) Memoirs of the Museum of Comparative Zodlogy i

AT HARVARD COLLEGE.

Vou SV No. 3. |

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GENESIS |
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BY

1 ALPHEUS BYA TT |

WITH FOURTEEN PLATES.

PUBLISHED IN CONJUNCTION WITH THE
SMITHSONIAN INSTITUTION.

CAMBRIDGE:
Printed for the sAluseum.

NOVEMBER, 1889.

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ADVERTISEMENT.

Tux present work is published by the SMITHSONIAN INSTITUTION in Co-
operation with the Museum oF ComPARATIVE ZooLocy, Cambridge, Mass.,
the drawings for the plates having been made at the expense of that estab-
lishment.

This work has been recommended by Mr. ALEXANDER AGASSIZ.

In accordance with the rule of the Institution, requiring the formal approval
by selected experts of every Memoir offered for publication in the Smithsonian
“ Contributions to Knowledge,” it was submitted for examination to CHARLES
A. Wurrr and to Wititiam H. Dati; by whom it was also strongly com-
mended, and it has been accordingly accepted for publication in the series of

“ Contributions.”
S. P. LANGLEY,
Secretary Smithsonian Institution.

SMITHSONIAN INSTITUTION,

Wasuineton, D. C., February, 1889.

CONTENTS.

ERBPACH = soot. GR S hs en eR ae Se ee el
Law of Morphogenesis, viii. Organic Equivalence, viii. Morphological Equiva-
lence, viii. Morphological Difference, ix. Acceleration in Development, ix. Gera-
tology, ix. Acceleration in Degeneration, x. The Three Phases of Development, x.
Law of Variation, x. Local Origin of Forms, xi.

a Se ar Oe

Origin and Characteristics of Suborders, 1-8. Nomenclature of the Stages of
Growth and Decline, 8-21. Theory of Radicals and Morphological Equivalence in
Progressive Forms, 21-28; in Retrogressive Forms, 28-40. Law of Acceleration,
40-48. Origin of Differentials, 48-538.

le INTBODUGHION. 25. 2-4

elo GEN WATSOGN 0". Sg cen ye eee eee ea ce ea See ane arte)
General Remarks, 54-56. Radical Stock, 57. Plicatus Stock, 57-62. Weehnero-
ceran Series, 57. Schlotheimian Series, 57, 58. Caloceran Series, 58-61. Vermi-
ceran Series, 61, 62. Levis Stock, 62-70. Arnioceran Series, 62, 63. Coroniceran
Series, 63-65. Agassiceran Series, 65, 66. Asteroceran Series, 66-68. Oxynoticeran
Series, 69, 70. Incerta Sedes, 70, note.

TLE, SGENESIS OF CHARAGIERISNIOS 40 25 908 ce ee Rd
Anagenesis, or the Genesis of Progressive Characteristics, 71-74. Catagenesis, or
the Genesis of Retrogressive Characteristics, 74-80. Differential Characteristics,
80-84.

EV. GHOLOGICAD AND HAUNAL REDATIONS 90 2 0 oe SG

Remarks, 85-89. Psiloceras and Caloceras, 89-93. Weehneroceras and Schlotheimia,

93-95. Vermiceras, 95, 96. -Arnioceras, 96, 97. Coroniceras, 97-99. Agassiceras,

99, 100. Asteroceras, 100, 101. Oxynoticeras, 101-103. Fauna of South Germany,

Table I., 103. Fauna of the Cédte d’Or, Table II., 103, 104. Fauna of the Rhone

Basin, Table III., 104-106. Fauna of England, Table IV., 106. Fauna of the Provy-

ince of Central Europe, Table V., 106-108. Fauna of the Province of the Mediter-

ranean, Table VI., 108-112. Summary, 112-119.

V.. Duscriptions oF GENERA AND SPECInS OF ARIFTIDA ©... . 3. ) ..; 120-991
Radical Stock, 120-125. First, or Psiloceran Branch, 120-125. Psiloceras, 120-

124. T'megoceras, 125. Plicatus Stock, 125-161. Second, or Schlotheimian Branch,
125-136. Wehneroceras, 125-127. Schlotheimia, 127, 128. Third, or Vermiceran
Branch, 136-161. Caloceras, 136-154. Vermiceras, 154-161. Levis Stock, 161-221.
Fourth, or Coroniceran Branch, 161-194. Arnioceras, 161-174. Coroniceras, 174-194.
Fifth, or Agassiceran Branch, 194-214. Agassiceras, 194-200. Asteroceras, 200-214.
Sixth, or Oxynoticeran Branch, 214-221. Oxynoticeras, 214-221.

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INDEX

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ORTHOCERAS
ORTHOCERAS
ORTHOCERAS
ORTHOCERAS

ORTHOCERAS

LIST OF CUTS IN THE

ELEGANS, APEX AND PRoToconcH

poLitumM, Apex AND PRoroconcH .

TRUNCATUM, TRUNCATED END AND Ptiue
‘ 1 Va 7 »

UNGINS, CICATRIX AND APEX

POLITUM, APEX

Vicmeen ROCK RAS InMMIRIGHT 3 7. 3. 6,

CALOCERAS APLANATUM

CALocERAS NEWBERRYI

CALOCERAS ORTONT

ARNIOCERAS NEVADANUM

ASTEROCERAS OBTUSUM, VAR. QUADRAGONATUM

Pet.

Figures 1-5, page 10

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6-8,

24 95
31-33,
Q4 2K
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PREFACE.

T is a common mistake to designate my classification as ‘“embryological.”

It will be found by those who read these pages, that the whole life

of the individual, and all its metamorphoses, have been deemed essential

standards for the estimation of affinities. Even the degradational meta-

morphoses of old age are used as characteristics of value in the generic
descriptions; it is properly speaking an ontological classification.

The researches were conducted almost wholly in Museums, because it
was found impracticable to study stratigraphical superposition in the field.
This part of the work has already been accurately done by local geolo-
gists, and my notes were largely made upon their collections. More
extended studies might have made the work more accurate than it is
but this was not possible for me.

I desire to record my deep sense of obligation to the late Prof. Louis
Agassiz, under whose direction my studies upon the Arietidss were begun.
His instruction and advice were none the less valuable because we differed
in theoretical views; to him I owe the methods of observation which are
used in all my work.

His son, Alexander Agassiz, has also laid scientific men in this country
under heavy obligations, and this essay could not have been completed or
published but for his sympathy, and for the liberal manner in which he
has sustained by large personal sacrifices the collections and the cause of
scientific research in the Museum of Comparative Zodlogy.

Professor Langley, Secretary of the Smithsonian Institution, has shown tie
greatest consideration and courtesy, and in undertaking the speedy pub-
lication of this memoir after the Museum of Comparative Zovlogy had
been obliged for want of funds to postpone its issue indefinitely, has saved
the results from becoming antiquated before they were made public.

My principal studies outside of this Museum were made in the Museum
of Stuttgardt, and there I received unwearied attention and help from
Prof. Oscar Fraas, and the use of superb collections. Professor Quenstedt
of Tiibingen gave me the benefit of much valuable information, and threw
open his collections without reserve, and I am indebted for similar favors
to Prof. Guido Sandberger at Wiirtzburg, Prof. Karl Zittel of the Museum
at Munich, and to Professor Mésch at Ziirich, The late M. Barrande,
Professor Gaudry and his assistant Dr. Fischer of the Jardin des Plantes,

( vii )

>

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Vill PREFACE.

Professor Hébert and his assistant M. Munier-Chalmas of the Sorbonne,
Paris, were equally kind and liberal. I desire also to thank M. Collenot,
M. Bréon, and Dr. Bochard;, for their kind attention and the free use of
the collections at Semur. Professor Owen and Dr. Henry Woodward of
the British Museum, Mr. Etheridge of the Geological Museum, the authori-
ties of the Bristol Museum, and Dr. Thomas Wright, gave me _ similar
opportunities for study, and Mr. Marder at Lyme Regis assisted me in the
field. Prof. Jules Marcou has materially aided the work by the loan of
rare books not obtainable elsewhere, and I am also indebted to Prof. J. D.
Whitney for similar loans from his library. Professor Emerson of Amherst
has given me valuable information, and the use of his collection. I was
unfortunate in finding the curators of collections either absent or sick at
Hanover and Heidelberg; but in all practicable cases ample opportunities
for study were given me, except at the Museum of York, England, where
unyielding regulations prevented access to the interior of the cases, and my
identifications there were consequently made without handling the speci-
mens. I am also indebted to Professor Cope and Dr. John A. Ryder
for the results of investigations which have thrown much light upon
vexatious questions of theory, and which have not been properly repre-
sented by quotations in the text of this work, the general remarks having
been necessarily cut down to the narrowest possible limits.

The essay on “ Fossil Cephalopods in the Museum of Comparative Zodlogy”’
was written in large part as an introduction to this monograph, but for obvious
reasons has not been used. The following conclusions, copied with some
emendations and corrections from that essay, may be useful, however, in giv-
ing the reader a view of the theoretical opinions entertained by the author.

1

1. Law of Morphogenesis.— We have endeavored to demonstrate that a natural
classification may be made by means of a system of analysis in which the individual
is the unit of comparison, because its life in all its phases, morphological and physio-
logical, healthy or pathological, embryo, larva, adolescent, adult, and old (ontogeny),
correlates with the morphological and physiological history of the group to which it
belongs (phylogeny).

2. Organie Hquivalence.— All new characteristics, even those which are purely
mechanical reactions of the tissues, arise in a similar manner, as reactions due to the
exciting agency of the more general or more localized physical causes. They are there-
fore necessarily, and because of this mode of origin, the corresponding organic, or suitable
complementary equivalents of these physical causes, both structurally and functionally.

3. After their origin, however, and during their subsequent history, organic equiva-
lents or characteristics are divisible into two categories: those which become morpho-
logical equivalents, and are essentially similar in distinct series, and those which are
essentially different in distinct series, and may be classed as morphological differentials.

4, Morphological Equivalence.—In the different genetic series of a type derived from
one ancestral stock there is a perpetual recurrence of similar forms in similar succcs-
sion, which are usually called representative and often falsely classified together, though
they really belong to divergent, genetic series.

1 Proc. Am. Ass. Adv. Sci., XXXII., 1888.

PREFACE. 1X

5. These forms and their similar characteristics are not derived by direct inheritance
from the common ancestor, in which all the forms are necessarily similar and primitive,
but originate everywhere independently of hereditary influences in the different series,
and also in all formations independently of chronological or chorological distribution.

6. This evolution of similar morphological changes in the forms of different genetic
series must be regarded as the similar reactions or efforts of a common organism in
direct response to similar generally distributed physical causes active in the same habitat,
and are therefore necessarily similar to each other, though in different genetic series.
As a whole, they may be said to express the general tendencies of modification, due to
the efforts of the common-radical and common organization while spreading in all direc-
tions and in different genetic lines to respond to similar physical causes, and meet their
requirements with suitable changes. They are, therefore, structural equivalents of each
other in different series, and functional equivalents of the general requirements of the
environment or habitat, or, in other words, purely physical selections.

7. Morphological Difference. — Differentials are absent in the first members of series,
on first appearance in their descendants transient, but afterwards tend to become inva-
riable, or fixed in the stock or series, being perpetuated by direct inheritance in succes-
sive generations, species, etc. They finally often disappear in the retrogressive or highest
and last occurring members of each series, or in aberrant forms when on the same level.

8. They have no determinate mode of succession, but are usually more or less isolated
modifications, and arise first in individuals or varieties, but afterwards become characteristic
of species, and finally of the major part of the direct line in species, or descendent series.

9. They are, therefore, strictly adaptive, variable characteristics, and not directed in
their occurrence or development by any more or less invariable law of successive modi-
fication, as are the morphological equivalents. We have failed in finding any differentials
of great importance whose prepotence as hereditary characteristics could not be accounted
for by the law of use and disuse in connection with habits. The differentials of small
series, species, genera, and families, which we have not been able to analyze thoroughly,
may be due to the action and reaction of individual animals upon each other, or, in
other words, to natural selection.

10. Differentials, therefore, can be separated from other characteristics of the same
parts by careful observation and close analysis of their behavior in series, but cannot
be specifically predicted from the study of other series; whereas, morphological equiva-
lents can be predicted with the same certainty as the recurrence of cycles in physical
phenomena. Thus we can say of any new series of Nautiloids or Ammonoids, that, the
habitat remaining similar, they will, whenever or wherever found, tend to develop arcuate,
coiled, close-coiled, or discoidal and finally involute forms in progressive series, and
reverse this process in retrogressive series.

11. Acceleration in Development.— All modifications and variations in progressive
series tend to appear first in the adolescent or adult stages of growth, and then to be
inherited in suecessive descendants at earlier and earlier stages according to the law of
acceleration, until they either become embryonic, or are crowded out of the organization,
and replaced in the development by characteristics of later origin.

12. Geratology.— Modifications which tend to appear in the old age of the individual
of progressive series correlate with the modifications taking place in pathological series
of all grades, and in geratologous and retrogressive forms of all kinds, however progres-
sive they may be in certain characteristics. Geratologous forms, therefore, show that
the development of retrogressive characters has been stimulated so as to take the place
of the hereditary progressive, thus either partially or completely replacing them. Partial
replacement is often accompanied by the early development of hereditary progressive

characteristics.

x PREFACE.

13. Acceleration in Degeneration. — Geratologous forms may, therefore, be the highest
members of progressive series, or the terminal members of retrogressive series, and the
stimulation of the development appears to take effect upon both progressive and retro-
gressive characteristics ; thus producing, at the same time and in the same animal, first, the
earlier development of some of the progressive characteristics combined with geratologous
characteristics ; secondly, the earlier development of geratologous characteristics and their
fusion with larval characteristics, which occasions the complete replacement of progressive
characters, and occurs only in the extreme forms of retrogressive series, and in parasites.

14. The law of acceleration in development seems, therefore, to express an inva-
riable mode of action of heredity, in the earlier reproduction of hereditary characteris-
tics of all kinds, and under all conditions. In progressive series it acts upon healthy
characteristics, and appears to be an adaptation to favorable surroundings, and in retro-
gressive series upon pathological characteristics, and is probably an adaptation to un-
favorable surroundings, usually leading to the extinction of the series or type.

15. The Three Phases of Development. — In following up series, it has been found that
the development of ancestral forms is simple and direct (Hpacme); that of their more
specialized descendants becomes gradually indirect (Acme), acquiring complicated inter-
mediate or larval stages; and that of the terminal retrogressive or geratologous and
pathological forms becomes again more or less direct (Paracme.)

16. The introduction of adaptive larval stages into the history of individual develop-
ment in any series appears to be due to the direct exciting action of the surroundings,
and their absence or subsequent suppression to some physical agency, changes of habit,
or protection, or pathological causes. All of these causes must, however, be considered
as similar in their effect upon the young. They are stimulants, producing acceleration
or excessively rapid development of the ancestral progressive characteristics, or of the
retrogressive, or primitive larval characteristics inherited from the progressive forms.

17. This agreement in the mode of development of the individual according to its
position in the history of the group completes the correlations which exist between the
history of the individual (ontogeny) and the history of the group to which it belongs
(phylogeny). Using Haeckel’s nomenclature, the three periods of ontogenesis, Anaplasis,
Metaplasis, and Cataplasis, correlate with the three periods of phylogenesis, Epacme,
Acme, and Paracme. In addition to this general correlation, we now find that during
the epacme of a group the development of individuals is anaplastic or progressively direct ;
during the acme of a group, metaplastic or progressively indirect; and during the
paracme of a group, cataplastic, or retrogressively direct. We have also found, that, in
the history even of small groups, the epacme, acme, and paracme may often succeed one
another in geologic time, and show similar correlations, so that we can often distinguish
epacmic faunas, acmic faunas, and paracmic faunas in chronological succession. In
series, also, epacmic forms, acmic forms, and paracmic forms, either in series of species
or Varieties, may occur in geological succession in different faunas, or in zodlogical grada-
tion in the same fauna.

18. Law of Variation.—The action of physical changes takes effect upon an irritable,
plastic organism, which necessarily responds to external stimulant by an internal reaction
or effort. This action from within upon the parts of organisms modifies their heredi-
tary forms by the production of new growths or changes, which are, therefore, adapted or
suitable to the conditions of the habitat, and are therefore physiologically and organically
equivalent to the physical agents and forces from which they directly or indirectly origi-
nated. In so far, then, as causes and habits are similar, they probably produce representa-
tion or morphological equivalence in different series of the same type in similar habitats ;
and in so far as they are different, they probably produce the differentials which distin-
guish series and groups from each other.

Spin ce

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PREFACE. >

19. The radical and epacmic forms of the Arietide probably originated in the North-
eastern Alps, and migrated from thence southerly and westerly into Italy, and also in
another direction westerly into South Germany and the Cédte-d’Or. In these last two
faunas new series of acmic forms arose by modification, and these and the paracmic
forms which seem to have arisen in the same basins flowed back into the Northeastern
Alps, and thence into Italy, during Bucklandian and later times. They were also dis-
tributed from these two basins to all others to the north and south of them in Central
Kurope. The Northeastern Alps and the South German and Céte-d’Or basins constitute
a Zone of Autochthones for the Arietidwe, and other faunas to the north and south of these
are what we have called Residual Faunas.

The materials in the Museum of Comparative Zovdlogy consist of various
collections made in England by Damon, Marder, and Wright; Boucault’s
famous collection from the Cote-d’Or, containing several of D’Orbigny’s types,
and in part named by him, or by direct comparison with his collection; a
special and very large general collection, especially rich, however, in South
German species, purchased from Dr. Krantz; a valuable exchange from the
Museum at Stuttgardt named by Professor Fraas; Professor Bronn’s collection
labelled by him; a number of valuable species, principally from Belgium, from
L. de Koninck’s collection; a similar lot presented by Prof. J. Marcou, from
various localities in Europe; and others not sufficiently important to be men-
tioned here.

ALPHEUS HYATEL.

CampBripGE, April, 1889.

cane semaine st en a peemcnmoeneumenceine. ~ cman eaten iene ae a Lacs SN een
a.

sree gence eenem

GENESIS OF THE ARIETIDA.

: &
INTRODUCTION.
ORIGIN AND CHARACTERISTICS OF SUBORDERS.

HE succession of forms among the silurian members of the genus Mimoceras

indicates that true gyroceran shells occurred among Ammonoidea, differing

from the similar forms among Nautiloids only in the possession of a globular pro-

toconch and a small ventral lobe. In some silurian and devonian Anarcestes these

permanent adult stages are repeated in the development of the young. Those in

Mimoceras compressum are truly cyrtoceran, or open curves at first; and in others,
as in a variety of Anarcestes fecundus described by Barrande, they are straight.

The next stage of growth is a loose-coiled or gyroceran form, like the adult
of Mimoceras. These stages can only be accounted for as hereditary tendencies
of growth in a type which is being rapidly changed from a primitive ancestral
straight form with simple sutures into a close-coiled nautilian shell.

Branco? describes and figures a specimen of Bactrites with a protoconch
similar to the very peculiar ovoid protoconch of Mim. compressum. He quotes
Beyrich, who gave him this specimen, as authority for the view that Bactrites
is connected with Mimoceras as Baculites is with the normal Ammonoids of the
Cretaceous. This idea was first published by Quenstedt in his “ Die Cephalo-
poden,’ and it is quite possible that Bactrites of the Devonian may be a de-
graded form of Mimoceras, but in that case the latter is also a degraded form of
Anarcestes, or transitional between it and Bactrites. To establish this proposi-
tion, forms of Mimoceras and Anarcestes should be produced in which uncoiling
occurred in adults after a close-coiled stage of growth had been passed through.
Such degraded forms are common in the Jura and Cretaceous, and enable the
observer to connect Baculites with the normal coiled Ammonoids of the same
formations. Whether this be so or not, the straight Bactrites-like young of
some forms of Anarcestes, the gyroceran young of others of the Goniatitine,
and the gyroceran adults and young of Mimoceras, indicate the derivation of
Goniatitinss to have been from silurian straight shells similar to Bactrites, if
not directly from that genus itself.

1 Genera Foss. Ceph., pp. 303, 304, 309, Proc. Bost. Soc. Nat. Hist., XXII., 1883.
2 Zeitsch, Deutsch. Geol. Gesell., XX XVII. p. 1.
ii

Dd GENESIS OF THE ARIETIDA.

We pointed out in “ Embryology of Fossil Cephalopods,”' that the loosely
coiled stages prevalent among Nautilinidee were repeated in the early stages
of development in some of the Goniatitinae and in the later Ammonoids. This
repetition was indicated by the form of the embryo which was flattened and
depressed, and also in the first sutures and in the embryonal umbilici. These
last are two conical or flattened depressions on either side of the protoconch, at
its junction with the apex of the conch. They were accounted for as remnants
of the umbilical perforation found in the young and adults of Mimoceras and
all coiled Nautiloids.

