presented to

of tbe

\Hniverait? of Toronto

Mr* Joseph Nason

,

I :

'
. , ' "

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A MANUAL OF PALEONTOLOGY

BY THE SAME AUTHOR,

i.

Second Edition, revised and enlarged.
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FOR THE USE OF STUDENTS,

WITH A GENERAL INTRODUCTION ON THE PRINCIPLES OF ZOOLOGY,
AND GLOSSARY OF SCIENTIFIC TERMS.

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INTRODUCTION TO THE STUDY OF BIOLOGY.

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TEXT-BOOK OF GEOLOGY,

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WILLIAM BLACKWOOD & SONS, EDINBURGH AND LONDON ;
and D. APPLETON & CO., NEW YORK.

MANUAL OF PALEONTOLOGY

FOR THE USE OF STUDENTS

WITH A GENERAL INTRODUCTION ON THE
PRINCIPLES OF PALEONTOLOGY

BY

HENRY ALLEYNE NICHOLSON

M.D. D.Sc. M.A. PH.D. F.R.S.E. F.G.S. &c.

PROFESSOR OF NATURAL HISTORY AND BOTANY IN UNIVERSITY COLLEGE, TORONTO ,

FORMERLY LECTURER ON NATURAL HISTORY IN THE MEDICAL SCHOOL

OF EDINBURGH ; ETC. ETC.

WILLIAM BLACKWOOD AND SONS

EDINBURGH AND LONDON

MDCCCLXXII

All Rights are reserved

P RE F AC E.

THE object of the present work is to furnish the student
of Geology and the general reader with a compendious
account of the leading principles and facts of the vast
and ever-increasing science of Palaeontology. In carry-
ing out this object, all superfluous details have been
rigidly excluded, and the Author has endeavoured to
restrict himself entirely to those facts which are abso-
lutely necessary to any one who would study Palaeon-
tology as a department of science, sufficiently distinct
to stand alone, and yet most closely connected with the
sciences of Zoology and Botany on the one hand, and
with Geology on the other hand.

In the First Part of the work is given a general ac-
count of the principles upon which the palaeontological
observer proceeds.

In the Second Part of the work, Palaeontology, or the
past history of the Animal Kingdom, is treated of ; and
here much more space has been devoted to the Inver-
tebrate than to the Vertebrate groups — upon the ground
that it is chiefly, or almost exclusively, with the former
that the ordinary palaeontological student has to deal.

The Third Part of the work gives a brief and very
general view of Palaeobotany, or the past history of the

vi PREFACE.

Vegetable Kingdom. This department of the subject
has not been treated at any length, partly because the
remains of plants are comparatively rare in the stratified
series, and partly because nothing less than a special
treatise would suffice to handle satisfactorily this obscure
and difficult branch of the subject.

The fourth and concluding portion of the work treats
of Historical, or, as it might be called, Stratigraphical,
Palaeontology — namely, of the application of Palaeon-
tology to the elucidation of the succession of the strati-
fied deposits of the earth's crust. This department of
the subject has also been very briefly disposed of, not
because its intrinsic importance does not warrant a
more extended treatment, but because it is the Author's
intention, as his leisure will permit, to devote a separate
treatise to the consideration of this wide and compara-
tively independent section of the science.

In conclusion, the Author would beg his readers to
remember that there is no science which is growing so
rapidly, and which is as yet so comparatively in its
infancy, as Palaeontology ; and that there is none in
which the conclusions of to-day are more liable to be
vitiated by the discoveries of the morrow. Even whilst
these sheets have been going through the press, facts
have been brought to light which ought to have found
their place in a Manual of this kind, but which have
been of necessity altogether passed over, or, at best,
have been merely alluded to. For all deficiencies, there-
fore, arising from this cause, the Author has to beg the
kind indulgence of his readers.

With regard to the Illustrations, the Author has
gratefully to acknowledge the kindness of Alfred R. C.

PREFACE. vii

Selwyn, Esq., Director of the Geological Survey of
Canada, who placed at the Author's disposal a number
of engravings of Silurian and Devonian fossils, from the
publications of the Survey. The Author has likewise
to acknowledge a similar obligation to Principal Daw-
son, of M'Gill University, Montreal, who kindly per-
mitted the use of several of the illustrations of his
' Acadian Geology.' A considerable proportion of the
engravings, however, are taken from D'Orbigny's beau-
tifully illustrated ' Cours Elementaire de Paleontologie,'
by an arrangement with the publishers of that work.

UNIVERSITY COLLEGE, TORONTO,
October 16, 1872.

CONTENTS.

PART I.-GENERAIi INTRODUCTION.

CHAPTER I.

PAGE

Definition of Palaeontology — Definition of the term " fossil " — Pro-
cesses of Fossilisation — Definition of "rock" — Classification of
Rocks, 1-5

CHAPTER II.

Characters of the Sedimentary Rocks — Mode of formation of the Sedi-
mentary Rocks — Definition of the term " formation " — Chief
divisions of the Aqueous Rocks — Mechanically -formed Rocks —
Chemically-formed Rocks — Organically-formed Rocks — Different
ages of the Aqueous Rocks — Chronological Succession of the
Stratified Rocks, 5-14

CHAPTER III.

Use of the term "contemporaneous," as applied to groups of beds —
General sequence of phenomena at the close of each Geological
Period — Migrations — Differences between the fossils of known
contemporaneous strata — Geological continuity — Relations be-
tween the Chalk and the Atlantic Ooze — Reappearance of similar
forms of life under similar conditions — Doctrine of " Colonies," 14-27

CHAPTER IV.

Causes of the Imperfection of the Palseontological Record — Causes of
the absence of certain animals as fossils — Unrepresented time —
Unconformity, sequence of phenomena indicated by — Leading
examples of unconformity — Thinning out of beds — Sudden ex-
tinction of Animals — Disappearance of fossils, . . . 27-39

CHAPTER V.

Conclusions to be drawn from Fossils — Age of Rocks — Mode of origin
of any Fossiliferous bed — Fluviatile, lacustrine, and marine deposits
— Conclusions as to Climate, 40-44

CHAPTER VI.

Primary divisions of the Animal Kingdom — Impossibility of a linear
Classification — Tabular view of the chief divisions of the Animal
Kingdom — General succession and progression of organic types, 44-55

X CONTENTS.

PART II.— PAL^EOZOOLOGY.

CHAPTER VII.

Zoological characters and chief divisions of the Protozoa — Relations of
the Protozoa to time — Characters of the Foraminifera — Variations
of the test of the Foraminifera— Structure of Eozoon — Distribu-
tion of the Forminifera in time — Characters of the Radiolaria, and
their distribution in time — Characters of the Sponges, and their
geological distribution — Stromatopora — Receptaculites, . 59-72

CHAPTER VIII.

General characters and chief divisions of the Ccelenterata— Distribu-
tion in time of Coelenterate animals — Orders of Hydrozoa not
represented as fossils — Fossil Medusae and Sea-blubbers — General
characters of the Corynida — Palseocoryne — Corynoides — General
characters of the Thecaphora — Dendrograpsus — Dictyonema —
Structure and probable affinities of Oldhamia — General characters
and distribution of the Graptolitidae — Structure of a simple Grapto-
lite — Reproduction of Graptolites — Monoprionidian and Diprion-
idian forms — Characters of the genus Graptolites — Didymo-
grapsus — Tetragrapsus — Dichograpsus — Rastrites — Diplograpsus
— Climacograpsus — Dicranograpsus — Phyllograpsus, . . 73-85

CHAPTER IX.

General facts as to the distribution of the Actinozoa in time — Divisions
of the Zoantharia — Characters of Z. malacodermata — Characters
of Z. sclerobasica, and their distribution in time — Nature of a
Sclerodermic coral — Structure of a simple coral— Gemmation and
fission amongst corals — Deep-sea corals and reef-builders —
Ancient coral-reefs — Divisions and distribution in time of the
Zoantharia sclerodermata — Characters of the Rugosa — Recent
Rugose corals — Operculate corals — Families and distribution in
time of the Rugosa — Tabular view of the divisions of the Zoan-
tharia sclerodermata and Rugosa — Characters of the Alcyonaria
— Distribution of the Alcyonaria in time, . 85-102

•

CHAPTER X.

Characters of the Annuloida — Characters of the Echinodermata — Dis-
tribution of Echinodermata in time — General characters of the
Echinoidea — Structure of the test in Echinoids — Spines and
tubercles — Apical disc — Regular and irregular Echinoids — Peris-
choechinidae — Distribution of Echinoids in time — Chief families of
Echinoidea, their characters and distribution, . . . 102-110

CHAPTER XL

Characters of the Asteroidea — Features distinguishing them from the
Echinodermata — General structure of a Starfish — Differences
among them — Diagram and structure of a Goniaster — The internal
and integumentary skeletons — Distribution of the Asteroidea in
time — Characters of the Ophiuroidea — General structure of an
Ophiuroid — Their distribution in time, .... 110-117

CONTENTS. XI

CHAPTER XII.

Characters of the Crinoidea — General structure of a Crinoid — Structure
of the column of the Crinoids — Structure of the calyx — Distribu-
tion of the Crinoids in time — Crinoidea articulata and tesselata
— Characters of the Cystoidea — Structure of the column, calyx,
and appendages of the Cystideans — Pectinated rhombs — Distribu-
tion of the Cystideans in time — Chief genera of Cystoidea — Cha-
racters of the Blastoidea — Structure of Pentremites — Distribution
of Blastoidea in time — Characters and distribution in time of the
Holothuroidea, 118-135

CHAPTER XIII.

Characters of the Annulosa — Characters of the Annelida — Characters
of the Tubicola — Distribution of the Tubicola in time — Cornulites
— Conchicolites — Serpulites — Trachyderma — Spirorbis — Serpula
— Ditrupa — Characters of the Errant Annelides — Scolithus —
Arenicolites — Tracks of Errant Annelides, .... 136-143

CHAPTER XIV.

Characters of Arthropoda — Distribution of Arthropoda in time — Cha-
racters of Crustacea — Morphology of a typical Crustacean — General
facts as to the past existence of Crustacea — Table of the divisions
of the Crustacea — Characters and divisions of the Cirripedia —
Structure of the shell in the Balanidse — Distribution of the Balan-
idae in time — Characters and distribution of the Verrucidse — Struc-
ture of the Pedunculated Cirripedes — Distribution of the Lepadidse
in time, . 143- 1 55

CHAPTER XV.

Characters and orders of the Entomostracous Crustaceans — Ostracoda
— Distribution of the Ostracoda in time — Estheria — Characters
and distribution in time of the Phyllopoda — Characters of the
Trilobita — General structure of a Trilobite — Appendages of Tri-
lobites — Systematic position of Trilobites — Distribution of Trilo-
bites in past time — Leading families of the Trilobita — Characters
and divisions of the Merostomata — Characters and distribution in
time of the Eurypterida — Characters and distribution in time of
the Xiphosura, I55'I75

CHAPTER XVI.

Characters of the Malacostrata — Characters of the Edriophthalmata
— Characters and distribution in time of the Amphipoda — Cha-
racters and distribution in time of the Isopoda — Characters of the
Podophthalmata — Characters and distribution of the Stomapoda
— Characters and distribution of the Decapoda — Macrura — Ano-

-Brachyura, ........ 175-180

CHAPTER XVII.

Characters of the Arachnida — General distribution of the Arachnida in
time — Characters and distribution of the Scorpionidse — Characters

Xll CONTENTS.

and distribution of the Araneida — Characters and distribution
of the Myriapoda — Characters and distribution in time of the
Insecta, 181-187

CHAPTER XVIII.

General characters of the Mollusca — General characters of the shell of
the Molluscs — General distribution of the Mollusca in time — Divi-
sions of the Mollusca — Characters of the Polyzoa — Structure of
the polypides and colonies of the Polyzoa — Divisions of the Poly-
zoa— Distribution of the Polyzoa in time, .... 187-198

CHAPTER XIX.

General characters of the Brachiopoda — Structure of the shell of the
Brachiopods — Oral processes and their supports — Divisions of the
Brachiopods — General distribution of the Brachiopoda in time —
Characters, distribution in time, and leading genera of the Tere-
bratulidse — Thecididae — Spiriferidae — Kininckida; — Rhynchonel-
lidae — Strophomenidse — Productidae — Craniadae — Discinidse —
Lingulidae, 198-214

CHAPTER XX.

General characters of the Lamellibranchiata — Shell of the Lamelli-
branchs — General distribution of the Lamellibranchiata in time —
Ostreidae — Aviculidse — Mytilidae — Arcadae — Trigoniadae — Union-
idse — Chamidae — Hippuritidae — Tridacnidae — Cardiadae — Lucin-
idae — Cycladidse — Cyprinidae — Veneridas — Mactridae — Tellinidae

— Solenidae — Myacidae — Anatinidse — Gastrochaenidae — Pholad-
idae, 214-240

CHAPTER XXL

General characters of the Gasteropoda — Shell of the Gasteropods —
Siphonostomatous and Holostomatous Univalves — Table of the
divisions of the Gasteropoda — General distribution of the Gastero-
poda in time — Strombidae — Muricidse — Buccinidae — Conidae —
Volutidae — Cypraeidse — Naticidae — Pyramidellidse — Cerithiadae
— Melaniadse — Turritellidae — Littorinidae — Paludinidae — Neritidse

— Turbinidae — Haliotidse — Fissurellidae — Calyptrseidae — Patel-
lidae — Dentalidse — Chitonidse — Opisthobranchiate Gasteropods —
Tornatellidae — Bullidae — Aphysiadae — Pleurobranchidae, . 240-262

CHAPTER XXII.

Heteropoda — Firolidae — Atlantidae — Pulmonate Gasteropods — Heli-
cidae — Limacidae — Limnasidas — Auriculidae — Cyclostomidae —
Aciculidae, 262-268

CHAPTER XXIII.

General characters of the Pteropoda — General distribution of the
Pteropoda in time — Hyalea — Theca — Conularia — Tenta-
culites, 269-272

CONTENTS. Xlll

CHAPTER XXIV.

General characters of the Cephalopoda — Mandibles of the Cephalo-
pods — Ink-sac, shell, and internal skeleton — Divisions — General
distribution of the Cephalopoda in time, .... 272-277

CHAPTER XXV.

General characters of the Tetrabranchiata — Anatomy of the Pearly
Nautilus — Shell of the Tetrabranchiata — Distribution of the
Tetrabranchiata in time — Nautilidae — Orthoceratidae — Ammoni-
tidae — Shell of the Ammonitidse — Distribution in time of the
Ammonitidas — Genera of the Ammonitidae, . . . 277-293

CHAPTER XXVI.

General characters of the Dibranchiate Cephalopods — Distribution of
the Dibranchiata — Octopoda — Argonautidae — Octopodidae — De-
capoda — Teuthidae — Sepiadae — Spirulidae — Belemnitidse, . 293-299

CHAPTER XXVII.

General characters of the Vertebrata — General structure of the Verte-
brate skeleton — Classes of the Vertebrata — General distribution
of Vertebrata in time, ....... 299-306

CHAPTER XXVIII.

General characters of the Fishes — Scales of Fishes — Skeleton of
Fishes — Limbs of Fishes — Median fins of Pishes — General dis-
tribution of Fishes in time, ...... 306-315

CHAPTER XXIX.

Teleostean and Ganoid Fishes — General characters of the Teleostei —
Sub-orders of the Teleostei — Malacopteri — Anacanthini — Acan-
thopteri — Plectognathi — Lophobranchii — General characters of
the Ganoidei — General distribution of the Ganoids in time —
Classification of the Ganoids — Amiadse — Lepidosteidae — Lepi-
dopleuridse — Crossopterygidae — Families and distribution of the
Crcssopterygious Ganoids— Ostracostei — Sturionidae, . . 315-333

CHAPTER XXX.

Elasmobranchii and Dipnoi — General characters of the Elasmo-
branchii — General distribution of the Elasmobranchii in time —
Holocephali — Plagiostomi, general characters and divisions of
Cestraphori — Cestracionts of the Upper Ludlow Rocks — Hybo-
donts and Acrodonts — Selachii — Batides — General characters of
the Dipnoi — Characters of the Barramunda — Palaeichthyes of Dr
Giinther, . ... . 334'345

CHAPTER XXXI.

Amphibia — General characters of the Amphibia — Distribution of

Amphibians in time — Urodela — Anoura — Labyrinthodontia, 346-353

XIV CONTENTS.

CHAPTER XXXII.

Reptilia — General characters of Reptiles — Distribution of Reptiles —
Characters and geological distribution of the Chelonia — Ophidia
— Lacertilia — Crocodilia, 353-3^8

CHAPTER XXXIII.

Extinct orders of Reptiles — Characters and distribution of the Ichthy-
opterygia — Sauropterygia — Pterosauria — Anomodontia — Deino-
sauria, 368-381

CHAPTER XXXIV.

General characters of the Birds — Skeleton — Pectoral limbs —Hind
limbs — General distribution in time — Foot-prints of Birds —
General characters and geological history of the Natatores — Gral-
latores — Cursores — Rasores — Scansores — Insessores — Raptores —
Saurune, 381-396

CHAPTER XXXV.

General characters of Mammals — Osteology of Mammals — Limbs —

Teeth — General distribution of Mammals in time, . . 397-406

CHAPTER XXXVI.

Orders of Mammalia — Characters and distribution of Monotremata —

Marsupialia — Edentata, ....... 406-417

CHAPTER XXXVII.

Orders of Mammalia continued — Characters and distribution in time
of the Sirenia — Cetacea — Calsenidoe — Catodontidse — Delphinidae
— Rhynchoceti — Zeuglodontidse, ..... 417-422

CHAPTER XXXVIII.

Orders of Mammalia continued — Characters and distribution of the
Ungulata — Perissodactyles — Rhinoceridse — Tapiridse— Palseother-
idse — Solidungula — Artiodactyles — Hippopotamidse — Sinda —
Anoplotheridse — Ruminantia — Camelidse — Moschidse — Cervidae-
Camelopardalidse — Cavicornia, ....... 423-441

CHAPTER XXXIX.

Orders of Mammalia continued — Characters and distribution in time
of the Hyracoidea — Proboscidea — Elephas — Mastodon — Deino-
therium, .......... 441-447

CHAPTER XL.

Orders of Mammalia continued — Characters and distribution in time
of the Carnivora — Pinnigrada — Plantigrada — Ursidaa — Melidse —
Digitigrada — Mustelidse — Viverridse — Hysenidse — Canidae —
Felidae, 447-456

CONTENTS. xv

CHAPTER XLI.

Orders of Mammalia continued — Characters and distribution in time
of Rodentia — Leporidae — Cavidse — Hystricidse — Castoridse —
Muridas — Dipodidse — Myoxidas — Sciuridae — Cheiroptera — Insec-
tivora — Talpidae — Soricidae — Erinaceidae, .... 456-463

CHAPTER XLII.

Orders of Mammalia continued — Characters and distribution in time
of the Quadrumana — Strepsirhina — Platyrhina — Catarhina —
Characters and distribution in time of the Bimana, . . 464-469

PART IIL-PALEOBOTANY.

CHAPTER XLIII.

Palseobotany — Divisions of the Vegetable Kingdom — General Rela-
tions of Plants to time, ....... 473-477

CHAPTER XLIV.

Pre- Carboniferous Floras — Cambrian Plants — Silurian Plants — De-
vonian Plants, ......... 477-484

CHAPTER XLV.

Carboniferous Plants — Origin and structure of Coal — Ferns — Calamites
— Calamodendron — Lepidodendroids — Sigillarioids — Coniferse —
Cycadacese — Angiospermous Exogens — Monocotyledons — Per-
mian Plants, ......... 485-496

CHAPTER XLVI.

Floras of the Secondary and Tertiary Periods — Triassic Plants-
Jurassic Plants — Cretaceous Plants — Eocene Plants — Miocene
Plants — Pliocene Plants, . . . . . . . 496-503

PART IV.-HISTORICAL PALEONTOLOGY.

CHAPTER XLVII.

Historical Palaeontology — Synopsis of the fossiliferous formations —
Rocks of the Laurentian Period — Life of the Period — Rocks of
the Huronian Period — Rocks of the Cambrian Period — Lower
Cambrian — Upper Cambrian — Life of the Cambrian Period —
Primordial Zone — Skiddaw and Quebec Groups, . . 507-514

CHAPTER XLVIII.

Rocks of the Silurian Period— Divisions of the Silurian Rocks in

Britain — In North America — Life of the Silurian Period, . 515-520

xvi CONTENTS.

CHAPTER XLIX.

Rocks of the Devonian Period — Old Red Sandstone — Devonian

Rocks of N. America— Life of the Devonian Period, . . 520-523

CHAPTER L.

Rocks of the Carboniferous Period — Life of the Carboniferous Period

—Rocks of the Permian Period — Life of the Permian Period, 524-530

CHAPTER LI.

Rocks of the Triassic Period — Rhsetic beds — Life of the Triassic
Period, 53<>535

CHAPTER LII.
Rocks of the Jurassic Period — Life of the Jurassic Period, . . 535-539

CHAPTER LIII.
Rocks of the Cretaceous Period — Life of the Cretaceous Period, 540-546

CHAPTER LIV.

Palaeontological break between the Secondary and Tertiary Rocks —
Classification of the Tertiary Rocks — Rocks of the Eocene
Period — Life of the Eocene period, 546-552

CHAPTER LV.
Rocks of the Miocene Period — Life of the Miocene Period, . 552-554

CHAPTER LVI.

Rocks of the Pliocene Period — Life of the Pliocene Period — Post-
Pliocene Period — Pre-Glacial Deposits — Pre-Glacial Mammals —
Glacial Deposits — Glacial Shells — Post-Glacial Deposits — Post-
Glacial Mammals, ........ 5 54" 5 62

GLOSSARY, 563-585

INDEX, - 586-601

PART I.

GENERAL INTRODUCTION

PAL/EONTO LOGY.

CHAPTER I.

>

INTRODUCTION.

DEFINITION OF PALAEONTOLOGY.

PALEONTOLOGY (Gr. palaios, ancient ; onta, beings ; logos, dis-
course) 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 subsequently discussed, the
palaeontological 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.

As Zoology, then, treats of the animals now inhabiting the
earth, and as Botany treats of the now existing plants,
Palaeontology may be considered as the Zoology and Botany
of the past. Regarding it from this, the only true point of
view, some knowledge of Zoology and Botany is essential to a
prosecution of the study of Palaeontology, and such details of
these sciences as may be deemed requisite will be introduced
in the proper place. The materials, again, which fall to be
studied by the palaeontologist, are derived entirely from the
proper province of the geologist. fossils are derived, from
rocks. It will therefore be necessary to trespass to some ex-

A

2 INTRODUCTION.

tent upon the peculiar domain of the geologist, and to obtain
some knowledge of the origin, composition, and mode of
occurrence of the rocks from which Palaeontology derives its
materials. Lastly, Palaeontology, apart from its own import-
ance as an independent science, is employed by the geologist
to assist him in his determination of the chronological succes-
sion of the materials which compose the crust of the earth.
Palaeontology, therefore, must be separately studied in its rela-
tion to historical Geology.

DEFINITION OF FOSSILS.

All the natural objects which come to be studied by the
palaeontologist are termed " fossils " (Lat. fossus, dug up). In
most cases, fossils, or, as they are often termed, " petrifactions,"
are actual portions of animal or vegetable organisms, such as
the shells of Molluscs, the skeletons of Corals, the bones of Ver-
tebrate 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 objects 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 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 extinct — 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 recent 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 discarded in this con-
nection. The terms " fauna " and " flora " are employed in
Palaeontology much as they are by the naturalist, to mean
the entire assemblage of the animals or of the plants respect-
ively 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. 3

FOSSILISATION.

Fossilisation may be applied in a general sense to all the
processes through which an organic body passes in order to
become a fossil. Here we need only consider the three lead-
ing 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 pro-
duced by pressure, by the deprivation of organic matter origi-
nally present, or by more or less complete infiltration 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 all formations almost contain some
fossils in which the original structure is more or less com-
pletely 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 ima-
gine 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 surround-
ing matter would insure that the clay would everywhere ad-
here 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 obvi-
ously have the following state of
parts. The clay which filled the
shell would form an accurate
cast of the interior of the shell,
and the clay outside would give
us an exact impression or cast
of the exterior of the shell (fig.

l). We should have, then, tWO Fig- i. — Trigonia longa, showing casts
j • of the exterior and interior of the shell.

casts, an interior and an exterior,

and the two would be very dif-

ferent to one another, since the inside of a shell is very unlike
the outside. In the case, in fact, of many univalve shells, the
interior cast is so unlike the exterior or unlike the shell itself,
that it maybe difficult to determine the true origin of the former.

4 INTRODUCTION.

It only remains to add that there is sometimes a further
complication. If the rock be very porous and permeable by
water, it may happen that the original shell is entirely dissolved
away, leaving the interior cast 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 interior and exterior cast-
trie space, that is, formerly occupied by 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 be really a much later formation, and which
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 even sometimes the in-
ternal minute structure, of the original organic body, but which,
nevertheless, 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 elegant ex-
ample of this is afforded by fossil wood which has been " silici-
fied " 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 which under the microscope 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 substance is by no means necessarily
flint, but may be iron-pyrites, oxide of iron, sulphur, &c. ; and it
is not uncommon to find many other fossils besides wood pre-
served in this way, such as shells, corals, or sponges.

DEFINITION OF ROCK.

The crust of the earth consists of various different materials,
produced at different successive periods, occupying certain
definite spaces, and not confusedly mixed together, but, on the
contrary, exhibiting a definite and discoverable order of arrange-

CLASSIFICATION OF ROCKS. 5

ment. 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 ap-
plying to all 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 rocks as
are the hardest and most compact granites or limestones.

CLASSIFICATION OF ROCKS.

For the purposes of the palaeontologist all the rocks which
enter into the composition of the solid exterior of the earth
may be divided into two great classes : — i. The Igneous
Rocks, which are formed within the body of the earth itself,
and which owe their structure and origin to the action of heat;
and 2, the Aqueous or Sedimentary Rocks, which are formed
at the surface of the earth, and which owe their structure and
origin to the mechanical action of water. The Igneous Rocks
are 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 unstratified masses. The Aqueous and Sedimentary
Rocks are formed at the surface by the disintegration and re-
construction of previously existing rocks, are mostly fossilifer-
ous, and are stratified — i.e., are arranged in distinct layers or
" strata." The Sedimentary Rocks, as containing fossils, are the
only rocks which it is essential for the palaeontologist to be
acquainted with, and we shall very briefly consider their lead-
ing physical characters, their chief varieties, their mode of ori-
gin, and their historical succession.

CHAPTER II.

SEDIMENTARY ROCKS.

THE Sedimentary or Fossiliferous Rocks form the greater por-
tion 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

6 INTRODUCTION.

composition. We may examine any given area, and find in it
nothing but one kind of rock — sandstone, perhaps, or lime-
stone. 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" rocks, 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 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 contributed 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 laminae ; 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 or 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 all the materials which they bring down at
their mouths, forming in this way their " deltas." Whenever
such a delta is cut through, either by man or by some channel
of the river altering its course, we find that it is composed of a
succession of horizontal layers or strata of sand or mud, varying
in mineral composition, in structure, or in grain, according to

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 7

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 — irrespective of the materials delivered
into it by rivers — is constantly preparing fresh stratified de-
posits by its own action. Upon every coast-line the sea is
constantly eating back into the land and reducing its compo-
nent 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 at the mouth of some ancient river,
forming its delta ; 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 terres-
trial organisms. In the last case, the majority, at any rate, of
the fossils would be the remains of marine animals.

The term "formation" is employed by geologists to express
"any group of rocks which have some character 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, includ-
ing under the last head all rocks which owe their origin to
vital action, as well as those produced by ordinary chemical
agencies.

A. MECHANICALLY-FORMED ROCKS. — These are all those
Aqueous Rocks of which we can obtain proofs that their
particles have been mechanically transported to their present

8 INTRODUCTION.

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 micro-
scopical 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 an exact equiva-
lent 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 sandstone, grits, and most
conglomerates and breccias. In the Argillaceous group are
those Aqueous Rocks which contain a certain amount of clay
or hydrated silicate of alumina. Under this head come clays,
shales, marls, clay-slate, and most flags or flag-stones.

B. CHEMICALLY-FORMED ROCKS. — In this section are com-
prised all those Aqueous Rocks which have been formed by
chemical agencies. As many of these chemical agencies, how-
ever, 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 import-
ant of the Chemically-formed Rocks are the so-called Calcare-
ous Rocks, comprising all those which contain a large propor-
tion of carbonate of line, or are wholly made up of this substance.
We may also shortly notice coal and gypsum.

Chalk is merely a limestone which is soft and pulverulent,
with an earthy fracture. It is nearly pure carbonate of lime,
and is to a great extent an organically-formed rock, consisting
mainly of the minute calcareous shells of Foraminifera, with
the calcareous shells of molluscs, sea-urchins, sea-mosses, and

CHIEF DIVISIONS OF THE AQUEOUS ROCKS. Q

the like. The nearest approach which we have at the present
day to chalk is probably to be found in the deposit called "ooze,"
which forms a considerable portion of the bed of the deep At-
lantic, and which will be afterwards noticed at greater length.

Limestone is a hard and compact rock, and its many
varieties are formed in different ways, and differ from one
another in more or less important points. Though the sea
contains carbonate of lime in solution, no marine limestones
appear to be formed by chemical agency alone, but in all these
the lime is abstracted from the sea-water by the agency of
marine animals. Primarily, therefore, marine limestones are
organically-formed rocks, consisting almost entirely of corals,
shells, Crinoids, and other calcareous organisms. Such lime-
stones may fairly be compared to the great coral-reefs of the
Pacific and other warm seas. It is to be remembered, how-
ever, that many marine limestones are secondarily mechani-
cally-formed rocks. In these cases, the calcareous matter of
the rock has been originally separated by living beings, but
has then been transported by the waves, or by currents, to
certain localities at a distance, where it has been heaped up to
form a bed of limestone.

Other limestone deposits, such as the stalactites and stalag- , '
mites of caves, and the "calcareous tufa" and "travertine " of
some hot springs, are purely chemical in their origin, and owe
nothing to the operation of living beings.

Gypsum, in chemical composition, consists of sulphuric acid
in combination with lime and two atoms of water ; or, in other
words, it is a hydrated sulphate of lime. It commonly occurs
as a whitish or yellowish-white rock, something like loaf-sugar
to look at, generally arranged in distinct beds, but sometimes
in irregular cakes or veins. It is pal aeon tologically important
as occasionally yielding well-preserved fossils ; but its exact
mode of origin has not yet been fully worked out.

Coal is, in all those forms to which the name would ordin- 6~.
arily be applied, an organically-formed rock, and may be re-
garded as formed of compressed vegetable matter. In all its
varieties — such as bituminous coal, anthracite, and lignite or
brown coal, — it approximates more or less closely in chemical
composition to wood. It consists, namely, of from seventy
to eighty per cent of pure carbon, with varying quantities
of hydrogen and oxygen, and a small amount of earthy or
mineral matter which constitutes the ash. All coals occur in
the form of beds, intercalated with other stratified rocks ; and
there are innumerable gradations between pure coal, earthy
coal, and carbonaceous shale, till we reach ordinary shale.

10 INTRODUCTION.

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 sometimes being afforded by
mineral characters. 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 remem-
bered, however, that superposition can at best give us but the
relative age of a bed as compared with other beds of the same
region. It cannot give us the absolute 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.

The second, and in the long-run more available, test of the
ages of the different sedimentary beds, is that afforded by their
organic remains. Still, this test is also by no means univer-
sally applicable, nor in all cases absolutely conclusive. Many
aqueous rocks are unfossiliferous through a thickness of
hundreds, or even thousands, 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 particular set of beds. As the result, however, of com-
bined palaeontological and geological researches, it is now pos-
sible for us to divide the entire series of stratified deposits 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, represents the life 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 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

CHRONOLOGICAL SUCCESSION OF AQUEOUS ROCKS. 1 1

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 palaeontology. Whenever, for instance,
we meet in Britain with the fossils known as Graptolites, we
may be sure that we are dealing with 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 Lower Silurian Rocks. Furthermore, if certain special
forms are present, we may be even able to say to what exact
part or subdivision of the Lower Silurian series they belong.

All these conclusions, however, would have to be accom-
panied by a tacit but well-understood reservation. No Grap-
tolites have ever been found in Britain out of rocks known
upon other grounds to be Silurian ; 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 Lower Silurians, might at any time be
found to have survived into the Upper Silurian period. We
should never forget, therefore, in determining the age of a rock
by palaeontological evidence alone, that we are always reason-
ing upon generalisations which are the result of experience
alone, and which may at any time be overthrown by fresh
discoveries.

CHRONOLOGICAL SUCCESSION OF THE AQUEOUS ROCKS.

As the result of observations made upon the superposition of
rocks in different localities, from their mineral characters, and
from their included fossils, geologists have been able to divide
the entire stratified series into a number of different divisions
or formations, each characterised by a general uniformity of
mineral composition, and by a special and peculiar assemblage
of organic forms. Each of these primary groups is in turn
divided into a series of smaller divisions, characterised and
distinguished in the same way. It is not pretended for a mo-
ment that all these primary rock-groups can anywhere be seen
surmounting one another regularly. There is no region upon
the earth where all the stratified formations can be seen to-
gether; and, even when most of them occur in the same
country, they can nowhere be seen all succeeding each other
in their regular and uninterrupted succession. The reason of
this is obvious. There are many places — to take a single ex-
ample— where one may see the Silurian Rocks, the Old Red
Sandstone, and the Carboniferous Rocks succeeding one an-

1 2 INTRODUCTION.

other regularly, and in their proper order. This is because
the particular region where this occurs was always submerged
beneath the sea while these formations were being deposited.
There are, however, many more localities in which one would
find the Carboniferous Rocks resting un conformably upon the
Silurians without the intervention of any strata which could be
referred to the Old Red Sandstone. This might arise from
one of two causes : i. The Silurians might have been elevated
above the sea immediately after their deposition, so as to form
dry land during the whole of the Old Red period, in which
case, of course, no strata of the age of the Old Red Sandstone
could possibly be deposited. 2. The Old Red Sandstone might
have been deposited upon the Silurian, and then the whole
might have been elevated above the sea, and subjected to an
amount of denudation sufficient to remove the Old Red Sand-
stone entirely. In this case, when the land was again sub-
merged, the Carboniferous Rocks, or any younger formation,
might be deposited directly upon Silurian strata. From one
or other of these causes, then, or from subsequent disturbances
and denudations, it happens that we can rarely find many of
the primary formations following one another consecutively
and in their regular order.

In no case, however, do we ever find the Old Red Sand-
stone resting upon the Carboniferous, or the Silurian Rocks
reposing on the Old Red. We have therefore, by a com-
parison of many different areas, an established order of succes-
sion of the stratified formations, as shown in the subjoined
ideal section of the crust of the earth (fig. 2).

The main subdivisions of the Stratified Rocks are known by
the following names : —

1. Laurentian.

2. Cambrian (with Huronian?).

3. Silurian.

4. Devonian or Old Red Sandstone.

5. Carboniferous.

6. Permian ) XT T> j 0 j <.

7. Triassic } New Red Sandston«-

8. Jurassic or Oolitic.

9. Cretaceous.

10. Eocene.

11. Miocene.

12. Pliocene.

13. Post-tertiary.

IDEAL SECTION OF THE CRUST OF THE EARTH. I 3

IDEAL SECTION OF THE CRUST OF THE EARTH.

Fig. 2.

f *~~~~- — — ^""" - x

/(•'

}> Post-tertiary and Recent.
|° Pliocene.

Miocene.
Eocene.

Cretaceous.

Oolitic or Jurassic.

Triassic.
Permian.

Carboniferous.

Devonian or Old Red Sandstone.

Silurian.

Cambrian.
Huronian.

Laurentian.

14 INTRODUCTION.

Of these primary groups, the Laurentian, Cambrian, Silu-
rian, Devonian, Carboniferous, and Permian are collectively
grouped together under the name of Primary or Paleozoic
Rocks (Gr. palaios, ancient ; zoe, life), because of the entire
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 intermediate between those of the Pal-
aeozoic period, and those of more modern strata. The Eocene,
Miocene, Pliocene, and Post-tertiary Rocks are grouped together
under the head of Tertiary or Kainozoic Rocks (Gr. kainos, new;
zoe, life), because their organic remains approximate in char-
acter to those now existing upon the globe.

CHAPTER III.

CONTEMPORANEITY OF STRATA AND
GEOLOGICAL CONTINUITY.

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 iden-
tical forms occur, they are ordinarily said to be " contempora-
neous ; " 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 unhesitatingly regarded as " geological equivalents/' and
would be classed as Silurian, Devonian, Carboniferous, and so
on. It is to be remembered, however, that it is not necessary,
to establish such a degree of equivalency between widely
separated groups of strata, that the fossils of each should be
to any great extent specifically identical. It is sufficient that,
whilst some few species are identical in both, the majority of
the fossils should be "representative forms," or, in other words,
nearly allied species. It will be shown, however, that groups
of strata widely removed from one another in point of distance
can only exceptionally be " contemporaneous," in the strict
sense of this term. On the contrary, in so far as we can judge
from the known facts of the present distribution of living beings,
the occurrence of exactly the same fossils in beds far removed
from one another is prima facie evidence, that the strata are

CONTEMPORANEITY OF STRATA. 15

not exactly contemporaneous, but that they succeeded one
another in point of time, though by no long interval geologi-
cally speaking.

Most of the facts bearing upon this question rnay be elicited
by a consideration of such a widely extended and well-known
formation as the Mountain Limestone or Sub-Carboniferous
Limestone. This formation occurs in localities as remote
from one another as Europe, Central Asia, North America,
South America, and Australia ; and it is characterised by an
assemblage of well-marked fossils, amongst which Brachiopods
belonging to the genus Produda may be specially singled out.
Now, if we believe that the Carboniferous Limestone in all
these widely distant localities was strictly contemporaneous,
we should be compelled to admit the existence of an ocean
embracing all these points, and, in spite of its enormous ex-
tent, so uniform in temperature, depth, and the other condi-
tions of marine life, that beings 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 uni-
formity 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. Indeed, this explanation would
almost necessarily lead us to the now abandoned theory that
each period in geological history was characterised by a special
group of organisms spreading over the whole globe, and that
there took place at the close of each period a general destruc-
tion 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 pro-
bable 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 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 " contemporaneous" 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

16 INTRODUCTION.

large as the area now covered by the Pacific, or larger, and yet
it could not include all those localities in which strata of Car-
boniferous age with identical or representative fossils are
already kno>vn to exist. At the close of the deposition of
the Carboniferous Limestone in its original area, the condi-
tions there present must be supposed to have become unsuit-
able 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 unsuitable
conditions must, it is hardly necessary to say, have been an
extremely slow and gradual one ; and would doubtless be con-
nected with the progressive shallowing of the sea, the diversion
of old currents 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 conditions as we have supposed
upon the animals inhabiting the area? a. Some of them
would, doubtless, be sufficiently hardy and accommodating to
bear up under the new state of things ; and these would per-
sist 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 Car-
boniferous Limestone up into the Yoredale Series, the Mill-
stone 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.

b. There would, in the second place, be a certain number of
species which would be utterly unable to withstand the altered
conditions 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 a single particular locality.

c. 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 locomo-
tion, can actually " migrate " in person, supposing they find
themselves placed under unfavourable conditions. There are

CONTEMPORANEITY OF STRATA. I/

many animals, however, such as most shell-fish, corals, sea-
urchins, &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 individual has no means of removing
his quarters to some more favoured spot, there may be a "migra-
tion " of the species from an unsuitable to a suitable locality.
This is effected through the medium of \heyoung, 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 re-
moval 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 consider-
ing : — When the conditions of life in the seas of the Carbonifer-
ous Limestone became unfavourable for the further existence of
their fauna, some species would migrate to a more congenial
area. In this way a greater or less number of the species
characteristic of the Carboniferous 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, perhaps merely succeed-
ing in maintaining a more or less precarious existence. In
either case, their remains would be preserved in the sedimen-
tary 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 contem-
poraneous." 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 contemporan-
eous. For deposits of this nature, believed to hold this relation
to each other, the term of " homotaxeous" 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
Silurian Rocks of Europe, North America, South America,
Australia, &c., contain very similar fossils, and are undoubtedly
" homotaxeous." Nothing, however, that we see at the present

B

1 8 INTRODUCTION.

day can justify us in believing that these widely separated de-
posits are strictly " contemporaneous," 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 Silu-
rian 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 Silu-
rian Rocks as a whole applies with still greater force to certain
of the minor subdivisions of the same, which contain many of
exactly 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 question,
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 an-
other, as far as the identical fossils are concerned, by lineal
descent. Similar remarks might be made about the Devonian,
Permian, Triassic, Jurassic, 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 by Professor Huxley.
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 de-
posits 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 im-
palpable chalky mud, or "ooze." All these different 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

CONTEMPORANEITY OF STRATA. 1 9

ooze of the deep Atlantic would contain innumerable Foram-
inifera, along with siliceous Sponges, Sea-urchins, and Crinoids.
We learn, therefore, from this, that contemporaneous deposits
not only do not necessarily contain the same fossils, but that,
if widely separated 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 fossils 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 together with that of the Mediter-
ranean, we should find the two areas to contain deposits actu-
ally synchronous as regards the time of their deposition, and
very near to one another in point of distance, and yet contain-
ing, upon the whole, entirely distinct groups of organic remains.
We learn, therefore, from this, that owing to the existence of
geographical barriers, it is possible for contemporaneous de-
posits to be found in close contiguity, in a single region, and
yet to contain very different fossils.

Again, we know from the researches of Professors Carpenter
and Wyville Thomson and Mr Gwyn Jeffreys, that deposits may
be formed, side by side, in a single ocean, and may yet differ
from one another altogether, both in mineral characters and in
their included fossils, though strictly contemporaneous in point
of time. Thus, in parts of the deep Atlantic where the tem-
perature of the bottom water is comparatively high, we have
the calcareous deposit of the ooze, abounding in Foraminifera.
Sponges, and Echinoderms. In certain other areas in the
same ocean, and in comparatively close contiguity with the
preceding, we have the temperature lowered by cold currents,
and we find a sandy deposit in process of formation, with a
fauna much more scanty than that of the ooze, and wholly
distinct from it. We thus learn that sedimentary deposits may
be strictly contemporaneous, and may be placed very near to
one another in point of distance, and yet may contain very
different fossils.

Lastly, synchronous deposits necessarily contain wholly dif-
ferent 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 contemporaneous 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

20 INTRODUCTION.

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 " contemporaneous ; " but they do not
contain the same fossils. This may be readily explained, how-
ever, 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.

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 Sedi-
mentary Rocks may be naturally divided into a certain num-
ber 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
processes 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.

Nowadays, most geologists hold that 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 commence-
ment of the next period. On the contrary, they hold 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
geological period — say, the Cretaceous period? If we reject

CONTEMPORANEITY OF STRATA. 21

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, however, of the forms which
migrated, in the process of migration, and by reason of coming
into contact with strange neighbours and untried conditions,
would probably undergo more or less modification. Ulti-
mately, 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 modification that they would no longer be
regarded as specifically identical with the original Cretaceous
forms, but would be looked upon simply as allied or " repre-
sentative " species, though really the lineal descendants 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 area should have the smallest
likeness in 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

22 INTRODUCTION.

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 charac-
teristic species of the Chalk period. In other words, such
deposits as we have been speaking of would contain an assem-
blage 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 interme-
diate deposits (in the Maastricht beds of Holland, the Pisolitic
Limestone of France, the Faxoe Limestone of Denmark, and
the Thanet Sands of Britain), and we find in them traces of
such an intermixture.

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, traces 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 sub-
sequent 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 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 almost certain that we
shall never 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,

CONTEMPORANEITY OF STRATA. 23

as memorials of, at any rate, part of the time which elapsed
between the close of the one formation and the commence-
ment 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 Laurentian period to the
present day. There was, and could have been, no such con-
tinuity in any one given area ; but the chain could never have
been snapped at one point and taken up at a wholly different
one. The links must have been forged in different places,
but the chain, nevertheless, remained unbroken. From this
point of view, there would be little impropriety in saying that
we are living in the Silurian period ; but we could only say so
in a very limited sense. While most geologists will readily
admit that there must have been such an actual continuity of
the great geological periods, from the earliest times up to the
present day, it remains certain 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 formations will
always be separated from one another by more or less evident
physical or palaeontological 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 be in nature
no hiatus in the long series of fossiliferous deposits.

The theory of " geological continuity," then, may in practice
be carried so far as to be useless, or even injurious to the progress
of science. This would seem to be the case with the attempt
to show that we " are still living in the Cretaceous period,"
and that the ooze now forming at the bottom of the deep
Atlantic is merely a continuation in point of time of the great
and well-known formation of the White Chalk. The points of
resemblance by which this is sought to be established are
these: i. The Atlantic ooze or "abyssal mud" is a whitish
or grayish-looking mud, containing about sixty per cent of
carbonate of lime, with from twenty to thirty per cent of silica,
and a variable quantity of alumina. When dry, and espe-
cially if consolidated, it may fairly be compared in mineral
composition to some varieties of Chalk or to Chalk-marl. 2.
The abyssal mud of the Atlantic is to a very large extent com-
posed of the microscopic shells of Foraminifera, some of which
are specifically identical with Cretaceous forms, whilst White
Chalk is known to be very largely composed of the debris

24 INTRODUCTION.

of these minute organisms. 3. The ooze contains siliceous
sponges, in many respects comparable to the sponges which
are so characteristic of the Cretaceous period. 4. The ooze
contains Echinoderms, especially Sea-urchins and Crinoids,
such as abounded in the Chalk period ; whilst one of the latter
is related to a Cretaceous type hitherto believed to be extinct.
5. We have reason to believe that the conditions under which
the Chalk was formed were very similar to those now present
in the Atlantic at great depths.

On the other hand, as pointed out by Sir Charles Lyell and
Mr Prestwich, the differences between the Atlantic ooze and
and the Chalk are, to say the least of it, quite as weighty as
the resemblances, if not more so. Chalk is composed of from
eighty to as much as ninety-nine per cent of carbonate of lime,
and has therefore a very small proportion of any siliceous
or aluminous impurity. Secondly, the occurrence of identical
species of Foraminifera in the two formations amounts to very
little ; for it is well known that such lowly organised forms of
life have an extraordinary power of persistence, surviving geo-
logical changes which are fatal to higher organisms. Lastly,
the most characteristic of the Chalk fossils, such as the various
forms of Cephalopoda and Bivalve Molluscs, are entirely want-
ing in the Atlantic ooze.

Mr Prestwich concludes that although it is probably true
that " some considerable portion of the deep sea-bed of the
mid-Atlantic has continued submerged since the period of
our Chalk, and although the more adaptable forms of life
may have been transmitted in unbroken succession through
this channel, the immigration of other and more recent faunas
may have so modified the old population that the original
Chalk element is of no more importance than is the original
British element in our own English people. As well might it
have been said in the last century that we were living in the
period of the early Britons, because their descendants and
language still lingered in Cornwall, as that we are living in the
Cretaceous period, because a few Cretaceous forms still linger
in the deep Atlantic. Period in Geology must not be con-
founded with ' system ' or * formation.' The one is only
relative, the other definite. A formation is deposited or takes
place during a certain time, and that time is the period of the
formation ; but a geological period may include several forma-
tions, and is defined by the preponderance of certain orders,
families, or genera, according to the extent of the period
spoken of; and the passage of some of the forms into the next
geological series does not carry the period with them, any more

CONTEMPORANEITY OF STRATA. 25

than would any particular historical epoch be delayed until the
survivors of the preceding one had died out. Period is an
arbitrary time-division. The Chalk or the ' London Clay '
formations mark definite stratigraphical divisions. We may
speak of the period of the London Clay, or we may speak of
the Tertiary period. It merely refers to the ' time when '
either were in course of construction. The occurrence of
Triassic forms in the Jurassic series, of Oolitic forms in the
Cretaceous series, and of Cretaceous forms in the Eocene, in
no way lessens the independence of each series, although it
may sometimes render it difficult to say where one series ceases
and the other commences. The land and littoral faunas are
necessarily more liable to change than a deep-sea fauna,
because an island or part of a continent may be submerged,
and all on it destroyed, while the fauna of the adjacent oceans
would survive ; and as we cannot suppose the elevation of
entire ocean-beds at the same time, the maritime fauna of one
period must be in part almost necessarily transmitted to the
next."

In accordance, therefore, with the principles here laid down,
we may conclude that it is not correct to say that we " are
living in the Cretaceous period," in any other sense than one
might say that we are living in the Silurian period, with this
difference, that the Cretaceous period is much nearer to us in
point of time than the Silurian, and that we can therefore trace
a relationship between certain .Cretaceous types and certain
living forms that we can not hope to establish in the case of
Silurian fossils.

It is to be observed, lastly, that certain classes of animals
are always likely to flourish in places and times in which
favourable conditions are present, wholly irrespective of any
genetic connection between successive faunae. Thus, the con-
ditions present in the deep Atlantic are such as favour the
existence of numerous Foraminifera, Sponges, Echinoderms,
&c. Similar conditions existed in the seas in which the Chalk
was deposited ; and we need not, therefore, be surprised at the
predominance of similar organisms in the Cretaceous period.
In the same way, there are portions of the Carboniferous
Limestone fairly comparable to the Chalk in mineral characters
(making due allowance for difference of age), and containing
forms of life which may be regarded as representative of the
Cretaceous fauna — such as Foraminifera, smooth Terebratulce,
Crinoids, and Sea-urchins. The conditions, however, present
in the deep Atlantic are not exactly similar to those under which
the Chalk was deposited, for there are certain great classes,

26 INTRODUCTION.

such as the Cephalopoda, which abounded in the Cretaceous
seas, but which seem to have no representative in the abyssal
mud of the Atlantic.

x DOCTRINE OF COLONIES. — It only remains in this connec-

tion to consider very briefly the doctrine of " colonies," laid
down by M. Barrande, the eminent Bohemian palaeontologist.
It has been laid down as a law that when once a species dis-
appears it never again makes its appearance in the geological
record. This is unquestionably 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 pointed out 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 Upper and Lower Silurian Rocks of Bohemia are
characterised by very distinct assemblages of fossils. It is
found, however, that the Lower Silurian Rocks contain in
places a group of fossils characteristic of the Upper Silurian
series. The beds containing this "colony" of Upper Silurian
forms are succeeded by strata filled with Lower Silurian fossils ;
and it is only after several alternations of this kind that the
Upper 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 Lower Silurian
animals at a time when other portions of Europe were covered
by a sea containing Upper Silurian animals, and suppose the
former area to have been shut off from the latter by a land-
barrier, we can readily understand how the " colonies " were
produced. If, from any cause, a channel of communication

IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 2/

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 Upper
Silurian species of the latter area would thus be imported, in
greater or less numbers, into the midst of the general Lower
Silurian fauna of Bohemia, and would be preserved in the
Lower Silurian Rocks. If, however, the channel of com-
munication 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 Lower
Silurian fauna would again reign supreme. A reopening of
the channel of communication would allow of a fresh immigra-
tion and the formation of a fresh " colony," and the process
might be indefinitely repeated. Finally, however, we must
suppose that the Bohemian area was permanently thrown open
to immigration from the general European area, when the
Upper Silurian fauna of the latter would succeed in per-
manently and completely displacing the old Lower Silurian
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 migra-
tion under certain peculiar and exceptional circumstances.

CHAPTER IV.

THE IMPERFECTION OF THE PAL&ONTOLOGICAL

RECORD.

As has been already pointed out, the series of the stratified
formations 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 de--?
posits, 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 " palaeontological record;" but, in truth, the record of
life is far more imperfect than the mere physical series of de-
posits. As we are here chiefly concerned with the biological

28 INTRODUCTION.

aspect of the question, we may advantageously consider some
of the main causes of the numerous breaks and gaps in the
palaeontological record at some length.

I. CAUSES OF THE ABSENCE OF CERTAIN ANIMALS IN
FOSSILIFEROUS DEPOSITS. — 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 belong-
ing to every period of the earth's history, there would still be
enormous deficiencies in the palaeontological 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 consider 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 entire classes of the Gregarinidcz and Infusoria* Animal-
cules, from their absence of hard parts, must ever remain un-
represented in a fossil condition. One or two of the latter,
however, possess an integumentary covering capable under
favourable circumstances of being preserved in rocks of recent
age. The Monera present no structures capable of fossilisa-
tion ; and the same may be said of the Amozbea, though one or
two of the latter have a carapace which might possibly be pre-
served. The remaining Rhizopodous orders — viz., the Fora-
jninifera, Radiolaria, and Spongidd — almost invariably develop
hard structures of lime or flint ; and all these orders, therefore,
have left abundant traces of their existence in past time.

b. Coelenterata. — Amongst the Ccelenterate animals, the
Fresh-water Polypes (Hydra), the Oceanic Hydrozoa, the Jelly-
fishes (Medusida), the Sea -blubbers (Litcernarida), the Sea-
anemones (Actinidce), and the Ctenophora are destitute of hard
parts which could be preserved as fossils. The Sea-blubbers,
however, supply us with an instance of how a completely soft-
bodied creature may leave traces of its past existence; for there
is no doubt that impressions left by the stranded carcasses of
these animals have been detected in certain fine-grained rocks
(the Lithographic Slate of Solenhofen). On the other hand,
the coralligenous Zoophytes or "corals" (comprising the Zoan-
t/iaria sderodermata and sclerobasica, and most of the Alcyonaria)
possess hard parts capable of preservation, and the same is the
case with most of the Hydroid Zoophytes. Accordingly, there
are few more abundant fossils than corals ; whilst the large ex-
tinct group of the Graptolites is generally placed in the vicinity
of the Sea-firs (Sertularians).

c. Annuloida. — In this sub-kingdom the great class of the
Echinodermata may be said to be represented more or less

IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 29

completely by all its orders. In the Sea-cucumbers (Holothur-
oidea\ however, the calcareous structures so characteristic of
the integuments of the other Echinoderms are reduced to their
minimum ; and accordingly the evidence of the past existence
of these creatures is of the most scanty description. The other
great class of the Annuloida (viz., the Scolecida) comprises
animals almost without exception destitute of hard parts, and
which mostly live parasitically in the interior of other animals
(e.g., the Tape -worms, Suctorial -worms, Round -worms, &c.)
We are therefore without any geological evidence of the former
existence of Scolecida, though no doubt can be reasonably
entertained but that the group dates back to a time long an-
terior to the present fauna.

d. Annnlosa. — Many of the lower Annulose animals, such
as Leeches, Earth-worms, and Errant Annelides, possess no
structures by which we could expect to get direct evidence of
their past existence. The last of these, however, have left
ample traces of their former presence in the form of burrows
or " tracks" upon the mud and sand of ancient sea-bottoms ;
and the so-called " Tubicolar " Annelides are well represented
by their investing tubes. In the case of the higher Annulosa,
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, further, are not only aqueous, but
are also marine, most fossils are those of sea -animals. It
follows, therefore, that the remains of air-breathing animals,
whether these be terrestrial or aerial, can only be preserved 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 Crustaceans ; since these not only have a resisting shell or
" exoskeleton," but are also generally aquatic in their habits.
The air-breathing classes of the Myriapoda (Centipedes and
Millipedes), the Arachnida (Spiders and Scorpions), and the
Insect a or true Insects, on the other hand, have been much
less commonly and completely preserved, though many of
them are perfectly capable of being fossilised. Almost all such
remains, however, 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

30 INTRODUCTION.

as coal and peat. There is, however, a considerable number
of aquatic insects (but exclusively in fresh water), and there
are many insects the larvae of which inhabit water, whether
this be fresh or salt ; so that instances of these occurring as
fossils are not very infrequent.

e. Mollusca. — This sub-kingdom requires little notice, since
the greater number of its members possess hard structures
capable of being preserved in a fossil condition. Thus, the
horny or calcareous polypidoms of many of the Polyzoa, the
shells of the Brachiopods, the true Bivalves, and most of the
Gasteropoda, the internal skeletons of the Cuttle-fishes, and
the chambered shells of the Tetrabranchiate Cephalopods, all
occur more or less abundantly as fossils. The entire class of
the Tunicaries, however, presents (with one or two exceptions)
no hard structures, and is hence not with certainty known by
any fossil representative. Amongst the Gasteropoda, again,

. the Sea-slugs and their allies (Niidibranchiata) possess no shell,
and are unknown to the palaeontologist; whilst the shell of the
I Land-slugs is extremely minute, and has not been certainly
, recognised as fossil. Lastly, the air-breathing terrestrial Mol-
luscs, from their habits, rarely occur as fossils ; whilst those
which inhabit rivers, ponds, and lakes are less largely repre-
sented than marine forms, owing to the preponderance of salt-
water deposits over those of fresh water.

f. Vertebrata. — The majority of Vetebrate 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 Lampreys), have no scales, and either possess no
" endoskeleton " or have one which is almost wholly cartila-
ginous. The only evidence, therefore, which could be obtained
of the past existence of such fishes would be afforded by their
teeth ; but these are wanting in the Lancelet, and are very
small 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 integu-
mentary plates as well. They have also left many traces of
their existence in the form of footprints. Most living Amphi-
bians, however, frequent fresh waters, or spend a great part of
their time upon the land ; and hence their remains would not
be apt to be preserved in marine deposits.

IMPERFECTION OF PAL^EONTOLOGICAL RECORD. 31

The abundance of Reptiles as fossils naturally varies much,
according 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 hard integumentary
skeleton. The Snakes are mainly represented by forms which
frequented water, and especially by marine forms. The Lizards
(Lacertilia) live mainly upon the land, and do not therefore
abound as fossils ; but some extinct forms (the Mosasauroids)
were marine in their habits, and have consequently been pretty
fully preserved. The Crocodilia, 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 seem to have fre-
quented the sea itself. Of the extinct orders of Reptiles, the
great Ichthyosauri and the Plesiosauri and their allies were
marine in their habits, and their remains occur in what may
fairly be called profusion. The Flying Reptiles, or Ptero-
dactyles, 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
Deinosaurs and Dicynodonts, again, come very much under the
laws which regulate the preservation of Mammals as fossils ;
and their remains are chiefly, but not exclusively, to be found
in fluviatile 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 ac-
cordance with these considerations the most abundant remains
of Birds are referable to large wingless forms, to which the
power of saving themselves from their enemies by flight was
denied, whilst most of their bones were filled with marrow in-
stead of air. Next in abundance after these come the remains
of birds which frequent the sea-shore, lakes, estuaries, or rivers,
or which delight in marshy situations.

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

32 INTRODUCTION.

aquatic Mammals — such as Whales, Dolphins, and the like—
are, of course, much more likely to have been preserved 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 Mam-
mals as fossils is due to the comparatively rare occurrence of a
stray individual being killed whilst swimming a river or some
other piece of water, or being mired in a bog, or to the bones
of one that had died on land being washed into some stream
by floods ; but there are other cases for which a different ex-
planation must be sought.

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 palseontological knowledge.
In this connection 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.
In considering such a case, the evidence may be divided into
two heads, the one palaeontological, the other purely physical,
and each may be looked at separately.

The Chalk, as is well known, constitutes in Britain the
highest 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 repre-
sented merely by the dividing-line between the highest beds of
the Chalk and the lowest beds of the Eocene?

Taking the palaeontological evidence first, it is found that
out of five hundred species of fossils known in the Upper Cre-
taceous beds, only one Brachiopod and a few Foraminifera
have hitherto been detected in the immediately overlying
Eocene beds. These latter, on the contrary, are replete with
organic remains wholly distinct from those of the Cretaceous
beds. It may be said, therefore, that the very extensive as-
semblage 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 de-
posited. 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

IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 33

introduced en masse into the same waters. This theory, how-
ever, 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 prefer-
able, therefore, to believe that no such violent processes of
destruction and re-peopling took place, but that the marked
break in the life of the two periods indicates an enormous
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 became again a fitting home for marine life, an immi-
gration into it would set in from neighbouring seas. By this
time, however, the Cretaceous animals must have mostly died
out, or must have become 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 observe at the present
day, the palaeontological break between the Chalk and the
Eocene indicates a perfectly incalculable lapse of time; for
all species change or die out slowly, marine species especially
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 are seen to rest upon an eroded and denuded
surface of Chalk, filling up " pipes " and winding hollows
which descend far below the general surface of the latter. Not
only so, but the base of the Eocene Rocks is commonly com-
posed of a bed of rolled and rounded flints, derived from the
Chalk, affording incontestable proof that the Chalk had been
greatly worn down and removed 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 pheno-
mena : — 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 sub-
jected to still further denudation, and an approximately level

c

34

INTRODUCTION.

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 sur-
face (fig. 3).

Fig. 3. — Section showing strata of Tertiary age (a), resting upon a worn and denuded
surface of White Chalk (ft), the stratification of which is marked by lines of flints.

In the unconformability, then, between the Chalk and the
Eocene Rocks, we have unequivocal evidence — irrespective of
anything that we learn from Palaeontology — that the break
between the two formations was one of enormous length. In
Britain the interval of time thus indicated is not represented
by any deposits ; and in Europe generally there are but frag-
mentary traces of such. We may be quite sure, however, that
during the time represented in Britain by the mere line of un-
conformability between the Chalk and the Eocene, there were
somewhere deposited considerable accumulations of sediment.
Whether we shall ever succeed in discovering these, or any
part of these, is, of course, uncertain. We may be certain,
however, that such deposits, if ever discovered, will prove to
be charged with the remains of animals more or less inter-
mediate in character between those of the Cretaceous and those
of the Eocene period ; and the huge gap now existing between
these formations will thus be more or less completely bridged
over.

Amongst other well-known instances of more or less general
unconformity in the stratified series, may be mentioned that
between the Lower and Upper Silurian (not always present),
that between the Lower and Upper Old Red Sandstone (also
not universal), that between the Carboniferous and Permian
Rocks, that, between the Permian and Triassic Rocks (not
universal), and that between the Lower and Upper Cretaceous

IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 35

Rocks. All these physical breaks are accompanied by more
or less extensive palaeontological breaks as well. Other breaks
which are rendered less important by the absence or scarcity
of fossils, or which are as yet not thoroughly established, are
those between the Lower and Upper Laurentian Rocks, the
Upper Laurentian and Huronian, and the Upper Cambrian
and Lower Silurian.

It may not be out of place to point out that the unconforma-
bilities here indicated must in no way be confounded with the
common cases in which beds of one age rest unconformably
upon beds far older than themselves. When, for example, we
find beds of Carboniferous age reposing unconformably upon
Silurian strata, this merely indicates that, in the particular lo-
cality under examination, the Devonian or Old Red Sandstone
is amissing. This absence of a whole formation in any given
region merely indicates that the area was dry land during the
period of that formation, or that if any rocks of this age were
deposited in this locality, they were removed by denudation
before the higher group was laid down. The instances above
spoken of, as where the Carboniferous Rocks are succeeded
unconformably by the Permian, though essentially of the same
nature, are distinguished by an important point. In the former
case we know what formation is wanting, and we can intercal-
ate it from foreign areas, and thus complete the series. In the
latter case we have two successive formations in unconformable
junction, and we are not acquainted with any intermediate
group of strata which could be intercalated from any other )
locality.

From the above facts, then, we learn that one of the chief
causes of the imperfection of the palaeontological record is to
be found in the vast spaces of time which separate most of the
great " formations," 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 deposi-
tion as to have allowed of great zoological changes in the
interim, and to have thus caused irremediable blanks in the
palaeontological 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 I

30 INTRODUCTION.

thickness, 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 unrepre-
sented time throughout the whole stratified series is convincing
proof that the palaeontological record is, and ever must be, a
mere excerpt from the biological annals of the globe.

III. THINNING OUT OF BEDS. — Another cause by which the
continuity of the palaeontological record is affected is what is
technically 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 therefore be thickest. Thus, if we take a
series of beds, such as sandstones 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 approaching 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

Fig. 4. — Diagram to show the " thinning out " of beds, a Sandstones and
Conglomerates ; b Limestones.

would at first be very thin, but in proceeding still in the direc-
tion 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 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 directions to-
wards the circumference (fig. 4).

IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 37

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 sedi-
ment was most abundantly conveyed, or where the other con-
ditions 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 derived from the Lower Carboniferous Rocks of
Britain. Here we may start in South Wales and in Central
England with the Carboniferous Limestone as a great calcare-
ous 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 West-
moreland, 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 lime-
stones, however, still bearing a considerable proportion to the
whole. Passing still further northwards, the limestones go on
thinning out, till in Central Scotland, in place of the dense cal-
careous 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 fol-
lows : — 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 mechani-
cal sediments were derived, must have been placed somewhere
to the north of Scotland, and the deepest part of the ocean
must have been somewhere about Derbyshire. Here the con-
ditions for lime-making were most favourable, and here conse-
quently we find the greatest thickness of calcareous strata, and
the smallest intermixture of mechanical deposits.

The palaeontological results of this are readily deducible.
The entire Lower Carboniferous series of Britain was probably
deposited in a single ocean, apparently destitute of land-bar-

38 INTRODUCTION.

riers ; and consequently, taken as a whole, the fauna of this
series may be regarded as one and indivisible. The condi-
tions, nevertheless, which obtained in different parts of this
area were very different; 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 Carbonifer-
ous 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 deposits belonging to a given period. We may have
the deep-sea deposits of the period only, or we may know no-
thing but its littoral accumulations. In either case it is clear
that there is an imperfection of the palseontological 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.

IV. SUDDEN EXTINCTION OF ANIMALS. — Whilst there can
be little doubt but that the changes in animal life indicated by
Geology were in the main gradually effected, there still remain
cases in which individuals seem to have been suddenly de-
stroyed in great numbers, and others of a more obscure nature
in which allied species succeed one another with an inexpli-
cable rapidity. As an example of the first class of cases, we
may take the great Marine Reptiles of the Lias, which often
exhibit indications of having met a sudden death, whilst they
show no traces of mechanical injury. It has been suggested by
Sir Charles Lyell, with great probability, that the sudden death
of marine animals, in these and other similar cases, might have
been caused by the sudden "periodical discharge of large
bodies of turbid fresh water into the sea."

As an example of the second class of cases — which more
especially bear upon the present question — we may take the
existence in the Lias of zones characterised by particular species
of Ammonites. These zones are usually of small thickness,
and the Ammonite characterising each is usually confined to
that particular horizon ; whilst several of these zones have been
found to be persistent over very wide areas. As we know of
no reason why one species of Ammonite should flourish where

IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 39

another allied species would not, we cannot at present account
for this sudden disappearance of one species and its seeming
immediate replacement by another. We may be sure, however,
that we have here an imperfection of the palaeontological record,
and that in reality any two zones must have been separated by
a long period, in which one species became extinct, or was so
far modified as to appear as a new species.

V. DISAPPEARANCE OF FOSSILS. — The last subject which
need be mentioned in connection with the imperfection of the
palseontological record is that of the disappearance of fossils
from rocks originally fossiliferous. This, as a rule, is due to
" metamorphism " — that is to say, the subjection of the rock to
a sufficient amount of heat to cause a rearrangement of its
particles. When of at all a pronounced character, the result
of metamorphism is invariably the 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 palaeonto-
logical record, and the irreparable loss of much fossil evidence.
The most striking example which is to be found of this is the
great Laurentian series, which comprises ,some 30,000 feet of
highly metamorphosed sediments, but which, with one not
absolutely certain exception, has as yet yielded no remains of
life, though there is strong evidence of the former existence in
it of fossils.

Another not uncommon cause of the disappearance of organic
remains from originally fossiliferous deposits is the percolation
through 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. The cleavage, however, 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 con-
tained fossils or not, though it may be quite impossible to
make out the exact nature and character of the organic
remains.

40 INTRODUCTION.

CHAPTER V.
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 maybe divided
into a number of definite groups or " formations," each of which
is characterised by its organic remains. It may simply be re-
peated here that these formations are not properly and strictly
characterised by the occurrence in them of any one particular
fossil. It may be that a formation contains some particular
fossil, or fossils, not occurring out of that formation, and that
in this way an observer may identify a given group with toler-
able certainty. It very often happens, indeed, that some parti-
cular stratum, or sub-group of a series, contains peculiar fossils,
by which its existence may be determined in various localities.
As before remarked, however, the great formations are charac-
terised properly by the association of certain fossils, by the
predominance of certain families or orders, or by an assemblage
of fossil remains representing the " life" of the period in which
the formation 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
important conclusions as to the mode in which the fossiliferous
bed was deposited, and thus as to the condition of the parti-
cular 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 de-
posited by the overflowing of an ancient stream. Secondly, if
the bed contain the remains of shell-fish, minute crustaceans,
or fish, such as now inhabit lakes, we know that it is " lacus-
trine," and was deposited beneath the waters of a former lake.
Thirdly, if the bed contain the remains of animals such as now

j 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, 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 fossili-

CONCLUSIONS TO BE DRAWN FROM FOSSILS. 41

ferous 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), wre 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 accumulation 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 want-
ing, 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 con-
clusions 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 undoubtedly 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 undoubt-
edly grown on the very spot where we now find them. Thus
it is now generally admitted that the great coal-fields of the
Carboniferous age are the result of the growth in situ of the
plants which compose coal, and that these grew on vast

INTRODUCTION.

marshy or partially submerged tracts of level alluvial land.
We have, however, 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 surround-
ing 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. 5).

CONCLUSIONS AS TO CLI-
MATE.— In many cases fossils
enable us to come to impor-
tant conclusions as to the
climate of the period in which
they lived, but only a few in-
stances of this can be here
adduced. As fossils in the
majority of instances are the

Fie. >>. — Erect Tree containing Reptilian • ' f • , •

remains! Coal-measures, Nova Scotia (after remains of marine animals, it

Dawson). js 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 climate of a given area does not neces-
sarily imply a correspondingly warm climate in the neighbour-
ing land. Land-climates can only be determined by the
remains of land-animals or land-plants, and these are com-
paratively 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.

b. 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 sup-
posed habits more or less uncertain and unsafe.

CONCLUSIONS TO BE DRAWN FROM FOSSILS. 43

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 recently been shown that many shells formerly believed
to be confined to the Arctic Seas have, by reason of the ex-
tension 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 conditions under which certain beds
were supposed to have been deposited.

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 establishment 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 con-
ducing to its extension.

Still, we are in many cases able to draw completely reliable
conclusions as to the climate of a given geological period, by
an examination of the fossils belonging to that period. Among
the more striking examples of how the past climate of a region
may be deduced from the study of the organic remains con-
tained in its rocks, the following may be mentioned : It has /.
been shown that in Eocene times, or at the commencement
of the Tertiary period, the climate of what is now Western
Europe was of a tropical or sub-tropical character. Thus the
Eocene beds are found to contain the remains of shells such
as now inhabit tropical seas, as, for example, Cowries and
Volutes ; and with these are the fruits of palms, and the
remains of other tropical plants. It has been shown, again, -
that in Miocene times, or about the middle of the Tertiary
period, Central Europe was peopled with a luxuriant flora
resembling that of the warmer parts of the United States, and
leading to the conclusion that the mean annual temperature
must have been at least 30° hotter than it is at present. It
has been shown that, at the same time, Greenland, now buried
beneath a vast ice-shroud, was warm enough to support a large
number of trees, shrubs, and other plants, such as inhabit the
temperate regions of the globe. Lastly, it has been shown,
upon physical as well as palaeontological evidence, that the

44 INTRODUCTION.

greater part of the North Temperate Zone, at a comparatively
recent geological period, has been visited with all the rigours
of an Arctic climate, resembling that of Greenland at the pre-
sent day. This is indicated by the occurrence of Arctic shells
in the superficial deposits of this period, whilst the Musk-ox
and the Reindeer roamed far south of their present limits.

CHAPTER VI.

DIVISIONS OF THE ANIMAL KINGDOM, AND
SUCCESSION OF ORGANIC TYPES.

IT seems hardly necessary to remark that Palaeontology, as
a science, is based upon the kindred sciences of Zoology and
Botany, and that no satisfactory acquaintance with the former
can be arrived at without the previous acquisition of some
knowledge of the latter. It cannot be pretended to teach here
even the rudiments of these sciences, but there are a few points
which may be noticed as having a special bearing upon the
study of Palaeontology.

CLASSIFICATION OF THE ANIMAL KINGDOM. — Leaving the
vegetable kingdom till we come to speak of fossil plants, a
few remarks may be made on the classification of the animal
kingdom. Vast as is the number of known animals, all,
whether living or extinct, may be classed under some five or
six primary divisions or "morphological types," which are
technically spoken of as the " sub-kingdoms." 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 constructed ; and they differ from one another simply in
the modifications of this common plan. No comparison,
therefore, is possible between an animal belonging to one sub-
kingdom, and one belonging to another, since their distinguish-
ing characters are the result of the modification of two essen-
tially different ground-plans. Hence, it is possible to arrange
the animals of any one sub-kingdom in something like a linear
series, in which the lowest of the series most closely approaches
the primitive or ideal form of the sub-kingdom, whilst the
highest exhibits the greatest amount of complexity ancl special-
isation 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

CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 45

animal, no amount of complexity, no specialisation of organis-
ation, 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. We must therefore abandon
the idea that it is possible to establish a linear classification of
the animal kingdom.

The following synoptical table gives briefly the leading
divisions of the animal kingdom, and the chief characters of
these : —

TABULAR VIEW OF THE CHIEF DIVISIONS OF THE
ANIMAL KINGDOM.

INVERTEBRATE ANIMALS.

SUB-KINGDOM I.— PROTOZOA.

Animal simple or forming colonies, usually very minute ; the body com-
posed of the structureless, jelly-like, albuminous substance called "sar-
code ; " not divided into regular segments ; having no nervous system ; no
regular circulatory system ; usually no mouth ; no definite body-cavity or
digestive system, or at most but a short gullet.

CLASS A. GREGARINID^E. — Minute Protozoa which inhabit the interior
of insects and other animals, and which have not the power of throwing
out prolongations of their substance (pseudopodia). No mouth.

CLASS B. RHIZOPODA (Root-footed Protozoa). — Protozoa which are
simple or compound, and have the power of throwing out and retracting
prolongations of the body-substance (the so-called "pseudopodia"). No
mouth, in most, if not in all.

Order i. Monera. — Ex. Protogenes.

Order 2. Amcebea. — Ex. Proteus Animalcule (Amceba).

Order 3. Foraminifera. — Ex. Lagena, Nodosaria, Globigerina.

Order 4. Radiolaria. — Ex. Thalassicolla, Polycystina.

Order 5. Spongida. — Ex. Fresh-water Sponge (Spongilla), Venus's
Flower-Basket (Euplectella).

CLASS C. INFUSORIA (Infusorian Animalcules). — Protozoa with a mouth
and short gullet ; destitute of the power of emitting pseudopodia ; furnished
with vibratile cilia or contractile filaments ; the body usually composed of
three distinct layers.

Order i. Ciliata. — Ex. Bell-animalcule (Vorticella), Paramcecium.

Order 2. Flagellala. — Ex. Peranema.

Order 3. Suctoria. — Ex. Podophyra.

SUB-KINGDOM II.—CCELENTERATA.

Animals whose alimentary canal communicates freely with the general
cavity of the body ; body composed essentially of two layers or membranes,
an outer layer or •" ectoderm," and an inner layer or "endoderm." No
circulatory system or heart, and in most no nervous system. Skin fur-
nished with minute stinging organs or "thread-cells." Distinct reproduc-
tive organs in all.

CLASS A. HYDROZOA. — Walls of the digestive sac not separated from

46 INTRODUCTION.

those of the general body-cavity, the two coinciding with one another.
Reproductive organs external.

Sub-class I. HYDROIDA (Hydroid Zoophytes).

Order I. Hydrida. — Ex. Fresh- water Polype (Hydra).
Order 2. Corynida. — Ex. Pipe-coralline (Tubularia).
Order 3. Sertularida. — Ex. Sea-firs (Sertularia).
Sub-class II. SIPHONOPHORA (Oceanic Hydrozoa).
Order 4. Calycophorida. — Ex. Diphyes.

Order 5. Physophorida. — Ex. Portuguese Man-of-War (Physalia).
Sub-class III. DISCOPHORA (Jelly-fish).

Order 6. Medusida — Ex. Trachynema.
Sub-class IV. LUCERNARIDA (Sea-blubbers).
Order 7. Lucernaridce. — Ex. Lucernaria.
Order 8. Pelagidce. — Ex. Pelagia.
Order 9. Rhizostomida. — Ex. Rhizostoma.
Sub-class V. GRAPTOLITID^E (extinct).

CLASS B. ACTINOZOA. — Stomach opening below into the body-cavity,
which is divided into a number of compartments by a series of vertical par-
titions or " mesenteries." Reproductive organs internal.

Order I. Zoantharia. — Tentacles simply rounded, in multiples of
five or six. — Ex. Sea-Anemones (Actinidae), Star-
corals (Astrseidse), Brain-corals (Meandrina), Madre-
pores (Madreporidse).

Order 2. Alcyonaria. — Tentacles fringed, in multiples of four. —
Ex. Dead-man's-toes (Alcyonium), Organ-pipe Coral
(Tubipora), Sea-rods (Virgularia), Sea-pens (Penna-
tula), Red Coral (Corallium).
Order 3. Ritgosa (extinct).

Order^ Ctenophora. — Animal oceanic, swimming by means of
bands of cilia or " ctenophores." — Ex. Pleurobrachia,
Venus's Girdle (Cestum).

S US-KINGDOM III. —A NNUL OIDA .

Animals in which the alimentary canal is completely shut off from the
general cavity of the body, and in which there is a distinct nervous system.
A true blood-circulatory system may or may not be present. In all there
is a peculiar system of canals, which usually communicate with the exterior,
and which constitute what is called the "water- vascular system." The
body of the adult is never composed of a succession of definite rings, or pro-
vided with successive pairs of appendages disposed symmetrically on the
two sides of the body.

The Annuloida are divided into two great classes :

A. ECHINODERMATA. — Integument composed of numerous calcareous
plates joined together, or leathery and having grains, spines, or tubercles
of calcareous matter developed in it. Water-vascular system (ambulacral
system) mostly employed in locomotion, and generally communicating with
the exterior. Adult generally more or less starlike or "radiate " in shape ;
young mostly showing more or less complete "bilateral symmetry," that is,
showing similar parts on the two sides of the body. Nervous system
radiate.

Order I. Crinoidea (Sea-lilies). — Ex. Feather-star (Comatula), Me-
dusa-head Crinoid (Pentacrinus), Stone-lily (Encri-
nus.)

Order 2. Blastoidea (extinct).
Order 3. Cystoidea (extinct).

CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 47

Order 4. Ophiuroidea (Brittle-stars) — Ex. Sand-stars (Ophiura),

Brittle-stars (Ophiocoma).

Order 5. Asteroidea (Star-fishes). — Ex. Cross-fish (Uraster), Sun-
star (Solaster), Cushion-star (Goniaster).
Order 6. Echinoidea (Sea-urchins). — Ex. Sea -eggs (Echinus),

Heart-urchins (Spatangus).
Order 7. Holothuroidea (Sea-cucumbers). — Ex. Trepangs (Holo-

thuria).

B. SCOLECIDA. — Body usually flattened, or cylindrical and worm-like ;
integument soft, without lime. Water-vascular system not assisting in
locomotion. Nervous system consisting of one or two ganglia or little
masses, and not disposed in a radiate manner.

Order I. Tteniada. — Ex. Tape-worm (Tsenia).

Order 2. Trematoda (Suctorial worms). — Ex. Liver-fluke (Dis-

toma).
Order 3. Turbellaria. — Ex. Planarians (Planaria), Ribbon-worms

(Nemertes).
Orders Acanthocephala (Thorn-headed worms). — Ex. Echino-

rhynchus.

Order 5. Gordiacea (Hair-worms). — Ex. Gordius.
Order 6. Nematoda (Thread- worms). — Ex. Round- worm (Ascaris),

Guinea-worm (Filaria), Vinegar-eel (Anguillula) .
Order 7. Rotifera (Wheel-animalcules). — Ex. Builder-animalcule

(Melicerta), Flexible Creeper (Notommata).

SUB-KINGDOM IV.—ANNULOSA.

Animal composed of numerous definite segments or " somites," arranged
longitudinally, one behind the other. Nervous system always present, con-
sisting typically of a double chain of nervous masses, or ganglia, which are
placed along the lower surface of the body, and form a collar around the
gullet. Limbs (when present) turned toward that side of the body on
which the main masses of the nervous system are situated.

DIVISION A. ANARTHROPODA. — Locomotive appendages, when pre-
sent, not distinctly jointed or articulated to the body.
CLASS I. GEPHYREA. — Ex. Spoon-worms (Sipunculus).
CLASS II. ANNELIDA (Ringed-worms).

Order I. Hirudinea. — Ex. Leeches (Sanguisuga, Hirudo).
Order 2. Oligochata. — Ex. Earth-worms (Lumbricus), Water-
worms (Nais).

Order 3. Tubicola. — Ex. Tube-worms (Serpula).
Order 4. Errantia. — Ex. Sand-worms and Sea-centipedes (Nereis),

Lob-worm (Arenicola), Sea-mouse (Aphrodite).
CLASS III. CH^TOGNATHA (Arrow- worms). — Ex. Sagitta.
DIVISION B. ARTHROPODA. — Locomotive appendages jointed or articu-
lated to the body.

CLASS I. CRUSTACEA. — Respiration aquatic, mostly by gills. Two
pairs of antennae. Limbs more than four pairs in number, carried upon the
thorax, and generally the abdomen also.

Order I. Ichthyophthira. — Ex. Lernsea.

Order 2. Rhizocephala. — Ex. Peltogaster.

Order 3. Cirripedia. — Ex. Barnacles (Lepas), Acorn-shells (Bal-

anus).

Order 4. Ostracoda. — Ex. Water-fleas (Cypris).
Order 5. Copepoda. — Ex. Cyclops.
Order 6. Cladocera. — Ex. Branched-horned Water-fleas (Daphnia).

48

INTRODUCTION.

Order 7. Phyllopoda. — Ex. Brine-shrimp (Artemia).

Order 8. Trilobita (Extinct).

Order 9. Merostomata. — Ex. King-crabs (Limulus).

Order 10. Lamodipoda. — Ex. Whale-louse (Cyamus).

Order II. Isopoda. — Ex. Wood-lice (Oniscus), Slaters (Ligia).

Order 12. Amphipoda. — Ex. Sandhopper (Talitrus), Fresh-water

Shrimp (Gammarus).

Order 13. Stomapoda. — Ex. Locust-shrimp (Squilla).
Order 14. Decapoda. — Ex. Lobster (Homarus), Cray-fish (Astacus),
Shrimps (Crangon) ; Hermit-crabs (Pagurus) ; Crabs
(Cancer, Carcinus), Land-crabs (Gecarcinus).

CLASS II. ARACHNIDA. — Respiration aerial, by pulmonary chambers or
air-tubes (tracheae) in the higher forms. Antennae converted into jaws.
Head and thorax amalgamated. Four pairs of legs. Abdomen without
limbs.

Order I. Podosomata (Sea-spiders). — Ex. Pycnogonum.

Order 2. Monomerosomata. — Ex. Mites (Acarus), Water-mites (Hy-

drachna), Ticks (Ixodes).
Order 3. Adelarthrosomata. — Ex. Harvest-spiders (Phalangidae),

Book-scorpions (Chelifer).

Order 4. Pedipalpi. — Ex. Scorpions (Scorpio).
Order 5. Aranetda. — Ex. House-spiders (Tegenaria), Field-spiders

(Epeira).

CLASS III. MYRIAPODA. — Respiration aerial, by tracheae (air-tubes) or
by the skin. Head distinct ; remainder of body composed of nearly simi-
lar segments. Legs more than eight pairs in number, and borne partly
upon the abdomen. One pair of antennae.

Order I. Chilopoda. — Ex. Centipedes (Scolopendra).
Order 2. Chilognatha. — Ex. Millipedes (lulus).
Order 3. Pauropoda. — Ex. Pauropus.

. CLASS IV. INSECTA. — Respiration aerial, by tracheae. Head, thorax,
and abdomen distinct. One pair of antennae. Three pairs of legs, and
generally two pairs of wings on the thorax. No locomotive limbs on the
abdomen.

Order i. Anoplura. — Ex. Lice (Pediculus).

Order 2. Mallophaga (Bird-lice).

Order 3. Thysanura (Springtails).

Order 4. Hemiptera. — Ex. Plant-lice (Aphides), Field-bug (Pen-

tatoma), Cochineal Insects (Coccus).
Order 5. Orthoptera. — Ex. Locusts (Acrydium), Grass-hoppers

(Gryllus), Crickets (Achetina), Cockroach (Blatta).
Order 6. Neuroptera. — Ex. White Ants (Termes), Dragon-flies

(Libellulidae), May-flies (Ephemeridae).
Order 7. Aphaniptera. — Ex. Fleas (Pulex).
Order 8. Diptera. — Ex. Gnats (Culex), Crane-flies (Tipula),

House-flies and Flesh-flies (Musca).
Order 9. Lepidoptera (Butterflies and Moths).
Order 10. Hymenoptera. — Ex. Bees (Apidae), Humble-bees (Bom-
bidae), Wasps (Vespidae), Ants (Formicidae), Saw-flies,
(Tenthredinidae).

Order n. Strepsiptera. — Ex. Stylops.
Order 12. Coleoptera (Beetles).

SUB-KINGDOM V.—MOLLUSCA.
Animal soft-bodied, generally with a hard covering or shell. Nervous

CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 49

system consisting of a single ganglion or of scattered pairs of ganglia. A
distinct heart and breathing-organ, or neither.

The Mollusca may be divided into the two following primary divisions,
containing the following classes : —

A. MOLLUSCOIDA. — Nervous system consisting of a single ganglion or of
a principal pair of ganglia. No heart, or an imperfect one.

CLASS I. POLYZOA. — Animal always forming compound growths or
colonies. No heart. The mouth of each zooid surrounded
by a circle or crescent of ciliated tentacles. — Ex. Sea-
mats (Flustra), Lace-coral (Fenestella).

CLASS II. TUNICATA. — Animal simple or compound, enclosed in a
leathery or gristly case. An imperfect heart. — Ex. Sea-
squirts (Ascidia).

CLASS III. BRACHIOPODA. — Animal always simple ; the body enclosed
in a bivalve shell. Mouth furnished with two long fringed
processes or "arms." — Ex. Lamp-shells (Terebratula).

B. MOLLUSCA PROPER. — Nervous system consisting of three principal
pairs of ganglia. Heart well developed, consisting of at least two chambers.

CLASS IV. LAMELLIBRANCHIATA (Bivalve Shell -fish). — No distinct
head ; no teeth. Body enclosed in a shell which is " bi-
valve," or composed of two distinct pieces. One or two
leaf- like gills on each side of the body. — Ex. Oyster
(Ostrea), Scallop (Pecten), Mussel (Mytilus).

CLASS V. GASTEROPODA. — A distinct head and toothed tongue. Shell
absent in some, but mostly present, and usually consisting
of a single piece ("univalve"). Locomotion effected by
creeping about on the flattened under surface of the body
(" foot "), or by swimming by means of a fin-like modifi-
cation of the same. — Ex. Whelks (Buccinum), Limpets
(Patella), Sea-lemons (Doris), Land-snails (Helix), Slugs
(Limax).

CLASS VI. PTEROPODA. — Animal oceanic, swimming by means of two
wing-like appendages, one on each side of the head. Size
minute. — Ex. Cleodora.

CLASS VII. CEPHALOPODA. — Animal with eight or more arms, placed
in a circle round the mouth. Mouth armed with jaws, and
and a toothed tongue. Two or four plume-like gills. In
front of the body, a muscular tube ("funnel") through
which is expelled the water which has been used in respira-
tion. An external shell in some, an internal skeleton in
others. — Ex. Calamaries (Loligo), Cuttle-fishes or Poulpes
(Octopus), Paper-Nautilus (Argonauta), Pearly Nautilus
(Nautilus).

VERTEBRATE ANIMALS.

SUB-KINGDOM VI. — VER TEBRA TA.

Body composed of a number of definite segments arranged longitudinally,
or one behind the other. The main masses of the nervous system are
placed on the dorsal aspect of the body, and are completely shut off from
the general body-cavity. The limbs (when present) are turned away from
that side of the body on which the main nervous masses are situated, and
are never more than four in number. In most cases a backbone, or
"vertebral column," is present in the fully-grown animal.

D

50 INTRODUCTION.

CLASS I. PISCES (Fishes). — Breathing-organs in the form of gills. Heart
usually of two chambers, rarely of three. Blood cold. Limbs, when present,
converted into fins.

Order I. Pharyngobranchii. — Ex. Lancelet (Amphioxus).

Order 2. Marsipobranchii. — Ex. Lamprey (Petromyzon), Hag-fish

(Myxine).

Order 3. Teleostei (Bony Fishes). — Ex. Eels (Muraenid?e), Her-
rings (Clupeidae), Salmon and Trout (Salmonidae), Cod
and Haddock (Gadidae), Flat-fishes (Pleuronectidae),
Perch (Percidae), Mackerel (Scomberidae).
Order 4. Ganoidd. — Ex. Bony Pike (Lepidosteus), Paddle-fish

(Spatularia), Sturgeon (Sturio).

Order 5. Elasmobranchii. — Ex. Sharks (Carcharidae), Dog-fishes
(Scylliadae), Saw-fishes (Pristis), Rays and Skates
(Raiidse).

Order 6. Dipnoi. — Ex. Mud-fish (Lepidosiren).

CLASS II. AMPHIBIA (Amphibians). — Breathing-organs in the young in
the form of gills alone, afterwards lungs, either alone or associated with gills.
Skull joined to the backbone by two articulating surfaces ("condyles").
Limbs never converted into fins. Heart in the young of two chambers
only, in the adult of three chambers. Blood cold.
Order I. Labyrinthodontia (extinct).
Order 2. Ophiomorpha. — Ex. Caecilia.

Order 3. Urodda (Tailed Amphibians). — Ex. Water - newts
(Triton), Salamanders (Salamandra), Axolotl (Sire-
don), Mud-eel (Siren).

Order^ Anoura (Tailless Amphibians). — Ex. Frogs (Rana),
Tree-frogs (Hyla), Toads (Bufo), Surinam Toads (Pipa.)
CLASS III. REPTILIA (Reptiles). — Respiratory organs in the form of
lungs, never in the form of gills. Heart three -chambered, rarely four-cham-
bered, the pulmonary and systemic circulations always connected together
directly, either in the heart itself or in its immediate neighbourhood. Blood
cold. Skull jointed to the backbone by a single articulating surface or
"condyle." Each half of the lower jaw composed of several pieces.
Appendages of the skin in the form of scales or plates.

Order I. Chelonia. — Ex. Turtles (Cheloniidae), Soft Tortoises
(Trionycidae), Terrapins (Emydid&e), Land Tortoises
(Testudinidae).

Order 2. Ophidia. — Ex. Vipers (Viperidae), Rattlesnakes (Crota-
lidae), Sea-snakes (Hydrophidae), Boas and Pythons
(Boidae).

Order 3. Lacertilia. — Ex. Lizards (Lacerta), Iguanas (Iguanidae),
Monitors (Varanidae), Chameleons (Chamasleontidae).
Order 4. Crocodilia. — Ex. Crocodiles, Alligators, Gavials.
Order 5. Ichthyopterygia (extinct). — Ex. Ichthyosaurus.
Order 6. Sauropterygia (extinct). — Ex. Plesiosaurus.
Order 7. Pterosauria (extinct). — Ex. Pterodactylus.
Order 8. Anomodontia (extinct). — Ex. Dicynodon.
Order 9. Deinosauria (extinct). — Ex. Iguanodon.

CLASS IV. AVES (Birds) — Respiratory organs in the form of lungs,
never in the form of gills. Lungs connected with air-receptacles placed in
different parts of the body. Heart four- chambered. Blood warm. Skull
connected with the backbone by a single articulating surface or " condyle."
Each half of the lower jaw composed of several pieces. Appendages of
the skin in the form of feathers. Cavities of the chest and abdomen not

CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 51

separated by a complete partition (diaphragm). Fore-limbs converted into
wings. Animal oviparous.

Order I. Natatores (Swimmers). — Ex. Penguins (Spheniscidae),
Gulls (Laridae), Ducks (Anatidae), Geese (Anserinae),
Flamingos (Phaenicopteridae).

Order 2. Grallatores (Waders). — Ex. Rails (Rallidae), Water-hens
(Gallinulae), Cranes (Gruidas), Herons (Ardeidae),
Storks (Ciconinae), Snipes and Woodcock (Scolop-
acidae), Plovers, Oyster-catchers, and Turnstones
(Charadriidae).

Order 3. Cursores (Runners). — Ex. Ostrich (Struthio), American
Ostrich (Rhea), Emeu (Dromaius), Cassowary (Casu-
arius), Apteryx.

Order^ Rasores (Scratchers). — Ex. Grouse, Ptarmigan, Par-
tridges, Pheasants, Turkey, Guinea-fowl, Domestic
Fowl, Pea-fowl (Gallinacei) ; Doves, Pigeons, Ground-
pigeons (Columbacei).

Order 5. Scansores (Climbers). — Ex. Cuckoos (Cuculidae), Wood-
peckers (Picidae), Parrots, Cockatoos, Parrakeets
(Psittacidae), Toucans (Rhamphastidae), Trogons
(Trogonidae).

Order 6. Insessores (Perchers). — Ex. Crows, Magpies, and Jays
(Corvidae), Starlings (Sturnidae), Finches, Grosbeaks,
Larks (Fringillidae), Thrushes, Blackbirds, Orioles
(Merulidae), Creepers and Wrens (Certhidae), Hum-
ming-birds (Trochilidae), Swallows and Martins
(Hirundinidse), Swifts (Cypselidae), King-fishers (Al-
cedinidae).

Order 7. Raptores (Birds of Prey).— Ex. Owls (Strigidae), Fal-
cons and Hawks (Falconidae), Eagles (Aquilina), Vul-
tures (Vulturidae).

Order 8. Saurura (extinct). — Ex. Archaeopteryx.
CLASS V. MAMMALIA (Mammals or Quadrupeds). — Respiratory organs
in the form of lungs, which are never connected with air-sacs placed in
different parts of the body. Heart four-chambered. Blood warm. Skull
united to the backbone by two articulating surfaces or " condyles." Each
half of the lower jaw composed of a single piece. Appendages of the skin
in the form of hairs. Young nourished by means of a special fluid — the
milk, — secreted by special glands — the mammary glands. Animal vivipa-
rous.

A. NON-PLACENTAL MAMMALS. — The young not provided with a
placenta.

Order I. Monotremata. — Ex. Duck-mole (Ornithorhynchus), Spiny
Ant-eater (Echidna).

Order 2. Marsupialia. — Ex. Kangaroos (Macropodidae), Kan-
garoo-bear (Phascolarctos), Phalangers (Phalangis-
tida), Opossums (Didelphidae), Tasmanian Devil
(Dasyurus).

B. PLACENTAL MAMMALS. — The young provided with a placenta.

Order 3. Edentata. — Ex. Sloths (Bradypodidae), Armadillos (Dasy-
podidae), Hairy Ant-eaters (Myrmecophagidae), Scaly
Ant-eaters (Manis).

Order^ Sirenia. — Ex. Manatee (Manatus), Dugong (Halicore).

Order 5. Cetacea. — Ex. Whalebone-whales (Balaenidae), Sperm-
whales (Physeteridae), Dolphins and Porpoises (Del-
phinidae).

52 INTRODUCTION.

Order 6. Ungulata (Hoofed Quadrupeds). — Ex. Rhinoceros;
Tapir ; Horse, Ass, and Zebra (Equidae) ; Hippopota-
mus ; Hogs and Peccaries (Suida) ; Camels and
Llamas (Camelidse) ; Giraffe ; Stags, Elk, Reindeer
(Cervidae) ; Antelopes (Antilopidae) ; Sheep and Goats
(Ovidse) ; Oxen and Buffaloes (Bovidae).

Order 7. Hyracoidea. — Ex. Hyrax.

Order 8. Proboscidea. — Ex. Elephants (Elephas).

Order 9. Carnivora. — Ex. Seals (Phocidae), Bears (Ursidae),
Racoons (Procyon), Badgers (Melidse), Weasels and
Otters (Mustelidae), Civets and Genettes (Viverridse),
Dogs, Wolves, and Foxes (Canidae) ; Hyaenas
(Hyaenidae), Cats, Lynxes, Leopards, Tigers, Lions
(Felidse).

Order 10. Rodentia. — Ex. Hares and Rabbits (Leporidae), Porcu-
pines (Hystricidae), Beavers (Castoridae), Mice and
Rats (Muridae), Dormice (Myoxidae), Squirrels and
Marmots (Sciuridse).

Order II. Cheiroptera. — Ex. Common Bats ( Vespertilionidae) ,
Horseshoe-bats (Rhinolophidae), Vampire-bats (Phyl-
lostomidse), Fox-bats (Pteropidae).

Order 12. Insectivora. — Ex. Moles (Talpidae), Shrew-mice (Sori-
cidae), Hedgehogs (Erinaceidae).

Order 13. Quadrumana. — Ex. Aye-aye (Cheiromys), Lemurs (Le-
muridae), Spider-monkeys (Ateles), Howlers (My-
cetes), Macaques (Macacus), Baboons (Cynocephalus),
Gibbons (Hylobates), Orang (Simia), Gorilla and
Chimpanzee (Troglodytes).

Order 14. Bimana. — Man (Homo Sapiens).

GENERAL SUCCESSION AND PROGRESSION OF ORGANIC
TYPES. — Whilst admitting the impossibility of arranging the
animal kingdom upon any linear plan, no doubt obtains as to
the fact that some of the fundamental " morphological types,"
or plans upon which animals have been constructed, are higher
than others. Every one admits, for example, that the Verte-
brate type is higher than the Molluscan or the Articulate type,
an admission which is not affected by the fact that the highest
Molluscs and Articulates are superior in point of organisation
i to the lowest Vertebrates. In the same way, within the limits
of each sub-kingdom, every one admits that some of the groups
are higher than the others. Every one, for example, would
admit that a Mammal is a superior animal to a Fish. It fol-
lows from this that a certain general arrangement of the animal
kingdom, as a whole, is possible, upon the comparative basis
of the morphological type of the sub-kingdoms. Similarly a
general and more exact arrangement of the classes and orders
of each sub-kingdom may be made by the degree of perfection
in which the type of the sub-kingdom is carried out in each.
-^ No generalisation of Palaeontology seems to stand on a

GENERAL SUCCESSION OF ORGANIC TYPES. 53

firmer basis than that which asserts that there has been a f
general succession of organic types, and that the appear- '
ance of the lower forms of life has in the main preceded that
of the higher forms in point of time. In other words, it is
one of the generalisations of Palaeontology that there has
not only been a succession, but also a progression, of organic
types in proceeding from the earliest fossiliferous deposits
up to the present day. Whilst this general law remains, asi
we believe, unassailable, there are some important considera-
tions which must not be lost sight of. In the first place, 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 certain to
push back still further into the remote vistas of the past the
point of time at which each morphological type first made its
appearance upon the globe. Still, there is little likelihood that
the relative times of appearance of the great groups, as com-
pared with one another, will be affected by the researches of
the future. It remains almost certain that we shall find that
the lower types were followed in point of time by the higher.
In the second place, we find all the primary types in exist-
ence before the close of the Silurian period ; and he would be
rash indeed who would dogmatically deny that they might all
have been present in the earlier Cambrian period. This, at
first sight, might seem almost to negative the above generalisa-
tion, but it does not affect its value if fairly examined. The
lower sub-kingdoms of the Invertebrate animals appeared so
early that their origin is lost in the mists of antiquity, and we
can say nothing positively as to the time when each came into
existence. The Cambrian deposits are underlaid by the vast
series of the Laurentian deposits, representing an incalculable
lapse of time. These ancient sediments, with one exception,
have hitherto proved barren of life, owing to the intense meta-
morphism to which they have been subjected, and they conse-
quently yield no evidence bearing on the question in hand.
They serve to show us, however, by their presence alone, that
we must in the meanwhile leave the Invertebrate sub-kingdoms
out of account altogether as bearing upon the question of the
succession and progression of organic types. We do not know
when these sub-kingdoms commenced, and hence we have no
right to assert either that they were all introduced simultane-
ously, or that they came into being successively. We may be
sure, however, of one thing — they did not commence at the
points where now we find their earliest traces. There remains,
then, only the sub-kingdom of the Vertebrate animals which can

54 INTRODUCTION.

reasonably be appealed to as evidence on this question. The
stratified series is long enough to render it certain that it con-
tains traces of the first appearance of, at any rate, the higher
classes of these, though we doubtless are ignorant of the abso-
lute moment at which each appeared. If, therefore, it can be
shown that there has been a progression as far as this sub-
kingdom is concerned, then there would, by analogy, be the
greatest probability that a similar progression has taken place
in all the sub-kingdoms.

So far as our present knowledge goes, it would appear that
there is 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. Not only does this hold
good for the classes of the Vertebrates, but the same general
statement may be made as to the orders of each class. Where
apparent exceptions occur, a reasonable explanation can be
given, or our knowledge can be shown to be defective. Space
will not allow a discussion of this question, but a single ex-
ample may be taken. So far as we know at present, the earliest
remains of vertebrate animals are those of Fishes — the lowest
class of the sub-kingdom — and these appear in the Upper
Silurian Rocks for the first time. Granting the probability that
Fishes may some day be found in the Lower Silurian Rocks,
or even in Cambrian deposits, there still seems no likelihood
that they will be deprived by any future discoveries of their
position as being the earliest of their sub-kingdom. The oldest
remains of Fishes, however, are by no means those which would
be expected, but belong to two of the higher orders of the class.
This seeming anomaly, however, disappears when we consider
that the two lowest orders of Fishes possess no structures by
which we can reasonably expect to find them recorded in a
fossil state. They may therefore have been in existence long
before the Ganoids and Placoids of the Upper Silurian Rocks,
and we have no right to assume that they were not. As to the
remaining great order of Fishes (the Teleostean Fishes), it is
certain that their appearance was much later, and they are gen-
erally regarded as inferior to the Ganoids and Placoids in zoo-
logical position. This, however, is a matter of opinion, and
reasons are not wanting for regarding them as the highest of
their class.

It only remains to add that nothing further is contended for
here than the general fact of there having been a progression
of morphological types, the lowest presenting themselves first,
the highest being the last to appear upon the scene. It is by no

GENERAL SUCCESSION OF ORGANIC TYPES. 55

means contended that the Ganoid fishes of the Upper Silurian
Rocks were in any way degraded members of their order, or
inferior in point of organisation to the Ganoids of the present
day. On the contrary, there is reason to think that many
types early presented a development more varied than that
exhibited by their successors. It is simply contended that, on
the whole, there has been a zoological progression as we ascend
from the Cambrian period to the present day. It is also tOj
be remembered, that though the commencement of the Inver-
tebrate sub-kingdoms may be unknown to us, a similar pro-
gression can be in many cases shown as regards the orders and
classes of these, even more completely than in the case of the
Vertebrate sub-kingdom.

PART II.

PART II.

CHAPTER VII.
SUB-KINGDOM L— PROTOZOA.

SUB - KINGDOM I. PROTOZOA. — Animal simple or composite,
generally of very minute size, composed of a strtictureless, jelly-like,
albuminoid substance (termed " sareodc"\ showing no compositio?i
out of definite parts or segments, having no definite body -cavity,
•presenting no traces of a nervotts system, and having either no ali-
mentary apparatus, or but a very rudimetitary one.

TABLE OF THE DIVISIONS OF THE PROTOZOA.

CLASS A. GREGARINID^. — Parasitic Protozoa, which are destitute of a
mouth, and do not possess the power of emitting processes of their body-
substance (pseudopodia).

CLASS B. RHIZOPODA. — Protozoa, which are destitute of a mouth, and
have the power of emitting extensile and contractile processes of the body-
substance (pseudopodia).

Order I. Monera. — Ex. Protogenes.
Order 2. Amcebea. — Ex. Amoeba.
Order 3. Foraminifera. — Ex. Nummulites.
Order ^ Radiolaria. — Ex. Haliomma.
Order 5. Spengida. — Ex. Spongilla.

CLASS C. INFUSORIA (Infusorian Animalcules). — Protozoa mostly with
a mouth, and rudimentary digestive canal ; destitute of the power of emit-
ting pseudopodia; furnished with vibratile cilia or contractile filaments;
the body usually with a distinct cuticle covering a layer of firm sarcode.

Regarded palaeontologically, we may eliminate from the Pro-
tozoa the entire class of the Gregarinidce, with the Rhizopodous
orders of the Monera and Amcebea, no trace of the past exis-
tence 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 Animalcules. Some of these, however, possess
horny or membranous cases which might possibly be preserved
in a fossil state ; and it has been alleged that the genus Peri-

6o

PROTOZOA.

dinium has been thus detected in the Cretaceous formation.
With this doubtful exception, however, no Infusorian animal-
cule 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 Fora-
minifera, Radiolaria, and Spongida, all of which secrete hard
structures, and all of which are more or less extensively repre-
sented as fossils, so that they demand our attention separately
and in detail.

I. — FORAMINIFERA.

The Foraminifera may be denned as Rhizopoda in which the
body is protected by a shell or " test" which is usually composed
of carbonate of lime, but which may consist of particles of sand
cemented together by some animal cement, or may be simply horny
(chitinous). The animal may be simple, or may repeat itself inde-
finitely by budding, and the body-substance gives out long and
thread-like processes (pseudopodia), which interlace with one an-
other to form a network, and often coalesce at their bases to form a
continuous layer of sarcode outside the shell. The pseudopodia
reach the exterior either by perforations in the walls of the shell, or
simply by the mouth of the latter (fig. 6, c b\

Fig. 6. — Morphology of Foraminifera. a Lagena vulgaris, a monothalamous Fora-
minifer ; b Miliola (after Schultze), showing the pseudopodia protruded from the oral
aperture of the shell ; c Discorbina (after Schultze), showing the nautiloid shell with
the foramina in the shell-wall giving exit to pseudopodia ; d Section of Nodosaria
(after Carpenter) ; e Nodosaria hispida ; f Globigerina biilloides.

FORAMINIFERA. 6l

From a palaeontological point of view the only part of a
Foraminifer 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 calcareous, or composed of carbonate of
lime, but it is rarely membranous, and it is not uncommonly
" arenaceous " — that is, composed of particles of sand cemented
together by some animal substance. Secondly, the shells of the
Foraminifera may be divided into two natural groups, accord-
ing as their walls are, or are not, perforated by apertures or
" foramina" through which the pseudopodia are protruded. In
those calcareous shells in which the walls are not perforated
the substance of the test is " porcellanous," homogeneous, and
opaque-white when viewed by reflected light. In those^ calcar-
eous shells in which the walls are perforated by pseudopodial
foramina, the substance of the test is "vitreous," transparent, and
glassy. The arenaceous shells may or may not be perforated,
their texture in either case remaining the same. Thirdly, there
are some convenient, though arbitrary, distinctions to be drawn
from the form of the shell. The simplest form amongst the
Foraminifera, and that in which all alike primitively commence
their existence, is that of a single spheroid of sarcode capable
of secreting for itself a hard covering, as in Lagena (fig. 6, a)
and Orbulina (fig. 7). This simple state of things is rarely
retained throughout life, but the primitive
mass of sarcode usually repeats itself by bud-
ding, till a compound mass is produced, con-
sisting of a number of little spheres of sarcode,
surrounded by a common calcareous or are-
naceous envelope or test. Each bud of the
compound Foraminifer is surrounded by its p.
own shell, so that the whole comes to be com- wnversa. A simple
posed of a number of chambers, each contain- y^S^^-
ing a mass of sarcode. The partitions, how- Apennine beds) of

., , S-rr Italy. D'Orbigny.

ever, or "septa, between the different cham-
bers, are perforated by one or more apertures (fig. 6, d), through
which pass connecting bands of sarcode ; so that the sarcode
occupying the different chambers is united into a continuous
and organic whole. Each member of the colony may give out
its own pseudopodia through perforations in its investing wall
(fig. 6, <:), or the pseudopodia may be simply emitted from the
mouth of the shell by the last segment only (fig. 6, b). In any
case the direction in which the buds are thrown out by the
primordial spherule of sarcode is governed by a determinate
law, and differs in different species, the form ultimately assumed

62

PROTOZOA.

by the shell depending wholly upon this. The forms, however,
assumed by the shells of Foraminifera are extremely variable,
even within the limits of a single species, and it would be im-
possible to notice even the chief types in this place. There
are, however, two or three important variations which may
be noticed. 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 Nodosaria (fig. 6, e). 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 Discorbina (fig. 6, c), or
Robulina (fig. 8). These are the so-called " nautiloid " Fora-

minifera, from the resem-
blance of the shell in figure
to that of the Pearly Nauti-
lus. From this resemblance
the nautiloid Foraminifera
were originally placed in the
same class as the Ammonites
( Cephalopoda), but their true
position was shown by the
examination of their soft
P*«s. In the typical nauti-
loid shell the convolutions
of the spiral all lie in one plane ; but in other cases, as in
Rotalia (fig. 9) the shell becomes turreted or top-shaped, in
consequence of the coils of the spiral passing obliquely round
a central axis. In other forms, such as Nummulites (fig. 13),

Fig' 8--

Fig. 9. — Rotalia Boueana. D'Orbigny.

Orlitolites, and Orbitoides, the shell, though consisting essen-
tially of a succession of chambers arranged in a spiral series, is
of a much more complex nature. Lastly, in addition to these
symmetrical forms, there are others, such as Globigerina (fig. 6,
/), in which the arrangement of the segments is very irregular.
Remains of Foraminifera have been found in all the great

FORAMINIFERA. 63

formations into which the stratified series is divided, from the
Laurentian period to the present day. In one of the limestones
of the vast Laurentian series of Canada occurs a singular body
which has been described as a gigantic Foraminifer, under the
name of Eozoon Canadense (fig. 10). Some observers doubt
the true organic nature of Eozoon, but the weight of authority
is decidedly in favour of the belief that the above is its real
character. If this be the case, Eozoon is not only the oldest of
the Foraminifera, but is the earliest fossil of any kind as yet
discovered. Eozoon consists of a chambered calcareous skele-

'»!.•* V«»* t/_*l*

Fig. 10. — Diagram of a portion of Eozoon (after Carpenter). — A, B, C, Three tiers of
chambers communicating with one another by constricted apertures ; a a The true shell-
wall, perforated by numerous pseudopodial foramina ; b b Intermediate skeleton ; c Pas-
sage of communication (stolon-passage) from tier to tier ; d Ramifying tubes in the inter-
mediate skeleton.

ton infiltrated by certain silicates in solution. These silicates
are chiefly white pyroxene, serpentine,' and Loganite, and they
are now found occupying all the spaces in the fossil which were
formerly filled with the sarcode of the animal. When, there-
fore, a specimen of Eozoon is treated with acid, the calcareous
matter is dissolved out, and what we have left consists of a
cast in the above silicates of the chambers formerly occupied
by the sarcode of the animal, together with the various passages
by which these chambers are connected, and the tubes by
which the pseudopodia were conducted to the exterior. That
such a replacement of an animal body by silicated minerals
is not an impossibility is shown by the occurrence of casts of
living Foraminifera (such as Amphistegina) in which the sarcode
is replaced by a green silicate (probably glauconite), which
forms an accurate cast of the interior of the shell. Eozoon
consists essentially of a series of chambers placed in tiers
(fig. 10, A, B, C) which are arranged one above the other.

64 PROTOZOA.

Sometimes its growth was very regular, but sometimes extremely
irregular. The chambers are more or less perfectly marked off
from one another by inflections of the test or " septa," per-
forated for the passage of bands of sarcode, by which the
chambers are brought into organic connection. The sarcode
occupying the tiers of chambers is bounded by a thin " proper
wall" (fig. 10, a a), perforated by numerous minute tubes by
which the pseudopodia reached the exterior. It is obvious,
however, that only the chambers of the uppermost tiers could
thus have the power of giving out pseudopodia. The various
tiers of chambers are connected with one another by a canal -
system, and are separated from one another by the develop-
ment of supplementary layers of calcareous matter, constituting
what is called the " intermediate skeleton." Eozoon appears
to have grown in reef-like masses, often of very great extent,
and it finds its nearest living allies in the recent Polytrema and
Carpenteria. Its shell-structure also shows points of affinity
with the extinct Nummulites and the recent Calcarina. Eozoon
has been detected, not only in the Laurentian series of Canada,
but in other rocks supposed to be of the same age in Bavaria
and in other parts of Europe. It also occurs in the Lower
Silurian marbles of Connemara in Ireland ; and it is said to
have been detected in rocks of Liassic age.

Having given a somewhat detailed account of the singular
Eozoon — justified by its importance — it will not be necessary
to speak at any length of the more modern representatives of
the order. In the Silurian Rocks remains of Foraminifera
have been detected in various localities, some of the forms
apparently being identical with existing types. Thus, Ehren-
berg showed that the Lower Silurian sandstones of the
neighbourhood of St Petersburg contained casts of Forami-
niferous shells in glauconite, some of which were referable
to the living genera Rotalia and Textularia. Over wide
areas in the Southern Alps, Russia, Spain, Armenia, and the
United States, beds of Carboniferous limestone are charged

with the shells of Fusnlina
(fig. u). Whole beds are
made up of the remains of
this minute fossil, and the
Fusulina limestonehasbeen
Justl7 paralleled with the

Carboniferous, Russia. Nlimmulitic Limestone Of

Eocene times.

In the Secondary Rocks, Foraminifera occur in great abun-
dance, but they are not, specially noticeable except for the part

FORAMINIFERA.

they play in the formation of Chalk. The great formation of
the White Chalk — forming the well-known chalk-cliffs of the
south of England, and attaining sometimes a thickness of not
less than 1000 feet — is to a very large extent composed of the
debris of the microscopic shells of Foraminifera. As already
pointed out, therefore, the White Chalk is to some extent
comparable with the ooze of the deep Atlantic, which is also
largely made up of the skeletons of these minute organisms.
Amongst the Foraminifera of the Chalk are the genera Globi-
gerina (fig. 6, /), Rotalia (fig. 9), and Textularia (fig. 12), all
of which are represented by living species, no difference being
distinguishable in the case of
the first between the Creta-
ceous and the modern form.
In the Cretaceous formation
(Upper Greensand) we have
also the gigantic Arenaceous
Foraminifer which consti-
tutes the genus Parkeria,
the shell of which attains a
diameter of two and a quarter
inches.

In the Kainozoic period the Foraminifera attained their
maximum of development, both as regards their size and the
number of generic types. The Eocene formation especially is
remarkable for the profusion of its Foraminiferous fauna. The
Middle Eocene in particular is characterised by the possession
of a very widely spread and easily recognised formation, known
as the Nummulitic Limestone, from the occurrence in it of a
large coin-shaped Foraminifer, the Nummulite (fig. 13). Num-
mulites attain a size of as much as three inches in circumference,
and their structure is very complex. According to Sir Charles

Fig. 12. — Textularia Meyetiana.
D'Orbigny.

Fig. 13. — Nummulites Icevigatus. Eocene.

Lyell, " the Nummulitic Limestone, with its characteristic
fossils, plays a far more conspicuous part than any other

E

66

PROTOZOA.

Tertiary group in the solid framework of the earth's crust,
whether in Europe, Asia, or Africa. It often attains a thick-
ness 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 fol-
lowed still further eastwards into India, as far as Eastern
Bengal and the frontiers of China." Another important
member of the Eocene Rocks is the Miliolite Limestone of
the Paris basin, so called because of the abundance in it of the
shells of a species of Miliola, of which a living form is shown
in fig. 6, b.

II. — RADIOLARIA.

The order Radiolaria is denned as comprising those members
of the Rhizopoda which possess a siliceous test or siliceous spicules,
and are provided with pseudopodia which stand out from the body
like radiating filaments, and occasionally run into one another
(fig. 14).

Fig. 14. — Recent Radiolaria. a Acanthometra ; b Haliomma, one of the Poly-
cystina, showing the siliceous test and radiating pseudopodia.

All the Radiolaria possess hard structures in the form of sili-
ceous spicules or a siliceous test ; but only one group, viz.,
that of the Pelycystina, has as yet been detected in a fossil
condition. The Polycystina (fig. 14, b) are all microscopic
organisms very closely allied to the Foraminifera, from which
they differ chiefly in the siliceous nature of their skeleton.
The test is glassy, composed of flint, perforated by numerous

SPONGIDA. 67

foramina for the emission of pseudopodia, and often provided
with spine-like projections. The Polycystina are best known
as occurring in the so-called " Infusorial Earth " of Barbadoes.
This is a Tertiary deposit, and consists largely of the shells of
Polycystina. They have not as yet been detected in any
Palaeozoic formation, but they are known to occur in the
Mesozoic series.

III. — SPONGIDA.

The Sponges may be denned as Rhizopoda composed of
numerous amcebiform masses of sarcode united into a composite
mass, which is traversed by canals opening on the surface, and is
almost always supported by an internal skeleton or framework of
horny fibres or of calcareous or siliceous spicula.

The only portion of the Sponges with which the palaeonto-
logist is concerned, is the skeleton. Whatever the nature of
this skeleton may be, it is so arranged that its parts surround
two sets of apertures which open on the surface of the sponge,
and which are connected with one another by a system of
canals ramifying in its deeper portions. Of the apertures
which penetrate the substance of the sponge in every direc-
tion, one set consists of large chimney-like openings, which are
called " oscula," or " exhalant apertures." There maybe only
a single osculum, or many may be present. The other set
consists of very much smaller openings, which are always very
numerous, and which are termed the " pores/' or " inhalant
apertures." The pores and oscula are connected by a system
of canals excavated in the substance of the sponge, and a con-
stant circulation of water can be kept up through the whole
mass, the former serving for the incoming currents, the latter
for the outgoing.

The Sponges are divided into three groups according to the
nature of the skeleton : i. Keratosa, comprising the ordinary
sponges of commerce, in which the skeleton is composed of
a horny substance called "keratode;" 2. Calcarea, or Calci-
spongice, in which the skeleton is composed of carbonate of
lime ; and 3. Silicea, or Vitrea, in which the skeleton is com-
posed of flint or silex.

The Horny Sponges, from the nature of their skeleton, are
not certainly known as fossils ; but traces of their past exist-
ence are said to have been obtained in the form of the spicules
with which the horny skeleton is sometimes furnished. The
Calcareous and Siliceous Sponges are both well represented in
a fossil condition, though the true nature of some of the more

68

PROTOZOA.

ancient examples is perhaps somewhat dubious. As far as
we know at present, the Calcispongice commence in the Silurian
Rocks, attain their maximum in the Secondary Rocks, and are
diminished in numbers at the present day ; though Haeckel's
recent discoveries have rendered this last assertion more than
problematical. The Silicispongice. seem to have come into
existence during the Secondary period, attaining a great de-
velopment during the Cretaceous epoch, and being well repre-
sented at the present day.

As regards Palaeozoic sponges, one of the earliest known
forms is the Archaocyathus (fig. 15) of Mr Billings, species of
which have been obtained from the Potsdam Sandstone and
Calciferous Sand-rock (Upper Cambrian?) of Canada. The

general form in this genus
is that of a hollow cone or
hollow cylinder, enclosing a
large cup-shaped cavity, and
tapering towards one ex-
tremity, which was presum-
ably fixed to some foreign
body. Specimens appear to
have reached a very large
size, a length of two or three
feet and a diameter of three
or four inches being some-
times attained. The sponge
consists of an outer wall,
usually perforated with nu-
merous small irregular aper-
tures, and a thin inner wall
pierced with many open-
ings (fig. 15, a). The space
between the outer and inner
wall is subdivided into a

number of vertical radiating partitions, thus very closely simu-
lating the structure of one of the septate corals. The genus,
however, is shown truly to belong to the Spongida by the
occurrence of numerous branching, cylindrical, or fusiform
siliceous spicula within the substance of the organism. In the
same geological horizon, and also in higher strata, occurs the
somewhat allied genus Calathium, in which the skeleton also
assumed a turbinate form.

Amongst the Lower Silurian genera of Sponges may be
mentioned P-akzospongia, Acanthospongia, Eospongia, Palceo-
and Astylospongia (fig. 16). In the last, we have a

Fig. 15. — Restoration of the lower part of
A rchceocyathus M inganensis ; a the pores of
the inner wall of the cup. (After Billings.)

SPONGIDA.

69

globular sponge, provided with a cup-shaped cavity, on which
the oscula open, whilst the pores open upon the external sur-
face of the sphere. It was a calcareous sponge, enjoying a
free mode of existence, and it presents points of decided
affinity to the recent genus
Grantia. In the Upper Silurian
Rocks occur many sponges,
one of the most interesting
genera being Amphispongia,
comprising calcareous sponges,
oblong or sub-clavate in shape,
containing a central cavity, and
probably opening above by a
single osculum. On this hori-
zon occurs also the genus Favo-
spongia ; and here, as well as in
the Lower Silurians, we have
the singular genus Stromato-

M

Fig. 16. — Section of Astylospongia
prcemorsa, a lower Silurian Sponge

ford, which will be spoken of (after Roemer)'
immediately. In the Devonian Rocks, the genus Sparsispongia
may be noted ; but the Carboniferous series has hitherto
proved singularly destitute of sponges. In the Permian Rocks
it is worthy of notice that there occurs a genus described by
Geinitz under the name of Spongillopsis, and believed by him
to be most nearly allied to the recent fresh-water sponges
(Spoil gilla). This is a remarkable fact as bearing upon Pro-
fessor Ramsay's view, that the Permian Rocks were deposited
in inland waters *of great extent.

Leaving the Palaeozoic series, the sponges of the Triassic
and Jurassic formations call for no special remark, except that
the latter series abounds with examples of the Caldspangitz.
It is in the Cretaceous system, however, in which we meet with
the greatest development of the sponges. The flints which
form such a characteristic feature in the White Chalk are, in
some measure at any rate, "connected with the periodic
growth of large crops of the sponges " (Owen) ; and in some
sections of flint are found minute " spherical bodies, covered
with radiating and multicuspid spines," which have been
termed Spiniferites or Xanthidia, and are probably the " gem-
mules " of sponges. (By some, however, these are regarded
as being the " sporangia " of the Desmidue, an order of the
Protophyta.) The two most notable genera of Cretaceous
Sponges are Siphonia and Ventriculites. The Siphonia (fig. 17)
belong to a group of sponges termed Pctrospongiada, from
their possession of a stony reticulate skeleton without spicula.

PROTOZOA.

They consist of a pear-shaped mass, supported upon a longer
or shorter stem, which breaks up at its base into a number of
root-like processes of attachment. At the summit of the pyri-
form head is a single chimney-like osculum. In many respects

Fig. 17. — Siplwnia,
ficns, a Cretaceous
Sponge. D'Orbigny.

Fig. 18. — Ventricnlites
radiatus. White Chalk.
(After Lyell.)

the Siphonicz present a curious resemblance to the Holtenice
of the Atlantic ooze, and, like these, they probably were
denizens of a deep sea. The genus, however, is not known
to occur in strata younger than the Chalk.

Still more closely allied to the living Holtenia are the Ven-
triculites of the Chalk (fig. 18). These "have usually the
form of graceful vases, tubes, or funnels, variously ridged or
grooved, or otherwise ornamented on the surface, frequently
expanded above into a cup-like lip, and continued below into
a bundle of fibrous roots. The minute structure of these
bodies shows an extremely delicate tracery of fine tubes, some-
times empty, sometimes filled with loose calcareous matter
dyed with peroxide of iron " (Wyville Thomson). Like the
Siphonice, the genus Ventricnlites is not known to occur above
the Chalk.

The Tertiary Sponges call for no special comment ; but it
may be noticed that the great apparent predominance of the

SPONGIDA. 7*

Horny Sponges in our present seas, may be explained by the
fact that the members of this group cannot be recognised in a
fossil state except by their siliceous spicula, and that these are
only sometimes present, and are necessarily very difficult of
detection. The genus Cliona alone, comprising the singular
boring sponges, has managed to survive from the commence-
ment of the Palaeozoic period to the present day. Shells
mined by species of this genus occur in the Silurian Rocks,
and the genus is well represented in recent seas.

FOSSILS OF DOUBTFUL AFFINITIES. — Before leaving the Pro-
tozoa, there are two fossils of doubtful relationships which may
be briefly noticed — viz., Stromatopora and Receptaculites. These
show points of affinity to the Foraminifera on the one hand,
and the Sponges on the other hand, whilst the former ap-
proaches the Corals in some respects. Both, however, may,
with the greatest probability, be regarded as peculiar types of
Sponges.

Stromatopora (fig. 19) forms hemispherical, globular, or
irregular masses, often of very considerable size, and sometimes

Fig. 19.— A small and perfect specimen of Stromatopora rugosa (Hall).
From the Memoirs of the Geological Survey of Canada.

demonstrably attached to shells. In its structure, Stromato-
pora consists of numerous thin, concentric laminae, penetrated
by minute tubes, the mouths of which appear on the surface

PROTOZOA.

of each lamina as minute pores. Species of the genus occur
in both Lower and Upper Silurian strata, and in the Devonian
series, apparently not completely disappearing till towards the
close of the Triassic period.

Receptaculites (fig. 20), in its most perfect condition, is
described by Mr Billings as being " of a discoid, cylindrical,

ovate, or globular shape,
hollow within, and usually,
if not always, with an
aperture in the upper side.
In or near the centre of
the lower side there is
generally to be seen a
small rounded protuber-
ance, indicating, most pro-
bably, the position of the
primitive cell or nucleus
from which the animal
commenced its growth.
. . . The body-wall is of

Fig. 2o.-piagram of the structure of Recep- *• SOmewhat Complex StrUC-

taculites, as it would be shown by a vertical sec- ture. It Consists of three
tion of a perfect specimen, a The aperture at the 1

summit ; b The inner integument ; c The outer parts an external anQ ail

integument ; « The usual position of the nucleus j internal integument, and,
v Ihe great internal cayity. The unshaded . '

bands running from the outer to the inner integu- between these, a peculiar

ment represent the tubes. (After Billings.) tubular Or Spicular skele-

ton." The inner and outer integuments are composed of
numerous rhomboidal calcareous plates, closely fitting together,
and arranged in peculiar curved rows, giving fragments of the
fossil very much the appearance of the engine-turned case of a
watch. The inner integument differs from the outer in being
pierced by numerous small apertures, which open into the
central cavity, an aperture being placed at every junction of
four plates. Lastly, the inner and outer integuments are con-
nected together by a number of small straight cylindrical tubes
or hollow spicula. The late Mr Salter regarded Receptaculites
as belonging to the Fbraminifera, and finding its nearest living
ally in Orbitolites. Mr Billings, however, points out that it
has some curious points of resemblance to the little seed-like
" gemmule " of the Fresh-water Sponge \ and he regards it as
being on the whole a Sponge, having relationships with the
Foraminifera. Receptaculites occurs in both Lower and Upper
Silurian strata, as does the nearly-allied or identical genus
Ischadites.

CCELENTERATA. 73

CHAPTER VIII.

SUB-KINGDOM II.— CCELENTERATA.
FOSSIL HYDROZOA.

SUB-KINGDOM II. CCELENTERATA. — Animals whose alimen-
tary canal communicates freely with the general cavity of the body
(" somatic cavity "), so that the body-cavity communicates with the
outer world through the mouth. Body composed of two funda-
mental layers, an outer layer or " ectoderm" and an inner layer or
" etidoderm" The parts of the body, and especially the organs
round the mouth, arranged in a star-like or radiated form.

TABLE OF THE DIVISIONS OF THE CCELENTERATA.

CLASS A. HYDROZOA. — The walls of the digestive sac not separated
from those of the general body-cavity, the two coinciding with one another.
Reproductive organs in the form of external processes of the body- wall.
Sub-class I. HYDROIDA (Hydroid Zoophytes).
Order I. fiydrida. — Ex. Hydra.
Order 2. Corynida. — Ex. Tubularia.
Order 3. Thecaphora. — Ex. Sertularia, Campanularia.
Sub-class II. SIPHONOPHORA (Oceanic Hydrozoa).
Order 4. Calycophoridce. — Ex. Diphyes.
Order 5. Physophoridtz. — Ex. Physalia.
Sub-class III. DISCOPHORA (Jelly-fishes).

Order 6. Medusida. — Ex. ^Egina. v

Sub-class IV. LUCERNARIDA (Sea- blubbers), v
Order 7. Lucernariadce. — Ex. Lucernaria.
Order 8. Pelagid<z. — Ex. Pelagia.

Order 9. Rhizostomida Ex. Rhizostoma.

Sub-class V. GRAPTOLITID^E (Graptolites. )

CLASS B. ACTINOZOA.— Animal with a differentiated digestive sac open-
ing below into the body-cavity, but separated from it by an intervening
" perivisceral space," which is divided into compartments by a series of
radiating vertical partitions or "mesenteries," to the faces of which the re-
productive organs are attached.

Order I. Zoantharia. — Ex. Sea-anemones, Star-corals, Brain-
corals.

Order 2. Alcyonaria. — Ex. Sea-pens, Fan-corals, Sea-shrubs, Red-
coral.

Order 3. Rugosa. — Ex. Cyathophyllum.
Order 4. Ctenophora Ex. Venus's Girdle.

The Ccdenterata appear to have commenced their existence
in the Cambrian period, at which time both the great classes
of the sub-kingdom were differentiated from one another. So
far as we can judge, the Coelenterate animals have attained
their greatest development at the present day ; but two large

74

CCELENTERATA.

groups (the Graptolitida and Rugosd) are wholly extinct, whilst
the group of the Tabulate Corals is now much reduced in
numbers. The above conclusion is further rendered uncertain
by the existence in the sub-kingdom of some groups which,
from their absence of hard parts, have left no traces of their
past existence.

FOSSIL HYDROZOA.

Of the living orders of Hydrozoa, the Fresh-water Polypes
(Hydrida] and the Oceanic Hydrozoa (Calycophorida and
Physophoridcz) have left no traces of their former presence, as
might have been anticipated from their want of hard structures.
The order of the Medusida and the sub-class Lucernarida
(Jelly-fishes and Sea-blubbers) are equally destitute of hard

parts, and their absence from the
palseontological record might have
been confidently predicted. Curi-
ously enough, however, traces of
both groups have been detected in
the fine-grained lithographic slates
of Solenhofen and Eichstadt. Of
the Medusida, the two living families
of the sEquoridce and Trachyne-
mida have been recognised by
their impressions ; and an ancient
member of the order Rhizostomida
represents the Lucernarida in the
same formation. With these ex-
ceptions, however, the only living
orders of Hydrozoa which have
fossil representatives are the Cory-
nida and Thecaphora, both of which
possess a chitinous or horny in-
tegumentary skeleton. In neither
case, however, can the evidence be
said to be wholly free from sus-
picion.

I. CORYNIDA Or TUBULARIDA

(Pipe-Corallines.) — Animal simple,

ofTul>uIar;aindivisa,na.tura.lsize. consisting of a Single polypite / OT

compound, consisting of several poly-

pites united to one another by a common flesh or ccenosarc. The
ccenosarc generally secretes a hard chitinous outer covering or
" poly par y ; " but the separate polypites are never protected by cup-

Fig. 21. — Corynida. Fragment

FOSSIL HYDROZOA. 75

like expansions of the polypary. Type of the order , Tubularia
(fig. 21).

Two genera, viz., PalcBocoryne and Corynoides, have been re-
ferred to the Corynida, but in neither case is the reference free
from doubt. Palaocoryne (fig. 22) is a minute organism which

Fig. 22. — Palaocoryne radiatum, enlarged fifteen diameters.
(After Duncan and Jenkins.)

was discovered by Dr Martin Duncan and Mr Jenkins grow-
ing attached to the margins of Lace-corals (Fenestellcz) in the
Carboniferous Rocks of Scotland. Its base is expanded, with
finger-like processes of attachment. From the base rises a
short robust stem, which is marked with flutings and super-
ficial granulations. The stem terminates in a single polypite,
the mouth of which is surrounded by a single whorl of slender
processes or " tentacles," in the centre of which is the mouth.
The entire polypary, as above described, is " calcareous, dense,
and ornamented." In one living form only (viz., Bimeria) is
the polypary continued along the tentacles and upper part of
the body of the polypite, and in this case the polypary is simply
of the consistence of parchment. This peculiarity, therefore,
with the possession of a calcareous polypary, renders the refer-

CGELENTERATA.

ence of Palczocoryne to the order Corynida not wholly free from

doubt.

The genus Carynoides was proposed by the author for some
singular fossils from the Lower Silurian
Rocks of Scotland. Each consists of
a cylindrical corneous tube (fig. 23),
tapering towards the base, where it is
furnished with two small spines, and
expanding above into a species of
toothed cup. Corynoides consists of a
single polypite, and in this respect may
be compared with some living Cory-
nida. It would seem, however, not to
have been attached to any foreign
body — as all living Corynids are —
and its true affinities are thus rendered
uncertain.
II. THECAPHORA (or Sertularida and Campanularida).—

Animal compound, rooted and plant-like, consisting of numerous

Fig. 23. — Corynoides call'
cularis, enlarged. (Origi-
nal.)

Fig. 24. — a Sertularia (Diphasia) pinnata, natural size ; d Fragment of the same en-
larged, carrying a male capsule (p\ and showing the hydrothecse (h) ; b Fragment of
Cantpanularia neglecta (after Hincks), showing the polypites contained in their hydro-
theca? (Jt), and also the point at which the coenosarc communicates with the stomach of
the polypite (p).

polypites united by common flesh or ccenosarc. The cctnosarc is
more or less branched, and secretes a strong chitinous investment or
" polypary? The polypites are also protected within " hydro-

FOSSIL HYDROZOA.

77

thecce" or little cup-like expansions derived from the polypary.
The process of reproduction is carried on by the development of
the reproductive elements within horny urn-like sacs, which are of
larger size than the " hydrotheccz" and are known as " ovarian
capsules" or " gonotheccz" (often called " gonophores"}. Type oj
the order, the Sea-fir (Sertrtlaria, fig. 24).

As in the case of the Corynida, there is some uncertainty as
to the existence of any fossil representatives of this order. No
undoubted Sertularian, at any rate, is as yet known to the
palaeontologist ; but there are several genera which may with
more or less probability be referred to this place. The most
important of these — as being those in which the reference is
probably correct — are certain forms usually referred to the

Fig 25 — Dendrograpsns Hallianus. a Portion of the frond, natural size; b Por-
tion of a branch, enlarged ; c The footstalk and some of the principal branches, natural
size. (After Hall.)

Graptolitida, of which the genera Dendrograpsus and Dicty-
oncma may be noticed in particular. The forms referred to
Dendrograpsus are exclusively confined to the Upper Cam-
brian and Lower Silurian formations. They consist of plant-
like spreading and branched growths, which are furnished with
a strong footstalk (fig. 25). In all probability the organism
was attached by the base of the footstalk to some foreign
body, but no actual demonstration of this has as yet been
obtained. The branchlets carry upon one side a series of

7 8 CCELENTERATA.

little chitinous cups or " cellules," each of which must have
contained a polypite, and which agree with the similar struc-
tures of the Graptolites in partially overlapping one another ;
thus differing from the " hydrothecae " of the Sertularians.

In Dictyonema (fig. 26) we have organisms resembling
Dendrograpsus in many respects, but not possessing any foot-

Fig. 26. — Dictyonema retiforme, Hall. (After Hall.)

stalk. 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, slender,
transverse processes or dissepiments, and they bear small
'''• horny cups or " cellules " like those of the Graptolites. Dic-
tyonema ranges from the Upper Cambrian to the Middle
Devonian. The genus bears a close superficial resemblance
to the Fenestellce or Lace-corals (belonging to the Poly zoo) ;
but the latter have a calcareous skeleton, and have no " cel-
lules." Besides the above-mentioned genera, Calfograpsus
and Ptilograpsus may with great probability be referred to the
Sertularida; as may, perhaps, be the obscure fossils Butho-
grapsus and Thamnograpsus. All these genera are Silurian or
Upper Cambrian in age.

FOSSIL HYDROZOA.

79

OLDHAMIA. — The singular fossils described under the genus
Oldhamia may be noticed here, as they have been referred to
the Hydrozoa; though their true nature is altogether uncertain.
Oldhamia occurs in certain green and purple grits of Lower
Cambrian age, at Bray Head, in Wicklow, Ireland. They
occur in great abundance, matted together, and spreading over
the surfaces of the strata. Old-
hamia antiqua, the commonest
species, consists of a central
thread-like axis from which
spring bundles or umbels of
short radiating branches (fig. 27),
at regular intervals. Each branch
" is formed of a series of articu-
lations marking the positions of
minute cells " (E. Forbes). Old-
hamia has been variously refer-
red to the Sertularian Zoophytes,
to the Polyzoa, and to the vege-
table kingdom. The most pro-
bable conjecture would refer the
genus to the calcareous sea-
weeds (Salter).

III. SUB-CLASS GRAPTOLITID^E
(Graptolites). — The Graptolites
form a very large and important
family of fossils which usually present themselves in the shape
of horny linear bodies, toothed or serrated upon one or both
sides, and often combined into more or less complex systems.
If we disregard the genus Dictyonema, which is best referred
elsewhere, the Graptolites have an extremely definite range in
point of time, being exclusively confined to the Upper Cam-
brian and Silurian deposits. They attain their maximum of
development in the Upper Cambrian Rocks (Quebec group of
Canada and Skiddaw Slates of England), are abundantly re-
presented in the Lower Silurian, and die out altogether before
the close of the Upper Silurian period.

Excluding the genera JDictyonema, Dendrograpsus, Ptilograp-
sus, and Callograpsus, the Graptolitidce may be defined by the
possession of a compound polypary, consisting of a tubular
chitinous investment enclosing the coenosarc, giving origin to
numerous cup-like " cellules " or " hydrothecae," each of which
protected a polypite. The polypary was free, and was not at-
tached to any foreign body ; and the polypites were not sepa-
rated from the coenosarc by any partition. Lastly, the poly-

Fig, 27. — Oldhamia antiqua, natural
size (after Salter). Cambrian.

8o

CCELENTERATA.

pary was almost always strengthened by a chitinous rod or fibre,
which is termed the " solid axis/' and which is somewhat analo-
gous to the chitinous rod described by Dr Allman in the
singular Polyzoon, Rhabdopleura.

From the above definition, it will be seen that the Grapto-

lites agree with the living Sertulari-
ans in possessing a corneous poly-
pary, which not only invests the cceno-
sarc, but is expanded into little cups
or " hydrothecae, " within which
each polypite is protected. The
Graptolites, however, differ from the
Sertularians in the fact that the poly-
pary was unattached, and apparently
free-floating, whilst it has not, except
in a few cases, anything like the plant-
like appearance of the latter. Further,
the hydrothecae of the Graptolites,
except in the genus Rastrites, always
more or less overlap one another ;
whereas those of the Sertularians are
not in contact. Lastly, no Sertula-
rian exhibits any structure which can
be compared with the " solid axis "
of the Graptolites.

Taking such a simple Graptolite
as G. priodon (fig. 28), or G. sa&tta-

Fig. 28.— Morphology of Grapto- -if A\ rlui

utes priodon. A, Graptolites pri- rius (fig. 29, A), as the type of the sub-

odon, Bronn, preserved in relief: place the nolvnarv is Seen to rnn si col-
lateral view slightly enlarged. B, Cldbb> Uie POiypary 1

Dorsal view of a fragment of the Of three elements, which are known

same species: considerably en- fu « crki;^ avic " fVi^ " ™™n->,™

larged. C, Front view of a frag- ES tne SOllO. aXIS, tn< COmmon

ment of the same, showing the Canal" and the " Cellules." The

mouths of the cellules: much en- /, «••% .... .. . . . ,.

larged. D, Transverse section of SOlld aXIS IS a Cylindrical fibrOUS

rod which gives support to the cor-
neous and flexible polypary. The
term " solid" is probably a misnomer; for it was almost certainly
hollow, and filled with living material. It appears to be absent in
the genus Rastrites, and in Retiolites Geinitzianus, but some un-
certainty rests upon this point. As a very general rule, it is
prolonged as a longer or shorter naked rod beyond one or both
ends of the polypary, and either extension may be more or less
dilated. Its basal prolongation, with or without an accom-
panying extension of the common canal, is termed the "radicle,"
or " initial point," as marking the organic base of the frond.
The " common canal " is the tube in which the coenosarc

FOSSIL HYDROZOA.

81

was enclosed ; but it commonly appears, in compressed speci-
mens, merely as a vacant space between the "cellules" and
the solid axis. The common canal gives origin, by a process
of budding, to the " cellules " or " hydrothecae," which are little
horny cups for the reception of the polypites. Each cellule

1)

Fig. 29. — A, Young individual of Graptolites Sagittarius, His., showing the slender
curved base of the frond, and the extension of the axis beyond its opposite end ; B, Base of
another individual of the same, in which there is an extremely long " radicle ; " C, Frag-
ment of G. Sagittarius, much enlarged to show the cellules — from a specimen in reHef ;
D, Specimen of Graptolites Clingani, Carr., showing the distal and proximal extensions
of the axis.

rests by its base upon the common canal, is separated from its
neighbours by " cell-partitions," and opens at its apex by a
distinct aperture or " cell-mouth," through which the polypite
could exsert its tentaculate head.

The reproductive process appears, in some cases, at any rate,
to have been carried on by the formation at certain seasons of
horny capsules, of much greater size than the cellules, within
which the generative elements were matured. In some cases
these " ovarian vesicles" have been found actually attached to
the fronds of Graptolites. In other cases, as described by the
writer, we find numerous bell-shaped horny capsules (fig. 30),
each with a little spine at its summit, scattered through the
rock in which the Graptolites occur, but only doubtfully
attached to the fronds of the latter. These we may infer to
have been " ovarian vesicles ; " but they differ from the bodies
so called in the Sertularians in becoming detached from the
parent colony.

Two leading types may be distinguished amongst the Grap-

82

CCELENTERATA.

tolites, which are termed respectively " monoprionidian " and

" diprionidian." The monoprionidian graptolites, such as G.

priodon (fig. 28), are distinguished by the fact that the polypary,

Fig. 30. — Supposed "Ovarian Capsules" or reproductive buds of Graptolites.

whether simple or branched, possesses but a single row of cel-
lules or " hydro thecae." In the diprionidian forms, on the other
hand, as in Diplograpsus (fig. 35), the polypary possesses a row
of cellules on each side. It is noticeable that the diprionidian
graptolites, with rare exceptions, are confined to the Lower
Silurian and Cambrian Rocks ; whilst the monoprionidian forms
range from the Cambrian to the summit of the Upper Silurian
series.

At least sixteen genera of Graptolites, as here restricted, are
known to science ; but it will be
sufficient to give the diagnostic
characters of a few of the com-
monest and more important
types. In the genus Graptolites
(figs. 28, 29), the polypary is
simple, linear, possessing but a
single row of cellules on one
side, and commencing by an at-
tenuated, usually curved, base.

Fig. 31. — Didymograpsus V-fractus.
Upper Cambrian (Skiddaw Slates).

Fig. 32 — Tetragrafisus quadribracJiia-
tus (after Hall). Upper Cambrian (Skid-
daw and Quebec groups).

Species of this genus are found from near the base of the

FOSSIL HYDROZOA.

Lower Silurian series to the very summit of the Upper Silurian
deposits.

In the genus Didymograpsus (fig. 31), the polypary con-
sists of two simple monoprionidian branches, which spring
from a common point, which is almost invariably marked by
a small spine-like "radicle." The genus attains its maximum
in the Quebec group of Canada and Skiddaw slates of Eng-
land (Upper Cambrian), and is well represented in the earlier
portion of the Lower Silurian period (Llandeilo Rocks) : but
no species of the genus is known as late as the Upper Silurian
period.

In the genus Tetragrapsus (fig. 32), the polypary consists of
four simple monoprionidian branches, springing from a central

non-celluliferous connecting
process, which bifurcates at
each end. The celluliferous
branches do not subdivide,
and the base may be en-
veloped in a peculiar cor-
neous "disc," as will be im-
mediately described in the
genus Dichograpsus. The
species of Tetragrapsus are
exclusively confined to the
Skiddaw and Quebec groups
(Upper Cambrian).

In the genus Dichograp-
sus there are more than four
(usually eight) simple mono-
prionidian branches, which
arise from the same number
of divisions of a non-cel-
luliferous basal process. In
many cases the divisions of
the basal connecting pro-
cess (fig. 33), are enveloped

33. — Dichograpsus octobrachiatiis, showing the central disc (after Hall).
Skiddaw and Quebec groups.

84

CCELENTERATA.

in a species of corneous " disc" or plate, which is believed
to have been composed of two laminae. The functions of
this disc are doubtful ; but it has been compared with the
" float " or buoy of the Physophorida, an order of the Oceanic
Hydrozoa.

In the genus Rastrites (fig. 34), the polypary consists of a

B

Fig. 34. Morphology of Rastrites. — A, Rastrites peregrinns, Barn, from the Mud-
stones of the Coniston Series, enlarged. B, Rastrites capillaris, Carr., from the Upper
Llandeilo Shales of Dumfriesshire, enlarged. C, Fragment of Rastrites Linnai, Barr. ,
from the Coniston Mudstones, enlarged. D, Fragment of R. peregrines, greatly en-
larged, showing the impressed line running up the centre of each cellule. (Original.)

slender axial tube, giving off on one side a series of linear tubu-
lar cellules or " hydro thecae," which are free throughout their
entire length. The genus differs from all the other Graptolites,
in the fact that the cellules do not overlap one another, but are
free through their whole length, whilst it is very doubtful if a
true " solid axis " is present. In Britain and North America
the species of Rastrites are exclusively confined to the Lower
Silurian Rocks, but in Bohemia they pass up into the lowest
beds of the Upper Silurian.

