

derived from the Lower Carboniferous rocks of Britain. Here we
may start in South Wales and in Central England with the Carbon-
iferous Limestone as a great calcareous mass over 1000 feet in
thickness, and almost without a single intercalated layer of shale.
Passing northwards, some of the beds of limestone begin to thin out,
and their place is taken by strata of a different mineral nature, such
as sandstone, grit, or shale. The result of this is, that by the time
we have followed the Carboniferous Limestone into Yorkshire and
Westmorland, in place of a single great mass of limestone, we have
an equivalent mass of alternating strata of limestone, sandstone, grit,
and shale, with one or two thin seams of coal—the limestones, how-
ever, still bearing a considerable proportion to the whole. Passing
still further northwards, the limestones continue to thin out, till in
Central Scotland, in place of the dense calcareous accumulations of
Derbyshire, the Lower Carboniferous series consists of a great group
of sandstones, grits, and shales, with thick and workable beds of
coal, and with but few and comparatively insignificant beds of
limestone.

The state of things indicated by these phenomena is as follows:
The sea in which the Lower Carboniferous rocks of Britain were
deposited must have gradually deepened from north to south. The
land and coast-line whence the coarser mechanical sediments were
derived, must have been placed somewhere to the north and north-
west of what is now Great Britain, and the deepest part of the ocean
must have been somewhere about Derbyshire. Here the conditions
for lime-making were most favourable, and here consequently we find
the greatest thickness of calcareous strata, and the smallest inter-
mixture of mechanical deposits.

The palzeontological results of this are readily deducible. The
entire Lower Carboniferous series of Britain was probably deposited
in a single ocean, apparently destitute of land-barriers ; and conse-.
quently, taken as a whole, the fauna of this series may be regarded
as one and indivisible. The conditions, nevertheless, which obtained
in different parts of this area were very dissimilar ; and, as a necessary
result, certain groups of animals flourished in certain localities, and
were absent or but scantily represented in others. In the deeper
parts of the area we have an abundance of Corals, with Crinoids,
and at times Foraminifera. In the shallower parts of the area there
is, on the other hand, a predominance of forms which affect water of
no great depth. Still there is no difference in point of time between
the deposits of different parts of the area; and in order to obtain a
true notion of the Lower Carboniferous fauna, we must add the
fossils derived from one portion of the area to those derived from
another.

In many cases, however, we are acquainted with but one class of

74 INTRODUCTION.

deposits belonging to a given period. We may have the compara-
tively deep-water deposits of the period only, or we may know
nothing but its littoral accumulations. In either case it is clear
that there is an imperfection of the paleontological record; for
we cannot have even a moderately complete record of the marine
animals alone of a particular period, unless we have access to a
complete series of the deposits laid down in the seas of that period.
A still more serious imperfection of the record arises where, as
commonly happens, the marine deposits of a given period are alone
known, and we are left without any knowledge of the lacustrine,
fluviatile, and terrestrial deposits of the same period.

According to the views of Dr John Murray and the Abbé Renard,
a very important deficiency exists in the series of sedimentary de-
posits known to us as forming the existing dry land, in so far as the
series is without any representatives of the peculiar deposits which
are now in process of formation in the deep sea. It has been
shown by these investigators that between depths of six or seven
hundred fathoms down to the greatest depths known, at distances
of two hundred miles or more from land, there are now being
formed certain remarkable deposits which may be spoken of as
“deep-sea muds” and “abyssal clays.” The deep-sea “muds” and
“oozes” are exceedingly fine, mud-like deposits, which differ from
true muds in not being made up of water-worn particles of clay or
other mineral substances, and in being largely composed of the skele-
tons of minute animal or vegetable organisms. Some of these deep-
sea muds are largely composed of the shells of Foraminifera (“ Glo-
bigerina ooze”); others are essentially made up of the siliceous tests
of Polycystina and allied organisms (“ Radiolarian ooze”); others
are built up principally of the shells of Preropoda (‘‘ Pteropod ooze ”) ;
while others are the result of the accumulation of the flinty envelopes
of Diatoms (“‘ Diatom ooze”). The ‘“ abyssal clays,” again, are red,
purple, chocolate-coloured, or brown clays, composed of nearly im-
palpable particles, and almost destitute of calcareous matter, but
sometimes containing particles of metallic iron or concretions of
manganese. ‘These abyssal clays, according to Dr Murray, are pro-
duced by the decomposition in sea-water of floating pumice and of
ashes, ejected from volcanoes and ultimately falling into the sea ;
and there is evidence to show that they are the result of an exces-
sively slow process of accumulation.

From a study of the deposits at present in process of formation in
the deep sea, far from land, it has been concluded by Murray and Re-
nard, as before said, that no similar or parallel deposits exist amongst
the varied marine sediments which compose so large a portion of the
present continents. On this view, the ordinary stratified rocks of
marine origin have all been formed in comparatively shallow water,

IMPERFECTION OF PALAZOONTOLOGICAL RECORD. 75

or, at any rate, at a comparatively short distance from land. <A con-
clusion so far-reaching as this requires, however, to be received with
the utmost caution ; the more so as it constitutes one of the most
weighty arguments in favour of the equally far-reaching conclusion,
that the present continental areas have been in the main regions of
elevation, and the existing oceans in the main areas of depression,
since the beginning of the Cambrian period, if not from a still earlier
period. ‘That a large number of the known sedimentary rocks have
been formed from the wear and tear of pre-existing rocks, or have
been the result of the accumulation of the skeletons of animals and
plants, in comparatively shallow water and at moderate distances
from a coast-line, may be taken as certain. With our present im-
perfect acquaintance, however, with the nature and origin of many
of the older sediments of the earth’s crust, it appears hazardous to
conclude that a// the sedimentary rocks have been laid down near
land. In various parts of the stratified series we meet with deposits
which may be paralleled with the Foraminiferal ooze, the Radiolarian
ooze, the Diatom ooze, or even the Pteropod ooze of the present day,
though it may be admitted that these deposits may sometimes have
been formed in a comparatively shallow sea. Moreover, it cannot, with
our present knowledge, be safely asserted that we have zo ancient
representatives even of the ‘‘abyssal clays” of the deep oceans of the
present day. On the contrary, it seems very possible that certain of
the sediments of such old systems as the Cambrian and Ordovician
were formed at great depths, and that they represent the modern
abyssal clays. This is particularly the case with some of the fine-
grained, red, brown, or green muds which occasionally form a con-
spicuous feature in the Cambrian and Ordovician series. Such
muds are not only singular for their extraordinary barrenness in fos-
sils, but there is good ground for thinking that they have been
formed by the decomposition of volcanic matter, while they com-
monly exhibit dendrites of manganese.

IV. DisAPPEARANCE OF Fossits.—The last subject which need
be mentioned in connection with the imperfection of the paleeontolo-
gical record, is that of the disappearance of fossils from rocks origin-
ally fossiliferous. This, as a rule, is due to “‘ metamorphism ”—that
is to say, the subjection of the rock to a sufficient amount of pres-
sure or heat to cause a rearrangement of its particles. When of at
all a pronounced character, the result of metamorphism is the more
or less complete obliteration of any fossils which might have been
originally present in the rock. ‘To this cause must be set down
many great gaps in the paleontological record, and the irreparable
loss of much fossil evidence.

Another not uncommon cause of the disappearance of organic
remains from originally fossiliferous deposits is the percolation through

76 INTRODUCTION.

them of water holding carbonic acid in solution. By this means
fossils of a calcareous nature are dissolved out of the rock, and may
leave no traces behind. This cause, however, can only operate to
any extent in more or less loose and porous arenaceous deposits.

Lastly, ‘‘cleavage” may be mentioned as a common cause of the
disappearance of fossils. But the cleavage must be very intense,
if it actually prevents the recognition of the deposit as one in
which fossils formerly existed, though cases are not uncommon in
which this occurs through thousands of feet of strata. As a more
general rule, however, it is not very difficult to determine whether a
cleaved rock has ever contained fossils or not, though it may be
quite impossible to make out the exact nature and character of the
organic remains.

ei

CARTAN Jed Bee
CONCLUSIONS TO BE DRAWN FROM FOSSILS.

WE have already seen that geologists have been led by the study of
fossils to the all-important generalisation that the vast series of the
Fossiliferous or Sedimentary rocks may be divided into a number of
definite groups or ‘‘systems,” each of which is characterised by its
organic remains. It may simply be repeated here that these systems
are not properly and strictly characterised by the occurrence in them
of any one particular fossil. It very often happens, indeed, that
some particular stratum, or sub-group of a series, contains peculiar
fossils, by which its existence may be determined in various local-
ities. As before remarked, however, the great systems are char-
acterised properly by the association of certain fossils, by the pre-
dominance of certain families or orders, or by an assemblage of fossil
remains representing the ‘‘life” of the period in which the system
was deposited.

Fossils, then, enable us to determine the age of the deposits in
which they occur. Fossils further enable us to come to very im-
portant conclusions as to the mode in which the fossiliferous bed was
deposited, and thus as to the condition of the particular district or
region occupied by the fossiliferous bed at the time of the formation
of the latter. If, in the first place, the bed contain the remains of
animals such as now inhabit rivers, we know that it is “‘ fluviatile ”
in its origin, and that it must at one time have either formed an
actual river-bed, or been deposited by the overflowing of an ancient
stream. Secondly, if the bed contain the remains of shell-fish, min-
ute crustaceans, or fish, such as now inhabit lakes, we know that it
is “lacustrine,” and was deposited beneath the waters of a former
lake. Thirdly, if the bed contain the remains of animals such as
now people the ocean, we know that it is ‘‘ marine” in its origin,
and that it is a fragment of an old sea-bottom.

We can, however, often determine the conditions under which a
bed was deposited with greater accuracy than this. If, for example,

78 INTRODUCTION.

the fossils are of kinds resembling the marine animals now inhabiting
shallow waters, if they are accompanied by the detached relics of
terrestrial organisms, or if they are partially rolled and broken, we
may conclude that the fossiliferous deposit was laid down in a
shallow sea, in the immediate vicinity of a coast-line, or as an
actual shore-deposit. If, again, the remains are those of animals
such as now live in the deeper parts of the ocean, and there is a very
sparing intermixture of extraneous fossils (such as the bones of birds
or quadrupeds, or the remains of plants), we may presume that the
deposit is one of deep water. In other cases, we may find, scattered
through the rock, and still in their natural position, the valves of
shells such as we know at the present day as living buried in the
sand or mud of the sea-shore or of estuaries. In other cases, the
bed may obviously have been an ancient coral-reef, or an accumula-
tion of social shells, like Oysters. Lastly, if we find the deposit to
contain the remains of marine shells, but that these are dwarfed of
their fair proportions and distorted in figure, we may conclude that
it was laid down in a brackish sea, such as the Baltic, in which the
proper saltness was wanting, owing to its receiving an excessive
supply of fresh water.

In the preceding, we have been dealing simply with the remains
of aquatic animals, and we have seen that certain conclusions can
be accurately reached by an examination of these. As regards the
determination of the conditions of deposition from the remains of
aerial and terrestrial animals, or from plants, there is not such an
absolute certainty. The remains of land-animals would, of course,
occur in “ sub-aerial ” deposits—that is, in beds, like blown sand,
accumulated upon the land. Most of the remains of land-animals,
however, are found in deposits which have been laid down in water,
and they owe their present position to having been drowned in rivers
or lakes, or carried out to sea by streams. Birds, flying Reptiles,
and flying Mammals might also similarly find their way into aqueous
deposits ; but it is to be remembered that many Birds and Mammals
habitually spend a great part of their time in the water, and that
these might therefore be naturally expected to present themselves
as fossils in Sedimentary rocks. Plants, again, even when undoubt-
edly such as must have grown on land, do not prove that the bed
in which they occur was formed on land. Many of the remains of
plants known to us are extraneous to the bed in which they are now
found, having reached their present site by falling into lakes or
rivers, or being carried out to sea by floods or gales of wind. ‘There
are, however, many cases in which plants have undoubtedly grown
on the very spot where we now find them. Thus it is now gener-
ally admitted that the great coal-fields of the Carboniferous age are
the result of the growth zz sztw of the plants which compose coal,

CONCLUSIONS TO BE DRAWN FROM FOSSILS. 79

and that these grew on vast marshy or partially submerged tracts of
level alluvial land. We have, moreover, distinct evidence of old
land-surfaces, both in the Coal-measures and in other cases (as,
for instance, in the well-known “dirt-bed” of the Purbeck series).
When, for example, we find the ~
erect stumps of trees standing at
right angles to the surrounding
strata, we know that the surface
through which these send their
roots was at one time the surface
of the dry land, or, in other words,
was an ancient soil (fig. 17).

CONCLUSIONS AS TO CLIMATE.
—In many cases fossils enable us
to come to important conclusions
as to the climate of the period in
which they lived, but only a few
instances of this can be here ad-
duced. As fossils in the majority
of instances are the remains of
marine animals, it is mostly the
temperature of the sea which can
alone be determined in this way ;
and it is important to remember
that, owing to the existence of
heated currents, the marine cli- Fig. 17.—Erect Tree containing Reptilian

: ? remains. Coal-measures, Nova Scotia. (After
mate of a given area does not ne- Dawson.)
cessarily imply a correspondingly
warm climate in the neighbouring land. Land-climates can only be
determined by the remains of land-animals or land-plants, and these
are comparatively rare as fossils. It is also important to remember
that all conclusions on this head are really based upon the present
distribution of animal and vegetable life on the globe, and are
therefore liable to be vitiated by the following considerations :—

a. Most fossils are extinct, and it is not certain that the habits and
requirements of any extinct animal were exactly similar to, or even
at all resembling, those of its nearest living relative.

6. When we get very far back in time, we meet with groups of
organisms so unlike anything we know at the present day as to
render all conjectures as to climate founded upon their supposed
habits more or less uncertain and unsafe.

c. In the case of marine animals, we are as yet very far from
knowing the exact limits of distribution of many species within our
present seas; so that conclusions drawn from living forms as to
extinct species are apt to prove incorrect. For instance, it has

80 INTRODUCTION.

recently been shown that many shells formerly believed to be con-
fined to the arctic seas have, by reason of the extension of polar
currents, a wide range to the south; and this has thrown doubt
upon the conclusions drawn from fossil shells as to the arctic con-
ditions under which certain beds were supposed to have been de-
posited.

d. The distribution of animals at the present day is certainly
dependent upon other conditions beside climate alone; and the
causes which now limit the range of given animals are certainly
such as belong to the existing order of things. But the establish-
ment of the present order of things does not date back in many
cases to the introduction of the present species of animals. Even
in the case, therefore, of existing species of animals, it can often be
shown that the past distribution of the species was different formerly
to what it is now, not necessarily because the climate has changed,
but because of the alteration of other conditions essential to the
life of the species or conducing to its extension.

Upon the whole, therefore, it would seem that conclusions as to
the climate of any particular area at any given point of geological
time must be accepted with considerable caution, unless in cases
where there happens to be direct physical evidence of an arctic
climate. It has, in fact, been even questioned that there existed
marked differences in the climate of different regions of the earth in
the earlier periods of the earth’s history. Rather, it has been held
that in ancient geological times an equable temperature reigned
over the whole globe, as the result of a relatively high internal
terrestrial heat, the earth’s surface and the air being thus main-
tained at a temperature sufficiently high to render the influence of
the sun’s rays of comparatively little importance. On this view it
was supposed that it was only when the earth’s internal heat had
been largely dissipated by radiation, that climatic zones were devel-
oped ; the temperature of each region coming ultimately to depend
mainly upon the amount of heat which it might receive, directly or
indirectly, from the sun. ‘The change from the one condition of
things to the other was usually supposed to have corresponded, in
a general way, with the commencement of the Tertiary period.

Apart, however, from the inherent improbabilities attaching to this
theory—so far, at any rate, as concerns the periods subsequent to the
introduction of animal and vegetable life upon the globe—it has
been shown by Professor Neumayr that the existence of definite
climatic zones can be demonstrated, by the evidence of fossils, in
periods at least as ancient as the Jurassic. As regards the Pale-
ozoic period, the principal argument for the assumption that the
earth enjoyed a uniformly high temperature, as pointed out by
Neumayr, is that the Paleeozoic animals, even in northern latitudes,

CONCLUSIONS LO, BE “DRAWN FROM FOSSILS. 8I

are often more nearly related to types now living in the tropics than
to any others. As regards certain types—such as the ancient and
persistent genus /Vawte/us—some weight may be reasonably attached
to this argument. Another argument for the assumed uniformity of
climate in Palzeozoic time may be based upon the extraordinarily
wide range in space of many Palzeozoic types of animals. Upon
the whole, however, the Palzeozoic animals differ so widely from
their nearest living relatives as to render it very hazardous to base
-on their supposed habits of life any decided conclusions as to Palze-
ozoic climate. Much the same may be said with regard to the
argument in favour of a very uniform and widely spread warm-
temperate climate during Carboniferous times, based upon the ex-
tension of the predominant Coal-plants to high northern latitudes.

Taken collectively, our knowledge would rather go to show that
considerable variations in climate have occurred in all periods sub-
sequent to the appearance of living beings upon the earth. Thus,
there is more or less weighty evidence in favour of the occurrence
of Glacial periods in various of the older formations, beginning as
early as the Cambrian period. In Mesozoic time, certainly, the
evidence adduced by Neumayr, Marcou, and Trautschold seems to
show conclusively that different regions of the earth enjoyed, as
they do at present, different climates. The first of these observers,
in particular, has shown that a study of the animal life of the Jurassic
deposits of the north hemisphere would support the conclusion that
there existed during the Jurassic period three well-marked climatic
zones—one boreal, one temperate, and one subtropical—and that
two of these, at any rate, can be recognised in the south hemi-
sphere also. .

WOlE 1 F

82

CiMAdes hl gawk

RELATIONS OF PALZONTOLOGY 10 GEOLOGY ae
BIOLOG Y—METHODS OF PALAONTOLOG Y—CLASSI-
FICATION OF THE ANIMAL, TINGYP OM:

In more than one of its aspects, Palaeontology stands in an intimate
relation with Geology. Thus, so far as it is concerned with investi-
gating the mode of life and distribution in space of fossil organisms,
Paleontology becomes directly connected with the physiographical
side of Geology. From another point of view, in so far as it in-
vestigates the relations of fossil organisms to “me, Paleontology
becomes closely interwoven with Historical or Stratigraphical Ge-
ology. In all its fundamental aspects, however, Paleontology is
essentially a branch of #zo/ogy—constituting a branch of Zoology
where it deals with animals, and of Bofany in so far as it deals with
plants. Palzontology, therefore, may be properly divided into the
two departments of ‘ Palzozoology” and ‘ Palzobotany.” The
principal ground for the use of the separate term “‘ Paleontology,”
as distinct from ‘‘ Zoology” and ‘‘ Botany,” is simply that in study-
ing extinct organisms we have to take into account ¢he time at which
these lived. It is therefore the element of time, and that alone,
which entitles us to speak of Palzontology as an independent
science.

The methods of paleontological study are precisely the same as
those of Zoology and Botany. It is true that the earlier palzeontol-
ogists attached a certain importance to the age of a fossil, as bearing
upon the determination of its affinities, and that it was sometimes
assumed that fossils from deposits of different geological ages were
necessarily referable to different specific types. At the present day,
however, it is recognised that the systematic position and relation-
ships of an extinct organism must be settled by an appeal to its
morphological characters, altogether or to a great extent irrespective
of the age of the deposit in which it occurs. The zoologist and the

RELATIONS OF PALZONTOLOGY TO GEOLOGY. 83

botanist similarly rely essentially upon Morphology in the determina-
tion of the relations of animals and plants ; and there is, therefore,
no real difference in the methods of study employed, whether the
organisms under examination be living or extinct.

In some respects, however, the zoologist has a great advantage
over the paleontologist. The student of living beings can investi-
gate the eztire organism, the soft parts as well as the hard; and he
can also study the “development” of the organism, and by tracing
it through its early stages can discover how it came to assume its
adult characters. The student of fossil organisms, on the other
hand, is restricted, with the rarest exceptions, to an investigation of
the Zard parts only. The conclusions of the palzontologist as to
the characters and affinities of fossil animals are necessarily based
upon a study of the skeletal structures, from which the characters
of the soft parts have to be inferred. Moreover, it commonly
happens that even the hard parts of the animal have been im-
perfectly preserved, and that the object to be studied is a mere
fragment of the skeleton, from which all the soft tissues have been
removed. Again, it is only in exceptional cases that we have any
means of making ourselves acquainted with the development of
fossil animals. Considering the generally fragmentary character of
the objects with which the paleontologist has to deal, and the almost
invariable absence in fossils of any traces of the soft parts of the
organism, it might be supposed that the study of fossils was attended
with insuperable difficulties. The most serious of these difficulties
are, however, overcome by means of the law of the “correlation of
organs,” the establishment of which by the illustrious Cuvier marks
an era in palzontological science.

Stated in its most general form, the law of the correlation of
organs is the law that all the parts of an organism stand in some
relation to one another, the form and characters of each part being
more or less closely dependent on, and connected with, the form
and characters of all the rest. In other words, an organism is not a
fortuitous collocation of unrelated parts, but is composed of mutually
adapted and related organs, the possession of any given organ, there-
fore, implying the possession of other “correlated” organs. Thus,
the possession of mammary glands is “correlated” with the posses-
sion of two occipital condyles and of a simple mandible ; a stomach
adapted for rumination is correlated with the possession of only two
functional toes to the foot, and the absence of the central upper
incisors ; an inflected angle of the lower jaw is usually correlated with
the possession of “marsupial bones” or “marsupial cartilages”; a
covering of feathers is correlated (in living forms) with saddle-shaped
faces to the bodies of the cervical vertebre. From the above ex-
amples it will be evident that, by means of the law of correlation, it

84 INTRODUCTION.

is often possible to infer from an isolated organ or structure the es-
sential characters of the remainder of the organism. Thus, if we were
acquainted with no other part of some animal than its skull alone,
and if we found that that skull possessed two occipital condyles, and
that each half of the lower jaw was composed of a single piece, we
should be justified in concluding that the animal to which the skull
belonged possessed mammary glands. We should also be justified
in inferring many other facts about it, as, for example, that it pos-
sessed (or might have possessed) a hairy covering to the body, that
its blood was hot, and that it possessed non-nucleated red blood-
corpuscles. Similarly, if we met with a mammalian lower jaw, the
angle of which was bent inwards, or “inflected,” we should have
a strong presumption that the animal to which it belonged possessed
‘marsupial bones” or cartilages on the brim of the pelvis, and that
the young were born in a very imperfect state of development. It
follows from what has been already said, that the law of the correla-
tion of organs plays a most important part in paleontological inves-
tigation, enabling the observer to more or less completely “‘ recon-
struct” an extinct organism by means of its fragmentary remains. It
is to be remembered, however, that the law is a purely empirical one,
and expresses nothing more than the result of experience; so that
structures which we now know only as occurring in association may
ultimately be found separate, and conjoined with structures of a
different character. Moreover, it is to be borne in mind that in any
two correlated structures it is not that each is correlated with the
other, but that ove of the two is correlated with the other. That is
to say, of any two correlated organs, A and B, it may be true that A
is never found without B, but it does not follow that B may not
occur without A. Thus, the presence of a stomach adapted for
“rumination” is invariably associated (in living types) with an im-
perfect development of the incisors of the upper jaw, the central
upper incisors being always wanting ; but it is not the case that an
incomplete condition of the upper incisors, or the absence of the
central ones, is necessarily correlated with the habit of chewing the
cud. The proper way of putting the case is to assert that certain
structures (A) are never found apart from other structures (B), though
the latter may be present without the former. When, therefore, we
find a lower jaw having its angle “inflected,” we may, with our
present knowledge, assert that the animal to which that jaw belonged
probably possessed “marsupial bones” or ‘‘ marsupial cartilages ”
upon the brim of the pelvis; although the presence of a certain
amount of inflection in the jaws of some Jzsecttvora would preclude

1 A remarkable instance where this correlation is at fault, and has led to the
reference of the bones of one animal to two distinct orders, will be noticed
among the A/ammalia under the head of Chalicotherium.

CLASSIFICATION OF THE ANIMAL KINGDOM. 85

our making this assertion absolutely positive. If, however, we were
to find a pelvis with marsupial bones, we should not be justified in
asserting that the owner of the same must have possessed an in-
flected angle to the lower jaw. On the contrary, we know that such
an assertion would be erroneous, since the ‘‘ marsupial bones” are
present in the Monotremes, in which the angle of the jaw has its
usual form.

CLASSIFICATION OF THE ANIMAL KINGDOM.

Vast as is the number of known animals, all, whether living or
extinct, may be classed under a limited number of primary divisions
or “morphological types,” which are technically spoken of as the
“sub-kingdoms.” There are also certain groups of animals (the
Molluscoids and Tunicates) which have not the value of ‘ sub-
kingdoms,” but which are so far separated by their characters from
their mearest relatives that it is expedient in the meanwhile to treat
them as constituting distinct divisions of the animal kingdom. All
the animals in any one sub-kingdom agree with one another in their
structural type, or in the fundamental plan upon which they are con-
structed, and they differ from one another simply in the modifications
of this common plan. Two animals belonging to different sub-king-
doms may be rendered closely similar to one another as the result of
similar adaptive modifications, but no amount of physiological like-
ness will counterbalance or efface the morphological unlikeness due
to the fact that each is constructed upon an essentially different
ground-plan. As the animals belonging to any given sub-kingdom
are separated solely by the characters due to varying modifications
of a common morphological type, it is possible to arrange the mem-
bers of each in an approximately linear series, in which the lowest
members most closely approach the primitive or ideal form of the
sub-kingdom, while the highest exhibit the greatest amount of com-
plexity and specialisation of this type. But it is not possible to
establish any such linear classification for the animal kingdom as a
whole. Given an animal of a lower “ sub-kingdom” than another
animal, no amount of complexity, no specialisation of organisation,
can raise the former above the latter. The one may be the result of
the high evolution of a low morphological type, the other may be the
result of the low evolution of a higher morphological type, but the
superiority of the ground-plan gives the latter the higher place. It is
obvious, therefore, that a linear classification is not possible; since
the higher members of each sub-kingdom are more highly organised
than the lower forms of the next sub-kingdom in the series, at the
same time that they are constructed upon a lower morphological
type.

86 INTRODUCTION.

It is, in fact, clear that a pictorial representation of the different
groups of the animal kingdom, in the order of their natural alliances,
would not exhibit a series of regularly ascending steps, but would
have the form of a branched and ramified genealogical tree. Such
a tree would exhibit one main stem, which would give origin to nu-
merous lateral stems. These latter would, in turn, subdivide, some
branches ascending in the course of their development, while others,
as the result of degeneration, would descend.

The terms. “class,” order,” 7“ genus,” “sub-genus) a sspeelewme
and “‘ variety,” are employed by the palzeontologist in precisely the
same sense, and with precisely the same limitations, as by the zoolo-
gist. We must notice, however, that a paleontological “ species” has
not always or necessarily the same value as that which a zoological
species ought invariably to possess. This arises from the fact that
the determination of fossil species is, almost without exception, based
solely upon the characters of the hard parts of the animal—these,
also, being often but imperfectly preserved. <A fossil species, there-
fore, cannot, from the nature of things, be as thoroughly defined as a
living one ; and it is both possible and probable that variations in the
form of the skeleton, especially if an integumentary one, may often
depend upon mere individual, sexual, or local peculiarities, which
could be at once discovered in the case of living forms, but which
can hardly be detected as regards extinct types. Moreover, there is
a practical inconvenience attending the use of the terms “ variety ”
and ‘‘sub-genus ” in paleontology, which is not found in zoology,
owing to the very different nature of the working material of these
two sciences. Many paleontologists, therefore, prefer, as we think
rightly, to follow the general practice of giving distinct names to
“varieties ” and “‘ sub-genera,” thus practically raising them to the
rank of “species” and “ genera”; and this practice can hardly be
injurious if accompanied with the well-understood reservation that
this is done as a matter of convenience only, and that a somewhat
wider and looser signification is to be given to the terms “ species ”
and ‘‘ genus ” in paleeontology than would be admissible in zoology.
At the same time, this practice may be, and has been, carried too
far ; and in the case of very variable or “ protean ” species, it is cer-
tainly advisable to adhere to the plan usually adopted by British
paleeontologists—namely, to define the species by its central type,
and to group the variable forms under this type as varieties. As
a general definition, however, of what is understood in palzeon-
tology as a species, we may follow Zittel. This distinguished
naturalist defines a paleontological ‘“‘species” as comprising “all
those individuals, or remains of individuals, which possess in com-
mon an assemblage of constant characters, and which constitute
collectively a distinctly circumscribed morphological series (‘ For-

> 6¢

CLASSIFICATION OF THE ANIMAL KINGDOM. 87

menkreis ”), apart from all considerations relating to their range in
time and in space.” Such a series may be connected by transitional
forms with other morphological groups without losing its claim to be
considered as constituting a ‘‘ species,” provided the series does not
shade off in all directions into allied groups.

The following synoptical table gives the leading divisions of the
animal kingdom, with typical examples of each. Forms marked
with an asterisk are extinct, and are only known in the fossil
condition :—

fase VIEW OF THE CHIEF DIVISIONS OF THE
ANIMAL KINGDOM.
INVA BIR IS ELEVA TIE SAIN OY GATES!
SUB=KINGDOM I.—PROTOZOA.

CLASS I.—GREGARINIDA.
Gregarina, Monocystts. No fossil forms of this class exist.

CLASS II.—RHIZOPODA.

1. MONERA —. 5 : . LProtameba. No fossil forms.

2. AMCEBEA . - : . Ameba, Diffiugia, Arcella. No fossil forms.

3. FORAMINIFERA . : . Gromia, Liloculina, Saccammina, Lituola,
Textularia, Lagena, Globigerina, Rotalza,
* Orbitotdes, Nummulina.

4. RADIOLARIA : ; . Lhalassicolla, Acanthometra, Podocyrtis, Eucyr-
tidium.

5. HELIOZOA . : . Actinophrys, Actinospherium. No fossil
forms.

CLASS Iil.—INFUSORIA.

i. CILIATA : : : . Laramecium. No fossil forms.

2 SUCEORIA . : : . <Acimeta. No fossil forms.

3. FLAGELLATA : . Codostga. No fossil forms.

4. CILIO-FLAGELLATA . . Ceratium, Peridinium. Doubtful fossil repre-
sentatives are known.

SUB-KINGDOM II.—PORIFERA.
CLASS I.—PLETHOSPONGIZ.

1. MYXOSPONGIZ . : . Halisarca. No fossil forms.

2. CERATOSPONGIZ. : . Luspongia. Fossil representatives of doubtful
occurrence.

3. MONACTINELLIDA ; . Spongilla, Cliona, * Scoliorhaphis.

4. TETRACTINELLIDZ . . Zethya, Geodia, Pachastrella, * Tethyopsts.

5. LITHISTID# ; ; . Discodermia, Corallistes, ™ Chenendopora,

* Doryderma, ~Aulocopium, ~* Stphonia,
* Ferea, * Astylospongia.

6. HEXACTINELLIDZ : . Holtenia, LEuplectella, Hyalonema, * Ventri-
culites, * Protospongia, * Caloptychiunt.

88 INTRODUCTION.

7a DOCRAC TIN ET LUDA poy. . Astreospongia.
8. * HETERACTINELLID . Lholiasterella, Asteractinella.

CLASS II.—CALCISPONGLZE.

1. HOMOCELA : : . Leucosolenia. No fossil forms known. (=As-
cones of Haeckel).
2 EE DEROCGHUART = : . Grantia, Sycon,* Protosycon( = Sycones of Haec-

kel), Leuconza, Leucandra, &c. (= Leucones
of Haeckel), *Corynella, * Sestrostomella,
* Pharetrospongia (Pharetrones).

SUB-KINGDOM III.—CC@ELENTERATA.

CLASS I.—HYDROZOA.
Sub-class I.—Hydroida (Hydroid Zoophytes).

i EVDRIDAS 5 ; . Hydra, No fossil forms.
2. CORYNIDA . ‘ : . Coryne, Tubularia, Hydractinia, * Parkeria.
3) LHECAPHORA,- ~: ; . Sertularia, Plumularia, Campanularia, * Den-
drograptus (?), * Callograptus (?).
4. TRACHYMEDUS ‘ . Lrachynema, Aegina, * Palegina.
Sub-class II.—Siphonophora.
I. CALYCOPHORIDZ : . Duphyes. No fossil forms.
2. PHYSOPHORIDA . ; . Lhysalia. No fossil forms.

Sub-class III.—Lucernarida.

I. CALYCOZOA . ; : . Lucernaria. No fossil forms.
2. ACRASPEDA (DISCOPHORA). Aurelia, Rhizostoma, * Rhizostomites.

* Sub-class IV.—Graptolitoidea.

I. MONOPRIONIDZ . ; . Monograptus, Didymograptus, Tetragraptus.
2. DIPRIONIDA : : . Diplograptus, Chmacograptus, Retiolites, Phyl-
lograptus.

Sub-class V.—Hydrocoralline.

a. Milleporidze 5 : . Millepora, * Axopora.
6. Stylasteridze : : . Stylaster, Allopora.
c. * Syringospheeridze : . Syringosphera, Stolicskaria.

*Sub-class VI.—Stromatoporoidea.
Stromatopora, Actinostroma, Labechia.

CLASS II.—ACTINOZOA.

I. ZOANTHARIA.
A. Actiniaria (Zoantharia

malacodermata) . . <dctinia. No fossil forms.
£. Antipatharia (Zoantha-
ria sclerobasica) . Antipathes.

C. Madreporaria (Zoantha-
ria sclerodermata).
a. Aporosa . . Lurbinolia, Oculina, Pocillopora, Maandrina,
* Columnaria, * Stauria, * Holocystis, Mose-
leya.
6, Rugosa ‘ . *Cyathophyllum, “Zaphrentis, * Cystiphyllum.

CLASSIFICATION OF THE ANIMAL KINGDOM. 89

c. Fungida
ad. Perforata

2. ALCYONARIA

Go

—

_

Fungia, * Anabacia.
Madrepora, Porites,
* Thecia.

* Favosites, *Syringopora,

a. Haimeidze Monoxenia, Hartea. No fossil forms.
6, Cornulariadze Cornularia. No fossil forms.

c. Alcyonidee Alcyontum. No fossil forms.

ad. Pseudaxonia . Corallium, Mopsea.

é. Tubiporide . Tubipora. No fossil forms.

J. Helioporidee L[Teliopora.

g. Gorgonidee Gorgonia, Gorgonella, Isis, Primmnoa.
Ah. Pennatulide . Pennatula, * Graphularia.

2. ~Heliolitide. fleliolites, Plasmopora.

j- *Halysitide . fTalysites.

k. *Tetradiide . Tetradium.

Z, *Cheetetide . Chetetes.

. * MONTICULIPOROIDEA.

. CTENOPHORA

. *PALECHINOIDEA
2. EUECHINOIDEA

. ~ENCRINASTERIZ
. ASTERL© VERZ.

. REGULARES
2. IRREGULARES

Aulopora, Cladochonuts.
(Zoological affinities uncertain).
Monticulipora.
fistulipora, Callopora.
Pleurobrachia, Beroe.

me. * Auloporidee

a. Monticuliporidze
6, Fistuliporidee
No fossil forms.

SUB-KINGDOM IV.—ECHINODERMATA.

DIVISION A.—ECHINOZOA.
,CLASS I.—ECHINOIDEA.

Archeocidarts, Bothrioctdarss.

Echinus, Cidaris, Spatangus, * Echinothurta.

CLASS II.—ASTEROIDEA.

Paleaster, Petraster.
Asterzas, Goniaster, Solaster.

CLASS III.—OPHIUROIDEA.

. EURYALIDA A sterophyton, * Onychaster.

. OPHIURIDA Ophiogly pha, * Aspidura.
CLASS IV.—HOLOTHUROIDEA.

Cucumaria, Psolus.
DIVISION B.—PELMATOZOA.
CLASS I.—CRINOIDEA.
. ~ PALZOCRINOIDEA Actinocrinus, Cyathocrinus.
. NEOCRINOIDEA Pentacrinus, *Encrinus, Antedon.
CLASS II.—*CYSTOIDEA.

. APORITIDE Cryptocrinus, Agelacrinus.

. DIPLOPORITIDA. Glyptospherites, Spheronites.

. RHOMBIFERI Echinospherites, Caryocrinus.

CLASS III.—* BLASTOIDEA.

Pentremites, Granatocrinus, Codaster.
Astrocrinus, Eleutherocrinus.

90 INTRODUCTION:

SUB-KINGDOM V.—ANNULOSA,
DIVISION I.—SCOLECIDA.
CLASS I.—PLATYELMIA (Flat-worms).

1 AEN TADAY — : : . Tenia. No fossil forms.

2. TREMATODA : , . Distoma. No fossil forms.

Be URBELLARTA, . . Llanaria, Nemertes. No fossil forms.
CLASS II.—NEMATELMIA (Round-worms).

1. ACANTHOCEPHALA . . Lchinorhynchus. No fossil forms.

2. GORDIACEA : . Gordius. No fossil forms.

3. NEMATOIDEA . : . Ascaris. No fossil forms.

CLASS III.—ROTIFERA (ROTATORIA).

The Wheel-animalcules are wholly unknown in the fossil condition.

DIVISION II.—ANARTHROPODA.
CLASS I.—GEPHYREA (Spoon-worms).

With the very doubtful exception of the Jurassic genus £fztrachys, no represen-
tative of the Spoon-worms is known in the fossil condition. Well-known
recent genera are Szfzzeculus and Echturus.

CLASS II.—MYZOSTOMIDA.

The type-genus is AZyzostoma. (Recent and fossil).

CLASS III.—ANNELIDA (Ringed-worms). |

HIRUDINEA ‘ : . Sanguisuga, Clepsine. No fossil forms.
. OLIGOCHATA . : . Lumbricus (Earth- worm). Not certainly
known in the fossil condition.

YO |

3) ROE CHARA.
a. Tubicola : : . Serpula, Spirorbis, * Cornulites.
6, Errantia A : . Nereis, Aphrodite, * Hunicetes, * Arabellites.
CLASS IV.—CHATOGNATHA (Arrow-worms).
This class comprises the single recent genus Sagit¢a, and has no
fossil representatives.
DIVISION III.—ARTHROPODA.
CLASS I.—CRUSTACEA.

Sub-class I.—Anchoracephala.

I. CIRRIPEDIA : é . Lepas (Barnacle), Balanus (Acorn - shell),
* Turrilepas.
2. RHIZOCEPHALA . : . Leltogaster, Sacculina. No fossil forms.

Sub-class II.—Entomostraca.

I. OSTRACODA : : . Cypris, Cypridina, * Beyrichia, * Primttia.

2. COPEPODA . f ; . Cyclops, Lernea, Argulus. No fossil forms.
3. CLADOCERA : ‘ . Daphnia. No fossil forms.

4. PHYLLOPODA : ; . Apus, Estheria, Branchipus.

5. PHVELOCARTDAGg:: . Nebalia, * Hymenocaris, *Ceratiocaris, *Dis-

c710caris.

€LASSIFICATION OF THE ANIMAL KINGDOM. OI

co, ~ TRILOBITA ; . Asaphus, Calymene, [llenus.,
S&S 47. XIPHOSURA : . Limulus (King-crab), *elcreurus.
O 6 (8. *EURYPTERIDA . . Lurypterus, Pterygotus.
Sub-class III.—Malacostraca.

1. AMPHIPODA : : . TLalitrus, Gammarus, * Prosoponiscus.
2. ISOPODA : ; é . Ldotea, Ontscus, Serolis, * Archeoniscus.
3. STOMATOPODA . : . Sguzlla (Locust-shrimp).
4. SCHIZOPODA ‘ ‘ . JLysts (Opossum-shrimp).
5. CUMACEA . . : . Diastylzs.
6. DECAPODA.

a. Macrura : ‘ . Homarus (Lobster).

6 Anomura . : . Pagurus (Hermit-crab).

én brachyura ) - : . Cancer (Crab).

CLASS II.—ARACHNIDA.

I. PODOSOMATA (PYCNOGONIDA) Pyczrogonum, Nynphon. No fossil forms.
2. ~ANTHRACOMARTI. . Arthrolycosa, Archttarbus, Anthracomartus.
S AGARINA . : : . Acarus, Ixodes, Hydrachna.
4. ADELARTHROSOMATA . . LPhalangium, Chelifer, Galeodes.
Se DEPALPI : , . Scorpio, * Paleophonus, * Proscorpius.
6. ARANEIDA . , . Legenaria, Epetra, * Protolycosa.
CLASS III.—MYRIOPODA.
I. ONYCHOPHORA . ; . Leripatus. No fossil forms.
2. PAUROPODA : : . Pauropus. No fossil forms.
3. “PROTOSYNGNATHA _. . Laleocampa.
4. CHILOPODA. ; 3 . Scolopendra, Lithobius, Geophilus.
5. ~ARCHIPOLYPODA : . <Archidesmus, Euphoberia, Archiulus, Xylobtus.
6. DIPLOPODA (CHILOGNATHA) /2lus, Polydesmus.

CLASS IV.—INSECTA.

I. ANOPLURA ; : . Lediculus. No fossil forms.
2. MALLOPHAGA . ‘ . Trichodectes. No fossil forms.
3. COLLEMBOLA . : . Podura.
4. THYSANURA : : . Lepisma, Petrobius.
5. * PALZODICTYOPTERA . Lugereon, Dictyoneura, Paleoblattina.
6. RHYNCHOTA (HEMIPTERA) JVepa, Cicada, Notonecta.
7. OTHOPTERA : : . Llatta, Mantis, Gryllus, Edipoda, Forficula.
8. NEUROPTERA.

a. Pseudoneuroptera . Libellula, Termes, Ephemera.

6, Neuroptera Vera . Myrmeleon, Hemerobius, Panorpa.

c. Trichoptera : . Lhryganea, Limnophilus.
9. APHANIPTERA . : . Lulex. No fossil forms.
fo. DIPTERA... ; . Culex, Musca, Tipula.
11. LEPIDOPTERA . : . Vanessa, Sphinx, Bombyx.
12. HYMENOPTERA . : . Apis, Vespa, Formica.
3. STREPSIPTERA . : . Stylops, * Triena.
14. COLEOPTERA . : . Melolontha, Carabus, Cicindela.

MOLLUSCOIDEA.
CLASS I.—POLYZOA.
Sub-class I.—Ectoprocta.

I. PHYLACTOLZEMATA . . Llumatella. No fossil forms.
2. GYMNOLAMATA.

a, Cyclostomata : . Tubulipora, Diastopora, * Fenestella, * Ptilo-
dictya.

Q2 INTRODUCTION.

I.

Ze

b, Cheilostomata ; . Cellepora, Eschara, Lepralia, Flustra, Bugula.
c. Ctenostomata : . Vesicularia, Alcyonidium. No fossil forms.

Sub-class II.—Entoprocta.

Loxosoma, Pedicellina. No fossil forms.

Sub-class III.—Aspidophora.
Rhabdopleura. No fossil forms,

CLASS II.—BRACHIOPODA.

INARTICULATA . : . Cranta, Discina, Lingula, * Lingulella,* Acro-
treta.
ARTICULATA : 5 . Lerebratula, Rhynchonella, *Spirifera, * Stro-

phomena, * Orthis, * Producta.

SUB=-KINGDOM VI.—MOLLUSCA.
CLASS I.—LAMELLIBRANCHIATA (CONCHIFERA or PELECYPODA).

I. OSTREACEA : : . Ostrea, * Gryphea, Anomia.

2. SPECDINACE AGH. : . Spondylus, Lima, Pecten.

3. MYTILACEA : : . Avicula, * Aviculopecten, Mytilus, Pinna.

4. ARCACEA , : ; . Arca, Pectunculus, Nucula.

5. SUBMYTILACEA . : . “Modiolopsis, Trigonia, Unio, Astarte, Crassa-
tella.

6. ERYCINACEA \. . *Erycina, Galeomma.

7. CARDIACEA : : . Lridacna, Cardium,* Lunulicardium.

8. CHAMACEA ; : . Chama, * Diceras, * Caprina, * Hippurites.

9. CONCHACEA j : . *Megalodon, Cyprina, Venus, Cyrena, Psam-
mobia, Solen, Donax.

10. MYACEA . : . Mactra, Mya, Glycimeris, Gastrochena.

11. ADESMACEA : : . Pholas, Teredo.

12. LUCINACEA 5 ; . Lucina, Corbis.

12 L BLLEINACEA : . TLellina, Scrobicularia.

14. ANATINACEA . .. . . Solemya, Anatina, Pholadomya, Clavagella.

S

CLASS II.—GASTROPODA.

Sub-Class I.—Branchiogastropoda.

. PROSOBRANCHIATA . . Buccinum, Strombus, Littorina, Natica, *Mur-
chisonia.
OPISTHOBRANCHIATA . . <Acteon, Bulla, Aplysia, Doris.

. PTEROPODA.

a. Gymnosomata ; . Clo, Pueumodermon. No fossil forms.

6b. Thecosomata 5 . Cavolinia, Clecdora, * Hyolithes, * Tentaculites.
. HETEROPODA ; : . Carinaria, Atlanta.

Sub-class II.—Pulmogastropoda.
. STYLOMMATOPHORA . 5 VELA ey IE ULHS
. BASOMMATOPHORA . . Limnea, Planorbis.
CLASS III.—POLYPLACOPHORA.
. CHITONIDZ : ; . Chiton, * Helminthochiton.
CLASS IV.—SCAPHOPODA.

. SOLENOCONCHIA . : . Dentalium.

CLASSIFICATION OF THE ANIMAL KINGDOM. 93

CLASS V.—CEPHALOPODA.

I. DIBRANCHIATA . : . Loligo, Sepia, Spirula, Octopus, * Belemmeites.
2. TETRABRANCHIATA . . Nautilus, * Orthoceras, * Ammonites, * Bacu-
lites.
TUNICATA.

[The Tunicates or Ascidians occupy a position intermediate between JZollusca
and Vertebrata. No fossil forms are known, except in late Tertiary deposits. ]

VERTEBRATE ANIMALS?
SUB-KINGDOM VII.—VERTEBRATA.

CLASS I.—LEPTOCARDIA.

PHARYNGOBRANCHEI : . Lranchiostoma (Amphioxus). No fossil forms.

CLASS II.—PISCES (FISHES).

I. CYCLOSTOMI (MARSIPO-
BRANCHII . : ‘ . Myxine, Petromyzon. No fossil forms.
2. ELASMOBRANCHEI.
a. ~ Ichthyotomi : . Pleuracanthus.
6. Selachii
(1) Tectospondyli . Cestracton, Lamna, Spinax.
(2) eterospondylt . Sguatina, Rata.
3. CHIMAROIDEI . . Chimera, * [schiodus.
4. DIPNOI : ; . Leprdosiren, Ceratodus.
5. GANOIDEI.
a. *Cephalaspidea . . Cephalaspis, Pteraspis.
6. *Placodermata.. . Lterichthys, Coccosteus.
c. ~ Acanthodea : . <Acanthodes, Diplacanthus.
d. Crossopterygea. . ™Holoptychius, Polypterus.
e. Acipenseroidea .. . Acipenser, * Paleoniscus.
jf. Lepidosteoidea . Lepidosteus, * Dapedius.
g. Amioidea. . Amia, * Caturus.
6. TELEOSTEI.
a. Physostomi . . Salmo, Esox, Stluris.
6. Anacanthini . : . Gadus, Rhombus.
c. Pharyngognathi . . Labrax, * Phyllodus.
d. Acanthopterygii . . Mugil, Perca.
e. Lophobranchii_ _.. . Solenostoma, Hippocampus.
f. Plectognathi . : . Balistes, Diodon.

CLASS III.—AMPHIBIA (AMPHIBIANS).

1. * LABYRINTHODONTIA.

a. Branchiosauria. . Protriton.
6, Afstopoda . : . Dolichosoma, Ophiderpeton.
c. Microsauria . . Orocordylus, Ceraterpeton.

d. Labyrinthodontia Vera . Archegosaurus, Mastodonsaurus.

1 The classification of Vertebrate Animals here followed is, in the main, the
one which has been adopted in the latest of the Catalogues of fossil Vertebrates
issued by the Trustees of the British Museum.

Q4 INTRODUCTION.

2. APODA (OPHIOMORPHA) Cecilia, Siphonops. No fossil forms.
3- CAUDATA (URODELA) . Molge, Megalobatrachus.

4. ECAUDATA (ANOURA). Rana, Bufo.

2. * SAUROPTERYGIA Plestosaurus, Pliosaurus, Nothosaurus, Lario-
SQUTUS.
3. CHELONIA.
Ge NUNeCAta a . Dermatochelys, * Protostega.
6. Testudinata or Theca-
phora : J Testudo, Chelone, Trionyx, Chitra, Emyda.
4. “ ICHTHYOPTERYGIA . Ichthyosaurus, Baptanodon.
5. * PROTEROSAURIA Proterosaurus.
6. RHYNCHOCEPHALIA.
*a. Simeedosauria Champsosaurus,
6, Sphenodontina Sphenodon, * Hyperodapedon.
*c. Homeeosauria flomeosaurus, Sapheosaurus.
7, SQUAMATA.
a. Lacertilia Lacerta, Varanius.
6, Rhiptoglossa Chameleon.
c. * Dolichosauria Dolichosaurus.
ad. ~ Pythonomorpha Clidastes, Mosasaurus.
é. Ophidia Python, Coluber, Vipera.
8. * DINOSAURIA.
a. Ornithopoda Leuanodon, Scelidosaurus.
6. Theropoda . Megalosaurus, Zanclodon.
c. Sauropoda Orintthopsis, Diplodocus.
g. CROCODILIA.

10

—

2.

CLASS IV.—REPTILIA (REPTILES).

. * ANOMODONTIA.

a. Pariasauria

6. Theriodontia

c. Dicynodontia .
Group Placodontia .

a. * Aétosauria
6, * Parasuchia
c. Eusuchia

* ORNITHOSAURIA.
a. Pterosauria .
6. Pteranodontia

CLASS

* SAURURZ
RATITA.
aa Odontolezcy
6, * A&pyornithes
c. Apteryges
d. * Immanes
e. Megistanes

Pariasaurus, Pariotichus.
Galesaurus, Clepsydrops.
Dicynodon, Oudenodon.
Placodus, Cyamodus.

Aétosaurus.
Parasuchus, Stagonolepis.
Crocodilus, * Steneosaurus.

Pterodactylus, Rhamphorhynchus.
Pteranodon.

V.—AVES (BIRDS).
Archaeopteryx.

flesperornis.
ipyornis.

Apteryx, * Megapteryx.
Dinornts, Palapteryx.
Casuarius, Drome@eus.

jf. Rhez Lehea.
g. Struthiones Struthio.
hi. Gastornithes Gastornis.
3. CARINAT.
a. * Odontotormee Ichthyornis.
6, Crypturi Tinamus. No fossil forms.

c. Impennes Aptenodytes, * Paleudyftes.
@. Tubinares Procellaria, Puffinus.
e. Pygopodes Alca, Colymbus.

f. Gaviz

Larus.

CLASSIFICATION OF THE ANIMAL KINGDOM.

. Limicole

. Alectorides
Fulicariz
Galline.

. Columbze

Anseres. s

z. Palamedee .

. Odontoglossi
Herodiones

. Steganopodes

. Accipitres

. Striges .

Psittaci .

Picariz .

z. Passeres

ND. PY. MQ

NaS

Mo SBS

Limicola, Scolopax.

Grus, Otts.

Rallus, Notornts.

Gallus, Crax.

Columba, Pterocles, * Didus.
Anser, Aas.

Chauna. No fossil forms.
Phenicopterus, * Elornis.
Ciconia, Ardea.
Phalacrocorax, Diomedea.
Aguila, Vultur.

Otus, Nyctea.

Psittacus, Cacatua.

Picus, Cuculus.

Passer, Corvus.

CLASS VI.—MAMMALIA (MAMMALS).

. MONOTREMATA

. MARSUPIALIA.

a. Polyprotodontia
6, Diprotodontia

1. EDENTATA .

Ny

$y

CETACEA.

a. Odontoceti

6. * Archeoceti .
c. Mystacoceti .
SIRENIA
UNGULATA.

a. Artiodactyla .
6, Perissodactyla
c. * Toxodontia.
d. * Condylarthra
e. Hyracoidea

f. * Amblypoda
g. Proboscidea .
Group * Tillodontia
RODENTIA.

a. Duplicidentata
6, Simplicidentata

. CARNIVORA.

a. Pinnipedia
6. Carnivora Vera
c. *Creodonta .

. LNSECTIVORA.

a. Insectivora Vera
6, Dermoptera .

. CHIROPTERA.

a. Microchiroptera
6. Megachiroptera

. PRIMATES.

a. Lemuroidea .
6, Anthropoidea

Sub-class I.—-Prototheria.

Oriithorhynchus, Echidna,

Sub-class II.—Metatheria.

Dasyurus, Perameles.
Macropus, Phascolenys.

Sub-class III.—Eutheria.

Cholepus, Manis, Dasypus.

Delphinus, Physeter.
Zeuglodon.

Balena, Balenoptera.
Flalicore, Manatus.

Sus, Cervus, Bos.
Rhinoceros, Tapirus, Equus.
Toxodon, Typotherium.
Periptychus, Phenacodus.
Hyrax. No fossil forms.
Coryphodon, Dinoceras.
Elephas, * Dinotherium.
Tillotherium.

Lepus, Lagomys.
Mus, Sciurus, Hystrix.

Phoca, Otaria.
Felts, Ursus, Mustela.
fTyenodon, Pterodon.

Talpa, Erinaceus.

Galeopithecus. No fossil forms.

Vespertilio, Rhinolophus.
Pteropus. No fossil forms.

Lemur, Indris.
Macacus, Siniza.

9

=

96

CA ERE ne ay
THE EVOLUTION OF ORGANIC TYPES IN TIME.

THE naturalists of last century, and of the earlier part of this century,
generally believed that the existing forms of animals and plants had
been simultaneously produced by a special act of creation, and that
they had not been preceded by pre-existent animals and plants.
The occurrence of fossils in the crust of the earth had, it is true,
been for long recognised, and had given rise to much learned con-
troversy. By some, fossils were looked upon as having been pro-
duced by inorganic agencies, and thus as not being really the remains
of animals and plants. Others, again, clearly recognised that fossils
were truly the remains of organisms, but regarded them as having
belonged to animals that had been destroyed in the Noachian
deluge.

At the present day it is universally recognised that our existing
animals and plants have been preceded by many antecedent faunze
and flore. It is also generally admitted that the existing animals
and plants are the modified descendants of older forms of life. The
actual deginnings of life upon the earth are still unknown to us, and
are likely ever to remain so. We have no reason to think that the
most ancient of known fossils belong to the animals which first came
into existence, but much reason to come to an opposite conclusion.
Paleontology teaches us that new forms of life have been from time
to time introduced upon the earth, and that forms already in exist-
ence have become extinct. The laws which have governed this in-
troduction of new and disappearance of old life-forms are still imper-
fectly known to us, but of the fact of this succession of organic types
in time no doubt whatever is possible. It is also quite certain that
there has been not only a successzon but likewise a progression of or-
ganic forms in proceeding from the most ancient of geological periods
to the present day. The whole subject of the evolution of life-forms
in time involves some of the most profound problems of Palzeontol-
ogy, and can be but very briefly glanced at here. The more im-

PEE EVOLU TON: OFF ORGANIC (LYPES IN TIME. 97

portant points in connection with this subject may, however, be
shortly considered under the following heads :—

1. The Primordial Types of Life-—As above remarked, we know
nothing, and are never likely to know anything, of the animals and
plants which really constituted the first living beings. Of the life of
the Archzean period we at present have no certain knowledge ; but
we find representatives of all the Invertebrate sub-kingdoms in the
earliest fossiliferous deposits (Cambrian and Ordovician), while Ver-
tebrates appear low down in the Silurian (in the Clinton formation
of North America). It may, however, be taken as certain that these
ancient fossils cannot possibly be the remains of the really primor-
dial forms of life. Thus, regarded as individuals, these old organic
types are as complex and as highly specialised in their structure as
are the animals now in existence. Moreover, the great Invertebrate
groups of the Axznulosa and Mollusca are found in the Cambrian
period to be represented by many diverse forms, and to have already
reached a stage of advanced development. It would, however, be
at variance with all that we learn from the study of existing organisms,
that these great morphological types should, to begin with, have
presented themselves under highly specialised forms. Rather must
we conclude that a very long period must have been required for the
evolution of these varied morphological types, and that the Cambrian
fauna was really preceded by many antecedent faunze which are at
present unknown to us.

2. The Introduction of New Species—From the beginning of the
Cambrian period onwards, new species of animals have been intro-
duced upon the earth, apparently almost continuously. We may
certainly say that the introduction of new species has been “ con-
tinuous,” if we use this term in the sense “‘of the continued opera-
tion of the cause or causes which introduced life at first” (Dawson).
It has long been recognised that at certain periods in geological his-
tory large numbers of new species were introduced, and this was
formerly explained on the supposition that life was periodically de-
stroyed by physical convulsions, and that each of these “ catas-
trophes” was followed by a creation of new animals and _ plants.
The apparent periodicity in the introduction of new species is, how-
ever, probably really due simply to the imperfection of the geological
record. In all those cases, therefore, where we meet with the appar-
ently sudden incoming of a large number of new life-forms, we may
take it for granted that we have to deal with a hiatus in the geolo-
gical record in the particular area in which this phenomenon is ob-
served. The new forms have, namely, been in existence elsewhere,
and what we are observing is not their first introduction upon the
earth, but merely their first introduction into the area in question.
As regards the period in which we are now living, any apparent ces-

VOL. 1 G

98 INTRODUCTION.

sation in the introduction of new species is probably mainly due to
the shortness of the period during which accurate observations have |
been carried on. Moreover, though our present species have existed
for a time which, relatively to man, is very long, this time, estimated
geologically, may be, and probably is, very short. It is, further, ex-
ceedingly probable that the introduction of new species would, under
any circumstances, be imperceptible to a single observer, or even to
many successive generations of observers, since the changes by which
species are evolved from pre-existing species are probably so slowly
produced as to be imperceptible except when fully completed.

3. Abrupt Appearance of New Species.—In a large number of in-
stances new morphological types appear to have come into existence
abruptly, no closely allied types being known to have preceded them.
This is necessarily the case with the animals of the most ancient of
the fossiliferous formations (viz., the Lower Cambrian) ; but a similar
phenomenon is observable in hosts of other instances, where we
might reasonably expect to find that the new types were preceded by
older relatives. It is obvious, however, that this apparently abrupt
appearance of a new morphological type—as, for example, the sudden
appearance of the great family of the Azdzste in the Cretaceous
period—arises from an imperfection in our knowledge. On any
theory of evolution, each morphological type must have come into
existence, coincidently, both in space and time, with a pre-existing
allied morphological type (Wallace). When, therefore, we find new
morphological types suddenly appearing on a given geological horizon,
in an area where no allied forms have been found in older de-
posits, we must come to one or other of two conclusions. Either
the apparent absence of allied types in older strata is due to the fact
that these strata have not been sufficiently investigated, or the appar-
ently sudden introduction of the new forms is due to the fact that
the case is not one of their first. coming into existence at all, but
simply one of their first appearance in the area under observation.
In many instances where new organic types suddenly appear in an
area, the older deposits in which we might expect to find the remains
of the predecessors of these, are missing altogether in the same area.
Thus, we cannot expect to find the immediate predecessors of the
numerous new life-forms which in Europe usher in the commence
ment of the Secondary period, till we find the deposits which were
laid down in the interval between the close of the Permian and the
beginning of the Triassic period. In many other instances, however,
where the series of the stratified deposits may be moderately com-
plete, the apparent abruptness of appearance of a given morpholo-
gical type is really due to the fact that the series has been imper-
fectly examined ; and further investigation would either show that
the type in question really began to exist at an earlier period, or

LHe EVOLUTION" OF ORGANIC TYPES IN TIME. 99

would bring to light allied types from which we might suppose it to
have descended.

4. Relative Persistence of Species in Time.—The duration in time,
or “‘ vertical range” of species, varies greatly in different cases. Some
species have an extraordinarily extended range, sometimes passing
through two or three geological systems, and in such cases they
generally exhibit numerous varieties. This is the case, for example,
with some of the Brachiopods, such as Strophomena rhomboidalis
and Atrypa reticularis. Others, again, are singularly restricted in
their range, and do not pass beyond the limits of a single subdivision
of a system, or, it may be, even of a single band or zone. No case
is known in which a species which has once fairly died out has re-
appeared at a later period, but there is no absolute impossibility in
the separate evolution of the same specific type at two separate
periods. As a general rule, it is the animals which have the lowest
and simplest organisation that have the longest range in time, and
the additional possession of microscopic or minute dimensions seems
also to favour longevity. Some of the Foraminifera, for example
(e.g., Saccammina Carter’), seem to have survived, with little or no
perceptible alteration, from the Ordovician period to the present day.
On the other hand, large and highly organised animals, though long-
lived as zudividuals, rarely seem to live long as sfeces, and have,
therefore, usually a restricted vertical range. Some gevera, as some
species, are short-lived ; whereas others extend through a succession
of geological periods with extraordinarily little modification. Among
these ‘‘ persistent types ” may be specially mentioned the genus Zz7-
gula among the Brachiopods, and /Vauti/us (in the wide sense of the
name) among the Cephalopods, of which the former commenced in
the Cambrian and the latter in the Ordovician, and both of which
are represented by living species.

5. Relative Range of Morphological Types in Space.—The range of
particular morphological types in space is as variable as it is in time.
Some forms appear to be wholly restricted to some particular area,
or, possibly, to a single locality; while others have an enormous
range, and are found at very widely distant points of the earth’s sur-
face. Ina general way, the types which have a wide range in “me
have also a wide range in space. Thus, species of Brachiopods
like Strophomena rhomboidalis and Atrypa reticularis, which range
through more than one geological system, have likewise a very
extended geographical distribution. Still, a species which is con-
fined to a single system may have an enormous range in space—as,
for example, the common Pvoducta semireticulata of the Lower
Carboniferous ; while in some cases types which are restricted to a
single “zone,” like certain Graptolites and Ammonites, are found to
range over very wide areas. The apparently simultaneous appear-

Tele) INTRODUCTION.

ance of groups of morphological types in corresponding geological
periods in widely separated areas of the earth’s surface is probably
fallacious. Such groups must have appeared first in one area, and
their extension therefrom must have been the result of subsequent
migration. The only other explanation of this phenomenon would
be that the same morphological types had been szmultaneously pro-
duced at several widely remote points ; but this hypothesis is appar-
ently irreconcilable with any theory of evolution.

6. Extinction of Morphological Types.—While new species have
been constantly appearing throughout geological time, old species
have as constantly been undergoing extinction. In some cases,
extinction seems to have taken place with extraordinary abruptness,
as seen, for example, in the sudden disappearance of the Audist@ at
the close of the Cretaceous period. In other cases, extinction has
been a gradual process. In either case, we are to a large extent
ignorant of the causes of extinction, and of the laws under which
the process is carried on. As a general rule, it may be taken for
granted that the sudden disappearance of a whole group of morpholo-
gical types is more apparent than real. When we have a sufficiently
complete series of deposits, it 1s usual to find that a group has
begun to dwindle down long before it finally disappears from the
scene. Thus, the Graptolites, the Trilobites, and the Orthocera-
tites exhibit a progressive diminution as regards the number of
specific types before we reach the point at which extinction takes
place. Why these, and other similar groups, should show such an
extraordinary power of rapid extension and of the development of
new specific or generic types when first introduced upon the earth,
and should thereafter progressively decay and ultimately become
extinct, is a problem for which the solution has yet to be found. In
any case, it 1s to be remembered that in many cases “ extinction ”
implies nothing more than continued existence under a new form.
That is to say, a species often becomes apparently extinct by becom-
ing gradually modified into a new species, in which case the parent-
form actually disappears, but the modified form represents it in later
deposits.

7. Evolution of Morphological Types from pre-existing Forms.—
Paleontology has furnished a mass of evidence in favour of the view
that the introduction of new species in past time has been by evo-
lution from pre-existing forms. Taken as a whole, therefore, the
evidence of Palzeontology points to the operation of some general
law of evolution, whereby the later forms of life have been derived
from the older ones. ‘The principal palzeontological facts which sup-
port the general theory of the evolution of organic types from pre-
existing forms may be briefly glanced at here under the following
heads :—

THE EVOLUTION OF ORGANIC TYPES IN TIME. IOI

(a.) In the first place, it is a powerful argument in favour of the
theory of evolution that the primary morphological types which we
recognise among existing animals are identical with the types upon
which fossil animals are constructed. While the great majority of
fossils are extinct, and while many of them are extremely unlike any
existing forms, no fossil animal has hitherto been detected which
cannot be referred to one or other of the existing sab-kingdoms. Few
fossil animals, indeed, possess peculiarities so great as to entitle them
to be placed in any cass, other than in one of the classes of recent
forms. On the other hand, the differences between some of the
ancient types of life and the existing ones are so great, that palzeon-
tologists have been compelled to construct new swd-classes, orders,
and gezerva for their reception.

(6.) Again, the investigation of fossil animals has tended to greatly
diminish the intervals by which allied groups of existing animals are
separated. Many fossil animals, namely, are what has been termed
‘“‘comprehensive” in their morphological characters. That is to say,
they combine in themselves structural peculiarities which in later
formations or at the present day are only found separately, in groups
more or less widely removed from one another. ‘These “synthetic
types” or “collective types” serve to bridge over the gaps between
related morphological types, and are thus of special interest from a
theoretical point of view. Thus, to take a single example only, the
two great classes of the Saurvopsida—viz., the Reptiles and the
Birds—are at the present day separated by a wide interval. Palez-
ontology, however, has brought to light a number of transitional fos-
sil forms—some referable to Birds and some to Reptiles—which
more or less markedly combine in themselves the distinctive charac-
ters of both groups, and thus partially fill up the gap which now
exists between these two great divisions of Vertebrates.

(c.) Again, many fossil animals exhibit what are termed “ general-
ised” characters. If, namely, we construct for ourselves a “ general”
or “ideal” zyfe for any great group of animals—a type which shall
possess all the essential characters of the group, without its non-
essential ones—then we find that the fossil animals of the same
group are generally nearer to this type than are its living represen-
tatives. Moreover, the older representatives of any given group are
usually nearer to the ideal type of the group—or are more “ general-
ised ”—than are the later representatives of the same group. All
zoologists, however, admit that the process of development in any
individual animal is one in which there is a gradual progress ‘from
the general to the special, the embryo being nearer to the general
type of the group to which it belongs than the adult is. In other
words, the embryo animal is more generalised than the adult, and
the process of development is one of specialisation. Admitting this,

102 INTRODUCTION.

it follows that the fossil forms belonging to any given group, in so
far as they are ‘‘ generalised ” in their characters, may fairly be said
to be “embryonic” types; and as the oldest forms of any given
group are usually the least specialised, so they are likewise the most
“embryonic.” It must be borne in mind, however, that if we speak
of fossil animals as being ‘‘ embryonic types,” we can only do so on
the distinct understanding that it is not thereby implied that they
were In any way degraded forms, or that they were at all less perfectly
constructed, or less thoroughly adapted for their surroundings, than —
their modern representatives.

(d.) Lastly, overwhelming evidence in favour of a general theory
of evolution is afforded by the similarity of the types of life in suc-
cessive faunee and flore. The animals and plants of each geological
system are more closely related to the animals and plants of the
system immediately below and to those of the system immediately
above, than they are to the organisms of any other rock-group in the
stratified series. This fundamental paleontological fact does not
admit of reasonable explanation except upon the view that the
organisms of each geological period are the modified descendants of
those of the preceding period, and are the progenitors of the organ-
isms of the next succeeding period. Each geological system has, of
course, more or fewer special types of life, which are confined to it,
and which, apparently from inability to adapt themselves to changes
in their environment, die out before the close of the system without
leaving descendants. Others undergo but slight modification, and
appear in the next system as new species, “representative” of the
species from which they sprang. Others, again, vary more pro-
foundly, and break up into diverging groups, represented in the
succeeding period by more or less widely distinct forms.

8. General Progression of Organic Typfes.—The history of living
forms, as preserved in the paleontological record, exhibits a distinct
upward progress from the lower to the higher, or from the more
generalised to the more specialised. At the present day, the animal
kingdom admits of division into a number of primary morphological
types, of which some are higher than others. Thus, the Vertebrate
type is zoologically higher than any type of the Invertebrates, and the
sub-kingdoms of the latter have also a certain relative rank according
to the complexity of their plan of organisation. In the same way,
within the limits of each sub-kingdom, some of the groups are more
‘¢ specialised,” and therefore higher in the scale, than others.

Not only do the primary morphological types differ from one an-
other in relative zoological rank, as estimated by relative complexity
of organic plan, but Paleontology shows clearly that there has been
a progression in the order of their development, the lower types hav-
ing, in the main, preceded the higher in time. It is true, as before

PEE VOLUTIONFORFORGANIGCSLYPES IN TIME. TOs

pointed out, that it is very doubtful if we are as yet acquainted with
the absolute time of the first appearance upon the globe of even one
of the sub-kingdoms. Future discoveries, therefore, are almost cer-
tain to push back still further into the remote vistas of the past the
point of time at which each morphological type first made its appear-
ance upon the globe. Nevertheless, there is little likelihood that the
relative times of appearance of the great groups, as compared with
one another, will be affected by any discoveries which we have yet to
make. Moreover, as regards the Invertebrate sub-kingdoms, we are,
_ perhaps, never likely to find any reliable evidence which would
enable us to fix with precision their relative order of appearance.
All of these sub-kingdoms appear in the Cambrian deposits, and the
utmost that we can be certain of is that they had been in existence
in times long anterior to the Cambrian. Owing, however, to the
very general metamorphism which has affected the pre-Cambrian
sediments, we cannot hope to ever obtain more than the most scanty
evidence, if any, as to the actual origin of the earliest types of
life. With regard to the Vertebrate animals, on the other hand, the
series of the fossiliferous rocks is long enough to render it certain
that within its limits we ought to find traces of the first appearance
of, at any rate, the higher classes of these, though we are doubtless
likely to remain ignorant of the precise stage in the series at which
each first made its appearance. If, therefore, it can be shown that
there has been a progression so far as this sub-kingdom is concerned,
then there would, by analogy, be the greatest probability that a
similar progression has taken place as regards all the sub-kingdoms.
So far as our present knowledge goes, it would appear certain that
there zs such a progression in the Vertebrate sub-kingdom. The
classes of Vertebrates make their appearance, on the whole, in the
order indicated by their zoological position, the lowest first and the
highest last. Where apparent exceptions occur, a reasonable explan-
ation can be given, or our knowledge can be shown to be defective.
Thus, the Fishes constitute the lowest group of Vertebrates, and in
accordance with this they are the first to make their appearance (in
the Silurian period). The Amphibians stand next to the Fishes in
zoological rank, and they are the next group of Vertebrates to make
their appearance, their earliest known representatives being found
towards the close of the Paleozoic period (in the Carboniferous
system). A little later than the Amphibia (in the Permian period)
appear the Reptiles, which constitute the next highest class of Ver-
tebrates. The class of Birds, the next in the series, possesses a
paleontological record so fragmentary that we may leave it out of
account in this connection ; but the last and highest group of Verte-
brates, that of the Mammals, appears for the first time towards the
close of the Triassic period. It need only be added, that the gene-

104 INTRODUCTION.

ral progression of zoological types, indicated by the successive intro-
duction of the great classes of Vertebrates in the order of their
zoological rank, is amply confirmed and strengthened by what is
known as to the geological history of all the great groups of animals
of which we have a fairly complete record. Even as regards the
Invertebrate sub-kingdoms, where we are admittedly ignorant of the
first appearance of the main divisions, we are nevertheless commonly
able to show that the minor groups have been successively intro-
duced in the order of their zoological rank. At the same time, it is
to be borne in mind that zoological groups do not usually appear for
the first time in either their lowest or highest forms. The earliest
representatives of each group are, on the other hand, very usually
‘* generalised ” types, which have the capacity for either elevation or
degeneration in their later development.

9. Zhe Absence of closely graduated transitional Forms between
allied Morphological Types.—While the general testimony of Palzeon-
tology is overwhelmingly in favour of the view that some general law
of evolution has operated in the production of the varied forms of
life which now exist or have existed in the past, there is no dvect
paleontological evidence which would certainly establish any partic-
ular theory as to the precise modus operandi of this law. With
regard more particularly to the theory of “the origin of species by
means of natural selection,” which the world owes to the genius of
Darwin, the evidence of Palzeontology cannot be said to be conclusive.
More especially, we have in most cases no sufficient evidence of the
former existence of the numerous and closely graduated transitional
forms between different species, which must, on this theory, have once
existed. It is an essential part of the theory of natural selection
that the production of any given species from any pre-existing species
can only have been effected through the intervention of a long series
of intermediate or transitional forms. It is true that many extinct
animals are known which are clearly transitional between existing
groups, now more or less widely separated from one another. It is
also true that in a certain number of instances (particularly among the
Molluscs) it has been found possible to connect two different specific
types by means of a long series of intermediate links, the separate
members of the series differing only in minute characters. As a
general rule, however, the known transitional forms between allied
groups are few in number, and are so far isolated from one another
and from the forms they connect as to be in themselves absolutely
distinct morphological types. It cannot be denied, therefore, that
palzontology has, so far, to a large extent, failed to bring forward
the numerous and closely graduated series of intermediate forms
which must at one time have existed, supposing “natural selection ”
to be the sole agent in the origination of new species. The absence

PoE EVOLUTION OF ORGANIC TYPES IN TIME. 105

of a sufficient number of such transitional forms, and the insufficient
connection between such as are known to exist, may doubtless be
in part explained by the known ‘imperfection of the geological
record”; but this does not appear to offer an adequate solution of
the difficulty. The theory of “the origin of species by means of
natural selection,” as elaborated by the master-mind of Darwin,
constitutes, nevertheless, an invaluable, indeed an indispensable,
guide in all branches of paleontological research.

EEE RATURE.

[With regard to the subjects dealt with in the introductory portion of
this work, the following are some of the original sources of information to
which the student may have recourse. It is to be remembered, however,
in the case of this, as of subsequent bibliographical lists of a similar char-
acter, that nothing more has been attempted than to give a selection of
the more important original memoirs. |

1. “ Anniversary Address to the Geological Society of London.” (Min-
ute Structure and Chemical Composition of the Calcareous Skele-
ton of Invertebrates ; Structure of Limestones, &c.) 1879. Sorby.

. “Anniversary Address to the Geological Society of London.” (Ge-
ological Contemporaneity and Persistent Types of Life.) 1862.
Huxley.

3. “ Address to the Geological Section of the British Association for the
Advancement of Science.” (Homotaxis.) 1884. Blanford.

4. “ Relative Ages of American and English Fossil Floras.” ‘ Geological
Magazine,’ 1884, p. 496. J. Starkie Gardner.

5. ““ Homotaxis and Contemporaneity.” ‘ Geological Magazine,’ 1886,
p- 293. Oldham.

6. “ The Application of Biology to Geological History.” ‘ Proc. Biolog-
ical Soc. of Washington,’ 1886. C. A. White.

7. “ The Inter-relation of Contemporaneous Fossil Faunas and Floras.”
woumer |Our. oct and Ants, vol. xxxiil., ps 364, 1687. C. A.
White.

8. “ The Origin of Species by means of Natural Selection.” (Chapters
x. and x1., on “the Imperfection of the Geological Record,” and
on “the Geological Succession of Organic Beings.”) Sixth Edition,
1872. Darwin.

g. “ Défense des Colonies.” 1865 and 1870. Barrande.

to. “ The Pre-Devonian Rocks of Bohemia.” (The “ Colonies” of Bar-
rande.) ‘Quart. Journ. Geol. Soc.,’ vol. xxxvi., 1880. J. E. Marr.

11. “On the Nomenclature, Origin, and Distribution of Deep-sea De-
posits.” ‘Proc. Roy. Soc. Edin., 1884. John Murray and A.
Renard.

12. “ Report on the Deep-sea Deposits.” ‘ Narrative of the Cruise of
H.M.S. Challenger,’ vol. 11., Part 11., 1885.

13. “ The Geographical and Geological Distribution of Animals.” 1887.
Heilprin.

14. “ Ueber klimatische Zonen wahrend der Jura- und Kreide-Zeit.’
‘Denkschriften der kais. Akad. der Wiss.’ Vienna. 1883. Neu-
mayr.

15. “ Les Ancétres de nos Animaux dans les Temps Géologiques.” 1888.
Gaudry.

WN

ewerar oY,
Segoe eve

VAS 06 Ramee ie

ree eee Oe ee) OV EV G.-Y

INVER PE DRA A

BY

Ho ALEEYNE NICHOLSON

Epos Lo Es

Crier PE ho VE
SUB-KINGDOM I—PROTOZOA.

THE sub-kingdom /vo¢ozoa, as the name implies, includes the most
lowly organised members of the animal kingdom, and may be de-
fined as comprising animals composed of undifferentiated protoplasm,
or, at most, of protoplasm so far differentiated as to have developed
an outer “wall” and a central “nucleus,” the organism in the
latter case becoming a “cell.” In no case are definite “ tissues” de-
veloped by the differentiation of a primitive cellular aggregate. There
is no proper “ body-cavity”, no nervous system; and either no alt-
mentary apparatus, or one of a rudimentary nature.

The Protozoa are small, commonly microscopic animals, for the
most part aquatic in their habits. The contractile, jelly-like proto-
plasm, or “sarcode,” of which the body is composed may be en-
tirely naked, or may have the power of secreting hard structures,
of horn, lime, or flint. The following table exhibits the chief groups
of the Protozoa.

Cass I. GREGARINID#.—Protozoa in which the body has the form of
a simple cell, without any mouth-aperture, and destitute of the power of
emitting “pseudopodia.” The Gregarines are for the most part internal
parasites, and possess no hard structures.

CLass II.—RHIZOPODA (SARCODINA).—Protozoa which are destitute
of a mouth, and have the power of emitting extensile and contractile pro-
cesses of protoplasm (“ pseudopodia”). The sarcode may or may not
have the power of secreting hard structures.

Order 1. MWonera.—Ex. Protamceba.
Order 2. Amebea.—Ex. Amceba.

Order 3. Foraminifera.—E-x. Globigerina.
Order 4. Raditolarza.—Ex. Haliomma.
Order 5. Helzozoa.—E x. Actinophrys.

I1IO PROTOZOA.

CLAss III.—INFUSORIA (Infusorian Animalcules).—Protozoa which
are typically provided with a mouth and rudimentary digestive cavity,
which do not possess the power of emitting pseudopodia, but which are
furnished with vibratile cilia or with contractile filaments. They are
mostly microscopic in size, and are mostly destitute of the power of se-
creting hard skeletal structures.

Regarded palzontologically, we may eliminate from the Protozoa
the entire class of the Gvegarinide, with the Rhizopodous orders of
the AZonera’ and Amebea, no trace of the past existence of which
has yet been obtained, or, from their soft-bodied nature, is ever
likely to be. For all practical purposes the same may be said of
the large and universally distributed class of the Infusorian Animal-
cules.2 Some of these, however, possess chitinous or membranous
cases, which might possibly be preserved in a fossil state; and
Ehrenberg has found in the flints of the Chalk certain microscopic
bodies, which he regarded as being the protective carapaces of
Feridinium and allied forms of Flagellate Infusoria. With this
doubtful exception, however, no Infusorian animalcule has ever been
detected in the fossil state, though the class has doubtless existed
from the most remote antiquity. There remain, then, only the
three Rhizopodous orders of the Foraminifera, Radiolaria, and Helz-
ozoa, in all of which the soft protoplasmic body is generally strength-
ened by hard structures of horn, lime, or flint. The last mentioned
of these orders comprises fresh-water organisms, in which a skeleton
is absent or imperfectly developed, and no traces of fossil Alelzozoa
have hitherto been met with. On the other hand, the Aoraminifera
and fadiolaria usually have a well-developed skeleton, and are
more or less extensively represented as fossils, so that they demand
attention separately and in detail.

FORAMINIFERA.

The Foraminifera may be defined as Rhizopoda in which the
body ts protected by a shell or “‘ test,” which ts composed of carbonate
of lime, or which may consist of particles of sand cemented together by
some animal cement, or may be simply horny (chitinous). The body-
substance gives out long and thread-like processes ( pseudopodia), which
interlace with one another to form a network, and often coalesce at
their bases to form a continuous layer of sarcode outside the shell.
The pseudopodia (fig. 18) reach the exterior either by perforations in

1 The ‘‘ coccoliths ” are sometimes regarded as being referable to the MWonera ;
but they will be considered here as belonging to the vegetable kingdom, and they
will be briefly described in speaking of fossil 4/ge.

2 “¢ Fossil Infusoria ” are often spoken of as forming more or less extensive de-
posits in the earth’s crust, but the organisms so named are really Dzatoms and
Polycystina.

FORAMINIFERA. ele!

the walls of the shell, or simply by the mouth of the latter, or by both
these sets of apertures combined.

From a paleontological point of view the only part of a Foram-
inifer with which we have to deal is the shell or “test,” and there
are several points to notice in this connection. Firstly, as regards
the actual composition of the shell, it is in the majority of cases cal-
careous, or composed of carbonate of lime, but it is rarely chitinous,
and it is not uncommonly “arenaceous”—that is, composed of

Fig. 18.—A many-chambered Foraminifer (Rotalia veneta) with the radiating and netted
pseudopodia protruded. Greatly magnified. (After Max Schultze.)

particles of sand cemented together by some animal substance or
by carbonate of lime. With the horny or chitinous /oramuinifera
(Gromide) we have nothing to do here, as they have never been,
and are never likely to be, detected in a fossil condition.

I12 PROTOZOA.

An advance upon the chitinous shell is that presented by the
so-called “‘arenaceous” Foraminifera (fig. 19), which are among the
largest of the living types, the test being sometimes half an inch or
more in length. In some cases the “arenaceous” test is nothing
more than a chitinous envelope, protected by a layer of mud, or
having sand-grains more or less largely embedded in its substance
(H. B. Brady). Typically, however, the test of the arenaceous
Foraminifera consists of sand-grains or other foreign particles united

Fig. 19.—Shells of Arenaceous Foraminifera. a, Test of Astrorhiza, greatly enlarged; B,
Test of Trochammina ringens, enlarged thirty times; c, Test of Tvochammina litutformts,
enlarged eighteen times. (After W. B. Carpenter and Brady.)

together by a variable amount of cementing material, this latter con-
taining from two to three per cent of carbonate of lime together
with a notable proportion of peroxide of iron. The arenaceous
Foraminifera have, as a rule, no pseudopodial apertures or “ fora-
mina” in the walls of the test, the pseudopodia being emitted from
a single general or “oral” aperture, or from a number of apertures
in the wall of the last chamber. ‘Though normally ‘“ imperforate,”
there are, however, certain forms of the arenaceous or sub-arenaceous
foraminifera (such as Valyulina, Nodosinella, and Endothyra) in
which the walls are pierced by pseudopodial foramina. Indeed,
some degree of porosity appears to be commonly present, and in
some forms there is no ‘oral aperture” to the test at all.

The great majority of the /oraminifera possess a shell composed
essentially of carbonate of lime, with or without variable quantities
of other constituents. Two chief varieties of these calcareous tests
are known, termed respectively the ‘‘ porcellanous” and the “ hya-
line” or “vitreous” types. In the so-called ‘ porcellanous” types,
the test is quite homogeneous in its composition, opaque-white
when seen by reflected light, and destitute of pores or foramina

FORAMINIFERA. mae

for the emission of pseudopodial filaments. In all the porcellanous
Foraminifera, therefore, the shell is ‘‘ zmferforate,” and the pseudo-
podia are emitted from a general ‘oral aperture.” There is also
reason to believe that the shell in these types is largely composed
of aragonite. Though normally calcareous, the test may be en-
crusted by sand-grains, or it may be composed of siliceous particles
embedded in a chitinous envelope, or, as shown by Dr H. B. Brady
to sometimes occur in examples of JZ/ola dredged from great
depths, it may even be genuinely siliceous. On the other hand,
in the so-called “hyaline” or ‘‘ vitreous” types of the Foraminifera,
the calcareous test (composed principally of calcite) is glassy and
transparent, and its walls are perforated by numerous minute tubes
through which the pseudopodia are emitted. In the series of the
hyaline Foraminifera, therefore, the test is said to be “perforate.”
Hence, in vertical sections of the shell of any such type (e.g., Glodr-
gerina), the test is seen under the microscope to be traversed by
closely set tubules, running at right angles to the outer and inner

Fig. 20.—a, Vertical section of Fig. 21.—Section of the shell of Rotalia Schrateri-
the test of Globigerina bulloides, ana, magnified, showing pseudopodial tubes in the
highly magnified, showing the walls (d). The test is also traversed by a series of
pseudopodial tubes; B, Tangen- radiating and transverse canals (a, 6, c). (After
tial section of the same, showing Williamson and Carpenter.)

the tubules in transverse section.
(Original.)

surfaces of the shell; while in tangential sections (z.e., sections
parallel with the surface) these tubules are transversely divided, and
appear as dark spots or clear pores (see figs. 20 and 21).

The presence, or absence, of pseudopodial tubes in the walls of
the test has been employed as a character whereby the entire group
of the Foraminifera might be divided into the two sections of the
Perforata and Lmperforata ; the former including the hyaline or

MOL. 1. H

114 PROTOZOA.

vitreous types, while in the latter are comprised the “ porcellanous,”
‘“‘arenaceous,” and “chitinous” types. It has been shown, however,
that this division is not strictly natural, since various arenaceous
types possess a test which is more or less extensively porous. It
would appear, in fact, that the composition of the shell is liable to
variation, in accordance with the nature of the material obtainable
by the organism at any particular station, and that it is therefore
possible to attach too great value to this character in framing a
classification of the Foraminifera.

Again, as regards the form of the shell, great differences exist
among the Foraminifera, and as concerns the mere external con-
figuration, this is so variable that little or no value can be attached
to it in classification. Moreover, in the two great series of the
Perforate and the Imperforate Foraminifera it is common to find
parallel or ‘‘isomorphic” groups. ‘That is to say, we meet with two
series of forms, repeating each other’s peculiarities and variations in
Jorm, but the shell in the one series being perforate, while in the
other it is imperforate.

The simplest form among the Foraminifera is that of a single
spheroid of sarcode, capable of secreting for itself a hard covering,
as in the flask-shaped Lagena (fig. 29, f) or the
globular Oréudina (fig. 22). Forms such as these
are said to be “unilocular” or ‘‘monothalamous,”
the test consisting of but a single chamber, not
subdivided by partitions or “septa.” In the more
complex /oraminifera, the sarcode of the body

Fig. 22.—Oréuling Undergoes a subdivision into partially separated
universa. A simple segments, produced by constrictions in the grow-

Foraminifer from the

Pliocene strata (Sub- ing protoplasm, and each of these segments be-
Tele LOsicayye comes more or less completely divided off from its

neighbours, or enclosed by a wall of shell. In
these “multilocular” or ‘“polythalamous” Foraminifera, therefore,
the shell ultimately comes to consist of a series of chambers,
separated by partitions of the test, and filled with sarcode. The
partitions, or ‘‘septa,” between the different chambers, are, however,
perforated by one or more apertures, through which pass connecting
bands, or “stolons,” of sarcode; so that the sarcode occupying the
different chambers is united into a continuous and organic whole.
Each segment may give out its own pseudopodia through perfora-
tions in its investing wall (fig. 18), or the pseudopodia may be
simply emitted from the mouth of the shell by the last segment
only. In any case, the direction in which the segments are devel-
oped is governed by a determinate law, and differs in different
species, the form ultimately assumed by the shell depending wholly
upon this. The forms assumed by the shells of /oraminzfera are,

FORAMINIFERA. 115

however, extremely variable, even within the limits of a single
species, and it would be impossible to notice even the chief types
in this place. There are, however, two or three important variations
which may be mentioned. If the buds are thrown out from the
primitive spherule in a linear series so as to form a shell composed
of numerous chambers arranged in a straight line, we get such a type
as JVodosaria (fig. 29, g). When the new chambers are added in a
spiral direction, each being a
little larger than the one which
preceded it, and the coils of the
spiral lying in the same plane, we
get such a form as C7istellaria
Giear2s)y) hese are the so-
called “‘ nautiloid ” Foraminifera,
named from the resemblance of
the shell, in figure, to that of the
BearyeNanulus: -Hrom this res 9 Me: 23> Cele ee
semblance the nautiloid Fova-

minifera were originally placed in the same class as the Ammonites
(Cephalopoda), but their true position was shown by the examination
of their soft parts. In the typical nautiloid shell the convolutions
of the spiral all lie in one plane; but in other cases, as in Aofalia
or Pulvinulina (fig. 24), the shell becomes turreted or top-shaped,
in consequence of the coils of the spiral passing obliquely round a

Fig. 21.—Pulvinulina Boueana. (D’Orbigny.)

central axis. In other cases, as in Zinoporus, the chambers are
arranged in an irregular or “‘acervuline” manner.

In the majority of the polythalamous Foraminifera, the successive
chambers of the test are so produced that the septum between any
two of them is formed solely by the anterior wall of the older cham-
ber, which thus constitutes the posterior wall of the newer one (fig.
25). In the highest types of the compound Foraminifera, however,
each chamber is provided with its own proper wall of shell, each
segment, as it is produced, forming for itself a posterior wall which
applies itself to the anterior wall of the preceding segment; so that
each septum (“septal plane”) is composed of ¢zwo lamelle, as seen

Li PROTOZOA.

in fig. 26, a (Carpenter). Moreover, ‘in the higher types of the
hyaline or vitreous series we frequently meet with an ‘ intermediate ’
or ‘supplemental’ skeleton, formed by a secondary or exogenous
deposit upon the outer walls of the chambers, by
0 which they receive a great accession of strength.
; This deposit not only fills up what would other-
wise be superficial hollows at the junctions of the
chambers (fig. 26, a @), or (as in Polystomella) at
the umbilical depression, but often forms a layer
of considerable thickness over the whole surface,
thus separating each whorl from that which en-
closes it; and it is sometimes prolonged into out-
growths that give a very peculiar variety to the
ordinary contour, as in some varieties of fofala
and Folystomella, but most characteristically in
Calcarina (fig. 26, B), and the stellate form of
Tinoporus. This intermediate or supplemental
d skeleton, wherever developed to any considerable
Fig. 25.—Section of extent, is traversed by a set of ‘canals,’ which
the shell of Vodosaria .
rapa, showing the are usually arranged upon a systematic plan, and
mode of formation of are sometimes distributed with considerable min-
Dees hay eq velics ag (Carpenter). The canals of this system
Primordial chamber. are doubtless filled in the living state by prolonga-
tions of the sarcode, which serve to keep up the
vitality of the intermediate skeleton. This intermediate skeleton,
with its canal-system, is largely developed in many of the highest
and largest of the types of the hyaline /oraminifera, and very
specially so in the “‘ Nummulites ” and their immediate allies.

As regards the distribution of the /oramuinifera in space, a few
forms (all belonging to the single family of the Gromid@) are fresh-
water in habit, but the vast majority are inhabitants of the sea.

As regards the marine forms, very many species live in compara-
tively shallow water, but certain forms are found at great depths in
the ocean. A small number of forms, belonging, according to Dr
Henry B. Brady, to eight or nine genera, are pelagic in their habits,
and “pass their existence, either in part or entirely, at the surface of
the ocean or in mid-water.” Though only a few genera have pelagic
representatives, these few are of great importance, owing to the ex-
traordinary profusion in which they occur individually. The princi- —
pal pelagic genus is Globigerina, most of the species of which live in
the open sea, though one species of the genus seems to always live
at the bottom. The shells of the pelagic Foraminifera, after the
death of the animal, fall to the bottom of the sea, where they ac-
cumulate to form (along with the shells of the species which live
habitually at the bottom) great deposits of “ Foraminiferal mud.”

FORAMINIFERA. yy,

The most important deposit of this nature at the present day is the
well-known “ Globigerina ooze,” which is found to cover vast areas
of the sea-bottom in all the great oceans, mostly at depths of from
600 to about 2500 fathoms, and which is of special interest from the
resemblances which it presents to the White Chalk. The “ Globi-
gerina ooze” is a whitish or greyish mud, principally composed of
carbonate of lime, but containing a considerable proportion of silice-

|
|
|
|
|
|
|
|

Fig. 26.—a, Diagram of one of the higher forms of the vitreous Foraminifera, showing the
double nature of the septa (4), the stolon-passages between successive chambers (a), and the
supplemental skeleton (d); B, Test of Calcarina Sfenglerz, magnified twelve diameters, show-
ing the spines formed by the supplemental skeleton; c, Part of a section of the test of
Calcarina, magnified fifty diameters, showing the tubulated ‘‘ proper walls” of the chambers
(zz), and the canal-system of the intermediate skeleton (¢d); p, Part of the test of Nzaz7ulina
levigata, highly magnified, showing the canal-system of the septa (s), and marginal cord (7).
(After Carpenter.)

ous matter, along with a variable quantity of subordinate ingredients
such as alumina. When examined microscopically, the Globigerina
mud (fig. 27) is found to consist principally of the entire or broken
shells of oraminifera, belonging mostly to the genera Glodigerina,
Orbulina, Hastigerina, and Pulvinulina, together with many of the
singular calcareous organisms known as “ coccoliths.” In the nature
of the organisms of which it is composed, the Globigerina ooze of the
present day presents the closest resemblance to White Chalk ; while
the chemical differences between them—especially as regards the
relative percentage of silica—admit, as will be more particularly

118 PROTOZOA.

pointed out hereafter, of satisfactory explanation. There are, how-
ever, other differences between the two, especially as regards the
characters of the Molluscan fauna of the latter, which would indi-
cate that the Globigerina ooze and the
White Chalk were not formed under
conditions precisely alike.

As regards the distribution of the
Foraminifera in time, representatives of
the group are found in almost all, or
in all, rock-groups in which limestones
are developed from the Ordovician
period onward. Leaving the much
disputed ozoon on one side, no re-
mains of Foraminifera have hitherto
been recognised as occurring in any
deposit older than the Ordovician. As
regards the older rocks, the remains of
foraminifera are usually found most
abundantly in limestones, or in calca-
reous shales, and particularly in the
_Fig. 27.—Section of hardened Glo- shaly partings which separate calcare-
bigerina ooze, enlarged about twelve 5
Linco Recent s(@rizmall) ous bands. In many cases, they have
| contributed notably to the composi-
tion of the solid crust of the earth, and have often built up massive
and widely extended limestones. In other cases, where they are
present in smaller quantity, they may be commonly detected in thin
sections of limestone. In some instances, the tests of Foraminifera
have been infiltrated, prior to fossilisation, with glauconite (silicate
of iron and potash), and the actual shell has subsequently been dis-
solved away. In some of the warmer seas of the present day,
green sands are found to be in course of deposition, the grains of
which are largely composed of internal casts in glauconite of the
shells of Foraminifera ; and it is probable that the green grains
of various deposits, and especially of the Cretaceous system, are
in part of a similar nature.

If we omit the group of the Receptaculitide, regarded by Hinde
as referable to the Forzfera, the Ordovician, Silurian, and Devonian
limestones exhibit in general a remarkable, and, in fact, an unac-
countable, absence of the remains of Foraminifera ; since the variety
of the types of these organisms represented in the limestones of the
Carboniferous period would justify the conclusion that the order is
one of very high antiquity. The remains of Foraminifera are not,
however, absolutely wanting in these ancient deposits, since the
recent genus Saccammina has been found to occur in rocks of
Ordovician age, while the Devonian limestones occasionally con-

FORAMINIFERA. 119

tain the tests of Aoraminifera. In the Carboniferous period, most
of the limestones can be shown by microscopical examination to
contain the shells of Foraminifera in larger or smaller numbers (see
fig. 4); and some of them are so largely composed of the cases of
these minute organisms as to become truly “ Foraminiferal lime-
stones.” Of this nature are the great Fusulina limestones of Russia
and North America, and the Saccammina limestone of Britain. It
is interesting to notice that the highly specialised genus Vummulina,
which attained such a vast development in the Tertiary period, is
represented for the first time in the Carboniferous limestone. In
_ the Permian limestones Foraminifera are tolerably abundant, but on
the whole nearly resemble their Carboniferous predecessors.

In the Mesozoic period, the remains of Aoramznifera are more or
less abundant in the Triassic and Jurassic systems, occurring in
limestones, shales, or marls, and sometimes being present in sufficient
numbers to give rise to regular Foram-
iniferal limestones. In the Cretaceous
period, the most remarkable Foramini-
feral rock is the White Chalk itself. This
well-known and widely extended forma-
tion can be readily shown by micro-
scopical investigation to be very largely
made up of the entire or broken shells
of foraminifera, amongst which the
genus Globigerina plays a predominant
part (fig. 28). There is thus a close
and striking similarity between the White
Chalk and the “Globigerina ooze” of
modern seas. The principal distinction
between Chalk and consolidated Globi-
gerina mud is found in the fact that the
latter contains a considerable proportion

sae - Fig. 28.— Section of White
of siliceous matter, while the former con- Chalk, from Sussex, enlarged

sists of from ninety-five to ninety-eight 2>out fifty times. (Onginal.)

per cent of carbonate of lime, and is

nearly or quite free from disseminated silica. This distinction is,
however, more apparent than real, and depends in reality upon the
changes which the Chalk has undergone subsequent to its original
deposition. The siliceous matter in the modern Globigerina mud is
due to the presence of a larger or smaller intermixture of the flinty
tests of Radiolarians, the spicules of siliceous Sponges, the tests of
Diatoms, and the like. There is no reason to doubt, however, that
the Chalk, when first laid down, similarly contained a larger or
smaller quantity of siliceous matter in the form of the skeletons
of flint-producing organisms such as Sponges. ‘The silica of these

120 PROTOZOA.

skeletons in course of time underwent solution, and the siliceous
Sponges are now found in the White Chalk only in the form of casts,
or with their original skeleton replaced by some such substance as
peroxide of iron. The dissolved silica thus produced was ultimately
segregated from the mass of the Chalk, and is now represented by
the nodules of flint which form such a characteristic feature of parts
of the White Chalk. It would appear, therefore, that the White
Chalk in its original chemical composition must have been very
closely similar to the modern Globigerina ooze ; and it is a reason-
able conclusion from its general purity that it must, like its modern
analogue, have been deposited in a deep and open ocean, at a con-
siderable distance from land. At the same time, the characters of
the JZollusca which are predominant in the Chalk, would go to show
that this remarkable Foraminiferal deposit must have been laid down
in general at depths less than those at which the modern Globigerina
ooze 1s now accumulated.

In the Tertiary period, lastly, the remains of Foraminifera are
abundant and varied, and are often present in such numbers as to
give rise to more or less extensive Foraminiferal limestones. The
most notable of these is the great ‘‘ Nummulitic limestone” of the
Eocene. In the later Tertiary deposits, the genera represented are
mostly those now in existence, and many of the species are identical
with living forrms. The Foraminifera, in fact, like other lowly
organised forms, have been very ‘‘persistent” types of life. A
number of the Cretaceous species, indeed, appear to be inseparable
from existing forms, while some living species are believed to date
from even an earlier period. As regards the genera, the prevalent
types in Carboniferous times still survive unchanged; and Dr Carpen-
ter has enunciated the conclusion that upon the whole “ there is no
evidence of any fundamental modification or advance of the Forami-
niferous type from the Palzeozoic period to the present time.”

CLASSIFICATION OF THE FORAMINIFERA. — The classification of
the Foraminifera has proved a matter of considerable difficulty.
The older arrangements were unnatural, as being based wholly on
the form of the shell, a point in which the foraminifera show a most
marvellous variability. For this reason, the artificial systems pro-
posed by D’Orbigny and Max Schultze have now been generally
abandoned, and their place has been taken by other more natural
schemes of classification, and especially by those put forward inde-
pendently and almost simultaneously by Professor von Reuss upon
the Continent, and by Dr W. B. Carpenter, Mr Parker, and Professor
T. Rupert Jones in this country. Both these arrangements agree in
the essential feature that they divide the /oraminifera into two great
primary divisions, in accordance with the nature of the shelly invest-
ment. In the one division (Jmferforata), the test is not perforated

FORAMINIFERA. I21

by pseudopodial apertures, and it may be either ‘‘arenaceous” or
“porcellanous.” In the other division, the test is perforated by
more or less numerous pseudopodial foramina, and to this division
the name of Ferforaza is applied. The following tables exhibit the
arrangements proposed by Carpenter, Parker, and Rupert Jones, on
the one hand, and Reuss, on the other hand; the former being the
most natural, and the one most widely adopted :—

A. CLASSIFICATION OF THE FORAMINIFERA, ACCORDING TO
CARPENTER, PARKER, AND RUPERT JONES.

Sub-Order I, IMPERFORATA.—Test membranous, calcareous, or are-
naceous, not perforated by pseudopodial foramina.

Family 1. Gromdda. Family 2. J/zlolida.
Family 3. Lztuolida.

Sub- Order IJ, PERFORATA.—Test perforated by pseudopodial foramina,
generally calcareous.

Family 1. Lagenzda. Family 2. Globigerinida.
Family 3. Mummulinida.

4. CLASSIFICATION OF THE FORAMINIFERA ACCORDING TO REUSS.
I. FORAMINIFERA WITH A NON-PERFORATE TEST.

A.—W ith arenaceous tests.

1. Lituolidea. 2. Uvellidea.
B.—With compact, porcellanous, calcareous tests.
1. Sguamulinidea. 3. Peneroplidea.
2. Miliolidea. 4. Orbttulitidea.

II. FORAMINIFERA WITH A PERFORATE TEST.

A.—With a glassy, finely porous, calcareous test.

1. Sperillinidea. 5. Polymorphinidea.
2. Ovulitidea. 6. Cryptostegia.

3. Rhabdotdea. 7. Textilaridea.

4. Crtstellaridea. 8. Casstdulinidea.

£.—With an exceedingly porous, calcareous test.
1. Rotalidea.

C.—With a calcareous shell, traversed by a ramified canal-system.

1. Polystomellidea. 2. Nummuletidea.

On the other hand, Dr H. B. Brady, one of the highest living
authorities on the Foraminifera, has recently pointed out that, in the
light of our present knowledge, the primary division of the order
into the two sections of the Ferforata and Lmperforata cannot be

122 PROTOZOA.

considered to be natural. It is now well known that many of the
Arenaceous Foraminifera, forming one of the principal groups in the
old section of the Zmperforata, have diffused pseudopodial apertures,
with or without a general aperture as well, so that their test is truly
“perforate.” The retention of the sections Perforata and Lmfperfo-
rata would therefore necessitate the splitting up of the Arenaceous
Foraminifera into two series, one with a “perforate” and the other
with an “imperforate” test. In view of this fact, Dr Brady has
abandoned the minute structure of the test as an exclusive basis for
the classification of the /oraminifera, and has proposed the follow-
ing arrangement of the order into families :—

ORDER FORAMINIFERA (RETICULARIA).

Family 1. GROMIDAZ.— Test chitinous; smooth or encrusted with
foreign bodies ; with a pseudopodial aperture at one or both extremities.
Ex.—Gromia, Microgromia, Lieberkiihnia.

Family 2. MILIOLIDZ.—Test imperforate ; normally calcareous and
porcellanous, sometimes encrusted with sand, or, under certain condi-
tions, chitinous or siliceous. A2.—&iloculina, Peneroplis, Orbttolites.

Family 3. ASTRORHIZID£.—Test composed of sand-grains or other
foreign bodies, usually more or less united into a coherent test by a
cementing material. Usually the test is monothalamous, often branched
or radiate, sometimes partially subdivided, but seldom or never -truly
septate. La.—Astrorhiza (fig. 19, A), Rhabdammina, Saccammina.

Famtly 4. LITUVOLIDZ.—Test arenaceous, usually regular in contour ;
septation of the polythalamous forms often imperfect; chambers fre-
quently labyrinthic. L2—Lztuola, Trochammina (fig. 19, B and C),
Endothyra.

Family 5. TEXTULARID#.—Tests of the larger species arenaceous,
with or without a perforate calcareous basis ; smaller forms hyaline and
perforated. Chambers arranged in two or more alternating series, or
spiral, or confused. 4A2.—Textularia, Valvulina.

family 6. CHILOSTOMELLIDA.—Test calcareous, perforate, polythala-
mous. Segments following each other from the same end of the long
axis, or alternately at the two ends, or in cycles of three ; more or less
embracing. Aperture a curved slit at the end or margin of the final
segment. L2.—Chilostomella.

Family 7. LAGENID&.— Test calcareous, finely perforated; either
monothalamous, or consisting of a number of chambers joined in a
straight, curved, spiral, alternating, or (rarely) branched series. Aperture
simple or radiate, terminal. No interseptal skeleton nor canal-system.
Ex.—Lagena, Nodosaria, Cristellaria.

family 8. GLOBIGERINIDZ.—Test free, calcareous, perforate ; cham-
bers few, inflated, arranged spirally. Aperture single or multiple, con-
spicuous. No supplementary skeleton nor canal-system. 42.—G/odz-
gerina, Orbulina.

Family 9. ROTALIDA.—Test calcareous, perforate ; free or adherent.
Typically spiral and “ rotaliform”—~z.e., coiled in such a manner that the
whole of the segments are visible on the upper surface, those of the last
convolution only on the inferior or apertural side, sometimes one face
being more convex, sometimes the other. Aberrant forms evolute, out-
spread, acervuline or irregular. Some of the higher modifications with

FORAMINIFERA. 123

double chamber-walls, supplemental skeleton, and a system of canals.
L£x.—Rotalia, Discorbina, Carpenteria, Calcarina, Tinoporus.

Family to. NUMMULINID#.—Test calcareous and finely tubulated ;
typically free, polythalamous, and symmetrically spiral. Usually a “ sup-
plemental skeleton” and canal-system. L2.—Nummulina, Polystomella,
fusulina, Nonionina.

In connection with the general subject of the classification of the
Foraminifera, the following remarks by Dr Brady may advantageously
be quoted ; since they not only have a most important bearing upon
the special point in question, but forcibly express the principles
which should guide the philosophic naturalist in his systematic treat-
ment of all such variable forms of life: ‘‘ A purely artificial classifi-
cation is ill adapted to the conditions presented by a class of organ-
isms like the Foraminifera, largely made up of groups of which the
modifications run in parallel lines. This ‘isomorphism,’ demon-
strated chiefly by the labours of Messrs Parker and Jones, whilst it
is the source of most of the difficulties the systematist has to con-
tend with, is, at the same time, the key to the natural history of the
order as at present accepted. It exists not merely between a single
series, in one of the larger divisions, with a single series in another,
but often amongst several series even of the same family. It not
unfrequently happens that a member of one group presents a greater
similarity to its isomorph in another group, with which it has no rela-
tionship, than it does to any other member of its own group. Take
a familiar illustration—suppose the fingers of the two hands to repre-
sent the modifications (‘species’) of two such parallel types of Fora-
minifera: the thumb of one hand resembles more closely the thumb
of the other hand than it does any other of the fingers on its own.
In other words, the extreme member of one series bears greater
similarity to its isomorph in the other series than it does to its own
nearer relations, and so on through the remaining members of the
respective groups. Under conditions like these, artificial subdivision,
based upon minor morphological characters, is certain to infringe
the order of nature, owing to its tendency in some cases to separate
forms closely allied, and in others to place together such as have no
natural affinity.”

The principal fossil groups of Foraminifera require a brief con-
sideration, but in the short summary of these which follows—as in
the case of similar summaries which will subsequently be given—it
will be understood that nothing further is proposed than to select for
notice and characterisation those /eading types of each great group of
fossils which may seem to demand mention on the ground of their
being common, or in other respects, geologically or zoologically, of
peculiar importance. For anything like a complete list of the known
structural types of each group, or the characters of all the recorded

124 PROTOZOA.

genera, the specialist will consult special treatises ; and it does not
appear to be necessary for the wants of ordinary students to do more
than to supply a brief statement of the conspicuous characters—
especially the differential characters—of the more widely distributed
and more important types in each group. Nor can even this limited
characterisation of leading types be carried out with equal fulness in
the case of all groups of fossils, or upon any absolutely uniform plan.
In the case, however, of Invertebrate fossils, as being those with
which the palzontologist is more especially called upon to deal, the
families of each group will, where possible, be defined, and some of
the chief generic types will be noticed. The subjoined engraving,
representing some of the principal type-forms of the Foramuntfera, is
from a drawing kindly made for the author by his friend, Dr Henry
Brady, who has so greatly contributed to our knowledge of this
difficult group of organisms.

The first family of the old division of the Imperforate Aoramuintfera,
that of the Gromzde, requires no special consideration from a palzeon-
tological point of view, as it is not represented by any fossil forms.
Most of the Gvomide are inhabitants of fresh waters, and they
possess a thin, chitinous, imperforate shell, sometimes encrusted
with foreign bodies, and with a general pseudopodial aperture at one
or both ends. Owing to the horny character of the shell, it is hardly
probable that any members of this family will ever be discovered in
the fossil condition.

In the family of the AZztolide, the test is opaque, porcellanous,
unilocular, or multilocular, and extremely variable in shape; the
oral aperture being simple and undivided, or being formed by
numerous pores. The family, as far as known at present, is not
represented in the Palzeozoic period, but ranges from the Trias to
the Recent period inclusive. One of the simplest forms of this
group is Cornuspira (fig. 29, a), in which the shell is a simple un-
chambered spiral, like the shell of a Planorbis. The genus is repre-
sented for the first time in the Lias, and is found under living forms
in our seas. /Vubecularia is a still older type, beginning in the Trias,
and its test, extraordinarily variable in shape, is usually parasitic upon
shells and other foreign bodies. In d@io/a, again (fig. 29, 4, repre-
senting the sub-generic form Quzngueloculina), the shell is still ex-
tremely variable in form, but it consists typically (4z/oculina) of a
series of chambers wound round an axis, in such a manner that each
embraces half the entire circumference. This genus dates from the
Trias, and is well represented in recent seas. It abounded in Eocene
times, one of the Tertiary limestones of the Paris basin being known
as the “ Miliolite limestone,” in consequence of its being largely
made up of the shells of a AZzZzola._ In Peneroplis (fig. 29, c), which
is Closely allied to Cornuspira, the shell is a flattened spiral, which

FORAMINIFERA. es

expands very rapidly in its last half turn, the mouth running along
the length of the base, and being constituted by numerous isolated

Fig. 29.—Types of Foraminifera. a, Cornuspira foliacea; b, Quingueloculina seminulum ;
c, Peneroplis pertusus ; d, Lituolaagglutinans ; e, Trochamimina pusilla; f, Lagena sulcata ;
g, Nodosaria radicula; h, Marginulina raphanus; 1, Frondicularia Archiaciana ; 7, Poly-
morphina lactea; k, Globigerina bulloides; 1, Textularia sagittula; m, Cassidulina levigata ;
n, Bulimina Buchiana; 0, Rotalia Beccarii; p, Truncatulina lobatula; r, Archediscus Kar-
veri; s, Polystomella crispa; t, Amphistegina Lessoni. All the figures are greatly enlarged,
the real diameters varying from 1-100 to r-10 inch. (H. B. Brady.)

pores. It ranges from the Eocene to the present day. Much more
complicated types of the AZzolde are Alveolina and Orbitolites.

126 PROTOZOA.

The former has a comparatively large fusiform shell, consisting of
many layers of chambers rolled up spirally round an elongated axis,
the last series opening by a row of pores. It dates from the Cre-
taceous period, and has largely contributed to the formation of
various of the Tertiary limestones. The latter is coin-shaped, some-
times more than half an inch in diameter, and very complex as
regards the arrangement of its chambers. The genus is especially
abundant in the Eocene Tertiary, but it dates from the Lias, and
occurs plentifully in recent seas.

The next family of the /oramuinifera is that of the Astrorhizide,
comprising a number of interesting types, sometimes of considerable
size, in which the test is composed of sand-grains or other foreign
particles, generally united by a cementing basis, but sometimes
slightly or not at all consolidated. The test may be monothalamous
or polythalamous, but in the latter case genuine internal septa do
not exist. The shell is often branched or radiate, and may attain a
considerable size. The type-genus of this family is Astrorhiza itself
(fig. 19, A), which is not known to occur in the fossil condition, its
test, though of considerable thickness, having its component grains
very imperfectly cemented together. A much firmer and more com-
pact shell is possessed by the genus Saccammina, which merits special
mention as being the only Foramini-
fer which in Britain can be said to
actually form a limestone. It con-
sists of free spherical, pyriform, or
fusiform chambers (fig. 30), some-
times separate, sometimes united
end to end in twos or threes, with
thick, internally labyrinthic walls.
The central chamber communicates
with the exterior by a single aper-
ture, and the average length of the

i

cn
lua

a

HT

\. Be) chambers of the British Carbonifer-
ae, 2S SCOouss species (Saccammina Carteri,

: Brady) is as much as 1-8th inch.
QoS 3 Se It forms beds of limestone in the
Fig. 30.—A, A slice of limestone with Sac- Carboniferous of the South of Scot-
cammina Cartert, enlarged five diameters, land and North of England : but
from the Carboniferous Limestone of EIf- ‘ 1 Z
hills, Northumberland. (After H. B. Brady.) the genus 1S not. known tomeccur
, Sph f th , of th tural size, : . cate
cUhibiine vanaconee” oan ae eae again till we meet it in the Post-
Pliocene, and, in a living state, in
the North Sea. The genus is, however, of a much higher antiquity
than the Carboniferous, since it is found to be largely represented
in the Ordovician limestones of Ayrshire.
In a number of very interesting forms of the Astrorhizide, the test

FORAMINIFERA. 127

is tubular, composed of arenaceous tubes, of which the sand-grains
may be loosely or firmly cemented together, and which may be free
or may be adherent along one side to foreign bodies. The tubular
test may be branched or radiate, or may simply be more or less
loosely coiled and contorted. One of the most remarkable recent
types of this group is Syzizgammina, in which the test 1s described
by Dr Brady as forming masses of branching, radiating tubes, arranged
in more or less distinct layers or tiers. In Ayperammina, again, the
test (fig. 31) has the form of a sandy tube, often of indefinite length,

Fig. 31.—The winding tubular test of Hyferammina vagans, adherent on one side to a piece
of broken shell. a@ Initial chamber ; 4 General pseudopodial aperture. The figure is enlarged
fifteen diameters. Recent. (After H. B. Brady.)

with the closed end commonly inflated so as to form a distinct
chamber, the pseudopodia being emitted from a general aperture at
the opposite end of the tube. The tube in this genus may be free,
or may be adherent to foreign bodies.

The forms just mentioned throw light upon some very remarkable
fossils which occur in great numbers in certain of the Ordovician
limestones of Britain and North America, and which have been
described under the generic name of Girvanella (= Strephochetus).
The fossils in question present themselves in the form of small
rounded or irregular nodules (fig. 32, A), which are sometimes so
abundant as to constitute a conspicuous element in the limestone.
When broken, these nodules show a distinctly concentric structure,
and when examined by means of thin sections (fig. 32, B), they are
found to consist of exceedingly minute circular tubes (about 1-45
millimetre in diameter), endlessly contorted and bent, and twisted

128 PROTOZOA.

together in loosely reticulate or vermiculate aggregations. The most
probable view of the relationships of this singular fossil is that it is an

Fig. 32.—a, Fragment of limestone from the Ordovician rocks of Craighead, Girvan, of the
natural size, showing numerous exceptionally large masses of Givvanella problematica; B,
Section of a minute mass of G77-vanella, enlarged about sixty times. (Original.)

Arenaceous Foraminifer, allied to the recent genera Syrinmgammina
and Alyperammina.

The last group of the so-called ‘“ Imperforate” Foraminifera is
that of the Zztuwofide, comprising an extensive series of arenaceous
types, in which the shell consists essentially of particles of coarse or
fine sand cemented together more or less firmly. In many cases
the cement is calcareous, and though
the shell is usually imperforate, the
walls are in other cases pierced by
pseudopodial apertures. Sometimes
the test consists of purely calea-
reous particles embedded in a cal-
careous cement. In Zzzuo/a itself,
the type of the group (fig. 29, @),
the test is generally crosier-shaped,
sometimes nautiloid, usually with a
rough exterior, and composed of
sand-grains agglutinated together.
The genus ranges from the Car-
Fig. 33.—Section of Carboniferous Lime- [b oniferous to the present day. At
stone from Spergen Hill, Indiana, U.S., : : ‘
showing numerous large-sized Foraminifera essentially Carboniferous type 1s
(Endotiyra) and a few oolitic grains ME En doryra, in which sheen Ware

nautiloid, or resembles that of a
Rotalia in shape, and is found abundantly in the Mountain Lime-
stone of Britain. It forms in America entire beds of the Carbon-
iferous Limestone (fig. 33). Allied to Lxdothyra is the Liassic

FORAMINIFERA. 129

genus Jzvolutina, formerly placed among the Rotaline Foraminifera.
In Zrochammina (fig. 29, e) the test is usually spiral, consisting of
one or many chambers, free or attached, and, though sandy, with
a smooth surface. It ranges from the Carboniferous to the present
day. Valvulina (fig. 34) also generally has a spiral shell which may
be free or attached, and is normally thick-walled, imperforate, and
sandy. Sometimes, however, the shell is porous and smooth,
and in other cases the sandy coating seems to be a mere en-
crustation on a calcareous and perforate shell, so that Valvulina
(which is by Brady included in the family of the Zextudaride) may
be regarded as a transitional type between the series of the imper-
forate and perforate Foraminifera. The genus makes its first ap-
pearance in the Carboniferous of Britain, is
abundant in the Tertiaries, and is represented
in existing seas. In the /Vodosinella of the
Carboniferous we have another curious type,
closely resembling the well-known (Vodosaria
in form, but having a sub-arenaceous, imper-
forate test. A still more singular form is the
Stacheta of the Carboniferous, in which the
test is also sub-arenaceous and imperforate,
but grows parasitically upon foreign bodies,
in the shape of a crust composed of “an
acervuline mass of chamberlets” (Brady).
Lastly, there is a peculiar group of the Zztu-
olide represented by the recent Cyclammina
and the extinct Loftusia, in which the test is
sandy, and the finely arenaceous shell-wall is pig. 5, a, valvulina pal-
irregularly cancellated, so as greatly to restrict @7achus, viewed in profile,
the actual cavities of the chambers. In Cy- The came iota from below.
i . : OF} Carboniferous Limestone. (Af-
clammina the shell is spiral and nautiloid, ¢é; Brady.)
with numerous chambers arranged in an in-
volute series. In the singular genus Loftusia (fig. 35), from the
Eocene Tertiary of Persia, the test is fusiform, and may attain a
length of from two to three inches. As regards its internal structure,
the shell is composed of a spirally rolled lamella, the volutions of
which run in the long axis of the test, and which is of a sandy
texture and is much cancellated (fig. 35, B). The spaces between
the volutions of the primary lamella are intersected by obliquely
directed partitions, which are also cancellated in structure, and are
connected by numerous irregular vertical pillars.

The genus Parkeria, which has commonly been referred here,
has been shown by recent investigations to be truly referable to the
fydrozoa, and to be related to the existing Aydractinza.

Coming next to the great series of forms which have usually been

VOL. 1. I

130 PROTOZOA.

grouped together under the name of “ Perforate Foraminifera,” the
first family we have to deal with is that of the Zextwlarida@, in which
the test may be arenaceous or calcareous, but usually possesses a
perforate calcareous basis. The smaller forms of the family have a

=

= = “triy

SS

TS

Y = eS
Z, PEE, Wat.
ie pana N 5 Lapp
wee re 4 See Us
LS YL Li
OTE AGMA t PAE,
f 3 aac idee %

Fig. 35.—a, A specimen of Loftusia persica, from the Eocene of Persia, of the natural size,
cut open to show its general plan of structure. (After Brady.) 8, Portion of a vertical section ot
Loftusia, showing the minute structure of the test, enlarged about ten times. (Original.)

hyaline calcareous shell, with large pseudopodial foramina. The
chambers are usually arranged in two or more alternating series,
generally in a straight line, but sometimes in a spiral. In many
cases (e¢.g., in Bigenerina) the test is dimorphous, the first-formed
chambers being in a double series, while the later ones are uni-
serial. In Zextu/aria itself (figs. 209,
7, and 36) the test is generally coni-
cal or wedge-shaped, and consists of
numerous chambers arranged in two
alternate parallel series. Azgenerina
is much the same as TZexfularia,
except that the last-formed seg-
ments are disposed in a single and
not a double series ; and both make
Fig. eee their first appearance in the Car-
boniferous, the latter being a com-
mon type in many formations and being specially abundant in the
Chalk. Sulmina (fig. 29, 2), dating from the Trias (Rheetic) on-
wards, consists of spheroidal segments which progressively increase
in size, and form an oblique spiral; while Casszdul/ina (fig. 29, m),
ranging from the Miocene to the present day, though truly biserial,
is more or less completely rolled up, and may thus be regarded as
an involute Zextularia. Lastly, Chrysidalina, dating from the
Chalk, is like Zextu/aria, but is triserial. :
Closely related to the Textularians are the forms included in the
small group of the Czzlostomellide, in which the test is many-
chambered, calcareous, and finely perforate. The segments follow

FORAMINIFERA. 131

each other from the same end of the long axis, or alternately at the
two ends, or in cycles of three, and the one last formed more or
less completely embraces those previously formed. In Cz%zlosto-
mella itself, the segments are oval, and each entirely envelops the
previous one; whereas in Aomorphina, the chambers alternate at
three sides so as to leave portions of two, in addition to the last one,
exposed to view. The former genus is confined to the Tertiary
deposits, and the latter is Cretaceous and Tertiary.

The great family of the Zagenzde comprises “hyaline” or ‘ vit-
reous” Foraminifera, with a calcareous shell, the walls of which are
pierced by numerous mzzu¢e pores, and are usually more or less
strikingly thin and glassy. In the compound forms of this group
the successive chambers have their posterior walls formed by the
front wall of the preceding segment, so that the septa are always
single, instead of being double, and there is never any ‘“inter-
mediate” skeleton. The family may be divided into two series,
Lagena itself being the type of the one, while /Vodosaria is the type
of the other. In ZLageza (fig. 29, 7) the shell is simple, flask-shaped,
unilocular, with a single prominent aperture. The genus commen-
ces in the Silurian, with forms little different from, or identical with,
existing types, is further developed in the Secondary and Tertiary,
and is well represented at the present day. Folymorphina (fig. 29, 7)
is allied to Zagena, but it is multilocular, the chambers being usu-
ally arranged in a double series. It is represented in the Tnias,
and survives under common types at the present day. In the
series of which /Vodosaria is the type, we have perforate Forami-
nifera consisting of a succession of chambers, each of which is
essentially similar to a Zagena, arranged in a series, which is usually
nearly or quite straight, though sometimes spirally involuted. In
Vodosaria itself (fig. 29, g) the chambers are simple, and are dis-
posed in a straight line. It ranges from the Permian to the present
day. Dentalina, ranging from the Carboniferous onwards, is funda-
mentally like /Vodosaria, but the shell is bent like a bow. Vagzn-
wlina comprises forms similar to /Vodosaria, but laterally compressed,
and begins in the Trias (Rheetic). Warginulina (fig. 29, Z) is slightly
curved, or is sometimes crosier-shaped, and also starts in the Trias.
tFrondiwularia (fig. 29, 7) has the shell flattened out and leaf-like,
and likewise makes its first appearance at the summit of the Trias.
Lastly, Cvestellaria (with Robulina) comprises forms more or less
spirally inrolled or crosier-shaped, which extend from the Trias to
the present day, and have a very wide development both individu-
ally and specifically.

In the family of the Glodigerinide, Dr Carpenter included all
those hyaline Foraminifera, in which the calcareous shell is perfor-
ated by large-sized pseudopodial foramina, but the group, as defined

66

132 PROTOZOA.

by Dr H. B. Brady, is a much more restricted one. The test is
always calcareous and perforate, and consists of a few inflated
chambers arranged spirally, or of a single chamber only. ‘There is
no “supplementary skeleton,” and there is a large single or mul-
tiple “general aperture” to the shell. The apparently simplest
form of the Globigerinide is Orbulina (fig. 22), in which the test
has the external form of a single globular chamber, the walls of
which are perforated by a double series of foramina, large and
small. It seems more than doubtful if the test, as represented
in fig. 22, possesses any “general aperture.” Doubt has been
thrown upon the true relationships of Orvbudina by the discovery
that in many specimens, especially in those of small size, the
apparently monothalamous sphere contains in its interior a young
Globigerina-shell, attached to the inside of the wall by slender
spicules. It has therefore been held that Ordulina is really a
form of Globigerina in which the last chamber includes all those
previously formed. The genus Ordulina has a world-wide dis-
tribution at the present day, and its earliest representatives appear
in deposits as old as the Trias (Rhetic). The genus Ovulites,
formerly placed in the immediate neighbourhood of Orvéulina, ap-
pears, according to recent researches, to be in reality a Calcareous
Alga. The only other member of the G7odigerinide which requires
notice is the type-genus G/odigerina itself (fig. 29, 2), in which the
test is polythalamous and coarsely perforated (fig. 20). The cham-
bers are few in number, and globose in form, and are usually arranged
in a turbinate spiral, thus resembling the shell of a Rotafa. The
chambers do not communicate with one another directly, but each
opens by a special aperture into a deep central or umbilical depres-
sion. In pelagic forms (as also in Ovdulina) the test, when perfect,
appears to be covered with long and extremely delicate spines.
Globigerina dates from the Trias, and is extremely abundant. It is
of special interest, as being the principal constituent of the “ ooze”
(fig. 27) found at great depths in the larger oceans at the present
day ; while its shells form an equally large portion of the White
Chalk (see p. 119). 7

In the large and important family of the Rofalde, the test is
typically composed “of a succession of coarsely porous or globiger-
ine segments,. arranged in a turbinoid spire, and communicating
with each other by a crescentic aperture situated at the junction of
the septal plane with the free surface of the convolution” (Car-
penter). The segments of the shell are typically so coiled that the
whole of the chambers are exposed to view on the upper surface,
whereas on the under side only the last convolution is visible, differ-
ent types varying as to which side of the shell is the more convex.
‘The shell-structure may be simple, but in other cases the test is

FORAMINIFERA. W223

complex and is furnished with a “supplemental skeleton” and “ canal-
system” (fig. 21). Among the typical Rotaline forms, the genus
Discorbina, with its coarsely porous shell, dates from the Chalk,
and is found living in our seas. Px/vinulina (fig. 24), on the other
hand, with a more finely porous shell, has been detected by Brady
in rocks of Carboniferous age, and is thus one of the earliest rep-
resentatives of the Rotalines. In fo/a/a itself (figs. 21 and 29, 0),
the test is also spiral and turbinoid, but its structure is more com-
plex than in the preceding, the shell-substance being compact and
very finely porous ; while each chamber is enclosed by a complete
wall of its own, and there are canal-like spaces between the two
lamelle forming each septum. In these respects, Rofalia closely
approaches the Nummuline type. The earliest Rofalie appear in
the Jurassic, but the genus attains its maximum in the Tertiary
period, and is well represented at the present day. The approxi-
mation to the Nummuline type is further manifested by Cadcarina
(fig. 26, B and c), in which the shell is spiral and discoidal, with
spur-like marginal appendages, and with a well-developed “‘ supple-
mental skeleton” and “canal-sytem.” The genus has been shown
by Brady to commence in the Carboniferous. In //lanorbulina the
shell is composed of numerous segments, at first spirally and then
cyclically disposed. It dates from the Tertiary period, but the
forms which are included under the sub-generic name of Z7un-
catulina (fig. 29, p) commence in the Carboniferous. Zinoporus,
dating from the Chalk, is in some respects intermediate between
Calcarina and Planorbulina, its general form being like that of the
former, while the irregular and partly cyclical arrangement of its
chambers recalls the latter. No “general aperture” is present, but
a “supplemental skeleton” and ‘‘canal-system” are developed, both
of these structures being wanting in the allied Gyfszna. Though not
known in the fossil condition, the genus /olytrema may be alluded
to here, since it has some curious resemblances to certain of the
folyzoa. It forms crusts, or, more commonly, branched outgrowths,
parasitically attached to foreign bodies; and it consists of numer-
ous intercommunicating irregular chambers, the walls of which are
penetrated by an extensive system of capillary canals, a true canal-
system being, however, absent. ol/ytrema seems to be the rep-
resentative in the Rotaline series of the singular genus Sfachera
among the Jmferforata. Lastly, an aberrant type of the Rotalines
is constituted by the genus Sf777//ina, in which the test has the
form of a calcareous tube, without any internal partitions, coiled
into a flat spiral, and either free or attached to some foreign body.
The genus begins in the Tertiary rocks, and is represented by
living forms.

Finally, we have the family of the Vummulinide, comprising the

134 PROTOZOA.

most complex and the most highly organised of all the Aoraminzfera.
In the forms included under this head, the shell is compound ; the
successive chambers are enclosed each in its proper wall (as diagram-
matically shown in fig. 26, a); there is generally a well-developed
‘intermediate ” or ‘‘ supplemental” skeleton, which renders the shell
strong and@ compact, and which is perforated by a “ canal-system,”
originating in the spaces between the two lamellae composing each
septum ; while the shell-substance is pierced by close-set and ex-
tremely fine tubules (fig. 37), the septa alone wanting these, so

Teel
ATF
ir SMUT LL
z fit mil
MMH) Tis

Fig. 37.—Transverse section of the test of Naszulina pristina, from the Carboniferous Lime-
stone, enlarged too diameters, showing the primordial chamber and the tubulated shell-wall.
(After H. B. Brady.)

that contiguous chambers usually communicate by but one large
aperture. The lower forms of the family have a thickened and
finely tubulated shell-wall, but have no intermediate skeleton. The
form of the shell is typically a discoidal spiral or a cycloidal disc.

There is a relationship of a decided character between the higher
Rotalines and the Wummulinide, as exhibited by forms like Rotaha
itself, and Calcarina on the one hand, and by Polystomella and Amz-
Phistegina on the other hand. In Polystomedla (fig. 29, s) the shell
is lenticular and discoidal, and is composed of successive chambers,
which are prolonged into wing-like (“‘alar”) prolongations, which ex-
tend inwards to the centre, thus concealing the earlier turns of the
spire from view, while the centre itself is occupied by a solid cal-
careous boss, penetrated by irregular canals. The ‘“ canal-system ”
is extraordinarily developed and very complex. Some of the simpler
types of Polystomella are grouped together under the name of /Von-
zonina ;, and the genus seems to make its first appearance in the
Upper Chalk, being well represented in the Tertiaries, and surviving
to the present day.

Amphistegina still more closely approaches the Rotalines, with
which it has sometimes been grouped. Its shell is spiral and dis-
coidal (fig. 29, 7), usually more or less inequilateral, each chamber
being saddle-shaped, and sending forth “ alar” prolongations which
reach nearly to the centre, where is placed a solid boss. The shell-
substance, with exception of the septa and the central boss, is pene-

FORAMINIFERA. 135

trated by numerous close-set, parallel, extremely minute tubules, but
the “‘canal-system ” is only imperfectly developed. Brady has shown
that the genus occurs in the Carboniferous ; but with this exception
it is Tertiary and Recent.

Another very ancient, and more anomalous, type of the Nummu-
line group is the Avchediscus of Dr Brady (fig. 29, ~), which occurs
also in the Carboniferous Limestone. In this curious form the test
is “convoluted, rounded, more or less unsymmetrical ; formed of a
non-septate tube coiled upon itself in a constantly varying direction ;
the shell-wall transversed by very numerous parallel minute tubuli ”
(Brady).

In the genus Vummulina itself (fig. 38) the shell is coin-shaped,
of large size, sometimes as big as a florin, or larger, composed of

Fig. 38.—Nummulina nummularia. a, The shell viewed from above; B, The same.
horizontally bisected ; c, The same vertically bisected; b, Vertical section of part of the
shell, highly magnified, showing the chambers of the median plane, the alar prolongations,
and the tubuli of the shell-substance. Eocene Tertiary.

numerous chambers arranged on one plane in a regular spiral. Each
chamber is saddle-shaped, the internal or “alar” prolongations of
each extending to the centre, so that each revolution completely
encloses and conceals from view all the preceding ones. The suc-
cessive chambers communicate by means of arched fissures, which
perforate each septum, close to the periphery of the previous turn of
the spire, while secondary and irregular pores in the septa discharge
the same function. The general shell-substance is traversed by ex-
tremely minute parallel tubuli (fig. 38, D, and fig. 37); and there is

136 PROTOZOA.

a supplemental skeleton (forming the so-called ‘marginal cord ”),
which, together with the septa, is penetrated by a well-developed
and ramified “ canal-system” (see fig. 26, D). By the researches
of Brady, we know now that the range of the genus Vummulina
in time must be carried back to the Carboniferous, one small form
(viz., Vummulina pristina, fig. 37) having been detected in the
Mountain Limestone of Belgium. A few ‘‘ Nummulites ” have also
been detected in strata of Jurassic and Cretaceous age, but the maxi
mum development of the genus is recorded in the early Tertiary
period (Middle Eocene). At this period in the earth’s history we
find the Nummulites existing in extraordinary profusion, and build-
ing up the widespread and massive series of calcareous deposits
which are known as the ‘*‘ Nummulitic Limestone.” According to
Sir Charles Lyell, “‘the Nummulitic Limestone, with its characteristic
fossils, plays a far more conspicuous part than any other Tertiary
group in the solid framework of the earth’s crust, whether in Europe,
Asia, or Africa. It often attains a thickness of many thousand feet,
and extends from the Alps to the Carpathians, and is in full force in
the north of Africa, as in Algeria or Morocco. It has also been
traced from Egypt, where it was largely quarried of old for the
building of the Pyramids, into Asia Minor, and across Persia, by
Bagdad, to the mouths of the Indus. It occurs not only in Cutch,
but in the mountain-ranges which separate Scinde from Persia, and
which form the passes leading to Cabul; and it has been followed
still further eastwards into India, as far as Eastern Bengal and the
frontiers of China.” In the later Tertiary period, the genus under-
went a striking degeneration ; and it is represented at the present
day by only a few small forms, which are found in arctic, temperate,
and tropical seas.

Very closely allied to Vummulina, and of equal or even greater
geological importance, is the
genus /usulina, the typical forms
of which (fig. 39) are spindle-

; i shaped in figure, and may be
cr ae compared to a Nummulite drawn

out at its umbilici. According

to Brady, however, some species of /usudima are discoidal and sym-
metrical, and thus not distinguishable in form from Mummulina ;
while in other species the test is spherical. In internal structure,
and especially in the minute tubulation of the shell-substance, the
genus approaches Vummulina, but a regular interseptal “ canal-
system ” appears to be wanting, and the chambers are broken up
into chamberlets. Most of the Fusulne are of considerable size,
often from a third to a half of an inch in length, and they often con-
stitute massive beds of limestone, which have been justly paralleled

FORAMINIFERA. 137

with the Nummulitic Limestone of the Eocene. Thus they form
whole beds of the Carboniferous Limestone in Russia, Central
Europe, Armenia, India, China, Japan, and the United States.
Though pre-eminently Carboniferous, they occur also in the
Permian.

The remaining types of the Wummulnida can be merely al-
luded to here. The genus O7vdztordes is extremely like /Vummu-
/ima in external appearance and form, and has been often mis-
taken for it, but it differs considerably in its internal structure,
and especially in the fact that its mode of growth is cyclical in-
stead of spiral, and the place of the ‘“alar prolongations” of the
chambers of the latter is taken by a multitude of chamberlets.
The genus appears first at the summit of the Cretaceous, but it
undergoes, along with its ally Vwmmulina, an extraordinary devel-
opment in the early Tertiary period, and it forms immense masses
of Eocene limestone in the Southern United States, the West Indies,
and in various parts of the Old World. A nearly allied genus is
Cycloclypeus, which is also coin-shaped, and is strictly cyclical in its
mode of growth. It occurs in the Miocene Tertiary, and the only
known recent types attain an extraordinary size (over two inches
in diameter). Oferculina, again, is much more closely related to
LVummulina proper in its internal structure, though it differs in
jorm, owing to the fact that the chambers of the spirally inrolled
shell have no “alar prolongations,” and thus approximate to the
Rotaline type. The genus commences in the Upper Cretaceous,
but is particularly developed in the Eocene of the South of Europe
and Africa. Lastly, Heterostegina (Tertiary and Recent) differs from
Operculina chiefly in having the principal chambers broken up into
chamberlets by secondary septa.

APPENDIX TO FORAMINIFERA.
EOZOON CANADENSE.

In connection with the subject of the Foramznzfera, it is necessary to
consider the structure and probable nature of the singular body to which
the name of Zozodn has been given, since this body, if organic at all,
' must be regarded as referable to the foregoing group of organisms.
There is, in fact, a special, twofold interest attaching to Lozoon, if it
should be proved that the body so named is truly organic. In that case,
Eozoon would, on the one hand, be the most ancient type of life which
has yet been detected by the researches of palzontologists, while, in the
second place, it would present us with a type of Foraminzfera of colossal
size, and in other respects of quite peculiar zoological interest. Since the
whole subject of the structure and relations of Lozoom is one of great
complexity, it would not be advisable to deal with it here in any detailed
manner, or to enter into the long and still unfinished controversy which
has been carried on as to the organic or inorganic nature of this remark-
able body. It will be sufficient to briefly describe the general form and

138 PROTOZOA.

mode of occurrence of Lozodn, the chief structural features which it
presents in thin sections, and the general explanation of these features
given respectively by those who regard it as Foraminiferal and those who
consider it to be a purely mineral structure. In addition, it may not be
out of place to indicate a few considerations based upon a prolonged and
careful microscopical investigation which the present writer has inde-
pendently carried out into the structure of this problematical body.

The peculiar structure which has been described under the name of
Eozoon Canadense occurs in the crystalline metamorphic limestones of
the Lower Laurentian in Canada, and it has also been detected in the
same country in similar limestones believed to be of the age of the Upper
Laurentian or Huronian. An allied form (species?) has been found in
rocks supposed to be Laurentian in Newfoundland ; and Dr Giimbel has
described a third form from crystalline limestone belonging to the
““Hercynian gneiss formation” (Lower Cambrian or Huronian?) of
Bavaria.

As regards its mode of occurrence, Eozodz appears to most com-
monly present itself in the form of spreading layers or confluent masses.
According to Sir William Dawson, however, comparatively small, isolated
specimens are found, which have a “ broadly-turbinate, funnel-shaped,
or top-shaped form, sometimes with a depression on the upper surface.”
The same observer has also described the occurrence of vertical tubes
of large size traversing masses of Zozoon, and has compared these with
the oscular canals of Sponges.

As regards its macroscopic characters, a mass of Lozo0n shows a con-
spicuous structure out of thin alternating lamine, arranged parallel with
one another and often more or less concentrically (fig. 40). The laminze

Fig. 40.—Fragment of Zozo6n, of the natural size, showing alternating laminz of loganite
and dolomite. (After Dawson.)

of such a mass are usually of different colours and composition; one
series being white, and composed of carbonate of lime —whilst the
laminz of the second series alternate with the preceding, are green in
colour, and are found by chemical analysis to consist of some silicate,
generally serpentine or the closely related “ loganite,” or white pyroxene.
In some instances, however, according to Dawson, all the laminz are
calcareous, the concentric arrangement still remaining visible in conse-
quence of the fact that the laminz are composed alternately of lighter
and darker coloured limestone. The calcareous layers (fig. 41, A) are
composed of coarsely crystalline calcite (as viewed macroscopically), and

FORAMINIFERA. 139

vary much in thickness, not only in different specimens, but commonly
in different parts of the same specimen. According to Dawson, in
isolated, inversely conical specimens it is the laminz at the base which
are the thickest. Very commonly, the laminz subdivide and coalesce
with one another. The serpentinous layers, which alternate with the
calcareous laminz, usually show a more or less conspicuous structure

A Zz
\\
Z iP a

: = Zz ~ FE Zp A fi Ys Py ( ‘
LLB ALIENS
c

Fig. 41.—Minute structure of Zozoén Canadense, from the Laurentian limestones of Canada.
A, Part of a vertical section of Zozoéx, enlarged about ten times, showing the alternating layers
of calcite (c) and serpentine (s); 8, Part of a calcareous lamina, cut vertically, showing the
“canal-system,” enlarged about forty-five times; c, Part of a calcareous lamina, cut horizontally,
and enlarged about sixty times, showing the large and small branches of the canal-system ; D,
Part of a vertical section ofa calcareous lamina, enlarged about one hundred times, showing the
finer divisions of the canal-system and the so-called ‘‘ proper wall” (w). c, Calcareous lamine ;
ae laminz ; w, The so-called ‘‘ proper wall” ; ca, Large branches of the canal-system.
(Original.

out of small rounded or lenticular masses. This characteristic botryoidal
structure of the serpentinous laminz is best studied in polished specimens
which have been treated with weak acids, so as to dissolve out the cal-
careous portions of the mass to a limited depth below the surface.

As regards the zcroscopic structure of Zozoon, the calcareous lamine,
in well-preserved examples, exhibit a very remarkable canaliculated or

140 PROTOZOA.

tubulated structure. In parts in which this structure is preserved, the
crystalline calcite of the calcareous laminz is seen to be traversed by
branching and dendritic canals (fig. 41, Band Cc). Some of these canals
(fig. 41, B) are of comparatively large size, and these are generally more
or less extensively occupied with an infilling of serpentine, though some-
times partially filled with calcite. In connection with these large canals
are much more delicate canaliculi or tubules (fig. 41, C and D), which run
more or less parallel with one another, or have a tufted arrangement, and
which are commonly filled with transparent ca/cite. At the edges of the
calcareous lamine these delicate and branching tubules often appear to
terminate in a narrow belt or selvage (the so-called “proper wall” or
** Nummuline layer” of Carpenter and Dawson), which has a transversely
striated aspect, as if composed of parallel fibres or traversed by innumer-

=

eS

Fig. 42.--Portion of one of the calcareous layers of Aozoé7, magnified 100 diameters. @ a,
The proper wall (‘‘ Nummuline layer”) of one of the chambers, showing the fine vertical tubuli
with which it is penetrated, and which are slightly bent along the line @’ a’; cc, The inter-
mediate skeleton, with numerous branched canals. The oblique lines are the cleavage-planes
of the carbonate of lime, extending across both the intermediate skeleton and the proper wall.
(After Carpenter.)

able minute tubuli (fig. 41, D, w). According to the observations of
Dawson, this narrow selvage, or “ proper wall,” consists of “ finely divided
tubes, similar to those of the canal-system, and composed of its finer sub-
divisions placed close together so as to become approximately parallel”
(fig. 42).

The actual structure of Eozodn being as above briefly described, we
may in the next place shortly consider the interpretation placed upon this
structure by those who regard it as organic in origin, and who, like W. B.
Carpenter, Dawson, and Rupert Jones, consider it to represent an ancient
type of the foraminifera. Upon this view—which a reference to the
subjoined diagrammatic figure (fig. 43) will render readily intelligible—
the calcareous laminz (4 4) of a mass of Zozoon represent the original
calcareous skeleton of a gigantic Foraminifer, while the serpentinous
layers represent the successive tiers of chambers separating successive
laminze of the skeleton. The calcareous skeleton itself has been largely

FORAMINIFERA. I41

crystallised or otherwise altered by the metamorphic agencies which
have affected the entire mass of the enclosing rock; and the original
chambers between successive layers of the shell have been filled up
with serpentine or some other silicate, which has taken the place of
the living matter which, to
begin with, is supposed to
have occupied these spaces. y
The serpentinous infilling has C
been deposited from solution series
p eae}
in water, and has not only Ves
usually occupied the large
chambers between the cal-
careous lamine, but has also
more or less extensively pen-
etrated into the larger canals
or even the minuter tubuli
which traverse the substance
of these lamine. Placing
this interpretation upon the
observed structure of Zozoon,
the central and principal por- Fig. 43.—Diagram of a portion of EZozodn cut verti-

tion of each calcareous lam- cally. a, B, C, Three tiers of chambers communicating
with one another by slightly constricted apertures ; aa,

ina (fig. ABTS b b) is regarded The true shell-wall, perforated by numerous delicate
as corresponding with the _ tubes; 44, The main calcareous skeleton (‘‘ intermedi-

« » ate skeleton’); c, Passage of communication (‘‘ stolon-
supplemental skeleton” of passage ’’) from one tier of chambers to another; d,

such a Foraminifer as Ca/- Ramifying tubes in the calcareous skeleton. (After
carina or Nummulina, while ©tpenter-)

the branching tubes which

traverse the lamina (fig. 43, d), are considered to represent the “ canal-
system” of the same. Moreover, the narrow, transversely striated band
or selvage, which normally bounds each calcareous lamina above and
below (fig. 43, @ a), is regarded as corresponding with the “ proper wall”
of such a Foraminifer as Vummulina, and has therefore been com-
monly spoken of as the “ Nummuline layer.” On this view, therefore,
the so-called “proper wall” is part of the actual skeleton, and the
vertical lines which traverse it represent minute tubules, which open
into the chambers and on the surface by correspondingly fine pores.
It need only be added that if the above explanation of the observed
structure of Eozoon be accepted, it then takes its place in the series
of the Foraminifera as a gigantic and aberrant member of the Vum-
mulinide, having a quite special interest and importance as both the
oldest known fossil and also the largest of known Protozoans.

On the other hand, very weighty objections have been urged against
the theory of the organic nature of Zozoox by many observers, and more
especially by Mobius in Germany and King and Rowney in Britain.

It would be out of place here to attempt to discuss these objections, but
the following are, in brief, the more important arguments which have
been brought forward against the organic nature of Zozoou and in favour
of the view that it is a purely mineral structure :—

a. The structure to which the name of Zozodz is applied is found in
highly crystalline rocks, and in parts of these which are much broken
and altered. Moreover, no unquestionable organic remains have been
discovered in association with Zozoon.

6. The general form of Zozodn is very irregular, and though its minute
structure (supposing it to be organic) would show that it belongs to the

7 OY eens gage

praaees/yy//f/ Ueey UY,

GH Mfr

a e* AY
Ul fe u
uy

142 PROTOZOA.

Foraminifera, it cannot be closely compared with any known type,
recent or extinct, belonging to this group of organisms.

c. The thickness of the calcareous laminze of Zozodz is not only very
variable in different'specimens, but is liable to great variation even in a
single specimen. On the supposition, however, that the calcareous
laminz represent the layers of the skeleton of a Foraminifer or other
calcareous organism, it would seem very improbable that such great
variations in their thickness should be found to exist.

d. On the hypothesis of the organic nature of “ozod, there is a strong
a priori improbability of such exceedingly minute structures as the
“canal-system” of a Foraminiferal test being preserved in rocks so
highly crystalline as are the Laurentian limestones.

é. The canals of the so-called “canal-system” are often flat, instead of
round, and are commonly unequal in point of size, while it is not unusual
to find them running obliquely to the calcareous lamine instead of ¢vazs-
versely. These considerations would tend to show that the “canal-
system” is of inorganic origin.

jf. The “ proper wall” is not truly tubulated, but is formed of minute
parallel fibres of serpentine. It is therefore a purely inorganic structure,
and is really of the nature of a vein of fibrous serpentine (“chrysotile ”).

Some of the above arguments against the organic nature of Lozoon
are of a general nature, and their weight must necessarily remain largely
a matter of individual judgment. Others are of a special character, and
deal with matters of observation, as to which there are differences of
opinion. The sfeczal arguments all hinge upon two points—viz., the
“canal-system” and the “ proper wall”—and with regard to these the
following considerations may be indicated: On the view that the
“canal-system” is of inorganic origin, it has usually been assumed that
it consists of branched fibres of sexPentene or of some other silicate,
developed in the calcareous laminz. The larger canals are, it is true,
commonly filled with serpentine, but it admits of demonstration that the
smaller canals are commonly, and in fact usually, occupied simply by
crystalline carbonate of lime. On this point, the author is able to fully
corroborate the observations of Carpenter and Dawson. In the second
place, it can be proved that the so-called “ proper wall” of Zozo06z is, as
a rule, calcareous, and that it cannot, therefore, be regarded as univer-
sally of the nature of fibrous serpentine (chrysotile). This can be best
shown by acting with acids on thin vertical sections of Lozoonu along a
narrow transverse band, leaving the two ends of the section untouched.
When this is done, it is found that along the narrow tract acted upon by
the acid, not only have the calcareous laminze been dissolved out, but
the so-called “ proper wall” has at the same time also disappeared, its
composition out of carbonate of lime being thus conclusively proved. In
some cases, the “ proper wall” does not appear to be wholly destroyed
by acids, and in such cases it may be supposed that the tubuli of this
structure have been injected with serpentine, and have thus been enabled
to resist the action of the solvent. The above observation, at any rate,
appears to show conclusively that the so-called “proper wall” cannot
be always of the nature of a layer or vein of fibrous serpentine (chryso-
tile), since it is very commonly and quite unquestionably soluble in weak
acids. At the same time, true chrysotile veins often intersect masses of
Eozoon, and it is quite probable that in some instances such veins have
been confounded with the peculiar striated selvage to the calcareous
laminze of Hozooz, which is really what should be understood as the
“proper wall.”

FORAMINIFERA. 143

Upon the whole, therefore, it would appear that the much- vexed
question of the true nature of Zozoon is still incapable of receiving its
final solution. It is clear that in any endeavour to solve this problem
only the dest specimens—those, namely, which possess the so-called
“canal-system” and “proper wall” in a well-preserved state—can be
taken into account; since it is one of the most ordinary experiences of
paleontologists to find that out of a series of specimens of some quite
indubitable fossil—such as a coral—only a very limited number retain
their internal structure in a recognisable condition. It is also a reason-
able argument that until mineralogists or petrologists are able to point in
some unquestionable mineral or rock to a structure strictly comparable
with the “canal-system” of Zozoo7, they are not entitled to assert posi-
tively that the latter has a purely inorganic origin. Lastly, some weight
must be attached to the argument that though aa/ogows structures
(banded rocks of various kinds) are known, nothing clearly inorganic has
yet been discovered the general structure of which can be regarded as
precisely parallel with that of Zozo0z.

In connection, finally, with the subject of Zozo0z, it may be noticed
that Sir William Dawson has given the name of Archeospherine to
small spherical masses of serpentine, sometimes single, sometimes united
together in small numbers, which he finds in the Laurentian limestones
of Canada, and which he states to be surrounded by a tubulated cal-
careous shell, resembling the “ proper wall” of Zozodn. He is of opinion
that these bodies are either detached chamberlets of Aozoon, or that
they are independent organisms, allied to Aozoon, but of a simpler
type.

144

CHAP TE Rach xX.
PROTOZOA — Continued.

RADIOLARIA.

Tue order of the Radiolarians comprises a vast number of Rhizo-
pods, in which ¢he sarcode-body consists of a central protoplasmic mass,
enclosed in a porous, membranous, or chitinous capsule, which is in
turn surrounded by a thick layer of sarcode. The intra-capsular sar-
code contains a central “‘ nucleus,” and the pseudopodia (fig. 44) have
the form of slender radiating filaments, which rarely anastomose with

Fig. 44.—Eucecryphalus Schultzet, with the pseudopodia extended, showing the perforated
siliceous test and the lobed protoplasmic body. (After Kélliker.)

one another. As a rule, the protoplasmic body secretes a radially
disposed skeleton composed of silica, of a-silicate, or of a horny sub-
stance (“ acanthin”’).

As regards the ske/efon of the Radiolarians, some forms (7/a/as-
sicolla, Thalassolampe, Collozoum, &c.) are wholly devoid of hard

RADIOLARIA. 145

structures. Moreover, among those types in which a skeleton is
developed, there are great differences as regards both the chemical
composition and the structure of this. As regards the first of these
points, the skeleton is never calcareous, but presents itself under one
or other of the following three modifications. In the first place, the
skeleton may be composed of pure silica. This is the case in the
Polycystina (the Spumellaria and Nassellarta of Haeckel), which
constitute the largest and most typical group of Radiolarians. In
another series of forms the skeleton is a compound of silica with
some organic compound, or is a ‘silicate of carbon” (Haeckel).
This occurs in the entire group of the Pheodaria, except in Dicty-
ocha and its allies. Lastly, in a third series of forms the skeleton
consists of a peculiar organic substance (“‘acanthin”) allied to
chitine or horn. The forms in which the skeleton is of this nature
are grouped together by Haeckel under the name of Acantharia.

As regards the form of the skeleton, the most usual type is that of
a latticed shell (fig. 45), enclosing the central capsule. In certain
Radiolarians, however, the skeleton consists of radially or tangen-

Fig. 45.—Skeletons of Polycystina. a, Stylodictya multispina ; 8, Podocyrtis Schomburgii ;
Cc, Eucyrtidiune lagena. (After Haeckel.)

tially disposed spicules ; or it may have the form of a simple ring, or
of a ‘‘ basal tripod with or without a loose tissue of trabeculee ” (Haec-
kel). In the Polycystina (Spumellaria and Nassellaria), the siliceous
bars of the skeleton are invariably solid, whereas in the PAeodaria
the parts of the skeleton are always hollow.

As regards their classification, Professor Haeckel raises the Radio-.
larians to the rank of a distinct c/ass of the Protozoa, and he divides
them into the following four legions or sub-classes :—

I. SPUMELLARIA.—Capsular membrane perforated by innumerable fine:
pores. Fundamental form originally spherical. Skeleton siliceous, or
WAG IEE IE K

146 PROTOZOA.

in some cases absent. No dark pigment-body (“phzodium”) in the
extra-capsular sarcode.

This division includes forms such as 7halassicolla and Collozoum, in
which the skeleton is wanting, with others having a skeleton of siliceous
spicules, and with a large number of the forms usually spoken of as
“ Polycystina” in which the skeleton has the form of a latticed siliceous
shell.

2. ACANTHARIA.—Capsular membrane perforated by numerous fine
pores. Fundamental form originally spherical. Skeleton composed of
‘“acanthin.” No dark pigment-body in the extra-capsular sarcode. This
group includes forms such as Acanthometra and its allies.

3. NASSELLARIA.—Capsular membrane perforated by a porous area, or
by one single large opening divided into numerous very fine pores.
Fundamental form originally egg-shaped. Skeleton siliceous. No dark
pigment-body (‘‘ pheeodium”) in the extra-capsular sarcode. This group
comprises all those “ Polycystzna” which are not included under the
head of Spumellaria.

4. PHHODARIA. — Capsular membrane double, perforated by one
simple main opening prolonged into a tube, commonly with one or two
small accessory openings. Fundamental form originally egg-shaped.
A dark pigment-body (‘“phzeodium”) is constantly present in the extra-
capsular sarcode. The skeleton is siliceous, being usually composed of
a compound of silica with some organic substance, but in other instances
(Dictyocha) consisting of pure silica.

As regards their distribution in space, the Radiolarians are exclu-
sively marine, and are found in all seas and at all depths. They are
commonly floating organisms, and are often present in enormous
numbers, the greatest variety of specific types, however, being found
in the warm seas of the tropics. Many Radiolarians are “ pelagic,”
and inhabit the surface-waters of all oceans; others are “ abyssal,”
and are confined to great depths in the sea; while others, again, are
‘“‘zonarial,” and are restricted to particular bathymetrical horizons
between the surface and the bottom. Over large areas of the deep
sea, principally at depths of from two thousand to over four thousand
fathoms, the bottom is found to be covered with extensive deposits
of “ Radiolarian ooze.” The deposit so called is a siliceous mud,
with little calcareous matter, which is composed more or less largely
of the siliceous tests of various Radiolarians. The skeletons of
Radiolarians are, however, also present, in smaller or greater num-
bers, in many of the marine deposits which are formed at compara-
tively limited depths.

As regards their distribution in time, the Radiolarians are abun-
dantly represented by fossil forms, and are now known to have a
high antiquity. Owing, however, to the vast number of forms in-
cluded in the Radiolaria, and the great complexity of their classifica-
tion, the study of the fossil types can hardly be undertaken except
by a specialist. For these reasons, nothing further will be here
attempted than merely to give a brief outline of the more important
facts relating to the past history of the Aadzolaria. ‘The student

RADIOLARIA. 147

desirous of fuller information, or anxious to study the fauna of any
particular Radiolarian deposit, will of necessity consult the works of
Ehrenberg, Rtist, Haeckel, and others, who have specially devoted
themselves to the study of these minute organisms.

As regards the past history of the great groups of the Radiolarians,
the Acantharia, in which the skeleton is composed of ‘ acanthin,”
are wholly unknown in the fossil condition. This is likewise the
case with the group of the P@eodaria—in which the skeleton is
composed of silicate of carbon—with the single exception of the
small group represented by Dayctyocha and its allies, in which the
skeleton is purely siliceous. In Diuctyocha (fig. 46, d), the skeleton
is composed of irregular bars of flint united into a loose network with
wide meshes. ‘The genus begins in the Upper Chalk, and is repre-
sented in Tertiary deposits and in recent seas.

With the above-noted exception, all the known fossil Radiolarians
belong to the group of the so-called ‘‘ Polycystina,” comprised in the
two divisions defined by Haeckel under the names Spumellaria and
NVassellaria. In all of these forms the skeleton is purely siliceous,
and it usually has the form of a porous latticed shell, the precise
shape of which varies in different types.

Until recently, Radiolarians had only been detected in the fossil
condition in deposits of Kainozoic and Mesozoic Age; and our
knowledge of Palzeozoic types of Radiolarians is still very incomplete.
According to Haeckel, however, Dr Rust (whose researches on this
subject are still unpublished) has discovered various types of Poly-
cystina, ‘‘of very simple form and primitive structure,” in rocks as
old as the Silurian, or even the Cambrian. ‘The remains of Radio-
larians have also been indicated as occurring in the Carboniferous
Limestone of England, but the true nature of these has not been
clearly established.?

Radiolarian remains have now been discovered in all the great
Mesozoic systems. From the Jurassic system, in particular, numer-
ous fossil Polycystina have been described by Zittel, Dunikowski,
and Rist. A noticeable Jurassic genus is Cenosphera, which is
also found in the Chalk, in the Miocene marls of Barbados, and in
recent seas, and which has relationships with Collosphera. Many of
the Jurassic Radiolarians occur in jasper, flint, or chert; but they
are especially abundant in what have been termed “ Radiolarian
quartzes.” These are cryptocrystalline quartzites or hard siliceous
rocks, which are composed ‘‘for the most part of the closely com-
pacted shells of Spumellaria and Jassellaria” (Haeckel). The

1 Considerable portions of the Carboniferous Limestone of Britain are occa-
sionally partially composed of the minute calcareous spheres which have been
described under the name of ‘‘ Calc?sphere.” These enigmatical bodies are now
composed of carbonate of lime ; but it has been conjectured that they were origin-
ally siliceous, and that they are really referable to the Radiolaria.

148 PROTOZOA.

jaspers with Radiolarians are considered by Haeckel as of the nature
of true ‘ silicified deep-sea Radiolarian ooze.” Many forms of Radi-
olarians have also been yielded by the so-called ‘‘ Radiolarian copro-
lites” of the Lias of Hanover. These are “ roundish or cylindrical
bodies, which may attain the size of a goose-egg; they probably
originated from Fish or Cephalopods, which had fed upon Crustacea,
Pteropoda, and similar pelagic organisms, whose stomachs were al-
ready full of Radiolarian skeletons” (Haeckel).

The Radiolarians which have hitherto been discovered in the
Cretaceous rocks are few in number, but Zittel has described several

Fig. 46.—Types of Polycystina. a, Podocyrtis Schomburgit ; 6, Dictyomitra Montgolferz ;
c, Haliomma dixiphos; d, Dictyocha Messanensts; e, Eucyrtidium elegans; f, Lychnocantum
lucerna. dis living, and is after Haeckel ; the remaining are Tertiary, and are after Ehrenberg.
All the figures are greatly enlarged.

species from the Upper Chalk of Germany. The Cretaceous genera
Dictyomitra (fig. 46, 6) and Stylodictya (fig. 45, A) are represented
in both Tertiary and recent seas.

In formations belonging to the Tertiary period, Radiolarians are
found in vast abundance in certain deposits (marls and clays), which
may be regarded as ‘fossil Radiolarian oozes.” These Tertiary
Radiolarian clays and marls appear to be very widely distributed,
but the most famous of these deposits is the Polycystine Marl of
Barbados, the age of which is Miocene. The so-called “ Barbados
earth” is a friable, earthy or chalky marl, which rises to heights of
over 1000 feet above the level of the sea, and is more or less
extensively composed of the shells of Radiolarians, with a variable
proportion of the calcareous tests of the Foraminifera. According

RADIOLARIA. 149

to Haeckel, the number of species of Radiolarians in the Barbados
earth is not less than four hundred, and is probably more than five
hundred. This eminent authority regards the Barbados earth as a
deep-sea deposit, and states that very many of the Barbados Radio-
larians “are to-day extant and unchanged in the Radiolarian ooze
of the deep Pacific Ocean.”

Very similar to the Barbados earth is the Polycystine marl or
“tripoli” of Sicily, Calabria, Greece, and Northern Africa, the age
of which is also Miocene. Another deposit of the same nature is
the tripoli or Radiolarian clay of the Nicobar Islands, which rises
to elevations of about 2000 feet above the level of the sea, and is
probably of Miocene or Oligocene age.

Of the more common Tertiary genera of Radiolarians, Haliomma
(fig. 46, c), Aeltodiscus, Actinomma, and Didymocyrtis belong to a
group of forms in which the skeleton consists of two, three, or
more porous spherical shells, included concentrically within one
another, the smaller within the larger, and united by radial bars.
In other cases, as in the genera Podocyrtis (fig. 46, a), Eucyrtidium
(fig. 45, Cc), Lychnocanium (fig. 46, f), and Dictyomitra, the skele-
ton has the form of a latticed shell, which may be undivided, or is
partially marked off into two or more compartments by transverse
constrictions. The two poles of the shell in these cases are quite
unlike each other, and the membranous capsule of the living animal
is included within the closed apical pole. In other cases, again, the
skeleton consists of a flat, or lenticular and biconvex plate, which is
sometimes double, and has a more or less complex internal structure.
This type of skeleton is found in such genera as Astromma, Trema-
todiscus, Rhopalastrum, Stephanastrum, and Stylodictya (fig. 45, A).

LITFERATU RE.
FORAMINIFERA.
1. “Introduction to the Study of the Foraminifera.” ‘ Ray Society.’
1862. W. B. Carpenter.
2. “Report on the Foraminifera.” ‘Rep. on the Sci. Results of the

Voyage of H.M.S. Challenger,’ vol. ix. 1884. Henry B. Brady.

3. “Carboniferous and Permian Foraminifera” (with a general Intro-
duction). ‘Monographs of the Palzontographical Society,’ 1876.
H. B. Brady.

4. “Handbuch der Palzontologie,” vol. i. pp. 61-114, 1876. Zittel.

5. “ Mikrogeologie.” Ehrenberg. 1854.

6. “Foraminiféres Fossiles du Bassin Tertiaire de Vienne.” D’Or-
bigny.

7. “Entwurf einer systematischen Zusammenstellung der Foramini-
feren.” ‘Sitzungsber. d. k. Akad. Wiss. Wien,’ 1861. Reuss.

8. “ Monograph of the Foraminifera of the Crag,” 1868. Rupert Jones,
Parker, and Brady.

150 PROTOZOA.

Q.

“Mémoires sur les Foraminiféres du Lias.” ‘Mém. de ’Acad. Im-
périale de Metz,’ 1858-1866. Terquem.

EOZOON.

. “The Dawn of Life.” J. W. Dawson. 1876.

2. “On the Occurrence of Organic Remains in the Laurentian Rocks

10.

(ee)

Io.

Il.

of Canada.” - Sir W. EH: Logan. “Quant, Journ’ G@eolesaen,
XX1. 45-50. 1865.

. “On the Structure of Certain Organic Remains in the Laurentian

Limestones of Canada.” J. W. Dawson. ‘Quart. Journ. Geol.
Soc.,’ xxi. 51-59. 1865.

. * Additional Note on the Structure and Affinities of Eozo6n

Canadense.” W. B. Carpenter. ‘Quart. Journ. Geol. Soc.,’
Xxl. 59-66. 1865.

. “Supplemental Note on the Structure and Affinities of Eozo6n

Canadense.” W- B- ‘Carpenter.<) “Quart: Journ) \Geaeusoer,
XXIl. 219-228. 1866.

. “On the So-called Eozodnal Rock.” King & Rowney. ‘Quart.

Journ. Geol. Soc.,’ xxii. 185-218. 1866.

. “Der Bau des Eozoén Canadense.” ‘ Palzeontographica,’ vol. xxv.

1878. Mobius.

. “ Mobius on Eozo6n Canadense.” ‘Amer. Journ. Sci. and Arts,’ 1879.

Dawson.

“New Facts relating to Eozo6n Canadense.” ‘Geological Magazine,’
1888. Dawson.

“Specimens of Eozoén Canadense, and their Geological and other
Relations.” Dawson. 1888.

RADIOLARIA.

. “Report.on the Radiolaria.” ‘Rep. on the Sci. Results of the

Voyage of H.M.S. Challenger,’ vol. xviii. (two volumes of text
and one of Plates). 1887. Haeckel.

. “Die Radiolarien.” 1862. Haeckel.
. “Ueber die Thalassicollen, Polycystinen, und Acanthometren des

Mittelmeeres.” ‘Abhandl. d. k. Akad. d. Wiss. Berlin.’ 1858.
Johannes Muller.

. “Mikrogeologie.” 1854. Ehrenberg.
. “Mikrogeologische Studien tuber das kleinste Leben der Meeres-

Tiefgriinde aller Zonen.” ‘Abhandl. d. k. Akad. d. Wiss. Berlin.
13/2 oe eee Oma

. ‘““Fortsetzung der Mikrogeologische Studien.” (Polycystinen-Mergel

von Barbados). ‘Abhandl. d. k. Akad. d. Wiss. Berlin.’ 1875.
Ehrenberg.

. * Ueber fossile Radiolarien der oberen Kreide.” ‘ Zeitschr. d. deutsch.

Geol. Gesellsch.,’ 1876. Zittel.

. ““Handbuch der Palzontologie.” 1877. Zittel.
. “Die Radiolarien- Fauna der Tripoli von Grotte.” ‘ Palzeonto-

graphica,’ vol. xxvi., 1880. Stdhr.
“Die Spongien, Radiolarien, und Foraminiferen der Unter-Lias- .
sischen Schichten von Schafberg bei Salzburg.” Denkschr. d. k.
Akad. d. Wiss. Wien.’ 1882. Dunikowski.
“Beitrage zur Kenntniss der fossilen Radiolarien aus Gesteinen des
Jura.” ‘ Paleeontographica,’ 1885. Rust.

151

CHA ke OX.

SUB-KINGDOM I1.—PORIFERA.

UNDER the name of Forifera are included all those singular organ-
isms which are commonly known as Sponges. Originally regarded
as being of a vegetable nature, the Sponges are now universally
admitted to be animals; though naturalists are not yet in absolute
agreement as to the precise position in the animal kingdom which
ought to be assigned to them. Owing to the close likeness of some
of the cell-elements of the Sponges to certain of the Protozoa, the
entire group has been often referred to this latter sub-kingdom.
Thus, some of the cells of a sponge are morphologically identical
with the Amaebe, while others present the closest possible resem-
blance to the Flagellated Zufusoria. Hence, a sponge has often been
regarded as being a kind of colony, the units of which are morpho-
logically Protozoans. Naturalists are, however, now agreed as to the
removal of the Sponges from the Protozoa ; and they are by many
authorities regarded as forming the lowest division of the Zoo-
phytes (Ce/enterata). Other authorities consider that the Sponges
represent a distinct morphological type, intermediate between the
Protozoa and the Ca/lenterata, and that they are therefore entitled to
take rank as a separate sub-kingdom, to which the name of Porijera
has been given. In the present state of our knowledge, this view
seems to be the one which is attended with the fewest difficulties,
and it will therefore be followed here.

The Sponges may be defined as multicellular organisms of variable
shape, the cells of which are typically disposed to form an outer mem-
brane, an inner membrane, and an intermediate stratum ; and which
are traversed by canals, which open on the surface, and which are
more or less extensively lined by flagellate cells. In most cases the cel-
lullar aggregate 1s supported by a framework of horny fibres, or of
jiinty or calcareous spicules. A definite mouth and stomach are want-
ing, and a nervous system 1s not known with certainty to be developed.

The entire aggregate of cells which constitutes a sponge is so

152 PORIFERA.

arranged as to be traversed by a series of canals, which convey water
in and out of the organism, and which are thus connected with
respiration and the procuring of food. Looking at the skeleton of a
dried sponge, the most obvious sign of the existence of this “ aqui-
ferous system ” is the presence of one or more large superficial open-
ings, together with a great number of much smaller apertures (fig. 47,

Fig. 47.—Diagrammatic representation of the structure of a simple Sponge, as seen when cut
in half vertically. The general ‘‘ sponge-flesh”’ is lightly shaded (7) ; the canal-system is black,
and the arrows show the course of the water-currents. / Z, ‘‘ Pores,” opening into ‘‘ inhalant
canals,” which conduct to the ‘‘ ciliated chambers” (ck). From these chambers proceed the
larger ‘‘ exhalant canals” (zc), which open into a general central space or “‘cloaca.” This space
terminates on the surface by a single large opening or ‘‘osculum” (9), which serves for the
exit of the water. (After Haeckel )

pp). These latter are termed the “ pores,” and though permanently
present in the skeleton, they are only temporarily present in the
soft parts, being produced afresh, when required, as openings be-
tween the sponge-bells of the ectodermal layer. ‘The “pores” (fig.
47, p p) open directly, or through the intervention of more or less
extensive subdermal cavities, into a series of canals, which ramify in

PORIFERA. nee

every direction through the sponge, and which are called “ inhalant
canals,” as it is through these that the water is conveyed to the
interior of the sponge. The “ inhalant canals ” ultimately open into
a second series of canals, which converge to form one or more large
tubes which open on the surface by a corresponding number of
large openings. ‘These large tubes (fig. 47, zc) carry the water out of
the organism again, and they are hence called “exhalant canals” ;
while their surface-openings are known as the ‘“oscula.” The
“‘oscula,” though capable of being temporarily closed, are perma-
nent, and are often placed on chimney-like elevations. If there
should be but one oscwWum, it is placed at the apex of the sponge
(fig. 47, 0), while the pores occupy the general external surface.
What is commonly called a “sponge” may consist of only a single
excretory opening or “ osculum,” together with the ‘‘ pores” belong-
ing to this (fig. 47); or it may consist of a larger or smaller number
of such “oscula,” each with its proper complement of “pores.” In
the latter case, each osculum, with its accompanying pores, consti-
tutes a “‘ person,” and the entire organism is known as a “ sponge-
stock.”

In a living sponge, in its active condition, a circulation of water
is kept up throughout the organism by means of this system of canals.
The water is admitted from the exterior by the pores, and is driven
through the deeper parts of the sponge by means of flagellate cells,
which line a series of globular chambers developed between the
inhalant and the exhalant canals (fig. 47, cz). From these “ flagellated
chambers” the water is driven into the exhalant canals, and finally
escapes again by the osculum or oscula. In this way, the separate
sponge-cells are enabled to carry on their nutritive and respiratory
processes.

In a few sponges (the A/yxospongie of Haeckel) there is no
skeleton, and the above description would, therefore, fully express
the general structure of the organism. In the vast majority of
sponges, however, the soft cellular body is supported by more or
less extensively developed hard structures, which collectively consti-
tute the ske/efon. ‘The nature of the skeleton varies greatly in dif-
ferent forms, and these variations have been largely made use of in
the identification and classification of the Sponges. Speaking gen-
erally, the skeleton has the form of a more or less coherent frame-
work, composed either of horny fibres, or of needles of mineral mat-
ter, or of both these elements in combination. ‘The different modi-
fications of the skeleton will be more particularly spoken of in deal-
ing with the different groups of sponges. It will be sufficient to
point out here that, apart from modifications in the form of the
skeletal elements, there are the following four principal types of
skeleton among the Sponges :—

154 PORIFERA.

1. In certain sponges (such as the Common Bath Sponges) the
skeleton (fig. 48, a) is wholly, composed of netted horny fibres, with-
out proper ‘‘ spicules.” The substance composing the fibres in such

B

Fig. 48.—Forms of the skeleton in the fibrous Sponges. a, Horny, non-spiculate skeleton of
the Bath Sponge, enlarged about fifty times; B, Horny fibre cored with sand-grains; c, Horny
fibre with projecting siliceous spicules (‘‘ Echinonematous” Sponge); pb, Fibre in which the
spongin has been more or less completely replaced by siliceous spicules (‘‘ Holorhaphidote ”
Sponge). B, Cc, and D are greatly enlarged, and are after Carter.

types is allied to horn, but not precisely of the same nature, and it
is known as “ spongin” or ‘‘ keratode.”

2. In another group of sponges, including most of the commoner
forms, the skeleton is more or less extensively composed of siliceous

a b

Fig. 49.—Spicules of Sponges. @, Monactinellid skeleton-spicule of Rexzera ; 6, Monactinellid
spicule of CZonxa ; c, Monactinellid spicule of Spongilla ; d, Tetractinellid skeleton-spicule of
Geodia ; e, Skeleton-spicule of a Lithistid Sponge (¥evea); 7, Flesh-spicule of Cribella ; g, Flesh-
spicule of Esperia ; h, Flesh-spicule of Hyalonema. All the figures are greatly enlarged. (After
Schmidt, Vosmaer, Zittel, &c.)

needles or “spicula,” of various forms (fig. 49). These spicules
may be embedded in various ways in a reticulated fibrous skeleton
of spongin (fig. 48, c) ; or the horny material may be greatly reduced,

PORIFERA. 19st

so that the skeleton-fibre consists essentially of minute flinty needles
(fig. 48, D).

3. In a third group of sponges, the skeleton is destitute of horny
matter, and consists wholly of siliceous spicules, which may be fused
with one another into a continuous framework, or may be so inter-
-locked by their ends as to produce practical rigidity, or may be simply
held in position by the fleshy substance of the sponge. In both this
group and the preceding, in addition to the spicules of the proper
skeleton, there are generally developed in the mesoderm numerous
still more minute microscopic needles of flint, which are known as
** flesh-spicules.” .

4. Lastly, there is a group of sponges in which the skeleton is
wholly made up of spicules of carbonate of lime.

In all sponges which possess hard structures of flint or ime, the
“‘ spicules” consist, each, of concentric layers of mineral matter de-
posited round a central fibre of organic matter which occupies an
‘axial canal” in the spicule. In the Calcspongie each spicule may
be regarded as essentially a single crystal of carbonate of lime. In
the ordinary recent siliceous Sponges, on the other hand, the spicules
are composed of colloidal silica, which is as clear as glass, wholly
non-crystalline, and entirely unaffected by polarised light between
crossed Nicols. The silica of recent sponge-spicules is also soluble
in hot solutions of caustic potash.

As regards the distribution of the Sponges zz space, the great
majority are marine, but representatives of the Spongzliide are found
in fresh waters in all the great continental regions except Australia.
Of the marine Sponges, the Calcspongie and Ceratospongie are
principally inhabitants of shallow water. On the other hand, the
Hexactinellid Sponges are mostly found in deeper water, the major-
ity living at depths of from 100 to 2500 fathoms. The Lithistid
Sponges, on the contrary, are found in comparatively shallow water,
being most abundant between depths of 10 to 150 fathoms.

In connection with the subject of the distribution in time of the
Sponges, it is necessary to briefly consider the different modes in which
the skeleton of the Sponges may be preserved in the fossil condition.
Taking first the Sponges which secrete a siliceous skeleton, it has been
pointed out above that the silica of the spicules or spicular network of
these, in the vecez¢ condition, is colloidal and non-crystalline, glassy, and
entirely unaffected by polarised light. Though unaffected by acids, the
spicules undergo solution in hot caustic potash, and there is reason
to know that they readily become changed, or even dissolved, under
certain natural conditions which it is difficult or impossible to imitate in
the laboratory. While the above is the condition of the siliceous spicules
in recent Sponges, these structures in fossil Sponges have, as a rule, under-
gone more or less change during the process of fossilisation, the following
being the principal forms of alteration which have been observed.

(a.) The silica af the spicules may be changed into an amorphous

156 PORIFERA.

condition. The alteration is in this case but slight, since the silica is
still in the colloidal state, and the principal change that has occurred is
that the spicules have lost their original glassy aspect, and have become
porcellanous and milky-white when viewed by reflected light.

(6.) The silica of the spicules may have become cryptocrystalline or
crystalline. In this form of alteration, the original colloidal silica of the
spicules has become changed into chalcedony or quartz, and the spicules
now exhibit with polarised light the same colour-changes as are shown
by the above minerals.

(c.) In a great many cases among fossil Sponges, the original flinty
skeleton has undergone more or less complete solution during fossilisa-
tion, the Sponge being now represented only by hollow casts of the
original skeleton in the matrix of the enclosing rock. In the case of
calcareous organisms it has long been well known to palzontologists
that the skeleton very commonly undergoes solution, leaving nothing but
a hollow mould or impression in the rock to mark its former existence.
Silica being a much more stable substance than carbonate of lime, it uséd
to be supposed that an originally flinty skeleton would not be liable to
undergo a similar solution. It has, however, been conclusively shown
by Zittel, Sollas, and Hinde, that this supposed stability of organic silica
is largely imaginary. According to the last-named observer, “it may be
accepted as proved that silica in the colloid state, in which it occurs in
the skeleton of recent siliceous Sponges, and also in the original condi-
tion of fossil Sponges, is extremely liable to chemical changes, and that it
is only when it is in the condition of chalcedony, or is crystalline, that it
can be regarded as stable. The changes in the siliceous skeletons of
fossil Sponges, mentioned above, show the tendency of the silica to pass
from the unstable colloid to the stable chalcedonic or crystalline condi-
tion. Under favourable conditions this chemical change has taken place
without destroying the form of the spicular skeleton, but in other circum-
stances the colloid silica of the skeleton has been wholly dissolved away,
and redeposited, usually in the chalcedonic condition, so as to form solid
beds of chert and bands of nodular flints.”

(d@.) In the cases just spoken of, the original siliceous skeleton of the
Sponge has undergone solution, and there is left in the rock a hollow
mould of the skeleton, this mould being commonly so accurate as to
preserve with fidelity the form of the component spicules of the
skeleton. Very usually, however, the mould thus formed becomes
ultimately completely filled up with some mineral substance de-
posited from the water which percolates through the rock; the result
being the formation of a “pseudomorph” of the original Sponge, or, in
other words, a body which has the exact form, and may even have the
microscopic structure, of the original Sponge, but which consists of some
secondary substance which has taken the place of the original skeleton.
The substance which has in this way replaced the original Sponge is
most commonly crystalline calcite, but peroxide of iron is likewise often
the replacing material, or, less commonly, iron-pyrites or glauconite ;
while in some cases it would appear that the replacing substance has
been chalcedonic silica. It only needs to be added in this connection
that the changes above spoken of do not necessarily affect an entire
Sponge, but that specimens often occur in which a portion of the
skeleton has been fossilised in one way, while another part may have
been preserved in a different manner.

The Calcispongig do not, as a rule, undergo fundamental alteration,
as regards their skeletal structures, during fossilisation. In some late

PORIFERA. ey,

deposits, the spicules of Calcareous Sponges are found in a condition not
recognisably different from that of recent examples. As a rule, “the
spicular fibres of fossil Calcisponges retain their original structure of
carbonate of lime, though the form of the component spicules has to a
large extent disappeared, and the fibres are now either of crystalline
grains of calcite or show a finely radiate prismatic structure” (Hinde).
In certain cases, however, the calcareous skeleton of a Calcisponge may
be found to be replaced, as occurs commonly in the case of Corals and
other calcareous organisms, by chalcedonic silica. Such “ silicified”
specimens have necessarily undergone an entire destruction of the
minute structure of the skeleton, though the form of the skeleton may be
perfectly well preserved.

As regards their general geological distribution, the Sponges are
very largely represented in past time, and have a very high an-
tiquity. The two recent groups of the JZyxospongie and Cerato-
spongie, being devoid of hard parts or having only a horny skeleton,
are unknown in the fossil condition, though doubtful examples of
the latter have been brought
forward. The Sponges with a
skeleton of siliceous spicules are
known to occur in deposits as
ancient as the Cambrian, the
oldest Sponge at present known
being the Protospongia fenestrata
(fig. 50) of the Menevian Slates
of St David’s, South Wales. In
strata of Ordovician age the re-
mains of Sponges are not very
uncommon, the groups of the
Lithistide and Hexactinellide be-
ing both represented, the former
by types like Andia, and the
latter by Hyalostelia, Recepta- Sis, soz Par ot the spicular mesh of Pref
culttes, and Jschadites. In the from the Menevian strata of South Wales. The
Silurian deposits the same groups (Maer Hinde ee distorted by cleavage.
of Sponges are well represented
by forms such as Axulocopium, Astylospongia, and Dictyophyton ;
while the group of the Monactinellid Sponges is represented by the
genus Climacospongia. If we except the aberrant group of the e-
ceptaculitide, the Devonian system has, so far, proved to be singularly
barren of Sponge remains, though a few types (Astreospongia,
Dictyophyton, &c.) have been detected in strata of this age. On
the other hand, the seas of the Carboniferous period were tenanted
by a vast abundance of Sponges, belonging to few generic types—
so far as yet known—but representing the distinct groups of the
Monactinellide, Tetractinellide, Lithistide, Hexactinellide, and

158 PORIFERA.

Fleteractinellide. So great was the profusion of Sponge-life during
Carboniferous times that thick beds of chert—as conclusively de-
monstrated by Hinde—were formed by the gradual accumulation of
siliceous spicules on the floor of the sea. These siliceous sponge-
beds are largely developed in the Carboniferous limestone and Yore-
dale beds of the North of England, Wales, and Ireland, and may
reach a thickness of more than fifty feet [in Ireland, a maximum
thickness of over 300 feet of these chert-beds has been observed].
The highest Paleozoic deposits—viz., the Permian—have hitherto
yielded few or no unequivocal remains of Sponges.

Coming to the Mesozoic deposits, the Trias has not yielded a
large number of Sponges, and the great majority of the known forms
of this period belong to the Cadcispongiz, and are referable to the
extinct group of the Pharetrones. On the other hand, an enormous
number of Sponges are known to occur in strata of Jurassic age,
almost all the hitherto recognised types of this period belonging to
the three groups of the Lzthistide, Hexactinellide, and Pharetrones
(Calcispongie). At the summit of the Jurassic system (in the Pur-
beck beds) we also meet with the first undoubted representative of
the fresh-water genus Sfongil/a. In the Cretaceous system, and
especially in its upper division, Sponges also occur in vast numbers,
the three groups above mentioned being those most largely repre-
sented. It is noticeable, however, that the aberrant Calcisponges
which form the group of the /Paretrones diminish in numbers to-
wards the close of the Cretaceous period ; while the groups of the
Monactinellide and Tetractinellide have a fair representation. In
parts of the Cretaceous system, and particularly in the Lower and
Upper Greensand, occur beds of siliceous rock, which have been
shown by Hinde to have been formed by the accumulation of the
microscopic spicules of various types of Sponges. In some cases,
these spicules are loosely compacted together, and give rise to a
porous siliceous rock. More commonly, however, the spicules have
undergone partial solution in sea-water, and the dissolved silica thus
obtained has been subsequently redeposited, and has formed a
siliceous cement which has bound together the undissolved spicules
in a general cherty matrix. In such cases, the true nature of the
rock can only be recognised by an examination of thin sections
(fig. 51) under the microscope.

There is, further, every reason to believe. that the nodular flints
which form such a striking feature in the White Chalk have been in
reality produced by the solution of the skeletons of flinty Sponges
and other siliceous organisms, and the subsequent redeposition of
the silica thus obtained in a solid form. It is well known, namely,
that the siliceous Sponges of the White Chalk have usually had
their original siliceous skeleton more or less wholly dissolved out,

PORIFERA. 159

the original skeleton being now represented either by empty casts in
the rock or by pseudomorphs of lime, peroxide of iron, or iron-
pyrites. The general freedom of the body of the White Chalk
from silica can thus be readily explained on the ground that the
siliceous organisms which it, to begin with, contained, underwent a
more or less complete solu-
tion. The dissolved silica
thus obtained must, however,
have been from time to time
redeposited in a solid form,
thus giving rise to the nod-
ules of flint which are so
largely disseminated through
parts of the White Chalk.
On this view, the silica of the \
Chalk-flints had an organic —
origin, though deposited from
solution in sea-water. On
this view, it is also possible
to account for the fact that |
the silica, in course of re- Fig. 51.—Section of chert from the Upper Green-
deposition, should not only sand, showing numerous sponge-spicules embedded in
have accumulated in a nod- ane matrix, enlarged forty diameters. (Af-
ular form round any foreign

bodies which may have been lying on the sea-bottom at the time,
but should also have commonly penetrated into the internal cavities
of organic bodies, or should even have given rise to tabular masses .
or to actual veins.

In deposits of Tertiary age, finally, remains of Sponges have
hitherto been detected in much smaller numbers than in the pre-
ceding Mesozoic strata. The great group of the Pharetrones among
the Calcaspongie seems to have become extinct with the close of the
Cretaceous period, and the Hexactinellids and Lithistids are for the
most part but poorly represented. In the Miocene strata of Algeria,
however, Pomel has described an abundant fauna of Hexactinellid
and Lithistid Sponges.

160

CFT A (Bae ie ee le
PORIFE RA— Continued.
CLASSIFICATION AND PRINCIPAL GROUPS OF THE SPONGES.

THERE is, perhaps, no single group of the animal kingdom in which

it has proved so difficult to establish a natural classification, as has
been found to be the case with the Sponges. Even at the present
day there is no extant classification which can be regarded as final.
It is, however, now generally admitted that the calcareous Sponges
are so far separated from all the other groups of Sponges as to pro-
perly constitute a distinct class of Sponges. The non-calcareous
Sponges may be grouped together in a second class under the name
of Plethospongie, proposed for them by Professor Sollas. As regards
the ordinal divisions of the Plethospongie, the grouping followed by
*Professor Zittel may be adopted, with some modification, and the
general classification of the Sponges is thus expressed in the following
table :—

SUB-KINGDOM PORIFERA.
Crass I. PLETHOSPONGL® (Sollas).

Order 1. Myxosponci® (Halsarca).

2. CERATOSPONGLE (Luspongia).

3. MONACTINELLID® (Halichondria, &c.)

4. TETRACTINELLIDE (Geodia, Tethya, &c.)
» 5- LITHISTIDA (Descodermia, &c.)

6. HEXACTINELLID (/oltenia, &c.)

7. OCTACTINELLIDE (Astreospongia).

8. HETERACTINELLIDE (Asteractinella, &c.)

>)

[The last six of the above-mentioned orders are regarded by Hinde as
sub-orders, and are included in the single order Sz/¢c¢spongze. |

PRINCIPAL GROUPS OF THE SPONGES. I6I

Crass II. CALcISPONGIZ.

1. ASCONES (Ascetta, &c.)
,, 2. LEUCONES (Leucandra, &c.)
> 3+ SYCONES (Grantia).

4. PHARETRONES (Corynella, &c.)

Family

Cxiass J. PLETHOSPONGILA.

The Sponges included in this class are occasionally destitute of
hard structures, but the great majority possess a skeleton, which may
be composed of horny fibres alone, or of siliceous spicules alone, or
which is formed by a combination of these two sets of structures.
In no case is the skeleton composed of carbonate of lime.

ORDER 1. Myxosponci®.—The Sponges of this order are entirely
destitute of skeletal structures, or, at most, possess a few scattered
siliceous spicules. The type-genus is Halzsarca, comprising a num-
ber of soft fleshy sponges, widely distributed in recent seas, which
form crusts upon submarine objects. No example of this order, as
might be expected from the soft nature of the organism, is known as
occurring in the fossil condition.

ORDER 2. CERATOSPONGI£.—In this group of Sponges, the skele-
ton is composed of the horny substance known as “spongin,” and
there are either no proper spicules, or in some cases a few siliceous
spicules may be scattered in the mesoderm. The horny fibre of the
skeleton forms a close reticulation or network (fig. 48, a), and can
be shown to consist of a delicate axial thread of organic matter sur-
rounded by a laminated horny sheath. In many cases, the horny
fibre includes numerous sand-grains or other foreign bodies in its
interior (fig. 48, B), these being taken in at the free-growing ends of
the fibres, to which they form a kind of core, replacing the soft or-
ganic axis which in some cases is alone present. The type of this
order is the recent genus Ausfongia, comprising the Turkey Sponges
of commerce. No undoubted fossil representatives of the Cerafo-
spongie have been as yet detected in the fossil condition, the cylin-
drical antler-shaped bodies from the Cretaceous rocks of Germany,
which Geinitz described under the name of Sfozgztes, being of an
altogether problematical nature.

ORDER 3. MONACTINELLID£.—This order comprises an extensive
series of Sponges characterised by the possession of a skeleton which
is typically composed of horny fibres with included spicules of flint.
The spicules vary much in form, but are always uniaxial, being most
commonly fusiform, pin-shaped, or bow-shaped (fig. 49, @, 4, ¢, and
fig. 52). In recent Monactinellids the proportion borne by the spi-
cules to the horny fibre is very variable, and in some types the skele-
ton consists almost wholly of uniaxial spicules without any, or with

VOL. I. L

162 PORIFERA.

very little, horny connecting-substance (fig. 48, D). In addition to
the proper skeleton-spicules, which are usually connected by a horny
fibre, there are developed in the mesoderm more or less numerous
disconnected, uniaxial, siliceous needles or “‘ flesh-spicules.”

The order of the Monactinelhde is represented by a very large
number of existing marine Sponges, as well as by the fresh-water
group of the Sfongiliide. Owing to the nature of the hard struc-
tures in this order, the entire skeleton does not readily admit of pre-
servation, and most of the known fossil forms are therefore repre-

Fig. 52.—Fossil Monactinellid Sponges. a, Part of the spicular network of Climacospongia
vadiata, Silurian, Tennessee, enlarged twelve times ; ; B, Part of the spicular network of Acan-
thoraphis intertextus, Chalk, Kent, enlarged ten times; Cc, Spicules of Spougilla Purbeckensis,
as shown in a thin slice of chert from the Purbeck formation, enlarged; p, Spicule of Renzera
gracilis, Carboniferous, Yorkshire, enlarged sixty times; E, Spicule of Renicra clavata, Carbon-
iferous, Yorkshire, enlarged sixty times ; F, Spicule of Axinella paxillus, Carboniferous, Lanca-
shire, enlarged thirty times. (C is after John Young, and the remaining figures are after Hinde. )

sented by mere fragments or by detached spicules. The record of
the distribution of the Monactinellid Sponges in past time is, there-
fore, necessarily a very imperfect one. The oldest types which have
been determined with any certainty occur in the Silurian deposits,
in which are found the large uniaxial spicules upon which Hinde has
founded the genus Afractosella. Of the same age is the genus
Chimacospongia (fig. 52, A), in which the skeleton is composed of
elongated acerate spicules arranged in a ladder-like manner. Cer-
tain tubular borings in Silurian shells have also been referred to the
operations of a Sponge (Vzoa prisca), supposed to be related to the
living boring Sponges (CZzona), but the nature of these is very doubt-
ful. On the other hand, fossil shells pierced by borings in all respects
similar to those produced by the recent Cone are not uncommon
in Secondary and Tertiary deposits. In the Devonian rocks, Monac-

PRINCIPAL GROUPS OF THE SPONGES. 163

tinellid Sponges are almost unknown, but strata of this age in Bel-
gium have yielded remains on which the genus ZLaszocladia has been
founded. In the Carboniferous system, on the other hand, particu-
larly in some of the chert-beds associated with the Mountain Lime-
stone and Yoredale series, the remains of Monactinellid Sponges are
comparatively abundant. The best known types of this age are
Reniera and Axinella, the former represented by cylindrical spicules
(fig. 52, D and £), and the latter by pin-shaped spicules (fig. 52, F).
In the genus Hap/istion more or less complete specimens have been
found, showing that the sponge possessed a fibrous skeleton com-
‘posed of minute, straight, or curved, acerate spicules.

In the Permian rocks no certain remains of Monactinellid Sponges
are known, the Sfongz/lopsis of Geinitz being apparently inorganic ;
and the Trias has also yielded so far no traces of this group. In
the Jurassic system also, vast as is the number of known Sponges
belonging to other orders, no type of the Monactinellids has hitherto
been recognised till the very summit of the formation is reached.
In the Purbeck beds, however, in chert containing the remains of the
fresh-water Cara, are found numerous spicules belonging to a fresh-
water Sponge, to which the name of Spongilla Purbeckensts has been
given (fig. 52, c). In the Cretaceous system, likewise, the remains
of Monactinellids are very rare, but the Upper Chalk has yielded
shells bored by species of CZiona, and also the skeleton of the genus
Acanthoraphis (fig. 52, B), in which the spicules are fusiform and
minutely tuberculate. In the Tertiary rocks, lastly, the Monactinel-
lids are mostly, if not wholly, represented by the tunnels bored in
shells by species of C7/zona.

ORDER 4. TETRACTINELLID#.—This order comprises marine
Sponges in which the skeleton consists of siliceous skeleton-spicules,
frequently arranged in bundles in a radiating manner, and held to-
gether by spongin. The characteristic skeleton-spicules are tetraxial,
the commonest form being that of an elongated rod carrying three
shorter summit-rays at the upper end (fig. 49, @). In addition to
the typical tetraxial spicules there are usually other uniaxial forms, as
well as smaller “ flesh-spicules,” generally of a globate, stellate, or
reniform shape.

The Tetractinellid Sponges are largely represented at the present
day, the genera Zethya and Geodia being well-known examples of
the group. Owing to the want of a continuous siliceous skeleton,
however, the Tetractinellids are not commonly preserved as fossils,
and they are usually represented by detached spicules only. The
oldest known examples of this order occur in the Carboniferous
rocks, which have yielded the remains upon which the genera
Geodites and Pachastrella have been founded. The former of these
is supposed to be allied to the recent Geodza, and is characterised

164 PORIFERA.

by the possession of elongated spicules with bifid or trifid summits,
associated with a dermal layer of globate or reniform spicules. The
genus Pachastrella, again, comprises “‘ massive, nodose, platter-shaped,
or irregularly expanded Sponges without a specialised dermal layer ”
(Hinde). The skeleton is composed of four-rayed spicules, asso-
ciated with acerate spicules.. The oldest species of Pachastrella are
found in the Carboniferous, but other forms of the genus have been
recognised in the Jurassic rocks, the Upper Chalk, and the Eocene
Tertiary. In the Upper Chalk occur the remains of various Tetrac-
tinellid Sponges, of which the genus Ze¢hyopsis is perhaps the most
characteristic. In this genus (fig. 53), the skeleton is composed
of radiately arranged trifid spicules,
mingled with acerates, while the
surface is covered with a layer of
minute trifid anchorate spicules
(Zittel).

ORDER 5. LiTHISTIDZ. — The
Sponges included in this order are
massive, stony, and _ thick - walled,
with a very variable external figure.
The skeleton is composed _princi-
pally of -four-rayed or irregular spi-
cules (fig. 54), which usually branch
at their extremities, their ends being
blunt, or being furnished with min-

Ty er MieR emcee AR rere itul articular surfaces. The skeletal
thyopsis Steinmanni, from the Upper spicules are not fused together, but
Finck) arsed 24 umes.” (After “are so ‘interlocked “by the umbecuqam=

ing of their branches or by the close
apposition of their expanded extremities ” (Hinde) as to give rise to
a practically continuous framework (fig. 54, B). There are generally
small monaxial “ flesh-spicules,” and also a dermal layer of trifid or
discoid spicules, in addition to the ordinary skeleton-spicules. There
may be a single terminal osculum only, or the Sponge may be
provided with numerous scattered oscula; while the canal-system
exhibits numerous modifications in different groups of the order,
and in some cases is not developed as a special structure.

ae % ry, ANG

ane

SYN
SAN"
a7

ar ES

The order of the Lithistid Sponges has been divided by Zittel into the
four following sub-orders :—

1. Rhizomorina.—In this group of Lithistids the skeleton-spicules are
elongated and irregularly branched (fig. 55, B), the branches terminating
in minute articular surfaces which unite adjoining spicules into an irreg-
ular and confused network. Typical genera are Cxemidiastrum, Selis-
cothon and Verruculina.

2. Megamorina.—In this group the skeleton-spicules are large and
either simple or irregularly branched, the branches terminating in obtuse

PRINCIPAL GROUPS OF THE SPONGES. 165

ends or expanded articular surfaces. The spicules form an open mesh-
work by the apposition of their terminal facets. Typical genera are
Doryderma, Pachypoterion, and Carterella.

3. Anomocladina.—In this group the skeleton-spicules have the form
of a central node from which radiate simple or bifurcate arms, which
have slightly expanded ends, and are variable in number. The skeleton
forms a regular network produced by the union of the expanded ends of
the spicular arms with the nodes, or sometimes with the branches of
adjoining spicules (fig. 55, A). Typical genera are Vetulina, Hindia,
and Astylospongia.

4. Tetracladina.—In this group, the spicules (fig. 54) consist of four
rays which meet in a non-inflated centre in such a way that one ray

Fig. 34.-—A, A single skeleton-spicule of the living Lithistid Discodermia polydiscus, magni-
fied 60 diameters; B, Small portion of the skeleton of Siphonia pyriforntts, similarly enlarged.
(After Sollas.)

forms a shaft from which the other three rays spring, approximately
meeting at angles of 120. The ends of the rays are branched, and
interlock with the ends of adjoining spicules to form a continuous mesh-
work. Typical examples are the genera Ferea (fig. 49, ce), Aulocopium,
and Szphonza (fig. 58).

The Lithistid Sponges are all inhabitants of the sea, and the
existing genera (Descodermia, Corallistes, Vetulina, &c.) are mostly

166 PORIFERA.

found in water of moderate depth.

As regards the distribution of

the order in time, one of the most ancient representatives of the

Fig. 55.—A, Part of the spicular network of As-
tylospongia, from the Silurian of Gotland, enlarged
60 times; B, Rhizomorine spicule of Seliscothon
JTantelli, from the Cretaceous rocks, enlarged 60
times. (After Hinde.)

group would appear, from the
researches of Dr Hinde, to be
the genus Archeoscyplia (based
upon the Archeocyathus Min-
ganensis of Billings), which oc-
curs in the Upper Cambrian
rocks (Calciferous series) of
Canada, along with allied types
such as Calathium. Closely
related forms are found at a
corresponding geological hori-
zon (the Durness Limestone)
in Britain. The skeleton in
Archeoscyphia Minganensis (fig.
56) has the form of a curved
funnel attached by its pointed
base, and with a deep central
cavity or “cloaca” apparently

without an internal wall. The constituents of the skeleton have a
radial disposition, and distinct spicules, usually four-armed, and inter-

aN anty }
AG

Fig. 56.—Restoration of the lower part of
Archeoscyphia Minganensts. a, The pores
of the inner wall of the cup. Ordovician.
(After Billings.)

Fig. 57.—Section of Astylospongia
premorsa, Silurian, Tennessee. (After
Roemer. )

linked by their subdivided ends, are present. The siliceous nature
and spicular structure of the skeleton in Archeoscyphia Minganensis
render it clear that we have to deal here with a genuine Sponge.

PRINCIPAL GROUPS OF THE.SPONGES. 167

In the Ordovician rocks we meet with species of the genera
fiindia and Astylospongia, both of which are represented, still more
abundantly in Silurian strata. The genus Astylospongia (fig. 57)
comprises globular or ovate, unattached sponges, furnished with a
cup-shaped or funnel-shaped depression at the summit. There are
two principal sets of aquiferous canals, those of the one series being
radial and directed from the surface towards the centre, while those
of the other series are radial, but are vertically disposed in a direction
parallel to the surface, so as ultimately to open into the summit-cup.
Astylospongia was formerly referred to the Hexactinellids, but recent
_researches have shown that it is truly referable to the Anomocladine
group of the Lithistids. The skeleton consists of siliceous spicules
(fig. 55, A) with solid nodes, from which radiate from six to nine
straight rays, the ends of which are branched and are furnished with
slightly expanded articular processes. The rigid skeletal network is
formed by the apposition of the branched ends of the spicules to the
nodes of adjoining spicules, or, sometimes, to the ends of their
immediate neighbours. More or less closely allied to Astlospongia
are the Silurian genera Paleomanon and Protachilleum, and probably
the Ordovician genus Losfongia ; while the Jurassic genera AZelonella
and Cylindrophyma, the Cretaceous Mastosza, and the recent Vetudina
are regarded by Zittel as belonging to the same family.

The genus Avznzdia comprises free, spherical or subspherical
sponges, in which the body is traversed by numerous canals which
radiate from a central space and open on the surface. The skeleton
consists of four-rayed spicules, the digitated ends of which embrace
the nodes or rays of adjoining spicules in such a way as to form a
regular meshwork. The species of the genus are chiefly found in
the Ordovician and Silurian rocks, but spicules have been recognised
by Hinde in strata of Carboniferous age.

No Devonian Lithistids are at present known, but a few forms of
this group (Cxemidiastrum and Doryderma) have been recognised
in the Carboniferous deposits. No forms of the Zzthistide@ are
known in the Permian or Triassic rocks, but very numerous types
of this order of sponges have been recognised as occurring in the
Jurassic deposits. In the Upper Jurassic rocks of Germany, in
particular, are numerous Lithistids, belonging to such genera as
Cuemidiastrum, Fyalotragos, Platychonia, Placonella, &c. It is,
however, in the upper portion of the Cretaceous system that the
Lithistid Sponges attain their maximum development, the genera
Chenendopora, Siphonia, Verruculina, Chonella, Jerea, Jereica, Bol-
zdium, Turonia, Plinthosella, &c., being characteristic and widely
distributed types. Of all the Cretaceous Lithistids none is more
generally familiar than the genus Szfonia (fig. 58), in which the
sponge consists of a pyriform or subspherical body, supported

168 . PORIFERA.

usually on a longer or shorter stem, and attached thereby to some
foreign body. In some cases, however, the stem is wanting, and
the sponge is attached simply by diverging root-fibres. The ex-
halant water-canals open at the summit of the sponge by oscula
situated within an apical cavity or cloaca, while the inhalant canals
open by pores on the lateral surfaces. The skele-
ton-spicules (fig. 54, B) are four-armed, the ends
of the rays being expanded and furnished with
tubercles and intervening depressions, by means of
which they are interlocked with the rays of adjoining
spicules so as to produce a rigid framework. As
pointed out by Sollas, there is a close agreement in
form between the spicules of Szshonza and those of
the recent genus Dzscodermia. ‘The genus /evea is
very closely allied to SzAhonza, but there is no general
cloacal chamber ; while in the related genus Ha/irhoa
the body of the sponge is lobed.

In the Tertiary period, lastly, the remains of
Lithistids are for the most part of infrequent oc-
currence, though numerous sponges belonging to
this order have been detected in Miocene strata
in Algeria.

ORDER 6. HEXACTINELLID2.—In this group of
the siliceous Sponges, the skeleton is composed of

y ‘| six-armed flinty spicules, the rays of which are at
Fig. 58.—Siphonia right angles to each other (fig. 59, B). In the
Hee era centre of each spicule are three canals cutting each
other at right angles, and forming an axial six-rayed
tube. In some Hexactinellid Sponges, the spicules are simply
united by the soft tissues. More commonly, the spicules are
fused with one another by the ends of corresponding rays, or are
united by means of amorphous silica, so as to form a trellis-work
of rectangular or polyhedral meshes, the individual spicules of
which may be only recognisable by the persistence of their axial
canals (fig. 63). The “ flesh-spicules” are fundamentally six-armed,
but may give off secondary branches so as to form a rosette.

The Hexactinellid Sponges may be divided into two groups ac-
cording as the skeletal spicules are fused with one another or are
free. In the group of the Dyzctyonima, comprising such genera as
Euplectella, Ventriculites, Tremadictyon, Celoptychium (fig. 59), and
many others, the skeleton is composed of six-armed spicules which
became fused with one another by a secondary deposit of silica, so
as to form a latticed trellis-work. On the other hand, in the group
of the Zyssakina, comprising such genera as Sfauractinella and
flyalostelia, the skeletal spicules are interlaced, and are usually

PRINCIPAL GROUPS OF THE SPONGES. 169

simply held in position by the soft parts of the sponge, no fusion
taking place between them.