In our “Genera of Fossil Cephalopods” we narrowed this generalization
by comparing the first whorl of the embryo in the close-coiled Goniatitina
and in all Ammonitine with Anarcestes, thus bringing the affinities of all the
Ammonoidea to a focus in the silurian genus Anarcestes. These and other
similar observations, published before and since the work quoted above, have
been founded upon the law of acceleration formulated also in the Preface of this
monograph, pp. v, vi, Art. 11 and 14.

Dr. Branco’s extensive and accurate researches? have shown that all ot
these opinions, though founded upon a few specimens only, were sound, and
that the law of acceleration can be relied upon as'a working hypothesis. Though
treating us otherwise with more than just appreciation, this author failed to
notice that we had used the law of acceleration in development, or made our
inductions with the view of demonstrating its truth as a working hypothesis,
and consequently attributed the discovery of this law to Wiirtenberger.

Among Nautiloids the straight shells in each series appeared first ; they were
succeeded by the cyrtoceran, gyroceran, and close-coiled. Among Ammonoids
there is only one series — Bactrites, Mimoceras, and Anarcestes — which is
parallel with any one series of the many occurring among Nautiloids. The
open-whorled: stages of the young of Anarcestes and other Goniatitinse repre-
sent a transitional and highly accelerated development. This transitional
character is also indicated by the fact that, except in Mimoceras and some
species of Anarcestes, the occurrence of the gyroceran form, even in the young,
is sporadic. It occurs, as demonstrated by Barrande, in one variety of Gym-
nites fecundus, and not in the other. Sandberger has shown similar though less
marked variations in the young of Anar. subnautilinus, and Branco has described
the embryo of var. vittiger of the same species as close-coiled. Other examples
might be given, but it only remains to notice Branco’s doubts of the accuracy
of our drawings of the young of Gon. atratus and Gon. Listeri. Both of these
were found by him to belong to his close-coiled division of the Asellati of
the Carboniferous. Our drawings were made with a camera. The details they
contain show, better than any defence we can make, that they were also
closely studied by the author, and often corrected before being placed upon
stone. They indicate that primitive gyroceran forms of young are occasionally
found even among the highest forms of carboniferous Goniatitine,

1 See especially articles ‘ Whorls ”’ and “ Umbilicus,’’ Bull. Mus. Comp. Zodl., LENG: 5;
2 Paleontogr., 1880, 1881, XXVI., XXVI.

ORIGIN AND CHARACTERISTICS OF SUBORDERS. é

The depressed semi-lunar whorl appears first in the adults of Anarcestes. It
is subsequently found in the young as a stage immediately succeeding the more
cylindrical whorl of the gyroceran stage, when that occurs. In very close-coiled
forms, the latter may be omitted, or be only slightly indicated, and then the
anarcestian whorl appears at the beginning of the apex. In fact, this tendency
in Latisellati, and especially in Angustisellati, affects the shape of the protoconch
which is excessively depressed in the embryos of the higher suborders.

We have, therefore, considered it convenient to designate the anarces-
tian form of whorl as the primary radical of the Ammonoidea, reserving the
terms primitive and transitional radicals for the straight and gyroceran modi-
fications as they appear in Bactrites and Mimoceras.

The different series of the Clymenine and Goniatitine, and the Arcestine,
often begin with, and maintain persistently in full-grown shells, the primary
radical form. The Ceratitinee, Lytoceratines, and Ammonitine, on the contrary,
have this depressed form but rarely, except in their protoconchial stage, —
and at the beginning of the apex or true conch, while it remains in what we
have called the goniatitic stage of development.

The Clymeninx of the Devonian begin, when zovlogically arranged, with
discoidal forms having depressed semi-lunar anarcestian whorls. These de-
pressed whorls are exchanged in the higher forms for compressed discoidal
whorls, and these in turn for compressed involute whorls. The suborder
includes several genera and in each there occur examples. of this mode of
succession, or rather procession, of forms, forming parallel series.

The sutures of the genera Beneckia, Longobardites, Lecanites, Norites,
Meekoceras, Hungarites, and Carnites show them to be true Ceratitine. We
should, with our present information, be disposed to include these, and all
the genera mentioned by Mojsisovics as belonging to his group of Ammonites
trachyostraca, in the Ceratitina, distinguishing them by their well-known and
peculiar sutures from the Arcestine, Ammonitine, and Goniatitine.

The more or less compressed whorl, which in section can be described as
helmet-shaped, is the natural successor of the depressed anarcestian whorl both
in the growth of individuals and in the evolution of series of species. We have
considered this in the work quoted, therefore, as the secondary radical.

The secondary radicals? are prevalent in the Ceratitine, as shown by the
extensive researches of Mojsisovics in the remarkable and masterly treatise
above quoted. They completely replace the primary radicals as generators
of series in the Trias, except in the paleozoic survivors of the suborder
Arcestins. So far as the sutures are concerned, however, the Ceratitine,
though distinctly characteristic of the triassic faunse, are like the Goniatitine.
The young of Longobardites is really a Goniatite, similar to Prolecanites,

1 Genera of Fossil Cephalopods, Proc. Bost. Soc. Nat. Hist., XXII. p. 812.

* We formerly included (Gen. Foss. Ceph., p. 324) in secondary radicals some quadragonal whorls like
those of the adults of Xenodiscus; but we are now disposed to consider this an error, arising from not hay-
ing observed that the young of these forms often possessed, during earlier stages of growth, the secondary
or helmet-shaped whorl. This evidence shows that, in the most ancient periods as well as in later times,
quadragonal whorls were derivative modifications of the compressed helmet-shaped secondary radicals.

4 GENESIS OF THE ARIETIDA.

Norites is considered by Mojsisovics as allied to Pronorites, a genus of Gonia-
titinee, and by Griesbach, Zittel, and the author as allied more nearly to
another genus of the same suborder, Sageceras. Throughout the group the
lobes and saddles form a simple series in which very little differentiation is
observable except in the highest forms. The ventral lobe is very broad and
short, and the siphonal saddle broad and shallow. The survival of prolecanitian
characters in these outlines is apparent the moment we dispense with the
denticulations of the lobes and reduce the sutures to their primitive outlines.
The Arcestinsee of the Dyas are known only by one species, described by
Waagen, Cyelolobus Oldhami,’ which has whorls of the anarcestian shape. It
is an involute species, and there may be others of this genus in the same
formation, not yet discovered, which have more discoidal whorls.

According to our mode of translating the affinities of the forms, they arrange
themselves as follows. Popanoceras of the Dyas, as the direct descendant of
Prolecanites, inherits the tendency to have lobes and saddles of very nearly
the same size, with lobes having trifid or bifid terminations similar to those of
the young of Monophyllites, and also transitional to the sutures of the dyassic
Cyclolobus, the most ancient of the true Arcestine. If we are right, the young
of this last form, when examined, will be found to be similar to Popanoceras
antiquum at a stage when its sutures have not yet acquired marginal lobes.

The siphonal saddle in these forms and in true Arcestine is small, often
attenuated, and .the ventral lobe large and often broad. ‘The remaining
lobes and saddles are more nearly of the same size, numerous, and formed
a gradually lessening series inclining towards the umbilicus. The same aspect
is common in the simpler shells of Megaphyllites and Monophyllites, but in
these the large phylliform saddles, with entire outlines at their bases, exhibit
closer approach to the Prolecanitide. Arcestinw, therefore, retain in their
sutures the proportions of paleozoic forms of Goniatitinze which have numerous
lobes, but depart from them in having more complicated and ornate marginal
digitations. The series, with some exceptions, have involved whorls which
can only be considered as parallel with the more involute shells of silurian
and devonian Anarcestes. With respect to its forms and the smoothness of the
shell this series is a survival of purely paleozoic modifications.

The Lytoceratine form a separate phylum, distinguished usually by the
absence of true pile (ribs), the larval form and characteristics of the adult
shell, and the leaf-shaped marginal saddles of the sutures. Lytoceras, in its
smooth or unpilated shell, rounded abdomen, peculiar siphonal saddle, and
phylliform marginal saddles, appears to be a more progressive form of the
same genetic series as Megaphyllites and Monophyllites of the Trias. Even
the peculiar coarse striations of the shells of these genera are often repeated
among the Lytoceratine of the Jura.

Megaphyllites of the Trias is evidently closely allied to Monophyllites.
The siphonal saddle is similar to that of Monophyllites, and the marginal

1 Arcestes priscus, Waagen, is probably also a species of Cyclolobus. Geol. Surv. Ind., Salt Range,
ser. 18, I. i, pl. ii. fig. 6

ORIGIN AND CHARACTERISTICS OF SUBORDERS. 5

saddles are phylliform. The young of Monophyllites Suessi, Moj.,' of the Trias,
has sutures similar to the adults of Popanoceras antiquum® and Kingianum of the
Dyas,’ which are true Goniatitine. The sutures of Popanoceras are in their
turn transitional between Monophyllites and the more normal Goniatitine: of
the genus Prolecanites.

Triassic Ammonoidea have shallow ventral lobes and very prominent broad
siphonal saddles, thus giving the first lateral saddles the aspect of being ad-
juncts of the siphonal saddle. . In consequence of the more direct descent
of Lytoceratinz of the Jura from primitive forms, their sutures persist in
retaining triassic outlines, having usually short abdominal lobes, large siphonal
saddles, with the superior laterals apparently set upon their sides, the larger
lobes expanded and profusely branching at the top, the saddles expanded
and profusely branching at the base, the auxiliary lobes and saddles more
numerous and more nearly equal to the larger lobes and saddles than in
Ammonitine. Neumayer has demonstrated trumpet-like apertures in Lyt. am-
mane* The frilled and elevated ridges in shells of many forms indicate that
these are perhaps not uncommon in this group.’

The normal forms of the Ammonitinz, the Arietidee of the Lower Lias,
can be united to the genus Gymnites through Psiloceras. Gymnites can be
traced back to the Goniatitinee through Arcestes of the Trias and Cyclolobus
of the Dyas. The Ammonitine do not, therefore, come directly from the
Goniatitine, as do the Lytoceratine, but are probably direct offshoots of the
lower Arcestine. The Ammonitine include not only the typical jurassic and
cretaceous forms, but also the allied radical genera Schlotheimia and Psilo-
ceras of the Lias, and Gymnites and Ptychites of the Trias.°

In Gymnites of the Trias, the primary radical is exchanged for the more
compressed discoidal secondary radical, but still smooth shell, which is also
characteristic of Psiloceras of the Lias. The sutures are correlatively modified,
and begin to assume the aspect and proportions of the true Ammonitine. The
siphonal saddle is more prominent, but still retains in many species the pointed
aspect derived from the Goniatitine. The narrow first lateral saddles are apt to
appear like adjuncts of the siphonal saddle, owing to the great size and breadth

1 Mediterr. Triasprov., pl. Ixxix. fig. 4 a-e.

2 Arcestes antiquus, Waagen, Salt Range, Pal. Ind., ser. 13, I. i, pl. i. fig. 10.

8 Russia and Ural, M. V. K., II. pl. xxvii. fig. 5.

4 Mojsis. et Neum., Beitr., II., 1883, 1884, pl. xx.

5 Schlonbach, Paleontogr., XIII. p. 169, pl. xxvii. fig. 3, describes Amm. hircicornis, one of the
Lytoceratine, having a series of prominent flaring ridges indicating permanent apertures of similar
form. The slight, blunt rostrum is a notable characteristic of these apertures. Unfortunately, very
few have been preserved, possibly owing to the fact that they were in most species, as in the two
mentioned, thin flaring ridges, easily destroyed. We can only suggest, therefore, that this form of
rostrum might have been peculiar to this suborder,

6 In “Genera of Fossil Cephalopods,” in 1883, we expressed this opinion as follows: ‘‘This genus
(Cyclolobus) is very important, since it enables us to show the gradations by which the Prolecanitide
approximate to Arcestes, Ptychites, and Monophyllites.’? Mojsisovics, with new materials from Spitz-
bergen, has lately demonstrated the correctness of this opinion in part, and gives conclusive evidence
of the probable derivation of Arcestes and Ptychites from Popanoceras, Arkt. Trias Fauna, Mem. Akad.
St. Petersb., XX XIII. No. 6, p. 66, pl. xv.

6 GENESIS OF THE ARIETID.

of the first lateral lobes and the shortness of the ventral lobe. The aspect of
the second laterals in many species, and the gradation from these into the
auxiliary lobes, show that they retain the more primitive aspect of the earlier
forms in this part of the sutures.
| Ptychites of the Trias has sutures similar to those of Gymnites, and the
modified aspect of marginal lobes and saddles in both genera shows that, in
spite of a near approach or resemblance in the sutures to many Lytoceratina,
| they cannot be considered as so nearly related to them as to Cyclolobus.
Mojsisovics says that the evidence of genetic connection of Psiloceras planorbe
and Gymuites meultus rests alone upon the resemblances of the auxiliary lobes
| and saddles, and that the resemblances in form only occur between the discoidal
Gymnites and the most involute Psiloceratites, the former being indeed much
more involute than the most involute of the Psiloceratites. The genus Halorites
of the Trias is regarded by Mojsisovics as the probable ancestor of the Arietide. I.
We cannot recognize that there are any very marked differences in the |
amount of involution or form between Gym. incultus and Gym. Palnai when
| compared with Psi. planorbe, and the resemblances of the sutures are exceed-
| ingly close, especially when the species of Psiloceras of the Mediterranean , ;
province are studied. The aspect of the shells in the three former are very |
similar, while in the types of Halorites already cited by Mojsisovics, Had.
Ramsaueri, semiplicatus, decrescens, and semiglobosus,' they are very distinct.
The range of form in Halorites embraces highly sculptured shells, altogether
triassic in aspect. Neumayr’s” and Wihner’s® researches entirely confirm the
position here taken and show that Psiloceras possessed a series of involute
shells. Psiloceras and Gymnites, therefore, appear to be two parallel genera
of the same group, in each of which ‘discoidal forms give rise to more involute |
shells. Gym. incullus may be traced into the more involute Gym. EHumboldti, and
the still more involute Gym. Crednert. The adolescent young of Gym. Palmai,
Mojsis.* and ieu/tus° show less involution than the adult, and we may confidently
expect that some correspondingly still less. involute discoidal ancestral forms
will be found. Mojsisovics has not yet published his observations in full, and
his evidence is therefore not completed ; but, so far as we now know, the deriva-
tion of Psiloceras seems to have been from Gymnites as a common ancestor and
not from any forms of the Ceratitine like Halorites or its allies.
Mojsisovics has said, that out of his group of Ammonites leiostraca the genus
Phylloceras alone persists and is but little changed in the Jura; whereas. the
Amm. trachyostraca, or Ceratitinss, are more largely perpetuated, though much
changed, in the true Ammonitine. Our view differs, since we consider all
groups of the T'rias to have been discontinued in the Jura except the Lytocera-
tine. It is probable that a close affinity existed between Psiloceras and Gym-
nites, and the former is a modified Triassic survivor in the Lias; but. the
constant reappearance of the psiloceran form in the young of undoubted Arietian

1 Amm. Gattungen, Verhand. Geol. Reichs., 1879, No. 7.
I 2 Unterst. Lias, Abhandl., Geol. Reich., VII. 8 Unt. Lias, Mojsis. et Neum., Beitr., III.
i 4 Med. Triasprov., pl. lvii. fig. 2. 5 Thid., pl. liv. fig. 3.

ORIGIN AND CHARACTERISTICS OF SUBORDERS. vs

species shows that we must reckon it among the Arietide. The genus Schlo-
theimia is also a purely jurassic series, though undoubtedly triassic in respect to
its sutures. The young of Schlotheimia catenata is an almost exact reproduction of
the form described by Mojsisovics as @yoceras Buonarotti in “ Jahrbuch Geologi-
schen Reichsanstalt,’' and afterwards referred to Celtites in his “ Mediterranean
Triasprovinz.”” The pil cross the whorls on the abdomen in the same way,
and the general aspect of this discoidal shell is similar. It seems quite likely
that this is a young shell of some species, and until its exact affinities can be
determined it is of no great value. At present it would be difficult to say
with any certainty to what genus it might be referred. Mojsisovics was evi-
dently in doubt, since he states that it may be a young form of some species
of Balatonites. The resemblance to the young of Schlot. catenata may be due
to a purely pathological deformation, since the crossing of the abdomen by the
pile occurs from disease in many species of the Arietide and other keeled groups
of the Jura, notwithstanding the fact that it is normal in others. These facts,
and the gradations of form between Schlotheimia and Psiloceras presented by the
genus Weehneroceras,’ and by the young of this last genus, lead us to think that
Schlotheimia was derived from Psiloceras. The Ammonitine of the Jura, so
far as known, show no special traces of their prolecantian descent, except in
the discoidal shells and phylliform sutures of the genera just mentioned, and in
the embryonic and generalized goniatitic characters of the apical stages of the
shell. The ventral lobe of the Ammonitins is deep and narrow, the siphonal
saddle small but more or less dentated by marginal lobes and saddles. The
lateral saddles are broad and not so deeply divided by marginal lobes as in
the Lytoceratinxs, the lobes are narrower at the tops than in that suborder, and
the saddles consequently narrower at their bases. The great size and small
number of the lobes is also a marked peculiarity. The superior lateral saddles
and lobes are especially remarkable for size, and the auxiliary lobes and saddles
much less important and more unequal as compared with the lateral lobes and
saddles than in Lytoceratinee. The marginal lobes and saddles are as a rule short
and pointed, and the saddles rounded, but not phylliform. Possibly another
distinction will eventually be demonstrated in the more constricted and rostrated
apertures of many of the Ammonitines. .The characteristics of the embryos and
of the earliest stages do not yet seem sufficiently well known to be used in
this connection.

The Ammonoids, therefore, according to our views, are not divisible into
two grand divisions, but have six suborders: the Goniatitinae, of the Silurian,
Devonian, Carboniferous, Dyas, and Trias; the Clymenine of the Devonian ;
the Arcestinss of the Dyas and Trias; the Ceratitine of the Dyas and Trias;
the Lytoceratine of the Trias, Jura, and Cretaceous; and the Ammonitins of
the Trias, Jura, and Cretaceous.

Unfortunately, there is not space enough within the necessary limits of
this monograph to discuss the classifications of Mojsisovics, Fischer, and Zittel,

A Vol SEG, 1869, pli xy. 2 Page 129, pl. xxix.
8 A new genus described in this memoir.

8 GENESIS OF THE ARIETIDA.

and the embryological divisions proposed by Branco.’ The classification
given above was necessary in order to introduce our remarks upon the Am-
monitine, and show clearly why we limited this suborder as defined above ;
any further discussion would lead us too far away from the immediate objects
of this memoir.

NOMENCLATURE OF Sraces or GROWTH AND DECLINE.

In a paper read before the Boston Society of Natural History, November
16, 1887, the author discussed the classification of the stages of growth and
decline, dividing them as follows : —

1. The earlier stages, embracing the ovum (monoplast, Lankester), the
monoplacula, and the diploplacula, were considered under one term, Protembryo,
because of their parallelisms with the single and colonial Protozoa.

2. The next, or blastula stages, were classified under the head of Mesem-
bryo, on account of their resemblances to the Mesozoa; the latter being those

forms usually included in the sub-kingdom of Protozoa, but which have true.

ova and spermatozoa, and can be therefore separated as one-layered, spherical
Blastrea, closely parallel with the blastula, and precisely intermediate between
Protozoa and Metazoa.

3. The gastrula stages were considered as referable to true Metazoa, and
were styled accordingly the Metembryo.

4. The earlier planula or ciliated stages were regarded as indicating a still
very remote ancestral type, in common with Semper, Lankester, and Balfour,
and were termed the Neoembryo.

5. The later ciliated stages— those which show the essential characters of
the type to which the embryos belong — were classified as the Typembryo; ex.
the veliger, nauplius, etc. The typembryos were considered as the last of
embryonic stages, and those which followed were regarded as true larvae on
account of their more demonstrable connections with well known forms. — It
was found by applying this classification to the fossil Cephalopoda that the pro-
toconch of Owen was the shell of a univalve typembryo, which must have been
a veliger not very widely removed in structure from the similar shells of the
embryos of Gasteropoda and Pteropoda.’

The principal difficulty of the application of this view lies in bringing the
wrinkled and curious forms which occur upon the apices of some Nautiloids into

1 Mojsisovics, Med. Triasprovinz; Fischer, Manuel de Conchyliologie ; Zittel, Handbuch der Paleon-
tologie; Branco, Paleontogr., RVI we VL

2 Robert Tracy Jackson, a pupil of the author, in an essay now in preparation (‘‘ Phylogeny of the
Pelycypoda’’), shows that the typembryo stage of mollusks is limited to an early period characterized by
the existence of a shell-gland and the plate-like beginnings of a shell. Later veliger stages, he says, are ref-
erable to the class or phylum of Mollusca, to which the embryo really belongs, and he names them ‘ Phyl-
embryo” stages. The ‘ prodissoconch”’ is a name given by Jackson to the embryonic, bivalvular shell of
Pelyeypoda, which is the equivalent of the protoconch of cephalous mollusca. The completed protoconch
of the cephalous mollusca, and prodissoconch of Pelycypoda, Jackson considers as a stage later than that at
which the phylembryonic characters are emphasized, and as the close of the embryonic shell period. His
paper will give types of these and other stages considered in the several classes of mollusks.