In the genus Diplograpsus (fig. 35), the polypary consists of
two simple monoprionidian stipes, firmly united to one another,
back to back. The frond, therefore, is "diprionidian," or carries
cellules on both sides. The solid axis is usually prolonged
beyond the base of the polypary as a longer or shorter process
or " radicle," which is often flanked by lateral spines. The
solid axis is also almost invariably prolonged beyond the op-
posite or " distal ;' end of the polypary as a naked rod. In the
nearly-allied genus Climacograpsus, the structure is much as
above described, but the cellules have such a structure that

FOSSIL ACTINOZOA.

their mouths appear to be sunk below the general surface of
the polypary, forming a row of rounded or quadrangular open-
ings on each side. Both Dip-
lograpsus and Climacograpsus
range in Britain and North
America from the Upper Cam-
brian to the summit of the
Lower Silurian series ; but in
Bohemia they rise into the
lower portion of the Upper
Silurian deposits. In the genus
Dicranograpsus the polypary is
at first diprionidian, but soon
splits into two monoprionidian
branches which carry the cel-
lules along their outer margins.
The genus is exclusively Lower
Silurian. Lastly, the beautiful
genus Phyllograpsus may be
regarded as composed of two
Diplograpsi placed at right
angles to one another. "It is
exclusively confined to the
Skiddaw and Quebec Rocks.*

* The Student, desirous of fuller
information on this subject, may con-
sult the author's ' Monograph of
the British Graptolitidae,' Part I.,
General Introduction ; where full de-
tails are given as to the morphology
and affinities of these singular fossils.

Fig- 35- — A, Diplograpsus pristis,
His., slightly enlarged, showing the
normal condition of the base ; B, Another
example of the same, slightly enlarged,
showing a long radicle, and long lateral
spines ; C, Another of the same, en-
larged, showing lateral spines, succeeded
proximally by a small bulb, but showing
no true radicle. (Original.)

CHAPTER IX.
FOSSIL ACTINOZOA.

OF the living groups of the Actinozoa (see Table, p. 73), the
Ctenophora and the Sea-anemones (Zoantharia malacodermata),
from their absence of hard parts, are unknown in a fossil con-
dition. The remaining groups — viz., the Zoantharia sclerobasica,
Zoantharia sderodermata, Alcyonana, &ft&Rugosa — secrete a hard
skeleton, which is known by the general name of the " coral "

86

CCELENTERATA.

or " corallum." All these groups, therefore, are known as
fossils -} but they are of very unequal importance. The Zoan-
tharia sckrobasica and Alcyoimria are known by very few fossil
representatives, and require to be little more than mentioned.
The Zoantharia sclerodermata and Rugosa, on the other hand,
have left very numerous and interesting traces of their former
existence — the latter being almost altogether extinct, — and
both will require to be noticed at some length. Regarded
as a whole, the class of the Actinozoa appears, so far as we yet
know, to have commenced its existence in the Upper Cam-
brian period, and to have attained its maximum of develop-
ment at the present day.

ORDER I. — ZOANTHARIA.

Tentacles simple, rounded ; soft parts in multiples of Jive or six.

Sub-order I. Zoantharia malacodermata. — Ex. Sea-anemone.
,, 2. Zoantharia sclerobasica. — Ex. Antipathes.
,, 3. Zoantharia sclerodermata. — Ex. Reef-building Corals.

A. ZOANTHARIA MALACODERMATA. — Though, from their soft
nature, unknown in a fossil condition, the Sea-anemones merit
a brief description here, as they may be taken as the types of
the order, and as the somewhat complicated structure of the
sclerodermic coral will thereby be rendered much more intel-
ligible.

Fig. 36. — A, Actinia meseinbryanthemu-m, one of the Sea-anemones (after Johnston).
B, Section of the same, showing the mouth (a), the stomach (b), and the body-cavity (c).

The body of a Sea-anemone (fig. 36) is a truncated cone, or
a short cylinder, termed the " column," and is of a soft,

FOSSIL ACTINOZOA. 87

leathery consistence. The two extremities of the column are
termed respectively the " base " and the " disc," — the former
constituting the sucker, whereby the animal attaches itself at
will, whilst the mouth is situated in the centre of the latter.
In a few cases ( Cerianthus and Peachia) the centre of the base
is perforated, but the object of this arrangement is unknown.
Between the mouth and the circumference of the disc is a flat
space, without appendages of any kind, termed the " peris-
tomial space." Round the circumference of the disc are
placed numerous tentacles, usually retractile, arranged in alter-
nating rows, and amounting to as many as 200 in number in
the common Actinia. The tentacles are tubular prolongations
of the ectoderm and endoderm, containing diverticula from
the somatic chambers, and sometimes having apertures at
their free extremities. The mouth leads directly into the
stomach, which is a wide membranous tube, opening by a
large aperture into the general body-cavity below, and extend-
ing about half-way between the mouth and the base. The
wide space between the stomach and column-wall is sub-
divided into a number of compartments by radiating vertical
lamellae, termed the " primary mesenteries," arising on the one
hand from the inner surface of the body-wall, and attached on
the other to the external surface of the stomach. As the
stomach is considerably shorter than the column, it follows
that the inner edges of the primary mesenteries below the
stomach are free ; and these free edges, curving at first out-
wards and then downward and inwards, are ultimately attached
to the centre of the base. Besides the primary mesenteries,
there are other lamellae which also arise from the body-wall,
but which do not reach so far as the outer surface of the
stomach, and are called "secondary" and "tertiary" mesen-
teries, according to their breadth. The reproductive organs
are in the form of reddish bands, which contain ova and sper-
matozoa, and are situated on the faces of the mesenteries.

B. ZOANTHARIA ScLEROBASiCA. — The members of this
group are all composite organisms, consisting of numerous
polypes, each of which has essentially the structure of a small
Sea-anemone, united together by a common organised medium
or " coenosarc" (fig. 37). Each polype has six tentacles,
and the entire organism is supported by an internal skeleton
or " corallum." The coral is horny, and it is what is called
" sclerobasic ; " that is to say, it forms an internal axis, over
which the coenosarc is spread, much as the bark encloses the
wood of a tree. As the polypes are sunk in the coenosarc,
and as this simply forms a rind for the coral, it follows that

CCELENTERATA.

the polypes are outside the corallum. In other words, the
polypes take no part in the secretion of the corallum; but this
is deposited solely by the coenosarc or common flesh by which
the polypes are connected together.

Fig. 37. — Part of a living stem of Antipathies anguina, of the natural size.

(After Dana.)

The Zoantharia sderobasica are not known as occurring in
either the Palaeozoic or Mesozoic period. They appear for
the first time in Tertiary deposits, and the genus Antipathes
is represented in strata of Miocene age.

C. ZOANTHARIA SCLERODERMATA. — This group includes
mdst of the so-called " corals," and is of very high geological
importance. All the members of this group secrete a skeleton
or " corallum," and this is necessarily the only part of the
animal with which the palaeontologist has to deal ; so that it
becomes necessary to enter into its structure at some length.
The animal itself, in the Zoantharia sderodermata, in its essen-
tial structure resembles a sea-anemone ; but it very often has
the power of repeating itself by budding (gemmation) or cleav-
age (fission), so that from a simple it becomes a compound
organism. It may therefore consist of a single "polype," or
of many similar polypes united by a common flesh or " cceno-
sarc." The corallum is what is called " sclerodermic," its
essential peculiarity being that it is secreted by the polype or
polypes. The sclerodermic coral, in fact, is an actual calcifi-
cation of part of the tissues of the polype. When, therefore,
we have a simple coral, produced by a simple member of this
group (as in fig. 38), we have clearly to do with nothing but
skeletal structures produced in the interior of the polype itself.
When, on the other hand, we have a compotmd sclerodermic
coral to deal with, we have usually more than this. We have,
namely, two parts or elements of the coral to consider: i.
The parts of the coral secreted by each individual polype; and,
2. The parts secreted by the ccenosarc which unites all the
polypes into an organic whole. A compound coral may be
theoretically regarded, therefore, as consisting of a greater or
less number of simple corals, such as the preceding, united
together by a greater or less quantity of calcareous matter

FOSSIL ACTINOZOA.

89

secreted by the coenosarc (fig. 40). The entire compound
corallum consists, therefore, of a greater or less number of

Fig. 38. — Petraia calicula.
Lower Silurian.

Fig. 39. — Za.phren.tis Stokesi.
Lower Silurian.

" corallites " bound together by a calcareous basis, which is
secreted by the coenosarc, and is called the " ccenenchyma."

Fig. 40. — SynJielia Sharpeana.

\

In practice, however, this theoretical view of the subject is not
always borne out. The compound corallum may, and often
does, consist (as in fig. 41) of a number of corallites produced

CCELENTERATA.

by budding or cleavage from a primitive corallite, having their
outer walls closely amalgamated, but not sunk in any general
coenenchyma. In other cases, the ccenenchyma, though not
actually absent, is very much reduced in quantity.

Fig. \\.'—Michelinia convexa (D'Orbigny). A compound sclerodermic Coral.

Devonian.

To comprehend the more intimate structure of a sclero-
dermic coral, we may take a single
" corallite" of a composite form — or,
better, the simple corallum secreted by
a form which never repeats itself by
gemmation or cleavage (fig. 42). Such
a coral consists of an outer wall, which
encloses an internal space or chamber,
and which assumes very various forms.
We may, however, take the simplest
and commonest form, in which the coral
is conical or turbinate in shape (fig. 42).
The outer wall of this cone is called the
" theca," and it encloses a space which
is variously subdivided below, but which
has the form of a shallower or deeper
conical cup towards its summit. This
vacant space is called the " calice," and
in the living state it contains the sto-
machal sac of the polype. The space below the calice is
broken up into a number of vertical compartments or "loculi,"

Fig. 42. — Cyathaxonia,
Dalmani. A simple sclero-
dermic coral, showing the
theca, with its costae, the
calice, with the columella
in its centre, and the septa.
A portion of wall of the
theca is broken, in order
to show the interior of the
calice.

FOSSIL ACTINOZOA. gi

by a series of upright partitions or " septa," which spring from
the inner surface of the theca, and advance toward its centre.
Very commonly some of the septa unite centrally with a
median calcareous rod, which extends vertically from the
bottom of the theca to the bottom of the calice (sometimes
projecting into the latter), and which is called the " columella."
The columella, however, is often wanting, or a spurious one
may be formed by the twisting together or coalescence of the
inner edges of the septa. In rare cases, also, the septa them-
selves are wanting. The septa, further, are of different
breadths. A certain number (fig. 43) extend quite to the

Fig. 43. — Diagrammatic sections of corals. A, Section of sclerodermic coral, showing
five primary septa, the columella, and costae (c) ; B, Section of Rugose coral, showing
four primary septa. Between the primary septa are seen the secondary and tertiary
septa.

centre of the coral, where they meet the columella (when this
is present). These are called the " primary septa." Others,
however, fall short of the columella by a greater or less dis-
tance ; and these are called "secondary" and "tertiary"
septa, according to their breadth.

The above is the essential structure of the typical form of a
simple sclerodermic coral, and it is easy to see that it is pro-
duced by the calcification, or conversion into carbonate of
lime, of the lower portion of a polype similar in structure to
an ordinary Sea-anemone. The " theca" of the coral corre-
sponds to, and is secreted by, the " column-wall " or general
wall of the body of the polype. The " septa," again, corre-
spond with the " mesenteries," and, like them, are " primary,"
" secondary," or " tertiary," according as they reach the centre
or fall short of it by a greater or less distance. We must re-
member, however, that it is only the inferior half of the body
of the polype which is thus calcified. The tentacular disc and
mouth are placed at some distance above the upper margin of
the theca, and the digestive sac occupies the calice; whilst

CCELENTERATA.

the whole ot the space comprised within the theca is lined by
the endoderm, and the whole of its outer surface is covered
by the ectoderm.

Whilst the above gives the fundamental structure of a simple
sclerodermic corallum, there are some ad-
ditional details which are of sufficient im-
portance to demand special notice. The
septa in the coralla of the Zoantharia
sderodermata, like the mesenteries of the
living animal, are in multiples of five or
six. It is not common, however, to find
the septa so few as would be represented
by these fundamental numbers. Com-
monly, in progress of growth, fresh septa
are formed between those originally pre-
sent, until there may be several " cycles "
of septa (fig. 43).

The septa may be considered as being
continued, in many cases, through the
theca, and beyond its external surface.
The outer surface of the theca thus comes
to be covered with a series of vertical
ridges or ribs, which are termed the " cos-
tae" (fig. 43, <r, and fig. 44). The costae
vary much as to the distance by which
they are separated from one another, and
as to their breadth, their solidity, and
their ornamentation with spines, tuber-
cles, or teeth.

In some cases the outer surface of the
theca is more or less covered by a thicker
or thinner envelope of calcareous matter,
constituting what is termed the " epi-
theca." In some cases, as in the genus
Montlivaltia (fig. 45), the epitheca is very
highly developed, and forms a dense
covering, but it is often extremely thin. It varies much as
to the extent to which it is applied to the theca ; and it may
be smooth, or may be marked by concentric or encircling
ridges.

The chief remaining structures which may be noticed are
what are called "pali," " dissepiments," and " tabulae." Pali
are " small processes which exist between certain septa and
the columella. They generally arise from the base of the vis-
ceral cavity, or close to it, and pass upwards, united by one

Fig. 44. — Turbinolia
sulcata. The upper figure
shows the exterior of the
theca with the costae. The
lower figure shows the ca-
lice, with the columella
and primary and second-
ary septa. Eocene.

FOSSIL ACTINOZOA.

93

edge to the columella, and by the other to the inner end or
margin of the septa. When there is no columella, they are
adherent to the septa, present a free edge
to the cavity in the axis of the corallum,
and arise with the septa" (Duncan).
The dissepiments are incomplete hori-
zontal plates which grow from the sides
of the septa, stretching from one septum
to another, and more or less interfering
with the continuity of the loculi, and
breaking them up into a series of cells.
The loculi may thus, when the dissepi-
ments are numerous, become more or
less completely vesicular. Lastly, the
tabula (fig. 46) are transverse plates or
floors running at right angles to the axis
of the corallite, and dividing the theca
into so many horizontal compartments or
stories, each of which is vertically subdivided by the septa,
when these exist. Very generally, however, the septa are
absent when the coral is " tabulate."

Fig. 45. — Montlivaltia
caryophyllata, showing
the greatly-developed epi-
theca covering the lower
part of the coral. Great
Oolite.

Fig. tfi.—Columnaria alveplata, showing the corallites partitioned off
into stories by tabulae. Silurian.

GEMMATION AND FISSION AMONGST CORALS. — Compound
Corals, as before remarked, are produced by a process of
budding (gemmation) or cleavage (fission) from an originally
simple form, or by a combination of both these processes.
Most commonly, the compound sclerodermic coral consists of
a number of " corallites," each produced by a separate polype,
and of a common calcareous basis, or " ccenenchyma," secreted
by the coenosarc. There may, however, be no coenosarc, and

94

OELENTERATA.

consequently no ccenenchyma ; and the compound coral may
consist simply of a congeries of corallites directly united to,
or springing from, one another.

Three chief forms of gemmation may be distinguished
amongst the compound Zoantharia — viz., basal \ parietal, and
calicular.

In basal gemmation the mode of increase is by means of
a rudimentary coenosarc, which is put forth by the original
polype, and from which the young polype-buds are produced.
It " affords very different products according as the coenosarc
remains soft, or deposits a ccenenchyma ; appears under the
form of stolons, or of stouter connecting stems ; or even
spreads out in several directions as a continuous horizontal
expansion ; " in which last case the youngest polypes are, of
course, those nearest to the periphery of the mass.

The parietal mode of gemmation is the commonest, and
it gives rise chiefly to dendroid, or tree-like, corals. In this
method the buds are produced from the sides of the original
polype, and they often repeat the process indefinitely.

Calicular gemmation is not known to occur in any recent
coral, but it was a common mode of increase amongst extinct

forms. In this method "the
primitive polype sends up from
its oral disc two or more simi-
lar buds ; these, in their turn,
produce other young polypes,
and thus the process is repeated
until an inverted pyramidal mass
of considerable size is produced,
all the parts of which rest
upon the narrow base of the
first budding polype" (fig. 47).
Fission in the Actinozoa differs
from gemmation chiefly in the
fact, that the polypes produced
fissiparously resemble one an-
other in organisation, and often
in size, as soon as they become
distinct. In gemmation, on
the other hand, the polype-bud consists primarily of a mere
process of ectoderm and endoderm, enclosing a caecal process
of the somatic cavity, and a mouth and other structures are at
first wanting. Amongst the coralligenous Actinozoa fission is
usually effected by " oral cleavage," the divisional groove com-
mencing at the oral disc, and deepening to a certain extent,

Fig. 47. — Calicular gemmation as
seen in Lonsdalea Jlorifonnis. Upper
Silurian.

FOSSIL ACTINOZOA. 95

the proximal extremity always remaining undivided. More
rarely, fission " is effected by the separation of small portions
from the attached base of the primitive organism, whose form
and structure they subsequently, by gradual development, tend
to assume."

" The coral structures which result from a repetition of the
fissiparous process are of two principal kinds, according as
they tend most to increase in a vertical or in a horizontal
direction. In the first of these cases the corallum is cczspitose,
or tufted, convex on its distal aspect, and resolvable into a
succession of short diverging pairs of branches, each resulting
from the division of a single corallite." In the second case
the coral becomes lamellar. " Here the secondary corallites
are united throughout their whole height, and disposed in a
linear series, the entire mass presenting one continuous theca."
Both these forms of corallum " are liable to become massive by
the union of several rows or tufts of corallites throughout the
whole or a portion of their height. An illustration of this is
afforded by the large gyrate corallum of Meandrina, over the
surface of whose spheroidal mass the calicine region of the
combined corallites winds in so complex a manner as at once
to suggest that resemblance to the convolutions of the brain
which its popular name of Brain-stone Coral has been devised
to indicate." (Greene, ' Manual of Ccelenterata,' p. 185 et seq.)

Fig. 48. — Phillipsastrcea Vemeuilli'. From the Devonian (Corniferous Limestone)

of N. America.

DEEP-SEA CORALS AND REEF-BUILDERS. — At the present
day, as has been specially insisted on by Dr Martin Duncan,
we find two great groups of the Sclerodermic Zoantharia — viz.,
those which inhabit tolerably deep water, and those which
build the great masses of coral which are known as " coral-
reefs." The deep-sea corals, though often attaining, as in-
dividuals, a considerable size, and though often compound,

96 CCELENTERATA.

never form massive aggregations or " reefs." This is due to
the fact that, when composite, the separate corallites are not
united together by a lax cellular comenchyma, so that the
colony cannot increase to an indefinitely large size. The
deep-sea corals seem to have existed in all the great geological
periods, from the Silurian upwards. The chief genera of this
group at the present day are Caryophyllia, Balanophyllia,
Flabellum, Desmophyllum, and Sphenotrochus, amongst the sim-
ple forms ; and Lophohelia, Amphihelia, Dendrophyllia, and
Astrangia, amongst the compound forms.

The reef-building corals, when simple, are provided with
special structures which enable the polypes to grow rapidly.
The great majority of the reef-builders, however, are com-
pound, and owe the large size to which they attain to the
fact that the corallites are mostly united by a loose cellular
ccenenchyma. The chief genera of reef-building Zoantharia
in Mesozoic, Kainozoic, and Recent times, are Mceandrina,
Madrepora, Parties, Astraa, Millepora, Heliopora, Cycloseris,
Trochoseris, Heliastrcea, Solenastrtza, Pachyseris, Turbinaria,
and Astraopora ; but many others might be mentioned.

Amongst the more ancient examples of coral-reefs may be
mentioned the Wenlock Limestone of the Upper Silurians in
England, some of the Devonian Limestones in North America,
and parts of the Carboniferous Limestone in various parts of
the world. In Mesozoic times coral-reefs existed towards the
close of the Trias in Western Europe, and largely in Oolitic
times both in Western Europe and in England. In the earlier
portion of the Tertiary period, again, vast coral-reefs were
formed in Central and Southern Europe, in Egypt, Syria, and
Arabia, and in parts of India.

DIVISIONS AND DISTRIBUTION IN TIME OF THE ZOANTHARIA
SCLERODERMATA. — The Zoantharia sderodermata are divided
into the four following groups, founded upon the characters of
the corallum :—

1. Tabulata. — Septa rudimentary, or entirely absent ; tabulae
well developed and dividing the space included within the
theca (the "visceral chamber") into a number of stories
(fig. 46).

2. Perforata. — Septa well developed ; dissepiments rudi-
mentary ; no tabulae ; calcareous tissue of the coral (" scler-
enchyma ") porous.

3. Aporosa. — Septa well developed, lamellar ; no tabulae ;
calcareous tissue of the corallum (" sclerenchyma ") compact
and imperforate.

4. Tubulosa. — Septa indicated by mere striae ; thecae pyri-
form, occasionally united by a basal ccenenchyma (fig. 94).

FOSSIL ACTINOZOA. 97

As regards the distribution in time of the above four groups,
the Tabulate Corals attain their maximum in the Palaeozoic
period, being well represented in the Silurian, Devonian, and
Carboniferous formations. The family „ Thecidcz is exclusively
Silurian ; but the familiar Seriatoporida, Favositidce, and Mille-
poridce survived to the present day; though there are many
breaks in our knowledge of their course.

The Perforata are, on the whole, most abundant in Mesozoic
and Cainozoic strata, and attain their maximum at the present
day. In the Palaeozoic series the group is represented by
Protarea (Silurian) and Pleurodictyum (Devonian), both belong-
ing to the family of \hQ(Poritidce. The great family of the
Madreporida, on the other hand, did not make its appearance
till the Cretaceous period.

The Aporosa are almost exclusively confined to the Meso-
zoic, Kainozoic, and recent periods, attaining their maximum
at the present day. In the Palaeozoic period the group is
only represented by the Silurian genus Pakeocyclus, belonging
to the Ftmgidtt. At the commencement of the Mesozoic
period, in the Trias, appears for the first time the great family
of the Astr&ida, so largely represented at the present day.
Almost all the Jurassic Corals belong to the Aporosa, and
the two families of the Turbinolidcz and Oculinidcz make their
first appearance here. In the Cretaceous Rocks the Aporosa
are largely represented, the family Astrceidce being particularly
rich in generic forms. In the Tertiary period the group is also
well represented.

The Tubulosa, comprising the single
family oi\he>Auloporid<z, are exclusively
Palaeozoic. In the Devonian period,
and doubtfully in the Silurian, we have
the genus Aulopora (fig. 49) ; and in the
Carboniferous Rocks occurs the genus
Pyrgia. There is, however, reason to
believe that these genera have been

r j j , i j • Fie. 49. — A ulopora serpens.

founded upon the young and immature Devonian,

forms of other corals.

ORDER II. RUGOSA. — The members of this order are almost
entirely extinct, and, with the exception of Holocystis elegans
from the Lower Cretaceous rocks, and a few more modern
forms, are not known to occur in deposits younger than the
Palaeozoic epoch. With the soft parts of the Rugosa we are,
for the most part, entirely unacquainted, and the definition of
the order must therefore be founded upon the characters of
the corallum. The corallum in the Rugosa is highly de-

G

98

CCELENTERATA.

veloped, sclerodermic, with a true theca, and often presenting
both septa and tabulae combined. The septa are in multiples
oifour (fig. 43), unlike the recent sclerodermic coralla, in which
they are in multiples of five or six. There is, further, no true
coenenchyma. Some of the Rugosa are simple ; but others are
composite, increasing either by parietal or by calicular gemma-
tion.

The Palaeozoic corals (figs. 50-55), with hardly an exception,

PALEOZOIC CORALS.

Fig. 50. — Syringopora retiformis.
A Silurian Tabulate Coral.

Fig. 51. — Syringopora verticillata.
Silurian.

Fig. 52. — Syringopora. Dalmani.
Silurian.

Fig. 53. — Syringopora compacta.
Silurian.

Fig. 54. — Strombodes pentagonus.
A Silurian Rugose Coral.

Fig- 55- — Strombodes gracilis.
Silurian.

belong either to the Rugosa or to the Tabulate division of the
Zoantharia sclerodermata. The former are readily distinguish-
able from the latter in having well-developed septa, as a rule,
and in invariably having their septa in multiples of four. Until

FOSSIL ACTINOZOA. 99

quite recently it was believed that all the Rugosa were Palaeo-
zoic, with the exception of the genus Holocystis, represented in
the Cretaceous period (Upper Greensand) by the single species
H. elegans. Recent researches, however, have brought to
light the existence in our present seas of at least two genera
(Haplophyllia and Guynia) which belong to the Rugose family
of the Cyathaxonidce ; and certain Tertiary Rugose Corals
have also been described (Martin Duncan). As the Rugosa
are in no fundamental structural character to be distinguished
from the Zoantharia sclerodermata, save in the number of their
septa, there would thus seem to be no good ground for main-
taining that there is any essential difference between the Palaeo-
zoic corals and those of more modern times.

Recently it has been shown that some very abnormal Ru-
gose corals were provided with a lid or operculum, closing the
mouth of the calice. In the genus Calceola (fig. 56), formerly
referred to the Brachiopoda, and very abundant in certain parts
of the Devonian system, the operculum consisted of a single
valve or piece. In Goniophyllum four valves were present, and
in Cystiphyllum prismaticum there were four or more valves in
the operculum. It is worthy of notice that some recent corals
(species of Primnoa, Paramuricea, and others) exhibit also a
more or less complete operculum. According to Professor
Agassiz, the Rugosa and the Tabtilate
division of the Zoantharia ought not
to be considered as belonging to the
Actinozoa, but should be placed amongst
the Hydrozoa. This radical change, how-
ever, cannot be accepted without the
production of very conclusive evidence in
its favour. A strong argument against re-
ferring the Rugose and Tabulate Corals, Fig> 56 _^alceola sanda.
as proposed by Agassiz, to the Hydrozoa, #««• An opercuiate Rugose
is their possession in most cases of well-
developed septa, implying, of course, the existence in the living
animal of mesenteries, structures which are wholly wanting in
the Hydrozoa.

As regards the distribution in time of the families of the
Rugosa, the most important group is that of the Cyathophyllidce,
which is abundantly represented in the Silurian, Devonian, and
Carboniferous Rocks. The family Cyathaxonidce is Silurian
and Carboniferous, and is represented by two living genera.
The family Cystiphyllidce is Silurian and Devonian. Lastly,
the family Stauridce is represented in the Silurian Rocks by
the genus Stauria, in the Devonian Rocks by the genus

IOO CCELENTERATA.

Metriophyllum, in the Permian Rocks by the genus Polycceha,
and in Tertiary deposits by the genus Conosmilia.

APPENDIX GIVING A TABULAR VIEW OF THE DIVISIONS OF THE

ZOANTHARIA SCLERODERMATA AND RUGOSA (AFTER

MILNE-EDWARDS AND JULES HAIME).

A. The Zoantharia Sclerodermata are defined by the possession of a
scleroclermic corallum, the parts of which are arranged in multiples of five
or six. Septa generally well developed, but not combined, as a rule, with
tabulae.

The following chief divisions of the Zoantharia Sclerodermata are, with
few alterations, those adopted by the above-mentioned authorities : —

I. TABULATA. — Septa rudimentary or absent ; tabulae well developed,

dividing the visceral chamber into a series of stories.

1. Thccidce. — Corallum massive ; a dense spurious ccenenchyma formed

by the lateral union of the septa ; tabulae numerous.

2. Favositidce. — Septa and corallites distinct ; little or no true ccenen-

chyma.

3. Seriatoporida. — Corallum arborescent ; sclerenchyma abundant and

compact ; tabulae few.

4. Milleporidtz. — Corallum massive or foliaceous ; septa not numerous;

sclerenchyma tabular or cellular.

II. PERFORATA. — Septa well developed ; no tabulae ; dissepiments rudi-

mentary; sclerenchyma porous.

5. Eupsammida. — Corallum simple or composite ; septa well developed

and lamellar ; columella spongiose.

6. PorititUe. — Corallum composed of spongy, reticulated sclerenchyma.

Septa never lamellar, but consisting wholly of a more or less definite
series of trabeculae ; no tabulae.

7. Madreporida. — Corallum usually composite ; coenenchyma abundant

and spongy ; thecae porous, not distinct from the coenenchyma ;
septa distinct, but slightly perforate.

III. APOROSA. — Septa well developed, completely lamellar, and primi-

tively consisting of six elements ; no tabulse ; sclerenchyma imper-
forate.

8. Fungida. — Corallum simple or compound ; thecae ill' developed, and

somewhat porous ; no dissepiments or tabulae ; synapticulae numer-
ous.

9. Astrceidce. — Corallum simple or compound ; no proper coenenchyma ;

numerous dissepiments; no synapticulae. Corallites well defined,
and separated from one another by perfect walls.

10. Oculinidce. — Corallum composite ; ccenenchyma abundant and com-
pact ; dissepiments few in number. Walls of the corallites without
perforations, not distinct from the coenenchyma.

11. Turbinolidce. — Corallum usually simple; no coenenchyma; septa
well developed ; no dissepiments, nor synapticulae.

IV. TUBULOSA. — Septa indicated by mere striae ; thecae pyriform ; coral-

lites sometimes connected by a creeping basal ccenenchyma.

12. Auloporidce. — This being the only family in the Tubitlosa, its charac-
ters are necessarily the same as those of the division itself.

B. ORDER RUGOSA. — Characterised by the possession of a sclerodermic
corallum, usually with septa and tabulae combined, the former being in
multiples of four. The corallites are always distinct, and are never united

FOSSIL ACTINOZOA. IOI

together by a true coenenchyma. The septa are usually incomplete, but
are never porous, and never bear synapticulse. The order is divided into
the following four families : —
Family I. Staurid<z.

Corallum simple or composite ; septa incomplete, united by lamellar

dissepiments ; four large primary septa, forming a cross.
Family 2. Cyathaxonidce.

Corallum simple; septa complete; no dissepiments or tabulae; with-
out four primary septa.
Family 3. Cyathophyllida.

Corallum simple or composite ; septa incomplete ; tabulae generally

present.
Family 4. Cystiphyllidfe.

Corallum simple, composed chiefly of a vesicular mass with but
slight traces of septa.

ORDER III. ALCYONARIA. — The Alcyonarian Zoophytes
differ from the Zoantharia in the fact that the polypes have eight
pinnately fringed tentacles, the mesenteries also being some multiple
of four. The Alcyonaria thus differ from the Zoantharia, and
agree with the Rugosa in the numerical proportion of their soft
parts. The Alcyonaria, however, differ from the Rugosa in
never possessing a sclerodermic coral divided by septa. When
they have a sclerodermic corallum at all, it either consists
simply of scattered spicules (as in Alcyoniuni), or, if thecal,
consists of simple tubes which are not subdivided by vertical
partitions or septa (as in the Tubiporida). We have, however,
nothing to do with these forms, as they are unknown in a
fossil condition. The only members of the Alcyonaria which
have left any traces of their past existence, are those which
possess a " sclerobasic " coral, in the form of a simple or
branched internal axis, which may be calcareous or corneous,
or partly the one and partly the other. Such forms are well
represented at the present day by the Sea-pens (Pennatulid<z\
the Sea-shrubs and Red Coral (Gorgonida), the Fan -corals
(Rhipidogorgia), and the like. They are, however, of very small
palaeontological importance.

The genus Protovirgularia has been constituted for the
reception of an obscure Silurian fossil, from its. supposed
affinity to the living Sea-rods ( Virgularia). This problematical
organism, however, is almost certainly not one of the Alcyona-
ria, and may, perhaps, belong to the Hydrozoa. With this
exception, and the still more dubious examples of Gorgonidcs.
from the Silurian Rocks, no Alcyonarian Zoophyte has been
detected in deposits older than the Chalk. One of the Pen-
natulida (viz., Graphularid} has been found in the London
Clay (Lower Eocene) ; and the same formation has likewise
yielded two species of Gorgonidcz (Mopsea and Websterid).

102 ANNULOIDA.

The genus Corattium (including the living Red Coral) has
likewise been found in deposits of Miocene age.

CHAPTER X.

SUB-KINGDOM III. — ANNULOIDA.
ECHINODERMA TA.

SUB-KINGDOM III. — ANNULOIDA. — Animals in which the
alimentary canal is completely shut off from the general cavity of
the body. Nervous system distinct. A peculiar system of canals,
usually communicating with the exterior and containing water
derived from the outside, and termed the "water-vascular" or
" aquiferous" system, is present in all. In none is the body of the
adtilt composed of definite segments, or provided with " bilaterally
disposed successive pairs of appendages"

This sub-kingdom was proposed by Huxley, as a provisional
arrangement, to include the two groups of the Echinodermata
(Sea-urchins, Star-fishes, &c.) and the Scolecida (Tape-worms,
Round-worms, Wheel-animalcules, &c.) Whether this arrange-
ment be ultimately retained or not, matters not at all to the
palaeontologist, as no member of the Scolecida is known in the
fossil condition. The palaeontologist, therefore, has simply to
deal with the Echinodermata, the complete distinctness of
which, as a group, is beyond question.

CLASS ECHINODERMATA.

The class Echinodermata comprises the animals known com-
monly as Sea-urchins, Star-fishes, Brittle-stars, Sea-lilies, and
Sea-cucumbers, and is distinguished by the fact that the external
envelope of the body (" perisome ") has the power of secreting
calcareous matter to a greater or less extent. The integument is,
therefore, either composed of calcareous plates articulated together,
or is coriaceous, and has granules or spicules of lime developed in
it. The water-vascular system usually communicates with the
exterior, and generally subserves locomotion. The adult animal
exhibits more or less distinctly a " radial symmetry" or star-like
arrangement of its parts, but the young animal is more or less
bilaterally symmetrical.

The Echinodermata are divided into the following seven
orders : —

ECHINOIDEA. 103

1. Echinoidea. — Ex. Heart-urchin (Spatangus).

2. Asteroidea. — Ex. Star-fish (Uraster).

3. Ophiuroidea. — Ex. Brittle-star (Ophiura).

4. Crinoidea. — Ex. Stone-lily (Encrinus).
( 5. Cystoidea. — Ex. Hemicosmites.

?**• { 6. Blasloidea Ex. Pentremites.

7. Holothuroidea. — Ex. Trepang (Holothuria).

The above is not a true or natural arrangement of the orders
of the EchinocUrmata, but it is convenient for many reasons to
consider them in this sequence. As regards the general dis-
tribution of the class, the Echinodermata are represented more
or less abundantly in all the great formations from the Upper
Cambrian to the present day. The orders Cystoidea and Blas-
toidea are not only extinct, but are exclusively Palaeozoic ; in the
Crinoidea we have an order which has passed its prime, and ap-
pears to be verging on extinction. On the other hand, the orders
Echinoidea, Asteroidea, Ophiuroidea, and Holothuroidea appear
to have attained their maximum of development at the present
day. The Asteroidea and Ophiuroidea commence in the Silu-
rian period. The Echinoids commence in the Upper Silurian,
but reach no marked development till we enter upon Mesozoic
deposits. Lastly, the Holothurians, as might be expected from
the soft nature of their integuments, are hardly known as fossils,
though they seem to have existed in the Mesozoic period.

ORDER I. — ECHINOIDEA.

The members of this order — 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 is composed of numerous calcareous plates,
immovably connected together. The intestine is convoluted, and
there is a distinct anus. The mouth is usually armed with cal-
careous teeth, and is always situated on the inferior aspect of the
body, but the position of the vent varies.

As a matter of course, the palaeontological student has to
deal with nothing except the test of the Echinoids and its
appendages, and these must be described in some detail.
The " test " of the Echinoidea may be regarded as essentially
composed of the so-called " corona" and of the " apical disc/'
though other less important elements are present as well. The
" corona " is the main element of the test, and includes all
the calcareous covering of the animal except the scattered
plates round the mouth and anus and the "apical disc." The
test is composed of numerous calcareous plates, firmly united

IO4

ANNULOIDA.

to one another by their edges, arranged in rows (fig. 57), and
bearing different names according to their position and func-
tion. In one or two exceptional cases the plates are so thin

Fig- 57. — Morphology of Echinoidea. i. Portion of the test of Galerites hemisfihericus
enlarged, showing an mter-ambulacral area (a), and an ambulacral area (li). 2. Galerites
hemisphericus viewed from above, a Inter-ambulacra ; b Ambulacra. 3. Genital and
ocular disc of Henticidaris intermedia enlarged. c Ocular plate ; d Genital plate ; e
Anal aperture ; f Madreporiform tubercle. 4. Spine of the same. (After Forbes.) The
tubercles are mostly omitted on figs 2 and 3 for the sake of clearness.

and are so united together that the entire test becomes flexible
and soft. 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 means of additions made to the edge
of each individual plate, by means of an organised membrane
which passes between the sutures, or the lines where the plates
come in contact with one another.

In all recent and most fossil Echinoids, the test is composed
of twenty rows of calcareous plates, which are arranged in ten
alternating zones or areas (fig. 58). Each zone, therefore, is
composed of two rows of plates. In five of these zones (fig.
57, i, and fig. 58) the plates are of large size, and are not
perforated by any apertures. These zones are called the " in-
ter-ambulacra! areas. " The remaining five zones alternate
with the former, and are composed of very much smaller
plates, which are perforated by minute apertures or pores.
Through these apertures are emitted the little suctorial tubes
of the water-vascular system — the so-called " ambulacral tubes"
or " tube-feet" — by means of which the animal moves. Hence
these zones of perforated plates are termed the " ambulacral
areas" or "poriferous zones."

ECHINOIDEA.

105

In one great group of the Echinoids, the ambulacral areas
pass from the centre of the base of the shell to its summit
(fig. 58;, when they are said to be " perfect" (ambulacra per-
fecta} or " simple." In another great group the ambulacral

Fig. 58. — Gulerites albogalerus. The first figure shows the under sun'ace 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.

areas are not thus continuous from pole to pole, but simply
form a kind of rosette upon the upper surface of the shell
(fig. 59). In these cases — as in the common Heart-urchins—

I'ig- 59- — Scutella subrotunda, showing petaloid ambulacra. Miocene.

the ambulacral zones are said to be " circumscript" (ambulacra
circumscripta) or "petaloid."

The most important external structures of the corona are
the tubercles and spines. The tubercles are rounded eleva-
tions upon which the spines are carried (fig. 60). They vary
much in their dimensions, and receive special names accord-
ing to 'their size or position on the test. Ordinarily the tuber-
cle consists of a rounded ball or hemisphere (the " mamelon ")
supported upon a conical process (the "boss") which arises
from the plate. The ball of the tubercle may or may not be
perforated for the insertion of a ligament which is attached to
the articular surface "of the spine. In many cases (as in fig.
60) the base of the tubercle is surrounded a round or oval
smooth and excavated space which is termed the " areola."
The spines are movable appendages which are jointed

io6

ANNULOIDA.

to the tubercles by a sort of "ball-and-socket" or "uni-
versal" 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 ex-
ceeding the diameter of the test. Sometimes they are slender,

Fig. 60. — Hetnicidaris crenularis, showing tubercles, the larger of which are
perforated, and are surrounded by an areola. Oolite.

tapering, and truly spine-like ; at other times they are thick-
ened, ovate, or almost globular (fig. 61). The spine fits on
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 of the ligament before spoken
of. Above the acetabulum or socket of the
spine there is a prominent ridge or ring, more or
less " milled," for the attachment of the muscular
fibres which move the spine.

The "apical disc" or "genital disc" occupies
the summit of the test, and is generally composed
of ten plates (fig. 57, 3). Five of these plates
are of comparatively large size, and are termed
the " genital plates," each being perforated by
the duct of an ovary or testis. Each genital plate occupies
the summit of one of the interambulacral areas. One of the
genital plates (the right antero-lateral plate) is larger than the
others, and supports a spongy tubercle, perforated with many
apertures, like the rose of a watering-pot, and termed the
" madreporiform tubercle" (fig. 57). This structure protects
the mouth of the canal by which water is admitted from the
exterior to the water-vascular system. Wedged in between
the genital plates, and occupying the summits of the ambulacral
areas, are five smaller, heart-shaped, or pentagonal plates, each
of which is perforated for the reception of an " ocellus " or
eye, and which are therefore termed the " ocular plates."

Fig. 61. — Spine
of Cidaris glan-
diferus.

ECHINOIDEA.

lO/

An important division of the Echinoids is constituted by the
position of the anal aperture. In one great group of Echinoids
the mouth is situated in the centre of the base (fig. 62), and
the vent is placed at the summit of the test, surrounded by the
genital disc. These are the so-called " regular " Sea-urchins

Fig. 62. — Salenia personata, a "regular" Echinoid. 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 mouth in the centre of the base.

(Echinoidea endocydica}. They have a test which is almost
always circular, or spheroidal, or, it may be, depressed ; and
the mouth is armed with a complicated masticatory apparatus.
In the second great group the mouth is situated on the lower
surface of the test, and is sometimes central, sometimes excen-
tric in position. The anus varies in position, but is never
placed on the summit of the test, opposite to the mouth. The
anus, therefore, is not surrounded by the genital disc. Most
commonly the anus is marginal, or is sub-marginal, coming to
be placed in this last case on the lower surface of the test near
the mouth (fig. 63). The Sea-urchins in which this state of

Fig. 63. — Discoidea cylindrica, an "irregular" Echinoid. 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.

parts obtains are termed the " irregular " Echinoids (Echinoidea
exocydicd). They are further distinguished by being mostly
oblong, pentagonal, heart-shaped, or discoidal in form, by
being mostly destitute of any masticatory apparatus, and by
having only four perforated genital plates.

Another group must be constituted for the reception of the
Sea-urchins of the Palaeozoic Rocks, which differ materially
from the Mesozoic, Kainozoic, and Recent Echinoids. Only

108 ANNULOIDA.

two genera are known in the Palaeozoic series, viz., Archceo-
cidaris and Palachinus, but these differ from all the modern
forms in the fact that the corona of the test was composed of
more than twenty rows of plates. The test was divided into
five ambulacral and five interambulacral areas, and the in-
crease in the number of plates arises from the fact that each
interambulacral area consists of three, five, or more rows of
plates (fig. 64). From this peculiarity the Palaeozoic urchins

Fig. 64. — ArchfBocidaris ellipticits. The left-hand figure shows a portion of an
ambulacral area enlarged. The right-hand figure exhibits a single plate.

were placed in a separate sub-order by M'Coy, under the
name of Perischoechinidce (the Tesselata of Pomel). The five
interambulacral areas are surmounted dorsally by the genital
plates, which are five in number, and in Palachinus are doubly
perforated. The five ambulacral areas are " simple," or are
continuous from pole to pole, being surmounted by the ocular
plates. These are said by Baily to be triply perforated in
PalcKhinus, but they are said by De Koninck to be wanting.
The test in both genera appears to be " regular."

As regards the distribution of the Echinoidea in time, the
genera Arch&ocidaris and Paltzchinus (the Perischoechinidce) are
exclusively Palaeozoic, the former being confined to the Devo-
nian, Carboniferous Limestone, and Permian, whilst the latter
occurs both in the Carboniferous and in the Upper Silurian.
The normal Echinoids abound in the Mesozoic series, espe-
cially in the Oolitic and Cretaceous Rocks, and are also well
represented in the Tertiary Rocks. Their distribution will be
shortly noticed under the head of each family.

The Echinoidea are divided into the following more im-
portant families, with their leading characters, distribution in
time, and a few illustrative genera : —

i. Ananchytida. — Mouth excentric, in front; anus behind,

ECHINOIDEA. 109

marginal, or supramarginal. Ambulacra composed of simple
pores, not petaloidal. Apical disc of four perforated genital
plates and five ocular plates. Spines minute. No masticatory
apparatus. Distrib. Jurassic and Cretaceous. ///. Gen. Ana-
nychytes.

2. Spatangidce (Heart-urchins). Test oval, oblong, or com-
monly heart-shaped, exhibiting distinct bilateral symmetry.
Mouth excentric. Anus posterior and supramarginal. Am-
bulacra petaloid, the anterior one unpaired, usually lodged in
a groove or " sulcus." Four genital pores. Mouth toothless.
Spines minute and hair-like. Distrib. Cretaceous to Recent.
///. Gen. Spatangus, Micr aster, Eupatagus, Amphidetus.

3. Cottyritidce or Dysasterida (sometimes placed with the
Ananchytidft) sometimes in the following order of the Echino-
neidce). Test circular or oval. Mouth excentric ; anus supra-
marginal. Ambulacra not petaloidal, meeting at two points
on the upper surface, which are more or less apart. Four
generative pores. Mouth toothless. Distrib. Oolitic and
Cretaceous. ///. Gen. Collyrites (Dysaster}.

4. Echinoneidce. — Test oval. Mouth nearly central; anus
basal or marginal. Ambulacra not petaloidal, continuous from
mouth to apical disc. Four generative pores. Mouth tooth-
less. Distrib. Cretaceous to Recent. ///. Gen. Echinoneus,
Pyrina.

5. Cassidulida. — Mouth central, or nearly so; anus supra-
marginal or infra-marginal. Ambulacra more or less petaloidal,
similar or dissimilar. Four generative pores. Apical disc
sometimes excentric. Mouth toothless. Distrib. Oolitic to
Recent. ///. Gen. Clypeus, Pygaulus, Pygurus.

6. Clypeasterida. — Mouth central ; anus marginal or infra-
marginal, posterior. Dorsal portions of the ambulacra petaloid.
Five genital plates surrounding the madreporiform tubercle.
Mouth toothed. Distrib. Cretaceous to Recent. ///. Gen.
Clypeaster, Scutella (fig. 59), Echinocyamus.

7. Echinocenidce. — Mouth central ; anus on the upper sur-
face behind, or on the lower surface, sometimes mounting so
high as to enter into the genital disc. Ambulacra simple,
narrow. Apical disc with five genital plates. Spines small.
Mouth toothed. Distrib. Oolitic and Cretaceous. ///. Gen.
Galerites (fig. 58), Echinoconus, Pygaster, Holectypus.

8. CidaridcR. — Test regular, spheroidal. Mouth central;
anus opposite the mouth, surrounded by the genital disc.
Ambulacra narrow, straight, or flexuous. Spines large, mostly
club-shaped. Mouth toothed. Distrib. Triassic to Recent.
///. Gen. Cidaris, Temnocidaris.

IIO ANNULOIDA.

9. Echinida. — Test regular, spheroidal. Mouth central ;
anus opposite the mouth, surrounded by the genital disc.
Ambulacra wide or narrow, usually wide centrally, diminish-
ing towards the mouth and anus. Mouth toothed. Spines
varied in length and shape.

Section a. Salenida. — Apical disk of more than ten
plates, large, with the anus placed excentrically in it.
Distrib. Oolitic to Tertiary. III. Gen. Salenia (fig. 62),
Acrosalenia.

Section b. Diademadce. — Ambulacral areas with two or
four rows of large tubercles. Distrib. Jurassic to Recent.
///. Gen. Diadema, Astropyga.

Section c. Hemicidarida. — Interambulacra with two
rows of large tubercles. Distrib. Triassic to Cretaceous.
III. Gen. Hemicidaris (fig. 60).

Section d. EcJunidce Proper. — Ambulacral and inter-
ambulacral areas with large tubercles. Distrib. Jurassic
to Recent. III. Gen. Echinus, Temnopleurus.

10. PeriscJioechinidcz. — Test regular. Mouth central, infe-
rior ; anus opposite to the mouth, surrounded by the genital
disc. Ambulacra simple, perfect. Corona composed of more
than twenty rows of plates, each interambulacral area consist-
ing of from three to six rows. Distrib. Upper Silurian to
Carboniferous. ///. Gen. Archceocidaris and Palachinus.

CHAPTER XI.

ASTEROIDEA AND OPHIUROIDEA.
ORDER II. ASTEROIDEA.

THE order Asteroidea or Stellerida comprises the ordinary
" star-fishes," and is defined by the fact that the body (fig. 65)
is star-shaped or pentagonal, and consists of a central " disc"
surroimded by five or more lobes or " arms." The arms are
truly prolongations of the body, are hollow, and contain prolonga-
tions of the stomach in their interior. The arms are, further,
grooved on their under surface for the reception of the ambulacral
or water-vascular vessels. From these grooves the tube-feet are
protruded in two or four rows. The integument (perisome} is
leathery, but is more or less calcified by the development in it of
plates, granules, and spines of carbonate of lime. The mouth is

ASTEROIDEA. 1 1 1

inferior in position, and is toothless. An anus is usually present,
but may be absent.

The two most striking features which distinguish the Star-
fishes from the Sea-urchins are the star-like figure of the
former, and the fact that the body is not enclosed in an
immovable calcareous box or " test/' as it is in the latter.
The integument of the Asteroidea is, however, so richly pro-
vided with calcareous matter, that though more or less soft
and flexible during life, it is quite capable of being preserved
in a fossil condition. It is, of course, wholly with the cal-
careous secretions of the animal that the palaeontologist has to
deal ; and we may, therefore, dispense with any further account
of the soft parts, beyond what is contained in the above defini-
tion.

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 Urasters and Cribella,
and the extinct Paltzasters (fig. 65),
may be taken as examples of this
state of parts. In other forms, as
in the Sun-stars (Solaster) and the
extinct Lepidasters and Plumasters.
the disc is very broad, exceeding or
equalling the length of the arms in its
diameter; whilst the rays vary in num-
ber, from eight or ten up to thirty
or more. In the Cushion-stars
(Goniaster and Goniodiscus}, again, HS?' twe
the body is pentagonal, disc-shaped,
and flattened on the two sides, and the arms can only be
recognised by the ambulacral grooves on the lower surface
(fig. 66).

On the upper surface of the body, placed nearly in the
centre of the disc, is the 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
" madreporiform 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

112

ANNULOIDA.

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 the so-called "oral plates" (fig. 66).
Radiating from the mouth are a series of furrows, varying in
number with the arms, and termed the " ambulacral grooves."
Each ambulacral groove is continued along the lower surface
of one of the arms, tapering gradually towards the extremity
of the latter. The floor of each groove is constituted by a
double row of minute calcareous pieces — the " ambulacral
ossicles" — which are movably articulated to one another at
their inner ends. At the bottom of each groove is lodged one

of the radiating canals of the
water-vascular system or am-
bulacral system, from which
are given off the rows of suc-
torial feet, or " tube feet."
It follows from this that the
radiating vessels of the am-
bulacral system are outside
the chain of ambulacral os-
sicles, so that these latter
are to be regarded as an
internal skeleton, and they
do not correspond with any
part of the skeleton of Echi-
noids * — at least they do
not correspond with the per-
forated ambulacral plates of
the Sea-urchins. The am-
bulacral ossicles" however, of the Star-fishes are of such a form
that by their apposition an aperture or pore is formed between
each pair. By means of these pores (fig. 66, a) the tube-feet
communicate with a series of little bladders placed above the
chain of ossicles. These perforations, however, do not corre-
spond with the perforated plates of the Echinoid test, and the
tube-feet of the Star-fishes pass through no " poriferous " plates
on their way to the exterior.

This may be rendered more intelligible by examining a

* The structures in the Echinus, which are truly homologous with the
ambulacral ossicles of the Asteroidea and Ophiuroidea^ are the so-called
"auricube."

Fig. 66. — Diagram of a Star-fish (Goniaster),
showing the under surface, with the mouth
and ambulacral grooves, a, Ambulacral os-
sicles, with the ambulacral pores between
them. b, Adambulacral plates, bounding
the ambulacral grooves ; m, Marginal plates
(wanting in many species); o, Oral plates,
placed at the angles of the mouth.

ASTEROIDE A. 1 1 3

section of the arm of a Star-fish from which the soft parts have
been removed (fig. 67). In such a section the ambulacral
ossicles (a, a) are seen in the centre of the lower surface,
united along the middle line by their inner extremities. They
are so placed as to form a kind of elongated pent-house, and
immediately beneath the line where the ossicles of one side
are articulated with those of the other side is placed the
ambulacral vessel (b). Superficial to this, again, is a nerve-
cord ; so that the whole chain of ambulacral ossicles is placed
in the midst of the soft parts of the animal, and is thus clearly
an internal skeleton. At their outer extremities the ambulacral
ossicles are articulated by the intervention of the " adambulac-
ral plates " (fig. 66, £), with plates belonging to the external
or integumentary skeleton, to be immediately described. As
before said, the shape of the ambulacral ossicles is such that a

Fig. 67. — Section of the ray of Uraster rubens. a, a Ambulacral ossicles ; b Position
of the ambulacral vessel; c, c Plates of the external skeleton; n Nerve-cord. The
dotted lines show the tube-feet proceeding from the ambulacral vessel.

pore is formed by the apposition of each pair; and by these
apertures each tube-foot communicates with a vesicle placed
internal to the chain of ossicles. It will be seen, however,
that the tube-feet (indicated by the dotted lines in the figure)
do not pass through these apertures, or through any other
pores of the skeleton, on their way to the surface. The
" poriferous zones " of the Sea-urchins are part of the external
skeleton, and are not represented in the Star-fishes. On the
other hand, the integumentary skeleton in the Star-fishes is
absent along the ambulacral areas, or along the areas occupied
by the ambulacral grooves.

Leaving the ambulacral ossicles or internal skeleton of the
Asteroidea, we come now to the integumentary skeleton. This
consists of a vast number of small calcareous pieces, or " os-
sicles," united together so as to form a species of chain-armour.

H

114 ANNULOIDA.

The ossicles are united with one another in a reticulated man-
ner, and the interspaces between them are filled by the coria-
ceous integument. In some genera there is a single or double
row of large plates round the borders of the disc and arms
(fig. 66, m). These are termed the " marginal plates. " The
integument in the Star-fishes is also furnished with spines,
tubercles, and granules of calcareous matter. The spines
vary in their development and in their position in different
Star-fishes ; but there is commonly a row of spines along each
side of each of the ambulacral grooves. In some genera (as
in Solaster, Luidia, Ctenodiscus, &c.) there are spines the
summits of which carry bunches or tufts of minute calcareous
processes. These are termed "paxillae." Lastly, in A steroidea,
as in Echinoidea, there are the modified pincer-like spines
which are known by the name of " pedicellariae."

As regards their geological distribution, the Asteroidea have
a long vertical range, extending from the Lower Silurian Rocks
to the present day. In Silurian seas Star-fishes abounded,
and the Upper Silurian Rocks especially contain their remains
in what may be considered as plenty. The leading Silurian
genera are Pateaster, Stenaster, Palasterina, Paltzocoma (Salter),
Palceodiscus, and Petraster. Some of the more familial* Silurian
forms are figured below (fig. 68). The next period in which

Fig. 68. — Silurian Star-fishes. A, Palasterina prim&va, Upper Silurian ; B, Palte-
aster Riithveni, Upper Silurian ; C, Palaocoma Colvini, Upper Silurian. (After
Salter.)

Star-fishes abound is the Oolitic or Jurassic (Mesozoic), the
more important genera being Ur aster, Luidia, Astropecten, and
Goniaster. All the Oolitic species are extinct, but the genera
have mostly survived to the present day. In the Cretaceous
period, also, many Star-fishes occur, the genera Oreaster, Go-
niodiscus, and Steilaster being the most noticeable. In the
Tertiary Rocks remains of Star-fishes are not abundant, but
the genera Goniaster and Astropecten are represented in the
London Clay (Eocene).

OPHIUROIDEA. 115

No thoroughly satisfactory classification of the Asleroidea
has been as yet proposed, but the following are the names of
the more important fossil genera, with their range in time : —

Stenaster. Lower Silurian.

Petraster.

Palceaster. Lower Silurian to Carboniferous.

Palasterina. Upper Silurian.

Palceocoma (Salter).

Palcpodiscus.

Lepidaster.

Pleuraster. Trias.

Uraster. Jurassic to Recent.

Solaster.

Astrogonium.

Goniaster.

Astropecten.

Luidia. :

Arthraster. Cretaceous.
Oreaster,

Stellaster. Cretaceous to Recent.
Goniodiscus.

ORDER III. — OPHIUROIDEA.

The Ophiuroidea are often grouped with the Asteroidea, and
the living members of the order are known commonly as
Brittle-stars and Sand-stars. They are distinguished from the
true Star-fishes by the fact that the "disc" contains all the
internal organs of the animal ; the " arms" are not grooved in-
feriorly for the emission of ambulacral tube-feet ; and the mouth
is provided with a masticatory apparatus. The Ophiuroids are
very conspicuously star-shaped, and consist of a central "disc"
and a series of radiating " arms " (fig. 69). The " disc " is
truly disc-shaped, and is covered with granules, spines, or
scales. From the disc proceed the arms, in the form of long
and slender processes, which may be simple or branched, but
which differ from the arms of Star-fishes in not containing any
prolongations from the stomach, and in never having their
under surfaces furrowed by ambulacral grooves. The arms,
in fact, are special processes superadded for the purposes of
prehension and locomotion, and rendered necessary by the
fact that the ambulacral system takes no part in the function
of locomotion, as it does in the Star-fishes. A madreporiform
tubercle, however, is present, and is placed on the inferior
surface of the body, being commonly concealed by one of the
plates surrounding the mouth. The mouth, as in the Star-
fishes, is placed in the centre of the lower surface of the disc ;

Il6 ANNULOIDA.

but the stomach terminates blindly ; and there is, therefore, no
anal aperture.

Each arm is furnished with an internal and an external
skeleton. The internal skeleton consists, as in the star-fishes,
of a chain of " ambulacral ossicles," placed along the centre
of the arm. The ossicles are, however, now amalgamated in
pairs, each coalescing with its fellow on the opposite side ; so
that in place of a double row of movably articulated ossicles,
we have a single row of bilaterally symmetrical pieces.

Fig. 69. — Recent Ophiuroids. a Ophiura texturata, the common Sand-star;
b Opkiocoma neglecta, the grey Brittle-star (after Forbes).

The external skeleton of the arms is composed of four rows
of plates, one on the dorsal surface, one on the ventral, and
one on each lateral surface. The lateral plates generally carry
more less developed spines. In the extinct genus Protaster
it is said that the plates of the ventral row are double ; and
Ptilonaster is stated to possess four ventral rows of plates.
The disc, as before said, has a well-developed external skeleton
of scales, granules, and spines ; but there are never any of
those modified spines which are known as " pedicellariae," and
which occur in the Asteroids and Echinoids.

OPHIUROIDEA. II/

As regards their distribution in time, the Ophiuroidea are
represented for the first time in the Upper Silurian Rocks by
the genus Protaster (fig. 70), unless Taniaster be rightly re-

Fig. 70. — Protaster SedRtuickii. Upper Silurian. A, Disc and bases of the arms,
magnified. B, Portion of an arm greatly enlarged.

ferred here, in which case the order begins in the Lower
Silurian. No other Palaeozoic genera have been satisfactorily
made out. In the Muschelkalk, the middle member of the
Trias, we have a well-marked species, the Aspidura loricata of
Goldfuss (fig. 71). In the Oolitic, Cretaceous, and Tertiary

Fig. 71. — Aspidura loricata. Muschelkalk.

Rocks, Ophiuroids are by no means uncommon, and they be-
long for the most part to genera which exist at the present day.
Great uncertainty prevails as to the generic characters of these
animals ; but the Mesozoic forms are for the most part gene-
rally referred to the genera Ophiokpis, Ophioderma, Ophiocoma,
Amphiura, and Acroura.

ANNULOIDA.

CHAPTER XII.

CRINOIDEA, CYSTOIDEA, AND BLASTOIDEA.
ORDER IV. — CRINOIDEA.

THE Crinoids or Sea-lilies are Echinodermata in which the body

is fixed, during the whole or
a portion of the existence of
the animal, to the sea-bottom
by means of a longer or shorter
jointed or flexible stalk. The
body is provided with solid
arms which are primarily
five to ten in number, are
independent of the visceral
cavity, and are grooved on
their upper surface. The
arms are furnished with lat-
eral processes or " pinnulce,"
and the reproductive organs
are lodged beneath the integu-
ment on the ventral surf ace of
these, and are not placed in
the body-cavity.

If we take such a living
Crinoid as Rhizocrinus (fig.
72), we shall be able to ar-
rive at a comprehension of
the leading characters of this
order. Rhizocrinus is one
of those Crinoids which is
permanently rooted to some
foreign object by the base
of a stalk which is composed
of a number of calcareous
pieces or articulations. In
some cases (as in Apiocrinus,
fig. 81), the base of the stem
or " column " is consider-
ably expanded. In other
cases the column is simply
" rooted by a whorl of ter-
minal cirri in soft mud " (Wyville Thomson). The joints of
the column are movably articulated to one another, the joint-

Fig. 72. — Crinoidea: Rhizocrinus Lofoten-
sis, a living Crinoid (after Wyville Thomson),
four times the natural size, a Stem ; b Calyx ;
c c Arms.

CRINOIDEA. 119

surfaces often having a very elaborate structure, so that the
entire stem possesses in the living state a greater or less
amount of flexibility. Each joint is perforated centrally by a
canal, which is, very inappropriately, termed the " alimentary
canal/' but which in truth has nothing to do with the digestive
system of the animal. At the summit of the stem is placed
the body, which is termed the " calyx/' and which is usually
more or less cup-shaped, pyriform, bursiform, or discoidal.
The calyx exhibits two surfaces, a dorsal and a ventral, of
which the dorsal is composed of calcareous plates articulated
by their margins, whilst the former is composed of a more or
less leathery integument strengthened by the deposition in it
of numerous small plates of carbonate of lime. The ventral
surface exhibits the aperture of the mouth, which may be sub-
central or may be very excentric, and which in many extinct
forms is wholly concealed from view. The ventral surface also
exhibits the aperture of the anus, which is usually placed ex-
centrically in one of the spaces between the arms, and which
is generally, if not universally, carried at the end of a longer
or shorter tubular eminence or process, which is called the
" proboscis." Owing to the animal being supported on a stalk,
it is evident that the " ventral " surface is turned upwards, and
the " dorsal " surface downwards. The column springs from
the centre of the dorsal surface ; and a stalked Crinoid may,
therefore, be compared to a Star-fish turned upside down, with
its lower or ambulacral surface superior, and its dorsal surface
looking downwards. The calyx contains the digestive canal
and the central portions of the nervous and water-vascular
(ambulacral) systems ; but it does not contain the reproduc-
tive organs, as is the case with the visceral cavity of the other
Echinoderms.

From the margins of the calyx, where the dorsal and ventral
surfaces join one another, arises a series of longer or shorter
flexible processes, which are composed of a great number of
small calcareous articulations, and which are termed the "arms"
(%• 73)- The arms are usually primarily five in number, but
they generally divide almost immediately into two branches,
each of which may again subdivide ; the branches thus pro-
duced perhaps again dividing, until a crown of delicate graceful
filaments is formed. The arms carry smaller lateral branches
or " pinnulas " on both sides ; and they are not hollow like the
arms of the Star-fishes, nor do they contain any prolongations
of the stomach. The upper surface of the arms and pinnuke
is covered with a soft membrane, and below this are placed
the reproductive organs. The generative organs are, there-

I2O

ANNULOIDA.

fore, not placed within the calyx, and it follows of necessity
that there is no generative opening or "ova-
rian aperture " in the walls of the calyx.
The ventral surfaces of the arms and pin-
nulae are furnished with grooves, which
in the living species are seen to be co-
vered with vibratile cilia. The brachial
grooves coalesce till they constitute five
primary grooves, which are continued from
the bases of the arms to the mouth. The
action of the cilia gives rise to a constant
current of sea-water, bearing organic mat-
ter in solution ; and this current proceeds
from the brachial grooves to the mouth.
In this way the animal obtains its food.
As the bases of the arms are separated
from the mouth by an intervening space,
it follows that the brachial grooves are

Fig. 73. — 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 ; and
above is a magnified figure of part of one arm with its pinnulae.

continued over the ventral surface of the calyx, till they reach
the oral opening.

CRINOIDEA.

121

There is no doubt that it is by the above arrangement that
the living Crinoids obtain their food, and the mechanism seems
to have been essentially the same in many extinct species. In
the Palaeozoic Crinoids, however, there seems to have been a
modification of this arrangement. In these forms, as in Actino-
crinus (fig. 75), the arms have much the structure of those of the
recent Crinoids, and are deeply grooved on theirventral surfaces.
The ventral surface of the calyx, however, exhibits no central
aperture, but only a proboscidiform tube, which arises from one
of the inter-radial spaces (i.e., one of the intervals between two
of the arms). This tube is often of great length, and a good
deal of controversy has taken place as to its nature. Without
entering into the conflicting views upon this subject, it may be
stated that the preponderance of authority is in favour of the
view that this " proboscis " is an anal tube, having the vent at

Fig. 74. — Calyx of
Actinocrinus rotundus.

Fig. 75. — Calyx of
Actinocrinus Koniticki.

Fig. 76. — Calyx of A.
Verneuillanus. The
arms are wanting,
and the apertures at
their bases are seen.

its extremity. Good observers, however, regard it as discharg-
ing the functions of both the mouth and the anus. Be this as
it may, the grooves on the ventral surfaces of the arms are
certainly not continued over the ventral surface of the calyx,
but, on the contrary, stop short at the bases of the arms. Their
further course was long a mystery ; but it is now known that
they are continued below the ventral surface of the calyx as a
series of covered passages or tunnels, the external apertures of
which are placed at the points where the arms spring from the
disc (see figs. 74-76). These covered channels are either
simply roofed over by the calcareous integument of the calyx,
or are rarely excavated in its walls ; and they converge to a
central point in the middle of the ventral surface of the disc.
Here, it is believed, is placed the mouth, concealed by the
calcareous plates of the perisome. From the known function
of the brachial grooves in the living Crinoids, this view would

122 ANNULOIDA.

seem to be the most probable one ; but, as before remarked,
good authorities regard the excentric " proboscis " as the
mouth.

In another group of Crinoids, represented by the living
Feather-stars (Comatula) and the extinct Saccosoma (fig. 77),

Fig. 77. — Saccosoma pectinata, a free Crinoid. Jurassic.

the animal is only stalked when young, and in its adult con-
dition leads a free life. The young form in the members of
this group is supported upon a jointed calcareous column, by
which it is fixed to some foreign object ; and at this stage it in
no respect differs from the ordinary stalked Crinoids. At a

CRINOIDEA. 123

certain period of its existence, however, the calyx drops off its
column, and becomes a locomotive animal. It now has a
near resemblance to one of the Brittle-stars (Ophiuroidea) ;
but is distinguished, not only by its developmental history,
but by the possession of lateral pinnae to the arms, and in
having the reproductive organs situated external to the body
proper. In the Feather-stars ( Comatula or Antedoti) the dorsal
surface of the disc, at the point where the column was origi-
nally inserted, carries a series of jointed filaments or " cirri,"
by which the animal can moor itself to any foreign object.
These may be regarded as homologous with the "side-arms"
of the column of certain Crinoids. When the animal is thus
temporarily moored by its dorsal cirri, it is placed in the
ordinary position held by the Crinoids — namely, with the
mouth and ventral surface of the disc looking upwards. When
creeping about, on the other hand, by means of the long and
flexible arms, the animal occupies the position held by the
Star-fishes and Ophiuroids — namely, with the mouth and ven-
tral surface of the disc directed downwards, or towards the
ground.

Having now given a general account of the structure of the
Crinoids, it remains to consider some of their parts in greater
detail. In the first place, as regards the " column," we find
that the stem of attachment is composed of a great number of
separate plates or "articulations" placed one above the other,
and so jointed to one another that whilst the amount of move-
ment between any two pieces must be very limited, the entire
column acquires more or less flexibility. The column is per-
forated by a round or five-sided canal which pierces every
joint, and runs along the entire length of the stem. In the
Palaeozoic Crinoids, with few exceptions, the column was
round ; but in Platycrinus it is oval or elliptical (fig. 73). In
the genera Pentacrinus (fig. 78) and Extracrinus the column is
pentagonal in outline ; but much less markedly so in the
former than in the latter genus. The joints articulate with
one another by surfaces or facets which are differently marked
in different cases. In the Palaeozoic forms, as in Platycrinus
(fig. 73), the articulating facets are marked by more or less
numerous striae which radiate from near the centre of the joint.
In most of the Mesozoic genera, on the other hand, as in
Pentacrinus (fig. 78), the articulating facets are united by
crenated ridges arranged in a pentapetalous figure. In many
cases, as in Extracrinus and Pentacrinus, the column is fur-
nished with more or less numerous "auxiliary" arms, or "side-
arms," the function of which is not altogether clear.

124 ANNULOIDA.

The dorsal surface of the cup or " calyx" is composed of a
number of calcareous plates accurately fitted together. The
number and arrangement of these vary much in different

Fig. 78. — Pentacrinus fasciculosus, showing the form of the column, and one of the
facets of a joint. The central figure shows the arms, and the summit of the column
with side-arms.

genera, and it will be sufficient to indicate here their general
disposition. Reposing directly upon the summit of the column

CRINOIDEA.

125

is a series of plates which are termed "basal" from their
position, and which constitute the " pelvis " of Miller. The
"basals" may be five, four, or sometimes three in number,
and they form the lowest portion of the cup. In some cases
the "basals" are succeeded by a second row or cycle of plates,
which should properly be regarded, with Professor Beyrich, as
a second series of basals, but which are sometimes regarded
as something special, and are termed the "parabasals" or
" sub-radials." The basals (fig. 79, b) are succeeded by a

Fig. 79. — Diagram to show the structure of the calyx in the fossil Crinoids ; b Basals;
r Radials; i Inter-radials ; a Anal plates. Calyx of Forbesiocrinus. (After Pictet.)

series of two or three rows of plates, which are directly super-
imposed upon one another, and which form the foundations of
the arms (r, r). These are termed the "radials" (the " cos-
tas " of Miller), and are termed " primary," " secondary," and
" tertiary," according to their distance from the basals. The
last radial plates, or those furthest from the column (some-
times called the " axillary radials "), give origin to the arms.
The radial plates are arranged in a series of vertical columns,
which extend from the summit of the basals to the bases of
the arms. Between the different columns of radial plates,
however, are intercalated certain other smaller plates, which

•

126 ANNULOIDA.

alternate with one another, and which are termed "inter-
radials " (/). Lastly, one of the interradial spaces, correspond-
ing with the anus, is usually much wider than the others, and
is furnished with an additional series of plates, which are called
the "anal plates" (a).

As regards their general distribution in time, the Crinoidea
present us with an excellent example of a group which early
attained its maximum of development, and which has now
dwindled down to some half-dozen surviving species. With
one or two doubtful exceptions, the Crinoids appear, so far as
yet known, to have commenced their existence in the Lower
Silurian period, and they are represented by numerous and
very varied forms in the seas of the Upper Silurian period.
Amongst the commoner Silurian genera may be mentioned Cro-
talocrinus, Glyptocrinus, Ichthyocrinus, Periechocrinus, Rhodo-
crinus, Poteriocrinus, and Taxocrinus. In the Devonian Rocks,
also, Crinoids are plentiful, and the genera Cupressocrinus, Hap-
locrinus, and Melocrinus, may be mentioned as peculiar to this
period. It is in the earlier portion, however, of the Carbonifer-
ous period that the Crinoids attain their highest development.
The Carboniferous Limestone is in many places, over wide
areas, and for a thickness of many yards, almost entirely made
up of the debris of Crinoids; and in many places it is so
charged with the remains of these organisms as to deserve and
acquire the name of " crinoidal limestone " or " entrochal
marble." Amongst the commoner Carboniferous genera may
be mentioned Cyathocrinus, Actinocrinus (fig. 74), Platycrinus
(fig. 73), Poteriocrinus, and Taxocrinus. It is in the Palaeozoic
period, then, that the Crinoids attain their maximum, both
numerically and as regards the number of genera and species.
Taken as a whole, the Palaeozoic Crinoids are distinguished
by the characters already mentioned ; namely, by having the
brachial grooves conveyed to the mouth in concealed channels

j or tunnels, in having mostly a rounded column, and in the
fact that the articular facets of the column-joints usually are
marked by numerous simple radiating striae. As a rule, also,
the Palaeocrinoids have a calyx, in which the dorsal surface has

~ a preponderating development as compared with the ventral
surface.

Coming to Mesozoic times, Crinoids are still abundant,
though certainly reduced in numbers as compared with their
development in the Palaeozoic period. Taken as a whole, the
Mesozoic Crinoids are characterised by having the brachial

1 grooves continued over the ventral surface of the disc, and by

; having the ventral portion of the calyx more extensively de-

CRINOIDEA.

127

veloped than the dorsal ; whilst the articular surfaces of the ,
column-joints are usually morticed to one another by means of
crenated ridges which have a flower-like arrangement. Neither
of these latter characters, however, is constant. In the Meso-
zoic Rocks, also, appear for the first time remains of the
free Crinoids allied to the living Comatulce. The genus Sacco-
soma (fig. 77) is exclusively Oolitic, and appears to form in
some respects a connecting link between the true Crinoids and
the Ophiuroidea. In the Chalk the genus Comatula seems to
be represented ; and the Cretaceous genus Marsupites (the
" Tortoise Encrinite ") presents us with a form which is inter-
mediate between the fixed Crinoids and the forms which lead
a free existence when adult.

Of the stalked Crinoids of the Mesozoic
period, the genera Encrinus, Pentacrinus,
Extracrinus, and Apiocrinns are especially
noticeable. In the genus Encrinus (fig.
80) the arms are composed of a double
series of alternating pieces, and carry pin-
nules on their inner surfaces. The joints
of the column are perforated by a small
round " alimentary canal." The best-known
species is the famous Lily-encrinite (E. lilii-
formis, fig. 80), which is characteristic of
the Muschelkalk, the middle member of
the Trias.

In the genus Pentacrinus and the nearly
allied Extracrinus, the calyx is short and
composed of few plates (five basals and five
radials). The column is pentagonal, with
whorls of side-arms, and the articulating
surfaces of the joints are marked with pen-
tapetalous ridges. The arms are long,
slender, and branched. Amongst the best-
known species are the Pentacrinus fascicu-
losus of the Lias, and other nearly allied
forms of the same formation.

In the Apiocrinidcz or " Pear-Encrinites "
(fig. 81), the animal was fixed to some
foreign object by a dilated base, and the
column was long and composed of numer-
ous joints. The articulating surfaces of the column-joints are
marked with simple ridges, and the stem is rounded and not
pentagonal. The last joints of the column gradually increase
in diameter, until they attain a size equal to the breadth of the

Fig. 80. — Encrinus lilii-
formis. Muschelkalk.

128

ANNULOIDA.

calyx. Upon the last of these developed column-joints rest
the basal plates of the calyx proper, and upon the margins ot
the calyx is inserted a circle of bifid and
pinnate arms. Although the calyx itself
is of large size, the internal cavity or vis-
ceral chamber, in which the soft parts of
the animal were contained, is comparatively
very small. The best-known species of
Apiocrinus are the A. rotundus of the
Great Oolite and the A. Roissyanus (fig.
81) of the Coral Rag.

In the Cretaceous period the Apiocrinida
are represented by the genus Bourgueti-
crinus, and the living genus Rhizocrinus
(fig. 72) would appear also to be a repre-
sentative of this family. The free Crinoids
are pretty well represented also in the
Cretaceous period, the White Chalk having
yielded the discs of Comatulce, along with
the singular " Tortoise-encrinite " (Marsu-
pites), which would seem to connect the
stalked Crinoids with the free forms.

In the Tertiary period the Crinoids are
reduced, so far as is certainly known, to
the single genus Pentacrinus, which is re-
presented at the present day by the living
Pentacrinus Caput-Medusce of the Antilles.
The best -known species is the P. sub-
basaltiformis of the Eocene.

A good classification of the Crinoids is
still a desideratum. Commonly they have
been divided into two groups termed re-
spectively Articulata and Tesselata, accord-
ing as the radial plates of the calyx are
freely articulated to one another, or are
immovably joined together without articu-
lation. This arrangement is a far from
satisfactory one ; but if accepted, we should
have all the Mesozoic and Kainozoic
Crinoids (except Marsupites) in the divi-
sion of the Crinoidea articulata. On the
other hand, the division of the Crinoidea
tessdata would correspond with the Palaso-
Crinoids, comprising all the species known
from the Palaeozoic formations.

81. — Apiocrinus
Mlddle °°~

CYSTOIDEA. 1 29

The division of the Crinoidea into stalked and free forms is
in many respects inapplicable as a basis of zoological classifi-
cation. There can, however, be no doubt but that the free
Crinoids are structurally an advance upon the fixed forms. It
is, therefore, of interest to note that the stalked Crinoids had
attained their maximum in the Palaeozoic Rocks, and had even
commenced to decline before the free Crinoids first made their
appearance in the Mesozoic Series.

ORDER V. — CYSTOIDEA.

The Cystoidea are Echinodermata in which the body was
enclosed in a series of calcareous plates accurately articulated by
their edges, and was fixed to the sea-bottom by a longer or shorter
flexible jointed stalk. There were rarely true arms, and if present,
these structures are much less developed than in the true Crinoids.

Fig. 82. — Hemicosmites fiyriformis, one of the Cystideans. The right-hand figure
shows the upper surface of the calyx.

In general form the Cystideans are globular, oval, pear-
shaped, conical, or sub-cylindrical, and they resemble the
Crinoids in consisting of a stem or " column " and a body or
"calyx." The column is composed of a succession of cal-
careous joints, and in no respect differs from the column of
the Crinoids. In Lepadocrinus (fig. 83, D), however, it is
doubtful if the column was affixed to any foreign body, for its
lower extremity is composed of a single, long, spindle-shaped
piece. The stalk also is asserted to be absent altogether in
Sphczronites pomum and in the genus Agelacrinites. The calyx
consists of a number of polygonal calcareous plates accurately
fitted together, and enclosing all the viscera of the animal.
Sometimes the plates are indefinite in number and arrange-
ment ; but in other cases the number of plates is limited, and
they are arranged according to a definite plan. In other cases

130

ANNULOIDA.

the number and arrangement of the plates may be definite on
one side of the calyx and indefinite on the other.

As regards the structure of the arms of the Cystideans,
there is a good deal of diversity. In some forms there were
no true arms, comparable with the arms of the Crinoids ; but
there were small jointed processes, which were attached to the
calyx, and which represent the " pinnulae " or lateral branches
of the arms of the Crinoids. In some cases, grooves — cor-
responding with the brachial grooves of the Crinoids — are
seen to extend from the point of attachment of each pinnula

Fig. 83. — Cystideans. A, Caryocrinns ornatus ; a, Column ; b, Calyx ; c, Scars
where pinnulae were attached ; d, Valvular pyramid. B, P leurocystites squamosus
(dorsal side) ; /, p, Two of the pectinated rhombs. C, Pseudocrinus bifasciatus. D,
Lepadocnntts Gebhardi.

to the summit of the calyx. In other cases, as in Apiocystites
and Callocystites, arms were present, but they were bent back-
wards and immovably soldered down to the surface of the
calyx. The arms spring in these cases from the apex of the
calyx, and are anchylosed by their dorsal surfaces to the body.
On their ventral surfaces the arms are grooved by furrows
which clearly correspond with the brachial grooves of the
Crinoids, and on each side of these grooves is a row of pin-
nulse. In one or two cases there is only a single row of pin-
nules, and the arm seems to have been fastened to the calyx

CYSTOIDEA. 1 3 1

by one of the lateral surfaces, instead of by the dorsal surface.
In one Cystidean only (viz., Comarocystites punctatus, Billings)
are there free arms as in the true Crinoids ; but further re-
searches will doubtless show that these appendages existed in
other species as well. In Comarocystites, however, the arms
differ from those of the Crinoids in being only four in number,
in not subdividing (though they carry lateral pinnag), and in
arising directly from the summit of the calyx.

Upon the upper surface of the calyx in the Cystideans are
two, or sometimes three, ajpejrtures, the functions and nature
of which have given rise to considerable controversy. The j
best known of these is a large opening which is pierced in one
side of the calyx, usually near the middle of the body, but
sometimes approximated to either the apex or the base. This
aperture is mostly defended by a "valvular pyramid;" or, in
other words, by a series of small plates, arranged in a pyra-
midal manner, and serving for the closure of the opening.
Much difference of opinion has prevailed as to the true nature
of this orifice. Von Buch believed that it was an " ovarian ?
aperture ; " Mr Billings regards it as discharging the functions
of both the mouth and anus ; whilst Professor Wyville Thom-
son, Mr Salter, and other high authorities, regard it as being
the anus, and as corresponding with the proboscis of the •
Crinoids. That it is not an " ovarian orifice " may be re-
garded as certain, so that the question is narrowed to its
being the anus alone, or an " oro-anal" orifice. In the living
Leskia mirabilis, one of the Sea-urchins, both the mouth and
vent are closed by converging triangular valves, which doubt-
less correspond with the " pyramid " of the Cystideans. This
recent form, however, is not sufficient to decide the present
question, since in it both the mouth and the anus exhibit this
valvular apparatus. Upon the whole, therefore, this question
must be regarded as undecided, though the analogies of recent
forms would lead to the belief that the "pyramid" of the
Cystideans is truly the anus, and that the mouth must be
sought for between the bases of the arms, when these are
present.

A second aperture is placed near the centre of the summit
of the calyx, between the bases of the arms, when these exist.
This opening has not been universally detected, and its true
nature is doubtful. By Mr Billings it is believed to be what
he terms an "ambulacral orifice;" i.e., an aperture by which
the ambulacral vessels passed from the interior of the shell to
the exterior. The analogies of recent forms, however, would
support the view that this aperture is the mouth, in which case

132

ANNULOIDA.

the " pyramid " must be the anus. There is, however, in some
cases a third aperture of small size, always placed near the
apex, and this has been regarded as being truly the anus.

Many Cystideans were further provided with a system of
minute pores or fissures, penetrating the plates of the calyx,
and usually arranged in definite groups. These groups are
termed " pectinated rhombs " (fig. 84), and their exact func-
tion is doubtful. By Messrs Billings and Rose, however, they
are believed, apparently with good reason, to have admitted
water to the body-cavity, and to have thereby subserved a
respiratory function.

r>

Fig. 84. — A, Pectinated rhomb of Glyptocystites multiporus (Billings). B, Pectinated
rhomb of Pletirocystites (Billings). C, Two plates of Callocystites Jewetti (Hall), show-
ing the pectinated rhombs (/). All enlarged.

As regards the distribution of the Cystideans in time, they
are not only wholly extinct, but they are exclusively confined
to the earlier portion of the Palaeozoic period. They appear
to have commenced their existence in the Upper Cambrian
period, the earliest known examples being two extremely
simple forms (Trochocystites and Eocystites] from the "primor-
dial zone" of North America. Other forms have been de-
scribed as occurring in the " primordial zone " of Bohemia.
In the Chazy and Trenton Limestones of North America, of
Llandeilo-Caradoc age (Lower Silurian), and on the same
horizon in Russia, Scandinavia, and Bohemia, Cystideans are
found, often in vast numbers, though in a very fragmentary
condition. In the Bala Limestone (Lower Silurian) of Britain,
Cystideans are abundant fossils. In the Upper Silurian (Nia-
gara and Lower Helderberg) of North America, and on the
same horizon (Wenlock and Ludlow) of Britain, Cystideans
still occur, though their remains are not so plentiful. Lastly,
in the Devonian Rocks occur forms which have been doubt-
fully referred to Cystideans, but the real nature of which is
uncertain. Upon the whole, then, the Cystideans appear to
have commenced in the Upper Cambrian Rocks, to have

CYSTOIDEA. 133

attained their maximum of development in the Lower Silurian
period, to have gradually diminished in numbers and in im-
portance during the Upper Silurian, and to have died out
at the commencement of the Devonian period, or shortly
thereafter.

Of the commoner genera, Hemicosmites (fig. 82), Caryocrinus,
and Echinosphazrites have all the plates of the calyx perforated
by numerous pores. Spharonites has each calycine plate per-
forated by two pores, and Apiocystites, Callocystites, Prunocys-
tites, and Echinoencrinus have the calycine pores arranged in
rhombs upon two or three of the plates of the calyx. In
Glyptocystites there are from ten to thirteen of these " pecti-
nated rhombs." In Malocystites, Apiocystites, Callocystites, and
Pseudocrinus the arms are recumbent and soldered to the
calyx. In Comarocystites there were four free arms with pin-
nulse. In Lepadocrinus the last joint of the column is very
much elongated, and pointed at its extremity ; and in Agela-
crinites and some other forms the calyx appears to have been
directly attached to some foreign body, and a column seems
to have been wanting.

ORDER VI. — BLASTOIDEA.

The Blastoidea or " Pentremites " are Echinodermata in
which the body is enclosed in an armour of closely-fitting calcareous
plates, and is fixed to some foreign object by a slender column.
From the summit of the calyx radiate five areas which are grooved
longitudinally, and striated across, and which carry a row of
jointed pinnulcz on each side. (Fig. 85.)

The Blastoidea nearly resembled the Cystideans in many
respects. The body or " calyx '; is enclosed in a series of
articulated calcareous plates consisting of three large basals,
carrying five forked plates, which are usually regarded as
corresponding with the "radials" of the Crinoids. At the
angles of junction of the forked "radial" plates rest five
smaller plates — the so-called " deltoid plates " — which con-
verge towards the centre of the summit of the calyx. Between
these deltoid plates — which are generally regarded as corre-
sponding with the " inter-radials " of the Crinoids — are the so-
called " pseud -ambulacra." The pseud - ambulacra radiate
from the summit of the calyx, and the apex of each is re-
ceived into the cleft formed by the bifurcation of one of the
"radial" plates. Each pseud-ambulacrum is furrowed by a
longitudinal groove down its centre, and is of a somewhat
petaloid shape, the areas on each side of the central groove

134

ANNULOIDA.

being transversely striated. Along the lateral margins of each
pseud-ambulacrum is a row of minute pores, which open into
internal sacs, and are believed to have had a respiratory func-
tion. Along each side of the longitudinal groove of each
pseud-ambulacrum there appears to have been attached a row
of small jointed processes or " pinnulse." The five pseud-
ambulacra, radiating from the summit of the calyx, give the
upper surface of the body somewhat the appearance of a
rlower-bud ; hence the name applied to the order (Gr. blastos,
a bud ; eidos, form). Upon the whole, it would seem most
probable that the pseud-ambulacra of Pentremites represent
the arms of the Crinoids, anchylosed with the calyx, and that
the longitudinal furrows of the pseud-ambulacra represent the
" brachial grooves " of the Crinoids.

Fig. 85. — Blastoidea. A, Pentremites pyriformis, side-view. B, Base of the same.
C, Summit of Pentremites conoideus. b, b, Basals ; d, <t, Radials ; /, /, Pseud-ambulacra.
C Shows the central pentagonal aperture, surrounded by the five openings at the summit
of the deltoid plates. Carboniferous.

* At the summit of the calyx of the Blastoidea are usually six
apertures. One of these is larger than the others, and is
placed in the centre of the calyx, at the point towards which
the grooves of the pseud-ambulacra converge. This central
aperture has generally been regarded as the mouth, but Mr

BLASTOIDEA. 135

Billings dissents from this view. The remaining five apertures
are placed at the summit of each deltoid plate, between two
pseud-ambulacra. Four of the apertures are equal in size,
and have generally been regarded as " ovarian ; " but they are
looked upon by the above-mentioned eminent authority as
being connected with the respiratory system. The fifth is of
larger size than the other four, and is usually regarded as
partly ovarian and partly anal ; but it is looked upon by Mr.
Billings as " oro-anal."

Like the Cystideans, the Blastoidea are not only extinct,
but are exclusively Palaeozoic. The Cystideans, however,
attained their maximum at a very early period of Palaeozoic
time ; whereas the Pentremites flourished most abundantly in
the Carboniferous seas, towards the close of the Palaeozoic
period. The Cystideans had nearly died out, or had become
quite extinct, by the close of the Upper Silurian period ; and
it is a noteworthy fact that it is just at that point that the
Blastoidea seem to make their first appearance. Very spar-
ingly represented in the Upper Silurian Rocks, the Blastoidea
increase largely in numbers during the Devonian period ; but
they attain their maximum of development in the seas of the
earlier portion of the Carboniferous period. With one ex-
ceedingly problematical exception, no member of the order
is known to have survived the close of the Carboniferous
epoch.

ORDER VII. — HOLOTHUROIDEA.

The last order of the Echinodermata is that of the Holothu-
rians or " Sea-cucumbers," in which the body is vermiform or
slug-shaped, and the calcareous matter secreted by the integument is
reduced to scattered spicules (Synapta), or rarely is present in the
form of imbricated scales (Psolus).

As might have been expected from the generally soft nature
of their integuments, the Holothuroids are hardly known as
fossils, and they merely require to be mentioned here. The
only remains referred with any probability to this order are
certain calcareous spicula which have been found in deposits
of both Mesozoic and Tertiary age, and which have been re-
garded as belonging to a Synapta, and the shield of a species
of Psolus which has been found in Post-Tertiary deposits in
Bute.

136 ANNULOSA.

CHAPTER XIII.

SUB-KINGDOM IV.— ANNULOSA.
FOSSIL ANNELIDA.

SUB-KINGDOM ANNULOSA. — The Annulose animals are distin-
guished by the possession of a body which is composed of numer-
ous segments arranged longitudinally one behind the other. A
nen>ous system is always present, and consists of a double chain
of ganglia running along the ventral surface of the body and
traversed anteriorly by the gullet. The limbs (when present] are
turned toivards that side of the body upon which the chief masses
of the nervous system are situated.

The sub-kingdom Annulosa may be divided into two primary
sections, according as the body is provided with articulated
appendages or not ; these divisions being known respectively
as the Arthropoda (or Articulatd) and Anarthropoda. The
first of these comprises the Crabs, Lobsters, and the like (Crus-
tacea), the Spiders and Scorpions (Arachnida), the Centipedes
and Millipedes (Myriapoda\ and the true Insects (Insecta).
The latter comprises the Spoon-worms (Gephyrea), the Leeches
(Hirudinea), the Earth-worms (Oligocfuzta}, the Tube-worms
( Tubicola), and the Sand-worms or Sea-worms (Errantid) ; the
last four groups constituting the class of the Ringed Worms or
Annelida.

Regarded as a whole, the great Annulose sub-kingdom
seems to have commenced at least as early as the Echinoder-
mata and the Ccelenterata. Both the Anarthropodous and
Arthropodous divisions of the sub-kingdom are represented in
the Upper Cambrian ; and the former, at any rate, is repre-
sented in the Lower Cambrian period, along with the earliest
traces of life known to us, except the Eozob'n of the Laurentian
Series.

ANNELIDA.

In the Anarthropodous division of the Annulosa the loco-
motive appendages are never distinctly jointed or articulated
to the body ; and the integument, though usually capable of
secreting chitine or horny matter, is almost always quite soft
and flexible. The Spoon-worms (Gephyrea), and two orders
of the Annelides (viz., the Leeches and the Earth-worms), are
wholly unknown in the fossil condition, and need not be con-
sidered here. There remain only two orders of the Annelides

ANNELIDA.

137

(viz., the Tubeworms or Tiibicola, and the Sand-worms or
Errantid) which come under the notice of the palaeontologist,
and neither of these requires much notice. In both orders, as
throughout the division, the integument is more or less soft,
and there are no internal hard structures ; hence it is more
than doubtful if we have any example of the fossilised body of
these creatures, though such have been alleged to occur. The
Tubicolous Annelides, however, protect themselves by a tube
of lime, sand, or adventitious particles, and these investing
tubes are often preserved in the fossil condition. The Errant
Annelides, again, have left traces of their past existence in the
form of filled-up burrows or meandering trails upon the soft
sand and mud of the sea-bottom ; and from these we know
that the Annelides commenced their existence at least as early
as the Lower Cambrian period, obscure traces of their presence
having been even detected in the Laurentian Series.

ORDER TUBICOLA. — The Tubicolous Annelides are distin-
guished by the fact that the body is protected by a tube within
which the animal can withdraw itself by means of tufts of bristles
carried on the sides of the body. The gills are placed on or near
the head, generally in two lateral tufts ; hence the name of
" Cephalobranchiatc, Annelides" applied to this order (fig. 86).

The protecting tube of the
Tubicolous Annelides may be
composed of carbonate of lime
(Serpula), of grains of sand
(Sabellarid), or of sand, pieces
of shell, and other adventitious
particles cemented together by
a glutinous secretion from the
body (Terebella) ; or it may be
simply membranaceous or lea-
thery (Sabella). Sometimes the
tube is free and non-adherent
(Pectinaria) ; more commonly it
is attached to some sub-marine
object by its apex or by one
side (Serpula and Spirorbis).
Sometimes the tube is single

(Spirorbis) ; sometimes the animal is social, and the tubes are
clustered together in larger or smaller masses (Sabellarid}.

When the tube is calcareous, it presents certain resemblances
to the shells of some of the Molluscs, such as Vermetus and
Dentalium. In the living state it is easy to make a distinction
between these, for the Tubicolar Annelides are in no way

Fig. 86. — Tubicola. a Serpula con-
tortuplicata, showing the branchiae and
operculum ; b Spirorbis corn-munis.

ANNULOSA.

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, how-
ever, the calcareous tubes of Annelides, such as Serpula, are
less regular and symmetrical than those of Vermetus, whilst the
latter is partitioned by shelly septa, which do not exist in the
former. Again, the tube of Dentalium is open at both ends,
whereas it is closed at one extremity in the Serpulce. In the
Annelidous genus Ditrupa, however, the tube is open at
both ends, so that this distinction is one not universally appli-
cable.

Tubicolar Annelides are known from the Silurian 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 Spirorbis
has survived from the Upper Silurian period to the present
day; and forms very nearly allied to, if not actually identical
with, the recent Serpulce, are found in almost all formations,
beginning with the Silurian.

The chief Palaeozoic genera of Tubicola are Cornvlites,
Conchicolites, Serpulites, Trachyderma, Spirorbis (Microcon-

chus), and Serpula. The
genus Cornulites (fig. 87)
is Silurian, and the best
known species is C. serpu-
larius. In this singular
form the tube is of con-
siderable length -- often
three or four inches — with
a wide aperture at one
end, and tapering gradu-
ally to its opposite extrem-
ity, which is often curved,
and seems to have been
attached to some solid
body. The tube is cal-
careous, with very thick
walls, the substance of
which is composed of a number of cellular cavities. Exter-
nally the tube is ringed with transverse annulations, and marked
with fine longitudinal striae. The internal cast of the tube has
the form of a series of inverted conical rings, of small width,
arranged in an imbricated manner. The tube appears to have
been solitary, and is rarely found attached.

Fig. 87. — Comulites serpularius. Upper
Silurian.

ANNELIDA.

139

Fig. ^.-Conchicolites gregariiis, growing upon
the shell of an Orthoceras. Lower Silurian.

In the genus Conchicolites (fig. 88) we have a much smaller
Annelide, living socially, and forming masses of clustered tubes
growing attached to dead
shells in Lower Silurian
strata. As in Cornulites,
the tube of Conchicolites ap-
pears to have been calcare-
ous, but it is comparatively
thin, and has none of the
vesicular structure so char-
acteristic of the former. The
tube of Conchicolites is made
up of a series of short coni-
cal rings, inserted into one
another in an imbricated
manner, with their broader
ends turned away from the

mouth of the tube. It is worthy of notice that the casts of
Conchicolites, from their possession of the above structure, ex-
hibit a close resemblance to the shells of the Silurian genus
Te?itaculites ; whilst casts of the shells of some species of the
latter are absolutely undistinguishable, if fragmentary, from
casts of the tubes of the former. This is a remarkable fact,
since Tentaculites has often been regarded as a genus of Tubi-
colar Annelides ; but there are strong reasons for believing
that it is truly referable to the Mollusca, and belongs to the
order of the Pteropods.

The genus Serpulites was instituted by Murchison for certain
smooth semi-calcareous tubes, often of great length, and ap-
parently unattached, which occur in the Silurian series. These
tubes in some species reach a length of over a foot, with a
diameter of an inch, and their true nature is very doubtful.
The genus Trachyderma, again, was proposed by Phillips for the
casts of membranous flexible tubes which are found in the
Silurian rocks. These are transversely wrinkled or plaited, and
though the tube itself has disappeared, there can be little doubt
entertained as to their Annelidous nature.

The genus Spirorbis (fig. 89) is characterised by the posses-
sion of a shelly calcareous tube, which is coiled into a flat
spiral, one side of which is cemented to some foreign body.
The spiral may be either right-handed or left-handed, and the
shell generally occurs in numbers together, attached to dead
shells or to the remains of plants. The genus commences to
be represented in the Upper Silurian Rocks, in which S. Lewisii
is an abundant fossil. Other species occur in the Devonian,

140

ANNULOSA.

and the little S. carbonarius (fig. 89) is a common species in
the Carboniferous Rocks, whilst more than one form has been
described from the Permian series. The genus continues to

Fig. 89. — Spirorbis (Microconchus) carbonarius ; natural size, attached to a fossil plant,
and magnified. Carboniferous. (After Dawson.)

be well represented in both Mesozoic and Tertiary deposits ;

and living forms, apparently little different from the fossil ones,

abound in recent seas.

The genus Scrpttla (fig. 90) possesses a long shelly tube,

usually more or less tor-
tuous, sometimes solitary,
sometimes aggregated, and
fixed to some foreign body
by part of its surface. Spe-
cies of this genus have
been described from the
Upper Silurian, Devonian,
and Carboniferous forma-
tions. In the Trias some
species occur, and many
forms are known from the
Oolitic and Cretaceous
formations, whilst they are
equally numerous in the
Tertiary series.

Of the other fossils re-
ferred to the Tubicolar
Annelides, the only one
which needs notice is the
genus Ditrupa. The tube
in this genus is unattached,
open at both extremities,
and very closely resem-
This genus does not seem to

Fig. 90. — Serpulaflagellum.
(Jurassic.)

Oxford Clay.

bling the shell of a Dentalium.

ANNELIDA.

have come into existence till the close of the Cretaceous
period ; but it is found in great abundance in the London Clay
(Eocene) and the Crag (Pliocene).

ORDER ERRANTIA. — The Errant Annelides are character-
ised by the fact that the body is furnished with lateral tubercles
carrying tufts of bristles. The animal leads a free life, and is
not confined to a tube. The gills are placed along the back or sides
of the body ; hence the name of " Dorsibra?ichiate Annelides" often
applied to this order (fig. 91).

Fig. 91. — Errant Annelides. A, Hairy-bait (Nephthys) ; B, Sea-mouse (Aphrodite] ;
C, Lob-worn (Arenicola). (After Gosse.)

Possessing no hard structures, the Errant Annelides are
hardly capable of being preserved in a fossil state. Certain
fossils, however, have been supposed to be the bodies of these
animals in a petrified state ; but it is very difficult to believe
that such is the true nature of the remains in question, and
it is almost certain that they are really nothing more than
the " tracks " of sea-worms. On the other hand, the Errant
Annelides are abundantly represented by their trails upon old
sea-bottoms or their burrows in sand or mud ; remains of which
occur in all formations, almost, from the Lower Cambrian up
to the present day.

The burrows of Annelides, as a matter of course, run in a
direction more or less opposed to the surfaces of the laminae
of the rock, being often quite vertical. Sometimes such bur-
rows are hollow, but they are more commonly filled up by the

142

ANNULOSA.

matrix of the rock. The most important genera which have
been founded upon remains of this kind are Scolithus, Histio-
dermay and Arenicolites, all of which occur in rocks of Cam-
brian age. Scolithus is founded upon long burrows, which are
nearly straight, and descend vertically through the rock (fig.
92). Histioderma is a somewhat curved burrow, from one to
nearly four inches in length, terminating by a trumpet-shaped
opening, which is placed in the centre of a small mound.
Armicolites includes very small burrows which form loops,
opening on the surface by two apertures placed close to one
another. The mouths of these burrows are thus placed in
pairs, one being believed to be an aperture of entrance for the
worm, the other of exit. The nature of none of these fossils

Fig. 92. — Annelide-burrows (Scolithus Canadensis), from the Potsdam Sandstone (Upper
Cambrian). (After Billings.)

is wholly free from doubt ; but the other genera, which have
been regarded as formed by burrowing Annelides, are still
more obscure and uncertain.

As regards the surface-tracks and trails of Errant Annelides,
much difference of opinion exists, and the whole subject is
shrouded in obscurity. Many of these tracks were regarded
by their describers as being actually the body of the worm, as
in Crossopodia (fig. 93). Others, as Gordia and Myrianites,
are undoubtedly tracks of some animal, but there is no
evidence as to their having been produced by Annelides.
Others, again, such as Palceochorda, which are also almost cer-
tainly the trail of some marine animal, have been described as
the remains of plants. A few of these fossils may truly be of

CRUSTACEA.

143

a vegetable nature, whilst as to others (such as Nereites] no
certain conclusion can be arrived at. Upon the whole, it
would be safest to adopt Mr. Salter's proposal, and refer all
these remains provisionally to the artificial genus Helminthites ,

Fig. 93. — Crossopodia Scotica, an Annelida track. Silurian. (After M'Coy.J

retaining Scolithus for the burrows. As regards the distribu-
tion of these remains, it is sufficient to say that they occur
more or less abundantly in almost all strata of a suitable
mineral character from the Cambrian Rocks upwards.

CHAPTER XIV.

ARTHROPOD A.

CRUSTACEA.

DIVISION ARTHROPODA, or ARTICULATA. — The members of
this division of the sub-kingdom Anmilosa are distinguished
from the preceding division of the Anarthropoda by the pos-
session of jointed appendages, articulated to the body. The body
is composed of a series of segments or "somites" arranged along a
longitudinal axis ; each segment occasionally, and some always,
being provided, at some period of life or other, with articulated
appendages. Both the segmented body and the articulated limbs

144 ANNULOSA.

are more or less completely protected by an external skeleton
formed by the deposition of horny (chitinous) matter in the integu-
ment.

The division Arthropoda includes four great classes of
animals which are very generally spoken of as the " Arti-
culate Animals." These classes are the Crustacea (Lobsters,
Crabs, &c.), the Arachnida (Spiders, Scorpions, &c.), the
Myriapoda (Centipedes and Millipedes), and the Insccta (In-
sects). All these classes came into existence in the Palaeo-
zoic period, the division being represented by Crustaceans as
early as the Upper Cambrian at any rate, and doubtfully in
the Lower Cambrian. Owing to the fact that the Crustaceans
alone lead an habitually aquatic life, the remains of this class,
as might be expected, preponderate largely over those of the
other three. The air-breathing classes of the Arachnida,
Myriapoda, and Insecta, naturally, have not left abundant
traces of their existence in past time, a state of things which is
assisted by the nature of their integuments, which are rarely
as hard and resisting as those of the Crustaceans.

CLASS I. — CRUSTACEA.

The Crustaceans are Articulate animals in which the breath-
ing organs (when distinct) are in the form of gills, and the mode
of existence is almost always more or less aquatic. The body is
protected by a chitinous or sub-calcareous exoskeleton or "crust"
and the number of pairs of articulated limbs is generally from five
to seiwi. Some of the locomotive appendages are often carried
upon the segments of the abdomen, and there are two pairs of
jointed feelers or " antenna"

The body of a typical Crustacean, such as a Lobster (fig.
94), consists of a definite number of somites placed one be-
hind the other, and divisible into three regions — a head, thorax,
and abdomen. Most authorities regard the body as being
typically composed of twenty-one somites, of which seven go
to the head, seven to the thorax, and seven to the abdomen.
All these somites, except the last, may be provided with a pair
of appendages each. The last segment of the abdomen, how-
ever, never carries any appendages. This segment is known
as the "telson" (fig. 94, i, /), and it is variously regarded as
a somite without appendages, or as an impaired appendage
placed in the middle line of the body. If this latter view be
adopted, the body of a typical Crustacean will consist of only
twenty segments, instead of twenty-one. The telson is very

CRUSTACEA.

greatly developed in some Crustaceans, such as the King-
crabs, and less so in the extinct Eurypterida.

Fig. 94. — Morphology of Lobster, i. Lobster with all the appendages, except the
terminal swimmerets, removed, and the abdominal somites separated from one another.
ca Carapace ; t Telson. 2. The third abdominal somite separated, t Tergum ; j Ster-
num ; p Pleuron ; a Propodite ; b Exopodite ; c Endopodite. 3. One of the last pair
of foot-jaws or maxillipedes. e Epipodite ; g Gill ; the other letters as before.

Generally speaking, a greater or less number of the somites
are amalgamated together, rendering it difficult to recognise
their existence unless they bear appendages — each pair of
appendages indicating a separate somite. Very commonly the
segments of the head and thorax are welded together into a
single mass, which is termed the " cephalothorax," and which

146 ANNULOSA.

really consists of fourteen coalescent segments. The cephalo-
thorax is generally covered by a great shield or buckler, which
(is termed the "carapace" (fig. 94, i, ca), which is produced
by an enormous development of the dorsal walls of one or two
of the cephalic somites.

Each segment of the body may be regarded as essentially
composed of a convex upper plate, termed the " tergum,"
which is closed below by a flatter plate, called the " sternum,"
the line where the two unite being produced downwards and
outwards into a plate which is called the " pleuron," or
"pleura" (fig. 94, 2).

Strictly speaking, the composition of the typical somite is considerably
more complex, each df the primary arcs of the somite being really com-
posed of four pieces. The teijgal arc is composed of two central pieces,
one on each side of the middle line of the body, united together, and con-
stituting the " tergum " proper. The superior arc is completed by two
lateral pieces, one on each side of the tergum, which are termed the
"epj.mera." In like manner the ventral or sternal arc is composed of a
central plate, composed of two pieces united together in the middle line,
and constituting the " sternum " proper, the arc being completed by two
lateral pieces, termed the "episterna." These plates are usually more or
less completely anchylosed together, and the true structure of the somite
in these cases is often shown by what are called " apodemata." These
are septa which proceed inwards from the internal surface of the: somite,
penetrating more or less deeply between the various organs enclosed by the
ring, and always proceeding from the line of junction of the different pieces
of the segment (fig. 95).

Each somite of the body may bear a pair of appendages,
and these appendages are very much modified in different

parts of the body, in order to fulfil
different functions. Usually, how-
e ever, a common morphological type
^?.... p may be recognised in the appe'nd-
V ji^ ages of the C/7/j7Vta?tf, though certain

•f elements of this type are often want-
s s ing or much modified. Typically,

Fig. 95. -Theoretical figure iiius- the appendages of the Crustacea

tratmg the composition of the tegu- . rr »•••_»•«

mentary skeleton of the Crustacea COnSlSt Of an Undivided basal por-

(after Milne-Edwards). D Dorsal f' " r>rr»rtr»Hi'f^ " m'xrinn- rn-i'm"r»

arc; /^Tergal pieces; ee Epime- tlOn °r .Prpppaite, ^ giving Origin

ral pieces ; V Ventral arc ; s * Ster- tO tWO diverging lOUltS. of which

nal pieces ; ff Episternal pieces : , -, • • ' fi i . i / , T

//insertion of the extremities. the inner is called the "endopo-

dite," whilst the outer is known

as the " exopodite." In such an appendage as the " swim-
meret " oif a Lobster (fig. 94, 2), these fundamental parts are
readily recognisable ; but either the exopodite or endopodite,
or both, may be wanting, or they may be very much modified
in shape and form.

CRUSTACEA. 147

It is impossible to give any general view of the appendages
of a Crustacean ; but it may be as well to name the appendages
which are present in one of the higher forms, such as the
Lobster, in which all the somites, except the telson, carry a
pair of appendages each. The somites of the head and thorax
are amalgamated into a single mass, termed the "cephalo-
thorax," which is protected above by the " carapace," and
carries the appendages on its lower surface. The first segment
of the head carries a pair_o_f eyes, which are " compound," and /
are borne upon long stalks, formed by the propodite of the
appendage. The second segment of the head carries a pair of
small jointed feelers, which are known as the " lesser antennae "
or " antennules." Each consists of a short propodite, and a *
much-segmented endopodite and exopodite, which are nearly
of equal length. The third segment of the head carries a pair
of very long feelers, which are known as the " great antennae." 3.
Each consists of a short propodite and a long and jointed
endopodite, with a rudimentary exopodite. The fourth seg-
ment of the head carries a pair of jaws, which are known as the
" mandibles." Each mandible consists of a large propodite, *
with no exopodite, but with a small endopodite, which is known
as the " mandibular palp." Between the bases of the man-
dibles also is placed the aperture of the mouth, which is
bounded in front \>y a plate, known as the "labrum" (upper
lip) or " hypostoma." and behind by a forked plate, known as
the " labium " (lower lip) or " metastoma." Thefiff/t segment
carries another pair of jaws, which are known as the first pair
of " maxillae ; " whilst the sixth segment carries another pair of s. (,.
the same, known as the second pair of "maxillae." The
seventh and last segment of the head carries the first of three
pairs of what are generally known as " foot-jaws " or " maxilli-
pedes." Each foot-jaw is merely an ordinary limb, consisting
of propodite, exopodite, and endopodite, but modified to assist
in mastication. The eighth segment (the first of the thorax)
carries a second pair of foot-jaws, and the ninth segment (the
second of the thorax) bears a third pair of the same. The
tenth segment (the third of the thorax) carries a pair of jointed
limbs, consisting of propodite and endopodite alone, without
any exopodite. These limbs are greatly developed, and their
extremities form a pair of pincers or " chelae," so that they /o.tt.
constitute the " nipping-claws " of the Lobster. The eleventh
segment (the fourth of the thorax) carries a second pair of
limbs, also " chelate," but much smaller than the preceding ;
and the twelfth segment (the fifth of the thorax) carries another
pair of the same. The thirteenth segment (the sixth of the

148 ANNULOSA.

thorax) carries a pair of limbs like the preceding, but with
simply-pointed extremities ; and the fourteenth segment (the
last of the thorax) carries another pair of the same ; so that
there are altogether five pairs of ambulatory limbs, carried
respectively by the loth, nth, i2th, i3th, and i4th somites of
the body ; or, in other words, by the last five segments of the
thorax. Of the seven segments of the abdomen — completing
the total of twenty-one — the first six carry each a pair of ap-
pendages, which are used as swimming organs, and which are
termed the " swimmerets." Each swimmeret (fig. 94, 2) con-
sists of a propodite and a flattened exopodite and endopodite;
and the last pair is greatly widened out and expanded, forming
with the telson a powerful swimming-tail. The telson or last
abdominal segment carries no appendages, and is simply
placed between the last pair of swimmerets.

As regards the general distribution of the Crustacea in time,
remains of the class are comparatively abundant in all forma-
tions except the very oldest ; as might have been expected
from the generally chitinous or sub-calcareous nature of their
integuments and their aquatic habits. Owing also to their
habit of periodically casting their shell, a single individual may
leave repeated traces of himself, and the number of fossils may
considerably exceed that of the individuals which actually
underwent fossilisation. The Crustaceans appear to have com-
menced their existence in the Cambrian period, remains of
members of this class being tolerably abundant in the higher
portion of this formation. The Palaeozoic formations, taken
as a whole, are characterised by the predominance of the
orders Trilobita, Eurypterida, Ostracoda, and Phyllopoda, of
which the two former are exclusively confined to this period.
All the other orders of Crustacea, which have left any traces of
their past existence at all, appear to have come into existence
before the close of the Palaeozoic period. Upon the whole,
however, there has been a marked progression in proceeding
from the older formations to the present day. The Trilobites
and Eurypterids of the older Palaeozoic Rocks, though highly
organised so far as their type is concerned, are in many respects
inferior to later forms, whilst they present some striking points
of resemblance to the larval forms of the higher groups. The
great group of the Stalk-eyed Crustaceans — undoubtedly the
highest of the entire class — is not represented at all till we
reach the Carboniferous Rocks : and it is not till we come into
the Secondary period that we find any great development of
this group, whilst its abundance increases to a marked extent
in the Tertiary period, and it attains its maximum at the

CRUSTACEA. 149

present day. Similarly, of the two sub-orders of the Merosto-
mata, the Eurypterida are confined to the earlier portion of the
Palaeozoic period, whilst the more highly organised and less
larval King-crabs (Xiphosura) did not make their appearance
till the Eurypterids had disappeared, at the close of the Car-
boniferous period.

The following table shows the orders of the Crustacea, and
a short account will be given of the distribution in time of
those which are known to occur as fossils. The structure also
of the extinct groups will be shortly described. The orders
marked with an asterisk do not occur as fossils, or only doubt-
fully so, and will not be considered here.

TABULAR VIEW OF THE DIVISIONS OF THE CRUSTACEA.

Sub-class I. EPIZOA (Haustellata).
Order I. Ichthyophthira.*
,, 2. Rhizocephala*

Sub-class II. CIRRIPEDIA.

( Balanidse.

Order 3. Thoracica. < Verrucidse.

( Lepadidse.
,, 4. Abdominalia*
,, 5. Apoda*

Sub-class III. ENTOMOSTRACA.
Order 6. Ostracoda.
„ 7. Copepoda*
,, 8. Cladocera*
,, 9. Phyllopoda. > Legion, Branchiopoda.

,, 10. Trilobita. \

,, II. Merostomata.

Sub-class IV. MALACOSTRACA.

Division A. EDRIOPHTHALMATA.
Order 12. Lcemodipoda*
,, 13. Isopoda.
,, 14. Amphipoda.

Division B. PODOPHTHALMATA.
Order 15. Stomapoda.
,, 1 6. Decapoda.

Tribe a. Macrura.
,, b. Anomura.
,, c. Brachyura.

SUB-CLASS CIRRIPEDIA.

Animal free when young, but permanently attached in the adult
condition to some foreign body by the anterior extremity of the
metamorphosed head. The visceral cavity of the adult protected
by a calcareous shell of several pieces, or by a coriaceous envelope.
Abdomen free. Thoracic segments usually carrying six pairs of
forked ciliated limbs.

150 ANNULOSA.

The Cirripedia include three orders, of which only the order
Thoracica has ever been found in a fossil condition, or is ever
likely to be so. In this order are the common Acorn-shells
(Balanidcz) and Barnacles (Lepadidtz), in which the body is
protected by a more or less complete calcareous shell. The
Acorn-shells are generally known as the " Sessile Cirripedes,"
because the shell is directly attached by its base to some
foreign body, whereas the Barnacles are commonly known as
the " Pedunculated Cirripedes," because the shell is supported
upon a stalk or " peduncle." Besides these, the order Thor-
acica comprises a third family, that of the Verrucidce, in which
the shell resembles that of the Balanidcz in being sessile, but
differs in being unsymmetrical, and in some other particulars.

It is with the shell of the Cirripedes that the palaeontologist
has to deal ; and we may, therefore, consider briefly the chief
parts of the shell in the Sessile and Pedunculated Cirripedes
respectively. It will not be necessary, however, to enter into
minute details on this complicated subject, and it will be
sufficient to indicate the leading facts of importance.

In the symmetrical Sessile Cirripedes or Balanidcz, 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 mem-
branous plate, which closes the lower aperture of the shell, and
which is termed the "basis" (fig. 96 A, /). The "basis" is
fixed by its outer surface to some foreign object, and is some-
times 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 pyra-
midal lid or " qperculum." Leaving the operculum out of
consideration at present, the sides of the shell are seen to be
composed of from four to eight separate pieces, valves, or, as
they are technically called, compartments. These compart-
ments are usually closely contiguous by their lateral margins,
and are separated by lines of division or " sutures ; " but they
are sometimes anchylosed together. Each compartment con-
sists of a central portion, which is termed the "paries5' (fig.
96, B/), which is attached by its base to the "basis" of the
shell. The "paries" grows downwards, so that the whole
shell increases by additions made round the base. The paries
of each compartment is flanked by wing-like portions, which
differ from the paries in appearance, and are called "radii"
and " alag," according to their shape (fig. 96, B, C). Some-
times the paries has a "radius" on both sides, sometimes

CRUSTACEA. 1 5 I

" alae " 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. 96, A) ; and the compartment im-
mediately opposite to this " rostrum." The remaining com-
partments are " lateral," the one nearest the carina " carino-
lateral," the one nearest the rostrum " rostro-lateral," and the
middle one simply " lateral" (fig. 96, A); but the three rarely
coexist.

Fig. 96. — Shell of Balanidae. A, Diagram of the shell of Balanns ; /, / Basis ; c Carina ;
k Rostrum ; m Rostro-lateral compartment ; n Lateral compartment ; o Carino-lateral
compartment. B, Compartment with two radii (r, r) flanking the paries (p). C,
Compartment with a radius (r) on one side, and an ala (a) on the other side of the paries.
D, Internal view of the scutum. E, Internal view of the tergum, showing the spur (s)
and the beak (/). (After Darwin.)

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 along the opposite margin. Similarly,
each tergum opens and shuts against its fellow along one mar-
gin (the "carinal" margin), and articulates with one of the
scuta along the opposite margin. The apex of the terga (fig.
96, 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 depressor
muscles.

152 ANNULOSA.

As regards the distribution of the Balanida in time, the
oldest known representative of the family, so far as is certainly
known, has been indicated by Mr Seeley as occurring in the
Lias, and has been made the type of a new genus under the
name of Zoocapsa. So far as is known, no member of the
group occurs in any Palaeozoic deposit ; and negative evidence
is in this case of considerable value, as the Balani possess a
shell which is readily preserved, whilst they adhere to all
sorts of marine bodies. With the above-mentioned exception
(which may, perhaps, be referred to the Verrucidce), no fossil
Balanoid has hitherto been discovered in sediments older
than the commencement of the Tertiary period. The genus
Balanus is the earliest of the group, and appears under several
specific forms in the Eocene Rocks. In the Miocene and
Pliocene deposits, the Balanidcz are abundantly represented
by Balanus itself, and in the latter by the genera Acasta,
Pyrgoma, and Coronula.

The remaining family of the Sessile Cirripedes is that of the
Verrucida, comprising only the single genus Verruca. In many
respects the Verrucidce approach the Balanidce, but the shell is
composed of six valves only, and is unsymmetrical, whilst the
scuta and terga (forming the operculum), though movable,
are not furnished with a depressor muscle. The Verrucidcz
appear, so far as is known, to have commenced their existence
towards the close of the Secondary period, the Chalk having
yielded one species. Verruca Stromia is found in the Coralline
and Red Crags (Pliocene), in Glacial deposits, and in existing
seas.

The third family of the Cirripedia Thoradca is that of the
Lepadida or Pedunculated Cirripedes, commonly known as
" Barnacles." In these (fig. 97) the animal differs from the
Sessile Cirripedes in having its anterior extremity greatly
elongated, forming a stalk or " peduncle ;> by which the animal
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 appendages. The peduncle is
cylindrical, of varying length, flexible, and furnished with pro-
per muscles. In some species the peduncle is naked, and can-
not be preserved in the fossil condition ; but in other cases
the peduncle is furnished with calcareous scales (Loricula and
Turrilepas, fig. 99), in which case it is readily preserved. The
" capitulum " (fig. 98), as before said, corresponds with the

CRUSTACEA.

153

shell of the Balani, and is generally much flattened. It con-
sists ordinarily of five or more valves united to one another
by membrane, usually with marked interspaces ; but the valves
may be rudimentary or wanting, and
the entire capitulum may be mem-
branous. The parts of the capitu-
lum correspond ideally with the parts
of the shell in the Balanoids. In
the latter, however, the shell is for
the most part composed of the " com-
partments," and the " operculum " is
comparatively small and insignificant.
In the Lepadoids, on the other hand,
the valves which correspond with the
operculum of the Balanoids are dis-
proportionately developed, and the
valves which correspond with the
compartments of the Balanoids are
much less conspicuous, and are often
partially absent. The most important
and persistent of the valves are the
" scuta " (fig. 98, b), which protect the
front part of the body, and correspond
with the valves bearing the same name
in the operculum of the Balanoids.
The next most important are the
" terga" (fig. 98, 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 capitu-
lum, the former, being much the most
important, and there may be a " sub-
carina " and " sub-rostrum/' The re-
maining valves, with the carina and
rostrum, correspond with the proper

shell of the Balanoids ; but they are often wanting or rudi-
mentary, and they require no further consideration here.

As regards the distribution of the Pedunculated Cirripedes
in time, until recently no member of the family was certainly
known to have existed in the Palaeozoic period. Mr Henry
Woodward, however, has described a very interesting form
from the Upper Silurian Rocks, under the name of Turrilepas
(fig. 99, A). In this singular fossil the peduncle was furnished

Fig. 97. — Anatifa lepas, a
recent Pedunculated Cirripede.
The lower figure shows the
scutum detached.

154

ANNULOSA.

with intersecting rows of plates, as in Loricula. These plates,
when detached and occurring in an isolated condition, might
very readily be mistaken for the shells of Pteropods. The
genus is known both from the Wenlock Limestone of Dudley
and the Ludlow Rocks of the Pentland Hills near Edin-
burgh. The Devonian, Carboniferous, and Permian forma-
tions have as yet yielded no certain traces of Pedunculated^
Cirripedes, if we reject, as we apparently must, \he\Aptychus
of the Carboniferous rocks, referred here by M. D'Orbigny.

Fig. 98. — Capitulum of a Pedunculated Cirripede. a Tergum ; b Scutum ; c Carina ;
d Upper latus ; ^ Carino-latus ; f Rostrum ; g Sub-rostrum ; h Rostral latus ; i Infra-
median latus ; k sub-carina. (After Darwin.)

With the exception of the very ancient Turrilepas, the oldest
pedunculated Cirripedes belong to the genus Pollicipes, species
of which have been discovered in the Rhaetic beds (Upper Trias),
and in the Lower Oolites (Stonesfield Slate). In the Cretace-
ous period, " the Lepadidae arrived at their culminant point ;
there were then three genera, and at least thirty-two species,
some occurring in every stage of this system ;; (Darwin). In
the Tertiary rocks are a few species of Scalpellum and Pollicipes ;
but no species of the now existing and widely distributed

CRUSTACEA.

155

genus Lepas or Anatifa has as yet been certainly detected in a
fossil condition (Darwin), though D'Orbigny states that he has

B

Fig. 99. — A, Turrilcfias Wrightii. Upper Silurian. (After Woodward.) a A plate
of the same magnified. B, Loricula pulchella. Chalk. (After Darwin.)

discovered a representative of this genus in the Miocene
Tertiary.

CHAPTER XV.

CR US TA CEA — Continued.
SUB-CLASS ENTOMOSTRACA.

THE Entomostracous Crustaceans are defined by Professor
Rupert Jones as follows : — " Animal aquatic, covered with a
shell, or carapace, of a horny consistency, formed of one or more
pieces, in some genera resembling a cuirass or buckler, and in others
a bivalve shell, which completely or in great part envelops the
body and limbs of the animal ; in other genera the animal is in-
vested with a multivalve carapace, like jointed plate-armotir ; the
branchifB are attached either to the feet or to the organs of mastica-
tion; the I i tubs are jointed, and more or less setiferous. The
animals, for the most part, undergo a regular moulting or change
of shell, as they grow ; in some cases this amounts to a species of
transformation. "

The orders commonly included in the sub-class Entomostraca
are the Ostracoda, Copepoda, Cladocera, Phyllopoda, Trilobita,
and Merostomata (comprising the sub-orders Xiphosura and
Eurypterida). Of these, the Copepoda and Cladocera may

156 ANNULOSA.

be left out of consideration, as they are not certainly known to
occur in the fossil condition. There are also good reasons for
the belief that the Trilobites should be placed amongst the
Malacostracous Crustaceans, in or near the order Isopoda. In
the absence, however, of unassailable evidence, the Trilobites
may be safely retained in the vicinity of the Phyllopods, to
which they show undoubted affinities.

ORDER OSTRACODA.

Minute 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 adduc-
tor muscle, the insertion of which is marked in the interior of each
valve by a tubercle, pit, or group of spots, or by both spots and a
pit. The branchice are attached to the posterior jaws, and there
are only two or three pairs of feet, which subserve locomotion, but
are not adapted for swimming.

Of the living Ostracode Crustaceans, a great many inhabit
fresh waters ( Cypris] ; others live in fresh or in brackish waters
( Candona) ; lastly, others are exclusively confined to the sea
( Cythere and Cypridina). They generally swarm in the locali-
ties in which they occur, and from their habit of periodically
shedding their valves, considerable accumulations of their shells
may be formed under favouring circumstances.

It is only the carapace-valves of the Ostracode Crustaceans
that are preserved in the fossil condition; and the general form
of the carapace is often very similar in different genera. Hence,
the palaeontologist 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 an-
other, or, lastly, the surface-ornamentation. Partly for this
reason, and partly because the number of known fossil Ostra-
coda is very large, it will not be advisable here to do more than
give an outline of the general distribution of the order in time.

The Ostracode Crustaceans appear to have been amongst
the earliest representatives of their class, abounding as they do
in many Lower Silurian deposits. Amongst the more import-
ant genera which are represented in the Silurian Rocks may
be mentioned Primitia (fig. 100, a), Leper ditia, Beyrichia, Ento-
mis, Cypridina, Cytherella, Cythere, and Bairdia. Of these the
genus Primitia is exclusively confined to the Silurian rocks,
whilst the great genus Leperditia arrived here at its greatest
development. On the other hand, the genera Cytherella,

CRUSTACEA.

157

Cythere, and Bairdia are represented by species now living.
Presumably all these genera were marine, and we know that
this was the case with many of them. The Devonian rocks
are comparatively poor in Ostracoda, all the known forms
(leaving Estherid out of consideration) belonging to the genera
Entomis, Leperditia, and Beyrichia. In the Carboniferous

Fig. 100. — Fossil Ostracode Crustaceans : — a Primitia strangitlata, Lower Silurian ;
b Primitia Logani, Lower Silurian ; c Beyrichia Klaedeni, Upper Silurian ; d d'
CytJierella inflata, Carboniferous; e Leperditia Anna, Lower Silurian ; f Leperditia
Canadeusis, Lower Silurian ; g Beyrichia impendens, Upper Silurian ; h Beyrichia
subarcuata, Carboniferous ; i Candona Tateana, Carboniferous. All enlarged.

Rocks no less than fifteen genera have been detected. Of
these the genera Leperditia, Bairdia, Beyrichia, Cythere, Cypri-
dina, Cypridella, and Entomis are the most important. The
Leperditia were formerly referred to the genus Cypris, the
species of which are exclusively fresh-water in their habits. It
is noticeable, however, that some of the Carboniferous species
have been referred, apparently on good grounds, to the recent
genus Candona, all the forms of which inhabit fresh water. It
is also noticeable that the genera Beyrichia and Entomis
appear to die out in the Carboniferous Rocks, and have not
been detected in any later formations. In the Permian Rocks
we have only the genera Bairdia, Cythere, and Cypridina, of
which the two former are represented by living forms. In the
Secondary and Tertiary deposits, remains of Ostracode Crust-
aceans are abundant, often occurring in myriads in certain
strata, to which they sometimes impart a fissile character. The
chief genera which are represented in Mesozoic and Kainozoic
time, are Cypris, Candona, Bairdia, Cythere, Cytherella, and
Cypridina, all of which are represented by living species at the
present day."'

r The facts here summarised are mainly drawn from the Memoirs of
Professor Rupert Jones, and his admirable Monographs on the Ostracoda,
published by the Paloeontographical Society.

158

ANNULOSA.

ESTHERIA. — Before going on to the order PhyHopoda, we
may briefly notice here the little fossils belonging to the genus
Estheria^ as these are in some respects closely allied to the
Ostracoda, or are intermediate between these and the true
Phyllopods. Upon the whole, however, Estheria would seem
to be most nearly allied to the living Limnadia, in which case
it would be rightly referred to the Phyllopoda. The body in
Estheria is enclosed in a bivalve carapace (fig. 101, A), and

Fig. 101. — A, carapace of Estheria ovata, magnified six diameters, Trias ; B, cara-
pace of Leaia Leidyi, magnified five diameters, Lower Carboniferous (after Rupert
Jones).

the feet are foliaceous. The valves of the carapace have a
well-marked beak or " umbp," 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, for which they have often been mis-
taken. The valves are usually sub-triangular, ovate, or sub-
quadrate in form, and they possess a horny texture.

The living Esthericz 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 presumption that the deposits in which fossil
Esthericz occur were deposited in fresh or brackish water ; but
they not uncommonly occur in conjunction with undoubted
marine remains. They appear, on the whole, to occur most
frequently in those accumulations that " have been decidedly
the result of brackish-water inundations, and of more perman-
ent lagoons " (Jones). Fossil Estherice 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 genus Leaia (fig. 101) is very nearly allied to Estheria^

CRUSTACEA. 159

and comprises small Bivalved Crustaceans, with " dark, horny,
sub-quadrate valves, obliquely ridged from umbo to angles,
and ornamented with distinct lines of growth parallel with the
border" (Jones). Leaia is a very widely distributed genus,
but all the known species belong to either the Carboniferous
or Permian Rocks.

ORDER PHYLLOPODA.

Crustacea, mostly of small size, the carapace protecting the head
and thorax, or the body entirely naked. Feet numerous, never less
than eight pairs, mostly foliaceous or leaf like, branchial in function.

Most of the living Phyllopods are inhabitants of fresh waters,
but some live in the sea (Nebalia\ and others affect waters
which are abnormally salt (Artemia). The two most interest-
ing recent forms, as bearing on fossil examples of the order,
are Limnadia and Apus, both of which live in fresh water. In
Limnadia the body is enclosed in an oval bivalve carapace,
and there are from eighteen to thirty pairs of membranous
leaf-like feet. In Apus the carapace is clypeiform, and protects
a considerable portion of the abdomen ; and there are sixty
pairs of feet, of which all but the first pair are foliaceous.

Leaving out of sight the genera Estheria and Leaia, the
Phyllopods are almost exclusively palaeozoic in their distribu-
tion, and are chiefly, though not exclusively, known by their
carapace- valves. The best known genera are the Hymenocaris
of the Lingula flags, the Caryocaris of the Skiddaw slates, the
Peltocaris and Discinocaris of the Lower Silurian, the Ceratio-
caris of the Upper Silurian, and the Dithyrocaris of the Car-
boniferous Limestone. These forms have a general resem-
blance to one another, and are believed to be most nearly allied
to the recent Apus, whilst they are exclusively palaeozoic. The
genus Aspidocaris, however, is allied to the preceding, and is
found in the Triassic period.

In Hymenocaris (fig. 102, b} the carapace is comparatively
large, sub-triangular, apparently not bivalved ; there are nine
free abdominal segments, and the last carries three pairs of
unequal lanceolate appendages. In Caryocaris the carapace is
bivalved, pod-shaped, and truncated behind, and the last ab-
dominal segment carries three spines. In Peltocaris and Dis-
cinocaris (fig. 102, c.} the carapace is rounded, with concentric
lines of growth, a dorsal furrow being present in the former,
but wanting in the latter. In both there is commonly a wedge-
shaped indentation in front, caused by the separation from the
carapace of the anterior portion of the head. In Gtratiocaris,

i6o

ANNULOSA.

again, the carapace appears to be bent, but not divided or
hinged, along the dorsal line, and its shape is pod-like (fig.
102, a), with an abrupt posterior truncation. The surface of
the carapace is marked with " fine, obliquely longitudinal, im-
bricated striae " (M'Coy).

Fig. 102. — Palaeozoic Phyllopods : — a Ceratiocaris papilio, Upper Silurian (Salter).
b Hyntenocaris vermicauda, Upper Cambrian (Salter). c Discinocaris Browniana,
Lower Silurian (Original), d Peltocaris aptychoides, Lower Silurian (Woodward).

ORDER TRILOBITA.

Crustaceans in which the body is usually more or less distinctly
trilobed; there is a cephalic shield, usually bearing a pair of sessile
compound eyes ; the thoracic somites are movable upon one another,
and are very variable in number ; the abdominal segments are
coalescent, and form a caudal shield ; there is a well-developed
upper lip or " hypostome"

As regards the general structure of the Trilobites, the body
was protected by a well-developed chitinous shell or " crust,"
which covered the whole dorsal surface of the body, and on
which no appendages have ever been discovered except the
eyes. The under surface of the body must, in many genera at

CRUSTACEA.

161

any rate, have been flexible and membranous; since many
species have the power of rolling themselves up into a ball like
the recent wood-lice (Oniscus). Other Trilobites, however,
never seem to have possessed any power of rolling up. The
dorsal crust usually exhibits more or less markedly a division
into three longitudinal lobes (fig. 103), from which the name

Fig. 103. — Morphology of Trilobites. i. Angelina Sedgwickii, Upper Cambrian.
2. Diagram of a Trilobite (after Salter) : a Glabella with its furrows; bb Free cheeks,
bearing the eyes (po) ; c c Fixed cheek, including the eye-lobe (d)', ee Facial suture.

of the order is derived. In some cases, however, as in the
genera Homalonotus and Illanus, this trilobation is only ob-
scurely marked. The crust exhibits a well-marked division
into three regions, which are commonly found detached and
separate from one another. These three regions are — i, a
cephalic shield; 2, a variable number of movable "body-rings"
or thoracic segments ; and 3, a caudal shield or "pygidium."

The cephalic shield or buckler (figs. 103 — 107) 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 portion of the
cephalic shield is usually elevated above the remainder. It is
termed the " glabella," and it protected the region of the
stomach. The form of the glabella varies a good deal.
Usually it is widest in front (fig. 105), but its width may be
nearly uniform (fig. 106), or it may be widest posteriorly, and
contracted in front, as in Calymene (fig. 107). 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 divided
into lobes by grooves, which originate in the axal furrows, and
pass inwards towards the middle line (fig. 103, 2). These

L

1 62

ANNULOSA.

furrows mark the position of the segments which compose the
glabella, and they are 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 Illanus (fig. 109), the gla-
bella is very indistinctly marked
off from the rest of the shield.

At each side of the glabella,
and continuous with it, is a small
semicircular area, which is
termed the " fixed cheek " (fig.
103, 2). 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. 103, 2, e e).
No such peculiar line of division
is known to exist in any recent
Crustacean ; but there is a faint
indication of it in Limidus, 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, 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 — i, ttye glabella
and fixed cheeks ; and 2, the amalgamated free cheeks. In
other cases, the facial sutures, instead of joining in front of the
glabella, are continued forward, till they cut the anterior mar-
gin 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 Trinudeus, Microdiscus, and
Agnostus), the facial suture is absent.

The posterior angles of the free cheeks are very commonly
prolonged into longer or shorter spines, and they bear the
eyes. The eyes are compound, and consist of an aggregation

Fig. 104. — Pliacops (Dalmanites)
Umiilurus, Upper Silurian.

CRUSTACEA.

163

of facets, covered by a thin cornea. They are generally cres-
centic or reniform in shape, and are invariably sessile, in the
sense that they are never supported upon movable stalks. In
some cases, however, they are carried upon longer or shorter
prominences. The eyes differ much in size, and they are
wanting in a few forms, such as the little Agnostt.

Fig. 105. — Bronteus hinatus.

Fig. 106. — Cheirurus pleur-
exanthemus.

Fig. 107. — Calymene
B lumeiibachii.

Behind the cephalic shield comes the thorax, composed of
a variable number of segments which are not soldered to-
gether, but are capable of more or less movement upon each
other. The amount of movement thus allowed varies, but in
several genera (e.g., Calymene and Jllcemis) 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 (Agnos-
tus\ to as many as twenty-six (Harpes ungula). Ordinarily the
thorax (fig. 108) is strongly trilobed, and each body- ring ex-
hibits the same trilobation, being composed of a central, more
or less convex portion, called the " axis," and of two flatter
side-lobes, termed the " pleurae." The pleurae are in one piece
with the axis, but are separated from it by a more or less pro-
nounced groove, the "axal furrow." Each pleura is grooved
longitudinally by a deep sulcus, and in many genera the ends
of the pleurae are furnished with facets, which have smooth
surfaces, and slide under the preceding pleura, in the act of
rolling up. In some genera, as in Illcenus (fig. 109), the axis
is very broad, the axal furrows are not marked, and the trilo-

164

ANNULOSA.

bation of the thorax becomes very indistinct This is likewise
the case, but to a less extent, in the genus Homalonotus.

Fig. 108. — Asapkns Canadensis (Chap-
man), Lower Silurian.

Fig. 109. — Illteiius
iiMsis (Murchison), Lower
Silurian.

The caudal shield or "pygidium" — commonly called the
" tail " —is composed of a greater or less number of segments
anchylosed or amalgamated. Commonly, the pygidium is tri-

Fig. no. — Glabella and pygidium of Dikelocepiialus magnificus, Quebec Group
(Upper Cambrian). After Billings.

lobed (fig. no), like the thorax, and consists of a central
elevated " axis '5 and of a marginal " limb." The limb is

CRUSTACEA.

I65

separated from the axis by axal furrows, and usually exhibits on
its surface the lines which indicate the component pleurae, as
well as the longitudinal furrows on the faces of these. The ex-
tremity of the pygidium is sometimes simply rounded; but it
may be prolonged into a shorter or longer spine or "mucro,"
and the ends of the pleurae may also be extended into spine-
like projections (fig. no).

Until recently, the only structure which had been discovered
on the under surface of any Trilobite was a broad plate situated
in front of the mouth, and doubtless corresponding with the
upper lip — " labrum " or " hypostome " — of living Crustaceans
(fig. in). The form of this hypostome very closely resembles
that of the lip-plate of the recent
Apus, one of the Phyllopods. Quite
recently, Mr Henry Woodward has
described a specimen of Asaphus
platycephalus, in which, in addition to
the lip-plate, there is a jointed fila-
ment (fig. in,/), apparently springing
from a maxilla, and being the re-
mains of a maxillary " palpus." Mr
Woodward, who is one of the highest ,,.

... ' . . „ Fig. TCI i. — Buccal organs of

living authorities upon the Crustacea, Asaphus piatycepiiaius. After

concludes that there is no reason to

doubt that Trilobites possessed an-

tennas and antennules, mandibles, and maxillae, and foot-jaws ;

though, with the exception of the above, no traces of these

organs have ever been detected.

Also recently, a specimen of the large Trilobite, Asaphus
platycephalus (fig. 112), has been described by Mr Billings as
possessing organs which this distinguished palaeontologist re-
gards as being the remains of legs. The structures in question
are in the form of eight pairs of apparently jointed appendages,
which correspond with the eight segments of the thorax, arising
near the middle line, and curving forwards. Mr Henry Wood-
ward corroborates the view propounded by Mr Billings, that
these structures are of the nature of ambulatory legs. Pro-
fessors Dana and Verrill, on the other hand, regard these re-
mains as being "the semi-calcified arches in the membrane
of the ventral surface, to which the foliaceous appendages or
legs were attached."

Whichever view be adopted as to the nature of this specimen,
it seems tolerably certain that most Trilobites cannot have
possessed limbs which were furnished with a chitinous exo-
skeleton, and were thus capable of being preserved in a fossil

i66

ANNULOSA.

condition. The great abundance of Trilobites as fossils, and
their excellent preservation, as a general rule, render it pro-
bable that the limbs of most were of a soft and fleshy nature.

At the same time it is
very possible that some
forms were possessed of
chitinous jointed limbs,
as great variations exist
in the character of the
appendages even within
the limits of a single
order. The general view
which has up to the time
of this discovery been
held is, that the body of
the Trilobite occupied
the median lobe of the
crust, commencing with
the glabella in front, and
terminating with the py-
gidium behind, whilst the
axial lobes protected a
series of delicate, mem-
branous respiratory feet.
It is supposed, however,
by Mr Woodward, that
the branchiae were borne

Fig. 112. — Asaphus platycefkalus, Lower Silurian.

on the under surface of
the caudal shield.

As regards the systematic position of the Trilobites, they
have very generally been placed in the neighbourhood of the
Phyllopoda, or of the much higher order of the Isopoda. They
have been placed near the Phyllopods chiefly from the posses-
sion of numerous (not definite) body-rings, from the resem-
blance of their hypostome to the lip-plate of the Phyllopodous
genus Apus, and from their supposed possession of membran-
ous gill-feet. The recent discoveries, however, of Messrs
Billings and Woodward would lead to the belief that the Tri-
lobites, if not actually belonging to the Isopoda, have at any
rate closer affinities with this order than with any other. They
agree with the Isopods in the possession of sessile compound
eyes, in having the abdominal somites coalescent, and in some-
times possessing the power of rolling themselves up into a
ball. They differ, however, from the Isopods in the very im-
portant character that the thoracic segments of the latter are

CRUSTACEA. l6/

always definite and are almost invariably seven in number. In
the meanwhile, therefore, it is safest to regard the Trilobita as
a peculiar order, the exact position of which in the Crustacean
class is still undetermined.

The general facts as to the distribution of the Trilobita in
past time are soon told. The Trilobites are exclusively Palaeo-
zoic, their range extending from the Upper Cambrian to the
Lower Carboniferous. If the Palceopyge Ramsayi of the Long-
mynd beds be a Trilobite, then the order has its commence-
ment in the Lower Cambrian. In the Upper Cambrian Rocks,
and especially in the strata which constitute the " Menevian
Group " of Salter, and the " Primordial Zone " of Barrande, is
a peculiar group of forms commonly spoken of as the " Prim-
ordial Trilobites." These belong mostly to the two families
'Agnostid(z)tt\&(Olenida% and to the genera Agnostus, Para-
d&xides, Olenus, Dikelocephalus, Conocoryphe, Angelina, Ellipso-
cephalus, &c.

Many of these forms are distinguished by degraded char-
acters, such as the absence of eyes, the want of the facial
suture, the segmentation of the glabella, or the multiplication
or diminution of the number of body-rings. It should not be
omitted to be noticed that the singular tracks which have been
described from the Potsdam Sandstone (Upper Cambrian) of
Canada, under the names of Prjjtichnites and Climactichnites,
are believed with good reason to be the tracks of Trilobites.
In the Lower and Upper Silurian Rocks the Trilobites attain
their maximum of development, the leading families being the
Asaphidck, Phacopidcs, Trinudeidce, Cheirurida, and Calymenidcfa 3
and the chief genera being Asaphus, Ogygia, Phacops, Trinu-
deus, Ampyx, Cheirurus, Encrinurus, Calymene, and Homalo-
notus. In the Devonian Rocks, again, Trilobites are tolerably
abundant, though less so than in the preceding series. The
commonest Devonian genera are Phacops, Homalonotus, and
Bronteus. Lastly, the order seems to die out before the close
of the Carboniferous period, being represented in the Carbon-
iferous Limestone solely by the three genera, Phillipsia, /*
Bradiymetopus, and Griffithides.

The following gives the leading characters of the more im-
portant families of Trilobites, with a few of the chief genera in
each family, and the range of the group in time : —

i. AGNOSTID^E. — Characterised by their small size, the head
and tail being covered by nearly equal and similar shields, and
the reduction of the body-rings to two in number (fig. 113).
There are no eyes, and the facial suture is wanting. The
family includes only one well-marked genus, viz. Agnostus,

1 68

ANNULOSA.

which ranges from the Upper Cambrian to near the summit
of the Lower Silurian Rocks.

2. OLENID^E OR PARADOXID^E. — Character-
ised by having long bodies, with numerous
free thoracic segments (from eight to twenty-
three in number). The caudal shield is small,
and generally consists of very few segments.
The pleurae are mostly prolonged into longer
or shorter spines, which are directed back-
wards. The family includes some of the
largest of the Trilobites, and is mainly char-
acteristic of the " Primordial Zone " (Upper
Cambrian). It occurs, however, in the lower

Fig. 114. — Parado.rides Micntac (?), Upper Cambrian. After Dawson.

Silurian, but appears to die out in the Caradoc period. The

CRUSTACEA.

169

chief genera are Olenus, Paradoxides, Dikelocephalus, Cono-
coryphe, Sao, Angelina, and Ellipsocephalus.

3. AsAPHiDj«. — Large Trilobites, generally oval, and never
furnished with spines or tubercles on 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, sometimes more, rarely
fewer (six in ^Sglina).

The family Asaphidce is characteristically Lower Silurian
in its distribution, commencing by a few forms in the Upper
Cambrian, and being hardly at all represented in Upper Silu-
rian strata. The most important genera are Asaphus, Ogygia,
Illcenus, ^Eglina, Barrandia, and Psiiocephalus.

4. TRINUCLEID^E. — Cephalic shield large, the posterior angles
of the cheeks prolonged into long spines. Body-rings- six
(sometimes five ?) in number. Facial suture sometimes absent

Fig. 115. — Triune leus Pougerardi, Lower- Silurian.

(Trimicleus) ', eyes sometimes wanting (Ampyx). The Trinu-
deidtz are exclusively Lower Silurian, though there are traces
of their existence in the higher portion of the Upper Cambrian.
The only genera referred to this family are Trinudeus, Ampyx,
and Dionide.

5. CHEIRURID^E. — Cephalic shield with the facial sutures
terminating on its exterior margins. Body-rings eleven.
Pleurae with free extremities. Caudal shield of few segments,
the ends of these being free. The family extends from the
Upper Cambrian to the Devonian, but it attains its greatest

170

ANNULOSA.

development in the Silurian period. The chief genera are
Cheirurus, Amphion, Sph&rexochus, Staurocephalus, Deiphon,
Encrinurus, and Cybele.

6. CALYMENID^:. — Crust granulated, often tuberculated.

Body-rings thirteen in number.
Facial sutures ending at the
posterior angles of the cephalic
shield. Body sometimes very
indistinctly trilobed (Homalono-
tus). The family appears to
commence at the base of the
Lower Silurian series or at the
summit of the Upper Cam-
brian, and ranges into the De-
vonian. The only genera are
Calymene and Homalonotus,
of which the former is mark-
edly trilobed, but the latter
very indistinctly so (fig. 116).
The best -known species are
Calymene Blumenbachii, which
ranges from the Caradoc (Lower
Silurian) to the Ludlow Rocks
(Upper Silurian), and Homa-
lonotus delphinocephalus, which
is a well-known Upper Silurian
Trilobite.