The recent Hexactinellids are all inhabitants of the sea, and are
mostly found in deep water, and paleontologists are now acquainted
with a very extensive series of fossil forms, dating from the Cam-

ac jn

MH
MK

a (

a0)
;
A.
iC

Fig. 59.—A, Side-view of a specimen of Caloptychium Seebach?, of the natural size, from the
Cretaceous formation; B, Portion of the hexradiate skeleton of the same, enlarged 65 times.
(After Zittel.)

brian period. The oldest known type of the Hexactinelide is the
genus Protospongia, species of which occur in deposits of Cambrian
age. In this genus, the sponge is cup-shaped, with a thin wall,
composed of large cruciform spicules arranged so as to form a quad-
rate network, the interspaces of which are filled up by similarly dis-

LH© PORIFERA.

posed cross-shaped spicules of smaller size (fig. 50). Owing to the
condition of preservation of the sponge, it is still not absolutely
certain whether the spicules were fused with one another or free,
but it would seem probable that the former was the case, and that
the genus belongs therefore to the Dictyonine section of the
Hexactinellids.

Another very ancient genus of this order is /yalostelia, one of
the Lyssakine section of the Hexactinellids, which is first known
in the Cambrian deposits,
is found in Ordovician and
Silurian strata, and is abund-
antly represented in the Car-
boniferous rocks. Detached
spicules from the Chalk
have “also. been retemed
here. The genus /yalos-
telia is related to the recent
genus /yalonema, compris-
ing the so-called “‘ Glass-rope
Sponges.” The body of the
Sponge in Hyalostelia is im-
perfectly known, but is com-
posed of siliceous spicules
some of which are of the
hexactinellid type, with one

Fig. 60.—A, Part of the anchoring-rope ot Hyad- ;
ostelia Smithii, from the Carboniferous Limestone, ray much elongated while
of the natural size; 8, Fragment of one of the anchor- 3 4 :
ing spicular rods of the same species, showing four others are variously modi-

recurved rays at the distal end, enlarged ten diame- fied
ters. (After Hinde.) ed.

The sponge was at-

tached to the sea-bottom by
a long “rope” of cylindrical or rod-like, siliceous “anchoring
spicules,” which often terminate at their distal ends in four recurved
rays (fig. 60). The “rope” is the part usually found in the fossil
condition, and in the case of the Hyalostelia parallela of the Car-
boniferous rocks it was originally described as a tubicolar Annelide,
under the name of Serxpula parallela.

In strata of Ordovician age, the Hexactinellid Sponges are rep-
resented not only by the genus Ayadostelia, but also by the singu-
lar group of the Receptaculitide, the true relations of which have
been recently determined by Dr George J. Hinde. The two prin-
cipal genera of this family—viz., Receptaculites and Lschadites—have
long been known to paleontologists, but the investigation of their
structure has proved to be attended with great difficulties, and
various opinions have been held as to their relations and systematic
position. In Receptaculites (fig. 61) the organism is a cup-shaped
or platter-shaped body which grows from a small inversely conical

PRINCIPAL GROUPS OF THE SPONGES. 171

nucleus, and may reach a foot or more in diameter, but is not
attached by a stem to the sea-bottom. In the nearly allied Zschaa-
ztes, the organism is conical, ovate, or pyriform in shape, with

summit-aperture leading into a central cavity. In Leceptaculites, on
the other hand, there is no distinct evidence that the cup-shaped
cavity was ever roofed over as it is in Jschadifes. ‘The internal

a

I

WAY = a] Ny?

(LK
Ce “y NSA

i
Fil

‘ Yo

NZ
NW < BASS
P77

== WS C= Se

] ; | ,

Fig. 61.—Morphology ot Receftaculites. a, Outline of a perfect, basin-shaped specimen of
Receptaculites Neptunz, viewed in profile, of the natural size; 8, Part of the outer integument
of the same, enlarged two diameters, and so far weathered as to show the four transverse or
horizontal rays which underlie the summit-plates of the skeleton-spicules; c, Side-view of a
fragment of the same, showing the skeletal spicules; pb, Vertical section of the same, magnified,
showi ing the skeletal spicules with their axial canals and expanded extremities. From the De-
vonian of Germany. (After Giimbel.)

structure of these singular organisms will be best understood by refer-
ence to fig. 62, which is an ideal figure constructed by Mr Billings
to show the morphological characters of Feceptaculites. It should
be noted, however, that this figure, though well representing the
structure of Receptaculites, gives an incorrect idea of the form of the
organism ; since the known species of this genus are cup-shaped
and open superiorly, as shown in fig. 60, a. The cup-shaped body
of Receptaculites is furnished with a thick wall composed of pillar-
like spicules arranged at right angles to the surface. These spicules
are shown in thin sections (fig. 61, D) to be furnished in their in-
terior with an axial canal, and they are expanded at their outer ends

by2 PORIFERA.

into rhomboidal “summit plates” (fig. 61, B), which fit into one
another so as to form a mosaic-like outer layer or membrane, the
a plates being disposed in de-
cussating lines. Immediately
below, or internal to, the sum-
mit-plates, the vertical spicules
give off four transverse or hori-
zontal rays, which only become
visible externally when the sur-
face-plates are worn away or
pyle are viewed from the inside (fig.
stg SN G1, B). At their inner ends,
OS Ce ee where they abut upon the
Jaaiiis me ; o SSD central cavity of the organism,
Ss eee eee: the vertical spicules expand so
Fig. 62.—Diagram Bp ane Shasceure of KRecep- as to form small horizontal
ieeules sat would be shown by avenical plates (fig. 62, 2)) wale
summit ; 4, The inner plates of the spicules; c, traversed by horizontal canals,
The summit-plates of the spicules ; 7, The usual
position of the nucleus; v, The great internal and areso apposed to each other
cavity. The unshaded bands running from the as to give rise to an inner cal-

outer to the inner integument represent the spic-
ules. (After Billings.) The for of this figure careous membrane. In one

agrees with that of /schadites, the body in Recef- : ; 5
taculites being of the nature of an open cup or SP€CleS of the genus, if not in
ye all, the plates of this inner
membrane are so disposed as to leave cylindrical canals at their
angles of junction, through which the water which has filtered be-
tween the summit-plates of the outer layer of plates is admitted to
the internal cavity of the organism. In most specimens of fecep-
taculttes the skeleton-spicules are now composed of calcite or per-
oxide of iron, but Hinde has adduced evidence to show that the
spicules were originally siliceous, and that their present condition is
the result of replacement. The species of /eceptaculites are widely
distributed in the Ordovician and Silurian deposits, and are also
well represented in the Devonian rocks, while a species is recorded
as occurring in the strata of Carboniferous age.

The genus /schadites* comprises fossils which are in many respects
closely allied to Receptaculztes, but in which the central cavity is roofed
over superiorly, instead of being widely open as it is in the latter genus.
The form of the organism is, therefore, that represented in the diagram-
matic figure of Receptaculites given above (fig. 62), being conical or
pyriform, usually with a summit-perforation opening into the central
cavity. The wall of the organism is composed of cylindrical, pillar-like
spicules, arranged at right angles to the surface, and in most respects
similar to the corresponding structures in Aeceptaculites. The outer
ends of these hexactinellid spicules are modified to form rhomboidal

1! The fossils to which the name Zetragonzs have been given belong in part to
/schadites, and are in part referable to the Hexactinellid genus Dzctyophyton.

PRINCIPAL GROUPS OF -EHE SPONGES. 173

“summit-plates,” which are nearly in contact, and are arranged in
obliquely curved intersecting rows, giving the external surface of the
fossil very much the appearance of the engine-turned case of a watch.
Internal to the summit-plate, each radial spicule gives off four transverse
or horizontal rays, as in the genus Aeceptaculites; but the inner ends of
the radial spicules simply terminate in pointed extremities, and there is,
therefore, no internal plated membrane such as characterises the latter
genus. The species of /schadites are found in the Ordovician rocks,
and, more abundantly, in Silurian deposits, but they are not known to
have survived into the Devonian period. Nearly allied to /schadttes is
the genus Acanthochonia, which is also of Silurian age. Lastly, the
genus Spherospongia includes pyriform or cup-shaped organisms, the
_ outer integument of which consists of regularly arranged hexagonal
calcareous plates, which represent the expanded outer ends (or “ summit-
plates”) of a series of Hexactinellid spicules. Immediately below, or
internal to, the summit-plate, each spicule gives off four transverse or
horizontal rays, but the actual stem of the spicule, or, in other words, its
radial ray, is either aborted or is represented only by a short knob-like
projection. The species of Sfhe@rospongia are confined, so far as known,
to the Devonian rocks. .

In spite of their abnormal form and structure, as compared with recent
types, there seems to be no reason for doubting that Dr Hinde is correct
in his view that the genera Receptaculites, Ischadites, Acanthochonia, and
Spherospongia constitute a peculiar group of Lyssakine Hexactinellid
Sponges, all the members of which are Paleozoic.

In rocks of Silurian age, the Hexactinellid Sponges are represented
not only by the Anchoring-Sponges belonging to the genus Hyalo-
stelia and by the abnormal genera of the Receptaculitide just noticed,
but also by the curious types known as Dictyophyton and Plectoderma.
The genus Dictyophyton comprises cylindrical or cup-shaped sponges,
apparently not attached to foreign bodies, in which the wall consists
of a connected spicular framework disposed so as to form a series of
quadrangular areas. The precise structure of the spicules and their
mode of union are points as yet imperfectly known. The species of
Dictyophyton are not only found in the Silurian rocks, but likewise
in Devonian strata, and species occur also in the Carboniferous
deposits. The Silurian genus P/ectoderma is related to Dictyophy-
ton, but the spicular network is much less regular.

In the Devonian deposits, the groups of Hexactinellids represented
by Spherospongia and Dictyophyton still persist, but our knowledge
of other types is very imperfect. In the Carboniferous period, again,
the Hexactinellids are chiefly represented by the genus Hyalostelia,
the anchoring fibres of which are not very uncommon in the lower
beds of the system; but other genera of the ZLyssakina (such as
Ffolasterella) are likewise represented.

In the Permian and Triassic systems, so far as our certain know-
ledge goes, Hexactinellid Sponges may be said to be still unknown ;
though the imperfectly examined Aothroconis of King, from the Per-
mian of the North of England, may possibly belong here.

174 PORIFERA.

On the other hand, in the Jurassic rocks the Hexactinellid Sponges,
though comparatively few in number in the lower division of the
system, attain a great development in the upper beds of the system,
in certain regions. Of the Jurassic Hexactinellids, Cvratecularia,
Verrucocelia, Tremadictyon (fig. 63), Sporadopyle, and Sphenaulax
possess a skeleton built upon the same type as the recent Zuvefe and
farrea . Pachyteichisma and TLrochobolus are early forms of the great

Fig. 63.—Portion of the skeleton of Tvemadictyon reticulatum, enlarged 50 diameters, from
the Jurassic rocks. (After Zittel.) The original spicules are soldered into a continuous trellis-
work by a coating of silica; but their position and hexradiate form is shown by their axial
canals. The ‘‘ crossing-nodes,” or points of intersection of the arms of each spicule, are solid.

family of the Ventriculitide, Cypellia, Stauroderma, and others repre-
sent the extinct family of the Staurodermide ; and Stauractinella
belongs to the group of Hexactinellids (Zyssakima) in which the
skeleton-spicules are only united by sarcode, so that they do not
form a continuous network.

In the Cretaceous deposits, and especially in the Chalk itself, the
Hexactinellids are very largely and abundantly represented. Of the
family of the Auvetide, with their regular spicular mesh and simple
spicular nodes, we have now few forms (Craticularia, Verrucocelia,
&c.) ; but the great family of the Ventricufitide and the groups allied
to this now undergo a marvellous expansion. In the Ventriculitide
proper, the sponge-body is of variable shape, but usually more or
less cup-shaped or infundibuliform (figs. 64 and 65), or cylindrical,
the wall being often folded. The skeleton-spicules are always united
into a continuous lattice-work, and their “ crossing-nodes” are not
solid. On the other hand, the point of intersection of the arms of
each hexradiate spicule forms an open octahedron, in the centre of

PRENCIPAE GROUPS) OR) THE SPONGES: 175

which the central canals of the six rays form a delicate axial cross.
The boundaries of the central space are formed by twelve oblique
uniting beams, the whole forming an elegant octahedron, which is
known as the “lantern” (see the same type of spicule in Ce/lofty-
chium, fig. 59, B). The sponge-body in the Ventriculitide was
attached to the sea-bottom by a root of fasciculate flinty fibres, and
a dermal layer in the form of a cribriform siliceous membrane was

Fig. 64.—Ventriculites sp. White Fig. 65.—Ventriculites striatus,
Chalk, Britain. from! te Cretaceous rocks of Han-
over, one-half of the natural size.

present. Typical Cretaceous genera of the Ventriculitide are Ven-
triculites itself (figs. 64 and 65), of which numerous species are known,
Rhizopoterion and Cephalites.

Closely allied to the preceding is the family of the Celoptychide,
comprising the beautiful Chalk Sponges which constitute the genus
Celoptychium (fig. 59). These are in most respects very similar to
Ventriculites, but have a flattened or discoid body supported on a
short stem, the skeleton being folded into laminated walls which
divide the central cavity into radial chambers.

The group of the Weandrospongide is also closely related to that
of the Ventriculitide, and comprises variably shaped sponges with
folded walls, the folds often anastomosing so as to give rise to open
tubes. The genera of this family—such as PVocoscyphia, Tremabolites,
Etheridgia, Toulminia, and Camerospongia (fig. 66)—are mostly Cre-
taceous, though a few types occur in the Jurassic deposits.

176 PORIFERA.

As regards the remaining groups of the Cretaceous Hexactinellids,
the body-wall in the family Cal/odictyonide is composed of hexacti-
nellid spicules the nodes of which are octahedral, and which give
rise by their union to an exceedingly regular open meshwork, while
the canal-system is wanting or rudimentary. The Cretaceous genera

Fig. 66.—Camerospongia fungiformis. Cretaceous.

Callodictyon and Pleuropfe are good representatives of this family.
In the Ale/itionide, are included Sponges in which the walls are
closely perforated by tubular canals like the cells of honeycomb, and
the spicules have simple nodes. ‘This family includes the Creta-
ceous genus Stauronema and the genus Aphrocaliistes, which ranges
from the Chalk to the present day. The family of the Cosccnopori-
d@ comprises variously shaped
Sponges, with a close and ‘irre-
gular skeletal network, and hay-
ing numerous straight, blind,
radiate canals which open alter-
nately on both sides of the
sponge-wall. In Coscinopora
itself (fig. 67), the cup-shaped
sponge-body is affixed to some
foreign object by ramified roots.
The lattice-work of the skeleton
is irregular, and the crossing-
nodes of the spicules are partly
Fig. 67.—Coscinopora cupuliformis, and - Sallie, ee! pap fone
rao ori surface enlarged. Grecia a ~~ lantern In tlne nearly
allied Guwuettardia, which is also
Cretaceous in its range, the wall is deeply folded in a stellate
manner, and the crossing-nodes of the spicules are solid. Nearly
related to the preceding is the family of the Staurodermide, which,
though principally Jurassic in its range, is not without Cretaceous
representatives (such as Ludbrochus).

The Tertiary Hexactinellids, finally, are comparatively few in num-
ber and are imperfectly known, but the order is represented at the
present day by such genera as Luplectella, Hyalonema, Aphrocaltistes,
floltenia, Eurete, Farrea, and many others.

Before leaving the Hexactinellid Sponges, a few words may be
added with regard to the Silurian genus Amphispongia, the char-

o,
"i, y
|
il ts Him
Wy
Wy)

PRINCIPAL GROUPS? OF THE. SPONGES. I7@f

acters of which are in some respects anomalous. In this curious
genus (fig. 68, ¢ and @) the sponge-body is elliptical, greatly com-
pressed, and free, without any traces of a canal-system. The basal

ra.
Sh

Ss

SH

GG
S

ye
Wh

a
ee.
™—-

9
@,

Fig. 68.—a, Side-view of a specimen of Astreospongia meniscus, of the natural size, Sil-
urian; 4, Spicules of the same, enlarged (after Roemer); c, A split specimen of Amzphi-
Sfongia oblonga, of the natural size, Siiurian; d, Part of the upper portion of the same,
enlarged. (Original.)

portion of the sponge consists of large conical spicules, arranged
with their pointed lower ends converging towards the middle line ;
while the upper portion consists of ‘‘ slender four- and five-rayed
spicules with the rays at right angles to each
other” (Hinde). The spicules are not fused
with one another, and their arrangement is
peculiar. In spite of its aberrant character,
however, it would seem that Amphispongia
should be regarded as belonging to the
Flexactinellide.

ORDER 7. OCTACTINELLID£.—This order
is represented only by the single genus 4s-
treospongia, and is characterised by the pre-
sence of skeleton-spicules which are normally
eight-rayed, six of the rays radiating at equal
angles from a central point (fig. 68, 4), while
the other two rays form a vertical axis. The
spicules are not fused with one another, and
the vertical rays are often obsolete or wholly
wanting. The sponges which constitute the
genus Astreospongia (fig. 68, a) are discoid Fig. 69.—Skeleton-spicule
or basin-shaped in form, without any stem of of “stractinelia exparsa,
attachment, and without any definite canal- ee ay ee
system. The spicules have the form above diameters. (After Hinde.)
described, and are now usually found in the
condition of calcite. According to the views of Dr Hinde, however,
the present calcareous condition of the spicules is the result of
secondary changes or replacement, and the skeleton was originally

VOL. I. M

178 PORIFERA.

siliceous. The oldest known species of Astre@ospongia appear in the
Silurian, but the genus is principally characteristic of the Devonian
system.

OrDER 8. HETERACTINELLIDZ.—This group has been founded
by Hinde to include certain Paleeozoic siliceous Sponges in which
the skeleton-spicules consist of “‘an indefinite number of rays, vary-
ing from six to thirty, radiating from a common centre” (fig. 69).
The body-spicules are irregularly disposed and are not fused with
one another; but the dermal spicules are interwoven together, and
their rays are partially or completely fused with one another. The
genera Zholiasterella and Asteractinella (fig. 69), included by Hinde
in this group, are confined to strata of Carboniferous age, and are
only known by detached spicules or imperfect fragments.

Cxiass II. CALCISPONGIZA.

The class of the Calcareous Sponges comprises, as the name im-
plies, all those sponges in which the skeleton is composed of spicules
of carbonate of lime. The spicules vary considerably in form, and
different forms are often associated in the same sponge. In living
Calcisponges the spicules are never fused with one another, nor
united by horny fibre, but in the group of fossil Calcisponges de-
scribed by Zittel under the name of Pharetrones, the skeleton is
formed by a reticulated calcareous fibre which is ‘‘ wholly composed
of spicules in close approximation to each other, and as closely in-
terwoven together as the strands of a rope” (Hinde). The follow-
ing are the principal types of spicules found in the calcareous
Sponges. (a) Simple uniaxial spicules, which may be associated
with the other forms of spicules, or, as in Pharetrospongia, may be
the only forms present. (6) Three-rayed spicules, in which all the
rays are in one plane and the rays and angles are equal (figs. 70 and
71, B). In some cases the spicules are triradiate, but two of the
three rays are paired and equal, and the third ray is longer or
shorter than the other two. (c) Four-rayed spicules, with three
rays equal and in one plane, but with a fourth ray directed at nght
angles or obliquely to the others.

The recent Calcisponges are all of small size and are inhabitants
of comparatively shallow water, all being marine. By Vosmaer the
Calcspongie are divided into the following two orders :—

ORDER 1. Homocceia.—In this order there are no special
“flagellated chambers,” and the canal-system can hardly be said to
exist in a definite form; but the thin walls of the sponge (fig. 70)
are perforated by numerous pores opening directly into a general
cavity, which is lined by. ciliated epithelium and terminates on
the surface by a single osculum. The order corresponds with the

PRINCIPAL GROUPS OF THE SPONGES. 179

Ascones of Haeckel, and includes the recent genus Leucosolenia
(= Ascetta). No fossil forms belonging to this order are known
to occur.

ORDER 2. HETEROCHLA.—In this order “ flagellated chambers ”
are present, and there is a canal-system of different form in the dif-
ferent families of the order. In the family of
the Syconide (=the Sycones of Haeckel) the
flagellated chambers are elongated, and con-
stitute a series of radial tubes which open di-
rectly into a central cloacal chamber. This
family includes such recent genera as Grantia
and Sycon, together with the Jurassic genus
Protosycon. his latter is the earliest repre-
sentative of the modern Calcisponges, and pos-
sesses a cylindrical or clavate body, with a long
tubular cloaca, and having the three-rayed or
four-rayed spicules so disposed as to form a
series of radial canals.

In the family of the Leuconide (=the Leu-
cones of Haeckel) the flagellated chambers are
mostly rounded, and are placed in communi-
cation with the cloacal chamber by exhalant
canals ; while the skeletal spicules are arranged
in no definite order. This family includes such
recent genera as Leuconia and Leucandra, de-
tached spicules of both of which have been
recognised in the Pliocene beds of St Erth,

Cornwall. Very closely allied to this family is ,,Fi8,Jo (iene rar
the group of the Zeschonide, of which no fossil eareousi shone ci cnlatged

y times. (After Haec
forms are known. kel.)

Lastly, we have the large and important
group of the Pharetronide (the Pharetrones of Zittel), all the
members of which are extinct. This group includes the largest
and most massive of all the Calcisponges, and its characters depart
in many important respects from those of all recent forms. The
Sponges included by Zittel under the name of /Pharetrones are
variably shaped, simple or branched sponges, with thick walls, and
attached by their bases to foreign bodies. In some forms (e.g., in
Feronella) the canal-system is not distinctly developed, but there is
usually a special system of irregular, branched water-canals. The
skeleton consists of calcareous spicules disposed to form a network
of solid anastomosing fibres (fig. 71, D), and there is a well-de-
veloped smooth or wrinkled dermal membrane.

The earliest known types of the Pharetrones appear in the De-
vonian rocks, and belong to the genus /erone//a, which in later

180 PORIFERA.

deposits is represented by very numerous forms. In this genus,
the sponge is simple or branched, there is no definite canal-system,
and the skeleton consists (where its structure can be determined at
all) of anastomosing calcareous fibres composed of comparatively large
three-rayed and four-rayed spicules surrounded by similar spicules
of small size. Little is known of the Pharetrones of the Carbon-
iferous and Permian deposits; but the Upper Triassic beds have
yielded numerous forms belonging to such genera as Ludea, Ver-
ticillites, Peronella, Corynella, and Stellispongia. In the Jurassic
and Cretaceous rocks the remains of Pharetrones are often very
abundant, and belong to very numerous genera. Of the many

Fig. 71.—Pharetrones. a, Tremacystia D’Orbignyz, from the Upper Greensand, of the nat-
ural size; B, Portion of the outer surface of the same, showing the pores and the spicules of the
dermal layer, enlarged thirty times; c, Detached three-rayed spicule, belonging to the dermal
layer, enlarged seventy-two times ; D, Fragment of the skeleton-fibre of E/aswzostonza scitulum,
showing large three-rayed and four-rayed spicules with small filiform spicules, from the Upper
Chalk, enlarged fifty times. (After Hinde.)

Jurassic genera, Corynel/a is perhaps the most important. In this
genus we have sponges allied to Peronedla, but usually possessing
a distinct canal-system, and having the reticulated skeleton-fibre
composed of ‘minute, filiform, three-rayed spicules disposed gen-
erally parallel with each other in the direction of the fibre” (Hinde).
Other largely represented Jurassic genera are Ste//ispongia, Sestro-
stomella, and Lymnorea. Of the Cretaceous Pharetrones, the genera
Peronella and Corynella still hold a predominant place, but many
other types are present, such as Oculospongia, Tremacystia, Elasmo-
stoma, and Pharetrospongia. In the genus Zremacystia (fig. 71, A)
the sponge-body is formed of connected hollow segments, with a
common axial tube, and the wall is formed by a single layer of re-
ticulated calcareous fibres penetrated by numerous minute canals.
The dermal layer (fig. 71, B and c) is formed of relatively large
three-rayed and four-rayed spicules; while the skeleton-fibres are

PRINCIPAL GROUPS OF THE SPONGES. I8I

composed of minute filiform triradiate spicules. In L/asmostoma
(fig. 71, D) the fibres of the skeleton are composed of large three-
rayed and four-rayed spicules, arranged in the centre of the fibre
and surrounded by smaller sinuous spicules. Lastly, in the genus
Pharetrospongia, regarded by Professor Sollas as a Halichondroid
Sponge, the skeleton-fibre is composed of minute, straight or slightly
curved, uniaxial spicules, arranged parallel with one another in the
direction of the fibre.

The latest known representatives of the Pharefrones occur in the
Maestricht Chalk, but no examples of this group of sponges have
_ been as yet detected in any strata of Tertiary age, nor are any re-
cent forms recognised which could be referred to this remarkable
division of Calcisponges.

PDE RAR URE:

. “ Porifera.” Bronn’s ‘Klassen und Ordnungen des Thier-Reichs,’

vol. 11. (New Ed.), 1882-87. G. Vosmaer.

“Die Kalk-Schwamme.” Haeckel. 1872.

“Handbuch der Palzeontologie,” vol. i., part 2, 1879. Zittel.

. “Studien uber fossile Spongien.” ‘Abhandl. d. k. bayer. Akad. der
Wiss.’ 1877 and 1878. Zittel. (The three important memoirs
published by Zittel under the above title are translated into
English by Mr W. S. Dallas in the “Annals and Magazine of

Natural History,” for 1877, 1878, and 1879).

5. “ Beitrage zur Systematik der fossilen Spongien.” ‘Neues Jahrbuch
fiir Mineralogie,’ &c., 1877, 1878, 1879. Zittel.

6. “Ueber Cceloptychium. Ein Beitrag zur Kenntniss der Organ--

isation fossilen Spongien.” ‘Abhandl. der k. bayer. Akad.

der Wiss.’ Bd. xu. 1876. Zittel.

—

ON

7. “Ueber Astylospongide und Anomocladina.” ‘Neues Jahrb. fir
Mineralogie,’ &c., 1884. Zittel.

8. “ Die Spongitarien des Nord-deutschen Kreide-gebirges.” ‘ Pal-
zeontographica,’ 1864. F. A. Roemer.

g. “ Paléontologie de la Province d’Oran.” 5th Fasc. “ Spongiaires,”
1872. Pomel.

Io. “ Lethzea Palzozoica.” Ferdinand Roemer. 1880.

It. ‘ Ventriculitide of the Chalk.” ‘Annals Nat. Hist., 1847-48. Toul-
min Smith.

12. “ Beitrage zur Kenntniss der Organisation und systematischen
Stellung von Receptaculites.” C. W. Gumbel. ‘Abhandl. der
k. bayer. Akad. der Wiss.’ Bd. xii. 1876.

13. “Catalogue of the Fossil Sponges in the British Museum.” 1883.
Hinde.

14. “A Monograph of the British Fossil Sponges.” Palzeontographical
Society, 1887-88. Hinde.

15. “On the Structure and Affinities of the Family Receptaculitide.”
~Ouart |OumuGeols soc Vol. xl 1884. Hinde:

16. “On Beds of Sponge-remains in the Lower and Upper Greensands
of the South of England.” ‘Phil. Trans.,’ 1885. Hinde.

17. ~ Notes on Fossil Calcispongiz.” ‘Ann. & Mag. Nat. Hist., 1882.
Hinde.

182 PORIFERA.

18.

19.

“Structure and Affinities of the Genus Siphonia.” ‘Quart. Journ.
GeolvSoc. Voli xox, 18775 co ollas:

“On Pharetrospongia Strahani.” ‘Quart. Journ. Geol. Soc.’ Vol.
LMM S774) oOllas:

. “On the Structure and Affinities of the Genus Protospongia.” ‘ Quart.

Journ. Geol. Soc.’ Vol. xxxvi. 1880. Sollas.

. “On the Flint Nodules of the Trimmingham Chalk.” ‘Ann. and

Mag. Nat. Hist.,’ 1880. Sollas.

. “On Fossil Sponge-Spicules from the Carboniferous Strata of Ben

Bulben.” ‘Ann. & Mag. Nat. Hist., 1880. Carter.

. “Further Observations on the So-called ‘Farringdon Sponges.’”

‘Ann. & Mag. Nat. Hist.,’ 1883. Carter.

. “Die Pharetronen aus dem Cenoman von Essen, und die systema-

tische Stellung der Pharetronen.” ‘ Palzontographica.’ Bd. 29,
1883. Dunikowski.

. “Beitrage zur Kenntniss der Spongien der bohmischen Kreide-for-

mation.” ‘Abhandl. der k. bohm. Gesell. der Wiss.’ 1883-85.
Pocta.

. “Descriptions of Fossil Reticulate Sponges, constituting the Family

Dictyospongide.” ‘Thirty-fifth Ann. Rep. on the State Cabinet.
1884. Hall.

. “Remarks on Dictyophyton.” ‘Bulletin of the Amer. Mus. Nat.

Hist.,’ 1881. Whitfield.

CHAPTER XII.

ZOSSILS, OF DOUGLTFOL APRINITIZES.

I. ARCHZOCYATHINE.

y

THE lowest Cambrian strata (“ Olenellus Beds”) of North America,
Spain, and Sardinia have yielded the remains of a number of re-
markable organisms, which may be collectively spoken of as the
Archeocyathine, but which cannot at present be definitely referred
to their place in the zoological series. The three genera which may
be regarded as typical of this group of organisms are Archeocyathus,
LEthmophyllum, and Spirocyathus, and the characters of these may
be briefly treated of here.

There is some difficulty in determining for which of the species
described by Mr Billings under the name of A*xcheocyathus this
generic title should be retained. If, however, we follow Hinde,
and accept Archaeocyathus profundus, Bill., as the type of the genus,
we have to deal with elongated, turbinate, more or less curved
fossils, sometimes more than a foot in length, with a diameter of
from two to four inches, having a general resemblance to such
Rugose Corals as the simple species of Cyathophyllum. ‘The conical
skeleton is hollow, with a deep, cup-shaped internal cavity, the sur-
face of which shows radiating ridges, and is bounded by a thin
inner wall (fig. 72, A). Both the inner and outer walls are per-
forated by pores, and the space between the two is traversed by
numerous vertical septa, which are in turn connected by delicate
dissepiments, giving the general structure a vesicular character (fig.
72, 8B). Archeocyathus profundus seems to have been undoubtedly
calcareous in its original constitution, and there is no evidence that
its skeleton was at any time composed of spicules. The original
specimens were obtained in the Cambrian strata of the Straits of
Belle Isle, Labrador.

The genus Ethmophyllum, as based upon the fossils described by
Mr Meek from the Cambrian strata of Nevada under the name of £.

184 FOSSILS OF DOUBTFUL AFFINITIES.

Whitneyt, comprises organisms with a general resemblance to Avcheo-
cyathus. The skeleton in this genus is also superficially very similar
to a simple Rugose Coral, being cup-shaped, turbinate, or cylindrical,
and either straight or curved (fig. 72 47s, a), the external surface
being sometimes concentrically annulated or vertically ribbed. There
is a deep internal cup (fig. 72 ds), the lining of which is perforated
by numerous round or oval pores,
similar perforations, arranged in
vertical and horizontal rows, exist-
ing in the outer wall as well. The
space between the inner and outer
membranes is subdivided by a
number (from six to over one
hundred) of vertical radiating par-
titions (fig. 72, B), which have
a general resemblance to the
“septa” of the Madreporarian
Corals. These radiating septa
are usually perforated by rounded
apertures, which place contiguous
interseptal chambers in communi-
cation; and they are commonly
connected together by irregular
transverse plates, resembling the

Fig. 72.—A, Longitudinal section of asmall “ dissepiments ? Ot many corals.
Rehely rechuced sa paths Lrofunaus, PN. The whole structure of the skele-
lated structure of the skeleton and the deep ton is thus more or less porous,

cup at the summit; sp, Part of a transverse

section of the same, enlarged, showing that and qa characteristic feature of the
the reticulated skeleton has a distinct radial

structure, the septa being connected by dissep- QeNUS is the presence of oblique
ye Cambrian, Labrador. (After Wal- funnel-shaped canals leading into
the internal cup. As in the pre-
ceding genus, the skeleton is now calcareous, and microscopic sec-
tions show nothing which would prove that its constitution was at
any time essentially different, or that definite spicules existed. By
Mr Walcott, the fossil described by Mr Billings under the name of
Archeocyathus Minganensis has been referred to the genus E£¢hmo-
phyllum, but, as previously pointed out, the researches of Dr Hinde
have shown that this form was originally siliceous, with a spicular
skeleton, and that it is truly referable to the Lithistid Sponges.

On the other hand, the fossils described by Billings from the
Cambrian rocks of Canada under the name of Avcheocyathus atlan-
vicus would seem to differ considerably in structure from A7zche@ocya-
thus proper (as based upon A. grofundus, Bill.); and they have
recently been referred by Hinde to a new genus under the name of
Spirocyathus (apparently related to the Protopharetra of Bornemann).

ARCHAOCYATHIN&. 185

The skeleton in Sfrrocyathus atlanticus is conical in form, with a
general resemblance to a simple coral, its interior being occupied by
a longitudinal tubular cavity (fig. 72 ézs, c and D). The space
between the inner and outer walls is occupied by reticulated calcar-
eous tissue, in which a radial structure is hardly recognisable, while
distinct vertical “septa” do not appear to be present. The spaces
or irregular canals formed
by this calcareous reticu-
lation open on both the
outer and inner surfaces
_ of the skeleton by round-

ed or oval pores. In
this case, also, the skele-
ton seems to have been
originally calcareous, and
there is no evidence of
any spicular structure.
Spirocyathus atlanticus
occurs in the Cambrian
rocks of Canada and the
United States, and ap-
parently allied types have
been discovered by Bor-
nemann in strata of the
same age in Sardinia,
and have been described

by him under the name ; Fig. 72 Zia a SPecuneD ot Ethmophyllun Rensse-
@ricun, Ford, of the natural size; 8, Transverse section
of Protopharetra. of the same, showing the outer and inner walls and the

The Archeocyathine radiating septa (s); Cc and p, Transverse and longitudinal
sections of SAzrocyathus atlanticus, Bill. sp. ~, Pores in
are = among the most _ the outer wall; 2’, Pores in the inner wall; ¢ The in-
sueraaeorelall knows Noni amen (aa waco)
fossils, and are therefore
of peculiar zoological interest. It is not, however, possible at
present to come to any absolutely certain conclusion as to their
systematic position. As their skeleton seems to have been un-
doubtedly originally calcareous, and as there is no certain evi-
dence (now that the form described by Billings as Archeocyathus
Minganensis is known to be a Sponge) that their structure was
spicular, it would not be possible to refer the group to the Pov-
jera. On the other hand, as pointed out by Hinde, the Arxcheo-
cyathine show certain unquestionable points of relationship to
the Madreporarian Corals. This is particularly seen in the reticu-
lated structure and usually more or less radiate arrangement of
the skeletal framework, the skeleton being in many respects com-

parable with that of such a Perforate Coral as Calostylis. At the

186 FOSSILS OF DOUBTFUL AFFINITIES.

same time, the skeleton departs widely in certain of its features
(such as the presence of a distinct perforated internal wall) from the
Madreporarian type. Upon the whole, therefore, in the present
state of our knowledge, it seems best to regard the Avcheocyathine
as a group of uncertain affinities, probably more closely allied to the
Madreporaria than to any other division of the animal kingdom.

II. PAscEOLUS, CYCLOCRINUS, AND NIDULITES.

We may briefly consider here a series of fossils the true affinities
of which are at present absolutely uncertain, and which have no par-
ticular claim to be taken up in this connection beyond the fact that
they have a superficial resemblance to Aeceptaculites and Lschadites,
and have therefore been commonly placed alongside of these
genera. It has, however, been demonstrated by Hinde that the lat-
ter are Hexactinellid Sponges, while it seems certain that the fossils
here referred to—viz., Pasceolus and Cyclocrinus—are, at any rate,
not referable to the /orifera, though their true position is quite
problematical.

The genus Pasceolus (fig. 73, a and 0) was created by Mr Bil-
lings for the reception of some curious Ordovician and Silurian
fossils of an ovate or globular form, varying in size from the dimen-
sions of a hazel-nut to those of an apple. The outer layer of
the fossil consists of ‘“‘ small convex elevations, composed of a very
thin minutely wrinkled layer, which is sometimes translucent ”
(Hinde). These surface elevations have the general aspect of being
hexagonal or pentagonal plates, but there is not sufficient evidence
that actual plates are present, and they may be, and probably are,
only definitely limited areas of a common calcareous membrane.
The inner, concave sides of these polygonal areas are directed 77-
wards, towards the central cavity of the fossil (the cup-like plates of
Cyclocrinus being turned outwards); and in well-preserved specimens
they exhibit a minutely porous aspect. ‘There is some evidence
that the organism was provided with a peduncle of attachment, and
in some species a lateral aperture has been described as present.
By Mr Billings, it was at first supposed that /asceolus might belong
to the Zunicata, but this view was subsequently abandoned by him.
By later paleontologists the genus has been doubtfully compared
with Receptaculites or with the Cystideans, but its zoological affinities
must in the meanwhile be regarded as entirely uncertain.

The genus Cyclocrinus was originally founded by Eichwald to in-
clude certain ovate or spherical fossils from the Ordovician rocks of
Esthonia, which appear to have been free, and which have a thin,
plated, external layer enclosing a large central cavity (fig. 73, e-A).
The outer integument is calcareous, and presents externally the

PASCEOLUS, CYCLOCRINUS, AND NIDULITES. 187

aspect of being divided into a series of hexagonal or pentagonal
areas of very regular form and size (fig. 73, 2). Each of these areas
has the form of a shallow cup-shaped depression, the lower or convex
end of which is directed towards the interior of the fossil, and,
according to Hinde, is perforated centrally by a small rounded aper-
ture which leads into the central cavity of the organism. According,
however, to Ferdinand Roemer, whose figures are here reproduced
(fig. 73, fand g), each of these cup-like plates terminates internally

fi
yh

~

Fig. 73.—a, Pasceolus Halti, of the natural size (after Billings); 4, Pasceolus globosus, of the
natural size (after Billings); c, Pasceolus (?) melliflua, of the natural size (after Salter) ; d, Four
of the integumentary plates of the same, enlarged; e, Cyclocrinus Spaskii, of the natural size
(after Ferd. Roemer); _/, Part of a vertical section of the same; g, Part of the last, showing the
structure of the integument, enlarged; 4, Part of the mould of the inner surface, enlarged ;
z, Diagram of a vertical section of Cyclocrinus (Nidulites) favus, showing the form of the body
and integumentary plates, and the supposed peduncle (original). All the specimens are from the
Silurian, except 4, which is from the Ordovician.

in a small pillar, and the genus is hence compared by this distin-
guished paleontologist with Receptaculites. Dr Hinde, on the other
hand, does not recognise in Cyclocrinus any features of resemblance
to Receptaculites, and considers that the genus is identical with
Nidulites.

The present writer has not had the opportunity of studying the
genus Cyclocrinus, and is therefore unable to express a positive

188 FOSSILS OF DOUBTFUL AFFINITIES.

opinion as to its identity with /Vidu/ites. It is clear, however, that
the two are, at any rate, very closely related, if not absolutely iden-
tical The name /Vidulites was proposed by Salter for certain sin-
gular Silurian fossils (subsequently described by Eichwald under
the name of JZastopfora), which have the form of ovate, glob-
ular, or pyriform, hollow bodies, with a thin calcareous external
wall, and probably attached to foreign bodies by a peduncle (fig.
73,72). The wall of MWdulites encloses a large central space, and -is
formed of short, wide, hex-
agonal calcareous tubes or
cells, which are united to-
gether at their basal ends and
also by their walls (fig. 74, A
and,s). ‘The outeptendsyer
these shallow tubes or cells
are open, while the inner
ends are closed by curved
basal plates, the convexities
of which are turned towards
the central cavity of the or-
ganism. Moreover, the closed
Fig. 74.—Structure of Nidulites (= Mastopora). end of each cell is perforated
a, Tangential section of the wall of Widzdites, show- by a small round central aper-
ing the cup-like plates of the integument transversely
divided, so as to give rise to a series of hexagonal ture (fig. 74; CG) so that each
cells, enlarged six times; B, Vertical section of the cell communicates freely with

wall of the same, showing the short hexagonal cups

or cells of the outer membrane longitudinally divided 1 ; 1
similarly enlarged; c, A few of the cup-like plates the great internal CavAly.

of the wall, viewed internally and showing the cen- With regard to the affini-
tral perforations in their bases, enlarged. Fromthe ,- : ae
Silurian rocks of the Island of Oesel. — (Original. ) ties and systematic position of
Nidulites and Cyclocrinus, it
is not possible at present to give any decided opinion. ‘There is no
positive character exhibited by these singular fossils which would
enable us to refer them definitely to any known division of the
animal kingdom. The resemblances which they present to the
Receptaculitide or to the Cystzdeans are quite superficial, and it is not
even clear that they are genuinely related to the equally enigmatical
genus Pasceolus. It may be pointed out, however, that there are some
curious points of resemblance between MWidudites and Cyclocrinus on
the one hand and certain of the Calcareous Algze (Szphonee verticil-
/ate) on the other hand; and it does not seem impossible that these
points of resemblance indicate a genuine relationship. If this con-
jecture should prove to be well founded, these singular fossils may
ultimately find a resting-place in the vegetable kingdom.

Be en te

Onur

Oo Noe

PASCEOLUS, CYCLOCRINUS, AND NIDULITES. 189

PRE RAT URE:

I. ARCHEOCYATHIN-.

“ Paleozoic Fossils of Canada,” vol. 1., 1861-65. Billings.
ihe Wawn of Life? (p: 151): Dawson. 1875.

. “Second Contribution to the Studies on the Cambrian Faunas of

Nori America “Bull: U:S: Geol Survey, No: 30: 1886.
Walcott.

“Die Versteinerungen des Cambrischen Schichtensystems der Insel
Sardinien.” 1886. Bornemann.

“On Archeeocyathus, Billings, and on other Genera allied to or associ-
ated with it, from the Cambrian Strata of North America, Spain,
Sardinia, and Scotland.” ‘Quart. Journ. Geol. Soc.,’ vol. xlv.
1889. Hinde.

II]. PASCEOLUS, NIDULITES, AND CYCLOCRINUS.

“ Paleozoic Fossils of Canada,” vol. i. 1861-65. Billings. (Pasceolus.)

*“ Nidulites.” ‘Quart. Journ. Geol. Soc.,’ vol. vii., 1851. Salter.

““Cyclocrinus.” ‘ Lethza Rossica.’ 1860. Eichwald.

“ Nidulites.” ‘Monograph of the Silurian Fossils of Girvan.’ 1878.
Nicholson and Etheridge, jun.

. “Lethezea Paleozoica.” 1880. Ferd. Roemer.
. “On the Structure and Affinities of the Family of the Receptaculitide.”

7 Ouart., Journ) Geol) Soc? 1834. | Hinde.

190

CHA Par keg <G0ik

SUB-KINGDOM I11.—CG@LENTERATA.

GENERAL CHARACTERS AND DIVISIONS OF C@i!LENTERATES—
HYDROZOA—DIVISIONS OF HYDROZOA.

THE sub-kingdom Caelenterata (Frey and Leuckart) may be con-
sidered as a modern representative of the Radzata of Cuvier.
From the Radiata, however, the Echinodermata and Rotifera have
been removed, the entire sub-kingdom of the Protozoa has been
taken away, and the Polyzoa have been relegated to a place near
the AZollusca. Deducting these groups from the old Radiata, the
residue, comprising most of the animals commonly known as Polypes
or Zoophytes, remains to constitute the modern Ce/enteraza.

The Coelenterata may be defined as radially symmetrical animals,
in which the mouth opens into a simple or variously divided space
(“calenteric cavity”), which acts as an alimentary cavity, and which
may or may not be divided into two portions, of which one forms a
rudimentary digestive tube. The body-wall consists of two funda-
mental layers (“‘ ectoderm” and “‘endoderm’), between which an inter-
mediate layer (““ mesoderm”) ts usually developed. Peculiar urticating
organs, or “‘ thread-cells,” are present. The nervous system is somie-
times Specialised, sometimes diffused , but no vascular organs are de-
veloped. Reproductive organs are invariably present at some period
or another of life, though asexual reproduction ts also very general.

The sub-kingdom Cev/enterata is divided into the two great
primary divisions or classes of the Aydrozoa and Actinozoa, and
the following table indicates the main subdivisions of these :—

TABLE OF THE DIVISIONS OF THE C@LENTERAES

CLASS I-A yvpROZOA

Sub-class 1. HyDRoIDA (Hydroid Zoophytes).
a. Hydrida.—Ex. Hydra.
6. Corynida.—Ex. Tubularia, Hydractinia.

HYDROZOA. 19I

c. Thecaphora.—Ex. Sertularia, Campanularia.

ad. Trachymeduse.—Ex. Trachynema.
Sub-class 2. SIPHONOPHORA (Oceanic Hydrozoa).

a. Calycophoride.—Ex. Diphyes.

6. Physophoride.—Ex. Physalia.

Sub-class 3. LUCERNARIDA (Sea-blubbers).

a. Calycozoa.—Ex. Lucernaria.

6. Acraspeda (Discophora).—Ex. Aurelia, Rhizostoma.
Sub-class 4. GRAPTOLITOIDEA (Graptolites).
Sub-class 5. HYDROCORALLIN# (Hydrocorallines).

a. Milleporide.—Ex. Millepora.

b. Stylasteride.—Ex. Stylaster.

Sub-class 6. STROMATOPOROIDEA (Stromatoporoids).

CLASS IIJ.—ACTINOZOA.

Order 1. ZOANTHARIA.—£x. Sea-Anemones (Actznid@) Corals
(Madreporaria).

ALCYONARIA.—E£». Sea-pens (Pexnatulide), Red Coral
(Corallium), Organ-pipe Coral (7dbzfora).

Order 3. CTENOPHORA.—£x. Venus’s Girdle (Cestzz2).

Order

N

As regards their general dzstribution tn time, the earliest known
remains of Coelenterates appear in the Upper Cambrian rocks, where
the sub-kingdom is represented by ancient types of the Wydrozoa.

Fig. 75.—Diagrammatic vertical section of a Sea-anemone. a, Mouth; s, Gullet; 4, Body-
cavity ; cc, Convoluted cords (‘‘ craspeda”) forming the free edges of the mesentery (vx); tt, Ten-
tacles; a, Reproductive organ contained within the mesentery. The ectoderm (e) is indicated
by the broad external line, the endoderm (¢’) by the thin line, and the space between that and
the ectoderm represents the mesoderm.

In the Ordovician rocks we find the two great classes of the /y-
drozoa and the Actinozoa thoroughly differentiated, and existing
under many and varied types, a fact which would lead us to as-
sign a very high antiquity to the early progenitors of this series

192 CCELENTERATA.

of animals. From the beginning of the Ordovician rocks onwards,
the Coelenterates are very abundant and important as fossils, the large
groups of the Graptolitoidea and Stromatoporoidea being wholly
extinct, and having no close relatives now in existence. Owing
to the fact, however, that other large groups (such as the Lucer-
narians, the Oceanic Hydrozoa, and the Ctenophora) are almost or
altogether without hard parts, and therefore only capable of pre-
servation in the fossil condition under very exceptional circum-
stances, the geological history of the sub-kingdom is very imperfect.

CLASS k= Ep ROZON

The class of the ydrozoa comprises those Ccelenterates 727 which
the walls of the body enclose a simple undivided cavity (the “ celenteric
cavity”), which acts both as a body-cavity and a digestive cavity. An
asophageal tube is not developed ; but the upper end of the alimentary

1 72

Fig. 76.—a, Diagram of Hydra, vertically bisected, and greatly magnified; B, Diagram to
show the structure of a compound Hydrozoén (Sertularia). ec, Ectoderm; ex, Endoderm ; 7z,
Mouth, opening into the ccelenteric space or body-cavity ; ¢, Tentacle ; 4, Nutritive polypite ; go,
Reproductive bud or ‘‘ gonophore,” consisting of a capsule enclosing a central axis to which re-
productive polypites are attached ; cs, Coenosarc; 72, Hydrorhiza ; Ze, Periderm; 2, Hydrotheca.

tract may be prolonged into radiating canals united by a peripheral
ving. The reproductive organs are external buds, and are often devel-
oped in specially modified sovids (fig. 76).

HYDROZOA. 193

The simplest type of the A/ydrosoa is the genus Hydra, compris-
ing the Fresh-water Polypes, in which the organism consists of a
single tubular or cylindrical ‘‘ polypite” (fig. 76), furnished at its
base or “ proximal” extremity with a disc-like sucker or ‘‘ hydro-

Fig. 77.—A, Part of the colony of Bougainvillea muscus, one of the composite Hydrozoa, of
the natural size. B, Part of the same enlarged ; 4, A polypite fully expanded ; 7, An incompletely
developed medusiform bud ; 7’, A more completely developed medusiform bud ;_/, Coenosarc with
its investing periderm and central canal. c, A free medusiform gonophore of the same; z,
Gonocalyx; #, Manubrium; c, One of the radiating gastro-vascular canals; 0, Ocellus; z,
Velum; ¢, Tentacle. (After Allman.)

thiza,” by which it can attach itself to foreign bodies. At the

opposite or “distal” end of the body is the opening of the mouth

(fig. 76, m), surrounded by a variable number of hollow, extensile

and tactile processes or ‘“‘ tentacles.” The body-wall is composed of
VOL. 1. N

194 CCELENTERATA.

an outer and inner membrane, known respectively as the ‘‘ ectoderm ”
and ‘‘endoderm,” and no hard external layer is produced. ‘The
mouth opens into a cylindrical body-cavity or “‘ ccelenteric space,”
which runs the whole length of the body, and is completely undi-
vided, no gullet being developed. ‘There are, therefore, no radiating
membranous partitions corresponding with the ‘‘ mesenteries” of the
Actinozoa. The animal can produce buds, which become devel-
oped into new “ polypites,” but these do not remain attached to the
parent polypite, and the organism does not, therefore, become com-
posite. Moreover, at certain seasons, the animal develops true
reproductive organs, which have the form of external buds. These
discharge the reproductive elements by rupture of their walls, but are
not themselves separated from the organism.

The ovum in all the “ydrozoa gives rise to a “ polypite ” similar in
structure to the entire organism in Hydra, but the primordial poly-
pite is often endowed with the power of throwing out buds which
remain, some or all of them, permanently united with the original
“zooid.” In this way is produced a composite organism (fig. 76, B,
and fig. 77), consisting of a greater or smaller number of zooids or
‘polypites,” united by a common fleshy stem or ‘‘ coenosarc.” Very
generally, the zooids become differentiated into two sets, which differ
in structure and in the part they play in the life of the colony. In
the one series the zooids constitute the ordinary nutritive ‘‘ polypites ”
of the colony (fig: 77, 2), and are concerned with supplying food to
the organism. In the other series the zooids—now spoken of by the
general name of the “ gonophores ”—have a reproductive function,
and are concerned with the production of the generative elements.
These generative zodids or “ gonophores” may remain permanently
attached to the parent colony (fig. 76, B), or they may become much
modified and may become detached to lead a free existence (fig. 77).
In this latter case, the detached generative zooids usually present
themselves in the form of ‘“ Jelly-fishes” or ‘“‘ Medusoids.”

The colonies of the composite /Zydrozoa are sometimes free, the
proximal end of the coenosarec not being adapted for fixation (as in
the S7phonophora and the Graptolitordea proper). In other cases
the colony is attached to some foreign body by a modified proximal
extremity or “hydrorhiza” (fig. 76, 7%).

In a number of the composite Zydvozoa no hard structures in the
shape of an external skeleton are developed. In many cases, how-
ever, the ectoderm secretes a firm horny outer layer or “ periderm ”
(fig. 76, fe), which may cover the ccenosarc only (as in Bougain-
villea, fig. 77), or may be extended into little cups or “ hydrothecze ”
within which the individual polypites are contained. When “ hydro-
thecee ” are present, the body of the polypite is contained within
the cup, and the distal extremity, with the mouth and tentacles,

HYDROIDA. 195

can be protruded from the terminal opening or “aperture” of the
, hydrotheca (fig. 76 B, %). In some cases, not only are the nutritive
_ polypites protected within “‘ hydrothecz,” but the generative buds or
gonophores are also provided with a horny or chitinous covering,
constituting what are known as “‘gonangia.” Lastly, in the group of
the Hydrocorallines, and in a few other cases, the colony has the
power of secreting carbonate of lime, and thus of giving rise to a
calcareous skeleton, which in many cases is superficially similar to
the “corallum” of certain of the <Actinozoa.

With regard to the distribution of the ydrozoa in space, the great
majority of the organisms included under this head are marine, but
in a few cases (e.g., AZydra) the organism is found in fresh water.
As to the general distribution of the class in “me, the Fresh-water
Polypes (Aydrida), the Oceanic Hydrozoa (Calycophoride and Phy-
sophoride), and the Calycozoa (Lucernaria, &c.) have left no traces
of their past existence, as might have been anticipated from their
want of hard parts. The Zvachymeduse and Acraspeda (Jelly-
fishes and Sea-blubbers) are equally destitute of hard structures, and
their absence from the paleontological record might have been
confidently predicted. Under favourable circumstances, however,
these soft-bodied organisms are capable of leaving impressions in
soft mud or sand, by which their past existence may be determined ;
and such impressions have been recognised in deposits even -as
ancient as the Cambrian. ‘The great group of the Graftolitoidea
is not only entirely extinct, but is wholly restricted to the older
Palzeozoic rocks. The equally great group of the Stromatoporoidea
is also extinct, and is principally confined to the earlier Palzeozoic
deposits, though fossils which are probably referable here are also
found in the Mesozoic rocks. The Corynida and Thecaphora, both
largely represented in recent seas, have left but few and imperfectly
connected traces of their existence in past time; and some of the
forms usually referred to these orders, and especially the more
ancient ones, are of more or less dubious affinities. The recent genus
flydractinia, among the Corynida, occurs, however, in rocks as old
as the Cretaceous. Lastly, the existing group of the Hydrocorallines
is represented by fossil forms, which begin as early as the Trias.

In the following more detailed summary of the main divisions of
the Hydrozoa and of their principal fossil forms, those groups which,
as above mentioned, are not known to be represented in past time
are left out of account.

SupB-CLASS HyYDROIDA.

The sub-class of the “ Hydroid Zoophytes” comprises a large
number of Aydrozoa in which the organism is attached, or is cap-

196 CCELENTERATA.

able of attachment, to foreign bodies by means of a modified prox-
imal extremity or ‘“‘hydrorhiza.” A few of the types included in
this sub-class are simple (¢.g., Hydra), but the organism consists

Fig. 78.—Recent Corynida. a, Portion of the colony of Hevigonimus minutus, with polypites
and reproductive buds, enlarged about 25 diameters; B, A single polypite of Azmerza vestita,
greatly enlarged, showing the extension of the polypary upon the bases of the tentacles. (After
Allman.)

typically of numerous simple polypites united by a branched
‘“‘ccenosarc,” and forming a plant-like or encrusting colony. Very

HYDROIDA. 197

usually, the colony develops hard structures (‘“‘polypary” or
“coenosteum ”), which may have the form of an external chitinous
layer, or, In some instances, is composed of carbonate of lime. Re-
production takes place by fixed generative buds, or by the develop-
ment of free reproductive zooids (“‘ gonophores ”).

Of the orders of the Hydroid Zoophytes, the only three which
have fossil representatives are the Corynida, the Zhecaphora, and
the Zrachymeduse.

ORDER 1. Corynipa.—The “ Tubularian Zoophytes” or Corynida
are mostly composite, forming more or less plant-like, or encrusting
colonies, fixed to foreign objects proximally, and usually furnished
with a skeleton or ‘‘polypary.” The skeleton is mostly in the form
of a chitinous investment, which encloses the ccenosarc (fig. 78, A),
but which is not developed into definite cups or ‘“‘ hydrothecz” for
the reception of the individual polypites. In some cases, however,
the skeleton consists of zooidal tubes, in which the polypites were
lodged, united by a general clathrate or tubulated ccenosarcal skele-
ton, as in the genus Aydractinia and its fossil allies. In the living
genus Szmeria, also, the polypary forms an investment for the poly-
pites, and is even prolonged upwards as far as the bases of the
tentacles fig. 78, B). Though the skeleton of the Corynida is usu-
ally chitinous in composition, it is occasionally calcareous (as in
some species of “/ydractinta and in the genus /arkevia).

There are many recent types of the Corynida, such as the com-
mon Pipe-corallines (Zubularia), which, from the nature of their
skeleton, might quite well have been preserved in the fossil condi-
tion. The only recent genus, however, of which any fossil repre-
sentatives are known is /ydractinia, the colonies of which are well
known as forming crust-like investments upon shells. The species
of Hydractinia form chitinous—or rarely calcaréous—crusts upon
the exterior of the shells of Gastropods (fig. 79, A), the shell thus
affected being often ultimately more or less largely dissolved away,
and replaced by the substance of the parasite. The skeleton of
fiydractinia, when fully grown, consists of numerous close-set ver-
tical columns (“radial pillars,” fig. 79, p 4), which are united at
irregular intervals by horizontal “laminz,” the number of these,
and the consequent thickness of the crust, varying in different indi-
viduals or in different species. The successive ‘‘laminz” are separ-
ated by narrow intervals or “interlaminar spaces” (fig. 79, 7), which
are broken into irregular chambers by the ascending “radial pillars.”
The “laminze” themselves are not continuous membranes, but are
formed by the anastomosis of numerous horizontal connecting-pro-
cesses or “arms” (fig. 79, Ec), which spring from the radial pillars
at tolerably regular intervals. The ‘‘laminz” are thus more or less
cribriform, the apertures in their substance serving as tubes for the

198 CCELENTERATA.

zooids of the colony, while the interlaminar spaces are filled with
the soft ccenosarc. The surface of the skeleton is covered with
projecting wart-like tubercles, interspersed with larger pointed
spines (fig. 79, B and c), these being really the upper projecting
ends of the “radial pillars.” The surface also shows (fig. 79, B) the
rounded pores which lodged the zooids, together with singular
branched grooves or open canals, which apparently serve for the
lodgment of processes of the coenosarec. In the living species of

[ESS

LN JM - |

RAI aEHADe

— SS
p i

Fig. 79.—a, A colony of Hydractinia pliocena, attached to the shell of a Gastropod, of the
natural size, Pliocene. 3B, Portion of the surface of the same enlarged, showing wart-like promin-
ences, branched ccenosarcal canals, and minute circular zodidal apertures. c, Vertical section of
the crust of the recent Hydractinia echinata, showing surface-tubercles and spines (s). The suc-
cessive laminz of the skeleton (Z, 7) are separated by ‘“‘interlaminar spaces” (7) which are broken
up into irregular chambers by “‘ radial pillars.” p, Vertical section of the crust of Hydractinia
echinata, greatly enlarged, showing its composition out of vertical processes (‘‘ radial pillars’)
united by horizontal bars or ‘‘arms” (c). E, Horizontal section of the same, showing the pillars
(f) and their connecting-processes (c), greatly enlarged. (After Allman, Carter, and the Author.)

fTydractinia the organism consists of the general crust-like coenosarc,
and of a large number of ‘“polypites” emitted from the surface of
the same. Many of these polypites have mouths and tentacles, and
are devoted to the nutrition of the colony ; others are non-tentacu-
late, and carry sac-like generative buds, which are not detached
from the parent-colony ; while others form long spirally coiled fila-
ments, apparently intended for defensive purposes.

The recent species of Hydractinia are all marine, and the skeleton
is in general composed of chitine; but in an African species, de-

HYDROIDA. 199

scribed by Mr Carter, the skeleton is calcareous. The earliest
known fossil forms of Aydractinta appear in the Cretaceous rocks,
and a number of Tertiary forms are known. In the Aydractinia
circumvestiens of the Pliocene Tertiary (which is probably identical
with the 4. plocena of Dr Allman), the skeleton is calcareous,
and forms thick crusts upon the shells of Gastropods (fig. 79, A).
The genera Zhalaminia (Jurassic and Cretaceous) and Spheractinia
(Jurassic) have been founded by Steinmann for forms apparently
allied to Aydractinia, and it is not impossible that the Jurassic
genus £//ipsactinia, of the same author, should likewise be placed
here.

In many respects related to Aydractinia is the singular Mesozoic
genus Parkeria, best known by the Farkeria spherica of the Green-
sand of Cambridge. The organism in Parkeria spherica (fig. 80)
is globular in form, and varies in diameter from a quarter of an
inch or less up to more than two inches, the surface being often
nodulated or covered with small rounded or elongated elevations.
The skeleton must have been free in
its adult condition, as a rule at any
rate; but in many cases it grew round
some foreign body, such as a frag-
ment of shell. As to its chemical
composition, there is no sufficient
reason to doubt that the skeleton
was originally composed of carbon-
ate of lime, though many specimens
are now found to be more or less
largely phosphatised. As_ regards
its minute structure, the skeleton is

< a i Fig. 80.—A large specimen ot Parkeria
found, when examined microscopi- sievica, from the Upper Greensand of

Cambridge, of the natural size. (Original.
cally by means of thin sections, to ““™Pnds® ofthenatural size. (Origmal.)

be composed of a characteristic minutely tubulated tissue, the
tubules of which are radial in arrangement. ‘This tubulated tissue
is built up into a set of radiating columns (“radial pillars,” fig.
81, #) and a series of concentrically disposed lamellz, the latter
being separated by interspaces (“interlaminar spaces”), which are
broken up into irregular ‘‘chamberlets” (fig. 81, ¢). The tubu-
lated tissue of the “radial pillars” is traversed by a variable number
of comparatively wide, circular or oval tubes, which open upon the
surface, or into the chamberlets—each successive row of chamber-
lets having at one time formed the surface of the skeleton—and
which may be regarded as having lodged the nutritive polypites of
the colony. Upon the whole, Parkervia may be regarded as repre-
senting an aberrant type of the Mydractinide, but the genus has
also relations to the Hydrocorallines. The little spheroidal fossils

200 CCGELENTERATA.

from the Chalk which have been placed in the genus Porosphera
have often been regarded as related to Parkeria, but their minute
structure would rather support their being placed among the
Sponges.

In connection with the preceding, a few words may be said with regard
to the singular genera J7ztcheldeanta and Solenopora, which are of
doubtful affinities, though the balance of evidence is in favour of referring
them to the Hydrozoa. The genus Mctcheldeanta comprises small

Fig. 81.—Vertical section across the centre of a specimen of Parkeria, enlarged twice.
p, One of the radial pillars; c, One of the chamberlets. (Original.)

spheroidal fossils rarely reaching half an inch in diameter, which some-
times occur in such vast quantities as to give rise to actual beds of the
Carboniferous Limestone (fig. 82). When examined microscopically, the
skeleton of MWztcheldeania is found to be formed of radiating capillary
tubes, which are disposed in concentric strata, and have a diameter of
from ;\; to j/; of a millimetre. These tubes have porous walls, and are
united by a still more minutely tubulated tissue ; but the structure of the
organism is too complex to be advantageously discussed here.

The genus Solenopora comprises calcareous organisms of varying
size, usually ranging from the dimensions of a pea up to those of an

HYDROIDA. 201

orange, and of irregular shape (fig. 83, A). Examined microscopically, the
organism in So/enxopfora is found to be wholly composed of radiating

Fig. 82.—A fragment of limestone rom the Lower Carboniferous Series of the south of Scot-
land, largely composed of Mitcheldeania gregaria, of the natural size. (Original.)

capillary tubes, arranged in concentric strata. The tubes (fig. 83, D) vary
from ;4 to s'5 millimetre in size, and are in direct contact throughout, no
interstitial tissue of any kind being developed. The tubes are irregular

MELLEL TTL ELLE
ee oe | \ eB ae }
Haye as
i ' 3 {) 3 ff

esitaiaara wit
WE esectas

NaOH Soe
_
5
L
eet ar nn:
Wr
root Oe iavus
wnat

mk rs geeeaa
s Seana
casey ass prnattition

ee teint,

Saat
se 1

—s
8 rege
eer cp ett Masa ar AORTA fan: IVini aT ts
AS
etna C CI YEON ce ime
ee
yO ceed Tae abana

Fig. 83-—a, A small specimen of Solenopfora compacta, Billings, from the Ordovician rocks of
Saak, Esthonia, of the natural size; 8, Surface of a piece of limestone largely made up of small
specimens of the same, from the same locality, of the natural size; c, ‘l'angential section of the

same, enlarged about 35 times; pb, Vertical section of the same, similarly enlarged.
(Original.)

in form, with thin, often undulated walls, which are not pierced by any
apertures or pores, but are often crossed by more or fewer transverse

202 CCQELENTERATA.

partitions or “tabule” (fig. 83, D). Very commonly the tubes exhibit
more or fewer inwardly directed partitions, which extend to a greater or
less distance into the cavity of the tube, and are the result of the cleavage
or “fission” of the tubes. The species of Solenopfora are entirely con-
fined to the Ordovician rocks, and sometimes occur in such profusion as
to give rise to beds of limestone. The best known species (viz., S.
compacta) has been recognised in the Ordovician limestones of Russia,
Britain, the United States, and Canada.

Both Mitcheldeania and Solenopora are remarkable for the extraordi-
nary minuteness of their component tubes, and in this respect they differ
from all known Ccelenterates. Apart from this feature, they present in
their structure a general resemblance to forms like Parkeriza, and they

Fig. 84.—Sertularida. a, Portion of the colony ot Difhasia (Sertularia) tamarisca, of the
natural size, showing hydrothece and female ovarian capsules (gonangia). Band c, Portions of
different branches of the same, enlarged: 4, Hydrothece ; a, Male gonangium; g, Female gon-
angium. (After Hincks.)

may therefore be provisionally placed among the Hydroid Zoophytes.
In some points, however, the genus WWztcheldeania would appear to be
rather related to the Hydrocorallines.

Among the other forms which have been referred to the Coryuzda are
the genera Corynoides and Paleocoryne. ‘The former of these may, per-
haps, be best regarded as an abnormal type of the Graptolitozdea, and
will be alluded to in speaking of these organisms. The genus Pa/l@o-
coryne, on the other hand, is founded upon structures which belong to the
fronds of certain of the Fenesteliid@, and it will therefore be treated of
in dealing with the Polyzoa.

HYDROIDA. 203

ORDER 2. THECAPHORA.—This order includes the Sea-firs and
their allies (Sertudarida and Campanularida), in which the organism
is fixed, and consists of a more or less plant-like colony (fig. 84, A),
composed of numerous polypites united by a common stem or
*“coenosare.” The ccenosarc usually consists of a main stem or
“‘hydrocaulus,” with many branches, and it is fixed to foreign bodies
by an adherent base or “hydrorhiza.”. The colony produces a
strong corneous or chitinous outer investment (the “periderm” or
“‘polypary”), which not only invests the ccenosarc, but is also pro-
longed into cup-like receptacles, which enclose the individual poly-
pites, and are known as the “hydrothece.” The reproductive
zooids (‘‘ gonophores”) are either set free as Jelly-fishes (as in the
Campanularians generally), or are developed within urn-like recep-
tacles (‘‘ gonangia” or “ gonothecze”), which are of larger size than

Fig. 85.—Dendrograptus Hailianus. a, Portion of the frond, natural size; 4, Portion of a
branch, enlarged; c, The footstalk and some of the principal branches, natural size. Upper
Cambrian (Potsdam Sandstone). (After Hall.)

the ordinary hydrothecze (fig. 84, B and). In this latter case, the
reproductive zooids are not liberated from the parent colony as
independent organisms. In the typical Sertularians, the hydrothecz
spring directly from the sides of the ccenosare and are not supported
on stems, and they may be biserial (as in Sertudarvia and Diphasia,
fig. 84, A), or they may, as in Flumularia and its allies, be de-
veloped on one side only of the divisions of the ccenosarc. On the
other hand, in the Campanularians the polypites are stalked and ter-
minal, each being placed at the end of a division of the ccenosarc.
The existing Zhecaphora are not only very abundant and very

204 CCELENTERATA.

widely represented in recent seas, but they possess a chitinous poly-
pary which seems to be quite as well suited for preservation in fine-
grained sediments as is that of the Graptolites. It is therefore a
matter difficult of explanation that, except in late Quaternary deposits,
no trace of an absolutely undoubted Sertularian or Campanularian,
similar to the ordinary existing forms of the order, has been as yet
discovered. On the other hand, the ancient Palzozic deposits have
yielded the remains of various extinct organisms, which have often
been referred to the Graptolitoidea, but which, with greater prob-
ability, may be regarded as early types of the Zhecaphora. One of
the most interesting of these is the Cambrian and Ordovician genus
Dendrograptus, in which the organism had the form of a spreading

ah

rT
: mmee
= a

VA
YY
Le
ZS
Se

Fig. 87.—A branch of
Ptilograptus plumosus,
Hall. Enlarged. Ordo-
Fig. 86.—Dictyonema retiforme, Hall. Silurian (Nia- vician (Quebec Group),

gara Group), United States. (After Hall.) Canada. (After Hall.)

and branched frond, furnished with a strong footstalk (fig. 85), by
which it was probably attached to some foreign body. The branchlets
carry upon one side a series of little chitinous cups or “‘ hydrothecze ”
(“‘cellules”), which agree with the similar structures of the Grapto-
lites in partially overlapping one another.

In Dictyonema (fig. 86) we have organisms resembling Dendro-
graptus in many respects, but not possessing any footstalk. The
frond is branched and plant-like, and is fan-shaped or funnel-shaped
in form. It is not certainly known whether the organism was attached
by its base or not ; but there is the strongest probability in favour of
its having been fixed. The branches radiate from the base, running
nearly parallel with one another, and often bifurcating. They are
united to one another at short intervals by numerous, irregular,

HYDROIDA. 205

slender, transverse processes or dissepiments, and they bear small
horny cups or “ hydrothecz” (“ cellules”) like those of the Grapto-
lites. Diuctyonema ranges from the Upper Cambrian to the Middle
Devonian. The genus bears a close superficial resemblance to the
Fenestelle or Lace-corals (belonging to the Polyzoa) ; but the latter
have a calcareous skeleton, and have no “‘hydrothecz.” Besides the
above-mentioned genera, Ca/lograptus and Ptilograptus (fig. 87) may
with great probability be referred to the Zhecaphora ; as may, per-
haps, be the obscure fossils Luthograptus and Thamnograptus. All
these genera are found in the Ordovician or Silurian rocks.

OLDHAMIA.—The singular structures described under the genus
Oldhamia may be noticed here, as they have been referred to the
ffTydrozoa ; though their true nature is altogether uncertain. O/d-
hamia occurs in certain green and purple grits of Lower Cambrian
age, at Bray Head, in Wicklow, Ireland, where the supposed fronds
are found in great abundance, matted together, and spreading over
the surfaces of the strata. A form of O/dhamza is also said to occur
plentifully in the Potsdam Sandstone
(Upper Cambrian) of Wisconsin, in
North America, and still another form
has been described by Barrois from
the Cambrian rocks of the Pyrenees.
Oldhamia antigua, the commonest
form, consists of a central thread-like
axis from which spring bundles or
umbels of short radiating branches
(fig. 88), at regular intervals ; whereas
in the so-called Oldhamia radiata the
branches radiate from a central point
in all directions. Oldhamia has been
variously referred to the Sertularian
Zoophytes, to the Polyzoa, and to the
Alge. It has not, however, been as
yet satisfactorily shown that O/dhamuia Teor ee Auten
1S truly organic, and “1b 11S quite pos- size (after Salter). Cambrian.
sible that the structure so called is the
result of purely inorganic agencies. If really organic, it would seem
more than probable that O/dhamia is referable to the vegetable king-
dom, and that it belongs to the A/ge. ‘This is the view held by
Barrois, who compares O/dhamia with some of the types of Alge
which are placed in the family of the Dasycladee.

ORDER 3. TRACHYMEDUS&.— The Zrachymeduse constitute a
peculiar group of the “ Jelly-fishes,” which agree with all the organ-
isms grouped under this popular designation in the possession of a
gelatinous swimming-bell, from the under side of which is suspended
a single “polypite.” From the margin of the swimming-bell depend

2

206 CCELENTERATA.

solid tentacular processes, and the substance of the bell is traversed
by simple radiating canals which communicate above with the gastric
cavity of the polypite. The reproductive organs are developed in
the course of the radiating canals of the disc, and the embryo is
developed directly into the adult form, without the intervention of
an intermediate fixed and sexless stage.

Though wholly devoid of hard structures, the Zrachymedusa@, as
will be more fully pointed out in dealing with the Acrasfeda, are
capable of leaving traces of their past existence in the form of im-
pressions left by their stranded bodies in fine mud. Impressions
of this nature have been recognised in the fine-grained lithographic
limestone (Jurassic) of Solenhofen, in Bavaria, and have been referred
to the genera Palegina and Trachynemites, representing respectively
the two existing groups of the “#e7nide and Trachynemide.

SuUB-CLASS LUCERNARIDA.

The division of the Lucernarida comprises a large number of
recent /Zydrozoa in which the base of the organism is developed
into a disc-shaped or cup-like structure (the “‘umbrella”), in the
walls of which the reproductive organs are developed, and which
carries on its concave side a single, more or less modified “ poly-
pite.” The “ Jelly-fish” thus constituted may develop itself directly,
or it may be only the generative form of a minute fixed organism
(“‘ Hydra-tuba”), from which it is produced by fission.

The peculiar group of Lucernarians (Ca/lycozoa) of which Lucer-
naria itself is the type, is wholly unrepresented by fossil forms, and
needs no further consideration here. On the other hand, the group
of the Acraspeda—or, as it is often called, Dzscophora—has left
various traces of its past existence, and is in many ways of palzon-
tological interest. The group of the Acraspeda comprises most of
the larger organisms which are usually spoken of as ‘ Jelly-fishes,”
though the structures so called are for the most part merely the gen-
erative zooids produced by a minute sexless Lucernarian. Such a
Jelly-fish (as, for example, the recent Azuze/za) consists of a great
gelatinous swimming-bell or ‘‘ umbrella,” from the under side of which
hangs a single polypite, the structure of which is greatly modified
in the RAizostomide. ‘The swimming-bell is traversed by a complex
system of canals, connected superiorly with the gastric cavity of
the polypite (fig. 89), and its margin usually carries more or fewer
‘“‘tentacles,” which are often of great length. ‘The mouth of the
polypite is extended into fringed or lobed processes, often of great
length (fig. 89, 7). Lastly, the reproductive organs are in the form
of four folded bands, which project into four special cavities (the
‘“‘sub-genital pouches ”) in the floor of the gastric cavity.

LUCERNARIDA. 207

The Acraspedote Jelly-fishes are wholly marine, and are often of
very large size. They usually swim near the surface, but they have
been observed to crawl about on the sea-bottom in shallow water,
and they have also been seen to lie at the bottom with the base of
the umbrella turned downwards and the tentacles directed upwards.
Though they possess no hard structures, and though their tissues are
saturated with water, and therefore singularly perishable, they are
nevertheless capable of producing impressions in sand or mud by
which their past existence, and even their form, may be determined.

LL

~~
Ss
~>

i
|

\
N

Z KK z 3 ‘a ae Z

Zyl

SS Ws YW, SE
AO Ve

iii

Nt :
ii

i

\

\ \
Wr 2
eo
/

if

SAS

\
/

Fig. 89.—Under side ot the umbrella ot Auvelia aurita, one of the Acraspedote Meduse,
reduced in size. JZ, One of the four oral lobes, in the centre of which is placed the mouth; ¢,
Tentacles attached to the margin of the umbrella; c, One of the radiating canals of the umbrella;
wz, Sense-organ; 7, Reproductive organ, projecting into a ‘‘sub-genital pouch” (go). (After
Claus and Sedgwick.)

The markings by which the former existence of Jelly-fishes may be
recognised are of different kinds in different cases. In one group of
cases the body of the Jelly-fish has fallen after death upon the fine
mud of the sea-bottom, or has been thrown up on the shore, and an
impression representing the swimming-bell, and in some cases the
tentacles, of the animal, has thus been formed in the soft sediment.
Upon impressions of this nature in the lithographic slates (Jurassic)
of Solenhofen, Haeckel has founded various genera. Some of these,
as previously noted, are believed to belong to the group of the
Trachymeduse ; but others, such as LRfzzostomites (fig. 90) and

208 CCELENTERATA.

Flexarhizites, are considered as referable to the Acraspeda, and to
be related to such living types as R/zzostoma.

Of a somewhat more questionable nature are the singular bodies
from the Cambrian rocks of Sweden, to which Nathorst has given
the name of M@edusites. ‘These bodies are usually in the form of
four-rayed or five-rayed stars, or have the shape of four-sided or five-
sided pyramids the angles of which are more or less prolonged ; and
they have no actual organic structure. By Nathorst, however, they
are regarded, with much probability, as being produced by the in-
filling of the cavities of dead Jelly-fishes with mud or sand. On
this view the central pyramidal body of A/edusztes represents the cast

eu,

Fig. 90.—The impression of the swimming-bell o1 a Jelly-fish (RAzzostomites admirandus)
preserved in the lithographic slate (Jurassic) of Eichstadt, in Bavaria, one-seventh of the natural
size. The missing parts are restored in outline. (Copied from Zittel.)

of the gastric cavity of the polypite, while the four or five arms which
radiate from this represent casts of the radiating angles of the mouth.
In support of this view, Nathorst points to the known habit of certain
Jelly-fishes of lying at the bottom with the umbrella turned down
and the mouth directed upwards, in the position figured in fig. 89,
and he shows how this would naturally facilitate the filling of the
gastric cavity with mud. Moreover, Nathorst has shown that bodies
exceedingly similar in form and marking to the Cambrian Medusites
can be produced by taking casts of the internal cavities of fresh
specimens of Jelly-fishes in dilute plaster of Paris.

Lastly, Nathorst has brought forward ‘evidence to show that Jelly-
fishes are capable of producing various peculiar markings by their

LUCERNARIDA. 209

movements when creeping about on the muddy bottom of the sea in
shallow water, or by the trailing of their tentacles over soft sediment.
In view of this evidence, he has suggested that the peculiar striated
and furrowed markings in the Cambrian rocks (‘ Fucoidal Sand-
stone”) of Sweden which have been described under the name of
Lophyton (fig. 91), are to be regarded as really produced by the
trails of Jelly-fishes. These peculiar markings were originally de-
scribed as the remains of land-plants, but it seems certain that this

Fig. 91.—Fragment ot Zophyton Linneanum. ower Cambrian.

cannot be their real nature. Nathorst has, in fact, produced pre-
cisely similar markings by allowing plants to trail over soft mud ;
and if the so-called Medusites of the Swedish Cambrian is rightly
regarded as founded on the casts of the gastric cavity of Jelly-
fishes, we have in these a proof that there existed at the time ani-
mals capable of producing the striated trails of the same deposits
to which the name of Zophyton+ was originally applied.

1 The fossil described by Hicks from the Cambrian rocks of Wales under the
name of Zophyton explanatum has been shown by Hinde to be really the anchor-
ing-rope of a Hexactinellid Sponge.

VOL. ie O

210

CHAPS Eke SCE

HVDROZOA — Continued.
SUB-CLASS GRAPTOLITOIDEA.

THE organisms comprised under the head of Gvaptolitordea (the
Rhabdophora of Allman) are commonly known as “ Graptolites,”
and constitute a remarkable assemblage of extinct Wydrozoa, all the
known forms of which are confined to the Upper Cambrian, Ordo-
vician, and Silurian deposits. The Graptolites may be defined (if
the abnormal genus Corynoides be excluded) as being composite
F1ydrozoa in which the organism consists of numerous polypites
united by a coenosarc ; the latter being enclosed in a tubular, chitin-
ous polypary, usually forming a complete external membrane of con-
siderable strength, while the former were protected within ‘‘ hydro-
thece.” The polypary may be undivided or branched, and was
invariably free, the organism apparently floating in the water with
the proximal end of the colony directed upwards. In most cases, the
polypary is strengthened bya peculiar rod-like axis (the “virgula ”),
which lies in a groove on the dorsal side of the polypary (z.e., on the
side opposite to that on which the hydrothecze are developed), and
may be prolonged beyond one or both ends of the colony. The
polypary is, typically if not universally, furnished at its proximal end
with a minute triangular or dagger-shaped body (the “sicula”),
which represents the embryonic skeleton.

As regards its development, the earliest condition in which a
typical Graptolite presents itself is that of a small triangular corneous
body, which has been termed by Professor Lapworth the “sicula ”
(fig. 92, A), and which is the starting-point of the entire polypary.
In its earliest stage (fig. 92, A a) the “‘sicula” is merely a triangular
horny sheath lodging the ccenosarc, but a rod-like axis or ‘ virgula ”
(fig. 92, A 6) is soon developed along its entire length, often pro-
jecting freely at one or both extremities. In the next stage (fig. g2,

GRAPTOLITOIDEA. 2

Ac) a bud, constituting the first hydrotheca, appears on one side,
near the thicker end of the “sicula.” If the form under observation
belongs to the group of Graptolites in which the polypary possesses
two rows of hydrothece (the “ diprionidian ” Graptolites), a second
bud next appears on the opposite side of the “sicula” to the first
one, and a little in advance of it. In the further development of the
polypary, the sicula appears to remain stationary, usually persisting

Fig. 92.—A, Early stages in the development of Graptolites: a, The earliest stage of the

**sicula,” in which no virgula is developed ; 4, Later stage, with a virgula ; Say sual later stage,
with a single primordial hydrotheca; d, Stage with two hydrothece. B, Base of Monograptus
gregarius, enlarged ; C, Monograptus Clingani, young specimen, of the ‘natural size, showing a
proximal and distal extension of the virgula ; p, Proximal portion of Didymograptus Murchisoni ; s
E, Proximal portion of Climacograptus nornalis, enlarged; F, Proximal portion of Disorpho-
craptus, enlarged. sSicula; wv Virgula. All the specimens are Ordovician or Silurian. (Partly
after Lapworth and Tullberg, and partly original.)

at the base of the organism as a dagger-shaped process, the broad
end of which is directed proximally (fig. 92, B—F). In some cases
the sicula becomes obsolete, or it may ultimately develop into a
branch, or, rarely, into a vesicle (as in Diplograptus physophora).
Taking a simple Graptolite, such as Wonograptus priodon (fig. 93),
as the type of the sub-class, the polypary will be seen to consist
of three principal morphological elements—viz., the ccenosarc, the
hydrothecee, and the virgula. The last mentioned of these—often
spoken of as the “‘axis”—1is one of the most characteristic of the
structures of the Graptolitic polypary, and has the form of a cylin-
drical fibre or rod, probably hollow internally, which gives support
to the flexible chitinous skeleton. It runs, in such types as Jono-
graptus, along the dorsal side of the polypary, opposite to the hydro-

ZN2 HYDROZOA.

thecee (fig. 93, B), whereas in the double Graptolites it occupies a
central or sub-central position, between the two rows of hydrothecze
which form the biserial colony. In any case it lies in a groove in
the periderm, and is really outside the cceno-
sarc. Very commonly, the virgula projects
beyond one or both ends of the polypary as
a longer or shorter naked rod (fig. 92, c, and
fig. 94, A); the proximal extension being
often spoken of as the ‘‘radicle,” though this
name has also been used for the “ sicula.”
- Running parallel with the virgula is the coeno-
sarc — often spoken of as the ‘‘ common
canal”—-which is enclosed in the tubular
periderm, and presents itself in compressed
specimens as a flat space of variable width
between the virgula and the bases of the
hydrothecee (fig. 94, ¢). Springing from the
coenosarc, lastly, is a series of chitinous cups
or ‘“ hydrothecz,” which have often been
spoken of as the “cellules” or “ denticles.”
Each hydrotheca rests by its base upon
the ccenosarcal canal, is separated from
its neighbours by a definite partition, and
Fig. * 93 Morphology of Opens» at 1ts apex by an “aperture; thnouee
De ae re ae which the contained polypite could protrude
served in relief—lateral view its tentaculate head. ‘The hydrothecze vary
slightly enlarged—from the Si- : ; tie
lurian rocks; 8, Dorsal view of Extremely in form and in the precise position
a fragment of the same species of the aperture in different types of Grapto-

—considerably enlarged; c, ~ : “ :
Front view of a fragment of the lites, or in different species of the same

tet es ae genus (fig. 94); and the lip of the aperture
Ste ae, Omer may be variously ornamented with spines.

Lastly, the hydrothecze are typically so dis-
posed that they more or less extensively overlap one another (fig.
oA Baandse):

While the above is the arrangement of parts in such a form as
Monograptus priodon, there are many departures from this typical
condition in other forms of the Graptolites. Thus, the general peri-
derm, instead of forming a dense continuous membrane, may, as
in Retiolites (fig. 106), be reduced to a mere network of chitinous
threads. In the same genus, the virgula is double, the two halves
being placed on opposite sides of the ccenosarc, and being
united with the peridermal network. Again, the hydrothecez,
instead of more or less largely overlapping one another, may, as in
Rastrites (fig. 98), spring quite separately and at greater or smaller
intervals from the coenosarc. Lastly, it has not been certainly estab-

D) :

IMAM LAL

2

fh CON,

))

MM MMM

5 DIY. .
UE LE. UL.

StL

>

GRAPTOLITOIDEA. 213

lished that the ‘“‘virgula” is invariably developed in all types of the
Graptolites, and the name of Akabdophora, proposed for the group
by Professor Allman, is, therefore, not wholly appropriate.

With regard to the reproductive process in the Graptolites there are
strong grounds for supposing that the generative elements were
developed in specially modified polypites, or ‘‘ gonophores,” after
a manner analogous to that which occurs in the Hydroid Zoophytes
generally. In some cases, these generative buds may have been
destitute of a hard covering, and therefore incapable of preservation ;

Fig. 94.—a, Monograptus colonus, enlarged ; p, A fragment of MWonograptus priodon; c, Mon-
ograptus colonus; D, Monograptus Clingani; E, Monograptus spinigerus; F, Monograptus
attenuatus; G, Monograptus fisingert, all greatly enlarged. s, Sicula; v, Virgula; c, Coen-
osarc 3; 4, Hydrotheca; 7#z, Aperture ‘of hy drotheca ; sf, Apertural spine. (After Lapworth.)

but in other cases there is evidence of the existence of chitinous
receptacles, of larger size than the hydrothecee, and of different form,
which may be compared with the “ gonangia ” or “‘ ovarian capsules ”
of the recent Sertularians, and may be supposed to have lodged the
reproductive zooids. Thus, occasional specimens of certain of the
diprionidian Graptolites have been found to carry on their sides
singular horny sac-like structures, which can hardly be regarded as
anything else than as of the nature of “ gonangia.” Moreover, it is

214 HYDROZOA.

very usual, as pointed out by the writer, to find in association with
Graptolites peculiar, bell-shaped or conical, chitinous capsules, which
may be spoken of by the general name of Dawsonz@ (fig. 95). These
capsules present different appearances in accordance with the direc-
tion in which they have been compressed, and they vary in shape
and size. Each is furnished with a little spine or mucro at its sum-
mit, and also with a marginal chitinous thread or fibre. These
singular bodies have not hitherto been certainly detected in direct
connection with the polypary of any Graptolite. They may, however,

Hi
Wit
Hii
Hi
Hl iI Ve iI

Fig. 95.—Various forms of bell-shaped chitinous capsules (Dawsonia) found associated with
Graptolites, and supposed to be of the nature of ‘‘ gonangia.” (Original.)

be regarded, with great probability, as being of the nature of “ gon-
angia,” though they probably differed from the structures so called
in the recent Sertularians in becoming detached from the parent
colony.

Two leading ¢ypes of structure may be distinguished amongst the
Graptolites, and these may be respectively termed the ‘‘ monoprioni-
dian” and ‘‘diprionidian” type. ‘The monoprionidian Graptolites
(Monoprionide) are distinguished by the fact that, whether the
colony be simple or branched, the hydrothecz are arranged in a
single series, and the coenosarc is thus single and not double. In
the typical Monoprionide the hydrothecze are uniserial over the
entire polypary (as in Monograpitus or Didymograptus). A transition
is, however, effected between the monoprionidian and diprionidian
groups of Graptolites by such intermediate types as Dzmorpho-
graptus (fig. 92, F) in which the proximal portion is monoprioni-
dian and the distal portion diprionidian, or Dicranograptus (fig.
103, A) in which the opposite state of things obtains. On the other
hand, in the proper Dzprionide the polypary is duplicate, and con-
sists of two separate rows of hydrothecze, which may spring from an
undivided common ccenosarc, but which, more usually, arise from

GRAPTOLITOIDEA. 215

two separate coenosarcal tubes which are closely apposed to one
another, back to back, along their entire length.

Before briefly considering some of the leading types of these
two great groups, attention may be directed
for a moment to the singular genus Cozy-
noides (fig. 96), which differs in important
respects from all the ordinary Graptolites.
In this curious form the organism consists
of a cylindrical chitinous tube, tapering to-
wards the base, where it is furnished with
_two small spines, and expanding above into
a species of toothed cup. The polypary
does not show any signs of having been
attached to any foreign body, and the sug- Fig. 96.—Corynoides cali-
gestion has been thrown out by Lapworth, age enlarged. (Origi-
that the type may be regarded as a
Graptolite which never proceeded beyond the stage of a “sicula.”

The type of the Monoprionidian Graptolites is the genus J/ono-
graptus itself (figs. 93 and 94), which is also the central genus of the
family of the AZonograpiide. In this genus the polypary is simple and
linear, possessing but a single row of hydrothecz on one side, and
commencing by an attenuated, often curved base. The polypary is
straight, curved, or helicoid in different forms ; and great variations
exist in the shape of the hydrothecze in different species (fig. 94),
these structures usually, but not always, overlapping to a greater or
less, extent. The “sicula”
is attached along the dor-
sal margin of the proximal
end of the polypary (fig.

92, -8).° All the ‘species of

Monograptus are confined

to the Silurian rocks proper

(the Upper Silurian of Mur-

chison), ranging from the

base to the summit of the

system. In the allied genus

Cyrtograptus (fig. 97) the

polypary is also unilateral, -

in so far as the hydrothecze

are produced from _ the

sicula in one direction only, Eg. alge ae et ees Car

but the polypary is now

branched. ‘This genus is also confined to the Silurian rocks proper.
Again, in the genus fastrites (fig. 98) the polypary resembles that of
Monograptus in form, but the hydrothecze are more or less linear,

216) HYDROZOA.

and are isolated from one another, instead of overlapping. ‘The
species of this genus are, like those of the preceding genera, re-
stricted to the Silurian rocks proper.

The family Zeptograptide has been founded by Lapworth for
a number of bilaterally-symmetrical branched Graptolites, which
agree with one another in having the hydrothece attached along

:

C
=
D

oS

Fig. 98.—aA, Nastrites peregrinus 3 B, Rastrites capil- Fig. 99.—Canograptus gracilis,
laris; C, Rastrites Linnet; p, Fragment of Rastrites of the natural size. sSicula. Ordo-
peregrinus, greatly enlarged. All the figures are magni- vician. (After Lapworth.)

fied. Silurian. (Original.)

the whole of one face to the coenosarc, and not overlapping. The
form of the polypary varies much in this family, consisting of two
long primary branches in Leptograptus itself, but being rendered
complex in Pleurograptus by the development of secondary branches
from each of the long primary stems, these in turn sometimes giving
off tertiary branches. In the beautiful genus Cenograptus (fig. 99),
again, the two primary stems originate from the centre of a tri-
angular sicula, and form an S-
shaped frond, the convex sides
of which give off simple branches.
All the above genera are found
in the Ordovician rocks, but do

Fig. 100.—Didymograptus V- fractus. not extend upwards into the

Ordovician (Skiddaw Slates). Silurian proper.

The great family of the Dzcho-
graptide comprises a large number of branched Graptolites, all the
forms of which are found in the Upper Cambrian and Ordovician
deposits. The simplest type of this family is the genus Dzdymo-
graptus (figs. 92, D, and 100), in which the polypary consists of two
simple branches springing from a small pointed “sicula.” The
angle included between the polypiferous sides of the two branches
(“angle of divergence”) is always less than 180°, the opposite

GRAPTOLITOIDEA. 217

angle (“‘sicular angle”) being necessarily over 180°. The species
of Didymograptus are confined to the Ordovician rocks. Closely
allied to the preceding is the genus Zetragrapfus (fig. 101) in
which the polypary consists of four simple branches springing
from a central, non-polypiferous connecting-process or ‘‘ funicle,”
which bifurcates at each end. The

base is sometimes provided with

a peculiar corneous disc, similar

to that which characterises various

species of Dichograptus. ‘The

species of TZetragraptus are all

Ordovician (Arenig). In the genus

Dichograptus (fig. 102), again, the EX

polypary consists of eight simple

branches, which arise from the

same number of divisions of a

non-polypiferous basal process or

“‘funicle.” In many cases, the di-

visions of the “‘funicle” are envel-

oped ina species of horny SFGISG ” Fig. to1.—Tetragraptus quadribrachi-
or plate (fig. 102), which is be- ere Crew
lieved to have been composed of

two lamine. The functions of this disc are doubtful, but it has
been compared with the “float” of the Portuguese-Man-of-war
(Physalia) or of Velella among the recent Oceanic Hydrosoa. The
species of Dichograptus are confined to the lower portion of the
Ordovician series (Arenig); but allied genera, in which the polypary
is irregularly branched, are found in the Upper Cambrian deposits,
and are represented in the Ordovician rocks.

The only remaining family of the Monoprionidian Graptolites is
that of the Dicranograptide, comprising the two genera Dicrano-
graptus and Dicellograptus, in both of which the polypary is com-
posed of two branches, and the terminations of the hydrothecze are
isolated and characteristically incurved, so as to bring the cell-
apertures within the line of margin of the branch (fig. 103). In
the genus Dzcellograptus (fig. 103, B) the two branches of the poly-
pary are wholly free, and diverge from a basal ‘“‘sicula,” in such
a manner as to resemble the genus Didymograptus. ‘The angle
included between the polypiferous sides of the branches (“angle of
divergence”) is, however, greater than 180°, while the opposite
angle (‘‘sicular angle”) is necessarily less than 180°. In the cu-
rious genus Dicranograptus (fig. 103, A) we have a transition be-
tween the Monoprionidian and Diprionidian groups of Graptolites,
the two branches composing the polypary being adherent by their
dorsal surfaces for a longer or shorter distance, and then diverging

218 HYDROZOA.

freely. The species of both these genera are confined to the
Ordovician rocks.

Coming next to the group of the Diprionidian Graptolites, the
typical family is that of the Diplograptide, of which the type-genus
is Diplograptus itself. In this genus the polypary (fig. 104) con-
sists—as it does in most of the genera of the family—of two sim-
ple monoprionidian branches,
which are closely united to
one another along their flatten-
ed dorsal surfaces, but are en-
closed in independent perider-
mal sheaths, and are therefore
really separate. The virgule
of the two branches coalesce,
and form a single rod-like
axis, which is embedded in a
groove between the ccenosar-
cal sheaths, and commonly
projects distally as a naked
fibre, while it appears proxi-
mally as a shorter or longer
‘‘radicle” (figs. 104 and 105).
In some of the Diplograpiide,
however, according to Lap-
worth, there is only a single
coenosarcal canal from which
the two rows of hydrothecz

Fig. 102.—Dichograptus octobrachiatus, showing the central disc. (After Hall.)
Ordovician (Skiddaw and Quebec groups).

spring. The hydrothecz themselves overlap each other to a greater
or less extent, the distal portion of each being free. The species of
Diplograptus are found in both the Ordovician and Silurian rocks.
In the nearly allied genus C/macograptus (fig. 105), the structure is
much the same as in Diplograptus, but the hydrothece are vertically
disposed, in such a manner that their mouths appear to be sunk
below the general surface of the polypary. The appearances pre-
sent by the polypary in this genus vary extremely, according to

GRAPTOLITOIDEA. ZO

the manner in which the organism has been compressed, or the
particular view of the cell-apertures which may be afforded by a
given specimen (fig. 105, C, D, E). The species of the genus are
all Ordovician and Silurian. Of the remaining genera of the
Diplograptide the only one which needs special notice is the
remarkable Dimorphograptus (fig. 92, F), in which the proximal
portion of the polypary is monoprionidian, while the distal portion
is diprionidian. ‘The polypary in its basal part thus resembles a
Monograptus, which genus it also approaches in the possession of

B

_ Fig. 103.—aA, Proximal portion ot the polypary ot Dicranograptus Nicholsoni, enlarged five
times; B, Proximal portion of the polypary of Dicellograptus complanatus, enlarged. Ordo-
vician. (After Hopkinson and Lapworth.)

an adherent “sicula”; while in its upper portion it has the char-
acters of an ordinary Diflograptus. ‘The known species of Dimor-
bhograptus are all Silurian.

Of the remaining families of the Diprionidian Graptolites, the
Laswgraptide are not thoroughly understood, but their distinguish-
ing feature is found in the fact that the biserial polypary is provided
with peculiar chitinous spines, arising from the hydrothecz, which
subdivide and inosculate with one another so as to surround the
colony with a kind of netted fringe of fine fibres. The type-genus,
Lastograptus, is Ordovician. The family of the Retiolitide is also
a peculiar one, the characteristic feature being that the periderm is
very much attenuated, and is supported upon a remarkable network

22@ HYDROZOA.

of chitinous fibres, thus producing a minutely latticed appearance
of the surface (fig. 106). According to Lapworth, the two virgulee
of the biserial polypary are separated, and are attached to opposite
sides of the peridermal network. The type-genus is Reziolizes itself,
the species of which are Ordovician and Silurian. Lastly, the family
of the Phyllograptide includes the single genus Phyllograptus, all
the species of which are confined to the lower portion of the
Ordovician system. In this genus (fig. 107) the polypary is leaf-

a N
4
| |
|
: B
: cs
A
€
iN Z*

Fig. 104.—a, Diplograptus folia- _ Fig. 105.—a, Aspecimen of Climacograptus normalis,
ceus, slightly enlarged; Bs, A Diflo- in relief and partially split in half, showing the virgula
graptus showing two long lateral embedded between the two branches of the duplex
spines, in addition to a central polypary; B, Transverse section of the polypary of the
‘“‘yadicle”; c, Base of a Dzplo- same; C, D, and £, Different views of the polypary of
graptus, enlarged. Ordovician. the same, showing the appearances produced by differ-
(Original. ) ences in the direction of compression. 7, Radicle;

v, Virgula; 4, Septum between the two halves of the
polypary; 4, Hydrotheca; 7z, Aperture. All the fig-
ures are enlarged. Silurian. (Original.)

like, and consists of four rows of hydrothecz placed back to back,
in such a manner as to resemble two Diplograpti intersecting one
another at right angles. In consequence of this peculiar structure
of the polypary, the Phyllograpit are sometimes spoken of as the
“‘tetraprionidian ” Graptolites.

The Graptolites have been considered with some detail on account
of their great importance in determining the chronological succession

GRAPTOLITOIDEA. 221

of the Ordovician and Silurian deposits, as has been amply demon-
strated by the researches of Lapworth, Linnarsson, and others.
Regarded as a whole, the Graptolites, as previously stated, are
restricted to the Upper Cambrian, Ordovician, and Silurian rocks,
but particular types have been shown to be characteristic of particu-
lar horizons in these rock-systems. This is not the place to give an
account of the general succession of the Graffolitoidea in time, or to
indicate the precise stratigraphical value of particular forms of the
group, but some general results may be briefly alluded to. The
great family of the J/onograptide is wholly confined to the Silurian
rocks proper (Upper Silurian of Murchison), the genus AZonograptus

|

\

PUL

Zz

wr

Zz

OK

y)
aN

2
D

.

Fig. 106.—Different views of portions Fig. 107.—Group of individuals of PhyZ/o-
of Retiolites venosus, enlarged nine graptus typus, from the Quebec group of
times, showing the netted periderm and Canada (after Hall). One of the four rows
the virgula. (After Hall.) of cells is hidden on the under surface.

itself extending from the base of this system to its summit. On the
other hand, the families of the Diplograptide and Retiolitide range
from the base of the Ordovician rocks to the middle of the Silurian.
The families of the Leptograptide, Dicranograptide, Lasiograptide,
and Phyllograptide are restricted to the Ordovician rocks, and the
species of Phyllograptus, the sole representative of the last of these
families, is only found in the basal beds (Arenig and Llanvirn beds)
of the Ordovician. Lastly, the great family of the Dzchograptide
commences in the Upper Cambrian period, culminates in the lower
Ordovician, and dies out altogether before the commencement of the
Silurian. The horizon of the Arenig rocks (Skiddaw and Quebec

222 HYDROZOA.

groups) is especially characterised by the presence of such genera as
Dichograptus and Tetragraptus, species of these genera being found
in rocks of this age in localities as remote as Canada, Britain, and
Australia. :

Finally, as regards the zoological affinities of the Graptolites,
paleontologists are now agreed in regarding these singular organ-
isms as an ancient and aberrant type of the Hydrozoa. In many
respects the Graptolites present a resemblance to the recent Sertu-
larians, this resemblance being shown not only in the fact that the
hydrothecze have a general likeness in form and arrangement in the
two groups, but also in the possession by certain of the former of
chitinous reproductive capsules, which admit of comparison with
the “ gonangia” of the latter. On the other hand, the polypary of
the Sertularians is always fixed, the hydrothecze are never in contact,
and the colony is not specially strengthened by a horny fibre. In
contradistinction, the Graptolites were free organisms, originating in
a basal “‘sicula,” the hydrothecz are usually (but not always) more
or less largely in contact, and the polypary is strengthened by the
peculiar chitinous rod which has been previously spoken of as the
“virgula.” In the singular recent genus Aabdopleura, one of the
marine Folyzoa, the polyzoary is strengthened by a peculiar hollow
chitinous axial tube, which has been compared by Professor All-
man with the ‘“‘virgula” of the Graptolites. There are, also, points
of resemblance between the Graptolites and those Polyzoa (such as
Vesicularia) in which the cells of the colony communicate by means
of acommon tube. None of the Polysoa, which possess a chitinous
- external skeleton, are, however, free and unattached, and the general
balance of evidence is unquestionably in favour of a reference of the
Graptolitoidea to the class of the Lydrozoa.

223

Glalwa Ie IIe ee We

TANGY RAO Z OA — Continued:
HYDROCORALLINES AND STROMATOPOROIDS.
SUB-CLASS HYDROCORALLIN-.

THE name of Aydrocoralline has been proposed by Professor
Moseley for two groups of marine Hydrozoa which produce a reg-
ular skeleton of carbonate of lime, and which, on the strength of
the skeleton alone, were formerly referred to the true Corals (Ac-
tinozoa). The two groups in question are the A/illeporide and
Stylasteride, the former being represented by the well-known JZ/e-
pora, which contributes largely to the formation of coral-reefs in
various regions. The “ccenosteum” or calcareous skeleton of
Millepora (fig. 108) is usually in the form of a foliaceous or
laminar expansion, or is simply branched, and though minutely
spongy, is of considerable density. The main mass of the skeleton
is essentially composed of a complex network of anastomosing cal-
careous fibres, so disposed as to give rise to a correspondingly com-
plex network of anastomosing and tortuous canals (fig. 109, cc). In
the living condition, this canal-system is filled with anastomosing
stolons of the ccenosarc, by which the different zooids of the colony
are placed in organic connection. The general spongy skeleton,
constituted as above described, is traversed at intervals by the
vertical tubes in which the zodids were contained. These tubes
are in two series, differing slightly in size, and they open on the sur-
face by apertures correspondingly different in dimensions, of which
the larger ones are called the “ gastropores” and the smaller the
“‘dactylopores” (fig. 108, g and @). The gastropores and dactylo-
pores may be irregularly distributed, or the dactylopores may be
arranged in more or less definite systems round the gastropores.
These two sets of tubes, as shown by Moseley, lodge respectively
larger and smaller zooids, which differ in structure and function.

224 HYDROZOA.

The large zooids (‘ gastrozooids ”) possess a mouth and digestive
cavity, and have from four to six short tentacles. On the other
hand, the smaller zoodids (‘‘dactylozooids”) have no mouth, and
possess short clavate tentacles on their sides: they are long and
slender, and perform the function of prehension for the colony.
Whatever may be the structure of the contained zooids, the zooi-
dal tubes are intersected internally by distinct transverse calcareous
partitions or “tabulze” (fig. 108, c, and fig. 109, B); but there are
no traces of radiating vertical partitions or ‘‘ septa.” The entire
coenosteum shows a more or less evident composition out of thin

Fig. 108.—a, Portion of the coenosteum of JZzllepora alcicornis, of the natural size; p, Part
of the surface of the same enlarged, showing the mouths of the ‘‘ gastropores ” (g) and “ dacty-
lopores ” (d), and the intermediate coenosteal tissue ; c, Vertical section enlarged, showing the
tabulate zodidal tubes. (Original.) >

concentric laminz, only a thin surface-layer being at any given
moment actually alive. ‘The reproductive process in AZ@illepora is
imperfectly known, but Mr Quelch has shown that in one species
of the genus the reproductive zooids are developed within special
globular cavities or “ampulle,’ which are contained within the
general spongy skeleton, and are covered by a thin porous layer.

The structure of M//lepora has been dwelt upon at some length,
as throwing considerable light upon the relationships of the extinct
Stromatoporoids, but the genus itself is of little palzeontological im-
portance. The earliest known forms of the genus appear in the

HYDROCORALLINES AND STROMATOPOROIDS. 225

Eocene rocks ; and in the same formation appears the allied genus
Axopora, which differs from MM//efora chiefly in the fact that the
tabulate zooidal tubes are traversed by a large fasciculate “ colum-
ella” or central rod. The Cretaceous genus Porosphera has been
regarded as related to JZ@//epora, but it appears to be truly referable
to the Sponges.

The second group of the Hydrocorallines is that of the Stvaster-
i@e, comprising a number of recent genera (S¢ylaster, Allopora,
Cryptohelia, Sporadopora, &c.), all of which are inhabitants of the
sea, and range from the neighbourhood of the coast-line to great
depths. The ccenosteum of the Stylasterids is calcareous, more or

B

Fig. rog.—Thin sections of MWzdlefora, sp., enlarged about thirty-five times. A, Tangential
section. B, Vertical section. g g, Gastropores; dd, Dactylopores; c c, Ccenosarcal canals.
(Original.)

less branched, forming a dendroid colony or flabellate expansion,
and exhibiting upon the surface, or on its sides, small rounded aper-
tures which usually have the appearance of being intersected margin-
ally by radiating partitions or septa, and thus simulate the “ calices ”
of an ordinary Madreporarian Coral (fig. 110). In other cases, the
surface shows a series of large apertures, with more numerous and
irregularly arranged smaller openings, the latter not being radially
arranged round the former. Thin sections of the ccenosteum (fig.
111) show that the general skeleton is composed of a dense, sub-
crystalline calcareous tissue, which is traversed in all directions by a
system of branched and anastomosing canals, which in the living
VOL. I. P

226 ; HYDROZOA.

condition are occupied by prolongations of the ccenosarc, and which
place the different zooids of the colony in direct connection. The
zooids are of two kinds, differing in size, structure, and function.
The larger zooids (‘ gastrozooids”) are provided with a mouth and
stomach-sac ; while the others (‘‘ dactylozooids”) are elongated and
destitute of a mouth, thus coming to represent tentacles in form.
The gastrozooids occupy, as in JA¢lepora, the large tubes of the
skeleton, and the dactylozooids are lodged in the small tubes.
Hence, when the dactylozooids are arranged in definite ‘‘ cyclo-
systems” round the gastrozooids, then each of the large apertures in
the skeleton comes to be surrounded by a circle of smaller elongated
pores, which are only separated laterally by thin partitions, and which

Fig. 110.—A, Portion of the ras of Stylaster sanguineus, of the natural size; B, Small
portion of a branch of the same, enlarged, showing the calices and ampulle. Living, in the
Australian seas. (After Milne- Edwards and Haime.)

thus give rise to the appearance of a central ‘ calice” surrounded by
radiated “‘septa” (fig. 111, C). In certain forms of the Stylasterids,
as in Allopora, the tubes lodging the gastrozooids are occupied in-
feriorly by a reticulate calcareous style or “columella” (a similar
structure occasionally existing in the dactylopores) ; and transverse
calcareous partitions or “tabule” are sometimes present, though
usually in small numbers. Lastly, reproduction in the Stylasterids
is effected by means of reproductive zooids developed within special
sac-like cavities or ‘ampullee,” which at certain periods communicate
with the exterior by means of minute pores.

As regards their distribution in time, a few species of Stylasterids
have been recognised in the Tertiary deposits, the recent genera

HYDROCORALLINES AND STROMATOPOROIDS. 227

Distichopora and Allopora being both represented by Tertiary forms.
There are also certain Cretaceous fossils, at present imperfectly
known, which, according to Moseley, are probably referable to this
group. The most ancient allies of the Stylasterids, however, would
appear, from the researches of the present writer, to be the singular
Triassic fossils for which Professor P. M. Duncan founded the genera

Fig. 111.—a, Vertical section ot the coenosteum of A Zlopora, sp., showing the reticulate coeno-
sarcal tissue and its canals, greatly enlarged. The section traverses a gastropore, which is seen
to be occupied below by a reticulate ‘‘columella” (s). 8, Horizontal section of the same, greatly
enlarged, intersecting one of the systems of zodidal tubes: s, Columella of the gastropore cut
across; @, One of the dactylopores cut across. Cc, Portion of the surface, enlarged, showing a gas-
tropore (g) surrounded by its circle of dactylopores (d). (Original.)

Syringosphera and Stolicskaria.1 The fossils included in these
genera are known as “ Karakoram stones,” and are found in strata
of supposed Triassic age in the Karakoram Mountains, in Kashmir.
They are spheroidal or spherical bodies (fig. 112) which vary from
an inch or less up to two inches or more in diameter, and which, in
unworn specimens, exhibit a warty, verrucose, or granular surface.
The surface also generally exhibits rounded pits or pores, which may
be uniformly distributed, or which are specially developed along
the equatorial diameter of the fossil. There are no traces of any
mark of attachment, and the organism must have been free. The

1 In 1865 Professor Reuss published descriptions and figures of some fossils.
from the Alpine Trias, for which he proposed the generic name of Heterastridium
(Sitzungsberichte der Wien Akad. Bd. 51, p. 385, Pls. I.-1V., 1865). It is clear
from these that Heterastridium is very closely allied to Stoltczkaria, if not abso-
lutely identical with it. In case of the identity of these two genera being estab-
lished, the name of Stoliczkaria will have to be abandoned in favour of that of
Fleterastridium, the latter having been published first.

228 HYDROZOA.

skeleton is calcareous, and its general substance is composed of a
characteristic, cancellated or tubulated ccenosarcal tissue, closely
resembling the ccenosarcal
tissue of Parkeria. ‘The tu-
buli of the general ccenosteal
tissue have a radial direction
from the centre to jthemene
cumference, as in Parkeria,
but there is no marked ar-
rangement into concentric
layers. As seen in cross-sec-
tions (fig. 113, A) this tubu-
lated tissue exhibits a char-
of ie dative ete the tieakereetcageim acteristic netted “appearance.
mir. The surface of the specimen is much worn, The general cancellated tissue
(Otel) the apertures of the zodidal tubes. of the skeleton is traversed by

numerous comparatively large
radiating tubes (fig. 113, 7), which open on the surface by the
rounded apertures above spoken of, and which may be regarded as

zooidal tubes. ‘These tubes, in some cases at any rate, are of differ-

(aa) A G CO B E

Fig. 113.— Minute structure of Stodiczkaria. a, Section of the skeleton taken tangentially to
the surface, enlarged twenty-five times, showing the general cancellated ccenosarcal tissue (¢) and
the transversely-divided zodidal tubes (¢) with their reticulate columellz (co); 8, Vertical section,
similarly enlarged, the letters as before. (Original.)

ent sizes, and correspond with the ‘“gastropores” and “ dactylo-
pores” of the Stylasterids, and each is provided with a reticulate
central style or “columella” (fig. 113, co). In cross-sections the

STROMATOPOROIDEA. 229

tubes often show the appearance of short inward projections, which
have the aspect of the radiating “septa” of a coral, but which are
doubtless of a wholly different nature.

The general structure of the skeleton in Stoficzkaria, and appar-
ently in Syzingosphera also, is thus in many respects similar to that
of the recent genera A//opora (fig. 111) and Sporadofora among the
Stylasterids. These singular organisms may therefore be regarded
as being referable to the Hydrocorallines, and as being related to the
Stylasteride. From these, however, they differ in their free habit,
and in the peculiar radial tubulation of the ccoenosarcal tissue ; and
they may thus be properly considered as constituting a special family,
to which the name of Syringospheride, proposed by Professor
Duncan, may be given. The resemblance between Séoliczkaria and
Syringosphera on the one hand and Parkeria on the other hand,
though superficially close, is not dependent on real identity of struc-
ture. They agree inthe general nature of the ccenosarcal tissue ; but
the skeleton in Parkeria is composed of concentric layers, separated
by tiers of chamberlets or by “interlaminar spaces,” and is traversed
by numerous radial pillars, while the zooidal tubes are irregular and
are devoid of a columellar style.

SUB-CLASS STROMATOPOROIDEA.

The Stromatoporoids constitute a large group of extinct Hydrozoa,
which, so far as certainly known, are confined to the Ordovician,
Silurian, and Devonian rocks. ‘The ccenosteum in the forms in-
cluded in this group is calcareous and often of large size; and
some of the limestones of the Silurian and Devonian period are
very largely made up of the skeletons of these organisms. The form
of the skeleton and the mode of growth are extremely variable, but
the most typical condition of the ccenosteum is that of a spheroidal
or irregular mass, or of a flattened expansion, attached basally to
some foreign body, and exhibiting a more or less conspicuous com-
position out of concentric calcareous laminze (fig. 114). In some
cases the skeleton is branched and dendroid, and in others it forms a
thin crust growing upon foreign bodies. In this latter case, as well
as in some massive types, the organism is attached by the whole of
its under surface ; but more usually the attachment is by a peduncle,
and the greater portion of the basal surface is covered by a thin,
concentrically wrinkled, calcareous membrane or “‘ epitheca.”

As regards the general structure of the skeleton of the Stromato-
poroids, the most obvious feature is that it is composed of numer-
ous concentric layers or “laminz,” which are separated by narrow
intervals or ‘‘interlaminar spaces.” In reality, however, the actu-
ally fundamental element in the skeleton is not found in these con-

230 HYDROZOA.

spicuous concentric laminze but in a series of vertical calcareous |
rods (‘radial pillars”), which are directed at right angles to the
lamine. The “lamine,” in fact, are not continuous calcareous
layers, but are in most cases really formed by numerous irregular
calcareous rods or processes which are given out by the “pillars” at
definite levels, and which join with one another and with the pillars
to form a reticulated or porous membrane. Hence, in a typical
Stromatoporoid, the last-formed concentric lamina, which consti-
tutes the outer surface of the organism, exhibits numerous minute
pores, which open internally into the uppermost “interlaminar

Fig. r14.—A specimen of a Stromatoporoid, of the natural size, showing the concentrically
laminated skeleton. ‘The under surface is concave and was probably attached to a foreign body.
From the Trenton Limestone of Canada. (After Billings.)

space,” and which probably served to give exit to the zooids of the
colony. The outer layer also commonly shows numerous small
granules or tubercles, which are really the free upper ends of the
vertical or radial pillars. These last-named structures are small cal-
careous columns, which have a general radial direction, and which
cross the interlaminar spaces vertically and thus connect successive
concentric laminge with one another. In some cases (as in the
genus Clathrodictyon) the pillars are merely short perpendicular
processes which run from the upper surface of one lamina to the
under surface of the next. In other cases (as in the genus Actn-
ostroma, fig. 115, B and c) the pillars run continuously through a con-
siderable number of laminz. In many cases, it can also be shown

STROMATOPOROIDEA. 231

that the radial pillars contain in their interior a minute axial canal
(as in Ladechia, fig. 116, A), but there is no ground for supposing
that this opened upon the surface by any aperture.

The zooids which composed the colony of the Stromatoporoids
were sometimes merely lodged in the pores which pierce the reticu-
‘lated concentric laminz, and there are no definite ‘“ zooidal tubes”
(fig. 115, A). In other cases, such tubes are present ; though their re-
cognition is not always easy, and they are often very irregular.
When well developed, the zooidal tubes are usually intersected by

IISLX AINE SRITEAS
BRIS ERB AY
¥ KIO PFW? PF
» tars:

was PS &S U A-4, ; @
Beet ae: neat Pe
Sb eee

SRS ae x on
SS woke

Fig. 115-—A, Tangential section of Actinostroma intertextum, showing the transversely-di-
vided radial pillars and the reticulated structure of the concentric laminz. , Vertical section of
the same, showing the radial pillars and the formation of the concentric lamine out of processes
which are given out horizontally by these. Enlarged twelve times. cand D, Parts of the same
sections enlarged further. From the Silurian rocks. (Original.)

a number of transverse calcareous partitions or “tabulz” (fig. 119,
B and D). In no case are the zooidal tubes provided with radi-
ating vertical partitions comparable with the “septa” of corals. It
would seem certain that in all the Stromatoporoids the part of the
colony which would be at any given moment actually alive, must
have been restricted to a thin external layer.

Among the more noticeable features presented by the Stromato-
poroids are the so-called “‘astrorhize” of many types. These are
stellate, often much branched, gutters or grooves which are found on
the external surface of the last-formed lamina, each stellate system
being placed at a little distance from its fellows. As each lamina

222 HYDROZOA.

of the colony has at one time formed the external surface, the ex-
terior of each exhibits astrorhizze, as a rule, when the specimen is
broken open. Very commonly, also, the astrorhize are placed in
successive groups one above the other, those of each vertical system
being united by a wall-less axial tube, which usually opens on the
outer surface by an aperture, which is often placed at the summit of
a conical or rounded prominence. The astrorhizal canals of the
Stromatoporoids may
be compared with the
peculiar grooves seen
on the externalsurface
of the crusts of the
recent Lydractinia, or
with the branching
and inosculating coen-
osarcal canals of AZz/-
lepora, and, like the
latter, they probably
transmitted stolons of
the coenosarc.

The Stromatopo-
roids may be divided
into two great groups,
the forms of one of
these having a resem-
blance to Hydractinia
in the structure of the
skeleton, while those
of the other possess
a coenosteum con-
structed more nearly
after the type of that
of A@illepora. In the
first of these primary

Fig. 116.—a, Tangential section of the Saar Cs a sections the skeleton
bechia conferta, from the Wenlock Limestone (Silurian), 5 :
enlarged twelve times. The section shows the transversely (as in Actinostroma,
divided radial pillars (J), with their axial canals, and their con- fig. Lit5: and Labechia,
necting processes (c). 3B, Vertical section of the same, simi- 2
larly enlarged, the letters as before. (Original.) fig. It 6) 1S composed

of ‘radial pillars ”
and ‘concentric lamine,” which remain definitely recognisable and
do not become fused with one another into a continuous reticulation.
The type of this section is the genus Actinostroma, in which the
Ccenosteum is massive or laminar, often of large size, and the
radial pillars are long and are continued without a break through
numerous successive lamine (fig. 115, B). The concentric lamine

STROMATOPOROIDEA. 220

are formed by radiating processes given out in whorls at definite
levels from the radial pillars, and uniting with one another in such
a way as to give rise to an angular meshwork. Hence, horizontal
sections of the species of this genus (fig. 115, A and c) exhibit
a structure not at all unlike that of a Hexactinellid Sponge, the
cut ends of the radial pillars constituting so many centres from
which the horizontal processes forming the laminze are given out
in a stellate manner. The earliest types of Actinostroma appear
in the Silurian rocks, but the genus is characteristically Devonian.
In the nearly allied genus Clathrodictyon, the radial pillars are com-
paratively ill developed, and do not pass from one interlaminar space
to another. The species of this genus, though not absolutely unrep-
resented in the Devonian, are characteristic of the Silurian period.

The singular genus ZLadechia is the type of another group of
Stromatoporoids. The ccenosteum in this genus (fig. 117) is usually
laminar, attached by a peduncle, and
having the under surface covered with
a wrinkled calcareous membrane or
“‘epitheca.” The upper surface shows
no traces of pores or zooidal apertures,
but is covered with numerous blunt
tubercles. Vertical sections (fig. 116, B)
show that these tubercles are the free :
upper ends of stout radial pillars, which Lee Cae
femmecemlccred with) one another by rcks of Gotland, ofthe natural size,

snowing the epithecate under side
numerous arched calcareous plates. and the tuberculate upper surface.
Horizontal sections (fig. 116, a) show ("sina
the cut ends of the radial pillars, united by the calcareous plates
above spoken of. The pillars are hollow, with a minute axial
canal, but they do not seem to be naturally perforated at their
summits. In the absence of definite zooidal pores, it must be
supposed that the surface was covered with the ccenosarc, from
which the polypites were budded off. The genus Ladechia ranges
from the Ordovician to the Devonian, and the allied Rosenel/a is
found in the Ordovician and Silurian rocks.

In this connection a few words may be here said with regard to
the extraordinary and problematical fossils from the Ordovician rocks
of North America for which Mr Billings founded the genus Beatricea.
The fossils in question have the form of cylindrical or angular stems
(fig. 118), which are nearly straight, are unbranched, and may attain
a length of several feet. The outer surface sometimes shows small
rounded tubercles, or may exhibit minute circular apertures, the
nature of which is quite uncertain. ‘Transparent transverse and
vertical sections (fig. 118, B and c) show that the fossil is prin-
cipally made up of a thick outer sheath of lenticular calcareous cells

234 HYDROZOA.

or vesicles, which are arranged in concentric layers round a large
axial tube running the whole length of the organism. This axial
tube is intersected by strongly curved calcareous partitions or
“tabule” ; and the vesicular tissue which surrounds it is sometimes
found to be traversed by columns which radiate outwards to the cir-
cumference, and which may be compared with the ‘radial pillars”
of Labechia. Upon the whole, with our present knowledge, it would

ee 8 fo,

Gin
ae Pee
sf FI esi ot e Ye.
x cae
f ie é % x, : Sy ee
CAR PN RRS
a: f Pe ? : SE <
‘is os
x Vv ; or 2
4
4 ane fe if raat i f
gM 4 meth Oh edé
py LEAS ae a ~
SS, AGN
ua s 1 So ncacalt
oO Sp ace
B e In be as ee 2
RASS Sw a
ee Bry h

Salt ay teak Wi a deataaa te Ta T
EN nx

{ATONE AOSTA SE™
=o erin
Sains.

rigor
wim ep
aay SS

rae
ae

N a
¢

Fig. 118.—a, A fragment of Beatricea undulata, slightly less than the natural size, from the
Ordovician rocks (Cincinnati Group) of North America. B, Cross-section, and c, Vertical section

of Beatricea nodulosa, from the same formation, slightly enlarged. The sections show the
peripheral vesicular tissue and the central tabulate tube. (Original.)

seem best to regard Beatricea as a very abnormal type of the Stro-
matoporoids, with relationships to Lavechia and /diostroma ; but the
position of this anomalous genus must be regarded as more or less
doubtful. |

The remaining forms of the Stromatoporoids present certain strong
resemblances in their structure to the existing genus J///egora, and

STROMATOPOROIDEA. 235

differ from the types previously considered in the fact that the radial
pillars and concentric laminz are so combined with one another as
to lose their distinctness as separate elements, and to become fused
with one another so as to form a continuously reticulated skeleton.
Moreover, the skeletal tissue has a peculiar microscopic structure,
being minutely porous or tubulated (fig. 119, a and B). Definite
zooidal tubes are also present, and these are crossed by more or less

Fig. 119.—a, Tangential section of Stromatopora Beuthii, enlarged twelve times, showing the
reticulate skeleton and the porous skeleton-fibre ; B, Vertical section of the same, similarly en-
larged, showing the tabulate zoédidal tubes; c and p, Tangential and vertical sections of Stvom-
atopora bicheliensis, similarly enlarged. Middle Devonian. (Original.)

extensively developed transverse partitions or “tabule” (fig. 119,
Band Dp). ‘The type of this group is the genus Stvomatofora itself,
in which the ccenosteum is massive or laminar and is usually fur-
nished with an epitheca. The skeleton is completely reticulate, the
radial pillars and their connecting-processes being completely fused
with one another, so as to give rise to a vermiculate tissue traversed
by minute, irregular, tabulate zodidal tubes. Very commonly, the

236 HYDROZOA.

massive skeleton is formed of a series of thick concentric strata
(“latilaminz”), each of which is made up of subordinate concentric
“Jamine.” The type of this genus is the Stvomatopora concentrica
of Goldfuss, a comparatively rare species in the Middle Devonian
of Germany and Britain. Upon this species Goldfuss founded the
genus Stromatopora, but the name has been erroneously given to
various Stromatoporoids of quite different affinities. Other species
of Stromatopora are found in the Silurian and Devonian rocks ; and
the allied genus Stromatoporella appears to be principally if not
wholly Devonian.

Lastly, there is a group of Stromatoporoids, represented by genera
such as /diostroma and Amphipora, in which the skeletal tissue re-
sembles that of Stvomatopora in its reticulated character, but the
coenosteum is cylindrical and often branched, and is provided inter-
nally with a comparatively large axial tube intersected by cross
partitions or “‘tabule.” The genera above-mentioned are both
Devonian, and the sole known species of Amphipora (viz., A.
ramosa) is an abundant and characteristic fossil in the Middle
Devonian of Germany and Britain, its slender cylindrical stems
occurring in great abundance in particular beds in this formation.

Before leaving the subject of the Stromatoporoids, allusion may be
made to the fossils which have been described under the name of Cauno-
pora. The fossils in question resemble the ordinary Stromatoporoids,
and indeed ave only Stromatoporoids of various species, with the pecu-
liarity that the general tissue of the ccenosteum is traversed by a number
of comparatively large, thick-walled vertical tubes, which open on the
surface by definite round apertures. These tubes often spring at the
base from horizontal stolons, and are usually connected here and there
by lateral tubes of a similar structure to themselves ; they usually, if not
always, have funnel-shaped, or sometimes horizontal, internal calcareous
partitions or “tabule,” and they occasionally possess rows of short
‘septal spines.” It has been shown that the same species of Stromato-
poroid may occur with or without these peculiar “‘ Caunopora-tubes,” and
there exists further an obvious likeness between these tubes and the
corallites of such corals as Aulopora and Syringopora. Upon the whole,
therefore, it may be regarded as probable, if not absolutely certain, that
the fossils usually grouped together under the name of “‘ Caunopora” are
Stromatoporoids which in course of growth have enveloped a colony of
some such coral as an Auwlopora or Syringopora, the latter not being
thereby killed, but continuing to grow and flourish as a “commensal”
within the tissues of the Stromatoporoid.

As regards the zoological affinities of the Stromatoporoids, their
general structure seems to render it certain that they are referable to
the Aydrozoa, of which they must be considered to form a special and
now unrepresented group. Certain forms (such as Actinostroma and
Labechia) show a decided relationship with the recent Aydractinza ;
while others (such as S¢vomatopora itself) are more closely connected

EIDE RATURE OF EMDROZOA. 23/7

with the Hydrocorallines, and especially with JZi/lepora. ‘These two
groups of Stromatoporoids are, however, united by various transi-
tional forms, and they possess structural peculiarities of sufficient
importance to preclude the reference of the entire series to any exist-
ing division of the Hydrozoa.

As to their general geological distribution, the Stromatoporoids are
not certainly known as occurring out of the Ordovician, Silurian, and
Devonian formations. Very few forms have yet been recognised in
the Ordovician rocks, but the genus Ladechia is well represented in
strata of this age. The aberrant genus 4eatricea is also Ordovician.
In the Silurian rocks, Stromatoporoids are exceedingly abundant,
often entering largely into the composition of the limestones of this
period. ‘The predominant Silurian genus is Clathrodictyon, but the
genera Actinostroma, Stromatopora, and Ladbechia are also represented.
It is, however, in the Devonian rocks, and particularly in the Middle
Devonian, that the Stromatoporoids attain their maximum develop-
ment, the group being represented in strata of this age by numerous
species of Actinostroma, Stromatopora, and Stromatoporella, as well
as by forms of /dostroma, Amphipora, &c. Stromatoporoids have
been said to occur in the Carboniferous rocks, but the true nature of
these has not as yet been satisfactorily investigated. There are also
certain Secondary fossils which, on further examination, may prove
to be referable to the present group.

PGE RAO, OF EL DROZO A:

I. CORYNIDA.

1. “ Fossil Hydractiniz.” ‘Geological Magazine,’ 1872. Allman.

“On the close Relationship of Hydractinia, Parkeria, and Stromato-
pora, with descriptions of new species of the former, both recent
and fossil.” “Annals Nat. Hist. 1877. Carter.

. “On New Species of Hydractiniidz, Recent and Fossil.” ‘Ann. Nat.

Elise,” 1676. Carter.

4. “ Description of Parkeria and Loftusia.” ‘Phil. Trans.,’ 1869. W.
B. Carpenter and H. B. Brady.

. “On the Structure and Affinities of the Genus Parkeria.” ‘ Annals
Nat. Hist.,? 1888. Nicholson.

6. “On certain anomalous Organisms which are concerned in the for-
mation of some of the Palzozoic Limestones.” (Mitcheldeania
and Solenopora.) ‘Geol. Magazine,’ 1888. Nicholson.

7. “ Ueber fossile Hydrozoen aus der Familie der Coryniden.” ‘ Pale-
ontographica,’ Bd. 25, 1877. Steinmann.

N

Go

ww

II. THECAPHORA AND GRAPTOLITOIDEA.

co

. “Graptolites de Bohéme.” Barrande. 1850.
9. “ Ueber Graptolithen.” Scharenberg. 1851.

238 HYDROZOA.

Io.

Iflic

“ Die Graptolithen. Versteinerungen der Grauwacken-formation.
Geinitz. 1852.

“‘ Graptolites of the Quebec Series.” ‘ Descript. of Canadian Organic
Remams. Decade un.” Halll 1365:

. “Monograph of the British Graptolitide.” Part 1., General Intro-

duction. Nicholson. 1872.

. “ Notes on the British Graptolites.” ‘ Geol. Mag., 1873. Lapworth.
. “On the Geological Distribution of the Rhabdophora.” ‘ Annals

Nat. Hist.,’ 1880. Lapworth.

. “On new British Graptolites.” ‘Annals Nat. Hist.,’ 1880. Lapworth.
. “On Scottish Monograptide.” ‘Geol. Mag.,’ 1876. Lapworth.
. “The Geology and Paleontology of the West of Scotland.” ‘Cata-

logue of the Western Scottish Fossils, 1876. Lapworth.

. “On the Graptolites described by Hisinger and the older Swedish

Authors.” 1882. Tullberg.

. “ Die Graptolithen-familie Dichograptide.” 1885. Herrmann.

III. TRACHYMEDUS# AND LUCERNARIDA.

. “Ueber fossile Medusen.” ‘Zeitschr. fiir Wiss. Zool.” 1865 and

1870. Haeckel.

. “ Ueber fossile Medusen.” ‘ Mém. Ac. imp. de St Petersbourg, 1871.

Brandt.

. “Om Aftryck af Medusor i Sveriges Kambriska Lager” (On Impres~

sions of Medusze in the Cambrian Rocks of Sweden). ‘ Kongl.
Svenska Vetenskaps-Akad. Handlingar, 1881. Nathorst.

IV. HYDROCORALLIN~.

. “Contributions to the Natural History of the United States.” Louis.

Agassiz. (The animal of A/zl/epora is figured, vol. i1., pl. xv., and.
the genus is referred to the Hydrozoa.)

24. “ Observations critiques sur la classification des Polypiers paléo-~

zoiques.” Compt. end? 1. bac, 1875. Dollius:

. “ Notes on Two.Species of Millepora,” &c. ‘Phil’ Trans; rages

Moseley. (This memoir also contains a note on the structure of
a Stylaster.)

. “Structure of a Species of Millepora occurring at Tahiti.” ‘ Annals.

Nat. Hist.,’ 1876. Moseley.

. “ Preliminary Note on the Structure of the Stylasteride.” ‘ Annals.

Natt. selisie alo 77s ee VLOSelLe ye
“On the Actinozoan Nature of Millepora alcicornis.” ‘Annals Nat.
Hist.,’ 1876. Nelson and Martin Duncan.

. “On the Structure of the Stylasteride.” ‘Phil. Trans.,’1878. Moseley..
. “Report on certain Hydroid, Alcyonarian, and Madreporarian

Corals.” ‘Report on the Scientific Results of the Voyage of
H.M.S. Challenger,’ vol. 1. 1881. Moseley.

. “Scientific Results of the Second Yarkand Mission ” (Syringospher-

idz). 1879. P. Martin Duncan.

. “On the Genus Stoliczkaria and its Distinctness from Parkeria.”

“Quart. Journ. Geol Soc. od2,, (Po Ve Duncan:

. “ Zwei neue Anthozoen aus den Hallstadter Schichten.” ‘ Sitzungsbe-~

richte d. k. Akad. d. Wiss. Wien., Bd. 11., 1865. Reuss.

LITERATURE OF HYDROZOA. 239

V. STROMATOPOROIDEA.

. “ Petrefacta Germaniz.” Goldfuss. 1826.
. “ Ueber die Natur der Stromatoporen.” Von Rosen. 1867.
. “ Die Stromatoporen des rheinischen Devons.” Bargatzky. 1881.

. “ Monograph of the British Stromatoporoids.” ‘ Palzeontographical

Society.’ Part I. General Introduction. 1886. Nicholson.

. “On some new or imperfectly known species of Stromatoporoids.”

‘Annals Nat. Hist.,’ 1886, 1887. Nicholson.

240

Cll AEP Ros Vale

SUB-KINGDOM C@LENTERA TA—continued.
CHARACTERS, STRUCTURE, AND DISTRIBUTION OF THE ACTINOZOA.

THE division of the Actznozoa comprises the Sea-anemones, the
Corals, and various allied forms, and is defined as including
Celenterate animals in which the mouth opens into an esophageal
tube, which in turn opens below into the general cavity of the body
(“‘ceelenteric space”). The esophagus ts separated from the body-wall
by an intervening “ perivisceral space,” which ts divided into a series
of compartments by radiating vertical membranous partitions or
“« mesenteries,” to the faces of which the reproductive organs are
attached.

The Actinozoa differ, therefore, fundamentally from the Aydrozoa
in this, that whereas in the latter the space (“ccelenteric” space)
included within the body-walls is simple and undivided, and there
is no proper alimentary tube, in the former there is a distinct
cesophagus (fig. 120, g), and the general cavity of the body is di-
vided into radial compartments by vertical membranous plates
(‘‘mesenteries ”).

The tissues of the Aczéznozoa consist of an external “ ectoderm ”
and an internal ‘‘endoderm,” between which is developed an in-
termediate layer or “‘mesoderm” (the “‘mesoglcea).. The ectoderm
covers the entire outer surface of the organism, and is prolonged
inwards at the mouth to form the lining of the cesophageal tube,
while the endoderm lines all the internal cavities of the body.
Both the ectoderm and endoderm are primitively cellular, but both
are liable to undergo more or less differentiation, muscular fibres,
nerve-cells, thread-cells, &c., being developed in process of growth.
The mesoderm is essentially composed of connective tissue, and
forms an intermediate layer (the ‘“‘Stiitz-lamelle” of the Germans)
which gives stability to the soft body of the animal.

The Actinozoa may be simple, as in the Sea-anemones, the organ-

ACTINOZOA. 241

ism consisting of a single “‘polype” ; or they may be composite, the
organism being composed of more or less numerous polypes con-
nected with one another directly, or united by a common “ cceno-
sarc.”

Taking a simple Actinozoon, such as a Sea-anemone (fig. 121),
as the type of the class, the body is seen to form a cylindrical tube,
the walls of which are
formed by the three layers
above spoken of, enclos-
ing an internal cavity
(the ‘‘visceral chamber”).
The base of the cylinder
is usually completely
closed, and often forms
a muscular disc of attach-
mene, (“pedal disc ”).
The distal end of the
cylindrical body, on the
other hand, is perforated
centrally by the oval fis-
sure of the mouth, and
is furnished round its
margin with a series of
hollow, muscular and tac-
mia tentacles.”. The
mouth opens into a mem-
branous cesophageal tube,
formed by an infolding
of the ectoderm and co .
endoderm, which hangs Fis 199A polypeof dstepdes esendaris argzent
down into the body- phagus ; w, Body-wall ; #e, Flat face of a mesentery ; /,

ae : Edge of a mesentery ; sf, One of the calcareous “‘septa”’
cavity, and terminates at ofthe corallum, intervening between the mesenteries; 7,

Beetartiemes above the | Rerotntve rans cn Coralinms ca, Columellas cr
proximal extremity of the ©

animal in a wide aperture by which it communicates freely with
the general cavity of the ‘ visceral chamber.”

The general space (“visceral cavity”) included within the body-
walls is subdivided into radiating compartments by a series of ver-.
tical membranous partitions, which spring from the body - wall
internally and are directed inwards, constituting what are known
as the ‘mesenteries.” Some of these partitions—known as the
“principal” or ‘‘ primary” mesenteries—extend all the way from
the body-wall to the side of the cesophagus ; and in the Adyonaria
all the mesenteries do so. In most cases, however, there are shorter
mesenteries, which fall short of the gullet, and which-are known as.

VOL: 5. Q

Z2A2 CGELENTERATA.

“secondary” and “tertiary” mesenteries according to their relative
length. Below the level of the bottom of the cesophagus the inner
edges of even the principal mesenteries are free (fig. 120, f); and
the intermesenteric compartments thus all open freely into a com-
mon space, while they may also communicate with one another by
means of perforations in their bounding mesenteries, placed near
the point where the latter join the upper end of the gullet. Lastly,

Fig. 121.—A, Actinia mesembryanthemum, one of the Sea-anemones (after Johnston); B,
section of the same showing the mouth (q@), the cesophagus (4), the body-cavity (c), and one of
the mesenteries (7).

attached to the faces of certain of the mesenteries, towards the
lower end of the body, are the band-like reproductive organs (fig.
1y2Os, 7)

As regards the development of the mesenteries, Lacaze-Duthiers has
shown that in the Actinzde and in Astrozdes the first step is the appear-
ance of a single pair of mesenteries developed at right angles to the oral
fissure, nearer to one side than the other, so as to divide the body-cavity
into two unequal chambers (fig. 122, 1, 1). In the larger of these cham-
bers appear the two next mesenteries (2, 2), one on each side. Two
additional mesenteries (3, 3) next appear in the smaller chamber, this
making in all szv mesenteries ; but this condition is evanescent, and two
further septa (4, 4) are developed on the opposite side of the first-formed
mesenteries to the third pair. At this stage, therefore, there are ezghz
mesenteries in all (fig. 122); but two further pairs of mesenteries are
produced, raising the number to Zwe/ve, and completing the series of the
“¢ principal” mesenteries.

According, therefore, to the observations of Lacaze-Duthiers, the
twelve “ principal” mesenteries of Astrozdes are developed in six pairs,
which are produced independently and at separate times; and this
arrangement seems to hold good in the typical Sea-anemones. The
two pairs of “ principal” mesenteries which correspond with the opposite
extremities of the longitudinal mouth, are known as the “ directive” mes-
enteries. The twelve mesenteries which succeed the twelve “ principal”

ACTINOZOA. 243

mesenteries, are developed in pairs in the interspaces between the six
pairs of the latter, and additional pairs may be subsequently developed
in a similar manner in cycles; but no new mesenteries are produced
in the chambers included between the two laminz which form each
pair of “principal” mesenteries.

On the other hand, according to the views of Milne-Edwards and
Haime, the mesenteries of the Sea-anemones, and of the ordinary
Zoantharian Corals, are developed in a primary cycle of six, to which a
second cycle of six is soon added. Should a further development of
mesenteries take place, a third cycle of twelve is produced, the new
laminz being formed simultaneously in the intervals between those
already in existence; and any further production of mesenteries is

Fig. 122.—Embryo of a Sea-an-

emone (Actinia mesembryanthe- Fig. 123. —Calcareous spicules

weunz), in which the first eight septa
have been developed (after Lacaze-
Duthiers). The numerals indicate
the order in which primitive septa
make their appearance.

(‘‘ dermosclerites’’) of the Gor-
gonide, greatly enlarged. aA, Gor-
gonia radula; B, Sclerogorgia
suberosa; C, Melithea ochracea.

(After Kolliker.)

supposed to take place in obedience to the same general law. So far
as the later cycles of septa in the Hexacoralla are concerned, the general
law has been laid down by von Koch that each new septum is produced
in the interspace between two older ones, and the septa of each succes-
sive cycle are produced, approximately, simultaneously.

In certain of the Actznozoa, such as the Sea-anemones, and the
Ctenophora, the body remains permanently soft; but most of the
animals belonging to this class produce hard structures, which vary
much in different cases, and are known by the general name of
the “corallum.” The simplest form of the corallum is that of de-
tached microscopic “spicules” of carbonate of lime, which are
more or less largely developed in the soft tissues, but do not unite
with one another to form a coherent skeleton. Such spicules are
of common occurrence in the Alcyonarians, and their shape (fig.
123) varies greatly in different types. They are most abundantly
developed in the ccenosarc, but may also be present in the walls
of the polypes. Though usually permanently separate, the spicules
may become so far fused with one another as to give rise to a
coherent external skeleton, as occurs in the Organ-pipe Corals
(Zubipora).

244 CCELENTERATA.

In other cases, as in the Red Coral (Corallium), the spicules
become fused so as to form a solid cylindrical calcareous axis, which
occupies the centre of the ccenosarc (fig. 124). Such a coenosarcal
axis 1s produced independently of the polypes of the colony, and
constitutes what is known as a ‘“sclerobasic” corallum. The form
of the sclerobase or axial corallum is simple or branched, in accord-
ance with the undivided or divided condition of the ccenosare ; and
its precise structure is very variable. In Corallium it is formed of
microscopic spicula united by a general calcareous matrix; but in
other cases the uniting matrix may be horny, while in the Anmz-

eed = 7
LAST
RYAN
y Yeap”
RAS
@
~ GO

Fig. 124.—A portion of a colony of Red Coral (Coraliium rubrum), longitudinally divided,
and having part of the ccenosarc with its embedded polypes removed. (After Lacaze-Duthiers.)
co, Coenosarc, with its embedded polypes, its outer portion traversed by reticulate canals; s, Sclero-
basic corallum, grooved for the reception of a series of longitudinal coenosarcal canals (ca); £ A,
Polypes having their tentacles (¢) protruded; @, Gullet; A’ 2’, Polypes retracted within the
coenosarc.

pathide and in many of the Gorgonide the sclerobase is not formed
by the fusion of calcareous spicules, but is the result of the secretion
of horny matter in successive concentric layers.

In the great majority of the coralligenous Actimozoa the corallum
is calcareous, and is not formed by the fusion of definite ‘ spicula,”
but is the result of the secretion of carbonate of lime by the outer
surface of the ectoderm. Such a corallum has been commonly
spoken of as “ sclerodermic.” The actual calcareous tissue (‘ scler-
enchyma”) which constitutes an ordinary Madreporarian coral has
a peculiar microscopic structure, appearing as if formed of bundles
of minute calcareous fibres, and commonly having a sub-crystalline
character. When these bundles of fibres are cut across transversely
(fig. 125, A), they give rise to a characteristic stellate structure, which
in some cases (¢.¢., Stylophora, Pocillopora, &c.) is of a very regular

ACTINOZOA. 245

nature. In many instances the entire corallum of a Madreporarian
consists of the ordinary fibrous sclerenchyma just alluded to. It is
not unusual, however, to find that in progress of growth the original
skeleton becomes thickened, and its internal cavities more or less
restricted, by a deposition of carbonate of lime of secondary origin.
This secondarily-formed calcareous tissue has been termed “stereo-
plasma” by Lindstrom, and it is often of lighter colour than the
sclerenchyma of the original skeleton (fig. 125, B), or is otherwise
distinguishable from the latter.

An ordinary sclerodermic coral may consist of a single cuplike
‘structure corresponding with a single polype, or of several such,

Fig. 125.—A, Portion of a tangential section of the corallum of the recent Stylophora palmata,
enlarged, showing the fibro-crystalline structure of the sclerenchyma. B, A few corallites of
Pachypora Nicholsont, Frech, transversely divided and considerably magnified, showing the
primordial wall (vw) and the dense lining of secondary ‘‘stereoplasma” (s). From the Middle
Devonian of Gerolstein. (Original.)

springing directly from one another, or united by a common cal-
careous tissue (“‘coenenchyma”) corresponding with the coenosarc
of the colony.

A typical simple sclerodermic corallum (fig. 126) is secreted by a
single polype, and its structure presents an obvious correspondence
with that of the animal which produces it. It is generally more or
less conical in shape, or sometimes discoid, and consists of an outer
wall and included space. ‘The wall corresponds with the lower part
of the column of the polype, and is known as the “theca.” It may
be very imperfect, or may be strengthened by a secondary calcareous
investment (“‘epitheca”). The theca encloses a space which cor-
responds with the lower part of the body-cavity of the polype, and
is known as the “visceral chamber.” Superiorly the theca termi-
nates in a shallower or deeper, cup-shaped depression, which contains
the cesophagus of the polype, and is known as the “‘calice.” Below

246 CCELENTERATA.

the calice, the visceral chamber is subdivided into a number of
vertical compartments (“loculi”) by a series of upright calcareous
partitions or “septa,” which spring from the inner surface of the
theca, and are directed inwards towards the centre. The septa are
calcifications formed within the intermesenteric chambers (fig. 120,
sp), so that each septum is placed between two mesenteries and
underneath a tentacle, and the total number of the septa is equal
to that of the mesenteries. The septa likewise increase in number
with the increasing growth of the polype, as the mesenteries do ;
and, like the latter, they vary in their width, so that they are often
spoken of as “‘ primary,” “ secondary,” and “ tertiary” septa.

The septa of both recent and fossil corals, when examined in cross-
sections, commonly show a composition out of two lamellz of dense,

Fig. 126.—Caryophyllia borealis. A simple sclerodermic Coral, twice the natural size.
(After Sir Wyville Thomson.)

usually light-coloured sclerenchyma (“ stereoplasma”), separated by a
median, generally dark line (fig. 127). .

This central dark line (the “ Primarstreif” of the Germans) has been
regarded as a mere line of calcification ; but it seems to be really a dis-
tinct median lamella, representing the primordial septum, while the
lateral layers of stereoplasma are of secondary origin. In some cases
(as in Caryophyllia borealis, fig. 127, A), it appears that this central plate
is itself double, and it is probable that it is always so in origin, even
though its component elements become completely fused in process of
growth.! In other cases (as in Helzophyllum and its allies), the septa

1 Hinde has clearly shown that the primary lamella of the septum is really
double in the genus Ses¢astr@a, and a somewhat similar structure of the septa
seems to obtain in the recent genus /labellum.

ACTINOZOA. 247

appear to consist principally, or only, of the thin primitive central lamella,
no secondary layer of stereoplasma, or but a very imperfect one, being
developed. In such cases, the outer wall of the coral is also very thin
(fig. 128, B). Where secondary stereoplasma is well developed, the
thickened outer ends of the septa usually become fused with one another,
so as to form a more or less dense outer investment to the visceral
chamber. Sometimes (as in S¢reptelasma, fig. 127, B), the external wall
of the corallum seems to be formed wholly by the thickened outer ends
of the septa; but in marty forms the primitive theca can be recognised
in the substance of the outer investment as a thin dark plate (fig. 127, 7)
formed by lateral outgrowths from the primordial septa. Hence in such
cases the peripheral ends of the septa continue to grow outwards subse-

Fig. 127.—A, Portion of a cross-section of the recent Caryophyllia borealis, enlarged to show
the structure of the septa. 8, A similar preparation of Streptelasmma corniculum, Ordovician,
N. America. c, A similar section of Zaphrentis Enniskillenz, Carboniferous. , Dark line oc-
cupying the middle of the septum; sz, Layer of stereoplasma; ¢, Theca, formed by out-growths
from the outer ends of the septa; s, Septum of the first order; s’, Septum of the second order ; d,
Dissepiments. (Original.)

quently to the formation of the original theca ; each septum thus coming
to consist of an intrathecal and an extrathecal portion.

In some corals (as, for example, in Pholidophyllum.), it can be clearly
shown that the septa are made up of calcareous trabeculz or spines
(the “ Vertical-leisten” of the Germans), which are directed upwards
and inwards towards the axis of the corallum, and which become united
with one another directly or by means of secondary sclerenchyma. In
Heliophyllum, Crepidophyllum, Phillipsastrea, and other allied genera
of Palzeozoic corals, these oblique septal trabeculee are greatly developed,
and are not obscured by the development of lateral layers of stereoplasma.
Hence in these genera cross-sections of the septa (fig. 128, B) exhibit
characteristic thickenings or cross-bars, which have been termed “ car-
ine,” and which are the result of the intersection of the septal spines
just spoken of, while the free edges of the septa are furnished with
pointed projections or teeth.

248 CCELENTERATA.

In many composite corals calcareous structures, as will be subse-
quently seen, are commonly developed externally to the thecz of
the polypes, constituting what is known by the general name of
‘““peritheca” or ‘‘exotheca.” In a simple sclerodermic coral, such
as we are here considering, the only exothecal structures are the so-
called ‘‘costz.” These are vertical ridges on the exterior of the
corallum, which correspond with the septa, and which, in fact, are
the exothecal edges of the septal laminze. In some cases, however,
we meet with similar vertical ridges (“‘rugze” or ‘“‘ pseudocostze”’) on
the exterior of the theca which do not correspond with the septa
within, in many instances alternating with the latter; but the true
nature of these is not clear. The costez, when present, vary much
as to their relative distance apart, their breadth, their solidity, and
their ornamentation with tubercles, granules, or teeth.

In the interior of the corallum various “ endothecal” structures
may be developed, all of which may be regarded as essentially pro-
duced by modifications of, or outgrowths from, the septa. In many

Fig. 128.—a, Transverse section of a simple Zoantharian Coral (Caryophyllia Bowerbankt),
enlarged. (After Milne-Edwards and Haime.) ¢, Theca; s, One of the primary septa; Z, One
of the ‘‘pali.” In the centre is seen the irregular ‘‘ columella.” 8, Transverse section of a
Rugose coral (Crepidophyllunt subcespitosum), enlarged four times (Original). 7, Theca; d,
‘‘ Dissepiments”’; s, One of the first order of septa ; s’, One of the second order of septa ; 7, “‘ Fos-
sula.” In the centre of the coral is a space occupied by tabule.

corals the septal laminze themselves are more or less rudimentary, and
may be represented only by vertical rows of spines (as in Favosites)
or by mere longitudinal striz (as in species of Cystiphyllum). When
the septa have the form of complete calcareous lamelle, they may
terminate internally by free edges, and the centre of the visceral
chamber may be completely vacant. In other cases, narrow vertical
plates which are known as “‘ pali” (fig. 128, A) are developed at the
inner ends of certain of the septa, and have the appearance of being
continuations of the latter, though detached from them. When a
“columella” is present, the inner edges of the pali are united with

ACTINOZOA. 249

this. The “columella” is the general name given to certain axial
structures which are commonly developed from the centre of the
base of the visceral chamber. The structure of the columella
varies in different cases, but it extends, typically, from the floor
of the visceral chamber to the bottom of the calice, into which
it projects for a greater or less distance ; and the principal septa are
often more or less closely connected with it. In some cases, the
columella is a solid calcareous rod, or it may be made up of reticu-
lated calcareous tissue (fig. 128, a) or of twisted calcareous fibres,
while in other instances its structure is even more complicated.
Theoretically, the ‘“‘interseptal loculi” are vacant spaces or verti-
cal compartments, bounded laterally by the septa, and extending
from the lower and lateral surfaces of the theca to the floor of the
calice. In practice, however, the continuity of the interseptal loculi
is usually more or less interfered with by the development of one or
more of the structures known as “‘synapticula,” “‘ dissepiments,” and
“tabule.” The ‘synapticula” are transverse calcareous bars which
stretch across the interseptal loculi, perforating the mesenteries, and

Fig. 129.—A, Portion of the corallum of Favosites favosa, of the natural size; Bp, Portion of
four corallites of Havosites Gothlandica, enlarged, showing the tabule.

form a sort of trellis-work uniting the faces of adjacent septa. They
are specially characteristic of the Fungide. The structures known
as “‘dissepiments” are present in the majority of corals, and have
the form of incomplete, oblique or approximately horizontal plates,
which stretch between adjacent septa, and break up the interseptal
loculi into secondary compartments or cells. Lastly, the ‘‘ tabulee”
may be regarded as highly developed dissepiments, and, like them,
are approximately horizontal, as a rule at any rate. They differ from
the dissepiments in the fact that they cut across the interseptal loculi
at the same level. When fully developed (fig. 129, B), they are
transverse plates, which extend completely across the visceral cham-

250 CCELENTERATA.

ber, and divide it into a series of storeys placed one above the other,
the only living portion of the coral being above the last-formed tabule.
In some cases, the tabule are “incomplete,” and are merely flat
tongue-shaped plates which extend from the inner surface of the
theca transversely into the visceral chamber. In other cases (as
in Michelinia), the tabule are imperfect, and become united with
one another so as to form a sort of vesicular tissue. In still other
cases (as in Syringopora) the tabule are funnel-shaped, and fit into
one another from above downwards.

As regards the process of development, the ordinary sclerodermic
corallum is the result of the secretion of carbonate of lime by a special
layer of ectodermal cells (“‘ calicoblast layer,” fig. 130, ca), and is therefore
truly external to the body of the polype by which it is produced. If the
formation of the corallum be observed in the embryo of Astrozdes, it 1s
found that the first step is the secretion of a ring-shaped “basal plate”
(fig. 130, da) between the lower surface of the polype and the substance to

oF |
PRE 2 eS fi
Ser cid a Be! AN
TEES, Sp SS Oy A
Bede 3) claace aaa Sai NSP
Pic cantilinoo Oona anoDS—— = “2ana™ ss SIS
Bua cent aia ca a

Ca

Fig. 130.—Diagrammatic vertical section or a young polype ot Astroides calicularis, showing
_the formation of the corallum, greatly enlarged. 4a, Basal plate, produced by a special layer
of ectodermal cells (ca); ef, Lateral wall of the corallum; se, One of the septa, pushing before
it a fold of the entire body-wall; ec, Ectoderm; ez, Endoderm; me, Mesoderm (“‘ supporting
lamella”); 22, Mesentery; @, Gullet. (Slightly altered from Bourne, and based ona figure
given by von Koch.)

which it has attached itself. The formation of the septa is subsequent to
that of the basal plate, these structures appearing as radially-disposed
ridges or folds of the base of the polype, each fold (fig. 130, se) being com-
posed of the three constituent layers of the body-wall. The septa are
thus, like the basal plate, really external to the polype; but in process
of growth they carry up with them the folds of the body-wall by which
they are covered, and they ultimately come to project into the inter-
mesenteric chambers, and to have all the appearance of being internal
structures.

The ¢heca is not an independent structure, as is the basal plate, but
seems to be usually the result of the bifurcation of the peripheral ends
of the septa, and the lateral fusion of these (fig. 127, A, Z). In some cases
the external investment of the corallum seems to consist solely of the
thickened outer ends of the septa (as in StvePtelasma, fig. 127, B) ; but in

ACTINOZOA. 251

other cases there is present, in addition, a secondary calcareous mem-
brane, which is known as the “ epztheca,” and which appears to be

secreted by the reflection of the ectoderm over the upper part of the
The “dissepiments,’ which are present in the interseptal

corallum.

loculi of most corals, are secreted by the ectodermal cells (“calico-

blasts”) of what were “ originally the interseptal parts of the base of the
The soft parts of the polype thus always lie above

polype” (Bourne).
the last-formed dissepiments, and the spaces between the latter and the
theca are not occupied by soft tissues of any kind.

In connection with the preceding, a few words may be said as to the
relations of the polype to the corallum which it secretes. As has been

_ mn
Mt ~~~.
eC
CH
toe NE Ee Bae
YY sh) fa eres BNC
SAR =e NSBR EY 777 EA y
Tae

~s-s. r

9,
4,
COT

CYT
S urcnuts

O

Fig. 131.—Diagrammatic vertical section ot MWzssa corymbosa, showing the relations of the

polype to the corallum.

od, Oral disc of the polype; a, (Esophagus, with the free edges of the

mesenteries seen below its inferior end; 7m, Flat surface of a mesentery; ec, Ectoderm (cross-

mesoderm ; ca, Special ectodermal layer (‘‘calicoblast layer’’) secreting the corallum (co); d, Dis-
(Slightly altered from

shaded); ez, Endoderm (unshaded), the dark line between this and the ectoderm representing the
sepiments ; ~ 7, Inversion of the polype constituting the ‘‘ Randplatte.”

Bourne.)
seen, the corallum is of ectodermal origin, and is therefore really external
In process of growth, however, the corallum becomes

to the polype.

pushed up into the polype from below, so to speak, and thus comes to be

apparently situated within the polype. What actually happens, as shown

in the accompanying diagram (fig. 131), is that the polype becomes in-

verted over the corallum, so as to form a layer external to the theca,
Thus a portion

which von Heider has spoken of as the “ Randplatte.”

252 CCELENTERATA.

of the polype comes to le external to the theca, while a portion lies
within the latter. It follows from this that the general body-cavity or
“coelenteric space” is divided by the theca into two parts, of which one
is intrathecal, while the other is extrathecal, the latter being divided into
chambers by mesenteries, just as the former is. [According to von Koch,
the originally continuous mesenteries are cut into two by the fusion of the
peripheral ends of the septa to form the theca, each mesentery thus
becoming divided into an extrathecal and intrathecal portion.] Above
the lip of the calice, the extrathecal and intrathecal portions of the cce-
lenteric space communicate with one another. It is the extrathecal por-
tion of the polype which forms the “ Randplatte” (fig. 131, 7 7); and the
so-called “epitheca,” when present, seems to be formed “from the free
edge of the soft tissues on the exterior of the corallum, as they retreat
farther and farther from the original surface of attachment” (Bourne).
In composite corals the “ coenosarc” is the result of the coalescence and
union of the ‘‘ Randplatten” of adjacent polypes ; and the general cal-
careous tissue (“‘coenenchyma”) which unites the various corallites is
secreted by the ccenosarc. Where a coenenchyma is present, the ex-
trathecal portions of the mesenteries are awanting.

The above gives the general structure of a typical simple sclero-
dermic corallum, as secreted by a single polype. A compound
sclerodermic corallum is the aggregate skeleton produced by a col-
ony of such polypes, and varies in form and size according to the
characters of the colony by which it is produced. In general, such

Fig. 132.—Astrea pallida, a compound sclerodermic Coral, in its living condition.
(After Dana.)

a colony consists (fig. 132) of a number of polypes, which may
spring directly from one another, or may be united by a common
flesh or ccenosarc; and corresponding elements are found in the
corallum. In the former instance, the compound corallum con-
sists of an assemblage of separate “corallites,” as the skeletons of
the individual polypes are called, these being united with one
another directly and in various ways. In the latter instance, the

ACTINOZOA. 253

corallum consists of a number of “corallites” together with a com-
mon calcareous basis or tissue, which unites the various corallites
into a whole, is secreted by the ccenosarc, and is known as the
** coenenchyma.”

The corallites of a composite sclerodermic coral are essentially
similar in structure to a simple corallum, such as has been previously
described. The “coenenchyma” is the name given to all those
calcareous structures which may unite the different corallites with
one another, and which is, therefore, of ‘exothecal” or “peri-
thecal” origin ; and its nature varies greatly in different cases. Most
usually, however, the ccenenchyma consists either of simply porous
or of compact sclerenchyma; though it may have the form of a
reticulated or vesicular tissue. In many of the composite coralla,
the corallites composing the colony are also invested inferiorly and
laterally by a general calcareous membrane or ‘“ epitheca,” which is
common to the entire growth.

A compound corallum is, of course, primitively simple, and it becomes
composite either by budding or by cleavage of the original polype, the
following being the principal methods in which this increase is effected.

1. Lateral or parietal gemmation.—In this mode of increase the original
polype throws out buds from some point on its sides between the base

Fig. 134.—Calicular gemmation as
seen in Lonusdaleia floriforniis. Car-
boniferous.

Fig. 133-—A branch of the recent
Dendrophyllia nigrescens showing la-
teral gemmation. a, A corallite; c,
Ccenenchyma.

and the circle of tentacles, and these buds, on becoming perfect coral-
lites, may repeat the process. Commonly the new corallites tend to
diverge from one another, the resulting form of corallum being dendroid
or branched. In other cases the new corallites grow up side by side, and
in contact with one another, the corallum thus becoming massive or
“astraeiform.” Composite corals produced by lateral gemmation may
have the corallites directly connected with one another, or united by a
more or less copious “ coenenchyma” (fig. 133).

254 CCELENTERATA.

2. Calicinal or calicular gemmation.—This consists in the production
of buds from the calicine dis¢ of the parent corallite, which may or may
not continue to grow thereafter, whilst the new corallites thus produced
generally repeat ‘the process. The simplest form of calicular budding is
seen in some of the Rugose corals (species of Cystiphyllum, Heliophyllum,
&c.), where the calicine disc gives off but a single bud, which may repeat
the process indefinitely, till the corallum presents the appearance of a
succession of inverted cones placed one above the other, only the upper-
most of these being actually alive. It is not clear, however, that the
phenomena here alluded to are really the result of budding, i in the proper
sense of the term. It is not clear, namely, that the original polype pro-
duces a calicine bud which kills its parent; and another explanation of
the observed facts would ascribe them rather to a process of “ rejuven-
escence” on the part of a single polype. On this view, the original polype
undergoes periodic contraction and partial death, only the central part
of the animal retaining its vitality. Each period of contraction is, how-
ever, followed by one “of active growth, and the coral thus comes ulti-
mately to assume the form of a succession of inverted cones.

In the more genuine forms of calicular budding, on the other hand, the
form of the corallum varies according as the buds spring from the margins
or centres of the calices, and as the new corallites remain free or become
united with another. In one form of the process, characteristic of certain
Palzeozoic corals, the original polype throws up from its calicine disc one
or more new corallites, which kill the parent. These, in turn, produce
others after a similar fashion, till the entire corallum assumes the form of
an inverted pyramidal mass resting upon the original budding polype
(fig. 134).

3. Intermural gemmation.—This mode of budding is seen in the
Favositide and in other extinct corals, and consists in the production of
new corallites from
the lip of the cali-
cine wall of a pre-
existing corallite, in-
stead of from the
actual calice itself.
Hence in cross-sec-
tions of such corals
the new corallites
appear to be wedged
in at the angles of

a : he a junction of the old
ig. 135.—Transverse and vertical sections of Mavosites, en-

larged, showing intermural budding. co, A young corallite. corallites (fig. 135; A),
(Original.) and it is not possible

to determine from
which of the tubes concerned the new bud has been given off. In long
sections, again, the new corallite appears as if produced by the splitting
of the conjoined wall of two adjacent corallites (fig. 135, B).

4. Basal or stolonal gemmation.—This mode of increase is specially
characteristic of the Alcyonarians, though not confined to these. In this
method the original polype sends forth “from its base creeping prolonga-
tions or “stolons” (fig. 136), from which new corallites are produced.
In other cases the same result is attained by the budding of new coral-
lites from a basal laminar expansion. In either case, the youngest coral-
lites are necessarily those nearest to the periphery of the colony.

5. fission. — Fissiparous multiplication commences by the partial

ACTINOZOA. 255

cleavage of the parent polype, the process of division commencing with
a constriction of the oral disc, which gradually deepens till the original
animal becomes divided into two more or less completely separate
polypes, which, however, remain connected proximally. The process
is not sharply distinguishable from gemma-
tion, and the form of corallum produced there-
by varies greatly in different cases. In many
instances the corallites produced by fission
may be divided for a considerable distance,
remaining connected by the basal portion of
the original polype only, the resulting corallum
being of a “ ceespitose” or tufted form, and
consisting of short diverging pairs of branches,
of which each pair represents the division of a
single corallite. In other cases, the separation he eo Die ees
of the secondary polypes is very imperfect, and Devonian.
the corallum tends to assume a massive or
lamellar form. In such cases the calices form continuous rows, with
more or less clearly distinguishable centres, and the calicine furrows
are often winding and contorted, as seen in the familiar Brain-corals
(Meandrina).

In such corals as Chetetes (fig. 137), the fissiparous development of
the new corallites can be generally recognised in sections without

Fig. 137.—Sections of Chetetes septosus, from the Carboniferous rocks, enlarged to show fission
of the corallites. a, Cross-section of a few corallites, some of which show the commencing fission
of a tube by the development of an internal longitudinal partition ( #); B, Vertical section, show-
ing a single corallite (c) splitting into two. (Original. )

difficulty. The commencing fission of a corallite is marked by the de-
velopment of an internal vertical partition, which is at first incomplete,
and which therefore appears in transverse sections as an inwardly directed
tooth-like process (fig. 137, A, A), looking like a septum. A correspond-
ing partition is then dev eloped opposite to the first one, and by the
inward growth and final junction of these, the original tube is ulti-
mately divided into two. In longitudinal sections (fig. 137, B), the fis-
sion of a corallite is marked by the appearance of a longitudinal parti-
tion in the interior of a tube, which thus becomes div ided into tw o—the
two new corallites being at first of small size, but gradually assuming
their full dimensions.

256 CCELENTERATA.

As regards the classification of the Actinozoa, no arrangement that
has yet been proposed can be regarded as more than provisional,
the true affinities of various important fossil groups being still uncer-
tain. Usually the Actznozoa have been divided into the four orders
of the Zoantharia, Alcyonaria, Ctenophora, and Rugosa. ‘The first
three of these divisions are largely represented by living forms, and
may be regarded as essentially natural groups; but the division of
the Rugosa is certainly unnatural, and cannot be retained in its old
sense. With our present knowledge—derived wholly from the skel-
etal structures—it is not possible to speak positively as to the precise
relationships of many of the organisms included in the old group of
the Rugosa. There is no good reason for separating certain of the
so-called Rugose Corals from existing groups of the Zvantharia
Aporosa ; but it would not appear to be expedient, in the meanwhile
at any rate, to refer the whole of the Augosa to the above-mentioned
division of the Madreporarians. ‘The three principal groups of the
Rugosa—viz., the Cyathophylloids, Zaphrentoids, and Cystiphylloids
—are closely connected with one another, and have certain peculiar
features of their own. For the reception of these, therefore, it seems
to be best, provisionally at any rate, to retain the general name of
Rugosa, but to regard the forms in question as constituting a special
section of the Madreporarians rather than a distinct order.

As regards their general distribution in space, all the recent Actin-
ozoa are inhabitants of the sea, and there is no reason to suppose that
any of the fossil forms were other than marine. The coralligenous
forms, generally spoken of as “Corals,” are partly inhabitants of
deep water, partly shallow-water types ; and the latter are well known
as giving rise in warm seas, and under suitable conditions, to those
great aggregations of coral which are known as “coral-reefs.” It is
not necessary to consider here the general phenomena of existing
coral-reefs, or to enter into a discussion of the vexed question as to
the laws and conditions under which the various forms of these
structures are produced. A few words may be said, however, as to
the nature of the materials which actually form a recent coral-reef,
as this is a point which has important geological bearings. In the
first place, though Corals properly so called are the principal agents
concerned in the construction of a coral-reef, they are not the only
ones, a very important part in the formation of the reef being played
by other organisms which secrete a calcareous skeleton. Thus, the
materials composing a coral-reef are largely the result of the accumu-
lation of the calcareous skeletons of animals other than corals, and
particularly of the Hydrocorallines and the Molluscs ; while the cal-
careous A/ge (Nullipores) take an important part in the formation
of some reefs. Again, it is only a portion—chiefly the outer edge—
of a modern coral-reef which is actually composed of living corals,

ACTINOZOA. any

growing in place; and a large portion of all reefs is formed by cal-
careous deposits of a fragmental character, which have been produced
by the action of the sea upon the reef, and which are therefore essen-
tially made up of larger or smaller pieces of coral mixed with the
entire or broken skeletons of other lime-secreting organisms. Lastly,
the materials composing a coral-reef are liable to undergo more or
less extensive secondary changes caused by the continued percolation
through them of water, these changes being in the direction of a more
or less complete crystallisation and of a consequent obliteration of
the original organic structure of the rock.

Essentially, therefore, a modern coral-reef is composed, on the one
hand, of more or less extensive calcareous masses formed by ¢he
growth in place of corals associated with other lime-secreting organ-
isms, and, on the other hand, of purely mechanical deposits produced
by the wear and tear of the preceding. As it is known that the reef-
building corals do not thrive at depths greater than about thirty
fathoms, it is certain that the portions of the reef actually formed of
corals which have grown in place must have originated in quite
shallow water. On the other hand, the detrital deposits formed by
the degradation of the original reef form a belt on the flanks of the
latter, and may extend into comparatively deep water. Moreover, the
portions of the reef which are of mechanical origin may considerably
exceed in amount those which are due to the direct growth of the
corals themselves.

The following are the more important kinds of calcareous rocks which
occur in existing coral-reefs :—

1. “ Coral-rock,’ properly so called, produced by the reef-corals gvow-
ing im place. Though essentially formed by the growing corals them-
selves, this rock is also largely made up of calcareous mud and the
entire or broken skeletons of various lime-producing organisms other
than corals, the interstices between the corals being thus completely
filled up. This is more especially the case near the surface of the reef,
where the branching and reticulated types of corals (such as the Madre-
pores) chiefly abound. ‘“ Coral-rock,” produced as above, is liable to
undergo secondary changes as the result of the percolation through it of
water, the original coralline structure being thus more or less extensively
obliterated, and the rock being converted into a compact and crystalline
limestone.

2. “ Reef-rock,’ produced by the action of the sea upon the reef, and
consisting of fragments of broken coral mixed with the entire or broken
remains of all sorts of calcareous organisms other than corals (Molluscs,
Echinoderms, Foraminifera, Nullipores, &c.), the whole being cemented
together by a matrix of crystalline calcite. This matrix is formed by the
percolation of water through the mass, this leading to partial solution of
the fragments, and to the subsequent deposition in the crystalline form of
the carbonate of lime thus obtained. “ Reef-rock” is always stratified,
and varies in texture, according to the size of the fragments of which it is
composed. Usually itis more or less compact and homogeneous ; and
its component organic fragments may be readily recognisable, or may

VOL. I. R

258 CG@:LENTERATA.

be more or less obliterated by secondary crystallisation. In some cases,
where the rock is composed of large fragments of coral cemented to-
gether by calcareous débris, a “coral-breccia” is produced. A some-
what similar rock (“boulder-rock”) is formed above the level of high
water by the fragments of coral which are heaped up by the waves, and
which become ultimately cemented together by the action of the spray.

3. “ Coral-mud,’ formed of fine calcareous mud derived from the wear
and tear of the reef by the action of the waves. Such deposits are neces-
sarily stratified, and they are more or less fine-grained, chalk-like in
appearance, and often friable. Though largely composed of minute
particles of carbonate of lime, these coral-muds are often extensively
made up of recognisable fragments of various calcareous organisms, or
of the minute tests of Foraminifera.

4. “ Sand-rock,” formed above high-water mark by the action of the
wind. Though subaerial in origin, the “sand-rock” is stratified ; and it
is composed of fine coral sand cemented together by the action of the
spray of the sea, or by the percolation through it of rain-water.

Coralline limestones have been formed in all the great geological
periods from the Ordovician onwards, and some of these undoubtedly
represent ancient coral-reefs. In an old coral-reef we should expect
to find the same two groups of calcareous rocks as have been above
noted as occurring in modern reefs. We ought, namely, to meet in
a fossil reef, on the one hand, with limestones formed mainly of
corals which actually grew in place, and, on the other hand, with
limestones produced by the contemporaneous degradation of the
reef and therefore made up of the débris of corals and other cal-
careous organisms. Owing, however, to the action of denudation,
it must be a matter of comparatively rare occurrence that both these
groups of deposits should be found occupying their natural relative
positions at the existing surface; and the rarity of such an occur-
rence must be in direct proportion to the antiquity of the supposed
reef. In amy case, it can only be under exceptional circumstances
that the original form of any ancient coral-reef can have been so far
conserved that it would be possible to determine that the reef was
originally a “fringing reef,” a “barrier,” or an “atoll.” In the
later Tertiary rocks, no doubt, denudation may have been com-
paratively speaking so slight that the original form of the reef may
admit of determination. Even in the Secondary rocks, however,
the changes produced by displacements of the strata and subse-
quent denudation are so great that the original form of the reefs
can hardly be more than a matter of inference. In the still more
ancient Paleozoic deposits, again, the dislocations due to earth-
movements have been so extensive, and the denudation subsequent
to these has been so long continued and so effective, that it must
always be hazardous to treat the existing outcrops of coralline lime-
stones as representing the original boundaries of old coral-reefs. Hence
there is a considerable element of uncertainty attaching to the so-

ACTINOZOA. 259

called “atolls” which have been described as occurring in rocks of
Devonian or Carboniferous age. Not only is it theoretically im-
probable that an “atoll” of such high antiquity as the Devonian
should have so far escaped destruction by denudation that its
original form should still be recognisable, but these supposed atolls
are found in areas which can be proved to have undergone extensive
disturbance. In such cases, therefore—as, for example, in the
“atolls” described by M. Dupont in the Devonian limestones of
Belgium—it must be borne in mind that the observed ring-like
arrangement of the limestones may well be explained as the result
of denudation acting upon a series of strata which contain coralline
limestones amongst their members, and which have been folded in a
complex manner.

Owing to their peculiar mode of formation, it is clear that those por-
tions of a coral-reef which are formed by corals growing in place must
always be terminated by more or less abrupt boundaries ; and, for the
reasons above given, it is doubtful if the existing outcrops of any of the
known Paleozoic limestones can be regarded as actually corresponding
with the edges of old reefs. Still it may be permissible to assert that
coral-reefs existed in Palaeozoic time, provided the term “reef” be used
in a wide sense. There are, namely, Palzozoic limestones which are
more or less largely composed of corals which grew zz sztu, and these
may be looked upon as constituting formations similar to existing coral-
reefs, though they are mostly of small thickness, and though their present
outcrops must be the result of denudation rather than of original ar-
rangement. On the other hand, very many of the coralline limestones of
the Paleozoic period have been only partially, or not at all, produced by
corals growing in place, but are essentially of the nature of “ reef-rock,”
being mainly composed of small corals, or of fragments of the larger
forms, intermingled with the débrzs of innumerable calcareous organisms
of other kinds, such as Crinoids, Brachiopods, Foraminifera, &c. The
oldest known coralline limestones occur in the Ordovician period ; but
still more extensive coralline deposits are found in the Silurian. The
corals of these belong principally to the Rugose and Perforate divisions
of the Madreporarza, but there are also various forms (such as the
Fleliolitide) belonging to the Adcyonaria. Moreover, these ancient
coralline limestones are largely, often preponderatingly, made up of the
remains of Stromatoporoids, which are referable to the A/ydrozoa, or
of Monticuliporoids, the precise zoological place of which is not ab-
solutely certain. In the Devonian period we meet with very extensive
coralline limestones which, zoologically speaking, are closely allied to
those of the Silurian, and in the formation of which the Stromatoporoids
again play a very important part. The vast coralline limestones of the
Carboniferous period are mostly characterised by the occurrence of
Rugose corals (Lithostrotion, Lonsdaleta, Cyathophyllum, &c.), along
with Perforate types, such as Syringopora,; but the Stromatoporoids
appear to be now wholly wanting. No true coralline limestones have
hitherto been recognised in the Permian rocks ; but towards the close of
the Triassic period, true coral-reefs were largely developed in Western
Europe. Still more extensive reefs were formed during Jurassic times
in South-western and Western Europe and in Britain, and true reefs also

260 CCELENTERATA.

existed in Europe during the earlier portions of the Cretaceous period.
In the earlier portion of the Tertiary period, again, vast coral-reefs were
formed in Central and Southern Europe, in Egypt, Syna, and Arabia,
and in parts of India. In the later portions of the Tertiary period, reefs
are much more sparingly developed in Europe, but they were at this time
formed on a large scale in the warmer regions of the earth’s surface. In
Mesozoic, Kainozoic, and recent times alike, the chief genera of reef-
building corals belong to the families of the Astreide, Poritide, and
Madreporide, though the Oculznzde and Fungide also contribute to the
formation of reefs.

With regard, finally, to the dzstribution in time of the Actinozoa,
the Ctenophora, being devoid of hard parts, are unknown in the
fossil condition, and need no further consideration here. On the
other hand, the Zoantharia (including the Augosa) and the Alcyon-
aria are very largely represented in past time, both sections of the
class being represented by extinct types in rocks as old as the Or-
dovician. Speaking generally, the Actnozoa of the Paleozoic
period belong principally to the Rugose and Aporose divisions of
the Zoantharia and to certain abnormal groups of the Adcyonaria,
though the Perforate Zoantharia are by no means unrepresented in
rocks of this age. On the other hand, the Mesozoic and Kainozoic
periods are characterised by the predominance of the Perforate and
Aporose Zoantharians, these being the chief representatives of the
class at the present day.

261

GAP lT ER XV

CHAK ACTERS AND DIVISIONS OF THE
ZLOANTHARTA.

MADREPORARIA APOROSA.

From a paleontological point of view the order Zoantharia is not
in a satisfactory position, since the only general definition of it
which can be given is one based upon the soft parts, and therefore
depending mainly upon characters which cannot be recognised in
the fossil forms. The living Zoantharians Aossess simple, usually
numerous tentacles, and the mesenteries are never eight in number.
The mesenteries typically exhibit a more or less clearly recognisable
bilateral arrangement, and usually show a hexameral symmetry ;
but some forms are completely radial, and the disposition of the
mesenteries in hexameral cycles is often departed from. In the
section of the Rugose Corals, more particularly, the symmetry is
typically tetrameral. A corallum may be wholly wanting (Actznz-
aria), or a horny sclerobasis may be developed (Aztipatharia). In
most Zoantharians (Aladreporaria) there is, however, a well-devel-
oped sclerodermic corallum, the symmetry of which varies in accord-
ance with that of the mesenteries.

The general arrangement and structure of the soft and hard
parts of the Zoantharians have been sufficiently discussed in dealing
with the Actinozoa as a whole; but there are some points connected
with the symmetry and arrangement of the mesenteries which may
be briefly alluded to here :—

Hexameral symmetry obtains as a general rule, though not uni-
versally, in the Actinzde (Sea-anemones), Antipathide, Madreporaria
Perforata, M. Fungida, and M. Aforosa,; the mesenteries and
septa being typically arranged in cycles of six pairs each (fig. 138).
On the other hand, tetrameral symmetry is commonly recognisable
in the Rugose Corals, though in some of the forms generally in-

262 ZOANTHARIA.

cluded in the Azgosa a tetrameral arrangement of the septa can-
not be clearly made out.

Though showing a general radial symmetry, the majority of
the Zoantharians at the same time exhibit a distinct bilaterality of
their parts. This bilateral symmetry is shown by the presence at
each end of the longitudinal gullet (fig. 138, @) of a pair of mesen-
teries which differ in the arrangement of their muscles from the
other mesenteries, and which are known as the “ directive” mesen-
teries. In certain of the Madreporarians (e.g., Mussa, Euphyliia,

Fig. 138.— Diagram of a cross-section of Caryo- Fig. 139.—Floor of the calice of a typi-
phyllia, the soft parts being unshaded and the cal Rugose Coral (Zaphrentis Enniskill-
corallum black. @, Gullet, with the ‘‘ directive ent), of the natural size, showing distinct
mesenteries ” (72) at each end; w, Body-wall ; bilaterality in the disposition of the septa.
s, Septum; z, Theca. (Slightly altered from von J, The “‘fossula.” From the Carbonifer-
Koch.) ous Limestone. (Original.)

and Lophohelia) there are, however, no “ directive mesenteries,” and
in such forms a complete radial symmetry obtains. On the other
hand, in the typical Rugose Corals very distinct bilateral symmetry
usually obtains, and is readily recognised by the general arrange-
ment of the septa, or by an exaggerated or reduced development of
certain of these structures. In many Rugose Corals this bilaterality
is rendered specially conspicuous by the presence of a shallower or
deeper groove or pit—the “‘fossula””—occupied by a limited num-
ber of septa of reduced size (fig. 139, f). Sometimes more than
one fossula may be present, and the position of the pit thus named
varies in different types of the Rugosa, being sometimes dorsal,
sometimes ventral, and sometimes lateral.

There seems to be every ground for believing that the “fossula” of
the Rugose Corals is connected with the development of the reproduc-
tive organs. On this point the observations which have been made by
Moseley on the anatomy of the polypes of the recent genus Serzatopora
are particularly instructive. It has been shown, namely, that in Sevzazo-
pora it is only two of the twelve mesenteries (viz., the pair of ventro-

MADREPORARIA APOROSA. 263

lateral mesenteries) which develop reproductive organs. These two
mesenteries are much longer than the others, and correspond to inter-
mesenteric pouches of excessive depth, which fit into deep conical pits in
the skeleton, bounded by septa of much reduced size. In accordance
with these observations, it may be assumed that the “fossula” of the
Rugose Corals served to lodge a special hypertrophied mesentery, or
group of mesenteries, carrying reproductive organs. It is noteworthy,
however, that in the recent Servzatopora (as also in Madrepora Durvillet)
the two mesenteries which are modified for reproductive purposes are o7
opposite sides of the polype,; whereas the fossula of the Azgosa is usually
unilateral.

As regards the classification of the Zoantharia, the order may be
divided into the three groups or sub-orders of the Actnzaria, Anti-
patharia, and Madreporaria. ‘The first of these comprises the Sea-
anemones ; and, from the absence of a corallum in these forms, is
sometimes spoken of under the name of Zoantharia malacodermata.
The second group—sometimes called Zoantharia sclerobasica—com-
prises the Axntipathide or “ Black Corals” and their allies, in
which a horny sclerobase is developed. Lastly, the great series
of the Madreporarians— sometimes spoken of as the Zoantharia
sclerodermata—comprises all the ordinary “Corals” of the present
day along with the extinct group of the Augosa, in all of which a
well-developed sclerodermic corallum is present.

All the Zoantharians are marine, and from their common posses-
sion of a calcareous skeleton they have been largely preserved in the
fossil condition. Owing to their want of hard parts, the Sea-anem-
ones (Actiniaria) have left no traces of their past existence, and
need, therefore, no further consideration here. The group of the
Antipatharia also requires merely to be mentioned, as no fossil
forms have been hitherto identified, the Zezopathes vetusta of Milne-
Edwards and Haime appearing to be a Gorgonian and therefore
referable to the Al/cyonaria. ‘There remains the great group of the
Madreporaria, which is represented in past time by a vast series
of fossil forms, and which requires, therefore, a somewhat detailed
examination.

MADREPORARIA.

The group of the Madreporarians or Zoantharia sclerodermata
comprises those Zoantharians in which a well-developed sclerodermic
corallum, which is not simply spicular, is present. ‘The septa of the
corallum are, typically, arranged according to either a hexameral or a
tetrameral system ; but in some cases some other numerical law may
govern the disposition of the septa, and in other cases no special
symmetry may be recognisable. The organism may be simple, con-
sisting of a single polype only, or composite, consisting of many

264 ZOANTHARIA.

polypes united with one another directly, or connected by a general
coenosarc.

A strictly natural classification of the Wadreporaria has still to be
framed. By Milne-Edwards and Haime they were divided into the
four sections of the Asorosa, Perforata, Tabulata, and Tubulosa ;
while these authorities considered the Augosa as a distinct order.
The section of the Zadulata (‘‘ Tabulate Corals”) has, however,
been shown to be a miscellaneous and artificial assemblage, and the
types formerly included in it have now found a place in the Aporose
or Perforate sections of the order, or have been relegated to the
Alcyonaria. The section of the Zzbulosa, again, is a small and
imperfectly understood one, and the forms included in it may be
temporarily placed in the A/cyonaria. Lastly, recent researches and
discoveries have rendered hardly tenable the retention of the Augosa
as a separate order of Actinozoa ; though the true affinities of many
of the so-called Rugose Corals are still very uncertain. In the present
state of our knowledge, the Wadreporaria may be divided into the
four primary sections of the Asorosa, Rugosa, Fungida, and Per-
Jorata. Of these, the /unugida do not appear to have come into
existence prior to the Jurassic period ; but the remaining three sec-
tions were differentiated as early as the Ordovician period.

SECTION I. MADREPORARIA APOROSA.

The division of the Aforosa comprises those Madreporarians in
which the corallum is composed of more or less compact and solid
sclerenchyma, the “theca” or wall surrounding the visceral chamber
being complete, and not perforated by apertures or pores (fig. 140).
An “‘ epitheca” may be present. The septa are well developed, and
usually have the form of solid lamelle, though they are in some
cases more or less cribriform. The interseptal loculi may be open
throughout, but endothecal tissue in the form of “ dissepiments” is
usually more or less largely developed, while “synapticula” and
“‘tabulz” are sometimes present. The corallum may be simple or
composite. The symmetry may be completely radial (dZussa and
Luphyllia), or bilateral. The arrangement of the septa is typically
hexameral, but may be tetrameral, pentameral, or otherwise abnormal.

It is difficult to speak positively as to the geological distribution of
the Madreporaria Aporosa, owing to the uncertainty which attaches
to the precise affinities of many fossil Corals. There are, however,
various Paleozoic types which may most suitably find a place here,
the Ordovician genus Columunaria (Favistella) being apparently the
most ancient of these. The Silurian genus Sfauria, in spite of its
tetrameral symmetry, may likewise be regarded as an Astreeid ; while
Duncanella and Cyathaxonia, the former Silurian and the latter Car-

MADREPORARIA APOROSA. 265

boniferous, may be looked upon as early types of the Zurbinolide,
as, perhaps, Pefraza and Polycelia may also be. Professor Duncan
further regards the Devonian genus Baétersbyia and the Carboniferous
fleterophyllia as representing a special group of Aporosa allied to the
Astreide. In the Secondary and Tertiary deposits the Aporose

Fig. 140.—Caryophyllia (Cyathina) Bowerbankt, from the Gault (Cretaceous). The left-hand
figure represents a specimen imperfect above, and enlarged, showing the tuberculated costz.
The right-hand figure is a magnified cross-section, showing the septa and pali. (After Milne-
Edwards and Haime.)

Madreporarians are represented by a vast number of types, which
do not essentially differ in plan of structure from existing forms.

The Madreforaria Aporosa are divided into the following
families :—

family 1. Turbinolide.—t\n this family the corallum is generally
simple, or when compound is destitute of a coenenchyma. ‘The wall
is solid and imperforate, and the septa are in the form of lamelle,
often granulated on their sides. The zuerseptal loculi are open from
top to bottom, no endothecal structures in the form of dissepiments
or synapticule being developed. A few Palzeozoic Corals (such as
Duncanella and Cyathaxonia) may be referred here, but the family
is mainly Secondary and Tertiary.

The number of forms included in the 7urdznolide is so large, that only
a few of the leading types of the family can be here referred to in the

266 ZOANTHARIA.

briefest way. In the genus Z7zrvdznolia itself (fig. 141), the corallum is
simple and conical, with a projecting styliform columella, but without
pali. The costeze are very prominent, and the spaces
between them are marked with rows of small dim-
ples, which look like perforations in the wall, but do
not really penetrate to the visceral chamber. The
genus is well represented in the Lower Tertiary
deposits, but is doubtfully recent. In Szuzlotrochus
and its allies there is no columella, and pali are
rarely present. The type-genus is Cretaceous and
Tertiary. The genus /labellum is the type of
another group of the family, and is distinguished
by the compressed and wedge-shaped form of the
corallum, the calice thus assuming an oval form.
The structure of the wall and septa in Flabellum
is peculiar, but is not so different from that of the
same parts in certain fossil corals of other groups
as to justify the removal of the genus from its pres-
ent position. The species of Flabellum are all
Tertiary and Recent. In Placotrochus and its allies
a columella of a lamellar form is present, and there
are rarely pali. The genus is Recent and Tertiary,
as also is the related genus Sphenotrochus. The
genus Zvrochocyathus 1s the type of an extensive
series of forms, in which there is a fasciculate col-
umella, and generally one or more cycles of pali.
Trochocyathus itself (including 7hecocyathus) dates
from the Lias, and ranges to the present day. Al-
lied to this is the well-known genus Caryophyllia
(figs. 140 and 126), which ranges from the Creta-
ceous period to the present day, and is distinguished
Tie Giro by its possession of a trabecular columella and a
sulcata. Theupperfigure Single crown of pali (fig. 128, A).
shows the exterior of the The remaining types included in the 7urvbznolide
a ee Ae Shows are more or lessabnormal. The genus Dasmza, for
the calice, with the col- example, is so peculiar, that it has been regarded
umella and primary and 4s the type of a separate family (Pseudoturbinolide),
secondary septa. Eo- foe: : A
cene. the distinctive feature being that the septa are ar-
ranged in groups of three, in such a way that each
septum might be regarded as formed by the coalescence of three ele-
ments. The genus is Cretaceous and Tertiary. The Recent genera
Guynia and Haplophyliia, again, are remarkable in the fact that the
symmetry of the corallum is tetrameral, and they thus serve to lead us to
such ancient types as the Cyathavonie of the Carboniferous rocks. In
the true Cyathaxonie (as typified by the Cyathaxonta cornu of the Moun-
tain Limestone) the corallum is simple and conical, the septa having a
tetrameral symmetry, and a “fossula” being present. There is a promi-
nent columella, and the interseptal loculi appear to be free from endo-
thecal structures. As the presence of a fossula, and the fact that the
septa have a tetrameral arrangement, cannot be considered as dis-
tinctive features, there would not appear to be sufficient ground for
excluding this genus from the Aforosa. The Silurian corals which have
been included in the genus Cyathaxonta belong, however, to the genus
Lindstremia, which may also be referable to this division of the /Zadre-
poraria, though it will be here provisionally placed among the Augosa.

MADREPORARIA APOROSA. 267

Another Paleozoic type that may with great probability be included
among the 7wvdznolzde, is the Silurian genus Duncanella. In this genus
(fig. 142) the coral-
lum is simple and
conical, with a deep
calice, and a well-de-
veloped wall marked
by costae and en-
circling striz. The
wall, however, is de-
ficient at the ex-
treme base of the
corallum, thus al-
lowing the primitive
septa to protude as
a little cone (fig.
142.) Shere: are
eighteen (sometimes
seventeen) septa, the
symmetry of which
is completely radial,
and which meet cen-
trally so as to form
a sort of pseudo-
columella (fig. 142,C). Fig. 142.—Duncanella borealis, from the Silurian of North
The interseptal lo- America. a, Side-view of the corallum, enlarged twice ; B, Base of
cull, as in the Zyy- the corallum, enlarged, showing the absence of the wall and the pro-

: ; trusion of the septa; c, Transverse section of the corallum, en-
binolide generally, larged nine times ; D, Vertical section of the corallum, enlarged four

are completely open, times. (Original.)

and are free from en-

dothecal structures of any kind, though the bottom of the visceral cham-

ber is more or less extensively filled up by a deposit of stereoplasma.
Lastly, it is probable that the imperfectly understood genera Petraza

and Polycelia, both of which are of Paleozoic age, may ultimately be

shown to be aberrant types of the 7urbinolide.

family 2. Oculinide.—The corallum in this family is always
composite (fig. 143), the new corallites being usually produced by
lateral gemmation, and being united by an abundant and compact
coenenchyma, the surface of which is smooth or striated, but is not
echinulate. The wall of the corallites is imperforate, not distinct
from the ccenenchyma, and the lower portion of the visceral cham-
ber usually becomes extensively filled up in process of growth by
a deposition of stereoplasma. The interseptal loculi are usually
open to the base, but dissepiments or (as in Lophohelia) tabule are
occasionally developed.

The Oculinide appear for the first time in the Jurassic rocks
(Euhelia, Enallohelia, &c.), and are also represented in the Creta-
ceous rocks (Syzhelia, fig. 143, Diblasus, Laryhelia, &c.) In the
Eocene Tertiary we meet with early types of the Recent genus
Oculina itself, with its arborescent corallum and nearly smooth
coenenchyma. The well-known living genera Amphihelia and

268 ZOANTHARIA.

Lophohelia \ikewise appear in the Tertiaries, the former in the
Eocene and the latter in the Miocene. Lastly, the widely dis-
tributed Recent genus Stylophora (fig. 144) appears as early as the
Eocene Tertiary. The corallum in this genus is readily recognised
by its granulated coenenchyma, the presence of a styliform columella,

Ai, i e c AR hy
“i in |
ay \

Fig. 143.—Synhelia Sharpeana. Cretaceous.

and the fact that there are six fully-developed septa, with an inter-
mediate cycle of six rudimentary septa.

Family 3. Pocilloporide.—TVhe corallum in this family is compo-
site, with a dense coenenchyma, the corallites having their visceral
chambers largely filled up inferiorly with solid stereoplasma (fig. 145,
c). The calices are oval, and are definitely oriented, their long axes

corresponding with that

a | b of the branches of the
corallum. The septa
are small, twelve in
number, with a distinct
bilateral arrangement.
The cavities of the pol-
ypes are placed in com-
munication (as in the
ptitintt hace, ths coli of Siropiors, sevetiniete, Aleyonarians) by @ net-
6, Surface of the same, enlarged. (After Zittel.) work of canals, which
traverse the superficial

region of the colony. The mesenteries of the ventro-lateral pair
are, moreover, much longer than the others, and are the only ones
which carry mesenterial filaments, and which develop reproductive
organs. In Serviatofora, as shown by Moseley, these two mesen-

MADREPORARIA APOROSA. 269

teries correspond with especially deep intermesenteric pouches,
which fit into deep pits in the floor of the visceral chamber. ‘These
pits are bounded by septa of much reduced size, and may be fairly
compared with the ‘‘ fossula” of the Augosa.

This family comprises only the two genera Pocillopora and Seria-
topora, both of which, as above shown, have certain very remarkable
characters, and make a decided approach to the Rugose Corals. In
Pocillopora (fig. 145), there is a small columella, and well-developed

_ Fig. 145.—a. Portion of the corallum of Pocillopora aspera, var. lata, Verrill, of the natural
size; B, Part of the surface of same, enlarged; c, Section of the corallites of the same, showing
the columella, enlarged; pb, Vertical section of the same, enlarged, showing tabule. (After
Dana.)

tabulz (fig. 145, D) are present. The genus ranges from the Mio-
cene Tertiary. In Seviatopora, on the other hand, there is a large
compact columella, and only traces of tabulz are present. No fossil
forms of this genus have been hitherto discovered.

Family 4. Astreide.—tIn this large family of the Aforosa the
corallum may be simple or composite. Endothecal tissue in the
form of dissepiments is well developed, and tabulz are present
in some forms. The septa are lamellar, their free edges being
sometimes smooth or entire, sometimes dentated or ragged. The
increase of the composite coralla (fig. 146) is effected by gemmation
or by fission, and the new corallites usually become united directly
by their walls or costz, or in other cases by vesicular exothecal
tissue, a solid coenenchyma being rarely developed.

If Columnaria be admitted into the Astreide, the family is
represented as early as the Ordovician period. The Silurian
genera Stauria and Acervularia (as typified by A. ananas), the
Devonian Sattersbyia, and the Carboniferous /fetervophyllia may
likewise be regarded as Palzozoic types of the Astreide, though
all depart in different respects from the ordinary forms of this family.
Leaving the Palzozoic period, we find a great development of
Astreide to take place towards the close of the Trias, where the

270 ZOANTHARIA.

family is represented by numerous and varied types; a still
further expansion takes place in the QOolites; very numerous
forms are met with in the Cretaceous, and though there is some

Fig. 146.—Thecosmilia annularis. Coral-rag, England.

decrease in the Tertiaries, this great family still holds its ground
as the most important group of the ‘‘reef-building” corals.

The family of the Astreidz admits of subdivision into a number of
minor groups, and comprises such a vast number of forms that it is
impossible to do more here than to allude to a few of the more important
types. In the first place, there is a large series of
forms (Astr@@ simplices) in which the corallum is
simple and solitary. These simple Astrzeans ap-
pear under many generic types in the Secondary
period, and have survived to the present day.
Well-known genera are Montlivaltia (fig. 147),
ranging from the Tras to the Recent period ;
Trochosmilia, ranging from the Jurassic to the
Miocene ; and Pavasmilza, ranging from the Cre-
taceous to the present day.

In a second group of the Astreeans (Astree
reptantes), comprising such genera as Rhizangia

fe as Re and Asétrangia, the corallum is composite, and
ia caryophyllate, show. consists of short corallites budded out from basal
ing the greatly-developed stolons or expansions. Szzangia is Cretaceous

epitheca covering the : ae oie eee ;
(operon ce che coral and Tertiary, while Astrangza is represented in

Grant Oblite: the Eocene Tertiary, and survives at the present
day.

In a third group of Astreans (Astr@e@ gemmantes) are comprised
compound forms, in which the mode of increase is “ by gemmation from
the wall below the calicular margin” (Martin Duncan). In this group
are included various Secondary, Tertiary, and Recent corals (Cladocora,
&c.), and Professor Martin Duncan also places here the remarkable

MADREPORARIA APOROSA. 271

Paleozoic genera Heterophyllia and Battersbyia. 1n the former of
these (fig. 148) the corallites are long and slender, increasing by budding
around the calicular margin. There is a thick wall, marked by prominent
coste, which may be variously ornamented. There may be only six
septa; but there is usually a larger number of these structures, their

Fig. 148.—Heterophyllia angulata, from the Carboniferous Limestone of Northumberland.
A, A fragment of the corallum, enlarged slightly. 8, Transverse section of the same, enlarged

seven times. cC, Longitudinal section, similarly enlarged: ¢ Tabula; ~ Cut edges of the septa.
(Original.)

arrangement being distinctly bilateral, and in many respects resembling
that seen in young examples of Zaphrentis. Some of the septa usually
became coalescent, so as to give rise to fan-like groups, while the longer
septa are continued to meet in the centre of the visceral chamber. There
is no true columella, but a “fossula” is often present (fig. 148, B); and
the septa are further peculiar in so far that the wall does not appear to

SiN Ze lp NEF, 5}
ea]
Ras SAN et

Iv ae mg
ISIS. WA AN AG

Fig. 149.—/sastrea oblonga ; portion of a small polished slab, of the natural size, and a few
calices enlarged. Jurassic (Portland Oolite).

be formed by an extension and fusion of their outer ends. Lastly, dis-
sepiments in limited number are present, and curved “ tabule” are well
developed (fig. 148, C). The genus is only known as occurring in the
Carboniferous rocks of Britain.

The genus Battersbyia (with which the /ascicwlaria of Dybowski may
be compared) was founded to include certain Devonian corals possessing

272 ZOANTHARIA.

a fasciculate corallum, composed of unequally-sized cylindrical corallites,
which are not in contact laterally, or only touch each other to a limited
extent. According to Professor Martin Duncan, the septa are variable
in number and size, and the endothecal tissues consist of an abundance
of vesicular dissepiments along with well-developed tabulee.

In a fourth group of Astreeans (Astree cespitose) the corallum is
more or less tufted or caespitose, the corallites being produced by fission
from a common parent, but having their terminal portions free. As
examples of this large and well-marked group may be taken the recent
Mussa, or such Secondary corals as Thecosmilia (fig. 146) and Clado-

phyliia, the former of these being
2S one of the most characteristic gen-
" SS ee era of the Jurassic rocks.

ABER ae eS, In a fifth group (Astve@@ conflu-
ueae Meng se K ee | entes) we have a number of well-
= * 30°37 known genera of Astreeans, in which
4 the composite corallum increases

mainly by fission, this being so far
imperfect that the calices of the dif-
ferent corallites are usually more or
less completely confluent with one
another. Familiar examples of this
group are the genera Dzp/orza (Cre-
taceous to Recent), MWeandrina
(Jurassic to Recent), Euphylita
(Jurassic to Recent), and /fhzAz-
dogyra (Jurassic and Cretaceous).

All the remaining Astrzeans are
‘agglomerate ” or “ astraeiform,”
consisting of numerous closely ap-
proximated corallites, which may
be united by their walls directly or
by ccenenchyma, and which give
rise by their union to massive
coralla. In certain of the forms
included in this group, such as
Favia (Jurassic to Recent), the
mode of increase is essentially by

: et ce) fission. In others, however, includ-

Fig. 150.—a, A small mass of Ho/ocystis ele- - :
gans, of the natural size; B, A few calices of Ing Many of the most typical forms
the same, enlarged. Cretaceous. (After Milne- of the entire family, the mode of
Bclyewos nae Ble wie) increase is essentially by gemma-

tion, the new buds being usually
thrown out either from the all or from the calice of the parent. A very
large number of generic types of this group are known, abounding in
the Secondary and Tertiary periods, and being extensively represented
at the present day. Among the more familiar genera may be mentioned
Heliastrea, Prionastrea, [sastrea (fig. 149), Septastrea, Convexastv@a,
Plestastrea, Stylina, and Latimeandra.

Finally, we may consider here certain forms of corals which depart
more or less widely from the ordinary type of the Astraeans, but which
are nevertheless to be regarded as belonging to this family. The first of
these is the recent genus (eru/ina, in which the corallum is composite
and usually foliaceous, with a basal plate which is perforated by foramina
and slits. In the possession of this perforated basal plate the genus

MADREPORARIA APOROSA. 273

approaches the Fwgzda, and it has been commonly regarded as con-
stituting a special family of the Aforosa (the Pseudofungide).

Another remarkable type is constituted by the genus Holocystzs of the
Lower Greensand (Cretaceous). In this genus (fig. 150) the corallum is
composite, the corallites being connected directly by their walls or by
coste. There is a styliform columella, and the septa are developed in
three cycles, there being four principal septa of much larger size than
the others. The symmetry is thus conspicuously tetrameral, and for
this reason Holocystis has generally been regarded as belonging to the
Rugosa. The visceral chambers of the corallites are also intersected by
tabule, these structures being likewise abundantly developed in the
allied genus Coccophyllum of the Alpine Trias.

The Silurian genus S¢awrvza, which has been usually referred to the
Rugosa (Tetracoralla), and which has been regarded as the type of
the special family of the Staurvzd@, may also be regarded as belonging to
the Astreide, since it differs from the typical Astrzeans in little else than
its marked tetrameral symmetry. The corallum in Stauréa (fig. 151) is

Fig. 152.—Transverse section of a single corallite

Fig. 151 —A few calices of Stauria of Stauria astreiforniis, from the Silurian of Got-
astretforniis, enlarged, showing the land, enlarged ten times. wv, Primordial wall; s,
four primary septa forming a four- Secondary layer of stereoplasma, the corresponding
branched cross. Silurian. (After layer in the interior of the corallite being shaded.
Milne-Edwards and Haime.) (Original.)

composite and astreeiform, increase being effected by calicular gemma-
tion, and the corallites being connected directly by their walls. There
is no columella, but there are four principal septa which form a com-
plete cross in each corallite (fig. 152). These four septa divide the vis-
ceral chamber into as many quadrants, each of which contains three long
and four short septa. The total number of septa is thus thirty-two, six-
teen long and sixteen short. The periphery of the visceral chamber is.
occupied by vesicular dissepimental tissue, while the central area is
traversed by horizontal tabula. The only known species of this genus
is the Staurvia astreiformis of the Wenlock Limestone.

It would also seem not improbable that the Paleozoic genus Acer-
vularia, properly so called (in so far as based upon Aces vularia ananas,
Linn., of the Wenlock Limestone of Gotland), will have to be placed
among the Astreidz, though this point does not admit of discussion
here. On the other hand, many of the forms usually referred to Acer-

VOLS L S

274 ZOANTHARIA.

vularia are of a different structure to A. azanas, and are referable to
the Cyathophylloid group of the Rugosa.