NOMENCLATURE OF STAGES OF.GROWTH AND DECLINE. ]

exact relations with the indubitable protoconchs occurring upon the apices of the
conchs of Ammonoids and Belemnoids. The wrinkled lump above referred to is
unquestionably a part of the shell. It is not only closely attached, but the longi-
tudinal striz of the apex of the true conch are continuous upon the proximate
parts of the lump. It had an aperture which must have remained open until the
body of the veliger had entirely left the interior of the protoconch, and was
then closed by the apical plate. There is a cicatrix upon the apex of the conch,
which is invariably concealed by the lump when it is present, and in some
examples we observed the fracture of the outer layer of the shell on the apex
of the conch and outside of the ordinary boundary of the cicatrix, which could
only have been caused by the violent removal of the lump. The wrinkled and
contracted aspect of the lump when preserved can be accounted for by assuming
it to have been composed of conchiolin. This also accounts for its almost invari=
able absence, since such an organ must have been easily lost or destroyed. The
lumps must consequently be regarded as the remnants of conchiolinous pro-
toconchs having elongated and narrow apertures; but probably they were,
when in a living condition, much larger and more oval, and more similar to the
protoconch of the Ammonoids. The continuity of the strie from the conch to
the protoconch also shows that the conch was built out from the aperture of the
protoconch, layer after layer, and the concentric markings, and form of the apex,
which correlates with that of the scar, sustain this idea. The figures on the fol-
lowing pages are less perfect than several other examples studied by the author
since these were drawn. They do not show the passage of the external longitu-
dinal striae from the apex of the conch on to the surface of the protoconch.

A living chamber among recent and fossil Nautiloids marked a period of
rest after a stage of growth. The septum, therefore, was not built until the
animal arrived near the final steps, or had altogether stopped building out the
sides of that part of the shell in which it lived. At any rate, we can say with-
out risk of error that the septum was the final step, or one of the final steps, in
the construction of a living chamber.

6. The first living chamber, or the first larval or neepionic! stage of a Nauti-
loid was, therefore, represented by the apex of the conch in that order; but the
first septum and siphonal ceecum did not exist at this stage, which is represented
by a straight or slightly curved widely spreading cone, — in fact, the empty apex
of the conch. The length of the first living chamber has not been ascertained ; but
that it was short seems probable from the form of the cone in Nautilus. Doubt-
less this remark does not apply to the earliest forms of closely coiled shells, in
which the cone was much slenderer than in existing Nautilus, and the first living

1 Noms, infant, or young animal. The term ‘+ silphologic ” was used for this stage in the article above
quoted. ‘This literally means ‘‘ grub’? stage, and it is not strictly applicable to a normal progressive stage
of development. Grubs, caterpillars, and the like, among insects, are degraded or retrogressive develop-
ments, as compared with the normal, probably hereditary Thysanuriform larve of what are commonly

_ called the lower orders of Insecta. Studies of insects lately made have convinced us of the truth of this

opinion, first published by Friedrich Brauer, and of the need of changing this term to the one used, and of
reserving silphologic as a general term for retrogressive stages, such as one finds in the larve: of Coleoptera,
Lepidotera, Hymenoptera, and Neuroptera,

pd

a

10 GENESIS OF THE ARIETIDAL.

chamber perhaps longer in proportion. The entire absence of a cecum, and of
all signs of a siphon, may be inferred with probable certainty in this first stage ;
and we proposed, in the paper referred to above, to name it the Asiphonula. This
form may indicate the previous existence of a common univalve ancestor for the
Cephalopoda which resembled the Pteropoda. Certainly the aspect of the calcare-
ous protoconch of Ammonoids and Belemnoids favors this idea, first suggested by
Von Jhering ; and the asiphonula adds another argument, since it has no siphon or
true septum. The young of the
Pteropoda, especially the ancient
forms, had calcareous protoconchs
in most forms; but doubtless there
TBR, “AW are more primitive shells in which
iy ff D> \ the protoconchs had _ the more
// primitive, embryonic, . conchioli-
nous stage of development. The
evidence, therefore, is not conclu-
sive, but it justifies the supposition
that Cephalopods and Pteropods
had originally some common an-
cestor, a true shell without septa
or siphon, and possessing a proto-
conch, which might have been
conchiolinous.

There is, however, another
group, the Scaphopoda, which
may claim to be considered in
this connection. According to
W. K. Brooks, the veliger is rep-
resented by the adult of Dentalium

Fig.

1-8. Apex and protoconch of Orth. elegans, Miinst., from
the side, below, and in front. In Fig. 2 the fine stria really
cross the shoulder of the apex (b), and reach to the proto-
conch (a). Named by Klipstein, Loc. St. Cassian, Coll. Brit-
ish Museum.

. 4,5. Apex and protoconch of another specimen mounted

with the first on the same card. Named by same, Loc. same,
Coll. same.

ig. 6-8. Views from the side, front, and below of the same

parts in Orth. politum, Klipst. The shading on the protoconch
of Fig. 8 does not indicate structure; this protuberance is
smooth. a, protoconch; b, shoulder of the area of the cica-
trix. Named by same, Loe. same, Coll. same.

in several of its leading charac-
teristics, and this must be regarded
therefore as the most generalized
type of the true Mollusca. It is
quite possible that the asiphonula
may have retained some of the
characters of the veliger, and may
have resembled Dentalium or

some common ancestor, and may have descended from this form without having
passed through any pteropod-like ancestral modification. The peculiar resem-
blances of the young of some of the Goniatitine and the adults of Tentaculites
among Pteropoda may be entirely due to homoplasy, and not to homogeny.’

phenomena with w
independent origin of similar ch
ous use of terms Heterology and Homolo
of Genera,

1 These terms were first used by Lankester (Jour. Micr. Sci., XVII., 1877, p. 486). They express

hich naturalists have long been familiar, ‘‘ homoplastic ’? meaning representation and
aracters, and ‘* homogenous’? meaning genetic connection. See also previ-
gy for the same phenomena by Cope, in his masterly essay, ‘‘ Origin
” Proc, Acad, Sci. Phila., 1868, and “ Origin of the Fittest,’ p. 90.

NOMENCLATURE OF STAGES OF GROWTH AND DECLINE, 11

It is obvious that we cannot ac-
count for the nautilus-like ven-
tral saddle of the earlier sutures
of the Ammonoids, the calca-
reous shell of the protoconch,
the coecal stage, the absence of
the collar in the lower Goniati-
tine and in the young of the
higher forms, the often central
position of the siphon in the
young, and many other charac-
ters, unless we admit a proba-
ble derivation of the Goniatitinee
from some straight microsipho-
nulate form of Nautiloid. It is,
therefore, highly probable that
the pteropod-like aspect of the
young of some Goniatitinas may
be a purely homoplastic charac-
ter, and be meaningless so far as
the genesis of the group is con-
cerned.

7. The next or second of the
neepionic stages was represented
by a living chamber, which was
completed by the building of the
first septum with its attached
cecum, indicating the primitive
beginnings of a siphon. This
stage we styled the Czcosipho-
nula, and we have considered the
possession of a cacum to be an
indication of the former exist-
ence of an ancestor having a
central series of cecal pouches.
These may have had functional
communication in some forms by
means of an endosiphon, as in
the Endoceratide, and in others,
either belonging to this family or
to a more primitive group, they
may have been closed cxca.

8. The next nepionic stage
was ended when the second sep-
tum was built in the modern

Fig. 9,10. Views from the side and below of the plug which the
animal of Orth. uncatum, Barr., habitually built on the exterior
of the broken or truncated end of its shell. The last suture
is shown in Fig. 9, and the internal shadowy markings are
apparent in both figures at a, g. These, however, in Fig. 9,
are too far removed from the exterior. When the outer layer
of the plug is penetrated, they are seen to be a part of its
structure. ‘The side view is also defective in the drawing of
the pseudo siphon (d). There should be three distinct steps
indicating three layers. ‘The external crenulated strie of the
plug appear at h. Loc. Bohemia, Coll. British Museum.

1 2. Views of the same from the side and below, to show

the external markings of the plug (h), which contrast strongly

with the perfectly smooth shell above the septum of trunca-
tion and internal strie (1) which appear when the. outer layer
is fractured. No septa ever occur in the plugs. These figures
are introduced in order to meet M. Barrande’s objections (Syst.
Syl. Pl. 488), that the examples of what we have called the
protoconch and apex of the true conch were in reality plugs
similar to those of Orth. truncatum. There is no need of mak-
ing any remarks; if our figures are correct, we are right in
our statements. It may, however, be well in this connection
to say that M. Barrande has done us the honor to make use of

a number of our figures, including in part the above.

Fig. 13-15. Views of the cicatrix and apex of Orth, unguis, Phill.,
after the shedding or remoyal of the protoconch as it usually
occurs, leaving the cicatrix uninjured. Fig. 13 shows the area
of the cicatrix much enlarged; b, conch or apex forming a
smooth shoulder; and ec, depressed surface of the cicatrix.
Fig. 14, view less magnified of apex; Fig. 15, section of same.
Loe. Dublin, Coll. British Museum.

Fig. 16. Apex of Orth. unguis, Phill. natural size, with first three
sutures.

Fig. 17. Apex of same species after the probably violent removal
of the protoconch, showing the fractured shell (b), and the
unusual aspect of the cicatrix. ‘This and Fig. 16 are types.
Loc. Yorkshire, Coll. British Museum.

Fig. 18. Front view of Fig. 19. The broken line (k) is hy potheti-
cal. It indicates the possible outline and position of the caecum,
supposing the oval area in the centre of Fig. 19 to have repre-
sented that organ.

Fig. 19. Apex of Orth. politum from below. The protoconch has also
been violently removed, and the opening plugged, apparently
from within. The dark spot on the right seemed to be a rup-
ture in the external surface. The oval shade in the centre indi-
cated an internal structure, which may have been the caecum In
the first air-chamber. Loc. St. Cassian, Coll. British Museum.

12 GENESIS OF THE ARIETIDA.

Nautilus, and in the vast majority of all known fossils of the order so far known
to the author this stage had similar characters. The siphon was larger at this
stage than subsequently, and possessed a prolongation which reached down into
and lined the primitive cecum. ‘This closed pipe was however more or less cylin-
drical, and formed a transition to a cylindrical, open, siphonal tube, when com-
pared with the caecum on the one hand and the siphon of the succeeding septa
on the other. The second septum was prolonged apically into a funnel, and this
was continuous with a true porous wall, which formed the remainder of the
pouch. We have already pointed out the probability that this wall was the
homologue of the calcareous sheaths or endocones which filled the interiors of
the siphons of Endoceratide. There is, therefore, as previously stated by the
author, a structural though highly concentrated and much modified remnant of
the adult siphonal elements of an Endoceras still preserved in this stage, even in
the existing Nautilus, and we propose to name it the Macrosiphonula.

9. The next neepionic stage in living Nautilus was the third living chamber
and third septum with its siphon. The siphon has a true funnel, and the siphonal

wall attached to it is less swollen out, and seems, upon re-examination of the .

junctions at the opening of the funnel in the second septum, to be discontinuous.
If we are correct, this stage has a small siphon consisting of the usual funnel and
tubular porous wall, as in the vast majority of all Nautiloidsand Ammonoids. We
proposed to name this, according to its aspect and structure, the Microsiphonula.
The microsiphonula, though a nepionic stage in the modern Nautilus, did: not
always occur among larval stages, but had in common with the macrosiphonula
a traceable beginning in the adult stages of ancestral types. The genesis of the
two forms of hic may be studied in the Endoceratide. In this family Cyrto-
cerina had a siphon, which continually increased in size, probably throughout life,
though more forms need to be described before one can be assured a this as a
fact. There is no doubt, however, that the next form, Piloceras, had what we can
safely call a macrosiphon of typical structure until very late in life. The large
shells collected in Newfoundland by the author had siphons of great. size, aiak
were only slightly contracted or remotely approximated to the tubular condition
of the Orthoceratide in the adolescent and adult stages.

This and other changes occurring in the adolescent stages induced us to
distinguish them by a special term, Nealogic. The adolescent or nealogic
stages, therefore, and the stages of the adult, or, as we have named them, the
EKphebolic stages, in Piloperas show for the first time a tendency to contract
the siphon or approximate to the microsiphonula, but they never had a true
microsiphon. The contracted siphon in these forms, as in the other genera of
this family, always had the holochoanoidal or complete funnel reaching from one
septum to the next, and a series of conical concentric endocones, or sheaths, as
they have been called by others, which stretched from the ends of the funnels,
and were the homologues of the porous walls of the segments of the siphon in
Nautilus.

The terminations of the endocones were prolonged into a central tube. or
endosiphon, which we have previously described, and which probably served as a

i

NOMENCLATURE OF STAGES OF GROWTH AND DECLINE. 13

functional siphon in these shells. Gerard Holm! first called attention to the
interesting character of the young stages of the siphon in Endoceras, and has
shown this organ to have been very large even in the young, having not only
a cecal beginning, as in other forms, but in several species having a swollen
or macrosiphonulate form which endured throughout several septa. In speci-
mens now in the Museum of Comparative Zodlogy, at least six septa were built
before any signs of contraction began to appear. In other cases figured by Holm
the siphonal cecum, though very large as compared with that of Orthoceras, was
attached to the first septum, as in all the shells so far known from that group,
and occupied only the first air-chamber. We should suggest to those having
materials for study, that the shells having this last character are very likely not
true Endoceratites, but perhaps the young of species of the genus Sannionites,
which, according to the classification followed by the author, is a genus distinct
from Endoceras, because the species possess a much slenderer siphon. Whatever
the fate of this suggestion, it is plain that transitional series exist in this group
between Sannionites and Cyrtocerina or Piloceras, and that gradations occurred
also in Piloceras, which show that contraction of the siphon began first in adults,
and then, according to the law of acceleration, was inherited in the nealogic
stages of immediate descendants, and finally became nepionic in the smaller
siphoned species of the genera Endoceras and Sannionites. This tendency to
contraction in the diameter of the siphon indicated the beginning of a series of
transformations which accompanied a decrease in size of the fleshy siphon, and
other correlative transformations, such as the decrease in length of the funnels, and
the contraction and straightening out of the calcareous endocones, so as to form
the walls of a tubular siphon. In other words, as the siphon contracted, the func-
tional endosiphon formed by the open and extended tips of the endocones was
finally brought into line with the funnels, and together with them formed the
microsiphon, which is consequently a degraded modification derived from the
funnels, endosiphon, and endocones of the Endoceratidee. The Orthoceratide and
all the remaining forms, with some notable exceptions which we shall take up
and describe in future papers, had a microsiphon. The whole microsiphon formed
a continuous open tube of narrow diameter, reaching from the last septum to the
nepionic septa, which represented the macrosiphonula. Doubtless the duration
of nzepionic stages will be found to vary somewhat in ancient forms, but the
indications, so far as known, are in favor of the theory that the vast majority of
even ancient forms had a microsiphon, which was developed comparatively early
in the life of the animal.

The nealogic stages of succeeding groups would be very interesting if
there were space to describe them, but we shall have to illustrate this part of
our work among the Ammonitine. The protoconchs of Ammonoidea, including
the genus Bactrites, had, as remarked above, globose forms with calcareous
shells, and these shells were continuous with the apex of the conch, but the
aspect of the junctions was quite distinct from those of Nautiloids. The con-
striction between them and the apex was very slight in the uncoiled young of the

' Dames et Kayser, Paleontol. Abhandl., [II., Part I.

14 GENESIS OF THE ARIETIDZ.

more primitive forms of several silurian and devonian species of Goniatitine, and
this is notably the case in Bactrites which has a straight shell. In these primitive
forms the apertures of the protoconchs must have been less contracted than in
most Nautiloids,

The apex of the conch did not expand so fast as in Nautiloids, but was more
nearly of the same diameter as the neck of the protoconch, and often remained
tubular for a considerable portion of the nepionic period. This was especially
evident in the more open whorls of the anarcestian larve, figured by Sandberger,
Barrande, and Branco. Among the close-coiled forms of paleozoic species, and in
still later occurring genera, the protoconch itself became depressed, and a deep
dorsal constriction resulted from the abruptness with which the apical part of the
conch turned in upon the inner (dorsal) side of the protoconch.

The calcareous nature of the shell, the depressed form and transversely con-
stricted aperture, and the closer union of protoconch and conch among Ammo-
noids, separated the young apparently so widely from those of Nautiloids, as to
lead Barrande, Munier-Chalmas, and Branco to deny that transitions occurred
between them. Another distinction of importance was, that the aperture of the
protoconch was closed, not by an apical plate, but by the first septum. In other
words, the asiphonula of Nautiloids disappeared as a distinct nepionic stage,
and the cxcosiphonula took its place in the development of the young among
Ammonoids. ‘This fact led Branco in his masterly work on the early stages to
assert, in common with Barrande and Munier-Chalmas, that the protoconch of the
Ammonoids was the homologue of the apex of the conch and first air-chamber in
the Nautiloids. Certainly the calcareous shell and the position of the first sep-
tum and cecum appear to be in favor of their view.

On the other hand, the student of embryology will be slow to admit that the
resemblances of the protoconch in Ammonoids to the veliger shell has no mean-
ing. Ifit have any meaning at all, and can be compared with the protoconchs
of the Cephalophora during the veliger stage, then during the whole of that
stage the typembryos of Ammonoids, like all other veligers, could not have had
a siphonal cecum or siphon. This is insured by the emptiness of the protoconch,
the siphonal cecum being present only in the aperture, and not penetrating far
back into or resting upon the first formed plate of the protoconch, as in the first
air-chamber of Nautiloids,

Another argument in favor of the view here advocated is the general fact,
cited in the paper quoted above, upon the “ Values in Classification of the Stages
of Growth and Decline,” that the typembryos, to which class of forms the veli-
ger belongs, cannot be said to have the essential characters of any specialized
division, like the Cephalopoda, but have to be compared with remote and gen-
eralized types from whom their principal characteristics were inherited.

The authors quoted above, holding the view that the protoconch was the
homologue of the first chamber and apex of Nautiloids, necessarily rejected our
theoretical explanation of the presence of the first septum and cecum in the
aperture as due to acceleration of development.

Nevertheless, this explanation still seems to us correct, and we have now a new

4

NOMENCLATURE OF STAGES OF GROWTH AND DECLINE. 15

point to make in its favor. If the protoconch of Nautiloids was an empty con-
chiolin shell and represented the veliger stage, it most certainly could not have
been the ancestral form from which the calcareous tendency of the same stage in
Ammonoids was derived. The characteristics of the asiphonula of Nautiloids are,
however, just what are needed to fill the gap. The apex at this stage in Nau-
tiloids is rounded and calcareous. The tendency to deposit calcareous matter
could therefore have been inherited from an ancestor corresponding to the asi-
phonula, and which we will name the Asiphonophora. The Asiphonophora must
have had a calcareous shell acquired as an adaptive character, without internal
calcareous septa or a siphon. This form could not have been by- any means so
far removed from the ancestor of the veliger as the immediately following an-
cestor of the macrosiphonula, which we have named the Macrosiphonophora.
This must have had septa and a central axis of ceca, or at any rate at least
one septum and a caecum.

The characters of the Asiphonophora, when transmitted to the Ammonoids
according to the law of acceleration, would have been inherited earlier than in
Nautiloids, would therefore have affected the growth of the protoconch, and
would have necessarily produced the calcified shell of this stage in Ammonoids.
The fusion of the protoconch with the conch in all Ammonoids was the imme-
diate result of this process, and in this way the more tubular form and freer
connection of the protoconch with the true conch, and the constant adhesion

of the former to the latter, can be explained.

The disappearance of the asiphonula as a distinct stage in the young of
the Ammonoids appears to us, therefore, not an argument against the deriva-
tion of the Ammonoids from Asiphonophora, but in favor of this opinion. In
fact, it seems to us that, in order to disprove it, opponents will have to find
a cicatrix upon the apex of the protoconch in the Ammonoidea. According to
the uncompromising attitude of those who insist upon the naked facts, and are
hostile to explanations, the protoconch is the apex of the conch in Ammonoids,
and the absence of any cicatrix upon the tip of this is a difficulty they can only
surmount by asserting that the general and special homologies we have traced,
and all the embryological and nepiological correlations, are purely homoplastic,
and do not indicate the derivation of the Ammonoids from any form of Nauti-
loid. They must also explain away the similarity of the protoconch in external
aspect to the veliger shell in Gasteropoda, since this is an earlier stage than
that of the apex of the true conch in Nautiloids, Ammonoids, and all cephalous
mollusks. Can any of these gentlemen tell us why the cicatrix does not appear
upon the protoconch of Ammonoids, and explain at the same time how that
shell came to be similar to the veliger shell in the Cephalophorous Mollusca
on the one hand, and the apex of the conch of Nautilus on the other?