7. PHACOPID^:. — "Eyes
largely faceted, the cornea con-
vex over each facet, forming a
granulated, not a smooth eye.
Facial suture ending posteri-
orly on the outer margin of
the cheek. Thorax with eleven
rings " (Salter). This family includes the single genus, (phacops,
divided into the sub-genera Trimerocephalus, Phacops, Acaste,
Chasmops, Dalmania, and Cryphceus. The family Phacopida
ranges from the base of the Lower Silurian series (perhaps from
the Upper Cambrian) to the summit of the Devonian series.
Amongst the Upper Silurian . species may be mentioned
Phacops caudatns and P. Downingitz, as well-known fossils ;
whilst P. latifroiis is a familiar and widely-distributed Devonian
species.

8. LICHAD/E. — Cephalic shield small, the facial sutures
cutting its outer margins. Glabella large, deeply furrowed.

Fig. 1 16. — Homalonotns delphinoce-
plialus. Upper Silurian.

CRUSTACEA. 17 1

Body-rings eleven in number. Pygidium with an undefined
axis and broad limb. The family includes the single genus
Lichas, and extends from the Lower Silurian into the De-
vonian.

9. PROETID/E. — Cephalic shield with the facial sutures not
uniting in front of the glabella. Body-rings nine or ten in
number. Axis elongated. This family ranges from the Lower
Silurian to the Carboniferous. Besides Proetus, this family in-
cludes Phillipsia and Griffithides.

10. ACIDASPID^E. — Surface ornamented. Body-rings from
eight to ten in number. The ends of the pleurae extended into
spines, and directed backwards. Pygidium of from two to
three segments, small, furnished with prominent spines. The
genus Acidaspis ranges from the Lower Silurian into the De-
vonian.

11. BRONTEID^E. — Body-rings ten in number. Pygidium
large, the axis extremely short, the margin entire. The family
includes only the genus Bronteus (fig. 105), and is confined to
the Upper Silurian and Devonian Rocks.

12. HARPEDID^E. — Cephalic shield horse-shoe-shaped, its
lateral angles greatly prolonged. Facial suture cutting the
exterior margin of the buckler. Body-rings numerous, some-
times no less than twenty-six in number. Pygidium small.
This family comprises only the genus Harpes, all the species
of which belong to the Lower Silurian, Upper Silurian, and
Devonian.

13. CYPHASPID^E. — Cephalic shield with the posterior angles
usually prolonged into spines, the facial suture cutting its ex-
terior margins. Body-rings from ten to twenty-two. Crust
spinulose or pitted. The chief genera of this family are
Cyphaspis and Aulacopleura (Arethusind), the former ranging
from the Lower Silurian to the Devonian, the latter exclusively
confined to the Silurian series.

ORDER MEROSTOMATA.

Crustaceans •, often of large size, in which the mouth is furnished
with mandibles and maxilla, the terminations of which become
walking or swimming feet, or organs of prehension (figs. 117,
1 1 8).

The order Merostomata comprises the two sub-orders of the
Xiphosura and Eurypterida. The former appears to have
commenced its existence in the Upper Silurian period, and is
represented at the present day by the Limuli or King-crabs.
The latter is wholly extinct, and is exclusively Palaeozoic, none

1/2

ANNULOSA.

of its members being known out of the Silurian, Devonian, and
Carboniferous formations.

Fig. 117. — Xiphosura. Limnhtspoly-
phemus, viewed from below, c The
cephalic shield carrying the sessile eyes
upon its upper surface ; o " Operculum,"
covering the reproductive organs ; b
Branchial plates ; a First pair of anten-
nae (antennules) ending in chelae. Below
these is the aperture of the mouth sur-
rounded by the spiny bases of the re-
maining five pairs of appendages, which
are regarded by Woodward as being
respectively, from before backwards, the
great antennas, the mandibles, the first
maxillae, the second maxillae, and a pair
of maxillipedes. All have their extremi-
ties chelate.

Fig. 118. — Eurypterida. Ptery-
gaius Anglicus, restored (after H.
Woodward), c c Chelate antenna? ;
o o Eyes, situated at the anterior mar-
gin of the carapace ; m m The mandi-
bles, and the first and second maxillae ;
n n The maxillipedes ; the basal mar-
gins of these are serrated, and are
drawn as if seen through the metas-
toma or post-oral plate, which serves
as a lower lip. Immediately behind
this is seen the operculum or thoracic
plate, which covers the two anterior
thoracic somites. Behind this are five
thoracic and five abdominal somites,
and lastly, there is the telson (/).

SUB-ORDER I. — EURYPTERIDA.

" Crustacea with numerous, free, thoracico-abdominal segments,
the first and second (?) of which bear one or more broad lamellar
appendages upon their ventral surface, the remaining segments
being devoid of appendages ; anterior rings united into a carapace,
bearing a pair of larval eyes (ocelli] near the centre, and a pair of
large, marginal, or sub-central eyes ; the mouth furnished with a
broad post-oral plate, or metastoma, and five pairs of movable

CRUSTACEA. 173

appendages, the posterior of which form great swimming-feet ; the
telson, or terminal segment, extremely variable inform; the in-
tegument characteristically sculptured" — (Henry Woodward.)

In the typical Eurypterids, such as Pterygotus (fig. 118) and
Eurypterus, the anterior portion of the body is covered by a
buckler or carapace, which bears a pair of minute larval eyes,
and a pair of large compound eyes placed marginally or sub-
centrally. On the under surface of the carapace are five pairs
of appendages. The first pair of these is usually regarded as
representing the antennae. The appendages of this pair are
mostly chelate, or converted into nipping-claws, but they are
sometimes simple, and they sometimes are spinous towards
their bases, and officiate as masticatory organs (Eurypterus
and Slimonia). The next three pairs of appendages are simply
pointed spinous organs (" pedipalrjs^"), but the last pair is
sometimes converted into rowing-organs (Stylonurus). The
last pair of appendages constitute two greatly-developed
swimming-feet, the bases of which are furnished with spines,
and form powerful jaws. The bases of these jaw-feet are covered
by a greatly-developed post-oral plate or " metastoma." Be-
hind the head come thirteen free segments, counting the telson
as one. The first two of these, immediately behind the cara-
pace, are covered below by a thoracic plate or " operculum,"
which doubtless protected the reproductive organs. The
other somites carry no appendages, though it is probable that
some of them bore membranous branchiae. The " telson " or
terminal segment of the abdomen (fig. 118, /), is sometimes
lanceolate or bilobate, as in Pterygotus and Slimonia, or some-
times narrow and sword-shaped, as in Eurypterus and Stylon-
•itrus. The surface of the crust is sculptured over the greater
part of its extent, with characteristic markings, which look
something like the scales of an ordinary Bony fish. These
" scale-marks/' however, are often wanting over parts of the
surface.

The Eurypterids range from the Upper Silurian, where they
attain their maximum, through the Devonian, into the Car-
boniferous Rocks, where they appear to die out. Traces, how-
ever, of these large Crustaceans are by no means wanting in
the Lower Silurian, though as yet undescribed. Of the typical
genera, Pterygotus extends from the Upper Silurian to the
Upper Devonian, and species of this genus seem to have
attained a gigantic size. (Pterygotus Anglicus is calculated to
have reached a length of six feet.) Slimonia is Upper Silurian,
and Stylonurus is both Upper Silurian and Devonian. Euryp-
terus is not known in the Silurian, but is represented by many

1/4 ANNULOSA.

species in the Devonian, and extends into the Carboniferous
Rocks. Hemiaspis, with only nine segments and the telson
behind the carapace, is exclusively Upper Silurian. Lastly,
Pseudoniscus, with the same number of free segments, is found
in the passage-beds between the Upper Silurian and Devonian.
In conclusion, it is interesting to note that these ancient
Crustaceans present many larval features, resembling the larvae
of the Decapoda, especially in the fact that the hinder portion
of the body is composed of free segments, which carry no
appendages.*

SUB-ORDER II. — XIPHOSURA (Ptzrilopoda).

" Crustacea having the anterior segments welded together to
form a broad convex buckler, upon the dorsal surface of which are
placed the compound eyes and ocelli; the former sub-centrally, the
latter in the centre in front. The mouth is furnished with a small
labrum, a rudimentary metastoma, and six pairs of appendages.
Posterior segments of the body more or less free, and bearing upon
their ventral surfaces a series of broad lamellar appendages; the
telson, or terminal segment, ensiform" — (Henry Woodward.)

The only living members of the Xiphosura are the Limuli,
commonly known as King-crabs or Horse-shoe Crabs. The
anterior portion of the body is covered by a broad horse-shoe-
shaped buckler (fig. 1 1 7), the upper surface of which bears a pair
of larval and a pair of compound eyes. On the lower surface
of the carapace is placed the aperture of the mouth, surrounded
by six pairs of limbs, the bases of which are spinous, and
officiate as jaws, whilst their terminations are converted into
chelae or nipping-claws. The first pair of appendages is placed
in front of the mouth, and represents the antennae, so that the
antennae of the King-crabs are chelate. Behind the cephalic
buckler comes a second shield, composed of six amalgamated
segments, below which are carried the reproductive organs and
branchiae, the former protected by a thoracic plate or " oper-
culum," the latter borne by five pairs of lamellar appendages.
Lastly, articulated to the posterior margin of the abdominal
shield, is a long sword-like spine or "telson" (fig. 117, /).

The Xiphosura seem to have commenced existence in the
Upper Silurian period, where they are represented by the
Neolimulus falcatus of Mr Henry Woodward. With this ex-

* The student desirous of fuller information on this subject, as on the
Xiphosura also, should consult the excellent memoirs by Mr Henry
Woodward, and especially his monograph of the Merostomata, published
by the Palseontographical Society.

CRUSTACEA.

175

ception, however, no Limuloid Crustaceans are known till the
Carboniferous Rocks are reached. Here we have the two
genera Prestwichia and Belimirns, the former represented by
two, the latter by four species. In Prestwichia (fig. 119), the
thoracic and abdominal segments are not separable from one
another, and the former
are anchylosed or amal-
gamated, as well as the
latter. In Belinurus there
are five thoracic and three
abdominal segments (as
in the preceding), but the
thoracic somites are free
and movable, whilst the
abdominal ones are an-
chylosed. The only other
genus of the Xiphosura
is {Limulud itself. This
genus is represented by
forms doubtfully here re-
ferable as early as the
Permian Rocks. An-
other dubious form oc-
curs in the Trias. Seven

species have been described from the Lithographic slates of
Solenhofen (Middle Oolites). One doubtful form occurs in
the Chalk, a single Tertiary species has been described, and
four species are known as existing at the present day.

Fig. 119. — Prestwichia (Limulus) rotundata,
Coal-Measures.

CHAPTER XVI.

CR USTA CE A— Concluded.
MALACOSTRACA.

THE Malacostracous Crustaceans are distinguished by the
possession of a definite number of body-segments, seven
somites generally going to make up the thorax, and an equal
number entering into the composition of the abdomen (count-
ing the telson as a somite). The Malacostraca are divided
into two primary sections, termed respectively Edriophthal-

1/6 ANNULOSA.

mata and Podophthalmata, according as the eyes are sessile or
are supported upon eyestalks.

DIVISION A. EDRIOPHTHALMATA. — The division of the
Sessile-eyed Crustaceans comprises those Malaco strata in
which the eyes are not supported upon stalks or peduncles,
and there is mostly no carapace. The eyes are sometimes
compound, sometimes simple, and are placed on the sides of
the head. The head is almost always distinct from the body ;
and there are typically seven pairs of feet in the adult.
(Hence the name of Tetradecapoda applied to this division by
Agassiz.) The Edriophthalmata include the orders Lcemodi-
poda, Amphipoda, and Isopoda, of which the two latter are
alone known in a fossil condition, whilst the last is the only
one of any importance.

ORDER AMPHIPODA.

Small Crustaceans in which the respiratory organs have the
form of membranous vesicles attached to the bases of the thoracic
limbs. Abdomen well developed, and composed of seven segments.
Seven pairs of thoracic limbs.

The most familiar recent forms of the Amphipoda are the
" fresh -water Shrimps" (Gammarus\ the Sand-hoppers (Tali-
trus), and the Shore-hoppers (Orchestid). The oldest repre-
sentative of the order is a doubtful form, which has been
described by Mr Woodward from the Upper Silurian Rocks
under the name of Necrogammarus. The Carboniferous genus
Gampsonyx has been referred here, but is more properly placed
amongst the Stomapoda. There are no other fossil Amphipods
of any importance.

ORDER ISOPODA.

Crustaceans in which the head is distinct from the segment
bearingthe first pair of feet. The eyes are compound and sessile.
There are usually seven pairs of thoracic appendages, borne upon
seven movable segments. The animal sometimes has the power
of rolling into a ball. The abdominal segments are coalescent,
and form a broad caudal shield, beneath which the branchicz are
carried.

Of the living Isopods, some (Bopyridce) are parasitic in
their adult condition upon other Crustaceans. Others, such as
the common Wood-lice (Oniscus], live habitually upon the land.
Others, again, are littoral in their habits, or frequent the sea.

The oldest known Isopod is a large form which has been
described by Mr Henry Woodward from the Devonian Rocks

CRUSTACEA.

177

under the name of Prcearcturus. It is believed to resemble

the living Arcturus Baffinsii. From the Carboniferous Rocks

an Isopod has been described under

the name of Acanthotelson. In the

Permian Rocks we have the genus

Prosoponiscus, which, however, has

been referred to the Amphipoda.

In the Upper Oolites (Purbeck

beds) occurs the Arch&oniscus

Brodiei (fig. 120), often in large

numbers. In the Chalk occurs the

genus Palaga, which ranges to the

Fig. ™>.—Arch<roniscus
Miocene Tertiary. Lastly, several £ fossil isopod, from the Upper

J . •> ' Oolites.

forms, some of which are of very

uncertain affinities, have been described from the Tertiary

Rocks.

DIVISION B. PODOPHTHALMATA. — The members of this
division are Malacostracous Crustaceans, in which the eyes
are compound, and are supported upon movable stalks or
peduncles, and the anterior portion of the body (cephalo-
thorax) is protected by a carapace. In this division are in-
cluded the two orders of the Stomapoda and Decapoda.

ORDER STOMAPODA.

Stalk-eyed Crustaceans in which there are generally from six
to eight pairs of legs, and the branchm are not enclosed in a cavity
beneath the thorax, but are either suspended beneath the abdomen,
or, more rarely, attached to the thoracic legs.

Of the living Stomapods the best-known forms are the
Locust-shrimps (Squilla), the Glass-shrimps (Erichthys], and
the Opossum-shrimps (Mysis). The earliest-known example
of the Stomapoda is the Gampsonyx fimbriatus of the Carboni-
ferous Rocks ; and the Pygocephalus Couperi of the same
formation is also probably to be referred to this order. The
genus Squilla itself does not appear to be represented in rocks
older than the Eocene Tertiary.

ORDER DECAPODA.

Crustaceans with Jive pairs of ambulatory legs, of which the
first pair is modified to form nipping-claws, some of the other
pairs behind this being often chelate as well. There is a large
cephalothoracic carapace, and the branchm are contained in cavi-
ties at the sides of the thorax.

M

1/8 ANNULOSA.

The order Decapoda includes the highest forms of the entire
class of the Crustaceans, such as the Lobsters, Hermit-crabs,
and Crabs, and it is divided into the following three tribes :—

TRIBE I. MACRURA. — The members of this tribe, such as
the Lobsters, Shrimps, Prawns, and Cray-fish, have a long and
well-developed abdomen, the posterior extremity of which
forms a powerful natatory organ or caudal fin. This is con-
stituted by a greatly-expanded pair of natatory appendages
(" swimmerets ") borne upon the last segment but one of the
abdomen, between which is placed the last segment or " tel-
son."

The Macrurous Decapods are unquestionably of a lower
type than the Brachyurous Decapods or Crabs ; so that it is
no matter of surprise to find that the former, so far as is
known, have enjoyed a vastly higher antiquity than the latter.
The Brachyura are not known in deposits older than the
Oolites. The Macrura, on the other hand, were in existence
before the close of the Palaeozoic period. In the Carboni-
ferous formation we have several forms of Prawn-like Crusta-
ceans belonging to the genus Anthrapalcemon (or Anthracopa-
fomori), of which a species is figured below (fig. 121). In

Fig. iz-L.—Anthrapalcemoti Salteri, Carboniferous. (After Salter.)

the Permian Rocks no Macrurous Decapods are known to
occur. In the Trias, examples of the genera Galatea and
Litogaster have been detected, and other forms have been
alleged to occur. In the Jurassic and Cretaceous strata
" Long-tailed " Decapods are extremely abundant, and are
often beautifully preserved. Amongst the more remarkable
of the Jurassic genera may be mentioned Eryon (fig. 122),

CRUSTACEA.

179

which commences in the Lias, but attains its maximum in the
Middle Oolitic strata, being especially abundant in the fine-
grained Lithographic Slates of Solenhofen. In this singular
genus, the carapace is large and broad, and nearly quadrate in
figure, whilst the antennae are very small. Another singular
genus from the Solenhofen Slates is Megachirus, in which the
first pair of legs is enormously elongated, but not terminated
by chelae. In the Cretaceous Rocks are numerous Macrourans,
belonging to the genera Meyeria, Enoploclytia, Hoploparia, &c.
In many parts of the Tertiary series, especially in the London
Clay (Eocene), are numerous remains of Macrura, some of

Fig. 122. — Eryon arctifonnis, Middle Oolites [Solenhofen Slates).

which have been referred, with more or less doubt, to such
living genera as Astacus and Palinurus.

TRIBE II. ANOMURA. — The Anomurous Decapods are dis-
tinguished by the condition of the abdomen, which is neither
so well developed as in the Macrura, nor so rudimentary as in
the Brachyura. The abdomen does not take any part in
locomotion, and does not terminate posteriorly in a caudal
fin. The penultimate segment of the abdomen, however, is
mostly furnished with more or less well-developed appendages.

i So

ANNULOSA.

The best-known living Anomura are the Hermit-crabs or Sol-
dier-crabs (Paguridof), the Crab-lobsters (Porcellatuz), and the
Sponge-crabs (Dromia).

The Anomura are of small importance as fossils. They
commence in the Secondary period, a few forms having been
described from the Oolites, and a greater number from the
Cretaceous Rocks. In the Tertiary period Anomurous Crus-
taceans are not uncommon ; and the genus Pagurus itself
appears to be represented in the Red Crag (Pliocene). The
Dromilites of the London Clay is supposed to be related to
the living Dromia.

TRIBE III. BRACHYURA. — The "Short-tailed" Decapods
or Crabs are distinguished by having a rudimentary abdomen,
which is tucked up beneath the cephalothorax. The carapace
is usually very large, and the extremity of the abdomen is not
provided with any appendages. Most of the Crabs are littoral
in their habits, and have legs formed for walking. Others are
adapted for swimming, and the Land-crabs habitually live
inland.

As before remarked, the Brachyurous Decapods are much
later in their appearance than the Macrura. The oldest

known Crab, at present, is
the Pal&inachus longipes, de-
scribed by Mr Henry Wood-
ward from the Forest Marble
(Lower Oolites). In the
Cretaceous series Crabs are
tolerably abundant, one Cre-
taceous form belonging to
the recent genus Cancer. In
the Tertiary Rocks, and es-
pecially in the London Clay
(Eocene), remains of Crabs
occur in profusion. The
chief Tertiary genera are
Xanthopsis, Xantholites, Cancer (fig. 123), Grapsus, and Ebalia.

Fig. 123. — Cancer \Carpilius) macrochelus,
Tertiary.

ARACHNIDA. l8l

CHAPTER XVII.

ARACHNIDA, MYRIAPODA, AND INSECT A.
CLASS ARACHNIDA.

THE Arachnida are Articulate animals, in which the respiratory
organs, when present, are in the form of pulmonary chambers or
sacs, or of ramified tubes (" trachea ") formed by an involution
of the integument and fitted for breathing air directly ; or both
these organs are combined. In no case are the breathing-organs in
the form of gills. There are four pairs of locomotive limbs, and
there are no limbs attached to the segments of the abdomen. There
is only one pair of antenna, and these are not present as antennce,
btitare converted into jaws or pincers. The head is amalgamated
with the thorax to form a cephalothorax, the eyes are sessile, and
the integuments are more or less chitinous.

The Arachnida are mainly distinguished from the Crustacea*
by the absence of gills, and the general presence of organs
adapted for breathing air directly. They are distinguished
from the Insects by the possession of four pairs of legs, by
never possessing wings, and by having simple eyes, whilst the
head is amalgamated with the thorax. From the Myriapods
they are distinguished by the fact that the legs of the latter are

Fig. 124. — A recent Scorpion (reduced). The great nipping-claws of the Scorpion are not
legs, but are a development of organs belonging to the mouth.

never less than nine pairs in number, whilst the segments of
the thorax are distinct from one another and from the head,

* Van Beneden would refer the Trilobites, King-crabs, and Eurypterids
to the Arachnida, but such a radical change must be supported by over-
whelming evidence before it can be accepted.

182

ANNULOSA.

and the segments of the abdomen carry legs. As is the case
with all the air-breathing Articulates, the remains of Arachnida,
though of considerable theoretical interest, are of very rare
occurrence as fossils. They will therefore be very briefly
noticed here. Of the groups of the Arachnida, the Mites
(Acarida), the Harvest-spiders (Phalangidce), the Book-scorpions
(Pscudoscorpionidoi), the Scorpions (Pedipalpi\ and the true
Spiders (Araneida)t have all been detected in a fossil condition.
The three first groups require no consideration here, being
almost unknown except as occurring in amber, which is a fossil
resin of late Tertiary age. The Scorpions and Spiders both
appear to have come into existence in the Carboniferous period,
and the forms which then existed do not appear to have been
strikingly different from living types.

ORDER PEDIPALPI. — The typical members of this order are
the Scorpions (Scorpionidcz), in which the abdomen is distinctly

Fig. 125. — Cyclophthalmus senior. A fossil Scorpion from the Coal-measures of Bohemia.

segmented, and not separated from the thorax by any marked con-
striction. The respiratory organs are in the form of pulmonary
sacs opening on the under surface of the abdomen by distinct
apertures or " stigmata." The jaws (maxillae) carry an enor-

MYRIAPODA. 183

i

mously-developed pair of nipping -claws (fig. 124), and the
antennae are also converted into chelae. The head carries six,
eight, or twelve simple eyes, and the last joint of the abdomen
(telson), terminates in a hooked claw, perforated for the trans-
mission of the duct of a poison-gland.

As regards their distribution in time, the Scorpions com-
mence in the Carboniferous period, where they are represented
by the genera Eoscorpius and Cyclophthalmus. The most
celebrated fossil Scorpion is the Cyclophthalmus senior (fig. 125)
of the Bohemian Coal-measures. This remarkable form re-
sembles the living Androctonus in having twelve eyes, but
these are disposed in a circle, whereas in the latter there are
six eyes on each side of the head.

ORDER ARANEIDA. — This order includes the true Spiders,
which are characterised by the amalgamation of the head and
thorax into a single mass, to which the generally soft and unseg-
mented abdomen is attached by a constricted portion or peduncle.
Respiration is effected by pulmonary sacs in combination with
air-tubes (tracheae). The head bears from six to eight simple
eyes.

The oldest-known Spiders occur in the Carboniferous Rocks.
In the Coal-measures of Upper Silesia, Romer has described a
Spider, which is allied to the living Lycosa, and which he has
termed Protolycosa anthracophila. Other fossil Spiders have
been described from the Lithographic Slates of Solenhofen
(Middle Oolite), and from the Tertiary Rocks, and a good
many species occur preserved in amber.

CLASS MYRIAPODA.

The Myriapods are Articulate animals in which the head is
distinct, and the remainder of the body is divided into nearly
similar segments. There is no marked boundary-line between the
thorax and abdomen, and the segments of the latter carry locomotive
limbs. There is one pair of jointed antenna, and the number of
legs is always more than eight pairs. Respiration is effected by
air-tubes (trachea).

The living Myriapods are divided into the three orders
Chilopoda, Chilognatha, and Pauropoda. In the Chilopoda are
the Centipedes, characterised by their masticatory mouth, and
carnivorous habits, by the possession of legs in single pairs
(usually from fifteen to forty pairs), and by having antennae of
from fourteen to forty or more joints. In the Chilognatha are
the Millipedes and Gallyworms, characterised by their vege-
tarian habits, by having the segments of the body so amal-

1 84

ANNULOSA.

gamated that the legs appear to be arranged in double pairs,
and by having antennas of six or seven joints. In the Pauro-
poda is the single genus Pauropus, characterised by having
only nine pairs of legs, and the antennae bifid, with three
long multi-articulate appendages.

Fig. 126. — Millipede (lulus).

The oldest-known Myriapods occur in the Coal-measures,
the two best-known] genera being Xylobius and Archiulns.
These genera belong to the order Chilognatha, and comprise,
therefore, vegetable-feeders. In Xylobius (fig. 127) the seg-

Fig. 127. — Xylobius Sigillarice, a Carboniferous Myriapod. (After Dawson.)
a, Natural size ; b, Anterior portion, enlarged ; c, Posterior portion, enlarged.

ments are divided by cross sutures into numerous fragments, in
a manner wholly unknown amongst recent forms. Several
species of this genus are known, of which the one figured
above derives its specific name from the fact that it is found
in the hollow trunks of Sigillaria. It must have possessed,
like the living Gallyworms, the power of rolling itself up into
a ball (Dawson). In the allied genus Archiulus, the segments
are not broken up into fragments, as they are in Xylobius.
The characters of both these genera are so peculiar that they
have been placed in a separate family under the name of
:Archiulidcz.\ Other Myriapods have been discovered in the
Carboniferous Rocks of North America and Britain, and have
been referred to the genus EupJwberia. The true place of

INSECTA. 185

these is uncertain, and they seem to have possessed the
anomalous character of a row of dorsal spines. In the Litho-
graphic Slates of Solenhofen (Middle Oolites) occur the
remains of an animal which is referred to the Myriapoda by
Count Miinster, under the name of Geophilus proavus. Other
Myriapods have been described from Tertiary strata and from
amber.

CLASS INSECTA.

The Insects are Articulate Animals, in which the head, thorax,
and abdomen are distinct from one another. The thorax consists
of three segments, each of which carries a pair of legs. Mostly
there are two pairs of wings borne by the two hinder segments of
the thorax. The abdomen never carries locomotive limbs, but the
last abdominal segments may carry reproductive or sensory appen-
dages. A single pair of jointed antenna is present, and the eyes are
generally compound. Respiration is effected by air-tubes (trachece).

As regards the general distribution of the Insecta in time,
the oldest-known forms are from the Devonian Rocks of North
America. Here occur the remains of several insects which
belong to the order of the Neuropterous Insects (or to the
(jPseudo-neuroptera)). Amongst the most remarkable of these is
the Platephemera antiqua of Mr Scudder (fig. 128). This
species must have attained a
large size — five inches in ex-
panse of wing — and it is re-
garded by Mr Scudder as
being referable to the Ephe-
merida (the May-flies). This
eminent authority, however,
regards it as a "synthetic
type ; " that is to say, as a
form combining peculiarities ,,. w.

~ i • i Fig. 128. — Wing of Platephemera antiqua

Of Structure Which are nOW (after Dawson), Devonian.

only found in different groups.

Three other genera belonging to the Neuroptera have been
described from the Devonian Rocks of North America, under
the names Homothetus, Lithentomum, and Xenoneura.

In the Carboniferous Rocks, the remains of Insects, as might
have been expected, are comparatively more abundant, though
still far from common. In the rocks of this period we have
representatives of the orders Neuroptera, Orthoptera, and Coleop-
terd (Beetles). The Neuroptera are represented by a remark-
able form, which has been referred to the Ephemeridce under
the name of Haplophlebium Barnesii (fig. 129). This insect

1 86

ANNULOSA.

must have attained a size much larger than that of any recent
Ephemerids, measuring fully seven inches in expanse of wing.

Fig. 129. — Haplophlebium Bantesii (after Dawson). From the Carboniferous Rocks
of Canada, a Profile of base of wing.

Another remarkable Carboniferous insect is the Archimulacris
Acadicus of Mr Scudder (fig. 130). It belongs to a group of
Insects which are tolerably abundant in
Carboniferous strata — viz., the Cockroaches;
but it does not agree with any living forms.
In the Secondary period, remains of In-
sects are much more abundant than in any
Palaeozoic deposit The Jurassic Rocks
have yielded the earliest examples of the
orders Hymenoptera and Hemiptera, whilst
the orders Neuroptera, Orthoptera, and
Coleoptera are well represented. In the
Tertiary Rocks, again, the remains of In-
sects become still more abundant, and in
some deposits they are found in the greatest
profusion. Whilst all the above-mentioned orders are repre-
sented, the Tertiary Rocks have also yielded the first traces
(with doubtful exceptions) of the orders Diptera zxi&Lepidoptera.
Amber, which is, geologically speaking, a very modern pro-
duct, has yielded the remains of a vast number of insects, all
of which belong to extinct forms.

The following are the names of the Orders of Insects which
are known in a fossil condition, with the date of their first
appearance : —

Fig. 1 30. — A rchimnl-
acris Acadicus (after
Dawson). From the
Carboniferous Rocks of
Canada.

SUB-KINGDOM MOLLUSCA. l8/

1. Neuroptera (Dragon-flies, White Ants, May-flies, &c.) Devonian.

2. Orthoplera (Cockroaches, Crickets, Locusts, &c.) Carboniferous.

3. Coleoptera (Beetles). Carboniferous.

4. Hymenoptera (Bees, Wasps, Saw-flies, Ants). Jurassic.

5. Hemiptera (Aphides, Field-bugs, Cicadas, &c.) Jurassic.

6. Lepidoptera (Butterflies and Moths). Tertiary.

7. Diptera (House-flies, Flesh-flies, Gnats, Crane-flies, &c.) Tertiary.

8. Thysanura (Spring-tails). Late Tertiary (in amber).

CHAPTER XVIII.
SUB-KINGDOM MOLLUSCA.

POLYZOA.

SUB-KINGDOM MOLLUSCA. — The Mollusca comprise the ani-
mals ordinarily known as Shell-fish, from their commonly pos-
sessing an exoskeleton or shell. The Molluscs are soft-bodied
and destitute of any evident segmentation. Commonly the integu-
ment secretes a hard calcareous or horny envelope, but this may be
absent. The alimentary canal is always present, and never com-
municates with the body-cavity. The nervous system consists
typically of three pairs of ganglia, disposed in a characteristically
scattered manner ; but in the lower forms a single ganglion alone
is present. A heart may or may not be present, and there may or
may not be distinct respiratory organs.

As a matter of course, it is only with the shell of the Mol-
lusca that the palaeontologist has to deal, and those forms
which are destitute of this structure are wholly unknown in the
fossil condition. The special characters of the shell will be
treated of in speaking of the separate classes. In the mean-
while it is sufficient to draw attention to some general consi-
derations. In the Sea-mosses and Sea-mats (Polyzoa], the
animal is compound, and the hard structures secreted by the
colony would not come under the common designation of
" shell." In these cases the investment of the colony would
rather be termed a "polypidom," and when of a horny nature,
it does indeed show a very close resemblance to the " polypary "
of the Sertularian Zoophytes. In the Ascidian Molluscs or
Sea-squirts (Tunicata), the animal is simply enclosed in a
leathery or cartilaginous case, in which calcareous matter is
very rarely developed. Hence we need feel no surprise that
the Tunicaries, with one or two very problematical exceptions,

1 88 MOLLUSCA.

are not known in the fossil state. The Lamp-shells and their
allies (Brachiopoda) possess a bivalve shell, consisting of two
pieces or " valves," which are more or less highly calcareous.
Coming to the higher Mollusca, the true bivalve Shell-fish
(Lamcllibranchiata)) as their common name implies, have also
a bivalve shell ; but this is distinguished from the shell of the
Brachiopods by sufficiently good characters. No Lamelli-
branch is destitute of a shell, and the remains of this class
occur more or less abundantly in all deposits except the most
ancient. The ordinary univalve Shell-fish (Gasteropoda), as
indicated by their common name, have usually a shell com-
posed of a single piece or "valve." In many Gasteropods,
however, there is either no shell at all, when the animal is said
to be "naked " (as in the Sea-slugs), or the shell is quite rudi-
mentary, and is concealed within the mantle (as in the ordin-
ary slugs). In other Gasteropods again (viz. in the Chitons), the
shell is " multivalve," consisting of eight pieces or valves placed
one behind the other. Most, however, of the " multivalve "
shells of older writers are really referable to the Cirripedia.
In the minute Oceanic Molluscs which form the class Ptero-
poda, the animal is sometimes naked, but is more usually
protected by a symmetrical glassy shell, which is always uni-
valve. In the class of the Cephalopoda, finally, great diversity
exists in the character of the skeleton. All the ordinary Cut-
tle-fishes have an internal skeleton, embedded in the mantle,
and not visible externally. This internal skeleton may be
calcareous or horny, and it may be of a very complicated
nature ; but it merely serves to support the soft parts of the
animal, and it does not form an external case in which the
animal lives. In one Cuttle-fish only (viz., the Argonaut or
Paper Nautilus), is there an external shell, but the nature of
this is quite peculiar, and it cannot be compared with the
shell of any of the ordinary Molluscs. In another group of
the Cephalopoda, represented at the present day by the Pearly
Nautilus, there is a well-developed external shell, which is
always composed of a single piece, and is always chambered,
the animal living in the last and largest chamber of the shell.

In composition the shell of the higher Mollnsca consists of
carbonate of lime — usually having the atomic arrangement of
calcite — with a small proportion of animal matter. In the
Pholadida, however, the calcareous matter exists in the allo-
tropic condition of arragonite, which is very much harder than
calcite. As regards their texture, three principal varieties of
shells may be distinguished — viz., the " porcellanous," the
" nacreous/7 and the " fibrous." In the nacreous or pearly

GENERAL CHARACTERS OF MOLLUSCA. 189

shells, as seen in " mother-of-pearl," the shell has a peculiar
lustre, due to the minute undulations of the edges of alternate
layers of carbonate of lime and membrane. The " fibrous "
shells are composed of successive layers of prismatic cells.
The " porcellanous " shell has a more complicated structure,
and is composed of three layers or strata, each of which is
made up of very numerous plates, " like cards placed on edge."
The direction in which these vertical plates are placed, is
sometimes transverse in the central layer, and lengthwise in
the two others ; or longitudinal in the middle, and transverse
in the outer and inner strata.

From their so commonly possessing hard structures, whether
external or internal, no fossils are more abundant or import-
ant than Molluscs. As regards the general distribution of the
Mollusca in time, the sub-kingdom commences its existence in
the Cambrian period, and there is no reason to suppose that
this is really its first appearance. In the Cambrian Rocks,
the classes of the Polyzoa, Brachiopoda, Pteropoda, Gasteropoda,
and Cephalopoda are certainly represented, and the Lamelli-
branchiata existed in Lower Silurian times, if not earlier.
Speaking generally, the chief representatives of the Mollusca
in Palaeozoic time are the chambered Cephalopods (Tetra-
branchiata) and the Brachiopoda; in Mesozoic time, the Cuttle-
fishes (Dibranchiate Cephalopods), the chambered Cephalo-
pods, and the Polyzoa ; in Kainozoic time, the Lamellibranchs
and Gasteropods. The Polyzoa are comparatively poorly re-
presented in Palaeozoic Rocks, and attain their maximum
towards the close of the Mesozoic period. The Brachiopods
are vastly more abundant in Palaeozoic deposits than in Meso-
zoic, and have gradually declined to the present day. The
Lamellibranchiata seem to have been gradually increasing in
importance since their first appearance in the Lower Silurian
seas, and they have attained their maximum at the present
day. The Gasteropods, upon the whole, like the Bivalves,
seem to have reached their culminating point in recent seas ;
whilst the Pteropods seem to have been as abundant in Silurian
seas as they are at present. The history of the Cephalopoda is
a remarkable one. The Tetrabranchiate forms, with chambered
shells, attained their maximum in the earlier portion of the
Silurian period, as regards their simpler types ; but the more
complex types of the group swarmed in the seas of the
Secondary period, and finally disappeared at the close of this
epoch. This group at the present day is represented solely
by the Pearly Nautilus. The Dibranchiate Cephalopoda, on
the other hand, represented at the present day by the Cuttle-

1 90 MOLLUSCA.

fishes, did not make their appearance till the commence-
ment of the Secondary period, and seem to have reached
their maximum in existing seas.

The sub-kingdom Mollusca is divided into two great divi-
sions, termed respectively the Molluscoida and the Mollusca
Proper. The division Molluscoida comprises the three classes
of the Polyzoa, Tunicata, and Brachiopoda, characterised by
having a nervous system consisting of a single ganglion or prin-
cipal pair of ga?iglia, whilst there is either no distinct organ of
the circulation or an imperfect heart. In the division of the
Mollusca Proper are comprised the classes of the Lamelli-
branchiata (Bivalves), Gasteropoda (Univalves), Pteropoda, and
Cephalopoda. All these classes are distinguished by having
a nervous system composed of three principal pairs of ganglia;
whilst there is a well-developed heart \ consisting of at least two
chambers.

CLASS POLYZOA OR BRYOZOA.

Animal composite, forming colonies, all the members of which
are produced by budding from a primitive being (zooid). Each
member of the colony (zooid) is enclosed in a double-walled sac,
the outer coat of which is mostly hardened by horny or calcareous
matter. There is no heart, and the mouth is surrounded by a
circle or crescent of hollow ciliated tentacles. The colonies are all
but invariably faced to some foreign object, and are in many cases
plant-like inform.

All the Polyzoa live in an associated form in colonies or
" polyzoaria," which are sometimes foliaceous, sometimes
branched and plant-like, sometimes encrusting, and very
rarely are free. Each " polyzoarium " consists of an assem-
blage of distinct but similiar zooids arising by continuous
gemmation from a single primordial individual. The colonies
thus produced are in very many respects closely similar to
those of many of the Hydroid Polypes, with which, indeed,
the Polyzoa were for a longtime classed. The " polyzoarium,"
however, of a Polyzob'n differs from the polypidom of a com-
posite Hydroid in the general fact that the separate cells of
the former do not communicate with one another otherwise
than by the continuity of the external integument; whereas
the zooids of the latter are united by an organic connecting
medium, or " ccenosarc," from which they take their origin.
On this point Mr Busk observes : —

" It has been before said that the Polyzoa are always asso-
ciated into compound growths, made up of a congeries of
individuals, which, though distinct, yet retain some degree of

POLYZOA.

intercommunication, comparable in kind perhaps, though not
in degree, to what obtains in many of the compound Ascidi-
ans. That this community exists is proved by the otherwise
inexplicable circumstance that the polyzoaria in many in-
stances present elements common to the whole growth, and
not belonging specially to any individual. The chief bond of
connection would appear to reside partly in the continuity of
the external integument, and partly also, in all probability, in
a slow interchange of the vital fluid with which the cavities of
the cells are charged."

In one sub-order of the Polyzoa ( Ctenostomatd), the polyzo-
arium consists of a series of cells arising from a common tube,
but this exception does not affect the value of the above
general distinction between the Polyzoa and the Hydroida.

A second point of difference is found in the invariably cor-
neous (or chitinous) texture of the polypidoms of the Hydroida^
whereas those of the Polyzoa may be corneous or fleshy, but
are in the majority of instances more or less highly charged
with carbonate of lime.

As before remarked, the colonies of the Polyzoa are pro-
duced by a process of continuous budding from a primitive
being or zooid. The budding takes place according to a
determinate law, differing in different forms, and the resulting
colony varies in shape according to the method of budding in
each species. All the zooids of the colony are termed " poly-
pides," and the entire colony consists simply of an aggregation
of precisely similar polypides, which may be simply united by
their external integuments or, more rarely, spring from a com-
mon tube. It is only with the outer investment of the colony
that the palaeontologist has to deal ; but it may be well briefly
to describe the structure of a typical polypide.

The polypide of a Polyzob'n (fig. 131, 2) consists essentially
of a double-walled sac, filled with fluid, and perforated by an
aperture where the mouth of the polypide is situated. In the
majority of cases the outer wall of the sac (termed the " ecto-
cyst") is of a horny consistence, or maybe more or less highly
calcareous. It forms a little chamber, which is technically
called the " cell." At one point, varying in its position, the
cell is furnished with an aperture or "mouth" (fig. 131, T),
whence the polypide can protrude its tentaculate head. The
inner wall of the sac (termed the " endocyst ") is invariably
flexible and membranous, and the space included within it is
filled with fluid, in which floats the alimentary canal. The
commencement of the alimentary canal is surrounded by a
series of hollow ciliated tentacles, which are mostly arranged

192

MOLLUSCA.

in a circle in the marine Polyzoa, but are disposed in the
shape of a horse-shoe in most of the fresh-water forms. The
digestive canal passes through the body-cavity, without open-
ing into it, and terminates in a distinct anus placed near the
mouth. The only other organs possessed by the polypide are
a nervous ganglion, and the organs of reproduction, each
zooid being hermaphrodite.

J

Fig. 131. — Morphology of Polyzoa. i. Portion of the coenpecium of Flustra truncata,
magnified. 2. Diagram of a Polyzoon (after Allman) : a Region of the mouth surrounded
by tentacles ; b Alimentary canal ; c Anus ; d Nervous ganglion ; e Investing sac (ecto-
cyst) ; f Testis ; f Ovary; £• Retractor muscle. 3. Bird's-head process, or "avicula-
rium," of a Polyzoon.

In order, then, to arrive at a clear conception of the struc-
ture of a Polyzoon, we have simply to imagine that such a
polypide as above described should have the power of repeat-
ing itself by gemmation, " thus producing one or more pre-
cisely similar systems, holding a definite position relatively to
one another, while all continue organically united."

The only element of the Polyzoa with which the palaeonto-
logist is concerned is the external investment of the colony—
the " ccenoecium " or " polyzoarium." This is formed by the
combined ectocysts of the various polypides, and it varies
greatly both in form and actual composition. In form, it may
be plant-like, rooted at one point, and rising into foliaceous
expansions or arborescent growths ; or it may spread over
some foreign object as a continuous crust. In consistence, it
may be fleshy, horny, sub-calcareous, or completely calcareous ;

POLYZOA.

193

Fig. 132. — Escharina Oceani, show-
ing the sub- terminal mouths of the cells.
Upper Cretaceous.

the simply fleshy forms, as a matter of course, never occurring
in a fossil condition.

The form of the " cell," formed by the ectocyst or outer
wall of each polypide, varies considerably, and important dis-
tinctions may be drawn from this character alone. In one
large group of the Polyzoa — the Cheilostomata — the mouth of
the cell is never quite terminal
in % position, but is always placed
upon the front of the cell, gene-
rally close to one end (fig. 132) ;
whilst the diameter of the mouth
is less than the diameter of the
cell. In most of these forms,
also, the mouth of the cell is
provided with a movable lid or
shutter, by which it can be closed
when the animal is retracted
within it. In another great group
—the Cydostomata — the cells are
tubular in form, and the mouth is terminal in position, whilst
its diameter usually equals that of the cell. In these forms,
also, there is no special apparatus for the closure of the mouth
of the cell.

The surface of the cell may be " either smooth and entire,
spinous or granulous ; perforated with minute pores, or cribri-
form 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."

There still remain three structures which are present in many
forms, and especially in the Cheilostomata, which require some
notice. The structures in question are known as the "ovicell,"
the " avicularia," and the " vibracula."

The " ovicell " is a structure especially characteristic of the
Cheilostomatous Polyzoa; but its presence is not universal, and
when present it may be inconspicuous. Its general form is that
of "a more or less rounded eminence situated above or behind
the cell. . . . The cavity of the organ is continuous with
the perivisceral space, through a passage situated at the upper
and back part of the cell, and through which it would appear
the ova are conveyed as into a sort of marsupial pouch. This
organ is wanting in the Cydostomata, in which its functions are

N

194 MOLLUSCA.

apparently supplied by a dilatation of the body of the cell
itself." (Busk.)

The " avicularia " and " vibracula " are peculiar appendages
of the ectocyst, supposed to be weapons of offence and defence,
or to subserve some unknown function in the economy of the
colony, and believed by Huxley to be peculiarly modified
polypides. The avicularia, or "bird's-head processes," 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 they are often closely similar
to the head of a bird (fig. 131, 3), and they perform a peculiar
snapping movement, which is continued long after the apparent
death of the colony. In many respects, the avicularia are
comparable with the " pedicellariae " of the Sea-urchins and
Star-fishes. In the "yibracula," the place of the mandible of
the avicularium is taken by a bristle or seta, which is capable of
extensive movement.

The following table exhibits the leading groups of the
Polyzoa : —

TABLE OF THE DIVISIONS OF THE POLYZOA.

ORDER I. — PHYLACTOL^MATA.

Tentacles arranged in the shape of a horse-shoe or crescent. Mouth
furnished with a valve-like organ or "epistome."

Sub-order I. Lophopea (fresh- water). — Arms of the tentacular disc (" lopho-
phore") free or obsolete ; consistence, horny or sub -calcareous.

Sub-order 2. Pedicellinea (marine). — Arms of the tentacular disc united
at their extremities ; consistence, soft and fleshy.

Sub-order 3. Rhabdopleurea (marine). — Ccencecium branched, adherent,
membranous, with a chitinous rod on its adherent side. Tentacular disc
horse-shoe-shaped. No epistome (?)

ORDER II. — GYMNOL^EMATA.

Tentacles arranged in the form of a more or less complete circle. No
valve-like organ, or "epistome," arching over the mouth.

Sub-order 4. Paludicellea (fresh-water). — Polypide completely retractile ;
evagination of tentacular sheath imperfect ; consistence, horny or sub-
calcareous.

Sub-order 5. Cheilostomata (marine). — Polypide completely retractile ;
evagination perfect ; orifice of cell sub-terminal, of less diameter than the
cell, and usually closed with a movable lip or shutter, sometimes by a con-
tractile sphincter; cells not tubular ; consistence, calcareous, horny, or fleshy.

Sub-order 6. Cyclostomata (marine). — Cell tubular ; orifice terminal, of
the same diameter as the cell, without any movable apparatus for its closure;
consistence, calcareous.

Sub-order 7. Ctenostomata (marine). — Orifice of the cell terminal, furnished
with a usually setose fringe for its closure ; cells distinct, arising from a
common tube ; consistence, horny or carnose.

POLYZOA.

195

Of the above sub-orders of the Polyzoa, only the marine
groups of the Cheilostomata and Cydostomata are known to
occur in the fossil condition ; their preservation being due to
their marine habits and their general possession of a calcareous
or sub-calcareous coenoecium. The general facts as to the dis-
tribution of the Polyzoa in past time have been already alluded
to. The (OldhamiaiQf the Cambrian Rocks and the Graptolites
have been referred to the Polyzoa ; but the former is probably
a plant, and the latter almost certainly belong to the Hydrozoa.
Leaving these out of account, the Polyzoa seem to commence
in the Upper Cambrian, and are well represented in the Silu-
rian, Devonian, Carboniferous, and Permian Rocks, but espe-
cially in the Carboniferous. None of the Palaeozoic genera
extend into the Secondary period. In the Secondary period
Polyzoa are very abundant, and they attain their maximum
of development in the Cretaceous period, the Chalk having
yielded over two hundred species belonging to this class. In
the Tertiary period, also, Polyzoa are abundant ; the Coralline
Crag (Pliocene) deriving its name from the great profusion of
its Polyzoan remains.

Of the Palaeozoic Polyzoa the most important forms belong
to the family of the Fenestellidce) or " Lace-corals." These
commence in the Lower Silurian, and extend to the Permian ;
but they are especially characteristic of the Carboniferous
Rocks. In Fenestella itself (fig. 133), the coenoecium forms a

Fig. 133. — Fenestella Lyelli. a Natural size ; b Portion enlarged; c Cells and spines
in profile. From the Carboniferous Rocks of Canada (after Dawson).

funnel-shaped or fan-shaped expansion, the base of which is
attached to some foreign object. The coencecium is composed
of a number of nearly parallel stems, united to one another by
numerous cross-bars or dissepiments, enclosing small inter-

196 MOLLUSCA.

spaces. The outer surface of the branches is minutely porous
or longitudinally striated. The inner surface of the branches
exhibits a central ridge or keel, separating the mouths of two
rows of cells. Sometimes there is an additional row of cells
on the mesial keel, and the dissepiments are usually destitute
of cells. The entire ccenoecium is calcareous. In the nearly
allied genus Retepora, the coencecium is also a fan-shaped ex-
pansion, and is also of a calcareous consistence. In place,
however, of transverse dissepiments, the branches of the ccenoe-
cium unite with one another in such a manner as to form ovate
interspaces or " fenestrules." The outer surface of the ccenoe-
cium is non-celluliferous and minutely striated. The inner
surface bears several rows of small cells.

In the genus Ptilopora (fig. 134) are forms essentially similar

Fig. 134. — Ptilopora pluma; the right-hand figure of the natural size, the left-hand
figure enlarged. Carboniferous.

to Fenestella, but having a feather-like arrangement, consisting
of a central stem giving off lateral branches, which are con-
nected by dissepiments, leaving oval fenestrules. In Glauco-
nome (Acanthocladia, King) are forms in which the ccencecium
consists of a central axis giving off lateral branches, which bear
longitudinally-disposed cellules, but which are not united by
transverse dissepiments. Lastly, in Archimedipora, which is
found abundantly in parts of the Carboniferous series of the
United States, the ccenoecium is wound in an oblique spiral
round a central axis. The only other Palaeozoic genus of any
special importance is Ptilodictya, the species of which are
especially characteristic of the Silurian Rocks. In this genus,
the ccenoecium is flattened, foliaceous, or more commonly

POLYZOA.

197

dichotomously branched. The cellules are placed obliquely
on both sides of the ccencecium, and have prominent oval
mouths.

In the Secondary period, the remains of Polyzoa are abund-
ant, and some of the genera are still represented in recent

Fig. 135. — Entalophora cellarioides, natural size and enlarged. Oolites.

seas.

Nearly twenty genera are known from the Jurassic
Rocks, amongst which may be mentioned Idmonea, Eschara,
Defranria, Diastopora, Bidiastopora, (fig. 136), and Entalophora

Fig. 136. — Bidiastopora cervicornis, natural size and enlarged. Oolites.

(fig. 135). All of these, except Eschara, belong to the group
of the Cydostomata, distinguished by their tubular cells, the
mouth of which equals in breadth the diameter of the cell.

It is in the Cretaceous period that the Polyzoa attain their
maximum, nearly two hundred species being known in the
Chalk. Most of the Cretaceous forms belong to the 'Eschar-
id<z, the genus Eschara being abundantly represented. All
the members of this family belong to the group of the Cheilos-
tomatous Polyzoa, in which the orifice of the cell is not terminal,
and is of less diameter than the cell itself.

In the Tertiary Rocks Polyzoa are likewise abundant, and
many of the genera are represented at the present day by

198

MOLLUSCA.

living forms. One of the greatest depots of fossil Polyzoa is
the White Crag of Suffolk, which is for this reason very inap-
propriately called the " Coralline Crag." Amongst the more
important Tertiary genera may be mentioned Eschara, Celle-
pora, Flustra, Tubulipora, Idmonea, and Fascicularia (or Meand-
ropora). One of the most singular of these is the genus Fasci-
cularia (fig. 137), in which the coenoecium is more or less

Fig. 137. — Fascicularia (Meandropora) cerebriformis, Miocene Tertiary.

spherical, composed of vertical laminae arranged somewhat
like the convolutions of the brain, and carrying the cell-mouths
at their extremities.

CHAPTER XIX.
BRACHIOPODA.

THE Brachiopoda are defined as Molluscous animals in which
the body is protected by a bivalve shell, which is lined by expansions
of the integument or " mantle" The mouth is furnished with
long, spirally-coiled, cirriferous processes or " arms" The animal
is never composite. (Fig. 138).

Fig. 138. — Brachiopoda. — Terebratula vitrea. i. Showing the ciliated " arms ; "
2. Showing the shell with its loop. (After Woodward.)

The Brachiopoda are essentially very similar in structure to
the Polyzoa, from which they are distinguished by the fact that

BRACHIOPODA.

IQQ

they are never composite, and by the possession of a bivalve,
calcareous, or sub-calcareous shell. They are commonly known
as " Lamp-shells," and are all inhabitants of the sea. All the
living forms are fixed to some solid object in their adult con-
dition ; but there is good reason to believe that many of the
fossil forms were unattached and free in their fully-grown con-
dition. From the presence of a bivalve shell, the Brachiopods
have often been placed near the true bivalve Molluscs (the
Lamellibranchiata) ; but their organisation is very much in-
ferior, and there are also sufficient differences in the shell to
justify their separation.

The two valves of the shell in any Brachiopod are articulated
together by an apparatus of teeth and sockets, or are kept in
apposition by muscular action alone. As regards the contained
animal, the position of the valves is anterior and posterior, so
that they are properly termed the " ventral " and " dorsal "
valves. One oif the valves is always slightly, sometimes greatly,
larger than the other, so that the shell is said to be " inequi-
valve" (fig. 139). On the other hand, a line drawn vertically

Fig. 139. — Rhynchonella sulcata. A, Profile view. B, View of the dorsal surface.
C, View of the base, a Ventral valve ; b Dorsal valve ; / Base ; c Beak ; k Foramen.
Lower Cretaceous.

from the beak of the shell to its base (in fig. 139 B, from c to/),
would divide it into two equal halves, so that the shell is said
to be " equilateral." In the true bivalve Shell-fish (Lamelli-
branchiata), 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 (" equi valve "), and a
line drawn from the beak to the base would almost always
divide the shell into unequal halves ; so that the shell is " in-
equilateral."

Ordinarily the ventral valve of the shell of the Brachiopods
is the largest of the two, and it is generally furnished with a
prominent curved "beak." Very commonly the beak is per-

T

20O

MOLLUSCA.

forated by a larger or smaller aperture, which is termed the
" foramen " (fig. 139, 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 Lingula\
the peduncle simply passes between the apices of the valves,
and there is no foramen ; whilst in others (as in Crania, fig.
161), the shell is merely attached by the substance of the ven-
tral valve. The dorsal valve, which is also usually the smallest,
is always free, and is never perforated by a foramen. Further,
as already remarked, there is reason to believe that many fossil
forms were free and unattached in their adult condition.

In most living Brachiopods the valves are articulated to one
another by two teeth which are developed upon the ventral
valve, and fit into corresponding 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
two " cardinal muscles." These are inserted on each side of
the centre of the ventral valve, and serve to open the shell.
The valves of the shell are closed by proper "adductor muscles"
(usually four in number), which also pass between the valves ;
and in those in which hinge-teeth are wanting, it is by these
muscles that the valves are kept together. These muscles
leave "scars" or impressions at their points of insertion and
origin : and the number and form of these scars afford impor-
tant diagnostic characters to the palaeontologist.

Very commonly, the beaks of the dorsal and ventral valves
are separated from one another by a narrower or wider space,
which is termed the "hinge-area" (fig. 140). In some genera,

. — Terebratella Astieriaiia, Cretaceous, e Hinge-area; m Ueltidium.

as in Spirifera, the area is very conspicuous ; in other cases it
is very narrow, or even does not exist. In front of the foramen
of the ventral valve, and very often forming part of its circum-
ference, there is commonly a triangular plate, which may be

BRACHIOPODA.

2O I

Fig. 141. — Minute structure
of the shell of Terebratula,
showing the flattened prisms
of the shell, and the canals.

composed of one or two pieces, and which is termed the " del-
tidium" (fig. 140, m). In other cases this structure is alto-
gether wanting.

In intimate structure, the shell of most of the Brachiopoda
(fig. 141) consists " of flattened prisms, of considerable 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.) In most cases, also, 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, usually widening as
they approach the external surface.
These canals give the shell a "punc-
tated " structure, and in the living ani-
mal they contain csecal tubuli, or pro-
longations, from the mantle, which are
considered by Huxley as analogous to

the vascular processes by which in many Ascidians the muscular
tunic, or "mantle," is attached to the outer tunic, or "test."
In some of the Brachiopoda (as in the Rhynchonellidce) the shell
is " impunctate," or is devoid of this singular canal system.

The inner surface of the valves of the shell is lined by ex-
pansions of the integument which secrete the shell, and are
called the " lobes " of the " pallium," or "mantle." The diges-
tive organs and muscles occupy a small space near the beak
of the shell, which is partitioned off by a membranous septum,
which is perforated by the aperture of the mouth. The re-
mainder of the cavity of the shell is almost filled by two long
oral processes, which are termed the " arms," and from which
the name of the class has been derived (fig. 138, i). These
organs are lateral prolongations of the margins of the mouth,
usually of great length, closely coiled up, and fringed on one
side with lateral processes, or " cirri." In many Brachiopods
the arms are supported upon a more or less complicated inter-
nal calcareous framework or skeleton, which is sometimes called
the "carriage-spring apparatus."

In some forms, as in the typical Terebratulce (fig. 138, 2), the
internal skeleton which supports the arms is a short shelly loop,
of a very simple character. In these cases it is only at their
bases that the arms are supported, and they are therefore
more or less movable. In other cases, as in the Spiriferidcz
(fig. 142), the arms must have been immovable, as they are
supported by two thin spirally-foiled lamellae, which form two

202 MOLLUSCA.

calcareous spires in the interior of the dorsal valve. In some
cases, the whorls of these spires are in turn furnished with
minute calcareous spines, showing that the cirri of the arms

Fig. 142. — Spirifera hysterica, Carboniferous. The right-hand figure shows the interior
of the dorsal valve, with the calcareous spires for the support of the arms.

were also supported by an internal skeleton. The form and
development of the calcareous supports of the arms, though
liable to vary with age, nevertheless furnish important characters
in the discrimination of fossil Brachiopods.

The Brachiopoda may be divided into two groups, called
respectively the Articulata and Inarticulata. In the former
the valves of the shell are united along a hinge-line, the lobes
of the mantle are not completely free, and the intestine ends
caecally. In this group are the recent Terebratulida and Rhyn-
chonellidcz. In the Inarticulata the valves of the shell are not
united along a hinge-line, the mantle-lobes are completely free,
and the intestine terminates in a distinct anus. In this group
are the Craniada, Discinida, and Lingulida.

The Brachiopods are of such importance as fossils that the
characters of the more important groups, with their geological
range, and leading genera will here be given, along with figures
of the commoner types. As regards the general distribution
of the class in time, the Brachiopoda are found from the Cam-
brian Rocks up to the present day, and present us with an
example of a group which appears to be slowly dying out.
Nearly two thousand extinct species have been described, and
the class appears to have attained its maximum in the Silurian
epoch, which is, for this reason, sometimes called the " Age
of Brachiopods." Numerous genera and species are found also
in both the Devonian and Carboniferous formations. In the
Secondary Rocks Brachiopoda are still abundant, though less
so than in the Palaeozoic period. In the Tertiary epoch a still
further diminution takes place, and at the present day we are
not acquainted with a hundred living forms. Of the families
of Brachiopoda, the Productidcs, Strophomenidce^ and Spiriferidce.
are the more important extinct types. Of the genera, the most

BRACHIOPODA. 203

persistent is the genus Lingula, which commences in the Cam-
brian Rocks, and has maintained its place up to the present
day, though it appears to be gradually dying out.

According to Woodward : — " The hingeless genera attainedN
their maximum in the Palaeozoic age, and only three now sur-
vive {Lingula, Distinct, Crania} — the representatives of as many
distinct families. Of the genera with articulated valves those
provided with spiral arms appeared first, and attained their
maximum while the Terebratulidcz were still few in number.
The subdivision with calcareous spires disappeared with the
Liassic period, whereas the genus Rhynchonella still exists.
Lastly, the typical group, Terebratulidce, attained its maximum
in the Chalk period, and is scarcely yet on the decline."

Of the families of the Brachiopoda, the Productidce and
Strophomenidce are exclusively Palaeozoic. The Spiriferidce
are mainly Palaeozoic, but extend into the Lias, where they
finally disappear. The Lingulidce commence in the Cambrian
period, and have survived to the present day. The Rhyncho-
nellidce, Craniadce, and Discinidce commence in the Silurian
period, and are represented by living forms in existing seas.
The Koninckinidce are exclusively Triassic. The Thecididcz ex-
tend from the Trias to the present day ; and the Terebratulida
appear to commence in the Devonian, and are well represented
by living forms. In the following are given the leading char-
acters and more important forms of the families of the Brachio-
poda : * —

FAM. I. TEREBRATULIDCE. — Shell minutely punctate : ven-
tral valve with a prominent beak, perforated by a foramen for
the emission of a muscular ped-
uncle, whereby the animal is
fixed to some submarine object.
Foramen partially surrounded
by a deltidium of one or two
pieces. Arms entirely or par-
tially supported by calcified
processes, usually in the form
of a loop, and always fixed to ~ ,

' Fig. 143. — Tj&ehratula. sacculus, Car-

the dorsal Valve (fig. I43.) boniferous. The right-hand figure shows

T,-. 4-1, ~ T< ~J * x.,/.~ "*. the interior of the dorsal valve with the

In the genus Terebratula it- loop. (After Dawson.)
self, and in Terebratulina, the
loop supporting the arms is very short, the former commencing

* Most of the details of this section are taken from the magnificent
Monograph of the Brachiopoda, published by the Palaeontographical
Society, and written by Thomas Davidson, Esq., F.R.S., the greatest
living authority upon the subject of the Brachiopods.

204

MOLLUSCA.

in the Devonian period, the latter in the Oolitic, and both
being represented by living forms. In the genus Waldheimia
there is a very long loop, which is bent backwards, and the
same is the case with Terebratella. The former appears to
commence in the Trias, the latter in the Cretaceous Rocks, and
both have survived to the present day. Forming a section of
the Terebratulidce, or sometimes regarded
as a separate family, are the two or three
species which make up the genus Strin-
gocephalus. These (fig. 144) are all De-
vonian, and are characterised by the pos-
session of a long loop, and a widely-
punctated shell. The beak of the ventral
valve is very prominent, and is pierced by
a foramen, which is large in the young,
and small in the adult shell ; and the ventral valve has a well-
developed mesial septum.

FAM. II. THECIDID^E. — Shell fixed to the sea-bottom by
the substance of the beak of the larger or ventral valve ;
structure punctated. Oral processes (arms) united in the form

Fig. 144. — Stringoce-
phalns Burtini, Devon-
ian.

T-

..r

Fig. 145. — Thecidium papillatnm. e Hinge-area ; n Hinge-teeth of ventral valve ;
r r Granulated border of the interior of the dorsal valve.

of a bridge over the visceral cavity ; cirrated arms folded upon
themselves, and supported by a calcareous loop. (Fig. 145-)

BRACHIOPODA.

205

The members of this family are all attached to some foreign
body by a portion of the beak of the ventral valve, which, in
the adult state, has either no foramen, or an exceedingly small
one. The ventral valve has a well-marked hinge-area and an
indistinct triangular deltidium. All the known species belong
to the single genus Thecidium, represented at the present day
by a single living species. In time, the genus TJiecidium
seems to have commenced in the Upper Trias, and is well re-
presented in parts of the Jurassic and Cretaceous Series.

FAM. III. SpiRiFERiDjE. — Animal free when adult, or rarely
attached by a muscular peduncle. Shell punctated or un-
punctated. Arms greatly
developed, and entirely
supported upon a thin,
shelly, spirally-rolled la-
mella (fig. 142 and fig.
146.)

The family of the Spir-
iferidtz is pre - eminently
Palaeozoic, 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, in the gen-
us Spirt/era, or Spirifer (fig. 148), the valves of the shell are
articulated by teeth and sockets, and the shell is not punctated.
The hinge-area is divided across in each valve by a triangular
fissure, which in the ventral valve is closed more or less com-

Fig. 146. — Atkyris sitbtilita. Lower Car-
boniferous. The right-hand figure shows the
interior of the dorsal valve, with the spiral sup-
ports for the arms. (After Dawson.)

Figs. 147 and 148. — Spirifera. sculptilis, Devonian. Sfarifera. mucrouata, Devonian.

pletely by a pseudo-deltidium, and in the dorsal valve is
occupied by the cardinal process. The true Spirifers are
mainly Silurian and Devonian, and the forms of the latter
formation often have the shell winged, or drawn out at the
lateral angles (fig. 148). The genus Spiriferina differs from
Spirifer chiefly in having the shell punctated, and extends
from the Devonian to the Lias. In the genus Cyrtia, the
shell is impunctate, and the deltidium is perforated by a small

206

MOLLUSCA.

foramen. This genus extends from the Upper Silurian to the
Trias. In the genus Athyris (fig. 146) there is no hinge-area
or deltidium, and the beak of the ventral valve does not appear
to be perforated by a foramen in the adult condition. All the
species of Athyris appear to be Palaeozoic, and they are es-
pecially characteristic of the Devonian period. In the genus
Spirigera (including Retzia) there is no true hinge-area, and
the beak of the ventral valve is terminated by a round foramen,
with a distinct deltidium. The members of this genus extend
from the Silurian to the Trias. In the genus Uncites the shell

Fig. 149. — Atrypa(Spirigerina)reticularis, Silurian.

is impunctate, there is no hinge-area, and the ventral valve has
a long incurved beak, which is perforated in the young shell
by a small foramen. The genus is, so far as known, exclusively
Devonian. Lastly, in the genus Atrypa (fig. 149) the shell is
impunctate, and the beak of the ventral valve is long and

incurved. The beak is perforated
by a small foramen, completed by a
deltidium. Owing to the curvature
of the beak, however, this foramen is
often concealed, so that the beak
seems to be imperforate ; hence the
name of the genus (Gr. a, without ;
trupa, aperture.) It is probable that
the shell was unattached in the later
portions of its existence. The genus
is exclusively Palaeozoic, appearing
to be confined to the Silurian and
Devonian formations. The best-
known species is A. reticularis, figured above.

FAM. IV. KONINCKINID^E. — Animal unknown. Shell free ;
valves unarticulated (?). Oral arms supported by two lamellae
spirally coiled (fig. 150).

The only genus of this family is Koninckia, represented by

Fig. 150. — J\omticKui Leon-
Jtardi, showing the spiral sup-
ports for the arms. Trias.

BRACHIOPODA. . 2O/

the single species K. Leonhardi of the Trias of St Cassian.
The shell resembles Producta in being eared, and the dorsal
valve is concave, and follows the curve of the ventral valve.
It differs from Producta in having the arms supported upon
spiral processes.

FAM. V. RHYNCHONELLID^E. — Animal free, or attached by a
muscular peduncle issuing from an aperture situated under the
extremity of the beak of the ventral valve. Arms spirally
rolled, flexible, and supported only at their origin by a pair of
short, curved, shelly processes. Shell-structure fibrous and
impunctate. (Fig. 151.)

Fig. 151. — Rhynchonella capax ; dorsal, profile, and ventral views.
Lower Silurian.

The Rhynchonellidcz range from the Lower Silurian to the
present day, in the person of the genus Rhynchonella itself; but
the remaining genera of the family are exclusively Palaeozoic.
The genus Rhynchonella (fig. 151) has the valves more or less
convex, smooth or plaited, united by teeth and sockets. The
shell is trigonal, generally with a mesial fold and sinus (fig. 139),
and having the beak of the ventral valve acute, incurved,
or prominent. The foramen is situated under the beak, open
to view, or concealed, and entirely or partially completed by
a deltidium. The species of the genus Rhynchonella are very
abundant in both Palaeozoic and Mesozoic deposits, and two
species are known at the present day.

In the genus Pentamerus (fig. 152), the shell is ovate, the
valves articulated by teeth and sockets, 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 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 diges-
tive organs, and the spiral arms must have filled the great

208

MOLLUSCA.

lateral spaces. In the interior of the smaller or dorsal valve
are two longitudinal septa, which often form a chamber cor-
responding to and apposed to the median chamber in the ven-

Fig. 152. — Pentamerus Knightii. The right-hand figure shows the internal septa
and dental plates of the shell. Upper Silurian.

tral valve. The Pentameri range from the Lower Silurian to
the Carboniferous inclusive ; but they are especially character-
istic of that portion of the Silurian series known as the Lland-
overy formation. They often occur in the greatest profusion,
and the species have in many cases an enormous geographical
range.

The two other genera generally placed in the Rhynchonel-
HdcK — viz., Camarophoria zndiPorambomtes, are of little impor-
tance. The former is confined to the Carboniferous and
Permian deposits, and the latter occurs exclusively in strata of
Lower Silurian age.

FAM. VI. STROPHOMENID^E. — Animal unknown ; some pro-
bably free — others attached, during the whole or a portion of
their existence, by a muscular peduncle. No calcified supports
for the arms. Shell with a straight hinge-line and a low trian-
gular area in each valve. Shell-structure fibrous or punctated.
The Strophomenidce are exclusively Palaeozoic, and include the

Fig. i^.-^Orthis David-
soni; dorsal and side view.
Silurian.

Fig. i$$.—Orthis porcata; dorsal and
side view. Silurian.

genera Orthis, Orthisina, Strophomena, Leptana, and David-
sonia, of which the first four only are sufficiently abundant to
need notice here.

BRACHIOPODA.

209

Fig. 155. — Or-
this elegantula,
Silurian.

In the genus Orthis the valves are articulated by teeth and
sockets, and usually are more or less transversely oblong (fig.
153). 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 com-
monly ornamented with striae, or furnished with
well-marked longitudinal ribs. The species of
the genus Orthis abound in the Silurian, Devonian, and Car-
boniferous periods, especially in the first of these ; but the
genus is not known to have survived the Carboniferous period.

In the genus Orthisina (fig. 156) the shell nearly resembles
that of Orthis ; but there is a double hinge-area, largest in
the ventral valve, the central fissures of
which are always covered by a convex delti-
•dium ; whereas in the latter genus they are
open. In some species (as in O. Verneuili)
the deltidium is perforated by a foramen
under the beak of the ventral valve. The
typical species of Orthisina are Silurian;
but the genus is stated by Mr Davidson to
range through the Devonian and Carbon-
iferous into, the Permian.

In Strophomma (fig. 157) 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

Fig. 156. — Orthisina
Verneuiliy Lower Silu-
rian.

Fig. 157. — Strophoniena antiquata, Silurian.

hinge-area, which is largest in the ventral valve. Each hinge-
area has a median notch, which, in the ventral valve, is par-
tially covered by a deltidium. The ventral valve may be

o

2IO

MOLLUSCA.

convex or concave, and the dorsal valve follows the curvature
of the ventral valve. The species of the genus Strophomena
are very abundant in the Silurian, Devonian, and Carbonifer-
ous formations, often attaining a large size ; but they do not
seem to have survived the close of the last-named period.

In the genus Leptana are forms smaller than the Stropho-
mence, but resembling them in many respects. The shell is
more or less completely semicircular (fig. 158), with a double
hinge-area, notched in the centre, the
fissure in the ventral valve being partly
covered by a deltidium. The valves
articulate by teeth and sockets, and the
surface is generally striated. The Lep-
tcentz extend from the Silurian Rocks
to the summit of the Lias, but are not
known in any younger deposits.

FAM. VII. PRODUCTION. — Animal un-
known. Shell entirely free, or attached
to submarine objects by the substance
of the beak; valves either regularly articulated, or kept in
place by muscular action alone. No calcified supports for
the oral processes. The Productidce are exclusively Palaeozoic,
and are especially characteristic of the Devonian, Carbonifer-
ous, and Permian deposits.

The two most important genera of the Prodnctidce are
Chonetes and Producta. In the genus Chonetes (fig. 159) the
shell is concavo-convex, transversely oblong, with a straight

Fig. 158. — Leptana seri-
cea. a Ventral valve ; b
Dorsal valve ; c Section of
the shell. Silurian.

labnaniatia., Carboniferous.

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, tubular spines. The species of

BRACHIOPODA.

211

Chonetes are distributed in the Silurian, Devonian, and Car-
boniferous periods, but they are most abundant in the last
of these.

In the genus Producta (fig. 1 60) the valves are not articu-
lated by any apparatus of teeth and sockets, and the shell

Fig. 160. — Producta, cora, Carboniferous, a Dorsal valve ; b Ventral valve.
(After Dawson.)

would appear to have been free in the adult condition. The
shell is generally transversely elongated, and is auriculate, or
furnished with ear-like expansions. There is a straight hinge-
line, usually shorter than the width of the shell. The hinge-
area is rudimentary or wanting. The ventral valve is convex,
the dorsal concave, following the curve of the former. The
surface is ribbed or striated, and the ribs carry a greater or
less 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
Carboniferous period.

FAM. VIII. CRANIAD/E. — Animal fixed to submarine ob-
jects by the substance of the ventral valve. Arms fleshy and

Fig. 161. — Crania Ignabergensis, Cretaceous.

spirally coiled. No hinge or articulating processes ; upper or
dorsal valve limpet-shaped (fig. 161). The family includes the

212 MOLLUSCA.

single genus Crania, which commenced in the Silurian period,
and has continued to exist without interruption to the present
day. The shell may be smooth, or striated with radiating
ribs, sometimes with spines or foliaceous expansions. The
ventral valve is the shallowest, and the shell is usually attached
by a portion of its substance. The dorsal valve is more or
less conical, and the valves are simply kept in apposition by
muscular action.

FAM. IX. DISCINID^E. — Animal attached by means of a
muscular peduncle passing through the ventral or lower valve,
by means of a slit in its hinder portion or a circular foramen
excavated in its substance. Arms fleshy. Valves unarticulated.
The Discinidfr range from the Silurian period to the present
day. The three most important genera are Discina, Tr emails,
and Siphonotreta.

In Discina (fig. 162) the shell is generally circular or orbicu-
lar in shape. The upper valve is limpet-shaped, smooth or

Fig. 162. — Disci>ui Circe, Silurian. Fig. 163. — Disciiia ljelopea, Silurian.

concentrically striated ; the ventral valve is flat or partly con-
vex, perforated by a longitudinal slit, which is placed in the
middle of an oval depressed disc. The valves are not articu-
lated to one another, but are kept together by muscular action
alone. The species of the genus Discina range from the
Silurian Rocks to the present day, seven species being now
living.

In the genus Trematis both valves are more or less convex,
and the general shape of the shell is more or less oval or sub-
orbicular. The ventral valve is furnished
with a slit for the passage of a peduncle
of attachment. This genus seems to be
exclusively Silurian.

In the genus Siphonotreta (fig. 164)
the shell is oval, inequivalve, with un-
articulated 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

BRACHIOPODA.

213

concentric lines of growth, and furnished with numerous deli-
cate tubular spines, which, however, are rarely preserved. All
the Sipkonotreta at present known belong to the Silurian period.

FAM. X. LiNGULiDyE. — Animal fixed by a muscular peduncle
passing out between the beaks of the valves. Arms fleshy, not
supported by calcified processes. Shell unarticulated, sub-equi-
valve, of a horny texture. The LinguMa range, in the person
of Lingula itself, from the Cambrian period to the present day.

In the genus Lingula (fig. 165) the shell is oblong, com-
pressed, the dorsal valve little smaller than tne ventral. The

Fig. 165. — Lingula, Eva, Lower Silurian. Dorsal and ventral valves.
(After Billings.)

shell is oval, rounded, or satchel-shaped, tapering more or less
towards the beaks. The surface is concentrically striated with
lines of growth. The genus commences to be represented in
the Cambrian Rocks, and has continued without interruption,
and with no perceptible change, to the present day.

In Obolns the valves are orbicular, sub-equal, smooth, the
ventral valve having a longitudinal furrow for the passage of

Fig. 166. — Obolella cingulata, Billings. Upper Cambrian.

fibres of attachment. The valves are unarticulated, and are
maintained in apposition by muscular action. All the known
species of Obolus are confined to the Silurian period, and are
especially characteristic of the Lower Silurian period. The

214 MOLLUSCA.

genus Obolella (fig. 166) of Mr Billings is only separated from
Obolus by certain internal characters. The little shells belong-
ing to this genus sometimes occur in myriads in the Potsdam
Group (Upper Cambrian) of North America.

CHAPTER XX.
LAMELLIBRANCHIA TA.

THE Lamellibranchiata or Bivalve Shell-fish are distinguished
by the fact that the head is not distinct, and the mouth is destitute
of any apparatus of teeth. The body is more or less completely
protected in a bivalve shell, co?nposed of two, usually symmetrical,
pieces or valves. There are generally two leaf -like lamellar gills
upon each side of the body.

The Lamellibranchs include all the ordinary Bivalve Shell-
fish, such as Oysters, Cockles, Mussels, and the like, and they
are all either marine or inhabitants of fresh water.

Though they agree with the Brachiopoda in possessing a
shell which is composed of two pieces or valves, there are,
nevertheless, many points in which the shell of a Lamelli-
branch is distinguishable from that of a Brachiopod, irrespec-
tive of the great difference in the structure of the animal in
each. The shell in the Brachiopoda, 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 Lamellibran-
chiata, 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 re-
gards the animal is always lateral, so that they are properly
termed " right " and "left " valves, instead of " ventral " and
" dorsal."

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 unsymmetri-
cal, one valve being much larger or deeper than the other.
Lastly, there are some cases in which the shell becomes very

LAMELLIBRANCHIATA.

215

nearly equilateral, the line drawn from the beaks to the base
dividing the shell into two almost equal halves.

h

B

A

Fig. 167. — Left valve of CytJierea chione (after Woodward). A, Anterior margin ;
B, Posterior margin ; C, Ventral margin or base ; « Umbo ; h Ligament ; / Lunule ;
£ Cardinal tooth ; tt Lateral teeth; a Anterior adductor; a' Posterior adductor; p Pal-
lial line ; s Pallial sinus, caused by the retractor muscles of the siphons.

The following are the chief points to be noticed in connec-
tion with the shell of any Lamellibranch : 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 " (fig.
167, //), and is always turned towards the mouth of the animal.
Consequently the side of the shell towards which the umbones
are turned is the " anterior" side, and it is usually the shortest
half 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 " side, or " base." The length of the shell
is measured from its anterior to its posterior margin, and its
breadth 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

2l6 MOLLUSCA.

said to be " edentulous." Posterior 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 liga-
ment 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 behind the beak, 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 liga-
ment and cartilage is sufficient of itself to open the shell.

The hinge-line is mostly curved, but it may be quite straight.
Generally the beaks are more or less 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 Arcada 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 some forms (fig. 167) 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 ; some-
times the cardinal teeth alone are present ; and in some cases
(Arcadce) there is a row of similar and equal teeth.

In the interior of the shell of the Bivalves are found certain
markings which are often of great importance to the palaeon-
tologist. The body is enclosed in an expansion of the dorsal
integument, which constitutes the "mantle" or "pallium,"
whereby the shell is secreted. Towards its circumference the
mantle is more or less completely united to the shell, leaving
in its interior, when the soft parts are removed, a more or less
distinctly impressed line, which is called the " pallial line " or
" pallial impression " (fig. 168, a). In some of the Bivalves the
two halves or " lobes" of the mantle are united at their mar-
gins, so that the animal is enveloped in an almost closed sac.

LAMELLIBRANCHIATA.

217

In these cases it is necessary that there should be orifices in
the mantle-sac by which water can be admitted to the gills, and
can be expelled again from the body. The margins or lips of
these orifices are usually drawn out or extended into longer or
shorter muscular tubes, which are termed the " siphons," and
which may be either separate, or may be united to one another
along one side. The Bivalves which possess these siphons
are said to be " siphonate," and there are two leading modi-
fications in the arrangement of these tubes. In the Siphonate
Bivalves which spend their existence buried in sand or mud,
as well as in many other cases, the siphons are long, and can
be partially or entirely retracted within the shell by means of
special muscles, called the " retractor-muscles of the siphons."
In these cases, the pallial line does not run in an unbroken
curve, but is deflected inwards posteriorly, so as to form an
indentation or bay, which is termed the " jDallial sinus " (fig.
1 68, 2). The presence, therefore, of an indented pallial line
shows that the animal possessed retractile siphons. In other

Fig. 1 68. — Shells of Lamellibranchiata. i. Cyclas amnica, a dimyary shell with an
entire pallial line. 2. Tapes pttllastra, a dimyary shell with an indented pallial line.
3. Feriia. ephippiuni, a monomyary shell. (After Woodward.) a Pallial line; b
Muscular impressions left by the adductors ; c Siphonal impression.

Bivalves the respiratory siphons are of small size, and are des-
titute of retractor muscles, so that they cannot be withdrawn
within the shell. In these cases the " pallial line," or the im-
pression caused by the attachment of the muscular border of
the mantle, is unbroken in its curvature, and presents no
indentation (fig. 168, i). In another group of the Bivalves
there are no respiratory siphons at all, and the mantle-lobes
are free, and are not united to one another at their edges. In
these cases also, the pallial line is unbroken or " simple."
When, therefore, we find a Bivalve shell in which the pallial
line is not indented by a sinus, we know that the animal which
inhabited the shell either possessed no siphons, or that if siphons
were present, they were small and not retractile.

2l8 MOLLUSCA.

In accordance with these considerations, the Lamdlibranchi-
ata are divided into two sections, according as respiratory
siphons are present or absent, and according to their nature
when they exist.

SECTION A. ASIPHONIDA. — Animal without respiratory si-
phons ; mantle-lobes free; the pallial line simple and not in-
dented (Integro-pallialia).

This section comprises the families Ostreidce, Aviculidce, My-
tilidce, Arcades, Trigoniadce, and Unionidce.

SECTION B. SIPHONIDA. — Animal with respiratory siphons ;
mantle-lobes more or less united.

Two subdivisions are comprised in this section. In the
first the siphons are short, and the pallial line is simple (Integro-
pallialia) ; as is seen in the families Chamidcz, Hippuritidce,
Tridacnidce, Cardiadce, Ludnidcs, Cycladida, and Cyprinidce.

The second subdivision (Sinu^allialiq) is distinguished

by the possession of long respiratory siphons, and a sinnated

pallial line, and it comprises the families Veneridcs, Mactridce,

Tellinida, Solenidce, Myaculce, Anatinidce, Gastrochcenidce, and

Pholadidce.

Besides the impressions left by the muscular border of the
mantle, and by the retractor muscles of the siphons, when
these are present, there are other impressions caused by the
insertion into the shell of the muscles by which the valves are
brought together — the " adductor muscles." The number of
adductor muscles never exceeds two, but there may be only
one ; and in accordance with this distinction the Bivalves have
been divided into the two groups of the Dimyaria and Mono-
myaria. These divisions, however, are of small actual value.
In most Bivalves there are two adductor muscles passing be-
tween the inner surfaces of the valves, one being placed
anteriorly, in front of the mouth, whilst the other is situated
posteriorly, in the neighbourhood of the vent. In the Mono-
myary Bivalves it is the posterior adductor which remains,
and the anterior adductor is absent. The adductors leave
distinct "muscular impressions," or scars, in the interior of the
shell, so that it is easy in any given specimen to determine
where there was only one adductor, or whether two were pre-
sent (see fig. 1 68).

The habits of the Lamellibranchiata are very various. Some,
such as the Oyster (Ostrea), and the Scallop (Pecteii), habit-
ually lie on one side, the lower valve being the deepest, and
the foot being wanting, or rudimentary. Others, such as the
Mussel (Mytilus\ and the Pinna, are attached to some foreign
object by an apparatus of threads, which is called the " byssus,"

LAMELLIBR ANCHI ATA. 2 1 9

and is secreted by a special gland. Others are fixed to some
solid body by the substance of one of the valves. Many, such
as the Myas, spend their existence sunk in the sand of the sea-
shore or in the mud of estuaries. Others, as the Pholades
and Lithodomi, bore holes in rock or wood, in which they live.
Finally, many are permanently free and locomotive.

As regards the general distribution in time of the Lamelli-
branchiata, the class seems to have commenced in the Lower
Silurian Rocks, and to have steadily increased up to the pre-
sent day, when it seems to have attained its maximum, both
as regards numbers and as regards variety of type. The recent
Bivalves are also superior in organisation to those which have
preceded them. In the Palaeozoic and earlier Secondary de-
posits the Bivalves belong mainly to the group of the Asiph-
onida, in which there are no respiratory siphons. In the later
Secondary and Tertiary Rocks, on the other hand, there is a
predominance of Siphonate Bivalves, in which the mantle-lobes
are united and there are respiratory siphons. Upon the whole,
the Lamellibranchiata are sparingly represented in the Lower
Silurian, more abundant in the Upper Silurian, reduced in
numbers in the Devonian, very plentiful in the Carboniferous,
scanty in the Permian and Trias, profusely represented in the
Jurassic Rocks, and very abundant in the Cretaceous and Ter-
tiary periods (Lobley). In the Carboniferous Rocks the family
of the Aviculidce is especially abundant. One very singular
and aberrant family — viz., the Hippuritida — is exclusively con-
fined to the Secondary period, and is not known to occur out
of the limits of the Cretaceous formation. The Venerida,
which are perhaps the most highly organised of the Lamelli-
branchiata, appear for the first time in the Oolitic Rocks, and,
increasing in the Tertiary period, have culminated in the
Recent period. The remains of Lamellibranchiata are very
abundant in many formations, and are of great palaeontological
importance. It will therefore be well to review the families*
of the class briefly, giving the leading characters, more impor-
tant genera, and geological distribution of each.

SECTION A. ASIPHONIDA.

FAM. i. OSTREID^E. — Shell inequivalve, slightly inequilateral,
free or attached ; hinge usually edentulous. Ligament internal.

* In the following synoptical view of the Lamellibranchiata, the classi-
fication adopted in Woodward's admirable Manual of the Mollusca has
been mainly followed.

22O

MOLLUSCA.

Lobes of the mantle entirely separated ; the foot small and
byssiferous, or wanting. A single adductor muscle.

In the typical Oysters, forming the genus Ostrea (figs. 169,

Fig. 169. — Ostrea Couloni, Lower Greensand. '

170), the shell is irregular, and is attached by the left valve,
which is also convex, and has a well-marked beak. The upper
valve is generally flat or concave, and is the smallest of the

Fig. 170. — Ostrea aguila, Lower Greensand.

two valves. The hinge is toothless. Both valves may be
more or less completely plain, and the upper one especially
often is so. The lower valve, however, is commonly plaited,
and both valves are sometimes thus ornamented, as in Ostrea
Marsliii of the Oolites (fig. 171).

In the sub-genus Gryphcza are included Oysters which were
either quite free or very slightly attached. The left or lower
valve (fig. 172) is much the largest, and has a very pronounced
incurved beak, whilst the right valve is small and concave. In
the sub-genus Exogyra, again, the beaks are " reversed "-—that
is to say, turned towards the posterior side of the shell. True
Oysters commence to be represented in the Carboniferous

LAMELLIBRANCHIATA.

221

seas, abound in the Secondary and Tertiary periods, and are
very plentiful at the present day. The sub-genera Gryphcea
and Exogyra are exclusively Mesozoic, the former abounding

Fig. 171. — Ostrea Marshii, Oxford
Clay (Middle Oolites).

Fig. 172. — {jfyjmcea tucurva, Lias.

especially in the lower portion of the Oolitic series, whilst the
latter is chiefly characteristic of the later Oolitic and Cretace-
ous deposits.

In the Aiiomia the shell is thin and translucent, and is fixed
to some solid body by a plug which passes through a hole or

Fig. 173. — Pgcten Islandicus, left valve. Post-Tertiary and Recent.

notch in the right valve. The typical fossil species are dis-
tributed from the Oolites upwards. The Oolitic genus Placu-
nopsis is also related to Anomia.

The genus Pecten includes the Scallops (fig. 173), in which

222 MOLLUSCA.

the shell rests upon the right valve, and the beaks are furnished
with ears. The anterior ears are usually the largest and most
prominent, and the shell is generally furnished with ribs radiat-
ing from the umbos. The right valve is the deepest, and is
notched below the anterior ear. Counting in its sub-genera,
nearly five hundred species of the genus Pecten are known in
the fossil state, commencing in the Devonian Rocks, and ex-
tending to the present day. The Palaeozoic Pectens are dis-
tinguished from their successors in more modern rocks by
having the posterior ears larger than the anterior; and they
are therefore placed by M'Coy in a new genus, under the
name of Aviculopecten. They are, however, usually regarded as
belonging to the Avicididce.

In the genus Lima (or Plagiostoma) the shell is equivalve and
free, whilst the beaks are separated from one another and are
eared. The genus is represented by numerous species in the
rocks of the Secondary period, and has survived to the present
day.

In Spondylus (fig. 174) the shell is inequivalve, and is fixed by
the right valve to some foreign body. The beaks are apart and

Fig. T.-]\.—Spondylus spinosus, Chalk.

eared, and the shell is covered with spines, foliaceous expan-
sions, or ribs radiating from the beak. The lower valve has a
triangular hinge-area, and there are two teeth in each valve.
The Spondyli seem to have commenced in the Cretaceous
period, in which they are very abundant, and they have con-
tinued through the Tertiary period to the present day.

Lastly, the Plicatula (fig. 175) approach the Spondyli nearly,
by 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 Plica-
tulce extend from the Trias to the present day, and they abound
to such an extent in parts of the Lower Greensand (Cretaceous),

LAMELLIBRANCHIATA.

223

as to have given rise to the name of " Argile a Plicatules " ap-
plied to the beds in question.

Fig. 175. — Plicatula placujiea, Lower Greensand.

FAM. 2. AVICULID^E. — Shell inequivalve, very oblique, at-
tached by a byssus ; hinge nearly or quite edentulous. Mantle-
lobes free; anterior adductor small, leaving its impression
within the umbo \ posterior adductor large and sub-central.
Foot small.

Leaving out of consideration the genus Aviculopecten, which
holds a dubious position, and has been already spoken of, the
chief fossil genera of the Aviculidce are Avicula, Posidonomya,

220

Fig. 176. — Avicula deinissa,
Lower Silurian.

Fig. 177. — Ambonychia xpdiata,
Lower Silurian.

Gervittia, Perna, Inoceramtis, and Pinna. In the genus Avicula
(fig. 176) the shell is oblique and very inequivalve. The right

224

MOLLUSCA.

valve has a notch under the anterior ear; and the hinge has
one or two cardinal teeth, sometimes with an elongated pos-
terior tooth. The true Aviculce are represented by veiy numer-
ous fossil species, extending from the Lower Silurian Rocks to
the present day. Of the sub-genera of Avicula, the three most
important fossil forms are Ambonychia, Pterinea, and Cardiola,
the place of the last in this family being somewhat doubtful.
In the AmbonychicR (fig. 177) the valves are gibbous, nearly
equal, and the anterior ear is almost obsolete. They extend
from the Lower Silurian to the Carboniferous. The Pterineas
(fig. 178) are very abundant in the Silurian Rocks, especially
in the upper division of the series, and they extend to the Car-

C

Fig. 178. — A, Pteriiiea snb-falcata ; B, Cardiola interrupta; C, Cardiola fibrosa.
(After M'Coy and Salter.) Silurian.

boniferous Rocks. They have a shell with large ears and very
oblique, the hinge-area being long and straight. The Cardiolce
have an oblique, equivalve shell (fig. 178, B), radiately ribbed,
with prominent beaks and a short hinge-area. They are mainly
characteristic of the Upper Silurian Rocks, but they have been
stated to occur in the Lower Silurian, and they are found in
the Devonian.

The shells of the genus Posidonomya are very thin, con-
centrically striated, equivalve and earless. They extend from
the Silurian to the Trias, but are especially characteristic of
the Carboniferous Rocks. Many of the smaller shells referred
to Posidonomya are undoubtedly referable to the Crustacean
genus Esther ia.

The genus Gervillia comprises a number of fossil shells,
which range from the Carboniferous Rocks to the Chalk, and
which are very like the true Aviculce. The shell is elongated,
the anterior ear small, and the posterior ear broad and wing-
like. ' Nearly allied to Gervillia is the genus Perna, which
commenced in the Trias, and is represented in recent seas.

Nearly related to both Gervillia and Perna is the genus
Inoceramus (figs. 179, 180), which is entirely confined to the
Secondary period, and is mainly characteristic of the Creta-

LAMELLIBRANCHIATA.

225

ceous series. The shells of this genus are inequivalve, with
radiating ribs or concentric furrows, and with prominent
beaks. The hinge-line is long and straight, with numerous

Fig. 179. — Inoceramus sulcatus. Gault (Cretaceous).

Fig. 180. — Inoceramus problematicus. (Jhaik.

caitilage-pits. Some of the Inocerami attain a length of two
or three feet, and fragments of them are often found perfor-
ated by boring sponges.

The last genus of the Aviculidce is Pinna, in which the shell
is equivalve and wedge-shaped, and the beaks are placed
quite on the anterior side of the shell. The Pinniz seem to
have commenced in the Devonian, but their existence prior
to the Carboniferous period is a matter of some uncertainty.
Many species are known in the Secondary and Tertiary
Rocks, and the genus is well represented by living forms.
The sub-genus Trichites is exclusively Oolitic,. and the shells
referred here sometimes attained an enormous size.

FAM. 3. MYTILID^E. — Shell equivalve ; umbones anterior;
hinge edentulous ; anterior muscular impression small, pos-
terior Jarge. Shell attached by a byssus. Mantle-lobes united
between the siphonal apertures. Foot cylindrical, grooved, and
byssiferous. The chief fossil genera of the Mytilidcz are
Mytilus, Modiola, Lithodomus, Modiolopsis, and Orthonota'.

In the genus Mytilus are the true Mussels, in which the
shell is wedge-shaped, and the beaks terminal. Numerous
fossil forms are known, commencing in the Permian. The
Modiola, or " Horse-mussels," have the beaks anterior, blunt,
not pointed, the hinge edentulous, and the shell oblong.

226

MOLLUSCA.

More than one hundred fossil species have been described,
commencing in the Lias, and extending to the present day.
The Palaeozoic Modiola are probably referable to different gen-
era. The Date-shells (Lithodomus) form a sub-genus QiModiola,
and are distinguished by their habit of forming perforations
in rocks, in which they live. They appear to date from the
Lower Oolitic Rocks, and are known to palaeontologists by
both their shells and their burrows.

The genus Modiolopsis (fig. 181), includes a number of
Silurian shells, the true place of which is somewhat uncertain.

Fig. 181. — Modiolopsis modiolaris. Lower Silurian.

The shell is equivalve, very inequilateral, the beaks anterior,
and the surface smooth, or marked by fine concentric lines of
growth; The shell is thin, and its posterior end is consider-
ably broader than the anterior.

The genus OrtJtonota likewise comprises a number of Silu-
rian Bivalves, and is also in a somewhat doubtful position.

The shell (fig. 182) is elongated,
equivalve, very inequilateral,
having the beaks placed close
to its anterior end. The shell
is thin, and its margins are
parallel.

FAM. 4. ARCADE. — Shell
equivalve ; hinge long, with
many comb-like teeth ; muscu-
lar impressions nearly equal;
mantle - lobes separated ; foot
large, bent, and deeply grooved. The most important fossil
genera of this family are Area, Cucullcea, Pectimculus, Nucula,
Ctenodonta, Cyrtodonta, and Leda.

The Arks (Area) have a straight hinge-line, with remote
beaks, separated from one another by an oval or lozenge-

Fig. 182. — Ortkoiiota paralleia.
Lower Silurian.

LAMELLIBR ANCH I ATA.

227

shaped ligamental area (fig. 183). The teeth are numerous

and transverse, and the surface is generally strongly ribbed.

Species of Area have been

described from the Lower

Silurian Rocks upwards. It

is probable, however, that

the older Palaeozoic forms

referred here really belong

to other genera, especially

Ctenodonta and Cyrtodonta.

In Cucttllcza the shell is
ventricose, and the hinge-
teeth are few and oblique,
and at each end of the hinge
become parallel with the
hinge-line. Species of this genus have been described from
the Lower Silurian upwards.

The Pectunculi have a nearly round and equilateral shell, the
beaks separated by a striated ligamental area, the hinge-line
curved, and the hinge-teeth forming a semicircular row. Pect-
unculus 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.

The Nucula (fig. 184) have a trigonal shell, the beaks of
which are reversed, and turned towards the posterior side of
the shell, which is also the shortest side. The hinge has

Fig. 183. — Area antiqua. Permian.

Fig. 184. — j.\ncnla bivirgata. Gault.

Fig. i»5. — Ctetiodonta contracta.
Lower Silurian, a Interior of right
valve ; b Exterior of the same.

numerous teeth on each side of a central internal cartilage-pit.
The Palaeozoic shells referred to Nucula probably belong to
other genera. Many species, however, are known from the
Secondary and Tertiary Rocks.

The genera Ctenodonta and Cucullella are both nearly re-
lated to one another and to Nucula, and both are exclusively
Palaeozoic, and are mainly, if not entirely, Silurian. The
Ctenodonta (fig. 185) are extremely like Nucula, but are dis-

228

MOLLUSCA.

tinguished by having an external ligament. The posterior side
of the shell is generally the shortest, but the reverse is some-
times the case.

The shells of the genus Cyrtodonta (Palaarca of Hall) are
very inequilateral, the umbones being anterior (fig. 186). The

Fig. 1 86. — Cyrtodonta Hindi (Billings). Lower Silurian, a Dorsal view ; b Side view.

hinge-area is undefined, and the surface 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 Cyrtodonta appear to be
exclusively confined to the Silurian and Devonian Rocks.

In the genus Leda the shell resembles that of Nucula, especi-
ally in having numerous teeth on either side of a central
cartilage-pit. The shell, however, is oblong, rounded in front,
and pointed behind. The occurrence of Leda in the Palaeozoic
period is dubious ; but numerous species are known from the
Secondary and Tertiary Rocks.

FAM. 5. TRIGONIAD^E. — Shell equivalve, trigonal ; hinge-teeth
few, diverging ; umbones directed posteriorly. Mantle open ;
foot long and bent. The most important genera of this family
are Trigonia, Myophoria, and Axinus.

LAMELLIBRANCHIATA.

229

In Trigonia (fig. 187) the shell is trigonal, with tubercles,
radiating ribs, or concentric ridges. The hinge-teeth are
two in one valve and three in the other. The Trigonics are

Fig. 187. — Trigonia scabra. Chalk.

essentially Mesozoic, being only known, in the fossil con-
dition, as extending from the Trias to the Chalk. They are
not known with certainty to be represented in the Tertiary
Rocks at all; but the Australian seas have yielded some
living forms.

The shells of the genus Myophoria have the umbones direct-
ed anteriorly, and are in most respects closely similar to Tri-
gonia. They belong exclusively to the Triassic period.

The genus Axinus (Schizodus) is also nearly related to Tri-
gonia y but the shell is thinner, and is smooth, and the posterior
side is not so distinctly angular, but is marked by an oblique
ridge. The shells of this genus extend from the Upper
Silurian to the Trias, but are especially characteristic of the
Permian Rocks.

FAM. 6. UNIONID/E. — Shell usually equivalve, with a large
external ligament. Anterior hinge-teeth thick and striated ;
posterior laminar or want-
ing. Mantle-lobes united
between the siphonal ap-
ertures. Foot very large,
compressed, byssiferous in
the fry. All the members
of the UnionidcB are in-
habitants of fresh water,
and they are, therefore, not
known as fossils except in
fluviatile and lacustrine de-
posits. The only two fossil
genera of the family are

TTM' _. J A j Fig. 1 88. — Unio Waldensis. Wealden

Unto and Anodon. (Lower cretaceous).

In the genus Unio (fig.

1 88) the shell is oval or elongated, somewhat resembling that
of a mussel (hence the name of River-mussels commonly

230 MOLLUSCA.

given to the Unios}. The species of this genus appear to
commence in the Lower Cretaceous Rocks, and they are
very abundant at the present day. The beaks of fossil speci-
mens are often deeply eroded, as are those of living forms.

The Anodons or Swan-mussels closely resemble the Unios,
but the shell is edentulous. The earliest fossil forms occur in
the Lower Tertiaries (Eocene).

SECTION B. SIPHONIDA.

Sub-division I. Integropallialia. — Siphons short, pallial line
simple.

FAM. 7. CHAMID^E. — Shell inequivalve, attached. Hinge-
teeth 2-1 (two in one valve and one in the other). Impres-
sions of the adductors large. Mantle closed ; pedal and
siphonal orifices small and nearly equal. Foot very small.
The most important fossil forms, of this family belong to the
genera Chama, Diceras, and Requienia.

In the genus C/iama the shell is attached usually by the
beak of the left valve, but sometimes by that of the right. The
upper valve is the smallest, and both bear foliaceous expan-
sions. The free valve carries one tooth which articulates with
two teeth in the attached valve. The Chamas do not appear
as fossils till we reach the Cretaceous Rocks, and they have
continued to exist up to the present day.

In the remarkable genus Diceras (fig. 189), the shell is

"sub-equivalve, attached by
either umbo; beaks very promi-
nent, spiral, furrowed externally
by ligamental grooves ; hinge
very thick, teeth 2-1, promi-
nent • muscular impressions
bounded by long spiral ridges,
sometimes obsolete " (Wood-
ward). The species of Diceras
are exclusively confined to the
Middle Oolites. In this for-
mation in the Alps they occur

Fig. ^.-Dicera^arietina. Middle jn such abundance ^ to give

rise to the name of " Calcaire

a Dicerates," applied to beds of the same age as the Coral
Rag of Britain.

The genus Requienia is exclusively confined to the Cre-
taceous period, and differs from Diceras chiefly in having a

LAMELLIBRANCH1ATA.

231

very inequivalve shell, always attached by its left valve. The
attached valve is the largest, and is spiral, whilst the free valve
is small and sub -spiral.

FAM. 8. HIPPURITID/E (Rudistes of Lamarck). — "Shell in-
equivalve, unsymmetrical, thick, attached by the right umbo ;
umbones frequently camerated ; structure and sculpturing of
the valves dissimilar ; ligament internal ; hinge-teeth 1-2 ;
adductor impressions two, large, those of the left valve on
prominent apophyses ; pallial line simple, sub-marginal." —
(Woodward).

The Hippuritida are not only entirely extinct, but are ex-
clusively confined to the Cretaceous Rocks, whence more than
one hundred species have been described. All the members
of this family were attached, and lived in beds like oysters.
The two valves of the shell are always altogether unlike in
sculpturing, appearance, shape, and size ; and the cast of the
interior of the shell is often extremely different to the form of
the shell itself. About a hundred
species of the family are known,
all of which are Cretaceous, oc-
curring in Britain, Southern
Europe, the West Indies, North
America, Algeria, and Egypt.
Species of this family occur in
such numbers in certain compact
marbles in the south of Europe,
of the age of the Lower Chalk,
as to have given origin to the
name of " Hippurite Limestones "
applied to these strata.

The Hippuritidce have been
especially studied by Dr S. P.
Woodward, who makes the fol-
lowing remarks upon their struc-
ture and affinities : — " They are
the most problematical of all fos-
sils ; there are no recent shells
which can be supposed to belong
to the same family ; and the con-
dition in which they usually occur
has involved them in greater ob-
scurity. The characters which
determine their position amongst the ordinary Bivalves are
the following : —

" i. The shell is composed of two distinct layers.

Fig. 190. — Hippitrites Toucasiana.
A large individual, with two smaller
ones attached to it

232

MOLLUSCA.

" 2. They are essentially unsymmetrical and right-and-left
valved.

"3. The sculpturing of the valves is dissimilar.

" 4. There is evidence of a large internal ligament.

" 5. The hinge-teeth are developed from the free valve.

" 6. The muscular impressions are two only.

" 7. There is a distinct pallial line.

" The outer layer of shell in the Hippurite and Radiolite
consists of prismatic cellular structure ; the prisms are perpen-
dicular to the shell-laminae, and subdivided often minutely.
The cells appear to have been empty, like those of Ostrea.
The inner layer which forms the hinge and lines the umbones,

is sub-nacreous, and very rarely preserved The

inner shell-layer is seldom compact, its laminae are extremely
thin, and separated by intervals like the water-chambers of

Spondylus The chief peculiarity of the Hippuri-

tidcz is the dissimilarity in the structure of the valves, but even
this is deprived of much significance by its inconstancy. The
free valve of Hippurites is perforated by radiating canals,
which open round its inner margin, and communicate with the
upper surface by numerous pores, as if to supply the interior

with filtered water In the closely allied genus

Radiolites there is no trace of such canals, nor in Caprotina"

The shell of Hippurites (fig. 190) is inversely conical or
cylindrical, and sometimes attains a length of a foot or more.

Fig. 191. — Caprina. Aguilloni. The right-hand figure shows the interior of

the left valve.

The shell is attached by the larger conical valve, and is closed
by a small depressed free valve, with a central umbo. In

LAMELLIBRANCHIATA. 233

Radiolites the shell is inversely conical, bi-conical, or cylin-
drical, with dissimilar valves. The upper valve is sometimes
flat, sometimes conical, and has a central umbo. In Caprina
(fig. 191) the valves of the shell are dissimilar, the fixed valve
being conical, whilst the free valve is oblique, or is spirally
rolled. The free valve is thick, and is " perforated by one or
more rows of flattened canals, radiating from the umbo, and
opening all round the margin" (Woodward). The cavity of
the free valve is sometimes chambered.

FAM. 9. TRIDACNID^E. — Shell equivalve ; ligament external ;
muscular impressions blended, sub-central. Animal attached
by a byssus, or free. Mantle-lobes extensively united ; pedal
aperture large ; siphonal orifices surrounded by a thickened
pallial border. Foot finger-like and byssiferous. The shell is
truncated in front, the surface ribbed, and the margins toothed.
The family contains the single genus Tridacna, which is not
known to have come into existence before the period of the
Miocene Tertiary.

FAM. 10. CARDIAD^E. — Shell equivalve, heart-shaped, with
radiating ribs ; cardinal teeth 2 ; lateral teeth i-i in each
valve. Mantle open in front ; siphons usually very short ; foot
large and sickle-shaped. The only two genera of this family
are Cardium and Conocardium.

In Cardium are comprised the true Cockles, in which the
shell is ventricose, the beaks pronounced, and placed nearly in
the centre of the dorsal margin (fig. 192), the margins crenated,

Fig. 192.— Cardium Hillanum. Upper Greensand.

and the pallial line more or less indented. It is doubtful it
any true Cardium has been detected in the Silurian Rocks.
With the Devonian, however, the genus begins to be well re-
presented, and it has continued up to the present day, attaining
its maximum in existing seas. The species figured above is
separated from the true Cockles by having the posterior slope
of the shell radiately striated, whilst the sides are concentri-
cally furrowed.

234 MOLLUSCA.

The genus Conocardium comprises a number of Palaeozoic
shells, in which the anterior side is conical and gaping ; whilst
the posterior margin is truncated, and there is a longer or
shorter siphonal tube placed near the beaks.

FAM. ii. LUCINID^E. — Shell orbicular, free; cardinal teeth i
or 2; lateral teeth i - i, or obsolete. Mantle - lobes open
below, with one or two siphonal orifices behind; foot elon-
gated, cylindrical, or strap-shaped. The most important fossil
genera of the Lucinidcz are Lucina and Corbis. Nearly two
hundred species of the former have been described, commenc-
ing with the Devonian; and about eighty species of the former
are known, commencing with the Lias.

FAM. 12. CYCLADID^E. — Shell sub-orbicular, closed; hinge
with cardinal and lateral teeth; ligament external. Mantle
open in front ; a single siphon, or two more or less united.
Foot large, tongue-shaped. The genera Cydas and Cyrena
compose this family, and both are inhabitants of fresh water ;
though the latter not uncommonly frequents brackish water,
and one species of the former has been described as marine.
In the Cydades the shell is thin, and there are two hinge-
teeth in one valve arid one in
the other. In Cydas itself
the shell is nearly equilateral,
but in the sub-genus Pisi-
dium, it is inequilateral, with
the anterior side the longest.
In Cyrena (fig. 193) the shell
is thick, and there are three

Fig. 193. — Cyrena autiqua. .Locene. .

hinge -teeth in each valve.

Both Cydas and Cyrena seem to have come into existence at
the commencement of the Cretaceous period (Wealden), and
they are abundantly distributed through the Tertiary Rocks.

FAM. 13. CYPRINID^E. — Shell equivalve, closed; ligament
external ; cardinal teeth 1-3 in each valve, and usually a
posterior tooth. Mantle-lobes united behind by a curtain
pierced with two siphonal orifices. Foot thick and tongue-
shaped. Of the genera of the Cyprinida, the more important
fossil forms belong to Cyprina, Astarte, Crassatella, Isocardia,
Cardita, and the extinct Megalodon, Anthracosia, Hippopodium,
and Pachyrisma. Taken as a whole, the Cyprinida have passed
their acme, and have begun to decline in numbers and im-
portance.

Cyprina has a large, strong, oval shell, covered with a thick
epidermis. Numerous fossil species are known, commencing
in the Trias.

LAMELLIBRANCHIATA.

235

Astarte includes thick, generally concentrically - furrowed
shells. Two hundred fossil species are known, commencing
in the Lias.

Crassatella (fig. 194) comprises thick, solid, ventricose
shells, attenuated posteriorly, and generally having a concen-

Fig. 194. — Crassatella ponderosa. Eocene Tertiary.

trically-furrowed surface. Unlike the two preceding genera,
Crassatella has the ligament internal. The genus commences
in the Cretaceous Rocks, is abundant in the Tertiaries, and is
well represented at the present day.

In the Heart-cockles (Isocardia) the beaks are remote and
sub-spiral, and the shell is heart-shaped. The Isocardicz do
not appear to have existed in the Palaeozoic period, but com-
mence in the Trias, are tolerably abundant in the Oolites and
Cretaceous Rocks, decline in numbers in the Tertiaries, and
are represented by a few forms in existing seas.

Cardita (fig. 195) includes Cockle-shaped shells, which
have radiating ribs, an external ligament, and a toothed

Fig. 195. — Cardita planicosta. Eocene Tertiary.

margin. The genus commences in the Trias, but attains its
maximum in the Tertiary period, about a hundred species
having been enumerated from rocks of this age.

236 MOLLUSCA.

Allied to Cardita is the extinct genus Hippopodium, well
known by the thick and solid H. ponderosum of the Lias.

Pachyrisma is another extinct genus, in which the shell is
also very thick and ponderous in its structure. It has large
sub-spiral umbones, and is peculiar to the Great Oolite.

Megalodon is likewise extinct, and includes massive shells,
with sub-spiral beaks and an external ligament. The genus
is doubtfully represented in the Silurian and Carboniferous
Rocks, and is characteristically Devonian.

Lastly may be mentioned the shells which are known as
AnthracosMRy which abound in parts of the Carboniferous
series. These are nearly allied to the extinct genus Cardinia,
if they do not actually belong to it. They are exclusively
Palaeozoic, and extend from the Upper Silurian to the
Carboniferous; whereas Cardinia is very doubtfully repre-
sented in rocks older than the Lias.

Sub-division II. Simipallialia. — Respiratory siphons large;
pallial line indented.

FAM. 14. VENERID^E. — Shell regular, sub-orbicular or oblong;
ligament external ; hinge with usually three diverging teeth in
each valve. Animal usually free and locomotive ; mantle with
a rather large anterior opening ; siphons unequal, more or less
united. Foot tongue- shaped, compressed, sometimes grooved
and byssiferous. The Veneridce are the most highly organised
of the Bivalves, and comprise some of the most beautiful
examples of the class. They commence in the Oolitic Rocks,
are abundant in the Tertiaries, and have attained their maxi-
mum at the present day. All the more important fossil forms
belong to the nearly-allied genera Venus and Cytherea. Both
of these commenced their existence in the Oolites, the former
being represented by about one hundred and fifty, the latter
by nearly a hundred extinct forms.

FAM. 15. MACTRID^E. — Shell equivalve, trigonal; hinge with
two diverging cardinal teeth, and usually with anterior and pos-
terior lateral teeth. Mantle more or less open in front ; siphons
united, with fringed orifices ; foot compressed. The only two
genera of any importance as fossils are Mactra and Lutraria,
both of which live buried in sand or mud. The Mactra have
a nearly equilateral shell, with a short pallial sinus, and an
internal ligament contained in a triangular pit. They appear to
have commenced in the Lias, and have attained their maximum
at the present day. In Lutraria the shell is oblong and gaping
at both ends, the pallial sinus is deep, and the internal ligament
is supported by a prominent cartilage-plate. The genus is not
known in rocks earlier than the Miocene Tertiary.

LAMELLIBRANCHIATA.

237

FAM. 1 6. TELLINID^E. — Shell free, usually equivalve and
closed; cardinal teeth t\vo at most, laterals i-i, sometimes
wanting. Ligament on the shortest side of the shell, some-
times internal. Mantle widely open in front. Siphons long
and slender ; foot tongue-shaped, compressed. Pallial sinus
very large. The chief fossil genera are Tellina, Psammobia,
and Donax. In Tellina the shell is very slightly in equivalve
(fig. 196) with a prominent external ligament. More than
a hundred fossil species
are known, dating from
the Oolitic period ; but
the genus has attained its
maximum at the present
day. In Psammobia the
shell is oblong, compres-
sed, and slightly gaping at
both ends ; whilst in Donax
the shell is wedge-shaped, the front rounded and produced,
the posterior side short. Both genera commence in the
Eocene Tertiary, and are represented by numerous species at
the present day.

FAM. 17. SOLENID^E. — Shell elongated, gaping at both
ends ; ligament external ; hinge-teeth usually 2-3. Siphons
short and united (in the long-shelled genera), or longer and

Fig. 196. — Tellina proximo,, right valve.
Post-Pliocene.

Fig. iq-j.—Myatruncata, Post-Pliocene
and Recent.

Fig. 198. — Portion of the hinge of
Mya areiiaria, showing the cartilage-
process.

partly separate (in the genera with shorter shells). Foot
very large and powerful. Gills prolonged into the bran-
chial siphon. This family is of small geological importance.
The Razor-shells (Solen) are represented by a few Tertiary
forms, commencing in the Eocene ; and the genera Cul-
telhis and Solecurtus commence their existence in the Creta-
ceous Rocks.

FAM. 1 8. MYACID.E. — Shell gaping posteriorly. Mantle
almost entirely closed ; siphons united, partly or wholly retrac-

238

MOLLUSCA.

tile. Foot very small. The more important genera of this
family are Mya, Corbula, Thetis^ Panopcea, and Saxicava.

In the Gapers (Mya\ the shell is oblong, inequivalve, and
gaping at both ends. The left valve is the smallest, and
it carries an internal ligament supported upon a prominent
cartilage-process (fig. 198). The Myas live buried verti-
cally 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 the shell is inequivalve, the left valve the
smallest, and with a prominent cartilage-process ; but the shell
is gibbous, and does not gape at its ends, whilst the pallial
sinus is small. Numerous fossil species are known, commenc-
ing in the Lower Oolites.

The genus TJietis is a small one, including thin, translucent,

sub-orbicular shells, with an ex-
ternal ligament. A few species
of the genus are known, com-
mencing with the Lower Cre-
taceous Rocks.

Panopcea resembles Mya in
having a thick oblong shell,
gaping at each end; but the
shell is equivalve, and the liga-
ment is external. Very numerous fossil species of this genus
are known, commencing in the Lower Oolites.

Saxicava, as its name implies,
includes shells which form bur-
rows in rocks. The adult shell
(fig. 199) is edentulous, equi-
valve, and oblong, gaping at the
ends, and furnished with an ex-
ternal ligament. The genus seems
to commence in the Eocene
Tertiary, and has continued to
the present day.

FAM. 19. ANATINID^E. — Shell
often inequivalve, with an external
ligament. Mantle-lobes more or
less united. Siphons long, more
or less united. Foot small. The
more abundant and important
fossil genera of this family are
Anatina, Pholadomya, and Myarites.

Fig. 199. — Saxicazxi ntgosa, left
valve. Post-Pliocene and Recent.

Fig. 200. — Anatina spatulata.
Kimmeridge Clay (Upper Oolites).

LAMELLIBRANCHIATA. 239

In the Lantern-shells (Anatina) the shell is oblong, gaping
posteriorly, and having the beaks directed towards the posterior
side (fig. 200). The hinge of each valve carries a spoon-
shaped cartilage-process. The
Anatince are doubtfully repre-
sented in the Devonian, and
still more dubiously in the
Silurian Rocks. They occur,
however, abundantly in the
Secondary Rocks, and are
present in smaller numbers in

the TertiarieS. Fig. 201. — Pholadomya cequivaivis.

The genus Pholadomya in-
cludes a large number of shells, which are equivalve, ob-
long, and gaping posteriorly (fig. 201). The shell is thin,
ventricose, and adorned with radiating ribs on the sides.
The ligament is external, and there is a large pallial sinus.
The species of Pholadomya are very numerous in the Secondary
Rocks, where they attain their maximum. They are much
reduced in number in the Tertiaries, and are barely repre-
sented at the present day.

The genus Myacites has a gaping ventricose shell, with the
umbones directed anteriorly, and the ligament external. They
are known in the Palaeozoic period, commencing in the Silu-
rian ; and they are represented in the earlier portion of the
Secondary period; but they seem to have died out in the
Chalk.

FAM. 20. GASTROCH.«NiDjE. — Shell equivalve, gaping, with
thin edentulous valves, sometimes cemented to a calcareous
tube. Mantle-margins thick in front, united, with a small
pedal aperture. Siphons very long, united. Foot finger-
shaped. The members of the GastrochcEnidce burrow in mud
or stone, and the only two fossil genera are Gastrochana and
Clavagella, the existence of AsfiergilluniAn. a fossil state being
doubtful.

In GastrocJuzna the shell is wedge-shaped, gaping in front
and closed behind. The fossil species commence in the In-
ferior Oolite, and the genus is represented at the present day.
In Clavagella (fig. 202) the shell is oblong, one of the valves
being free, whilst the other forms part of a more or less elon-
gated calcareous tube, which is often divided by a longitudinal
partition arid terminates' in tubular openings. The fossil
Clavagellce commence in the Upper Greensand, and the genus
is represented by several living species.

FAM. 21. PBOLADID.E. — Shell gaping at both ends, without

240

MOLLUSCA.

Fig. 202. — Glaziagella cretacea. Chalk.

hinge or ligament, often with accessory valves. Animal club-
shaped or worm-like, with a
short truncated foot. Mantle
closed in front ; siphons long,
united to near their extremi-
ties.

In the genus Pholas the
shell is cylindrical or oval,
the valves are edentulous, and
there is no ligament or a rudi-
mentary 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. Many
fossil species of the genus are known, commencing in the
Jurassic Rocks.

In the genus Teredo 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 transverse furrow; hinge-margins re-
flected in front, marked by the anterior muscular impressions :
umbonal cavity with a long curved muscular process." — (Wood-
ward.) Species of Teredo 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.

CHAPTER XXL
GASTEROPODA.

THE Gasteropods are Molluscs in which the body is furnished
with a distinct head, and the mouth is provided with a mastica-
tory apparatus or " lingual ribbon" Locomotion is effected by
means of a broad, horizontally-flattened, ventral disc — the "foot"
— or by a vertically-flattened, Jin-like modification of the same.
The body is never included in a bivalve shell ; and may be naked.
Usually, however, there is a " univalve " shell, or in some cases a
" multivalve " shell.

This class includes all those Molluscous animals which are

GASTEROPODA. 241

commonly known as " Univalves," such as Land-snails, Sea-
snails, Whelks, Limpets, &c. In the Chitons, however, the
shell is composed of eight pieces (" multivalve ") ; and in the
Slugs, the shell is minute and is completely concealed in the
mantle ; whilst in the Sea-slugs and Sea-lemons the animal is
" naked," and is destitute of a shell.

In their habits the Gasteropods show great differences,
most' of them being free and locomotive, though some are
sedentary. The typical forms move about more or less
actively by the successive contractions and expansions of a
muscular organ developed upon the ventral surface of the body
and known as the " foot." In many cases the posterior por-
tion of the foot secretes a calcareous, horny, or fibrous plate,

Fig. 203. — Amfiullaria cajuiliczdata, one of the Apple-shells, o Operculum ;
s Respiratory siphon.

which is called the " operculum " (fig. 203, o), and which serves
to close the aperture of the shell when the animal is retracted
within it. Lastly, in one aberrant group of the Gasteropods
(Heteropodd) the animal is fitted for swimming in the open
ocean, by the conversion of the " foot " into a vertically-
flattened fin.

The respiratory process in the Gasteropods differs consider-
ably in different cases ; and the class may be divided into two
principal sections, according as the animal is fitted for breath-
ing air directly or through the medium of water. The air-
breathing Gasteropods are known as the Pulmonata or Pul-
monifera, and comprise forms which either live on land (Snails,
Slugs, &c.), or which inhabit fresh water (Pond-snails, &c.)
The water-breathing Gasteropods are mostly provided with
distinct gills or " branchiae," and they form the section of the
Branchifera. They are mostly inhabitants of the sea; but
some of them inhabit fresh water.

242

MOLLUSCA.

Shell of the Gasteropoda. — The shell of the Gasteropoda is
composed either of a single piece (univalve), or of a number
of plates succeeding one another from before backwards (mul-
tivalve). The univalve shell 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 alteration, as is seen in the common Limpet (Patella). In
the great majority of cases, however, the cone is considerably
elongated, so as to form a tube, which may retain this shape
(as in Dcntalium), but is usually coiled up into a spiral. The
" spiral univalve " (fig. 205) may, in fact, be looked upon as the
typical form of the shell in the Gasteropoda. 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 in the same plane, when the shell
is said to be " discoidal " (as in the common fresh-water shell
Planorbis). 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," " trochoid," " turbinated,"
&c. This last form (fig. 204) is the one which may be looked

Fig. 204.— Cassis caucellata, a Spiral Gasteropod. \a " Spire," placed at the posterior
end of the shell ; b " Mouth," placed at the anterior end of the shell ; c Inner or colu-
mellar lip ; d Outer lip ; e Notch for the passage of a respiratory siphon.

upon as most characteristic of the Gasteropods, the shell being
composed of a number of whorls passing obliquely round a
central axis or " columella," having the embryonic shell or
" nucleus " at its apex, 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." The lines or grooves
formed by the junction of the whorls are termed the " sutures,"

GASTEROPODA.

243

and the whorls above the body-whorl constitute the " spire"
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
the "aperture" of the shell is termed the "peristome," and is
composed of an outer and inner lip (fig. 204), of which the
former 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." 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.

Fig. 205. — Scalaria
GrcKulandica^ a Ho-
lostomatous Univalve.
Post-Pliocene.

Fig. 206. — Fusus tprnatus, a Si-
phonostomatous Univalve. Post-
Pliocene.

In the multivalve Gasteropods, the shell is composed of
eight transverse imbricated plates, which succeed one another
from before backwards, and are embedded in the leathery or
fibrous border of the mantle, which may be plain, or may be
beset with bristles, spines, or scales.

In the marine Univalves two important variations exist in
the form of the mouth of the shell. In one group (fig. 205)

244 MOLLUSCA.

the mouth of the shell is unbroken or " entire," not having
any notch or indentation of its margin. The shells in which
the mouth has this form are termed " holostomatous ; n and
for the most part they belong to Gasteropods which are phyto-
phagous, or live upon vegetable food. The possession, how-
ever, of a holostomatous shell in reality simply proves that the
animal had no respiratory " siphons," or tubes formed by the
folding of the mantle. In a second group the aperture of the
shell (fig. 206) is notched in front ; and the shell is said to be
" siphonostomatous." There may be a posterior notch as
well as the anterior one, and one or both of these notches may
be produced into longer or shorter canals. The Siphonosto-
matous Univalves are mainly carnivorous in their habits ; but
the notched mouth does not necessarily indicate the nature of
the food. The possession of a Siphonostomatous shell, on the
contrary, merely indicates that the animal possessed tubular
inflections of the mantle, or " respiratory siphons," by which
the water is conveyed to and from the gills.

Divisions of the Gasteropoda. — The following table shows
the chief divisions of the Gasteropoda : —

TABLE OF THE GASTEROPODA.

SECTION A. BRANCHIFERA. — Respiration aquatic, by the walls of the
mantle-cavity or by gills.

ORDER I. PROSOBRANCHIATA. — The branchiae situated (prosori)
in advance of the heart.

Division a. Siphonostomata. — Margin of the shell-aperture
notched or produced into a canal. This division comprises the
families of the Strombidcc (Wing-shells), Muricidcc, Buccinidce
(Whelks), Conidce (Cones), Volutidce (Volutes), and Cypraida
(Cowries).

Division b. Holostomatd. — Margin of the shell-aperture " en-
tire" rarely notched or produced into a canal. This division
includes the families of the Naticidce, Pyramidellid<z, Cerithiada,
Melaniadce, Turritellidcz, Littorinidce (Periwinkles), Paludinidce
(River-snails), Neritida, Turbinid<z (Top-shells), Haliotida% Fis-
stirellidtz (Keyhole-limpets), Calyptrceidtz (Bonnet-limpets), Patel-
lidce (Limpets), Dentalidce (Tooth-shells), and Chitonidce.
ORDER II. OPISTHOBRANCHIATA. — Branchise placed towards the
rear {opisthen} of the body.

Division a. Tedibranchiata. — Brdnchia covered by the shell or
mantle. A shell in most. Sexes united. The division includes the
families of the Tornatellidce, Bullidce (Bubble-shells), Aplysiada
(Sea-hares), PUurobranchiadae^ and Phyllidiada.

Division b. Nudibranchiata. — Animal destitute of a shell in the
adult condition. Branchiae external, on the back or sides of the
body. This division includes the various naked Gasteropods
commonly known as Sea-lemons and Sea-slugs.
ORDER III. NUCLEOBRANCHIATA, or HETEROPODA. — Shell pre-
sent or absent. Animal free-swimming and oceanic, with a fin-like

GASTEROPODA. 245

tail or flattened ventral fin. This order includes the two families of
the Firolidce and Atlantidce.

SECTION B. PULMONIFERA. — Respiration aerial, by means of a pul-
monary chamber.

ORDER IV. INOPERCULATA. — Shell not provided with an oper-
culum. This order comprises the families of the Heliddce (Land-
snails), Limacida (Slugs), Oncidiada^ Limnceida (Pond-snails), and
Auriculid(Z.

ORDER V. OPERCULATA. — Shell provided with an operculum. In
this order are the families Cyclostomidce and Aci&tlida.

Distribution of the Gasteropoda in time. — As regards the
general distribution of the Gasteropods in past time, all the
families of the Prosobranchiata are known by fossil representa-
tives. Of the Opisthobranchiata the Tectibranchiate section
is tolerably well represented in past time ; but the section of
the Nudibranchiata, from the total absence of the shell, is not
known at all in the fossil condition. Both families of the
Heteropoda are represented by fossil forms. The Pulmonate
Gasteropods, from the fact that they either live on land or
inhabit fresh water, are necessarily not so fully represented in
past time as are the Branchiate Gasteropods. Still, nearly
all the families of the air-breathing Univalves have fossil
representatives.

Taken as a whole, the Gasteropoda are represented in past
time from the Upper Cambrian Rocks upwards. Of the
Branchifera, the Holostomata are more abundant in the Palaeo-
zoic period ; and the Siphonostomata predominate more in the
Secondary and Tertiary periods, attaining their maximum at
the present day. The place of the carnivorous Siphonostomata
in the Palaeozoic seas appears to ha've been filled by the
Tetrabranchiate Cephalopods. The Branchiate Gasteropods
of fresh water are chiefly represented as fossils by the genera
Paludina, Valvata, and Ampullaria.

The Heteropoda are likewise of very ancient origin, having
commenced their existence in the Upper Cambrian deposits.
The genera Better ophon, Porcellia, Cyrtolites, and Madnrea,
are exclusively Palaeozoic ; Bellerophina is found in the
Gault (Secondary), and Carinaria has been detected in the
Tertiaries.

The Pulmonate Gasteropoda, as was to be anticipated, are
not found abundantly as fossils, occurring chiefly in lacustrine
and estuarine deposits, in which the genera Limncea, Physa,
Ancyius, &c., are amongst those most commonly represented.
These, however, are entirely Mesozoic and Kainozoic. In
the Palaeozoic period the sole known representatives of the

246 MOLLUSCA.

Pulmonifera are the Pupa vetusta and Zonites priscus of the
Carboniferous Rocks.

In the following* are given the characters of those families
of the Gasteropoda which occur in the fossil state, with the
leading genera of each family and their range in time.

SECTION A. BRANCHIFERA. — Respiration aquatic, generally
by gills.

ORDER I. PROSOBRANCHIATA. — Gills situated in advance of
the heart.

Division a. Siphonostomata. — Mouth of the shell notched, or
produced into a canal.

FAM. i. STROMBID^E. — Shell with an expanded lip, deeply
notched near the canal. Operculum claw-shaped. Foot nar-
row, adapted for leaping. All the existing genera of the
Strombidce are represented in the fossil state, but the family
does not seem to have come into existence before the Jurassic
period, and it attained its maximum in the Tertiary period.

Fig. 207. — Pteroceras oceani. Neocomian.

The genus Strombus has a shell with a short spire, a long
aperture, and an expanded outer lip, there being a posterior as
well as an anterior notch. The Strombs are represented in

* Tn the characters of the families of the Gasteropoda, as in those of the
Lamellibranchiata, Woodward's 'Manual of the Mollusca' has been mainly
followed.

GASTEROPODA. 247

the Cretaceous and Tertiary Rocks; but they attain their
maximum in existing seas.

The Scorpion-shells form the genus Pteroceras (fig. 207), in
which the shell of the adult has its outer lip furnished with
long claws, one of which forms a posterior canal close to the
spire. Many fossil species are known, commencing in the
Lias.

In the genus Rostellaria, 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.
Lastly, the genus Seraphs comprises smooth shells, with a
short or obsolete spire, a thin outer lip, and a long narrow
mouth. The fossil species date from the Eocene Tertiary.

FAM. 2. MURICID/E. — Shell with a straight anterior canal,
the aperture entire posteriorly. Foot broad. The Muritida
are essentially characteristic of the Tertiary and Recent
periods. They commence, however, in the Jurassic Rocks, in
some doubtful examples, and they aje certainly represented
in the Cretaceous Rocks by not a few forms.

In the genus Murex the canal is often very long, and may
be partially closed ; the shell is ornamented with longitudinal
ridges or rows of spines (yarices\ and the aperture is rounded.

In the nearly-related Typhis (fig. 208) there are tubular
spines between the varices, and the last of these lodges the
posterior siphon. Both
Murex and Typhis com-
mence in the Eocene Ter-
tiary, and have attained
their maximum in existing
seas.

Pisania commences to
be represented in the
Eocene, as do the genera
Ranella, Triton, and Can-
cellaria. Fasciolaria and
Pyrula commence their

.-, f^ Fig. 208. — lyphis tubifer. Rocene 1 ertiary.

existence in the Cre-
taceous Rocks ; and Turbinella and Trichotropis do not make
their appearance till the Miocene. Lastly, the great genus
Ftistts, distinguished by the spindle-shaped, many-whorled
shell, and long straight canal (fig. 209), appears to have its
commencement in the Oolites. Fusi become very numerous
towards the close of the Cretaceous period, and they are
very plentiful in the Tertiaries. One of the common fossils

248 MOLLUSCA.

of the Red Crag (Newer Pliocene) is the reversed shell,
Fusus contrarius, which is now known to exist in the living
state as well.

Fig. 209. — Fusus Necomieiisis. Fig. 210. — Buccinum nndatum (var.)

Lower Greensand. Post- Pliocene and Recent.

FAM. 3. BUCCINID^E. — Shell notched anteriorly, or with the
canal reflected, producing a kind of varix on the front of the
shell. With the exception of the extinct genus Purpurina of
the Lower Oolites, and some species of Buccinum in the Cre-
taceous Rocks, the family of the Buccinidcz is exclusively con-
fined to the Tertiary and Recent periods. The two great
families, therefore, of the Muricidcz and Buccinida are essen-
tially characteristic of the later periods of the earth's history.
The most important fossil genera of the Buccinida are Buc-
cinum, Terebra, Nassa, Purpura, Cassis, and Olivet.

The Whelks form the genus Buccinum (fig. 210), dis-
tinguished by the ventricose body-whorl, large aperture, and
short reflected canal. Some few species of Buccimim are
found in the Upper Cretaceous Rocks ; but the genus is
essentially Tertiary and Recent.

Terebra comprises the Auger-shells, distinguished from the
Whelks by their long, pointed shells, consisting of many whorls,
and having a small mouth. They commence in the Eocene
Tertiary. The Dog-whelks (Nassa) also commence in the
Eocene, and are distinguished from the Whelks chiefly by
having the columellar lip expanded and callous, with a tooth
near the anterior canal. The shells of the genus Purpura

GASTEROPODA.

249

have a short spire and wide aperture, with an expanded and
flattened inner lip. They commence in the Miocene Tertiary.
The Helmet-shells (Cassis] begin in the Eocene, and are dis-
tinguished by their short spire, large body-whorl, long aperture,
recurved canal, and expanded inner lip. Lastly, the Olives
(Oliva) and Rice-shells (OUvella) are characterised by their
cylindrical polished shell, with a short spire, a long narrow
aperture, notched in front, and obliquely-striated columella.
The living Olives are tropical and sub-tropical in their dis-
tribution, and the fossil species commence in the Eocene
Tertiary.

FAM. 4. CONID.E. — Shell inversely conical, with a long nar-
row aperture, the outer lip notched at or near the suture. The
Conidce. commence in the Cretaceous Rocks, abound in the
Tertiaries, and attain their maximum at the present day.

The true Cones form the genus Conus, and are distinguished
by their short spire and regularly conical
shell, of which the outer lip is notched
near the suture. The Cones are repre-
sented in the Chalk, but are mainly Ter-
tiary and Recent. The genus Pleurotoma
is distinguished by a spindle-shaped shell,
with a long spire, the outer lip having
a deep slit near the suture. The genus
commences in the Chalk, and has an
enormous development in the Tertiaries,
from which nearly three hundred species
are known. The maximum, however, is
attained in existing seas, in which there
are very numerous species.

FAM. 5. VQLUTID^E. — Shell turreted or
convolute, the aperture notched in front ;
the Qolumella obliquely plaited. No
operculum. Foot very large ; mantle
often reflected over the shell. The living
members of the Volutidce are chiefly in-
habitants of warm seas, and are often
remarkable for their brilliant colours.
The family does not appear to have ex-
isted till towards the later portion of the
Cretaceous period ; but it is abundantly
represented in the Tertiaries, and attains
its maximum in existing seas. The most
important genera are Voluta and Mitra.

The true Volutes form the genus Valuta (fig. 211), charac-

Fig. 211. — Valuta, elongata.
Chalk.

250 MOLLUSCA.

terised by the short spire, large, deeply-notched aperture, and
columella with several plaits. Species of Valuta occur in the
Cretaceous period, but the genus is mainly Tertiary and Recent.

In the genus Mitra the shell is spindle-
shaped, with a long spire, and small
mouth. The Mitrce commence in the
Cretaceous period, but the fossil species
are mainly distributed through the Ter-
tiary formations.

FAM. 6. CYPR^ID^E. — Shell convo-
lute, enamelled ; spire concealed ; aper-
ture narrow, channelled at each end.
Outer lip thin in the young shell, but
thickened and inflected in the adult.
Foot broad ; mantle forming lobes which
Fig. 2i2.^cyp>-cea eiegaus. meet over the back of the shell. The
only important genus of this family is
that of Cyprcea (fig. 212), comprising the numerous and well-
known living shells which are commonly called Cowries. The
Cyprace are mainly, but not exclusively, inhabitants of warm
seas, and they attain their highest development between the
tropics. The 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. 212) the spire is completely concealed within
the shell, the entire surface is generally covered with shining
enamel, the inner lip is crenulated, and the outer lip is thick-
ened, inflected, and crenulated. The small Cowries of which
Cyprcza Eiiropcea is the type, are not known as occurring in the
fossil condition.

Division b.Holostomata. — Margin of the shell-aperture "entire"
rarely notched or produced into a canal.

FAM. 7. NATICID^E. — Shell globular, of few whorls, with a
small spire ; outer lip acute ; inner lip (pillar) often callous.
Foot very large ; mantle-lobes hiding more or less of the shell.
This family is stated to commence in the Upper Silurian
Rocks ; but there is more or less uncertainty as to the true
affinities of the Palaeozoic fossils which are referred here.
The most important fossil genus is Natica itself.

The shell in Natica (fig. 213) is thick, smooth, and polished,
often with coloured markings. The inner lip is callous, and
the shell is umbilicated. Fossil Naticce have been described
from the Upper Silurian, Devonian, Carboniferous, and Per-
mian Rocks; and they are very abundant in all the Secondary

GASTEROPODA. 251

and Tertiary formations. The sub-genus Naticopsis is Carbo-
niferous, Naticella is Triassic, and Globulus is found in the
Eocene.

FAM. 8. PYRAMIDELLID^E. — Shell turreted, with a small
aperture ; sometimes with one or more prominent plaits on the
columella. Operculum horny and imbricated. The Pyrami-
dellidcz commence in the Lower Silurian Rocks, and appear to
be on the decline at the present day. The chief fossil forms
belong to the genera Chemnitzia, JEulima, Loxonema, and
Macrocheilus.

Gkemnitzia includes a number of slender, turreted, many-
whorled shells, with plaited whorls, and a simple aperture. The
genus appears to commence in the Permian Rocks, and whilst
more than one hundred and fifty fossil species are known, the
number of living forms is very small. Many of the shells, how-
ever, included under this head, are of very doubtful affinities.

Fig. 213. — Natica clausa. Fig. 214. — Macrocheilus sub-

Post- Pliocene. costatus. Devonian.

Eulima includes small, polished, elongated shells, with level
whorls and a reflected inner lip. Eulima are of doubtful oc-
currence in the Carboniferous Rocks, are sparingly represented
in the Secondary Rocks, but are tolerably abundant in the
Tertiaries.

The genera Loxonema and Macrocheilus (fig. 214), lastly,
include Palaeozoic shells, whose true place is in many cases
uncertain. The former extends from the Lower Silurian to
the Trias, but the latter is mainly, if not exclusively, confined
to the Devonian and Carboniferous Rocks.

MOLLUSCA.

FAM. 9. CERITHIAD^E. — Shell spiral, turreted ; aperture
channelled in front, with a less distinct posterior canal. Lip
generally expanded in the adult. Operculum horny and
spiral. The Cerithiadcz are exclusively confined to the Second-
ary, Tertiary, and Recent periods, and are represented in the
Tertiary Rocks by a vast number of forms. The most import-
ant fossil forms belong to the genera Cerithium, Pvtamides,
Nerincea, and Aporrhais, of which Nerinaa is extinct, and is
exclusively confined to the Secondary period.

For all practical purposes Cerithium and Potamides may be

considered together, as no
strict line of demarcation
can be drawn between the
fossil forms. In both, the
shell is turreted and many-
whorled (fig. 215), with or
without varices.

The aperture of the shell
is small, with a tortuous an-
terior canal, and an ex-
panded outer lip. Most of
the living forms are inhabi-
tants of fresh or brackish
waters, and they are chiefly
found in hot climates. The
fossil forms, to the number
of nearly five hundred,
commence in the Trias, but they attain their maximum of
development in the Eocene Tertiary.

In the genus Nerincea (fig. 2 1 6), the shell is turreted, many-
whorled, and nearly cylindrical. The columella carries con-
tinuous ridges, and similar ridges exist on the interior of the
whorls, so that casts of the interior of the shell are often very
unlike the form of the exterior. The aperture of the shell is
channelled in front. The species of Nerincea are exclusively
Jurassic and Cretaceous, and are very numerous. One of the
limestones of the Jura, believed to be of the age of the Coral
Rag (Middle Oolite) of Britain, abounds to such an extent
in these shells as to have gained the name of " Calcaire a
Nerinees."

In the genus Aporrhais, lastly, the shell is turreted, and the
outer lip of the adult is greatly expanded and lobed. The
species of this genus are marine in their habits. A great many
Jurassic and Cretaceous shells, generally referred at present to
Rostdlaria, probably belong really to Aporrhais ; but the de-

Fig. 215. — Cerithi- Fig. 216. — Nerin&a
inn liexagonum. Eo- bisulcata. Chalk,
cene Tertiary.

GASTEROPODA. 253

termination of these fossils by the shells alone is attended with
great difficulties.

FAM. 10. MELANIAD^E. — Shell spiral, turreted; aperture
often channelled or notched in front ; outer lip acute. Oper-
culum horny and spiral. Many fossil shells have been referred
to the Melaniada, but it is probable that most of these belong
to the Palaeozoic genus Loxonema and the Mesozoic Chem-
nitzia. The true Melanice do not appear to have commenced
their existence till the Eocene Tertiary. All the living species
inhabit fresh water, generally in the warmer parts of the world ;
and it is probable that all the fossil species occur only in fluvia-
tile and lacustrine deposits.

FAM. ii. TURRITELLID^E. — Shell tubular or spiral, often
turreted; upper part partitioned off; aperture simple. Oper-
culum horny, many-whorled. Foot very short. Branchial
plume single. The Turritellidcz are not known to have existed
in the Palaeozoic period ; but they appear to commence about
the middle of the Jurassic period, abounding in the Tertiaries,
and attaining their maximum in existing seas. The chief
fossil genera are Turritella, Vermetus, and Scalaria.

In Turritella (fig. 217) the shell is turreted. many-whorled,
and spirally striated ; the aperture is
small and rounded, and the peristome
thin. Species of Turritella have been
described from the Palaeozoic and older
Mesozoic formations, but almost cer-
tainly belong to the genera Murchisonia
and Loxonema. The genus is for the
first time represented with certainty in
the Lower Cretaceous Rocks (Neo-
comian), and many fossil species are
found in the Tertiaries.

The genus Vermetus comprises tubu-
lar shells, the chief interest of which

,-, 11 -i • i .1 Fig. 217. — Turntella angu-

is the strong resemblance which they iata. Neocomian.

show to the Annelidous genus Serpula.

The shell is attached, 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 Ser-
pula. Fossil Vermeti are known from the Lower Cretaceous
upwards.

The genus Scalaria comprises the Wentle-traps, in which

254

MOLLUSCA.

the shell is very like that of Turritella, but the whorls are
ornamented with transverse ribs, and the peristome is continu-
ous round the circular aperture (fig. 205). The Scalarice com-
mence in the Middle Oolites (Coral Rag), and attain their
maximum in existing seas.

FAM. 12. LITTORINID^E. — Shell spiral, top-shaped, or de-
pressed; aperture rounded and entire, operculum horny
and pauci-spiral. The exact range of the Littorinidce. in
time is uncertain, owing to the difficulty of determining the
true affinities of many fossil Univalves. Several Palaeozoic
and Mesozoic shells have been referred to Littorina, and
the genus Rissoa commences in the Permian. The family,
however, is mainly characteristic of the Tertiary and Recent
periods.

In the genus Littorina 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 Middle Tertiaries to the present
day.

In the genus Solarium (fig. 218) the shell is much depressed;

there is a large and deep umbilicus,
running from the base to the apex
of the shell, and the aperture of the
shell is rhombic. Doubtful Second-
ary forms of this genus are known ;
but the undoubted species com-
mence in the Eocene Tertiary. The
genus Phorus also comprises shells,
the true range of which is very un-
certain. Undoubted species, how-
ever, date from the Cretaceous
period. Lastly, in the genus Rissoa
the shell is very small, pointed, and
many-whorled, with a small round
aperture surrounded by a continuous
peristome. Many fossil species are
known, commencing in the Permian
Rocks, abounding in the Oolites, and being very abundant in
the later Tertiaries.

FAM. 13. PALUDINID^E. — Shell conical or globular; aper-
ture rounded and entire; operculum horny or shelly. The
Paludinida are essentially inhabitants of fresh water ; though
they sometimes live in brackish, or even in 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

Fig. 218. — Solarium ornatujn.
Gault (Upper Cretaceous).

GASTEROPODA.

255

or lacustrine in their origin. The three chief or only living
genera are, Paludina, Valvata, and Ampullaria. The two
former date from the Cretaceous period, the first possibly
from the Jurassic, and both abound in the Wealden and in
many Tertiary deposits. The existence of Ampullarice in a
fossil state is attended with considerable uncertainty, chiefly
from the great difficulty, or impossibility, of separating them
from species of the marine genus Natica.

FAM. 14. NERITID^E. — Shell thick, globular, with a very
small spire ; aperture semi-lunate, its cglumellar side expanded ;
outer lip acute. Operculum shelly, sub-spiral. The Neritida
are not known as occurring in the Palaeozoic Rocks, but are
found from the Jurassic period onwards, attaining their maxi-
mum at the present day.

In the genus Nerita (fig. 219) the shell is thick, with a broad
columella, the inner edge of which is straight and toothed.

Fig. 219. — Nerita Schemidelliana. Eocene Tertiary.

The outer lip is thickened and often denticulated internally.
The true Nerites are inhabitants of warm seas ; and they date
in past time from the Lias. The nearly-allied genus Neritina
includes the so-called "fresh-water Nerites," which agree in
most characters with Nerita, but inhabit fresh or brackish
waters. The fossil species commence in the Eocene Tertiary.
Lastly, the genus Pileolus comprises small limpet-shaped shells,
with a semi-lunar aperture below. The only fossil species are
from the Lower Oolites (Great Oolite).

FAM. 15. TURBINID^:. — Shell turbinated (top-shaped) or
pyramidal, nacreous (i.e. pearly) inside. Operculum horny and
multi-spiral, or calcareous and pauci-spiral. The family of the
Turbinida has a very high antiquity, dating from the Lower
Silurian ; but many of the older shells referred to this family
are of more or less doubtful affinities. The most important
fossil genera are Turbo, Trochus, and Euomphalus.

In the genus Turbo (fig. 220) the shell is turbinated, with a

256

MOLLUSCA.

round base. The whorls are convex ; the aperture is large and

rounded ; and the operculum is calcareous. A great number

of fossil species of this genus have been
described, commencing in the Lower
Silurian ; but there is considerable
doubt as to the true position of many
of the older forms.