There does not, further, seem to be any sufficient reason for excluding
the Ordovician genus Columnaria (= Favistella) from the Astreide. In
this genus the corallum (fig. 153) is massive, and is composed of pris-
matic or polygonal coral-
lites, which are usually
more or less completely
united by their walls.
The septa (fig. 154, A)
are well developed, and
are lamellar in form,
each corallite contain-
ing about thirty of these
structures, disposed in
two cycles, and alter-
nately long and _ short.
The long septa are not
of equal length, one

Fig. 153.—A colony of Columnaria calicina, Nich., from being often much longer
the Hudson River Group of Canada, of the natural siz. than the others ; and

(Original) they fall short of the

centre “of the Syaseeral
chamber, no columella being present. Endothecal tissue in the form of
dissepiments is very imperfectly developed, but numerous tabulz (fig.
154, B) are present.

Finally, the remarkable recent genus J/oseleya must be noticed
here. In this genus, as described by Mr Quelch, the corallum is

Fig. 154.—Sections of a corallite of Columnaria calicina, from the Ordovician of North
America, enlarged ten times. a, Cross-section; 8, Longitudinal section. v, Primordial wall;
s, Secondary layer of stereoplasma, the corresponding layer in the interior of the corallite being
shaded; ¢, Tabule; 7, Cut edges of septa. (Original.)

composite, the only known specimen consisting of a single large coral-
lite, round which smaller corallites are produced by calicinal marginal
budding. The wall is very thin, with a slight epitheca ; and the septa

MADREPORARIA APOROSA. 275

are very numerous and are arranged in several cycles, their inner edges
being dentate and giving rise superiorly to an irregular pseudo-colu-
mella. The septa are not alternately equal, and the symmetry appears
to be completely radial. Endothecal tissue is largely developed, the
dissepiments being vesicular in the periphery of the visceral chamber,
but uniting to form distinct tabulee centrally. In the possession of
an exterior vesicular zone and the presence of a central tabulate area,
the genus JZoseleya resembles the extinct genus Cyathophyllum ; and
it is referred by Quelch to the family Cyathophyllide. Upon the
strength of this resemblance, indeed, the authority just mentioned
refers the Cyathophyllide, along with the remaining corals usually
grouped under the head of Augosa, to the division of the A/adre-
poraria Aporosa. It is possible that future researches may justify
the merging of the Augosa in the Aforosa, but it does not appear
in the meanwhile that there is sufficient evidence to warrant a change
sO sweeping. Even as regards the genus Cyathophyllum itself and
its immediate allies, the resemblances to Moseleya are not without
noteworthy counterbalancing differences, as, for example, the general
bilaterai symmetry of the former, and the usual development of the
septa in a pinnate manner along three principal lines. Still more
weighty, of course, are the differences which separate the Zaphren-
toidea and the Cystiphylloidea from Moseleya. Upon the whole,
therefore, as will be more fully shown in what follows, there ap-
pears to be sufficient ground for the retention of the Auwgosa as a
special division of the AZadreporaria, though certain of the Rugose
corals of former writers may well be placed among the AZorosa.

276

CHAPTER. XQvVLEk
LOANTHA RI A—continued.
SECTION II. MADREPORARIA RUGOSA (TETRACORALLA).

THE corallum in the Wadreporaria Rugosa may be simple or com-
posite, and is composed of compact, solid sclerenchyma, the theca
being complete and imperforate. The septa are usually well devel-
oped and lamellar, with smooth or dentated edges; but they are
sometimes rudimentary. The symmetry of the corallum is almost
always obviously bilateral ; and the septa are generally of two orders,
alternately long and short. The septa are, typically, developed
according to a tetrameral system, new septa being produced along
one median and two lateral lines, while a fourth line is commonly
marked by a long or short septum ora fossula. A well-marked septal
‘“‘fossula” is usually present, and generally corresponds with a much
reduced primary septum, but there may be three or four fossule.
Endothecal tissue in the form of dissepiments is usually largely
developed; and very generally the dissepiments unite with one
another in the central portion of the visceral chamber so as to
form well-marked “tabule.” The mode of increase in the com-
posite coralla is mostly by lateral or calicular budding, and a true
coenenchyma is wanting.

It has been supposed by some naturalists that the so-called
Rugose corals might possibly be referable to the Hydrozoa, and,
at any rate, that they are not truly Madreporarian. On the other
hand, Mr Quelch has recently abolished the -ugosa as a distinct
division, and has united the corals formerly placed therein with the
Madreporaria Aporosa. Some of the forms included in the old
order of the Augosa may, as previously seen, be referred without
difficulty to the Aforosa, and as regards most of the others the view
advocated by Mr Quelch can be supported by evidence of no small
weight. The resemblances, namely, between the corallum of the
typical Rugosa and that of the MWadreporaria Aporosa are so numer-

MADREPORARIA RUGOSA. 277

ous and so important, that it is impossible to imagine that the coralla
in the two cases were secreted by different methods, or bore dis-
similar relations to the soft parts of the animals producing them.
Thus, in both groups alike the simple form of corallum (fig. 155)
consists of an outer wall or ‘‘theca,” enclosing a central space or
‘visceral chamber,” which is ordinarily divided into a series of
compartments by vertical partitions or “septa”; in both alike the
“visceral chamber” may be partitioned off into storeys by horizontal
plates or “tabule”; in both alike the interseptal loculi are liable to
be more or less subdivided by ‘‘ dissepiments” ; and in both alike

Fig. 155.—Morphology of the Ruwgosa. a, Fragment of Zaphrentis gigantea, showing the
septa (s), with the sparse dissepiments crossing the interseptal loculi, the epitheca (e), and the
thin proper wall (w); B, Transverse section of Zaphrentis Guerangeri, showing the septa and
dissepiments, the central area occupied solely by the tabule, and the ‘‘ fossula” (/); c, Longi-
tudinal section of the last, showing the arrangement of the tabulz. (A is after Edwards and
Haime ; B and c are after Mr James Thomson.)

)

the axial rod, known as the “columella,” may be developed. In
both groups, moreover, the corallum is often composite, and may
be regarded as a variously formed aggregate of “corallites,” each
of these subordinate elements of the colony being essentially similar
in structure to the typical simple corallum.

In spite of the above-mentioned general resemblances, it will
be found, however, that the central and most typical group of the
old order Augosa—viz., the group of the Zaphrentoid corals—is
separated from the division of the Madreporaria Aporosa by im-
portant morphological and developmental characters. But the
Zaphrentoids are very intimately connected by many intermediate
links with the Cyathophylloidea, the group of Augosa which most
nearly approaches the Astreide. The Cyathophylloids, again, have a

278 ZOANTHARIA.

close connection with the typical Cyst#phylloidea, and, through these,
with the most abnormal of all the forms included in the Rugosa
(viz., Calceola and its allies). Upon the whole, therefore, in the present
condition of our knowledge, it seems best to retain the name Augosa
for the three groups of the Zaphrentoid, Cyathophylloid, and Cysti-
phylloid corals, and to regard these as constituting a special division
of the Madreporaria.

While the corallum of the Augosa, as above limited, is in general
structure quite similar to that of the Wadreporaria Aporosa, it pos-
sesses Certain special peculiarities, which must be briefly noticed here.
The structure of the ¢/eca or wall of the corallum in the Augosa is
generally in agreement with that of the Aporosa, the outer invest-
ment of the visceral chamber being formed by the coalescence of
lateral outgrowths from the peripheral margins of the septa, as seen,
for example, in Zaphrentis (fig. 127, C). In other cases (as in Aelio-
phyllum and Crepidophyllum), the septa appear to end abruptly in
the wall, which is very thin, and seems to be developed indepen-
dently of the septa. In Streptelasma, again, a dense false wall is
formed by the junction of the much-thickened outer ends of the
septa (fig. 127, B). A true “epitheca” has been very commonly
described as present in the simple Rugose Corals, but it is very diffi-
cult to demonstrate the existence of this in microscopic sections, as
a structure distinct from the true wall, and it seems probable that
what has been generally called the “epitheca” is in many cases
really the “theca.” In certain of the compound Rugose Corals, on
the other hand, there exists a general epitheca enclosing the entire
colony inferiorly. As regards their internal structure, the septa are
usually composed, as in the Afsorosa generally, of a median plate
(“primordial septum”) bounded on both sides by a layer of dense
secondary sclerenchyma or “‘stereoplasma.” In some cases, as in
Pholidophyllum, the septa can be shown to be formed by the coal-
escence of obliquely directed calcareous trabeculze, the free ends of
which project at the inner margins of the septa. In Helophyllum
and its allies, the septa are thin, and are either unthickened by
secondary stereoplasma, or have only a very thin layer of this sub-
stance on the sides of the primordial septum. In these cases the
oblique trabeculze (‘‘ Septaldornen ” of the Germans) above spoken of
are greatly developed, and give rise to the peculiar structures known
as “carine,” which will be more fully considered later on.

The most important features in the structure of the corallum of
the Augosa are, however, connected with the arrangement and mode
of development of the septa. ‘The most obvious of the peculiarities
of a typical Rugose coral is the conspicuously bilateral disposition
of its parts (see fig. 139). The causes of this bilaterality will be best
understood by a consideration of the structure of a simple Rugose

MADREPORARIA RUGOSA. 279

coral, such as Streptelasma corniculum or Omphyma subturbinata.
From an investigation of such types it was shown by Kunth that
the symmetry of the corallum is tetrameral, and is governed by four
principal septa placed at right angles to one another. The bilater-
ality of the corallum depends upon the mode in which new septa are
developed in relation to three out of these four principal:septa. The
most important of the three principal septa in question is placed
along the convex (or “ dorsal”) side of the corallum, and new septa
are developed on both sides of this in a pinnate or feather-like
manner (fig. 156, A). This dorsal median septum may be longer or
shorter than the other septa, or of normal size, and it may be con-

Fig. 156.—a, Streptelasma corniculum, viewed from its convex (or “ dorsal”) side, showing
the intercalation of new septa on both sides of the “cardinal septum” (4), of the natural size.
B, Side-view of the same specimen, showing the development of new septa on one side of one of the
“‘alar” septa (s). From the Ordovician rocks of North America. (Orginal.)

veniently spoken of as the “cardinal septum” (the “ Hauptseptum ”
of Kunth). The septa produced on the two sides of the “cardinal
septum ” gradually get less and less oblique to the latter, till we reach
two septa placed laterally, at right angles to the “cardinal septum,”
which may be spoken of as the “alar” septa (the “‘Seitensepta” of
Kunth). On the ventral side of each alar septum—~v.e., on the side
furthest removed from the “ cardinal septum ”—new septa are devel-
oped in an oblique manner (fig. 156, B, s). The remaining septum
of the quartette of principal septa is placed in the middle line on the
concave (or “ventral”) side of the corallum, and it does not serve
as a starting-point for the development of new septa, and therefore

280 ZOANTHARIA.

does not show any feather-like disposition of the septa on its sides.
It may be longer or shorter than the others, and may be spoken of
as the “counter” septum (the “Gegenseptum ” of Kunth).

Hence, the surface of the theca of a simple Rugose coral such as
Streptelasma corniculum is marked out by these four principal septa
into as many quadrants, as shown in the annexed sketch (fig. 157)
of a specimen of this coral, viewed from the base, and therefore
greatly foreshortened. ‘Thus the dorsal or convex side is divided
into two “cardinal” quadrants, occupied by the pinnately developed
septa which flank the “cardinal septum” (fig. 157, 2). The two

Fig. 158.— Transverse section of
Paleocyclus porpita, from the Silurian

Fig. 157.—Plan of the septa in a speci- of Gotland, enlarged three times.
men of Streptelasma corniculum, viewed i‘ Cardinal” septum, contained in ,
from below, the radiating lines indicating the fossula; ss, ‘‘Alar” septa; g,°
the peripheral margins of the septa as ap- “*Counter” septum. In the section
pearing on the surface of the corallum. figured there are only forty septa, but
hf, The ‘‘cardinal septum’; ss, The there are usually forty-four, twenty-
‘‘alar” septa; g, The ‘‘ counter septum.” two long and twenty-two short.
(After Kunth.) (Original. )

‘counter ” quadrants, on the other hand, are occupied by the septa
developed along the ventral side of the “alar” septa (fig. 157, ss),
and they merge with one another in the mesial ventral line, owing
to the fact that the “counter septum” (g) is not a source for the
development of new septa. It follows from the above that an inspec-
tion of the surface of a well-preserved example of Streptelasma cor-
niculum or Omphyma subturbinata enables us to recognise by the
disposition of the septa the position of the “cardinal” and “alar”
septa, but that the ‘‘ counter septum” cannot be thus recognised.

It was further pointed out by Kunth that though the four principal
septa above spoken of divide the corallum into four quadrants, it does
not necessarily follow that these contain the same number of septa
each. On the contrary, it is not unusual to find that the ‘“ counter
quadrants” contain conjointly a greater number of septa than do the
two “cardinal quadrants.”

MADREPORARIA RUGOSA. © 281

Thus in Pal@ocyclus porpita (fig. 158), the number of septa in each
quadrant is sometimes the same—namely, nine—making, with the four
principal septa, a total of forty. In most examples of this coral there
are, however, forty-four septa in all, the two counter-quadrants con-
taining each eleven septa, while the cardinal quadrants have nine
each.

The peculiar arrangement of the septa above indicated can be
recognised in a large number of the simple Rugose corals by a
mere inspection of the surface of well-preserved examples. Where
the surface is badly preserved, and the observer has to rely upon
thin sections, the “cardinal” and ‘‘counter” septa can usually
_ be readily recognised, but it is often a matter of difficulty to deter-
mine the “alar” septa. In some of the most completely radial
forms—as in some species of Cyathophyllum—the position of the
four principal septa may cease to be recognisable in transverse
sections of the corallum. Lastly, in cases where the septa are rudi-
mentary—as in the Cystiphylloids generally—it may be impossible
to demonstrate the tetrameral arrangement of the septa, though in
other cases (as in Goniophyllum) no such difficulty obtains.

As regards the relative /ength of the septa, the most usual arrange-
ment is to find that the septa are alternately equal (approximately
equal, that is to say); so that the septa consist of a long series and
a short series alternating with one another. Hence, the septa are
often said to be of two “orders,” but the septa of each order are
by no means always quite equal in length, nor is it to be supposed
that the septa of each order were simultaneously developed.

In a great many of the Augosa, the bilaterality of the corallum is
especially marked by the unequal development, as regards length, of the
“ cardinal” and “ counter” septum, one or other of which usually occupies
the so-called “fossula.” The “fossula” or “ fossette” (fig. 139), as pre-
viously explained (see p. 262), is a more or less conspicuous groove or
depression in the calice, due to a reduction in size of the septa at that
point, necessitated, in all probability, by the existence in the living polype
of one or more hypertrophied mesenteries carrying the reproductive
organs. Asa rule, there is only one “ fossula,’ which may be median or
lateral in position, the latter being, however, very unusual. Sometimes
there are three fossulaze, one median, and two lateral; while in other cases
(2.g., Omphyma) there are four of these calicine grooves, two median, and
two lateral. In this last case (fig. 159, A), the four fundamental septa
occupy the four fossulz, the cardinal septum being the best developed.
In the much more common case of there being only a single median
fossula, this is almost always related to either the “cardinal” or the
“counter” septum. The most usual arrangement is for the fossula to be
placed on the convex (or “ dorsal”) side of the simple coralla, in which
case it is intersected mesially by the “ cardinal septum,” which is then
much reduced in stze. This disposition of parts occurs in Pal@ocyclus
porpita (fig. 158), in the genus Sz¢vepfe/asma, and in most of the species
usually referred to Zaphrentis. Sometimes, as in Lophophyllum, the
“cardinal” septum is very short, and occupies the dorsally-placed fossula,

282 ZOANTHARIA.

while the “ counter” septum is especially long. On the other hand, the
fossula may be placed on the concave (or ‘“‘ ventral”) side of the simple
coralla, as in some of the species generally placed in Zaphreniis (e.g.,
in Zaphrentis Enniskillent, fig. 139). In this case the fossula is inter-
sected by the “counter” septum, which is reduced in size, or may be
altogether rudimentary or obsolete ; while the “cardinal” septum may
have its normal dimensions, or may be specially developed. In rare
cases the fossula (when single) is lateral in position, and 1s occupied by
one of the “ alar” septa.

The interseptal loculi in the Rugose corals are generally more or
less largely occupied by endothecal tissue in the form of dissepi-
ments and tabulz, both these structures being usually conjoined.
The dissepiments are principally developed in the peripheral area

Fig. 159.—Structure of Omphyma subturbinata, from the Silurian of Britain. a, Transverse
section, enlarged slightly, showing the four fossulz, the arrangement of the septa, and the large
central area occupied by the tabulz: /, Cardinal septum; ss, Alar septa; g, Counter septum. B,
Longitudinal section, slightly enlarged: e¢, Peripheral zone of vesicular dissepimental tissue; 7,
Tabule. (Original.)

of the visceral chamber, and have the form of curved calcareous
plates directed obliquely from one septum to the next one. In
transverse sections (fig. 159, A) the cut edges of the dissepiments
appear as transverse lines passing directly or in a curved manner
across the interseptal loculi, and connecting together adjacent
septa. In longitudinal sections (fig. 159, B) the dissepiments are
usually seen to give rise to an outer zone of lenticular vesicles (e)
which are directed obliquely inwards and downwards from the in-
ternal surface of the wall towards the centre of the visceral chamber.
In the central region of the corallum the dissepiments become more
nearly horizontal and are developed in adjacent interseptal loculi at
the same level, their coalescence giving rise to the flat or curved
transverse partitions which are known as “tabule” (fig. 159, B, 7).
The central tabulate area of the visceral chamber varies much in
extent, but is best developed in those types (such as Amfplexus,

MADREPORARIA RUGOSA. 283

Omphyma, Campophyllum, &c.) in which the septa are short and do
_ not extend far from the wall inwards.

The development of the peripheral zone of vesicular dissepimental
tissue is also very variable, its extent being in inverse proportion to that
of the central tabulate area. It is very well developed in Cyathophyllum
and in the Cyathophylloid corals generally, though considerably reduced
in such types as Omphyma and Campophyllum. in Zaphrentis and the
Zaphrentoid corals in general the dissepimental vesicular zone is greatly
reduced, and may be practically absent, the central tabulate area being
greatly developed. On the other hand, in Cystzphyl/um and its imme-
diate allies the central tabulate area is invaded by the dissepiments, and
the entire visceral chamber becomes filled with a vesicular tissue, the
_central cells of which are usually of comparatively large size, and repre-
sent tabule. In Paleocyclus porpita, and in some very flat discoid
types (such as Microcyclus), the depth of the visceral chamber is in-
sufficient to permit of the development of dissepiments or tabulz. These
structures are likewise obsolete in the aberrant genus Cadceola,; while
they are very imperfectly developed in the genus Lindstremia, owing
to the fact that the lower part of the visceral chamber becomes filled by
secondary stereoplasma.

As regards exothecal structures, the corallum of the Rugose corals
generally exhibits externally more or less conspicuous vertical ridges,
which are spoken of as “rugs,” and which are separated by inter-
vening depressions or grooves. In some cases, these longitudinal
ridges may correspond with the outer edges of the septa within, and
may thus resemble the structures known in the Aporose corals as
““coste.” In most cases, however, the ridges correspond with the
interseptal loculi, and thus alternate with the septa. In some cases
(e.g., in Pholidophyllum) Lindstrom has described the vertical ridges
as Carrying rows of minute, overlapping, calcareous plates or scales.
Other superficial exothecal structures are occasionally developed
in Rugose corals, such as the surface-tubercles of some species of
Zaphrentis, the root-like processes of attachment of Omphyma, &c.,
and the connecting-processes which unite adjacent corallites in £77-
dophyllum. The remarkable opercular plates of such genera as
Gontophyllum and Calceola must also be regarded as of an exothecal
nature. It must be regarded as doubtful, however, if anything
which can properly be described as a “‘ coenenchyma ” is developed
in any composite Rugose coral. In such types, the corallites may
remain isolated except at their point of origin from the colony ; or,
if in contact, they may either be united by the fusion of their walls,
or the walls may be absent and the corallites are united to one
another by the extension and confluence of their septa, as seen, for
example, in the genus P%illipsastrea (fig. 160).

_ As regards their classification, the Rugosa are here considered as a
mere section of the Madreporaria, instead of as a distinct order of
Corals, and the signification of the name has been considerably

284 ZOANTHARIA.

narrowed by the removal to the AZorosa of various types originally
referred to this group. ‘Thus, the Paleozoic genera Stauria and
Cyathaxonia, previously generally placed among the Augosa, are here
relegated to the Agorosa, while Professor Martin Duncan has been
followed in the reference to the same group of the Secondary genus
Holocystis, the Tertiary Conosmilia, and the recent Haplophylia and
Guynia. As thus limited, the Augosa constitute a moderately natural
assemblage of forms, which may be subdivided into three main

\"\ BINS >

Fig. 160.—Phillipsastrea Verneuilli. From the Devonian (Corniferous Limestone)
of N. America. (After Billings.)

sections, which are typified respectively by the genera Cyathophyl-
lum, Laphrentis, and Cystiphyllum, and which may therefore be
spoken of as the Cyathophylloidea, Zaphrentoidea, and Cystiphyl-
loidea.1 As regards their distribution in time, all these groups are
confined, so far as at present certainly known, to the Paleozoic
period, and their characters and principal types will now be briefly
considered.

I. CYATHOPHYLLOIDEA.

The section of the Cyathophylloidea comprises those Rugosa in
which the peripheral region of the visceral chamber is more or less
extensively occupied by vesicular dissepimental tissue, the lenticular
cells of which are directed obliquely inwards and downwards, their
convex sides being turned upwards (fig. 161, B). The central area
of the visceral chamber is occupied by tabulz, but the tabulate area
is often much restricted. ‘The length of the septa is very variable,
but these structures are always present and are generally alternately
long and short, the septa of each order being approximately equal. |
In most forms there is a well-developed fossula, and the symmetry
is conspicuously bilateral. In others the fossula is rudimentary or

1 The elaborate classification of the Rugose corals put forward by Dybowski
has not been adopted here, partly because many of the forms placed in this group
by this observer are here removed elsewhere, and partly because the details of his
proposed arrangement are largely unnatural.

CYATHOPHYLLOIDEA. 285
obsolete, and the symmetry becomes more or less radial. <A true

columella may or may not be present, and the corallum may be
simple or composite.

The Cyathophylloids, so far as certainly known, are confined to
the Ordovician, Silurian, Devonian, and Carboniferous deposits, and

are thus wholly Palzeozoic.

ah

A
}}

1v,
iy)

}

E

7 LY)
y
if

Tp
*

Fig. 161.—Structure of Cyathophyllum heterophyllum, from the Middle Devonian of Gerol-
stein. A, Transverse section of the corallum, slightly enlarged; B, Longitudinal section, also
slightly enlarged, showing the outer vesicular zone (¢), and the central area of anastomosing
tabule (4). This is one of the species of Cyathophyllum in which a “‘fossula” is not clearly

recognisable, the symmetry thus becoming completely radial. The septa nearly reach the centre,
and their inner portions are considerably thickened. (Original.)

Upon the ground of a close structural resemblance between the genus
Cyathophyllum itself and the recent genus Moseleya, Mr Quelch, as pre-
viously noted, has proposed the removal of all the Cyathophyllizde to the
Aporose Madreporarians, and the placing them in the immediate vicinity
of the Astrveide,; but this change can hardly be accepted. It is true
that there are certain species of Cyathophyllum which are so far similar
to Woseleya that they show an almost complete radial symmetry, a “ fos-
sula” not being distinctly developed, while a tetrameral arrangement of
the septa is not recognisable. Even within the limits of the genus
Cyathophyllum itself, there are, however, species with a well-developed
fossula and a distinctly bilateral arrangement of parts; while other
allied genera are as conspicuously bilateral as is the genus Zaphrentzs,
and possess a “fossula” of precisely the same type as that of the latter.
Moreover, through such genera as Omphyma and Campophyllum a com-
plete transition is effected between the typical Cyathophylloids and the
typical Zaphrentoids. Lastly, through Cystiphyllum it becomes easy

to pass from Cyathophyllum or Actinocystis to such aberrant types as
Goniophyllum and Rhizophyllum.,

Family 1. Cyathophyllide.—The chief family of the Cyatho-
phylloid corals is that of the Cyathophylide, comprising all those
members of the present section in which the septa are smooth, and
consist of a median plate (“ primordial septum ”) thickened on both
sides by a layer of stereoplasma or secondary calcareous deposit.

286 ZOANTHARIA.

Of the many genera of this family the three leading types are
Cyathophyllum, Lithostrotion, and Omphyma.

In the genus Cyathophyllum itself, the corallum may be simple or
composite, the compound forms being sometimes massive (fig. 162),
sometimes fasciculate. The septa are numerous, alternately long and
short, the longer ones being
continued to, or nearly to,
the centre of the visceral
chamber, where they are
usually more or less twisted,
and give rise to a sort of
spurious columella (fig.
161, A). The external dis-
sepimental zone is largely
developed, and is com-
posed of oblique vesicles
of small size (fig. 161, B);
while the internal tabulate
area is comparatively small
and incompletely devel-
oped, the tabulz having a
vesicular character. The

Fi 6 A i Cyathophyllunt hexagonum “fossula” is small or obso-
ig. 162.—A specimen of Cyathophyll :

from the Devonian Limestone of Gerolstein, of the nateral, ete; ime symmetry in the
size. (After Zittel.) latter case becoming more

or less completely radial ;
whereas when the fossula is recognisable, the symmetry is obviously
bilateral. Many species of the genus are known, the earliest forms
appearing in the Ordovician and the latest in the Carboniferous rocks.
The genus is especially well represented in the Devonian and Carboni-
ferous rocks.
The Silurian and Devonian genus Actinocystis differs from Cyatho-
phyllum proper, chiefly in the fact that the septa are imperfect, passing

. Fig. 164.—A rachnophyl-
Fig 163.—Avrachnophyllum (Stronebodes) lume (Stronebodes) gracile.
pentagonum. Silurian, Canada. Silurian, Canada.

externally into vesicular tissue, which also largely replaces the central
tabulate area. Allied genera are the Spongophyllum and Endophyllum
of the Devonian rocks, in which the corallum is composite, and the septa
are also more or less incomplete.

The genus Acervularia, as based on the 4. ananas of the Silurian

CYATHOPHYLLOIDEA. 287

rocks, may perhaps be referred, as previously remarked, to the As¢reide ;
but many of the astrziform corals usually placed in this genus, and
especially the so-called “ Acervularie” of the Devonian rocks, are nearly
allied to Cyathophyllum. The corals in question agree in general struc-
ture, and particularly in the possession of an exterior vesicular zone, with
Cyathophyllum, but differ from this in the fact that the central tabulate
area is partitioned off and enclosed by a secondary and interior wall or
“mural investment.” Another type which may be placed in this neigh-
bourhood is the Silurian genus Avachnophyllum (= Strombodes), in which
the corallum is composite and astrziform (figs. 163 and 164), but the
walls of the corallites, as also the septa, are very imperfectly developed,
while the visceral chamber is almost filled with vesicular tissue disposed
centrally in funnel-shaped layers.

As the type of another group of the Cyathophyllide, the great genus
_ Ltthostrotion, so characteristic of the Carboniferous deposits of many
parts of the world, may be taken. The
corallum in this genus (fig. 165) is al-
ways composite, sometimes massive,
sometimes fasciculate, according as the
prismatic or cylindrical corallites are
or are not in direct contact with one
another. In internal structure, Lztho-
strotzon is built upon the type of
Cyathophyllum, each corallite having
an external vesicular zone and an inter-
nal tabulate area (fig. 166, B). The ve-
sicular zone is narrow, and the tabulate
area is wide, and is traversed centrally
by a well-developed styliform columella.
The septa are alternately long and
short, their disposition being clearly
tetrameral ; and the symmetry is dis-
tinctly bilateral, a well-marked fossula
being often recognisable. Thus, in the
species here figured (fig. 166, A), there
are fifty-six septa in all in each corallite,
twenty-eight of these being long ones
and a similar number being short. Of
the twenty-eight long septa, the four ae is ; aie
leading septa are readily determined, ,,/i8,x65,7 Fragment ofa mass of Litho
The “cardinal septum” (%) is shorter Carboniferous. (After De Koninck.)
than the others, and is placed in the
fossula, while the “counter septum” (g) is placed at the opposite end of
the compressed columella, a definite middle line to the corallite being
thus established. At right angles to the centre of this line are the two
“alar septa” (ss), and the remaining twenty-four long septa form four
groups of six septa each, corresponding with the four quadrants of the
corallite. Some of the species of Zzthostrotzon are not as regularly con-
structed as the above, but the same general type is preserved throughout
the genus.

The genus Diphyphyllum, ranging from the Silurian to the Carbon-
iferous, appears to resemble Zz¢hostrotion in general structure, but the
corallites of the fasciculate corallum are devoid of a columella. The
genus ELrzdobhyllum, of the Silurian and Devonian rocks, again, seems
to differ from Diphyphylium principally in the fact that the long, cylin-

288 ZOANTHARIA.

drical corallites are united together by horizontal connecting-processes of
an exothecal nature.

Lastly, a natural transition is effected between the typical Cyatho-
phyllids and the typical Zaphrentide by means of such genera as

Fig. 166.—Structure of Lzthostrotion Martini, from the Carboniferous Limestone. a, Trans-
verse section, enlarged about 3% times; B, Vertical section, similarly enlarged. 4, Cardinal
septum, situated in the fossula; g, Counter septum; ss, Alar septa: co, Columella; e, Vesicular
tissue; ¢, Tabule. (Original.)

Omphyma and Campophyllum. The genus Omphyma is wholly confined
to the Silurian rocks, and comprises simple, turbinate or cylindro-conical
corals, the wall of which gives out root-like processes of attachment of an
exothecal nature (fig. 167, a). The calice shows four shallow fossulz,
placedat right angles
to one ancther, and
lodging the four lead-
ing septa; and the
same structure is
shown in transverse
sections of the cor-
allum (fig. 159, A).
The septa are nu-
merous, and are al-
ternately long and
short ; but even the
longest septa extend
a limited distance
only into the visceral
chamber, thus leav-
ing a very extensive
central area, which
is occupied by the
tabule (fig. 159, B).
Fig. 167.—Omphyma subturbinata, from the Silurian of Gotland, The genus agrees im
reduced in size. a@, Side view of the corallum: 4, View of the calice this respect with the
showing the four fossule. (After Milne-Edwards and Haime.) Zaphrentoids, but it
shows its relation-

ship with Cyathophyllum by the possession of an external zone of ves-
icular tissue, though this is comparatively of small thickness, and is

CYATHOPHYLLOIDEA. 289

composed of comparatively large vesicles. In the reduction of the ex-
ternal vesicular zone and the proportionate development of the central
tabulate area, the Devonian and Carboniferous genus Campophyllum
closely resembles Omfhyma, and also approaches the Zaphrentoids. The
genus further resembles these latter, and differs from Omhymza, in the
possession of a single very large fossula, giving rise to a conspicuous
bilaterality of the corallum.

Family 2. Heliophyllide.—The members of this family agree in
many respects with the typical Cyathophyllide, but are markedly
distinguished from these by the characters of the septa. These
structures in the present family are thin, and are composed essen-
tially of nothing more than the primordial septal plate, occasionally
with a thin coating of stereoplasma towards their bases. The septa
are thickened on their sides by conspicuous lamellar ridges (rep-
resenting the septal spines of such forms as /Pholidophyllum),
which are directed obliquely inwards and upwards from the exterior
of the visceral chamber towards the centre of the same, and which

nt

‘th nad)

‘)

re.

a

IX)

My

i

B

Fig. 168.—Structure of the corallum of Heliophyllum elegantulum, from the Devonian (Ham-
ilton Group) of North America. a, Transverse section, enlarged nearly twice; °B, Longitudinal
section of the same, taken just below the calice, similarly enlarged. . #, Cardinal septum, in the
fossula; g, Counter septum; ¢, Peripheral vesicular zone; 7, Central-tabulate area; 7, Oblique
septal ridges (‘‘ carinal ridges”) on the sides of the septa. (Original.)

form a marked feature in longitudinal sections of the corallum (fig.
168, B). In transverse sections of the corallum (fig. 168, a) these
oblique septal ridges appear as conspicuous cross-bars or “ carinze,” ?
which run transversely to the septal laminze and produce a most char-
acteristic appearance. On the free edges of the septa, again, the
septal ridges appear as prominent transverse ridges or teeth. Owing
to the development of the septal ridges just spoken of, the septal

1 The appropriate name of ‘‘carine” was given to these septal bars by Miss
Mary E. Holmes, M.A.
VOI vI- At

290 ZOANTHARIA.

laminee often become more or less zigzag in the peripheral part of
the corallum.

As regards the other characters of the Helophylide, the outer ends
of the septa terminate with apparent abruptness in a thin outer invest-
ment, which is not improbably rather of the nature of an epitheca
rather than of a true “wall.” In some cases (Phillipsastrea) the
corallites have no definite outer investment, the septa of adjacent
tubes becoming confluent. As in the Cyathophyllida, there is a
well-developed external vesicular zone, and a comparatively small
central tabulate area. The range of the family is from the Silurian
to the Carboniferous, but the great majority of the species are
Devonian, the group being, as a whole, as characteristic of the De-
vonian period as the family of the Clstophylliide is of the succeed-
ing Carboniferous period. The three leading genera are Helophyl-
lum, Crepidophyllum, and Phillipsastrea.

In the genus Heliophyllum itself the corallum is simple (fig. 169) or
composite ; the carinate septa are numerous and alternately long and
short, the latter, however, being of considerable length; and the longer
septa are, many of them, continued inwards to near the centre of the
visceral chamber, where they become twisted, and coalesce to form a
spurious columella, which is of large size, and often projects prominently
into the floor of the calice (fig. 168, A). The symmetry of the corallum is
distinctly bilateral, a well-marked “fossula”
being present. The “cardinal septum” is
shorter than the other long septa,and, along
with two short septa, occupies the fos-
sula. The exterior vesicular zone is well
developed, dissepiments being exceedingly
abundant, and there is a small tabulate
central area (fig. 168, B). The species of
the genus are principally Devonian, but
some Silurian corals have also been re-
ferred here. The genus Helzophyllum has
commonly been regarded as a mere sub-
genus of Cyathophyllum, but if due weight
be given to the peculiar structure of the
septa, it can hardly be placed in the family
wet _ of the Cyathophyliide at all. The genus

Fig. 169.—A young form of ee Crepidophyllum is in general structure es-
en rane he ee a lus (On. sentially similar to Hediophyllum, but the
ginal.) central tabulate area is enclosed in a dis-

tinct accessory wall or inner mural invest-
ment, which is usually open on one side so as to communicate freely with
the large fossula (fig. 128, B). The corallum may be simple or compound,
and all the known species of the genus are found in the Devonian rocks.

Lastly, in the genus PAz/iépsastrea (=Smithia) the corallum is com-
pound, and the internal structure of the corallites is essentially the same
as in Heliophyllum.: The corallites, however, are devoid of a wall, and

1 This statement is based on a microscopic examination of Phdllipsastrea
Verneutlli, of the American Devonian rocks, the type-species of the genus.

CYATHOPHYLLOIDEA. 291

become united to one another by the confluence of the outer ends of the
septa (fig. 160). The septa are “carinate,” and alternately long and
short, a distinct fossula being usually present, and the symmetry thus
becoming clearly bilateral. The species of PArllipsastr@a are prin-
cipally Devonian, but the range of the genus extends into the Carbon-
iferous period.

family 3. Clisiophyllide.—The corals of this family agree with
the Cyathophylide and Helophyllide in the general character of
possessing a well-marked exterior vesicular zone and a central tabu-
late area. The central tabulate area is, however, traversed in this
family by an extensively developed and complex spurious columella,
formed partly of vertical, often twisted plates which have a general
radial direction, and partly of vesicular tabulz which intersect the
former in an obliquely ascending direction. This massive pseudo-
columella appears in the floor of the calice as a rounded or conical
boss of greater or. less size, the surface of which, in well-preserved
specimens, shows radiating, often spiral ridges. The septa are
numerous, of two sizes, alternately equal. The symmetry is usually
markedly bilateral, a well-developed “‘ fossula,” lodging the ‘ cardinal

YC

Rca

<A

\

Cai tt ep
SER Aae ma

Seca ie aS

SOS

Fig. 170.—Morphology of the Clistophyllide. a, Transverse section of Dibunxophylium sp.,
from the Carboniferous rocks of the North of England, slightly enlarged; B, Longitudinal
section of the same. 4, ‘‘ Cardinal septum” situated in the ‘‘ fossula”; g, ‘‘ Counter septum” ;
e, Outer zone of vesicular dissepiments; 7, Central area of anastomosing tabule; c, The
columellar plate. (Original.)

septum,” being present. The ‘‘ cardinal septum ” is shorter than the
other long septa, and the “‘ counter septum ” is often specially devel-
oped. ‘The septa are thickened by lateral deposits of stereoplasma,
and are not “carinate.” The corallum may be simple or composite.
The Chsiophylide are mainly, if not exclusively, confined to the

Milne-Edwards and Haime state that a columella is present, but no traces of this
structure appear in thin sections.

292 ZOANTHARIA.

Carboniferous period, the principal genera being C7liszophyllum,
Dibunophyllum, Cyclophyllum, Aulophylum, and Lonsdaleia.

In the genus CZistophyllum the general structure of the simple coral-
lum is as described in the above characterisation of the family Cézszo-
phyllide. The great central pseudocolumellar mass is composed of a
number of tolerably regular, radial and somewhat spiral lamellae, which
may be regarded as corresponding with prolongations of the septa, and
which are intersected by obliquely directed vesicular tabule (fig. 171, B).
As seen in the floor of the calice, the pseudocolumella forms a large
rounded boss, marked by spiral radiating ridges. The zone immediately
external to the pseudocolumella is occupied by inosculating tabule,

Fig. 171.—A, Cross-section of two corallites of Lonxsdaleia duplicata, Lower Carboniferous, en-
larged ; B, Cross-section of the corallum of Clistophyllum Keyserlingi, Lower Carboniferous, of
the natural size. (After James Thomson and the Author.)

forming large vesicles ; and external to this region is a deep peripheral
zone of small oblique dissepimental vesicles, traversed by the septa.
The septa are numerous, alternately long and short, and a well-marked
septal fossula is present. The species of Cl¢szophyllum are probably
wholly confined to the Carboniferous period, though some Devonian and
Silurian corals have been referred here.

The Carboniferous genus Dzbunophyllum (fig. 170) is very closely
related in general structure to Clzs¢ophyllum, but the pseudocolumellar
area is divided into two by a vertical partition, or columellar plate,
one end of which is usually connected with the “counter septum,” while
the other is directed to the “cardinal septum” in the fossula, the bilateral
symmetry of the corallum being thus exceedingly well marked. Again, in
the Carboniferous genus Awlophyllum, and the nearly allied or identical
Cyclophyllum, the pseudocolumellar area is enclosed by a kind of inner
mural investment or accessory wall, and is prolonged at one point into a
lateral tongue-like extension directed to the fossula. The pseudocolumella
has a minutely vesicular structure, the vesicles being formed by radial
lamellze intersected by obliquely ascending arched dissepiments. <Azdo-
Phyllum stands in the same relation to Clszophyllum that Crepidophyllum
holds to Helzophyllum, or that the Devonian Acervularie (so-called) hold
to Cyathophyllum.

ZAPHRENTOIDEA. 293

Axophyllum, again, comprises simple Clisiophylloid corals of Car-
boniferous age, in which there is a large vesicular pseudocolumella
piercing a central tabulate area, which is enclosed by an accessory wall,
and is in turn surrounded by a vesicular zone. Lastly, we may include ©
here the Carboniferous genus Lossdaleza (fig. 134), in which there is a
composite, fasciculate, or astrzeiform corallum. Each corallite has, as
usual in this family, a large pseudocolumella, formed of twisted lamelle,
and having a vesicular structure (fig. 171, A). The columella traverses a
well-developed tabulate area, but the genus differs from the other types
of the family in the fact that the outer zone of the corallum is occupied
wholly by large lenticular vesicles, the septa being here obsolete, and
being developed in the central region only. In the series of the C//szo-
phyllide, Lonsdaleta holds the place occupied by Lzthostrotion in the
series of the Cyathophyliide.

Il. ZAPHRENTOIDEA.

The section of the ZaphArentotdea comprises those Rugose Corals
in which there is a comparatively limited amount of dissepimental
endotheca, the visceral chamber never being sheathed with a zone

Fig. 172.—Morphology ot Zaphrentis. a, Transverse section of a fully-grown individual of
Zaphrentis Enniskillent, from the Carboniferous Limestone, enlarged about twice. 8, Trans-
verse section of a very young example of the same, enlarged six times. c, Part of the theca of
the same, enlarged, showing one long and two short septa, the bases of these structures forming
the wall. The septa have a primordial lamina thickened by stereoplasma. bp, Long section of
the same, showing the tabula. (Original.)

of vesicular tissue ; while there is, on the other hand, a proportion-
ately extensive development of ‘the tabule. [In the Hadrophyllide

204 ZOANTHARIA.

and in Paleocyclus porpita, the corallum is so short that neither dis-
sepiments nor tabulz are developed at all.] The septa are thickened
with stereoplasma (fig. 127, B and c), and are not “carinate.” As
a rule, the septa are of two orders, alternately long and short. In
all the typical members of the section, the symmetry is conspicu-
ously bilateral, and a tetrameral disposition of the septa can usually
be readily determined. There is generally a well-marked fossula
(fig. 172, f), placed dorsally and containing the “cardinal septum ”; or
ventral in position, enclosing the “‘counter septum”; or rarely lateral
and traversed by one of the “‘alar septa.” In some forms a fossula
is not determinable (e.g., in some species of Stveptelasma and in
Lindstremia generally). In the
genera just mentioned it is also
usual for the lower part of the
visceral chamber to be more or
less largely filled up with a de-
posit of stereoplasma. The Zaph-
rentoid Corals are exclusively
Paleozoic, and range from the
Ordovician to the Carboniferous
period, or, if the genus Polycelia
be admitted here, to the Permian.
Family 1. Laphrentidea.—The
typical family of the Zaphrentoid
Corals is that of the Zaphrentide,
of which the genus Zaghrentis
itself 1s the. central fommay) ite
family is characterised by the
marked bilaterality of the coral-
lum, a well-developed fossula be-
ing present, while the develop-
ment of the septa is usually char-
acterised by the inequality in size
of certain of these structures.
The septum which occupies the
Fig. 173.—Zaphrentis cornicula, the walls fossula ey be either the “ car-
of the calice broken away, and showing the dinal septum ” or the “counties
“fossula,”” of the natural size. Devonian, “5 5 : Bais
America. (Original.) septum,” but in either case it is
shorter than the other long septa.
Neither a true columella nor a pseudocolumella are developed, and
there is a thick theca formed by the coalescence of outgrowths from
the outer ends of the septa (fig. 172, c). It is doubtful if a true
epitheca is present.

Only the more important of the genera of the Zaphrentide can be here
noticed, the chief being Zaphrentis itself. In this genus (fig. 173) the

ZAPHRENTOIDEA. 295

corallum is simple, conical, turbinate, or cylindrical in form, more or less
curved, and showing a conspicuous fossula in the obliquely placed calice.
The fossula in different species is on the convex side of the corallum
(“dorsal”), or on the concave side (“ventral”), or in rare cases is lat-
eral. The septum included therein is usually very short (fig. 172, A and
B), and may be obsolete, while more or fewer of the septa on each side
generally bend round, and, partly coalescing, enclose the wide inner
end of the fossular groove. The septa are moderately numerous, al-
ternately long and short, the latter being commonly rudimentary and
sometimes partly obsolete. The long septa extend a considerable dis-
tance inwards towards the centre of the visceral chamber, and often
show a’ tendency to coalesce in groups. Dissepiments are sparingly
developed in the outer zone of the corallum, but tabulz are largely
developed, and pass from side to side of the visceral chamber (fig.
172, D), often becoming united to form large arched vesicles. The
species of Zaphrentis are mainly Carboniferous and Devonian, but
some forms referred to the genus are Silurian.

The Devonian and Carboniferous genus Amplexus is closely similar
to Zaphrentis, but the simple corallum is usually cylindrical in form,
while the septa are much less perfectly developed, being confined to the
margin of the visceral chamber, and thus leaving exposed a large central
space occupied by nearly horizontal, complete tabulz.

In the Carboniferous genus Lophophyllum there is a simple conical
corallum of small size (fig. 174), which agrees with Zaphrentis in the
scanty development of dissepiments and the possession of complete
arched tabulz. There is also a small fossula, which lodges the “ cardinal
septum ” (fig. 174, B, /), this being shorter than the other septa. On the

Fig. 174.—Structure of Lophophyllum eruca, from the Carboniferous Limestone, Scotland.
A, Side-view of the corallum, enlarged slightly; 8, Transverse section of the same, enlarged four
times ; C, Longitudinal section of the same, similarly enlarged. 4%, Cardinal septum; g, Counter
septum ; ¢, Tabule. (Original.)

other hand, the “counter septum” (fig. 172, B, g) is greatly developed,
being much longer than the other septa, and having its inner extremity
swollen. This enlarged septum has been regarded as a true columella,
but an examination of very young specimens shows that its real nature is
as just described. The remaining septa are unequal in size, but a division
into alternately long and short septa cannot be recognised.

In the Carboniferous genus Menophyllum, again, there are three
fossulee, the largest being on the dorsal side of the corallum, and lodging
the “cardinal septum,” while the other two are lateral and lodge the

296 ZOANTHARIA.

“‘alar septa,” the tabulate area in the floor of the calice thus assuming the
form of a half-moon. Lastly, in the Devonian genus Azzsophyllum
(fig. 175), the cardinal and alar septa are specially developed, and
form three prominent ridges in the cup
Ofithteicalice:

Outside of the typical family of the
Zaphrentide are various Zaphrentoid
corals which in the present state of our
knowledge can only provisionally be ar-
ranged in groups, and the true affinities
of which are not always clear. One
group of forms, which may be provision-
ally spoken of as that of the Hadrophyl-
fide, comprises certain singular little
discoid corals for which the genera
oe eee oe aoe Hadrophyllum, Baryphyllum, Combo-
same, viewed from above—Devonian. PAyllum, and Microcyclus (fig. 176) have
(After Milne-Edwards and Haime.) been founded. In these singular types

the simple corallum has the form of a
flattened disc, the calice being so shallow as hardly to deserve the name,
while the base is also often flat, the corallum thus becoming coin-shaped.
There is generally a marked septal fossula, and the symmetry is con-
spicuously bilateral. The septa are smooth-edged, and irregular in

Fig. 176.—Microcyclus discus, from the Devonian (Hamilton Group) ot North America. a,
Upper surface of the corallum; 8, Under surface of the same. The cross shows the natural size
of the corallum. (Original.)

length, and the interseptal loculi are filled up with stereoplasma, no
dissepiments nor tabule being developed. All the types of this group,
so far as 1s certainly known, are found in rocks of Devonian age.

The type of a second group (Pal@ocycltde) is constituted by the
singular Pal@ocyclus porpita (fig. 177) of the Silurian rocks of Gotland.!
The corallum in this form is discoidal, the flat circular base being covered
with a concentrically striated basal plate. The septa are forty-four, or
rarely forty, in number, alternately long and short, the “cardinal septum”
being shorter than the other septa, and being placed in a well-marked
“fossula” (figs. 158, and 177, A), the symmetry thus becoming bilateral.
The “counter septum” is not specially developed. All the septa are
tuberculated and have crenulated edges. There are no dissepiments nor
tabula, but the interseptal loculi are not filled up with stereoplasma. In
this respect, as also in the crenulated form and more regular develop-

1 Paleocyclus porpita certainly occurs also in the Wenlock Limestone of
Britain (Dudley), but the P. Fletcherd of, the same formation does not appear to
be properly referable to the genus Pa/@ocyclus, but belongs to Pholzdophyllum.

ZAPHRENTOIDEA. 297

ment of the septa, Paleocyclus porpita differs from the group of which
fladrophyllum is the type. The affinities of Pal@ocyclus cannot be
regarded as clearly established. It is possible that the genus, instead
of being placed here, should be looked upon as holding the same

Fig. 177.—Paleocyclus porpita, from the Wenlock Limestone of Gotland. a, Upper surface
(calice) of the corallum, showing the cardinal septum in the fossula(%); B, Side-view of the
corallum; c, View of the flat under side of the corallum, with the concentrically striated
epitheca. All the figures are enlarged about twice. (Original.)

position to the Helzophyliide that Hadrophyllum and its allies do to
the Zaphrentide.

The genus Strefiel/asma may be regarded as the type of another group
of Zaphrentoid Corals, to which the name Streftelasmid@ may be given.
The corallum in this genus is simple and turbinate or conical in form.
A true “theca” does not seem to be present, but the septa become much

Fig. 178.—Structure of Streptelasma corniculum, from the Ordovician rocks (Cincinnati
Group) of North America. a, Transverse section; B, Longitudinal section of the corallum,
enlarged twice. The transverse section shows the thick false wall formed by the fusion of the
outer portions of the septa. 4, Cardinal septum situated in the fossula; g, Counter septum.
= the specimen figured there are one hundred and eight septa, alternately long and short.
(Original.)

thickened towards their outer edges, being fused with one another by
their lateral margins for a considerable distance, and thus giving rise toa
dense false wall (figs. 127, Band 178, A). The septa are numerous, of two
orders, alternately long and short, the latter being buried for the greater
portion of their length in the false wall. The symmetry is distinctly bi-

298 ZOANTHARIA.

lateral, the cardinal and alar septa being clearly recognisable, in well-pre-
served specimens, by the pinnate arrangement of the costal furrows on
the exterior of the corallum (fig. 156). The cardinal septum is reduced
in size, and usually occupies the centre of a large fossula (fig. 178, A), but
in some species (¢.¢., in S. eurofeum) a fossula is wanting. The lower
part of the visceral chamber is more or less extensively filled up with
stereoplasma, and the upper part of the same is crossed by irregular
tabulz, dissepiments being also developed in moderate numbers. The
centre of the visceral chamber is occupied by a large, irregularly reticu-
lated or trabecular pseudocolumella (fig. 178, A), with which the inner
ends of the long septa are directly connected, and which is highly
characteristic of the genus. The species of Stveftelasma are mainly
Ordovician, but Silurian forms have also been recorded. The genus
Ptychophyllum (if judged by the structure of the mushroom - shaped
P. patellatum of the Silurian rocks) is very closely related to Szref-
telasma, the principal difference being that in this case the pseudo-
columella is produced by a twisting together of the
thickened inner ends of the longer septa. If, as
maintained by Lindstrém, these two genera are to
be regarded as identical, the name of Ptychophyl-
lum will have to be suppressed in favour of the
older title of Streptelasma.

Lastly, we may possibly place among the Zap/-
rentotdea the small, simple Palzozoic corals
which constitute the genus Lindstremia (fig. 179).
These forms agree with the typical Rugosa in
the pinnate arrangement of the septa and the
resulting bilateral symmetry of the corallum, but
they do not appear to possess a fossula. The

Fig. 179.—Lindstre- distinctive feature in the genus is the fusion of
fe prnellines A por. the septa by their inner ends to form a sort of
ion of top of the theca : A
is broken, in order to Ppseudocolumella, which is often of great size and
show the interior of the projects into the floor of the calice. The lower
callce. pS iEan: portion of the visceral chamber is more or less

extensively filled up by stereoplasma, but dissepi-
ments and tabulz are scantily developed in its upper portion. The
species of Lindstremia are mostly Ordovician and Silurian, but the
genus survives into the Carboniferous period.

III. CystTIPHYLLOIDEA.

The section of the Cystiphyllotdea comprises those Rugose Corals
in which endothecal tissue in the form of dissepiments is in general
extensively developed, while tabulz are absent or are incompletely
developed, and the septa are more or less imperfect, and may be
reduced to mere marginal striz. When the septa are so far de-
veloped as to enable this point to be determined, it can be shown
that the symmetry of the corallum is distinctly bilateral, and in some
cases a well-marked fossula is present. ‘The Cystiphylloid corals are
wholly Paleozoic, and are confined to the Silurian and Devonian
rocks.

family 1. Cystiphyllide.—This is the typical family of the Cysti-

CYSTIPHYEEOIDEA: 299

phylloid corals, and is characterised by the fact that the endothecal
structures are more or less completely reduced to a vesicular tissue,
composed of lenticular cells, which are often of specially large size
in the centre of the visceral chamber, and in this region represent

WINS

Fig. 180.—Structure of Cystiphyllum cylindricum, Lonsd., from the Wenlock Limestone of
Ironbridge. aA, Transverse section, enlarged twice; B, Part of a vertical section, similarly en-
larged. (Original.)

tabule (fig. 180). The septa are rudimentary, but are usually recog-
nisable as more or less distinct striz or ridges on the surface of the
calice.

The type-genus of this family is Cystiphyllum itself, in which the
corallum is almost invariably simple (it 1s composite in the C. frute-
cosum of the American Devonian rocks), and is usually conical in form
(fig. 181), though in some cases greatly flattened. The wall is well
developed, and the visceral chamber is entirely filled with a vesicular
tissue of obliquely disposed lenticular cells, which in the central region
of the corallum often show a well-marked arrangement in funnel-shaped
layers. The calice sometimes exhibits nothing but the rounded upper
surfaces of the lenticular vesicles just spoken of, but its surface com-
monly shows more or less marked radial ridges or radiating rows of
tubercles, which represent the septa. In some cases, as in the De-
vonian C. swlcatum and C. lamellosum, a well-marked dorsal fossula is
present; and in the latter species it is sometimes even possible to
recognise a disposition of the septal ridges in four groups, correspond-
ing with the four quadrants of a typical Rugose Coral. All the known
species of Cystifhyllum are found in the Silurian or Devonian rocks,
one of the commonest species being the C. veszculosum (fig. 181) of the
Devonian rocks of North America and Europe. Through Actinocystes
a transition can without violence be effected between the genus Cyséz-
phyllum on the one hand and Cyathophyllum on the other hand.

Family 2. Calceolide.—This family has been founded for a
number of remarkable Paleozoic corals, of which the principal
genera are Gontophyllum, Rhizophyllum, Areopoma, and Calceola.
The corallum in this family is simple and conical in form, very

300 ZOANTHARIA.

commonly more or less angulated, and assuming a pyramidal or
quadrilateral figure. Internally, the structure may not differ essen-
tially from that of Cystphyllum, the visceral chamber being filled
with an endothecal vesicular
tissue, and the septa being in-
complete or rudimentary (fig.
182, B). Sometimes the septa
are obsolete, but they are usu-
ally recognisable as radiating
ridges or rows of tubercles in
the calice, or they may even
form radiating lamellz which
intersect the marginal region of
the visceral chamber. The
essential character of the family,
however, is found in the fact
that the calice is closed by a
variously constructed lid or
“operculum,” composed of one
Or more pieces (fig. «desu.
In this feature, the corals of
the present family differ from
all recent Madreporarians,
though a species of operculum
is found in some living Al-
cyonarians (Primnoa and Lar-
amuriea). The structure and
affinities of the family of the
Operculate Corals have been
admirably worked out by Lind-
strom; and all the known
genera of the family are Silu-
rian or Devonian.

In the Silurian Goniophyllum
tgs ae nt ee (fig. 182) the corallum is distinctly
ig. 181.—Cystiphyllunt vesiculosumt, showing O91 : : Es

‘*rejuvenescence,” the corallum consisting of a quadrilateral, Its four sides being

succession of cups produced by budding from the flattened. The internal structure

original polype. One side of the calice is broken jg wholly vesicular. the cells of the
away, and shows the internal structure. Of the ee 2 “:
natural size. Devonian, America and Europe. central region of the visceral

(Original. ) chamber being of large size and

representing tabula. The quad-
rangular calice is deep, and is furnished with marked septal ridges, of
which four—one in the middle of each side—are specially prominent,
the longest being the “ cardinal septum,” while the other three are the

“counter” and “alar” septa. The septa are not mere calicine striz, but

are truly lamellar, though they are marginal. The calice is closed with

CYSTIPHYLEOIDEA: 301

an operculum of four calcareous plates, of which the dorsal and ventral
ones are trapezoidal and the lateral ones are triangular.

In Rhktzophyllum the conical or pyramidal corallum is attached to
foreign objects by root-like exothecal processes developed from its flat-
tened under surface, the upper surface being rounded. The calice has
septal striz and a distinct fossula, the internal structure is wholly of

Fig. 182.—A, Goniophyllune pyramidale, from the Silurian of Gotland, showing the operculum
in place, twice the natural size; B, Transverse section of the same species, slightly enlarged. (a is
after Lindstrém ; B is original.)

oblique vesicles, and the operculum is in the form of a single semicircular
plate. The species of the genus are mostly Silurian, but one form is
found in the Lower Devonian.

Still more closely allied to Cystifhyllum is the genus Ar@opoma, com-
prising only the A. (Cystiphyllum) prismaticum of the Silurian rocks.
The corallum in this form is subangular, more or less clearly four-sided,
the calice having radial rows of septal tubercles, and the surface exhibit-
ing distinct ruge. Internally the structure is wholly vesicular, and the
calice is closed by an operculum of subtriangular valves.

Lastly, in the genus Calceo/a (fig. 183), the slipper-shaped corallum is
free, and has the form of a slightly curved four-sided pyramid, of which
one side is broad and flat, the opposite side being
equally broad but convex, while the lateral faces
are much reduced, and are only represented by
the rounded junctions of the two broad faces.
The calice is deep, corresponding in form to the
exterior, and marked internally with distinct
septal striz. The “cardinal septum” is clearly
marked, and is placed in the centre of the vaulted
side of the corallum, sometimes in a distinct
groove or fossula, while the septa on both sides of :
this have a pinnate arrangement. The “counter pie 1g3.—-The corallum of
septum” is 1n the middle of the flat side of the Cakeola sandalina (a small
corallum, and is also often in a distinct fossula. Seale), from the Middle

; : evonian of Gerolstein, view-
The calice is closed by a half-moon-shaped oper- ed from its rounded side, of
culum, which resembles the valve of a Brachi- the natural size.
opod in form and sculpturing, its under sur-
face, however, showing a prominent median and fainter lateral septal
ridges. The internal structure is dense, the thick wall apparently solid,
but showing, according to the observations of Kunth, a finely vesicular
structure. The only known species of this genus is the Calceola sandalina
of the Middle Devonian rocks, an abundant and characteristic fossil in

302 ZOANTHARIA.

—

strata of this age in Europe. It may be noted in connection with Calceola
sandalina that the internal structure of the curious Cystzphyllum lamel-
Josum of the same geological horizon exhibits, in its young stages, a curious
resemblance to that of the present form, the latter, however, not being
known to possess an operculum. This fact, along with the general
identity in structure between Av@opoma prismaticum and the typical
Cystiphylla, may be taken as fully corroborating Lindstrém’s conclusion
that these remarkable Operculate Corals cannot be separated from the

Madreporaria kugosa.

3°35

Gliese DER. Xe

LOANTHA RITA—continued.
MADREPORARIA FUNGIDA AND PERFORATA.,
SECTION III. MADREPORARIA FUNGIDA.

THIS section includes simple or composite Madreporarians, in which
the interseptal loculi are crossed by trellis-like calcareous bars (“ syn-
apticula”). In the composite forms, where adjacent corallites are
connected by prolongations of their septa (“ septo-costze ”), the inter-
spaces between these prolongations are also synapticulate. The
septa are lamellar, and are usually solid, though occasionally per-
forations exist. When there is a basal plate it is usually perforated
by apertures, but it may be imperforate. Endothecal structures
(dissepiments and columella) may or may not be developed. Ten-
tacles in the living forms ‘short, lobe-like, scattered, sometimes
obsolete ” (Duncan).

So far as certainly known, the section of the MWadreporaria Fun-
gida has no Paleozoic representatives ; but the Secondary and Ter-
tiary deposits have yielded a iarge number of fossil forms, only a
few of the more important of which can be alluded to here.

By Professor Martin Duncan the section of the /ungida is di-
vided into the following five families :—

Family 1. Plesiofungide.—TVhis family is related to the Aporosa,
and comprises simple or composite /umgida, in which dissepiments
exist in addition to the synapticula, and the septa are usually solid
and imperforate. The principal genus in this family is Zhammnas-
trea, including a large number of species, which range from the
Trias to the Miocene Tertiary, and have a very wide geographical
distribution. In this genus the corallum is composite and is usu-
ally massive or lobate in form, sometimes laminar or encrusting ;
while the corallites have ill-defined walls. The calices (fig. 184, A)
have distinct centres, but are shallow, and the septa become con-

304 ZOANTHARIA.

fluent with those of neighbouring cups by means of septo-costal
prolongations. The septa appear to be sometimes perforated,
sometimes imperforate (Duncan), and both dissepiments and syn-
apticula are developed, a variably shaped columella being also

Ss 1EP ESS aN

Fig. 184.—A, Surface of Thammnastrea agaricites, from the Cretaceous deposits of Gosau; B,
Surface of Comzoseris conferta, from the Oligocene Tertiary of Vicenza, enlarged twice. (After
Zittel.)

present. Closely allied to Zhamunastrea is the Jurassic genus
Clausastrea.

Family 2. Fungide.—In the true /ungide the corallum is simple
or compound, the interseptal loculi showing numerous synapticula,
but there being no dissepiments. ‘The septa are usually imperfor-
ate, and the basal wall is generally perforated. As restricted by
‘Duncan, this family comprises no other fossil genus than the J/zcra-
bacia of the Cretaceous rocks. In this genus the corallum is of
small size, free and unattached, of lenticular form, with a convex
base covered with a perforated basal plate.

Family 3. Lophosertde.—In. this family the corallum may be
simple or compound, the wall being imperforate, and the septa also
usually solid. There are synapticula, but no dissepiments. The
simple forms of this family may be turbinate, discoid, or attached
by a .wide base, and are represented in Secondary and Tertiary
deposits by various generic types (Zrochoseris, Cycloseris, Podoseris,
&c.) The composite types have their calices united by confluence
of the septo-costze, and usually possess a thin laminar or frond-like
corallum. Besides such recent genera as Lophoseris and Mycedium,
we have here a number of fossil types, some of which (such as
Protoserts and Comoserts, fig. 184, B) are found in rocks as ancient
as the Jurassic.

family 4. Anabactde.—This small family includes only the two
genera Anabacia and Genabacia, the former being simple and the
latter composite, and both being confined to the Jurassic rocks.
The septa in these genera are perforated, and the wall is indistinct,

MADREPORARIA FUNGIDA. 305

while there are synapticula but no dissepiments. Azadacza is dis-
coid in form, and of small size, and its basal wall is wanting.

Family 5. Prestoporttide.—This family includes /uzgzda in which
the septa are trabeculate and the septa regularly porous, thus ap-
proaching the JZadreporaria Perforata. When a wall is present, it
is imperforate. Synapticula are present, and dissepiments may or
may not exist. Most of the genera included in this family (Leffo-

Fig. 185.—Cyclolites elliptica, viewed from above, rom below, and from the side. Cretaceous.

Lhyllia, Cyclolites, Microsolena, &c.) are Jurassic or Cretaceous, the
well-known genus Cyc/olites occurring in both of these formations.
In this genus (fig. 185), the corallum is simple and free, discoid,
with a flat or slightly concave base, and either circular or elliptical
in outline. The under surface of the corallum is covered with a
well - developed, concen-
trically striated basal plate.
The septa are trabecular
and more or less_ per-
forated, and there is either
no columella or a rudi-
mentary one.

Forming a. transition
between the typical Fun-
gida and the typical Perfor-
ata is the Jurassic genus
Microsolena (fig. 186), in
which the corallum is mas-
sive, of variable shape, but
usually more or less lobed.
geet eal walluiscrovened: Tis e06, Vinement of Miorsinline canons, apdlthees
with a strong epitheca, and
the calices are not circumscribed by a definite wall. The septa are
trabecular and perforated, and synapticula are abundantly developed.

VOI i U

306 ZOANTHARIA.

SECTION IV. MADREPORARIA PERFORATA.

This section includes simple or composite Madreporarians in
which the calcareous tissue (sclerenchyma) of the corallum is more
or less conspicuously porous or reticulate (fig. 187, c); the visceral
chambers of the corallites being thus placed, in the compound
forms, in communication with one another. The septa may be
solid, but are usually more or less porous, being often represented
by irregular trabeculz, or, in other cases, by rows of calcareous
spines. Dissepiments are usually present, and tabulz are com-
monly developed. The existing d/adreporaria Ferforata fall into
the three groups of the Lu¢sammide, Madreporide, and FPorttide,
while we may place here the three extinct groups of the Favositide,
Syringoporide, and Thecide. ‘These three last-mentioned groups

NY, OL ea
NACE NSAI
EY

KGS a 3 Ast
th Oi; ue Ye AV) 2 RG
Vged “— aj Se
UL ; fs pe oF ,
AW Sy; CK s

a

x

Fig. 187.—a, Dendrophyllia elegans, trom the Oligocene Tertiary of Brockenhurst, of the nat-
ural size ; B, Transverse section of the same, enlarged (after Zittel);.c, Portion of a section of a
recent species of Dezdrophyllia, showing the porous structure of the skeleton.

are essentially Palzeozoic, the Favositide alone having any Mesozoic
representative (the <Koninckta of the Cretaceous rocks). Of the
three existing groups of the Perforata, the FPoritide appear to be
the most ancient, the Ordovician genus /Pvofarea belonging to this
family, while the Calapecia (Columnopora) of the same formation
links the Poritide with the favositide. The Devonian genera
Areopora and Cletstopora, and the Carboniferous genus Pal@acis
(fig. 188) may also be referred to the Poritide. The Eupsammide
are also an ancient group, being represented in the Silurian rocks
by the genus Calostylis. On the other hand, the Wadrefortde@ are
of comparatively modern origin, the first known types appearing in
the Tertiary deposits. Upon the whole, however, the existing groups
of the ELupsammide, Poritide, and Madreporide do not present

MADREPORARIA PERFORATA. SOW

themselves in any prominent manner till the Tertiary period is
reached, and they have attained their maximum at the present day.
In the following brief summary of the characters and distribution
in time of the leading groups of the Perforate Madreporarians, it
will be best to take first the three recent families above mentioned.
family 1. Eupsammide.—tn this family the corallum may be sim-
ple or compound, the wa// of the corallites being perforated, while

Fig. 188.—Paleacis cyclostonza, from the Carboniferous rocks of Scotland. a, Upper surface
of a colony enlarged twice; B, Vertical section of the corallum, showing the reticulated struc-
ture of the skeleton, enlarged. (Original.)

the principal septa may be entire and imperforate. The smaller
septa are, however, usually perforate, and in other cases all the septa
are trabecular. There is a limited development of endothecal tis-
sue, the interseptal loculi thus remaining more or less open. ‘This
family is principally Tertiary and Recent, but the genus Calostylis is
Silurian, and there are also Cretaceous types (Stephanophyllia, &c.)

Fig. 189.—Calostylis Andersoni, from the Wenlock Limestone of Shropshire. a, A broken
specimen, enlarged slightly; Bb, Transverse section, enlarged five times; Cc, Vertical section,
similarly enlarged, showing the thick wall and the trabecular character of the septa. (Original.)

It is clear, therefore, that our knowledge of the past history of the
family is extremely imperfect.

The most ancient type of this family is the genus Ca/ostylzs, first
described by Lindstrém from the Wenlock Limestone of Gotland, but
occurring also in deposits of the same age in Britain. In this genus the

308 ZOANTHARIA.

corallum (fig. 189) is cylindrical, and may be simple, or may become
composite by the production of lateral buds. The wall is thick and por-
ous, but is covered here and there with a thin striated epitheca. The
septa are so highly perforated as to become more or less trabecular (fig.
189, B and C), and they may unite centrally to form a species of spongy
columella ; but dissepiments are very imperfectly developed. There is
no reason to doubt the correctness of Lindstrém’s reference of Calostylis
to the Eupsammide, with which the genus agrees in all essential char-
acters. No type of the Euzfsammide has hitherto been detected in
any Palzozoic deposit of later age than the Silurian, nor in any of the
older Mesozoic rock-groups ; but in the Cretaceous rocks we meet with
the genus Szephanophyliia. In this genus the corallum is free, simple,
and discoid, with an open circular calice; and species of the genus
range from the Cretaceous to the present day. In Salanophyliza,
ranging from the Eocene Tertiary to the present day, the corallum is
also simple, but is usually permanently fixed to some foreign body. An
allied type is the Phocene and Recent genus 7hecopsammia, which is
considered by Professor Martin Duncan to be related in some respects
to the Silurian genus Ca/ostylzs. Also allied to Balanophyliza is the
Eocene genus Exdopachys (fig. 190), in which the corallum is simple and

Fig. 190.—Exdopachys Maclurii, viewed in profile and from above. Eocene Tertiary.

compressed, and a spongy columella is present, while the keeled base is
continued into two wing-like expansions. The type of another group of
the Eupsammide is the well-known genus Dendrophyllia (fig. 187), in
which the corallum is composite and generally of a dendroid form, the
corallites being cylindrical, and having a spongy columella. The species
of Dendrophyliia range from the Eocene Tertiary to the present day.

family 2. Madreporide.—lIn this family the corallum is invariably
composite, the mode of increase being by gemmation, and the constitu-
ent corallites of the colony being united by an abundant spongy ccen-
enchyma. The corallites have porous walls, which are not distinct
from the ccenenchyma, and the septa are usually fairly developed,
and are lamellar. The interseptal loculi have dissepiments, but a
columella is wanting. As here defined, the family of the AZadepor-
zd@e includes only the single genus d/adrefora, including a vast
number of forms, ranging in time from the Eocene Tertiary to the
present day. The corallum (fig. 191) in this genus is very variable
in shape, being most usually branched or tufted; the corallites are
tubular, with more or less projecting calices ; and the visceral cham-

MADREPORARIA PERFORATA. 309

ber is divided into two halves by two of the six principal septa, which
are specially developed, and nearly meet along their inner edges.
family 3. Poritide.—In this extensive family the corallum is always
composite, the constituent corallites being united directly or by the
intervention of a more or less copious ccenenchyma. In either case
the calcareous tissue of the corallum is spongy or reticulate, and the
porous walls of the corallites are mostly not separable from the

Fig. 191.—Wadrepora plantaginea, of the natural size, showing the porous
ccenenchyma and the tubular corallites. Recent.

coenenchyma, when this latter exists. ‘The septa may be rudimen-
tary or obsolete, but they are usually present, and have the form of
vertical rows of spinules, which often anastomose, and give rise to a
sort of trellis-work. Rarely, the septa are imperforate and lamellar.
In some cases tabule are present, and a columella may or may not
be developed. The oldest types of the Poritide appear in the Ordo-
vician rocks, but the family is represented in the Palaeozoic deposits
by but a few isolated genera (Protarea, Araopora, Paleacis, &c.),

310 ZOANTHARIA.

and is mainly Mesozoic and Tertiary, numerous forms existing at
the present day.

The group of the Porctzde which is most nearly allied to the Jad-
reporide is that of which Zzrdbinaria is the type, characterised by
the fact that the corallites have distinct walls and are united by an
abundant reticulate or spongy ccenenchyma. 7wvrdinaria itself ranges
from the Miocene Tertiary to the present day, and allied types are
Actinacis (Cretaceous to Oligocene) and Astreopora (Eocene to Recent).
More or less closely allied to the preceding are the little Carboniferous
corals which constitute the genus Pa/@aczs.1_ In this genus the corallum
(fig. 188) is composed of short and wide corallites, united together directly
or by the intervention of a limited amount of ccenenchyma. The tissue
of the skeleton is more or less trabecular (fig. 188, B), and the septa are
obsolete, being represented only by rows of granules in the interior of the
deep calices. The species of Pa/@acis are found growing upon the stems
of Crinoids and other foreign bodies in the Lower Carboniferous rocks
of both Europe and North America.

The genus Porites is the type of another group of the Povitéde, char-
acterised by the reticulated sclerenchyma, the almost total or total absence
of a coenenchyma, and the generally trabecular septa. The species of

Cee YY CMLL:

VS — HILL:

Fig. 192.—Cleistopora geometrica, Edw. & Haime, sp. aA, Upper surface of a full-sized
individual, of the natural size; B, A single calice enlarged; c, Vertical section of a specimen
growing upon a Brachiopod, enlarged five times; b, Tangential section of the same specimen
similarly enlarged. (Original.)

Porttes are abundant at the present day, and are largely concerned
with the building up of coral-reefs ; while the earliest types of the genus
occur in the Cretaceous rocks. Allied to Porites are various Tertiary

1 Misled by certain peculiarities in the minute structure of the skeleton, the
present writer was formerly induced to believe that Paleaczs did not properly
belong to the corals.

MADREPORARIA PERFORATA. Sl

genera, such as Lztharea, Rhodarea, &c. We may also place here the
ancient genera Sty/ar@a and Protarea, both of which commence in the
Ordovician rocks, the latter surviving into the Devonian period. In the
Devonian rocks we find, further, the singular genus C/ezstopora, repre-
sented only by the little C. geometrica of the European Devonian rocks,
in which the corallum (fig. 192, A) is composed of short polygonal coral-
lites, forming a discoid colony which is usually attached by its under
surface to some foreign body. The corallites are united by fusion of
their walls, which are slightly porous, and the septa are only present as
marginal striz (fig. 192, B). The characteristic feature about the genus,
however, is that the whole of the visceral chamber, below the calice,
is filled with reticulated or trabecular calcareous tissue (fig. 192, C
and D).

Lastly, a third group of the Porit¢de is typified by the genus A/veopfora,
the most characteristic feature of the group being that the walls of the
corallites (fig. 193, A) are spongy and porous, while the septa (fig. 193, B)
are trabecular, and well-developed tabulz are usually present. The

Fig. 193.— Alveofora spongiosa, one of the recent Poritide (after Dana). A, Some or the
corallites cut vertically and enlarged, showing the tabule and the perforated walls; B, View of
the calices from above, enlarged.

genus A/veopora itself ranges from the Eocene Tertiary to the present
day, but the genus Arvgofora, properly referred here by Waagen, is
found in the Devonian deposits of Australia and the Carboniferous rocks
of India. In this ancient type the corallum is massive, and is composed
of polygonal corallites, which have their walls fused with one another.
The walls are composed of spongy tissue, with irregular pores, the septa
being trabecular or reticulate, while tabula may be more or less exten-
sively developed. The Cretaceous genus Konznckia, though incompletely
investigated, may also be placed here as a provisional arrangement ;
while the recent genus Favosztipfora, as described by Mr Saville Kent,
would appear to form a connecting link between <A/veopora and fa-
vosites.

Family 4. Favositide.—This large and important family of Corals
is characterised by the possession of a variably shaped corallum
composed of polygonal or sub-cylindrical corallites, which are
usually in close contact throughout their entire extent, but are not
completely united by fusion of their walls. The walls of the
corallites are porous, the visceral chambers of adjacent corallites

Bie ZOANTHARIA.

being thus placed in direct communication; but the perforations
are not irregular, and are restricted to definite, circular or oval
apertures known as ‘‘ mural pores.” There is no true coenenchyma ;
and the condition of the septa is extremely variable, these structures
being sometimes obsolete, sometimes in the form of marginal ridges,
and most commonly in the form of vertically disposed rows of
spinules. ‘Tabule are usually well developed and complete, but

Fig. 194.—Thin sections of Favositoid Corals, showing the phenomena presented by the mural
pores. a, Tangential section of Favosztes sp., from the Devonian of Queensland, enlarged six
times. alk Vertical section of the same similarly enlarged; in two of. the tubes the section
traverses the centre of the visceral chambers, but in one it corresponds in part with the wall of
the corallite. Band B’, Tangential and vertical sections of A lweolites Labechez, E. & H., from
the Wenlock Limestone of Ironbridge, enlarged ten times. [The septal thorns which characterise
this species, as also A. Sattersbyz, E. & H., are mostly omitted in the drawing.] cand c’, Tan-
gential and vertical sections of Pachyfora sp., from the Corniferous Limestone of the Falls of the
Ohio, enlarged ten times. In all the figures the letter Z indicates the mural pores. (Original.)

they are sometimes imperfect. The corallum increases by the form
of budding which Waagen has defined as “ inter-mural gemmation ”
Geempeen4):

The family of the avositide is obviously allied to that of the
FPoritide, from which it is separated principally by the fact that the
walls of adjacent corallites are not undistinguishably fused (though
they may appear to be so in specimens in bad preservation), while
the perforations in the walls are in the form of more or less definite

MADREPORARIA PERFORATA. 313

“mural pores.” As here restricted, the family is exclusively Palzo-
zoic in its range, the earliest known types appearing in the Ordo-
vician, while the latest are found in the Carboniferous rocks. The
great majority of forms, however, are Silurian and Devonian.

There are certain appearances in thin sections of the Favosttide, as
seen under the microscope, which it is desirable to understand. In the
first place, the individual corallites of the colony have distinct walls.
Hence, in thin sections (fig. 194, A and C), the partition which separates
contiguous tubes usually exhibits a central dark or light line (the “ prim-
ordial wall”) bounded on each side by a layer of fibrous “ stereoplasma.”
In badly preserved specimens it may not be possible to demonstrate the
- primordial mural plate in thin sections, but the real distinctness of the
corallites is shown by the fact that in fractured examples the individual
tubes commonly separate from one another along the line of this plate,
each tube thus retaining its own proper wall.

In the second place, the so-called ‘‘ mural pores” of the Favosztzd@ are
rounded or oval apertures, usually arranged in longitudinal series, which
perforate the walls of adjacent corallites and place adjoining visceral
chambers in direct communication. They are sometimes not completed,
since the thin “ primordial wall” which separates contiguous tubes is
sometimes not actually perforated. The mural pores are most regular in
form and distribution in the genus Favosztes, in which the pores are often
surrounded by slightly raised margins, and are arranged in one or more
series along the flat faces of the prismatic corallites (fig. 195, D). In such
genera as Pachypora, where the corallites have greatly thickened walls,
the mural pores assume the character of ¢wdes rather than of mere Zores,
and in such cases they often perforate the walls in a tortuous manner.
As regards their recognition in thin sections, mural pores appear in
transverse sections of the tubes (fig. 194, A, B, C) as gaps or deficiencies
in the wall forming the circumference of the corallite, the size of this gap
depending on the size of the pores. In vertical sections (fig. 194, A’, B’, C’)
the pores may similarly present themselves as gaps in the walls of the
corallites. It very commonly happens, however, that a vertical section
may in part ruz along the actual wall of the corallites, instead of merely
dividing the tube longitudinally ; and when this happens, the mural pores
are seen as round or oval perforations in the wall within the space
mcluded between the lateral boundaries of the tubes.

The principal genus of the Favositide is Favosites (= Calamopora,
Goldfuss) itself, the species of which range from the Ordovician to
the Carboniferous inclusive. In this genus the corallum (fig. 195)
is commonly massive and often of large size, but in other cases it
may be lobate or branched. The corallites are numerous, usually
more or less conspicuously polygonal, with thin and distinct walls.
The mural pores are arranged in rows along the flat faces, or, more
rarely, along the angles, of the prismatic corallites. In the former
case, each face of the tube may carry one, two, or three rows of
pores, this being, gexerad//y, a constant feature in different species.
There are numerous tabule, and these structures are usually ‘“‘ com-
plete” (z.e., they stretch entirely across the visceral chamber) ; but

314 ZOANTHARIA.

they may be “incomplete.” In no instance are the tabulz “ cys-
toid ”’—that is to say, they do not anastomose so as to give rise to a
vesicular tissue of arched cells. The septa in avosites are some-
times wanting, but are usually represented by vertical rows of
pointed tubercles or of slender calcareous spines. As previously
mentioned, the tabulz in some species of Favosites are ‘“incom-

0D.

2S.

Fig. 195.—a, A specimen of Havosites Gothlandica, Lam., from the Niagara Limestone (Wen-
lock) of Owen Sound, Ontario, of the natural size; Bn, A small example of the same species from
the Wenlock Limestone of Dudley, with comparatively minute corallites, of the natural size; c,
Fragment of the same species, with large-sized corallites, from the Wenlock Limestone of Got-
land, of the natural size; p, Part of two corallites of the same species, from the Corniferous
Limestone (Devonian) of Woodstock, Ontario, slightly enlarged. (Original.)

plete,” having the form, some or all of them, of thin, close-set trans-
verse plates which only extend across about one-third or one-half
of the diameter of the visceral chamber. This condition of the
tabulz is characteristic of such forms as the Devonian / hemt-
spherica (fig. 196), and the generic name of “Lmmonsta has been
proposed for these. 3
Nearly allied to Havosites is the genus Pachypora, in which the

MADREPORARIA PERFORATA. 215

corallum is usually lobate or dendroid, and the corallites have their
walls more or less extensively thickened by a secondary deposit of
stereoplasma, the visceral chambers thus becoming more or less
contracted, especially in the peripheral region of the colony (fig. 197).

oS: eS
900 fesc8 Gee,
PES REN SF
OIA nz
SEE eR SMITTY Ww Se

ORES ES Ee ESCORT C)

eee ceirerey) Av

SES Ree Oe

Weostecemsscesstercsessgtecseceed <7) i “P

ORE EER EOIN Say VE
pememreces) ZS |i)

=e E333 gtste 35 Beagete 5 dl

3 J5estsese oz SS qe
HR HR Il HL
LTE TT PAS HL

ATT H PM TAY

S63) geil B

Fig. 196.—Fragment of Havosites (Em- Fig. 197.-—A, Transverse section of a few coral-
mionsia) hemispherica, of the natural size. lites of Pachypora Nicholsont, Frech, from the De-
Devonian, America. (After Billings.) vonian of the Eifel, enlarged seven times, showing

the thickened walls of the corallites; B, Vertical
section of a few tubes of the same. Z, Mural pores.
(Original.)

The tabule in this genus are straight and complete; the septa are
usually rudimentary ; and the mural pores are generally large and uni-
serial, being converted into tubes in the more highly thickened por-
tions of the corallites. The species of Pachygora are mostly Silurian
and Devonian, but some forms appear to occur in the Carboniferous
rocks. Closely related to Pachy-
fora is the Silurian and Devonian
genus Striatopora (fig. 198), in
which the corallites also have
greatly thickened walls, but the
calices are surrounded by a cup-
shaped thickened margin, the
floor of which is striated by
rudimentary septal ridges. An- Fig. 198.— Fragment of Striatopora flexuosa
: : of the natural size, and two calices enlarged.
other allied type is the genus Silurian. (After Hall.)
Trachypora, the species of which
are principally Devonian. Here we may also place the curious
Silurian genus Zacerigora, in which the mural pores are uniserial
and of large size, and the septa are in the form of marginal ridges.
The genus A/veolites is the type of another group of Favositide
in which the corallites are usually more or less compressed, so as
to appear triangular, or semilunar, or crescentic when transversely
divided. The septa are usually present in the form of one, two,

216. ZOANTHARIA.

or three elongated tooth-like ridges (fig. 199); but in some species
the corallites possess strong ascending calcareous spines, the nature
of which is different. ‘The mural pores are uniserial and of large
size, and the tabulz are complete and more or less horizontal.
The species of A/veolites usually have
a branched or massive corallum, the
latter usually formed of superimposed
crusts; and they are found in the
Silurian and Devonian deposits. An
allied genus, with a similar geological
range, 1s Cezzizes, in which the coral-
lites are greatly compressed, and are
much thickened towards their mouths.
Another group is constituted by
the genera Pleurodictyum and Michel-
znia, in both of which the tabuleze
are more or less “cystoid” or ves-
Fig. 199.—Calices of Alveolites sub- 1cular, and the mural pores are
acsiewlaris, Lam eceaty cutee’, very irregular. It is, indeed, very
2M BES (OES Gruss) doubtful if these two genera can
be separated, and in case of their

union the name of Michelinia will have to be abandoned. In
Pleurodictyum (fig. 200) the corallum is discoid ; with a flat or con-
cave base, covered with an epithecal plate, and attached at one point
to a foreign body. The corallites are polygonal, and diverge from
the centre of the base, those on the circumference being nearly hori-
zontal or even bent downwards, while the median ones are more or
less perpendicular. The mural pores are numerous and quite irreg-
ular ; and in one species there is the singular feature that the mural
pores of the under sides of the peripheral corallites pass directly
through the basal plate of the colony, which thus becomes perforated.
The tabulz often inosculate, and become to some extent vesicular,
but these structures are comparatively few in number, and the “ cys-
toid” character of the tabule is thus little marked. The genus
Pleurodictyum is wholly Silurian and Devonian, so far as known,
if Michelinia be excluded from it. The best known species is the
P. problematicum of the Devonian rocks of Europe, the singular
discoid casts of which (fig. 200, A) are commonly found in the
Lower Devonian of the Eifel. In these casts the conical columns
(fig. 200, B) represent the moulds of the visceral chambers of the
corallites, and the little cylindrical rods connecting these are the
result of the infilling of the mural pores. <A singular feature in these
casts is, that there is generally to be seen a curious cylindrical
twisted body (fig. 200, A) in the centre of the base. This “worm-
hike body” has been very generally recognised in specimens of

MADREPORARIA PERFORATA. 317

Pleurodictyum, of different species and from widely remote regions.
There is little reason to doubt that it represents the tube of an
Annelide which lived as a “‘commensal” with the coral, in the same

Fig 200.—a, Lower surface of the cast of Pleurodictyum problematicum, Goldf., from the
Lower Devonian of Germany, of the natural size (after Roemer), showing the vermitorm body in
the centre; B, A few of the separate casts of the tubes of Pleurodictyum problematicum, Goldf.,
from the Devonian of the Eifel, showing the casts of the mural pores, enlarged (after Milne-
Edwards and Haime); c, Upper surface of the corallum of Pleurodictyum stylophorum, Eaton,
from the Hamilton group of North America, of the natural size, showing the form of the calices
(Original) ; p, Lower surface of another example of the same, of the natural size, showing the stri-
ated epitheca, and the point where the corallum was attached to the stem of a Crinoid (Original).

way as a Sipunculid (Aspidostphon) is found in constant association
with the corallum of the existing Heferopsammita.

The genus JWchelinia is in all its essential characters identical
with Pleurodictyum, but the corallum is massive (fig. 201), and the
tabule are numerous, and inosculate so as to give rise to a tissue of
arched vesicles. The epitheca, also, commonly gives off root-like
processes of attachment. The species of Micheltnza are all Devonian
and Carboniferous.

It remains to briefly notice certain transitional types by which the Fav-
osttid@ are connected with the Poritzde on the one hand and the Sy7zz-
goporid@ on the other hand. Thus, anear approach to A/veofora among
the Poritide is effected by the remarkable Ordovician genus Calapecia
(=Columnopora).1 The corallum in this genus is massive, and is com-

1 An examination of the original specimens has clearly shown that the forms
described by Billings under the name of Ca/afacza are identical with those

318 ZOANTHARIA.

posed of polygonal corallites, which are usually directly connected by their
walls, and agree with those of the avosztid@ in possessing a primordial
mural plate. A true coenenchyma is in general wanting, but in some

Fig. 201.—Aichelinia convexa (D’Orbigny). Devonian.

specimens the corallites are in places connected by the intervention of a
small quantity of exothecal tissue. The walls of the corallites are per-
forated by rows of large mural pores, which are placed close together and
give the wall a lattice-like appearance. The septa are in the form of

Fig. 202.—a, A fragment of a colony of Syringolites Huronensis, Hinde, of the natural size ;
b, A single calice of the same, enlarged eight times, showing the central tube, and radiating lines
of septal tubercles ; c, Part of a corallite of the same, split open, and enlarged six times, showing
the composition of the central tube out of invaginated tabule; p, Part of a corallite of the same,
viewed from the exterior and enlarged six times, showing the mural pores. Niagara Limestone,
Manitoulin Island, Ontario. (Original.)

marginal ridges, and the tabulz are complete and horizontal, and do not
give rise to a vesicular tissue by their union.

described by the present writer under the head of Columnopora, and the latter
name must therefore be abandoned. Of the forms included by Billings under
Calapacia, only one—viz., C. Anticostiensts—was figured,.and this proves to be
really quite different from the others, and to be nearly related to the genera Syr7zn-
gophyllum and Thecostegites.

MADREPORARIA PERFORATA. 319

On the other hand, a distinct transition between Favosttes and Syrin-
gopora is effected by the Silurian genus Syrzzgolztes, in which the coral-
lum (fig. 202) is quite similar in general structure to Favosztes, being
composed of thin-walled polygonal corallites, the faces of which are per-
forated by longitudinal rows of distant mural pores, but the tabulz are
curved, and are depressed centrally so as to produce by their invagination
a vertical median tube running down the middle of each visceral chamber.
The Devonian genus Aoemeria, again, seems to offer a similar transition
between Pachyfora and Syringopora. In this remarkable type, the
corallum is closely similar in general structure to that of Pachypora,
being composed of contiguous polygonal corallites, with distinct walls
which are greatly thickened internally by a secondary deposit of stereo-
plasma, and are perforated by well-marked tubular mural pores, but
the tabule are funnel-shaped and are invaginated in a manner precisely
similar to that which is so characteristic of Syrzngopora.

The genus Romingerta, of the Silurian and Devonian rocks of
North America, affords another transitional link between the -avo-
sttide and the Syringoporide. ‘The corallum in this genus (fig. 203)
is lax and spreading, erect or semi-erect, and
composed of cylindrical tubular corallites which
are produced by gemmation in umbellate whorls
or verticils. The tubes are largely free, but
where their walls come in contact, the visceral
chambers are placed in communication by dis-
tinct mural pores. The tabulz are remote, and
in general horizontal, and the septa are repre-
sented by vertical rows of calcareous spines. =)

Family 5. Syringoporide.—Vhis family includes — yi, 353. Portion of
a number of Paleozoic corals in which the skele- the corallum of Rowzin-

: : ‘ : geria umbellifera, of the
ton is composite, usually fasciculate in form (figs. natural size. Devonian
204-207), and is composed of cylindricai coral- Se oe
lites which in general are not in actual contact, |
but mostly have their visceral chambers placed in direct communica-
tion by means of hollow, cylindrical connecting-processes or horizontal
platforms, which are periodically produced. In many cases the coral-
lites come into actual contact in parts of the corallum, and where
this occurs their walls are pierced by mural pores similar to those
of the Favositide. ‘The tabule are well developed, and are usually
funnel-shaped, but they are sometimes vesicular, or may, rarely, be
simply curved. ‘The septa are in the form of vertical rows of cal-
careous spines. ‘The mode of increase is by basal or stolonal gem-
mation, or by the production of new buds from the connecting-
processes or floors. The oldest members of this family appear in
the Ordovician rocks, and the last appear in the Carboniferous.

The affinities of the Syz7ngoporide have been much disputed, and
the type-genus Syzizgopora has commonly been placed among the
Alcyonaria, and has been regarded as a near ally of the recent

320 ZOANTHARIA.

Tubipora. To the present writer the evidence in favour of the
view that the Syzingoporide constitute a peculiar group of the
Madreporaria FPerforata, and that they are nearly related to the
Favositide, appears to be exceedingly strong, and may be briefly
summed up as follows :—

a. The hollow connecting-processes of Syrimgopora are morpho-
logically nothing more than mural pores as existing between coral-
lites which are not in actual contact, and, like mural pores, they place
the visceral chambers of contiguous tubes in direct communication.

6. In many members of the Syrzingoporide the corallites do

Fig. 204.—Syritngopora retiforniis. Fig. 205.—Syringopora verticillata..
Silurian. Silurian.

Fig. 206.—Syringopora Dalmani. Fig. 207.—Syringopora compacta.
Silurian. Silurian.

partially come into direct contact, and wherever this occurs, mural
pores of the ordinary Favositoid type are developed.

c. The septa have the form of vertical rows of calcareous spines,.
as is also the case in the typical members of the Favositide.

ad. The Favositoid genera Syringolites and Roemerta possess the
infundibuliform tabule of Syrzngopora in combination with the
contiguous corallites and serially disposed mural pores of Favoszzes
and Pachypora.

e. On the other hand, the Syringoporoid genera Canunapora,
Chonostegites, Thecostegites, and Syringophyllum have the general
characters of Syringopora as regards the form of the corallum and
the mode of increase, but resemble different members of the Favo-
sttide in the characters of the tabulz, and, occasionally, in the
possession of ‘‘ mural pores.”

MADREPORARIA PERFORATA. 321

Ff. Lastly, the skeleton in Syzingopora and its allies is never
composed of: spicules, as it is in Zwbifora, but its microscopic
structure agrees precisely with that of the corallum in the JZadre-
porarta generally.

It should be added, however, that though it would appear highly
probable that the real affinities of the Syzngoportide are with the
Madreporaria, the members of this family show a resemblance to
the Alcyonarians in the fact that their common mode of increase is
by stolonal or basal gemmation, and in this respect they differ
altogether from the typical Perforate Madreporarians ; though this
single feature cannot be allowed to counterbalance their numerous
and striking points of resemblance to the Favositide.

The typical genus of the Syrixgoporide is Syringopora itself, in which
the corallum commences as a prostrate network of tubes, resembling in
form a colony of Aulopora. In process of growth, this basal network
sends up numerous vertical, flexuous, cylindrical corallites, which are not
in direct contact, though sometimes (¢.g., in S. davata) they become
directly united here and there. The corallites are enclosed, each, in a
thick proper wall, and they are usually united by hollow cylindrical con-
necting-processes (figs. 204-207) which occasionally (¢,g., in S. ¢abulata)
assume the form of horizontal laminar floors. These connecting-processes
place the visceral chambers of adjoining tubes in direct communication,
and, as shown in thin sections (fig. 208), they are traversed by con-
tinuations of the endothecal tissue of the polypes themselves. The septa
are sometimes nearly obsolete, but they usually have the form of vertical
rows of calcareous spines. The tabulz are well developed, and are in
general more or less regularly funnel-shaped (fig. 208, A), and give rise
by their invagination to a more or less continuous tube occupying the
axis of the visceral chamber. The species of Syvéngofora are abundant
in the Silurian, Devonian, and Carboniferous deposits, and often reach
a large size.

In the Silurian genus Caznapora, the general form of the corallum is
like that of Syringopora, but when connecting-processes are present
these are very short, and the corallites are usually partially in contact,
in which case they assume a polygonal form and are perforated by mural
pores. The tabulz are sometimes funnel-shaped, sometimes simply
curved, and the septa are spiniform.

We may also include in this family the remarkable Devonian genus
Chonostegites, which proves to be a link between the Syrzugoporide
and Favosttide, and has, indeed, been included in the latter family.
The corallum in this genus is massive, and is composed of cylindrical
corallites which may be partially in contact, but are usually separate
and are connected by numerous close-set, concentrically disposed, hori-
zontal connecting-floors or laminar expansions. These periodic floors
are so far exothecal that they are extensions from the walls of the coral-
lites, but they are hollow, and are filled with prolongations of the en-
dothecal tissues of the corallites themselves, so that they place the
visceral chambers of. contiguous tubes in direct communication. In
places, the corallites come into direct contact, and in this case their
visceral chambers communicate by mural pores precisely similar to
those of the Favosttide. The septa have the form of rows of cal-
careous spines, and the tabulz differ from those of Syringopora and

VOU, 1. =

322 ZOANTHARIA.

agree with those of MJzchelinia in being vesicular or “cystoid” in
structure.

ih

i,
fi

ia I
i) |

Fig. 208.—a, Part of a longitudinal section of Sy7zzgopora
reticulata, Goldf., from the Carboniferous Limestone of
Kendal, Westmorland, enlarged five times, showing the spini-
form septa and the funnel-shaped tabule with their central
tube. Owing to the flexures of the corallites, the section cuts
the tubes in different parts, sometimes passing close to the
wall and showing the cut ends of the spiniform septa, some-
times passing through the axis of the visceral chamber and
bisecting the axial tube, and sometimes cutting the axial tube
and its enveloping tabulz in an oblique manner. B, Part of
a transverse section of the same specimen, enlarged five times,
showing the spiniform septa, and the cut edges of the tabule
surrounding the central tube. (Original.)

The increase of the corallum is by basal gemmation, or by

budding from the hollow
periodic expansions in
the intervals between
the old. cups. * ingidite
mode of increase, Chozo-
stegztes resembles Sy-
ringopora, and the hol-
low periodic floors may
be considered as homo-
logous with the hollow
connecting-tubes of the
latter. On the other
hand, in the possession
of vesicular tabule and
in the presence of mural
pores in parts where the
corallites touch each
other, the genus closely
approaches to MMzchelz-
nta. Nearly related to
Chonostegites is the Or-
dovician and _ Silurian
genus Syringophyllum,
and we may also place
here the Devonian genus
Thecostegites. In both
these genera the coral-
lum consists essentially
of cylindrical, tabulate
corallites which are
placed in connection
with one another by
hollow, periodically pro-
duced, laminar floors,
into which the endothe-
cal tissues of the polypes
are directly continued ;
but in some cases these
floors are successively
superimposed on one
another, and give rise
by their union to a kind
of spurious coenenchy-
ma. The strictureljor
the skeleton in these
genera is, however, too
complex to allow of its
being advantageously
considered here.

Family 6. Thecide.—This family includes only the aberrant genus
Thecia,' the structure of which is too complex to permit of more than

1 As the result of extended investigations, the writer has been led to materially
modify the views which he formerly expressed (‘ Paleeozoic Tabulate Corals’) as

MADREPORARIA PERFORATA. 323

the briefest description in this place. The corallum in Zzecza is
generally in the form of a laminar expansion, furnished inferiorly
with a striated epithecal membrane. In their early condition, the
corallites are often oblique to the basal plate, and in this stage they
have thin and apparently distinct walls, the visceral chambers being
_ crossed by complete tabulz, and the general appearance being not
unlike to that of some species of Favosites. Very soon, however,
the corallites become perpendicular to the basal plate, and they then
appear to lose their distinct walls and to become united by the
intervention of a thick, vertically tubulated calcareous tissue, which
may be regarded as probably of the nature of a spurious ccen-
enchyma, and from which the walls of the individual corallites are
wholly inseparable. The surface, therefore, exhibits the stellate
calices of the corallites separated by an apparently dense interstitial
tissue, marked superficially by minute tubercles, and by radiating,
often vermicular, grooves which extend from one calice to another.
The visceral chambers of adjacent corallites are placed in direct
communication by means of well-marked, often bent, horizontal
tubes, which represent elongated mural pores. The septa are gener-
ally twelve in number in each corallite, and have the form of irregular
vertical ridges, with very broad bases, which only extend a short way
inwards into the visceral chamber, and appear sometimes to terminate
along their inner edges in blunt spines. The tabulz are complete,
horizontal, or slightly curved, and tolerably numerous.

The known species of Z%ecza are Silurian, the most familiar being
the common Z: Swindernana of the Wenlock Limestone. The
coral described by Rominger from the corresponding horizon in
America under the name of Zhecia major appears to differ in im-
portant respects from the European species of Zhecza, and would
appear to be nearly related to the Favositoid genus Lacerzpora.

The family of the Zeced@, as above defined, is separated from
the Favosttide by the complete fusion of the corallites in the ter-
minal portion of their course, and by the peculiar nature of the
tubulated ccenenchymal tissue which separates adjoining visceral
chambers. The fact that the corallites have as a rule twelve septa
each, would support the view that Zecta is to be regarded as refer-
able to the Zoantharia rather than to the A/cyonaria ; and the pres-
ence of tubes directly connecting the cavities of adjoining polypes
would show that the genus belongs to the Madreforaria Perforata.

to the structure and affinities of Zzecza. The exothecal tubules were previously
regarded as corresponding with the ‘‘ mesopores”’ of He/iolites, and the genus
was on this ground placed among the Alcyonaria. The examination of well-pre-
served specimens by means of thin sections would, however, appear to prove
conclusively that this is not their nature, and that they are really what Milne-
Edwards and Haime described as a ‘‘ spurious ccenenchyma.”’

324

CneAS Pl ER aeG

GENERAL CHARACTERS AND DIVISIONS Oe
TE ALC ON ATCA,

THE second great division of the Actnozoa is that of the Alcyonaria
or Octactinia, defined by the possession of polypes with eight pin-
nately fringed tentacles, the mesentertes and intermesenteric chambers
being also eight tn number. The corallum ts usually sclerobasic, or

4” do ‘4

Fig. 209.—Transverse section of a polype of A/-
cyonium, enlarged. (After O. and R. Hertwig.)
The numbers indicate the four pairs of mesenteries.
s, CEsophagus transversely divided; ¢z, One of
the eight longitudinal ‘‘ retractor” muscles of the
mesenteries ; ve, Ventral side of polype ; do, Dorsal
side. Nos. 11, and 44, are the ‘‘directive” mes-
enteries.

spicular, or formed of both an
axtal sclerobasts and detached
spicules. Ln other types, the pol-
ypes composing the colony may be
provided with separate “ thece.”

The Alcyonarta are essen-
tially distinguished from the
Zoantharia by the possession
of eight unpaired mesenteries
and eight tentacles (reduced in
some rare cases to six or four).

The mesenteries (fig. 209) are
symmetrically grouped round the
cesophagus, so that there is a
dorsal intermesenteric space, and
a ventral one, together with three
lateral compartments on each
side. The “ directive” mesen-
teries of the ventral side (fig. 209,
Nos. 1, 1), have the longitudinal
retractor muscles attached to

their opposed faces; whilst the opposed sides of the dorsal directive
mesenteries have the transverse muscles. The mesenteries are not in
pairs ; and the order in which they appear has not been precisely in-
vestigated, the numbering given in the annexed figure not being certainly
known to express the order in which these structures are developed.

CHARACTERS AND DIVISIONS OF ALCYONARIA. 325

With the exception of the two genera MJonoxenia (Haimeia, E.
and H.) and Hartea, the Alcyonaria are all composite, the tubular
polypes being united by a ccenosarc, and their body-cavities being
placed in communication by means of anastomosing canals, which
ramify in the coenosarc, and permit of a free circulation of nutrient
fluids. The form of the colony differs greatly in different cases, but
none possess the power of independent locomotion, most being
rooted to foreign objects, or sunk in the mud. ‘The polypes, in
most of the essential points of their organisation, agree with those
of the Zoantharia, the mouth opening into a tubular gullet, which in
_turn communicates freely with the body-cavity, and the cesophagus
being connected with the body-wall by means of a series of vertical
membranous laminz or ‘ mesenteries.” The mesenteries, however,
are only eight in number, and are not paired, one of the tentacles
corresponding with and opening into each intermesenteric chamber.

The guilet in the Adcyonaria is so placed that its long axis (fig.
209) corresponds with the dorso-ventral plane of the body of the
polype, and it very commonly is furnished on its ventral side with a
ciliated groove (the “‘ siphonoglyphe” of Mr Hickson).

In many instances the colony in the Alcyonaria is dimorphic,
consisting of two sets of zooids, which differ from one another in
structure and function. The zooids of the one series (generally
called ‘‘autozooids) have the normal size, and possess the structures
proper to the mature polypes ; while those of the other series (gen-
erally called “ siphonozooids”) are reduced in size, and want certain
structures of the normal polypes, such as tentacles, mesenterial fila-
ments, or reproductive organs. No siphonozooids have been recog-
nised in Zubipora or in most of the Gorgontde, and von Koch
doubts if the structures described as such by Moseley in Helopora
are really of this nature.

The mode of increase in the Adcyonaria is typically by basal or
stolonal gemmation, the parent throwing out basal extensions, which
commonly unite to form a creeping network or a crust-like expansion,
from which new polypes are thrown up at intervals. In other cases
the stolons are produced from the sides of the polypes at different
levels above the base ; and in still other cases (e.g., in Adcyontum) the
stolons coalesce to form a common fleshy mass or ccenosarc. In
some cases, as in the /elolitide, the peculiar mode of increase
which has been described by von Koch as ‘“ccenenchymal gemma-
tion” is observed, but the nature of this will be described hereafter.

There are no skeletal structures in AZonoxenta (Haimeta), but with
this exception a corallum of some sort or another is produced in all
the Alcyonaria. According to the investigations of von Koch, the
skeletal structures of the Aldcyonarza may be ectodermal or meso-
dermal in origin. The ectoderm commonly produces hard struc-

326 CHARACTERS AND DIVISIONS OF ALCYONARIA.

tures of a horny character, in general hardened by the deposition of
carbonate of lime. In some cases (¢.g., in Cornularia) these horny
structures remain external, forming a sheath to the colony; but in
other cases the colony becomes in process of growth inverted over
the skeleton, which then forms a central horny axis or ‘‘ sclerobase”
supporting the soft parts (fig. 210).
The mesoderm may also produce
skeletal structures in the form of
variously-shaped crystalline spicules
or “sclerites” (fig. 123), which are
composed of an organic basis har-
dened by carbonate of lime. In
some Alcyonarians the skeleton con-
sists solely of these mesodermal
spicules, which may remain en-
tirely free and detached (as in AZ
cyontum), or may be fused with one
another directly (as in Corallium
and Zubipora), or may be partly

Fig. 210.—Diagrammatic vertical section :
through a young colony of Gorgonia, showing free and partly united by horny

the relation of the sclerobase to the soft parts. : ‘
a, Horny axis or sclerobase, supporting the matter (as mn Sclerogorgia). In

colony; ¢, Ectoderm represented by the thick other types. again. as in Gorvonta
dark line; 4%, Two polypes; c, One of the yP ee ( : Ss
coenosarcal canals, connecting the visceral and Teas: the skeleton is twofold,
chambers of the polypes with one another. spas
For the sake of clearness, the horny axis has consisting on the one hand of an
been represented of disproportionate thick- gyxjq] sclerobase of ectodermal ori-
ness. (After von Koch.) ,
gin, and on the other hand of free

spicules developed within the mesoderm. ‘The skeleton of Hedopora,
finally, is peculiar in its structure, and is probably ectodermal in
origin.

The Alcyonaria, so far as the living types are concerned, are
divided by von Koch into the following groups :—

SUB-ORDER I. ALCYONACEA.—Sedentary Alcyonarians in which an
axial skeleton is usually wanting. When such a skeleton exists (as in
Corallium) it is of mesodermal origin, and is not secreted by a continuous
epithelial layer.

Family 1. Haimeide, . ‘ . Monoxenia, Hartea.
" 2. Cornularide, : . Cornularia, &c.
" 3. Aleyonidze, = : . Alcyonium, &c.
" 4. Pseudaxonia,. ; . Corallium, Mopsea, &c.
" 5. Qubiponda. ys . Lubipora.
" 6. Helioporide, . : . LHeliopora.

_ SUB-ORDER II. GORGONACEA.—Sedentary Alcyonarians in which there
is a firm sclerobasic axis secreted by a continuous epithelial layer. The
colony is not polymorphic.

Family 7. Gorgonide, . ; . Gorgonia, Isis, &c.

PSEUDAXONIA. 327

_ SUB-ORDER II]. PENNATULACEA.—Free-living Alcyonarians consist-
ing of a stem and polypiferous branches. The colony is polymorphic.

Family 8. Pennatulide, . ‘ . Pennatula, Verettllum, &c.

So far as the sub-orders are concerned, the above classification is
only partially available for paleontological purposes, as based upon
characters which are not recognisable in fossil forms. ‘There are,
moreover, certain extinct groups of corals (Halysitide, Tetradiide,
Chetetide, &c.) which we must provisionally place among the
Alcyonarians, but which cannot, with our present knowledge, be
included in any of the three sub-orders above mentioned.

As regards the distribution in time of the Alcyonarians, the fami-
lies of the Haimeide, Cornularide, Alcyonide, and Tubiporide have
no fossil representatives, so far as is certainly known ; and only the
last mentioned of these requires further notice here. On the other
hand, the families of the Psexdaxonia, Gorgonide, Pennatulide, and
Fflelioporide are all sparingly represented by fossil types in the
Secondary and Tertiary deposits. The extinct family of the He/zo-
fitide is mainly Paleozoic, its earliest representatives appearing in
the Ordovician rocks. In addition to the preceding, there are the
four families of the Halysitide, Tetradide, Chetetide, and Aulopor-
zd@, the members of which are apparently exclusively Palzeozoic, but
the true relationships of which are more or less uncertain. Still
more uncertain is the systematic position of the extinct groups of
the Monticuliporide and Fistuliporide, which will be here treated
of apart from the ALyouaria.

In the following brief account of the fossil Alcyonarians, only
those families will be considered which are known to have fossil
representatives ; but the family of the Zudiporide also demands a
short notice, from its supposed relationship to Syzingopora.

PSEUDAXONIA.

This group of the Alcyonarians comprises forms in which the
skeleton is composed of mesodermal spicules, the sclerobasic axis,
when present, not being secreted by a continuous epithelial layer.
The spicules are sometimes (Briareum) completely detached, though
even in this case they may form in part a tolerably well-defined axis.
On the other hand, in the well-known Red Coral (Corallium rubrum)
there is a dense calcareous sclerobase which is composed of spicules
or sclerites embedded in and united by a fibro-crystalline calcareous
matrix (fig. 211). The sclerobasic axis of Cora//ium is unjointed
and is branched, and its surface exhibits longitudinal grooves which
lodged the larger ccenosarcal canals (fig. 124). In Melthea and
Mopsea, again, there is a sclerobasic axis, but this is jointed, and is com-

328 CHARACTERS AND DIVISIONS OF ALCYONARIA.

posed alternately of soft and hard segments, the former being com-
posed of separate sclerites united by horny matter, while the latter
are made up of fused spicules. In Sclerogorgia, finally, there is an
unjointed axis, consisting of horn with embedded sclerites, while
there are also free spicules in the soft tissues.

As regards the geological distribution of the Psewdaxonia, the
genus Corallium appears to be represented in rocks as ancient as

Fig. 211.—Part of a longitudinal section of Covaliium rubrum, magnified 180 times, showing
the spicules of the skeleton united by a crystalline or fibrous matrix, produced by the calcification
of the soft interspicular tissues. (Original.)

the Jurassic, and the Eocene Tertiary has yielded the remains of
the genera /opsea and Websterta, of which the former still survives,
while the latter is confined to the Eocene and is of uncertain
affinities.

TUBIPORID-.

This group of the Alcyonarians comprises only the recent genus
Tubipora, including the familiar ‘‘ Organ-pipe Corals.” There is a
well-developed corallum in Zudifora composed of numerous cylin-
drical tubes or thecze, separated by small intervals, and connected
with one another by horizontal calcareous floors, which form a series
of concentric laminz parallel with the upper surface of the colony.
These floors are produced by the coalescence of horizontal stolons
given out from the upper ends of the polypes, and new corallites are
budded out from their upper surface. Internally they are traversed
by horizontal canals which communicate with the visceral chambers

TUBIPORIDA. 329

of the polypes by numerous rounded apertures placed at the points
where the corallites are embraced by the floors (fig. 212, a and B).

Fig. 212.—a, Part of a tube of Tubipora musica, Linn., divided longitudinally, showing the
openings of the canal-system of the connecting-floors into the visceral chamber of the polype; pB,
Part of a horizontal section taken at the level of one of the connecting-floors, showing the canal-
system of the connecting-floor ; c, Part of a corallite of Tudzfora divided longitudinally, showing
the axial tube; in the lower portion of the figure the axial tube is laidopen. All the figures are
enlarged five times. (Original.)

In the interior of the corallites there commonly exists a hollow cal-
careous tube (fig. 212, c), which occupies the axis of the visceral

Fig. 213.—a, Transverse section of a corallite of Tubzpora musica, Linn., taken at the level of
one of the connecting-floors, enlarged twenty times, showing the tubuli of the wall; B, Portion of
the surface of one of the connecting-floors, enlarged twenty times, showing the external openings
of the tubuli of the skeleton; c, Fragment of the corallum of 7wdzfora, enlarged sixty times,
showing the composition of the skeleton out of spicules. (Original.)

chamber, and is dilated and fused with the enclosing theca at the
level of the successive connecting-floors. This axial tube is only

330 CHARACTERS AND DIVISIONS OF ALCYONARIA.

occasionally present ; and no traces of proper “ tabulee” (in the strict
. sense) have been noticed to occur. There are also no structures
which admit of being regarded as septa.

As regards the microscopic structure of the corallum of Zuédzfora,
the entire calcareous skeleton is permeated throughout by a system
of minute parallel tubules, which sometimes branch, and which
open on the surface by well-defined rounded apertures (fig. 213, A
and B). ‘These canaliculi run at right angles to the walls of the
corallites and also to the connecting-floors, and they render the
skeleton of Zudzfora completely and minutely porous. Moreover,
thin sections show that the skeleton is made up of a network of
irregular fusiform spicules which are firmly united with one another
(igs 21.356):

The genus Zudzpora is not known to occur in a fossil condition,
but the structure of its skeleton is a matter of considerable paleon-
tological importance, as high authorities regard the genus as the
closest living ally of the Palzeozoic genus Syzingopora. Reasons
have been previously given (p. 320) for considering that Syrzngopora
and its allies are closely related to the /avosttide, and that they
truly form a group of the Wadreporaria FPerforata. It is sufficient,
therefore, to point out here that the skeleton of Zudzpfora differs
fundamentally from that of Syzzmgopora in the following points :—

a. The entire skeleton is traversed by minute canaliculi, no
traces of which are found in the compact corallum of Syringopora.

6. The skeleton is composed of distinct spicules.

c. The axial tube, when present, is not formed of invaginated
“tabule,” as in Syvingopora, and there is no evidence of the exist-
ence of proper ‘‘tabulz” at all.

ad. No proper septa exist, whereas well-developed spiniform septa
are present in Syringopora. |

Upon the whole, therefore, it would appear that there is no suff-
cient evidence at present available which would support the reference
of Syringopora and its allies to the Zudbiporide.

GORGONID-.

The family of the Gorgonide@, as defined by von Koch, includes
those Alcyonarians in which the colony is fixed, and is sup-
ported by an axial sclerobase, which is secreted by a continuous
layer of epithelium. The sclerobase may be purely horny (as in
Gorgonia itself), or it may be composed of alternate horny and
calcareous joints (as in Jszs). The polypes are all similar to one
another, and polymorphism has not been observed. ‘This family is
of little paleontological importance; but the genus /szs has been
recognised in deposits as ancient as the Cretaceous. Remains re-

PENNATULIDZ. 331

ferable to the recent genera Primnoa and Gorgonella have also
been detected in the Miocene Tertiary rocks.

PENNATULIDA.

This family includes a number of Alcyonarians in which the
colony is not fixed to any foreign object, and is composed of a
central ccenosarcal stem or rachis carrying polypes superiorly, these
being commonly arranged on longer or shorter lateral branches.
The polypes are dimorphic, and the skeleton usually has the form
of an unbranched, horny or partially calcified sclerobase. This
group is also of small paleontological importance, but the genus
Pavonaria has been recognised in deposits of late Cretaceous age,
and the remains of Graphularia have been found in the Eocene
and Miocene Tertiary.

HELIOPORID&.

This family, as here defined, comprises only the single genus
fleliopora, in which there is a well-developed sclerodermic corallum
(fig. 214, A) composed of tabulate tubes of two sizes, the larger of
these being furnished with radiating pseudosepta, which do not
correspond in number with the mesenteries of the living polypes.
The larger tubes of the colony (‘‘autopores”) have usually been
regarded as the true corallites, and the smaller interstitial tubes
(“‘siphonopores ”) have been commonly considered as constituting a
“‘coenenchyma”; but the researches of Moseley on the living
Fleliopora cerulea have rendered it probable that the colony is really
dimorphic, the sexual zooids occupying the large tubes, while the
small tubes lodge imperfect sexless zooids. The large tubes or
“autopores” are crossed by well-developed horizontal “ tabulz,”
and are completely separated from one another by the smaller tubes
or ‘“siphonopores,” which are also tabulate (fig. 214, c). Apart
from their larger size, the autopores are further distinguished by the
fact that they exhibit internally a variable number of longitudinal
ridges which resemble the radiating “septa” of the Zoantharian
corals. In the living Helopora cerulea there are usually twelve of
these radiating ridges in each autopore, but they can hardly be said
to have any existence as definite structures, and appear rather to be
formed by the projection into the cavity of the autopore of the
prismatic siphonopores which bound the latter. In //. Partschiz,
of the Cretaceous rocks, the autopores possess from twenty-five to
twenty-eight radial ridges which extend inwards to some distance,
while 47. macrostoma, of the same formation, has numerous septal
ridges, but these are shorter. In any case these septal ridges not

332 CHARACTERS AND DIVISIONS OF ALCYONARIA.

only are not at all constant in number, but do not correspond with
the mesenteries of the living polypes, these being always ezgA7¢ in
number. Hence, the radial ridges of Ae/opora must be regarded
as ‘‘pseudosepta,” and they are not homologous with the “septa” of
the Madreporarians. The “siphonopores” or interstitial tubes are
destitute of pseudosepta, and in the case of the living H. caerulea
they are occupied by structures which Professor Moseley regards as

Fig. 2r4.—A, Colony of the recent Heliopora caerulea, of the natural size; B, Portion of the
surface of the same, enlarged, showing the apertures of the larger and smaller zodids; c, Ver-
tical section of a few of the ‘‘ siphonopores”’ enlarged, showing the tabula. (After Dana.)

probably of the nature of rudimentary, sexless polypes. These
‘“‘siphonozooids” have the form of sacs lined by the endoderm,
closed externally, but communicating with the cavities of the auto-
zooids by means of canals in the soft tissues.
As regards its minute structure, the skeleton of Aelzopora con-
sists of fibro-crystalline carbonate of lime having a very peculiar and
characteristic arrangement. When examined in thin sections (fig.
215), the corallum is seen to be composed of radially disposed, par-
allel, prismatic rods, the apices of which project above the general
surface as prominent blunt papillze which occupy the angles of junc-
tion of contiguous siphonopores, and constitute a diagnostic feature of

HELIOPORID. 228

the genus Ae/zofora. ‘The rods are generally placed, each, at the
junction of four siphonopores, and are, therefore, essentially quad-
rilateral They are firmly united with one another along their
opposed sides by dentated sutures, and they are excavated along
their angles by the siphonopores. Each rod possesses a single or
multiple, generally elongated, apparently structureless axis, round
which the calcareous tissue is disposed in radiating plates of great
tenuity, which look in cross-sections (fig. 215, A) like fibres. The
peculiar prismatic rods just described may be regarded as modified
spicules, which become laterally anchylosed. In the fossil species of

AY
i
i

Ss

“ RRS SSNS NS aad aS oD
Sn ees
eee - S :
a 5 a Aca SS >
ELE EERE —_
. me _s SS my, — =, Sorry
we ‘ : > S NN ite =
AX

lac

We

LUI CLE.
A Oe

SSS Z
Yee

YY

Lt

ZZ
nce
te

(es
a

Fig 215.—a, Tangential section of the corallum of the recent Heliofora cerulea, enlarged
twenty times ; B, Longitudinal section, similarly enlarged. az, Autopore; sz, Siphonopore; a,
Tube of a parasitic Annelide (Leucodora); s, Suture between two adjoining spicules; za, Tab-
ula. (Original.)

fleliopora the skeletal structure is commonly largely affected by
mineralisation, but in some cases (eg., in 4. Blainvilleana) the
minute structure of the corallum can be shown to be essentially
similar to that of the recent A cerulea. Even where obliterated
by crystallisation, the minute structure can be inferred to have been
spicular, as the surface always shows the characteristic projecting
papillae formed by the free ends of the skeletal rods.

It is worth noting in connection with the skeleton of Helzofora that
the corallum in the recent H. ceru/ea is commonly traversed by numer-
ous Annelide-tubes belonging to a species of Leucodora. These tubes
are intermediate in size between the autopores and siphonopores (fig.
215, A), are very regularly distributed, and have their mouths flush with
the general surface ; while they are not mere borings, but are coated by

334 CHARACTERS AND DIVISIONS OF ALCYONARIA.

a layer of the coral-substance. For these reasons they have all the
aspect of belonging to the corallum itself, and if they occurred in the
fossil species of the genus their real nature might very readily be
mistaken.

The mode of growth of the corallum in He/ofgora is peculiar.
The siphonopores appear to increase by means of “ intermural gem-
mation,” and not, as in the fe/oltzde generally, by fission. On
the other hand, the autopores, as can readily be observed in the
growing ends of the colony, are produced by what von Koch has
called “‘coenenchymal gemmation.” In this process—which will
be spoken of again in connection with /e/zo/zzes—new autopores are
produced by the apparent fusion and coalescence of a number of the
siphonopores. According to Moseley’s observations on the recent
Ff. cerulea, this is effected by an arrest of growth of one or more
of a group of siphonopores set apart for the production of a fresh
autopore. ‘‘ The arrested cell or cells form a central floor to the
new calicle, around which lies a circular zone of contiguous, deeper,
and older cells. The inner walls of these cells—z.e., those nearer
to the centre of the growing calicle—cease to grow, whilst their
outer ones continue to develop, and being fused together form the
lateral walls of the calicle. The plications in the wall of the fully
formed calicle are to a great extent the result of this peculiar mode
of growth.” The conversion of a group of imperfect polypes into a
single complete polype is doubtless a sufficiently remarkable phen-
omenon ; but it is probable that, in reality, it is only a single siphono-
zooid which ultimately becomes developed into an autozooid, the
remainder of the siphonozooids concerned in the process becoming
aborted. An analogous phenomenon has been observed by von
Koch (‘Zoologischer Anzeiger,’ 1881) in the case of certain of
the Pennatulide, in which the siphonozooids become converted into
autozooids. The subject is one of great paleontological importance,
since the same phenomenon—as will be subsequently shown—is
observed in /e/iolites and its allies; and it has been contended by
Lindstrom that this fact is seriously opposed to the view that the
interstitial tubes of e/zolites are of the nature of “‘siphonopores ”
rather than of “‘ccenenchymal tubes.” The observations of Moseley
upon Heliopora cerulea and of von Koch on the Pennatulide de-
prive this contention, however, of the weight which might otherwise
be attached to it.

Since the researches of Moseley upon fYeliopora caerulea, it has
been usual to include He/olites and its allies in the family of the
Ftelioporide. ‘The latter, however, possess a skeleton widely differ-
ent from that of Ae/zopora in its minute structure, while the auto-
pores are provided with an approximately constant number of septa,
the nature of which appears to be different from that of the pseudo-

HELIOLITIDZ. 335

septa of Helopora. For these reasons, amongst others, He/iolites
and its relations may be placed, provisionally at any rate, in a
separate family.

The recent Heliopora cerulea is found in the Indian and Pacific
oceans, and fossil species of the genus are found in the Cretaceous
and Eocene deposits. The imperfectly known genus Polytremacis,
from the Cretaceous rocks, appears to be closely related to
fleliopora.

HELIOLITIDA.

_ This family comprises a number of Palzeozoic corals, of which
the type is the widely distributed and abundant genus /e/olites it-
self, and is closely similar to the preceding group in its general
characters. The corallum (fig. 216) is composite, and consists of
two sets of tubes, of different sizes, of which the larger (“‘auto-

cu

i(

ret
ie

|

i
He
th

Fig. 216.—a, Small colony of Helrolites tnterstinctus, Linn., of the natural size; B, Small por-
tion of the surface of the same, magnified, showing the autopores (a) and the mouths of the
siphonopores (4); c, Vertical section of the same, enlarged, showing the tabulate autopores (a),
and the similarly tabulate siphonopores (6). (Original.)

pores ”) are, as a rule, completely separated from one another by the
intervention of the smaller (“‘siphonopores”). Both sets of tubes
are provided with tabule (fig. 216, c), and the autopores are fur-
nished with lamellar, or rarely spiniform, septa, the number of
which is almost invariably twelve in each corallite. In some cases
the septa unite centrally to form a reticulate pseudocolumella.
The siphonopores increase principally by fission, though partly by
intermural gemmation, while the autopores are produced by

336 CHARACTERS AND DIVISIONS OF ALCYONARIA.

“‘ccenenchymal gemmation.” The structure of the skeleton is not
spicular.

As regards the minute characters of the skeleton, the autopores
and siphonopores are ¢/zm-walled, and no traces of the peculiar pris-
matic rods of the corallum of Aelopfora can be detected. The
siphonopores are generally so largely developed as to form a com-
plete zone, of one or more rows, of small tubes between adjacent
autopores (fig. 216, B); but in He/olites dubius (fig. 217, A) the
number of the siphonopores is much reduced, and contiguous auto-
pores are largely in contact. Both sets of tubes are furnished with

Fig. 217.—A, Cross-section of Hedlzolztes dubius, from the Ordovician rocks of Esthonia, en-
larged ten times; B, Vertical section of the same, similarly enlarged, showing the spiniform
septa; c, Tangential section of Heliolites porosus, from the Middle Devonian of Biichel, showing
“*coenenchymal gemmation,” enlarged ten times; D, Part of another cross-section of the same,
enlarged about twenty times, showing fission of the siphonopores. sz, Siphonopores ; az, Auto-
pores; au’, Autopore being developed by ‘‘ccenenchymal gemmation”; Z, Incomplete septum
in a siphonopore, indicating partially accomplished fission of the tube. (Original.)

tabulz, which are more numerous in the siphonopores than in the
autopores (fig. 216, c). The siphonopores are without septa, but
the autopores possess septal ridges or spines, which are very variable
in their development, but are almost always twelve in number in
each autopore. In some species (/e/tolites tnterstinctus, H. Mur-
chisont, &c.) the septa are lamellar, but are rudimentary, and may
even be represented only by slight bendings of the walls of the auto-
pores. In other species (7 porosus, H. parvistella, &c.) the septa

HELIOLITIDA. 33h

are lamellar, and extend to a considerable distance into the interior
of the visceral chamber, sometimes meeting to form a reticulated
pseudocolumella (4. zutricatus), or even showing alternate large
and small septa (as in some examples of /e/olites porosus). Lastly,
the septa may be in the form of twelve longitudinal rows. of spines
(as in Heliolites dubius, fig. 217, A and B, and in the true Helolites
megastoma of M‘Coy).

As regards the mode of growth of the corallum in /e/olites and
its allies, the siphonopores are usually developed fissiparously (fig.
217, D), though intermural gemmation also occurs. On the other
hand, the autopores are produced by ‘‘ccenenchymal gemmation,”
in a fashion essentially similar to that which has been already de-
scribed as occurring in Helopora. In Heltolites dubtus, in which the
siphonopores are reduced to a minimum (fig. 217, A and B), a single
siphonopore may sometimes be observed to be developed vertically
and directly into an autopore.. More usually, an autopore is pro-
duced by the arrested development of a group of siphonopores
(as in Helopora) ; and the process can be observed readily both in
transverse and longitudinal sections. In the former (fig. 217, Cc)
the enclosure of a group of siphonopores within an external wall,
and the gradual development of the septa can be readily made out ;
while in long sections a few of the siphonopores are seen to be
suddenly arrested in their growth, and commonly to be cut off by
a common tabula, their place vertically being taken by a single
autopore.

As regards their zoological position, the He/olitide show points
of relationship on the one hand to the Alcyonarza, and on the
other hand to the Zoantharia. In the general features of the cor-
allum (apart from the minute structure of the skeleton) the mem-
bers of this family show a striking resemblance to the unquestionably
Alcyonarian genus Ffeliopfora, and in both groups we find the sin-
gular phenomenon of “‘ ccenenchymal gemmation.” This remarkable
mode of increase, however, occurs also in the family of the /7stul-
poride ; so that undue weight must not be assigned to this alone.
On the other hand, in the fact that the number of the septa is
almost constantly twelve, while these structures are sometimes alter-
nately long and short, and are occasionally in the form of rows of
spines, we have a decided approach to various groups of the Zoan-
tharia. The small tubes of the corallum of the Aedoltide have
commonly been regarded as cenenchymal in their nature, but
Moseley’s observations on AHeopora would strongly support the view
here taken, that these structures are really tenanted by rudimentary
polypes (“siphonozooids”), and that the corallum is therefore really
dimorphic. It has been already pointed out that the fact that the
large corallites are formed by an arrested development and appa-

VOL..I. ¥

338 CHARACTERS AND DIVISIONS OF ALCYONARIA.

rent coalescence of a number of the small tubes does not really
militate against the view that the latter are of the nature of

‘ siphonopores.”

As regards their distribution in time, all the members of the
Fleliolitide are Paleozoic, and all are confined to the Ordovician,
Silurian, and Devonian periods.

The type-genus of the Helzolitide is Heliolites itself, in which the
corallum is massive or branched, and the siphonopores are polygonal,
and usually regular in form, and possess complete walls (figs. 216, 217).
The species of He/zolztes range from the Ordovician to the Devonian,
and are very abundant in the Silurian rocks proper.

In the genus Plasmotora (fig. 218) the corallum is like that of
Fleliolites in general structure and appearance, but the walls of the

a B, \ ay sateen aici, PO eel MMe et LS ay fA \ ‘ . a :
dy'¥ \ a) edhe. NEN
A f ; yp SJ

Fig. 218.—a, Transverse section of a specimen of Plasmofora petaliformis, Lonsd., from the
Wenlock Limestone of Gotland, enlarged five times; B, Transverse section of Plasmopora scita,
E. and H., from the Wenlock Limestone of Gotland, enlarged five times; c, Vertical section of
the same specimen, similarly enlarged. (Original.)

siphonopores are incomplete or obsolete, and their tabule are thus
enabled more or less largely to coalesce, and give rise to a vesicular
tissue of lenticular cells (fig. 218). There are generally from two to five
rows of siphonopores between adjoining autopores, and the septa may be
either lamellar or spinulose. The species of Plasmopora are principally
found in the Ordovician and Silurian rocks, but Devonian forms are also
known. The Silurian deposits also contain various corals closely related
to Plasmopora, for which the names of Propora and Pinacopora have
been proposed, but these titles cannot be considered as of more than
sub-generic value. In both these groups the siphonopores are much
reduced in number, and the autopores are correspondingly close-set ; the
calices of the autopores being elevated above the general surface in
Propora, but flush with the surface in Pzzacopora, and the corallum in
the latter being typically discoid in form.

HALYSITIDA, 339

HALYSITID.

This family comprises only the familiar Ordovician and Silurian
corals known commonly as “Chain-corals,” and constituting the
single genus /a/ysites. The corallum
in Hlalysites (fig. 219) is fasciculate and
reticulate, composed of long, tubular,
cylindrical corallites, which are placed
side by side in intersecting and anasto-
mosing laminz or lines, any given coral-
lite being united with its neighbours to
the nght and left along its whole length,
and each lamina of the corallum con-
sisting of no more than a single linear
series of tubes. Each tube is enclosed
in a strong imperforate wall, surrounded
on its free sides by a thick epitheca ;
and there may be a distinct division of

)

22iG8

2 = (6
= See)
Owe
=>)
Ze

os

So
ae Seo

=e
Slate Ss
SS SS
ZF abseg|
a S
‘s}
——

Zoaim oe)

es)
MwA
SOOO Wy)
ysl vy / bh,
YO" 1,

the corallites into two series of different “ay re Yd AO
. ° . . AWS Se) SS Ay =
sizes, in which case a single small tube 1 AN A fle?)
is placed between each pair of the larger \\ eso: yf

tubes. In other cases all the tubes are :
pmoieimnesize and structure. Septa May Fig. o19—2, Upper surface of a
be wanting, and, when present, have they ieenc vee eee
form of vertically disposed rows of spines, of the natural size; 4, Part of the
: same enlarged. (Original.)

in cycles of twelve. The tabulz are

complete, horizontal, or slightly concave, not vesicular, the smaller
corallites (when present) being much more closely tabulate than the
larger ones.

The species of Ha/ysttes may be divided into two groups, according
as the corallum is composed throughout of corallites of one size, or
consists of two sets of corallites of different sizes. The common
ff, escharoides of the Silurian rocks (fig. 219, and fig. 220, A) is an
example of the forms in which all the corallites are similar. On
the other hand, in the familiar 4. catenu/aria of the same formation,
the corallum consists of large corallites separated by the intervention
of small, closely tabulate tubes (fig. 220, B and c). Septa are some-
times absent (fig. 220, B), but in other instances they are well devel-
oped (fig. 220, A). When present, the septa always have the form
of vertical rows of spines, twelve of such rows being usually recog-
nisable in each corallite. The mode of growth of the corallum is
by “stolonal gemmation,” the colony in its early condition being not
unlike that of an Axulopora.

The zoological position of the genus //a/ysztes cannot be regarded
as certain, but it would appear, on the whole, to be most nearly

340 CHARACTERS AND DIVISIONS, OF ALCVYONARTZAS

related to the Helolitide. At the same time, there are indications
of a possible relationship between F/adysztes and the Syringoporide.
This is particularly shown by the peculiar coral described by Mr
Etheridge from the Arctic Silurian rocks under the name of Aadly-
sites catenulatus, var. Fetldent, which has the form of Halysttes, but

Fig. 220.—a, Transverse section of Halysztes escharoides, Lam., from the Silurian of Gotland,
enlarged ten times, showing the spiniform septa, and the absence of a series of small corallites ;
B, Transverse section of Halysites catenularia, Linn., from the Wenlock Limestone of Dudley,
enlarged five times, showing the absence of septa, and the presence of a series of small corallites ;
c, Vertical section of a few corallites of the last specimen, enlarged five times, showing the large
and small corallites, and the difference in the tabulation of these. (Original.)

in which the corallites resemble those of Syzimgofora in being fur-
nished with connecting-tubes. This singular type cannot, however,
be regarded as properly belonging to Hadlysztes.

TETRADIIDA.

This small family includes only the single genus Zetradium,
which, so far, has only been detected in the Ordovician rocks of
North America. In this genus the corallum (fig. 221) is massive,
and is composed of long, prismatic and closely contiguous corallites,
which are of small size, and have imperforate walls. The tubes are
furnished with longitudinal inflections or plications, generally four in
number in each tube, which do not reach the centre of the visceral
chamber, and which give a characteristic cruciform or petaloid aspect
to cross-sections of the corallites (fig. 221, B). These longitudinal
plications are apparently to be regarded as of the nature of septa
or pseudosepta. The tubes are crossed by numerous tabule (fig.
221, C), which are sometimes complete, but are at other times per-
forated by central apertures (as in the tabule of some species of
Stenopora). The mede of increase appears to be by fission.

Tetradium appears to be related to Halysztes, but its true affinities
and zoological position are uncertain.

CH AETETIDA, 341

CHATETIDA.

This family includes only the single genus Che‘eées, all the known
species of which are found in the Carboniferous rocks, though vari-

the same.

Fig. 221.—a, Fragment of a large corallum of Tetradiune minus, Safford, from the Cincinnati
Group of North America, of the natural size; B, Transverse section of the same, enlarged ten

times, showing the petaloid form of the tubes and the short septa; c, Vertical section of the same,
similarly enlarged, showing the tabule. (Original.)

ous Monticuliporoids have been formerly referred to the same genus.
The type-species is the C. radians of the Carboniferous Limestone

4 é 2 aa
Aare ame : fume
3 4 S ee
4 = &
4 S ‘4 % . £ Fi
ae J 2 if
a : b.8
Pa ok
, 2 Z
=
seeks! A 2
. j
4 2 Pe
2 of
% 5 & 2s F 4 EA g
4 4 ee ‘Zs Ae 3
y t FA B ge i
% é 4 BS =G: z
oe ee ee
m7 TF Wet ft
y é ‘ p.e § 3
é ee 5 bi ae

Fig. 222.—A, Tangential section of Chetetes Etheridgii, from the Carboniferous Limestone of
Westmorland, enlarged about ten times; B, Longitudinal section of the same, similarly enlarged.
a, Imperfect longitudinal partition produced by uncompleted fission of an old corallite. (Original.)

of Russia, but the characters of all the known species are essentially
The corallum in Chefefes is massive or laminar, often

342 CHARACTERS AND DIVISIONS, OF, ALCYONARIA:

of large size; and consists of long, tubular, prismatic corallites,
which are not only in close contact throughout, but are so com-
pletely incorporated by fusion of their walls that rough fractures
almost always expose the interior of the tubes. The corallites are
all of one kind, are irregularly polygonal, and possess completely
imperforate walls. The tubes are traversed by a few complete
tabulee (fig. 222, B), which are commonly developed periodically at
successive levels ; but there are no septa. The increase of the cor-
allum is by fission of the old tubes; and hence in cross-sections
(fig. 222, A) it is common to observe imperfect longitudinal partitions
projecting into the visceral chambers of the corallites, and indicating
the uncompleted fission of the tubes.

The zoological affinities of the genus CA@/efes are quite uncertain,
and it is not even clear that it is referable to the A/cyonarza.
Many authorities regard the genus as belonging to the Folyzoa
rather than to the Calenterata ; but the fissiparous mode of its
development, and the total absence of pores or canals connecting
adjoining tubes, would militate strongly against its being referred to
the former group.

AULOPORID.

This small and imperfectly understood group comprises the
Palzeozoic genera Axulopora, Cladochonus (Pyrgia), and Monilipora,
of which the first may be taken as the type. The corallum in
Aulopora (fig. 223, A) has the form of a creeping, branched, or
reticulate system of tubes, attached by the whole of the lower sur-
face to the exterior of a shell, coral, or other foreign bodyaneiae
prostrate stems or stolons send up at longer or shorter intervals
reclined tubular or trumpet-shaped corallites, which are free termin-
ally, and do not grow up to form a fasciculate mass. As regards
their internal structure, the corallites are commonly furnished with
curved or horizontal tabule, and rudimentary septa are present in
the form of marginal strize or rows of tubercles. The walls of the
corallites are imperforate, and the mode of increase of the corallum
is by stolonal gemmation. The species of Aulopora range from
the Ordovician to the Carboniferous inclusive. |

Cladochonus (Pyrgia) closely resembles Aulopfora, but the colony
is only attached to foreign bodies by isolated points of attachment,
and grows in an erect manner rather than as a creeping network.
In its young state, the corallum consists of a single trumpet-shaped
corallite (fig. 223, c and b), attached by processes springing from
its lower surface. Zontlopora possesses an Auloporoid corallum,
which is attached parasitically to the stems of Crinoids in a ring-like
manner, the walls of the trumpet-shaped corallites having a peculiar

LITERATURE OF ACTINOZOA. 343

cancellated structure. Both these genera are confined to the Car-
boniferous period.

The true relationships of the Auloporide are uncertain. A close
resemblance exists between the adult colonies of Axz/ofora and the
young stages of both Syzzngopora and Falysites, but it is questionable

~ SK :

~
==
SS

SSS

RX
WS
NSS

Fig. 223.—a, Portion of Aulopora tubeformis, of the natural size; and p, Portion of the same,
enlarged (after Goldfuss). Devonian. cand p, Cladochonus (Pyrgia) Michelint, of the natural
size, and enlarged (after Milne-Edwards and Haime). Carboniferous.

if this likeness bespeaks any real affinity to either of these genera.
In the stolonal method of gemmation characteristic of the Aulopo-
roids we have a marked Alcyonarian feature, and the group may
therefore be provisionally placed in the division of the A/cyonarta.

Pig RAD ORE Oke Nel iN@OZOA:

al

. “ Manuel d’Actinologie et de Zoophytologie.” De Blainville. 1834-37.

2. “ Histoire des Animaux sans Vertébres,” vol. 11. Lamarck. (Ed. 2,
1836.)

3. “ Histoire Naturelle des Coralliaires ou Polypes proprement dits.”
Milne-Edwards and Haime. 1855-60.

4. “Recherches surles Polypiers.” ‘Ann. des Sciences Nat.’ Milne-

Edwards and Haime. 1848-52.

“Iconographie Zoophytologique.” Michelin. 1840-47.

“ Beitrage zur physiologischen Kenntniss der Korallenthiere im All-
gemeinen und besonders des rothen Meeres.” ‘Abhandl. d. Berl.
Akad.’ Ehrenberg. 1832.

7. “Zoophytes.” ‘Report of the Exploring Expedition under Captain

Wilkes.’ Dana. 1848.
8. “ Die Korallthiere des rothen Meeres.” Klunzinger. 1877-79.

CxS

344 LITERATURE OF ACTINOZOA.

QO.

IO.

It Ws

“Die Bindesubstanz der Ccelenteraten.” ‘Icones Histiologice.’
Kolliker. 1866.
*“ A Revision of the Families and Genera of the Sclerodermic Zoan-

tharia or Madreporania.” “Journ. Linn! Soc. (Zool)? vols
Martin Duncan. 1884.
“Report on the Reef Corals.” ‘ Challenger Reports, vol. xvi.

Quelch. 1886.

. “On the Helioporidze and their Allies” “Challenger Reports, ol

i. Moseley. 1881.

. “On the Anatomy of Mussa and Euphyllia and the Morphology of

the Madreporarian Skeleton.” ‘Quart. Journ. Micro. Sci.,’ vol.
xxvill. Bourne. 1887.

. “Das Skelet der Alcyonarien.” ‘Morphologisches Jahrbuch.’ Von

Koch. 1878.

15. “* Die Gorgoniden des Golfes von Neapel.” Von Koch. 1887.
. “Die ungeschlechtliche Vermehrung (Theilung und Knospung)

einiger palzeozoischen Korallen.” ‘ Palzeontographica.’ Neue
Holgeyixe sOnelochs garage:

. “ Beitrage zur Kenntniss fossiler Korallen.” ‘ Zeitschr. d. deutschen

Geolog. Gesellschaft, Jahrg. 1869-70. Kunth.

. “Introduction a l’étude des Polypiers Fossiles.” Fromentel. 1858-

it,

. ‘Handbuch der Palzcontologie?” Bd. 1. Lief 2.) VoniZirrelee:
. “Polypiers Fossiles des Terrains Paléozoiques.” Milne-Edwards

and Haime. 1851.

. “Monograph of the British Fossil Corals.” ‘ Palzeontographical

Society.’ Milne-Edwards and Haime. 1851-54.

. “ British Fossil Corals.” (Supplement to the preceding.) ‘ Palzeon-

tographical Society.’ Martin Duncan. 1865-72.

=» lwethzeal Palecozorca.7) Lick 25. Herdinand) Noememumtece

‘““Monographie der Sclerodermata Rugosa aus der Silur-formation
Estlands,” &c. Dybowski. 1873.

. “ Reports on the British Fossil Corals.” ‘ Rep. Brit. Assoc.,’ 1869-

7) Martine» unean:

. “On the Affinities of the Palzeozoic Tabulate Corals with Existing

Species, “Aimer jour Ser and Ant 137255 Vieulr

. “Affinities of the Anthozoa Tabulata.” ‘Ann. of Nat. Hist.’ ser. 4,

VO xvii elo OMe linc strom:

. “On the Structure and Affinities of the Palazozoic Corals of the

Paleozoic Period.” Nicholson. 1879.

. “Monograph of the Girvan Silurian Fossils.” Nicholson and Ethe-

ridge, jun. 1878-80.

. “Die Korallen der Nattheimer Schichten.” ‘ Palzeontographica,’ vol.

xxl. Becker and Milaschewitsch. 1875.

. “ Petrefaktenkunde Deutschlands.” (Korallen.) Quenstedt. 1881.
. * Nouvelles Recherches sur les Animaux Fossiles du Terrain Car-

bonifére dela Belgique.” Premiere Partie. 1872. De Koninck.

. “ Petrefacta Germaniez.” Goldfuss. 1826-33.
> British) Ralzcozo1e Hossilss aus Cova alot.
. “Index to the Generic Names applied to the Corals of the Palzeozeic

Formations.” ‘ Bihang till K. Svenska Vet-Akad. Handlingar.’
Balivilie aiCoswa le inGistromar

. “ Obersilurische Korallen von lshau-Tien.” (In Richthofen’s ‘ China.’)

Lindstrom.

LITERATURE OF ACTINOZOA. 345

. “ Palzeozoiska Formationernas Operkelbadrande Koraller.” (Opercu-

~ late Corals of the Palaeozoic Formations.) Lindstrém. 1882.

. “ Fossil Corals of the State of Michigan.” Rominger. 1876.

“ Die Cyathophylliden und Zaphrentiden des deutschen Mitteldevon.”
Frech. 1886.

. “Die Korallenfauna des Oberdevons in Deutschland.” ‘ Zeitschr. d.

deutschen Geolog. Gesellschaft.’ Jahrg. 1885. Frech.

. “Ueber einige Anthozoen des Devon.” ‘Zeitschr. d. deutschen

Geolog. Gesellschaft.’ Jahrg. 1881. Schliiter.

. “On the Genera Heterophylha, Battersbyia, Palezeocyclus, and Astero-

smilia.” ‘ Phil. Trans.,’ 1867. Martin Duncan.

. “Ueber die verwandschaftlichen Beziehung einiger Korallengattun-

gen.” ‘Palezontographica.’ Neue Folge, ix. 1883. Pratz.

346

Caden Ea ER eal:
THE MONTICULIPOROIDS.

WE may consider here the remarkable groups of organisms (JZon-
ticuliporide and Fistuliporide), which have been collectively spoken
of as the “‘ Monticuliporoids,” and the precise systematic position of
which is still uncertain. ‘The Monticuliporoids, in fact, exhibit a
combination of characters; and paleontologists have therefore, so
far, come to no final decision as to the true relationships of these
puzzling organisms, some authorities regarding them as a peculiar
group of Corals, while others consider them to be referable to the
Polyzoa.

The structural characters of the Monticuliporoids are very com-
plex, and are for the most part only capable of complete elucidation
by means of microscopic examination, while the number of different
forms included in the group is very large. For these reasons, noth-
ing more will be here attempted than to give a brief outline of the
general morphology of the entire series, with the distinctive char-
acters of the two families of the Monticuliporide and Fistuliporide,
and a brief notice of the more important types included in these.

In all the Monticuliporoids, the skeleton is composed of closely
approximated, prismatic or sub-circular tubes, sometimes all similar
to one another, sometimes of different sizes, which are provided with
distinct walls. In the centre of the colony the tubes are always
thin-walled, more or less polygonal in shape, and similar to one
another in internal structure ; but as they approach the surface, they
diverge from one another by the intercalation of new tubes, their
walls commonly becoming at the same time thickened, and their in-
ternal characters being modified. It is in the outer, or “ mature,” re-
gion of the colony (fig. 224, E, #7) that a second set of tubes is usually
developed in those cases in which the colony is dimorphic. The
exterior of the colony commonly exhibits at intervals definite areas
(“‘ monticules” and “‘ maculze”), which are elevated or depressed as
regards the general surface, and consist of larger or smaller tubes

THE MONTICULIPOROIDS. 347

than the average (fig. 224, mo). The walls of the tubes are imper-
forate ; tabule are always present; and true “septa” are probably
always wanting, though “ pseudosepta,” in the form of radial plates
or spines, are in rare cases developed.

The form of the skeleton in the Monticuliporoids is extremely variable,
though it is in general tolerably constant for each species. In many
forms the skeleton is dendroid or ramose (fig. 224, B), consisting of
cylindrical or subcylindrical stems, which have a fixed base and branch
more or less freely above, the entire surface being covered with the
openings of the tubes. In others, the skeleton is so far modified from
the preceding that it assumes the form of an erect, laminar or frondescent

Fig. 224.—a, Fragment of the frondescent corallum of Monticulipora mamtmtulata, D’Orb.
(= Peronopora molesta, Nich.) showing ‘“‘ monticules” (70); B, Fragment of the dendroid corallum
of Callopora ? (Hetervtrypa) rugosa, E. and H.; c, Discoid corallum of Aszplexopora discoidea,
James; D, Hemispherical corallum of Callopora nummiformis, Dyb., viewed sideways; E, The
same vertically fractured, showing the divergence of the tubes and the peripheral ‘‘ mature”
region (vz). All the figures are of the natural size, except E, which is reduced. (Original.)

colony, composed of two strata of tubes the mouths of which open on the
two sides of the expansion (fig. 224, A). In numerous other types (fig.
224, D) the colony is hemispherical, the usually flattened or concave base
being covered with a concentrically wrinkled epitheca, while the mouths
of the tubes cover the entire upper surface. In still other forms, the
tubes are very short, and the colony has the form of a thin, flat or concave
disc, with a striated basal plate (fig. 224, c). In other cases, the skeleton
assumes a lobate or massive form ; and in others it is encrusting, and is
attached parasitically to foreign bodies.

A very important distinction between different types of the Mon-
ticuliporoids is based upon the homomorphic or heteromorphic con-
dition of the colony. In some forms (viz., in J/onotryfa) the tubes
are essentially similar throughout the colony in size and internal
structure, any difference which may be observed between different

348 THE MONTICULIPOROIDS.

tubes appearing to depend upon their relative age only. On the
other hand, most Monticuliporoids exhibit a distinct dimorphism,
the colony being composed of at least two kinds of tubes, which
differ in size and in internal structure. ‘The relative proportions of
these two sets of tubes to one another vary in different forms, but
the larger ones may be spoken of as ‘‘ autopores,” and the smaller
ones as “ mesopores.” The “ autopores” may be regarded as having
lodged the perfect zooids of the colony, and they are distinguished
both by their comparatively large size (fig. 225, a), and also by the
nature of their tabulse, these structures being usually comparatively

Sears

}

meaicenhny ee

‘Ol
a

yt

Ee lee
TL

440 1_f
Ao maser,

Fig. 225.—a, Tangential section of Callopora nummiformis, Dyb., from the Silurian rocks of
Esthonia, enlarged twenty times; B, Vertical section of the same, similarly enlarged. a, Auto-
pore; 7#z, Mesopore. (Original.)

few and remote, or being specially modified in form. On the other
hand, the “‘ mesopores,” or “interstitial tubes,” occupy, in greater or
less number, the spaces between the autopores, and are not only
smaller than the latter, but are more closely tabulate (fig. 225, m2).
The mesopores have often been considered as merely of the nature
of a “ccenenchymal” or “interstitial” tissue, but they may be
regarded, with great probability, as really having lodged imperfect
zooids, and as corresponding with the “ siphonopores” of the Ae/zo-
poride and Helolitide.

In addition to the preceding, many Monticuliporoids

whether

otherwise homomorphic or heteromorphic—possess yet a further
series of tubes, which have been spoken of as ‘“ acanthopores” or
‘“‘spiniform corallites.” These are minute cylindrical tubes, with
thick and laminated walls (fig. 226), which run in the substance of

THE MONTICULIPOROIDS. 349

the walls bounding contiguous autopores or mesopores, and the free
ends of which usually project above the general surface as spines or
blunt tubercles (fig. 227). The “acanthopores,” when present, are
only developed in the peripheral or “‘ mature ” region of the colony ;
and they are readily recognised in tangential sections (fig. 226, ac), as
round bodies which usually show a minute central tube surrounded
by a thick and dark-coloured wall of laminated calcareous tissue.
Waagen has expressed the opinion that the ‘“‘acanthopores” are
only immature tubes, but this is conclusively shown to be erroneous
by the fact that, while immature tubes can be readily demonstrated
in ali specimens, the ‘‘acanthopores” are strictly confined to par-
ticular sfeczes of Monticuliporoids, and are uniformly absent in others.

Fig. 226.—A few corallites of /7s- Fig. 227.—a, Profile view of a portion of the
tulipora eriensis, Rom.: a, Auto- surface of Dekayia aspera, showing acantho-
pores ; 7z, Mesopores ; ac, Acantho- pores; 6, The same, viewed from above. Enlarged
pores. Enlarged about forty times. about forty times. (After Nicholson and Foord.)

Moreover, they differ entirely in structure from the young tubes,
and unlike the corallites (whether young or old) they project above
the general surface of the colony in the form of spines. Again,
when they are limited in number, the acanthopores occupy definite
positions as regards the ordinary tubes of the colony ; and, finally,
in many forms (fig. 230, D) the acanthopores are so numerous as to
render the hypothesis that they are of the nature of young corallites
quite untenable. It may, then, be taken as certain that the acan-
thopores represent a special morphological element in the Monti-
culiporoid colony ; but it is difficult to give any satisfactory explan-
ation as to their true nature. They may be regarded, with
considerable probability, as of the nature of aborted zooids ; and
possibly their nearest analogue is to be found in the “ avicularia ”
of the recent Polyzoa. This suggestion is supported by the fact
that in some living Polyzoans (as in Lefegora) the avicularia are
attached to thickened tubes immersed in the substance of the
skeleton, the appearance of which in thin sections is very similar to
that observed in sections of those Monticuliporoids which possess
acanthopores.

350 THE MONTICULIPOROIDS.

In many Monticuliporoids the surface is studded at intervals with
small elevations which are known as “ monticules” (fig. 224, a),
and which are usually constituted by groups of corallites of larger
than the average size. In other cases, there are scattered depressed
areas, usually stellate in form, which are occupied by the “ meso-
pores” only, and which are known as “ macule.” These can be
shown to be really of the nature of centres of growth for the colony.

So far as is certainly known, the walls of the tubes in the Monti-
culiporoids are wholly destitute of mural pores, or foramina of any
kind, the chambers of contiguous tubes being thus completely sep-
arated from one another. Considering the vast number of thin

Fig. 228.—a, Part of a typical specimen of Jlonotrypella pulchella, EK. and H., from the Wen-
lock Limestone of Dudley, of the natural size; B, Part of the surface of the same, embracing one
of the clusters of large corallites, enlarged. (Original.)

sections of the Monticuliporoids which have been examined by
competent observers, the imperforate condition of the walls of the
tubes in the Monticuliporoids must be regarded as free from doubt ;
and it constitutes one of the most marked features by which these
organisms are separated from the Cyclostomatous folyzoa. Mural
pores have been described by De Koninck, and also by the present
writer and Mr R. Etheridge, jun., as occurring in the genus S¢enopora ;
but the exhaustive investigations of Waagen and Wentzel have shown
that even in this genus the walls are really imperforate, and that the
structures described as pores in such forms as Szenopora facki must
admit of a different interpretation. Mr Ulrich has also described
pores as occurring in a Monticuliporoid, but it may be suggested
with much probability that, in this case, the organism observed is
really referable to some other group.

In almost all the Monticuliporoids the tubes are crossed by trans-
verse calcareous partitions or ‘‘tabulse,” which are in general very
numerous (fig. 225, B), though occasionally limited in their develop-
ment. Usually, in the dimorphic forms, the autopores have few and
remote tabulee, while the mesopores have a much greater abundance
of these structures. Mostly, the tabulz are “complete,” forming
horizontal partitions which extend entirely across the tubes (fig.

THE MONTICULIPOROIDS. 351

225, B). In other cases, one half of the tube is crossed by straight
tabule, while the other half is occupied by curved or “cystoid”
tabule, forming a series of lenticular vesicles on one side (fig.
230, F). In other cases (Prasofgora), “cystoid” tabule are devel-
oped all round the periphery of the tube, and the centre is occupied
by straight tabule. Lastly, in istulipora, the walls of the meso-
pores are incompletely developed, and the tabulz unite to form a
tissue of lenticular vesicles between the autopores, the genus thus
bearing the same relation, in this respect, to Callopora that Plasmo-
pora does to Heliolites among the Aelolitide.

The great majority of the Monticuliporoids exhibit no radial
structures in the tubes which could be compared with the “septa”
of an ordinary coral. Ina few forms, such structures do occur, but
it is doubtful if in any such instance we have to deal with structures
really developed in mesenteries, and therefore really homologous
with the ‘‘septa” of the Zoantharia. Thus in Séstulipora, each
autopore is provided with two longitudinal folds, situated opposite
one another, towards one end of the visceral chamber. Again, in
a hitherto undescribed species of Callofora (fig. 229, A) each

Fig. 229.—a, A large specimen of Callopfora Foordit, of the natural size; pn, Tangential section
of the same, showing the pseudoseptal folds in the autopores, enlarged twenty times; c, Vertical
section of the same, similarly enlarged. a, Autopores; #z, Mesopores. From the Ordovician
rocks of Esthonia. (Original.)

autopore is provided with from two to five radial plications of the
wall, which closely resemble the “septa” of Zetradium, and give a
characteristic floriform appearance to cross-sections of the corallites.
Moreover, in typical examples of Jonticulipora mammulata, D’Orb.
(= Peronopora molesta, Nich.), the author has detected radially dis-
posed spines (fig. 230, D), which have much the appearance of the
radial spines of /avosites and Syringopora ; and similar structures
have been recognised by other observers in other forms.

Lastly, as regards the mode of growth of the skeleton, new tubes
are most usually produced by “intermural gemmation,” in a manner

352 THE MONTICULIPOROIDS.

precisely similar to that which obtains in the Favosttide. It is for
this reason that rough fractures of the Monticuliporoids expose the
walls of tubes, whereas in the genus C/e@/efes, where the growth is
fissiparous, fractures usually lay open the visceral chambers of the
corallites. It is, however, interesting to note that fisszon also occurs
not rarely in the Monticuliporoids, though it is not so common a
mode of increase as gemmation. In the mesopores of Fistulipora
and some allied types fission seems to be the ordinary mode of
increase, as it is in the case of the siphonopores of the Hedohtide.
This fact would go far to prove that the mesopores are not merely
coenenchymal ; since fission can hardly occur unless we suppose the
existence of separate zooids endowed with the power of division.
The occurrence of fission in the autopores of the Monticuliporoids
is also strongly against the reference of these organisms to the
Cyclostomatous /olyzoa, since these latter invariably increase by
means of gemmation. A still more interesting fact is the occur-
rence—as described by Waagen—of “ccenenchymal gemmation ”
among the Fistuliporoids, autopores in these cases being formed by
the abortion and apparent fusion of a group of mesopores, in a
manner precisely similar to that previously noted as occurring in
Fleliopora and Hleliolites. ‘This fact would also bear very strongly
against the view that the Monticuliporoids are to be regarded as
belonging to the Polyzoa.

It must be admitted, however, that the zoological affinities of the
Monticuliporoids are still a matter of uncertainty. In many of their
features, both structural and developmental, they show marked rela-
onehips with the Actnozoa generally, and with the Adyonaria in
particular, while in others they approach the Polyzoa ; and it must,
in the meanwhile, remain a matter of individual opinion whether the
Monticuliporoids should be regarded as a very peculiar group of
Corals or as an equally peculiar group of Polyzoans. It would be
out of place here to enter into any detailed discussion of a question
so complex, but it may be of advantage to summarise briefly the
chief points which must be taken into consideration in coming to
any decision as to the systematic position of the Monticuliporoids.

Leaving the external form of the skeleton entirely out of con-
sideration, the gezeral features which favour the reference of the
Monticuliporoids to the Ce/enterata are the following :-—

1. The common dimorphism of the colony in the Monticuliporoids
finds its best parallel in Helzopora and FHe/zolztes, the Coelenterate nature
of which is undoubted. In particular, the structural relationships between
Fistulipora and Heltolites, or Plasmopora, are exceedingly close; the
skeleton consisting in both of large, sparsely tabulate tubes G autopores ”)
separated by smaller, closely tabulate tubes (“ mesopores” or “siphono-
pores ”), and the former of these possessing radial structures of the nature

of “ septa” or “ pseudosepta.”

THE MONTICULIPOROIDS. 353

2. The Monticuliporoids increase by fission as well as by gemmation,
whereas the recent Polyzoa appear to be uniformly characterised by a
gemmiparous mode of development, which varies in its precise details in
different groups. Moreover, the gemmation of the Monticuliporoids is
‘“‘intermural,” and is precisely similar to that which obtains among the
Favositide.

3. “ Ccenenchymal gemmation ” occurs in the Fzs¢tuléporide, this mode
of increase being otherwise absolutely characteristic of We/zopora and of
the Heliolitide.

4. The walls of the tubes in the Monticuliporoids are imperforate ;
whereas in the calcareous Polyzoa the skeleton seems to be almost
always (probably always) porous, and the cavities of contiguous cells are
usually placed in direct communication by means of connecting-foramina
or tubes.

5. The abundant development of “tabule” in the Monticuliporoids is
a feature in which these organisms resemble a large number of un-
doubted Corals.

6. Certain Monticuliporoids possess in their autopores radial folds or
plications which may be compared with the “ pseudosepta” of Hedzo-
pora,; while others (Monteculipora mammulata) possess radially disposed
calcareous spines, which are closely similar to the septal spines of /avos-
ites, of Syringopora, and of certain species of Helzolztes.

On the other hand, there are the following considerations which
would point to a relationship between the Monticuliporoids and the
Polysoa, or which, at any rate, would more or less diminish the import-
ance of some of the features above mentioned as showing the Ccel-
enterate affinities of these organisms.

1. The polyzoary of Heteropora (which is undoubtedly a Polyzoan)
consists of large tubes scattered among smaller ones, though there does
not appear to be any essential difference in the structure of these
respectively.

2. “ Tabule” are by no means confined to the Ccelenterates, precisely
similar structures—so far as appearance goes—being present in un-
doubted Polyzoa (e.g., in Heteropora, Domopora, Fascicularia, Alveo-
laria, &c.)

3. Radial structures in the form of rows of spines are present in a
number of Polyzoa (e.g., in Heteropora, Discoporella, &c.)

4. There are various Polyzoa (such as Rhombopora Hamiltonensis,
Certopora interporosa, and some of the Fenestellids) which possess struc-
tures apparently very similar to the “acanthopores” of many Monti-
culiporoids. Structures presenting in some respects the same aspect are
found in the recent Retepore, in which they serve to carry the avicularia.

5. Portions of the skeleton of /7stulipora incrustans, Phill., have been
shown by John Young to become thickened, and to exhibit a finely
tubulated structure similar to that seen in the skeleton of the Femes-
tellide.

6. According to the observations of Lindstrdm, certain of the Monti-
culiporoids pass through early stages of development in which the
skeleton is of a distinctly Polyzoan type. As an example of this, we
may ‘ake the singular Callopora heterosolen, the basal (and therefore ~
first-formed) portion of which exhibits Polyzoan characters, while the
main mass of the skeleton is of the ordinary Monticuliporoid type.

Wile 1. Z

354 THE MONTICULIPOROIDS.

7. Lastly, certain extinct forms the Polyzoan nature of which seems
unquestionable are hardly distinguishable, as regards minute structure,
from other forms which have always been regarded as Monticuliporoids.
Thus, an extremely close structural resemblance obtains between Cevzo-
pora interporosa, on the one hand, and Latostomella (Monticulipora)
tumida, on the other hand.

As regards their geological distribution, the forms usually regarded
as Monticuliporoids are exclusively Paleozoic, and range from the
Ordovician to the Permian inclusive. In the Ordovician rocks, in
particular, Monticuliporoids are enormously abundant, and they also
constitute a conspicuous feature in the Silurian deposits, while their
number is much reduced in the Devonian, Carboniferous, and Per-
mian strata. As a rule, particular types are confined to special
geological horizons, but the vertical distribution of the group still
requires to be worked out in detail. So far as certainly known, the
genus Sztexofora—a name which has served to cover many different
types of the Monticuliporoids—is confined exclusively to the Car-
boniferous and Permian deposits. It is not at all improbable that
representatives of the Monticuliporoids will be found to have sur-
vived into the Secondary period, while there are even Tertiary fossils
which show remarkable points of resemblance to this ancient group
of organisms.

With regard to the classification of the Monticuliporoids, two
principal types of structure may be recognised, represented respec-
tively by the genera MWonticulipora and Fistulipora, as these are now
restricted. These two types of structure may be taken with con-
venience as the foundation of the two families of the Wlonticuliporide
and f/istuliporide. It must be admitted, however, that these two
families are connected together by transitional forms ; and it is prob-
ably impossible, in the present state of our knowledge, to so define
them as to render them mutually exclusive.

MONTICULIPORID&.

The skeleton of the Wonticuliporide is very variable in form, and
may be either composed of essentially similar tubes throughout, or
may be made up of large tubes (“autopores”) and of a limited
number of smaller, closely tabulate tubes (‘‘mesopores”). The
interstitial tubes or “‘mesopores” are not sufficiently developed to

isolate the autopores, while they are provided with complete walls
and their tabulz are straight. ‘‘ Acanthopores” are very commonly
present. Septal spines are rarely developed. The mode of growth
of the skeleton is by intermural gemmation, commonly associated
with fission.

This family includes the genera Monticulipora, Monotrypa, Mono-

MONTICULIPORID. 355

trypella, Dianulites, Diplotrypa, Dekayia, Stenopora, &c., and ranges
from the Ordovician to the Permian period.

The type of the genus Jonticulipora is the MZ. mammulata, D’Orb.,
of the Ordovician rocks of North America, which Mr Ulrich identifies
with the form described by the writer under the name of Peronopora
molesta. In this form, the corallum (fig. 224, A) has usually the shape of
a laminar erect expansion, composed of two layers of tubes which open on
the two sides of the frond. The large tubes or ‘“‘autopores” are placed
close together, and just before reaching the surface their walls become

Strat atk ale

‘
xs
‘)

Oe

Fig. 230.—Morphology of Monticulipora nammulata, D’Orb. (=Peronopora molesta, Nich.),
Ordovician, Cincinnati. aA, Tangential section taken immediately below the surface, enlarged
twenty times. B, Tangential section taken at a greater depth below the surface, similarly en-
larged. c, Vertical section, showing one side of the double frond, similarly enlarged. ob, ©, and
F, Portions of the preceding sections enlarged forty times: a, Autopores; 7z, Mesopores; ac,
Acanthopores ; fa, One of the ‘‘ cystoid” tabulez of an autopore, the rest of the tube being crossed
by straight tabula. (Original.)

considerably thickened ; hence there is a considerable difference between
sections taken just below the actual surface (fig. 230, A and D) and those
taken at a little depth (fig. 230, Band E). Interstitial tubes or mesopores
are developed in small number, and are easily recognised in long sections
by their close tabulation (fig. 230, F). Acanthopores are developed in
great numbers, and form a ring round each autopore (fig. 230, D), but
they are difficult to recognise except in tangential sections taken close to
the surface. The autopores are furnished with two sets of tabule, each
tube showing a series of vesicular or “cystoid” tabulz on one side (fig.
230, F, a) with a series of straight tabule in the other half of the tube.
Owing to this peculiarity in the tabulation of the autopores, tangential
sections (fig. 230, B) exhibit the cut edges of the cystoid tabule in the

356 THE MONTICULIPOROIDS.

form of a curved or horse-shoe-shaped line in the interior of each auto-
pore. In some examples of this species, the autopores are provided with
radially disposed pseudoseptal spines (fig. 230, D), but these are not recog-
nisable.in other specimens.

Of the remaining genera of the Wonticuliporide only two or three can
be briefly noticed here. The genus J/onotrypa is characterised by the
fact that the tubes are essentially similar to one another, being polygonal,
thin-walled, and furnished with few remote tabulee, while mesopores are
absent, as, usually, are acanthopores also. The genus ranges from the
Ordovician into the Devonian. Monotrypella is very similar to Mono-

Fig. 231.—Sections of Wonotrypella pulchella, EK. and H., from the Wenlock Limestone of
Britain, enlarged about eighteen times. a, Tangential section; B, Longitudinal section.
(Original.)

trypa, but the corallites become thickened by stereoplasma as they
approach the surface, their walls, however, always remaining distinct
(fig. 231).

The Ordovician genus Dzanulites (as based upon Dianulites fastigz-
atus, Eichw.) is essentially similar to Wonotrypa as regards the nature
and structure of the corallites, but the corallum is inv “ersely conical in
form, and is provided with a striated epithecal membrane, so that the
calices open at the upper end of the colony only, and the organism is
superficially quite lke a simple coral in appearance. The genus Azm-
plexopora, ranging from the Ordovician to the Carboniferous, nearly
resembles A/onotrypella in structure; but numerous acanthopores are
developed, which often form complete rings round the autopores.
Dekayia, again, resembles MJonotrypella in having only a single set of
tubes, without mesopores, but the walls of the autopores are united, and
there are numerous large acanthopores, the apices of which project
above the surface as prominent blunt spines (fig. 227). The genus is
only known from the Ordovician rocks.

Lastly, in the Carboniferous and Permian genus SZezopfora, the colony
consists of oval or circular or subpolygonal autopores, the walls of which
on approaching the surface become thickened with annular deposits of
stereoplasma, which are separated by unthickened nodes (fig. 232, C), this
peculiarity giving a very characteristic appearance to longitudinal sec-
tions. In the centre of the colony the corallites are polygonal and thin-
walled, and do not exhibit the characteristic annulations of the genus.

FISTULIPORID&. 357

Mesopores are not developed, but there are usually numerous acantho-
pores (fig. 232, A and B). The tabule are usually straight and complete,
but they are sometimes perforated by central apertures (fig. 232,C). The
walls of the autopores in Stenxopfora have been described as being per-
forated by mural pores, but, as previously noted, the researches of

ee SY
Vg LS, KW
A ZAWY i mM l)
EZ 1 \
“a ii \_ GX KZ
if N le a7
iy - WY

VE

Y

a
&

iN]

Ze?
EY,

rm

ye
Say) py,

y eo

ip UES ; Y

SD

Dy

SS

es
=
=

S AE Na!
SS i, ) Hes
Y Li;
\ Zy}
% aN /, Dye NU
WZZANS \S
@ . iS
i
SAA S=— G
iz Z5 .

Fig. 232.—Sections of Stexofora Howsii, from the Carboniferous rocks of England, enlarged
about eighteen times. A and 3B, Tangential sections; c, Longitudinal section, showing the
periodic thickenings of the walls of the tubes. (Original.)

Waagen and Wentzel have rendered it certain that the supposed mural
pores must be otherwise explained, and that the walls of the tubes are
really imperforate.

FISTULIPORID.

The skeleton in this family is of very variable form, and is com-
posed of large tubes (“‘autopores”) which are in general more or
less completely isolated (fig. 233) by the development of a copious
series of smaller tubes (‘‘mesopores”), these latter being often
aggregated into star-shaped groups or “macule,” which serve as
centres of growth for the colony. The walls of the autopores are
either completely unthickened (Cal/opora and Prasopora), or are
specially thickened on one side (/istulipora). ‘The mesopores are
furnished with more numerous tabule than the autopores; and in
some cases (/istulifora) their walls are incomplete, thus allowing
their tabulz to coalesce so as to form an interstitial tissue of lentic-
ular vesicles. The mode of increase as regards the autopores is
typically by “‘ccenenchymal gemmation,” the mesopores increasing
by means of fission. Pseudoseptal spines are occasionally devel-
oped, and pseudoseptal folds are commonly present. Acanthopores
are occasionally, but not usually, developed.

358 THE MONTICULIPOROIDS.

Since “coenenchymal gemmation” is at present only known as
occurring (apart from the present family) in the unquestionably
Actinozoan groups of the Aeloporide and Heliolitide, it would
seem that the presence of this mode of increase in the Fistuliporoids,
first pointed out by Waagen,
is an almost incontrovertible
proof that the latter should
be referred to the Alcyonar-
ian Zoophytes. If this be
admitted, however, it would
follow, almost inevitably,
that the MMonticuliporide
should also be regarded as
Alcyonarians, since there
exists an exceedingly close

Fig. 233.—Tangential section of Fistulipora tri- ele ROasl between ues
foliata, from the Middle Devonian of Gerolstein, en- and the Fistuliporoids. No
lauged about forty ties, showing the (riplate auto” arrangement, tm tea amen
Nicholson and Foord.) would refer /zstulipora and

Callopora to one great di-
vision of the animal kingdom (Ca/enterata), and would place Jon-
ticulipora, Diplotrypa, and allied types in another great division
(Polyzoa) could possibly be sustained.

The type-genus of the Fistuliporoids is 7s¢/zpora itself, in which the
variously shaped corallum is composed of oval or cylindrical autopores,
which are furnished towards one side with two longitudinal folds
(“pseudosepta”), giving to the tubes in cross-sections a characteristic
bilobed or trifoliate appearance (fig. 233), and which are separated by one
or more rows of mesopores (fig. 234, D). The walls of the mesopores are
ncompletely developed, and their tabulz therefore coalesce to give rise
9 a vesicular tissue occupying the spaces between the autopores (fig.
234, E). Acanthopores are occasionally developed, and in some cases
pseudoseptal spines have been observed.

The species of /7Zstudipora are Silurian, Devonian, and Carboniferous,
and are in general readily recognised by the trifoliate form of the auto-
pores in cross-sections, the abundance of the mesopores, and the fact that
the tabulze of the mesopores coalesce to form a tissue of lenticular vesicles
occupying the spaces between the autopores, and resembling the simi-
larly formed vesicles which separate the autopores in Plasmopora and
Propora. In some forms, the two pseudoseptal folds which are so char-
acteristic of the genus are little developed (compare fig. 234, D, with fig.
233), and the trifoliate shape of the tubes is proportionately obscured.
The peculiar horse-shoe-shaped sinus along one side of the autopores,
formed by the pseudosepta, has been considered, with much probability,
as corresponding in the living animal with a ciliated groove (“ siphono-
glyphe”) such as is found in the cesophagus of the Alcyonarians. Another
characteristic feature in many species of the genus is that the portion of
the wall bounding the sinus just spoken of is considerably thickened, and

FISTULIPORID&. 359

in well-preserved specimens sometimes exhibits a peculiar striated aspect,
as if it were finely tubulated.

The genus Cal/ofora, as maintained by Waagen, must find a place in
the immediate neighbourhood of F7stu/zpora. The typical species of this
genus resemble /7s¢u/ifora in most respects, but the autopores are, as
a rule, without pseudoseptal folds, and the mesopores have complete walls
and are furnished with straight tabulz, which do not coalesce to form an
interstitial vesicular tissue (fig. 225, B). In some cases, traces of pseudo-

Fig. 234.—Fistulipora incrustans, from the Carboniferous rocks of England. a, A colony
growing on the stem of a Crinoid, of natural size; B, Broken extremity of the same, showing
the thickness of the colony; c, Portion of the surface, enlarged almost twenty times; D. Tan-
gential section, similarly enlarged; :, Vertical section, similarly enlarged. a@, Autopores; 77,
Mesopores; c, Primordial tubes of the colony. (After Nicholson and Foord.)

septa are present in the autopores, and in one species (Cal/lopora Foordaii,
fig. 229) these structures are exceptionally developed. Pseudoseptal
spines are occasionally present in this genus. The walls of the autopores
in Callopora are not specially thickened in the “mature” region of the
corallum, as is shown by the structure of the type-species of the genus
(Callopora elegantula, Hall). Hence, forms like Callofora(?) ramosa,
E. and H., of the Ordovician rocks of North America, which have been
referred here by Mr Ulrich, must find a place elsewhere, as the autopores
become markedly thickened in the peripheral portion of the corallum.

360 THE MONTICULIPOROIDS.

The species of Cal/opora appear to be confined to the Ordovician and
Silurian rocks.

Lastly, the Ordovician genus Prasopora differs from Callopora mainly
in the fact that the autopores are furnished marginally with a series of
vesicular or “ cystoid” tabulze, which enclose a central area traversed by
straight tabulee.

LITERATURE OF MONDICULIPOROIDS:

1. ‘ Polypiers Fossiles des Terrains Paléozoiques.” Milne-Edwards and
Haime. 1851.
“Die Chetetiden der ostbaltischen Silurformation.” | Dybowski.
1877.
. “On the Structure and Affinities of the Genus Monticulipora and
its Subgenera.” Nicholson. 1881.

N

Go

4. “American Palzozoic Bryozoa.” Ulrich. (A series of papers in
the ‘ Journal of the Cincinnati Society of Natural History,’ 1879-
1884).

5. “Contributions to the Micro-Palzontology of the Cambro-Silurian
Rocks of Canada.” Foord. 1883.

6. “On the Genus Fistulipora, M‘Coy, with Descriptions of several
species.” ‘Annals and Magazine of Nat. Hist.’ 1885. Nichol-
son and Foord.

7. “On the Tasmanian and Australian Species of the Genus Stenopora,
Lonsdale.” ‘Annals and Magazine of Nat. Hist.’ 1886. Nichol-
son and Etheridge, jun.

8. “ The Salt-Range Fossils—Ccelenterata.” ‘ Palzeontologia Indica.
1886. Waagen and Wentzel.

Clee) ad MBS” OEE
SUB-KINGDOM IV.—ECHINODERMATA.

GENERAL CHARACTERS OF THE ECHINODERMATA.

THE sub-kingdom of the Zchinodermata comprises the animals
usually known as Sea-urchins, Star-fishes, Brittle-stars, Sea-cucum-
bers, Sea-lilies, &c., and may be briefly defined as follows :—

Simple marine organisms, which are mostly bilaterally symmetrical
when young, but which tn the adult condition have thts bilateral sym-
metry more or less extensively masked by a radial (usually pentamerous)
arrangement of their parts. An alimentary canal ts present, with or
without a distinct anus, separate from the proper body-cavity. A
system of water-vessels, often communicating directly with the exterior,
and generally connected with protrusible tubes (“feet”), ts present.
The nervous system 1s radiate, consisting of an esophageal ring and
radiating branches. The integument ts characteristically hardened by
the deposition in tt of carbonate of lime in the form of plates, granules,
or spicules.

The adult Echinoderms always exhibit a more or less conspicuous
radiate structure, the symmetry of the body being essentially penta-
merous ; but the larval forms are usually distinctly bilateral, and bi-
lateral symmetry is in general more or less clearly recognisable in the
fully grown animal. The radial symmetry of the body of the adult
is exhibited not only in the external skeleton, but also in many of
the internal organs, and especially in the nervous and ambulacral
systems. The alimentary canal, unlike that of the Ccelenterates, is
always completely shut off from the general cavity of the body, a
mouth being always present, and an anal aperture usually existing as
well. When a mouth and anus are present, these openings may be
at opposite poles or on the same side of the body, the mouth being
usually central in position, while the anus may be completely ex-
centric. In the free-living Echinoderms, the mouth is usually either
terminal and placed in front, or is situated in the centre of the in-

362 ECHINODERMATA.

ferior surface of the body. On the other hand, in the stalked Crinoids
and certain other forms, the ventral surface is directed upwards, and
the mouth is thus placed on the superior aspect of the body.
Among the most characteristic of all Echinodermal structures are
the so-called ‘‘ water-vessels ” or ‘‘ambulacral” vessels. This system
consists of a series of musculo-membranous tubes filled with a watery
fluid, and connected with the function of respiration, while at the
same time commonly subserving
locomotion. It consists essen-
tially (fig. 235) of a circular
vessel which surrounds the com-
mencement of the alimentary
canal, and gives off secondary
vessels in a radiating manner.
The “radiating vessels” usually
give off at right angles numerous
short lateral tubes (the ‘“tube-
feet” or -“ pedicels ”) > tandiame
“circular vessel” is generally
placed in communication with
the exterior by a special canal
(‘‘stone-canal ” or “‘ water-tube ”)
which opens on the surface by
a spongy calcareous plate (“ma-
dreporite”). Though commonly
subserving locomotion, the am-
bulacral vessels are probably
primarily respiratory in function ;
and they not uncommonly give
off leaf-like or branched external
processes (“‘ambulacral gills”),
which serve as respiratory or-
2 Reece moe )=60fegcans. ‘There is also a second
Fig. 235.—Diagram of tne ambulacral system vascular system, consisting of an
of Echinus. m2, Madreporite; s, Stone-canal ; . ‘ F
r, Central esophageal ring: fA, Polian Oral ring and radial trunks, which
vesicles; a@ a, Radiating ambulacral vessels. are situated between the water-

Only the bases of four of the radiating ves-
sels are shown; and a few of the tube-feet (4), yessels and the nerve-bands.

with their secondary vesicles or ‘‘ampullz” (z), < +6. ; :
are shown on one side of one of the radiating The oral ring 1s in relation with
canals a peculiar organ, formerly de-
scribed as a heart, but probably to be regarded as a kidney, which
in many Echinoderms seems to communicate with the exterior by
means of the madreporite.

The sexes are almost always distinct in the Echinoderms, and the
reproductive organs are usually lodged in the interior of the body,

definite openings for the escape of the generative elements existing

GENERAL CHARACTERS OF THE ECHINODERMATA. 363

in the body-wall. In the Crinoids, on the other hand, the repro-
ductive organs are lodged in the “arms,” and permanent generative
apertures are rarely, if ever, present. As regards their position, the
generative glands (ovaries or testes) alternate in the Echinoderms
generally with the radiating nerve-cords and ambulacral vessels, and
are therefore ‘“interradial,” while the latter are “radial” ; but in the
Crinoids the genital cord, being lodged in the arms, is necessarily
radial in position.

The integument of the Echinoderms has the power of secreting
carbonate of lime, and a more or less definite integumentary skeleton
is thus usually produced. Not only is this exoskeleton in general
readily preserved in the fossil state, but its minute structure is so
characteristic that even the smallest fragment can usually be recog-
nised’ with certainty by the help of the microscope. In the first
place, the calcareous tissue of the Echinodermal exoskeleton has a
very characteristic crystalline structure. ‘‘ Each plate, each spine, and
each joint is mineralogically and optically, as it were, made out of a
single crystal of calcite, having its principal axis perpendicular to the
plane of the plate, or parallel to the axis of a spine or joint, the
’ growth from first to last being in perfect crystalline continuity ”
(Sorby). In recent Echinodermal skeletons, this crystalline struc-
ture is only recognisable by the optical phenomena displayed by
thin sections under the microscope; but the skeleton of fossil
forms, as the result of mineralisation, usually exhibits, in its minutest
fragments, the unmistakable rhombohedral cleavage of calcite. In
the second place, the skeleton of the Echinoderms has an equally
characteristic organic structure, being made up of reticulated and
anastomosing calcareous rods, which are produced by the calcifica-
tion of a network of organic fibres, the uncalcified intervals of which
are filled in the fresh state with living matter. All Echinodermal
ossicles and plates exhibit this characteristic netted structure (fig.
236), but different forms differ in the size and disposition of the
meshes ; the commonest and simplest arrangement being that of
parallel strata of perforated calcareous laminz connected with one
another by vertical pillars. In other cases, as in the spines of the
Echinoids, the structure consists of radially-disposed, vertical, netted
plates united by numerous short horizontal rods; and other types
exhibit other special modifications.

In altered specimens, the minute reticulated structure of the
skeleton may be largely obliterated, or even wholly unrecognisable,
but the characteristic cleavage usually remains. Owing to the per-
sistence of the characteristic micro-structure of the skeleton, even
detached and otherwise indeterminable fragments of Echinoderms
can commonly be recognised with certainty under the microscope,
and valuable assistance is thus often afforded to the palzeontologist

364. ECHINODERMATA.

in his researches. Thus the singular fossils described by Eichwald
under the name of Lolboporites can by this means be clearly deter-
mined to be of Echinodermal origin. ‘These curious remains occur
in the Ordovician rocks of Russia and Canada, and though variable
in shape, have most commonly the form of inversely conical, ovoid,
or clavate bodies, about a quarter of an inch or less in their long
diameter, and composed of calcite with its characteristic cleavage.
The narrower end of the body is usually smooth, and the sides or
upper surface generally pitted with shallow depressions. Described
originally as corals, the microscopic appearances of thin sections
render it certain that the fossils placed under Lolboporites are parts

SS A> %
\C >) RSE St
SES . \
IN Sean ae
x ‘ RNY
Sr SN S
ASTRA ,

SV

Fig. 236.—Minute structure of Echinodermal plates. a, Part of a small plate (madreporite ?)
of an Echinoderm from the Carboniferous rocks of Scotland, highly magnified; B, Part of an
RE eeeny tc plate of Lepidocentrus, from the Devonian of the Eifel, highly magnified.
(Original.

of the exoskeleton of some Echinoderm. It is difficult to speak
precisely as to their nature, but they may be compared with the
large tubercles or swollen spines which are developed in the integu-
ment of certain Star-fishes (¢.g., Pentaceros).

As regards their classification, the Echinodermata may be divided
into seven primary groups, which are now usually regarded as
classes—viz., the Crinotdea, Cystotdea, Blastoidea, Ophiuroidea, As-
teroidea, Echinoidea, and Holothuroidea. Of these, the first is to a
considerable extent extinct, and the two next are entirely so; while
they exhibit certain structural peculiarities which separate them from
the other classes. More particularly, the members of these three
classes—viz., the Crinoids, Cystoids, and Blastoids—all possess a
dorsally-developed, jointed calcareous stalk, which serves to fix them
to foreign objects, and which may be only temporarily present.
From the presence of this jointed stem, these three classes are
grouped together in a single great division, under the name of /ed-
matozoa. On the other hand, the Echinoids, Asteroids, Ophiuroids,
and Holothuroids are devoid of this stalk at all periods of develop-

GENERAL CHARACTERS.OF THE ECHINODERMATA. 365

ment, and usually creep about by the aid of their tube-feet, with
the oral surface of the body turned downwards. They are there-
fore grouped together in a common division under the name of
LEchinoszoa.

As regards their destribution, all the recent Echinoderms are mar-
ine, and from their habit of life and their possession of a calcareous
exoskeleton, the members of this sub-kingdom are largely represented
as fossils, ranging from the Upper Cambrian period onwards. ‘The
classes of the Cystordea and Adastoidea are not only extinct, but are
exclusively Palzeozoic; while in the Cvznotdea we have a group
which has passed its prime, and appears to be verging on extinction.
On the other hand, the classes Echinoidea, Asteroidea, Ophiuroidea,
and olothuroidea appear to have attained their maximum of de-
velopment at the present day. The Asteroidea and Ophiuroidea
commence in the Ordovician period. The £chinotds commence in
the Ordovician, but reach no marked development till we enter
upon Mesozoic deposits. Lastly, the Molothurians, as might be
expected from the soft nature of their integuments, are hardly known
as fossils, though they seem to have existed at any rate as early as
the Carboniferous period.

366

Cea Pal eX Glia
DIVISION A.—ECHINOZOA.

Cxiass I. ECHINOIDEA.

THE members of this class—commonly known as Sea-urchins—are
characterised by the possession of a more or less globular, heart-
shaped, discoidal or depressed body, encased in a “test” or shell, which
zs composed of numerous calcareous plates, in general immovably con-
nected together. The intestine 1s convoluted, and there is a distinct
anus. The mouth 1s always situated on the inferior aspect of the
body, but the position of the vent varies.

The ambulacral system of the Echinoids consists of its usual
parts, and the five radial vessels given off from the circular ceso-
phageal ring are situated within the shell of the animal. It follows
from this that the tube-feet given off from the radial vessels can
only reach the exterior by passing through perforations in the plates
of the calcareous test. Hence the outer surface of a Sea-urchin
exhibits five longitudinal areas which are “radial” in position and
correspond with the five radiating ambulacral vessels, and the plates
of which are more or less extensively perforated for the protrusion
of the tube-feet. These so-called ‘“‘ ambulacral” or “ poriferous ”
areas are separated by five zones which are “ interradial” in position,
have imperforate plates, and are known as the “ interambulacral ”
areas. The external opening of the ambulacral system is closed by
a spongy or porous plate—the “ madreporite ”—which is almost in-
variably situated on the apex of the test in one of the interradii.
In the extinct Lchinocystites (Cystocidaris) alone the madreporite
is removed from its normal position, and is placed “close to the
apical pole.” .

As regards the digestive system, the mouth is always placed on
the under surface of the body, and may be central or excentric in
position. The mouth is sometimes edentulous, but in other cases a
complicated apparatus of calcareous teeth is developed. The anus

ECHINOIDEA. 367

in many cases is placed at the summit of the test, and is surrounded
by the so-called ‘‘apical disc” or ‘‘ dorso-central system”; but it is
in other cases marginal or submarginal, being then separated from
the apical disc, and being almost always situated in the posterior
interradius. In “&chinocystites (Cystocidaris) alone the anus is ex-
centric and interradial, but is placed near the apex.

The radial nerve-cords run along with the radiating ambulacral
vessels in the inside of the shell, and become connected at their
terminations with a series of perforated plates (“ocular plates”’)
which form part of the so-called “‘ apical disc,” and which are “ radial ”
in position. The generative glands occupy the “ interradial” areas,
and their ducts normally open by perforations in the so-called “ gen-
ital plates,” which lhkewise form part of the “apical disc.”

It is necessarily principally with the test of the Echinoids and its
appendages that the palzontologist is concerned, and these struc-
tures must therefore be considered in some detail. The test of the
Echinoidea may be regarded as essentially composed of the so-called

Fig. 237.—Echinoidea. Test of Echinus esculentus, viewed from above. a, One of the
ambulacral areas; za, One of the interambulacral areas.

“corona” and of the “apical disc” ; though minor and less constant
plates are likewise developed in the membranes surrounding the
mouth and anus respectively.

The “corona” forms the main element of the test, and is com-
posed of numerous calcareous plates, more or less firmly united to
one another by their edges, arranged in rows, and bearing different

368 ECHINOZOA.

names according to their position and function. In the singular
Urchins which constitute the family of the Zchznothuride, as also
in various Paleozoic Echinoids, the plates of the test overlap one
another in an imbricating manner, so that the shell becomes flexible.
As a rule, however, the corona forms an immovable case or box
within which the animal is contained; and its growth is carried on
by additions made to the edge of each individual plate by the
progressive calcification of an organised membrane which passes
between the “sutures,” or the lines where the plates come in con-
tact with one another. The first circle of the coronal plates is
developed round the mouth, and the vertical growth of the test is
carried on by the intercalation of successive rows of plates between
those already formed and the apical disc.

The corona is composed of ten alternating meridional zones, of
which five are radial in position and are perforated, while five are
interradial and are imperforate. In all the recent Echinoids, and
in all the fossil forms except the Palechinoids and the Cretaceous

Tetracidaris, each of these ten

a zones is composed of two rows of

Aas plates, there being thus twenty
meridional rows of plates alto-
gether. ‘The five interradial zones
are spoken of as the “ interam-
bulacral areas,” and are composed
of large-sized plates, which are not
perforated by any apertures (fig.
237, ta, and figs 233).1@)sueeeme
five radial zones, on the other
hand, are termed the “ ambulacral
areas” or “‘ poriferous zones,” and
are composed of comparatively

Fig. 238.—A, Portion of the test of Holecty- sana paces, MICE Ae sear
pus hemisphericus, enlarged, showing an inter- by minute pores for the emission

ambulacral area (a), and an ambulacral area

(4). B, Dorso- central system of Hemzcidaris of the “ tube-feet ” (fig. 237; % and
permedia, enlarged 6 Ostler plates, fig. 238, 2). As a rule, the am-
porite. (After Forbes.) bulacral pores are in pairs, but in

a few cases the pores are unpaired.
The pores of each pair may be similar or dissimilar in shape, and
in many cases they are united by transverse furrows.

In many Echinoids the ambulacral tube-feet can be protruded
along the entire length of the ambulacral areas, which are perforated
along their entire course from the centre of the base of the corona to
the summit of the same, and which are then said to be “ perfect”
(ambulacra perfecta) or “simple” (figs. 237 and 239). In many
other Echinoids, on the other hand, the ambulacral areas are not

ECHINOIDEA. 369

thus continuously perforated from pole to pole, but they are “ in-
terrupted,” only their upper portions being regularly poriferous.

Fig. 239.—Echinoconus conicus (=Galerites albogalerus). The first figure shows the under
surface with the mouth and anus; the middle figure is a side-view; and the right-hand figure
shows the upper surface, with the ambulacral areas converging to the apical disc. White Chalk.

In such cases (fig. 240) the ambulacral zones are widened out
superiorly, and form a kind of rosette upon the upper surface of the

Fig. 240.—Scutella subrotunda, showing petaloid ambulacra. Miocene.

test, when they are said to be “circumscript” (ambulacra circum-
scripta), or ‘ petaloid.”

The most important external structures of the corona are the
tubercles and spines. The tubercles are rounded elevations upon

Fig. 241.—Hemicidaris crenularis, showing tubercles, the larger of which are perforated,
and are surrounded by an areola. Jurassic.

which the spines are carried (fig. 241). They vary much in their

dimensions, and receive special names, according to their size or

position on the test. Ordinarily the tubercle consists of a rounded
VOL... 1. BIS

370 ECHINOZOA.

ball or hemisphere (the ‘“‘mamelon”) supported upon a conical pro-
cess (“the boss”) which arises from the plate. The ball of the
tubercle may or may not be perforated for the insertion of a liga-
ment which is attached to the articular surface of the spine. In
many cases (as in fig. 241) the base of the tubercle is surrounded by
a round or oval, smooth and excavated space which is termed the
areola, OK. seromicule:,

The spines are movable appendages which are jointed to the tuber-
cles by a sort of “ball-and-socket” or “universal” joint. They
are used defensively and in locomotion, and vary
much in length and shape. Sometimes they are
very minute; at other times they attain a length
considerably exceeding the diameter of the test.
Sometimes they are slender, tapering, and truly spine-
like; at other times they are thickened, ovate, or
almost globular (fig. 242). The spine fits on to the
rounded head of the tubercle by a concave articular
surface (“acetabulum”), and there may or may not
be a pit at the bottom of this, for the attachment

Fig. 242.—Spine Of the ligament before spoken of. Above the acetab-
of Se ulum or socket of the spine there is a prominent
ridge or ring, more or less “‘ milled,” for the attach-

ment of the muscular fibres which move the spine.

At the summit of the corona in all Echinoids is found the single
or double row of plates which constitutes the “apical disc” or dorso-
central system, corresponding with the “calyx” of the Crinoids. In
the most typical forms (‘ Regular” Echinoids) the plates of the
apical disc surround the membrane (“‘ periproct ”) in which the anus
is situated (fig. 243, A); but in the so-called “ Irregular” Echinoids
(fig. 243, B) the apical disc simply occupies the summit of the
test, and the anus is excentric, and is entirely removed from the
disc. In its most ordinary condition (as in the genus Z£chinus, fig.
237), the apical disc is composed of ten plates arranged in two
alternating rows of five plates each. The uppermost row consists
of a cycle of five large plates of a pentagonal form, which are perfor-
ated each by the duct of a testis or ovary, and are therefore known
as the “genital plates.” (In the Palzeozoic Echinoids from three
to five pores pierce each genital plate.) One of the genital plates
is larger than the others, and supports a spongy tubercle perforated
by many minute apertures, like the rose of a watering-pot, and termed
the ‘‘madreporite” or “madreporiform tubercle” (fig. 243, ma).
The madreporite varies much in size, and sometimes forms almost
the whole of the apical disc. The genital plates occupy the summits
of the interambulacral areas, and are therefore interradial in position.
Wedged in between the genital plates, and occupying the summit

ECHINOIDEA. a7

of the ambulacral areas, are five smaller, heart-shaped or pentagonal
plates, which are known as the “ocular plates,” each of which is
perforated by a minute pore lodging the rudimentary sense-organ
(“ocellus”) in which the radial ambulacral nerve terminates.

The anus in the Echinoids is situated in a membrane (“peri-
proct”), which is more or less largely hardened by the development
in it of small calcareous plates, which may be wholly irregular, or
may form one or more regular cycles (fig. 243, az). As previously
seen, the periproct in the ‘‘ Regular” Sea-urchins is placed in the
centre of the apical disc (fig. 243, A), whereas in the “ Irregular”
Urchins it has no connection with this structure, and is wholly

Fig. 243.—a, Apex of the shell of Czdaris taperialis (Recent), enlarged, after Van der Heeven ;
B, Apex of the shell of Wzcrvaster (Cretaceous), showing the condition of the apical disc in the
**Trregular” Echinoids, after Zittel. az, Anus, surrounded by the plated ‘“‘periproct”’; 2, One
of the genital plates; 0, One of the ocular plates ; za, Madreporite ; 47, the two posterior am-
bulacral areas, constituting the ‘‘ bivium.”

excentric. The mouth in the Echinoids, like the anus, is situated
in a coriaceous membrane (“ peristomial” membrane) hardened by
plates and granules of lime. Hence in macerated or fossil speci-
mens the under surface shows, in place of the true mouth-opening,
a wide vacant space (“‘peristome”) originally occupied by the per-
istomial integument. The peristome may be rounded or oval, or
bilabiate, or, very commonly, pentagonal, often with incisions at the
angles for the accommodation of the so-called “ oral gills.”

The internal skeleton of the Echinoids is represented by the so-
called “auricule” of certain types. These are calcareous arches
which are ambulacral or “radial” in position, and spring from the
inner surface of the lower edge of the test, just where the imper-
fectly calcified peristomial membrane begins. Each forms an arch
over one of the radiating ambulacral vessels; and the auricles cor-
respond, therefore, with the so-called ‘‘ambulacral ossicles” of the
Star-fishes.

are ECHINOZOA.

Though superficially conspicuously “ radial” in its symmetry, the test
of the Sea-urchins can nevertheless be shown, with more or less clear-
ness, to have also a bilateral symmetry. This can be demonstrated by
the position of such an unpaired organ as the “ madreporite,” and is more
conspicuously exhibited in the “Irregular” Sea-urchins than in the
“ Regular” forms, though recognisable even in the latter. Thus, if the
test of a Regular Sea-urchin (figs. 237 and 243) be viewed from above
while held in such a position that the madreporite is placed on the side
farthest from the spectator and on his right hand, it will be seen that
facing the spectator is an unpaired ambulacral area (“ radius”), while on
the side nearest him is an unpaired interambulacral area (“interradius ”).
A line drawn through the centre of these two unpaired areas gives a
middle line to the body, the structures on either side being for the most
part symmetrically disposed. It will further be seen that three ambula-
cral areas (the “ trivium”) are directed towards the side farthest from
the spectator (the “anterior” side) ; while two (the “ bivium”) are directed
“posteriorly,” or towards the side facing the spectator. The unpaired
ambulacral area is therefore “ anterior,’ and the unpaired interambula-
crum is “ posterior.” In the “ Irregular Sea-urchins” the bilaterality is
still more marked, the unpaired anterior ambulacrum being usually dif-
ferent to the others in form or size; while the anus is commonly placed
on the ventral side of the body, in the unpaired posterior interambulacrum.

As regards classification, the class of the Echinoidea is divided
by Zittel into the two orders of the Pavlechinotdea, in which the test
consists of more or fewer than twenty meridional rows of plates, and
the Euechinoidea, in which there are constantly twenty rows of plates
in the shell. The Palechinoids comprise the three groups of the
Cystocidaride, Bothriocidaride, and Perischoéchinide, and the Eu-
echinoids are divided into the two groups of the Regwlares and [rre-
gulares, according as the test is of the “regular” or “irregular ” type.

As regards their distribution in time, all the Echinoids of the
Palzeozoic formations except Locidaris belong to the order of the
Palechinoidea, and a single member of this division (Azaulocidarts)
is known to exist in strata of Triassic age, the division being other-
wise unrepresented in Mesozoic or Tertiary deposits. The earliest
types of the Palechinoids are found in the Ordovician rocks. On the
other hand, the Euechinoids make their first appearance, so far as
certainly known, in the Permian (Zocdavis), and attain a marvellous
development in the Jurassic and Cretaceous periods. In the Tertiary
rocks, on the contrary, the number of known fossil forms is reduced,
most of the Kainozoic types being characteristic of shallow water,
and many of the genera being still in existence. Upon the whole,
the Euechinoids may be considered as having attained their maxi-
mum development in the period of the Chalk.

In the following condensed account of the characters and geolo-
gical distribution of the chief groups of the Echinoids, the less im-
portant types are necessarily omitted. The arrangement adopted by
Zittel has been followed in the main.

PALECHINOIDEA. 373

ORDER I. PALECHINOIDEA.

This order comprises all those Urchins in which ¢he Zest 7s made up
of more or (rarely) fewer than twenty meridional rows of plates: while
the plates of the apical disc are perforated by two or more pores each,
or may be in part imperforate. Asa general rule, there is an increase
in the number of rows of plates forming the test of the Palechinoids,
as compared with that of the Euechinoids, the interambulacral areas
usually consisting of more than two rows of plates each (fig. 244).
In some cases, the ambulacral as well as the interambulacral areas
may consist of more than two rows of plates each, as, for example,

Fig. 244.—Palechinus ellipticus. The \eft-hand figure shows a portion of an ambulacral area
enlarged. The right-hand figure exhibits a single interambulacral plate.

in the genus JZelonites (fig. 247). On the other hand, in the genus
Lothriocidaris there is a reduction instead of a multiplication of the
normal number of rows of plates in the test, the interambulacral
areas consisting of one row of plates only. Furthermore, in many
of the Palechinoids the test becomes more or less flexible, owing to
the fact that the plates are not suturally united by their margins, but
overlap by means of bevelled edges, the structure of the shell thus
resembling that seen in the existing group of the Zchinothuride. In
all the Palechinoids there is a large peristomial aperture, and a well-
developed masticatory apparatus (‘ Aristotle’s lantern”) was present.
In all except Echinocystites (Cystocidaris), the test is ‘‘regular,” the
anus being placed at the summit of the shell and surrounded by the
apical disc. ‘The genital plates are perforated by from three to five
pores each ; and the ocular plates have usually two pores each, but
are in other cases imperforate (fig. 244).

The order of the Palechinoids includes the three sub-orders of the
Cystocidaride, Bothriocidaride, and Pertschoéchinide, all of which
are wholly confined to the Paleozoic period, with the exception of
the last, which is represented in the Trias by the imperfectly known
genus Aznaulocidaris. It is interesting to note that this ancient

374 ECHINOZOA.

series of Echinoids possesses both “regular” and “irregular” types,
and in this respect runs parallel with the later group of the Euechin-
oids. It is to be remembered, however, that the abnormal Zchino-
cystites (Cystocidaris) exhibits an irregularity of structure which
differs considerably from that which characterises the “ Irregular”
Euechinoids.

The sub-order of the Cystocidaride comprises only the aberrant
genus Echinocystites (= Cystocidaris, Zittel), in which the interambu-

Fig. 245.— a, Apical disc of Palechinus, enlarged (after Baily); 8B, Apical disc of Medlonites
(after Meek and Worthen): g, One of the genital plates; 0, One of the ocular plates.

lacral zones are composed each of several rows of plates, and the
anus is excentric. The two known species of the genus are found
in the Silurian rocks of Britain.

The test in Echznocystites is spheroidal or ovoid, with narrow ambulacral
and broad interambulacral areas, the latter being formed by several
irregular rows of imbricated calcareous plates, carrying spines. The
mouth is on the under surface, central in position, with a well-developed
masticatory apparatus ; while the anus is excentric, but has the unique
position of being not widely remote from the apex in one of the inter-
ambulacral spaces. The madreporite is also quite peculiar in not being
at the apex of the shell, but in being placed excentrically in one of the
interambulacra. Another remarkable point is that the anus is closed by
a valvular pyramid of calcareous plates, a feature highly characteristic of
the Cystideans.

The sub-order of the Bothriocidaride includes the single genus
Bothriocidaris, in which the interambulacral areas are composed
each of a single row of plates, and the anus is placed in the centre
of the apical disc. The two known species of the genus have been
found in the Ordovician rocks of Russia (Esthonia).

PALECHINOIDEA. 375

The test in Bothrioctdaris is spheroidal and “ regular,” the anus being
situated in the centre of the apical disc, and the ambulacra being
“perfect.” The plates of the test are immovably connected, and the
interambulacral zones are composed of a single row of plates only, while
the ambulacral zones have two rows ‘each (fig. 246, a). There are thus
fifteen meridional rows of plates in the test in all. The peristomial

Se

oe

Fig. 246.—Bothriocidaris Pahleni, Ordovician. a, The test viewed sideways, of the natural
size; 4, The apical disc and anus, enlarged; c, The mouth, enlarged. (Copied from Zittel, after |
Fr. Schmidt.)

membrane (fig. 246, c) is furnished with triangular valvular plates sur-
rounding the mouth-opening, and similar plates encircle the aperture of
the anus (4).

The sub-order of the Perischoéchinide comprises all the known
remaining types of the Palechinoids, and is characterised by the fact
that the test is composed of more than twenty meridional rows of
plates, and is “regular” in type, the anus being situated in the
centre of the apical disc. The interambulacral areas always possess
more than two rows of plates each, and the ambulacral areas likewise
may consist of more than two rows each (as in Ae/onites and Oligo-
porus, fig. 247). The mouth is placed in the centre of the lower
surface, and is furnished with a masticatory apparatus, while the
anus is situated at the summit of the test. The genital plates have
from two to five pores, and the ocular plates may have two pores
each or may be imperforate (fig. 245). Very commonly the test
becomes more or less flexible in consequence of the imbrication of
its component plates, the edges of which are often bevelled. All the
Peristhotchinide are Palzozoic, with the exception of the Triassic
genus Anaulocidaris. ‘The earliest types are found in the Silurian,
but the group attains its maximum in the Carboniferous rocks.

Of the genera of the Perischoéchinide, Palechinus possesses a
spheroidal test (fig. 244), the plates of which abut against one another
without any overlapping. The ambulacral areas are comparatively
narrow, of two rows only, each plate perforated by two pores. The
interambulacral areas are broad, and are composed of from four to eight
rows of plates. The apical disc (fig. 245, A) has five triply perforated
genital plates, and an equal number of doubly perforated ocular plates
(Baily), but the latter are wanting in P. sfhericus. A single species of.