It must be observed, also, that we do not insist that the primary radical of
the Ammonoids, Anarcestes, was necessarily descended directly from Endoceras,
but that it had probably come from a prototype like the veliger, possibly, as
suggested by Brooks, from a class now only represented by the genus Dentalium.
The next step, according to our translation of the evidences, must have been

16 GENESIS OF THE ARIETID.

the Asiphonophora, which may have been more of a Pteropod or Scaphopod
than a Cephalopod. So far as the shell goes, there are no similarities to the
peculiar shell of Dentalium, but perhaps more to that of a Pteropod.

The next step in this line of genesis must have been the ancestral generator
of the characters of the czcosiphonula, which we propose to call the Caecophora,
a form which must have been a reality in some shape, and in some species
doubtless had the characters of the ccosiphonula in its ephebolic stages.
This class of forms, though having septa and a central axis, which we might
have to consider as a primitive siphon, was nevertheless quite distinct from
those which followed.

The next link in the genealogical tree must have been the ancestor of the
peculiarities of the macrosiphonula, and this is luckily a well known form.
The Endoceratide enable us not only to see that the previous train of induc-
tion is legitimate, but to connect our line of hypothetical forms with the next
in the evolution of the group. The Endoceratidee are true Macrosiphonophora,
according to the nomenclature adopted here, and are transitional to the more
highly specialized and stable modification which had what we have termed the
microsiphon.

When this organ came into being in the direct line of change, the evolution
of the forms also changed its character. The more rapid or accelerated modes
of change were replaced by slower processes. The changes occurring in the
types preceding, and including the Endoceratidse (Macrosiphonophora), were,
if we can judge by the abrupt transitions of the genera in this family, more
rapid and more important in their effects on structures than was the rule
subsequently. This is also shown in the structural changes taking place in
the embryos of Nautiloids and Ammonoids, as compared with the slow and
comparatively slight changes of the subsequent stages of growth. The rapid
acceleration of the macrosiphonulate character during the evolution of the
Endoceratidz, the still more rapid acceleration which took place in the evo-
lution of the microsiphon among Ammonoids, and the fusion, through accelera-
tion in development, of the characters of the asiphonula with the protoconch, all
bear witness to the truth of this induction.’

The neepionic stages in ancient asellate forms of the Ammonitine, as has
been shown above, may be considered as indicating the primitive radical, the
straight orthoceran, and the gyroceran, or loosely coiled nautilian shells; but in

1 We have already traced the more rapid evolution of the ancient forms of Cephalopoda, and need not
go into the matter any further in this monograph than to state that these facts accord with the law an-
nounced in Genera of Fossil Cephalopods (Proc. Bost. Soc. Nat. Hist., XXII. p. 262), which reads as
follows: ‘‘ These facts, and the acknowledged sudden appearance of all the distinct types of Invertebrata
in the Paleozoic, and of the greater number of all existing and fossil types before the expiration of paleo-
zoic time, speak strongly for the quicker evolution of forms in the Paleozoic, and indicate a gen>ral law
of evolution. This, we think, can be formulated as follows: types are evolved more quickly, and exhibit greater
structural differences between genetic groups of the same stock, while still near their point of origin than they do
subsequently. The variations or differences may take place quickly in the fundamental structural charac-
teristics, and even embryos may become different when in the earliest period, but subsequently only more
superficial structures become subject to great variations.’’ See also Foss. Ceph. Mus. Comp., in Proc. Am.
Assoc. Ady. Sci., XX XII., 1883, p. 338,

NOMENCLATURE OF STAGES OF GROWTH AND DECLINE. a7

all other forms, especially in the devonian latisellate and triassic angustisellate
embryos, the tendency to become closely coiled, and to inherit the depressed
primary radical whorl of Anarcestes, produced the Goniatitinula, and affected
even the protoconch. ‘The protoconch through heredity becomes depressed fusi-
form by lateral expansion in the Angustisellati, and the embryonic nautiloid
character of the first septum in the asellate forms and its tendency to form
a broad ventral saddle in the latisellate and a narrow ventral saddle in the
angustisellate embryo is correlative with this progression of form.

The goniatitinula is a true larva, corresponding to adults within the order.
We use the term because it is the characteristic larval form: of the Ammonoidea,
which was introduced at first among adult Goniatitinez, and in the higher forms
of this group became, by acceleration, fused with the microsiphonula.

The remarkable researches of Branco enable us to state that this progres-
sion in complication of the embryo in form and sutures has no counterpart
in the parallel series of any pre-existing series of adult shells, except among
Nautiloidea ; consequently the angustisellate peculiarities of the ventral saddles
and deep lateral lobes characteristic of the latisellate and angustisellate em-
bryos of the Devonian and Trias were not due to inheritance from primitive
adult radicals, but were later modifications originating in the cacosiphonula
from close coiling. They -were correlative with the earlier or accelerated
development of the depressed whorl, and the quicker growth in bulk of the
whorl. Similar tendencies have been observed repeatedly in different progres-
sive series of Nautiloidea. Thus, wherever we have been able to trace the series
of species from a straight, or loose-coiled, to a close-coiled nautilian form, this
as a rule has more complicated sutures. The universal result of such progres-
sive specialization among the adult forms of Nautiloids is closer coiling, due to
quicker growth in bulk of the whorl, and is accompanied also by the evolution
of a larger ventral saddle. It is not surprising that similar mechanical results
should follow in the septa of the embryos of Ammonoidea, when similar changes
in the mode of growth occurred through the accelerated inheritance of the
depressed anarcestian radical whorl, and closer coiling in the ceecosiphonula.

Branco has observed the shortening of the larval stages in the Latisellati
as compared with the Asellati, and the still greater acceleration of development
occurring in the Angustisellati, and the correlation of these with the general pro-
gress in complication of the sutures of the adults of the same divisions in time.
This confirms our previously published opinions of the relation of embryos
and adults, and also agrees with those here published regarding the inheritance
of the primary, radical, smooth form in the depressed embryos of Latisellati and
Angustisellati, and the correlative evolution of the sutures and coiling.

The microsiphonula appeared in the Ammonoidea with the second septum,
in what is morphologically the second air-chamber when compared with Nauti-
lus, though actually the first existing in the apex of the true conch. This
microsiphonula is also an accelerated form, since the siphon becomes very rapidly
or even abruptly attenuated. The collar or distinctive organ of the siphon among
the normal Ammonoids was not formed until later, though the precise period

2
oO

18 GENESIS OF THE ARIETIDA.

has not been ascertained in any one form, so far as we know. The microsi-
phonula occurred, as might have been expected, earlier than the true goniatitic
stages, or goniatitinula, in those species which had the nautiloidean stage with
ventral saddle also prolonged into the second septum, as in the Asellati figured
by Sandberger, and (ron. atratus figured by Branco. The goniatitinula became
distinguishable when the first ventral lobe appeared. This was undivided, as
in the lower Anarcestes and in the Magnosellaride among Goniatitine. This
stage is prolonged through one or more septa in the higher Goniatitine, and
also in the Lytoceratinzs and Ammonitins, and the whorl also at this time
strikes one as similar to Anarcestes, or depressed semilunar in section, as stated
above, and in these the goniatitinula is completed.

The duration of the nepionic period can in a general way be described
as coincident in extent with the duration of the smooth shell, which is always
found at the centre of the umbilicus, however much the shell may be subse-
quently ribbed and ornamented. This period would of course include many
more transformations than the goniatitinula, especially among the higher and
later occurring species of the Mesozoic.

Haeckel designated all of the progressive stages which succeeded the true
ovarian stages and included the nepionic and nealogic stages, and their
structural relations, under the term Metamorphology.’ This term is, however,
somewhat indefinite and artificial when limited in this way, since the ovarian
stages are necessarily of very different duration in distinct groups, and cannot
be considered as the natural limit of the embryologic period. We should, as
above stated, be disposed to think that some such limit as here proposed would
be nearer to the true one, namely, to consider the typembryos as the last of
the true embryologic stages. This nomenclature would enable an author to
give an approximate idea of the stage at which the metamorphologic stages
began in any type. Thus, they would have begun in Nautiloids with the asi-
phonula, and in the absence of this among Ammonoids with the ceecosiphonula.
In the absence of this last, if it is absent among the lower Sepioidea, the meta-
morphologic stages, according to the same rule, would begin with the first stage
immediately succeeding the protoconchial stage. Whenever this last is absent,
as it certainly is among the highest of the Sepioidea having meroblastic ova,
then its equivalent stage, which represents what is left of the veliger, should
be taken as the last of the embryologic stages.

As has been noted above, the nzpionic period is always smooth, and is
visible at the centre of the umbilicus in most discoidal shells, and the demar-
cation is therefore visible between this and the nealogic period; but, as can be
observed on most specimens, an attempt to separate the characters of the latter
from the characters of adults is attended by greater difficulties. It is, however,
essential to distinguish the category of ephebolic or adult characters from the
nealogic, because in each form of any series there are usually found certain novel
characters, which appear for the first time in that particular series. These make
their first appearance almost invariably during the ephebolic period.

1 Morph. d. Organismen, II. p. 22.

NOMENCLATURE OF STAGES OF GROWTH AND DECLINE. 19

The ephebolic characters are as a rule inherited or homogenous within the
special series in which they originated, but are not transmitted from one series
to another except through the medium of the nealogic stages of what we have
called the tertiary radicals, and they are not, so far as we know, ever concen-
trated in the earliest larval or nepionic stages; they occur too late in the
history of types.

We classify in the nealogic and ephebolic stages such characters as follows:
the sharply defined ridge-like pile and tubercles, the channels with their lateral
ridges, and keels, and especially the hollow keel, the highly developed rostrum
of the higher suborders, especially Ammoniting, the lateral lappets of the aper-
tures, and the branching marginal lobes and saddles of the sutures of suborders
above Goniatitine. Speaking in a general way, we should include in these
categories those progressive characters which appear late in the life of the
shell among the higher suborders, and at the acme of their development in
time, which are not found in the stock of discoidal radical forms. When the
shell began to assume the ribs or pile, as we prefer to call them, the nealogic
period may be said in a general way to have been entered upon. It has been
found that these stages of growth indicated genetic relationship with radical
forms, which were not infrequently merely different genera or species within
the limits of the same family, and often occurred on the same or only slightly
different horizons. The nealogic stages of the higher Ammonoids, Ammoni-
tine and Lytoceratine, have not the constancy and general importance of the
nepionic stages, but are transient in the history of the types, appearing and
disappearing in the same limited series of forms. They consist of the less im-
portant modifications which first appeared in the adolescent or adult stages at
a late period in the history of a type, and were then inherited in the nealogic
stages at earlier ages in successive species of the same series, according to the
usual action of the law of acceleration. The nealogic category cannot be as
definitively separated from the characteristics of adults as from those of the
larve. Their first appearance in adults indicated the establishment of a new
species in any given series, since they are invariably differences so far as their
predecessors and congeners in the same series are concerned. However much
they may represent or reproduce the characters of species in other series, they
are essentially differentials as regards the adult stages of ancestral species of
the same series. Thus the nealogic characters are as a rule ephebolic, and not
nealogic, in origin among the Cephalopoda, and usually become nealogic through
inheritance. We shall have frequent occasion farther on to call in the evidence
of the ephebolic stages, and to show, as in the Endoceratide, that, as a rule,
characteristics originated in this stage of growth, as indeed must have been the
case with the caecum and the microsiphon.

At the termination of the progressive stages, which ended with the full
development of the ephebolic characters, the first stage of decline, or the gera-
tologic period, began to make its appearance, and became more and more appar-
ent as the specimens advanced in age. It was found that, as has been observed

1 See, for secondary and tertiary radicals, p. 22 et seq.

20 GENESIS OF THE ARIETIDA.

in other animals, especially in man himself, the decline was marked by degra-
dation of certain characters, and the number of parts undergoing degeneration
was gradually increased, until finally the whole of the body was more or less
affected.

This period has been frequently described by the author in previous publi-
cations, and will be more fully described farther on. It is necessary now only
to call attention to the fact, that the geratologic or old-age period can be natu-
rally subdivided into two quite distinct stages. The first, or Clinologic stage,
included the retrogressive transformations during which the nealogie and ephebolic
characters became resorbed one after another, usually in reverse order to the succession in
which they were introduced during the progressive stages of growth. The size of the
whorl also, sooner or later according to the species, showed retrogression during
this period. All of these retrogressive tendencies reached their extreme ex-
pression in the last and final stage of the ontogeny of the individual. In this
stage the spines, pile, and often the keel and channels, when present, were
lost, and the size of the whorl was so much reduced in all its diameters that it
became more or less rounded, whatever the angularity of the whorl during the
ephebolic period. This stage we have designated by the term Nostologic, on
account of the likeness to its own nepionic period, which was finally acquired by
the smooth, almost rounded whorl after the loss of its progressive characters.

Geratology, or the study of the relations of these old-age stages, shows, as we
shall try to demonstrate farther on, that the clinologic characters can be used to
predict the degradational modifications which appeared in any series of orna-
mented shells when placed under such unfavorable conditions that their descend-
ants became degraded, and series of more and more retrogressive forms were
gradually brought into existence. A number of such series have been traced by
several authors, and they usually end with a perfectly straight form. This form
terminated the phylogeny of the series in a manner comparable to that in which
the nostologic stage terminated the ontogeny of the individual. It is usually
separated also by a gap from all other species, which has not yet been fully filled
by intermediate species. This nostologic adult form, the so-called genus Baculites,
is not only comparable in this way and by means of its smooth and compressed
cylindrical whorl with the last stage of ontogeny, but it is also a very complete
reversion to the aspect of the earliest radicals of its own class, the Orthoceratite
and Endoceratite.

This nomenclature is similar to that originated and published by Haeckel, and
at first sight may appear to many naturalists as identical; but it is really only
complementary. It is based upon strictly structural and morphological grounds,
whereas Haeckel's nomenclature’ was entirely physiological. This eminent author
regarded the ontogeny of an individual as a cycle divisible into three periods ;
first, the progressive stages of Anaplasis, or those of progressive evolution; sec-
ondly, the stages of fulfilled growth and development, Metaplasis ; thirdly, those
of decline, Cataplasis. He also appreciated and gave full weight to the general
physiological correlations which are traceable between the history of a group and

1 Morphol. d, Organismen, II. pp. 18-23.

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THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 21

the life of an individual, and in accordance with these ideas designated the pro-
gressive periods of expansion in the phylogenetic history of a group as the
Epacme, the period of greatest expansion in number and variety of species and
forms as the Acme, and the periods of decline in numbers of species, etc., as the
Paracme.

Haeckel used also the term Anaplastology for the physiological relations of
the stages of progressive growth and those of the epacme of groups, Metaplas-
tology for those of the adult and the acme of groups, and Cataplastology for
those of the senile stages and the paracme of groups. These terms seem to
cover the same ground as those we have employed, but they were in reality
chosen for the purpose of classifying physiological relations. Thus the anaplastic
relations of the neepionic and nealogic stages to the phenomena occurring dur-
ing the epacme of groups, the metaplastic relations of the ephebolic stages to the
phenomena occurring at the acme of groups, and the cataplastic relations of the
geratologic stages to the phenomena occurring during the paracme of groups, are
the functional relations of the structural modifications occurring in the ontogeny
of individuals to those which are characteristic of the phylogeny of groups.

THrory or RADICALS AND Morpno.ocicaL EquiIvVALENCE IN
PROGRESSIVE Forms.

The simpler characters of the sutures in the adults of more ancient forms, as
compared with the more modern species of the same series, has been noticed by
Wiirtenberger, Zittel, Neumayr, Waagen, and Branco,! in different groups of
Ammonitine. The first is very decided in his statement, that the Ammonitine
he has studied form perpetually diverging series, which spring from certain
common ancestral forms.

The constant repetition of discoidal and involute forms in series, which are
otherwise distinct in respect to their sutures and minor characteristics of develop-
ment and shell markings, produces a similarity in the succession of the forms. It
is practicable to compare the evolution of discoidal into more involute forms of
any one series with a similar genetic procession in any other series. Thus in the
General Summary, Plate XIV., we can compare the discoidal forms of Ver. Cony-
beari, Fig. 20, with Arn. tardicrescens, Fig. 26, Cor. rotiforme, Fig. 30, and Ast. Tur-
nert, Fig. 36, and in the same way the involute forms of As/. Collenoti with Oayn.
oxynotum, Greenough, and Lotharingum ; and these comparisons also hold good for
Schlot. Boucaultiana, and the terminal forms like Woh. Emmerici and Psil. mesogenos,

which are also involute. In exceptional series the whorls do not become more

involute in the higher species, but are nevertheless modified in those character-
istics which usually accompany and correlate with increase of involution. Thus
the lateral diameter of the whorl decreases, the sides become more and more

1 Wiirtenberger, Stammesgesch. d. Amm., Darwinistische Schriften, Nr. 5, Leipzig, 1880, p. 91. Zittel,
Ueber Phylloceras tatricum, Jahrb. d. k. k. geol. Reichsant., 1869, p. 65, Neumayr, Die Phylloceraten d.
Dogger und Malm, Ibid., 1871, pp. 347, 348; also, Zeits. d. deutsch. geol. Gesellsch., 1875, p. 866. Waagen,
Die Formenreihe d. Amm. subradiatus, Benecke’s Geognost. paleont. Beitr., II. p. 202. Branco, Paleontogr.,
RXV 1 ROX VAT

1
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4

22 GENESIS OF THE ARIETIDA.

convergent outwardly, and the abdomen narrower, though the shell may still re-
main discoidal; ex. Caloceras and Coroniceras, Plate XIV. Fig. 11-16, 28-32.

The Ammonoids of the Lias also have a tendency to produce keels, ribs, etc. in
addition to the parallel procession of the forms just described. Thus, when we study
the parallelisms occurring in different series or genera of the Ammonitine in the
same family or group, we find that equivalent species in different series are due
not only to the increasing involution of the whorls, but also to the development
of similar structural characteristics. Most paleontologists are not aware of these
facts, and therefore are apt to consider species of distinct series as closely allied.
It is usual, for example, to classify all the species of the Arietidee having quadrago-
nal whorls, deep channels, prominent keels, and well developed pile, as species
of the same genus, Arietites,’ whereas they are more closely allied to Psil.
planorbe, their radical ancestor, than they are to each other. Errors of this kind
are common, and have been still more general. Thus most modern improve-
ments in taxonomy in all the branches of the animal kingdom have consisted
in doing away with classifications made by the association of representative
forms, or, as they are here called, morphological equivalents.

The Arietidx sprang from discoidal species of Psiloceras, having smooth shells
and phylliform sutures. Other groups occurring later in time are traceable to
forms of more advanced structure, so far as the shape and ornaments of the
whorl and the sutures are concerned. In every case, however, progressive groups
have been traced directly to forms having discoidal shells. The discoidal radicals
of different series have been invariably found to be nearly related to each other,
and to preceding discoidal radical types, while their descendent species are diver-
gent, and essentially distinct. However closely they might have resembled each
other as morphological equivalents, they possessed the homogenous differential
characteristics of their own genetic series.

I have elsewhere noted the facts tending to establish the probable existence
of a continuous line or radical stock of types or species.? The paleozoic primary
radicals are similar to Anarcestes; the mesozoic or secondary radicals are like
Dinarites Mahomedanus, Ceratites Sturt, Gymnites, and Psiloceras; they occur largely
in the Trias, and are species with discoidal but rather compressed smooth shells.
The tertiary radicals, though discoidal, may be highly ornamented with pile and
spines, and have sometimes very broad or coronate whorls; they occur largely
in the Jura.? The primary and secondary radicals, if we follow Haeckel’s nomen-

1 Zittel’s Handbuch d. Pal., I. p. 455.

2 Gen. of Foss. Ceph., Proc. Bost. Soc. Nat. Hist., XXIII., 1883, pp. 823-825.

8 Tirolites and Tropites are acmic or tertiary radicals occurring in the Trias. They are certainly coro-
nate forms, with pil, tubercles, and open umbilici. If any one will compare the young of Balatonites or
Tropites with the adults of the smooth species of Dinarites and Ceratites as figured by Mojsisovics, he will
be able to see that the radical stock is a definable series of forms, with characteristics not only shown in the
adults of simpler smooth genera and species, but necessarily repeated in the young of more modified species,
like Balatonites, Tropites, etc. It must be remembered, however, that all forms will not have the smooth,
compressed secondary radical reproduced in their young; many of them lost this, or had it only very
slightly, since it was replaced by the broader-abdomened tuberculated tertiary radical, as in the young of
Trachyceras aon. The young of Tropites has a form and sutures similar to those of Glyphioceras diadema
of the Carboniferous, and the stock of tertiary radicals may therefore be said to have begun even in the

Paleozoic.

THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 23
clature, are epacmic, and the tertiary are what we should call acmic radicals.
Cel. Pettos is an excellent example of an acmic radical in the Jura. It stands
morphologically and chronologically at the centre of the affinities of the group
of Dactyloide and Stephanoceratide, that is, of the larger part of the odlitic
Ammonitine. It is, in its relation to these, and to the characteristics of their
nealogic stages of development, an epacmic radical, but with regard to Psilo-
ceras, and more ancient secondary radical forms, it is a tertiary or acmic radical.
It has a flattened abdomen, very divergent sides, like those of Steph. coronatum,
and similar acmic radical forms, and a line of coarse tubercles along the sides.
Though altogether distinct from Psiloceras, it is also a perfectly discoidal form.
The direct descendants of Pettos, which belong properly to the stephanoceran
and allied groups, are also discoidal forms, though the series often have involute
species, such as Maer. macrocephulum, ete.

Tertiary radicals in what we propose to call the Pettos Stock, or Spinifera,
according to the evidence of the younger stages and the characteristics of adults,
have but one row of large spines in adults, and whorls which are very gibbous or
trapezoidal in section, that is, with abdomen broader than dorsum. The whorl
may sometimes be smooth, with only one row of lateral spines, but is usually
strongly pilated, the pile being single on the sides and as a rule bifurcated only
on or near to the abdomen. ‘The sutures have a more or less close resemblance
to those of Der. Dudressier’, or Cel. Pettos. The line of descent being broken,
we shall, in the imperfect list below, give some forms having two lines of tuber-
cles. These, however, have young which, until a late stage, show only one outer
line of lateral tubercles, as in the adults of the two species cited above. Steph.
nodosum of the Lower Odlite is the tertiary radical of that genus, and of Macro-
cephalites, Spheroceras, Morphoceras, Reineckia, Cadoceras, Quenstedioceras,
Aspidoceras, Olcostephanus, and Pachydiscus. All of these genera have some
forms which are either closely similar to the radical in the adult stages, or else
have young with a nodosum-like stage. Peloceras athieta has a similar history,
though it is like Dactylioceras in its nealogic stages, it has two lateral rows of
large spines, and is similar to Asp. perarmatum in the adult. The huge coronate
forms of the Upper Jura, like Olcostephanus Gravesianus, etc., and the single-
spined forms like Aspidoceras Hdwardsianus, and shells like Asp. perarmatum,
Rupellense, etc., with two rows of spines, are obviously in the line of stock forms.
In fact, one can select from the discoidal shells of these groups a more or less
closely allied series of stock forms, from each of which a separate genus or series
of genera arose, until we find in the Cretaceous a new beginning in Hoplites
ftoyerianus and Cornuelianus for the species of that large genus, and of Acantho-
ceras, Pulchellia, and possibly Holcodiscus and Costidiscus.

The cretaceous group, with nodose keels or lines of tubercles in place of a
keel, also belong to the Spinifera, but they form a separate phylum connected, in
common with such forms as Acanthoceras mammillare, with the Hoplites series,
and their radical is also Royerianus. The radical of Cosmoceras, Cos. Taylori of
the Lias, is a species with two rows of spines allied to Deroceras armatum, and
the adult characteristics of this species are repeated in the young stages of the

24 GENESIS OF THE ARIETID.

normal forms of that genus. Wiirtenberger has come to similar conclusions, and
has traced a large part of the same genera back to the same origin in the work
quoted above. We differ in details, and in the way in which we treat the stem
of stock forms, but these differences will probably disappear after further re-
searches have been made. His book is full of the evidences of careful work, and
we do not feel disposed to offer any criticisms until there is an opportunity to
publish our own observations in detail. The young forms of the Spinifera in the
later nepionic stage, have a very close resemblance to the young of Tropites
before the keel appears, and also an obvious reference to Tirolites of the Trias,
and to the more remote and possible ancestor, Glyph. diadema, in the Carboniferous.

Per. Defranci is the radical of all of the species of the large genus Peri-
sphinctes, and has no tubercles in the adult, but in the young there is a prolonged
stage like the adult of discoidal coeloceran species, and in still younger stages a
pettos-like stage. This genus embraces a very large number of species which
have been traced out by Wiirtenberger, and referred by him to a species closely
allied to the one quoted above in the Lower Odlite. The absence of tubercles,
and the rounded form of the whorl in this group, and the frequent absence
of the trapezoidal form and tubercles even in the early stages of many species,
show that it is distinct from the Spinifera. We propose to designate it by the
term Plicatifera.

The tertiary radicals of the keeled groups, the Carinifera, as we propose to
call them, have also close structural relations, but are modifications of what we
have called the quadragonal form. Nevertheless, in the young and the adults
there is a tendency to reproduce the tertiary radical of the Spinifera. This
is to be seen in Wihner’s figures of Caloceras (Arietites) Coregonense, and that
keen observer describes the resemblance of the young just before the keel ap-
pears to Cal. Pettos of the Middle Lias. Similar facts can be noted in the young
of other forms of the Arietidse, but the keeled stage acquires prepotency in the
Arietide. Their quadragonal, keeled, and channelled forms began in Caloceras,
and from this genus sprang the similar tertiary radicals of the later Jura. The
adical stock is continued by such species, as follows: Amaltheus Hawskerense,
Phymatoceras enervatum, EHildoceras Walcott, and Harpoceras Sowerbyi, which last
has a thodified quadragonal form until a late stage of growth in some varieties,
Oppelia hecticus also has in some varieties a quadragonal form until a late stage,
though not so discoidal as most of the preceding. In the Cretaceous, there
is Schlanbachia tricarinatus and Westphalicus, which are true stock forms of the
Cariniferae.”

Haploceras, Desmoceras, Silesites, Pictetia, and the like, have tertiary radicals
similar to the typical forms of Lytoceras, and belong therefore to the Lytoceratine.

1 Mojsis. et Neum., Beitr., VI., 1888, pl xxii.

2 If should be noticed in this connection that the characteristics of the so-called pettos-like young of the
earlier occurring species of the Carinifera are favorable to Mojsisovics’s view that the Arietide sprang from
Halorites. This genus is closely related to Tropites, and the form and sutures of the young of several
species in the Arietide certainly show affinities for Tropites. On the other hand, as we have maintained
above, the affinities and gradations of all the species of the Arietide lead us back into Psiloceras, and the
alliance of that genus with Gymnites seems to be closer than with any other in the Trias,

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THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 25

Cal. tortile, Cal. laqueum, and Schiot. catenata, in the Plicatus Stock of the
Arietide, are more closely allied to one another and to Psil. planorbe than are the
morphological equivalents among their descendants to one another. However
closely the descendent involute forms may simulate one another, their nepi-
onic and nealogic stages are generally distinct, and indicate the series with
its peculiar differential characters. Arn. miserabile or semicostatum, and Agas.
levigatum, are more nearly related to each other and to Psi, planorbe
in the Levis Stock than are any of the descendent morphological equiva-
lents. ‘There are several forms closely representative of one another, and ap-
parently almost identical, among these morphological equivalents. Thus the
adults of Ver. Conybeari are apparently very closely allied to Oor. bisuicatum,
and to some forms of As¢. Turnerd and Arn. ceras ; but all of these are more
distinct in their nealogic stages than in the adults. The Arietidee present in
this respect a similar picture (Summary Plates) to that of the whole group of the
fossil Cephalods. Thus the adults of the earlier and simpler radical species, from
which the later and more complicated forms must have been derived, are more
closely related in structure than any of their adult descendants. The Cyrtocera-
tites, Orthoceratites, Gyroceratites, the Nautilini, and the anarcestian Goniatites of
the Silurian, are more nearly related in structure and development, in the simi-
larity of the adult sutures, the absence of pil and tubercles, and the mode of
growth, than are their direct descendants, the genera of the Nautiloidea and the
Ammonoidea in the Carboniferous and Jura.

The Nautiloids and the Ammonoids had morphological equivalents, but close
parallelism is not constant or frequent, and occurred principally among later
forms. We have elsewhere discussed this question, and need only notice well
known cases; such as the extraordinary likeness of Clydonautilus to the higher
forms of Goniatitine due to its divided ventral lobe, of Centroceras to Agonia-
tites, and of Subclymenia to Agoniatites, and also the better known example
of the Clymeninz of the Devonian and the Aturia group of the Tertiary. Such
cases of morphological equivalence are disposed of by the use of the convenient
expression, that these are mere analogies. This expression, however, fills noth-
ing but a verbal gap. It neither explains parallelisms, nor the confusion they
have occasioned and still occasion in our classifications, nor the constant ten-
dency of straight shells to become coiled and of already coiled discoidal shells
in progressive series to become involute, to whatever series they may belong, or
wherever they may be found, thus producing morphological equivalents in great
numbers.

The only comparison that represents all these relations to my mind is that
of a number of divergent branches united at their bases or radical ends into a
common trunk. The branches are composed of groups, which, though distinct,
and having differential characteristics, are nevertheless similar in the forms pro-
duced, and in the order of procession of these forms.

The equivalent forms of the larger branches would be admitted to have origi-
nated independently of the direct influence of inheritance. We think that this
is also true in the smaller series, since in no case can the similarities of the

4

26 GENESIS OF THE ARIETIDA.

equivalents, however close, have been derived or carried across the genetic lines
of descent from an equivalent representative species of one branch to that of
another. Nor could the similarities of such forms have been derived in any
series from the radical species, because involved whorls, keels, channels, etc. did
not exist in the discoidal stock forms. Parallel series and equivalent forms, also,
occur often in such zodlogical and geological relations that any sequence or
descent of one from the other is improbable; as, for example, Aturia of the
Tertiary, and Clymenine of the Devonian; or Centroceras of the Devonian,
or Subclymenia of the Carboniferous, and Agoniatites which began in the
Silurian.

These facts speak with great force for the continuity in descent of the dis-
coidal shells, and for the existence of a primitive trunk line of generalized
radicals, beginning with the earliest times and lasting into the Jura. The uni-
versality of the phenomena leads at first to the supposition that we can account
for morphological equivalence of species in different series by some invariable
law of growth, such as is evidently the cause of the more exact parallelisms
which occur between different individuals of the same species. We might con-
sider each species as representing a hereditary grade of structure in the develop-
ment of a series, just as any period in the life of an individual would represent a
stage of development, inherited from some ancestral form.

We were led into this error at first, but it is an inadmissible supposition in
the light of the facts given above. These show, that the representative forms
are absolutely new forms in their respective genera or groups, possessing char-
acters not found in the stock or chronological trunk of discoidal radicals, and
their resemblances are therefore homoplastic, and not homogenous.

There are also many kinds of series among fossil Cephalopoda, and in some
of these forms similar to those of the Ammonoids and Nautiloids are not pro-
duced, as in the Sepioids and Belemnoids. In these orders entirely new modi-
fications accompanied equally complete changes in habits and habitat. The
crawling and shell-covered, littoral, radical Orthoceras has in these orders be-
come changed into a swimming and predatory mollusk, the shell having become
internal. It seems evident in these cases, that the forces of the surroundings
and new habits deflected the Sepioids and Belemnoids from the more normal
course taken by the Nautiloids and Ammonoids, and thus made the repetition of
form or equivalence in the shells impossible, except very rarely, and then only in
a very limited sense. Such, for example, are the similarities which exist between
the internal shell of Spirula and the external shell of Lituites, or between the
pseudo shell of the female Argonauta,’ and the true external shell of one of the
compressed Ammonitine, like Cosmoceras or Hoplites.

The disappearance of the siphon in the Sepioids, and the naked young of the
existing forms of this order, show that too much weight can hardly be given to
the modifying and eventually controlling influence of changes of habit, or, what
is the same thing, the effects of the surroundings in any new habitat, whether

1 See Evolution of Cephalopoda, Science, TIL, No. 52, 58, 1884; Foss. Ceph. of Mus. Comp. Zool., Bul-
letin, I, No. 1; Proc. Am. Ass. Ady. Sci., XXIII., 1883, p 341.

THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 27

sought by the animal or forced upon it by geologic changes. Professor Cope,’
in his masterly work on the “ Origin of the Fittest,” and in pamphlets previously
published, described “homologous” and ‘ heterologous” series equivalent to
what we have called homoplastic and homogenous series, and gives numerous
instances from.all departments of the animal kingdom of exact and inexact
parallelisms sustaining the position taken above. This eminent author discusses
at length the location of growth force due to use or habits, and shows this to be
an efficient cause of modification, thus bringing out clearly and demonstrating
a new law of variation. His opinions with regard to ‘‘mimetic analogy” in
external and internal characters differs only in so far as we have preferred to use
the term morphological equivalence, because we thought it expressed more
exactly the phenomena of homoplasy. He says (p. 96), “I believe such coin-
cidences express merely the developmental type common to many heterologous
(homoplastic) series of a given zodlogical region.” With regard to the effects
of habit, we should also refer to Cope’s remarks (p. 198), and examples with
which he explains the origin of generic characters in the ossification of the
cranial walls in the Batrachia, and the origin of horns among Ruminants, as due
to habits of defence, concluding (p. 200) that the use of the angles of the parts in
question (the head) would result in a normal exostosis of a simple kind in the
frogs, or as horn cores in the Ruminantia. Waagen, in his “ Jurassic Cephalopoda
of Kutch,” ? has made a valuable contribution to the facts in tracing several par-
allel series of Lytoceratine in India and Central Europe. ‘‘The most important
facts which result from the investigations explained in the present volume are
these two: first, that in Kachh, in the same manner as in Europe, developmental
series exist, which are in part identical with the European ones; and second, that
the succession of the identical species in time during the jurassic period in Kachh
has been governed by exactly the same laws as have been observed in Europe.”

‘For facts (parallel series*) like those mentioned, which would be augmented
by a good many instances if other groups of Ammonites were as well known as
Phylloceras, the only explanation is, that the changes of form in the organic
world were dependent upon laws which were innate in them and had not to
rely exclusively on outer circumstances. The latter factors, as struggle for
existence, geographical separation, etc., certainly influenced the production of
forms greatly ; but the fundamental law upon which these influences acted very
likely was not the law of variation, as stated by Darwin, but the law of develop-
ment, or the tendency of the organisms to produce an offspring varying in a cer-
tain well defined direction. If this law be true, the time will come when we shall
be able to indicate a priori, with tolerable certainty, what species a given form
can or might produce.”

1 Origin of Genera, Proc. Acad. Nat. Science, 1863; Methods of Creation, Ibid., 1871, p. 229; and
Origin of the Fittest, p. 95 et seq.

2 Paleontol. Ind., Juras. Fau. of Kutch, I., Ceph., pp. 242, 243.

3 Waagen’s parallel series end in the evolution of identical forms or species from or through different
species. We have never met an example of this kind which did not admit of explanation as the result of
migration. Waagen’s remarks, however, apply to parallel series in general, whether the forms ultimately
evolved are the same, or merely resemble one another more or less closely.

28 GENESIS OF THE ARIETIDA.

We reproduce this conclusion in full, though, as may be seen by reading the
preceding pages, we differ essentially as to the causes that produced parallelism
between different series in the same or different localities. Nevertheless, Waagen
agrees with us in rejecting the doctrine of natural selection as a fundamental
cause of parallelism, and has also stated in 1875, from independent observations,
the possibility of doing what we have been putting in practice ever since 1866;
namely, predicting what sort of species would be found as descendants of certain
given forms, and then subsequently finding them. This experience has also
been shared by Professor Cope, who makes similar statements of his own obser-
vations among fossil and recent Batrachians and Reptiles. ‘The method pursued
by both of us differs from that ordinarily used by naturalists in predicting the
existence of new forms, in that it relies upon the action of the law of accelera-
tion, and the constant recurrence of similar forms in different series of the
same stock, or, as we have explained above, upon the law of morphological
equivalence.’

Turory or Rapicats AND MorpnoLoaicAL EQUIVALENCE IN
RETROGRESSIVE Forms.

There are certain species among complicated acmic forms which became the
ancestors of uncoiled degenerate series, that can be properly termed nostologic
forms on account of their complete reversion to the uncoiled forms of the radical
groups among Nautiloids. These were not confined to any special class of forms,
though more frequent among the higher than among the trunk stock of radical
forms. They are what we have called geratologous radicals. Thus Lobites of
the Trias must have sprung from some geratologous radical among the Goniati-
tine; and Hauer’s Cochloceras with its turrillites-like whorls, and the straight
Rhabdoceras, both have sutures which indicate derivation from some genus like
Helictites or Choristoceras among Ceratitinse of the Trias, ribbed shells with very
simple sutures Choristoceras, also, had discoidal species in the Rheetic beds.

We treat these forms as probably degradational, because of their simpler
ornamentation and sutures, and also because the similar uncoiled shells among
Gasteropoda and among Ammonitine may be followed until they grade into
closely coiled and more complicated shells, from which they probably arose.’
The geratologous forms have a most important bearing on the conclusions reached
in this essay. They terminate the geologic history of their suborders, just as the
Turrillites and Baculites, and others, appear as the final forms of Ammonitine.
They were also coextensive with the existence of the cephalopod type, and were
evidently liable to be evolved at any time in their history, and to increase in

1 The law of acceleration and of morphological equivalence has been stated in the Preface, pp. iv. and v.

2 These lines were written before Zittel’s superb work, ‘‘ Handbuch der Paleontologie,” had appeared,
in which (p. 431) he associates these forms in exactly the same order. Although his text does not allude to
the genesis of the forms, his mode of arrangement shows that he probably had the same idea in mind.

8 Parallelisms of Individuals and Order among Tetrabranchiate Mollusks, Mem. Bost. Soc. Nat. Hist.,
J., 1866-67, and Proceedings of same, I., 1866, p. 802. Genetic Relations of Stephanoceras, Proc. Bost.
Soc. Nat. Hist., 1876, XVIII. p. 380. Also Genesis of Tertiary Species of Planorbis at Steinheim, p. 8.

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THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 29

numbers whenever conditions became unfavorable to the evolution of normal
progressive forms. The degenerative nature of the uncoiled Ammonitine and
Lytoceratinee of the Cretaceous has been ver generally recognized. They were
regarded as diseased forms by Von Buch and Quenstedt, and Neumayr’s dis-
covery of the prevalence of simpler sutures even in the normal forms of the Cre-
taceous has completed this wonderful picture of wholesale degradation. It can
be confidently stated, that the well known cretaceous genera of uncoiled shells,
Crioceras, Ancyloceras, Ptychoceras, Hamites, and Baculites, are the morpho-
logical equivalents of similar forms occurring earlier in the Jura, but that they
are not their lineal descendants. The series of Cosmoceras (Anum.) bifurcatum
worked out by Quenstedt,’ and studied also in detail by the author, had shells
which became gradually uncoiled. Quenstedt named the uncoiled forms Ham-
ites, but has correctly traced them to the coarsely tuberculated species Cos.
bfurcatum. There is also a finely tuberculated specimen, baculatus, with a
broader abdomen, which does not otherwise differ from bifurcatum. To this
last he is disposed with good reason to refer an arcuate and a straight baculites-
like shell. This same tendency is observable among the shells of the Planorbidx
at Steinheim.? Among living shells of a closely allied, if not identical, species of
Planorbis at Magnon,® similar but exaggerated and evidently diseased forms
occur, and the physical conditions are such that we can attribute the tendency to
the unfavorable and abnormal nature of the surroundings.

We have previously pointed out, that such uncoiled shells could not have
had the same habits as closely coiled ones. The appearance of a rostrum
in the Ammoniting indicates that they had become exclusively crawling ani-
mals, in consequence of the disappearance of the ambulatory pipe or hyponome.
In the shells of uncoiled Ammonitine the rostrum though smaller is still present.
Scaphitoid, ancyloceratoid, hamitoid, and ptychoceratoid shells, to whatever gen-
era they may be eventually referred, have one peculiarity in common, the liv-
ing chamber is bent backwards, forming a shepherd’s crook. The absence of the
hyponome and the presence of the rostrum in these forms show that they could
not have been swimmers, like the modern Nautilus with its large hyponome and
corresponding sinus in the aperture and in the striw of growth along the outer
(ventral) side of the whorls. The shepherd’s crook added to the rostrum in the
living chambers of the shells mentioned above indicates not only a wide departure
in habits from the close-coiled Nautiloids, but also from the close-coiled Ammo-
nitine, since such creatures could not have crawled with facility. They must have
been stationary, either hanging among the branches of plants and feeding upon
them, or living with their lower portions buried in the ground and cleaning the
surrounding surfaces for their food. Other suppositions might be made, but all
hypotheses would. involve a wide departure from the habits of their immediate
ancestors, and from those of their morphological equivalents, Lituites, Gyroce-
ratites, or other uncoiled Nautiloids, none of which have the reversed shepherd’s

1 Der Jura, p. 400, plates lv., Ixxii.; Amm. Schwab, Jura, p. 576, plate Ixx.
2 Gen, of Plan. at Steinheim, Summ. Pl. ix.
8 Ann. Soc, Malacol, Brussels, VI., 1871, Planorbis complanatus (forme scalaire), by M. Lois Piré.