In the genus Trochus the shell is
pyramidal, with a nearly flat base ; the
aperture is oblique and rhombic in
shape, and the operculum is horny. A
great number of species of this genus,
also, have been described, commenc-
ing in the Silurian Rocks. As in the
case of Turbo, however, the affinities

of many of the older forms are very problematical.

The genus Euomphalus (fig. 221)15 entirely extinct, and is

essentially Palaeozoic, ranging from the Silurian to the Trias,

Fig. 220. — Turbo subcostatus.
Devonian.

Fig. 221.— Euomphalus De Cewt (Billings)^ a Front view ; b View of the umbilicus.

Devonian.

but being most abundant in the Carboniferous Rocks. The
shell in this genus is depressed or discoidal, the whorls lying
nearly or quite in the same plane. The whorls are angulated
or coronated, the aperture is polygonal, the umbilicus is very
large, and there is a shelly operculum. The genus Ophileta is
closely allied to Eiiomphalus, if not identical with it.

FAM. 1 6. HALIOTID^E. — Shell spiral, ear-shaped, or trochoid;
aperture large, nacreous. Outer lip notched or perforated.
No operculum. Mantle-margin with a posterior fold or siphon,
occupying the slit or perforation in the shell.

The living genera Haliotis and Scissurella are not known in

GASTEROPODA.

257

rocks older than the Miocene Tertiary. The extinct genera
Pleurotomaria and Murchisonia are, on the other hand, of great
antiquity, the latter being exclusively Palaeozoic, and the
former mainly so.

The genus Haliotis comprises the so-called " ear-shells,"
distinguished by their ear-shaped shell, with a minute spire,
an enormous aperture, and a series of round perforations in
the outer angle of the shell. A few fossil species are known,
commencing in the Miocene.

In the genus Srissurella, which also commences in the
Miocene, the shell is thin, with a large and greatly expanded
body-whorl, and the place of the perforations of Haliotis is
taken by a simple slit in the margin of the outer lip.

The genus Plettrotomaria comprises a great number of
Palaeozoic univalves, which occur in the Silurian, Devonian,
and Carboniferous formations. In sediments later than the
Carboniferous the genus is largely represented, extending even
to the close of the Mesozoic period. In the Jurassic period
especially the genus has a great development, most of the
forms being more ornate than those from the older rocks.
In the Cretaceous Rocks the genus finally dies out, with
the sole exception of a single living species. The form of
the shell in Pleurotomaria (fig. 222) differs considerably in
different cases. Very
commonly the shell is
very similar to that of
Trochus. In other cases
it more nearlyresembles
Turbo ; and sometimes
it is very much flatten-
ed out and depressed.
The shell consists of
few whorls, of which
the last may be discon-
nected from the others,
and is essentially dis-
tinguished by its sub-
quadrate aperture, with
a deeper or shallower
slit in the outer lip. 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 Trochus and Turbo.

Murchisonia (fig. 224) is another genus of great importance

R

Fig. 222. — Pleurotomaria Agave. Lower
Silurian (Billings).

Fig. 223. — Pleurotomaria Dryope. Lower
Silurian (Billings).

258

MOLLUSCA.

to the student of the older rocks, as it is exclusively confined
to the Palaeozoic period, ranging from the Lower Silurian to
the Permian. The shell in Murchisonia closely resembles
that of Pleurotomaria, but is usually more elongated and com-
posed of a greater number of whorls. The outer lip is deeply
notched, and the whorls have the same band on their exterior
as is present in Pleurotomaria. The aperture of the shell is
slightly channelled in front, and the surface is often variously
sculptured and adorned.

We may place here, provisionally, the Palaeozoic genus
Holopea (fig. 225), the exact affinities of which are doubtful.

The shell in this genus is
spiral, the aperture oval,
and the outer lip sinuated
near the base. The genus
has been compared to the
violet-snail (lanthina) of
the Atlantic, in which
case its place should be
here; but its true posi-
tion is altogether uncer-
tain. It is exclusively
Silurian in its range ; and
it is probable that the
genus Platyceras should
be united with it, in which
case the vertical range
will be extended at any
rate to the Carboniferous.
FAM. 17. FISSURELLID^E : — Shell conical, patelliform, with a
notch in the anterior margin, or a perforation at the apex,
which is occupied by the anal siphon. Muscular impression
horse-shoe shaped, open in front. The existence of the Fis-
surellidcz in the Palaeozoic period is open to considerable
doubt ; but a good many fossil forms are known from the
Secondary and Tertiary Rocks.

The genus Fissurella comprises the so-called " Keyhole
Limpets," distinguished by having the apex of the shell per-
forated by a larger or smaller, generally oval aperture. Doubt-
ful examples of the genus have been indicated as occurring in
the Devonian and Carboniferous ; but there are a good many
unequivocal species in the Secondary and Tertiary Rocks. In
the Oolitic genus Rimula the perforation, instead of being at
the apex of the shell, is placed a little above the anterior
margin. Lastly, in Emarginula the anterior margin is fur-

Fig. 224. — Murcki-
sonia g racilis ( H al 1) .
Lower Silurian.

Fig. 225. — Hotopea
Guelphensis (Billings).
Middle Silurian.

GASTEROPODA. 259

nished with a longitudinal notch or slit. The species of this
genus date from the Trias.

FAM. T 8. CALYPTR^ID^: : — Shell limpet-shaped, with a more
or less spiral apex; interior simple, or divided by a shelly
process to which the adductor muscles are attached. Exclud-
ing shells whose true position is uncertain, it would appear
very questionable if any of the Calyptrceida are found in the
Palaeozoic Rocks. They are by no means abundant in the
Secondary formations ; and though more plentiful in the Ter-
tiaries, they attain their maximum in existing seas.

The genus Calyptrcea 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.
With doubtful exceptions, the fossil species of Calyptrcea are
all of Tertiary age. In the genus Crepidula there is a shelly
partition covering the posterior half of the interior of the shell.
The fossil species date from the Eocene Tertiary. In the
genus Pileopsis (or Capulus) are included the " Bonnet-lim-
pets," in which the apex of the shell is spirally recurved. If
Platyceras be excluded from this genus, the species of Pileopsis
date from the Lias ; but the former is Palaeozoic.

FAM. 19. PATELLID^:: — Shell conical, with the apex turned
forwards ; muscular impression horse-shoe shaped, open in
front. Foot as large as the margin of the mantle. Respira-
tory organ in the form of one or two branchial plumes,
lodged in a cervical cavity, or of a series of lamellae sur-
rounding the animal between the body and the mantle. The
Patellidcz commence to be represented in the Lower Silurian
Rocks, and have continued to the present day.

Fig. 226. — Metoptoma nycteis. _ a Side view ; b View of the upper side.
Lower Silurian (Billings).

The genera Patella (including the common Limpets), Ac-
&a, and Metoptoma can hardly be separated in practice
from one another. Patella and Acmcea, at any rate, are
palseontologically indivisible, since the only distinctions be-
tween them are in the nature of the respiratory organs. In-

260 MOLLUSCA.

eluding these genera, therefore, in one, the range of the
Limpets is from the Silurian upwards.

The genus Metoptoma (fig. 226) very closely resembles
Patella, but the muscular scar consists of a number of dis-
connected cavities. In the typical species, also, the anterior
side, under the apex of the shell, is truncated or nearly straight.
Species of Metoptoma are particularly abundant in the Lower
Silurian series ; but they range as far as the Carboniferous.

FAM. 20. DENTALIDJE : — Shell tubular, symmetrical, curved,
open at both ends. Aperture circular. Foot pointed, with
symmetrical side-lobes. The " Tooth-shells " are generally
placed here, in the vicinity of the Limpets ; but they are re-
ferred by Huxley to the class of the Pteropoda. The family
comprises the single genus Dentalium, well known by the
tubular, smooth, or longitudinally striated shell, open at both
ends. The fossil species are liable to be confounded with the
tubes of Tubicolar Annelides, or a reverse mistake to this may
be made. Several species have been described from the
Devonian, and more especially from the Carboniferous Rocks,
some of them of large size ; but more or less doubt obtains as
to the true nature of these. The Secondary Rocks have
yielded a considerable number of species, and they become
still more numerous in the Tertiaries.

FAM. 21. CHITONID^E : — Shell multivalve, composed of eight
transverse plates, disposed one behind the other in an imbricat-
ed manner. Animal with a broad creeping foot; branchiae
forming a series of lamellae between the foot and the mantle,
round the posterior part of the body. The Chitonidcz com-
prise only the single genus Chiton, with several
more or less distinct sub-genera. The species of
the family commence in the Lower Silurian, and are
rare as fossils, attaining their maximum at the pre-
sent day.

The distinctive peculiarities of the shell of the
Chitons (fig. 227), by which they may always be
separated from the Cirripedes, are the following :—
i. The shell never consists of more or fewer than
eight pieces. 2. The valves of the shell are al-
Grijn- ways placed one behind the other in a unilinear
series. 3. The six middle plates of the shell are
divided, each, by lines of sculpturing into three dis-
tinct areas — a dorsal and two lateral areas. 4. Each plate
is imbedded in the mantle of the animal by forward extensions
of its front edge, which are termed the "apophyses."

The Chitons are represented by fossil species in the Silurian,

GASTEROPODA.

26l

Fig. 228. — Cinulia Avellana (Avellana
cassis, D'Orbigny). Chalk.

Devonian, Carboniferous, and Permian Rocks, and are not so
excessively rare in the Carboniferous Limestone. They are
very poorly represented in the Secondary Rocks, and are by
no means abundant in the Tertiaries.

ORDER II. OPISTHOBRANCHIATA : — Gills placed towards the
rear of the body.

FAM. 22. TORNATELLID^E : — Shell external, spiral or con-
voluted ; aperture long and narrow ; columella plaited. The
Tornatellida are mainly Mesozoic, ranging from the Trias or
from the base of the Jurassic series to the Chalk inclusive,
and attaining their maximum in the Cretaceous series.
Several genera are entirely
extinct, of which the most im-
portant is Cinulia (fig. 228).
In this genus the shell is
globular, with a small spire,
the outer lip reflected and
crenulated interiorly, and the
columella with tooth - like
folds. All the species are
Cretaceous. In the genus
Tomatella, the shell is ovate,
with a well-marked spire, the outer lip thin, and the colu-
mella with a strong fold. The fossil species range from the
Trias upwards, and the genus, though on the decline, is re-
presented by several living species. Many of the Secondary
species belong to more or less distinct sub-genera ( Cylindrites,
Acteonella, and Acteonind).

FAM. 23. BULLID^ : — Shell convoluted, thin ; spire small or
concealed ; lip sharp. Animal often more
or less completely investing the shell.
The Bullida commence their existence in
the Jurassic period, and have continued
to the present day. The only important
genus is Bulla, comprising the so-called
"Bubble-shells" (fig. 229). The species
of this genus are not uncommon in the fossil condition, com-
mencing in the Oolites.

FAM. 24. APLYSIAD^: : — Shell absent or rudimentary, con-
cealed by the mantle when present. Animal slug-like ; sides
extensively lobed and reflected over the back and shell. One
or two shells from the younger Tertiary rocks have been re-
ferred, with great doubt, to the genus Aplysia.

FAM. 25. PLEUROBRANCHID^: .-—Shell limpet-like or con-
cealed, rarely wanting. Mantle or shell covering the back of

Fig. 229. — Bulla supra-
jurettsis. Middle Oolites.

262

MOLLUSCA.

the animal. Two doubtful species belonging to the genus
Umbrella have been described from the Tertiaries ; but the
family is otherwise unknown in the fossil condition.

CHAPTER XXII.

GA STEROPODA— Continued.

HETEROPODA AND PULMONIFERA.

ORDER III. HETEROPODA OR NUCLEOBRANCHIATA : — The
Gasteropods of this order 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 vertically-fiatte?ied ventral fin. They are found swim-
ming 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 operculum. In other
cases, as in Carinaria (fig. 230), the body is large, and there is

Fig. 230. — Heteropoda. Carinaria, cymbium. /Proboscis; £ Tentacles;
£ Shell ; / Foot ; d Disc. (After Woodward.)

Branchiae ;

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 Firolidce and Atlantidce.
The former of these is represented by a single species only,
from the Miocene Tertiary. The latter had a great develop-
ment in Palaeozoic seas, and is represented in the formations
of this period by several remarkable genera.

FAM. i. FIROLID^ : — Body large, never completely pro-
tected by a shell, often shell-less. Sometimes a small delicate

GASTEROPODA. 263

hyaline shell, placed on the back, protecting the gills. The
only genus of this family which is represented in a fossil state
is Carinaria (fig. 230), a single species of which has been found
in deposits of Tertiary age (Miocene).

FAM. 2. ATLANTID^E : — Animal furnished with a well-de-
veloped shell, into which it can retire. Shell symmetrical,
discoidal, destitute of septa, often provided with an operculum.
This family is represented by the genera Bellerophon, Maclurea,
Cyrtolites, Ecculiomphalus, and Porcellia, most of which are
exclusively Palaeozoic, whilst the others are mainly so.

In the genus Bellerophon (fig. 231) the shell is symmetrical,
convoluted, the coils of the shell usually lying in one plane.

Fig. 231. — Bellerophon Argo (Billings), a Front view ; b side view. Lower Silurian.

The whorls are few, smooth or sculptured, and there is a
dorsal keel along the convex margin of the shell. The aper-
ture is often more or less expanded, and is in most instances
emarginate or deeply notched on the dorsal side. The genus
ranges from the Lower Silurian to the Carboniferous. The
Bellerophina of the Gault (Upper Cretaceous) is doubtfully
allied to Bellerophon, and may belong to -the Pteropoda.

The genus Maclurea is very remarkable in its structure, and
all the known species are entirely confined to the Lower
Silurian Rocks. The shell (fig. 232) in this singular genus is
" discoidal, few-whorled, longitudinally grooved at the back,
and slightly rugose with lines of growth ; dextral side convex,
deeply and narrowly perforated ; left side flat, exposing the
inner whorls ; operculum sinistrally sub-spiral, solid, with two
internal projections, one of them beneath the nucleus, very
thick and rugose" (Woodward). Maclurea has been variously
regarded as " dextral " or " sinistral ; " but the probabilities are
in favour of the view that it is truly dextral. In this case, the
flat side of the shell is the umbilicus, and the spire must be
regarded as sunk below the general surface of the shell. (On
this view the specimen figured at b, fig. 232, is represented up-
side down.) The species of Maclurea occur chiefly at the base

264

MOLLUSCA.

of the Lower Silurian series both in North America and in
Scotland, occurring in some localities in the greatest profusion.

Fig. 232. — Mad-urea crenulata. a Spire ; b front , c base. Lower Silurian.

The genus Ophileta (fig. 233) of the Silurian Rocks may be
mentioned here, though its true affinities are extremely doubt-

Fig. 233. — Ophileta bella (Billings). Different views of a nearly perfect specimen.
Quebec Group (Upper Cambrian ?)

ful. The shell in this genus is discoidal, and very closely
resembles that of Eiwmphalus. The aperture, however, is
stated by Mr Billings to have a sinus in the
lower lip and a notch in the upper lip-
characters which are not present in Mac-
hirea. It is a matter of question whether
Ophileta should be regarded as comprising
species of Machtrea with slender whorls,
or whether it should be placed in the Tur-
binidce, in or near Euomphalus, or whether
it should not be placed in the Haliotidcz and
be regarded as a discoidal Pleurotomaria.

In the genus Cyrtolites (fig. 234) the shell
is thin, symmetrical, discoidal, or coiled into
the shape of a horn, the whorls more or less disconnected,
furnished with a keel, and sculptured. The species of this

Fig. 234. — Cyrtolites
ornatus. Lower Silu-
rian.

GASTEROPODA. 265

genus range from the Lower Silurian to the Carboniferous
Rocks, and are, therefore, exclusively Palaeozoic.

In Ecculiomphalus (fig. 235) the shell is very like that of
CyrtolitcS) but the whorls are few in number, and are widely
separated from one another. The shell is thin, and the coils

Fig. 235. — Ecculiomphalus distans. Quebec Group (Upper Cambrian?)

lie in the same plane. The species of this genus range from
the Lower Silurian to the Carboniferous, and have been com-
pared to Euomphali imperfectly rolled up ; but the true affini-
ties of the genus are doubtful.

Lastly, the genus Porcellia includes shells which are com-
posed of many whorls coiled into a flat spiral. The whorls are
keeled, and the aperture has a dorsal slit. The species of this
genus are mainly Palaeozoic, but range into the Trias.

SECTION B. PULMONIFERA : — Respiration aerial, by means
of a pulmonary chamber. The Pulmonifera include the ordin-
ary Land-snails, Slugs, Pond-snails, &c., and are usually provided
with a well-developed shell ; though this may be rudimentary
(as in the Slugs), or even wanting. In the Land-snails and
Pond-snails there is a well-developed shell into which the
animal can retire completely. The Slugs, again, have a merely
rudimentary shell which is completely concealed within the
mantle. The completely shell-less forms are necessarily wholly
unknown as fossils. The Slugs, with a rudimentary shell, are
only doubtfully represented .in a fossil state, and that only in
the Tertiary Rocks. The abundance of the shell-bearing forms
as fossils depends mainly on the habits of the animal. The
Land-snails, being terrestrial in their habits, are, necessarily,
but sparingly represented as fossils, and they do not date back

266 MOLLUSCA.

to a time anterior to the Carboniferous. The Pond-snails, be-
ing exclusively confined to fresh water, are only known as fossils
in fluviatile and lacustrine deposits, and they are exclusively
Secondary and Tertiary, not being known in the Palaeozoic
period. The Pulmonifera are divided into the two orders of
the Inoperculata and Operculata, according as the shell is des-
titute of an operculum, or is provided with this apparatus.

ORDER IV. INOPERCULATA : — Shell not provided with an
operculum.

FAM. i. HELICID^E : — Shell well developed, capable of con-
taining the entire animal. With the exception of Pupa and
Zonites (the last a sub-genus of Helix), all the Helicida belong to
the Tertiary and Recent periods. As they are all terrestrial in
their habits, they are necessarily of rare occurrence as fossils,
occurring chiefly in fluviatile and lacustrine deposits. The two
genera above mentioned have been found in the Coal-Measures,
and are the oldest forms of the group. The chief fossil genera
are Helix, Bulimus, Achatina, Pupa, and Clausilia.

In the genus Helix are the ordinary Land-snails (fig. 236),
in which the shell is conical, sometimes depressed, or some-
times discoidal ; the aperture transverse, crescentic or rounded,
and the columella perforated or imperforate. The Land-snails,
with one exception, are all confined to the Tertiary and Recent
periods. The exception to this statement is the Zonites priscus
(fig. 236), discovered by Dr Dawson in the Coal-Measures of

I

Fig. 236. — Zonites (Conulus) priscus (after Dawson). a Specimen enlarged twelve
diameters ; b Sculpture, magnified. Coal-Measures, Nova Scotia.

Nova Scotia. This is a true Land-snail referred to Zonites or
Conulus, a sub-genus of Helix itself.

In Bulimus the shell is turreted or oblong, the columella
generally simple, and the outer lip usually expanded and
thickened. In the nearly allied genus Achatina the columella

GASTEROPODA.

267

is twisted, and the lips of the shell- aperture are thin. Both
genera date their existence from the Eocene Tertiary.

In the genus Pupa the shell is cylindrical or oblong, with a
round, often toothed, aperture. The oldest member of this
genus is the Pupa vetusta (fig. 237), discovered by Dr Dawson
in the Coal-Measures of Nova
Scotia, in the hollow trunk of an
erect Sigillaria. This ancient
form is remarkably like some
living " Chrysalis-shells," and
there appears to be no reason
for framing a new genus (Den-
dropupa] for its reception. With
the exception of this little shell,
all the fossil species of Pupa are
confined to the Tertiary period,
commencing in the Eocene.

In the genus Clausilia the
shell is spindle-shaped, coiled
into a left-handed spiral ("sin-
istral"), with an elliptical aper-
ture, partially contracted by
shelly processes. The Clausi-
lia, so far as known, date their
existence from the Eocene
Tertiary.

FAM. 2. LIMACID^E : — Shell rudimentary, usually internal or
concealed by the mantle. The " Slugs " are included in this
family, and they are only known in the fossil state by doubtful
remains in the Miocene and Pliocene Tertiary. A species of
Testacella has also been indicated as occurring in the Miocene.
• FAM. 3. LIMN/EID^E : — Shell well developed, thin and horn-
coloured. Aperture simple ; lip sharp. The
Limnceidce are all inhabitants of fresh water,
and they are found in fluviatile and lacus-
trine deposits. They are believed to com-
mence in the Jurassic period, members of
this family having been described from the
Lias and from the Purbeck beds (Upper
Oolites). It is not, however, until we reach
the base of the Cretaceous system (Weald
Clay) that these forms appear in any abun-
dance. Fig.

The genus Limnaa (fig. 238) includes the *•*****' Eocene-
so-called " Pond-snails," characterised by their thin, spiral,

Fig. 237. — Pupa {Dendropupa) vetusta.
(After Dawson. ) a Natural size ; b En-
larged ; c Apex enlarged ; a Sculpture,
magnified. Coal-Measures.

268 MOLLUSCA.

elongated shells, with a large body-whorl and an obliquely-
twisted columella. The species of this genus commence in
the Wealden (Lower Cretaceous) — perhaps in the Upper
Oolites — and are abundantly represented throughout the Ter-
tiary series.

In the genus Physa (fig. 239) the shell is left-handed (" sinis-
tral "), ovate, thin, and polished, with the aperture rounded in
front. Species of this genus have been indi-
cated as occurring in the Purbeck beds (Up-
per Oolites) and Wealden (Cretaceous).
Most of the fossil species, however, belong to
the Tertiary period, and the genus attains its
maximum at the present day.

The genus Ancylus comprises the so-called
" River-Limpets," at once distinguished by
their thin, conical, limpet-shaped shells. A few
fossil species are known, chiefly, if not exclu-
Fig. 239.— Physa sively, confined to the Tertiary period.

cohimnans. Eocene. r™ 7^7 7 • • -i

Ine genus Planorbis comprises a number
of well-known fresh-water shells, in which the shell is discoidal
and 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, whence a large
number of forms has been obtained.

FAM. 4. AURICULTDJE : — Shell spiral, with a horny epidermis;
aperture elongated and denticulated. The species of this
family inhabit salt marshes and places overflowed by the sea.
They are of little importance as fossils, dating from the Eocene
Tertiary.

ORDER V. OPERCULATA : — Shell furnished with an oper-
culum.

FAM. 5. CYCLOSTOMID^E : — Shell spiral, rarely elongated,
often depressed. Aperture nearly circular.
Operculum spiral. The genus Cydostoma
(fig. 240) includes almost all the fossil
species of this family, and dates from the
Eocene Tertiary. All the members of this
family are terrestrial in their habits, and
they are of small importance as fossils.

FAM. 6. ACICULID^E : — Shell elongated,
Fig. 240.— Cyciastoma cylindrical j operculum thin and sub-
Amoudn. Eocene Ter- spiral. A species of Aticula has been in-
dicated as occurring in the Pliocene Terti-
ary j but the family is otherwise unrepresented by fossil forms.

PTEROPODA.

269

CHAPTER XXIII.

CLASS PTEROPODA.

THE Pteropoda are defined by being free and pelagic, swimming
by means of two wing-like appendages (epipodia), developed
from each side of the anterior extremity of the body. The
flexure of the intestine is neural.

As to the position of the Pteropoda in the Molluscan scale,
they must be looked upon as inferior in organisation to any of
the Gasteropoda, of which class they are often regarded as the
lowest division. They permanently represent, in fact, the tran-
sient, larval stage of the Sea-snails.

The living Pteropods are all of small size, and are found
swimming at the surface of the open ocean, often in enormous
numbers. Locomotion
is effected by two wing-
like fins (fig. 241) devel-
oped from the sides of
the head. In some cases
the body is naked and
unprotected; but there
is commonly a symmetri-
cal glassy shell, either
consisting of a dorsal and

11, •, j

Ventral plate United, Or

forming a spiral.

The Pteropoda are divided into two orders, termed Thecoso-
mata and Gymnosomata; the former characterised by possess-
ing an external shell and an indistinct head ; the latter by
being devoid of a shell, and by having a distinct head, with
fins attached to the neck.

The Gymnosomatous Pteropods, in which there is no shell,
as a matter of course, are wholly unknown in the fossil con-
dition. The Thecosomatous Pteropods, in which there is a
shell, are divided into two families — the Hyaleida and Lima-
cinidtz. The latter comprises forms in which there is a small
spiral shell, which is sometimes provided with an operculum ;
but it is unrepresented in a fossil state. The former family
comprises forms in which the shell is symmetrical, straight or
curved, globular or needle-shaped, and it is represented by a
considerable number of fossil forms, most of which are ex-
tremely unlike any known living examples of the class, being
often of comparatively colossal dimensions. ' The fossil forms

Fie. 241. — Pteropoda. a Cleodora pyramidata ;
£ Cmuria columaella. (After Woodward.)

2/O

MOLLUSCA.

Fig. 242. — Hyalea Orbignyana.
Tertiary.

mostly belong to the genera Hyalea, Cuvieria, Cleodora, Theca,
Pterotheca, Tentaculites, and Conularia; but other less import-
ant types are known to have existed in past time. Of the
above-mentioned generic forms, the first three are well repre-
sented at the present day by living forms. The remaining
four are almost exclusively Palaeozoic, Conularia alone surviv-
ing into the earlier portion of the Mesozoic period. Not only
is this the case, but the forms in question all commence their
existence in the Lower Silurian or Upper Cambrian, and none
of them except Conularia transgresses the upper limit of the
Devonian Rocks. Lastly, almost all these forms are of com-
paratively gigantic size, and they differ in many respects from
living forms.

In the genus Hyalea (fig. 242) the shell is globular, trans-
lucent, the dorsal plate ex-
tended into a hood ; the aper-
ture is contracted, with a late-
ral slit on each side. The
fossil species are only known
Miocene in the Miocene and Pliocene
Tertiary, and the genus at-
tains its maximum in existing seas. Cleodora has a pyramidal
shell, and dates from the Miocene; and Cuvieria (fig. 241)
has a cylindrical shell, and dates from the Pliocene. Both
these genera attain their maximum at the present day.

The genus Theca (the Hyolithes of Continental and American
palaeontologists) comprises a number of singular forms in

which the shell is straight, sheath-
shaped, tapering to a point, triangular,
and destitute of lateral appendages
(fig. 243). The mouth of the shell
is trigonal, sometimes closed by an
operculum, sometimes furnished with
curved lateral appendages. The length
of the shell is commonly about an inch
or an inch and a half. Nearly ninety
species of this genus are enumerated
by M. Barrande, distributed in the
Upper Cambrian, Silurian, and Devon-
ian formations, but not extending into
the Carboniferous period.
The genus Pterotheca of Salter is exclusively Silurian, and is
characterised by having the " shell transversely oval, bilobed,
with wavy sides and a strong median keel ; ventral plate short,
narrow, and flat."

Fig. 243. — i neca operculata.
and its operculum. (After Sal-
ter.) From the Tremadoc Slates
(Upper Cambrian ?)

PTEROPODA.

271

Fig. 244. — (^onularia or-
itata. Devonian.

The genus Conularia is one of the most extraordinary of the
extinct genera of the Pteropods, if only for the enormous size
attained by many examples. The shape
of the shell is very like that of some
living Pteropods, but specimens occa-
sionally reach the length of nearly a foot,
with a breadth of more than an inch.
The shell in Conularia (fig. 244) is
straight, tapering towards one end, and
having a sub-quadrate or rhomboidal
aperture at the other. The form of the
shell is generally distinctly four-sided,
the sides being finely striated with trans-
verse lines. The shell is generally of
extreme tenuity j but the internal cavity
is sometimes restricted by concentric
lamellae, and the apex maybe partitioned
off. M. Barrande enumerates eighty-three
species of Conularia, most of which are
Palaeozoic, commencing in the lowest Silurian deposits. The
genus, however, extends into the Mesozoic Rocks, the last
species, so far as at present known, appearing in the Lias.

Lastly, the genus Tentaculites comprises a number of singular
Palaeozoic fossils, the true position of which cannot be said
to be absolutely free from doubt. Most authorities now place
Tentaculites, with apparently good reason, in the Pteropoda ;
but others would still refer this genus to
the Tubicolar Annelides. It must be ad-
mitted, also, that in some respects Ten-
taculites approximates pretty closely to the
Annelidous genera Conchicolites and Cor-
nulites. Upon the whole, however, the
mode of occurrence of Tentaculites and
its undoubted free habit of existence leave
little doubt as to its true place being
amongst the Pteropods. The shell of
Tentaculites (fig. 245) has the form of a
straight conical tube, tapering towards one Fig. 245. —

' . • j j i j j ornatus. Upper Silurian.

extremity to a pointed closed apex, and Europe and North America,
expanding towards the other to a circular
aperture. The walls of the shell are thin, and are surrounded
"with numerous thickened rings or annulations, sometimes with
intermediate striae, over a whole or part of the length of the tube.
The size of Tentaculites varies much in different cases, being
sometimes less than a couple of lines in length, and sometimes

2/2 MOLLUSCA.

attaining a length of an inch or more. Fifty-two species of
Tentaculites are enumerated by M. Barrande, commencing in
the Lower Silurian and ranging into the Devonian. The genus
is essentially Silurian, and examples of some species often
occur in myriads through a considerable thickness of strata.

CHAPTER XXIV.
CLASS CEPHALOPODA.

CLASS IV. CEPHALOPODA. — The members of the Cephalo-
poda are denned by the possession of eight or more arms placed
in a circle round the mouth ; the body is enclosed in a muscular
mantle-sac, and there are two or four plume-like gills within the
mantle. There is an anterior tubular orifice (the " infundibulum"
or "funnel"), through which the effete water of respiration is
expelled.

The Cephalopoda, comprising the Cuttle-fishes, Squids, Pearly
Nautilus, &c., constitute the most highly organised of the
classes of the Mollusca. They 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 surround 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 majority of the living Cephalopods are naked, possess-
ing only an internal skeleton, and this often a rudimentary
one ; but the Argonaut (Paper Nautilus) and the Pearly Nau-
tilus are protected with an external shell, though the nature of
this is extremely different in the two forms.

The body in the Cephalopoda is symmetrical, and is enclosed
in an integument which may be regarded as a modification of
the mantle of the other Mollusca. Ordinarily there is a toler-
ably distinct separation of the body into an anterior cephalic
portion (prosoma), and a posterior portion, enveloped in the
mantle, and containing the viscera (metasoma). The head is
very distinct, bearing a pair of large globular eyes, and having
the mouth in its centre. The mouth is surrounded by a circle

CEPHALOPODA.

273

of eight, ten, or more, long muscular processes, or "arms "

(fig. 246), which are generally provided with rows of suckers.

In the Octopod Cuttle-fishes there are only eight arms, and

these are all nearly alike. In the

Decapod Cuttle-fishes there are

ten arms, but two of these — called

" tentacles " — are much longer

than the others, and bear suckers

only at their extremities, which

are enlarged and club-shaped.

In the Pearly Nautilus the arms

are numerous, and are devoid of

suckers.

The parts of the Cephalopoda
which may be preserved in a fossil
condition, and which thus inte-
rest the palaeontologist, are the
mandibles, the ink-bag, and the
skeleton, whether this be internal
or external.

The mandibles are contained
within the mouth or " buccal
cavity" of the animal, and have
the form of powerful jaws, work-
ing vertically like the beak of a Fig. 246._Cephaiopoda.
bird. They are horny or calcare- Atiantica, one of the Cuttle-fishes

j • i ii (after Woodward).

ous, and in shape closely resem-
ble the beak of a parrot, with this difference, that the largest
of the two mandibles is placed inferiorly. Mandibles of this
nature are present in both the Cuttle-fishes and the Pearly
Nautilus, and they doubtless existed in all the extinct forms.
They not uncommonly occur as fossils, but they do not appear
to have been observed out of the Jurassic and Cretaceous
Rocks. They are commonly called " Rhyncholites/' and genera
such as Rhynchoteuthis have been founded upon them (fig.
247).

The ink-bag is a special gland possessed by the Cuttle-fishes,
for the purpose of secreting an inky fluid, which the animal can
discharge into the water, so as to enable it to escape when
menaced or pursued. The secretion of the ink-bag consists of
finely-divided particles of carbon suspended in fluid, and it is
extremely indestructible. The ink-bag, with its contained se-
cretion, is not uncommonly found in the fossil condition ; but
it has only been observed in strata of Secondary age. In the
Tetrabranchiate Cephalopods, in which there is an external

s

2/4

MOLLUSCA.

shell, and this means of defence is not needed, there is no ink-
bag.

The shell of the Cephalopoda is sometimes external, some-
times internal. The internal skeleton is known as the " cuttle-

Fig. 247. — Rkynclioteuthis Astieriaiui. Lower Greensand (Cretaceous).

bone," " sepiostaire," or " pen " (gladius), and may be either
corneous 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 " splanchno-
skeleton." In Spirula 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 inter-
nal, and differs, therefore, entirely from the external shell of the
latter. The only living Cephalopods which are provided with
an external shell are the Paper Nautilus (Argonauta\ and the
Pearly Nautilus (Nautilus pompilms] ; but not only is the struc-
ture 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 two of the 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, 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 re-
garded as a " pedal shell." The shell of the Pearly Nautilus
(fig. 248), on the other hand, is a true pallial shell, and is se-
creted 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

CEPHALOPODA. 2/5

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 Dibranchiata and Tetrabran-
chiata. The former is characterised by the possession of two
gills only, and by the fact that the shell, if external (as it very
rarely is), is never chambered. In this order are comprised
the living Cuttle-fishes, Squids, and Paper Nautilus, with the
extinct family of the Belemnitida. The latter is distinguished
by the presence of four gills, and by the possession of an exter-
nal many-chambered shell. This order is abundantly repre-
sented in past time, but has no other living representative than
the Pearly Nautilus alone. The following table gives the char-
acters and leading genera of the families of Cephalopoda : —

SYNOPSIS OF THE FAMILIES OF THE CEPHALOPODA.
CLASS CEPHALOPODA.

ORDER I. DIBRANCHIATA.

Animal with two branchiae ; not more than eight or ten arms,
provided with suckers ; an ink-bag Shell commonly internal and
rudimentary ; rarely external, but not chambered.
SECTION A. OCTOPODA.

Arms eight, suckers sessile.
Fam. I. Argonautidce.

Female provided with a calcareous, external, monothalamous
shell, secreted by the webbed extremities of two of the dorsal
arms. Gen. Argonauta.
Fam. 2. Octopodida.

Shell internal, rudimentary, uncalcified. No pallial^fins in
most. 111. Gen. Octopus, Tremoctopus, Eledone, Pinnoctopus.
SECTION B. DECAPODA.

Arms eight, 'with twoclavale " tentacles ;" suckers pedunculated.
Fam. 3. Teuthida.

Shell an internal horny "pen" or "gladius." Fins mostly
terminal. 111. Gen. Loligo, Onychoteuthis, Ommastrcphes.
Fam. 4. Belemnitidce.

Shell internal, composed of a conical chambered portion
("phragmacone") with a marginal siphuncle, produced into a
horny plate or "pen," and lodged in a cylindrical fibrous
"guard." 111. Gen. Belemnites, Belemnitella, Belemnoteuthis.
Fam. 5. Sepiada;.

Shell calcareous, consisting of a broad, laminar plate, termi-
nating in an imperfectly-chambered apex (" phragmacone"). 111.
Gen. Sepia, Beloptera, Spirulirostra.
Fam. 6. Spirulidce.

Shell internal, nacreous, chambered, discoidal ; the whorls
separate ; a ventral siphuncle. Gen. Spirula.
ORDER II. TETRABRANCHIATA.

Animal with four gills ; arms more than ten, without suckers ;
no ink-bag ; shell external, chambered, and siphuncled.

276 MOLLUSCA.

Fam. i. Nautilidtz.

Sutures of the shell simple ; the siphuncle central, sub-central,
or near the concavity of the curved shells, simple.
Sub-family Nautilidce proper.

Body-chamber capacious ; aperture simple ; siphuncle
central or internal. 111. Gen. Nautilus, Lituites, Trocho-
cei'as.
Sub-family Orthoceratidfe.

Shell straight, curved, or discoidal ; body-chamber
small ; aperture contracted ; siphuncle complicated. 111.
Gen. Orthoceras, Phragmoceras, Cyrtoceras.
Fam. 2. Amnwnitidce.

Shell discoidal, curved, spiral, or straight ; body-chamber
elongated ; aperture guarded by processes, or closed by an oper-
culum ; sutures angulated, lobed, or foliaceous ; siphuncle external
or dorsal (on the convex side of the curved shells). 111. Gen.
Ammonites, Ceratites, B acuities, Turrilites, Scaphites, Ancyloceras.

As regards their general distribution in time, the Cephalo-
pods are largely represented in all the primary groups of strati-
fied rocks from the Lower Silurian up to the present day. Of
the two orders of Cephalopoda, the Tetrabranchiata is the oldest,
attaining its maximum in the Palaeozoic period, decreasing in
the Mesozoic and Kainozoic epochs, and being represented at
the present day by the single form, Nautilus pompilius. Of the
sections of this order, the Nautilidce proper and the Orthocer-
atidce are pre-eminently Palaeozoic, and the Ammonitida are
not only pre-eminently but are almost exclusively Secondary.
Of the abundance of the two former families in the Silurian
seas some idea may be obtained when it is mentioned that over
a thousand species have been described by M. Barrande from
the Silurian basin of Bohemia alone. ThzNautitida proper have
gradually decreased in numbers from the Palaeozoic, through
the Secondary and Tertiary periods, to the present day. The
Orthoceratidcz died out much sooner, being exclusively Palaeo-
zoic, with the exception of the genera Orthoceras itself and
Cyrtoceras, which survived into the commencement of the Se-
condary period, finally dying out in the Trias.

The second family of the Tetrabranchiata — viz., the Ammo-
nitidce. — is almost exclusively Secondary, being very largely re-
presented by numerous species of the genera Ammonites, Cera-
lites, Baculites, Turrilites, &c. The only Palaeozoic genera are
Goniatites and Bactrites, of which the former is found from the
Upper Silurian to the Trias, whilst the latter is a Silurian
and Devonian form. The genus Ceratites is characteristically
Triassic, but it is said to occur in the Devonian Rocks, and
some species are Cretaceous. All the remaining genera are
exclusively Secondary, the genera Baculites, Turrilites, Hamites
and Ptychoceras being confined to the Cretaceous period.

TETRABRANCHIATE CEPHALOPODS. 2//

Of the Dibranchiate Cephalopods the record is less perfect,
as they have few structures which are capable of preservation.
They attain their maximum, as fossils, shortly after their first
appearance in the Secondary Rocks, where they are represented
by the large and important family of the BeUmnitidcR. Some
of the Teuthidcz and Sepiadce are found both in the Secondary
and in the Tertiary Rocks, and two species of Argonaut have
been discovered in the later Tertiaries. No example of a Di-
branchiate Cephalopod is known from the Palaeozoic deposits,
and the order attains its maximum at the present day.

CHAPTER XXV.
TETRABRANCHIATE CEPHALOPODS.

THE Tetrabranchiate Cephalopods are characterised by being
creeping animals, protected by an external, many-chambered shell,
the septa between the chambers of which are perforated by a mem-
branous or calcareous tube, termed the " siphuncle" The arms
are numerous, and are devoid of suckers ; the. branchice 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.

The Tetrabranchiate Cephalopods have an enormous de-
velopment in past time, several thousand species, mostly
belonging to extinct types, being known from the Palaeozoic
Rocks alone. In the Mesozoic Rocks the members of this
order were almost equally abundant. In the Tertiary Rocks
the order is reduced to the single genus Nautilus, represented
at the present day by the single species Nautilus pompilius
(the Pearly Nautilus). The palaeontological importance of this
order being so great, it may be as well to preface the account
of the extinct forms by a short description of the structure of
the living Nautilus pompilius, as described by Professor Owen,
from the only perfect specimen which has as yet been obtained.

The soft structures in the Pearly Nautilus may be divided
into a posterior, soft, membranous mass (mctasoma), containing
the viscera, and an anterior muscular division, comprising the
head (prosoma) ; the whole being contained in the outermost,
capacious chamber (the body-chamber) of the shell, from which
the head can be protruded at will. The shell itself (fig. 248)
is involuted and many-chambered, the animal being contained
successively in each chamber, and retiring from it as its size

2;8

MOLLUSCA.

becomes sufficiently great to necessitate the acquisition of more
room. Each chamber, as the animal retires from it, is walled
off by a curved, nacreous septum ; the communication between
the chambers being still kept up by a membranous tube or
siphuncle, which opens at one extremity into the pericardium,

Fig. 248. — Pearly Nautilus (Nautilus pompilius). a Mantle ; b Its dorsal fold ;
c Hood ; o Eye ; / Tentacles ; f Funnel.

and is continued through the entire length of the shell. The
position of the siphuncle is in the centre of each septum.

Posteriorly the mantle of the Nautilus is very thin, but it is
much thicker in front, and forms a thick fold or collar sur-
rounding the head and its appendages. From the sides of the
head spring a great number of muscular prehensile processes
or " arms," which are annulated, but are not provided with cups
or suckers. In the centre of the head is the mouth, surrounded
by a circular fleshy lip, external to which is a series of labial
processes. The mouth opens into a buccal cavity, armed with
two horny mandibles, partially calcified towards their extremi-
ties, and shaped like the beak of a parrot, except that the under
mandible is the longest. There is also a "tongue/' which is
fleshy and sentient in front, but is armed with recurved teeth
behind. The gullet opens into a large crop, which in turn
conducts to a gizzard, and the intestine terminates at the base
of the funnel. On each side of the crop is a well-developed
liver.

The heart is contained in a large cavity, divided into several

TETRABRANCHIATE CEPHALOPODS.

chambers, and termed the " pericardium " (Owen). The re-
spiratory organs are in the form of four pyramidal branchiae,
two on each side.

The chief masses of the nervous system are the cerebral and
infra-cesophageal ganglia, which are partially protected by a
cartilaginous plate, which is to be regarded as a rudimentary
cranium, and which sends out processes for the attachment of
muscles. The organs of sense are two large eyes, attached by
short stalks to the sides of the head, and two hollow plicated
sub-ocular processes, believed to be olfactory in their function.

The reproductive organs of the female consist of an ovary,
oviduct, and accessory nidamental gland.

There is no ink-bag, and the funnel does not form a com-
plete tube, but consists of two muscular lobes, which are simply
in apposition. It is the organ by which swimming is effected,
the animal being propelled through the water by means of the
reaction produced by the successive jets emitted from the
funnel. The function of the chambers of the shell appears to
be that of reducing the specific gravity of the animal to near
that of the surrounding water, since they are probably filled
with some gas secreted by the animal, or with water itself. The
function of the siphuncle is unknown, except in so far as it
doubtless serves to maintain the vitality of the shell.

SHELL OF THE TETRABRANCHIATA. — The shells of all the
Tetrabranchiata agree in the following points : —

1. The shell is external.

2. The shell is divided into a series of chambers by plates
or " septa," the edges of which, where they appear on the shell,
are termed the " sutures."

3. The outermost chamber of the shell is the largest, and is
the one inhabited by the animal.

4. The various chambers of the shell are united by a tube,
termed the " siphuncle."

Agreeing in all these fundamental points of structure, two
very distinct types of shell may be distinguished as charac-
teristic of the two families Nantilidce and Ammonitidce, into
which the order Tetrabranchiata is divided.

In the family Nautilidce (fig. 249), the " septa " of the shell
are simple, curved, or slightly lobed ; the " sutures " are more
or less completely plain ; and the " siphuncle " is central, sub-
central, or internal (i.e., on the concave side of the curved shells).

In the family Ammonitida (fig. 249), on the other hand, the
septa are folded and complex ; the sutures are angulated, zig-
zag, lobed, or foliaceous ; and the siphuncle is external (i.e.,
on the convex side of the curved shells).

280

MOLLUSCA.

In both these great types of shell, a series of representative
forms exists, resembling each other in the manner in which the
shell is folded or coiled, but differing in their fundamental
structure. All these different forms may be looked upon as
produced by the modification of a greatly-elongated cone, the
structure of which may be in conformity with the type either of
the Nautilidcz or of the Ammonitidcz. The following table
(after Woodward) exhibits some of the representative forms in
the two families : —

Nautilida.

Shell straight .... Orthoceras .

„ bent on itself . . Ascoceras .

„ curved .... Cyrtoceras .

„ spiral Trochoceras

„ discoidal .... Gyroceras .

,, discoidal and produced Lituites . .

involute Nautilus .

0 .0 0

Ammonitida.

Baculites.

Ptychoceras.

Toxoceras.

Turrilites.

Crioceras.

Ancyloceras.

Ammonites.

Fig. 249. — Diagram to illustrate the position of the siphuncle and the form of the septa
in various Tetrabranchiate Cephalopoda. The upper row of figures represents transverse
sections of the shells, the lower row represents the edges of the septa, a a A mmonite or
Baculite ; b b Ceratite ; ccGoniatite; ddClymenia; ee Nautilus or Orthoceras.

DISTRIBUTION OF TETRABRANCHIATA. IN TIME. — Regarded
as a whole, the Tetrabranchiate Cephalopods form a group
which early attained its maximum, and which is now almost
extinct. The greatest development, in point of numbers, took
place in the Palaeozoic period ; and the forms then existing
belonged to decidedly simpler types than those which followed
them. The greatest number of types existed during the Meso-
zoic period ; and here the order still maintained a great abun-
dance of individuals. With the close of the Secondary epoch
a large number of complex types disappeared wholly, and the
order was left without any representative in the Tertiary Rocks
except the simple and ancient genus Nautilus.

NAUTILID.'E. 28l

As regards the two great sections of the order, the Nauti-
lidce are the most ancient, dating their existence from the
Lower Silurian, if not from the Upper Cambrian. Not only
is this the case, but they are pre-eminently Palaeozoic, very few
forms surviving into the Secondary period, and only one into
the Tertiary. The Ammonitidcz, on the other hand, are pre-
eminently Mesozoic, and no member of this group is known
to have survived into the Kainozoic period. This group,
however, is represented by two comparatively simple types in
the Palaeozoic period, commencing their existence from the
Silurian.

In the following are given the characters and distribution in
time of the leading forms of the Tetrabranchiate Cephalo-
pods : —

NAUTILID^E.

FAM. I. NAUTILID^E. — Sutures of the shett simple ; thesiphunde
simple, central, sub-central, or near the concavity of the curved
shells.

SUB-FAMILY i. NAUTILID/E PROPER. — Body-chamber capa-
cious ; aperture of the shell simple ; siphuncle central or in-
ternal. The genera of this sub-family are Nautilus, Lituites,
Trochoceras, and Clymenia ; of which the last three are ex-
clusively Palaeozoic, whilst the first ranges through all the
great formations from the Silurian upwards, and is represented
at the present day by the Pearly Nautilus.

In the genus Nautilus (fig. 250) the shell is involute or dis-
coidal, consisting of a few whorls coiled into a flat spiral. The

Fig. 250. — Nautilus Danicus. Upper Cretaceous (" Danien " of D'Orbigny).

body-chamber is of large size, and the siphuncle is central, or
nearly so. The genus Nautilus ranges from the Upper Silu-

282

MOLLUSCA.

Fig. 251. — Lituites cornu-arietis.
Lower Silurian.

rian to the present day, having its maximum of development
in the Carboniferous period. The Palaeozoic forms are mostly

discoidal, having the whorls more
or less completely exposed. The
Nautili Q{ later deposits are mostly
like the living species in having
each whorl overlapping the pre-
ceding, so that merely an " um-
bilicus " is visible. Many of the
extinct forms, belonging to all
ages, agree with the living Naut-
ilus in having the surface quite
smooth ( Lcevigati ). Others,
which are especially character-
istic of the Jurassic Rocks, have
the surface striated (Striati).
Others, chiefly of Cretaceous
age, have the surface marked by distinct ribs (Radiati).

In the Upper Silurian and Devonian Rocks Nautili are few;
in the Carboniferous, many species are known; in the Permian

Rocks and Trias are
but few species; but the
Jurassic and Cretaceous
Rocks have yielded a
considerable number.
Lastly, several Tertiary
species are known, all
of which agree with the
living Nautilus pompilius
in having their surface
completely smooth.

In the genus Lituites
(fig. 251) the shell is at
first coiled discoidally
with close or discon-
nected whorls ; but the
last chamber is pro-
duced into a straight
or slightly-curved line.
The siphuncle is placed
in the centre of the septa
of the shell. All the
known species of Lituites are confined to the Silurian forma-
tion ; but some occur in deposits the age of which is pro-
bably Upper Cambrian.

Fig. 252. — Clyinenia Sedgwickii. Devonian. The
lower figure shows the form of the suture.

NAUTILID^E.

283

The genus Trochocems is one which was founded by M.
Barrande to include certain singular Silurian Cephalopods in
which the shell is doubly curved. In the typical forms —
corresponding with Turrilites amongst the Ammonitidcz — the
coils of the shell are in contact and pass obliquely round a
central axis, so that the shell becomes turreted. In other
cases, however, the shells are simply bent, and we have an
approach to the genus Cyrtoceras.

In the genus Clymenia (fig. 252) the shell is discoidal, coiled
into a flat spiral, and closely resembling some of the older
forms of Nautilus. The inner side of each whorl is deeply
excavated for the reception of the convexity of the internal
whorl. The septa are simple, like those of Nautilus, or are
slightly lobed, and the siphuncle is internal, placed on the
concave side of the whorls. Numerous species of Clymenia are
known, all belonging to the Devonian period ; and some of
the Upper Devonian limestones of
Germany are so profusely charged
with fossils of this genus as to have
received the name of " Clymenien-
kalk."

SUB - FAMILY 2. ORTHOCERAT-
ID^L. — Shell straight, curved, or
discoidal ; body - chamber small ;
aperture of the shell small, some-
times extremely contracted; siph-
uncle complicated. The Ortho-
ceratidcz commence in the lowest
Silurian deposits, and attain their
maximum of development in the
Silurian Rocks. The family is well
represented in the Devonian and
Carboniferous Rocks, but is much
reduced in numbers in the Per-
mians. The last appearance of the
family is in the Triassic Rocks,
where it is represented by the
genera Orthoceras and Cyrtoceras.
The chief genera of this sub- F-

. . ° rig. 253. — Orthocerax crebn-

lamily are Ort/lOCeraS, G-OmpriO- septum. Lower Silurian. The lower
/vr/70 T>hrn<rtnn/-s"riic rW//j/v*-/r c figure is a section, showing the form

ceras, ./-//; agmoceras, Cyrtoceras, and pos;tion Of the siphuncle.
Gyroceras, and Ascoceras.

In the genus Orthoceras (fig. 253) the shell is straight, the
siphuncle central or excentric, often of a very complex struc-
ture, and the aperture of the shell sometimes contracted. The

284

MOLLUSCA.

Orthocerata are pre-eminently fossils of the Silurian, Devonian,
and Carboniferous Rocks. They are, however, found in the
Permians, and, passing into the Mesozoic series, they make
their last appearance near the summit of the Triassic Rocks.
They sometimes attained an enormous size, occasionally ex-
ceeding six feet in length, with a diameter of more than a foot.
Some idea of the vast numbers of these Cephalopods in the
Palaeozoic seas may be obtained from the statement that M.
Barrande enumerates more than five hundred species as occur-
ring in the small Silurian basin of Bohemia alone. The
numerous species of Orthoceras are divided by the above-
named distinguished palaeontologist into two principal sections
— the Short-coned Orthoceratites, and the Long-coned Ortho-
ceratites — 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 forms come into the second group.
The nature of the siphuncle is very different in different
Orthocerata, and more or less well marked sub-genera have
been founded upon the characters of this structure. In the
sub-genus Huronia the siphuncle is of very large size, each
joint being cylindrical below but inflated above, the outer
walls of the siphuncle being connected with an internal central

tube by radiating plates. In the forms
termed Cochleati the siphuncle consists
of a succession of spheroidal bead-like
joints. In the sub-genus Endoceras the
siphuncle is very large, marginal, ex-
centric, or central, and it is partitioned
off by funnel-shaped diaphragms. There
is, however, considerable difference of
opinion as to the true nature of the
siphuncle in this sub-genus. Lastly, in
the sub-genus Gonioceras the transverse
section of the shell is flattened, and the
sutures are undulated.

The genus Cyrtoceras (fig. 254) very
closely resembles Orthoceras, but the
shell is curved instead of being straight,
and the siphuncle is either sub-central,
or is more commonly internal — i.e., on
the concave side of the shell. Cyrtoceras has about the same
vertical range as Orthoceras, ranging from the Silurian through
all the Palaeozoic formations, and disappearing in the Trias.
The genus is characteristically Silurian, and M. Barrande has

Fig. 254.- -Cyrtoceras iso-
dorus (Billings). Lower
Silurian.

NAUTILID.E.

285

described nearly two hundred and fifty species from rocks of
this age in Bohemia.

Fig. 255. — Pkra^n: r.is (Cnmptilites) ventricosus. Upper Silurian. The right-
lirmd figure shows the form of the aperture.

In the genus Phragmoceras
(fig. 255) the shell is curved,
and its aperture is contracted
in the most extraordinary
manner in the middle, so as
to assume somewhat of the
shape of a keyhole. The
siphuncle in the majority of
cases is placed upon the con-
cave side of the shell. In
other cases, the ventral side
of the Mollusc corresponds
with the convex side of the
shell. The species of Phrag-
moceras are Silurian and De-
vonian, mainly the former ;
and M. Barrande enumerates
thirty-eight species as occur-
ring in the Silurian basin of
Bohemia.

In the genus Gomphoceras,
the shell is spindle-shaped, or Fig as^_AM0efnu <;„***»«* (Bii-

globular, tapering towards itS lings), showing the form of the septa.

apex. The aperture is con- Lower s

tracted in the middle, like that of Phragmoceras, and the

siphuncle is generally sub-central. In most cases the ventral

286 MOLLUSCA.

side of the shell is relatively the most convex, but the reverse
of this sometimes occurs. The species of Gomphoceras range
from the Silurian to the Carboniferous, but belong mainly to
the former. M. Barrande enumerates no less than seventy-
three species as occurring in the Silurian Rocks of Bohemia.

The genus Ascoceras (fig. 256) comprises some singular forms
in which the shell is globular or flask-shaped, and the septa do
not run at right angles to the axis of the shell, but nearly
parallel with it, being at the same time curved in an extra-
ordinary manner. The air-chambers also are restricted to a
portion only of the shell. In Aphragmites the air-chambers are
not persistent. Both these genera are exclusively confined to
the Silurian Rocks, abounding chiefly in the upper division of
the series.

Lastly, in the genus Gyroceras the shell is coiled into a flat

spiral, the volutions of which are not contiguous. The siphuncle

is excentric. This genus is, perhaps, hardly separated from

Lituites by any sufficiently good characters. The species of

•the genus are mainly Upper Silurian and Devonian.

AMMONITID^E.

FAM. II. AMMONITID^E. — Shell discoidal, curved, spiral, or
straight ; body-chamber elongated ; aperture guarded by processes,
or closed by an operculum; sutures angulated, lobed, or foliaceous ;
siphimcle external or dorsal, on the convex side of the curved shells.

The chief point by which the Ammonitida are distinguished
from the Nautilida is the nature of the septa between the air-
chambers. The latter have septa which are simply curved,
and which consequently exhibit plain or very slightly lobed
edges or sutures. In the Ammonitidce, on the other hand, 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 surface of the shell in the
form of angulated, lobed, or foliaceous lines (fig. 257).

The angulated or digitated portions of the suture, which are
directed inwards, away from the mouth of the shell, are called
the " lobes" The elevations between the " lobes/' which
point towards the mouth of the shell, are called the " saddles."
These parts have the following arrangement (fig. 257) : — In
the middle of the back or convex surface of the shell, tra-
versed by the siphuncle, is a single unpaired lobe which is
termed the "dorsal lobe" (D). The lobe on each side of this
is the " lateral-superior " lobe (L). The lobe next to this

AMMONITID^:.

287

again is the " lateral- inferior " lobe; and the lobes which
follow this (of a variable number) are the " auxiliary " lobes
(A1, A2, A3, A4). Lastly, there is a second unpaired lobe im-
mediately opposite to the dorsal lobe, placed upon the con-
cave side of the shell, and termed the " ventral " lobe. The
" saddles " are similarly subdivided. Between the dorsal and
lateral-superior lobes comes the "dorsal saddle" (SD). Next
to this, between the superior-lateral and inferior-lateral lobes
is placed the "lateral saddle" (SL) on each side; and this
is followed by a variable number of " auxiliary saddles "
(S1, S2, S3, S4\

Fig. 257. — One-half of the suture of Ammonites Truellii. D, Dorsal lobe, traversed
by the siphuncle ; L, Lateral- superior lobe ; E, Lateral-inferior lobe ; A*, A2, A3, A4, Aux-
iliary lobes; SD, Dorsal saddle ; SL, Lateral saddle ; S1, S2, S3. S4, Auxiliary saddles.

The aperture of the shell in the Ammonitidcz is commonly
furnished with lateral processes of greater or less length ; and
in some, if not in all cases, it was further protected by a horny
or shelly operculum. Sometimes the operculum consists of a
single piece : but in other cases it is divided into two sym-
metrical halves by a straight median suture. The opercula of
this latter kind were originally described as separate fossils,
under the name of Trigonellites.

As regards the general distribution in time of the Ammon-
itidcz, the earliest-known forms of the group appear in the
Silurian Rocks; the genus Bactrites in the Lower Silurian,
and Goniatites in the Upper Silurian. No other Palaeozoic
types of the group are known ; but with the commencement
of the Mesozoic period begins an era in which an enormous
development of the Ammonitidcz took place. The genus
Ceratites is characteristically Triassic. The Jurassic Rocks
are chiefly distinguished by species of the genus Ammonites
itself, though other generic types are not wanting. Lastly, in
the Cretaceous Rocks we find, along with Ammonites proper,

288

MOLLUSCA.

several remarkable forms, such as Turrilites,B acuities, Hamites,
Scaphties, and Ptychoceras. With the close of the Cretaceous
period the Ammonitidce disappeared altogether, and no ex-
ample of this large and varied family has as yet been detected
in the Tertiaries, or is known to exist in Recent seas.

GENERA OF AMMONITID^E.

The genus Goniatites (fig. 258) comprises ancient forms of
the Ammonitidae, in which the shell is discoidal ; the sutures

are simply lobed or angulated ; and
the siphuncle is dorsal. The earliest-
known forms of this genus are found
in the Upper Silurian Rocks, the last
in the Trias, and the most in the Car-
boniferous.

The genus Bactrites comprises forms
quite similar to Goniatites, except that
the shell, instead of being rolled up, is
straight. The genus represents Ortho-
ceras. from which it differs in the

Fig. 258. — Goniatites (Aganidcs] Jossa. Carboniferous.

possession of lobed septa, and in the position of the siph-
uncle. The known species range from the Lower Silurian to
the Devonian.

The genus Ceratites (fig. 259) comprises forms which re-

AMMONITID^E.

289

semble Goniatites in having a discoidal shell, the coils of which
lie in one plane and are contiguous. It is distinguished, how-
ever, from Goniatites on the one hand and Ammonites on the
other, by having the
" lobes " of the suture
denticulated or cren-
ulated, whilst the
" saddles " are simply
rounded. The species
of Ceratites are typi-
cally Triassic, the best-
known form being the
C. nodosus of the
Muschelkalk. Some
species, however, oc-
cur in the Cretaceous
Rocks, though no
member of the genus
has as yet been de-
tected in the intervening Jurassic deposits.

The genus Ammonites comprises by far the greater number
of the Ammojiitidcz, over five hundred species being already
known. The shell in Ammonites is spirally rolled up into a
flat spiral, all the volutions of which are contiguous (figs.

Fig. 259. — Ceratites nodosus.
(Middle Trias).

Muschelkalk

Fig. 260. — Ammonites Humphresianus. Inferior Oolite.

260, 261). The innermost whorls of the shell are more or less
concealed ; the septa are undulated ; the sutures are lobed,
foliaceous, or ramified; and the siphuncle is dorsal. The
species of the genus Ammonites range from the Trias to the

2QO

MOLLUSCA.

Chalk, and are thus exclusively confined to the Secondary period.
Within these limits, each rock-group is characterised by par-
ticular species, the number of individuals being often very great,
and the size which is sometimes attained being nothing short of

Fig. 261. — Ammonites bifrons. Lias.

gigantic. In the Lias particular species of Ammonites succeed
one another regularly, each having its own definite horizon,
which it does not transgress. It is thus possible to distinguish
a certain number of zones, each characterised by a particular
Ammonite. Some of these zones are very persistent and ex-
tend over very wide areas, thus affording valuable aid to the
geologist in his determination of rocks. It is to be remem-
bered, however, that there are other species which are not thus
restricted in their vertical range, even in the same formations
in which definite zones occur.

The numerous species of Ammonites are divided into groups
as follows (Pictet) : —

SECTION A. Back with an entire keel.

1. Arietes . . . Lower Oolites. — Ex. A. bisulcatus.

2. Falciferi . . Lower Oolites. — Ex. A. serpentinus.

3. Cristati . . . Cretaceous. — Ex. A. inflatus.

SECTION B. Back crenated or tuberculated.

4. Amalthei . . Oolites. — Ex. A. cordatus.

5. Pulchelli (or Rhotomagenses) . . Cretaceous. — Ex. A. crenatus.

SECTION C. Back compressed and sharp.

6. Clypeiformi (or Disci) . . . Oolites. — Ex. A. discus.

AMMONITID-dE.

2QI

SECTION D. Back channelled.

7. Dentati . . . Oolitic and Cretaceous. — Ex. A. Jason.

8. Gemmati . Trias. — Ex. A. Aon.

9. Flexuosi . .

10. Compressi

11. Armati .

12. Angulicostati

13. Capricorni

14. Heterophylli

15. Z*£Btf . .

1 6. Planulati .
17 ."ICoronati .

1 8. Macrocephali

19. Globosi

20. Fimbriati

SECTION E. Back squared.

. Cretaceous. — Ex. A. radiatus.

Cretaceous. — Ex. A. Beaumontianus.
. Oolitic. — Ex. A. perarmatus.
. Oolitic and Cretaceous — Ex. A. Milletianus.

SECTION F. Back round.

Lias. — Ex. A. planicostatus.

Oolitic. — Ex. A. heterophyllus.

Cretaceous. — Ex. A. Mayorianus.

Oolitic. — Ex. A. annulatus.

Oolitic. — Ex. A. Humphresianus.

Oolitic and Cretaceous. — Ex. A. microstoma.

Trias. — Ex. A. globus.

Jurassic and Cretaceous. — Ex. A. sub-fimbriatus.

In the genus Crioceras are included forms which resemble
the Ammonites in all essential characters, but in which the
volutions of the shell are not contiguous. The shell, there-
fore, is discoidal, with separate whorls, thus corresponding
with Gyroceras amongst the series of the Nautilidce. All the
known species of Crioceras belong to the Cretaceous period,
ranging from the Lower Greensand to the Gault.

In the genus Toxoceras the shell is simply arcuate, or bent
like a horn, and is never spirally rolled up ; so that this genus
represents Cyrtoceras in the series of the Nautilidcz. The
species of Toxoceras range from the lower Oolites to the Gault,
but the genus is characteristically Cretaceous.

In the genus Ancyloceras (fig. 262) the shell at first re-

Fig. 262. — Ancyloceras Matheronianus. Gault.

sembles that of Crioceras, consisting of several volutions which
are coiled into a flat spiral, but which are not in contact with
one another. The shell differs from Crioceras, however, in the
fact that the last volution is produced at a tangent, and is ulti-

2Q2

MOLLUSCA.

mately bent back in the form of a crosier. The species of
Ancyloceras are Jurassic and Cretaceous, ranging from the In-
ferior Oolite to the Chalk.

In the genus Scaphites, the shell resembles that of Ancylo-
ceras in consisting of a series of volutions coiled into a flat

spiral, and having the last volution de-
tached from the others, produced, and
ultimately bent back in the form of a
crosier. Scaphites differs from Ancylo-
ceras in the fact that the volutions of
the enrolled part of the shell are in con-
tact, instead of being separate as they
are in the latter. The produced whorl,
also, is rarely of any great length, but
is speedily bent back upon itself. All
the species of Scaphites are Cretaceous,
ranging from the Lower Greensand to
the Chalk.

In the genus Helicoceras the shell is
coiled into a turreted spiral, the volu-
tions of which are not contiguous. The
shell is, also, left-handed or " sinistral."
With the exception of a single species
from the Inferior Oolite, all the species
of Helicoceras belong to the Cretaceous
period.

In the genus Turrilites the shell
agrees with that of the preceding in
being composed of volutions which
pass obliquely round a central axis
(fig. 263), so as to form a turreted
spiral. The shell is, also, left-handed
or " sinistral." In Turrilites, however,
the whorls of the shell are in contact,
instead of being disconnected as they
are in Helicoceras. The genus corre-
sponds with Trochoceras in the series of
the Nautilida. All the species of Tur-
rilites are Cretaceous, ranging from the
Gault to the Chalk.

In the genus Hamites the shell is an

extremely-elongated cone, which is bent upon itself more than
once, in a hook-like manner, all the volutions being separate.
Numerous species of Hamites are known, all of them being Cre-
taceous, and ranging from the Lower Greensand to the Chalk.

Fig. 263. — Turrilites
catenatus. Gault.

DIBRANCHIATE CEPHALOPODS. 293

In the genus Ptychoceras the shell is, also, a much elongated
cone, which is simply bent upon itself once, the two straight
portions of the shell being in contact. The range of this genus
is the same as that of Hamites, extending from the Lower
Greensand to the Chalk.

Lastly, in the genus Baculites the shell is simply a straight
elongated cone, not bent in any way. Baculites corresponds,
therefore, with Orthoceras in the series of the Nauttiidce* The
range of Baculites is the same as that of the preceding — from
the Lower Greensand to the Chalk ; but the genus is most
abundant in the Chalk itself.

CHAPTER XXVI.
DIBRANCHIATE CEPHALOPODS.

THE Dibranchiate Cephalopods or Cuttle-fishes are character-
ised as being swimming animals, almost invariably naked, with
never more than eight or ten arms, which are always provided
with suckers. There are two branchia, which are furnished
with branchial hearts ; an ink-sac is always present ; the funnel
is a complete tube, and the shell is internal, or, if external, is not
chambered.

The Cuttle-fishes are rapacious and active animals, swim-
ming 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 some-
times attain to a great size. They may be divided into two sec-
tions, Octopoda and Decapoda, according as they have simply
eight arms, or eight arms and two additional " tentacles."

The parts of a Dibranchiate Cephalopod which may be pre-
served in a fossil condition are the mandibles, the ink-sac, the
shell (if such be present), and the internal skeleton. The occur-
rence of the mandibles and ink-sacs of Dibranchiate Cephalo-
pods in a fossil state has been already spoken of (p. 273), and
need not be further noticed here. An external shell is pre-
sent only in the Argonaut amongst living Cuttle-fishes, and
similar structures are of rare occurrence as fossils in some of
the youngest portions of the earth's crust. The internal
skeleton of the Cuttle-fishes differs very much in its characters

294 MOLLUSCA.

in different cases. In the Calamaries the skeleton is in the
form of a horny " pen," consisting of a median shaft and of
two lateral expansions or wings. In the Sfpiada the skeleton
has the form of a broad, laminated, calcareous plate, having a
more or less perfectly chambered apex or " mucro." In the
singular Spirula the skeleton has the form of a chambered
tube coiled into a spiral, the coils of which are separate from
one another. Lastly, in the extinct family of the Belemnitidce,
there was a complicated internal support. It is, then, chiefly
from the preservation of their internal skeletons that the
Dibranchiate Cephalopods are known to have existed in past
periods of the earth's history. In addition, however, to the
skeleton, mandibles, and ink-bag, cases are not altogether un-
known in which the hooks of the suckers, and even the out-
lines of the arms and body, have been preserved in a fossil
condition.

As regards their general distribution in time, the record of
the Dibranchiate Cephalopods is much less complete than that
of the Tetrabranchiata. In the vast series of the Palaeozoic
formations no trace has ever been discovered of the existence
of any member of this order. Shortly after the commence-
ment of the Mesozoic period appear the first Belemnites ; and
all the Secondary formations after the oldest teem with the
remains of this family of the Dibranchiata. Remains of the
living families of the Teuthida and Sepiada are also not un-
known in the Mesozoic Rocks, but no trace of the great group
of the Bekmnitidce. has hitherto been detected in Tertiary de-
posits. Upon the whole, the order must be regarded as having
attained its maximum at the present day. In the following
are given the characters, chief genera, and distribution in time
of the families of the Dibranchiate Cephalopods.

SECTION A. OCTOPODA. — The Cephalopods comprised in
this section are distinguished by the possession of eight arms,
which are provided with sessile suckers. The body is short
and bursiform, ordinarily without fins. The shell is internal
and rudimentary; in one instance only (Argonaut) external.

FAM. i. ARGONAUTID^E. — Female provided with a delicate,
symmetrical, involuted shell, which is secreted by the webbed
extremities of the two dorsal arms, and is not attached in any
way to the body of the animal. Male much smaller than the
female, shell-less. This family includes only the single genus
Argonauta (the Paper Nautilus). One or two species of
Argonaut have been discovered in the Pliocene Tertiary.

FAM. 2. OCTOPODID^E. — Shell internal, rudimentary, repre-
sented by two short styles encysted in the substance of the

DIBRANCHIATE CEPHALOPODS.

295

mantle. This family includes the living Poulpes and their
allies, but has no fossil representatives.

SECTION B. DECAPODA. — The Cuttle-fishes of this section
have eight " arms " and two additional "tentacles/' which are
much longer than the true arms, and carry suckers on their
extremities only, which are expanded and club-shaped. The
suckers are pedunculated, the body is furnished with lateral
fins, and the shell is always internal.

FAM. 3. TEUTHID^E. — Shell consisting of an internal horny
"pen" or "gladius," composed of a central shaft and two
lateral wings. Several of such pens may exist in a single
individual, packed one behind the other. Fins mostly ter-
minal and angular. This family comprises the living Cala-
maries and Squids, and the following fossil genera have been
founded upon " pens " which have been discovered in various
Secondary deposits.

a. Teudopsis. — Pen lanceolate, produced in front, dilated and
spatulate behind. Five species of this genus have been de-
scribed from the Lias.

b. Beloteuthis. — Pen lanceolate, pointed in front, with two
small wing-like expansions behind (fig. 264). Six species have
been described by Count Minister from

the Upper Lias of Wiirtemberg.

c. Leptoteuthis. — Pen horny, hastate,
broad in front, pointed behind. A single
species is known from the Oxford Clay
(Jurassic).

d. Besides the above, remains found
in the Jurassic Rocks have been referred
to the living genera Enoploteuthis and
Ommastrephes ; and the extinct genus
Acanthoteuthis has also been placed in
this family.

FAM. 4. SEPIAD^E. — Internal skeleton
in the form of a broad, laminated, calcare-
ous plate, with an imperfectly-chambered
apex (or " mucro "). The chambered
portion of the skeleton corresponds with
the " phragmacone " of the Belemnites.
The fossil species of this family range from the Middle Oolites
upwards, and belong to the following three genera : —

a. Sepia. — Shell broad and thick in front, laminated, and
terminating in a prominent mucro. The fossil forms belong
to the Oxford Clay (Jurassic) and Eocene Tertiary, and the
genus attains its maximum at the present day.

Fig. 264. — Belotenthis sub-
costata. Jurassic (Lias).

296

MOLLUSCA.

b. Spirulirostra. — The shell (fig. 265) in this singular genus
consists of a chambered portion or phragmacone coiled into a
spiral, the volutions of which are separated. This is lodged in
a pointed calcareous portion or " rostrum." The only known
species of this genus is found in the Miocene Tertiary.

Fig. 265. — Spinihrostra Bellardii. Miocene Tertiary.

c. Beloptera. — Shell consisting of a nearly straight chambered
portion or "phragmacone," perforated by a siphuncle, and
lodged in a pointed calcareous rostrum which is furnished with
lateral wings. Two species only of this genus are known, both
from the Eocene Tertiary.

d. Belemnosis. — This genus has been founded for the recep-
tion of an Eocene fossil closely resembling Beloptera^ but differ-
ing in not possessing any lateral expansions.

FAM. 5. SPIRULID^E. — Shell nacreous, discoidal, composed
of volutions which are not in contact with one another. The
shell is divided into a series of air-chambers by curved shelly
partitions, pierced by a ventral tube or " siphuncle." The
entire shell corresponds with the " phragmacone ;> of the skele-
ton of the Belemnites. Spirulirostra and Beloptera are often
referred to this family ; but if these be placed in the Sepiadce,
the family of the Spirulidce is then without any known fossil
representative.

FAM. 6. BELEMNITID^E. — Shell internal, composed of a
conical chambered portion (" phragmacone "), with a marginal
or ventral siphuncle, lodged in a cylindrical fibrous " guard,"
and produced in front into a thin horny or shelly plate or
" pen " (the " pro-ostracum "). The Bdtmnitida are exclusively
confined to the Secondary Rocks, ranging from the top of the

DIBRANCHIATE CEPHALOPODS.

297

Trias to the Chalk. The following are the more important
genera belonging to this family : —

a. Belemnites. — The skeleton of the Belemnite consists of a
sub - cylindrical, longer or shorter,
fibrous body (fig. 266), which is
termed the "rostrum" or "guard."
The length of the guard varies very
much in different cases, and it is the
part of the Belemnite which is most
commonly found in a fossil condi-
tion. At the front or broad end, the
guard is hollowed out into a conical
excavation, which is termed the
" alveolus." Within the alveolus,
in perfect specimens, is contained
the " phragmacone." This consists
of a conical series of chambers, se-
parated from one another by curved
shelly partitions or septa, which
are perforated by apertures for the
passage of the " siphuncle." The
siphuncle traverses the middle of
the ventral wall of the phragmacone,
and the whole series of chambers is
enclosed in a thin shell-wall (the
"conotheca" of Huxley). Anteri-
orly the conotheca or investment of
the phragmacone is prolonged for-
wards into a horny or shelly plate,
which corresponds with part of the
" pen" of the Calamaries, and which
is termed the " pro-ostracum " (fig.
266, r). The form of the " pro-
ostracum " varies greatly in different
cases, and it affords important char-
acters in the discrimination of spe-
cific and generic forms in the Belem-
nitid(Z. Owing, however, to its ex-
treme tenuity, it is very rarely found
preserved in a fossil condition, and
its value to the working palaeonto-
logist is thus greatly reduced.

Not only is the internal skeleton

of the Belemnite known, but various specimens have been dis-
covered, from which much has been learnt as to other points

Fig. 266. — Diagram of Belem-
nite (after Professor Phillips), r
Horny or shelly pen or " pro-
ostracum ; " ^Chambered "phrag-
macone" in its cavity (a) or "al-
veolus ;" g " Guard."

298 MOLLUSCA.

of its anatomy. Thus we know that the body was furnished
with lateral fins, that there were eight arms and two longer
" tentacles," that the suckers were provided with horny hooks,
that there was a large ink-sac, and that the mouth was armed
with horny mandibles.

The following table of the sections and sub-sections of the
species of the genus Belemnites is the one given by Dr S. P.
Woodward : —

Section I. Acoeli.

Without dorsal or ventral grooves.
Sub-section I. Acuarii.

Without lateral furrows, but often channelled at the extreme

point. (Ex. B. acuarius. Lias.)
Sub-section 2. Clavati.

With lateral furrows. (Ex. B. davatus. Lias.)
Section II. Gastrocceli.

Ventral groove distinct.
Sub-section I. Canaliculati.

No lateral furrows. (Ex. B. canaliculatus. Inf. Oolite.)
Sub-section 2. Hastati.

Lateral furrows distinct. (Ex. B. hastatus. Oolite.)
Section III. Notocoeli.

With a dorsal groove, and furrowed on each side. (Ex.
B. dilatatus. Neocomian. )

The species of the genus Belemnites range from the top of
the Trias, where the earliest forms appear, to the
Upper Greensand, in which the genus finally dis-
appears. The species are most numerous in the
Jurassic Rocks, and often occur in the greatest
abundance in particular beds or particular localities.
It would seem not improbable that the genus Belop-
tcrct, befoj^noticed, should be referred to the Belem-
\nifiSze, ancPthe genus Belemnosepia, (or Geoteuthis),
formerly referred *Q the Teuthidce, appears to be al-
most certainly referable here.

b. Belemnitella. — In this genus (fig. 267) the skele-
ton is very similar in its general arrangement to that
of Belemnites ; but there is a straight -fissure in the
guard, at its upper end, on the ventral side of the
wall of the alveolus. The species of this genus are

F; 26 — exclusively Cretaceous, and are only found in the
Beiemniteiia upper portion of this formation, ranging from the
SBT"** Upper Greensand to the Chalk.

c. Belemnoteuthis. — " Shell consisting of a phrag-
macone, like that of the Belemnite ; a horny dorsal pen with
obscure lateral bands ; and a thin fibrous guard, with two
diverging ridges on the dorsal side. Animal provided with

VERTEBRATA. 299

arms and tentacles of nearly equal length, furnished with a
double alternating series of horny hooks, from 20 to 40 pairs
on each arm ; mantle free all round ; fins large, medio-dorsal."
— (Woodward.) Only one species is known, from the Oxford
Clay (Middle Oolites). High authorities, such as Owen and
D'Orbigny, question the validity of this genus, and regard it
as being founded upon specimens of Belemnites.

d. Xiphoteuthis. — Guard narrow and cylindrical, containing
a very long, deep-chambered, narrow phragmacone. Pro-
ostracum greatly developed (nearly a foot in length), very
narrow at its base, widening out anteriorly, and finally ter-
minating in a pointed apex. Only a single species is known,
from the Lias.

CHAPTER XXVII.
SUB-KINGDOM VERTEBRATA.

THE sub-kingdom Vertebrata may be shortly defined as includ-
ing animals in which the body is composed of a succession of
definite segments, arranged along a longitudinal axis ; the main
masses of the nervous system (brain and spinal cord] are situated
along the dorsal surface of the body, and are completely shut off
from the general body-cavity. The limbs are never more than
four in number, and are always turned away from that aspect of
the body upon which the main masses of the nervous system are
situated. In all, the nervous axis is primitively supported by a
cellular rod, which is termed the "notochord;" but in most the
notochord is replaced in the adult by the bony axis known as the
" spine" or " vertebral column."

The past existence of Vertebrate animals is chiefly recognised
by the preservation of their hard structures. These hard struc-
tures are of two kinds — some belonging to the internal or true
skeleton (endoskeleton), others being of the nature of horny
or bony plates, scales, or appendages of various kinds, de-
veloped in the integument (exoskeleton). The nature of the
exoskeleton in the Vertebrates differs very much in different
cases, and it will be considered when treating of the separate
groups. It will be well, however, to give an extremely
general and brief view of the structure of the endoskeleton,
taking for this purpose a Mammal as a typical form. In this
way the student will be enabled readily to trace the modifica-
tions of the skeleton in the lower forms, and will without

300 VERTEBRATA.

difficulty comprehend the terms which are necessarily em-
ployed in the definitions of the various groups. It may be
added here, before proceeding further, that it does not seem
requisite to treat the Vertebrata with the same fulness as the
Invertebrate. The fossil remains of Vertebrates are in many
cases of the highest theoretical interest, but they come much
less frequently under the notice of the ordinary student than
do the remains of the Invertebrates. No practical study, also,
of the fossil Vertebrates can be carried out without a consider-
able acquaintance with Comparative Osteology. Lastly, the
remains of Vertebrate animals generally occur in such a frag-
mentary condition that a sufficient series of specimens for pro-
fitable study can rarely be obtained, except under peculiarly
favourable circumstances, in special cases, or where access can
be had to a first-rate museum. For these and other reasons it
is thought enough, in a treatise intended for the working palae-
ontologist, to give a general account of each class of the Verte-
brata^ with definitions of the orders, and a brief notice of the
leading forms of each. Only in cases of special interest will any
details of a more minute character than the above be given.

The skeleton of the Vertebrata may be regarded as consisting
essentially of the bones which go to form the head and trunk
on the one hand (sometimes called the " axial " skeleton), and
of those which form the supports for the limbs ("appendicular"
skeleton) on the other hand. The bones of the head and
trunk may be looked upon as essentially composed of a series
of bony rings or segments, arranged longitudinally, one behind
the other. Anteriorly these segments are much expanded, and
likewise much modified, to form the bony case which encloses
the brain, and which is termed the cranium or skull. Behind
the head the segments enclose a much smaller cavity, which is
called the " neural " or spinal canal, as it encloses the spinal
cord ; arid they are arranged one behind the other, forming
the vertebral column. The segments which form the verte-
bral column are called " vertebras," and they have the follow-
ing general structure : — Each vertebra (fig. 268, A) consists of
a central piece, which is the fundamental and essential element
of the vertebra, and is known as the " body " or " centrum" (c).
From the upper or posterior surface of the centrum spring two
bony arches (n n), which are called the " neural arches " or
" neurapophyses," because they form with the body a canal — the
" neural canal " — which encloses the spinal cord. From the
point where the neural arches meet behind, there is usually
developed a longer or shorter spine, which is termed the " spi-
nous process " or " neural spine " (s). From the neural arches

GENERAL CHARACTERS OF VERTEBRATA. 3<DI

there are also developed in the typical vertebra two processes
(a a), which are known as the "articular" processes, or "zyga-
pophyses." The vertebrae are united to one another partly
by these, but to a greater extent by the bodies or " centra."
From the sides of the vertebral body, at the point of junction
with the neural arches, there proceed two lateral processes
(d d), which are known as the " transverse processes."

Fig. 268. — A, Lumbar vertebra of a Whale : c Body or centrum ; n n Neural arches ;
j Neural spine ; a a Articular processes ; d d Transverse processes. B, Diagram of a
thoracic vertebra : c Centrum ; n n Neural arches enclosing the neural canal ; J Neural
spine; r r Ribs, assisting in the formation of the haemal arch; j> p Costal cartilages;
b Sternum, with haemal spine. (After Owen.)

These elements form the vertebra of the human anatomist,
but the "vertebra" of the transcendental anatomist is com-
pleted by a second arch which is placed beneath the body of
the vertebra, and which is called the " haemal " arch, as it
includes and protects the main organs of the circulation.
This second arch is often only recognisable with great diffi-
culty, as its parts are generally much modified, but a good
example may be obtained in the human chest, or in the caudal
vertebra of a bony fish.

As a general rule, the vertebral column is divisible into a
number of distinct regions, of which the following are recog-
nisable in man and in the higher Vertebrata : — i. A series of
vertebrae which compose the neck, and constitute the " cer-
vical region " of the spine (fig. 269, c\ 2. A number of vertebrae
which usually carry well-developed ribs, and form the " dorsal
region'' (d). 3. A series of vertebrae which form the region
of the loins, or "lumbar region" (b}. 4. A greater or less
number of vertebrae which constitute the " sacral region," and

302

VERTEBRATA.

are usually amalgamated or " anchylosed " together to form a
single bone, the " sacrum " (s). 5. The spinal column is com-
pleted by a variable number of vertebrae which constitute the
"caudal" region, or tail (t).

Fig. 269. — Skeleton of the Beaver {Castor fiber), showing the different regions of the
vertebral column, c Cervical region ; d Dorsal region ; b Lumbar region ; s Sacrum ;
t Caudal region.

As regards the skull of the Vertebrates, the most important
points to be noticed are the manner in which the cranium
articulates with the vertebral column, and the structure of the
lower jaw or " mandible." In Birds and Eeptiles the skull
articulates with the first vertebra of the neck by means of a
single articulating surface or " condyle," carried upon the
occipital bone. In the Amphibians, again, and in the Mam-
mals, there are two " occipital condyles," by which the skull
is jointed to the neck. The lower jaw is sometimes want-
ing, but, when present, it consists in all Vertebrata of two
halves or " rami," which are united to one another in front,
and articulate separately with the skull behind. In many
cases, each half, or " ramus," of the lower jaw consists of
several pieces united to one another by sutures ; but in the
Mammalia each ramus consists of no more than a single
piece. The two rami are very variously connected with one
another, being sometimes only joined by ligaments and mus-

GENERAL CHARACTERS OF VERTEBRATA. 303

cles, sometimes united by cartilage or by bony suture, and
sometimes fused or anchylosed with one another, so as to
leave no evidence of their true composition. The mode by
which each ramus of the lower jaw articulates with the skull
also varies. In the Mammalia the lower jaw articulates with
a cavity formed on what is known to human anatomists as the
temporal bone ; but in Birds and Eeptiles, the lower jaw articu-
lates with the skull, not directly, but by the intervention of a
special bone, known as the "quadrate bone" or "os qvadratvm."

As regards the limbs of Vertebrates, whilst many differences
exist, which will be afterwards noticed, there is a general
agreement in the parts of which they are composed. As a
rule, each pair of limbs is joined to the trunk by means of a
series of bones which also correspond to one another in general
structure. The fore-limbs, often called the " pectoral " limbs,
are united with the trunk by means of a bony arch, which is
called the " pectoral " or " scapular " arch ; whilst the hind-
limbs are similarly connected with the trunk by means of the
" pelvic arch." In giving a general description of the parts
which compose the limbs and their supporting arches, it will
be best to take the case of a Mammal, and the departures
from this type will then be readily recognised.

The pectoral or scapular arch consists usually of three bones,
the "scapula" or shoulder-blade, the "coracoid," and the
"clavicle" or collar-bone; but in the great majority of the
Mammals, the coracoid is anchylosed with the scapula, of
which it forms a mere process. The scapula or shoulder-
blade (fig. 270, s) is usually placed outside the ribs, and it
forms, either alone or in conjunction with the other bones of
the shoulder-girdle, the cavity with which the upper arm is
articulated. The coracoid, though rarely existing as a distinct
bone in the Mammals, plays a very important part in other
Vertebrates. The clavicles are often wanting, or rudimentary,
and they are the least essential elements of the scapular arch.
The fore-limb proper consists, firstly, of a single bone which
fonns the upper arm, and which is known as the humerus (h).
This articulates above with the shoulder-girdle, and is followed
below by the fore-arm, which consists of two bones, called the
radius and ulna. Of these the radius is chiefly concerned
with carrying the hand. The radius and ulna are followed by
the bones of the wrist, which are usually composed of several
bones, and constitute what is called the carpus (d). These
support the bones of the root of the hand, which vary in
number, but are always more or less cylindrical in shape.
They constitute what is called the metacarpus. The bones of

304

VERTEBRATA.

the metacarpus carry the digits, which also vary in number,
but are composed each of from two to three cylindrical bones,
which are known as the phalanges (p).

Homologous parts are, as a rule, readily recognisable in the
hind-limb. The pelvic arch, by which the hind-limb is united
with the trunk, consists of three pieces — the ilium, ischium,
and pubes — which are usually anchylosed together, and form
conjointly what is known as the innominate bone (fig. 271, i). In

y....

Fig. 270. — Pectoral limb
(arm) of Chimpanzee. (After
Owen), c Clavicle ; 5 Scapula
or shoulder-blade; h Humerus;
r Radius; «Ulna; d Bones of
the wrist, or carpus; m Meta-
carpus ; p Phalanges of the
fingers.

Fig. 271. — Hind-limb of the
Chimpanzee. i Innominate
bone ;f Thigh-bone or femur ;
t Tibia ; s Fibula ; r Bones of
the ankle, or tarsus ; m Meta-
tarsus ; p Phalanges.

most Mammals, the two innominate bones unite in front by a
ligamentous or cartilaginous union, and they constitute, with
the sacrum, what is known as the pelvis. The hind-limb pro-
per consists of the following parts : — i. The thigh-bone or
femur, corresponding with the humerus in the fore-limb. 2.

VERTEBRATA. 305

The bones of the shank, corresponding with the radius and
ulna of the fore-limb, and known as the tibia and fibula. Of
these, the tibia is mainly, or altogether, concerned in carrying
the foot, and it is thus shown to correspond to the radius,
whilst the fibula corresponds to the ulna. 3. The small bones
of the ankle, known as the tarsus, and varying in number in
different cases. 4. A variable number of cylindrical bones
(normally five), which are called the metatarsus, and which
correspond to the metacarpus. 5. Lastly, the metatarsus car-
ries the digits, which consist, each, of from two to three small
bones ox phalanges, as in the fore-limb.

The sub-kingdom Vertebrata is divided into the following
five classes : —

1. PISCES (Fishes). — Respiration by means of gills ; heart
usually two-chambered ; an exoskeleton, in the form of horny
scales or bony plates, generally present; blood cold. Limbs,
when present, in the form of fins, or expansions of the integu-
ment supported by bony or cartilaginous spines or " rays."

2. AMPHIBIA (Amphibians). — Respiration at first exclusively
by gills, afterwards by lungs, either alone or associated with
gills. Heart of the adult three-chambered ; blood cold. The
skull connected with the vertebral column by two occipital
condyles. The limbs, when present, never converted into fins,
and composed of the same parts as in the higher Vertebrates.

3. REPTILIA (Reptiles). — Respiration aerial, by lungs, and
never by gills. Pulmonary and systemic circulations connected
together either within the heart or in its immediate neighbour-
hood. Heart of the adult three-chambered in most; rarely
four-chambered. Blood cold. Skull united to the vertebral
column by one occipital condyle. Exoskeleton in the form
of horny scales or bony plates, or both combined.

4. AVES (Birds). — Respiration aerial, by lungs, and never
by gills. Bronchial tubes opening on the surface of the lungs
into air-sacs. A greater or less number of the bones almost
always hollow and filled with air. The skull connected with the
vertebral column by a single occipital condyle. Heart four-
chambered ; the pulmonary and systemic circulations distinct,
and the blood warm. Epidermic appendages in the form of fea-
thers. Pectoral limbs in the form of wings. Animal oviparous.

5. MAMMALIA (Quadrupeds). — Respiration aerial, by lungs,
and never by gills. The terminations of the air-passages (bron-
chi) never connected with air-sacs. Heart four -chambered ;
the pulmonary and systemic circulations distinct ; the blood
warm. Skull connected with the vertebral column by two arti-
culating surfaces or condyles. Some part or other of the integu-

u

306 VERTEBRATA.

ment provided at some time or other with epidermic append-
ages in the form of hairs. The young nourished for a shorter
or longer time by means of a special fluid — the milk — secreted
by special glands — the mammary glands. Animal viviparous.
As regards the general distribution in time of the Vertebrata,
the earliest known traces of the existence of this sub-kingdom
are found in the Upper Silurian Rocks. Here are the remains of
Ganoid and Plagiostomous fishes ; and we may fairly anticipate
that further research will ultimately result in putting back the
first appearance of Fishes at any rate to the Lower Silurian.
The class of the Amphibians is not known to have come into
existence prior to the commencement of the Carboniferous
period, but it had attained a great development before the
close of this epoch. The class of the true Reptiles is repre-
sented, by more or less doubtful examples only, in the newer
Palaeozoic deposits. In the Mesozoic Rocks, however, the
development of this class was so great that the Secondary
period has been termed the " Age of Reptiles." The class
Aves is doubtfully represented by foot-prints in strata of the
age of the Trias ; but no Palaeozoic remains of this class have
been as yet detected. The earliest undoubted remains of
Birds occur in the Jurassic series, and the class has continued
to be represented more or less abundantly to the present day.
Lastly, the class of the Mammalia, so far as at present known,
finds its earliest fossil representative in strata of the age of the
Trias (New Red Sandstone). The Mammals, however, can-
not be said to be in any way abundant as fossils, till we reach
the Eocene Tertiary. From this point onward the remains of
Mammals are as abundant as, in the nature of the case, they
could reasonably be expected to be.

CHAPTER XXVIII.
FISHES.

THE first class of the Vertebrata is that of the Fishes (Pisces),
which may be broadly defined as including Vertebrate animals
which are provided with gills throughout the whole of life ; the
heart, when present, consists (with one exception} of a single auricle
and a single ventricle ; the blood is cold ; the limbs, when present,
are in the form of fins, or expansions of the integument.

In form, Fishes are adapted for rapid locomotion in water,
the shape of the body being such as to give rise to the least

FISHES. 307

possible friction in swimming. To this end also, as well as
for purposes of defence, the body is usually enveloped with a
coating of scales developed in the inferior or dermal layer of
the skin. The more important modifications in the form of
these dermal scales are as follows: I. Cycloid scales (fig. 272),
consisting of thin, flexible, horny scales, circular or elliptical
in shape, and having a more or less completely smooth outline.
These are the scales which are characteristic of most of the
ordinary bony fishes. II. Ctenoid scales (fig. 273), also con-
sisting of thin horny plates, but having their posterior margins

Fig. 272. — Cycloid scale. Fig. 273. — Ctenoid scale. Fig. 274. — Ganoid scale.

fringed with spines, or cut into comb-like projections. III.
Ganoid scales, composed of an inferior layer consisting of bone,
covered by a superficial layer of hard polished enamel (the so-
called "ganoine"). These scales (fig. 274) are usually much
larger and thicker than the ordinary scales, and though they
are often articulated to one another by special processes, they
only rarely overlap. IV. Placoid scales, consisting of detached
bony grains, tubercles, or plates, of which the latter are not
uncommonly armed with spines.

It is very important for the geologist to recognise the charac-
ters of these different scales, as he may have to decide upon
the characters of a fossil fish merely from detached scales.
Such decisions, however, are always more or less hazardous,
since the scales of the different orders of the living fishes are
not invariably of the same kind in all the forms of the order.
Thus, ganoid scales are not peculiar to the order of the Ganoid
fishes, but occur also in some of the Bony Fishes (Teleostei).
The scales, also, form at best but one character, and they can
hardly be said to constitute the most important character of
any fish. A classification, therefore, which is based primarily
upon the nature of the scales, necessarily is more or less "artifi-
cial," and is liable to bring into juxtaposition forms which have
no real affinity to one another. For these reasons, most
zoologists do not accept the classification of the Fishes into the
four orders of the Cycloideit Ctenoidei, Ganoidei, and Placoidei,
since this classification, though sanctioned by such an eminent

308 VERTEBRATA.

authority as Professor Agassiz, is founded solely upon the
nature of the integumentary covering. The palaeontologist,
however, whose materials often consist of nothing more than
detached scales, is not rarely driven, by the necessity of the
case, to provisionally classify his specimens in accordance with
the nature of these appendages.

As regards their true osseous system or endoskeleton, Fishes
vary very widely. In the Lancelet there can hardly be said
to be any skeleton, the spinal cord being simply supported by
the gelatinous notochord, which remains throughout life. In
others the skeleton remains permanently cartilaginous ; in
others it is partially cartilaginous and partially ossified ; and,
lastly, in most modern fishes it is entirely ossified, or converted
into bone. Taking a bony fish (fig. 275) as in this respect a
typical example of the class, the following are the chief points
in the osteology of a fish which require notice :—

The vertebral column in a bony fish consists of vertebras
which are hollow at both ends, or biconcave, and are techni-
cally said to be " amphicoelous." The cup-like margins of the
vertebral bodies are united by ligaments, and the cavities
formed between contiguous vertebrae are filled with the gela-
tinous remains of the notochord. This elastic gelatinous sub-
stance acts as a kind of ball-and-socket joint between the
bodies of the vertebrae, thus giving the whole spine the extreme
mobility which is requisite for animals living in a watery
medium. The ossification of the vertebrae is often much more
imperfect than the above, but in no case except that of the
Bony Pike (Lepidosteus) is ossification carried to a greater
extent than this. In this fish, however, the vertebral column
is composed of " opisthoccelous " vertebrae — that is, of vertebrae
the bodies of which are concave behind and convex in front.
The entire spinal column is divisible into not more than two
distinct regions, an abdominal and a caudal region. The ab-
dominal vertebrae possess a superior or neural arch (through
which passes the spinal cord), a superior spinous process
(neural spine), and two transverse processes to which the ribs
are usually attached. The caudal vertebrae (fig. 275) have no
marked transverse processes ; but in addition to the neural
arches and spines, they give off an inferior or /uzmal arch
below the body of the vertebrae, and the haemal arches carry
inferior spinous processes (haemal spines).

The ribs of a bony fish are attached to the transverse pro-
cesses, or to the bodies, of the abdominal vertebrae, in the form
of slender curved bones which articulate with no more than
one vertebra each, and that only at a single point. Unlike the

FISHES.

309

ribs of the higher Vertebrates, the ribs do not enclose a thoracic
cavity, but are simply imbedded in the muscles which bound
the abdomen. Usually each rib gives off a spine-like bone,
which is directed backwards amongst the muscles. Inferiorly
the extremities of the ribs are free, or are rarely united to der-
mal ossifications in the middle line of the abdomen \ but there
is never any breast-bone or sternum properly so called.

Fig. 275.— Skeleton of the common Perch (Perca fluviatilis). p Pectoral fin ; v One
of the ventral fins ; a Anal fin, supported upon interspinous bones (z) ; c Caudal fin ;
d First dorsal fin ; d' Second dorsal fin, both supported upon interspinous bones ; */
Interspinous bones ; r Ribs ; ^ Spinous processes of vertebrae ; h Haemal processes of
vertebras.

The only remaining bones connected with the skeleton of
the trunk are the so-called interspinous bones (fig. 275, i z).
These form a series of dagger-shaped bones plunged in the
middle line of the body between the great lateral muscles
which make up the greater part of the body of a fish. The
internal ends or points of the interspinous bones are attached
by ligament to the spinous processes of the vertebrae ; whilst
to their outer ends are articulated the " rays " of the so-called
" median " fins, which will be hereafter described. As a rule,
there is only one interspinous bone to each spinous process,
but in the Flat-fishes (Sole, Turbot, &c.) there are two.

Beside the fins which represent the limbs (pectoral and
ventral fins), fishes possess other fins placed in the middle line
of the body, and all of these alike are supported by bony spines
or "rays," which are of two kinds, termed respectively "spi-
nous rays " and " soft rays." The " spinous rays " are simple
bony spines, apparently composed of a single piece each, but
really consisting of two halves firmly united along the middle
line. The " soft rays " are composed of several slender spines

3io.

VERTEBRATA.

proceeding from a common base, and all divided transversely
into numerous short pieces. The soft rays occur in many fishes
in different fins, but they are invariably found in the caudal
fin or tail (fig. 275, c). The rays of the median fins, whatever
their character may be, always articulate by a hinge-joint with
the heads of the interspinous bones.

The sktill of the bony fishes is an extremely complicated
structure, and it is impossible to enter into its composition
here. The only portions of the skull which require special
mention are the bones which form the gill-cover or operculum.
For reasons connected with the respiratory process in fishes,
there generally exists between the head and the scapular arch
a great cavity or gap on each side, within which are contained
the branchiae. The cavity thus formed opens externally on
each side of the neck by a single vertical fissure or " gill-slit,"
closed by a broad flap, called the "gill-cover" or "operculum,"
and by a membrane termed the " branchiostegal membrane."

The gill-cover (fig. 276, /, o, s, i) is composed of a chain of
broad flat bones, termed the opercular bones. Of these, the

Fig. 276. — Skull of Cod (Morrfnta vu?g-aris)—Cuv\er. a Urohyal ; b Basihyal; c
Ceratohyal ; d Branchiostegal rays ; p Prae-operculum ; o Operculum proper ; j Sub-oper-
culum; z Inter-operculum; in Mandible; n Intermaxillary bone.

innermost articulates with the skull (tympano-mandibular arch),
and is called the " prae-operculum ;" the next is a large bone

FISHES. 3 1 1

called the " operculum " proper ; and the remaining two bones,
called respectively the " sub-operculum " and " inter-opercu-
lum," form, with the operculum proper, the edge of the gill-
cover. These various bones are united together by membrane,
and they form collectively a kind of movable door, by means of
which the branchial chamber can be alternately opened and
shut. Besides the gill-cover, however, the branchial chamber
is closed by a membrane called the " branchiostegal mem-
brane," which is attached to the os hyoides. The membrane
is supported and spread out by a number of slender curved
spines, which are attached to the lateral branches of the hyoid
bone, act very much as the ribs of an umbrella, and known as
the "branchiostegal rays" (fig. 276, d).

The limbs of fishes depart considerably from the typical form
exhibited in the higher Vertebrates. One or both pairs of
limbs may be wanting, but when present the limbs are always
in the form of fins — that is, of expansions of the integument
strengthened by bony or cartilaginous fin-rays. The anterior
limbs are known as the pectoral fins, and the posterior as the
ventral fins ; and they are at once distinguished from the
so-called " median " fins by being always disposed in pairs,
usually symmetrically. Hence they are often spoken of as the
paired fins.

The fore-limbs or pectoral fins possess in a modified form
most of the bones which are present in the anterior extremities
of the higher Vertebrata. They vary much in size and in other
characters. Sometimes they are enormously expanded, as in
the Flying-fish (Exoccztus) • and at other times they form merely
a pair of paddles, as in the extinct Pterichthys. The hind-
limbs or ventral fins are wanting in many fishes, and they are
less developed and less fixed in position than are the pectorals.
In some cases the ventral fins are " abdominal " in position,
and are placed more or less towards the hinder part of the
body (as in the Sharks, Ganoids, and Mud-fishes). In other
cases, they are "thoracic,5' that is, they are placed beneath the
pectorals ; and in some cases they are situated on the sides of
the neck in advance of the pectorals, when they are said to be
"jugular." In these cases, the pelvic arch is attached to the
pectoral arch, and is therefore wholly removed from its normal
position.

In addition to the pectoral and ventral fins — the homologues
of the limbs — which may be wanting, fishes are furnished
with certain other expansions of the integument, which are
" median'5 in position, and must on no account be confounded
with the true " paired " fins. These median fins are variable

312

VERTEBRATA.

in number, and in some cases there is but a single fringe
running round the posterior extremity of the body. In all
cases, however, the median fins are " azygous " — that is to
say, they occupy the middle line of the body, and are not
symmetrically disposed in pairs. Most commonly, the median
fins consist of one or two expansions of the dorsal integument,
called the "dorsal fins" (fig. 277, d d'} ; one or two on the
ventral surface near the anus — the "anal fins" (fig. 277, a) ;
and a broad fin at the extremity of the vertebral column, called
the " caudal fin " or tail (c). In all cases, the rays which sup-
port the median fins are articulated with the so-called inter-
spinous bones, which have been previously described. Though
called "median," from their position in the middle line of the
body, and from their being unpaired, the median fins of Fishes,
as shown by Goodsir and Humphrey, are truly to be regarded
as formed by the coalescence of two lateral elements in the
mesial plane of the body.

Fig. 277. — Outline of a fish (Perca granulata), showing the paired and unpaired fins.
/ One of the pectoral fins ; v One of the ventral fins ; d First dorsal fin ; d' Second dor-
sal fin ; a Anal fin ; c Caudal fin.

The caudal fin or tail of fishes is always set vertically at the
extremity of the spine, so as to work from side to side, and it
is the chief organ of progression in the fishes. In its vertical
position and in the possession of fin-rays, it differs altogether
from the horizontal integumentary expansion which constitutes
the tail of the Whales, Dolphins, and Sirenia (Dugong and
Manatee). In the form of the tail, fishes exhibit two very dis-
tinct types of structure, termed respectively the " homocercal "
and " heterocercal " type of tail (fig. 278). The homocercal
tail is the one which most commonly occurs in our modern
fishes, and it is characterised by the fact that the two lobes of

FISHES.

313

Fig. 278.— Tails of different fishes.
a Homocercal tail (Sword-fish) ; b Het-
erocercal tail (Sturgeon.)

the tail are equal, and the vertebral column, instead of being
prolonged into the upper lobe of the tail, stops short at its
base. In the heterocercal tail, on the other hand, the vertebral
column is prolonged into the up-
per lobe of the tail, so that the
tail becomes unequally lobed, its
greater portion being placed be-
low the spine. Even where the
vertebral column is not pro-
longed into the upper lobe, the
tail may nevertheless become
heterocercal, in consequence of
a great development of the
haemal spines as compared with
the neural spines of the vertebrae.
As regards their general dis-
tribution in time, the geological
history of fishes presents some
points of peculiar interest. Of
all the classes of the great sub-
kingdom Vertebrata, the fishes
are the lowest in point of or-
ganisation. It might therefore
have been reasonably expected that they would present us
with the first indications of vertebrate life upon the globe ;
and such is indeed the case. After passing through the enor-
mous group of deposits known as the Laurentian, Huronian,
Cambrian, and Lower Silurian formations — representing an
immense lapse of time during which, so far as we yet know,
no vertebrate animal had been created — we find in the Upper
Silurian Rocks the first traces offish. The earliest of these, in
Britain, is found in the base of the Ludlow Rocks (Lower Lud-
low Shale), and belongs to the placoganoid genus Pteraspis.
Also in the Ludlow Rocks, but at the summit of their upper
division, are found fin-spines and shagreen, probably belonging
to Cestraciont fishes — that is to say, to fishes of as high a
grade of organisation as the Elasmobranchii. So abundant
are the remains of fishes in the next great geological epoch —
namely, the Devonian or Old Red Sandstone — that this period
has frequently been designated the " Age of Fishes." Most of
the fishes of the Old Red Sandstone belong to the order Gan-
oidei. In the Carboniferous and Permian Rocks, which close
the Palaeozoic period, most of the fishes are still Ganoid, but
the former contain the remains of many Plagiostomous fishes.
At the close of the Palaeozoic and the commencement of the

VERTEBRATA.

Mesozoic epoch, the Ganoid fishes begin to lose that predomi-
nant position which they before occupied, though they continue
to be represented through the whole of the Mesozoic and Kain-
ozoic periods up to the present day. The Ganoids, therefore,
are an instance of a family which has endured through the
greater part of geological time, but which early attained its
maximum, and has been slowly dying out ever since. Towards
the close of the Mesozoic period (in the Cretaceous period) the
great order of the Teleostean or Bony fishes is for the first time
known certainly to have made its appearance. The orders
of the Marsipobranchii, Pharyngobranchii, and Dipnoi have
not left, so far as is known, any traces of their existence in
past time. Judging from analogy, however, it is highly pro-
bable that the two former of these must have had a vast anti-
quity, and it is not impossible that the so-called " Conodonts"
from the Lower Silurian Rocks of Russia may yet be shown to
be the horny teeth of fishes allied to the Lampreys. At pre-
sent, however, the weight of evidence is in favour of looking
upon these problematical little bodies as probably referable to
some of the Invertebrate.

These so-called " Conodonts " are microscopic in their
dimensions, and have tEe form oT " minute, glistening, slender,
conical bodies, hollow at the base, pointed at the end, more or
less bent, with sharp opposite margins" (Owen). They show
no trace of dental structure, and Professor Owen concludes
that they " have most analogy with the spines, or hooklets, or
denticles of Naked Molluscs and Annelides."

It is also to be borne in mind that, though it has not yet
been possible to definitely refer any fossil fishes to the order
of the Dipnoi, recent discoveries have rendered it extremely
probable that some well-known extinct types really belong to
this order. Thus, the great " Barramunda " ( Ceratodus Fosteri)
of the rivers of Queensland would seem to be truly referable to
the Triassic genus Ceratodus, in which case this latter must be
removed to the Dipnoi. This remarkable fish also presents
some striking points of resemblance with certain extinct
Ganoids, such as Dipterus. Upon the whole, therefore, there
are good grounds for accepting Dr. Giinther's suggestion that
the Dipnoi should be regarded as a mere sub-order of the
Ganoids.

In the following chapter are given the orders of the Fishes,
with the leading characters and geological distribution of each.
The order, however, of the Pharyngobranchii (comprising only
the living Lancelet), and that of the Marsipobranchii (compris-
ing the Lampreys and Hag-fishes), may be here dismissed, as

TELEOSTEI. 3 1 5

they are not known to be represented by any fossil forms.
There remain, therefore, for consideration the orders of the
Teleostei (Bony Fishes), Ganoidei (Ganoids), Elasmobranchii
(Sharks and Rays), and Dipnoi (Mud-fishes).

CHAPTER XXIX.

ORDERS OF FISHES.

ORDER I. TELEOSTEI. — This order includes the great majority
of fishes in which there is a well-ossified endoskeleton, and it
corresponds very nearly with Cuvier's division of the " osse-
ous " fishes. The Teleostei are defined as follows : — The skele-
ton is usually well ossified ; the cranium is provided with cranial
bones, and a mandible is present ; whilst the vertebral column
almost always consists of more or less completely ossified vertebrce.
The pectoral arch has a clavicle; and the two pairs of limbs, whe7i
present, are in the form of fins supported by rays. The gills are
free, pectinated or tufted in shape, a bony gill-cover and branchio-
stegal rays being always developed. The branchial artery has its
base developed into a bulbus arteriosus ; but this is never rhythmi-
cally contractile, and is separated from the ventricle by no more
than a single row of valves.

The scales in the Teleostean fishes are generally thin, horny,
flexible plates, which overlap one another, and have the " cy-
cloid " or " ctenoid " characters. The order, therefore, corres-
ponds, in a general way, with the orders Ctenoidei and Cycloidei
of Agassiz. Some of the Teleostean fishes, however, are pro-
vided with ganoid scales.

Excluding the Leptolepidce, which are sometimes referred to
this order, the Teleostei do not seem to have any representatives
in times anterior to the Cretaceous period — that is, towards the
close of the Mesozoic period. From this time on, however, Bony
Fishes with cycloid or ctenoid scales are the chief fossil repre-
sentatives of the whole class of the fishes, and the order
appears to have attained its maximum at the present day.

The order Teleostei is divided into the following sub-orders :

SUB-ORDER A. MALACOPTERI, Owen (= Physostomata, Miil-
ler). — This sub-order is defined by usually possessing a com-
plete set of fins, supported by rays, all of which are " soft " or
many-jointed, with the occasional exception of the first rays in
the dorsal and pectoral fins. A swim-bladder is always present,

ORDERS OF FISHES.

and always communicates with the oesophagus by means of a
duct, which is the homologue of the windpipe. The skin is
rarely naked, and is mostly furnished with cycloid scales ; but
in some cases ganoid plates are present.

The more important families comprised in this sub-order are
the Murcenida (Eels), the Chtpeidce (Herrings), the Pikes
(Esocida), the Cyprinida (Carp, Chub, Barbel, &c.), and the
Salmottida (Salmon and Trout). Few of these families ap-
peared in rocks older than the Eocene Tertiary. The Salmon-
idcz are only sparsely represented in deposits older than those
of the Post-Tertiary epoch. The Cyprinidcz and Esocidcz are
both represented in the fresh-water deposits of the Tertiary
period, and the Murcenidce appear for the first time in the
Eocene. The genus Osmeroides (fig. 279) has been referred

Fig. 279. — i. Beryx (Osmeroides) Letvesiensts, a Percoid fish from the Chalk ;
2. Osmeroides Mantelli, a Salmonoid fish from the Chalk.

to a position in the neighbourhood of the Salmonidce, and
dates from the Cretaceous period. The Clupeoids, also,
make their first appearance in the Cretaceous period. Also
in this group are the Sheat-fishes (Siluridce), which are chiefly
noticeable because they are amongst the small number of
living fishes possessed of structures of the same nature as

TELEOSTEI. 317

the fossil spines known as " ichthyodorulites." The structure
in question consists of the first ray of the pectoral fins, which
is largely developed and constitutes a formidable spine, which
the animal can erect and depress at pleasure. Unlike the old
" ichthyodorulites," however, the spines of the Siluridce have
their bases modified for articulation with another bone, and
they are not simply hollow and implanted in the flesh. The
" Siluroids " are also remarkable for their resemblance to cer-
tain of the extinct Ganoid fishes (e.g., Pterichthys, Coccosteus,
&c.), caused by the fact that the head is protected with an exo-
skeleton of dermal bones. The Siluroid fishes, however, are
hardly represented at all in the fossil state, being only known
by two or three doubtful Tertiary examples:

SUB-ORDER B. ANACANTHINI. — This sub-order is distin-
guished by the fact that the fins are entirely supported by
" soft" rays, and never possess " spiny" rays ; whilst the ven-
tral fins are either wanting, or, if present, are placed under the
throat, beneath or in advance of the pectorals, and supported
by the pectoral arch. The swim-bladder may be wanting, but
when present it does not communicate with the oesophagus by
a duct.

The only important families in this sub-order are the Gadida
(Cod-family) and the PletironectidcB (Flat Fishes). The Gadidce

Fig. 280. — Rhombus miniums. A small fossil Turbot from the Eocene Tertiary of

Monte Bolca.

comprise the living Cod, Haddock, Whiting, &c., and appear
to date their existence from the Eocene Tertiary. The Pleuro-
nectidtz comprise the living Sole, Flounder, Plaice, and the
like, in which the body is very much compressed from side to

318 ORDERS OF FISHES.

side, and is bordered by long dorsal and anal fins. The bones
of the head are twisted in such a manner that both eyes are
brought to one side of the body. The fish keeps this side up-
permost, and is dark-coloured on this aspect ; whilst the oppo-
site side, on which it rests, is white. The mouth has the two
sides unequal, the pectorals are rarely of the same size, the
ventrals look like a continuation of the anal fin, and the bran-
chiostegal rays are six in number. The Pleuronectida are only
known by two or three fossils, of which the oldest is the little
Rhombus minimus (fig. 280) of the Eocene deposits of Monte
Bolca.

SUB-ORDER C. ACANTHOPTERI. — This sub-order is character-
ised by the fact that one or more of the first rays in the fins are
in the form of true, unjointed, inflexible, " spiny" rays. The
exoskeleton consists, as a rule, of ctenoid scales. The ventral
fins are generally beneath or in advance of the pectorals, and
the duct of the swim-bladder is invariably obliterated.

The chief living families of this sub-order are the Perch
family (Pcrcida), the Mullets (Mugilida}, the Mackerel family
(Scomberida], the Gurnards (Sclerogenidce), the Blennies (Blen-
niid(£\ the Gobies (Gobiida\ and the Chaetodons (Ch&todon-
tidce). The fossil representatives of this sub-order are mainly
Tertiary; but the genus Beryx (fig. 279) dates from the Cre-
taceous period. In the Eocene Tertiary of Monte Bolca occur
several remarkable forms, of which one of the most singular is
the Chaetodont genus Platax (fig. 281).

SUB-ORDER D. PLECTOGNATHI. — This sub-order is charac-
terised by the fact that the maxillary and premaxillary bones
are immovably connected on each side of the jaw. The endo-
skeleton is only partially ossified, and the vertebral column
often remains permanently cartilaginous. The exoskeleton is
in the form of ganoid plates, scales, or spines. The ventral
fins are generally wanting, and the air-bladder is destitute of
a duct.

This sub-order includes the living Trunk-fishes (Ostracion-
tida), File-fishes (Balislidce}, and Globe-fishes (Gymnodontidce).
The fossil forms are few in number, and the earliest date from
the Eocene Tertiary. They are chiefly noticeable for the re-
semblance to the true Ganoid fishes, produced by their parti-
ally ossified endoskeleton and by their possession of ganoid
scales.

SUB-ORDER E. LOPHOBRANCHII. — This is a small and unim-
portant group, mainly characterised by the peculiar structure
of the gills, which are arranged in little tufts upon the branchial
arches, instead of the comb-like plates of the typical bony

GANOIDEI. 319

fishes. The endoskeleton is only partially converted into bone,
and the exoskeleton, by way of compensation, consists of
ganoid plates. The swim-bladder is destitute of an air-duct.

This sub-order comprises the living Pipe-fishes (Syngna-
thidce) and Sea-horses (Hippocampidce). A few fossil forms are
known, dating from the Eocene Tertiary.

Fig. 281. — Platax altissimus, a Chsetodont from the Eocene Tertiary of Monte Bolca.

ORDER II. GANOIDEI. — The order of the true Ganoid
Fishes may be defined by the following characters. — The endo-

320 ORDERS OF FISHES.

skeleton is only partially ossified, the vertebral column mostly re-
maining cartilaginous throughout life, especially amongst the extinct
forms of the Palczozoic period, in which the notochord is persistent.
The skull is furnished with distinct cranial bones, and the lower
jaw is present. The exoskeleton is in the form of ganoid scales,
plates, or spines. There are usually two pairs of limbs, in the
form of fins, each supported by fin-rays. The fir sir ays of the fins
are mostly in the form of strong spines. The pectoral arch has a
clavicle, and the posterior limbs (ventral fins] are placed close to the
anus. The caudal fin is mostly unsymmetrical or " heterocercal."
The sivim-bladder is always present, is often cellular, and is pro-
vided with an air-duct. The intestine is often furnished with a
spiral valve. The gills and opercular apparatus are essentially
the same as in the Bony fishes. The heart has one auricle and a
ventricle, and the base of the branchial artery is dilated into a
bulbtis arteriosus, which is rhythmically contractile, is furnished
with a distinct coat of striated muscular fibres, and is provided
with several transverse rows of valves.

Of these characters, those which it is most important to
remember are the following : —

I. The endoskeleton is rarely thoroughly ossified, but varies a
good deal as to the extent to which ossification is carried. In
some forms, including most of the older members of the order,
the chorda dorsalis is persistent, no vertebral centra are de-
veloped, and the skull is cartilaginous, and is protected by
ganoid plates. Even in these forms, however, the peripheral
elements of the vertebrae are ossified. In others, the bodies of
the vertebrae are marked out by osseous or semi-cartilaginous
rings, enclosing the primitive matter of the notochord. In
others, the vertebrae are like those of the Bony fishes — that is
to say, deeply biconcave or " amphiccelous." In one Ganoid,
however — the Bony Pike {Lepidosteus) — the vertebral column
consists of a series of " opisthocoelous " vertebrae — that is to
say, vertebrae which are convex in front and concave behind.
This is the highest point of development reached in the spinal
column of any fish, and its structure is more Reptilian than
Piscine.

II. The exoskeleton consists, in all Ganoid fishes, of scales,
plates, or spines, which are said to possess ganoid characters.
The peculiarities of these scales are that they are composed of
two distinct layers — an inferior layer of bone and a superficial
covering of a kind of enamel, somewhat similar to the enamel
of the teeth, called "ganoine." In form the ganoid scales
most generally exhibit themselves as rhomboidal plates, placed
edge to edge, without overlapping, in oblique rows, the plates

GANOIDEI.

321

of each row being often articulated to those of the next by
distinct processes. In other cases the ganoid structures are
simply in the form of detached plates, tubercles, or spines; and
in some cases their shape is even undistinguishable from the
horny scales of the typical Teleostean fishes. In all cases,
however, whatever their form may be, they have the distinctive
ganoid structure, being composed of an inferior layer of true
bone and a superior layer of enamel. It is to be remembered,
however, that these ganoid plates and scales are not confined
to the fishes of the order Ganoidei, but that they occur in two
sub-orders of the Bony Fishes — namely, the Plectognathi and
Lophobranchii — and in some others of the Teleostei as well.

III. As to the fins, both pectorals and ventrals are usually
present, and the ventrals are always placed far back, in the
neighbourhood of the anus, and are never situated in the im-
mediate vicinity of the pectorals. In some living and many
extinct forms the fin-rays of the paired fins are arranged so as
to form a fringe round a central lobe (fig. 282). This struc-

Fig. 282.— Ganoid Fishes. A, Polypterus (recent) ; ~^>,Osteolepis (extinct), a One
of the pectoral fins, showing the fin-rays arranged round a central lobe ; b One of the
ventral fins ; c Anal fin ; d Dorsal fin ; cf Second dorsal fin.

ture characterises a division of Ganoids called by Huxley, for
this reason, Crossopterygida, or " fringe-finned." The form of
the caudal fin varies, the Ganoids being in this respect inter-
mediate between the Bony fishes, in which the tail is " homo-
cereal," and the Sharks and Rays, in which there is a " hetero-
cercal" caudal fin. In the majority of Ganoids, then, the tail
is unsymmetrical or " heterocercal," but it is sometimes equi-
lobed or "homocercal."

322 ORDERS OF FISHES.

As regards 'the general distribution in time of the Ganoidei,
the oldest representatives of the fishes belong, so far as is yet
known with certainty, to this order. The order, namely, is
represented in the Upper Silurian Rocks of Bohemia and
Britain by several Ganoid fishes, which have been referred to
five distinct genera. In the Devonian Rocks, or Old Red
Sandstone, the Ganoids attain their maximum. The singular
family of the Cephalaspida appears to die out finally at the
close of this period, and the great group of the Crossopterygida
attained here its highest development, being represented at the
present day by the single genus Polypterus. The Carboniferous
and Permian Rocks contain an abundance of Lepidoganoids.
In the Mesozoic period, the Lepidoganoids are very largely
represented by various extinct types, many of which belong to
the family of the Lepidosteida — represented at the present day
by the Bony Pike or Gar-pike of North America. Here, also,
we have for the first time representatives of the family of the
Sturionidce, to which the living Sturgeons belong. Lastly, in
the Oolitic Rocks appear for the first time Lepidoganoids with
homocercal tails, and they continue to be represented up to
the present day. In the Tertiary Rocks true Sturgeons (Aci-
penser) make their appearance ; but the Ganoids are now con-
siderably outnumbered by the Teleostean fishes ; and the latter
have a still more marked predominance at the present day.

The classification of the Ganoid Fishes has hitherto proved a
matter of extreme difficulty ; and probably no arrangement
that has been as yet proposed can be regarded as being, in all
its details, more than provisional. A convenient primary
division is that into Lepidoganoids, in which the body is
furnished with scales of moderate size, and the endoskeleton
is generally more or less perfectly ossified ; and Placoganoids,
in which the skeleton is imperfectly ossified, and the head and
more or less of the body are protected by large ganoid plates,
which in many cases are united together by sutures. Accept-
ing this division, the order Ganoidei may be divided into the
following sub-orders : —

SECTION i. LEPIDOGANOIDEI.
Sub-order A. Amiada.

B. Lepidosteidce.

C. Lepidopleuridce.

D. Crossopterygidte.

E. Acanthodidce.

SECTION 2. PLACOGANOIDEI.
Sub-order F. Ostracostei.
G. Sturionida.

GANOIDEI. 323

The position of at least two of these sub-orders (viz., Acan-
thodidce and Ostracostei) in the order of the Ganoids is question-
able ; whilst the Sturionidce have been referred elsewhere. In
any case, the number of forms included in these sub-orders is
so large that nothing more can be done here than simply to
draw attention to some of the more striking examples of each.

SUB-ORDER A. AMIAD^E. — In this sub-order are included
Ganoids in which the scales are rounded and overlap one an-
other, and the tail is homocercal. The vertebral column is
ossified, and the external appearance approaches closely to
that of an ordinary Teleostean fish. A few fossil forms from
the Tertiary Rocks have been more or less doubtfully referred
to this group ; and the sub-order is represented at the present
day by various American fishes, all belonging to the genus
Amia.

SUB-ORDER B. LEPIDOSTEID^E. — Scales rhomboidal, not
overlapping; tail heterocercal, sometimes homocercal ; paired
fins not lobate ; fin-borders generally with fulcral scales ; true
branchiostegal rays. This sub-order is represented at the
present day by the Gar-pike (Lepidosteus) of the North Ameri-
can continent, and it attained its greatest development in the
Mesozoic period. The exact range of the sub-order in time is
uncertain, as it has not yet been determined what forms should
be included in it. If Cheirolepis be excluded, the sub-order is
not represented at all in the Devonian Rocks. In the Car-
boniferous and Permian Rocks the sub-order is mainly repre-
sented by the genera Paltzoniscus and Amblypterus (fig. 283), in
which the tail is heterocercal, and the jaws are furnished with

Fig. 283. — A mblypterus macropterus. Carboniferous.

numerous minute teeth. Numerous species of these genera are
known in the above-mentioned formations, and both appear for
the last time in the Trias. In the Secondary Rocks Lepido-
steids are extremely abundant, the chief forms belonging to the

324

ORDERS OF FISHES.

families Dapedida, Lepidotida, and Leptolepidce. In the Dapedi-
d<z (fig. 284, i), the tail-fin is only slightly heterocercal, and the

Fig. 284. — i. Dapedius tetragonolepis. 2. Leptolepis sprattiformis.
3. Lepidotus Valdensis.

back teeth are obtuse. Dapedius itself is compressed and deep-
bodied, and is exclusively confined to the Lias. The front-teeth
in this genus are notched or bifurcate. ^Echmodus is also

Fig. 285. — Tetragonolepis (restored). Lias.

exclusively Liassic ; but Semionotus and Pholidophorus range
upwards to the Chalk or to the highest Oolitic strata. The
Oolitic genus Tetragonolepis (fig. 285) is closely similar to Da-

GANOIDEI.

325

pedius, but the front teeth are not notched. The body is
greatly compressed, and there is a single long dorsal fin.
The place of this genus is disputed, and it is often referred
to the Pycnodonts. The Lepidotidcz have a homocercal tail
(fig. 283, 3), and possess obtuse teeth. The type -genus,
Ltpidotus, ranges from the Lias to the Eocene Tertiary.
The Leptolepidce (fig. 283, 2) have also a homocercal tail, and
possess small rounded scales. The species of this family are
all Secondary in their distribution.

SUB-ORDER C. LEPIDOPLEURID^:. — "Ganoids with hetero-
cercal equilobate tails. Body rhomboidal, covered with
rhombic scales, articulated by strong ribs traversing their
anterior margins internally. Dorsal fin equal to half the
length of the trunk. Anal fin also with an elongate base.
Ventrals, when present, small. Paired fins non - lobate.
Branchiostegal rays not taking the form of broad plates.
Notochord persistent. Arches well ossified." — (Young.) The
two most important families of this sub-order are the Platy-
somida and Pycnodontida ; of which the former is mainly
Carboniferous and Permian, whilst the latter is almost ex-
clusively Mesozoic. In the genus Platysomus (fig. 286) the

Fig. 286. — Platysomus gibbosus. Middle Permian.

tail is heterocercal, the dorsal and anal fins are long, the
pectorals are small, and the ventrals appear to be wanting.
The teeth are conical and uniserial, and the body is deep
and compressed from side to side. The Platysomi are mainly
found in the Permian Rocks. In the true Pycnodonts the
teeth are multiserial, and are adapted for crushing ; consisting
of " a circular or transversely oval crown, flattened above,
and sessile on the bone to which it is attached; or of an

326 ORDERS OF FISHES.

obtusely conical crown, which is broader than its peduncle of
support" (Young). The Pycnodonts are mainly Oolitic, but
a few Cretaceous species are known, and one form has been
described from the Eocene Tertiary. The Triassic Placodus,
formerly referred to this family, is now known to be truly
Reptilian.

SUB-ORDER D. CROSSOPTERYGID^E. — "Dorsal fins two, or,
if single, multifid or very long ; the pectoral, and usually the
ventral, fins lobate ; no branchiostegal rays, but two principal,
with sometimes lateral and median, jugular plates, situated
between the rami of the mandible ; caudal fin diphycercal, or
heterocercal ; scales cycloid or rhomboid, smooth or sculp-
tured."— (Huxley.)

All the Ganoids of this sub-order are pre-eminently dis-
tinguished by the structure of the paired fins, the pectorals
always, and the ventrals usually, consisting of a central lobe
or stem, which is covered by scales, and to the sides of which
the fin -rays are attached. The nearest approach to this
structure amongst living fishes is found in the paired fins of
the Barramunda (Ceratodus Fosteri) of the rivers of Queens-
land. In this singular fish, which is at present referred to the
order of the Dipnoi, the pectoral and ventral fins are supported
by a median, many-jointed, cartilaginous rod, to which nume-
rous lateral branches are attached. The scales in this sub-
order are sometimes rhomboidal, not overlapping one another;
at other times they are cycloidal in shape, and are arranged
in an imbricate manner.

Professor Huxley divides the Crossopterygida into the fol-
lowing families. (See ' Memoirs of the Geological Survey of
Great Britain. Decade X.5) :-

Fam. I. — POLYPTERII.

Dorsal fin very long, multifid ; scales rhomboidal.
Polypterus (fig. 282).

Fam. 2. — SAURODIPTERINI.

Dorsal fins two ; scales rhomboidal, smooth ; fins sub -acutely
lobate.

Diplopterus, Osteolepis (fig. 282), Megalichthys.

Fam. 3. — GLYPTODIPTERINI.

Dorsal fins two ; scales rhomboidal or cycloidal, sculptured ;

pectoral fins acutely lobate j dentition dendrodont.
Sub-fam. A. with rhomboidal scales.

Glyptol&mus (fig. 287), Glyptopomus, Gyroptychius.
Sub-fam. B. with cycloidal scales.

Holoptychius (fig. 288), Glyptolepis, Platygnathus \Rhizodus,
Dendrodus, Cricodus, Lamnodus}.

GANOIDEI. 327

Fam. 4. — CTENODIPTERINI.

Dorsal fins two ; scales cycloidal ; pectorals and ventrals acutely
lobate ; dentition ctenodont.

Dipterus \Ceratodus? Tristichopterus ?]

Fam. 5. — PHANEROPLEURINI.

Dorsal fin single, very long, not subdivided, supported by many
interspinous bones ; scales thin, cycloidal ; teeth conical ; ven-
tral fins very long, acutely lobate.
Phaneropleuron (fig. 290).

Fam. 6. — CCELACANTHINI.

Dorsal fins two, each supported by a single interspinous bone ;
scales cycloidal ; paired fins obtusely lobate ; air-bladder ossi-
fied. Ccelacanthus, Undina, Macropoma.

As regards the distribution of the Crossopterygida in time,
Professor Huxley remarks: — " Of the six families which com-
pose it, four are not only Palaeozoic, but are, some exclusively,
and all chiefly, confined to rocks of Devonian age — an epoch
in which, so far as our present knowledge goes, no fish belong-
ing to the sub-orders of the Amiadce, and Lepidosteidce (un-
less Cheirolepis be one of the latter) makes its appearance.
Rapidly diminishing in number, the Crossopterygidae seem to
have had several representatives in the Carboniferous epoch ;
but after this period (unless Ceratodus be a Ctenodipterine}
they are continued through the Mesozoic age only by a thin,
though continuous, line of Ccelacanthini, and terminate, at the
present day, in the two or three known species of the single
genus Polypterus"

Of the extinct types of this sub-order, some are sufficiently
important to merit especial mention. In the family of the
Sanrodipterini, the genus Osteolcpis (fig. 282) has a very hetero-
cercal tail and smooth scales. The first dorsal is placed near
the centre of the back, and the mouth is furnished with sharp
teeth. All the species of this genus are Devonian. The Car-
boniferous genus Megalichthys appears also to belong here.
In this singular genus are large " sauroid " fishes with hetero-
cercal tails, rhomboidal scales, and great conical incurved teeth,
which are mostly smooth, but are sometimes finely ridged.

Of the Glyptodipterini with rhomboidal scales, Glyptolamus
(fig. 287) may be taken as the type. In this singular fish, the
body is elongated and the head depressed. There are two
dorsal fins which are placed very far back, and the ventrals
have a similar posterior position. The tail is " divided into
two equal lobes by the prolonged conical termination of the
body," becoming thus " diphycercal." Glyptolamus is exclu-
sively confined to the Devonian period.

328

ORDERS OF FISHES.

Of the Glyptodipterines with cycloidal scales, the most
important form is Holoptychius (fig. 288). In this genus
there are two dorsal fins placed very far back, and the

Fig. 287. — Glyptolcemits Kinnairdi. Restored. A. Scale of the same. Devonian.

Fig. 288. — Holoptychius nobilissimus. Restored. A, Scale of the same. Devonian.

ventrals are similarly approximated to the tail, as in Glypto-
Iczmus. The body, however, is covered with large scales of a
cycloidal form, which overlap one another, and have wrinkled
surfaces ; and the tail is inequilobed. The teeth are of two
sizes, and the larger ones are longitudinally striated at their
bases. The true Holoptychii are Devonian in their distribu-
tion. In the Carboniferous Rocks, however, occurs the nearly
allied genus Rhizodus (fig. 289), in which the teeth agree with
those of Holoptychius in being of two sizes, but they differ in
being trenchant on both sides. Rhizodus must have attained
a large size, and must have been highly predaceous in its
habits.

The type-genus of the Ctenodipterini is Dipterus, in which
the position and form of the fins are very much the same as
in Holoptychius. The body is also covered with cycloidal
overlapping scales ; but these scales are smooth. The head
is protected by a kind of helmet formed of the anchylosed

GANOIDEI.

329

cranial bones, and the teeth are conical in form and nearly
equal in size. The species of Dipterus are all Devonian.

Fig. 289. — Jaw of Rhizodus Hibberti. Carboniferous.

The family Phanopleurini comprises only the single genus
Phaneroplenron (fig. 290), which is probably exclusively De-
vonian. In this singular genus the scales are very thin,
cycloidal, and overlapping one another. The dorsal fin is
extremely long, and is confluent with the tail-fin, and the pec-
torals and ventrals are acutely lobate. The jaws are armed
with a single series of short conical teeth, and the notochord
was persistent.

Fig. 290. — P haneropleuron A ndersoni and scale. Devonian.

Lastly, the family of the Ccdacanthi comprises forms which
range from the Devonian to the Cretaceous period, and which
are distinguished, in the typical genera, by having hollow fin-
spines, by having two dorsal fins, each supported by a single
interspinous bone, by having cycloidal overlapping scales, and
by the remarkable peculiarity that the swim-bladder was ossi-
fied. The type-genus Calacanthus seems to range from the
Carboniferous to the Trias.

330

ORDERS OF FISHES.

SUB-ORDER E. ACANTHODID^E. — Scales exceedingly small,
shagreen -like ; the front of each fin provided with a strong
spine, simply implanted in the flesh; no distinctly ossified
cranial bones ; no operculum ; tail heterocercal. In their fin-
spines, and in some other points, fat Acanthodida approximate
closely to the Elasmobranchii ; but they are generally regarded
as an order of the Ganoidei. The Acanthodida are mainly
Devonian, but some forms occur in the Carboniferous Rocks,
and a species from the Permian Rocks has been doubtfully
referred here. Acanthodes (fig. 291) has a single dorsal fin, and

Fig. 291. — i. Acanthodes Mitchelli. 2. Climatius scutiger.
3. Diplacanthus gracilis. Devonian.

is represented in both Devonian and Carboniferous deposits.
Diplacanthus (fig. 291, 3) has two dorsal fins, and is exclusively
confined to the Devonian Rocks.

SUB-ORDER F. OSTRACOSTEI. — The Ganoids of this sub-
order are characterised by having the head, and generally the
anterior portion of the trunk as well, encased in a strong ar-
mour composed of numerous large ganoid plates, immovably
united to one another. The posterior extremity of the body
is more or less completely unprotected ; and whilst the noto-
chord is persistent, the peripheral elements of the vertebrae
are ossified. The fishes belonging to this section are the
most ancient of their class, commencing in the Upper Silurian
Rocks. They extend through the Devonian series, but are
not known to have survived into the Carboniferous period.

GANOIDEI. 331

They have generally been placed amongst the Ganoids ; but
Professor Huxley has pointed out that they present, many of
them, features by which they approximate closely to the Silu-
roids amongst the Teleosteans. The more important genera
included in this sub-order are Cephalaspis, Pteraspis, Coccosteus,
and Pterichthys.

Cephalaspis (fig. 292) is the type of the family of the Cephal-
aspidcz, and is readily recognised by the fact that the cephalic
shield has its posterior angles produced into long " cornua,"

Fig. 292. — Cephalaspis Lye Uii. (After Page.) Old Red Sandstone.

giving it the shape of a " saddler's knife." Besides these la-
teral cornua, there is a " posterior cornu " or spine, formed by
a prolongation backwards of the hinder margin of the shield in
the middle line. The orbits are approximated, and are placed
nearly in the centre of the cephalic shield. No jaws or teeth
are known, and the mouth was probably soft, and adapted for
suction. The head-shield exhibits vascular canals, and shows
very distinct bone-cells when examined in thin sections under
the microscope. The body is covered with ganoid scales, and
there is a well-marked dorsal fin. Pectoral fins have also been
described, and the tail is clothed with a heterocercal fin. In
the nearly allied Auchenaspis, the structure is very similar to
the above, but there is no spine or " posterior cornu/' and
there is instead a neck-plate formed by an extension backwards
from the cephalic shield. The Cephalaspidtz are mainly found
in the Old Red Sandstone, the commonest species being C.
Lyellii. Other species are found in the " passage-beds "
between the Silurian and Old Red, and the genus is not
wholly unrepresented in the Upper Silurian deposits.

In the genus Pteraspis (fig. 293) the head is defended, as in
Cephalaspis, by a shield or buckler, which is composed of seve-
ral pieces firmly anchylosed. The shield consists of a central
disc, the lateral angles of which are produced into short cornua,

332 ORDERS OF FISHES.

whilst it is extended into a rostrum in front. The posterior
spine is very small, and is attached to the disc as a separate
piece. The orbits are situated laterally.
The minute structure of the shield is very
complex, consisting of three layers. The
innermost layer is laminated, and is tra-
versed by vascular canals. The middle
layer is made up of polygonal cavities ;
and the outer layer is structureless or
fibrous, and is finely striated or grooved.
The body was covered with scales ; but
nothing is known of the nature of the fins.
The genera Cyathaspis and Scaphaspis
have been founded upon forms which have

usuall7 been Placed under Pteraspis, and
of Ludiow. (After Mur- which differ in more or less essential
points from the typical species of this
genus. The genus Pteraspis, so far as yet known, comprises
the most ancient of the fishes, commencing as it does in the
earlier portion of the Ludiow formation (Upper Silurian).
Other species are known in the Old Red Sandstone ; but the
genus appears to have entirely disappeared before the close of
the Devonian period.

In the genus Coccosteus the head was protected by a great
shield, the plates of which are covered with small hemispheri-
cal tubercles. There is also a ventral or "sternal" shield,
which, according to Huxley, seems to have had no direct con-
nection with the cephalic buckler. The mouth was furnished
with a distinct lower jaw or "mandible/' composed of two
rami, carrying small teeth. The notochord was persistent, but
the neural and haemal spines of the vertebrae, and the rays of
the dorsal and anal fins, are well ossified. A heterocercal tail-
fin was doubtless present as well. The genus Coccosteus is
essentially Devonian ; but a species has been discovered by
M. Barrande in the Upper Silurian of Bohemia.

In the genus Pterichthys (fig. 294) are some very remarkable
fishes, first discovered in the Old Red Sandstone by the late
Hugh Miller, and nearly related in most respects to Coccosteus.
The whole of the head and the anterior part of the trunk were
defended by a buckler of large ganoid plates suturally united,
those covering the trunk forming a back-plate and a breast-
plate articulated together at the sides. The rest of the body
was covered with small ganoid scales. A small dorsal fin, a
pair of ventrals, a pair of pectorals, and a heterocercal tail-fin
were present. The form of the pectoral fins is the peculiar

GANOIDEI. 333

characteristic of the genus. These were in the form of two
long curved spines, somewhat like wings, covered by finely-
tuberculated ganoid plates. From their form they cannot
have been of much use in swimming ; but they probably, as
suggested by Owen, enabled the animal to shuffle along the
sandy bottom of the sea, if stranded at low water. All the
species of Pterichthys are exclusively confined to the Old Red
Sandstone.

Fig. 294. — Pterichthys comutus. Old Red Sandstone.

SUB-ORDER G. STURIONID^E. — In this sub-order the skeleton
is almost altogether cartilaginous, and the notochord is per-
sistent. The exoskeleton is usually in the form of large gan-
oid plates, which are united into a shield over the head, but
are detached over the body. Sometimes the exoskeleton is
almost absent, and in no case is the mouth furnished with
teeth. The tail is heterocercal.

This sub-order comprises the living Sturgeons, and is not
known with certainty to have corne into existence before the
Eocene Tertiary, where it is represented by the Acipenser toli-
apicus of the London Clay. In the Lias, however, occur two
species of the singular genus Chondrosteus, which have usually
been referred here, and have been regarded as being most
nearly allied to the Paddle-fishes (Spatularici] of North America.
The skull, however, is more completely ossified than is the case
with any living members of the Sturionufa; and the true place
of Chondrosteus must be regarded as uncertain.

334 ORDERS OF FISHES.

CHAPTER XXX.
ORDERS OF FISHES— Continued.

ORDER III. ELASMOBRANCHII ( = Selachia, Muller ; PZacoidei,
Agassiz ; Holocephali and Plagiostomi, Owen). — This order in-
cludes the Sharks, Rays, and Chimaerae, and corresponds with
the greater and most typical portion of the Chondropterygidce. or
Cartilaginous Fishes of Cuvier. The order is distinguished by
the following characters : — The skull and lower jaw are well
developed, but there are no cranial bones ; and the skull consists of
a single cartilaginous box, without any indication of sutures.
The vertebral column is sometimes composed of distinct vertebra,
sometimes cartilaginous or sub-notochordal. The exoskeleton is in
the form of placoid granules, tubercles, or spines. There are two
pairs of fins, represe?iting the limbs, and supported by cartilaginous
Jin-rays ; and the ventral fins are placed far back near the anus.
The pectoral arch has no clavicle. The heart consists of a single
auricle and ventricle, and the bulbus arteriosus is rhythmically
contractile, is provided with a special coat of striated muscular
fibres, and is furnished with several transverse rows of valves.
The gills are pouch-like.

In most of the above characters it will be seen at once that
the Elasmobranchii agree with the Ganoid fishes, especially as
regards the structure of the heart. The following points of
difference, however, require more special notice :—

I. The exoskeleton is what is called by Agassiz "placoid."
It consists, namely, of no continuous covering of scales or
ganoid plates, but of more or less numerous detached grains,
tubercles, or spines, composed of bony matter, and scattered
here and there in the integument. In the case of the Rays,
these placoid ossifications often take a very singular shape,
consisting of an osseous or cartilaginous disc, from the upper
surface of which springs a sharp recurved spine, composed of
dentine.

II. The gills are fixed and pouch-like, and differ very mate-
rially from those of the Bony and Ganoid fishes. In the case
of the Sharks and Rays, the gill-pouches open upon the sur-
face by a series of separate apertures, which are placed on the
sides of the neck in the former, and on the under surface of
the body in the latter. In neither is there any gill-cover or
operculum, nor are there any branchiostegal rays. In one
section of the order, however — viz., the Holocephali — though
the internal structure of the gills is essentially the same as in

ELASMOBRANCHII. 335

the Sharks, there is only a single branchial aperture or gill-slit
externally, and this is protected by a rudimentary operculum
and branchiostegal rays.

The order Elasmobranchii is divided into the two sub-orders
of the Holocephali and Plagiostomi. The former comprises the
living Chimczrce, characterised by the mouth being terminal,
and there being only a single gill-slit The latter comprises
the living Port Jackson Shark, the true Sharks and Dog-fishes,
and the Rays, characterised by having the mouth transverse
and placed on the under surface of the head, whilst there are
several apertures to the gills.

As regards their general distribution in time, the Elasmo-
branchii are nearly as ancient as the Ganoids. At the top of
the Upper Ludlow Eocks, or at the close of the Upper Silurian
epoch, there have been discovered the remains of undoubted
Plagiostomous fishes, most nearly allied to the existing Port
Jackson Shark (Cestracion Philippi). These remains consist
chiefly of defensive spines, which formed the first rays in the
dorsal fins, and upon these the genus Onchus (fig. 295) has been
founded. Besides these there have been found portions of skin
or " shagreen," with little placoid tubercles, like the skin of a
living shark. These have been referred to the genera Sphago-
dus and Thelodus. They are the earliest known remains of
Plagiostomous fishes, and with the exception of the few re-
mains from the Lower Ludlow Rocks, they are the earliest
known remains of fishes in the stratified series. The discovery
of these remains, at that time the earliest known traces of
Vertebrate life, is due to the genius of Sir Roderick Murchi-
son, the author of ' Siluria.'

Most of the fossil Elasmobranchii belong to the division
Cestraphori of Owen, so called because they are provided with
the large fin-spines which are known to geologists as " ichthyo-
dorulites." The two families of this division — the Cestracionts
and Hybodonts — are largely represented in past time, the
former chiefly in the Palaeozoic period, the latter chiefly in the
Mesozoic Rocks. Subjoined is an illustration of the " ichthyo-
dorulites " and teeth of some of the Palaeozoic Cestraphori.

The true Sharks are represented in the Mesozoic deposits
(e.g., by teeth of Notidanus in the Oolites); but they are chiefly
Cretaceous and Tertiary. The teeth of Odontaspis, Galeocerdo,
and Carcharodon, are good examples from the Eocene of the
Isle of Sheppey. The true Rays are older than the true
Sharks, the Carboniferous fossil Pleuracanthus being probably
the spine of a Ray (fig. 296). Numerous remains of Rays,
chiefly in the form of the pavement-like teeth, are known,

336 ORDERS OF FISHES.

both from the Secondary and Tertiary Rocks. The last divi-
sion of the Elasmobranchii — viz., that of the Holocephali — is
poorly represented in past time by the Mesozoic and Kaino-
zoic Ischiodus, Elasmodtis, Ganodus, and Edaphodtis.

In the following a more detailed account is given of the
characters of the various groups of the Elasmobranchii, with
the leading characters and more important fossil forms of
each : —

SUB-ORDER A. HOLOCEPHALI. — This sub-order includes cer-
tain curious fishes, of which the only living forms are the
Chimarida. The notochord is persistent, but the neural
arches and transverse processes are cartilaginous. The jaws
are bony, and are covered by broad plates representing the
teeth. The exoskeleton consists of placoid granules. The
first ray of the anterior dorsal fin is in the form of a powerful
defensive spine, like the " ichthyodorulites " of many fossil
fishes. The ventral fins are abdominal, and the tail is hetero-
cercal. There is only a single external gill-aperture, covered
with a gill-cover and branchiostegal membrane ; but only a
small portion of the borders of the branchial laminae is free.
The mouth is placed at the extremity of the head.