370 ECHINOZOA.

the genus occurs in the Silurian rocks, but a number of forms are found
in the Carboniferous Limestone.

In the genera Melonites and Oligoporus, of the Carboniferous rocks,
we have large spherical Urchins, in which the test appears to have been
rigid, though some of the plates are occasionally bevelled off, so as to
articulate in an overlapping manner with one another. In J/elonttes
(fig. 247) there is a multiplication of the plates of both the interambulacral
and ambulacral areas, the former consisting in the middle of seven or eight
rows, while the latter are of eight or ten rows, or, in a British species, of
from twelve to fourteen rows. The central two rows of ambulacral plates
are larger than the rest and elevated above them, and each plate of these
areas is doubly perforated. The apical disc (fig. 245, B) is composed of

Fig. 247-—A, Portion of an ambulacral area of Welonites niultiporus. 8, Portion of an am-

bulacral area of Oligoforus Dane: 7, Lateral row of interambulacral plates. Carboniferous.
(Meek and Worthen.)

the normal ten plates, but the ocular plates are sometimes imperforate,
and the genital plates are furnished with from three to five pores.

Oligoporus (fig. 247, B) is very similar to J/e/onites, but the ambulacral
areas consist each of only four rows of plates.

Allied to MWelonztes is the Carboniferous genus Lefzdesthes, in which
the ambulacra are composed of no less than ten rows of plates, the inter-
ambulacra being comparatively narrow and composed of six or seven
rows of plates. The plates of the test, as in various other Palechinoids,
are imbricated, the test thus becoming flexible, as it is in the recent genus
Asthenosoma. The imbrication in the flexible Palechinoids differs from
that of the Echinothuride in the fact that the overlapping of the inter-
ambulacral plates is from below upwards, and that of the ambulacral
plates from above downwards, the reverse of this taking place in Astheno-
soma and its allies.

A well-known Carboniferous genus is Avch@ocidaris (fig. 248), in which

EUECHINOIDEA. 377

the test is spheroidal, the ambulacra are only two-rowed, and the inter-
ambulacra are wide and are composed of three or more rows of plates.
The interambulacral plates (fig. 248, 4) carry each a large perforated
tubercle, surrounded by a ring, supporting a long echinulate spine (d).
As shown by Mr John Young, the test must have possessed a certain
degree of flexibility, as the edges of some of the interambulacral plates
are bevelled off. The Devonian and Carboniferous genus Lepidechinus

Fig. 248.—Archeocidaris Wortheni, from the Carboniferous Limestone of North America.
a, Fragment of the under side, with the teeth, of the natural size; 6, An interambulacral plate,
viewed from above and sideways, showing the hexagonal form, and the spine-bearing tubercle;
¢, Portion of an ambulacrum, enlarged: d, One of the spines, of the natural size. (Copied from
Zittel—after Hall.)

differs from the preceding in the fact that the plates of the test are
strongly imbricated, the shell thus becoming quite flexible. The ambu-
lacral areas are two-rowed, but the interambulacra have from nine to
eleven rows of plates. .

Differing in some respects from the preceding are the genera Perischo-
domus, Rhoéchinus, and Lepidocentrus, of which the two first are Car-
boniferous, while the last is found in the Devonian rocks. In all these
genera, the test is rendered flexible by the overlapping of the inter-
ambulacral plates.

Lastly, the Triassic genus Azaulocidaris, known by detached plates
and spines, is allied to Arch@ocidaris, and, so far as known, is the latest
representative of the division of the Palechinoids.

ORDER II. EUECHINOIDEA.

This division comprises all those Sea-urchins in which doth the
ambulacral and interambulacral areas are constantly two-rowed, the
test thus consisting of twenty rows of plates. The genital and ocular
plates are almost always perforated by a single opening each ; and
a masticatory apparatus may be present or absent. The test may be
“< vegular” or “ irregular.”

378 ECHINOZOA.

The order of the Euechinoids includes all the normal Sea-
urchins, and the distribution of the group in time is remarkable.
No Euechinoid has hitherto been detected in any Palzozoic de-
posit anterior to the Permian, but a vast development of the forms
of this division takes place in rocks of Mesozoic age, while all the
Tertiary and Recent Urchins also belong to this group. In the
Jurassic and Cretaceous rocks the Euechinoids attain their maxi-
mum development, and very numerous forms are also known from
the Tertiary formations.

The Euechinoidea may be divided into the two sub-orders of the
Regulares and Irregulares, the characters and chief groups of which
will be briefly treated of in the following pages.

REGULAR EUECHINOIDS.

The sub-order Regulares (Echinoidea endocyclica) includes all those
Euechinoids in which the test is “regular,” the mouth being inferior
and central, while the anus occupies the centre of the superior sur-
face, and is surrounded by the apical disc. The form of the test is
usually spheroidal, and the ambulacral areas are perfect, and are all
alike. The mouth is furnished with a masticatory apparatus. In
Tetracidaris the interambulacra are in part four-rowed, but in all
others they are two-rowed, as are the ambulacra in all cases. The
members of this sub-order appear to be the most ancient forms
of the Euechinoids, being tolerably well represented in the Trias,
and even occurring in the still older Permian formation (Zocdavis.)
They are largely represented in the Jurassic and Cretaceous forma-
tions, but begin to diminish in numbers
in the Eocene Tertiary. The Regulares
may be divided into the four princi-
pal families of the Czdaride, Salenide,
Lchinothuride, and Glyphostomata, the
more important forms of which are
noticed below.

family 1. Cidaride.—In this family
the test is spheroidal, and more or less
flattened at the oral and anal poles.
: The ambulacral areas (fig. 249), are

Fig. 249.—Under surface of the test VEry Narrow, often flexuous, and never

OF ee he Week) | provided with’ large tubercles malime

interambulacral areas are wide, and

carry large perforated tubercles, surrounded by an areola, and

supporting the primary spines. ‘The spines are of two sizes, the

primary ones usually more or less cylindrical, clavate, or fusiform,
and generally longitudinally ridged or tuberculate (fig. 242).

REGULAR EUECHINOIDS. 379

Of the genera of this family, Czdarzs itself (fig. 249) is the most im-
portant, ranging from the Trias to the present day. Rhabdocidaris is
Jurassic and Cretaceous ; Diflocidarzs is Jurassic; and the Porocidaris
of the Secondary and Tertiary periods has now been detected by Sir
Wyville Thomson in a living condition. In the aberrant Cretaceous
genus T7etracidaris, the interambulacral zones are composed each of four
rows of plates, reduced to two rows in the neighbourhood of the apex.

The genus Zoctdaris, based upon a form which occurs in the Permian
rocks of Germany, has been generally placed among the Palechinoids, in
the vicinity of Arvcheocidaris. According to the recent researches of
Kolesch, however, the interambulacral and ambulacral areas in £. Key-
serlingi are two-rowed, and the genus is therefore properly referable to
the Euechinoids. The Devonian and Carboniferous Urchins which have
been referred to Zoczdaris have more than twenty rows of plates in the
corona, and must therefore be removed from this genus as now under-
stood. With our present knowledge, therefore, the Permian Zoczdaris
must be regarded as the oldest type of the Euechinoids.

Family 2. Salenide.—In this family the test is generally spher-
oidal, hemispherical, or depressed, and the ambulacral areas are
always narrow, sometimes straight, sometimes flexuous, and without
large primary tubercles. The interambulacral areas are always pro-
vided with two rows of large tubercles,
with crenulated bosses, which may or
may not be perforated. The lead-
ing character of the family, however,
is to be found in the apical disc (figs.
250 and 251), which is of unusually
large size, and possesses a supernum-
erary or ‘‘suranal” plate in addition
to the ten normal plates. This sur-
anal plate (fig. 250, s) is placed in
front of the anus, and it may be
single, or it may be represented by _ Fig. 250.— Apical disc of Peltastes

: Wrightiz, one of the Salenide. a,
several (not more than eight) ele- Anus; yg One of the genital plates:
ments. From a morphological point %,0% 9,the ostlar plates; Suranal
of view the suranal plate may be Wee Greensand). (After

: ght.

compared with the “ dorso-central ”

plate of the Crinoids, while the genital and ocular plates respectively
correspond to the basals and radials of the Crinoidal calyx. The
“‘madreporite” is imperfectly developed, and often hardly recog-
nisable. The peristomial membrane is furnished with calcareous
plates which differ from the peristomial plates of the Czdarid@ in
the fact that the rows of ambulacral pores are not continued over
them to the mouth.

The genus Sa/enia itself (fig. 251) appears for the first time in the
Cretaceous rocks, and still survives at the present day. e/fastes, with
a similar range in time to Sa/enza, differs from the latter in the fact that

380 ECHINOZOA.

the anus is placed in the middle line ; and the Gonzophorus of the Chalk
is a closely allied form. Acrosalenda, again, ranges from the Lias to the
Chalk.

Family 3. Lchinothuride.—In this small but highly remarkable
division of the L£chinotdea the test is “regular,” the anus being

Fig. 251.—Salenia personata. The left-hand figure represents the upper surface of the shell,
and shows the anus surrounded by the apical disc. The right-hand figure shows the under side
with the peristomial space.

placed in the centre of the apical disc, and the ambulacral areas
being continuous ; but the plates of both the ambulacral and inter-
ambulacral areas are imbricated and overlap one another (fig. 252),
the test thus becoming flexible. In this abnormal character, the
Echinothuride agree with some of the Paleozoic Urchins, but they

Fig. 252.—Portion of one of the ambulacral areas of Echinothuria floris, enlarged four
times. Chalk. (After Wright.)

differ from these, and agree with the ordinary Regular Echinoids in
having the test composed of no more than twenty rows of plates.

The only fossil forms of this group, as yet discovered, are refer-
able to the Cretaceous genus Lchinothuria, the true affinities of —
which have now been elucidated by the discovery of the extraor-
dinary living types referred to the genera Asthenosoma and Phor-
mosoma.

Family 4. Glyphostomata.—In this family the ambulacral areas
are not much narrower than the interambulacral, and both as a rule
carry primary tubercles. The peristomial membrane usually carries
irregular calcareous ossicles, but is not completely plated, and the
peristome is furnished with more or less marked incisions at its
angles. ‘Auricule” are present. This family is divisible into the

REGULAR EUECHINOIDS. 381

two minor groups of the Diadematide and the £chinide, both of
which appear in the Secondary period, and are represented at the
present day.

In the Diadematide, the pairs of ambulacral pores (fig 253) form
a single row on each side of the ambulacral areas, except near the
apex and the peristome, where more than one row of pore-pairs
may be developed. The test is generally circular or pentagonal,

Fig. 253.—Portion of the test of Pseudodiadema Fittontz, enlarged four times. a, Ambulacral
area; 7, Interambulacral area. Lower Greensand (Cretaceous). (After Wright.)

more or less depressed and flat below. The ambulacral areas are
wide, and carry two rows of large primary tubercles, equal in size to
the two or more rows of tubercles upon the interambulacra. The
tubercles are sometimes perforated, sometimes imperforate, and
they may or may not be crenulated. The spines are cylindrical and
slender, and usually of considerable length. In the living Dradema
the spines are long, tubular, and covered with imbricated scales

Fig. 254.—Hemicidaris crenularis, showing tubercles, the larger of which are perforated,
and are surrounded by an areola. Jurassic.

arranged in oblique rings. The Déadematide are very extensively
represented in the Secondary rocks, the earliest forms appearing in
the Upper Trias; the Tertiary forms are less numerous, and a
limited number of types referable to the group still exist.

Of the genera of this family, Hemictdaris (fig. 254) has a spheroidal,
more or less depressed test, with a general resemblance to that of the

382 ECHINOZOA.

Cidaride. The ambulacral areas, however, though narrow and mostly
undulated, are wider than in the Czdavid@, and are provided with com-
paratively large tubercles, which may be developed inferiorly only
(Hemicidaris), or which may extend along the entire length of the area
(Acroctdaris). The interambulacral areas are wide, and carry very large
perforated tubercles with crenulated bosses. The spines are usually long,
cylindrical, and tapering. The type-genus of this family is Hemzczdaris
(fig. 254), which ranges from the Upper Trias to the Lower Cretaceous
inclusive. In Acrocidaris, of the Jurassic and Cretaceous periods, the
ambulacral areas are comparatively wide. In the genus Pseudodiadema,
which ranges from the Lias to the Eocene Tertiary, the spines are solid
and microscopically. striated, and the tubercles are perforated (fig. 253).
On the other hand, in the genus Cyphosoma and in a number of allied
forms, the tubercles are imperforate. The species of Cyphosoma are
mostly found in the Chalk, but some occur in the Eocene, and a single
species survives at present. 7emipedina, again, which begins in the
Jurassic rocks, and which is also represented at the present day by a

single living species, is like Psewdodiadema, but the tubercles are not
crenulated. This is also the case with the extensive genus Gouiopygus
(fig. 255), which is principally Cretaceous in its range, though also occur-

Fig. 255.— Goniopygus niajor, viewed from above and sideways, of the natural size.
Cretaceous.

ring in the Eocene rocks. In the great size of the apical disc this genus
reminds us of Sa/enza, but it wants the supernumerary “suranal” plate
of the latter. Among the many other genera of this sub-family, Cottaldia
(Chalk to Recent), Glypticus (Jurassic), Codiopsis (Cretaceous), and Zem-
nechinus (Pliocene) may be specially mentioned ; but the number of types
included in this group is too large to permit of further particularisation.

In the sub-family of the Achinzde, the general structure of the
test is much the same as in the Dzadematide, but the ambulacral
plates consist of at least three ‘‘ pore-plates ” fused together, and the
pairs of ambulacral pores are arranged in three or more rows (rarely
in two rows only) on each side of each ambulacrum (fig. 256, 4).
The test is usually globular or hemispherical, and the ambulacral
areas are comparatively wide, and carry two or more rows of tubercles.
The interambulacral areas are wide, and carry primary tubercles,
which are always imperforate, and are never of very large size. The
spines are short and awl-shaped, and their surface is marked with
fine longitudinal lines.

REGULAR EUECHINOIDS. 383

In many genera of the Echznzd@ each ambulacral plate carries three
pairs of pores, and types exhibiting this character appear as early as the
Jurassic period. One of the leading genera thus characterised 1s Szom-
echinus (fig. 256), which is found in both the Jurassic and Cretaceous
deposits. An allied Jurassic genus is Polycyphus,; while Salmaczs and
Echinus proper begin in the Eocene Tertiary, and are represented at the
present day by living species. On the other hand, in other genera of the
Etchinide each ambulacral plate carries more than three pairs of ambu-
lacral pores. The forms of this group are comparatively modern, a few

Fig. 256.—Stomechinus lineatus, from the Jurassic rocks (Coral Rag) of Germany. a, A
specimen viewed in profile, of the natural size; 6, Part of the oral region of the same. (After
Zittel.)

types (Phymechinus, Pedinopsis, &c.) occurring in the Upper Jurassic or
Cretaceous rocks, but the majority being Tertiary or Recent. The two
most important members of this section are SAherechinus and Strongylo-
centrotus, both of which begin in the Pliocene Tertiary, and are repre-
sented by living species.

IRREGULAR EUECHINOIDS.

The sub-order of the /rregulares (Echinoidea exocyclica) includes
all those Euechinoids in which the test is “irregular,” the anus being
excentric, and not connected with the genital disc. The mouth is
placed on the lower surface, and may be central or excentric in
position, while a masticatory apparatus may or may not be present.
The test is bilaterally symmetrical, commonly of an oblong, penta-
gonal, heart-shaped, or discoidal figure (as in the common ‘“ Heart-
urchins” and “Cake-urchins”). ‘There are commonly only four
genital plates in the apical disc, and the ambulacra may be either
simple or petaloid.

The Irregular Euechinoids have been divided into two groups,
according as they possess a masticatory apparatus (Grathostomata),
or are without teeth (Azelostomaia) ; but these two groups are very
closely connected, and it seems that too much weight has been

384 ECHINOZOA.

attached to the value in classification of this particular character.
Moreover, it has not in all cases been certainly ascertained whether
or not a masticatory apparatus is actually present. Here, therefore,
it will be sufficient to divide the Irregular Euechinoids into the six
families of the Conoclypetde, Clypeastride, E-chinoconide, Cassidulide,
Flolasteride, and Spatangide. ‘The oldest types of the whole series
(Pygaster and Galeropygus) appear in the Lias, and numerous forms
are known in the later Mesozoic and Tertiary deposits, while the
group is largely represented at the present day.

Family 1. Conoclypeide.—The Urchins of this family have a
rounded or ovoid, gibbous test, covered with small tubercles and
spines. The ambulacra are petaloid, but are continued inferiorly as
faras the mouth. There are only four genital plates, and the madre-
porite is of large size. ‘The mouth is placed in the centre of the
inferior surface, and the anus is submarginal. Teeth are present,
and “‘ auricles” are also developed. All the members of this family

Fig. 257.—Conoclypus conoideus, from the Eocene rocks of Germany, viewed sideways and
from below, reduced in size. (After Zittel.)

except one are referable to the single genus Conoclypus (fig. 257), the
species of which range from the Chalk to the present day, being most
abundant in the Eocene Tertiary.

Family 2. Clypeastride.—In this family the test is usually circular
or elliptical, generally depressed, the surface covered with small
tubercles surrounded by sunken, ring-like aveo/e, and carrying hair-
like spines. The dorsal portions of the ambulacral zones are wide
and petaloid, and the ambulacral pores are confined to the apical
“rosette” thus formed. The mouth is inferior, central, and armed
with teeth ; and the anus is marginal or infra-marginal. The madre-
porite occupies almost the whole of the apical disc, and the genital
plates (four or five in number) are only indicated by their pores.

IRREGULAR EUECHINOIDS. 385

The interior of the shell, as a rule, is more or less subdivided by
calcareous pillars or septa. The Clypeastrids range from the Chalk
to the present day, but the early forms of the group are small.

The typical Clypeastrids have the test more or less gibbous superiorly,
the two most important genera being Echinocyamus and Clypeaster. The
first of these includes small oval Urchins, which range from the Chalk to
the present day ; while the latter (fig. 258) comprises large, massive, ellipti- °
cal or pentagonal types, with a conspicuously developed ambulacral rosette.

oF 2°\c gy

~e\0 COV
© cO\ao*
rs

cjeoceo

COC

oO.
aye
18}

Y,
13)

—]
c
u
Oo
pio OC
;

ty 7 ¢ - w
PES ~ 8) 5c
Ape Poe alec
“
“Oo yt <4 7
9:6 Het

Fig. 258.—Clypeaster grandifiorus, from the Miocene Tertiary, viewed from above and below,
slightly reduced in size. (Copied from Zittel, after Desor.)

The oldest known species of Clyfeaster appear in the Eocene Tertiary,
but there are numerous Miocene and Pliocene forms, and the genus is
well represented in recent seas.

In another group of Clypeastrids, exemplified by such genera as Scu-
tella and Echinarachiius, the test is so flattened as to become discoid
or cake-like. The genus Sczfella (fig. 240) is wholly confined to the
Eocene and Miocene deposits, while the closely allied types placed
under Echinarachnius are still represented in existing seas.

Family 3. LEchinoconide.—In this family the test is usually cir-
cular or subpentagonal, the ambulacral areas being narrow, and
running continuously from the apical disc to the peristome (fig. 259).
Both the ambulacral and interambulacral areas carry small, crenu-
lated, and perforated tubercles, which support short and awl-shaped
spines. The mouth is inferior and central, and the excentric anus
may be superior in position, but is usually inferior or marginal.
There may be only four genital plates in the apical disc.

VOL. I. 2B

386 ECHINOZOA.

The position of the family Echznocontde has been rendered doubt-
ful by the researches of Professor Martin Duncan, who has shown
that the type-genus, “chinoconus, usually regarded as possessing teeth
and “auricles,” is really destitute of both these structures. In ac-
cordance with this, Dr Duncan would remove the genus Echinoconus
to the family of the Casstdufide. ‘The forms included in the family

Fig. 259.—Dzuscoidea cylindrica. The right-hand figure shows the summit of the shell, with
the genital disc. The left-hand figure shows the base of the shell, on which are situated both the
mouth and anus. Cretaceous.

Echinoconide are almost wholly confined to the Jurassic and Creta-
ceous rocks, so far as at present known; but a living species of
Pygaster has been detected, and this genus, at any rate, must have
representatives in the Tertiary rocks.

The genus Lchinoconus (=Galerites) is exclusively confined to the
Cretaceous rocks, £. vulgaris and £. conticus (=Galerites albogalerus)
being very common species in the White Chalk.
The test in this genus (fig. 239) is rounded or
subpentagonal, often conical, with a nearly flat
base. The anus is infra-marginal or nearly mar-
ginal. Dz¢scotdea (fig. 259) 1s also confined to
the Cretaceous rocks, and is nearly related to the
preceding, but the margins of the interambulacral
areas in the interior of the test are strengthened
by longitudinal thickenings or ribs. olectypus,
again, is closely allied to Dzscozdea, but the test
is depressed (fig. 260), and there are no internal

Fic, 260.Test of Hole. ribs. The species of this genus are Jurassic and
typus hemisphericus, viewed Cretaceous. Lastly, in the genus Pygaster (fig.
from above—Jurassic. (After 261), the anal aperture is of great size, oblong
Edward Forbes.) ss : : :

or pyriform in shape, and situated on the: superior

aspect of the shell. All the five genital plates
are present, and are perforated for the generative ducts. The species
of this genus are mostly Jurassic and Cretaceous, but a recent species is
known to exist.

Family 4. Cassidulide.—This family comprises irregular Urchins
in which the mouth is invariably edentulous, and is placed centrally
or subcentrally on the inferior surface, while the anus is excentric,
and is generally placed on the upper surface (fig. 262). The test
is generally oval or elliptical, and the ambulacral zones are approxi-

IRREGULAR EUECHINOIDS. 387

mately similar, and may be either simple (Zchinonide) or petaloid
(Echinolampade). Only four genital plates are furnished with per-

Fig. 261.—Pygaster truncatus, viewed from above, from behind, and from one side.
Cretaceous.

forations for the generative ducts. The range of the family is from
the Jurassic to the present day inclusive.

In one series of the Cass¢dudid@—sometimes spoken of as the Echzno-
mzde—the ambulacra are simple and linear, and the mouth is central or

Fig. 262.—Hyboclypus gibberulus, viewed from above, from one side, and from below.
Jurassic.

subcentral. A good example of this is the Jurassic genus Hyboclypus
(fig. 262), in which the mouth is removed towards the anterior side, the
anus is in a longitudinal dorsal valley, and
the apical disc is elongated, so that the pos-
terior two ambulacra become disjoined from
the anterior three. Other examples of this
group are the Cretaceous and Eocene genus
Pyrina,and the Miocene and Recent genus
Echinoneus. In another group of the Cas-
sidulide—sometimes spoken of as the Ech-
znolampade—the ambulacra are petaloid,
and are generally sunk in the vicinity of
the mouth in grooves separated by the
swollen interambulacra, giving rise to a
peristomial rosette or “ floscelle.” Some of

5 Fig. 263.—Echinobrissus clunicu-
the members of this group make a near ap- laris, Jurassic, viewed from above.

proach to the preceding, being withoutacon- (After Wright.)

spicuous oral rosette, and having ambulacra

of a but very slightly petaloidal form; and these have sometimes been
separated to form a distinct group (Echinodrisside). Of the many forms

388 ECHINOZOA.

included in this group the genus Lchinobrissius is one of the most widely
distributed, species of the genus being very abundant in the Jurassic
rocks, but extending also into the Cretaceous. In this genus (fig. 263),
the test is concave below, and the anus is placed in a dorsal sulcus.
Other well-known genera are MVucleolites (Chalk to Recent), Pygurus
(Jurassic and Cretaceous), Clypeuws (Jurassic), Pygaulus (Cretaceous),
Cassidulus (Cretaceous and Tertiary), Echinanthus (Cretaceous and
Tertiary), and the Tertiary and Recent Catopygus and Echinolampas.

Family 5. Holasteride.—This family comprises ovoid Urchins,
with simple ambulacra, and a generally very gibbous test. The
apical disc is usually drawn out in an antero-posterior direction, the
elongation being sometimes so great that the two posterior ambulacra

Fig. 264.—Collyrites (Dysaster) Eudesi, viewed from above, from one side, and from below.
Jurassic.

are widely separated from the three anterior ones on the summit of
the shell (fig. 264). The peristome is excentric, generally oblique
or bilabiate ; and the anus is inframarginal or marginal. The mem-
bers of this family are mostly Jurassic and Cretaceous, but a number
of recent forms are known to exist.

In one group of this family (the Collyritide of D’Orbigny, or the
Dysasteride of other writers), the apical disc is greatly elongated, and
the narrow ambulacral areas thus become
more or less “disjunct,” the two hinder
ambulacra meeting superiorly at one end
of the disc, while the three anterior ambu-
lacra meet at the other end of the same.
The principal genus of this group is Co/-
lyrites itself (figs. 264 and 265), in which
the test is oval or somewhat heart-shaped,
the mouth being inferior and excentric, and
the anus being supramarginal. The ele-
ments of the apical disc are detached from
one another, the anterior portion contain-
ing four perforated genital plates and three
ocular plates, while the posterior portion,

a connected with the preceding by a narrow
Fig. 265.—Upper surface of the series of supernumerary plates, contains
test of Collyrites elliptica, showing 3
long apical disc and disjunct ambu. -the*two other ocular plates; (ilteemusme
lacra. Jurassic. (After Zittel.) represented by numerous species in the
Jurassic and Cretaceous rocks. Closely
allied to the preceding, and with a similar geological range, is the genus
Dysaster.

IRREGULAR EUECHINOIDS, 389

In another series of the Holasterid@—sometimes spoken of as the
Ananchytide or Echinocoride—the apical disc may be either elongated

or compact, but in either case the
five ambulacra all meet in it.
The chief genus of this group
is Ananchytes (fig. 266) itself, in
which the test is ovate, and highly
convex above, the peristome is ad-
vanced forwards and is two-lipped,
and the anus is inframarginal.
The species of this genus are
confined to the Chalk, the com-
monest form being the well-
known and highly variable A.
ovata. The genus fHolaster is
nearly related to Axanchytes, but
the test is sub-cordate, the apical
disc is more elongated, and the
anus is marginal or supramar-
ginal. The species are chiefly
Cretaceous, but are found in the
Tertiary deposits in Australia. In
Cardiaster, again, which is also
Cretaceous, there is the addi-
tional character of the existence
of a “fasciole,” which passes be-
neath the anus and is continued
on the sides of the test. As will

Fig. 266.—Under surface of the test of Azan-
chytes ovata, showing the position of the mouth
and anus. Jurassic. (After Forbes.)

be seen immediately; the presence of “fascioles”—that is to say, of cir-
cumscribed bands of microscopic granules, occupying definite areas and

positions on the test—is highly
characteristic of the Sfatan-
gid@, towards which Cardiaster
thus makes an approach.

Family 6. Spatangide.—In
the members of this family—
often spoken of as ‘ Heart-
urchins ”—the test is mark-
edly bilateral, and is usually
conspicuously heart - shaped
(fig. 267). The mouth is ad-
vanced far forwards on the
under side, and the anus is
supra-marginal, and is placed
in the posterior interambu-
lacrum. The ambulacra are
petaloid, and the unpaired
anterior ambulacrum always
differs more or less from the

Fig. 267.— Upper surface of Micraster coranguinune.

Cretaceous. (After Forbes.)

others, being usually lodged in a groove or “sulcus” (fig. 267).
The mouth is typically bilabiate, but is in some cases five-sided ;

390 ECHINOZOA.

and, as in the preceding two families, teeth are invariably wanting.
The tubercles of the test are mostly small, and carry hair-like
spines; but there are larger, crenulated, and perforated tubercles for
the support of larger spines. As a rule, bands of microscopic tuber-
cles known as ‘“‘fascioles” (fig. 268) are present, and occupy differ-
ent positions in different genera.
Sometimes the “fasciole” sur-
rounds the ambulacral rosette,
when it is said to be “ peripeta-
lous” ; sometimes it is ‘‘ internal,”
surrounding the unpaired ambu-
lacrum; sometimes it surrounds
the sides, and is said to be

Fig. 268.—Gualteria Orbignyana, viewed : x
both from above and below. The left-hand ‘‘ lateral ie at other times it runs

figure shows the “‘fasciole” cutting the ambu- :

ie oe a es 2 round the test, and is termed
‘“‘marginal” ; and, lastly, it may
be limited to the base of the anal aperture, when it is termed

‘¢ sub-anal.”

Of the genera of SHatangide characterised by a pentagonal mouth, the
chief is Zoxaster, the species of which are wholly Cretaceous. Of the
more normal Heart-urchins, with a bilabiate mouth, //zcraster (fig. 267)
possesses a sub-anal fasciole, and is widely distributed in the Chalk, the
genus being also represented in the Tertiary rocks of Australia. Epzaster,
likewise found in the Chalk, has no sub-anal fasciole, but is otherwise
similar to Micraster. Hemiaster, very abundant in the Cretaceous
period, but also represented by Tertiary and living species, has a peri-
petalous fasciole. Lzuzthza (Periaster) has both a peripetalous and a
lateral fasciole, and ranges from the Chalk to the present day. Gwualterza
and Macropneustes are Eocene types; while Schzzaster, Brissus, Bres-
sopsis, Echinospatagus (Amphidetus), Eupatagus, and Spatangus are
well-known Tertiary and Recent genera.

391

Crew ra 2 ROP Sex re

ASTEROIDEA, ORATOROLGEA AND VHOLOGMLORO LD EA.

Ciass II. ASTEROIDEA.

THE class Astevoidea comprises the ordinary Star-fishes, and is
defined by the following characters: Zhe body (fig. 269) zs star-
shaped or pentagonal, and consists of a central body or “disc” sur-

Fig. 269.—Astropecten irregularis, viewed from the upper surface; 7z Madreporite. Recent.

rounded by five or more lobes (“ arms,” or “vrays”), which radiate
JSrom the body, are hollow, and contain prolongations of the viscera.
The body is not enclosed in an immovable box, as in the Lchinozdea,
but the integument (“ perisome”) ts coriaceous, and ts strengthened by

392 ECHINOZOA.

irrecular calcareous plates, or studded by calcareous spines. No dental
apparatus ts present. The mouth ts inferior, and central in position ;
the anus either absent or dorsal. The ambulacral tube-feet are pro-
truded from grooves on the under surface of the rays.

In their form the Star-fishes differ considerably, though in most
the figure is markedly stellate. The animal consists of a central
body or “disc,” which gives off radiating processes or “‘arms,” but
the size of the disc is very different in different species, and the
arms vary greatly in length and in number. In many living and
extinct forms the “disc” is inconspicuous, and appears to be formed
simply by the junction of the bases of the arms, which in this case
are normally five in number. ‘The living
Asterias and Cribrelle, and the extinct
Paleasters (fig. 270), may be taken as
examples of this state of parts. In other
forms, as in the Sun-stars (So/aster) and
the extinct Leszdasters and Plumasters,
the disc is very broad, exceeding or
equalling the length of the arms in its
diameter ; whilst the rays vary in number,
from eight or ten up to thirty or more.
eS | ._ In the Cushion-stars (Gonzaster and

ig. 270.—Paleaster Niagarensis, oe 5 3
Hall. Ordovician. Goniodiscus), again, the body is pen-
tagonal, disc-shaped, and flattened on
the two sides, and the arms can only be recognised by the ambu-
lacral grooves on the lower surface (fig. 271).

On the upper surface of the body, placed nearly in the centre of
the disc, is the minute aperture of the anus, when this is present ;
but the genera Astropecten, Ctenodiscus, and Luidia are destitute of
a vent. Also on the upper surface is the “‘ madreporite ” or ‘‘ madre-
poriform tubercle,” in the form of a spongy or striated disc placed at
the angle of junction of two rays. It has the same function as in
the Echinoids, serving to protect the entrance to the water-vascular
system. Ordinarily there is a single madreporiform tubercle, but
in some genera there are two, three, or more tubercles ; and there
seems in some cases to be a correspondence between the number
of the arms and the number of madreporic plates.

Placed in the centre of the lower surface is the mouth, at the
angles of which are five pairs of so-called “oral plates” (fig. 271, 0),
which must not be confounded with plates similarly named in the
Crinoids; but there are no teeth. Deep furrows, known as the
‘‘ambulacral grooves,” radiate from the mouth, one along the under
surface of each of the arms, gradually narrowing as the extremity of
the latter is approached. The roof of each groove is constituted by
a double row of minute calcareous pieces—the ‘“‘ ambulacral ossicles ”

ASTEROIDEA. 393

—which are movably articulated to one another at their inner ends.

Running in the roof of the groove, below the line of union of the

two rows of ambulacral ossicles, is one of the radiating ambulacral

vessels, from which are given off the rows of suctorial ‘‘ tube-feet.”
The integumentary skeleton of the Asteroids is less developed

than in the Echinoids, and has the form of innumerable small

calcareous pieces, or “ossicles,” united together so as to form a

species of chain-armour. ‘The os-

sicles are generally united with one

another in a reticulated manner,

and the interspaces between them

are filled by the coriaceous integu-

ment; but they may be directly 4, ck!

united by their edges. In many

genera a specially developed series

of ossicles forms a row of plates,

known as the ‘adambulacral

plates” (fig. 271, 4), on each side

of the ambulacral furrows. In

many genera, also, there is a single _ Fig. 271.—Diagram of a Star-fish (Goni-

aster), showing the under surface, with the
or double row of large plates, known mouth and ambulacral grooves. a, Ambula-
as the “ marginal plates ” (fig. 271, cral ossicles, with the ambulacral pores be-

? f tween them; 4, Adambulacral plates, bound-
it), round the margins of the disc. ing the ambulacral grooves; 7, Marginal

: : plates (wanting in many species); 0, Oral

and arms, along the line separating plates, placed at the angles of the mouth.
the dorsal and ventral surfaces.
Spines are commonly developed, especially along the margins of
the ambulacral grooves, but these structures are in no case movably
articulated. The so-called ‘“‘pedicellarie” of the Asteroids, as in
the Echinoids, may be regarded as peculiarly modified pincer-like
spines ; but the size of these is too small to render it likely that
they can be commonly preserved in the fossil condition. In some
genera (as in Solaster, Luidia, Ctenodiscus, &c.), there are large
spines the summits of which carry bunches or tufts of minute cal-
careous processes, and which are known as “‘paxille.” In other
cases, as in Pentaceros, there are very much thickened spines, which
may assume considerable dimensions. It is not improbable that the
Ordovician fossils upon which the genus Aolboporites has been
founded, are really of the nature of dermal spines belonging to
some Asteroid like Fentaceros.

The ambulacral system of the Asteroids is essentially similar in
its arrangement to that of the Echinoids. ‘The external opening of
the water-vessels is always placed interradially, between the two
posterior rays (when five rays are present), and is provided with a
porous “ madreporite,” two, three, or more of these being occasion-
ally present. The madreporite admits the water to the short

304 ECHINOZOA.

“‘sand-canal,” which opens into the circular vessel surrounding the
gullet. From the circular canal arise radiating ambulacral vessels,
which correspond in number with the number of the arms, and
which are lodged, along with the radiating nerves, in deep ‘‘am-
bulacral grooves” on the under surface of the arms. Each radi-
ating vessel gives off two or four rows of cylindrical tube-feet or
“pedicels,” the ends of which are usually sucker-like, and which are
used in locomotion. ‘The tube-feet are protruded by means of
vesicles or ‘‘ampullz,” which spring from their bases, and are situ-
ated superiorly to the radiating vessel. As compared with the
Echinoids, the essential peculiarity of the ambulacral system is that
the radiating ambulacral vessels are situated externally, and are not
covered over by a calcified integument. There are, therefore, no
structures in the Asteroids which can be compared with the per-
forated ambulacral plates of the Sea-urchins, and the tube-feet of
the former do not pass through any portion of the integumentary
skeleton on the way to the surface. On the other hand, the radi-
ating ambulacral vessels of the Star-fishes are protected by an zw/er-
nal skeleton, which is not present in the Echinoids, or which is only
imperfectly represented in some types of the latter by the so-called
‘‘auricule.” This internal skeleton has the form of a double

Fig. 272.—Diagrammatic section of the ray of Asterias rubens. a a, Ambulacral ossicles ;
4, Position of the ambulacral vessel; cc, Plates of the external skeleton; 2, Nerve-cord. The
dotted lines show the tube-feet proceeding from the ambulacral vessel, but the ampullz are not
represented.

series of elongated calcareous plates, the so-called ‘‘ ambulacral
ossicles,” which form the roof of the ambulacral groove on the
under side of each arm, and are so apposed to one another as to
form a kind of elongated pent-house, beneath which is placed the
radiating ambulacral vessel (fig. 272, a a). ‘The ambulacral ossicles
on the one side of the ambulacral groove may be directly apposed
to the ossicles of the corresponding row on the other side of the
groove (as in the typical Star-fishes), or the ossicles of the one row
may alternate with those of the opposite row (as in the ancient group
of the Lzcrinasterie). In either case the ambulacral ossicles are

ASTEROIDEA. 395

so excavated on their sides as to give rise by their apposition later-
ally to a series of pores, by means of which the ampullee communi-
cate with the bases of the tube-feet. Hence, the ampullez are
situated in the interior of the arms, superiorly to the chain of
ambulacral ossicles, while the radiating ambulacral vessels and
tube-feet are placed zujeriorly to the same.

In addition to these ambulacral vessels, Star-fishes possess a system
of respiratory organs which are known as the dermal branchize or
“‘papule.” These are delicate czecal processes of the integument,
the cavities of which are in direct relationship with the general
body-cavity. In one order of recent Star-fishes (Phanerogonia) they
are restricted to the dorsal surface, while in the C7y/zogonza they are
distributed over the whole body.

The generative organs of the Asveroidea are situated within the
‘“‘arms,” above the chain of ambulacral ossicles, and they discharge
their products by means of minute sieve-like openings in the angles
between the arms, the size of these apertures being too small to
admit of their recognition in a fossil condition.

The living Asteroids have a wide range in space, being princi-
pally shallow-water forms, but extending from the littoral zone to
great depths in the sea. As regards their dstribution in time, the
Star-fishes are a group of great antiquity, the earliest members of
the order appearing in the Ordovician (Upper Cambrian ?) strata.
Most of the Paleozoic types are peculiar, but the recent genus
Astropecten is stated to occur in rocks as old as the Devonian.

As regards their classification, the Asteroids may be divided into
two primary groups, or sub-classes, according to the arrangement of
the ambulacral ossicles. In one great group (Zuasteroidea), the two
rows of ambulacral ossicles which roof over each ambulacral furrow
are placed opposite to each other. The forms of this group are
not unrepresented in the Paleozoic rocks, but they are principally
characteristic of the Secondary and Tertiary deposits, and are the
only types now in existence. On the other hand, most of the
Palzeozoic Star-fishes belong to the series of the Lzcrinasteria, in
which the two rows of ambulacral ossicles in each arm are so placed
as to alternate with one another. No form belonging to this group
of Star-fishes appears to have survived the Paleeozoic period. Owing
to their rare occurrence as fossils, and their generally imperfect state
of preservation, Star-fishes are not of special interest to the palzeon-
tological student, and it will be sufficient here to briefly indicate
the chief characters of some of the more important of the known
fossil forms.

The section of the Ezcrinasterie, in which the ambulacral ossicles
are alternately placed, is, as above remarked, exclusively Palzeozoic,
and the widely distributed genus Pa/easter may be taken as its

306 ECHINOZOA.

central type. In this genus (fig. 273) the body is five-armed, the
disc being very small; and the ambulacral grooves on the under
side of the arms are furnished with two rows of alternately placed
ambulacral ossicles, bounded on each side by a row of “ adambu-
lacral plates,” which are, in turn, bordered by a series of large ‘‘ mar-

BAD

Fig. 273.—Paleaster eucharis, Devonian (after Hall). a, Under side of a specimen, four of the
arms being cut short ; B, Upper side of the same. a, Ambulacral ossicles, lying in the ambulacral
grooves; 6, Adambulacral plates; 7, Marginal plates; 0, One of the oral plates; ¢, Madrepori-
form tubercle.

ginal” plates. On the dorsal surface are three or more rows of
plates which are united by intermediate ossicles, and do not appear
to be separated by intervening pores. The genus Pad/easter com-
prises some species of considerable size, and ranges from the Ordo-
vician to the Carboniferous. The Ordovician genus Uvasterella

Fig. 274.—A, Palasterina primeva, Silurian; B, Paleaster Ruthvent, Silurian ;
c, Paleocoma Colvini, Silurian. (After Salter.)

( = Stenaster) is in many respects like Padeaster, but the ambulacral
grooves are bordered by a row of adambulacral plates, without a
second row of marginal plates. /e¢raster, also Ordovician, has an
incomplete series of disc-plates between the adambulacral and mar-

ASTEROIDEA. 397

ginal rows of plates, but is doubtfully separable from Padeaster ;
while the Ordovician and Silurian Pa/asterina (fig. 274, A) has the
disc still more extensively developed, and is further distinguished by
the fact that the plates of the adambulacral series which are placed
at the angles of the oral aperture are large and triangular. The
Silurian genus Pa/@odiscus, again, has a discoid form, the body being
pentagonal, without distinct arms, and the mouth being furnished
with five pairs of triangular oral plates. Lastly, the Silurian genus
Paleocoma (fig. 274, C) is an aberrant form of this group, with slightly
prominent arms, laterally bordered by long spines, the intervals
between which are filled up by a netted membrane.

In the Devonian rocks, various forms of the Eucrinasteri@ have
been detected, the chief genus in this formation being Asszdosoma,
in which the disc is of large size, with five small arms, and the
structural characters are in many respects peculiar. Thus, the arms
are covered superiorly with two or four rows of closely apposed
plates, which are continued over the disc, leaving a central star-
shaped space apparently covered only by a leathery skin; while the
madreporite is stated to be placed interradially on the under side
near the mouth. The known species of this singular genus are
found in the Devonian rocks of Germany. elanthaster, of the
Devonian rocks of Germany and Britain, is imperfectly known, and
may possibly be an Ophiuroid. It has a large disc, and from four-
teen to sixteen arms.

The sub-class of the Zwasteroidea is distinguished from the pre-
ceding by the fact that the pairs of ambulacral ossicles are placed
opposite to each other, and are directly united by their inner ends.
The members of this group appear in rocks as ancient as the De-
vonian, while all the Mesozoic, Kainozoic, and Recent Star-fishes
are referable to this series.

The following classification of the Ewasteroidea has recently been pro-
posed by Sladen, some of the less important families being omitted :—

ORDER I. PHANEROGONIA.—Marginal plates large and well devel-
oped ; papulz restricted to the dorsal surface. Ambulacral plates well
spaced ; tube-feet in two rows.

Families.—Porcellanasteridz (Porcellanaster, Ctenodiscus), Astropect-
inidz (Astropecten, Luidia), Pentagonasteridze (Astrogonium, Stellaster,
Gontodiscus), Antheneidz (Govzzaster), Pentacerotide (Pentaceros).

ORDER II. CRYPTOGONIA.—Marginal plates inconspicuous; papulz
distributed over the whole body. Ambulacral plates crowded and narrow;
tube-feet in two or four rows.

Families.—Solasteride (Solaster, Crossaster), Pterasteride (Pteraster,
Hymenaster), Echinasteridz (Echinaster, Cribrella), Asteriidz (Asterias),
Brisingidz (Brzsznga).

The forms of the Ewasteroidea which have been detected in the
Devonian rocks belong mostly to extinct genera (Xenaster, Eolutdia,

398 ECHINOZOA.

and FPalastropecten), but the still existing genus Astropecten (Asterias
of many authors) is represented by a single species (Stiirtz), and
the same genus is said to occur in the Carboniferous rocks. If some
doubt attaches to the Palzeozoic forms which have been referred to
Astropecten, unquestionable remains of species of this genus occur in
the Mesozoic and Tertiary rocks, the earliest appearing in the Lias.
The genus belongs to the group of Star-fishes (Panerogonia) in
which the tube-feet are in two rows and the “ papule” confined to
the dorsal surface, and is recognised by its five-rayed form, and
flattened disc and arms, the edges of which carry a double row of
large “marginal plates” (figs. 269 and 275). The lower of the two

Fig. 275.— Under surface of Astropecten Phillipsii, of the natural size.
Jurassic. (After Wright.)

rows of marginal plates is furnished with spines, and the whole
of the upper surface is covered with tubercles crowned by groups
of minute prickles.

Other genera of Phanerogonia which are abundantly represented
in the Jurassic, Cretaceous, and Tertiary rocks, and which still sur-
vive, are Gontaster, Astrogonium, Gontodiscus, and Stellaster. The
first-named genus comprises the so-called ‘‘Cushion-stars,” and is
characterised by the fact that the body has the form of a pentagonal
disc (fig. 271), in which the arms are principally recognisable by the
presence of the ambulacral furrows on the inferior surface. The
disc is bordered by a double row of large ‘‘ marginal plates,” and
the upper and lower surfaces are covered with small, four-sided or
polygonal plates. Besides the above, the existing genera Pentaceros
(Oreaster) and Luidia appear in the Jurassic, though the occur-
rence of the latter is not certainly established. Among the C7yféo-

OPHIUROIDEA. 399

gonia, the recent genus So/as¢er, comprising the familiar ‘‘ Sun-stars,”
is represented by a single known Jurassic species, and is easily re-
cognised by its wide disc and short arms, and by the fact that the
dorsal integument is studded at intervals with prominent “ paxille.”
Another still living genus, which is known to have existed in rocks
as old as the Lias, is Asterias (or Uraster of many authors). This
familiar genus belongs to the group of Star-fishes in which the am-
bulacral tube-feet are in four rows, and is the only form of this
group which has hitherto been found fossil. The disc is small, and
the arms are long, and are variable in number, while the dorsal
integument is hardened by netted ossicles, many of which are
developed into projecting tubercles or blunt spines. The extinct
genera of Mesozoic Star-fishes, such as the Jurassic Plumaster
and Zropidaster, do not exhibit any special peculiarities demanding
notice here.

Crass III. OPHIUROIDEA.

The class of the Opfiurotdea comprises the small but familiar
group of the “ Brittle-stars” and “Sand-stars,” and is characterised
by the fact that the body ts stellate, consisting of a central “ disc,” in
which the viscera are contained, and of elongated “arms,” which are
sharply separated from the disc, do not contain prolongations of the
alimentary canal, and are not furnished inferiorly with open ambu-
lacral grooves.

The body in the Ophiuroids always has the form of a rounded
or pentagonal disc (fig. 276), and carries long slender arms, which
are typically simple, though they are branched in many of the Eury-
alids, and which are essentially employed as locomotive and prehen-
sile organs. The arms do not contain diverticula from the alimentary
canal, but they lodge the radiating ambulacral vessels and nerve-
cords, these structures not being situated in open “ambulacral
grooves,” as in the Asteroids, but being covered in by the coriace-
ous or plated integument. On the under side of the body, in the
centre of the disc, is seen the stellate opening of the mouth (fig.
276, Cc); and the reproductive organs open also on the under side
by ten fissures or slits, a pair of these being situated at the base of
each of the five arms. Owing to the absence of an anus, there is
no aperture on the upper surface of the body.

With regard to the integumentary skeleton of the Brittle-stars, it
is impossible to enter here into the interesting features shown in the
embryonic condition of certain Ophiuroids, at which stage it can be
shown that the exoskeleton of the dorsal surface is in many respects
homologous with the apical disc of the Echinoids and the calyx of
the Crinoids. In the adult condition, the integumentary skeleton
of the Ophiuroids is of a very complicated character; but the im-

400 ECHINOZOA.

portance of the group from a paleontological point of view is not
sufficient to justify its being treated of here except as regards its
general features. The upper surface of the disc of an Ophiuroid
is covered throughout with calcareous plates, scales, or granules.
A large central plate (dorsocentral”) is sometimes recognisable,
and a pair of large plates (‘radial shields”) is usually developed on
the dorsal aspect of the disc at the point of origin of each of the

Fig. 276.—Ophiuroidea. O~phioglypha lacertosa. a, Outline, of the natural size; B, The disc
viewed from above, twice the natural size; c, The disc viewed from below, showing the mouth
and genital fissures, twice the natural size. (Original.)

five arms (fig. 276, B). On the under side of the disc the arms,
with their ventral rows of plates, are continued to the mouth, but
the spaces between the arms (“‘interbrachial areas”) are covered
with plates, scales, or minute tubercles of lime (fig. 276, c). The
stellate aperture of the mouth is bordered with a system of peristo-
mial ossicles, some of which act as teeth; while at its angles, one in
each interbrachial space, are situated five large ‘‘mouth-shields ”

OPHIUROIDEA. AOI

(fig. 276, c), which are homologous with the “oral plates” of the
Crinoids. In the majority of the Brittle-stars one (or more) of the
oral plates is enlarged, and represents in function the ‘‘ madreporite ”
of the Star-fishes.

The arms are, typically, protected by four rows of calcareous
plates, one dorsal, one ventral, and two lateral (fig. 277). The
lateral, or ‘‘adambulacral,” plates carry rows of spines, and not only
cover the sides of the arm, but also encroach upon the inferior sur-
face. The ventral shields (“‘superambulacral plates”) are so related
to the lateral plates, that a pair of pores is
formed on each side of each of the former,
by means of which the tube-feet gain the
exterior. In the Euryalids, the arms are
covered with a leathery skin, containing
minute granules and scales.

In addition to the proper integumentary
skeleton, the Ophiuroids possess an zxzernal
or ambulacral skeleton, consisting of a linear
series of large calcareous discs or “‘ vertebral
ossicles,” which occupy the greater part of
the interior of each arm, and are grooved open ea ane
inferiorly for the reception of the ambulacral cross-section of the arm of an
! é Ophiuroid (slightly altered
Reread racials Merve (te) 277): 9 “Nese! Vom\Sladen), “ao; Ambulacral
discs correspond with the “ambulacral ossi- psicie inmovahly une he
cles” of the Star-fishes, but the ossicles of opposite side; , Superior

‘ ; plate of the arm; s, Lateral
each pair are anchylosed with one another. plate; Z Inferior plate; ~,
Successive vertebral discs are movably arti- eee ee Sa eS
culated with one another, and the entire Uae oa ae ¢, Tube-
series is largely supplied with muscles. The
first two pairs of ambulacral ossicles in each series have their lateral
elements disjunct, instead of being fused in the middle line, the
pieces of the first pair taking part in the formation of the calcified
peristome, and thus becoming connected with the armature of the
mouth.

The ambulacral system of the Ophiuroids is constructed upon
essentially the same type as in the Asteroids and Echinoids, but its
place as a locomotive apparatus is taken by the arms, the tube-feet
being tentacle-like, without terminal suckers, and with no specially
developed “ampulle.” The special peculiarity of the ambulacral
system in the Ophiuroids, as compared with that of the Asteroids, is
that the grooves on the under side of the row of ambulacral ossicles,
in which lie the radiating ambulacral vessels, are not open, as they
are in the latter, but are closed in by the passage over them of the
integument. Another peculiar feature, in all except the extinct
Protophiurida, is the position of the ‘‘ madreporite” on the inferior

VOL. I. DAMS

402 ECHINOZOA.

surface of the body and its connection with the oral plates, with one
of which it is generally confluent. |

As regards the digestive system, the Ophiuroids differ from the
majority of the Asteroids in the fact that the alimentary canal ter-
minates blindly, and there is, therefore, no anal aperture upon the
dorsal surface of the disc.

Lastly, as regards the reproductive system, the generative glands
in the Ophiuroids are placed interradially, and their ducts open into
singular folded pouches or “ bursze,” which in turn communicate
with the exterior by means of slit-hke openings (the ‘“ genital
fissures”), which are placed, singly, or rarely in pairs, on the sides
of the arms inferiorly, at their junction with the disc (fig. 276, c).
Calcareous plates are sometimes developed in the walls of these bur-
see, and currents of sea-water flow in and out of the genital fissures.
It is probable, therefore, that these “genital burs” are partly res-
piratory in function, and that they correspond with the so-called
‘“‘hydrospires” of the Cystoids and Blastoids.

The living Ophiuroids are all inhabitants of the sea, and the
marine deposits of almost all the great geological periods have
yielded examples of the group, the oldest known forms occurring in
Ordovician strata. Most of the remains of Ophiuroids, and par-
ticularly those of the more ancient formations, are, however, more
or less imperfect, while fossils of this group are, as a rule, exceedingly
rare. It will be sufficient here, therefore, to deal with the fossil
forms of Ophiuroids very briefly.

The existing Ophiuroids fall naturally into two sections—the
Euryalida and Ophiurida—the characters of which are sufficiently
distinct. In the Zuryalda, the arms may
be simple, but are more usually branched,
and in either case their integument is
leathery, the arms being devoid of the rows
of plates so characteristic of the typical
Brittle-stars. The type of this group is
the genus Astrophyton (Luryale), com-
prising the well-known ‘“ Medusa - head
Stars,” characterised by their much-
branched arms. The only two extinct
genera which appear to be referable to the

Fig. 278—Onychaster flexitis, Luryalida are Eucladia and Onychaster.
viewed sideways, of the natural ‘The former of these is found in the Silu-
size, with the arms rolled up. ; aes : ;
From the Carboniferous Lime- rian rocks of Britain, and is characterised
ana Scenes oa niece Bite) by the possession of a granulated disc and

of five bifurcating arms. The genus Ony-
chaster (fig. 278) is based upon forms found in the Carboniferous
Limestone of North America, and is characterised by the possession

OPHIUROIDEA. 403

of a small disc, and of five simple round arms, which are covered
with a granulated integument, and carry spines on their ventral
aspect. As in the living Euryalids, the arms could be rolled up
towards their ventral side at their tips.

The second section of the living Ophiuroids—that of the Op/zu-
vida—comprises the typical forms of the order, and is characterised
by the fact that the arms are always simple and are protected by four
rows of integumentary plates (fig. 279). The integument of the disc

em,
Wi 4;

AN
is =

an
i

ViNGG >»
AM |
Liye -
! — an ja)
r Za id 4 y
reso WZ
: Gard
WV

Wy BM Wa Yj, ZS

/ || WSS

EM NINN EZ
LT GS Ihe Z yy ry

Aa [ZE ‘

Fig. 279.—Under surface of Ophioderma (Ophioglypha ?) Gaveyz, of the natural size.
Jurassic (Lias). (After Wright.)

is soft, or is covered with granules or plates of carbonate of lime.
The earliest types of this group appear in the Lower Devonian
(Ophiurella primigenta, Stirtz); and numerous forms are found in
the Secondary and Tertiary rocks. A well-known Triassic genus is
Aspidura (= Acroura), the remains of which are widely distributed
in the Muschelkalk (fig. 280). The Jurassic Ophiuroids belong
principally to the genera Ophioderma (fig. 279), Ophioglypha, and
Geocoma, of which the last is peculiar to the Jurassic rocks, while
the two former are represented in the Cretaceous and Tertiary rocks,

AO4 ECHINOZOA.

and survive at the present day. The recent genus Op/zolepis is found

in the Pleistocene, and possibly occurs in Tertiary deposits also.
Finally, there are various Palzeozoic Ophiuroids which cannot

be included in either of the preceding sections, and which may be

Fig. 280.—A spidura loricata. Muschelkalk.

provisionally placed in a special division (Protophiurida), though
their characters are not completely understood. All the forms here
in question agree with the typical Ophiurids in having five simple
plated arms, but the “‘madreporite” is placed on the dorsal aspect
of the body, and the under surface of the arms exhibits a double,

Fig. 281.—a, Outline of Eugaster Logani, of the natural size—Devonian. B, Base of an arm
of the same viewed from below, enlarged. c, Outline of Protaster Forébesi, of the natural size—
Silurian. vb, Base of an arm of same, viewed from below, enlarged. £, Portion of the arm of
Ptilonaster princeps, viewed from below, enlarged—Devonian. a, Ventral (superambulacral ?)
plates; 46, Adambulacral plates; Z, Pore. (After Hall.)

in place of a single, row of plates (fig. 281, B). Two views may be
held as to the nature of the double (or sometimes quadruple) row
of plates exhibited on the under side of the arms of the Protophiu-
rids. On one view, these plates are considered as being integument-

OPHIUROIDEA. AO5

ary, and as corresponding with the ventral shields (‘‘ superambula-
cral plates”) of the normal Ophiuroids, their special peculiarity on
this theory of their nature being their duplication. On the other
hand, it may be held that the ventral or superambulacral plates of
the ordinary Brittle-Stars are not developed at all in the ancient
types in question, and that the double row of plates above alluded
to are really the “ambulacrai ossicles” or “ vertebral discs,” which
would, on this view, differ from the corresponding structures in the
normal Ophiuroids by being separate, instead of being anchylosed
in pairs. If this latter view be correct, the Protophiurids may have
either had open ambulacral grooves, as in the Asteroids, or the
under side of the arms may have been closed by soft skin, as in the
Euryalids. Whichever of these two views is the correct one, the
plates of the double ventral row of the Protophiurids may either be
placed opposite one another, or they may alternate, and they are
also so disposed as to give origin to a double series of pores.

Of the genera of Protophiurids, Profaster (fig. 282) is found in
the Ordovician and Silurian rocks, and is characterised by its round
scaly disc, and by the fact
that the arms are provided
inferiorly with a double row
of plates, and carry bunches
of lateral spines (fig. 282, B).
In the Devonian genus £z-
gaster (fig. 281, A) the gen-
eral structure is very similar
to that of Profaster, but the
disc is prolonged along the
bases of the arms, and the
plates of the disc are articu-
lated by their edges, and do
not overlap. The under side
of the arms (fig. 281, B) ex-
hibits a double row of alter-
nating plates, and _ lateral
spines appear to have been
wanting. In the genus
Ptilonaster, again, the arms
exhibit on their under surface
jour rows of plates and a
double row of pores. This pFie, 2x Pogter, SedewichtSiluian, x
genus is also Devonian. ofanarm, greatly enlarged. (After Salter.)
Lastly, the genus Zenzaster,
from the Ordovician rocks of Canada, is in many respects like
Protaster, but the two rows of plates which occupy the under sur-

406 ECHINOZOA.

face of the arms have the peculiarity that each is constricted in
the middle, a feature which would rather lead to the belief that
these plates are truly of the nature of ‘“ambulacral ossicles.”

Cuiass IV. HoLOTHUROIDEA.

The class of the Holothuroidea includes the animals usually
known as “‘Sea-cucumbers,” distinguished from the other Echino-
derms by their elongated, vermiform, or slug-like form, and their
leathery muscular integuments. ‘The mouth and anus are usually
terminal in position, and the radial symmetry of the body is not
conspicuously shown externally except by the crown of oral ten-
tacles, and, often, by the bands of tube-feet. Palseontologically
speaking, the Holothurians are of little importance, since they
possess few structures which are capable of preservation in a fossil
condition. Unlike the other Echinoderms, the Holothurians ex-
hibit a very limited tendency to a calcification of their tissues. No
proper ‘‘ test,” in fact, exists in any Holothurian, but the skin con-
tains numerous isolated, mostly microscopic bodies, of special
forms in different types. These calcareous structures (fig. 283)
may be globular, wheel-shaped, spicular, anchor-shaped, &c., and

Fig. 283.—Integumentary ossicles of recent and fossil Holothurians. a, A plate of Achistrumz
Nicholsoni, enlarged forty-five times, from the Carboniferous rocks of Scotland ; 6, Hooklet of
the same, similarly enlarged; c, Anchor and anchor-plate of a recent species of Syxafpta, en-
larged; ad, Plate of Chirodota? Traguairiz, enlarged forty-five times, from the Carboniferous
rocks of Scotland ; e, Plate of the recent Thyonidium pellucidunt, enlarged. (After R. Etheridge,
jun.)

in rare cases (as in Psolus) have the form of comparatively large
imbricated scales, which constitute a kind of external shell. When-
ever the integumentary calcifications are plate-like, they exhibit
under the microscope the peculiar netted structure which is char-
acteristic of the Echinodermal test. In addition to the integument-
ary hard structures, there exists a ring of calcareous pieces sur-
rounding the mouth, and serving for the attachment of five great
longitudinal muscles.

Owing to their want of hard structures of any size, the geological
history of the Holothurians is necessarily a very imperfect one, being

HOLOTHUROIDEA. 407

based only on the occasional recognition of the microscopic plates or
spicules of the integumentary skeleton. The oldest remains which
can be certainly affirmed to be those of Holothurians are the micro-
scopic plates and spicules described by Mr R. Etheridge, jun., as
occurring in the Carboniferous rocks of Scotland. Some of these
have the form of rounded, perforated calcareous plates, about 7; inch
in diameter, associated with simple calcareous hooks or one-fluked
anchors, the shaft of the anchor having a perforation or ‘‘ eye” at
its base (fig. 283, a and 4). These plates and hooklets have been
referred to a special genus under the name of Achistrum ; and they
may be compared with the anchors and anchor-plates of the living
genus Synapta (fig. 283, c). Others have the form of circular,
generally concavo-convex, wheel-like plates, about 73, inch in diam-
eter, with a group of central pores and a series of marginal perfora-
tions (fig. 283, d@). These resemble the wheel-shaped integumentary
plates of such living types as Zhyonidium (fig. 283, e) or Chirodota,
and they may be provisionally placed in the latter genus.

It is probable that investigations conducted with sufficient care
will ultimately show that the minute plates and spicules of Holo-
thurians have been more generally preserved in the fossil condition
than has been usually assumed to be the case. In the meanwhile,
with the exception of the remains above noted, no undoubted traces
of the former existence of Holothurians have been found until the
Jurassic rocks are reached. Here, the occurrence of minute wheel-
like plates, resembling the ‘‘ wheels” of the recent Czvodota has
been recorded. Pocta has described plates of /so/us from the
Chalk of Bohemia, and Schlumberger has recently found the
characteristic armature of Syzapta, Chirodota, and Thyonidium in
the Middle Eocene of the Paris basin; while CZzrodo¢a occurs in
the Pliocene of Northern Italy, and plates belonging to Psol/uws have
been found in Post-tertiary deposits in Bute.

408

Cir a ory

DIVISION B. PELMATOZOA.

THE three groups of Echinoderms known as the Crinoids, Cystoids,
and Blastoids agree with one another in certain common characters,
and may be included in a single primary section termed /e/matozoa.
In all these forms the body is fixed, either temporarily or perman-
ently, by the dorsal surface, often having a jointed stem or peduncle ;
and the mouth is placed on the opposite side of the body. In its
fully developed condition, the peduncle has the form of a jointed
stem, containing a neuro-vascular axis in its interior. ‘The body
itself is enclosed in a variously modified series of calcareous plates,
which represent ‘the apical disc of the Echinoids, and the upper
surface may be provided with jointed appendages (the “ arms”).
The circular ambulacral vessel has no direct communication with the
exterior, or only a limited one, and the radiating ambulacral vessels
(when present) are respiratory in function, and are not subservient to
locomotion.

Cuiass J. CRINOIDEA.

The Crinoids or “Sea-lilies” may be defined as Echinoderms in
which ¢he body is fixed, during the whole or a portion of the existence
of the animal, to the sea-bottom by means of a jointed, flexible stalk or
peduncle, which springs from the centre of the dorsal or aboral surface.
The body ts cup-shaped or discoidal, and its dorsal surface 1s protected
by a system of calcareous plates. The mouth is situated on the upper
surface, generally in the centre. From the margin of the cup-shaped
body spring jointed flexible appendages or “arms,” which are primt-
tively five in number, and which carry lateral jointed processes or
“< pinnules.” The upper or ventral surfaces of the arms are furnished
with grooves corresponding with the “ambulacral grooves” of the
Asteroids. The water-vascular system has only a limited communica-
tion with the exterior, and 1s not connected with locomotion. The

CRINOIDEA. 409

reproductive organs are situated beneath the skin in the grooves on the
ventral surface of the arms or pinnules.

As the study of the fossil Crinoids is attended with considerable
difficulties, it may be well to give here a brief account of the general
anatomy and development of one of the ‘“‘ Feather-stars ” (Comazu/a),
no other recent type of the group being readily obtainable for pur-
poses of investigation. All the known Crinoids are attached to
foreign bodies by a jointed stem or “column” in their young con-
dition ; but in the adult state they may either retain this stem of
attachment, and thus remain permanently fixed, or they may become

KL EWS NN AN S >
hy Ha ‘ YX Ss i]
a St L tke Sy Ei
A PIES ) im:
- oA D

a ff ht
/ /

Fig. 284.—Crinoidea. Axtedon (Comatula) rosacea, a free Crinoid, viewed from its
dorsal or aboral aspect.

detached from the stem and may lead a free existence. In accord-
ance with this, the Crinoids may be divided into the two groups of
the ‘‘ Pedunculate Crinoids” and the “ Free Crinoids.” In the
Pedunculate Crinoids, where the stalk of attachment is permanently
retained (fig. 289), the animal may be compared with a Star-fish
turned upside down, the column springing from the centre of the
“dorsal” (or “abactinal”) surface, while the “ventral” (or “ac-

ALO) PELMATOZOA.

tinal”) surface, with the mouth-opening, is turned upwards. In the
Free Crinoids, in which the adult is devoid of a peduncle of
attachment, the animal has it in its power to move about freely by
swimming ; while it can at the same time assume the position char-
acteristic of the Stalked Crinoids, since it can fix itself to foreign
objects with the mouth turned upwards and the dorsal surface
directed downwards.

The “ Feather-stars,” as exemplified by the common Azfedon
(Comatula) rosacea of British seas (fig. 284), belong to the group
of the ‘‘ Free Crinoids,” being attached by a stalk in their young
state only. The adult animal is free, and consists of a pentagonal
or cup-shaped body or “ calyx,” which gives origin on its sides to
five jointed processes or “‘arms.” The calyx encloses the visceral
mass or disc, the upper or ‘‘ actinal” surface of which exhibits the
apertures of the mouth and anus. ‘The five “arms” bifurcate
almost immediately after their origin from the calyx, so as to give
rise to ten long slender processes, which are transversely jointed, and

br <r

Fig. 285.—Side-view of the calyx of Axtedon sp., enlarged, the cirri being mostly removed,
and the bases of only two rays being shown. cd, Centrodorsal plate, with the origins of the
dorsal cirri (c); 7, One of the ‘‘ primary radials”; sv, One of the ‘‘ secondary radials”; av, One
of the ‘‘axillary radials,” carrying the bifurcations of the arm; 47, First ‘‘ brachial” plate.
(Original.)

are fringed on both sides by delicate filaments or “ pinnule.” The
dorsal surface of the body carries a number of delicate jointed
flexible processes (figs. 284 and 285, c), which are attached to the
so-called “‘centrodorsal” plate, and are known as the “cirri.” By
means of these the animal can moor itself temporarily to foreign
objects, with the mouth turned upwards.

CRINOIDEA. AII

The dorsal or aboral integument is hardened in Azntedon by the
formation within it of a system of calcareous plates, which collec-
tively constitute the “cup” or “calyx,” and which in large part
correspond with the “apical disc” of the Echinoids. ‘The central
piece of the calyx is known as the “ centrodorsal ” plate (fig. 285, cz),
and is developed from the topmost joint of the stem in the young
Feather-star. It carries the cirri, and has soldered on to it five
“radial” plates (fig. 285, ~), which represent the “ocular plates” of
the Echinoids. ‘There are thus afparently no representatives of the
“genital plates” of the Echinoids. In the great majority of the
recent Feather-stars, however, these plates are really present, though
they exist only in a metamorphosed condition. They are, in fact,
fused together to form a so-called “ rosette-plate,” which is con-
cealed from view externally, and lies hidden between the centro-
dorsal and radial plates. This “rosette-plate” consists, therefore,
of the amalgamated interradial plates which are known as the
““basals” in the stalked Crinoids. Following the first cycle of

Yee °
= co 000000%

wooo caG0000;

ait
Fig. 286.—a, Ventral or actinal surface of the body of Comatula (Antedon) rosacea, enlarged,
showing the central mouth (0), the excentric, proboscidiform anus (a7), and the brachial grooves
(ag), continued from the bases of the arms across the disc to the mouth. B, Side-view of the lower
part of Antedon levis, showing the calyx, the bases of the arms (4), and the roots of the dorsal
cirri, a single cirrus (c) being left complete, enlarged. (After P. Herbert Carpenter.)

“radials” in Aztedon are two other circles of radial plates (the
“second radials” and “axillary radials”), the outermost circle
carrying the bases of the jointed arms (fig. 285, sz and ar).
The upper or ventral surface of the body is covered with an
imperfectly calcified, coriaceous skin, and carries the aperture of the
mouth. In Comatula rosacea the mouth is central (fig. 286, A, 0),

AI2 PELMATOZOA.

as it is in all the ordinary Crinoids; but in some Feather-stars
(species of Actinometra) it may be quite excentric. The anus (az)
is usually supported on a tubular projection, and is excentric in
position. ‘The arms of Comatula rosacea exhibit on their ventral
surface a deep furrow or groove, the elevated margins of which
are cut out into minute crescentic respiratory leaves, at the base of
each of which is a group of three tentacles, connected with a cavity
in the interior of the respiratory leaf,
and communicating by a common
trunk with the radiating water-vessel.
The floor of the ambulacral furrows
is ciliated, and underneath each runs
a radiating water-vessel, together with
a blood-vascular trunk, and a nerve-
band which is in intimate relation
with the ambulacral epithelium. In
the centre of the arm, between the
calcareous skeleton and the water-
vessel, are three tubular prolongations
of the body-cavity. The middle and
largest one of these (fig. 287, ov) con-
tains one of the generative glands ;
while the upper and lower (the “ sub-
tentacular” and “cceliac” canals) are
much smaller, and permit of a circula-
tion of water derived from the body-
cavity. ‘The slender lateral ‘‘ pinnules ”
carried by the arms, as regards their
internal anatomy, have precisely the
Fig. 287.0: Cfossseetion of a pinnuley Structure of the arms *Unemeclmes:
of the Arctic Feather-star, magnified The ciliated grooves on the ventral

seventy-five times. (From Ludwig ;

after P. H. Carpenter.) 7, Calcareous aspect of the arms are continued over
skeleton, containing the axial nerve- h f. f the di A
cord (a); ag, Ambulacral groove; x, the upper suriace of the disc to reac
Radial nerve; 4, Radial blood-vessel ; =

wo Ambulacral vessel: T, Tentacle, the subcentrally or excentrically placed

ov, Ovary, with the subtentacularcanal mouth; and the animal feeds upon
above, and the ceeliac canal below; : :
ev, Genital blood-vessel. the minute organisms conveyed to the
mouth by the water-currents set up
along these grooves. ‘The mouth opens into a spirally coiled ali-
mentary tube, which forms most of the so-called ‘‘ visceral mass,”
and is wholly contained within the calyx, no diverticula from it
extending into the arms.

The water-vascular system consists of a circumoral ring, and of
the radiating water-vessels, which run along the brachial furrows.
These give off the tentacles, which are destitute of suckers, and
are essentially respiratory in function. The circular ring communi-

fn
Tonner
Ne
i
UUTTUM

Tes TTY

CRINOIDEA. 413

cates by numerous water-tubes with the body-cavity, to which the
sea-water is freely admitted by minute pores in the body-wall ;
while some of these pores are said by Perrier to lead directly
into the oral water-vascular ring, though this is denied by Hamann.

The vascular system is extraordinarily developed, and its upper
portion consists of an oral ring, which gives rise to the radial
vessels, and is also connected with a peculiar organ apparently
serving as a kidney, as well as with numerous ‘“intervisceral ”
vessels. There is no aboral vascular ring, but the vessels become
connected inferiorly with a singular quinquelocular structure known
as the “chambered organ,” which is contained within the centro-
dorsal plate of the calyx. The chambered organ is enclosed in a
peculiar fibrillar sheath, the nature of which will be spoken of
immediately, and it sends prolongations into all the arms, along
canals contained within the skeleton of the latter, and also into
the dorsal cirri.

In the Crinoids generally, the structure of the vascular system is, up to
a certain point, much the same as it 1s in Comatula. Occupying the
dorsoventral axis of the body is the lobated kidney, enclosed in a sheath
of vessels. Dorsally, these resolve themselves into a central group (of
one or more), and five peripheral vessels, the latter expanding in the
lower part of the calyx into the five chambers of the “ chambered organ.”
In the Pedunculate Crinoids the chambers narrow again, and the group
of vessels is continued down the central canal of the column. In Pez¢a-
crinus, which has cirri at regular intervals, the five peripheral vessels ex-
pand in each cirrus-bearing joint into five dilatations, which thus give rise
to a miniature “chambered organ,” each chamber of which gives off a
single vessel to a cirrus.

The nervous system of the Feather-stars is also extraordinarily
developed as compared with that of the other Echinoderms. As
has been previously seen, there is found under the floor of each
of the brachial grooves a fibrous nerve-band (fig. 287, ), which
corresponds morphologically with one of the radiating nerve-fibres
of a Star-fish. In addition to these ambulacral nerves, the ‘‘ cham-
bered organ,” above spoken of in connection with the vascular sys-
tem, is enclosed in a peculiar fibrillated sheath, which has been
shown by Dr W. B. Carpenter to be of a nervous nature. It gives
off a series of radial prolongations or ‘‘axial cords” (fig. 287, a),
which occupy median canals within the skeleton of the arms and
pinnules, and send numerous branches to the muscles and the
integument (fig. 287, a). In the stalked Crinoids the fibrillar
nerve-sheath is likewise prolonged, along with the blood-vessels,
into the central canal of the column or peduncle. No represen-
tative of this peculiar system of nerves is known in the unstalked
Echinoderms (£chinozoa).

AIA PELMATOZOA.

Though free in its adult condition, the Rosy Feather-star passes
through a stage of its development in which it is attached by a
delicate jointed stalk to some foreign object (fig. 288). When
first discovered in this condition, it was supposed to be a distinct
type of the Crinoids, and was described under the name of Fenzta-
crinus Leuropeus. ‘The Comatula, therefore, represents temporarily,
in this stage of its development, the permanent condition of the
Pedunculate Crinoids.

As regards the development of Comatuda, the larva is at first cylindri-
cal, with four transverse bands of cilia, a hinder tuft of cilia, and an ali-
mentary canal furnished with a lateral aperture, its general aspect closely
resembling that of the embryos of certain Annelides. The skeleton of the
calyx is developed anteriorly, that of the column
posteriorly, the former being the first to appear.
In its early condition (fig. 288) the calycine skele-
ton consists of a row of five “basal” plates (0),
together with three or five small “ underbasals,”
which rest below upon the so-called “ centrodor-
sal plate” (cd), and fuse with it at an early period.
The basals are succeeded above by a cycle of
five “ oral” plates (0), in the centre of which the
permanent mouth is finally developed. Five
“radial” plates (7) are next developed as a cycle
between the oral and basal plates: and to the
radials are rapidly added the plates of the arms
proper (the “brachials). Inferiorly, the centro-
dorsal plate rests upon a short jointed column
(fig. 288, c), at the bottom of which is an ex-
panded “ dorsocentral” plate (d), forming a disc
of attachment; and the larva now passes into
what is known as its “ Pentacrinus stage.” In
the further progress of growth the arms increase
in length, and the oral plates diminish in size
and ultimately disappear. At the same time the
centrodorsal plate increases in size, so as to en-
close the basal plates, which in turn become
fused with one another, and remain only as the
so-called “rosette” on the upper surface of the
centrodorsal. The latter also develops jointed

Wis, See ne arvaeoniCoa! cirri from its outer suface, and finally becomes
tula (Antedon) rosacea, en- Metached from the next joint of the column be-

larged (after Sir Wyville Jow, when the animal enters upon its free stage of
Thomson). 00, Oral plates ; ike

yr, Radial plates; 64, Basal 4I!€.
plates ; cd, Centrodorsal plate ;
c, Column; d, Disc of attach-
ment (dorsocentral plate).

As regards the essential features in their
anatomy, the “Stalked” Crinoids do not
differ “materially fromthe “Free” forms” of the: group aye t@ne
particularly, there is a substantial identity in structure in the two
sections of the order as regards the form and arrangement of the
alimentary canal, the ambulacral and vascular systems, and the ner-
vous and reproductive organs. As the majority of the fossil Crin-

AIS

CRINOIDEA.

ns 9 CAIN
ee Uta, Sacre: eS reek

Se SY
Sa
enERE ED

EGE. See

+r
an reso ep Oe
> chet F pool pe tASTiy ote
%5 oe S ON el ee al
gyr7 2 © 2 ho ie. 4 wir
7 ee aes 4 i

Pc aibitaa ae ee

‘3 ooh” ail

alked Crinoid, slightly enlarged.

t

Ss

Fig. 289.—Pentacrinus Maclearanus, a living

AI6 PELMATOZOA.

oids, however, belong to the Pedunculate division of the group, it is
necessary to study the skeleton of these in greater detail.

A pedunculate Crinoid, such as Pentacrinus (fig. 289), consists of
a cup-shaped body or ‘‘ calyx,” which encloses the principal viscera,
and is furnished with a crown of pinnate “arms,” and which is
attached to some foreign object by means of a stalk or ‘‘ column,”
composed of a number of calcareous pieces or ‘‘articulations.” In
some cases (as in Apiocrinus) the base of the “column” is consid-
erably expanded. In other cases the column is simply “rooted by
a whorl of terminal cirri in soft mud” (Wyville Thomson). The
column may be extremely short, or even wanting in the adult, or
may reach the extraordinary length of sixty or seventy feet. The
whole column is composed of a series of ring-like or pentagonal
joints, which are generally movably articulated with one another,
and are furnished with special muscles, the joint-surfaces often
having a very elaborate structure, and the entire stem possessing in
the living state a larger or smaller amount of flexibility. Very
often more or fewer of the column-joints carry lateral jointed pro-
cesses or “cirri” (fig. 289). Each joint of the stem, further, is
perforated centrally by a canal, which lodges an extension from
the “chambered organ” and its fibrillar nerve-sheath.

As regards its shape, the “column” of the Stalked Crinoids is very
commonly round, but it is sometimes oval or elliptical (as in Platycrinus,
fig. 300), and it is not infrequently pentagonal (as in Axtracrinus, fig.
290). The separate joints or “articulations” of the column are usually
so connected with one another that whilst the amount of movement
between any two pieces must be very limited, the entire stem is more or
less flexible. The articular surfaces or facets by which contiguous joints
are connected, are differently marked in different cases. In many forms,
the articulating facets are marked by more or less numerous radiating
striz, which run from the central canal of the joint to its margin. In
other cases, as in Pentacrinus and Extracrinus (fig. 290), the articular
faces are united by crenated ridges arranged in a pentapetalous figure.
Though usually articulated movably, the stem-joints are occasionally
united here and there by the peculiar mode of union known as “syzygy.”
By this is understood the immovable union of two originally separate
joints by close ligamentous connection and subsequent more or less
complete fusion, the primitive line of division usually remaining visible
as a line of suture.

The uppermost joint of the column is often larger than, and differently
shaped from, the inferior joints, and may, as in Afzocrinus, enter largely
into the formation of the calyx. In many cases, as in Pemtacrinus and
Extracrinus (figs. 289 and 290), the column is furnished with more or
less numerous auxiliary arms or “‘side-arms,” which represent the “ cirri”
of the Comatulids. The column generally increases in height by the
addition of new joints at its summit, and also by the intercalation of
others between those previously formed in the upper, and therefore the
youngest, part of the stem ; and the whole series is traversed centrally by
a variously shaped tube—the misnamed “alimentary canal” of old writers

417

CRINOIDEA.

cme
ae
2
vo
as
AS
em]
Og
ue
aS

lverticu

ly noted, lodges the neuro-vascular a

» aS previous

—which
The neuro-vascular tube of the stem sends off d

and root-like processes of attachment, when these structures are present.

In some cases,

It is very commonly round, but it may be pentapetalous.

s running para

llel with and around a central

there are four or five canal

is uncertain.

le of tubes

ig (RC

tube, but in this case the function of the oute

ay

ectesveeevecaereceraedd’”

“1S.

oints of Extracrinus subangular

ém-j

The small figures show the st

de-arms.

its sl

h

wit

Fig. 290.—Extracrinus briaroides, from the Lias, showing the crown of arms, and the column

form, or

9 Py

he cup-shaped

Summit t

The column carries at its
bursiform body of the animal, or ‘‘calyx” (fig. 291).

As the

column is produced from the aboral pole of the animal, it is the

2410)

VOL. I.

418 PELMATOZOA.

dorsal side of the calyx which is turned downwards, while the
ventral or oral side is turned upwards. ‘The dorsal or inferior side
of the calyx is entirely enclosed in a series of polygonal calcare-

ous plates, which are more or less closely joined together.

\ NS
Re Ws.
a =

YH)

Rae

My) rip WN
Hi ole
Ny

Fig. 291.—Side-view of the
calyx of Poteriocrinus multiplex,
from the Carboniferous Limestone
of Russia, of the natural size,
showing the top-joints of the
column (c) and the bases of the
arms. 46, The cycle of ‘‘ under-
basals”; Z, The ‘‘basals”; 7,
The ‘“‘primary radials”; 47, The
“second radials” (or first ‘* brach-

In some
cases the plates are united by firm sutures ;
while in others the plates are more or less
movably articulated; and in still other
cases certain of the plates may be con-
nected by the peculiar mode of immovable
union, which has been already described
under the name of ““syzyey.” as aemame
cases, as in the Devonian genus //ys¢77-
crinus, the calycine plates are furnished
externally with movably articulated spines,
resembling the prickles of the Echinoids.

The following is the general arrange-
ment of the calycine plates in the Stalked
Crinoids (figs. 291 and 292). Resting
directly upon the summit of the highest
joint of the column is the cup-shaped basal
portion of the calyx, which is known as
the “‘ basis,” and which may consist of a
single or double row of plates. In those
Crinoids in which the basis is composed

ials’”’ of some authors). (After

Zittel.) of a single row of plates only — hence

termed ‘‘monocyclic” Crinoids—its com-
ponent plates rest directly upon the top-joint of the column, and are
known as the “‘basals.” The ‘basals” are interradial in position,
and are homologous with the “genital plates” in the apical disc of
the Echinoids. The basals are usually five in number, but may be
reduced to four, three, or two; and they may be invisible externally
owing to their concealment by the radials (as in most Comatul@).
In the so-called ‘‘ dicyclic” Crinoids, on the other hand, the true
‘“‘basals” retain their constant interradial position, but are separated
from the top-joint of the column by an intercalated row of plates
termed the ‘“underbasals” (figs. 291 and 292, 6), the basis thus
consisting of two successive cycles of plates.1 The underbasals are
radial in position, and have no representative in the calyx of the
‘““monocyclic” Crinoids. It is not clear that they possess any
homologues in the apical disc of the Sea-urchins, as do the basals
and radials of the Crinoidal calyx. They were formerly compared

1 In the nomenclature of some writers, the plates of the dicyclic calyx are known
respectively as the ‘‘basals” and ‘‘ parabasals”’; but the nomenclature of Dr P.
Herbert Carpenter, employed above, undoubtedly expresses the true homologies
of the monocyclic and dicyclic forms.

CRINOIDEA. AIO

collectively to the “suranal” or dorsocentral plate of the Salenzade,
which is represented in the larvee of other Urchins; but it is now
generally admitted that the homologue of this plate in the Crinoids is
the plate supporting the discoidal base of the larval stem (fig. 288, @).
Succeeding the basals, and alternating with them, are one or more
cycles of plates, which are directly superimposed upon one another in
longitudinal rows, and which form the foundations of the arms. The
lowest of these, up to the first bifurcation, are known as the “ radials ”
(figs. 291, 292, 7), and are termed “ primary,” “secondary,” or “ter-
tiary ” radials, according to their distance from the basals. The last

Fig. 292.—Diagram of the dissected calyx of Rhodocrinus, a ‘‘ dicyclic” Crinoid, viewed from
Eo (after Schultze). 4, Underbasals; 4, Basals; 7, First radials; z, Interradials; a, Anal
plates.

)

radial plates, or those furthest from the column, are the “axillary
radials, and give origin to the lowest plates of the arms (“brachial ”
plates); or, if the cycle of the primary radials alone is developed,
the first brachials rest upon these. The “radial” plates are
arranged in a series of five vertical columns, which are, as the name
implies, radial in position; and the primary radials are homolo-
gous with the “ocular plates” in the apical disc of the Echinoids.!

1 From the strict morphological point of view, these primary radials are the
only plates to which the name ‘‘ radials” is applicable, all those which follow
them being really arm-joints (‘‘brachials’’). It is, however, convenient for
descriptive purposes to give the name of ‘‘ radials” to all those plates which are

420 PELMATOZOA.

Between the five columns of radial plates, corresponding with the
five arms, there may be intercalated certain other smaller plates,
which, from their position, are spoken of as “interradials” (fig.
292,72). When “‘interradials” are developed, one of the interradial
spaces, corresponding with the anus, is usually wider than the others,
and is furnished with an additional series of calcareous pieces, which
are termed ‘‘anal plates” (fig. 292, a).

As above mentioned, the first brachial plates rest directly upon
the highest row of radials; and the “arms,” therefore, spring from
the margins of the calyx, where the dorsal and
ventral surfaces join. ‘The arms are formed of a
single or double longitudinal row of “ brachial
ossicles,” the plates in the latter case alternating
with one another. The brachial plates are in
many cases traversed by a single or double canal,
which transmits the axial nerve-cord (fig. 287).
In most cases, the brachial ossicles are movably
articulated with one another, having their op-
posed surfaces separated by interarticular sub-
stance, and being provided with muscular fasci-
culi. In other cases, however, the arm-plates
are fixed in immovable junction by “syzygy,”
and may coalesce with one another. The arms
are primarily five in number, and they may re-
main simple. Most commonly, however, the

o arms are more or less branched, and they gener-

ig. 293.—Portion of , : abe
an arm of Platycrinus, ally carry on their sides short, jointed filaments
showing the lateral pin- or “ pinnules,” the structure of which repeats

that of the arms on a smaller scale (fig. 293).
Pinnulz may be wanting (as in Cyathocrinus), and it is not always easy
to distinguish between “ pinnules,” properly so called, and ‘‘ armlets”
(z.e., short divisions of the arms themselves) ; since the real distinc-
tion between these structures depends upon their contained soft parts,
and is therefore unavailable as regards fossil forms. The proper
“arms,” namely, lodge the sterile genital cord, while it is within
the pinnules that the fertile portions of the genital glands are con-
tained. Owing to the position of the reproductive glands beneath
the soft skin of the pinnules, it follows that there exists no gener-
ative opening, or ‘‘ ovarian aperture,” in the walls of the calyx, such
as 1s present in the Cystideans.

The ventral surfaces of the arms and pinnules, as in Comatua,
are furnished with furrows—the ‘‘ambulacral grooves” or “ food-

situated in the direction of the rays, as far as the first axillary joint ; and when
the arms are numerous, some authors speak of secondary and tertiary radials
according to the number of axillaries between the basals and the free arms.

CRINOIDEA. 421

grooves ”—which ultimately coalesce to form five primary grooves,
which are continued across the ventral surface of the disc to the
mouth (fig. 286, a). These ambulacral grooves, in living forms, are
ciliated, and along them currents of water are kept up, by which
organic particles are conveyed to the mouth. In a number of types,
including numerous extinct and a few living forms, the ambulacral
furrows are covered in superficially by two, or, more rarely, by four
rows of alternating calcareous plates of small size.

The upper or ventral surface of the visceral mass or disc is in
all living Crinoids, whether stalked or free, covered with a leathery
skin containing calcareous granules or plates, which are sometimes
scattered, but sometimes very closely placed ; and it exhibits the five
principal ambulacral grooves as generally open furrows passing from
the bases of the arms to the mouth (fig. 286, a). The mouth itself
is central in position, or, rarely, excentric (Actnometra), and may be
surrounded with five triangular “ oral plates,” which alternate with
the ambulacral grooves. In most Comatu/e, the oral plates are
present only in the early stages of development (fig. 288), and dis-
appear in the adult; though they are relatively large and well de-
veloped in Zhaumatocrinus. Almost all the Secondary and Tertiary
Crinoids resembled the ordinary living forms in the possession of a
plated ventral perisome and open ambulacral grooves; and hence
such forms have been grouped together by Dr P. H. Carpenter under
the name of ‘Neocrinoids.” In all recent Crinoids, further, the
upper surface of the body exhibits the aperture of the anus, which
is generally excentric, though central in position in some Actinometre,
and which is usually placed at the summit of a proboscidiform emin-
ence (fig. 286, A).

On the other hand, in the so-called ‘ Palzeocrinoids,” embracing
under this name all the Crinoids of the Paleozoic rocks, the upper
surface of the calyx rarely exhibits open ambulacral grooves, nor is
the mouth-opening generally exposed to view. On the contrary, the
oral aperture and food-grooves are more or less completely concealed
beneath a superficial plated covering, the structure of which varies in
different groups. In very many cases, as in the Actnocrinide,
Platycrinide, Rhodocrinide, &c., the ventral surface of the calyx is
roofed over by a flat or vaulted canopy of calcareous plates, which
are firmly united with one another, and completely conceal the sub-
jacent mouth-opening and ambulacral grooves. Five plates which
meet in the centre of this vault correspond to the “ oral plates ” of the
Neocrinoids. One of these is larger than the rest, and immediately
behind it the vault is perforated by a single, excentric, or, rarely,
central aperture, which is often prolonged into a tubular “ proboscis,”
and which is to be regarded as the anus. In all such cases, the
ambulacral grooves are continued beneath the above-mentioned

422 PELMATOZOA.

canopy, from the bases of the arms, across the ventral aspect of the
calyx, as somany tunnels. During life these lodged both the food-
grooves and the water-vessels beneath them, and there is evidence
that the latter opened into a circular vessel surrounding the mouth
and representing the circular ambulacral vessel of the Echinoderms
generally. Hence in specimens of such forms, where the arms have
been detached (figs. 294-296), the upper side of the calyx is seen

Fig. 294.—Calyx Fig. 295.—Calyx Fig. 296.—Calyx of A. Ver-

of Actinocrinus ro- of Actinocrinus Ko- neutllanus. The arms are
tundus. ninCki. . wanting, and the apertures of

the food-grooves at their bases
are seen.

to be covered with a plated dome, and the points of insertion of the
arms are marked by the openings of the food-grooves on their way
inwards to the concealed mouth.

In the great family of the Cyathocrinide, among the Palzo-
crinoids, the mouth and convergent food-grooves are concealed
from view by a vault which is chiefly composed of the “oral”
plates in the centre, together with the united covering-plates of the

ambulacra (fig. 297, A). These
el are all of a much less massive
f a ae . character than in the forms
a

(Js above mentioned, and are
c . a Soe

+—, readily destroyed. When these

tegminal plates have not been
: preserved—as is very common-
A B ly the case—then the upper

Fig. 297,—Upper surface of the calyx of Cy- Sunace of the Che (fig. 2975
athocrinus malvaceus, showing the superficial B) exhibits a large central peri-

plating of the disc preserved (A) and the same re- : : L:
moved (x). anz, Ambulacral grooves, in the one stomial opening, to which the

figure roofed in by a double row of minute ossi- five ambulacral grooves con-

cles, and in the other figure open; a, ‘Anal :

plate”; 0, Peristome; az, Anus. (After Zittel.) verge, together with an excen-
trically placed and often pro-

boscidiform anus. In this family, the peristome is surrounded by five

large calyx-interradials, of which one (the “anal plate,” fig. 297, a)

is excavated on one side, and corresponds with the anus. The

CRINOIDEA, 423

general structure of the “tegmen calycis” in the great Paleozoic
family of the Poreriocrinide is the same as in the Cyathocrinide, but
both the interradials and the “oral plates” are often inconspicuous,
or imperfectly developed. In these forms, also, the excentric anus
is prolonged into a proboscidiform tube, which is often of great
size (fig. 298).

As regards the classification of the Crinoids, the first well-ground-
ed systematic arrangement was that proposed by Johannes Miller,
who divided the order into the three
sections of the Zesse//ata, the Articulata,
and the Costata. The first of these
sections included the Palzozoic Crin-
oids, and its name was based on the
fact that in these the plates of the
calyx are united by sutures which do
not admit of movement. The section
of the Articulata, again, included the
living, Tertiary, and Secondary Crin-
oids (Marsupites alone excepted), in
which the calycine plates are mov-
ably articulated ; while the section Cos-
fata comprised only the aberrant Ju-
rassic genus Saccocoma. Zittel, in his
admirable ‘Handbuch der Palzeon- hace \
tologie,’ has followed Miiller’s classi- Nee Ce
fication, with various emendations and
modifications. Muller’s classification,
though a great advance upon that pro-
posed by his predecessors, cannot be
considered, even as modified by Zittel,
to be a strictly natural one, since forms
which agree in all the other main points =
of their organisation may differ as re- Fig. 208.—Calyx and part of the
gards the mode in which the calycine BES ql Oops radiains, show-
erate sjommed together. 9) Thus: the Sarhomcou. » (fer De Koninck
family of the Jchthyocrinide, though
closely resembling the other Paleeozoic Crinoids in its essential or-
ganisation, is characterised by the possession of movably articulated
radial plates, and thus should properly fall under the section of the
Articulata. The classification which will be here followed is that
adopted by Dr P. Herbert Carpenter and by Mr Charles Wachs-
muth, in which the C7vinordea are divided into the two primary
sections of the Paleocrinoidea and Neocrinoidea. In the division
of the Paleocrinoidea are comprised all the known Paleozoic
Crinoids, and the distinguishing characters of the division are,

SE;

Sg
oo)

A2A PELMATOZOA.

roughly speaking, that the calyx is disproportionately large and
massively constructed as compared with the arms, interradials
being usually present and often united with the radials in such
a way as to form a portion of the calyx; while the anal inter-
radius is specially developed, thus rendering the cup unsymmet-
rical. Moreover, the mouth and food-grooves are generally con-
cealed from view by the development of a more or less definite
“vault” above the proper ventral surface of the calyx. On the
other hand, the Weocrinoidea are all Secondary, Tertiary, or Recent,
and are roughly distinguished from the Palzeocrinoids by the com-
paratively small size of the usually symmetrical calyx and the pro-
portionately large development of the arms. The interradials, if
present, are rarely incorporated into the calyx, and with one excep-
tion (Zhaumatocrinus) an ‘‘anal” interradius cannot be recognised.
The higher radial plates are more or less movably articulated, and
do not enter into the composition of the calyx. Lastly, the ventral
surface of the visceral mass is not covered by a plated dome, but
the mouth and ambulacral grooves are exposed to view. Speak-
ing generally, the division Paleocrinoidea may be regarded as cor-
responding with Muller’s division of the Zesse//ata, while the section
LVeocrinoidea corresponds with the Avticulata and Costata of the
same author.

As regards the distribution of the Crinoids zz space, the order is
represented by comparatively few forms in recent seas, and these
have mostly a very local range. All the existing forms belong to the
division of the Neocrinoids, and the majority of them are referable
to the free-living family of the Comatufde, of which there are not far
from two hundred known forms, belonging to six genera (Aznfedon,
Actinometra, Atelecrinus, Eudiocrinus, Promachocrinus, and Thauma-
tocrinus). On the other hand, there are only about forty known
living types of the ‘‘ Pedunculate ” Crinoids, belonging to some half-
a-dozen genera (Pentacrinus, Rhizocrinus, Bathycrinus, Flyocrinus,
Metacrinus, and Holopus). ‘The Comatulide have a very wide range
in space, being found in almost all seas, but they are essentially
inhabitants of shallow water. Many of the living stalked Crinoids,
on the other hand, such as Bathycrinus and Hyocrinus, are only found
at great depths in the sea. They do not range, however, below
2500 fathoms, while one species of Anfedon occurs at a depth of
2900 fathoms.

As regards their distribution in time, the entire group of the
Paleeocrinoids is restricted to the Palzeozoic period, and may be said
to have attained its maximum development in rocks as ancient as
the Silurian. Throughout all Palzeozoic time the Crinoids are the
predominant types of the Echinoderms, and many of the Ordovician,
Silurian, Devonian, and Carboniferous limestones are so extensively

PALAZZOCRINOIDEA. 425

composed of the fragmentary remains of these organisms that they
may be properly spoken of as ‘“crinoidal limestones” and “ en-
crinital marbles.” The Permian formation (Dyas) is singularly poor
in remains of Crinoids, and the commencement of Mesozoic time
appears to have been signalised by the complete disappearance of
the Palzocrinoids, and the coming in of the Neocrinoids. The first
forms of this latter group make their appearance in the Trias (Excrinus,
&c.), and numerous types are known in the Jurassic and Cretaceous
rocks, but the Crinoids no longer play a part of such conspicuous
importance as we have seen to have been the case in the Palzeozoic
period. The earliest forms of the great modern family of the Com-
atulide appear in the lower part of the Jurassic system (Middle Lias).
The Tertiary formations are by no means rich in Crinoids, and the
comparatively limited recent Crinoidal fauna must be regarded as a
survival from the earlier part of the Mesozoic period, most of the
living types being closely connected with forms which existed at the
time when the Triassic and Jurassic deposits were laid down.

In the following synopsis of the families of the C7znxozdea, the char-
acters and distribution in time of the leading groups will be briefly
touched upon, but the less important families can only be defined
in the shortest manner possible. The arrangement followed is, in
the main, that adopted by Wachsmuth and Springer as regards the
Palzocrinoids and by Dr P. Herbert Carpenter as regards the Neo-
crinoids.

Division A. PALZOCRINOIDEA.

The division of the Pateocrinoidea corresponds with Miuller’s
division of the Zesse//ata, as redefined by Zittel, mus the two Meso-
zoic genera Marsupites and Uintacrinus. ‘The calyx in the Palzo-
crinoids is comparatively large, with massive plates, and is usually
unsymmetrical, the arms being proportionately small. Interradials
are usually present, while the anal interradius is specially developed
and is readily recognisable. A certain number of the plates above
the primary radials are, as a rule, “closely united to one another and
to the interradials, so as to form the walls of a relatively large and
substantial calyx” (P. H. Carpenter). The ventral surface is covered
by a more or less extensive vault, the centre of which is generally
occupied by the united oral plates, concealing the mouth and the
origins of the ambulacra (fig. 297).

Family 1. Actinocrinide.—The calyx in this family is always
“monocyclic,” there being three to five basals, but no “ under-
basals” (fig. 299). The plates of the cup are firmly united by
suture, and the radials take part in the formation of the calyx. In-
terradial plates are developed, and the lowest “anal” interradial
rests directly upon the basals. The arms may be uniserial or biserial

426 PELMATOZOA.

—i.e., they may consist of a single or double row of brachials—but
they are most commonly the latter. ‘The ventral surface of the
calyx is covered with a vault of heavy plates which are closely con-
nected together. The geological range of the family is from the
Ordovician to the Carboniferous inclusive.

The type-genus of this family is Actzzocrznus itself, in which the calyx,
though very variable in shape (figs. 294-296), always possesses three
basals, which form a hexagon, and are united superiorly with the five
primary radials and the lowest of the anal interradials. There are three
cycles of radials, and the highest radials carry each a double series of
brachial plates, which support the variously divided arms. There are
three or more anal plates, of which the lowest (fig. 299, a) always rests
upon the basals directly. There is a variable number of interradials,
and the column is round. The upper surface of the cup is vaulted over
with calcareous plates, and the brachial grooves are continued beneath
the vault thus formed, as so many
tunnels, to the central and con-
cealed mouth. The anus may or
may not be extended into a pro-
boscis, and it is sometimes very
excentric, sometimes subcentral.
It has been shown that in some
of the Actinocrinide (as in forms
belonging to other families) there
exists in the interior of the calyx
a singular convoluted calcareous
plate, of a reticulated texture,
shaped somewhat like an ordin-
ary Bubble-shell (BzZ/a), occupy-
ing the vertical axis of the body,
and often of large size. This has
been compared with the calca-
reous structures present in the
” te ‘“‘sand-canal” of various Echino-
Action (her Sohatees He agaRs Sf derms ; but it is probably rather
Radials; z, Interradials; a, The lowest of the an extreme development of, the
anal plates. discoidal calcareous plates which

; have been described as strength-
ening the double wall of the spirally-twisted alimentary canal in the
living Comatule. The genus Actinocrinus appears to commence in
the Silurian, and is also represented in the Devonian; but it attains
its maximum in the Carboniferous, and is wholly unknown in later
deposits. Agaricocrinus and Batocrinus are Carboniferous forms very
closely allied to Actznocrinus. The Silurian genera Periechocrinus and
Megistocrinus are close allies of Actinocrinus, and the Carboniferous
Aniphoracrinus and Dorycrinus only differ from it in comparatively
trifling particulars.

In the Silurian and Devonian genus MJelocrinus, there are four or
three basals, the lowest anal plate is separated from the basals by the
primary radials, and the arms are in the form of five free rays giving off
lateral armlets. <Ae/ocrinus is often regarded as the type of the separate
family of the Melocrinéd@, to which Wachsmuth and Springer also refer
the genus Glyftocrinus, which will be briefly noticed later.

PALAOCRINOIDEA. 427

Among the other genera of the Acténocrintde@ may be mentioned
Stelidiocrinus, Briarocrinus,and Carpocrinus, which have been regarded
as the types of as many families, and all of which are found in the
Silurian rocks.

family 2. Barrandeocrinide.—This family has been founded by
Angelin for the reception of the single genus Barrandeocrinus, which
occurs in the Silurian rocks of Gotland. In this genus the arms
are arranged in pairs, and are reflexed in such a way that their
dorsal surfaces rest upon the outer surface of the calyx, while they
are at the same time confluent laterally.

family 3. Platycrintide.— This family is characterised by the
possession of a ‘‘monocyclic” calyx, with three, or sometimes two,

|

|

|

ll

i
i

Fig. 300.— Platycrinus tricontadactylus. Carboniferous. The left-hand figure shows the
calyx, arms, and upper part of the stem, and the figure next this shows the surface of one of the
joints of the column. ‘The right-hand figure shows the proboscis.

basals and five radials. There are from three to five plates in each
interradial space ; but the anal interradials do not come in contact
with the basals, except in some forms (Hexacrinus). ‘The arms are
at least ten in number (fig. 300), and may be uniserial or biserial.
The column is round or elliptical, and the neurovascular axial canal
is of small size. The geological range of the family is from the Silu-
rian to the Carboniferous inclusive, but the maximum development
is attained in the Carboniferous Limestone.

The type-genus of the Platycrintde is Platycrinus itself, in which the
cup is composed of three basals and a single cycle of radials, amongst

428 PELMATOZOA.

which the anal interradial is not intercalated. The succeeding radials
are embraced in the free arms, and do not form part of the calyx. The
arms are numerous and bifurcated, and all the divisions carry pinnules.
There are three or five interradials in each of the interradial spaces, and
there may be one large, or three small anal plates. The column is rounded
near the calyx, but its lower joints are oval and compressed. There is,
typically, a large anal proboscis. In connection with the proboscis of
Platycrinus, we may just notice the well-known fact that in many speci-
mens (as is the case with other Crinoids possessing a similar elongated
anal tube) there is found in close apposition with the proboscis, and often
placed upon its actual summit, the shell of a fossil Univalve (apparently
almost always, or always, a species of Platyceras). It was originally
supposed that the Crinoid had been fossilised in the act of eating the
Mollusc—the anal tube being regarded as the mouth—but all the living
Crinoids feed upon microscopic animalcules, and this supposition is
therefore, Aza facze, an improbable one. It has also been shown by
Meek and Worthen that the P/atyceras must have lived for a long time
attached to the proboscis of the Crinoid, since the lip of its shell has
closely adapted its form to that of the surface to which it is attached.
We may therefore safely accept the conclusion reached by these
observers, that the P/atyceras was in the habit of attaching itself para-
sitically to the side or summit of the proboscis of Platycrinus and other
Crinoids, thus obtaining a share of the minute animalcules upon which
its host lived.

The genus Platycrinus, as defined by Wachsmuth and Springer, is
almost entirely confined to the Carboniferous period, being represented
by many species in the Carboniferous Limestone. One or two small
forms, however, occur in the Devonian. The genus Hexacrinus is
closely allied to Platycrinus, but it possesses a large anal plate, which
rests directly upon the basals (as in Actinocrinus). The genus is strictly
Devonian, and the species are mostly European.

By Wachsmuth and Springer the genus Hevxacrinus is regarded, prob-
ably correctly, as the type of the distinct family of the Hexacrinzde, to
which they also refer Hystricrinus and Dichocrinus. Of the remaining
genera of the P/atycrinzde@, the only one which needs special mention is
the somewhat aberrant Ordovician and Devonian genus Coccocrinus. In
this genus, the vault is entirely formed by five large oral plates, which
rest upon the interradials and conceal the mouth.

Family 4. Rhodocrinide.—The forms included in this family have
a dicyclic calyx (fig. 292), but the underbasals may be very small,
and are sometimes completely concealed from external view (Glypzo-
crinus). The underbasals are usually five in number, sometimes
three: and there are five basals. Interradials are well developed,
but the anal interradius is ‘‘scarcely distinct” (Wachsmuth and
Springer). A very characteristic feature, however, is that the first
radials are separated by interradials which rest upon the basals.
The arms may be uniserial or biserial. The species of this family
range from the Ordovician to the Carboniferous inclusive.

The type-genus of this family is Rodocrznus itself, which ranges from the
Silurian to the Carboniferous. The underbasals in this genus (fig. 292)
are five in number, and are well developed. The five lowest interradials

PALZOCRINOIDEA. 429

rest upon the basals, and form with the first radials a ring of ten plates ;
while the arms, varying in number from ten to twenty, are bifurcated two
or three times during their course. Allied to Rhodocrinus is the genus
Ollacrinus (Gilbertsocrinus) of the Carboniferous Limestone.

The genus G/yftocrinus has been commonly referred to the Rhodocrin-
zd@, but it is now placed by Wachsmuth and Springer in the Zelocrinide,
while other authorities regard it as the type of a separate family (Glyf/o-
crintd@). In this genus, the turbinate calyx possesses underbasals, but
these are of small size, and may be quite rudimentary. The calycine

Fig. 301.—a, Calyx and arms of Eucalyptocrinus rosaceus, viewed trom one side, of the
natural size—Devonian (after Schultze); 8, Calyx of Glyptocrinus basalis, viewed from one side,
of the natural size—Ordovician (after M ‘Coy).

plates are ornamented with characteristic radiating ridges (fig. 301, B) ;
the arms are uniserial ; and the column is annulated or moniliform. All
the species of Glyptocrinus appear to belong to the Ordovician period.

Family 5. Calyptocrinide.—In the remarkable forms included in
this family, the calyx is regular and ‘“‘monocyclic,” flattened or
hollowed out basally, and passing superiorly into a flask-shaped
tegmen, which is narrowed above, and terminates in a centrally
placed anal aperture surrounded by regularly arranged polygonal
plates. The arms are, typically, twenty in number, biserial, and
not projecting beyond the level of the upper limit of the calyx ; and
they are situated between riblike processes of the upper margin of
the cup, or in special lateral niches formed by vertical outgrowths
from the wall of the calyx. The members of this family are exclu-
sively confined to the Silurian and Devonian formations, the prin-
cipal genus being ELucalyptocrinus.

In Eucalyptocrinus (fig. 301, A), the calyx is inverted upon itself, the
calycine cup being deeply concave at its base, so as to look like the bot-
tom of a wine-bottle. Within this basal funnel are situated the four small
basals, which are succeeded by five large primary radials. These are
strongly bent, one-half of each passing up into the basal funnel, while
the other half appears on the lower and lateral aspects of the cup. Two
other rows of radials succeed these, the tertiary radials being unusually
large, and each supporting the bases of two arms. The interradial

430 PELMATOZOA.

plates are developed in a most singular manner, so as to form a series of
five linear, clavate processes, which separate and support the arms ; five
other precisely similar processes being borne by the axillary radials.
The arms thus come to lie in deep grooves
or niches in the sides of the calice, the
upper surface of which they do not reach.
The upper surface is completely vaulted
over, and is mainly formed by the upper
ends of the ten interbrachial processes
just spoken of, in the centre of which is a
small circular anal aperture, surrounded by
five or more plates. The species of Euca-
lyptocrinus are found in the Silurian and
Devonian rocks; and the Silurian genus
Flypanthocrinus differs principally from the
preceding in the fact that the base of the
calyx is not funnel-shaped. The Silurian
genus Corymbocrinus (fig. 302) has been
likewise placed in the neighbourhood of
Eucalyptocrinus, but is now considered by
Wachsmuth and Springer as belonging
rather to the family of the Actinocrinide.
In this genus the calyx resembles that of
Eucalyptocrinus in having a deep funnel-
Pa See sage ok and arms of shaped depression at its base, but the
orymbocrinus polydactylus. Wen -
lock Limestone of Britain. (After arms are long and much divided. Lastly,
M‘Coy.) the genus Cad/icrinus, also Silurian, is in
most structural features closely allied to
Eucalyptocrinus, and appears to represent an earlier phase in the devel-
opment of the family.

family 6. Crotalocrinide.—In this small and remarkable family,
the calyx is “‘dicyclic,” with small underbasals and large basals.
The arms are uniserial, without pinnee, but furnished with numerous

Fig. 303.—a, Calyx and arms of Cvrota/ocrinus Loveni, cut across to show how the arms
are rolled up; B, A portion of the network formed by the arms, enlarged. Silurian. (After
J. Miller.)

branches, by the coalescence of which they become more or less
extensively connected with one another laterally, generally forming
wide, inrolled, foliaceous expansions. The anus, so far as known,
has the form of an excentric, proboscidiform, plated tube. The

PALZZOCRINOIDEA. 431

centre of the vault is occupied by five oral plates, while the
ambulacral grooves of the arms and their lateral branches are
covered in by small calcareous plates. The genera of this family are
Silurian, but C7lezocrinus, if rightly referred here, is Ordovician.

The type-genus of this family is Crotalocrinus (Anthocrinus), one of
the most beautiful Crinoids of the Wenlock Limestone of Gotland and
Britain. The calyx consists of five small underbasals and five large
basals, with a single zone of radials, while interradials are wanting,
with the exception of a single small anal plate. The arms are bifur-
cated, and the subdivisions unite with one another by means of lateral
processes, thus giving rise to a network, perforated by numerous aper-
tures (fig. 303). The Silurian genus E7allocrinus is nearly allied to
Crotalocrinus, but the arms become free towards their extremities.

Family 7. Ichthyocrinide.—In this family the calyx is ‘‘ dicyclic,”
but the three underbasals are
small, and are mostly not visible
externally. The radials articu-

F

Basfn sos
late upon one another, and are apeee geo
= . a) tl
united laterally by the peri- 2a fe Spee ee
somic plates of the disc. The SAS eee

ee ese Sees 5
arms are short, bifurcating, and soe Eee
often in contact laterally, thus Be. al boe &

ae i

forming an upward continua-
tion of the calyx (fig. 304, a);
while pinnules are apparently
wanting. The disc had open
ambulacral grooves, and was
covered with perisomic plates,
like that of a recent Crinoid. zi
Its central part was occupied RS 7B
by five oral plates, which in Fig. 304.—a, Side-view of the calyx of /chthyo-

some species, if not in all, crixus /evis, from the Silurian (Niagara Lime-
, f stone) of North America; n, Calyx and upper
were separate irom one another, part of the column of Taxocrinus tuberculatus,

from the Silurian (Wenlock Limestone) of Brit-
so as to open the mouth to the in” ‘(Arer Hall and MCoy.) bgt Bri
exterior. The members of this
family are found in the Silurian, Devonian, and Carboniferous

deposits.

oe
LX) 0

The typical genera of the /chthyocrintde—such as Ichthyocrinus itself
(Silurian to Carboniferous), Lecanocrinus (Silurian and Devonian), and
Mespilocrinus (Carboniferous)—are characterised generally by the im-
perfect separation of the calyx and arms, the latter being commonly
in close apposition laterally (fig. 304, A). On the other hand, the genus
Taxocrinus (fig. 304, B) represents a section of the family—sometimes
raised to the rank of a separate family (Zaxocrinid@)—in which the
arms are well developed and repeatedly bifurcated. The species of
Taxocrinus are found in the Silurian, Devonian, and Carboniferous

AB? PELMATOZOA.

rocks ; and the genus /orbestocrinus, with a similar geological range,
is principally distinguished from this by the more abundant develop-
ment of the interradial plates.

family 8. Haplocrinide.—In this family the calyx is small and
spheroidal, and is composed of basals and radials, underbasals
being absent. The ventral surface of the calyx exhibits five large
“oral” plates, forming a low pyramid, which is excavated along the
sutures of the plates to receive the bases of the arms (fig. 305).
There is no definite anal plate, but the anal opening perforates one
of the oral plates, which is somewhat larger than its fellows. The
arms are poorly developed. The family, as defined by Wachsmuth
and Springer, includes only the two genera Hafplocrinus (fig. 305)
and Adl/agecrinus, of which the former is mainly if not wholly De-
vonian in its range, while the latter is exclusively confined to the

Fig. 305.—Haplocrinus meespiliformis. The calyx viewed from below, from one side,
and from above, and enlarged. Devonian.

Carboniferous rocks. Both genera comprise very small Crinoids,
which are in some respects simpler in their construction than the
normal members of the order, and may be considered as perma-
nently representing the larval condition of the Paleeocrinoids.
Allagecrinus is remarkable for the inequality in the size of its
radials, some of which may be axillary and bear two arms. For
this reason it is regarded by some authors as the type of a distinct
family.

Family 9. Symbathocrinide.—In this family the calyx is small,
and is composed of basals and radials only. The central portion
of the ventral surface of the calyx exhibits a circle of oral plates.
The arms are uniserial, exceedingly long, and folded together. The
principal genera of this family are Syméathocrinus (Devonian and
Carboniferous), Prsocrinus (Silurian), and Z7zacrinus (Devonian and
Carboniferous).

Family 10. Cupressocrinide.—In this family the large, basin-shaped
calyx is apparently of the “dicyclic” type, the underbasals being
anchylosed to form a solid disc, which some authors regard as
being an enlarged top stem-joint, in which case the calyx would
be “monocyclic.” Upon this disc rest five basals, followed by
five radials, the upper edges of which are truncated and form a

PALZOCRINOIDEA. 433

horizontal line. Reposing directly upon the radials are the five
first brachials, which are as wide as the radials, but are of very
small vertical thickness. The arms are mas-
sive, moving as in one piece, uniserial, and
undivided. They gradually diminish towards
their apices, and by the accurate apposition
of their edges together, form a pentagonal
pyramid. The arm-plates bear numerous
small and incurved pinnules, six or more on
either side of each joint. These roof in the
deep ambulacral grooves, which seem also to
have had a definite calcareous skeleton of
their own. Between the bases of the arms,
in the interior of the cup, is placed a so-called
“consolidating apparatus,” formed of five
laterally anchylosed calcareous pieces, which
apparently really represent “the united
muscle-plates of the radials” (P. H. Car-
penter). This peculiar apparatus covers the Fig 306.—Side-view of the
greater part of the ventral surface of the (7° CF REG,
calyx, and the mouth appears to have been ofthe naturalsize. Devonian.
a. eee (After Schultze.)

placed in its centre. The column is obtusely

quadrangular, annulated, and traversed by a large central canal
surrounded by four smaller tubes.

The only genus of this family is Cugressocrinus itself, the species
of which are exclusively Devonian, and appear to have been wholly
confined to the European area. The characters of the genus need
not be more fully discussed, the principal ones having been men-
tioned in the diagnosis of the family.

family 11. Gasterocomide.—in this family the calyx (fig. 307) is
small and spheroidal, and is typically dicyclic, the underbasals

WAIN AW
\\ MY
WK GC

Fig. 307.—Gasteroconta antigua, from the Devonian rocks of the Eifel, enlarged twice. a,
The calyx viewed from the side; 4, The anal aspect of the calyx; c, The ventral surface of the
calyx. (After Schultze—copied from Zittel.)

being usually represented by a simple pentagonal plate. ‘This plate

may, however, be merely an enlarged top stem-joint (as in Cupres-

socrinus), and Zittel regards Manocrinus as being monocyclic. ‘There

are five basals, and generally an equal number of radials, with one
WOL. 1. 2 E

A34 PELMATOZOA.

or more interradials in the anal interradius. In /Vanocrinus, how-
ever, there are only four arm-bearing radials, one of which is
axillary. In the type-genus Gasterocoma, one of the basals is
notched for the anal opening, which is situated between it and the
first anal plate. The arms are recumbent or widely divergent, and
the stem is generally four-sided, and is perforated by four canals,
surrounding, or confluent with, a larger central canal. The two
principal genera of this family are Gasterocoma (Epactocrinus) and
Nanocrinus, both of which are found in the Devonian deposits of
Europe.

family 12. LHybocrinide.—The members of this small family
exhibit embryonic characters, and have a ‘‘monocyclic” base,
with imperfectly developed radials, and a very small ventral sac.
The basals are five in number, and are very large. The arms are
simple and without pinnules; and one or more of them may be
undeveloped, or only represented by recurrent ambulacra which
run over the outer surface of the calyx. The genera included
by Wachsmuth and Springer in this family are Hybocrinus, Hybo-
cystites, Hloplocrinus, and Baerocrinus, all of which are confined to
the Ordovician rocks.

Family 13. Heterocrinide.—In this family are comprised Paleo-
crinoids with a relatively large ventral and small dorsal development
of the calyx. ‘The basis, as in the preceding family, is ‘‘ monocyclic,”
thus differing from that of the Cyathocrintde and Poteriocrinide, in
which underbasals are present. The arms are much more developed
than in the “ydbocrinide, and are furnished with long pinnules. The
principal genera are Heterocrinus and Stenocrinus, both of which are
found in the Ordovician rocks of North America.

Family 14. Anomalocrinde.—tIn this family the only genus is
Anomatlocrinus, the species of which are found in the Ordovician
rocks of North America. The calyx in this genus is large and
depressed, with a ‘‘ monocyclic” basis. The pinnules of the arms
are not given off alternately from opposite sides (as in Crinoids
generally), “‘ but from every successive joint on one side at a time, ~
from one bifurcation to the next, where they change on both rami
to the opposite” (Wachsmuth and Springer).

Family 15. Belemnocrinide.—The only genus included in this
family is the Belemnocrinus of the Carboniferous Limestone of North
America. In this genus, the basis is ‘‘monocyclic,” with no under-

basals, but with relatively large basals. The ventral side of the
calyx is well developed, but the visceral cavity is extremely small.
There is an anal plate placed in a line with the radials. The anal
proboscis is large and porous. Lastly, the pinnules of the arms are
given off regularly at every second or third joint, and not alternately
from all the brachials. According to Wachsmuth and Springer, the

PALZOCRINOIDEA. 435

genus forms a connecting-link between the e/erocrinide and the
Cyathocrinide.

Family 16. Cyathocrinide.—In this important family of Crinoids,
the calyx is irregular, and is of the “‘ dicyclic” type, consisting of five
underbasals (fig. 308, 4), five basals (J), five primary radials (7), and
from one to three anal interradials (2). The ventral surface of the
calyx is mainly formed by the large interradial plates, between which
are the ambulacral grooves, roofed over with small calcareous plates
(fig. 297). The arms are uniserial, long, repeatedly bifurcated

Fig. 308.—a, Diagram, showing the dissected calyx of Barycrinus (after Hall): 4, Under-
basals; 2, Basals; 7, Lowest of the three radials (‘‘ primary radials”); a, Anal plate. B, Calyx
and part of the arms of Cyathocrinus planus, of the natural size. Carboniferous.

(fig. 309), and without true pinnules. The family of the Cyatho-
crinidé is Closely allied to that of the Poteriocrinide, but the arm-
joints are differently articulated in the two, and the arms are repeat-
edly bifurcated in the former group; whereas in the latter the arms
may remain simple after the first bifurcation, or branch irregularly,
and they, further, carry pinnules. The range of the Cyathocrinide in
time is from the Silurian to the Permian inclusive.

The principal genus in this family is Cyathocrinus itself (fig. 309),
which ranges from the Silurian to the Permian, but attains its maximum
development in the Carboniferous Limestone. In this genus the calyx
is small and basin-shaped, with long, frequently divided arms. The
ventral side is slightly convex, and a plated anal tube is present. The
column is round, and is composed of very narrow articulations, which
are perforated by a five-angled neurovascular canal. Barycrinus, of
the Carboniferous rocks of North America, is nearly related in most
respects to Cyathocrinus; while Dendrocrinus (Ordovician), Caradbo-

436

PELMATOZOA.

crinus (Ordovician), and Homocrinus (Silurian and Devonian) are other
leading genera of this family.

family 17. Potertocrinide.—In this family the calyx is “ dicyclic,”
and is essentially similar to that of Cyathocrinus, consisting of five
underbasals, five basals, five primary radials, and from one to

WSK

OTA eS + 5
Peat Agee Oem SB)
ppned) SRNL

aOR ea rineree yea:

DIL jg uevUS aCe

Wo

TESS 4

eA
M
Le.

WON

=
wane
SAS JSPR AN -,
NYS Sines SARE Sakae
N VSs San Fae
TH 7 '\ errr ~ S se
Si ae poe) IS OSS
as ERNEST SEGA y TSS
a SSS ADA RIA NS aes ; ANGST
PN . Ns > CN
EZ
Ot)
(}
ep,
Bs om of
su

vt ie
ig Sf!
t

, Wh, h- Z ey) >
Ws HY), “fi \) i
ee, Sv Vy
\ Vid iH | 1)
hi lh
i Ws pop

Fig. 309.—Side-view
of the calyx and arms
of Cyathocrinus longi-
manus, of the natural
size, Silurian. (After
Angelin — copied from
Zittel.)

arms are provided with long pinnules.

five interradials (fig. 291). The arms are simple
or bifurcated, and carry long pinnules. The ven-
tral surface of the calyx is elevated and convex,
and a greatly developed anal tube or proboscis is
usually present (fig. 298). The genera of this
family appear to be principally, if not wholly, con-
fined to the Devonian and Carboniferous rocks,

by far the larger number of forms belonging to
the latter.

The principal genus of this family is Poferiocrinus
itself (fig. 298), which is closely allied to Cyathocrinus,
from which it 1s distinguished principally by the more
elevated form of the ventral sac, the great develop-
ment of the anal tube, and the structure of the arms.
These latter organs may be simple or branched, but
in either case are provided with pinnules, while the
radials are truncated superiorly, where they articu-
late with the brachials. On the other hand, in
Cyathocrinus the arms are without pinnules, and
the first radials (fig. 308, 7) articulate with the second
by means of horse-shoe-shaped facets. The species
of Poteriocrinus are mainly Carboniferous, but a few
forms are known from the Devonian rocks. Closely
allied genera are Zeacrinus (Carboniferous) and
Scaphiocrinus (Carboniferous and Devonian).

Family 18. Astylocrinide.—The calyx in this
family is free, the peduncle of the larva being
evanescent ; and it is composed of firmly united
massive plates (fig. 310). Typically, the calyx is
“ dicyclic,” but &driocrinus, if rightly referred
here, has no underbasals. ‘There are two cycles of
radials, the second of which is axillary, and the
Anal interradial plates are

developed, and the dorsal side of the calyx does not carry cirri. The
type-genus of this family is Agasstzocrinus (= Astylocrinus), which

is found in the Carboniferous Limestone of North America.

The

genus L£ariocrinus, from the Silurian rocks of North America, has
also been provisionally placed in this family by Wachsmuth and

Springer.

In Agasstzocrinus (figs. 310, 311) the calyx was attached in its early
condition by a larval peduncle, but the adult was free.

The underbasals

PALEOCRINOIDEA. A37

become united to form an almost solid disc, which is slightly hollowed
above, and exhibits a group of pits, which probably lodged extensions of
the “ chambered organ.” The Silurian genus La7zocrinus was also free
in its adult condition, but underbasals are wanting, and it possesses other
peculiarities as well.

Family 19. Catillocrinide.—In this small family, the calyx is of
small size and of the “ monocyclic” type. The radials are remark-
ably unequal in point of size, two of them being greatly developed,
and forming the larger part of the margin of the calyx. These carry
a much larger number of the arms than the three small radials.
‘The arms are simple, uniserial, and long, and the column is round.

Fig. 310.—Side-view of a complete Fig. 311.—Dissected calyx of Agassizocrinus. 3,
example of Agassizocrinus dactyli- Underbasals; 4, Basals; 7, Radials; a, Anal plates.
Jormis (=Astylocrinus levis, F. (After Hall.)

Roemer). Carboniferous, North Am-
erica. (After Meek and Worthen.)

The type-genus is Cazz//ocrinus, the geological horizon of which is
the Carboniferous rocks of North America.

family 20. Calceocrinide (= Chetrocrinde).—This family includes
only the aberrant genus Calceocrinus ( == Chetrocrinus), which ranges
from the Ordovician to the Carboniferous. In this genus the small
and irregular calyx, with its crown of arms, is fixed in such a way as
to hang downwards from the summit of the column. The calyx is
“monocyclic,” and there are only three basals, which, in the natural
position of the cup, are situated posteriorly. The radials are of un-
equal size, only three of them bearing arms. The basals and radials
are united by ligaments and muscles, so that a distinct articulation
is formed at this point in the cup. The arms are bifurcated, and
those on the posterior side are the strongest.

438 PELMATOZOA.

DIvIsIon B. NEOCRINOIDEA.

This division of the C7vnotdea corresponds with the Articulata of
Miiller (with the addition of the genera AZarsufites and Uintacrinus),
together with the Costata of the same author. As defined by Dr
P. Herbert Carpenter, the forms included in the /Veocrinotdea possess
a relatively minute, usually symmetrical, regularly pentamerous calyx,
the arms being in general greatly developed. There are, as a rule,
five equal and similar basals, and five also equal and similar radials.
Underbasals are rarely present (Zcrinus, E-xtracrinus, and Marsu-
pites). Interradials are rarely developed, and, when present, no
special “‘ anal” interradius (except in Zaumato-
crinus alone) is recognisable. The higher radials
do not enter largely into the composition of the
calyx, and are usually more or less movable,
being generally united to the succeeding plates
by a muscular articulation. ‘The ventral surface
of the calyx is not concealed by an external

canopy or vault of calcareous plates, but the
fs = aperture of the mouth, with the ambulacral
grooves converging to it, is exposed to view.
The ambulacral grooves may be more or less
roofed in by calcareous plates, and “oral” plates,
when present, ‘“‘may be limited to larval exist-
ence, or remain through hfe partially covering
the peristome, but capable of being separated
so as to open the mouth to the exterior” (P.
H. Carpenter). All the Neocrinoids are Second-
ary, Tertiary, or Recent, no Paleozoic represent-
atives of the division being at present known.

Family 1. Encrintde.—In this family the calyx
is shallow and basin-shaped, with a “ dicyclic”
basis. There are five underbasals, which are
of very small size, and are concealed by the
uppermost joint of the column. ‘These are
succeeded by five large basals, followed in turn

Fig. 312.—Encrinus by five radials, the whole of these plates being
liltiformis. _ Muschel- firmly united by suture. The primary radials are
kalk. The lower figure : ; F
shows the articulating followed by two others, the second of which is axil-
eee Le ia the lary and bears two arms, which sometimes fork

again, so that there are ten, or, rarely, twenty divi-
sions in all. The arms (fig. 312) are often biserial, are abundantly
furnished with pinnules, and form by their apposition a kind of
pyramid. The upper column-joints (fig. 312) are generally alter-
nately large and small. The joint-surfaces are furnished with

9991999999 9S.
Se

5
HG

a

ay

set

a)

aa

Jb
3
4

aid
‘

Zz
Spud
3

i
WY,

2449

NEOCRINOIDEA. 439

radial ridges, and each exhibits in the centre a small round or
pentagonal neurovascular canal (see the lower figure in fig. 312).
Lastly, the visceral mass was enclosed in a plated perisome essen-
tially similar to that of the recent Crinoids.

The only clearly established genus belonging to this family is
Encrinus itself, all the species of which are Triassic. <A well-known
species of this genus is the Lily-encrinite (Z. “Ziiformus, fig. 312),
the heads of which are not very rare in some localities in the
Muschelkalk of Germany.

Family 2. Lugeniacrinide.—In this singular family, the calyx
(fig. 313) is apparently composed only of primary radial plates,
which rest directly upon the enlarged uppermost joint of the column.
Basals have not been detected, but it is prob-
able that they were present in a rudimentary
form. There are two additional rows of radials,
which bear ten uniserial arms, and the base of
the column is expanded, and serves to cement
the animal to foreign bodies. The geological
range of the family is restricted to the Jurassic
and Cretaceous rocks.

The principal genus of this family is Awgenza-
crinus itself (fig. 313), which occurs in the
Jurassic and Cretaceous deposits of Europe.
The column-joints and clove-shaped calyx of
species of this genus are not uncommon, but
the arms have never been found attached to the
cup, and no example of a complete calyx has @2Ne 2 aN
yet been detected. rN peas iy Nes

Family 3. Holopide.—In this aberrant fam- ee eae
ily the calyx is without a column, and is __ Fig. 313.— E£ugeniacri-

- : nus caryophyllatus, with-
firmly adherent to foreign bodies by the un- out the arms, restored.
der surface of the wide cup. The basals are eee a
fused with one another, and usually with the
radials also, in which latter case the presence of distinct basals can
only be inferred. The arms (where known) are thick, massive, and
spirally inrolled.

In the recent genus Aolopfus the basals and radials are “‘ com-
pletely anchylosed into an asymmetrical tube-like calyx, which is
fixed by an irregularly expanded base” (P. H. Carpenter). Allied
to this extraordinary living type are a few fossil forms from the
Mesozoic and later Tertiary deposits. Of these the genera Cotyde-
crinus (Cotylederma) and Ludesicrinus are confined to the Lias ;
while Cyathidium is found in the late Cretaceous deposits (Faxoe
Limestone) and in the Eocene Tertiary.

family 4. Hyocrinide.—This family includes only the living

440

PELMATOZOA.

genus Hyocrinus, which is in some respects related to the Palzo-

Fig. 314.—A piocrinus
Rotssyanus. Middle Oo-
lite (Jurassic).

crinoids. In this genus the calyx-plates are thin,
and the cup consists of both basals and radials,
the former being only three in number. The
radials are five in number, and each carries a
single undivided arm. The arm-joints are united
by “‘syzygy” into groups of two or three, the
terminal joint of each group bearing a long pin-
nule. There are five large “oral” plates round
the mouth. The stem consists of short cylin-
drical joints, the articular surfaces of which are
simple or slightly striated.

family 5. Plicatocrinide.—This family in-
cludes only the Jurassic genus P%catocrinus,
which is considered by Zittel as nearly allied to,
or identical with, Ayocrinus. Basal plates are,
however, said to be absent; while the arms are
short, and the joints are not united by ‘“‘syzygy,”
and are provided with short pinnules.

family 6. Aptocrinide.—In this family the
calyx is regular, and the upper stem-joints are,
typically, wider than those below, the upper
part of the column thus passing gradually into
the base of the cup. The basals (are)iiveram
number, and are surmounted by three cycles of
radials, each cycle being normally pentamerous.
The stem is expanded at its base for attachment
to foreign bodies, or is furnished with branching
roots or cirri (fig. 314), and the apposed faces
of its component joints are marked with radial
strie. The earliest types of this family (4Zz0-
crinus and Millericrinus) appear in the Jurassic
rocks, and became extinct in the Lower Creta-
ceous period.

In the genus Apzocrinus, comprising the so-called
““ Pear-encrinites,” there is a long cylindrical stem,
rooted to foreign bodies by an expanded base (fig.
314). The upper joints of the stem are narrower, as
regards vertical height, than the lower ones, while
they are widened out laterally, so as to pass gradually
into the massive pyriform cup. The uppermost joint
of the stem is much enlarged, and carries the five
basals, which are in turn succeeded by three rows of
radials. The species of Afpzocrinus are found in

the Jurassic and Lower Cretaceous rocks. In the genus J/2llerecrinus,
with a very similar geological range, the upper stem-joints are only

NEOCRINOIDEA. 441

very gradually widened out, and the top one is not very greatly larger
than those below it.

family 7. Bourgueticrinide.—In this family the calyx is very
simple, consisting of five basals and five radials. The stem-joints
are dice-box-shaped, their faces bearing transverse ridges with fossze
at their sides which lodge the interarticular igaments. The stem
is attached below by a branching root or by radicular cirri, and
there are five or ten slender arms, the joints of which are united
in pairs, with a pinnule on the distal joint of each pair only. The
disc bears five oral plates of variable size, and the brachial ambu-
lacra have two rows of covering-plates.

This family differs essentially from the Afzocrinzde in the relatively
small size of the calycular cavity and in the more or less dice-box-
shaped character of the stem-joints. In the type-genus Bourguetz-
crinus there is a small pyriform calyx, passing gradually downwards
into the thickened upper part of the stem, the top joints of which are
much enlarged, while it is fixed below by a root-like prolongation.
Bourgueticrinus is essentially a Cretaceous genus, but has been de-
scribed as occurring both in Jurassic and in Tertiary strata, solely,
however, on the very uncertain evidence afforded by stem-joints. The
family is represented by two living genera. Aathycrinus ranges from
Iooo to 2400 fathoms in the Atlantic, but is not yet known in the
fossil state ; while RAzzocrinus, which occurs at smaller depths, ranges
back to the Eocene Tertiary. In the former type the basals are small
and firmly united, while the radials are long and comparatively free, and
there are ten arms. On the other hand, Af%zzocrinus has long basals
and short, closely united radials, as in Bourgueticrinus,; while there are
but five arms, the joints of which are united by “ syzygy,” only the upper
joint of each pair bearing a pinnule. In both genera the upper stem-
joints are thin and discoidal, while the ambulacral furrows of the arms
and pinnules are protected by delicate calcareous plates. The disc of
Rhizocrinus is, further, covered by large “ oral” plates, which are much
reduced or absent in Bathycrinus.

Family 8. Pentacrinide.—This family is defined by Dr P. H.
Carpenter as comprising forms in which the calyx is small relatively
to the stem and arms, and is “composed of five basals and five
radials, with underbasals in one genus. ‘The rays divide from one
to eight times. The stem bears verticils of cirri at intervals. Two
joints are united by syzygy at each node, to the upper one of which
the cirri are articulated. The internodes are traversed by five liga-
mentous bundles, which are interradially disposed, and give rise to
a more or less petaloid figure on the joint-faces. No root nor
radicular cirri.” The range of the family is from the Trias to the
present day.

The type-genus of this family is Pestacrinus itself, which has the

geological range of the family. In this well-known genus (fig. 289) the
joint-faces of the pentagonal stem are marked by crenated ridges

A42 PELMATOZOA.

arranged in a floriform manner, each petaloid sector having from five
to eight large teeth at the sides. There are only three radials, and the
arms rarely divide more than thrice. The genus Wetacrinus, only known
by living forms, differs from Pextfacrinus chiefly in the possession of
from four to six radials, the characters of the joint-faces being the same
in both genera. Lastly, the Mesozoic genus Axtracrinus (fig. 290) is
separated from Pentacrinus by the possession of a ring of underbasals,
and by the much more frequent subdivision of the arms. The faces of
the stem-joints in this genus are also different, the petaloid sectors being
linear, and having delicately crenulated edges. In all three genera the
visceral mass is surrounded by a plated perisome, which unites the lower
part of the rays and arms.

Family 9. Marsupitide.—This family comprises free Crinoids,
in which the larval peduncle is lost in the adult. A “ centro-
dorsal” plate is present, but this does not
bear cirri. The calyx may be monocyclic
or dicyclic, and there are no definite in-
terradial plates. The only genera in-
cluded in this family are AZarsupites and
Uintacrinus, both of which are confined
to the Cretaceous period.

The genus JJarsupites comprises the so-
called ‘‘ Tortoise -encrinites” of the Chalk,
and is characterised by the possession of a
globular calyx, composed of large thin plates,
carrying bifurcated uniserial arms. The calyx
is dicyclic, the underbasals, five in number,
surrounding a central pentagonal plate, which

: Weer. has usually been regarded as an enlarged top
ees ha RS aaa stem-joint (“centrodorsal”). There is, how-
Marsupites ornatus, from the €Vver, reason to think that it is rather homol-
Chalk. ogous with the suranal plate of Sa/enza, and

therefore a “dorsocentral” plate. There are
five basals and three rows of radials, but regular interradials are not
developed. The ventral surface of the calyx is vaulted, and covered
with small calcareous plates; and the anus is sub-central. The genus
Uintacrinus resembles MJarsupites in its general form, and in the pos-
session of a pentagonal “centrodorsal” (?) which does not carry cirri.
On the other hand, the globular calyx is monocyclic, and there are ten
arms, the bases of which are united laterally by numerous perisomic
plates, as in the Pentacrinide.

Family 10. Comatulide.—This family of Crinoids comprises the
‘‘Feather-stars,” all of which (except Z/zolMericrinus) lose the larval
peduncle, and are therefore free in the adult condition (fig. 284).
The base of the calyx is closed by a “ centrodorsal” plate (fig.
285, cd), which represents the enlarged top stem-joint, and upon
which jointed cirri are developed. ‘The calyx is apparently “‘ mono-
cyclic,” but underbasals have recently been discovered in the larva

NEOCRINOIDEA. 443

of the Rosy Feather-star, and there are grounds for believing that
their presence is characteristic of the family. They never reach any
great size, however, and fuse at an early period with the enlarged
top stem-joint or ‘‘centrodorsal.” The basals are very generally
rudimentary, being reduced to a small “‘rosette-plate,” concealed
between the centrodorsal and the primary radials. In Azelecrinus
and Zhaumatocrinus, however, and in most fossil Comatfule, the
basals persist and are visible externally. There are three, or,
rarely, two cycles of radials; and, except in Zhaumatocrinus, de-
finite calyx-interradials are not developed. There are five or ten
arms, which are either simple or more or less divided. A large
number of living forms of the “ Comatule” are known, with a
very wide range in space. As regards their distribution in time,
the earliest types of the Feather-stars are found in the Jurassic

Fig. 316.—Centrodorsal (cd) and radial pentagon (7) of Axtedon tucurva, eniarged six times.
Cretaceous (Upper Greensand). aA, Side-view; B, View from above; c, View from below. (After
P. H. Carpenter.)

rocks (Antedon, Actinometra, &c.), and there are also various Cre-
taceous and Tertiary types. The parts most commonly preserved
in a fossil condition are the centrodorsal plate and radial penta-
gon (fig. 316); and upon remains of this nature, before their
true character was understood, the generic name of Solanocrinus
(““ Glenotremites”) was founded. The names of <A/zonia, Gany-
meda, &c., were also based upon the isolated centrodorsals of
fossil Comatule.

The extensive genus Azzedon possesses a central or subcentral mouth
and ten or more arms, while the basals of the recent species form a
“rosette,” and are invisible externally. The earliest fossil species appear
in the Lias. LEzudiocrinus resembles Antedon, but has only five arms.
The genus is represented by a single Cretaceous form, but living types
are known. Actinometra differs from Anfedon in the fact that the
mouth is excentric or marginal in position. The genus ranges from the
Jurassic period to the present day. Lastly, in the Jurassic and Creta-
ceous genus Zhzolliericrinus, the centrodorsal plate exhibits a cavity
which is usually filled by the first joint of the persistent stem, the lower

A44A PELMATOZOA.

joints of which are dice-box-shaped. The genus has therefore been
compared to an Axtedon with a Bourgueticrinus stem.

family 11. Saccocomide.—This remarkable family comprises only
the single genus Saccocoma, which is represented by one species
(S. pectinata, fig. 317) only, from the Upper Jurassic rocks (Litho-

Fig. 317.—Saccocoma pectinata, from the Upper Jurassic of Bavaria. The left-hand figure
shows the complete organism, with the arms inrolled.

graphic Slates) of Bavaria. In this singular genus, the organism is
free, the larval peduncle being evanescent. The calyx is composed
of a single minute basal supporting a cycle of five, thin, closely
united radials, ornamented externally with ten radiating ribs,
and the ventral surface is occupied by five oral plates. There are

NEOCRINOIDEA. AAS

five arms, which bifurcate once, and have the power of rolling
up. The arms carry a few long pinnules like those of Myocrinus,
and possess small undivided spine-like processes. The skeletal
tissue is throughout peculiar in not being dense, but in having a
tolerably loose reticulated structure. The characters of Saccocoma
are so peculiar, that the genus was placed by Muller in a separate
division of Crinoids, to which he applied the name of Cos¢ata.

APPENDIX.

Since the preceding pages were written, some important discoveries
have been made respecting the nature of the ventral covering in Excrinus
and 7axocrinus, the latter genus having a plated disc exactly like that
of a Neocrinoid, with open ambulacra and an exposed mouth surrounded
by five oral plates. There can be little doubt that the other /chthyo-
crinid@ were essentially in the same condition: while Zzcrinus proves
to be very closely allied to the Carboniferous Poderiocrinide, such as
Lrisocrinus and Stemmatocrinus.

Under these circumstances, it is no longer possible to regard the
Neocrinoidea and Paleocrinoidea as well-defined primary groups, though
the names may be conveniently retained as expressing a general strati-
graphical distinction between the older and the younger Crinoids. Messrs
Wachsmuth and Springer have already suggested the outlines of a new
classification which, with slight modification by Dr P. H. Carpenter—to
whom the author is indebted for the present note—will probably result in
something like the following scheme.

ORDER I. COADUNATA.

Crinoids in which the interradials, where present, are incorporated into
the calyx, the latter generally also including the higher radials, which are
immovably united by suture ; while an anal system is well developed.
The mouth and ambulacra are subtegminal, the centre of the vault
being occupied by five oral plates, and the arms are usually biserial.

SUB-ORDER I. CAMERATA.

Actinocrinidz, Rhodocrinidz, Reteocrinidz, Glyptocrinide,
Melocrinidz, Platycrinide, Hexacrinide, Barrandeocrinide, Calypto-
crinide.

SUB-ORDER II. RETICULATA.
Family—Crotalocrinide.

ORDER II. INADUNATA.

Crinoids in which the arms are free from the first radials. The calyx
generally has an anal side, and frequently a dicyclic base. Interradials
may or may not be present. The mouth may be concealed beneath an
oral pyramid, or in the centre of a plated disc with open ambulacra.

SUB-ORDER I. LARVIFORMIA.— Interradial and anal plates rarely
present. Base monocyclic: arms uniserial. Ambulacra closed, and
mouth concealed by an oral pyramid.

446 PELMATOZOA.

Families—Haplocrinidz, Symbathocrinidze, Cupressocrinidz, Gastero-
comide.

SUB-ORDER II. FISTULATA.—Interradial and anal plates generally
well developed. Base usually dicyclic, and arms often biserial. Oral
plates generally reduced, and the calyx covered by a plated perisome
which often bears open ambulacra. The posterior interradius may be
greatly developed to form the ventral sac or anal proboscis.

Families — Hybocrinidz, Heterocrinidz, Anomalocrinide, Belen

crinidz, Cyathocrinidz, Poteriocrinidz, Encrinidz, Astylocrinide,
Catillocrinide, Calceocrinide.

ORDER III. ARTICULATA.

Crinoids in which the higher radials are more or less movably articu-
lated on one another, though often united laterally by the plated perisome
of the disc. The ambulacra are generally open and the mouth exposed,
though often surrounded by oral plates. Interradial and anal plates
rarely present : arms uniserial.

SUB-ORDER [. IMPINNATA.
Family—lIchthyocrinide.

SUB-ORDER II. PINNATA.
Families—Pentacrinidz, Comatulidz, Apiocrinide, Bourgueticrinide,
Eugeniacrinidz, Holopidz, Marsupitide, Plicatocrinide, Hyo-

crinidz, Saccocomide.

447

Copa rallies Ks X OCW I:

PELMATOZOA—continued.
GSO LEA AND BLAS TOVD EA:
Cuass II. CystoipEa.

THE Cystideans are an extinct group of Echinoderms in which ¢he
body (or calyx”) ts spherical or ovate, and ts enclosed tn a case com-
posed of more or fewer calcareous plates, which are usually united by
suture but trregularly arranged, and do not exhibit perfect radial sym-
metry. The plates of the calyx are tn general pierced by more or less
numerous pores, which probably communicated with internal organs,
and which may be regarded as almost certainly connected with the
Junction of respiration. A jointed column may be present or absent.

Fig. 318.—Hemiscosmites pyriforniis, one of the Cystideans. The right-hand figure
shows the upper surface of the calyx.

The upper surface of the calyx usually shows radiating ambulacral
grooves, a central oral aperture, and a lateral anal (?) opening, with
sometimes a small ovarian (?) opening. Arms are tmperfectly developed,
or may be wanting.

In general form the Cystideans are globular, oval, pear-shaped,

448 | PELMATOZOA.

conical, or subcylindrical, and they generally resemble the Crinoids
in consisting of a stem or “column” and a body or “calyx.” ‘The
stem is sometimes long (as in Caryocrinus); but it is usually feebly
developed, and: often attenuated towards its base, sometimes ter-
minating in a single long spindle-shaped piece (Lepadocrinus, fig.
326, D), in which case it probably did not serve as an organ of
attachment. In other cases the stem is rudimentary (as in LZchino-
spherites) or it may be even absent altogether, the organism being
then mostly attached to foreign objects by the base of the calyx, or,
maine lyamiine es

The calyx is composed of a number of polygonal plates, which
usually exhibit no marked radial disposition, though they are some-
times of limited number and arranged according to a definite plan.
In other cases the calyx-plates are indefinite in number and ar-
rangement ; and in some forms the number and arrangement of
the plates may be definite on one side of the calyx and indefinite

Fig. 319.—Upper surface of the calyx of Glyptospherites Leuchtenberg?, from the Ordovician
rocks of Russia. 7z, Mouth, covered by the oral plates ; az, Ambulacral grooves ; #, Socket for
one of the armlets ; az, Anus, without its covering-plates ; 0, Supposed ovarian aperture.

on the other. The base of the calyx is usually readily recognised
by the presence of the articular surface for the top joint of the
stem, or by being fixed to some foreign object ; and the upper sur-
face generally shows two or three openings, the nature and functions
of which have been much disputed. One of these openings is
central or subcentral in position (319, 7), and is often protected in
well-preserved specimens with a covering of five small plates, repre-
senting the orals of the Crinoids, while it forms the point of con-
vergence of from two to five, simple or branched grooves which run
over the ventral surface of the calyx (am). These grooves clearly
correspond to the “‘ambulacral grooves” or “‘food-grooves” of the
Crinoids, and there can therefore be no doubt that the aperture in

CYSTOIDEA. 449

question is the mouth. A second aperture (fig. 319, az) is placed
excentrically, usually on the upper surface of the calyx, and in good
specimens is furnished with five or six triangular calcareous plates,
which are arranged to form a sort of cone or “ valvular pyramid,”
and which serve for the closure of the opening. It is not neces-
sary to discuss the various views which have been put forward as
to the functions of this orifice, but there is every reason to believe
that it is really the anus. In many cases there is a third opening,
which is always of small size and always placed near the mouth
(fig. 319, 0). This aperture has been commonly regarded as being
of the nature of an “ovarian ” aperture or genital pore.

-In well-preserved examples, the upper surface of the calyx com-
monly exhibits simple or branched grooves (fig. 319, am), which
radiate from the mouth, and obviously are of the nature of “‘ambu-
lacral grooves” or ‘‘food-grooves.” In some cases, as, for example,
in Cadlocystites (fig. 320) and in Lepadocrinus
(fig. 326, c), the ambulacral groove is bordered
on each side with a row of delicate jointed
pinnulee, which are also grooved on their ventral
faces. In such cases, the ambulacral grooves
may be looked upon as representing recumbent
arms which have become soldered down to the
surface of the calyx. In cases where the am-
bulacral groove is bordered by a single row of
pinnules, the arm may be supposed to be fast-
ened down to the calyx by one of its sides, Mi8,320-7Side-view of

z the calyx of Cadlocystites
instead of by the dorsal surface. In other Zewertdé, from the Silu-
: rian of North America,
Cystideans the upper surface of the calyx ex- showing the ambulacral
‘ie : : = = d th a
hibits irregularly scattered articular facets, which, Sins of i) pm tles on

in the perfect condition, served for the attach- Lee Ane:
ment of small unbranched jointed filaments. Hall.)

These may be regarded as of the nature of

‘“‘armlets” or simple arms, rather than as pinnule. They are
seen in such genera as Glyptospherites (fig. 319, fp), Caryocrinus
(fig. 326, A), and Pleurocysiites (fig. 326, B), and they can be some-
times shown to possess a ventral groove, which is provided with
small calcareous covering-plates. Lastly, in the genus Comarocystites
there are four free arms, which differ from the structures just spoken
of, and agree with the arms of the Crinoids generally, in being pro-
vided with lateral pinne.

In some forms of the Cystideans (Cryptocrinus, Malocystites, &c.)
the plates of the calyx appear to be completely imperforate. In the
majority of cases, however, the walls of the calyx are more or less
extensively perforated by pores or fissures, which usually open
directly on the outer surface of the body, but are in other cases

MOE. I. 2 F

A50 PELMATOZOA.

closed by an exceedingly thin calcareous membrane, while they in-
variably traverse the entire thickness of the plates. Their arrange-
ment differs much in different types of the Cystideans, and they
afford therefore important evidence in classification. In certain
forms (such as Glyptospherites, Gomphocystites, &c.) the pores are
conjugate, or are united in pairs, the individual plates possessing

A

Fig. 321.—A, Part of the calyx of Zocystites ? longidactylus, from the Cambrian rocks of North
America, enlarged, showing pores passing between adjoining plates; B, Plate of Glyptospherites
Leuchtenbergi, enlarged, showing double pores; c, Plate of Echinospherites aurantium, show-
ing diffused pore-rhombs, enlarged, from the Ordovician rocks of Russia. (A is after Walcott.)

several of such pairs (fig. 321, B). In other forms, the pores are
arranged in rows, a row on one plate being united by grooves or
fissures, sometimes on the exterior of the calyx or at other times
on its interior, with a corresponding row on an adjoining plate.
These rows of connected pores (fig. 322) are arranged so as to form
lozenge-shaped or rhombic figures ; in such a manner that one-half of

Fig. 322.—a, Pore-rhomb of Glyftocystites multiporus (Billings); 8, Pore-rhomb of Pleuvo-
cystites (Billings); c, Two plates of Cadlocystites fewettzz (Hall), showing the pore-rhombs (4).
All enlarged.

each rhomb belongs to one plate and the other half to its contiguous
neighbour, while the grooves connecting the two component rows of
pores pass across the line of suture between the two plates, either
externally or internally. In some types, as in Echinospherites (fig.
321, C) and Caryocystites, these ‘“‘pore-rhombs” are very numerous,
and are present upon nearly all the plates of the calyx. In other

CYSTOIDEA. A5I

cases (as in Caryocrinus and Hemicosmites) they are only developed
on the side-walls of the calyx, and are absent from its upper surface.
In other cases, again, as in Pleurocystites (fig. 326, B) or Callocystites
(fig. 322, C), the pore-rhombs, or ‘‘ pectinated rhombs,” as they have
been often termed, are comparatively few in number, and their
component halves not only stand on contiguous plates, but may be
separated externally by an interval.

It would seem extremely probable that the differences in the form
and arrangement of the pores in different groups of Cystideans,
which have been pointed out above, are really an indication of a
fundamental difference in the nature and function of these structures.
In those Cystideans which possess “ pore-rhombs” (2homdébzferr),
there seems no reason to doubt that these structures were connected
with internally-placed, folded tubes similar to the ‘‘ hydrospires” of
the Blastoids, and that they acted as respiratory organs. On the
other hand, it has been suggested by Lovén, with much probability,
that the linked pores of Glyptospherites and its allies (Diploporitide)
were connected with the ambulacral system, and that, like the pores
in the test of the Urchins, they were occupied by pedicels. On
this view, ‘‘ hydrospires”” are wanting in the types in question, and
the function of respiration would be discharged by the tube-feet.
If this suggestion be accepted, the Diploporous Cystoids would be
comparable to the Sporadiporous Holothurians or to such Urchins
as Melonites. They would, however, differ from the Urchins gener-
ally in the want of definite radial symmetry in the plates of the
test, and also in the fact that the pores for the tube-feet per-
forate the plates of the zzzterambulacral areas, instead of being con-
fined to the ambulacral areas only.1 The Cystoids (Agoritide)
in which neither pores nor ‘“pore-rhombs” are developed, occupy
a dubious position from a systematic point of view. They differ
widely from the preceding groups in some respects, and it is pos-
sible that they may ultimately find a place elsewhere.

As regards their distribution in time, the Cystideans are not only
wholly extinct, but they are entirely restricted to the Palzeozoic
period, ranging from the Cambrian period to the Carboniferous
Limestone, but attaining their maximum of development in deposits
of Ordovician age. The few Cambrian forms which have hitherto
been detected are only known from imperfect examples, and their
precise structure is incompletely understood. Upon such remains
have been founded several genera (Locystites, Trochocystites, Proto-
cystites, &c.), but these do not at present admit of precise definition.

1 In such Urchins as Scztella (fig. 240) the branches of the ambulacral grooves
on the actinal surface extend into the interambulacral regions, and are lined by
minute tube-feet, while in Zchinanthus there are isolated ‘‘ locomotive” pores
scattered over many of the interambulacral plates.

452 PELMATOZOA.

In one of these ancient types, from the Cambrian rocks of North
America, which Mr Walcott has doubtfully referred to the genus
Focystites, there appears to be the exceptional character that the
pores are formed by the apposition of corresponding indentations in
the edges of contiguous plates (fig. 321, A). In the Ordovician
series, and particularly in strata of Llandeilo-Bala age, the remains
of Cystideans are sometimes abundant, and the group attains here
its maximum. In the Silurian period Cystideans are less abundant,
and in the Devonian formation only very few forms (Zzaracrinus,
Ateleocystites, Strobilocystites, &c.) are known to occur. Lastly, if
Codaster be removed to the Blastoids, the group of the Cystideans
is chiefly represented in Carboniferous deposits by the aberrant
genus Agelacrinus.

As regards their classification, the Cystideans may be conveniently
divided into the three orders of the Aforitide, Diploporitide, and
Rhombifert, according as the calycine plates are imperforate, are
pierced by yoked pairs of pores indiscriminately distributed, or
have their pores arranged in “pore-rhombs”; and the characters
and principal genera of these three groups may be very briefly
glanced at here.

ORDER 1. APORITID#.—In this group are comprised all those
Cystideans in which the calyx-plates are destitute of pores. Of the
genera of this group Cvyftocrinus (fig. 325, B) has a globular calyx,
composed of comparatively few plates arranged in a tolerably definite
manner, there being three basals, succeeded by two cycles of pen-
tagonal plates. ‘The central mouth is, in perfect specimens, covered
by a vault of small calcareous plates, and the laterally placed anus
is provided with a ‘“‘valvular pyramid.” The stem and arms are
unknown, and the genus is confined to the Ordovician rocks.
Malocystites, from the Ordovician deposits of. Canada, possesses an
indefinite number of plates in the calyx, and the mouth is excentric,
and is surrounded by radiating ambulacral furrows. In Axomalo-
cystites (—=Ateleocystites, Billings) the calyx is also composed of an
indefinite number of plates, which are ornamented with transverse
striz. One side of the calyx is convex, while the other is flat or
concave, and the summit is provided with delicate armlets or pin-
nule. The species of this genus range from the Ordovician to the
Devonian. The most remarkable type of the imperforate Cysti-
deans, however, is that presented by Agelacrinus and Ldrioaster,
which have sometimes been regarded as constituting a special
family (Agelacrinide). In the genus Agelacrinus (including Aemz-
cystites, Hall) the body (fig. 323, A) is in the form of a depressed
or convex disc, attached by the whole of its under surface to
some foreign body, and therefore devoid of a peduncle. The
upper or ventral surface of the disc is covered with numerous

CYSTOIDEA. 453

small calcareous plates, which may or may not overlap in an
imbricating manner, and exhibits in its centre the opening of the
mouth, protected by four “oral” plates. Radiating from the mouth
are five curved ambulacral grooves, and in one of the interradial
spaces is situated the opening of the anus (0), protected by a
“‘ pyramid ” of calcareous plates.
The species of Agelacrinus are
found in the Ordovician, Silu-
rian, Devonian, and Carbonifer-
ous rocks. The genus £ar10-
aster (fig. 323, B), from the Or-
dovician rocks, agrees in most
of its general characters with
Agelacrinus, but the ambulac-
ral grooves are furnished with
a double row of pores on each
side.

ORDER 2. DIPLOPORITID.
—TIn the Cystideans which are
included in this group, the
pores are linked or united in
pairs, and the individual calyx-
plates are pierced by several of
such pairs (fig. 321,B). There
is, as before pointed out, much
probability in the view put
forth by Lovén, that the yoked
pores of the Dzploporitide
served for the passage of tube-
feet, and that they thus differ
in their real nature from the
“pore-rhombs” of the Rhom-
biferous Cystoids. If this view

5 Fig. 323.—a, Upper surface ot Agelacrinus Cin-
be correct, the present group 1S _ cinmnatiensis, enlarged two and a half diameters.

7 Ordovician (after Hall). 8B, Upper surface of an
very sharply separated from both imperfect specimen of Edrvioaster Bigsbyz, of the

the other groups of Cystoids. natural size. Ordovician (after Billings). 0, Anal
aperture.
As the type of the Dzflopo-
vitide, the Ordovician genus Glyptospherites may be taken, in which
the globular calyx (fig. 319) is composed of numerous polygonal
plates, each of which is perforated by a larger or smaller number of
conjugate pores. The mouth is central, and is covered by five oral
plates, while converging to it are five branching ambulacral grooves,
at the terminations of which are the articular facets to which the
armlets or pinnulz were attached. On one side is the compara-
tively large opening of the anus, and between the two is a small

A54 PELMATOZOA.

aperture which has been usually regarded as a genital pore. The
calyx was furnished with a stem composed of thin annular joints.
The genus Sfheronites, also Ordovician in its range, is allied to
the preceding in several points, but there
was no stem, and the calyx was adherent
by its base to foreign bodies. In the
Silurian genus Gomphocystites (fig. 324) the
calyx has a very peculiar shape, being
pyriform, very narrow below, and inflated
at its summit. The calyx-plates are in
numerous cycles, and have superficial
granules, along with yoked pores. The
mouth is central, and is surrounded by
five spirally wound ambulacral grooves.
In Holocystites, again, the calyx (fig. 325,
F) is long and subcylindrical, and is com-
posed of six or more ranges of hexagonal
or polygonal plates. The mouth is cen-
tral, and the calyx was furnished with
a short stem, or was sessile. The genus is
found in the Silurian rocks of North
America and Europe.

ORDER 3. RHOMBIFERI.—The Cysti-

deans included in this order are charac-
Fig. 324.—Side-view of the cast terised by the possession of pores ar-
of the calyx of Gomphocystites : : :
Oe ae ee ee ranged In Trows, corresponding rows 1n
of North America. (After Hall.) adjoining plates being connected, exter-
nally or internally, by grooves or slits
which cross the lines of suture between the plates. The pores are
thus arranged in groups, which are usually more or less lozenge-
shaped, and which are known as “pore-rhombs.” ‘The pore-
rhombs were probably connected internally with organs similar to
those which will be described in dealing with the Blastoids as
‘“‘hydrospires,” and their function seems to have been certainly
respiratory.

In one section of this order the plates are indefinite in number,
and the pore-rhombs are distributed indifferently over the whole
calyx, and are exceedingly numerous. A good example of this
section is the well-known Ordovician genus Zchinospherites (fig. 325,
A), in which the calyx is of large size, globular, and stemless, its
base being attached to foreign bodies. The calyx-plates are very
numerous, polygonal, with pore-rhombs on every side (fig. 321, C).
At the apex is the mouth, and the anus is lateral and is protected
by a large “valvular pyramid,” while a small ovarian (?) opening is
placed between the two. Caryocystites, also Ordovician, is nearly

Yi
ee 9
iy,

= === 5 === S=Ee ————
aaa S55 =
= = =
. ‘ mare SSS
SS

CYSTOIDEA. A55

related to Echinospherites, but the calyx is more of an ovoidal form,
and the plates are ridged or striated. Allied genera are Paleocysittes
and Comarocystites, both from the Ordovician rocks of North
America, and the latter remarkable in having a small number of
pinnate arms.

In a second group of the Rhombifert, the pore-rhombs are con-
fined to the sides of the calyx, and the upper surface is formed of
imperforate plates, while the arrangement of the calycine plates

Fig. 325.—A, Echinospherites aurantium ; %, Cryptocrinus levis ; c, Echinoencrinus Senken-
bergi; D, Echinoencrinus (?) armzatus ; E, One of the “‘ pectinated rhombs” of the last, enlarged ;
F, Holocystites cylindricus. v, Valvular anal pyramid. All the specimens are viewed from one
side. (a, B, and c are after von Buch; D is after Edward Forbes; and F is after Hall.)

generally is to a greater or less extent radial. A good example of
this group is afforded by the genus Caryocrinus (fig. 326, A), which
is widely distributed in the Silurian rocks of North America. In
this genus there is a long and cylindrical column, which carries an
ovoid calyx, the upper surface of which exhibits the articular facets
to which free-jointed armlets or pinnulz were attached. The lateral
calyx-plates show externally lines of pores radiating from their centres,
and an internal examination shows that these pores are connected
by canals into pairs, so as to form a series of ‘‘rhombs.” Aemzcos-
mutes (fig. 318) is an allied genus, which is found in the Ordovician
and Silurian deposits of Europe.

Finally, in a third group of the Rhombifert are included forms in
which the calyx-plates are generally more or less definite in number,
and more or less clearly arranged in a quinary manner, while the
“‘pore-rhombs” are limited in number, and are often so disposed that

456 PELMATOZOA.

the component halves of each are separated externally by an interval
(fig. 322, c). Of the more important genera of this group, Pleuro-
cystites is remarkable in having the perisomatic plates on the dorsal
side of the calyx large and definitely arranged, while those of the
ventral side are numerous and indefinite. The summit of the calyx
carries two jointed armlets (fig. 326, B), and there are three “ pore-
rhombs,” or, as these structures were termed by Edward Forbes,
“pnectinated rhombs.” The genus is found in the Ordovician rocks
of Canada. In the Ordovician genus Echinoencrinus (fig. 325, C)
the calyx is composed of four series of plates, there being four basals,

Fig. 326.—a, Caryocrinus ornatus: a, Column; 4, Calyx; c, Scars where pinnule were
attached; @, Valvular pyramid. 3, Pleurocystites sguamosus (dorsal side): ~ ~, Two of the
pore-rhombs. c, Lepadocrinus (Pseudocrinus) bifasciatus. Dv, Lepadocrinus Gebhardi.

and five plates in every cycle above this. There are.three “ pectin-
ated rhombs,” and the anal opening is of large size and is placed on
one side. The Silurian Cystideans referred to this genus by Edward
Forbes under the names of £. daccatus and £. armatus (fig. 325, D)
differ in some important points from the type of Echinoencrinus.
Glyptocystites, of the Ordovician rocks of America and Europe, is
allied to the preceding, but possesses numerous “ pore-rhombs ” (ten
to twelve in number), no other genus of this section having more
than three or four of these organs. In Lepadocrinus—with which
Zittel unites Psexdocrinus and Afiocystites—the calyx is ovoid, more
or less quadrangular, with a long stem, which becomes attenuated

BLASTOIDEA. 457

below, or ends in an elongated and pointed ossicle (fig. 326, D).
The mouth is central, and there are two or four ambulacral grooves,
which in well-preserved examples are bordered by short pinnules
(fig. 326, c). The anus is excentric, and is furnished with valvular
plates, and there are three reniform or triangular pore-rhombs. The
genus is principally Silurian. Lastly, in Cad//ocyséttes, as in the pre-
ceding genus, the calyx consists of four zones of plates, of which the
lowest consists of four basals. ‘The mouth is central, and there are
five ambulacral grooves (fig. 320), which are bordered by well-devel-
oped pinnules. The anus is excentric, and there are four pectinated
trhombs. The species of Cad/ocystizes are found in the Silurian rocks
of North America.

Cuass III. BLASTOIDEA.

This class includes extinct Echinoderms in which ¢#e body.
(“calyx”) ts pyriform, clavate, ovate, or globular, and 1s attached by
a short jointed peduncle, which is in some cases wanting. The calyx
exhibits complete radial symmetry, and is enclosed in a covering of
suturally united calcareous plates, consisting of basals, radials, and
interradials. The upper surface exhibits five ambulacral areas,
usually of a more or less petaloid shape, which radiate from the
mouth, the latter being superior and central, and being concealed by a
covering of small calcareous plates, some of which represent the “ orals”
of the Crinoids, while the ambulacral grooves are protected by a double
row of “‘covering-plates.” Small jointed appendages or “pinnules”
are attached, in a single or double row, to the sides of the ambulacral
fields, but no true arms are present. ‘‘ Hydrosptres,” opening by five
or ten apertures round the mouth or by tnterradial fissures, are present,
but are limited to the radial and tnterradial plates, never extending on
to the basals.

The Blastoids form a peculiar group of Palzeozoic Echinoderms,
in which the body is generally supported by means of a short
peduncle composed of discoidal joints, though in some cases no
stem appears to have been present. The calyx is globular, ovoid,
clavate, or bell-shaped, and is remarkable for its regular radial sym-
metry. Underbasals, such as are found in the “ dicyclic” Crinoids,
are not developed, but the calycine plates consist of a cycle of
basals, a row of radials, and a circle of interradial (“deltoid ”) plates.
The basals (fig. 327, a and 328, B) are three in number, two
being comparatively large and of equal size, while the third is much
smaller. Following the basals is a cycle of five “radials,” which
are usually of large size, and form the sides of the calyx (figs. 327
and 328, d). The radials have been sometimes spoken of as the
“forked plates,’ owing to the fact that each is deeply divided or

458 PELMATOZOA.

incised distally, in such a way that the two arms of the plate
enclose the lower end of one of the ambulacral fields. The radials
differ from the corresponding plates of the Crinoids in the import-
ant fact that they do not form the starting point for a crown of
‘“‘arms.” Placed towards the summit of the calyx, at the angles of
junction of the radials, are five triangular, rhomboidal, or pen-
tagonal interradial plates, which have commonly been spoken of as
the “ deltoids ” (fig. 327, A and B, z). The cycle of the deltoids is
interrupted by the ambulacra, and a considerable portion of their
entire area may be hidden from view beneath the adjoining plates

Fig. 327.—Structure of Blastoids. a, Calyx of Pextvemztes, dissected, showing the basals (4),
the forked ‘‘radials” (¢), and the interradial or ‘‘deltoid” plates (z). 3B, Side-view of the calyx
of Pentremites cervinus—the letters as before. c, Section across the calyx of Granatocrinus
ellipticus, showing the hydrospires cut transversely in their course below the ambulacral areas.
D, Section across one of the ambulacral areas of Pentremites Godoni, showing the compound
nature of the hydrospires, enlarged. (After Hall and Rofe.)

of the ambulacral fields. The ‘‘deltoids” of the Blastoids cor-
respond very closely with the large interradials of Cyathocrinus, as
shown in fig. 297, and, through these, with the interradial systems
of the other Crinoids.

The most complicated structures in the test of the Blastoids are
those connected with the ambulacral areas. The ambulacral fields
(formerly spoken of as the ‘‘pseudambulacra”) are always five in
number, and pass in a radiating manner from the centre of the
summit of the calyx to its margins. It is these which give to the
summit of the body its resemblance to a flower-bud (figs. 327, B, and
328, A) upon which the name of the class is founded (Gr. d/astos,
a bud; and ezdos, form). Though usually broad and petaloid in
shape, the ambulacra are sometimes narrow, and their length varies
in different types of the class. In a typical Blastoid, such as a
species of Pentremites, the ambulacra have the following structure.
Running down the centre of each of the petaloid ambulacral fields
is a well-marked median groove, often with crenulated edges
(fig. 329, B, ag), which in perfect specimens is roofed over by a
double row of small calcareous ossicles or ‘‘ covering-plates (fig. 329,

BLASTOIDEA. A59

A, c). This median groove clearly corresponds with the “food-
groove” of the arm and disc of a Crinoid, and may therefore be
termed the “ambulacral groove.” The ambulacral groove is ex-
cavated in the middle line of a long pointed plate (fig. 329, B, Z)
which runs down the centre of the ambulacral field and was termed
by F. Roemer the “lancet-plate.”. The two halves of the lancet-
plate, in well-preserved specimens, are seen to be crossed by numer-

an D

Gh

Fig. 328.—a, and B, Side-view and base of Pentremites pyriforniis: 66, Basals; dd, Radials ;
~~, Ambulacral fields. c, Summit of Granatocrinus Norwoodi (after Meek and Worthen), en-
larged, showing the plated membrane covering the mouth (vz), the spiracles (sf), the anus (az),
and the summits of the ambulacral fields (a7). pb, Summit of Pentrenzttes sulcatus (after Ferd.
Roemer), showing the mouth denuded of its covering-plates and placed in the centre of the
Secs (sf): an, Anal opening ; az, One of the ambulacral fields. From the Carboniferous
rocks.

ous transverse grooves, which open centrally into the main ambula-
cral groove. As the lancet-piece is narrower than the ambulacral
field, there exists on each side of the former an interval, separating
the sides of the lancet-plate from the forks of the bounding radial
on each side. This interval is occupied on each side by a row of
small quadrilateral ossicles or “‘side-plates” (fig. 329, s), which
complete the ambulacral field superficially. Each ambulacral area
is thus traversed from end to end by two lines of suture (fig. 329,
B), which separate the median lancet-plate from the side-plates at
its edges.

460 PELMATOZOA.

In Pentremites and in most other genera of Blastoids, the side-
plates are so shaped as to leave along their outer ends a series of
apertures or ‘‘ marginal pores” (fig. 329, 4), by means of which
water is admitted to the ‘‘ hydrospires.” -In many cases, however,
the marginal pores are not merely spaces between the attenuated
outer ends of the side-plates, but they are in part formed by a series
of still smaller ossicles, which are known as the “ outer side-plates ”
(the ‘supplemental pore-plates” of Roemer). In entremites the
side-plates are marginal, and leave the whole upper surface of the
lancet-plate exposed to view ; but in other cases they encroach upon

ag ‘sp m sp zl

My

es

ih
ARAN

|
A

Bene Ey"

|

i

if

ANIKI,

iN
I

IN\\
|

\

i

il
it

mw

i
:
|

Stull

oN

Fig. 329.—A, Upper portion of one of the ambulacra of Pentremites sulcatus, enlarged,
showing the ‘‘covering-plates”’ (c) of the ambulacral groove, passing superiorly into the plated
canopy (vz) which conceals the mouth. 3B, Ambulacrum of Penxtremites pyriformis, from which
the covering-plates have been removed, showing the ambulacral groove (ag), the lancet-plate (2),
the side-plates (s) with their marginal pores, and the spiracles (sf) at the upper end. c, Am-
bulacrum of the same species, from which the lancet-plate and most of the side-plates have
been removed, showing the ‘‘under lancet-plate” (2), the tops of the hydrospires, (Z), and the
ambulacral opening. (After R. Etheridge, jun., and P. H. Carpenter.)

the lancet-plate, and leave visible little more than the central food-
groove.

The lancet-plate is pierced by a canal which lodged the radial
water-vessel, and which opens into a circular ambulacral canal sur-
rounding the mouth. The removal of the lancet-plate allows the
top of the ‘“ hydrospires” to be seen (fig. 329, c, Z). In the genus
FPentremites, however, and in some other types, there is situated
beneath the lancet-plate, in the middle line of the ambulacral field,
an elongated, trough-like plate, which Messrs Etheridge and Car-
penter have termed the “ under lancet-plate” (fig. 329, #2).

True “arms,” comparable with the structures so called in the
Crinoids, are not developed in the Blastoids. Along the outer edge

BLASTOIDEA. 461

of each ambulacral field there was situated, however, a single or
double row of slender jointed “ pinnules.” The sockets for these
are placed between each pair of marginal pores, but the delicate
pinnules themselves are rarely preserved.

In perfect specimens of the Blastoids, the apex of the ventral sur-
face (fig. 328, Cc) appears to have been closed by a canopy of small
calcareous plates, some of which represent the orals of Crinoids ;
but in the majority of examples these have been destroyed in the
process of fossilisation. In the Blastoids, therefore, as in the
Palzocrinoids generally, the mouth was really subtegminal, and was
not visible externally in the natural condition. When the covering-
plates, however, have been lost, the mouth is seen as a central aper-
ture placed at the point of convergence of the ambulacral fields
(fig. 328, D). The vault of plates concealing the mouth passes
laterally without a break into the “ covering-plates” of the ambu-
lacral grooves. The anus is excentric, and pierces one of the
interradials (‘‘ deltoid” plates).

The most remarkable organs in the Blastoids are the respiratory
tubes or ‘‘ hydrospires,” which are probably always present in one
form or another, though they have not
been universally detected. In Pentremites Tae epha
(fig. 330) the hydrospires lie underneath ae ye
the lateral portions of the ambulacral pL TESS Lie
fields, one on each side of each ambu- Laer Sr
lacrum, so that there are ten of these Pa ds
organs in all. When the lancet-plate is
removed from an ambulacrum in this
genus, the outer sides of the hydrospires
are seen on each side (fig. 329, c, 4),
with the “under lancet-plate” in the
centre. Each hydrospire consists of a
flattened lamellar tube, with thin calcare-
ous walls, more or less extensively folded, _ Fis. 330.—Cross-section of the

: : 2 calyx of Pentrenttes sulcatus,
and terminating internally by closed and from the Carboniferous rocks of
somewhat dilated ends, the reduplications eke ee ceia eee
of the tube being placed lengthways be- eee ey Domenie
neath the ambulacrum. Water is admitted (After Zittel.)
into the hydrospires by slits on their outer
faces in direct connection with the rows of “ marginal pores” between
the overlying “ side-plates” of the ambulacrum (fig. 330, 2 A). At
their upper ends the hydrospires are placed in further communica-
tion with the exterior by a ring of five or ten openings surrounding
the peristome. These apertures (formerly called “ ovarian open-
ings”) are usually spoken of as the “spiracles” (fig. 328, c), and
they probably served for the escape of water from the hydrospires.

f

\, 1 VF -
LMM TD, ,
Mis pe ~

462 PELMATOZOA.

The general arrangement of the hydrospires in the majority of the
Blastoids is essentially similar to that which obtains in Pentremztées, as
above briefly described ; but there are some remarkable departures from
this type. Thus in Codaster (=Codonaster) there are only eight hydro-
spires, and these open externally by slits separated by intervening ridges,
which occupy four of the five interradial areas on the ventral surface of
the body, and which have a direction parallel with that of the ambulacra
(fig. 331, A). In Phenoschisma the arrangement is the same, but the

Fig. 331.—a, Upper surface of the calyx of Codaster trilobatus, var. acutus, from the Car-
boniferous Limestone, enlarged, showing the numerous hydrospire-slits (f) in all the interradii
except the anal one. (After M‘Coy.) B, Side-view of the calyx of Orophocrinus (Codontites)
stelliformis, from the Carboniferous Limestone of North America, of the natural size. c, Upper
surface of the calyx of the same (after Meek and Worthen), enlarged. a, Anal aperture; 7,
Ambulacra ; J, in fig. c, Hydrospire-clefts or ‘‘ spiracles.”

hydrospire-slits occupy the anal as well as the other four interradii.
Lastly, in the genus Ovophocrinus (fig. 331, C) the “spiracles ” or external
openings of the hydrospires are in the form of ten clefts, of variable
length, which extend along the sides of the ambulacra.

There can be little doubt that the “‘ hydrospires ” of the Blastoids,
like the less highly developed structures of the same kind in the
Cystoids, are essentially respiratory in function. ‘They present in
many respects a remarkable resemblance to the folded genital
‘“‘bursee” of the Ophiuroids, as regards both their structure and
their mode of termination on the surface of the body. It is
therefore probable that the hydrospires, like the “‘ bursze” of the
Brittle-stars, were connected with the discharge of the reproductive
elements into the external medium.

As regards the distribution in time of the Blastoids, no member
of the order has been as yet certainly detected in the Ordovician
rocks. In the Silurian rocks of North America a few forms have
been found, and in the Devonian deposits both of the New and
Old World various genera are represented, such as Pentremitidea,
Eleutherocrinus, Codaster, and Eleacrinus. It is in the Carbonifer-
ous rocks, however, that the Blastoids attain their maximum devel-
opment, the type-genus Pentremites (fig. 332, a and 6)—sometimes
written Pentatremites or LPentatrematites—appearing here for the

BLASTOIDEA. 463

first time. The other genera most largely represented in the
Carboniferous rocks are Granatocrinus, Schizoblastus (fig. 332, ©),
Codaster (fig. 331, A), Orophocrinus (fig. 331, B), and Jesoblastus.
Above the horizon of the Carboniferous Limestone no remains of
Blastoids have been as yet discovered.

As regards their classification, the Blastoids are divided by Mr
Etheridge, jun., and Dr P. H. Carpenter, into the two primary
groups or orders of the Aeguwlares and Jrregulares, the former
including pedunculate types with a symmetrical base and having
equal and similar ambulacra, while the latter comprises sessile forms

Fig. 332.—a, Pentremites pyriforniis, viewed sideways, showing a portion of the column;
6, Summit of the calyx of Pentrencites cervinus, showing the ambulacral areas and the apical
apertures ; c, Side-view of Schizoblastus melonoides ; d, Summit of Schizoblastus neglectus. (Figs.
@ and @ are of the natural size; c and d@ are slightly enlarged.) (After Hall, and Meek and
Worthen.)

in which the base is usually unsymmetrical, and one ambulacrum
and the corresponding radial are different from their fellows. The
following table exhibits the families adopted by the authorities just
named, with the genera included in each :—

ORDER I. REGULARES.

Family 1. Pentremitide.—Base usually convex and often much elon-
gated. Spiracles five, but sometimes more or less completely divided by
a median septum. Their distal boundary formed by side-plates. Hy-
drospires concentrated at the lowest part of the radial sinus. The genera
Pentremites (fig. 328), Pentremitidea, and Mesoblastus are included in
this family.

Family 2. Troostoblastide.—Ambulacra very narrow, and descending
sharply outwards from the much-restricted peristome. Deltoids usually
limited to the summit and rarely visible externally. Lancet-plate entirely
covered by the side-plates. Spiracles generally double, appearing as
linear slits at the sides of the deltoid ridge, but not bounded distally by
side-plates. The genera Zvoostocrinus, Metablastus, and Tricelocrinus
belong here.

Family 3. Nucleoblastide.—Calyx usually globular or ovoidal, with
flattened or concave base and linear ambulacra. Spiracles distinctly
double, and chiefly formed by the apposition of notches in the lancet-

464 PELMATOZOA.

plate and deltoids. This family includes E/eacrinus (with an anal plate) ;
and Schizoblastus (fig. 332, c and @), Cryptoblastus, and Acentotremites
(without an anal plate).

Family 4. Granatoblastide.—Calyx globular or ovoidal, with a flattened
or concave base and linear ambulacra. Spiracles five, piercing the del-
toids ; or ten, grooving their lateral edges. This family includes the
genera Granatocrinus and Heteroblastus.

Family 5. Codasteride.—Base usually well developed and sometimes
very long. Some or all of the hydrospire-slits pierce the calyx-plates on
the sides of the radial sinus, restricted portions of which may remain
open as the spiracles. This family includes the genera Codaster (fig.
331, A), Phenoschisma, Orophocrinus (fig. 331, B and C), and Crypio-
schisnia.

ORDER II. IRREGULARES.

Family 6. Astrocrinide.—This family includes certain singular un-
stalked and unsymmetrical Blastoids, in which one ambulacrum and one
radial are different from the rest. In Astrocrinus and Eleutherocrinus
the basals are unsymmetrical, and the azygos radial is small and without
definite limbs, its ambulacrum being short, wide, and horizontal. On the
other hand, in Pentephyllum the basals are symmetrical, and the odd
ambulacrum is linear.

LITERATURE OF ECHINODERMATA:

GENERAL.

1. “Ueber den Bau der Echinodermen.” ‘Abhandlungen der Berlin
Akad.’ 1853. Joh. Miller.

2. ‘“ Morphologische Studien an Echinodermen.” H. Ludwig. Leipzig,
1877-82.

3. “Histoire naturelle des Zoophytes Echinodermes.” Dujardin and
Hupe. Paris, 1862.

4. “ Monographie d’Echinodermes vivants et fossiles.” Louis Agassiz.
1838-41.

5. . Handbuch der Palzontologie,” Abth. L., Liei 3. Zitteayaiage!

6. “Beitrage zur Histologie der Echinodermen,” I.-1V. Hamann.
1884-809.

7.. “ Die Stamme des’ Thierreichs.”. Bd. I. Neumayr.

8. “ Bronn’s Klassen und Ordnungen des Thierreichs” (Echinoderms).
2d Ed. 1889. Ludwig.

g. ** Notes on Echinoderm Morphology,” I.-XI. ‘Quart. Journ. Micro.
SG) Wi 7.026 ae Et ae aipenver,

ECHINOIDEA.

10. “ Catalogue raisonné des familles, des genres, et des espéces de la
classe des Echinodermes.” Louis Agassiz and Desor. 1847.

11. “ Revision of the Echini.” Alexander ‘Agassiz. ‘Memoirs of the
Museum of Comparative Zoology at Harvard,’ vol. ill. 1872-74.

12. “Monograph of the British Fossil Echinodermata.” Thomas
Wright. ‘ Palzeontographical Society.’

13. “Etudes sur les Echinoidées.” Svenska Vetensk. Handl.” Bd. xi.
Tov4. sleoven:

LITERATURE OF ECHINODERMATA. 465

moeourtalesia.” lbid, Bd. xix. JLovén, 1883)
. “Report on the Echinoidea.” ‘Challenger Reports,’ vol. 11. 1881.

Alexander Agassiz.

. “Report on the ‘ Blake’ Echini.” Alexander Agassiz. 1883.
. “Synopsis des Echinides fossiles.” Desor. 1855-59.
. “ Paléontologie francaise.” Terrains crétacés. Echinides irreguliers,

vol. vi. 1856-57. D’Orbigny.

. “Paléontologie francaise” (a continuation of the preceding).

Cotteau.

. “Monograph of the Echinodermata of the British Tertiaries.”
grap

‘ Paleeontographical Society.’ Edward Forbes.

. “ Petrefaktenkunde Deutschlands.” Bd. ii. Echiniden. Quenstedt.

1872-75.

. “Petrefacta Germanie.” Bd.i. Goldfuss. 1826-33.
. “Paleozoic Fossils.” M‘Coy. 1851. (Perischoechinide.) Also

“Carboniferous Fossils of Ireland.” 1844.

24. “ Echinothuridz and Perischoechinide.” R. Etheridge, jun. ‘ Quart.

, Journ. Geol. Soc.,’ vol. xxx. pp. 307-316. 1874.

. “Echinologie helvetique.” De Loriol. 1868-1875.
. “Die Echiniden der vicentinischen und veronesischen Tertiarablager-

ungen.” ‘Palzontographica.’ Dames. 1877.

ASTEROIDEA AND OPHIUROIDEA.

. “System der Asteriden.” Miller and Troschel. 1843.
. “Ophiuridze and Astrophytide.” Theodore Lyman. ‘Illustrated

Catalogue of the Museum of Comparative Zoology at Harvard.’
1865.

. “Additamenta ad historiam Ophiuridarum.” Litken. 1859.
. “ Report on the Asteroidea.” ‘Challenger Reports,’ vol. xxx. 1889.

Sladen.

. “North American Star-fishes.” A. Agassiz. 1877.
. “Report on the Ophiuroidea.” ‘Report on the Scientific Results of

the Voyage of H.M.S. Challenger, vol. v. Lyman. 1882.

. * Revision de la Collection du Musée d’histoire naturelle de Paris.”

“Arch. Zool. Expérim. et générale, vols. iv. andv. 1875, 1876.
Perrier.

. “Anatomie comparée du squelette des Stellérides.” Ibid., vol. vii.

1878. Viguier.

. “British Fossil Echinodermata.” ‘The Asteroidea. Thomas

Wright. ‘ Palzontographical Society.’ 1862 and 1866.

. “ British Fossil Asteriade.” ‘Mem. Geol. Survey,’ vol. ii, Part 11.,

and Decade i. Edward Forbes. 1848 and 1850.

. “New Palzeozoic Star-fishes.” Salter. ‘Ann. and Mag. Nat. Hist.,’

Ser Lavo. xx |) 1857.

. “Asteriadz of the Lower Silurian Rocks of Canada.” Billings.

‘Geol. Surv. of Canada,” Decade ii. 1858.

. “The Genus Paleaster,” &c. James Hall. ‘Twentieth Ann. Rep.

on the State Cabinet.’ 1868.

. * Neue Asteriden aus devonischem Dachschiefer von Bundenbach bei

Birkenfeld.” ‘ Palzeontographica, vol. ix. 1862. Ferd. Roemer.

. “Ueber einige Asteroiden der rheinischen Grauwacke.” ‘ Sitzungs-
g

berichte d. Wien Akad.’ Bd. Ixiii. 1871. Simonowitsch.

. “ Beitrag zur Kenntniss Palzeozoischer See-Sterne.” ‘ Palzeontograph-
8 grap

ica.” Bd. xxxii. 1886. Stiirtz.

VOL. I. 2G

A466 LITERATURE OF ECHINODERMATA.

65.

66.

HOLOTHUROIDEA.

. “Die Seewalzen, eine systematische Monographie.” Lampert. 1885.
. “Monographie de l’etage Bathonien de la Moselle.” Terquem and

Jourdy.

. “On the presence of scattered Skeletal Remains of Holothuroidea in

the Carboniferous Limestone Series of Scotland.” ‘Proc. Royal
Physical Soc. of Edinburgh.’ 1880-81. R. Etheridge, jun.

. “Note sur les Holothuridées du Calcaire Grossier.” Schlumberger.

CRINOIDEA.

. “A Natural History of the Crinoidea,” ce, JS; Milleriaieene

. “Memoir on the Pentacrinus Europeus.” J. V. Thomson. 1827.

. “ Ueber den Pentacrinus caput-Medusz.” J. Miller. 1843.

. “ Development of Comatula.” Sir Wyville Thomson. ‘ Phil. Trans.’

1865.

. “On the Structure, Physiology, and Development of Antedon rosa-

ceus” Dr W-BsCarpenter, = Proc Royy 506 ate;

. “Anatomy, Physiology, and Development of Comatula.” Dr W. B.

Carpenters) hil ilirans:ouetooe:

. “On the Oral and Apical Systems of Echinoderms.” ‘ Quart. Journ.

Micro, Sci... Volswxv itl. xix UP SE Carpenters

. ““Report on the Crinoidea.” ‘ Report on the Scientific Results of the

Voyage of H.M.S. Challenger,’ vol. xi; 1884. Pi HE @arpenter

- “Report on the Crinoidea:” Part Il. The Comatulze | hcpyongeme

Scientific Results of the Voyage of H.M.S. Challenger,’ vol. xxvl.
1888. P. H. Carpenter.

. “The Early Stages in the Development of Antedon rosaceus.” H.

Bury. 1888.

. “Revision of the Palzocrinoidea.” Wachsmuth and Springer.

Philadelphia. 1879-86.
fonographie der Echinodermen der Ejifler Kalk.” Schultze.
‘Denkschr. derk. k. Akad. der Wiss. Wien.’ 1867. j

. “Recherches sur les Crinoides du terrain carbonifére de la Bel-

gique.” De Koninck and Le Hon. 1854.

. “The Crinoidea of the Lower Silurian Rocks of Canada.” E. Bil-

lings. ‘Figures and Descriptions of Canadian Organic Remains.’
Decade iv. 1859.

. “Paleontology of Illinois,” vol. v. Meek and Worthen. 1873.

(Carboniferous Crinoids and Blastoids.)

. “Paleontology of Ohio,” vols. 1. and 11. Meek. 1873 and 1875.

(Descriptions of Silurian and Carboniferous Crinoids.)

. “Handbuch der Palezontologie,” Bd. 1., Lief. 3. 1879. Zittel.
. “Discovery of the ventral structure of Taxocrinus and Flaplocrinus,

and consequent modifications in the Classification of the Crin-
oidea.” Wachsmuth and Springer. 1889.

CYSTOIDEA.

“On the Cystidea of the Lower Silurian Rocks of Canada.” E. Bil-
lings. ‘Figures and Descriptions of Canadian Organic Remains.’
Decade i. 1858.

“Notes on the Structure of the Crinoidea, Cystidea, and Blastoidea.”
E. Billings. ‘ Palzeozoic Fossils,’ vol. 1. 1874.

LITERATURE’ OF ECHINODERMATA. 467

» Ueber Cystideen.” Von Buch. 1845. (Translated in ‘ Quart.

Journ. Geol. Soc. Lond.’ 1845.)

. “Russische Sphzroniten.” Von Volborth. 1846.
. “ British Fossil Cystidez.” Edward Forbes. ‘Mem. Geol. Survey,’

vol. 11. part ii. 1848.

me awentiecn Keport om the State Cabinet.” “James Hall 13968.

(Silurian Cystideans.)

. “Systéme Silurien du Centre de la Bohéme.” (Cystideans.) -Bar-

rande (W. Waagen). 1888.

BLASTOIDEA.

. “Monographie der fossilen Crinoideen-Familie der Blastoideen.”

Ferdinand Roemer. 1851.

. “Catalogue of the Blastoidea in the Geological Department of the

British Museum.” 1886. R. Etheridge, jun., and P. H. Car-
penter.

= Notes on Echinodermata.” Rofe. ‘Geol. Mag.,’ Dec. 1, vol. 1.

1865.

468

Glick Pale Ros DOG Giele

SUL-KINGDOM V.—ANNULOSA.

CHARACTERS AND DIVISIONS OF ANNULOSA—THE SCOLECIDA
AND ANARTHROPODA.

SUB-KINGDOM ANNULOSA.—The Annulose animals are characterised
by the possession of a body which ts usually more or less elongated,
and 1s always bilaterally symmetrical instead of being radially dis-
posed. Very commonly the body ts divided into similar (homonomous)
segments, whith may be definite or indefinite, and are arranged along
an antero-posterior axis. Lateral appendages may be absent or
present, and when present, are symmetrically disposed. A nervous
system is present, and consists of one or two ganglia placed in the
anterior part of the body, or of a ventrally-placed, double ganghated
chain.

The sub-kingdom of the Azzulosa may be divided into the three
primary sections of the Scolecida, the Anarthropoda, and the Arthro-
poda, of which the two former are often separated to form a single
great division of the animal kingdom under the name of Vermes.
The division of the Arthropoda comprises the Crustaceans, the
Arachnids, the Myriopods, and the Insects, the great majority of
which are provided with a resisting exoskeleton, which is typically
composed of chitine, but is often more or less largely calcified.
Hence, the record of this division in past time is a comparatively
complete one, its earliest representatives appearing in deposits of
Cambrian age. ‘The division of the Axarthropoda comprises the
typical ‘‘ Worms ” (Leeches, Earthworms, Sea-worms, &c.), in
which exoskeletal structures are often completely wanting, or are
only partially developed. Hence the paleontological history of
these animals is a necessarily very imperfect one. We have, how-
ever, unquestionable proofs of the existence of Sea-worms in rocks
as ancient as the Ordovician, at any rate; and, if we may judge
from the evidence of “tracks” or ‘‘ burrows,” the lower Cambrian

ANARTHROPODA. 469

(and possibly even the Laurentian) deposits contain the remains of
animals belonging to this division. Finally, the division of the
Scolecida comprises the various ‘‘ Worms” which from their com-
monly parasitic habit are generally known as the £7/oz0a, together
with the group of the Wheel-animalcules or Rotjera. To say noth-
ing of the microscopic dimensions of the Rotifers and many of the
Lintozoa, none of the Scolecids are provided with hard structures,
which, under ordinary conditions, could possibly be preserved in the
fossil state. It would, therefore, be no matter of surprise to find
that we have absolutely no record of the existence of these animals
in past time. There are, however, a few remains which have been
referred to the Zzfozoa, and which may be noted here. ‘The most
satisfactory of these is a worm which was found by von Heyden in
the abdomen of a fossil Beetle from the Miocene Brown Coal of
Germany, and which has been referred to the Hairworms ( Gordiacea)
under the name of AZermis antiqua. ‘The same genus has been
detected in amber, along with minute filamentous worms which
have been referred to the ematoda, and have been placed under
the genera Anguillula and Enchytreus. ‘These are the sole remains
of Scolecids which have hitherto been detected, and it is there-
fore unnecessary here to deal further with this division of the
Annulosa.

ANARTHROPODA.

The animals included in this section are usually spoken of as
‘“Worms,” and constitute the highest division of the ‘‘ Vermes,” as
this name is now understood. Under this head are placed the
Spoon-worms (Gefhyrea), the Arrow-worms (Chesognatha), and
the Ringed Worms (Aznelida), together with the small and aberrant
group of the AZyzostomida. ‘The division is characterised generally
by the usually elongated, vermiform body, which is, typically, com-
posed of numerous, clearly recognisable segments. ‘The segments
are in general nearly similar: and when lateral locomotive appen-
dages are developed, these are not composed of successive joints,
and are not articulated to the body.

Of the four groups included under the head of Azarthropoda,
the Annelides are comparatively well represented as fossils, com-
mencing in the Cambrian period. On the other hand, the Che/og-
natha are wholly unknown in the fossil condition; as also are the
Gephyreans, unless Ehlers be correct in referring to this group
certain obscure remains from the Lithographic Slate (Jurassic) of
Germany, for which he proposed the name of Lfztrachys. ‘The
Myzostomida, however, have been certainly recognised in the fossil
condition, though their geological history is still imperfectly known.
Myzostoma, the type-genus of this curious and abnormal group,

470 ANNELIDA.

comprises small, symmetrical, unsegmented animals, with a dis-
coidal body furnished below with five pairs of unjointed feet ter-
minated by hooks, which form cysts, somewhat like plant-galls, _
upon the calyx, arms, or pinnules of Comatu/e and other Crinoids.
In various fossil Crinoids the arms or pinnules have been found to
be distorted by the cysts of some form belonging to the JZyzostom-
zda, and further investigation will probably show that this group is
really one of great antiquity.

ANNELIDA.

The class of the Azne/ida comprises the so-called Ringed Worms,
including the Leeches (//zvudinea), the Earthworms and their allies
(Oligocheta), and the Sea-worms (Polycheta). The body in the
Annelides is always elongated, and is composed of numerous seg-
ments, all the segments, except those at the anterior and posterior
extremities of the body, being in general similar to one another.
In the Leeches, the segments carry no lateral appendages, and
locomotion is effected by means of suctorial discs. In the Oligo-
cheetous worms, the segments are provided with locomotive appen-
dages in the form of horny setze, embedded basally in the integument.
Lastly, in the Folycheta the segments carry, as a rule, tufts of
horny bristles attached to unjointed lateral protuberances or “ foot-
tubercles ” (parapodia).

As regards their adstribution in time, the Oligocheta are wholly
unknown as fossils, and no reliable traces of the past existence of
the AZzrudinea have hitherto been discovered ; though some prob-
lematical fossils from the Lithographic Slate (Jurassic) of Germany
have been regarded as the remains of Leeches. The order of the
Polycheta, on the other hand, comprises worms which are marine
in habit and are at the present day very widely distributed, so that
we should expect to find ample evidence of their former existence.
As the integument of the Polychzetous worms is more or less soft,
and as the only hard structures developed within the tissues are
the horny jaws and the locomotive bristles, it can only be under
exceptionally favourable circumstances—as, for example, in the
fine-grained Jurassic lithographic slates of Germany —that the
actual Jody of these animals can have been preserved in the
fossil condition. Many of the /olycheta, however, protect them-
selves by an investing tube which may be composed of lime, or
of sand or other adventitious particles cemented together; and
the cases of these “‘ Tubicolous” worms are often preserved. ‘The
free-swimming or ‘‘ Errant” Polycheta, again, have left evidence of
their past existence in their fossilised jaws, as well as by less un-
equivocal remains in the form of filled-up burrows or meandering

POLYCHAITA. 471

trails upon the soft sand or mud of the sea-bottom. In this way
we know that the Polychetous Annelides commenced their exist-
ence at least as early as the Cambrian, while obscure traces of
their presence have even been detected in the Laurentian period.
Owing to their comparatively frequent occurrence as fossils, it is
necessary to study this group of Worms in greater detail.

POLYCHATA.

SuB-ORDER I. Tusicora.—The Worms included in this sub-
order are distinguished by the fact that they inhabit variously
formed tubes, to which they are not organically connected, and in
which they can move freely by means of their setigerous foot-tuber-
cles. | Owing to their possession of an investing tube, branchize are
only developed in the anterior region of the body (fig. 333), this
being the only part which is ordin-
arily exposed to the action of the
sea-water; hence the Zzézcola are
sometimes called the ‘cephalo-
branchiate ” Annelides.

The protecting tube of the Tubic-
olous Annelides may be composed
of carbonate of lime (Sevpula), of
grains of sand (Sade//aria), or of
sand, pieces of shell, and other ad-
ventitious particles cemented to-
gether by a glutinous secretion from
the body (Zézebella); or it may be
simply membranaceous or leathery ,jyuplicata, showing the branchie: and
(Sabella). Sometimes the tube is operculum ; 4, SAzrvorbis communts.
free and non-adherent (ectinaria) ;
more commonly it is attached to some submarine object by its
apex or by one side (Sevpu/a and Sfirorbis). Sometimes the tube
is single (Spzvorbis, generally) ; sometimes the animal is social, and
the tubes are clustered together in larger or smaller masses
(Sabellaria).

When the tube is calcareous, it presents certain resemblances to
the shells of some of the Molluscs, such as Vermetus and Den-
talium. In the living state it is easy to make a distinction between
these, for the Tubicolar Annelides are in no way organically
attached to their tubes, whereas the Molluscs are always attached
to their shell by proper muscles. In the fossil condition, however,
it may be very difficult to refer a given calcareous tube to its proper
place. As a general rule, however, the calcareous tubes of Annel-
ides, such as Sevpudla, are less regular and symmetrical than those

A72 ANNELIDA.

of Vermetus, whilst the latter are partitioned by shelly septa, which
do not exist in the former. Again, the tube of Dentalum is open
at both ends, whereas it is closed at one extremity in the Sevpude.
In the Annelidous genus Dtrupa, however, the tube is open at
both ends, so that this distinction is one not universally applicable.

Tubicolar Annelides are certainly known from the Ordovician
rocks upwards, almost every great period having representatives of
the order, though many of the fossils referred to this group are of
a more or less problematical nature. The genus SZirorbis has
survived from the Silurian period to the present day; and forms
apparently not separable from the existing genus Sezfuda are known
in deposits at any rate as old as the Carboniferous.

Of the fossil Tubicolar Annelides which are likewise known by
still existing types, and the true relations of which are therefore
beyond dispute, the three chief genera are Sevpula (including Ver-
milia and Lilograna), Spirorbis, and Ditrupa. In the genus Serpula
(fig. 334), there is a long shelly
tube, usually more or less tortu-

| Ps NINN ous, sometimes solitary, some-
| | SG Tih times aggregated, which is fixed
i Si to some foreign body by a smaller
J |, Vaal )) | Dy or larger portion of its surface.
‘ll Nh | i) MAW \ = The genera Vermila and Filo-
HN \), il ! i) ah grana are principally distinguish-
ye i NK = wo) | able from Serxpula proper by
Mi | SN a characters belonging to the ani-
iN | Sn mal and not to the tube which
uy ai it inhabits. It is doubtful, there-
i Ki \\z DN fore, if these three types can be
" i hi y ii) hE i separated in the fossil condition
i i] ein \3 MN from one another ; though it has
i ih ME i): 3 hi been adduced as a distinctive
Te A ‘ A J Dy cM oes us ea Ba the
a ay NN SHAME Wj mouth of the tube: oiten pos-
N S “3 s ul Le di ih i i) V sesses from one to three tooth-
=“ ne z vas yy 4 like projections.
As regards its microscopic
Ee apf FEE: Oxford Clay. structure, the tube of Serpula

appears to be mainly composed
of delicate concentric laminze of carbonate of lime, with a consider-
able proportion of animal matter. Some of the layers, and par-
ticularly those near the exterior, may be of considerable thickness,
and may exhibit a peculiar tubulated structure, being traversed by
minute branching canals, the direction of which is at right angles to
the long axis of the tube itself (fig. 335, a). In other cases, the

POLYCHATA. A73

tube is composed of numerous concentric laminz separated by inter-
_vening rows of tolerably large-sized vesicles (fig. 335, B), while in
other forms the laminated tissue preponderates and the vesicular
tissue is imperfectly developed and is only present in parts of the
tube.

As regards the geological range of Sezfw/a, the earliest unequiv-
ocal types are found in the Carboniferous rocks,! but the genus has
been asserted to occur in still older deposits. In the Trias and
Lower Jurassic rocks Sevpu/e are not infrequent, but are usually
solitary in habit ; whereas social types of the genus are not uncom-
mon in the later Jurassic deposits, and entire beds of limestone in
the Lower Cretaceous rocks are sometimes made up of the tubes of

Fig. 335.— Microscopic structure of the tube ot some Tubicolar Annelides. a, Cross-section of
the tube of Se7puda sp. (Recent), showing laminated and tubulated calcareous tissue; B, Cross-
section of the tube of a Tertiary species of Sevpuda, showing laminated and vesicular tissue; Cc,
Cross-section of the tube of Cornudites sp. (Silurian), showing an internal layer of laminated and
tubulated tissue, with an outer layer of a vesicular structure; D, Oblique section of a tube of
Conchicolites gregarius (Ordovician). The figures show only parts of the sections, and are all
enlarged. (Original.)

these Annelides. Numerous forms likewise occur in the Tertiary
rocks.

In the genus Szvorbis (figs. 336-338), the tube is calcareous, and
is coiled into a flat spiral, one side of which is cemented to some
foreign body. The spiral may be either right-handed (‘ dextral”) or
left-handed (“sinistral”), and the last volution is usually more or
less elevated, and is often extended into a free bent tube of no great
length. Internally the tube is usually open throughout, but in some
forms it is divided into chambers by a few calcareous partitions.
The tube is usually adorned externally with concentric striz or
annulations, sometimes with tubercles or spines ; and all the known
forms are of small size. In some species the tube is constantly
solitary, but in other cases great numbers are found together. The

1 The Serpula parallela, M‘Coy, of the Carboniferous rocks, as previously
shown, is really the siliceous ‘‘rope”’ of one of the Hexactinellid Sponges
(Ayalostelia).

A74 ANNELIDA.

name Microconchus has been proposed for forms of Sfzvorbis, which
are not simply cemented by the under surface to some foreign sub-
stance, but which make a depression or groove in the body to which
the tube is attached. The living species of Szvordzs are all marine,
but some of the extinct forms of the Carboniferous period are com-
monly found attached to the stems and leaves of undoubted terrestrial
plants, a fact which would seem to show that some of these ancient
types were able to exist in brackish, or, possibly, even in fresh water.

Fig. 336.—a, Spzrorbis omphalodes, natural size and enlarged — Devonian, Europe and
America; 4, SAzvorbis Arkonensis, of the natural size and enlarged; c, The same, with the
tube twisted in the reverse direction—Devonian, America. (Original.)

Fig. 337.—a, 4, Spivorbis laxus, enlarged—Silurian, America; c, Spzvorbis spinuliferus, of the
natural size and enlarged—Devonian, Canada. (After Hall and the Author.)

Fig. 338.—Spivorbis (Microconchus) carbonarius, natural size, attached to a fossil plant,
and magnified—Carboniferous. (After Dawson.)

The earliest known species of Sf/zvorbis occur in the Ordovician
rocks, and the genus is abundantly represented in the Silurian,
Devonian, and Carboniferous rocks, the tubes often occurring in
great numbers attached to the exterior of shells or corals. The
Spirorbis helicteres of the Carboniferous rocks sometimes occurs in
the Carboniferous rocks of Scotland in quantities sufficient to make
up bands of limestone of some thickness. Other species have been
described from the Permian rocks, and the genus continues to be
well represented in both Mesozoic and Tertiary deposits, while liy-

POLYCHATA. 475

ing forms, apparently little different from the fossil ones, abound in
recent seas.