30 GENESIS OF THE ARIETIDZ.

crook in the living chambers or the rostrum. These cases also illustrate Dohrn’s
theory’ of change of function, and the effects produced upon organs thereby,
which has been of the greatest use in our researches. Semper’s researches and
experiments? explain changes*in organisms in the same way, as probably caused
by changes in the surroundings which have led to the adoption of new habits, and
the consequent modification or suppression of already existing organs, and some-
times to the building up of entirely new organs or parts. It is interesting to
note, that our investigations, though necessarily confined to purely morpho-
logical phenomena, have led to theoretical results similar to the conclusions of
Dohrn, Semper, and others.

We can account for the existence of the parallel series on the basis of the
following law of relation to the surroundings:

The response or reaction of the forms of different series to the action of the ordinary
surroundings in the same habitat produced progressive morphological equivalence, when the
external influences were favorable to growth.’

The enviroment may assuredly be assumed to have been favorable in the case
of the parallel series of normal forms of the Ammonitinz and other chambered
shells, whether occurring in India or Europe. ‘The diversity of these causes
was very considerable, but it was not of such a nature as to imply a change
of habitat, or any fundamental change not favorable to the growth of the shell.
The average size of Goniatitinse is considerably below that of the Ceratitinse, and
these in turn, as well as the Lytoceratinze and Ammonititine of the Trias, are
smaller as a rule than the same suborders during the Jura and earlier Cretaceous,
The steady increase in size in all the progressive series of the Arietids culminating
in the huge shells of Coroniceras shows this very plainly, as may be seen upon
consulting the Summary Plates, and the same is true of Planorbide at Steinheim.

When the environment, however, became unfavorable to growth, we find
retrogression and retrogressiye equivalence. Lobites is a genus of small species;
Choristoceras, Cochloceras, and Rhabdoceras are also smaller than most of the
Ceratitinz. The deformed species of the bifurcatus series are smaller than the
normal bifurcatus. All of the scaphitoid shells are notably smaller than their
congeners, and though there are many large Crioceratites, Ancyloceratites, and
Baculites, there are, so far as we know, no exceptions to the rule in cases which
have been traced to close-coiled forms. Retrogression is also exhibited in the
decreasing size of the retrogressive forms of Agassiceras, Asteroceras, and
Oxynoticeras.

In the pathological species with extremely retrogressive forms there is an
evident exhaustion of the normal powers of growth and development, and prema-
ture senility. This is shown in the uncoiling, destruction of the ornaments, and
often also by the retention of nepionic and nealogic characteristics in adults.
The form and sutures of straight shells in the Jura and Cretaceous, for example,

1 Der Ursprung und der Princip des Functionswechsel, Leipzig, 1875.

2 Wachsthum’s Beding. d. Lym. stagnalis, Verhandl. d. Wurzb. phys. med. Gesell. N. F., IV.; also
Naturl. Existenzbedin, d. Thiere, Leipzig, 1880; and Animal Life, ete., Appleton’s International Scientific
Series, 1881.

3 See also Preface, pp. iv. and v.

eee caaaranaen

THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 3k

differ but little at any age. The four or six lobes of the young are retained
throughout life, and have comparatively simple margins. The adult, however,
is not similar to a true larval form except in the same sense that an old whorl is
similar to its own young, or the toothless gums of an old man are similar to the
same parts before the teeth appear. The Baculites are not as a rule strictly
tubular whorls, as in the nepionic stages of other Ammonitine, but are gener-
ally more or less compressed in the adults, like the aged whorls of close-coiled
shells. The development skipped the normal progressive stages of the proximate
close-coiled ancestors, and, like syphilitic children, these shells had no proper
adult stages, but assumed senile, degradational characteristics while still young,
and are, as we have said above, purely nostologie forms.

The law of evolution for geratologous forms seems therefore to be as follows:

Lhe response or reaction of the forms of different series to the action of the ordinary
surroundings in the same habitat produced retrogressive morphological equivalence, when
the external influences were unfavorable to growth,

We cannot account for the number of uncoiled Ammonoids in the Upper Cre-
taceous, their wide distribution, and the undeniable fact, that they were the
members of an order then rapidly nearing extinction, unless we imagine the gen-
eral conditions of life during this period to have become unfavorable. The
unfavorable causes produced in the forms of the groups as a whole similar modifi-
cations to those caused by the unfavorable effects of the local surroundings in Cos.
ifurcatum, and other shells in more limited localities during the jurassic period.

The bifurcatus shells and the uncoiled cretaceous Ammonoids are not isolated
individuals, —like the turrillitic deformities of Ammonitine figured by D’Orbigny
under the name of Zuwrr. Boblayi, Valdani, and Coynarti, or the planicostan
deformities figured in Qor. rotiforme, Plate ILI. Fig. 7-13, and the scalariform
Planorbidee of Magnon, or multitudes of similar instances known to every student
of these fossils, — but series of varieties, species, and genera. These can only be
accounted for as the result of hereditary tendencies acting upon races and species,
through successive generations, for periods of time more or less prolonged.

The evidence is very strong, that Baculites, Scaphites, etc. of the Cretaceous
are not necessarily species of the same genus, but probably always polyphylettic
in origin. The Baculites of North America have so close resemblance to those
of Europe, that they are usually considered as allied species; but there are
indications in the peculiar nodular markings and great size of many species,
which lead us to think that they originated from American stocks. Several
species of American Scaphites have common characteristics in the sutures, and
in the aspect of the ribs and tubercles, and the abdomen, which suggest affinity
with Placenticeras. Meek’s plates of Scaphites, published in his Invertebrate
Paleontology,’ exhibit common characteristics so far as the sutures are concerned,
especially the large size and length of the first lateral lobes, but he gives no
figures of the tuberculated young of Placenticeras placenta, which make this com-
parison closer. The Amm. Mullanus on Plate LVIII. Fig. 1, 1a, from Upper Cre-
taceous, Chippeway Point, near Fort Benton, has exactly the form in some

1 U.S. Geol. Survey of Territ., Hayden, [X., plate xxxiv., and Placenticeras on plate xxiii.

32 GENESIS OF THE ARIETIDA.

examples; also the sutures, Plate VI. Fig. 9, of the young of Scaph. ventricosus,
Plate VI. Fig. 7 b, 8-8 b, of the same locality; the pile, the involution of the
whorls, and the sutures are also similar. It differs only in possessing the scaphi-
toid living chamber, which is well marked. This group of Scaphites are stouter,
and have different sutures from Placenticeras.'

In Europe Stephanoceras refractum, the Amm. refractus of authors, is a true
Scaphites, but no one thinks of calling it Scaphites, and it is usually referred
to the group of normal Ammonitinz, in common with several other distorted
forms. In an article on “Genetic Relations of Stephanoceras,’* we discussed
the affinities of this and similar distorted forms, trying to show the former
existence of a general tendency to imitate the scaphitoid mode of growth in
Stephanoceras Gervili’, microstomum, and platystomum. These species rebuilt a living
chamber at each arrest of growth, which was eccentric, having a flatter curva-
ture, and being smaller than the included whorl. This living chamber was also
resorbed at each period of renewed growth, as in Scaphites.

The well known form <Amm. vertebralis Sow., of the Upper Jura, was
described by Quenstedt as a diseased scaphitoid form, derived from Arun.
cordatum, and this conclusion has also been confirmed by my own observations.
Slephanoceras bullatum® has a shell which is precisely like typical Scaphites in
the form and aspect of the last whorl, but does not depart from the spiral as
in Scaphites. It is, in other words, intermediate between Scaphites and the
normal closely coiled Ammonitine of the Stephanoceran group. The Ami,
microstomus impresse of the Upper Jura is figured by Quenstedt as a form of
Steph. microstomun, to which it has a close similarity, although smaller, and the
author concentrates his knowledge of the relation of these forms in one sen-
tence, “Scaphites sind haufig nur kranke Ammoniten,’’—Scaphites are often
only diseased Ammonites. This statement, which was also Von Buch’s opinion,
requires a qualification, since they are not simply sick or diseased Ammonoids,
occurring sporadically like occasional distortions, but races or stocks with cata-
plastic tendencies inherited and increasing in successive generations.

The distribution, affinities, and cataplastic nature of these forms indicate
local origin, but during the cretaceous period unfavorable conditions prevailed
so generally that series of them were produced independently, and apparently
simultaneously, in many localities in Europe and in this country. Thus, equiv-
alent series of nostologic forms, like Scaphites, Ancyloceras, and Baculites, arose
in groups of species, which were not genetically connected with one another, but
more or less closely with widely separated and distinct genera of the progressive
Ammonitine and Lytoceratine.*

1 These remarks, however, are considered to be simply suggestions, which the author purposes to follow
out and publish with proper details.

2 Proe. Bost. Soc. Nat. Hist., XVIII., 1876, pp. 870-384.

8 Die Ceph., p. 61.

4 Zittel, in his admirable ‘‘ Handbuch der Paleontologie,”’ I. pp. 440-446, adopts Neumayr’s opinion as
to the connection of the typical cretaceous genera of Hamites, etc. with the Lytoceratinz, founding his belief
in their genetic connection upon the sutures and smooth shell. On pages 481, 482, he confirms Neumayr’s
and Uhlig’s opinion of the variety of genera from which the more ornamented shells of Ancyloceras, Crio-

ceras, etc. had been derived.

THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 30

Neumayr was the first to trace systematically the uncoiled forms of the
Cretaceous to several groups and distinct species of normal close-coiled Am-
monitine,’ thus confirming Pictet’s isolated but suggestive observations on
Acanthoceras angulicostatum, and declared that Acanthoceras, Olcostephanus, and
Hoplites were the radicals of the uncoiled forms previously included under a
number of generic names by D’Orbigny and other authors, and also traced the
genera Hamites and Turrilites to an origin in Lytoceras. Uhlig? holds views
similar to Neumayr, tracing most of the Crioceratites to Hoplites, but con-
siders that Olcostephanus, Acanthoceras, and Aspidoceras had also crioceratitic
derivatives. Our conclusions, therefore, are in accord with the results of the
researches of Quenstedt, Neumayr, and Uhlig upon the same class of forms.

The Ammonitinz of the Lias and Qélites in extreme old age, as a rule, lost
the tubercles, pile, and often the keel, the whorls became smooth, and decreased
in size, tending to take on a rounded or triangular outline in section, according
to the group in which the species belongs. Thus, in Plate I, Fig. 24 and 25
show the changes which took place in the old whorl of Cal. raricostatum, and Fig. 1
and 2 the similar effects in the old age of Cul. carusense. The whorl in both be-
came rounded, and lost its ribs, ete. On Plate V. Fig. 8, 9, may be seen the old age
of Cor, Gmuendense, and on Plate VI. Fig. 1, 2, the similar old age metamorphoses
of Cor. trigonatum. In these last the quadragonal whorl of the adult became tri-
gonal, instead of being rounded by senile degradation as in the first instance.
On Plate X. Fig. 1-3, there are illustrations of individuals of Asf. obtusum, which
can only be accounted for as the results of premature old age in this species,
since the young until a late period of growth are identical, and both Professor
Fraas of Stuttgardt and the author have identified them under this name.

These. changes are all due to the loss of power in the old animal, which
can no longer maintain its normal rate of increase in size as it grows. Thus
the smaller discoidal whorls of Caloceras with low keels became rounded, and
the quadragonal whorls of the keeled and channelled Coroniceras became tri-
gonal. The latter is really a stage of reduction in size, intermediate between
the quadragonal form and completely degenerate rounded whorl of extreme
age, but, so far as is now known, this last stage was not reached by the progres-
sive forms of the Arietidse except in Oxynoticeras.*

Notwithstanding the evident loss of power, and the consequent and well
marked changes taking place in the old whorl of many species of Vermiceras,

1 Zeits. deutsch. geol. Gesell., 1875, pp. 874, 875, 924, 935, and subsequently with Uhlig in Paleon-
togr., X XVII.

? Denksch. Acad. Wien, 1883, XLVI. p. 258.

® One of the finest illustrations of the effects of senility upon the shells of the Ammonitine of the
Jura is given by Waagen (Geol. Surv. of India, Ceph., Jurass. Fauna von Kutch, pl. xi. fig. 1). In a
large specimen of Perisphinctes aberrans, the old-whorl became smooth, greatly reduced in size, rounded,
less involute, and finally exhibited a series of heavy folds on the sides. These senile folds are also common
in the old of many forms of the Upper Jura, but are rarer and smaller in the Oélites and Lias. They may
be due to prolonged arrests of growth, and the decline of the power to resorb the thickened edges of the
apertures, after each period of rest. But, whatever the cause, they certainly indicated a loss, not an in-
crease of strength. This is shown by the degradation in size and form of the whorls in such examples

as are given below in the descriptions of Cor. Bucklandi, Cor. trigonatum, Ast. obtusum, and especially Oxyn.
Lotharingum.

5

34 GENESIS OF THE ARIETID.

Coroniceras, and Asteroceras, the stages of decline in individuals are not usually
attended by such complete metamorphoses in these normal progressive forms
as in Oxynoticeras and many others among the jurassic Ammonitine. The
keel persisted, and is generally still visible even in extreme age, though often
greatly reduced in size; the whorl also usually continued the same rate of
growth so far as dorso-abdominal diameter is concerned. It therefore appeared
to increase in size throughout life when viewed laterally, even in very large
individuals of Vermiceras, Coroniceras, and Asteroceras. It is to be anticipated,

"in some very rare cases of exceptional longevity even in these species, that the
keel would be absent and the whorl would become rounded. This happened in
senile specimens of Oayn. Lotharingum, which apparently possessed less power
of resisting the effects of extreme age. This is a very interesting fact, since
Oxynoticeras is the paracmic series of the Arietide, and according to our views
would be likely to exhibit strongly marked degradational characters.

It is obvious that the decrease in the size of the whorl, if continued long
enough in old age, must have finally caused the last whorl to strike off from
the regular line of the spiral, as in the Crioceras. We searched the collections
of Europe during the year 1873 for a specimen of a normal species of large
size and sufficiently advanced in age to refute or confirm this view, and finally
found one, through the aid of Professor Mésch, in the Museum under his charge
at Zirich. This was a large fossil of the Neocomian from Sentis, in which the
adult whorls were ribbed, but the outer whorl old, smooth, and contracted to such
an extent that at a short distance from its termination it was separated by a
distinct gap from the abdomen of the next inner whorl. Professor Mésch was
impressed by this fact, and gave this specimen, which he considered a new
species, the manuscript name of Amm. (Scaphites) umbilicus, which it probably
still retains.

I have examined all the figures of M. Barrande, anticipating the finding of
some marks of senility in individuals among the lower types of Nautiloids, and
have not been disappointed. M. Barrande classifies the form of the siphon as
“the cylindrical, the nummuloid, and the mixed”; and though he nowhere,
so far as I can find, describes these metamorphoses of the siphon as stages of
development, yet this was probably his real view, since in all his figures, suffi-
ciently complete to show the young, when the siphon is nummuloidal in the
adult it is cylindrical in the young.' Barrande’s figures also exhibit clearly
the degradation of the nummuloid siphon, and its return during old age to the
cylindrical form;? but I cannot find that this eminent author regarded these
metamorphoses as having been caused by senility.

1 Phrag. simples, pl. xix. fig. 9, Gomph. Belloti, pl. xxxti. fig. 6, Phrag. perversum, var. subrecta, pl. ¢.
fig. 11-17, Cyrt. Logani, pl. clxxxii. fig. 2-10, and Cyrt. indomitum, pl. clxiii. fig. 5, all show the development
of the nummuloid siphon from the smaller cylindrical tube of the young, or else it has a lessened diameter
approximating to the cylindrical condition in the young.

2 Cyrt. rebelle, pl. elxiv. fig. 7, exhibits the change during growth of the siphon, which transforms it
from a nummuloidal to a cylindrical tube, and causes the shifting of the position from close proximity to
the convex side to near the centre of the last formed septum. Orthoc. docens, pl. ccl. fig. 7, exhibits a
similar series of metamorphoses, but the siphon remains at the centre of the whorl.

"
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THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 55

Degradation in the ornaments, markings, etc., occurred, but is less marked
and rarer on account of the frequent absence of the shell. Prof. James Hall
has figured cases of senile degradation! in Orthoceras, and we have ourselves
seen several similar examples.

We have not been able to trace any remarkable changes in old age among
the silurian, devonian, or carboniferous goniatitine. ‘The dyassic and _ triassic
forms of Ammonoidea with highly ornamented shells have not, as far as known,
exhibited cases of senile metamorphosis in any noticeable abundance, and there
is a marked absence of these in Mojsisovies’s plates, although a few are figured.

There is an easily observed increase in the effects of old age upon. the last
whorls of the shell in the Jura. Every group, however, does not show the effects
of senility equally. There are not only less remarkable metamorphoses in the
radical genus Psiloceras, but also less in the Arietide, as a whole, than in the Am-
monitinee of the Upper Jura. This retrogression’ correlates directly with the
increasing prevalence of geratologous uncoiled shells in the Cretaceous. There
is, therefore, among Ammonoidea a general progress up to the Jura, which is
definitely expressed in the life of the individual as well as in the life of the
type, and a general decline in the later Jura and Cretaceous, which is also defi-
nitely expressed in a similar way. Ge ratologous types and forms are also less
frequent among the paleozoic and earlier mesozoie than in later mesozoic series.
Individuals apparently had greater strength as individuals in these earlier periods, senile
melamorphoses being less marked in their old age. The phenomena presented by
radical types also accord with this statement. If we pick out those types which
were the progenitors of series, they appear to have been less affected by degra-
dational changes than the more specialized forms which arose from them. This
fact, however, as we have often stated, corresponds directly with the more com-
plicated organization of derivative forms, as contrasted with the simpler structures
of radical forms. There are more characters introduced in the adults of special-
ized derivatives, and the necessary disappearance and degradation of these marks
the old age of the individual in such types with more obvious modifications.

As we have stated above, however, geratologous metamorphoses do occur
even in Orthoceratites, and series of Nautiloidea. The Lituites of the Phillips-
burg (Canada) and Fort Cassin limestones,? which we are now studying, and the
Lituites and Trocholites described by Holm,’ have in their youngest stages forms
which indicate derivation from nautilian shells, thus proving that they are not
radical forms, but degenerate uncoiled derivatives of prepaleozoic or paleozoic
stocks of close-coiled Nautiloids, of which they are the last survivors. Trocho-
ceran species belong to several different genera, and are all degenerate forms.

? Orthoe. fusiforme, figured in Nat. Hist. of New York, Paleont., I., pl. xx. fig. 1, is a very large specimen,
with the last three sutures nearer together than the preceding, and this generally indicates advanced age
among Ammonitine. The increasing width between the folds in the shell of Orth. crotalum, Hall, Paleont.,
V., pt. 2; pl: ali. fig. 1, 9, 6, though characteristic of the living chamber, as described by him, probably
became permanently characteristic of the senile stages. Very large specimens of Endoceras not infrequently
show approximation of the sutures and less distinct annulations than in the adult stage, though this does not
appear to be an invariable accompaniment of age, as in the Ammonitine.,

? Whitfield, Bull. Am. Museum, New York, I., No. 8.
8 Dames et Kayser, Pal. Abh., III., pl. i. and y.

36 GENESIS OF THE ARIETID/.

Ascoceratites, Discoceratites, and Ophidioceratites also indicate lost faunas, in
which such types had their now unknown, but progressive progenitors.

Notwithstanding, however, these geratologous series and the facts already
stated, the shells of the surviving stocks of Nautiloidea were not usually so per-
ceptibly changed in old age as the more specialized shells of Ammonoidea. So
far as known, the shell of a nautiloid, whether fossil or recent, though it may
lose tubercles and perhaps become somewhat changed, neither becomes very
decidedly depressed nor decreases perceptibly in the involution of its whorls
during old age. This remarkable exhibition of persistent growth force in indi-
viduals, when taken in conjunction with the slight senile metamorphoses of the
smooth radical types of the Ammonoidea and the persistence of the keel in the
normal progressive forms of the Arietids, the persistence of Nautiloidea until the
present time, and the absence of nostologic series in Nautiloids of the Mesozoic
and Neozoie, all show how complete is the correspondence between the ontogeny
of individuals and the phylogeny of the groups to which they belong.

Alcide d’Orbigny drew attention to the old age of the individual among
Ammonitine in his “ Paléontologie Francaise.” He divided the life of the indi-
vidual into five periods, distinguishable from each other by the external character-
istics of the shell; namely, the first period, or “ période embryonnaire,” during
which it is smooth and the abdomen round; the second period, or “ premiére
période @accroissement,” which is marked by the advent of the tubercles, or ribs
and keel, if there are to. be any upon the adult shell; the third period, or
“derniére période d’accroissement,” during which the tubercles or ribs and the
keel are fully developed, and the whorl takes on its adult configuration ; the
fourth period, or “ premiére période de dégénérescence,” during which the ribs or
tubercles begin to separate more widely and become depressed ; and the fifth
period, or “ deuxiéme période de dégénérescence,” when all these ornaments are
obsolete, and the exterior is smooth again as in the young.