The Chiniceroid fishes are not known to have existed at all
during the Palaeozoic period ; but they are not uncommon in
the Secondary period and in the Tertiaries. They are exclu-
sively known by means of their jaws and teeth and their fin-
spines or " ichthyodorulites." The dental plates are united to
the beak-shaped jaws; and the dorsal fin-spines are always
movable and jointed — instead of being supported on a cartilage
imbedded in the muscular tissue of the back (as in the Spina-
cidce and Cestraciontidce). Of the fossil Chimaeroids, the genera
Ischiodns and Ganodus are exclusively Mesozoic ; Edaphodus
ranges from the Cretaceous series to the Eocene Tertiary; and
Elasmodus is only known from the Eocene.

SUB-ORDER B. PLAGIOSTOMI. — This sub-order is of consider-
ably greater importance, as it includes the well-known Sharks
and Rays. The vertebral centra are usually more or less ossi-
fied, and even when quite cartilaginous, the centra are marked
out by distinct rings. The skull is in the form of a cartila-
ginous capsule, without distinct cranial bones. The mouth is
transverse, and is placed on the under surface of the head.
The exoskeleton consists of placoid granules, tubercles, or
spines. The branchial sacs open externally by as many dis-
tinct apertures as there are sacs, and there is no operculum.
A pair of tubes proceed from the pharynx to open on the upper
surface of the head by two apertures, which are termed

ELASMOBRANCHII. 337

" spiracles." By means of these water can be admitted to the
pharynx, and thence to the gills.

By Professor Owen the Plagiostomi are divided into three
sections, termed respectively the Ctstraphori, the Selachii, and
the Batides.

a. Cestraphori. — In this division there is a strong spine in
front of each dorsal fin, and the back teeth are obtuse. The
only living representative of this group is the Port Jackson
Shark (Cestradon Philippi), characterised by its pavement of
plate-like crushing teeth, adapted for comminuting small Mol-
luscs and Crustaceans. It is exclusively an inhabitant of the
Australian and Chinese seas, and is remarkable for its close re-
semblance to a large group of extinct forms, of which the best
known are the genera Hybodus and Acrodus from the Second-
ary Rocks.

The Cestraphori are known in a fossil state mainly by their
fin-spines, or " ichthyodorulites," and their teeth. It is obvious,
however, that it must be often very difficult or altogether impos-
sible to determine absolutely whether a spine or a piece of shag-
reen belongs to a Cestraciont or to a true Shark. Some of the
forms, therefore, to be immediately mentioned, must be regarded
as being only provisionally placed amongst the Cestraciontidce.

With this proviso, the earliest known traces of Cestraciont
fishes appear to be in the Upper Ludlow Rocks, at the sum-
mit of the Silurian series. Here, within the limits of a single
stratum, well known as the " bone-bed," occur remains which
have been with more or less probability referred to Cestra-
cionts. Some of these (fig. 295) are in the form of compressed,

Fig. 295. — A, Spine of Onchus tenuistriatus. B, Shagreen-scales of Thelodus.
Both from the bone-bed of the Upper Ludlow Rocks.

slightly curved spines, the sides of which are grooved longi-
tudinally. These have been referred to a provisional genus,
under the name of Onchus, and there appears to be little doubt
as to their truly belonging to fishes of some kind. It is, how-
ever, quite possible that they really belong to Pteraspis, in
which case they must be removed from their present place.

Along with the spines of Onchus are found fragments of
prickly skin or shagreen, which have been referred to the
temporary genus Sphagodus, along with minute cushion-shaped
bodies, which are doubtless placoid scales, and which have

Y

338

ORDERS OF FISHES.

been referred to another genus under the name of Thelodus
(fig. 295, B). In the same bed are found jaw-like bodies, with
tooth-like processes of different sizes, which have been named
Plectrodus, and have been supposed to be the jaws of fishes.
The true nature of these, however, is doubtful, and they cer-
tainly do not belong to Plagiostomous fishes. Possibly they
are the prickly margins of the cephalic bucklers of Cephalas-
pidean fishes.

It should be mentioned, also, that M. Barrande enumerates
Ctenacanthus amongst the fishes found in the Upper Silurian
rocks of Bohemia, this genus being otherwise only known in
the Devonian and Carboniferous formations.

In the Devonian Rocks the remains of Cestraphori are not
uncommon. The more important fossil spines of the deposits
of this period have been referred to the 'genera Onchus, Ctena-
canthus, Homacanthns, and Cosmacanthus. The fossil teeth
belong chiefly to the genera Ctenodus, Ctenoptychius, Cladodus,
and Conchodus.

In the Carboniferous period the remains of Cestraphori are
comparatively very abundant, though confined generally to

Fig. 296. — i. Fin-spine of Pleiiracanthus (one of the Rays); 2. Cyracanthiis; 3.
Ctenacanthus; 4. Tooth of Petalodus; 5. Psammodus; 6. Ctenoj>tychiiis. All from the
Carboniferous Rocks.

particular localities. The spines of the Carboniferous strata
have been referred to many genera, of which the most import-
ant are Ctenacanthus (fig. 296, 3), Gyracanthns (fig. 296, 2), Ho-

ELASMOBRANCHII.

339

macanthus, Oracanthus, OncJms, Leptacanthus, and Edestes. The
fossil teeth of the Carboniferous Rocks have also been referred
to many genera, of which the more important are Cochliodus
(fig. 297), Psammodus, Orodus, Petalodus (fig. 296, 4), Ctenop-
tychius (fig. 296, 6), Cladodus,
Centrodus, Glossodus, and Petro-
dus. Two types may be distin-
guished in these teeth. In one
type, as in Cochliodus (fig. 297)
or Psammodus, the teeth have
the form of broad crushing
plates, adapted for the com-
minution of Molluscs or Crus-
taceans. In fact, in these forms

the teeth Very Closely resemble
, - . , / . J nerous).

those ot the living Fort Jackson
Shark (Cestratioii). In the other type, as in Cladodus, Orodus,
and Glossodus, the teeth are of what is called the " Hybodont"
form, having a general conical shape, and consisting of a cen-
tral principal cone, flanked by smaller secondary cones.

In the Permian series the remains of Cestraphori are scanty,
but they are very numerous in all the great formations of the
Secondary period. The four most important Mesozoic genera
are Hybodus, Acrodus, Strophodus, and Ptychodus. The almost
exclusively Triassic genus Ceratodus has generally been referred
here also, but its true affinities are with the Dipnoi.

In the genus Hybodus (fig. 298) the teeth are shark-like, but
are not so trenchant as they are in the true Sharks. They

Fig. 297. — Dental plates of Cochliodus
Mountain Limestone (Carbon-

Fig. 298.— Tooth
of Hybodus.

Fig. 299. — Fin-spine of Hybodus. Cretaceous.

consist of a central "principal" cone, with smaller "second-
ary" cones on each side. The fin-spines (fig. 299) in this
genus are longitudinally grooved, and carry a series of small
teeth on their hinder or concave margin. Species of Hybodus
abound in the Triassic and Jurassic formations, and occur,
though less abundantly, in the Cretaceous Rocks.

In the genus Acrodus (fig. 300) the teeth are more like those
of the Port Jackson Shark. The front teeth are pointed, and

340 ORDERS OF FISHES.

resemble those of the Hybodonts,but the back teeth are adapted
for crushing shell-fish. Each of these crushing teeth has an elon-
gated form, with a rounded
surface, which is covered
with fine transverse striae
proceeding from a central
longitudinal line. From their
general form, colour, and
Fig. 3oo.— Tooth of Acrodus tiobiiis. Lias. striation, they are common-
ly called "fossil leeches" by

the quarrymen. As in the case biHybodus, the species viAcrodus
are exclusively Mesozoic, ranging from the Trias to the Chalk.
The teeth of Strophodus are elongated, very similar to those
of Acrodus in their general form, but truncated at both ends,
and having their surface reticulated. Like the preceding, the
species of Strophodus range from the Trias to the Chalk.

In the genus Ptychodus, lastly, the teeth are more or less
quadrate in form, and the summit of the crown of the tooth is
thrown into parallel transverse folds, ridges, or plications,
surrounded by a granulated area. All the species of this genus
are Cretaceous.

A few Tertiary forms of the Cestraphori have been described;
but the affinities of most of these are doubtful. At the present
day the family is represented by the single living species, the
Port Jackson Shark (Cestracion Philippi).

b. SelachiL — This group comprises the Dog-fishes and Sharks,
characterised by the elongated, not rhomboidal, form of the
body, and by the lateral position of the gill-slits on the sides
of the neck. The teeth are sharp and conical, and are arranged
in several rows, of which the outermost alone is employed, the
inner ones serving to replace the former when worn out.

This family attains its maximum at the present day, and its
earliest authentic representatives appear in the Jurassic period.
Some Palaeozoic fossils, however, have been, with more or less
probability, referred to Sharks, or placed in the neighbourhood
of the living Monk-fishes (Squatina). With the exception of
occasional vertebrae, all the known remains of Selachians con-
sist of teeth.

In the Jurassic series are found teeth of Notidanus and
Sphmodus. In the Cretaceous Rocks are numerous teeth,
referred to the genera Corax, Galeocerdo^ Otodus, Lamna,
Oxyrhina, and Odontaspis, all of which continue to be repre-
sented in the Tertiary deposits. The teeth of Carcharodon
(fig. 303) also occur in the Cretaceous series, but the genus is
mainly Tertiary. The teeth of Carcharodon are triangular,

ELASMOBRANCHII.

341

serrated on both sides, and sometimes of immense size (five or
six inches in length). In Otodus (fig. 302) the teeth are not
denticulated at their edges, and they have a secondary tooth

Fig. 301. — Oxyrhinaxipho- Fig 302. — Otodus obliqitus. Fig. 303. — Carcharodon pro-
don. Miocene. Eocene. ductus. Miocene.

at each side of the base. The teeth of Oxyrhina (fig. 301),
lastly, are large and compressed, differing from those of Otodus
chiefly in wanting the lateral projections at the base. Upon
the whole, the deposits which have yielded the greatest abund-
ance of the teeth of these extinct Sharks, are the Upper Green-
sand (Cretaceous) and the London Clay (Eocene Tertiary).

c. Batides. — This group
includes the Rays and
Skates, and is distinguished
by the fact that the bran-
chial apertures are placed
on the under surface of
the body, forming two
rows of openings a little
behind the mouth. In
the typical members of
the group, the body is
flattened out so as to form
a kind of disc (fig. 304),
the greater part of which
is made up of the enor-
mously developed pectoral
fins. Upon the upper sur-
face of the disc are the
eyes and spiracles ; upon
the lower surface are the
nostrils, mouth, and bran-
chial apertures. The flat-
tened bodies of the Rays, however, must be carefully dis-
tinguished from those of the Flat-fishes (Pleuronectidce). In

Fig. 304. — Batides. Raia marginata, one
of the Skates. Reduced one-sixth. (After
Gosse.)

342 ORDERS OF FISHES.

the former, the flat surfaces of the body are truly the dorsal
and ventral surfaces. In the latter, as before remarked, the
body is flattened, not from above downwards, but from side
to side, and the head is so twisted that both eyes are brought
to one side of the body.

The tail in the Rays is long and slender, usually armed with
spines, and generally with two or three fins (the homologues
of the dorsal fins). The mouth is paved with flat teeth of a
more or less rhomboidal shape. The integument is often
furnished with placoid structures of a peculiar shape, consist-
ing of oval or rounded osseous discs, from the centre of each
of which springs a curved spine of dentine. The tail also is
sometimes armed with a doubly-serrated defensive spine.

The Rays are known in the fossil condition by their flat
crushing teeth mainly, but also by their fin-rays, bony discs,
and defensive spines. The earliest trace of the Rays is found
in the Carboniferous Rocks, where occurs the doubly-serrated
spine which is referred to the genus Plairacanthus (fig. 296, i).
In this singular form, however, the spine seems to have been
inserted at the back of the head, instead of in the tail, as in the
living Sting-rays. In the Jurassic Rocks occur the remains of
Rays, which have been referred to the genera Squaloraia,
Spathobatis, Arthropterus, &c. In the Tertiary Rocks the re-
mains of Rays are tolerably
abundant, and consist almost
exclusively of the dental plates.
These consist (fig. 305) of gene-
rally flat plates, usually some-
what rhomboidal in shape,
often placed close together and
sometimes united laterally by
sutures, so as to " form a kind

Fig. 305. — Teeth of a fossil Ray (Mylio- /• •> ,-,

Ltis Edivardsif). Eocene. of mosaic pavement on both

the upper and lower jaws "

(Owen). Most of the fossil forms belong to the genus Mylio-
batis, which comprises the living Eagle-rays. All the fossil
species of this family belong to the Tertiary period.

ORDER IV. — DIPNOI ( = Protopteri, Owen). — This order is
a very small one, and includes only the singular Mud-fishes
(Lepidosiren and Ceratodus) ; but it is nevertheless of great im-
portance as exhibiting a distinct transition between the Fishes
and the Amphibia. So many, in fact, and so striking, are the
points of resemblance between the two, that until recently the
Lepidosiren (fig. 306) was always made to constitute the lowest
class of the Amphibia. The highest authorities, however, now

DIPNOI. 343

concur in placing it amongst the fishes, of which it constitutes
the highest order. The order Dipnoi is defined by the follow-
ing characters : — The body is fish-like in shape. There is a skull
with distinct cranial bones and a lower jaw, but the notochord is
persistent, and there are no vertebral centra, nor an occipital con-
dyle. The exoskeleton consists of horny, over lapping scales, having
the " cycloid" character. The pectoral and ventral limbs are both
present, but have (in Lepidosireti] the form of awl-shaped, filiform,
many-jointed organs, of which the former only have a membranous
fringe infer iorly. The ventral limbs are attached close to the anus,
and the pectoral arch has a clavicle ; but the scapular arch is at-
tacked to the occiput. The hinder extremity of the body is fringed
by a vertical median fin. The heart has two auricles and one ventri-
cle. The respiratory organs are twofold, consisting on the one hand
of free filamentous gills contained in a branchial chamber, which
opens externally by a single vertical gill-slit ; and on the other
hand of true lungs in the form of a double cellular air-bladder,
communicating with the oesophagus by means of an air-duct or
trachea. The branchicz are supported upon branchial arches, but
these are not connected with the hyoid bone ; and in some cases, at
any rate, rudimentary external branchicz exist as well. The
nasal sacs open posteriorly into the throat.

Fig. 306. — Dipnoi. Lepidosiren annectens.

Until lately the only known members of the order Dipnoi
were the Lepidosirm paradoxa of South America and the Lepi-
dosiren (Protopterus) annectens of Africa. No fossil also could be
referred with any certainty to this order. Recently, however,
there has been discovered a most remarkable fish in the rivers
of Queensland (Australia), which is almost certainly referable to
this order, and which throws great light upon several fossil
forms. The organisation of this fish is so extraordinary, and
its affinities with some of the extinct Ganoids are so numerous
and important, that it will be well to quote at some length the
description of it given by Dr. Albert Giinther, one of the most
eminent of living ichthyologists. The fish in question has
been named the Ceratodus Fosteri, and it is known locally as
the " Barrarmmda." It is said to attain a length of about six

344 ORDERS OF FISHES.

feet, but its average length is about three feet. The Barra-
munda " is eel-shaped, but considerably shorter and thicker
than a common eel, and covered with very large scales. The
head is flattened and broad, the eye lateral and rather small,
the mouth in front of the broad snout and moderately wide.
The gill openings are a rather narrow slit on each side of the
head. There are no external nostrils. The tail, which is of
about the same length as the body without the head, is com-
pressed, and tapers to a point, but it is surrounded by a very
broad fringe, supported by innumerable fine and long fin-rays.
There are two fore and two hind paddles, similar to each other
in shape and size, and very different from the fins of ordinary
fishes ; their central portion being covered with a scaly skin,
and the entire paddle surrounded by a rayed fringe. If we
were to cut off the hind part of the tail of a fish, the piece
would bear a strong resemblance to one of the paired paddles.
The vent is situated in the median line of the abdomen be-
tween the paddles.

" In order to obtain a view of the inside of the mouth, it is
necessary to slit it open, at least on one side. We then notice
that there are a pair of nasal openings within and on each side
of the cavity of the mouth. The palate is armed with a pair
of large, long, dental plates, with a flattish undulated and
punctated surface, and with five or six sharp prongs on the
outer side, entirely similar to the fossil teeth described under
the name of Ceratodus. Two similar dental plates of the lower
jaw correspond to the upper, their undulated surface fitting
exactly to that of the opposite teeth. Beside these molars,
the front part of the upper jaw (vomer) is armed with two
obliquely placed incisor-like dental lamellae, which have no
corresponding teeth in the lower jaw. As we know the kind
of food taken by the Barramunda, the use of these teeth is
apparent. The incisors will assist in taking up or even tear-
ing off leaves, which are then partially crushed between the
undulated surfaces of the molars.

" The skeleton consists of a cartilaginous basis, in the form
of a long tapering chord for the body and tail, and in that of a
capsule for the head. No segmentation into separate vertebrae
is visible in any part of the notochord ; but it supports a con-
siderable number of apophyses, the abdominal of which bear
well-developed ribs, all being solid cartilaginous rods, with a
thin sheath of bone. In the same manner no part of the brain-
capsule is ossified, but it is nearly entirely enclosed in thin
bony lamellae. This is also the structure of the appendages of
the skull, as the mandible and the hyoid and scapulary arches.

ELASMOBRANCHII. 345

From a study of the skull, it becomes apparent at once why
in fossil teeth of Ceratodus nothing or very little of the bone
attached to them has been preserved. These teeth rest on
cartilage as well as on bone, the latter being a very thin and
porous layer which could not be preserved, unless the pro-
gress of stratification had been going on with as little disturb-
ance as in the Solenhofen Schiefer ; but the matrix in which
fossil Ceratodont teeth are found shows that it was formed
under very different conditions, and it is certainly not of a
nature to permit the supposition that thin porous lamellae of
bone would have been preserved entire.

" The structure of the skeleton reminds us much of that of the
sturgeons, Chimsera, and especially of Lepidosiren ; and of all
the modifications by which it differs from these types, perhaps
none is of greater interest than that observed in the paddles.
The central part of the paddle, which we have found externally
to be covered with scales, is supported by a jointed axis of
cartilage extending from the root to the extremity of the pad-
dle ; each joint bears a pair of three- or two- or one- jointed
branches. This is the case in the hind as well as fore paddles,
and we are justified in supposing that those extinct Ganoids of
which impressions of paddles with scaly centres have been
preserved, were provided with a similar internal skeleton."

Upon the whole, Dr. Giinther concludes : — i. That the Bar-
ramunda is not generically separable from the almost exclusively
Triassic genus Ceratodus, which was founded simply upon de-
tached teeth ; 2. That the Barramunda is very closely allied to
certain of the Crossopterygious Ganoids, such as the Dipterus
of the Old Red Sandstone, the chief difference being, that the
tail of the latter is heterocercal ; 3. That the order Dipnoi
should be considered merely as forming a sub-order of the
Ganoidei ; 4. That the Ganoidei may be united with the Elas-
mobranchii into a single group, which may be termed Palaich-
thyes, and which is characterised by having a " heart with a
contractile bulbus arteriosus, intestine with a spiral valve, and
optic nerves non-decussating;" 5. That the Ganoidei are the
Fresh-water Palceichthyes, and the Elasmobranchii are the
Marine Palczichthyes.

If the views of this high authority be ultimately adopted, it
will have to be admitted that the Dipnoi, instead of being un-
known in a fossil state, have enjoyed a vast antiquity, dating
their existence from the Lower Old Red Sandstone.

346 AMPHIBIA.

CHAPTER XXXI.
A M P H I B I A.

THE class Amphibia comprises the Frogs and Toads, the Sala-
mandroids, the C<zrili<z, and the extinct Labyrinthodonts, and
may be briefly denned as follows : — As is the case with the
Fishes, branchice, or filaments adapted for breathing air dissolved
in water, are always developed upon the visceral arches for a longer
or shorter time. On the other hand, the Amphibians differ from
the Fishes in the fact that true lungs are always present in the
adult ; the limbs are never converted into fins ; and when median
fins are present, as is sometimes the case, these are never furnished
with fin-rays. The limbs, when present, exhibit in their skeleton
the same parts as do the limbs of the higher Vertebrates. The
skull always articulates with the vertebral column by means of two
occipital condyles. The heart consists of two auricles and a single
ventricle. The nasal sacs communicate posteriorly with the
pharynx; and the rectum, ureters, and ducts of the reproductive
organs open into a common chamber or "cloaca."

The great and distinguishing character of the Amphibia is
the fact that they undergo a metamorphosis after their exclusion
from the egg. They commence life as water-breathing larvae,
provided with gills or branchiae ; but in their adult state they
invariably possess lungs ; the branchiae in the higher forms dis-
appearing when the lungs are developed, but being in other
cases permanently retained throughout life.

In the earliest embryonic condition the branchiae are exter-
nal, placed on the side of the neck, and not situated in an
internal chamber as in Fishes. In some cases the external
branchiae only are present, and they are, in any case, the gills
which are retained in those forms in which the branchiae are
permanent (Perennibranchiata). In the tailed Amphibians
( Urodeld) and in the Frogs and Toads (Anoura) two sets of
gills are developed — an external set, which is very soon lost,
and an internal set, which is retained for a longer or shorter
period. As maturity is approached, true lungs adapted for
breathing air are developed. The development, however, of
the lungs varies with the completeness with which aerial respi-
ration has to be accomplished ; being highest in those forms
which lose their gills when grown up (Caducibranchiata), and
lowest in those in which the branchiae are retained throughout
life (Perennibranchiatd).

The class Amphibia is divided into the four orders of the

URODELA. 347

Ophiomorpha, Urodela, Anoura,dJ\&Labyrinthodontia. The first
of these includes only the serpentiform animals known as
Ccecilice, and not having any certain fossil representatives, may
be altogether passed over here. The order Urodela comprises
the so-called "tailed " Amphibians of the present day, such as
the Newts and Salamanders. The earliest traces of this order
in past time occur in the Tertiary deposits. The order Anoura
includes the so-called " tail-less" Amphibians, such as the Frogs
and Toads, and is likewise not known to have existed in periods
anterior to the Tertiary. Lastly, the order Labyrinthodontia
is entirely extinct, and is known to have existed only during
the Carboniferous, Permian, and Triassic periods.

ORDER I. URODELA (= Ichthyomorpha, Owen ; Saurobatra-
chia). — This order is commonly spoken of collectively as that
of the " Tailed" Amphibians, from the fact that the larval tail
is always retained in the adult. The Urodela are characterised
by having the skin naked, and almost invariably destitute of
any exoskeleton. The body is elongated posteriorly to form a
compressed or cylindrical tail, which is permanently retained
throughout life. The dorsal vertebrae are biconcave (amphi-
ccelous], or concave behind and convex in front (opisthoc<zlous\
and they have short ribs attached to the transverse processes.
The bones of the fore-arm (radius and ulna) on the one hand,
and those of the shank (tibia and fibula) on the other, are
not anchylosed to form single bones.

The best known of the existing Urodela are the Newts
(Triton], the Salamanders (Salamandra\ the Mud-eels (Siren),
the Axolotl (Siredon\ and the Giant-Salamanders (Menopoma).
Some of these are " perennibranchiate," retaining the bran-
chiae throughout life ; others lose the branchiae, becoming thus
" caducibranchiate," but retain the branchial apertures behind
the head ; others, lastly, lose both the branchiae and the bran-
chial apertures. Most of the Urodela have the four limbs
well developed, but some possess only the anterior limbs.

The geological history of the Urodela is short and of little
importance. No trace of the order has hitherto been discovered
in any deposits older than the Tertiary. The only exception
to this statement is constituted by the fossil described from the
Lower Permian Rocks by Geinitz under the name of Palao-
siren, and regarded by him as being most nearly allied to the
Siren lacertina. It is probable, however, that Palceosiren is
really referable to the Labyrinthodontia. In strata of Tertiary
age have been discovered the remains of Newts and Sala-
manders. The most remarkable fossil referable to this order
is the Andrias Scheuchzeri (fig. 307) of the Miocene beds of

348

AMPHIBIA.

Fig. 307. — A ndrias Scheuchzeri. Miocene Tertiary.

ANOURA.

349

Oeningen. This singular fossil was described by its original
discoverer as human, under the name of Homo diluvii testis ;
but it is really the skeleton of a Salamandroid of large size.
It is very closely allied to the Giant Salamander (Menopoma,
or Sieboldia, maxima] of Java/

ORDER II. ANOURA ( = Batrachia, Huxley ; Theriomorpha,
Owen ; Chdonobatrachia, &c.) — This order includes the Frogs
and Toads, and is perhaps best designated by the name of
Anoura, or "Tail-less" Amphibians. The name Batrachia,
employed by Huxley, is inexpedient, partly because it is used
by Owen to designate the entire class Amphibia, and partly
because, in common language, it is usual to understand by a
" Batrachian" any of the higher Amphibians; such, for instance,
as a Labyrinthodont.

The Anoura, or Tail-less Amphibians, are characterised by
the following points : — The adult is destitute of both gills and
tail, both of which structures exist in the larva, whilst the two
pairs of limbs are always present. The skin is soft, and there
are rarely any traces of an exoskeleton. The dorsal vertebrae
are "procoelous " or concave in front, and are furnished with

Fig. 308. — Skeleton of the common Frog (Rana temporaria). d Dorsal vertebrae,
with long transverse processes.

long transverse processes, which take the place of ribs, which
are only present in a rudimentary form. The radius and ulna
in the fore-limb, and the tibia and fibula in the hind-limb, are

350 AMPHIBIA.

anchylosed to form single bones (fig. 308). The mouth is
sometimes edentulous, but the upper jaw has usually small
teeth, and the lower jaw sometimes. The hind-limbs usually
have the digits webbed for swimming, and are generally much
larger and longer than the fore-limbs.

The geological history of the Anoura, as in the case of the
Urodela, is of small importance. The two chief groups of the
living A?wura — namely, the Frogs and the Toads — are both
represented in past time ; but they do not appear to have come
into existence till after the commencement of the Tertiary
period. Most of the fossil forms have been detected in de-
posits of Miocene age.

ORDER IV. LABYRINTHODONTIA. - - The members of this,
the last order of the Amphibia, are entirely extinct. They
were Batrachians, probably most nearly allied to the Urodela,
but all of large size, and some of gigantic dimensions, the skull
of one species (Labyrinthodon Jcegeri] being upwards of three
feet in length and two feet in breadth. The Labyrinthodonts
were first known to science simply by their footprints, which
were found in certain sandstones of the age of the Trias.
These footprints consisted of a series of alternate pairs of
hand-shaped impressions, the hinder print of each pair being
much larger than the one in front (fig. 309). So like were
these impressions to the shape of the human hand that the
unknown animal which produced them was at once christened
Cheir other ium, or " Hand-beast." Further discoveries, how-
ever, soon showed that the footprints of Cheirotherium had
been produced by different species of Batrachians, to which the
name of Labyrinthodonts was applied in consequence of the
complex microscopic structure of the teeth.

The order Labyrinthodontia is thus defined by Professor
Huxley : — " The body is salamandriform, with relatively weak
limbs and a long tail. The dorsal vertebrae, when completely
ossified, are biconcave, with double transverse processes. The
ribs have distinct ckpitula and tubercula.

" In the thoracic region, three superficially sculptured exo-
skeletal plates, one median and two lateral, occupy the place
of the interclavicle and clavicles. Between these and the pelvis
is a peculiar armour, formed of rows of oval dermal plates,
which lie on each side of the middle line of the abdomen, and
are directed obliquely forwards and inwards, to meet in that line.

"The skull has distinctly ossified epiotic bones, in the same
position and of the same form as those of fishes. The cranial
bones are sculptured, and many exhibit peculiar smooth sym-
metrical grooves — the so-called ' mucous canals.'

LABYRINTIIODONTIA.

351

" The parietes of the teeth are deeply plaited and folded, so
as to give rise to a complicated
* labyrinthine ' pattern in the
transverse section of the tooth. ';

The points in which the Laby-
rinthodonts differ from the mo-
dern Urodela are chiefly to be
found in the fact that the head
is defended by an external cov-
ering or helmet of hard and
polished osseous plates, in the
possession of ventral integument-
ary scutes, in the existence of
exoskeletal plates occupying the
place of the interclavicle and cla-
vicles, in the amphiccelous form

Fig. 309. — Foot-prints of a Labyrinthodont (CJuirotkerium), from the Trias. The
upper figure shows a single foot-print enlarged ; the lower figure shows a slab, with
several prints, and traversed by reticulated desiccation-cracks.

352

AMPHIBIA.

of the dorsal vertebrae, and in the complicated structure of the
teeth. These last-mentioned organs are not only often very
numerous, but are of large size. The subjoined illustration
(fig. 310) shows the beautiful and complex structure of the
teeth, from which the name of the order is derived.

Fig. 310. — Section of the tooth of Labyrinthodon (Mastodonsaurus] y<egeri.

The Labyrinthodonts range from the Carboniferous Rocks
to the Trias ; but some of the forms commonly included in
this order may perhaps belong elsewhere. One type of the
Labyrinthodonts is constituted by the singular genus Archego-
saurus, and the less known Apateon — both from the Carboni-
ferous Rocks. Archegosaunis is remarkable in having the
notochord persistent, and in the possession of permanent bran-
chial arches. It has been- made by Professor Owen the type
of a separate group, the Ganocephala; but it is probably an
immature and larval form. The occipital condyles, also, do
not seem to have been ossified in the Archegosauria.

Of the Carboniferous Labyrinthodonts the most important
genera are Anthracosaurus, Pholidogaster, Ophiderpeton, Ich-
thyerpeton, Urocondylus, Lepterpeton, Baphetes, Raniceps, Den-
drerpeton, Hylerpeton, and Hylonomus ; though the affinities of
some of these are more or less doubtful. Most of the Car-
boniferous Labyrinthodonts were of comparatively small size ;
but some, such as Baphetes (fig. 311) and Anthracosaurus, must
have attained gigantic dimensions. All the above-mentioned
genera seem to have possessed well-ossified vertebrae, with well-
developed limbs, the form of the body being mostly salaman-
driform, but sometimes fish-like, or serpentiform.

LABYRINTHODONTIA.

353

In the Permian Rocks, a few remains of LabyrinthodontS
have been discovered, the genus Zygosaurus being peculiar to
this period.

Fig. 311. — Baphetes planiceps, from the Carboniferous Rocks of Nova Scotia. (After
Dawson.) a Anterior part of the skull, viewed from beneath, and much reduced ; b One
of the largest teeth, natural size.

In the Triassic Rocks the remains of LabyrinthodontS
are abundant, the most important genus being Labyrinthodon
or Mastodonsaurus. This genus is known mainly by foot-
prints and by crania ; and the size attained by some species
must have been colossal. No remains of this order have
hitherto been discovered in rocks younger than the Trias.

CHAPTER XXXII.
REPTILIA.

THE true Reptiles and the Birds, unlike as they are in external
appearance, are nevertheless related to one another by various
points of affinity ; so that they may well be included in a
single division, which has been termed Sauropsida by Huxley.
The Sauropsida are defined by the possession of the following
characters : — At no period of existence are branchice, or water-
breathing respiratory organs, developed upon the visceral arches ;
the red corpuscles of the blood are nucleated ; the skull articulates
with the vertebral column by means of a single articulating surface
or condyle ; and each half or " ramus " of the lower jaw is com-
posed of several pieces, and articulates with the skull, not directly,
but by the intervention of a peculiar bone, called the " quadrate
bone" or " os quadratum " (fig. 312).

z

354 REPTILIA.

These being the common characters of Reptiles and Birds,
by which they are collectively distinguished from other Verte-
brates, it remains to inquire what are the characters by which
they are distinguished from one another. The following, then,
are the characters which separate the Reptiles from the Birds :
— The blood in Reptiles is cold — that is to say, slightly warmer
than the external medium — owing mainly to the fact that the
pulmonary and systemic circulations are always directly con-
nected together, either within the heart or in its immediate neigh-
bourhood, so that the body is supplied with a mixture of venous
and arterial blood, in place of pure arterial blood alone. The
terminations of the bronchi at the surface of the lung are closed,
and do not communicate with air -sacs, placed in different parts of
the body. When the epidermis develops horny structures, these
are in the form of horny plates or scales, and never in the form of
feathers. The fore-limbs are formed for various purposes, includ-
ing in some cases even flight, but they are never constructed tipon
the type of the " wings " of Birds. Lastly, with one or two doubt-
ful exceptions, whilst the ankle-joint is placed between the distal
and proximal portions of the tarsus, the tarsal and metatarsal
bones of the hind-limb are never anchylosed into a single bone.

These are the leading characters by which Reptiles are dis-
tinguished from Birds ; but we must not forget the other dis-
tinctive peculiarities in which Reptiles agree with Birds, and
differ from other Vertebrates — namely, the absence of branchiae
at all times of life, the possession of only one occipital con-
dyle, and the articulation of the complex lower jaw with the
skull by means of a quadrate bone.

It is now necessary to consider these characteristics of the
Reptilia a little more minutely. The class includes the Tor-
toises and Turtles, the Snakes, the Lizards, the Crocodiles, and
a number of extinct forms ; and with the exception of the Tor-
toises and Turtles they are mostly of an elongated cylindrical
shape, provided posteriorly with a long tail. The limbs may
be altogether absent, as in the Snakes, or quite rudimentary,
as in some of the Lizards, but as a general rule both pairs of
limbs are present, sometimes in the form of ambulatory legs,
sometimes as swimming-paddles, and in some extinct forms
modified to subserve an aerial life. The endoskeleton is
always well ossified, and is never cartilaginous or semi-cartil-
aginous, as in many Fishes and some Amphibians. The skull
articulates with the atlas by a single condyle. The lower jaw
is complex, each half or ramus being composed of from four to
six pieces, united to one another by sutures (fig. 312). In the
Tortoises, however, these are anchylosed into a single piece,

GENERAL CHARACTERS OF REPTILES. 355

and the two rami are also anchylosed. In most Reptiles, how-
ever, the two rami of the lower jaw are only loosely united —
in the Snakes by ligaments and muscles only, in the Lizards
by fibro-cartilage, and in the Crocodilia by a regular suture.
In all, the lower jaw articulates with the skull by a quadrate
bone (fig. 312, a) ; and as this often projects backwards, the

b

Fig. 312. —Skull of a Serpent (Python), b Articular portion of the lower jaw ;
a Quadrate bone ; c Squamosal portion of the temporal bone.

opening of the mouth is often very extensive, and may even
extend beyond the base of the skull. Teeth are usually pre-
sent, but are not sunk in separate sockets or alveoli, except in
the Crocodiles and in some extinct forms. In the Tortoises
and Turtles alone of living types there are no teeth, and the
jaws are simply sheathed in horn, constituting a kind of beak
like that of a bird.

Ribs are always present and always well developed, but they
differ much in form. It is not correct, however, to regard the
presence of ribs as separating the true Reptiles from the Am-
phibia, as is sometimes stated. Some of the most Lizard-like
of the Amphibians, such as the Siren, possess short but well-
developed ribs, and rudiments of ribs are traceable in other
orders; whilst in the Cczrilice they are large and well developed.

As regards the exoskeleton, all Reptiles have horny epider-
mic scales, and they are divided into two great sections — called
respectively Squamata and Loricata — according as the integu-
mentary skeleton consists simply of these scales, or there are
osseous plates developed in the derma as well. In the Tor-
toises, the epidermic plates unite with the bony exoskeleton
and with the true - endoskeleton to form the case or box in
which the body of these animals is enclosed.

The class Reptilia is divided into the following nine orders,
of which the first four are represented by living forms, whilst
the remaining five are extinct : —

356 REPTILIA.

1. Chelonia (Tortoises and Turtles).

2. Ophidia (Snakes).

3. Lacertilia (Lizards).

4. Crocodilia (Crocodiles and Alligators).

5. Ichthyopterygia.

6. Sauropterygia.

>• Recent.

7. Anomodontia.

> Extinct.

8. Pterosauria.

9. JDeinosauria.

As regards their general distribution in time, the Reptilia
attained their maximum of development in the Mesozoic
period, which has hence often been called the "Age of Reptiles."
If the Elgin Sandstones, containing the remains of Telerpeton
and Stagonolepis, be of Triassic age — as seems almost certain
— then no Reptile has as yet been discovered in the Devonian
Rocks. In the Carboniferous Rocks, the place of the true
Reptiles seems to have been taken by the Amphibian group of
the Labyrinthodonts. It is possible, however, that the little
Hylonomus, of which three species were discovered in the Coal-
strata of Nova Scotia by Dr Dawson, may be Lacertian in its
affinities. It is also possible that the vertebrae from strata of
the same age described by Professor Marsh under the name of
Eosaurus Acadiensis, may belong to a marine reptile allied to
Ichthyosaurus. In the Permian Rocks the first undoubted
Reptilian remains occur, the Protorosaurus of this period being
probably a Lacertilian.

Throughout the whole Mesozoic series, Reptilian remains
are abundant and belong to numerous and strange types.
Chelonians and true Crocodiles, with Lizards allied to existing
forms, make their first appearance in deposits belonging to this
period. The extinct orders of the Ichthyopterygia, Saurop-
terygia, Anomodontia, Pterosauria, and Deinosauria, not only
first appear in Mesozoic deposits, but are exclusively confined
to rocks of this age. In the Tertiary period, lastly, the
remains of Reptiles are comparatively rare, and the number
of types is much reduced. The living order of the Ophidia,
however, makes its first appearance in the Tertiary deposits.
In the following view of the characters and distribution in time
of the orders of the Reptiles, it will be advisable to consider
the recent orders first, though this is not in accordance with
their natural arrangement.

ORDER I. CHELONIA. — The first order of living Reptiles is
that of the Chelonia, comprising the Tortoises and Turtles, and
distinguished by the following characters: — There is an osseous
exoskeleton which is combined with the endoskeleton to form

CHELONIA.

357

a kind of bony case or box in which the body of the animal is
enclosed, and which is covered by a leathery skin, or, more
usually, by horny epidermic plates. The dorsal vertebrae are
immovably connected together, and are devoid of transverse
processes. The ribs are greatly expanded (fig. 313, r), and

Fig. 313. — Skeleton of Tortoise (Ewys Enropcea?, the plastron being removed, en
Carapace ; r Ribs, greatly expanded, and united by their edges ; ^ Scapular arch, placed
within the carapace, and carrying the fore-limbs; / Pelvic arch, also placed within the
carapace, and carrying the hind-limbs.

are united to one another by sutures, so that the walls of the
thoracic cavity are immovable. All the bones of the skull
except the lower jaw and the hyoid bone are immovably united
together. There are no teeth, and the jaws are encased in
horn so as to form a kind of beak. The heart is three-
chambered, the ventricular septum being imperfect.

Of these characters of the Chelonia, the most important and
distinctive are the nature of the jaws, and the structure of the
exoskeleton and skeleton. As regards the first of these points,
the lower jaw in the adult appears to consist of a single piece,
its complex character being masked by anchylosis. The sepa-
rate pieces which really compose each ramus of the jaw are

358 REPTILIA.

immovably anchylosed together, and the two rami are also
united in front by a true bony union. There are also no
teeth, and the edges of the jaws are simply sheathed in horn,
constituting a sharp beak. As regards the second of these
points, the bony case in which the body of a Chelonian is
enclosed consists essentially of two pieces, a superior or dorsal
piece, generally convex, called the " carapace," and an inferior
or ventral piece, generally flat or concave, called the "plastron."
The carapace and plastron are firmly united along their edges,
but are so excavated in front and behind as to leave apertures
for the head, tail, and fore and hind limbs. The limbs and
tail can almost always be withdrawn at will under the shelter
of the thoracico-abdominal case formed in this way by the
carapace and plastron, and the head is also generally re-
tractile.

The carapace or dorsal shield is composed of the flattened
spinous processes of the dorsal vertebrae, the expanded ribs,
and usually a series of marginal bones — the whole covered by
horny epidermic plates or by a leathery skin. The plastron
or ventral shield is composed of nine bony pieces, which are
probably integumentary ossifications, but which are sometimes
regarded as composing a modified and greatly - expanded
breast-bone. The scapular and pelvic arches, supporting re-
spectively the fore and hind limbs, are placed within the cara-
pace. As in the Crocodilia, clavicles are wanting.

From the aquatic habits of many of the members of this order
they are by no means uncommon in the fossil condition. The
Turtles frequent the sea, and thus come naturally to be fossils
in marine deposits ; and the preservation of all the Chelonians
alike is rendered easy by the indestructible nature of the case
in which their bodies are enclosed.

The Chelonians may be divided into sections according as
the limbs are natatory, are adapted for an amphibious life, or
are fitted for terrestrial progression. In the first of these sec-
tions are the true Turtles (Cheloniidce), which frequent the
sea, and are distinguished by their depressed and flattened
carapace, and by their oar-like limbs. In the second section
are the River and Marsh Tortoises, comprising the Soft Tor-
toises (Trionycidce) and the Terrapins (Emydidtz). In the
third section are the true Land-tortoises (Testudimdcs)^ distin-
guished by their strongly convex carapace, and limbs adapted
for walking upon the land. All these three sections are repre-
sented in past time, the Turtles, Trionydds^ and Emydida
appearing for the first time, so far as is certainly known, in the
Jurassic series, whilst the Testudinidcz do not appear till the

CHELONIA.

359

commencement of the Tertiary epoch. The earliest known
traces of Chelonians occur in the Permian Rocks, in the lower
portion, that is, of the New Red Sandstone of older geologists.
These traces, however, are not wholly satisfactory, since they
consist solely of the footprints of the animal upon the ripple-
marked surfaces of the sandstone. Of this nature is the
Chelichnus Duncani, described by Sir William Jardine in his
classical work on the
' Ichnology ' of Annan-
dale in Dumfriesshire.
With doubtful excep-
tions, the first unequi-
vocal remains of Che-
lonians appear in the
Jurassic series. The
Cheloniidce make their
first undoubted ap-
pearance with the Che-
lone planiceps of the
Portland stone (Upper
Oolite). In the Cre-
taceous series are seve-
ral turtles, one of which
is figured below (fig.
314). In the Tertiary
Rocks the remains of
Turtles are abundant,
and especially so in the
London Clay (Eocene).
Species of Emydidcz
have been cited from
the Jurassic series,

some of which appear to be free from doubt. A species of
Emys occurs in the Wealden, and numerous forms of this
family have been detected in formations of Tertiary age, es-
pecially in the Eocene and Miocene. The Trionytidcz, except
for a femur described by Owen from the Lias, are not known
to have existed prior to the commencement of the Tertiary
period. Numerous species of Trionyx, however, occur in the
Eocene, and others have been described from the Miocene
and Pliocene. The Testudinidce or Land-tortoises appear to
have commenced their existence in the Miocene Tertiary.
The most remarkable form of this group is the great Colosso-
chelys Atlas of the Tertiary deposits of the Sivalik Hills, which
is believed to have reached the gigantic length of twenty feet.

Fig. 314. — Chelone Benstedi. Lower Chalk.

360 REPTILIA.

ORDER II. OPHIDIA. — The second order of Reptiles is
that of the Ophidia, comprising the Snakes and Serpents, and
distinguished by the following characters : —

The body is always more or less elongated, cylindrical, and
worm-like, and whilst possessing a covering of horny scales, is
always unprovided with a bony exoskeleton. The dorsal ver-
tebrae are concave in front (procoelous), with rudimentary trans-
verse processes. There is never any sternum, nor pectoral
arch, nor fore-limbs, nor sacrum, and as a rule there are no
traces of hind-limbs. Rudimentary hind-limbs, however, are
occasionally present (e. g., in Python and Tortrix). There are
always numerous ribs. The two halves or rami of the lower
jaw are composed of several pieces, and the rami are united
anteriorly by ligaments and muscles only, and not by cartilage
or suture. The lower jaw, further, articulates with the skull by
means of a quadrate bone (fig. 312, #), which is always more
or less movable, and is in turn united with the squamous por-
tion of the temporal bone ("mastoid bone"), which is also
movable, and is not firmly united with the skull. The superior
maxillae are united with the praemaxillae by ligaments and mus-
cles only, and the palatine arches are movable and armed with
pointed recurved teeth. Hooked conical teeth are always pre-
sent, but they are never lodged in distinct sockets or alveoli.
Functionally, they are capable of performing nothing more
than merely holding the prey fast, and the Snakes are provided
with no genuine masticatory apparatus. The heart has three
chambers, two auricles and a ventricle, the latter imperfectly
divided into two cavities by an incomplete septum. The lungs
and other paired organs are mostly not bilaterally symmetrical,
one of each pair being either rudimentary or absent.

The three most important groups of the existing Ophidians
are the Colubrine Snakes, the Constricting Snakes, and the
Viperine Snakes. In the first of these the upper jaws carry
solid teeth, with or without canaliculated fangs as well. In
the second group are the Boas and Pythons, distinguished by
their great size, enormous muscular power, and numerous
strong recurved teeth. In the third group are Snakes, in which
the upper jaws carry only a pair of perforated poison-fangs.

Most of the existing Snakes are terrestrial in their habits,
and are therefore not likely to be preserved in stratified de-
posits. Many of these, however, take to the water occasionally,
and some habitually frequent rivers or the sea itself. All the
above-mentioned groups of Ophidians are represented in past
time, but they are neither abundant nor of importance as fossils.
No remains of Ophidians are known to occur in any Palaeozoic

LACERTILIA, 361

or Mesozoic deposit. The earliest known traces of any ser-
pent are in the Lower Kainozoic Rocks, the oldest being the
Palceophis toliapicus of the London Clay of Sheppey. The
nearly-allied Palaophis typhaus of the Eocene beds of Brackle-
sham appears to have been a Boa-constrictor-like snake of
about twenty feet in length. Other species of Palceophis have
been described from the Tertiary Rocks of the United States,
and the genus Dinophis has been formed for the reception of
another gigantic constricting Serpent from the same formation.
In some of the later deposits have been found the poison-
fangs of a venomous snake. Upon the whole, however, the
Snakes must be looked upon as a comparatively modern group,
and not as one of any great geological antiquity.

ORDER III. LACERTILIA. — The third order of Reptiles is
that of the Lacertilia, comprising all those animals which are
commonly known as Lizards, together with some serpentiform
animals such as the Blind-worms. The Lacertilia are dis-
tinguished by the following characters : —

As a general rule, there are two pairs of well-developed
limbs, but there may be only one pair, or all the limbs may be
absent. A scapular arch is always present, whatever the con-
dition of the limbs may be. An exoskeleton, in the form of
horny scales like those of the Snakes, is almost always present.
The vertebrae of the dorsal region are procoelous or concave in
front, rarely amphiccelous or concave at both ends. There is
a single transverse process at each side, and the heads of the
ribs are simple and undivided. There is either no sacrum, or
the sacral vertebrae do not exceed two in number. The teeth
are not lodged in distinct sockets. The eyes are generally
furnished with movable eyelids, and are always so in the com-
pletely snake-like forms. The heart consists of two auricles
and a ventricle, the latter partially divided by an incomplete
partition. There is a urinary bladder, and the aperture of the
cloaca is transverse.

As a general rule, the animals included under this order
have four well-developed legs, and would therefore be popu-
larly called " Lizards." In some (Chirotes) there are no hind-
feet ; in some (Bipes) the fore-limbs are wanting ; and others
(Anguis, Pseudopus, and Amphisbczna) are entirely destitute
of limbs, thus coming closely to resemble the true Snakes
or Ophidians in external appearance. These serpentiform
Lizards, however, can be distinguished from the true Snakes,
amongst other characters, by the structure of the jaws. In
the Snakes, as before said, the two rami of the lower jaw are
loosely united in front by ligaments and muscles, and are

362 REPTILIA.

attached behind to a movable quadrate bone, which is in turn
connected with a movable squamosal, this giving an enormous
width of gape to these animals. In the Lizards, however, even
in those most like the Snakes, the halves of the lower jaw are
firmly united to one another in front, and though the quadrate
bone is usually more or less movable, the jaws can in no case
be separated to anything like the extent that characterises the
Ophidia.

The Lizards are distinguished from the Crocodiles, amongst
other characters, by the fact that the integumentary covering is
in the form of horny scales, never with bony "scutes," whilst
the teeth are rarely or never sunk into distinct sockets. In many
cases the teeth are anchylosed to the summit of the margin of
the jaw ("acrodont" dentition); in other cases they are at-
tached by their sides to the inner surface of the jaw (" pleuro-
dont" dentition).

The whole order of the Lacertilia is very often united with
the next group of the Crocodilia, under the name of Sauria.
The term " Saurian," however, is an exceedingly convenient
one to designate all the reptiles which approach the typical
Lizards in external configuration, whatever their exact nature
may be ; and from this point of view it is often very useful as
applied to many fossil forms, the structure of which is only im-
perfectly known. It is therefore perhaps best to employ this
term merely in a loose general sense.

It is hardly possible, with our present knowledge, to speak
very positively as to the exact range of the Lacertilia in time.
This uncertainty arises from two causes — firstly, that there is
some doubt as to the exact age of some deposits which have
yielded Lacertilian remains ; and secondly, that the affinities of
some extinct Reptiles are a matter of considerable question.
Upon the whole, the oldest known Lacertilian would appear to
be the Protorosaurus of the Middle Permian Rocks ; though
good authorities have placed this form in the Crocodilian group
of the Thecodontia. Protorosaurus attained a length of between
three and four feet, and differs from all existing Lizards in
having its teeth implanted in distinct sockets — this being a
Crocodilian character. In other respects, the Permian reptile
approximates closely to the living Monitors ( Varanidcz), and its
slightly-cupped vertebrae would lead to the belief that it was
aquatic in its habits.

In rocks known, or supposed, to be of Triassic age, nume-
rous Lacertilian reptiles have been discovered, of which the
most important are Telerpeton, Hyperodapedon, and Rhyncho-
saurus. Telerpeton occurs in strata near Elgin, in Scotland,

LACERTILIA. 363

which have been variously referred to the Upper Devonian
and to the Trias, but which almost certainly belong to the latter.
Professor Huxley concludes that Telerpeton " presents not a
single character approximating it towards the type of the Per-
mian Protosauria, nor to the Triassic Rhynchosaurus, and other
(probably Triassic) African and Asiatic allies of that genus,
nor to the Mesozoic Dinosauria; still less can it be considered
a ' generalised ' form, or as, in any sense, a less perfectly organ-
ised creature than the Gecko, whose swift and noiseless run
over walls and ceilings, surprises the traveller in warmer cli-
mates than our own." In its dentition, Telerpeton seems to
have been " acrodont," and it differs from most existing Lizards
merely in having amphiccelous, and not proccelous, vertebrae.

Hyperodapedon was originally discovered in the " Elgin Sand-
stones " along with Telerpeton, and it has since been found in
strata of Triassic age in India. It was described by Professor
Huxley as " a Saurian reptile about six feet long, remarkable
for the flattened or slightly concave articular surfaces of the
centra of its vertebrae, and for its well-developed costal system
and fore and hind limbs ; but more particularly characterised
by its numerous series of sub-cylindrical palatal teeth." Upon
the whole, Huxley concludes that Hyperodapedon is most
nearly allied to the living Sphenodon (Hatteria) of New Zealand,
upon the grounds that both " have amphiccelous vertebras
(those of the ancient reptile being far less fish-like than those
of the modern one, be it noted) ; both have beak-like praemax-
illae, not anchylosed together ; both have the inferior zygoma
complete ; both have similarly-formed lower jaws ; in each a
single row of teeth in the mandible bites between two rows of
teeth fixed to a plate, which is formed by a union of the maxil-
la with the palatine bone — a structure which is quite anom-
alous amongst Lacertilians ; and, finally, in both, these teeth
wear down to the bone of the jaw by masticatory attrition."

The genus Rhynchosaurus is in a doubtful position, but
may conveniently be considered
here. By Huxley its affinities
are regarded as being Lacertili-
an, but by Owen it is looked
upon as belonging to the Ano-
modontia, and as being most
nearly allied to Oudenodon. In

many points RJiynchosaiirUS ap- Fig. 315.— Skull of Rhynchosaurus arti-

proaches the existing Lizards,

but its vertebrae are amphiccelous, and the structure of the

mouth is quite unlike that of any living Lacertilian. The skull

REPTILIA.

(fig. 315) is pyramidal, and the jaws do not exhibit any traces
of teeth. If the mouth be really edentulous, then Rhynchosau-
rus should probably be removed from the Lacertilia\ but this
point cannot in the meanwhile be definitely decided in the
affirmative.

Amongst other Triassic, or supposed Triassic, Lacertilians,
may be mentioned Saurosternon and Pristerodon^ from strata
believed to be of Triassic age in Africa, and Clepsysanrus and
Centemodon from deposits of the same age in North America.

In the Jurassic period, the remains of Lacertilians are not
unknown, but call for little special notice. Several forms of
little importance have been described from the Middle Oolites.
In the fresh-water strata of the Purbeck series (Upper Oolites),
occur the remains which have been referred to the genera
Nuthetes, Macellodon, Saurillus, and Echinodon. These are,
perhaps, the first traces in the stratified series of remains, the
affinities of which to the typical Lacertidce. cannot be disputed.

In the Cretaceous series occur the small Lizards which con-
stitute the genera Raphiosaurus, Coniosaums, and Dolichosau-
rus. Here also, and almost exclusively confined to strata of
this age, occur the singular Lacertilians which form the group
of the " Mosasauroids." These remarkable Reptiles were of
gigantic size, Mosasaurus princeps being believed to have at-
tained the enormous length of not less than seventy-five feet.
The teeth in these reptiles (fig. 316) are long, pyramidal, and

Fig. 316.— Skull of Mosasaurus Cam/eri, much reduced. Maastricht Chalk.

slightly curved ; but they are anchylosed to the jaw, and are
not sunk into distinct sockets, as in the living Crocodiles.

CROCODILIA. 365

From the shortness of the humerus, and the indications that
the vertebral column was unusually flexible, and that the tail
was laterally compressed, it was early conjectured that the
Mosasauroids were marine and aquatic in their habits. This
conjecture has been raised to the rank of a certainty by the
discovery that the fore and hind limbs of the Mosasauroids
were in the form of fin-like paddles, like those of the Ichthyo-
saur and Plesiosaur. There can therefore be no doubt that
Mosasaurus — like the living Amblyrhynchus — was aquatic in its
habits, and frequented the sea-shore, coming, in fact, only oc-
casionally to the land. The best-known genus is Mosasaurus,
of which the most celebrated species is the M. Camperi (fig.
316) of the Maestricht Chalk. Other genera belonging to this
group are Leiodon, Baptosaurus, and Halisaurus. Recently,
Marsh has described bony dermal scutes as present in several
Mosasauroids (e.g., Holcodus, Leiodon, and Edestosaurus], thus
rendering their Lacertilian affinities doubtful.

In the Tertiary Rocks the remains of Lacertilians are not by
any means unknown, but none of the forms of this period are
sufficiently important to demand especial attention. Most of
the Tertiary Lacertilians, however, are of small size, and ap-
pear to have been terrestrial in their habits, thus approximating
to the typical existing Lizards.

ORDER IV. CROCODILIA. — The last and highest order of
the living Reptilia is that of the Crocodilia, including the living
Crocodiles, Alligators, and Gavials, and characterised by the
following peculiarities : —

The body is covered with an outer epidermic exoskeleton
composed of horny scales, and an inner dermal exoskeleton
consisting of squared bony plates or scutes, which may be con-
fined to the dorsal surface alone, or may exist on the ventral
surface as well, and which are disposed on the back of the
neck into groups of different form and number in different
species. The bones of the skull and face are firmly united to-
gether, and the two halves or rami of the lower jaw are united
in front by a suture. There is a single row of teeth, which are
implanted in distinct sockets, and hollowed at the base for the
germs of the new teeth, by which they are successively pushed
out and replaced during the life of the animal. The centra of
the dorsal vertebrae in all living Crocodilia are procoelous, or
concave in front, but in the extinct forms they may be either
amphicoelous (concave at both ends) or opisthocoelous (con-
cave behind). The vertebral ends of the anterior trunk-ribs
are bifurcate. There are two sacral vertebrae. The cervical
vertebrae have small ribs (hence the difficulty experienced by

366

REPTILIA.

the animal in turning quickly) ; and there are generally false
abdominal ribs produced by the ossification of the tendinous
intersections of the recti muscles. There are no clavicles.
The heart consists of four completely distinct and separate
cavities, two auricles, and two ventricles, the ventricular sep-
tum— as in no other Reptiles — being complete. The right and
left aortse, however, or, in other words, the pulmonary artery
and systemic aorta, are connected together close to their origin
by a small aperture {foramen Panizzce), so that the two sides
of the heart communicate with one another. The aperture of
the cloaca is longitudinal, and not transverse, as in the Lizards.
All the four limbs are present, the anterior ones being penta-
dactylous, the posterior tetradactylous. All are oviparous.

The chief points by which the Crocodiles are distinguished
from their near allies, the Lacertilians, are the possession of
a partial bony dermal exoskeleton in addition to the ordinary
epidermic covering of scales, the lodgment of the teeth in
distinct sockets, and the fact that the mixture of venous and
arterial blood, which is so characteristic of Reptiles, takes
place, not in the heart itself, but in its immediate neighbour-
hood, by a communication between the pulmonary artery and
aorta directly after their origin.

The order Crocodilia is divided into three sub-orders, termed
Proccelia, Amphicotfia, and Opisthocoslia according as the dorsal
vertebrae are concave in front, concave at both ends, or con-
cave behind. The sub-order Proaxlia comprises all the living
forms — namely, the Crocodiles proper, the Alligators, and the
Gavials. The first of these have the fourth tooth in the lower
jaw (fig. 317) larger than the others, forming a canine tooth,

Fig. 317. — Skull of young Crocodilus biporcatus (after Van der Hoven).

which is received into a notch excavated in the alveolar border
of the upper jaw, so that it is visible externally when the mouth
is closed. In the Alligators (fig. 318), the fourth tooth in the
lower jaw forms a canine which is received into a pit in the
palatal surface of the upper jaw, where it is completely con-
cealed when the mouth is shut. In the Gavials the snout is

CROCODILIA. 367

greatly prolonged, and the teeth are pretty nearly equal in size
and similar in form in the two jaws.

The Procodian Crocodiles occur for the first time in the
Greensand (Cretaceous Series) of North America. In Europe,
however, the earliest remains of Proccelian Crocodiles are from
the Lower Tertiary Rocks (Eocene). It is a curious fact that
in the Eocene Rocks of the south-west of England, there occur
fossil remains of all the three living types of the Crocodilia —
namely, the Gavials, true Crocodiles, and Alligators ; though
at the present day these forms are all geographically restricted
in their range, and are never associated together.

Fig. 318. — Lower jaw of an Alligator. Eocene Tertiary, Isle of Wight.

The Amphicoilian Crocodiles are characterised by their
biconcave vertebrae, and are entirely extinct, being confined
altogether to the Mesozoic period. The biconcave vertebras
show a decided approach to the structure of the backbone in
fishes ; and as the rocks in which they occur are mostly marine,
there can be little doubt but that these Crocodiles were, in
the majority of cases at any rate, inhabitants of the sea. The
typical members of this sub-order range from the Lias to the
Chalk ; and the most important genera are Teleosaurus, Steneo-
saurus, Dakosaurus, Makrospondylus, Goniopholis, and Sucho-
sanrus, the two last mentioned occurring in the fresh-water
deposits of the Wealden (Cretaceous).

The Stagonolepis of the Elgin Sandstone, with its pitted dermal
bony scutes, is now believed to be truly referable to the Croco-
dilia. As before said, the Elgin Sandstones are probably Triassic.

We may briefly consider here a group of Reptiles which
have been regarded as Crocodilian, but which are placed by
Owen in a separate order under the name of Thecodontia, and
which are looked upon by Huxley as being Deinosaurian. The

368 REPTILIA.

" Thecodont " Reptiles are defined as follows : — " Vertebral
bodies biconcave ; ribs of the trunk long and bent, the anterior
ones with a bifurcate head ; sacrum of three vertebras ; limbs
ambulatory, femur with a third trochanter. Teeth with the
crown more or less compressed, pointed, with trenchant and
finely serrate margins, implanted in distinct sockets." — (Owen.)

The Thecodont Reptiles are Triassic, and the three most im-
portant genera are Thecodontosaurus, Palczosaurus, and Belodon,
the last from undoubted . Triassic strata, whilst the two former
occur in a dolomitic conglomerate near Bristol, which has
sometimes been thought to be Permian, but which is also
almost certainly Triassic. In some respects these reptiles
make an approach to the Lacertians ; but, on the whole, little
doubt can be entertained as to their truly belonging to the
Amphicoelian Crocodiles.

The sub-order of the Opisthocalian Crocodiles, including
those forms in which the anterior trunk vertebrae are concave
behind, is one which can be only provisionally retained. Pro-
fessor Owen includes in this section the two genera Strepto-
spondylus and Cetiosaurus ; but the latter is referable to the
Deinosauria, and will be treated of when that order is con-
sidered. The genus Streptospondylus has been founded on
vertebrae obtained from the Oolitic and Wealden formations ;
but there are doubts as to the true position of the reptile to
which these belonged.

CHAPTER XXXIII.
EXTINCT ORDERS OF REPTILES.

IT remains now to consider briefly the leading characters of
five wholly extinct orders of Reptiles, the peculiarities of which
are very extraordinary, and are such as are exhibited by no
living forms.

ORDER V. ICHTHYOPTERYGIA, Owen ( = Ichthyosauria, Hux-
ley).— The gigantic Saurians forming this order were distin-
guished by the following characters : —

The body was fish-like, without any distinct neck, and pro-
bably covered with a smooth or wrinkled skin, no horny or
bony exoskeleton having been ever discovered. The vertebrae
were numerous, deeply biconcave or amphicoelous, and having
the neural arches united to the centra by a distinct suture.
The anterior trunk-ribs possess bifurcate heads. There is no

ICHTHYOPTERYGIA.

369

sacrum, and no sternal ribs or sternum, but clavicles were pre-
sent, as well as an interclavicle (episternum) ; and false ribs
were developed in the walls of the abdomen. The skull had
enormous orbits separated by a septum, and an elongated
snout. The eyeball was protected by a ring of bony plates in
the sclerotic. The teeth were not lodged in distinct sockets,
but in a common alveolar groove. The fore and hind limbs
were converted into swimming-paddles, the ordinary number
of digits (five) remaining recognisable, but the phalanges being
greatly increased in number, and marginal ossicles being added
as well. A vertical caudal fin was in all probability present.

Fig. 319. — Ichthyosaurus communis. Lias.

The order Ichthyopterygia includes only the gigantic and
fish-like Ichthyosauri (fig. 319), all exclusively Mesozoic, and
abounding in the Lias, Oolites, and Chalk, but especially char-

Fig. 320. — Two vertebrae of Eosaiirus Acadiensis (Marsh). Coal-measures of
Nova Scotia. (After Dawson.)

acteristic of the Lias. There is no doubt whatever but that the
Ichthyosauri were essentially marine animals, and they have
been often included with the next order (Sauropterygia) in a
common group, under the name of Enaliosauria or Sea-lizards.

2 A

370 REPTILIA.

In 1 86 1 Professor Marsh discovered in the Coal-measures
of Nova Scotia two large amphicoelous vertebrae, which he
described under the name of Eosaumis Acadiensis. These
vertebras (fig. 320) are of very large size (about two and a half
inches in diameter), and they are deeply excavated at both
ends. They are regarded by Professor Marsh as indicating
the existence in the later Carboniferous period of a gigantic
reptile allied to Ichthyosaurus. By Huxley, however, it is
believed that these remains may truly belong to some large
Labyrinthodont.

In the biconcave vertebrae and probable presence of a ver-
tical tail-fin, the Ichthyosaurus approaches the true Fishes.
There is, however, no doubt as to the fact that the animal
was strictly an air-breather, and its reptilian characters cannot
be questioned, at the same time that the conformation of the
limbs is decidedly Cetacean in many respects. Much has
been gathered from various sources as to the habits of the
Ichthyosaurus, and its history is one of great interest. From
the researches of Buckland, Conybeare, and Owen, the fol-
lowing facts appear to be pretty well established : — That the
Ichthyosauri kept chiefly to open waters may be inferred from
their strong and well-developed swimming-apparatus. That
they occasionally had recourse to the shore, and crawled upon
the beach, may be safely inferred from the presence of a strong
and well-developed bony arch, supporting the fore-limbs, and
closely resembling in structure the scapular arch of the Orni-
thorhynchus or Duck-mole of Australia. That they lived in
stormy seas,, or were in the habit of diving to considerable
depths, is shown by the presence of a ring of bony plates in
the sclerotic, protecting the eye from injury or pressure. That
they possessed extraordinary powers of vision, especially in
the dusk, is certain from the size of the pupil, and from the
enormous width of the orbits. That they were carnivorous
and predatory in the highest degree is shown by the wide
mouth, the long jaws, and the numerous, powerful, and pointed
teeth. This is proved, also, by an examination of their petri-
fied droppings, which are known to geologists as " coprolites,"
and which contain numerous fragments of the scales and bones
of the Ganoid fishes which inhabited the same seas.

ORDER VI. SAUROPTERYGIA, Owen ( = Plesiosauria, Huxley).
— This order of extinct reptiles, of which the well-known Ple-
siosaurus may be taken as the type, is characterised by the
following peculiarities : —

The body, as far as is known, was naked, and not furnished
with any horny or bony exoskeleton. The bodies of the ver-

SAUROPTERYGIA. 37 1

tebrae were either flat or only slightly cupped at each end, and
the neural arches were anchylosed with the centra, and did
not remain distinct during life. The transverse processes of
the vertebrae were long, and the anterior trunk-ribs had simple,
not bifurcate, heads. No sternum or sternal ribs are known
to have existed, but there were false abdominal ribs. The
neck, in most, was greatly elongated, and composed of numer-
ous vertebras. The sacrum was composed of two vertebrae.
The orbits were of large size, and there was a long snout, as
in the Ichthyosauri, but there was no circle of bony plates in
the sclerotic. The limbs agree with those of the Ichthyosauri
in being in the form of swimming-paddles (fig. 321), but differ
in not possessing any supernumerary marginal ossicles. A
pectoral arch, formed of two clavicles and an interclavicle
(episternum), appears to have been sometimes, if not always,
present. The teeth were simple, and were inserted into dis-
tinct sockets, and not lodged in a common groove.

Fig. 321. — Plesiosaurus dolichodeirus. Lias.

The most familiar and typical member of the Sauropterygia
is the Plesiosaurus (fig. 321), a gigantic marine reptile> chiefly
characteristic of the Lias and Oolites. As regards the habits
of the Plesiosaurus, Dr Conybeare arrives at the following con-
clusions : — " That it was aquatic is evident from the form of
its paddles ; that it was marine is almost equally so from the
remains with which it is universally associated ; that it may
have occasionally visited the shore, the resemblance of its ex-
tremities to those of the Turtles may lead us to conjecture ;
its movements, however, must have been very awkward on
land ; and its long neck must have impeded its progress

3/2 REPTILIA.

through the water, presenting a striking contrast to the organi-
sation which so admirably fits the Ichthyosaurus to cut through
the waves." As its respiratory organs were such that it must
of necessity have required to obtain air frequently, we may
conclude " that it swam upon or near the surface, arching
back its long neck like a swan, and occasionally darting it
down at the fish which happened to float within its reach. It
may perhaps have lurked in shoal water along the coast, con-
cealed amongst the sea-weed ; and raising its nostrils to a
level with the surface from a considerable depth, may have
found a secure retreat from the assaults of powerful enemies ;
while the length and flexibility of its neck may have com-
pensated for the want of strength in its jaws, and its incapacity
for swift motion through the water."

The geological range of the Plesiosaurus is from the Lias to
the Chalk inclusive, and specimens have been found indicat-
ing a length of from eighteen to twenty feet.

About twenty species of Plesiosaurus have been described
in all. Of the remaining genera of the Sauropterygia, Notho-
saurus, Simosaurus, Placodus, Pistosaurus, and Conchiosaurus
are Triassic. In Nothosaurus the neck is long, composed of
at least twenty vertebrae. The dorsal vertebrae are biconcave,
and the limbs are converted into swimming-paddles. The
teeth are numerous and conical, and are implanted into dis-
tinct sockets. Several species are known, all Triassic, and
especially characteristic of the Muschelkalk. Simosaurus had
a large head with enormous orbits, and teeth sunk into dis-
tinct sockets. This genus is exclusively confined to the Mus-
chelkalk. In Placodus (fig. 322), the teeth are in distinct

sockets, and resemble those of
many fishes in being round-
ed and obtuse, forming broad
crushing plates adapted for the
comminution of shell-fish. The
upper jaw contains a double
series of these teeth, an outer
or maxillary series, and an in-
ternal or palatal series ; but
the under jaw has only a sin-
gle row of teeth.

Lastly, in Pliosaurus we

Fig. 322. — Under surface of the upper jaw i ,-i •>-,• j ,

\KFiacodusgigas. Muschelkalk. have a huge reptile, allied to

the Plesiosaurus in its fin-like

paddles, but having an enormous head supported upon a short
neck. The teeth are simple and conical, and in large speci-

ANOMODONTIA.

373

mens attain a great size. Pliosaurus is confined to the Middle
and Upper Oolites.

ORDER VII. ANOMODONTIA. — The members of this order
are especially characterised by the structure of the mouth, the
jaws being converted into a kind of beak, which was pro-
bably sheathed in horn, and resembled the jaws of a Turtle.
Sometimes the mouth appears to have been wholly destitute
of teeth, but in other cases there was a single pair of teeth
implanted in the upper jaw, growing from persistent pulps,
and assuming the character of great tusks. The dorsal verte-
brae are biconcave, and the anterior trunk-ribs have bifurcate
heads. The sacrum is large, composed of several vertebrae.
The animal seems to have been organised for terrestrial pro-
gression, the pectoral and pelvic arches being strong, and the
limbs well developed.

By Owen the genera Dicynodon, Oudenodon, and Rhyncho-
saurus are included in this order; but the last of these is
regarded by Huxley as a Lacertilian. In Dicynodon (fig. 323,

Fig. 323. — A, Skull of Dicynodon lacerticeps , showing the maxillary tusk. B, Skull
of Oudenodon Bainii. From the Trias of South Africa, (After Owen.)

A), the anterior portions of the jaws appear to have been al-
together toothless ; and they form a kind of beak, which was
probably sheathed in horn. The lower jaw has no teeth ; but

3/4 REPTILIA.

each superior maxilla carries an enormous tusk-like tooth
growing from a persistent pulp. In Oudenodon, on the other
hand, the mouth is beak-shaped (fig. 323, B), and seems to
have possessed no teeth of any kind. Dicynodon and Oudeno-
don are known only from strata of supposed Triassic age in
India and South Africa. Rhynchosaurus also, if truly refer-
able here, is Triassic, occurring in Europe.

ORDER VIII. PTEROSAURIA. — This order includes a group
of extraordinary flying Reptiles, all belonging to the Mesozoic
epoch, and exhibiting in many respects a very extraordinary
combination of characters. The most familiar members of
the order are the so-called " Pterodactyles," and the following
are the characters of the order : —

No exoskeleton is known to have existed. The dorsal
vertebrae are proccelous, and the anterior trunk-ribs are double-
headed. There is a broad sternum with a median ridge or
keel, and ossified sternal ribs. The jaws are always armed
with teeth, and these were implanted in distinct sockets. In
some forms (Ramphorhynchus) there appear to have been no
teeth in the anterior portion of the jaws, and these parts seem
to have been sheathed in horn, so as to constitute a kind of
beak. A ring of bony plates occurs in the sclerotic coat of
the eye. The pectoral arch consists of a scapula and distinct
coracoid bone, articulating with the sternum as in Birds, but
no clavicles have hitherto been discovered. The fore-limb
(fig. 324) consists of a humerus, ulna and radius, carpus, and
hand of four fingers, of which the inner three are short and
unguiculate, whilst the outermost is clawless and is enormous-
ly elongated. Between this immensely-lengthened finger, the
side of the body, and the comparatively small hind-limb, there
must have been supported an expanded flying-membrane or
" patagium," which the animal must have been able to employ
as a wing, much as the Bats of the present day. Lastly, most
of the bones were " pneumatic " — that is to say, were hollow
and filled with air.

By the presence of teeth in distinct sockets, and, as will be
seen hereafter, especially in the structure of the limbs, the
Pterodactyles differed from all known Birds, and there can
be little question as to their being genuine Reptiles. The only
Reptile, however, now existing, which possesses any power of
sustaining itself in the air, is the little Draco volans, but this
can only take extended leaps from tree to tree, and cannot be
said to have any power of flight properly so called. That
the Pterodactyles, on the other hand, possessed the power of
genuine flight, is shown by the presence of a median keel upon

PTEROSAURIA.

375

the sternum, proving the existence of unusually-developed
pectoral muscles ; by the articulation of the coracoid bones
with the top of the sternum, providing a fixed point or fulcrum
for the action of the pectoral muscles ; and, lastly, by the exist-
ence of air-cavities in the bones, giving the animal the neces-
sary degree of lightness. The apparatus, however, of flight was
not a " wing," as in Birds, but a flying-membrane, very similar
in its mode of action to the patagium of the Mammalian order
of the Bats. The patagium of the Bats, however, differs from
that of the Pterodactyles in being supported by the greatly-
elongated fingers, whereas in the latter it is only the outermost
finger which is thus lengthened out.

Fig. 324. — Pterodactylus crassirostris. From the Lithographic Slates of Solenhofen.

(Upper Oolite).

The difficulty as to the position of the Pterosauria is evaded
by Mr Seeley by placing them in a distinct class, which he
terms Ornithosauria, and which he regards as most nearly
related to, but coequal with, the class Aves.

The Pterosauria are exclusively Mesozoic, being found from
the Lower Lias to the Middle Chalk inclusive, the Lithographic
Slate of Solenhofen (Upper Oolite) being particularly rich in
their remains. Most of them appear to have attained no very
great size, but the remains of a species from the Cretaceous
Rocks have been considered to indicate an animal with more
than twenty feet expanse of wing, counting from tip to tip.

In the genus Pterodactylus proper, the jaws are provided

376 REPTILIA.

with teeth to their extremities, all the teeth being long and
slender.

In Dimorphodon, the anterior teeth are large and pointed,
the posterior teeth small and lancet-shaped.

In Ramphorhynchus, the anterior portion of both jaws is
edentulous, and may have formed a horny beak, but teeth are
present in the hinder portion of the jaws.

ORDER IX. DEINOSAURIA. — The last order of the Reptiles
is that of the Deinosauria, comprising a group of very remark-
able extinct forms, which are in some respects intermediate in
their characters between the Cursorial birds and the typical
Reptiles ; whilst they have been supposed to have affinities
to the Pachydermatous Mammals. Most of the Dtinosauria
were of gigantic size, and the order is denned by the following
characters : —

The skin was sometimes naked, sometimes furnished with a
well-developed exoskeleton, consisting of bony shields, much
resembling those of the Crocodiles. A few of the anterior ver-
tebrae were opisthocoelous, the remainder having flat or slightly
biconcave bodies. The anterior trunk-ribs were double-headed.
The teeth were confined to the jaws and implanted in distinct
sockets. There were always two pairs of limbs, and these
were strong, furnished with claws, and adapted for terrestrial
progression. In some cases the fore-limbs were very small in
proportion to the size of the hind-limbs. No clavicles have
been discovered.

The teeth are sometimes implanted in distinct sockets, and
they are never anchylosed with the jaws. The ischium and
pubes are much elongated ; the inner wall of the acetabulum
is formed by membrane ; the tibia has its proximal end pro-
longed anteriorly into a strong crest ; and the astragalus is
bird-like (Huxley).

The most remarkable points in the organisation of the
Deinosauria are connected with the structure of the pelvis and
hind-limb, the characters of which, as pointed out by Huxley,
approximate to those of the same parts in the Birds, and
especially in the Struthious Birds. This approximation is
especially seen in the prolongation of the ilium in front of the
acetabulum (fig. 325), the elongation and slenderness of form
of the ischium, and the slenderness of the pubes. The astra-
galus is like that of a bird, and in some cases appears to have
become anchylosed with the distal end of the tibia. The
metatarsal bones, however, remain distinct, and are not an-
chylosed with any of the tarsal bones to form a " tarso-meta-
tarsus."

DEINOSAURIA.

377

The Deinosauria are exclusively Mesozoic, ranging from the
Triassic to the Cretaceous formation, but abounding especially
in the Oolitic and the
earlier portion of the Cre-
taceous period. By Pro-
fessor Huxley the " The-
codont" Reptiles are re-
garded as belonging here,
as has been already re-
marked. The same high
authority has also pro-
posed the establishment
of a new order termed
Ornithoscelida to include
the ordinary Deinosaurian
Reptiles along with the
singular Compsognathus.

A large number of gen-
eric types are included in
the Deinosauria, of which
Iguanodon, Megalosaurus,
Cetiosaurus, and Compsog-
nathus may be especially
mentioned. Other less
important forms are Poi-
kilopleuron, Lcelaps, Euske-
lesaurus, Hylceosaurus, Hy-»
psilophodon, and Hadro-

SaUrUS. Fig 32S._/^ Oj Deinosaur. il Ilium ; is

The Iguanodon is main- Ischium ;/ Femur ; / Tibia ; 5 Fibula ; as Astra-

i -r i • i /". galus ; ca Calcaneum ; m Metatarsus. (After

ly, if not exclusively, Cre- Huxley.)
taceous, being especially

characteristic of the great delta-deposit of the Wealden. The
length of the Iguanodon has been estimated as being probably
from fifty to sixty feet, and from the close resemblance of its
teeth to those of the living Iguanas, there is little doubt that
it was herbivorous and not carnivorous. The femur of a large
Iguanodon measures from four to five feet in length, with a cir-
cumference of twenty-two inches in its smallest part. From
the disproportionately small size of the fore-limbs, and from the
occurence of pairs of gigantic three-toed footsteps in the same
beds, it has been concluded, with much probability, that Igu-
anodon, in spite of its enormous bulk, must have walked tem-
porarily or permanently upon its hind-legs, thus coming to pre-
sent a most marked and striking affinity to the Birds.

378

REPTILIA.

The teeth of Iguanodon (fig. 326) present a singularly close
resemblance in shape to those of the comparatively pigmy
Iguanas of the present day. Their crown is obtusely sub-tri-
angular, with longitudinal ridges, and having the surface of the

Fig. 326. — Teeth of Iguanodon Mantellii. Wealden.

enamel crenated on one or both sides. They present the ex-
traordinary feature that the crown became worn down flat by
mastication, showing that Iguanodon employed the teeth in the
actual trituration of the vegetable matter on which it fed.

The gigantic Cetiosaurus of the Oolitic and Cretaceous
Rocks was originally placed amongst the Crocodilia; but the
researches of Professor Phillips have shown that it belongs
really to the Deinosauria. Having obtained a magnificent
series of remains of this reptile, Professor Phillips has been
able to determine many very interesting points as to the
anatomy and habits of this colossal animal, the total length
of which he estimates as being probably not less than sixty
or seventy feet. As to its mode of life, this accomplished
writer remarks : —

" Probably when ' standing at ease ' not less than ten feet in
height, and of a bulk in proportion, this creature was un-
matched in magnitude and physical strength by any of the
largest inhabitants of the Mesozoic land or sea. Did it live in
the sea, in fresh waters, or on the land ? This question can-
not be answered, as in the case of Ichthyosaurus, by appeal to
the accompanying organic remains ; for some of the bones lie

DEINOSAURIA. 379

in marine deposits, others in situations marked by estuarine
conditions, and, out of the Oxfordshire district, in Sussex, in
fluviatile accumulations. Was it fitted to live exclusively in
water ? Such an idea was at one time entertained, in conse-
quence of the biconcave character of the caudal vertebrae, and
it is often suggested by the mere magnitude of the creature,
which would seem to have an easier life while floating in water,
than when painfully lifting its huge bulk, and moving with slow
steps along the ground. But neither of these arguments is
valid. The ancient earth was trodden by larger quadrupeds
than our elephant ; and the biconcave character of vertebrae,
which is not uniform along the column in Cetiosaurus, is perhaps
as much a character of a geological period as of a mechanical
function of life. Good evidence of continual life in water is
yielded in the case of Ichthyosaurus, and other Enaliosaurs,
by the articulating surfaces of their limb-bones, for these, all of
them, to the last phalanx, have that slight and indefinite adjust-
ment of 'the bones, with much intervening cartilage, which fits
the leg to be both a flexible and forcible instrument of nata-
tion, much superior to the ordinary oar-blade of the boatman.
On the contrary, in Cetiosaur, as well as in Megalosaur and
Iguanodon, all the articulations are definite, and made so as
to correspond to determinate movements in particular direc-
tions, and these are such as to be suited for walking. In par-
ticular, the femur, by its head projecting freely from the ace-
tabulum, seems to claim a movement of free stepping more
parallel to the line of the body, and more approaching to the
vertical than the sprawling gait of the crocodile. The large
claws concur in this indication of terrestrial habits. But, on
the other hand, these characters are not contrary to the belief
that the animal may have been amphibious ; and the great
vertical height of the anterior part of the tail seems to support
this explanation, but it does not go further. For the later
caudal vertebrae, instead of being much compressed, as in
Teleosaurus, are nearly circular in the cross section, and are
interlocked by posterior zygapophyses, extended over half or
the whole length of a vertebrae. We have therefore a marsh-
loving or river-side animal, dwelling amidst filicine, cycadace-
ous, and coniferous shrubs and trees full of insects and small
mammalia. What was its usual diet? If ex ungue leonem,
surely ex dentedbum. We have indeed but one tooth, and that
small and incomplete. It resembles more the tooth of Iguan-
odon than that of any other reptile ; for this reason it seems
probable that the animal was nourished by similar vegetable
food which abounded in the vicinity, and was not obliged to

380

REPTILIA.

contend with Megalosaurus for a scanty supply of more stimu-
lating diet."

Megalosaurus is a gigantic Oolitic Reptile, which occurs also
in the Cretaceous series (Weald Clay). Its length has been
estimated at between forty and fifty feet, the femur and tibia
each measuring about three feet in length. As the head of
the femur is set on nearly at right angles with the shaft, whilst
all the long bones contain large medullary cavities, there can
be no doubt but that Megalosaurus was terrestrial in its
habits. That it was carnivorous and destructive in the highest
degree is shown by the powerful, pointed, and trenchant teeth.

The teeth in Megalosaurus are conical, compressed, with
finely -serrated edges. The fore -limbs are extraordinarily

Fig. 327. — Cranium of Megalosaurus, restored. (After Professor Phillips.)

smaller than the hind-limbs. The teeth do not become worn
by mastication ; and there appears to have been no exoskeleton.
One of the most remarkable of the Deinosauria is the little
Compsognathus longipes of the Lithographic Slate of Solenhofen,
regarded by Professor Huxley as the type of a special group
(Compsognatha) of his order Ornithoscelida. The special
characters distinguishing this group are, that the cervical region
of the spine is long, and the femur is shorter than the tibia ;
whereas in the typical Deinosauria the neck is relatively short,
and the femur is as long as, or longer than, the tibia. Comp-
sognathus is not remarkable for its size, which does not seem
to have been much more than two feet, but for the striking
affinities which it exhibits to the true Birds. The head of
Compsognathus was furnished with toothed jaws, and supported

BIRDS. 381

upon a long and slender neck. The fore-limbs were very short,
but the hind-limbs were long and like those of Birds. The
proximal portion of the tarsus resembled that of Birds in being
anchylosed to the lower end of the tibia ; but the distal portion
of the tarsus — unlike that of Birds — was free, and was not an-
chylosed with the metatarsus. Huxley concludes that " it is
impossible to look at the conformation of this strange Reptile,
and to doubt that it hopped or walked in an erect or semi-
erect position, after the manner of a bird, to which its long
neck, slight head, and small anterior limbs must have given it
an extraordinary resemblance."

CHAPTER XXXIV.
BIRDS.

THE fourth class of the Vertebrata is that of Aves, or Birds.
The Birds may be shortly denned as being " oviparous
Vertebrates with warm blood, a double circulation, and a
covering of feathers " (Owen). More minutely, however, the
Birds are denned by the possession of the following char-
acters : —

The skull articulates with the vertebral column by a single oc-
cipital candy le. Each half or ramus of the lower jaw consists of
a number of pieces, which are separate from one another in the
embryo ; and the jaw is united with the skull, not directly, but by
the intervention of a quadrate bone (as in the Reptiles]. The fore-
limb in no existing birds possesses more than three fingers or
digits, and the metacarpal bones are anchylosed together. In all
living Birds the fore-limbs are useless as regards prehension, and
in most they are organs of flight. The hind-limbs in all Birds
have the ankle-joint placed in the middle of the tarsus, the proxi-
mal portion of the tarsus coalescing with the tibia, and the distal
portion of the tarsus being anchylosed with the metatarsus to con-
stitute a single bone known as the " tarso-metatarsus."

The heart consists of four chambers, two auricles and two ven-
tricles; and not only are the right and left sides of the heart com-
pletely separated from one another, but there is no communication
between the pulmonary and systemic circulations, as there is in
Reptiles.

The respiratory organs are in the form of spongy cellular lungs,
which are not freely suspended in pleural sacs ; and the bronchi

382 BIRDS.

open on their surface into a number of air-sacs, placed in different
parts of the body.

All birds are oviparous, none bringing forth their young alive,
or being even ovo-viviparous. All birds are, lastly, provided
with an epidermic covering, so modified as to constitute what are
known as feathers.

The entire skeleton of the Birds is singularly compact,rand at
the same time singularly light. The compactness is due to the
presence of an unusual amount of phosphate of lime ; and the
lightness, to the absence in many of the bones of the ordinary
marrow, and its replacement by air.

As regards the vertebral column, Birds exhibit some very in-
teresting peculiarities. The cervical region of the spine is
unusually long and flexible, since the fore-limbs are useless as
organs of prehension — and all acts of grasping must be exer-
cised either by the beak or by the hind-feet, or by both acting in
conjunction. The number of vertebrae in the neck varies from
nine to twenty-four, and their structure is always such as to
allow of considerable freedom of motion one upon the other.
The dorsal vertebrae vary from six to ten in number, and of
these the anterior four or five are generally anchylosed with
one another, so as to give a base of resistance to the wings.
In the Cursorial Birds, however (such as the Ostrich and
Emeu), and in some others (such as the Penguin), in which
the power of flight is wanting, the dorsal vertebras are all more
or less freely movable one upon another. There are no lumbar
vertebrae, but all the vertebrae between the last dorsal and
the first caudal (varying from nine to twenty) are anchylosed
together to form a bone which is ordinarily known as the
" sacrum." To this, in turn, the iliac bones are anchylosed
along its whole length, giving perfect immobility to this region
of the spine and to the pelvis.

The coccygeal or caudal vertebrae vary in number from
eight to ten, and are movable upon one another. The most
noticeable feature about this part of the spinal column is what
is known as the " ploughshare-bone." This is the last joint of
the tail, and is a long, slender, ploughshare-shaped bone, de-
stitute of lateral processes, and without any medullary canal
(fig. 330, B). In reality it consists of two or more of the
caudal vertebrae, completely anchylosed, and fused into a
single mass. It is usually set on to the extremity of the spine
at an angle more or less nearly perpendicular to the axis of the
body; and it affords a firm basis for the support of the great
quill-feathers of the tail (" rectrices "). In the Cursorial Birds,
which do not fly, the terminal joint of the tail is not plough-

CHARACTERS OF BIRDS. 383

share-shaped. In the extraordinary Mesozoic bird, the Archce-
opteryx macrura, there is no ploughshare-bone, and the tail
consists of twenty separate vertebrae, all distinct from one
another, and each carrying a pair of quill -feathers, one on
each side. As the vertebras of the ploughshare-bone are
distinct from one another in the embryos of existing birds, the
tail of the Arch&opteryx is to be regarded as a case of the per-
manent retention in the adult of an embryonic character. In
the increased number of caudal vertebras, however, and in some
other characters, the tail of the Archtzopteryx makes a decided
approach to the true Reptiles.

The various bones which compose the skull of Birds are
amalgamated in the adult so as to form a single piece, and the
sutures even are obliterated, the lower jaw alone remaining
movable. The occipital bone carries a single occipital condyle
only, and this is hemispherical or nearly globular in shape. The
"beak" (fig. 328), which forms such a conspicuous feature in all

Fig. 328. — Skull of Spur-winged Goose (Plectroptems Gambensis).

birds, consists of an upper and lower half, or a "superior" and
" inferior mandible." The upper mandible is composed almost
entirely of the greatly-elongated intermaxillary bones, flanked
by the comparatively small superior maxillae. The inferior
mandible is primitively composed of twelve pieces, six on each
side ; but in the adult these are all indistinguishably amal-
gamated with one another, and the lower jaw forms a single
piece. As in the Reptiles, the lower jaw articulates with the
skull, not directly, but through the intervention of a distinct
bone — the quadrate bone or tympanic bone — which always re-
mains permanently movable, and is never anchylosed with the
skull. In no bird are teeth ever developed in either jaw, but
both mandibles are encased in horn, forming the beak, and
the margins of the bill are sometimes serrated.

The thoracic cavity is bounded by the dorsal vertebrae, which

BIRDS.

are usually, as before said, anchylosed with one another to a
greater or less extent. Laterally, the thorax is bounded by
the ribs, which vary in number from six to ten pairs. In most
birds each rib carries a peculiar process — the "uncinate pro-
cess " — which arises from its posterior margin, is directed up-
wards and backwards, and passes over the rib next in succes-
sion behind, where it is bound down by ligament. The first
and last dorsal ribs carry no uncinate processes, and in some
cases the processes continue throughout life as separate pieces
(fig. 329, B). Anteriorly, the ribs articulate with a series of

B

Fig. 329. — A, Breast-bone, shoulder-girdle, and fore-limb of Penguin (after Owen):
b Sternum, with the sternal keel ; j J Scapulae; k k Coracoid bones; c Furculum or
merry-thought, composed of the united clavicles ; h Humerus ; » Ulna ; r Radius ; t
Thumb ; ?« Metacarpus ; / Phalanges of the fingers. B, Ribs of the Golden Eagle : a a
Ribs giving off(£ b) uncinate processes ; c c Sternal ribs.

straight bones, which are called the " sternal ribs," but which
in reality are to be looked upon as the ossified " costal carti-
lages." These sternal ribs (fig. 329, B) are in turn movably
articulated to the sternum in front, and " they are the centres
upon which the respiratory movements hinge " (Owen). In
front the thoracic cavity is completed by an enormously-ex-
panded sternum or breast-bone, which in some birds of great
powers of flight extends over the abdominal cavity as well, in
some cases even reaching the pelvis. The sternum of all
birds which fly, is characterised by the presence of a greatly-
developed median ridge or keel (fig. 329, A), to which are

CHARACTERS OF BIRDS. 385

attached the great pectoral muscles, which move the wings.
As a general rule, the size of this sternal crest allows a very
tolerable estimate to be formed of the flying powers of the
bird to which it may have belonged ; and in the Ostriches and
other birds which do not fly, there is no sternal keel. At its
anterior angles the sternum exhibits two pits for the attach-
ment of the coracoid bones.

The scapular or pectoral arch consists of the shoulder-blade
or scapula, the collar-bone or clavicle, and the coracoid bone,
on each side. The scapula, as a rule (fig. 329, A, s s) is a
simple elongated bone, not flattened out into a broad plate,
and carrying no transverse ridge, or spinous process. Only a
portion of the glenoid cavity for the articulation with the head
of the humerus is formed by the scapula, the remainder being
formed by the coracoid. The coracoid bones (fig. 329, A, k k)
correspond with the coracoid processes of man, but in birds
they are distinct bones, and are not anchylosed with the scap-
ula. The coracoid bone on each side is always the strongest
of the bones forming the scapular arch. Superiorly it articu-
lates with the clavicle and scapula, and forms part of the gle-
noid cavity for the humerus. Inferiorly each coracoid bone
articulates with the upper angle of the sternum. The position
of the coracoids is more or less nearly vertical, so that they
form fixed points for the action of the wings in their down-
ward stroke. The clavicles (fig. 329, A, c) are rarely rudimen-
tary or absent, and are in some few cases separate bones. In
the great majority, however, of birds, the clavicles are anchy-
losed together at their anterior extremities, so as to form a
single bone, somewhat V-shaped, popularly known as the
" merry-thought," and technically called the " furculum." The
outer extremities of the furculum articulate with the scapula
and coracoid ; and the anchylosed angle is commonly united
by ligament to the top of the sternum. The function of the
clavicular or furcular arch is "to oppose the forces which tend
to press the humeri inwards towards the mesial plane, during
the downward stroke of the wing " (Owen). Consequently the
clavicles are stronger, and their angle of union is more open,
in proportion to the powers of flight possessed by each bird.

As regards the structure of the wing proper, the humerus is
short and strong, and articulates superiorly with an articular
cavity formed partly by the coracoid and partly by the scapula.
The fore-arm is composed of a radius and ulna, of which the
former is the smallest and most slender. The carpus is reduced
to two small bones wedged in between the distal end of the
fore-arm and the metacarpus. The metacarpus consists of

2 B

386 BIRDS.

two bones which in all existing birds are anchylosed at both
ends, but which are free in the remarkable extinct Archaop-
teryx. The metacarpal, which corresponds to the radius, is the
larger of the two, and it carries the digit which has the greatest
number of phalanges. At the proximal end of the radial
metacarpal is generally attached a single phalanx, constituting
the so-called " thumb." The digit which is attached to the
ulnar metacarpal never consists of more than a single phalanx.

As regards the structure of the posterior extremity or hind-
limb, the pieces which compose the innominate bones (namely,
the ilium, ischium, and pubes) are always anchylosed with one
another ; and the two innominate bones are also always an-
chylosed, by the medium of the greatly-elongated ilia, with the
sacral region of the spine. In no living bird, however, with
the single exception of the Ostrich, are the innominate bones
united in the middle line in front by a symphysis pubis. The
stability of the pelvic arch, necessary in animals which sup-
port the weight of the body on the hind-limbs alone, is amply
secured in all ordinary cases by the anchylosis of the ilia with
the sacrum.

As in the higher Vertebrates, the lower limb (fig. 330, A)
consists of a femur, a tibia and fibula, a tarsus, metatarsus,
and phalanges ; but some of these parts are considerably ob-
scured by anchylosis. The femur or thigh-bone (fig. 330, A,/)
is generally very short, comparatively speaking. The chief
"bone of the leg is the tibia (t\ to which a thin and tapering
fibula (r) is anchylosed. The upper end of the fibula, how-
ever, articulates with the external condyle of the femur. The
ankle-joint is placed, as in Reptiles, between the proximal and
distal portions of the tarsus. The proximal portion of the
tarsus is undistinguishably amalgamated with the lower end of
the tibia. The distal portion of the tarsus is anchylosed with
the whole of the metatarsus to constitute the most character-
istic bone in the leg of the Bird — the " tarso-metatarsus " (m).
In most of the long-legged birds, such as the Waders, the dis-
proportionate length of the leg is given by an extraordinary
elongation of the tarso-metatarsus.

The tarso-metatarsus is followed inferiorly by the digits of
the foot. In most birds the foot consists of three toes directed
forwards and one backwards — four toes in all. In no wild
bird are there more than four toes, but often there are only
three, and in the Ostrich the number is reduced to two. In
all birds which have three anterior and one posterior toe, it is
the posterior thumb or hallux (that is to say, the innermost
digit of the hind-limb) which is directed backwards ; and it

CHARACTERS OF BIRDS.

387

invariably consists of two phalanges only. The most internal
of the three toes which are directed forwards, consists of three
phalanges ; the next has four phalanges ; and the outermost
toe is made up of five phalanges (fig. 330, A). This in-
crease in an arithmetical ratio of the phalanges of the toes,
in proceeding from the inner to the outer side of the foot,
obtains in almost all birds, and enables us readily to detect
which digit is suppressed, when the normal four are not all

Fig. 330. — A, Hind-limb of the Loon (Colyntbus glacialis) — after Owen: i Innominate
bone ; j Thigh-bone or femur ; / Tibia, with the proximal portion of the tarsus anchy-
losed with its lower end ; r Fibula ; m Tarso-metatarsus, consisting of the distal portion
of the tarsus anchylosed with the metatarsus ; p p Phalanges of the toes. B, Tail of the
Golden Eagle : j Ploughshare-bone, carrying the great tail-feathers.

present. Variations of different kinds exist, however, in the
number and disposition of the toes. In many birds — such as
the Parrots — the outermost toe is turned backwards, so that
there are two toes in front and two behind. In others, again,
the outer toe is normally directed forwards, but can be turned
backwards at the will of the animal. In the Swifts, on the
other hand, all four toes are present, but they are all turned
forwards. In many cases — especially amongst the Natatorial

388 BIRDS.

birds — the hallux is wholly wanting, or is rudimentary. In the
Emeu, Cassowary, Bustards, and other genera, the hallux is
invariably absent, and the foot is three-toed. In the Ostrich
both the hallux and the next toe (" index ") are wanting, and
the foot consists simply of two toes, these being the outer toe
and the one next to it.

As regards the geological distribution of Birds, there are
many reasons why we should be cautious in reasoning upon
merely negative evidence, and more than ordinarily careful not
to infer the non-existence of birds during any particular geolo-
gical epoch, simply because we can find no positive evidence
for their presence. As Sir Charles Lyell has well remarked,
" the powers of flight possessed by most birds would insure
them against perishing by numerous casualties to which quad-
rupeds are exposed during floods ; " and, " if they chance to
be drowned, or to die when swimming on water, it will scarcely
ever happen that they will be submerged so as to become pre-
served in sedimentary deposits," since, from the lightness of the
bones, the carcase would remain long afloat, and would be
liable to be devoured by predaceous animals. As, with a few
utterly trivial exceptions, all the deposits in which fossils are
found have been laid down in water, and more especially as
they are for the most part marine, these considerations put for-
ward by Sir Charles Lyell afford obvious ground against the
anticipation that the remains of birds should be either of fre-
quent occurrence or of a perfect character in any of the fossil-
iferous rocks. In accordance with these considerations, as a
matter of fact, most of the known remains of birds are either
fragmentary, or belong to forms which were organised to live a
terrestrial life, and were not adapted for flight.

The earliest remains which have been generally referred to
birds are in the form of footprints (fig. 331) impressed upon
certain sandstones in the valley of the Connecticut River in
the United States. These sandstones are almost certainly
Triassic, and if the ornithic character of these footprints be
admitted, then Birds date their existence from the commence-
ment of the Mesozoic period, and, for anything we know to
the contrary, may have existed during the Palaeozoic epoch.

The evidence as to the ornithic character of the footprints
in the American Trias is as follows : —

Firstly, The tracks are, beyond all question, those of a biped
— that is to say, of an animal which walked upon two legs.
No living animals walk habitually upon two legs except Man
and Birds, and therefore there is a prima facie presumption
that the authors of these prints were birds.

DISTRIBUTION OF BIRDS.

389

Secondly, The impressions are mostly tridactylous — that is to
say, formed by an animal with three toes on each foot, as is
the case in many Waders and most Cursorial Birds.

Fig- 33I--

-Footprint supposed to belong to a Bird,
of Connecticut.

Triassic Sandstones

Thirdly, The impressions of the toes show the same numeri-
cal progression in the number of phalanges as exists in living
birds — that is to say, the innermost of the anterior toes has
three phalanges, the middle one has four, and the outermost
toe has five phalanges.

Taking this evidence collectively, it would have seemed, till
lately, tolerably certain that these impressions were formed by
Birds. We must not, however, lose sight of the possibility
that these impressions may have been formed by Reptiles
more bird-like in their characters than any of the living forms
with which we are acquainted. The recent researches of
Huxley, Cope, and others, go to show that the Deinosaurian
Reptiles possessed the power of walking, temporarily or per-
manently, on the hind-legs, and many curious affinities to the
true Birds have been pointed out. It is therefore by no means
impossible that these footprints of the Connecticut valley are
truly Reptilian.*

The size and other characters of the above-mentioned im-
pressions vary much, and they have certainly been produced

* The occurrence of many four-toed impressions in these same Sandstones,
and the further discovery of the bones of Deinosaurian Reptiles in the same
beds, have rendered the Reptilian nature of many of these footprints almost
certain ; but some may possibly have been formed by Birds.

390 BIRDS.

by several different animals. In the largest hitherto discov-
ered, each footprint is twenty-two inches long, and twelve
inches wide, showing that the feet were four times as large as
those of the African Ostrich. The animal, therefore, which
produced these impressions — whether Avian or Reptilian —
must have been of gigantic size.

The first unmistakable remains of a bird have been found
in the Solenhofen Slates of Bavaria, of the age of the Upper
Oolites. A single unique specimen, consisting of bones and
feathers, but unfortunately without the skull, is all that has
hitherto been discovered ; and it has been named the Archce-
opteryx macrura. The characters of this singular and aberrant
bird, which alone constitutes the order Saururce, will be shortly
given, and need not be repeated here.

Other doubtful remains of birds have been alleged to occur
in the Mesozoic series, but many of these certainly belong in
reality to Pterodactyles. In the Cretaceous Rocks, however,
of the United States, occur the bones of several Wading Birds
(Laornis, Telmatornis, and Palczotringd). Recently, Professor
Marsh has described some additional remains of Birds from
the Cretaceous Rocks. Some of these belong to a new genus,
Graculavus, allied to the existing Cormorants. Others belong
to a gigantic swimming bird of remarkable affinities, but hav-
ing its nearest allies in the living Colymbidce. The genus
Hesperornis and family Hesperornida are proposed for its re-
ception.

In the Tertiary Rocks there are, comparatively speaking,
many remains of birds. In the Eocene Rocks of France has
been found a large bird, as big as an Ostrich, the so-called
Gastornis Parisiensis ; and in England, in the same formation,
we have a small Vulture (Lithornis vulturinus), and a King-
fisher (Halcyornis toliapicus). In the Eocene of Glaris, in Swit-
zerland, occurs also the oldest known Insessorial or Passerine
bird, the Protornis Glarisiensis, which was about as big as a lark.

Numerous remains of birds have likewise been found in the
Miocene and Pliocene deposits. Amongst these we have Par-
rots, Trogons, Secretary Birds, Petrels, Cranes, Guillemots,
&c. With the exception, however, of the Mesozoic Archceop-
teryx, by far the most remarkable remains of birds have been
found in the Post-tertiary or Pleistocene deposits. All the
remains now alluded to are those of gigantic wingless birds ;
and it is .worthy of notice that they are almost exclusively
found in regions now tenanted by smaller wingless birds,
whilst there is reason to believe that some of them have been
in existence during the human period. Most of the remains

NATATORES. 39 1

in question have been found in New Zealand, where there
have been obtained the bones of several species of large wing-
less birds, referred by Owen to the genera Dinornis, Palap-
teryx, and Aptornis. The Dinornis gigantens must have been
one of the most gigantic of the whole class of birds, the tibia
measuring upwards of a yard in length, and the skeleton indi-
cating a bird which stood at least ten feet in height. In an-
other species, the Dinornis elephantopus, the " framework of
the skeleton is the most massive of any in the whole class of
birds/' and " the toe-bones almost rival those of the Elephant "
(Owen). The feet were furnished with three anterior toes,
and are of interest as presenting us with an undoubted bird
big enough to produce the largest of the footprints of the
Triassic Sandstones of Connecticut. There is reason to be-
lieve, from the traditions of the Maories, that the Dinornis was
living at no very remote period, and that it has been exter-
minated by man.

In Madagascar, bones have been discovered of a bird as
large as, or larger than, the Dinornis giganteus, which has been
described under the name of the dEpiornis maximus. With
the bones have been found eggs measuring from thirteen to
fourteen inches in diameter, and computed to be as big as
three ostrich-eggs, or one hundred and forty-eight hens' eggs.
Unlike New Zealand, where there is the Apteryx, Madagascar
itself has no living wingless birds ; but in the neighbouring
island of Mauritius the Dodo has been exterminated less than
three hundred years ago ; and the little island of Rodriguez, in
the same geographical province, has in a similar period lost
the wingless Solitaire (Pezophaps).

In the following are given the characters of the orders of the
Birds, with the range of each in time, so far as known : —

ORDER I. NATATORES. — The order of the Natatores, or
Swimmers, comprises a number of birds which are as much or
even more at home in the water than upon the land. In
accordance with their aquatic habit of life, the Natatores have
a boat-shaped body, usually with a long neck. The legs are
short, and placed behind the centre of gravity of the body,
this position enabling them to act admirably as paddles, at the
same time that it renders the gait upon dry land more or less
awkward and shuffling. In all cases the toes are " webbed,"
or united by membrane to a greater or less extent. In many
instances the membrane or web is stretched completely from
toe to toe ; but in others the web is divided or split up between
the toes, so that the toes are fringed with membranous borders,
and the feet are only imperfectly webbed.

392 BIRDS.

Amongst the more important families of the Natatores may
be enumerated the Penguins (Spheniscidce), the Auks (Alcida),
the Gulls and Terns (Larida], the Petrels (Procellarida\ the
Pelicans (Pelicanus], the Cormorants (Phalacrocorax), the Gan-
nets (Su/a), the Ducks (Anatida\ the Geese (AnseriruK\ and
the Swans (Cygnida).

As might have been expected, the remains of Natatorial
Birds are, speaking comparatively, not uncommon as fossils.
The earliest traces of this order in past time appear in the
Cretaceous series, which has yielded in Europe the Cimolornis
(supposed to be allied to the Albatross), and in North America
the genera Graculavus, Hesperornis, Laornis, Telmatornis, and
Palczotringa. The Eocene Tertiary has a form believed to be
nearly allied to the living Pelicans, and another supposed to be
related to the Mergansers. The Ducks and Flamingos appear
for the first time in the Miocene, and the Post-tertiary deposits
have yielded remains of Geese, Gulls, Terns, Divers, and Guil-
lemots, or of birds allied to these.

ORDER II. GRALLATORES. — The birds comprising the order
of the Gr dilator es, or Waders, for the most part frequent the
banks of rivers and lakes, the shores of estuaries, marshes,
lagoons, and shallow pools, though some of them keep almost
exclusively to dry land, preferring, however, moist and damp
situations. In accordance with their semi-aquatic, amphibious
habits, the Waders are distinguished by the great length of
their legs ; the increase in length being mainly due to the
great elongation of the tarso-metatarsus. The legs are also
unfeathered from the lower end of the tibia downwards. The
toes are elongated and straight, and are never completely
palmate, though sometimes semi-palmate. There are three
anterior toes, and usually a short hallux, but the latter may be
wanting. The wings are long, and the power of flight usually
considerable ; but the tail is short, and the long legs are
stretched out behind in flight to compensate for the brevity
of the tail. The body is generally slender, and the neck and
beak usually of considerable length.

Amongst the more important Grallatorial Birds are the Rails
(Rallidce), Water-hens (Gallinufa), Cranes (Gruidce), Herons
(Ardeida!\ Storks (Ciconince), Snipes (Scolopaadcz), Sandpipers
(Tringidce), Curlews (Numenius), Plovers (Charadriid<z\ and
Bustards (Otidce).

As in the case of the Natatores, the earliest traces of the
Waders appear to belong to the Cretaceous period. These
consist of bones which have been referred to a Snipe-like bird
(Scolopax), and which have been obtained from the Greensand

CURSORES.

393

of New Jersey. In the Eocene Rocks, the most important form
is the Numenius gypsorum, which has been discovered in the
Gypseous series of Montmartre, and which is supposed to have
been allied to the Ibis. In the later Tertiary deposits occur
the remains of birds allied to, if not identical with, the living
Cranes ( Grus\ Bustards ( Otis), Rails (Rallus), and Coots (Fulica).
ORDER III. CURSORES. — The third order of Birds is that of
the Cursores, or Runners, comprising the Ostriches, Rheas,
Cassowaries, Emeus, and the singular Apteryx of New Zealand.
In many respects the Cursores are to be looked upon as an
artificial assemblage; but in the meanwhile it will be most
convenient to consider them as forming a distinct division.
The Cursores are characterised by the rudimentary condition
of the wings, which are so short as to be useless for flight, and
by the compensating length and strength of the legs. In ac-
cordance with this condition of the limbs, many of the bones
retain their marrow, and the sternum is destitute of the pro-
minent ridge or keel, to which the great pectoral muscles are
attached (hence the name of Ratita, applied by Huxley to the

Fig. 332. — Apteryx A ustralis. (Gould.)

order). In the Ostrich, the pubic bones of the pelvis unite to
form a symphysis pubis as they do in no other bird, and in all
the pelvic arch possesses unusual strength and stability. The

394 BIRDS.

legs are extremely robust and powerful, and the hind-toe is
entirely wanting, except in the Apteryx, in which it is rudimen-
tary. The anterior toes are two or three in number, and are
provided with strong blunt claws or nails. The plumage pre-
sents the remarkable peculiarity that the barbs of the feathers,
instead of being connected to one another by hooked barbules,
as is usually the case, are remote and disconnected from one
another, presenting some resemblance to hairs.

The living Cursorial Birds are the Ostrich (Struthio camelus),
the American Ostriches (Rhea), the Emeu (Dromaius), the
various species of Cassowary (Casuarius), and the Apteryx
(fig. 332). Of the extinct forms of the Cursores,\&z most ancient
appears to be the Gastornis Parisiensis of the Eocene Tertiary.
This bird seems to have attained the size of an Ostrich, and it
appears to have points of affinity with the Natatorial and Gral-
latorial Birds. In the superficial deposits of New Zealand have
been found, as already mentioned, the remains of several species
of Dinornis and Palapteryx, along with bones of the now ex-
isting Apteryx. In similar deposits in Madagascar occur the
bones of the gigantic s£piornis ; and in the bone-caves of
Brazil have been found remains of the American Ostriches
or Rheas.

ORDER IV. RASORES. — The fourth order of Birds is that of
the Rasores, or Scratchers, often spoken of collectively as the
" Gallinaceous" Birds, from the old name of "Gallinae," given
to the order by Linnaeus. The Rasores are characterised by
the convex, vaulted upper mandible, having the nostrils pierced
in a membranous space at its base. The nostrils are covered
by a cartilaginous scale. The legs are strong and robust,
mostly covered with feathers as far as the joint between the
tibia and tarso-metatarsus. There are four toes, three in front
and one behind, the latter being short, and placed generally at
a higher level than the other toes. All the toes terminate in
strong blunt claws suitable for scratching (Gallinacet), or in
more slender claws adapted for perching (Columbacei). The
order Rasores comprises the various species of Grouse (Tetra-
onidce), the Partridges, Francolins, and Quails (Pcrdidda>\ the
Turkeys, Fowls, Pheasants, and Pea-fowl (Phasianidcz), the
Pigeons and Doves {Columbida\ and the recently extinct Dodo
(Didus ineptus).

The earliest remains of the Rasorial Birds appear in the
Eocene Tertiary, where traces of a Partridge have been found.
In Post-Tertiary deposits occur the remains of birds more or
less closely allied to the existing Pigeons, Grouse, Quail,
Pheasant, Fowl, and Tinamou.

SCANSORES— INSESSORES — RAPTORES. 395

ORDER V. SCANSORES. — The order of the Scansorial or
Climbing Birds is easily and very shortly denned, having no
other distinctive and exclusive peculiarity except the fact that
the feet are provided with four toes, of which two are turned
backwards and two forwards. Of the two toes which are
directed backwards, one, of course, is the hallux, or proper
hind-toe, and the other is the outermost of the normal three
anterior toes. This arrangement of the toes enables the Scan-
sores to climb with unusual facility. Their powers of flight, on
the other hand, are generally only moderate and below the
average.

The most important families of the Scansores are the Cuckoos
(Cuculidtz), the Woodpeckers and Wry-necks (Picidce},t\iz Par-
rots (Psittacidce), the Toucans (Rhamphastid<z\ and the Tro-
gons (Trogonida).

The Scansores are of small importance as fossils, but the
remains of Parrots, Trogons, Woodpeckers, and Cuckoos have
been detected in the later Tertiary and Post-tertiary deposits.

ORDER VI. INSESSORES. — The sixth order of Birds is that of
the Insessores, or Perchers — often spoken of as the Passeres,
or "Passerine" Birds. They are defined by Owen as fol-
lows : —

"Legs slender, short, with three toes before and one behind,
the two external toes united by a very short membrane."

The Insessores form the largest order of existing birds, com-
prising all the ordinary "song-birds," and including a great
number of families. The earliest known representatives of the
order in past time are the Protornis Glarisiensis of the Eocene
Schists of Claris, and the Haley ornis toliapicus of the London
Clay of Sheppey — the former somewhat resembling the living
Larks, whilst the latter is supposed to be related to the King-
fishers. Besides these, a few unimportant forms have been
discovered in the later Tertiary and Post-tertiary deposits.

ORDER VII. RAPTORES. — All the members of this order are
characterised by the shape of the bill, which is "strong, curved,
sharp-edged, and sharp-pointed, often armed with a lateral
tooth " (Owen). The upper mandible is the longest, and is
strongly hooked at the tip. The body is very muscular ; the
legs are robust, short, with three toes in front and one behind,
all armed with long, curved, crooked claws or talons ; the
wings are commonly pointed, and of considerable size, and the
flight is usually rapid and powerful.

The order Raptor es is divided into the two sections of the
Nocturnal and Diurnal Raptor es, comprising respectively the
forms which fly by night and those which fly by day. In the

39^

BIRDS.

former are only the Owls, and in the latter are the Hawks,
Falcons, Eagles, and Vultures.' The earliest representative of
the Raptores in past time is the Lithornis vulturinus of the Lon-
don Clay of Sheppey, a bird probably related to the existing
vultures. In the Gypseous series of Montmartre (Eocene),
there are also remains of an Owl (Strix\ and of a Harrier
( Circus). In later Tertiary and Post-tertiary deposits occur
unimportant remains of Eagles, Hawks, and Vultures.

ORDER VIII. SAURUR.E. — This order includes only the ex-
tinct bird, the Archczopteryx macrura, a single specimen of
which — and that but a fragmentary one — has been discovered
in the Lithographic Slates of Solenhofen (Upper Oolites).
This extraordinary bird (fig. 333), appears to have been about
as big as a Rook ; but it differs from all known birds in having
two free claws belonging to the wing, and in having a long
lizard-like tail, longer than the body, and composed of separate
vertebrae.

Fig. 333. — Archceopteryx macr-ura, showing tail and tail-feathers,
with detached bones.

The tail was destitute of any ploughshare-bone, and each
vertebra carried a single pair of quill-feathers. The metacar-
pal bones also were not anchylosed, as they are in all other
known birds, living or extinct. Milne Edwards concludes
that Archczopteryx was probably a vegetable feeder, and that it
ordinarily perched upon trees.

MAMMALIA. 397

CHAPTER XXXV.

MAMMALIA.
GENERAL CHARACTERS OF THE MAMMALIA.

THE last and highest class of the Vertebrata, that of the Mam-
malia, may be shortly defined as including Vertebrate animals
in which some part or other of the integument is always provided
with hairs at some time of life; and the young are nourished for
a longer or shorter time, by means of a special fluid — the milk —
secreted by special glands — the mammary glands. These two
characters are of themselves sufficient broadly to separate the
Mammals from all other classes of the Vertebrate sub-kingdom.
In addition, however, to these two leading peculiarities, the
Mammals exhibit the following other characters of scarcely less
importance :—

1. The skull articulates with the vertebral column by means
of a double articulation, the occipital bone carrying two con-
dyles, in place of the single condyle of the Reptiles and Birds.

2. The lower jaw or mandible consists of two halves or
rami, united anteriorly by a symphysis, but not necessarily an-
chylosed; but these are each composed of a single piece,
instead of being complex and consisting of several pieces, as
in the Reptiles and Birds. Further, the lower jaw always ar-
ticulates directly with the squamosal element of the skull, and
is never united to an os quadratum, as in the Sauropsida.

3. The two hemispheres of the cerebral mass, or brain proper,
are united together by a more or less extensively developed
" corpus callosum " or commissure.

4. The heart consists — as in Birds — of four cavities or cham-
bers, two auricles and two ventricles. The right and left sides
of the heart are completely separated from one another, and
there is no communication between the pulmonary and systemic
circulations.

5. The cavities of the thorax and abdomen are completely
separated from one another by a muscular partition — the dia-
phragm or midriff.

6. The respiratory organs are in the form of two lungs placed
in the thorax, but none of the bronchi end in air-receptacles,
distributed through the body, as in Birds.

As regards the Osteology of the Mammals, the following
points should be noticed : —

With the exception of the Whales and Dolphins (Cetacea),

MAMMALIA.

and the Dugongs and Manatees (Sirenia), the vertebral column
is divisible into the same regions as in man — namely, into a
cervical, dorsal, lumbar, sacral, and caudal or coccygeal region
(see fig. 269). In the Cetacea and Sirenia the dorsal region of
the spine is followed by a number of vertebrae which compose
the hinder extremity of the body, but which cannot be separ-
ated into lumbar, sacral, and caudal vertebrae.

In spite of the great difference which is observable in the
length of the neck in different Mammals, the number of verte-
brae in the cervical region is extraordinarily constant, being
almost invariably seven, as in man. In this respect there is no
difference between the Whale and the Giraffe. The only ex-
ceptions to this law are the Manatus australis, one of the Sea-
cows, which has usually six cervical vertebrae ; and the three-
toed Sloth (Bradypus tridactylus), which is commonly regarded
as possessing nine, though competent anatomists would refer
the posterior two of these to the dorsal region.

The dorsal vertebrae are mostly thirteen in number, but they
vary from ten to twenty-four. In Man there are twelve, in one
of the Armadillos only ten, and in the three-fingered Sloth the
maximum is attained. The lumbar vertebrae are usually six or
seven in number, rarely fewer than four. In Man they are five
in number, and they are reduced to two in the two-toed Sloth,
one of the Ant-eaters, and the Duck-mole.

The first vertebra, or atlas, always bears two articular cavi-
ties for the reception of the two condyles of the occipital bone,
and the second vertebra, or axis, usually has an " odontoid "
process on which the head rotates. In the true Whales, how-
ever, in which the cervical vertebrae are anchylosed together to
a greater or less extent, and the neck is immovable, the odon-
toid process is also wanting.

The number of lumbar and sacral vertebrae, as we have seen,
varies in different Mammals ; but ordinarily some of the verte-
brae are anchylosed into a single bone, and have the iliac bones
abutting against them, thus constituting the " sacrum" of human
anatomists. In the Cetacea and Sirenia, in which the hind-
limbs are wanting, and the pelvis rudimentary, there is no
" sacrum."

The thoracic cavity or chest in Mammals is always enclosed
by a series of ribs, the number of which varies with that of the
dorsal vertebrae. In most cases each rib articulates by its head
with the bodies of two vertebrae, and by its tubercle with the
transverse process of one of these vertebrae (the lower one).
In the Monotremata (e.g., the Duck-mole), the ribs articulate
with the body of the vertebra only ; and in the Whales, the

GENERAL CHARACTERS OF THE MAMMALIA. 399

hindermost of the ribs, or all of them, articulate with the trans-
verse processes only, and not with the centra at all.

There are usually no bony pieces uniting the ribs with the
sternum or breast-bone in front, as in Birds ; but the so-called
" sternal ribs " of Aves are represented by the " costal carti-
lages" of the Mammals. In some cases, however, the carti-
lages of the ribs do become ossified and constitute sternal ribs.
Sometimes, as in the Armadillos, there is a joint between the
vertebral rib and costal cartilage. More rarely, as in the Mono-
tremes, an intermediate piece is found between the vertebral
and costal portions of the rib. Only the anterior ribs reach
the sternum, and these are called the " true " ribs ; the poste-
rior ribs, which fall short of the breast-bone, being known as
the " false " ribs.

The sternum or breast-bone is formed of several pieces placed
one behind the other, but usually anchylosed together to form
a single bone. It is placed upon the ventral surface of the
body, and is united with the vertebral column by the ribs and
their cartilages. It is generally a long and narrow bone, but in
the Cetacea it is broad. It is only in some burrowing animals
(such as the Moles) and in the true flying Mammals (the Bats),
that the sternum is provided with any ridge or keel for the at-
tachment of the pectoral muscles, as it is in Birds. The ster-
num is primitively composed of three pieces, an anterior piece
or prcesternum, a middle piece or mesosternum, and a posterior
piece or xiphisternum. The praesternum is the " manubrium
sterni " of human anatomy, and is the portion of the sternum
which lies in front of the attachment of the second pair of ribs.
All the other ribs are connected with the mesosternum. The
xiphisternum is the " xiphoid cartilage " of human anatomy, and
it commonly remains throughout life more or less unossified.
In the Monotremes there is a T-shaped bone above or in front
of the praesternum, but this is probably to be regarded as be-
longing to the shoulder-girdle, and as representing the " epi-
sternum " or " interclavicle" of the Reptiles.

The normal number of limbs in the Mammalia is four, two
anterior and two posterior ; and hence they are often spoken
of as "quadrupeds," though all the limbs are not universally
present, and other animals have four limbs as well. The ante-
rior limbs are not known to be wanting in any Mammal, but
the posterior limbs are absent in the Cetacea and Sirenia.

As regards the structure of the anterior limb, the chief
points to be noticed concern the means by which it is con-
nected with the trunk. The scapula or shoulder-blade is never
absent, and it is in the form of a broad flat bone, applied to the

400 MAMMALIA.

outer aspect of the ribs, and much more developed than in the
Birds. The coracoid bone, which forms such a marked feature
in the scapular arch of Aves, is fused with the scapula, and
only articulates with the sternum in the Duck-mole and Echidna
(Monotremata). In all other Mammals the coracoid forms
merely a process of the scapula, and does not reach the top of
the breast-bone. The collar-bones or clavicles never unite in
any Mammal to form a "furculum," as in Birds : but in the
Monotremes they unite with an " inter-clavicle " placed in front
of the sternum. The clavicles, in point of fact, are not present
in a well-developed form in any Mammals except in those
which use the anterior limbs in flight, in digging, or in prehen-
sion. The Cetacea, the Hoofed Quadrupeds ( Ungulata), and
some of the Edentata, have no clavicles. Most of the Carni-
vora and some Rodents possess a clavicle, but this is imperfect,
and does not articulate with the top of the sternum. The In-
sectivorous Mammals, many of the Rodents, the Bats, and all
the Quadrumana, have (with man) a perfect clavicle articulat-
ing with the anterior end of the sternum.

The humerus, or long bone of the upper arm (brachium\ is
never wanting, but is extremely short in the Whales, in which
the anterior limbs are converted into swimming-paddles.

In the fore-arm of all Mammals the ulna and radius are re-
cognisable, but they are not necessarily distinct; and the radius,
as being the bone which mainly supports the hand, is the only
one which is always well developed, the ulna being often rudi-
mentary. In the Cetacea the ulna and radius are anchylosed
together ; and in most of the Hoofed Quadrupeds they are an-
chylosed towards their distal extremities.

The fore-arm is succeeded by the small bones which com-
pose the wrist or " carpus." These are eight in number in man,
but vary in different Mammals from five to eleven.

The metacarpus in man and in most Mammals consists of
five cylindrical bones, articulating proximally with the carpus,
and distally with the phalanges of the fingers. The most re-
markable modification of this normal state of things occurs in
the Ruminants and in the Horse. In the Ruminants, in which
the foot is cleft, and consists of two perfect toes only, there are
two metacarpal bones in the embryo ; but these are anchylosed
together in the adult, and form a single mass which is known
as the " canon-bone " (fig. 334, ca). In the Horse, in which
the foot consists of no more than a single digit, there is only a
single metacarpal bone, on each side of which are two little
bony spines — the so-called "splint-bones" — which are attached
superiorly to the carpus. These are to be regarded as rudi-

GENERAL CHARACTERS OF THE MAMMALIA. 401

mentary metacarpals ; but by Cuvier they were looked upon as
imperfect fingers. In most of the other Ungulates there are at
least three metacarpals, and in the Elephants there are five.

The normal number of digits
is five, but they vary from one
to five. The middle finger is
the longest and most persistent
of the digits of the fore-limb ;
and in the Horse it is the only
one which is left (fig. 334, A).
The thumb is very frequently
absent. In the Ruminants there
are only two fingers which are
functionally useful, these carry-
ing the hoofs. In many Rumi-
nants, however, there are two
rudimentary and functionally
useless digits in addition.

Normally each digit has three
phalanges, except the thumb,
which has only two. In the
Whales and Dolphins ( Cetacea),
in which the anterior limbs form
swimming - paddles very like
those of the Ichthyosaurus and
Plesiosaurus, the phalanges are
considerably increased in num-
ber as they are in those Rep-
tiles. In all the Mammalia,
too, except the Cetacea, it is the
rule that the terminal phalanx
in each digit should carry a
nail, claw, or hoof.

Whilst the anterior limbs are never absent in any Mammal,
the posterior limbs are occasionally wholly wanting, as in the
Cetacea and Sirenia. Generally speaking, however, the poste-
rior limbs are present, and the pelvic arch has much the same
structure as in man. The two halves of the pelvis — the ossa
innominata — consist each of three pieces in the embryo (viz.,
the ilium, ischium, and pubes), which meet to form the cup-
shaped cavity known as the " acetabulum," with which the head
of the thigh-bone articulates. In the adult Mammal these
three bones are anchylosed together, and the two ossa inno-
minata unite in front by means of a symphysis pubis, con-
stituted either by a cartilaginous union (synchondrosis), or by

2 c

Fig- 334- — A, Fore-leg of the Horse: r
Radius ; c Carpus ; ca Canon-bone ; p
Splint-bone ; a First phalanx or " great
pastern;" b Second phalanx or "small
astern ; " c Ungual phalanx or " coffin-
ione." B, Fore-limb of a Deer: r Radi-
us ; c Carpus ; ca Canon-bone ; j Supple-
mentary toe.

>P

hi

402 MAMMALIA.

merely ligamentous attachment. In some Mammals, however,
such as the Mole, and many of the Bats, the pubic bones re-
main disunited during life. As a rule also, the ossa innomin-
ata are firmly united with the vertebral column. In the Ceta-
ceans, in which the hind-limbs are wanting, and there is no
sacrum, the innominate bones are rudimentary, and are not
attached in any way to the spine.

The only other bones which are ever connected with the
pelvis are two small bones 4 which are directed upwards from
the brim of the pelvic cavity in Marsupials and Monotremes.
These are the so-called " marsupial bones " regarded generally
as not forming parts of the skeleton properly so called, but
as being ossifications of the internal tendons of the " external
oblique" muscles of the abdomen (fig. 336).

In those Mammals which possess hind-limbs, the normal
composition of the member is of the following parts : — i. A
thigh-bone or femur ; 2. Two bones forming the shank, and
known as the tibia and fibula ; 3. A number of small bones
constituting the ankle or tarsus ; 4. The " root " of the foot,
made up of the " metatarsus ; " 5. The phalanges of the toes
(see fig. 271).

The thigh-bone or femur articulates with the pelvis, usually
at a very open angle. In Man it is distinguished by being the
longest bone of the body, and by having the axis of its shaft
nearly parallel to that of the vertebral column. In most Mam-
mals the femur is relatively shorter, and the axis of its shaft
deviates considerably from that of the spine, being sometimes
at right angles, or even at an acute angle.

Of the bones of the leg proper the tibia corresponds to the
radius in the fore-limb, as shown by its carrying the tarsus ;
and the fibula is the representative of the ulna. The articula-
tion between the tibia and fibula on the one hand, and the
femur on the other, constitutes the " knee-joint," which is usu-
ally defended in front by the " knee-pan " or patella, a large
sesamoid bone developed in the tendons of the great extensor
muscles of the thigh. The patella is of small size in the Car-
nivora, but does not appear to be wanting in any except the
Marsupials. In many cases the tibia and fibula are anchylosed
towards their distal extremities. In the Horse the fibula has
much the same character as in Birds, being a long splint-like
bone which only extends about half-way down the tibia. In
the Ruminants the reverse of this obtains, the upper half of the
fibula being absent, and only the lower half present.

The tibia articulates with the tarsus, consisting in Man of
seven bones, but varying in different Mammals from four to nine.

GENERAL CHARACTERS OF THE MAMMALIA. 403

The foot consists normally of five toes connected with the
tarsus by means of five metatarsal bones, which closely re-
semble the metacarpals. In the Ruminants there are only two
metatarsals, and these are anchylosed in the adult, and carry
two toes. In the Horse there is only one complete metatarsal
supporting a single toe. As a rule, the number of digits in the
hind-limb or foot is the same as that in the fore-limb or hand ;
but this is not always the case.

The cranial bones are invariably connected with one another
by sutures, and in no other examples than the Monotremes are
these sutures obliterated in the adult. The occipital bone
carries two condyles for articulation with the first cervical
vertebra. The lower jaw is composed of two halves or rami,
which are distinct from another in the embryo, and may or
may not be anchylosed together in the adult. However this
maybe, in no Mammal is the ramus of the lower jaw composed
of several pieces, as it is in Birds and Reptiles, nor does it
articulate with the skull by the intervention of an os quadratum.
On the other hand, each ramus of the lower jaw in the Mam-
mals is composed of only a single piece, and articulates with
the squamosal element of the skull, or, in other words, with the
squamous portion of the temporal bone.

Teeth are present in the great majority of Mammals ; but
they are only present in the embryo of the Whalebone Whales,
and are entirely absent in the genera Echidna, Mams, and
Myrmecophaga. In the Duck-mole (Ornithorhynchus] the teeth
are horny, and the same was the case in the extinct Rhytina
amongst the Sirenia. In all other Mammals the teeth have
their ordinary structure of dentine, enamel, and crusta petrosa,
these elements being variously disposed in different cases. In
no Mammals are the teeth ever anchylosed with the jaw, and
in all the teeth are implanted into distinct sockets or alveoli,
which, however, are very imperfect in some of the Cetacea.

Many Mammals have only a single set of teeth throughout
life, and these are termed by Owen " monophyodont." In
most cases, however, the first set of teeth — called the " milk "
or " deciduous " teeth — is replaced in the course of growth by
a second set of "permanent" teeth. The deciduous and per-
manent sets of teeth do not necessarily correspond to one
another ; but no Mammal has ever more than these two sets.
The Mammals with two sets of teeth are called by Owen
" diphyodont."

In Man and in many other Mammals the teeth are divisible
into four distinct groups, which differ from one another in
position, appearance, and function ; and which are known

404 MAMMALIA.

respectively as the incisors, canines, prcemolars, and molars
(fig. 335). "Those teeth which are implanted in the prae-
maxillary bones, and in the corresponding part of the lower
jaw, are called ' incisors,' whatever be their shape or size.
The tooth in the maxillary bone which is situated at or near
to the suture with the praemaxillary, is the ' canine/ as is also
that tooth in the lower jaw which, in opposing it, passes in
front of its crown when the mouth is closed. The other teeth
of the first set are the ' deciduous molars ; ' the teeth which
displace and succeed them vertically are the ' praemolars ; '
the more posterior teeth, which are not displaced by vertical
successors, are the ' molars ' properly so called." — (Owen.)
The deciduous dentition, therefore, of a diphyodont Mammal,
consists of only three kinds of teeth — incisors, canines, and

Fig. 335. — Teeth of the right side of the lower jaw of the Chimpanzee (after Owen).
* Incisors ; c Canine ; pm Praemolars ; in Molars.

molars. The incisor and canine teeth of the deciduous set are
replaced by the teeth which bear the same names in the per-
manent set. The deciduous " molars," however, are replaced
by the permanent " praemolars," and the " molars " of the per-
manent set of teeth are not represented in the deciduous series,
only existing once, and not being replaced by successors.

All these four kinds of teeth are not necessarily present in
all Mammals, and, as will be afterwards seen, the characters of
the teeth are amongst the most important of the distinctions by
which the Mammalian orders are separated from one another.
The variations which exist in the number of teeth in different
Mammals are usually expressed by a " dental formula," which
presents the " dentition " of both jaws in a condensed and
easily-recognised form.

GENERAL CHARACTERS OF THE MAMMALIA. 405

According to Owen, the typical permanent dentition of a
diphyodont Mammal would be expressed by the following
formula : —

3—3 i— i 4—4 3—3

The four kinds of teeth are indicated in such a formula by the
letters — incisors i, canines c, praemolars pm, molars m. The
numbers in the upper line indicate the teeth in the upper jaw,
those in the lower line stand for those in the lower jaw; and
the number of teeth on each side of the jaw is indicated by
the short dashes between the figures.

As regards their general distribution in time, as a matter of
course, the remains of Mammals are scanty, and occupy but
a small space in the geological record; since the greater
number of the Mammalia are terrestrial, and the greater
number of the stratified fossiliferous deposits are marine. The
Mammals, too, are the most highly organised of the entire
sub-kingdom of the Vertebrata ; and therefore, in obedience to
the well-known law of succession, they ought to make their
appearance upon the globe at a later period than any of the
lower classes of the Vertebrata. Such, in point of fact, is to a
great extent the case ; and if the geological record were perfect,
the law would doubtless be carried out to its full extent.

It is in the upper portion of the Triassic Rocks — that is to
say, not long after the commencement of the Mesozoic or
Secondary epoch — that Mammals for the first time make their
appearance ; three or four species being now known in a zone
of rocks which are placed at the summit of the Trias, just where
this formation begins to pass into the Lias. The earliest of these
—the oldest known of all the Mammals — appears at the upper
part of the Upper Trias (Keuper) and also at its very summit
(Penarth beds), and has been described under the name of
Microlestes antiquus. The nearest ally of Microlestes amongst
existing Mammals would seem to be the Marsupial and insec-
tivorous Myrmecobius, or Banded Ant-eater of Australia. As
only the teeth, however, of Microlestes have hitherto been dis-
covered, it is impossible to decide positively whether this
primeval Mammal was Marsupial or Placental.

The next traces of Mammals occur in the Stonesfield Slate
(Lower Oolites), and here four species, all of small size, are
known to occur. Most of these were Marsupial, but it is
possible that one was Placental. They form the genera Amphi-
lestes, Amphitherium, Phascolotherium, and Stereognathus. After
the Stonesfield Slate another interval succeeds, in which no

406 ORDERS OF MAMMALIA.

Mammalian remains have hitherto been found ; but in the fresh-
water formation of the Middle Purbeck, at the top, namely, of
the Oolitic series, as many as fourteen small Mammals have
been discovered. These constitute the genera Plagiaulax,
Spalacotherium, Triconodon, and Galestes. Another gap then
follows, no Mammal having hitherto been discovered in any
portion of the Cretaceous series (with doubtful exceptions).

Leaving the Mesozoic and entering upon the Kainozoic
period, remains of Mammals are never absent from any of the
geological formations. From the base of the Eocene Rocks
up to the present day remains of Mammals commonly occur,
constantly increasing in number and importance, till we arrive
at the fauna now in existence upon the globe.

In the following are given the characters of each order of
the Mammalia, with the range in time, and, so far as known,
the more important fossil forms of each. The number, how-
ever, of known fossil Mammals is so great, and in many cases
they exhibit so many peculiarities and divergences from exist-
ing forms, that nothing more can be attempted here than to
give a brief and general sketch of the palaeontological history of
the class ; attention being drawn, where it may seem necessary,
to extinct types of special interest.

CHAPTER XXXVI.

ORDERS OF MAMMALIA.

ORDER I. MONOTREMATA. — The first and lowest order of the
Mammalia is that of the Moiiotremata, containing only two
genera, both belonging to Australia — namely, the Duck-mole
(Ornithorhynchus) and the Porcupine Ant-eater (Echidna].

The order is distinguished by the following characters : —
The intestine opens into a " cloaca," which receives also the
products of the urinary and generative organs, which discharge
themselves into a urogenital canal — the condition of parts
being very much the same as in Birds. The jaws are either
wholly destitute of teeth (Echidna), or are furnished with horny
plates which act as teeth. The pectoral arch has some highly
bird-like characters, the most important of these being the
extension of the coracoid bones to the anterior end of the
sternum. The females possess no marsupial pouch, but the
pelvis is furnished with the so-called " marsupial bones," be-

MARSUPIALIA. 407

lieved to be ossifications of the internal tendon of the external
oblique muscle of the abdomen. The corpus callosum is very
small, and has been asserted to be altogether wanting. There
are no external ears. The mammary glands have no nipples,
and their ducts open either into a kind of integumentary pouch
(Echidna} or simply on a flat surface ( Ornithorhynchui). The
young are said to be destitute of a placenta, or, in other words,
no vascular connection is established between the foetus and
the mother. The feet have five toes each, armed with claws,
and the males carry perforated spurs on the back of the tarsus
(attached to a supplementary tarsal bone).

As regards their geological history, the Monotremes are not
known to be represented at all in past time ; and this need not
excite any surprise, seeing that the order is represented at the
present day by no more than two genera, both confined to a
single geographical region. Upon theoretical grounds, how-
ever, it may be expected that we shall ultimately discover that
the antiquity of the order Monotremata is extremely high.

ORDER II. MARSUPIALIA. — The order Marsupialia forms
with the Monotremata the division of the Non-placental Mam-
mals. With the single exception of the genus Didelphys, which
is American, all the Marsupialia belong to the Melanesian pro-
vince ; that is to say, they all belong to Australia, Van Diemen's
Land, New Guinea, and some of the neighbouring islands.

The following are the characters which distinguish the
order : —

The skull is composed of distinct cranial bones united by
sutures, and they all possess true teeth ; whilst the angle of
the lower jaw is almost always inflected. The pectoral arch
has the same form as in the higher Mammals, and the coracoid
no longer reaches the anterior end of the sternum. All pos-
sess the so-called "marsupial bones" (fig. 336), attached to
the brim of the pelvis. The corpus callosum is very small,
and has been asserted to be absent. The young Marsupials
are born in a very imperfect condition, of very small size, and
at a stage when their development has proceeded to a very
limited degree only. It is believed that there is no placenta
or vascular communication between the mother and foetus,
parturition taking place before any necessity arises for such an
arrangement. As the young are born in such an imperfect
state of development, special arrangements are required to
secure their existence. When born, they are therefore, in the
great majority of cases, transferred by the mother to a peculiar
pouch formed by a folding of the integument of the abdomen.
This pouch is known as the " marsupium," and gives the name

408

ORDERS OF MAMMALIA.

to the order. Within the marsupium are contained the nipples,
which are of great length. Being for some time after their
birth extremely feeble, and unable to perform the act of suc-
tion, the young within the pouch are nourished involuntarily,
the mammary glands being provided with special muscles
which force the rnilk into the mouths of the young. At a
later stage the young can suckle by their own exertions, and

they leave the pouch and return to
it at will. In a few forms there is
no complete marsupium as above
described ; but the structure of the
nipples is the same, and the young
are carried about by the mother,
adhering to the lengthy teats.

The so-called " marsupial bones "
(fig. 336) doubtless serve to support
the marsupial pouch and its con-
tained young, but this cannot be
their sole function, since they occur
in the Monotremes, in which there
is no pouch.

They consist of two small bones,
which spring from the brim of the
pelvis, and which are merely ossi-
fications of the internal tendons of
the " external oblique " muscles of
the abdomen.

The Marsupialia may be pri-
marily divided into the vegetable-
eating and the rapacious or car-
nivorous forms — the former characterised by the rudimentary
condition or absence of the canine teeth, the molars mostly
having broad grinding crowns ; whilst in the latter there are
well-developed canines, and the molars mostly have trenchant
edges. In the phytophagous section are the living Kangaroos
(Macropodidcz], the Wombat (Phascolomys), the Kangaroo-rats
(Hypsiprymnus\ and the Phalangers (Phalangistidce). In the
carnivorous section are the true Opossums (Didelphidtz), the
Banded Ant-eater (Myrmecobius\ the Thylatinus, and the
" native devil " or Dasytirus.

As regards their distribution in time, the Marsupialia pro-
bably constitute the oldest of the Mammalian orders. Owing,
however, to the detached and fragmentary condition of almost
all Mammalian remains — consisting in many cases of the
ramus of the lower jaw, or of separate teeth — it is not possible

Fig. 336. — One side of the pel-
vis of a Kangaroo, showing the
"marsupial bones" (;«)• After
Owen.

MARSUPIALIA.

409

to state this with absolute certainty. The oldest known
European Mammal is the Microlestes antiquus of the Upper
Trias, only a few teeth of which have been as yet detected.
The earliest horizon on which Microlestes occurs is in a " bone-
bed " in the Keuper of Wiirtemberg ; but it has also been
detected in the higher " Rhaetic " beds. Professor Owen
believes that the Hypsiprymnopsis of Mr Boyd Dawkins, from
the Rhaetic marls of Somersetshire, is also referable to Micro-
lestes. Upon the whole, it is most probable that Microlestes
was Marsupial ; and it appears to be most nearly related to
the little insectivorous Myrmecobius or Banded Ant-eater of
New South Wales (fig. 337).

Fig. 337. — Myrmecobius fascia ins.

Nearly allied to Microlestes is a small Mammal, a lower jaw
of which has been obtained from the Trias of North America,
and which has been described under the name of Dromatherium
sylvestre. This little animal (fig. 338) appears also to be Mar-
supial, and to be most nearly related to Myrmecobius. Each

F'g- 338.— Lower jaw of Dromatherinnt sylvestre (after Emmons). From rocks
supposed to be of Triassic age, in North Carolina.

ramus of the lower jaw contains " ten small molars in a con-
tinuous series, one canine, and three conical incisors — the
latter being divided by short intervals " (Owen).

4IO ORDERS OF MAMMALIA.

The next Mammaliferous horizon above the Trias is the
Stonesfield Slate in the Lower Oolites ; and there is no doubt
that some, if not all, of the Mammalian remains of this belong
to small Marsupials. Four genera of small Mammals are
known from this horizon — viz., Amphilestes^ AmphitJierium,
Phascolotherium, and Stereognathus. In Amphitherium (fig.
339), the molars are cuspidate, and the animal was doubtless

Fig. 339. — Ramus of the lower jaw of A mphitheriu m (Thylacotheriunt)
Prevostii. Stonesfield Slate.

insectivorous. It is believed by Owen to be Marsupial, and
to be most nearly related to Myrmecobius. Amphilestes and
Phascolotherium (fig. 340) are also believed by the same high
authority to have been insectivorous Marsupials, and the latter
is supposed to find its nearest living ally in the Opossums of
America. Lastly, the Stereognathus of the Stonesfield Slate is
in a dubious position. It may have been Marsupial ; but,
upon the whole, Professor Owen is inclined to believe that it
was placental, hoofed, and herbivorous.

With the occurrence of small Marsupials in England within
the Oolitic period, it is interesting to notice how the fauna of
that time approached in other respects to that now inhabiting
Australia. At the present day, Australia is almost wholly
tenanted by Marsupials ; upon its land-surface flourish Arau-
caricz and Cycadaceous plants, and in its seas swims the Port-
Jackson Shark ( Cestracion Philippi) ; whilst the Molluscan
genus Trigonia is nowadays exclusively confined to the Aus-
tralian coasts. In England at the time of the deposition of
the Stonesfield Slate, we must have had a fauna and flora very
closely resembling what we now see in Australia. The small
Marsupials Amphitherium and Phascolotherium prove that the
Mammals were the same in order; cones of Araucarian pines,
with tree-ferns and fronds of Cycads, occur throughout the
Oolitic series; spine-bearing fishes, like the Port -Jackson
Shark, are abundantly represented by genera such as Acrodus
and Strophodus; and lastly, the genus Trigonia^ now exclu-
sively Australian, is represented in the Stonesfield Slate by
species which differ little from those now existing.

Another singular point of resemblance is established by the

MARSUPIALIA.

411

occurrence in the rivers of Queensland of the " Barramunda,"
which is referred to the genus Ceratodus — a genus which, though
pre-eminently Triassic, nevertheless extended its range into
the Jurassic period.

Towards the close of the Oolitic period, in the Middle Pur-
beck beds, we have evidence of a number of small Mammals, all
of which are probably referable to the Marsupialia. Fourteen
species are known, all of small size, the largest being no bigger
than a polecat or hedgehog. The genera to which these little
quadrupeds have been referred are Plagiaulax, Spalacotherium,
Triconodon, and Galestes. The first of these — viz., Plagiaulax
(fig. 340, 4) — is believed to be most nearly allied to the living

Fig. 340. — Oolitic Mammals, natural size. i. Lower jaw and teeth of Phascolotherium',
2. of Triconodon; 3. of A mphitheri um ; 4. of Plagiaulax.

Kangaroo-rats (Hypsiprymnus] of Australia ; and it is held by
good authorities to have been phytophagous, as are its living
relatives. Professor Owen, on the other hand, maintains that
Plagiaulax was carnivorous. The remaining three genera —
viz., Spalacotherium, Triconodon (fig. 340, 2), and Galestes — ap-
pear to have been certainly insectivorous, and find their nearest
living allies in the Australian Phalangers and the American
Opossums.

In the older Tertiary Rocks the remains of Marsupials are
not abundant. In the Eocene Tertiary (Gypseous series of
Montmartre), however, occurs an Opossum, which is very
closely allied to the existing American forms, and which has
been named the Didelphys Gypsorum. Other species of the
same genus have also been discovered in deposits of Miocene
age.