In the genus Ditrupa, the tube is free and unattached, open at
both ends, and calcareous in composition, its general aspect being
very similar to that of the shell of a Dezzalium. The genus appears
to have existed in Carboniferous times, but it is not found in any
abundance till the Tertiary period is reached. Species of this genus
are abundant in the London Clay (Eocene) and in the Red Crag
(Pliocene).

In the Paleozoic rocks there occur the remains of various or-
ganisms which have been commonly referred to the Tubicolous
Annelides, but which differ more or less extensively in structure and
character from any existing types, their precise nature being thus
rendered more or less doubtful. Some of the more important of
these may be briefly considered here. Among the most problemat-
ical of these are the fossils for which the names of Serpudlizes and
Trachyderma have been proposed. Under the head of Serpulites
are included smooth, arcuate, semi-calcareous, glossy, apparently
unattached, tubular fossils, which sometimes reach a length of a
foot, with a diameter of an inch. In the most typical forms of
Serpulites the tube exhibits two small longitudinal ridges or tubular
ribs, placed respectively along the convex and concave faces of the
fossil; but these thickened borders do not appear to be constantly
present. Forms of Sevfulifes are found in the Paleozoic rocks from
the Ordovician to the Carboniferous inclusive, but their true affinities
are by no means certain. The name of Zrachyderma (apparently
the same as the Scolecoderma of Salter) was proposed by Phillips for
the casts of membranous, flexible tubes which are found in Ordo-
vician and Silurian deposits. These are transversely wrinkled or
plaited, and as they are usually found to cross the strata obliquely
or vertically, it is probable that they are really Annelidous in their
nature.

More remarkable than the preceding is the Ordovician, Silurian,
and Devonian genus Cornulites (figs. 339, 340), in which the animal
was solitary, and inhabited a conical calcareous tube of considerable
size. The tube of Cornulites (fig. 339) is ringed with well-marked
transverse annulations, and is usually ornamented with fine longitud-
inal striz. The tube gradually tapers towards its lower end, where
it appears to have been attached to foreign bodies, the attachment
taking place by the pointed and usually bent initial portion of the
tube, and not (as in Or¢onia) by the whole of one side. Moreover,
many adult examples show no signs of having been attached by the
pointed base, so that the tube was probably not invariably fixed to
foreign bodies, but may have been free. The tube may be three
or four inches long, straight or slightly curved, and with a wide

476 | ANNELIDA.

aperture at its broad end. The internal cast of the tube has the
form of a series of inverted conical rings, of small width, arranged
in an imbricating manner. ‘The most remarkable feature about
Cornulites is, however, the peculiar micro-structure of the thick
calcareous wall. Thin sections of the tube show that it is composed
principally of lenticular calcareous vesicles of considerable size (figs.
335, C, and 339, B), resembling in form the vesicles of a Cystiphyl-
loid coral. ‘These vesicles are sometimes traversed by irregular
laminated bands or fibrous layers, and a similar layer seems to line
the interior, and cover the exterior of the tube. The inner laminated
layer (fig. 335, C) is sometimes of considerable thickness, and is

oe ain er @ ami)

ANN X $ jj
iy fie i 4
Sei
OK ANI

)
iby

i
ie a il Hin

Fig. 340.—Cornulites sp. Silurian. The
right-hand figure represents a cast of the
tube. The left-hand figure represents a

Fig. 339.—Cornulites serpularius, from the specimen broken below. (Original.)
Wenlock Limestone. a, Tube of the natural
size; B, Portion of a cross-section of the tube
enlarged. (Original.)

traversed by-minute transverse tubuli similar to those seen in the
laminated calcareous tissue of some recent Sevpude. As the tube
in some Sevpule (fig. 335, B) also shows a vesicular character, the
microscopic structure of the tube of Cornudites is not so abnormal as
it has generally been supposed to be, and its Annelidan nature is,
on the whole, rather supported by its minute structure than dis-
proved.

In the genus Orfonia (fig. 341) are included conical, slightly
flexuous calcareous tubes, which have a general resemblance to
Cornulites, but are of comparatively small size, and are cemented
by the whole of one surface to some foreign body such as a shell or
a coral. ‘Though often found in considerable numbers, the tubes
are essentially solitary in habit. The tube is ringed with imbricating

POLYCHATA. AGG

annulations, and the free surface of the tube, in some species, appears
to have a cellular structure, similar to that which is seen in the tube
of Cornulites ; but the microscopic characters of Ovtonza have not

Fig. 341-—a, Tubes of Ortonia conica growing upon the valve of Stvophomena alternata,
natural size; B, A single tube of the same, enlarged. Ordovician. (Original.)

as yet been worked out. The known species of Orfonza are found
in the Ordovician, Silurian, Devonian, and Carboniferous rocks.
It may be noted in this connection that the tubes of some species
of Ortonia, except for being attached along one side to foreign
bodies, present a considerable
general likeness to the tubes of
the genus TZentaculites, which
genus high authorities have re-

1D

garded as Annelidan. There i
are, however, important distinc- fy
tions between these two types, Bi

and the genus TZentacudlites will
be considered here under the
Prteropoda, to which group, in
the author’s opinion, it is pro-
perly referable. =
A similar superficial likeness _ Fig. 342.—Conchicolites gregarius, growing
to Zentaculites is exhibited by (Ouse sg ee ig Ta
the Ordovician genus Conchico-
lites, which is certainly Annelidan. In this genus (fig. 342) the
animal was social, and formed masses of clustered tubes, growing
side by side, attached by their bases to the outside of the dead
shells of Orthocerata or Brachiopods. Each tube is made up of
short imbricating rings, each of which partially overlaps the one
below. Hence the cast of the tube (the right-hand figure in fig.

478 ANNELIDA.

342) appears to consist of short conical segments, the broad ends
of which are turned away from the mouth of the tube. Though
the general aspect of the tubes of Comchicolites is very similar to
that of Cornudites, the micro-structure of the tube is very different
in the two genera. In Cornudizes, as has been shown, the tube has
a characteristic vesicular structure (fig. 335, c). On the other
hand, thin sections of the tube of Conchicolites (fig. 335, D) show
it to be devoid of this cellular structure, and to be composed of
imbricating calcareous plates, which are fibrous in character, and
which overlap in such a way that the broad upper ends of the
successive rings are directed towards the interior of the tube.
SUB-ORDER II. ERrantia.— The Polychzetous Annelides in-
cluded in this sub-order are free-living animals which do not form
for themselves investing-tubes. The body is usually elongated,
each segment carrying on its sides tufts of horny sete, attached to

Fig. 343.-—a, Head of Wevezs incerta, viewed from beneath, and enlarged (after Quatrefages) :
d, The principal pair of chitinous jaws (the dark dots on the lobe behind these are smaller den-
ticles); fa’, Internal pair of palpi; Aa, External or greater pair of palpi; ¢ 77, Tentacles. B,
Foot-tubercle of erezs, enlarged: zo, Notopodium; ze, Neuropodium; c, Dorsal cirrhus; ¢’,
Nena! cirrhus; 664, Branchial filaments ; a, Acicule; ss, Sete attached to the dorsal and
ventral oars.

fleshy, double tubercles or “ parapodia” (fig. 343, B). The mouth
is furnished with horny or partially calcified jaws (fig. 343, A). The
branchiz are attached to the sides of the body, or to the dorsal
surface. ‘Though the integument of the Errant Annelides secretes
chitinous matter to a certain extent, a resistant exoskeleton is not
developed, the only hard structures present being the chitinous
setae and the horny jaws, the lower pair of the latter (and sometimes
the upper pair also) being more or less completely calcified. Owing
to the soft nature of their integument and foot-tubercles, it can only
be under the most favourable conditions that the actual dody of an
Errant Annelide can be preserved in the fossil state. Specimens

POLYCHATA. A79

of this nature do, however, occur occasionally in finely-levigated
sediments, such as the Lithographic Slates (Jurassic) of Germany
and the Eocene Slates of Monte Bolca. Impressions of this kind
not only exhibit the form of the body, but may show the lateral
setee (fig. 344) and the jaws in place; and upon such Ehlers
founded the genera Lunzcites, Lumbriconereites, and Meringosoma,
all of which were originally described from the Lithographic Slates
(Jurassic) of Germany.

Apart from the comparatively very rare cases in which, as above
described, the body of the worm is
itself partially preserved, it has been
shown by Hinde and others that the
horny jaws of Annelides are by no
means of rare occurrence even in
strata as ancient as the Ordovician,
so that the Palzeozoic seas must
have been tenanted by vast numbers
of these animals. The jaws of An-
nelides (fig. 345) usually present
themselves as minute, dark, shining
objects, wholly unconnected with
one another, or with the remains of
the animal to which they originally
belonged. Though probably partly
calcified, the jaws seem to be in the
main composed of chitine, as they
are not destroyed by the action of
mineral acids. They average about
zz inch in length, but a few reach a
length of a third of an inch. In
jorm, the jaws are very variable.
In one type (fig. 345, A), the jaw
is long and narrow, with a series of
nearly similar teeth on one margin ;
in another common form, the jaw is
furnished with a powerful anterior
hook, which may be immediately
succeeded by a series of small teeth,
or may have the latter on the straight
edge of a wide posterior extension

Z “SF ————
SIO SS

ioe

= ————

: sens : Fig. 344.—The impression of an Errant
(fig. 345; B) , other varieties are in Annelide (Eunicites avitus), from the

the shape of simple hooks with g_ Lithographic Slates of Eichstadt, of the

r : 5 3 natural size. (After Zittel.)
wide flange-like extension behind

(fig. 345, C); while others are falciform, with a series of small teeth
on the curved upper edge. There are other variations in the shape

480 ANNELIDA.

of these minute fossils, and owing to the isolated condition in which
they occur, it is difficult to refer them to genera and species. Most
of the fossil forms resemble the jaws of the living family of the
Eunicea, and such have been referred to the genera Eumicites (fig.
345, A), Arabellites (fig. 345, B), Lumbriconereites, &c. Others
correspond with the recent genus G/ycera, and have been placed
under Glycerites (fig. 345, C); while Verezdavus appears to represent
the existing family of the Lycoridea.

As regards their distribution in time, Hinde has shown that these
fossil jaws are abundant in some parts of the Ordovician, Silurian,
Devonian, and Carboniferous formations ; and they are also known
to exist in Mesozoic and Tertiary deposits in actual connection

Fig. 345.—Jaws of Annelides from the Ordovician rocks (Cincinnati group) of North America.
A, Jaw of Eunicites varians, enlarged 3% times; B, Jaw of Avadellites cornutus, enlarged
twelve times; c, Jaw of Glycerites sulcatus, enlarged fifteen times. (After Hinde.)

with the bodies of their original possessors. If Rohon and Zittel
should prove to be correct in their view that the so-called ‘‘ Cono-
donts” are really of the nature of the jaws of Annelides, then these
minute fossils occur in rocks as ancient as the Upper Cambrian ;
but the nature of these problematical bodies will be dealt with
more fully later on.

Apart from the above-mentioned indubitable remains of Errant
Annelides, numerous more or less distinct worm-like markings,
which are found in muddy and sandy sediments throughout almost
the whole of the series of stratified rocks, have been referred to ani-
mals of this group. Some of these (such as JVereztes and Phyllo-
docites) have been described as being of the nature of the petrified.
bodies of Sea-worms ; but as they exhibit absolutely no structure,
it is in the highest degree improbable that this explanation of their
origin is correct. The true nature, in fact, of most of the remains
here in question must be regarded as exceedingly uncertain. Some
are, probably, really referable to the vegetable kingdom ; others are
almost certainly formed by Molluscs, or by Crustaceans; others
are of entirely dubious affinities ; while others are, doubtless, really
due to the operation of Errant Annelides. It may be added that
the fossil remains which have been referred to Nemertean Worms
cannot at present be separated, in any satisfactory manner, from
those formed by Errant Annelides. ‘Thus the so-called /Vemertites

POLYCHATA. ASI

of the Silurian is just as likely to be Annelidan as Nemertean, and
the nature of the Legnodesmus of the Solenhofen Slates is wholly
problematical. In fact, the entire subject of the remains of fossil
Errant Annelides is one of the most obscure and difficult with
which the paleontologist is called upon to deal; and all that can
be done here is to glance at some of the leading points of interest
connected with it, under the following heads :—

I. Burrows of Habitation.—Various recent Annelides live buried
in the sand or mud, between tide-marks or in shallow water, and
communicate with the surface by means of a perpendicular shaft
or burrow. Such shafts may, for convenience’ sake, be termed
“burrows of habitation,” though the animal forms a fresh one at
will, as it moves from one spot to another; and, as a matter of
course, they run in a direction more or less opposed to the surfaces
of the laminz of the rock, being often quite vertical. Sometimes

Fig. 346.—Annelide-burrows (Scolithus Canadensis) from the Potsdam Sandstone (Upper
Cambrian). (After Billings.)

such burrows are hollow, but they are more commonly filled up by
the matrix of the rock. Among the genera which have been founded
upon remains of this kind are Scolithus, Hltsttoderma, and Arent-
colites, all of which occur in rocks of Cambrian or Ordovician age.
Scolithus is founded upon long burrows, which are nearly straight,
and descend vertically through the rock (fig. 346). They often
become somewhat widened out superiorly, and are generally found
in great numbers together. They occur abundantly in the Pots-
dam Sandstone (Upper Cambrian), and Clinton formation (Silurian)
of North America, and also in the hard sandstones of the Stiper
Stones in Shropshire (Ordovician). They have been supposed to
have been formed by sea-weeds, but there is little doubt that they
VOL. I. 2H

482 ANNELIDA.

are truly the burrows of Annelides. The somewhat problematical
fossil upon which the genus /7zstioderma is founded is described
as a curved burrow, from one to nearly four inches
in length, terminating in a trumpet-shaped open-
ing, which is placed in the centre of a small
mound. The genus Avenicolites, again (fig. 347),
includes small double burrows, which form loops,
shaped like the letter U, opening on the surface
Py Sees by two apertures placed close to one another.
mus. Fromthe Long- Lhe mouths of these burrows are thus placed in
Pee are Cam- pairs, one orifice being supposed to be an aper-

ture of entrance for the worm, and the other one
of exit. Burrows of this nature occur abundantly in the Lower
Cambrian strata of the Longmynd, and are also far from uncommon
in deposits of Ordovician age.

Il. Wandering Burrows.—Various recent Annelides, among
which the common Lug-worm (Avenicola piscatorum) is a notable
example, form long, wandering, irregular, and tortuous tunnels in
the sand of the sea-shore, at a little distance below the surface. In
these cases the worm subsists upon particles of organic matter dis-
seminated through the sand or mud, through which, therefore, it
literally eats its way. The burrows thus formed are, consequently,
very irregular; they principally have a horizontal direction; if
formed by many individuals, they may cross or intersect one
another in various ways; and as the worm proceeds on its course,
they become filled up in the rear of the advancing animal by the
sand which has been passed through the alimentary canal, some of
this sand being often voided at some point at the surface to form
the tortuous “‘ worm-casts,” with which every wanderer on the sea-
shore is so familiar. Bodies which we may reasonably assume to
be of essentially the same nature as the filled-up “ wandering bur-
rows” of worms like the living Lug-worm, are well known to all
workers amongst the more ancient, muddy and sandy strata of
the earth’s crust, and they have received various names, and have
had very various origins ascribed to them. They usually present
themselves as irregularly cylindrical, worm-like elevations of the
surfaces of the strata (fig. 348), which usually are more or less
parallel with the laminze of deposition, but often run somewhat
obliquely to these, so as to thread successive laminz to one
another. Generally, they differ slightly in texture and colour from
the surrounding rock—as can well be supposed, if their origin be
as above described—and from their somewhat superior hardness,
they resist disintegration by weathering, and thus come to stand
out prominently above the surface. Though they may be much
matted together, and may thus appear to branch, it is only in some

POLY CHANDA. 483

cases that they really subdivide. It would appear that many of
the fossils of the Paleeozoic rocks which have been referred to the
Fucoids, under the generic titles Paleochorda, Paleophycus, &c.,
may be really the filled-up burrows of wandering marine worms,
and such remains may at present be grouped together under the
common name of //lanolites.

While the above explanation will aceount sufficiently for many
of the objects which have been described under the name of Pad@o-
chorda, and which are here spoken of under the title of P/anolites,
there are many similar fossils for which Nathorst would account in
a different and a quite satisfactory manner. It has been shown,

Fig. 348.—P/lanolites vulgaris, the filled-up burrows of a marine worm.
Silurian (Clinton Group), Canada. (Original.)

namely, by this well-known observer, that plaster-of-Paris casts of
the shallow grooves which worms make in crawling over the sur-
face of fine mud, present cylindrical vermiform markings precisely
similar in form and appearance to the fossils here spoken of under
the name of Planolites. Nathorst therefore concludes that most,
if not all, of such fossils are really convex casts of what were origin-
ally grooves or furrows ; and he supports this contention by show-
ing that the worm-like markings in question are found to stand out
in demi-relief from the wader surfaces of the strata. On this explana-
tion—which would probably account satisfactorily for very many of
these worm-like fossils—the structures here spoken of would really
be of the nature of ¢vacks, rather than of filled-up durrows. At the

A484 ANNELIDA.

same time, there are undoubtedly some examples which may be
regarded as burrows and not as tracks, since there are specimens in
which the cylindrical worm-like markings pass obliquely from one
lamina to another, instead of being confined to a single surface of
deposition. Another point that may be noted in connection with
this subject is, that it has been shown by Nathorst that the tracks
of certain Annelides upon the surface of mud or sand are branched.
_ The fact, therefore, that many of the fossils described under such
titles as Paleochorda and Paleophycus are seen to branch, would not
be in itself sufficient to preclude acceptance of the explanation of
their origin put forward by Nathorst.

In connection with the burrows of worms, a word may be said as
to the curious vermiform bodies which occur abundantly in the
Lithographic Slates (Jurassic) of Solenhofen, and which have been
described under the name of ZLumbricaria. ‘The fossils in question
are about as thick as a quill in some cases, but in others are only
of the dimensions of twine, and they form convoluted and confused
elevations on the surface of the beds. They have generally been
looked upon as of the nature of casts of the alimentary canal—true
‘“‘worm-casts” in fact—of marine worms; and, judging from their
appearance, this explanation of their nature is probably correct.

Ill. Zvrails and Tracks.—Lastly, we have to deal briefly with a
great group of fossils which have been supposed to be of the nature
of the “‘ trails” of Errant Annelides—that is to say, markings formed
by the animal dragging its soft body over the surface of wet sand or
mud, between tide-marks or in shallow water. Markings of this
nature are extremely abundant in many of the older rocks, and in
many cases no doubt can be entertained as to their being really the
tracks of some marine animal. Even in these cases, however, it is
at present impossible, in the majority of instances, to discriminate
between the trails produced by Annelides and those formed by
Univalve Molluscs or by Crustaceans. There are, nevertheless,
certain tracks which may be regarded with considerable probability
as Annelidan. This is especially true of the Silurian fossils upon
which the genera /Vereizes (fig. 349, B) and Phyllodocites (fig. 349, A)
have been founded. In these cases we have long, sinuous, and
often sharply-bent impressions on the surfaces of the strata, which
consist of a central, broader or narrower axis, representing the body
of the worm, and of a series of lateral, more or less leaf-like mark-
ings, representing the foot-tubercles. These tracks, and others like
them, have commonly been supposed to represent the actual dody of
the Annelide, now replaced by mud; but, as before remarked, it is
very difficult to conceive of such a replacement, and it is more likely
that we have simply the trail of the animal formed by its serpentine
wandering over the surface of soft mud.

POLYCHATA. 485

Another fossil, which is extremely abundant in the Silurian rocks
of some localities, and which has generally been supposed to be the

Ae
(AA
A
|

iy

\
i

el |

Sen

| &)

oe d

\\
i

TTT “=: ry Suc WY I Ta
EM: LA
MUI, ees E ill

ay NWA iy Pie

SSS
Fig. 349.—A, A small portion of the trail of Phyllodocites ¥acksont, from the Silurian slates
of Wurtzbach, of the natural size (after Geinitz); 8, Small portion of the trail of Veveztes
Loomisii, from the same locality, natural size (after Geinitz); c, Fragment of a slab, showing
Myrianites tenuis, from the Silurian slates of Thornilee, Peeblesshire, of the natural size. The
slab has split at different levels in different parts, and the fossil is seen to cut vertically across the
laminz of deposition, the surfaces thus formed being concentrically striated. (Original.)

track of an Annelide, is MZyrianites. In ordinary specimens of this
genus (fig. 349, C) all that is seen is that the surfaces of the strata
are marked by winding and tortuous linear impressions, of extremely

486 ANNELIDA.

small comparative width, and easily recognisable from the matrix by
their darker colour and slightly different texture. These meandering
markings wind over the surface of the stone in indefinite undulations,
often appearing to cross one another; and no one, looking at such
a specimen, would be inclined to doubt that he had to deal with
the trails left upon the mud of the seashore by some soft-bodied
marine animals, though he might question if these could be An-
nelides. Other specimens, however, of the same fossil, which have
been carefully examined by the author, prove conclusively that, in
spite of appearances, MZyrianites is not only not Annelidan in its
nature, but that it cannot possibly be the ¢vack of any animal what-
ever. It can be shown, in fact, that the narrow serpentine markings
upon the surface of the stone, which are universally understood
under the name JA/yrvianites, are really the cut edges of thin vertical
laminar expansions, sinuously folded, and seen in horizontal section.
In fig. 349, C, a portion of one of the specimens referred to is

Fig. 350.—Cvrossopodia Scotica, a supposed Annelide track. Silurian. (After M‘Coy.)

figured, from which it will be seen that the fossil cuts directly across
the lamine of deposition, its actual surface (where exposed by exfolia-
tion of a part of the slab) being marked with concentric striz. It
is therefore quite clear that AZyrianizes was really a thin, erect, folded,
leaf-like expansion, of some kind or another, and that what paleeon-
tologists have described under this name is only the horizontally-cut
edge of this expansion as seen on the surface of the stratum, What
Myrianites really is, is quite an open question. It is, perhaps, a
peculiar form of Fucoid. ‘That it is not Annelidan seems perfectly
certain.

Another fossil which has generally been regarded as referable to
the Errant Annelides is the Cvossopodia of M‘Coy (fig. 350), also

POLYCHATA. - 487

very abundant in certain Silurian strata. In this fossil there is a
central narrow groove, which winds in serpentine bends over the
surface of the stone, and is supposed to represent the body of the
animal, bounded on each side by a broader and generally ill-defined
space, supposed to represent the foot-tubercles. That Cvossopodia,
however, should be the petrified Jody of an Errant Annelide seems
almost incredible, and that it is even the “vack of one of these
creatures is extremely improbable. In well-preserved specimens of
any size, the impressions known ‘under this name are seen to wind
backwards and forwards over the stone in a succession of long loops
which are placed quite close together, and which could hardly have
been produced by any animal in a movement of forward progression.
There is, indeed, some evidence that the impressions of Cvossopodia
really cut directly across the laminze of deposition to some depth,
and that they have some direct, though at present not understood,
connection with AZyrianites.

As might have been expected, any fossils which can be supposed
with any probability to be the tracks of Annelides, or of other
marine animals, present themselves as depressed or concave markings
on the upper surfaces of the strata. The casts of these markings,
however, are often to be observed on the wzder surfaces of the beds,
and these, as a matter of course, present themselves as convex or
elevated impressions. When the beds are vertical, or when the
specimens are not found actually zz szfu, it is impossible to distin-
guish between these two classes of specimens; especially as some
elevated impressions, supposed to be tracks, do really occur on the
upper surfaces of the strata. Such impressions, in the opinion of
Principal Dawson, ‘“‘ have been left by denudation of the surround-
ing material, just as footprints on dry snow sometimes remain in
relief after the surrounding loose snow has been drifted away by
the wind, the portion consolidated by pressure being better able to
resist the denuding agency.”

As has been already pointed out, however, there is strong reason
for accepting the conclusion of Nathorst that many of the elevated
worm-like markings that are seen in muddy and sandy sediments are
in reality casts of grooved tracks or furrows which have been pro-
duced by the movements of Annelides and other marine animals
over fine silt.

Before leaving this obscure subject finally, it may be well to
notice briefly one or two considerations which bear upon the ques-
tion of the origin and real nature of markings such as we have been
considering. In the first place, the late Mr Albany Hancock, in
an extremely able memoir, advocated the view that the vermiform
fossils of the older rocks may have been, in general at any rate,
produced by Crustaceans. He showed that similar markings are

488 ANNELIDA.

produced, at the present day, by small Amphipod Crustaceans
(Sulcator arenarius and Kroyera arenaria), which burrow immedi-
ately below the sand on the sea-shore, and give rise to the following
appearances: (1.) Large tracks, about 3-8ths of an inch wide,
slightly raised, ribbon-like in shape, with a median groove, often
intricate and convoluted, sometimes knotted, and several feet in
length; (2.) Narrow wedge-shaped furrows, 2-1oths of an inch
wide, winding capriciously and often abruptly over the surface ;
(3.) Nodulated or articulated tracks, consisting of a small furrow,
with a rounded ridge on one side. Mr Hancock showed that
tracks of these three kinds are actually produced by the above-
named small Crustaceans, which burrow beneath the sand, but a
short way below the surface, “‘the arch or tunnel thus formed par-
tially subsiding, as the creature moves forwards, and breaking along
the centre,” thus giving rise to a median groove. There is no
doubt that the phenomena so carefully observed by Mr Hancock
throw considerable light upon the subject of the supposed Anne-
lide tracks of muddy and sandy sediments; but there is room for
much hesitation before concluding that any of these tracks, in the
older rocks at any rate, were really formed by Crustaceans like the
living Sulcator arenarius. One ground for such hesitation need
alone be brought forward here—namely, that the so-called ‘‘ Anne-
lide-tracks” of the older Palzeozoic rocks often occur in vast num-
bers, in finely-levigated deposits, and throughout a thickness of
sometimes hundreds of feet of strata, and that it is almost incon-
ceivable that traces of the makers should not have been detected
in the same beds, supposing them to have been formed by animals
which, like Crustaceans, have a skeleton highly susceptible of
preservation in the fossil condition.

In the second place, there are good grounds for ascribing certain
forms of “tracks,” which have often been regarded as Annelidous,
to the operation of Univalve Molluscs. It is well known that many
Gasteropods, in crawling over the surface of sand or mud, give rise
to sinuous or intercrossing trails, the general feature of which is the
presence of a median furrow or groove, which may or may not be
bordered by a series of lateral markings on each side. Thus, the
annexed engraving (fig. 351) shows the track of a common living
Gasteropod (Purpura lapillus) when moving over firm sand, and it will
be at once seen that the markings produced by this Univalve are
exceedingly similar to the supposed Annelide-trails upon which the
genus Cvossofodia has been founded, both consisting of a central
groove, bounded by lateral raised margins. While it may therefore
be regarded as very probable that some supposed worm-tracks have
been formed by Molluscs, it cannot be altogether overlooked that
we do not usually meet with the fossil shells of such Molluscs in

POLYCHATA. 489

the deposits in which the trails occur, as we might reasonably
expect to do.

Principal Dawson, again, suggests “that Algz and also land-
plants, drifting with tides and currents, often make the most remark-
able and fantastic trails,” which might easily be mistaken. for the

Fig. 351.—Track of the living Purpura lapillus on firm sand, reduced three diameters.
(From a drawing made by the late Robert Gray.)

tracks of Annelides. This suggestion is a very valuable one, but
certainly will not explain the origin of the majority of the so-called
** Annelide-tracks” of the Paleozoic rocks, the regular serpentine
form of which is one of their most remarkable features.

Lastly, some observers are disposed to see in these supposed
tracks and trails the remains of various forms of A/ge, the drifted

490 ANNELIDA.

stems of which, lying on the surface of mud or sand, have, by their
slow decay, given rise to the worm-like markings which we have
been here considering. The evidence in favour of this view does
not appear to be satisfactory, but it is impossible to pursue further
this intricate subject in this place. The student desirous of fuller
information on this difficult question may be referred more particu-
larly to the important and beautifully illustrated memoir which Pro-
fessor Nathorst has published upon the tracks and markings produced
by various living forms of Invertebrates.

Oo

ul

EIPTERASURE:

. “A Contribution to the Study of the British Carboniferous Tubicolar

Annelides.” ‘Geological Magazine.’ 1880. R. Etheridge, jun.
“Notes on the Annelida Tubicola of the Wenlock Shales.” ‘ Quart.
Journ. Geol. Soc.,’ vol. xxxviili. 1882. Vine.

. “Cornulites, Tentaculites, and Conchicolites.” Nicholson. ‘Amer.

Journ? Sci-and Arts? 1872.

. “On the Genus Ortonia.” Nicholson. ‘Geol. Mag.,’ Dec. 1, vol. ix.

1872

_ “ Ueber fossile Wiirmer aus dem lithographischen Schiefer in Bayern.”

‘Palzeontographica,’ Bd. xvi. 1867-70. Ehlers.

. “On Annelide Jaws from the Cambro-Silurian, Silurian, and Devonian

_ Formations in Canada, and from the Lower Carboniferous in
Scotland.” “Quart. Journ: Geol. Soc.,’ vol. xxxv. 1870; “Hiumde:
“On Annelide Jaws from the Wenlock and Ludlow Formations of
the West»of England.” ‘Quart. Journ. Geol. Soc.,’ vol. xxxvi.
1880. Hinde.
“On Annelide Remains from the Silurian Strata of the Isie of Got-
land.” ‘ Bihang till K. Svenska Vet.-Akad. Handlingar,’ Bd. vii.
1882. Hinde.

.“* Ueber» Conodonten.”. ‘ Sitzungsberichte d| k. bay Akad

Wiss.’ 1886. (Maintaining the view that the “ Conodonts” are
the jaws of Annelides.) Rohon and Zittel.

. “Om Spar af nagra Evertebrerade Djur M. M. och deras Palzonto-

logiska Betydelse (On the Tracks of some Invertebrate Animals
and their Palzeontological Significance).” ‘Kongl. Svenska Vet-
enskaps-Akad. Handlingar.’ 1881. Nathorst.

. “Paleontology of New York,” vols. i. and ii. 1843 and 1852. Also

vol. vil. Suppl. 1888. James Hall.

. “Fossils of the Longmynd.” Salter. ‘Quart. Jour. Geol. Soc.,’ vol.

xiii, 1857. Also ‘Mem. Geol. Survey,’ vol. iii., Appendix. 1866.

. “Vermiform Fossils from the Mountain Limestone.” Albany Han-

cock. ‘Ann. and Mag. Nat. Hist.,’ ser. 3, vol. ii. 1858.

. “The Taconic System.” Emmons. 1844.
. “The Silurian System.” Murchison. 3d ed. 1859. (Description

of Annelides by Macleay.)

. “Petrefacta Germaniz.” Goldfuss. 1826.
. “Ueber ein A*quivalent der takonischen Schiefer Nord-Amerikas in

Deutschland.” Geinitz and Liebe. ‘Verhandl. d. k. Leopold.
Carolin. deutsch. Akad. 1867.

“Impressions and Footprints of Aquatic Animals on Carboniferous
Rocks.” Principal Dawson. ‘Amer. Journ. Sci. and Arts.’ 1873.

die a4

491

Gm APTER “XXXVI.
AKLARORODA.
CRUSTACEA.

THE division of the Arthropoda or “ Articulate Animals” com-
prises the four great classes of the Crustacea (Lobsters, Crabs, &c.),
the Arachnida (Spiders and Scorpions), the JZyriofoda (Centipedes
and Millepedes), and the JZmsecta (the Insects properly so called),
and is distinguished as follows :—

The body ts composed of a sertes of segments or “somites,” which
are usually definite in number, and which are arranged along a lon-
gitudinal axis. Each segment may be provided with a single pair of
appendages, and these are always jointed, and are articulated to the
body. Both the segmented body and the articulated appendages are,
as a rule, furnished with a chitinous, often more or less extensively
calcified, exoskeleton, formed by a hardening of the integument. The
appendages are hollow, and the muscles are prolonged into their in-
tertor. The nervous system consists, typically, of a double chain of
ganglia placed along the ventral surface of the body, united by lonsgt-
tudinal commissures, and traversed anteriorly by the esophagus. The
heart, when present, ts situated dorsally. When distinct respiratory
organs are present, they may be in the form of gills or branchia, or
they may be saccular or tubular involutions of the integument ( pul-
monary sacs or trachee) adapted for breathing air directly.

If the King-crabs and the Eurypterids be retained in the C7ws-
tacea, then the classes of the Arachnida, Myriopoda, and Lnsecta
comprise those Arthropods which breathe air directly, and which
are thus, in general, adapted for a terrestrial life. On the other
hand, the Cvwstacea are essentially water-breathing animals, and
even those forms which are terrestrial in their habit, possess respir-
atory organs in the form of branchiz. From their generally aquatic
mode of life, and the usually more resistant character of their exo-
skeleton, the Crustacea are more abundantly represented in the

AQ2 ARTHROPODA.

fossil condition than is any of the other classes. All the four
great classes of Arthropods are, however, known to have been in
existence in rocks as old as the Silurian, while the Crustaceans
were thoroughly differentiated in the Cambrian period. It is,
therefore, clear that the point of divergence of the four primary
groups of Arthropods must be sought for in a period long anterior
to the Cambrian ; and it is hardly probable that we shall ever be-
come acquainted with the primitive form from which the ‘ phylum ”
of the Arthropoda took its origin.

Ciass I. CRUSTACEA.

The class of the Crustacea may be generally defined as compris-
ing Arthropods which are essentially water-breathers, and usually are
provided with gills or branchiea. The segments of the body are usu-
ally definite in number, and some of them almost invariably carry
jointed appendages. The head, typically, carries two pairs of anten-
ne; some of the appendages are modified to act as masticating or-
gans ; and the segments of the abdomen are commonly furnished with
locomotive appendages. The body ts protected by a chitinous or
partially calcified exoskeleton or “‘ crust,’ and the number of am-
bulatory limbs ts mostly from five to seven. The Crustacea, in
general, pass in development through a distinct metamorphosis, but
the nature of this differs in different cases.

The body of a typical Crustacean, such as a Lobster, generally
exhibits a division into three regions—a head, a thorax, and an
abdomen — each of which is composed of a certain number of
somites, which may be free, or may be more or less indistinguish-
ably fused with one another. Very commonly, the segments of
the head and thorax are united together into a ‘‘ cephalothorax,”
which may be protected by a common shield or “carapace”
(fig. 352, ca). The segments of the abdomen may be separate
and movable on one another, or a smaller or larger number of
the terminal segments may be fused to form a caudal shield or
“‘pygidium.” ~ The. last segment of the abdomen (fig.) 35277)
is known as the “telson,” and is generally without appendages,
while the anus opens on its lower surface. The “telson” has been
variously regarded as an unpaired appendage, as a segment devoid
of appendages, or as representing an aborted vegzon of the body,
the latter being the view which, on various grounds, seems to be
the most probable one.

Each segment of the body of a Crustacean may be regarded
as essentially composed of a convex upper plate (‘“‘tergum”),
closed below by a flatter ventral plate (“sternum”), the line
where the two unite being produced downwards and outwards, or

CRUSTACEA. 493

outwards only, into a plate which is known as the “pleuron” or
“pleura” (fig. 353). Each segment of the body may carry a pair
of appendages (even the telson being sometimes furnished with
such); and the typical appendage of the Crus¢acea consists of an
undivided basal portion, or “ protopodite,”
to which are attached two diverging branches
(fig. 353). The outer of these branches is
termed the ‘‘exopodite,” and the inner the
“endopodite”; but one or other, or both,
of these terminal divisions of the appendage
may be suppressed.

Mnewhead “imjithe Crustacea as a rule
carries in front a pair of eyes, which in
the higher forms are “compound,” being
made up of a variable number of separate
lenses united side by side. The eyes may
be fixed directly to the head, as in the
“ Sessile-eyed”” Crustaceans (Hedriophthal-
mata), or may be carried upon longer or
shorter movable peduncles, as in the “ Stalk-
eyed” Crustaceans (Podophthalmata). Be-
hind the eyes, the head carries, in general,
two pairs of jointed feelers or “‘antennez,”
the first pair (“‘antennules”) being com-
paratively small, while the hinder pair
(“great antennze”) is of larger size. The
segments immediately posterior to this carry
three pairs of jaws—the ‘‘ mandibles,” and
the first and second pairs of ‘‘ maxillee.”
All these are modified appendages, and
therefore are in pairs, and work from side
to side. The mandibles constitute the most
powerful pair of jaws, and consist usually
of a strong toothed protopodite to which a _ Fig. 3s2.—Tobster with all
short endopodite (the “mandibular palp ”) is the appendages except the ter-

minal swimmerets removed,

attached. Between the bases of the mandi- and the abdominal somites

: separated from one another.
bles is the aperture of the mouth, bounded Fw IOStEUMars. C2.) Carapace:
‘ oe bas fering th hali d thor-
in front by an undivided chitinous plate (the Z2ic"Seements. 1 to 6, The
Saypestonte Of labrum 7), and behind by fst si scements of the: ab:

J : cp domen. No. 6 carries the last
a usually forked lower lip or *‘metastoma.” pairofswimmerets. 7, Telson.
The first pairs of thoracic appendages are
generally intermediate in structure between walking-legs and jaws,
and constitute what are known as “ foot-jaws” or ‘“ maxillipedes” ;
while the hinder ones are more especially devoted to locomotion.

The thoracic appendages vary, however, extremely in form and

AOA CRUSTACEA.

structure in different groups of the Crustaceans. In the Decapod
Crustaceans five pairs of the thoracic appendages are in the form
of walking-legs; while other groups (such as the Isopods) have
seven pairs of ambulatory limbs ;
and in others, again, the number of
locomotive thoracic limbs may be
greater or less than the above. ‘The
abdominal appendages are very vari-
able in form and function, but they
are mostly primarily concerned in
locomotion, though often modified
to serve as respiratory organs, or, in
the females, carrying the eggs.

As regards their classification, the
Crustacea may be divided into the
two primary sections of the Lzzfomo-
straca and the Malacostraca. ‘The
first of these includes a great num-

Fig. 353-—The third abdominal somite ber of comparatively simple Crusta-
of the Lobster, separated. 7, Tergum;s, Ceans, 1n which the number of the
Sternum; /, Pleura; a, Protopoditeof the :
appendage; 4, Exopodite;c, Endopodite.e Segments and appendages 1S’ WELy.

variable, sometimes rising above the
normal, and sometimes falling below it. The second division in-
cludes the more highly organised Crustaceans, in which the num-
ber of the segments and appendages is definite. The Cirripedes
(with the AAzzocephala) may be provisionally regarded as a third
division under the name of Axchoracephala, characterised by the
fact that the adult is attached to foreign bodies by the metamor-
phosed head. The orders included in these three divisions are
shown in the following table :—

SuB-CLASS J]. ANCHORACEPHALA.

Order 1. Cirripedia.

SuB-cLAss IJ. ENTOMOSTRACA.

Order 1. Ostracoda.
Copepoda.

Legion, Lophyropoda.

Legion, Branchiopoda.
. Lyrilobita.

. Aiphosura.

f
. Cladocera.
. Phyllopoda.
l
. Lurypterida. J

2
3
4

» 5. Lhyllocarida.
6
i
8

Legion, Merostomata.

CIRRIPEDIA. AQ5

SuUB-CLASS IIT. MALACOSTRACA.
Division A. HEDRIOPHTHALMATA.

Order 1. Amphipoda.
a) 2s Lsopoda.

Division B. PODOPHTHALMATA.

Order 1. Cumacea.
» 2. Stomatopoda.
» 3. Schizopoda.
» 4. Decapoda.

As regards the general distribution of the Crustacea in time, re-
mains of animals belonging to this class are abundant in the fossil-
iferous formations generally, from the Cambrian onwards. Nor are
these remains confined to purely marine formations, since many
Crustaceans are inhabitants of fresh or brackish waters, and the
remains of such are of common occurrence in lacustrine or estuarine
deposits. The most ancient group of the Crustaceans is that of the
Trilobites, which is represented early in the Cambrian period, and
continued to exist till the close of Paleozoic time (Permian).
Nearly as old a group is that of the Pylocarida, the latest repre-
sentatives of which appear in the Trias. The Eurypterids, again,
like the Trilobites, are exclusively Palzeozoic, the earliest forms of
this group appearing in the Ordovician period. Most of the other
orders of Crustaceans appear to have come into existence within the
limits of the Paleozoic period, though some doubt may be felt as
to the systematic position and affinities of some of the ancient forms
which have been referred to certain of the higher orders of the class.
The Decapod Crustaceans, which represent the highest stage of
development in the class, have their beginnings in the Paleozoic
period, but they do not attain a dominant position till the Mesozoic
deposits are far advanced, and they have attained their maximum
at the present day.

Susp-cLAss I. ANCHORACEPHALA.
ORDER CIRRIPEDIA.

The order of the Cz7rvifedia includes a series of aberrant Crusta-
ceans, of which the most familiar forms, and the only ones which
occur in the fossil condition, are the Acorn-shells and their allies
(Balanide and Verrucide) and the Barnacles (Lepadide). The
essential feature of the order is that ¢e larva has the form of
a free-swimming “nauplius,” but the adult 1s fixed by means of tts
modified antenne, and ts enclosed in an integumentary sac, within

496 CRUSTACEA.

which a many-valved shell is typically developed. The abdomen ts
rudimentary, and the thorax usually carries six pairs of multiartic-
ulate limbs (“cirri”), each of which consists of a protopodite carrying
a long, jointed endopodite and exopodite.

The typical Crrrifedia are distinguished by the fact that in the
adult condition they are permanently fixed to some solid object by
the anterior extremity of the greatly metamorphosed head ; the first
three cephalic segments being much developed, and enclosing the
rest of the body. The larva is free and locomotive, and the subse-
quent attachment, and conversion into the fixed adult, is effected
by means of a peculiar secretion, or cement, which is discharged
through the antenneze of the larva, and is produced by special cement-
glands. In the Czrrifedia, therefore, the head of the adult is per-

Fig. 354.—Morphology of Cirripedia. a, Lefas fectinata, one of the Barnacles, one side of
the shell being removed, enlarged four times: c, Peduncle; d, Cement-duct; 0, Ovary; s,
Ovisac; zv, Vas deferens; #4, Penis. B, Pecilasma fissa, enlarged five times; c, Peduncle.
c, Balanus balanoides, viewed from above, of the natural size. pv, Balanus tintinnabulume,
with the shell on one side removed to show the animal ; a, One of the valves (“‘scutum ”) of the
operculum; 6, Another valve (‘“‘tergum’”’) of the operculum. (After Darwin and Pagenstecher.)

manently fixed to some solid object, and the visceral cavity is pro-
tected by an articulated calcareous shell, or by a coriaceous envelope
(fig. 354). The posterior extremity of the animal is free, and can
be protruded at will through the orifice of the shell. This extremity
consists of the rudimentary abdomen, and of six pairs of forked,
cirrated limbs, fringed with hairs, which are attached to the thorax,
and serve to provide the animal with food. The two more important
types of the Cyrripedia are the Acorn-shells (Balanide and Verru-
cide) and the Barnacles (Lefadide). In the former the animal is
sessile, the larval antennze, through which the cement exudes, being
embedded in the centre of the membranous or calcareous “ basis ”
of the shell. In the latter the animal is stalked, and consists of a
“peduncle” and a “capitulum.” The peduncle consists of the

CIRRIPEDIA. AQ7

anterior extremity of the body, with the larval antenne, usually
cemented to some foreign body. ‘The capitulum is supported upon
the peduncle, and consists of a case composed of several calcareous
plates, united by a membrane, enclosing the remainder of the
animal.

The group of the AAzsocephava differs in many respects from that
of the typical Cirripedes, cement-glands being absent, and the animal
being fixed parasitically to the bodies of other Crustaceans by means
of branched root-like processes derived from the metamorphosis of
the antennz, while the alimentary canal and limbs are absent.

The order of the C7rrvzpedia is divisible into four principal divi-
sions—the Zhoracica, the Abdominalia, the Apoda, and the Rhzz0-
cephala—of which only the sub-order of the Zhoracica is known to
possess fossil representatives. This sub-order includes the Acorn-
shells and Barnacles, in which the body is protected by a more or
less complete calcareous shell; and as it is with the shell that the
palzeontologist has to deal, some details must be given as to its
general structure.

As regards the microscopic structure of the shell, the calcareous
tissue of the exoskeleton is exceedingly hard and compact, and
shows in thin sections a finely granular structure. In the Lepa-
doids the shell-structure is very dense, with an obscure fibrous
arrangement, but in many Balanoids a coarse cellular or tubular
structure is present, the tubes being of large size, and being crossed
by transverse partitions.

In the symmetrical Sessile Cirripedes or Balanide, commonly
known as Acorn-shells, the animal is protected by a calcareous shell
formed by calcifications within the walls of the first three cephalic
segments. The animal is placed within the shell, head downwards,
and is fixed to the centre of a shelly or membranous plate, which
closes the lower aperture of the shell, and which is termed the
eieasisca(nes 255, 4,7). (he “basis” is fixed) by its outer surface
to some foreign object, and is sometimes compact, sometimes porous.
Above the basis rises a limpet-shaped, conical, or cylindrical shell,
which is open at the top, but is capable of being completely closed
by a pyramidal lid or “‘operculum.” Leaving the operculum out of
consideration at present, the sides of the shell are seen to be com-
posed of from four to eight separate pieces or valves, or, as they
are technically called, compartments. ‘These compartments are
usually closely contiguous by their lateral margins, and are separ-
ated by lines of division or ‘‘sutures”; but they are sometimes
anchylosed together. Each compartment consists of a main central
portion, which is termed 'the “ paries” (fig. 355, B, 4), and which is
attached below to the “basis” of the shell. The “ paries” grows
downwards, so that the whole shell increases by additions made

Vow. 2a

498 CRUSTACEA.

round the base. The paries of each compartment is flanked by
wing-like portions, which differ from the paries in appearance,
and are called “radu” and “alee,” according to their shape (fig.
355, B, C). Sometimes the paries has a “radius” on both sides,
sometimes “alee” on both sides, and sometimes an ala on one side
and a radius on the other.

The separate compartments of the shell receive special names
according to their position. The compartment at the end of the
shell where the animal thrusts out its cirrated limbs, is called the
“carina” (fig. 355, 4); and the compartment immediately opposite
to this the “rostrum.” ‘The remaining compartments are “lateral,”
the one nearest the carina ‘‘carino-lateral,” the one nearest the
rostrum ‘‘rostro-lateral,” and the middle one simply “lateral” (fig.
355, A); but the three rarely coexist.

The “operculum” or lid of the shell consists of two pairs of
valves, known as the “scuta” and “ terga,” forming a little pyramid
or cone, attached within the orifice of the shell by a membrane.
Each scutum opens and shuts against its fellow along one margin
(the ‘‘occludent” margin), and articulates with one of the terga

Fig. 355.—Shell of Balanida. a, Diagram of the shell of Balanus: 17, Basis; c, Carina;
Rk, Rostrum; 7, Rostro-lateral compartment; ~, Lateral compartment; 0, Carino-lateral com-
partment. B, Compartment with two radii (7 7), flanking the paries (4). c, Compartment with
a radius (7) on one side, and an a/a (a) on the other side of the paries. bp, Internal view of the
scutum. E, Internal view of the tergum, showing the spur (s) and the beak (¢). (After Darwin.)

along the opposite margin. Similarly, each tergum opens and shuts
against its fellow along one margin (the “carinal” margin), and
articulates with one of the scuta along the opposite margin. ‘The
apex of the terga (fig. 355, E) often forms a prominent beak, and
the basal margin is furnished with a process or ‘‘spur.” The scuta
and terga are not only movable, but are furnished with proper de-
pressor muscles.

CIRRIPEDIA. 499

As regards the geological distribution of the Balanida, the oldest
known types are the Protobalanus and Paleocreusia of the Devonian
rocks of North America. ‘The former of these is a minute Balanoid
which possessed the unique peculiarity that the shell consists of no
less than twelve compartments (the “rostrum,” the “carina,” and
five pairs of “lateralia”). In the genus Paleocreusia, again, the
shell was embedded in the substance of the corallum of Favosites,
and the compartments of the shell are fused to form a single un-
divided plate, covering a tubular sub-cylindrical basis.

With the above-mentioned exceptions, no Palzozoic representa-
tives of the Balanoids have hitherto been recognised, the Balanus
carbonarius of the Carboniferous rocks of Saxony being, according
to Zittel, not a Cirripede at all. In the Mesozoic rocks, moreover,
no undoubted representative of the Balanoids is known till the
Upper Chalk is reached, a species of Chthamalus appearing in this
formation. The fossil described by Seeley as a Balanoid from the

aN BG z . ‘3 Zi
Gi HereterTOVes
\

Vit ee
Ss
AWENS P
aN > \ 7
y E
4 aw
RSE
NN
GAs
,
ne
te , \
a
VAS ’ y
: Sie
FA Rh
~j 4 3

Fig. 356.—Balanus concavus, of the natural size, from the Pliocene Tertiary (Crag). a, Side-
view of the shell; 4, Tergum; c, Scutum. (After Darwin—copied from Zittel.)

Lias, under the name of Zvocapsa, does not appear to be properly
referable to this group. In the Tertiary rocks, the remains of
Balanoids are not uncommon, the recent genus Balanus (fig. 356)
occurring in deposits as old as the Eocene, and being still more
abundantly represented in the Oligocene, Miocene, and Pliocene.
In the later Tertiaries the group is further represented by forms
belonging to the genera Chthamalus, Acasta, Pyrgoma, and Coronula,
all of which are known by living types.

The remaining family of the Sessile Cirripedes is that of the
Verrucide, comprising only the single genus Verruca. In many
respects the Verrucide approach the Ladlanide, but the shell is
composed of six valves only, and is unsymmetrical, whilst the scuta
and terga (forming the operculum), though movable, are not fur-
nished with a depressor muscle. The Verrucide appear, so far as

500 CRUSTACEA.

is known, to have commenced their existence towards the close of
the Secondary period, the Chalk having yielded two species. Ver-
ruca Stromia is found in the Coralline and Red Crags (Pliocene),
in Glacial deposits, and in existing seas.

The third family of the C7zrripedia Thoracica is that of the Lefa-
dide or Pedunculated Cirripedes, commonly known as “ Barnacles.”
In these (fig. 357) the animal differs from the Sessile Cirripedes in
having its anterior extremity greatly elon-
gated, forming a stalk or ‘“ peduncle” by
which it is fixed to some foreign object.
At its free extremity the peduncle bears the
‘“‘capitulum,” which corresponds to the shell
of the Balanoids, and is composed of various
calcareous pieces, united by a membrane,
moved upon one another by appropriate
muscles, and protecting in their interior the
body of the animal with its various appen-
dages. The peduncle is cylindrical, of vary-
ing length, flexible, and furnished with proper
muscles. In some species the peduncle is
naked, and cannot be preserved in the fossil
condition ; but in other cases the peduncle
is furnished with calcareous scales (Loricula
and Zurrilepas, fig. 359), in which case it
is readily preserved. The)“ capitulmman
(fig. 358), as before said, corresponds with
the shell of the alanz, and is generally
much flattened. It consists ordinarily of
five or more valves united to one another
by membrane, usually with marked inter-
spaces; but the valves may be rudimentary
or wanting, and the entire capitulum may be
membranous. The parts of the capitulum
correspond ideally with the parts of the

sli ae I ne os shell in the Balanoids. In the latter, how-
a recent Pedunculated Cirri: ever, the shell is for the most part composed
pede.’ The lower figureshows “of the “Compartments,” and ‘then jemem
culum” is comparatively small and insignifi-

cant. In the Lepadoids, on the other hand; the valyes@yiitem
correspond with the operculum of the Balanoids are disproportion-
ately developed, and the valves which correspond with the com-
partments of the Balanoids are much less conspicuous, and are
often partially absent. ‘The most important and persistent of the
valves are the “‘scuta” (fig. 358, 4), which protect the front part of
the body, and correspond with the valves bearing the same name in

CIRRIPEDIA. 501

the operculum of the Balanoids. The next most important are the
“terga” (fig. 358, a), which protect the dorso-lateral surface. A
pair of scuta and a pair of terga are present, and these are the
largest of all the valves. The “carina” and “rostrum” are placed
along the edges of the ca-
pitulum, the former being
much the most important ;
and there may be a ‘‘sub-
carina” and ‘‘sub-rostrum.”
The remaining valves, with
the carina and rostrum, cor-
respond with the proper
shell of the Balanoids ; but
they are often wanting or
rudimentary, and they re-
quire no further considera-
tion here.

As regards the distribu-
tion of the Lepadoid Cirri-
pedes in time, the oldest
known types belong to the
genus Zurrilepas (= Plum-
ulites), several forms of
which have been detected
in the Ordovician, Silurian, h
and Devonian formations. Fig. 358.—Capitulum of a Pedunculated Cirripede.
In this singular genus (fig. @, Tergum; 4, Scutum; c, Carina; d, Upper latus;

: é, Carino-latus;_/, Rostrum; g, Sub-rostrum; /, Ros-
359; a) are included elon- tral latus; z, Infra-median latus; £, Sub-carina. (After
gated bodies covered with D2win.)
from four to six intersect-
ing rows of calcareous plates. The plates are triangular in form,
with a curved lower margin, and marked with transverse strie ;
those of the median series being keeled. When detached and
occurring in an isolated condition (fig. 359, a), these plates are
not unlike the shells of certain Pteropods, while they may be, and
have been, mistaken for the plates of Chitons. They are also not
very unlike the plates of some Cystideans (A‘eleocystites). By Bar-
rande, Zurrilepas was regarded as the capitulum of a Lepadoid, in
which there was either no peduncle or a short one; but Dr Henry
Woodward is probably correct in the view that the fossils really
represent a scaly peduncle similar to that of the genus Lovicula,
and that the capitulum is still unknown. On the other hand, the
Strobilepis of the Devonian rocks of North America seems to be
really founded upon the capitulum of a Lepadoid. Allied to
Turrilepas is the Silurian genus Azatifopsis, of which only the

ee S{i)] INS
Fee lL A

u
‘
'

z

502 CRUSTACEA.

detached valves are known, these being somewhat quadrilateral in
shape, and having the lower part of the base marked vut into one
or two horizontal segments, which are more or less separated from
the body of the valve. In the Carboniferous and Permian rocks
no Lepadoids are known, but the genus /o/licipes is represented
in the later Triassic (Rhezetic deposits). Other forms of Fodlicipes
are Jurassic, but the genus attained its maximum of development
in the Cretaceous period, at which time the group of the Lepadoids
seems to have reached its culminating point. ‘Tertiary species of
Pollicipes are also known, and the genus survives at the present

Fig. 359.—a, Turrilepas (Plumulites) Wrightii—Silurian. (After Woodward.) a, A plate of
the same magnified. p, Loricula pulchella—Chalk. (After Darwin.)

day. Some Jurassic types formerly ascribed to Pol/icipes have been
separated by Zittel to form the genus Avcheolepas. The genus
Loricula 1s wholly Cretaceous, and comprises forms with a small
capitulum and a short, plated peduncle (fig. 359, B), the organism
being attached by one side to the shells of Ammonites. The exten-
sive genus Scalpellum has numerous living types, and also about
thirty fossil representatives, of which the oldest appears in the Cre-
taceous rocks. On the other hand, the recent genus Leas (Ana-
tifa) is not certainly known to occur in the fossil condition, even
in the late Tertiary or Quaternary deposits, though the allied
Pecilasma is doubtfully represented in the newer ‘Tertiaries.

593

Gri weal E Ry xSXLxXe
CRUSTA CE A—continued.
SuB-CLASS I].—ENTOMOSTRACA,

Sup-cLass II. Enromostraca (Gzathopoda, Woodward). — The
division of the Entomostracous Crustaceans includes a large number
of comparatively simple types, in which the limbs and segments are
usually indefinite in number, the former either fewer or more than
fourteen ; and the character of the appendages is very varied. ‘The
limbs are principally developed in the cephalic region, and their
bases generally act as jaws. The characteristic larval form is that of
a “nauplius.” The orders of the Lurypterida and Xiphosura (with
the probable addition of the 7Z7/odita), here placed among the
Entomostraca, are grouped together by Professor Claus in a special
section, which he terms Gvgantostraca, and which he regards as
probably related to the Arachnida.

The Zxtomostraca are divided into three great divisions, or
“legions,” the Lophyropoda, LBranchiopoda, and Merostomata.

Division A. LOPHYROPODA.

The members of this division possess few branchize, and these are
attached to the appendages of the mouth. ‘The feet are few in num-
ber, and mainly subserve locomotion ; the carapace is in the form
either of a shield protecting the cephalothorax, or of a bivalve shell
enclosing the entire body. The mouth is mostly not suctorial, but
is furnished with organs of mastication.

This division comprises the two orders Ostracoda and Copepoda.

ORDER I. Ostracopa.— Small Crustaceans having the entire body
enclosed in a shell or carapace, which is composed of two valves united
along the back by a membrane. The valves are capable of being closed
by an adductor muscle, the insertion of which in the interior of each

504 CRUSTACEA.

valve ts marked by a tubercle, pit, or group of spots, or by both spots
and a pit. There are seven pairs of appendages, of which the first
two are antenna, and the posterior appendages are adapted for creeping
or swimming.

The Ostracoda are all small Crustaceans in which the body is
enclosed within a bean-shaped or mussel-shaped shell, composed of
two valves united along the back by an elastic ligament (fig. 360, B).
The animal can open the valves of the shell along their ventral
margin, and can protrude the appendages and the caudal extremity
of the abdomen. ‘The first two pairs of appendages are antennules

if
|| Wy

WW

7

Fig. 360.—Recent Ostracoda. a, Cyfridina Messinensis, viewed from the side, and greatly
enlarged, one-half of the shell being removed. 3B, Cyfris fusca, viewed from the side, and less
highly magnified, the shell-valves being retained, but slightly displaced. a, Antennules; az,
Antenne; 0, Eye; o’, Ocellus; c, Heart; s, Stomach; 4 Whip-like appendage for the retention
of the brood ; a6, Extremity of the abdomen; 7, Mandibular appendage ; 7x, The first, second,
and third maxille.

and antennee (fig. 360, a), which can be used as locomotive limbs.
These are followed by a pair of mandibles, succeeded by a pair of
maxillz ; and the next two pairs of appendages may be either jaws
or legs. The sixth and seventh pairs of appendages are leg-like,
and variously formed in different cases. A median eye, or two
lateral eyes are present. Branchial plates are attached to some of
the jaws, and a distinct heart may be present (Cyfvidina) or absent
(Cypris and Cythere). The young forms are usually “ nauplii,” but

OSTRACODA. 505

there may be no metamorphosis. Parthenogenesis is a not uncom-
mon phenomenon in the Ostracodes.

The Ostracoda, often called ‘“ Water-fleas,” are represented by
very numerous forms both in fresh water and in the sea. The com-
monest fresh-water types are the little Cypvzdes (fig. 360, B). The
marine Ostracodes (Cythere, Cypridina, &c.), are mostly shallow-
water forms, and are of small size; but there are deep-sea types
which attain comparatively gigantic dimensions (nearly an inch in
length). Numerous fossil forms of the Ostracodes are known, their
remains occurring in all formations, from the Cambrian onward.

It is only the carapace-valves of the Ostracode Crustaceans that
are preserved in the fossil condition, with the rarest exceptions ; and
the general form of the carapace is often very similar in different
genera. Hence the palzontologist has to rely, in the discrimination
of these minute fossils, upon small variations of shape, differences
in the thickness of the valves, the characters of the edges of the
valves, or the manner in which they are hinged to one another, or,
lastly, the surface-ornamentation. Besides the difficulty attaching to
the study of the fossil Ostracoda from their small size and general
similarity of appearance, it is often by no means easy to distinguish
between the cephalic and the posterior extremity of the body.
When not alike, the most contracted extremity is to be regarded as
the head, and the widest as the hinder end of the carapace. The
former, as a rule, carries grooves or tubercles, when such structures
are present at all. The tubercles of the test, where developed, ap-
pear to represent the eye; and the grooves and intervening lobes,
which are found in many forms, have been aptly compared by Bar-
rande to the furrows and lobes of the glabella of Trilobites. There
are many types, however, in which there are no conspicuous external
markings, and in which the two ends of the carapace are similar.
The Mesozoic and Tertiary Ostracoda are very small, and the same
is true of a large number of Paleozoic species; but among the
latter we find some comparatively large types, which, like Leperditza
ffisingeri, may reach fifteen millimetres or more in length. Asa
rule, also, the Palzeozoic Ostracoda are plain, or are simply striated
or granular; whereas the Mesozoic and Tertiary forms are com-
monly ornamented with projecting tubercles, or in various other
ways. As regards their general distribution in time, the Ostracoda
certainly commence in the Upper Cambrian, and are even doubt-
fully represented in the lower division of this formation. They
existed under many and varied types in the Ordovician and Silurian,
and are abundant in all the succeeding formations, till the Recent
period is reached. As matter of course, the remains of this group
of Crustaceans with which we have chiefly to do, are principally
those of the marvzme members of the order, and this is especially

506 CRUSTACEA.

true as regards the Palzeozoic species. In later deposits, however,
the occurrence of Ostracodes of types now found in fresh or brackish
water 1s by no means uncommon.

The total number of fossil Ostracoda is very large, the difficulties
attending their study, for reasons already stated, are quite excep-
tionally great ; and it is impossible, in many cases, for the student
to discriminate species, or, often, even genera, unless he should have
made the group a subject of special investigation. Here, therefore,
no attempt will be made to give even the briefest analysis of the
families or genera of the order; but it may be well to shortly char-
acterise some of the common or more remarkable types, with special
reference to the Paleozoic forms, with which, upon many grounds,
it is desirable that the student should have some acquaintance.

Among the Palaeozoic Ostracodes, the first group that may be
noticed is that of which Leferdztia (fig. 361, Cc and D) is the type
(Leperditide). In this genus the two valves are unequal in size,
smooth, nearly oblong, bean-shaped, with the posterior end wider
than the anterior. ‘There is a small tubercular eye-spot, placed on
the head, near the hinge, and underneath and behind this is a
slightly inflated area, corresponding with an excavation of the shell
interiorly, and exhibiting reticulated or areolar muscular markings.
Behind the eye-spot is generally a vertical groove, which begins at
the dorsal margin, and extends a short way across the valves. The
genus ranges from the Ordovician to the Carboniferous. JLsochilina
(fig. 361, B) nearly resembles the preceding, but the valves are
equal. It is not uncommon in the Ordovician rocks.

The genus Primitia (fig. 361, E-G) comprises another group of
Palzeozoic Ostracodes, which is essentially characteristic of the
Cambrian, Ordovician, and Silurian deposits, though apparently
also represented in the Carboniferous. In this genus the carapace
is equivalve, convex, and oblong in shape, indented with a vertical
dorsal groove of variable depth. Related to Primztia is the familiar
genus Beyrichia (fig. 361, H and 1), which is confined to the Cam-
brian, Ordovician, and Silurian rocks, and which sometimes is pres-
ent in such vast numbers as to give rise, by the accumulation of the
carapace-valves, to regular bands of limestone. ‘The carapace of
Beyrichia is more particularly distinguished by the possession of
two or three transverse grooves, which start at the hinge, and pass
partially or wholly across the valves. In the curious Beyrichia (?)
oculifera, the eye-spot forms a prominent and faceted tubercle, un-
like that of any other Ostracode (fig. 361, 1). Two other members
of the ancient family of the Leferditide may be just mentioned—
namely, A7zrkéya and Moorea, of which the former ranges from the
Silurian to the Permian, while the latter is principally Carboniferous,
and is doubtfully represented in the Jurassic rocks.

OSTRACODA. 507

Another great group of the Ostracoda is that of the Cypridinide,
in which the carapace is compact, smooth, or punctate, or striated,
with a deep incision in the anterior margin for the exit of the larger

Fig. 361.—Types of Ostracoda. a, The test of Cyfr7zs faba, from the Miocene, viewed side-
ways, and enlarged fifteen times ; a’, The same, viewed from the dorsal margin; B, /sochilina
Ottawa, enlarged four times (left valve and ventral view)—Ordovician ; c, Leferditia Foseph-
ana, of the natural size (right valve and anterior view)—Ordovician ; D, Leferditia solitaria,
enlarged, showing the eye-spot and muscular impression—Silurian ; E, Pr7ztéa sp.—Silurian ;
F, Primitia strangulata, Ordovician, enlarged; Gc, Right and left valves of Primitia tarda—
Silurian ; H, Beyrichia complicata —Ordovician ; 1, Beyrichia (?) oculifera, showing the elevated
eye-spot, greatly enlarged—Ordovician ; J, Extom7s tuberosa, Jones (=E. felagica, Barr.), right
valve, enlarged twice—Silurian; k, EAztomds tmpendens, enlarged—Silurian; L, Cypridina
Wrightiana, \eft valve, enlarged four times—Carboniferous; mM, Dorsal view of a small example
of Extomoconchus Scouleri, enlarged four times—Carboniferous; N, Left valve of Polycope
simplex, enlarged eight times—Carboniferous; 0, Cyfris Browniana, viewed dorsally, enlarged
twenty-five times—Pleistocene; Pp, Candona candida, viewed ventrally, and similarly enlarged
—Post-Tertiary and Recent; Q, Cythere convexa, right valve, similarly enlarged—Pliocene and
Recent ; R, Interior of left valve of the same. (After Barrande, Rupert Jones, M‘Coy, Hall,
and G. S. Brady.)

antenne. Numerous living forms of the Cypvidinide are known,
and the family is represented in past time principally by the three
generic types, Cypridina, Entomis, and L:ntomoconchus, the last two

508 CRUSTACEA.

of these being entirely extinct. In Cyfridina (fig. 361, L) the cara-
pace is produced in front into a beak-like projection, below which
is a hollow or notch facing the ventral margin. Many of the so-
called Cypridine of the older Palzeozoic rocks are now known to
be referable to other types, but the genus is well represented in the
Carboniferous, and exists at the present day. Lz/fomis (fig. 361,
j and k) ranges from the Ordovician to the Carboniferous, but
attains its maximum in the Devonian rocks. ‘The carapace in this
genus resembles that of some of the Leperdztide in having a dorsal
groove, indenting the valves transversely, and sometimes reaching
the ventral margin, and having a rounded tubercle placed at or near
its lower end. One species of this genus (Zxtomis serratostriata),
formerly known as a Cygridina, is so abundant in certain of the
Devonian strata of Germany as to have gained for these the name
of “ Cypridinen-Schiefer.” ztomoconchus (fig. 361, M), again, is a
large form, with a thick and globose carapace, having a much less
developed notch in front than in Cypridina. It is confined to the
Carboniferous rocks. Among other Carboniferous Cypridinide
may be mentioned the genera Cyfrella, Cypridella, Cypridellina,
Sulcuna, and Rhombina, all of which are characteristic of the
Carboniferous rocks.

Another group of the Ostracodes (Polycopide@) is that character-
ised by the genus Polycope (fig. 361, N), in which the carapace-
valves are subequal and thin, not markedly notched in front, and
having no beak. ‘Though represented by living species, the only
undoubted members of this genus which have been detected in a
fossil state are from the Devonian and Carboniferous rocks.

The genus Cytherel/a is the type of another group (Cytherellide),
in which the valves are very thick and calcareous, and are not
notched in front. In Cytherella itself the right valve is much
larger than the left, overlapping the latter throughout the whole
circumference, and ‘presenting round the entire inner margin a
distinct groove, into which the valve of the opposite side is re-
ceived” (G. S. Brady). The genus ranges from the Carboniferous
to the present day; and we may provisionally place with it the
Cytherellina and chmina of the Silurian.

Lastly, we have the great group of Ostracodes represented by the
families of the Cysride and Cytheride, “including all the fresh-
water and a vast majority of the marine Os¢racoda, and embracing
all the forms classed by the earlier writers under the two great
genera Cypris and Cythere” (G. S. Brady).

In the Cyprida, as typified by CyZris itself (fig. 361, A and 0),
the valves are thin and smooth, and more or less sinuate below.
Most of the Cygrvzde@ are inhabitants of fresh water, and the fossil
forms are principally found in lacustrine or fluviatile deposits, often

BRANCHIOPODA. 509

occurring in astonishing abundance. A few forms (such as Bazrdia
and Pontocypris) are marine in habit. The family of the Cypride
seems to have attained its maximum at the present day, but is rep-
resented in deposits as old as the Carboniferous by forms which
are believed to be referable to the living genera Candona and
Bairdia. Specimens of the Carboniferous genus Faleocypris have
been found, showing the eye, the antennz, and the jointed limbs,
of which there are two pairs behind the mandibles, the last pair
being strongly incurved.

In the family of the Cyz¢heride, lastly, the shell is minute, thick,
inequivalve, and generally elongated or reniform in shape. ‘The
dorsal margin of the carapace has two denticles in the right valve
fitting into corresponding sockets in the left valve. The surface is
smooth, or is variously ornamented with tubercles or spines. The
genera of Cytheride are mainly Recent and Tertiary ; but the genus
Cythere ranges from the Silurian to the present day, and there are
various Secondary types belonging to the genera Cythereis and
Cytheridea.

ORDER II. CopEpopa.— Small Crustaceans having bifid natatory
Jeet, and the head and thorax usually covered with a carapace. Two
caudal locomotive appendages are often present ; but the abdomen does
not carry limbs. Segmentation 1s distinct in the free forms ; but tt is
more or less lost in the females of the parasitic types.

The order of the Cofegoda comprises numerous small Crusta-
ceans, which inhabit both fresh and salt water, many types being
parasitic in habit. No certain examples of the Copepods have
hitherto been detected in the fossil condition.

DIvIsION B. BRANCHIOPODA.

The Crustaceans included in this division have many branchie,
and these are attached to the legs, which are often numerous, and
are formed for swimming. In other cases the legs themselves are
flattened out so as to form branchiz. The body is either naked,
or is protected by a carapace, which may enclose either the entire
body, or the head and thorax only. The mouth is provided with
organs of mastication.

The Lranchiopoda comprise the Cladocera, the Phyllopoda, the
Phyllocarida, and probably the Z7zlodzta, though this last departs
in many respects from the first three groups.

OrvDER I. CLADOCERA.—The members of this order are sma//
Crustaceans, which have a distinct head, and have the whole of the
remainder of the body enclosed within a bivalved carapace. The feet
are few in number (usually four, five, or six pairs), and are mostly
respiratory, carrying the branchia. Two pairs of antenne are

510 CRUSTACEA.

present, the larger pair being of large size, branched, and acting as
natatory organs.

The types of this order are mostly confined to fresh water, a few
forms being found in brackish pools. No undoubted representa-
tives of the C/adocera have been hitherto detected in the fossil
state, though a few small fossil types have been referred to this
order.

ORDER II. PHyYLLopopsa.—Cvustacea, mostly of small size, gener-
ally having the front part of the body protected by a shield-like cara-
‘pace, or sometimes having the body enclosed in a bivalve shell. The
Jeet are usually numer-
ous, and more or fewer
of them are leaf-like in
jorm, and act as respira-
tory organs.

The living types of the
Phyllopods (Ajuws, fig.
362, Lranchipus, Lim-
nadia, Lstheria, &c.)
are mostly inhabitants of
fresh water, but species
of Lstheria are found in
brackish water, and the
Artemie@ live in salt
lakes, or in the brine
pans of salt-works. As
a type of the Phyllopods
the recent genus Asus
(fig. 362) may be taken, ©
in which the anterior
part of the body is
covered with an oval
carapace, carrying a pair

Fig. 362.—Afus cancriformis, a recent Phyllopod, of compound ee hi aie

viewed from above, and enlarged. 1ts upper surface in front.

The under surface carries

sixty pairs of feet, of which the first is divided into three slender

whip-like branches on each side, while the others are of the genuine

‘“‘ pnhyllopodous” type, being leaf-like in form, and acting as breath-
ing-organs in function.

If the recent genus /Vebazia and its numerous fossil allies are
removed to form the order PhyMocarida, then the number of known
fossil Phyllopods is comparatively small. By far the most important
type, from a paleontological point of view, is the genus Zs¢hevia
(fig. 363, A), which is nearly related to the living Lzmnadia, and

PHY LLOPODA. S511

which in some respects constitutes a connecting-link between the
Phyllopods and the Ostracodes. The body in Lstherza is enclosed
in a bivalve carapace, and the feet are foliaceous. The valves of
the carapace have a well-marked beak or “ umbo,” and are hinged
to one another along a dorsal line. From these circumstances, and
from their being marked with numerous concentric lines of growth,
the carapace-valves of Estheria very closely resemble the shells of
certain Bivalve Molluscs (Posidonia and VPosidonomya), for which
they have often been mistaken. The valves are usually sub-
triangular, ovate, or sub-quadrate in form, and they possess a horny
texture.

The living “sthevi@ are, without exception, inhabitants of fresh,
or, rarely, brackish water; and no one of the recent twenty-four
species has been detected in the sea. This would afford a strong

Fig. 363 —a, Carapace of Estheria ovata, magnified six diameters—Trias ; B, Carapace of
Leaia Leityz, magnified five diameters—Lower Carboniferous. (After Rupert Jones.)

presumption that the deposits in which £s¢herie@ occur were laid
down in fresh or brackish water ; but such fossils not uncommonly
occur in conjunction with undoubted marine remains. They
appear, on the whole, to occur most frequently in those accumu-
lations that “have been decidedly the result of brackish-water
inundations, and of more permanent lagoons” (Jones). Fossil
Estherie occur in the Devonian, Carboniferous, Permian, Triassic,
Jurassic, Cretaceous, and some Tertiary deposits; but they appear
to have attained their maximum development towards the close of
the Triassic period. The allied genus Schzsodiscus is Devonian, and
Lstheriella is found in the Trias.

The genus Zeaza (fig. 363, B) is very nearly allied to Lstheria,
and comprises small Bivalved Crustaceans, with ‘ dark, horny, sub-
quadrate valves, obliquely ridged from umbo to angles, and orna-
mented with distinct lines of growth parallel with the border”
(Jones). Leaza is a very widely distributed genus, but all the
known species belong to either the Carboniferous or Permian rocks.
It has been suggested, however, that the obscure Ordovician genera
Myocaris and Ribeiria are allied to Leaza.

512 CRUSTACEA.

Lastly, we may notice that a Phyllopod nearly allied to the living
fresh-water genus Branchipus has been detected by Dr Henry Wood-
ward in the Eocene formation, and has been described by him under
the name Aranchipodites vectensis. The much older Branchipusites
(rightly Branchipodites) anthracinus, of the Coal-measures, has been
supposed to have similar relationships, but it does not appear to be
truly a Phyllopod.

ORDER II]. PHyLLocartpa.—This order was founded by Packard
to include the recent genus /Vesala along with certain extinct types
of the Crustacea, which in some respects form a connecting-link
between the Phyllopods and the Malacostracous group of the Schiz-
opods, though they appear to be properly referable to the Branchr-
opoda. The principal living form of the Phyllocarida is Nebalia,
which must be regarded as constituting
with its immediate allies the family of the
Nebaliade, and which must be taken as
giving the essential characters of the order.
In the genus Vebata (fig. 364), the an-
terior part of the body is covered with a
folded, but unhinged, cephalothoracic shield
or carapace, which is connected with the
body in its cephalic part only, and extends
down the sides so as to enclose the mouth
organs and the greater part of the other
appendages. ‘The valves of the carapace
are not separated along the back, but are
moved by an adductor muscle. In front
of the carapace, and movably articulated
to it, is a rostral plate ; and there are also
two compound stalked eyes, the cornea
of which is not faceted. ‘Two pairs of
antennze are present. The segments of
h the thorax, though enclosed by the cara-
7 pace, are free, and carry eight pairs of

! 4 foliaceous feet, which are of the “ phyllo-

podous” type, and officiate as branchie.

iy The abdomen is composed of free rings,
Fig. 364.—Nebalia Herbstiz, en- ; : ;

larged about three times. Recent. the first four somites of this region carry-

ing as many pairs of biramose legs, while

there are also two pairs of rudimentary caudal limbs. No telson

is present in /Vedal/a and its allies, but there is a well-developed

telson in the Ceratiocaride. ‘There is no metamorphosis in de-

velopment.

The living types of the Phyllocarida belong to the genus Webala

and the closely related ebaliopsis and Paranebalia, and are all small

PHYLLOCARIDA. 513

Crustaceans, which are exclusively marine in habit. The recent
forms constitute a special division of the order (/Vebaliade), dis-
tinguished, among other characters, by the want of a telson; and
they are not known to be directly represented in the fossil state.
On the other hand, there are numerous fossil Crustaceans, chiefly
of Palzeozoic age, which appear to be properly referable to the
Phyllocarida, and which may be regarded as constituting a special
division of this order (Ceratiocaride), distinguished more particu-
larly from the /Vebaiiade by the presence of a well-developed telson.
The earliest forms of this peculiar group of ‘‘ Pod-shrimps,” as they
have been termed, appear in the Cambrian period, while the group

Fig. 365.—Palzozoic Phyllocarida. a, Ceratiocaris papilio—Silurian (Salter) ; 6, Hynzenocaris
wermicauda—Upper Cambrian (Salter); c, Disctnocaris Browniana, without the ‘‘rostrum ”—
Ordovician (Original); d, Peltocaris aptychotdes—Ordovician (Woodward).

attains its maximum development in the Silurian, and underwent
almost total extinction subsequent to the close of the Carboniferous
period. The number of genera included in the family of the
Ceratiocarideé is very large, and many of these are only imperfectly
understood. It will therefore be sufficient here to allude briefly
to some of the more important and better known types.

As the type of this group may be taken the genus Ceratiocaris
itself (fig. 365, a) in which the anterior portion of the body is en-
closed in an elongated or pod-like carapace, composed of two oval

VOL. I. 2%

514 CRUSTACEA.

valves, contracted in front and with an abrupt posterior truncation.
The carapace-valves are united along the back by a median line of
attachment, and are commonly marked with fine linear striee, while
a lanceolate rostrum is developed in front. There were fourteen
or more body-rings, of which the last five or six were free, some or
all of these supporting lamellar appendages which seem to have
been branchial in function. At the hinder end of the body is a
powerful pointed telson, with two smaller lateral spines. The
thoracic limbs are unknown, but toothed jaws have been in some
instances recognised, either detached or in connection with the
body of their former possessor. The oldest species of Cevatiocaris
appear in the Ordovician rocks, but the genus attained its maximum
in the Silurian period, and the last known forms occur in the Lower
Carboniferous deposits. Some of the species attained to a great
size, C. Ludensis growing to a length of two feet.

In the Cambrian rocks is found the allied genus Aymenocaris
(fig. 365, 4), in which the large sub-triangular carapace is not bi-
valved but is simply folded. There are generally nine free abdom-
inal segments, the hinder termination of the body being adorned
with three pairs of unequal spines. ‘The Cambrian rocks of North
America have yielded the remains of the related genus /vofocarts,
which differs from AMymenocaris principally in the possession of
thirty narrow abdominal rings, and in the fact that there is a large
telson ending in two terminal spines. Of the same general type
as the preceding is the Ordovician genus Cavyocaris, which agrees
with Ceratiocaris in the fact that the carapace is bivalved, instead of
being simply folded. The carapace is pod-like in form, and trun-
cated behind, and the abdomen terminates in three spines. The
researches of Novak have, further, shown that the singular Crus-
taceans described by Barrande from the Silurian rocks of Bohemia
under the names of Azzstozoé, Callozoé and Orozoé, and originally
regarded by this observer as gigantic Ostracodes, are really referable
to the Ceratiocaride. The carapace of Avistozoé (fig. 366) reaches
three inches in length, and is composed of two valves united along
a straight dorsal margin, its general shape being oval, with a pointed
anterior and rounded posterior margin, and its front portion carrying
prominent rounded tubercles. Novak has shown that the fossil
described under the name of 4actropus is really a portion of the
abdomen of Avzistozoé, and that the so-called Ceratiocaris debilis is
the telson of the same genus. |

Of the later forms of the Ceratiocaride, the Devonian rocks of
North America have yielded the remains of the curious genus
Lchinocaris, in which there is an ovoid folded carapace, adorned
anteriorly with tubercles, and apparently without a rostrum. There
are seven free abdominal segments, and a strong trifurcate telson.

PHYLLOCARIDA. 515

Lastly, in the Carboniferous and Devonian genus Dthyrocaris (fig.
367), there is a broad carapace composed of two semi-oval valves
ridged along the back in the middle line and laterally, and there is
only one free body-ring. The rostrum is unknown, but there is a
powerful trifurcate telson.

Another remarkable series of the Phyocarida comprises forms
with a thin, concentrically striated carapace, which may be simple, or
may be divided into two halves and sutured along the back, and which
is commonly notched in front for the reception of a triangular mov-
able “rostrum.” -A number of curious, and in some cases prob-
lematical, fossils, the oldest of which are found in the Ordovician,
while the last appear in the Trias, have been included in this
group, and only a few of the more important can be noticed here.
A typical genus of this group is the Fe/focaris of the Ordovician
rocks (fig. 365, 2), in which the carapace is approximately circular,

Fig. 366.—Carapace of A77s-

tozoé memoranda, from the Fig. 367.—Dithyrocaris
Silurian rocks of Bohemia, of Scouler?, viewed from
the natural size, viewed side- above, reduced slightly in
ways, with the dorsal margin to size. Carboniferous Lime-
the left. (After Barrande.) stone. (After M‘Coy.)

and consists of two valves of a semicircular form, which are united
along the back by a straight dorsal suture, and which are deeply
notched in front for the reception of a movable parabolic plate or
“rostrum.” The Ordovician and Silurian genus Afptychopsts is very
similar in general characters to Pe/focaris, but the rostrum is trian-
gular in form. In the Silurian genus P%erocaris the same general
type of structure is retained, but the valves are only united for a
short space anteriorly, while they diverge behind, so as to form a
wide posterior notch. On the other hand, in the remarkable Silurian
genus Drscinocaris (fig. 365, ¢), the concentrically striated carapace is
circular in form, and shows no median line of suture on its dorsal
surface, while there is a deep triangular notch in front for the recep-
tion of the rostrum. One species of this genus attains a diameter

516 | CRUSTACEA.

of seven inches across the carapace. Various Devonian fossils have
been placed, under special generic names, in the immediate neigh-
bourhood of Descenocarts, and the Triassic genus Aspzdocaris is also
regarded as closely allied to this genus.

OrvER IV. Tritopira.—The Trilobites are Palzeozoic Crusta-
ceans in which ¢he body is more or less distinctly trilobed, and the
head, thorax, and abdomen are distinct. The head ts covered with a
cephalic shield, which usually bears a pair of compound sessile eyes,
ocellt being apparently never developed. The somites of the thorax are

Fig. 368.—The skeleton of a Trilobite (Angelina Sedgwickii), partially dissected. a, Head-
shield; B, Movable rings of the thorax; c, Tail or abdomen. gg, Glabella, in this species
without furrows ;_7, Fixed cheeks; ¢, Eye-lobe; 0, Eye; 4 Facial suture; fv, Free cheeks;
s, Head-spines; 4, Pleure ; £4, Anchylosed pleurze of pygidium.

movable upon one another, and carry jointed legs to which branchie
were attached. The abdominal segments are fused to form a caudal
shield, and support below jointed appendages similar to those of the
thorax. A well-developed upper lip (“ hypostome”) is present, and
some of the cephalic appendages are modified to act as mouth-organs.
As regards the general structure of the Z7zodita, the body was
protected by a well-developed calcareous shell or ‘‘ crust” which
covered the whole dorsal surface of the body, and which usually

TRILOBITA. 517

exhibits more or less markedly a division into three longitudinal
lobes (fig. 368), from which the name of the order is derived. In
some cases, however, as in the genera HYomalonotus and Lllenus,
this trilobation is only obscurely marked. Within the limits of the
same species, Barrande has observed that the individuals may some-
times present themselves under two forms, one broad and the other
long, and he regards the broad forms as the females, and the long
forms as the males, of the species.

The crust exhibits a well-marked division into three regions, which
are commonly found detached and separate from one another.
These three regions are—1, a cephalic shield; 2, a variable num-
ber of movable “‘ body-rings” or thoracic segments ; and 3, a caudal
shield or ‘‘ pygidium.”

The cephalic shield or buckler (fig. 368) is generally more or
less semicircular in shape, and is composed of a central and two
lateral pieces, of which the two latter may or may not be united in
front of the former. The central por-
tion of the cephalic shield is usually
elevated above the remainder. It is
termed the “ glabella” (fig. 368, ¢), and
it protected the region of the stomach.
The form of the glabella varies a good
deal. Usually it is widest in front
(fig. 369), but its width may be nearly
uniform, or it may be widest pos-
teriorly and contracted in front, as
in Calymene. ‘The glabella is bounded
at the sides by two grooves, which
are known as the “ axal furrows,” and
is marked off behind by a third groove,
which is termed the “ neck-furrow.”
The surface of the glabella may be
quite smooth, but it is ordinarily di-
vided into “lobes” by ‘ grooves,”
which originate in the axal furrows,
and pass inwards towards the middle
line (fig. 369). These furrows mark
the position of the segments which
compose the glabella, and they are BE oO ara ira eee
sometimes continuous from side to
side. Usually there are three pairs of these furrows, a lower or
basal, a middle or ocular, and an upper or frontal furrow ; but
there may be an additional pair of furrows in front of these. In
some cases, as in //enus (fig. 374), the glabella is very indistinctly
marked off from the rest of the shield.

518 CRUSTACEA.

The grooves of the glabella probably mark off so many segments, to
which organs of prehension and mastication were attached inferiorly,
and they are marked internally by corresponding ridges, to which muscles
must have been attached. Sometimes (/enus, Ellipsocephalus, Encrin-
urus, &c.) they are obsolete, as also occurs in particular species of other
genera (7rvinucleus and A: glina). ‘Typically, three pairs of grooves are
present, but some species of Phacops have four, and so have other types.

In certain Trilobites there are found two pores, or, in other cases,
funnel-shaped depressions, one on each side of the glabella, in the axal
furrow which separates this region from the cheeks. M‘Coy thought
that these “cephalic pores” might have been the points of origin of a
pair of antennz. It 1s certain, however, that this cannot be the true
explanation of these structures ; and they may be perhaps accounted for
as marking the point of origin of deep internal processes of the exo-
skeleton to which muscles were attached, while it has also been suggested
that they may indicate the position of a pair of “ ocelli.”

At each side of the glabella, and continuous with it, is a small
semicircular area, which is termed the “ fixed cheek” (fig. 368, 7).
The glabella, with the “ fixed cheeks,” is separated from the lateral
portions of the cephalic shield, termed the ‘‘ movable” or “ free”
cheeks, by a peculiar suture or line of division, which is known
as the “facial suture” (fig. 368, 7). No such line of division
is known to exist in any recent Crustacean; but there is a faint
indication of it in Zzmzlus, and some doubtful traces of it in certain
other forms. ‘The course taken by the facial sutures differs in
different cases, and causes an important difference in the structure
of the cephalic shield. In some cases (Asaphus, Phacops, Homa-
Zonotus, &c.) the facial sutures, starting from the posterior margins
of the buckler, skirt the fixed cheeks, and join one another in front
of the glabella. In these cases it is obvious that the free cheeks
form a single piece, so that the entire shield consists of but two
portions—r, the glabella and fixed cheeks ; and 2, the amalgamated
free cheeks. In other cases (Paradoxides, [llenus, Proetus, &c.),
the facial sutures, instead of joining in front of the glabella, are
continued forward, till they cut the anterior margin of the shield
separately. In these cases the free cheeks are discontinuous, and
the cephalic shield consists of three portions. In a few genera (as in
Trinucleus, Microdiscus, and Agnostus) the facial sutures are absent,
in which case the free and fixed cheeks are fused with one another.

The posterior angles (“‘ genal angles”) of the free cheeks are very
commonly prolonged into longer or shorter spines, and the free
cheeks also bear the eyes. The eyes are compound, and consist of
an aggregation of facets, covered by a thin cornea. ‘They are gen-
erally crescentic or reniform in shape, and are invariably sesszée, in
the sense that they are never supported upon movable stalks. In
some cases, however, they are carried upon longer or shorter prom-
inences. ‘The eyes differ much in size, and they are wanting in a

/

TRILOBITA. 519

few forms, such as Agnostus, Ampyx, some of the Zrinuclet, and
certain forms of Conocephalus. ‘Though facets are usually easily
detected in such as have eyes of any size, there are some (Lvozteus,
Arethusina, Proetus, &c.) in which the eyes are smooth. In any
case, the number of lenses varies greatly, there being as few as four-
teen facets, or as many as fifteen thousand in each eye in different
types (Barrande).

Behind the cephalic shield comes the thorax, composed of a
variable number of segments which are not soldered together, but
are capable of more or less movement upon each other. The
amount of movement thus allowed varies, but in several genera
(e.¢., Calymene and /ienus) it was sufficiently great to allow of the
animal completely rolling itself up after the manner of a hedgehog.
The number of body-rings or segments in the thorax varies from no
more than two (Agnostus) to as many as twenty-six (/arpes ungula),
or twenty-nine. Ordinarily the thorax (fig. 373) is strongly trilobed,
and each body-ring exhibits the same trilobation, being composed of

Fig. 370.—Bvronteus lunatus. Fig. 371.—Cheirurus pleur- Fig. 372.—Calymene
exanthemus. Blumensachit.

a central, more or less convex portion, called the ‘‘ axis,” and of two
flatter side-lobes, termed the “‘ pleurz.” The pleurz are in one piece
with the axis, but are separated from it by a more or less pronounced
groove, the ‘“‘axal furrow.” In one type of pleure, each of these
structures carries a deep longitudinal groove or sulcus upon its upper
surface (as in Asaphus, Ogygia, Phacops, Calymene, &c.) In another
type, on the other hand (as in Cheirurus, Bronteus, Acidaspis, &c.),
the place of the sulcus is taken by a similarly situated oblique 7dge.
The pleurz are always bent downwards towards their ends, and also
commonly bent backwards as well, the point where the backward
curvature begins being the “fulcrum” of Salter. In the Trilobites

520- CRUSTACEA.

with grooved pleurz, more especially, the pleuree imbricate and
overlap ; and the “fulcrum” of each is often bevelled off, so as to
form a facet upon which the pleura immediately in front plays, thus
allowing the animal to 7vo// ug. In the state of complete enrol-
ment, the under surface of the pygidium is closely applied to the
corresponding surface of the head-shield, thus entirely concealing
the ventral aspect of the animal. Some forms (such as Homadlonotus,
Lichas, Triarthrus, Olenus, Paradoxides, A7ghna, &c.) are not known
to have been endowed with the power of rolling up. Though the
trilobation of the thorax is usually very well marked (figs. 370-373),
at other times the axis is very broad, and the axal furrows more or
less inconspicuous. ‘This is the case in ///enus (fig. 374), and to a
less extent in Hlomadlonotus.

The caudal shield or ‘‘ pygidium ”—commonly called the “tail ”
—is composed of a greater or less number of segments anchylosed

B= Se

Fig. 374.—lllenus Barriensis

Fig. Bie oan Canadensis (Chap- (Murchison), Silman

n). Ordovician.

or amalgamated with one another. Commonly, the pygidium is
trilobed (fig. 373), like the thorax, and consists of a central elevated
“axis” and of a marginal “limb.” The limb is separated from
the axis by axal furrows, and usually exhibits on its surface the
lines which indicate the component pleurze, as well as the longi-
tudinal furrows on the faces of these. The extremity of the pygi-
dium is sometimes simply rounded, with an “entire” margin ; but
it may be prolonged into a shorter or longer spine or “‘ mucro ” (fig.
369), and the ends of the pleurse may also be extended into spine-
like projections (fig. 375). The number of rings in the tail varies
from two (Sao hirsuta) to twenty-eight (species of Amphion).

TRILOBITA. Sel

With regard to the condition of the wader surface of the Trilo-
bites, the progress of our knowledge has been slow, and is still in
some respects far from complete. Specimens showing the inferior
surface are exceedingly rare, and until of late years the only struc-
ture which had been detected on this aspect of the animal was the

- 375-—Glabella and pygidium of Dikedlocephalus magnificus, Quebec group (Lower
Ordovician). (After Billings.)

er
OQ
Oo

upper lip. The margin of the head-shield (as that of the pygidium
also) is turned under in the form of a broader or narrower down-
ward and inward inflection or “doublure” (fig. 377, @), and to the
centre of this is attached the lip-plate or “‘hypostome.” The form
of this varies, but usually it is either an oval gibbous plate or it is
broad and deeply forked behind (figs. 376,
377, 2). Beside this lip-plate, in a speci-
men of Asaphus platycephalus, Dr Henry
Woodward detected a jointed filament (fig.
376, ), apparently attached to a maxillary
plate, and representing a “maxillary pal-
pus.” At a later period, Mr Billings de-
scribed a specimen of Asaphus platycepha-
/us, showing the under surface of the body,

: . meet Fig. 376.— Buccal organs of
with a pair of apparently jointed appen- Asashus platycephalus (after
dages attached to each segment of the P/cedwar’). tome
thorax ; but the nature of these structures
as ambulatory legs was not universally admitted. The correctness
of the view held by Mr Billings as to the nature of the thoracic
limbs in Asaphus platycephalus has, however, been completely
established by a specimen of Asaphus megistos, from the Ordovi-
cian rocks of Ohio, which shows the under surface with its appen-

522 CRUSTACEA.

dages, and which has been described by Dr Mickleborough and
Mr Walcott. In this remarkable specimen (fig. 377), all the seg-
ments of the thorax, as well as those of the pygidium, are pro-
vided with jointed limbs, while branchial filaments (4) are likewise
present. Apart from the
interesting specimens
above noticed, the con-
dition of the under sur-
face of the ‘Tnilobites,
with its appended struc-
tures, has been fully in-
vestigated by Mr Charles
D. Walcott, whose re-
searches have been car-
ried on by the method
of making thin transverse
and longitudinal sections
of rolled-up specimens.
This able observer has
shown that the visceral
cavity of the Trilobites
(fig. 378, &) was bounded
inferiorly by a thin mem-
brane, which was attached
to the lower margin of
the dorsal crust all round.
This ventral membrane
was supported by calci-
fied arches, which in turn
supported the appendages

Meath eee th
Fig. 377-— Under surface of the body of Asaphus meg- benez ih aid 2 ue Ese
zstos, from the Ordovician rocks of Ohio, with the miss- latter, it is now estab-

ing parts restored in outline. ad, and d’, Doublure or : .
infolded margin of the cephalic shield, thorax, and pygid- lished that there existed

ium respectively. All the rings of the thorax and tail - j <!
carry jointed limbs, and branchial filaments (4) are also a row of articulated ap

present. In front, the bases of the last pair of cephalic pendages on each side
eae Wale) is shown (vm). 7, The hypos- OF the middle line below

(fig. 379). In the genus
Calymene, as will be seen from the accompanying illustrations, the
thoracic appendages were in the form of slender, five-jointed legs,
in which the terminal segment forms a pointed claw, and the basal
segment carries a jointed appendage, regarded by Mr Walcott as
homologous with the “epipodite” of many recent Crustaceans.
On each side of the thoracic cavity there is, also, attached a row of
bifid spiral appendages (fig. 378, e), of the nature of gills; and
branchial appendages were probably attached to the bases of the

TRILOBITA. 523

thoracic limbs as well. ‘The abdominal or pygidial rings carried
appendages also, a pair to each segment, but these do not appear
to have differed in form from the thoracic hmbs. With regard, fin-
ally, to the appendages of the head, the mouth is situated behind
the hypostome, and is bounded by four pairs of jointed manduca-
tory appendages, the basal joints of which are, partly or wholly,
modified to act as jaws. The hindmost cephalic appendages (fig.
379, 4) are larger than the anterior ones, and may be regarded as
foot-jaws.

In connection with the exoskeleton of the Trilobites, a few words
may be said as to the mznuuze structure of the crust. ‘Thin vertical
sections (fig. 380, B) show that the crust is traversed by vertical
canals or tubes of different sizes, the general tissue being finely

\\ Ul

Fig. 378.—Transverse section of the thorax of Calymene senaria, partially restored (after C.
D. Walcott). a@, Dorsal crust ; 4, Visceral cavity, continued laterally to the pleural margins of
the dorsal crust; c, Legs, restored; ad, Epipodite; e, Spiral gills. Enlarged six times.

tubulated so as to resemble somewhat the dentine of teeth, and
there being usually a system of comparatively large vertical tubes as
well. ‘Tangential sections (fig. 380, A and C) may only exhibit the
openings of the larger set of tubes, or may show the minute and
close-set apertures of the small tubuli as well. Where a large set of
tubes is clearly developed, the minute structure of the crust is very
similar to that of the shell of the recent Zzmudus ; but the presence
of these large tubes cannot be regarded as a distinctive feature, since
similar canals are present in the shell of the Lobster, in parts at any
rate.

With regard to the development of the Trilobites, the eggs have
been noticed by both Barrande and Walcott. They are spheroidal
or cylindroidal in shape, and mostly about a twenty-fifth to a fiftieth
of an inch in diameter, and they seem to have been deposited in
clusters. The larval condition of the Trilobites is only known in

524 CRUSTACEA.

certain cases, and it is possible that the young may often have been
naked. This subject has been chiefly worked out by Barrande, who
has shown that, so far as our
present knowledge goes, the
development of the Trilobites
follows one or other of four
principal lines. In one group
of forms (e.g., Sao hirsuta), the
most minute larve observed
possess a head-shield, but have
no pygidium, while the thorax is
either wanting or rudimentary.
In another type (Agnostus), the
larva has both the head-shield
and pygidium in a developed
condition, but the thorax is
wanting. In a third, all the
three regions of the body are
present, but the thorax and
pygidium are at first incom-
plete ; and in a fourth group,
though the thorax possesses
the number of rings proper to

h idium is im-
Fig. 379.— Restoration of the under surface ot fae adult, the PYS d :

Calymene Blumenbachii, showing the appendages. perfect.
da, Doublure of the cephalic shield; 4, Hypos-

rome; The last pair of cephalic sppendsets As to their made talents
a, Thoracic limbs; @’, Abdominal limbs. (After Trilobites, as before remarked,
Walcott.) seem to have delighted in muddy

bottoms, though often found in
limestones, and they must have frequented particular localities in vast
numbers. In connection with this subject, we may briefly notice certain
tracks or markings in the rocks, which may perhaps have been pro-

A

Fig. 380.—A, Tangential section of the crust of Calymene senaria, showing the openings of
large and small tubes; B, Vertical section of the same; c, Tangential section of the crust of
Asaphus Canadensis, showing a minutely porous structure. All the figures are greatly magnified.
(Original.)

duced by these extraordinary extinct Crustaceans, or by their allies the
King-crabs and Eurypterids. The most interesting of the tracks in ques-
tion are those which have been described by Professor Owen from the
Potsdam Sandstone (Upper Cambrian) of Canada, under the name of

TRILOBITA. 525

Protichnites. The tracks upon which this genus is founded (fig. 381, A
and B) consist essentially of a median groove, with a number of depres-
sions or footprints on each side in corresponding pairs, these being often
arranged in answering groups, of seven or eight pairs each. Sometimes
the pits or footprints are replaced by shallow grooves, on each side of the
main median groove (fig. 381, B). The tracks of Protichnztes indicate
the existence in the Upper Cambrian of some animal of very considerable
size, since they are sometimes half a foot or more in width. That the
animal producing these tracks was a Crustacean can hardly be doubted ;
the median groove being made by the tail-spine, and the lateral mark-
ings by the feet; and as we know that large Trilobites actually lived
during this period, it seems most reasonable to suppose that we have in
these the real makers of the tracks. Sir William Dawson, however, has
shown that tracks of a closely similar nature are formed by the living

y)

}

yy

)

i

NY)

ie

\\

\

p

\\

K

\\
AG

WicA
WB

Fig. 381.—Supposed Crustacean tracks and burrows. A, Portion of the track of Pvrotich-
nites alternans, from the Potsdam Sandstone, reduced to one-tenth of the natural size; B,
Portion of the track of Protichuites lineatus, from the same formation, similarly reduced; c,
Portion of Climactichnites Wilsoni, from the Potsdam group, reduced to one-thirtieth of the
natural size; D, Rusichnuites (Rusophycus) bilobatus, from the Clinton formation (Silurian), re-
duced one-half. (After Owen and Hall.)

King -crabs (Lzulus), and he would therefore ascribe Protichnttes
rather to the Eurypterids. The same eminent observer has also shown
that smaller forms of Protichnites occur in the Carboniferous ; and he
ascribes these to the Limuloid genus Zelznurus. The curious track
known as Climactichnites (fig. 381, C) 1s likewise found in the Potsdam
formation, and consists of a band about six inches wide, crossed by
straight ridges, and bounded by beaded margins. These were probably
formed by the same animal as that which produced Pvroftichnites, and
Dawson has shown that the living Lz7/us, when it uses its swimming-
feet, gives rise to a ladder-like track of the same kind. Prof. Chapman
believes that both Protichuztes and Climactichnites are really of vegetable
origin. The only other fossil which need be mentioned in this connec-
tion is the curious Azszchuztes, which is of common occurrence in the
Ordovician and Silurian rocks of North America, and is also found
in the Carboniferous. Originally described as a plant under the name
of Rusophycus, its name was changed by Dawson to Rusichnttes, in
accordance with his belief that it really represents the casts of the bur-

526 CRUSTACEA.

rows of Trilobites, and that it can be shown to be sometimes connected
with footprints consisting of a double series of transverse markings. In
form, Rusichnites (fig. 381, D) presents itself as an oval, cylindroidal
body, deeply furrowed, or bilobed, by means of a longitudinal sulcus,
the lateral halves being transversely ridged or grooved. The body
thus constituted may be independent, or may stand in apparent con-
nection with a cylindrical and slender appendage.

With regard to their systematic position, the Trilobites have been
usually regarded as Entomostracous Crustaceans, with relationships
to the Phyllopods and to the JZerostomata ; but they have been
sometimes considered as related to the Isopods. With regard to
these last, there is no doubt a considerable general likeness between
such an Isopod as Sevo/is and various forms of the Trilobites ; and
a tangible point of resemblance is found in the fact that in many
Isopods the caudal segments coalesce to form a shield like the
pygidium of the Trilobites. On the other hand, the segmentation
of the body in the Trilobites is indefinite, the number of limbs is
large, and thoracic branchiz are developed ; whereas in the Isopods
the segmentation of the body is definite, there are only seven pairs
of legs, and the branchiz are abdominal. With the Phyllopods,
the Trilobites are in agreement as regards the indefinite segmenta-
tion of the body; and the recent genus Apus possesses a lip-plate
which in form is very similar to that of the Trilobites. The Trilo-
bites, however, have a calcareous crust ;
their imbs are jointed, and not phyllo-
podous; and the segments of the ab-
domen are anchylosed. Dhteneame
finally, remarkable points of relationship
between the Trilobites and the JZero-
stomata, and particularly between the
former and the Limuloid types of the
latter. Thus, the Trilobites show affin-
ities with the JZerostomata in the pos-
session of a very similar head-shield to
that of the latter, the presence (particu-

Fig. 382.—Larva of Lzmulus on larly in some extinct Limuloids) of dis-
Dobra » greatly enlarged. (After tinct indications of a “ facial suture,” the

existence of compound sessile eyes, and
the microscopic structure of the crust. Moreover, the larva of the
recent Limulus (fig. 382) is destitute of the tail-spine of the adult,
and in many respects shows a striking resemblance to certain of the
Trilobites, and particularly to the genus Z7nucleus. There are,
however, various striking points of difference between the Trilo-
bites and the Limuloids. Thus the former always possess free
thoracic segments, and the appendages carried on these differ en-

TRILOBITA. ey

tirely from those borne on the same region in any of the JZero-
stomata. Again, the Trilobites have no “ ocelli,” and have a well-
developed hypostome. On the other hand, the thoracic somites
in the Limuloids may be completely anchylosed (as they are in
Limulus itself); ocelli are present as well as compound eyes; and
the hypostome is rudimentary or absent. Upon the whole, in spite
of the above-mentioned differences, it would seem that the Trilo-
bites are more nearly related to the JZervostomaza than to any other
group of the Cvwustacea, and if, as maintained by Claus and other
high authorities, the latter are properly referable to the Arachnida,
it will be apparently necessary to transfer the Z7z/odita also to this
class of the Avthropoda. Apart, however, from the difficult ques-
tion as to whether the Limuloids and Eurypterids are referable to
the Arachnida or to the Crustacea, it may be questioned if there
is sufficient justification, in the present state of our knowledge, for
placing these two groups along with the Trilobites in the common
division to which Claus has given the name of Gigantostraca. The
differences between the 7Z7z/odita on the one hand, and the Xzpho-
sura and Eurypterida on the other hand, are, at any rate, so
numerous that it would be a matter of difficulty to frame a defini-
tion of the Gzgantostraca which would embrace these three orders,
and would at the same time exclude all the other groups of the
Crustacea.

The general facts as to the dstribution of the 7rzlobita in past
time are soon told. The Trilobites are exclusively Palzeozoic, their
range extending from the Upper Cambrian to the Permian. If the
problematical Paleopyge Ramsayt of the Longmynd beds be a Tri-
lobite, then the order has its commencement in the Lower Cambrian.
In the Upper Cambrian rocks the order attained a wonderful devel-
opment, the number of generic and specific types already known
from this formation being very large, while individuals are sometimes
extremely abundant. Some of these so-called “‘ Primordial” Trilo-
bites attain a very great size, being only surpassed amongst later
forms by some species of Asaphus. They mostly belong to the
families of the Agnostide, Conocephalde, and Paradoxide, and to
the genera Paradoxides, Conocoryphe, Sao, Ellipsocephalus, Hydro-
cephalus, Artonellus, Dikellocephalus, &c. Along with these, however,
are genera such as Agnostus, which pass up into the Ordovician.
Some of the “ Primordial” Trilobites are not so highly organised
as their successors, as shown by the occasional absence of eyes,
or want of the facial suture, by the imperfect segmentation of the
glabella, or by the multiplication or diminution of the number of
the body-rings ; but others do not exhibit any inferiority to those
of later periods.

In the Ordovician and Silurian rocks the Trilobites attain their

528 CRUSTACEA.

maximum of development, the leading families being the Asaphide,
Phacopide, Trinucleida, Chetruride, and Calymenide, and the chief
genera being Asaphus, Ogygia, Phacops, Trinucleus, Ampyx, Chetru-
rus, Lncrinurus, Calymene, and Homalonotus. In the Devonian
rocks, again, Trilobites are tolerably abundant, though less so than
in the preceding series. The commonest Devonian genera are
Phacops, Homatonotus, Proetus, and Bronteus. Lastly, the order
seems to die out before the close of the Paleozoic epoch, being
represented in the Carboniferous period solely by the four genera
Phillipsia, Brachymetopus, Griffithides, and Proetus ; while in the
Permian rocks only a single species of PAz/psia has hitherto been
detected.

In the following, a brief summary of the families of the 77/odzta,
indicating the principal genera of each, and their distribution in
time, will be given. No strictly zoological arrange-
ment of these families is as yet possible, except in a
general sense, but the classification proposed by M.
Barrande, one of the most illustrious paleeontologists
of this century, has been in the main adhered to.

FAMILY 1. HARPEDID&.—Cephalic shield large,
ee and horse-shoe-shaped, its posterior angles greatly
Pe eS prolonged, and its margin or “limb” perforated by
Cunmian of Bohemia. pores (fig. 383). The glabella is conical and pro-

minent, with slightly marked furrows, and the eyes
are small, and consist of a few lenses. ‘There are from twenty-five
to twenty-nine thoracic segments, and the pygidium is extremely
small, and consists of three or four amalgamated segments. The
species of /Zarpes, the sole genus comprised in
this family, are principally Ordovician and Silu-
rian, but a few Devonian forms are known.

FaMILY 2. REMOPLEURIDZ.—In this family the
head is greatly developed, semicircular in shape,
the genal angles produced into spines. The
glabella is smooth, or possesses three pairs of
lateral grooves, and the facial sutures unite in
front of it. The eyes are very long and are
reticulated. There are eleven to thirteen body-

Fig. 384.—Remo- Tings, with grooved pleure, and the pygidium is
Pee oe “ae Nte, Very small, and is often reduced to two segments.
Barrande.) This family contains only the single genus Remio-

pleurides (fig. 384), which is confined to the Ordo-

vician and Silurian deposits.
FAMILY 3. PARADOXIDZ or OLENIDZ.—Head-shield well devel-
oped, crescentic, the genal angles produced. The glabella, typi-
cally, widest anteriorly, with well-marked grooves. The facial

TRILOBITA. 529

sutures nearly parallel, cutting the head-shield separately ; the eyes
large. The body is very long (fig. 385, a); the thorax has from
twelve to twenty segments, with grooved pleure; the pygidium
being usually small and of few segments. The family is essentially
characteristic of the Cambrian deposits, ranging through all the
divisions of this formation.

The principal genus of this group is Paradoxides itself (fig. 385, a,
and fig. 386), with its long and trilobed body, sometimes reaching
a length of two feet or more. The thorax in this genus is greatly

Fig. 385.—Paradoxide and Conocephalide. a, Paradoxides Bohemicus, reduced in size; 4,
Ellipsocephalus Hoffi; c, Sao hirsuta; d, Conocoryphe Sultzeri—all the above, together with
fig. g, are from the Upper Cambrian or ‘‘ Primordial Zone” of Bohemia); e, Head-shield of
Dikellocephalus Celticus, from the Lingula Flags of Wales; 7, Head-shield of Coxocoryphe
Matthewi, from the Upper Cambrian (Acadian Group) of New Brunswick ; .2, Aguostus rex,
Bohemia; %, Tail-shield of Dzkellocephalus Minnesotensis, from the Upper Cambrian (Potsdam
Sandstone) of Minnesota. (After Barrande, Dawson, Salter, and Dale Owen.)

elongated, and consists of sixteen or twenty rings, while the axis of
the pygidium often contains two segments only. The eyes are
long, reniform, and smooth. The genus is characteristic of, and
confined to, the Cambrian period. //utonia and Anopolenus, with
a similar geological range, are closely related to Paradoxides; but
the former of these two genera has a narrow glabella and a tuber-
culated surface, while the latter has the last two pleurze of the thorax
dilated and bent backwards, and the pygidium has wide lateral lobes.
The genus Olenellus resembles Paradoxides in most respects, but
VOL. I. 205

530 CRUSTACEA.

there are only thirteen or fourteen segments in the thorax, and the
lateral lobes of the pygidium are undeveloped, the elongated and
pointed axis alone remaining. ‘The genus O/ened/us appears to be
characteristic of the Lower Cambrian deposits, while Paradoxides
distinguishes the Middle Cambrian fauna, and Olenus (or Dikello-
cephalus) the Upper Cambrian.

In Aydrocephalus, again, the glabella is immensely inflated, with
a median longitudinal groove ; and the facial sutures cut the outer

Fig. 386.—Paradoxides Micmac. St John’s Group (Cambrian), Newfoundland.
After Dawson.)

margins of the head-shield, so that the free cheeks become much
reduced in size, and the genal spines are attached to the fixed
cheeks. Eyes are wanting, and there are only twelve body-rings.
A more important and widely distributed genus of this family is
Olenus (fig. 387), in which the general characters are very similar
to those of Paradoxides, but the glabella is contracted in front so
as to become conical, and its furrows are often extended completely

TRILOBITA. | 531

across it: there are only fourteen body-rings ; and the pygidium is
well developed. avadolina includes O/ent with only twelve body-
rings, and with a spined margin to the pygidium; while Pe/tura
embraces forms in which the hinder angles of
the head-shield are rounded, and the glabella
is prolonged forwards to the front margin.
Olenus and its sub-genera are confined to the
Cambrian period, and specially distinguish the
Upper Cambrian desposits. Characteristic of
the same geological horizon is the genus
Dikellocephalus (figs. 375, and 385, #) in
which the most striking feature is the broad,
fanlike, often spined tail, with its short many-
tinged axis. Ihe facial sutures cut the
margin of the head-shield separately in front, Fig. 387.—Odenus micru-
and the grooves of the glabella are like those ii eee en ee
of many O/enz in joining from side to side.

Family 4. CONOCEPHALID#.—This family is a convenient one to
retain, though it does not seem at present possible to separate it
from the preceding by any rigid definition. Its members resemble
the Paradoxide in general characters, but the glabella is narrow in
front, or, at any rate, not dilated in this region, and the tail is
usually fairly well developed, while the thoracic rings are not so
numerous as in the typical forms of the latter. Moreover, most of
the members of the Conocephalide have the power of rolling up into
a ball. The type-genus is Conocoryphe or Conocephatites (fig. 385,
d and /), which has resemblances to both Olenus and Calymene, its
glabella approaching that of the latter in its comparatively great
posterior width and its contraction in front. Eyes are usually, but
not always present ; the facial sutures are discontinuous ; the fixed
cheeks are large and the free cheeks small; and there are fourteen
or fifteen body-rings, while the tail has from two to eight rings.
The genus is represented by very numerous species in the Upper
Cambrian, and also occurs in the Ordovician rocks. //pso-
cephalus (fig. 385, 4) is related to the preceding, but the glabella
is subquadrate, smooth, and convex, and there are twelve to four-
teen body-rings. Angelina (fig. 388) is another Upper Cambrian
genus, with affinities to Olenus. Its glabella, however, is destitute of
grooves, and the tail is composed of four or five rings, while the
body-segments are fifteen in number. The genus Sao (fig. 385, ©),
of the same formation, is a link between the present family and the
Paradoxide. It is distinguished by its prominent furrowed glabella,
the possession of seventeen body-rings, and the minute tail of two
segments only. Avionellus, also Cambrian, has sixteen body-rings,
and three caudal segments; and the allied genus Aenocephalus, of

532 CRUSTACEA.

the same age, is chiefly separated from the former by its much more
convex glabella. Lastly, Bathyurus (Upper Cambrian and Ordovi-
cian) and Bathyure/lus (Ordovician) form in some respects inter-
mediate types between the Conocephalde and the Asaplide ; and
the Olenoid genus Z77arthrus survives to near the middle of the
Ordovician period.

Family 5. BoHEMILLIDZ.—This family contains only the Ordo-
vician genus Bohemilla, characterised by its greatly developed head ;
the glabella being of large proportionate size, with four pairs of
lateral grooves, the hinder ones of which pass completely from side
to side, so as to divide this region of the head into regular rings or

Fig. 338.—A ngelina Sedgwicki7, in its natural condition, and distorted by cleavage.
Upper Cambrian. (After Salter.)

segments, closely resembling those of the thoracic axis. The eyes
are large and reticulated; the course of the facial sutures is un-
known ; the genal angles are prolonged into long spines, directed
transversely rather than backwards; and the thorax and pygidium
are not clearly marked off from one another, the former consisting
apparently of five segments and the latter of two.

Family 6. CALYMENID#&.—In this family the crust is often tuber-
culated or granulated ; the head is well developed ; the glabella is
widest behind; and the facial sutures are discontinuous, and
terminate at the posterior angles of the cephalic shield. ‘There
are thirteen segments in the thorax, with grooved pleure ; the tail
is of moderate size; and the condition of the eyes is variable. In

TRILOBITA. 533

Calymene itself (fig. 372) the head is usually crescentic, with
rounded genal angles; and the glabella is conical, strongly convex,
with deep axal furrows, and divided by three deep lateral grooves
on each side, all the “lobes” thus formed being globose, and the
hindmost being the largest. The eyes are minute and reticulated,
but are rarely recognisable. The tail is convex, with a well-marked
axis, and the hypostome is quadrate and forked posteriorly. The
animal possessed in perfection the
power of rolling up into a ball, speci-
mens commonly occurring in this
condition. ‘The species of Calymene
are principally Ordovician and Silu-
rian, and the three most familiar
species are the nearly allied C. Blu-
menbachit, C. senaria, and C. brevt-
capitata. ‘The genus is also known
to have survived, in North America,
into the commencement of the De-
vonian period.

The genus Aomalonotus is the
only other member of the Cady-
menideé, and is distinguished from
Calymene by the greatly elongated
and faintly trilobed body (fig. 389).
The glabella, further, is smooth or
exhibits but faint traces of lobation.
The species of Homalonotus are Si-
lurian and Devonian, and the genus
has a wide distribution in space. A
very familiar species is the Homalo-
notus delphinocephalus of the Silurian
rocks.

family 7. ASAPHIDE. — Large
Trilobites, generally oval, and never Pig se ee De
furnished with spines or tubercles on cephalus. Silurian.
their surface. The eyes smooth, and
the facial sutures terminating on the posterior margin. The
cephalic and caudal shields generally of large size, the glabella
of the former often obscure, and the latter sometimes exhibiting
no indication of its component segments. The body-rings usually
eight in number, with grooved pleure. The family is character-
istically Ordovician, and the two principal genera are Asaphus
and Ogygia. In the genus Asaphus (figs. 390, 392, 393) the
general trilobation is somewhat indistinct, and the caudal shield is
generally equal to the head in size. The genal angles of the head-

534 CRUSTACEA.

shield may be rounded or spinose, and the glabelia is not marked off
by conspicuous axal furrows. The facial sutures are discontinuous,
the eyes crescentic, the hypostome deeply forked, and the pygidium
may or may not show a conspicuous axis, its hinder extremity being
usually rounded, and its margin always entire. This important
genus is characteristic of the Ordovician rocks, and the species
have a world-wide distribution, some of the forms attaining the
extraordinary size of two feet in length. The genus Asaphus has
been divided into a number of sub-genera, of which Jsofe/us and
Megalaspis are the most important. In the former of these (fig.
392) the axis is very wide, the glabella is imperfectly marked off,

\ \\ \\ \
ih \\!
A Kp yp ion

UT

Fig. 390.—Asaphus tyrannus. Ordo- Fig. 391.—Ogygia Buchiz. Ordovician.
vician. (After Salter.) (After Salter.)

and the pleurz have rounded ends. In Megalaspis (fig. 393), on
the other hand, the axis is narrow, the glabella is very short, and
the head-shield is usually greatly extended in front.

The genus Ogygza is closely allied to Asaphus in general form and
proportions ; but the axis of the pygidium is more conspicuously
marked than in most Asaphz (fig. 391), the hypostome is rounded
and not cleft, the glabella is distinctly furrowed, and the pleuree of
the thoracic segments have only rudimentary “fulcra.” The species
of Ogygia are confined to the Ordovician rocks. ‘This is also the
case with the genus /Vzode, which is in some respects intermediate
between Asaphus and Ogygia, having the round hypostome and
lobed glabella of the latter, while it approaches the former in its
wide glabella and its obtuse and faceted pleuree. The Ordovician

TRILOBITA. 535

genus Styg7za is related to Ogygia, but the head-shield and pygidium
are very similar. Lastly, the Upper Cambrian genus Pszlocephalus
forms a link between Asaphus and //enus ; while the genus Vi/eus
might be almost indifferently placed with either the Asaphide@ or the
Lllenide. :

FamiLy 8. ILL£N1ID#.—In this family the head and tail are greatly
developed, and, as in the Asaphide, are approximately equal in size
(fig. 394). The glabella is broad and rounded, destitute of lobes,
and with the axal furrows hardly at all marked. . There are eight to

Ss
= =<
SSSs

ae \ eS \ \
ill SSNS 1
FI}
,

ll
is

Fig. 393.—Asaphus (Megalas-
pis) extenuatus, of the natural
Fig. 392.—A saphus (Isotelus) platycephalus. size. Ordovician, Sweden. (After

Ordovician. Angelin.)

ten body-rings ; and the axis of the tail is truncated or wanting, and
in no case exhibits definite segmentation. The free cheeks are ex-
tremely small; the facial sutures are separate; and the eyes are
crescentic.

If WVileus be regarded as belonging to the Asaphide, the only
well-defined genus in this family is ///enus itself (fig. 394). In this
genus the head is large, convex, and tumid, as is also the tail, the
glabella and pygidial axis being hardly marked out, and being
wholly unsegmented. In the typical forms of this group (L/lenus
proper), the axis of the thorax is not disproportionately wide, and

536 CRUSTACEA.

the axal furrows are distinct ; but in others (Gumastus), the thoracic
axis 1s extremely wide, and is hardly separated from the pleurz by

Fig. 394.—a, A complete example of //Zenus Davisiz, in its unrolled state—Ordovician; B,
eee of the same; c, Lé/enus (Bumastus) Barriensis, rolled up—Silurian. (After
alter.
recognisable axal furrows (fig. 374). In the former of these sections
there are ten body-rings ; whereas in Oct//enus and Panderia there

Fig. 395.—a, 4@glina prisca—Ordovician; B, Head-shield of Chezrurus juvenis—Ordovician 5
c, Head-shield of Aszphion Fischeri—Ordovician ; D, Side view of the head-shield of Spher- .
exochus mirus—Ordovician and Silurian. (After Barrande and Salter.)

are only eight body-rings, and in Dysp/anus there are nine. The
species of ///enus are exclusively confined to the Ordovician and
Silurian periods.

TRILOBITA. a7

FAMILY 9. AXGLINIDZ.—This family contains only the single
genus 4g/ina (fig. 395, A), of the Ordovician rocks, and is chiefly
distinguished from the preceding by the much larger size of the
eyes, and the smaller number of body-rings. The head and tail are
both of large size, the latter with a truncated axis; the glabella is
not conspicuously marked out; the facial sutures are discontinu-
Ous; and the eyes are extremely large and reticulate; while the
segments of the thorax are reduced to five or six in number.

FAMILY 10. CHEIRURID£&.—In this large and important family
the head-shield is well developed, with discontinuous facial sutures,
which terminate on its outer margin. The glabella is usually highly
convex or tumid, with well-marked axal furrows and lateral grooves.
There are ten to twelve, rarely fifteen or eighteen, generally eleven,
body-rings, and the pygidium is small, of from three to five segments,
the pleurze terminating in free ends. The family ranges from the
Upper Cambrian to the Devonian, but is principally characteristic of
the Ordovician and Silurian rocks. In Cheirurus itself (figs. 395, B,
and 396) the head is semicircular, with
rounded or pointed genal angles, and with
a strongly-arched glabella, which is deeply
grooved by the lateral furrows. There are
generally eleven body-rings, with ridged or
slightly grooved pleurz ; and the tail has
a well-marked axis of four rings, its pleuree
being prolonged into points or spines.
Ampluon (fig. 395, C) is nearly related to
Cheirurus, but has from fifteen to eighteen
body-rings, and exhibits minor differences
as well. /lacoparia, again, agrees with —— sl
Cheirurus in having eleven body-rings, and ee, Can =
also in the form and lobation of the gla- \ (eae
bella, but it is destitute of both eyes and Sg J
facial sutures, as is also the genus Avera. SURG i
Spherexochus, lastly (fig. 395, D), while a
agreeing with Cherrurus generally, is dis- Fig. 396.—-Cheirurus ZNSIGHIS,
tinguished by the extreme inflation of the OLR gee ea Pg
glabella, and the presence of no more than
three segments in the pygidium ; while the basal lobes of the gla-
bella are completely isolated, and there are only ten body-rings.
We may. also place here the very singular and aberrant genera
Staurocephalus and Detphon. In the former of these the general
characters correspond with those of Chezrurus, but the anterior or
*‘ frontal” portion of the glabella is enormously swollen, and forms
a great globular projection in advance of the line of the cheeks.
The species of Staurocephalus are Ordovician and Silurian. In the

538 CRUSTACEA.

still more curious Dezphon, of the Silurian rocks, the fixed cheeks
are rudimentary, and are reduced to two curved spines, which spring
from the sides of the swollen glabella, and carry the faceted eyes,
while the free cheeks are obsolete. The axis of the tail is formed
of four or five rings, and the pleuree are prolonged into two spines
on each side, one of these being formed by the first segment only,
while the other, and much larger, one is made up of the amalgamated
extremities of the remaining segments.

FAMILY 11. ENCRINURIDZ.— This family is confined to the
Ordovician and Silurian periods, and is related to the preceding
through the intervention of Amphion. The head is fairly devel-

Fig. 397-—A, Head-shield of Eucrinurus Fig. 398.—a, Cybele Lovenz, of the
punctatus — Silurian; B, Head-shield of natural size; B, Cast of the pygidium
Cromus intercostatus—Silurian ; c, Head- of Cybele verrucosa, enlarged twice.
shield of Cydele bellatula — Ordovician. From the Ordovician rocks of Girvan.
(After Barrande.) (After R. Etheridge, jun., and the

Author.)

oped, the genal angles rounded or pointed, and the facial sutures
discontinuous, and cutting the outer angles of the cephalic buckler.
Eyes are present, though not of large size, and the glabella may
or may not exhibit distinct lateral grooves. The surface is tuber-
culated, and some or all of the body-rings may bear spines. ‘The
thorax generally consists of eleven segments; and the tail, though
moderate in size, has a well-marked axis, which is composed of
very numerous rings.

In L£ucrinurus (fig. 397, A) the glabella is pyriform, strongly
tuberculated, with the lateral furrows almost obsolete. The body-
rings are eleven in number, and the axis of the pygidium is com-
posed of extremely numerous rings. In this genus, as in its near

TRILOBITA. 539

ally Cyéele, the pygidium is long and triangular, and has its pleurze
bent backwards so as ultimately to become parallel with the axis
(fig. 398, B). The range of the genus Eucrinurus is principally
Silurian, but the genus likewise occurs in the higher portion of the
Ordovician series. The genus Cydele (= Zethus, Volborth) is dis-
tinguished from Zucrinurus chiefly by its clavate glabella (fig. 397, C)
and its possession of twelve body-rings, which are usually produced
into spines (fig. 398, A). The facial sutures cut the margin of the
head-shield close to the genal spines, and the tail resembles that of
LEncrinurus in form. The genus is characteristic of the Ordovician
rocks. Lastly, in the Silurian genus Cvomus (fig. 397, B) the gla-

Fig. 3099. — Acidaspis Dufrénoyi, Fig. 400.—a, Head-shield and tail of Lichas
from the Silurian rocks of Bohemia. palmata; B, Head-shield of Acidaspis Hoer-
(After Barrand—Copied from Zittel.) mest. Silurian rocks of Bohemia. (After Bar-

rande.)

bella has four well-marked lateral grooves; the eyes are small and
ovoid ; and the pygidium looks like a continuation of the thorax,
its axis being composed of from twelve to twenty-eight rings, and
its pleuree terminating in free points.

FAMILY 12. DINDYMENID#.—In Dindymene, of the Ordovician for-
mation, the only genus which can be certainly referred to this family,
the head-shield is semicircular, with a tumid glabella, destitute of
lateral grooves. There are no eyes, nor facial sutures; and the
cheeks are tumid, as in Z7nucleus. There are ten body-rings, and
the tail is large and distinctly segmented.

540 CRUSTACEA:

FaMILy 13. Acipaspip#.—Like the preceding, this family contains
only a single genus—viz., Acidasfis itself. In this characteristically
Silurian type (fig. 400, B), the usual form of the head-shield in the
Trilobites is somewhat masked, the trilobation being rendered indis-
tinct by the presence of an additional and secondary pair of axal
furrows, which mark off a central inflated portion of the glabella.
The thorax has nine or ten rings, with ridged pleurz, which are
terminated by spines; while the tail is very small, and has its
margin fringed with spines (fig. 399). The facial sutures are
continuous, or are sometimes wanting; and the eyes are of small
size and smooth. The species of Acdaspis are found in the Silurian
and Devonian rocks, and are usually readily recognised by their
highly ornamented and spinose crust.

FamILy 14. LichHap#.—The principal or only genus in this family
is Lichas' itself (fig. 400, A), in which the body is broad and oval,
and the crust is superficially more or less
granulated or tuberculated. The head-
shield is transversely elongated and
very convex, and the glabella as a rule
is not very clearly separated from the
cheeks. The frontal grooves of the
glabella are extended backwards, so
as to enclose a central lobe. The
facial sutures cut the anterior margin
separately, and the eyes are small and
smooth. ‘There are nine or ten tho-
racic rings, with grooved pleurz; and
the pygidium is larger than the head,
and often presents prominent spinose
ends to its component rings. The
species of Zzchas are Ordovician, Si-
lurian, and Devonian.

FAMILY 15. BRONTEIDH. — This

Fig. 4o1.—a, Head-shield of Bron- family includes only the genus S7on-
ious conpanifir, from the Silurian Zeus, the species of which are found in
(After Barrande.) the Ordovician, Silurian, and Devonian

rocks. In this well-marked type (fig.
401) the body is broad, and could be rolled up, both the head-
shield and the pygidium being of great size. The tail is particu-
larly large, and is always more or less fan-shaped, the axis being
short and rudimentary, while the “limb” is greatly developed.
The head-shield is trilobed, the glabella being dilated in front, the

1 The genus ZLzchas has been very fully treated of by Magister Friedrich
Schmidt (‘ Revision der Ostbaltischen’Silurischen Trilobiten,’ Abth. II., 1885),
by whom it has been split up into a number of sub-generic groups.

TRILOBITA. 541

facial sutures being separate, and the eyes sickle-shaped. ‘There
are ten thoracic segments, and the pleure are ridged.

FAMILY 16. PHAcopip#&.—In this, one of the best-marked and
most typical of the families of the Trilobites, the head is well de-
veloped, the glabella conspicuously broadest in front, with three or
four lateral grooves, and the facial sutures united in front of the gla-
bella, and cutting the outer margins of the cephalic buckler behind.
The eyes are usually large, and are faceted (fig. 403); there are
eleven body-rings, with grooved pleure ; and the condition of the
pygidium is variable. The hypostome is convex, and more or less

Fig. 402.—a, Phacops Stern- Fig. 403.—Phacops (Dat-
bergt, from the Silurian rocks manttes) longicaudata. Silu-
of Bohemia; B, Head-shield rian (Wenlock) of Britain and
of Phacops (Trimerocephalus) North America.

Volborthz, Silurian, Bohemia.
(After Barrande. Copied from
Zittel.)

triangular in shape. The genus Phacofs itself (with the sub-genera
Trimerocephalus, Phacops proper, Acaste, Pterygometopus, Chasmops,
Dalmanites, and Crypheus) constitutes the entire family, and ranges
from low down in the Ordovician series to the Upper Devonian
rocks.

As regards the sub-genera of Phacops, Trimerocephalus includes
Silurian and Devonian forms, in which the glabella is tumid in front
(fig. 402, B) ; the glabella-furrows are faint or wanting ; and the pygidium
is of small size. In Phacops proper (fig. 402, A) the genal angles of the
head-shield are rounded ; the two anterior pairs of glabella-furrows are
inconspicuous, and the glabella is very wide in front; the pleure are
rounded ; and the pygidium is of few segments, with an entire margin.

542 CRUSTACEA.

The species included under this head are Silurian and Devonian. Dal-
manttes (or Dalmania) includes forms with the pleurz pointed and bent
backwards, the pygidium being conspicuously segmented, and often end-
ing in a spine (fig. 403). There are three glabella-furrows on each side,
and the genal angles of the head-shield are long and produced. The
species of this group are principally Silurian, but some of the forms are
Ordovician and others are Devonian. Chasmops includes Ordovician
species in which the genal angles are produced ; the anterior glabella-
lobes are laterally extended ; the pleuree have truncated ends ; and the
pygidium is of large size. Pterygometopus also includes Ordovician
species, in which the frontal lobes of the glabella are laterally extended,
and are intersected by the facial sutures. In Acasfe are comprised
Ordovician and Silurian species in which the glabella is not tumid, and
exhibits all its furrows in a well-developed form, while the pygidium is
often pointed. Lastly, Cxyp@us includes Devonian types, and is princi-
pally distinguished by the fact that the margin of the pygidium is toothed
or serrated.

FaMILy 17. PRoETID#.—In this family the body is oval, dis-
tinctly trilobed, and capable of being rolled up. The head is of
variable size, semicircular, sometimes with
rounded, sometimes with spinose genal
angles. The glabella is distinctly marked
off from the cheeks, and the hindmost pair
of glabella-furrows commonly circumscribe
a basal lobe. The facial sutures cut the
anterior margin of the head-shield separ-
ately. There are from eight to twenty-
two body-rings, with grooved pleure, and
the pygidium is distinctly segmented, and
usually has an entire margin. The eyes
have distinct facets, but are covered by a
smooth cornea.

In Proetus itself (fig. 404, Cc) the head-
shield is semicircular; the glabella has
three pairs of lateral furrows; the eyes
are large, semicircular, of numerous facets,
covered by a thin cornea ; there are eight
or ten body-rings, and the tail has an

Fig. 4o4.—a, Head-shield of ‘‘entire” border. The genus ranges from
Ce ee ee the Ordovician to the Carboniferous.
oe sie Seen wake or ~CyPhaspis (fig. 404, B), of the Ordovi-
Bohemia. (After Barrande.) cian, Silurian, and Devonian rocks, differs

from the preceding chiefly in its more
convex glabella, with circumscribed basal lobes, its ovoid and
remote eyes, and the generally greater number (fifteen to seventeen)
of the body-rings. Avethusina (fig. 404, A), with a similar range
in time, has its glabella much shortened, while the body-rings are as

TRILOBITA. 543

many as twenty-two in number. Carvmon is an Ordovician genus
allied to Proetus, but it has neither eyes nor facial sutures, and it
possesses eleven body-rings. The genus Marfides (apparently =
Lrinnys of Salter) is an interesting type, which appears to be in-
termediate between the Proetide and Olenide@, and which carries
back the range of the former into the Upper Cambrian. It has
the “limb” of the head-shield very wide, and covered with a net-
work of radiating and bifurcated nervures. On the other hand,
the Proetide are represented in the Carboniferous rocks, not only
by Pvroetus itself, but also by the genera PAilipsia, Griffithides,
and Lrachymetopus, one species of the first of these genera having
been detected in deposits of Permian age. These types are there-
fore the most modern examples of the order Z7z/odita at present

Fig. 405.—a, Grifiithides globiceps, from the. Carboniferous Limestone; B, Ph7llipsia Derii-
ensis, from the Carboniferous Limestone; c, Glabella and free cheek of the same; D, Hypostome
of the same ; E, Body-ring of the same. All the figures are enlarged. (After Henry Woodward.)

known to us. In the genus /P/zllipsia (fig. 405, B-E) the body is
oval in form, and can be rolled up. The glabella (fig. 405, c) has
nearly parallel sides, with two or three lateral furrows, the hind-
most of which circumscribe a nearly circular basal lobe on each
side. There are only nine body-rings. The tail is semi-oval, dis-
tinctly segmented, and with an “entire” margin; and the eyes are
large, reticulated, and reniform. Gviffithides (fig. 405, A) resembles
Phillipsia in having nine body-rings, but the glabella is pyriform,
without lateral furrows, and with the basal lobes inflated, while
the eyes are small, lunate, and smooth. Srachymetopus, finally,
much resembles the preceding in form, but the glabella is small,
with lateral furrows but with no basal lobes. The eyes are small
and smooth, and no facial sutures are visible. The head-shield is
covered with a “small bead-like ornamentation ” (Henry Wood-

544 CRUSTACEA.

ward). The thorax is unknown, but the pygidium is large, and
the segments of the axis are beaded.

FamiLy 18. TRINUCLEIDZ.—In this singular family (fig. 406) the
head-shield is enormously developed, with a wide margin or “limb,”
which is usually perforated by rounded pores. The glabella is well
marked, but eyes are usually wanting, and the facial sutures may be
absent. The body-rings are reduced to five or six in number, with
grooved pleuree; and the tail is wide and sub-triangular. The
family contains three principal genera, viz., Z7inucleus, Dionide, and
Ampyx, all of which are Ordovician or Silurian in their range ; and
its zoological affinities seem to be with the Harpedide. In the
well-known and widely-distributed genus Z7nucleus (figs. 406, 407)
the body is distinctly trilobed; the “limb” of the head-shield is

Fig. 406.—T7rinucleus Pongerardi—Ordovician. The right-hand figure represents
a vertical section of a rolled-up specimen.

composed of two lamelle, and is perforated by numerous larger or
smaller foramina ; and the ‘‘genal angles” are prolonged into con-
spicuous spines which are usually single, but are forked in 7: Ponger-
arat. The glabella is prominent and pyriform, with mere traces of
lateral grooves, the facial sutures being rudimentary, and the cheeks
being tumid, and generally furnished on each side with a small
tubercle seemingly representing the eyes. There are six body-rings ;
and the tail is triangular, with a distinct axis, and having its margin
entire and striated. The genus Z7zzucleus is wholly confined to the
Ordovician rocks, and is specially characteristic of the Bala beds.
The genus Dronide has a sub-quadrangular glabella ; and the “limb ”
of the head-shield, though perforated, is rudimentary, and by absence
of the facial sutures becomes continuous with the cheeks. ‘The eyes
are wanting, and there are six body-rings. In the curious Ordovi-
cian and Silurian genus Ampyx (fig. 408) the head is sub-triangular,

TRILOBITA. 545

with spinose genal angles, and without a perforated “limb.” The
glabella is prolonged forwards in front of the head-shield as a trian-
gular process, which is often extended into a long spine, while its
lateral grooves are obsolete, and eyes are wholly wanting. ‘The
facial sutures are present and are discontinuous. ‘There are five or
six body-rings, and the tail is sub-triangular. The species of Ampyx

Fig. 407.—Tvinucleus concentricus. Ordo- Fig. 408.—A myx nudus. Ordovician.
vician. (After Salter.) (After Salter.)

are mostly Ordovician, but a few Silurian forms are known. LZndy-
muonia (Ordovician) is allied to both Z7inucleus and Ampyx, but
wants the perforated border of the former, and the prolonged glabella
and genal spines of the latter.

FAMILY 19.—AGNosTID#&.—This, the last, family of the Trilobites
includes a number of small forms of this order, which
range from the Upper Cambrian to near the summit of
the Ordovician. The cephalic and caudal shields in
this group are nearly equal, and are very similar to one
another in form and markings. The thoracic segments
are reduced to two only in number, with grooved
pleure ; and both eyes and facial sutures are totally
wanting. The type-genus of the family is Agnostus it-
self (fig. 409), which is represented by numerous forms d
in the Upper Cambrian and Ordovician rocks. Mficro- Fig. 409.—

F : ; - Agnostus prin-
discus of the Upper Cambrian (sometimes placed in ‘eds. Upper
the Z7inuclerde or in the Olenide) agrees with Agnostus a eae
in its want of facial sutures and eyes, but it has four
body-rings, and the axis of the tail is segmented. Lastly, the
Shumardia of the Ordovician (Quebec Group) is like Agnostus,

VOL. I. 2M

546 CRUSTACEA.

but has both the axis and lateral lobes of the pygidium distinctly
segmented.

Division C. MEROSTOMATA.

The members of this group are Crustaceans, often of gigantic
size, in which the mouth is furnished with mandibles and maxilla,
the terminations of which become walking or swimming feet,
and organs of prehension. ‘Two orders are included under the
Merostomata—viz., the recent King-crabs (X7phosura) and the ex-
tinct Eurypterids. By Professor Claus these orders are regarded
as forming a special division of Arthropods, with relationships to
the Arachnida, to which he applies the name of Gvganfostraca.
Professor Ray Lankester has also shown that there are various
remarkable features of relationship between Zzmu/us and the Scor-
pions ; and the same point has been brought out by Van Beneden
from his researches into the development of the King-crabs. More-
over, the investigations of Mr Benjamin Peach would show that
there are close and important relationships between the Scorpions
and the Paleozoic group of the Eurypterids.

ORDER J. XipHosURA (Pc@cILopopA).— This order includes
Crustacea in which the antertor segments are amalgamated to form a
large cephalic buckler, upon the dorsal surface of which are placed the
eyes (when present). Ox the under side of the head-shield is placed
the mouth, which ws furnished with a rudimentary metastoma,
and 1s surrounded by six pairs of appendages, the bases of all but
the first pair being modified to act as masticating organs. The seg-
ments behind the head-shield may be fused with one another, or may
be more or less completely free , and they carry upon their under sur-
Jace a series of lamellar appendages which are branchial in function.
The last segment of the body forms a sword-lke movable telson.

The only existing genus contained in the order X7phosura is
Limulus, comprising the King-crabs or Horse-shoe Crabs. In this
genus (fig. 410) the anterior segments—usually regarded as repre-
senting the head and thorax—are fused to form a horse-shoe-shaped
cephalothoracic shield. The upper surface of this carries subcen-
trally a pair of large compound eyes, and also a pair of small larval
eyes placed in the middle line in front. On the under side of the
head-shield is the mouth, surrounded by six pairs of jointed limbs,
the last five pairs having their basal joints spinose, and thus
adapted to act as jaws. ‘The first pair of appendages — often
regarded as representing the antennze—are placed in front of
the mouth and terminate in nipping-claws. The next four pairs of
appendages are also generally chelate, while each of the last pair
of legs is terminated by two flat spines, with a whorl of similar
spines proximally, being thus adapted for locomotion. Behind

MEROSTOMATA. 547

the cephalic buckler comes a second, somewhat rhomboidal shield,
the segments of which are immovably welded together, and which
is usually regarded as representing the abdomen, though some
authorities consider it as the thorax. The lateral margins of
this abdominal shield carry movable spines, and on its under sur-
face in front are placed the generative openings, protected by a
broad, divided “operculum,” which is formed by the first pair of
abdominal limbs. The oper-
culum not only covers the
reproductive apertures, but
more or less extensively con-
ceals the remaining five pairs
of abdominal limbs. These
latter are much modified, and
support a number of delicate
lamelle arranged like the
leaves of a book, which act
as branchiz. Lastly, the ab-
dominal shield has movably
articulated to its hinder mar-
gin a long ensiform “telson”
(fig. 410).

The integument of Lzmu-
Jus is thoroughly hardened by
the deposition of chitine, and
forms a resisting shell. Thin
sections show that this is
largely composed of a pecu-
liar finely tubulated tissue,
which has very much the ap-
pearance of dentine under the
microscope (fig. 411, A). In
the inner layer of the shell,
the minute tubuli just men-
tioned are accompanied by a
limited number of vertical

. Fig. 410.—Limulus meoluccanus, viewed from the
canals of larger S1Z€ (fig. 4I1I, dorsal aspect, and reduced in size. (Recent.)
A, c), the structure thus com-
ing closely to resemble that shown in vertical sections of the shell
of the Trilobites.

The embryo of Limulus (fig. 382) is destitute of the tail-spine of
the adult, this structure only existing in a rudimentary form; and
in this stage of its existence, as previously noticed, it bears a strong
resemblance to certain of the Trilobites.

It is not necessary here to enter into the vexed question as to

he
ney
a
3

Sr ges eS
wishin

es

548 CRUSTACEA.

whether Zzmz/us should properly be placed among the Crustacea or
the Arachnida. It is sufficient to note that the X7phosura are clearly
related to the Eurypterids on the one hand and the Trilobites on
the other hand ; and that when the natural systematic arrangement
of the Arthropoda shall have been finally settled, these three orders
will necessarily be placed close together. The Xzphosura and the
Lurypterida, in particular, are closely connected together by means
of Hemzaspis and its allies. So much so is this the case, that while
Dr Henry Woodward places HYemzaspis and the genera related to it
among the Eurypterids, these forms are placed by Zittel among the
Xiphosurans, an arrangement which will be followed here.

The existing species of Lzmu/us are aquatic in habit and are
inhabitants of the sea. The oldest fossil types of the Xiphosura

Fig. 411.—A, Part of a transverse section of the tail-spine of Lzmulus: a, Outer cuticular
layer; 4, Intermediate finely tubulated layer; c, Internal layer of finely tubulated tissue with
interspersed larger tubes. B, Part of a tangential section of the inner layer of the cephalic
buckler ; @, Portion of the section showing the minute dots representing the transversely divided
tubuli, together with the cut ends of the larger tubes, which are alone shown at e. (Original.)

(Hemiaspis, Neolimulus, &c.), appear in the Silurian rocks. Other
ancient types of the order (Gefznurus and Prestwichia) appear in the
Carboniferous formation. The oldest types of Zzmudus itself are
found in the Triassic rocks.

The Xzphosura are divided by Zittel into the two families of the
Flemiaspide and the Limulide, the former including all the Palzo-
zoic types of the order, while the genus Zzmu/us alone is comprised
in the latter. In the Hemaspide, the cephalic shield is separated
from the thorax, and sometimes possesses a “facial suture.” ‘The
thorax! is composed of five or six segments which are usually free

1 By Packard the head-shield of the Hemzaspid@ is regarded as representing

the entire cephalothorax ; and the free segments which immediately follow this
are considered as belonging to the abdomen and not to the thorax.

MEROSTOMATA. 549

(fig. 412); and the abdomen consists of three or more rings, and
is terminated by a spine-like telson. The appendages are as yet
unknown.

The genus Hemdzaspis (fig. 412, A) comprises some singular Silurian
Crustaceans, in which there is a semicircular head-shield with a central
glabella, and indications of facial sutures and eyes. The thorax is tri-
lobed, and consists of six free segments. There are three free segments
in the abdomen, and these are followed by a long spiniform telson.
The genus Pseudoniscus, also from the Silurian rocks, resembles emzz-
aspis nN many points, and particularly in the possession of free thoracic
segments, but there is no distinct line of demarcation between the thorax
and the abdomen (fig. 412, B). Another Silurian genus, also closely re-

_Fig. 412.—A, Hemiaspis limuloides (after H. Woodward); B, Pseudoniscus aculeatus (after
Nieszkowski) ; c, Bunodes (Exapinurus) Schrenkii (after Nieszkowski). All from the Silurian.

lated to the preceding, is Bunodes (Exapinurus), in which the thorax
likewise consists of free rings, but the last two are fused with one another.
There are three movable abdominal rings and a spine-like telson (fig.
412, C), and the animal possessed, like so many of the Trilobites, the
power of rolling itself into a ball.

In the remarkable genus described by Dr Henry Woodward from the
Silurian rocks of Britain under the name of Veolimulus (fig. 413), the
head-shield has a general resemblance to that of the recent Zz7u/us, and
there are traces of a divisional line crossing the head and apparently cor-
responding with the “facial suture” of the Trilobites. Compound eyes
and ocelli seem to be present, and there are six free thoracic segments,

550 CRUSTACEA.

followed, probably, by three free abdominal rings, of which only two have
been preserved. A long spiniform telson may be conjecturally added to
complete this ancient Limuloid Crustacean. In the Devonian rocks, the
only genus of Xiphosurans which has hitherto been recognised with cer-
tainty is the Prozolémulus of Packard, which appears to be nearly related
to Weolimulus. In the Carboniferous rocks, on the other hand, the
Limuloids are represented by a number of forms, the most important
genus being Prestwchia (fig. 414), which has the general form of /Veo-
4imulus, but in which the thoracic and abdominal segments are not
marked off from one another, and are all anchylosed. The genus £w/-
roops, trom the Coal-measures of North America, is hardly separable
from the preceding, but the eyes are situated on the anterior edge of the

‘|
Aa
Te
\\aa ’

ARAN

Fig. 413.—Neolimulus falcatus, enlarged Fig. 414.—Prestwichia rotundata.
about three times. Silurian. (After Henry Coal-measures.
Woodward.)

cephalic buckler. Another well-known Carboniferous genus is Beiinurus,
which agrees with the preceding in having five thoracic and three abdo-
minal segments, together with a long tail-spine, but in which the thoracic
rings are free and movable, while those of the abdomen are anchylosed
with one another. It would also seem probable that the singular Crus-
tacean fossils which have been described from the Coal-measures under
the name of Cyclus, are really, as maintained by Dr Henry Woodward,
the young forms of such Carboniferous Xiphosurans as 4elznurus and
Prestwichia. The very similar Triassic fossils, for which the generic
name of Halycine has been proposed, are probably also the larval forms
of Limuloid Crustaceans.

The family of the Zzmutide is distinguished from that of the
Femiaspide by the fact that the cephalic and thoracic segments are
amalgamated to form a cephalothoracic shield, the upper surface of
which bears two compound eyes and a pair of simple eyes. The
abdominal segments are amalgamated with one another to form a

MEROSTOMATA. Ber

second post-cephalic shield, which is terminated by the movable,
spine-like telson. The only genus of this family is Lzmulus itself,
the characters of which have been already treated of in some detail.
The earliest undoubted fossil species of Zzmu/us appear in the Trias
of Europe, and other representatives of the genus are found in the
Jurassic rocks (the Lithographic Slates of Germany), and in the

Fig. 415.—Zurypterus Fischeri, from the Silurian rocks of Oesel, viewed from above and re-
stored, the size being about one-fifth of nature. The segments behind the carapace are numbered,
the first six being sometimes considered as thoracic. (After Friedrich Schmidt. Copied from
Zittel.)

Cretaceous and Tertiary deposits. Of the existing species of the
genus, one is found on the east coast of North America, and others
occur on the eastern shores of Asia and in the Malayan Archipelago.

OrveER IJ. Eurypreripa.—The Eurypterids are /arge Crusta-
ceans (fig. 415), 0 which the body is elongated and compressed, and
the chitinous integument is ornamented with a characteristic scale-like

552 CRUSTACEA.

sculpturing. The anterior part of the body ts covered with a cara-
pace, which carries a pair of large, marginal, or subcentral eyes, and
a pair of small ocelli placed near the centre. On the under side of
the carapace is the opening of the mouth, furnished behind with a large
undivided metastoma and with a series of jointed appendages (five or
six pairs in number), of which the first are preoral, and represent
antennae, while the remainder are modified for mastication or locomo-
tion, the last pair forming usually great swimming-feet. Behind the
carapace the body consists of numerous free thoracico-abdominal seg-
ments, certain of the anterior of which are furnished below with
divided lamellae, which concealed the branchia. The hinder segments
carry no appendages, and the abdomen terminates in a spine-like or
paddle-shaped telson.

The integument of the Eurypterids is hardened by chitine, and
when transparent fragments are examined under the microscope,
these exhibit a reticulated structure, numerous clear rounded
corpuscles, of various sizes, appearing to be disseminated in a
horny matrix ; the crust thus assuming a punctated or porous aspect.
The characteristic ‘‘ scale-marking ” is the result of the development
at intervals of curved linear thickenings of the exoskeleton.

The anterior part of the body in the Eurypterids is covered by a
comparatively short, semicircular, or subquadrate carapace, which is
considered by Woodward, Schmidt, and Zittel as representing the
head only, but which is regarded by Claus and Hall as a cephalo-
thorax. The upper surface of the carapace carries a pair of large,
prominent, faceted, compound eyes, which may be subcentral, or
may be placed on the margin of the head-shield. There is also a
pair of small ocelli, usually placed close together, subcentrally.

On the under side of the carapace is the opening of the mouth,
surrounded by a series of jointed appendages. The first pair of
appendages (fig. 416, az) are przeoral in position, and represent the
antenns. ‘They terminate in pincers in Prerygotus (fig. 416, an),
but are stated by Fr. Schmidt to have the form of very slender
jointed organs in urypierus. The remaining appendages are
similar to those of Zzmulus in having their bases spinous, and in
officiating as jaws. Woodward recognises four pairs of these; but
according to Fr. Schmidt there are five pairs, the total number of
appendages on the under side of the head-shield being thus six
pairs. ‘The anterior appendages behind the antennze may represent
mandibles and maxillz, and they have the form of slender jointed
organs, with dilated and serrated basal joints (fig. 416, gz). The
last pair of appendages, regarded by Woodward as maxillipedes
(fig. 416, mx), are of great size, and while their bases are dentated
to fit them for mastication, they are usually dilated distally so as to
form powerful swimming-paddles. The mouth is a longitudinal

MEROSTOMATA. 553

fissure on the under side of the head, surrounded by the toothed
bases of the limbs, and provided behind with a large undivided
metastoma (fig. 416, 7), while in some cases a hypostome or upper
lip appears to be present as well.

Behind the carapace the body consists of thirteen free segments,
counting the telson as one. By Claus and Hall the whole of these
segments are regarded as belonging to the abdomen. By other

{ C re:
Mg ECG (ae aids :

(

Fig. 416.—Under side of the head and the following segments of Prerygotus Anglicus, restored.
0, The large compound marginal eyes; az, The first pair of appendages, chelate, and repre-
senting antenne; 7, Three pairs of slender ‘‘ gnathopods,” with spinose bases, placed on the
sides of the mouth-opening (according to Fr. Schmidt, there are four pairs of these organs) ;
mx, the last pair of appendages (‘‘ maxillipedes”), developed into great swimming-feet, but
acting by their bases as jaws; 7, Metastoma, drawn as if it were transparent, so as to show the
toothed bases of the last pair of appendages below it; of, Operculum. The ‘“‘scale-marking” is
only represented on the segments behind the operculum. (After Henry Woodward.)

authorities, however—as, for example, by Fr. Schmidt—the anterior
six of these segments are regarded as belonging to the thorax, while
the posterior seven are looked upon as forming the abdomen. Im-
mediately behind the carapace, on the inferior aspect of the body,
is a broad lamellar plate, which is divided into two lateral halves by
a narrow median process (fig. 416, of), and which is known as the
“operculum.” . This plate, like the structure which bears the same
name in the King-crabs, doubtless protected the openings of the

ae

554 CRUSTACEA.

reproductive organs, and also served to conceal the leaf-like gills,
fragments of which are sometimes found in the fossil state. Accord-
ing to Fr. Schmidt, the segments immediately following the ‘ oper-
culum” have their ventral side formed, each, by a pair of lamellar
plates, which meet in the middle line, and which are regarded by
this observer as modified thoracic appendages carrying branchiz.
According to the investigations of Mr Benjamin Peach, some
Eurypterids were further provided with well-developed pectinated
organs, apparently similar in form and structure to the so-called
“combs” (pectines) of the existing Scorpions. Lastly, the seven
hindmost segments of the body are undoubtedly devoid of appen-
dages of any kind, and the last of these is the “telson.” The form
of this varies, being lanceolate or bilobate in Prerygotus and Slimonia,
but narrow and sword-shaped in Eurypzerus and Stylonurus.

There are at present no materials available for working out the
development of the Eurypterids, but there is every reason to sup-
pose that the berry-like bodies which are found in the Old Red
Sandstone of Scotland, and which have been described under the
name of Parka decipiens, are really the eggs of Crustaceans belong-
ing to this order.

There can be no question as to the importance of the relation-
ships between the Eurypterids and the Scorpions; and many high
authorities consider that the order Eurypterida should be removed
from the Crustacea and placed in the series of the Avachnida.
There is, however, no reason for doubting that the Eurypterids were
water-breathing animals, provided with branchiz ; and as the nature
of the respiratory organs constitutes, perhaps, the most weighty of
the distinctions between the closely related classes of the Crustacea
and the Arachnida, it would seem proper to regard the Lurypterida
as an ancient type of the Crustacea, in which are preserved certain
of the characters which must have been possessed by the ancestral
Arthropods from which these two classes originally diverged.

The nature of the deposits in which the remains of Eurypterids
are found, and of the fossils associated with them, would prove that
these animals were essentially marine, their habits, probably, being
very similar to those of the existing King-crabs. It is, however,
possible that certain of the Eurypterids were inhabitants of brackish,
or even of purely fresh, waters. As regards their geological range,
the Eurypterids seem to have appeared for the first time in the
Ordovician rocks, but comparatively little is known of the early
representatives of the order. On the other hand, Eurypterids abound
in the Silurian rocks, and it is in this system of deposits that the
order seems to have attained its maximum development. Numer-
ous Devonian Eurypterids are also known, and the genus Lurypiterus
is represented in the Carboniferous rocks, while a doubtful repre-

MEROSTOMATA. 555

sentative of the order (Campylocephalus) has been recorded from the
Permian rocks of Russia. With the close of the Palseozoic period,
however, the order appears to have undergone complete extinction.

The four most important genera of the Eurypterids are Lurypterus,
Pterygotus, Slimonia, and Stylonurus. In Eurypterus (fig. 415) there
are five pairs of legs attached to the under surface of the head-shield, all
of which have their bases modified to act as masticatory organs, and the
last pair of which are developed into powerful swimming-paddles. There
is also, according to Fr. Schmidt, an additional, preoral pair of appen-
dages, in the form of delicate jointed filaments, which represent the
antenne but are not chelate. Most of the species of Auryplerus are
found in the highest deposits of the Silurian rocks ; but there are a few
Devonian species, and the Carboniferous rocks have likewise yielded
representatives of the genus (e.g., the 4. Scoulerz of the Scotch Car-
boniferous rocks).

The genus Prerygotus (fig. 416) is principally Silurian and Devonian,
the largest species (Pterygotus Anglicus)—sometimes attaining a length
of nearly six feet—being found in the Old Red Sandstone of Scotland ;
but Barrande has described forms of the genus from the Ordovician
rocks of Bohemia. /Perygotus differs from ELurypterus, among other
characters, in the marginal position of the large compound eyes, and
in the fact that the preeoral appendages (antennz) are very long and
terminate in nipping-claws. The telson of Prerygotus, further, is broad
and lanceolate, whereas that of Luryfterus is long and pointed.
The Silurian genus S/z7zonza resembles Pterygotus in the form of the
telson and in the marginal position of the compound eyes, but differs
from it in the quadrate form of the head-shield and in the structure of
the limbs. Finally, the Silurian and Devonian genus Stylonurus resem-
bles Eurypterus in the possession of an ensiform telson, and in its general
structure ; but the last two pairs of limbs are developed into long slender
rowing-organs, which reach nearly to the hinder extremity of the body.

556

CHAP FER ox xc
CRUSTACEA—continued.

SuB-CLASS III].—MALACOSTRACA.

THE Crustaceans included in the sub-class Mad/acostraca (Thorac-
poda, Woodward) are distinguished by the possession of a generally
definite number of body-segments ; seven somites going to make up
the thorax, and an equal number entering into the composition of
the abdomen (counting, that is, the telson as a somite). The
Matacostraca are divided into two primary divisions, termed res-
pectively the Hedriophthalmata and the Podophthalmata, according
as the eyes are sessile or are supported upon eye-stalks.

Division A. HEDRIOPHTHALMATA.

This division comprises those JZa/acostraca in which the eyes are
sessile, and the body is mostly not protected by a carapace. It
comprises the two orders of the /sopoda and Amphipoda. ‘The eyes
are generally compound, but sometimes simple, and are placed on
the sides of the head. The head is almost always distinct from
the thorax, and the mandibles are often furnished with a palp.
Typically there are seven pairs of feet in the adult, hence this di-
vision has been called Zetradecapoda by Agassiz.

OrvER J. AmpHipopa.—The members of this order are Crus-
taceans, mostly of small size, in which ¢he body ts laterally compressed,
and the thorax consists of seven segments, carrying seven pairs of legs.
The abdomen 1s mostly well developed, and consists of seven segments.
The gills are lamellar or vesicular, and are attached to the basal
joints of the thoracic legs. The seven pairs of thoracic limbs are dt-
rected partly forwards and partly backwards. It is from this latter
circumstance that the name of the order is derived.

The order of the Amphipods comprises both marine and fresh-
water forms, many familiar types, such as the Sand-hoppers (Zait-

HEDRIOPHTHALMATA. 557

rus) and Shore-hoppers (Ovchestia), being more or less amphibious
in habit, while some genera (such as Gammarus) possess both
marine and fresh-water representatives. The geological history of
the Amphipods is still very imperfectly known. If the incompletely
understood Paleozoic genera Gamipsonyx, Paleocaris, Paleorchestia,

Fig. 417-—Gamarus locusta, enlarged about four times. Recent. (After Spence Bate
and Westwood).

and the forms allied to these, be excluded from the order, the num-
ber of known fossil forms of the order is very small. If the genus
Necrogammarus described by Dr Henry Woodward from the
Silurian rocks of Britain, be truly referable here, it is the oldest
type of the Amphipods at present known. Hardly less certain is
the position of the Permian genus Pvosoponiscus (Paleocrangon),

Fig. 418.—Pvrosoponiscus (Paleocrangon) problematicus, viewed from one side, and partially
s : : d : zs
restored. From the Magnesian Limestone (Permian) of Durham. (After Spence Bate.)

which Mr Spence Bate has described as related to the living Pedra
antigua. The fossil forms of the Amphipoda from the Tertiary
series are almost exclusively from fresh-water deposits, and either
belong to such existing genera as Gammarus or are nearly allied to
other living types. No fossil representatives of the little group

558 CRUSTACEA.

of parasitic Amphipods included under the name of Lemodipoda
have been as yet discovered.

OrpDER II. Isopopa.—In this order the head is always distinct
from the segment bearing the first patr of feet. The respiratory organs
are not thoracic, as in the preceding order, but are attached to the
inferior surface of the abdomen, and consist of leaf-ke branchie,
which in the terrestrial species are protected by plates which fold over
them. The thorax ts composed of seven segments, bearing typically
seven pairs of limbs, which, in the females, have marginal plates,
attached to their bases, and serving to protect the ova. The num-

Fig. 419.—Recent Isopoda. a, [dotea entomon, enlarged; B, Arcturus longicornis, enlarged ;
c, Serolis Scythei : an, Antenne; a, Antennules. (After Gerstaecker, Spence Bate and West-
wood, and Liitken.)

ber of segments in the abdomen varies, but is never more than
seven. The abdominal segments are in many Isopods coalescent,
and form a broad caudal shield, beneath which the branchiz are
carried (fig. 419, A).

The recent Isopods are for the most part of small size, and are
of the most varied habit. Many forms are strictly marine, some
forms occurring even at great depths (over 2000 fathoms), but very
many types are either inhabitants of shallow water or live between
tide-marks. Some forms, such as the Lopyride, are parasitic in the
adult condition. Many Isopods live in fresh waters, some of these
belonging to genera which are also represented by marine forms.
Other Isopods, like the Wood-lice (Ozz¢scide) are terrestrial in
habit.

THORACOSTRACA OR PODOPHTHALMATA. 559

As in the case of the Amphipods, the geological history of the
Isopods is very imperfectly known. The Palzozoic Arthropods
which have been referred here, such as the problematical Arthro-
pleura of the Carboniferous rocks, and the form described by Dr
Henry Woodward from the Old Red Sandstone under the name of
Prearcturus, are of doubtful affinities. The earliest unquestionable
Isopods are found in the Jurassic rocks
(the Lithographic Slates of Germany),
in which the order is represented by
the extinct genera Urdaand giles. In
the Upper Jurassic (Purbeck beds) of
Britain is found the Avcheoniscus Brodiet
(fig. 420), often in considerable num-
bers, the genus being apparently refer-
able to the recent family of the 4Agzde.
To the same family belongs the extinct
genus Palega, species of whicharefound _ Fig. 420.—Avcheoniscus Brodiei,
: ; a fossil Isopod from the Purbeck
in the Cretaceous and Tertiary rocks. Beds.

A tolerably abundant Tertiary genus is

Lospheroma, which belongs to the recent family of the Spheromide.
Lastly, the terrestrial family of the Wood-lice (Ozzscide) is repre-
sented in late Tertiary deposits by such existing genera as Armaazllo,
Porcellio, and Ontscus itself.

Division B. THORACOSTRACA OR PODOPHTHALMATA.

The Crustaceans included in this division possess compound eyes
which are usually placed upon movable peduncles ; while the anterior
part of the body is covered with a “carapace” or shield, which
covers the head and the anterior thoracic segments at any rate, and
often protects the entire cephalothorax. The body consists of nine-
teen undoubted segments, of which thirteen belong to the cephalo-
thorax and six to the abdomen. If the ocular ring and the telson
be counted as segments, there are then twenty-one segments alto-
gether. All of the Zkoracostraca except certain of the Shrimps
(Peneide) pass through “ Zoea” stages in their development. The
division Zhoracostraca comprises the four orders of the Cumacea,
the Schizopoda, the Stomatopoda, and the Decapoda, of which the
last includes the most highly organised and familiar examples of
the class Crustacea. Of these orders, the first two have no direct
fossil representatives, though we may consider in connection with
the Schizopods certain Palzeozoic Crustaceans, which are possibly
ancestral types of the order. The Stomatopods are represented by
few fossil forms, beginning, perhaps, in the Carboniferous rocks.
On the other hand, there are numerous known fossil forms of the

560 CRUSTACEA.

Decapod Crustaceans, especially in the Mesozoic and Tertiary de-
posits; but the paleontological interest of these is comparatively
small, and it will be sufficient here to give a brief sketch of the
general geological history of the three great tribes into which the
order Decapoda is divided.

OrpER I. Cumacea.—This order includes small marine Crus-
taceans, in which there is a short carapace covering the head and the
anterior thoracic segments. The eyes are sessile, and the mouth-organs
resemble those of the Isopoda. The two anterior pairs of legs at least
possess natatory exopodites, and the branchie are attached to the
epipodites of the maxillipedes. The abdomen is elongated and com-
posed of six segments, and a telson may be present or absent.

The Cumacea are regarded by G. O. Sars as an order of Crustacea
related on the one hand to the Schizopods or Macrurous Decapods,
and on the other hand to the /sofoda. No fossil forms of the order
are known.

ORDER II. Scuizopopa.—This order includes the ‘‘ Opossum
Shrimps” (JZyszs) and their allies, comprising small Crustaceans
which are in many respects related to the Decagoda. According to

G. O. Sars, the Schizopods occupy ‘“‘the most primitive position

0 See
Y . (———=—
. = =

N \ PRR : ~~
AR RRS
NAS ASV m

Fig. 421.—‘‘ Opossum Shrimp” (JZysis oculata). 2, Marsupial pouch. (After G. O. Sars.)

within the division Podophthalmia, being apparently the least modi-
fied forms, in which the original characters distinguishing the pro-
genitors of the whole division would seem to exhibit least change.”
The correctness of this view is shown by the fact that many of the
Podophthalmate Crustaceans pass in their development through a
‘* Mysis-stage,” 1n which they present marked Schizopodous char-
acters. The Schizopods are characterised by the fact that ‘the

THORACOSTRACA OR PODOPHTHALMATA. 561

thoracic limbs are eight on each side, and are provided each with an
exopodite and endopodite (fig. 421), the exopodites being natatory in
Junction. A cephalothoracic shield is present, and there ts usually
only a single pair of maxillipedes. The gills are attached to the
thoracic legs, or, exceptionally, to the abdominal feet. The ova are
carried beneath the thorax of the female, usually in a marsupial pouch
Jormed by leaf-lke plates produced from the bases of the legs (fig.
421, m). The telson often possesses minute terminal appendages or
spines.

The Schizopods are distinguished from the Decapods by the
larger number of the thoracic limbs, and by the fact that these
appendages have well-developed exopodites, as well as by the fact
that the gills are not carried in branchial chambers formed by a
downward prolongation of the sides of the carapace. In JZyses and
its allies true branchiz are wanting. With the single exception of
the AZysis relicta of the great lakes of Sweden and North America,
all the Schizopods are inhabitants of the sea,
extending their range to considerable depths.

No undoubted fossil forms of the Schizopoda
are as yet known, but a brief consideration may
be given here to the singular Palseozoic genera
Paleocaris and Ganipsonyx, which some author-
ities regard as aberrant members of the Amphz-
poda, but which are considered by Packard as
being probably ancestral types of the Schizopods.
The genus Pa/eocaris (fig. 422) includes peculiar
elongated Crustaceans from the Coal-measures
of North America and Britain, in which there is
a short cephalothoracic shield, but the hinder
thoracic segments are free. There are two
pairs of antenne, of nearly equal length, and
the limbs do not appear to be bifid. The
telson has a pair of “stylets” on each side,
and the condition of the eyes has not been
clearly ascertained. The genus Acanthotelson,
also from the Coal-measures, appears to be re-
lated to Paleocaris, as, possibly, are the genera Pe Sieh Sheen
Palworchestia (Carboniferous) and LVectotelson From. Me Coa: meanires
(Permian), but the true relationships of these Meek and Worthen.)
forms are very uncertain. Another Carbon-
iferous genus which may perhaps find a place here is Gampsonyx,
including small Crustaceans which have a general resemblance to
the Amphipods in appearance, but in which the lmbs seem to
have been of the Schizopodous type.

OrvER III. Sromatopopa.—This order includes the recent

VOL. 1. 2N

562 CRUSTACEA.

Locust-shrimps (Sguz//a), all of which are inhabitants of the sea.
The Crustaceans of this order (fig. 423) have a@ short cephalothoracic
carapace, which does not protect the hinder
segments of the thorax. There are five
pairs of maxillipedes, and three pairs of
thoracic legs. The branchie are not en-
closed tn a cephalothoracic gill-chamber
on each side, but are in the form of tufts
attached to the abdominal feet. The eyes
and antenne are attached to a somite
which 1s not soldered to the cephalo-
thorax.

As regards their distribution in time,
it is doubtful if any Palzeozoic types of
the Crustacea can be referred to this
order, but the genera JVecroscilla and
Diplostylus, of the Coal-measures, may
possibly be ancient representatives of
the Stomatopoda. Inthe Jurassic rocks
(Lithographic Slates) of Germany is
found the genus Scu/da, which is re-
lated to the recent genus Sguzd/a, and
species of the latter have been de-
Fig. 423.—Squzlla mantis, the Locust- ae ah is ae BS

$ro% Sasa while others occur in the Eocene
Tertiary.

ORDER IV. Decapopa.—This order includes the Shrimps and
Lobsters, the Hermit-crabs, and the true Crabs, and comprises the
most highly organised of all the Crustacea. Most of the Decapods
are aquatic in their habits, and they are usually protected by strong
resisting shells. There is always a complicated set of ‘‘ gnathites,”
or appendages modified for masticatory purposes, surrounding the
mouth. Zhe ambulatory feet are made up of five pairs of legs
(hence the name of the order); ¢he first patr—and often some
other pairs behind this—being ‘‘ chelate,” or having their extremities
developed into nipping-claws. The branchie are pyramidal, and are
contained in cavities at the side of the thorax. The carapace ts
well developed, and covers all the segments of the head and
thorax.

The Decafoda are divided into three tribes, termed respectively
the Macrura, Anomura, and Brachyura, and characterised by the
nature of the abdomen.

TrinpE A. Macrura.— This tribe includes the ‘ Long-tailed
Decapods,” such as the Lobsters, Cray-fish, Shrimps, and Prawns,
in which the abdomen is well developed, often longer than the

THORACOSTRACA OR PODOPHTHALMATA. 563

cephalothorax, and its posterior extremity is in the form of a
powerful natatory organ or caudal fin. The recent Macrurans are
mostly marine in habit, but some typical forms (the Cray-fishes) are
inhabitants of fresh water. The earliest fossil representatives of the
Macrura are certain Shrimp-like Crustaceans which appear in the
Devonian and Carboniferous rocks, but the group undergoes a great
development in the Mesozoic period, and many Tertiary forms are
known as well. It will be suf-
ficient here to give a general
sketch of the geological history
of the group, without discussing
its different families in any de-
tailed manner.

The oldest known Macruran
is the Shrimp-like Paleopale-
mon of the Devonian rocks of
North America, the general
characters of which would jus-
tify its reference to the exist-
ing family of the Shrimps and
Prawns (Caridide). To the
same family may be referred
the Carboniferous genera Az-
thrapalemon (fig. 425), Cran-
gopsis, and Pygocephalus. In
Anthrapalemon, there is a
well-developed carapace, which
is furnished with a beak or
“rostrum,” and possesses ser-
rated lateral margins. There
are five pairs of thoracic legs ;
the abdomen is composed of ..

: Fig. 424.—The common Cray-fish (A stacus fluvt-
free segments, and there is a azzvis), viewed from below. a, Antennules; 4,
caudal fin, formed by the tel- Antenne; c, Eyes; d, Opening of antennary

gland ; e, Last pair of foot-jaws ;_4 One of the great
Sumeneawituetiicnlast pair of cele: g, Fifth thoracic limb; 4, Swimmerets; 2,
: pair of swimmerets ; 7, € opening o
swimmerets. No undoubted the anus below the telson.
representatives of the JZacrura
have hitherto been detected in the Permian rocks, but the Trias
has yielded a number of Long-tailed Decapods belonging to the
families of the Shrimps (Pexeus and ger), the Lryonide, and the
Glypheide (Pemphix, Lithogaster, &c.) It is, however, in the
Jurassic rocks that the Macrura attain their maximum develop-
ment as fossils, all the recent families of the order having now
come into existence, and some of them attaining here their cul-
minating point. The Shrimps (Cavidid@) are represented by genera

5040 CRUSTACEA.

such as Peneus and ger; the Spiny Lobsters (Palnuride) are
exemplified by the singular J/ecochirus (fig. 426) of the Solenhofen
Slates, in which the first pair of ambulatory limbs are enormously

elongated, but do not terminate in

\i 3 f pincers; the Glypheide are repre-

\ sented by Glyphea itself, and the

ei “IN| qe genus Pseudastacus takes the place of
Wn. the modern Lobsters. The most re-

YY |

markable group of the Jurassic MJac-
rura is, however, that of the Exyonzde,
of which the principal genus is Zvyox
itself. This interesting family has rep-
resentatives in the Trias, and is very
widely distributed in the Jurassic and
Cretaceous rocks, while recent investi-
gations have shown that a few forms of
the group (such as Widlemoésia) still
maintain their existence at the bottom

Fig. 425.—A nthrapalemongracilis, of the deep SES In Lryon (fig. 427),
of the natural size. From the Coal- the carapace is large and broad) and
measures of North America. (After . 5
Meek and Worthen.) nearly quadrate in figure, whilst the

antennee are very small; the first four
pairs of ambulatory legs are chelate, and the first pair are much
longer than the others ; and the caudal extremity is constituted by
the triangular telson and the dilated last pair of swimmerets. Beau-

tifully preserved examples of Avyon are found in the Lithographic

Fig. 426.—Mecochirus longincanus, from the Lithographic Slates of Eichstadt,
one-half the natural size. (After Zittel.)

Slates of Germany, and in the same deposits are found the remains
of ‘“ Phyllosome,” which are to be regarded as the larval stages of
the former. In the Cretaceous ,rocks, Macrurous Decapods are
tolerably numerous, and belong to all the principal sections of the

THORACOSTRACA OR PODOPHTHALMATA. 565

tribe. Among the more characteristic Cretaceous genera may be
mentioned Lxoploclytia, Hoploparia, Meyeria, Palinurus, and Scyl-
farus. Very abundant also in parts of the Cretaceous series are
the great chelee of burrowing Crabs belonging to the genus Ca/-
Jianassa, a type which appeared in the Jurassic rocks, and which
survives at the present day. In the Tertiary rocks, finally, the
remains of JZacrura are
comparatively scanty, and
present few points of special
interest. The recent genus
Flomarus, including the
common Lobster, appears
in the Oligocene deposits,
and in the fresh-water Ter-
tiary deposits of North
America are found the re-
mains of Cray-fishes (As¢a-
cus) essentially similar to
existing forms.

TrisE B. ANOMURA.—
The Decapods which be-
long to this tribe are dis-
tinguished by the condition
of the abdomen, which is
neither so well developed
as in the JZacrura, nor so
rudimentary as in Crabs.
The last pair of thora- Fig. 427.—Evryon arctiformis. Jurassic rocks.
cic limbs are reduced in (Solenhofen Slates.)
size. Further, the abdo-
men does not terminate posteriorly in a caudal fin, as in the
Macrura.

The division Axomura must be regarded as an artificial assem-
blage, composed of modified forms of both the Jacrura and
Brachyura. It is, in fact, impossible to draw a rigid line between
the Anomura and the Lrachyura—the two tribes being connected
by transitional forms, which might with equal propriety be placed in
either. The most characteristic forms of the Axomura are the
“ Hermit-crabs” (Pagurus, Cenobita, &c.), and the “ Plated
Lobsters” (Galathea). The Hermit-crabs are interesting on ac-
count of their habit of protecting the soft abdomen within the
empty shell of some Mollusc (fig. 428). Many of the Hermits,
such as the Cenobite of the tropics, are terrestrial in their habits,
and commonly employ the shells of snails for their borrowed dwell-
ing. As the Cenobite migrate to the sea for the purpose of pro-

566 CRUSTACEA.

ducing their eggs, it is conceivable that by their agency a curious
and puzzling intermixture of land-shells with marine types of Mol-
luscs might be effected.

With regard to the distribution of the Azomura in time, our
knowledge is at present very imperfect. If the group of Decapods
represented by the living Sponge-crabs (Dvomia) be referred to the
Brachyura, then it is doubtful if any remains of the Axomura have
been found in any Mesozoic deposit, while Paleeozoic forms are

Fig. 428.—Hermit-crab (C@xoézta) in its borrowed shell. After Morse.

wholly unknown. The claws of a form resembling Gadlathea have
been recorded as occurring in the Faxoe Chalk ; but with this ex-
ception the earliest unquestionable remains of Anomurous Decapods
are referable to the genus Pagurus, and are found in the Eocene
deposits.

TRIBE C. BRacHyuRA.—The “short-tailed ” Decapods, or Crabs,
are distinguished from the two preceding tribes by the rudimentary
condition of the abdomen, which is very short, and is tucked up
beneath the cephalothorax, the latter being disproportionately large.
There is no caudal fin, and there are from one or two (males) to four
(females) pairs of abdominal appendages, which are employed by
the females in carrying the ova. The Crabs are mostly furnished
with ambulatory limbs, and are rarely formed for swimming, most
of them being littoral in their habits, and some even living inland.

With regard to their geological history, it is very doubtful if any
genuine representatives of the Brachyura have been hitherto de-
tected in the Paleeozoic series. The Gvtocrangon granulatus of the
Devonian rocks, the Brachypyge carbonis of the Carboniferous, and
the Hemitrochiscus paradoxus of the Permian deposits, which have
been supposed to be ancient types of the Brachyura, are all more
or less problematical in nature. Even in the Jurassic rocks the

LITERATURE OF CRUSTACEA. 567

evidence of the existence of genuine Crabs is not perfectly clear ;
since the Paleinachus longipes ci the Forest Marble (Lower Oolites),
described by Dr Henry Woodward as a Crab, is not completely
known, and the Jurassic genus
Prosopon may perhaps be refer-
able to the Axomura. In the
Cretaceous rocks there are various
Decapods of the family of the
Sponge-crabs, which form a tran-
sitional group between the Brachy-
ura and Azxomura, such as the
genus Dromiopsis ; but there are
also genuine Crabs, such as Pa/@o-
corystes, E-ucorystes, Necrocarcinus,
L£tus, and Xantho, <P resenting Fig. 429 —Paleocarpilius macrocheilus.

several of the existing families of Eocene.

the Lrachyura. ‘The Eocene de-

posits, and particularly those of Britain (the London Clay), have
proved very rich in the remains of Brachyurous Decapods, some of
the forms of this period belonging to extinct genera (such as J/icro-
mata, Psammocarcinus, Paleocarpilius, fig. 429, Lobocarcinus, Xan-
thilites, and, above all, Xanthopsis), while others are referable to
such existing genera as Cancer and Xantho. ‘The later Tertiary
deposits have yielded comparatively few remains of Bvachyura, and
these of little special interest, but the fresh-water genus Ze/phusa and
the terrestrial genus Gecarcinus are both represented in the Miocene
deposits of Geningen.

me i

ILI S ISSA ORI, Ol (INU IVA Cia yae

GENERAL.

1. “ Gliederfussler.” ‘Bronn’s Klassen und Ordnungen des Thierreichs,’
vol. v. Gerstaecker. 1866-80.

2. Article “ Crustacea,” in ‘Encyclopzedia Britannica,’ 9th ed. vol. vi.
Henry Woodward. 1877.

3. “ Histoire Naturelle des Crustacés.” Milne-Edwards. 1834-40.

4. “Histoire Naturelle des Crustacés fossiles.” Brongniart and Des-
marest. 1822.

5. “Catalogue of the British Fossil Crustacea.” Henry Woodward.
1877.

6. “Crustacea of the United States Exploring Expedition.” Dana.
1852-53.

7. ““Handbuch der Palzontologie.” Bd. I., Abth. 2. 1885. Zittel.

CIRRIPEDIA.

8. “ Monograph of the Cirripedia.” Darwin. ‘Ray Society.’ ‘“ Lepa-
did,” 1851. ‘‘ Balanide,” 1854.

£68

9.

Io.

LITERATURE OF CRUSTACEA.

“Fossil Lepadidze of Britain.” Darwin. ‘ Paleontographical
SOcleby. » tO5i-

“Fossil Balanidz of Britain.” Darwin. ‘ Palzontographical
SOcleby a 1o54-

. “Report on the Cirripedia.” ‘Challenger Reports.’ Vols. viii. and

Me PLOGs, loose mld Oe ke

. “On a New Genus of Cirripedia.” Henry Woodward. ‘ Quart.

Journ. Geol. Soc.,’ vol. xxi. 1865. (Zuvrrilepas.)

. “Systeme Silurien de la Bohéme.” Barrande. Vol. i., Supplement.

1872. (Plumulites and Anatifopsts.)

. “ Monographie des Crustacés fossiles du terrain crétacé du duché de

Limbourg.” 1854. Bosquet.

. “Ueber fossile Lepadiden.” ‘Sitzungsber. d. k. k. Akad. d. Wissen-

chaften, Wien. Bd. 49. 1864. Reuss.

. “Bemerkungen tiber einige fossile Lepaditen aus dem Lithogra-

phischen Schiefer und der oberen Kreide.” ‘Sitzungsber. d.
bayer. Akad.’ 1884. Zittel.

. “ Paleontology of New York.” Vol. vii. 1888. (Protobalanus, &c.)

Halland Clarke:

OSTRACODA.

‘“‘ Natural History of British Entomostraca.” Baird. ‘ Ray Society.’
1850.
“Monograph of the Recent British Ostracoda.” G. S. Brady.
> cans? Linn SOc sa Gob:

20. “ Oversigt af Norges marine Ostracoder.” G.O. Sars. 1865.

1. “Monographie der Ostracoden.” ‘Wiegmann’s Archiv.’ Bd. xx.

HOAs Zewker,

. “ Monograph of the Entomostraca of the Cretaceous Formation of

England.” Rupert Jones. ‘ Palzontographical Society.’ 1849.

. “Monograph of the Tertiary Entomostraca of England.” Rupert

Jones. ‘ Palzeontographical Society.’ 1856.

. “Palaeozoic Bivalved Entomostraca.” Rupert Jones. ‘Ann. and

Mag. Nat. Hist.’ 1855-1869.

. “Carboniferous Entomostraca of Britain.” Rupert Jones, J. W.
Kirkby, and G. S. Brady. ‘ Palzontographical Society.’ 1874
and 1884.

. “Post-Tertiary Entomostraca of Scotland.” G. S. Brady, H. W.

Crosskey, and D. Robertson. ‘ Palzontographical Society.’
1874.

. “Monograph of the Ostracoda of the Antwerp Crag.” G.. 3:
Brady.» [rans .Zooly s0ceavol xc | 1373,
28. “Systéme Silurien “de la Bohéme.” Barrande. Vola) Suppie=

ment. 1672.

. “Description des Entomostracés fossiles des terrains tertiaires de la

France et de la Belgique.” ‘ Mém. de Acad. Roy. de Belgique.’
Volexxivaero52essbesquer

PHYLLOPODA AND PHYLLOCARIDA.

. “Zur Kenntniss des Baues und der Entwickelung von Branchipus

stagnalis und Apus cancriformis.” ‘Abh. d. k. Ges. d. Wissen-
schaften.’ Gottingen.. 1873. Claus.

EPPERATURE “OF “CRUSTACEA. 569

. “A Monograph of the Phyllopod Crustacea of North America.”

‘Twelfth Ann. Report of the U.S. Geol. and Geog. Survey of
the Territories.’ 1883. Packard.

“Report on the Phyllocarida.” ‘Challenger Reports, vol. xix.
Foog., G:.O.Sars:

“Fossil Estheriz.” Rupert Jones. ‘ Paleeontographical Society.’
1862.

“ Peltocaris, a New Genus of Crustacea.” Salter. ‘Quart. Journ.
Beak oge VOlaxi P.675., 1603.

. “ Hymenocaris.” Salter. ‘Mem. Geol. Survey,’ vol. i11., Appendix.

1866.
“Crustacean Teeth of the Carboniferous and Silurian.” Henry
Woodward. ‘Geol. Mag., vol. 11. 1865.

. “ Discinocaris.”. Henry Woodward. ‘Quart. Journ. Geol. Soc.,’

vol. xxii. 1866.

. “Aspidocaris.” Reuss. ‘Sitzungsber. d. Akad. Wien.’ 1867.
. “Systeme Silurien de la Bohéme.” Barrande. Vol. i., Supplement.

1872.

. “ Dithyrocaris.”. Henry Woodward and R. Etheridge, jun. ‘ Geol.

Mag? vol; x. 1873.

. “A Monograph of the British Palaeozoic Phyllopoda (Phyllocarida,

Packard).” Part i. Ceratiocaridz. ‘ Palzontographical So-
ciety.’ 1888. Rupert Jones and Henry Woodward.

. “ Ceratiocaridz from the Chemung and Waverley Groups.” ‘ Rep.

of Progress: 2d Geol. Survey of Pennsylvania.’ 1884. Beecher.

. “Remarques sur le genre Aristozoé, Barrande.” ‘ Sitzungsber. d. k.

Bohm. Ges. d. Wissenschaften.’ 1885. Novak.

TRILOBITA.

. “ Systéme Silurien de la Bohéme.” Vol. i., 1852, and Supplement,

1872. Barrande.

5. “ Crustacea formationis transitionis.” 1878. Angelin.
. “Monograph of the British Trilobites.” ‘ Paleontographical So-

ciety.’ 1864-67. Salter.

. “ Ueber einige BOhmische Trilobiten.” 1845. Also, ‘“‘ Untersuchungen

uber Trilobiten.” 1846. Beyrich.

. “Organisation of Trilobites.” Burmeister. ‘Ray Society.’ 1846.
. “British Organic Remains.” Salter. ‘Mem. Geol. Survey,’ decade

1. 1849. Also ‘Mem. Geol. Survey,’ vol. iii. 1866.

. “ Catalogue of British Fossil Crustacea.” Henry Woodward. 1877.
. “ Paleozoic Fossils of Canada.” Vol. i. 1861-65. Billings.
. “Prodrom einer Monographie der béhmischen Trilobiten.” 1874.

Hawle and Corda.

. “Paleontology of New York.” Vols. i. and ii., 1847-52, Hall; and

vol. vii., 1888, Hall and Clarke.

cs Revision der ostbaltischen Silurischen Trilobiten.” ‘Mém. de
Acad. imp. de St Pétersbourg.’ 1881, 1883, 1885. Friedrich
Schmidt.

. “ The Tnilobite.” ‘Bull. Mus. Comp. Zool.’ Vol. viii. 1881. Wal-

cott.

. “Monograph of the British Carboniferous Trilobites.” ‘ Palaeonto-

graphical Society.’ 1883-84. Henry Woodward.

570 LITERATURE OF CRUSTACEA.

XIPHOSURA AND EURYPTERIDA.

. * Recherches sur l’anatomie des Limules.” ‘Annales des Sci. Nat.’

A. Milne-Edwards. 1873.

. “On the Anatomy and Development of the American King-Crab.”

Owen. “Trans; Eimn: Soc. 0 1672:

. “Development of Limulus polyphemus.” A. S. Packard. ‘Mem.

Boston Soc. Nat. Hist.’ 1871.

. “The Anatomy, Histology, and Embryology of Limulus polyphemus.”

‘Anniversary Mem. of the Boston Soc. of Nat. Hist.’ 1880.
Packard.

. “Zur Embryologie und Morphologie des Limulus polyphemus.”

Dohrn. - \lenaische Zeitsehia 1671.

. “ Recherches sur Vhist. nat. et Anat. des Limules.” Van der Hoeven.

1838.

. “Limulus an Arachnid.” ‘ Quart. Journ. Mic. Sci.’ Ray Lankester.

188i. °

. “On the relation of the Xiphosura to the Eurypterida.” Henry

Woodward. ‘Quart. Journ. Geol. Soc.’ 1872.

. “Die Crustaceen-fauna der Eurypterus-Schichten von Rootzikill auf

Oesel.” “Mém. de PAcad. imp. de St.” Pétersboure. iaeanen
Schmidt. 1883.

. “ Monograph of the Genus Pterygotus.” Huxley and Salter. ‘ Mem.

Geol. Survey,’ monograph i. (with atlas). 1859.

. “ Monograph of the British Fossil Crustacea belonging to the Order

Merostomata.”” Henry Woodward. ‘ Palzontographical So-
ciety.’ 1866-78.

. “British Palaeozoic Crustacea belonging to the Order (erostomata.”

Henry Woodward. ‘Geol. Magazine,’ vol. ix. 1872. (ffemt-

aspts.)

. “Ona New King-Crab from the Upper Silurian.” Henry Woodward.

loid., vol. v. 1868. (eolimulus.)

. “Contributions to British Fossil Crustacea.” Henry Woodward.

‘Geol. Magazine,’ vol. vi. 1870. (Cyclus.)

. “Exapinurus and Pseudoniscus.” Nieszkowski. ‘Archiv fir Na-

turkunde Liv. Ehst. und Kurlands,’ ser. 1. vol. 1. 1859.

»*Eurypterus:” sJames Halli “Pal, Ne York, vole im ege:

MALACOSTRACA.

. “A History of the British Sessile-eyed Crustacea.” 1863-68. Spence

Bate and J. O. Westwood.

. “Catalogue of the specimens of Amphipodous Crustaceans in the

Collection of the British Museum.” Spence Bate. 1862.

. “Untersuchungen iiber die Bildung und Entwickelung der Wasser-

asseln.” | Rathkeaieg2.

. “Crustacea Amphipoda borealia et arctica.” Boéck. 1871.
. “On a Fossil Crustacean found in the Magnesian Limestone of

Durham,” &c. - Spence Bate. ‘Quart. Journ. Geol) Soe voles
1859. (Prosoponiscus.)

. “Fin Beitrag zur Kenntniss der fossilen Asseln.” ‘ Sitzungsber. d.

bayer. Akad.’ 1882. Von Ammon.

. “On Eocene Crustacea from Gurnet Bay, Isle of Wight.” ‘ Quart.

Journ. Geol. Soc.’ 1879. Henry Woodward.

97:

LITERATURE OF CRUSTACEA. 571

. “Contributions to British Fossil Crustacea.” Henry Woodward.

“Geol. Magazine,’ vol. vii. 1870. (Palega.)

. “Report on the Cumacea.” ‘Challenger Reports,’ vol. xix. 1887.

GOs Sars:

. “Monographie over de ved Norges Kyster forekommender Mysider.”

G. O. Sars. 1870-79.

- “Report on the Schizopoda.” ‘Rep. on the Sci. Results of the

Challenger Exped.’ vol. xi... 1885. G. O. Sars.

. “ Paleontology of Illinois.” Vols. 11. and iil. 1866 and 1868. Meek

and Worthen. (Pale@ocaris, Gampsonyx, Acanthotelson, and
Anthrapalemon.)

. “Archzoniscus Brodiel.” Westwood, in Brodie’s ‘Insects of the

Secondary Rocks.’ 1845.

. “Report on the Stomatopoda.” ‘Challenger Reports,’ vol. xvi.

1886. Brooks.

. “Ona Fossil Squilla from the London Clay of Highgate.” ‘ Quart.

Journ. Geol. Soc.’ 1879. Henry Woodward.

. “ Versuch einer Naturgeschichte der Krabben und Krebse.” Herbst.

1782-1804.

. “Monograph of the Malacostracous Crustacea of Great Britain.”

Bell. ‘ Palzeontographical Society.’ 1857 and 1862.

. “Fossilen Krebse von Bayern.” Minster. ‘ Beitrage zur Petre-

faktenkunde,’ vol. 11. 1839.

. “ Neue Gattungen fossiler Krebse.” Von Meyer. 1840.
weeeakecozoic Macruira. Salter, “@uart. Journ. Geol. Soc., vols:

xvi. and xix. 1861 and 1863. (Azthrapalemon.)

. “ Palzozoic Macrura.” Huxley. ‘Quart. Journ. Geol. Soc.,’ vols.

xi. and xvill. 1857 and 1862. (Pygocephalus.)

. “Notice of New Forms of Fossil Crustaceans from the Upper

Devonian Rocks of Ohio.” (Pal@opalemon.) ‘Amer. Journ.
Sci. and Arts.’ 1880. Whitfield.

. “Jurassische und Triassische Crustaceen.” ‘ Palazontographica.’

1854. Von Meyer.

. “On New Crustacea from the Lower Carboniferous Rocks of Esk-

dale and Liddesdale.” ‘Trans. Roy. Soc., Edin.’ 1880 and
1882. Benjamin N. Peach.

“Die Macruren-Decapoden der Senon- und Cenoman- Bildungen
Westfalens.” ‘ Zeitschr. d. deutsch. Geol. Ges.’ 1862. Schliiter.

572

CH AeA ERD DG Nae

ARTHROPODA—continued.
ARACHNIDA AND MYRIOPODA.

Crass II. ARACHNIDA.

THE Avachnida—including the Spiders, Scorpions, Mites, &c.—
possess almost all the essential characters of the Crustacea, to which
they are very closely allied. Thus, the body is divided into a vari-
able number of somites, some of which are always provided with
articulated appendages. <A pair of ganglia is primitively developed
in each somite, and the neural system is placed ventrally. The
heart, when present, is always situated on the opposite side of the
alimentary canal to the chain of ganglia. The respiratory organs,
however, whenever these are differentiated, are never in the form of
branchiz as in the Cvusfacea, but are in the form either of pul-
monary vesicles or sacs, or of ramified tubes, formed by an involu-
tion of the integument, and fitted for breathing air directly. Fur-
ther, there are never more than four pairs of ambulatory limbs, and
no locomotive appendages are developed upon any of the abdominal
segments. Antennz are not present (as such), and the eyes are
simple and sessile. The head and thorax are united to form a
cephalothorax (the thoracic segments in rare cases remaining free),
and in some cases the cephalothorax is fused with the abdomen.

Speaking generally, therefore, the Avachnida are distinguished
from the Crustacea by the possession of four pairs of watking-legs,
the want of locomotive appendages on the abdomen, and the absence of
antenne ; while the breathing-organs (when differentiated) are adapted
“or breathing air directly, and are never in the form of branche.

The integument of the Arachnida is in general more or less ex-
tensively hardened by chitine, and commonly forms a resistant exo-
skeleton. Viewed under the microscope, the chitinous exoskeleton
of such an Arachnidan as a Scorpion (fig. 430, a and B) exhibits a

a

ARACHNIDA. 573
finely punctate or minutely porous structure, along with numerous
oval pits of different sizes, each of which exhibits a central dark
spot or ring. ‘These latter are not perforations, ‘but are the sockets
of hairs. ‘The skin of a fossil
Scorpion from the Carbonif-
erous rocks (collected by the
Geological Survey of Scot-
land) also exhibits a minutely
reticulate or porous structure,
and presents larger oval pits,
which show a central dark
spot, and which seem to be
quite similar to the _hair-
sockets of the recent Scor-
pions (fig. 430, Cc and D).
There are also still larger
oval perforations, which are
surrounded by a fibrous ring,
and which are true /ferfora-
tions, passing completely
through the thin integument.
These may represent the

Fig. 430.—A, Exoskeleton of a recent Scorpion
enlarged, and (8) still more highly magnified, show-

sockets of large bristles, from
which the delicate chitinous
membrane forming the origi-
nal floor of the socket (traces

ing minute pores together with larger pits to which

hairs were attached. c, Portion of the skin of a
fossil Scorpion from the Carboniferous rocks of Scot-
land, enlarged, showing pits for the attachment
of hairs. The large oval perforations probably also
represent the sockets of hairs, of larger size. ,
Portion of the same enlarged further, showing a
finely reticulate or porous structure. (Original.)

of which are still sometimes
visible) has disappeared ; or
they may be truly pores. In the latter case, they do not appear to
have any representative in the integument of the recent Scorpions.
The segments of the head and thorax in the Arachnida are gen-
erally amalgamated to form a ‘‘ cephalothorax,” which is in some
cases (So/ugide) segmented. ‘The upper surface of the head carries
the eyes, which are always simple and are never supported upon
movable peduncles. There are no proper ‘‘antenne,” but the place
of these is taken by a pair of prehensile organs known as the
*‘ cheliceree,” “‘falces,” or ‘‘ mandibles” in different groups of the
class (fig. 431, ¢). There is a single pair of “ maxille” or proper
jaws, which carry long jointed appendages—the ‘‘ maxillary palpi.”
The palpi are sometimes leg-like in form (‘ pedipalpi”), or they
may, as in the Scorpions, be converted into nipping-claws (fig.
431, m). Immediately posterior to the mouth is a lower lip or
““labium,” which is unpaired in the Spiders, but in some cases is
partially divided by a longitudinal groove, and is thus seen to repre-
sent a second pair of maxillz. The four segments of the thorax

574 ARTHROPODA. |

carry, as a rule, four pairs of jointed ambulatory legs. Abdominal
limbs are present in the embryo of various Arachnida, but ambula- |
tory appendages are never developed on the abdominal somites of ;
the adult. In the Scorpions, the first abdominal segment carries a
minute “operculum,” formed by the coalescence of a pair of ap-
pendages, which covers the opening of the reproductive organs ;
and the second abdominal segment carries the peculiar organs which

I ee SS So fe ™
1 ¢ a |

w yzsyl ep 2 . “h / ;

SSS |. PRE \ |
s AER \\ SIN
SER, VS

Pe = | A

| OR

oN
\ aI ENG)

Fig. 431.—a, Scorpio afer, viewed from above, and somewhat reduced in size; B, Upper sur-
face of the cephalothorax of the same, enlarged; c, Buthus Kochi, with the terminal segments
and the ends of the appendages on one side omitted. 22, Maxillary palpi (behind these are
the four pairs of ambulatory legs) ; c, Chelicere ; ¢, Telson; 0, Lateral ocelli; 0’, Central, larger
ocelli; , Opercular plate, covering the opening of the reproductive organs; 7, One of the
‘*combs 3 s, One of the stigmatic openings. (c is after Prof. Ray Lankester.)

are known as the ‘“‘combs.” The extremity of the abdomen carries
in the Spiders the so-called ‘‘ spinnerets” (two, four, or six in num-
ber), which have sometimes been regarded as modified abdominal
appendages. A “telson” is present in the Scorpions, in which it
forms a poisonous “‘ sting”; and a jointed caudal filament is present
in Thelyphonus.

The higher Avachnida are air-breathers, and possess distinct res-
piratory organs in the form of “ tracheze” or “‘ pulmonary sacs,” the

ARACHNIDA. Eyas

former being tubular and the latter pouch-like in form. The air is
admitted to the breathing-organs by paired apertures (“stigmata”),
which are mostly placed on the ventral aspect of the abdomen.
Many of the lower Arachnida have no differentiated respiratory
organs ; and the Pycnogonids, if rightly placed in this class, are
water-breathers.

As regards their distribution in space, the higher Arachnida are
essentially terrestrial in habit. Many of the lower forms are inter-
nal or external parasites. A few of the Mites live in the sea or
between tide-marks, and the singular Pantopods (/Pycnogonida) are
wholly marine in habit: but the zoological position of these last is
uncertain.

As regards their distribution in time, our knowledge of the history
of the Arachnida is still very incomplete. Many of the lower
forms are incapable of preservation, while the terrestrial habits of
most of the higher forms sufficiently account for their comparative
rarity as fossils. The oldest known representatives of the class are
the Scorpions, which appear, under forms not very widely different
from those now in existence, in the Silurian rocks. ‘The earliest
types of the true Spiders (Profolycosa and Phalaranea) appear in
the Coal-measures, where also appear forms allied to the recent
Thelyphonus. The great majority of the Palzozoic Arachnids,
however, differ in various points from existing forms, and have
been placed by Scudder in a special order (Anthracomart:), which
is confined to the Palzeozoic period. In the Mesozoic rocks no
undoubted remains of Arachnids have hitherto been detected. On
the other hand, in the Tertiary rocks are found representatives of
all the living orders of Arachnids, except the problematical group
of the Pycnogonida, which is not known at all in the fossil state.
Most of the Tertiary Arachnids have been found in amber—the
fossil resin of certain Conifers—and the state of preservation of
these is often marvellously perfect. The more important facts
relating to the fossil Avachnida may be briefly noticed under
the following heads :—

1. ACARIDA.—This group of the Avachnida comprises the Mites
and Ticks, in which the cephalothorax and abdomen are fused into
a single mass, while the mouth-organs are generally adapted for
piercing and suction. Breathing organs may be wanting, but
when present, are in form of trachez. All the principal existing
families of Mites are known to be represented in amber (Tertiary).
Galls formed by Mites have also been detected on the leaves of
fossil Willows in the Tertiary beds of Europe.

2. ANTHRACOMARTI.—This order has been founded for the re-
ception of certain Paleozoic Arachnids, in which the body is some-
what compressed, the cephalothorax and abdomen are distinctly

576 ARTHROPODA.

separated from one another, and the former is usually composed of
more or fewer wedge-shaped, foot-bearing segments. The abdomen
consists of from four to nine somites, and the “palpi” are not
much longer than the legs, and are not terminated by pincers or
claws (Scudder). Of the genera included in this extinct group, all
of which are confined to the Carboniferous period, Architarbus
(fig. 432, B) is found in the Coal-measures of both Europe and
North America. In A. sudovals the cephalothorax is shorter than
the abdomen and carries four pairs of legs and a pair of palpi, the
form of which is unknown. The abdomen consists of nine seg-

Fig. 432.—a, Eophrynus Prestvici?, viewed ventrally, and somewhat enlarged—Carboniferous ;
B, Architarbus subovalis, enlarged four times, and viewed from below—Carboniferous (after H.
Woodward).

ments, of which the anterior ones are much narrower than the
hinder ones. In Anthracomartus, also distributed in the Coal-
measures of Europe and North America, the cephalothorax is quad-
rangular, and is only about half as wide as the abdomen, the latter
region consisting of seven segments. In Arthrolycosa, from the
Coal-measures of Illinois, the cephalothorax, on the other hand, is
round, and is much larger than the abdomen, the latter region con-
sisting of seven distinct segments and being comparatively narrow.
Lastly, in the singular genus Lophrynus (fig. 432, A), the cephalo-
thorax is triangular and extended in front, and carries the four pairs
of legs and a pair of slender palpi. The abdomen is twice as large

ont — ol
ee

ARACHNIDA. 577

as the cephalothorax, and its upper surface is tuberculated, while on
its ventral aspect are seen the openings of six pairs of stigmata.

3. ADELARTHROSOMATA.—Under this name may be included
Arachnidans such as the “ Book-scorpions” (Pseudoscorpionid@)
and the “ Harvest-men” (Phalangide), in which the abdomen is
more or less distinctly segmented, but is not clearly separated from
the cephalothorax, the two regions being of equal width and con-
joined together; while the respiratory organs have the form of
tracheze. Various Tertiary forms of the Pseudoscorpions have
been detected—principally in amber—but these all belong to exist-
ing genera (Chelifer, Chernes, &c.) Of the Phalangide no other
fossil forms are known except those which occur in amber, and of
these a number of types, belonging to several genera, have been
described.

4. PEDIPALPI.—Under this head may be included the two groups
of the Scorpions (Scorpiodea) and the Phrynidea, in which the abdo-
men is segmented, with or without a ‘post-abdomen,” and the
breathing-organs are in the form of pulmonary sacs. The Scorpions
are characterised by their compressed bodies, and by the clear separ-
ation of the cephalothorax from the long and segmented abdomen.
The abdomen proper consists of seven wide somites, of which the
first carries on its ventral surface the opening of the generative
organs, closed by a delicate lid or operculum (fig. 431, g); the
second carries a pair of peculiar comb-like appendages (‘ pectines ”),
the precise function of which is not known; and the next four
exhibit the oblique apertures (“stigmata”) of the four pairs of pul-
monary sacs. The abdomen proper is followed by six narrower
segments, which constitute a “ post-abdomen,” and of which the
last (the “telson”) is hooked, and is converted into a poisonous
“sting.” The cephalothorax is covered by a shield-like carapace,
the upper surface of which carries a variable number of simple eyes,
one pair of which is larger than the others, and is placed dorsally,
while the smaller eyes are marginal. The first pair of cephalic
appendages, corresponding with the ‘“‘falces” of the Spiders, are
converted into nipping-claws (“‘ chelicerze”) ; the maxillary palpi are
very large and end in pincers; and a partially divided lower lip is
present. The four thoracic segments carry the four pairs of walking-
legs.