The recapitulation in which he sums up the results of this remarkable series
of observations is equally truthful and instructive. The following paragraph
conveys the sense of the original, though its piquancy and force is lost in trans-
lation. “These modifications are not due to chance, but to decided regularly
occurring periodical metamorphoses, which affect the larger number of the
Ammonites, and which invariably operate in a regular order of succession. In
fact, each one, though smooth in the youngest period, covers itself at a later time
in the course of growth with tubercles around the umbilicus, afterward with ribs,
striations, or tubercles upon the back (abdomen). It is then in the adult stage.
Having arrived at the maximum of external complication, all of these ornaments
begin to show signs of alteration ; it (the shell) degenerates; its striations and
dorsal (abdominal) ribs first disappear; then follow its lateral ribs or tubercles,
and in old age it becomes fully as simple externally as it was during the em-
bryonic period.” *

1 There are apparent exceptions to this law, as observed above, in the heavy folds of the senile stages
of many forms in the Upper Jura, and some in the Lower Jura. The young of these forms, which have not
yet been investigated closely, ‘will, however, probably explain this discrepancy by showing that the senile
folds correspond with larval folds, as is the case in Oxynoticeras of the Lias.

THE THREE MODES OF DEVELOPMENT. 37

The accomplished author of the “ Paléontologie Francaise” denied that the
internal parts were affected by old age, “ne montrent qu’une complication
’ This error was corrected by
Quenstedt who pointed out that the closer approximation of the sutures in large
individuals was due to senility, and the author is now able to record that he has
either observed or seen figured similar cases of approximate sutures, indicating
senile degradation in all of the different forms of chambered shells, except in
Belemnoids, which have not yet been investigated.

D’Orbigny and Quenstedt were both satisfied with noting the details of
the old stage in the individual, the diseased aspect of certain forms, and their
reproduction of the characters of their own young and of those of older forms,
but did not attempt to explain the wider meaning of these parallelisms. In
former papers we have asserted that the close similarity between the smooth,
straight Baculites of the Cretaceous, the extreme nostologic form of the Ammo-
noids, and the smooth, straight Orthoceras of the Cambrian, the common radical
from which both Ammonoids and Nautiloids sprang, is parallel with the resem-
blances which exist between the nostologic or oldest stages of the individual and
its own young.

This resemblance between radical and geratologous forms in smaller groups,
like the Arietide, was slighter, and often consisted merely in the smoothness
of the shell, or loss of the keel, or decrease in the amount of involution of
the whorl. As?. Collenoti and Psil. planorbe both have the compressed helmet-
shaped outline of the whorl in section, and are smooth, though Collenoti exag-
gerates this form, or is more involute and flatter than planorbe. The most
remarkable cases of geratologous reversion in the Lias are found in Ozynoticeras
Lotharingum, in which the old whorl loses its keel, and exactly reassumes through
degeneration the compressed helmet-shaped aspect of the adults of Psd. planorbe.
Iiven this extreme example among Arietide, however, is not in any sense
an uncoiled shell. It is very nearly a complete parallel with the smooth
keelless proximate radical form Psiloceras, and may therefore be termed a noso-
logic species. It barely attains this extreme rank in degeneration, whereas other

toujours croissante et jamais de dégénérescence.’

species, such as As?. Oollenoti, which retain the keel and do not decrease in size of
whorl, are only clinologic approximations.

The resemblances which occur between the young and old of the same indi-
vidual in the same parts and organs take place because the organs lose their
power to exercise the functions which distinguished them in the adult, and
becoming useless, are either partly or wholly atrophied and resorbed.

Tur TuHree Moprs or DEVELOPMENT.

The likeness between the younger stages of growth and the senile stages
of decline in the same individual is, as we have just shown, due to the disap-
pearance in old age of the specialized ephebolic characteristics acquired in the
progressive nealogic and adult stages of growth. In groups the resemblances
between radical and geratologous forms is occasioned by a similar suppression in

38 GENESIS OF THE ARIETIDA.

the latter of the more specialized ephebolic characteristics which arose in the
group during its acme of evolution in time.

We now propose to take one step more, and try to show that this tripartite
correlation in the development of the individual and in the evolution of the
type correlates with a similar cycle in the modes of development of the indi-
vidual, which we have classified as the direct radical, or anaplastic mode, the
complex, or metaplastic mode, and the direct geratologous, or cataplastic mode.
We are thus carrying to definite conclusions and confirming by application the
laws announced by Haeckel in his “ Morphologie der Organismen,”’* and by the
author independently with regard to the ontogeny of the Cephalopoda, in his
essay on the “ Parallelism between the Individual and Order in Tetrabranchiate
Cephalopods.”’ ?

Haeckel was a strong advocate of the general efficacy of natural selection
as a motive force of far greater importance in the evolution of types than has
been granted in this and other publications by the author, and did not give as
much weight to the correlations between the ontogenetic and phylogenetic cycles.
If these have the correlations here claimed, then we can see that a theory like
that of natural selection, which does not recognize the action of some law which
has affected both the individual and the type in the same way, cannot be recon-
ciled with the observed facts in the evolution of forms. A theory of evolution
must necessarily, while admitting the origin of new characters by external causes,
also recognize the limitations due to the force of heredity in conserving the type.
It must admit fully the plasticity of organisms, and the power of external condi-
tions to effect fundamental changes in structure by means of internal reactions, —
that is, through the action of either conscious or unconscious effort,— but not
deny to heredity its fullest effect in the tendency of like to produce like. It
should emphatically deny that heredity tends to produce like with variations, or
that there is any such thing as a tendency to variation which is inherent and
not produced by external forces. It must recognize not only the three physio-
logical phases of epacme, acme, and paracme, but that all the phenomena of
evolution accord with this cycle. It should show that not only the general
physiological phenomena, but also the relative strength of the individual, as
testified by the slight effect of old age upon the shell in the oldest and
simplest types, and the more rapid evolution of paleozoic as compared with
mesozoic types, and of geratologic types at the termini of each special group of
forms in time, are strictly in accord, and testify ‘to the existence of a common
law governing and producing cycles. It must also recognize that there is a
growing stability in types, and less important structural variations at the acme of
a group than during its epacme or paracme; and that its habitat was freer
at first than it was subsequently during its acme.’ The struggle for existence
between species, if there were any at first, (which we do not believe,) must have
been very slight compared with what it became during the crowded acme, and

1 Vol. IL. pp. 18, 22, 320.
2 Mem. Bost. Soc. Nat. Hist., I. p. 195 et seq., and Proc. of same, X., 1866, p. 302.
8 See Genera of Fossil Cephalopoda, p. 261, and Fossil Cephal. Mus. Comp. Zodl., p. 339.

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THE THREE MODES OF DEVELOPMENT. 39

this shows conclusively the comparatively small influence of natural selection
except during the acme of groups.

Another series of facts in favor of the views here advocated is to be found
in the cycle formed by the modes of development. The more ancient and sim-
pler forms of Cephalopoda, like Orthoceras and most of the earlier forms of
Nautiloidea, had a direct mode of development, during which the individual
passed through certain well marked changes; but these were less numerous and
not so crowded together as in types with more complicated development. The
young and adults of the same individual among straight radical shells differed
comparatively little in form and ornamentation. The siphon in Piloceras, and
in some species of Endoceras, for example, was comparatively little changed in
adults from what it had been in the young, and Cyrtocerina as described above,
probably remained completely macrosiphonitic throughout life.

When closer coiling was introduced and more concentrated development
occurred, as in the higher Nautiloidea and Ammonoidea, we found, as one of
the results, the omission of some hereditary stages. As we have said above,
the first air-chamber disappeared in Ammonoidea, having become fused with
the protoconch, which stage acquired through this earlier inheritance a ten-
dency to secrete a calcareous shell, and in consequence of this fusion the
excosiphonula was also carried back and appeared earlier in the life of the shell
and animal,

The neepionic or true larval stages, as we have said above, became more
accelerated in the angustisellate young of the Lytoceratine and Ammonitine,
and the succeeding or nealogic stages were introduced with a profusion of orna-
ments and increased complications in the outlines of the sutures, curves of the
septa, structure of siphon, increased involution, and changes of structure and
form in the whorls, which multiplied the metamorphoses and made the different
stages of growth more distinct than in the Goniatitinse and Nautiloidea.

The complex mode of development of the normal acmic forms, due to the
introduction of these new characteristics, is easily perceived in most of the
Ammonitine, even without breaking down the whorls to examine the young.
The ornaments and pile on the exposed sides of the whorls show this in most
species of the Jura with sufficiently discoidal shells.

The paracmic forms, and especially the degenerate uncoiled species of
every group, exhibit a return to the direct mode of development, and a lessen-
ing of the variety and number of structural changes. These suppressions be-
came, as we have described them above, so well marked in all the straight
baculites-like forms, that a tyro cannot fail to notice the fact. The smooth,
slightly compressed whorl retained nearly the same form throughout life, the
sutures retained the primitive number of nepionic lobes, and the. marginal
digitations were comparatively simple even in adults.

Similar phenomena occurred in every group. Thus in the Arietide the
radical Psiloceras planorbe had the anaplastic or comparatively direct mode of
development, while the descendent species in both these genera had more com-
plicated, metaplastic transformations, due to the introduction of a quadragonal

40 GENESIS OF THE ARIETIDA.

form, with keels, channels, etc.! The metaplastic mode of development of the
progressive forms was again exchanged in the still higher and more specialized
but degenerate and geratologous forms, like Ast. Collenoti and the Oxynoticeran
series, for the cataplastic mode. The young more closely resembled the later
stages, and passed into them with less abrupt transitions, because of the action
of the law of acceleration, and the consequent omission of ephebolic character-
istics. The same process took place in each genus of the Arietida, more or less
according to its place in the cycle, and in our descriptions of the species and
series the evidence will be given.

Law or ACCELERATION.”

Whenever the character or form, whether healthy or pathological, became
fixed in the organism, it became at the same time subject to the law of ac-
celeration. Its previously transient and sporadic appearance ceased, and a
series came into being having this character, whatever it might be, constantly
reproduced in earlier stages of the species.

The fixity of many characters on first appearance may be reasonably doubted,
but not their subsequent tendency to acceleration. The hollow keel of Oxyn.
oxynotum is a novel character, and it seems to be present in every mature speci-
men of the species. Nevertheless, in this and in all cases like this, there is a
dearth of evidence of a positive nature, and some specimens may yet be found
which did not possess it. There are however, examples without number like
the variable first appearance of the abdominal channel in Schlotheimia, of the
keel in Caloceras, and of the pilwe in Arnioceras and Agassiceras. The young had
fold-like pile in Schlotheimia, which crossed the abdomen. The single channel
which was subsequently produced is a progressive stage, arising partly from the
suppression of the folds along the median line, and partly from extra growth of
the pile on either side of the abdomen. Sometimes the suppression of the pile
along the median line of the abdomen never took place, the abdomen remaining
completely pilated throughout life. This occurred as a sporadic or varietal ephe-
bolic character in Schlot. catenala, but in the higher, later occurring, and more

1 See Chapter III. of this memoir.

2 T have used the term Law of Concentration in several recent essays, instead of, as formerly, ‘* Law of
Acceleration,’”? because my attention had been attracted to phenomena which showed that an animal having
accelerated dévelopment of characteristics did not necessarily have a quick development, but on the con-
trary might grow, so far as time is concerned, even more slowly than others of its own group. It became
essential, then, to get rid of the impression, which I had held in common with some other embryologists,
that an animal which skipped many characteristics of its ancestors, or of its own type, had necessarily a
quicker growth and development. Undoubtedly, in many instances, especially where acceleration is due to
pathological causes, such is the result; but this does not occur in all cases, or perhaps necessarily in any
case. In trying to introduce this idea I went too far, and in substituting the term ‘‘ Concentration’? for
“ Acceleration ’? made a change which was not an improvement. In this memoir, therefore, I have returned
to the older and more appropriate term which stands at the head of this section, The term ‘‘ abbreviated
development” is often used, as it has been by Balfour, for extreme examples of acceleration, and it also im-
plies no necessary relation of time. This term, however, was not invented to express a law of develop-
ment, and its author did not take into consideration the fact, that such cases are only the extreme expression
and the necessary result of a universal law of organic evolution.

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LAW OF ACCELERATION. 4]

compressed, involute forms like Sehlot. Charmassci, the suppression, so far as we
know, always occurred in normal forms at some nealogic stage, and the presence
of a channel is constant even in the young. If the pile again crossed the
abdomen, thus obliterating or obscuring the channel, during the life of the
same individual, it occurred as a degradational character in the senile stages.
Extreme cases of degradation in species did not occur in Schlotheimia, but if
there had been any such nostologic forms, they would have inherited this ten-
dency to obliterate the channel during the nealogic stages. The law of ac-
celeration of development was quite as effective in its action upon geratologous
as upon progressive characters, as will be seen when we treat of this class of
characters farther on.

Besides the examples given above of the inheritance of characters in larger
and smaller series, we add the following in order to make our meaning still clearer.
The form, shape, and characteristics of the secondary radical, Psi. planorbe, are
prominently shown in the young of Arnioceras, Plate II. Fig. 10-15, and in the
Embryology of Cephalopods, Plate II. Fig. 9, 10, until a late period of the
growth of the shell, but are less noticeable in the young of the descendent
species, Cor. kridion, in which indeed they are perceptible only in the transition
form between this species and senzicostatum. Most of the specimens have young
like that figured on Plate III. Fig. 2, and are stouter than the flat discoidal Psil.

planorbe. These and the young of other species of Coroniceras inherit the stouter

quadragonal whorl and peculiar ribs and tubercles, the keel, and the channels,
at earlier stages of their growth than those in which they first appeared in ances-
tral shells, as may be seen by comparing Arn. semicostatum with the young of
Coroniceras, Plate III. Fig. 19, and Fig. 5, 6, 8-10.

One of the most convincing examples of the law of acceleration which we
have studied can be illustrated by using Wright’s book, “Lias Ammonites.”? He
shows the latscostan form of the young on Plate XXXIV., and in Fig. 4-6 the
adult of Androgynoceras hybridum, his Agoceras heterogencum. A more accelerated
form is shown on Plate XXXV. Fig. 4-6, in which the young are similar to
lateecosta for a less prolonged period of their growth. Wright's oc. Henleyi,
Plate XXXIII., is also a specimen of the same species with a prolonged late-
costan stage of growth. Lip. Henleyi, figured by Wright as Mgoc. striatum,
Plate XLIIL, is also highly accelerated, and most of the specimens have young
shells with no traces of their lateecostan ancestry, reproducing only the char-
acteristics of the adult whorls of And. hybridum. Lip. Bechei, also figured by
Wright, Plate XLIL, is still more accelerated in its mode of development, since
the young has no resemblance to the adult of And. hybridum. From the smooth
stage of the nxpionic period of growth it passes abruptly to a stage in which the
shell resembles the adult form of And. Henley’. The whorls at this stage show
the specific characters of the adult of And..Henleyi ; they are too involute and
too heavily ribbed and tuberculated in proportion to their size to be compared
with the adult of And. hybridum.

Wiirtenberger’s book is devoted to the exposition of this law of heredity

1 Paleontological Soc., XXXII., 1878.
6

42 GENESIS OF THE ARIETID.

among the Ammonites. This author, in his “Studien tiber die Stammesgeschichte
der Ammoniten,” ! traces the Armatus or Aspidoceras stock of the Upper Jura to
the Planulati; that is, to the genera Coeloceras and Dactylioceras, which last I
had previously described and traced to an origin in Deroceras Dudressiert of the
the Lower Lias2 His work is a summary of evidently extensive observations
upon the Ammonites of the Upper Jura, all of which he traces directly or indi-
directly to the Planulati. Whether he can sustain this opinion will be questioned
by some until he has published his plates. He has, however, studied the series
according to proper methods of analysis, and should be given the credit of the
doubt. We also, though the author fails to notice the fact, have traced Pelloceras
athleta to the same species in the Lias, Amm. annulatus Quenst., and published the
remark ® that they were genetically connected by intermediate forms. Our obser-
vations, therefore, closely accord upon this very important species, and we also
agree in the view that most of the jurassic genera we have included in the
Spinifera and Plicatifera can be traced to Ca/. Pettos as the probable radical.*

In his fourth chapter Wiirtenberger gives the history of the evolution of the
Lallierianus series, in which he traces degeneration in the lobes and saddles,
showing that changes of all kinds appear first on the outer (adult or senile) whorl
of the ancestral forms, and encroach more and more on the inner (younger)
whorls in descendants. Neumayr® considers that Wiirtenberger was the dis-
coverer of the law of acceleration in development, and this author states that he
first published his new discoveries in “ Ausland ” of 1873,— about five years
after the appearance of precisely similar statements in such scientific periodicals
as the Proceedings of the Philadelphia Academy, by Professor Cope, and the
Proceedings and Memoirs of the Boston Society of Natural History,” by the
author. Professor Cope has lately republished his discoveries in a volume en-
titled “ The Origin of the Fittest,” and in these masterly essays those who are
interested may get a full view of his mode of explaining this law, and will find
very complete series of illustrations of the character and meaning of parallel
series and other related phenomena.

The decision as to who discovered the law of acceleration is only historically
interesting ; but it is of general importance that so many persons agree, and
that an eminent paleontologist like Neumayr, who has studied such phenomena
among fossils, considers the law to be true in its application, as tested by him,
with some exceptions. He does not state the exceptions, however, and they
cannot be discussed. The opinions of Wiirtenberger and Neumayr that some
species inherited characteristics at later stages than those in which they occurred
in any ancestral species or pair, seem at present to rest upon the insecure basis
of the apparent need of this assumption in order to account for acceleration as

1 Ernst Gunther, Leipzig, Darwinistische Schriften, No. 5.

2 Non-reversionary Series of the Liparoceratide, etc., Proc. Bost. Soc. Nat. Hist., January, 1872, and
Appendix to the same, with a geological table, Ibid., May 20, 1874.

8 Proc. Bost. Soc. Nat. Hist., Appendix to Non-reversionary Series of the Liparoceratide, 1874, p. 33.

4 See above, pp. 23, 24.
5 Zeitsch. d. deutsch. geo]. Gesellsch., p. 868.
6 See above, page 28, note 3, and Proc. Bost. Soc. Nat. Hist., 1870, pp. 72, 73.

LAW OF ACCELERATION. AZ

being due to the law of natural selection. We do not deny the existence of
such examples; we are only anxious to hear of their existence, and to be able
to examine the evidence.

Weissmann‘ also seems to have been unacquainted with the same literature,
and claims the discovery of the law of acceleration for Wiirtenberger. Weiss-
mann’s interpretations of the phenomena were in part very similar to our own.
He rejected Wiirtenberger’s theory of the origin of acceleration through the
action of natural selection, and states that it is due to the innate law of growth,
which rules every organism. In many places he explains this law of growth as
a mechanical law, and the origin of variations as due to the innate response of
the organism to external forces exciting it to suitable changes. This law of
variation through mechanical causation is identical with that advocated by Cope,
Ryder, and the author; but with regard to this there can probably be no contro-
versy about priority. Dr. A. $8. Packard has shown that such views are essen-
tially rehabilitations and improvements upon Lamarck’s theory of effort, and he
has appropriately named us the Neo-Lamarckian school.

This eminent author (Weissmann) has apparently abandoned this position in
his later works. He claims that the protoplasmic basis of organisms is alone
the vehicle of heredity, and substantially imperishable or continuous; that all
variations taking place in the organisms, unless they affect this basis so as to
modify the ovum, are not inherited; that the variations of males and females are,
when inherited in the offspring, the originators of new characters through the
new combinations which necessarily arise, and he also regards natural selection
as the prime agent in the preservation and perpetuation of these variations.’ We
have been unable to find any characters which were not inheritable in some series.
The behavior of all characteristics which have been introduced into any series
of species shows them to be subject to the law of acceleration, in whatever way
they have originated, whether primarily as adaptive characters, according to our
hypothesis, or by natural selection and through the combination of the sexual
variations, as supposed by Weissmann. All of the degenerative changes took
place in retrogressive series, in precisely the same way as is described above for
progressive changes. Thus, the degradational characters and uncoiling became
noticeable in the old of individuals and of species first, and then appeared, in
obedience to the law of acceleration of development, at earlier stages in suc-
ceeding or derivative forms, until finally they entirely replaced the normal
progressive characteristics of the nealogic stages. A straight Baculites-like modi-
fication could not have been produced by the unfavorable surroundings directly
from any close-coiled form; it must have arisen from the intermediate arcuate
and crioceran modifications. If this be true, heredity must have played its part
even in the extreme modifications of abnormal geratologous series, however
improbable this may seem.