In the later Tertiary and Post-tertiary period the order of
the Marsupialia is represented by some very remarkable forms.
The remains in question have been found in the bone-caves of
Australia — the country in which Marsupials now abound above
every other part of the globe ; and they show that Australia,

412

ORDERS OF MAMMALIA.

at no distant geological period, possessed a Marsupial fauna,
much resembling that which it has at present, but compara-
tively of a much more gigantic size. In the remains from the
Australian bone-caves, almost all the most characteristic living
Marsupials of Australia and Van Diemen's Land are repre-
sented ; but the extinct forms are usually of much greater size.
We have Wombats, Phalangers, Flying Phalangers, and Kan-
garoos, with carnivorous Marsupials resembling the recent
Thylacinus and Dasyurus. The two most remarkable of these
extinct forms are Diprotodon and Thylacoleo. In most essen-
tial respects Diprotodon resembled the Kangaroos, the denti-
tion, especially, showing many points of affinity. The hind-

limbs, however, of Diprotodon
were by no means so dispro-
portionately long as in the
Kangaroos. In size, Dipro-
todon must have many times
exceeded the largest of the
living Kangaroos, since the
skull measures three feet in
length (fig. 341).

Smaller than Diprotodon is
NototJierium, a genus which is
also most nearly allied to the living Kangaroos.

Thylacoleo (fig. 342), like Plagiaulax, is in a disputed posi-

Fig. MI.—

t Diprotodon Austraiis.

Fig. 342.— Skull of Thylacoleo. Post-Tertiary deposits of Australia. (After Flower.)

EDENTATA. 413

tion. By Professor Owen it is regarded as being strictly car-
nivorous, and as finding its nearest living ally in the Thylacine.
The great feature in the dentition is the presence in either jaw
of one huge, compressed, and trenchant prsemolar. This is
regarded by Owen as a " carnassial ; " but Professor Flower,
with greater probability, regards it as corresponding to the
great cutting praemolar of the Kangaroo-rats (Hypsiprymnus),
a view which is further borne out by the small size of the
canines in Thylacoleo. Upon the whole, therefore, Flower
concludes that " Thylacoleo is a highly-modified and aberrant
form of the type of Marsupials now represented by the Macro-
podidce and Phalangistida, though not belonging to either of
these families as now restricted," and he believes that its diet
was of a vegetable nature. Under any view of its habits,
Thylacoleo is a very remarkable type of the Marsupials ; and it
must have attained a very great size, since the length of the
crown of the great praemolar is not less than two inches and a
quarter.

ORDER III. EDENTATA, or BRUTA. — The lowest order of the
placental or monodelphous Mammals is that of the Edentata,
often known by the name of Bruta. The name Edentata is
certainly not an altogether appropriate one, since it is only in
two genera in the order that there are absolutely no teeth.
The remaining members of the order have teeth, but these are
always destitute of true enamel, are never displaced by a
second set, and have no complete roots. Further, in none of
the Edentata are there any median incisors, and in only one
species (one of the Armadillos) are there any incisor teeth at
all. . Canine teeth, too, are almost invariably wanting. Cla-
vicles are usually present, but are absent in the Scaly Ant-
eater (Manis}. All the toes are furnished with long and
powerful claws. The mammary glands are usually pectoral,
but are sometimes abdominal in position. The testes are
abdominal in position. The skin is often covered with bony
plates or horny scales.

The order Edentata is conveniently divided into two great
sections, in accordance with the nature of the food, the one
section being phytophagous, the other insectivorous. In the
former section is the single group of the Sloths (Bradypodidce).
In the latter are the two groups of the Armadillos (Dasypodidce\
and the various species of Ant-eaters (the latter constituting
Owen's group of the Edentuld).

The Edentates, like the Marsupials, are singularly circum-
scribed at the present day. No member of the order is at the
present time indigenous in Europe. Tropical Asia and Africa

414

ORDERS OF MAMMALIA.

have the Scaly Ant-eaters or Pangolins ; and in Africa occurs
the Edentate genus Orycteropus. South America, however, is
the metropolis of the Edentata, the order being there repre-
sented by the Sloths, the Armadillos, and the true Ant-eaters.
It is also in South America that by far the greater number of
extinct Edentates have been found ; and, as in the case of the
Australian Marsupials, the fossil forms are gigantic in size
as compared with their living representatives.

The oldest known representative of the Edentata is the
Macrotherium of the Miocene Tertiary of France. This is a
gigantic Edentate, intermediate in some respects between the
Pangolins (Manis) and the Aardwark (Orycteropus]. There
does not appear to have been any dermal armour, and the
teeth are rootless and destitute of enamel. The ungual pha-
langes are bent like those of the Pangolins, and the animal
doubtless possessed long curved claws. From the Upper
Miocene of Attica, M. Gaudry has also described a gigantic
Edentate, allied to Macrotherium, and larger than a Rhino-
ceros. The name assigned to this singular form is Ancylo-
therium Pentelici.

In comparatively recent deposits in South America are
found remains of Edentates corresponding to the three groups
which now inhabit that continent — viz., the Sloths, Armadillos,
and Hairy Ant-eaters. The Sloths (Bradypodidcz) are repre-
sented in the Post-tertiary deposits of South America by a
group of gigantic forms, the most important of which belong
to the genera Megatherium, Mylodon, and Megalonyx.

Megatherium (fig. 343) was a colossal Sloth-like Edentate,

Fig. 343. — Megatherium Cnvien. Post-Pliocene, South America.

EDENTATA.

415

which attained a length of eighteen feet, with bones as mas-
sive as, or more so than, those of the Elephant. The jaws are
destitute of canine and incisor teeth, but there are five upper
and four lower molars on each side. All the molars have the
form of quadrangular prisms, the crowns of which are furnished
with well-marked transverse ridges : and they grew from per-
manent pulps. The limbs are extremely massive, and the
pectoral arch has a clavicle. The digits are very large and
strong, and some of them are furnished with well-developed
claws. The tail is enormously thick. Unlike the living
Sloths, Megatherium must have been terrestrial in its habits,
and must have lived upon the foliage of trees which it up-
rooted for itself.

The genus Mylodon comprises large Sloth-like animals, of
which the best known is the Mylodon robustus (fig. 344). In
its size, Mylodon robustus was smaller than the Megatherium,
but it reached a length of eleven feet. In many respects

Fig. 344.— Skeleton of Mylodon robustus. Post-Pliocene, South America.

Mylodon is very like Megatherium, and the number of the
teeth is the same — viz., five upper and four lower molars on
each side. The crowns of the molars, however, were flat,
instead of being ridged. The fore -feet are pentadacty-

41 6 ORDERS OF MAMMALIA.

lous, and the posterior tetradactylous, the two external digits
being nailless.

Megalonyx, unlike the preceding, has been found in both
North and South America. It has the same number of teeth as
Megatherium and Mylodon, but the crowns of these are exca-
vated centrally and have a prominent margin. The fore-limbs
are shorter than the hind-limbs, and the calcaneum is unusually
long. Megalonyx was probably about the size of an ox.

Just as the Sloths of the present day were formerly repre-
sented in the same geographical area by the gigantic Megathe-
roids, so the little banded and cuirassed Armadillos of South
America were formerly represented by gigantic species, con-
stituting the genus Glyptodon. The Glyptodons (fig. 345)
differed from the living Armadillos in having no bands in their
armour, so that they must have been unable to roll themselves
up. It is rare at the present day to meet with any Armadillo
over two or three feet in length ; but the length of the Glypto-
don davipes, from the tip of the snout to the end of the tail,
was more than nine feet.

Fig. 345. — Glyptodon davipes. Post Pliocene, South America.

There are no canine or incisor teeth in the Glyptodon, but
there are eight molars on each side of each jaw, and the crowns
of these are fluted and almost trilobed. The head is covered
by a helmet of bony plates, and the trunk was defended by an
armour of almost hexagonal bony pieces united by sutures, and
exhibiting special patterns of sculpturing in each species. The
tail was also defended by a similar armour, and the vertebras
were mostly fused together so as to form a cylindrical bony
rod. The feet are massive, and the ungual phalanges short and
compressed.

Besides the various species of Glyptodon, South America has
also yielded the remains of several true species of Dasypus,
nearly allied to the living Armadillos. These have been found

SIRENIA. 417

in the ossiferous caverns of Brazil ; in which occur also other
Edentates, which have been referred to separate genera, but the
affinities of which are somewhat dubious.

CHAPTER XXXVII.
ORDERS OF MAMMALIA— Continued.

ORDER IV. SIRENIA. — This order comprises no other living
animals except the Dugongs and Manatees, which are often
placed with the true Cetaceans (Whales and Dolphins) in a
common order. There is no doubt, in fact, but that the Sirenia
are very closely allied to the Cetacea, and though they are to
be regarded as separate orders, yet they may be advantage-
ously considered as belonging to a single section, which has
been called Mutilata, from the constant absence of the hind-
limbs.

The Sirenia agree with the Whales and Dolphins in their
complete adaptation to an aquatic mode of life (fig. 346) ;
especially in the presence of a powerful caudal fin, which differs
from that of Fishes in being placed horizontally and in being
a mere expansion of the integuments, not supported by bony
rays. The hind-limbs are wholly wanting, and there is no sa-
crum. The anterior limbs are converted into swimming-paddles
or " flippers." The snout is fleshy and well developed, and
the nostrils are placed on its upper surface, and not on the top
of the head, as in the Whales. Fleshy lips are present, and
the upper one usually carries a moustache. The skin is covered
with fleshy bristles. The head is not disproportionately large,
as in the true Whales, and is not so gradually prolonged into
the body as it is in the latter. There may be only six cervical
vertebrae. The teats are two in number and are " thoracic,"
— i. e., are placed on the chest. There are no clavicles, and
the digits have no more than three phalanges each. The testes
are retained throughout life within the abdomen, but vesiculae
seminales are present. The animal is diphyodont, the perma-
nent teeth consisting of molars with flattened crowns adapted
for bruising vegetable food, and incisors, which are present in
the young animal, at any rate. In the extinct Rhytina it does
not appear that there were any incisor teeth.

The only existing Sirenia are the Manatees (Manatus) and

2 D

4i8

ORDERS OF MAMMALIA.

the Dugongs (Halicore), often spoken of collectively as " sea-
cows/' and forming the family of the Manatidce.

Fig. 346. — Sirenia. Dugong (Halicore).

The most important, if not the only, fossil remains which
can be referred with certainty to the Sirenia, are those upon
which the genus Halitherium has been founded. The upper
incisors in this genus are tusk-like, the lower incisors small,
and the molars furnished with tubercular crowns. Halitherium
appears to be in some respects intermediate between the
Dugongs and Manatees ; and several species of the genus are
known, ranging from the Eocene to the Pliocene Tertiary.

The genus Deinotherium referred to this order by De Blain-
ville, and still retained in this position by Pictet, will be here
considered as belonging to the order of the Proboscidea.

ORDER V. CETACEA. — In this order are the Whales, Dol-
phins, and Porpoises, all agreeing with the preceding in their
complete adaptation to an aquatic life. The body is com-
pletely fish-like in form ; the anterior limbs are converted into
swimming-paddles or " flippers ; " the proximal bones of the
fore-limbs are much reduced in length, and the succeeding
bones are shortened and flattened, and are enveloped in a
tendinous skin, thus reducing the limbs to oar-like fins ; there
are no external ears ; the posterior limbs are completely absent;
and there is a powerful, horizontally-flattened, caudal fin, some-
times accompanied by a dorsal fin as well. In all these char-
acters the Cetacea agree with the Sirenia, except in the one
last mentioned. On the other hand, the nostrils, which may
be single or double, are always placed at the top of the head,
constituting the so-called " blow-holes " or " spiracles ; " and
they are never situated at the end of a snout. The body is
very sparingly furnished with hairs, or the adult may be com-
pletely hairless. The teats are two in number and are placed
upon the groin. The head is generally of disproportionately
large size, and is never separated from the body by any distinct
constriction or neck. The lumbar region of the spine is long,

CETACEA. 419

and, as in the Sirenia, there is no sacrum, and the pelvis is
only present in a rudimentary form. There are no clavicles,
and some of the digits may possess more than three phalanges
each. Lastly, the adult is either destitute of teeth or, with ex-
ception of the Zeuglodonts, is monophyodont — that is to say,
possesses but a single set of teeth, which are never replaced by
others. When teeth are present, they are usually conical and
numerous, and they are almost always of one kind only.

The Cetacea may be divided into the two sections of the
BalcznidcE, comprising only the " Whalebone Whales," in which
true teeth are absent ; and the " Toothed Whales " or Odonto-
ceti, comprising the living families of the Delphinida (Dolphins
and Porpoises), the Catodontida (Sperm Whales), and the Rhyn-
choceti (" Ziphioid " Whales), with the extinct family of the
Zeuglodontida.

Fig. 347. — Skull of the Right Whale (Balcena ntysticetus) — after Owen.

Fam. i. Balcznida. — The Bal<znid<z or Toothless Whales are
characterised by the total absence of teeth in the adult (fig.
347). Teeth, however, are present in the fcetal Whale, but
they never cut the gum. The place of teeth is supplied by a
number of plates of whalebone or " baleen " attached to the
palate ; hence the name of " Whalebone Whales " often given
to this family. They are the largest of living animals, and may
be divided into the two sections of the Smooth Whales, in which
the skin is smooth, and there is no dorsal fin (as in the Green-
land Whale), and the Furrowed Whales, in which the skin is
furrowed, and a dorsal fin is present (as in the so-called Finner
Whales and Hump-backed Whales).

The Bal&nidcz are of little geological importance. In Plio-
cene deposits have been found remains referred to the Rorquals ;
and bones of the Whalebone Whales have also been found
in various Post-Tertiary accumulations. It is probable, like-

42O

ORDERS OF MAMMALIA.

wise, that the ear-bones or " cetotolites " which occur in the
Red Crag (Pliocene) are, in some instances at any rate, refer-
able to members of the Baltznidce.

Fam. 2. Catodontidce. — The family of the Catodontidce, or
Physeterida, comprises the Sperm Whales or Cachalots, with
which we commence the series of the Toothed Whales (Odon-
toceti). They are characterised by the fact that the palate is
destitute of baleen plates, and the lower jaw possesses a series
(about fifty-four) of pointed conical teeth, separated by inter-
vals, and sunk in a common alveolar groove, which is only im-
perfectly divided by septa. The upper jaw is also in reality
furnished with teeth — but, with a single partial exception, these
do not cut the gum.

Remains of Cachalots (Physeter) occur in the Pliocene and
Post-Tertiary deposits, and their existence has even been indi-
cated in the Miocene Tertiary. They are, however, of no
special importance.

Fam. 3. Delphinida. — This family includes the Dolphins,
Porpoises, and Narwhal, and is characterised by usually pos-
sessing teeth in both jaws ; the teeth being numerous, and
conical in shape. The nostrils, as in the last family, are united,
but they are placed further back, upon the top of the head.
The single blow-hole or nostril is transverse and mostly cres-
centic or lunate in shape. The head is by no means so dispro-
portionately large as in the former families, usually forming
about one-seventh of the entire length of the body.

Fig. 348. — The common Dolphin (Delphinus delphis).

The genus Delphinus, comprising the common Dolphins,
appears to date from the Miocene Tertiary, and is well repre-
sented in deposits of Pliocene age. In Miocene strata also
occur the Delphinoid remains which have been referred to the
genera Stereodelphis and Champsodelphis.

Fam. 4. Rhynchoceti. — This family is allied to the Cacha-
lots or Sperm Whales, and includes the so-called " Ziphioid
Whales." They are distinguished by the possession of a

CETACEA. 421

pointed snout (the " beak " or " rostrum "), single blow-hole,
and small dorsal fin ; and by their dentition. The upper jaw
is edentulous, any teeth which may be present not cutting the
gum. The lower jaw, on the other hand, possesses usually a
single pair of teeth, which are sometimes tusk-like, but which
in other cases are concealed by the gum.

The rostrum of these Cetaceans is of great density, and has
often been preserved in a fossil state, usually presenting itself
as a bony cylinder or elongated cone, generally more or less
water-worn. Upon fossils of this nature have been founded
the genera Choneziphius and Belemnoziphius, both of which
occur in the so-called " Crags " (Pliocene). The genus Ziphius
also occurs in the Crag, but unlike the preceding it is repre-
sented by existing species. Besides the "beaks," some fossil
teeth have been found, which may perhaps be referable to mem-
bers of this family.

Fam. 5. Zeuglodontidce. — The members of this family differ
from all existing Odontoceti in the possession of molar teeth im-
planted by two distinct fangs. The Zeuglodonts are entirely
extinct, and they are exclusively confined to the Eocene, Mio-
cene, and Pliocene periods. The chief genera are Zeuglodon
and Squalodon.

Zeuglodon (fig. 349) is distinguished by its elongated snout,
conical incisors, and molar teeth with triangular serrated
crowns, implanted in the jaw by two roots. Each molar looks

Fig. 349. — Zeuglodon cetpides. A, Molar tooth, natural size ; B, Vertebra, reduced.
From the Middle Eocene of North America. (After Lyell.)

as if it were composed of two separate teeth united on one side
by their crowns ; and it is this peculiarity which is expressed
by the generic name. The species of Zeuglodon are Eocene
and Miocene, one of the best known being the great Z.

422 ORDERS OF MAMMALIA.

cetoides of the Middle Eocene (Jackson Beds) of the United
States, which attained a length of seventy feet.

By Professor Huxley, Zeuglodon is regarded as intermediate
between the true Cetaceans and the Carnivorous family of the
Seals. On this point, this eminent naturalist remarks : — "The
skull of this great Eocene sea-monster, in fact, shows, by the
narrow and prolonged interorbital region ; the extensive union
of the parietal bones in a sagittal suture ; the well-developed
nasal bones ; the distinct and large incisors implanted in prse-
maxillary bones, which take a full share in bounding the fore-
part of the gape ; the two-fanged molar teeth with triangular
and serrated crowns, not exceeding five on each side in each
jaw ; and the existence of a deciduous dentition, — its close re-
lation with the Seals. While, on the other hand, the produced
rostral form of the snout, the long symphysis, and the low cor-
onary process of the mandible, are approximations to the
Cetacean form of those parts."

The genus Squalodon is nearly related to Zeuglodon^ but the
teeth are more numerous ; and the double-fanged molars are
more compressed and pyramidal in form. " The nasal bones
are very short, and the upper surface of the rostrum presents
the groove, filled up during life by the prolongation of the eth-
moidal cartilage, which is so characteristic of the majority of
Cetaceans " (Huxley). The species of Squalodon all belong
to the Miocene and Pliocene Tertiary.

The genus Saurocetes has been founded for the reception of
another Zeuglodont, in which there were double-fanged teeth
with conoid crowns. The remains on which this genus are
based, are from strata of Tertiary age, near Buenos Ayres, and
they indicate an animal much smaller than the true Zeuglodons.

Lastly, it would appear probable that the genus Balcenodon,
founded upon teeth from the Red Crag (Pliocene), is really re-
ferable to this family, and probably to the genus Squalodon.
In part, however, teeth of Ziphioid Whales have also been in-
cluded under this title. By Owen Balanodon is regarded as
comprising teeth of a Cetacean nearly allied to the living
Sperm Whale.

UNGULATA. 423

CHAPTER XXXVIII.
ORDERS OF MAMMALIA— Continued.

ORDER VI. UNGULATA. — The order of the Ungulata, or
Hoofed Quadrupeds, is one of the largest and most important
of all the divisions of the Mammalia. It comprises three
entire old orders — namely, the Pachydermata, Solidungula, and
Ruminantia.

The first of these old divisions — that of the Pachydermata —
included the Elephants, Rhinoceros, Hippopotamus, Tapirs,
and the Pigs, all characterised, as the name implies, by their
thick integuments. The name is still used to express this fact,
though the order is now abandoned, and is merged with that
of the Ungulata; the Elephants alone being removed to a
separate order under the name of Proboscidea.

The second old order — that of the Solidungula or Solipedes

—included the Horse, Zebra, and Ass, all characterised by the

fact that the foot terminates in a single toe, encased in an

expanded hoof. The name Solidungula is still retained for

these animals, as a section of the Ungulata.

The third old order — that of the Ruminantia — includes all
those animals, such as Oxen, Sheep, Goats, Camels, Giraffes,
Deer, and others, which chew the cud or "ruminate," and have
two functional toes to each foot, encased in hoofs. The name
Ruminantia is still retained for these animals, as constituting
a most natural group of the Ungtilata.

All these various animals, then, are now grouped together
into the single order of the Ungulata, or Hoofed Quadrupeds,
and the following are the characters of the order : —

All the four limbs are present, and that portion of the toe
which touches the ground is always encased in a greatly-ex-
panded nail, constituting a "hoof." There are never more
than four full-sized toes to each limb. Owing to the encase-
ment of the toes in hoofs, the limbs are useless for prehension,
and only subserve locomotion ; hence clavicles are always want-
ing in the entire order. There are always two sets of enamelled
teeth, so that the animal is diphyodont. The molar teeth are
massive and have broad crowns, adapted for grinding vegetable
substances.

The order Ungtdata is divided into two primary sections : —
the Perissodactyla, in which the toes or hoofs are odd in num-
ber (one or three), and the Artiodactyla, in which the toes are
even in number (two or four).

424 ORDERS OF MAMMALIA.

SECTION A. PERISSODACTYLA. — The section of the Perisso-
dactyle Ungulates includes the Rhinoceros, the Tapirs, the
Horse and its allies, and some extinct forms, all agreeing in
the following characters : —

The hind-feet are odd-toed in all, and the fore-feet in all
except the Tapirs. The dorso-lumbar vertebrae are never less
than twenty-two in number. The femur has a third trochanter.
The horns, if present, are not paired. Usually there is only
one horn, but if there are two, these are placed in the middle
line of the head, one behind the other. In neither case are
the horns ever supported by bony horn-cores. The stomach
is simple, and is not divided into several compartments ; and
there is a large and capacious caecum.

The three existing genera of Perissodactyle Ungulates —
namely, the Horse, Tapir, and Rhinoceros, are widely removed
from one another in many important characters ; but the inter-
vals between them are filled up by an extensive series of fossil
forms, commencing in the Lower Tertiary Strata.

Fam. i. Rhinoceridcz. — This family comprises only a single
genus, the genus Rhinoceros. The Rhinoceroses are extremely
large and bulky brutes, having a very thick skin, which is
usually thrown into deep folds. The muzzle is rounded and

H H

blunt, and there are ' molars, with tuberculate crowns.

7 — 7

There are no canines, but there are usually incisor teeth in both
jaws. The skull is pyramidal, and the nasal bones are enor-
mously developed. The feet are furnished with three toes each,
encased in hoofs. The nasal bones usually support one or two
horns, which are not paired. The horn is composed of longi-
tudinal fibres, which are agglutinated together, and are of the
nature of epidermic growths, somewhat analogous to hairs.
When two horns are present, the hinder one is carried by the
frontal bones, and is placed in the middle line of the head
behind the anterior horn. The posterior horn is usually much
shorter than the anterior one, and if not, it differs in shape.
The Rhinoceroses live in marshy places, and subsist chiefly on
the foliage of trees. They are exclusively confined at the pre-
sent day to the warmer parts of the Old World ; but an extinct
species (Rhinoceros tichorhinus) formerly inhabited England,
and ranged over the greater part of Europe.

The fossil species of Rhinoceros are numerous, commencing
in the Miocene Tertiary, and ranging through the Pliocene
and Post-Pliocene deposits. The species of Rhinoceros may
be divided into groups, as follows : —

i. Those in which the nostrils are separated by a bony sep-

UNGULATA. 425

turn (" cloison "), and the incisor teeth are wanting in the adult
(£. tichorhinus).

2. Those in which there is no bony partition between the
nostrils, and the incisors are of medium size (Rhinoceros mega-
rhinus].

3. Those in which there is no " cloison," and the incisors
are of large size (Rhinoceros incisivus).

4. Those in which there is an imperfect bony partition be-
tween the nostrils (Rhinoceros Etruscus and R. hemitcechus').

The most important extinct forms of the genus Rhinoceros
are the R. tichorhinus, R. megarhinus, R. hemitcechus ( — R.
leptorhinus, Owen), R. Etruscus, and the hornless species con-
stituting the sub-genus Acerotherium.

The Rhinoceros tichorhinus is generally known as the
" Woolly Rhinoceros," from its possession of a woolly cover-
ing. Its skin was foldless, and it possessed two horns, of
which the anterior one was very large. The limbs are ex-
tremely stout, and the nostrils are completely separated by an
osseous septum. R. tichorhinus is essentially a northern form,
and has the same distribution in space as the Mammoth, except
that it did not cross Behring Straits, and is therefore not
found in America. In time, it is younger than the Mammoth,
not being found in the prae-glacial forest-bed of Norfolk, and
occurring for the first time in the Lower Brick-earths of the
Thames valley (proe-glacial, but younger than the "forest-
bed"). It is, therefore, essentially a Post-glacial Mammal,
and it is mainly found in quaternary cave-deposits and valley-
gravels. A molar tooth of this well-known form is figured
below (fig. 351).

Fig. 350. — Penultimate molar of the Fig. 351.— Penultimate molar of the
lower jaw of Rhinoceros megarhinus, lower jaw of Rhinoceros tichorhinus,
two-thirds of the natural size. Post- two-thirds of the natural size. Post-
Pliocene. Pliocene.

The Rhinoceros hemitcechus of Falconer ( = the R. leptorhinus
of Owen) is also provided with two horns, but is of a much

426 ORDERS OF MAMMALIA.

more slender build than the Tichorhine form. The nasal
bones are slender, and the nostrils are separated by a partially-
ossified septum. The adult animal possesses neither incisor
nor canine teeth. Like the preceding, R. hemitcechus is ex-
clusively Post-Pliocene in its distribution, and is found in
cave-deposits and in the Thames-valley Brick-earths.

The Rhinoceros megarhinus of Christol ( = the R. leptorhinus
of Cuvier and Falconer) is also bicorn, and resembles R. hemi-
tcechus in being of comparatively slender build. It is dis-
tinguished, however, by the enormous development of the
nasal bones and the absence of the " cloison " or bony parti-
tion between the nostrils. This form (fig. 350) is found in the
Pliocene beds of Italy and France, and also occurs in the
prae-glacial forest-bed of Cromer and the Lower Brick-earths
of the Thames valley.

Rhinoceros Etruscus is also bicorn, and has the nostrils par-
tially separated by a " demi-cloison " or incomplete bony par-
tition, which "strengthened the basement of the anterior horn."
This species is found in deposits of Pliocene age, and occurs
also in the Post-Pliocene (as in the Cromer forest-bed).

In the Miocene period occur various remains of hornless
species of Rhinoceros, which have often been united into a
separate genus, or sub-genus, under the name of Acerotherium.
Some of these forms have all the feet three-toed, and they
constitute the Rhinoceros incisivus of Cuvier. The typical
species of Acerotherium, on the other hand, are stated to agree
with the living Tapirs in having the fore-feet four-toed.

Fam. 2. Tapir ida. — The Tapirs are characterised by the
possession of a short movable proboscis or trunk. The skull
is pyramidal, and the nasal bones project over the nasal cavity.
The skin is hairy and very thick. The tail is extremely short.
The fore-feet have four toes each, but these are unsymmetrical,
and the hind-feet have only three toes, all encased in hoofs.

3 — 3
The jaws are furnished with incisor teeth, ( ), small can-

O O

«T >T

ines, and 4 — 7 molars.
6 — o

The genus Tapirus, including the existing Tapirs, appears for
the first time in deposits of Miocene age, and is represented
by various species in Pliocene and Post-Pliocene strata. The
genus Lophiodon comprises Tapiroid Ungulates, which are
essentially, if not exclusively, of Miocene age. They differ
from the Tapirs almost solely in the characters of some of the
molar and prsemolar teeth. Lastly, the genus Coryphodon,
likewise nearly related to the Tapirs, is found exclusively in
the Eocene Tertiary.

UNGULATA.

427

Fam. 3. Palaotheridce. — This family includes certain ex-
tinct Ungulates from the Eocene and Miocene Tertiary. They
are characterised by the possession of three toes to all the feet,
by having canines, and by the fact that the lower molars have
a doubly crescentic form. The canines are longer than the
other teeth, and the dental formula is —

3 — 3 J — I 4 — 4 3 — 3

/ ; c- — -; pm- — r; m-— = 44.

3—3

4—4 3—3

The chief, if not the only, genus in this family is Palceotherium
itself. Several species of this genus are known, varying in size
from a sheep up to a horse. From the size and form of the
nasal bones, it is deduced, with great probability, that the Palae-
othere possessed a short movable proboscis or trunk (fig. 352).

Fig. 352. — Outline of Palceo therium magnum, restored, after Cuvier. Upper Eocene.

All the known species of Palceotherium are Eocene or Miocene,
and the genus attained its maximum in the former period.

Fam. 4. Solidungula or Equidce. — This family comprises the
Horses, Asses, and Zebras, characterised by the fact that the
feet have only a single perfect toe each, enclosed in a single
broad hoof. There is a discontinuous series of teeth in each
jaw ; and in the males, canines are present, but these are
wanting in the females. The dental formula is —

.3—3

i — i

pm

3—3

m

= 40.

3—3 i— i 3—3 3—3

The skin is covered with hair, and the neck is furnished with
a mane.

428 ORDERS OF MAMMALIA.

Three fossil genera of this family are known — viz., Anchi-
therium, Hipparion, &&& Equus , the last of which is represented
at the present day by the existing Horses, Asses, and Zebras.

Anchitherium comprises some singular forms from the Upper
Eocene and Lower Miocene. In this genus each foot is fur-
nished with a single functional hoofed toe, flanked by two
small hoofed digits, which are sufficiently developed to touch
the ground. Anchitherium is nearly related to Palceotherium.

Hipparion is confined to the Upper Miocene and Pliocene
deposits, and is distinguished by the fact that each foot pos-
sessed a single fully-developed toe, bordered by two function-
ally useless toes, which did not touch the ground, but simply
dangled on each side of the central toe.

In the genus Equus, the foot consists of a single developed
toe, but there are two rudimentary toes in the form of little
bony spines — the so-called " splint-bones " — which are attached
to the carpus on either side of the metacarpal of the single
functional toe. In the Pliocene period appear, for the first
time, remains of horses which, like the present form, possessed
only a single toe encased in a single hoof. It is interesting to
observe that one of the Pliocene horses (Equus curvidens)
occurs in South America, though this continent certainly pos-
sessed no native horse at the time of its discovery by the
Spaniards. About twenty horses — one of them standing no
more than two and a half feet in height — have been described
from North America, in which continent no indigenous horse
existed at the time of its discovery. The Equus fossilis of the
Post-Pliocene and Recent deposits is specifically undistinguish-
able from the common horse (Equus caballus}.

SECTION B. ARTIODACTYLA. — In this section of the Ungu-
lates the number of the toes is even — either two or four — and
the third toe in each foot forms a symmetrical pair with the
fourth. The dorso-lumbar vertebrae are nineteen in number,
and there is no third trochanter on the femur. If true horns
are present, these are always in pairs, and are supported by
bony horn-cores. The antlers of the Deer are also paired, but
they are not to be regarded as true horns. The stomach is
always more or less complex, or is divided into separate com-"
partments, and the aecum is comparatively small and simple.

The section Artiodactyla comprises the Hippopotamus, the
Pigs, and the whole group of the Ruminants, including Oxen,
Sheep, Goats, Antelopes, Camels, Llamas, Giraffes, Deer, &c.
Besides these there is an extensive series of fossil forms com-
mencing in the Eocene or Lower Tertiary period, and in many
respects filling up the gaps between the living forms.

UNGULATA. 429

The group of the Artiodactyle Ungulates may be divided
into two sections termed respectively Omnivora and Rumi-
nantia, according as they live upon a miscellaneous (but chiefly
vegetable) diet, or are exclusively vegetable-feeders and chew
the cud. In the former are the living families of the Hippo-
potamidce, and Suida (Swine), with the extinct group of the
Anoplotherida. In the latter are the Camelidce, Moschidce
(Musk-deer), Cervidce (Deer), Camelopardalidce (Giraffes), and
Cavicornia (Antelopes, Sheep, Goats, and Oxen).

OMNIVORA.

i. Hippopotamida. — This group contains only the single
genus Hippopotamus, characterised by the massive heavy body,
the short blunt muzzle, the large head, and the presence of

2 2

teeth of three kinds 'in both jaws. The incisors are - — , the

2 2
-.- y *7 * fa A

canines extremely large, , and the molars, ' — '- or - — -

i — i 7 — 7 6 — 6'

with crowns adapted for grinding vegetable substances. The
upper canines are short, but the lower canines are in the form
of enormous tusks, with a chisel-shaped edge. The feet are
massive, and are terminated by four hoofed toes each. The
eyes and ears are small, and the skin is extremely thick, and
is furnished with few hairs. The tail is very short.

Several extinct species of Hippopotamus are known, but
there is only one well-established living form, the Hippopo-
tamus amphibius or River-horse, and this is confined to the
African continent.

The genus Hippopotamus may be divided into two sub-
genera, in accordance with the number
of the incisor teeth. In the sub-genus
Tetraprotodon, comprising the living
species and most of the fossil forms,
there are four incisors in each jaw. In
the sub-genus Hexaprotodon, compris-
ing several Miocene species from
-India, there are six incisors in each
jaw.

The best -known fossil species of
Hippopotamus in Europe is the H. Fig. 353.— Molar tooth of Hip-
major, which is found both in Pliocene ^rafS. *lS*PtiU2L
and in Post-Tertiary deposits. This

species is very nearly allied to the living H. amphibius; but it
extended its range over the whole of the south of Europe.

43O ORDERS OF MAMMALIA.

In the Tertiary deposits of the Siwalik Hills in India (Mio-
cene) have been discovered several species of Hippopotamus,
belonging to the sub-generic type, Hexaprotodon.

2. Suida. — The group of the Suida, comprising the Pigs,
Hogs, and Peccaries, is very closely allied to the preceding ;
but the feet have only two functional toes, the other two toes
being much shorter, and hardly touching the ground. All the
three kinds of teeth are present, but they vary a good deal.
The canines always are very large, and in the males they usu-
ally constitute formidable tusks projecting from the sides of
the mouth. The incisors are variable, but the lower ones are
always inclined forwards. The molars vary from three to

seven on each side of the mouth (^ — * or Z — '-}. The stom-

3—3 7—7

ach is mostly slightly divided, and is not nearly so complex as
in the Ruminants. The snout is truncated and cylindrical,
fitted for turning up the ground, and is capable of consider-
able movement. The skin is more or less abundantly covered
with hair, and the tail is very short, or represented only by a
tubercle.

The most important genera of the Suida are Sus (Pigs),
Dicotyles (Peccaries), Charopotamus, Hyopotamus, and Anthra-
cotherium, of which the three last are extinct.

The genus Sus, comprising the true Pigs, appears to have
commenced its existence in the Miocene Tertiary. Several
species are known from Pliocene deposits ; and the Wild
Boar (Sus scrofa) has been found in Post-Pliocene accumula-
tions (commencing in the prae-glacial forest-bed of Norfolk).

The genus Dicotyles, comprising the existing Peccaries, is
at present confined to the American continent. The same
country also has yielded five fossil species, which have been
found in the bone-caves of Brazil, and two of which appear to
have been much larger than the living forms.

Chceropotamus comprises some Upper Eocene Suida, which
possess seven molars on each side of each jaw, the first of
these (prsemolars) being compressed, whilst the others are
tuberculate. The canines are short, and are not exserted, as
they are in the Wild Boar. Hyopotamus is another genus, in
which the canines are short. All the species of this latter
genus belong to the Upper Eocene and Lower Miocene Ter-
tiary. Lastly, the genus Anthracotherium is nearly allied to
Chczropotamus, with which it agrees in the number and general
form of the praemolar and molar teeth. All the known species
of this genus belong to the Lower Miocene.

3. Anoplotheridcz. — Forming a kind of transition between

UNGULATA. 43 1

the Swine and the true Ruminants, is the extinct group of the
Anoplotheridcz, from the Lower Tertiary Rocks. The Anoplo-
theria (fig. 354) were slender in form, with long tails, and feet
terminated by two hoofed toes each, sometimes with small
accessory hoofs. The dentition consisted of six incisors in
each jaw, small canines not larger than the incisors, and seven
molars on each side, there being no interval or diastema be-
tween the molars and the canines.

Fig. 354. — A noplotherinm commune. Eocene Tertiary.

There was thus a continuous series of teeth in each jaw, the
dental formula being—

3-3 i- 1 4-4 3-3 ~

The most important genera of this family are Anoplotherium
and Xiphodon of the Upper Eocene, Chalicotherium of the
Miocene, and Dichobune of the Middle Eocene ; but many less
important genera are known.

RUMINANTIA.

The last section of the Artiodadyle Ungulates is the great
and natural group of the Ruminantia, or Ruminant animals.
This section comprises the Oxen, Sheep, Antelopes, Giraffes,
Deer, Camels, &c., and is distinguished by the following char-
acters : —

The foot is what is called " cloven," consisting of a symmet-
rical pair of toes encased in hoofs, and looking as if produced
by the splitting into two equal parts of a single hoof. In addi-
tion to these functional toes, there are usually two smaller sup-
plementary hoofs placed at the back of the foot. The meta-
carpal bones of the two functional toes of the fore-limb, and
the metatarsal bones of the same toes of the hind-limb, coalesce

432

ORDERS OF MAMMALIA.

to form a single bone, known as the " canon-bone." The
stomach is complex, and is divided into several compartments,
this being in accordance with their mode of eating. They all,
namely, ruminate or " chew the cud " — that is to say, they first
swallow their food in an unmasticated or partially-masticated
condition, and then bring it up again, after a longer or shorter
time, in order to chew it thoroughly.

The dentition of the Ruminants presents peculiarities almost
as great and as distinctive as those to be derived from the di-
gestive system. In the typical Ruminants (e.g., Oxen, Sheep,
Antelopes), there are no incisor teeth in the upper jaw, their
place being taken by a callous pad of hardened gum, against
which the lower incisors impinge (fig. 355). There are also no

m

Fig. 355. — Skull of a hornless Sheep (after Owen), i Incisors; c Canines ;
in Molars and prjemolars.

upper canine teeth, and the only teeth in the upper jaw are six
molars on each side. In the front of the lower jaw is a con-
tinuous and uninterrupted series of eight teeth, of which the
central six are incisors, and the two outer ones are regarded by
Owen as being canines. Upon this view, canine teeth are pre-
sent in the lower jaw of the typical Ruminants, and they are
only remarkable for being placed in the same series as the in-
cisors, which they altogether resemble in shape, size, and direc-
tion. Behind this continuous series of eight teeth in the lower
jaw there is a vacant space, which is followed behind by six
molars on each side.

UNGULATA. 433

The dental formula, then, for a typical Ruminant animal is —

o — o o — o

t c — . *m t-3 -w3-=3

3—3' i— i ' * 3—3' 3—3

The departures from this typical formula occur in the Camelidce,
the Moschidce, and in some of the Deer. Most of the Deer con-
form in their dentition to the above formula, but a few forms
(e. g., the Muntjak) have canine teeth in the upper jaw. These
upper canines, however, are mostly confined to the males; and
if they occur in the females, they are of a small size. The
dentition of the Camelidce (Camels and Llamas) is still more
aberrant ; there being two canine-like upper incisors and upper
canines as well. The lower canines also are more pointed and
stand more erect than the lower incisors, so that they are easily
recognisable.

The group of the Ruminantia includes the families of the
Camelidce (Camels and Llamas), the Moschidce (Musk-deer), the
Cervidce (Deer), the Camelopardalidce (Giraffe), and the Cavicor-
nia (Oxen, Sheep, Goats, Antelopes).

a. Camelidce. — The Camels and Llamas constitute in many
respects an aberrant group of the Ruminantia, especially in
their dentition, the peculiarities of which have been spoken of
above, and need not be repeated here. In their feet, too, the
Camelidce are peculiar. The feet are long and terminate in
only two toes, which are covered by imperfect nail-like hoofs,
covering no more than the upper surface of each toe. The
two hinder supplementary toes, which are mostly present in the
Ruminants, are here altogether wanting ; and the soles of the
feet are covered by a callous horny integument, by which the
two toes of each foot are conjoined, and upon which the ani-
mal walks. The head in all the Camelidce is destitute of horns,
and the nostrils can be closed at the will of the animal.

The two living genera of the Camelidce are Camelus, compris-
ing the true Camels, and Auchenia, comprising the Llamas and
Alpacas of South America. Both of these genera are repre-
sented by fossil forms, the former by two species which occur
in the Tertiary deposits of the Siwalik Hills, in India, and the
latter by two species which occur in the bone-caves of Brazil,
and one of which exceeded the horse in size.

Besides these existing genera, there are the two extinct genera
Merycotherium and Macrauchenia. The first of these is only
known by some molar teeth, which have been discovered in
the drift of Siberia, and which resemble those of the Camel in
form. Macrauchenia is a remarkable extinct genus, which is in
many respects intermediate between the Perissodactyle and

2 E

434 ORDERS OF MAMMALIA.

Artiodactyle Ungulates. In fact, as the feet appear to be un-
doubtedly three-toed, it can only with some violence be consi-
dered here as belonging to the Artiodactyles. At the same
time, it shows many remarkable points of affinity to the Came-
lidcz, and it may be regarded as a generalised type, presenting
resemblances on the one hand to Palceotherium, and on the
other hand to the Llamas (Auchenia). Only a single species is
known, which equals the Rhinoceros in size, and occurs in
Post-Tertiary or late Tertiary strata in South America.

b. Moschidce. — The second group is that of the Musk-deer,
characterised by the total absence of horns in both sexes, and
by the presence of canines in both jaws, those in the upper jaw
being in the form of tusks in the males, but being much smaller
in the females.

The family Moschidce is a small one, and is of little geologi-
cal importance. A species of Moschus, allied to the living
Musk-deer, has been found in India, and another form has been
indicated as occurring in the later Tertiary deposits of Europe.
The genus Amphitragiilus has been founded upon remains from
the Lower Miocene of France ; and the nearly-allied Dremo-
therium has been discovered in the Miocene deposits of France
and Attica.

c. Cervidce. — This family is of much greater importance than
that of the Mosckidtf, including as it does all the true Deer.
They are distinguished from the other Ruminants chiefly by
the nature of the horns. With the single exception of the
Reindeer, these appendages are confined to the males amongst
the Cervidce, and do not occur in the females. They do not
consist, as in the succeeding group, of a hollow sheath of horn
surrounding a central bony core, nor are they permanently re-
tained by the animal. On the other hand, the horns, or, as
they are more properly called, the antlers, of the Cervidce are
deciduous, and are solid. They are bony throughout, and are
usually more or less branched, and they are annually shed and
annually reproduced at the breeding season. They increase
in size and in the number of branches every time they are
reproduced, until in the old males they may attain an enor-
mous size.

The living Cervidce are very generally distributed, but no
member of the group has hitherto been discovered in either
Australia or South Africa, their place in the latter continent
seeming to be taken by the nearly-allied Antelopes (distin-
guished by their hollow horns).

The true Cervidce do not seem to make their appearance
before the Miocene period, in which they are represented by

UNGULATA.

435

the extinct genus Dorcatkerhtm, and by species of the living
genus Cervus. The former of these appears to have been
furnished with upper canines ; and the animal had antlers
supported upon bony peduncles, in both of these respects re-
sembling the living Muntjak (Cervus Afuntfak) of India.

The number of known fossil Deer is very considerable, but
many forms are only known by fragmentary remains ; and it
will be sufficient here to speak of some of the more important
examples.

*ig. 356. — Cervus tnegaceros (Megaceros Hibertiicus). The " Irish Elk."
Post-Pliocene.

The true Elks, represented by the living Moose (Alces mal-
c/iis, or A. palmatus), are distinguished by their antlers with-
out either basal or mesial " tines," but terminated by a great

436 ORDERS OF MAMMALIA.

palmation digitated on its outer side only. Antlers of a
species undistinguishable from the existing Moose have been
found not uncommonly in Post-Pliocene deposits in various
parts of Europe, but this animal does not make its appearance
till after the close of the Glacial period.

The Reindeer (Cervus tarandus] of Northern Europe and
North America is remarkable for being the only member of
the Cervidce. in which both sexes have horns. The horns are
of large size, cylindrical, divided, with basilar and median
tynes. Remains of the Reindeer are 'found, often in con-
siderable abundance, in various Post - Pliocene deposits in
Europe, extending as far south as the Pyrenees.

Intermediate between the Reindeer and the Fallow-deer
is the celebrated Post-Pliocene species, which is commonly
known as the "Irish Elk" (Cervus megaceros, or Megaceros
Hibernicus}. This extinct form (fig. 356) is remarkable for its
great size and for the enormous dimensions of the spreading
antlers, which are expanded towards their extremities, and
attain an expanse of as much as ten feet from tip to tip. The
Cervus megaceros is exclusively Post-Tertiary, but does not
appear, so far as is known with certainty, to have survived into
the Prehistoric period.

The true Stags (Cervus), to which the Irish Elk seems pro-
perly to belong, are typified by such species as the Red Deer
( Cervus elaphus] of Europe, and the Wapiti ( Cervus Canadensis]
of North America. The former of these occurs in a fossil
state in Post-Pliocene and* Recent deposits in Europe, and the
latter is represented in accumulations of the same age in
America by a closely-allied or identical form.

The Roebuck (Cervus capreolus], distinguished by its
branched antlers, with a median, but without a basilar, tyne,
is also known in a fossil condition in Post-Pliocene deposits
in Europe, appearing before the commencement of the Glacial
period.

The Miocene and Pliocene deposits, lastly, have yielded
remains of Cervidce, which have been referred to various
species ; but none of these are sufficiently important to merit
especial mention.

d. Camelopardalida. — This family includes only a single
living animal — the Camelopardalis Giraffa, or Giraffe — some-
times called the Camelopard, from the fact that the skin is
spotted like that of the Leopard, whilst the neck is long, and
gives it some distant resemblance to a Camel. There are no
upper canines in the Giraffe, and both sexes possess two small
frontal horns, which, however, are persistent, and remain per-

UNGULATA. 437

manently covered by a hairy skin, terminated by a tuft of long
stiff bristles. The neck is of extraordinary length, but, never-
theless, consists of no more than the normal seven cervical
vertebrae. The fore-legs appear to be much longer than the
hind-legs, and all are terminated by two toes each, the supple-
mentary toes being altogether wanting.

Fossil species of Giraffe have been discovered in the Ter-
tiary deposits of the Siwalik Hills in India and in the Upper
Miocene of Attica; and a species has also been described
from France. This last, however, would seem to be referable
to the genus Helladotherium, founded for the reception of some
singular fossils from the Upper Miocene Tertiary of Attica.
In this remarkable genus there appear to have been no horns,
and 'the teeth present certain resemblances to those of the
Antelopes.

e. Cavicornia. — The last family of the Ruminants is that of
the Cavicornia or Bovida, comprising the Oxen, Sheep, Goats,
and Antelopes. This family includes the most typical Rumi-
nants, and those of most importance to man. The upper jaw
in all the Cavicornia is wholly destitute of incisors and canines,
the place of which is taken by the hardened gum, against which
the lower incisors bite. There are six incisors and two canines
in the lower jaw, placed in a continuous series, and the molars
are separated by a wide gap from the canines. There are six
molars on each side of each jaw. Both sexes have horns, or
the males only may be horned, but in either case these ap-
pendages are very different from the " antlers " of the Cervidce.
The horns, namely, are persistent, instead of being deciduous,
and each consists of a bony process of the frontal bone — or
"horn-core" — covered by a sheath of horn. The feet are
cleft, but are furnished with accessory hoofs placed on the
back of the foot.

The Cavicornia comprise the three families of the Antilopidcz,
Ovida, and Bovidcz. The Antelopes form an extremely large
section, with very many species. They are characterised by
their slender deer-like form, their long and slender legs, and
their simple, cylindrical, annulated, or twisted horns, which are
usually confined to the males, but sometimes occur in the
females as well.

The above definition will not apply in all points to some
singular extinct forms usually referred to the Antilopida, nor
to one aberrant existing form — viz., the Prong-buck (Antilope
furcifer, or Antilocapra Americana). This extraordinary and
unique species differs from the typical Antelopes in having no
accessory hoofs, in having horns which have a snag in front,

438

ORDERS OF MAMMALIA.

and in the fact that the outer sheath of the horn is deciduous,
and not permanent. For these reasons, it has been proposed
to place the Prong-buck in a separate family (the Aniilocaprida) ;
but it is more convenient here to consider it as an aberrant
member of the Antilopidce.

Several species of Antelope have been described from the
Miocene and Pliocene deposits of Europe, but none of them
are of any special importance. Fossil Antelopes have also
been discovered in the bone-caves of Brazil, though no mem-
ber of this family is known at the present day as existing in
South America. By far the most remarkable fossils, however,
which have been generally referred to the Antilopidce, are those
on which the genera Sivatherium and Bramatherium have been
founded.

Sivatherium (fig. 357) is known by the single species S.
giganteum, discovered by Dr Falconer and Sir Proby Cautley
in the Tertiary deposits of the Siwalik Hills in India. The

Fig- 357- — Skull of Sivatlierium giganteum. Pliocene, India. (After Murie.)

most important peculiarity in Sivatherium is the structure of
the horns, of which the animal possessed two pairs. Both
pairs of horns were supported by bony " cores/' so that there
can be no hesitation in referring Sivatherium to the group of

UNGULATA. 439

the Cavicornia. The anterior horns, as shown by the shape
of the horn-cores, were simple; and if the posterior horns had
been of a similar form, then Sivatherium might have been
fairly regarded as merely a gigantic four -horned Antelope,
similar to the living Antilope (Tetraceros) quadricornis of
India. The posterior horns, however, are not only much
larger than the anterior, but they possess two snags or
branches — a peculiarity not to be paralleled amongst existing
Cavicornia, except in the Prong-buck. Dr Murie, however, in
an admirable paper on the affinities of Sivatherium, has drawn
attention to the fact that the Prong-buck sheds the sheath of
its horns annually, and has suggested that this may have also
been the case with the extinct form. This hypothesis is ren-
dered probable, amongst other reasons, by the fact that no
sheath has as yet been discovered surrounding the horn-cores
of either pair of horns in the Sivatherium. Upon the whole,
therefore, the above-mentioned zoologist would refer Siva-
therium to a distinct group which he terms Sivatherida, and
regards as being most nearly related to the Antilocaprida.

Bramatherium has been found in deposits of the same age as
Sivatherium, with which it agrees in its colossal dimensions
and its possession of two pairs of hollow horns. It differs from
Sivatherium, however, in certain details of minor importance.

The Sheep and Goats (Ovida) have mostly horns in both
sexes, and the horns are generally curved, compressed, and
turned more or less backwards. The body is heavier, and the
legs shorter and stouter, than in the true Antelopes. In the
true Goats (Capra) both sexes have horns, and there are no
lachrymal sinuses. The true Sheep (Ovis) are destitute of a
beard, and the horns are generally twisted into a spiral. Horns
may be present in both sexes, or in the males only.

The Sheep and Goats are of no importance as fossils, unless,
indeed, as believed by high authorities, the Musk-ox should be
referred to the Ovidcz. Here, however, it will be considered
as belonging to the Bovidce. Remains of both Sheep and Goats
have been discovered in various Post-Tertiary deposits in
Europe, but they present nothing of special interest.

The true Oxen (Bovida) are distinguished by having simple
horns, of a rounded shape, not twisted into a spiral. A few
remains of Bovidcz have been found in deposits of Pliocene
age, but the Oxen are essentially Post-Pliocene and Recent.
The most important Fossil Oxen are the Urus, the Aurochs,
the Bos longifrons of Owen, and the Musk-ox.

The Aurochs or Lithuanian Bison (Bos bison] can hardly be
considered as a fossil form, as it occurs in a living state in

440

ORDERS OF MAMMALIA.

Europe at the present day. Remains, however, of this large
ox are found in various prehistoric deposits.

The Bos longifrons of Owen, or " Small Short-horn," is in a
similar position to the Aurochs. According to Mr Boyd
Dawkins, this form (which is identical with the Bos frontosus
of Nilsson) has not been proved to occur in any Post-Pliocene
deposit, though it occurs plentifully in the bone-caves and
alluvia of the Recent or prehistoric period. It is believed by
the same high authority that the Bos longifrons is the ancestor
of our present Welsh or Scotch Cattle.

The Urus or Wild Bull (Bos primigenius\ though much
larger than our ordinary oxen, is believed to be specifically
undistinguishable from the domestic Ox (Bos taurus\ and it
was probably the parent of the larger varieties of European

Fig- 358.— Skull of the Urus (Bos primigenius). Post-Pliocene and Recent.

Oxen. It was a contemporary of the Mammoth, Woolly
Rhinoceros, Cave Lion, Cave Bear, Irish Elk, and other Post-
Pliocene Mammals, and it was in existence up to at least the
twelfth century.

The last of the Oxen which deserves notice is the curious
Musk-ox (Ovibos moschatus). This singular animal is at the
present day a native of Arctic America, and is remarkable for
the great length of the hair. It is called the Musk-ox, because
it gives out a musky odour. Like the Reindeer, the Musk-ox
had formerly a much wider geographical range than it has at
present — the conditions of climate which are necessary for its
existence having at that time extended over a veiy much

HYRACOIDEA — PROBOSCIDEA. 44!

larger area than at present. The Musk-ox, in fact, in Post
Tertiary times is known to have extended over the greater part
of Europe, remains of it occurring abundantly in certain of the
bone-caves of France. As already mentioned, high authorities
regard the Musk-ox as being truly a large Sheep, and as being,
therefore, referable to the Ovidce.

CHAPTER XXXIX.
ORDERS OF MAMMALIA— Continued.
HYRACOIDEA AND PROBOSCIDEA.

ORDER VII. HYRACOIDEA. — This is a very small order which
has been constituted by Huxley for the reception of two or
three little animals, which make up the single genus Hyrax.
These have been usually placed in the immediate neighbour-
hood of the Rhinoceros, to which they have some decided
affinities, and they are still retained by Owen in the section of
the Perissodactyle Ungulates.

The order is distinguished by the following characters : —
There are no canine teeth, and the incisors of the upper jaw
are long and curved, and grow from permanent pulps, as they
do in the Rodents (such as the Beaver, Rat, &c.) The molar
teeth are singularly like those of the Rhinoceros. According
to Huxley, the dental formula of the aged animal is —

. 2 — 2 o — o 4 — 4 3 — 3

^»4=5;*» 3-5-36,

The fore-feet are tetradactylous, the' hind-feet tridactylous, and
all the toes have rounded hoof-like nails, with the exception of
the inner toes of the hind-feet, which have an obliquely-curved
nail. There are no clavicles. The nose and ears are short,
and the tail is represented by a mere tubercle.

The living species of Hyrax inhabit Syria, Palestine, and
South Africa. No fossil representative of the order has as yet
been discovered. The Hyracotherium of the Eocene Tertiary,
however, received its name from its supposed affinities to the
living Hyrax.

ORDER VIII. PROBOSCIDEA. — The eighth order of Mammals
is that of the Proboscidea, comprising no other living animals

442

ORDERS OF MAMMALIA.

except the Elephants, but including also the extinct Mastodon
and Deinotherium.

The order is characterised by the total absence of canine
teeth ; the molar teeth are few in number, large, and trans-
versely ridged or tuberculate ; incisors are always present, and
grow from persistent pulps, constituting long tusks (fig. 359).

Fig- 359- — Skull of the Indian Elephant (Elephas Indicus). /Tusk-like upper incisors ;
m Lower jaw, with grinding molars, but without incisors ; n Nostrils, placed at the ex-
tremity of the proboscis.

In all the Elephants there are two of these tusk-like incisors in
the upper jaw, and the lower jaw is without incisor teeth. In
the Deinotherium this is reversed, there being two tusk-like
lower incisors and no upper incisors. In the Mastodons, the
incisors are usually developed in the upper jaw, and form tusks,
as in the Elephants ; but sometimes there are both upper^and
lower incisors, and both are tusk-like. The nose is prolonged
into a cylindrical trunk, movable in every direction, highly
sensitive, and terminating in a finger-like prehensile lobe (fig.
359). The nostrils are placed at the extremity of the proboscis.
The feet are furnished with five toes each, but these are only
partially indicated externally by the divisions of the hoof. The
feet are furnished with a thick pad of integument, forming the

PROBOSCIDEA.

443

palms of the hand and the soles of the feet. There are no
clavicles. The testes are abdominal throughout life. There
are two teats, and these are placed upon the chest.

The order Proboscidea comprises the three genera, Elephas
(with both living and extinct representatives), Mastodon, and
Deinotherium, the two latter being extinct. The order came
into existence in the Miocene period, in which it is represented
by all these three genera. The genus Elephas comprises the
living Asiatic and Indian Elephants. In all the Elephants,
whether living or extinct, the " tusks " are formed by an enor-
mous development of the upper incisors. The milk-tusks are
early shed, and never attain any great size. The permanent
tusks, however, grow from persistent pulps, attaining in old
males an enormous size. The lower incisors are absent, and
there are no other teeth in the jaws except the large molars,
which are usually two in number on each side of each jaw.
The molar teeth are of very large size, and are composed of
a number of transverse plates of enamel united together by
dentine. In the Indian Elephant the transverse ridges of
enamel are narrow and undulating, whilst in the African
Elephant they enclose lozenge-shaped intervals.

The surfaces of the molars are approximately flat, and the
plates of enamel form patterns which are very characteristic of

Fig. 360. — Molar of the Mammoth (ElepJtas primigeuius), upper jaw, right side,
half natural size. Post-Pliocene, a Grinding surface ; b Side view.

the different species. Subjoined are illustrations of the molars
of three of the most important Post-Pliocene Elephants (figs.
360-362).

444

ORDERS OF MAMMALIA.

No Elephant has as yet been discovered in the Miocene
deposits of Europe, but six species are known from strata of
this age in India. In the Pliocene period, Europe possessed
its Elephants, of which the most important is the Elephas
antiquus (fig. 362). This is essentially a southern form, and
is found in Pliocene strata in France and Italy. It survived
the Glacial period, and is found abundantly in various Post-
Pliocene deposits. It abounded in Post-Pliocene times chiefly
in Southern Europe, south of the Alps and Pyrenees ; and it is
only on the northern edge of this area that its remains are
found commingled with those of the Mammoth.

Fig. 361. — Molar tooth of Elephas meridionalis, one-third of natural size.
Pliocene and Post-Pliocene. (After Lyell.)

Fig. 362. — Molar tooth of Elephas antiquus. Penultimate molar, one-third 01
natural size. Post-Pliocene and Pliocene. (After Lyell.)

Of the Post-Pliocene Elephants by far the best-known and
most important is the Mammoth (Elephas primigenius}. This
remarkable form (fig. 363) was essentially northern in its dis-
tribution, never passing south of a line drawn through the
Pyrenees, the Alps, the northern shores of the Caspian, Lake
Baikal, Kamschatka, and the Stanovi Mountains (Dawkins).
It occurs in the prae-Glacial forest-bed of Cromer in Norfolk,
survived the Glacial period, and is found abundantly in Post-
Glacial deposits in France, Germany, Britain, Russia in Europe,
Asia, and North America, being often associated with the Rein-

PROBOSCIDEA.

445

deer, Lemming, and Musk-ox. That it survived into the ear-
lier portion of the human period is unquestionable, its remains
having been found in a great number of instances associated

B

bfl

-

with implements of human manufacture ; whilst in one instance
a recognisable portrait of it has been discovered, carved on
bone. From its great abundance in Siberia, it might have been
safely inferred that the Mammoth was able to endure a much

446 ORDERS OF MAMMALIA.

colder climate than either of the living species. This inference,
however, has been rendered a certainty by the discovery of the
body of more than one Mammoth embedded in the frozen soil
of Siberia. These specimens had been so perfectly preserved
that even microscopical sections of some of the tissues could
be made ; and in one case even the eyes were preserved.
From these specimens, we know that the body of the Mam-
moth was covered with long woolly hair.

Amongst other Elephants which occur in Post-Pliocene de-
posits, may be mentioned, as of special interest, the pigmy
Elephants of Malta. One of these — the Elephas Melitensis,
or so-called " Donkey-Elephant " — was not more than four
and a half feet in height. The other — the Elephas Falconeri,
of Busk — was still smaller, its average height at the withers not
exceeding two and a half to three feet.

The Mastodons in most respects closely resemble the true
Elephants, from which they are distinguished by their denti-
tion. As in the Elephants, the upper incisors grow from per-
manent pulps, and constitute long tusks ; but in the majority
of cases the Mastodons also possess lower incisors as well.

Fig. 364. — Third milk-molar of the left side of the upper jaw of Mastodon
Arvernensis, showing the grinding surface. Pliocene. (After Lyell.)

The two lower incisors, however, though tusk-shaped, did
not develop themselves to any extent, and often disappeared
in adult life. A more important distinction between the Ele-
phants and Mastodons is that the molar teeth of the latter are
not only more numerous, but have the peculiarity that their
crowns are furnished with nipple-shaped eminences or tubercles
placed in pairs (fig. 364). The Mastodons appear to have
commenced their existence in the Miocene period, being re-

CARNIVORA.

447

presented in strata of this age by four European and three
Indian species. In the Pliocene period, also, remains of
Mastodon are not infrequent;
and in North America the great
M. Ohioticus occurs plentifully in
deposits of Post-Pliocene age.

The last of the Probostidea is
the remarkable Miocene Mam-
mal known as the Deinotherium,
which is still referred by some
high authorities to the order
Sirenia.

This extraordinary animal has
hitherto only been found in
Miocene deposits, and little is
known of it except its enormous
skull (fig. 365). Molars and
praemolars were present in each
jaw, and the upper jaw was des-
titute of canines and incisors.

very large tusk-like incisors, which were not directed forwards
as in the true Elephants, but were bent abruptly downwards
(fig. 365). The animal must have attained an enormous size,
and it is probable that the curved tusks were used either in
digging up roots or in mooring the animal to the banks of
rivers, for it was probably aquatic or semi-aquatic in its habits.

Several species of Deinotherium have been indicated as
occurring in Europe, and a species has been noticed in the
Tertiary deposits of the Siwalik Hills by Dr Falconer and Sir
Proby Cautley.

Fig. 365. — Skull of Deinotherium
giganteum. Miocene Tertiary.

In the lower jaw were two

CHAPTER XL.

ORDERS OF MAMMALIA— Continued.
CARNIVORA.

ORDER IX. CARNIVORA. — The ninth order of Mammals is that
of the Carnivora, comprising the Fera, or Beasts of Prey, along
with the old order of the Pinnipedia, or Seals and Walruses,
these latter being now universally regarded as merely a group
of the Carnivora modified to lead an aquatic life.

448 ORDERS OF MAMMALIA.

The Carnivora are distinguished by always possessing two
sets of teeth, which are simply covered by enamel, and are
always of three kinds — incisors, canines, and molars — differ-
ing from one another in shape and size. The incisors are

• -3 •?

generally - - (except in some Seals) ; the canines are always
3 3

- and are invariably much larger and longer than the in-

cisors. The prsemolars and molars are mostly furnished with
cutting or trenchant edges ; but they graduate from a cutting
to a tuberculate form, as the diet is strictly carnivorous, or
becomes more or less miscellaneous. In the typical Carnivores
(such as the Lion and Tiger), the last tooth but one in the
upper jaw, and the last tooth in the lower jaw, are known as
the " carnassial " teeth, having a sharp cutting edge adapted
for dividing flesh, and generally a more or less developed tu-
berculated heel or process. A varying number, however, of the
molars and praemolars may be " tuberculate/' their crowns
being adapted for bruising rather than cutting. As a general
rule, the shorter the jaw, and the fewer the praemolars and
molars, the more carnivorous is the animal. The jaws are so
articulated as to admit of vertical but not of horizontal move-
ments ; the zygomatic arches are greatly developed to give
room for the powerful muscles of the jaws ; and the orbits are
not separated from the temporal fossae.

In all the Carnivora\\\z clavicles are either altogether want-
ing, or are quite rudimentary. The toes are provided with
sharp curved claws.

The order Carnivora is divided into three very natural sec-
tions :—

Section I. Pinnigrada or Pinnipedia. — This section comprises
the Seals and Walruses, in which the fore and hind limbs are
short, and are expanded into broad, webbed swimming -paddles
(fig. 366, B.) The hind-feet are placed very far back, nearly
in a line with the axis of the body, and they are more or less
tied down to the tail by the integuments.

Section II. Plantigrada. — This section comprises the Bears
and their allies, in which the whole, or nearly the whole, of the
foot is applied to the ground, so that the animal walks upon
the soles of the feet (fig. 366, A.)

Section III. Digitigrada. — This section comprises the Lions,
Tigers, Cats, Dogs, &c., in which the heel of the foot is raised
entirely off the ground, and the animal walks upon the tips of
the toes (fig. 366, C.)

As regards their general distribution in time, if the little Mi-

CARNIVORA.

449

crolestes of the Upper Trias be Marsupial, as is almost certainly
the case, then the order Carnivora is comparatively modern, the
earliest undoubted remains having been found in the Eocene
Tertiary. In the Eocene period, however, the families of the
Canidce and Felidce appear to have been already differentiated.
The Ursidce, Viverrid(z,Mustelidce,Hy<znidcz, and Phocidce, do not
seem to have made their appearance before the Miocene period.
In the Pliocene and Post-Pliocene periods almost all the existing
types of the Carnivora are represented by extinct forms, whilst
in the latter the remains of various living species are found
associated with other animals which have at the present day
entirely passed away. In the following are given the charac-
ters and chief fossil forms of the families of the Carnivora.

Fig. 366. — Feet of Carnivora (after Owen). A, Plantigrada, Foot of Bear ;
B, Pinnigrada, Hind-feet of Seal; C, Digitigrada, Foot of Lion.

SECTION I. PINNIGRADA. — This section of the Carnivora
comprises the amphibious Seals and Walruses, which differ
from the typical Carnivores merely in points connected with
their semi-aquatic mode of life. The body is elongated, some-
what fish-like in shape, and terminated by a short conical tail.
All the four limbs are present, but they are very short, and the
five toes of each foot are united by the integuments, so as to
form powerful swimming-paddles. The hind-feet are placed
very far back, their axis nearly coinciding with that of the body
(fig. 366, B). Owing to this circumstance the hinder end of
the body forms an admirable swimming apparatus, similar in
its action to the horizontal tail-fin of the Cetacea and Sirenia.
The tips of the toes are furnished with strong claws, but the
powers of terrestrial locomotion are very limited. The ears are

2 F

45 O ORDERS OF MAMMALIA.

of small size, and are mostly only indicated by small apertures,
which the animal has the power of closing when under water.
The bones are light and spongy, and beneath the skin is a layer
of fat or blubber. The dentition varies ; but teeth of three
kinds are always present, in the young animal at any rate.
The canines are always long and pointed, and the molars are
generally furnished with sharp cutting edges.

The Seals (Phocida) are distinguished by having incisor
teeth in both jaws, and by the fact that the canines are not
immoderately developed. As regards their distribution in
time, the Seals are indicated as occurring in the Miocene and
Pliocene Tertiary; but their remains are by no means as
abundant as might have been anticipated from their aquatic
habits. Remains of Seals, however, are by no means very rare
in Post-Tertiary deposits.

The Walruses (Trichedda) are distinguished from the Seals
by their enormously -developed upper canines, which grow
from persistent pulps, and constitute great pointed tusks.
Remains of the Walrus have been found in some of the later
Tertiary deposits, but they are merely fragmentary, and are of
little importance.

SECTION II. PLANTIGRADA. — The Carnivorous animals be-
longing to this section apply the whole or the greater part of
the sole of the foot to the ground (fig. 366, A) ; and the por-
tion of the sole so employed is destitute of hairs in most
instances (the sole is hairy in the Polar Bear).

The typical family of the Plantigrade Carnivora is that of
the Ursida or Bears, in which the entire sole of the foot is
applied to the ground in walking. The Ursidcz are much less
purely carnivorous than the majority of the order, and, in
accordance with their omnivorous habits, the teeth do not
exhibit the typical carnivorous characters. The incisors and
canines have the ordinary carnivorous form, but the "carnas-
sial" or sectorial molar has a tuberculate crown instead of a
sharp cutting edge. The dental formula is—

4=4 2-2

. pm = //f - =

3—3 i— i 4—4 3—3

The claws are large, strong, and curved, but are not retrac-
tile. The tongue is smooth ; the ears small, erect, and rounded ;
the tail short ; the nose forms a movable truncated snout \ and
the pupil is circular.

The oldest known member of the Ursidce is the Amphicyon
of the Miocene Tertiary. In this genus the molars are tuber-
culated, as they are in the true Bears ; but, unlike the latter,

CARNIVORA.

there is an additional molar on each side of the upper jaw.
Several species have been described from deposits of Middle
Tertiary age.

The true Bears ( Urstis) do not appear, so far as is certainly
known, to have commenced their existence before the Pliocene
period, the best-known species of this epoch being the Ursus
Arvernensis. In the Post-Tertiary period the two most im-
portant species are the Ursus priscus and Ursus spelczus, of
which the former is probably identical with the living Grizzly
Bear ( Ursus ferox). The Cave-bear (Ursus spelceus, fig. 367)

Fig. 367.— Skull of Ursus sjtel<zus. Post-Pliocene.

is a gigantic Bear, which, as its name implies, has been found
mainly in cavern-deposits. The size of this species con-
siderably exceeded that of any existing Bear, and it is espe-
cially characteristic of the later portion of the Post-Pliocene
period.

More or less nearly allied to the true Bears are the little
living animals which are known as Coatis (Nasud), Racoons
(Procyoii), and Kinkajous (Cercoleptes\ all of which at the
present day are confined to the American continent. The
bone-caves of Brazil have yielded remains of two species of
Nastta, and a Racoon has been found in Post-Tertiary de-
posits in Illinois. No certain remains of Cercoleptes are known ;
but the Arctocyon primcevus of the Eocene Tertiary of France
has been compared with the existing Kinkajous.

The only remaining family of the Plantigrada is that of the
Melida or Badgers, characterised by their elongated bodies
and short legs, and by the fact that the carnassial tooth has a
partly cutting edge, and is not wholly tuberculate as in the
Bears.

452 ORDERS OF MAMMALIA.

Remains of Badgers have been found in Post-Tertiary de-
posits in Europe, and they are probably referable to the exist-
ing Mdes taxus. The Gluttons (Gulo) are also only known
from Post-Tertiary accumulations, and the so-called Gulo
spelczus of the cavern-deposits of Europe does not appear to
be separable from the common Wolverine (Gulo luscus).

SECTION III. DIGITIGRADA. — In this section of the Carni-
vora the heel is raised above the ground, with the whole or
the greater part of the metacarpus, so that the animals walk
more or less completely on the tips of the toes (fig. 366, C).
No absolute line, however, of demarcation can be drawn
between the Plantigrade and Digitigrade sections of the Car-
nivora, since many forms (e-g., Mustelidcz and Vrverrida) ex-
hibit transitional characters, and it has even been proposed
to place these in a separate section, under the name of Semi-
plantigrada.

The first family of the Digitigrada is that of the Mustelidcz
or Weasels, including a number of small Carnivores, with short
legs, elongated worm-like bodies, and a peculiar gliding mode
of progression (hence the name of Vermiformes, sometimes
applied to the group).

The most important fossil forms of the Mustdida belong to
the genera Mustela (comprising the Weasels and Stoats), and
Lutra (comprising the Otters). The Weasels appear to have
come into existence in the Miocene period, being represented
by several species in deposits belonging to this age. They
occur also in Pliocene and Post-Tertiary deposits. The Otters
are likewise known by their remains in strata of Miocene and
Pliocene age, and they occur in Post-Tertiary times.

The second family of the Semi-plantigrade Carnivores is that
of the Vtverridce, the Civets and Genettes. They are all of
moderate size, with sharp muzzles and long tails, and more or
less striped, or banded, or spotted. The carnassial molar is
trenchant ; the canines are long, sharp, and pointed ; and the
tongue is roughened by numerous prickly papillae. The claws
are semi-retractile, and the pupils can contract, on exposure to
light, till they resemble a mere line.

The genus Palceonyctis of De Blainville has been founded
upon a lower jaw obtained from the Eocene Tertiary of France,
and apparently referable to this family. The Miocene rocks
of France have yielded the remains of several species which
have been placed in the existing genus Viverra. Lastly, the
Hyanictis and Ictitherium of the Upper Miocene deposits of
Attica, appear to be intermediate in their characters between
the Viv err idee and ffycenidce.

CARNIVORA. 453

Forming a transition between the Viverridcz and the Felidce
is the family of the Hycznidcz, distinguished by the fact that,
alone of all the Carnivora, both pairs of feet have only four
toes each. The hind-legs are shorter than the fore-legs, so that
the trunk sinks towards the hind-quarters, and the tail is short.
The tongue is rough and prickly. The head is extremely
broad, the muzzle rounded, and the muscles of the jaw ex-
tremely powerful and well developed. The claws are non-
retractile. All the molars are trenchant except the last upper
molar, which is tuberculate. The upper carnassial has a small
internal tubercle, and the lower carnassial is wholly trenchant.

The earliest fossil member of the Hycenidce is the Hycena
Hipparionum of the Pliocene of France, and other species have
been obtained in the same country from strata of the same age.
Of the Post-Tertiary Hyaenas, the best known and most im-
portant is the great Cave-hyaena (Hycena spelcea, fig. 368).
This species in many respects resembles the Hyczna crocnta of

Fig. 368. — Skull of Hyana spelcea. Post- Pliocene.

South Africa ; and it inhabited Britain and the greater part of
Europe during the Post-Pliocene period. Its remains often
occur in great abundance, and no doubt can be entertained as
to its having survived into the human period.

Here may be considered the genus Hyanodon, which cannot
be referred either to the Hycznidcz or Felidce. This remark-
able genus has been detected in the Eocene Tertiary of Eng-
land, and the Miocene in France, and is noticeable for the
great number of its molars, as compared with the existing
Fdidce. The dental formula is —

-3 — 3 i — i 4 — 4 3 — 3

'&ri=i'.*'J:$s"J=J-*

All the praemolars and molars possessed trenchant edges,

454

ORDERS OF MAMMALIA.

and were compressed, so that the dentition of this extinct genus
is more highly carnivorous than is the case with any existing
Carnivore.

The next family is that of the Canidce, comprising the Dogs,
Wolves, Foxes, and Jackals. The members of this family are
characterised by having pointed muzzles, smooth tongues, and
non-retractile claws. The fore-feet have five toes each,

the hind-feet have only four. The molar teeth are

sometimes

7—7

7—7

7—7
, and of these, two or three on each side are

tuberculate. The carnassial has a tolerably large heel or
process.

Fig. 369. — Skull of Jackal (Canis aureus).

The true Dogs and the Wolves, forming the genus Canis,
and the Foxes ( Vulpes), can hardly be distinguished from one
another, as fossils, with any certainty. The oldest known
member of the Canidce is the Canis Parisiensis of the Upper
Eocene Tertiary (Gypseous series of Montmartre), which ap-
pears to be nearly allied to the existing Arctic Fox ( Vulpes
lagopus). Other species of Canis occur in the Miocene, Plio-
cene, and Post-Tertiary deposits ; and the so-called Canis
familiaris fossilis of the caves of Germany, Belgium, and France,
appears to be very nearly allied to the domestic Dog of the
present day. Similarly, the so-called Canis spelceus, and Canis
vulpes spelceus are nearly, if not quite, identical with the exist-
ing Wolf and Fox of Europe. Lastly, the Galcecynus of the
Pliocene schists of Oeningen, and the Pal&ocyon (Lund) of the
Brazilian caves, are two extinct genera which may be provision-
ally referred to the Canidce.

The last group of the Digitigrada is that of the Felidce, or Cat
tribe, comprising the most typical members of the whole order
of the Carnivora, such as the Lions, Tigers, Leopards, Cat, and
Panthers. The members of this family all walk upon the tips

CARNIVORA. 45 5

of their toes, the soles of their feet being hairy, and the whole
of the metacarpus and heel being raised above the ground (fig.
366, C). The jaws are short, and, owing to this fact, and to
the great size of the muscles concerned in mastication, the head
assumes a short and rounded form, with an abbreviated and
rounded muzzle. The molars and praemolars are fewer in
number than in any other of the Carnivora (hence the short-
ness of the jaws), and they are all trenchant, except the last
molar in the upper jaw, which is tuberculate. The upper car-
nassial has three lobes, and a blunt heel or internal process.
The lower carnassial has two cutting lobes, and no internal
process. According to Owen, the dental formula is —

. 3 — 3 l — I 3 — 3 l — l

'3=5; ^I-_zi;^2=r2;^I— , = 30.

The legs are nearly of equal size, and the hind-feet have only
four toes each, whilst the fore-feet have five. All the toes are
furnished with strong, curved, retractile claws, which, when not
in use, are withdrawn within sheaths by the action of elastic
ligaments, so as not to be unnecessarily blunted.

Fig. 370. — Skull of Lion (Felis led).

The Felidce probably came into existence in the Eocene
period ; but there is considerable uncertainty as to the remains
which have been cited from deposits of this age. Several spe-
cies of Felis have been indicated as occurring in Miocene
deposits, and still more numerous forms have been determined
from Pliocene strata. The most important and best known of
the Post-Pliocene Felida is the great Cave-lion (Felis spelcea\
which does not appear to be separable by any character of im-
portance from the existing Lion (Felis leo\ This species in-
habited Britain in times subsequent to the Glacial period, and

456 ORDERS OF MAMMALIA.

was a contemporary of the Cave-hyaena, Cave-bear, Woolly
Rhinoceros, and Mammoth. There can also be no doubt but
that the Cave -lion survived into the earlier portion of the
human period.

The only other member of the Felidcz which deserves men-
tion, is the "sabre-toothed" Tiger (Machairodus), species of
which are known to have existed from the Miocene period up
to the Post-Pliocene. In this singular genus the upper canines
were greatly elongated, trenchant, and sabre - shaped, with
finely-serrated margins. There is no upper true molar, and
the praemolars are reduced to two on each side of each jaw.
The dental formula is —

.3—3 I— I 2—2 0—0

' 3—3 ; c 7=1 ; /« « ; *i=r=26-

Species of Machairodus must have been as large as a Lion ;
and the genus is not only European, but is also represented by
a form in South America, and another in India.

CHAPTER XLI.

ORDERS OF MAMMALIA— Continued.
RODENTIA, CHEIROPTERA, AND INSECTIVORA.

ORDER X. RODENTIA. — The tenth order of Mammals is that
of the Rodents, often spoken of as Glires, comprising the Mice,
Rats, Squirrels, Rabbits, Hares, Beavers, &c.

The Rodentia are characterised by the possession of two
long curved incisor teeth in each jaw, separated by a wide in-
terval from the molars. The lower jaw never has more than
two of these incisors, and the upper jaw very rarely; but some-
times there are four upper incisors. There are no canine
teeth, and the molars and praemolars are few in number (rarely
more than four on each side of the jaw). The feet are usually
furnished with five toes each, all of which are armed with claws ;
and the hallux, when present, does not differ in form from the
other digits.

The most characteristic point about the Rodents is to be
found in the structure of the incisors, which are adapted for
continuous gnawing — hence the name of Rodentia. The in-
cisor teeth are commonly two in each jaw, and they grow from

RODENTIA.

457

persistent pulps, so that they continue to grow throughout the
life of the animal. They are large, long and curved (fig. 371,

Fig. 371. — A, Skull of the Beaver (after Owen). B, Diagram of the incisor teeth 01
a Rodent, showing the chisel-shaped point : a Enamel ; d Dentine.

B), and are covered anteriorly by a plate of hard enamel. The
back part of each incisor is composed only of the comparatively
soft dentine, so that when the tooth is exposed to attrition, the
soft dentine behind wears away more rapidly than the hard
enamel in front. The result of this is that the crown of the
tooth acquires by use a chisel-like shape, bevelled away behind,
and the enamel forms a persistent cutting edge (fig. 371).

The gnawing action of the incisors is assisted by the articu-
lation of the lower jaw, the condyle of which is placed longi-
tudinally and not transversely, so that the jaw slides backwards
and forwards. The molars, consequently, have flat crowns, the
enamelled surfaces of which are always arranged in transverse
ridges, in opposition to the antero-posterior movement of the
jaw.

The earliest known traces of the Rodents in past time have
been discovered in the Eocene Tertiary. The order comprises
a large number of families, only the more important of which
can be noticed here.

Fain. i. Leporida. — In this family are the Hares and Rabbits
(Lepus], and the Pikas (Lagomys), distinguished amongst the
Rodents by the possession of two small incisors in the upper
jaw, placed behind the central chisel-shaped incisors, so that
there are four upper incisors in all. The molars and prsemolars
are rootless, and the dental formula is —

.2 — 2

o — o

; pm

i— i ' - o—o' •"" 2—2' 3—3
The clavicles are imperfect. The fore-legs are furnished

45 8 ORDERS OF MAMMALIA.

with five toes, and are considerably shorter than the hind-legs,
which have only four toes. The two orbits communicate by
an aperture in the septum. Generally there is a short erect tail.

Species of Lepus, more or less nearly allied to the existing
Hares and Rabbits, are found in the Miocene and Pliocene
Tertiary of Europe ; whilst the Post-Tertiary deposits of the
same area have yielded remains almost or quite identical with
living species. The cave-deposits of Brazil have also yielded
the bones of a hare very nearly allied to the living Lepus
Brasiliensis. The Calling Hares or Pikas (Lagomys), which
are distinguished by their nearly complete clavicles and rudi-
mentary tail, and which at the present day are characteristic of
Siberia, are found in the Pliocene of Oeningen and in Post-
Tertiary deposits in Britain and Southern Europe.

Fam. 2. Cavidcz. — In this family are the living Capybaras
(Hydrochcerus), Agoutis (Dasyprocta), Pacas (Coelogenys), &c.,
characterised by their absence of clavicles, their rudimentary
tail, their unguiculate toes, and their general possession of
eight rootless molars in each jaw. Almost all the existing
members of this family belong to South America, and this
continent has been peopled during Post-Tertiary times with
numerous species more or less nearly allied to living forms.
Thus, the Brazilian bone-caves have yielded to the researches
of Lund remains of Guinea-pigs (Ancema), Agoutis, Pacas, and
Capybaras, all of which appear to belong to extinct species.

Fam, 3. Hystricidcz. — In this family are the well-known Por-
cupines, distinguished from the other Rodents by the fact that
the body is covered with long spines or " quills," mixed with
bristly hairs. They have four molars on each side of each jaw,
and they possess imperfect clavicles.

Remains of Porcupines allied to the existing species of
Hystrix have been detected in the Pliocene and Post-Pliocene
deposits of Europe and Asia. On the other hand, the bone-
caves of Brazil have yielded the remains of a Porcupine with
a prehensile tail, allied to the living Cercolabes of South
America.

Fam. 4. Castoridce. — The best-known example of this family
is the Beaver (Castor fiber}. The distinctive peculiarities of
the family are the possession of distinct clavicles, the posses-
sion of five toes to each foot, and the fact that the hinder feet
are mostly webbed, adapting the animal to a semi-aquatic life.

The genus Castor, comprising the existing Beaver, and
characterised by the possession of a flattened scaly tail, is re-
presented by fossil species in the Miocene and Pliocene de-
posits of Europe. The Castor spelceus of the European cave-

RODENTIA. 459

deposits does not appear to be specifically separable from the
existing Beaver (Castor fiber]. The great Trogontherium (fig.
372) of the Post-Tertiary de-
posits of Europe, also appears
to be generically inseparable
from Castor. The Castoroides
Ohioensis of the Post-Tertiary
period of North America
seems to be rightly referred
to a separate genus. The
only known species attained

J i . • Fie. 372. — J aw of i rogon thenum C nviert.

a comparatively gigantic size, Post-Pliocene,

reaching a length of about

five feet. The Chalicomys of the European Miocene and
Pliocene deposits appears to be nearly related to the Beavers ;
and the bone-caves of Brazil have yielded a species of Myopot-
amus nearly allied to the existing Coypu (Myopotamus coypus)
of South America.

Fam. 5. Muridcz. — The fifth family of Rodents is that of the
Murida, comprising the Rats, Mice, and Lemmings. In this
family the tail is long, always thinly haired, sometimes naked
and scaly. The lower incisors are narrow and pointed, and
there are complete clavicles. The hind-feet are furnished with
five toes, the fore-feet with four, together with a rudimentary
pollex.

Remains of Rats and Mice have been obtained in the Mio-
cene and Pliocene Tertiary of Europe, and the Post-Tertiary
forms are in several cases very nearly if not altogether un-
distinguishable from existing forms. The genus Cricetus, com-
prising the existing Hamster, is represented in Post-Tertiary
deposits by a form probably identical with the living C. vulgaris.
The Lemmings (Myodes) are represented by at least one species
in Post-Tertiary deposits in Britain, occurring after the Glacial
period, and being contemporary with " palaeolithic" man. The
Voles or Campagnols (Arvicola) commence in the Pliocene,
and are abundantly represented in Post-Tertiary deposits. The
Post-Glacial deposits of Britain have yielded remains of the
Arvicola pratensis, A. agrestis, and A. amphibia, the last of
which (the well-known " Water-rat") occurs also in Prae-
Glacial accumulations.

Fam. 6. Dipodidce. — The sixth family of the Rodents, which
is sufficiently important to need notice, is that of the Dipodidcz
or Jerboas, mainly characterised by the disproportionate length
of the hind-limbs as compared with the fore-limbs. The tail
also is long and hairy, and there are complete clavicles.

460 ORDERS OF MAMMALIA.

Remains of a species of Jerboa (Dipus) have been discovered
in Miocene deposits in France, but they are of no special im-
portance.

Fam. 7. Myoxidce. — The members of this family are com-
monly known as Dormice, and they are often included in the
following family of the Squirrels and Marmots.

They resemble the Squirrels in most respects, but they have
only four molars on each side of the upper jaw, whereas the
latter possess five. Two species of Myoxus have been detected
in the Upper Eocene (Gypseous series of Montmartre), and a
third species has been determined from beds of Miocene age.
Several species have been detected in Post-Tertiary deposits,
of which the most remarkable is the comparatively gigantic
Myoxus Melitensis of the Maltese Post-Pliocene.

Fam. 8. Sciuridcz. — This is the last family of Rodents which
calls for any special mention, and it comprises the true Squir-
rels, the Flying Squirrels, and the Marmots.

The members of this family are distinguished by their pointed
or compressed incisors and their tubercular molars, the upper
jaw having five of the latter on each side, whilst the lower jaw
has only four. The genus Sciurus, comprising the true Squir-
rels, is represented from the Eocene Tertiary upwards, but
none of the fossil forms are of special interest. The genus
Arctomys, comprising the Marmots, is represented in the Plio-
cene by a single species, and by several forms in the Post-
Tertiary. The Pouched Marmots (Spermophilus), lastly, ap-
pear for the first time in the Miocene ; and Britain possessed
two species in times posterior to the Glacial period.

ORDER XL CHEIROPTERA. — This order is undoubtedly " the
most distinctly circumscribed and natural group " in the whole
class of the Mammalia. In many respects, however, it would
be advantageous to regard the Cheiroptera as a sub-order of
the next order (namely the Insectivord), specially modified to
lead an aerial life ; just as the Pinnigrada are regarded as a
mere section of the Carnivora specially modified to suit an
aquatic life.

The Cheiroptera are essentially characterised by the fact that
the anterior limbs are longer than the posterior, the digits of
the fore -limb, with the exception of the pollex, being enor-
mously elongated (fig. 373). These elongated fingers are
united by an expanded membrane or "patagium," which is
also extended between the fore and hind limbs and the sides
of the body, and in many cases passes also between the hind-
limbs and the tail. The patagium thus formed is naked, or
nearly so, on both sides, and it serves for flight. Of the fingers

CHEIROPTERA.

461

of the hand, the pollex, and sometimes the next finger as well,
are unguiculate, or furnished with claws ; but the other digits
are destitute of nails. In the hind-limbs all the toes are un-
guiculate, and the hallux is not in any respect different from
the other digits. Well-developed clavicles are always present,
and the radius has no power of rotation upon the ulna. The
mammary glands are two in number, and are placed upon the
chest. There are teeth of three kinds, and the canines are
always well developed. The molars are tuberculate or grooved
in the frugivorous forms, and cuspidate in the insectivorous
species. The ulna is sometimes quite rudimentary. The
bones are not pneumatic.

Fig- 373.— Skeleton of Fox-bat (Pteropus)— after Owen.

The living Bats are divided into the two groups of the
Frugivorous Bats, comprising the single family of the Pteropidcz
(Fox-bats or Roussettes), and the Insectivorous Bats, com-
prising the three families of the Vespertilionidce, the Rhinolo-
phidos (Horse-shoe Bats), and the Phyllostomida (Vampire
Bats). The Cheiroptera are represented for the first time in
the Eocene Tertiary of Europe, and that by a form very
similar to the existing European Bats. The fossil in question
is the Vespertilio Parisiensis (fig. 374) of the Gypseous series
of Montmartre (Upper Eocene). Other species of small In-

462 ORDERS OF MAMMALIA.

sectivorous Bats ( Vespertilid) have been discovered in Miocene,
Pliocene, and Post-Tertiary deposits. The Horse-shoe Bats
(Rhinolophus) have as yet only been discovered in cave-
deposits. Lastly, the Vampire Bats are represented by no
less than five species in the Post-Pliocene cave-deposits of
Brazil, in which country is found the living Phyllostoma
spectrum.

Fig. 374. — Vespertilio Parisiensis. Upper Eocene.

ORDER XII. INSECTIVORA. — The twelfth order of Mammals
is that of the Insectivora, comprising a number of small Mam-
mals which are very similar to the Rodents in many respects,
but want the peculiar incisors of that order, and are likewise
always furnished with clavicles.

In the Insectivora, all the three kinds of teeth are usually
present, but the exact nature of the dentition varies consider-
ably in different cases. The incisors and canines present
little special, but the molars are always serrated with nume-
rous, small, pointed eminences or cusps, adapted for crushing
insects. With one exception, clavicles are always present in a
complete form. All the feet are usually furnished with five
toes ; all the toes are furnished with claws ; and the animal
walks on the soles of the feet, or is plantigrade.

The earliest traces of Insectivorous Mammals are in the
Eocene Tertiary (the Spalacodon of the Upper Eocene of
Hordwell, discovered by Mr Flower). The order, however,

INSECTIVORA.

Fig. 375. — Insectivora. Skull of
the common Hedgehog (Erinaceus
Europceus).

does not become well represented till we reach the Miocene
period.

The three leading families of the Insectivora are the Talpidce
or Moles, the Soricidcz or Shrew-
mice, and fasErinaceida or Hedge-
hogs.

Fam. i. Talpidce. — The body in
this family is covered with hair ;
the feet are formed for digging and
burrowing, and the toes are fur-
nished with strong curved claws.

The earliest remains of Talpidce
appear for the first time in the
Miocene Tertiary ; but they are of
little importance. The common Mole (Talpa Europcea) occurs
in Post-Pliocene deposits in Britain and on the Continent.
Several genera (Dimylus^ Palceospalax, Geotrypus, &c.)~ have
been founded upon remains of Mole-like animals from the
Miocene and later Tertiary deposits.

Fam. 2. Soricidcz. — The Soricidce or Shrew-mice are distin-
guished by having the body covered with hair, and the feet
not adapted for digging ; whilst there are external ears, and
the eyes are well developed. Of all the Insectivora, no divi-
sion is more abundant or more widely distributed than that of
the Shrew-mice. In general form and appearance the Shrews
very closely resemble the true Mice (Muridce) and the Dor-
mice (Myoxidcz), but they are in reality widely different, and
must not be confounded with them.

Remains of Shrews (belonging to the genera Sorex, Mysa-
rachne, and Plesiosorex) have been discovered in the Miocene
deposits of Europe. Several existing species (such as Sorex
araneus and S. fodiens] occur in Post-Tertiary cave-deposits
and ossiferous breccias. Lastly, the Desmans (Mygale) are
represented from the Miocene Tertiary onwards.

Fam. 3. Erinaceidcz. — The last family of the Insectivora is
that of the Hedgehogs, characterised by the fact that the upper
part of the body is covered with prickly spines, the feet are
not adapted for digging, and the animal has mostly the power
of rolling itself into a ball at the approach of danger.

Several species of Hedgehog have been found in the fossil
state, commencing in the Miocene Tertiary. The Erinaceus
fossilis of the Post-Tertiary period, does not appear to be
separable from the common species (Erinaceus Europczus}.

464 ORDERS OF MAMMALIA.

CHAPTER XLII.
ORDERS OF MAMMALIA— Concluded.

QUADRUMANA AND BlMANA.

ORDER XIII. QUADRUMANA. — The thirteenth order ot Mam-
mals is that of the Quadrumana, comprising the Apes, Mon-
keys, Baboons, Lemurs, &c., characterised by the following
points : —

The hallux (innermost toe of the hind-limb) is separated
from the other toes, and is opposable to them, so that the
hind-feet become prehensile hands. The pollex (innermost
toe of the fore-limbs) may be wanting, but when present, it
also is usually opposable to the other digits, so that the animal
becomes truly quadrumanous, or four-handed.

2 — 2 3 — 3

The incisor teeth generally are - — , and the molars -

3 2—2' 3—3

with broad and tuberculate crowns. Perfect clavicles are
present. The teats are two in number, and are pectoral in
position.

The Quadrumana are divided by Owen into three very
natural groups, separated from one another by their anato-
mical characters and by their geographical distribution as
follows : —

STREPSIRHINA.

This section of the Quadrumana is characterised by the
possession of twisted or curved nostrils, placed at the end
of the snout. The incisor teeth are generally much modified,

«^ __,_ _ ^ t *y -,- ^

and are in number as a rule ; the praemolars are -

3 — 3 3 — 3

2 2

or - — and the molars are tuberculate. The second digit
2 — 2'

of the hind-limb has a claw, and both fore and hind feet have
five toes each, all the thumbs being generally opposable. In
the true Lemurs, all the digits, except the second toe of the
hind-feet, are furnished with nails.

This section is often called that of the Prosimicz, and it in-
cludes several families, of which the Aye-Ayes, Pottos, and
true Lemurs are the most important.

No member of the Strepsirhine division of the Quadrumana
has as yet been discovered in the fossil condition. When,

QUADRUMANA. 465

however, those regions of the world have been properly ex-
plored in which these forms occur at the present day, we shall
doubtless find extinct representatives of this group. The
Strepsirhine Monkeys, namely, are at present confined to
Madagascar, Western Africa, and the Indian Archipelago ;
and these regions are as yet almost unknown, palaeontologi-
cally speaking.

PLATYRHINA.

The section of the Platyrhine Monkeys is exclusively con-
fined to South America, and one of its leading characters is to
be found in the almost universal possession of a prehensile
tail ; this being an adaptive character by which the animal
is suited to the arboreal life which so many of the South
American Mammals are forced to lead. There are neither
cheek-pouches nor natal callosities, and there is an additional
praemolar, and sometimes a molar less than in man and the
Old World Monkeys. The nostrils are simple, wide apart,
and placed nearly at the extremity of the snout. The prae-

3 — 3
molars are - - in number, and have blunt tubercles. The

3 — 3

thumbs of the fore-hands are either wanting altogether, or, if

present, are not opposable, though versatile.

The fossil remains of Platyrhine Monkeys are only known
to occur in South America, to which country all the existing
forms are confined. Here, in deposits of late Tertiary or
Post-Tertiary age, have been found remains of Monkeys re-
ferable to the existing genera Cebus, Callithrix, and lacchus,
along with a large form which constitutes the extinct genus
Protopithecus, and which is allied to the recent Mycetes.

CATARHINA.

The third and highest section of the Quadrumana is that of
the Catarhina or Old World Monkeys. In this section the
nostrils are oblique, and are placed close together, and the
septum narium is narrow. The thumbs of all the feet are
opposable, so that the animal is strictly quadrumanous. In
Colobus alone the anterior thumbs (pollex) are wanting. The
dental formula is the same as in man, viz. : —

.2 — 2 i — i , .2 — 2 3 — 3

z - - ; c - - ; pmf j m * — * = 32.

2 — 2 i — i 2 — 2 3 — 3

The incisors, however, are projecting and prominent, and
the canines — especially in the males — are large and pointed.
Moreover, the teeth form an uneven series, interrupted by a

2 G

466 ORDERS OF MAMMALIA.

diastema or interval. The tail is never prehensile, and is
sometimes absent. Cheek-pouches are often present, and the
skin covering the tubera ischii is almost always callous and
destitute of hair, constituting the so-called " natal callosities."
With the single exception of a Monkey which inhabits the
Rock of Gibraltar, all the Catarhina are natives of Africa
and Asia.

The earliest traces of the Catarhine Monkeys (constituting
the oldest known relics of the entire order of the Qitadrumana)
appear in the Eocene Tertiary ; and they occur only in the
Old World, so far as is yet known. The Macacus eocanus of
the London Clay has now been referred to Hyracotherium ;
but the Coznopithecus lemur oides of Riitimeyer, from deposits of
Eocene age, appears to be an undoubted Monkey. Ccenopi-
thecus, however, cannot be referred with any certainty to the

Fig. 376. — Lower jaw of PliopitJiecus (Pitkecus) antiquus. Miocene.

Catarhina, its most marked affinities being with the genus
Mycetes on the one hand, and the Lemuridcz on the other. In
the Miocene deposits of Greece occur the remains of a Macaque
(Mesopithecus Pentelict) ; and in deposits of the same age in
France have been found the remains upon which have been
founded the genera Pliopithecus (fig. 376) and Dryopithcfus.
The former of these appears to have been most nearly allied
to the recent genus Semnopithecus, in which case it must have
possessed a tail and cheek-pouches. The latter appears to have
been more nearly allied to the living Gibbons (Hylobates), in
which case it must have been destitute of a tail and of cheek-
pouches.

Besides the above, the Pliocene (or Miocene) deposits of
India have yielded the remains of Semnopithecus, Macacus,

BIMANA.

467

and a form allied to the Orang. The Pliocene deposits of
France contain remains of the genera Semnopithecus, Macacus,
and Cercopithecus ; and a jaw of Macacus has been obtained
from similar deposits in Essex.

ORDER XIV. BIMANA. — This, the last remaining order of
the Mammalia, comprises Man (Homo) alone, and it will there-
fore require but little notice here, the peculiarities of Man's
mental and physical structure properly belonging to other
branches of science.

Zoologically, Man is distinguished from all other Mammals
by his habitually erect posture and bipedal progression. The
lower limbs are exclusively devoted to progression and to sup-
porting the weight of the body. The anterior limbs are shorter
than the posterior, and have nothing whatever to do with pro-
gression. The thumb is opposable, and the hands are pre-
hensile, the fingers being provided with nails. The toes of the
hind-limb are also furnished with nails, but the hallux is not
opposable to the other digits, and the feet are therefore useless
as organs of prehension. The foot is broad and plantigrade,
and the whole sole is applied to the ground in walking.

The dentition consists of thirty-two teeth, and these form a
nearly even and uninterrupted series, without any interval or
diastema. The dental formula is —

I — I

2 — 2

3' — 3

377-— A> Skull of the Orang-outang. B, Skull of an adult European.

The brain is more largely developed and more abundantly
furnished with large and deep convolutions than is the case
with any other Mammal. The mammae are pectoral, and the
placenta is discoidal and deciduate.

468 ORDERS OF MAMMALIA.

Man is the only terrestrial Mammal in which the body is
not provided with a covering of hair.

Palseontologically, there is little to be said about Man — or,
rather, so much might be said on this subject that its discus-
sion can only be properly taken up in a special treatise.
Man appeared upon the earth, so far as we know, only in the
last or Post-Tertiary period of Geology, and his remains, in
the form of bones or implements of various kinds, have been
detected in various Post-Tertiary accumulations, such as valley-
gravels and cave-deposits. The chief facts as to the past exist-
ence of man which concern the palaeontological student may
be briefly stated as follows : —

1. Man unquestionably existed during the later portion of
what Sir Charles Lyell has termed the " Post-Pliocene " period.
In other words, Man's existence dates back to a time when
several remarkable Mammals, to be afterwards mentioned, had
not yet become extinct ; but he does not date back to a time
anterior to the present Molluscan fauna.

2. The antiquity of the so-called Post-Pliocene period is
a matter which must be mainly settled by the evidence of
Geology proper, and need not be discussed here.

3. The extinct Mammals with which man coexisted in
Western Europe are mostly of large size, the most important
being the Mammoth (Elephas primigenius), the Woolly Rhino-
ceros (Rhinoceros tichorhinus), the Cave-lion (Felis spelaa),
the Cave-hyaena (Hycena spelced), and the Cave-bear (Ursus
spelceus). We do not know the causes which led to the ex-
tinction of these Post-Pliocene Mammals ; but we know that
no Mammalian species has become extinct during the historical
period.

4. The extinct Mammals with which man coexisted are re-
ferable in many cases to species which presumably required a
very different climate to that now prevailing in Western Europe.
How long a period, however, has been consumed in the bring-
ing about of the climatic changes thus indicated we have no
means of calculating with any approach to accuracy.

5. Some of the deposits in which the remains of man have
been found associated with the bones of extinct Mammals, are
such as to show incontestably that great changes in the phy-
sical geography and surface-configuration of Western Europe
have taken place since the period of their accumulation. We
have, however, no means at present of judging of the lapse of
time thus indicated except by analogies and comparisons which
may be disputed.

6. The human implements which are associated with the

BIMANA. 469

remains of extinct Mammals, themselves bear evidence of an
exceedingly barbarous condition of the human species. Post-
Pliocene or " Palaeolithic " Man was clearly unacquainted with
the use of any of the metals. Not only so, but the workman-
ship of these ancient races was much inferior to that of the
later tribes, who were also ignorant of the metals, and who
also used nothing but weapons and tools of stone.

7. Lastly, it is only with the human remains of the Post-
Pliocene period that the palaeontologist proper has to deal.
When we enter the " Recent " period, in which the remains of
Man are associated with those of existing species of Mammals,
we pass out of the region of pure palaeontology into the do-
main of the Archaeologist and the Ethnologist.

PART III.

PAL^OBOTANY

PAL^OBOTANY.

CHAPTER XLIII.

GENERAL RELATIONS OF PLANTS TO TIME.

THE subject of Palaeobotany or Palaeophytology is one which
is far too vast to be treated of in a work of this nature ; whilst
it is one which is of less importance to the general student than
that of Palaeozoology. For this reason, nothing further will be
attempted here than to give the briefest and most elementary
outline of the general distribution t)f plants in past time, to
which will be added a short summary of the chief forms of
vegetable life which characterise each of the great formations.
The following table shows the leading groups into which the
Vegetable Kingdom is divided : —

DIVISIONS OF THE VEGETABLE KINGDOM.

I. CRYPTOGAMIC PLANTS (Gr. kruptos, concealed ; gamos, marriage),
distinguished by having no distinct flowers or fruit. They include —

a. Thallogens. — Ex. Sea- weeds (Alga), Lichens, Mushrooms.

b. Anogens — Ex. Liverworts, Mosses.

c. Acrogens. — Ex. Club-mosses (Zy<r0/W/tf«?^), Ferns, Horse-tails (Equi-
setacece).

II. PHANEROGAMIC PLANTS (Gr. phaneros, conspicuous ; gamos, mar-
riage), distinguished by having distinct flowers and seeds. They are
divided into —

a. Endogens. — Ex. Grasses, Palms, Lilies. These have endogenous stems,
showing no rings of growth, and the young plant possesses but a single
seed-lobe or " cotyledon." Hence they are often called Monocotyledons.

b. Exogens. — Ex. Pines and Cycads, with most ordinary shrubs, trees,
and flowering plants. The Pines and Cycads, with the fossil Sigillarice,
have the seed naked, and are hence called Gymnosperms (Gr. gumnos, naked ;
sperma, seed). Ordinary trees and shrubs, on the other hand, have the
seed covered, and are therefore called Angiosperms. Both the Gymno-
sperms and Angiosperms have an exogenous mode of growth, with a true
bark and annual rings of growth. The seed also possesses two seed-lobes or
" cotyledons ; " and they are therefore often spoken of as Dicotyledons.

474 PAIwEOBOTANY.

The remains of Plants appear for the first time, so far as yet
known, in the Lower Cambrian series (jhtEophyton of the Fucoi-
dal Sandstone of Sweden) ; and from this time onward they are
never absent altogether from any of the great geological forma-
tions. The affinities of this earliest known plant are so dubi-
ous that it cannot be employed as proving the first appearance
of any of the great groups of plants. The Upper Cambrian
and Lower Silurian Rocks have yielded various remains of an
unquestionable vegetable nature, but of doubtful affinities — re-
ferred, however, with more or less probability, to Sea-weeds
(" Fucoids "). In the Upper Silurian Rocks have been detected
various Sea-weeds (Spirophyton, &c.), the spore-cases of Lyco-
podiaceous plants (Pachytheca}, Lepidodendron, and remains of
the remarkable generalised type Psilophyton, which is in some
respects intermediate between the Lycopodiacece (Club-mosses)
and the Ferns. In the Devonian period — as we now know,
from the researches of Dr Dawson of Montreal in particular-
plants are very abundant, and belong to varied types. The
great group of the Gymnospermous Exogens is here represented
by remains of various Conifers (Dadoxylon, Ormoxylon, and
Prototaxites}. The Ferns are represented by numerous species,
in many cases not far removed from types now in existence ;
and it is interesting to notice that Tree-ferns (Psaronius and
Caulopteris) are not wanting amongst these. The Lycopodiacea
or Club-mosses are represented in the Devonian Series by nu-
merous remarkable types, such as Lepidodendron, Lcpidophloios,
Cordaites, and Lycopodiies. The Sigillarioid plants, regarded
by different authorities as being Coniferous, or Lycopodiaceous,
or as being intermediate between the Acrogens and Gymno-
sperms — are represented by species of Sigillaria itself, with its
Stigmaria roots. The Horse-tails or Eqnisetacece are repre-
sented by species of the remarkable genus Catamites. The
genus Antkolithes, commonly supposed to be the spike of fruc-
tification of some phanerogamic plant, and now known to bear
the probably Gymnospermous fruit, Cardiocarpon — is repre-
sented by two species in the Devonian Rocks. Lastly, the
Devonian formation of the State of New York has yielded the
remains of an Angiospermous Exogen, which has been described
by Dr Dawson, under the name of Syringoxylon mirabile.

We thus see, even from such an imperfect summary as the
above, that we must abandon the old view that nothing like a
general and varied flora existed in times anterior to the Coal-
measures. We see that at a point of Palaeozoic time as early
as that represented by the Devonian formation, the earth ex-
hibited a far from scanty vegetation, composed of true land-

GENERAL RELATIONS OF PLANTS TO TIME. 4/5

plants, and embracing representatives of almost all the great
groups of plants which at present grow upon its surface. Thus,
we find in the Devonian Rocks representatives of the groups of
the Horse-tails, Club-mosses, Ferns, and Gymnospermous and
Angiospermous Exogens. We have, however, no certain re-
presentative of the great group of the Endogens, whilst the
Angiospermous Exogens are known by a single genus only,
represented by a single species. Upon the whole, therefore,
the vegetation of the Devonian period is characterised by the
predominance of Cryptogams and Gymnospermous Exogens.

Passing on to the Carboniferous period, we have to consider
the largest and most varied of the Palaeozoic floras, but one
which is in most respects very similar to that of the Devonian
period. Some Devonian genera of plants do not pass up into
the over-lying formation, and some of the Carboniferous genera
have not been recognised in the Devonian ; whilst hardly any
species are common to the two floras. Still, the general fades
of the Carboniferous vegetation is much the same as that of
the Devonian ; and the same groups predominate in the former
as in the latter, The predominant groups of plants in the Car- <f ,
boniferous Rocks are the Ferns (Filices), the Sigillarioids, the
Lepidodendroids, and the Calamites, of which all except the
Sigillarioids are certainly Cryptogams. Here, also, we have
the first instance of the occurrence of a Fungus (Archagari-
a>n). The Conifera are well represented by several genera
(Araucarioxylon, Dadoxylon, &c.), but no remains of trees
belonging to the Angiospermous Exogens have been as yet
detected. There are, however, a few flowering plants (such as
the Monocotyledonous Pothocites of the Scotch Carboniferous).
Lastly, the Carboniferous Rocks have yielded remains of the
genus Nwggerathia, referred by Brongniart to the peculiar Gym-
nospermous group of the Cycadacetz, but regarded by others as
belonging to the Ferns.

In the Permian period, the vegetation is nearly related to
that of the Coal-measures. We have still numerous Ferns
(Neuropteris, Pecopteris, Sphenopteris\ Tree-ferns (Psaronius\ the
Lycopodiaceous Lepidodendron, and Calamites. The Conifers,
also, are abundant, and belong to several genera. Some of the
Conifers, however (as Ullmania), bear genuine cones, and the
Sigillarioids, which are so characteristic of the Carboniferous
period, have apparently altogether disappeared in the Permian.

With the Trias we commence the great series of Mesozoic a&»
deposits, and there is a marked change in the vegetation of this
period as compared with that of the Carboniferous and Permian
epochs. The Lepidodendroids and Sigillarioids have now com-

476 PAL^EOBOTANY.

pletely disappeared. The Calamites of the Coal-measures are
represented by true Horse-tails (Equisetites). Ferns and Coni-
fers are still abundant, and some of the latter ( Voltzia) are by
no means unlike existing forms. Lastly, there is an abundance
of remains of Cycadaceous plants {Pterophyllum, Podozamites,
&c.)

The Jurassic and Lower Cretaceous deposits are similarly
characterised by an abundance of Cycads, Ferns, and Conifers,
the first of these in particular constituting a marked feature in
the vegetation.

In the Upper Cretaceous period we have the first appearance,
in any quantity, of ordinary Angiospermous Exogens, similar to
those which predominate at the present day in the flora of
temperate regions. Besides Ferns and Cycads more or less
allied to Jurassic forms, we have now numerous Dicotyledonous
trees, such as the Oak, Beech, Fig, Poplar, Walnut, Willow,
Alder, &c., belonging to familiar genera now in existence.
Here, also, we have trie first appearance, so far as is certainly
known, of the group of the Palms.

Of the vegetation of the Tertiary period, it is sufficient to
remark here that now there is a marked predominance of
Angiospermous Exogens and of Endogens as compared with
Cryptogams and Gymnospermous Exogens. Not only is this
the case, but many of the Tertiary plants approximate closely
to existing forms, this approximation becoming more and more
marked as we recede from the Eocene and approach the Re-
cent period.

Before closing this brief review of the succession of plants
upon the globe, it may be well to notice shortly a generalisa-
tion which was long since made by M. Adolphe Brongniart.
This distinguished observer, in dividing the series of stratified
deposits in accordance with the fossil plants contained in them,
p named the Palaeozoic period the " Age of Acrogens," the
Secondary period (exclusive of the Cretaceous) the " Age of
Gymnosperms," and the Cretaceous and Tertiary periods the
" Age of Angiosperms.J> This generalisation, though still ex-
pressing a general truth, can only be accepted with consider-
able reservation. Gymnosperms, and even Angiosperms, are
not unknown in the Palaeozoic period ; and if the Sigillarioids
should be referred to the former group of plants, then the later
Palaeozoic period would have as good claim to be called the
" Age of Gymnosperms " as the Secondary period. Again, as
pointed out by Sir Charles Lyell, the Lower and Upper Creta-
ceous floras differ from one another in the most striking manner,
the Lower Cretaceous agreeing in this respect with the Jurassic

PRE-CARBONIFEROUS FLORAS. 477

series, whilst the Upper Cretaceous series is linked on by its
plants to the Tertiary formations. The line, therefore, between
the Age of Gymnosperms and the Age of Angiosperms must
be drawn between the Lower and Upper Cretaceous, and not
at the base of the Cretaceous series.

CHAPTER XLIV.
PRE-CARBONIFEROUS FLORAS.

CAMBRIAN PLANTS. — The Laurentian and Huronian deposits
have as yet yielded no remains of plants ; but the occurrence
of graphite in large quantity in the former of these would
strongly support the view that the Laurentian period was not
without an abundant vegetation. The Lower Cambrian Rocks
have yielded many so-called " fucoids ; " but these are almost
invariably to be referred to the tracks and burrows of marine
worms. The only apparently unequivocal plant of the Lower
Cambrian period is the Eophyton (fig. 378) of the "Fucoidal
Sandstone " of Sweden. '

The singular fossils referred to this genus consist of straight,
furrowed, and striated stems, which can hardly be anything else
than the remains of plants. The affinities, however, of these
ancient fossils are quite undetermined, except that it seems
pretty certain that they cannot be referred to the Alga.

In the Upper Cambrian Rocks (Potsdam Sandstone) of
North America occur various so-called " Fucoids " (Palceophy-
cus, &c.) The true nature of these, however, is in many cases
very doubtful, and it is questionable if any of them can really
be regarded as plants.

Here, also, we may briefly consider certain remains dis-
covered by the author in the Skiddaw Slates of the North of
England, a formation which is probably referable to the Upper
Cambrian, but which good authorities regard as belonging to
the Lower Silurian series. The remains in question were
originally referred provisionally to the genera Btithotrephis and
Eophyton^ and the fossils which led to the former determina-
tion appear to be indubitable plants. They are thus described
by Dr Dawson in a note communicated to the author : —

I. Buthotrephis Harknessii. — This consists of what have been cylindrical
branches, given off from a central stem, and producing a few branchlets in
the manner of Pinnularia. Under the microscope the branches show a

478

PAL^OBOTANY.

vesicular structure; but this I believe to have been produced by the weather-
ing out of minute globular concretions, probably of calcareous matter. The
appearances are rather those of roots or slender herbaceous stems than of
Algae. If found in the Coal-measures it would probably be regarded as an
obscure Pinnularia.

2. Buthotrephis radiatus. — This shows radiating branchlets or leaves,
with the same vesicular structure as the preceding, and having some re-
semblance to the whorls of Annnlaria, though without any midrib.

It is quite possible that both of the above may belong to the same species.
If a land-plant, allied to Annularia, the first may represent the roots or sub-
aquatic stems, and the second its whorls of leaves. If an Alga, the first
may represent branching fronds, and the latter the fructification. Under the
former supposition, they may be compared with Annnlaria laxa of the
Devonian, and the radiating root-like bodies associated with it. — (Dawson,
' Report on Devonian Flora.') Under the supposition that the plants are
Algae, they may be compared with SpJuzrococcites Schurtzanus of Goeppert,
from the Lower Silurian (Etage D.) of Bohemia, though they do not come
under the technical definition of Sternberg's genus Spluzrococcites.

Fig. 378. — Fragment of Eophyton Linueanum. Lower Cambrian.

SILURIAN PLANTS. — The remains of plants in the Silurian
series are few in number and require little consideration. In

PRE-CARBONIFEROUS FLORAS.

479

the Lower Silurian Rocks no undoubted traces of land-plants
have hitherto been detected. The deposits of this period,
however, have yielded numerous fossils which have been re-
ferred to " Fucoids," under the generic titles of Palceophycus,
Licrophycus, Buthotrephis, Phytopsis, Sphenothallus, &c. Some
of these appear to be nothing more than the tracks of Annel-
ides. Others appear to be unquestionable plants ; but nothing
positive can be stated as to their affinities. They may be Algce,
or they may belong to plants higher in the vegetable scale.
Subjoined is an illustration of a characteristic Canadian species
described by Mr Billings (fig. 379).

Fig. 379. — Licrophycits Ottawaeiisis, a " Fucoid" from the Trenton Limestone
(Lower Silurian) of Canada. After Billings.

In the Upper Silurian Rocks are also numerous remains ot
" Fucoids " (Arthrophycus, Dichwlites, Chondrites, Spirophyton,
&c.), which do not differ in any important point from those ot
the inferior division. Some of these can hardly be anything
but true plants, and would certainly seem to be the remains of

480 PAL^EOBOTANY.

genuine Sea-weeds. Besides these problematical fossils, how-
ever, the Upper Silurian Rocks have been shown to contain
the remains of genuine land-plants. Thus, remains of the
Lycopodiaceous genus Lepidodendron (Sagenaria) have been
discovered in the Upper Silurian of Germany and Bohemia.
At the summit of the Upper Silurian series in Britain have
been detected numerous seed-vessels or " sporangia " referred
by Hooker to a Lycopodiaceous plant under the generic title
of Pachytheca. Lastly, the Upper Silurian of North America
has yielded remains of the characteristic Devonian genus Psilo-
phyton, which will be described immediately.

DEVONIAN PLANTS. — The plants of the Devonian period
belong to the groups of the Equisetacea (Horse-tails), Lyco-
podiacece (Club-mosses), Filices (Ferns), Sigillarioids, and Coni-
fer a — the whole constituting an abundant terrestrial vegetation.
Besides the above, however — as already mentioned — the re-
mains of a true Angiospermous Exogen have in one instance
been detected in Devonian strata (Dawson).

The Equisetacece are represented by species of the remarkable
genus Calamites, the characters of which will be briefly spoken
of when treating of the Coal-plants.

The Lycopodiacea are represented by the genera Lepidoden-
dron, Lycopodites, Leptophlaum, Lepidophloios, Cordaites, and
Psilophyton. The Lepidodendroids will be shortly discussed
under the head of the plants of the Carboniferous series ; but
Cordaites and Psilophyton merit special notice here. The
genus Cordaites is common both to the Devonian and the
Carboniferous formations, and includes broad, striated, parallel-
veined leaves, which are extremely abundant in certain beds.
They possess broad clasping bases, and may attain a length of
a foot and a breadth of as much as three inches. Their affini-
ties are disputed j but they are regarded by Dr Dawson as
referable to some Lycopodiaceous plant.

The genus Psilophyton of Dawson (fig. 380) commences its
existence in the Upper Silurian Rocks ; but it is character-
istically Devonian, and is not known to be represented in the
Carboniferous period. The following is given by Dr Dawson
as the definition of the genus : —

" Stems branching dichotomously, and covered with inter-
rupted ridges. Leaves rudimentary, or short, rigid, and pointed ;
in barren stems, numerous and spirally arranged; in fertile
stems and branchlets, sparsely scattered or absent ; in decor-
ticated specimens represented by minute punctate scars. Young
branches circinate ; rhizomata cylindrical, covered with hairs
or ramenta, and having circular areoles irregularly disposed,

PRE-CARBONIFEROUS FLORAS.

481

Fig 380. — Psilophyton prtnceps (Dawson). a
Rhizome ; b Stem ; c Termination of a branch ;
d Vernation ; e Fructification, — all of the natural
size ; g Areole of rhizome enlarged ; h Restoration
of the plant, reduced. Devonian of Canada.

2 H

482 PAL^EOBOTANY.

giving origin to slender cylindrical rootlets. Internal structure
— an axis of scalariform vessels, surrounded by a cylinder of
parenchymatous cells, and by an outer cylinder of elongated
woody cells. Fructification consisting of naked oval spore-
cases, borne usually in pairs on slender curved pedicles, either
lateral or terminal/'

Species of Psilophyton occur all through the Devonian series
of North America, and they are also not wanting in the Old
Red Sandstone of Britain. The genus is regarded by Dr
Dawson as comprising "synthetic or generalised plants, having
rhizomata resembling those of some ferns, stems having the
structure of Lycopodium, and rudimentary leaves also resem-
bling those of Lycopodiacecz, branchlets with circinate verna-
tion like that of Ferns, and sporangia of a type quite peculiar
to themselves."

The Ferns of the Devonian period are very numerous, and
upon the whole present a close resemblance to those of the
Carboniferous period. The smaller forms are represented by
such genera as Cyclopteris, Nenropteris, Sphenopteris, Alethop-
teris, Pecopteris, &c. Besides these, however, there occur the
trunks of large Tree-ferns, which are referred to the genera
Psaronius, Caulopteris, and Protopteris. Subjoined is an illus-
tration of a Fern from the Devonian of Europe (fig. 381).

The Sigillarioids of the Devonian series comprise forms
referable to the well-known genera Sigillaria (with Stigmarid)
and Calamodendron ; though the affinities of the last are not
well understood. The characters of these genera will be
noticed in treating of the plants of the Carboniferous series.

The Coniferce of the Devonian Rocks belong to the genera
Dadoxylon, Ormoxylon, and Prototaxites. All of these are
exogenous trees with concentric rings of growth, and the two
former are undoubtedly Coniferous, as their woody tissue
exhibits discs under the microscope. Prototaxites, unlike the
preceding, occurs in the Lower Devonian series, and is there-
fore the oldest Exogenous tree at present known to us. The
woody fibres do not exhibit punctations, and there is there-
fore some doubt as to the exact position of this genus.

In addition to the preceding forms, the Devonian Rocks have
yielded examples of the fossils known as Sternbergia, Cyperites,
Aster ophyllites, Anmtlaria, Pinnularia, Cardiocarpon, and Tri-
gonocarpon. Of these, the genus Sternbergia comprises cylin-
drical, transversely-marked fossils, which are now known to
be nothing more than the casts of the pith-cylinders of other
plants. They seem chiefly to belong to Conifers of the genus
Dadoxylon, but they are referable also to Sigillaria, and even

PRE-CARBONIFEROUS FLORAS.

483

to Lepidodendron. When the plant to which they belong is
itself preserved, there is no difficulty in recognising the true

Fig. 381. — Sphenopteris lajcus. Devonian.

nature of the Sttmbcrgia ; but when the outer wood has been
denuded, it becomes almost impossible to determine to what
plant they may have belonged. The genus Cyperites comprises
elongated linear leaves, which appear truly to be the leaves
of Sigillarice. The genus Aster ophyllites (fig. 382) comprises
elegant plants with ribbed and jointed stems. The joints of
the stems give off verticils of leaves, or branchlets bearing
whorls of leaves, which are narrow, elongated, and furnished
with a single midrib. This genus is not only found in the
Devonian Series, but is commonly represented in the Coal-
measures, to which the species here figured belongs.

The genus Annularia comprises plants which are of doubt-
ful affinities, but which possessed slender stems bearing at in-
tervals whorls of leaves. The Annularice appear to have been

PAL^EOBOTANY.

floating plants, and they occur in both the Devonian and
Carboniferous formations.

Fig. 382. — Asterophyllitesfoliosus. Coal-measures. (After Lindley and Hutton.)

The fossils known as Pinnularice are slender stem-like bodies,
with a smooth or striate surface, producing at right angles long
slender branchlets. The genus Pinnularia is regarded by
Dawson as being founded upon the roots of other plants, such
as Asterophyllites or Calamites.

Lastly, we find in the Devonian Rocks the little fruits
known as Cardiocarpon and Trigonocarpon, which are so abun-
dant in the Coal-measures. The Cardiocarpa appear mostly
to have been winged achenes or " samaras ; " but it is not
altogether certain by what plants they were produced. It is
now known, however, that the so-called Antholithes consists of
a spike, bearing Cardiocarpa protected by bracts ; and there is
a considerable probability that they were produced by Sigil-

larioid trees. Trigonocarpon (fig. 383)
comprises nut-like fruits, often of
considerable size, and commonly
three- or six- angled. The exterior of
the fruit was probably fleshy, and well-
preserved specimens show the integu-
ments, and the internal cavity at one
time filled by the albumen and em-
bryo. Trigonocarpon is probably the
fruit of a Conifer, and it shows a de-
cided resemblance to the solitary fruit of the existing Taxoid
genus, Salisbnria. Possibly, however, Dr Dawson is correct
in his conjecture that most of the Trigonocarpa belonged really
to Sigillarioid plants.

Fig. 383. — Trigonocarpon ova-
turn. Coal-measures. (After
Lindley and Hutton.)

THE CARBONIFEROUS AND PERMIAN FLORAS. 485

CHAPTER XLV.
THE CARBONIFEROUS AND PERMIAN FLORAS.

CARBONIFEROUS PLANTS. — The most extensive and the best
known of the Palaeozoic Floras is that which flourished during
the Carboniferous period. At this time were formed those
vast accumulations of vegetable matter which we know as
coal; and much of our information as to the Carboniferous
plants is due to the value of coal, and to the vigour with which
coal-mining has been prosecuted.

Coal consists of nearly pure carbon, with varying proportions of hydrogen
and oxygen and a small quantity of mineral matter. The following are the
conclusions arrived at by Dr Dawson as to the minute structure of coal : —
I. The so-called "mineral charcoal" or "mother coal" consists chiefly of
" bast-tissue " or of elongated cells derived from the inner bark of Sigillaricp
and Lepidodendra. 2. Besides the above, the mineral charcoal contains in
many instances scalariform tissue derived from Ferns, Sigillarite, Lepido-
dendra, &c. 3. The coarse and laminated portions of the coal are made
up of vascular bundles, derived apparently in the main from Ferns, along
with other vegetable fragments, and in some cases, though not to a great
extent, the sporangia of some of the Carboniferous Cryptogams. 4. In
many parts of the coal occur discigerous or punctated woody fibres, be-
longing to Dadoxylon, Sigillaria, and Calamodendron. 5. A considerable
portion of the coal is made up of " epidermal tissue," which is "a dense
cellular tissue representing the outer integuments of various leaves, herba-
ceous stems, and fruits. " 6. The layers of bright shining coal are com-
posed of the flattened stems, and chiefly of the bark, of Sigillarice and
other trees. 7. Some layers of coal are occasionally composed mainly of
the compressed leaves of Cordaites. 8. Sporangia are often present in
coal ; but they rarely exist in such a proportion as to any extent actually to
form the coal themselves.

As has been already observed, the types of plants which
are found in the Carboniferous Rocks are to a great extent
identical with those which composed the Devonian flora.
Specifically, however, the coal-plants are almost always distinct
from the Devonian forms. The number of plants already
known to have existed during the Carboniferous period is so
great, that nothing more can be done here than to draw the
attention of the student to some of the more important and
characteristic types.

a. Filiccs. - - The Ferns of the Carboniferous period are
extremely numerous, and include both herbaceous forms like
the majority of existing species, and arborescent forms similar
to the living Tree-ferns of New Zealand. The latter belong
to the genera Psaronius, Caulopteris, and Palceopteris, of which
the two former occur in the older Devonian period. Of the

486

PAIwEOBOTANY.

smaller ferns, the genera Sphenopteris, Pecopteris, Alethopteris,
Odontopteris, Neuropteris, Hymenophyllites, and Cyclopteris may
be mentioned as the most important and widely distributed.
In the genus Neuropteris (fig. 384) the midrib of the leaflets is

Fig. 384. — Neuropteris heterophylla. Coal-measures of Europe. The lower figure
shows a single leaflet enlarged.

evanescent, either not distinct, or disappearing towards the
apex. Species of this genus are found in the Coal-formation
over almost the whole world. In Alethopteris the leaflets are
attached by their bases to the stem and to one another, and
are provided with a very distinct midrib from which the veins
are given off nearly at right angles. The commonest species
is the cosmopolitan Alethopteris (Pecopteris') lonchitica, which
nearly resembles the living Brackens (Pteris aquilina). Nearly
allied to Alethopteris is the genus Pecopteris, which includes a

THE CARBONIFEROUS AND PERMIAN FLORAS. 487

large number of characteristic Carboniferous species. In
Odontopteris (fig. 385) the frond is pinnate, the leaflets being
attached by their entire bases, and the veins are generally
given off from the base. The species here figured is a widely-
distributed one, occurring in both Europe and North America.

Fig. 385. — Odontopteris Schlotheimii. Carboniferous of Europe and North America.

In the genus Sphenopteris, the leaflets are narrow towards their
bases, often assuming a wedge-like form, the nervures dividing
in a pinnate manner from the base.

Lastly, in the genus Hymenophyllites the frond exhibits a
general resemblance to Sphenopteris, but the margin is divided
into lobes, into each of which a single nervure is continued.

b. Calqinites* — Amongst the commonest and most charac-
teristic of the plants of the Carboniferous period are the
striated fossils which are known as Catamites. Long as these
have been known, and carefully as they have been studied,
there is still no unanimity of opinion as to the affinities of
these plants. The prevalent modern view, however, is that
Calamites are truly referable to the Equisetacea, and that they
may be regarded as gigantic Horse-tails — though they differ
in many respects from any existing forms. The Calamites
were " slender, ribbed, and jointed externally, and from the
joints there proceeded, in some of the species, long, narrow,
simple branchlets ; and, in others, branches bearing whorls of
small branchlets or rudimentary leaves. The stem was hollow,
with thin transverse floors or diaphragms at the joints, and it

488

PAL^OBOTANY.

had no true wood and bark, but only a thin external shell of
fibres and scalariform vessels. The Catamites grew in dense

fig. 386. — Calamites cantue/ormis. Carboniferous of Europe and North America.

brakes on the sandy and muddy flats, subject to inundation,
or perhaps even in the water, and they had the power of
budding out from the base of the stem, so as to form clumps

THE CARBONIFEROUS AND PERMIAN FLORAS. 489

of plants, and also of securing their foot-hold by numerous
cord-like roots proceeding from various heights on the lower
part of the stem. The fruit was a long cone or spike, bearing
spore-cases under scales" (Dawson, Acadian Geology, p. 441).
Besides the true Calamites, the Carboniferous Rocks have also
yielded the remains of the genus Equisetites, which differed
from the Calamites, and agrees with the existing Horse-tails
in having sheaths at the joints.

Calamites often attain a comparatively gigantic size — twenty
feet or more in length ; and though they generally occur as
prostrate and flattened stems, they are not uncommonly found
in an erect and uncompressed condition, standing as they grew.
The fossils known as Asterophyllites have been referred to
Calamites, of which they were at one time supposed to consti-
tute the foliage ; but this opinion has been shown to be pro-
bably incorrect.

c. Calamodendron. — A good deal of the confusion which has
prevailed as to the true nature of Calamites appears to have
arisen out of the problematic fossils now generally referred to
the genus Calamodendron. As ordinarily found, Calamodendra
present themselves in the form of jointed and longitudinally-
ribbed cylindrical steins, which are hardly separable from
Calamites, except that they show no " areoles," or points
whence leaves or branchlets have been given off. From the
examination, however, of complete specimens, it has been
shown that Calamodendron, as thus constituted, is really nothing
more than the cast of the pith or medullary cavity of a com-
plex woody stem, thus resembling in its nature the fossils
known as Sternbergia. Round the internal axis thus consti-
tuted there is found in perfect examples a thick woody envel-
ope, composed of ligneous wedges arranged concentrically and
separated by intervening tracts of cellular tissue (or " medul-
lary rays "). The external surface of the stem is not known,
but the woody wedges are stated to consist of " elongated
cells, and porous, discigerous, or pseudo-scalariform tissue."
The affinities of Calamodendron are uncertain. It is regarded
by different authorities as belonging to the Gymnospermous
Exogens or to the Acrogens, or as a connecting form between
these groups. In any case, it is necessary to distinguish very
carefully between Calamodendron and Calamites, the latter
being clearly separated by the absence of a woody envelope,
and the presence of whorled leaves or branchlets at the arti-
culations of the stem.

d. Lepidodendroids. — Under this head we have to consider
the genera Lepidodendron and Lepidophloios, generally regarded

490

PALyEOBOTANY.

as gigantic extinct members of the Club-moss family (Lycopo-
diacece). The genus Lepidodendron (fig. 387) comprises nume-

Fig. 387. — Lepidodendron Sternbergii. Carboniferous.

rous large arborescent plants, which attain their maximum in
the Carboniferous period, but which appear to commence in
the Upper Silurian, and are well represented in the Devonian.
The trunk in some cases reached a length of fifty feet or more,

THE CARBONIFEROUS AND PERMIAN FLORAS. 49 1

and the branches are given off in a regular, bifurcating manner.
The bark is marked with numerous rhombic or oval scars,
arranged in quincunx order, and indicating the points where
leaves were formerly attached. The branches were covered
with slender, pointed leaves, closely crowded together; and
the fructification was carried at the ends of the branches in
the form of cones or spikes. These cones have generally been
described under the name of Lepidostrobi ; and they consist of
a central axis, surrounded by imbricated scales or bracts, each
of which supports a sporangium or spore-case.

In internal structure, Lepidodendron possesses a large cen-
tral pith, surrounded by a continuous sheath of scalariform
vessels. Outside this, again, is a thick bark, composed mainly
of elongated fibres or " bast-tissue," with a thin dense outer
rind.

The genera, or sub-genera, Sagenaria> Knorria, and Aspidiaria,
are properly to be referred to Lepidodendron. The genus Le-
pidophloios, however, is represented in both in Devonian and
Carboniferous Rocks by forms which are generically distinct
from Lepidodendron. The genus includes Lycopodiaceous
trees which have " thick branches, transversely elongated leaf-
scars, each with three vascular points, and placed on elevated
or scale-like protuberances, long one-nerved leaves, and large
lateral strobiles in vertical rows or spirally disposed " (Daw-
son).

e. Sigillarioids. — The three chief genera included under this
head are Sigillaria, Rhytidolepis, and Favularia, of which the
first is the most important. The Sigillarioids commence their
existence, so far as known, in the Devonian period, but they
attain their maximum in the Carboniferous ; and — unlike the
Lepidodendroio\s — they are not known to occur in the Per-
mian period. They are comparatively gigantic in size, often
attaining a height of from thirty to fifty feet or more; but
though abundant and well preserved, great divergence of
opinion prevails as to their true affinities. The name of Sigil-
larioids (Lat. sigilla, little seals or images) is derived from the
fact that the bark is marked with seal-like impressions or leaf-
scars (fig. 388).

According to Dawson, Sigillaria proper is distinguished by
its strong ribs, " which are usually much broader than the
oval or elliptical tripunctate areoles, and are striated longi-
tudinally." The stem consists of a central pith, which is trans-
versely partitioned, as in the so-called Sternbergice. The pith
is surrounded by a woody cylinder, consisting of ligneous
wedges, composed of punctated (discigerous) and scalariform

4Q2 PAL^OBOTANY.

vessels, and separated by medullary rays. Outside the woody
axis is an inner bark composed of long durable fibres of
" bast-tissue," the whole surrounded by a thick outer bark of
dense cellular tissue. " The trunk when old lost its regular
ribs and scars, owing to expansion, and became furrowed like
that of an Exogenous tree." The roots, as will be seen im-
mediately, constitute the fossils known as Stigmaria. The

Fig. 388. — Fragment Q{ Sigillaria Gr&seri. The left-hand figure shows a small
portion enlarged. Carboniferous.

leaves are believed to be the so-called Cyperites, long, narrow,
rigid, and two- or three- nerved. The fruits are supposed to
be Trigonocarpa, " borne in racemes on the upper part of the
stem." Upon the whole, Dr Dawson is disposed to adopt the
view, originally put forth by Brongniart, that the Sigillaria
find their nearest living allies in the Cycads, and that if not
actually referable to the Gymnospermous Exogens, they may
be intermediate between these and the higher Acrogens.

Mr Carruthers, on the other hand, describes Sigillaria as
consisting of a central cellular pith or medulla, surrounded by
a sheath consisting wholly of scalariform vessels, the whole
enveloped in an external cortical mass of cellular tissue. The
medullary sheath is perforated by meshes for the passage out-
wards of the vascular bundles which go to the axial appendages
(the leaves and branches) ; but there are no true medullary
rays. Upon these grounds, Mr Carruthers decides against
the view that Sigillaria is a Gymnospermous Exogen, and he
regards it as Cryptogamic and Lycopodiaceous. He also dis-

THE CARBONIFEROUS AND PERMIAN FLORAS. 493

credits the assertion that discigerous tissue is present, and
describes the fruit as consisting of cones or strobiles.

Leaving the botanical position of Sigillaria thus undecided,
we find that it is now almost universally conceded that the
fossils originally described under the name of Stigmaria are
the roots of Sigillaria, the actual connection between the two
having been in numerous instances demonstrated in an un-
mistakable manner. The Stigmaricz (fig. 389) ordinarily pre-
sent themselves in the form of long, compressed or rounded

Fig. 389. — Stiginariajicoides. Quarter natural size. Carboniferous.

fragments, the external surface of which is covered with
rounded pits or shallow tubercles, each of which has a little
pit or depression in its centre. From each of these pits there
proceeds, in perfect examples, a long cylindrical rootlet ; but
in many cases these have altogether disappeared. In its
internal structure, Stigmaria exhibits a central pith surrounded
by a sheath of scalariform vessels, the whole enclosed in a
cellular envelope. The Stigmaricz are generally found ramify-
ing in the " underclay," which forms the floor of a bed of coal,
and which represents the ancient soil upon which the Sigillaria
grew.

Of the remaining genera of the Sigillarioids, Rhytidolepis is
the most important. It is characterised by the possession of
large, hexagonal, tripunctate areoles, and narrow, often trans-
versely striate ribs. In Favularia, lastly, the smaller branches
were destitute of ribs, with elliptical, spirally-disposed areoles.
The stem branched dichotomously — like that of a Lepidoden-
dron — and the leaves were broad, with numerous parallel veins,
approximating to the leaves of Cordaites.

f. Conifera. — True Conifers have long been known to occur
in the Carboniferous Rocks. They belong to the genera
Dadoxylon, Palaoxylon, Araucarioxylon, and Pinites. They

494 PAL^OBOTANY.

are recognised by the great size and concentric rings of their
prostrate, rarely erect trunks, and by the fact that the micro-
scope exhibits punctated fibres in their wood. Their fruit is
unknown, unless, as is very probable, it is constituted by the
so-called Trigonocarpa, If this be the case, the Carboniferous
Conifers must have been " Taxoid," resembling the recent
Yews in producing berries instead of true cones. The so-
called Sternbergicz, as has been already pointed out, are " pith-
cylinders/' or, in other words, casts of the pith, of Dadoocylon,
They appear, however, to belong also to Sigillaria and Lepido-
phloios.

g- C2cJ*ji9££&' ~ ' The peculiar group of Gymnospermous
Exogens represented at the present day by the Cycads is not
known with certainty to be represented in the Carboniferous
Rocks. Noeggerathia has been referred here, and the Cyca-
daceous genus Pteropiiyllum has also been alleged to occur.
Brongniart has also conjectured that the Sigillarioids are in
reality most nearly allied to the Cycadacecz ; and this opinion
is supported by other high authorities.

h. Angiospermous Exogens. — The occurrence of true Angio-
sperms in the Carboniferous period is very doubtful. No
Exogenous wood which is not Coniferous has been as yet
detected. The fossil known as Antholithes, which was at one
time conjectured to be possibly the infloresence of an An-
giosperm, has now been shown to be really a raceme bearing
the fruit termed Cardiocarpon ; and it remains uncertain to
what plant this really belongs.

i. Monocotyledons . — The occurrence of Endogens in the
Coal-formation is also attended with some uncertainty. The
genus Nceggerathia has sometimes been referred to the Palms,
and the same group has been asserted to be represented by
species of Palmacites. The only apparently unequivocal proof
of the occurrence of Carboniferous Endogens is, however,
afforded by the so-called Pothocites, which appears to have
been the spadix of an Aroideous plant.

PERMIAN PLANTS. — The Permian Flora is, upon the whole,
very nearly allied to that of the Coal-measures, though the
Permian species are mostly distinct, and there are some new
genera. Thus, we find species of Lepidodendron, Catamites,
Equisetites, Asterophyllites, Anmdaria, &c. — all genera which
are highly characteristic of the Carboniferous period. On the
other hand, the Sigillarioids of the Coal appear to have finally
passed away with the close of the Carboniferous period.

Ferns are abundant in the Permian Rocks, and belong for
the most part to the well-known Carboniferous genera Alethop-

THE CARBONIFEROUS AND PERMIAN FLORAS. 495

teris, Neuropteris, Sphenopteris, and Pecopteris. There are also
Tree-ferns referable to the genus Psaronius. The singular

Fig. 390. — Neeggerathia expaiisa. Permian.

genus Neeggerathia (fig. 390) is also represented in the Permian
Rocks.

Fig. 391. — Walchia pintformis ; a Branch ; b Twig. From the Permian of Saxony.

(After Gutbier.)

The Conifers of the Permian period are numerous, and

496 PAL^OBOTANY.

belong in part to Carboniferous genera. A characteristic
genus, however, is Walchia (fig. 391), distinguished by its lax
short leaves. This genus, though not exclusively Permian, is
mainly so, the best-known species being the W. piniformis.
Here, also, we meet with Conifers which produce true cones,
and which differ, therefore, in an important respect from the
Taxoid Conifers of the Coal-measures. One of the most
characteristic of these is the Ullmania selaginoides, which oc-
curs in the Magnesian Limestone of Durham, the Middle
Permian of Westmorland, and the " Kupfer-schiefer " of
Germany.

CHAPTER XLVI.

FLORAS OF THE SECONDARY AND TERTIARY

PERIODS.

TRIASSIC PLANTS. — With the Trias we commence what has
been aptly termed the "Age of Cycads," from the predomi-
nance of the plants of this group in the Mesozoic vegetation.
The Cycads are a group of Gymnospermous Exogens, the
form and habit of growth of which present considerable re-
semblance to those of young Palms (fig. 392). The trunk is

Fig. 392. — Zaniia spiralis, a living Cycad. Australia.

unbranched, often shortened, and bearing a crown of pinnate
fronds. The leaves are usually " circinate " — that is, they un-
roll in expanding, like the fronds of Ferns. The ovules are
borne upon the edge of altered leaves, or are carried on the
scales of a cone. All the existing species of Cycads are

FLORAS OF SECONDARY AND TERTIARY PERIODS. 497

natives of warm countries, occurring in South America, the
West Indies, Japan, Australia, Southern Asia, and South
Africa. As has been already remarked, the occurrence of
genuine Cycads in the Carboniferous vegetation has not been
demonstrated, and the same holds good of all the Palaeozoic
floras. True Cycads, therefore, so far as known, make their
first appearance in the Trias, at the commencement of the Me-
sozoic period, where they are represented by the genera Ptero-
phyllum, Zamites, and Podozamites. Cycads continue to be
abundantly represented throughout the whole Mesozoic series;
but they have only been detected by a single dubious example
in strata of Tertiary age. The name " Age of Cycads," as
applied to the Secondary epoch, is, therefore, from a botanical
point of view, an exceedingly appropriate one.

Besides Cycads, the Triassic Rocks have yielded the re-
mains of Ferns, Equisetites, Calamites, and Conifers. The
Ferns belong mostly to the genera
Neuropteris, Pecofiteris, Acrostichites,
Crematopteris, Cydopteris, and Ano-
mopteris. A characteristic species of
the first of these is figured below
(fig. 393). The Conifers of the Trias,
lastly, are abundant, the most char-
acteristic genus being Voltzia. This
genus is related to the existing Cy-
presses, and many species of it are
found in the Triassic Rocks.

Fig- 393- — Neuropteris elegans. Trias.

JURASSIC PLANTS. — Taken as a whole, the Jurassic period
is characterised by the prevalence of Ferns, Cycads, and
Conifers ; no Palms or Angiospermous Exogens having been
as yet shown to occur.

The Cycads are extremely abundant, and belong chiefly to
the genera Pterophyllum, Otozamites, Zamites, Bucklandia, Cros-
sozamia, Williamsonia, Mantellia, &c. The " dirt-bed," as it

2 I

498

PAL/EOBOTANY.

is called, of the Purbeck beds, consists of an ancient soil, in
which stand erect the trunks of Conifers and the stems of
Cycads of the genus Mantellia (fig. 394). The fronds of

Fig. 394. — Mantellia (Cycadeoidea) megalophylla, a Cycad from the Purbeck
"dirt-bed." Upper Oolites.

Fig. 395. — Coniopteris Murravana. Great Oolite.

Cycads occur also in great abundance in various Jurassic
strata, especially in the lower portion of the series ; and the

FLORAS OF SECONDARY AND TERTIARY PERIODS. 499

cones likewise have been in some instances preserved. The
Conifers are represented by various genera more or less nearly
allied to the present Araucarice, and cones have been in a
few instances detected.

Ferns occur very abundantly in the Jurassic series, the
commonest genera being Coniopteris (fig. 395), Odontopteris
(fig. 396), Sphenopteris, Cyclopteris, Phlebopteris, Pecopteris,
Polypodites, Pachypteris, and T&niopteris.

Endogens are by no means unknown in the Jurassic series,
though no representative of the group of the Palms has been
as yet detected. Amongst the most important of the Oolitic
Endogens may be mentioned the Aroideous fruit described by
Mr Carruthers under the name of Aroides Stutterdi, and the
fruits known as Podocarya and Kaidacarpum, both of which
belong to the living order of the Pandanece, (Screw-pines).

Fig. 396. — Odontopteris cycadea. Lower Lias.

CRETACEOUS PLANTS. — The Lower Cretaceous Plants
greatly resemble those of the Jurassic period, consisting
mainly of Ferns, Cycads, and Conifers. The Upper Creta-
ceous Rocks, however, both in Europe and in North America,
have yielded an abundant flora which resembles the existing
vegetation of the globe in consisting mainly of Angiospermous
Exogens and of Monocotyledons. In Europe, the plant-re-
mains in question have been found chiefly in certain sands in

5oo

PAL^EOBOTANY.

the neighbourhood of Aix-la-Chapelle, and they consist of
numerous Ferns, Conifers (such as Cycadopteris), Screw Pines
(Pandanus], Oaks (Quercus), Walnut (Juglans], Fig (Ficus],
and many Proteacece, some of which are referred to existing
genera (Dryandra, Banksia, Grevillea, &c.)

In North America, the Cretaceous strata of New Jersey,
Alabama, Nebraska, Kansas, &c., have yielded the remains of
numerous plants, many of which belong to existing genera.
Amongst these may be mentioned Tulip-trees (Liriodendrwi},
Sassafras (fig. 397), Oaks (Quercus), Beeches (Fagus), Plane-

Fig. 397. — Cretaceous Angiosperms.— a, Sassafras Cretaceum; b, Liriodendron
Meekii; c, Leguminosites Marcouanus; d, Salix MeekiL (After Dana.)

trees (Platanus), Alders (Alnus\ Dog-wood (Cornus), Willows
(Salix}, Poplars (Popuhis), Cypresses (Cupressus), Bald Cy-
presses (Taxodiuni), Magnolias, &c. Besides these, however,
there occur other forms which have now entirely disappeared
from North America — as, for example, species of Cinnamomum
and Araucaria.