The Scorpions possess a resistant chitinous exoskeleton, readily
capable of preservation in the fossil condition (see p. 573). It is
also probable that some of the more ancient forms were littoral in
habit, which would account for the occurrence of their remains in
strata of marine origin. The Scorpions are the most ancient group
of the Arachnida, being represented in the Silurian rocks of both
the Old and New Worlds. Various Carboniferous Scorpions are

MOE. I. 270

578 ARTHROPODA.

also known, and these ancient types do not appear to have differed
from the living representatives of the group except in comparatively
non-essential characters.

The genus Paleophonus (fig. 433) has been detected in the Silu-
rian strata of Gotland and of Scotland, and comprises Scorpions
which differ from all existing types in the fact that the walking-legs
gradually taper to their ends, which terminate in points or simple
claws. The maxillary palpi form strong nipping-claws, and the
median eye-tubercles are placed not far from the anterior margin of
the cephalothorax. The genus Proscorfius occurs in the Silurian
deposits of North America, and differs from the preceding in the

Fig. 433.—Ventral aspect of a species of

Paleophonus, from the Silurian rocks of Les- Fig. 434.—A specimen of Zoscorpius carbon-
mahagow, Lanarkshire. Enlarged nearly avius, from the Carboniferous rocks of Illinois,
twice. (After Benjamin N. Peach.) of the natural size. (After Meek and Worthen.)

fact that the legs are long, with blunt terminal joints ending in two
claws. The median dorsal eye-tubercles are placed on the anterior
margin of the cephalothorax, and the lateral eyes are on ridges, as
in the living Scorpions. The genus Zoscorpius (fig. 434) is confined
to the Carboniferous rocks, and species have been detected in the
Coal-measures of both Europe and North America. J/aszovia is
probably identical with Zoscorfius. The genus is nearly related to
Proscorpius, from which it differs in having the median dorsal eye-
tubercles of smaller size, and not placed close to the anterior margin
of the cephalothorax. The Coal-measures of Europe and North
America have also yielded the remains of Scorpions on which the
genus Cyclophthalmus—including the first fossil forms known to

es

Sth gee ds

ARACHNIDA. 579

science—was founded. In this genus (fig. 435) the median dorsal
eye-tubercles are of very large size, and occupy almost half of the
cephalothorax towards the anterior margin, while the lateral eyes
form a semicircle behind and to the sides of the great dorsal eyes,
and the palpi are developed into nipping-claws of very large size.
According to Mr Scudder, the four genera just mentioned constitute
a special division of the Scorpions (Azz¢hracoscorpit), characterised,
among other points, by the fact that the dorsal eye-tubercles are
either placed on the anterior margin of the cephalothorax or a short
distance behind it. On the other hand, in the Scorpions of the

Pig. 435-—Cyclophthalmus senior. A fossil Scorpion from the Coal-measures of Bohemia.

more modern type (JVeoscorpit), the median eye-tubercles are, as a
rule, far removed from the anterior margin of the cephalothorax, and
are placed behind the lateral eyes. It is a singular fact that while
the Anthracoscorpi are wholly confined to the Paleozoic rocks, no
example of the /Veoscorpii has hitherto been detected in the Mesozoic
or in the earlier Kainozoic deposits. The only known fossil repre-
sentative of the JVeoscorfiz, in fact, is a late Tertiary form (Z7tyus
eogenus) which has been discovered in amber.

The remaining section of the Pedipalpi is that of the PArynidea,
which differs from the Scorpions in the fact that the cephalothorax
is sharply separated from the abdomen, and is occasionally divided
into two distinct regions. The maxillary palpi are greatly developed,

580 ARTHROPODA.

but terminate in claws or in imperfect pincers, and the abdomen
does not terminate in a “sting.” The existing genus Phrynus has
been detected in Tertiary deposits, while the recent genus ZheZy-
phonus is represented in the Carboniferous rocks by the genus
Geralinura.

5. ARANEIDA.—This division of the Arachnida includes the true
Spiders, characterised by the soft and imperfectly segmented ab-
domen, which carries two, four, or six “‘spinnerets” posteriorly, and
is united in front with the cephalothorax by a constricted peduncle.
The maxillary palpi are slender and leg-like, and never terminate in
nipping-claws, while the “falces” or “mandibles” are hooked, and
contain a poison-gland in their base. The most ancient represen-
tatives of the Spiders, so far as at present known, are the Protolycosa
anthracophila, and Phalaranea borassifolia of the Coal-measures of
Europe, both of which have been referred to the section of the
Territelarie. No Mesozoic Spiders have hitherto been discovered ;
but about seventy genera have been recognised as occurring in
Tertiary deposits—many of them in amber. About one-half of the
known Tertiary genera of Spiders are without representatives at the
present day.

Crass III. Myriopopa.

The class of the JZyriofoda includes the multisegmentate, worm-
like Arthropods known as the Centipedes and Millepedes, and is
characterised by the fact that the head is distinct, and the remainder
of the body ts divided into nearly similar segments, the thorax exhibit-
ing no clear line of demarcation from the abdomen. There is one pair
of antenna, and the number of the legs is always more than eight pairs.
Respiration ts by trachea.

In this class of the Arthropoda the head is always distinctly
marked off from the rest of the body, and consists of five or six
amalgamated somites. The head carries a single pair of jointed
antennz, which are usually simple (fig. 436), but are bifid, and
carry many-jointed appendages in the aberrant genus auropus.
Behind the antenne there is generally a variable number of simple
sessile eyes. The mouth is placed on the under side of the head,
and is provided with mandibles and maxille. The Centipedes also
possess two pairs of “ foot-jaws,” of which the hindmost pair (fig.
436, f) are of large size, and are terminated by perforated hooks,
which communicate with internally-placed poison-glands. These
appendages, however, are not carried upon the head, but are
attached to a special segment formed by the amalgamation of the
anterior thoracic rings. ‘The segments behind the head are numer-
ous, and there is no distinct line of demarcation between those

MYRIOPODA. 581

which belong to the thorax and those which are referable to the
abdomen. The post-cephalic segments, with the exception of the
last, usually carry a single pair of jointed legs each. Among the
living Myriopods, Pauropus has only nine pairs of legs; but, with
this exception, eleven pairs of legs is the smallest number possessed
by any existing type. In the Millepedes (DzAlofoda) each apparent
segment carries two pairs of legs (fig. 437); but this is really due to

Fig. 436.—Lithobius forficatus, Fig. 437.-—lulus
a recent Centipede, enlarged, and MAXIMUS, a re-
viewed dorsally. az, Antenne ; cent Millepede.

hh, Head; 7 Foot-jaw.

the coalescence of the somites in pairs, each apparent segment being
in reality composed of two amalgamated somites.

In the abnormal genus Pauropus respiration is cutaneous, but in
all other living Myriopods the breathing-organs are in the form of
“‘ tracheze ”"—that is to say, tubes which open on the surface of the
body by minute apertures or ‘‘ stigmata,” and which convey the air
into the interior of the body. In /ervipfatus the trachez open ex-
ternally by irregularly placed “‘ stigmata” over the whole surface of
the body. In the Centipedes the “stigmata” are placed on the
sides of the body on alternate segments. In the Millepedes (Diflo-

582 ARTHROPODA.

oda), on the other hand, in which the segments are amalgamated
in pairs, the stigmata are placed on every apparent ring.

The recent Myriopods are grouped into the four orders of the
Chilopoda (Centipedes), Diplopoda (Millepedes), Pauropoda (Pauro-
pus), and Onychophora (Peripatus). To these Scudder has added
the two extinct orders of the Protosyngnatha and Archipolypoda for
the reception of the Paleozoic types of Myriopods.

As regards their distribution in time, all the recent Myriopods
are terrestrial in habit. As a necessary result of this, the remains
of Myriopods are not abundant as fossils, and have been mostly
found in deposits of distinctly fresh-water or estuarine origin. ‘The
occurrence of Myriopods in unequivocally marine strata is, however,
by no means unknown, though difficult with our present knowledge
to satisfactorily explain. The two living orders of the Pauropoda
and Onychophora—represented each by a single genus only—are
unknown as fossils, and require no further consideration here. The
other two existing orders—viz., the Chzlopoda and Diplopoda—are
represented only by Tertiary types, with the possible exception of a
Cretaceous form of the latter order. On the other hand, a con-
siderable number of Palzeozoic Myriopods are known, which differ
more or less widely from all existing types, and for the reception of
which Mr Scudder has founded the two orders of the Protosyngnatha
and Archipolypoda. ‘The only known representative of the Profo-
syngnatha is the genus Paleocampa, which is found in the Coal-
measures of North America. The oldest Myriopods, however,
belong to the Archipolypoda, and remains of early forms of this order
have been described by Mr Peach as occurring in the Old Red
Sandstone of Scotland. It is, however, in the Carboniferous rocks
that this ancient group of Myriopods attains its maximum develop-
ment, about thirty different species having been already described
from the Coal-measures of the Old and New Worlds. ‘There are
also a few Myriopods known to occur in the Permian rocks of
Europe, which probably belong to the same order. In the follow-
ing a brief account is given of the four orders of Myriopods which
are known to be represented by fossil forms.

ORDER I. PROTOSYNGNATHA.—This order comprises only the
single genus FPaleocampa, of which only a single species (2.
anthrax) has been hitherto recorded. In this remarkable genus
(fig. 438) the body is comparatively short and worm-like, consisting
of few segments, each body-ring being furnished with a single dorsal
and ventral plate. Each segment carries a pair of stout fleshy legs,
and the upper surface is furnished with large tubercles, each of
which supports a cluster of long needles, and which are arranged in
longitudinal rows. The sole known species of Pa/eocampa is found
in the Coal-measures of Illinois; and the possession of the bundles

MYRIOPODA. 583

of long bristles above mentioned gives to the fossil the aspect of the
caterpillar of such a Moth as the Tiger-moth.

OrvbER II. CurLopopa.—This order includes the recent Centi-
pedes (fig. 436), characterised by their elongated depressed bodies,
each body-ring being protected by a dorsal plate above, and a cor-
responding ventral plate below. ‘The first two pairs of thoracic
appendages are converted into foot-jaws, the second pair being of
large size and hooked, and being connected with poison-glands.
All the remaining body-rings carry a single pair of jointed legs each,
and the tracheal stigmata are usually placed on alternate segments.
The generative organs open at the posterior end of the body.

With the exception of the problematical Geophilus proavus of
the Lithographic Slates (Jurassic) of Germany, the oldest known

Fig. 438.—A specimen of Paleocanipa anthrax, from the Coal-measures of Illinois,
enlarged twice. (After Scudder.)

remains of Centipedes are of Tertiary age. Most of these have
been found in amber, and they all fall under existing families of the
order.

OrvDER III. ArcHipotypopa.—This order has been founded by
Scudder for the reception of a number of Palzeozoic Myriopods, and
is characterised as follows: The body in the Archipolypoda is fusi-
form and elongated, composed of many segments, and thickest in
the anterior half or third. The cephalic appendages are borne upon
a single apparent segment. ‘The body-segments are provided each
with a pair of ventral plates and a more or less divided dorsal plate,
“the latter occupying the upper surface and most of the sides of the
body, and divided more or less conspicuously into a ridged anterior
and a lower posterior portion, the anterior frequently bearing spines
or tubercles.” The ventral plates are as broad as the body, each
bearing a pair of long corneous legs, approximated at the base, and

584 ARTHROPODA.

furnished outside the legs with large stigmata directed transversely
to the axis of the body (Scudder). This order comprises all the
Paleozoic Myriopoda with the exception of the Carboniferous genus
Paleocampa, and it is not known to have any representatives in
the Mesozoic or Kainozoic rocks. ‘The most ancient types of the
Archipolypoda at present known are those recorded by Page and Peach
as occurring in the Old Red Sandstone of Scotland (Kampecaris and
Archidesmus). With these exceptions, all the members of the order
are either Carboniferous or Permian in age. The three most im-
portant genera of the Archipolypoda are Euphoberia, Archiulus, and
Xylobius. In the genus Luphoberia (fig. 439) the dorsal shields
are divided each into two more or less closely consolidated, but dis-
tinctly separate sub-segments, one of which is much more elevated
than the other. The segments are generally from two to three
times broader than long, and they carry subdorsal and lateral rows
of large spines, which are forked and terminate in simple ends.
The species of Huphoberia are found in the Coal-measures of North

Fig. 439.-—Portion of the body of Auphoberia armigera, from the Coal-measures of Illinois,
of the natural size (after Meek and Worthen). The dark spots on the dorsal shields are pits left
by the breaking off of the dorsal spines.

America and Britain. The genus Acantherpestes includes Carbon-
iferous Myriopods which differ from uphoberia chiefly in having
the spines bifurcated at the tip, though there are other characters
of difference as well. Acantherpestes major, of the Coal-measures
of Illinois, attained a length of about a foot, and “‘ was armed with
coarse branching spines more than a centimetre long” (Scudder).
Mr Scudder regards this species as having been amphibious in
habit, as he considers that certain lateral openings which it exhibits
were branchial in character.

The genera Archiulus and Xylobius constitute a special family
(Archiulide) of the Archipolypoda, characterised by the fact that the
dorsal plates are ‘“ closely consolidated, but still distinctly separable,”
though the anterior is rarely much elevated above the posterior
sub-segment. The body is “almost smooth or covered more or
less abundantly with serially disposed papillee, from which in some
cases hairs or small spines arise” (Scudder). These genera are
closely allied in some respects to the Millepedes (Dzp/opoda), though
they would seem on the whole to be properly referable to a

LITERATURE. 585

separate order. In Axchiulus the dorsal plates are entire, generally
from two to three times broader than long, and furnished with
a few bristle-bearing papille. The best known species of this
genus have been found in the
Coal-measures ; but some im-
perfectly described Myriopods
from the Permian rocks of
Bohemia may also belong
here. The genus Xy/odzus re-
sembles Archiulus in general
features, but the segments are
divided by longitudinal su-
tures into numerous quadrate

sections. All the known
species of this genus are from
the Coal-measures. Fig. 440.—Xylobius Sigillarie, a Carboniferous

Beeaemilieh yDrricrona. Marored (te: Dawes). « Nanelsze; 4 Au
(CHILOGNATHA).—This order _ larged.
includes the recent Mille-
pedes, and is characterised by the fact that the body is usually
cylindrical, and the body-rings (except the most anterior ones) are
fused in pairs, each apparent segment thus coming to carry two
pairs of legs. The legs are small and spring from the under sur-
face of the segments, and each apparent ring carries a pair of
stigmata. There are no “foot-jaws,” and the generative apertures
are placed anteriorly, at the base of the second or third pair of
legs.

The oldest known fossil representative of the Dzplopoda is a
form (Zulopsis cretacea) which has been described from the Creta-
ceous rocks of Greenland. All the other hitherto recorded fossil
Millepedes are of Tertiary age, the majority of the known types
having been found in amber.

PEPE RA TORE:

ARACHNIDA AND MYRIOPODA.

1. “ Die Arachniden.” Hahn and Koch. 1831-49.

2. “ Die Insecten und Spinnen der Vorwelt.” Giebel. 1856.

3. “On Fossil Arachnidz, including Spiders and Scorpions.” Brodie.
1882.

4. “ Die im Bernstein befindlichen Crustaceen, Myriapoden, Arachniden,
und Apteren der Vorwelt.”. Koch and Berendt. 1854.

5- “Fossil Spiders.” ‘Harvard University Bulletin, vol. 1. 1882.
Scudder.

6. “ Systematische Uebersicht der fossilen Myriopoden, Arachnoideen

586 LITERATURE.

10.

und Insecten.” In Zittel’s ‘ Handbuch der Palzontologie.’ Bd. I.,
Abth. li. 1885.9 seudder

. “Systematic Review of our present knowledge of Fossil Insects, in-

cluding Myriapods and Arachnids.” ‘Bull. of the U.S. Geol.
Survey,’ vol. v. 1886. Scudder.

. “Articulated Fossils of the Coal- Measures.” ‘Geol. Survey of

Illinois,’ vol. i. 1868. Meek and Worthen.

““Einige Spinnen und ein Myriapode aus der Braunkohle von Rott.”
‘Verhandl. d. naturh. Vereins d. preuss. Rheinl.’ Bd. V. 1878.
Bertkau.

“On the discovery of a new and very perfect Arachnide from the
Ironstone of the Dudley Coal-field” (Lophrynus Prestviciz).
‘Geol. Mag.’ 1871. Henry Woodward.

11. “Arthrolycosa.” “SAmer Journ: Sci. and,Arts.” 13742 btaneee

“New species of Fossil Scorpions from the Carboniferous Rocks of
Scotland and the English Borders.” ‘Trans. Roy. Soc. Edin.,’
vol. xxx. 1882. Benjamin N. Peach.

“On a Silurian Scorpion from Gotland.” ‘Kongl. Vetenskaps-
Akad. Handl.’ Bd. XXI. 1885. Thorell and Lindstrom.

“Ancient Air-breathers.” ‘Nature.’ 1885. Benjamin N. Peach.

. “Ona Fossil Scorpion from the Silurian Rocks of America.” ‘ Bulle-

tin of the Amer. Museum of Nat. Hist.,’ vol. i. 1885. Whitfield.
“On a Chilognathous Myriapod from the Coal-Formation of Nova
Scotia.” ‘ Quart. Journ. Geol. Soc.,’ vol. xvi. 1859. Dawson.
““On some Fossil Myriapods from the Lower Old Red Sandstone of
Forfarshire.” “ * Proce. Roy: Phys. Soc: Edin., vel ivi
Benjamin N. Peach.

. “On the Carboniferous Myriapods preserved in the Sigillarian stumps

of, Novawscotia.” ‘Mem. Bost. Soc. Nat. Hist.,’ voliiigesiage:
Scudder.

. “Archipolypoda, a subordinal type of spined Myriapods from the

Carboniferous Formation.” J/dzd., vol. 11. 1882. Scudder.

» “The affinities of Paleocampa.” ‘Amer. Journ. Se. and me,

vol. xxiv. 1882. Scudder.

. “Two new and diverse types of Carboniferous Myriapods.” ‘Mem.

Bost. Soc. Nat. Hist.’ vol. 11. 1884. Seudder.

. “On some Spined Myriapods from the Carboniferous Series of

England.” ‘Geol. Magazine.” 1887. Henry Woodward.

Cleavle | ie DO GUEe

ARTHROPODA — continued.

CLASS DVS INSECTA.

THE Jnsecta are defined as Articulate animals in which the head,
thorax, and abdomen are distinct ; there are three pairs of legs borne
on the thorax; the abdomen is destitute of legs; a single pair of
antenne is present; mostly, there are two pairs of wings on the
thorax. Lespiration is effected by trachea.

The integument of the Jzsecfa, in the mature condition, is more
or less hardened by the deposition of chitine, and usually forms a
resisting exoskeleton, to which the muscles are attached. The
segments of the head are amalgamated into~a single piece, which
bears a pair of jointed feelers or antenne, a pair of eyes, usually
compound, and the appendages of the mouth. ‘The segments of
the thorax are also amalgamated into a single piece; but this,
nevertheless, admits of separation into its constituent three somites
(fig. 441). These are termed respectively, from before backwards,
the ‘‘ prothorax,” “‘ mesothorax,” and ‘“‘ metathorax,” and each bears
a pair of jointed legs. In the great majority of Insects, the dorsal
arches of the mesothorax and metathorax give origin each to a pair
of wings.

Each leg consists of from six to nine joints. The first of these,
which is attached to the sternal surface of the thorax, is called the
“coxa,” and is succeeded by a short joint, termed the “‘ trochanter.”
The trochanter is followed by a joint, often of large size, called the
“femur,” succeeded by the so-called ‘ tibia,” and this has articulated
to it the “tarsus,” which may be composed of from one to five
joints.

The wings of Insects are expansions of the sides of the meso- and
meta-thorax, these expansions being supported by slender but firm
tubes, known as the “nervures.” Each nervure consists of a cen-
tral trachea or air-tube, running in the centre of a larger blood-tube ;

5388 ARTHROPODA.

so that the wings not only act as organs of flight, but at the same
time assist in the process of respiration. Normally, two pairs of
wings are present, but one or other may be wanting.

The arrangement of the ‘‘nervures” of the wings is definite and
characteristic in different groups of the Insects. In the most typical
forms of wing, as in the Orthoptera (fig. 442, A), there are six prin-
cipal veins, which arise, in groups of three, from two principal roots,
one anterior and the other
posterior. According to
the nomenclature followed
by Heer and Scudder,
these six principal veins
es ae 2 are termed, from before

A Cape §=Dackwards, the marginal,
= mediastinal, scapular, ex-
ternomedian, internomed-
zan, and anal veins. The
general arrangement of
these veins (fig. 442, A) is
as follows: “The margz-
nal vein (ma) is placed at,
or close to, the anterior
margin of the wing; and
“the ‘mediastinal’ and
‘scapular’ veins, which
are superior (z.e., part from
the main vein on the upper
or anterior side), terminate
upon the anterior margin.

Fig. 441.--Diagram of the external anatomy of an The ‘internomedian’ and
Insech . @, Head carrying the eyes (>and antennas(an);" anak’ “take the Miata
p ‘ gment of the thorax, with the first pair of legs; :

c, Second segment of the thorax, with the second pair COUISE, and their branches

of legs and the first pair of wings; d@, Third segment of : :
the thorax, with the third pair of legs and the second @I€ inferior, or, at least,

pair of wings ; e, Abdomen, without limbs, but carrying directed towards the inner
terminal appendages concerned in reproduction; /, i
Femur ; ¢, Tibia; za, Tarsus. margin ; while the ‘ exter-
nomedian,’ which is inter-
posed between these two sets, terminates at the tip of the wing,
and branches indifferently on either side” (Scudder). In some
groups of the Insects there may be a suppression of certain of
these six primary veins, and the above general arrangement is liable
to characteristic modifications in different cases. The value of the
characters derived from the neuration of the wings is, however, im-
paired by the fact that entomologists have not adopted a uniform
nomenclature of the nervures in different orders of the Zzsecta.
In the Coleoptera (Beetles) the wings of the anterior pair become

SSS ae
Mi <= E

INSECTA. 589

hardened by the deposition of chitine, so as to form two protective
cases for the hinder membranous wings. In this condition the
anterior wings are known as the “elytra,” or “ wing-cases.” In
some of the HYemzpzera this change only affects the inner portions
of the anterior wings, the apices of which remain membranous, and

me
\

1 : /
ve H
vi
272

Fig. 442.—a, Schematic view of the right anterior wing of a Palzozoic Cockroach, greatly
enlarged. (After Scudder.) sa, ‘‘ Marginal” vein, which in this case merely thickens the
margin of the wing; ze, ‘‘ Mediastinal” vein; sc, ‘‘Scapular” vein; ex, ‘“‘ Externomedian”
vein; zz, “ Internomedian” vein; az, ‘‘ Anal” vein. x, Anterior wing of Butterfly (Castzia
veraguana), enlarged ; co, ‘‘Costal” vein; su, ‘‘Subcostal” vein; sc, ‘‘ Scapular” vein ; CX,
Branches of the ‘‘externomedian” vein; zz, ‘‘Internomedian” vein; v7, ‘‘Internal” vein.
(After J. O. Westwood.)

to these the term “hemelytra” is applied. In the Dépzera the pos-
terior pair of wings are rudimentary, and are converted into two
capitate filaments, called “halteres” or “balancers.” In the S¢rep-
siptera the anterior pair of wings are rudimentary, and are converted
into twisted filaments.

590 ARTHROPODA.

The typical number of somites in the abdomen of the /zsecfa is
ten or eleven, and this number can sometimes be recognised in the
Orthoptera and some other forms. In the Hymenoptera and Lepr-
doptera not more than nine or ten can be recognised, and in many
cases even fewer can be made out. The abdominal somites are
usually more or less freely movable upon one another, and never
carry locomotive limbs. The extremity of the abdomen is, however,
commonly furnished with appendages, which are connected with the
generative function, and not infrequently serve as offensive and de-
fensive weapons. Of this nature are the ovipositors of Ichneumons
and other insects, and the sting of Bees and Wasps. In the Earwig
(Forficula) these caudal appendages form a pair of forceps; whilst
in many insects they are in the form of bristles, by which powerful
leaps can be effected, as is seen in the Spring-tails (Podure).

Generally speaking, the young insect is very different in external
characters from the adult, and it requires to pass through a series
of changes, which constitute the “‘ metamorphosis,” before attaining
maturity. In some Insects, however, there appears to be no meta-
morphosis, and in some the changes which take place are not so
striking or so complete as in others. By the absence of metamor-
phosis, or by the degree of its completeness when present, Insects
are divided into sections, called respectively Ametabola, Hemimeta-
bola, and Holometabola, which, though not, perhaps, of a very high
scientific value, are nevertheless very convenient in practice.

The ‘‘ Ametabolic” Insects are those which have no proper
“metamorphosis,” the young stages of the Insect resembling the
adult in all essential points except in size. This absence of a meta-
morphosis is only seen in Insects which are destitute of wings in
the adult condition, and which are therefore often spoken of as the ©
Aptera. In the so-called ‘‘ Hemimetabolic” Insects, where an “ in-
complete” metamorphosis exists, the young insect is at first very
different from the adult, and in the process of conversion into the
latter it undergoes changes of form, while it at the same time
remains capable of locomotion and of nourishing itself. In its first
condition, after emergence from the egg, it is known as a “ larva,”
and at this stage it presents no traces of wings. In its second con-
dition—the stage of the “‘pupa”—it possesses rudimentary wings,
but is still active and feeds. In its third stage, as the perfect insect
or “imago,” the wings are fully developed, and the insect acquires
the power of flight. Lastly, the Insects which undergo a “ complete ”
metamorphosis, and which are therefore said to be ‘‘ holometabolic,”
pass through the same series of changes as those observed in the
case of the Hemimetabolic forms, but the larva, pupa, and imago
differ from one another more widely than is the case in the latter,
and the insect in the “ pupa” stage is quiescent and does not feed.

INSECTA. 591

The great majority of existing Insects are terrestrial in habit, and
almost all of those which are aquatic are inhabitants of fresh water.
For these reasons, the remains of Insects are by no means abund-
antly preserved in the fossil condition, and are chiefly found in
association with deposits of coal, or in lacustrine or fluviatile strata.
Moreover, the remains of this class of Arthropods are generally
found (except when preserved in amber) in a more or less frag-
mentary condition, and, under any circumstances, they cannot be
satisfactorily deciphered except by practised workers in the depart-
ment of Entomology. Between two and three thousand species of
fossil Insects have been already described, but for the reasons just
stated, it would be impossible here to deal with these in even a very
general manner. The student desirous of acquiring a detailed know-
ledge of the fossil Insects must have recourse to special works on
the subject, and, especially, to the admirable treatises published by
Mies seudder (see “iiterature of Insecta’). All that can be at-
tempted here is to give a brief outline of the general geological
distribution of the class, and of the leading characters and range in
time of the great orders of /usecta.

As regards the general geological distribution of the Jvsecfa, the
oldest known insect is the Paleoblattina Douvillet, recently described
by Brongniart from rocks belonging to the inferior portion of the
Silurian (Upper Silurian) rocks of France. With the exception of
this ancient type, the earliest remains of Insects are found in the
Upper Devonian rocks of North America. ‘It is, however, only
when we reach the productive Coal-measures that we arrive at
insect-faunas of considerable extent, such as those especially of
Commentry in France and of Mazon Creek in Illinois. Other con-
siderable deposits are found in the Coal-fields of the Saarbriick and
Wettin basins of Germany, the Belgian and British Coal-fields, and
in America the Coal-basins of Nova Scotia and Pennsylvania. The
Permian offers comparatively few species, but some of these are of
particular interest (e.¢., Lwgereon), and the Trias is almost wanting
in fossil insects, except in the South Park of Colorado, where about
twenty species have recently been obtained, affording transitional
forms among the Cockroaches. Later Mesozoic deposits have
yielded nothing in America, but much in England, where nearly all
the strata from the Lower Lias to the Wealden have been pro-
ductive. On the Continent of Europe prolific Liassic deposits have
been discovered at Dobbertin in Germany and Schambelen in Swit-
zerland, while the Oolitic beds of Solenhofen are world-renowned.
Scanty returns have come from the Cretaceous, but the early Ter-
tiaries have yielded an abundant harvest in the amber deposits of
the Baltic shore, the marls of Aix, and in America at Florissant and
Green River, while the Middle Tertiaries of Oeningen, Radoboj,

592 ARTHROPODA.

Parschlug, and Auvergne, and the Rhenish Brown Coals have been
scarcely less prolific” (Scudder).

All the known Palzeozoic Insects are referred by Mr Scudder to
‘a single homogeneous group of generalised Hexapods,” which this
eminent authority has named /ad@odictyoptera, and which “ should
be separated from later types more by the lack of those special
characteristics which are the property of existing orders than by
any definite peculiarities of its own.” With the exception of a few
forms from the Trias of North America, which are allied to the
Cockroaches, all the types included by Scudder under the name of
Paleodictyoptera are restricted to the Paleozoic period. Of the
modern orders of Insects, the great divisions of the Orthopiera,
Neuroptera, and Coleoptera possess representatives in rocks of
Triassic age; while the Hemiptera, Diptera, Lepidopiera, and
Flymenoptera existed under well-marked forms in the Jurassic
period.

In the following brief summary of the orders of Insects, with more
especial reference to their geological history, Mr Scudder’s treatise
on fossil Insects in Zittel’s ‘ Handbuch der Paleeontologie’ has been
followed, with some variation as to the classification adopted :—

Division A. AMETABOLIC INSECTS.

Of the four existing orders of Ametabolic or Apterous Insects,—
viz., the Anoplura (“Lice”), Mallophaga (“ Bird-lice”), Collem-
bola (“‘Springtails”), and Zhysanura,—only the last two are known
to be represented by fossil forms, and these only in deposits of
Tertiary age. Thus, forms allied to the existing Podura and
Smynthurus have been recorded as occurring in amber (early
Tertiary), while a species of the recent genus Lepzsma has been
similarly preserved, along with a number of other allied but extinct
types. The Oligocene deposits of Florissant, Colorado, have also
yielded examples of insects belonging to the order Zhysanura.

DIVISION B. HEMIMETABOLIC INSECTS.

OrpDER J. PALHODICTYOPTERA.—This order has been founded
by Mr Scudder for the reception of a number of Paleozoic and a
few Triassic Insects, with the following characters: ‘‘ Body generally
elongated, mouth-parts variously developed ; antennze filiform. Tho-
racic joints subequally developed; legs moderately long. Meso-
thoracic and metathoracic wings closely similar, equally mem-
branous ; the six principal veins (fig. 442, 4) always developed, the
marginal simple, and forming the costal border, the mediastinal
simple, or with superior branches only; the other veins usually

HEMIMETABOLIC INSECTS. 593

dichotomise ; stout and well-defined cross-veins rare; membrane
generally reticulate. Wings in repose lying on the abdomen, the
anal area of the hind-wings, though usually of great distal extension,
never plaited, though sometimes broadly folded. Abdomen usually
long and slender, the last joint often furnished with simple articu-
lated appendages ” (Scudder).

The Falcodictyoptera, as above defined, comprise generalised
Insects, in which there was an “incomplete” metamorphosis, and
the four wings were membranous, equally developed, and charac-
terised by a simple type of neuration. Mr Scudder recognises
within the limits of the /av/eodictyoptera four principal types of
structure, representing the existing orders of the Orthoptera, Neu-
roptera, Hemiptera, and Coleoptera, and in accordance with this
he has divided the order into four primary groups (the Orthopteroid,
Neuropteroid, Hemipteroid, and Coleopteroid groups). The earliest
known form of the Faleodictyoptera is the Paleoblattina Douvillet
of the Silurian rocks of Calvados, which is at present the most
ancient representative of the entire class of the Insects, and the
affinities of which are uncertain. Other forms of the order appear
in the Upper Devonian rocks of
North America ; numerous Carbon-
iferous and a few Permian forms
are known; and the last represen-
tatives of the order appear in the
Triassic rocks of North America.

The Orthopteroid section of the
Paleodictyoptera includes a group of
forms representing the modern Cock-
roaches, and a second group which
shows relationships to the existing
“ Stick-insects” (Phasmide). Apart
from the Silurian genus fa/leodlat-
tina, various Carboniferous types
are known which are allied to the
existing Cockroaches, but differ
from these in the neuration of the
wings; and upon such have been
founded the genera Archimylacris,

ae

M) lacris, Progonoblattina (fig. 443), Fig. 443.—Pvrogonoblattina helvetica, an

Etoblattina, &c. Of these, the last- Orthopteroid type of the Palgodictyoptera,
. : from the Carboniferous rocks of Switzer-

mentioned genus occurs also in the land, restored. (After Heer.)

Trias of North America, along with

other allied forms. The precursors of the modern Phasmide@ are

the “ Protophasmids ” of the Carboniferous rocks, comprising various

genera which resemble the existing ‘‘Stick-insects” in the form of

VOL. I. Zi

Garr

504 3 ARTHROPODA.

the body, but in which the wings have the characteristic features of
those of the Paleodictyoptera generally, being equally developed,
with a simple neuration, the anterior pair being unthickened and
transparent. The two best known genera of this group are Z7fano-

ZF Vw NN ——WS WS >
! EAN A \ AAG \ SS we \ \ SS
EARLS WWE RR “S| ne SWS
= R \\\ Vy NA N SNe ee SUNN NSS SSSSaane
Wi) sm ey et) <= Sa)
Na ry = Jf a Se SSQ_7~—w"s
SS, LRA INNS
= ZA ARE NY « |
Wy ei

Boy, A
f ae
WYLUE Wie
- f Ze ff sx
Dy Yh, Oh IN
ad ar Wy YU, (ENN
WG LINO
L S

ALARA
ee ee SSS IS SS

Fig. 444.—Hafplophlebium Barnesti (after Dawson). From the Carboniferous rocks
of Canada. a, Profile of base of wing.

phasma and Protophasma, both from the Carboniferous rocks. The

same formation has also yielded a number of other allied types,

upon which have been founded the-genera Dauctyoneura, Haplophle-

dium (fig. 444), Paolia, Breyeria, &c.

The Neuropteroid section of the Paleodictyoptera includes a num-

~ ber of Palzeozoic insects, which

SATALITyy «© «appear upon the whole to be

A most nearly allied to the existing

May - flies (Zphemeride). ‘The

most ancient types of this section

appear in the Upper Devonian

rocks of Canada, and upon these

have been founded the genera

Platephemera (fig. 445), Llomothe-

Fig. 445.-—Wing of Platephemera antigua, tus, Xenoneura, and Lithentomum.

Gey Devonian rocks of Canada. A number of allied types, which

have been referred to such genera

as Miamia, Lithomantis, Hemeristia, &c., have been detected in the
Coal-measures of both Europe and North America.

Of the Hemipteroid section of the /Paleodictyoptera the most
remarkable type is the Permian genus Lugereon (fig. 446). In this
remarkable genus the mouth-organs are lancet-shaped, the antennze
are slender and many-jointed, and the front and hind wings are

HEMIMETABOLIC INSECTS. 595

of large size, transparent, and essentially similar in form and neura-
tion. The Permian genus “/z/gorina is allied to the preceding ;
whereas in the PA¢hanocoris of the Coal-measures, the front wings
differ in character from the hind wings, and assume the features of
“‘hemelytra.”

Lastly, Mr Scudder forms a section of ‘ Coleopteroid” /ade-
odictyoptera for the reception of Paleozoic insects, which may be
regarded as precursors of the modern Beetles (Coleoptera), and

1 SS Oe
Llp Wy,

—v SYS > CES:
Qe GSS Se il
Saif

Fig. 446.—Zugereon Bockingi, from the Lower Permian rocks of Germany. (After Dohrn—
copied from Zittel )

which resemble the latter in having the anterior pair of wings
hardened by chitine so as to form cases (“elytra”) for the pro-
tection of the membranous hind-wings. ‘The existence of insects of
this type in the Carboniferous period is shown by the presence in
fossil wood from the Coal-measures of borings similar to those
produced by existing Beetles. The elytra of Coleopteroid in-
sects have also been recently discovered in the Carboniferous
rocks of Silesia, but the characters of these have not yet been fully
determined.

ORDER II. RuyNcHota (Hemiptera).—Mouth suctorial, beak-
shaped, consisting of a jointed rostrum, composed of the elongated
labium and labial palpi, which together form a jointed, tubular sheath

596 ARTHROPODA.

Jor the bristle-shaped, styliform mandibles and maxille. Eyes com-
pound, usually with ocelli as well. Two pairs of wings in most;
sometimes wanting. Pupa generally active.

The recent Ahynchota are of very varied habit, and they may be
divided into two principal sections in accordance with the structure
of the wings. In one great section of the order (Homoptera) the
anterior and posterior wings are both membranous, the former being
simply of firmer texture than the latter. To this section belong
such existing types as the Aphides, the Cicadas (fig. 447, c), the
Lantern-flies, &c. In the other great section of the order (Heter-
optera) the anterior wings are hardened at their bases by chitine and
remain membranous towards their apices (fig. 447, B), constituting

Fig. 447.—Recent Rhynchota. a, 7Thrifs, enlarged ; B, Nepa cinerea, enlarged ; c, Cicada
Angilica, the wings on the right side of the body being omitted ; p, Larva of the same; E, Pupa
of the same. (Figs. c, D, and E are after Westwood.)

protective cases (“‘hemelytra”) for the wholly membranous hind
wings. In this section are included the numerous forms of Land-
bugs and Water-bugs.

As regards their geological distribution, the place of the Rhynchota
in the Paleozoic rocks is taken by the Hemipteroid forms of the
Paleodictyoptera. In the Jurassic rocks, however, appear for the
first time well-marked representatives of both the above-mentioned
sections of the order ; the Homopterous forms being represented by
types allied to the Cicadas, while the Heteropterous division is
represented by forms closely allied to, or identical with, the existing
Water-scorpions (/Vega) and the Land-bugs. The little Plant-lice
(Aphis, &c.) appear in the Cretaceous rocks (Wealden) ; and a vast
number of Tertiary types of the AAynchota have been described,
most of these presenting no marked peculiarities as compared with
living types. The Paleontina oolitica of the Stonesfield Slate of

HEMIMETABOLIC INSECTS. 597

England, regarded by Mr Butler as being a Butterfly, is considered
by Mr Scudder as truly a Cicada.

ORDER III. OrtTHOpTERA.—In this order the mouth ts mastica-
tory ; the wings are four, sometimes wanting, the anterior pair mostly
smaller than the posterior and of a semt-coriaceous or leathery consist-
ence. The posterior wings, when not in use, are plaited longitudinally
like a fan or may be transversely folded. The interspaces between the
nervures are filled with transverse reticulations, and the anal area of
the wing ts of large size. The antenne are usually filiform, and the
Jemales are usually provided with an ovipositor.

The earliest types of the Ovthoptera appear in the Trias, where
the order is represented by several forms of Cockroaches. In the
Jurassic rocks are found forms belonging to the families of the Ear-
wigs (Baseopsis, of the Lias), the Locusts (Gryl/acris and Locusta),
and the Crickets (Gry//us), while the Grasshoppers (Acvidide) are
doubtfully represented in deposits of Mesozoic age. All the pre-
ceding families continue to be well represented in the Tertiary
rocks, and in deposits of this age appear also forms belonging to
the families of the Wantide and Phasmide.

ORDER IV. NEvUROPTERA.—Mouth usually masticatory ; wings
jour in number, all membranous, generally nearly equal in sise,
traversed by numerous delicate nervures, which have a longitudinal
and transverse direction, thus giving them a reticulated, lace-like
aspect (fig. 448). Metamorphosis in some groups incomplete, in other
groups complete. The larva active, hexapod, the pupa active or
guiescent.

The insects included in the order /Veuroptera differ so widely
in their characters, habits, and metamorphoses that they may be
divided into the three primary groups of the Pseudoneuroptera, the
Neuroptera vera, and the Z7ichoptera, of which the first consti-
tutes a transitional group between the typical /Veurvoftera and the
Orthoptera.

The Pseudoneuroptera are characterised by their incomplete meta-
morphosis, the larve being commonly inhabitants of water, and the
pupz being active. Of the groups included in this section of the
order, the Termites or “ White Ants” are represented in rocks as
old as the Lias, and abounded in Tertiary times. The May-flies
(Ephemeride) and the Dragon-flies (Lzbe//ulide) likewise commenced
their existence in the Jurassic rocks, and have many Tertiary repre-
sentatives. Beautifully preserved examples of the Dragon-flies have
been yielded by the fine-grained Lithographic Slates of Solenhofen
(fig. 448), while still older forms have been recognised in the Lias.
Lastly, the family of the Per/zde, including the recent ‘ Stone-flies,”
is represented in the Eocene Tertiary.

The group of the (Veuroptera vera includes those members of

598 ARTHROPODA.

the order in which there is a complete metamorphosis, the pupa
being inactive, and comprises the Ant-lions (J/yrmeleontide), the
Aphis-lions (Hemerobiida), the Scorpion-flies (Panorpide), and the
Sialide. The first of these groups is doubtfully known by fossil
forms in the Tertiary rocks, but the three last have representatives
in the Jurassic rocks, and are also found more or less abundantly in
deposits of Tertiary age.

Lastly, the group of the Z7ichoptera comprises the Caddis-flies
(Phryganeide), in which the anterior wings are generally hairy, the
larvee are aquatic and usually reside in tubular cases formed of

Sau CLL
Fa ES Ea
wy OEE, 49) ¥
<= od n
EOE é Hou
citeccaonees eee SETA ESS Sere
§ SE GI Te Weer acces
SERA OOOO at Ls
LER Sis

Fig. 448.—Petalia longialata, a fossil Dragon-fly from the Lithographic Slates (Jurassic) of
Solenhofen. (Copied from Scudder and Zittel.)

small foreign bodies, and the pupze are inactive during the greater
part of their life. A few Mesozoic forms of the Caddis-flies are
known, and various Tertiary types have been recognised. The
principal paleontological interest of the Caddis-flies arises, however,
from the fact that the tubular cases of the larvee, formed of small
fragments of stone or of minute shells cemented together, are capable
of preservation in the fossil state. Such cases have been found in
the Cretaceous rocks of Bohemia and in various Tertiary deposits,
and they sometimes occur in such numbers as to give rise to deposits
of considerable thickness. Of this nature is the so-called “‘ Indusial
Limestone” of Auvergne, which covers considerable areas, and attains
a thickness of eight or ten feet.

q _—-

———a

HOLOMETABOLIC INSECTS. 599

Division C. HOLOMETABOLIC INSECTS.

ORDER I. APHANIPTERA.—/Vings rudimentary, in the form of
scales situated on the mesothorax and metathorax. Mouth suctorial.
Metamorphosis complete.

This order includes only the Fleas, and requires no further con-
sideration here, since no fossil representatives of the group are known
to exist.

OrvDER IJ. Diprera.—This order includes the ‘‘ Two-winged
Flies,” and is characterised by the fact that the mouth ts suctorial
and ts also adapted for piercing ; the anterior wings are membranous,
with a small basal lobe (“alula”), not closely reticulated, but with a
Jew, definitely-placed cross-veins. The posterior wings are rudimentary,
and are represented by a pair of clubbed filaments (‘ halteres’”’).

As regards the distribution of the Dzfzera in time, a few repre-
sentatives of the order have been detected in rocks as old as the
Jurassic, but the majority of the fossil forms are found in Tertiary
deposits, being especially abundant in amber. Most of the existing
families of Diptera are represented by fossil forms, but none of these
present any points of special interest.

ORDER III. Leprpoprera.—This order includes the Butterflies
and Moths, and is characterised by the fact that the mouth of the
adult 1s completely adapted for suction, the mandibles being rudiment-
ary. oth pairs of wings are present, and are membranous, being
covered with rows of flattened hairs or scales. The neuration of the
wings (fig. 442, B) 7s simple, the nervures being rarely united by cross-
veins. The “marginal” vein is wanting ; while the“ scapular” and
“externomedian” veins generally form between them a median cell,
and give origin to most of the secondary nervures. The metamorphosis
2s complete, the larva (“caterpillar”) being worm-like, and the pupa
(“chrysals”) being completely enclosed in a horny integument.

As regards their distribution in time, undoubted remains of
several species of Lepidoptera (such as the Sphinx Snellent of the
Solenhofen Slates) have been detected in the Jurassic rocks; and
the tunnels of the larve of small Moths have been noticed in fossil
leaves of Cretaceous age; but the number of recognised Mesozoic
Lepidoptera is very limited. In the Tertiary rocks the remains of
Lepidoptera are still exceedingly rare, but both the Moths and the
Butterflies are now represented by fossil forms. About a dozen
Tertiary species of Butterflies are known altogether, and most of
these belong to extinct genera (JZylothrites, Neorinopsis, &c.)

ORDER IV. HyMENOPTERA.—This order includes the Ants, Bees
and Wasps, Gall-flies, &c., and is characterised by the fact that the
mouth-organs are adapted partly for suction and partly for biting, the
mandibles being well developed. Both pairs of wings are usually

600 ARTHROPODA.

present, the front pair being larger than the hinder pair. The wings
are membranous, with a few distant nervures, which are generally con-
nected by cross-veins so as to form large polygonal cells. The females
usually with an ovipositor, which may be converted into a “ sting”
(aculeus).

As regards their distribution in time, very few fossil forms of the
L1ymenoptera are known in deposits older than the Tertiary. Of
the very limited number of Mesozoic forms one of the most ancient
is the Paleomyrmex prodromus, described by Heer from the Liassic
rocks of Switzerland, which belongs to the family of the Ants
(Lormicide), a family which has also representatives in later Jurassic
deposits. In the Tertiary rocks the remains of Aymenoptera are
more abundant, almost all the existing families of importance being
represented ; but none of the fossil forms are of special interest.

ORDER V. STREPSIPTERA.—females without wings or feet, para-
silic. Males possessing the posterior pair of wings, which are large,
membranous, and folded longitudinally lke a fan. The anterior pair
of wings rudimentary, represented by a pair of singular twisted organs.
Jaws rudimentary.

The Strepsiptera constitute a small order, which includes certain
minute parasites of Bees and other ymenoptera. ‘The females are
grub-like, but the males are winged. A single example of one of
the winged males of this singular group of insects has been detected
in amber, and has been referred to the extinct genus Z7zena.

ORDER VI. CoLEoPTERA.—This great order of Insects includes
the “Beetles,” which are characterised by their strong chitinous
integument and the complete adaptation of the mouth-organs for
biting, the mandibles being well developed. Zhe anterior wings are
useless as organs of flight, and are hardened by chitine, so as to form
protective cases (elytra) for the posterior wings, these being membranous,
and being folded transversely and longitudinally in repose. The nerv-
ures of the hind-wings are few and distant, cross-veins being rarely
developed. The inner margins of the elytra (fig. 449) are generally
straight, and when in contact they form a longitudinal suture.

As regards their distribution in time, the oldest types of the
Coleoptera, recognised by Mr Scudder, belong to the Curculonide
(Weevils), and appear in the Triassic rocks (Curculionites pro-
dromus). ‘The Jurassic rocks have yielded a number of types of
this family also; while Heer describes other forms from the Creta-
ceous rocks of Greenland; and about one hundred species of
Weevils, belonging mostly to existing genera, have been mentioned
or described from the Tertiary rocks. ‘The great existing families
of the Chrysomelide, Buprestide, and Carabide (fig. 449, B) are
also all represented by Triassic forms; and all have more or less
numerous Jurassic and Tertiary representatives. Of the remaining

LITERATURE. 601

families of the Coleoptera the majority of the leading groups of the
present day, such as the Zenebrionide, Cerambycide, Scarabaeidae,
Elateride, Staphylinide, Coccinellide, Hydrophilide, and Dytiscde
possess more or less numerous Jurassic representatives, and all

Fig. 449.—aA, Dytiscus Lavateri, restored, from the Miocene deposits of Oeningen, of the
natural size; B, Thurmannia punctulata, one of the Carabide, restored, and enlarged three
times, from the Lias of Schambelen; c, Coccinella decempunctata, enlarged twice, “from the
Miocene deposits of Oeningen. (After Heer.)

occur under many specific forms in the Tertiary rocks. Many of
the smaller families of Beetles are also known by fossil forms, but
the order has attained its maximum development at the present
day.

DItERATURE.

1. “Insecta,” in Zittel’s ‘Handbuch der Palzontologie, Bd. II., Lief. Be
1885. Scudder.

. “Systematic Review of our present Knowledge of Fossil Insects.”
‘Bull. of the U.S. Geol. Survey.’ No. 31, 1886. Scudder.

. “The Tertiary Lake-basin at Florissant.” ‘Bull. U.S. Geol. Survey

of the Territories,’ vol. vi. 1881. Scudder.

4. “ Winged Insects from a palzontological point of view, or the Geo-
logical History of Insects.” ‘Mem. Bost. Soc. Nat. Hist, vol. 111.
1885. Scudder.

“Die Insecten und Spinnen der Vorwelt.” 1856. Giebel.

“A History of the Fossil Insects in the Sesser Rocks of Eng-.
land.” 1845. P. B. Brodie.

7. ‘Die fossilen Insecten der Kohlenformation von Saarbrticken.”

Von Goldenberg. ‘Palzontographica.’ 1854.
8. “Eugereon Bockingi, eine neue Insectenform, aus dem Todtlie-
gende.” Dohrn. ‘Palzontographica.’ 1866.

@, Die Insectenfauna der Tertiargebilde von Oeningen und von Rad-

oboj in Croatien.” 1847-53. Oswald Heer.

i)

Oo

nun

602 LITERATURE.

20.

. “Die Urwelt der Schweiz.” 2d Ed. 1879. English translation.

1876. Oswald Heer.

. “Apercu sur les insectes fossiles en général.” 2d. Ed. 1883. Charles

Brongniart.

2. ‘ Lebenszeichen vorweltlicher im Bernstein eingeschlossener Thiere.”

1856. Menge.

. “Descriptions of Fossil Insects found at Mazon Creek.” ‘Geol.

Survey of Illinois, vol. 11. 1868. Scudder.

. “The Devonian Insects of New Brunswick.” ‘Anniv. Mem. Bost.

Soc. Nat Hist? ese, “Scudder

. “The Carboniferous Hexapod Insects of Great Britain.” ‘“ Mem.

Bost. Soc. Nat. Hist. 1883. Scudder.
‘“‘ Palzodictyoptera, or the Affinities and Classification of the Palzo-
zoic Hexapoda.” Ibid. 1886. Scudder.

. “New Genera and Species of Fossil Cockroaches from the older

American Rocks.” ‘Proc. Acad. Nat. Sci. Philadelphia.’ 1885.
Scudder.

“On a remarkable Fossil Insect from the Coal-Measures of Scot-
land.” ‘Quart. Journ: Geol? Soc.;) vol. xxxil. 1670: seems
Woodward.

“On some New British Carboniferous Cockroaches.” ‘Geol. Maga-
zine. 1887. Henry Woodward.

“Die Ahnen unserer Schmetterlinge in der Secundar- und Tertiar-
periode.” ‘Berl. Entom. Zeitschr., Bd. XXIX 1685e@ppen-
heim.

GHnArTER XAXXHE

MOLLUSCOIDEA.

POLYZOA.

WE may consider here, under the name of Jo/uscoidea, the two
groups of animals which are known respectively as the /o/ysoa and
the Lrachiopoda. These two groups, in many respects closely
allied to one another, present affinities on the one hand to the
Worms, and on the other hand to the MWo//usca, with both of which
they have been arranged by different systematists. In the present
state of our knowledge, however, it seems best to consider these
two groups separately, without referring them definitely to either of
the two sub-kingdoms above mentioned. The Tunicates, which
have also often been included amongst the Molluscoids, may like-
wise be in the meanwhile regarded as a separate division, which
finds its most natural position between the J/o//usca and the Ver-
tebrata. It is not necessary, however, to further consider the
Tunicates in this work, since the paleontological history of this
group of animals is an almost absolute blank. No fossil remains
of Tunicates have, in fact, been hitherto discovered except the
minute spicules of a species of Leffoclinum in the Pliocene beds of
St Erth. Many existing Tunicates, however, both simple and com-
pound, are known to possess more or less numerous calcareous
spicula in their tissues, and by the help of these it may ultimately
be found possible to trace back the existence of these singular or-
ganisms to an earlier period of the earth’s history.

The dMJoluscoidea may be briefly defined as unsegmented, simple
or compound animals, with bilateral symmetry. The mouth is
furnished with a crown of ciliated tentacles, or with spirally-rolled
ciliated processes. The nervous system consists of a single gan-
glion, or of an cesophageal nerve-ring with more than one ganglion.
A heart is absent or present. Under this head may be placed the
two classes of the Polysoa and the Brachiopoda.

604 MOLLUSCOIDEA.

POLYZOA.

Crass I. Potyzoa (Lryozoa).—The members of this class are
mostly composite animals, each zooid of which possesses, typically, a
Jreely suspended alimentary canal, with mouth and anus, enclosed with-
in a double-walled sac. The mouth is surrounded with a circle or
crescent of hollow ciliated tentacles, and the nervous system consists of
a single ganglion placed between the mouth and the anus.

With the single exception of the genus Zoxosoma, all the Polyzoa
live in an associated form in colonies or ‘ polyzoaria,”’ which are

Fig. 450.—Diagram showing the
structure of a single polypide of a
Polyzoan (after Busk). 7, Tentacles;
mz, Mouth; g, Nerve-ganglion; a,
Gullet 3; s, Stomach; 2, Intestine;
a, Anus; 0, Ovary; x, Testis; 2,
Funiculus; ov, Aperture of the
zoczclum ; v, Tentacular sheath;
d, Perivisceral cavity ; ~, Retractor
muscles; ¢, Ectocyst.

sometimes foliaceous, sometimes branch-
ed and plant-like, sometimes laminar,
sometimes encrusting, and very rarely
are free. Each “ polyzoarium” consists
of an assemblage of distinct but similar
zoolds arising by continuous gemmation
from a single primordial individual.
The entire colony—or its entire der-
mal system—is called the “ polyzoar-
ium”. or ‘‘ coencecium/”s; “the (segamae-
zooids are called ‘“ polypides”; and
the littke chambers in which each is
contained are called the “cells @aion
“ZO Ge Cla: «

A typical polypide of a Polyzoon (fig.
450) consists of a membranous sac (“en-
docyst”) the external surface of which, ex-
cept at its anterior end, is generally hard-
ened by an investing horny or calcified
layer, which is known as the “ ectocyst.”
Freely suspended in the _perivisceral
fluid filling the space enclosed with-
in the endocyst is the alimentary canal,
which consists of a mouth, gullet, stom-
ach, intestine, and anus. The mouth
(fig. 450, 7) is placed anteriorly, and is
surrounded by a crown of tubular, non-
retractile tentacles, which are ciliated,
and act as respiratory organs. In differ-
ent types of the class, the tentacles are
arranged in a circle or are disposed so
as to form a horse-shoe or crescent.
The alimentary canal is bent upon it-

self in such a way that the anus (fig. 450, a) comes to be placed
near the mouth, being usually placed outside the tentacular circle

POLYZOA. 605

(in the ‘‘ Ectoproctous” Polyzca), but sometimes within it (in the
“‘Entoproctous” /olyzoa). The alimentary canal is moored to
the body-wall by muscular bands, those springing from the bottom
of the cell serving to retract the polypide within its chamber,
while the protrusion of the tentaculated anterior extremity is
effected by muscular fasciculi which run in a circular manner in
the wall of the cell.

Each polypide possesses a single nervous ganglion (fig. 450, g),
which is placed upon one side of the gullet, between it and the anal
aperture. The different polypides may also be connected together
by a remarkable organic structure, which was at one time believed
to be of a nervous nature, and was termed the “colonial nervous
system,” but which is now generally spoken of as the ‘“ endosarc.”
This singular connective system, by which the different polypides
of the colony are organically united, commences as a peculiar cel-
lular cord, the “ funiculus” (fig. 450, z), which stretches from the
base of the stomach to the bottom of the zocecium, and upon which
the testis is developed. At the point where the funiculus is fixed
to the bottom of the cell, a perforation in the ectocyst exists, and
filaments of the funiculus thus either pass into adjacent polypides,
or become connected with a common branched fibre which runs
through the stolons of the colony (as in Bowerbankia). In many
cases the endosarcal cords give off branching fibres, and they have
a general likeness to a nervous system. Histologically, however,
the endosare does not consist of nervous elements, and it may be
regarded as a kind of ccenosarcal structure, which is largely con-
nected with the production of the generative elements, and from
which, possibly, the polypides are produced by gemmation.

The polypide of the Fo/ysoa is generally hermaphrodite, the ovary
(fig. 450, 0) being usually situated near the summit of the cell,
attached to the inner surface of the endocyst, while the testis (x) is
placed at the bottom of the cell, and is attached to the ‘“ funiculus.”
The generative elements are usually set free into the perigastric
space, the ova being thus fecundated within the body-cavity of the
parent polypide. ‘The fertilised ova may pass into special dilata-
tions of the cell (‘“ovicells”), or the embryos may be hatched
within the perivisceral cavity of the parent.

The embryo is, to begin with, ciliated and freely locomotive, but
ultimately fixes itself, and, except in Zoxosoma, begins to produce a
colony by means of budding. The new buds are usually produced
from the dorsal wall of the polypide, or from its sides, or sometimes
from its anterior extremity. Fission, so common among the Ccel-
enterates, has never been noticed to occur. The ultimate form of
the polyzoary depends upon the precise method in which the new
buds are developed. The separate polypides of the colony are ap-

606 MOLLUSCOIDEA.

parently always more or less clearly united with one another by an
organic connection. In many cases this communication between
the different polypides is effected by means of the structure which
has been previously spoken of as the “‘endosarc.” In other cases
the walls of the cells are pierced by pores or traversed by tubuli, by
means of which the perivisceral cavities of adjoining polypides are
placed in communication.. In other cases, again, there exists a
common lamina, the extension of which precedes the production
of new cells. Lastly, in the group of Folyzoa known as the
Ctenostomata, there exists a common tube with which all the poly-
pides of the colony are connected.

The structures in the Folyzoa with which the paleontologist is
more especially concerned are those developed from the external

Fig. 451.—A, Fragment of Stomatopora (Alecto) dilatans, a recent Cyclostomatous Polyzoén,
enlarged. B, A few cells of Swetttia Marionensis, a recent Cheilostomatous Polyzoén, enlarged :
wt, Aperture of the cell; a, Avicularium; 0, Ovicel!. (After Busk.)

investing layer or ‘“ ectocyst,” which form the skeleton of the colony,
and which alone are capable of being preserved in the fossil condi-
tion. In rare cases among the existing Po/yzoa the ectocyst may be
absent, or may be gelatinous in consistence ; but it is usually either
purely chitinous or more or less extensively calcified. The ectocyst
forms for each polypide of the colony a more or less complete
“cell”; but the cell is invariably furnished at one point with an
“aperture” or “mouth,” whence the polypide can pretrude its
tentaculate head. In various forms, however, the anterior wall of
the ectocyst may be imperfectly hardened, or may remain mem-
branous. The form of the “cells” or ‘zocecia” in the Polysoa
varies extremely in different groups, and important distinctions are

POLYZOA. 607

based upon this character. Thus, in the so-called ‘‘ Cyclostomatous ”
Polyzoa the cells are tubular in form (fig. 451, A), and the aperture
is terminal in position, and is approximately equal to the cell itself
in diameter, while there is no special movable apparatus for its
closure. On the other hand, in the so-called ‘‘ Cheilostomatous ”
Polyzoa (fig. 451, B) the mouth of the cell is never quite terminal
in position, but is always placed upon the front of the cell, generally
close to the anterior end, while its diameter is less than that of the
cell, and it is provided with a movable opercular valve.

The surface of the cell may be “either smooth and entire, spin-
ous or granulous ; perforated with minute pores, or cribriform with
larger openings ; reticulate or ribbed, &c.,—all of which conditions,
with certain precautions, afford excellent diagnostic characters ”
(Busk). The margins of the mouth of the cell, also, may be
“simple or thickened, unarmed or beset with erect ‘ marginal
spines,’ which again may be either rigid or articulated at the base,
simple or branched.”

Though the separate zocecia of a Polyzoan colony are usually
apparently quite separate and distinct from one another, except by
continuity of their external investment, it has been shown that
contiguous cells are commonly placed in direct connection with

Fig. 452.—A, Longitudinal section of a few tubes of the recent 7Texzysonia stellata, enlarged,
showing the porous walls of the cells; B, Central portion of a transverse section of a branch of
Cellepora ramulosa (Recent), showing tubes connecting the cavities of adjoining cells, enlarged ;
c, Part of a tangential section of the polyzoary of Domopora stellata (Recent), enlarged to show
the connecting-tubuli. (Original.)

one another by what have been called ‘‘communication-plates ”
or ‘‘rosette-plates.” These are portions of the cell-wall pierced
by one or more minute pores which transmit processes of the
structure which has been previously described as the “ endosarc.”
In many of the calcareous Folyzoa also, the walls of the cells
are pierced by more or less numerous pores, which open into the
cavity of the cell (fig. 451). In certain of the Cyclostomatous
Polyzoa, as also in some Cheilostomatous forms, where the walls of
the cells are of considerable relative thickness, these pores assume

608 MOLLUSCOIDEA.

the form of tubes, which place the perivisceral cavities of contiguous
cells in direct communication, as is seen, for example, in such recent
genera as Cellepora among the Chezlostomata, and Domopora and
Heteropora among the Cyclostomata. ‘These connecting-tubes (fig.
452) are usually wide and trumpet-shaped at the points where they
open into the cavities of the cells, and are contracted in the middle
portion of their course; and they, doubtless, are simply a further
development of the simple pores seen in many other forms.

Again, in various of the Paleeozoic Polyzoa, and particularly in
the family of the Feneste/ide, a portion of the polyzoary consists of
dense calcareous tissue which exhibits under the microscope a finely
punctated appearance. When sufficiently thin sections of this
punctated layer are prepared, and examined with a sufficiently high
magnifying power, the tissue is seen to be penetrated by innumer-
able exceedingly minute tubuli (fig. 453), which run at right angles
to the surface of the polyzoary. Nothing certain has, however, been
ascertained as to the nature and function of these tubuli. In some
types, such as Rhombopora
(Ceriopora) interporosa, of
the Carboniferous rocks,
the thickened walls of the
cells near their mouths are
penetrated by dark rod-like
structures which run at
right angles to the surface.
These structtires @iamemon
larger size than the tubuli
of the Fenestellids, but they
sometimes exhibit a clear
central space, and it is pro-
bable that they are really
of the nature of tubes.

In a great number of the
Fig. 453.—A portion of the punctated layer on the

non-poriferous side of a Fenestellid (P/yllopora sp.), cut recent Polyzoa, the poly-
parallel with the surface and greatly enlarged. De- zoarium is furnished with

vonian, Canada. (Original.) : 5
singular appendages, which
are known as ‘“avicularia” and ‘‘vibracula,” and which are to be
regarded as specially modified zooids. The avicularia or “ bird’s-
head processes ” (fig. 454, B and c) differ a good deal in shape, but
consist essentially of ‘‘a movable mandible and a cup furnished
with a horny beak, with which the point of the mandible is capable
of being brought into apposition” (Busk). In shape, the avicularia
often closely resemble the head of a bird; and they are in many
respects comparable with the “ pedicellariz” of the Echinodermata,
keeping up a constant snapping movement which continues long

POLYZOA. 609
after the death of the general colony. In the “vibracula” (fig.
454, A), the place of the mandible of the avicularium is taken by a
bristle, or seta, which is capable of extensive movement.

Owing to the minute size of the avicularia and vibracula and
their readily perishable structure, it could hardly be expected that
the fossil Polysoa should exhibit similar organs except under the
most favourable conditions of preservation ; and as a matter of fact,
these appendages have not hitherto been recognised except in a few
instances. The former existence of avicularia may, however, be
in many cases inferred by the presence of cicatrices or pore-like

Fig. 454.—A, Three cells of MWastigophora Hyndmanni, showing vibracula (v)—the left-hand
cell also shows an occium; B, Sessile avicularium of Scrvupocellaria scruposa; and c, Pedun-
culate avicularium. 46, Beak; c, Chamber of the avicularium; 7, Muscles; 4, Peduncle.
All the figures are enlarged. (After Hincks and Busk.) =

depressions on the surface of the cells. In some instances it can
be shown, as, for example, in the recent Rezepora, that the avicularia
are really attached to thickened tubes which pass deep into the
substance of the polyzoary, and which can therefore be readily
recognised in thin sections (fig. 455, A). This observation is of
considerable interest as affording a possible explanation of certain
thickened tubular structures which are found in some of the Palzo-
zoic Polyzoa. The structures in question have the form of tubes
with thickened fibrous walls, embedded in the solid tissue of the
polyzoary ; and when cut across transversely in thin sections (fig.
455, B and C), they exhibit a minute central clear spot surrounded
VOL. I. 2Q

610 MOLLUSCOIDEA.

by a dark margin. They were first recognised by Mr John Young
as occurring in some of the Feneste/ide (fig. 467),and they were
compared by this observer with the ‘‘acanthopores” of the Monti-
culiporoids. They occur, however, in other Paleozoic Folyzoa
beside the Lace-corals (as in Coscinium and in species of Rhom-
bopora), and it may be conjectured that they are of the same nature
as the small thick-walled tubes in the polyzoary of the existing
Retepora (fig. 455, A), in which they support the avicularia.

In many of the Folysoa the cells are furnished with special dila-
tations, which serve as marsupial pouches for the ova, and which
are known as the “‘ovicells” or “ocecia.” In general, these pecu-
liar brood-pouches have the form of helmet-shaped or sac-like cham-
bers springing from the anterior end of the cell (fig. 451, B, 0), with

Fig. 455.—A, Tangential section of a recent species of Retefora, taken parallel to the non-
poriferous surface of the polyzoary, enlarged, showing the thickened tubes (4) to which the
avicularia were attached; B, Tangential section of Rhombopora (Ceriopora) Hamiltonensis,
from the Devonian rocks of Canada, enlarged, showing thickened tubes (); c, Tangential sec-
tion of Coscintum (Coscinotrypa) cribriforme, from the Devonian rocks of Canada, enlarged,
(Gone similar thickened tubes (J). c, Cavity of a cell; 74 One of the “‘fenestree” of Retepora.

riginal.)

the cavity of which they communicate by an aperture or fissure in
their hinder wall. Ovicells are not only found in the recent Chez/-
ostomata generally, but occur also in numerous Secondary and Ter-
tiary types. Mr Ulrich has likewise recognised in certain of the
Fenestellids structures which appear to be of the nature of ovicells ;
but with this exception no traces of these organs have hitherto been
detected in the Paleozoic Polyzoa.

In various of the Cyclostomatous /o/yzoa the mouths of a greater
or less number of the cells may be closed by a calcareous mem-
brane, covering parts of the surface more or less completely. In
other cases (as in Mesenteripora and sometimes in the Paleozoic
Polypora), individual cells may have their mouths closed by a cal-
careous lid, which may exhibit a minute central perforation, or, in

POLYZOA. 611

other cases, a projecting tubule. Mr Waters has further shown that
in the Cyc/ostomata it is not uncommon for a calcareous plate to be
developed at the point where the zocecial tube rises free from the
polyzoarium ; while in other cases, two of these “ closing-plates ”
are developed close together. Probably of a similar nature to the
“‘closing-plates ” just mentioned are the transverse calcareous parti-
tions which are developed in the tubes of various Cyclostomatous
Polyzoa, both recent and fossil, and which have been spoken of as
“tabulee,” from their similarity to the structures known by this name
in many Corals. These so-called “tabule” differ from the ‘ clos-
ing-plates ” described by Mr Waters in being developed in the deeper

Fig. 456.—Minute structure of the recent Heteropora pelliculata, Waters (=H. neozelanica,
Busk). A, Tangential section of the polyzoary, enlarged about fifty times, showing the proper
zocecia (a, a) and interstitial tubes (4) connected by numerous minute tubules (c). The cells
are furnished with numerous radiating spines or ‘“‘rays.’’ B, Part of a longitudinal section,
enlarged about twenty times, showing connécting-pores, ‘‘rays,” and delicate transverse parti-
tions or ‘‘tabule.” (Original.)

as well as in the more superficial portions of the colony, and they
are sometimes present in considerable numbers. They occur in
various genera, as, for example, in eferopora (fig. 456, B), Alveo-
laria, Fascicularia, Lichenopora, &c.; and they are probably con-
nected with the periodic death and renovation of the polypides
which is known to occur in many recent /o/yzoa.

In certain of the Folyzoa, finally, the cells are furnished with
delicate, radially disposed spines, which present a superficial re-
semblance to the “septa” of such corals as /avosztes and certain
of the Heoltide, and which may be spoken of as “rays.” These
curious structures (fig. 456, A) have the form of minute calcareous

612 MOLLUSCOIDEA.

spines which are directed into the interior of the cell-cavity, their
free ends being sometimes globular or button-like. They have
been recognised by the present writer in the recent Meteropora
pelliculata and in some species of Lichenopora (Discoporella) ; while
Mr Waters has detected them in Ezz¢alophora intricaria, and in species
of Zubulipora and Lichenofora ; and apparently identical structures
have been shown by Mr John Young to exist in certain of the Fenes-
tellide. So far as known, these “rays” are confined to certain of
the Cyclostomatous Po/yzoa, and their precise morphological signifi-
cance has not as yet been determined. According to a curious
observation of Mr Waters, the zocecia of Lichenopora grignonensts
not only possess ‘‘rays” in their interior, but are also furnished
with similar spines projecting from portions of the exzermaZ surface.

As regards their classification, the Polyzoa may be divided into
the three primary sections of the Ectoprocta, Entoprocta, and Aspido-
phora, of which the last two require no further characterisation here,
as they are not known to possess any fossil representatives. The
division of the Lctoprocta, on the other hand, includes the great
majority of the living Polysoa and the whole of the fossil forms,
though the essential feature of the division is the position of the
anal opening outside the tentacular circle——a character which,
necessarily, can only be positively determined in lving examples.
The £ctoprocta may be divided into the two orders of the Phylacto-
lemata and Gymnolemata, the former characterised by the almost
universal feature that the tentacular crown is horse-shoe-shaped, and
by the possession of a peculiar valve-like organ (‘‘ epistome”) arch-
ing over the mouth; while the tentacular crown in the latter is
circular and there is no epistome. The Phylactolematous /o/ysoa
are confined to fresh waters, and they need not be considered here
further, as no fossil examples of the order have ever been detected.
The order of the Gymmnolemata, on the other hand, is of great im-
portance, as comprising the vast majority of the existing marine
Folysoa and all the known fossil forms. The order may be divided
into the three sub-orders of the Cyclostomata, the Chezlostomata,
and the Cvenostomata, the first two characterised by the form of
the cell and the absence or presence of an opercular valve to the
cell-aperture, while the last is distinguished by the fact that the
cells arise from a common tube, their mouths being terminal and
furnished with a setose fringe for their closure.

As regards their azstribution in time, the earliest known forms of
the Folyzoa are found in the Ordovician rocks, and all the later
Palzeozoic formations abound in Polyzoan remains. Even in the
Ordovician rocks the Gymnolemata are represented by numerous
and very widely different types, and the primitive forms of the class
must have existed in Cambrian or in even earlier periods. The

POLYZOA. 613

Paleozoic Polysoa appear to be for the most part referable to the
Cyclostomatous division of the Gymnolemata, and no unequivocal
examples of the Chez/ostomata have been hitherto recognised in
any Palzozoic formation. The form described by the present
author from the Ordovician rocks as Appothoa? inflata is refer-
able to Stomazopora (as this genus is usually understood), and in
that case is Cyclostomatous, as also is the Aippothoa devonica of
Gehlert. It is, however, possible that the Palszeozoic genus Paées-
chara, of Hall, is really Cheilostomatous. While the Paleozoic
Polyszoa, therefore, must in the meanwhile be referred in a general
way to the Cyclostomata, it has to be borne in mind that many of
them exhibit very peculiar characters, and that certain forms are
apparently transitional between the Cyclostomata and the Chezlos-
tomata. It is, in fact, not improbable that fuller investigation of
the characters and structure of the Paleozoic /o/ysoa will render it
necessary to recast the classification of the Gymnolemata ; and steps
in this direction have already been taken by Mr Ulrich. It does
not seem possible, however, to accomplish this satisfactorily at
present, since we are not only still imperfectly acquainted with the
minute structure of many Paleozoic FPolyszoa, but there are various
Palzozoic organisms, the precise place of which in the zoological
series has not yet been ascertained with certainty. This is notably
the case with the great Palzozoic group of the Monticuliporoids,
which, for reasons previously given (see p. 352), have been here
placed provisionally beside the Ccelenterates, while they are regard-
ed by Lindstrom, Ulrich, and other authorities as belonging to the
Polyzoa. It is also not impossible that we may have in the Pale-
ozoic rocks representatives of other groups of the existing Polyzoa
than the Cyclostomata and Chetlostomata. Thus, the singular
genus Ascodictyon, of the Silurian, Devonian, and Carboniferous
rocks, may possibly be, as suggested by Mr Vine, a representative
of the Czenostomata, or may even be referable to the section of the
Entoproctous /olyzoa.

The earlier Secondary deposits (Trias and Lias) have hitherto
yielded very few remains of Folyzoa ; but numerous forms of this
class are known in the later Jurassic and in the Cretaceous rocks,
the Upper Chalk, in particular, being extraordinarily rich in the
remains of these organisms. In the earlier part of the Secondary
period, by far the larger number of the known odyzoa are still re-
ferable to the Cyclostomata, but in the later portion of the Cretaceous
period the Chezlostomata are likewise largely represented. In the
Tertiary rocks, again, not only are the remains of Po/ysoa abundant,
but the majority of the forms represented are now referable to the
Chetlostomata, the Cyclostomatous types undergoing a decided re-
duction, All the great divisions of the Tertiary rocks have yielded

614 MOLLUSCOIDEA.

more or less numerous /odyzoa (fig. 457); but the Upper Oligocene
of Germany, the Miocene deposits of France, Austria, Switzerland,

9 6 O".0.:

‘a. @@O

» @ "5
om,

Fig. 457-—Types of Tertiary Polyzoa. a, A few cells of Alicroporella violacea (Pliocene and
Recent), magnified; B, Cellepora coronopus, of the natural size, and a portion of the surface en-
larged (Pliocene); c, A small piece of Cellaria (Salicoruaria) crassa, of the natural size
and enlarged (Pliocene); p, Lawnulites guadrata, of the natural size, and a small portion of the
upper surface enlarged (Tertiary); E, A fragment of Scrzfocellaria elliptica, viewed from
behind, enlarged (Tertiary); Fr, A small piece of Crista denticulata (Tertiary), enlarged; G, A
fragment of Tubulipora flabellaris (Tertiary), enlarged; u, A fragment of Diastopora simplex,
enlarged (Tertiary); 1, A piece of Vixcularia Haidingeri, natural size and enlarged (Tertiary) ;
J, [dimonea fenestrata, natural size and enlarged (Tertiary); kK, Hornera reteporacea, natural
size and enlarged (Tertiary). (After Busk and Reuss.)

and Italy, and the Pliocene beds (‘‘ Coralline Crag”) of Britain,
have proved particularly rich in the remains of these organisms.
In the following general account of the characters and chief groups

CYCLOSTOMATA. 615

of the fossil Polyzoa, no attempt will be made to give a complete
review of the different families. Not only is the classification of
the fossil /olysoa in an admittedly unsatisfactory state, but the
characters of many of the fossil types cannot be rendered intelli-
gible without the free use of illustrations, even where these are
thoroughly understood ; while there are many types the structure of
which is at present only imperfectly known. Nothing further will
therefore be attempted here than to shortly characterise some of
the more important and more widely distributed groups, and to
indicate the chief forms of these and their general geological range ;
all the fossil types here referred to being provisionally distributed
between the Cyclostomata and the Cheilostomata.

SuB-ORDER I. CYCLOSTOMATA.

This sub-order, as has been previously seen, includes Gymno-
lematous Polyzoa, in which the cells are more or less tubular, the
cell-aperture being terminal, usually of the same diameter as the
tube itself, and not provided with a movable operculum for its
closure. In a large number of the Cyclostomata, the tubes (fig.
451, A) are free for a larger or smaller portion of their length, so
that the surface of the colony is partly formed by the lateral walls
of the zocecia; while in other types (fig. 456, B) the tubes are in
contact throughout their entire length, the cells thus opening at
right angles to the axis or surface of the colony, and the whole
exterior being thus occupied by the cell-apertures. This difference
probably expresses a genuine structural distinction, and upon it Mr
Waters has proposed to divide the Cyclostomata into the two divi-
sions of the Paralledata, with partially free tubes, and the Rectangu-
Jata, with the tubes in contact throughout.

In most of the Cyclostomata the calcareous walls of the cells are
pierced by smaller or larger pores, but in some cases the walls
appear to be completely imperforate. In many forms all the cells
are similar to one another, but in others (¢.g., in Heteropora) the
colony consists of two sets of tubes, which are similar in internal
structure, but differ in point of size. In other forms referred to
this sub-order an interstitial vesicular tissue appears to be developed
between the proper zocecia. ‘‘ Ovicells” are developed in certain
of the Cyclostomata, but they have not been observed in others, and
they do not play such a conspicuous part as they do in the C/ezlos-
tomata. In various forms of the Cyclostomata, finally, radiating
spines or ‘“‘rays” are developed in the cells, while the structures
previously alluded to as ‘‘closing-plates” and ‘“ tabule” are not
uncommonly present.

The Cyclostomata are the most ancient group of the Folyzoa,

616 MOLLUSCOIDEA.

being represented by numerous forms in all the great geological
formations from the Ordovician onwards. With a few possible ex-
ceptions, as already noted, the whole of the Paleozoic Polyzoa may
be provisionally referred to the Cyclostomata ; but while some of
even the oldest forms belong to quite normal groups of this sub-
order, others differ widely from the regular type, and will probably
be ultimately referred elsewhere. Leaving these last out of con-
sideration, the Cyclostomata may be said to attain their maximum
development in the Jurassic and Cretaceous rocks, a decided diminu-
tion in their numbers taking place in the Tertiary period.

Taking the normal groups of the Cyc/ostomata first, and leaving
out of sight certain comparatively unimportant types, the family of
the Crzszzde comprises a small number of dendroid forms, in which
the polyzoary consists of calcareous segments united by corneous
joints, the tubular zocecia being either uniserial or biserial (fig.
457, F). The type of this family is C7zsza itself, which is represented
by numerous Tertiary and recent species.

The family of the Zudbuliporide (Stomatoporide) comprises forms
in which the polyzoary is usually creeping and wholly adherent by
its under surface, or partially free and erect. The tubular zocecia
may be disposed uniserially, or biserially, or irregularly grouped,
their upper ends being more or less extensively free. The ovicells
are represented by ‘‘an inflation of the zoarium at certain points, or
a modified cell” (Hincks).

In the genus 77zulzpora itself the colony is more or less extensively
attached by its base (fig. 457, G), and the tubular zocecia are free for a
great part of their length and radiate from an excentric point. The
species of this genus range from the Cretaceous rocks to the present
day. The forms included under the head of Stomatopora (Alecto) differ
considerably in their characters. In one group of forms comprised under
this generic name the colony is completely adherent to foreign bodies,
and the tubular cells are more or less extensively immersed, being free
close to their mouths only; so that a more or less strap-shaped, often
branched frond is produced (figs. 451, A, and 459, B and C), the walls of
the zocecia being at the same time porous, and usually either biserial or
multiserial. In some forms (Pvodoscina), the polyzoary has the above
characters, but is partially free and erect. Forms of the type here in-
dicated are found in rocks as ancient as the Ordovician, while numerous
species still exist. On the other hand, there have been included in
Stomatopora various forms in which the polyzoary consists of a creeping
adherent network, formed of uniserial or sometimes alternatingly biserial
cells, which spring directly from each other, each new tube being pro-
duced from the anterior end of the lower surface of the preceding cell
(figs. 458 and 459,D). The tubes are thick-walled and destitute of pores,
and the colony often closely resembles an Az/opora inform. Indeed, the
only essential distinction between such colonies and Az/opora is to be
found in the fact, that in the typical species of the latter there appears to
be a creeping basal network from which the tubes are sent up at inter-
vals, instead of springing directly from one another ; but it is not clear

CYCLOSTOMATA. 617

how far even this distinction can be relied upon. Forms of this second
type occur from the Ordovician rocks onwards. It would seem that
these two groups of Stomatopore should be generically separated from one
another, as the differences above pointed out are of substantial import-

Fig. 458.—A specimen Fig. 459.—a, A fragment of shell with Stovzato-
of Stowzatopora dichotonza, pora auloporoides and S. inflata growing on it, of
from the Great Oolite, of the natural size, from the Cincinnati group (Ordo-
the natural size. (After vician) of America; B, Stomatopora auloporoides,
Zittel.) enlarged ; c, Part of the same, enlarged still further ;

D, Stomatopora inflata, enlarged; E, Fragment of
Hedevella Canadensis, from the Devonian rocks of
Canada, of the natural size and enlarged. (Original.)

ance. It would also seem certain that the Silurian and Devonian genera
Reptaria and Hederella (fig. 459, E), sometimes placed among the Corals,
should be referred to this family. In these doubtfully distinct genera the
colony is branched and adherent to foreign bodies by its lower surface,
the branches consisting of long, narrow tubular cells, which spring in an
alternating manner from one another, each branch being thus biserial.

Allied to the preceding is the family of the Dvastoporide, in
which the polyzoary is usually encrusting and discoid or fan-shaped,
though sometimes foliaceous and erect. The tubular cells are in

Fig. 460.—Mesenteripora (Bidiastopora) cervicornis, natural size and enlarged. urassic.
= b] >

great part immersed, their ends only being usually free, and the

peripheral part of the colony may be formed of small, angular

“verminal” cells. The species of Dzastofora, in a restricted sense

(=) ) 5)

form small crusts upon foreign bodies, and range from the Jurassic
. 5 4 . 5 . .

to the present day. Allied types appear in the Silurian rocks, and

618 MOLLUSCOIDEA.

have been referred by Mr Vine to the genus Drastoporella. The
foliaceous and erect forms of Dastopora are sometimes included
under the separate generic name of JZesenteripora, or, if consisting
of two layers of cells placed back to back, of Bzdiastopora (fig. 460).

Berenicea comprises forms which hardly appear to be separable
from Diastopora ; but the typical forms placed under this head con-
sist of crusts of superimposed cells. The genus has been quoted
from the Ordovician rocks, and there are numerous undoubted
Secondary, Tertiary, and Recent species.

Also related to the Zudbuliporide is the family of the Axtalophor-
zd@, in which the polyzoary is erect and free, rising from an expanded
adherent base, and formed of long tubular cells which usually open
all round the stems. The genus Lutalophora (Pustulopora) itself
ranges from the Jurassic to the present day, and has the cells open-

Fig. 461.—Entalophora (Pustulopora) cellarioides, of the natural size and enlarged. Jurassic.

ing irregularly on all sides of the branches. ‘The name of Sfevopora
is usually given to forms essentially similar to the preceding, but
having the cells so disposed that the cell-mouths form simple circles
or spirals round the stems. Species of Sszropora appear as early
as the Silurian period, and numerous Secondary and Tertiary types
are known, while the genus still survives.

In the family of the /dmoneide, the polyzoary is erect, and almost
always more or less branched, the branches being usually round,
and sometimes anastomosing with one another. The tubular cells
open on one side only of the polyzoary. In the genus Ldmonea
itself (fig. 457, J) the cells are disposed in transverse or oblique
rows on each side of the front faces of the branches, which are
divided mesially by an angulation or longitudinal keel. The genus
ranges from the Chalk to the present day. In the genus Hornera (fig.
457, K), again, the polyzoary is branched and sometimes reticulated,
the cells opening on one side of the branches only, their mouths
being commonly placed in somewhat rhomboidal spaces marked
out by wavy anastomosing ridges. Interstitial pores occur between

CYCLOSTOMATA. 619

the cell-mouths, and may be developed on the non-celluliferous
dorsal surface. The earliest undoubted species of Hormera occur
in the Cretaceous rocks, and there are numerous Tertiary and recent
types.

The family of the Zichenoporide comprises discoid polyzoaria,
which sometimes in process
of growth become confluent,
Or may even become mas-
sive, the colony being fixed
by a broad adherent base
or by a narrow peduncle.
The zocecia are tubular and
CECE, and are in complete Fig. 462.—Botryllopora socialis, from the Devonian

rocks of Canada. a, A small colony attached to a
contact throughout, Or are coral, of the natural size; 4, A single disc of the same,
free towards their extrem- Suse) eee ortebereame, calargec
mies, Lhe walls of the
zocecia may be porous or imperforate, and the proper zocecia may
be separated by intermediate cancellated or porous spaces.

The most ancient type of the Lichenoporid@ appears to be the genus
Botryllopora of the Devonian rocks (Hamilton formation) of Canada and
the United States. In this genus (fig. 462) the polyzoary consists of
separate or confluent discs, which are attached by the whole of the under
surface to foreign bodies. Each disc shows a series of elevated ridges
or ribs, which radiate from a central area and are separated by inter-
vening furrows. The ribs carry the apertures of the tubular zocecia, and
the spaces between them appear, in well-preserved specimens, to be
minutely porous. The genus Lichenopora (Discoporella) comprises
forms in which the polyzoary has the form of a simple disc or of
numerous confluent discs, each disc being composed of tubular cells,
which are arranged in lines radiating from a central space, and separated
by intervening intervals. The zocecia are free towards their mouths, and
project above the general surface ; and the spaces between them, as well
as the central area, are occupied by smaller interstitial tubes or “ cancelli.”
In some forms, both the proper zocecia and the “ cancelli” are provided
with delicate capitate “rays.” In many structural features Lzchenopora
closely approaches Heteropora, but the zocecia of the latter are in contact
throughout, and are not free towards their extremities. The forms with
confluent discs are sometimes separated to constitute the separate genus
Radiopora. ‘The earliest types of Lichenopora (if considered as embrac-
ing Radiopora) appear in the Trias ; while the genus has Jurassic, Cre-
taceous, and Tertiary representatives, and still survives at the present
day. Inthe genus Domopora (Defrancia) the polyzoary is discoidal or
massive, simple or lobed, attached by the whole base or by a stalk, or
sometimes free. The zocecia are “ disposed in radiating lines, consisting
of one or more series, on the free extremity of the stem or lobes”
(Hincks), and their mouths do not project above the general surface.
The walls of the zocecia are penetrated by numerous delicate tubull.
This genus should perhaps be removed to the family of the Heteroforide.
The species of Domopora appear first in the Jurassic, and are abundant
in the Chalk, while Tertiary and living forms are also known.

620 MOLLUSCOIDEA.

The singular genus A/weolaria (fig. 463) may likewise be associated
with the Lzchenoporide—the only described species being the A. semzz-
ovata of the Red Crag (Pliocene) of Britain. In this remarkable form the
polyzoary is massive and globose, consisting of numerous mushroom-
shaped discs or cups, which are arranged in radiating and diverging
lines, the cups of each vertical series springing directly from one another
(fig. 463, C); and the different groups being so disposed that they form
a series of thick concentric layers. Each concentric stratum is thus
made up of a number of discs which are firmly united by their edges,
but are free towards their bases; and each disc is enclosed in a strong
calcareous membrane, the upper surface alone being free, and ex-

45

Fig. 463.—A lveolaria semiovata, from the Red Crag (Pliocene) of Britain. a, A specimen of
the natural size ; B, A portion of the surface enlarged ; c, Part of a vertical section enlarged ; D,
Part of a tangential section enlarged. (Original.)

hibiting the apertures of the cells. The laterally-united discs are poly-
gonal, and the surface (fig. 463, A and B) thus shows a number of poly-
gonal cups bounded by strongly elevated ridges, each of which, in turn,
exhibits a raised median line corresponding with the free edge of the
epithecal membrane. For the same reason, tangential sections (fig.
463, D) show that the tubes are divided into polygonal groups, each of
which is bounded by a strong external wall. The tubes themselves are
in close contact throughout, their mouths not projecting above the
general surface. The walls of the tubes are apparently completely im-
perforate ; but “‘closing-plates” or “ tabule” are often developed.

The family of the rondiporide (Theonoide) includes forms in
which the polyzoary is composed of long contiguous tubes, the

CYCLOSTOMATA. 621

mouths of which are commonly disposed in groups of different size
and form, separated by porous or imperforate interspaces. The
genera Frondipora and Fasciculipora (Fungella) are both represented
by species which range from the Chalk to the present day, and there
are several other genera which are found in the Cretaceous or
Tertiary rocks. Of the Tertiary forms the most interesting is the
genus Fasacularia (Meandropora), which is exceedingly abundant
in the Red Crag (Pliocene) of Britain. In this genus (fig. 464) the

Fig. 464.—Fascicularia (Maeandropora) cerebriformis. ‘Tertiary.

polyzoary is more or less massive, generally globose, and often of
large size, composed of long calcareous tubes arranged in bundles,
the tubes of each bundle being in contact, and the bundles being
enclosed laterally in a calcareous membrane. The bundles diverge
from the base of the colony, and may be connected by horizontal
and concentric plates, or may be confluent by their sides and thus
give rise to vertical convoluted laminz. ‘The tubes are destitute of
“rays,” but exhibit horizontal ‘‘ tabule,” and have minutely porous
walls. In the common /asccularia aurantium of the Red Crag the
tubes open on the surface in sinuous anastomosing ridges, while in
the allied /: fubzpora, of the same formation, they open on rounded
eminences.

The family of the eferoporide is in some important respects
related to that of the Lzchenoporide, and comprises the genera
fleteropora and Heteroporella. ‘The polyzoary in this family may
be erect and branched, or may be encrusting ; and is composed of
tubular zocecia which are interspersed among similarly tubular but
somewhat smaller ‘‘cancelli,” all the tubes being in close contact
throughout, and the mouths of the zocecia not projecting above the
general surface. The walls of the zocecia and interstitial tubes or
cancelli are penetrated by minute tubules, which place contiguous
cells in communication (fig. 456); and in some species at any rate,
delicate radiating spines (‘‘rays”) are developed. There is also
generally a larger or smaller number of “‘ closing-plates ” or ‘‘ tabulz,”
which are principally developed in the deeper parts of the colony.
In the genus feteropora itself, the colony is erect and branched, the
tubes being vertical in the centre of the branches, but bending out-

622 MOLLUSCOIDEA.

wards to reach the surface, their walls being considerably thickened
in the outer part of their course (fig. 456, 8). The earliest forms of
Fleteropora appear in the Jurassic rocks, and the genus has survived
to the present day. The forms included by Busk in Heteropore/la
are Cretaceous and Tertiary, and the polyzoary is said to differ from
that of He¢eropora in being discoid and encrusting.

The family of the Fenestelide or “ Lace-corals” constitutes one
of the largest and most important groups of the Paleozoic Polyzoa,
no Secondary or Tertiary types belonging to this family having been

D

Fig. 465.—Heteropora pelliculata, Waters (=H. neozelanica, Busk), a recent species of
Heteropora. A, A fragment of the polyzoary of the natural size; B and c, Portions of the surface
of different specimens, “enlarged, showing the apertures of the zocecia and cancelli; p, A portion
of the surface of another specimen in which the mouths of the cancelli and some of the zocecia are
in places covered by a calcareous pellicle, enlarged. (After Busk, Waters, and the Author.)

hitherto recognised. In all the members of this family the polyzoary
is reticulated, generally fan-shaped or funnel-shaped, and composed
of rigid, calcareous, parallel or slightly diverging branches, which may
be united by cross-bars or “‘ dissepiments,” or may be sinuous and
may unite regularly by anastomosis ; the frond coming in both cases
to be perforated by symmetrically disposed, sub-quadrate or oval
spaces or ‘‘fenestrules” (figs. 466 and 467). The zocecia have the
form of short, utricular tubes, arranged in two or more series on one
side only of the branches, the reverse side being non-poriferous, and
being commonly finely striated. When true “ dissepiments” are
present, they are non-poriferous. ‘The mouths of the zocecia are

CYCLOSTOMATA. 623

more or less circular, and are often provided with a projecting lip or
‘¢ peristome.”

The minute structure of the polyzoary in the /eneste/ide@ appears
to be very uniform. ‘The cells themselves are formed of a layer of

Fig. 466.—Fenestella Lyelli. a, Natural size; 4, Portion enlarged ; c, Cells and spines in
profile. From the Carooniferous rocks of Canada. (After Dawson.)

perfectly homogeneous compact calcite, which is strengthened by a
basal striated membrane; while the reverse or non-poriferous side
of the polyzoary is composed of a thick stratum of calcareous tissue

te

SS

Fig. 467.—Minute structure of Fenestella tuberculocarinata, from the Carboniferous rocks of
Scotland. a, Section taken parallel to the non-poriferous surface, showing thickened tubes (for
the support of ‘‘avicularia” ?), enlarged. , Section parallel to the celluliferous surface of the
polyzoary, showing the biserial cells (c): d, Dissepiments ; 4, Fenestrules. (Original.)

traversed by exceedingly minute tubuli, the direction of which is
perpendicular to the surface, and which communicate to thin sec-
tions of this region of the skeleton an exceedingly characteristic

624 MOLLUSCOIDEA.

appearance (fig. 453). In some cases, as previously noted, the dor-
sal or non-poriferous side is traversed by remote, thick-walled, and
comparatively large tubes (fig. 467, A), which may project above
the surface of the polyzoary, and which may, perhaps, have served
for the support of processes similar to the ‘‘avicularia” of the recent
FPolyzoa. In certain forms of the Feneste/lide (species of Fenestella
and Polypora), it has been shown by Mr John Young that the poly-
zoary was furnished on its margins or external surface with certain
remarkable appendages, which were originally described by Professor
Martin Duncan and Mr Jenkins under the name of Paleocoryne,

Ts J,
Y LE /)//

Fig. 468.—Branched appendage of a Fenestellid (the Paleocoryne radiatum of Duncan and
Jenkins), enlarged fifteen diameters. (After Martin Duncan and H. M. Jenkins.)

and which were regarded by these observers as belonging to the
fTydrozoa. The appendages in question (fig. 468) are of small
size, and have the form of short, robust, calcareous stems, which
spring from an expanded base, and are usually marked with longi-
tudinal flutings or superficial granulations, while the free extremity
generally terminates in a whorl of similarly fluted and ornamented
cylindrical processes. In some cases, as shown by Mr John Young,
the terminal processes may be curved or hooked, or they may be
even united by lateral cross-bars. The observations of Mr Young
prove conclusively that the structures described under the name of
faleocoryne truly form parts of the Polyzoan to which they are

CYCLOSTOMATA. 625

attached, since thin sections prove the absolute continuity of the
substance of the two; while the processes themselves consist, as
does the polyzoary from which they spring, of an external finely-
tubulated layer and an internal homogeneous stratum. The nature
and use of these singular appendages cannot at present be more
than guessed at.

As regards the chief types of the Fevzestellide, the genus Fenestella
itself ranges from the Silurian to the Permian inclusive, and comprises a
large number of species, the greater part of which belong to the Devonian
and Carboniferous rocks. In this genus (figs. 467, 468, and 469, Cc and

ELI

Gh
ty

ry

on 22 es }

pie ; a MH lt

aE 5 up a

aA £o% boy

ese 38 on } \

2ak7 \' /

eax eo tale g LAY

oo gs ALP

2 150 9 2 One4,

oe iee ee!

© €> LY 4a Ss oe)

23 LAMY PS
\ eg Pe UH RO
< Se :

Fig. 469.—A, Poriferous side of Polypora rigida (Devonian); B, Non-poriferous side of the
same ; Cand D, Poriferous and non-poriferous sides of Henestella biseriata (Devonian) ; E, Section
of Phyllopora sp. (Devonian), showing the anastomosing branches and the form and arrangement
of the cells; Fr, Non-poriferous side of the same; G, Transverse and vertical section of Ca7-
tnopora Hindei (Devonian), showing the greatly developed keels, with the biserial cells at their
bases ; H, Section of the same parallel with the poriferous face ; 1, Part of the non-poriferous side
of the same. All the figures are enlarged. (Figs, a—p are after Hall; =E—1 are original.)

D), the polyzoary is fan-shaped or infundibuliform, the cells being de-
veloped on one side only, this being generally, if not always, the zzer
side of the colony. The branches are straight, and are connected at
short intervals by regularly placed, non-poriferous cross-bars, or “‘ dissepi-
ments.” The zocecia are always biserial, the two rows of each branch
being separated by a median ridge or keel. In its general structure the
Devonian genus Carinopora (fig. 469, G—I) resembles Fenestella, the poly-
zoary being funnel-shaped, with the cells opening on the zzszde, and each
branch having a double row of cells separated by a median keel. In this
genus, however, the keels on the branches are enormously developed,
and the external aspect of the polyzoary resembles that of Phyllopora.
The genus Sescoscinium, also from the Devonian rocks, is considered
by Ulrich as identical with Carvinopora, but in this case the zocecia open
WAGES IIe 2 R

626 MOLLUSCOIDEA.

on the oztstde of the funnel-shaped polyzoary. The remarkable De-
vonian genus Unztrypa, again, resembles the two preceding types in
general structure ; but the projecting keels which separate the two rows
of cells on each branch are widened at their summits, and are connected
with one another by thin lateral processes placed at variable distances.
In the Carboniferous genus Pézlopora (fig. 470) are included forms which
agree in essential structure with /emestel/a, but differ in the feather-like
form of the frond, the polyzoary having a central stem which gives off
lateral branches in a pinnate manner, these latter being connected by
dissepiments separated by oval fenestrules. The genus Archimedes
(Archimedipora) is another remarkable Carboniferous type, in which the
general structure is like that of Fevestel/a, but the reticulate polyzoary is
wound in an obliquely spiral manner round a central screw-like axis (fig.
471,c). The genus Helzcopora has a similarly spiral zoarium, but there

mil

yi (4

Ne
i

See

ANGLES
STF titan
lg

’ mn

ay

Fig. 470.—Ptilopora pluma ; the right-hand figure of the natural size, the left-hand
figure enlarged. Carboniferous.

is no central axis developed. Lyvofora, from the Carboniferous rocks of
North America, resembles /ezested/a in general features ; but the net-like
polyzoary is bounded by solid lateral supports, which spring, like the two
branches of the letter U, from a small base of attachment. Lastly, the
genus Fenestralia, likewise from the Carboniferous rocks of North
America, differs from /eveste//a principally in the fact that there are wo
rows of cells on each side of the median keel in each branch.

The Carboniferous genus Actznostoma resembles Fenestella in having
a fenestrated polyzoary which is poriferous on one side only; but the
branches are not keeled, the cell-mouths are furnished with radiating
teeth or “‘ rays,” and the zocecia have a second supplementary pore close
to the proper aperture. The widely distributed genus Polyfora (fig. 469,
A and B, and fig. 471, @) agrees with Femeste//a in general structure, but
the branches are not keeled, and there are from three to six rows of cells
to each branch. As in Fezestel/a, however, the branches are connected
by solid, non-poriferous “ dissepiments.” On the other hand, in the genus
Phyllopora (the Retepora of many authors) the branches which compose
the funnel-shaped polyzoary are not joined by dissepiments, but are
sinuous, and anastomose with one another at short and regular intervals,
so as to give rise to a symmetrically disposed system of “ fenestrules ”
(fig. 469, E and F). The zocecia are placed on the inner side of the frond,

CYCLOSTOMATA. G27

each branch having from two to five rows of cells. The species of Phy/-
lopora range from the Ordovician rocks to the Permian. Lastly, in the
Carboniferous genus Govzocladia the branches anastomose as in Phy/-
lopora, but they are keeled on both sides, and there are three or four rows
of cells on each side of the median keel on the poriferous side.

The family of the Acanthocladide comprises a number of Palez-
ozoic Polyzoa which are in many respects allied to the Fenesteliide.

st i \\
iN \

WA
a) \Y \

on = =

‘ = OL O=O-0

Fig. 471.—Carboniferous Polyzoa. a, Fragment of Polypora dendroides, of the natural size—
Ireland ; 2’, Small portion of the saiue, enlarged to show the cells; 6, Piznatopora (Glauconomte)
pulcherrima, a fragment, of the natural size—Ireland; 4’, Portion of the same, enlarged; c,
The central screw-like axis of Archimedes Wortheni, of the natural size — Carboniferous,
America; ¢’, Portion of the exterior of the frond of the same, enlarged; ¢’, Portion of the
wai of the frond of the same, showing the mouths of the. cells, enlarged. (After M‘Coy and

all.

In this family the polyzoary is ‘‘ poriferous on one side only, den-
droid, pinnate, or forming fenestrated expansions, and consisting of
strong central stems and numerous smaller lateral branches which
proceed from their opposite margins. The lateral branches are free,
or may unite (in the fenestrate genera) with those of the adjacent
branches. Non-poriferous dissepiments are absent ” (Ulrich).

628 MOLLUSCOIDEA.

The genus Acanthocladia is Carboniferous and Permian, and possesses
a polyzoary which is bilaterally branched in a single plane, and which is
celluliferous on one side only, the reverse side being solid and striated.
The zocecia are placed on the main stem and branches, and are multi-
serial. The Carboniferous genus Piznatopora (the Glauconome of many
authors) resembles the preceding in general form (fig. 471, 6 and 6’), but
the cells are biserial, and the stems have a more or less well-developed
keel. The Carboniferous genus Septopora resembles Pinnatopora gen-
erally, but becomes fenestrated by the union
of the lateral branches of the polyzoary ; while
the same thing occurs in the Permian genus
Synocladia. In this last genus the lateral
branches are directed obliquely upwards, and
carry two rows of pores each, while the main
stems carry from three to five rows of pores
separated by a median keel.

The families of the Ptlodictyonide, Stic-
toporide, and Cystodictyonide may be briefly
considered together, since they contain
Palseozoic olyzoa which are superficially
very similar to one another, and which are
in many respects really allied, though they
differ in the internal structure of the poly-
zoary. Owing, however, to the fact that
various types have been hitherto insuff-
ciently examined by means of microscopic
sections, it is not always possible to separ-
ate these families accurately, or to refer a
particular form to one or other of them.
The family of the tlodictyontide, more
especially, cannot at present be precisely
defined, since the structure of the type-
species of the genus /#lodictya—viz., the
P. lanceolata, Goldf. sp. of the Silurian
Fig. 472.-_A specimen of yocks—has not yet been thoroughly in-

Ptilodictya (Heterodictya) gi- ; s
gantea, from the Devonian vestigated. Judging, however, from ex-
rocks of Canada, of the natural :

size. The polyzoary is splitin ternal characters alone, it would seem
half along tis median plane, and orobable that the Devonian Polyzoammmte:

shows in places portions of the : :
striated calcareous membrane scribed by the writer under the name of
produced by the coalescence of : 3 é : :
the two layers of cells compos- Fleterodictya gigantea IS Congeneric with
ee ee Ptilodictya lanceolata, as understood by
Lonsdale ; and we may therefore take the
former as exhibiting the essential characters of the genus P#/odictya.
The polyzoary in Ptilodictya (Heterodictya) gigantea has the form
of a flattened, unbranched, two-edged frond, which reaches several
inches in length and an inch or more in width (fig. 472), with a

thickness in the centre of about two lines. The polyzoary consists

CYCLOSTOMATA. 629

of two strata of tubular zocecia, the bases of which unite to form a
median calcareous striated layer, along the line of which the frond
readily splits. The zocecia are disposed in parallel longitudinal
lines, those of the central rows being themselves longitudinal, while
those of the lateral regions of the colony are directed obliquely
upwards and outwards, the arrangement of the cells being thus
feather-like (fig. 472). The two flattened surfaces of the polyzoary
are wholly covered by the minute, oval cell-apertures. As regards
the internal structure, the zocecia have strong, fibrous and imper-
forate walls, and the cells are traversed by numerous transverse
calcareous partitions or ‘“‘tabulz,” many of which, however, are
incomplete, and do not extend the whole way across the tube in

~/Myk SS
BRE|A 6.

I-REZ2
L<2O
z=
ES Ir “>
MY A~ GN Ug
rw EN A

(

Fig. 473-—Minute structure of Ptzlodictya (Heterodictya) gigantea, Nich., from the Cornifer-
ous Limestone (Devonian) of Canada. a, Vertical and longitudinal section, showing the well-
developed tabulz ; 8, Vertical and transverse section, showing the incomplete condition of many
of the tabule; c, Tangential section. All the figures are enlarged eighteen times. (Original.)

which they occur (fig. 473). The cells run obliquely to the
surface, and are in contact throughout, no interstitial tubes or
cells being developed.

If the form just described is to be taken as a true Pe/odictya, then
the essential characters of the genus /#/odictya and of the family
Piilodictyonide are that the polyzoary is leaflike, and composed of
two layers of tubular zocecia, which are attached back to back, a
spurious mesothecal membrane being formed by the coalescence of
their bases ; the cells are in contact throughout, no interstitial cells
being present; the cell-mouths are simple; and cross-partitions or
“‘tabule” are abundantly developed in the tubes. Owing to the
uncertainty which at present attaches to the limits of the family
Ptilodictyonide, it is impossible to speak definitely as to the geolog-
ical range of the family; but P. Zanceolata, Goldf., is Silurian, and
P. (Heterodictya) gigantea is Devonian.

-There are various Paleozoic Polyzoa that have been commonly
placed in the genus P¢zlodictya, which agree with the preceding in vari-
ous general characters, but differ in important structural features. Thus,

630 MOLLUSCOIDEA.

there are numerous Ordovician and Silurian types, of which we may
take Pizlodictya (Stictopora ?) falciformis as an example, in which the
polyzoary is in the form of an unbranched, or slightly branched, flattened
frond (fig. 474, a), composed of two layers of cells placed back to back, a
more or less recognisable calcareous membrane (the “ mesotheca” of
Hall) being produced by the coalescence of their bases. In the par-
ticular type here selected as an example of this group the polyzoary is
usually unbranched, sickle-shaped, and thin-edged, the margins being
longitudinally striated, and occasionally perforated by the apertures of
minute and imperfect cells. The zocecia (figs. 474, c, and 475, A) are tubu-
lar, and in close contact throughout, no interstitial cells being developed;

f

Fig. 474.—Ptilodictya (Stictopora ?) Fig. 475.—Structure of Ptilodictya (Sticto-
Jalciformis. a, Small specimen of the fora?) falciformis. a, Tangential section, en-
natural size; 6, Cross-section, showing larged, showing the lozenge-shaped tubes; B,
the shape of the frond; c, Portion of the ‘Transverse section, enlarged, showing the arrange-
surface, enlarged. Trenton Limestone ment of the two layers of cells. (Original.)
and Cincinnati Group, America. (Or-
iginal.)

and the apertures are oval or lozenge-shaped. The tubes (fig. 475, B)
are rectangular to the flat surfaces of the polyzoary, and they do not
appear to be traversed by “ tabulz.” An essentially similar structure is
exhibited by the Silurian Polyzoan described by Hall under the name of
Clathropora frondosa, which constitutes the type of the genus Clathro-
pora. in this case, however, the polyzoary is composite, and is formed
by the inosculation of a series of thin leaf-like bilaminar fronds, which
anastomose in such a way as to leave regularly placed oval perfora-
tions or fenestrules ; the minute structure of the tubes resembling that
observed in Pétlodictya falciformts.

A number of Ordovician, Silurian, and Devonian Folyzoa, more
or less closely allied in general characters to the types treated of
above, have been placed in the family of the Szctoporide. It does
not, however, appear possible at present to give any precise defini-
tion of the family, since Hall and Ulrich, who have more especially
studied the forms in question, are not agreed as to the limits of the
genus Stictopora, the type of the whole family. The forms which
have been generally included under the name of Sécfopora are
compressed or leaf-like Folysoa, consisting of two layers of cells

CYCLOSTOMATA. 631

placed back to back, and usually more or less branched, the edges
of the frond being non-celluliferous, and the cell-mouths being oval
or circular.

The family of the Cystodictyonide is defined by Ulrich as com-
prising forms of Paleeozoic Polyzoa in which the polyzoary consists

t
Seip
ie
MDa

oe
ditt

Fig. 476.—Cystodictya Gilberti, from the Devonian rocks of North America. a, Part of the
polyzoary, enlarged (after Hall); B, Tangential section taken just below the surface, showing
the trilobed apertures of the cells ; c, Tangential section taken at a deeper level than the preced-
ing, showing the interstitial vesicular tissue ; D, Part of a specimen split along the median plane,
enlarged ; E, Part of the surface, enlarged, showing the porous intercellular tissue; F, Cross-
section of the polyzoary, enlarged. (Original.)

of two layers of cells placed back to back, with tubular zocecia,
which are separated by irregular vesicular tissue. The cell-mouths
have a small tooth-like
projection on each side,
giving the aperture a char-
acteristic trilobed form
Ge 476, B); and the
margins of the zoarium
are sharp or rounded, and
are non-poriferous.

As an example of this
family may be taken the

Devonian Cystodictya Gil- Fig. 477-—Fragment of Coscinium (Cosctnotrypa)
bert2 (fig. 476), in which ¢76rtforme, of the natural size and enlarged. Devonian,

the polyzoary is irregularly ered Mey)

branched, and consists of

two layers of cells which open on its opposite surfaces, and are united
by a striated mesothecal layer formed by the union of the bases of the

632 MOLLUSCOIDEA.

cells (fig. 476, D and F). The cell-mouths are trilobed, and the surface
in well-preserved specimens exhibits shallow interapertural pits (fig. 476,
E), which in thin sections are seen to be produced by irregular vesicles
occupying the intervals between the proper zocecia (fig. 476, C). This
species is abundant in the Devonian rocks of North America, but is
placed by Hall in the genus Szzctopora. The genus Coscinium of Key-
serling (= Coscinotrypa, Hall) possesses an internal structure essentially
similar to that of Cystodictya, but the polyzoary forms a wide netted
expansion (fig. 477), perforated by numerous oval “fenestrules,” the
edges of which are sharp, and are non-celluliferous. In this genus the
interstitial vesicular tissue between the zocecia is largely obliterated by
a finely tubulated calcareous deposit (fig. 455, C).

The family of the Ceramoporide has been founded by Mr Ulrich
for a number of Paleozoic FPolyzoa in which the polyzoary is usually
incrusting, the cell-apertures being triangular or ovate, generally with
a prominent and arched lip on one side. The type-genus of this
family is Ceramofora itself, which ranges from the Ordovician to the
Devonian, and forms thin crusts upon corals, shells, &c. The cells

Fig. 478.—Fragment of Fig. 479.—Rhabdomeson gracile, from the Car-
Rhonbopora Hamtlton- boniferous rocks of Scotland. a, Tangential section,
ensis, of the natural size enlarged. B, Vertical section, enlarged, showing the
and enlarged. Devonian, central tube: c, The proper cell- “mouth ; V, ~The
Canada. (Original.) outer chamber or ‘‘ vestibule.” (Original.)

in this genus are angular, with a strongly arched lip and oblique
aperture, and they usually radiate from one or more centres of
growth.

Finally, the family of the Aabdomesontide includes a number of
small Paleozoic Polyzoa, in which the polyzoary is ramose, and is
composed of slender, cylindrical, solid or tubular branches, the cell-
apertures being placed on all sides of the branches (fig. 478). The
proper cell-mouth is placed at a little distance below the surface,
and opens into a so-called “vestibule” or outer chamber, which
constitutes the apparent cell-aperture on the surface (fig. 479, B).
The cavities of the zocecia may be crossed by a limited number
of ‘“‘tabulee,” and the apertures are sometimes provided with per-
forated ‘closing-plates” ; while thick-walled tubes (for the support

CHEILOSTOMATA. 633

of “‘avicularia” ?) may be developed in the interzocecial spaces (figs.
479, A, and 455, C).

In the genus Rhombopora (fig. 478) the zocecia radiate in all directions
from an imaginary axis, and the proper cell-apertures are placed at the
bottom of oval or rhomboidal “vestibules.” The species of this genus
range from the Silurian to the Carboniferous inclusive. The genus
Rhabdomeson is principally, if not exclusively, Carboniferous in its range,
and comprises forms which are essentially similar to Rhombopora in
general characters, but differ in the fact that the zocecia radiate in all
directions from an axial calcareous tube (fig. 479, B) running up the
centre of the stems.

SUB-ORDER II. CHEILOSTOMATA.

In this sub-order are included all those Gymnolematous Polyzoa
in which the aperture of the cell is subterminal, of less diameter
than the cell itself, and usually closed by a movable lip or operculum
(fig. 480). The essential char-
acter of the Chezlostomata is,
therefore, the position of the
cell-mouth on the anterior face
of the zocecium, instead of at
its extremity. The aperture
can also be usually closed by
a semicircular movable lid,
which may or may not be
calcified, and which is almost
always destroyed in fossilisa-
nome, the “extent to which
calcification of the ectocyst \
HOOUS in the Chetlostomata Fig. 480.—Cells of Cheilostomatous Polyzoa,
pee eerily im different types ised Mage Opream, & Oval
Sometimes the polyzoary re-
mains completely corneous (as in the //ustrid@), in which case it is
incapable of preservation in the fossil condition ; whereas in other
cases the entire cell-wall may be calcified. There are many forms,
however, in which an intermediate state of parts obtains, the hinder
and lateral portions of the cell being calcified, wnile a larger or
smaller area of the anterior wall, particularly in the neighbourhood
of the mouth, remains in a membranous or horny state. Hence, in
such cases the cells, in the fossil condition, are more or less largely
open in front. In other cases, where the polyzoary is incrusting,
the posterior wall of the cells may be uncalcified.

“ Avicularia” and ‘‘vibracula” aré commonly developed in the
Cheilostomata, and in the case of the living forms afford valuable
characters in classification. In fossil forms, however, these minute

\\\ :
i \

634 MOLLUSCOIDEA.

appendages can hardly ever be preserved, though their former exist-
ence may be inferred from the presence of “special pores” which
are usually placed near the mouth, or the existence of thickened
tubular supports which penetrate the substance of the polyzoary and
are thus recognisable in thin sections (fig. 455, A).

The “ovicells” or marsupial pouches of the Chezlostomata are
very characteristic structures, though they may be wanting, or may
be so deeply immersed in the skeleton as to be inconspicuous.
Most usually, the ovicells have the form of globular or helmet-
shaped sacs (fig. 480, B) appended to the anterior end of the cells,
and placed in communication with the cavity of the latter by special
openings.

New cells are produced by budding from the anterior ends or
lateral margins of the pre-existing cells, and all the zocecia remain
to some extent directly connected with one another. In the C4ez/-
ostomata generally contiguous cells are placed in communication
with one another by means of perforated portions of their cell-walls
(“‘ rosette-plates ”), the number and position of these structures
varying in different cases. These ‘ rosette-plates” correspond with
the pores which are so commonly developed in the cell-wall of the
Cyclostomatous Polyzoa, but their presence can only be detected
in the fossil forms in cases where the condition of preservation is
exceptionally good.

As regards the distribution of the Chezlostomata in time, it is
doubtful, as previously noted, if any representatives of this sub-order
have hitherto been detected in the Paleozoic rocks, though there
are some Paleozoic types (such as Paleschara) which may belong |
here. On the other hand, in the Secondary rocks, from the Jurassic
onwards, we meet with an abundance of the remains of Cheilosto-
matous Polysoa, while a vast number of Tertiary forms have been
described. As the characters which separate the different groups
of the Chezlostomata are for the most part difficult of recognition,
and as the classification of the group is still in a more or less
unsettled condition, it will be necessary here to deal with the
families of the sub-order very briefly. The arrangement here
followed is, in the main, that adopted by Hincks, but only those
families which from their size or paleontological significance are of
special importance, are alluded to.

In the family of the Ce//ularitde, the polyzoary is erect and
dichotomously branched, with linear divisions, composed of cells
arranged in the same plane. The genus Ce//ularia has no fossil
representatives, but Scrupocellaria (fig. 457, E) is known both by
Recent and Tertiary species. |

In the family of the Ce//aritde (Salicornariade of Busk), the poly-
zoary is erect and dichotomously divided, the branches being cylin-

CHEILOSTOMATA. 635

drical, and the zocecia disposed round an imaginary axis. The type-
genus is Ce//aria (=Saticornaria), in which the surface (fig. 457, C)
is divided into rhomboidal or hexagonal spaces, representing the
front walls of the cells; and irregularly disposed avicularia are present.
The species of this genus range from the Chalk to the present day.

The family of the Vencularitd@ is typified by the genus Vincularia,
the species of which are Cretaceous, Tertiary, and Recent. In this
genus (fig. 457, 1) the polyzoary is erect, branched, and rigid, the
zocecia being disposed alternately round an imaginary axis, and hav-
ing a raised border in front.

The great family of the AZembraniporide includes forms in which
there is a calcareous or corneo-calcareous polyzoary, composed of
horizontal and contiguous cells, the colony forming an incrusting
expansion, or in some cases giving rise to an erect growth. The
zocecia are generally separated by raised margins, the front wall
remaining more or less uncalcified. Owing to the membranaceous
structure of the anterior walls of the cells, the front of the zocecia in
fossil specimens always appears to be more or less largely open. In
the extensive genus AZembranipora (fig. 481), the cells are surrounded
by a well-marked elevated border,
the space included within which
is technically spoken of as the
fates the entire “area” may
be occupied by a horny mem-
brane, in which the true cell-aper-
ture is pierced; and when this is
Mieweise the entire “area” in the
fossil condition is open. In other
cases a larger or smaller part of the :
membrane occupying the “area” ,, Mg. #81: -Membranitors ocean, show
may be calcified, the remainder Upper Cretaceous.
being left permanently soft. In
these cases the “‘ area” of the cell in fossil examples exhibits a more
or less extensive deficiency or ‘‘ aperture,” which is always of greater
size than the proper cell-mouth itself. The polyzoary in the genus
Membranipora is always incrusting, and the numerous species of the
genus range from the Chalk to the present day. A similar geological
range 1s possessed by the genus Bzfustra, in which the polyzoary is
generally erect and foliaceous, and is typically composed of two layers
of cells placed back to back.

In the family of the J%croporide the polyzoary is incrusting, or
sometimes free and unilaminar, and the zocecia resemble those of
the preceding family in being surrounded by elevated margins (fig.
482, A), but the front wall of the cells is completely calcareous.
The genus Aficropora (fig. 482, a) comprises forms in which the

636 MOLLUSCOIDEA.

cell-mouth is surrounded by a thickened border, and the species con-
tained in it range from the Chalk to the present day.

The family of the C7zé77linide comprises forms in which the poly-
zoary 1s sometimes incrusting, sometimes free and foliaceous. ‘The
zocecia have their front wall more or less fissured, or traversed by
radiating ribs separated by intervening furrows, which may be closed
or perforated (fig. 482, B). The type-genus of this family is C7zd-
rilina itself (=Lepraha in part), of which both recent and fossil
forms are known, the earliest of the latter appearing in the Cretaceous
deposits.

The family of the Wicroporelide also includes a number of the
incrusting or erect types of Polyzoa which were included by older

Fig. 482.—a, Cells of Wicropora complanata (Tertiary and Recent), enlarged; B, Cells of
Cribrilina radiata (Cretaceous, Tertiary, and Recent), enlarged; c, Cells of MJzcroporella inz-
pressa (Tertiary and Recent), enlarged. (After Hincks.)

writers under the comprehensive name of Lepraia , the essential
characters of the family being found in the fact that the cell-aperture
is more or less semicircular, with an entire lower margin, while the
front wall of the zocecia exhibits a semilunate or circular ‘ special
pore” (fig. 482, c). The type-genus of this family is Mcroporella
itself, the species of which are Tertiary and Recent.

The great family of the Zscharide (including under this name
also the AZyriozotde of Hincks) comprises forms in which the poly-
zoary is always completely calcareous, and may be incrusting, or
erect and foliaceous, or sometimes dendroid. The zocecia are with-
out a membranous area or raised margins, the cell-wall being entire
or variously punctured, but always without special pores opening
into the perivisceral cavity. In the Tertiary and Recent genus
Schizoporella (fig. 483, B) the polyzoary is sometimes incrusting,
sometimes free and foliaceous, and the lower lip of the cell-aperture
has a distinct notch or sinus, representing the median pore in the
Microporellide. In the genus ippothoa the form of the cell-mouth
is very similar to that seen in Schzzoforel/a, but the zocecia are “ dis-

CHEILOSTOMATA. 627;

tant, caudate, and connected with one another by a slender prolonga-
tion of the lower extremity, so as to form a linear series” (Hincks).
The earliest forms of this type appear in the Cretaceous rocks, and
the genus still survives. The genus £Zschara, as formerly under-
stood, has been reconstructed by modern authorities, and its most

Fig. 483.—a, Cells of Lepralia pallasiana (Tertiary and Recent), enlarged. p, Cells of
Schizoporella unicornis (Tertiary and Recent), enlarged. c, Cells of AZucronella coccinea (Ter-
tiary and Recent), enlarged: a, Avicularium; 9, Ovicell. (After Busk and Hincks.)

characteristic forms find a place in the genus Zepralza, as at present
restricted. In this genus, the polyzoary may be incrusting or erect
(fig. 484), and the foliaceous forms may be unilaminar, or may be
composed of two layers of cells united back to back. The zocecia
are ovate, with a more or less
horse - shoe - shaped aperture, the
lower lip of which is entire (fig.
483, A). The species of this genus
range from the later Secondary
period to the present day. In the
genus forel/a, the original cell-
mouth is semicircular, but there
is formed round this a secondary bad
and larger mouth which encloses Fig. pe hae ee Ranvilliana.
an avicularium. The species of
this genus are Tertiary and Recent. The genus Srtta (fig.
451, B) resembles the preceding in most characters, but the
secondary mouth is elongated and is channelled in front, while
the lower lip of the primary aperture is dentate. The species
of Smittia are Tertiary and Recent. Jucronella is another allied
genus, in which the peristome (fig. 483, C) is elevated in front into a
more or less prominent mucro. ‘The species of the genus are Ter-
tiary and Recent.

Related to the preceding, but perhaps forming the type of a
separate family (Aeteporide), is the genus fRetepora (fig. 485), in

638 MOLLUSCOIDEA.

which the polyzoary is erect and calcareous, and usually has the
form of a reticulate or fenestrated expansion, which is adherent by
means of an incrusting base. ‘The zocecia are developed on the
front face only of the zoarium, the dorsal surface being smooth or
striated, and carrying avicularia supported upon tubercles. The
cells are closely united or immersed, and on the lower margin of the
cell-mouth is a prominent rostrum carrying an avicularium. ‘The
species of /ezefora range from the Chalk to the present day.

The family of the Ceeforide includes forms with a calcareous
polyzoary, which may be incrusting, or ramose, or massive, and

B

Fig. 485.—Retepora cellulosa, from the Red Crag (Pliocene). _a, A fragment, of the natural
size ; B, Part of the poriferous surface, enlarged. (After Busk—copied from Zittel.)

which consists of irregularly heaped up zocecia, which are urceolate
in form and have sub-terminal mouths. The principal genus in this
family is Ced/epora itself (fig. 457, B), in which the cell-mouths have
in their immediate vicinity one or more ascending rostra carrying
avicularia. The genus is widely distributed in the Tertiary rocks,
and numerous existing species are known.

Lastly, we have the singular family of the Se/enarvizde, including
the allied genera Selenaria, Cupularia, and Lunulites (fig. 457, D),
in which the polyzoary is unattached, and consists of a plano-con-
vex or concavo-convex disc, composed of only one layer of cells,
the mouths of which open on the convex surface. The three
genera above mentioned are the principal ones comprised in this
family, and they range from the Chalk to the present day.

JUIN yA TM ONRID.

1. “Catalogue of the Marine Polyzoa in the Collection of the British
Museum” (Cheilostomata). 1852. Busk.

2. “ Catalogue of the Cyclostomatous Polyzoa in the Collection of the
British Museum.” 1875. Busk.

3. “ Report on the Polyzoa.” ‘ Challenger Reports,’ vol. x., 1884, and vol.
xvil., 1886. Busk.

4. “Monograph of the Fossil Polyzoa of the Crag.” Busk. ‘ Paleeon-
tographical Society.’ 1859.

Ovi

LITERATURE OF POLYZOA. 639

. “History of the British Marine Polyzoa.” 1880. Hincks.
. “Bryozoa marina in regionibus arcticis et borealibus viventia.”

1867. Smitt.

. “ Kritisk forteckning 6fver Skandinaviens Hafs-Bryozoer.” 1864-68.

Smitt.

= Handbuch der Palzeontologie.” Bd. I., Lief: 4. 1880. Zittel.
. ““Prodromus of the Zoology of Victoria” (Polyzoa). Decades III.-

Mice He MacGillivray.

. “Paléontologie Francaise” (‘Terrains Cretacés et Jurassiques’).

D’Orbigny. 1840-53.

11. “ Polyparien des Wiener Tertiarbeckens.” Reuss. 1847.

2. “ Palzontologische Studien uber die zlteren Tertiarschichten der

Alpen.” Reuss. 1869.

. “ Bryozoen des sachsischen Elbthalgebirges.” ‘ Palaontographica,’

Bde Xe” 1872-74. Reuss.

. “Die Polyparien des Norddeutschen Tertiargebirges.” ‘ Palzon-

tographica, Bd. 1X. 1863. F. A. Roemer.

. “Die Bryozoen der bdhmischen Kreideformation.” ‘ Denkschr. d.

Wien. Akad,’ Bd. XXIV. 1877. Novak.

. “Description des Bryozoaires fossiles de la formation jurassique.”

“Meém. Soc: geol. France.” -Ser. 2. vol. v. 1854. . Jules Haime.

17. “ Die Bryozoen der Maestrichter Kreidebildungen.” 1851. Hagenow.
18. “Monograph of Permian Fossils.” King. ‘ Paleeontographical

Society.’ 1849.

. “Synopsis of the Carboniferous Fossils of Ireland.” M‘Coy. 1844.
. “British Palzozoic Fossils.” M‘Coy. 1851.
Poeealcontolosy of New York,” vol, i, 1851, and vol., vi., 1887.

James Hall.

. “Descriptions of Bryozoa from the Palzeozoic Rocks of the Western

States and Territories.” Prout. ‘ Trans. Acad. Sci. of St Louis,’
vol. 1.

. “American Paleozoic Bryozoa.” ‘Journ. Cincinnati Society of Nat.

ist, 1652-64. OF Ulrich:

. “Contributions to American Palzontology,”’ vol. i. 1886. E. O.

Ulrich.

. “Report on the Palzontology of Ontario.” 1874. Nicholson.
. “A Review of the British Carboniferous Fenestellide.” ‘Quart.

Journ. Geol. Soc.,’ vols. xxxv. and xxxvi. G. W. Shrubsole.

. “A Review of the Family Diastoporide.” ‘Quart. Journ. Geol.

Soe VOl xxxvin 16oo, Gaks Vine:

. “Reports on Fossil Polyzoa.” ‘Brit. Association Reports.” 1880-

1883. G. R. Vine.

. “New Carboniferous Polyzoa.” ‘Quart. Journ. Geol. Soc.,’ vol. xxx.,

1874. Professor John Young and Mr John Young.

. “On new Carboniferous Polyzoa.” ‘Ann. and Mag. Nat. Hist.’

Ser. 4. vols. xii. and xv., 1874-75. Professor John Young and
Mr John Young.

. “Fossil Chilostomatous Bryozoa from Australia.” ‘Quart. Journ.

Geol. Soc.’, vols. xxxvii., 1881, xxxvili., 1882. A. W. Waters.

. “On Tertiary Cyclostomatous Bryozoa from New Zealand.” Ibid.,

vol. xliii. 1887. A. W. Waters.

. “On Fossil Cyclostomatous Bryozoa from Australia. Ibid., vol. xl.

1884. A. W. Waters.

. “La Faune des Bryozoaires Garumniens de Faxe.” ‘Ann. de la Soc.

Malacologique de Belgique,’ t. xxi. 1886. Pergens and Meunier.

640

CHAP LER see
MOLLUSCOIDEA — continued.
BRACHIOPODA.

BracuHiopopa (Padliobranchiata).—The members of this class are
defined by the possession of a body protected by a bivalve shell, which
2s lined by an expansion of the integument, or “mantle.” The mouth
7s furnished with two long spirally-coiled cirriferous processes or
“arms,” which act as respiratory organs. The nervous system con-
sists of an esophageal ring, upon which infra-esophageal and supra-
esophageal ganglia are developed. One or two pairs of tubular
““nephridia” are present, which act as ducts to the reproductive
organs. The sexes are distinct or united.

The Srachiopoda are essentially very similar in structure to the
Folyzoa, from which they are distinguished by the fact that they are
never composite, and by the possession of a bivalve, calcareous, or
sub-calcareous shell. All the living forms, except Zingula (Glottidia)
pyramidata (fig. 486) are fixed in their adult condition to some
foreign object, but many of the fossil forms seem to have been
permanently free and unattached.

As regards the anatomy of their soft parts, the internal organs in
the Brachiopoda are enclosed within two integumentary expansions
which constitute the “lobes” of the ‘‘ mantle,” and which are gener-
ally regarded as being placed on the dorsal and ventral aspects of
the body respectively. The space included between these two flaps
of the integument is the ‘pallial cavity,” the viscera and muscles

being situated towards the beaks of the shell, and separated from
the mantle-cavity by a membranous partition, which is perforated
by the aperture of the mouth (fig. 487). The larger part of the
mantle-cavity is occupied by two long oral processes, commonly
spoken of as the ‘“‘arms,” which are the principal organs of respira-
tion, and also serve to bring food-particles to the mouth by the cur-

BRACHIOPODA. 641

rents set up by the vibrating cilia with which they are covered.
The “arms” are homologous with the tentacular crown (‘lopho-
phore”) of the olyzoa, and have the form of lateral tubular pro-
longations of the margins of the mouth, usually of great propor-
tionate length, coiled up spirally and fringed with ciliated lateral
processes or “cirri” (fig. 487). Ina few forms the arms«can be
protruded from between the opened valves of the shell, and in
many types they are supported upon a more or less complicated

Fig. 486.—Morphology of Brachiofoda. a, Lingula (Glottidia) pyramidata (after Morse):
f; Peduncle; s, Sand-tube, encasing base of peduncle. B, Lingula anatina (after Cuvier): A,
The peduncle. c, Waldheiniia cranium, with adherent young, attached to a stone (after
Davidson): #, Peduncle; v, Ventral valve; d, Dorsal valve. pb, Crania [enabergensis, attached
by its ventral valve to a piece of coral (Chalk).

internal calcareous framework or “loop,” the structure of which
will be considered in greater detail hereafter.

On the inner side of the cirri of the arms is a ciliated furrow or
“brachial groove,” which conducts to the opening of the mouth,
and which serves for the conveyance of nutritive particles carried in
the water-currents set up by the cilia. The mouth conducts by an
cesophagus to a globular stomach, surrounded by a well-developed
granular “liver.” The intestine is sometimes short, sometimes long
and coiled, and it may either terminate in a distinct anal aperture
(as in Limgula and the other genera of Inarticulate Brachiopods), or
it may end blindly in the middle line (as in Zevebratula and the
Articulate genera of Brachiopods generally). A distinct heart is
present, in some cases at any rate, and has the form of a contractile

MOLe 1. 2S

642 MOLLUSCOIDEA.

vesicle situated on the dorsal side of the stomach. The body-cavity
proper is filled with a corpusculated fluid, and sends out branched
prolongations into the substance of the pallial lobes. These so-

SoS
pa a a a
7g CaS
a = = -$4.

Fig. 487.—Anatomy of Waldheimia flavescens. a, View of the animal after the ventral valve
of the shell has been removed, enlarged. 8, Longitudinal section, enlarged: d, Spirally-coiled
‘farm,” with lateral cirri (2); a, Adductor muscle; c, c, Divaricator muscles; s, Septum; v,
Mouth; z, Terminal portion of the alimentary canal. (After Davidson.)

called ‘‘ pallial sinuses ” often leave well-marked branching “ vascular
impressions ” on the internal casts of the fossil Brachiopods (fig. 488).
The central nerve-system of the Brachiopods has the form of a

Fig. 488.—Internal cast of Rhynchonella acuminata, from the Carboniferous rocks, viewed
ventrally and from the umbonal aspect. a, Mark left by the adductor muscle; x, Cardinal
muscular impression ; P, Mark left by the peduncle; v, ‘“‘ Vascular impressions”; 0, Ovarian
impressions. (After Davidson.)

circum-cesophageal ring, with a large sub-cesophageal ganglion, and
sometimes small supra-cesophageal ganglia as well. The sexes are

BRACHIOPODA. 643

sometimes united, but are more commonly distinct, and the repro-
ductive elements reach the exterior by means of two or four tubular
“nephridia,” which open on the one hand into the body-cavity, and
on the other hand into the pallialchamber. The generative glands
are developed in the lobes of the mantle, and commonly leave im-
pressions on internal casts of the shell (fig. 488, 0). The embryo
is ciliated and freely locomotive, but becomes fixed in the course of
its development.

The shell of the Brachiofoda is essentially calcareous, but it may
be largely composed of horny matter (as in Dyscina), or the car-
bonate of lime may be largely replaced by phosphate (as in Zzzgu/a).

LOTS ALY
Wy ONL ie oi y

7

.$ Wy Sa
~. NS = SAS <—we
SAO SAN WSs TESTE

AS2 5 S 3

a

Fig. 489.— Minute structure of the shell of the Brachiofoda. A, Tangential section of the
shell of the recent Waldheimia flavescens, greatly enlarged, showing the tubuli and the ends of
the flattened fibrous prisms of the shell; 8, Vertical section of the same, less highly magnified ;
c, Tangential section of the shell of Cyrtzxza Hamiltonensts, from the Devonian rocks of Canada,
greatly enlarged, the tubuli being mostly filled with peroxide of iron; D, Vertical section of the
same, less highly magnified. (Original.)

In the genus just mentioned, the shell consists of alternating layers
of horny and calcareous composition, the calcareous layers being
traversed by fine tubuli. As regards its microscopic structure, the
shell of the Brachiopods consists of ‘‘ flattened prisms, of consider-
able length, arranged parallel to one another with great regularity,
and at a very acute angle—usually only about 10° or 12°—with the
surfaces of the shell” (Carpenter). The oblique fibrous prisms
which compose the shell are best seen in vertical sections (fig.
489, B), but their irregular and closely dove-tailed extremities are
also shown in tangential sections (fig. 489, A and c). In some

644 MOLLUSCOIDEA.

types of the Brachiopods, as in the genus AAyuchonella, the shell-
structure is simply fibrous. In many forms, however, the shell is
perforated by a series of minute canals, which pass from one surface
of the shell to the other, in a more or less vertical direction, being
in general more or less dilated just before they reach their termina-
tion on the exterior of the shell (fig. 489, B and D), ‘These canals
give the shell a “‘punctated” structure, and in the living animal
they contain czecal tubuli, or solid prolongations, derived from the
mantle. In some forms (as in Producta and Chonetes) the tubuli
do not reach the exterior of the shell, the outer layer being simply
fibrous. Though the shell is in some groups of the Brachiopods
always ‘‘ punctate,” there are nearly allied types in which the shell
may be ‘“‘impunctate” in one case and ‘ punctate” in another.
Thus, the shell is simply fibrous in Rhynchonella, but is tubulated
in the nearly related genus, or sub-genus, Ahyuchoporina.

The two valves of the shell in any Brachiopod are articulated
together by an apparatus of teeth and sockets, or are kept in apposi-
tion by muscular action alone. As regards the contained animal,

Fig. 490.—Rhynchonella sulcata. a, Profile view; B, View of the dorsal surface ; c, View of the
base. a, Ventral valve; 4, Dorsal valve; 7, Base; c, Beak; £, Foramen. Lower Cretaceous.

the position of the valves is anterior and posterior, so that they are
properly termed the ““ventral” and *’dorsal” valves. One ot game
valves is always slightly, sometimes greatly, larger than the other,
so that the shell is said to be ‘‘inequivalve” (fig. 490). On the
other hand, a line drawn vertically from the beak of the shell to its
base (in fig. 490, B, from ¢ to f) would divide it into two equal halves,
so that the shell is said to be “equilateral.” In the true Bivalve
Shell-fish (Lamelibranchiata), on the contrary, the valves of the
shell are placed upon the sides of the contained animal, so that
they are “right and “left,” instead of being dorsal and ventral.
Further, the two valves are usually of the same size (‘“ equivalve ”),
and a line drawn from the beak to the base would almost always
divide the shell into unequal halves; so that the shell is “‘inequi-
lateral.”

BRACHIOPODA. 645

Ordinarily, the ventral valve of the shell of the Brachiopods is the
larger of the two, and it is generally furnished with a prominent
‘curved ‘‘ beak.” Very commonly the beak is perforated by a larger
or smaller aperture, which is termed the “foramen” (fig. 490, B),
and which serves for the transmission of a muscular peduncle or
stem by which the shell is attached to some foreign object. In
some cases, however (as in Lingua, fig. 486, B), the peduncle
simply passes between the apices of the valves, and there is no
foramen ; whilst in others (as in Cvanza, fig. 486, D), the shell is
merely attached by the substance of the ventral valve. The dorsal
valve, which is also usually the smaller, is always free, and is never
perforated by a foramen. Further, as already remarked, there is
reason to believe that some fossil forms were free and unattached
in their adult condition.

The Lrachiopoda are divided into two primary sections according
as the valves are held together by muscular action alone, and there
is no “hinge” developed (‘‘ Zzarticulata”), or as the valves are pro-

Fig. 491.—Muscular system of Waldheimia flavescens. M, Ventral valve; nN, Dorsal valve;
7, Loop; v, Mouth; z, Extremity of intestine; @ a, Adductor; c, Divaricators; c’, Accessory
divaricators; 4, Ventral adjustors; 4’, Peduncular muscle; 4”, Dorsal adjustors; p, Peduncle.
(After Hancock.)

vided with a proper “hinge” (‘‘ Avticulata”). In the Articulated
Brachiopods the valves are united at their beaks by means of two
teeth which are developed on the ventral valve, and fit into cor-
responding sockets in the dorsal valve. Behind the dental sockets
of the dorsal valve there is usually a prominent process (“ cardinal
process”), to which are attached the so-called “ cardinal ” or “ divari-
cator” muscles (fig. 491, c). These are inserted on each side of
the centre of the ventral valve, two pairs being usually present ; and
they serve to open the shell, no structure corresponding with the

646 MOLLUSCOIDEA.

“ligament” of the Bivalve Molluscs being developed. One pair of
‘¢ divaricators ” is of much smaller size than the other, and the name
of “accessory divaricators” is given to these. The valves, on the
other hand, are held together by a pair of ‘‘adductor” or ‘‘ occlusor ”
muscles (fig. 491, @), which pass from one valve to the other, in the
neighbourhood of the beaks. ‘The adductors bifurcate about the
middle, so as to produce a large quadrangular impression on the
internal surface of the dorsal valve (fig. 492, B, a a) and a single
divided impression towards the centre of the ventral valve (fig.
492, A, a). ‘There are also, in some cases, muscles connected with
the movements of the peduncle; and others (the ‘‘ dorsal” and
‘ventral adjustors”), which have the function of erecting the shell
and also that of attaching the peduncle to the shell. In the Inar-

Fig. 492.—A, Interior of the ventral valve of Waldheimia flavescens: 7, Foramen; d, Delti-
dium ; z, Teeth; a, Adductor impressions ; c, Impressions of the divaricator muscles; c’, Acces-
sory divaricators; 4, ‘‘ Ventral adjustors” ; 6’ Peduncular muscle. B, Interior of the dorsal valve
of Waldheimia flavescens: cc’, Cardinal process; 4 6, Hinge-plate; s, Dental sockets; 2,
Loop ; g, Crura of the loop; a a, Adductor impressions ; c, Point of attachment of the accessory
divaricator ; 4, Point of attachment of the peduncular muscles; ss, Septum. (After Davidson.)

ticulated section of the Brachiopoda, as in Lingula, the arrangement
of the muscles by which the valves are opened and shut is still more
complicated.

The “arms” or “brachial processes” are in some cases simply
coiled up within the shell, but in other cases, as previously noted,
they are supported by a more or less complicated calcareous skeleton,
which is known as the “loop” or ‘‘apophysis” (fig. 492, B). When
present, the loop is always attached to the dorsal valve of the shell,
and though it serves to support the brachial membrane, it does not
strictly follow the course of the arms. In its simplest form, the loop
is a thin ribbon-shaped calcareous lamella, the two ends of which

BRACHIOPODA. 647

spring from near the hinge of the dorsal valve, while the free end
of the loop is folded back upon itself (fig. 492, B). ‘‘In some
genera it extends to upwards of three-fourths of the length of the
shell, as in Waldheimia ; but in others it is short, and projects but
little beyond the hinge-line. In some genera it is attached only to
the hinge-plate, as in Zerebratula, Waldheimia, &c.; in others, to
a central longitudinal plate or septum, as in Zerebratella, &c. In
certain families the apophysis presents the form of two spirally-coiled
lamellee, which nearly fill the interior of the shell; the ends of the
spirals being directed outwards or towards the cardinal angles, as in
Spirifera (fig. 493), Athyris, &c.; or horizontally, the apices facing
each other towards the centre of the shell, as in Glassza. Again,
the spirals are sometimes vertical, their inner sides being pressed
together and flattened, with their terminations close together and
facing the bottom and centre of the dorsal valve, as in Afrypa”
(Davidson). The spiral processes are also commonly connected by
a more or less complicated system of lamellee, which vary in shape

ot D ee eet cs
90022? 22
er pDr2sPW

qa
ATL
\

Fig. 493.—Spivifera hysterica—Carboniferous. The right-hand figure shows the interior of
the dorsal valve, with the calcareous spires for the support of the arms. gg, Cardinal angles ;
é, Hinge-area; £, Triangular peduncular foramen.

and character in different types, and are of great value in the dis-
crimination of certain genera. In the Rhyuchonellide, the loop is
represented only by two short, slender, curved lamelleze; while in
some cases the sides of the loop carry minute calcareous spines,
showing that even the cirri of the arms were supported by an
internal skeleton. In whole families, lastly, as, for example, in the
Strophomenide and Productide, the arms are entirely devoid of
calcified supports.

Very commonly, the beaks of the dorsal and ventral valves of
the Brachiopoda are separated from one another by a narrower or
wider space, which is termed the “hinge-area” (fig. 493, ¢). The
“area” is more or less triangular in form, generally developed on
the ventral valve only, but sometimes formed by both valves con-
jointly, and commonly transversely striated. In such genera as
Spirtfera and Cyrtina the hinge-area is of very large size, but it may
be very narrow, and in many cases it does not exist at all. Another
structure that is commonly present in the Articulated Brachiopods

648 MOLLUSCOIDEA.

is what is known as the “deltidium.” This is a triangular calcareous
plate, sometimes single, sometimes composed of two lateral halves
(fig. 492, @), which is developed in front of the foramen of the
ventral valve, and may either completely enclose the foramen (as in
Rhynchonella), or may simply form the lower boundary of this aper-
ture. What is called a “ pseudo-deltidium,” again, is a triangular
calcareous plate which grows downwards from the upper end of
the triangular foramen in such genera as Sfirvifera, and which
partially closes this opening.

As regards their distribution in space, all the Brachiopoda are
marine, the number of known existing species and varieties being
under one hundred and fifty. The range of the living Brachiopods
in depth is very variable, even as regards individual species, some
forms commonly living between tide-marks, or in quite shallow
water, while others extend to depths of nearly three thousand fathoms.
Upon the whole, however, the Brachiopods must be regarded as
inhabitants of comparatively shallow water, since about half of the
known living species are confined to depths of less than one hundred
fathoms.

Leaving the problematical Zozodn out of sight, the Brachiopods
are amongst the oldest forms of animal life, representatives of this
class appearing in the Lower Cambrian deposits. Owing to the
great number of fossil Brachiopods, and also owing to the fact that
particular types are commonly confined to particular geological
horizons, the study of this group of animals is one of great palee-
ontological and stratigraphical importance. Out of one hundred
and thirty-nine genera recorded by Davidson, one hundred and six
appeared first in the Palaeozoic rocks ; thirty-four genera are repre-
sented in the Mesozoic deposits ; and twenty-one in the Kainozoic
and Recent deposits taken together. The genera Lingula, Discina,
Crania, Terebratula, and Rhynchonella appear at some point or
another in the Paleozoic series, and still exist. About eight genera
are represented in the Cambrian ; whereas no less than sixty-seven
genera are represented in the combined Ordovician and Silurian
deposits, after which the number of genera becomes progressively
reduced, fifty-two generic types being present in the Devonian, forty
in the Carboniferous, and twenty in the Permian. Of the known
Mesozoic genera about sixteen are peculiar to this period ; while of
the thirteen Tertiary genera no less than twelve survive at present ;
and there are eight exclusively recent genera.

Upon the whole, the hingeless or Inarticulate group of the Brachi-
opods is the most ancient, all the Cambrian genera, with the excep-
tion of Orthis, belonging to this division. Of the Cambrian genera,
Lingula, Discina, and Cranza still survive. While less than one
hundred and fifty species exist at present, the united Ordovician and

BRACHIOPODA. 649

Silurian systems have yielded nearly two thousand species. Vast as
is the number of Ordovician forms, the Silurian rocks are still more
rich in this group of fossils; and the class of the Brachiopoda may
be considered as attaining its maximum in the Silurian period, which
has, for this reason, been not unaptly spoken of as the “‘ Age of
Brachiopods.” In the Devonian rocks more than thirteen hundred
species of Brachiopods are known, and though many of these be-
long to genera which were previously in existence, others belong to
types, such as Uneites, Stringocephalus, Davidsonia, &c., which are
peculiar to this system of rocks. The great genus Zevebratula has
its first representatives in the Devonian. In the Carboniferous rocks
the number of species has undergone a marked reduction, the prin-
cipal forms belonging to the great Palzeozoic families of the Stxopho-
meniae, Spiriferide, and Productide. The genus FProducta attains
here its maximum, some of the species having an enormous geo-
graphical extension. In the Permian rocks only about thirty species
of Brachiopods are known, and these belong mostly to the families
of the Productide and Strophomenide.

With the beginning of the Mesozoic period, the decay of the
Brachiopodous “phylum” which set in during Devonian times be-
comes still more pronounced. The Triassic rocks, like the Permian,
exhibit a singular poverty in the remains of Brachiopods, but the
group is fairly represented in both the Jurassic and Cretaceous
deposits. Upon the whole, however, the reduction of the number
of species which is so marked in the later Paleozoic rocks 1s pro-
gressively continued through the Mesozoic period. Moreover, some
of the most characteristic of the Paleeozoic families (the Afryprde,
Trimerellide, Productide, and Obolide) have totally disappeared ;
while the great families of the S¢tvophomenide and Spiriferide are
only represented by a few surviving types, and disappear wholly in
the Jurassic rocks. On the other hand, the families of the Zevebra-
tulide and Rhynchonellide now assume a marked predominance ;
the latter, however, being almost exclusively represented by species
of the genus Akynchonella itself. Finally, in the Tertiary rocks
Brachiopods are few in number, and belong almost wholly to exist-
ing genera, while a number of the sfeczes still survive.

As regards classification, the Brachiopoda may be divided into the
two orders of the /narticulata and the Articulata, the characters and
families of which will be briefly treated of in what follows.

ORDER [. INARTICULATA

(= Tretenterata, Lyopomata, Pleuropygia).

This division of the Brachiofoda comprises those forms in which
the valves of the shell are not hinged, but are held together by

650 MOLLUSCOIDEA.

muscles only, the mantle-lobes are completely free, and the intestine
terminates in a distinct anus. This order includes the Paleozoic
families of the Obofide and Trimereliide, and the three families of
the Lingulide, Discinide, and Craniade, which commence in the
Lower Paleozoic rocks and are all represented by living species at
the present day.

FamiLy 1. LincuLIpD&.—In this family the animal is fixed by a
muscular peduncle which passes out between the beaks of the valves
(fig. 486, B). The shell is almost equivalve, oblong or ovate in
form, and composed of alternating corneous and calcareous layers,
the latter being phosphatic and perforated by minute tubuli. The
arms are fleshy, spirally rolled, and not supported by calcified pro-
cesses. The family includes the genus Zzuguda along with some
allied (sub-generic?) forms,
and ranges from the Lower
Cambrian to the present day.

In the genus Lingua (fig.
494) the shell is oblong,
compressed, the dorsal valve
little shorter than the ven-
tral. The .shell is) eval
rounded, or satchel-shaped,
tapering more or less to-
wards the beaks. The sur-
Fig. 494.—Lingula Eva. Ordovician. Dorsal and face is concentrically striated

ventral valves. (After Billings.) with lines of growth. The

genus commences to be rep-

resented in the Cambrian rocks, and has continued without interrup-
tion, and with no perceptible change, to the present day.

P| \ iN
ff ‘
fe Nh a\s
ANN
HT \Sy) AN
LSS it \
| i S |
th NW
ie INF)
\ = 7 W\\(
S — N\\\\
\\ Ly)

The genus, or sub-genus, Zzzgu/ella (fig. 495, D) differs from Lzngula
proper in the fact that there is a distinct groove in the beak of the ventral
valve for the passage of the peduncle. This type comprises the oldest
of British Brachiopods, ZL. ferruginea being a small form which occurs
low down in the Lower Cambrian. Another species—viz., L. Daviszz—
is extremely abundant in the so-called “ Lingula Flags” (Upper Cam-
brian). The sub-genus Lizugulepis is very similar to Lzmgula proper,
but the ventral valve is furnished with a feeble median septum. ‘The
type is the L. pznn@formis of the Cambrian rocks of North America.

FAMILY 2. OsoLtip#.—This family comprises forms closely allied
to the preceding, but the beaks of the valves are thickened at their
margin, and that of the ventral valve is provided with a groove for
the passage of the peduncle. In structure, the shell is calcareo-
corneous. ‘The family is principally Cambrian, Ordovician, and
Silurian, the genus Schmidtia surviving into the Devonian period,

BRACHIOPODA. 651

and the genera (Veobolus, Lakhmina, and Schizopholis being Car-
boniferous.

In the genus QOédolus (fig. 495, B and c) the shell is orbicular,
with subequal, smooth valves, the ventral valve having a longitu-

ANS

AY

‘
SEN
=
SAN

at

SK
Ss

SS

<
~

ASSN

es:

SS

S

SS

Fig. 495.—Lingulide, Discinide, and Ololide. A, Trematis filosa, Ordovician; B, Cast of
Obolus Davidsonz, Silurian ; c, Interior of the dorsal valve of the same; pb, Lingulella Davisiz,
Upper Cambrian; &, Ventral valve of Acrotreta Nicholson7, of the natural size and enlarged,
and F, Side-view of the ventral valve of the same, enlarged, Ordovician ; G, Interior of the dorsal
valve of thesame. (A is after Billings, and the other figures after Davidson.)

dinal groove for the passage of the peduncle-fibres. Usually there
is a weak median septum in the ventral valve. The species of this
genus are wholly Ordovician and Silurian, and are especially char-
acteristic of the former of these systems. The little Obolus Apollinis

Fig. 496.—Kutorgina cingulata. (Billings.) Upper Cambrian.

occurs in vast numbers in the Ordovician ‘‘ Ungulite. Grit” of
Russia.

The genus Odolel/a, of the Cambrian and Ordovician formations, is
nearly allied to Odo/zs, but the arrangement of the muscular impressions
is different. The genus Xutorgina (fig. 496) is essentially similar to the
preceding, but the shell is sub-quadrate, and there is a straight hinge-line.

652 MOLLUSCOIDEA.

The genus is characteristic of the Cambrian rocks of Canada. Schmidtia,
of the Silurian and Devonian rocks, has a minute oval shell, the ventral
valve of which is convex, with a pointed beak below which an “area” is
developed ; and the genus Lepzobolus of the Ordovician rocks of North
America is closely allied to this, but differs in its internal characters. In
the Cambrian genus Acrothele, the shell is nearly circular, and the ven-
tral valve is somewhat conical, the beak being sub-central and perforated
by a foramen, while the beak of the dorsal valve is marginal.

In the genus Szfhonotreta (fig. 497) the shell is oval, inequivalve, with
unarticulated valves. The beak of the ventral valve is perforated by a
foramen which opens on its back, and communicates with the interior by
a cylindrical tube. The surface of the shell is
covered with concentric lines of growth, and fur-
nished with numerous delicate tubular spines,
which, however, are rarely preserved. All the
Siphonotrete at present known belong to the
Ordovician and Silurian periods.

ie ‘ In the genus Acrotrefa (fig. 495, E—G) the

git ie UG dorsal vilve is nearly Bes i ventral is

conical and patelliform, the surface being con-
centrically striated. The beak of the ventral valve is perforated by a
round foramen, from which a pedicle-groove extends to the posterior
margin, and is bounded laterally on either side by a small false area.
The genus is wholly Ordovician.

In the neighbourhood of Acrotreta, Dr Fischer, with some doubt,
places the Silurian genus Ezchwa/dia, which has been commonly referred
to the articulate family of the Ahynchonellida, but in which hinge-teeth
and sockets appear to be absent. The shell in this curious genus is sub-
trigonal or oval, and the ventral valve has its apex perforated by a
peduncular foramen, while the dorsal valve is provided with a prominent
median septum. - The structure of the shell is very peculiar, the most
conspicuous feature connected with this being that the greater part of
the surface is covered with a special alveolated layer, the hexagonal
pits of which are arranged in decussating oblique lines.

Lastly, the Carboniferous rocks of India have yielded certain curious
types which have been placed in this family, and have been referred to
the genera Veobolus, Lakhmina, and Schizopholis. In all these genera
the shell is of small size, and either suborbicular or trapezoidal in shape.

Famity 3. Discinip#.—TIn this family the shell is corneo-cal-
careous, with unequal valves, the animal being attached by a
muscular peduncle passing through the ventral or lower valve by
means of a slit in its hinder portion, or a circular foramen exca-
vated in its substance. The arms (fig. 499) are fleshy and spirally
coiled, and are not provided with calcified supports. The Descinzde
range from the Ordovician period to the present day.

In the genus Dzsczna (figs. 498-500) the shell is sub-orbicular, with
conical, nearly equal valves, of which the dorsal is the deepest, while the
ventral valve is flatter, and the beaks of both are sub-central. In the
typical forms of Dzsczza, the ventral valve has an elongated marginal
opening, which is prolonged on the surface into an anterior groove tra-
versing the shell obliquely and terminating internally in a second groove
which runs in an opposite direction to the first. In the centre of the

BRACHIOPODA. 653

ventral valve is a subtriangular plate, which conceals the minute tubular
foramen. In the forms which are included in the sub-genus Ordzculozdea,
the general structure is the same as in Desczza proper, but the valves are
much elevated, and the minute foramen is situated at the posterior ex-
tremity of a groove, which is prolonged externally only, but has no inter-
nal continuation. The forms comprised in the sub-genus JL7scznzsca,
again, possess a longitudinal foramen situated between the beak of the

Fig. 498.—Dzscina (Or- Fig. 499.—The animal of Fig. 500. — Ventral
biculoidea) nitida, from Discina, as seen on the re- valve of Discina Circe,
the Carboniferous rocks moval of the ventral valve and from the Trenton Lime-
of North America. d, part of the ventral mantle- stone (Ordovician) of
Dorsal valve; v, Ventral lobe. 4, Expanded surface of Canada, showing the
valve. (After Zittel.) the peduncle. (After Wood- pedicle- groove. (After

ward.) Billings.)

ventral valve and its hinder margin, in the centre of a depressed oval
disc, the valve itself being flat or concave. The species of D¢sczza, in
the general sense, range from the Ordovician to the present day. In
the genus 77vematzis (fig. 495, A) both the valves are more or less convex,
and the general shape of the shell is sub-orbicular or transversely oval.
The dorsal valve is the most convex, its beak being marginal, with a
false ‘“‘area” below it. The ventral valve is flatter, and has a wide mar-

Fig. 501.—Crania [gnabergensis. Cretaceous.

ginal slit for the passage of the peduncle. The surface is radiately
striated, and is ornamented with small superficial pits. The species
of this genus are Ordovician and Silurian.

FAMILY 4. CRANIAD#.—In this family the shell is calcareous,
more or less circular in shape (fig. 501), the ventral valve being
the shallowest, and being usually fixed by the substance of the test

654 MOLLUSCOIDEA.

to some foreign object. The dorsal valve is conical or limpet-
shaped, and the shell in both valves is tubulated. In the interior
of each valve are four principal muscular impressions, formed by
the adductors, and in the interior of the ventral valve, centrally, is
placed a triangular protuberance, which serves to support the bases
of the fleshy arms. The family ranges from the Ordovician to the
present day.

The only well-established genus in this family is Cranza itself,
which commenced to exist in the Ordovician period, and which is
represented at the present day by several living species. The shell
in Crania may be smooth, or striated with radiating ribs, sometimes
with spines or foliaceous expansions, while the internal margins of
the valves are expanded and often granulated. The ventral valve
is fixed by its lower surface to foreign bodies, while the free dorsal
valve is more or less conical (fig. 501).

In the sub-genus Pseudocrania (Ordovician to Devonian), the shell is
only slightly inequivalve and is free, while the inner margins of the
valves are smooth. In this family may perhaps be placed the singular

Fig. 502. -— Trimerella Fig. 503.—Tvrimerella Fig. 504. — Monomerella
acuminata —cast. Silu- grandis—cast. Silurian. prisca—cast. Silurian. (After
rian. (After Davidson and (After Davidson and Davidson and King.)

King.) King.

Ordovician genus Schizocrania, in which the shell resembles Cvanza in
general characters, and is fixed by the flattened ventral valve, while the
dorsal valve is conical and is radiately striated. The ventral valve, how-
ever, exhibits a triangular notch on its posterior side, extending nearly
to the centre, and there are six muscular impressions in the dorsal
valve.

FaMILy 5. TRIMERELLIDZ.—This family is related to that of the
Obolide, and comprises forms in which the shell is thick and cal-

BRACHIOPODA. 655

careous, with unequal valves ; the beaks usually prominent, or some-
times obtusely rounded, and either massive and solid, or divided by
a partition into two chambers. There is a well-developed hinge-area
(fig. 503), and a wide deltidium, bounded by two ridges, the inner
ends of which serve as teeth, though true teeth are not present.
Each valve is furnished with muscular platforms, which, in the
typical species, are elevated and doubly vaulted. The principal, or
only, genera of the family are Z7imerella, Dinobolus, and Mono-
merella, and the family is confined entirely to the Ordovician and
Silurian rocks. The differences between the above-mentioned genera
depend mostly upon internal characters, which can hardly be made
clear except by an examination of actual specimens, and as these
very generally occur in the form of internal casts, the study of the
forms of this group is attended with exceptional difficulties.

ORDER IJ. ARTICULATA
(=Chistenterata, Arthropomata, Apygia).

In this order of the Brachiopods the valves of the shell are hinged,
usually by means of teeth and sockets ; the lobes of the mantle are
not completely free; and the intestine ends blindly. This order
includes the families of the Productide, Strophomenide, Koninck-
imide, Spiriferide, Atrypide, Rhynchonellide, Terebratulide, Stringo-
cephalide, and Thecidide, of which only the Rhynchonellida, Tere-
bratulide, and Thecidiide are represented by living forms.

FaMILy 1. PRopuctip#&.—In this family the shell is entirely free,
or is attached to submarine objects by the substance of the ventral
valve or by means of spines. The valves may be regularly articulated,
or may be kept in place by muscular action alone. ‘There is a
straight hinge-line, and the outer surface is more or less largely fur-
nished with tubular spines, while the inner surface exhibits numerous
funnel-shaped punctures. The arms are not provided with calcified
supports, but there are well-marked muscular and vascular impres-
sions. The ventral valve (fig. 505, ve) is convex, while the dorsal
valve (do) is concave, and is furnished with a prominent cardinal
process (ca), to which the divaricator muscles are attached. The
interior of the dorsal valve exhibits a pair of large central dendritic
adductor-impressions, separated by a median ridge (a a), a pair of
reniform vascular impressions (7), and two shelly prominences (f),
which probably served to support the bases of the arms. ‘The
interior of the ventral valve exhibits a pair of large dendritic ad-
ductor-impressions, situated close beneath the incurved beak, a pair
of large lateral striated divaricator-impressions (¢ @), and two anterior
depressions (s) which probably lodged the spiral arms.

656 MOLLUSCOIDEA.

All the members of the Productide are Paleozoic, the earliest
forms appearing in the Silurian, while the last are found in the Per-
mian deposits.

In the genus Producta (or Productus) itself (figs. 505-507) the
valves are not articulated by teeth and sockets, and appear to have
been generally free in the adult condition. In some cases, how-
ever, where the shell is furnished with long spines, it may be sup-
posed that these structures served to moor the animal in the soft
ooze of the sea-bottom. In the curious Producta complectens, Mr R.
Etheridge, jun., has shown that the shell was firmly attached by the

YAS
Sune
3

Yi Hy
COAL

4 4 f

I)

HATA)
I f Ati NY

Fig. 505.—Structure of Producta gigantea, from the Carboniferous Limestone. a, Interior of
the dorsal valve; B, Interior of the ventral valve, a portion of the projecting beak being removed ;
c, Ideal section of both valves, in place, in the middle line; p, Hinge-line of the dorsal valve.
a a, Adductor impressions ; d d, Divaricator impressions (in the ideal fig. c the letters a and d
indicate the adductor and divaricator muscles respectively); z, Reniform vascular impressions ;
p, Processes supporting the bases of the arms; s, Hollows occupied by the spiral arms; ca,
Cardinal process ; , Hinge-line ; do, Dorsal valve; ve, Ventral valve. (After Woodward.)

twisting of some of the spines of the ventral valve round the column
of a Crinoid. In the still more singular Producta proboscidea, the
ventral valve is prolonged beyond the dorsal, and its edges are
rolled together and form an elongated tube, by which the shell was
attached to some foreign body. The shell in Pvoducta is generally
transversely elongated in shape, and is ‘“ auriculate” or furnished
with ear-like expansions. ‘There is a straight hinge-line, usually
shorter than the greatest width of the shell, the hinge-area being
linear or wanting. The ventral valve is convex, with a large, bent,
and imperforate beak—the dorsal valve being concave, and follow-
ing the curve of the former. The surface is ribbed or striated, and

BRACHIOPODA. 657

the ribs carry a larger or smaller number of longer or shorter tubular
spines, which are especially abundant upon the auricular expansions.
The species of Producta range from the Devonian to the Permian,
but the genus is essentially and especially characteristic of the Car-
boniferous period. ji

The genus Sztrophalosia (fig. 508, B) ranges from the Devonian to the
Permian, and is distinguished from Producta chiefly by the fact that the

ES

\ MiG
N\ WE

YW
<>,
YAS

S
\
Ly LYS Z
Zu,
i i ‘ -
i \\ Z Wy
in
Fig. 506.—Dorsal and profile views of Producta Fig. 507.—Dorsal aspect of Producta
semireticulata. Carboniferous. horrida. Permian. (After King.)

valves are not edentulous, but are articulated by teeth and sockets ;
while each valve has a distinct hinge-area, and the ventral valve has a
foramen covered with a deltidium. Az/osteges, again (fig. 508, A), from
the Permian, has no teeth or dental sockets—in this respect agreeing
with Producta—but the ventral valve has a wide hinge-area, pierced by
a foramen, which is covered by a convex pseudo-deltidium. <Az/osteges
is probably only a sub-genus of S¢rophalosza, but the shell is free, whereas

Fig. 508.—a, Aulosteges Wangenheimii—Permian, showing the hinge-area and deltidium; 8,
Strophalosia Goldfussi, viewed dorsally—Permian ; c, Productella onusta—Devonian—interior
of the dorsal valve, showing the cardinal process (c), the muscular scars (vz), and the reniform
vascular impressions (v). (After Davidson and Hall.)

in the latter the shellis attached by the beak ofthe ventral valve. Lastly,
in the Devonian Productella (fig. 508, C) the valves are articulated by
teeth and sockets, and a hinge-area is present in both valves, but the
latter is narrow and linear, and the ventral valve is extremely convex
and gibbous.

In the genus Chometes (fig. 509) the shell is concavo-convex, trans-

VOL, I- Py “Ie

658 MOLLUSCOIDEA.

versely oblong, with a straight hinge-line. The hinge-line is as wide as
the shell, or the shell is eared. The ventral valve is convex, the dorsal
concave, and both have a distinct hinge-area, with a central fissure,
closed in the ventral valve by a pseudo-deltidium. The upper edge of
the hinge-area of the ventral valve is furnished with a row of delicate

Fig. 509.—Chonetes Dalmaniana. Carboniferous.

tubular spines. The species of Chometes are distributed in the Silurian,
Devonian, and Carboniferous periods.

FAMILY 2. STROPHOMENID2.—lIn this great family of Brachio-
pods the shell is rounded or subquadrate, generally compressed,
plano-convex, concavo-convex, or biconvex, the beaks being rarely
prominent, and the hinge-line being straight and long. The shell
seems usually to have been attached by a muscular peduncle. There
is a low hinge-area in each valve, often with a triangular fissure,
sometimes closed by a pseudo-deltidium, beneath the beaks. The

Fig. 510.—Interior of the dorsal valve (A) and ventral valve (B) of Orthzs striatula, from the
Middle Devonian of the Eifel. 4%, Hinge-area; ¢, Hinge-teeth; a a, Adductor impressions;
d, Impressions of the divaricators and peduncle-muscles ; 0, Ovarian spaces. (After Davidson.)

ventral valve has two powerful hinge-teeth (fig. 510, ¢); and the
dorsal valve has a prominent cardinal process, between two short
brachial processes. The interior of the dorsal valve (fig. 510, a)
exhibits four adductor-impressions (a), and well-marked vascular
impressions which enclose wide ovarian spaces (0). The interior
of the ventral valve (fig. 510, B) shows two narrow, centrally-placed

BRACHIOPODA. 659

adductor-impressions (a), flanked by fan-shaped scars (@) produced
by the conjoined divaricators and peduncle-muscles, the whole
enclosed in a saucer-shaped depression. The arms are devoid of
spiral supports, and the shell is usually penetrated by microscopic
tubuli, which are comparatively large and remote.

The three principal genera of the Strophomenide are Strophomena,

Fig. 511.—Orthis calligram-
mea, var. Davidsoni; dorsal Fig. 512.—Orthis porcata; dorsal and
and side view. Ordovician. side view. Ordovician.

Orthis, and Leptena, and with the doubtful exception of some
Mesozoic forms of the last of these, the entire family is confined to
the Palzeozoic period.

In the genus Or¢his the valves are articulated by teeth and
sockets, and usually are more or less transversely oblong (figs.

SZ

Fig. 513.—a and a’, Orthis (Platystrophia) biforata, Ordovician ; 4, Orthis fabellulum, Ordo-
Vician ; ¢ and c’, Exterior and interior of the dorsal valve of Orthis subguadrata, Ordovician ;
a, Strophomena deltoidea, Ordovician. (After Meek, Hall, and Salter.)

510-514). There is a straight hinge-line, generally shorter than
the width of the shell. Each valve has a hinge-area, notched in
its centre by a triangular fissure through which the fibres of the
peduncle were transmitted. The shell is often more or less flattened
or depressed, and the surface may be smooth, but is more commonly

660 MOLLUSCOIDEA.

ornamented with strize, or furnished with well-marked longitudinal
ribs. The species of the genus Ov¢/zs begin in the Cambrian, and
abound in the Ordovician, Silurian, Devonian, and Carboniferous
periods, especially in the first two of these; but the genus is not
known to have survived the Carboniferous period. This genus is
one of the most important and widely distributed groups of Palzo-
zoic Brachiopods, and the species belonging to it may generally be
distinguished from the closely related Strophomene by the fact that
the shell is seldom flat, one valve being usually much more convex
than the other; while the general form is compact and not ex-
tended, and the hinge-line is often shorter than the greatest width

Fig. 514.—a, Dorsal aspect of Stvophomena alternata, from the Ordovician of North America ;
6, Ventral aspect of Strophemena filitexta, Ordovician, North America; c, Orthis testudin-

aria, Ordovician; d a’, Orthis plicatella, Ordovician; ee’ e’, Leptena sericea, Ordovician.
(After Meek, Hall, and the Author.)

of the shell. The muscular scars are quadrate, and not extended
either vertically or laterally. Lastly, the ‘cardinal process ”—that
is, the projection of the dorsal valve, to which the ‘ divaricator
muscles” are attached—djis undivided and linear. Though the
species of Orthis most nearly resemble certain forms of Stvopho-
mena, and are very liable to be confounded with these, one or
two species (such as Orthis biforata—513, a) closely simulate the
genus Sfivifera in general form.

In the sub-genus Platystrophia, of which Orthzs biforata of the Ordo-
vician rocks (fig. 513, @)1s a characteristic form, the shell is generally
transversely elongated, with a long hinge-line, both valves convex, and
the ventral valve with a deep median sinus. A hinge-area and triangu-
lar deltidial fissure are present in both valves. The valves are radially
plaited, and the beaks are prominent and incurved. The sub-genus
ranges from the Ordovician to the Carboniferous.

The genus Skenidium (fig. 515, D—G) is in many respects allied to
Orthis, but the ventral valve is much elevated, with a high triangular

BRACHIOPODA. 661

area, in the centre of which is a deltoid foramen often partially closed by
a pseudo-deltidium ; while the dorsal valve is furnished with a prominent
median septum, which is continuous with the cardinal process superiorly,
and may be bifurcated at its anterior extremity. The species of Skevz-
dium are Ordovician and Silurian, and it seems probable that the genus
is identical with the Devonian J/ystrophora of Kayser.

In the Silurian and Devonian genus 7vopidolepius (fig. 515, A—C), the

Fig. 515.—A, Dorsal view of the shell of Tvopzdoleptus carinatus, Devonian (Hamilton group)
of North America, of the natural size; B, Interior of the dorsal valve of the same; c, Interior
of the ventral valve of the same; bD, Dorsal aspect of Skenidium tnsigne, from the Silurian
(Lower Helderberg) of North America; §£, Cardinal aspect of the same enlarged, showing the
high area of the ventral valve, and the triangular foramen partially closed by a pseudo-deltidium ;
F, Base of the same; G, Interior of the dorsal valve of the same, showing the median septum.
(After Hall.)

shell is concavo-convex, radiately ribbed, with a straight hinge-line and
a double area, that of the ventral valve perforated by a large foramen.
The ventral valve carries two strong, crenulated and diverging teeth,
and the dorsal valve has two correspondingly crenulated dental sockets,
a well-marked median septum, and a prominent cardinal process which
almost entirely fills the foramen in the ventral
valve. The species of Zvropidoleptus are Silurian
and Devonian.

In the genus Orthisina (= Klitambonites and
Hemtpronttes) the shell resembles that of Orthzs,
but the ventral valve is pyramidal, and has*a
very high area, directed more or less at right
angles to the median plane of the valves, while
the dorsal valve is furnished with a smaller area.
In both valves there is a triangular fissure in the
hinge-area, covered by a pseudo-deltidium, that of
the ventral valve being often perforated by a peduncular foramen.
The typical forms of Or¢hzscna are found in the Ordovician deposits.

Fig. 516. — Orthisina
Verneutlz. Ordovician.

In the genus Strophomena (figs. 513, 514, and 517) the shell is
depressed, generally semicircular, the hinge-line as long as the width
of the shell, or longer. The surface may be smooth, but is most
commonly striated or ribbed. ‘There is a double hinge-area, which
is largest in the ventral valve. Each hinge-area has a median notch,

662 MOLLUSCOIDEA.

which, in the ventral valve, is partially covered by a deltidium. The
ventral valve may be convex or concave, and the dorsal valve follows
the curvature of the ventral valve. The species of the genus S7vo-
Phomena are very abundant in the Ordovician, Silurian, Devonian,
and Carboniferous formations, often attaining a large size; but they
do not seem to have survived the close of the last-named period.
Speaking generally, the species of Strophomena may be distin-
guished from those of Orvthis and Leftena—both of which they

Fig. 517.—Strophomena antiquata. Ordovician and Silurian.

much resemble occasionally—by attention to the following points :
The shell is wswa//y flat and semi-oval, its length and breadth being
about equal, and the hinge-line always equalling and often exceeding
in length the transverse diameter of the shell. Rarely, the shell is
bent and transversely extended, as in Leftena. ‘The cardinal pro-
cess is large and bifid; and the muscular impressions are quadrate

and laterally expanded.

The name of Strophodonta has been given to forms of Stvophomena
in which the hinge-line is crenulated, and there is no fissure in the hinge-

W
~

Af

Mn

M
[

Fig. 518.—Plectambonites (Strophomena) rhomboidalis. Silurian.

area of the ventral valve. The name of Plectambonttes (Leptagonia),
again, has been given to forms of Sfrophomena in which the shell is con-
cavo-convex, transversely semicircular, radially striated, and often con-
centrically wrinkled in the neighbourhood of the beaks (fig. 518). The
valves in these types are generally strongly geniculated, the umbonal
region being flattened, while the margins of the shell are bent towards
the dorsal aspect. Forms belonging to this group are found in the
Ordovician, Silurian, Devonian, and Carboniferous formations ; a typical

BRACHIOPODA. 663

example, and one of very wide geographical range, being the familiar
Plectambonites (Strophomena) rhomboidalis (fig. =18), which begins in
the Bala beds (Ordovician), and survived into the Carboniferous period.

The genus Streptorhynchius (Orthotetes) comprises forms like Stropho-
mena, With a biconvex or concavo-convex, radially striated shell. The
beak of the ventral valve is long, often twisted, with a high area and a
pseudo-deltidium ; the area of the dorsal valve being linear. The genus
ranges from the Devonian to the Permian, characteristic species being
the S. wmbraculum of the Middle Devonian and the S. crenistria of the
Carboniferous.

In the genus Zeftena are forms smaller than the majority of the
Strophomene, but in many respects resembling these. ‘The shell is
more or less completely semicircular (figs. 514, e¢, and 519), trans-
versely elongated, with a double hinge-area, notched in the centre,
the fissure in the ventral valve having a deltidium,
and the surface being generally striated. Speak-
ing generally, the species of Leftena can usually ¥ be
be separated from those of Strophomena or
Orthis by the form of the transversely elongated
shell, the valves of which are strongly bent, so
that one (the dorsal) is always very concave, and
the other (the ventral) correspondingly convex. pe eee
Moreover, the muscular impressions are elon- eee l Me lieske) Section
gated instead of being laterally expanded, as
they are in the genus Strofhomena. ‘The genus Leftena ranges
from the Ordovician to the Carboniferous. A few forms from the
Lower Jurassic rocks have also been referred to the genus Leftena,
but some of these are now placed in the succeeding family, in the
genus Koninckella, and it is very doubtful if the others are properly
referable to Leptena.

Finally, the genus Davidsonia includes certain singular Brachio-
pods, in which the shell is thick and solid, and is attached to foreign
bodies by the substance of the ventral valve. The ventral valve has
a wide area, with a triangular fissure covered by a convex deltidium;
and though there are no calcified brachial supports, the position of
the arms is indicated by two spirally-grooved elevations in the in-
terior of the valve. The species of Davidsonia are found in the
Devonian rocks, and the genus should perhaps be referred to the
following family.

FAMILY 3. KONINCKINID£.—This family is incompletely known,
and includes small Brachiopods, in which the shell is plano-convex
or concavo-convex, the hinge-line being straight or curved, and a
hinge-area being absent. There may or may not be a foramen in
the beak of the ventral valve, and the arms are supported upon two
loosely-inrolled spiral lamellee, the apices of the coils being directed
towards the ventral valve. ‘The typical forms of this family range

Dy .

664 MOLLUSCOIDEA.

from the Devonian to the Lias, but the Silurian genus Calospira
may possibly belong here.

In the genus Koninckina, comprising only the K. Leonhardi (fig. 520)
of the Upper Trias, the shell is circular, concavo-convex in form, very
thick, with a smooth surface and an impunctate shell-structure. The
hinge-line is straight, with teeth and sockets, but without an area or
deltidium. The ventral valve is very convex, and a large part of the
cavity of the shell is occupied by the spirally-coiled brachial processes.
Nearly allied to Koninckina is the Devonian genus Axoplotheca, in
which the spirals for the arms are more largely developed than in the
former.

Lastly, the genus Kozinckella has been founded by Munier-Chalmas
for the reception of some of the small Brachiopods of the Lias which

Fig. 520.—Koninckina Leonhard, from the Fig. 521.— Kon-
Trias of St Cassian. The left-hand figures inckella liasina.
show the ventral and dorsal aspects of the Lias. The small
shell, of the natural size. The right-hand cross below. the
figure is enlarged, and shows the spiral brachial figure indicates the
processes. (After Zittel.) real size of the shell.

were formerly referred to LeA¢ena. In this genus the shell (fig. 521) is
concavo-convex, smooth, and in general aspect not unlike a Lepffena, but
the arms are supported by spiral brachial processes of two or three coils,
which carry lateral calcareous spines for the support of the cirri of the
arms. The type of this genus is the Konnckella liasina of the Lias.

FAMILY 4. SPIRIFERID#.—In this family the shell is biconvex,
its minute structure being sometimes punctated, sometimes fibrous.
The arms were entirely supported upon two spirally-rolled calcareous
lamella, which spring from the hinge of the dorsal valve—the bases
of the spires being turned towards each other, while their apices
are directed laterally towards the cardinal angles of the shell (fig.
493).

The family of the Speriferide is pre-eminently Paleozoic, but
several forms extend into the older Secondary rocks. No member
of the family, however, has yet been found in rocks younger than
the Lias. Of the genera of the family, the most important is the
genus Spirifera, or Spirifer (figs. 522, 523, 524, and 526), in which
the valves are articulated by teeth and sockets, and the shell is not
punctated. ‘The hinge-line is long and straight, and the well-marked
hinge-area is divided across in each valve by a triangular fissure,

= PP 2g

BRACHIOPODA. 665

which in the ventral valve is closed more or less completely by a
pseudo-deltidium, and in the dorsal valve is occupied by the car-
dinal process. The true Spirifers are mainly Silurian, Devonian,
and Carboniferous, and the forms of the second of these formations
often have the shell winged, or drawn out at the lateral angles (fig.
523). In the Permian rocks a few species of the genus are found.
The forms included under the name of Sprriferina (fig. 525) range
from the Devonian to the Lias, and differ from Sfz77fera proper in

oe AT vey ag

SS a
CARDS NRO SS
a

%s acai Se Ss
SAS eS >
~) SS >

ee ee ea
ao — = EILEEN
es KRISS

.
\
Ses
j
Fig. 522.—Sfirifera sculptils. Fig. 523.—Spirifera neucronata.
Devonian. Devonian.

the fact that the shell is punctated, and in the presence of a strong
median septum in the ventral valve between the dental plates, while
the surface of the shell is usually covered with small tubular
spines.

Suessta, of the Lias, resembles Sfz7zfera in general form, and in the
impunctate structure of the shell, and agrees with Sfzriferzna in the
possession of a median septum between the dental plates in the ventral
valve, while the “ crura” of the brachial spirals are united by a transverse
band. The Carboniferous Syrzzgothyris, again, resembles Sfiriferina
in the punctation of the shell ; but the upper ends of the dental lamellze

Fig. 524.—Spirifera Niagar- Fig. 525.—Spiriferina ros- Fig. 526.—Spirifera tri-

emsis. Silurian, America. trata. Lias. gonalis. Carboniferous
Limestone.

are connected with two horizontal plates, which bend downwards in the
middle line, and form by their apposition a tubular fissure beneath the
beak of the ventral valve.

In the genus Cyrtza the shell resembles Sfzrzfera in most respects ;
but the valves are very unequal, the dorsal valve is approximately flat,
and the ventral valve is pyramidal, with a very large triangular hinge-
area and a long and narrow foramen, which is partially closed by a
pseudo-deltidium. Cyrtina (fig. 527, C and D) resembles Cy7v¢za in the
shape of the valves, but the shell is punctate, whereas in the latter it is

666 MOLLUSCOIDEA.

impunctate. The genus Cyréa is Silurian and Devonian, a familiar
species being the C. exporrecta of the Wenlock Limestone, while the
species of Cyrzézza range from the Devonian to the Trias.

More important than either of the preceding is the genus Athyris
(including under this head the Spivigera of D’Orbigny), which

Fig. 527.—A, Retzia serpentina, with part of the dorsal valve removed to show the spires;
6, Uncites gryphus, with the spires (s), from the Devonian ; c, Side view of Cyrtina heteroclita
—Devonian; p, The same viewed from the dorsal aspect; E, Athyris concentrica—Devonian ;
F, Merista levis—Silurian; Gc, Meristella angustifrons—Silurian, enlarged; u, Cast of the
same. (After Davidson and Hall.)

ranges from the Silurian to the Trias. The shell in this genus
(figs. 527, E, and 528) is convex, with unequal valves, the beak of
the ventral valve being incurved,
and either perforated by a small
round foramen, or having the
foramen concealed or closed in
the adult state. (The wxame
Athyris, like that of Azrypa, is
Fig. 528.—Athyris subtilita—Lower Car- a zoological misnomer, since in
boniferous. The right-hand figure shows the both genera the beak of the ven-
interior of the dorsal valve, with the spiral : :
supports for the arms. (After Dawson.) tral valve is‘ really perforated, in
the young state at any rate. Some
authorities, however, retain the name of Sfzrigera for those forms
in which the foramen remains throughout life, and employ that of
Athyris for those in which this aperture becomes closed in the adult
condition, the latter having the additional distinctive character that
the interior of the dorsal valve is partially divided by a longitudinal
septum.) The spiral supports for the arms in A?¢hyris are largely
developed, and their pointed extremities are directed towards the
lateral angles of the shell (fig. 528, ¢).

BRACHIOPODA. 667

Merista (fig. 527, F), of the Silurian and Devonian, is like Athyrzs in
general characters, but there is a longitudinal septum in the ventral valve,
which is supported by strongly-arched transverse plates, together form-
ing what is known as the “shoe-lifter process.” JA/eristella (fig. 527, G
and H, and fig. 529) closely resembles the preceding, but the septum and
supporting arched plates are wanting in the ventral valve. The genus is

Fig. 529.—a, Cast of the interior of the ventral valve of Meristella nasuta, from the Devonian
(Original); 4, Interior of the ventral valve of the same (after Billings).

Silurian and Devonian, and a well-known and familiar species is the
Mertstella tumitda of the Silurian rocks.

In the Silurian and Devonian genus WVucleosfira, the shell has a punc-
tated structure, with a short hinge-line, and a false area with a minute
peduncular foramen beneath the beak of the ventral valve. There is a
low median process in the interior of the ventral valve ; and the dorsal

Fig. 530.—1. Interior of a specimen of Uncites gryphus, from the Middle Devonian, in which
the greater part of the dorsal valve has been removed. ‘The spires are destroyed, but their
*‘crura” remain. 2. Restored interior of the dorsal valve of the same: a, Cardinal process ;
4, Principal stems of the spires (d); c, Band connecting the ‘‘crura” of the spires; ¢, Pouch-
shaped expansions of the beaks. (After Davidson.)

valve has a spatula-shaped cardinal process, which extends upwards
below the beak of the ventral valve, and to the base of which the “ crura”
of the brachial spires are attached.

The genus AeZzza includes a large number of species which range from
the Silurian to the Trias. The shell in this genus (fig. 527, A) is oval,
usually radiately striate or ribbed, the beak of the ventral valve being

668 MOLLUSCOIDEA.

perforated by a foramen, below which is a deltidium. The shell-struc-
ture is punctated, and the brachial spires are similar to those of Spzrzfera.
The names of 7vematospira and Rhynchospira have been proposed for a
number of Silurian and Devonian Brachiopods which are closely allied to
Retzia, but which differ from the typical forms of this genus in some
secondary characters.

Lastly, the genus Uncztes may be placed in this family, though
its characters are in some respects peculiar. The valves in Uncttes
(figs. 527, B, and 530) are convex, radially striated, and of an im-
punctate structure. The beak of the ventral valve is very promin-
ent and strongly curved. ‘The foramen in the beak of the ventral
valve disappears early, and there is no true hinge-area, but a large
concave deltidium is present, which partially conceals the incurved
beak of the dorsal valve. The margins of the beaks are bent in
wards, so as to form pouch-shaped expansions external to the hinge.
Well-developed brachial processes, of the form characteristic of the
Spiriferide, are present.

The genus Uzcztes is confined to the Devonian rocks, the type being
the familiar U. gryphus of the Middle Devonian of Europe.

FamILy 5. ATRypIp#.—In this family the shell-structure is im-
punctate, and the ventral valve has an incurved beak, with a curved
hinge-line and no _ hinge-area.
The essential character of the
family, however, is that the
dorsal valve is provided with
two spirally-coiled _ brachial
supports, the apices of which
are directed towards the in-
terior of the valve(mes 54a):
The geological range of the
family is from the Ordovi-
cian to the Trias.

The type of this family is
the genus Afrypa itself, in
which the shell (fig. 532) is
biconvex, generally radiately

Fig. 531.—Atrypa reticularis, from the Silurian ribbed, and often ornamented
rocks of North America, enlarged. The greater with squamose lines of growth.

part of the dorsal valve has been removed, to show :
the loop and spiral brachial processes. (After Hall.) Though named in accordance

with the belief that the beak
of the ventral valve was imperforate, a small foramen is really pres-
ent in this genus (fig. 531), sometimes concealed, and sometimes
bounded in front by a small deltidium. The spiral brachial pro-
cesses are large and conical, and are directed with their apices

BRACHIOPODA. 669

turned into the hollow of the capacious and ventricose dorsal valve.
The species of A¢rypa range from the Ordovician to the Trias in-
clusive, an exceedingly familiar and widely distributed species

Fig. 532.—Atrypa reticularis. Silurian and Devonian of Europe and America.
(After Billings.)

being the A. reticularis (fig. 532) of the Silurian and Devonian
rocks.

The Silurian and Devonian genus C@/ospira is generally regarded asa
close ally of Azvyfa. The brachial supports in this genus are of few
coils, and have the peculiarity that the apices of the spires are directed
towards each other. The Ordovician and Silurian genus Zygosfira
is also nearly related to A¢rypa, but the bra-
chial spires have their apices directed obliquely
into the cavity of the dorsal valve, and point
towards each other. On the other hand, in
the genus Dayza (fig. 533) the spires have
their apices turned obliquely into the cavity
of the dorsal valve in such a manner as to
point away from each other, thus facing the
sides of the shell. The type of the genus
Dayia is the familiar Silurian Brachiopod
formerly known as Rhynchonella navicula,
but now termed Dayza navicula.

FAMILY 6. RHYNCHONELLID#.—In this eee the dor:

family the animal is free, or attached by a sal valve of Dayia navicula, Si-
lurian, enlarged. (After David-

muscular peduncle issuing from a foramen _ son.)
beneath the beak of the ventral valve.
The arms are spirally coiled, and are supported at their origins only
by a pair of short, curved, calcareous processes. The shell-struc-
ture is usually fibrous and impunctate, but in a few forms it is
tubulated. The shell is biconvex, usually with a curved hinge-line,
and a prominent pointed beak in the ventral valve. The geolo-
gical range of the family is from the Ordovician to the present
day, but the great majority of the genera are confined to the
Paleozoic rocks.

The type-genus of this family is RAynchonella, in which the valves
are more or less convex, smooth, or plaited, and united by teeth and
sockets. The shell (fig. 534) is trigonal, generally with a sinus in

670 MOLLUSCOIDEA.

the ventral valve and a corresponding fold in the dorsal valve, and
having the beak of the ventral valve acute, incurved, and prominent.
The foramen is situated beneath the beak, open to view or con-
cealed, and entirely or partially completed by a deltidium. The
numerous species of Ahynchonella begin in the Ordovician rocks,
and the genus is well represented in the Silurian, Devonian, and
Carboniferous rocks. In the Secondary series the genus exhibits a

ci f

—

(i
NG

Fig. 534.—AhAyuchonella capax; dorsal, profile, and ventral views. Ordovician.

marked development in the Jurassic period ; but there are few Ter-
tiary species, and only six living forms are known.

The Permian Brachiopods which have been included under the name
of Rhynchoporina resemble Rhynchonella in all essential respects, but
the shell is punctated. In the Silurian genus Eafonza, hitherto only
found in North America, the teeth in the ventral valve are prolonged
into elevated ridges which enclose the muscular impressions, these latter
being divided by a median septum, a more developed septum being pre-
sent in the dorsal valve as well. In the Triassic genus Dzmerela,
again, there is a large triangular foramen beneath the beak of the ventral
valve, and the dorsal valve has a prominent median septum which divides
the umbonal half of the cavity of the shell into two chambers. In Zezo-

be

Fig. 535.—Letorhynchus Huronensis, viewed dorsally (a), ventrally (4), and in profile (c).
Devonian. (Original.)

>

rhynchus (fig. 535) are various Devonian Brachiopods, very closely allied
to Rhynchonella proper, but having the plications of the shell obsolete
on the lateral angles, while well marked on the mesial fold and sinus.
The beak of the ventral valve is pierced by a foramen, in at any rate the
early stages of growth, and there is a well-defined septum in the dorsal
valve. 7Zyiplesza (Silurian) has a triangular pedicle-notch beneath the
beak of the ventral valve, the hinge-line being straight, with a well-
defined hinge-area ; while the cardinal process in the dorsal valve is pro-
minent and bifurcated, and the shell itself is trilobate. Inthe Ordovician

BRACHIOPODA. 671

genus Camarella the shell is almost equivalve, the ventral valve having
an incurved imperforate beak ; and the dental lamellze converge to form
beneath the beak of the ventral valve a small triangular chamber, from
which a median septum is continued. A similar median septum is con-
tinued in the dorsal valve from the bases of the brachial
processes. Lastly, the genus Stenzoschisma (=Camaro-
phoria, King) possesses a shell lke that of Rhyncho-
nella, but the teeth in the ventral valve are supported by
converging lamellz, which unite to form a low median
septum, while a more pronounced septum is developed
in the interior of the dorsal valve. The species~of
this genus are abundant in the Devonian rocks of North
America, while other species occur in the Carboniferous
and Permian rocks.

All the preceding forms are naturally associated _ Fig. 536.—Sten-
oschisma (Came-

with one another by their structural characters; but arophoria) zlobu-
there is another great group of Brachiopods usually (ee: eee
placed in the Ahyuchonellide, and agreeing with

this family in many points, of which the genus Pentamerus is the
type, and which presents certain distinctive features of its own.
In Pentamerus (fig. 537) the shell is ovate, the valves articulated by
teeth and sockets, and the surface generally ribbed or striated, but
sometimes smooth. The beaks are incurved, that of the ventral
valve concealing a triangular fissure. Inside the ventral valve “ two
contiguous vertical septa coalesce into one median plate, extending

Fig. 537-—Pentamerus Knightit. The right-hand figure shows the internal septa and
dental plates of the shell. Silurian.

from the beak to a greater or less distance; and then diverge and
form the dental plates, enclosing a triangular chamber of much
smaller dimensions than the lateral ones” (Davidson). The small
central chamber must have been occupied by the digestive organs,
and the spiral arms must have filled the great lateral spaces. In
the interior of the smaller or dorsal valve are two longitudinal septa,
which often form a chamber corresponding with and apposed to the
median chamber in the ventral valve. The /enfamervi are confined
to the Silurian and Devonian deposits, particular species being often

672 MOLLUSCOIDEA.

restricted to definite horizons, while some forms have a very wide
geographical range. Well-known Silurian species are P. Knzghtii,
P. oblongus (fig. 538), and P. undatus, while P. globus and P. acuto-
Jobatus are Devonian, and the familiar P. galeatus is found in both
sets of deposits.

In the typical forms of Penxtamerus the shell is more or less globose,
the ventral valve is much the largest, and the median septum in the same
valve is very long. In certain Silurian species, however, which have
been placed in Penxtamerus, and for which Mr Billings proposed the
name of Stricklandia (= Stricklandinia), the two valves (fig. 539) are

WM—=T-s FPU—~M
= Mt bn Wi . \N
Z Zoom A ~
VW > IOAN i >
mT

Fig. 538.—Large specimen of Pentamerus oblongus. Fig. 539. — Stricklandia

Silurian. (Original.) Davidsoni, viewed sideways
and __ dorsally. Silurian.

(After Billings.)

not very disproportionately unequal, the shell is often more or less de-
pressed, and in the ventral valve there is but a short mesial septum
which supports a V-shaped chamber beneath the beak ; whereas in the
dorsal valve there are only two short socket-plates. Pentamerella, Am-
phigenia, Gypidula, and Anastrophia are other generic or sub-generic
titles which have been proposed for forms more or less closely allied to
Pentamerus itself. The first three of these occur in the Devonian, but
the last is found in the Silurian deposits of North America.

The genus Porambonites occupies a doubtful position, being some-
times placed in the present family, and sometimes referred to the
Strophomentde. In this genus the shell is globose and almost equivalve,
with a mesial fold and sinus in front; and the beak of the ventral valve
has a small foramen. The hinge-teeth in the ventral valve are supported
by strong dental lamella, which unite to form a small median septum.

BRACHIOPODA. 673

The surface is apparently smooth, but is in reality ornamented with
minute, close-set circular pits disposed in radiating lines. The species
of Porambonites are characteristic of the Ordovician rocks, and are
especially abundant in deposits of this age in the Baltic provinces of
Russia.

FAMILY 7. TEREBRATULID#.—The shell in the Zerebratulid@ is
minutely punctate in structure, and is rounded or oval in form, the

A s 1D \\\ ye, i FOS <
ATI SR N
pi
q pi Wy
7 Sa vn
WRAL Ler i(
sere, }) I

Fig. 540.—Interior of the ventral valve (a) and dorsal valve (bs) of the recent Waldheimia
Jiavescens. a’, Beak of the ventral valve with the foramen (/); ¢, Hinge-teeth; 4, Septum of
dorsal valve ; Z, Brachial loop; s, Dental sockets ; 2 a, Adductor-impressions ; 6 4, Ventral ad-
justors; ¢ c, Divaricator-impressions; 4’, Peduncular muscles; c’, Cardinal process. (After
Davidson.)

surface being smooth or striated. The beak of the ventral valve
(fig. 540, a’) is prominent, and is perforated by a foramen, through
which passes the peduncle of attachment, and which is partially
surrounded by a deltidium of one or two pieces. The arms are
supported by a loop-shaped brachial process (fig. 540, 7), which

SSS
—S—SsSs
—=

Fig. 541.—a, Terebratula quadrifida—Lias ; b, Terebratula spheroidalis—Inferior Oolite ;
¢, Terebratula digona—Bradford Clay, Forest Marble, and Great Oolite (Jurassic). (After
Davidson.)

varies in length and form in different types of the family, and which

springs from the hinge of the dorsal valve. As regards its geolo-

gical range, the family of the Zervebratulide is represented in de-

posits as old as the Devonian, or even the Silurian; but it attains

its maximum development in the Mesozoic and Kainozoic deposits,
WOL. I. 2U

674 MOLLUSCOIDEA.
and it is represented at the present day by a number of living
forms.

In the genus Zerebratula itself, as now usually restricted, the
shell (fig. 541) is oval or circular, with a smooth surface, and either
simply rounded in front, or exhibiting a mesial fold in the ventral
valve, to which corresponds a sinus, with a lateral fold on each side,
in the dorsal valve. The beak of
the ventral valve is short, with a
wide foramen, below which is a
deltidium. The brachial loop (fig.
542) is short, and does not extend
to more than a third of the distance
between the hinge-line and the an-
: terior “margin of the shell ihe

Fig. 542.—Terebratula sacculus—Car- Oldest forms of the Zevebratule ap-
boniferous. The right-hand figure shows : :
the interior of the dorsal valve with the P€ar in the Devonian, and other
loop. (After Dawson.) forms are found in the Carbonif-
erous and Permian deposits. These
early examples of the genus differ from later types in the possession
of strong dental supports beneath the hinge of the ventral valve.
Throughout the Secondary rocks, and especially in the Jurassic and
Cretaceous formations, the genus is largely represented, while there °
is also a limited number of Tertiary types, and several living species
are known.

In Terebratulina (fig. 543) the exterior of the shell is ornamented with
dichotomous radial strize, and the brachial loop is very short, and is con-
verted into a simple ring. The species
of Terebratulina range from the Jurassic
to the present day.

The genus Waldheimia is the type of
another series of the Zevebratulid@, in
which the brachial loop is elongated, its
length equalling at least half that of the
S shell itself (fig. 540). In addition to the
ub, Spc Terebeatulina suistrinta, presence of a long brachial loop, another
(After Zittel.) distinctive character of Waldheimia is

. the existence of a more or less developed
median septum in the interior of the dorsal valve. The species of Wald-
heimta appear to commence in the Lias, and the genus is well represented
at the present day. There are no dental plates in the ventral valve of
Waldhetmia, but such plates are developed in the closely allied Zezllerza
of the Jurassic, Cretaceous, and older Tertiary formations.

In the Silurian, Devonian, and Carboniferous genus Ceztronella (fig.
544), the shell has the general characters of 7erebratu/a, but the brachial
loop consists of two delicate ribbon-like lamellae, which extend about
one-half the length of the shell. “These lamellz at first curve gently
outwards, and then approach each other gradually, until at their lower
extremities they meet at an acute angle; then, becoming united, they
are reflected backwards towards the beak, in what appears to be a thin,
flat, vertical plate. Near their origin each bears upon the ventral side

BRACHIOPODA. 675

a single triangular crural process” (Billings). The species of this genus
seem to be mainly confined to the Paleozoic rocks of North America ;
but European forms are
known. The Silurian and
Devonian genus Leftocelia
seems to be nearly allied
to Ceztronella, but the shell
is radiately-ribbed, whereas in
the latter genus it 1s smooth.
The Silurian and Devonian
genera Rensseleria and Me-
ganterts likewise include
ancient types of the Zeredbra-
tulide. Fig. 544.—Lateral (a) and dorsal (4) views of Cen-

tronella glans-fagea, from the Devonian rocks of
In the genus Terebratella North America, Of the natural size; c, Brachial loop

(fig. 545) the shell is some- of the same, enlarged. (After Hall—copied from

times smooth, sometimes ra- @#ttel.)

diately-ribbed, and there is

an incomplete deltidium (7) below the foramen. In the dorsal valve

is a well-developed mesial septum, with which the brachial loop becomes

secondarily connected by means of transverse calcareous processes, one

on each side. The genus Zevedbyatel/a begins in the Lias, is well repre-

sented in the Cretaceous formation, and still exists at the present day.
Various Mesozoic, Tertiary, and Recent Brachiopods are closely re-

Fig. 545.— Terebratella Astieriana—Cretaceous. ¢, Hinge-area; 7, Deltidium.

lated to Terebratella, with which they agree in the fact that the brachial
loop, in addition to its normal attachment to the hinge-line, has a second-
ary connection with a median septum in the dorsal valve. Among the
forms in question, Lyra (Terebrirostra) has a greatly elongated beak to
the ventral valve, and is confined to the Cretaceous period. The genus
Trigonosemus, also Cretaceous, has an incurved beak, a large cardinal
process, and an extensive hinge-area. In the genus JZagas, of the Cre-
taceous period, the dorsal septum is so greatly developed as almost to
divide the cavity of the shell into two halves ; while in Wegerlza (Chalk
to Recent) the brachial loop is not only attached to the hinge-plate, but
is doubly connected with the dorsal septum. The Jurassic and Creta-
ceous Kzugena, and the recent Louchardia and Kraussina are other
types belonging to the same group.

FamiLy 8. ARGIOPIDA.—In this family there is a large foramen
for the transmission of the peduncle of attachment, and the dorsal

676 MOLLUSCOIDEA.

valve is provided with one or more sub-marginal septa, with which
the brachial loop becomes more or less extensively fused. The
shell-structure is punctate. The range of the family is from the
Jurassic period to the present day.

The type-genus of this family is Azgzoge itself, which ranges from
the Upper Jurassic to the present
day. In this genus the shell (fig.
546) is transversely oval, with a
straight hinge-line and an area to
each valve, and having a large fora-
men, with a rudimentary deltidium.
The interior of the dorsal valve is

furnished with from three to five
of Azite demiiis (Recent) caged, Sub<Matginal “septa (s) ; while ste
spowing the subamareical sepia (9 2x4 brachial loop follows the margin of

the shell, and becomes attached to
the septa, thus becoming four-lobed, being at the same time partially
confluent with the shell. Czs¢e//a (Lias to Recent) closely resembles
Argiope in general characters, but there is only a single septum in
the dorsal valve, and the brachial loop is two-lobed.

FAMILY 9. STRINGOCEPHALID#.—In this family the shell is
rounded ; the beak of the ventral valve possesses a foramen and

nie
\
i

wee NS
P

GSHoweO
7

Fig. 547.—A, Interior of the dorsal valve of Stvingocephalus Burtint, Middle Devonian; B,
Shell of the same viewed in profile and showing the interior : a, Adductor impression ; Z, Cardinal
process; Z, Hinge-plate; c, Crura of loop (2); @, Dorsal septum; v, Ventral septum; 7, Dental
sockets. The radial processes of the loop are shown in a by dotted lines. (After Davidson.)

deltidium ; the cardinal process of the dorsal valve is greatly de-
veloped ; and the brachial loop is marginal, and carries internally-
directed radial processes. The only genus comprised in this family
is Stringocephalus itself, which is confined to the Silurian and De-
vonian rocks.

BRACHIOPODA. 677

_ ‘The type-species of Stringocephalus is the well-known S. Burtini
of the Middle Devonian of Europe. In this well-known species
(figs. 547 and 548) the shell is sub-orbicular, with a prominent beak
to the ventral valve, and often growing to a great size. There is a
large foramen below the beak of the ventral valve, which is triangular
in the young shell, but ultimately becomes oval and reduced in size
by the growth of the deltidium. The ventral
valve has prominent teeth, fitting into corre-
sponding sockets (¢) in the dorsal valve. The
cardinal process (f) in the dorsal valve is very
prominent, and its free end is bifurcated to
receive a well-developed median septum (vz) in
the ventral valve. A corresponding, but much
smaller septum (d@) is present in the dorsal valve. Fig. 548. — Str-ingoce-
The hinge-plate (2) of the dorsal valve gives {4a/“s Buriint_Devon
origin to a large brachial loop (/), consisting of

two crura (¢) which are reflected backwards about the middle of the
valve, and then, bending forwards, give origin to a wide ribbon-

Fig. 549.—Thecidium papillatum. e, Hinge-area; 7, Hinge-teeth of ventral valve
y yr, Granulated border of the interior of the dorsal valve. Cretaceous.

shaped band, which is sub-marginal in position, and gives off radiat-
ing shelly processes along its inner margin.

FAMILY to. THECIDIIDZ.—In this family the shell is usually
fixed to the sea-bottom by the substance of the beak of the ventral
valve ; the arms are united in the form of a bridge over the visceral

678 MOLLUSCOIDEA.

cavity, are folded upon themselves, and are supported by a cal-
careous loop; and the mantle is strengthened by a copious develop-
ment of calcareous spicula. The inner layer of the shell is fibrous,
but the outer layer is tubulated. The geological range of the family
is from, the Carboniferous to the present day.

The type-genus of this family is Zhectdium (= Thecidea) which
commences in the Upper Trias, is well represented in parts of the
Jurassic and Cretaceous rocks, and survives under two specific forms
at the present day. In this genus the shell (fig. 549) is plano-
convex, and is fixed by the substance of the beak of the ventral
valve, or may be free in the adult condition. ‘The hinge-line is
straight, with powerful hinge-teeth in the ventral valve, this valve
being further distinguished by the presence of a large triangular
hinge-area, in which is a pseudo-deltidium. The margins of both
valves exhibit internally a broad granulated and thickened border.
In the dorsal valve is a prominent cardinal process, flanked by the
dental sockets, below which the brachial supports unite to form a
slender bridge. The loop follows
the margin of the shell, generally
forming more or fewer lobes, and
is either confluent with the shell,
or is connected with a calcareous
network formed by the largely
developed spicula in the mantle.