EOCENE PLANTS. — The Plants of the Eocene period ap-

AX

FLORAS OF SECONDARY AND TERTIARY PERIODS. 50 1

proximate on the whole to the existing vegetation of the earth.
They are, however, in the main most closely allied to forms
which now are found in tropical or sub-tropical regions. In
the London Clay occur numerous fruits of Palms (Nipadites^
fig. 398), along with various other plants, most of which in-
dicate a warm climate as prevailing in the South of England
at the commencement of the Eocene period. In the Eocene
strata of North America occur numerous plants, such as Palms,
Conifers, Magnolia, Cinnamon, Fig, Dog-wood, Maple, Hick-
ory, Poplar, Plane-trees, &c. Upon the whole, the Eocene
flora of North America is nearly re-
lated to that of the Miocene strata
of Europe, as well as to that now
existing in the American area. We
may conclude, therefore, that " the
forests of the American Eocene re-
sembled those of the European Mio-
cene, and even of modern America"
(Dana).

MIOCENE PLANTS. — The deposits
of the Miocene period have yielded
an extraordinarily large number of
plants, only a few of the more im-
portant of which can be indicated
here. Our chief sources of informa-
tion as to the vegetation of the Miocene period are derived
from the Brown Coals of Germany and Austria, the Lower

Fig. 398. — Nipadites ellip-
ticus. London Clay of Shep-
pey.

Fig. 399. — Miocene Palms. A, Chamarops Helvetica; B, Sabal major.
Lower Miocene of Switzerland and France.

and Upper Molasse of Switzerland, and the Miocene strata of
Greenland. The lignites of Austria have yielded very numer-

502

PAIwEOBOTANY.

otis plant-remains, chiefly of a tropical character \ one of the
most noticeable forms being a Palm of the genus Sabal (fig.
399, B), now found in America. The plants of the Lower
Miocene of Switzerland are also mostly of a tropical character,
but include several forms now found in North America, such
as a Tulip-tree (Liriodendron} and a Cypress (Taxodium).
Amongst the more remarkable forms from these beds may be
mentioned Fan-Palms (Cham&rops, fig. 399, A), numerous
tropical ferns, and two species of Cinnamon. The plant-
remains of the Upper Molasse of Switzerland indicate an
extraordinarily rank and luxuriant vegetation, composed
mainly of plants which now live in warm countries. Among
the commoner plants of this formation may be enumerated
many species of Maple (Acer), Plane-trees (Platanus, fig. 400),
Cinnamon-trees, and other members of the Lanracea, many
species of Proteacecz (Banksia, Grevillea, &c.), several species
of Sarsaparilla (Smilax\ Palms, Cypresses, &c.

Fig. 400. — Platanus aceroides. — a
Leaf ; b The core of a bundle of
pericarps ; c A single fruit or peri-
carp, natural size. Upper Miocene.

Fig. 401 . — Cinnamo-
m u m poly mo rph u >n . a
Leaf ; b Flower. Upper
Miocene.

In Britain, the Lower Miocene strata of Bovey Tracy have
yielded remains of Ferns, Vines, Fig, Cinnamon, Proteacece,
&c., along with numerous Conifers. The most abundant of
these last is a gigantic pine — the Sequoia Couttsicz — which is
very nearly allied to the huge Sequoia ( Wellingtonia) gigantea
of California. A nearly-allied form (Sequoia Langsdorffii) has
been detected in the leaf-bed of Ardtun in the Hebrides.

In Greenland, as well as in other parts of the Arctic regions,
Miocene strata have been discovered which have yielded a .
great number of plants, many of which are identical with
species found in the European Miocene. Amongst these

FLORAS OF SECONDARY AND TERTIARY PERIODS. 503

plants are found many trees, such as Conifers, Beeches, Oaks,
Maples, Plane-trees, Walnuts, Magnolias, &c., with numerous
shrubs, ferns, and other smaller plants.

Taking the Miocene flora as a whole, Dr Heer concludes
from his study of about 3000 plants contained in the European
Miocene alone, that the Miocene plants indicate tropical or
sub-tropical conditions, but that there is a striking intermixture
of forms which are at present found in countries widely re-
moved from one another. It is impossible to state with cer-
tainty how many of the Miocene plants belong to existing
species, but it appears that the larger number are extinct.
According to Heer, the American types of plants are most
largely represented in the Miocene flora, next those of Europe
and Asia, next those of Africa, and lastly those of Australia.
Upon the whole, however, the Miocene flora of Europe is
mostly nearly allied to the plants which we now find inhabit-
ing the warmer parts of the United States ; and this has led
to the suggestion that in Miocene times the Atlantic Ocean
was dry land, and that a migration of American plants to
Europe was thus permitted. This view is borne out by the
fact that the Miocene plants of Europe are most nearly allied
to the living plants of the eastern or Atlantic seaboard of the
United States, and also by the occurrence of a rich Miocene
flora in Greenland. As regards Greenland, Dr Heer has de-
termined that the Miocene plants indicate a temperate climate
in that country, with a mean annual temperature at least 30°
warmer than it is at present.

The present limit of trees is the isothermal which gives the
mean temperature of 50° Fahr. in July, or about the parallel
of 67° N. latitude. In Miocene times, however, the Limes,
Cypresses, and Plane-trees reach the 79th degree of latitude,
and the Pines and Poplars must have ranged even further
north than this.

PLIOCENE PLANTS. — The vegetation of the Pliocene period
is, upon the whole, so closely allied to that now existing as to
call for no special mention. It is worthy of notice, however,
that the Pliocene flora of Europe was strikingly similar to that
now existing in North America. Thus, we find in the Plio-
cene of Europe genera such as the Locust-trees (Robinia},
the Honey-locusts (Gleditschia], the Sumach (Rhus], the Bald
Cypress (Taxodium), the Tulip-tree (Liriodendrori), the Sweet-
gum Tree (Liquidambar\ the Sour-gum Tree (Nyssa), &c.,
which do not now occur in Europe, but are at present charac-
teristic forms in the flora of temperate North America.

PART IV.

HISTORICAL PALAEONTOLOGY

HISTORICAL PALEONTOLOGY.

CHAPTER XLVL
LAURENTIAN AND CAMBRIAN PERIODS.

IN this portion of the work it will be endeavoured very briefly
to give a view of the forms of life which characterised each of
the great geological periods. The subject of the fossils which
characterise each particular stratum or group of strata in the
earth's crust is one far too vast to be grappled with here, and
can only be properly considered in a special treatise. All that
will be attempted here is to give a short synopsis of the de-
posits of each successive era, followed by a general account of
the " life " of the period in which those deposits were laid
down. Such an account may be advantageously prefaced by
a tabular view of the more important fossiliferous deposits,
commencing with the most ancient.

TABULAR VIEW OF FOSSILIFEROUS STRATA.

I. PALAEOZOIC OR PRIMARY EPOCH.
( Terrains Paleozo'iques. )

i. LAURENTIAN.

a. Lower Laurentian. — British — Wanting. Foreign — Great series of

metamorphic rocks in Canada, gneiss, mica-schist, quartzite, and
limestones, with a total thickness of about 20,000 feet.

b. Upper Laurentian. — British — Fundamental Gneiss of the Hebrides (?) ;

Hypersthene Rocks of the Isle of Skye (?). Foreign — Labrador Series
of Canada, having a thickness of 10,000 feet, and resting unconform-
ably upon the Lower Laurentian.

2. HURONIAN.

British — Wanting (?). Foreign — About 18,000 feet of metamorphic rocks
resting unconformably upon the Laurentian series of Canada. Per-
haps the equivalent of the Lower Cambrian of other regions.

508 HISTORICAL PALEONTOLOGY.

3. CAMBRIAN.

a. Lower Cambrian. — British — Longmynd group of Shropshire; Harlech

Grits ; Llanberis Slates ; Green and purple slaty rocks of Wicklow,
containing Oldhamia. Foreign — Fucoidal Sandstone of Sweden, with
Eophyton ; Etages A and B of Barrande in Bohemia ; Huronian series
of Canada (?).

b. Upper Cambrian. — British — Lingula Flags of Shropshire and Wales.

Tremadoc Slates (?). Skiddaw Slates (?). Foreign — "Primordial
zone" of Bohemia; Alum-schists of Sweden and Norway; Potsdam
Sandstone and Calciferous Sand-rock of North America ; Quebec
group of Canada (?).

4. SILURIAN.

a. Lower Silurian. —

Britain.

1. Lower Llandeilo or Arenig Group.

2. Upper Llandeilo or Llandeilo Flags.

3. Caradoc, Bala, or Coniston Group.

4. Lower Llandovery Group.

North America.

1. Trenton Period (comprising the Chazy, Birds-eye, Black River,

and Trenton Limestones).

2. Hudson Period (comprising the Utica Shales and Hudson River

Group).
Bohemia.
\ Etage D of Barrande.

b. Upper Silurian.

Britain.

I. Upper Llandovery (comprising the Tarannon Shales and May
Hill Sandstone).

Wenlock Group (comprising the Woolhope Limestone, Wen-
lock Shale, and Wenlock Limestone).

Ludlow Group (comprising the Lower and Upper Ludlow
formations).
North America.

Niagara period (comprising the Oneida Conglomerate, Medina
Sandstone, Clinton Group and Niagara Limestone).

Salina period (comprising the Guelph Limestone and Onondaga
Salt Group).

Lower Helderberg period (comprising the Tentaculite and Water-
lime Groups, the Lower Pentamerus Limestone, the Delthyris
Shaly Limestone, and the Upper Pentamerus Limestone).
Bohemia.
Etage E.

F.

G.

5. DEVONIAN.

a. Lower Devonian. — British — Arbroath Paving Stones of Scotland ; Lin-

ton Group of Devonshire. Foreign — Oriskany Sandstone (?) and
Corniferous series of North America.

b. Middle Devonian. — British — Bituminous Schists of Caithness ; Ilfra-

combe Group of Devonshire. Foreign — Eifel Limestone of Europe ;
Hamilton series of North America.

TABLE OF FOSSILIFEROUS STRATA. 509

c. Upper Devonian. — British — Sandstones of Dura Den ; Sandstones of
Denholm Hill in Roxburghshire ; Kiltorcan beds of Ireland ; Pilton
and Petherwyn Group of South of England. Foreign — Clymenien-
Kalk, and Cypridinen-Schiefer of Germany ; Portage, Chemung, and
Catskill Groups of North America.

6. CARBONIFEROUS.

a. Lower Carboniferous. — British — Carboniferous Slates of Ireland ; Moun-

tain Limestone ; Yoredale Series. Foreign — Sub- Carboniferous Group
of North America.

b. Upper Carboniferous — British — Millstone Grit ; Coal- Measures. Foreign

— Equivalent beds in various parts of the world.

7. PERMIAN.

a. Lower Permian. — British — Lower Red Sandstones of North of Eng-

land. Foreign — Rothliegendes of Germany.

b. Middle Permian. — British — Marl Slate and Magnesian Limestone.

Foreign — Mergel-schiefer, Kupfer-schiefer, and Zechstein of Germany.

c. Upper Permian. — British — Gypseous Marls and Red Sandstones of the

North of England. Foreign — Bunter-schiefer of Germany.

II. MESOZOIC OR SECONDARY EPOCH.
( Terrains Secondaires. )

8. TRIASSIC SERIES.

a. Lower Trias. — British — New Red Sandstone of Lancashire and

Cheshire. Foreign — Bunter Sandstein of Germany.

b. Middle Trias. — British — Wanting. Foreign — Muschelkalk of Germany.

c. Upper Trias. — British — Red marls, salt, &c. (Keuper), of Cheshire ;

Penarth, Rhsetic, or Avicula contorta beds of Somersetshire, Glamor-
ganshire, &c. Foreign — Keuper beds of Germany ; Kossen (St
Cassian) and Hallstadt beds of the Austrian Alps.

9. JURASSIC SERIES.

a. Lower Oolites. — British — Lias, Inferior Oolite, Fuller's Earth, Great

Oolite, Stonesfield Slate, Cornbrash, and Forest Marble. Foreign —
The Sinemurien, Liasien, Toarcien, Bajocien, and Bathonien of
D'Orbigny.

b. Middle Oolites. — British — Kelloway Rock, Oxford Clay, Coral Rag.

Foreign — Nerinean Limestone of the Jura, Diceras Limestone of the
Alps.

c. Upper Oolites — British — Kimmeridge Clay, Portland Stone, Purbeck

beds. Foreign — Lithographic Slate of Solenhofen.

10. CRETACEOUS SERIES.

a. Lower Cretaceous. — British — Hastings Sands, Weald Clay, Lower

Greensand, Kentish Rag. Foreign — Neocomian of Neufchatel, Weal-
den of Hanover.

b. Upper Cretaceous. — British — Gault, Blackdown beds, Upper Green-

sand, Chalk Marl, White Chalk. Foreign — Quader Sandstein and
Planer Kalk of Germany, Hippurite Limestone of the South of
Europe, Maestricht Chalk, Faxoe Limestone, Sands and Marls of New
Jersey in North America.

5IO HISTORICAL PALEONTOLOGY.

III. KAINOZOIC OR TERTIARY EPOCH.
(Terrains Tertiaires.}

11. EOCENE SERIES.

a. Lower Eocene. — British — Thanet Sands, Plastic and Mottled Clays of

Woolwich, London Clay. Foreign — Sables de Bracheux and Argile
plastique of France. Claiborne beds of Alabama, United States.

b. Middle Eocene. — British — Bagshot, Bracklesham and Barton beds,

Headon Series, St Helens or Osborne Series. Foreign — Calcaire
Grossier of France ; Nummulitic Limestone of the Alps; Jackson
beds of the United States.

c. Upper Eocene. — British — Bembridge beds, Hempstead beds (Lower

Miocene?). Foreign — Gypseous Series of Montmartre in France,
Vicksburg and White River beds in the United States.

12. MIOCENE SERIES.

a. Lower Miocene. — British — Bovey Tracy lignites and clays, Leaf-beds of

Mull in the Hebrides. Foreign — Brown Coals of Germany and
Croatia, Lower Molasse of Switzerland.

b. Upper Miocene. — British — Ferruginous Sands of North Downs (?).

Foreign — Faluns of Touraine, Epplesheim Sands, Upper Molasse of
Switzerland, Oeningen beds of Switzerland, Siwalik beds of India.

13. PLIOCENE SERIES.

a. Older Pliocene. — British— White Crag and Red Crag of Suffolk.

Foreign — Upper and Middle Crags of Antwerp, Sub-Apennine beds.

b. Neiver Pliocene. — British — Norwich Crag. Foreign — Lacustrine Strata

of the Val d' Arno, near Florence.

14. POST-TERTIARY SERIES.

a. Post- Pliocene. — Cave-deposits, High-level and low-level gravels, Glacial

deposits, Forest-bed of Cromer, &c.

b. Recent. — Peat-mosses, recent river-gravels, lacustrine mud,&c.

LAURENTIAN PERIOD.

ROCKS OF THE PERIOD. — The Laurentian Rocks have their
typical development in North America, especially in Canada.
In northern New York strata of -this age rise into the lofty
and rugged elevations of the Adirondacks, and similar rocks
occur in another area to the south of Lake Superior. The
Laurentian series is of vast thickness, and is divided into
a lower and upper division. The Lower Laurentian group
attains the enormous thickness of about 20,000 feet, and is
composed entirely of metamorphic rocks, consisting mainly of
gneiss interstratified with mica-schist, with great beds of quartz,
and massive beds of crystalline limestone, of which one varies
from 700 to 1500 feet in thickness. Conglomerates also oc-
cur, and there are vast deposits of magnetic and specular iron-
ore. Graphite or black-lead occurs disseminated in strings,
veins, and beds, through hundreds of feet of Lower Laurentian
strata, and its amount is calculated by Dr Dawson to be equal

HURONIAN PERIOD. 511

in quantity to the coal-seams of an equal area of the Carbon-
iferous rocks.

Not only is the Lower Laurentian series of vast thickness
and greatly metamorphosed, but it must have been elevated
above the sea, and subjected to vast denudation, prior to the
deposition of the upper group. This is shown by the fact
that the Upper Laurentian lies unconformably upon the trun-
cated edges of the Lower Laurentian. The Upper Lauren-
tian group is about 10,000 feet thick, and consists wholly of
stratified crystalline rocks. These consist mainly of gneissic
and felspathic rocks, often characterised by the occurrence of
lime-felspar or Labradorite. The series is extensively devel-
oped in Labrador, and is sometimes spoken of as the " Labra-
dor series."

In Britain it has been conjectured, with great probability, that
the "fundamental gneiss" of the Hebrides and the "hypers-
thene rocks " of the Isle of Skye belong to the Laurentian series.

LIFE OF THE LAURENTIAN PERIOD. — The Laurentian rocks
are often spoken of as the Azoic series (Gr. a, without ; zoe,
life) ; but the name appears to be inappropriate, because there
is good evidence to show that living beings were in existence
in the Laurentian period. In the first place, it is certain that
the Laurentian rocks, though now highly metamorphic, were
originally deposited as ordinary sedimentary beds of sandstone,
conglomerate, shale, and limestone. There is, therefore, no
reason whatever for supposing that the seas of the Laurentian
period differed in any respect from modern seas, so far at any
rate as to render the existence of living beings impossible j
while we know that one of the results of metamorphic action
is the obliteration of the fossils in the rock affected. Secondly,
by the researches of Sir William Logan there was discovered
in one of the limestones of the Lower Laurentian group, the
body which has been described under the name of Eozoon
Canadense, and which is believed to be a gigantic Foraminifer.
The organic nature of this body was first detected by Dr Daw-
son of Montreal, and his opinion as to its nature has since
been confirmed by the highest authorities. Thirdly, there is
good reason to believe that the graphite of the Laurentian
rocks is nothing more than metamorphic coal, and that it is
derived from vegetables which flourished during the Lauren-
tian period.

HURONIAN PERIOD.

The rocks of the Huronian series rest unconformably upon
the denuded edges of the Laurentian rocks on the borders of

512 HISTORICAL PALEONTOLOGY.

Lakes Superior and Huron. They are about 18,000 feet in
thickness, and consist of quartzites (altered sandstones), sili-
ceous slates, conglomerates, and limestones. The conglome-
rates sometimes contain pebbles derived from the subjacent
Laurentian rocks. No fossils have hitherto been found in
any part of the Huronian series, and its exact age is therefore
doubtful. Not improbably it may correspond with the Lower
Cambrian rocks of other regions, but it may represent an
independent formation to be intercalated in point of time
between the Laurentian and Cambrian groups.

CAMBRIAN PERIOD.

ROCKS OF THE PERIOD. — The exact limits of the Cambrian
Rocks are as yet not well denned, different authorities taking
different views as to the strata which should be considered
under this head. The name " Cambrian " is derived from the
fact that these strata are the lowest rocks visible in North
Wales and its borders (Cambria). The Cambrian rocks are
generally divided into a Lower and Upper division, and they
are well developed in various parts of Europe and America.
The following gives a general idea of the nature, distribution,
and mineral characters of the Cambrian rocks : —

I. Cambrian Rocks of Britain. — The Lower Cambrian rocks
of Britain are best seen in the Longmynd Hills in Shropshire,
and consist of about 25,000 feet of variously-coloured sand-
stones, grits, and shales, often ripple-marked, and exhibiting
rain-prints, but with very few fossils. These are succeeded by
a great series of micaceous flagstones, slates, and shales, which
vary in thickness from 6000 to 2000 feet, and are, in part
at any rate, of Upper Cambrian age. They are known as the
Lingula Flags, from the occurrence in them of a Brachiopod
belonging to the genus Lingula. In North Wales the Lower
Cambrian strata are often highly metamorphosed, and the cele-
brated Welsh roofing-slates are also derived from this division.
Cambrian rocks occur in other parts of Britain, and the follow-
ing table exhibits their leading members :—

1. Lower Cambrian :

a. Longmynd beds (25,000 feet).

b. Llanberis slates (3000 feet).

c. Harlech grits (6000 feet).

d. Oldhamia slates of -Ireland.

2. Upper Cambrian :

e. Lingula Flags of Wales (about 6000 feet).

/. Tremadoc Slates of North Wales (2000 feet).

g. Skiddaw Slates of the north of England (7000 feet).

CAMBRIAN PERIOD. 513

The last-mentioned group of rocks, namely, the Skiddaw
Slates of the north of England, is in a doubtful position.
They consist of about 7000 feet of dark-coloured shales and
slates, and they are most clearly the equivalent of the Quebec
group of Canada, containing many of the same fossils. Upon
the whole, it seems safer in the meanwhile to regard them as
Upper Cambrian. .

II. Cambrian Rocks of Bohemia and Sweden. — In Bohemia,
M. Barrande has succeeded in demonstrating as underlying
the Lower Silurian rocks of that country a zone of rocks,
which correspond to the Lingula Flags of Britain, and are
therefore of Upper Cambrian age. This zone contains many
remarkable and characteristic fossils, and is often spoken of as
the " Primordial Zone." In Sweden and Norway the Lower
Cambrian rocks are represented by a sandstone containing
impressions supposed to be referable to sea-weeds or " fucoids."
This " Fucoidal sandstone " is succeeded by beds of so-called
" alum-schist/' which are of Upper Cambrian age, and corre-
spond with the Lingula Flags of Britain.

III. Cambrian Rocks of North America. — The Cambrian
rocks are represented in North America by the Potsdam sand-
stone and the Calciferous series. The Potsdam Sandstone is
mostly a laminated sandstone, or grit in the State of New
York, but limestones are present in addition in the Mississippi
basin, and it consists of a great thickness (2000 to 7000 feet)
of slates, sandstones, and limestones, along the Appalachian
chain. It contains a good many fossils, among which are
Trilobites resembling those of the " Primordial Zone " in
Bohemia.

The Calciferous series consists of a hard calcareous sand-
stone, or " sand-rock " in the State of New York ; but it con-
sists of sandstone with well-developed magnesian limestone in
the basin of the Mississippi ; and along the Appalachian chain
it consists of sandstones and limestones, subordinated to great
masses of shale. In their last-mentioned development the
Calciferous rocks have been termed the " Quebec group," and,
as before said, they are undoubtedly the equivalent of the
Skiddaw Slates of Britain. They attain a thickness of from
5000 to 7000 feet ; but it is not clear whether they are truly
referable to the Upper Cambrian or to the base of the Silurian
system. Most probably they are transition beds between the
two formations.

LIFE OF THE CAMBRIAN PERIOD. — In the Lower Cambrian
Rocks fossils have hitherto proved extremely scarce. The
commonest organic remains are the burrows and tracks of

2 K

5 14 HISTORICAL PALEONTOLOGY.

Annelides (Arenicolites, Histioderma, &c.) Besides these, the
Longmynd beds of Shropshire have yielded a supposed Trilo-
bite (Palaopyge). The green and purple slaty rocks of Wick-
low have yielded two species of the singular fossil Oldhamia
(fig. 27), which may be a Hydroid Zoophyte, but which is
more probably a calcareous sea-weed. Lastly, the " Fucoidal
Sandstone " of Sweden, besides the obscure remains which are
known as " fucoids," has yielded the remarkable fossil known
as Eophyton (fig. 378), which is most probably a plant, along
with a small Lingula.

In the Upper Cambrian Rocks, fossils become tolerably
abundant, and belong to varied types. The most character-
istic forms are Trilobites, the characters of which are so
peculiar as to have gained them the name of " primordial,''
applied also to the strata in which they are found. The
chief genera are Paradoxides (fig. 114), Conocephalus, Sao,
Conocoryphe, Ellipsocephalus, Microdiscus, Agnostus, &c. The
" Primordial Zone " of Bohemia has also yielded a few
Pteropods, Brachiopods, and Echinoderms. The Potsdam
Sandstone of North America contains various primordial
Trilobites (especially those of the genus Dikelocephalus], Bra-
chiopods of the genera Obolus, Obolella, and Lingula, Gastero-
pods of the genera Pleurotomaria and Ophileta, Annelide-bur-
rows (Scolithus), and numerous so-called " fucoids." Lastly,
in the Potsdam Sandstone have been detected the earliest
footprints, if they may be so termed, which have been as yet
discovered. These have been described under the names of
Protichnites and Climactichnites, and they have probably been
produced by large Crustaceans.

The Lingula Flags of Britain owe their name to the occur-
rence in them of a large satchel-shaped Lingula (L. Davisii).
Trilobites of the genera Olenus, Agnostus, Paradoxides, &c.,
occur, and remains of Phyllopodous Crustaceans (Hymeno-
caris] are by no means rare.

The Skiddaw and Quebec groups, as already mentioned,
are in a doubtful position, and are often regarded as being
referable to the Lower Silurian. They are chiefly noticeable
for the great abundance of Graptolites which they have been
shown to contain. Many of these belong to genera which
pass up into the Silurian rocks (Didymograpsus, Diplograpsus,
and Climacograpsus) ; but others belong to types which are
exclusively confined to this horizon, and which are remarkably
complex as compared with later forms. Amongst these may
be mentioned the genera Tetragrapsus (fig. 32), Dichograpsus
(fig. 33), Loganograpsus, and Phyllograpsus.

SILURIAN PERIOD. 515

CHAPTER XLVIII.

SILURIAN PERIOD.

ROCKS OF THE PERIOD.

FOLLOWING the Cambrian comes the great Silurian series of
rocks, first clearly established and definitely worked out by
Sir Roderick Murchison, the founder of the Silurian system.
The exact limit between the Cambrian and Silurian formations
is one which is not clearly defined, since there does not appear
to be any general physical break between the two groups.
The line of demarcation between them is, in the present state
of our knowledge, an arbitrary line, and is derived chiefly from
the characters of the Trilobites. There are rocks, however,
such as the Tremadoc Slates, the Skiddaw Slates, and the Cal-
ciferous and Quebec groups, in which there is an intermixture
of Cambrian with true Lower Silurian types. These rocks,
therefore, might be regarded as Upper Cambrian or as Lower
Silurian, or as passage-beds between the two. It is to be
remembered, also, that the Tremadoc Slates and Lingula Flags
are regarded by Sir Roderick Murchison as being the base-
ment-beds of the Lower Silurian.

The name " Silurian " was proposed by Sir R. Murchison
for a great series of strata lying below the Old Red Sandstone,
and occupying those parts of Wales and England which were
at one time occupied by the " Silures," a tribe of ancient
Britons. The Silurian rocks are largely developed in Wales,
the north of England, Scotland, and Ireland, in various parts
of Europe, especially Bohemia, Saxony, Russia, and Sweden,
and in the North American Continent. The entire series is
divisible into the two sections of the Lower and Upper Silurian
rocks, each in turn split up into smaller subdivisions, the names
of which have usually been taken from localities where they are
unusually well developed, or where they were first studied.

In Britain the Silurian Rocks are divided into the following
groups from below upwards : —

a. Lower Llandeilo group, -j

b. Upper Llandeilo group, I eilnr;an

c. Bala, Caradoc, or Coniston group, [ ^

d. Lower Llandovery group, )

e. Upper Llandovery group, \

f. Wenlock group, > Upper Silurian.

g. Ludlow group, )

5l6 HISTORICAL PALAEONTOLOGY.

a. The Lower Llandeilo or Arenig group derives its name from
the town of Llandeilo, in Wales, where it consists of dark- coloured
micaceous flags, with earthy shales and gritty sandstones.

b. The Upper Llandeilo group consists of a great series of
micaceous flags and dark-coloured shales, often with inter-
stratified igneous matter. In Scotland the group consists of
a great assemblage of shales and grits, the former mostly very
dark in colour, often anthracitic, and charged with the remains
of Graptolites.

c. The Bala, Caradoc, or Comston group consists in Wales
of slates, grits, and sandstones, with two interstratified lime-
stones, the whole attaining a thickness of about 5500 feet.
In the north of England this group consists of black flaggy
beds, a well-marked limestone with intercalated shales, and
black mudstones replete with Graptolites.

d. The Lower Llandovery group consists of slates and sand-
stones, with great beds of conglomerate.

e. The Upper Llandovery group forms in Britain the base of
the Upper Silurians, and rests unconformably upon the Lower
Llandovery. It consists of limestones, shales, conglomerates,
sandstones, and slates, attaining a total thickness of nearly
2000 feet.

f. The Wenlock group consists of a great mass of shale and
flagstone (Wenlock Shale), underlaid and surmounted by lime-
stones, the whole attaining a thickness of 3000 feet.

g. The Ludlow group consists of shales, limestones, and
sandstones in Wales, and of grits and shales in the north of
England, having a total thickness of from 2000 to 4000 or
5000 feet.

In North America the Silurian series is magnificently devel-
oped, and is capable, like that of other parts of the world, of
being separated into a Lower and Upper division. The
annexed table shows the subdivisions of the Silurian series as
developed in the State of New York, and their supposed
British equivalents — the table being in ascending order :—

Silurian Strata of New York. British equivalents.

1. Trenton period (comprising the Chazy, Bird's ^ The Lower Silurian
eye, Black River, and Trenton limestones. I series (comprising the

> Llandeilo, Bala, and

2. Hudson period (comprising the Utica slates Lower Llandovery
and Hudson River shales). ' groups).

•\ The lower portion of

3. Niagara period (comprising the Oneida I the Upper Silurian series
conglomerate, Medina sandstone, Clinton group, > (comprising the Upper
and Niagara limestone). Llandovery and Wen-

J lock).

SILURIAN PERIOD. 517

4. Salina period (comprising the Guelph lime- ) NQ British ivalent
stone and Onondaga salt group). )

5. The Lower Helderberg period (comprising^ The ^ h . rf
the Tentacuhte and Water - lime groups the I the ^ ^ gjj^
Lower Pentamerus limestone, the Delthyns Lies(co^prisingtheLud.
shaly limestone, and the Upper Pentamerus j CTOlm\
limestone).

In Bohemia, as shown by M. Barrande, the Silurian series
likewise admits of a subdivision into an Inferior and a Supe-
rior division. The former comprises the single " e'tage D,"
and is characterised by a fauna to which M. Barrande has
applied the term of " second fauna," the so-called "primordial
zone" having yielded the "first fauna" of the same palaeonto-
logist. The Upper Silurian series comprises the etages E, F, G,
and H, and is characterised by the possession of the " third
fauna."

LIFE OF THE SILURIAN PERIOD. — In the lower portion of
the Cambrian series, as we have seen, organic remains are ex-
ceedingly scanty ; but in the upper portion of the same, fossils
are tolerably abundant, and belong in part to types which pass
upwards into the overlying Silurian series. The fossils of the
Silurian series are almost exclusively marine, the only excep-
tions being some remains of land-plants, such as stems of
Lepidodendron (Sagenaria) and the sporangia of Lycopodiace-
ous plants (Pachytheca), the latter having been discovered in
the very highest beds of the system. The only other vegeta-
ble remains which have been detected in undoubted Silurian
deposits belong to what are loosely termed " fucoids " (Licro-
phycus, Arthrophycus, Palceophycus, Buthotrephis, &c.), and
these are tolerably abundant in various parts of the series.

The sub-kingdom of the Protozoa is represented by For-
aminiferous shells and by Sponges. The latter are tolerably
abundant in both the Lower and Upper Silurian and belong
to various genera (Palaospongia, Acanthospongia, Astylospongia,
Amphispongia, &c.) Here, also, we meet with the singular
genera Receptaculites and Ischadites, which have been variously
regarded as gigantic Foraminifers, as Sponges, or as inter-
mediate forms between the Foraminifera and the Spongida.

The sub -kingdom of the Coslenterata is represented in
Silurian times by the Graptolites and by numerous Corals.
The typical Graptolites commence their existence in the Skid-
daw and Quebec Groups (Upper Cambrian ?), and are highly
characteristic of the Silurian Rocks. If we except the genus
Dictyonema, which is probably referable to the Sertularians, no
species of Graptolite is known to have survived the close of
the Silurian period. Neglecting their earlier appearance, the

5l8 HISTORICAL PALEONTOLOGY.

genera Didymograpsus and Dicranograpsus are exclusively,
and the genera Diplograpsus, Climacograpsus, and Rastrites are
pre-eminently, characteristic of the Lower Silurian period.
The genera Graptolites and Retiolites are those which espe-
cially characterise the Upper Silurian deposits, though both
commence in the inferior division of the series. Corals are
exceedingly abundant in many parts of the Silurian series,
certain formations, such as the Wenlock Limestone of Eng-
land and the Niagara Limestone of North America, being
in places so largely composed of these fossils that they have
been regarded as ancient coral-reefs. Almost all the Silurian
corals belong to the groups of the Rugosa and Tabulate

The Echinodermata are largely represented in Silurian de-
deposits, more especially by Crinoids and Cystideans. The
former are extremely abundant, and belong in many instances
to peculiar types. The Cystideans are pre-eminently Lower
Silurian, though they occur also in the upper division of the
series. They are especially characteristic of the Bala or
Caradoc period. The true Star-fishes (Asteroidea) are repre-
sented even in the Lower Silurian rocks ; whilst the Brittle-
stars (Ophiuroidea) are represented by the genus Protaster.
The Sea-urchins (Echinoided) are not represented at all except
in the Upper Silurian, and there only by the aberrant genus
Palachinus.

The Annelida are represented in the Silurian rocks by the
tracks and burrows of Sea-worms (Helminthites and Scolites),
and by the tubes of Tubicola (Serpulites, Ortonia, Conchicolites,
Cornulites, Spirorbis, &c.) The little spiral tubes of Spirorbis
are commonly found in the Upper Silurian rocks attached to
the shells of Orthocerata and the like.

The Arthropoda appear to have been represented wholly by
Crustaceans, no Arachnids, Myriapods, or Insects being yet
known with certainty to occur. The most important Silurian
Crustaceans belong to the Trilobita, Phyllopoda, Eurypterida,
and Ostracoda. The Trilobites are extraordinarily abundant,
and every subdivision of the Silurian series has its characteristic
species. The " primordial Trilobites " are only represented
by such forms as Agnostus and O lemts. The Lower Silurians
have many types, amongst which Asaphus, Ogygia, Trinucleus
Calymene, Cheirurus, Illcznus, and Phacops may be mentioned
as the most important, though most of these range into the
Upper Silurians as well. The Silurian Phyllopods are toler-
ably plentiful in both divisions of the series and belong chiefly
to the genera Ceratiocaris, Peltocaris, and Discinocaris. The
Eurypterids are represented in the Lower Silurians, but they

SILURIAN PERIOD. 519

are pre-eminently characteristic of the higher beds of the
Upper Silurian. Lastly, the Ostracoda are often extremely
abundant, and belong chiefly to the genera Leper ditia, Pri-
mitia, Beyrichia, and Entomis.

The sub-kingdom Mollusca is very largely represented in
Silurian deposits, and the Brachiopods and Tetrabranchiate
Cephalopods in particular enjoyed a vast extension and a de-
velopment which has never since been attained. The Brachi-
opods are so abundant in all parts of the series that the
Silurian period has been spoken of as the "Age of Brachi-
opods." The chief families are the Strophomenida, Rhy?i-
chonellidcz, Spiriferida, and Lingulidce. The genus Pentamerus
is especially characteristic of the Llandovery Rocks, or of what
has been termed the " Middle Silurian " by Sir Charles Lyell.
The Caradoc period is noticeable for the great number of
Or -t 'hides, mostly belonging to simple plaited forms. The ex-
clusively Silurian genera, however, are very few, but Obolus,
Siphonotreta, and Trematis are not known to have survived
into the Devonian period. Bivalves, such as Modiolopsis,
Ctenodonta, Lyrodesma, Ambonychia, Pterinea, Cardiola, &c.,
are far from uncommon ; whilst the Gasteropods are largely
represented by such forms as Pleurotomaria, Metoptoma,
Holopea, Cydonema, and Murchisonia. The Heteropods are
represented by Maclurea, Bellerophon, Cyrtolites, and Ecculiom-
phalus ; and the Pteropods abounded under the generic forms of
Theca (Hyolithes), Conularia, Tentaculites, and Pterotheca. The
Tetrabranchiate Cephalopods are extraordinarily abundant ;
but they belong almost exclusively to the sections of the
Naiitilida and Orthoceratidce ; the Ammonitidce being repre-
sented only by the genus Goniatites, which has not as yet been
recognised in the Lower Silurian deposits. The family of the
Orthoceratidcz attains here its maximum of development, over
one thousand species having been described by M. Barrande
from the Silurian basin of Bohemia alone. Their highest de-
velopment, however, is in the upper and not in the lower
division of the series.

The sub-kingdom Vertebrata is not known to be represented
in the Lower Silurian period at all ; but remains of various
fishes have been detected in the Upper Silurian series. In
Britain, the earliest fish-remains have been discovered in the
Lower Ludlow Shale, and consist of the cephalic bucklers of
Pteraspidean fishes. In the well-known stratum at the summit
of the Ludlow Rocks, familiar under the name of the " bone-
bed," have been discovered the defensive spines on which the
genus Onchus has been founded, and the shagreen-scales

520 HISTORICAL PALEONTOLOGY.

which constitute the genera Thelodus and Sphagodus. These
spines are believed to indicate the existence in the Upper
Silurian seas of Cestraciont fishes allied to the living Port-
Jackson Shark, whilst the latter may have belonged to some
form like the existing Dog-fishes. It must be admitted, how-
ever, that the true nature of these fossils is still open to ques-
tion. From the Upper Silurian series of Bohemia M. Bar-
rande describes no less than five fishes — viz., Coccosteus primus,
C. Agassizi, Asterolepis Bohemicus, Gompholepis Panderi, and
Ctenacanthus Bohemicus, of which the first four belong to the
Ganoids, whilst the last is supposed to be a Cestraciont or a
Selachian.

CHAPTER XLIX.

DEVONIAN PERIOD.

ROCKS OF THE PERIOD.

THE Silurian Rocks are succeeded upward by a great system of
rocks, mainly of the nature of sandstones and conglomerates,
to which the name of Old Red Sandstone has been applied.
The name Devonian formation is also employed to designate
these same strata, rocks supposed to belong to this period
being largely developed in Devonshire, in England. It is
probable, however, that the Devonian rocks represent a por-
tion only of the Old Red Sandstone, and that they cannot be
regarded as the full equivalent of the Old Red Sandstone of
other regions. The term " Devonian " may, however, when
thus understood, be usefully employed as a general term for
all the strata which intervene between the Silurian System and
the succeeding formation of the Carboniferous rocks.

The uncertainty as to the exact position of the Devonian
Rocks of Devonshire in the series of the Old Red Sandstone,
or the uncertainty as to whether they represent the Old Red
Sandstone in whole or in part, arises from this — that though
both formations are fossiliferous, the peculiar fossils of each
are never found associated together. The peculiar fossils of
the Old Red Sandstone proper are not found in the rocks of
Devonshire ; and the fossils of the latter, though found in
equivalent strata on the Continent of Europe, do not occur in
the beds to which the name of Old Red Sandstone was origi-
nally applied. This, however, may be largely due to the fact

DEVONIAN PERIOD. 521

that, while the Devonian strata are undoubtedly marine in
their origin, there seems reason to conclude that the Old Red
Sandstone proper was, in part at any rate, a fresh-water de-
posit. The two groups, therefore, might be truly contempora-
neous, and yet might not contain the same fossils.

The Old Red Sandstone is pre-eminently a British forma-
tion, and is divisible into three groups — the Lower, Middle,
and Upper Old Red.

The Lower Old Red reposes with perfect conformity upon
the highest beds of the Upper Silurians, the two formations
appearing to pass into one another by an intermediate series
of " passage-beds," which contain large Crustaceans of the
family of the Eurypterids. The Lower Old Red consists
mainly of massive conglomerates, with sandstones, shales, and
concretionary limestones. Its organic remains consist chiefly
of plants, Crustaceans, and fishes.

The Middle Old Red of Scotland consists of dark-grey flag-
stones, bituminous, flaggy shales, and conglomerates, some-
times accompanied by shales having irregular calcareous no-
dules embedded in them. The fossil remains are chiefly fishes,
with one Crustacean, and a few plants.

The Upper Old Red of Scotland consists of pebbly con-
glomerates, sandstones, and shales, and contains many fishes,
a good many fragments supposed to belong to sea-weeds, and
some undoubted land-plants.

In North and South Devon there occurs, underlying the
Carboniferous Rocks, a great series of strata which has been
regarded as the equivalent of the Old Red Sandstone. Though
certainly referable, in great part at any rate, to the period of
the Old Red Sandstone, it does not appear that the Devonian
Rocks can be regarded as the equivalent of the Old Red
Sandstone of Scotland. The Devonian Rocks, however, are
largely represented on the continent of Europe, and they are
richly fossiliferous ; though they do not contain any of the
characteristic Crustaceans, and only one or two generic re-
presentatives of the characteristic fishes of the Scotch Old
Red.

The Devonian Rocks of Devonshire consist essentially of
greenish slates, alternating with sandstones, conglomerates,
and well-developed bands of blue crystalline limestone and
calcareous slates.

In no country in the world probably is there a finer and
more complete exposition of the strata intervening between
the Silurian and Carboniferous formations than in the United
States. The following are the main subdivisions of the Devo-

Upper Devonian.

522 HISTORICAL PALEONTOLOGY.

nian Rocks of the State of New York, in which, probably, the
series is most typically displayed : —

1. Oriskany period (Oriskany Sandstone),* "J

2. Corniferous period (comprising the I Lower Devom'an

Cauda-Galli grit, Schoharie grit, and i
Upper Helderberg group), /

3. Hamilton period (comprising the Mar-

cellus, Hamilton, arid Genesee
groups),

4. Chemung period (comprising the Por-

tage and Chemung groups),

5. Catskill period (Catskill Sandstone),

LIFE OF THE DEVONIAN PERIOD. — Taken as a whole, the
life of the Devonian period may be regarded as transitional
between that of the underlying Silurian and overlying Carboni-
ferous period. As far, however, as our present knowledge
allows of our forming a definite opinion, the Devonian fauna
and flora approximate more nearly to those of the succeed-
ing Carboniferous than to those of the antecedent Silurian
period. This is especially shown in the Devonian plants,
which, as has been already pointed out, in almost all cases
agree generically with those of the Carboniferous ; whilst
in some cases they are even specifically identical. Thus, the
Devonian land supported an abundant vegetation, in which
Lepidodendroids, Sigillarioids, Calamites, Ferns, and Conifers,
mostly of Carboniferous types, play a prominent part. There
are, however, some forms, which, like Psilophyton, are as yet
not known to have occurred in the Carboniferous deposits.

The Protozoa are represented in the Devonian rocks by For-
aminifera and Sponges. Of the latter, Sparsispongia is the
most characteristic genus. (Steganodictyum is the buckler of a
Pteraspidean fish.)

The Cozlenterata are represented by the Hydrozoal genus
Dictyonema, which has often been referred to the Graptolites,
and by very numerous and varied forms of corals. No true
Graptolites have been as yet detected, unless Dictyonema be
one. The corals still belong mainly to the groups of the
Rugosa and Tabulata. The section of the Tubulosa (Aulopor-
idce) is represented here for the first time. Here also occur
the singular operculate Rugose corals upon which the genus
Calceola is founded.

The Echinodermata are represented in the Devonian period
by numerous Crinoids (Cupressocrinus, Aplocrinus, Platycri-

* The Oriskany Sandstone, though here placed in the Devonian, is pro-
bably really the summit of the Upper Silurian.

DEVONIAN PERIOD. 523

nus, &c.), along with Pentremite s ; whilst Cystideans are stated
to make their last appearance here.

The Articulates are represented by numerous Crustaceans,
and by a few insects — the latter being the first of their class.
The Crustaceans are abundant, the chief forms being Trilobites
(Phacops, Bronteus, Homalonotus, &c.), large Eurypterids (Ptery-
gotus, Stylonurus, Eurypterus, &c.), and Ostracodes (Entomis,
Leper ditia, Beyrichia, &c.) The bivalved carapaces of the last
mentioned of these groups are very abundant in certain De-
vonian beds, and the so-called " Cypridinen-schiefer " of the
Devonian series of Germany derives its name from the occur-
rence in it of vast numbers of the little Entomis ( Cypridina)
serrato-striata. In certain Devonian beds, also, the remains of
the Crustacean genus Estheria are very abundant. The Devo-
nian Insects appear on the whole to have the closest affinity
with certain of the existing Neuroptera or Pseudo-neuroptera.

The Mollusca are largely represented in Devonian time, and
the Brachiopods are especially abundant. The most charac-
teristic forms are those of the genera Stringocephalus (fig. 144)
and Uncites, along with numerous broad-winged Spirifers (such
as S. mucronata, fig. 148). Lamellibranchs (such as Megalo-
don and Pterinea\ Gasteropods (Macrocheilus, Trochus, Pleuro-
tomaria, &c.), and Pteropods (Conularia) are well represented
in the Devonian Rocks. As in the case of the Silurian period,
no certain traces of the existence of Dibranchiate Cephalo-
pods have been as yet detected in the Devonian. The Tetra-
branchiate Cephalopods, however, are known by true Nautili
and Orthocerata, and by the genus Clymenia. The family of
the Ammotttiida is also represented by the genera Goniatites
and Bactrites.

The sub-kingdom of the Vertebrata is still represented by
fishes only ; but these are so abundant that the Devonian
period has been commonly called the " Age of Fishes." Most
of the Devonian Fishes belong to the order of the Ganoids,
and especially to the two groups of the Crossopterygidcz and
Ostracostei. The genera Cephalaspis, Pteraspis, Pterichthys,
and Coccosteus, do not survive this period, and there are many
other peculiar Lepidoganoids as well. Besides Ganoids, nu-
merous remains of Elasmobranchii have been detected, these
being referable both to the Cestraphori and to the Selachii. It
is probable, also, that some of the Devonian fishes are rightly
referable to the order Dipnoi, finding their nearest living
allies in the Mud-fishes of South America and Africa, and the
Barramunda of Australia.

524 HISTORICAL PALEONTOLOGY.

CHAPTER L.

CARBONIFEROUS PERIOD.
ROCKS OF THE PERIOD.

OVERLYING the great formation of the Old Red Sandstone, or
Devonian Rocks, sometimes unconformably but more often in
perfect conformity, we have the large and important series of
the Carboniferous Rocks, so called because workable beds of
coal are more commonly developed in this than in any other
formation. It must not be forgotten, however, that coal is not
exclusively a Carboniferous product, but that workable seams
of coal occur in several formations younger than the Carboni-
ferous. In all cases, too, the coal forms but a very small pro-
portion of the actual thickness of the Carboniferous Rocks,
occurring in comparatively thin beds intercalated in a great
series of sandstones, shales, and limestones.

The Carboniferous Rocks are largely developed in Britain,
on the continent of Europe, and in North America, and are
known to occur in other parts of the world also. Their general
composition, however, is, comparatively speaking, so uniform,
that it will be sufficient to take a general view of the formation
without considering each area separately. As a general rule,
the Carboniferous Rocks may be divided into the following
three groups, from below upward :—

1. The Carboniferous Slates and Mountain Limestone, mainly
and most typically calcareous. Sometimes termed the Sub-
carboniferous group.

2. The Millstone Grit, essentially arenaceous and conglome-
ratic.

3. The Coal-measures, composed of alternating shales, sand-
stones, and other strata, with workable beds of coal.

I. The CARBONIFEROUS, SUB-CARBONIFEROUS, or MOUNTAIN,
LIMESTONE constitutes ordinarily the base of the Carboniferous
system. In Ireland, however, and elsewhere, the lowest beds
of the Carboniferous series are slates and grits, which attain a
maximum thickness of 5000 feet, and have been termed the
Carboniferous Slates. Their fossils are partially referable to
good Carboniferous types, and partly to Devonian forms, so
that they may be regarded as passage-beds. The Carboni-
ferous limestone proper in its most typical development, as in
Wales and the west of England, consists of a great mass of
nearly pure limestone, from 1000 to 2000 feet thick, with a

CARBONIFEROUS PERIOD. 525

few beds of shale. In other places, however, it is more or
less broken up into a series of different beds of limestone,
alternating with sandstones, grits, and shales, and sometimes
containing beds of coal. In North America it is never purely
calcareous, but consists mainly, or entirely, of sandstones and
shales, sometimes with thin beds of coal, or deposits of clay
iron-ore. Westward, however, it becomes more highly cal-
careous.

II. THE MILLSTONE GRIT. — The highest beds of the Car-
boniferous limestone are succeeded, usually conformably but
sometimes unconformably, by a series of sandy and gritty beds
which have been termed the Millstone Grit. In its most
typical form the Millstone Grit consists of a series of hard
quartzose sandstones, the component grains of which are some-
times so large as to be more properly called small pebbles,
when the rock becomes a fine conglomerate. In other cases
regular conglomerates are present, and there are sometimes
shales, limestones, and thin beds of coal. The thickness of
the Millstone Grit varies from 1000 to 1700 feet as a rule;
but sometimes its thickness is very greatly diminished. Fos-
sils are scarce, and offer no peculiarity.

III. THE COAL-MEASURES. — The Coal-measures proper
succeed the Millstone Grit conformably, and consist of a great
series of shale, sandstone, grit, and coal, attaining a total
thickness, when well developed, of from 7000 to 15,000 feet.
Except in Scotland, where workable coal-seams occur below
the horizon of the Millstone Grit, it is mostly from the true
Coal-measures that coal is obtained ; the largest and most
productive coal-fields of the world occurring in Britain, North
America, and Belgium. In their mineral nature, the Coal-
measures, all over the world, exhibit a wonderful general uni-
formity of composition. They consist, namely, of dark, often
nearly black, earthy and laminated shales, yellow, brown, and
purple sandstones, sometimes spotted, but very rarely red in
colour, along with occasional beds of limestone and clay iron-
ore, and beds of coal of varying thickness. These alternating
beds may follow one another in any order, and may be re-
peated over and over again, the total thickness sometimes
reaching the enormous amount of 14,000 feet, or nearly three
miles. In the South Wales coal-field the series consists as
usual of sandstones, shales, and coals, alternating with one
another, and indicating a slow, but probably intermittent,
depression of the area which they now occupy. In this coal-
field there are about 80 distinct beds of coal, each of which
represents an ancient land-surface. Each of these beds re-

526 HISTORICAL PALEONTOLOGY.

poses upon a sandy shale or clay, which is known as the
"imderclay" or " floor" of the coal, and through which spread
numerous fossils referred to the genus Stigmaria, and now
known to be the roots of plants (Sigillaria). Each seam is
also surmounted by a bed of shale, forming the so-called
" roof" of the coal, and in this are found numerous flattened
and compressed branches and stems of plants.

LIFE OF THE PERIOD. — The vegetation of the Carboniferous
period is exceedingly luxuriant ; but its characters have been
already so fully discussed as to render unnecessary anything
further here than a mere allusion to its chief members. The
chief feature in the Carboniferous flora is the great predominance
of Cryptogams as compared with Phanerogams. The former
are amply represented by numerous Ferns, Calamites, Lepido-
dendroids, and, perhaps, Sigillarioids. The latter, with few
exceptions, are represented only by Gymnospermous Exogens.

The Protozoa are represented in the Carboniferous rocks by
a few Sponges and by the shells of Foraminifera, of which the
genus Fusulina (fig. n) is the most characteristic. The tests
of this form are sometimes so abundant as almost to make up
the whole of certain limestones.

The Ccelenterates are represented almost exclusively by
Corals, which abound especially in some of the limestones of
the Lower Carboniferous series. Most of the Carbonifer-
ous Corals belong to the Tabulate division of the Zoantharia
Sclerodermata, or to the Rugosa, and amongst the more impor-
tant genera may be mentioned Lithostrotion, Syringopora, Lons-
daleia, Cyathophyllum, Amplexus, Favosites, and Chcztetes.

Of the Echinodermata the most abundant are the Crinoids,
which occur in vast profusion in most of the limestones of the
Carboniferous series. The most important genera are Actino-
crimts, Platycrinus, Cyathocrinus, Poteriocrinus, and Rhodocri-
nus. In some parts of the Carboniferous, Pentremites are also
exceedingly abundant. Lastly, the Echinoids are represented
by the two aberrant genera, Archczocidaris and Palcechinus,

Annelides are not abundant, with the single exception of
the little Spirorbis, or Microconchus, carbonarius, which some-
times occurs in great plenty. The Crustaceans belong chiefly
to the groups of the Ostracoda and Phyllopoda. The Trilo-
bites make here their last appearance ; the genera Phillipsia^
Griffithides, and Brachymetopus, being the last of the race.
The Eurypterids also appear to die out finally in the Carbon-
iferous. On the other hand, the Xiphosura are now repre-
sented by the genera Belinurus and Prestwichia (fig. 119) ; and
the Macrourous Decapods appear to commence their existence

CARBONIFEROUS PERIOD. 527

at this point. Of the Phyllopods, the best-known genera are
Dithyrocaris and Leaia. The little Ostracoda are often exceed-
ingly abundant, some of them belonging to marine, and others
to fresh-water or brackish-water forms. About thirteen genera
have been already detected in rocks of Carboniferous age, the
most important being Leperditia, Bairdia, Cypridina, Cythere,
Candona, and Beyrichia, of which the last appears to die out
here. Besides Crustaceans, the Arthropods are represented
by Arachnida, Myriapoda, and Insecta.

The Mollusca are very largely represented in Carboniferous
seas. Polyzoa are very abundant, the most characteristic forms
belonging to the genera fenestella, Ptilopora, Retepora, and Ar-
chimedipora. Brachiopods occur in profusion, and belong as
a rule to very well marked types. The great family of the
Productidcz attains here its maximum, most of the remaining
forms belonging to the genera Spirifera, Strophomena, Orthis,
Lingula, Terebratula, and Discina. Bivalves are very numerous,
and the family of the Aviculida reaches here its maximum of
development. Other well-known Carboniferous Bivalves be-
long to the genera Edmondia, Posidonomya, Conocardium, and
Cardiomorpha. The Gasteropods are represented mainly by
the characteristically Palaeozoic genera Macrocheilus and Lox-
onema, the almost exclusively Palaeozoic Euomphalus, and the
persistent genus Pleurotomaria. Heteropods (Bellerophon and
Porcellia) and Pteropods (Conularia) are also not unknown.
No Dibranchiate Cephalopods are as yet known to occur, but
the Tetrabranchiates are well represented — the Nautilidtz by
forms of Orthoceras and Cyrtoceras, and the Ammonitida by
Goniatites.

The Vertebrates are now represented by Amphibians, in
addition to Fishes. The latter are still chiefly Ganoid, the
commonest forms belonging to the genera Palceoniscus, Rhizo-
dus, and Holoptychius. Besides these occur numerous teeth
and fin-spines referred to Elasmobranchii, the most important
genera founded on these remains being Psammodus, Orodus,
Cochliodus, Cladodus, Ctenacanthus, Pleur acanthus, Gyracanthus,
Leptacanthus, and Orthacanthus. The Amphibians appear to
belong exclusively to the extinct order of the Labyrinthodon-
tia, referred to many genera, of which the most important are
Archegosaurus, Anthracosaurus, and Baphetes. Some of the
remains, however, of the air-breathing Vertebrates of the Car-
boniferous period are perhaps higher in the scale than Laby-
rinthodonts ; and they have been supposed to indicate the
existence at this time of true Reptiles.

$28 HISTORICAL PALAEONTOLOGY.

PERMIAN PERIOD.

ROCKS OF THE PERIOD. — The Carboniferous series is suc-
ceeded by a group of beds, which complete the Palaeozoic
formations, and which were termed Permian Rocks by Sir
Roderick Murchison, from the province of Perm, in Russia,
where they are extensively developed. Formerly these rocks
were grouped with the succeeding formation of the Trias under
the common name of " New Red Sandstone." This name
was given them because they contain a good deal of red sand-
stone, and because they are superior to the Carboniferous
rocks, while the Old Red Sandstone is inferior. Nowadays,
however, the term " New Red Sandstone " is rarely employed,
unless it be for red sandstones and associated rocks, which are
seen to overlie the Coal-measures, but which contain no fossils
by which their exact age may be made out. Under these
circumstances it is sometimes convenient to employ the term
" New Red Sandstone." The New Red, however, of the older
geologists is now broken up into the two formations of the
Permian and Triassic rocks, the former being the top of the
Palaeozoic series, and the latter constituting the base of the
Mesozoic.

The Permian rocks, as a rule, repose unconformably upon
the underlying Carboniferous rocks, but seem to pass upward
conformably into the Trias, in most instances. The division,
therefore, between the Permian and Triassic rocks, and, con-
sequently, between the Palaeozoic and Mesozoic series, is not
founded upon any marked or universal physical break, but
upon the difference in the life of the two periods.

The Permian rocks exhibit their most typical features in
Russia and Germany, though they are very well developed in
parts of Britain, and they occur in North America. When
well developed, they exhibit three main divisions : a lower set
of sandstones, a middle group, generally calcareous, and an
upper series of sandstones, constituting respectively the Lower,
Middle, and Upper Permians.

In Russia, Germany, and Britain, the Permian rocks con-
sist of the following members :—

i. The Lower Permians consisting mainly of a great series
of sandstones, of different colours, but usually red. The base
of this series is often constituted by massive breccias with
included fragments of the older rocks, upon which they may
happen to repose ; and similar breccias sometimes occur in
the upper portion of the series as well. The thickness of this

PERMIAN PERIOD. 529

group varies a good deal, but may amount to 3000 or 4000
feet.

2. The Middle Permians, consisting, in their typical de-
velopment, of laminated marls, or " marl-slate," surmounted
by beds of magnesian limestone (the " Zechstein " of the Ger-
man geologists). Sometimes the limestones are degenerate or
wholly deficient, and the series may consist of sandy shales
and gypsiferous clays. The magnesian limestone, however, of
the Middle Permians is, as a rule, so well marked a feature
that it was long spoken of as the Magnesian Limestone.

3. The Upper Permians, consisting of a series of sandstones
and shales, or of red or mottled marls, often gypsiferous, and
sometimes including beds of limestone.

In North America, the Permian rocks appear to be confined
to the region west of the Mississippi, being especially well de-
veloped in Kansas. Their exact limits have not as yet been
made out, and their total thickness is not more than a few
hundred feet. They consist of sandstones, conglomerates,
limestones, marls, and beds of gypsum.

LIFE OF THE PERIOD. — The Permian Rocks have yielded
a very considerable number of plants, most of which are speci-
fically distinct from those of the Coal-measures. Though the
species, however, are distinct, many of the Permian genera
date back to the antecedent Carboniferous period. Thus,
besides several genera of Carboniferous Ferns, the Permian
Rocks contain the well-known genera Lepidodendron and Cala-
mites. The Sigillarioids, however, seem to have finally dis-
appeared. Conifers are by no means uncommon, and some
of these ( Ullmania} produce true cones. The genus Walchia
comprises the most characteristic of the Permian Conifers.

The Protozoa are represented in the Permian deposits by a
few Sponges and Foraminifera. The Coelcnterates are repre-
sented by Corals, but these are rarely abundant. The Rugosa
are reduced here to the single genus Polyccelia. Crustaceans
are also by no means largely represented. The Trilobita
have disappeared, as have the Eurypterids. The King-crabs
(Limulus] are, however, represented by one species. Ostracoda
are tolerably abundant, and the genus Prosoponiscus has been
regarded as referable to either the Isopoda or the Amphipoda.
Lastly, the genus Hemitrochiscus has been founded for the
reception of a Permian fossil which has been regarded as the
remains of a true Crab. If this determination be correct, the
tribe of Brachyurous Decapods has its commencement here.

Molluscs occur in greater abundance than any of the pre-
ceding. The genera Fenestella and Acanthocladia represent the

2 L

530 HISTORICAL PALAEONTOLOGY.

Polyzoa. The most important genera of Brachiopods are
Spirifera, Producta, Strophalosia, Camarophoria, and Lingula.
Bivalves are moderately numerous, the commonest forms be-
longing to the family Trigoniada and to the genus Axinus
(Schizodus). Other forms belong to the genera Mytilus, Bake-
wellia, and Avicula. Gasteropods and Cephalopods are, upon
the whole, very poorly represented in the Permian series.

The most important Permian fossils are referable to the
Vertebrata, Fishes are comparatively very abundant, and be-
long almost entirely to the order of the Ganoids. The most
characteristic genera are Pal&oniscus, Platysomus, Pygopterus,
Gyropristis, Acrolepis, and Ccelacanthus. The Amphibians are
represented by various forms belonging to the Labyrinthodontia.
True Reptiles are represented by the Protorosaurus of the
" Kupfer-schiefer " of Germany, and somewhat doubtfully by
the Chelonian footprints (Chelichnus) from the Permian Sand-
stones of Dumfriesshire.

CHAPTER LI.

TRIASSIC PERIOD.

ROCKS OF THE PERIOD.

WE come now to the consideration of the great Mesozoic, or
Secondary series of formations, consisting, in ascending order,
of the Triassic, Jurassic, and Cretaceous systems. The Trias-
sic group forms the base of the Mesozoic series, and corre-
sponds with the higher portion of the New Red Sandstone of
the older geologists. Like the Permian Rocks, and as implied
by its name, the Trias admits of a subdivision into three
groups — a Lower, Middle, and Upper Trias. Of these sub-
divisions the middle one is wanting in Britain ; and all have
received German names, being more largely and typically de-
veloped in Germany than in any other country. Thus, the
Lower Trias is known as the Bunter Sandstein; the Middle
Trias is called the Muschelkalk, and the Upper Trias is known
as the Keuper.

I. The lowest division of the Trias is known as the Bunter
Sandstein, from the generally variegated colours of the beds
which compose it (German, bunt, variegated). The Bunter
Sandstein of the continent of Europe consists of red and

TRIASSIC PERIOD. 531

white sandstones, with red clays, and thin limestones, the
whole attaining a thickness of about 1500 feet. The term
" marl " is very generally employed to designate the clays of
the Lower and Upper Trias, but the term is inappropriate, as
they contain no lime, and are therefore not genuine marls.
In Britain the Bunter Sandstein consists of red and mottled
sandstones, with unconsolidated conglomerates, or " pebble-
beds," the whole having a thickness of about 1200 feet. The
Bunter Sandstein, as a rule, is very barren of fossils.

II. The Middle Trias is not developed in Britain, but it
is largely developed in Germany, where it constitutes what is
known as the Muschelkalk (Germ. Muschel, mussel ; kalk, lime-
stone), from the abundance of fossil shells which it contains.
The Muschelkalk consists of compact grey or yellowish lime-
stones, sometimes dolomitic, and including occasional beds of
gypsum and rock-salt.

III. The Upper Trias, or Keuper^ as it is generally called,
occurs in England ; but is not so well developed as it is in
Germany. In Britain the Keuper is about 1000 feet in thick-
ness, and consists of white and brown sandstones, with red
marls, the whole topped by red clays with rock-salt and
gypsum.

The Keuper in Britain is extremely unfossiliferous ; but it
passes upwards with perfect conformity into a very remarkable
group of beds, at one time classed with the Lias, and now
known under the names of the Penarth beds (from Penarth, in
Glamorganshire), the Rhaetic beds (from the Rhaetic Alps), or
the Avicula contorta beds (from the occurrence in them of
great numbers of this peculiar Bivalve). These singular beds
have been variously regarded as the highest beds of the Trias,
or the lowest beds of the Lias, or as an intermediate group.
The phenomena observed on the Continent, however, render
it best to consider them as Triassic, as they certainly agree
with the so-called St Cassian or Kossen beds which form the
top of the Trias in the Austrian Alps.

The Penarth beds occur in Glamorganshire, Gloucestershire,
Warwickshire, Staffordshire, and the north of Ireland; and
they generally consist of a small thickness of dark grey and
black shales, surmounted conformably by the lowest beds of
the Lias. The most characteristic fossils which they contain
are the three Bivalves Cardium Rhc&ticum, Avicula contorta,
and Pecten Valoniensis ; but they have yielded many other
fossils, amongst which the most important are the remains of
Fishes and small Mammals (Microlestes).

In the Austrian Alps the Trias terminates upwards in an

532

HISTORICAL PALAEONTOLOGY.

i.

Koessen beds.

(Synonyms, Upper St
Cassian beds of Escher \
and Merian).

2. Dachstein beds.

extraordinary series of fossiliferous beds, replete with marine
fossils. Sir Charles Lyell gives the following table of these
remarkable deposits : —

Strata below the Lias in the Austrian Alps, in Descending Order.

/Grey and black limestone, with calcareous
marls having a thickness of about 50
feet. Among the fossils, Brachiopoda
very numerous ; some few species com-
mon to the genuine Lias ; many pecu-
liar. Avicula contorta, Pec ten Valo-
niensis, Cardium Rh&ticum, Avicula
incequivalvis, Spirifer Miinsteri, Dav.
Strata containing the above fossils al-
ternate with the Dachstein beds, lying
next below.

White or greyish limestone, often in beds
three or four feet thick. Total thick-
ness of the formation above 2000 feet.
Upper part fossiliferous, with some
strata composed of corals. (Lithoden-
dron.) Lower portion without fossils.
Among the characteristic shells are He-
micardium Wulferii, Megalodon triqueter,
and other large bivalves.

Red, pink, or white marble, from 800 to
1000 feet in thickness, containing more
than 800 species of marine fossils, for
the most part mollusca. Many species
of Orthoceras. True Ammonites, besides
Ceratites and Goniatites, Belemnites (rare),
Porcellia, Pleurotomaria, Trochus, Mono-
tis salinaria, &c.

A. Black and grey lime-
stone 150 feet thick, al-
ternating with the un-
derlying Werfen beds.

B. Red and green shale
and sandstone, with
salt and gypsum.

In the United States, rocks of Triassic age occur in several
areas between the Appalachians and the Atlantic seaboard ;
but they show no such triple division as in Germany, and their
exact place in the system is uncertain. The rocks of these
areas consist of red sandstones, sometimes shaly or conglomer-
atic, occasionally with beds of impure limestone. Other more
extensive areas where Triassic rocks appear at the surface, are
found west of the Mississippi, on the slopes of the Rocky Moun-
tains, where the beds consist of sandstones and gypsiferous
marls. The American Trias is chiefly remarkable for having
yielded the remains of a small Marsupial (Dromatherium) and

Hallstadt beds
(or St Cassian).

A. Guttenstein beds.

B. Werfen beds, base of

Upper Trias ?
Lower Trias of some
geologists.

Among the fossils
are Ceratites
cassianus, My-
acites fassaen-
sis, Naiicella
costata, &c.

TRIASSIC PERIOD.

533

numerous footprints, which have generally been referred to
Birds (Brontozoum), along with the tracks of undoubted Rep-
tiles (Otozoum, Anisopus, &c.)

LIFE OF THE TRIASSIC PERIOD. — The Triassic period, as
regards its plants and animals, is in many respects intermedi-
ate between the Palaeozoic and the later Mesozoic deposits,
whilst being itself decidedly Mesozoic. Amongst the plants
there are some Palaeozoic types (such as Calamites) ; but there
is no longer a marked predominance of Cryptogams, and the
leading forms are Ferns (Pecopteris, Neuropteris, Acrostichites ,
&c.), Cycads (Pterophyllum, Podozamites, &c.), and Conifers
(chiefly belonging to the genus Voltzia).

The Protozoa are represented in Triassic times by several
sponges (AmorphospongiO) Cupulispongia, Leiospongia, &c.)
Corals are by no means infrequent in the Muschelkalk, and in
some of the limestones of the Upper Trias ; but they are other-
wise rare. They belong mostly to Secondary types, such as
Montlivaltia, Synastraa, Acrosmilia, Eunomia, &c. The Echi-
noderms are rarely abundant, but two forms are exceedingly
characteristic of the Muschelkalk. These are the beautiful
Lily-encrinite, Encrinus liliiformis (fig. 80), and the little
Ophiurid, Aspidura loricata (fig. 71).

Articulates are not abundant, with the exception of Ostra-
coda, which are sometimes very plentiful. The other common
forms are referable to Estheria; but Macrurous Decapods have
also been detected. Besides Crustaceans, several forms of
Insects have been discovered.

The Mollusca are exceedingly abundant in parts of the Tri-
assic series, and they exhibit an extraordinary intermixture of
Palaeozoic and Mesozoic types. This is shown in a synoptical
manner in the following table of the Mollusca of the Upper
Trias of the Austrian Alps, given by Sir Charles Lyell in his
' Elements of Geology : ' —

Genera of Fossil Mollusca in the St Cassian and Hallstadt Beds.

Common to Older Rocks.

Cyrtoceras.

Orthoceras.

Goniatites.

Loxonema.

Holopella.

Murchisonia.

Euomphalus.

Porcel lia.

Megalodon.

Cyrtia.

Characteristic Triassic
Genera.

Common to Newer Rocks.

Ceratites.

Ammonites.

Scoliostoma (or

Belemnites.

Cochlearia).

Nerinsea.

Naticella.

Opis.

Platystoma.

Cardita.

Isoarca.

Trigonia.

Pleurophorus.

Myoconchus.

Myophoria.

Ostrea. I sp.

Monotis.

Plicatula.

Koninckia.

Thecidium.

534 HISTORICAL PALAEONTOLOGY.

From the above table it will be seen, that amongst the Gas-
teropoda the Trias has yielded the characteristically Palaeozoic
Loxonema, Holopeila, Murchisonia, and Euomphalus, all of
which commence their existence in the Silurian period. With
these are forms like Scoliostoma and Platystoma, which are
characteristically Triassic, and these are associated with such
a typical Jurassic genus as Nerincza. Amongst the Bivalves,
we find the Palaeozoic Megalodon side by side with the Triassic
Monotis and Myophoria, these being associated with the Tri-
gonice, Plicatulce, and Oysters of later deposits. The Brachi-
opods exhibit the Palaeozoic Cyrtia, with the Triassic Koninc-
kia, and the modern genus Thecidium. Lastly, amongst the
Cephalopods, this same intermingling of old and new types is
shown in its most striking form. The ancient genera Orthoceras,
Cyrtoceras, and Goniatites appear here for the last time upon
the scene. With these are the first Dibranchiate Cephalopods,
represented by the great Mesozoic genus Belemnites. The
Ammonitida, with the disappearance of the comparatively
simple Goniatites, are represented by the more complex Cera-
iites, which is exclusively Triassic; whilst the still more com-
plicated genus Ammonites makes its first appearance here, and
is never again wanting till we reach the close of the Mesozoic
period.

The Vertebrata are represented in the Triassic period ap-
parently by members of all the existing classes. Fishes are
very numerous, and belong chiefly to the Hybodonts, Acro-
donts, and Ganoids. Amongst the more important forms we
find the Palaeozoic genera Palczoniscus and Amblypterus, with
the Secondary Hybodus and Acrodus, and the Triassic genus
Saurichthys. We may also assert now with tolerable safety,
that the order of the Dipnoous Fishes was represented in
Triassic times by various species of the genus Ceratodus.

The Amphibians of the Trias are known both by the actual
bones and teeth, and still more commonly by their footprints.
They belonged exclusively to the order of the Labyrinthodon-
tia, which disappears finally at the close of this period.

Of the living orders of the Reptiles, the Chelonians are only
known by more or less doubtful footprints ; the Lacertilians
are represented by Telerpeton and Rhynchosaurus (the last often
referred to the Dicynodonts) \ the Crocodilia are represented
by Stagonolepis, Belodon, Thecodontosaurus, and Palczosaurus
(the last two referred by Huxley to the Deinosaurs) ; and the
Ophidians do not appear to have yet commenced their exist-
ence. Of the extinct orders of Reptiles, the Pterosaurs are
unknown in the Trias, and the Ichthyosaurs are not with cer-

JURASSIC PERIOD. 535

tainty known to have existed. The Plesiosaurs are represented
by species of Plesiosaurus itself, and by the allied genera Simo-
saurus, Nothosaurus, Pistosaurus, &c. The Anomodontia are
represented by the genera Dicynodon and Oudenodon ; whilst
Rhynchosanrus is referred by Owen to this group. Lastly, the
Deinosaurs are represented, according to Huxley, by several
forms, amongst which the most important are the "Thecodont"
Palceosaurus and Thecodontosaurus, both of which have been
referred by other writers to different groups of the Reptilia.

The existence of Birds during the Triassic period must, as
yet, be regarded as uncertain. The only evidence as to their
existence which has been hitherto obtained, consists in the
paired footprints which have been already spoken of as occur-
ring in the Triassic strata of the Connecticut Valley. These
footprints are very numerous, and are often pf very large size ;
and there is no doubt but that many of them were produced
by animals walking upon two legs. Some of them, however,
have been unquestionably produced by Reptiles ; and it must
at present remain uncertain whether all have been thus formed,
or whether some may not have been formed by Birds. The
probabilities, however, are in favour of the view that some of
these tracks are truly ornithic.

Lastly, the Mammals are represented in the Trias only by
the small forms referred to the genera Microlestes and Droma-
therium^ both of which are probably referable to the order of
the Marsupials.

CHAPTER LII.

JURASSIC PERIOD.

ROCKS OF THE PERIOD.

SUCCEEDING to the Trias, we have a great series of Rocks
which are known as the Oolitic Rocks, from their commonly
containing oolitic limestones, or as the Jurassic Series, from
their being largely developed in the mountain -range of the
Jura, on the western borders of Switzerland. The Jurassic
rocks are very extensively developed in Britain, where they
consist of the following members in ascending order :

I. Lias.

II. Lower Oolites (consisting of the Inferior Oolite, Fuller's

Earth, Great Oolite, Stonesfield Slate, &c.)

536 HISTORICAL PALEONTOLOGY.

III. Middle Oolites (Oxford Clay and Coral-rag).

IV. Upper Oolites (Kimmeridge Clay, Portland Stone, and

Purbeck beds).

I. The Lias succeeds the uppermost beds of the Trias with
perfect conformity, and passes upward, generally conformably,
into the lowest beds of the Lower Oolites. It consists essen-
tially of a great series of bluish or greyish laminated clays,
alternating with thin bands of blue or grey limestone, the
whole assuming at a distance a characteristically striped and
banded appearance.

II. The Lower Oolites consist of calcareous freestones (In-
ferior Oolite), shales, clays, and marls (Fuller's earth), fine-
grained Oolitic limestones (Great Oolite), with calcareous
flags at the base (Stonesfield slate), and superiorly shelly lime-
stones and calcareous sandstones (Forest - marble and Corn-
brash), the whole having a thickness of from 400 to 500 feet.
In Yorkshire the Lower Oolites consist of limestones with car-
bonaceous shales and thin seams of coal, which are sufficiently
extensive and constant to be worked for coal. Of this age,
also, is probably the coal-field of Brora, in Sutherlandshire, in
the north of Scotland.

III. The Middle Oolites are composed of a great mass of
dark-blue tenacious clay (Oxford clay), with a maximum thick-
ness of 700 feet, surmounted by from 150 to 250 feet of lime-
stones, known as the Coral-rag, from the number of corals con-
tained in them.

IV. The Upper Oolites consist in Britain of laminated, some-
times carbonaceous or bituminous clays (Kimmeridge clay),
forming the base of the group, and having a thickness of 500
or 600 feet. These are succeeded by sandstones and lime-
stones (Portland stone) of about 120 feet in thickness; and
the formation is capped by a remarkable group of alternating
strata of fresh-water, brackish-water, and marine beds, with old
land-surfaces, the whole known as the Purbeck beds, and
having a united thickness of about 150 feet. Of the same age
as the Upper Oolites in Britain is the Solenhofen slate of
Bavaria, an exceedingly fine-grained stone, which is largely
used in lithography, and is celebrated for the number and
beauty of its organic remains, especially those of Vertebrates.

Rocks belonging to the Jurassic series, in the form of lime-
stones and marls, have been detected by their fossils in the
Laramie Mountains and in other portions of the Rocky Moun-
tains, and also at various points in Arctic America. The ex-
tent, however, of these beds is unknown, and no subdivisions
have hitherto been established in them.

JURASSIC PERIOD. 537

LIFE OF THE PERIOD. — The vegetation of the Jurassic
period is characterised by the abundance of Ferns, Cycads,
and Conifers — the Cycadacecz attaining here their maximum of
development.

The Protozoa are represented by numerous Foraminifera
and by Sponges. Of the former the genera Invofatina, Nodo-
saria, Cristellaria, Detitalina, and Frondicularia may be men-
tioned as amongst the most important. Of the latter the chief
forms belong to Cribrospongia, Actinospongia, Porospongia,
Goniospongia, Perispongia, Chenendopora, and Scyphia.

The Coelenterates are represented in the Jurassic period by
numerous corals, which are exceedingly abundant in some of
the limestones of the series (such as the Coral-rag and the
Great Oolite). The number of Oolitic genera of Corals is
very large, but the commonest and most characteristic forms
belong to Thamnastrtza, Isastraa, Prionastrtza, Anabacia, Mont-
livaltia, Thecosmilia, Eunomia, Protoseris, Comoseris, Den-
drarea, Dactylarea, Loboccznia, Aplophyllia, Trochocyathus, and
Stylina.

The Echinoderms are very largely represented all through
the Jurassic Series. The Crinoids are represented both by
stalked forms (Pentacri?ius, Extracrinus, Apiocrinus, &c.) and
by free forms (Saccosoma). Echinoids are extremely abundant
in many parts of the series, the commonest generic types being
Hemicidaris, Diadema, Pseudodiadema, Nudeolites, Dysaster
(Collyrites), Acrosalenia, and Cidaris. True Star-fishes ( Ur aster,
Tropidaster, Plumaster, Solaster, and Astropecteri) are not un-
known, and Ophiuroids (Ophioderma, Ophiolepis, Acroura, &c.)
are far from uncommon.

As regards the Arthropods, Crustaceans are abundantly
found in certain beds (especially in the Solenhofen Slates).
The orders which are most largely represented are the Decapoda
(with many forms, both Macrurous and Brachyurous), the Cir-
ripedia, and the Ostracoda. Besides Crustaceans, the Oolitic
rocks have yielded numerous Insects, belong to the orders
Coleoptera, Neuroptera, Orthoptera, Hemiptera, Diptera, and
Hymenoptera. True Spiders have also been detected.

Coming to the Mollusca, Brachiopods are still abundant,
though they do not fill such a predominant place in the marine
fauna as in many Palaeozoic deposits. The Palaeozoic genera
Lept&na and Spirifera appear here (in the Lias) for the last
time ; and most of the Jurassic forms belong to the modern
genera Terebratula and Rhynchonella. Bivalves are very abun-
dant, and approximate in many respects to existing forms.
The sub-genera Gryphcea and Exogyra amongst the Oysters,

538 HISTORICAL PALEONTOLOGY.

along with numerous forms of Ostrea itself, and the genera
Trigonia, Lima (Plagiostomd), Pholadomya, Cardinia, and
Avicula may be mentioned as comprising most of the com-
moner forms. One of the most remarkable, however, of the
Oolitic genera of Lamellibranchs is Diceras (fig. 189), com-
prising certain singular shells allied to the existing Chama.
These are so abundant in a limestone of the Alps of the age
of the Coral-rag as to have gained for this formation the name
of " Diceras Limestone."

Of the Gasteropoda there are many examples of the ancient
genus Pleurotomaria ; but on the whole the Univalves have a
modern aspect. Holostomatous Univalves, such as Nerita,
Patella, Natica, Turritella, Chemnitzia, and Nerincza, still hold
a predominant place ; and species of the last-named genus are
especially characteristic of parts of the series. The Tertiary
and modern genus, Cerithium, also makes its first appearance
here. Though the Holostomata still predominate, there is now
a fair proportion of the carnivorous siphonostomatous Univalves,
and many of these are referable to existing genera. Thus,
with the extinct Purpuroidea are found forms belonging to
such genera as Pteroceras, Rostellaria, Buccinum, Fusus, Murex,
and Pleurotoma. The Cephalopoda are exceedingly abundant
all through the Jurassic series, and are represented by both
Dibranchiate and Tetrabranchiate types. The Dibranchiate
BelemnitidcK here attained their maximum of development,
many beds being literally charged with the guards of these
extinct cuttle-fishes. The Tetrabranchiates are represented
by various species of the persistent genus Nautilus, but more
especially by species of Ammonites, which are extraordinarily
plentiful and of the most varied forms. Speaking generally,
Ammonites and Belemnites may be stated to be the charac-
teristic fossils of the Jurassic period.

In the fresh-water strata of the Oolites (Purbeck beds), the
Molluscs, as a matter of course, belong to forms which now
inhabit fresh water. Thus, amongst the Bivalves we have the
genus Cyrena, and amongst the Gasteropods we meet with the
genera Planorbis, Physa, Paludina, and Melanopsis. As regards
the Vertebrates, little need be said about the Jurassic fishes,
which belong to the Ganoidei and ElasmobranchiL The Ganoids
now possess, many of them, symmetrical tails, and the most
important genera are Tetragonolepis, Dapedius, ^Echmodus,
Pycnodus, Leptolepis, and Aspidorhynchns. The Cestraphom
are represented by Hybodonts (Hybodus and Strophodus] and
Acrodus. Lastly, the true Sharks are not without Jurassic
representatives (Notidanus).

JURASSIC PERIOD. 539

The Reptilia have an enormous development in Oolitic
times, and are represented both by forms allied to those now
in existence and by types which are now altogether extinct. Of
the living forms there are as yet no Ophidians, but the Che-
lonians are represented by various genera (Idiochelys, Eury-
stermim, and Chelone). The Lacertilians are represented by
several forms of no special importance, and the Crocodilia were
represented by species with amphicoelous vertebrae ( Teleosaurus
and Steneosaurus). Of the extinct orders of Reptiles, the Ichthyop-
terygia, comprising only the genus Ichthyosaurus, form a very
marked feature in the Reptilian fauna of the Jurassic period.
Numerous species of Ichthyosaurus are known ; and the remains
of individuals are very abundant in certain beds, especially in
the Lias. The Sauropterygia are represented by numerous
species of Plesiosaurtis, remains of which are also very abun-
dant in the Lias and in other parts of the Oolitic series. The
Pterosauria are represented by all their chief genera (Ptero-
dactylus, Dimorphodon, and Ramphorhynchus] ; and though
commencing in the Lias, they are most abundant in the Solen-
hofen Slate. The Dicynodonts appear to have died out ; but
the Deinosaurs are largely represented, chiefly by the genera
Megalosaurus and Cetiosaurus.

The Birds have no other representative in the Oolitic period
than the extraordinary Archaopteryx macrura of the Solenhofen
Slates — the first undoubted indication of birds in the geolo-
gical record. As has been before pointed out, this Jurassic
bird differed in several most important characters from all
known members of the class, whether living or extinct ; its
most striking peculiarity being the possession of a long, lizard-
like tail composed of free vertebrae, of which each supported a
pair of quill-feathers.

The Mammals, taking all things into consideration, are well
represented in the Jurassic series, their remains belonging to
the two horizons of the Stonesfield Slate (Lower Oolites) and
the Purbeck beds (Upper Oolites). The Stonesfield Mammals

—viz., Amphitherium, Amphilestes, Phascolotherium, and Stereog-
nathus — are all of small size ; and the first three appear to be
certainly Marsupial. Stereognathus may be also a Marsupial,
but its true affinities are uncertain. The Purbeck Mammals

—Triconodon, Spalacotherium, Galestes, and Plagiaulax — were
likewise all of small size, and they appear to have been all
Marsupial ; the three first-named being probably insectivorous,
whilst the last appears to have been a vegetable-feeder.

540 HISTORICAL PALEONTOLOGY.

CHAPTER LIII.

CRETACEOUS PERIOD.

ROCKS OF THE PERIOD.

THE next series of rocks in ascending order is the great and
important series of the Cretaceous Rocks, so called from the
general occurrence in the system of chalk (Lat. creta, chalk).
As developed in Britain and Europe generally, the following
leading subdivisions may be recognised in the Cretaceous
series : —

1. Wealden, } T ^

T f? j XT v / Lower Cretaceous.

2. Lower Greensand or Neocomian, j

3. Gault, -I

4* r j?Pi? Greensand' 1 Upper Cretaceous.

5. Chalk,

6. Maastricht beds, J

I. The Wealden formation, though of considerable impor-
tance, is a local group, and is confined to the south-east of
England, France, and some other parts of Europe. Its name
is derived from the Weald, a district comprising parts of
Surrey, Sussex, and Kent, where it is largely developed. Its
lower portion, for a thickness of from 500 to 1000 feet, is
arenaceous, and is known as the Hastings Sands. Its Upper
portion, for a thickness of 150 to nearly 300 feet, is chiefly
argillaceous, consisting of clays with sandy layers, and occa-
sionally courses of limestone. The geological importance of the
Wealden formation is very great, as it is undoubtedly the
delta of an ancient river, being composed almost wholly of
fresh-water beds, with a few brackish-water and even marine
strata, intercalated in the lower portion. Its geographical
extent, though uncertain, owing to the enormous denudation
to which it has been subjected, is nevertheless great, since it
extends from Dorsetshire to France, and occurs also in North
Germany. Still, even if it were continuous between all these
points, it would not be larger than the delta of such a modern
river as the Ganges. The river which produced the Wealden
series must have flowed from an ancient continent occupying
what is now the Atlantic Ocean ;' and the time occupied in
the formation of the Wealden must have been very great,
though we have, of course, no data by which we can accu-
rately calculate its duration.

CRETACEOUS PERIOD. 541

The fossils of the Wealden series are, naturally, mostly the
remains of such animals as we know at the present day as in-
habiting rivers. We have, namely, fresh-water mussels ( Unio],
river-snails (Paludina), and other fresh-water shells, with nume-
rous little bivalved Crustaceans, and some fishes.

II. The Wealden beds pass upward, often by insensible
gradations, into the Lower Greensand. The name Lower
Greensand is not an appropriate one, for green sands only
occur sparingly and occasionally, and are found in other for-
mations. For this reason it has been proposed to substitute
for Lower Greensand the name Neocomian, derived from the
town of Neufchatel — anciently called Neocomum — in Switzer-
land. If this name were adopted, as it ought to be, the
Wealden beds would be called the Lower Neocomian.

The Lower Greensand or Neocomian of Britain has a thick-
ness of about 850 feet, and consists of alternations of sands,
sandstones, and clays, with occasional calcareous bands. The
general colour of the series is dark brown, sometimes red, and
the sands are occasionally green, from the presence of silicate
of iron.

The fossils of the Lower Greensand are purely marine, and
among the most characteristic are the shells of Cephalopods.

The most remarkable point, however, about the fossils of
the Lower Cretaceous series, is their marked divergence from
the fossils of the Upper Cretaceous rocks. Of 280 species of
fossils in the Lower Cretaceous series, only 51, or about 18
per cent, pass on into the Upper Cretaceous. This break in
the life of the two periods is accompanied by a decided phy-
sical break as well, for the Gault is often, if not always, uncon-
formably superimposed on the Lower Greensand. At the
same time, the Lower and Upper Cretaceous groups form a
closely-connected and inseparable series, as shown by a com-
parison of their fossils with those of the underlying Jurassic
Rocks and the overlying Tertiary beds. Thus, in Britain no
marine fossil is known to be common to the marine beds of
the Upper Oolites and the Lower Greensand; and of more
than 500 species of fossils in the Upper Cretaceous Rocks,
almost every one died out before the formation of the lowest
Tertiary strata, the only survivors being one Brachiopod and a
few Foraminifera.

III. The lowest member of the Upper Cretaceous series is
a stiff, dark-grey, blue, or brown clay, often worked for brick-
making, and known as the Gault, from a provincial English
term. It occurs chiefly in the south-east of England, but can
be traced through France to the flanks of the Alps and Ba-

542 HISTORICAL PALAEONTOLOGY.

varia. It never exceeds TOO feet in thickness ; but it con-
tains many fossils, usually in a state of beautiful preservation.

IV. The Gault is succeeded upward by the Upper Green-
sand, which varies in thickness from three up to 100 feet, and
which derives its name from the occasional occurrence in it of
green sands. These, however, are local and sometimes want-
ing, and the name " Upper Greensand;J is to be regarded as a
name and not a description. The group consists, in Britain,
of sands and clays, sometimes with bands of calcareous grit or
siliceous limestone, and occasionally containing concretions of
phosphate of lime, which are largely worked for agricultural
purposes.

V. The top of the Upper Greensand becomes argillaceous,
and passes up gradually into the base of the great formation
known as the true Chalk, divided into the three subdivisions
of the chalk-marl, white chalk without flints, and white chalk
with flints. The first of these is simply argillaceous chalk,
and passes up into a great mass of obscurely-stratified white
chalk in which there are no flints. This, in turn, passes up
into a great mass of white chalk, in which the stratification is
marked by nodules of black flint arranged in layers. The
thickness of these three subdivisions taken together is some-
times over 1000 feet, and their geographical extent is very
great. White Chalk, with its characteristic appearance, may
be traced from the north of Ireland to the Crimea, a distance
of about 1140 geographical miles, and, in an opposite direc-
tion, from the south of Sweden to Bordeaux, a distance of
about 840 geographical miles.

VI. In Britain there occur no beds containing Chalk fossils,
or in any way referable to the Cretaceous period, above the
true White Chalk with flints. On the banks of the Maes,
however, near Maestricht, in Holland, there occurs a series of
yellowish limestones, of about 100 feet in thickness, and un-
doubtedly superior to the White Chalk. These Maestricht
beds contain a remarkable series of fossils, the characters of
which are partly Cretaceous and partly Tertiary. Thus, with
the characteristic Chalk fossils, Belemnites, Baculites, Sea-Ur-
chins, &c., are numerous Univalve Molluscs, such as Cowries
and Volutes, which are otherwise exclusively Tertiary or Re-
cent.

Holding a similar position to the Maestricht beds, and
showing a similar intermixture of Cretaceous forms with later
types, are certain beds which occur in the island of Seeland,
in Denmark, and which are known as the Faxoe Limestone.

VII. In North America, the Lower Cretaceous Rocks are

CRETACEOUS PERIOD. 543

not represented at all, or very feebly; but there is a very
extensive development of rocks of Upper Cretaceous age in
the United States. According to Dana, " the Cretaceous
Eocks occur — i. At intervals along the Atlantic border, south
of New York, from New Jersey to South Carolina ; 2. Exten-
sively over the States along the Gulf 'border ; and 3. Through
a large part of the Western interior region, over the slopes of
the Rocky Mountains, from Texas northward, to the head-
waters of the Missouri on the east of the summit of the chain,
and far into the Colorado region on the west. Still farther
north-west in British America, they appear on the Saskat-
chewan and Assiniboine, and also on the Arctic Sea, near the
mouth of the Mackenzie." The rocks of these areas consist
chiefly of sands, marls, clays, and limestones ; but it is to be
remembered that there is no white Chalk. Green sands are
often present, as in New Jersey, where they are called " marls,"
and are largely worked for agricultural purposes, their fertilis-
ing properties being due to the presence of a small percentage
of phosphate of lime.

LIFE OF THE CRETACEOUS PERIOD. — As regards the vegeta-
tion of the Cretaceous period, the plants of the Inferior divi-
sion of the series agree with those of the antecedent Jurassic
period in consisting chiefly of Ferns, Cycads, and Conifers.
In the Upper Cretaceous Rocks, on the other hand, we find a
vegetation composed largely of Angiospermous Exogens, many
of which belong to existing genera.

The Protozoa are very largely represented in the Cretaceous
period by Foraminifera and Sponges. The microscopic shells
of the former are often excessively abundant ; and the white
chalk is to a large extent composed of the exuvia of these
minute organisms. Amongst the more important genera may
be mentioned Texttdaria, Globigerina, Rotalia, Lituola, Nodo-
saria, Flabellina, Cuneolina, Cristellaria, Bulimina, Dentalina,
&c. Sponges are very numerous, especially in the Upper
Greensand and White Chalk. The most important genera are
Siphonia, Ventriculites, Manon, Choanites, Cliona, Scyphia,
Chenendopora, Guettardia, and Polypothecia ; but many other
forms might be mentioned.

The Ccelenterates are represented by Corals, belonging
mainly to the genera Trochocyathus, Cyclocyathus, Trochosmilia,
Parasmilia, Cyathina, Micrabacia, Stephanophyllia, &c. In the
Upper Greensand, also, occurs the little Holocystis elegans, long
believed to be the last of the Rugose Corals.

The Echinoderms are exceedingly abundant in the Creta-
ceous rocks, but belong mainly to the Echinoids. Crinoids,

544 HISTORICAL PALAEONTOLOGY.

though not altogether rare, are very perceptibly reduced in
numbers, the more important forms being MarsupiUs, Penta-
crinus, Bourgueticrinus, and Comatula. Sea-urchins, on the
other hand, are so numerous as to constitute one of the most
marked features in the Cretaceous fauna. The leading genera
are Micr aster, Ananchytes, Galerites, Hemipneustes, Diadema,
Discoidea, Salenia, Cidaris, Catopygus, Pygaster, Pygaulus,
Holaster, &c.

The Arthropods are represented by various Crustaceans be-
longing mainly to the Macrurous and Brachyurous Decapods,
and to the Cirripedes. The little Ostracodes are also abun-
dant in many parts of the series, especially in the fresh-water
strata of the Wealden.

Coming to the Mollusca, the Polyzoa have a great develop-
ment in the Cretaceous deposits, the family of the Eschar idee.
here attaining its maximum. Amongst the more characteristic
Cretaceous genera may be mentioned Eschara, Escharina,
Vincularia, Membranipora, Flustra, Reticulipora, Hornera,
Tubulipora, &c.

Brachiopods are not especially numerous, and belong mainly
to Terebratula, Terebratella, Terebratulina, Rhynchonella^ and
Crania. Bivalves are very abundant, and some of them are
very characteristic. Amongst these are numerous species of
Ostrea, Exogyra, Lima, Plicatula, Pecten, and Spondylus, with
the various species of Inoceramus, and the great family of the
Hippuritidce. With the exception of a few Jurassic species,
the genus Inoceramus is exclusively Cretaceous, being repre-
sented in deposits of this period by numerous species, and not
being known to have survived it. The Hippuritidce, or Rudis-
tes of Lamarck, comprise a great number of very aberrant
Bivalves, all of which were attached and lived associated in
beds, like Oysters. The two valves of the shell are always
unlike in sculpturing, in appearance, and in shape, and the cast
of the interior is often very unlike the form of the outer surface
of the shell. A great many species of this family are known,
chiefly referable, to the genera Hippurites, Radiolites, and Ca-
prina. The family appears to be exclusively Cretaceous ; and .
the most characteristic members of the Cretaceous series of the
south of Europe consists of certain compact marbles, which
are known as " Hippurite Limestone," from the abundance of
shells of this family.

Gasteropods are not particularly numerous in the Cretace-
ous Rocks, and belong chiefly to such modern genera as Turri-
tella, Natica, Solarium, Scalaria, Rostellaria, Dentalium, Phorus,
&c. Along -with these are species of the persistent genus Pleu-

CRETACEOUS PERIOD. 545

rotomaria, and the Mesozoic Nerintza. Towards the close of the
Cretaceous period, we meet for the first time with Gasteropods
of the existing genera Voluta, Mitra, Cyprcea, Fasciolaria,
Strombus, &c.

The most characteristic Molluscs of the Cretaceous period
are Cephalopods. The Dibranchiate section of this order is
represented by species of Belemnites itself and by the genus
Belemnitella. Of the Tetrabranchiates we find species of the
old genus Nautilus ; but this section is represented mainly by
complex and beautiful forms of the Ammonitida. The genus
Ammonites itself, dating its existence from the Upper Trias, is
represented by many Cretaceous species, and finally disappears
with the close of this period. Ancyloceras dates from the
commencement of the Jurassic period, and also dies out in the
Chalk. Finally, the Ammonitidce are represented by the genera
Baculites, Turrilites, Scaphites, Hamites, Ptychoceras, Toxoceras,
and Crioceras, which make their first appearance in the Creta-
ceous rocks, but which are not known at present to occur in
any later deposit.

Remains of Fishes are by no means rare in the Cretaceous
rocks. Teleostean Fishes appear here, and are well represented
by forms more or less allied to existing types (Beryx, Osmero-
ides, &c.) Ganoids (such as Lepidotus, Caturus, Pycnodus, &c.)
are plentiful ; but are of little special importance. Of the
Cestracionts, we have the old genus Awodtts, and the Creta-
ceous genus Ptychodus. Hybodonts also occur, and teeth of
true Selachians (Lamna, Carcharias, Odontaspis, &c.) are not
wanting.

The Reptiles of the Cretaceous belong mostly to the orders
of the Pterosauria, Ichthyopterygia, Sauropterygia, and Deino-
sauria — all of which die out with the Cretaceous period. The
best known of the Deinosaurs is Iguanodon, which is confined
exclusively to the Lower Cretaceous period, but the genera
Ichthyosaurus^ Plesiosaurus, and Pterodactylus, extend their
range into the Upper Cretaceous. The only exclusively Cre-
taceous group of Reptiles is that of the Mosasauroids, which
are known to have existed up to the last phase of this period
(Maestricht beds). The Mosasauroids are found in Europe,
but more abundantly in North America ; and the recent dis-
covery by Professor Marsh, that the body was, in some cases,
furnished with a covering of bony scutes, would seem to re-
move them from the Lizards, amongst which they have been
generally placed.

Birds have not been shown with certainty to have existed
during the Cretaceous period in Europe, though various re-

2 M

546 HISTORICAL PALEONTOLOGY.

mains of this age have been with more or less probability re-
garded as being Ornithic. The Upper Cretaceous rocks of
the United States have, however, yielded the remains of un-
doubted birds (Laornis, Telmatornis, Scolopax, and Palaotringa).
More remarkable than any of the above are the recently-dis-
covered Hesperornis and Ichthyornis, of which the former is a
large Diver-like bird, whilst the latter exhibits the singular
peculiarity that the vertebrae are biconcave. Mammals have
not hitherto been detected in any Cretaceous deposit.

CHAPTER LIV.
EOCENE PERIOD.

BEFORE commencing the study of the subdivisions of the
Kainozoic series, there are some general considerations to be
noted. In the first place, there is a complete and entire phy-
sical break between the rocks of the Mesozoic and Kainozoic
periods. In no instance are Tertiary strata to be found rest-
ing conformably upon any Secondary rock. The Chalk has
invariably suffered much erosion and denudation before the
lowest Tertiary strata were deposited upon it. This is shown
by the fact that the actually eroded surface of the Chalk can
often be seen, or, failing this, that we can point to the presence
Of the chalk-flints in the Tertiary strata. This last, of course,
affords unquestionable proof that the Chalk must have been
subjected to enormous denudation prior to the formation of
the Tertiary beds, all the chalk itself having been removed,
and nothing left but the flints, while these are all rolled and
rounded.

In the second place, there is a complete break in the life
of the Mesozoic and Kainozoic periods. With the excep-
tion of a few Foraminifera, and one Brachiopod (the latter
doubtful), no Cretaceous species is known to have survived the
Cretaceous period ; while several characteristic families, such
as the AmmonitidcE and Hippuritida, died out entirely with the
close of the Cretaceous rocks. In the Tertiary rocks, on the
other hand, not only are all the animals and plants more or
less like existing types, but we meet with a constantly-increas-
ing number of living species as we pass from the bottom of the
Kainozoic series to the top. Upon this last fact is founded

EOCENE PERIOD. 547

the modern classification of the Kainozoic rocks, propounded
by Sir Charles Lyell.

It follows from the constant want of conformity between
the Cretaceous and Tertiary rocks, and still more from the
entire difference in life, that the Cretaceous and Tertiary
periods are separated by an enormous lapse of unrepresented
time. How long this interval may have been, we have no
means of judging exactly, but it very possibly was as long as
the whole Kainozoic epoch itself. Some day we shall doubt-
less find, at some part of the earth's surface, strata which were
deposited during this period, and which will contain fossils
intermediate in character between the organic remains which
respectively characterise the Secondary and Tertiary periods.
At present, we have only slight traces of such deposits, as, for
instance, the Maastricht beds.

CLASSIFICATION OF THE TERTIARY ROCKS. — The classifica-
tion of the Tertiary rocks is a matter of unusual difficulty, in
consequence of their occurring in disconnected basins, form-
ing a series of detached areas, which hold no relations of
superposition to one another. The order, therefore, of the
Tertiaries in point of time, can only be determined by an
appeal to fossils ; and in such determination Sir Charles Lyell
proposed to take as the basis of classification \he proportion of
living or existing species of Mollusca which occurs in each stratum
or group of strata. Acting upon this principle, Sir Charles
Lyell divides the Tertiary series into four groups : —

i. The Eocene formation (Gr. eos, dawn; kainos, new), con-
taining the smallest proportion of existing species, and being,
therefore, the oldest division. In this classification only the
Mollusca are taken into account ; and it was found that of
these about three and a half per cent were identical with
existing species.

II. The Miocene formation (Gr. meion, less ; kainos, new),
with more recent species than the Eocene, but less than the
succeeding formation, and less than one-half the total number
in the formation. As before, only the Mollusca are taken into
account, and about 17 per cent of these agree with existing
species.

III. The Pliocene formation (Gr. pleion, more ; kainos, new),
with more than half the species of shells identical with existing
species ; the proportion of these varying from 35 to 50 per
cent in the lower beds of this division, up to 90 or 95 per cent
in its higher portion.

IV. The Post-Tertiary Formations, in which all the shells
belong to existing species. This, in turn, is divided into two

548 HISTORICAL PALAEONTOLOGY.

minor groups — the Post-Pliocene and Recent Formations. In
the Post-Pliocene formations, while all the Mollusca belong to
existing species, most of the Mammals belong to extinct
species. In the Recent period, the quadrupeds, as well as the
shells, belong to living species.

The above, with some modifications, was the original classi-
fication proposed by Sir Charles Lyell for the Tertiary rocks,
and now universally accepted. More recent researches, it is
true, have somewhat altered the proportions of existing species
to extinct, as stated above. The general principle, however,
of an increase in the number of living species, still holds good ;
and this is as yet the only satisfactory basis upon which it has
been proposed to arrange the Tertiary deposits.

EOCENE FORMATION.

The Eocene rocks are the lowest of the Tertiary series, and
comprise all those Tertiary deposits in which there is only a
small proportion of existing Mollusca — from three and a half
to five per cent. The Eocene rocks occur in several basins in
Britain, France, the Netherlands, and other parts of Europe,
and in the United States. The subdivisions which have been
established are extremely numerous, and it is often impossible
to parallel those of one basin with those of another. It will
be sufficient, therefore, to accept the division of the Eocene
formation into three great groups — Lower, Middle, and Upper
Eocene — and to consider some of the more important beds
comprised under these heads in Europe and in North America.

I. LOWER EOCENE. — The base of the Eocene series in
Britain is constituted by about 90 feet of light-coloured, some-
times argillaceous sands (Thanet Sands), which are of marine
origin. Above these, or forming the base of the formation
where these are wanting, come mottled clays and sands with
lignite (Woolwich and Reading series), which are estuarine or
fluvio-marine in origin. The highest member of the Lower
Eocene of Britain is the " London Clay," consisting of a
great mass of dark-brown or blue clay, sometimes with sandy
beds, or with layers of " septaria," the whole attaining a thick-
ness of from 200 to as much as 500 feet. The London Clay
is a purely marine deposit, containing many marine fossils,
with the remains of terrestrial animals and plants ; all of which
indicate a high temperature of the sea and tropical or sub-
tropical conditions of the land.

II. MIDDLE EOCENE. — The inferior portion of the Middle
Eocene of Britain consists of marine beds, chiefly consisting

EOCENE PERIOD. 549

of sands, clays, and gravels, and attaining a very considerable
thickness (Bagshot and Bracklesham beds). The superior
portion of the Middle Eocene of Britain, on the other hand,
consists of deposits which are almost exclusively fresh-water
or brackish-water in origin (Headon and Osborne series).

The chief Continental formations of Middle Eocene age are
the " Calcaire grossier " of the Paris basin, and the "Num-
mulitic Limestone " of the Alps.

III. UPPER EOCENE. — If the Headon and Osborne beds of
the Isle of Wight be placed in the Middle Eocene, the only
British representatives of the Upper Eocene are the Bern-
bridge and Hempstead beds — though the latter are regarded
by Sir Charles Lyell as being of Lower Miocene age. These
strata consist of limestones, clays, and marls, which have for
the most part been deposited in fresh or brackish water.

IV. EOCENE BEDS OF THE PARIS BASIN. — The Eocene
strata are very well developed in the neighbourhood of Paris,
where they occupy a large area or basin scooped out of the
Chalk. The beds of this area are partly marine, partly fresh-
water in origin ; and the following table (after Sir Charles
Lyell) shows their subdivisions and their parallelism with the
English series : —

GENERAL TABLE OF FRENCH EOCENE STRATA.
UPPER EOCENE.

French Subdivisions. English Equivalents.

A. I. Gypseous series of Mont- I. Bembridge series.

martre.

A. 2. Calcaire silicieux, or Tra- 2. Osborne and Headon series.

vertin Inferieur.

A. 3. Gres de Beauchamp, or 3. White sand and clay of Barton

Sables Moyens. Cliff, Hants.

MIDDLE EOCENE.

B. I. Calcaire Grossier. I. Bagshot and Bracklesham beds.

B. 2. Soissonnais Sands, or Lits 2. Wanting.

Coquilliers.

LOWER EOCENE.

C. I. Argile de Londres at base of I. London Clay.

Hill of Cassel, near Dun-
kirk.

C. 2. Argile plastique and lignite. 2. Plastic clay and sand with lig-
nite (Woolwich and Reading
series).
C. 3. Sables de Bracheux. 3. Thanet sands.

V. EOCENE STRATA OF THE UNITED STATES. — In North
America, Lower Eocene Rocks are extensively developed at

550 HISTORICAL PALAEONTOLOGY.

Claiborne, Alabama, and consist of clays, lignites, marls, and
impure limestones. The fossils of the Claiborne series are
much the same in their characters as those of the London
clay, and the lignites contain numerous plant-remains.

The Middle Eocene group is represented in North America
by lignitic clays and marls which occur at Jackson, Mississippi.
Amongst the more remarkable fossils of the Jackson beds are
the teeth and bones of Cetaceans of the genus Zeuglodon.

Rocks of Upper Eocene age occur in North America at
Vicksburg, Mississippi, and consist of lignites, clays, marls,
and limestones. On the White River they are about 1000
feet thick, and consist of clays, sandstones, and limestones, of
fresh-water origin. Among their most remarkable fossils are
the remains of Mammals, of which about forty species have
been already determined.

LIFE OF THE EOCENE PERIOD.

Little need be added here as to the life of the Eocene
period, fossils being so abundant as to render it impossible to
do more than indicate some general considerations. Upon
the whole, the plants and animals of the Eocene period closely
resemble those now in existence upon the globe ; not, how-
ever, necessarily in the exact localities in which they are now
found. Thus, the modern representatives of the plants and
animals of the Eocene Rocks of Europe are not to be found
in Europe itself, but in some tropical or sub-tropical region.
The climatic conditions of Europe in the Eocene period were
very different to those at present subsisting, and the animals
and plants were correspondingly different. Still, there are
few Eocene fossils which have not their modern representa-
tives in warm countries.

The Protozoa are represented in Eocene times chiefly by
ForaminiferO) which are often extraordinarily abundant, and
the shells of which may in some cases be said without exagge-
ration to compose whole mountain-masses. The great and
widespread formation of the Nummulitic Limestone is largely
made up of the shells of Nummulites and Orbitoides, some of
the former occasionally reaching a size of more than an inch
in diameter. One of the limestones of the Paris basin is
largely composed of the shells of a species of Miliola. Nume-
rous other forms occur ; and the genus Nummulites is exclu-
sively confined to this formation.

Corals are not particularly abundant in the Eocene rocks,
but they are mostly of types identical with, or nearly allied to,

EOCENE PERIOD. 551

those now existing. The Tabulata are represented by no
more than one genus, and the Eocene forms belong mainly to
the Zoantharia, Aporosa, and Perforata. Besides Zoantharia,
the family of the Pennatulidce (Sea-pens, &c.) is represented
by the genus Graphularia, and the family of the Gorgonidcz
(sea-shrubs), by the genera Mopsea and Websteria.

As regards the Mollusca, Brachiopods and Polyzoa are not
abundant, and the former are represented in Eocene times
chiefly by the existing genera Terebratula and Rhynchonella.
Lamellibranchs and Gasteropods, the latter especially, are
exceedingly abundant, and almost all existing genera are now
represented ; though less than five per cent are identical with
existing species. The Gasteropods are chiefly siphonostoma-
tous, and belong to such familiar genera as Voluta, Mitra,
Conus, Pleurotoma, Fusus, Cyprcza, Oliva, Ancillaria, Rostel-
laria, &c. The fresh-water and brackish-water beds of the
formation have also yielded numerous species of Cerithium,
along with Limncea, Planorbis, Melania, &c. The Ammonites,
Turrilites, Baculites, Belemnites, &c., of the Cretaceous period
have now disappeared, and the Cephalopoda are represented
mainly by the genus Nautilus, though Dibranchiates (such as
Belosepia) are not unknown.

The most important fossils of the Eocene Rocks belong to
the sub-kingdom of the Vertebrata. Fishes are numerous,
sometimes (as in the limestone of Monte Bolca) extraordinarily
so. They belong in the vast majority of instances to the
Teleostei, the remains of Ganoid fishes being comparatively
very rare. True Sharks are represented by numerous teeth,
referable to the genera Carcharodon, Otodus, Lamna, Galeo-
cerdo, &c. ; and Rays are represented by their pavement-like
dental plates (Myliobatis}.

The Reptiles of the Eocene period all belong to the existing
orders of the Chelonians, Ophidians, Lacertilians, and Croco-
dilians. The Chelonians are very abundant, and belong for
the most part to existing genera. The Ophidians make their
first appearance in the Eocene (Palceophis). The Crocodilians,
lastly, are very abundant, speaking comparatively; and Eng-
land possessed in' Eocene times representatives of the three
existing genera of this order — viz., Crocodilus, Alligator, and
Gavialis.

As regards the Birds, it is sufficient to say that all the exist-
ing orders of Aves appear to have been represented in Eocene
times, often by forms which differ little from existing types.

As regards the Mammals, the Eocene deposits have yielded
remains of Marsupialia, Sirenia, Cetacea, Ungulata, Carnivora,

552 HISTORICAL PALEONTOLOGY. .

Cheiroptera, Rodentia, and Insectivora. No traces, however, have
hitherto been found in the Eocene of the orders Probostidea
and Edentata, and the Quadrumana are represented only by
two doubtful forms. The Marsupials are represented in
the Eocene by Diddphys^ the Sirenia by Halithcrium, and
the Cetaceans by the singular and aberrant family of the Zeu-
glodonts. The Ungulates are represented by a great series of
forms, of which the most important are the two extinct groups
of the Pal&otheridtz and Anoplotherida, the former representing
the Perissodactyles, the latter the Artiodactyles. Besides these,
however, there occur numerous other extinct forms, chiefly
referable to the genera Coryphodon, Lophiodon, Chceropotamus ,
Anthracotherium, Hyopotamus, Pliolophus, Dichodon, Dichobune,
Xiphodon, &c.

The Carnivora are represented by the extinct Hycenodon,
the Cheiroptera by species of the existing genus Vespertilio, the
Rodentia by Shrew-mice (Myoxus), and the Insectivora by
Spalacodon.

CHAPTER LV.

MIOCENE PERIOD.

ROCKS OF THE PERIOD.

THE Miocene formations comprise those Tertiary deposits
which contain less than about 35 per cent of existing species
of Mollusca, and more than 5 per cent, or those deposits in
which the proportion of living shells is less than of extinct
species. The Miocene formations are divisible in Europe into
a Lower Miocene and Upper Miocene group.

I. LOWER MIOCENE. — The Miocene formations are very
poorly represented in Britain, their leading development being
at Bovey Tracy, in Devonshire, where there occur sands, clays,
and beds of lignite or woody coal. These strata contain nume-
rous plants, among which are Vines, Figs, the Cinnamon-tree,
Palms, and a number of Conifers. Other plant-bearing strata
in the Hebrides, on the west coast of Scotland, have been
referred to the Miocene age.

In France, the Lower Miocene is represented in Auvergne,
Cantal, and Velay, by a great thickness of nearly horizontal
strata of sand, sandstone, clays, marls, and limestones, all of

MIOCENE PERIOD. 553

fresh-water origin. Other Miocene deposits occur in Austria,
Germany, Switzerland, and the Siwalik hills in India.

II. UPPER MIOCENE. — The typical European deposits of
Upper Miocene age occur in the valley of the Loire, in France,
and are known as the " Faluns," a provincial term given to
shelly sands employed to spread upon soils which are deficient
in lime. The Faluns occur in scattered patches, which are
rarely more than 50 feet in thickness, and consist of sands
and marls. The fossils are chiefly marine, but there occur
also land and fresh-water shells, and the remains of numerous
Mammals.

In Switzerland, between the Alps and the Jura, there occurs
a great series of Miocene deposits, known collectively as the
" Molasse," from the soft nature of a greenish sandstone,
which constitutes one of its chief members. It attains a thick-
ness of many thousands of feet, and rises into lofty mountains,
some of which — as the Rigi — are more than 6000 feet in
height. The middle portion of the Molasse is of marine
origin, and is shown by its fossils to be of the age of the
Faluns ; but the lower and upper portions of the formation
are mainly or entirely of fresh-water origin. The Lower
Molasse (of Lower Miocene age) has yielded about 500 species
of plants, mostly of tropical or sub-tropical forms. The Upper
Molasse has yielded about the same number of plants, with
about 900 species of Insects, such as wood-eating Beetles,
Water-beetles, White Ants, Dragon-flies, &c.

MIOCENE OF NORTH AMERICA. — Miocene deposits are
found in the United States in New Jersey, Maryland, Virginia,
California, Oregon, &c., and they attain sometimes a thickness
of 1500 feet. They consist chiefly of clays, sands, and sand-
stones: and in Virginia there is a bed of what is wrongly
called " Infusorial Earth," which attains a thickness of many
feet, and consists almost wholly of the siliceous cases of cer-
tain low forms of plants (Diatoms). The strata of the White
River, with remains of numerous Mammals, formerly spoken
of as Upper Eocene, are sometimes referred to the Miocene
formation. The fossils of the American Miocene are chiefly
Molluscs (of which 15 to 30 per cent are living species).

LIFE OF THE MIOCENE PERIOD. — The vegetation of the
Miocene period has been already spoken of, and need not be
again discussed here. The Invertebrates of the Miocene also
need no special mention, since they are very similar in type to
those now in existence, though mostly specifically distinct.
The Fishes, Reptiles, and Birds of the Miocene likewise call
for no special comment. The Miocene Mammals, on the

554 HISTORICAL PALEONTOLOGY.

other hand, belong in great part to extinct types, and are
sufficiently remarkable in their characters to demand some
notice. In addition to the orders known to be represented in
the Eocene Tertiary, we meet now with remains referable to
the Edentata, Proboscidea, and Quadrumana ; whilst some
existing groups of the older orders are now represented for the
first time.

The Edentates are represented by the gigantic Macrotherium,
which appears to have been nearly allied to the Scaly Ant-
eaters or Pangolins, and by the still more gigantic Ancylotherhim.

Of the Sirenia we have the genus Halitherium, and of the
true Cetacea we have the remains of Squalodonts and Dolphins.

Of the Ungulates the Rhinoceridtz are represented in Miocene
times by Acerotherium, the Equidce. by Anchitherium and Hip-
parion, the Hippopotamidce by species of Hippopotamus itself,
the Suida by species of SHS, the Moschidcz by Dremotherium,
the Cervidce by Dorcatherium, the Camelopardalida by Hellado-
therium, and the Cavicornia by the extraordinary Sivatherium
and Bramatherium. The Bovida do not appear as yet to
have come into existence.

The Probosddea are represented in the Miocene period by
all the known sections of the order — namely, by Elephants,
Mastodons, and the Deinotherium.

Of the Carnivora we have Miocene representatives of the
Felidcz (Machairodus), the Canida, Hycmida, Viverridce, and
MustelidcB. The Insectivora are represented by species of
Erinaccus and Talpa, and the Rodents by species of Castor,
Mus, Lepus, &c. Lastly, the Quadrumana are represented by
the two extinct genera Pliopithecus and Dryopithecus.

CHAPTER LVI.

PLIOCENE AND POST-PLIOCENE PERIODS.
ROCKS OF THE PLIOCENE PERIOD.

THE Pliocene formations contain from 40 to 95 per cent of
existing species of Mollusca, the remainder belonging to extinct
species. They are divided by Sir Charles Lyell into two
divisions, the Older Pliocene and Newer Pliocene.

The Pliocene deposits of Britain occur in Suffolk, and are
known by the name of " Crags," this being a local term used

PLIOCENE AND POST-PLIOCENE PERIODS. 555

for certain shelly sands, which are employed in agriculture.
Two of these Crags are referable to the Older Pliocene — viz.,
the White and Red Crags, — and one belongs to the Newer
Pliocene, viz., the Norwich Crag.

The White or Coralline Crag of Suffolk is the oldest of the
Pliocene deposits of Britain, and is an exceedingly local for-
mation, occurring in but a single small area, and having a
maximum thickness of not more than 50 feet. It consists of
soft sands, with occasional intercalations of flaggy limestone.
Though of small extent and thickness, the Coralline Crag is of
importance from the number of fossils which it contains. The
name "Coralline" is a misnomer; since there are few true
Corals, and the so-called "Corals" of the formation are really
Polyzoa, often of very singular forms. The shells of the Coral-
line Crag are mostly such as inhabit the seas of temperate
regions ; but there occur some forms usually looked upon as
indicating a warm climate.

The Upper or Red Crag of Suffolk — like the Coralline Crag
—has a limited geographical extent and a small thickness,
rarely exceeding 40 feet. It consists of quartzose sands, usu-
ally deep red or brown in colour, and charged with numerous
fossils.

Altogether more than 200 species of shells are known from
the Red Crag, of which 60 per cent are referable to existing
species. The shells indicate upon the whole a temperate or
even cold climate, decidedly less warm than that indicated by
the organic remains of the Coralline Crag. It appears, there-
fore, that a gradual refrigeration was going on during the
Pliocene period, commencing in the Coralline Crag, becoming
intensified in the Red Crag, being still more severe in the
Norwich Crag, and finally culminating in the Arctic cold of the
Glacial period.

Besides the Mollusca, the Red Crag contains the ear-bones
of Whales, the teeth of Sharks and Rays, and remains of the
Mastodon, Rhinoceros, and Tapir.

The Newer Pliocene deposits are represented in Britain by
the Norwich Crag, a local formation occurring near Norwich.
It consists of incoherent sands, loams, and gravels, resting in
detached patches, from 2 to 20 feet in thickness, upon an
eroded surface of Chalk. The Norwich Crag contains a mix-
ture of marine, land, and fresh-water shells, with remains of
fishes and bones of mammals ; so that it must have been de-
posited as a local sea-deposit near the mouth of an ancient
river. It contains altogether more than 100 marine shells, of
which 89 per cent belong to existing species. Of the Mam-

556 HISTORICAL PALEONTOLOGY.

mals, the two most important are an Elephant (Elephas meri-
dionalis), and the characteristic Pliocene Mastodon (M. Arver-
nensis), which is hitherto the only Mastodon found in Britain.

The following are the more important Pliocene deposits
which have been hitherto recognised out of Britain :—

1. In the neighbourhood of Antwerp occur certain " crags,"
which are the equivalent of the White and Red Crag in part.
The lowest of these contains less than 50 per cent, and the
highest 60 per cent, of existing species of shells, the remainder
being extinct.

2. Bordering the chain of the Apennines, in Italy, on both
sides are a series of low hills made up of Tertiary strata, which
are known as the Sub-Apennine beds. Part of these is of
Miocene age, part is Older Pliocene, and a portion 'is Newer
Pliocene. The Older Pliocene portion of the Sub-Apennines
consists of blue or brown marls, which sometimes attain a
thickness of 2000 feet.

3. In the valley of the Arno, above Florence, are both
Older and Newer Pliocene strata. The former consist of blue
clays and lignites, with an abundance of plants. The latter
consist of sands and conglomerates, with remains of large Car-
nivorous Mammals, Mastodon, Elephant, Rhinoceros, Hippo-
potamus, &c.

4. In Sicily, Newer Pliocene strata are probably more largely
developed than anywhere else in the world, rising sometimes
to a height of 3000 feet above the sea. The series consists
of clays, marls, sands, and conglomerates, capped by a com-
pact limestone, which attains a thickness of from 700 to 800
feet. The fossils of these beds belong almost entirely to living
species, one of the commonest being the Great Scallop of the
Mediterranean (Pecten Jacobaus].

5. Occupying an extensive area round. the Caspian, Aral,
and Azof Seas, are Pliocene deposits known as the " Aralo-
Caspian " beds. The fossils in these beds are partly fresh-
water, partly marine, and partly intermediate in character, and
they are in great part identical with species now inhabiting
the Caspian. The entire formation appears to indicate the
former existence of a great sheet of brackish water, forming an
inland sea, like the Caspian, but as large as, or larger than, the
Mediterranean.

6. In the United States, strata of Pliocene age are found in
North and South Carolina. They consist of sands and clays,
with numerous fossils, chiefly Molluscs and Echinoderms.
From 40 to 60 per cent of the fossils belong to existing
species. On the Loup Fork of the river Platte, in the Upper

POST-PLIOCENE PERIOD. 557

Missouri region, are strata which are also believed to be refer-
able to the Pliocene period, and probably to its upper division.
They are from 300 to 400 feet thick, and contain land-shells,
with the bones of numerous Mammals, such as Camels, Rhino-
ceroses, Mastodons, Elephants, the Horse, Stag, &c.

LIFE OF THE PLIOCENE PERIOD. — As regards the life of
the Pliocene period, it is sufficient to indicate two general
considerations. In the first place, we have to notice that the
introduction upon the globe of existing species of animals was
carried on rapidly during this period. In the older Pliocene
deposits the number of shells of existing species is only from
40 to 60 per cent ; but in the Newer Pliocene the proportion
of existing species rises to as much as 80 to 95 per cent. The
Mammals still all belong to extinct species, but modern types
gradually supersede the more antique forms of the Eocene and
Miocene periods. In the second place, there is good evidence
to show that the Pliocene period was one in which the climate
of the northern hemisphere gradually became colder. In the
Miocene period, as we have seen, Europe possessed a climate
probably very similar to that now enjoyed by the Southern
States of the Union, and certainly very much warmer than its
present climate. In the Older Pliocene, northern forms, on
the other hand, predominate among the shells, though some
of the types of warmer "regions still survive. In the Newer
Pliocene, the Mollusca are almost exclusively such as inhabit
the seas of temperate or even cold regions. It might be
thought that the occurrence of Mammals such as the Elephant,
Rhinoceros, and Hippopotamus, would prove that the climate
of Europe and the United States must have been a hot one
during the later portion of the Pliocene period. We have,
however, reason to believe that many of these extinct quadru-
peds were more abundantly furnished with hair, and more
adapted to withstand a cool temperature, than any of their
living congeners.

Amongst the Pliocene Mammals may be mentioned the
following, as comprising the more important forms : —

Mastodon Arvernensis.
Elephas meridionalis.
Elephas antiquus.
Rhinoceros megarhinus.

Tapirus Arvernensis.
Machairodus ctiltridens.
Ursus Arvernensis.
Equus plicidens.

Hippopotamus major.

POST-PLIOCENE PERIOD.

Later than any of the Tertiary formations are a series of de-
posits which are spoken of as Post-Tertiary or Quaternary,
and which are characterised by the fact that all the contained

558 HISTORICAL PALAEONTOLOGY.

shells belong to existing species. The Post-Tertiary deposits
are divided by -Sir Charles Lyell into Post-Pliocene, in which
the shells belong entirely to existing species, but some of the
Mammals are extinct ; and the Recent, in which the shells and
the Mammals alike belong to existing species.

The Recent deposits do not properly concern the Palaeonto-
logist, but the Zoologist, since they contain the remains of none
but existing animals. The Post-Pliocene deposits, on the
other hand, contain the remains of various extinct Mammals,
and therefore properly form part of the domain of the palaeon-
tologist. The deposits of the Post-Pliocene period may be
divided into those which preceded the Glacial period, those
which were formed during the Glacial epoch, and those which
are Post-Glacial.

I. PRE-GLACIAL DEPOSITS. — The chief pre-glacial deposit of
Britain is found on the Norfolk coast, reposing upon the Newer
Pliocene (Norwich Crag), and consists of an ancient land-sur-
face which is known as the " Cromer Forest-bed."

This consists of an ancient soil, having embedded in it the
stumps of many trees, still in an erect position, with remains
of living plants, and the bones of recent and extinct quadru-
peds. It is overlaid by fresh-water and marine beds, all the
shells of which belong to existing species, and it is finally sur-
mounted by true "glacial drift." While all the shells and
plants of the Cromer Forest-bed and its associated strata belong
to existing species, the Mammals are partly living, partly ex-
tinct. Thus, we find the existing Wolf, Bison, Reindeer,
Beaver, Walrus, &c., side by side with three extinct Elephants,
the Rhinoceros, and Hippopotamus, and a gigantic extinct
Beaver. Among the Elephants are two Pliocene species, viz.,
Elephas meridionalis and Elephas antiquus. The third species
is the Mammoth (Elephas primigenius), which has not as yet
been detected in strata of Pliocene age. The following list is
given by Mr Boyd Dawkins as comprising the most important
Mammals as yet known in the " Forest-bed : " —

LIST OF PRE-GLACIAL MAMMALS.

Ursus Arvernensis.

Ursus spelaus (? Etruscus).

Sorex.

Mygale moschata.

Talpa Europcea,

Cervus megaceros ?

Cervus capreolus.

Cervus elaphus.

Cervus Sedgwickii.

Cervus ardeus.

Bos primigenius.
Hippopotamus major.
Equus fossilis.
Rhinoceros megarhinus.
Rhinoceros Etruscus.
Elephas antiquus.
Elephas meridionalis.
Arvicola amphibia.
Castor fiber.
Trogontherium Cuvieri.

POST-PLIOCENE PERIOD. 559

II. GLACIAL DEPOSITS. — Under this head is included a
great series of deposits which are widely spread over both
Europe and America, and which were formed at a time when
the climate of these countries was very much colder than it is at
present, and approached more or less closely to what we see at
the present day in the Arctic regions. These deposits are
known by the general name of the Glacial deposits, or by the
more specialised names of the Drift, the Northern Drift, the
Boulder-clay, the Till, &c.

These glacial deposits are found in Britain as far south as
the Thames, over the whole of Northern Europe, in all the
more elevated portions of Southern and Central Europe, and
over the whole of North America, as far south as the 39th par-
allel. They generally occur as sands, clays, and gravels,
spread in widely-extended sheets over all the geological forma-
tions alike, except the most recent, and are commonly spoken
of under the general term of " Glacial drift." They vary much
in their exact nature in different districts, but they universally
consist of one, or all, of the following members : —

1. Unstratified clays, or loams, containing numerous angular
or sub-angular blocks of stone, which have often been trans-
ported for a greater or less distance from their parent rock,
and which often exhibit polished, grooved, or striated surfaces.
These beds are what is called Boulder-clay, or Till.

2. Sands, gravels, and clays, often more or less regularly
stratified, but containing erratic blocks, often of large size, and
with their edges unworn, derived from considerable distances
from the place where they are now found. In these beds it is
not at all uncommon to find fossil shells ; and these, though of
existing species, are mostly of an Arctic character, comprising
a majority of forms which are now exclusively found in the icy
waters of the Arctic seas. These beds are often spoken of as
"Stratified Drift."

3. Stratified sands and gravels, in which the pebbles are
worn and rounded, and which have been produced by a re-
arrangement of ordinary glacial beds by the sea. These beds
are commonly known as " Drift-gravels," or " Regenerated
Drift."

The fossils of the Glacial deposits are almost exclusively
shells, which belong to existing species, but are referable to
species now inhabiting cold regions. The most important
Glacial shells are the following : —

560 HISTORICAL PALAEONTOLOGY.

Pecten Islandicus.
Astarte borealis.
Leda oblonga.
Saxicava rugosa.
Tellina proximo,.
Tel Una solidula.
Leda truncata.
Astarte compressa.

Trophon clathratum.
Natica clausa.
Scalaria Grcenlandica.
Bucdnum undatum.
Purpura lapillus.
Fusus Islandicus.
Littorina littorea.

III. POST-GLACIAL DEPOSITS. — Under this head are in-
cluded various fluviatile deposits, such as brick-earths, low-
level and high-level gravels, and all those accumulations which
are generally understood by the terms " cave-deposits," " ossi-
ferous breccias," and the like. The fossils of these deposits
consist chiefly of the bones of Mammals, both living and
extinct, in many instances mixed with the bones, or, more
commonly, the implements of man in his earliest and rudest
condition. Most of the Pre-glacial Mammals which have
been previously enumerated, survived the Glacial period, and
appear in Post-glacial deposits; but along with these are
other forms — some extinct, some still in existence — which are
not known to have lived in times prior to the Glacial epoch.
The following list is given by Mr Boyd. Dawkins of the
Mammals which inhabited Britain during the Post-glacial
epoch : —

LIST OF POST-GLACIAL MAMMALS.

Palaeolithic Man.

The Glutton (Gulo luscus).

The Cave Bear ( Ursus spelaus) ?

The Grizzly Bear (Ursus ferox) ?

The Cave Lion (Felis leo=Felis spelaa).

The Cave Hyaena (Hycena spel&a).

The Panther (Felis pardus).

The Musk-sheep (Ovibos moschatus).

The Tichorhine Rhinoceros (R. tichorhinus).

The Mammoth (Elephas primigenius).

The Lemming (My odes Icmmtis).

The Cave Pika (Lagomys).

The Pouched Marmot (Spermophilus).

Spermophilus erythrogenoides.

GEOGRAPHICAL SUCCESSION OF ORGANIC FORMS.

A few words may be said here on a law which may be called
the " law of the geographical succession of organic forms,"
and which is illustrated more completely by the Mammalia
than by any other extinct animals. An examination, namely,
of the facts of the geological distribution of Mammals, leads to
the striking generalisation that " the present distribution of
organic forms dates back to a period anterior to the origin of

GEOGRAPHICAL SUCCESSION OF ORGANIC FORMS. 561

existing species " (Lyell). In other words, though the extinct
Mammals of the later geological deposits of any given country
differ specifically from those now existing in the same country,
they are nevertheless referable to the same orders, and are in
every respect more closely allied to the present Mammalian
fauna than to that of any other country. A few examples will
render this perfectly clear.

Australia at the present day is an altogether peculiar zoolo-
gical province, characterised by the abundance and variety of
Marsupials which inhabit it. In the Post-tertiary deposits of
Australia, however, we are presented with proofs that Marsu-
pials were just as characteristic of Australia during late geolo-
gical epochs as they are now. In the Post-pliocene period
we know that Australia was occupied by Kangaroos, Kan-
garoo-rats, Wombats, Phalangers, and Carnivorous Marsupials,
in every way representing the living Marsupials in zoological
value, but specifically distinct, and generally of gigantic size.

In the same way, South America at the present day is espe-
cially characterised by a Mammalian fauna containing many
peculiar forms, the Edentata being especially conspicuous, and
having a larger representation than in any other region.
Similar but distinct forms, however, are found to have existed
in South America anterior to the creation of any existing
species. Thus, the modern Sloths of South America are re-
presented by the colossal Mylodon, Megalonyx, Scelidotherium,
and Megatherium. The little armour-plated Armadillos are
represented by the equally colossal Glyptodon. The Llamas-
representing in South America the Camels of the Old World —
are represented by the curious extinct genus Macrauchenia.
The Platyrhine Monkeys have their extinct representatives.
Fossil Tapirs take the place of the two existing species ; and
the Peccaries are represented by at least five extinct species
of Dicotyles. The bone-caves of Brazil have also yielded re-
mains of Sloths, Coatis, Kinkajous, Armadillos, Guinea-pigs,
Agoutis, Capybaras, Pacas, Coypus, Vampire Bats, and Cerco-
labes, allied to, yet distinct from, the species now inhabiting
South America.

Similarly, India is at present the only country in which
four-horned Antelopes occur; and it is in the Siwalik Hills
that there have been found the two gigantic four-horned An-
telopes, which constitute the genera Sivatherium and Brama-
therium.

In Europe, again, the Mammalian fauna of the later Ter-
tiary periods is much more closely allied to that now charac-
terising the Old World, than to that of the New. We have

2 N

562 HISTORICAL PALEONTOLOGY.

the Lion, Bear, Wolf, Fox, and other well-known Carnivora.
Elephants, Ehinoceroses, and Hippopotami, then as now, are
characteristic Old World forms. The Ruminants are equally
characteristic of the eastern hemisphere, though not exclu-
sively confined to it, and they have numerous and varied re-
presentatives in later Tertiary deposits. The Giraffe is repre-
sented by the Helladotherium, and the Bactrian Camel by the
Merycotherium of the Siberian Drift. The fossil Quadrumana,
too, of Europe, all belong to the Catarhine section of the
order.

It is unnecessary to pursue the subject further, but no law
is more firmly established than this : " That with extinct as
with existing Mammalia, particular forms were assigned to
particular provinces ; and that the same forms were restricted
to the same provinces at a former geological period as they
are at the present day " (Owen). It is to be borne in mind,
however, that the law, as just stated, holds good for the later
Tertiary period only, and does not apply, in any manner that
admits of being traced, to the earlier geological epochs.

GLOSSARY.

ABDOMEN (Lat. abdo, I conceal). The posterior cavity of the body, contain-
ing the intestines and others of the viscera. In many Invertebrates there
is no separation of the body-cavity into thorax and abdomen, and it is only
in the higher Annulosa that a distinct abdomen can be said to exist.

ABEREANT (Lat. aberro, I wander away). Departing from the regular type.

ABNORMAL (Lat. ab, from ; norma, a rule). Irregular ; deviating from the
ordinary standard.

ABRANCHIATE (Gr. a, without; bragchia, gill). Destitute of gills or bran-
chiae.

ACANTHOPTERYGII (Gr. akantha, spine ; pterux, wing). A group of bony
fishes with spinous rays in the front part of the dorsal fin.

ACARINA (Gr. akari, a mite). A division of the Arachnida, of which the
Cheese-mite is the type.

ACEPHALOUS (Gr. a, without ; kephale, head). Not possessing a distinct
head.

ACETABULA (Lat. acetabulum, a cup). The suckers with which the cephalic
processes of many Cephalopoda (Cuttle-fishes) are provided.

ACETABULUM. The cup-shaped socket of the hip-joint in Vertebrates.

ACRODONT (Gr. akros, high ; odous^tooih). Applied to Lizards, in which the
teeth are anchylosed with the summit of the jaw.

ACROGENS (Gr. akros, high ; gennao, I produce. ) Plants which increase in
height by additions made to the summit of the stem, by the union of the
bases of the leaves.

ACTINOZOA (Gr. aktin, a ray ; and zoon, an animal). That division of the
Ccelenterata of which the Sea-anemones may be taken as the type.

ALVEOLI (Lat. dim. of alvus, belly). Applied to the sockets of the teeth.

AMBULACRA (Lat. ambulacrum, a place for walking). The perforated spaces
or "avenues" through which are protruded the tube-feet, by means of
which locomotion is effected in the Echinodermata.

AMBULATORY (Lat. ambulo, I walk). Formed for walking. Applied to a
single limb, or to an entire animal.

AMMONITID^;. A family of Tetrabranchiate Cephalopods, so called from the
resemblance of the shell of the type-genus, Ammonites, to the horns of the
Egyptian God, Jupiter- Ammon.

AMCEBA (Gr. amoibos, changing). A species of Rhizopod, so called from the
numerous changes of form which it undergoes.

AJVKEBIFORM. Resembling an Amoeba in form.

AMORPHOZOA (Gr. a, without ; morphe, shape ; zoon, animal). A name some-
times used to designate the Sponges.

AMPHIBIA (Gr. amphi, both; bios, life). The Frogs, Newts, and the like,
which have gills when young, but can always breathe air directly when
adult.

AMPHICCELOUS (Gr. amphi, at both ends ; koilos, hollow). Applied to verte-
brae which are concave at both ends.

564

GLOSSARY.

AMPHIPODA (Gr. amphi, and pous, a foot). An order of Crustacea.

ANAL (Lat. anus, the vent). Connected with the anus, or situated near the

anus.
ANARTHROPODA (Gr. a, without ; arthros, a joint ; pous, foot). That division

of Annulose animals in which there are no articulated appendages.
ANCHYLOSIS or ANKYLOSIS (Gr. ankulos, crooked). The union of two bones

by osseous matter, so that they become one bone, or are immovably joined

together.
ANGIOSPERMS (Gr. angeion, a vessel ; sperma, seed). Plants which have their

seeds enclosed in a seed-vessel.
ANNELIDA (a Gallicised form of Annulata). The Ringed worms, which form

one of the divisions of the A nartkropoda.
ANNULATED. Composed of a succession of rings.

ANNULOIDA (Lat. annulus, a ring ; Gr. eidos, form). The sub-kingdom com-
prising the Echinodermata and the Scolecida(=Echinozoa).
ANNULOSA (Lat. annulus). The sub-kingdom comprising the Anarthropoda

and the Arthropoda or Articulata, in all of which the body is more or less

evidently composed of a succession of rings.
ANOMODONTIA (Gr. anomos, irregular; odous, tooth). An extinct order of

Reptiles, often called Dicynodontia.
ANOMURA (Gr. anomos, irregular ; oura, tail). A tribe of Decapod Crustacea,

of which the Hermit-crab is the type.
ANOPLOTHERID^: (Gr. anoplos, unarmed ; ther, beast). A family of Tertiary

Ungulates.
ANOURA (Gr. a, without ; oura, tail). The order of Amphibia comprising the

Frogs and Toads, in which the adult is destitute of a tail. Olten called

Batrachia.
ANTENNA (Lat. antenna, a yard-arm). The jointed horns or feelers possessed

by the majority of the Articulata.
ANTENNULES (dim. of Antennae). Applied to the smaller pair of antennae in

the Crustacea.
ANTIBRACHIUM (Gr. anti, in front of ; Irachion, the arm). The fore-arm of

the higher Vertebrates, composed of the radius and ulna.
ANTLERS. Properly the branches of the horns of the Deer tribe (Cervidce),

but generally applied to the entire horns.
APIOCRINID.E (Gr. apion, a pear; krinon, lily). A family of Crinoids — the

" Pear-encrinites."
APLACENTALIA. The section of the Mammalia, comprising the two divisions

of the Didelphia and Monodelphia, in which the young is not furnished

with a placenta.
APODA (Gr. a, without ; podes, feet). Applied to those fishes which have no

ventral fins. Also to the footless Ccecilice amongst the Amphibia.
APODAL. Devoid of feet.
APTERA (Gr. a, without ; pteron, a wing). A division of Insects, which is

characterised by the absence of wings in the adult condition.
APTEROUS. Devoid of wings.
APTERYX (Gr. a, without; pterux, a wing). A wingless bird of New Zealand,

belonging to the order Cursores.
ARACHNIDA (Gr. arachne, a spider). A class of the Articulata, comprising

Spiders, Scorpions, and allied animals.
ARBORESCENT. Branched like a tree.
ARCH^OPTERYX (Gr. archaios, ancient ; pterux, wing). The singular fossil

bird which alone constitutes the order of the Saurarce.
ARENACEOUS. Sandy, or composed of grains of sand.
ARTICULATA (Lat. articulus, a joint). A division of the animal kingdom,

comprising Insects, Centipedes, Spiders, and Crustaceans, characterised by

the possession of jointed bodies or jointed limbs. The term Arthropoda is

now more usually employed.
ARTIODACTYLA (Gr. artios, even ; daktulos, a finger or toe). A division of

the hoofed quadrupeds (Unyulata) in which each foot has an even number

of toes (two or four).

GLOSSARY. 565

ASCIDIOIDA (Gr. asJcos, a bottle ; eidos, a form). A synonym of Tunicata, a
class of Molluscous animals, which have the shape, in many cases, of a
two-necked bottle.

ASEXUAL. Applied to modes of reproduction in which the sexes are not
concerned.

ASIPHONATE. Not possessing a respiratory tube or siphon. (Applied to a
division of the Lamellibranchiate Molluscs).

ASTEROID (Gr. aster, a star ; and eidos, form). Star-shaped, or possessing
radiating lobes or rays like a star-fish.

ASTEROIDEA. An order of Echinodermata, comprising the Star-fishes, char-
acterised by their rayed form.

ASTOMATOUS (Gr. a, without; stoma, mouth). Not possessing a mouth.

ATLAS (Gr. the God who holds up the earth). The first vertebra of the neck,
which articulates with and supports the skull.

AVES (Lat. avis, a bird). The class of the Birds.

AVICULARIUM (Lat. avicula, dim. of avis, a Bird). A singular appendage,
often shaped like the head of a bird, found in many of the Polyzoa.

Axis (Gr. axon, a pivot). The second vertebra of the neck, upon which the
skull and atlas usually rotate.

AZYGOUS (Gr. a, without ; zugon, yoke). Single ; without a fellow.

BALANID^E (Gr. balanos, an acorn). A family of sessile Cirripedes, commonly
called "Acorn- shells."

BALEEN (Lat. balwna, a whale). The horny plates which occupy the palate
of the true or " whalebone" Whales.

BATIDFS (Gr. bates, a bramble). The family of the Elasmobranchii comprising
the Rays.

BATRACHIA (Gr. batrachos, a frog). Often loosely applied to any of the Am-
phibia, but sometimes restricted to the Amphibians as a class, or to the
single order of the Anoura.

BELEMNITID^E (Gr. belemnon, a dart). An extinct group of Dibranchiate
Cephalopods, comprising the Belemnites and their allies.

BIFID. Cleft into two parts ; forked.

BILATERAL. Having two symmetrical sides.

BIMANA (Lat. bis, twice ; manus, a hand). The order of Mammalia compris-
ing man alone.

BIPEDAL (Lat. bis, twice ; pes, foot). Walking upon two legs.

BIVALVE (Lat. bis, twice ; valvce, folding-doors). Composed of two plates or
valves ; applied to the shell of the Lamellibranchiata and Brachiopoda, and
to the carapace of certain Crustacea.

BLASTOIDEA (Gr. blastos, a bud ; and eidos, form). An extinct order of Echi-
nodermata, often called Pentremites.

BRACHIOPODA (Gr. brachion, an arm ; pous, the foot). A class of the Mollus-
coida, often called "Lamp-shells," characterised by possessing two fleshy
arms continued from the sides of the mouth.

BRACHIUM (Gr. brachion, arm). Applied to the upper arm of Vertebrates.

BRACHYURA (Gr. brachus, short ; oura, tail). A tribe of the Decapod Crusta-
ceans with short tails (i.e., the Crabs).

BRADYPODIDJE (Gr. bradus, slow ; podes, feet). The family of Edentata com-
prising the Sloths.

BRANCHIA (Gr. bragchia, the gill of a fish). A respiratory organ adapted to
breathe air dissolved in water.

BRANCHIATE. Possessing gills or braiichiaB.

BRANCHIFERA (Gr. bragchia, gill; andphero, I carry). A division of Oaslero-
podous Molluscs, in which the respiration is aquatic, and the respiratory
organs are mostly in the form of distinct gills.

BRANCHIO-GASTEROPODA (= Branchifera).

BRANCHIOPODA (Gr. bragchia; and pous, foot). A legion of Crustacea, in
which the gills are supported by the feet.

BRANCHIOSTEGAL (Gr. bragchia, gill; stego, I cover). Applied to a membrane
and rays by which the gills are protected in many fishes.

566 GLOSSARY.

BRUTA (Lat. brutus, heavy, stupid). Often used to designate the Mammalian
order of the Edentata.

BRTOZOA (Gr. bruon, moss ; zoSn, animal). A synonym of Polyzoa, a class of
the Molluscoida.

BUCOAL (Lat. lucca, mouth or cheeks). Connected with the mouth.

BURSIPORM (Lat. bursa, a purse ; forma, shape). Shaped like a purse ; sub-
spherical.

BYSSIFEROUS. Producing a byssus.

BYSSDS (Gr. bussos, flax). A term applied to the silky filaments by which
the Pinna, the common Mussel, and certain other bivalve Mollusca, attach
themselves to foreign objects.

CADUCIBRANCHIATE (Lat. caducus, falling off; Gr. bragchia, gill). Applied
to those Amphibians in which the gills fall off before maturity is
reached.

CADUCOUS. Applied to parts which fall off or are shed during the life of the
animal.

C2ECAL (Lat. ccecus, blind). Terminating blindly, or in a closed extremity.

C^CUM (Lat. ccecus). A tube which terminates blindly.

C^ESPITOSE (Lat. ccespes, a turf). Tufted.

CAINOZOIC. (See Kainozoic.)

CALAMITES (Lat. calamus, a reed). Extinct plants with reed-like stems, be-
lieved to be gigantic representatives of the Equisetacece.

CALCAREOUS (Lat. calx, lime). Composed of carbonate of lime.

CALICE. The little cup in which the polype of a coralligenous Zoophyte
(Actinozo&n) is contained.

CALYCOPHORID^E (Gr. kalux, a cup ; and phero, I carry). An order of the
Oceanic Hydrozoa, so called from their possessing bell-shaped swimming
organs (nectocalyces).

CALYX (Lat. calyx, a cup)'. Applied to the cup-shaped body of Vorticella
(Protozoa), or of a Crinoid (Echinodermata).

CAMPANULARIDA (Lat. campanula, a bell). An order of Hydroid Zoophytes.

CANINE (Lat. canis, a dog). The eye-tooth of Mammals, or the tooth which
is placed at or close to the prsemaxillary suture in the upper jaw, and the
corresponding tooth in the lower jaw.

CAPITULUM (Lat. dim. oicaput, head). Applied to the body of a Barnacle
(Lepadidce), from its being supported upon a stalk or peduncle.

CARAPACE. A protective shield. Applied to the upper shell of Crabs, Lob-
sters, and many other Crustacea; also to the case with which certain of the
Infusoria are provided. Also the upper half of the immovable case in
which the body of a Chelonian is protected.

CARINAT.E (Lat. carina, a keel). Applied by Huxley to all those birds in
which the sternum is furnished with a median ridge or keel.

CARNIVORA (Lat. caro, flesh ; voro, I devour). An order of the Mammalia.

CARNIVOROUS (Lat. caro, flesh ; voro, I devour). Feeding upon flesh.

CARNOSE (Lat. caro). Fleshy.

CARPUS (Gr. karpos, the wrist). The small bones which intervene between
the fore-arm and the metacarpus.

CATARHINA (Gr. kata, downwards ; rhines, nostrils). A group of the Quadru*
mana.

CAUDAL (Lat. cauda, the tail). Belonging to the tail.

CAVICORNIA (Lat. cavus, hollow ; cornu, a horn). The " hollow-horned "
Ruminants, in which the horn consists of a central bony "horn-core" sur-
rounded by a horny sheath.

CENTRUM (Gr. kentron, the point round which a circle is described by a pair
of compasses). The central portion or " body" of a vertebra.

CEPHALASPID^E (Gr. kephale, head ; aspis, shield). A family of fossil fishes.

CEPHALIC (Gr. kephale, head). Belonging to the head.

CEPHALO-BRANCHIATE (Gr. kephale; and bragchia, gill). Carrying gills upon
the head. Applied to a section of the Annelida, which, like the Serpulce,
have tufts of external gills placed upon the head.

GLOSSARY. 567

CEPHALOPHORA (Gr. kephale; andphero, I carry). Used synonymously with
Encephala, to designate those Mollusca which possess a distinct head.

CEPHALOPODA (Gr. kephale ; and podes, feet). A class of the Mollusca, com-
prising the Cuttle-fishes and their allies, in which there is a series of arms
ranged round the head.

CEPHALOTHORAX (Gr. kephale; and thorax, chest). The anterior division of
the body in many Crustacea and Arachnida, which is composed of the
coalesced head and chest.

CERVICAL (Lat. cervix, neck). Connected with the region of the neck.

CESTRAPHORI (Gr. kestra, a weapon ; pliero, I carry). The group of Elasmo-
branchii represented at the present day by the Port Jackson Shark.

CETACEA (Gr. ketos, a whale). The order of Mammals comprising the Whales
and Dolphins.

CHEIROPTERA (Gr. cheir, hand ; pteron, a wing). The order of Mammals com-
prising the Bats.

CHEL.E (Gr. elide, a claw). The prehensile claws with which some of the
limbs are terminated in certain Crustacea, such as the Crab, Lobster, &c.

CHELATE. Possessing chelae ; applied to a limb.

CHELICER.S: (Gr. chele, a claw ; and keras, a horn). The prehensile claws of
the Scorpion, supposed to be homologous with antennae.

CHELONIA (Gr. chelone, a tortoise). The order of Keptiles comprising the
Tortoises and Turtles.

CHELONOBATRACHIA (Gr. chelone, a tortoise ; batrachos, a frog). Sometimes
applied to the Amphibian order of the Anoura (Frogs and Toads).

CHILOGNATHA (Gr. cheilos, a lip ; and gnathos, a jaw). An order of the My-
riapoda.

CHILOPODA (Gr. cheilos ; and podes, feet). An order of the Myriapoda.

CHITINK (Gr. chiton, a coat). The peculiar chemical principle, nearly allied
to horn, which forms the exoskeleton in many Invertebrate Animals, espe-
cially in the Arthropoda (Crustacea, Insecta, &c.)

CIRRI (Lat. cirrus, a curl). Tendril-like appendages, such as the feet of Bar-
nacles and Acorn-shells (Cirripedes), the lateral processes on the arms of
Brachiopoda, &c.

CIRRIFEROUS or CiRRiGEROUS. Carrying cirri.

CIRRIPEDIA, CIRRHIPEDIA, or CiRRHOPODA (Lat. cirrus, a curl ; and pes, a
foot). A sub-class of Crustacea with curled jointed feet.

CLADOCERA (Gr. klados, a branch ; keras, a horn). An order of Crustacea with
branched antennae.

CLAVATE (Lat. clavus, a club). Club-shaped.

CLAVICLE (Lat. clavicula, a little key). The " collar-bone," forming one of the
elements of the pectoral arch of Vertebrates.

CLOACA (Lat. a sink). The cavity into which the intestinal canal and the
ducts of the generative and urinary organs open in common, in some In-
vertebrates (e.g., in Insects), and also in many Vertebrate animals.

CLYPEIFORM (Lat. clypeus, a shield ; and forma, shape). Shield-shaped ; ap-
, plied, for example, to the carapace of the King-crab.

CCELENTERATA (Gr. koilos, hollow ; enteron, the bowel). The sub-kingdom
which comprises the Hydrozoa and Actinozoa. Proposed by Frey and
Leuckhart in place of the old term Radiata, which included other animals
as well.

CCENENCHYMA (Gr. koinos, common ; enchuma, tissue, literally an infxision).
The common calcareous tissue which unites together the various corallites
of a compound corallum.

CCENCECIUM (Gr. koinos, common ; oikos, house). The entire dermal system
of any Polyzoou : employed in place of the terms polyzoary or polypidom.

COENOSARC (Gr. koinos, common ; sarx, flesh). The common organised me-
dium by which the separate polypites of a compound Hydrozoon are con-
nected together.

COLEOPTKRA (Gr. koleos, a sheath; pteron, wing). The order of Insects
(Beetles) in which the anterior pair of wings are hardened, and serve as pro-
tective cases for the posterior pair of membranous wings.

568 GLOSSARY.

COLUBRINA (Lat. coluber, a snake). A division of the Opkidia.
COLUMBACEI (Lat. columba, a dove). The division of Rasoriai birds compris-
ing the Doves and Pigeons.
COLUMELLA (Lat. dim. of columna, a column). In Conchology, the central

axis round which the whorls of a spiral univalve are wound. Amongst the

A ctinozoa, it is the central axis or pillar which is found in the centre of the

thecae of many corals.
COLUMN. Applied to the cylindrical body of a Sea-anemone (Actinia) ; also

to the jointed stem or peduncle of the stalked Crinoids..
CONCHIFERA (Lat concka, a shell ; fero, I carry). Shell-fish. Applied in a

restricted sense to the bivalve Molluscs, and used as a synonym for Lamelli-

brancldata.
CONDYLE (Gr. kondulos, a knuckle). The surface by which one bone articulates

with another. Applied especially to the articular surface or surfaces by

which the skull 'articulates with the vertebral column.
CONIROSTRES (Lat. conns, a cone ; rostrum, a beak). The division of Perching

Birds with conical beaks.

COPEPODA (Gr. kope, an oar ; podes, feet). An order of Crustacea.
CORACOID (Gr. korax, a crow ; eidos, form). One of the bones which enters

into the composition of the pectoral arch in Birds, Reptiles, and Mono-

tremes. In most Mammals it is a mere process of the scapula, having, in ,

man, some resemblance in shape to the beak of a crow.
CORALLIGENOUS. Producing a corallum.
CORALLITE. The corallum secreted by an Actinozob'n which consists of a single

polype ; or the portion of a composite corallum which belongs to, and is

secreted by, an individual polype.
CORALLUM (from the Latin for Red Coral). The hard structures deposited in,

or by, the tissues of an Actinozob'n — commonly called a " coral."
CORIACEOUS (Lat. corium, hide). Leathery.
CORYNIDA (Gr. korune, a club). A group of the Hydroid Zoophytes, so called

from their sometimes possessing clubbed tentacles.
COST^E (Lat. costa, a rib). Applied amongst the Crinoidea to designate the

rows of plates which succeed the inferior or basal portion of the cup (pel-
vis). Amongst the Corals the " costie " are vertical ridges which occur

on the outer surface of the theca, and mark the position of the septa

within.

COSTAL (Lat. costa, a rib). Connected with the ribs.
CRANIUM (Gr. kranion, the skull). The bony or cartilaginous case in which

the brain is contained.

CRINOIDEA (Gr. krinon, a lily; eidos, form). An order of Echinodermata, com-
prising forms which are usually stalked, and sometimes resemble lilies in

shape.

CROCODILIA (Gr. krokodeilos, a crocodile). An order of Reptiles.
CROSSOPTERYGID.-E (Gr. krossotos, a fringe ; pterux, a fin). A sub-order of

Ganoids in which the paired fins possess a central lobe.
CRUSTACEA (Lat. crusta, a crust). A class of Articulate animals, comprising

Crabs, Lobstei*s, &c., characterised by the possession of a hard shell or

crust, which they cast periodically.
CRYPTOGAMS (Gr. kruptos, concealed ; gamos, marriage). A division of plants

in which the organs of reproduction are obscure and there are no true

flowers.
CTENOID (Gr. kteis, a comb ; eidos, form). Applied to those scales of fishes,

the hinder margins of which are fringed with spines or comb-like projections.
CTENOPHORA (Gr. kteis, a comb ; and phero, I carry). An order of Adinozoa,

comprising oceanic creatures, which swim by means of "ctenophores," or

bands of cilia arranged in comb-like plates.
CURSORES (Lat. curro, I run). An order of Aves, comprising birds destitute

of the power of flight, but formed for running vigorously (e.g., the Ostrich

and Emeu).

CUSPIDATE. Furnished with small pointed eminences or " cusps."
CUTICLE (Lat. cuticula, dim. of cutis, skin). The pellicle which forms the

GLOSSARY. 569

outer layer of the body amongst the Infusoria. The outer layer of the

integument generally.
CYCLOID (Gr. kuklos, a circle ; eidos, form). Applied to those scales of fishes

which have a regularly circular or elliptical outline with an even margin.
CYCLOSTOMI (Gr. kuklos, and stoma, mouth). Sometimes used to designate

the Hag-fishes and Lampreys, forming the order Marsipobranchii.
CYST (Gr. kustis, a bladder or bag). A sac or vesicle.
UYSTOIDEA (Gr. kustis, a bladder; and eidos, form). An extinct order of

Echinodermata.

DECAPODA (Gr. deka, ten ; podes, feet). The division of Crustacea which have

ten ambulatory feet ; also the family of Cuttle-fishes, in which there are

ten arms or cephalic processes.
DECIDUOUS (Lat. decido, I fall off). Applied to parts which fall off or are

shed during the life of the animal.
DECOLLATED (Lat. decollo, I behead). Applied to univalve shells, the apex of

which falls off in the course of growth.

DEINOSAURIA (Gr. deinos, terrible ; saura, lizard). An extinct order of Rep-
tiles.
DENDRIFORM, DENDRITIC, DENDROID (Gr. dendron, a tree). Branched like a

tree, arborescent.

DERMAL (Gr. derma, skin). Belonging to the integument.
DESMIDI^E. Minute fresh- water plants, of a green colour, without a siliceous

epidermis.

DEXTRAL (Lat. dextra, the right hand). Right-handed. Applied to the di-
rection of the spiral in the greater number of univalve shells.
DIAPHRAGM (Gr. diaphragma, a partition). The "midriff" or the muscle

which in Mammalia forms a partition between the cavities of the thorax

and abdomen.
DIASTEMA (Gr. dia, apart ; histemi, to place). A gap or interval, especially

between teeth.
DIATOMACE.E (Gr. diatemno, I sever). An order of minute plants, which are

provided with siliceous envelopes.
DIBRANCHIATA (Gr. dis, twice ; bragchia, gill). The order of Cephalopoda

(comprising the Cuttle-fishes, &c.) in which only two gills are present.
DICYNODONTIA (Gr. dis, twice; kuon, dog; odovs, tooth). An extinct order

of Reptiles.
DIDELPHIA (Gr. dis, twice ; delphus, womb). The subdivision of Mammals

comprising the Marsupials.
DIGIT (Lat. digitus, a finger). A finger or toe.

DIGITIGRADA (Lat. diyitus ; gradior, I walk). A subdivision of the Carnivora.
DIGITIGRADE. Walking upon the tips of the toes, and not upon the soles of

the feet.
DIMYARY (Gr. dis, twice ; muon, muscle). Applied to those bivalve Molluscs

(Lamellibranchiata) in which the shell is closed by two adductor muscles.
DIPHYODONT (Gr. dis, twice; phuo, I generate; odous, tooth). Applied to

those Mammals which have two sets of teeth.
DIPNOI (Gr. dis, twice ; piwe, breath). The order of Fishes represented by

the Lepidosiren.
DIPTERA (Gr. dis, twice ; pteron, wing). An order of Insects characterised by

the possession of two wings.
DISCOID (Gr. diskos, a quoit ; eidos, form). Shaped like a round plate or

quoit.
DISCOPHORA (Gr. diskos, a quoit ; phero, I carry). This term is applied to the

Medusce, or Jelly-fishes, from their form ; and is sometimes used to desig-
nate the order of the Leeches (Hirudinea), from the suctorial discs which

these animals possess.
DISSEPIMENTS (Lat. dissepio, I partition off). Partitions". Used in a restricted

sense to designate certain imperfect transverse partitions, which grow from

the septa of many corals.
DISTAL. Applied to the quickly-growing end of the hydrosoma of a Hydro-

570 GLOSSARY.

zoon; the opposite, or "proximal," extremity growing less rapidly, and
being the end by which the organism is fixed, when attached at all.

DIURNAL (Lat. dies, day). Applied to animals which are active during the
day.

DORSAL (Lat. dorsum, back). Connected with the back.

DORSIBRANCHIATE (Lat. dorsum, the back ; Gr. bragchia, gill). Having ex-
ternal gills attached to the back ; applied to certain Anneiides&nd Mollusca.
The term is of mongrel composition, and " notobranchiate" is more cor-
rectly employed.

ECHINODERMATA (Gr. echinos; and derma, skin). A class of animals com-
prising the Sea-urchins, Star-fishes, and others, most of which have spiny
skins.

ECHINOIDEA (Gr. echinos; and eidos, form). An order of Echinodermata, com-
prising the Sea-urchins.

ECHINULATE. Possessing spines.

ECTOCYST (Gr. ektos, outside ; kustis, a bladder). The external investment of
the coencecium of a Polyzob'n.

ECTODERM (Gr. ektos, and derma, skin). The external integumentary layer of
the Ccelenterata.

EDENTATA (Lat. e, without ; dens, tooth). An order of Mammalia often
called Bruta.

EDENTULOUS. Toothless, without any dental apparatus. Applied to the
mouth of any animal, or to the hinge of the bivalve Molluscs.

EDRIOPHTHALMATA (Gr. hedraios, sitting ; ophthalmos, eye). The division
of Crustacea in which the eyes are sessile, and are not supported upon
stalks.

ELASMOBRANCHII (Gr. elasma, a plate ; bragchia, gill). An order of Fishes,
including the Sharks and Rays.

ELYTRA (Gr. elutron, a sheath). The chitinous anterior pair of wings in
Beetles, which form cases for the posterior membranous wings. Also ap-
plied to the scales or plates on the back of the Sea-mouse (Aphrodite).

EMBRYO (Gr. en, in ; bruo, I swell). The earliest stage at which the young
animal is recognisable in the impregnated ovum.

ENALIOSAURIA (Gr. enalios, marine ; saura, lizard). Sometimes employed as
a common term to designate the extinct Reptilian orders of the Jchthyosauria
and Plesiosauria.

ENCEPHALOUS (Gr. en, in ; kephale, the head). Possessing a distinct head.
Usually applied to all the Mollusca proper, except the Lamellibranchiata.

ENDOCYST (Gr. endon, within ; kustis, a bag). The inner membrane or in-
tegumentary layer of a Polyzob'n. In Cristatella, where there is no " ecto-
cyst," the endocyst constitutes the entire integument.

ENDODERM (Gr. endon; aud derma, skin). The inner integumentary layer of
the Ccelenterata.

ENDOPODITE (Gr. endon ; and pous, foot). The inner of the two secondary
joints into which the typical limb of a Crustacean is divided.

ENDOSKELETON (Gr. endon; and skeletos, dry). The internal hard structures,
such as bones, which serve for the attachment of muscles, or the protec-
tion of organs, and which are not a mere hardening of the integument.

ENSIFORM (Lat. ensis, a sword ; forma, shape). Sword-shaped.

ENTOMOPHAGA (Gr. entoma, insects ; phago, I eat). A section of the Marsu-
pialia.

ENTOMOSTRACA (Gr. entoma, insects ; ostrakon, a shell). Literally Shelled
Insects, applied to a division of Crustacea.

ENTOZOA (Gr. enlos, within ; zoon, animal). Animals which are parasitic in
the interior of other animals.

EOCENE (Gr. eos, dawn ; kainos, new or recent). The lowest division of the
Tertiary Rocks, in which species of existing shells are to a small extent
represented.

EPIDERMIS (Gr. epi, upon ; derma, the true skin). The outer non-vascular
layer of the skin, often called the scarf-skin or cuticle.

GLOSSARY. 571

EPIMERA (Or. epi, upon ; meron, thigh). The lateral pieces of the dorsal arc

of the somite of a Crustacean.
EPIPODIA (Gr. epi, upon ; pous, the foot). Muscular lobes developed from

the lateral and upper surfaces of the " foot" of some Molluscs.
EPIPODITE (Gr. epi, upon ; pous, foot). A process developed upon the basal

joint, or " protopodite," of some of the limbs of certain Crustacea.
EPISTERNA (Gr. epi, upon ; sternon, the breast-bone). The lateral pieces of

the inferior or ventral arc of the somite of a Crustacean,
EPISTOME (Gr. epi; and stoma, mouth). A valve-like organ which arches

over the mouth in certain of the Polyzoa.
EPITHECA (Gr. epi ; and theke, a sheath). A continuous layer surrounding

the thecse in some Corals externally.
EPIZOA (Gr. epi, upon ; zoo'n, animal). Animals which are parasitic upon

other animals. In a restricted sense, a division of Crustacea which are

parasitic upon fishes.
EQUILATERAL (Lat. aguus, equal ; latus, side). Having its sides equal.

Usually applied to the shells of the Brachiopoda. When applied to the

spiral shells of the Foraminifera, it means that all the convolutions of the

shell lie in the same plane.
EQUISETACEA (Lat. eyuus, horse ; seta, bristle). A group of Cryptogamous

plants, commonly known as " Horse-tails."
EQUIVALVE (Lat. wquus, equal ; valvce, folding-doors). Applied to shells

which are composed of two equal pieces or valves.
ERRANTIA (Lat. erro, I wander). An order of Annelida, often called Nereidea,

distinguished by their great locomotive powers.
EURYPTERIDA (Gr. eurus, broad ; pteron, wing). An extinct sub-order of

Crustacea.
EXOPODITE (Gr. exo, outside ; pous, foot). The outer of the two secondary

joints into which the typical limb of a Crustacean is divided.
EXOSKELETON (Gr. exo, outside ; skeletos, dry. The external skeleton, which

is constituted by a hardening of the integument, and is often called a

" dermoskeleton."

FASCICULATED (Lat. fasciculus, a bundle). Arranged in bundles.

FAUNA (Lat. Fauni, the rural deities of the Romans). The general assem-
blage of the animals of any region or district.

FEMUR. The thigh-bone, intervening between the pelvis and the bones of
the leg proper (tibia and fibula).

FIBULA (Lat. a brooch). The outermost of the two bones of the leg in the
higher Vertebrata ; corresponding to the ulna of the fore-arm.

FILICES (Lat. filix, a fern). The order of Cryptogamic plants comprising the
Ferns.

FILIFORM (Lat.fihim, a thread ; forma, shape). Thread-shaped.

FISSION (Lat. findo, I cleave). Multiplication by means of a process of self-
division.

FISSIPAROUS (Lat. findo ; and pario, I produce). Giving origin to fresh struc-
tures by a process of fission.

FLORA (Lat. Flora, the goddess of flowers). The general assemblage of the
plants of any region or district.

FOOT- JAWS. The limbs of Crustacea, which are modified to subserve mastica-
tion.

FOOT-SECRETION. The term applied by Mr Dana to the sclerobasic corallum
of certain A ctinozoa.

FOOT-TUBERCLES. The unarticulated appendages of the Annelida, often
called parapodia.

FORAMINIFERA (Lat. foramen, an aperture ; fero, I carry). An order of Pro-
tozoa, usually characterised by the possession of a shell perforated by
numerous pseudopodial apertures.

FRUGIVOROUS (Lat. frux, fruit; voro, I devour). Living upon fruits.

FUCOIDS (Lat. fucus, sea- weed ; Gr. eidos, likeness). Fossils, often of an
obscure nature, believed to be the remains of sea-weeds.

5/2 GLOSSARY.

FURCULUM or FURCULA (Lat. dim. of f urea, a fork). The " merry- thought "
of birds, or the V-ishaped bone formed by the united clavicles.

FUSIFORM (Lat. fusus, a spindle; and forma, shape). Spindle-shaped, or
pointed at both ends.

GALLINACEI (Lat. gallina, a fowl). Sometimes applied to the whole order of
the Rasorial Birds, but properly restricted to that section of the order of
which the common Fowl is a typical example.

GANGLION (Gr. gagglion, a knot). A mass of nervous matter containing
nerve-cells, and giving origin to nerve-fibres.

GANOID (Gr. ganos, splendour, brightness). Applied to those scales or plates
which are composed of an inferior layer of true bone covered by a superior
layer of polished enamel.

GANOIDEI. An order of Fishes.

GASTEROPODA (Gr. gaster, stomach ; pous, foot). The class of the Molhisca
comprising the ordinary univalves, in which locomotion is usually effected
by a muscular expansion of the under surface of the body (the " foot").

GEMMAE (gemma, a bud). The buds produced by any animal, whether detached
or not.

GEMMATION. The process of producing new structures by budding.

GEMMIPAROUS (Lat. gemma, a bud ; pario, I produce). Giving origin to new
structures by a process of budding.

GEPHYREA (Gr. gephura, a bridge). A class of the Anarthropoda, comprising
the Spoon-worms (Sipunculus) and their allies.

GIZZARD. A muscular division of the stomach in Birds, Insects, &c.

GLADIUS (Lat. a sword). Applied to the horny eudoskeleton or "pen" of
certain Cuttle-fishes.

GLENOID (Gr. glene, a cavity ; eidos, form). A shallow cavity ; applied espe-
cially to the shallow articular cavity in the shoulder-blade to which the
head of the humerus is jointed.

GRALLATORES (Lat. grallce, stilts). The order of the long-legged Wading
Birds.

GRAPTOLITID^E (Gr. grapho, I write ; lithos, stone). An extinct sub-class of
the Hydrozoa.

GREGAKINIDA (Lat. gregariiis, occurring in numbers together). A class of the
Protozoa.

GUARD. The cylindrical fibrous sheath with which the internal chambered
shell (phragmacone) of a Belemnite is protected.

GYMNOL^EMATA (Gr. gumnos, naked ; laimos, the throat). An order of the
Polyzoa in which the mouth is devoid of the valvular structure known as
the "epistome."

GYMNOPHIONA (Gr. gumnos, naked ; ophis, a snake). The order of the Am-
phibia comprising the snake-like Ccecilice.

GYMNOPHTHALMATA (Gr. gumnos ; and ophthalmos, the eye). Applied by Ed-
ward Forbes to those Medusce in which the eye-specks at the margin of the
disc are unprotected. The division is now abandoned.

GYMNOSOMATA (Gr. gumnos ; and soma, the body). The order of Pteropoda
in which the body is not protected by a shell.

HALLUX (Lat. allex, the thumb or great toe). The innermost of the five

digits which normally compose the hind foot of a Vertebrate animal. In

man, the great toe.

HEMIPTERA (Gr. hemi; and pteron, wing). An order of Insects in which the
, anterior wings are sometimes " hemelytra."
HERMAPHRODITE ((3r. Hermes, Mercury ; Aphrodite, Venus). Possessing the

characters of both sexes combined.
HETEROCERCAL (Gr. heteros, diverse; kerkos, tail.) Applied to the tail of

Fishes when it is unsymmetrical, or composed of two unequal lobes.
HETEROPODA (Gr. heteros, diverse ; podes, feet). An aberrant group of the

Gasteropods, in which the foot is modified so as to form a swimming

organ.

GLOSSARY. 573

HIRUDINEA (Lat. hirudo, a horse-leech). The order of Annelida comprising

the Leeches.
HISTOLOGY (Gr. histos, a web ; logos, a discourse). The study of the tissues,

more especially of the minuter elements of the body.
HOLOCEPHALI (Gr. holos, whole ; kephale, head). A sub-order of the Elasmo-

branchii comprising the Ckimcerce.
HOLOSTOMATA (Gr. holos, whole ; stoma, mouth). A division of Gasteropodous

Molluscs, in which the aperture of the shell is rounded, or " entire."
HOLOTHUROIDEA (Gr. holothourion ; and eidos, form). An order of Echinoder-

mata comprising the Trepangs.
HOMOCERCAL (Gr. homos, same ; kerkos, tail). Applied to the tail of Fishes

when it is symmetrical, or composed of two equal lobes.
HOMOLOGOUS (Gr. homos ; and logos, a discourse). Applied to parts which

are constructed upon the same fundamental plan.
HUMERUS. The bone of the upper arm (brachium) in the Vertebrates.
HYALINE (Gr. hualos, crystal). Crystalline or glassy.
HYBODONTS (Gr. hubos, curved ; odous, tooth). A group of Fishes of which

Hybodus is the type-genus.
HYDROIDA (Gr. hudra; and eidos, form). The sub-class of the Hydrozoa,

which comprises the animals most nearly allied to the Hydra.
HYDROTIIECA (Gr. hudra; and theke, a case). The little cbitinous cups in

which the polypites of the Sertularida and Campanularida are protected.
HYDROZOA (Gr. hndra ; and 200/1, animal). The class of the Coelenterata

which comprises animals constructed after the type of the Hydra.
HYMENOPTERA (Gr. hitmen, a membrane ; pteron, a wing). An order of In-
sects (comprising Bees, Ants, &c.) characterised by the possession of four

membranous wings.

HYOID (Gr. U ; eidos, form). The bone which supports the tongue in Ver-
tebrates, and derives its name from its resemblance in man to the Greek

letter U.
HYPOSTOME (Gr. hupo, under ; stoma, mouth). The upper lip, or "labrum,"

of certain Crustacea (e.g., Trilobites).
HYRACOIDEA (Gr. hurax, a shrew ; eidos, form). An order of the Mammalia,

constituted for the reception of the single genus Hyrax.

ICHTHYODORULITE (Gr. ichthus, fish ; dorus, spear ; lithos, stone). The fossil
fin-spines of Fishes.

ICHTHYOMORPHA (Gr. ichthus ; morphe, shape). An order of Amphibians,
often called Urodela, comprising the fish-like Newts, &c.

ICHTHYOPHTHIRA (Gr. ichthus ; phtheir, a louse). An order of Crustacea com-
prising animals which are parasitic upon Fishes.

ICHTHYOPSIDA (Gr. ich thus; opsis, appearance). The primary division of
Verteorata, comprising the Fishes and Amphibia. Often spoken of as the
Branchiate Vertebrata.

ICHTHYOPTERYGIA (Gr. ichthus ; pterux, wing). An extinct order of Reptiles.

ICHTHYOSAURIA (Gr. ichthus ; saura, lizard). Synonymous with Ichthyopterygia.

ILIUM. The haunch-bone, one of the bones of the pelvic arch in the higher
Vertebrates.

IMAGO (Lat. an image or apparition). The perfect insect, after it has under-
gone its metamorphoses.

IMBRICATED. Applied to scales or plates which overlap one another like tiles.

INCISOR (Lat. incido, I cut). The cutting teeth fixed in the intermaxillary
bones of the Mammalia, and the corresponding teeth in the lower jaw.

INEQUILATERAL. Having the two sides unequal, as in the case of the shells
of the ordinary bivalves (Lamellibranchiata). When applied to the shells
of the Foraminifera, it implies that the convolutions of the shell do not lie
in the same plane, but are obliquely wound round an axis.

INEQUIVALVE. Composed of two unequal pieces or valves.

INFUNDIBULUM (Lat. for funnel). The tube formed by the coalescence or
apposition of the epipodia in the Cephalopoda. Commonly termed the
"funnel," or " siphon."

5/4 GLOSSARY.

INFUSORIA (Lat. infusum, an infusion). A class of Protozoa, so called be-
cause tbey are often developed in organic infusions.

INOPERCULATA (Lat. in, without ; operculum, a lid). The division of pul-
monate Gasteropoda in which there is no shelly or horny plate (operculum)
by which the shell is closed when the animal is withdrawn within it.

INSECTA (Lat. inseco, I cut into). The class of articulate animals commonly
known as Insects.

INSECTIVORA (Lat. insectum, an insect; voro, I devour). An order of
Mammals.

INSECTIVOROUS. Living upon Insects.

INSESSORES (Lat. insedeo, I sit upon). The order of the Perching Birds, often
called Passer es.

INTERAMBULACRA. The rows of plates in an Echinoderm which are not per-
forated for the emission of the "tube-feet."

INTERMAXILL^B, or PR^IMAXILL^. The two bones which are situated between
the two superior maxillfe in Vertebrata. In man, and some monkeys, the
praemaxillae anchylose with the maxillae, so as to be irrecognisable in the
adult.

INVERTEBRATA (Lat. in, without ; vertebra, a bone of the back). Animals
without a spinal column or backbone.

ISCHIUM (Gr. ischion, the hip). One of the bones of the pelvic arch in Verte-
brates.

ISOPODA (Gr. isos, equal ; podes, feet). An order of Crustacea in which the
feet are like one another and equal.

JUGULAR (Lat. jngulum, the throat). Connected with, or placed upon, the
throat. Applied to the ventral fins of fishes when they are placed beneath
or in advance of the pectorals.

KAINOZOIC (Gr. Icainos, recent ; zoe, life). The Tertiary period in Geology,

comprising those formations in which the organic remains approximate

more or less closely to the existing fauna and flora.
KERATODE (Gr. keras, horn ; eidos, form). The horny substance of which the

skeleton of many sponges is made up.
KERATOSA. The division of Sponges in which the skeleton is composed of

keratode.

LABIUM (Lat. for lip). Restricted to the lower lip of Articulate animals.
LABRUM (Lat. for lip). Restricted to the upper lip of Articulate animals.
LABYRINTHODONTIA (Gr. lalmrinthos, a labj'rinth ; odous, tooth). An extinct

order of Amphibia, so called from the complex microscopic structure of

the teeth.
LACERTILIA (Lat. lacerta, a lizard). An order of Reptilia comprising the

Lizards and Slow-worms.

L^GMODIPODA (Gr. laimos, throat ; dis, twice ; podes, feet). An order of Crus-
tacea, so called because they have two feet placed far forwards, as it were,

under the throat.
LAMELLIBRANCHIATA (Lat. lamella, a plate ; Gr. braffchia, gill). The class of

Mollusca, comprising the ordinary bivalves, characterised by the possession

of lamellar gills.

LAMELLIROSTRES (Lat. lamella, a plate ; rostrum, beak). The flat-billed Swim-
ming Birds (Natatores), such as Ducks, Geese, Swans, &c.
LARVA (Lat. a mask). The insect in its first stage after its emergence from

the egg, when it is usually very different from the adult.
LARYNX. The upper part of the windpipe, forming a cavity with appropriate

muscles and cartilages, situated beneath the hyoid bone, and concerned in

Mammals in the production of vocal sounds.
LENTICULAR (Lat. lens, a bean). Shaped like a biconvex lens.
LEPIDODENDRON (Gr. lepis, a scale ; dendron, a tree). A genus of extinct

plants, so named from the scale-like scars upon the stem left by the falling

off of the leaves.

GLOSSARY. 575

LEPIDOPTERA (Gr. lepis, a scale ; pteron, a wing). An order of Insects, com-
prising Butterflies and Moths, characterised by possessing four wings which
are usually covered with minute scales.

LEPIDOTA (Gr. lepis, a scale). Formerly applied to the order Dipnoi, con-
taining the Mud-fishes (Lepidosireri).

LEPTOCARDIA (Gr. leptos, slender, small ; cardia, heart). The name given by
Muller to the order of Fishes comprising the Lancelot, now called Pharyn-
gobranchii.

LOPHOPHORE (Gr. lophos, a crest ; and phero, I carry). The disc or stage
upon which the tentacles of the Polyzoa are borne.

LOPHYROPODA (Gr. lophouros, having stiff hairs ; and podes, feet). A section
of Crustacea.

LORICATA (Lat. lorica, a cuirass). The division of Reptiles comprising the
Chelonia and Crocodilia, in which bony plates are developed in the skin
(derma).

LUCERNARIDA (Lat. lucerna, a lamp). An order of the Hydrozoa.

LUMBAR (Lat. lumbus, loin). Connected with the loins.

LUNATE (Lat. luna, moon). Crescentic in shape.

LYCOPODIACE.E (Gr. lupos, a wolf ; pous, foot). The group of Cryptogamic
plants generally known as " Club-mosses."

MACRURA (Gr. makros, long ; oura, tail). A tribe of Decapod Crustaceans with
long tails (e.g., the Lobster, Shrimp, &c.)

MADREPORIFORM. Perforated with small holes, like a coral ; applied to the
tubercle by which the ambulacral system of the Echinoderms mostly com-
municates with the exterior.

MALACOSTRACA (Gr. malakos, soft ; ostralcon, shell). A division of Crustacea.
Originally applied by Aristotle to the entire class Crustacea, because their
shells were softer than those of the Mollusca.

MAMMALIA (Lat. mamma, the breast). The class of Vertebrate animals which
suckle their young.

MANDIBLE (Lat. mandibulum, a jaw). The upper pair of jaws in Insects ;
also applied to one of the pairs of jaws in Crustacea and Spiders, to the beak
of Cephalopoda, the lower jaw of Vertebrates, &c.

MANTLE. The external integument of most of the Mollusca, which is largely
developed, and forms a cloak in which the viscera are protected. Techni-
cally called the "pallium."

MANUS (Lat. the hand). The hand of the higher Vertebrates.

MARSIPOBRANCHII (Gr. marsipos, a pouch ; bragchia, gill). The order of
Fishes comprising the Hag-fishes and Lampreys, with pouch-like gills.

MARSUPIALIA (Lat. marsupium, a pouch). An order of Mammals in which the
females mostly have an abdominal pouch in which the young are carried.

MASTICATORY (Lat. mastico, I chew). Applied to parts adapted for chewing.

MAXILLA (Lat. jaws). The inferior pair or pairs of jaws in the Arthropoda
(Insects, Crustacea, &c. ) The upper jaw-bones of Vertebrates.

MAXILLIPEDES (Lat. maxillce, jaws ; pes, the foot). The limbs in Crustacea
and Myriapoda which are converted into masticatory organs, and are com-
monly called " foot-jaws."

MEDULLA (Lat. marrow). Applied to the marrow of bones ; or to the spinal
cord, with or without the adjective " spinalis."

MEDUSA. An order of Hydrozoa, commonly known as Jelly-fishes (Disco-
phora, or Acalephce), so called because of the resemblance of their tentacles
to the snaky hair of the Medusa. Many Medusae are now known to be
merely the gonophores of Hydrozoa.

MEROSTQMATA (Gr. meron, thigh ; stoma, mouth). An order of Crustacea in
which the appendages which are placed round the mouth, and which offi-
ciate as jaws, have their free extremities developed into walking or pre-
hensile organs.

MESENTERIES (Gr. mesos, intermediate ; enteron, intestine). In a restricted
sense, the vertical plates which divide the somatic cavity of a Sea-anemone
(Actinia) into chambers.

GLOSSARY.

MESOPODIUM (Gr. mesos, middle ; pous, foot). The middle portion of the
"foot" of Molluscs.

MESOSTERNUM (Gr. mesos, intermediate ; sternon, the breast-bone). The
middle portion of the sternum, intervening between the attachment of the
second pair of ribs and the xiphoid cartilage (xiphisternum).

MESOTHORAX (Gr. mesos; and thorax, the chest). The middle ring of the
thorax in Insects,

MESOZOIC (Gr. meson ; and zoe, life). The Secondary period in Geology.

METACARPUS (Gr. meta, after ; karpos, the wrist). The bones which form the
"root of the hand," and intervene between the wrist and the fingers.

METAMORPHOSIS (Gr. meta, implying change ; morphe, shape). The changes
of form which certain animals undergo in passing from their younger to
their fully-grown condition.

METAPODIUM (Gr. meta, after ; pous, the foot). The posterior lobe of the foot
in Mollusca; often called the "operculigerous lobe," because it develops
the operculum when this structure is present.

METASTOMA (Gr. meta, after ; stoma, mouth). The plate which closes the
mouth posteriorly in the Crustacea.

METATARSUS (Gr. meta, after ; tarsos, the instep). The bones which inter-
vene between the bones of the ankle (tarsus) and the digits in the hind-foot
of the higher Vertebrates.

METATHORAX (Gr. meta, after ; thorax, the chest). The posterior ring of the
thorax in Insects.

MIMETIC (Gr. mimetikos, imitative). Applied to organs or animals which re-
semble each other in external appearance, but not in essential structure.

MOLARS (Lat. mola, a mill). The "grinders" in man, or the teeth in diphyo-
dont Mammals which are not preceded by milk-teeth.

MOLLDSCA (Lat. molds, soft). The sub-kingdom which includes the Shell-
fish proper, the Polyzoa, the Tunicata, and the Lamp-shells; so called from
the generally soft nature of their bodies.

MOLLUSCOIDA (Mollusca; Gr. eidos, form). The lower division of tho Mollusca,
comprising the Polyzoa, Tunicata, and Drachiopoda.

MONODELPHIA (Gr. monos, single ; delphus, womb). The division of Mammalia
in which the uterus is single.

MONOMYARY (Gr. monos, single; muon, muscle). Applied to those bivalves
(Lamellibranchiata) in which the shell is closed by a single adductor muscle.

MONOPHYODONT (Gr. monos ; phuo, I generate; odous, tooth). Applied to
those Mammals in which only a single set of teeth is ever developed.

MONOTHALAMOUS (Gr. monos ; and thalamos, chamber). Possessing only a
single chamber. Applied to the shells of Foraminifera and Mollusca.

MONOTREMATA (Gr. monos ; trema, aperture). The order of Mammals com-
prising the Duck-mole and Echidna, in which the intestinal canal opens
into a "cloaca" common to the ducts of the urinary and generative organs.

MULTILOCULAR (Lat. multus, many; loculus, a little purse). Divided into
many chambers.

MULTIVALVE. Applied to shells which are composed of many pieces.

MULTQNGULA (Lat. multus, many; ungula, hoof). The division of Perisso-
dactyle Ungulates, in which each foot has more than a single hoof.

MYRIAPODA or MYRIOPODA (Gr. murios, ten thousand ; podes, feet). A class
of Arthropoda comprising the Centipedes and their allies, characterised by
their numerous feet.

NACREOUS (Fr. nacre, mother-of-pearl, originally Oriental.) Pearly; of the

texture of mother-of-pearl.

NATATORES (Lat. nare, to swim). The order of the Swimming Birds.
NATATORY (Lat. nare, to swim). Formed for swimming.
NAUTILOID. Resembling the shell of the Nautilus in shape.
NERVURES (Lat. nervus, a sinew). The ribs which support the membranous

wings of insects.

NEURAL (Gr. neuron, a nerve). Connected with the nervous system.
NEURAPOPHYSIS (Gr. neuron, a nerve ; apophusis, a projecting part). The

GLOSSARY. 577

" spinous process " of a vertebra, or the process formed at the point of
junction of the neural arches.

NEUROPTERA (Gr. neuron ; and pteron, a wing). An order of Insects charac-
terised by four membranous wings with numerous reticulated nervures
(e.g., Dragon- flies).

NOCTURNAL (Lat. nox, night). Applied to animals which are active by night.

NORMAL (Lat. norma, a rule). Conforming, to the ordinary standard.

NOTOBRANCHIATA (Gr. notos, the back ; and bragchia, gill). Carrying the
gills upon the back ; applied to a division of the Annelida.

NOTOCHORD (Gr. notos, back ; chorde, string). A cellular rod which is devel-
oped in the embryo of Vertebrates immediately beneath the spinal cord,
and which is usually replaced in the adult by the vertebral column. Often
it is spoken of as the " chorda dorsalis."

NUDIBRANCHIATA (Lat. nudus, naked ; and Gr. bragchia, gill). An order of
the Gasteropoda in which the gills are naked.

NUMMULITES (Lat. nummus, a coin). A large coin-shaped Foraminifer of the
Eocene period.

OCCIPITAL. Connected with the occiput, or the back part of the head.

OCEANIC. Applied to animals which inhabit the open ocean ( = pelagic).

OCELLI (Lat. diminutive of oculus, eye). The simple eyes of many Echino-
derms, Spiders, Crustaceans, Molluscs, &c.

OCTOPODA (Gr. oclo, eight ; pous, foot). The tribe of Cuttle-fishes with eight
arms attached to the head.

ODONTOCETI (Gr. odous, tooth; ketos, whale). The "toothed" Whales, in
contradistinction to the " whalebone " Whales.

ODONTOID (Gr. odous ; eidos, form). The "odontoid process " is the centrum
or body of the first cervical vertebra (atlas). It is detached from the atlas,
and is usually auchylosed with the second cervical vertebra (axis), and it
forms the pivot upon which the head rotates.

ODONTOPHORE (Gr. odous, tooth; phero, I carry). The so-called "tongue,"
or masticatory apparatus of Gasteropoda, Pteropoda, and Cephalopoda.

OESOPHAGUS. The gullet or tube leading from the mouth to the stomach.

OLIGOCH^TA (Gr. oligos, few ; chaite, hair). An order of Annelida, compris-
ing the Earth-worms, in which there are few bristles.

OMNIVOROUS (Lat. omnia, everything ; voro, I devour). Feeding indiscrimin-
ately upon all sorts of food.

OPERCULATA (Lat. operculum, a lid). A division of pulmonate Gasteropoda,
in which the shell is closed by an operculum.

OPERCULUM. A horny or shelly plate developed in certain Mollusca upon the
hinder part of the foot, and serving to close the aperture of the shell when
the animal is retracted within it ; also the lid of the shell of a Balanus or
Acorn- shell ; also the chain of flat bones which cover the gills in many
fishes.

OPHIDIA (Gr. ophis, a serpent). The order of Reptiles comprising the Snakes.

OPHIDOB ATRACHIA (Gr. ophis ; batrachos, a frog). Sometimes applied to the
order of Snake-like Amphibians comprising the Ccecilice.

OPHIOMORPHA (Gr. ophis ; morphe, shape). The order of Amphibia compris-
ing the Ccecilice.

OPHIUROIDEA (Gr. ophis, snake ; oura, tail ; eidos, form). An order of Echino-
dermata, comprising the Brittle-stars and Sand-stars.

OPISTHOBRANCHIATA (Gr. opisthen, behind ; bragchia, gill). A division of
Gasteropoda in which the gills are placed on the posterior part of the body.

OPISTHOCCELOUS (Gr. opisthen, behind ; koilos, hollow). Applied to vertebrae,
the bodies of which are hollow or concave behind.

ORAL (Lat. os, mouth). Connected with the mouth.

ORNITHODELPHIA (Gr. ornis, a bird ; delphus, womb). The primary division
of Mammals comprising the Monotremata.

ORNITHOSCELIDA (Gr. ornis, bird ; skelos, leg). Applied by Huxley to the
Deinosaurian Reptiles, together with the genus Compsognathus, on account
of the bird-like character of their hind-limbs.

2 O

5/3

GLOSSARY.

ORTHOCERATID.E (Gr. orthos, straight ; Jceras, horn). A family of the Nau-

tilidce, in which the shell is straight, or nearly so.
ORTHOPTERA (Gr. orthos, straight ; pteron, wing). An order of Insects.
OSSICULA (Lat. diminutive of os, bone). Literally small bones. Often used

to designate any hard structures of small size, such as the calcareous plates

in the integument of the Star-fishes.
OSTRACODA (Gr. ostrakon, a shell). An order of small Crustaceans which are

enclosed in bivalve shells.
OTOLITHS (Gr. ous, ear ; and lithos, stone). The calcareous bodies connected

with the sense of hearing, even in its most rudimentary form.
OVARIAN VESICLES or CAPSULES. The generative buds of the Sertularida.

PACHYDERMATA (Gr. pachus, thick ; derma, skin). An old Mammalian order
constituted by Cuvier for the reception of the Rhinoceros, Hippopotamus,
•Elephant, &c.

PALAEONTOLOGY (Gr. palaios, ancient ; and logos, discourse). The science of
fossil remains or of extinct organised beings.

PALJEOTHERID.E (Gr. palaios, ancient ; ther, beast). A group of Tertiary
Ungulates.

PALAEOZOIC (Gr. palaios, ancient ; and zoe, life). Applied to the oldest of the
great geological epochs.

PALLIOBRANCHIATA (Lat. pallium ; and Gr. bragchia, gill). An old name for
the Brachiopoda, founded upon the belief that the system of tubes in the
mantle constituted the gills.

PALLIUM (Lat. pallium, a cloak). The mantle of the Mollusca. Pallial :
relating to the mantle. Pallial line or impression : the line left it) the dead
shell by the muscular margin of the mantle. Pallial shell ; a shell which is
secreted by, or contained within, the mantle, such as the " bone " of the
Cuttle-fishes.

PALPI (Lat. palpo, I touch). Processes supposed to be organs of touch,
developed from certain of the oral appendages in Insects, Spiders, and Crus-
tacea, and from the sides of the mouth in the Acephalous Molluscs.

PAPILLA (Lat. for nipple). A minute soft prominence.

PARAPODIA (Gr. para, beside ; podes, feet). The imarticulated lateral loco-
motive processes or " foot-tubercles " of many of the Annelida.

PARIETAL (Lat. paries, a wall). Connected with the walls of a cavity or of
the body.

PATAGIUM (Lat. the border of a dress). Applied to the expansion of the in-
tegument by which Bats, Flying Squirrels, and other animals support them-
selves in the air.

PATELLA. The knee-cap or knee-pan. A sesamoid bone developed in the
tendon of insertion of the great extensor muscles of the thigh.

PECTINATE (Lat. pecten, a comb). Comb-like ; applied to the gills of certain
Gasteropods, hence called Pectinibranchiata.

PECTORAL (Lat. pectus, chest). Connected with, or placed upon, the chest.

PEDAL (Lat. pes, the foot). Connected with the foot of Mollusca.

PEDICELLARLE (Lat. pedicellus, a louse). Certain singular appendages found
in many Echinoderms, attached to the surface of the body, and resembling
a little beak or forceps supported on a stalk.

PEDICLE (Lat. dim. of pes, the foot). A little stem.

PEDIPALPI (Lat. pes, ,foot ; and palpo, I feel). An order of Arachnida com-
prising the Scorpions, &c.

PEDUNCLE (Lat. pedunculus, a stem or stalk). In a restricted sense applied
to the muscular process by which certain Brachiopods are attached, and
to the stem which bears the body (capitulum) in Barnacles.

PEDUNCULATE. Possessing a peduncle.

PELAGIC (Gr. pelagos, sea). Inhabiting tbe open ocean.

PELVIS (Lat. for basin). Applied, from analogy, to the basal portion of the
cup (calyx) of Crinoids. The bony arch with which the hind -limbs are
connected in Vertebrates.

PERENNIBRANCHIATA (Lat. perennis, perpetual ; Gr. bragchia, gill). Applied to

GLOSSARY. 579

those Amphibia in which the gills are permanently retained throughout

life.

PERGAMENTACEOUS (Lat. pergamena, parchment). Of the texture of parchment.
PERIOSTBACUM (Gr. peri, around ; and ostrakon, shell). The layer of epidermis

which covers the shell in most of the Mollusca.

PERISOME (Gr. peri ; and soma, body). The coriaceous or calcareous integu-
ment of the Echinodermata.
PERISSODACTYLA (Gr. perissos, uneven ; daklulos, finger). Applied to those

Hoofed Quadrupeds (Ungulata) in which the feet have an uneven number

of toes.

PETALOID. Shaped like the petal of a flower.
PHALANGES (Gr. phalanx, a row). The small bones composing the digits of

the higher Vertebrata. Normally each digit has three phalanges.
PHANEROGAMS (Gr. phaneros, visible ; gamos, marriage). Plants which have

the organs of reproduction conspicuous, and which bear true flowers.
PHARTNGOBRANCHII (Gr. pharugx, pharynx ; bragchia, gill). The order of

Fishes comprising only the Lancelet.
PHARYNX. The dilated commencement of the gullet.
PHRAGMACONE (Gr. phragma, a partition ; and konos, a cone). The chambered

portion of the internal shell of a Belemnite.
PHYLACTOLJEMATA (Gr. phulasso, I guard ; and laimos, throat). The division

of Polyzoa in which the mouth is provided with the arched valvular process

known as the "epistome."

PHYLLOPODA (Gr. phullon, leaf ; and pous, foot). An order of Crustacea.
PHYSOPHORID.S: (Gr. phusa, air-bladder ; and phero, I carry). An order of

Oceanic Hydrozoa.

PHYTOID (Gr. phuton, a plant ; and eidos, form). Plant-like.
PHYTOPHAGOUS (Gr. phuton, a plant ; and phago, I eat). Plant-eating, or

herbivorous.

PINNATE (Lat. pinna, a feather). Feather-shaped : or possessing lateral pro-
cesses.
PINNIGRADA (Lat. pinna, a feather ; gradior, I walk). The group of Carni-

vora, comprising the Seals and Walruses, adapted for an aquatic life. Often

called Pinnipedia.

PINNULE (Lat. dim. of pinna). The lateral processes of the arms of Crinoids.
PISCES (Lat. piscis, a fish). The class of Vertebrates comprising the Fishes.
PLACENTA (Lat. a cake). The " after- birth," or the organ by which a vascu-
lar connection is established in the higher Mammalia between the mother

and the foetus.

PLACENTAL. Possessing a placenta ; or connected with the placenta.
PLACOID (Gr. plax, a plate; eidos, form). Applied to the irregular bony

plates, grains, or spines which are found in the skin of various fishes

( Elasmobranchii) .
PLAGIOSTOMI (Gr. plagios, transverse ; stoma, mouth). The Sharks and Rays,

in which the mouth is transverse, and is placed on the under surface of the

head.
PLANTIGRADE (Lat. planta, the sole ef the foot ; gradior, I walk). Applying

the sole of the foot to the ground in walking.

PLASTRON. The lower or ventral portion of the bony case of the Chelonians.
PLATYRHINA (Gr. platus, broad ; rhines, nostrils). A group of the Quadrumana.
PLEURODONT (Gr. pleuron, rib, side ; odous, tooth). Having the teeth anchy-

losed with the inner side of the jaws.

PLEURON (Gr. pleuron, a rib). The lateral extensions of the shell of Crustacea.
PNEUMATIC (Gr. pneuma, air). Filled with air.
PODOPHTHALMATA (Gr. pous, f oot ; and ophthalmos, eye). The division of

Crustacea in which the eyes are borne at the end of long footstalks.
POLLEX (Lat. the thumb). The innermost of the five normal digits of the

anterior limb of the higher Vertebrates. In man, the thumb.
POLYCYSTINA (Gr. polus, many ; and kustis, a cyst). An order of Protozoa,

with foraminated siliceous shells.
POLYPARY. The hard chitiuous covering secreted by many of the Hydrozoa.

580 GLOSSARY.

POLYPE (Gr. polus, many ; pous, foot). Restricted to the single individual of
a simple Actinozoon, such as a Sea-anemone, or to the separate zooids of a
compound Actinozoon. Often applied indiscriminately to any of the Ccelen-
terata, or even to the Polyzoa.

POLYPIDE. The separate zob'id of a Polyzoon.

POLYPIDOM. The dermal system of a colony of a Hydrozoon, or Polyzoon.

POLYPITE. The separate zob'id of a Hydrozoon.

POLYTHALAMOUS (Gr. polus ; and thalamos, chamber). Having many cham-
bers ; applied to the shells of Foraminifera and Cephalopoda.

POLYZOA (Gr. polus ; and zoon, animal). A division of the Molluscoida com-
prising compound animals such as the Sea-mat — sometimes called Bryozoa.

POLYZOARIUM. The dermal system of the colony of a Polyzoon (= Polypidom).

PORCELLANOUS. Of the texture of porcelain.

PORIFERA (Lat. porus, a pore ; &ndfero, I carry). Sometimes used to desig-
nate the Foraminifera, or the Sponges.

POST-ANAL. Situated behind the anus.

POST-CESOPHAGEAL. Situated behind the gullet.

POST-ORAL. Situated behind the mouth.

PRjEMAXiLLJE — see Intermaxillse.

, PR^EMOLARS (Lat. prce, before; molares, the grinders). The molar teeth of
Mammals which succeed the molars of the milk-set of teeth. In man, the
bicuspid teeth.

PRjE-ossoPHAGEAL. Situated in front of the gullet.

PR.& -STERNUM. The anterior portion of the breast-bone, corresponding with
the inanubrium sterni of human anatomy, and extending as far as the point
of articulation of the second rib.

PROBOSCIDEA (Lat. proboscis, the snout). The order of Mammals comprising
the Elephants.

PROCCELOUS (Gr. pro, before ; koilos, hollow). Applied to vertebrae, the bodies
of which are hollow or concave in front.

PROPODIUM (Gr. pro, before ; pous, foot). The anterior part of the foot in
Molluscs.

PROSOBRANCHIATA (Gr. proson, in advance of; bragchia, a gill). A division
of Gasteropodous Molluscs in which the gills are situated in advance of the
heart.

PROSOMA (Gr. pro, before ; soma, body). The anterior part of the body.

PROTHORAX (Gr. pro ; and t/iorax, chest). The anterior ring of the thorax of
insects.

PROTOPHYTA (Gr. protos ; and phuton, plant). The lowest division of plants.

PROTOPLASM (Gr. protos; and plasso, I mould). The elementary basis of or-
ganised tissues. Sometimes used synonymously for the "sarcode" of the
Protozoa.

PROTOPODITE (Gr. protos, first ; and pous, foot). The basal segment of the
typical limb of a Crustacean.

PROTOZOA (Gr. protos ; and zoon, animal). The lowest division of the animal
kingdom.

PROXIMAL (Lat. proximus, next). The slowly-growing, comparatively-fixed
extremity of a limb or of an organism.

PSEUDOPODIA (Gr. pseudos, falsity ; and poiis, foot). The extensions of the
body-substance which are put forth by the Rhizopoda at will, and which
serve for locomotion and prehension.

PTEROPODA (Gr. pteron, wing ; and pous, foot). A class of the Mollusca which
swim by means of fins attached near the head.

PTEROSAURIA (Gr. pteron, wing ; saura, lizard). An extinct order of Reptiles.

PUBIS (Lat. pubes, hair). The share-bone ; one of the bones which enter into
the composition of the pelvic arch of Vertebrates.

PULMOGASTEROPODA (= Pulmonifera).

PULMONARIA. A division of Arachnida which breathe by means of pulmo-
nary sacs.

PULMONIFERA (Lat. pulmo, a lung ; and/m>, I carry). The division of Mol-
lusca which breathe by means of a pulmonary chamber.

GLOSSARY. 581

PULMONATE. Possessing lungs.

PYKIFOEM (Lat. pyrus, a pear ; and/orww, form). Pear-shaped.

QUADRUMANA (Lat. quatuor, four ; manus, hand). The order of Mammals
comprising the Apes, Monkeys, Baboons, Lemurs, &c.

RADIATA (Lat. radios, a ray). Formerly applied to a large number of animals
which are now placed in separate sub-kingdoms (e.g., the C'celenterata, the
Echinodermata, the Infusoria, &c.)

RADIOLARIA (Lat. radius, a ray). A division of Protozoa.

RADIUS (Lat. a spoke or ray). The innermost of the two bones of the fore-
arm of the higher Vertebrates. It carries the thumb, when present, and
corresponds with the tibia of the hind-limb.

RAMUS (Lat. a branch). Applied to each half or branch of the lower jaw, or
mandible, of Vertebrates.

RAPTORES (Lat. rapto, I plunder). The order of the Birds of Prey.

RASORES (Lat. rado, I scratch). The order of the Scratching Birds (Fowls,
Pigeons, &c.)

RATIT^ (Lat. rates, a raft). Applied by Huxley to the Cursorial Birds, which
do not fly, and have therefore a raft-like sternum without any median
keel.

RECTUM (Lat. rectus, straight). The terminal portion of the intestinal canal,
opening at the surface of the body at the anus.

REPTILIA (Lat. repto, I crawl). The class of the Vertebrata comprising the
Tortoises, Snakes, Lizards, Crocodiles, &c.

REVERSED. Applied to spiral univalves, in which the direction of the spiral
is the reverse of the normal — i.e., sinistral.

RHIZOPHAGA (Gr. rhiza, root ; phago, I eat). A group of the Marsupials.

RHIZOPODA (Gr. rhiza, a root ; and pous, foot). The division of Protozoa com-
prising all those which are capable of emitting pseudopodia.

RHYNCHOLITES (Gr. rhunchos, beak ; and lithos, stone). Beak-shaped fossils
consisting of the mandibles of Cephalopoda.

RODENTIA (Lat. rodo, I gnaw). An order of the Mammals; often called Glires
(Lat. glis, a dormouse).

RUGOSA (Lat. rugosus, wrinkled). An order of Corals.

RUMINANTIA (Lat. ruminor, I chew the cud). The group of Hoofed Quadru-
peds (Ungidata) which " ruminate " or chew the cud.

SACRUM. The vertebrae (usually anchylosed) which unite with the haunch-
bones (ilia) to form the pelvis.

SAND-CANAL (= STONE-CANAL). The tube by which water is conveyed from
the exterior to the ambulacral system of the Echinodermata.

SARCODE (Gr. sarx, flesh ; eidos, form). The jelly-like substance of which
the bodies of the Protozoa are composed. It is an albuminous body contain-
ing oil-granules, and is sometimes called " animal protoplasm."

SARCOIDS (Gr. sarx ; and eidos, form). The separate amoebiform particles
which in the aggregate make up the " flesh " of a Sponge.

SAURIA (Gr. saura, a lizard). Any lizard-like Reptile is often spoken of as a
" Saurian ; " but the term is sometimes restricted to the Crocodiles alone,
or to the Crocodiles and Lacertilians.

SAUROBATRACHIA (Gr. saura; batrachos, frog). Sometimes applied to the
order of the tailed Amphibians (Urodela).

SAUROPSIDA (Gr. saura; and opsis, appearance). The name given by Huxley
to the two classes of the Birds and Reptiles collectively.

SAUROPTERTGIA (Gr. saura; pterux, wing). An extinct order of Reptiles,
called by Huxley Plesiosauna, from the typical genus Plesiosaurus.

SAURUR.E (Gr. saura; oura, tail). The extinct order of Birds comprising
only the A rchceopteryx.

SCANSORES (Lat. scando, I climb). The order of the Climbing Birds (Parrots,
Woodpeckers, &c.)

SCAPULA (Lat. for shoulder-blade). The shoulder-blade of the pectoral arch

582 GLOSSARY.

of Vertebrates; in a restricted sense, the row of plates in the cup of
Crinoids, which give origin to the arms, and are usually called the " axil-
lary radials."

SCLERENCHYMA (Gr. sJcleros, hard ; and enchuma, tissue). The calcareous
tissue of which a coral is composed.

SCLEROBASIC (Gr. skleros, hard ; basis, pedestal). The coral which is pro-
duced by the outer surface of the integument in certain Actinozoa (e.g.,
Red Coral), and forms a solid axis which is invested by the soft parts of the
animal. It is called " foot-secretion " by Mr Dana.

SCLERODERMTC (Gr. skleros ; and derma, skin). Applied to the corallum which
is deposited within the tissues of certain Actinozoa, and is called "tissue-
secretion" by Mr Dana.

SCLEROTIC (Gr. skleros, hard). The outer dense fibrous coat of the eye.

SCOLECIDA (Gr. skolex, worm). A division of the Annuloida.

SCUTA (Lat. scutum, a shield). Applied to any shield-like plates; especially
to those which are developed in the integument of many Reptiles.

SELACHIA or SELACHII (Gr. selachos, a cartilaginous fish, probably a shark).
The sub-order of Elasmolranchii comprising the Sharks and Dog-fishes.

SEPIOSTAIRE. The internal shell of the Sepia, commonly known as the
"cuttle- bone."

SEPTA. Partitions.

SERPENTIFORM. Resembling a serpent in shape.

SERTULARIDA (Lat. sertiim, a wreath). An order of Hydrozoa.

SESSILE (Lat. sedo, I sit). Not supported upon a stalk or peduncle ; attached
by a base.

SET.E (Lat. bristles). Bristles or long stiff hairs.

SETIFEROUS. Supporting bristles.

SETIGEROUS (=Setiferous).

SETOSE. Bristly.

SIGILLARIOIDS (Lat. sigilla, little images). A group of extinct plants of which
Sigillaria is the type, so called from the seal-like markings on the bark.

SILICEOUS (Lat. silex, flint). Composed of flint.

SINISTRAL (Lat. sinistra, the left hand). Left-handed ; applied to the direc-
tion of the spiral in certain shells, which are said to be "reversed."

SIPHON (Gr. siphon, a tube). Applied to the respiratory tubes in the Mol-
lusca ; also to other tubes of different functions.

SIPHONOPHORA (Gr. siphon ; wadphero, I carry). A division of the Hydrozoa
comprising the Oceanic forms (CalycopJwridce and Physophoridce).

SIPHONOSTOMATA (Gr. siphon ; and stoma, mouth). The division of Gastero-
podous Molluscs, in which the aperture of the shell is not "entire," but
possesses a notch or tube for the emission of the respiratory siphon.

SIPHUNCLE (Lat. sipkunculus, a little tube). The tube which connects to-
gether the various chambers of the shell of certain Cephalopoda (e.g., the
Pearljr Nautilus).

SIPUNOULOIDEA (Lat. siphunculus, a little siphon). A class of Anarthropoda
(Annulosa).

SIRENIA (Gr. seiren, a mermaid). The order of Mammalia comprising the
Dugongs and Manatees.

SOLIDUNGULA (Lat. solidus, solid ; ungula, a hoof). The group of Hoofed
Quadrupeds comprising the Horse, Ass, and Zebra, in which each foot has
only a single solid hoof. Often called Solipedia.

SOMATIC (Gr. soma, body). Connected with the body.

SOMITE (Gr. soma). A single segment in the body of an Articulate animal.

SPERMATOZOA (Gr. sperma, seed ; and zoon, animal). The microscopic fila-
ments which form the essential generative element of the male.

SPICULA (Lat. spiculum, a point). Pointed needle-shaped bodies.

SPIRACLES (Lat. spiro, I breathe). The breathing-pores, or apertures of the
breathing-tubes (tracheae) of Insects. Also the single nostril of the Hag-
fishes, the "blow-hole" of Cetaceans, &c.

SPLANCHNOSKELETON (Gr. splagchna, viscera ; skelelos, dry). The hard struc-
tures occasionally developed in connection with the internal organs or viscera.

GLOSSARY. 5 83

SPONGE-PARTICLES— see Sarcoids.

SPONGIDA (Gr. spoggos, a sponge). The division of Protozoa commonly known

as sponges.
SQUAMATA (Lat. squama, a scale). The division of Reptiles comprising the

Ophidia and Lacertilia, in which the integument develops horny scales, but

there are no dermal ossifications.
STELLERIDA (Lat. stella, star). Sometimes employed to designate the order of

the Star-fishes.
STELLIFORM. Star-shaped.
STERNUM (Gr. sternon). The breast-bone.
STOLON (Gr. stolos, a sending forth). Offshoots. The connecting processes

of sarcode, in Foraminifera ; the connecting tube in the social Ascidians ;

the processes sent out by the coenosarc of certain Actinozoa.
STOMAPODA (Gr. stoma, mouth ; pous, foot). An order of Crustacea.
STOMATODE (Gr. stoma). Possessing a mouth. The Infusoria are thus often

called the Stomatode Protozoa.
STREPSIPTERA (Gr. strepho, I twist; and pteron, wing). An order of Insects

in which the anterior wings are represented by twisted rudiments.
STREPSIRHINA (Gr. strepho, I twist ; rhines, nostrils). A group of the Quad-

rumana, often spoken of as Prosimice.
STYLIFORM (Lat. stylus, a pointed instrument; forma, form). Pointed in

shape.

SUB-CALCAREOUS. Somewhat calcareous.
SUB-CENTRAL. Nearly central, but not quite.
SUB-PEDUNCULATE. Supported upon a very short stem.
SUB-SESSILE. Nearly sessile, or without a stalk.
SUTURE (Lat. suo, 1 sew). The line of junction of two parts which are

immovably connected together. Applied to the line where the whorls

of a univalve shell join one another ; also to the lines made upon the

exterior of the shell of a chambered Cephalopod by the margins of the

septa.

SWIMMERETS. The limbs of Crustacea, which are adapted for swimming.
SYMPHYSIS (Gr. sumphusis, a growing together). Union of two bones in

which there is no motion or but a very limited amount.
SYNAPTICULE (Gr. sunapto, I fasten together). Transverse props sometimes

found in Corals, extending across the loculi like the bars of a grate.

TABULA (Lat. tabula, a tablet). Horizontal plates or floors found in some

Corals, extending across the cavity of the " theca " from side to side.
TACTILE (Lat. tango, I touch). Connected with the sense of touch.
TARSO-METATARSUS. The single bone in the leg of Birds produced by the

union and anchylosis of the lower or distal portion of the tarsus with the

whole of the metatarsus.
TARSUS (Gr. tarsos, the flat of the foot). The small bones which form the

ankle (or "instep" of man), and which correspond with the wrist (carpus)

of the anterior limb.
TECTIBRANCHIATA (Lat. tectiis, covered ; and Gr. bragchia, gills). A division

of Opisthobranchiate Gasteropoda in which the gills are protected by the

mantle.

TEGUMENTARY (Lat. tegumentum, ^ covering). Connected with the integu-
ment or skin.

TELEOSTEI (Gr. teleios, perfect; osteon, bone). The order of the "Bony Fishes."
TELSON (Gr. telson, a limit). The last joint in the abdomen of Crustacea;

variously regarded as a segment without appendages, or as an azygous

appendage.

TERGUM (Lat. for back). The dorsal arc of the somite of an Arthropod.
TERRICOLA (Lat. terra, earth ; and colo, I inhabit). Employed occasionally

to designate the Earth-worms (Lumbricidce).
TEST (Lat. testa, shell). The shell of Mollusca, which are for this reason

sometimes called " Testacea;" also, the calcareous case of Echinoderms ;

also, the thick, leathery, outer tunic in the Tunicata.

584

GLOSSARY.

TESTACEOUS. Provided with a shell or hard covering.

TETRABRANCHIATA (Gr. tetra, four ; bragchia, gill). The order of Cephalopoda
characterised by the possession of four gills.

THALASSICOLLIDA (Gr. thalassa, sea ; kolla, glue). A division of Protozoa.

THECA (Gr. theke, a sheath). A sheath or receptacle.

THECOSOMATA (Gr. theke ; and soma, body). A division of Pteropodous
Molluscs, in which the body is protected by an external shell.

THERIOMORPHA (Gr. ther, beast ; morphe, shape). Applied by Owen to the
order of the Tail-less Amphibians (Anoura).

THORAX (Gr. a breastplate). The chest.

TIBIA (Lat. a flute). The shin-bone, being the innermost of the two bones of
the leg, and corresponding with the radius in the anterior extremity.

TOTIPALMAT^E (Lat. totus, whole ; palma, the palm of the hand). A group
of Wading Birds in which the hallux is united to the other toes by mem-
brane, so that the feet are completely webbed.

TRACHEA (Gr. tracheia, the rough windpipe). The tube which conveys air
to the lungs in the air-breathing Vertebrates.

TRACHEAE. The breathing- tubes of Insects and other articulate animals.

TRACHEARIA. The division of Arachnida which breathe by means of tra-
cheae.

TRILOBITA (Gr. treis, three ; lobos, a lobe). An extinct order of Crustaceans.

TROCHANTER (Gr. trecho,! turn), A process of the upper part of the thigh-
bone (femur) to which are attached the muscles which rotate the limb.
There may be two, or even three, trochanters present.

TROCHOID (Gr. trochos, a wheel ; and eidos, form). Conical with a flat base ;
applied to the shells of Foraminifera and Univalve Molluscs.

TROPHI (Gr. trophos, a nourisher). The parts of the mouth in insects which
are concerned in the acquisition and preparation of food. Often called
" instrumenta cibaria."

TROPHOSOME (Gr. trepho, I nourish ; and soma, body). Applied collectively
to the assemblage of the nutritive zob'ids of any Hydrozoon.

TRUNCATED (Lat. trunco, I shorten). Abruptly cut off; applied to univalve
shells, the apex of which breaks off, so that the shell becomes ''decol-
lated."

TUBICOLA (Lat. tuba, a tube ; and colo, I inhabit). The order of Annelida
which construct a tubular case in which they protect themselves.

TUBICOLOUS. Inhabiting a tube.

TUNICATA (Lat. tunica, a cloak). A class of Molluscoida which are enveloped
in a tough leathery case or "test."

TURBINATED (Lat. turbo, a top). Top-shaped ; conical with a round base.

ULNA (Gr. olene, the elbow). The outermost of the two bones of the fore-
arm, corresponding with the fibula of the hind-limb.

UMBELLATE (Lat. umbella, a parasol). Forming an umbel — i.e., a number of
nearly equal radii all proceeding from one point.

UMBILICUS (Lat. for navel). The aperture seen at the base of the axis of
certain univalve shells, which are then said to be "perforated" or "um-
bilicated."

UMBO (Lat. the boss of a shield). The beak of a bivalve shell.

UMBRELLA. The contractile disc of one of the Lucernarida.

UNCINATE (Lat. uncinus, a hook). Provided with hooks or bent spines.

UNGUICULATE (Lat. unguis, nail). Furnished with claws.

UNGULATA (Lat. ungula, hoof). The order of Mammals comprising the Hoofed
Quadrupeds.

UNGULATE. Furnished with expanded nails constituting hoofs.

UNILOCULAR (Lat. unus, one ; and loculus, a little purse). Possessing a single
cavity or chamber. Applied to the shells of Foraminifera and Mollusca.

UNIVALVE (Lat. unus, one ; valvce, folding-doors). A shell composed of a
single piece or valve.

URODELA (Gr. oura, tail ; delos, visible). The order of the Tailed Amphi-
bians (Newts, &c.)

GLOSSARY. 585

VARICES (Lat. varix, a dilated vein). The ridges or spinose lines which mark

the former position of the mouth in certain univalve shells.
VASCULAR (Lat. vas, a vessel). Connected with the circulatory system.
VENTRAL (Lat. venter, the stomach). Eclating to the inferior surface of the

body.
VERMES (Lat. vermis, a worm). Sometimes employed at the present day in

the same, or very nearly the same, sense as Annuloida, or as Annuloida

plus the A narthropoda.

VERMIFORM (Lat. vermis, worm ; and forma, form). Worm-like.
VERTEBRA (Lat. verto, I turn). One of the bony segments of the vertebral

column or backbone.
VERTEBRATA (Lat. vertebra, a bone of the back, from vertere, to turn). The

division of the Animal Kingdom roughly characterised by the possession

of a backbone.

VESICLE (Lat. vesica, a bladder). A little sac or cyst.
VIBRACULA (Lat. vibro, I shake). Long filamentous appendages found in

many Polyzoa.

VIPERINA (Lat. vipera, a viper). A group of the Snakes.
VIVIPAROUS (Lat. vivus, alive ; and pario, I bring forth). Bringing forth

young alive.

WHORL. The spiral turn of a univalve shell.

XIPHISTERNUM (Gr. ziphos, sword ; stemon, breast-bone). The inferior or
posterior segment of the sternum, corresponding with the " xiphoid carti-
lage" of human anatomy.

XIPHOSURA (Gr. xiphos, a sword ; and oura, tail). An order of Crustacea,
comprising the Limuli or King-Crabs, characterised by their long sword-
like tails.

ZEUGLODONTID.E (Gr. zeugle, a yoke ; odous, a tooth). An extinct family of
Cetaceans, in which the molar teeth are two-fanged and look as if com-
posed of two parts united by a neck.

ZOOID (Gr. zoon, animal ; and eidos, like). The more or less completely in-
dependent organisms produced by gemmation or fission, whether these
remain attached to one another or are detached and set free.

ZOOPHYTE (Gr. zoon, animal ; phuton, plant). Loosely applied to many
plant-like animals, such as Sponges, Corals, Sea-anemones, Sea- mats, &c.

INDEX.

Absence of certain animals in fossiliferous
deposits, how accounted for, 27-39.

Acanthocladia, 196, 529.

Acanthodes, 330.

Acanthodidce, 322-330.

Acanthopteri, 318.

Acanthonpongia, 68.

Acanthotelson, 177.

Acanthoteuthis, 295.

Acarida, 182.

Acasta, 152.

Acaste, 170.

Acer, 502.

Acerotherium, 425, 426.

Achatina, 266.

Acicula, 268.

Aciculidce, 268.

Acidaspidce, 171.

Acidaspis, 171.

Acipenser, 322, 333.

-Acmoea, 259.

Acorn-shells, 150.

Acrodont Lizards, 362.

ulerodws, 335, 337, 339, 340, 410.

Acrogens, 473 ; age of, 476.

Acrotepis, 530.

Acrosalenia, 110.

Acrostichites, 497, 533.

u4cr<mra, 117.

Acteonella, 261.

.dcteonma, 261.

.AcZtma, 86, 87.

Actinocrinuii, 121, 126.

Actinospongia, 537.

J.cii?iozoa, 73; characters, 85; distribu-
tion in time, 86.

Adductor muscles of Lamellibranchiata,
218.

jEchmodus, 324.

jEglina, 169.

jEpiornis, 390, 394.

jEquoridce, 74.

Aganides, 288.

Age of Acrogens, 476; of Gymnosperms,
476; of Angiosperms, 476.

Agelacrinus, 129, 133.

Agnostidce, 167

Agnostus, 162, 163, 167, 168.

.4£ces, 435.

Alcyonaria, 73; characters of, 101; dis-
tribution of, in time, 101.

Alcyonium, 101.

Alethopteris, 482, 486, 494.

^ce, 473, 477.

Alligator, 366, 367.

s, 500.

Alum-schists, of Sweden, 510.

Amber, insects preserved in, 186.

Amblypterus, 323, 534.

Amblyrhynchus, 365.

Ambonychia, 223, 224.

Ambulacral ossicles of Star-fishes, 112, 113.

Ainia, 323.

Amiadas, 322, 323, 327.

Ammonites, 289 ; sections of, 290.

Ammonitidce, 279, 280, 281; characters
of, 286; shell of, 279, 286.

Amcebea, 59.

Amphibia, 305; characters of, 346; orders
of, 347 ; distribution of, in time, 347.

Amphicoelia (Crocodilia), 36(>, 367.

Ainphwyon, 450.

Amphidetus, 109.

Amphihelia, 96.

Amphilestes, 405, 410.

Amphion, 170.

Amphipoda, 176.

Amphisbcena, 361.

Amphispongia, 69.

Ainphistegma, 63.

Amphitherium, 405, 410, 411.

Amphitragulus, 434.

Amphiura, 117.

Amplexus, 526.

Ampullaria, 245, 255.

Ampyx, 167, 169.

Anabacia, 537.

Anacanthini, 317.

Ananchytes, 109.

Ananchytidce, 109.

Anarthropoda, 136.

Anatifa, 153, 155.

Anatina, 238, 239.

^4vi««mwZoe, 218, 238.

Anchitherium, 428

Ancyloceras, 291, 292.

Ancylotherium, 414.

Ancylus, 268.

Andrias, 347, 348.

Angelina, 161, 167, 169.

Angiosperms, 473.

Anguis, 361.

Animal Kingdom, divisions of, 44-52.

Anisopus, 533.'

,4nnelMta, 136 : characters of, 136 ; distri-
bution of, in time, 137.

^nnwZaria, 478, 482, 483, 494.

Annuloida, 102.

Annulosa, 29, 47 ; characters of, 136 ; dis-
tribution of, in time, 136.

INDEX.

587

Anodon, 229, 230.

Anoema, 458.

Anogens, 473.

Anomia, 221.

Anomodontia, 373.

Anomopteris, 497.

Anomura, 179, 180.

Anoplotheridce, 430, 431.

Anoplotherium, 430.

-4n<mra, 346, 347, 349.

Ant-eaters, 413.

_4?ited<m, 123.

Antholithes, 474, 484, 494.

Anthracopalcemon, 178.

Anthracosia, 234, 236.

Anthracosaurus, 352.

Anthracotherium, 430.

Antttocapra, 437.

Antilocapridce, 438, 439.

Antilope, 437, 439.

Antilopidce, 437, 438.

Antipathes, 88.

Antwerp Crag, 556.

Apateon, 352.

Aphragmites, 286.

Apiocrinidce, 127, 128.

Apiocrimis, 118, 128.

Apiocystites, 130, 133.

Aplysia, 261.

Aplysiadce, 261.

Aporosa, 96; distribution of, in time, 97.

Aporrhais, 252.

Apteryx, 393, 394.

Aptornis, 390.

Aptychus, 154.

^^ms, 159, 165, 166.

Aralo-Caspian beds, 556.

J.rae/imda, characters of, 181; orders of,

182; distribution of, in time, 182.
Araneida, 182, 183.
Araucaria, 497, 500.
Arawarioxylon, 475, 493.
,4rca, 226, 227.
ylrcadee, 216, 218, 226.
Archceocidaris, 108, 110.
Archceocyathus, 68.
Archceoniscus, 177.
Archceopteryx, 383, 386, 390, 396.
Archagaricon, 475.
Archegosauria, 352.
Archegosaurus, 352.
Archimedipora, 196.
Archimulacris, 186.
Archiulidce, 184.
Archiulus, 184.
Arctocyon, 451, 460.
Arctomys, 460.
.4rc£wras, 177.
Arenicolites, 142.
Arethusina, 171.
Argonauta, 274, 275, 294.
Argonaut idee, 275, 294.
Armadillos, 413, 416.
Arms of Star-fishes, 111, 113; of Ophiu-

roids, 116; of Crinoids, 119; of Cys-

tideaus, 130; of Blastoidea, 134; of

Brachiopoda, 201.
Aroides, 499.
Arteniia, 159.
Arthr aster, 115.
Arthrophycus, 479.
Arthropoda, 143, 144.

Arthropterus, 342.

^ rticulata (Brachiopoda), 202 ; (Crinoi-
dea), 128.

Artiodactyla, 423, 428.

Arvicola, 459.

Asaphidce, 167.

Asaphus, 164, 165, 166, 167.

Ascidian Molluscs, 187.

Ascoceras, 283, 285, 286.

Asiphonida, 218, 219.

Aspergillum, 239.

J.spMMisr<'a, 491.

Aspidocaris, 159.

Aspidorhynchus, 538.

Aspidura, 117, 533.

^Isfacws, 179.

Astarte, 234, 235.

Jls^eroirfea, characters of, 110 ; distribu-
tion of, in time, 114.

Asterolepis, 520.

Asterophyllites, 482, 483, 484, 489, 494.

J.s£nm, 96.

Astrceidce, 97, 100.

Astrceopora, 96.

Axtrangia, 96.

Astrogonium, 115.

Astropecten, 111, 114.

Astropyga, 110.

Astylospongia, 68, 69.

Athyris, 206.

Atlantic Ooze, 23.

Atlantidce, 262, 263.

Atrypa, 206.

Auchenaspis, 331.

Auchenia, 433, 434.

Aulacopleura, 171.

Aulopora, 97.

Auloporidce, 97, 100.

Auriculidce, 268.

Aurochs, 439.

,4ves, 381.

Avicula, 223, 224.

Avicula contorta beds, 531.

Avicularia, 194.

Aviculidce, 219, 223.

Aviculopecten, 222, 223.

Axinus, 229, 530.

Bactrites, 276, 287, 288.

Baculites, 276, 287, 293.

Bagshot series, 549.

Bairdia, 156, 157.

Bakewellia, 530.

Bala beds, 516.

Balcena, 419.

Balcenidce, 419, 420.

Ealcenodon, 422.

Balanidce, 150, 152.

Balanophyllia, 96.

Balanus, 151, 152.

Balistidce, 318.

Banksia, 499, 502.

Baphetes, 352, 353.

Baptosaurus, 365.

Barnacles, 152.

Barramunda, 314, 343, 344, 345.

Barrandia, 169.

Batides, 337, 341.

Batrachia, 349.

Belemnitella, 290.

Belemnites, 297; sections of, 298.

Belemnitidce, 275, 277, 294, 296.

588

INDEX.

Selemnosepia, 298.

Belemnosis, 296.

Belemnoteuthi*, 298.

Belemnoziphitis, 421.

Belinurus, 175.

Bellerophina, 245, 263.

Bellerophon, 245, 263.

Belodon, 368.

Beloptera, 296, 298.

Beloteuthis, 295.

Bembridge beds, 549.

Beryx, 316, 318.

Beyrichia, 156, 157.

Bidiastopora, 197.

Bimana, 466.

Bimeria, 75.

-Bipes, 361.

Birds, characters of, 381 ; distribution of,
in time, 388 ; orders of, 391-396.

Bivalve Molluscs, 214.

Blastoidea, characters of, 133 ; distribu-
tion of, in time, 135.

Blenniidce, 318.

Bopyridce, 176.

Bos, 439, 440.

Bourguaticrinus, 128.

Bovey Tracy lignites, 502.

Bovidce, 437, 439, 440.

Brackiopoda, characters of, 198 ; shell of,
199 ; families of, 203 ; distribution of,
in time, 202, 203.

Brachymetopiis, 167.

Brachyura, 180.

Bradypodidcn, 413, 414.

Bradypus, 398.

Bramatherium, 438, 439.

Branchifera (Gasteropoda), 241, 244, 246.

Bronteidce, 171.

Bronteus, 163, 167, 171.

Brontozoum, 533.

Bruta, 413.

Bryozoa (see Polyzoa).

Buccinidce, 248.

Buccinum, 248.

Bucklandia, 497.

Bulimuj, 266.

£«Ma, 261.

Bullidce, 261.

Banter Sandstein, 530, 531.

Burrows of Annelides, 141, 142.

Buthograpaus, 78.

Buthotrephis, 477, 479.

Caducibranchiate Amphibians, 340.

Ccecilice, 347, 355.

Calamaries, 295.

Cala mites, 474, 475, 480, 487, 488, 489, 494,

529.

Calamodendron, 482, 483.
Calathium, 68.
Calcaire grossier, 549.
Calcareous Sponges, 67.
Calceola, 99.

Calciferous Sand-rock, 513.
Calcispongice, 67, 68.
Callithrix, 465.
Callocystites, 130, 132, 133.
Callograpsus, 78, 79.
Calycophoridce, 73, 74.
Calymene, 163, 167, 170.
Calymenidce, 170.
Calyptrcea, 259.

Calyptrceidoe, 259.

Calyx of Crinoids, 119 ; of Cystoidea, 129 ;
of Blastoidea, 133.

Camarophoria, 208, 530.

Cambrian period, rocks of, 512 ; life of,
513 ; flora of, 477.

Camelidce, 433.

Camelopardalidce, 433, 436.

Camelopardalis, 436.

Camelus, 433.

Campanularida, 76.

Cancellaria, 247.

Cancer, 180.

Candona, 156, 157.

Canidce, 449, 454.

Canis, 454.

Capitulum of Lepadoids, 152, 153.

Capra, 439.

Caprina, 233.

Caprotina, 232.

Capulus, 259.

Caradoc beds, 513.

Carboniferous period, rocks of, 524 ; life
of, 526 ; flora of, 485.

Carboniferous Slates, 524.

Carcharodon, 335, 340.

Cardiadce, 218, 233.

Cardinia, 236.

Cardiocai-pum, 474, 482, 484, 494.

Cardiola, 224.

Cardiomorpha, 527.

Cardita, 234, 235.

Cardium, 233.

Carinaria, 245, 262, 263.

Carnivora, characters of, 447, 448 ; Pinni-
grade, 449 ; Plantigrade, 450 ; Digiti-
grade, 452 ; distribution of, in time, 449.

Carpenteria, 64.

Carriage - spring apparatus of Brachio-
pods, 201.

Caryocaris, 159.

Caryocrinus, 130.

Caryocystites, 133.

Caryophyllia, 96.

Cassidulida, 109.

Cassis, 242, 248, 249.

Castor, 458, 459.

Castoridce, 458

Castoroides, 459.

Casuarius, 394.

Catarhine Monkeys, 465, 466.

Catodontidce, 419.

Catopygus, 544.

Caturus, 545.

Caulopteris, 474, 482, 485.

Cave Bear, 451.

Cave Hysena, 453.

Cave Lion, 455.

Cave Pika, 560.

Cavicornia, 433, 437.

Cavidce, 458.

Cebus, 465.

Cellepora, 198.

Cellules of Graptolites, 79, 81.

Centemodon, 364.

Centipedes, 183.

Centrodus, 338, 339.

Cephalaspidce, 322, 331.

Cephalaspis, 331.

Cephalopoda, characters of, 272 ; distri-
bution of, in time, 276 ; Tetrabranchiate,
277 ; Dibranchiate, 293.

INDEX.

589

Ceratiocaris, 159, 160.

Ceratites, 276, 287, 288, 289, 534.

Ceratodus, 327, 339, 342, 343, 344, 345.

Cerithiadce, 252.

Cerithium, 252.

Cercolabes, 450.

Cercoleptes, 451.

Cercopithecus, 466.

Cervidce, 433, 434.

Cervus, 435, 436.

Cestracion, 337, 339, 340, 335.

Cestraciontidce, 337.

Cestraphori, 335, 336, 337, 338, 339, 340.

Cetacea, characters of, 418; distribution
of, in time, 419.

Cetiosaurus, 368, 378, 379.

Cetotolites, 420.

Chceropotamus' 43k -

Chcetodontidce, &¥&

Chalicomys, 459.

Chalicotherium, 431.

Chalk, 540; compared with the Atlantic
Ooze, 23.

Chama, 230.

Chamcerops, 501.

Chamidce, 218, 230.

Chainpsodelphis, 420.

Chasmops, 170.

Cheilostomata, 193, 194, 195.

Cheirolepis, 323, 327.

Cheiroptera, characters of, 460 ; distribu-
tion of, in time, 461.

Cheirotherium, 350, 351.

Cheiruridce, 167, 169.

Cheirurus, 163, 167, 170.

Chelichmis, 359.

Chelone, 359.

Chelonia, characters of, 356 ; distribution
of, in time, 359.

Cheloniidce, 358, 359.

Chemnitzia, 251, 253.

Chemung period, 522.

Chenendopora, 537.

Chilognatha, 183, 184.

Chilopoda, 183.

Chimceridce, 336.

Chirotes, 361.

Chiton, 260.

Chitonidce, 260,

Chfetetes, 526.

Chondrites, 479.

Chondrosteus, 333.

Chonetes, 210, 211.

Choneziphius, 421.

Cidaridte, 109.

Cidaris, 106, 109.

Cimolornis, 392.

Cinnarnomum, 500, 502.

Cinulia, 261.

Circus, 396.

Cirri of Brachiopods, 201.

Cirripedia, characters of, 149 ; orders of,
150 ; distribution of, in time, 152 ; Ses-
sile, 150 ; Pedunculated, 152.

Cladocera, 155.

Cladodus, 338, 339.

Claiborne beds, 550.

Clausilia, 266, 267.

Clavagella, 239, 240.

Cleavage, 39.

Cleodora, 269, 270.

ClepsysauriM, 364.

Cliinacograpsus, 84, 85.

Climactichnites, 167.

Climatius, 330.

Cliona, 71.

Clupeidce, 316.

Clymenia, 281, 282, 283.

Clypeaster, 109.

Clypeasteridce, 109.

Clypeus, 109.

Coal, structure of, 485.

Coal-measures, 525.

Coccosteus, 331, 332, 520.

Cochliodus, 339.

Ccelacanthini, 327, 329.

Ccelacanthus, 327, 329, 530.

Ccelenterata, characters of, 73; divisions

of, 73 ; distribution of, in time, 73, 74.
Coelogenys, 458.
Coanenchyma, 89.
Coenoecium, 192.
Ccenopithecus, 466.
Coleoptera, 185, 186, 187.
Collyrites, 109.
Collyritidce, 109.
Colobus, 465.
Colonies, 26.
Colossochelys, 359.
Colubrine Snakes, 360.
Columbacei, 394.
Columella of Corals, 91 ; of the shell of

Gasteropods, 242.
Column of Crinoids, 118, 123.
Colymbidce, 390.
Comarocystites, 131.
Comatula, 122, 123, 127, 128.
Common canal of Graptolites, 80.
Compsognatha, 380.
Compsognathus, 377, 380.
Conchicolites, 138, 139.
Conchifera (see Lamellibranchiata).
Conchiosaurus, 372.
Conchodus, 338.

Conclusions to be drawnfrom Fossils, 40-44.
Conidas, 249.
Coniopteris, 498.
Coniosaurus, 364.
Coniston series, 516
Conocardium, 233, 234.
Conocoryphe, 167, 169.
Conodonts, 314.
Conosmilia, 100.
Constricting Snakes, 361.
Contemporaneity of strata, 14-20.
Continuity, Geological, 20-26.
Conularia, 270, 271.
Conuhis, 266.
Conus, 249.
Copepoda, 155.
Coralline Crag, 555.
Corallium, 102.
Coral-reefs, ancient, 95, 96.
Corals, gemmation and fission of. 93-95.
Corals, simple and compound, 88, 89, 90,

91, 92, 93.
Coral-Rag, 536.
Coraa;, 340.
Corbis, 234.
Corbula, 238.
Cordaites, 474, 480.
Cornbrash, 536.
Corniferous period, 519.
Cornulites, 138.

590

INDEX.

Cornus, 500.

Coronula, 152.

Corynida, 74,75, 76.

Corynoides, 75, 76.

Coryphodon, 426.

Cosmacanthus, 338.

Crag, Antwerp, 556 ; Coralline, 555 ; Nor-
wich, ib. ; Red, ib. ; White, ib.

Crania, 203, 211, 212.

Craniadce, 202, 211.

Crassatella, 234, 235.

Crematopteris, 497.

Crepidula, 259.

Cretaceous period, rocks of, 540 ; life of,
545 ; flora of, 499.

Cribella, 111.

Cribrospongia, 537.

Cricetus, 459.

Cricodus, 326.

Crinoidea, characters of, 118 ; distribution
of, in time, 126.

Criuoidal limestone, 126.

Crioceras, 291.

Cristellaria, 537, 543.

Crocodilia, 365-368.

Crocodilus, 366.

Cromer Forest-bed, 558.

Crossopodia, 142, 143.

Crosmpterygidce, 321, 322, 326, 327.

Crossozamia, 497.

Crotalocrinus, 126.

Crustacea, characters of, 144; orders of,
149 ; distribution of, in time, 148.

Cryphceus, 170.

Cryptogams, 473.

Ctenacanthus, 338, 520.

Ctenodipteri, 327, 328.

Ctenodiscus, 111, 114.

Ctenodonta, 226, 227.

Ctenodus, 338.

Ctenoidei, 307, 315.

Ctenoid scales of fishes, 307.

Ctenophora, 73, 85.

Ctenoptychius, 338, 339.

Ctenostomata, 191, 194.

Cucttlidce, 395.

Cucullcea, 226, 227.

Cultellus, 237.

Cupressocrinus, 126.

Cupressus, 500.

Cupulispongia, 533.

Cursores, 393.

Cuttle-fishes, 2P3.

Cuvieria, 269. 270.

Cyathaspis, 332.

Cyathaxonia, 90.

Cyathaxonidce, 99, 101.

Cyathina. 543.

Cyathocrinus, 126.

Cyathophyllidce, 99, 101.

Cyathophyllum, 523.

Ct/6efc, 170.

Cycadacece, 473, 475, 494, 496, 497.

Cycadeoidea, 498.

Cycadopteris, 499.

Cycladidce, 218, 234.

Cyclas, 234.

Cycloidei, 307, 315.

Cycloid scales of fishes, 307.

Cyclophthalmus, 182, 183.

Cyclopteris, 482, 486, 497.

Cycloseris, 96.

Cyclostoma, 268.

Cyclostomata, 193, 194, 195.

Cyclostomida:, 268.

Cylindrites, 261.

Cyperites, 482, 483, 492.

Cyphaspidce, 171.

Cyphaspis, 171.

Cyprcea, 250.

Cyprceidce, 250.

Cypridella, 157.

Cypridina, 156, 157, 523.

Cyprina, 234.

Cyprinidce, 218, 234, 316.

Cypris, 156, 157.

Cyrena, 234.

Cj/rtwi, 205, 534.

Cyrtoceras, 276, 283, 284, 291, 534.

Cyrtodontar, 226-228.

Cyrtolites, 245, 263, 264.

Cystiphyllidce, 99, 101.

CystiphyUum, 99.

Cystoidea, characters of, 129 ; distribution

of, in time, 132.
Cythere, 156, 157.
Cytherea, 236.
Cytherella, 156, 157.

Dactylarea, 537.

Dadoxylon, 474, 475, 482, 493, 494.

Dakosaurus, 367.

Dalmania, 170.

Dapedidce, 324.

Dapedius, 324.

Dasypodidce, 413.

Dasypus, 416.

Dasyprocta, 458.

Dasyurus. 408.

Davidsonia, 208.

Decapoda (Crustacea), 177 ; (Cephalo-
poda), 295.

Deep-sea corals, 95.

Defrancia, 197.

Deinosauria, characters of, 376 ; distribu-
tion of, in time, 377.

Deinotherium, 418, 442, 443, 447.

Deiphon, 170.

Delphinidce, 419, 420.

Delphinus, 420.

Dendrarea, 537.

Dendrerpeton, 352.

Dendrodus, 326.

Dendrograpsus, 77-79.

Dendrophyllia, 96.

Dendropupa, 267.

Dentalidce, 260.

Dentalina, 537.

Dentalium, 137, 138, 242, 260.

Derivative rocks, 8.

Desmophyllum, 96.

Devonian period, rocks of, 520 ; life of,
521 ; flora of, 480.

Diadema, 110.

Diademadce, 110.

Diastopora, 197.

Dibranchiate Cephalopods, characters of,
293 ; families of, 275 ; distribution of, in
time, 294.

Diceras, 230.

Dichobune, 431.

Dichograpsus, 83.

Dicotyledons, 473.

Dicotyles, 430.

INDEX.

591

Dicranograpsus, 85.

Dictuolites, 479.

Dictyonema, 77-79.

Dicynodon, 373, 374.

Didelphidce, 408.

Didelphys, 407, 411.

Didus, 894.

Didymograpsus, 82, 83.

Digitigrada (Carmvora), 448. '

Dikelocephalus, 164, 167, 169.

Dimorphodon, 376.

Dimyary Bivalves, 218.

Dimylus, 463.

Dinophis, 361.

Dinornis, 390, 394.

Dinosauria (see Deinosauria).

Dionide, 169.

Diplacanthus, 330.

Diplograpsus, 82, 84, 85. /

Diplopterus, 326.

Dipnoi, characters of, 343; distribution of,

in time, 314, 343, 345.
Dipodidce, 459.

Diprionidian Graptolites, 82, 84.
Diprotodon, 412.
Diptera, 186, 187.
Dipterus, 327, 328, 345.
Dipiis, 460.
Distinct, 203, 212.
Duscinidce, 202, 212.
Discinocaris, 159, 160.
Discoidea, 107.
Discorbina, 60, 62.
Dissepiments (Corals), 93.
Dithyrocaris, 159.
Ditrupa, 138, 149.
Dolichosaurus, 364.
Donax, 237.
Dorcatherium, 434.
Dremotherium, 434.
Dromaius, 394.
Dromatherium, 409, 532.
Dromia, 180.
Dromilites, 180.
Dryandra, 499.
Dryopithecus, 466.
Dysaster, 109.
Dysasteridce, 109.

Ebalia, 180.

Ecculiomphalus, 263, 265.

Echidna, 406, 407.

Echinidce, 110.

Echinoconidce, 109.

Echinoconus, 109.

Echinocyamus, 109.

Echinodermata, characters of, 102; orders
of, 103 ; distribution of, in time, 103.

Echinodon, 364.

Echinoencrinus, 133.

Ec?iinoidea, characters of, 103; distribu-
tion of, in time, 108 ; families of, 109.

Echinoneida, 109.

Echinoneus, 109.

Echinosphcerites, 123.

Echinus, 110, 112.

Edaphodus, 336.

Edentata, characters of, 413 ; distribution
of, in time, 414.

Edestes, 338.

Edestosaurus, 365.

Edmondia, 527.

Edriophthalmata, 175, 176.

Elasmobranchii, characters of, 334 ; fam-
ilies of, 335; distribution of. in time,
335.

Elastnodus, 336.

Elephas, 442-446.

Elk, 435 ; Irish, 435, 436.

Ellipsocephalns, 167, 169.

Emarginula, 258.

Emydidce, 358, 359.

.Ewys, 357, 359.

Enalwsauria, 369.

Encrinurus, 167, 170.

Encrinus, 127, 533.

Endoceras, 284.

Endogens, 473.

Enoploclytia, 179.

Enoploteuthis, 295.

Entalophora, 197.

Entomis, 156.

Entomostraca, 155.

Entrochal Marble, 126.

Eocene period, rocks of, 546; life of, 550 ;
flora of, 500.

Eocystites, 132.

Eophyton, 474, 477, 478.

Eosaurus, 356, 369, 370.

Soscorpius, 183.

Eospongia, 68.

Eozoon, 63.

Ephemeridce, 185.

Epitheca (Corals), 92.

Equidce, 427.

Equisetacece, 473, 474, 480, 487.

Equisetites, 476, 489, 494.

Equus, 428.

Erichthys, 177.

Erinaceidce, 463.

Erinacevs, 463.

Errantia, 137, 141, 142.

J?rj/o«, 178, 179.

Eschara, 197, 198.

Escharidcv, 197.

Escharina, 193.

Esocidce, 316.

Estheria, 157, 158, 159, 224, 533.

Eulima, 251.

Eunomia, 533.

Euoinphalus, 255, 256, 264, 265, 534.

Eupatagus, 109.

Euphoberia, 184.

Eupsammidce, 100.

Eurypterida, 145, 148, 171, 172, 173.

Eurypterus, 173.

Eurysternum, 539.

Euskelesaurus, 377.

Exogens, 473.

Exogyra, 220.

Extracrinus, 123, 127.

Facial suture of Trilobites, 162.

Fagus, 500.

Faluns, 553.

Fascicularia, 198.

Fasciolaria, 247.

Favosites, 523.

Favositidce, 97, 100.

Favospongia, 69.

Favularia, 491, 493.

Felidce, 449, 453, 454, 455, 456.

FeZis, 455.

Fenestella, 195, 196, 529.

592

INDEX.

Fenestellidce, 195.

Ficus, 499.

Filices, 475, 485.

Firolidce, 262.

Fission of Corals, 94.

Fissurella, 258.

Fissurellidce, 258.

Flabellum, 96.

Flints, origin of, 69.

Flora of the Cambrian period, 477 ; of the
Silurian period, 478 ; of the Devonian
period, 480 ; of the Carboniferous, 485 ;
of the Permian period, 494 ; of the Trias,
496 ; of the Jurassic period, 497; of the
Cretaceous period, 499 ; of the Eocene,
500 ; of the Miocene, 501 ; of the Plio-
cene, 503.

Flustra, 198.

Foraminifera, characters of, 60 ; test of,
61, 62 ; distribution of, in time, 62-66.

Forest Marble, 536.

Formation, definition of, 7.

Fossil, definition of, 2.

Fossilisation, 34.

Frondicularia, 537.

Fucoidal Sandstone of Sweden, 477, 514.

Fucoids, 477, 479, 474.

Fulica, 392.

Fuller's-Earth, 536.

Fungidce, 97, 100.

Fusulina, 64.

Fiisus, 243, 247, 248.

Gadidce, 318.

Galcecynus, 454.

Galatea, 178.

Galeocerdo, 335, 840.

Galerites, 104, 109.

Gaieties, 406. 411.

Gallinacei, 394.

Gammanm, 176.

Gampsonyx, 176, 177.

Ganocephala, 352.

Ganodus, 336.

Ganoidei, characters of, 320 ; sub-orders

of, 322 ; distribution of, in time, 322.
Ganoid scales, 307.
Gasteropoda, characters of, 240 ; shell of,

242 ; families of, 244 ; distribution of, in

time, 245.

Gastornis, 390, 394.
Gastrochcena, 239.
Gastrochoenidce, 218, 239.
Gault, 540.
Gavial, 366.

Gemmation of Corals, 93-95.
General succession of organic types, 52-55.
Geological continuity, 20-26
Geological record, imperfection of, 32.
Geophilus, 184.
Geoteuthis, 298.
Geotrypus, 463.
Gephyrea, 136.
Gervillia, 223, 224.
Giraffe, 436, 437.
Glabella of Trilobites, 161.
Glacial deposits, 559.
Glacial shells, 559.
Glaucoiwme, 196.
Gleditschia, 503.
Glires, 456.
Globigerina, 60, 62, 65.

Globulus, 251.
Glossodus, 339.
Glyptocrinus, 126.
Glyptocystites, 132, 133.
Glyptodipterini, 326, 327, 328.
Glyptodon, 416.
Glyptolcemus, 326, 327, 328.
Glyptolepis, 326.
Glyptopomus, 326.
Gobiidce, 318.
Gomphoceras, 283, 285.
Gompholepis, 520.
Goniaster, 111, 112, 114, 115.
Goniatites, 276, 287, 288, 289, 534.
Gonioceras, 284.
Goniodiscus, 111, 114, 115.
Goniapholis, 367.
Gonipphylliim, 99.
Goniospongia, 537.
Gordia, 142.
Gorgonidce, 101.
Graculavus, 390.
Grallatores, 392.
Grantia, 69.
Graphularia, 101.
Grapsus, 180.
Graptolites, 80, 81, 82.
Graptolitidce, characters of, 79; distri-
bution of, in time, 79, 82.
Great Oolite, 536.

Greensand, Lower, 540 ; Upper, 542.
Grevillia, 499, 502.
Griffithides, 167, 171.
Grus, 392.
Gryphona, 220, 221.
Guard of Belemnite, 297.
Guettardia, 543.
Gulo, 452.
Guynia, 99.
Gymnodontidce, 318.
Gymnolcemata (Polyzod), 192.
Gymnosomata (Pteropoda), 269.
Gymnosperms, 473.
Gypseous Series of Montmartre, 549.
Gyracanthus, 338.
Gyroceras, 283, 286, 291.
Gyroptychius, 326.
Gyropristis, 530.

Hadrosaurus, 377.

Halcyornis, 390, 395.

Halicore, 418.

Haliomma, 66.

Haliotidce, 256, 264.

Haliptis, 256, 257.

Halisaurus, 365.

Halitheriurn, 418.

Hamilton period, 522.

Hamites, 276, 288, 292.

Hamster, 459.

Haplocrinus, 126.

Haplophlebium, 185, 186.

Haplophyllia, 99.

Harlech Grits, 512.

Harpedidce, 171.

Harpes, 163, 171.

Hatteria, 363.

Headon Series, 549.

Heart-urchins, 109.

Helderberg series, Lower, 517; Upper,

522.
Heliastrcea, 96.

INDEX.

593

Helicidce, 266.

Helicoceras, 292.

Heliopora, 96.

Helix, 266.

Helladotherium, 437.

Helminthites, 143.

Helminthochiton, 260.

Hemiaspis, 174.

Hemicidaridce, 110.

Hemicidaris, 104, 106, 110.

Hemicosmites, 129, 133.

Hemipneustes, 544.

Hemiptera, 186, 187.

Hemitrochiscus, 529.

Hermit Crabs, 180.

Hesperornidce, 390.

Hesperornis, 390.

Heterocercal, tail of Fishes, 312, 313.

Heteropoda, characters of, 262 ; families

of, 262; distribution of, in time, 245,

262.

Hexaprotodon, 429, 430.
Hipparion, 428.
Hippocampidce, 319.
Hippopodium, 234, 236.
Hippopotamidce, 429.
Hippopotamus, 429.
Hippurite Limestone, 231.
Hippurites, 232.
Hippuritidce, 218, 219, 231, 232.
Histioderma, 142.
Holcodus, 365.
Holectypus, 109.
Holocephali, 335, 336.
Holocystis, 97, 99.
Holopea, 258.
Holoptychius, 326, 328.
Holostomata (Gasteropoda), 244, 245, 250.
Holothuroidea, 135.
Holtenia, 70.
Homacanthus, 338.
Homalonotus, 161, 164, 167, 170.
Homocercal, tail of Fishes, 312, 313.
Homotaxeous deposits, 17.
Howothetus, 185.
Hoploparia, 179.
Horse, 427, 428.
Hudson River period, 516.
Huronia, 284.

Huronian period, rocks of, 511.
Hycena, 453.
Hycenictis, 452.
Hycenidce, 449, 452, 453.
Hycenodon, 453.
Hyalea, 270.
Hyaleidce, 269.
Hybodonts, 339.
Hybodus, 335, 337, 339, 534.
Hydrida, 74.
Hydrochceruis, 453.
Hydroida, 73.
Hydrozoa, characters of, 73 ; divisions

of, 73 ; distribution of, in time, 74.
Hyloeosaurus, 377.
Hylerpeton, 352.
Hylobates, 466.
Hylonomus, 352, 356.
Hymenocaris, 159, 160.
Hymeiiophyllites, 486, 487,
Hymenoptera, 186, 187.

Hyolithes, 270.
Hyopotamus, 430.
Hyperodapedon, 362, 363.
Hypostome, of Trilobites, 165.
Hypsilophodon, 377.
Hypsiprymnopsis, 409.
Hypsiprymnuf, 408, 413.
Hyracoidea, 441.
Hyracotherium, 441, 466.
Hyrax, 441.
Hystricidce, 458.
Hystrix, 458.

lacchus, 465.

lanthina, 258.

Ibis, 392.

Ichthyerpeton, 352.

Ichthyocrinus, 126.

Ichthyodorulites, 317, 335, 336, 337.

Ichthyomorpha, 347.

Ichthyopterygia, 368, 369, 370.

Ichthyosauria, 368.

Ichthyosaurus, 369, 370.

Ictittierium, 452.

Idiochelys, 539.

Idm-onea, 197, 198.

Igvanodon, 377, 378.

Illcenus, 161, 16-2, 163, 164, 169.

Imperfection of the Palseontological

Record, 27-39.

Inarticulata (Brachiopoda), 202.
Inferior Oolite,
Infusoria, 28, 59.
Infusorial Earth, 67.
Ink-bag, of Cuttle-fishes, 273.
Inoceramus, 223, 224, 225.
Insecta, characters of, 185 ; orders of,

187 ; distribution of, in time, 185, 186.
Insectivora, characters of, 462 ; families

of, 463 ; distribution of, in time, 462.
Insessores, 395.
Integropallialia (Lame llibranchiata),

218.

Involutina, 537.
Irish Elk, 435, 436.
Irregular Echinoids, 107.
Isastrcea, 537.
Ischadites, 72.
Ischiodus, 336.
Isocardia, 234, 235.
Isopoda, characters of, 176; distribution

of, in time, 176, 177.
s, 184.

Jackson beds, 550.
Jelly-fishes, 74.
Jerboa, 460.
Juglans, 499.

Jurassic period, rocks of, 535 ; life of,
537 ; flora of, 497.

Kaidacarpum, 499.
Kangaroo, 408, 412.
Kangaroo-rat, 408, 411, 413.
Keratosa (Spongida), 67.
Keuper, 531.
Kimmeridge Clay, 536.
King Crabs, 174.
Knorria, 491.
Koninckia, 206, 534.

2 P

594

INDEX.

Koninckinidce, 203, 206.
Kossen beds, 531, 532.

Labyrinthodon, 353, 350.
Labyrinthodontia, characters of, 350 ;

distribution of, in time, 352.
Lace-corals, 195.
Latertidce, 364.

Lacertilia, 356 ; characters of, 361 ; dis-
tribution of, in time, 362.
Lcelaps, 377.
Lcemodipoda, 176.

Lagena, 60, 61.

Lagomys, 457, 458.

Lamellibranchiata, characters of, 214 ;
shell of, 215 ; divisions of, 218 ; dis-
tribution of, in time, 219; families
of, 219-240.

Lamna, 340.

Lamnodus, 326.

Laornis, 390, 892.

Lauracece, 502.

Laurentian period, rocks of, 510 ; life of,
511.

Leaia, 158, 159.

Leda, 226, 228.

Leguminosites, 500.

Leiodon, 365.

Lemming, 459.

Lerrmridce, 464, 466.

Lepadidas, 150 ; shell of, 152, 153.

Lepadocrinites, 129, 130, 133.

Lepas, 153, 154, 155.

Leperditia, 156, 157.

Lepidaster, 111, 115.

Lepidodendroids, 475, 489.

Lepidodendron, 474, 475, 480, 483, 490,
491, 494, 529.

Lepidoganoids, 322.

Lepidopleuridce, 325.

Lepidophloios, 474, 480, 489, 491.

Lepidoptera, 180, 187.

Lepidosiren, 342, 343, 345.

Lepidosteidce, 322, 323.

Lepidosteus, 320, 323.

Lepidostrobus, 491.

Lepidotidce, 324, 325.

Lepidotus, 825.

Leporidce, 457.

Leptacanthus, 338.

Leptcena, 208, 210.

Lepterpeton, 352.

Leptolepidce, 315, 324, 325.

Leptolepis, 324.

Leptophlosum, 480.

Leptoteuthis, 295.

Lepus, 457, 458.

Leskia, 131.

Lias, 535.

Lichadce, 170.

Lichas, 171.

Licrophycus, 479.

Ligament, of Bivalve Molluscs, 215.

I/i7»a, 222.

Limaeidcz, 267.

Limacinidce, 269.

Limnadia, 159.

Lirnncea, 245, 267.

Limnceidce, 267.

Limulus, 163, 171, 172, 174, 175.

Lingula, 203, 213, 530.

Lingula Flags, 512, 514.

Lingulidce, 202, 203, 213.
Liquidambar, 503.
Liriodendron, 500, 501, 603..
Lithentomum, 185.
Lithodomus, 225, 226.
Lithornis, 390, 395.
Litogaster, 178.
Littorina, 254.
Littwinidce, 254.
Lituites, 281, 282, 286.
Lituola, 543.
Lizards, 361.
Llanberis Slates, 512.
Llandeilo Rocks, 516.
Llandovery Rocks, 516.
Loboccenia, 537.
Loganograpsus, 514.
London Clay, 548.
Longmynd Rocks, 512.
Lonsdaleia, 94.
Lophiodon, 426.
Lophobranchii, 318, 821.
Lophohelia, 96.
Lophopea, 194.
Loricata (Reptilia), 355.
Loricula, 152, 154, 155.
Lower Cretaceous Rocks, 541.
Lower Oolites, 535.
.Lo:to?i07na, 251,253, 534.
Lticemarida, 73, 74,
Lucina, 234.
Lucinidce, 218, 234.
Ludlow Rocks, 516.
Luidia, 111, 114.
Lutra, 452.
Lutraria, 236.

Lycopodiacece, 474, 480, 482, 490.
Lycopodites, 474, 480.
Lycosa, 183.

Macacus, 466.

Macellodon, 364.

Machairodus, 456.

Maclurea, 245, 263, 264.

MacraUchenia, 433, 434.

Macrocheitus, 251.

M acropodidce, 408, 413.

Macropoma, 327.

Macrospondylus, 367.

Macrotfterium, 414.

Macrura, 178, 179.

Mactra, 236.

Mactridce, 218, 236.

Madrepora, 96.

Madreporidas, 97, 100.

Madreporiform tubercle, 106.

Maestricht beds, 540.

Malacodermata (Zoantharia), 86.

Malacopteri, 315.

Malacostraca, 175.

Malocystites, 133.

Mammalia, characters of, 397; skeleton
of, 398 ; dentition of, 403 ; distribution
of, in time, 405; orders of, 406.

Mammoth, 443, 444, 445.

Manatidce, 418.

Mandibles, of Cephalopods, 273.

Manis, 413, 414.

Manon, 543.

Mantellia, 497, 498.

Marsipobranchii, 314.

Marsupial bones, 408.

INDEX.

595

Marsupialia, characters of, 407; distribu-
tion of, in time, 408.

Marsupites, 127, 128.

Mastodon, 442, 446, 447.

Mastodonsaurus, 353.

Meandrina, 95, 96.

Meandropora, 198.

Medusidce, 73, 74.

Megaceros, 435, 436.

Megachirus, 179.

Megalichthys, 326, 327.

Megaiodon', 234, 236, 534.

Megalonyx, 414, 416.

Megalosaurus, 377, 380.

Megatherium, 414, 415.

Melania, 253.

Melaniadce, 253.

Meles, 452.

Melidce, 451.

Melocrinus, 126.

Membranipora, 544.

Menopoma, 347, 349.

Merostomata, characters of, 171 ; sub-
orders of, 171.

Merycotherium, 433.

Mesopithecus, 466.

Metamorphism, 39.

Metoptoma, 259, 260.

Metriophyllum, 100.

Meyeria, 179.

Michelinia, 90.

Micrabacia, 543.

Micraster, 109.

Microconchus, 140.

Microdiscus, 162.

Microlestes, 405, 409, 531.

Middle Oolites, 536.

Migrations, 16.

Miliola, 60.

Millepora, 96.

Milleporidce, 97, 100.

Millstone Grit, 524, 525.

Miocene period, rocks of, 552; life of,
553; flora of, 501.

Jlfifrra, 249, 250.

Modiola, 225, 226.

Modiolopsis, 225, 226.

Molasse, 553.

Mole, 463.

Mollusca, characters of, 187 ; shell of, 187-
189; distribution of, in time, 189.

Mollusca Proper, characters of, 190 ; divi-
sions of, 190.

Molluscoida, characters of, 190 ; divisions
of, 190.

Monera, 28, 59.

Monitors, 362.

Monocotyledons, 473.

Monomyary Bivalves, 218.

Monoprionidian Graptolites, 82.

Monotis, 534.

Monotremata, characters of, 406.

Montlivaltia, 92, 93, 533.

Mopsea, 101.

Mosasauroids, 364, 365.

Mosasaurus, 364, 365.

Moschidce, 433, 434.

Moschus, 434,

Mountain Limestone, 524.

Mugilidce. 318.

Muntjak, 433, 435.

Murcenidce, 316.

Murchisonia, 257, 258, 534.

Murex, 247.

Muricidce, 247.

Muridce, 459, 463.

Muschelkalk, 531.

Musk-ox, 440.

Mustela, 452.

Mustelidce, 449, 452.

Mutilata, 417.

A/2/a, 237, 238.

Myacidce, 218, 238.

Myacites, 238, 239.

Mycetes, 4<i5, 466.

Mygale, 463.

Myliobatis, 342.

Mylodon, 414, 415, 416.

Myodes, 459.

Myophoria, 228, 229, 534.

Myopotamus, 459.

Myoxidce, 460, 463.

Myoxus, 460.

Myrianites, 142.

Myriapoda, characters of, 183 ; distribu-

tion of, in time, 184.
Myrmecobius, 405, 408, 409.
Mysarachne, 463.
Mysis, 177.
Mytilidce, 218, 225.
Mytilus, 225, 530.

Nacreous Shells, 188.

Nassa, 248.

Nasua, 451.

Natatores, 391.

Natica, 250.

Naticella, 251.

Naticidce, 250.

Naticopsis, 251.

Nautilidce, characters of, 281 ; shell of,

279, 281 ; distribution of, in time, 281.
Nautiloid Foraminifera, 62.
Nautilus, Pearly, 277 ; Paper, 294.
Nautilus. 274, 276, 277, 278, 280, 281, 282.
Nebalia,, 169.
Necrogammarus, 176.
Neolimulus, 174.
Nereites, 143.
Nerinea, 252, 534.
Nerita, 255.
Neritidce, 255.
Neritina, 255.
Neuroptera, 185, 186, 187.
Neuropteris, 475, 482, 486, 495, 497, 533.
Nipadites, 500, 501.
Nodosaria, 60, 62.
Nceggerathia, 475, 494, 495.
Norwich Crag, 555.
Nothosaurus, 372.
Notidanus, 335, 340.
A/ ototherium, 412.

tfucleobranchiata (see Heteropoda), 262.
Nucleolites, 537.
Nucula 226, 227.
Nudibranchiata, 245.
Numenius, 392.
Nummulites, 62, 64, 65, 549.
Nummulitic Limestone, 65.
Nuthetes, 364.
, 503.

Obolella, 213, 214.
Obolus, 213.

596

INDEX.

Oceanic Hydrozoa, 74.

Octopodidce, 275, 294.

Oculinidce, 97, 100.

Odontaspis, 335, 340.

Odontoceti, 419.

Odontopteris, 486, 487, 498, 499.

Ogygia, 167, 169.

Oldhamia, 79, 195.

Old Red Sandstone, 520, 521.

Olenidce, 167, 168.

Olenus, 167, 168.

Oligochceta, 136.

Oliva, 248, 249.

Olivella, 249.

Ommastrephes, 295.

Onchus, 335, 337.

Oniscws, 161, 176.

Oolitic period, rocks of, 535; life of, 537;
flora of, 497.

Ooze, Atlantic, 23.

Opercidata, 266, 268.

Operculum, of Cirripedes, 150; of Euryp-
terids, 173 ; of Limulus, 174 ; of Gas-
teropoda, 241 ; of Maclurea, 263 ; of
Theca, 270.

Ophiderpeton, 352.

Ophidia, characters of, 360; distribution
of, in time, 860.

Ophileta, 256, 264.

Ophipcoma, 117.

Ophipderma, 117.

Ophiolepi*, 117.

Ophiomorpha, 347.

Ophiura, 116.

Ophiuroidea, characters of, 115; distribu-
tion of, in time, 117.

Opisthobranchiata, 245.

Opisthocoelia (CrocodHia), 366, 368.

Opossum, 411.

Oracanthtts, 338.

Orbitoides, 62.

Orbitolites, 62, 72.

Orbulina, 61.

Orchestia, 176.

Oreaster, 114, 115.

Organic types, succession of, 52-54.

Oriskany Sandstone, 522.

Ormpxylon, 474, 482.

Ornithorhynchus, 406, 407.

Omithoscelida, 377, 380.

Omithosauria, 375.

Orodus, 339.

Ort/m, 208, 209.

Orthisina, 208, 209.

Orthoceras, 276, 283, 284, 534.

Orthoceratidce, 276, 283.

Orthonota, 225, 226.

Orthoptera, 185, 186, 187.

Ortonia, 518.

Osborne series, 549.

Osmeroides, 316.

Osteolepis, 321, 326, 327.

Ostraciontidce, 318.

Ostracoda, characters of, 156; distribution
of, in time, 156, 157, 533.

Ostracostei, 323, 330.

(Mrea, 220, 221.

Ostreidce, 218, 219.

0«is, 392.

Otodus, 340, 341.

Otozamites, 497.

Otozoum, 533.

Oudenodon, 363, 373, 374.

Ovarian capsules of Graptolites, 81.

Ovarian pyramid of Cystideans, 131.

Ovibos, 440.

Ovicell, 193.

Oindce, 437, 439, 441.

Owis, 439.

Oxford Clay, 536.

Oxyrhina, 340, 341.

Pachydermata, 423.

Pachypteris, 498.

Pachyrisma, 234, 236.

Pachyseris, 96.

Pachytheca, 474, 480.

Paddlefish, 333.

Paguridce, 180.

Pagurus, 180.

Palcearca, 228.

Palceaster, 111, 114, 115.

Palcechinus, 108, 110.

Palcega, 177.

Palceiehthyes, 345.

Palceinachus, 180.

Palceochorda, 142.

Palceocoma, 114, 115.

Palceocoryne, 75.

Palceocrinoids, 123, 126.

Palceocyclus, 97.

Palceocyon, 454.

Palceodiscus, 114, 115.

Palaeolithic Man, 468.

Palceomanon, 68.

Palceoniscus, 323, 530, 534.

Palceonyctis, 452.

Palaeontological Record, imperfection of,

27-39.

Palaeontology, definition of, 1.
Palceophis, 361.
Palceophycus, 477, 479.
Palceopteris, 485.
Palceopyge, 167.
Palceosaurus, 368.
Palceosiren, 347.
Palceospalax, 463.
Palceospongia, 68.
Palceotheridce, 427.
Palceotherium, 427.
Palceotringa, 390, 392.
Palceoxylon, 493.
Palapteryx, 390, 394.
Palasterina, 114, 115.
Pali (Corals), 92.
Palinurus, 179.

Pallial line, of Bivalve shells, 216.
Pallial sinus, 217.
Palmacites, 494.
Paludicellea, 194.
Paludina, 245, 255.
Paludinidce, 255.
Pandanece, 499.
Pandanus, 499.
Panopoea, 238.
Paper Nautilus, 294.
Paradoxidce, 168.
Paradoxides, 167, 168, 169.
Paramuricea, 99.
Parasmilia, 543.
Parkeria, 65.
Passeres, 395.
Patella, 242, 259.
Patellidce, 259.
Pauropoda, 183, 184.

INDEX.

597

Pauropus, 184.

Pearly Nautilus, 274, 277, 278.

Peccary, 430

Pecopteris, 475, 482, 486, 495, 497, 498, 533.

Pecten, 221, 222.

Pectinaria, 137.

Pectinated rhombs of Cystideans, 132.

Pectunculus, 226, 227.

Pedicellarise, 114.

Pedicellinece, 194.

Pedipalpi, 182.

Pedunculated Cirripedes, 150, 152.

Peltocaris, 159, 160.

Pen, of Cuttle-fishes, 294.

Penarth beds, 531.

Pennatulidce, 101.

Pentacrinus, 123, 124, 127, 128.

Pentamerus, 207, 208.

Pentremites, 133, 134.

Percidce, 318.

Perdicidce, 394.

Perennibranchiata (Amphibia), 346.

Perforata, 96 ; distribution of, in time, 97.

Peridinium, 59.

Periechocrinus, 126.

Perischoechinidce, 108, 110.

Perispongia, 537.

Perissodactyla, 423, 424.

Permian period, rocks of, 528 ; life of,
529 ; flora of, 495.

Perna, 223, 224.

Petalodus, 339.

Petraia, 89.

Petraster, 114, 115.

PetroduK, 339.

Petrospongiadce, 69.

Pezophaps, 391.

Phacopidce, 167, 170.

Phacops, 162, 167, 170.

Phalangidce, 182.

Phalangistidce, 408, 413.

Phanerogams, 473.

Phaneropleurini, 327, 329.

Phaneropleuron, 327, 329.

Pharyngobranchii, 314.

Phascolomys, 408.

Phascolotherium, 405, 410.

Phasianidce, 394.

Phillipsa§trcea, 95.

Phillipsid, 167, 171.

Phlebopteris, 498.

Phocidce, 449, 450.

Pholadidce, 218, 239.

Pholadomya, 239.

Pholas, 240.

Pholidogaster, 352.

Pholidophorus, 324.

Phorus, 254.

Phragmacone, of Spirula, 296; of Belem-
nite, 297.

Phragmoceras, 283, 285.

Phylactolcemata, 194.

Phyllograpsus, 85.

Phyllopoda, characters of, 159 ; distribu-
tion of, in time, 159.

Phyllostomidce, 461.

Phyllostoma, 462.

Physa, 245, 268.

Physeter, 420.

Physophoridce, 73, 74, 84.

Physostoinata, 315.

Phytopsis, 479.

Pileolus, 255.

Pileopsis, 259.

Pinites, 493.

Pinna, 223, 224.

Pinnigrada, 448.

Pinnipedia, 447, 448.

Pinnularia, 477, 478, 482, 483.

Pisania, 247.

Pisces, characters of, 306; orders of, 315;

distribution of, in time, 313.
Pisidium, 234.
Pistosaurus, 372.
Placodus, 326, 372.
Placoganoids, 322.
Placoidei, 307.
Placoid scales, 307.
Placunopsis, 221
Plagiaulax, 406, 411.
Plagiostoina, 222.
Plagiostomi, 335, 336.
Planorbis, 242, 268.
Plantigrada, 448.
Platanus, 500, 502.
Platax, 318, 319.
Platephemera, 185.
Platyceras, 258, 259.
Platycrinus, 120, 123, 126;
Platygnathus, 326.
Platyrhina, 465.
Platysomidce, 325.
Platysomus, 325, 530.
Platystoma, 534.
Plectognathi, 318, 321.
Plectrodus, 338.
Plesiosauria, 370.
Plesiosaurus, 371, 372.
Plesiosorex, 463.
Pleuracanthus, 335, 338, 342.
Pleuraster, 115.
Pleurobranchidce, 261.
Pleurocystites, 130.
Pleurodictyum, 97.
Pleurodont Lizards, 362.
Pleuronectidce, 317, 318.
Pleurotoma, 249.
Pleurotomaria, 257, 264.
Plicatula, 222, 223.
Pliocene period, rocks of, 554 ; life of, 557.

flora of, 503.
Pliopithecus, 466.
Pliosaurus, 372.
Plumaster, 111.
Podocarya, 499.
Podophthalmata, 176, 177.
Podozamites, 476, 497, 533.
Poikilopleuron, 377.
Pollicipes, 154.
Polyccelia, 100, 529.
Polycystina, 66, 67.
Polypodites, 498.
Polypothecia, 543.
Polypterini, 326.
Polypterus, 321, 322, 326, 327.
Polytrema, 64.
Polyzoa, characters of, 190 ; orders of,

194 ; distribution of, in time, 195.
Polyzoarium, 190.
Populus, 500.
Porambonites, 208.
Porcellana, 180.
Porcellia, 245. 263. 265.
Porites, 96.

INDEX.

Poritidce, 97, 100.

Porospongia, 537.

Portland Stone, 536.

Posidonomya, 223, 224.

Post-Glacial deposits, 560.

Post-Glacial Mammals, 560.

Post-Pliocene deposits, 557.

Post-Pliocene Mammals, 557.

Potamides, 252.

Poteriocrinus, 126.

Pothocites, 475, 494.

Potsdam Sandstone, 513, 514.

Prce-arcturus, 177.

Prse-Glacial deposits, 558.

Prse-Glacial Mammals, 558.

Prestwichia, 175.

Primitia, 156, 157.

Primnoa, 99.

Primordial Zone, 167, 168, 513, 514.

Prionastrcea, 537.

Pristerodon,'364.

Proboscidea, characters of, 442 ; distribu-
tion of, in time, 443.

Proboscis, of Crinoids, 119, 121.

Proccelia (Crocodilia), 366, 367.

Procyon, 451.

Producta, 210, eil, 530.

Productidce, 202, 210.

Proetidce, 171.

Proetus, 171.

Prongbuck, 437, 438,. 439.

Pro-ostracum, 297.

Prosobrarichiata, 245.

Prosoponiscus, 177, 529.

Protarea, 97.

Protastcr, 116, 117.

Proteacece, 499, 5i)2.

Protichnites, 167.

Protolycosa, 182.

Protopithecus, 465.

Protopteri, 842.

Protopteris, 482.

Protornis, 390, 395.

Protorosaurus, 356, 362, 530.

Protoseris, 537.

Prototaxites, 474, 482.

Protovirgularia, 101.

Protozoa, characters of, 59 ; divisions of,
59 ; distribution of, in time, 59, 60.

Prunoeystites, 133.

Psammobia, 237.

Psamrnodus, 338, 339.

Psaronius, 474, 475, 482, 485, 495.

Pseudocrinus, 130, 133.

Pseudoneuroptera, 185.

Pseudoniscus, 174.

Pseudoscorpionidce, 182.

Psilocephalus, 169

Psilophyton, 474, 480-482.

Psittacidce, 395.

Psolus, 135.

Pteraspis, 331, 332, 337.

Pterichthys, 331-333.

Pterinea, 224.

Pteris, 486.

Pteroceras, 246, 247.

Pterodactylus, 374, 375.

Pterophyllum, 476, 494, 497, 533.

Pteropidce, 461.

Pteropoda, characters of, 269 ; shell of,
269 ; orders of, 269 ; distribution of, in
time, 269, 270.

Pterosauria, characters of, 374 ; distribu-
tion of, in time, 375.
Pterotheca, 270.
Pterygotus, 172, 173.
Ptilodictya, 196.
Ptilograpsus, 78, 79.
Ptilomaster, 116.
Ptilopora, 196.
Ptychoceras, 276, 288, 293
Ptychodus, 339, 340.
Pidmonifera, 241, 245, 265.
Pt*pa, 246, 267, 267.
Purbeck beds, 536.
Purpura, 248.
Purpurina, 248.
Purpuroides, 638.
Pycnodontidce, 325.
Pygaster, Io9.
Pygaulus, 109.
Pygidium, 161, 164.
Pygocephahis, 177.
Pygopterus, 530.
Pygurus, 109.
Pyramidellidce, 251.
Pyrgia, 97.
Pyrgoma, 152.
Pyrina, 109.
Pyrula, 247.
Python, 355, 360.

Quadrumana, characters of, 464 ; sections
of, 464 ; distribution of, in time, 464-466.
Quebec group, 513, 514.
Quercus, 499, 500.

Radiata, 73.

Jiadiolaria, characters of, 66 ; distribu-
tion of, in time, 66.

Radiolites, 232.

.Ram, 341.

Rallus, 392.

Ramphorhynchw, 374, 376.

.Rawa, 349.

Ranella, 247.

Raniceps, 352.

Raphiosaurus, 364.

Raptores, 395.

Rasores, 294.

Rastrites, 80, 84.

Ratitce, 893.

Rays, 341, 342.

Recent peripd,548, 558.

Receptaculites, 71, 72.

Red Coral, 102.

Red Crag, 555.

Reef-building Corals, 95, 96.

Regular Echinoids, 107.

Rein-deer, 436.

Reptilia, characters of, 353 ; orders of,
355 ; distribution of, in time, 356.

Requienia, 230.

Retepora, 196.

Reticulipora, 544.

Retiolites, 80.

Retzia, 206.

Rhabdopleura, 80, 194.

Rhsetic beds, 531.

Rhamphastidce, 395.

.R/iea, 394,

Rhinoceridce, 424.

Rhinoceros, 424-426.

Rhinolophidce, 461.

INDEX.

599

Rhinolophus, 462.

Rhizocrinus, 118, 128.

Rhizodus, 326, 328, 329.

Rhizopoda, 59, 60.

RMzostoinidce, 74.

Rhodocrinus, 126.

Rhombus, 317, 318.

Rhus, 503.

Rhynchoceti, 419, 420.

Rhyncholites, 273.

Rhynchonella, 199, 203, 207.

Rhynchonellidce, 201-203, 207.

Rhynchosaurus, 362-364, 373, 374.

Rhynchoteuthis, 273, 274.

Rhytidolepis, 491, 493.

Rimula, 258.

Rissoa, 254.

Robinia, 503.

Robulina, 62. "

Rodentia, characters of, 456 ; distribution

of, in time, 457.
Roebuck, 436.
Rostellaria, 247, 252.
Rotalia, 62, 64.
Rudistes, 231.
Rugosa, 97 ; distribution of, in time, 99 ;

families of, 101.
Ruminantia, characters of, 431 ; families

of, 433.

SABAL, 501.

Sabella, 137.

Sabellaria, 137.

Saccosoma, 122, 127.

Sagenaria, 480, 491.

Salamander, 347.

Salenia, 107, 110.

Saleniadce, 111).

Sato, 500.

Salmonidce, 316.

Sao, 169.

Sassafras, 500.

Sauria, 362.

Saurichthys, 534.

Saurillvs, 364.

Saurocetes, 422.

Saurodipterini, 326, 327.

Sauroid Fishes, 327.

Sauropsida, 353.

Sauropterygia, 370-372.

Saurosternon, 364.

Saururce, 390, 396.

iSaxicava, 238.

Scalaria, 243, 253. •

Scales of Fishes, 307.

Scalpellum, 154.

Scansores, 394.

Scaphaspis, 332.

Scaphites, 288, 292.

Schizodus, 229, 530.

Scissurella, 256, 257.

Sciuridce, 460.

Sciurus, 460.

Sclerenchyma, 96.

Scierobasica (Zoantharia), 87.

Sclerobasic Corals, 87.

Scleroderrnata (Zoantharia), 88.

Sclerodermic Corals, 88.

Sclerogenidce, 318.

Scolecida, 102.

Scoliostoma, 534.

Scolites, 142.

Scolithus, 142.

Scolopax, 392, 546.

Scomberidce, 318.

Scorpion, 181-183.

Scorpionidce, 182.

Scutella, 104, 109.

Scyphia, 537. ,

Sea-anemones, 80, 81.

Sea-cucumbers, 135.

Seals, 449, 450.

Sea-Mosses, 187.

Sea-Urchins, 103.

Sedimentary Eocks, origin of, 6.

Selachii, 337, 340.

Semionotus, 324.

Semnopithecus, 466.

Sepia, 275, 295.

Sepiadce, 275, 294, 295.

Septa, of corals, 91, 92; of the shell of

Tetrabranchiate Cephalopods, 279, 280.
Sequoia, 502.
Seraphs, 247.
Seriatoporidce, 97, 100.
Serpula, 137, 138, 140.
Serpulites, 139.

Sertularida, characters of, 76 ; distribu-
tion of, in time, 77.
Sessile Cirripedes, 150-152.

Sharks, 336, 340.

Shell, of Balanoids, 150 ; of Lepadoids,
152; of Mollusca, 187; of Brachiopoda,
199 ; of Lamellibranchiata, 214 ; of
Gasteropoda, 242 ; of Pteropoda, 269 ;
of Tetrabranchiate Cephalopods, 279.

Shrew-mice, 463.

Sieboldia, 349.

Sigillaria, 474, 482, 491-494.

Sigillarioids,474,475, 480, 482, 491-494, 529.

Silicispongia, 67, 68.

Silurian period, rocks of, 515; life of,
517 ; flora of, 478.

Siluridce, 316, 317.

Simosaurus, 372.

Sinupallialia (Lamellibranchiata'), 218,
236.

Siphonia, 66, 70.

Siphonida (Lamellibranchiata}, 218, 219.

Siphonostomata (Gasteropoda), 244-246.

Siphonotreta, 212, 213.

Siren, 347.

Sirenia, characters of, 417 ; distribution of,
in time, 418.

Sivatherium, 438, 439.

Skiddaw Slates, 512, 514.

Slimonia, 173.

Sloths, 413, 414.

Smilax, 502.

Snakes, 360.

Solarium, 254.

Solaster, 111, 114.

Solecurtus, 237.

SoZm, 237.

Solenastrcea, 96.

Solenidce, 218, 237.

Solid axis, of Graptolites, 80.

Solidungula, 423, 427.

Solipedia, 423.

Sorese, 463.

Soricidce, 463.

Spalacodon, 462.

talacotherium, 411.
arsispongia, 69.

6oo

INDEX.

Spatangidce, 109.

Spatangust 109.

Spathobatis, 342.

Spatularia, 333.

Spermophilus, 460.

Sphcerexochus, 170.

Sphcerococcites, 478.

Sphceronites, 129, 133.

Sphagodus, 335, 337.

Sphenodon, 363.

Sphenodus, 340.

Sphenopteris, 475, 482, 483, 486, 495, 493.

Sphenothallus, 479.

Sp/ienofroc/iws, 96.

Spinacidce, 336.

Spiniferites, 69.

Spirtfer, 202, 205.

SpiriferidcR, 201-203, 205.

SpiVyerina, 205.

Spirigera, 206.

Spirophyton, 474, 479.

Spirorbis, 137, 138, 139.

&pirula, 274, 275, 294

Spirulidce, 275, 296.

Spirulirostra, 296.

Spondylus, 222.

Spongida, characters of, 67 ; distribution
of, in time. 67, 68.

Spongilla, 69.

Spongillopsis, 69.

Squa'lodon, 421, 422.

Squaloraia, 842.

Squamata (Reptilia), 355.

Squatina, 340.

Squilla, 177.

Stagonolepin, 356, 367.

Stauria, 99

Stauridce, 99, 101.

Staurocephalus, 170.

St Cassian beds, 531.

Steganodictyum, 522.

Stellaster, 114, 115.

Stenaster, 114, 115.

Sfcerwoscmnts, 367.

Stephanophyllia, 543.

Stereodelphis, 420.

Stereognathus, 405, 410.

Sternbergia, 482, 483, 489, 491.

Stigmarm, 474, 482, 493.

Stomapoda, characters of, 177 ; distribu-
tion of, in time, 177.

Stonesfleld Slate, 536 ; Mammals of, 410.

Strata, contemporaneity of, 14.

Strepsirhina, 464.

Streptospondyltis, 368.

Stringocephalus, 204.

Stn'a;, 395.

Strom atopora, 69, 71.

Strombidce, 246.

Strombodes, 98.

Strombus, 246.

Strophalosia, 530.

Strophodus, 339, 340, 410.

Strophomena, 208, 209.

Strophomenidce, 202, 203, 208.

Struthio, 394.

Sturionidce, 322, 333.

Stylina, 537.

Stylonurus, 173.

Siichosaurus, 367.

Sudden Extinction of marine animals,38,39.
, 430.

Su$, 430.
Synapta, 135.
Synastrcea, 533,
Syngnathidce, 319.
Synnelia, 89.
Syringopora, 98.
Syringoxylon, 474.

Tabulse, 93

Tabulata, 96 : distribution of. in time,

97.

Tceniaster, 117.
Tceniopteris, 498.
Talitrus, 176.
TaZpa, 463.
Talpidce, 463.
Tapiridce, 426.
Tapirus, 426.
Taxocrinus, 126.
Taxodium, 500, 501, 503.
Tectibranchiata, 244.
Tcleosaurus, 367.
Teleostei, characters of, 315; distribution

of, in time, 315 ; sub-orders of, 315-319.
Telerpeton, 356, 362, 363.
Tellina, 237.
Tellinidce, 218, 237.
Telmatornis, 390, 392.
Temnocidari-s, 109.
Temnopleurus, 110.
Tentaculites, 139, 270, 271, 272.
Terebella, 137.
Terebra, 248.
Terebratella, 200, 204.
Terebratula, 198, 201, 203.
Terebratulidce, 202-204.
Terebratulina, 203.
Teredo, 240.

Tertiary Rocks, classification of, 547.
Tesselata (Crinoidea), 128.
Test, of Foramintfera, 61; of Echinoidea,

103 ; of Cirripedia, 250.
Testacella, 267.
Testudinidce, 358, 359.
Tetrabranchiata, characters of, 277 ; shell

of, 279 ; distribution of, in time, 280.
Tetraceros, 439.
Tetradecapoda, 176.
Tetragonolepis, 324.
Tetragrapsus, 82, 83.
Tetraonidce, 394.
Tetraprotodon, 429.
Teudopsis, 295.
Teuthidce, 275, 277, 294. 298.
Textularia, 64, 65.
Thallogens, 473.
Thamnastrcea, 537.
Thamnograpsus, 78.
Thanet Sands, 548.
7'Aeca, 270.
Thecaphora, 74, 76.
Thecidce, 97, 100.
Thecididce, 204.
Thecidinm. 204. 205, 534.
Thecodontia, 367.
Thecodontosaurus, 368.
Thecosmilia, 537.
Thecosomata (Pteropodd), 269.
Thelodus, 335, 337, 338.
Thetis, 238.

Thinning out of beds, 36-38.
Thoracica (Cirripedia), 150.

INDEX.

60 1

Thylacinus, 408.

Thylacoleo, 412, 413.

Thysanura, 187.

Tornatella, 261.

Tornatellidce, 261.

Tortoises, 358, 359.

Toucan, 395.

Toxoceras, 291.

Trachyderma, 139.

Trachynemidce, 74.

Tracks, of Annelides, 141, 142.

Tremadoe Slates, 512, 515.

Trematis, 212.

Trenton period, 508, 516.

Triassic period, rocks of, 530; life of, 533:

flora of, 496.
Trichecidce, 450.
Trickites, 225.
Trichotropis, 247.
Triconodon, 406, 411
Tridacna, 232.
Tridacnidce, 218, 232.
Trigonia, 228, 229.
Trigomllites, 287.
Triyoniadce, 218, 228, 530.
Trigonoearpum, 482, 484, 492, 494.
Trilobita, characters of, 160 ; distribution

of, in time, 167; families of, 167-171.
Trimerocephalus, 170.
Trinucleidce, 167, 169.
Trinucleus, 162, 167, 169.
Trionycidce, 358, 359.
Trwnyx, 359.
Tristichopterus, 327.
Triton, 247.

Trochoceras, 281, 283, 292.
Trochocyathus, 537, 543.
Trochocystites, 132.
Trochoseris, 96.
Troehosmilia, 543.
Trochus, 256.
Trogonidce, 395.
Trogontherium, 459. .
Tropidaster, 537.
Tubicola, characters of, 137 ; distribution

of, in time, 138.
Tubiporidce, 101.
Tubitlaria, 74.
Tubulipora, 198.

Tubulosa, 96 ; distribution of, in time 97
Tunicata, 187.
Turbinaria, 96.
Turbinella, 247.
Turbinidce, 255, 264.
Turbinolia, 92.
Turbinolidce, 97, 100.
Turbo, 255, 256.
Turrilepas, 152, 153, 154, 155.
Turrilites, 276, 288, 292.
Turritella, 253
Turritellidce, 253.
Turtles, 358, 359.
Typhis, 247.

(Tllmania, 475, 496, 529.

Umbrella, 262.

Uncites, 206.

Unconfonnability, of strata 33.

Undina, 327.

Ungulata, characters of, 423 ; divisions of,

4jiO.

C/mo, 229.

, 218, 229.
Univalve Shells, 240, 241.
Unrepresented time, 32-36.
Upper Cretaceous Rocks, 540.
Upper Oolitic Rocks, 536.
Uraster, 111, 113, 114 115
Urocondylus, 352.
Urodela characters of, 347 ; distribution

of, m time, 347, 349.
Ursidce, 449, 450.
LTrsus, 451.
J7rws, 439, 400.

Valvata, 245, 255.

Vegetable kingdom, divisions of 473

Venendce, 218, 219, 236.

Ventriculites, 67, 70.

Fent^, 236.

Vermetus, 137, 138, 242, 253

Ferrwca, 152.

Verrucidce, 150, 152

F<5f^S"ilSSS2SM1 of' 299'' skeleton

ol, 300 ; distnbntion of, in time 306
Vespertilio, 461, 462.
Vespertilionidce, 461.
Vibracula, 194.
FincwZaria, 544.
Viperine Snakes, 360.
Virgularia, 101.
Fi'verra, 452.
Viverridce, 449, 452, 453
FoZtewz, 476, 497, 533
Valuta, 249, 250.
Volutidce, 249.
s, 454.

Walchia, 495, 496, 529.

Waldheimia, 204.

Wealden, 540.

Websteria, 101.

Wellingtonia, 502.

Wenlock series, 516.

Whalebone Whales, 419.

White Crag, 555.

Williainsonia, 497.

Woolwich and Reading Series, 548.

Xanthidia, 69.

Xantholites, ISO.

Xanthopsis, 180.

Xenoneura, 185.

Xiphodon, 431.

^pAoswm, characters of, 174; distribu-

tion of, in time, 174, 175
Xiphoteuthis, 299.
Xylobius, 184.

Zamia, 496.
Zamites, 497.
Zaphrentis, 89.
Zechstein, 529.
Zeuglodon, 421.
Zeitglodontidce, 419, 421.
Ziphioid Whales, 419, 420.
Ziphius, 421.

Zoantharia,73,86;Malacodermata 85 86-
' '

Zoocapsa, 152.
Zygosaurus, 353.

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"As a school-book nothing can match the Advanced Text-Book of Geology by
Professor Page of Newcastle." — Mechanics' Magazine.

THE GEOLOGICAL EXAMINATOR. A Progressive Series

of Questions adapted to the Introductory and Advanced Text-Books of
Geology. Prepared to assist Teachers in Framing their Examinations,
and Students in testing their own Progress and Proficiency. By the
Same. Fourth Edition. 9d.

THE CRUST OF THE EARTH: A Handy Outline of Geology.

By the Same. Is.

"An eminently satisfactory work, giving, in less than 100 pages, an admirable
outline sketch of Geology, . . . forming, if not a royal road, at least one of the
smoothest we possess, to an intelligent acquaintance with geological phenomena." —
Scotsman.

" Of singular merit for its clearness and trustworthy character." — Standard.

SYNOPSES OF SUBJECTS Taught in the Geological Class,

College of Physical Science, Newcastle-on-Tyne, University of Durham.
Fcap., cloth, 2s. 6d.

HANDBOOK OF GEOLOGICAL TERMS, GEOLOGY, AND

PHYSICAL GEOGRAPHY. By the Same. Second Edition, enlarged.
7s. 6d.

INTRODUCTORY TEXT-BOOK OF PHYSICAL GEO-
GRAPHY. With Sketch-Maps and Illustrations. By the Same. Fifth
Edition. 2s.

ADVANCED TEXT-BOOK OF PHYSICAL GEOGRAPHY.

By the Same. With Engravings. 5s.
"A thoroughly good Text-Book of Physical Geography."— Saturday Review.

EXAMINATIONS ON PHYSICAL GEOGRAPHY. A Pro-

gressive Series of Questions, adapted to the Introductory and Advanced
Text-Books of Physical Geography. By the Same. 9d.

ADVANCED TEXT-BOOK OF BOTANY. For the Use of

Students. By ROBERT BROWN, M.A., PH.D., F.R.G.S., Lecturer on
Botany under the Science and Art Department of the Committee of the
Privy Council on Education. [In the pi-ess.

WILLIAM BLACKWOOD & SONS, EDINBURGH AND LONDON.

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