Besides the Liassic types in-
cluded under the names of Lude-
sella, Davidsonella, and Bactrynium,
this family includes the remarkable
Carboniferous types described by
Waagen under the names of O/d-
hamina and Lyttonia. In these
singular forms the shell is of large
size, flat or gibbous, and attached
by the ventral valve. The hinge-
line is straight and short, without

Fig. 550.—A, Interior of the ventral valve GME! alice) OIE pseudo-deltidium. 2 In-
cus corks of Indi: 9, Carcinel ey eran See Oe a
dorsal valve. (After Waagen.) a median septum, flanked on both

sides by numerous, transverse and
oblique, lateral septal ridges. The dorsal valve is rudimentary,
“forming together with the brachial apparatus one strongly-lobed
shelly plate, which fits between the external septa of the large valve ”
(Waagen). These abnormal types have hitherto been detected only
in the Carboniferous rocks of India, and they are regarded by
Waagen as forming a special sub-family of the Zhecidide.

4 OO Nom

LITERATURE OF BRACHIOPODA. 679

EIDE RAGURE:

. “Manuel de Conchyliologie.” Paul Fischer. 1887.

. “Manual of the Mollusca.” S. P. Woodward. 4thed. 1880.
wdtandbuch der Palzcontologie.” Bd. I, Liefi 4. 1880: Zittel:

. “ Monograph of the British Fossil Brachiopoda.” ‘ Palzeontographical

Society.’ (With Supplements.) 1851-85. Davidson. (The first
part contains a Memoir by Professor Owen on the Anatomy of
Terebratula, and one by Dr W. B. Carpenter on the Intimate
Structure of the Shell of the Brachiopoda.)

AS Monograph of Recent Brachiopoda.” ‘Trans. Linn. Soc.’

(Zoology), vol. iv., 1886-87. Davidson.

. “On the Earliest Forms of Brachiopoda hitherto discovered in the

British Palzeozoic Rocks.” ‘ Geological Magazine,’ vol. v., 1868.
Davidson.

. “On the Genera and Species of Spiral- bearing Brachiopoda.”

‘Geological Magazine.’ Dec. II., vol. viii. 1881. Davidson.

Ou the mdarimerclida “Quart, Journ. Geol, Soc, vol) xxx., 1874.

Davidson and King.

. “On some Characters of Lingula anatina, illustrating the study of

fossil oPalhobranchs:” “Ann. Nat, Hist... Ser, vol. xit., 1873.
King.

. “A Monograph of the Permian Fossils of England.” ‘ Palzonto-

graphical Society, 1850. King.

11. “ Ueber Terebrateln, mit einem Versuch sie zu classificiren und zu
beschreiben.” Berlin, 1834. Von Buch.

12. “A Revision of the Terebratulidz and Lingulide.” ‘American
Journal of Conchology,’ vol. vi., 1870. Dall.

13. “ Petrefaktenkunde Deutschlands.” Bd. IJ. Die Brachiopoden.
1871. Quenstedt.

14. “Systeme Silurien du Centre de la Boheme.” - Vol. v., Brachiopodes.
1879. Barrande.

15. “ British Palzeozoic Fossils.” M‘Coy. 1852.

16. “Figures and Descriptions of British Palzeozoic Fossils.” 1841.
Phillips.

17. “ Paleontology of New York.” James Hall. Vols. 1.-iv. 1843-67.
Vol. iv. of this great work is specially devoted to the Brachiopoda,
and the earlier volumes are largely concerned with descriptions
of forms belonging to this class.)

18. “ Reports of the State Cabinet” (the 13th, 15th, 16th, 2oth, 23d, 24th,

and 29th). 1860-75. Hall.

19. “ Paleozoic Fossils.” Vols. i. and 11., 1861 and 1874. Billings.

““ Monographie des genres Productus et Chonetes.” De Koninck.
1847.

21. “ Salt Range Fossils.” ‘ Palzeontologia Indica,’ 1879-85. Waagen.

2. “ Bidrag till Kannedomen om Gotlands Brachiopoden.” ‘ Ofversigt

af k. Vet. Akad. Férhandl.’ Bd. XVII. 1860. Lindstr6m.

. “Ueber die Brachiopoden der Késsener Schichten.” ‘ Denkschr. d.
k. Akad. d. Wiss. Wien.’ Bd. VII. 1854. Suess.
. “Zusammenstellung und Beschreibung simmtlicher im Uebergangs-

gebirge der Eifel vorkommenden Brachiopoden.” ‘ Palzeonto-
Srapnica, ~ Bde ills +1354. Schnur.

. “Die Brachiopoden des Mittel- und Ober-Devon der Eifel.” ‘ Zeitschr.

d. deutsch. Geol. Gesellschaft... Bd. XXIII. 1871. Kayser.

680

CT ar Re Xe exer

SOB KINGDOM MOLLOSCA-

GENERAL CHARACTERS OF THE MOLLUSCA—GENERAL CHARACTERS
OF THE LAMELLIBRANCHIATA.

THE Mollusca may be defined as soft-bodied, bilaterally symmetrical,
not definitely segmented animals. The anterior part of the body is
very generally developed into a distinct head, bearing one or more pairs
of soft tactile processes or tentacles. The mouth is anterior, the alt-
mentary canal is completely shut off from the general cavity of the
body, and the anus ts primitively posterior. The nervous system con-
sists of a small number of paired ganglia. A distinct vascular sys-
tem and a systemic heart are present. One or more pairs of kidneys
(sometimes a single kidney) are present as saccular organs (“ne-
phridia”), which open internally into the body-cavity, and communt-
cate with the exterior by a pore placed near the anus. Commonly
there ts an external or internal “ shell.”

The body of a Mollusc exhibits a distinct dorsal and ventral
surface, and a right and left side. The dorsal surface is covered
by a fold of the integument which constitutes what is called the
“mantle” or “pallium,” and which may be greatly expanded later-
ally, or may form a complete sac enclosing all the viscera. The
so-called “‘mantle-cavity” or “pallial chamber” is the space in-
cluded between the lateral prolongations of the mantle and the
sides of the body.

From the ventral side of the body there is, typically, developed
an unpaired median muscular mass, which constitutes what is called
the “foot.” The foot (fig. 551, 7) may show a distinct division
into an anterior, a middle, and a posterior region; and it is often
furnished with distinct lateral prolongations (“‘epipodia”). The
foot undergoes remarkable modifications in different groups of the
Mollusca.

The alimentary canal commences at the mouth (fig. 551, 72),

GENERAL CHARACTERS OF THE MOLLUSCA. 681

which may or may not be provided with an apparatus of teeth, or
may be furnished with tactile processes. The digestive tube is com-
monly of considerable length, and usually shows a gullet, into which
salivary glands pour their secretion, a stomach, and an intestine.
The rectum terminates at the anal aperture (fig. 551, @), which is
primitively at the hinder end of the body, but which in many forms
ultimately becomes shifted further forward. The blood is colour-
less ; and a definite heart, consisting of a ventricle and one or two

Piles:

e

Th ed
TE lS .

vn 7 f X vg

Fig. 551-—Diagram of a Mollusc (altered from Lankester). 2, Mouth; a, Anus; Z, Liver:
J, Foot; sh, Shell, attached to the mantle; 2, Heart; fe, Pericardium ; z, Kidney, opening in-
ternally into the pericardium, and externally near the anus (2); 4r, Gill; eg. One of the cerebral
ganglia, connected by commissures with the pleural ganglion (fg) and the pedal ganglion (4);
va, Visceral nerve-cord extending backward, and carrying visceral ganglia (wg).

auricles, is always present, and always has the function of propell-
ing the aerated blood through the body.

Respiratory organs are not always developed, the function of
respiration being in some cases discharged by the thin walls of the
mantle-cavity. In the majority of the Molluscs, however, there are
definite respiratory organs, a portion of the mantle being specialised
for this purpose. Inthe Zamel/libranchiata, and the branchiate Gas-
tropoda, the breathing-organs are in the form of lamellar or pectin-
ate gills; and the same is the case with the Cephalopoda. In the
pulmonate Gastropoda, in which respiration is aerial, a pulmonary
sac or air-chamber is produced by the folding of a portion of the
mantle, over the interior of which the pulmonary vessels are dis-
tributed, and the external opening of which is placed on the side
of the neck.

The nervous system consists of paired ganglia united by com-

6S2 MOLLUSCA.

missures. The most important ganglia are (1) a pair of “cerebral ”
ganglia, placed above the gullet; (2) a pair of “pedal” ganglia
placed below the gullet, and supplying the foot and adjacent parts ;
and (3) a group of ‘‘ visceral” ganglia placed towards the posterior
part of the body.

Reproductive organs are always present, and the sexes may be
distinct or united. There is usually a well-marked metamorphosis
in development, and the embryo very commonly passes through a
“‘trochosphere” stage, in which it swims about actively by means
of a circlet of cilia placed in front of the mouth, and closely re-
sembles the larva of many Annelides. ‘The young Mollusc pos-
sesses a glandular involution of the dorsal integument, which pro-
duces an embryonic shell, and this may either be cast off as de-
velopment proceeds, or may remain permanently as part of the
shell of the adult. In the Spiral Gastropods the embryonic shell
or “nucleus” is placed at the apex of the permanent shell, whereas
in the Bivalves it is situated at the beak or “ umbo.”

The Molluscs very generally develop an integumentary skeleton
in the form of a “shell,” which in all forms, except in the Argonaut,
is secreted by the mantle. In chemical composition the shell con-
sists of carbonate of lime disseminated throughout an organic
matrix. The atomic arrangement of the carbonate of lime differs
in different cases, some Molluscs having the shell wholly composed
of calcite, while in others it is wholly composed of aragonite, and
in many forms it consists of an inner layer of aragonite and an
outer layer of calcite. Very generally the outer surface of the shell
is covered by an easily recognisable horny external layer (the “‘ epi-
dermis” or “periostracum”), but this may be exceedingly thin, or
may disappear altogether in the course of growth. Some of the
more important points in the microscopic structure of the shell will
be briefly noticed in dealing with the different groups of Molluscs.
While the presence of a shell is very characteristic of the Molluscs,
there are many so-called “naked” forms, in which the adult is
either totally devoid of a shell, or possesses only a rudimentary
shell enclosed in the substance of the mantle.

The JAZollusca may be roughly divided into two great sections,
respectively termed the Acephala and the Lxcephala (or Cephalo-
Phora), characterised by the absence or presence of a distinctly
differentiated head. The headless, or Acephalous, Molluscs corre-
spond to the class Lamellibranchiata ; also distinguished, at first
sight, by the possession of a bivalve shell. The Encephalous
Molluscs are more highly organised, and are divided into the two
principal classes of the Gastropfoda (including the Preropoda) and
the Cephalopoda, with which may be associated the two small and
aberrant groups of the Polyplacophora (Chitons) and Scaphopoda

LAMELLIBRANCHIATA. 68 3

(Tooth-shells). The shell in the Encephalous Molluscs is of a
very different nature in different cases, but all the members of this
section possess a complicated series of lingual teeth, and they have
for this reason been grouped together by Professor Huxley under
the name of Odontophora.

As regards their dstribution in space, all the members of the
Mollusca are aquatic in their habits with the exception of a portion
of the Pulmonate Gastropods, many of these, however, being in-
habitants of water, though others are strictly terrestrial. The
water-inhabiting Molluscs may live in the sea, or in brackish or
fresh waters. Owing to their generally living in water, and
owing also to their so commonly possessing hard structures, whether
external or internal, no fossils are, more abundant or more import-
ant than the remains of the JZollusca. As regards the general ds-
tribution tn time of the Molluscs, all the principal classes (viz., the
Lamellibranchiata, Gastropoda, and Cephalopoda) are represented
in the Upper Cambrian deposits, and it is therefore clear that we
have at present no knowledge of the really primordial types of the
sub-kingdom. Speaking generally, the chief representatives of the
Mollusca in Palzeozoic time are the chambered Cephalopods ( Zé¢ra-
branchiata), the Dibranchiate Cephalopods apparently not having
come into existence, while the Lamellibranchs and Gastropods
show a comparatively limited development. In Mesozoic time,
the Dibranchiate Cephalopods make their first appearance, and
undergo a vast development, while the Tetrabranchiate division of
this class has also a wonderful representation. ‘The Lamelli-
branchs are very largely represented in the Mesozoic deposits, but
the Gastropods still play a subordinate part. In Kainozoic time,
on the other hand, the Cephalopods undergo an extraordinary re-
duction, the group of the Tetrabranchiates becoming almost extinct,
while the Lamellibranchs and Gastropods, the latter particularly,
assume a predominant position. At the present day, the Lamelli-
branchs and Gastropods are the two leading classes of Molluscs,
and both seem to have attained their culminating point in existing
seas.

Crass I]. LAMELLIBRANCHIATA.

The Lamellibranchiata (= Conchifera or FPelecypoda) are often
familiarly spoken of as the “ Bivalve Molluscs,” and are characterised
by the absence of a distinctly differentiated head, and by having the
mantle divided into two lobes, right and left, each of which secretes a
shelly investment, so that the body is more or less completely enclosed
in a bivalve shell. There are one or two pairs of lamellar gills on
each side of the body. An odontophore ts wanting. The sexes are
distinct or united.

684 ; MOLLUSCA.

The body in the Lamellibranchs is bilaterally symmetrical, and is
enclosed in a largely developed ‘‘ mantle” or “ pallium,” which is
divided into two lateral halves, the
right and left “‘lobes” of the mantle.
The two lobes of the mantle are
united along the dorsal side of the
body, and are prolonged laterally as
two great flaps, which conceal the
body, and enclose inferiorly a cham-
ber known as the ‘ mantle-cavity.”
The lower or ventral edges of the
mantle-lobes are normally free; but
in many Bivalves they become more
or less fused with one another (fig.
552), so that the animal is enclosed
in a complete sac, in which certain
openings are left anteriorly and pos-
teriorly. Two of these apertures are
at the posterior end of the animal,
and serve to permit the ingress into
the mantle-cavity of the water required
for respiration and for the purpose of

oh Se obtaining food, and the egress of the

Fig. 552.-—Diagrammatic vertical and
transverse section of Mya arenaria. 6, SaMe. The lower or ventral aperture
Back, or.’ ‘dorsal margin of the shell; “is inhalant in‘ function ;9the pmeemme

s s, The two valves of the shell, right i
and left; 2 m, The two halves, or dorsal aperture is exhalant ; and the

“lobes,” of the mantle, producing the : é at Gale
shell; gg, The gills, two pairs on each anus is always placed in the vicinity
side ; 2, The heart; 7, Intestine; , The OF the latter, so that excrementitious

matters are carried away in the out-
going currents of water. In many cases these two openings. into
the mantle-sac are drawn out into longer or shorter muscular tubes,
which are known as the “siphons.” In those Bivalves which have
the ventral margins of the mantle-lobes /vee, the in-going and out-
going currents of water still enter and leave the mantle-cavity by
openings at its posterior end.

In those Bivalves which have the mantle-lobes fused along their
ventral edges, a third aperture is necessary in order to allow of the
protrusion of the “foot.” This aperture is always placed ventrally
and towards the anterior end of the animal. In the forms with
free mantle-lobes no special opening is needed for the protrusion of
this organ. :

The ‘‘foot” of the Bivalves is not so extensively developed as in
the Gastropods. Usually it forms a hatchet-shaped muscular organ,
which may be used in locomotion, but is hardly ever adapted for
crawling. In other cases it is cylindrical in shape, and in the

LAMELLIBRANCHIATA. 685

sedentary Bivalves it is more or less completely aborted. In many
cases, especially in the young, there is developed, on the under
surface of the foot, in the middle line, a peculiar “‘ byssal gland.”
This gland secretes a viscid material which is moulded into threads
by grooves on the external surface of the foot, and which gives rise
to a tuft of silky fibres (the ‘“‘ byssus”), serving to moor the animal
to foreign objects, and often having a special notch or aperture in
the shell for its emission.

The sHe// of the Bivalves is the result of the deposition of lime-
salts in the outer layer of the mantle, chiefly along its ventral mar-
gins ; and as the mantle is divided into a right and left ‘‘ lobe,” so
the shell also is divided into a right and left “‘ valve.” The outer
surface of the shell is usually covered by thinner or thicker horny
“epidermis” or cuticle, but this may become obsolete in the adult.
The calcareous tissue of the shell itself is very generally disposed in
two distinct strata, of which the outer is prismatic, and the inner is

F + ‘ : Bt
eS We fe 7 2 iy
Wd Cf ein Fi > ie
id ©. ie ; tilt }
wes ¢ le ALALe 2
Y. He Ghar p
= foil JS So 1 aS
BD i i 2 > ag
i ve DR Ps Ie ot less
4 ji 3 ye 5 ;

ran

Fig. 553-—A, External surface of Pizza, showing the ends of the prisms of the outer shell-
layer, greatly enlarged; B, Polished surface of mother-of-pearl, enlarged eighty-five times.
(After W. B. Carpenter.)

laminated. The outer prismatic layer is secreted by the free edges
of the mantle-lobes, and grows, therefore, at the circumference of
the shell only. It consists, in the majority of cases, of polygonal
calcareous prisms, placed side by side in close contact, and directed
perpendicularly to the surface of the shell. Hence sections of this
layer taken parallel with the surface exhibit the transversely-divided
prisms as a pavement of hexagonal or polygonal cells ; and the same
appearance is seen on examining the surface of this layer under a
sufficient magnifying power (fig. 553, A). The prisms of the outer
layer of the shell vary considerably in diameter, length, regularity,
and precise mode of arrangement in different Bivalves. The inner

686 MOLLUSCA.

layer of the shell is laminated, and is secreted by the whole outer
surface of the mantle. Hence, this stratum is produced in successive
layers throughout the entire life of the animal, each new layer ex-.
tending a little beyond the one last formed; and in this way are
produced the concentric “lines of growth,” which are so character-
istic of the shells of the Bivalves. The calcareous laminze compos-
ing the inner layer of the shell are disposed approximately parallel
to the surface. In many cases (fig. 553, B) the laminze are very
delicate, and are more or less crumpled or undulated, so that when
the minute undulations of the successive layers of this stratum are
exposed on the surface, the rays of light are broken up in such a
way as to give rise to the iridescence and play of colours character-
istic of ‘“‘mother-of-pearl” or ‘‘nacre.” In other cases, however,
the laminee of this internal stratum are thicker, and are not minutely
undulated, and this layer then assumes a ‘‘ porcellanous” character.

As regards the chemical composition of the shell in the Bivalves, con-
siderable differences obtain as to the precise condition in which the
carbonate of lime presents itself. In some cases (as, for example, in
Ostrea), both the outer and inner layers of the shell are composed of
calcite, whereas in others both layers are formed of aragonite. In other
cases, again (as in Pz77a), the outer prismatic layer is composed of cal-
cite, while the inner laminated layer is formed of aragonite. Owing to
the greater destructibility and instability of aragonite as compared with
calcite, these differences in composition lead to considerable differences
in the mode of preservation of different types of the Bivalves. Thus,
forms in which the shell is wholly composed of aragonite are often repre-
sented in the fossil state solely by moulds and casts; while in those in
which the two layers of the shell differ in composition, the inner ara-
gonite-layer of the shell may have been wholly removed, while the outer
calcite-layer may be well preserved.

Though the Bivalves agree with the Lvachiopoda in possessing a
shell which is composed of two pieces or valves (small accessory
plates are present in Phol/as, &c.), there are, nevertheless, many
points in which the shell of a Lamellibranch is distinguished from
that of a Brachiopod, irrespective of the great difference in the
structure of the animal in each. The shell in the 4rachiopoda, as
we have seen, is rarely or never quite equivalve, and always has its
two sides equally developed (equilateral); whilst the valves are
placed antero-posteriorly as regards the animal, one in front and
one behind, so that they are “dorsal” and “ventral.” In the
Lamellibranchiata, on the other hand, the two valves are usually
of nearly equal size (equivalve), and are more developed on one
side than on the other (inequilateral); whilst their position as
regards the animal is always J/azera/, so that they are properly
termed “right” and “leit” valves, instead “of “ventral” sama
“* dorsal.”

LAMELLIBRANCHIATA. 687

It is to be remembered, however, that many of the Bivalves, such
as the Oysters, habitually lie on one side, in which case the valves,
though really right and left, are called ‘‘upper” and “lower.” It is
to be borne in mind, also, that the two valves, especially in the
attached Bivalves, may be very unsymmetrical, one valve being
much larger or deeper than the other. Lastly, there are. some
cases (e.g., Lectunculus) in which the shell becomes very nearly
equilateral, the line drawn from the beaks to the base dividing the
shell into two almost equal halves.

The following are the chief points to be noticed in connection
with the shell of any Lamellibranch (fig. 554): Each valve of the
shell may be regarded as essentially a hollow cone, the apex of
which is turned more or less to one side; so that more of the shell
is situated on one side of the apex than on the other. The apex
of the valve is called the ‘“‘umbo,” or “ beak,” and is mostly turned
towards the mouth of the animal. Consequently, the side of the

h

—— U

4 NE L

C

Fig. 554.—Left valve of Cytherea chione. (After Woodward.) a, Anterior margin; p,
Posterior margin; c, Ventral margin or base. uw, Umbo; 4, Ligament; Z, Lunule; c, Cardinal
tooth; 77, Lateral teeth; a, Anterior adductor; a’, Posterior adductor; Z, Pallial line; s, Pallial
sinus, caused by the retractor muscles of the siphons.

shell towards which the umbones are turned is the “anterior” side,
and it is usually the shortest half of the shell. In some Bivalves,
however, the beaks are “reversed,” and are turned towards the
posterior side of the shell. The longer half of the shell, from which
the umbones turn away, is called the “ posterior” side, but in some
cases this is equal to, or even shorter than, the anterior side. The
side of the shell where the beaks are situated, and where the valves
are united to one another, is called the “dorsal” side; and the
opposite margin, along which the shell opens, is called the “ ventral”

688 MOLLUSCA.

side or “base.” The /ength of the shell is measured from its an-
terior to its posterior margin, and its dveadth from the dorsal margin
to the base.

At the dorsal margin the valves are united to one another, for a
shorter or longer distance, along a line which is called the “ hinge-
line.” The union is effected in most shells by means of a series of
parts which interlock with one another (the “ teeth”), but these are
sometimes absent, when the shell is said to be ‘‘ edentulous.” Pos-
terior to the umbones, in most Bivalves, is another structure passing
between the valves, which is called the “ligament,” and which is
usually composed of two parts, either distinct or combined with one
another. These two parts are known as the “external ligament ”
(or the ligament proper) and the “cartilage,” and they constitute
the agency whereby the shell is opened ; but one or other of them
may be absent. The ligament proper is outside the shell, and
consists of a band of horny fibres, passing from one valve to the
other just deiznd the beaks, in such a manner that it is put upon the
stretch when the shell is closed. ‘The cartilage, or internal ligament,
is lodged between the hinge-lines of the two valves, generally in one
or more “pits,” or in special processes of the shell. It consists of
elastic fibres placed perpendicularly between the surfaces by which
it is contained, so that they are necessarily shortened and compressed
when the valves are shut. To open the shell, therefore, it is simply
necessary for the animal to relax the muscles which are provided
for the closure of the valves, whereupon the elastic force of the
ligament and cartilage is sufficient of itself to open the shell.

Generally the hinge-line is curved, but it is sometimes straight.
The beaks are mostly more or less closely contiguous ; but they may
be removed from one another to a greater or less distance, and in
some anomalous forms they are not near one another at all. In
the genus Azca the two beaks are separated from one another by
an oval or lozenge-shaped flat space or area. When teeth are
present, they differ much in their form and arrangement. In many
forms (fig. 554) the teeth are divisible into three sets—one group,
of one or more teeth, placed immediately beneath the umbo, and
known as the “cardinal teeth”; and two groups on either side of
the preceding, termed the “lateral teeth.” Sometimes there may
be lateral teeth only; sometimes the cardinal teeth alone are
present ; and in some cases (Avcide) there is a row of similar and
equal teeth.

While the opening of the valves of the shell of a Lamellibranch
is effected by the elastic force of the ligament, the closure of the
valves is effected by the contraction of one or two powerful muscles,
which are known as the “adductor muscles.” In the majority of
Bivalves—hence termed Dzmyaria—there are two adductor muscles,

LAMELLIBRANCHIATA.

689

which pass from the inner surface of one valve to that of the other,
one being placed anteriorly in front of the mouth, while the other
is situated posteriorly close to the termination of the intestine (fig.

555, @ and a’). Moreover, among
the Dimyary Bivalves the adductors
present two markedly different con-
ditions. In one group of forms —
hence termed Homomyaria—the an-
terior and posterior adductors are
approximately equal in size. In a
second series—hence termed /fe¢ero-
myaria —the anterior adductor is
very small, and the posterior adduc-
tor is very large. Examples of this
latter condition are found in the
Mussels, Pearl-mussels, &c. On the
other hand, in Ostrea, Fecten, and
certain other Bivalves—hence called
Monomyaria — the anterior adductor
is absent, and the posterior adductor
alone remains. ‘The adductors leave
distinct “muscular impressions” in
the interior of the shell (fig. 556),
so that it is easy to determine, by a
simple inspection of the dead shell,
whether a given Bivalve has been
‘“‘ dimyary ” or “ monomyary.”
Besides the scars left by the ad-
ductor muscles, or muscle, there are
other impressions in the interior of
the valves which are produced by
the attachment of muscles. Thus,
the “foot” is very commonly pro-
vided with ‘‘ pedal muscles,” which
leave small scars in the inside of the
shell. When they are well devel-
oped, the “pedal impressions” are
twofold, consisting of an impression
formed by the “ protractor” muscle
which exserts the foot, and of another,
posteriorly-placed scar formed by the
“retractor” muscle which withdraws

\
ro)

r ASAP AAA Ae ranean

ae.
=m
RS

ALN IO IRL AANA S SAL
iti
= SS
y ===
na DN

lol ff SES = iS
(2 SES . S

Sees" ae
Fp 9 =: =sec
SSS
PP SSS
| ha a

Fig. 555.— Anatomy of Mya arenarvia.
(After Woodward.) The left valve of
the shell and the left mantle-lobe are
removed, and half of the siphons has
been cut away. a, Anterior adductor ;
a’, Posterior adductor ; 6, Visceral mass ;
c, Chamber of the mantle-cavity into
which the anus (vw) opens; 7, Foot; g,
Branchiz; 4, Heart; 7z, Cut ventral
edge of the mantle; 0, Mouth; s, In-
halant siphon; s’, Exhalant siphon; /,
Labial palpi. ‘The arrows indicate the
direction of the water-currents.

the foot (fig. 556, a, Af and 7A), a second retractor being some-
times inserted behind the anterior adductor.
Again, the muscular margin of the mantle is attached to the

VOL. I.

2X

690 MOLLUSCA.

interior of each valve along a line running at a little distance within,
and parallel with, the ventral margin of the shell. In this way is
formed a more or less well-marked impression in the interior of each
valve, which is termed the “ pallial line” (fig. 556, m). The form
assumed by the “ pallial line” differs in different Bivalves accord-
ing as respiratory “‘siphons” are present or absent. In all those
Bivalves, namely, in which the mantle-lobes are free, and in which

m

Fig. 556.—A, Interior of the left valve of Anodonta cygnea; B, Interior of the right valve ot
Artemis exoleta (after Woodward); c, Interior of the left valve of Pectex varius (after Wood-
ward). @, Impression of the anterior adductor; Za, Impression of the posterior adductor; 77,
Pallial line ; s, Sinus in the pallial line caused by the insertion of the retractor muscles of the
siphons; Z/, Scar of the protractor muscle of the foot; 7, Scar of the anterior retractor muscle
of the foot ; 7’, Scar of the posterior retractor muscle of the foot. In Pecten varius (c), though
the shell is monomyary, the scar left by the posterior adductor (fa) is double, and there is a large
scar (fe) formed by the muscular base of the foot.

there are consequently no siphons, the ‘‘ pallial line” runs in an un-
broken curve round the lower part of the valve (fig. 556, A, 7).
The pallial line is similarly unbroken in those Bivalves which possess
short siphons, but which do not possess a specially developed “ re-
tractor muscle” for the withdrawal of the siphons within the shell.
The name of Jxtegropalialia is given to all such Bivalves as the
above, in which the pallial line is “entire,” or unindented, and there

LAMELLIBRANCHIATA. 691

are either no siphons or but short ones. On the other hand, in
those Bivalves which have long respiratory siphons there exists on
each side a specially developed ‘retractor muscle,” the function of
which is to withdraw the siphons within the shell. The insertion of
this siphonal retractor causes an indentation in the pallial line pos-
teriorly (fig. 556, B, s), the depth of this depending upon the size
of the siphonal muscles. In all those Bivalves, therefore, which
possess retractile siphons, the pallial line is deflected posteriorly into
a larger or smaller ‘‘ pallial sinus” or ‘‘siphonal impression ;” and
those Bivalves in which this sinus exists are grouped together under
_the name of S7zzupalhatia.

There is no distinctly differentiated head in any of the Lamelli-
branchs (hence the name of “ Acephalous Molluscs” commonly
given to the class), and the mouth is simply placed at the anterior
end of the body. It is furnished with ciliated, leaf-like, membranous
processes, or “ labial palpi” (fig. 555, 7), which are two or four in
number, and serve to conduct the in-going water-currents to the
mouth. ‘The mouth is not furnished with any arrangement of teeth,
and the animal lives upon the microscopic particles of nutrient
matter brought to the mouth by the in-going currents of water,
which are kept in movement by the action of the cilia covering the
gills. These organs (fig. 555, ¢) are leaflike, and are attached by
their bases to the sides of the body, their free ends depending into
the mantle-cavity. Most Bivalves have two of these lamellar
branchize on each side of the body, but the external pair may be
wanting.

As has been already mentioned, the arrangements for the admis-
sion of water to the gills, and its expulsion again from the mantle-
cavity, are essentially the same in all Bivalves. In almost all cases
the in-going current of water enters the pallial chamber posteriorly
and ventrally, while the out-going current escapes posteriorly and dor-
sally. In those Bivalves which have free mantle-lobes (‘‘ Asiphonate
Bivalves”’), the apertures for the water-currents are simply produced
by the apposition of the hinder edges of the mantle-lobes to each
other. On the other hand, in those Bivalves which have the mantle-
lobes united (“‘Siphonate Bivalves,” fig. 555), the margins of the
“inhalant” and “ exhalant” apertures are drawn out or extended
into longer or shorter muscular tubes or ‘‘siphons.” The siphons
may be separate, or they may be united to one another along one
side, and they can usually be partially or entirely retracted within
the shell by means of special muscles, called the “‘ retractor muscles
of the siphons.” These siphons are more specially characteristic of
those Lamellibranchs which spend their existence buried in the sand,
protruding their respiratory tubes in order to obtain water, and with
it such nutrient particles as the water may contain. As has been

692 MOLLUSCA.

previously seen, the presence or absence of retractile siphons can be
readily determined merely by inspection of the dead shell.

The Lamellibranchiata are wholly aquatic, living in either salt or
fresh water, and their habits are very various. Some, such as the
Oyster (Ostrea), and the Scallop (/ectez), habitually lie on one side,
the lower valve being the deepest, and the foot being wanting, or
rudimentary. The former is fixed by the substance of the valve, but
the latter swims by rapidly opening and closing the shell. Others,
such as the Mussel (AZyti/us) and the Pinna, are attached to some
foreign object by a “ byssus.” Others are fixed to some solid body
by the substance of one of the valves. Many, such as the JZyas,
spend their existence sunk in the sand of the sea-shore or in the mud
of estuaries. Others, as the Pholades and Lithodomz, bore holes in
rock or wood, in which they live. Finally, many are permanently
free and locomotive.

The Lamellibranchiata have often been divided into two primary
sections, according as “‘ siphons” are or are not developed. In one
of these sections—Asizphonida—the mantle-lobes are free, and there
are no respiratory siphons, so that the pallial line is simple and is
not indented. In the other great section— Szphonida—the mantle-
lobes are more or less united, and respiratory siphons are present.
In certain groups of the Siphonate Bivalves the siphons are short,
without specially developed retractor-muscles, and the pallial line is
therefore simple, the name of lxzegropaliaha being given to such
forms. On the other hand, in many types of the Siphonate Bivalves
—hence termed S7zupaliiatia—there are long siphons, the greatly
developed retractor-muscles of which are attached to an indenta-
tion or bay in the pallial line. This classification is doubtfully
natural, and is largely inapplicable to fossil forms ; for which reasons
the arrangement adopted by Dr Paul Fischer in his ‘ Manuel de
Conchyliologie’ has, in the main, been here followed in preference.
Owing, however, to the great importance in the study of the fossil
Bivalves of the various internal markings of the shell, it may be of
use here to indicate generally the principal groups of Lamellibranchs
which agree with one another in the general nature of the impres-
sions left by the pallial line and adductors ; a guide being thus given
to the families amongst which the affinities of a given fossil shell
must be sought. From this point of view, the Bivalves fall into the
four following sections, the families of which, though often allied,

have no necessary zoological relationship with one another :—-

(1.) The following families of Lamellibranchiata are ‘‘monomyary,”
and have an “entire” pallial line, no siphons being developed—viz., the
Ostreide, Anomiide, Spondylidea, Limide, and Pectinide. This group
of families corresponds with the W/onomyaria of some writers.

(2.) The following families are “ heteromyary,” and have no siphons, the

LAMELLIBRANCHIATA. 693

pallial line being “entire”—viz., the Aviculide and Mytilide (= the
Hleteromyaria of Bronn).

(3-) The following families are “ homomyary,” and have an “entire”
pallial line, the animal being in some cases devoid of siphons, while in
other cases short, non-retractile siphons are present—viz., the Arvcide,
Nuculide, Modiolopstde, Trigonitde, Unionidae, Cardinide, Carditide,
Grammysiide, Astartide, Crassatellide, Erycinide, Galeommide, Tri-
dacnide, Cardide, Lunulicardide, Chamide, Rudiste, Megalodontide,
Cyprinide, Ungulintde, Unicardiide, and Tancrediide.

(4.) The following families are “ homomyary,” and are provided with
retractile siphons, the pallial line thus becoming “ sinuated”— viz., the
Veneride, Donacide, Psammobiide, Solenide, Mactride, Myide, Glyct-
meride, Gastrochenide, Pholadide, Teredinide, Lucinide, Tellinide,
_ Scrobiculariide, Solemyide, Arcomyide, Anatinide, Precarditde (?),
Pholadomyide, and Clavagellide.

ce

As regards their general distribution in time, the Lamellibranchs
are a very ancient group, the earliest representatives of the class
(Glyptarca, &c.) being found in the Upper Cambrian rocks. Upon
the whole, the Asiphonate Bivalves are more characteristically Palee-
ozoic, while those in which the mantle-lobes are united and there are
respiratory siphons, are principally found in the Secondary and Ter-
tiary rocks. One of the principal Paleozoic groups is that of the
Aviculide, while the AZytilide are also largely represented. Mono-
myary types appear in the later portion of the Palzeozoic period,
numerous forms (Aviculopecten, &c.) allied to the recent Scallops
occurring in the Carboniferous rocks. With the commencement of
the Secondary period, in the Trias, many old types disappear, and
new ones take their places. Monomyary Bivalves are now numer-
ous, but among the Dimyary forms the Asiphonate families still pre-
dominate. The forms with long retractile siphons (S7zupallialia)
begin with a few types in the Trias, and gradually become more
numerous as we pass upwards. The Veneride, which are perhaps >
the most highly organised of the groups of the Lamellibranchs, ap-
pear for the first time in the Jurassic rocks, and increasing in the
Tertiaries, have culminated in the Recent period. The singular
group of the Azdiste is exclusively confined to the Cretaceous
period.

694

CPUASE (ene are vale

LAMELLIBRANCHIATA—continued.

DIVISIONS OF LAMELLIBRANCHIATA.

VARIOUS attempts have been made to divide the Lamellibranchiata
into sections equivalent to the ‘‘ orders” of the higher animals, but,
so far, little success has attended these efforts, and no arrangement
which has hitherto been proposed can be regarded as thoroughly
satisfactory, more especially from a paleontological point of view.
In what follows, the Lameliibranchiata are divided into a number of
sections, which it is convenient to speak of as so many “ orders,”
though it cannot be asserted that they have a value equivalent to
the divisions known by this title among Vertebrate animals. As
regards these primary sections, Dr Paul Fischer has been followed,
and under each section will be given the characters and geological
range of the more important families included in it.

OrDER I. OSTREACEA.

In this order the mantle-lobes are completely free ; a single ad-
ductor muscle (the posterior) is alone present, the animal being thus
‘“monomyary ”; there are two branchize on each side of the body ;
and the foot is wanting, or is present in a rudimentary form and
secretes a “byssus.” The shell is inequivalve ; the hinge is eden-
tulous ; the ligament is internal; and the pallial line 1s “ entire,”
and sometimes not distinct. This order includes the two families of
the Ostrerde and Anomide.

FAMILY I. OsTREID#.—In this family the shell is generally in-
equivalve and fixed to foreign bodies by the substance of the left
valve, but is in other cases free; the beaks are subcentral, or, in
many cases, twisted; the ligament is internal, and is lodged in a
triangular cartilage-pit ; the single muscular impression is subcentral,
or excentric and posterior ; the pallial line is not distinct ; and the

OSTREACEA. 695

shell-structure is laminated. This family is exclusively confined to
salt water, and comprises the Oysters. Numerous Secondary and
Tertiary representatives of the family are known, but the few Pale-
ozoic types which have been referred here are probably really of a
different nature.

The principal genus included in the Os¢reide, as here understood,
is Ostrea itself, the essential characters of which are those of the

Fig. 557-—Ostrea (Exogyra) Coulent. Lower Greensand.

family itself. The shell described by De Koninck from the Car-
boniferous Limestone under the name of Os¢vea nobilissima has
generally been quoted as the oldest known type of the genus Os¢rea,
but it is referred by Fischer to the genus Pachypteria (? Spondylide).
In the Secondary and Tertiary rocks, however, we meet with a vast

Fig. 558.—Ostrea (Alectryonia) Marshii. . Fig. 559.—Gryphea incurva. Lias.
Oxford Clay (Middle Oolites).

number of fossil Oysters, which have commonly been distributed
among several more or less well-marked sections of the genus, of
which the following are the most important. In the typical forms
of the genus (Ostrea proper) the valves are pretty nearly of the same
length, the lip of the right valve is not serrated, and the external

696 LAMELLIBRANCHIATA.

surface is marked with concentrically-disposed foliaceous ridges or
with roughly radial ribs. The umbo is not incurved, and below it
is a transversely striated ligamental pit. The Edible Oyster (0.
edulis) is a familiar example of this section of the genus, and essen-
tially similar forms are known to have existed in the Jurassic rocks.
In the sub-genus Aéectryonia (fig. 558) both the valves are strongly
ribbed or folded, the edges of the valves being thus indented in a

Fig. 560.—ELxogyra aqguila. ower Greensand.

zigzag manner; while the adductor impression is placed far back.
Forms of this type began to exist as early as the Trias, and the
recent O. crista-galli is a familiar example of a now living form of
the group.

In the sub-genus Gryfhea (fig. 559), the two valves are of un-
equal length, the left valve fixed in early life, but often becoming
free in the adult condition, while its beak is prolonged and incurved,
being bent either forwards or backwards. The right valve, on the
other hand, is small in size, and is flat or concave in shape, looking
like a kind of operculum to the left valve. The species of Gryphaea

Fig. 561.—Exogyra virgula. Upper Oolites.

are pre-eminently Jurassic and Cretaceous, but a few Tertiary and
Recent forms of the group are known.

In the sub-genus Lxogyra, again, the shell is very inequivalve
(figs. 557, 560, and 561), and is fixed by the substance of the thick
and concave left valve, the right valve being flat and resembling an
‘“‘operculum ” in form. The beaks of both valves are rolled up,
being “reversed ”—that is to say, turned towards the posterior side

OSTREACEA. 697

of the shell—and the ligamental area is oblique and narrow. The
species of Lxogyra are abundant in the Jurassic and Cretaceous
deposits.

The name of Pernostrea has been proposed by Munier-Chalmas
for certain Jurassic Oysters which differ from Os¢vea proper chiefly
in having the ligament contained in from four to eight transverse
grooves or pits (as i in Perna).

FaMILy 2. ANOMIID2.—In this family the shell is inequivalve,
and is fixed to foreign objects, either in early life or permanently,
by a byssus, which traverses a notch or foramen in the right valve,
and is ordinarily calcified at its termination. The muscles of the
byssus leave one or more impressions on the interior of the left
valve. There is an internal ligament; the hinge is edentulous ;
the pallial line is simple ; and the shell exhibits a laminated struc-
ture. The range of the family is from the Devonian to the present
day, and the chief genera are Anomia and Placuna.

In the genus Axomia (fig. 562) the shell is suborbicular and
ostreiform, the left or upper valve being convex, while the right or
under valve is flat or concave. In the margin of the right valve, near

Fig. 562.—A noma Casanovet, from the Eocene Tertiary. enlarged. A, Interior of the left
valve; B, Interior of the right valve : 2, Foramen for the passage of the byssus; 7, Impressions
left by the muscles of the byssus ; vz’, Adductor impression. (After Hoernes.)

the hinge, is a deep notch or sinus, which in process of growth may
be converted into a complete foramen, and which serves to transmit
the byssus, by means of which the shell is attached to foreign bodies.
The end of the byssus is calcified, and it forms a solid plug which
fills up the notch or foramen in the valve. The interior of the right
valve shows only the impression of the single adductor, but the in-
terior of the left valve exhibits in addition one to three scars produced
by the muscles of the byssus. All the living forms of Azomza are
marine, and the genus is represented in past time by numerous

698 LAMELLIBRANCHIATA.

Tertiary species, and, more rarely, by Cretaceous and Jurassic
types. The Zzmanomia of the Devonian rocks is, however, very
closely related to Azomia proper, from which it differs in the
pointed shape and radial striation of the valves, and in the fact
that the byssal foramen is trigonal in form.

The extinct genus Placunopsis, ranging from the Carboniferous Lime-
stone to the Jurassic, resembles Azomza in many respects, but the right
valve is not perforated ; the ligament is lodged in a transverse, sub-
marginal groove; and the adductor impression is large and subcentral.
The genus P/acuna comprises flattened and cake-like, orbicular shells,
which are unattached to foreign bodies. The elastic ligament is sup-
ported by two diverging ridges in the right valve, with corresponding
grooves in the left valve. The typical forms of the genus are recent, but
types of no more than sub-generic value occur in the Tertiary rocks.
The Jurassic genus Hyfotrema is intermediate between Anomia and
Placuna, since it possesses a byssal foramen which is completely closed
in the adult.

ORDER II. PECTINACEA.

In this order, the mantle-lobes are completely free; there is a
single adductor only; there are no siphons; there are two branchize on
each side of the body; and the foot is rudimentary and often bys-
siferous. The shell-structure is tubulated or lamellated, but without
a proper prismatic layer. The shell is inequivalve or sub-equivalve ;
the ligament is lodged in a pit between the beaks; the hinge is
generally toothed ; and the pallial line is entire. This order con-
tains the three principal families of the Spondylide, Limide, and
Fectinide, all the recent forms of which are marine.

FaMILy 1. SPONDYLID#&.—In this family the shell is inequivalve,

Fig. 563.—Sfoudylus spinosus. Chalk.

and is attached to foreign bodies by the beak of the right valve,
which is larger than the left. The hinge of each valve has two
teeth, between which is the cartilage-pit. The adductor impression

PECTINACEA. 699

is subcentral. The two principal genera of this family are Sfon-
aylus and Plicatula.

The genus Sfondylus, comprising the ‘Thorny Oysters,” has an
equivalve shell, the right valve being the deepest, and serving for
the attachment of the shell to foreign bodies (fig. 563). The beaks
are separated and are eared, and the shell is covered with spines,
foliacequs expansions, or ribs radiating from the beak. The lower
valve has a triangular hinge-area, and there are two teeth in each
valve. The Sfondy4i seem to have commenced in the Jurassic
period (? Trias), are abundant in the Cretaceous, and have con-
tinued through the Tertiary period to the present day.

Fig. 564.—Pdicatula placunea. Lower Greensand.

The genus Piicatula (fig. 564) approaches Sfondylus nearly in
having an inequivalve shell, which is attached by the right valve,
and by having two hinge-teeth in each valve. ‘The shell, however,
is rarely eared, the hinge-area is obscure, and the valves are not
spiny, though they may be plaited. The Pécatule extend from the
Trias to the present day, and they abound to such an extent in
parts of the Lower Greensand (Cretaceous), as to have given rise to
the name of ‘“ Argile a Plicatules” applied to the beds in question.
Lastly, the genus Zerguemza, of the Triassic and Liassic rocks, re-
sembles Spondylus in many respects, but is at once distinguished by
the fact that the hinge is edentulous. In this respect the genus
resembles the Oysters, from which it is separated by the fact that
the shell is attached by the 7zg#¢ valve, and not by the left. Fischer
also includes in this family, with doubt, the Carboniferous genus
Pachypteria.

FaMmiLy 2. Limip#.—The shell in this family is auriculate, and
equivalve or nearly so, and it may be free or may be attached by
a byssus, which passes out by a sinuosity in the nght valve or by a
notch below the anterior ears. The beaks are pointed and straight,
and a portion of the hinge-area and ligament is left externally visible ;
while hinge-teeth may be wanting or present. The earliest types of
the family appear in the Carboniferous rocks ; there are numerous
Secondary and Tertiary forms; and the present seas contain a
limited number of existing species.

700 LAMELLIBRANCHIATA.

In the genus Zzma or Radula the shell is equivalve and free, and
the beaks are separated from one another and eared (fig. 565). The
surface is generally adorned with
radiating ribs or strize, and there is a
median cartilage-pit, and a triangular

71)
ML!

Gf BAT) ° . °
. Joa e hinge-area. The genus (including
Vis i BA Plagiostoma) appears to occur in the
Aide ! i) KW Carboniferous, is abundantly repre-
a eal sented in the Triassic, Jurassic,
eee vat Cretaceous, and Tertiary rocks, and
ey exists in diminished numbers at the

NN
i \ present day. Zzmea, ranging from
the Trias to the Recent period,
differs from Zzma principally in hav-
ing the hinge-line closely toothed.
FAMILY 3. PECTINIDZ.—In this
family the foot is tongue-shaped and
byssiferous; the margins of the
figs - mantle-lobes carry ocelli; and the
adductor impression is a little ex-
centric. The. shell is sub-equivalve or equivalve, nearly equilateral,
auriculate, free or occasionally attached by the right valve. Gener-
ally there is a notch under the ear of the right valve for the passage

wn

iy
NESE
W's YG YY) Se Dy use

KC revert

“yy ez
Vii; A
bei, CB

yy
Mig ba
1 My

iis ox

ih és
AN
<<

U

l/
Wy
Ul

/

“Ypy Uy Wy,
wy 3

ty
WV
Uy

Wh
Why
lly

WU

YY

Uy

“
Mil

Fig. 566.—Pecten [slandicus, left valve. Post-Tertiary and Recent.

of the byssus; and the cartilage-pit is internal, of triangular shape,
and placed between the beaks, being rarely broken up into detached
pits. All the members of this family are marine, its earliest forms

PECTINACEA. 701

appearing in the Devonian rocks, while numerous living types
exist.

The genus //7zui¢es comprises a number of forms in which the
shell is free when young, but becomes in adult life attached by the
right valve, the shell becoming at the same time thick and irregular.
The left valve is free, and the hinge-line is edentulous. Numerous
fossil forms of A/zznzfes are known, the earliest appearing in the
Trias, and the genus still survives.

In the genus /ecfen, comprising the Scallops, the shell (fig. 566)
rests upon the right valve, and the beaks are furnished with ears.
The anterior ears are the largest and most prominent, and the shell
is generally furnished with ribs radiating from the umbos. There
is a single, median, triangular cartilage-pit. The right valve is the
deepest, and is notched for the byssus below the anterior ear.
Using the name /ecfez in its modern and restricted signification, it
is probable that all the Palzeozoic shells so named are really refer-
able to allied genera (Avzculopecten and Pernopecten more especially).
The genus, however, is largely represented both in the Secondary
and Tertiary deposits, and exists under numerous and varied forms
at the present day.

The name of £7folium has been given to forms of Pecten in which the
shell is smooth, the hinge-line is rendered angular by the outward exten-
sion of the ears, and there is no byssal notch under the anterior ear of
the right valve. Numerous forms
of this type occur from the Ju-
rassic onwards; but the Pale-
ozoic shells which have been
placed here are probably refer-
able to allied genera, such as
Pernopecten. Inthe genus Per-
nopecten, of the Devonian and
Carboniferous rocks, are com-
prised ancient types of Scallops,
with small, nearly equal, ears,
the central triangular cartilage-
pit being flanked by a row of
smaller pits on each side (thus
approaching Perna), and the
surface being nearly or quite
devoid of radiating ridges. The
genus Crenipecten, with a simi- Fig. 567.—Internal cast of Aviculopecten. Car-
lar geological range to Perno- boniferous. (After M‘Coy.)
pecten, has the hinge furnished
with a row of small cartilage-pits along its entire length, no central pit
being present.

Of the Paleozoic types of the /ectinide, the most important is
the large and widely distributed genus <Avzcwlopecten, which, as its
name implies, affords a transitional link between the present family

702 LAMELLIBRANCIHIIATA.

and that of the Aviculide. The shell in this genus (fig. 567)
has the general form and aspect of that of Fecten itself; but
the anterior ear is flattened, and smaller than the posterior one.
There is a byssal notch beneath the anterior ear; but there is
no median cartilage-pit, and the ligament is confined to a narrow
facet along the hinge-margin. ‘The muscular impression and pallial
line are as in Fecten. The hinge-line is usually shorter than the
transverse diameter of the shell, and the surface is generally adorned
with radiating ribs. The species of Avzculopecten are distributed
between the Devonian and Permian, but they are most characteristic
of the Carboniferous rocks, in which they are extremely abundant.
In the absence of a median cartilage-pit, and the lodgment of the
ligament in a groove along the hinge-line, the genus approaches the
Aviculide, but its shell is stated by Meek to have the corrugated and
laminated structure of /ecfen, and not the prismatic structure of the
former. The genus S¢reblopteria of the Carboniferous and Permian
rocks comprises forms which agree with Aviculopecten in having the
ligament in a groove along the margin of the ears ; but the posterior
ear is hardly marked off from the hinder margin of the shell, and
an oblique posterior cardinal tooth is present.

OrpDER III. MyTILACEA
(= Heteromyaria, Bronn).

In this order the mantle-lobes are free, the pallial line is entire, and -
there are usually two adductor muscles. (In the Tertiary genus Dress-
senomya the pallial line is sinuated ; while the recent genus Prasina
is monomyary.) The anterior adductor is small; the posterior is of
large size. The foot is tongue-shaped and usually byssiferous. The
shell possesses an external, often largely developed, prismatic layer,
and may be inequivalve or equivalve. The ligament is generally
contained in several marginal grooves or in an oblique furrow ; and
the hinge may or may not be provided with teeth. The two prin-
cipal families contained in this order are the Aviculide and Myiilide,
and the recent forms are in part marine, and in part inhabitants of
fresh waters.

FAMILY 1. AVICULID#.—In this family the mantle-lobes are free,
the foot is small and byssiferous, and the shell-structure consists of
an internal nacreous layer and an external prismatic layer. ‘The
anterior adductor! is small, and leaves its impression at the base of

1 The muscle which is here spoken of as the ‘‘ anterior adductor” is sometimes
regarded as, in some cases, being really the anterior retractor of the foot. On
this view, there is no anterior adductor muscle in some of the most typical forms
of the Aviculid@, the animal being monomyary.

MYTILACEA. 703

the anterior ear ; the posterior adductor impression is large and sub-
central. The shell is inequivalve or subequivalve, oblique, with a
straight hinge-line, and furnished on one or both sides with wing-
like expansions or ears. Under the anterior ear of the right valve
is a notch or aperture for the transmission of the byssus. The
family of the Avzculide is a very large one, and has a most extensive
development in past time, beginning under various types in the
Ordovician rocks, and being continued thereafter to the present
day. The principal forms included in this family may be briefly
considered under the following groups :—

Fig. 568.—Types of Aviculide. a, Avicula Cottaldina—Cretaceous; B, Avicula contorta—
Upper Trias; c, Vudlsella falcata—Eocene; D, Pseudomonotis speluncaria—Permian; §, In-
terior of the shell of the same, showing the adductor impression and pallial line ; Fr, Posidonomya
Becheri—Lower Carboniferous.

Firstly, we have the great group of shells, of which AvicuZa itself
(fig. 568, A and B) is the type. In this genus the shell is oblique
and inequivalve, the right valve being smaller and less convex than
the left. The right valve has a byssal notch under the anterior ear,
and the hinge has one or two cardinal teeth, sometimes with an
elongated posterior tooth. The ligament is partly external, partly
contained internally in a deep groove. ‘The species of Avicula
range from the Ordovician period to the present day, numerous
forms of this genus occurring in the Secondary and Tertiary

rocks.

fore or less closely allied to Avicula are the Paleozoic genera Lezof-
teria (Devonian and Carboniferous), Zonopteria (Carboniferous), Pferon-
ztes (Devonian and Carboniferous), Lzmoptera (Devonian), and Lopteria
(Ordovician). Also related to Avicu/a is the genus Pseudomonotis (Eumt-
crotis, Meek), in which the shell is but slightly oblique, and is inequivalve,

7 O04 LAMELLIBRANCHIATA.

the left valve convex, with a prominent beak. The hinge is nearly or
quite toothless, and the anterior ear is small or undeveloped, while a deep
byssal notch in front is present (fig. 568, D and E). The earliest forms of
Pseudomonotis are found in the Devonian rocks, but the genus attains its
maximum in the Triassic and Jurassic rocks. A well-known species from
the Permian rocks of Europe is P. sfeluncaria (fig. 568, D). In the
singular Triassic genus Cassianella (fig. 570, D and E) the shell is thick
and very inequivalve, the right valve being flat or concave, while the left
is strongly convex. The hinge-line is straight, with few teeth, the liga-
ment being lodged in a triangular groove behind the beaks ; a byssal
notch is absent; and the shell is eared.

Another, but limited, group is that represented by Vudsel/a and
Mateus, together with some Secondary and Tertiary forms of small
importance, characterised by the common feature that the ligament
is lodged in a single pit extending from the beak internally. In
Vulsella (fig. 568, c) the shell is nearly equivalve and earless, the
hinge being toothless, and a byssal notch being absent. “The genus
dates from the Eocene Tertiary, and still survives. On the other

| (7 z= === PS
we Nig Le

his

Fig. 569.—Perna Mudlleti (A), and a portion of its hinge-line (B). Lower Greensand.

hand, the “‘ Hammer-oysters ” (AZad/ews) are not known in the fossil
state, and are distinguished by their very long ears and central
beaks.

A third, much more important, group of the Aviculide is that
represented by /ervna and its allies, all of which have a straight
hinge-line, crossed by numerous transverse furrows for the lodgment
of the ligament. In Perna (or Melina) itself (fig. 569) the shell
varies in form, but there is generally a long posterior ear; there are
numerous close-set cartilage-pits, and the right valve has a byssal

MYTILACEA. 705

notch. The genus begins in the Trias, is well represented in
the later Secondary and Tertiary deposits, and still survives under
a few forms. A large and well-known species is the Perna Mullett
of the Neocomian rocks. Allied to the preceding is the genus
Gerviliia (fig. 570, A), in which the shell is elongated and very
oblique, with a broad and wing-like posterior ear. The hinge-line
is furnished with numerous cartilage-pits (fig. 570, B), and the
anterior ear is comparatively small, while the beaks are nearly or
quite terminal in position. The species of Gervz//ia abound in the
Triassic, Jurassic, and Cretaceous rocks, and a single species of the

Bra ever l if vy ii

bit)

TT OMTTERHERTATILR
i WAKO

Fig. 570.—Types of Aviculide. a, Gervillia Hartmanni—Lias; B, Part of hinge of the same,
enlarged ; c, Hoérnesia Foannis-Austrie, slightly enlarged—Trias; pb and E, Casstanella gry-
pheata, of different ages—Trias. (After Miinster and Laube.)

genus is found in the Eocene rocks. In the Trias are found various
forms of the closely allied Hoérnesza (fig. 570, C), in which the left
valve is greatly inflated, with a strongly incurved beak, while the
hinge-line is crenulated, and a single strong tooth exists in both
valves. Sakewellia, of the Permian, resembles Gevvidiia in general
form, but the hinge is provided with anterior and posterior teeth,
and the cartilage-pits are few in number. The Devonian genus
Actinodesma is probably a still older relative of Gervzdia.

Nearly related to both Geruz/lia and Ferna is the important and.
widely-distributed genus /moceramus (figs. 571, 572), which is entirely
confined to the Secondary period, and is mainly characteristic of the
Cretaceous series. The shells of this genus are inequivalve, with

VOL. I. UN,

706 LAMELLIBRANCHIATA.

radiating ribs or concentric furrows, and with prominent beaks.
The shell is earless, and the hinge-line is long and straight, with
numerous cartilage-pits. Some of the /woceramz attain a length of

Fig. 571.—luoceramus sulcatus. Gault (Cretaceous).

two or three feet, and fragments of them are often found perforated
by boring sponges. The shell in the /zocerami consists of a thin
internal nacreous layer, with a generally very thick outer prismatic

Fig. 572.—lnoceramus problematicus. Chalk.

stratum, but either the internal or the external layer may be destroyed
in the process of fossilisation.

The Jurassic and Cretaceous genus Awcella (fig. 573) is related to the
preceding, but may be considered as the type of a separate group of the
Aviculide. \n this genus, the shell (fig.
573) 18 very inequivalve, the left valve
being convex and the right valve flat, and
the beaks of both valves being inflated
and incurved. The ears are imperfectly
developed; the surface is concentrically
striated; the ligament is external and

SSS linear; and the hinge is hardly or not at

Fig. 573. — Aucella muosquensis, all toothed. The Carboniferous genera,

Ee Jurassic, Russia. (After Zit- Rytotia, Posidoniella, and Aphanaia, and

the Triassic genus Rhyuchopterus, are
placed by Fischer in the same group with AuzcelJa.

Gy 4 Y le: ELS

The genus A/onotis is the type of another group of the Aviculida,
in which the shell is equivalve, compressed, with small beaks, the
ears more or less confluent with the shell, the hinge without teeth,
and the hgament linear. Monofzs itself is confined to the Trias,
occurring in rocks of this age in both the Old World and the New.
Very closely related to the preceding are the Triassic genera Dao-

MYTILACEA. 707

nella (fig. 574) and falodia, in which are comprised flat, equi-
valve, radiately-striated shells, more or less markedly inequilateral
in shape, with a straight hinge-line, without a hgamental pit or teeth,
and with no ears. Also belong-
ing to this group is the remark-
able genus Posidonomya (= Po-
sidonia), in which the shell (fig.
568, F) is thin, concentrically
striated, with a straight hinge-
line, destitute of hinge-teeth,
and without developed ears.
The species of /ostdonomya |
_ Tange from the Silurian to the Fig. 574.—Daonella (Halobia) Lonemetli.
Jurassic rocks, and have a gen-
eral resemblance in shape to specimens of £s¢heria. ‘The species
of this genus commonly occur gregariously, and particular species
are commonly characteristic of particular horizons.

The important Paleozoic genus /erinea is the type of another
group of the Avzculide, in which the shell (figs. 575, 576) is equi-

‘liriass

SS in Ws) ANY
\ Wy VW
ZAIN
Sa J} PA AANAR
eee

WY

Fig. 575.—a, Ptertnea subfalcata, Fig. 576.—Pterinea (Avicula) demissa.
Silurian. (After M‘Coy.) s, Interior Ordovician rocks (Hudson River group) of
of the left valve of Pterinea levis, De- North America.
vonian. (After Zittel.)

valve, inequilateral, and winged, with a byssal notch below the
anterior ear. The hinge has two or more cardinal teeth, with
oblique lateral teeth, and there is a large, longitudinally-striated
ligamental area for the reception of the internal ligament. ‘The

708 LAMELLIBRANCHIATA.

small impression of the anterior adductor is placed below the an-
terior ear, and the surface is radiately striated. The species of
Prerinea have a wide distribution in the Ordovician, Silurian, De-
vonian, and Carboniferous rocks. ‘The Devonian genus G/yfiodes-

Fig. 577.—A ubonychia radiata.
Ordovician.

ma is allied to Prerinea, but the liga-
ment is external, and the hinge has
two strong lateral teeth, together
with numerous irregular transverse
plications along its margin.

The genus Ambonychia (fig. 577)
is the type of another group of the
Aviculide, and is widely distributed
in the Paleozoic rocks, ranging from
the Ordovician to the Carboniferous.
In this genus the shell (fig. 577) is
equivalve and very inequilateral, the
beaks being pointed, and placed at
the anterior end of the long straight
hinge-line. The ligament is internal,
and is lodged in longitudinal grooves
running parallel with the cardinal
margin. ‘There is no anterior ear,
but a wide byssal aperture is present,

while the posterior ear is broad and aliform. ‘The Devonian
genera Mytilarca and Gosseletia may be placed in the neighbour-

hood of Ambonychia.

A transition between the Aviculide and the AZyiitlide is effected

Fig. 578.—J/yalina crassa, interior of a broken right valve, showing the hinge.
Carboniferous Limestone. (Original.)

by the remarkable genus MWyadna (fig. 578), in which the shell is
inequivalve, and mussel-shaped, with terminal beaks, and a flat and
thickened cardinal area marked with longitudinal cartilage-grooves,
and sometimes with the umbones septate. The genus JZyalina is

MYTILACEA. 709

stated to range from the Silurian to the Permian, but it is princi-
pally characteristic of the Carboniferous and Permian rocks.
Though the shell of AZyaina resembles that of the AMtetde in
form, the shell-structure agrees with that of the Avzcudzde in the
presence of a well-developed external prismatic layer.

We pass naturally from the Aviculide to the AZvtiilde through
the genus /izza and its allies, which have often been regarded as
constituting a special family (Pixznuzde). In Pinna, the type-genus

i ae ‘

HELE NAN

BREE AY
LA

Cann Space:
sa a a a a oe STE ea
Sere

ah ae ey OE

we

mt f—t

esa
Seager o e
eo

— TZ
oy
er tt
=F ee
teeter isa
; eee
err |
see
Aeros
—
ee

ET Si Ss
—

as

ys,

(ener a SE MT ia ae 2 ee
a.

1 &

a a

iO ned

i t\ ‘ uN

ANN
\\

as te 2 hel week iy Sols meee TTS TERT o
eS ae © Se PT eer oe a LJ
as

age
(FIP Tis
a

aoes
sare.
ae
ate
Pea
a
rae
sateeee
eee

Dt aad ad
fy em a ier

Fig. 579.—a, Pinna flabelliformis, the hinder part of the shell being broken away, reduced in
size; B, Aviculopinna membranacea. From the Carboniferous Limestone of Belgium. (After
De Koninck.)

of this group, the shell (fig. 579) is equivalve and wedge-shaped ;
the beaks are placed quite at the anterior end of the shell, and the
posterior end is truncated and gaping. The hinge is toothless, and
there is an elongated ligamental groove. The shell consists almost
entirely of the external prismatic layer, the inner nacreous layer
being of extreme tenuity. The earliest types of Pina appear in
the Devonian rocks, and some of these have been separated by
Hall to form the genus Pa/eopinna, on the ground of the convexity

JMO LAMELLIBRANCHIATA.

of their valves and the fine striation of the surface. In the Car-
boniferous rocks the genus is represented by large forms, and
numerous later types are known, the existing species having a wide
range in space.

In the Jurassic and Cretaceous genus 77zchztes the shell is of large
size and great thickness, with a marked fibrous structure, the valves being
of unequal size, with twisted beaks and undulated margins. The hinge-
line is linear and edentulous, and the impression of the posterior ad-
ductor is very long and narrow. Lastly, in the Carboniferous and Per-
mian genus Aviculopinna (fig. 579, B), the beaks are placed a little way
behind the anterior extremity of the shell, and the surface is nearly
smooth, and is marked with concentric striz.

Famity 2. Mytitip#.—TIn this family the foot is cylindrical,
grooved, and byssiferous, and there are two adductor impressions,
that of the anterior adductor being small and terminal in position, .
while that of the posterior adductor is of large size. The shell is
mostly equivalve, wedge-shaped or oval, with anteriorly-placed beaks,
not alate, and without a byssal notch; the byssus passing between
the slightly gaping ventral margins of the valves. The cardinal
margin is oblique; the hinge is edentulous; and the ligament is
long, linear, and marginal. The pallial line (except in Drezssenomya)
is entire. The shell is composed of an inner nacreous layer and
an outer cellulo-prismatic stratum, with a horny epidermis. The
Mytilide are partly marine and partly inhabitants of brackish or
fresh water, and the earliest types of the family appear to be found
in the Devonian rocks. |

In the genus MWytlus are the true “ Mussels,” in which the shell
is very inequilateral and wedge-shaped, and the beaks are terminal
in position. Numerous fossil
forms are known, commencing
in the Trias, and the genus
is largely represented at the
present day. The Palzeozoic
shells which have been placed
under AZytzdus probably belong
really to other genera. yeane
genus Modiola, comprising the
‘“* Horse - mussels,” is hardly
separable, so far as the shell
—— is concerned, from JZytzlus

Fig. 580.—Exterior and interior of the left valve proper, the principal differ-
OEE Cee from the Eocene Tertiary ences being that the shell is

rather oblong than cuneiform,
and the beaks are rounded, and are placed a little behind the
anterior extremity (fig. 580). The genus J/odio/a appears to be

MYTILACEA. Fate

represented in formations as ancient as the Devonian and Car-
boniferous, but most of the fossil species are Secondary and Ter-
tiary, and there are also numerous living forms. ‘The Recent and
Tertiary genus Sefztifer, again, differs from JZyt/us in having a cal-
careous shelf within the beak for the attachment of the anterior
adductor muscle. The ‘“ Date-shells” (Zzthodomus) are nearly re-
lated to Modiola, and are distinguished by their long, cylindrical,
anteriorly-inflated shell, and by their habit of forming perforations
in rocks, in which they live. They appear to date from the Car-
boniferous rocks, and are known to palzontologists by both their
shells and their burrows. Cvenel/a, of the Cretaceous, Tertiary, and
Recent deposits, is another ally of dZodzola.

The genus Dveissena (including Congeria) comprises Mussel-
shaped Bivalves, with terminal beaks (fig. 581), and a small byssal
notch in the right valve, but differing from J/ytZus in having keeled
valves, and in the fact that the internal lining of the shell is not
nacreous. The hinge is toothed, and the anterior adductor is
attached (as in Septzfer) to a calcareous shelf within the beak.
The living species of Dvezssena are inhabitants of fresh or brackish

Fig. 581.—Dreissena (Congeria) conglobata, from the Upper Miocene of the Vienna basin.
(After Zittel.)

waters, and have a very wide distribution. Fossil forms of the
genus are found, often in extraordinary profusion, in the Miocene
and Pliocene deposits of Central and Eastern Europe, certain of
the Tertiary beds of Austria and Hungary being, for this reason,
spoken of as the ‘“Congerien-schichten.” The Miocene genus
Dreissenomya is related in most respects to Dreissena, but exhibits
the remarkable feature that the pallial line is sinuated.

It is, lastly, probable that the thin-shelled Carboniferous Bivalves
which constitute the genus Azthracoptera are brackish-water forms,
and are allied to Drezssena. In general form Axnthracoptera re-

MZ LAMELLIBRANCHIATA.

sembles Myalina, but it is destitute of the thick striated hinge-
plate of the latter, and the ligament is external.

ORDER IV. ARCACEA.

In this order the mantle-lobes are completely separate, or may
form two respiratory siphons; the foot is byssiferous or grooved ;
and there are two adductors. ‘The shell is ordinarily equivalve, and
the hinge is furnished in both valves with a series of equal and
similar teeth. This division of Bivalves includes the two families
of the Arcide and Nuculide, both of which have representatives in
rocks as ancient as the Ordovician, at any rate.

FamMILy 1. ARciID&.—TIn this family the muscular impressions
are nearly equal, the foot is large, bent, and deeply grooved, and
the mantle-lobes are separate. The shell is equivalve, and the
hinge is long and carries numerous comb-like teeth. The ligament
is usually external, attached to a striated area below the beak, but
it may be internal, and contained within
a single groove. The family of the Az-
cide appears to be represented in the
Upper Cambrian deposits (G/yptarca)
and is largely developed in existing seas.

In the genus Azca (fig. 582) the shell
is transversely elongated and inequilateral,
the surface being generally ornamented
with radial ribs or striz. ‘The hinge-line
is straight, and is furnished with numerous
transverse equal teeth, ” Whe wbeasman.
remote from one another, and are separ-
ated by an oval or lozenge-shaped, striated
ligamental area. Taken as a whole, the
genus Arca ranges from the Upper Cambrian to the present day,
the oldest types (Glyptarca) appearing in the Lower Tremadoc
beds.

The genus Avca has been broken up into numerous sub-genera, of
which the two most important are Cardonarca and [soarca. ‘The former
of these comprises some types from the Carboniferous Limestone, in
which the beaks are tumid and incurved, and the hinge has two strong
oblique teeth in front, and numerous transverse teeth behind. The forms
included under the head of /soarca belong to the Jurassic and Cretaceous
rocks, and have an elongated, very inequilateral shell, with the beaks
near the anterior end. The beaks are inflated and incurved, and the
hinge-line is slightly curved, and has a row of transverse teeth on each
side.

Fig. 582.—Arca antigua. Permian.

Closely allied to Avca is the genus Cucud/ea, in which the shell is
trapezoidal and ventricose ; the hinge-line is straight ; and the hinge-

ARCACEA. va

teeth are few and oblique, and at each end of the hinge become
parallel with the cardinal margin. ‘The genus Cucu//ea, in the wide
sense, ranges from the Carboniferous period to the present day, but
it is a matter of great difficulty to separate the fossil forms of this
genus from those belonging to Avca.

The genus Cucud/@a has been divided into sub-genera, of which the
two most important are JZacrodon and Parallelodon. In the former of
these (fig. 583, E) the shell is greatly elongated, with a long hinge-line,
the portion of which in front of the beaks carries a number of short

Fig. 583.—Types of Arvcide and Nuculide. A, Interior of Lyrodesma Cincinnatiensis, show-
ing the hinge, enlarged three times—Ordovician (after Hall); 8, Interior of Tellinomya pectun-
culoides, showing the hinge and adductor scars, enlarged twice—Ordovician (after Hall); c, In-
terior of the right valve of Pectunculus subpilosus—Tertiary ; D, Interior of the valve of Lmz-
opsis aurita—Pliocene; E, Interior of Mlacrodon Hirsonensts—Jurassic.

oblique teeth, while the portion behind the beaks supports a few elon-
gated teeth which run nearly parallel with the cardinal margin. Forms
of this type are not uncommon in the Secondary rocks, but the earliest
representatives appear in the Devonian rocks, and a single species exists
at the present day. The sub-genus Parallelodon is very closely allied
to Macrodon, possessing the same elongated posterior teeth directed
parallel to the hinge-line, but the anterior teeth are also sub-horizontal.
The species of this type are principally Carboniferous and Permian.

In the genus Pectunculus (fig. 583, Cc), the shell is nearly round and
almost equilateral ; the beaks are separated by a striated ligamental
area of triangular form; the hinge-line is curved, and the hinge-
teeth are oblique and form a semicircular row. fectunculus is a
comparatively modern genus, and does not seem to have come into
existence before the Cretaceous period. Numerous species are
known in the Tertiary rocks, and there are about sixty living types
of the genus.

a

ZT: LAMELLIBRANCHIATA.

Limopsts, ranging from the Trias to the present day, has an orbicular,
but slightly oblique shell (fig. 583, D), with a central triangular cartilage-
pit, and a row of transverse teeth on each side of this. Lastly, the Mio-
cene and Pliocene genus /Vwculina has the shell oval or subtrigonal,
with the anterior side abbreviated ; the hinge-line being curved, and

carrying a row of short transverse teeth completed posteriorly by one
elongated lamelliform lateral tooth.

In connection with the present family we may consider the ex-
tinct genera Cardiola and Cyrtodonta, with some forms allied to the
last of these, the precise affinities of these being
uncertain. In the genus Cardiola (fig. 584)
the shell is thin, equivalve, and oblique, with
convex valves and prominent incurved beaks,
and having the surface adorned with radiating
grooves, which are crossed by concentric fur-
rows in such a way as to give rise to radiating
rows of tubercular eminences. There is a large
triangular, transversely-grooved ligamental area
below the beak, and the hinge-line is straight ;
but teeth have not been certainly detected in
Fig. 584.—Cardiolacor- the typical forms of the genus, and the mus-

nucopie, from the Devon- - ;
ian rocks of Germany, of ular impressions are unknown. Numerous

Se sie. (After ‘species of the genus have been recognised in

the Silurian and Devonian rocks, a character-
istic species from the former system being the well-known Cardzola
interrupta.

The shells of the genus Cyrtodonta (Palearca ot Hall) are ventri-
cose and very inequilateral, the umbones being anterior (fig. 585).
The hinge-area is undefined, and the surface is generally smooth.
There are a few (three) anterior cardinal teeth, and “two or three
remote oblique posterior teeth parallel to the hinge-margin ” (Salter).
The species of Cyvtodonta appear to be exclusively confined to the
Ordovician, Silurian, and Devonian rocks, but the genus is said to
occur in the Upper Cambrian. Vanuxemia comprises forms of the
genus with nearly terminal beaks. In the genus J/ega/omus, again
(fig. 586), are comprised forms essentially similar to Cyrtodonta
(possibly identical with it), but having an excessively thickened and
massive shell, which is usually strongly inflated. The valves are
equal ; the beaks strongly incurved and placed anteriorly ; the hinge-
line furnished with three or four (?) strong transverse teeth ; and the
anterior muscular impression extremely deep. ‘The forms of this
genus appear to be confined to the Silurian rocks, and often attain a
great size, but they usually occur in the state of casts only.

FamiLy 2. NucuLID£.—This family comprises a number of marine
Bivalves, in which the mantle-lobes may be open, or siphons may be

ARCACEA. | 716

present, while the foot is discoid, and there are two nearly equal
adductors. The shell is equivalve, with an internal or external liga-
ment, but without a ligamental area; and the hinge is furnished
with numerous narrow teeth. The pallial line may be entire or
sinuated. This family includes two related groups, typified respec-
tively by Wucula and Nuculana (Leda), the former group being char-
acterised by the fact that the pallial line is entire and the posterior

Fig. 585.—Cyrtodonta Hindi. (Billings.) Ordovician. a, Side view; 4, Dorsal view.

side of the shell is short, while in the latter the pallial line is more or
less sinuated and the posterior side of the shell is long.

In the genus /Vucu/a itself (fig. 587) the shell is trigonal or oval,
and the beaks are reversed and turned towards the posterior side of
the shell, which is also the shortest side. The interior of the shell
is nacreous and the ventral margin may be smooth or finely dentic-
ulated. The hinge is angulated, and shows a central internal carti-
lage-pit, flanked on each side by numerous teeth. The Secondary
and Tertiary rocks have yielded a considerable number of species of
LVucula, and there are many living forms. The Palzozoic shells
which have been referred to Vucu/a probably belong really to other
types (Zel//inomya, &c.)

In the neighbourhood of the preceding may be placed the Silurian and
Devonian genus Czcullella (fig. 589, B), in which the hinge-line is straight

716 LAMELLIBRANCHIATA.

or slightly curved, and the hinge is essentially similar to that of Vucuda,
except that the ligament is external; but there exists a long inter nal
septum, which extends from below the beak towards the anterior muscu-
lar impression. The genera Clezdophorus (Ordovician and Silurian) and
Redonta (Cambrian and Ordovician) appear to be related to Cucullella,

Fig. 586.—Wegalomus compressus. A, Side view of the cast of the shell, natural size; p, The
same viewed from above: ad, Cast of the adductor impression ; 7, Pallial line. (Original. )

since both possess a vertical internal plate, which commences in front of
the beaks, and is continued downwards behind the anterior adductor, a
deep slit being left in the cast of the shell by its removal.

Also in the neighbourhood of /Vucu/a may be placed the genus
Tellinomya (= Ctenodonta, Salter), though this type shows decided

=

Mil \

Zo
(Ai >
(7

if
xf

Fig. 588.—Tellinomya contracta.
Ordovician. a@, Interior of right
valve; 4, Exterior of the same.

Fig. 587-—Nucula bivirgata. Gault.

affinities with Pectunculus among the Arcade. In Zellinomya (figs.
583, B, and 588) the posterior side of the shell may or may not be
the shortest, and the ligament is external, and is not placed, as in

ARCACEA. 717

NVucula, in an internal pit. The shell is generally oval or elon-
gated, smooth, or marked with fine concentric lines; there is no
ligamental area (as there is in Pectunculus), but the hinge carries
numerous small transverse teeth. The species of Ze//¢nomya range
from the Ordovician to the Carboniferous, and the forms placed by
Hall under the genus FPad/@onezlo are probably congeneric with the
above.

The genus /Vuculana (Leda) is the type of another group of the
present family, which is distinguished by the fact that the shell is
more or less produced posteriorly, and also usually by a more or
less marked sinuation of the pallial line (589, a); for which reasons
these forms are sometimes considered as constituting a separate
family (Vuculanide). In Nuculana (Leda) the shell (fig. 589, a)

Fig. 589.—Types of Nuculide. A, Interior of the right valve of Nuculana (Leda) lanceolata—
Pliocene; 8, Cucullella ovata—Silurian; c, Voldia striatu/a—Cretaceous, enlarged; pb, In-
terior of the left valve of Voldza mya/ts—Pliocene.

resembles that of /Vucu/a, but is rounded in front and produced
behind, while the pallial line is generally more or less indented. The
hinge has numerous small teeth on either side of a small central
cartilage-pit. Various species of the genus have been described
from the Palzozoic rocks, beginning in the Devonian, and it is
abundantly represented in the Secondary, Tertiary, and Post-Ter-
tiary deposits, as well as by living forms. Yoda (fig. 589, c and
D) resembles the preceding in most respects, but the teeth are comb-
like, and there is a large pallial sinus. The genus is perhaps rep-
resented as early as the Devonian or Carboniferous, but can hardly
be distinguished from /Vucu/ana in the fossil condition.

In the neighbourhood of Wuculana may be placed the Ordovician
genus Lyrodesma, in which there is an equivalve oblique shell, truncated
posteriorly, with an external ligament, and having a hinge of several

AWS | LAMELLIBRANCHIATA.

transverse teeth radiating in a fan-shaped manner from the beak (fig.
583,A). The Ordovician genus Actinodonta only differs from Lyrodesma
in having a longer hinge-line, and in the fact that the central hinge-teeth
are short or obsolete.

ORDER V. SUBMYTILACEA.

This order is defined by Fischer as comprising marine or fresh-
water Bivalves, in which the mantle-lobes are free, with thickened
margins ; the foot may or may not be byssiferous, and there are
(except in J7Ziillerta only) two adductor muscles. The shell is
almost always equivalve, the interior of the valves sometimes
nacreous, sometimes not; the hinge is furnished with teeth, which
are differentiated into a ‘‘ cardinal” and two “lateral” series; the
ligament is external; and the pallial line is simple. Dr Fischer
includes in this order a number of families, of which the most
important are the MJodiolopside, Trigontide, Unionide, Cardiniide,
Carditide, Astartide, and Crassatellide.

FAMILY 1. MoproLopsip#.—TIn this family the shell is equivalve
and very inequilateral, the beaks being placed subterminally towards
the anterior end of the shell. There are two adductor impressions,
of which the anterior is smaller than the posterior, and the pallial
line is entire. The ligament is external, and the hinge may or may
not be furnished with teeth. The principal genus of this family is
Modiolopsts itself (fig. 590), in which the shell is elongated, re-

Fig. 590.—odiolopsis miodiolaris. Ordovician.

sembling that of a MZodio/a in shape, with anterior beaks, and
having the surface smooth, or marked by fine concentric lines of
growth. The posterior end of the shell is broader than the an-
terior ; the hinge-line is long and nearly straight, and there is a long
ligamental groove extending to the posterior extremity, no teeth
being apparently developed. The impression of the anterior ad-
ductor is small but deep, that of the posterior adductor being wide
and ill-defined. The species of Modzolopsis are Ordovician and

SUBMYTILACEA. 719

Silurian. The Devonian genus Modiomorpha is closely related to
Modiolopsis, but the left valve has a single cuneiform tooth, which
fits into a corresponding cavity in the right valve.

FamILy 2. TRIGONIID#.—The members of this family are marine,
with a large bent foot, which does not secrete a byssus, and with
free mantle-lobes. The shell (fig. 592) is equivalve, subtrigonal,
nacreous internally, with an external ligament placed behind the
beaks, and a simple pallial line. The hinge-teeth are few in number
(fig. 591), varying from one to three in each valve. The only living
genus in this family is Z7zgonza itself, but various extinct types may
be associated with this. :

In the genus 777gonia (figs. 591-593) the shell is thick, nacreous
internally, trigonal in shape, and very inequilateral, the beaks being

Fig. 591.—Interior of the left
valve of Trigonia pectinata.
Recent. “7, Hinge-line, with
teeth and sockets; a, Anterior
adductor impression; a’, Pos- Fig. 592.—Tvigonia costata, from the
terior adductor impression. Jurassic rocks.

directed backwards. The anterior side of the shell is rounded, and
the posterior side is produced and obliquely truncated, constituting
a special ‘‘area,” which is often ornamented differently to the rest
of the shell, from which it is divided off by a more or less pro-
nounced ridge running from the beak to the hinder margin. The
so-called ‘‘ escutcheon” is a smaller area, which is cut off from the
rest of the shell by a second oblique ridge running close to the
dorsal margin of the shell
behind the beaks: The
hinge of the right valve is
furnished with two diverging
teeth, the faces of which are
strongly striated ; while that
of the left valve has a strong :
central tooth, striated on Fig. 593.— 7rigonia scabra. Chalk.

both sides, and two lateral,

externally striated teeth. The surface of the shell is rarely almost
smooth, the majority of species exhibiting a characteristic ornamen-

720 LAMELLIBRANCHIATA.

tation, consisting sometimes of concentric lines, but more usually
taking the form of radial rows of tubercles or diverging ribs. By the
form of the shell and the ornamentation of the surface the species
of Zrigonia may be divided into a number of minor groups. The
earliest types of Z7zgonia appear in the Lias, and the genus exhibits
an extensive development in the later Jurassic and Cretaceous for-
mations. A few Tertiary species are known, and the Australian
seas are inhabited by five existing forms.

The Triassic genus Myophoria (fig. 594) comprises sub-triangular
shells, obliquely keeled, smooth, concentrically striated, or with a
partial development of radiating ribs. ‘The left valve has three, and
the right two,. cardinal teeth. In the genus Schizodus (=the
Axinus of many authors, but not of Sowerby) are comprised a
number of Carboniferous and Permian Bivalves, in which the shell
(fig. 595) is obliquely ovate, and is in many respects externally

Fig. 595.—Cast of Schzz-
odus obscurus, from the
; Permian rocks, of the nat-
Fig. 594.—Myophoria lineata. ‘Trias. ural size. (After Zittel.)

similar to Ayophoria, except that the surface is smooth and non-
plicate, while the posterior side is bounded by an obscure oblique
ridge, and is not markedly angular. The right valve has two di-
verging teeth, and the left valve has a strong central tooth, with a
smaller marginal tooth on each side. The Devonian genus Cwur-
tonotus and the Carboniferous Do/aéra may be provisionally asso-
ciated with the present family.

FamMILy 3. Unionrp#.—In this family the foot is large and com-
pressed, not byssiferous except in the fry; the mantle-lobes are more
or less free, being usually united between the siphonal apertures ;
and there are two adductor muscles. The shell is ordinarily equi-
valve, nacreous internally, with a thick epidermis, and a large
external ligament. The hinge may be edentulous or furnished with
well-developed teeth, and the pallial line is entire. All the members
of this family are inhabitants of fresh water, and they are, therefore,
not known in the fossil condition except in fluviatile and lacustrine
deposits. If Anthracosta and Carbonicola be removed to the Car-
dinitde, the genera Unio and Anodonta are the only types of this
family which need consideration here.

SUBMYTILACEA. 72N

The shell in the genus Uvzio (fig. 596) is generally oval or
elongated, the beaks being placed towards the anterior end, and
a prominent external ligament
being present. The surface is
smooth, concentrically striated,
or in some cases ribbed, and
is covered with a thick horny
epidermis, which is often de-
stroyed over the beaks. The
hinge of the right valve has
two anterior lateral teeth, and
a long laminar posterior lateral
tooth; while that of the left
valve has a single anterior
lateral tooth, a cardinal tooth,
and two laminar posterior lat-
eral teeth. The most ancient fossil representatives of the River-
mussels appear in the Purbeck beds (Upper Jurassic), and other
forms (Unio Valdensis, &c.) are found in the Wealden deposits. A
considerable number of Tertiary types of Uzzo have been recognised,
principally in the Miocene beds, but the genus attains its maximum
at the present day.

The genus Axodonta or Anodon comprises the living Swan-
mussels, and is distinguished from Uxzo by the tenuity of the shell
and the edentulous character of the hinge. The shell forms an
elongated oval, compressed in the young condition but convex
when old, with anteriorly placed beaks; and it often attains a
considerable size. The earliest undoubted fossil forms of this
genus appear in the Eocene Tertiary; but the Upper Devonian
rocks of Ireland and Scotland have yielded the remains of a large
Bivalve which has been referred here under the name of Anodonta
(Archanodonta) Jukesi.

FAMILY 4. CarpDINuD#.—This family was proposed by Zittel
to include a number of Bivalves, in which there is an equivalve,
oval, or trigonal shell, which is not nacreous internally, and in which
the surface is smooth or concentrically striated. The ligament is
external, the pallial line is entire, and the muscular impressions are
deep and simple. ‘The cardinal teeth are generally small, but the
lateral hinge-teeth are more or less developed, and are often very
thick. The forms included in this family are all extinct, and present
relationships on the one hand to the Unzonide and on the other
hand to the Astartide. From the fossils with which they are
associated, they would appear to have been marine, or to have
inhabited brackish waters.

In the genus Cardinia (fig. 597, B) the shell is trigonal or ovate,

MOE. 1. 2aA

Fig. 596.—Uxio Valdensis. Wealden (Lower
Cretaceous).

722 LAMELLIBRANCHIATA.

very inequilaterai, posteriorly attenuated, and not ventricose. The
ligament is external, in a deep furrow, and the cardinal teeth are
feebly developed or wanting, while there is a single prominent
lateral tooth on each side. The surface is smooth or concentrically
striated, and the beaks are not eroded. ‘The genus is extinct, and
is confined to the Triassic and Jurassic rocks. Z7zgonodus, of the
Trias (fig. 597, C), is closely allied to Cardinia, but the cardinal

Fig. 597.—Types of Cardiniide. a, Anthracosia Lottneri, from the Coal-measures of Ger-
many; B, Interior of the right valve of Cardinia Listeri, Jurassic; c, Cast of the interior and
hinge-line of 7vigonodus Sandbergi, from the Trias of Wiirtemberg; D, Interior of the left valve
of Guerangeria Davousti, from the Inferior Devonian of France. (After Zittel, Chlert, and
Woodward.)

teeth are more fully developed, the right valve having one and the
left valve two. Various Palzozoic shells have been referred to
Cardinia, but the true affinities of these are doubtful.

We may place in this family the Devonian and Carboniferous
genus Carbonicola, comprising Unionoid Bivalves, with thick shells,
an external ligament, and a concentrically-striated surface. The
beaks are not eroded; and the hinge has a thick cardinal tooth in
the right valve, with a long lamellar lateral tooth on each side.

The genus Azthracosia comprises a number of thin-shelled
Bivalves in which the shell is long-oval and inequilateral (fig.
597, A), and the surface is smooth or concentrically-striated. The
ligament is external, and the hinge seems to have been provided
with a single cardinal tooth in each valve, without lateral teeth.
The Axnthracosie are found in abundance in parts of the Coal-
measures and Lower Permian series, and they may perhaps have
been inhabitants of brackish water.

Lastly, we may place here the Lower Devonian genus Gueran-

SUBMYTILACEA. WO
geria, of GEhlert, in which the shell (fig. 597, D) is long-oval and
very inequilateral, with small subterminal beaks, and a concentri-
cally-striated surface. The ligament is external; both valves have
an elongated posterior lateral tooth; and the right valve has a
cardinal tooth which fits into a corresponding socket in the left
valve.

FaMILY 5. CARDITIDA.—In this family the mantle-lobes are free,
the foot is byssiferous or is grooved inferiorly, and there are two
adductor muscles. The shell is equivalve, solid, cordate, oval, or
transversely elongated, and generally adorned with radiating ribs.
The pallial line is entire; the ligament is almost always external ;
and the hinge is massive, and supports one or two oblique cardinal
teeth and sometimes lateral teeth as well. The members of this
family are marine in habit, and the two most important recent
genera are Venericardia and Cardita, which are closely related to
one another, and are separated principally by characters connected
with the living animal, the former having a large foot which is
grooved and non-byssiferous, while in the latter the foot is short
and secretes a byssus.

In both Venericardia and Cardita the shell (fig. 598) is massive,
more or less cockle-shaped, inequilateral, and adorned with radiat-

Fig. 598.—Venericardia (Cardita) planicosta. Eocene Tertiary.

ing ribs, the ventral margin being denticulated or crenulated. The
ligament is external, and the hinge-plate is thick and furnished with
powerful cardinal and variably developed lateral teeth. The genus
Cardita ranges in time from the Trias to the present day; while the
species of Venericardia abound in the Cretaceous and Tertiary rocks,
and a few forms still survive.

With the preceding may be associated, provisionally at any rate,
a number of wholly extinct genera. Of these the genus Pleuro-
phorus (fig. 599) possesses an oblong shell, with anterior, almost
terminal beaks, and a massive hinge. Each valve has two diverg-
ing cardinal teeth, with a single elongated lateral tooth placed
posteriorly ; and the anterior adductor impression is very deep,

GDL LAMELLIBRANCHIATA.

and is bounded behind by an elevated ridge. The species of
Pleurophorus range from the Devonian to the Trias, but they are
most characteristic of the Permian formation. Possibly allied to
the above is the Matheria of the Ordovician rocks of Canada, in
which the beaks are placed anteriorly
and the ligament is external; and the
Silurian genus Axodontopsis may, per-
haps, also find a place here.
In this neighbourhood Dr Fischer
Segoe Hi likewise places the extinct genera JZyo-
Fig. 599.—Interior of the left 5 -
valve of Pleurophorus costatus, concha and Llippopodium. In the
Kony rman. rocks) te” former of these the’ shell Gsmtmickmems
mussel-shaped, with nearly terminal
beaks, and having the ligament external and contained in a
groove. ‘The hinge is massive and curved, and in the right valve
carries a single oblique tooth. ‘The anterior adductor impression
is deep, and the pallial line is entire. The species of Jyoconcha
are essentially characteristic of the Secondary rocks, though the
genus has been stated to occur in the later Palzozoic deposits.
In the genus AZippopodium (fig. 600) the shell is oblong, massive,
and ventricose, with nearly terminal incurved beaks, an external

Fig. 600.—H7ppopodium ponderosum. Lias.

ligament, and an entire pallial line. The hinge carries in each
valve an oblique tooth, which becomes obsolete with age. The
genus is confined to the Jurassic rocks, a familiar species being
the Aippopodium ponderosum of the Lias.

FamiLy 6. ASTARTIDA.—In this family the mantle-lobes are free,
and the foot is long and pointed. The shell is equivalve, thick,
trigonal or oval, with a more or less distinct “lunule.” The liga-
ment is external, and the hinge thick, with two or three cardinal
teeth in each valve, the lateral teeth being obsolete. ‘There are
two adductor impressions, of which the anterior is the deepest, and
the interior of the shell is not pearly. ‘The members of this family
are all marine, and the principal genera are Astarfe and Ofzs.

SUBMYTILACEA. 725
In the genus Astarte (fig. 601) the shell is thick, and usually
concentrically furrowed, subtrigonal, rounded, or oval in form,
inequilateral, and usually with a _ well-
marked “lunule.” The ligament is ex-
ternal, and there are two cardinal hinge-
teeth in each valve, the front tooth of
the right valve being large and_ thick.
The genus Asfarfe is stated to occur in
the Paleozoic series, from the Silurian
onwards ; but the affinities of the supposed
ancient representatives of this type are Fig. Pek Ree ear
uncertain. From the Mesozoic deposits right valve of Astarte detrita.
‘numerous species of Astarte have been ob- J™5*
tained, and the genus attained its maximum development at this
period. The Tertiary species are fewer in number, and about a
score of living species are known. The Carboniferous genus
Astartella and the Cypricardella (Microdon) of the
Devonian and Carboniferous rocks appear to be
related to Astarte. ‘The genus Pachydomus, of the
Devonian rocks of Australia and Tasmania, may,
perhaps, also be placed in this family. =
Of the remaining genera of the Astartide, the __. Fis-_602.—Inte-
2 i : : ‘ rior of the right
only one which need be specially noticed 1s Ofzs, valve of Opis Zunu-
of which numerous species are found in the Triassic, “" J™*
Jurassic, and Cretaceous rocks. In this genus the shell (fig. 602)
is heart-shaped and keeled, with prominent incurved beaks, a
distinct lunule, and a single cardinal tooth in each valve.
FAMILY 7. CRASSATELLIDZ.— The general characters of the
animal in this family are similar to those in the Astartide.

Fig. 603.—Crassatella ponderosa. Eocene Tertiary.

The shell also agrees with that of the Astartide in being equi-
valve, massive, and subtrigonal, with a distinct “lunule.” ‘The
shell is, however, more or less produced posteriorly, and the liga-
ment is lodged in an internal groove. The type of this family
is Crassatella itself (fig. 603), in which the shell is thick, solid, and

726 LAMELLIBRANCHIATA.

ventricose, attenuated posteriorly, and having a concentrically fur-
rowed surface. There is a distinct “lunule,” and the hinge is broad,
with strong cardinal teeth and feebly developed lateral teeth, while
there is a well-marked pit in the hinge-plate of each valve for the
reception of the internal ligament. The genus is marine; the
earliest forms appearing in the Cretaceous rocks, while numerous
Tertiary and about thirty-five Recent species are known. The Cre-
taceous genus Cvassate/lina has been associated with Cvassated/a,
but it agrees with the Astartide in having an external ligament.

ORDER VI. ERYCINACEA.

This order is defined by Fischer as comprising marine Bivalves,
with a byssiferous foot, and without respiratory siphons, but with the
exceptional character that the branchial aperture is placed anteriorly,
in front of the pedal opening, instead of being placed posteriorly
below the exhalant or anal aperture. The shell is small and thin,
equivalve, free, the hinge being toothed or toothless, and an internal
cartilage-pit and generally an external ligament being present. There
are two adductors, and the pallial line is entire. This order includes
the two small families of the Erycinide and Galeommide.

FAMILY I. ERYCINIDA.—The shell in this family is small and thin,
oval or trigonal in form, equivalve, mostly inequilateral, and smooth or
finely striated. The hinge carries one or two cardinal teeth, but lateral
teeth are not constant. The internal ligament is contained in an oblique
groove between the hinge-plates of the valves, and the external ligament
is feebly developed.

The genus -vyczza includes a large number of small shells which are
found in Tertiary deposits, and are specially abundant in the Eocene
rocks. A single species has been described from the Cretaceous rocks
of North America. Very closely related to E7yczna, if generically separ-
able from it, is the genus Ke//za, which is not known in the fossil condi-
tion (as distinct from the preceding). Related genera are Lefton and
Montacuta, both of which are known by Tertiary forms, and still survive.

FAMILY 2. GALEOMMID&.—In this family the shell is small, thin, equi-
valve, and subequilateral, and is more or less gaping. The hinge may
be edentulous, or may be provided with one or two teeth ; and the liga-
ment is internal, and is lodged ina median pit. All the forms included in
this family are marine, the two principal genera being Galeomma and
Scintilla, both of which are represented by living forms. The oldest
species of Galeomma are found in the Pliocene deposits, while Sczntclla
appears as early as the Eocene.

OrpDER VII. CARDIACEA.

The Lamellibranchs included in this order are inhabitants of the
sea or of brackish water, and possess a byssiferous or grooved foot ;
while there are two adductor muscles. (According to the views of

CARDIACEA. 72g

some malacologists, Z77#dacna is monomyary.) The shell is equi-
valve and thick, the hinge with or without teeth, the ligament exter-
nal, and the pallial line simple or slightly indented. This division
includes the two principal families of the Z7idacnide and Cardide.

FaMILy 1. TRmpacnip&.—JIn this family the shell is equivalve,
thick, not nacreous internally, and usually truncated or gaping in
front, the ventral margin being undulated or dentate, and the sur-
face ribbed. The hinge has a single cardinal tooth and one or two
posterior lateral teeth in each valve, and the ligament is external.
The foot is finger-like and usually secretes a byssus; the mantle-
lobes are extensively united ; and the impressions of the adductors
are blended together and are subcentral in position. (According to
some authorities, the anterior adductor is really absent.)

In the genus Z7idacna itself (fig. 604) the shell is massive, of
large size, and subtrigonal in form ; and there is a wide byssal aper-
ture just in front of the beaks. On the other hand, in the closely

Fig. 604.—Tridacna media. Tertiary. Interior of right valve.

allied A/zppopus the shell is closed, and the pedal aperture is only
indicated by small serrations of the margin of the valves. Z7¢dacna
is only known in a fossil condition by a few species from the later
Tertiaries. The Paleozoic Eurydesma has also been referred to this
family.

FAMILY 2. CARDIID#.—In this family are included the “‘ Cockles,”
in which the mantle is open in front to allow of the passage of a
large and sickle-shaped foot, while it is closed behind and gives
origin to two longer or shorter siphons. ‘The shell is equivalve and
is not nacreous, usually heart-shaped in form, with radiating ribs,
and with the ventral margin toothed or wavy. The ligament is ex-
ternal, and the hinge carries one or two cardinal teeth in each valve,
usually with lateral teeth as well. There are two adductor-muscles,
and the pallial line is entire or slightly indented.

In the genus Cardium are comprised the true Cockles, in which
the shell is ventricose, the beaks pronounced, and placed nearly in

728 LAMELLIBRANCHIATA.

the centre of the dorsal margin, the margins crenated, and the
pallial line more or less indented. The surface is adorned with
radial ribs or strize, which often carry spines. A very large number
of recent species of Cardiuwm are known, and between three and
four hundred fossil forms have been referred here. Certain Palz-
ozoic types have been placed under this head, but the affinities of
these are doubtful. On the other hand, the genus is largely repre-
sented by undoubted types throughout the Mesozoic and Kainozoic
series. The genus Cavdium has been broken up into numerous
minor groups, most of which can be with difficulty, or not at all,
recognised in the fossil condition. Papyridea, Levicardium, and
Lithocardium are Secondary to Recent types closely allied to Car-
dium proper. Protocardia (fig. 605) has the posterior slope of the
shell radiately ribbed, while
the rest of the shell is con-
centrically striated. —femz-
cardium has keeled valves,
the shell appearing cordate
as viewed from behind or in
front. Lymnocardium and
Adacna include _ brackish-
water and fresh-water Cockles,
Fig. 605.—Cardium (Protocardia) Hillanunt. in which the cardinal teeth
Upper Greensand. are small or obsolete; and
the species of the former are
common in some of the fluviatile and estuarine deposits of the
Upper Tertiary period. The recent species of Adacna are found
abundantly in the Black Sea and Caspian Sea, and in the Sea of
Aral, often in quite brackish water, and the fossil species are extra-
ordinarily plentiful in the Tertiary deposits of Austria, Hungary, and
Southern Russia. The genus is remarkable for the exceeding vari-
ability of the hinge as regards the number of teeth. Ayssocardium,
again, includes Eocene and Miocene Cockles, in which the shell is
truncated anteriorly, and possesses a large byssal sinus.

The most remarkable of the early types of the Cardid@ is the
genus Conocardium (= Pleurorhynchus), which ranges from the Or-
dovician to the Carboniferous, but is specially characteristic of the
Devonian and Carboniferous formations. The shell in this genus
(fig. 606) is keeled, and very oblique, the azzerior end (sometimes
regarded as the posterior end) of the shell being short and abruptly
truncated, so as to appear as a cordate flattened area when the
shell is viewed from the front. Just below the beaks the shell is
produced anteriorly into a long cylindrical tubular projection or
beak. ostertorly the shell is elongated and contracted, the valves
being widely deficient or gaping at the extremity. The hinge-line

CHAMACEA. 729

is long and straight; and two cardinal teeth, with a hinder lateral
one, appear to be present.

Famity 3. LUNULICARDUD#.—This family is one of very uncertain
value, and embraces only the imperfectly understood genus Lwsuelt-
cardium of Miinster. In this genus the shell is obliquely oval,
equivalve, and inequilateral, the surface being adorned with radiat-
ing ribs. The anterior end of the shell is truncated, and the pos-

Fig. 606.—A, Conocardium giganteun, showing the truncate anterior and produced posterior
end of the shell, with the tubular prolongation of the former; B, Conocardium infiatum, viewed
from above: c. The same viewed laterally. Carboniferous. (After M‘Coy.)

terior end is sub-alate. The cardinal line is “marked by a lunate
hiatus in each valve, which was probably occupied by the ligament”
(Hall). The hinge and muscular markings are unknown. In this
genus, as in Conocardium, the truncated end of the shell is some-
times regarded as the fosterior end. The species of Lunulicardium
are found in the Silurian and Devonian rocks, being very abundant
in the Silurian rocks of Bohemia.

ORDER VIII. CHAMACEA.

In this order, represented at the present day by the single genus
Chama, the mantle is closed, the mantle-cavity communicating with
the exterior by apertures for the foot and for the in-going and out-

730 | LAMELLIBRANCHIATA.

going currents of water; and the foot is rudimentary. ‘The shell is
irregular, very inequivalve, always attached to foreign objects by the
substance of one valve. In structure, the shell is thick, and consists
of an internal porcellanous and an external prismatic layer, often
with special and remarkable modifications in particular types. The
hinge is thick, and is provided with cardinal teeth, but lateral teeth
are wanting. The ligament may be external or internal, or is want-
ing altogether. The pallial line is entire, and the two adductors
leave well-marked scars, or may be inserted upon special internal
calcareous septa. This order includes the two families of the
Chamide and the fudiste.

FAMILY 1. CHAMID&.—In this family the shell is inequivalve,
and is generally attached to foreign objects by the substance of one
of the valves. ‘The ligament is normally external, and lies in a deep
groove, but it may become more or less completely concealed from
view. ‘The hinge is massive, and usually carries two teeth in one
valve and one in the other. The adductor impressions are very
large, and the pallial line is entire. The family includes the single
recent genus Chama, together with a number of exceedingly remark-
able Mesozoic Bivalves, such as Duceras, Reguienia, Monopleura,
Caprina, Caprotina, &c. The structure of these latter is, however,
so complicated that they cannot be advantageously treated of here
except in an exceedingly brief manner ; since a full understanding
of their characters can only be obtained by the examination of
actual specimens.

In the genus Chama (fig. 607) the shell is attached to foreign
objects by the beak of the left valve, or, more rarely, by that of
the right valve. The beaks of both valves are incurved and are
directed anteriorly. The free valve is the
smallest, and the surface of both valves is
furnished with foliaceous expansions, derived
from a thick external prismatic layer, below
which is situated an internal porcellanous
layer. ‘The massive hinge usually carries a
single tooth in the free valve, articulating
with two teeth in the attached valve. The
recent species of Chama are all inhabitants
of the sea. The fossil species commence
in the Cretaceous rocks, a number of forms
Feo peenes OF USS cress fomiarc) to cake Tertiary deposits.
mellosa. Eocene Tertiary. In the genus LRequienia (fig. 608) the shell

is exceedingly inequivalve, the right valve
being small, subspiral, and operculiform, while the left valve is of
large size and is spirally rolled up, its beak serving for the attach-
ment of the shell to some foreign body. ‘The ligament is external,

CHAMACEA. 7a

and is prolonged on the outside of the left valve to its beak ; and
the hinge is edentulous or has a single tooth. The genus is distin-
guished from Chama by its generally smooth or striated surface, and
the want of the foliaceous expansions of the latter. The species of
Requienta are exclusively confined to the Cretaceous period.

In the genus Diceras (fig. 609) the shell is slightly inequivalve,
the beaks being very prominent and spirally rolled up in both valves.

Fig. 608. — Reguienia
ammonia, one-fourth of
the natural size. a, Point
of attachment. Cretaceous
rocks. (After Woodward.)

Fig. 609.— Diceras arietina. Upper
Jurassic.

Either the right or the left valve may be the largest, and in that case
serves for the attachment of the shell to foreign bodies by means of
the umbo. The ligament is external, and is prolonged to the apices
of the beaks in external furrows. The hinge is very thick, with prom-
inent teeth (two in one valve and one in the other); and the
muscular impressions are bounded by long spiral
ridges. The species of Dzceras are exclusively
confined to the Middle and Upper Jurassic
rocks, abounding especially, in some regions, in
beds of the age of the Coral-rag of Britain.

In the genus Monopleura (fig. 610) the shell
is very inequivalve, and is fixed by the apex of
the right valve, which is the larger of the two,
and is conical in form, being either straight, or
more or less spirally inrolled. The left valve
is small, and either flat or widely conical, with
a submarginal umbo. The ligament is pro- ees ye ee
longed externally in grooves, which run to the ¢iobata, of the natural
beaks in each valve. The surface is generally Ce er eene
radially striated. The species of this genus are
wholly confined to the Cretaceous rocks, and principally characterise
the lower division of this formation. Closely allied to Monopleura,
and also confined to the Cretaceous rocks, is the genus Caprofina.

32 _ LAMELLIBRANCHIATA.

Here also must be placed the remarkable Cretaceous genera
Caprina, Plagioptychus (=Caprina in part), and Lchthyosarcolites
(= Caprinella and Caprinula), in all of which the shell (fig. 611)
is very inequivalve, thick-walled, and either fixed by the apex of
the right valve, or, in some cases, free. In all these forms the
shell-structure consists of a thin external prismatic layer, and a
greatly developed internal laminated or porcellanous layer, the
laminze of which may be more or less extensively separated by
vacant spaces (the so-called ‘‘ water-chambers”). In the substance
of the left valve in these genera there is, further, developed a

Fig. 611.—Plagioptychus (Caprina) Aguilioni. The right-hand figure shows the
interior of the left valve.

system of radial canals which run from the beak to the free
margin of the valve, where they terminate in foramina, and which
are sometimes simple and sometimes complex in their arrangement.
FAMILY 2. Rupist#® (Aiippuritide).—In this family the shell is
very inequivalve (fig. 612), unsymmetrical, massive, the two valves -
being dissimilar in structure and sculpturing. The shell is attached
by the apex of the elongated right valve, which is conical in form ;
while the left valve is depressed, often operculiform, and has a
central umbo. There is no ligament; but the free upper valve is
fixed into the conical lower valve by powerful teeth and processes,
and is only capable of movement in a vertical direction. There are
two large adductor impressions, those of the left valve being upon
prominent apophyses. The pallial line is simple and submarginal.

The shell-structure in the Wzppuritzd@ is exceedingly peculiar, and has
been described by Zittel as follows: “ The /owery valve consists of two
layers, the outer of which is formed of perpendicular prisms having a
direction parallel to the long axis of the shell, and intersected by numer-

CHAMACEA. 738

ous transverse lamella, which are horizontal, or are directed somewhat
obliquely outwards and upwards, the intersection of the two series giving
rise to a lattice-like structure (fig. 614). The shell splits easily along the
line of these transverse lamella, the upper surfaces of which—as also of
the thickened upper margin of the shell—exhibit radially disposed vas-
cular impressions. The inner stratum of the shell is white, porcellanous
and laminated in structure. Sometimes the parallel lamellz are sepa-
rated by vacant spaces (fig. 613), thus giving rise to intervening lacunze
(‘water-chambers’). This is especially the case in Azppurites, in which
the greater portion of the conical lower valve is formed by the inner
shell-layer. The two shell-layers separate readily from one another; and

Ne

is

ic
)
p

6)

Fig. 613.— Vertical section of a
broken shell of Hzppurites organ-
zsans, without the body-chamber,

Fig. 612.— Hippurites Toucasi- showing the horizontal partitions
anus. A large individual, with two and intervening spaces (‘“‘ water-
smaller ones attached to it. Creta- chambers”’), of the natural size.
ceous. (After Zittel.)

as the inner one, at least in SAhk@rulites and Radzolztes, resists destruc-
tion during fossilisation less completely than the outer one, it commonly
happens that only the outer layer is preserved, and the mould of the
body-chamber appears to be separated from the latter by a vacant space.
Still more commonly, the inner layer has undergone transformation, and
has been replaced by crystalline calcite. The uAfer valve consists, like
the lower one, of two layers, but the cellulo-prismatic outer stratum is
mostly of small thickness, and in Azpfurctes is traversed by a compli-
cated system of canals, while the inner porcellanous and laminated layer
is frequently converted into crystalline calcite.” It is usually supposed
that the outer layer of the shell in the HzApuritide corresponds with the
external prismatic layer in such Bivalves as Pimva, but it differs from
the latter in the great size of the component prisms, and in the fact that

7 34 LAMELLIBRANCHIATA.

these are directed Aarallel to the surface of the shell instead of perpen-
dicular to the surface. Moreover, the intersection of the prisms by hori-
zontal or oblique lamelle gives rise to an altogether unique vesicular
structure. Further, the prisms in the outer shell-layer in the. ordinary
Bivalves are solid, whereas in the Hzppuritide they are hollow, and were
probably occupied in life by some organic infilling.

The shell of Azppurites (fig. 612) is inversely conical or cylin-
drical, and sometimes attains a length of two or three feet. The
shell is attached by the larger conical valve, and is closed by a small
depressed free valve, with a central umbo. In fadzoltes the shell
is inversely conical, bi-conical, or cylindrical, with dissimilar valves.
The upper valve is sometimes flat, sometimes conical, and has a

Fig. 614.—Minute structure of the shell of Spherulites (Radiolites) Mortonz, from the Upper
Greensand, Cambridge. a, Transverse section, enlarged ten times, showing the large hollow
prisms of the outer layer (7) transversely divided, the thin inner layer (2) being converted into
crystalline calcite; B, Vertical section, similarly enlarged, showing the prisms of the outer layer
with their intersecting cross-partitions. (Original.)

central or lateral umbo. The external shell-layer in the lower valve
is exceedingly thick, and is made up of hollow calcareous prisms,
which run parallel with the surface and are intersected by close-set
oblique transverse plates (fig. 614); while the inner shell-layer is
comparatively thin. In the typical forms of Radzolites the lower
valve commonly exhibits on one side two bands running from the
beak to the upper margin, which are smooth or striated differently
from the rest of the valve. In the closely allied genus Spherulites
these bands are wanting.

The Audiste are not only entirely extinct, but are exclusively
restricted to rocks of Cretaceous age, being especially characteristic
of the middle and upper divisions of this formation, particular types
commonly being confined to special stratigraphical horizons. ‘The
Cretaceous deposits of Britain, Europe, Algeria, Asia Minor, Persia,

CONCHACEA. 736

and North America have yielded the remains of these singular
Molluscs ; but they are especially abundant in Southern Europe,
where they often give rise to great beds of marble (‘ Hippurite
Limestones,” ‘“‘ Rudisten-Kalk”). In all the Audzste the two valves
of the shell are more or less conspicuously dissimilar in shape and
size, and often in external sculpturing or internal structure. They
appear to have lived in shallow water, and to have grown in great
beds or banks, much as Oysters do.

ORDER IX. CONCHACEA.

In this order, the inhalant and exhalant openings of the mantle
are usually prolonged into siphons; the foot may or may not be
byssiferous ; and there are two adductor muscles. The shell is
equivalve, regular, and free ; the ligament is almost always external ;
the hinge has cardinal teeth, generally with lateral teeth as well ;
and the pallial line is usually sinuated, but may be entire. The
Bivalves included in this order are mostly marine, but sometimes
inhabit brackish or fresh waters. The principal families included
under this head by Fischer are the JMegalodontide, Cyprinide,
Veneride, Cyrenide, Ungulinide, Unicardiudae, Tancrediide, Don-
acide, Psammobide, and Solenide.

FaMILy 1. MEGALODONTID&.—In this family the shell (fig. 615) is
equivalve, very thick, and mostly smooth or concentrically striated,

——

Fig. 615.—MJegalodon cucullatus, from the Middle Devonian of Paffrath. (After Zittel.)

the beaks being turned to the anterior side of the shell. The hinge-
plate is very broad, each valve carrying one or two strong cardinal
teeth, with feebly developed lateral teeth. The ligament is external,
and the posterior adductor impression is placed upon a more or less
prominent ridge. All the genera of this family are extinct, the prin-
cipal type being JZegalodon itself. In this genus (fig. 615) the shell

736 LAMELLIBRANCHIATA.

is massive, with subspiral beaks and an external ligament. The right
valve has two striated cardinal teeth, and the left valve has one, par-
tially-divided cardinal tooth. ‘The species of A/ega/odon range from
the Devonian to the Trias, a familiar species being the JZ. cucul-
Zatus of the Middle Devonian rocks. Allied to the preceding is the
Jurassic genus Pachyrisma, in which the shell is thick and pon-
derous, and the umbones are subspiral.

FAMILY 2. CyPRINID#.—In this family the mantle-lobes are united
behind by a curtain pierced by two siphonal orifices, and the foot is
thick and tongue-shaped. ‘The shell is equivalve, thick, the beaks
directed anteriorly and often inrolled,
and the hinge is furnished with cardinal
and lateral teeth. The ligament is ex-
ternal, and the pallial line is entire.

The principal genus in this family is
Cyprina itself, in which the shell is
large, strong, and rounded, with a thick
epidermis, and a strong external liga-
ment. The hinge carries two cardinal
teeth in each valve, with a single lateral
tooth posteriorly, and variably developed
anterior lateral teeth (fig. 616). The
pe ee Mes ee Gp genus Cyprina is represented in recent
rina Saussuri, Cretaceous. seas by the familiar C. Js/andica, and

there are numerous Secondary and Ter-
tiary species, commencing in the Lias.

The genus Ssocardia (fig. 617) comprises the ‘‘ Heart-cockles,”
in which the shell is cordiform and inflated, and the beaks are
remote and subspiral. The ligament splits in front, and is con-
tinued in two separate furrows as far
as the beaks. The hinge in each valve
possesses two cardinal teeth and a pos-
terior lateral tooth. ‘The genus JLsocardia
is represented by living forms, and the fossil
species date from the Jurassic rocks.
Most of the Jurassic ‘ Heart - cockles,”
however, belong to the related genus Azzso-
cardia, in which the beaks are approximated
and the ligament is not split.

Cypricardia (= Trapezium) has a trapezoi-
Big. OL CIS crassa. dal shell, usually radiately striated, the hinge
1ocene. e . . .

with three radiating cardinal teeth and a pos-

terior lateral tooth in each valve, and the posterior side often keeled.
The true Cypricardie are probably wholly Mesozoic and Kainozoic, and
a few recent species of the genus are known. It is possible, however,
that the Paleozoic genera Cypricardinia (Silurian to Carboniferous) and

CONCHACEA. 737

Gontophora (Silurian and Devonian) should find a place in the neigh-
bourhood of Cyfricaradza.

FaMILY 3. VENERID£.—In this family the animal is free and
locomotive ; the mantle has a large anterior opening for. the foot ;
and respiratory siphons, which may be separate or more or less
united, are developed. The foot is tongue-shaped and compressed,
in some cases grooved and byssiferous. The shell (fig. 618) is
regular, suborbicular or oblong, equivalve, and furnished with an
external ligament. The hinge usually carries three diverging car-
dinal teeth, and the development of the lateral teeth is variable.
The pallial line usually shows a deeper or shallower sinus, but in
some cases is entire. The Vezeride are all marine, and the family
includes some of the most highly organised and most beautifully

Fig. 618.—Venus cincta, from the Miocene rocks of Austria. (After Zittel.)

coloured examples of the entire class of the Lameliibranchiata. No
Paleeozoic representatives of the family have been as yet detected.

In the genus Venus (fig. 618) the shell varies greatly in form and
in surface-ornamentation, and is principally distinguished by its wide
hinge-plate, furnished in each valve with three diverging cardinal
teeth. The genus, in its typical form, appears to begin in the
Jurassic rocks, and the Tertiary rocks have yielded a large number
of forms, while about two hundred species are known to exist at the
present day. Very nearly related to Venus is the genus Cytherea
(Meretrix), which is largely represented at the present day, and has
numerous fossil forms, commencing in the Jurassic rocks.

In the genus Dostnza (Artemis) the shell is orbicular, compressed,
and concentrically-striated, with a deep “lunule” and a deep and
pointed pallial sinus (fig. 556, B). The earliest fossil forms appear
in the Cretaceous rocks. Venerupis, again, has the shell radiately
ribbed, and at the same time furnished with concentric ridges, the
general form of the shell being oblong. In Zafes, lastly, the shell
is oblong, with anteriorly placed beaks, a concentrically-striated

VOL. I. 3A

738 LAMELLIBRANCHIATA.

surface, and a broad pallial sinus. The genus is known by Cre-
taceous, Tertiary, and Recent species.

In the singular genus Zetis, now usually reared here, the shell
is gibbous and very thin, and there is an exceedingly deep, angular,
pallial sinus, which extends nearly to the beaks. The known species
of this genus are found in the Cretaceous rocks. Finally, the genus
FPetricola, now usually regarded as the type of a separate family,
comprises Bivalves which differ from the Venerzde in their habit of
burrowing into rocks or sand, or in being fixed into crevices by a
byssus. The shell in this genus is thin and tumid, with a short
anterior side and a deep pallial sinus. The range of the genus is
from the Cretaceous period to the present day.

FAMILY 4. CYRENID&.—In this family the mantle is open in
front ; a single siphon is present, or, more usually, two more or less
united ; and the foot is large and tongue-shaped. The shell is sub-
orbicular, closed, with a thick epidermis and a concentrically-striated
surface, the hinge with cardinal and lateral teeth, and the ligament
external. The pallial line is simple or slightly sinuated. The
members of this family inhabit fresh or brackish waters, and their
remains are commonly found in estuarine or lacustrine deposits of
Mesozoic and Tertiary age.

In the genus Cyvena (fig. 619) the shell is thick, and rounded
or subtrigonal, the beaks being commonly eroded. ‘The hinge in
each valve has three cardinal teeth, and a single lateral tooth in
front and behind. The forms
which are included under the
name of Cordicula differ from
Cyrena proper principally in
the fact that the lateral teeth
are elongated and are trans-

Fig 619.—Cyvrena antigua. Eocene. versely striated. The oldest

representatives of these two

types appear in the Jurassic rocks, and there are numerous living

forms, the Cretaceous and Tertiary rocks having also yielded many
characteristic species.

The genus Spherium (Cyclas) comprises fresh-water forms in
which the shell is of small size, thin, more or less orbicular, and
nearly equilateral. ‘The right valve has one cardinal tooth, often
bifid, and the left valve has two. The genus /2szdium differs from
the preceding in little except that the shell is inequilateral, the
anterior side being the longest. Both these types are now in ex-
istence, and the earliest fossil forms commence in the Eocene
Tertiary.

FAMILY 5. UNGULINID#.—In this family the mantle-lobes are free ;
and the foot is long and vermiform, and does not secrete a byssus. The

CONCHACEA. 739

shell is equivalve, slightly inequilateral, orbicular in form, and more or
less tumid. The hinge has usually two cardinal teeth in each valve,
without lateral teeth. The ligament is wholly or partially internal, and
the pallial line is entire.

The type-genus of this little group is Usgulina, which is represented
by living species and by a few Tertiary forms.

FAMILY 6. UNICARDIID£.—JIn this family the shell is equivalve,

slightly inequilateral, oval or rounded, and concentrically striated. The
hinge carries a single cardinal tooth in each valve; the hgament is lodged
in an external marginal groove ; the adductor impressions are elliptical ;
and the pallial line is entire. The genus Unzcardium is the type of this
family, and its species range from the Trias to the Chalk. Fischer
also includes here his genus Pseudedmondia, of the Carboniferous rocks,
founded for the reception of certain forms of Edwondia in which the liga-
ment is external, and is placed in a marginal groove.
_ FAMILY 7. TANCREDIID.—This family includes transversely triangu-
lar shells, resembling Dozax in form, with an external ligament, and an
entzre pallial line. The hinge has in each valve two cardinal teeth (some-
times only a single tooth in one valve), with lateral teeth as well, at any
rate posteriorly. The type of this family is the extinct genus Zancredia,
in which the shell is attenuated in front, and obliquely truncated behind.
The species of this genus range from the Trias to the Chalk.

FamiLty 8. Donacip#.—In this family the animal is marine or
estuarine in habit, with a large foot, and short separate siphons.
The shell is equivalve, more or less wedge-
shaped, close, and non-nacreous. The
hinge carries one or two cardinal teeth in
each valve, with inconstant lateral teeth ;
the ligament is external; and the pallial
line is deeply indented.

In the genus Donax (fig. 620), the shell 5:5 650.—Interior of the
is wedgeshaped, the front rounded and right valve of Donax retusa.
produced, and the posterior side short and
obliquely truncated. There are numerous living species of this
genus, and a small number of fossil forms, the oldest undoubted
types appearing in the Eocene deposits. The Jurassic genus
Isodonta (Sowerbya) may be placed
in the neighbourhood of Dovzax.

FaMILy 9. PsaMMosup#.—This ~%% Ss
family includes marine Bivalves, {| a ae M
with long separate siphons and a i
tongue-shaped foot. The shell is
Fig. 621.—Interior of the right valve of

Psammobia rudis. Eocene.

transversely elongated, equivalve,
sub-equilateral, slightly gaping at
both ends, with an external ligament, and a deeply sinuated pallial
line (fig. 621). The hinge usually carries two cardinal teeth in
each valve, but there are no lateral teeth.

The type of this family is the genus Psammobra, in which the

740 LAMELLIBRANCHIATA.

shell is oblong, compressed, and nearly equilateral (fig. 621).
There are many recent species of this genus, together with a
moderate number of Tertiary forms, but the earliest appearance of
the genus seems to be in the Cretaceous rocks. The Jurassic
genus Quenstedtia appears to be nearly allied to Psammobza.

FAMILY 10. SOLENIDA£.—In this family respiratory siphons are
present, and are usually short and more or less united, but may be
longer and separate. The foot is very large, and more or less
cylindrical in shape; and the branchiz are prolonged into the
branchial siphon. ‘The shell is transversely elongated, more or
less gaping at both ends, equivalve, and covered with epidermis.
The hinge is variable, carrying from one to three cardinal teeth in
each valve, without lateral teeth. The ligament is external, and
the pallial line is more or less sinuated. The recent members of
this family are all marine or estuarine in habit, and the group attains
its maximum development at the present day.

Of the genera of this family, So/ecurtus (fig. 622) has an elongated
shell with subcentral beaks, the dorsal and ventral margins being

NS
=

Z hy
F_fouyey

Fig. 622.—Solecurtus Deshayesi. Eocene. Fig. 623.—Interior of the right valve of
(After Zittel.) Szligua polita.. Recent.

nearly parallel, and the surface generally marked with oblique lines.
The genus begins in the Cretaceous rocks and still survives. In
the genus St/gua (fig. 623) the shell agrees in form with that of Sode-
curtus, and also has the beaks placed a little in front of the centre,
but an oblique internal rib runs from below the beak to the ventral
margin. This genus ranges in time, as does the preceding, from the
Cretaceous to the present day. Cwu/fellus, ranging from the Eocene
to the present day, resembles the preceding in most characters, but
the beaks are placed very far forwards, and the shell thus becomes
very inequilateral. In the genera Hzszs and So/en are included the
typical ‘‘ Razor-shells,” in which the shell is greatly elongated, with
the beaks placed almost at the anterior end of the shell, and with
both extremities widely gaping. zszs begins in the Tertiary rocks
and is represented at the present day, its chief distinction from So/ex
being that the shell is somewhat curved, whereas in the latter it is
straight. So/en itself is said to occur in deposits as old as the
Devonian, but the earliest undoubted species are found in the

MYACEA. 741

Trias, and the genus still survives. The Carboniferous genus
Solenopsis, with prominent beaks and a closed anterior end, and
the Devonian Padeosolen may represent ancient types of the So/en-
za. Here also, perhaps, may be placed the Palzeozoic genus
Orthonota, the typical forms of which are Devonian, though species
have been described from rocks as
old as the Ordovician (fig. 624). In
this genus the shell is greatly elongat-
ed and very inequilateral, the anterior
end being rounded and the posterior
end truncate, and the beaks being
Eleseisto sthe ‘anterior end; The
muscular impressions and pallial line
have not been made out; and the. Fig. 624.—Orthonota (Orthodesma) par-
hinge is only imperfectly known, but eae

is apparently edentulous. The hinge-line is straight, and in the
typical forms of the genus is continued in a straight line in front of
the beaks. In one group of forms, however, sometimes distinguished
under the name of Ovthodesma, the hinge-line is bent or contracted
in front of the beaks, and is straight behind (fig. 624).

ORDER X. MYACEA.

In this order the mantle-lobes are united, a pedal aperture exist-
ing in front and two siphons behind. ‘The siphons are long, and
may be united or separate. The foot may or may not be byssiferous,
and there are two adductor muscles. ‘The shell is free, equivalve
or inequivalve, with an internal or external ligament, and a variable
pallial line, while the characters of the hinge also differ in different
families of the order. The chief families of this order are the
Mactride, Myide, Glycimeride, and Gastrochenide.

Famity 1. Macrrip&.—TIn this family the mantle is more or
less open in front; the siphons are united, with fringed orifices ;
and the foot is compressed. The shell is equivalve, trigonal, gen-
erally gaping behind; the ligament being typically internal and
lodged in a deep triangular pit between the beaks. ‘The left valve
has a widely bifurcated cardinal tooth, which is received between
the diverging branches of a right cardinal tooth; and lateral teeth
are usually present in addition in front and behind. ‘The pallial
line is usually deeply sinuated. The members of this family are
all marine, and the two principal genera are Mactra and Lutraria.

In the genus MZactra (fig. 625) the shell is trigonal in form,
slightly gaping behind, with a short pallial sinus. The internal
ligament is contained in a triangular pit, but there is also an
external ligament lodged in a groove. ‘The recent species of

742 LAMELLIBRANCHIATA.

Mactra \ive buried in sand or mud. The fossil forms begin in the
Jurassic rocks, but the genus does not show any extensive develop-
ment till the Tertiary rocks are reached.

In the genus Lutrarta the shell is oblong and gaping at both
ends; the pallial sinus is deep, and the internal ligament is sup-
ported by a prominent, spoon shaped
cartilage-plate. The earliest undoubted
fossil forms of this genus appear in the
Tertiary rocks, and about thirty living
species are known.

FamiILy 2. Myip#.—In this family
the mantle is almost entirely closed,
but there exists in front an aperture for
the small triangular foot, while poste-
riorly are two long siphons, more or less
completely united with one another (fig.
555), and partly or wholly retractile.
The shell is inequivalve, thick, gaping
posteriorly, and not nacreous internally.

Fig. 625.—Mactra podolica. Mi- [he internal ligament is supported upon

Sa ane, Austria. (After_ 4 spoon-shaped process developed from

the hinge-plate of the left valve. The

members of this family are marine or estuarine in habit, and the
principal genera are MZya, Corbu/a, and /Veera.

In the genus JZya the shell is pleas inequivalve, and gaping at
both ends. The left valve is the smallest, and it carries an internal
ligament supported upon a prominent cartilage-process (figs. 626,

Fig. 627.—Portion of the hinge
Fig. 626.—Mya truncata. FPost-Pliocene of Mya arenaria, showing the car-
and Recent. tilage-process.

627). The Myas live buried vertically in sand or mud. They are
not known to have existed before the period of the Middle Tertiary
(Miocene), and almost all the fossil species are in existence at the
present day.

In Corbula (fig. 628) the shell is inequivalve, the left valve the
smallest, and with a prominent cartilage-process ; but the shell is

MYACEA. 743

gibbous, and does not gape at its ends, whilst the pallial sinus is
small. The recent species of Cordula live partly in the sea, and
partly in estuaries or at the mouths of rivers. ‘There are numer-
ous fossil forms of the genus, espe-
cially in the Cretaceous and Ter-
tiary rocks; but the oldest forms
appear in the Trias.

The genus JVeera is allied to Cor-
bula, but the shell is nearly equi-
valve, the right valve being slightly Fig. 628.—Corbula pisum, viewed from
the smallest, and the shell is pro- the left and right sides. Eocene.
duced and open posteriorly. The
earliest types of /Veera appear in the Upper Jurassic rocks, and
the genus still survives.

FAMILY 3. GLYCIMERID#&.—In this family the mantle-lobes are
united, and there are long siphons, which are united wholly or in
great part. The shell is equivalve or nearly so, gaping at both ends,
and covered with a thick epidermis, which is prolonged over the
siphons. The hinge has one or two weak cardinal teeth, or is tooth-
less. The ligament is external, and the pallial sinus varies in depth.
The Bivalves included in this family are all marine, and are either
free or burrow in mud.

In Glycimerts (= Panopea) the shell (fig. 629, A) is thick, oblong,
inequilateral, and gaping at both ends. A single cardinal tooth is

Fig. 629.—A, Interior of the right valve of Glycimeris (Panopea) Americana, from the
Miocene rocks of North America, one-third of the natural size; B, Interior of the left valve of
Cyrtodaria (Glycimeris) siligua, Arctic seas, two-thirds of the natural size. (After Woodward.)

present in each valve ; the pallial line is continuous, and the pallial
sinus is very deep. Several Recent species of Glyczmeris are known,
and there are also various Tertiary forms, the earliest types of the
genus seeming to occur in the Cretaceous rocks. Allied to the pre-
ceding is the genus Cyrtodaria (= the Glycimeris of many authors).
in which the shell agrees generally with that of Glycimeris, but the
pallial line is interrupted, and the pallial sinus is very slight (fig.
629, B).

In the genus Saxzcava (fig. 630) the animal burrows in rocks, or
fixes itself in crevices by means of a byssus. The adult shell is

744 LAMELLIBRANCHIATA.

thick and oblong, more or less inequivalve, irregular, and often
gaping. ‘The hinge is generally edentulous, and the pallial line is
interrupted. “The genus” seems @ to
commence in the Eocene Tertiary,
and has continued to the present day.

FAMILY 4. GASTROCHANIDA.—In
this family the mantle-lobes are
united; there are long _ siphons,
joined together; and the foot is of
small size, finger-shaped, and not
byssiferous. The shell is equivalve, inequilateral, thin, wedge-
shaped, and gaping in front. The beaks are placed anteriorly,
and the anterior side of the shell is short. ‘The hinge is toothless ;
the ligament is external ; and the pallial sinus is deep. The mem-
bers of this family burrow in rocks, corals, &c., or bury themselves
in mud; and a longer or shorter shelly tube, to which the shell
itself is commonly cemented, is often developed. The tubes and
shells of Gastrochena are not very rarely found in the fossil state
in rocks of Secondary and Tertiary age, and a number of living
species are known. ‘The allied genus /istudaria ranges from the
Cretaceous rocks to the present day.

Fig. 630.—Saxicava rugosa, left valve.
Post-Pliocene and Recent.

ORDER XI. ADESMACEA.,

In this order the mantle-lobes are united, and there are long
siphons joined along almost their entire length. ‘The foot is gener-
ally well developed, and there are two adductor muscles. ‘The shell
consists essentially of two valves, but accessory plates or an adven-
titious calcareous tube may be developed in addition. A portion
of the cardinal margin is reflected above the beaks, and the um-
bonal cavity is divided internally by a prominent process. The
hinge and ligament are not developed. ‘The members of this order
are inhabitants of the sea or of brackish waters, and they all form
perforations in stone or wood. ‘The order is divided by Fischer
into the two closely related families of the Pholadide and Teredinide.

FAMILY 1. PHOoLADID#.—In this family the animal is club-shaped
or worm-like, with a short truncated foot, and long siphons united
to near their extremities. The shell is gaping at both ends, with a
portion of the cardinal margin reflected over the beaks, and usually
having the dorsal region protected by one or more accessory plates.
The members of this family are almost exclusively marine, and form
burrows in stone or wood. In some cases (as in Pholas itself) the
young are similar to the adult ; whereas in other cases (Pholadidea,
Teredina, &c.) a marked metamorphosis takes place in development.
This metamorphosis consists essentially in the formation of a cal-

ADESMACEA. 745

careous plate which fills up the anterior vacuity in the valves, and
in the production from the hinder end of the shell of cup-shaped
appendices which may coalesce to form a longer or shorter tube.

In the genus /o/as, the shell is cylindrical or oval, and the front
portion of the valves is marked with conspicuous radiating ridges
or rows of spines. ‘The valves are edentulous ; and there is no liga-
ment, or a rudimentary one. The pallial sinus is very deep, and the
dorsal margin of the shell is protected by accessory valves. The
Pholades inhabit burrows which they form for themselves in clay,
peat, or rock, and they are known in the fossil condition not only
by their shells but also by their burrows, the latter affording useful
indications of the existence of old shore-lines. Various extinct
forms are known from the Tertiary rocks, and the genus appears to
be represented in the Cretaceous and Jurassic deposits.

In the recent genus Pholadidea the shell has a transverse furrow, and
the anterior vacuity of the valves becomes filled up with a callous plate.
In the genus, or sub-genus, Parapholas, again, the anterior aperture be-
comes similarly closed by a callous plate, but the valves show two ob-
lique furrows running from the beaks to the ventral margin (fig. 631).

Fig. 631.—Parapholas mersa, viewed from one side and above. Cretaceous.
(After Stoliczka.)

The species of Parapholas range from the Cretaceous rocks to the pres-
ent day. In the allied 1/aréesca the anterior vacuity is also closed by a
callous plate, and the beaks are covered by a simple shield-like lamina.
The living species of JZartes¢a burrow in wood, and the earliest fossil
forms have been detected in the Carboniferous rocks. The recent genus
Aylophaga also comprises wood-boring forms, and is represented in rocks
as ancient as the Jurassic and Cretaceous by allied types (Xylophagel/a).
Lastly, Fischer places in this family the Eocene genus 7eredina, in which
there is a globular shell, the anterior vacuity of which is closed by a cal-
lous plate, while the beaks are covered by a dorsal plate, and the valves
are fused with a long calcareous tube, developed posteriorly.

FAMILY 2. TEREDINIDA.—This family includes only the single
genus Zevedo, the characters of which are, therefore, those of the
family. In Zevedo, the shell is ‘globular, open in front and behind,
lodged at the inner extremity of a burrow partly or entirely lined by
shell ; valves three-lobed, concentrically striated, and with one trans-
verse furrow ; hinge-margins reflected in front, marked by the anterior
muscular impressions ; umbonal cavity with a long curved muscular

746 LAMELLIBRANCHIATA.

process” (Woodward). Species of Zevedo occasionally reach a very
large size, and they are known in the fossil state both by their shells
and by their burrows in wood. The genus seems to have com-
menced in the Lias, and is well represented at the present day.
Numerous Tertiary species are known, but the recognition of the
existence of the “ Ship-worms” in past time very generally depends
simply upon the presence of their filled-up burrows in fossil wood.

ORDER XII. LUCINACEA.

This order includes marine Lamellibranchs, with typically but a
single branchia on each side and with two adductor muscles, the
mantle-lobes being more or less free, and the foot usually vermiform.
The shell is free, non-nacreous, the hinge with cardinal and lateral
teeth, and the pallial line entire. The only family included in this
order is that of the Zucinide, the precise limits of which, as regards
fossil forms more particularly, are still uncertain.

Famity 1. Lucinip#.—The mantle-lobes in this family are open
below, with one or two siphonal apertures behind, and the foot is
elongated, cylindrical, or strap-shaped. The shell is orbicular and
free, with one or two cardinal teeth, and generally a single lateral
tooth on each side. The ligament is partially or wholly internal, or

«

a
A Vall

Fig. 632.—a, Interior of the right valve of Cordis pectunculus—Eocene } B, Interior of the
right valve of Diplodonta Jupinus—Miocene; C, Interior of the left valve of Lucina striatula—
Jurassic.

in some cases (Diplodonta) external. The anterior adductor impres-
sion is usually elongated. Taken as a whole, the family is principally
Secondary, Tertiary, and Recent, its Palaeozoic representatives being
mostly imperfectly understood, and referred here with doubt. In
Lucina itself, the type of the family (fig. 632, c), the shell is
rounded, with a lunule beneath the beak ; the ligament is in a deep
groove, sometimes nearly or quite internal; and the teeth have the
typical arrangement of the entire group, though some are occasion-

TELLINACEA. 747

ally obsolete. Little can be said with certainty as to the Palzeozoic
shells usually referred to Zucina, but the genus is abundantly repre-
sented in Secondary and Tertiary deposits ; and ancient representa-
tives of the genus have been described from the Silurian and De-
vonian rocks. Cordis (fig. 632, A), with many species from the
Trias onwards, is very like Zucina, but has the surface concentri-
cally furrowed, with denticulate edges. Dzflodonta (Cretaceous to
Recent) has two cardinal teeth in each valve, the anterior in the
right and the posterior in the left being bifid (fig. 632, B). Lastly,
the genus Axzzus of Sowerby may perhaps be referred here, though
the hinge is toothless or has only a feeble tooth in the right valve.
The range of this genus is from the Eocene to the present day.

OrvDER XIII. TELLINACEA.

In this order the foot is very large; there are two adductor
muscles ; there is only a single gill on each side; and the siphons
are long and completely separate. The shell is free, non-nacreous,
the hinge with cardinal and lateral teeth, and the pallial line deeply
sinuated. This order includes the two families of the Ze//inzde and
Scrobiculariide, all the members of which are marine in habit.

FAMILY 1. TELLINID#.—In this family the shell is free, usually
equivalve and closed, with smooth margins. ‘The hinge has at most
two cardinal teeth in each valve, with a lateral tooth on each side,
- or without lateral teeth. The ligament is external, and the pallial
sinus is very deep.

The principal genus in this family is Ze//ma itself, which includes
about three hundred living species and a considerable number of
fossil forms, mostly from the
Tertiary rocks. In this genus
the shell is oval or transversely
elongated, very slightly inequi-
valve, the anterior side being
rounded, and the posterior side
often angulated. The beaks are Fig. 633.—Tellina proxima, right valve.
often placed nearly in the mid- Post-Pliocene.
dle of the shell; the ligament is
prominent and external; and the pallial sinus is very broad and
deep. The oldest undoubted forms of Ze/na appear in the Lower
Cretaceous rocks. .

FAMILY 2. SCROBICULARIID#.—In this family the animal agrees
with that of Ze//ima in general structure, and the characters of the
shell are in most respects the same; but the ligament is internal,
and is lodged in a pit below the beaks, an external ligament being
sometimes imperfectly developed as well. ‘The two principal genera

b

748 LAMELLIBRANCHIATA.

are Scrobicudaria and Semele, both of which are represented by Ter-
tiary and Recent species.

ORDER XIV. ANATINACEA.

This order includes marine Bivalves with a moderate - sized,
grooved, or byssiferous foot, distinct siphonal orifices, a single
branchia on each side, and two adductor muscles. The shell is
thin, usually with a pearly internal layer and a finely granulated
external layer. The hinge may or may not carry teeth, and the
pallial line is mostly sinuated, but may be entire. The principal
families included in this order are the Solemytde, Arcomyide, Anat-
inde, Grammyside, Precardiide, Pholadomyide, and Clavagellide.

FAMILY I. SOLEMYIDA.—This family includes the single genus
Solemya, which ranges from the Devonian to the present day. In
this genus the shell is equivalve, inequilateral, transversely elongated,
obtuse and gaping at both ends, with the epidermis prolonged
beyond the ventral margin. ‘The beaks are inconspicuous; the
ligament is partly internal and partly external; the hinge is tooth-
less, or has a single cardinal tooth in each valve; and the pallial
line is obscure. The Devonian and Carboniferous genus CZn0-
pistha appears to be related to Solemya.

FAMILY 2. ARCOMYID#&.—The forms included in this family are
all extinct, and have usually been included in the Pholadomyide,
from which they are distinguished by the finely granulated character
of the exterior of the shell. The shell is equivalve, inequilateral,

Fig. 634.—A rcomya (Homontya) calceifornis, viewed from the dorsal side, two-thirds of the
natural size. Lower Jurassic rocks. (After Zittel.)

very thin, with an edentulous hinge, but with a thickened cardinal
margin. ‘The ligament is external and prominent, and the pallial
line is sinuated.. The principal genera included in this family are
Arcomya (fig. 634), Gontomya, and Pleuromya, all of which are con-
fined to the Secondary rocks, the first and last ranging from the
Trias to the Chalk, while Gonzomya is Jurassic and Cretaceous.
FaMILy 3. ANATINID#.—In this family the mantle-lobes are more

ANATINACEA. 749

or less united ; there are long siphons, more or less extensively con-
joined, and the foot is of small size. The shell is thin, usually
nacreous internally, and commonly granulated externally, and as a
rule somewhat inequivalve. The ligament is wholly or partially in-
ternal, usually in a spoon-shaped cartilage-pit, flanked by one or two
cardinal teeth, and often containing a detached ossicle. ‘The pallial
line is usually sinuated. All the members of this family are inhabi-
tants of the sea.

In Anaztina itself (fig. 635) the shell is oblong, very thin, gaping
behind, and having the beaks turned towards the posterior side of
the shell, which is more or less attenuated.
The hinge of each valve carries a spoon-
shaped cartilage-process, and the beak is
usually supported by an oblique, back-
wardly directed internal ridge. The pal-
lial line is deeply sinuated. The earliest
undoubted forms of Azatina are found
in the Lower Cretaceous rocks, and the
genus survives at the present day. ‘The
genus Zhracia, ranging from the Trias to
the present day, is in most respects very
similar to Azatina, but the shell is inequi-
valve (the right valve being larger than
the left), and there is a short external Orr
“ : ons : Fig. 635.—Anatina sfatulata.
ligament, in addition to the internal car- _ Kimeridge Clay (Upper Oolites.)
tilage. In Pandora the shell is also thin
and inequivalve, but it does not gape behind. ‘The species of this
genus range from the Eocene to the present day; and the species
of the allied genus Zyonsta have a similar range in time. Lastly,
the Cretaceous genus Lzop~istha appears to belong here, though the
pallial line is apparently not sinuated. Numerous Palzozoic Bivalves
have been referred to the Avatnide, but most of these are character-
ised by an entire pallial line and an external ligament, and may be pro-
visionally placed in the family of the Grammyside. It is possible,
however, that the genus Al/orisma (fig. 636, C) should find a place
in the Anatinide, with which it agrees in the possession of a sinu-
ated pallial line, and in having the external surface of the valves
granulated. ‘The shell in this genus is transversely elongated, equi-
valve, with anteriorly-placed, almost terminal beaks, and a concen-
trically-striated surface. The hinge is edentulous, and an external
ligament is present. The species of AMorvisma range from the
Devonian to the Permian rocks.

FAMILY 4. GRAMMyYSIIDZ.—This family comprises a number of
Palzozoic Bivalves which differ from the typical Avatinide in hay-
ing an entire pallial line, and also in the fact that the ligament is

750 LAMELLIBRANCHIATA.

external. The shell in the forms included here is equivalve, oval
or transversely elongated, convex, and thin. The hinge is edentu-
lous, and the cardinal border is straight. Fischer regards this family
as representing in the Paleozoic deposits the Avcomyide of the
Secondary period, but the affinities of most of the genera provision-
ally associated with Grammysia must be regarded as very uncertain.

In the Silurian and Devonian genus Grammysia (fig. 636, B) the
shell is transversely elongated, equivalve, with the beaks placed very

(SS = y y }}) | ii) TY \\ \

Fig. 636.—A, Right side of Paleanatina typa, showing the superior size of the left beak—
Devonian (after Hall); 8, Grammysia cingulata—Silurian; c, Adlorisma sulcata—Carbon-
iferous (after Phillips); Dp, Leptodomus truncatus—Silurian (after M‘Coy).

far forwards and incurved, a deep “‘lunule” being present below
them. The hinge-line is straight, and the hinge is edentulous ; and
a single or double fold extends backwards from the beaks to the
middle of the ventral margin.

The following Palaeozoic genera agree with Grammysza in more or
fewer characters, and may be provisionally associated with it, though
they diverge in important respects from the above general definition of
the family Grammysitde. \n Cardiomorpha (Silurian to Carboniferous)
the shell is shaped like that of /socardza, with approximated, almost ter-
minal beaks, and a simple pallial line. The hinge is toothless, and there
is an elongated groove for the external ligament. In the genus Lepfodo-
mus, with a similar geological range to the preceding, the shell (fig. 636, D)
is thin and elongated, with tumid incurved beaks, a well-marked posterior
slope, and a deep “lunule.” The hinge is toothless, and the surface is
marked with concentric ridges which split anteriorly. The widely distrib-
uted Carboniferous genus Edmondia has “a transversely-oval, equi-
valve, edentulous shell, with an internal lamellar cartilage-support. The
dorsal margins are erect and simple, and the pallial line is entire” (R.
Etheridge, jun.) In the genus Sanguznolites, principally if not exclu-
sively Carboniferous in its range, the shell is “ transversely oblong and

ANATINACEA. 751

equivalve, but very inequilateral, possessing an external ligament, and a
strong external oblique posterior ridge, the pallial line being entire” (R.
Etheridge, jun.) The Carboniferous genus Azthracomya, in which there
is a thin concentrically-striated oblong shell, with anterior beaks and an
external ligament, may perhaps also find a place here. The Devonian
genus Palganatina (fig. 636, A) more probably belongs to the Axatnide,
since the shell is inequivalve (the left valve being larger than the right),
and there are indications of the presence of an internal ligament ; but the
form of the pallial line has not been clearly ascertained. The Devonian
genus Czmztaria also occupies an uncertain position; and there are
various other Palzeozoic types which may possibly be referable to this
family, but which cannot be discussed here.

FAMILY 5. PR®CARDIIDZ.—This family has been constituted by
Hoernes for the reception of a number of Silurian Bivalves, of which
the genus /recardium is the type. The forms here in question
have thin equivalve or inequivalve shells, which have a marked
general resemblance to the Cockles, but which are without the
characteristic teeth of the Cardizde—the hinge being, in fact,
edentulous, or furnished with transverse folds. The adductor
impressions and pallial line in Precardium and its allies are un-
known ; but Fischer suggests that the genus Cardiola may possibly
be found to belong to this singular group.

FaMILy 6. PHOLADOMYID&.—lIn this family the mantle-lobes are
united ; and there are very long siphons, conjoined along their
entire length. ‘The foot is small, and a single gill is present on
each side. The shell is equivalve, inequilateral, thin, convex,
adorned with radiating ribs, pearly internally, but not granulated
externally. The hinge is toothless; the ligament is external; and
the pallial line is sinuated. This family has close relationships
with the Azcomyide and also with the Avzatinide, and the only
genus included in it by Fischer is Pholadomya itself, which is
extremely abundant in the Jurassic, Cretaceous, and Tertiary rocks,
but is only known at the present day to be represented by two or
three species, all of which inhabit great depths in the sea.

In Pholadomya (fig. 637) the shell is equivalve, oblong, and
gaping posteriorly, thin, ven-
tricose, and adorned with
radiating ribs on the sides.
The anterior side of the shell
is short and rounded, and the
beaks are prominent. The hinge
is toothless, and the cardinal Fig. 637.—Pholadomya equivalvis. Chalk.
margin behind the beaks is
often folded in so as to give rise to an elongated false area or
escutcheon.

FAMILY 7. CLAVAGELLIDZ.—In this family the mantle-lobes are

752 LAMELLIBRANCHIATA.

united, and there are long conjoined siphons, with a single branchia
on each side. The shell is in the young state similar to that of
Thracia, but one or both of the valves ultimately become fused
with a secondarily-produced adventitious calcareous tube, of con-

siderable size (fig. 638).

The genus C/avagel/a itself comprises forms which burrow in

Fig. 638.—Clavagella cretacea. Chalk.

rocks, corals, &c., and in which
the shell is inequivalve, the left
valve being fused with a long cal-
careous tube (fig. 638), while the
right valve lies freely in the in-
terior of the tube, the latter being
often divided by a_ longitudinal
partition. This singular genus is
known to have existed in rocks as
old as the Cretaceous, and still
survives. In the nearly allied
genus Aspergillum (Pliocene and
Recent), both the valves of the
shell are fused with the calcareous

tube, which is closed below by a perforated disc with a minute

central fissure.

753

Cina ek XOXO IT.

Crass II. Gastropopa (or GASTEROPODA).

THE members of this class are Alol/usca with a more or less distinct
head, and a generally unsymmetrical body. The mantle is never
divided into two lobes, and the shell, when present, ts untvalve. The
“* foot” is well developed, and usually has the form of a broad hort-
sontallyjiattened ventral disc, upon which the animal creeps.

The body in the Gastropods is composed of three principal por-
tions—a head, foot, and visceral sac—the last of these being more
or less completely protected by a fold of the dorsal integument, con-
stituting the “mantle.” The body is distinctly unsymmetrical, and
the mantle is never divided into a right and left lobe, while the vis-
ceral sac is often coiled up spirally. The foot is typically in the
form of a broad flattened muscular disc, developed upon the ventral
surface of the body, and not exhibiting any distinct division into
parts. In the Hezeropoda, however, and in the Wing-shells (S¢vom-
bide), the foot exhibits a division into three portions: an anterior,
the “propodium ”; a middle, the ‘‘mesopodium ” ; and a posterior
lobe, or ‘‘metapodium.” In the Aezeropoda, the foot is flattened,
and forms a ventral fin, by means of which the animal swims, back-
downwards.

In some, again, the upper and lateral surfaces of the foot are
expanded into muscular side-lobes, which are called ‘ epipodia.”
In the Pteropodous division of the Gastropods the epipodia are the
only portions of the foot which are developed, and they constitute a
pair of fins attached to the sides of the head. In many cases the
metapodium, or posterior portion of the foot, secretes a calcareous,
horny, or fibrous plate, which is called the ‘‘ operculum” (fig. 639,
9), and which serves to close the orifice of the shell when the animal
is retracted within it.

The sell of the Gastropods is a secretion from the mantle, and
is always present in the embryo. It is, however, wanting in the
adults of the Nudibranchs and in some other forms, and it is in other

MOU. 1. 2.3

754 GASTROPODA.

cases very minute, and hidden in the mantle (as, for example, in the
Slugs). From the very general occurrence of a shell which is “ uni-
valve,” or composed of a single piece, the Gastropods are commonly
spoken of as the ‘‘ Univalve Molluscs.” In its chemical composi-
tion the shell is composed of carbonate of lime (sometimes in the
condition of calcite, sometimes in that of aragonite). Its inner
layer is often nacreous, and it grows by additions made to its free
margin by the muscular edge (“collar”) of the mantle, in which

Fig. 639.—Ampullaria canaliculata. o, Operculum; s, Respiratory siphon.

numerous pigment-glands are contained. Primitively the shell is
covered witha horny cuticular layer (‘‘ epidermis ”), but this often
disappears with age. In many cases, the mantle becomes reflected
over the shell, the outer surface of which may thus become covered
with a layer of enamel (as in the Cowries).

The shell of the Gastropods is to be regarded as essentially a
cone, the apex of which is more or less oblique. In the simplest
form of the shell, the conical shape is retained without any altera-
tion, as is seen in the common Limpet (/a¢ed/a). In the great
majority of cases, however, the cone is considerably elongated, so
as to form a tube, which is usually coiled up into a spiral. The
‘spiral univalve” (fig. 640) may, in fact, be looked upon as the
typical form of the shell in the Gastropoda. In some cases the
coils of the shell—termed technically the ‘‘ whorls ”—are hardly in
contact with one another (as in Vermetus). More commonly the
whorls are in contact, and are so amalgamated that the inner side
of each convolution is formed by the pre-existing whorl. In some
cases the whorls of the shell are coiled round a central axis 27 the
same plane, when the shell is said to be ‘ discoidal” (as in the com-
mon fresh-water shell lanorbis). In most cases, however, the
whorls are wound round an axis in an oblique manner, a true
spiral being formed, and the shell becoming “turreted,” “ tro-

GASTROPODA. 755

choid,” “‘turbinated,” &c. This last form is the one which may
be looked upon as most characteristic of the Gastropods, the shell
being composed of a number of whorls (fig. 640, zw) passing
obliquely round a central axis or
“columella” (co), having the em-
bryonic shell or ‘‘nucleus” at its
apex (a), and having the mouth
or “‘ aperture” of the shell placed
at the extremity of the last and
largest of the whorls, termed the
“body-whorl” (zh'). The lines
or grooves formed by the junc-
tion of the whorls are termed the
“sutures ” (sw), and the whorls
above the body-whorl constitute
fe’ spire ’(S) of the’shell. The
axis of the shell (columella), round
which the whorls are coiled, is
usually solid, when the shell is
said to be “imperforate”; but
it is sometimes hollow, when the
shell is said to be ‘‘ perforated,”
and the aperture of the axis near
the mouth of the shell is called
the “‘ umbilicus.” ~The margin of Fig. 640.—Longitudinal section of 77ztox
the “aperture” of the shell is soc rere oe pa Ne The
termed the “peristome,” or “peri- last yhorl ofthe spire; zw, The Body wher
treme,” and is composed of an "or canal.

outer and inner lip, of which the

former (fig. 640, L) is often expanded or fringed with spines. When
these expansions or fringes are periodically formed, the place of the
mouth of the shell at different stages of its growth is marked by
ridges or rows of spines, which cross the whorls, and are called
“varices.” In certain groups of the Gastropods (olostomata) the
aperture of the shell is unbrokenly round or “ entire,” but in other
groups (Szphonostomata) it is notched, or produced into a canal.
Often there are two of these canals, an anterior and a posterior, and
the function of these is to protect the respiratory siphons. The
animal withdraws into its shell by a retractor muscle, which passes
into the foot, or is attached to the operculum; its scar or impression
being placed, in the spiral Univalves, upon the columella. In the
great majority of the Univalves the shell is coiled to the left, the
“mouth” of the shell being thus on the right-hand side (fig. 640).
In such cases the shell is said to be right-handed or “ dextral.” In
other cases, however, the shell is coiled to the right, and the mouth

eel

756 GASTROPODA.

is on the left, when the shell becomes ‘‘reversed” or ‘ sinistral.”
The left-handed spiral may be the normal condition of the shell, or
it may be only a variety of a normally dextral form.

As regards their internal anatomy, the head of the Gastropods is
usually very distinctly marked out, and is generally provided with ten-
tacles and eyes. Within the pharynx is found the singular dental appar-
atus which is known as the “‘odontophore.” The essential portion
of this is a chitinous band, which is beset with minute transversely-
arranged teeth, and is known as the “radula” or “lingual ribbon.”
The radula is supported upon a cartilaginous cushion, which can be
made to rotate by special muscles, the ribbon thus coming to act as
a file, rasp, or chain-saw. The arrangement of the teeth in the
radula varies much in different cases, but they are usually disposed
in a median series, flanked by two or more lateral rows; and their
form and disposition are so constant as to afford one of the most
valuable aids to the classification of the recent Gastropoda. As,
however, the characters of the radula cannot be determined in the
case of fossil Gastropods, a classification based upon the structure
of this organ is necessarily defective from a paleontological point
of view.

Respiration in the Gastropods is variously effected ; the members
of one great section (Lranchiogastropoda) being, with few excep-
tions, constructed to breathe air dissolved in water, while in
another division (Puldmogastropoda) the respiration is aerial. In
the former division, respiration may be effected in several ways.
Firstly, there may be no specialised respiratory organ, the blood
being simply exposed to the water in the thin walls of the mantle-
cavity (as in some of the Heteropoda). Secondly, the respiratory
organs may be in the form of outward processes of the integument,
exposed in tufts on the back and sides of the animal (as in the
Nudibranchiata), ‘Thirdly, the respiratory organs are in the form
of pectinated or plume-like branchiz, contained in a more or less
complete branchial chamber formed by an inflection of the mantle.
In many members of this last section the water obtains access to
the gills by means of a tubular prolongation or folding of the
mantle, forming a “siphon” (fig. 639, s), the effete water being
expelled by another posterior siphon similarly constructed. The
number of gill-plumes differs in different groups. In most cases
there is only a single branchial plume, placed on the right side of
the neck; in other cases an additional gill is present on the left
side ; and in other forms, again (e.g., Pazel/a), the gills are multiple
and are arranged in a circle. Lastly, in the Pulmonate Gastropods
the breathing-organ is a pulmonary chamber, formed by an inflec-
tion of the mantle, the walls of which are richly supplied with blood,
while air is admitted to its interior by a distinct aperture. A tran-

GASTROPODA. Te

sition between the Branchiate and Pulmonate groups is effected by
forms like Ampullaria, in which gills are present, but the walls of
the mantle-cavity are in parts highly vascular, and are thus adapted
for aerial respiration. Another link between these two groups is
afforded by forms like the Cyclostomide and the Helicinide, in
which the general organisation of the animal is that of the Proso-
branchiate Gastropods, but the breathing-organ is a pulmonary
chamber.

A few Gastropods retain the eggs within the uterus until they are
hatched ; but the majority are oviparous. The eggs are often laid
in the form of a string or band (“nidamental ribbon”) ; or they may
be enclosed in horny capsules (as, for example,.in the common
Whelk). The young, when first hatched, are provided with an
embryonic shell, which in the adult may become concealed in a
fold in the mantle, or may be entirely lost. In the common spiral
Univalves the embryonic shell remains at the summit of the spire,
as the ‘‘ nucleus” of the adult shell. In the branchiate Gastropods
the embryo is protected by a small nautiloid shell, and passes
through a “‘veliger” stage, swimming freely by means of a ciliated,
often lobed ‘‘velum.” Among the Pulmonate Gastropods, those
which are strictly terrestrial pass through no metamorphosis, the
“velum” being absent in the embryo.

As regards their classification, the Gastropods may be divided
into the two primary groups, or sub-classes, of the Branchiogastropoda
and the Pulmogastropoda, the general distinction between the two
divisions being that the animal in the former is adapted for an
aquatic mode of respiration, while in the latter the breathing-organ
is a pulmonary sac. The division of the Branchiate Gastropods
may, again, be divided into the four orders of the Prosobranchiata
(the ordinary Univalves), the Opisthobranchiata (the Sea-slugs), the
Pteropoda (the Winged Snails), and the Heteropoda ; while the Pul-
monate Gastropods may be divided into the two orders of the
Stylommatophora and Basommatophora, in accordance with the
position of the eyes. The Chitons (/olyplacophora) and the
Dentalide (Scaphopoda), often included among the Gastropoda,
will be here regarded as constituting two separate classes of
Mollusca.

As regards their distribution in space, the Heteropods, the Ptero-
pods, the Opisthobranchiates, and the great majority of the Proso-
branchiates are inhabitants of the sea. Certain groups of the Proso-
branchiates, however, are found either in brackish or in fresh waters ;
while the terrestrial groups of the Cyclostomide, Actculide, and Helt-
cinide, often placed among the Pulmonate Gastropods, are now
usually regarded as being essentially Prosobranchiates modified for
an aerial mode of respiration. The Pteropods and the Heteropods

.
)

758 GASTROPODA.

are oceanic in habit, and are found swimming in the open sea, near
the surface, far from land; but the majority of the marine Proso-
branchs and the Opisthobranchs are inhabitants of shallow seas, or
live between tide-marks. In depths beyond five hundred fathoms
the number of Gastropods is greatly reduced ; but a few forms are
found to inhabit depths of between two and three thousand fathoms,
or even more. The Pulmonate Molluscs, lastly, are exclusively ter-
restrial in habit, or live in fresh waters. In the latter case, the
animal either comes to the surface from time to time, for the pur-
pose of obtaining air, or, if the water be too deep to allow of this,
its pulmonary chamber is so far modified that it is enabled to
breathe the oxygen dissolved in the surrounding water.

As regards their distribution in time, the Branchiate Gastropods
are necessarily more largely represented as fossils than the Pul-
monate forms. The record of the Prosobranchiates, owing to their
possession of a calcareous shell and their aquatic habits, is a very
full one. On the other hand, the Opisthobranchiates are but
imperfectly represented in past time, the entire group of the Nudi-
branchs being unprovided with a shell, and being therefore unknown
in the fossil condition. The oceanic group of the Heteropods (if
the Bellerophontide be placed elsewhere) is only represented in the
latest Tertiary deposits ; while the Pteropods, also pelagic in habit,
occur as fossils in the older Palzeozoic rocks, but are singularly
absent from the greater part of the Mesozoic and Kainozoic for-
mations. Of .the Pulmonate Gastropods, those forms which live
habitually in fresh water (e.g., the Zizmneide) are naturally more
largely represented in the fossil condition than the purely terrestrial
forms (¢.g., the elcid); but the remains of the latter are not un-
common in deposits which have been formed under suitable
conditions.

The Gastropods appear for the first time in the Upper Cambrian
deposits, from which a number of forms have been obtained, all
belonging to the holostomatous division of the Prosobranchiates,
the two principal genera being MWurchtsonia and Pleurotomaria.
The Upper Cambrian rocks have also yielded the oldest examples
of Ayolithes and its allies, which are usually regarded as belonging
to the Prerofoda. In the Ordovician and Silurian rocks are found
very numerous types of the Prosobranchiate Gastropods, all of
which—with the apparent exception of such forms as Swdbudites
and uchrysalis—are holostomatous. ‘The predominant groups
in these ancient deposits are the Auomphalide, Pleurotomarude,
and Lellerophontide. The Pteropods are represented by the
aberrant types Conularia, Hyolithes, and Tentaculites. In the De-
vonian, Carboniferous, and Permian formations the general character
of the Gastropodous fauna undergoes little change, the predominating

GASTROPODA. 759

forms still belonging to the holostomatous Prosobranchiates and the
Pteropods. ‘The latter, however, are now in part represented by
such normal forms as S¢y/o/a. In the Carboniferous rocks, further,
appear the first representatives of the Pulmonate Gastropods (Zon-
ates, Physa, &c.)

In the Trias the Gastropodous fauna has, in the main, a Palzeo-
zoic facies, but unquestionable siphonostomatous Prosobranchiates
appear here (Cerithium, Purpurina, &c.) The peculiar Paleozoic
Pteropods (with the exception of Conu/aria) have now disappeared.
In the Jurassic rocks a further change occurs, and a marked develop-
ment of the siphonostomatous Prosobranchiates now takes place.
The first Opisthobranchs appear at this stage, and we meet here
with a number of existing genera of fresh-water Gastropods (P/an-
orbis, Paludina, Melanta, &c.) In the Cretaceous rocks the siphon-
ostomatous Prosobranchiates continue to increase in number, and
in the Tertiary period they become the predominant group, the
Gastropods as a whole becoming at the same time the predominant
group of the JZo//usca, a condition of things which still subsists at
the present day.

760

CHA PCE Re Soo
DIVISIONS. OF. LHE ~GASTROPOLE
Susp-CLass I. BRANCHIOGASTROPODA.

THIS primary division of the Gastropods is distinguished, speaking
generally, by the fact that the animals included in it are water-
breathers, respiration being effected by the thin walls of the mantle-
cavity, by external branchial tufts, or by pectinated or plume-like
gills contained in a more or less complete branchial chamber. The
groups of the Cyclostomide, Aciculide, and Helicinide, from the
general characters of their organisation, must, however, be placed in
this division ; although the animal in these is terrestrial, and is fur-
nished with a pulmonary chamber adapted for breathing air directly.

This sub-class comprises the four orders of the Prosobranchiata,
Opisthobranchiata, Pteropoda, and Fleteropoda.

ORDER I. PROSOBRANCHIATA.

The great majority of the members of this order are aquatic in
habit, and possess gills situated in front of the heart, the auricle of the
heart being thus placed in front of the ventricle. The Cyclostomide,
Aciculide, and Helicinide alone possess a pulmonary chamber. The
gills are, typically, plume-like, and are lodged in a branchial chamber
formed by a fold of the mantle, which may or may not be so dis-
posed as to form an anterior and posterior tube or “siphon,” for
the entrance and escape of water from the branchial chamber. The
foot in the Prosobranchiates is large and adapted for creeping, and
the sexes are distinct. ‘Those members of the order which possess
an anterior siphon for the admission of water to the branchial cavity,
have the mouth of the shell notched in front, or produced into a
canal in which the siphon is lodged (fig. 642); while a similar notch
or canal may exist at the posterior end of the shell-aperture (fig.
643). The shell in these forms is said to be “siphonostomatous.”

PROSOBRANCHIATA. 761

In a great many forms, on the other hand, siphons are not devel-
oped, and the mouth of the shell is simply rounded or “entire”
(fig. 641), when the shell is said to be “ holostomatous.”

The great majority of the Prosobranchiata are inhabitants of the sea,
but certain groups are restricted to fresh or brackish waters ; while
the Cyclostomide, Aciculide, and Helicintde are terrestrial in habit. As
regards their distribution in time, the paleontological record is fuller
in the case of the Prosobranchiates than it is in the case of any
other division of the Gastropods. The Paleozoic types of the
Prosobranchiates belong almost exclusively to forms in which the
shell is “ holostomatous.” On the other hand, forms with the
“siphonostomatous ” type of shell-mouth do not make an undoubted

Fig. 641.—Scalaria Gren- Fig. 642.—Oliva por- Fig. 643.—Cerithiune
landica, a holostomatous phyria, a_ siphonosto- aluco, showing an an-
Univalve. matous Univalve. terior and _ posterior

notch for the siphons.

appearance till the Trias is reached, and they become the predomi-
nant group of Prosobranchiates in the Tertiary rocks, which position
they still hold.

The possession of a ‘‘holostomatous” or ‘‘siphonostomatous ”
shell has been employed as the basis for a separation of the Proso-
branchiata into two primary sections—viz., the “olostomata and
Siphonostomata—but these names, though convenient as general
terms, do not indicate natural divisions. In the more modern and
more scientific classification now generally in use among Malacolo-
gists the characters of the “radula” or lingual ribbon are those
mainly relied upon as distinguishing the primary groups of Proso-
branchiates. The form of the “radula” is, however, necessarily
unknown in the case of fossil forms, and it is therefore only by
means of analogies—which may or may not be trustworthy—that
the extinct groups of Prosobranchiates can be ranged in a series

762 DIVISIONS OF THE-GASTROPODA:

the groups of which are based upon the structure of this organ.
All that will be attempted here, therefore, is to give a brief outline
of the characters and geological range of the principal families of
Prosobranchiates, without regard to the arrangement of these in
larger groups. In this outline the ‘‘holostomatous” families, as
the most ancient and the least highly organised, naturally take
precedence of the forms with a ‘“‘siphonostomatous” shell.

FAMILY 1. PATELLIDZ.—In this family the animal usually pos-
sesses a series of branchize arranged marginally in a more or less
complete cycle round the foot. ‘The shell is conical, with the apex
turned more or less clearly towards the front; and the muscular
impression is horse-shoe-shaped and open in front, continuous or
broken up into separate cavities. The genus Acmea, often regarded
as the type of a special family, differs from Pazel/a proper in the fact
that there is always a cervical branchial plume, the marginal gills
being sometimes present, sometimes absent. As these types, how-
ever, cannot be distinguished from one another by their shells alone,
this distinction is palzeontologically inapplicable.

The typical species of Pazel/a, such as the common Limpet (P.
vulgata), have usually a radially-ribbed shell, with the apex sub-
central and turned forwards. Such types are clearly recognisable
in the Cretaceous and Tertiary rocks. In /e/con, again, the shell
is radially-ribbed, and the apex is shifted far forwards. Such types
abound in the Jurassic and Cretaceous rocks, and still survive. In
Acmea, finally, the apex is usually subcentral and the surface is

generally smooth or feebly striated. This type cannot be clearly
separated from the preceding except by an examination of the
animal, but many of the fossil Limpets doubtless belong here. A
Limpet of this type has been described by Hall from the Upper
Cambrian (Potsdam Sandstone) of North America under the generic
name of Paleacmea.

Most of the Paleozoic Limpets belong to the genera 77yb/¢dium and
Metoptoma, which agree with one another in the fact that the shell (fig.
644) is in the form of an obtuse or shallow cone, with the apex placed
very far forwards, so as to be submarginal. In 7ryblédium, as shown by

PROSOBRANCHIATA. 763

Lindstrém, the muscular scar is in the form of six pairs of disconnected
impressions, arranged in an oblong circle which is open in front. The
species of this genus are principally Ordovician and Silurian. Jeéof-
zoma, as now restricted, differs from the preceding in having the anterior
side broadly truncated (fig. 645, F), and in the fact that the muscular scar
is in the form of a continuous horse-shoe. The genus appears to range
from the Ordovician to the Carboniferous, but as the interior markings
of many species are unknown, it is impossible at present to sharply
separate this type from 77yblidium.

FaMILy 2. FiIsSURELLIDZ.—In this family the animal has the
gills symmetrically disposed on the two sides of the body. The
shell is conical and limpet-shaped, with a notch in the anterior

Fig. 645.—Fissurellidz, Capulide, and Patellide. a, Fissurella labiata—Eocene; 8B, Rimula
Blainvillei— Eocene; c, Emarginula Guerangeri—Cretaceous; D, Hipponyx cornucopie—
Eocene; £, Crefidula costata—Miocene; F, Metoptoma imbricata—Carboniferous; G, Patella
costaria—Eocene.

margin, or a perforation at or near the apex, corresponding with the
anus (fig. 645, Aandc). The muscular impression is horse-shoe-
shaped and is open in front.

The genus Fissurel/a (fig. 645, A) comprises the so-called “ Key-
hole Limpets,” distinguished by having the apex of the shell perfo-
rated by a larger or smaller, generally oval aperture. Very dubious
examples of the genus have been described from the Devonian and
Carboniferous rocks, but the earliest undoubted types appear in the
Jurassic rocks, from which time the genus has continued to the
present day. In the genus Azmula (fig. 645, B), ranging from the
Lias to the present day, the perforation, instead of being at the apex
of the shell, is placed a little above the anterior margin. Lastly, in
Emarginula (fig. 645, Cc) the anterior margin is furnished with a
longitudinal notch or slit. The oldest species of this genus has

704. DIVISIONS OF THE GASTROPODA.

been found in the Carboniferous Limestone, but most of the fossil
forms are Cretaceous and Tertiary.

FaMILY 3. CAPULIDZ (= Ca/yptreide).—In this family the shell
is conical and patelliform, with a more or less spiral apex, the interior
being simple, or divided by a shelly process to which the adductor
muscle is attached. The margin of the shell-aperture is thin and
entire, often more or less modified in outline by the habit which the
animal possesses of fixing itself, with the aperture closely fitted, to
some foreign body, such as a Crinoid.

The genus Ca/yptrea, in the wide sense in which it has gener-
ally been defined, includes the so-called ‘‘ Cup-and-saucer Limpets,”
in which the interior has a half-cup-shaped process attached to the
apex of the shell, and open in front. The earliest forms of this
type appear in the Cretaceous rocks, and the genus still survives.
In the genus Crepidula (fig. 645, E) there is a shelly partition cover-
ing the posterior half of the interior of the shell. The fossil forms
of this genus date from the Cretaceous period. Azpponyx, again,
comprises thick and obliquely conical shells, with a posterior apex,
and often provided with a shelly basis marked by a distinct horse-
shoe-shaped muscular impression (fig. 645, D). The genus ranges
from the Cretaceous rocks to the present day.

By far the most important genus of this family, palzeontologically
speaking, is Capulus (Pileopsis) itself, including the so-called ‘‘ Bon-
net-limpets” of the present day. The Paleozoic shells which have
been included under the name of Platyceras (= Acroculia) appear to
be identical with Capudlus, or, at any rate, to be distinguished from
this by characters of no more
than sub-generic value. In the
genus Capulus, employing this
name in the general sense in-
dicated above, the shell is con-
ical, with a posterior sub-spiral
apex, and, generally, a _horse-
shoe-shaped muscular impres-
sion. The aperture is greatly
enlarged, and its margins are
essentially entire; but owing to

the fact that the shell is usually
Pigs 646.— capuelus (0 ayeaes) smiricosus. affixed for lengthened periods to

foreign bodies, the lips may be-
come more or less sinuated or undulated (figs. 646, 647). The
shells of this genus may, as a rule, be recognised by their obliquely-
spiral or straight, conical shape, their wide aperture, and the
absence of a columella. ‘They may be dextral or sinistral, and
the surface may be simply marked with concentric lines of growth,

PROSOBRANCHIATA. 765

or may be ornamented with spines. The genus is abundantly
represented in the Silurian and Devonian periods, and less abun-
dantly in the Carboniferous; while
ancient types have been described from
the Upper Cambrian and Ordovician
rocks. Many Secondary and Tertiary
species are known, and the compara-
tively few living species are widely dis-
tributed over the globe.

According to Lindstrém, the name of
Platyceras may be retained for the Silu- Se enig a nates:
rian forms of Cafzzlus, as presenting cer- 7, (Cee er een tae
tain constant differences, and, in particu- ural size. Devonian, Canada. (Or-
lar, as not having been clearly shown to _ iginal.)
possess the horse-shoe-shaped muscular
scar of the latter. The same authority unites with Platyceras the Pale-
ozoic types described under the names of Platystoma (Conrad) and Stro-
phosiylus (Hall). Orthonychia, again, includes forms with a nearly
straight shell, the spire being very small, and the terminal portion of
the shell very large.

FAMILY 4. VELUTINID&.—The principal genus in this family is
Velutina, in which the shell is thin, with a large body-whorl and
small spire, and having a large rounded aperture with an entire
margin. The genus is principally Recent and Tertiary, but a few
Secondary types have been described.

FAMILY 5. PLEUROTOMARIIDA.—lIn this family the shell is nacre-
ous, very variable in form, but usually coiled into an elevated or flat
spiral. The outer lip of the shell-aperture (fig. 648) exhibits a notch
or slit, which in course of growth becomes progressively filled up,

Fue
Se TUT iw
, Tia

ah:

Fig. 648.—Side-view of the recent Pleurotomaria Quoyana, showing the slit in the outer
lip (s); and upper view of Pleurotomaria platyspira, showing the slit-band.

thus giving rise to a revolving band upon the whorls ; or which may
become partially closed and converted into one or more perforations.
The animal is provided with a circular horny operculum.

The family Pleurotomaritde has relationships with the Halotde,
the Bellerophontide, and the Euomphatide ; and the great majority
of the genera included in it are extinct. If Scssuvella be placed

766 DIVISIONS OF THE GASTROPODA.

among the Zyochide, the only genus of the family which still sur-
vives is Pleurotomaria itself.

The genus Pleurotomaria is a “ persistent type,” the oldest forms
appearing in the Upper Cambrian, while four living species have
been detected. ‘The genus is very largely represented 1 in the Ordo-
vician, Silurian, Devonian,
and Carbouliern foeke
A very limited number of
species has been hitherto
obtained from the Permian
deposits. In the Meso-

ni zoic rocks the genus again
Fig. 649. eae Ordovician. shows 2 great develop-
ment, the Secondary forms
being commonly more or-
nate than those from older
rocks. Very few Tertiary
species are known, and the
few living species are found
in the Antilles and in the

Fig. 650. ey oe eae Ordovician. J Tene Se hacen

Pleurotomaria (figs. 649,
650) differs considerably in different types, being most generally
similar to that of Zvochus or Turbo, but being in other cases very
much flattened out and depressed. The shell consists of a few
whorls, which are generally in close contact; but the last whorl
may be disconnected from the others, or the shell may be entirely
evolute (Odontomaria). ‘The aperture of the shell is subquadrate,
and the outer lip (fig. 648) exhibits a deeper or shallower slit. As
the shell grows, this slit becomes progressively filled up, forming a
well-marked band on the whorls. By this character Pleurotomaria
may generally be distinguished readily from such shells as 7rochus
and Turbo.

Many subordinate types are included in the comprehensive genus
Pleurotomaria, in the wide sense. Thus a number of Secondary types
admit of separation from Plewrotomaria proper by their possession of a
very deep slit and a narrow band, and these may be grouped together
under the name of Lepfomaria. Inthe Carboniferous Polytremaria the
band on the whorls is partially obliterated, and is perforated by a linear
series of minute foramina. In the Jurassic Dztremaria there 1s a kidney-
shaped aperture, consisting of two foramina united by a slit, in the band
near the outer lip. Lastly, in the Devonian Odontomaria the shell is
tubular and evolute.

The Silurian genus Euomphalopterus is regarded by Lindstrae as an

extreme form of Pleurotomaria. In this type the shell is a depressed
spiral, the slit-band forming a wide alation, perforated by canals which

PROSOBRANCHIATA. 767

open into the cavity of the shell internally, and externally by minute
pores on the margin of the wing. Again, in the Triassic and Jurassic
genus 7vrochotoma (fig. 651, B) the shell is trochoid, with a concave base,
and there is a single elongated perforation in the slit-band, near the
margin of the outer lip. The ancient Ordovician types Scaltes, Rhaph-
zstoma, and Helicotoma, of which the two last are probably identical,

Fig. 651.—a, Scalites angulatus, Ordovician, North America. (After Hall.)
B, Trochotoma affinis, Jurassic.

appear to be really referable to Plewvotomaria. In Scalites (fig. 651, A)
the shell is spiral, with a flattened spire, the body-whorl ventricose, the
“suture” canaliculated, the lip truncated, and the columella imperforate
and curved. In Rkaphistoma the spire is still more depressed, the
“suture” is close, instead of being grooved, there is an umbilicus
of moderate size, and the aperture is somewhat trigonal and slightly
notched.

The genus Porcellia (fig. 652), sometimes regarded as belonging
to the Bellerophontide, seems
to be really referable to the
Pleurotomaride. In this
genus the shell is discoidal
and many-whorled, the outer
lip having a deep slit, and
the whorls having a well-
marked revolving band run-
ning along the centre of the
dorsal side. The species of
Forcellia appear to range
from the Devonian to the

: Fig. 652.—Porcellia puzo, viewed sideways (A) and
Trias. from the front (B). Carboniferous.

Lastly, the important genus
Murchisonia (fig. 653) is nearly related to Plewrotomaria, the line
of separation between the two groups being, in fact, one which can-
not be sharply defined. The shell in the typical forms of AZwurchi-
sonia is long and turreted, the number of the whorls being greater

768 DIVISIONS OF THE GASTROPODA.

than in Pleurotomaria. ‘The outer lip is deeply notched, and the
outer side of the whorls shows the characteristic slit-band of the
family. The aperture of the shell is slightly channelled in front,
and the surface is often variously sculptured and
adorned. The genus ranges from the Ordovi-
clan to the Permian rocks, and possibly is repre-
sented in the Alpine Trias.

FAMILY 6. BELLEROPHONTIDZ.—In this family
the shell (figs. 654, 655) is ‘‘ nautiloid, generally
symmetrical, spirally inrolled; the spire is con-
cealed by the succeeding whorls; the aperture is
of large size; the outer lip is arched, sharp-edged,
simple, or greatly expanded, carrying in the middle
line a sinus or notch, continued on the convex-
ity of the last whorl by a slit-band or by a series
of perforations” (Fischer). This family includes
_ the extinct genus Lellerophon and its allies, and
Se ae has been often referred to the order of the Hezer-
OFTEN Be opoda. The shell in Bellerophon is, however, of

considerable thickness, and the genus is com-
monly found associated with forms which undoubtedly inhabited
water of comparatively small depth. For these reasons, amongst
others, the Bellerophontide can hardly be associated with a purely
oceanic group such as the Heteropods. On the other hand, the
presence of a dorsal revolving band on the whorls, and of a sinus or
notch in the outer lip, brings the shell in relation with that of the

Fig. 654.—Bellerophon Argo (Billings). a, Front view; 6, Side view. Ordovician.

Pleuvotomariide ; while an affinity with the Hatotide is established
by the presence in some forms (Z7emanotus) of a row of apertures
on the dorsal keel of the shell. All the members of the Le/ero-
phontide are extinct, and if the problematical Cretaceous genus
Bellerophina be excluded, they are exclusively confined to the
Palzeozoic rocks.

In the genus Bellerophon (figs. 654, 655) the shell is symmetri-
cally convoluted, the coils of the shell lying in one plane. The

PROSOBRANCHIATA. 769

whorls are few, smooth or sculptured, and there is a dorsal band or
keel along the convex margin of the shell. The aperture is often
more or less expanded, and is in most instances emarginate or
deeply notched on the dorsal side, the columellar lip being generally
more or less callous. The genus ranges from the Upper Cambrian
to the Permian, but attains its maximum in the Carboniferous
Limestone. 4ucanza (Silurian to Carboniferous) includes forms not
generically separable from Sedlerophon, but distinguished by the
fact that all the volutions are visible and increase gradually in size

Fig. 655.—edllerophon bicarenus, from the Carboniferous rocks of Belgium. (After Zittel.)

to the expanded mouth. The genus Zvemanotus (Silurian) resembles
Bucania in the form of the shell; but the dorsal band is replaced
by a series of perforations which become successively filled up in
process of growth, and which appear to correspond with the siphonal
apertures in the shell of Aavotis. Closely allied to Zremanotus is
the Silurian and Devonian genus Sa/gingostoma, in which there is a
single elongated aperture on the dorsal margin of the body-whorl at
some distance behind the margin of the liv.

In the neighbourhood of Lelleropfhon must also be placed the
genus Cyrtolites, in which the shell is symmetrical, discoidal, or
coiled into the shape of a horn, the whorls being in
contact or more or less disconnected. The aper-
ture is rhomboidal, with a median sinus, and a
band or keel is developed on the convexity of the
last whorl, while the surface is often sculptured.
The genus ranges from the Ordovician to the
Carboniferous.

The affinities of the genus Bedlerophina, of the Gault
(Cretaceous), are quite uncertain, though it has often Bist 6r6s a2 Gyrtes
been associated with Bellerophon. The shell in this “tes ornatus. Ordo-
genus is globular, spirally inrolled, and nautiloid, but ‘*"*™
the outer lip has no sinus or notch, and the convexity
of the whorls is not furnished with a keel or band. It is not improbable
that this genus is really referable to the Heterofoda, but the structure
of the shell is at present imperfectly known.

VOL. I. BEC

770 DIVISIONS OF THE GASTROPODA.

Famity 7. HatioTip#.—In this family the shell (fig. 657) is
spiral and ear-shaped, nacreous internally, and with a large aper-
ture. The body-whorl exhibits on the left side a series of rounded
perforations, which become successively filled
up, the last few, however, remaining always
open. The last of these apertures corre-
sponds with the anus and transmits a fold
of the mantle, while the others give passage
to tentaculiform prolongations of the pallial
border. ‘This family contains only the genus
FTatotis, comprising the recent “ Ear-shells.”
The oldest example of this genus is the #7.
antigua of the Maestricht Chalk, and a few
Tertiary species are known.

FAMILY 8. Sromatup#.—In this family
the shell is spiral or ear-shaped, with a short
spire, and an expanded entire aperture. The
Seen the Pliocene interior is nacreous, and the shell is destitute

of the perforations which characterise Halio-
tis. The principal genus in this family is Stomazia, the earliest
undoubted representatives of which appear in the Jurassic rocks,
while others are Cretaceous and Tertiary, and a few forms still
survive.

FamMILy 9. EvomMPpHALIDZ.—As defined by De Koninck, the
genera comprised in this family possess a spiral shell, sometimes
elevated, sometimes discoid, the whorls being in contact or disjunct,
and a larger or smaller umbilicus being present. ‘The outer lip of the
aperture exhibits one or two (rarely three) larger or smaller sinuses,
of which the surface often shows only slight traces, except that their
existence is usually marked by keels or by imbricated lamelle of
growth. ‘The inner portion of the shell is often partitioned off by
successively produced transverse septa; and a shelly operculum is
sometimes present. Professor De Koninck includes in this family
a number of extinct, mostly Palzeozoic, genera, which are probably
in some cases referable to different groups, but which will be here
considered together, as a matter of convenience. On the other
hand, none of the genera placed here by De Koninck are admitted
into this family by Lindstrom except Huwomphalus proper, while by
this authority Zoxonema is associated with Huomphalus.

The two principal types included in the Zuomphalde, as defined
by De Koninck, are Straparollus and Euomphalis, which many
authorities have regarded as so nearly related as to have merely the
standing of sub-genera, while Lindstrom considers them as belong-
ing to entirely different families. In Straparollus (fig. 658) the
shell is thick, typically conical, with a more or less prominent spire

PROSOBRANCHIATA. S/%

and a large umbilicus, the whorls being rounded and non-angulated,
the mouth round or oval, and the surface smooth or striated. The
species of this genus range from the Silurian to the Trias. Appar-
ently related to the preceding is P/a-
tyschisma, in which the shell is thin,
obtusely conical, ventricose, umbili-
cated, and smooth, “with a shallow
sinus in the outer lip, but with no
defined band” (R. Etheridge, jun.)
The genus appears to range from the
Silurian to the Carboniferous. Fig. 658.—Straparollus Dionysii, from

The genus Euomphalus (fig. 659), the Carboniferous Limestone of Bel-
as defined by Lindstrém, comprises *"” See ee
discoidal shells, in which the whorls are contiguous or disjunct ;
the umbilicus is wide; and the outer lip of the aperture possesses
on its upper side a shallow notch or sinus, which gives rise to
a more or less elevated revolving ridge or keel in the middle or
upper part of the convexity of the whorls. The mouth of the
shell is more or less angulated,
while the apex is filled up with
a secondary deposit of shell,
and the interior is often di-
vided off by transverse shelly
partitions. The species of
Luomphalus range from the
Silurian to the Carboniferous,
one of the most familiar types :
being thie 2: pentangulatus Fig. 659.— Euomphalus pentangulatus, of the
(fig. 659) of the Carbonifer- Inka: Ghee Wee Limestone of
ous Limestone. The well-
known Silurian shells which have been described under the names
of Euomphalus discors and E. rugosus have been shown by Lind-
strom to have possessed a nacreous shell, and to be referable to the
Turbinide.

The name of Schizostoma is applied by De Koninck to forms
with a shell (fig. 660) essentially similar to that of Lwomphalus, as
above described, but having two spiral keels, one on the upper and
one on the lower aspect of the convexity of the whorls. It would
seem that Ophileta is a synonym of Schzzostoma, and in that case
forms of this type range from the Ordovician to the Carboniferous.
The forms to which the name of Leculiomphalus has been applied
(fig. 661) would appear, again, to be essentially identical with
Euomphalus, from which they differ simply in the fact that the
shell is evolute, the whorls not being in contact. Forms of this
type are known to range from the Ordovician to the Carboniferous.

# 2D |
\\ \ \

772 DIVISIONS OF THE GASTROPODA.

The name of Celocentrus (= Cirrus, De Koninck) is given by
Zittel to certain Paleeozoic types which have a general resemblance
to Luomphalus, the shell being a flat spiral, with a large umbilicus
(fig. 662). The shell differs from that of Awomphalus proper in
the fact that the mouth is round, the outer lip is not sinuated, the

i)

ab.

Fig. 660.—Schizostoma (Ophileta) bella (Billings). Different views of a nearly perfect
specimen. Quebec Group (Ordovician).

whorls are more or less rounded, and the volutions support one or
two rows of prominent spines.

Discohelix includes discoidal shells, concave on both faces, with
the whorls flattened at the circumference, and furnished with two
marginal keels, the aperture being quadrangular. Forms of this
type appear to be principally characteristic of the Upper Trias and

Fig. 661.—Ecculiomphalus distans. (Quebec Group (Ordovician).

of the Jurassic rocks. ¢/rontia (Eocene) appears to be nearly
related to Descoheltx.

The remarkable Paleozoic genus A/aclurea (fig. 663) may be
provisionally placed here; though its precise affinities are very
doubtful, and it is regarded by Fischer as probably related to the

PROSOBRANCHIATA. TiS

NNeritide. In this genus the shell is discoidal, of few whorls, longi-
tudinally grooved at the back, and ornamented with lines of growth.

Fig. 662.—Ca@locentrus (Cirrus) Goldfussi. Devonian.

The upper side of the shell (drawn as the lower side in fig. 663, 4)
is convex, and deeply umbilicated by the sinking of the spire below

IN

= =

Fig. 663.—JJaclurea crenulata, Ordovician (Quebec Group), Canada. a, Upper side, with
the spire; 4, Side view of the shell; c, Base. Properly speaking, figure 4 should have been
drawn with the flattened base undermost and the hollow spire above. (After Billings.)

the general surface ; while the base is flattened and exposes the inner
whorls. The mouth of the shell is closed by a shelly operculum,

= = ——

Fig. 664.—Pleuronotus (Euomphalus) De-Cewi (Billings). a, Front view; 4, View of the
umbilicus. Devonian, North America.

which is “ sinistrally sub-spiral, solid, with two internal projections,

one of them beneath the nucleus, very thick and rugose” (Wood-
ward). The genus is essentially characteristic of the summit of the

774 DIVISIONS OF THE GASTROPODA.

Cambrian and the base of the Ordovician series (the Quebec Group
and Chazy Limestone in North America, the Durness Limestone in
Scotland, &c.)

Finally, we may notice here the Devonian fossil for which Billings
proposed the name of Luomphalus De-Cewi, and upon which Hall
has based the genus Pleuronotus. In this form (fig. 664) the shell
is discoidal, with a wide shallow umbilicus and a concave spire, the
outer lip of the aperture showing a dis-
tinct sinus. “The surface onthe sum
mit and external side of the whorls is
‘“‘marked by a distinct band, to the
margins of which the surface-striz con-
verge on the two sides, and upon which
they make a regular retral curve” (Hall).
This last character renders it probable,
as suggested by Hall, that Pleuronotus
should be referred to the family of the
Pleurotomaride.

FaMILY 10. SOLARID#. — In this
family the shell is obtusely conical or
depressed, with a large and deep um-
bilicus running from the base to the
apex of the shell. \Uhereeissiwommd
creous layer, and the aperture is entire.
The principal genus in this family is Solarium itself (fig. 665),
comprising the familiar ‘‘Staircase Shells.” In this genus the
edge of the umbilicus is typically crenulated, and the aperture is
rhombic. The species of Solarium range from the Cretaceous
(Trias?) to the present day.

FaMILy 11. TRocHip#.—In this family the shell is conical,
pyramidal, top-shaped, or helicoid, the aperture being entire, and
either quadrilateral or round in form. ‘The shell
is macreous, and the operculum is horny, cir-
cular, and multispiral, with a central nucleus.
The members of this family are all marine, and
are mostly found between tide-marks or in shal-
low water; a few forms, however, being inhabi-
tants of deep water.
on In the genus Z7vochus (fig. 666) the shell is

Fig. 666.— Trochus pyramidal, with a nearly flat base, and the aper-
ee Pliocene Ter ture is oblique and rounded in shape. The range

of the genus is from the Silurian to the present
day, but the determination of many of the fossil forms is un-
certain, since it is by the structure of the operculum that the
genus is essentially distinguished from Zurbo and Astralium, and

Fig. 665.—Solariun ornatumt.
Gault (Upper Cretaceous).

PROSOBRANCHIATA. 775

opercula, even when shelly and massive, are not often met with
in the fossil condition.

Monodonta in its general characters resembles Zvochus, but the
columella is thickened and carries a prominent tooth. The genus ranges
from the Tertiary period to the present day, and doubtful representatives
of it have been indicated as occurring in older times. In Delphinula the
shell is orbicular and depressed, the whorls angulated or
coronated, often spiny, the mouth round, the peristome
entire, and the umbilicus open. The genus seems to
begin in the Jurassic rocks. In Usmbonium the shell is
circular, with a short spire and a large body-whorl, the
surface being polished, and the umbilical region covered
with a prominent callosity. The genus begins in the
Devonian, and still survives. Lastly, according to the
views of Lindstrém, we must include in this family the _ Fig. 667-—Sevs-
genus Scissuvella (fig. 667), in which the shell is thin, A Tee.
with a greatly expanded body-whorl, and the outer lip is
furnished with a deep slit. The earliest forms of Sczssuvel/a appear in
the Cretaceous rocks, and the genus still survives.

FAMILY 12. TuRBINID@.—The shell in this family is solid and
nacreous internally (except in Phastanella), turbinated or trochoid
in form, with an entire, round or oval aper-
ture, and a rounded or flat base. The oper-
culum is calcareous, paucispiral, with a central
or excentric nucleus. ‘The members of this
family are marine, and inhabit shallow water.

In the genus Zurbo (fig. 668) the shell is
turbinated, with a round base, the whorls
being convex, and the aperture large and
rounded. The species of the genus range
from the Silurian to the present day, about -
Peeaundred fossil species haymg been de- “Fis. 68-— 1ato subcostatus.
scribed ; but owing to the non-preservation
of the opercula there is much doubt as to the true position of
many of the older forms.

In Astralium (Imperator) the shell is trochoid, with a flat or concave
base, and with keeled or foliaceous whorls and an angulated aperture.
The genus ranges from the Trias to
the present day. The genus Ovzos-
toma (fig. 669) comprises Silurian and
Devonian forms, in which the shell is
discoid, with a short spire, the whorls
being in contact, but the last whorl
sometimes partially disjunct. The
surface is usually spirally ribbed;
there is a wide and open umbilicus ; EaeenGo Or iustoren (Enea onal)
and the aperture has thin lips, with- discors. Silurian, Britain.
out a sinus. The inner layer of the
shell is nacreous, and there is a solid calcareous operculum. Some of
the most familiar of the Silurian forms, such as O. dscors (fig. 669), O.

776 DIVISIONS OF THE GASTROPODA.

rugosum, and O. sculptum, have been described as species of Euom-
phalus.

In Cyclonema (fig. 670, B) the shell is turbinated and imperforate, and
the surface is adorned with raised
spiral lines intersected by finer trans-
verse siriz. The genus ranges from
the Ordovician to the Devonian. The
Devonian genus /sonema resembles
Cyclonema, but the whorls are angular
and the aperture is rhombic. In
Eunema (fig. 670, A), again, the spire
is elevated, the whorls are more or
less angular, and the surface is adorn-

Fig. 670.—a, Eunema strigillatunz, ed with elevated spiral ribs. The
Ordovician (Trenton Limestone), Canada; genus begins in the Ordovician, and
Penn Bre eg en See the typical forms are Paleozoic. The
Zittel.) Secondary genus Amdberleya, however,

seems to differ from Awzema princi-
pally, if not solely, in the fact that the spiral ribs are replaced or accom-
panied by rows of tubercles or nodosities. The Silurian and Devonian
genus Zyvochonema resembles Cyclonema, but there is a wide umbilicus,
bordered by an elevated ridge. In the Silurian genus Cvaspedostoma
the shell is globular, the surface has transverse lamellar nbs, and there
is a circular mouth “ enclosed within an enormously enlarged and thick-
ened border” (Lindstrém).

The genus Phasianella (fig. 671) represents another type of the
Turbinide, in which the shell is not nacreous, and its surface is
smooth and polished. The spire is long, the body-whorl is large,
and the aperture is oval. The genus ranges from
the Devonian to the present day.

FAMILY 13. XENOPHORIDZ.—This family includes
only the genus Xezxophora (Phorus), in which the
shell (fig. 672) is trochoid, with a concave or flattened
base and keeled whorls, but differs from that of the
Trochide in not being nacreous. Very commonly,
foreign bodies, such as shells or small pieces of
stone, are attached to the surface and margins of

- the shell. The genus ranges from the Devonian to
_ Fig. 671.—Phasi- the present day.
ieee eta Famity 14. Neritip#.—TIn this family the shell
is thick and globular, with a very small spire, and
without an umbilicus. The aperture is semilunate, its columellar
side thickened and expanded, and often toothed (fig. 673), and the
outer lip acute. There is a calcareous, sub-spiral operculum, pro-
vided with a process on its inner side. The ‘‘ Nerites” are in-
habitants partly of salt water and partly of fresh or brackisn waters.
In many cases the inner turns of the spire become absorbed in
process of growth, so that casts of the interior of the fossil forms
often show no traces of a spire.

PROSOBRANCHIATA. ih

In the genus JVerita (fig. 673) the shell is thick, with a broad
columella, the inner edge of which is straight and toothed. The
outer lip is thickened and often denticulated internally. The true
Nerites are inhabitants of warm seas ; and typical forms of the genus

Fig. 672.—Xenophora (Phorus) canaliculata. Cretaceous.

appear first in the Cretaceous rocks, though nearly related types are
known from the Triassic and Jurassic rocks.

The Triassic and Jurassic genus Verztodomus closely resembles Verzta,
but the columellar lip of the aperture is thickened and callous, and is
without teeth. In the nearly allied Vervztoma, of the Jurassic rocks, the
shell is thick and ventricose, and the columellar lip is callous, and is not
toothed, while there is a notch or sinus in the middle of the outer lip.

Fig. 673.—Verita (Velates) Schuideliana. Eocene Tertiary.

The genus /Verztina, again, includes the so-called “ Fresh-water Nerites,”
which agree in most characters with /Verzfa, but inhabit fresh or brackish
waters, and have a comparatively thin smooth shell. The oldest forms
of Werztina seem to appear in the Lias, and the genus is abundantly
represented in the fresh-water deposits of the Tertiary period, while
many recent forms exist. Lastly, the genus P2/eo/ws comprises small
limpet-shaped shells, with a semilunar aperture. The range of the
genus is from the Jurassic to the Eocene.

FamILy 15. NeriTopsip4#.—In this family the shell resembles
that of /Verita or (Vatica in shape, and is thick and imperforate.
The aperture is entire, semilunate, or oval in form; and there is a
thick shelly operculum, oval in shape, and non-spiral. In Werttopsis
the shell is shaped like that of /Vevzta, of few volutions, and with a

778 DIVISIONS OF THE GASTROPODA.

short spire; and the columellar lip of the aperture is largely exca-
vated about its middle. The genus ranges from the Trias to the
present day. The name of Fedfarion has been given to oval or
nearly circular calcareous plates, concave above and flattened below,
which are found in the Jurassic rocks, and which are now known to
be the opercula of species of /Vevztopsis. Similar opercula occur in
the Upper Trias and in the Tertiary rocks. The extinct genus
Naticopsis (fig. 674) includes thick, imperforate, naticoid shells, with

Fig 674.—-a, Naticopsis plicistria, Carboniferous Limestone. (After M‘Coy.) 3, Waticopsis
ampliata, Carboniferous Limestone. (After De Koninck.)

a short spire and a large body-whorl. The aperture is oval, and the
columellar lip is callous and flattened, the outer’ lip being thin. A
calcareous operculum is present. The genus ranges from the De-
vonian to the Upper Trias.

FAMILY 16. HELICINID#.—This family includes the recent Fe/z-
cina and its allies, in which the shell is helicoid and globular, with a
short spire, the interior turns of the spire being absorbed in course
of growth. The aperture is semicircular, and a horny or calcareous
operculum is present. This family has been generally included
among the Pulmogastropoda, upon the ground that the breathing-
organ is in the form of a pulmonary chamber, and the animal is
terrestrial ; but the true relationships of the group appear to be with
the Weritide. All the undoubted forms of this family are Recent ;
but Fischer is inclined to place here the Carboniferous genus
Dawsonella, which has been commonly included among the Ae/-
cide. In this genus the shell is like that of AYe/7x in shape, with a
small aperture, the outer lip of which is thickened, while the col-
umellar lip is expanded into a large callosity, which covers the
whole umbilical region.

FAMILY 17. Naticip#.—In this family the shell is globular, of
few whorls, with a small spire (fig. 675); the aperture oval, rounded
in front, and narrow behind, with an acute outer lip, and commonly
with a callous inner lip. The foot is very large, and the mantle-
lobes hide more or less of the shell. ‘The operculum is pauci-

PROSOBRANCHIATA. 779

spiral, with an excentric nucleus, and may be either horny or
calcareous.

The shell in (Vatica (fig. 675) is globular, with a large body-
whorl, usually smooth and polished, and often with coloured mark-
ings. The inner lip is callous, and the shell
is umbilicated, though the umbilicus may be
partially or wholly filled up. A large number
of recent, and a still larger number of fossil,
forms of JVatica are known, species having
been described from rocks as old as the Silu-
rian. It is, however, very questionable if any
true forms of JVatica are known from any
Palzeozoic deposit, anterior to the Carbonifer- _ ae
ous at any rate. The most typical forms of *" Be pita cause
LVatica, in a strict sense, possess a wide umbil-
icus and a twisted columella, and the oldest shells of this type are
from the Eocene Tertiary.

Ampullina includes Eocene and Miocene forms, in which the columella
is only slightly thickened and is not twisted. Aszauropsis includes a
number of fossil forms, of which the earliest perhaps appear in the Car-
boniferous Limestone, while many others are founc in the Secondary
rocks and the Eocene. In these types there is no umbilicus or only a
narrow umbilical fissure, and the spire is moderately high. Lzzatza,
again, includes a series of forms, ranging from the Trias to the present
day, in which the aperture is semilunar, and the umbilicus is of moderate
or small size, and is without a spirally-twisted callus. The Eocene and
Oligocene genus Deshayesza has the inner lip covered with a thick callo-
sity, which largely conceals the umbilicus and is toothed on its apertural
edge. The Jurassic and Cretaceous genus 7y/ostoma, lastly, includes
forms with an elevated spire, and without an umbilicus, the outer lip
being thin and sharp.

The genus WVarica (Vanzkoro) includes forms in which the shell
has a general likeness to that of /Vatica (fig. 676), but the surface
is spirally striated, or
cancellated. The aper-
ture is semilunate or
oval, and the columella
is excavated or umbili-
cated. The genus ranges
from the Jurassic period
to the present day. /Vatz-

cella (Silurian to Trias) Fig. 676.—Narica (Van- Fig. 677. —Sigaretus
7. tkoro) Genevensis, from the clathratus, from the
resembles JV arica, but Cretaceous rocks. Eocene.

has no umbilicus or a
small one. Lastly, in Sigaretus (fig. 677) the shell is ear-shaped,
with a spirally-striated surface, a minute spire, and a very large

780 DIVISIONS OF THE GASTROPODA.

body-whorl and wide aperture. The species of this genus are
Tertiary and Recent.

FamiLy 18. PALupDINIDZ.—In this family the shell is conical or
globular, with a thick epidermis, and with convex whorls, the aper-
ture being entire and sometimes furnished with a continuous lip
The operculum may be horny or shelly. The members of this
family are essentially fresh-water forms, though some are found in
brackish waters, and Amfullaria is known in some cases to inhabit
salt water. As a matter of course, therefore, they are chiefly, if not
exclusively, found as fossils in deposits which are believed to be
fluviatile, lacustrine, or estuarine in origin.

The genus Vivipara (Paludina) comprises forms with a conical
shell, a generally smooth surface, and a horny operculum, an umbili-
cus being sometimes present, sometimes absent (fig. 678, a). The
oldest forms of Vivipara, in the wide
sense, are found in the Lower Cre-
taceous rocks (Wealden Beds), and
a large number of Tertiary and Re-
cent species are known. Sithynia
resembles Vivzpara, but the oper-
culum is partially calcified ; and its
range in time is the same, though

Fig. 678.—a, Paludina lenta, Pliocene ; the known fosell (on ia
B, Valvata piscinalis, wiewenl Grom Sa number. In Valvata (fig. 678, B)
Ae ae from below. (After Searles the shell may be top-shaped or dis-

coidal ; an umbilicus is present, and
the peristome is entire. The earliest undoubted forms of this genus
appear in the Upper Jurassic rocks (Purbeck Beds), and a small
number of Tertiary and Recent forms are known. Lastly, in Am-
pullaria (fig. 639) the shell is globular, with a short spire and a
ventricose body-whorl, and with or without an umbilicus. The
operculum may be horny or calcareous. The geological range of
Ampullaria is a matter of uncertainty, from the difficulty, or impos-
sibility, of separating the shells of this genus from those of WVatica
and its allies. Forms from rocks as old as the Lias have been re-
ferred to Ampullarza, but it is doubtful if any representatives of the
genus are known to occur in the fossil condition.

FAMILY 19. Rissoip#.—In this family the shell is spiral, usually
with an elevated spire, the aperture being entire and rounded, and
the operculum horny and spiral. The members of this family are
partly marine, partly inhabitants of brackish waters or marshes ; and
the two principal genera comprised in it are Rzssoa and Hydrobza.

In the genus Azssoa (fig. 679) are included small, thick shells,
generally more or less ribbed or striated, pointed in shape, many-
whorled, and with a small round aperture surrounded by a continu-

PROSOBRANCHIATA. 781

ous peristome. The species of A7zssoa are inhabitants of the sea,
and the range of the genus in time is from the Jurassic to the
present day. Forms of sub-generic value, or allied types, are /zs-
soina (Jurassic to Recent), Kezlostoma (Chalk to
Oligocene), Dizastoma (Eocene), and Pverostoma
(Eocene).

fydrobia is nearly related to Rzssoa, but the shell
is usually thin and smooth. The species of this
genus are mostly inhabitants of brackish or fresh
waters, but a few live in the sea. The earliest forms
of Hydrobia are recorded from the Jurassic rocks,
puevthe) genus is) mainly ‘Tertiary and Recent. _
The genus Assminea differs from Hydrobia almost ae se
wholly as regards the animal, but forms are stated Pige0.5* (Ait
to occur in rocks as old as the Eocene. Searles Wood.)

FAMILY 20. LirrorinipA&.—JIn this family the
shell is spiral, top-shaped, not nacreous internally, with a rounded
and entire aperture and a simple thin outer lip. The operculum
is horny and paucispiral. The members of this family are wholly
marine ; and their shells are very similar to those of the Zvochide
and Zurbinide, except that there is no nacreous layer developed.

In the genus Zz¢/orina are the true Periwinkles, distinguished by
their thick, generally top-shaped and pointed shells, of few whorls,
and with an imperforate columella. The undoubted fossil species
range from the Jurassic to the present day. In
the Tertiary and Recent genus Lacuna, the shell
resembles Zz¢torina in most respects, but it is
thin, and the columella is flattened and is bor-
dered by an umbilical fissure. We may also
include here the Silurian and Devonian genus
ffolopea (fig. 680), in which the shell is spiral,
and either conical, or, more usually, naticoid, Fig. 680.-= Holopen
with a short spire and a large body-whorl. The §we##ensis. (Billings.)
surface is smooth or marked with faint trans-
verse strize ; the outer lip is thin; the aperture is entire; and there
may or may not be a narrow umbilicus.

FAMILY 21. SCALARIID&.—lIn this family the shell is spiral and
turreted, many-whorled, the volutions marked with longitudinal
ribs; and the aperture is round and furnished with a continuous
peristome. The shell is perforated, but the umbilicus is often closed
or concealed ; and the operculum is horny and spiral.

In Scalaria itself are included the ‘‘ Wentle-traps,” in which the
shell is elongated and many-whorled (fig. 681), and the volutions
are adorned with transverse ribs, while the peristome is continu-
ous round the circular aperture. The earliest forms of this genus

782 DIVISIONS OF THE GASTROPODA.

appear in the Trias, and a number of Jurassic and Cretaceous
species are known; while the genus is largely represented in the
Tertiary rocks and at the present day. In the Jurassic genus
Exelissa, the essential characters agree with
those -of Scalaria, ‘but. the shell sis) on semaalll
size, the aperture is constricted, and the last
whorl may be partially disjunct. The Triassic
genus Cochlearia differs from Sca/avza in having
the whorls keeled and spirally striated, the trans-
verse ribs being feebly or not at all developed,
while the mouth is thickened and trumpet-shaped ;
and the Devonian genus Scoliostoma resembles
Cochlearia except that the last volution is bent
upwards and. the surface is cancellated. Lastly,
we may place here the ancient genera Callonema
and /Zolopella, which agree with the typical mem-
bers of this family in having a conical shell with
Fig. 681.—Scalavia an aperture surrounded by a continuous peristome.
Grenlandica. Post- ; 9c
Pliocene and Recent. Callonema ranges from the Ordovician to the De-
vonian, and has the surface ornamented by re-
mote, transverse, lamellar ribs; while in /Zo/opella the ribs are
reduced to mere striae, or are obsolete.

FAMILY 22. IANTHINID/.—The type of this family is the singular
pelagic genus /anthina, in which the shell is thin and turbinated,
with an oval or subquadrate aperture, the outer lip being thin, and
the columella slightly twisted. On the ground of similarity as re-
gards the characters of the radula, Janthina is placed by Fischer in
the vicinity of the Scalarzd@e. ‘The only known fossil forms are
from the Pliocene deposits of Italy.

FAMILY 23. TURRITELLIDZ.—In this family the shell is spiral,
many-whorled, turreted, the surface spirally ribbed or striated. The
aperture is round or subquadrate, entire, but sometimes slightly
notched in front. The outer lip is thin, and the operculum is
horny. All the members of this family are marine, and, if Vermetus
and Cecum be excluded, the principal representative of the group is
Turritella itself (fig. 682), the characters of which are therefore
those given above. Many living Zurritelie are known, and a still
larger number of fossil forms have been described, the earliest un-
questionable representatives of the genus occurring in the Jurassic,
or perhaps in the Triassic deposits. Most of the fossil species, how-
ever, are found in the Tertiary rocks.

FAMILY 24. VERMETID#.—In this family the shell (fig. 683) is
tubular, more or less spiral at first, but with its last turns disjunct.
The aperture is round, and is entire or furnished with a lateral slit.
A horny circular operculum is usually present. All the members of

PROSOBRANCHIATA. 783

this family are marine, and the two principal types are Vermetus and
Stligquarta. ‘The genus Vermetus is remarkable for the resemblance
of its tubular shell to the calcareous tubes of Sexpula. The shell is
usually attached to some foreign body, and though regularly spiral
when young, is always irregular in its growth when adult. The fossil
species are best distinguished from Serpula by the fact that the tube
is repeatedly partitioned off by calcareous septa as the animal grows.
It is, however, often a matter of extreme difficulty to determine
whether a given specimen be a Vermetus or a Serpula. The range
of Vermetus in time, using this name in its wide sense, is from the
Carboniferous period to the present day; but most of the fossil
forms belong to the later Secondary and Tertiary deposits. In the

Fig. 682.—Turritella angulata. Fig. 683.—S7liquaria anguiva.
Neocomian. Pliocene and Recent.

genus Sz/iquaria (fig. 683) the shell resembles that of Vermetus in
most respects, but it is free, and the tube has a continuous longi-
tudinal slit, which may be replaced by a row of pores, running along
the whole length of the shell on one side. The genus ranges from
the Cretaceous to the present day.

FAMILY 25. Ca&cip#.—This family comprises only the genus
Cecum, in which the shell is free, and, to begin with, forms a small
flat spiral. With age, however, the shell becomes decollated, and
has in its adult state the form of a curved cylindrical tube, the
truncated end of which is closed by a transverse calcareous partition.
A number of recent and a few fossil forms of the genus are known,
the oldest of the latter being found in the Eocene Tertiary.

FAMILY 26. PyRAMIDELLID#.—In this family the shell is spiral
and turreted, often with a polished surface. The aperture is small
and entire, sometimes with one or more prominent plaits on the
columella. The operculum is horny, ear-shaped, and paucispiral.
All the members of this family are marine, and most of the living
forms are of small size.

784. DIVISIONS OF THE GASTROPODA.

In Pyramidella (fig. 684, B) the shell is slender and turreted,
and the columellar lip is plaited. The genus is represented by a num-
ber of Recent and Tertiary species, while still older forms occur in
the Cretaceous rocks. Odostomia, with a similar geological range,
includes minute turreted shells
very similar in most respects
to Pyramidella, but having a
single tooth-like columellar fold.
Turbonilla, with the same range
in time, nearly resembles the
preceding, but the columellar
lip is simple, or has a feeble

Fig. 684.—a, Eulima vagans, Jurassic (after oblique fold. Chemnitsia (fig.
Morris and Lycett) ; B, Pyramidella leviuscula, 684, C) includes a number of
Pliocene (after Searles Wood); c, Chementtzia
internodula, Eocene (after Searles Wood). slender, turreted, many-whorled

) shells, with plaited whorls and
a simple aperture, the columellar lip having neither teeth nor folds.
Numerous fossil forms are known in the Triassic, Jurassic, and
Cretaceous deposits, in marine sediments only ; and there are also
Tertiary species. It is doubtful if the distinction between Chem-
nitzia and Turbonilla can be maintained. LZudima (fig. 684, A)
includes small, polished, elongated shells, with level whorls and a
reflected inner lip. The genus ranges from
the Trias to the present day, a large number
of species occurring in the ‘Tertiary deposits.
JViso, with the same geological range, has the
shell umbilicated, but otherwise resembles £w-
lima.

FAMILY 27. PSEUDOMELANIID2.—This family
has been founded for the reception of certain
extinct marine Gastropods, of which Loxonema
and Macrochetlus are the two most important
types. In this family the shell is many-whorled
and turreted, with an oval aperture, which is
typically entire, but is occasionally notched in
front. The columella is simple, or may be
slightly folded anteriorly. The forms included

Fig. 685.—Zoxone- In this family have a general resemblance to
ma rusvers, Carbon” VYelania, but they are found in deposits of
(Siege Piutllies.) marine origin, whereas the A/e/ani@ are inhabi-

tants of fresh water. |

The shell in Loxonema (fig. 685) is long and turreted, with -con-
vex whorls, which have no spiral band; and the surface is covered
with longitudinal, often more or less arched striz or ribs, while
the outer lip is more or less sinuated. The genus ranges from the

PROSOBRANCHIATA. 785

Silurian to the Trias, but attains its maximum development in the
Carboniferous Limestone.

The genus Macrocheilus (fig. 686) includes thick smooth shells,
with a moderately long spire and a pointed
apex, and with convex whorls. The aperture
is oval, not distinctly notched ; the inner lip is
callous, and the columella is imperforate and
obtusely folded in front. The genus ranges
from the Devonian to the Trias, the majority
of the known species being Carboniferous.
No species of the genus has been detected in
the later Secondary or Tertiary deposits, but a
living Japanese shell has been referred here.
The Devonian and Carboniferous genus Or¢ho-
nema appears to be related to Loxonema, and
the Carboniferous genus Solenzscus has been
placed here, though the aperture is canalicu-
lated in front. Lastly, the Secondary and ais
Tertiary genus Psewdomelania finds a place in Fig. 686.—Macrocheilus
this family. aS: Middle De-

FAmMILy 28. MELANIIDZ.— In this family
the shell is spiral and turreted, covered with a thick epidermis, and
often much eroded towards the apex of the spire. ‘The aperture is
oval, and either entire or channelled or
notched in front (fig. 687), the outer lip
being acute. The operculum is horny
and spiral. The members of this family
are essentially fresh-water Gastropods,
a few forms only inhabiting brackish
waters.

In Mel/ania itself the shell is usually
adorned with striz, ribs, or spines, and
the aperture is entire and pointed above
fieeada7. A) ihe recent species -of
Melanta have an exceedingly wide geo-
graphical range, and fossil forms are
found in moderate numbers in the Cre-
taceous and Tertiary deposits. In Pleu-
rocera the aperture is canaliculated be- ae Oe ens Ree :
low, and the outer lip is sinuated. The (77m, ae Medatis (Nike:
recent forms of this type are North
American, and the genus has numerous representatives in the
Cretaceous and Tertiary deposits. In J/e/anopsts, lastly, the aper-
ture is deeply notched, and the spire is often shortened ; while in
Pirena (fig. 687, Cc) the aperture has the same form, but the shell

VOL, I. g} 1D)

786 DIVISIONS OF THE GASTROPODA.

is turreted. Both genera range from the Cretaceous period to the

present day.

FAMILY 29. CycLostomip®.—In this family are included terres-
trial Gastropods, which possess a pulmonary chamber, and which

have therefore been commonly included among
the Pulmogastropoda. The shell is of variable
shape, spiral, sometimes conical (fig. 688),
sometimes depressed or discoidal. ‘The aper-
ture is nearly circular, and the peristome is
simple or reflected. An operculum is present,
and is usually more or less extensively calcified.
The principal genus in this family is Cyclostoma

Fig. 688.—Cyclostoma (fig. 688) itself, which has been split up into a

Arnoudit. Eocene Ter-

tlary.

number of subordinate groups. The oldest
forms of Cyclostoma, in the general sense, ap-

pear in the Cretaceous rocks, and a number of Tertiary species are
known, while the genus is largely represented at the present day.
FAMILY 30. AcicULID#.—This family includes small terrestrial

Fig. 689.—Subulites
terebriformis, Silurian,
North America. (After
Hall.)

Gastropods, provided, like the preceding, with a
pulmonary chamber. ‘The shell is elongated and
cylindrical, with a blunt apex, and a thickened
peristome. There is an operculum, but this is
never ‘calcified. The recent gents -Agzed/geis
represented in the later Tertiary deposits.

The genus 7runcatella—sometimes regarded as
the type of a separate family (77vuncatellid@)—com-
prises littoral or fresh-water Gastropods, sometimes
semi-terrestrial in habit, and related on the one hand
to Acicula, and on the other hand to the Azssozde.
The nature of the breathing-organs has not been
clearly ascertained. The shell in 77vucatella is elon-
gated and cylindrical, often truncated in the adult
state, and with an entire oval aperture. Species of
the genus have been detected in the Tertiary de-
posits, the oldest appearing in the Eocene.

FAMILY 31. SUBULITID2.—In this family the
shell (fig. 689) is elongate and fusiform, with a
smooth surface. The aperture is long and nar-
row, and is distinctly canaliculated in front. This
family includes some Palzeozoic and Triassic Gas-
tropods, of which Swdulites is the type, in all of
which the peristome is incomplete and the shell
notched in front. By Lindstrom the members
of this group are regarded as the most ancient

representatives of the division of the Siphonostomatous Proso-

branchs.

PROSOBRANCHIATA. 787

In Subulites (? = Polyphemopsis, Portlock) the shell is elongated,
slender and fusiform, with a smooth surface and a shallow suture.
The shell is thin and fragile, and is truncated
or rounded in front (fig. 689). The aperture is
long and narrow; the outer lip is thin, and the
inner lip is involute; and there is a distinct
notch in front. The range of the genus is from
the Ordovician to the Carboniferous. The genus
fuchrysalis, ranging from the Silurian to the
Trias, closely resembles Szdudites in the shape
and other characters of the shell, and is, perhaps,
hardly separable from the preceding. Lastly, in
the Ordovician genus Fusispfira (fig. 690) the
shell is fusiform, with an elevated spire and con-
vex whorls. The aperture is oval or elliptical,
and is prolonged below into a shallow canal ;
while the columella is twisted, but is without
folds.

FAMILY 32. NERINEID#.—In this family the
shell is turreted, thick, and solid, and the aper- _. aise

; ; : mas Fig. 690.—Fusispira
ture is canaliculated in front. The outer lip is sredriyrmis. — Ordo-
acute, and is sinuated superiorly or posteriorly, (After Hall). eet
a slit-band which runs continuously below the
suture being thus produced. The columella and parietes of the
aperture are furnished with continuous folds, which are prolonged

Fig. 691.—Nerinea Fig. 692.—Nerinea Goodhallit,
bisulcata. Chalk. In one-fourth of the natural size.
the lower part of the The left-hand figure represents
specimen the shell is a vertical section of the shell.
preserved, while the Coral Rag, England.

upper part shows the
cast of the interior.

into the interior of the spire. All the members of this family are
extinct, and all are confined to the Secondary period.

738 DIVISIONS OF THE GASTROPODA.

The principal or sole genus in this family is /Verinea itself,
which has been divided into several sub-genera. In this genus
the shell (figs. 691 and 692) is turreted, many-whorled, and nearly
cylindrical. The columella carries continuous ridges, and similar
ridges exist on the interior of the whorls, so that casts of the
interior are often very unlike the exterior. The genus /Vervznea
is wholly Jurassic and Cretaceous, a very large number of species
being found in the former of these systems, and particularly in
strata of the age of the Coral Rag.

FAMILY 33. CERITHIIDZ.—In this family the shell (fig. 693) is
spiral and turreted. The aperture is oval or quadrate, and is
channelled in front, the canal being short and often bent back-
wards. The outer lip is generally expanded in the adult, the
columella is sometimes thickened, and the operculum is horny and
spiral. The members of this family are marine or live in brackish
waters, some forms frequenting salt marshes or the mouths of rivers.
More than three hundred recent species, and over a thousand fossil
forms, of this family have been described, the most ancient types
appearing in the Trias. The known forms belong to the_ two
comprehensive genera Cerithium and Fotamides, each of which
has been split up into minor groups, to some of which a generic
value is sometimes attached.

In Cerithtum proper (fig. 693) the shell is without an epidermis,
the operculum is paucispiral, and the aperture has
a well-developed, backwardly-bent canal. The
species of Cervithium are essentially marine, and
the genus has been broken up into sub-generic
groups (/idula, LEustoma, &c.), the distinctive
characters of which are mostly of small import-
ance. ‘The species of Cerithium abound in the
Secondary and Tertiary rocks, and in warm seas
at the present day. The oldest forms appear in
the Alpine Trias.

The genus FPotamides closely resembles Cevs-
thium in general characters; but the surface is
NS / covered with epidermis, the aperture has only a
Fig.693.—Cerithium short canal or a notch in front, and the operculum
se eg Focene is multispiral. The species of otamides live in

brackish waters or at the mouths of rivers. In
the fossil condition the shells of Po¢amzdes cannot be certainly
distinguished from those of Cervzthium, but it is usual to consider
that the representatives of this family which occur in estuarine or
fresh-water deposits are referable to the former genus, while those
which occur in purely marine deposits belong to the latter. On this
view, the species of Potamides are Cretaceous, Tertiary, and Recent,

PROSOBRANCHIATA. 789

The genus has been split up into several sub-genera (Bzttiwm, Trt-
Joris, Ceritella, &c.), but these are of little importance.

FAMILY 34. APORRHAID#.—In this family the shell is fusiform,
turreted or conical; the aperture is prolonged in front into a canal ;
the outer lip is expanded, aliform or digitate ; and the operculum is
horny. The members of this family are
all marine, and they are closely allied to
the Strombide. The two principal genera
in this family are AZorrhais itself and
Alaria.

In Afgorrhais (fig. 694) the shell is
spindle-shaped, with a turreted spire, and
the outer lip of the adult is greatly ex-
panded and lobed, the inner lp being
callous. The aperture is narrow, and is
prolonged into a longer or shorter anterior
canal, while its posterior angle is prolonged
into an open tube, and the outer lip is
sinuated in front. The genus has been
broken up into numerous minor groups,
and is represented by numerous Jurassic,
Cretaceous, and Tertiary forms, and by a
few recent species. The genus <A/aria
Bomprees forms with a general resem- Nie (ot, deerrhans farke-
blance to Afgorrhais; but there is no Starkie Gardner.)
posterior canal, and the outer lip has no
proper sinus in front. The species of A/arza, in the wide sense of
the name, are confined to the Jurassic and Cretaceous deposits,
being especially abundant in the former.

FAMILY 35. STROMBID#.—In this family the shell is conical or
fusiform, with a pointed spire. ‘The aperture is prolonged into a
canal in front; and the outer lip is expanded, and has a notch or
sinus in front, near the canal. The operculum is horny and claw-
shaped. The foot is narrow and adapted for leaping, and there is
a long proboscis, with two tentacles carrying the eyes at their apices.
The members of this family are all marine.

In the genus Strombus the shell has a short spire and a large
body-whorl, and the long aperture is prolonged into a short canal
in front and has a notch behind. The outer lip is expanded, and
is more or less deeply indented or notched in front, near the canal.
The genus is represented by a number of recent species, and by a
moderate number of Cretaceous and Tertiary species.

The genus Pteroceras (or Pterocera) comprises the so-called
“ Scorpion-shells,” in which the shell of the adult (fig. 695) has its
outer lip furnished with long claws, one of which forms a posterior

790 DIVISIONS OF THE GASTROPODA.

canal close to the spire. Many fossil species are known, commenc-
ing in the Lias.

In the genus Aostellaria (fig. 696), the spire is long, and has the
posterior canal running up it. Many fossil species are known,
commencing in the Cretaceous rocks. The outer lip is always
expanded, and in some forms is enormously so. One of the most
familiar species is the great 2. ampla (fig. 696) of the London
Clay (Eocene).

Lastly, in the genus Zerebellum (= Seraphs) the shell is elongated
and subcylindrical, with a short or obsolete spire. The aperture is
long and narrow, with a thin outer lip and a short canal. ‘There is

Fig. 695.—Pteroceras oceani. Neocomian.

an emargination of the outer lip in front. The genus is Tertiary
and Recent, most of the fossil forms being found in the Eocene
rocks.

FAMILY 36. CypR&1p&.—JIn this family the shell is spirally
rolled up, but the spire is more or less completely concealed, owing
to the fact that the shell becomes overlaid by a coating of enamel.
The aperture is long and narrow (fig. 697), and is channelled at both
ends. The outer lip is thin in the young shell, but is thickened
and strongly inflected in the adult. ‘The foot is broad, and the
mantle forms lobes which meet over the back of the shell.

The principal genus in this family is Cyfvea itself, comprising
the numerous and well-known living shells commonly spoken of as
Cowries. The Cyfree are mainly, but not exclusively, inhabi-
tants of warm seas, and they attain their highest development

PROSOBRANCHIATA.

791

between the tropics. A single species has been found in the
highest Jurassic beds in Sicily (Zittel), but with this exception the

Fig. 696.—Rostellaria antpla, reduced one-third. Eocene Tertiary.

fossil species date from the Cretaceous period, and abound in

the Tertiaries.

The shell of the Cowries in the young state is furnished with a

prominent spire, and has a thin outer lip. In
the adult state (fig. 697) the spire is com-
pletely concealed within the shell, the entire
surface is generally covered with shining
enamel, the inner lip is crenulated, and the
outer lip is thickened, inflected, and crenu-
lated. The small Cowries of which the com-
mon Cyprea (Trivia) Europea is the type,
are not known to occur in the Secondary
rocks, but have a few Tertiary representatives.
They are distinguished from the ordinary
Cowries by the fact that the upper surface is
adorned with transverse ribs. The genus
Ovulum is closely related to Cypre@a, but the

Fig. 697.—Cy prea elegans.
Eocene Tertiary.

aperture is drawn out anteriorly and posteriorly, and the inner lip
is smooth. ‘The genus dates from the Eocene, and possesses a
number of existing representatives. rato, again, ranging from

792

DIVISIONS OF THE GASTROPODA.

the Chalk to the present day, differs from the Cowries in having
a cone-shaped shell, with a short but visible spire.
FaMILY 37. CassipDID#.—In this family the shell is ventricose,

with a short spire and a large body-whorl.

The aperture is long

and narrow, notched in front, or with a short recurved canal (fig.

698). The inner lip is callous, and the

—— outer lip is thickened and often plaited or

- === - enticulated. ‘The members of this family
= ae ea

oh) | ual
‘ Ip al

vata AW hi
\ f
i

are all marine, and the oldest forms belong-
ing to it appear in the Upper Cretaceous
rocks.

The genus Casszs (fig. 698) comprises the
‘‘ Helmet-shells,” distinguished by their short

spire, large body-whorl, elongated aperture,
short recurved anterior canal, and expanded
inner lip. The earliest forms of Casszs ap-
pear in the Eocene Tertiary, and the genus
still survives. Casstdaria (Upper Cretaceous
to Recent) closely resembles Casszs, but the
canal is elongated and produced. Lastly, Ozscea, with the same
range in time as Casstdaria, has the aperture truncated in front,
with a straight canal or notch.

FamiLty 38. DoLtup#.—In this family the shell is thick and ven-
tricose, with a large body-whorl and a wide oval aperture. The
whorls are longitudinally ribbed, and there
is a short anterior canal, which may be
straight or recurved. This family includes
only the genus Dolium, the species of which
are marine. ‘The fossil forms are chiefly
Tertiary, but a Cretaceous species of the
genus is known.

FAMILY 39. FicuLtip#.—JIn this family ,
the shell is thin and ventricose, spirally
ribbed or cancellated (fig. 699). The aper-
ture is of large size, and is prolonged in
front into a long canal. This family in-
cludes only the genus /icula (Pyrula in
part), in which the shell is pyriform, with
a very large body-whorl and a-short spire,
and with a sharp outer lip. The recent
species of Ficu/a are inhabitants of the sea, and the earliest fossil
forms of the genus appear in the Cretaceous rocks.

FamiILy 40. TRITon1mD#.—In this family the shell is spindle-
shaped, with a straight or somewhat bent canal. ‘The whorls are
often adorned with varices, and a horny operculum is present.

Fig. 698.—Cassis canalicula-
tus. Recent.

Fig. 699.—/cula (Pyrula)
reticulata. Miocene Ter-
tiary. (After Zittel.)

PROSOBRANCHIATA. 793

The members of this family are all marine, and the two principal
genera contained in it are Z7itonium (= Triton) and Ranella. The
former of these ranges from the Cretaceous period to the present
day, while the species of the latter are Tertiary and Recent.

FAMILY 41. Buccinrp#.—In this family the shell is conical, with
a large aperture, which is notched in front,
or prolonged into a very short canal, which
is reflected so as to produce a sort of varix
on the back of the shell anteriorly. All
the members of this family are marine,
and the three most important genera com-
prised in it are Buccinum, Nassa, and KY
Leburna. QQ \y

The Whelks form the genus Buccinum \ ,
(fig. 700), distinguished by the ventricose
body-whorl, large aperture, and short re-
flected canal. Some few species of Buc-
cinum are found in the Cretaceous rocks ;
but the genus is essentially Tertiary and
Recent.

The genus Vassa (fig. 701) comprises
the “‘ Dog-whelks,” in which the shell has a ae tay:

1g. 700. uccinum glaciale.
a general resemblance to that of Buc- Post-Pliocene and Recent.
cinum, but the columellar lip is expanded
and callous, and generally shows a tooth-like fold near the anterior
canal. More than two hundred recent species of /Vassa are known,
and a large number of Pliocene and Miocene
species have been described. In the early Ter-
tiary deposits the genus is sparingly represented,
and the oldest types appear in the Chalk.

In the genus £éurna, the shell is umbilicated
when young, but the inner lip is callous, and in the
adult condition is expanded so as to cover the
umbilicus. The genus is wholly Tertiary and
Recent. Lastly, the genus Lrachytrema includes Pee Bie
Jurassic types of the Buccinide, in which the shell (After Searles Wood.)
is turbinated, solid, and of small size, with nod-
ulated, ribbed, or cancellated whorls. The columella is smooth,
and there is a short oblique canal. By Fischer the genus is doubt-
fully referred to the Cerithide.

FAMILY 42. COLUMBELLID#.—In this family the shell is ovate or
fusiform, with a short spire and a large body-whorl. ‘The aperture
is long and narrow; the outer lip is thickened and toothed inter-
nally, and the inner lip is toothed or granulated in front. The
members of this family are all marine, and the three principal genera

\\\\\\\\\Ah NK \ Vi
wr

794 DIVISIONS OF THE GASTROPODA.

comprised in it are Columbella (Tertiary and Recent), Columbellina
(Cretaceous), and Columbellaria (Jurassic and Cretaceous).

FaMILy 43. PuRpURID#&.—In this family the shell is oval or fusi-
form, with a short spire. The columellar lip is expanded and more

Fig. 702.— Purpura tetragona. Plio- Fig. 703.—Purpuroidea nodulata.
cene. (After Searles Wood.) Jurassic. (Copied from Zittel.)

or less flattened, and there is a short anterior canal. "The members
of this family are all marine, and the principal genera are Purpura,
Purpuroidea, and Rapana.

In the genus Purpura (fig. 702) the shell has a short spire and
a large body-whorl; the columellar lip is smooth and flattened ;

Fig. 704.— Fusus Neocomiensis. Fig. 705.—Fusus (Chrysodomus) con-
Lower Greensand. trarius. Pliocene (Red Crag).

and there is a short oblique canal or notch in front. The genus is
exclusively Tertiary and Recent, and the fossil forms are few in
number.

In the Jurassic and Cretaceous genus Purpuroidea (fig. 703) the
shell is oval and ventricose, with a short pointed spire and a large

PROSOBRANCHIATA. 795

body-whorl. The whorls are convex and have a row of tubercles
below the suture. The outer lip is thin, the columella is smooth,
and there is a short wide canal. Lastly, in apana the shell is
ventricose, with a short spire, the aperture is produced in front,
and the columella is umbilicated. The genus ranges from the
Cretaceous to the present day.

FaMILy 44. Fusip&.—In this family the shell is elongated or
fusiform, dextral, or sinistral, usually without varices. The aperture
is moderately long, and is produced in front into a long straight
canal. The operculum is horny. The members of this family are
all marine, and the principal genera placed under this head by Zittel
are Lusus, Pisania, Fasctolaria, Turbinella, and Pyrula.

In the genus Fwsws the shell is spindle-shaped (figs. 704 and
705) and many-whorled, with an elongated straight canal. <A
very large number of Recent and fossil forms of Fwsus have been
recorded, and the genus has been broken up into a large num-
ber of minor groups or sub-genera, the characters of which cannot
be discussed here. Using the term
in its wide sense, /usus ranges from
the Jurassic period to the present day,
attaining its maximum development in
the Eocene and Miocene periods. An
abundant form in the Red Crag (Newer
Pliocene) is the well-known /usus
(Chrysodomus) contrarius, in which the
shell is reversed (fig. 705). This species
has now been found in the living con-
dition. Susus (Chrysodomus) tornatus is
a common fossil in the Glacial deposits
of Canada (fig. 706), and still survives
in the neighbouring seas.

In fisania the shell is generally of
small size, with an elevated spire and a
short canal. The surface is smooth or
spirally striated, and the outer lip is
crenulated. The genus is exclusively pee ee BOE cea
Tertiary and Recent. of Canada:

In fasciolaria the shell is fusiform and
elongated, with smooth, angulated, or tuberculated whorls. The
aperture is elongated, and is prolonged anteriorly into a wide,
generally straight canal. The outer lip is thin, and the columellar
lip is tortuous, with several oblique folds. The genus ranges from
the Chalk to the present day.

In Zurbinella the shell is thick, with a short spire and a long
straight canal, the columella having several transverse folds. Lastly,

796 DIVISIONS OF THE GASTROPODA.

the genera Melongena, fulgur (fig. 707), and Zudicla, form portions
of the old genus Pyrula, and all possess a pear-shaped ventricose
shell, with a short spire and a large body-whorl. Melongena has

Fig. 707. — Fulgur
canaliculatus. Mio-
cene.

a short wide canal and nodose or spinose
whorls, and is exclusively Tertiary and Recent.
Fulgur and Tudicla, on the other hand, have a
long straight canal; and both genera have recent
representatives, the former commencing in the
Miocene, and the latter in the Cretaceous de-
posits.

FaMILy 45. Muricip#.—In this family the
shell has a moderately high spire, and the sur-
face is adorned with foliaceous expansions, spines,
or well-marked varices. The aperture is round
or oval, entire posteriorly, and prolonged an-
teriorly into a straight or slightly oblique canal,
which is generally partially closed in. The
members of this family are all marine, and
with the exception of a few Cretaceous forms,

they are confined to the Tertiary and Recent periods.
In the genus JZurex (fig. 708) the shell is sometimes elongated,
sometimes ventricose, and the surface is adorned with varices in the

form of longitudinal ridges or
rows of spines. The aperture is
rounded, and the canal is usually
greatly prolonged, and is always
partially closed in. ‘Taken in its
wide sense, the genus Murex
ranges from the Chalk to the pre-
sent day, a large number of spe-
cies having been obtained from
the Tertiary rocks. In the nearly
related genus Zyphis (fig. 709)
there are tubular spines between
the varices, and the last of these
lodges the posterior siphon,
while the canal is completely
closed in. The species of Z)-
phis range from the Chalk to

Fig. 708.— deiwickia Nilecene: .
en7ee ee a Mipeene>. texthe present day. Lastly, in the

genus Z7vophon the shell is fusi-

form, with numerous narrow varices, the canal being open and

slightly bent to one side. The genus is Tertiary and Recent.
FAMILY 46. VoLuTip#.—In this family the shell is turreted or

convolute, with a shining, often enamelled, surface, and a large body-

Sirf tel SO

PROSOBRANCHIATA. 797

whorl. The aperture is notched in front or produced into a short
canal, and the columella is ob-
liquely plaited. There is usu-
ally no operculum, the foot is
very large, and the mantle is
often reflected over the shell.
The living members of the
Volutide are chiefly inhabi-
tants of warm seas, and are
often remarkable for their
briluant colours. The family
does not appear to have exist-

ed till towards the later portion MS ee nd es

of the Cretaceous period; but

it is abundantly represented in the Tertiaries, and attains its maxi-
mum in existing seas. The most important genera are Voluta, Vol-
utomitra, Mitra, and Marginella.

The true Volutes form the genus Voluta
(fig. 710), characterised by the short spire,
large, deeply-notched aperture, and columella
with several plaits. A large number of recent,
and still more numerous fossil, forms of Voluta
are known, the earliest types appearing in the
Cretaceous rocks. The genus has_ been
divided into a number of sub-genera, one of
the most important of which is Volutilithes,
represented by numerous forms in the Creta-
ceous and older Tertiary deposits.

Mitra, Volutomitra, and Turricula, are
hardly distinguishable as fossils, all of them
possessing a spindle-shaped shell, with a long
spire and a small aperture, an anterior notch
or short canal being present, and the colu-
mella being obliquely plaited. The typical
Mitre have the outer lip thickened and
smooth within, and are characteristic of the
Tertiary and Recent periods. In Zurricula
the outer lip is striated internally, and the
surface is transversely ribbed. Forms of
this type range from the Cretaceous rocks
to the present day. In Volutomitra (Ter-
tiary and Recent) the outer lip is thin and
simple.

In Marginella, lastly, the shell is smooth,
with a short or concealed spire; and the aperture is truncated

SPRATERABEY NN

Fig. 710.—Voluta elongata.
. Chalk.

7098 DIVISIONS OF THE GASTROPODA.
in front, with a wide notch, a plaited columella, and a thickened
outer lip. The genus is Tertiary and Recent.

Famity 47. Harpip®.—The type of this family is the genus
Ffarpa, in which the shell is ventricose, with a short spire and a
large body-whorl ; the whorls are convex and adorned with transverse
ribs, and the aperture is large and notched in front. The genus
comprises marine types, and is confined to the Tertiary and Recent
periods.

FamILy 48. Oxtvip#.—In this family the shell is elongated and
solid, with a narrow aperture, a sharp smooth outer lip, and a callous
columellar lip. ‘The members of this family are marine, and are
essentially inhabitants of warm seas.

The ‘ Olives” (OZva) and “ Rice-shells ” (OZvel/a) are character-
ised by their cylindrical polished
shell (fig. 711, A), with a short spire,
a long narrow aperture, notched
in front, and an obliquely striated
columella. The living Olives are
tropical and subtropical in their
distribution. A single species of
Olivella has been detected in the
Cretaceous rocks of California,
but with this exception, the Olives

Fo OL at Moe eo wholly Tertiary and Recent.

B, Ancillaria glandina, Kocene. The genus Ancllaria (fig. 711,

B) is nearly related to Ova, but

the spire is produced, and is covered with shining enamel. Species

of Ancillaria occur in the Upper Cretaceous rocks, but the genus is
mainly Tertiary and Recent.

FAMILY 49. CANCELLARID#.—The type of this family is the
genus Cancellaria, in which the shell is oval or turreted, with a large
body-whorl ; and the aperture notched or canaliculated in front. The
columella is obliquely plaited, and the surface is cancellated. The
genus ranges from the Chalk to the present day.

FamMILy 50. Conrp#.—lIn this family the shell is inversely coni-
cal, with a very short spire and an elongated body-whorl. The
aperture is long and narrow, notched in front, the columellar lip
not plaited, and the outer lip smooth and often notched at or
near the suture. The members of this family are all marine, and
they are principally Tertiary and Recent, the oldest types being
Cretaceous.

The principal genus of this family is Conus itself, using this
name in a comprehensive sense. The ‘‘Cones” are distinguished
by their short spire and regularly conical shell (fig. 712). Very
numerous recent species of Cozuws are known, and also a consider-

PROSOBRANCHIATA. 799

able number of fossil forms, the earliest representatives of the genus
appearing in the Middle Cretaceous rocks. The genus Conordis, of
the Eocene and Oligocene, nearly resembles Conus, but the spire
is elevated and pointed, the shell thus becoming biconical.

FAMILY 51. PLEUROTOMID&.—In this family the shell (fig. 713)
is spindle-shaped, with an elevated spire and an elongated aper-
ture, produced in front into a straight canal. The outer lip has

Fig. 712.—Conus deperditus. Fig. 713.—Pleurotoma
Eocene. rostrata. Eocene.

a slit or sinus posteriorly, near the suture. The principal, or
sole, genus comprised in this family is Pleurotoma itself, which
attained an enormous development in the Tertiary period, and is
still very largely represented. A few forms of Pleurotoma are
known to occur in the Cretaceous rocks ; but, according to Zittel,
more than nine hundred Tertiary species are known, while over six
hundred and fifty recent species exist. The genus Plewrotoma has
been divided by conchologists into a number of subordinate groups,
which are sometimes regarded as subgenera, sometimes as inde-
pendent genera.

FAMILY 52. TEREBRIDA.—This family comprises only the genus
Terebra, in which the shell is many-whorled and turreted, and
the body-whorl is of small size. The aperture is small, and there
is a short canal or notch in front; while the outer lip is thin and
sharp. The living species of Zevebva inhabit warm seas; and the
oldest fossil forms appear in the Eocene Tertiary.

8CO

CHAE Pik SOOCrS

DIVISTONS OF GASTROPODA—continued.

BRANCHIOGASTROPODA — continued.

ORDER IJ. OPISTHOBRANCHIATA.

THE Opisthobranchiate Gastropods are distinguished by the fact
that the branchize are situated behind the heart, and the auricle is
behind the ventricle of the heart. ‘The gills are not usually con-
tained in a special branchial chamber, and are commonly more or
less exposed to view. The shell. is wanting or present, being in the
latter case often rudimentary. The sexes are united in the same
individual.

The Opzsthobranchiata, or “‘ Sea-slugs,” may be divided into two
sections, the Zecttbranchiata and Nudibranchiata, according as the
branchize are protected or are uncovered. In the Nudibranchiate
forms, the branchize, when differentiated, are placed externally on
the back or sides of the body, and the animal, in the adult condi-
tion, is destitute of a shell. Owing to their want of hard structures,
no traces of the Nudibranchs have ever been detected in the fossil
condition. On the other hand, in the Tectibranchiate forms, the
mantle more or less extensively covers the gills, and very generally
secretes a shell, which may be so greatly developed as to entirely
enclose the animal when withdrawn within it. Owing to their pos-
session of a shell, the majority of the families of the Tectibranchs
are known to occur in the fossil state, the earliest forms appearing
in the Carboniferous rocks. The number of fossil Tectibranchiates
is, however, very limited as compared with that of the Prosobranchi-
ate Gastropods, the following four families being those which have
yielded fossil representatives :

FamiILy 1. ACTHONID# (TORNATELLID#).— In this family the
shell is spiral or convoluted; the aperture is long and narrow,
rounded or sometimes channelled in front; and the columella is

OPISTHOBRANCHIATA. Sol

generally plaited. The living examples of this family are mostly
small and thin-shelled, but some of the fossil forms are of consider-
able size and are thick-shelled. The family attains its maximum in
the Secondary period.

In the genus Acteon (Tornatella) the shell is ovate, with a well-
marked spire, the outer lip thin, and the columella with one or more
strong folds. The genus ranges
from the Trias to the present day.
In Acteonina, ranging from the
Carboniferous Limestone to the
present day, the shell is elongated,
and the columellar lip is without
folds. In Acteonella the shell is
ventricose, with a very large body-
whorl, and the columella shows
three strong oblique folds in front. This genus is characteristic of
the Middle and Upper Cretaceous deposits, having a remarkably
wide range in space, and being sometimes represented by very
numerous individuals in particular zones.

In the genus C7zu/ia (fig. 714) the shell is globular, with a small
spire ; the outer lip is reflected and crenulated interiorly ; and the
columella exhibits toothlike folds. ‘The genus is exclusively con-
fined to the Cretaceous rocks. In Cydindrites, again, the shell is
cylindrical, and smooth, with an elongated aperture and a fold on
the columella. The genus ranges from the Trias to the Cretaceous
rocks.

Lastly, the genus Azngicula (fig. 715) is now
usually placed in this family. The shell in this
genus is ventricose, with a small spire, the colum-
ella callous and deeply plaited, and the outer lip Fig. 715.—Rngicula
thickened and reflected. The earliest forms of (hoes Whey
Ringicula appear in the Cretaceous rocks, but
the genus attains its maximum in the later Tertiaries and at the
present day.

Family 2. BuLLID#&.—In this family the shell is convoluted and
thin, with a sharp outer lip and an elongated
aperture. The spire is small or concealed,
and the shell is often more or less complete-
ly invested by the soft parts of the animal.
A large number of fossil forms of this family,
beginning in the Trias, are known, and the
group has attained its maximum at the pres-
ent day. The three principal genera are Bulla, Scaphander, and
Cylichna.

The genus ula (fig. 716) comprises the so-called ‘ Bubble-

VOL. I. 3 E

Fig. 714.—Cinulia avellana. Chalk.

Fig. 716.— Bulla supra-
jurensis. Middle Oolites.

802 DIVISIONS OF THE GASTROPODA.

shells,” in which the shell is ventricose, with a very large body-
whorl and a deeply sunk spire. The fossil types are principally
found in the Tertiary deposits. The Recent and Tertiary genus
Scaphander is closely related to Sulla. Lastly, in Cylchna the
shell is solid, and cylindrical in form, with a narrow aperture and a
thickened columella. The species of this genus are numerous, and
range from the Trias to the present day.

FaMILy 3. ApLysiaD@.—In this family there is a thin horny
shell, which is concealed by the reflection of the mantle over the
back and sides of the animal. Two fossil species of ApZysza are
stated to occur in the Pliocene deposits of Sicily.

FAMILY 4. PLEUROBRANCHID&.—In this family the shell is
limpet-like, or concealed, or may be wanting. The genus Umbrella
appears to be represented in the Pliocene deposits, and dubious
Secondary forms of the same have also been described.

ORDER III. HETEROPODA.

The Gastropods included in the order of the Heferopoda or
Nucleobranchiata differ from the typical members of the class in
being organised to lead an existence in the open ocean, locomotion
being effected by a fin-like tail, or by a fan-shaped verticallyflattened
ventral fin. They are found swimming at or near the surface of the
ocean ; and the body may be completely protected by a shell, within
which the animal can retire, and which can be closed by an oper-

si ZF i

Fig. 717. eRe Carinaria cymbium. p, Proboscis; ¢, Tentacles; 6, Branchiz ;
Shell; 4 Foot; d, Disc. (After Woodward.)

culum. In other cases, as in Cavinaria (fig. 717), the body is
large, and there is only a small shell protecting the gills and heart.
In other cases, again, the shell is completely wanting. The order
is divided into the two families of the /7voWde and Atlantide, both
of which comprise transparent delicate animals, which are either
wholly naked or possess a shell of extreme tenuity and fragility.

PTEROPODA. 803

The members of the /ivofde are either shell-less, or possess a
small hyaline shell, placed on the back, protecting the gills. The
only member of this family which is known to be certainly repre-
sented in the fossil state is the existing genus Carinaria (fig. 717),
a single species of which has been found in deposits of Miocene
age.

In the Avantide the animal is furnished with a well-developed
but fragile shell, completely enclosing the body. In Adanfa itself
the shell is rolled into a flat spiral, and the body-whorl is keeled,
and exhibits a dorsal slit at the aperture, thus resembling the shell
of the Lellerophontide. A single species of At/an¢a has been found
in the Tertiary deposits of San Domingo. Owing to the close re-
semblance of the shell of e//erophon and its allies in external form
to that of At/anfa, the former have been commonly regarded as
Heteropods. The comparative thickness and solidity of the shell
of the Lellerophontide, however, and the common association of the
forms of this family with fossils of an unquestionable shallow-water
type, forbid the reference of these singular Palzeozoic Gastropods
to the present order.

ORDER IV. PTEROPODA.

The Pteropods or ‘‘ Winged Snails” are pelagic Molluscs, found
swimming near the surface in the open sea, the living forms being
all of small size. They have no distinctly differentiated head, and
the mouth is placed anteriorly in the centre of the fore-part of the
foot, which is rudimentary. The lateral parts of the foot (‘ epi-
podia”) are, however, developed into a pair of wing-like fins (fig.
718), by means of which the animal swims actively. The posterior
part of the foot (‘‘metapodium”) is
rudimentary, but in some cases may
develop an operculum. In some
groups (Gymunosomata) the mantle is
rudimentary, and the adult is not pro-
vided with a shell. In other groups
(Thecosomata) the mantle is well de-
veloped, and secretes a shell. In both
sections of the order the embryo is as
furnished with a shell, but the ‘aia Za ane ne ee ake ihe
shell is soon lost in the Gymmnosomata ; BUD. attached! to the sides of the
whereas in the great majority of the
Thecosomata, the adult develops a secondary and permanent shell,
of which the embryonic shell usually forms the initial portion. The
shell of the Zhecosomata generally is calcareous in composition, and
in all the living forms is very delicate in texture. The so-called

804 _. DIVISIONS OF THE GASTROPODA.

“shell” of Cymbulia is of a cartilaginous consistence, but it does
not correspond with the shell of the other Thecosomatous Pteropods
in its nature or origin. In the majority of the shell-bearing Ptero-
pods the shell is symmetrical, but in the Zzmacinide it is coiled into
a spiral. The Pteropods are all hermaphrodite, and the young pass
through a metamorphosis.

The VPteropoda have been very generally regarded as a distinct
class of the Mollusca; but the most recent investigations, more
especially those of Dr Pelseneer, prove that in the essential details
of their organisation they do not differ materially from the Gastvro-
poda, of which class they should be considered as a division or
order. The Pteropods fall naturally into the two sections of the
Gymnosomata and the Zhecosomata, the former devoid of any shell
in the adult condition, while the latter (with the exception of the
aberrant genus Cymbulia) possess an external calcareous shell.
Owing to their having no hard parts capable of preservation in the
fossil condition, the Gymnosomatous Pteropods have left behind
them no traces of their past existence, and therefore require no
further consideration here. On the other hand, the Thecosomatous
Pteropods are known to occur as fossils, though opinions differ as
to the true nature of many of the organisms which have been re-
ferred here.

As regards their distribution in time, the Tertiary rocks have
yielded the remains of indubitable Pteropods, which differ in no
respects from existing forms, and are, in fact, largely referable to
existing genera. ‘The whole series of the Secondary rocks has, on
the other hand, yielded no remains of organisms which can be
asserted to be unequivocal Pteropods. It is not, indeed, till we
reach the Devonian and Silurian deposits that we meet with fossils
which in all essential respects agree with the living Pteropods, and
which appear to belong to such existing genera as S¢ylola (Creseis).
It is true that these ancient representatives of Szy/zo/a have had their
‘claim to be regarded as Pteropods strongly disputed, but it will be
pointed out hereafter that there is at present no sufficient ground
for denying their Pteropodal nature. The case, however, is different
with the three remarkable groups of fossils typified respectively by
the genera Zentaculites, Hyolithes, and Conularia, the age of which
is exclusively or mainly Paleozoic. These ancient types differ in
many respects from the typical Pteropods, and their true nature
and position must be regarded in the meanwhile as more or less
open to question. If these aberrant and problematical genera be
provisionally included among the Thecosomatous Pteropods, the
following are the principal families included in this division of the
order :—

FAMILY 1. LIMACINID#&.—lIn this family the shell is twisted into

PTEROPODA. | 805

a left-handed spiral, and a spiral operculum is present. The anus is
on the right side, and the pallial cavity is dorsal in position. It is
not certain that any fossil forms of this family have been detected,
but some minute shells from the Eocene, Miocene, and Pliocene
deposits have been referred with considerable probability to the
existing genus Limacina (Spirals).

FaMILy 2. Cavo.iniip#.—In this family the shell is bilaterally
symmetrical and is not rolled up into a spiral. The anus is on the
left side, and the pallial cavity is ventral. The shell has a variable
form, but is essentially a hollow cone, which may be flattened dorso-
ventrally or may be circular in section. The initial portion of the
shell is generally distinct from the rest, and represents the larval
shell (Pelseneer).

The types which have been described under the names C7vesezs,
flyalocylix, Clio (sensu restricto), and Styfola, are included by Dr
Pelseneer under the common generic name of Cio (= Cleodora).
In all these forms the shell (fig. 722, c) is a conical tube, sometimes
circular in outline, sometimes oval, sometimes laterally keeled, the
apex of the shell being pointed, or exhibiting a bulbiform enlarge-
ment due to the presence of a distinctly defined embryonic shell.
Unquestionable remains of this group of Pteropods are found in the
Miocene and Pliocene deposits.

In the Silurian and Devonian rocks of both the Old and New
Worlds there occur minute conical calcareous tubes, which have been
generally referred to Stylola or Cresets.
As the type of these may be taken StyZola
(Creseis) fissurella of the Devonian rocks of
North America. In this remarkable form
(fig. 719) the shell is a very delicate cal-
careous tube, of a conical form, circular
in section, and without internal partitions,
either longitudinal or transverse, the aver-
age length of the tubes being from one to
three millimetres. The apex of the tube A B C
is commonly slightly bulbous (fig. 719, A), —_Fig. 719.—a and_B, Specimens
and is fe. aiaktd off o a ‘ ey See eee
emeamier irom the rest of the shell. The (Hmilton Group) of North

z ; i America, enlarged about six
surface is without annulations, and may be_ times, showing the embryonic
- shell at the apex; c, Apical por-
smooth, or marked by fine transverse strig, tion of the tube of Tentaculites
: ca: ‘listriatus, from th
sometimes with longitudinal striz as well guna GHEEee 16 eae
Bae gio, ce). Scyio/a pssurcila is exceed- <™>ryenic shell: (After Hall)
ingly abundant in parts of the Devonian
rocks of North America, and sometimes gives mse by the ac-
cumulation of its shells to thin bands of limestone (fig. 720),

which may have a considerable geographical range. Dr Pelseneer

"E
22

806 DIVISIONS OF THE GASTROPODA.

denies that the so-called ‘‘ Styliole” of the Silurian and Devonian
rocks can be referred to the Pzeropoda on the grounds of their great
size, the absence of an embryonic
shell, and the fact that no existing
species of C/o has the shell longi-
tudinally striated. The first two of
these objections, however, do not
apply to Stylola fissurella and its
allies, since the tube is smaller than
that of some of the existing species
of CZzo, and an embryonic shell is
present; while the third objection
would appear to be of anything but
a conclusive character. It is cer-
tainly remarkable that, admitting the
Pteropodal nature of Stylola fissur-
ella, no traces of forms of the same
genus should have hitherto been met
with in the later Palzeozoic and in
Fig. 720.—Thin section of limestone the Secondary deposits, and that the
from the Devonian rocks of Canandaigua, : ‘
North America, composed almost entirely Q{€NUS 1S not known to be again
ireed twenty timer Odcaniy ” “represented. till the Miocene apenod

is reached. Paleontology, however,
is rich in examples of gaps of this kind, and little importance can
be attached to a seeming hiatus, which may any day be partially
filled up.

Of the remaining genera of the Cavoliniide, Cuvierta has a straight
conical shell, the hinder pointed half of which is generally caducous in
the adult. The genus is represented by existing species and by late
Tertiary types. Lastly, in Cavo-
linia (Hyalea) the shell (fig. 721)
is globular, the dorsal plate com-
paratively flat, and prolonged into
a hood, the ventral plate bulging
Fig. 721.—Cavolinia (Hyalea) Orbignyana. and convex, the aperture con-

tee ee tracted, with a lateral slit on each

side, and the hinder end with one

to three spines. ‘The genus is represented by Miocene and Pliocene
forms as well as by existing species.

FAMILY 3. CYMBULIID#.—This family includes only the recent
genus Cymbulia, which differs from all the other Thecosomatous
Pteropods in the possession of a straight, bilaterally symmetrical,
cartilaginous “‘ pseudoconch,” which is formed by the thickening of
the integument, and is not homologous with the shell of the ordinary
Pteropods. As the ‘‘ shell” of Cyméufia is not capable of preserva-

PTEROPODA. 807,

tion in the fossil state, no record of the past existence of the genus
can be obtained.

Famity 4. Hyo.irHip&.—With this family we enter upon the
consideration of a series of remarkable Paleozoic fossils, which
have been generally referred to the Prerofoda, though their true
affinities cannot be considered as certainly established. The type
of this family is the genus /Zyolithes (= Theca and Pugiunculus),
which has been generally regarded as allied to the recent Clo or
Styliola (fig. 722, c), though the dimensions of the shell much
exceed those of the ordinary species of the latter, and there are
other differences as well. The shell (fig. 722, D, Fr, H) in Ayolithes
is bayonet-shaped or conical, usually straight, but sometimes curved,

Fig. 722.—a, Pterotheca corrugata—Ordovician (after Salter); 8, Pterotheca transversa—
Ordovician (after Salter); c, Styliola (Clio) depressa—Miocene; v, Hyolithes (Theca) oper-
culatus; and E, its operculum— Upper Cambrian (after Salter); F, Hyolithes aratus—Upper -
Cambrian ; and G, Cross-section of the same (after Salter); H, Hyolithes acutus—Silurian (after
Eichwald).

of thin texture, transversely striated or smooth, sometimes with
marginal ribs, but without lateral appendages. The mouth of the
shell is trigonal, and in some forms, at any rate, is provided with
an operculum (fig. 722, E), or occasionally furnished with curved
lateral appendages. The length of the shell varies, but is com-
monly from an inch to an inch and a half. The species of
ffyolithes are most abundant in the Upper Cambrian and Ordovi-
cian rocks ; but there are various Silurian and Devonian forms, and
the genus is recorded as occurring in both the Carboniferous and
the Permian rocks. /Pverotheca (fig. 722, A and B), of the Ordo-
vician, in many respects resembles /yolthes; but the median
dagger-shaped shell is bordered by lateral concentrically-striated
expansions or alations, thus coming to superficially resemble the
carapace of certain of the Phyllopods.

The Devonian genus Co/eofrion has a cylindrical and conical

808 DIVISIONS OF THE GASTROPODA.

shell, the exterior of which is marked with chevron-shaped strie.
Possibly allied to the preceding types, but of wholly uncertain
affinities, are the genera Yemziceras and Salterefla. In the first of
these are conical elongated shells, of circular section, in which the
walls are thickened by the deposition of concentric calcareous
lamelle, till only a small tubular space is left in the centre. The
genus 1s Ordovician. Sadltere/la, of the Upper Cambrian and Ordo-
vician rocks, comprises conical tubes, resembling the preceding in
shape, but consisting of several hollow cones placed one within the
other.

FAMILY 5. CONULARIIDH.—This family includes only the re-
markable genus Conularia (fig. 723), the true relationships of
which have not been clearly established, though the genus is
usually placed among the Preropoda. ‘The shell in Conularia is
very thin, and is pyramidal in shape, the transverse section being
rhomboidal or four-sided. The apex is often deciduous, and the
internal cavity may be partitioned off near the apex by one or more
transverse plates. ‘The aperture of the shell is contracted, and is
partially closed by tongue-like prolongations
from its corners. Each of the four faces of
the shell may be provided along its entire
length with an internal median longitudinal
fold, sometimes with two such, but these may
be wanting or rudimentary. Externally, each
face of the shell is divided into two equal
halves by a longitudinal groove, corresponding
with the internal fold above mentioned ; and
the surface is ornamented with transverse,
smooth, or tuberculated ridges, which are
angulated in the middle line of each face, so
as to form a series of obtuse angles, the apices
| ak, . of which point towards the aperture.
es Fig. 723.--Conularia or- 3 : ; :
| mata. Devonian. The genus Conu/aria attains its maximum
} in the Ordovician and Silurian rocks, some
| of these early types attaining a length of nearly a foot, with a

breadth of more than an inch. The Devonian and Carboniferous
rocks have yielded a few species, and two forms occur in the Per-
i} : mian, while a single species has been detected in the Trias, and
i another has been recorded from the Lias.
| 7 FamiLy 6. TENTACULITIDZ.—This family comprises only the
i genus Zentaculites, in which the shell (fig. 724) is comparatively

thick and solid, and has the form of a straight, elongated, conical
tube, from half a centimetre up to three centimetres in length, which
if tapers to a closed apex at one end, and expands towards the other
| to a circular aperture. The tube is always circular in outline, and

PTEROPODA. syele)

the apex is often partially filled up with a secondary calcareous
deposit, or may be partitioned off by one or more curved transverse
plates (fig. 725, A). The initial portion of the shell may be smooth
and without annulations, and may be simply pointed. In other
cases, the apex is distinctly bulbiform (fig. 719, Cc),
its starting-point being a dilated chamber, which
appears in no respect to differ from the ‘‘ em-
bryonic shell” of C/o and other Pteropods. The
whole of the tube, except the initial portion, is
annulated by abruptly elevated rings, which be-
come more remote as the aperture is approached ;
and the surface between the annulations is marked
by fine encircling striz, sometimes accompanied
by longitudinal strize as well.

As regards its minute structure, thin sections Fig. 724.—Tenta-
show that the tube of Zentaculites is composed (“ies ernatus, St
of two distinct layers of a different nature (fig.

725, B and c). The outer layer is very dense, and is thickened
at intervals so as to form the annulations which are so character-
istic of the genus. The inner layer is composed of transparent
calcite, traversed by parallel lamelle of a dark colour, which are
approximately parallel to the surface of the tube. Both layers

Fig. 725.—Minute structure of Textaculites attenuatus, from the Devonian rocks (Hamilton
Group) of Canada. a, Section of the apex of a tube, showing curved transverse partitions ;
B, Transverse section of the tube (the oval form of the tube is the result of pressure); c, Ver-
tical section, taken through the middle of the tube; pD, Vertical section traversing the wall of the
tube, and ite its peculiar tubulated structure. The figures are enlarged about twenty times.
(Original.

are more or less extensively penetrated by a system of exceedingly
minute tubuli (fig. 725, D), the direction of which is approximately
at right angles to the surface.

The genus Zeéztaculites ranges from the Ordovician to the De-
vonian, occurring for the most part in limestones, and being often
present in vast numbers in particular beds. In no case is the shell
attached to any foreign body.

The affinities of Zentaculites cannot, in the present state of our
knowledge, be determined with absolute certainty. The compara-

S10 DIVISIONS OF THE GASTROPODA.

tive thickness and solidity of the shell, together with its remarkable
minute structure, must be considered as points which militate against
a reference of the genus to the Pteropods. On the other hand, its
free habit of existence, its general form, its mode of occurrence, and
its occasional possession of a distinct initial chamber or embryonic
shell would support the view that it belongs to the Péeropoda. ‘The
occasional presence of curved internal septa is a point of small
weight, one way or the other, since such transverse partitions are
not absolutely unknown in recent Pteropods (Cuwvieria). Still less
stress can be laid upon the argument that Zeztaculites can hardly be
regarded as a Pteropod, seeing that the normal forms of the Pzero-
poda do not make their appearance till the Tertiary rocks are
reached. Any weight that might be supposed to be carried by such
an argument is counterbalanced by the fact that in Styliola jissurella
and its allies we have Palzeozoic forms which have not been shown to
differ materially from existing types of Pteropods. By some palez-
ontologists Zentaculites is regarded as belonging to the Tubicolar
Annelides ; and casts of the shell of Zenzaculites are undoubtedly
very similar to casts of the tube of Cornulites. ‘The microscopic
structure of the tube of Zentaculites is, however, widely different
from that of Cornulites, while the tube shows no signs of having
been at any time of life attached to any foreign body. It is, how-
ever, quite possible that some of the forms which have been referred
to Zentaculites are really Annelidan in nature. Thus, Hall has
pointed out that all the forms from the Ordovician rocks of North
America which have been placed in Zentaculites are curved and are
longitudinally striated ; and he regards these, therefore, as probably
truly belonging to Cornulites or to some related Annelidan genus.

Sup-Ciass II. PULMOGASTROPODA.

The Pulmonate Gastropods are essentially distinguished by the
fact that the breathing-organ is a pulmonary chamber, formed by an
inflection of the mantle, to which air is directly admitted by an ex-
ternal aperture ; while the sexes are united in the same individual.

The most typical members of this division of Gastropods, such as
the Land-snails and Slugs, are terrestrial in habit. Others, like the
Limneide, inhabit fresh waters, and either come to the surface to
obtain air, or, in some cases, have the power of using the lung-
chamber as an organ of aquatic respiration. A few forms only
(Stphonariide, Gadiniide) are inhabitants of salt water.

The condition of the shell varies much, a few forms (e.g., Ox-
cidium) being wholly without a shell. In the Slugs, a shell is
present, but is of small size, and is concealed within the mantle.
In the ordinary Snails, again, and in the Pond-snails, there is a well-

PULMOGASTROPODA. SII

developed external shell, within which the animal can entirely with-
draw itself.

As regards their adstribution in time, the completely shell-less
forms are necessarily altogether unknown in the fossil condition,
and the forms with a rudimentary and concealed shell are only
known in the latest Tertiary deposits. The abundance of the or-
dinary shell-bearing forms as fossils depends mainly on the habits of
the animal. As the preservation of an ancient land-surface in the
crust of the earth is a matter of rare occurrence, the strictly ter-
restrial Pulmonates are not largely represented in the fossil state,
their remains, in fact, occurring principally in lacustrine or fluviatile
deposits intermingled with the shells of fresh-water types of Pul-
monates. These latter are found in moderate numbers in fresh-
water deposits of Secondary and Tertiary age. The oldest known
types of the Pulmonate Gastropods have been found in the Carbon-
iferous rocks.

The sub-class Pulmogastropoda may be divided into the two orders
of the Stylommatophora and the Basommatophora ; but only a few of
the more important families composing these can be noticed here.

OrDER I. STYLOMMATOPHORA.

The Pulmonates included in this order have the eyes placed at
the extremities of long feelers, which are retractile and capable of
invagination. ‘The shell may be rudimentary or even absent, but
is usually well developed. The following are, from a palzonto-
logical point of view, the most important families included in this
order :—

FAMILY 1. TESTACELLID&.— This family includes carnivorous
Pulmonates, with a spiral shell of very variable size. In TZestacella
itself, the animal is slug-like, and there is a minute ear-shaped shell
placed at the hinder end of the body. Fossil forms of this genus
have been found in the later Tertiary deposits.

In Glandina, on the other hand, there is a well-developed spiral
shell, within which the body of the animal can be withdrawn. The
recent types of this genus inhabit warm regions, and the fossil forms
date from the Upper Cretaceous period.

FAMILy 2. Limacip#.—In this family are comprised the ‘‘ Slugs,”
in which there is a minute rudimentary shell concealed within the
mantle. Species of Zzmax have been recognised as occurring in the
late Tertiary and Quaternary deposits.

FAMILY 3. HELIcID#.—This family includes the ordinary ‘‘ Land-
snails,” in which there is a well-developed shell, capable of contain-
ing the entire animal. A large number of fossil representatives of
this family are known, chiefly belonging to the Tertiary period, but

812 DIVISIONS OF THE GASTROPODA.

occurring also in deposits of Secondary age, and even in rocks as
old as the Carboniferous formation. If Dazwsonella be regarded as
a member of the Helicnide (see p. 778), the oldest representatives
of the Helicide are the Zonttes (Conulus) priscus and the Pupa (Den-
dropupa) vetusta of the Coal-measures of North America, both of
which were first discovered and described by Sir William Dawson. —
In the genus /Ze/7x are the ordinary Land-snails, of which about
two thousand living species are known, belonging to a large number
of subgeneric groups. The shell in He/zx is very variable in shape,
sometimes conical, sometimes depressed, and sometimes discoidal ;
the aperture being transverse, crescentic or rounded in shape, and
the columella being perforated or imperforate. The most ancient
of the typical /e/ices appear in the Eocene rocks, and a large num-
ber of Tertiary species have been recognised.
In Zonites the shell is thin, usually hyaline, in the form of a

Fig. 726.—Zonttes (Conulus) priscus (after Dawson). a, Specimen enlarged twelve diameters ;
6, Sculpture, magnified. Coal-measures, Nova Scotia.

depressed spiral, with a simple and sharp-edged peristome, and
almost always umbilicated. The oldest example of this genus is
the Z. priscus (fig. 726) of the Coal-measures of Nova Scotia. Other
species occur in the later Tertiaries; and the Avcheozonites of the
Oligocene and Miocene deposits is nearly related to Zonztes.

In Bulimus the shell is oval or turreted, the columella is straight,
the aperture is oblong, and the outer lip is expanded and thickened.
Bulimulus includes forms with a shell very similar to that of Bw/-
mus, but with a generally thin lip and an elongated aperture. The
earliest forms of Ludimus appear in the Upper Cretaceous rocks.
In the genus Achatina the shell is like that of Budimus, but the
columella is twisted. No undoubted fossil representatives of this
genus have been recognised.

In the genus C/ausilia the shell is spindle-shaped, and is. coiled
into a left-handed spiral, the aperture being elliptical, and partially
contracted by two folds of the inner ip. The mouth of the shell

PULMOGASTROPODA. 813

is closed when the animal is withdrawn within it by a movable
calcareous plate (“‘clausilium”). A large number of recent species
of Clausilia are known, but the fossil
forms are not numerous, and the
oldest of them appear in the Eocene.

In the genus /xupa the shell is
cylindrical or oblong, with a rounded,
often toothed aperture and a reflected
outer lip. The oldest known type
of this genus is the Pupa (Dendro-
pupa) vetusta of the Coal-measures
of Nova Scotia, discovered by Sir
William Dawson in the hollow trunk
of an erect Sigv//arta. The aperture
in this form (fig. 727) is devoid of
teeth. An allied type is the Pusa
vermilionensis of the Coal-measures
of the United States. With these

exceptions, the fossil Pupe@ are all _ Fig. 727.—Pupa (Dendropupa) vetusta

: (after Dawson). a, Natural size; 4, En-
of Tertiary age. larged ; c, Apex enlarged ; d, Sculpture,

Lastly, in the genus Swccinea the magnified. Coal-measures.
shell is thin and ovate, with a small
spire and a large body-whorl, the aperture large and obliquely
oval, and the outer lip thin. The ‘‘ Amber-snails” live in moist
places on land, and the known fossil species are confined to the
Tertiary rocks. S. oblonga and S. putris are very common in the
Loess.

ORDER II. BASOMMATOPHORA.

In this order of Pulmonates the eyes are placed at the base of
two feelers, which are contractile, but are not capable of invagina-
tion. Of the families of this order, the Auriculide and Limnetde
are inhabitants of fresh waters, or are amphibious, or in other cases
live in moist places on land, while the aberrant groups of the
Siphonaride and Gadinitde are marine in habit.

FAMILY 1. AURICULIDZ.—In this family the shell is spiral, with
a horny epidermis; the aperture is elongated, generally with a
toothed outer lip; and the columella is folded. ‘The members of
this family inhabit salt-marshes and places overflowed by the sea.
The principal genus is Auvicula itself, which ranges from the Upper
Jurassic rocks to the present day, but the fossil forms are of com-
paratively little importance.

FAMILy 2. LiIMN#ID#.—In this family the shell is well developed,
thin and horn-coloured, and of very variable shape. ‘The aperture
is simple, and the outer lip is sharp. The ZLzmncede are all in-

814 DIVISIONS OF THE GASTROPODA.

habitants of fresh water, and they are found in fluviatile and lacus-
trine deposits. ‘They commence in the Jurassic period, members
of this family having been described from the
Lias (?) and from the Purbeck beds (Upper Jur-
assic). It is not, however, until we reach the
base of the Cretaceous system (Weald Clay) that
these forms appear in any abundance.

The genus Limnea (fig. 728) includes the so-
called ‘‘ Pond-snails,” characterised by their thin,
spiral, elongated shells, with a large body-whorl
and an obliquely-twisted columella. The species
of this genus commence in the Upper Jurassic
(Purbeck Beds), and they are abundantly repre-
sented in the Tertiary series.

In the genus Pysa (fig. 729) the shell is left-handed (“ sinistral ”),
ovate, thin, and polished, with the aperture rounded in front. Wal-
cott has described a species of Physa as occurring in the Lower
Carboniferous rocks of Nevada. With this exception, the oldest
species of the genus occur in the Purbeck beds (Upper Jurassic)
and Wealden (Lower Cretaceous). Most of the fossil species, how-
ever, belong to the Tertiary period, and the genus attains its maxi-
mum at the present day.

The genus Planorbis (fig. 730, A and B) comprises a number of
well-known fresh-water shells, in which the shell is discoidal and

Fig. 728.—Limnea
pyramidalis. Eocene.

Fig. 730.—a, Planorbis complanatus, viewed from below
and in front—Pliocene and Recent; B, Planorbis discus—
’ Eocene—viewed from above and in front, reduced one-half ;
Fig. 729.—Physa colum- c, Ancylus Matheronit— Tertiary—viewed sideways and

naris. Kocene. from above, the latter figure enlarged.

many-whorled, the aperture crescentic, and the lip thin. The fossil
species of this genus date from the Lias (?), but are not plentiful
except in the Tertiary deposits, from which numerous forms have
been obtained.

Lastly, the genus Axcylus (fig. 730, C) comprises the so-called
‘River-limpets,” distinguished by their thin limpet-shaped shell, the
apex of which is approximated to the hinder margin. The fossil
species are few in number, and the earliest forms appear in the
Miocene deposits.

PULMOGASTROPODA. S15

FAMILY 3. SIPHONARIIDZ.—This family comprises certain marine
Gastropods, of amphibious habits, which agree with the normal
Pulmonates in the possession of a pulmonary chamber. ‘The shell
is limpet-shaped, unsymmetrical, and usually radially nbbed. The
muscular impression in the interior of the shell is interrupted by a
lateral sinus corresponding with the opening of the pulmonary sac.
The type-genus of this family is SzpZonaria itself, the living species
of which are found in tropical seas. The earliest fossil forms appear
in the Eocene deposits, but the shell is with difficulty distinguished
from that of the Paze/iide.

Famity 4. Gapiniip&.—This family comprises marine Pulmo-
nates, which possess a patelliform shell, and differ from the preced-
ing family only as regards the armature of the mouth. No undoubted
fossil forms of the family are known, but Professor von Zittel is
disposed to refer here the genus Va/enctennesta, in which the shell
is like that of a large limpet, but the apex is much incurved, and
an internal sulcus and corresponding superficial fold extend from
the apex to the right margin, and exist in a less developed form on
the left side. This remarkable genus occurs in abundance in the
brackish-water Upper Miocene deposits (‘‘Congeria-beds”) of
south-eastern Europe.

816

CTT ERE ee Ge:
POLYVYPLACOPHORA AND SCAPHOPODA.

Crass III. POLYPLACOPHORA.

Tue class of the Polyplacophora comprises only the family of the
Chitonide, which differs in many important respects from the Gastro-
pods, and presents certain relationships with the Worms. The body
in the Chitonide (fig. 731, A) is elongated and worm-like, bilaterally
symmetrical, with the mouth

t at the anterior end, and the

anus at the hinder extremity
of the body. ‘There is no
differentiated head, nor are
cephalic tentacles develop-
ed. The under sumaceron
the foot forms a creeping
disc ; and the gills are nu-
merous (fig. 731, g), and are
contained in an imperfect
pallial chamber or groove,
between the margins of the

’ foot and the edge of the

Fig. 731.—a, Under surface of a species of Chzton

(after Cuvier): ¢, Fringe of tentacles round the mouth mantle. The upper surface

Oil of Cito seuamosus, reduced onchat Of the bodyisicomanedims

(After S. P. Woodward.) the mantle, which secretes
a “multivalve” shell (fig.

731, B), composed of eight transverse imbricated plates, which suc-

ceed one another from before backwards, and are embedded in the

leathery or fibrous border of the mantle.

The shell of the Chitons (fig. 731, B, and fig. 732) consists of
eight valves placed in a line, the anterior or ‘‘ cephalic” valve and
the posterior or “‘anal” valve invariably differing from the six “ in-
termediate” valves, which are similar to one another. Each of the
intermediate valves is divisible by lines of sculpturing into a central

POLYPLACOPHORA. 817

area (fig. 732, B, m) and two lateral areas (/). The upper or
exposed surface of the valves is spoken of as the ‘‘tegmentum,”
while the “articulamentum” is a peripheral zone which supports
and is partly covered by the \
tegmentum. The shell is en-
tirely surrounded by, and more
or less extensively embedded
mene. “girdle” or ‘“‘zona”
formed by the border of the
mantle, and variously covered
on its upper surface with
scales, spines, or bristles.
The cephalic and the six in-
termediate plates have their
apices at their posterior mar-
gin, but the apex of the anal
plate is usually anterior.

The cephalic valve is usu-

Sis ; Fig. 732.—a, Cephalic valve, B, one of the in-
ally semicircular in shape, and termediate valves, and c, anal valve of Chzton
: : meagnificus, viewed from the dorsal aspect: 72,
its front edge 1S generally Central area of the valve; Z, One of the lateral

areas of the valve; c c, Apophyses or sutural

: : ce ;
prolonged into an insertion- lamine ; 64, Sinus and jugal area. (After Gray.)

plate,” or forward extension

of the “‘articulamentum,” by which it is embedded in the mantle.
The intermediate valves are transverse in shape as a rule, and
their front edges are furnished with forward extensions of the arti-
culamentum, which serve to unite the successive valves, and are
known as the ‘‘ apophyses” or ‘‘sutural laminz” (fig. 732, ¢). Pos-
teriorly the intermediate plates usually possess “‘insertion-plates.”
The anal valve is variable in form and sculpturing, as well as in the
position of its apex, but it has in front a pair of apophyses, separated
by a median sinus (4), and it possesses an insertion-plate posteriorly.
The insertion-plate of the anal valve may be similar in form to that
of the cephalic valve, or may be different from it, and by this char-
acter the Chitons are grouped as ‘“‘regular” or “ irregular.”

The tegmentum of the recent Chitons exhibits two sets of superficial
circular apertures, one set large (“ megalopores ”), the other set of much
smaller size (“micropores”). These apertures lead into corresponding
sets of tubes, large and small, which perforate the shell vertically, and
open below into a plexus of horizontal canals running in the space be-
tween the apposed surfaces of the tegmentum and articulamentum. These
horizontal canals open internally, and lodge processes derived from the
mantle, which send out ramifications into the canals connected with the
““megalopores” and “micropores.” These ramifications finally expand
into differently-sized papilliform bodies (“ megalzsthetes” and “ micres-
thetes”), which appear to be peculiar organs of touch. Further, as shown
by Moseley, a number of the “megalesthetes” are in some cases spe-

wer. T: 208

818 POLYPLACOPHORA AND SCAPHOPODA.

cially modified in structure, and become converted into minute eyes
which are distributed over the exposed surface of the tegmentum.

The Chitons are inhabitants of the sea, and they are of rare
occurrence as fossils, being more abundant in the Paleozoic than
the Mesozoic or Kainozoic deposits. Under the name of Holochiton,
Fischer has united the recent genus Lepfochiton and a number of
Palzeozoic types which have been placed in groups under special
names (felminthochiton, Gryphochiton, &c.) ‘The general characters
of the ‘‘ Holochitons” are the possession of an oval or elongated
shell, in which the ‘insertion-plates” are obsolete or more or less
developed, their margins being in the latter case entire, and showing
neither fissures nor denticulations. ‘Taken as a whole, the Pale-
ozoic Chitons are characterised by the elongated form of the shell,
the narrowness of the valves (fig. 733), the absence or rudimentary

condition of the insertion-plates, and the

a b widely separated sutural laminze. In their
narrow valves and elongated form the
Palzeozoic Chitons resemble the recent
genus Cryptoplax ( = Chitonellus), but the
shell in the latter is formed wholly by the
articulamentum, the valves are more or
less separated, and the insertion-plates
have fissured margins. As regards their
geological distribution, the ‘ Holochi-
tons” range from the Ordovician to the
Permian rocks, but the majority of the
known forms are Carboniferous. Some

Fig. 733.—Holochiton (Grypho- :
chiton) priscus, from the Carbon- of the Carboniferous types, however,

iferous Limestone of Belgium. a,

Four consecutive plates; 4, Anal possibly belong to Cryptoplax ( Chitonel-

late s fi th teri d :
from the interior, (After De 24S). Lhe conical calearcous)yplatesmes

OMICS GoD ISE! ION) LuBELy) the Silurian rocks of Gotland, which

have been described under the name of
Chelodes, are regarded by Lindstrom as referable to the Chztonide.
The plates of Che/odes show remarkable resemblances to those of
the Chitons, but they are altogether peculiar in the fact that not
only are there no insertion-plates, but the sutural laminze are also
wholly unrepresented.

But few representatives of the Polyplacophora have hitherto been
found in the Secondary and Tertiary rocks, and these few appear to
belong to the genus C%z¢on itself, in which the insertion-plates are
well developed and possess fissured margins, those of the cephalic
and anal valves being alike in form.

SCAPHOPODA. 819

Crass IV. SCAPHOPODA.

This class of Moiluscs includes only the single family of the
Dentalitde, the characters of which would assign to it a position in
some respects intermediate between the Lamellibranchs and the
Gastropods. The type of the group is the genus Dentalium, the
animal of which is bilaterally symmetrical, and is enclosed in a con-
tinuous mantle, which secretes a tubular shell, which is open at both
ends. From the large anterior aperture of the shell is protruded the
foot, with a circle of tentacles surrounding the mouth, but there is
no distinct head. ‘The oral tentacles appear to discharge a respi-
ratory function, but there are no specialised branchize, nor is a
definite heart present. The nervous system is of the Molluscan
type; the kidneys are paired; the sexes are distinct; and the
pharynx is furnished with a radula.

The shell in the Dentalizde is in the form of a slightly curved
calcareous tube (fig. 735), of conical form, but not spirally coiled.
The shell is open at both
ends, the anterior aperture
being larger than the pos-
terior, and the latter being
sometimes simple, some-
times crenulated or fissured.
Theconcave side of the tube
corresponds with the dorsal
side of the animal, and the
ventral side is convex. No
operculum is developed.

The Dentalide are all
marine, and live buried in
sand or mud, with the wide
anterior extremity of the
shell downwards. ‘The fos-
sil forms begin at least as
early as the Devonian, and
some Ordovician and Si-

: Fig. 734.—Dentalium vul- Fig. 735.— Den-
lurian types have been re- gare, of the natural size, with talium Mie
the oral tentacles protruded from Miocene. After

corded, though these are the anterior opening of the shell. Deshayes.)

not free from doubt. (After Lacaze- Duthiers.)

In the genus Dentalium
(figs. 734 and 735) the tubular shell is smooth, or longitudinally
striated, or annulated; the anterior aperture is simple and is not
contracted ; and the posterior aperture is typically truncated and
entire. Lz¢alis is hardly separable from Dentalium proper, but there
is a short slit at the posterior aperture on the ventral (convex) side

820 POLYPLACOPHORA AND SCAPHOPODA.

of the tube. The fossil species of Dentalium may be confounded
with the tubes of Tubicolar Annelides, or a reverse mistake to this
may be made. Species of Denzalium have been described from the
Ordovician rocks of Russia by Eichwald, but the nature of these is
not absolutely certain. Undoubted forms of the genus appear in
the Devonian rocks, and a number of Carboniferous species are
known. In the Secondary and Tertiary rocks the genus is well
represented, the later forms being usually more ornate as regards
the characters of the surface than are the older types.

In the genus Szphonodentalium (Gadus) the tubular shell may or
may not be contracted towards its anterior extremity, but is always
attenuated behind ; and the posterior aperture is incised or lobulated.
The surface is smooth or finely striated. The genus ranges from
the Cretaceous rocks to the present day. Lastly, in the Recent
and late Tertiary genus Cadulus, the tube is swollen in its middle,
and both its apertures are entire, the hinder one being crenulated.

Cyaan Ek XE
CHASSO Vi CEPHAL OPODA.

THE members of the class Cephalopoda are bilaterally symmetrical
Molluscs, with a large head, and having the body enclosed in a
muscular mantle. The fore-part of the foot ts split up into eight or
more muscular processes or “arms,” which surround the mouth ; while
the epipodia are well developed, and give rise, by apposition or fuston,
to a muscular tube (“funnel”) through which the effete water of res-
piration is expelled. One or two pairs of gills are contained within
the pallial sac, and the sexes are always distinct.

The Cephalopoda, comprising the Cuttle-fishes, Pearly Nautilus,
&c., constitute the most highly organised of the classes of the
Mollusca. ‘Vhey are all marine and carnivorous, and are possessed
of considerable locomotive powers. At the bottom of the sea they
can walk about, head downwards, by means of the arms which sur-
round the mouth, and which are usually provided with numerous
suckers or “acetabula.” They are also enabled to swim, partly by
means of lateral expansions of the integument’ or fins (not always
present), and partly by means of the forcible expulsion of water
through the tubular “funnel,” the reaction of which causes the
animal to move in the opposite direction.

The body in the Cefhalopoda is bilaterally symmetrical, the
cephalic region being conspicuously marked out, and being sepa-
rated from the visceral region, which is enclosed in the mantle (fig.
736). The head bears a pair of large globular eyes, and has the
mouth placed in the centre of its anterior surface. The mouth is
surrounded by a circle of long muscular processes or “ arms,”
formed by the splitting up of the margins of the foot. In the
Cuttle-fishes there are always either eight or ten “arms,” and
these are provided with muscular suckers, which can be used in
prehension. In the Pearly Nautilus, on the other hand, the arms
are numerous, and are not furnished with suckers. ‘The lateral
margins of the foot (“epipodia”) are, again, either placed in

822 CEPHALOPODA.

apposition (Vauti/us) or are actually united (Cuttle-fishes), in such
a manner as to form a muscular tube, known as the “ funnel.”
The funnel (fig. 736, 7) is placed on the lower surface of the
body, with its anterior extremity projecting beyond the mantle,

A WY

Fig. 736.—Diagram of the structure of a Cuttle-
fish. ph, Pharyt nx, with the horny mandibles;
sa, Salivary glands ; @, (Esophagus ; s, Stomach ;
c, Gastric cecum; zz, Intestine; Z, Liver; x,
(Esophageal nerve-collar; g, One of the gills,
with the branchial heart at its base ; Z, Ink-bag,
its duct opening along with the intestine and
generative duct at the base of the funnel; ov,
Ovary; d, Oviduct (the nidamental and accessory
glands are omitted); 4, Funnel, Z, Pen, lying in
the mantle dorsally.

while it opens behind into the
pallial chamber. It serves for
the elimination of the water
which has been used in respi-
ration, and the out-going cur-
rents also carry away with them
the excretions of the kidneys
and of the ink-sac, together
with the feces. By the con-
tractions of the mantle, the
water contained in the pallial
sac can also be driven through
the funnel in a succession of
jets, driving the animal back-
wards through the water.

The mouth in the Cephalo-
pods conducts into a powerful
buccal cavity or pharynx (fig.
736, £2) containing two power-
ful mandibles, working verti-
cally, resembling the beak of
a parrot in shape, and either
horny (as in the Cuttle-fishes),
or partially calcified (as in
Vautilus). There is also a
toothed tongue or ‘radula.”
The intestine is short, and the
anal opening is placed at the
base of the . funnels ime
Cuttle-fishes possess a special
glandular organ, the ‘“ink-
bag” (fig. 736, 2), which
secretes an inky fluid, which
the animal can discharge into
the water, so as to facilitate
its escape when menaced or
pursued. The duct @etm@ine

ink-sac opens, along with the intestine, at the base of the funnel ;
but in the Pearly Nautilus and its extinct allies the ink-gland is

entirely absent.

A well-developed heart is present in the Cephalopods, and the

CEPHALOPODA. 823

respiratory organs are in the form of plume-like gills placed sym-
metrically on the sides of the body within the pallial sac. The
Cuttle-fishes (Dibranchiate Cephalopods) have two gills, one on
each side, while the Pearly Nautilus and its allies (Tetrabranchiate
Cephalopods) have four gills, two on each side. ‘The currents of
water needed in respiration are maintained by the alternate contrac-
tions and expansions of the muscular walls of the mantle-sac. In
each expansion the water finds its way into the pallial chamber by
the opening between the rim of the mantle and the neck; and in
each contraction it is expelled through the tube of the funnel, which
is so constructed as to allow of the egress but to prevent the ingress
of the water.

The nervous system of the Cephalopoda is highly developed, and
its central masses form an oesophageal nerve-collar, which is pro-
tected by a cartilaginous plate.

The sexes are in different individuals, and the males and females
are commonly more or less unlike externally, the former often having
one of the arms specially modified to serve as an intromittent organ.
The ducts of the generative glands open at the base of the funnel,
and each individual, besides the essential organs of reproduction
(testis or ovary), generally possesses accessory glands. The most
important of these accessory glands in the females are known as
the ‘“‘nidamental glands,” and they secrete a viscid material which
unites the eggs together.

The shell of the Cephalopoda is sometimes external, sometimes
internal. The internal skeleton (fig. 737) is known as the “ cuttle-
bone,” ‘“‘sepiostaire,” or “‘pen” (g/adius), and may be either cor-
neous or calcareous. In some cases it is rendered complex by the
addition of a chambered portion or ‘‘ phragmacone,” which is to be
regarded as a visceral skeleton or “‘splanchnoskeleton.” In Spzrula
(fig. 737, ¢) the phragmacone is the sole internal skeleton, and is
coiled into a spiral, the coils of which lie in one plane, and are near
one another, but not in contact. It thus resembles the shell of the
Pearly Nautilus, but it is zzéerna/, and differs, therefore, in this re-
spect from the ex¢erna/ shell of the latter, though it is so far ex-
ternal that the last chamber lodges part of the viscera. The only
living Cephalopods which are provided with an external shell are the
Paper Nautilus (Avgonauta) and the species of Pearly Nautilus
(Nautilus) ; but not only is the structure of the animal different in
each of these, but the nature of the shell itself is entirely different.
The shell of the Argonaut is involuted, but is not divided into
chambers, and it is secreted by the webbed extremities of the two
dorsal arms of the female. The arms are bent backwards, so as to
allow the animal to live in the shell, but there is in reality no organic
connection between the shell and the body of the animal. In fact,

824. CEPHALOPODA.

the shell of the Argonaut, being confined to the female, and serving
by its empty apex as a receptacle for the ova, may be looked upon
as a ‘“‘nidamental shell,” or, as it is secreted by a modified portion
of the foot, it may more properly be regarded as a “ pedal shell.”
The shell of the Pearly Nautilus, on the other hand, is a true pallial
shell, and is secreted by the body of the animal, to which it is
organically connected. It is involuted, but it differs from the shell
of the Argonaut in being divided into a series of chambers by shelly

Fig. 737-—a, Internal skeleton of Sepia ornata ; 6, Pen of Histioteuthis Bonelliana ;
c, Shell (“‘ phragmacone ”’) of Sfzrula fragilis ; d, Animal of Spirula Peroniz.

partitions or septa, which are pierced by a tube or “ siphuncle,” the
animal itself living in the last chamber only of the shell.

The Cephalopoda are divided into two extremely distinct and
well-marked orders, termed the Dzbranchiata and Tetrabranchiata,
in accordance with the number of gills possessed by the animal.
The former comprises all the true Cuttle-fishes ; whilst the latter,
though abundantly represented in past time, has no other living
representatives than three or four species of the genus Vautilus.

As regards their adzstribution tn space, the Cephalopods are ex-
clusively inhabitants of the sea, and sometimes attain a great size.
They live partly in the open sea and partly in shallow water close
to shore, and are carnivorous in habit.

As regards their general distribution in time, the oldest forms of

CEPHALOPODA. 825

the Cephalopoda (Orthoceras and Cyrtoceras) appear in the Upper
Cambrian rocks. All the known Palzeozoic representatives of the
class belong to the order of the Zetrabranchiata, whereas the order
of the Dzbranchiata makes its first appearance in rocks of Triassic
age. The Tetrabranchiates attain their maximum in the Secondary
period, about six or seven thousand fossil forms being already known
from strata of Paleozoic and Mesozoic age. On the other hand,
but few Tertiary Tetrabranchiates have been recorded, and the
order is represented at the present day by the single genus Vawtilus.
The order of the Dzdranchiata, on the contrary, attains its maximum
development at the present day.

826

CTA PAM Re powers
DIVISIONS OF THE CEPHALOPODA.

ORDER JI. TETRABRANCHIATA.

THE Tetrabranchiate Cephalopods are distinguished by the posses-
sion of az external many-chambered shell, the last and largest chamber
of which lodges the body of the animal. The chambers are separated
by calcareous partitions or “septa,” perforated by a membranous tube
or “ siphuncle.” The head is furnished with numerous fleshy “ ten-
tacles,” which are not provided with suckers ;, the branchie are four
in number, two on each side of the body ; the funnel does not form a
complete tube ; and there is no ink-bag.

This order of the Cephalopods is represented at the present day
by the single genus /Vautilus, with four living species, and we may
take the well-known Pearly Nautilus (V. fompzlius) as the type of
the division. The body of the Pearly Nautilus consists (fig. 738)
of a posterior visceral mass and an anterior cephalic region, the
whole being contained in the capacious outermost chamber (body-
chamber) of the shell, from which the head can be protruded at
will. ‘The shell is rolled up into a flat spiral, and the position of
the animal is such that the “funnel” (fig. 738, 7) is turned towards
the convex side of the shell, which is thus the ventral side, the
concave side being dorsal. The visceral mass is included in the
mantle, which is thin behind, but becomes thicker in front,
being reflected on the dorsal side as a kind of collar over the con-
vexity of the preceding whorl, which it invests with a black shelly
deposit. The animal is attached to the shell by a double shell-
muscle, while the posterior extremity gives off a membranous tube
or “‘siphuncle,” which pierces the successive septa centrally, and is
continued backwards through the entire series of air-chambers.

The front portion of the “foot” surrounds the animal’s mouth,
and is furnished with a number of cylindrical, retractile “ tentacles,”
which are not provided with suckers. Dorsally a portion of the

TETRABRANCHIATA. 827

foot is thickened, and forms a fleshy fold or “ hood” (fig. 738, ¢),
which abuts against the preceding whorl of the shell. On the ven-
tral side the median portion of the foot is converted into two mus-
cular lobes, which are placed in apposition but are not fused with
one another, thus forming the “funnel.” As in all the Cephalopods,
the funnel serves for the expulsion of the currents of water which
have passed over the gills, as also for the escape of the undigested
portions of the food and the generative products.

The mouth is placed in the centre of the head, and is armed with
two horny mandibles, partially calcified towards their extremities,
and shaped like the beak of a parrot, except that the inferior man-

S

Fig. 738.—Pearly Nautilus (Nautilus pompilius). a, Mantle; 4, Its dorsal fold;
c, Hood; 0, Eye; ¢, Tentacles ; 4 Funnel.

dible is the longest. A ‘‘radula” is present, and the intestine
terminates at the base of the funnel. The heart is contained in a
large viscero-pericardial sac (or ‘ pericardium”), and consists of a
ventricle, which receives four branchial veins; but there are no
“branchial hearts.” The branchiz are contained within the mantle-
cavity, and are four in number, two on each side. No ink-gland is
developed. The sexes are distinct, and the reproductive organs of
the female consist of an ovary, with two oviducts (the left rudi-
mentary), and an accessory nidamental gland.

The only structures possessed by the Pearly Nautilus which are
capable of preservation in the fossil condition are the mandibles and
the shell, since the foot in this genus secretes no structure which
can be compared with the “operculum ” of the Gastropods. Leay-
ing out of sight the ‘‘ Aptychi” of the Ammonites, it is from fossil

828 DIVISIONS OF THE CEPHALOPODA.

beaks or shells that we derive our knowledge of the extinct Tetra-
branchiates ; and it is therefore necessary to study these parts in
some detail, and with reference to the entire order.

In the living Pearly Nautilus the horny mandibles, which com-
pose the “beak,” are calcified towards their tips, the upper mandible
more extensively so than the lower one. Similar beak-like jaws
have been long known as occurring in the Secondary and Tertiary
rocks, and they have been described under the name of Rhyncholites.
The Jurassic and Cretaceous fossils included under the name of
Rhynchoteuthis (fig. 739) are very similar to Ahyncholites, and are
doubtless the calcified mandibles of some species of Vautilus, or of

Fig. 739.—Rhynchoteuthts Astierianus. Lower Greensand (Cretaceous).

some allied type. In the Palseozoic rocks, in which the JVaufilotdea
are abundantly represented, the fossil beaks, except for a Carbon-
iferous ‘“‘ Rhyncholite,” are unknown.

The se in all the Tetrabranchiates resembles that of the Nau-
tilus in having a larger or smaller body-chamber, preceded by a
chambered portion, which is divided into compartments by shelly
partitions or “ septa” (fig. 738). The chambers are usually spoken
of as the ‘‘air-chambers,” on the belief that they are filled with some
gas secreted by the animal itself, but some authorities take the view
that they are naturally filled with water. In all the Tetrabranchiates
the chambers are traversed throughout by an originally membranous
tube or ‘ siphuncle,” which is connected with the hinder end of the
visceral sac.

In the Pearly Nautilus, as before pointed out, the animal is so
related to its shell that the “‘funnel” is turned towards the convex
side of the latter, the aperture of the shell showing a corresponding
sinuation on that side. Hence, in the living Pearly Nautilus the
convex side of the shell is ventral, and the shell is “ exogastric.”
In various fossil Nautiloids, however, it can be shown that the shell-
aperture is excavated on the inner or concave side, at which point
we must suppose the ‘“‘funnel” to have been placed. In such

TETRABRANCHIATA. 829

“ endogastric” types the concave side of the shell is the ventral
side, the dorsal side being convex. In a great many fossil forms,
however, there is no clear evidence as to the position of the animal
in relation to its shell; and in such cases, as in the Ammonites, it
is advisable to employ the terms ‘‘ external” and “internal” for the
convex and concave sides of the shell, since we do not know which
side is ‘‘ dorsal” or ‘‘ ventral.”

The shell of the Tetrabranchiates may be regarded as essentially
a more or less elongated cone, the pointed end of which is parti-

Tir
(SO
D
Pe ‘
7
p Weer eae
)
p
>

yy daa ey
RD rn
De NTN ers
TANT AG
meas

IFT

“WSs

AN
A

\ A z
: A

Fig. 740.—Fragment of Actinoceras Fig. 741.—Restoration of Orthoceras,
crebriseptus—Cincinnati Group, North the shell being supposed to be divided
America, of the natural size. The lower vertically, and only its upper part being
figure is a section showing the air- shown. a, Arms; #, Muscular tube
chambers, and the form and position (‘‘funnel”) by which water is expelled
of the siphuncle. (After Billings.) from the mantle-chamber ; c, Air-cham-

bers; s, Siphuncle.

tioned off into air-chambers, while the body-chamber is situated at
the wide end (figs. 740 and 741). In some cases, as in Orthoceras
and Baculites, the shell retains permanently its primitive form as a
straight cone. In other cases the originally straight cone may be
slightly bent (Cyrtoceras) ; twisted into a hook (amizes) ; doubled
on itself (Ptychoceras); or coiled into an open spiral, the turns of
which may lie in one plane (Gyroceras) or may pass obliquely round
an imaginary axis (/e/icoceras). Very generally the volutions of the

830 DIVISIONS OF THE CEPHALOPODA.

shell are in contact with one another, in which case the coils may
lie in one plane (Vautilus, Ammonites, &c.), or they may pass ob-
liquely round an axis (Zurrilites). In the discoidal types (such as
Nautilus and the Ammonites) the last volution may more or less
completely conceal the preceding turns of the spiral. In other
cases the earlier coils of the shell remain visible, and the shell
becomes umbilicated.

The surface of the shell in the Tetrabranchiates may be nearly
smooth, or may show nothing more than delicate lines of growth.
In other cases the surface may be more or less conspicuously
adorned with various kinds of sculpturing, which may have a direc-
tion corresponding with the long axis of the shell, or may be at right
angles to this. Thin sections show that the shell is composed of
two principal layers, of a different nature. The outer layer forms a
thin porcellanous stratum, which is lined throughout by a thicker
nacreous layer, which alone forms the septa between the air-
chambers.

The “septa,” or partitions between the successive air-chambers,
vary greatly in number in different types of the Tetrabranchiates.

= /
ai. ig
we

Fig. 742.—Diagram to illustrate the position of the siphuncle and the form of the septa in
various Tetrabranchiate Cephalopods. The upper row of figures represents transverse sections
of the shells, the lower row represents the edges of thesepta. aa, Ammonite or Baculite; 6b,
Ceratite; cc, Goniatite; dd, Clymenia; ee, Nautilus or Orthoceras.

Whatever their number may be, they are usually placed in each
individual at approximately uniform distances apart in each succes-
sive portion of the shell; but the last two or three septa are com-
monly closer to one another than the rest, probably in consequence
of an impairment of the vitality of the animal with advancing age.
Up to a certain period of the animal’s life, new chambers are suc-
cessively formed as the increasing size of the body necessitates the
acquisition of more room, but the process by which the animal
moves forwards prior to the development of a fresh septum is not
perfectly understood. The edges of the septa, where they become

TETRABRANCHIATA. 831

continuous with the shell-wall, are known as the ‘‘ sutures,” and the
form of these necessarily varies with that of the septa themselves.
In one great division of the Tetrabranchiates (viz., the Vazt:lordea)
the septa are simply curved or slightly lobed, and the “sutures”
are more or less completely plain. In the other great division of
the order (viz., the Ammonoidea) the septa are folded and complex,
and the “sutures” are angulated, zigzag, lobed or foliaceous (fig.
742). The form of the “sutures” cannot be determined from the
exterior, so long as the shell is preserved; but in fossil forms, in
which the shell itself is commonly more or less extensively removed,
the form of the sutures can be readily studied, and affords charac-
ters of high morphological value.

The “siphuncle” in the Tetrabranchiate Cephalopods has the
form of a tube connected in front with the hinder end of the
body, and continued backwards throughout
the entire series of air-chambers. The pre-
cise function of the siphuncle is uncertain,
but it probably serves to maintain the vitality
of the shell. In the Pearly Nautilus the
siphuncle is a membranous tube, the walls
of which are to some extent strengthened
by the deposition of calcareous granules.
In some fossil Tetrabranchiates these calca-
reous deposits are so extensively developed
that the wall of the siphuncle may become
completely calcified. The proper sheath of
the siphuncle, formed in this way, must,
however, be carefully distinguished from cer-
tain other calcareous envelopes which may
come to more or less completely enclose
the siphuncular tube. Thus, in the Pearly
Nautilus each septum is prolonged backwards
at the point where it is perforated by the
siphuncle as a short shelly tube — “neck”
or “funnel” —which encloses the anterior =
portion of each segment of the siphuncle. Ay AES ae ae a
In some _ Tetrabranchiates these ‘* septal showing the “‘septal necks”
necks” do not merely form short collars CORE a eae oe
round the siphuncle, but each is continued
backwards from the septum in which it originates to the septum
next behind (fig. 743, s¢); so that the proper siphuncle becomes
enclosed in a complete secondary investment. In the majority
of the Nautiloids the septal necks are directed, as in the Pearly
Nautilus, dackwards from each septum, and such forms are said to
be ‘‘retrosiphonate.” On the other hand, the majority of the

832 DIVISIONS OF THE CEPHALOPODA.

Ammonoid Tetrabranchiates have the septal necks continued
jorwards from the producing septa, and are therefore said to be
‘“‘prosiphonate.” In many of the extinct types of the Vautilordea
the internal structure of the siphuncle is highly remarkable, the
cavity of the tube often becoming contracted by organic deposits of
secondary origin; but the structures in question will be more fully
considered later on. Lastly, important distinctions are drawn in
the Tetrabranchiates from the position of the siphuncle in relation
to the shell. In the Ammonotdea the siphuncle is always marginal,
and is mostly placed on the external side of the shell. In the WVaz-
tiloidea, on the other hand, the siphuncle may pierce the septa
centrally (as in the Pearly Nautilus) ; or it may be subcentral ; or in
other cases it may be marginal, being then sometimes external,
sometimes internal in position (fig. 742).

The development of the shell of the Pearly Nautilus is, unfor-
tunately, unknown ; but it has been shown that there are important
distinctions in the form and structure of the initial chamber of the

Fig. 744.—Development of Tetrabranchiate Cephalopods. a, The inner end of the shell of
Nautilus pompilius, enlarged, showing the initial chamber and the cicatrix; B, Cyrtoceras
preposterum—Silurian, showing the commencement of the shell; and (c) the initial chamber
viewed from below, showing the cicatrix ; p, Inner portion of the shell of Gontatites bicanalic-
ulatus—Devonian, showing the inflated protoconch ; E, First turn of the spire of Gonzatites sub-
lamellosus —Devonian 3 F, Crioceras Studeri—Cretaceous, enlarged, showing the protoconch ;
G, Protoconch and first turn of the spire of Ammonites gquadrisulcatus—Cretaceous, enlarged.
(After Barrande.)

shell in the two groups of the Vaut:lordea and Ammonoidea respec-
tively. In the Ammonoids the initial chamber of the shell (fig.
744, D—G) constitutes an inflated, spheroidal, oval, or pyriform sac,
the so-called “‘ protoconch” (or ‘‘ovisac”), which corresponds with
the ‘‘ nucleus” of the shell of the Gastropods, and is separated by a
constriction from the first air-cchamber. The siphuncle commences
as a closed and dilated tube, which deeply indents the front wall of

TETRABRANCHIATA. 833

the protoconch, but does not penetrate into the cavity of the latter.
Munier-Chalmas has shown, further, that the cavity of the proto-
conch is traversed by a tubular organ or “ prosiphon,” which abuts
against the front wall of the chamber, but does not communicate
with the proper siphuncle, the place of which it is supposed to take
in early life. In the /Vauzelordea, on the other hand, the initial
chamber of the shell (fig. 744, A, B, C) is a simple cone, which is
not constricted off from the first air-chamber and is not inflated.
The initial element of the siphuncle is a somewhat dilated cecal
tube, which indents the front wall of the initial chamber, but does
not enter its cavity. The external surface of the initial chamber is
usually marked by a network of transverse and longitudinal strie,
which mostly become obsolete in the adult shell. The hinder
extremity of the initial chamber also exhibits an oval, rounded, or
slit-like scar or cicatrix (fig. 744, Aandc). The presence of this
cicatrix would seem to show, as held by Hyatt, that the initial
chamber of the Nautiloids does not correspond with the ‘ proto-
conch ” of the Ammonoids ; and it seems not improbable that there
existed in the former a deciduous protoconch, which is now repre-
sented only by a small vacuity in the centre of the shell (in the
spirally-inrolled types). Hyatt, indeed, has described and figured
the remains of this protoconch as occurring in certain species of
Orthoceras. On this view, the initial chamber of the shell of the
Nautiloids is really the first air-chamber, and the cicatrix in its
posterior wall marks the point where this communicated with the
caducous protoconch.

The order of the Ze¢vrabranchiata may be divided into the two
sub-orders of the Vautzlordea and Ammonoidea, typified respectively
by the Nautili and the Ammonites. The Ammonoidea are regarded
by Fischer as a separate order of the Cephalopoda ; while the char-
acters of the protoconch are regarded by some as affording ground
for a reference of this division to the Dibranchiates rather than to
- the Tetrabranchiates.

Regarded as a whole, the Tetrabranchiate Cephalopods form a
group which early attained its maximum, and is now almost extinct.
The Palzeozoic Tetrabranchiates are in the main of a decidedly
simpler type than those which followed them. ‘The largest number
of generic types existed during the Mesozoic period, and the forms
of this epoch are morphologically the most complex. With the close
of the Secondary period disappeared almost all the characteristic
Mesozoic types, and the order was left without any representative in
the Tertiary rocks except the simple and ancient genus Vautz/us and
its immediate allies. As regards the two great sections of the order,
the Vautiloidea are the most ancient, dating their existence from
the Upper Cambrian. Not only is this the case, but they are pre-

MOL. UT: 3G

834 DIVISIONS OF THE CEPHALOPODA.

eminently Palzeozoic, only a few generic types surviving into the
Secondary period. On the other hand, the Ammonordea are pre-
eminently Mesozoic in their range, being represented in the Pale-
ozoic deposits earlier than the Carboniferous only by such compara-
tively simple types as Clymenta and Gontatites. With but limited
and local exceptions, the Ammonoidea are not known to have sur-
vived into even the commencement of the Kainozoic period ; and
all the living Zetrabranchiates belong to the single genus /Vauzzlus.

SUB-ORDER I. NAUTILOIDEA.

In this division of the Zetrabranchiata the shell is straight or bent,
or variously coiled, the aperture being simple or contracted, and the
ventral side being commonly indicated by an emargination of the
apertural edge. The sutures are simple, rarely undulated or den-
ticulate ; and the septa are concave towards the shell-aperture. The
siphuncle is variable in position, and its cavity is often contracted by
internal deposits. The ‘septal necks” are usually short, though
sometimes long, and are generally directed backwards, the shell
being ‘‘retrosiphonate.” The initial chamber is conical, and has a
cicatrix.

This sub-order includes the genus /Vau¢c/us, and a large number
of wholly extinct types. The general characters of the shell have
already been spoken of in dealing with the Zetrabranchiata as a
whole; but there are a few special points which may be shortly
noticed here.

The aperture of the body-chamber in the Nautiloids is variably
shaped. In some cases, as in Orthoceras, the aperture is simple, as
it is in the Pearly Nautilus ; but the lateral margins of the aperture
may be prolonged forwards, so that a sinus is produced on the con-
vex and concave sides of the shell. The
most marked and constant of these si-
nuses may be assumed to correspond with
the funnel, and therefore to represent the
ventral side of the animal; and, as pre-
viously pointed out, this is in Wautilus |
the convex side of the shell. While the
aperture in many Nautiloids is simple,
it becomes in other cases contracted by

Fig. 745.-—Aperture of the she’ the bending inwards of. the lateralijare-
a Ree Ae ee longations of the mouth, so as to be
converted into a dorsal and ventral open-

ing connected by an intervening passage. In some cases the
dorsal and ventral margins as well as the lateral ones are bent
inwards, in which case the aperture (fig. 745) assumes a T-shaped

NAUTILOIDEA. 835

or key-hole-like character. According to the views of Barrande,
the broad transverse part of the aperture represents in such cases
the position of the head, while the rounded extremity of the verti-
cal portion of the aperture corresponds with the funnel. It is
clear, however, that with an aperture so contracted, the animal
must have been incapable of protruding the head, as the living
Pearly Nautilus can.

The dorsal and ventral aspects of the animal have no constant
relation to the concave and convex sides of the shell among the
LVautiloidea. In the Pearly Nautilus the convex side is the ventral
one, but even within the limits of the same genus it is usual to meet
with forms having the convex side .
ventral associated with others in s
which the concave side is ventral.

The osztion of the siphuncle is
by no means constant among the
Nautiloids, and bears no fixed rela-
tion to the aspects of the body of
the animal, though it is commonly
placed towards the ventral side.
The siphuncle is upon the whole,
however, most generally situated
centrally or subcentrally, and when
removed towards the margin it is
usually external in the curved
shells, though it may be internal.
As regards its structure the siph-
uncle of the Nautiloids is, to begin
with, a simple membranous tube,
but it may become complex in
process of growth. In many cases
the cavity of the siphuncle be-
comes contracted by the formation
in its interior of annular deposits
of calcareous tissue (fig. 746, 07),
which were termed by Barrande
6c obstruction-rings” : and these may Fig. 746.—Vertical section of Orthoceras

: angulatum, Silurian, showing the siphuncle
be so extensively developed as to (s) contracted by the development of “ ob-
struction-rings” (07) opposite the septa.

completely obstruct the tube. (After Foord.)

The ‘‘ septal necks” of the Nau-

tiloids are almost always directed backwards, the shell thus being
“‘retrosiphonate” (fig. 743). In the two genera JVothoceras and
Bathmoceras alone are the septal necks turned forwards, so that
the shell is ‘‘prosiphonate.” In many forms, as in the existing

Pearly Nautilus, the septal necks are short; but in other cases

836 DIVISIONS OF THE CEPHALOPODA.

they extend from septum to septum, and they may even fit into
one another like so many funnels (as in the genus Exdoceras).

Lastly, the ‘“‘ su¢urves,” or the lines formed by the intersection
of the septa with the surface of the shell, are simply curved, sig-
moidally bent, or in some cases undulated. In a few cases short
external and internal bendings of the suture (“lobes”) may be
developed, but these never constitute a conspicuous feature.

As regards their distribution in time, the earliest types of the
LVautiloidea appear in the Upper Cambrian deposits, in which the
genera Orthoceras and Cyrtoceras are represented. In the Ordovician
rocks an enormous number of Nautiloids are known to occur, no
less than four hundred and sixty-three species having been recorded
by Barrande from rocks of this age in Bohemia alone. The maxi-
mum development of the group takes place, however, in the Silurian
period, the Bohemian area having yielded to the researches of Bar-
rande over a thousand species from deposits belonging to this
system. In the later Palaeozoic rocks the Nautiloids exhibit a pro-
gressive diminution in numbers, and only the genera autilus and
Orthoceras survive the close of this epoch, the latter finally dying
out in the Trias. The few known Tertiary types belong to VVautlus
or to closely allied forms, and the sole existing representatives of the
sub-order are four living species of LVautzlus.

The sub-order Vautiloidea may be divided into the following
families (see Foord’s “‘ Catalogue of the Fossil Cephalopoda in the
British Museum ”’) :—

FAMILY 1. ORTHOCERATIDA.—In this family the shell is straight
or slightly curved, the aperture is simple, and the siphuncle is .
usually slender and cylindrical. This family comprises the single
genus Orthoceras (figs. 747, 748), in which the shell is in the form
of a conical tube which is usually straight, but may be slightly
curved. The aperture of the shell is not contracted, and the body-
chamber is of large size. The septa are concave, usually horizontal,
and generally far apart; and the siphuncle is usually slender and
cylindrical, and may be central, subcentral, or excentric in position.
The numerous species of Orthoceras are divided by Barrande into
two principal sections—the Short-coned and Long-coned forms—
according as the shell has the form of a short cone with a large
apical angle, or of a prolonged cone with a small apical angle. The
first of these groups is a very small one, and almost all the more
common Orthocerata belong to the second section. ‘Though the
shell is typically straight, it may be gently curved throughout (as in
O. angulatum) ; or it may be slightly bent towards the point of the
cone, but otherwise straight (as in O. wmguzs). In the smaller forms,
the initial chamber, with its cicatrix, is sometimes preserved.

The oldest known species of Orthoceras appears in the Upper

NAUTILOIDEA. 837

Cambrian (Upper Tremadoc beds of Wales), and very numerous
forms of the genus have been recorded from the Ordovician rocks.
The genus attains its maximum in the Silurian, more than five
hundred species having been described by Barrande from rocks of
this age in Bohemia. In the Devonian and Carboniferous rocks a
great reduction in the number of species takes place ; a few Permian

Fig. 748.—a, Cast of the shell
of Orthoceras Hisingeri, from the
Silurian rocks of Gotland, of the

Fig. 747.-a, A broken specimen of
Orthoceras ornatum, of the natural size,
yom the Silurian rocks of Gotland ;_ 4, natural size ; 4, Transverse section

Waste secon of vhe teae showing of the shell, showing the siphuncle ;
the position of the siphuncle ; c, Portion ape 2
of the surface, enlarged. (After Foord.) c, Portion of the surface, enlarged.

(After Foord.)
types are known; and the last representatives of the genus are found
in the Alpine These.

FAMILY 2. ENDOCERATID#.—In this family the shell is straight
or slightly curved; the siphuncle is marginal or sub-marginal, of
large size ; and the septal necks are invaginated so as to form a wide
tube within which the siphuncle is contained.

838 DIVISIONS OF THE CEPHALOPODA.

The type-genus of this family is Adoceras, in which the shell is
straight and resembles that.of Orvthoceras in form. ‘The septal necks
(fig. 749, sf) are prolonged backwards to such an extent that each
becomes inserted into the mouth of the neck of the septum next
behind, thus forming a complete and wide tube which encloses the
siphuncle. This siphuncular tube is marginal or sub-marginal, and
may attain a diameter of one-half of that of the shell. The siphun-
cular tube is provided internally with a series of funnel-shaped
sheaths (fig. 749, sZ), which are not very numerous, and occur at
irregular intervals. ‘These were termed by Hall “ embryo-sheaths,”
upon the belief that they were connected with reproduction ; but

S (ap

Fig. 749.—A, Transverse section of the shell of Exdocevas ; B, Vertical section of part of the
anal ue Peni Wahlenbergi, from the Ordovician rocks of Sweden (after Foord): s, Cavity
of the siphuncle; sf, One of the ‘‘septal necks”; s, One of the siphuncular sheaths; ez,
Endosiphon.

their true nature is not absolutely certain. In well-preserved ex-
amples, the great siphuncular space contains in its interior a cylin-
drical slender tube or “‘ endosiphon ” (fig. 749, B, e), which probably
represents the calcified wall of the proper siphuncle. With the
doubtful exception of one Silurian species (Z. ? Ommaneyz) the genus
Endoceras is confined to the Ordovician rocks. uxdoceras Wahlen-
bergt (the &. duplex of many writers) is abundant in the Ordovician

' deposits of Scandinavia and Russia, and sometimes attains a length

of six feet or more. Casts of the great siphuncular tube are not
uncommon, and have the form of cylinders marked with oblique
annulations.

In the genus P2/oceras the shell is more or less broadly conical,

NAUTILOIDEA. 839

slightly curved, with a large marginal siphuncular tube, formed by
the prolongation and conjunction of the septal necks, and provided
internally with one or more funnel-shaped sheaths, which are united
at the top with its margin. ‘‘ These sheaths apparently communi-
cated with one another by means of the endosiphon, which passed
from the initial chamber into the siphun-
cular cavity by means of a large foramen,
situated on the inner curvature of the
siphuncle a little above the apical point”
(Foord). The species of /2/oceras are con-
fined to the summit of the Cambrian and
the base of the Ordovician deposits (the
Durness Limestone of Britain and the Cal-
ciferous formation and Quebec group of
North America).

The genus Cyrtocerina (fig. 750), of the Gui ee ne naiities,
Lower Ordovician rocks (Quebec Group) of Canada. (After Billings.)
Canada, is perhaps allied to Prloceras. In
this type, the shell is broadly conical and is curved, and there exists
on the concave side of the shell a wide marginal siphuncular tube.

FAMILY 3. ACTINOCERATID£.—In this family thé shell is straight
or slightly curved, and the siphuncle is of large size and is composed

pee
=i
— 4 ——-=

Fig. 751.—Weathered fragment of Actin- Fig. 752.—Fragment of Actinoceras Bigs-

oceras Bigsbyz, of the natural size, from the éyz, from the Ordovician rocks of Kentucky,
Ordovician rocks of Lake Huron. s, Septa; of the natural size. s, One of the septa; /,
ez, Endosiphon, with some of its tubuli (7). Foramina in the siphuncle by which the
(After Foord.) tubuli thrown out by the endosiphon may

have communicated with the septal cham-
bers. (After Foord.)

of nummuloid segments or discs, its internal cavity being more or
less extensively contracted by the development of ‘‘obstruction-rings.”

840 DIVISIONS OF THE CEPHALOPODA.

The type of this family is the genus Actnoceras (figs. 751 and
752), in which the shell is elongate-conical, and often of large size.
The siphuncle is very large, its diameter sometimes equalling half
that of the shell; and it is greatly inflated between the septa, so that it
comes to present a series of segments of a compressed-globular form.
In the centre of the main siphuncular tube is a cylindrical “ endo-
siphon” (fig. 751, ez), and the space between this and the wall of
the former is largely occupied by secondary calcareous deposits
(“‘ obstruction - rings”) developed at the “necks” of the septa.
‘““The endosiphon is provided with a distinct wall, and gives off at
regular intervals between the septa a number of radiating canals or
tubuli (fig. 751, 7), which apparently penetrate the shelly covering or
wall of the siphuncle” (Foord). The foramina by which these tubuli
open externally form a ring round each segment of the siphuncle
(fig. 752, 7), and they may perhaps have served to transmit blood-
vessels to the lining-¢membrane of the air-chambers. ‘The genus
Actinoceras ranges from the base of the
Ordovician (Upper Cambrian ?) to the
Carboniferous limestone, the A. gzgan-
teum of this latter formation attaining
a length of from four to six feet.

Allied to <Actinoceras are the genera
Discosorus, Huronia, and Sactoceras,
all of which are confined to the Silurian
rocks.

FAMILY 4. GOMPHOCERATIDA. — In
this family the shell may be approxi-
mately straight or more or less exten-
sively curved, and the aperture of the
shell is contracted and T-shaped (fig.
745). The principal genus in this
family is Gomphoceras, with which may
\ MO be included the forms usually spoken

Nk a” of as Phragmoceras.

a ee ee ee In the most typical forms of Gom-
Barrande.) _ phoceras (fig. 753) the shell is approxi-

mately straight, or is very slightly
curved, and the ventral side is always more convex than the dorsal,
the shell being thus ‘“‘ exogastric”; while the siphuncle is situated
towards the convex or ventral aspect. The aperture of the shell
(fig. 745) is T-shaped; and the transverse orifice, corresponding
with the head, may be widely expanded or may be contracted
in the middle. The siphuncle is commonly subcentral, the septa
are simply curved, and the body-chamber is of large size. The
name of Phragmoceras has been given to forms of Gomphoceras in

Ae Ul
\\ \\N\ = =f. ey

(es

NAUTILOIDEA. 841

which the shell (fig. 754) is more or less curved, the dorsal side
being convex and the ventral side concave, and the shell being thus
*‘ endogastric ;” while the siphuncle runs on the ventral aspect. The
form of the aperture is not affected by this reversal of the curva-
ture of the shell, except that the smaller opening of the T-shaped
mouth, corresponding with the funnel of the animal, is now turned
towards the concave side of the shell. ,
The genus Gomphoceras (including Phragmoceras) has been stated
to range from the Ordovician to the Carboniferous ; but, according
to Foord, the pre-Silurian and post-Silurian types referred to this
genus are of doubtful affinities, or are certainly known to be refer-

Fig. 754.—Gowphoceras (Phragmoceras) ventricosum. Silurian. The right-hand
figure shows the form of the aperture.

able to other genera. ‘The genus is therefore restricted, so far as
clearly ascertained, to the Silurian period.

FAMILY 5. ASCOCERATID#.—In this family the shell, when fully
grown, is sac-like and truncated below, the body-chamber occupying
most of the ventral side, while the last few septa are specially modi-
fied. The aperture may be simple or contracted.

The type of this family is the genus Ascoceras (fig. 755), which is
defined by Foord as follows: ‘‘The shell is of a sac-like form,
essentially straight, but always more convex on the ventral than on
the dorsal side. The apex is unknown, the shell being always
truncated. The transverse section may be elliptical or circular.
The body-chamber occupies nearly the whole length of the shell on
the ventral side, and contracts into a neck-like prolongation towards
the aperture, which is simple. The last few septa are abnormal ;
they have the usual shape and position on the ventral side of the
shell, but on the dorsal side they coalesce, and sweeping upwards
in a sigmoid curve (as seen in section, fig. 755, a) form a series of

842 DIVISIONS OF THE CEPHALOPODA.

vaulted chambers, convex towards the aperture, and encroaching
considerably upon the body-chamber. ‘This extraordinary confor-
mation of the septa on the dorsal side was doubtless caused by the
shrinking of the animal in its shell on that side; whereby a cavity
was created between the shell-wall and the mollusc, and then parti-
tioned off in the manner above described. The short siphuncle is
submarginal and near the ventral or convex border of the shell; it
diminishes rapidly in size towards the body-chamber. The test is

Fig. 755.—Ascoceras Bohemicum, Silurian, Bohemia. a, Longitudinal section, showing the
septa (s s) and siphuncle (sz); 4, Ventral aspect of the cast of the shell, showing the reduction in
size of the body-chamber caused by the encroachment of the septa; c, Dorsal view of the same
specimen ; d, Body-chamber, without the air-chambers ; ¢, Transverse section taken in the centre
of the fossil; 4 Truncated posterior extremity, showing the position of the siphuncle (sz); 2,
Anterior extremity, showing the simple form of the aperture (af). ‘The letters v and d’ indicate
the ventral and dorsal sides respectively. (After Barrande.)

relatively thick considering the size of the shell; its ornaments may
consist of transverse lines or of annulations.”

By the researches of Lindstrom it has recently been proved that
Ascoceras begins in the form of an Orthoceras, having a cylindrical
shell, with remote, simply curved septa, and a slender tubular
siphuncle, and that the sac-like shell above described is only the
final portion of the structure. When the organism has attained its
full growth, and has formed the inflated Ascoceras-shell, the older,
Orthoceratoid portion becomes decollated or cast off. It is, there-
fore, a matter of extreme rarity to find a complete specimen of
Ascoceras, exhibiting both the older and later portions of the shell.

NAUTILOIDEA. 843

The species of Ascoceras are found in the Silurian rocks in Europe,
and in the Ordovician rocks in North America. The Silurian genus
Glossoceras resembles Ascoceras in general structure, but the aper-
ture is contracted and lobed. The name of Aphragmites, again, is
given to forms in which the peculiar arched septa at the side of the
body-chamber are absent, the shell otherwise resembling Ascoceras.

FAMILY 6. POTERIOCERATID&.—The principal genus included in
this family is Poterioceras, in which the shell is fusiform in shape,
inflated in the central portion of its length, contracted towards the
aperture, and very slender in its apical portion. The siphuncle is
subcentral or marginal, and is inflated between the septa. The
shell has a general resemblance to Gomphoceras, but the aperture
is simple. The species of /oterioceras range from the Ordovician
to the Carboniferous. }

FAMILY 7. CYRTOCERATID#.—This family includes only the genus
Cyrtoceras, in which the shell (fig. 756) is more or less curved, but

Fig. 756.—Cyrtoceras obliguum, Middle Devonian, Germany, about two-thirds of the natural
size. a, Front view; 6, Side view. (After Foord.)

does not form a complete volution, and the body-chamber is of
large size. The septa are simple, concave forwards, and the
siphuncle may be internal, external, or subcentral in position, and
may be cylindrical or beaded. The shell is conical, or sometimes
subcylindrical in form, some species being of the ‘‘ brevicone” type,
while others are ‘“‘longicone.” The genus Cy7/oceras ranges from

844 DIVISIONS OF THE CEPHALOPODA.

the Cambrian to the Carboniferous, and attains its maximum in the
Silurian period, more than three hundred species having been de-
scribed by Barrande from the Silurian deposits of Bohemia alone.

Famity 8. Liruirip#.—The shell (fig. 757) in this family has
its earlier portion coiled into a flat spiral, while the later portion,
including the whole or the greater part
of the body-chamber, is produced in a
straight line. The volutions of the
spiral part of the shell may or may
not be in contact, and the siphuncle
is subcentral or internal. The septa
are simple and concave, and the sur-
face is transversely striated or ribbed.

In Lutuztes itself the uncoiled por-
tion of the shell is very long, and the
aperture is contracted, with a deep

nee Si ventral sinus. The genus is found in

Big. 757.—£ituiies cornw-arietis. 4. Ordovician and Silurian rocks.

The Silurian genus Ophzdioceras re-
sembles Lz¢uzfes in most respects, but the disjunct portion of the
shell is short, and contains a portion only of the body-chamber.
Lastly, in the genus Lzscoceras, also from the Silurian, the terminal
and produced portion of the shell is short, but the aperture differs
from that of Ophzdioceras in being simple. |

FamILy 9. TROCHOCERATID&.—In this family the shell is rolled
up into a spiral, the coils of which do not lie in a single plane. In
Trochoceras the shell is unsymmetrically coiled, and the last volu-
tion may be partially disjunct. The septa are concave, and the
siphuncle is usually placed between the centre and the convex ex-
ternal margin; while the aperture is simple. The genus ranges
from the Ordovician to the Devonian, but the great majority of the
species are Silurian. The Silurian Adelphoceras differs from Zvrocho-
ceras in having a contracted aperture to the shell.

FAMILY 10. NAuTILip#.—lIn this family the shell is spirally in-
rolled, the coils lying in one plane, and the aperture being simple
or contracted. Of the numerous generic types included in this
family, the following are the most important :—

In the Ordovician genus Zvocholites the shell is discoidal and
umbilicated, and the septa are concave, the suture-lines being
simple or feebly lobed. The siphuncle is sub-marginal, placed
towards the internal side, and the septal “necks” are long, and
reach from one septum to the next.

In Gyroceras (fig. 758) the shell is in the form of a flat spiral, the
coils of which are not in contact with one another. ‘The aperture
is simple, with a ventral and dorsal sinus; the sutures are simple;

NAUTILOIDEA. 845

‘the siphuncle is variable in position, but is usually placed between
the centre and the convex side; and the surface is commonly
adorned with tubercles or ribs. The
genus ranges from the Silurian to the
Carboniferous.

In Hercoceras the shell is discoidal,
with contiguous whorls and a wide um-
bilicus. The aperture is contracted ; the
sutures are simple; the siphuncle is sub-
marginal and external; and the surface
is adorned with transverse striz or a
row of projecting tubercles. The two
known species are Silurian.

Ge
y Vz, as ay
ih Go f . > 7
{( WH, p)) p\ SSS
d Ny if )) \\ \ SYS SS
SSNS

| WSS
In the genus JVautilus itself (fig. ; ‘
#59) the shell is involute or discoidal, 758 Gyreceras ornatum.

consisting of a few whorls coiled into

a flat spiral, the volutions being in contact, and the last turn of
the shell commonly more or less concealing the previous ones. In
the young condition of the shell a central vacuity exists behind the
conical initial chamber ; but in the typical forms of the genus this
becomes ultimately filled up by a secondary deposit of shell, or
becomes concealed by the later volutions. The body-chamber is
capacious, and the aperture is simple and has a ventral sinus. The

Fig. 759.—Nautilus Danicus. Upper Cretaceous.

septa are concave forwards, and the suture-lines are simple or may
show a slight ventral or dorsal “lobe.” The siphuncle is subcen-
tral in position, or may be placed between the centre and either
the ventral or the dorsal margin, and it is never contracted by
internal deposits; while the septal ‘‘necks” are always short.
The surface may be quite smooth (Levzgati), or adorned with
transverse striz (S¢vzatz), or with markedly distinct ribs (Radiazz),
The genus /Vauti/us has been split up into a number of minor

846 DIVISIONS OF THE CEPHALOPODA.

groups, to some of which a generic value is now usually attached. |
Using the name in the wide sense in which it has been commonly
employed, the genus may be said to range from the Ordovician to
the present day; but the
older types are almost cer-
tainly not congeneric with
those of later periods.

The name of Drsczes is
given to forms generally in-
cluded in the comprehensive
genus JVautilus, in which
the shell is widely umbili-

ari inm we __.. cated, with a persistent cen-
Fig. 760.—Nautilus (Vestinautilus) Koninckit. : 5

Carboniferous. tral vacuity; the volutions
being four-sided, and the
septa showing a deep ventral lobe. ‘The forms of this type are
Carboniferous. Zemnochetlus (Devonian to Trias) and Zremazto-
discus (Carboniferous) likewise include widely umbilicated Nautili,
in which the centre is perforated. A similar condition of parts
exists in Vestinautilus (fig. 760), but in this
type the whorls are trapezoidal in section and
are very wide towards the aperture. The
outer side of the shell is strongly keeled with
lateral longitudinal ribs separated by a dorsal
furrow. ‘The genus is confined to the Carbon-
iferous rocks.

Lastly, in Aturza the shell is involute and
destitute of an umbilicus; and the sutures are
strongly bent in a zigzag manner, with a deep
lateral “lobe.” The siphuncle is marginal and
is placed on the internal side of the shell, the
septal “necks” (fig. 743,.s¢) being very long
and being invaginated in such a manner as
to form a complete siphuncular investment.
The known species of Aturza are found in the

_ Eocene and Miocene deposits.

Hee Dee: FaMILy 11. Bactritip#.— This family in-
ee ee Se ee cludes only the genus Bactrites (fig. 761), in
—copied from Zittel.) | which the shell is straight and conical, with a

circular or elliptical section, resembling that of
Orthoceras in form. ‘The siphuncle is delicate and marginal in
position; and the septal necks are long and funnel-shaped. The
sutures are undulated, with a backwardly-directed sinus correspond-
ing with the siphuncle. Owing to the characters of the suture-
lines, the genus Lactrites has been regarded as related to the

NAUTILOIDEA. 847

Goniatites, and as representing an ancient type of the Ammonoids,
but it is now generally placed among the Nautiloids. The species
of the genus are Silurian and Devonian.

PROSIPHONATE NAUTILOIDS.

All the groups of the Nautiloids which have been previously
considered are ‘‘retrosiphonate,” having the septal necks directed
backwards. On the other hand, the genera Vothoceras and Lath-
moceras are “‘prosiphonate,” the septal necks being directed
towards the aperture of the shell. The genus Lathmoceras is
Ordovician, and is characterised by the possession of a straight
cylindro-conical shell, the septate portion of which is always trun-
cated. The aperture is simple, and the siphuncle is marginal, and
is ensheathed by numerous short invaginated funnels derived from
the closely-set septa. In the Silurian genus /Vothoceras the shell
is nautiloid and widely umbilicated; the sutures are simple and
concave ; the siphuncle is ventral in position ; and the septal necks
are short and are directed forwards.

848

lala eA ella ke
TETRABRANCHIATE CEPHALOPODS—continued.

SuB-ORDER II. AMMONOIDEA.

In this division of the Tetrabranchiate Cephalopods, the shell is
usually rolled up into a spiral disc, but may be turreted, straight,
hook-like, &c. The aperture may be simple, or may be furnished
with lateral and ventral processes. The siphuncle is slender, cylin-
drical, marginal in position, and never contracted internally by
shelly deposits. The septal ‘“‘ necks” are generally directed forwards,
though in some forms (e.g., Gonzatitid@) the reverse of this obtains.
The septa are more or less folded or lobed, and the sutures are
waved, angulated, or bent into “lobes” and ‘‘ saddles.” ‘The struc-
tures known as the “‘ Aptychus” and “ Anaptychus” are commonly
present. Lastly, the shell commences with a globular or inflated
‘“‘protoconch,” which is more or less
clearly constricted off from the first
septal chamber (fig. 744, D—G).

The general structure of the shell
and its mode of development have been
already treated of (see p. 829 and p.
832); but there are some _ special
features in the shell of the Ammonozdea,
as compared with that of the JVauzzl-
oidea, which require consideration here.

The dody-chamber of the Ammonoidea
is of variable size, but in a number of
forms it is remarkable for its great

Fig. 762. — Section of Avietites length as compared with its diameter
1 oom ibe owns Be (fig, 762), this implying that hempeam

of the animal was very long and nar-
row. In some cases, indeed, the body-chamber may occupy an
entire volution of the shell, or even a volution and a half.

AMMONOIDEA. 849

The agerture of the shell in the Ammonoids is commonly fur-
nished with lateral extensions or “ears,” while its ventral or external
side may be prolonged into a long pointed process or lobe. In this
way a kind of cowl is
sometimes formed above
the aperture, and the
width of the opening
may be considerably
contracted by the in-
ward bending of these
lobes (fig. 763). In the
Goniatitide and Clyme-
nude the aperture re-
sembles that of Vautclus
in being simple, with a ;
ventral sinus. In many Fig. 763.—Stephanoceras Brackenridgii, viewed laterally

ihe and in front, showing the extensions of the margin of the
cases the shell exhibits aperture. Jurassic.
at intervals transverse
ridges or contractions (‘“‘ varices”), which represent the periodically
formed mouths of the shell.

The ventral and dorsal sides of the shell of the Ammonoids
cannot be always determined with certainty. There are, however,
strong grounds for considering
the external or convex side of
the bent shells to be ventral,
while the concave or internal side
is dorsal.

The siphuncle in the Ammon-
oids is always cylindrical, and is
never furnished internally with
secondary calcareous structures re-
sembling the “ obstruction-rings ”
of many Nautiloids. Usually the
sheath of the siphuncle is calci-
fied, so that a continuous shelly
tube is produced. The siphuncle
commences by an inflated por-
tion (fig. 764, a), which indents Fig. 764.—Section of Ammonites (Cosmo-

ceras) Parkinsoni, in the mesial plane, show-

the protoconch (pr) on one side ; ing the ‘“‘prosiphon” (J), the siphuncle (sz)
a ae : & = with its dilated commencement (a), and the
saeeinis, tO Deon with, either~ protoconch G). (After Munier-Chalmas.)
internal or central in position.
In the majority of the Ammonoids the siphuncle ultimately comes
to be placed on the external margin of the shell (fig. 764, s7), but
in the Clymeniide it remains internal. ‘The septal ‘‘ necks” of the
Ammonoids are variable in their development, as also in position.

(0 | Pe 3H

850 TETRABRANCHIATE CEPHALOPODS.

In most cases the shell is ‘‘ prosiphonate,” the septal necks being
directed forwards, and being at the same time usually feebly devel-
oped. In the Clymentide and Gontatitide the shell is “retrosi-
phonate,” the septal necks being directed backwards; and in the
former family these structures are so largely developed that they
extend from one septum to the next behind.

The septa of the first-formed chambers of the shell of the Ammo-
noids are simply curved, or may be more or less bent, whereas in
the adult portion of the shell they are always undulated or folded,
the degree to which this takes place varying in different types. In
the more specialised forms of the Ammonoids the septa “are nearly
flat in the middle, and folded round the edge (like a shirt-frill) where
they abut against the outer shell-wall” (Woodward). ‘The result of
this is that the ‘‘ sutures,” or edges of the septa, appear on the sur-

rel

mall

Fig. 765.—One-half of the suture of Awemonites (Amaltheus) Truellez ; p, Siphonal or ven-
tral lobe, traversed by the siphuncle (7); L, Superior-lateral lobe; &, Inferior-lateral lobe; al,

Az, A, a4, Auxiliary lobes ; sp, External saddle; st, Lateral saddle ; sl, s2, s3, sf, Auxiliary
saddles.

face of the shell in the form of angulated, lobed, or foliaceous lines
(fig. 765).

The angulated or digitated portions of the suture which are
directed backwards, away from the mouth of the shell, are called
the “‘ Jobes.” The elevations between the “ lobes,” which point to-
wards the aperture of the shell, are called the ‘‘ saddles.” These
parts (fig. 765), as seen in one of the spirally-coiled Ammonoids,
have the following arrangement: In the middle of the convex or
ventral side of the shell is a single unpaired lobe, which is traversed
mesially by the siphuncle, and is termed the ‘ external,” ‘ ventral,”

r “siphonal” lobe (D). The lobe on each side of this (L) is known
as the ‘“ superior-lateral lobe.” The lobe on each side next to this
again (E) is the so-called ‘‘ inferior-lateral lobe”; and the lobes which
follow this (of a variable number) are distinguished as the ‘‘ auxiliary
lobes” (at, a7, a3, a*). Lastly, there is a second unpaired lobe im-
mediately opposite to the ventral lobe, placed upon the concave side

AMMONOIDEA. 851

of the shell, and known as the “ internal,” “‘ dorsal,” ‘‘ antisiphonal,”
or “columellar” lobe. The “saddles” are similarly subdivided and
distinguished. Between the ventral and superior-lateral lobes comes
the ‘‘ external saddle” (sp). Next to this, between the superior-
lateral and inferior-lateral lobes, is placed the first ‘lateral saddle ”
(s L), followed on each side by a variable number of “auxiliary sad-
@lecii (St, iS2,:s*, S*);

Associated with various forms of Ammonoids, sometimes situated
within the body-chamber of the shell, or at other times wholly
detached, are found the peculiar bodies to which the name of
“‘Aptychi” has been applied. <A typical Aptychus (figs. 766, 767)

SUI S SA |||!
aN ‘\ \ \

Fig. 766.—Afptychus (Trigonellites) Fig. 767. — Aptychus carinatus,
lamellosus. Jurassic. (After Wood- within the body-chamber of an Am-
ward.) monite.

consists of two bilaterally symmetrical halves, which are somewhat
semicircular in shape, and are apposed to one another by their
straight inner margins, which are destitute of teeth. In some cases
the Aptychus is thin and horny, but it is usually more or less exten-
sively calcified, and its thickness is sometimes considerable. In the
thick shelly types, the principal layer of the Aptychus has a peculiar
cellular structure. The surface may be smooth or variously sculp-
tured, and the inner face is commonly marked by concentric lines
of growth. In the bodies to which the name of Syzaptychus has been
given, the general structure is similar to that of Aptychus, but the
two halves of the structure are fused in the middle line. Bodies of
this type have been found in the body-chamber of species of Sca-
phites. In Anaptychus, again, the structure is a thin, apparently
horny, undivided plate, which is concentrically striated. Bodies of
this nature have been found in association with certain forms of
Ammonites and Goniatites. Some of the fossils which have been

852 TETRABRANCHIATE CEPHALOPODS.

described as the cephalic bucklers of Phyllocaridan Crustaceans
(such as some of the forms referred to Cardiocaris and Spathiocaris)
are in reality the “‘ Aptychi” of Goniatites. Many theories have
been held as to the nature of the ‘‘ Aptychi” of the Ammonoids,
but there are only two views which can be regarded as at all prob-
able. On one of these views, the Aptychi are to be regarded as
protective plates developed in the walls of the nidamental gland, in
which case all examples of Ammonites possessing these structures
are necessarily females. The more probable theory, however, is
that put forward by Sir Richard Owen—viz., that the Aptychus is
formed by the deposition of horny matter or lime within a structure
corresponding to the “hood” of the existing Pearly Nautilus. On
this view the Aptychus would act as an operculum, when the animal
was withdrawn within the shell. In those Ammonoids which are
devoid of Aptychi it must be supposed that the “ hood” remained
permanently uncalcified, as it does in the Pearly Nautilus.

As regards their zoological affinities, the Ammonoids have been
generally regarded as belonging to the Tetrabranchiate division of
the Cephalopoda, in which case the shell, like that of the Pearly
Nautilus, must have been external. It has, however, been also
held that the Ammonoids are really referable to the Dibranchiate
division of the Cephalopods, in which case the shell, like that of
the existing Szru/a, must have been internal. The grounds for
this view are chiefly derived from the mode of development of the
shell of the Ammonoids, which resembles that observed in Spirula
—the protoconch being in each case inflated and destitute of a
cicatrix, while a ‘“‘ prosiphon” is present. The “ Aptychi” of the
Ammonoids have also been compared to the “nuchal cartilages ”
of the Cuttle-fishes. Upon the whole, however, the balance of
evidence is in favour of the reference of the Ammonoids to the
Tetrabranchiata—the groups of the Clymenitde and Goniatitide
affording a transition between the two great sections of the Am-
monoidea and LVautiloidea.

As regards the general distribution in time of the Ammonotdea,
the most ancient types of the group belong to the genus Gonzatztes,
in the wide sense of this name, and are found in the highest Silurian
and the lowest Devonian deposits. The genus CZymenza, which,
like Gontatites, is comparatively simple in morphological type, is
also found in Devonian strata. The earliest forms of the ‘“‘ Am-
monites” are found in the Permo-Carboniferous rocks of India, but
in other regions the earliest representatives of this great section
of the Ammonoids appear in the Trias. In the Mesozoic period
the Ammonoids undergo a vast development, the principal and
most widely distributed type being that of the ‘‘ Ammonites.”
In the Cretaceous rocks, however, numerous new and _ varied

AMMONOIDEA. 853

generic types are found, such as Baculites, Hamittes, Turrilites,
Piychoceras, &c. With the close of the Cretaceous period, the
entire group of the Ammonotdea underwent an apparently sudden
and all but complete extinction, no undoubted examples of this
division of Cephalopods being known in any unequivocal Tertiary
strata, with the exception of certain ‘‘ Ammonites” which have been
found in the Eocene deposits of California.

In the following brief summary of the families of the Ammonoidea
the arrangement adopted by Zittel has been adhered to :—

FAMILY 1. CLYMENIID@.—In this family the suture-lines show
simple lobes and saddles (fig. 768) ; the septal “necks” are directed
backwards, the shell being
“‘retrosiphonate”; and the
siphuncle is placed on the
internal side of the shell.

The only genus included
in this family is Clymenia
itself (fig. 768), in which
the shell is coiled into a
flat spiral, the whorls of
which are in contact. The
inner side of each whorl
is deeply excavated for the
reception of the convexity
of the preceding whorl,
and the inner coils of
the spire are exposed to
view. The body-chamber
is long; the aperture has
a ventral sinus; and the
surface is smooth or
marked with fine trans- Fig. 768.—Clymenia Sedgwicki?z. Devonian. The
verse striz. The sutures lower figure shows the form of the suture.
are simply folded or lobed,
and the siphuncle is marginal, and is placed on the internal or
concave side of the shell. The septal ‘‘ necks” resemble those of
the Pearly Nautilus in being directed backwards, and they are some-
times short, or at other times invaginated into one another. ‘The
protoconch resembles that of the Gonéatitide in form, and is with-
out a cicatrix. The known species of CZymenza are confined to the
Upper Devonian rocks, some of the limestones of this age in Ger-
many being spoken of as the “‘ Clymenienkalk,” owing to their being
profusely charged with fossils of this genus.

FAMILY 2. GONIATITIDZ.—In this family the shell is spirally
coiled, with more or less embracing whorls; the suture-lines are

854 TETRABRANCHIATE CEPHALOPODS.

simply lobed or angulated, and are not foliaceous; the septal
“necks” are directed backwards; and the siphuncle is marginal,
and is placed on the external side of the shell. The “ protoconch”
(fig. 744, D and £) is inflated, and is devoid of a cicatrix.

This family comprises the comprehensive genus Gonzatites, which
has been divided by Hyatt into a considerable number of generic
groups, which need not be characterised here. In all the forms
included under the general name of Gonzatz/es the shell (fig. 769) is
discoidal, the extent to which the inner turns are exposed varying
widely in different forms. In some cases there is a wide umbilicus,
and the inner volutions are extensively exposed ; whereas in other
forms the umbilicus is much reduced in size, and the last whorl
more or less completely conceals those which preceded it. ‘The
body-chamber is usually long; and the sur-
face is generally smooth, but may be adorned
with tubercles or ribs. The sutures show
simple, sometimes rounded, sometimes an-
gulated lobes and saddles. The septal
“necks” resemble those of the /Vautc:ide
and of Clymenta in being directed back-
wards, the shell being thus ‘‘ retrosiphonate.”
On the other hand, the slender siphuncle
resembles that of the Ammonites in being

i i |

Fig. 769.—Goniatites (Gastrioceras) Fosse. Carboniferous.

marginally placed on the exzerna/ side of the shell. In some cases
simple or divided ‘‘ Aptychi” have been shown to be present.
The genus Gonzatites, using the name in the wide sense, com-

AMMONOIDEA. 855

prises about three hundred species, all of which are confined to the
Palzozoic rocks. The earliest types appear in the later Silurian
deposits, and have very simple suture-lines. In the Devonian and
Carboniferous rocks numerous forms of Goniatites are known; and
the latest representatives of the group are found in the Permo-
Carboniferous beds of the Salt Range in India. In certain of the
Devonian and Carboniferous Goniatites the sutures become com-
plicated by the increase of the number of lobes and saddles, till
a near approach is made to the structure of the septa in the
Ammonites.

FAMILY 3. ARCESTID#.—In this family the shell is discoidal,
and the body-chamber is very long, extending over one or one and
a half whorls. The surface of the shell is smooth, or may be
adorned with transverse strize, ribs, or folds. The suture-lines show
very numerous lobes and saddles, and both of these are laterally
incised, thus becoming foliaceous (fig. 770). No ‘‘ Aptychus” is
present. [In some forms a horny “Anaptychus” appears to have
existed. |

The members of this, as of all the remaining families of the
Ammonoidea, are distinguished from the Clymentide and Goutati-

RGSS Ore se NX
re Py ee eae

Fig. 770.—Suture of Cyclolobus Oldham, one of the Arcestide. _Permo-Carboniferous, India.
(After Waagen—copied from Zittel.)

tide by the greater complexity of their septa and the more ornate
form of the sutures resulting from this; while the septal ‘ necks”
are always turned forwards, and the shell is thus ‘‘ prosiphonate.”
Formerly all these forms were grouped under a comparatively small
number of genera, such as Ceratites, Ammonites, Hamites, Turrt-
lites, Baculites, &c., distinguished principally by the mode of growth
and the resulting form of the shell. By far the most important of
these groups was the comprehensive genus Ammonites, embracing
the great series of forms commonly known as “ Ammonites.”
Through the researches of Hyatt, Neumayr, Mojsisovics, Waagen,
von Zittel, and other well-known investigators, it has now been shown
that the old genus Ammonites can no longer be maintained, but
that the types formerly included under this name admit of a natural

856 TETRABRANCHIATE CEPHALOPODS.

division into a number of genera, which in turn constitute a number
of distinct families. These modern divisions of the old genus
Ammonites are distinguished by such morphological characters as
the size of the body-chamber, the form of the sutures, the shape of
the aperture, and the presence or absence of an “ Aptychus.” The
mere form of the shell is a matter to which comparatively small
weight is attached. Hence genera such as Saculites, Turrilites,
and the like, in which the most obvious peculiarity is the external
configuration of the shell, are now distributed, on the ground of
their internal structure, among the different families into which the
genus Ammonites has been broken up.

The three principal genera of the Arcestide are Arcestes, Cyclo-
lobus, and Lobites. In the genus Avceszes the shell is involute, the
last whorl being of large size, more or less completely concealing the
inner whorls, from which it often differs in character. The umbilicus
becomes constricted in course of growth, and is commonly completely
closed by a callous deposit. The aperture is without lateral lobes,
and the surface is smooth or furnished with fine transverse strie.
The species of Avcestes are almost exclusively Triassic, though early
types (Avcestes priscus, Waagen) appear in the
Permo-Carboniferous rocks of India, in which
also is found the nearly allied genus Cyclolo-
bus (fig. 770). The genus Lodztes agrees with
Arcestes in the general form of the shell, the
long body-chamber, and the common closure
of the umbilicus by a callosity. The surface,

: ; however, is commonly marked with radial
a pene folds (fig. 771), sometimes intersected by

longitudinal striz. The aperture may be
simple, but is usually prolonged into a projecting hood. The
species of this genus are confined to the Trias.

FAMILY 4. TRopitip#.—In this family the shell is discoidal, with
a long body-chamber, extending over more than one whorl. The
surface is more or less richly ornamented, with radial ribs which
often carry spines or tubercles. ‘The sutures are foliaceous, the
lobes and saddles being laterally incised. The principal genus of
this family is Zropztes itself, the species of which are found in the
Trias principally, but survive into the Lias.

FAMILY 5. CERATITIDZ.—In this family the form of the shell is
variable, and its surface is ornamented with ribs or tubercles. The
body-chamber is short, not extending over more than one-half or
three-quarters of a volution. The sutures mostly show simple non-
serrated “saddles,” while the “lobes” are denticulated (fig. 772).
The aperture is simple, and an “ Aptychus” is not known to have
been present.

AMMONOIDEA. 857

The type of this family is the genus Ceravtfes (fig. 772), in which
the shell is discoidal, the whorls in contact, and the inner volutions
exposed to view. The lobes of the suture are denticulated or
crenulated, while the saddles are simply rounded. The genus is
characteristically Triassic,
and the majority of the
species are found in the
Muschelkalk. In the
Triassic genus TZvrachy-
ceras (fig. 773) the gen-
eral characters resemble
those of Ceraztzes, but the
saddles are in general
laterally incised instead
of being quite simple.

The preceding genera
possess a discoidal shell,
the whorls of which Bre Fig. 772.—Ceratites nodosus. Muschelkalk
in contact, but there are (Middle Trias).
three Triassic genera in-
cluded in this family in which the form of the shell is different.
Thus, in Choristoceras the shell forms a flat spiral, the inner whorls
of which are contiguous, while the last whorl is disjunct. In Cochlo-
ceras, again, the shell is turreted, while there is the additional
peculiarity that the lobes,
as well as the saddles,
of the suture are simple.
Lastly, in ARhabdoceras the
shell is straight, the lobes
of the suture being like-
wise free from denticula-
tions.

FaMILY 6. CLADISCI-
TID#Z.—In this family the
shell is discoidal, and the
body-chamber is long, ex-
tending over one whorl or
thereabouts. The shell is
thick and laterally flattened, the surface being spirally striated or
smooth. The suture shows foliaceous saddles and finely incised
lobes. This family was founded by Zittel to include certain Triassic
‘** Ammonites,” most of which belong to the genus C/adiscites itself.

FAMILY 7. PINACOCERATID#.—The shell in this family has the
form of a compressed disc, usually with a smooth surface. The
body-chamber is short, occupying from a half to two-thirds of the

> i ren
rags

Fig. 773.—Tyrachyceras Aon. Trias.

858 TETRABRANCHIATE CEPHALOPODS.

last volution. The suture has very numerous lobes and saddles,
which are sometimes incised, sometimes comparatively simple, one
or more adventitious lobes being usually
present. An “ Aptychus” is not known to
have existed.

The genus Pinacoceras itself includes
a number of Triassic ‘‘ Ammonites,” which
sometimes attain to a great size (a yard or
more in diameter), and are distinguished
by the extraordinary complexity of the
suture-lines. On the other hand, in the
genus Sageceras, though the sutures show
very numerous lobes and saddles, this com-
! plexity does not exist, the saddles being
ne ees of Pe tongue-shaped and entire, while thewiebes
oceras heterophyllum. Ju- : : : 3
rassic. are simply indented. ‘The species of this

genus are chiefly Triassic, but early types
appear in the Permo-Carboniferous (“ Salt-Range Group”) of India.

Famity 8. PHYLLOCERATID&.—In this family the shell (fig. 774)
is discoidal, the body-chamber occupying from one-half to three-
fourths of a volution. ‘The surface is smooth or adorned with

Fig. 775.—Outline of Phylloceras Fig. 776.—Suture-line of Phylloceras hetero-
heterophyllum, showing the lobes fPhyllum. vp, Siphonal lobe; L, Superior-lateral
and saddles. pb, Siphonal lobe; L, lobe; L’, Inferior-lateral lobe; a@ a, Auxiliary
Superior-lateral lobe; L’, Inferior- lobes ; @, External saddle; Z, Lateral saddle.

lateral lobe; a a, Auxiliary lobes;
v, Antisiphonal lobe; d, External
saddle; Z, Lateral saddle.

transverse strize; and the aperture is simple. The lobes and sad-
dles of the suture-line (fig. 776) diminish gradually in size in pro-
ceeding from the external towards the internal side of the shell;

AMMONOIDEA. 859

and the saddles terminate in bladder-shaped rounded ends. An
‘““ Aptychus” is not known to have been present.

The type-genus of this family is Phy//oceras, comprising involute
““ Ammonites,” with a widely expanded body-chamber, a com-
pressed form, and either no umbilicus or a small one (fig. 774).
The surface usually exhibits fine transverse strize, which are directed
forwards ; and the external margin is never keeled or tuberculated.
The aperture is simple, with short ventral lobes. The most char-
acteristic feature, however, is the presence of numerous saddles,
which gradually diminish in size from without inwards, and which
end in rounded or bladder-shaped extremities (fig. 776). The
species of Phylloceras range from the Lias to the Cretaceous
rocks, but the genus is preceded in the Trias by allied types
(Megaphyliites).

FAMILY 9. LyTOCERATID#.—Shell extremely variable in shape ;
the body-chamber in the coiled types occupying from two-thirds to
three-quarters of the last volution. The surface is adorned with
simple, wavy, or nodose ribs, which may be straight or bent. The

Fig. 777-—Suture-line of Lytoceras Liebigt, Jurassic. s, Siphonal lobe; Es, External saddle.

suture-line exhibits few (generally six), deeply incised lobes and
saddles ; the superior, and commonly also the inferior, lateral lobe
being divided into two symmetrical halves, while the saddles may
also be more or less clearly bilateral (fig. 777). An “ Aptychus”
is only known in the single genus Bacu/dizes (Zittel).

The type-genus of this family 1s ZLy¢oceras itself, which, like all
the ‘“‘ Ammonites,” possesses a discoidal shell. As shown, however,
by Neumayr, the characteristic suture-line of Lytoceras is possessed
by a number of forms, such as Turrelites, Baculites, Hamites, &c., in
which the shell may be coiled into a turreted spiral, or may be
straight, hook-shaped, &c. The shell in Ly/oceras (fig. 778) is dis-
coidal and widely umbilicated, the whorls contiguous but hardly
or slightly overlapping. The surface is usually adorned with radial
lines of growth, or periodic contractions of the shell, with corre-
sponding prominent fringed ribs (“fimbrie”) at intervals. The
aperture is simple, with an internal lappet resting on the preced-
ing whorl. The suture-line (fig. 777) is complex, the lateral lobes

860 TETRABRANCHIATE CEPHALOPODS.

and saddles being divided into small symmetrical digitations. The
species of Zytoceras range from the base of the Lias to the middle

Fig. 778.—Lytoceras fintbri-
atun. Lias.

of the Cretaceous system.

The genus JZacroscaphites (fig. 779)
comprises a portion of the forms included
in the old genus Scaphites, and the suture-
lines agree with those of Lyfoceras and its
allies in the fact that the lateral lobes are
divided into two symmetrical halves. The
first portion of the shell is coiled into a
flat spiral, the volutions of which are in
contact, but the last-formed portion of the
shell is disjunct and is prolonged in a
straight line, its terminal extremity being
bent upwards and backwards. ‘The species
of this genus are confined to the Lower
Cretaceous rocks. :

In the genus Aamites (fig. 780) the shell is an extremely elon-
gated cone, which is bent upon itself more than once in a hook-

Fig. 779. — Macroscaphites
Tvanii,. Cretaceous. (Neo-
comian.)

like manner, all the volutions being separate.
The surface is usually adorned with trans-
verse ribs, and the body-chamber is very
long. The suture resembles that of the
Lytoceratide in the fact that the superior-
lateral lobe (as also commonly the inferior-
lateral lobe) is divided into two symmetrical '
halves, the saddles also being bilaterally
symmetrical. ‘The species of Alamztes range
from the Neocomian to the Chalk, and
some forms attain a considerable size.
The Cretaceous (Neocomian) genus Hamu-
fina differs from SZamites in the fact that
the elongated shell is only bent once, its
two portions being parallel to one another
but not in contact. In the genus Ptycho-
ceras, again, the shell (fig. 781) has the
form of a greatly elongated cone, which is
once bent upon itself, the two straight por-
tions of the shell being in contact. ‘The
thicker limb of the shell is transversely
ribbed; and the sutures have the same
form as those of Afamuztes. The species of

Ptychoceras are exclusively Cretaceous, and range from the Neo-

comian to the Gault.

In the genus Zurrilites (fig. 782) the shell has the form of a

AMMONOIDEA. S61

turreted spiral, being composed of volutions which pass obliquely
round a central axis, an umbilicus being present or absent. The
shell is usually sinistral, but is sometimes dextral. The surface
is adorned with ribs or nodosities; and the lateral lobes of the
suture-line are symmetrically divided. In TZwurrilites proper (fig.

Fig. 780.—Hamiites rotundus, restored. Cretaceous. (Gault.)

782) the volutions of the shell are in contact, whereas in He/sco-
ceras the shell is coiled into an open spiral, the coils of which do
not touch. Certain of the forms which have been placed in the
genus Ffeferoceras (such as HY. polyplocum) agree in the form of
their sutures with Zwurrilites, from which they
only differ in the fact that the terminal portion
of the shell is coiled into an open spiral, the
last whorl sometimes being prolonged in a
straight line. All the types in question are
Cretaceous, and range from the Neocomian to
the Chalk.

Lastly, the genus Laculites is included in the
family Lyzoceratide from the form of its suture-
lines, the superior-lateral lobes being symmetri-
cally divided. The shell in this genus (fig.
783) is in the form of a straight elongated
cone, with a long body-chamber, the aperture
of which is simple and is prolonged ventrally.
In some forms a divided “‘ Aptychus” has been
shown to exist. The species of this genus .
range from the Neocomian to the highest beds _ Fig. 781.—Peychoceras
of the Chalk. ine Newnan

FAMILY 10. PTycHITIDZ.— This family in-
cludes forms of ‘‘ Ammonites,” of variable shape, the spirally
coiled shell being flat or ventricose, with a wide or narrow um-
bilicus. The body-chamber occupies from two-thirds to three-
fourths of a volution. The sutures are sometimes simply angu-
lated and resemble those of the Goniatites; or the saddles are

ape nmny

862 TETRABRANCHIATE CEPHALOPODS.

round and the lobes denticulated, as in Ceratites ; or both sad-
dles and lobes are incised. No “ Aptychus” is present (Zittel).
The genera included in this family are mostly Triassic, the type-

ya,
—\
sail

Dally

m7 :

Y

Fig. 782.— Turrilites catena- Fig. 783.— Baculites

tus. ‘The lower figure repre-
sents the entire shell; the up-
per figure represents the base

anceps, showing part of
the body-chamber and
a portion of the septal

of the shell seen from below. chambers. Chalk.
Gault.

genus being Ptychizes itself, in which the sutures have both the lobes
and the saddles incised.

FamMILy 11. AMALTHEIDA.—This family includes ‘“ Ammonites,”
in which the shell is discoidal and laterally compressed (fig. 784,
785), and the last whorl conceals a considerable portion of the
preceding volutions. The body-chamber occupies about two-thirds

AMMONOIDEA. 863

of the last volution. The external side of the shell is acute, or is
provided with a projecting keel, which is often hollow. The sutures
are usually deeply incised, but may resemble those of Cera#ites in
form. A horny “ Anaptychus” has been shown to exist in a
number of forms.

The type-genus of this family is Ama/theus itself, in which the
shell (figs. 784, 785) is furnished along its external margin with an

Fig. 784.—A maltheus (Ammonties) mar- Fig. 785.—Amaltheus (Ammonites)
gartiaius. Lias. cordaius. Jurassic (Coral Rag).

acute or transversely plaited keel. The surface may be smooth,
striated, or transversely ribbed. The aperture is furnished with a
ventral process, and the sutures have deeply incised lobes and
saddles. Numerous species of this genus are found in the Jurassic
rocks, beginning in the Lias.

Nearly allied to the preceding is the genus Sch/oenbachia (figs.
786, 787), in which the external side is broad, and is furnished
with a strong median
keel, in the hollow of 4
which the thick siph- Aah hf JA
uncle is usually con- \\ i 4
tained. The surface is / ’ AA
transversely ribbed, and sg iu iB
the aperture is falciform, | \\—=Saetr=
and is provided on its | ==
ventral side with a for-
wardly directed process.
The species of this genus
are exclusively Cretace-

Fife
f ;

ous, and range from the Fig. 786. —Side-view _ of Fig. 7$7.—End-view
a : Schloenbachia Rotssyana. Cre- of Schloenbachia cris-
Neocomian to the Chalk. 2csne Z Pe ba eae

In the Cretaceous
genus Buchiceras the external edge of the shell is acute or keeled,
but the sutures resemble those of Ceratites so closely that the
forms of this type were formerly referred to the latter. Lastly,

864 TETRABRANCHIATE CEPHALOPODS.

the genus Oxynoticeras includes a number of Jurassic and Cre-
taceous ‘ Ammonites,” which differ. from those comprised in
Amaltheus chiefly in the form of the suture-lines.

FAaMILy 12. ASGOCERATID#.—The shell in this family of “ Am-
monites” is discoidal, compressed, and usually widely umbilicated ;
the surface generally with simple transverse ribs. The body-chamber
occupies about three-fourths of the last
volution, and the aperture is without
lateral extensions. The suture is incised,
with two lateral lobes, incompletely de-
veloped auxiliary lobes, and a bifurcated
antisiphonal lobe. An ‘ Anaptychus”

is present (Zittel).

S44 = The type-genus of this family is
Xe pe Fgoceras (fig. 788), in which the sur-
LS face shows simple transverse ribs spread
out or split ventrally. The external side
of the shell is rounded, without either a
Mee PE cs 9 median keel or furrow. The species of
cornum. Lias. this genus are confined to the Lias. The
most important genus in this family is,
however, Ariedites (fig. 789), in which the shell is flat and discoidal,
widely umbilicated, and many-whorled. The external margin is
more or less flattened, and is provided with a median keel bordered
by a lateral furrow on each side.
The surface has simple straight ribs,
which often have tubercles developed
on them near the ventral margin.
The body-chamber is long (fig. 762),
and occupies one volution or more.
A large number of species are known,
all of which are confined to the
Fig. 789.—Arietites CE bisul- rope Da, ss Due 4 The
" catus, reduced in size. Lias. ZUSUS, Zk: bisulcatus, and A. von
jormis being familiar species. If
the name of Ammonites is to be employed at all as a generic

designation, it must be for the forms here in question.

FAMILY 13. HARPOCERATID#.—In this family the shell (fig. 790)
is discoidal, compressed, and umbilicated ; the external margin is
obtusely or acutely keeled ; and the surface is adorned with falciform
ribs or striz. The aperture is falciform, and is furnished with
rounded auricles and a long, pointed, ventral process. ‘The suture
is digitated, and the antisiphonal lobe is undivided. A calcified
‘““ Aptychus ” is present.

The type of this family is the genus Harfoceras, of which very

ran

it)
-

Bal Ay

AMMONOIDEA. 865

numerous species are known, none of which transcends the limits of
the Jurassic system. Familiar forms are the H. ({ildoceras) bifrons

Fig. 790.—Harpoceras (Hildoceras) bifrons. Lias.

(fig. 790) and . serpentinum of the Upper Lias. Allied to Harfo-
ceras is the Jurassic genus Offelza, in which the shell is involute,
and the umbilicus is much reduced in

s1ze. cl

FAMILY 14. HAPLOCERATID#.—In this &\\\\ il f | f
family the shell is discoidal, with a wide ANG /
or narrow umbilicus ; the external margin
being rounded, or in a few cases feebly
keeled. The surface is adorned with fine
lines of growth or curved ribs, commonly
with falciform constrictions or varices.
The aperture has feebly developed auricles;
the suture-line is deeply incised ; and an
‘“* Aptychus” has hitherto been recognised

OW 20

Fig. 791.—Desmoceras (Am-
in a few forms only. monttes) ligatum. Cretaceous

(Neocomian).

The family of the Hafloceratide ranges
from the Lower Jurassic rocks to the Chalk, and the principal
genera are Haploceras and Desmoceras (fig..791).

FAMILY 15. STEPHANOCERATID&.—The form of the shell in this
family is variable, but the external margin is in general broad and
rounded, and is never keeled; while the surface is almost always
adorned with transverse ribs, which may carry tubercles, and usually
bifurcate near the ventral border (fig. 792). The body-chamber
occupies from one-half to two-thirds of the last volution. The
aperture is commonly furnished with wide lateral extensions or lap-
pets, which may be inflected to form a sort of cowl (fig. 763). The

VOL. I. 301

866 TETRABRANCHIATE CEPHALOPODS.

lobes and saddles of the sutures are incised, and a calcified “‘ Apty-
chus ” is present.

In Stephanoceras itself (792) the shell is discoidal and usually
widely umbilicated, and the surface is ornamented with strong ribs,

ye
My

Fig. 792.—Stephanoceras (Anenonites) Hunephrestanum. Inferior Oolite.

which are simple internally, but become once or more divided on
approaching the external border ; the point of bifurcation being in
general marked by the development of a more or less prominent

\ \ \\"\ 1] a) f')
\\ \\\\\\ \( HL yp,

K \\ AME A] /
NY iit 7 iy yp
CS Wh SY

WSs Q SENT Tos

Fig. 793-—Caloceras (Ammonites) Fig. 794.—Ce@loceras (Ammonttes)
annulatum. Lias. conumune. Laas.

tubercle. The species of the genus are confined to the Jurassic
rocks.

Very closely allied to the preceding is the genus Ce/oceras, but
the types included under this name have a long body-chamber (ex-
tending over more than one whorl), while the aperture of the shell

AMMONOIDEA. 867

is simple and without side-lappets. The surface-sculpture is similar
to that of Stephanoceras. All the species of Caloceras are found in
the Lias, two well-known forms being
C. (Ammonites) annulatum (fig. 793),
and C. (Ammonites) commune (fig.
794).

In Cosmoceras (fig. 795) the shell
is discoidal and the surface-ribs are
bent forwards, and often have tuber-
cles or spines developed along their
external ends. The aperture of the Fig. 795.—Cosmoceras (Ammonites)

5 : 3 ason, reduced in size. Jurassic
shell is furnished with long lateral (Oxford Clay).
extensions, which may disappear with
age. ‘The species of Cosmoceras are Jurassic and Lower Cretaceous.

In Perisphincies (fig. 796) the shell is discoidal, and usually widely
umbilicated, with a rounded external border. ‘The surface-ribs
divide, each, near the siphonal margin, into two or more branches.
The body-chamber extends over two-thirds or the whole of the last
whorl, and the aperture is simple, with lateral extensions or auricles.

GX

aN
f \i

WIE
(Zs

=——,)),”
i

Fig. 796.—Perisphinctes (Ammonites) Fig. 797. — Hoplites (Ammonites)
Martinst. Inferior Oolite. Jalcatus. Cretaceous.

\

\

A very large number of species of this genus are known, ranging
from the Inferior Oolite to the Lower Cretaceous.

In the genus Hoplites (fig. 797) the shell differs from that of
Perisphinctes in being involute, with the umbilicus narrow, and
the whorls high. The surface-ribs spring from tubercles near the
umbilical margin, which divide as they proceed outwards, and are
generally interrupted by a broad furrow along the line of the external
border of the shell. The species of this genus are characteristic of
the Cretaceous system.

In Acanthoceras the shell (fig. 798) is discoidal and umbilicated,
and the sculpture consists of strong, straight, undivided, or divided

Ne ud

868 TETRABRANCHIATE CEPHALOPODS.

ribs, which increase in width in proceeding from the umbilicus to- '
wards the external margin, and are often adorned with tubercles. ,
In the genus Aspidoceras, again, the shell (fig. 799) may be flat and

widely umbilicated ; or it may be inflated and involute, witha narrow
umbilicus. The sculpture consists of one or two rows of tubercles, {
which occasionally become obsolete in late life, while ribs are as a :
rule only present in young examples. ‘The numerous species of ft

\ \ ies
YW hy i}

IA

ed ZA Z2.we YW
= \G\ Ny fp ZZ 2 ISN \\\\ i@ YEE
es Ca: a A
" COV Ay’ “SS
SS fi 4 ES WHS =
SSS oA PGS
Uf Yj HN N SS
A AQ NS
(EWES
Fig. 798.—Acanthoceras Deverianum. Fig. 799.—Asfpidoceras longispinum.
Cretaceous (Lower Chalk). Jurassic (Kimeridge Clay).

Acanthoceras are wholly Cretaceous, while Aspidoceras ranges from
the Middle Jurassic to the Lower Cretaceous. Allied genera are
Simoceras and Peltoceras, both of which are confined to the Jurassic
series.

All the preceding forms of the Stephanoceratide possess a spirally-
coiled shell, the volutions of which are contiguous and lie in a single
plane; and all belong to the great group of the “ Ammonites.”
There are, however, other types, with a vari-
ously coiled shell, which, as judged by their )
general morphological characters, appear to be
properly referable here. Amongst the types
in question is the genus Scaphites, as re-
stricted by the removal to the Lytoceratide
of the forms which constitute the genus JZa-
croscaphites. In Scaphites proper the shell (fig.

800) consists of a series of volutions coiled

| into a flat spiral, but having the last whorl

ae ee aoe detached from the others, produced, and ulti-

lis. UpperCretaceous. mately bent back in the form of a crosier.

The suture-line shows several auxiliary lobes ;

and an “ Aptychus” is present. All the known species of Scaphiées
are confined to the Cretaceous system.

In the genus C7zoceras (fig. 801) the shell is rolled into a spiral,

AMMONOIDEA. 869

the turns of which lie in one plane, but the volutions are not in
contact with one another. The surface-sculpture consists of trans-
verse ribs, usually with rows of tubercles or short spines. The
suture is much ramified, but only consists of four principal lobes,
viz., a siphonal lobe, superior-lateral lobe, inferior-lateral lobe, and

iv iy, ? Ip

fw \ \
\D\\\

CM \ \ \ | yj ZZ
mi\\\y yy \\ Vv Wf f>
P €\\ if / GA
AW A \\

PA \\’ \ \\ \ WS alll iin, A
MSS
SS

eS

=
———4
—G SS

a ao ij XK
E uth tN HANS \ KAS S
HUW WW \SS
Fig. 801.—Crioceras Encerici. Fig. 802.—Heteroceras Emerict.

Cretaceous. Cretaceous.

antisiphonal lobe. The body-chamber is long, and the aperture is
simple and without side-lappets. The species of C7zoceras are Cre-
taceous, ranging from the Lower Greensand to the Gault. Some
of the forms which have been placed under the genus /eéeroceras
appear to be nearly related to Cvzoceras. In these forms the first
portion of the shell resembles Zurrziites in being obliquely coiled
and turreted, with contiguous whorls; but the last volution is de-
tached from the rest, and is produced and recurved (fig. 802).

The forms for which the name of Zoxoceras is employed have an
elongated, arcuate or bow-shaped shell, which is not coiled into. a

Fig. 803.—Axcyloceras Matheronianum. Gault.

spiral ; and the structural characters agree with those of Cvzoceras.
The species of Zoxoceras are found in the Lower Cretaceous rocks ;
but it is not clear that the genus has not been founded upon broken
examples of Cvioceras.

870 TETRABRANCHIATE CEPHALOPODS.

Also very closely allied to Cvzoceras, if not absolutely identical
with it, is the genus Azcyloceras (fig. 803), in which the shell agrees
with that of the former in consisting in its earlier portion of several
volutions, which are coiled into a flat spiral, but are not in contact
with one another. The shell differs, however, from that of Crzoceras
in the fact that the last volution is produced at a tangent, and is
ultimately bent back in the form of a crosier. The sutures are
divided into six lobes, which are very unequal in size, and are
digitated in a complex manner. ‘The genus is Jurassic and Creta-
ceous, ranging from the Inferior Oolite to the Neocomian.

871

CA hE KR XIE.
DIBRANCHIATE CEPHALOPODS.

Tue Dibranchiate Cephalopods or ‘‘ Cuttle-fishes ” are characterised
as being szzmming animals, almost invariably naked, with never
more than eight or ten arms, which are always provided with suckers.
There are two branchie, which are furnished with branchial hearts :
an ink-sac ts always present; the funnel ts a complete tube ; and the
shell (when present) ts internal, or, tf external, ts not chambered.

The Cuttle-fishes (fig. 804) are rapacious and active animals,
swimming freely by means of the jet of water expelled from the
funnel. The arms constitute powerful offensive weapons, being
excessively tenacious in their hold, and being sometimes provided
with a sharp claw in the centre of each sucker. They are mostly
nocturnal or crepuscular animals, and they sometimes attain to a
great size.

The general anatomy of the Cuttle-fishes has already been briefly
discussed (see p. 821), and it only remains to allude shortly to cer-
tain points which possess a special paleontological interest. Under
certain exceptionally favourable circumstances the outline of the
body has been preserved in the fossil Dibranchiates, and in such
cases the horny hooks with which the suckers are occasionally fur-
nished may be recognisable, and it may even be possible to deter-
mine the number of the ‘‘arms.” The mandibles of the Cuttle-
fishes differ from those of the Tetrabranchiates in not being calcified,
and these structures are therefore not preserved in the fossil condi-
tion. On the other hand, the Dibranchiates possess in the ink-sac
a structure which is quite capable of petrifaction, the carbonaceous
particles suspended in the “ink” being very indestructible. Hence
the fossilised ink-bag of the Dibranchiates is of tolerably frequent
occurrence.

The skeleton in the Dibranchiates may be rudimentary or wholly
absent, as in the majority of the Octopods. In the female Argo-
naut, again, there is a delicate, involute, extervma/ shell, which is

872 _ _DIBRANCHIATE CEPHALOPODS.

secreted by the two dorsal arms, and has no connection with the
mantle of the animal. In the great majority of the Dibranchi-
ates, however, there exists an zzzernaZ shell which is contained within
the mantle, and varies in structure in different types. In some
cases, the shell has the form of an elongated, horny, feather-shaped

x

rate ol’ lt

by <2 Ge

ieee * Ory
te te

Fig. 804.—a, The Common Calamary (Loligo vulgaris), reduced in size: a, One of the ordinary

arms ; ¢, One of the longer arms or ‘‘tentacles.” 8, Skeleton or “‘ pen” of the same, one-fourth

natural size (after Woodward). c, Side-view of one of the suckers, showing the horny hooks
surrounding the margin. p, View of the head from in front, showing the bases of the arms (a)
and tentacles (¢), the mouth (vz), and the funnel (/).

body or “pen” (fig. 737, 4), which is situated dorsally in a closed
sac of the mantle. In other cases, as in Sefza (fig. 737,9@)) tie
internal shell is calcareous in composition. The posterior end of
this skeleton may exhibit in a rudimentary form a chambered sac
or “‘phragmacone,” but in many cases no trace of this structure can

DIBRANCHIATE CEPHALOPODS. 873

be detected. In the extinct family of the Belemnitide, the skeleton
consists of a well-developed chambered cone (the ‘‘ phragmacone ”),
which is divided by arched septa into a succession of air-chambers,
the septa being pierced by a tube or “siphuncle.” ‘The phragmacone
in this family is prolonged forwards on its dorsal side into a flattened
“pen” (the ‘‘pro-ostracum”), while it is protected posteriorly by
a solid calcareous investment or sheath (the guard”). In the
existing genus S/zvuzZa the shell is internal, but is reduced to the
chambered “‘ phragmacone,” which is coiled into a flat spiral, the
coils of which are not in contact (fig. 737, ¢ and 2).

The phragmacone commences in a globular or inflated ‘“‘ proto-
conch” or “initial chamber ”
(fig. 805, pz), which is dis-
tinctly constricted off from
the first air-chamber, and
which is devoid of a cica-
trix. The siphuncle com-
mences as a cecal tube (c)
pushed into the protoconch; w
and a “prosiphon” (jf) is
present. It will be thus seen
that the protoconch of the
Dibranchiates is essentially
similar to that of the Am-
monoids, a fact which has
led some naturalists to the
belief that the latter are truly
Dibranchiate, and that their
shell was therefore internal.
In all the Dibranchiates in Fig. 805.— Longitudinal section of the shell of
which a phragmacone is com- (2c commencensent of the aiphuncle; ss Siph:
Bee veloped, the siphun-. wastes Ong of he genta sy Vental wall of the
cle is constantly veztra/ in
position, and in SfzruZa it is consequently placed along the concave
side of the shell.

As regards their classification, the Dibranchiata are divided into
two sub-orders, the Octofoda and the Decapoda, the former charac-
terised by the possession of eight arms only, while in the latter
there are eight comparatively short arms and two long arms or
“tentacles.” The Decapoda constitute the most important of these
groups, and are divided by Fischer into the three sections of the
Phragmophora, Sepiophora, and Chondrophora, in accordance with
the nature of the skeleton.

As regards the distribution of the Dibranchiate Cephalopods in
time, no Palzeozoic types of the order have hitherto been detected.

874 DIBRANCHIATE CEPHALOPODS.

The oldest known representatives of the order appear in the Trias,
and belong to the extinct families of the Belemnitide and Belem-
noteuthide. ‘The Belemnitide show a great development in the
Jurassic rocks, and in the same deposits occur the remains of
Cuttle-fishes essentially similar to those now in existence (forms of
the Chondrophora). The typical members of the Belemnitide dis-
appear with the close of the Cretaceous period, but a few forms of
this important Mesozoic family survive into the Tertiary. At the
present day, the sole survivor of the section of the Phragmophora is
the genus Sfirula. ‘The oldest types of the Seszophora appear in
the Tertiary deposits. In the following are given the characters and
distribution in time of those families of the Dibranchiates which are
known to occur in the fossil condition.

SuB-ORDER I. DECAPODA.

The forms included in this sub-order invariably possess an in-
ternal shell, and the head is always furnished with eight equal
‘“‘arms” and two longer “tentacles” (fig. 804, a). The mantle is
usually furnished with lateral or terminal fins, and the suckers of
the arms are pedunculate, or may be modified into horny hooks.

The sub-order is subdivided by Fischer into the three following
families :—

1. Phragmophora.—Cuttle-fishes in which the skeleton is furnished
with a “ phragmacone,” or chambered portion, in which a siphuncle is
developed. La. Spirula, Belemunites.

2. Sepiophora.—Cuttle-fishes in which the skeleton is calcareous, but
there is either no phragmacone, or a quite rudimentary one without a
siphuncle. Lx. Sepa.

3. Chondrophora.—Cuttle-fishes in which the shell has the form of a
homy > pens’ 227 Lolgp,

SECTION A. PHRAGMOPHORA.

In this section the shell consists of a ‘‘ phragmacone,” with or
without certain accessory structures. ‘The phragmacone (fig. 805)
resembles the shell of the Tetrabranchiates in consisting of a succes-
sion of air-chambers separated by shelly partitions or “septa,” which
are perforated by a “‘siphuncle” ; and it more particularly resembles
the shell of the Ammonoids in the fact that the ‘‘ protoconch” is
inflated and is provided with a “ prosiphon.” ‘The skeleton is, how-
ever, zzzernal, and possesses also other peculiarities which are not
found in the shell of any of the Tetrabranchiates. ‘The only existing
representative of this section is the genus Spzru/a, but numerous
fossil forms are known. The Phragmophora may be divided into the
following three families :—

PHRAGMOPHORA. 875

FAMILY 1. SPIRULID#.—This family includes only the recent
genus Spiruda (fig. 737, ¢ and d, and fig. 805), in which the shell is
reduced to the phragmacone. ‘This is coiled into a flat spiral, the
coils of which are not in contact, and it commences in an inflated
protoconch. The septa between the successive air-chambers are
concaye ; and the siphuncle is marginal, and is placed on the ventral
or concave side of the shell. The siphuncle is completely enclosed
within a series of septal “‘ necks,” which are directed backwards, and
are long enough to reach from one septum to another. No fossil
representatives of the genus have hitherto been recognised.

FAMILY 2. BELEMNITID&.—In this family the shell has the form
of a conical “‘ phragmacone,” with a ventral siphuncle (fig. 806, a),
which is lodged within a solid fibrous calcareous sheath or ‘ guard”
(4), and which has its dorsal margin prolonged into a thin horny or
shelly plate or ‘‘ pro-ostracum ” (c¢), corresponding with the “ pen”

Fig. 806.—A, Restoration of the animal of the Belemnite; B, Diagram showing the complete

skeleton of a Belemnite, consisting of the chambered phragmacone (a), the guard (4), and the horny
pen (c); c, Specimen of Belemnites canaliculatus, from the Inferior Oolite. (After Phillips.)

of the Chondrophora. The arms in the Belemnitide were furnished
with hooklets, and an ink-bag was present. The members of this
family are all extinct, and range from the Trias to the Miocene
Tertiary.

The most important genus in this family is Be/emneies itself, in
which the portion of the shell most commonly preserved is the

876 DIBRANCHIATE CEPHALOPODS.

subcylindrical, conical, or fusiform “ guard” or “rostrum.” At its
anterior broad extremity the “guard” is hollowed out into a

Fig. 807.—Diagram of Belem-
nite (after Professor Phillips).
7, Horny or shelly pen or
““ pro - ostracum”; 4, Cham-
bered ‘‘phragmacone” in its
cavity or ‘‘alveolus” (a); g,
“Guard.”

conical excavation, termed the ‘ alveolus”
(fig. 807, a). Within the alveolus, in well-
preserved specimens, is found the “ phrag-
macone.” This (fig. 807, #) consists of a
conical series of chambers, enclosed in a
thin proper wall (the ‘ conotheca” of Hux-
ley), and separated from one another by
curved shelly partitions or “ septa,” which
are perforated by apertures for the passage
of the “siphuncle.” The siphuncle is mar-
ginal, and traverses the middle of the ven-
tral wall of the phragmacone. The outer
or anterior chamber of the phragmacone is
of tolerably large size ; and the conotheca is
prolonged forwards on its dorsal side into a
horny or more or less calcified plate, known
as the “ pro-ostracum.” This corresponds
with the “pen” of the ordinary Cuttle-
fishes, and from its extreme tenuity is never
perfectly preserved, and, indeed, is com-
pletely wanting in the great majority of
specimens.

The “ guard” of the Belemnites consists
of prismatic calcareous fibres, which are
directed perpendicularly to the surface, and
radiate in all directions from an axial line,
which is not strictly central, but is some-
what nearer the ventral than the dorsal side.
The growth of the guard is effected by the
deposition of successive conical layers or
sheaths, which are secreted over the entire
surface, but are thickest behind, and become

gradually attenuated in front. The surface

of the guard is smooth; or may be wholly
or partially granulated or wrinked ; or, again,
may be marked with branched vascular im-
pressions, which are especially conspicuous
on the ventral side. In many cases a well-
marked groove —the “ventral furrow ”—

runs from the edge of the alveolus backwards on the ventral side,
extending for a short distance only, or reaching to the point of the
guard (fig. 806, c). In many cases the apical portion of the guard
shows two symmetrical grooves—the “‘ dorso-lateral grooves ”—which

PHRAGMOPHORA. 877

diverge slightly and become shallower as they extend forwards, and
which mark the dorsal side of the shell.

Between three and four hundred species of the genus Lelemnites
are known, the maximum development of the group taking place in
the Jurassic rocks. The oldest forms appear in the Lower Lias, and
the last in the Chalk, but the genus appears to have wholly died out
with the close of the Cretaceous period.

According to Zittel, the Holle ans sections of the genus Ledemizztes
may be recognised : —-

i Acuarit. —Guard conical, with two or three apical grooves, but
without a “ventral furrow” or “ dorso-lateral grooves.” (£2. We acuartus,
Upper Lias.)

2. Canaliculatz—Guard elongated, conical, or fusiform, with a deep
“ventral furrow.” (4x. B. canaliculatus, Inferior Oolite, fig. 806, C.)

3. Clavaiz.—Guard elongated, more or less clavate posteriorly, without
a “ventral furrow,’ but with well-marked lateral grooves. (Za. B
clavatus, Lias.)

4. Bipartiti.—Guard slender, cylindrical, with or without a “ ventral
furrow,” but with deep ‘“dorso-lateral grooves.” (Z£x. B. bipartilus,
Neocomian.)

5. Hastatz.—Guard elongated, narrower in front, thicker behind, and
terminating in a point posteriorly. A deep “ventral furrow” is present,
together with shallow lateral grooves. (Ax. B. hastatus, Oxford Clay.)

6. Conophori.—Guard conical, pointed behind.-. No ventral furrow is
present, but a corresponding furrow proceeds from the edge of the
alveolus backwards on the dorsal aspect of the shell.
Lateral grooves are wanting or feebly developed. (Ex.
B. conophorus, Neocomian.)

7. Dilatati—Guard short, laterally compressed, flat-
tened or four-sided. A dorsal furrow, as in the preced-
ing group, is present, and the lateral grooves are more
or less developed. (Ex. B. dilatatus, Neocomian.)

Closely allied to Lelemnites proper, and probably
not generically separable, are the forms included
under the name of Gelemnitella. In these types
(fig. 808) the guard is cylindrical, with a short
pointed mucro behind. ‘Two diverging dorso-lateral
lines exist on each side; and there is a slit-like
ventral furrow, which begins at the margin of the
alveolus, but does not reach the hinder end of he Ce
the same. The ventral side of the guard shows ella mucronata.

: : Chalk.
very well-marked vascular impressions. ‘The known
species of Belemmnitella are confined to the Upper Cretaceous rocks.

The most ancient type of the Lelemnitide is the genus Aulaco-
ceras, which is found in the Upper Trias of the Alps. In this
genus the guard is elongated and clavate in form, with a deep
lateral groove on each side. ‘The phragmacone is at least twice
as long as the guard, and slowly increases in width anteriorly.

878 DIBRANCHIATE CEPHALOPODS.

The siphuncle is marginal, enclosed in a calcareous sheath, and
contracted where it pierces the successive septa. Afractites, also
from the Alpine Trias, differs from Axudacoceras chiefly in the want
of lateral furrows.

In the singular genus Xzphoteuthis, of the Lower Lias, the guard
is cylindrical; the phragmacone is greatly elongated, and increases
very slowly in width ; and there is a narrow ‘“‘ pro-ostracum,” which
is at least five times as long as the guard.

In the Tertiary rocks, the family of the Belemnitide is represented
by the genera Lelemnosis, Leloptera, and Spirulirostra. ‘The only
known species of e/emnosis is found in the Eocene rocks (London
Clay), and has a short obtuse guard, with a terminal pore. The
phragmacone has horizontal septa and a marginal siphuncle. The
genus Lelopiera is also known by a single species only, and likewise
occurs in the Eocene rocks. In this curious type the shell consists
of two conical segments joined point to point, and further united
by wing-like lateral expansions. The posterior portion of the
skeleton represents the guard, while the phragmacone is lodged in
the anterior portion.

Lastly, in the genus Sfirulirostra (fig. 809) the skeleton consists
of a triangular, pointed guard, which is hollowed out in front for the

Fig. 809.—Spzrulirostra Bellardii. Miocene Tertiary.

reception of a chambered portion or phragmacone. ‘This latter is
spirally bent, and the septa are pierced along its concave or ventral
side by a marginal siphuncle. ‘The only known species of Sfzrud-
rostra is found in the Miocene deposits of Italy.

FaMILy 3. BELEMNOTEUTHID&.—In this family the skeleton is
internal, and resembles that of the Aelemnitide in consisting of a
“‘ ouard,” a chambered ‘‘ phragmacone,” and a thin shelly “ pro-
ostracum.” The guard is, however, reduced to a thin calcareous

SEPIOPHORA. 879

layer, which invests the conical phragmacone. The members of
this family are confined to the Upper Trias and the Jurassic rocks,
and the principal genus is Lelemnoteuthis (fig. 810) itself. In the
Oxford Clay, specimens of Belemnoteuthis have been found in which
the outline of the soft parts has been more or less perfectly pre-
served. From these it is known that the animal had eight arms,
with two “tentacles,” furnished with horny hooks. The hinder end
of the body was furnished with terminal fins ; and there was a large
ink-sac situated a little in front of the phragmacone. The phragma-
cone itself seems to have reached to nearly one-third of the length
of the body.

SECTION B. SEPIOPHORA.

In this section of the Decapods the skeleton is internal and is
calcareous, consisting of a well-developed ‘‘ pro-ostracum,” termin-

S\N)

\

\

S <<
LAY

SS
~ > S>

gies
INS

B
—————— Fig. 811.—Side-view (a) and ventral view
SS = (B) of the shell of Sepia Orbignyana. f,
> 5 3S **Pro-ostracum” ; #z, Mucro, hollowed out
5 hen Sepa ; in front for the rudimentary phragmacone ;
Fig. 810.—Restoration of Belemno- d, Dorsal side of the shell; v, Ventral side.
teuthis, from the Oxford Clay. (After D’Orbigny.)

ating posteriorly in a rudimentary phragmacone and rostrum. No
siphuncle is developed.

The type of this section is the existing genus Sefza, in which the
shell (“‘sepion” or “sepiostaire”) consists of an elongated, oval,
calcareous “pro-ostracum” (fig. 811, 4), which is rounded in front,

880 DIBRANCHIATE CEPHALOPODS.

and terminates posteriorly in small pointed “mucro” (m). The
front portion of the mucro is hollowed out, and contains a rudimen-
tary ‘‘phragmacone,” in which, however, a “siphuncle” is wholly
wanting. The pro-ostracum forms the largest portion of the shell,
and is thickened in front and concave on its inner side behind.
The convex dorsal side is formed of two strata of comparatively
dense calcareous tissue, partially separated by a chitinous lamella.
The concave inner side, on the other hand, is formed of a large
number of delicate parallel calcareous plates, which are not in con-
tact, but are united by vertical pillars, giving rise to a spongy tissue,
the spaces of which are filled by gases secreted by the animal. The
rudimentary phragmacone is imperfectly chambered, and the minute
‘‘mucro” is the representative of the “ guard” of the Belemnites.

A few fossil types of Segza are known, the oldest appearing in the
Eocene deposits. In the Eocene genus 4e/osepgza the “sepion” is
like that of Segza, and has a short, slightly bent rostrum. Internally
the rostrum is hollowed out for the reception of a chambered phrag-
macone, and on the inner side of this is an oblique funnel-shaped
cavity, which is regarded by Munier-Chalmas as representing the
siphuncle. Anteriorly the rostrum is continued into a calcareous
pro-ostracum, the dorsal surface of which is rugose.

SECTION C. CHONDROPHORA.

In this section of the Decapods the skeleton is internal, and has
the form of a long, thin, pointed or feather-shaped “‘ pen,” which is |
not calcified, or only partially so, but is composed
of a horn-like substance (‘‘ conchiolin ”).

This section includes a large number -of the
commoner Cuttle-fishes of the present day, such
as the familiar Calamaries (Zofgo, fig. 804).
Various fossil forms are also known from the
Jurassic and Cretaceous rocks, the “ pens) son
these being often accompanied by the remains
of the ink-sac. The fossil “pens” consist gen-
erally partly of horny and partly of calcified la-
mellze, and some of them attain a considerable
size. A number of genera have been founded
upon these fossil pens, such as Phylloteuthis, Belo-
\ teuthis (fig. 812), Geoteuthis, Leptoteuthis, Plesio-

Fig. 812.—Beloten. leuthis, &c.; but the differential characters of these
Cee ae Jv are not of sufficient importance to require discus-
sion here. In some of these types, as in Pleszofeu-

this, the pen is very long and sword-shaped, and is without lateral
wings. More commonly, as in Le/oteuthis (fig. 812), the pen is

OCTOPODA. 881

more or less feather-shaped, and consists of a central shaft bordered
by lateral wings. In some cases, as in Leffoteuthis and Plesioteuthis,
the actual impression of the body of the animal is preserved, and
from such examples it is known that the arms were not furnished
with horny hooks.

SuB-ORDER II. OcTopopDa.

The forms included in this section of the Dibranchiates are char-
acterised by the possession of eight equal arms, the internal skeleton
being rudimentary or absent. The suckers of the arms may be
modified into horny hooklets. In the female of the Paper Nautilus
(Argonauta) the two dorsal arms are widely expanded, and secrete
a delicate calcareous external shell, which is not connected by
muscles with the body of the animal. The shell of the female Ar-
gonaut is one-chambered, spirally coiled and involute, its external
border being keeled, and its surface tuberculated. The genus is
represented in the Pliocene Tertiary by one or two species, and
several living forms are known.

According to von Zittel, the genus Acanthoteuthis is founded upon
the remains of an Octopod Cuttle-fish preserved in the fine-grained
Lithographic Limestone (Jurassic) of Solenhofen, and showing the
form of the body and the outline of the arms, the latter carrying
each two rows of falciform horny hooks.

ELTERATURE OF MOLLUSCA

GENERAL.

1. “ Manuel de Conchyliologie et de Paléontologie Conchyliologique.”
Paul Fischer. 1887.

2. “ Handbuch der Palzontologie.” Bd. I. Abth. 2, Lief. 1-3. 1881-84.
Von Zittel.

3. “ Manual of the Mollusca.” S. P. Woodward. 4th ed., with “ Ap-
pendix of Recent and Fossil Conchological Discoveries,” by
Ralph Tate. 1880.

“ Handbuch der Conchyliologie.” Philippi. 1853.

. “Malacozoa.” In ‘Bronn’s Klassen und Ordnungen des Thier-

Reichs.’ 1862-66. Keferstein.

. “Traité élémentaire de Conchyliologie.” 1835-39. Deshayes.

“The Genera of Recent Mollusca.” 1858. H.and A. Adams.

. “Mineral Conchology of Great Britain.” 1812-30. J. Sowerby.

LAMELLIBRANCHIATA.

[Apart from the general works above quoted, the following are some of
the more important sources of original information, with more
especial reference to the fossil forms. |

9. “On the Microscopic Structure of Shells.” ‘Reports of the British
Association.’ 1844 and 1847. W. B. Carpenter.
WOR. 1: 2

882

32:
33:

LITERATURE OF MOLLUSCA.

“Tegumentary Organs.” ‘Todd and Bowman’s Cyclopzdia of Anat.
and Phys.’ (Supplement). 1859. Huxley.

. “ Description des animaux sans vertebres découvertes dans le bassin

de Paris.” 1860-66. Deshayes.

. “ Description des coquilles fossiles des environs de Paris.” 1824-37.

Deshayes.

. “The Pelecypoda, with a Review of all known Genera of this Class,

Fossil and Recent.” ‘ Palzontologia Indica,’ vol. i. 1871.
Ferd. Stoliczka.

. “A Report on the Invertebrate Cretaceous and Tertiary Fossils of

the Upper Missouri Country.” ‘U.S. Geol. Survey of the Ter-
ritories,’ vol. ix. 1876. Meek.

. “ Paleontology of New York.” Vols. i.-v. (more especially vol. v.)

1843-85. Hall.

. “ Paleontology of Illinois.” Vols. 11. and iii. 1866 and 1868. Meek

and Worthen.

. “British Palaeozoic Fossils.” 1851-1852. M ‘Coy.
. “Geology of Yorkshire.” 2ded. 1836. Phillips.
. “Faune du Calcaire Carbonifére de la Belgique.” Part-5. 1885.

De Koninck.

. “The Paleozoic Conchology of Scotland.” ‘Proc. Roy. Physical

Soc. Edin.’ 1882. R. Etheridge, jun.

. “A Monograph of the Crag Mollusca.” Part ii., Bivalves. ‘ Palzeon-

tographical Society.’ 1851 and 1856. Searles V. Wood.

. “A Monograph of the Eocene Mollusca.” Parts 1.-11i., Bivalves.

‘Palzontographical Society.’ 1861, 1864, and 1870. Searles V.
Wood.

. “A Monograph of the Mollusca of the Great Oolite.” Part 11.,

Bivalves. ‘ Paleeontographical Society.’ 1854. Morris and
Lycett.

. “Supplementary Monograph on the Mollusca from the Stonesfield

Slate, Great Oolite, Forest Marble, and Cornbrash.” Jdzd.
1863. Lycett.

. “A Monograph of the British Trigoniz.” Jézd. 1872-1876.

Lycett.

. “A Monograph of the Permian Fossils of England.” Jézd@. 1850.

King.

. “Structure and Affinities of the Hippuritide.” ‘ Quart. Journ. Geol.

Soc: volux: 1854.5 9-2. Woodward:

- oysteme Silunen du Centre de la Boheme.” Vol. vi. )(@raucmaee

Acéphalés.) Barrande. 1881.

. “Die Bivalven der Gosaugebilde in den nordéstlichen Alpen.”

‘Denkschriften der k. Akad. der Wiss,’ vol. xxv. 1866. Von
Zittel.

. “Die Fauna der Schichten von St Cassian.” J/ézd., vol. xxv. 1866.

Laube.

. “Die Land- und Siiss-Wasser-Conchylien der Vorwelt.” 1870-75.

F. Sandberger.

GASTROPODA (INCLUDING PTEROPODA).

“Cretaceous Gasteropoda of Southern India.” ‘ Palzeontologia
Indica.’ 1868. Stoliczka.
“On the Silurian Gastropoda and Pteropoda of Gotland.” ‘ Kongl.

34.
35:
36.

37:
38.
39:
40.

Al.
42.
43.
44.

45.
46.

47.
48.

49.
50.
5I.

Be:
53

54.

LITERATURE OF MOLLUSCA. 883

Svenska Vetenskaps-Akad. Handlingar.’ Bd. 19. 1884. Lind-
strom.

“Faune du Calcaire Carbonifére de la Belgique.” (Parts iii. and iv.)
1881 and 1883. De Koninck.

“Petrefactenkunde Deutschlands.” Bd. vii. (Gasteropoden.) 1881.
Quenstedt.

“ Paléontologie frangaise.” ‘Terrains Crétacés.’ Vol. ii. 1842-43.
‘Terrains Jurassiques.’ Vol. ii. 1850. D’Orbigny. (With con-
tinuation by Piette. Vol. iii. 1867-82.)

“Die Land- und Siiss-Wasser-Conchylien der Vorwelt.” 1870-75.
F. Sandberger.

“Mollusca from the Great Oolite.” Univalves. ‘ Paleeontographical
Society.’ 1850. Morris and Lycett.

““A Monograph of the British Jurassic Gasteropoda.” ‘ Palaonto-
graphical Society.’ 1887. Hudleston.

““A Monograph of the Eocene Mollusca.” ‘ Palazontographical
Society.’ Part i., Univalves. 1852, 1856, and 1858. Frederick
EK. Edwards.

““A Monograph of the Crag Mollusca.” Jézd. 1848. (Part 1,
Univalves.) Searles V. Wood.

“Systéme Silurien du Centre de la Bohéme. Vol. iii., Pteropodes.
1867. Barrande.

“Monographie der fossilen Pteropoden.” ‘Neues Jahrb. ftir Miner-
alogie.” 1847. G. Sandberger.

“Pteropoden aus dem Devon und Oligocéan von Hessen und
Nassau.” ‘ Palzeontographica.’ Vol. xi. 1864. Ludwig.

“Paleontology of New York.” Vol. v. Part ii. 1879. Hall.

“Report on the Pteropoda.” ‘Challenger Reports.’ Vol. xxiii.
1888. Pelseneer.

POLYPLACOPHORA

“Report on the Polyplacophora.” ‘Challenger Reports.’ Vol. xv.
1886. Haddon.

“On the Presence of Eyes in the Shells of certain Chitons, and on
the Structure of these Organs.” ‘Quart. Journ. Micro. Sci.’
New Ser., vol. xxv. 1885. Moseley.

“Faune du Calcaire Carbonifere de la Belgique.” Part iv. 1883.
De Koninck.

“On a New Species of Helminthochiton from the Upper Bala of
Girvan, Ayrshire.” ‘Geol. Mag.’ 1885. Henry Woodward.
“On the Silurian Gastropoda and Pteropoda of Gotland.” ‘ Kongl.
Svenska Vetenskaps - Akad. Handlingar.” Bd. 19. 1884.

(Chelodes.) Lindstrom.

SCAPHOPODA.

“Anatomie et Monographie du genre Dentalium.” ‘Mém. Soc.
hist. nat. de Paris,’ t. 1. 1825. Deshayes.

“ Histoire de organisation et du développement du Dentale.” ‘Ann
Sen Nat. Zool. Ser iv. Vols: vit-vill. 1856-57. Lacaze-
Duthiers.

“On the Cretaceous Dentaliide.” ‘Quart. Journ. Geol. Soc.’ Vol.
xxxlv. 1878. J. Starkie Gardner.

884 LITERATURE OF MOLLUSCA.

55:

56.
57-

58.
59:

60.
OI.
62.
63.
64.
65.
66.
67.
68.
69.
70.

7M.

1D,
73:
74.

75:

76.
77:

78.
79:

80.

CEPHALOPODA.

“Mémoires pour servir a histoire et ?anatomie des Mollusques.
(Cephalopodes.): 1817. Cuvier.

‘“‘Memoir on the Pearly Nautilus.” 1832. Owen.

“Systeme Silurien du Centre de la Bohéme.” Vol. i. 1867-77.
Barrande. A .

‘““Cephalopodes : Etudes générales.” 1877. Barrande.

‘“ Beitrage zur Entwickelungsgeschichte der fossilen Cephalopoden.”
‘Palzontographica.’ Bd. xxvi. and xxvil. 1879-80. Branco.
“Embryology of the Tetrabranchiates.” ‘Bull. Mus. Comp. Zool-

Opin? = VOlii oy 2) ellyatts

‘““Genera of Fossil Cephalopoda.” ‘Proc. Soc. Nat. Hist. Boston.’
Vol. xxii. 1884. Hyatt.

““Petrefactenkunde Deutschlands.” Abth. I. Die Cephalopoden.
1846-49. Quenstedt.

‘““A Monograph of the British Fossil Cephalopoda.” (Part I. Intro-
duction and Silurian Species.) 1882. J. F. Blake.

“Catalogue of the Fossil Cephalopoda in the Collection of the
British Museum.” Vol.i. 1889. A. H. Foord.

“Faune du Calcaire Carbonifére de la Belgique.” Parts i. and ii.
1878 and 1880. De Koninck.

‘““Paléontologie frangaise.” ‘Terrains crétacés.’ 1840. ‘Terrains
Jurassiques.’ 1852. D’Orbigny.

“Fossil Cephalopoda of the Cretaceous Rocks of Southern India.”
‘Palzeontologia Indica.’ 1865. Stoliczka and Blanford.

“Jurassic Fauna of Kutch.” (Cephalopoda.) ‘ Palzeontologia
Indica.’ 1871. Waagen.

“Salt Range Fossils.” (Cephalopoda.) ‘ Palzontologia Indica.’
1879-80. Waagen.

“ Beitrage zur Kenntniss der Cephalopoden-Fauna der Hallstadter
Schichten.”. “Denkschr. d.° Wiener Akad? Bd> icone:
Von Hauer.

‘“Nachtrage zur Kenntniss der Cephalopoden-Fauna der Hallstadter
Schichten.” ‘Sitzungsberichte d.k. k. Akad.’ Wien. Vol. xli.
1860. Von Hauer. .-

“Das Gebirge um Hallstadt.” ‘Abhandl. d. k. k. Geol. Reich-
sanstalt.’ Bd. vi. 1873 and 1875. Mojsisovics.

‘“‘ Die Cephalopoden der Mediterranen Trias-provinz.” ‘ Abhandl. d.
k. k. Geol. Reichsanstalt.’ Bd. x. 1882. Mojsisovics.

““Cephalopoden der Stramberger Schichten.” ‘ Palzontol. Mit-
theilungen aus dem Museum des bayr. Staates.’ Bd.i1. 1868.
Von Zittel.

“‘ Cephalopoden der oberen deutschen Kreide.” ‘ Palszeontographica.’
Bd. xxi. and xxiv. 1871, 1876. Schlitter.

“ Der Jura.” 1858. Quenstedt.

“Ueber Ammoniten.” ‘Sitzungsber. d. Wiener Akad.’ 1865 and
1870. Suess.

‘““Ueber Kreide-Ammoniten.” J/ézd. 1875. Neumayr.

‘‘Die Ammoniten der Kreide und die Systematik der Ammo-
nitiden.” ‘Zeitschr. d. deutschen geol. Gesellsch. Bd. xxvii.
1875. Neumayr.

‘“‘Palzeontologische Mittheilungen.” (Ueber jurassische Cephalo-
poden.) 1862. Oppel.

92.

LITERATURE OF MOLLUSCA. 885

. “Sur la Classification des Ammonites.” ‘ Bull. de la Soc. Géol.

de France.’ 1873. E. Favre.

. “Mollusca of the Chalk of England: Cephalopoda.” ‘ Palzeonto-

graphical Society.’ 1853, 1854, and 1856. Sharpe.

. “ Monograph of the Eocene Mollusca of England: Cephalopoda.”

‘ Palezeontographical Society.’ 1849. Edwards.

. “A Monograph of the Lias Ammonites.” ‘ Palzontographical

Society.’ 1880-85. Wright.

. “A Monograph of the Inferior Oolite Ammonites.” Jézd. — 1887.

Buckman.

. “ Report on the Invertebrate Cretaceous and Tertiary Fossils of the

Upper Missouri Country.” ‘United States Geol. Survey of the
Territories.’ Vol. ix. 1876. Meek.

. “Cephalopoda.” In Tate and Blake’s ‘Yorkshire Lias.’ 1876.

J. F. Blake.

. “Belemnites from the Oxford Clay.” ‘Phil. Trans.’ 1844. Owen.
. “Structure of Belemnites.” ‘Mem. Geol. Survey.’ 1864. Huxley.
. “Monograph of the Belemnitide.” ‘ Palzeontographical Society.’

1865-69. Phillips.

. “Observations on some Belemnites and other fossil remains of

Cephalopoda in the Oxford Clay, near Trowbridge, Wiltshire.”
‘Phil. Trans.’ 1848 and 1850. Mantell.

“Bemerkungen zur naheren Kenntniss der Belemniten.” 1830.
Graf Munster.

END OF THE FIRST VOLUME.

PRINTED BY WILLIAM BLACKWOOD AND SONS.

3, CLARKE, &Co,

seistSuSTAR

‘am
* : r
& a
: *
Rata’ e
» ~

—

. 64

a |
P

—-
.
,

SES
yPe

if cafe . ;

i

¥,
i
f

SMITHSONIAN INSTITUTION

Il | :

iii

9088 00748 5444