1 Studies in the Theory of Descent, Eng. ed., transl. by Meldola, I. pp. 274, 277.

2 Standard Natural History, edited by Kingsley, Introduction; and also Cope’s “ Origin of the Fittest,”
in which see index, Lamarck.

8 Continuitiit der Keimplasmas; also Ueber der Vererbung; see also, as in favor of the views here ad-
vanced, Kolliker’s criticism, Karyoplasma und Vererbung, Zeit. Wissensch. Zool., XLIV., 1886.

Saeenener es

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44 GENESIS OF THE ARIETIDA.

We would also suggest that the phenomena of parallelism, or the evolution
of similar forms in different series which can be predicted, is obviously contrary
to any law which does not assume that adaptive characters are equally inherit-
able with differentials. Again, the minuteness and slight importance of some
differentials, like the collar of the siphuncle in Ammonoids, which are neverthe-
less persistent throughout several geologic periods and constant in every series,
do not appear to be accounted for by Weissmann’s hypothesis. This collar
appeared first in the adults of the Goniatine, and became engrafted in the early
stages by the law of acceleration, like other characteristics. It should be re-
membered also that parallel series were continually evolved, while this differential
remained comparatively unchanged, and that the alteration of the entire form of
the whorl by involution, and the evolution of complicated from simpler radical
sutures took place over and over again in different series arising from the same
stock. How could males and females have combined to produce similar series of
variations, and also unimportant but still persistent differences? How could
characteristic of slight importance to the life of the species have made a deep
and lasting impression on the ovum, while others of obviously greater moment
to the organism were transient in different series ?

There is one phase of the law of acceleration which requires to be dwelt
upon as the best means of conveying its full meaning to those not yet accus-
tomed to note its action in their researches. It expresses the mode by which
the continual replacement! of the older by newer and later acquired character-
istics takes place in every genetic series, and therefore explains the mechanism of
gradation, whether progressive or retrogressive. Changes in environment, which introduce
new adaptive characteristics in the nealogie or adult stages, necessarily add these to the
hereditary stages of the younger periods of growth, and thus shorten the development of the
latter by direct replacement.

Heredity, as is well known, can continue for indefinite periods to reproduce
a useless part or organ, provided it does not interfere with the growth and
normal development of useful structures. When interference occurs, as is well
known to all physiologists, their resorption is a normal process, due to the fact
that they have become through disuse merely passive stores of food for the more
active worker cells.

Though species sometimes pass through more than one horizon, they are, as a
rule, limited to the levels upon which they first appear. This fact, and the fre-
quent differences in the sediments, which often correspond to differences in the
faunas, indicate that the different varieties or species characterizing distinct
horizons are more or less directly due to the changes in the surroundings, which
occurred in passing from one geologic level to another. We can fully understand
the phenomena of acceleration in development only when we begin by assum-
ing that the characteristics last introduced in the history of any type were more
suitable to the new conditions of life on the horizon of occurrence of the species,
than those which characterized the same stock in preceding horizons. These
characters would then necessarily, on account of their greater usefulness and

1 Genesis of Planorbis at Steinheim, p. 28.

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LAW OF ACCELERATION. 45

superior adaptability, interfere with the development of the less useful ancestral
stages, and thus tend to replace them. The necessary corollary of this process
would be the acceleration of the previously existing nealogic stages in direct pro-
portion to the number of new characters successively introduced into the direct
line of modification during the evolution of a group.

The importance of this law becomes more apparent when consideration is
claimed for it as a working hypothesis for the explanation of such obscure prob-
lems as occur among insects. The complicated metamorphoses of the Hymen-
optera, Diptera, and some Coleoptera, for example, in which feetless and headless
larvee appear, can be attributed to acceleration, like the more normal examples
among fossil Cephalopoda. They illustrate the suppression of ancestral thysanu-
riform stages, which when present in the active larve of lower orders indicate
that all insects were derived from some ancestor possibly similar to the adult
of such forms as Lepisma or Campodea. This gives new interest to the theoreti-
cal views of Brauer and Sir John Lubbock, who first pointed out the nepionic
characteristics of the adults among Thysanura.

It seems to us equally applicable to the explanation of the medusaless meta-
morphoses of the fresh-water Hydra, as compared with the marine Tubularia in
which the medusa stage is prevalent, and also to the accelerated development
of the pelagic meduse, Geryonia and others, in which the hydra-like stage has
vanished.

In Tenia, also, the earlier stages are so accelerated that the secondary sac,
furnished with cutting blades, worked by special muscles, and used for digging
through the tissues, is still called an ovum by many naturalists, though it is mor-
phologically the remnant of an active form producing the young Txnia by an
involution or bud from its walls. The ancestors of Tania must first have
acquired a cercaria or nurse form with cutting blades, and then, the evolution
having reached its highest progressive acme, the reverse process of resorption
through acceleration began. The constant exercise of the blades by the cer-
caria. and the use of a horny case for the ovum caused these to be retained, while
the other characteristics of the cercarian stage disappeared, or else like the blades
became more or less fused with the ovarian stages.

Perhaps the most. remarkable instance of the loss of progressive characters
correlating with a highly accelerated mode of development is man himself;!
and his example will serve a good purpose in making clear what we mean by
a geratologous retrogression, which is often evidently due to a great change in
habits, bringing about specialization in certain parts, enlarging and prematurely
developing them at the expense of many of the normal progressive characters of
the ancestral type. The Caucasian type,in losing the prognathism of the An-
thropoids, which is certainly a highly specialized characteristic of the adult forms
among the apes, has in a morphological sense made a step backwards instead of
forwards. The larger size of the brain as compared with the lower part of the
face and jaws is also an embryonic characteristic of all the Vertebrata, even

1 See Cope, Origin of the Fittest, pp. 11, 12, 147, 148, chaps. viii., ix., also Haeckel, Gen. Morphologie,
II. p. 446, and Anthropogenie, for similar views.

46 GENESIS OF THE ARIETIDA.

fishes and birds at an early stage exhibiting this peculiarity. Dr. C. S. Minot?
has declared, upon similar grounds, that there was nothing in man’s structure
which justifies us in considering him as morphologically a higher animal than the
more specialized Mammalia. Though not willing to indorse this statement as a
whole, it is in part true.

Notwithstanding the increased functional power of the brain, the loss of cer-
tain characters which once marked the progress of ancestral structures remains
to be accounted for. In fact, as suggested by Professor Shaler, the body and its
organs exhibit the evidence of having belonged originally to a horizontal type,
and in accommodating itself toa vertical position has succeeded in adapting its
parts to meet new and more complex conditions, and a new position with relation
to gravity, without having made very essential changes in hereditary structures.
Man is a walking simian biped, or, as Cope describes him, a “ pentadactyle plan-
tigrade bunodont.”* Nevertheless man is also a highly specialized type. The
extraordinary development of the legs, the increased size of the big toe, the dif-
ferentiation of the feet, the broadening out of the chest and sigmoid curve of the
backbone, the differentiation and shortening of the arms, the changes in the pel-
vis, and other correlative specializations, have probably been introduced through
the exercise of the parts in an upright position, as was originally pointed out
by Lamarck.’

There is, of course, a vast gap to be bridged between man and Ozynoticeras
oxynotum, but they are none the less types belonging to the same general category
of geratologous forms. They have arisen suddenly, and present alike the com-
mingling of degenerative and specialized characters. Such geratologous species
show us that any form having a highly accelerated development, and producing
suddenly some new and unexpected characteristics, as, for example, the hollow
keel of Oxynoticeras, or the peculiarities of man’s structure, may have, in asso-
ciation with these, many retrogressive characteristics.

The extreme example of Baculites-like shells are very distinct from these,
and show us that the development of geratologous characteristics may some-
times take place without the introduction of new characteristics. In such cases,
the adults may resemble their own young more completely than in man, or in
other examples given above, and may be similar in aspect to the primitive radical
of the whole group, as is Baculites when compared with Orthoceras. Such con-
siderations and others given above have led us to compare this class of forms in
which degeneration is complete with the oldest stage of decline in the individual,
and we have accordingly placed them in the same category as nostologic forms.
This serves to distinguish them from partially degraded forms, which can be
called geratologous, or from forms that resemble the first senile stages of the
individual, and can be termed clinologic forms.

In order to account for high degrees of specialization, and their tendency to

1 Amer. Assoc. Adv. of Science, August, 1881.

2 Origin of the Fittest, p. 266, referring of course to the retention in the organization of ancient ances-
tral characters.

% Philosophie Zoologique, I., Pt. I, chap. viii, Quelq. Observ. rel. 4 ]’Homme.

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LAW OF ACCELERATION. 47

extreme acceleration in development, the author, in a previous paper,’ imagined
the special means of protection often afforded to the young in such types to be
the efficient cause. But the Marsupialia are not the most highly specialized
mammals, nor are some of the penguins the most specialized birds, and yet both
protect the young in pouches. Distoma and many other parasites are highly
protected, and yet in these we find exceedingly long and complicated adaptive
series of metamorphoses, with a high degree of protection in some cases, and in
others more accelerated modes of development with less protection, as in Tsenia.
Balfour in his “ Comparative Embryology ” subsequently adopted the same ex-
planation in order to account for cases of “ abbreviated development,” some of
which he noted, but without, however, recognizing them as due to any general
law or tendency of development, or making quotations of Cope’s, Packard’s, or
the author’s researches in this direction,

The Diptera and other insects, whose larvee are placed in protected situations
where soft foods abound, and have consequently lost their useless jaws, eyes, legs,
and hard chitinous covering, and in some cases even the differentiated segmenta-
tion of their ancestral forms, are very remarkable examples of acceleration in
development. Doubtless the supply and kinds of food, and perhaps protection,
may have had much to do with these changes, as pointed out by several ento-
mologists. The constant correlation of habits and structure in larve is, however,
independent of protection; and it is evident that such a limited cause could not
have produced, as an effect, the universal tendency of acceleration. The hyper-
metamorphosis of some insects and parasites also shows that protected habitats,
or special maternal organs for protection, are not essential to acceleration, since
the most complicated and indirect modes of development occur as in Sitaris,
where the young are protected during certain stages and unprotected at others.

Acceleration occurs whether an animal is protected or unprotected, whether
furnished with one kind of food or another, in all sorts of habitats, and whether
it belongs to a progressive or retrogressive series. This can be supported by
many examples among recent animals, described by other authors than those
specially interested in proving the truth of this law.

With regard to the accelerated forms of shell-covered Cephalopods, they are
usually, if belonging to the geratologous category, smaller, narrower, or less gib-
bous, and sometimes much compressed, as in Ast. Collenoli and in Oxynoticeras,
when compared with their immediate progenitors. The more cylindrical whorls
of Lituites, Ophidioceras, etc., and the compressed cylindrical forms Crioceras,

- Hamites, or Baculites, show facts of the same nature. All of these more com-

pressed or more cylindrical shapes were obviously not adapted to the office of
accommodating living young; they indicate in a very positive manner that
there was less space within their whorls, and consequently less protection for
the young, than in the more gibbous shells of congeneric normal forms. It is
obvious that no special provision for protection existed for the young in such
shells, or in Stephanocera refractum, or Scaphites, which did not also exist in the
normal forms with complex modes of development. from which they were derived.

1 Genesis of Planorbis at Steinheim, p. 29.

48 GENESIS OF THE ARIETIDA.

There is also no ground for assuming exceptional protection in the cases of
dwarfs, which have accelerated development of retrogressive characters, as, for
example, in those of As¢. ob¢usum, which we shall describe in detail farther on.

OrIGIN OF DIFFERENTIALS.

Differentials are essential characteristics, which distinguish one group from
another, and, unlike morphological equivalents, are apparently directly inherited
in successive generations of the series from the distal or proximate radicals. Thus
the distinct stocks of the Nautiloids, Ammonoids, Belemnoids, and Sepioids, may
be followed without difficulty. The Goniatitinee, Arcestinee, Lytoceratinse, Ammo-
nitins, and Ceratitine, among Ammonoids, are examples of suborders less easily
separated. Vermiceras, Coroniceras, Amaltheus, Oxynoticeras, and Asteroceras are
examples of genera affording still greater diagnostic difficulties. In all of these
the differentials can with certainty be considered hereditary, since after their
introduction in the earlier members of a group they are perpetuated, not only
in the earlier species or forms, but more or less even among the most aberrant
and geratologous members of the group. Differentials are often described as in-
variable, but this is an imaccurate expression, which is not in practice trusted by
any naturalist of the present time. They are perhaps, when compared with other
characters, relatively constant, but in all complete series necessarily pass through
stages or phases of evolution. On first appearance, they are apt to be more or
less variable within the limits of the species in which they originate, then they
become constant in descendent forms of the same series, and finally in extremely
geratologous (nostologic) forms they may be in large part or wholly obsolete.

The close-coiled character of the young was certainly a differential among
Ammonoidea, but this became constant only in the mesozoic forms. The con-
traction which marked the tendency to reduce the size of the siphon was not very
important at first, and was variable in position among the Endoceratida. It was,
as has been said, probably fixed at the first septum in Sannionites, and became
perhaps invariably fixed at this stage in the Orthoceratide, assuming in them
the aspect which subsequently also characterized the close-coiled nautilian shells,
and the entire stock of the Ammonoidea and Belemnoidea. The contraction in
these orders defined or cut off the primitive caecum from the parts of the siphon
formed subsequently, and its invariable occurrence at one place in the neepionic
history of such a vast number of forms is very important in its bearing upon the
mode of origin of other and less important differentials.

There is no explanation of the introduction of these characters which permits
us to separate them, as belonging to a distinct category, from characters which
are adaptive. Nor can we say that any of them more deeply affected the ovum
than any other characters. They were simply the earliest in time, and made
their appearance in adults first as ephebolic characters, and then as suitable
characters were inherited, and, being replaced in due course of time by newer
modifications, were gradually forced back through the nealogic stages until they
secured representation in the neepionic stages. This seems to be a reasonable

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ORIGIN OF DIFFERENTIALS. 49

explanation of the observed phenomena; but that the characters, as in Weiss-
mann’s theory, singly or in part could have affected the ovum when they first
appeared, does not seem to be sustained by the facts. The examples cited above
of the transmission of the characteristics of the asiphonula and cecosiphonula
to the typembryo of the Ammonoidea give similar evidence with regard to the
origin of embryonic characters, and are directly against Weissmann’s position.

Barrande and Munier-Chalmas have tried unsuccessfully to prove the abso-
lute invariability of differentials among fossil Cephalopoda by means of the great
apparent differences between the embryos of Nautiloids and Ammonoids, but
the discovery of a protoconch in Orthoceratidz has demonstrated their error,*
and we confidently anticipate the discovery of some form in which the proto-
conch will exhibit intermediate characters.

The rostrum in the Ammonoids contrasts decidedly with the central sinus of
the same region of the aperture in Nautiloidea, and is a differential of importance,
which ought to be mentioned here. The rostrum of the mesozoic forms indicates
that the Ammonoids did not possess the ambulatory pipe or hyponome? of Nau-
tiloids, which causes the ventral sinus in the aperture and striae of growth in that
order. As noted above, they could not have been swimmers in the same sense as
the existing Nautilus, and they must have been for the most part strictly littoral
crawlers. The habit of crawling as a slower mode of progression combined with
varied habitats of shallower waters, may have been the cause of the higher spe-
cialization and greater variety of forms and structures which they exhibit. The
change from a ventral sinus to a rostrum in the aperture began among the higher
Goniatites during paleozoic time, and is shown by the narrower ventral sinus
of the aperture, and in the lines of growth on the shell. This sinus also is more
distinctly marked, and is present oftener, in the devonian forms of Goniatitine
than in the carboniferous species.

The Clymening of the Devonian have very small ventral sinuses in many
forms, and in others the hyponome may have been absent. The specimens ob-
served by the author have not as a rule exhibited the lines of growth with great
clearness, but many of Giimbel’s figures give the striations, and in some species
they pass straight across the venter. The Ammonoids of the Trias are appar-
ently completely transformed, the rostrum and the ventral saddle in the lines
of growth indicating the constant absence of a hyponome.

As the ambulatory hyponome disappeared, all the sutures became more
complicated or ammonoidal, and, in correlation with the greater lengthening
of ventral and dorsal lobes, the central zone of the septum changed from con-
cave to convex. When one tries to attribute the origin of convexity in the
septa, or the multiplication and lengthening of lobes, or the marginal digita-
tions of the sutures among ammonoids to fortuitous variations, he finds at once
that their history in the groups of the order is correlative with the phenomena
of morphological equivalence. As was long ago observed by Von Buch, and

1 Science, IIT., No. 52, 1884, p. 126; and also above pp. 10, 11.
2 See Foss, Ceph. Mus. Comp. Zodl., Proc. Am. Ass. Adv. Science, XXXII, 1883, p. 340; also Science,
III., No 52, 1884, p. 123; and above, p. 29.
7

50 GENESIS OF THE ARIETIDA.

by several naturalists since his time, the complication of these characteristics
increases in each group of Ammonoidea, in strict accord with the amount of invo-
lution of the whorls of the shell. The reason for this correlation is easily given.
Involute shells have broader sides and must necessarily have a larger num-
ber of lobes and saddles, or, if these do not increase in number, then they must
necessarily deepen and have more profuse marginal digitations. Origin through
fortuitous variation is consequently inadmissible, since one can predict the
changes which are to occur under certain specified conditions.

On the other hand, the assumption that these characteristics are advanta-
geous differences, acquired through the struggle for existence, seems to be ruled
out by the same facts. Characters and differences which were shared by many
series, whether living and contending in the same horizons and localities, or
occupying distinct horizons and widely separated localities, must have been due
to causes which modified the forms by acting from within the organism. The
external causes, as pointed out by several authors mentioned above, could not
have had such similar effects, since they were assuredly diverse on distinct hori-
zons and in different localities. The only cause of modification which could
have produced similar change in different groups must have been the efforts —
either as voluntary or involuntary mechanical reactions, or both'— of the ani-
mals in response to the requirements of the surroundings in the same habitat.
As has been said above, all external marks of similar reactions in the animals
themselves, such as parallel forms and characters, tend to disappear when the
habitat has become changed. That the differentials we have been treating of
are of the same nature as parallelisms, in so far as those appearing in one series
resembled those appearing in other series, or in so far as they correlate with such
characters, will not, we think, be doubted by an experienced observer.

While it is extremely difficult to account for the lengthening of the lobes, or
the multiplication of marginal digitations, by means of natural selection, it is not
difficult to understand that these complications might have been the result of the
habit of holding the comparatively large shell high above the arms. The branch-
ing of the posterior ends of the lobes would tend to give greater steadiness of
carriage to the shell, and the efforts of the animal to use these organs while
crawling would probably tend to increase them in size and length, and in the com-
plication of the outlines. The length of the rostrum was not great in most forms
of Ammonoidea, but in some groups it was quite prominent, as in the Amaltheidee.
Its length in all groups, together with its position, was, however, sufficient to
show that the shell must have been carried while crawling more elevated above
the arms than in Nautiloids, and therefore in a position bringing greater strain
upon the parts of the mantle most used in balancing this organ.

Waagen?’ with his usual keenness has observed, that the annular muscle could
not have served solely for holding the Nautilus within the shell, but must

1 Henslow in his interesting book, ‘‘ The Origin of Floral Structures,’’ (Appleton’s Intern. Sci. Series,
1888, p. 88,) takes somewhat similar ground, and says that “the forms and structures of flowers are the
direct outcome of the responsive power of protoplasm to external stimuli.” Also pp. 123, 147, 333-337. See

also quotation from Packard’s ‘* Cave Faunas of North America,” p. 52, note 1, of this memoir.
2 Ansatz d. Haftsmusk. b. Naut. u. d. Amm., Paleontogr., XVII. p. 190.

ORIGIN OF DIFFERENTIALS. 51

have been also useful as an air-tight band around the animal, fastening the
mantle closely to the shell. The very slight impression made in the inner
surface of the living chamber shows that this muscle was not very strong,
nor very useful for purposes of prehension, and we are disposed to agree with
Dr. Waagen’s remark, and even perhaps go a little further. Finely preserved
casts of the living chambers of Ammonoids, from Solenhofen and other places,
do not afford traces of this annular band, and it seems to have been of a similar
nature, but of not so great importance in this order, as the pallial muscles among
the Lamellibranchs. The animal of Nautilus was probably held in its shell almost
exclusively by pressure, and this band of muscles perhaps served to secure the
posterior parts from being disturbed by the movements of the outer parts of
the body while the animal was using its hyponome. The supposed muscular
band of Oppelia steraspis, figured by Waagen,! runs forward on the sides much
nearer to the lateral edges of the aperture than in Nautilus. This fact also
indicates that the Ammonitins could not have used the fore parts of the body
in the same way as the Nautiloids.

The convexity of the central zone of the septum is certainly a differential
among Ammonoids when compared with Nautiloids, but it is in strict correla-
tion with the arising and lengthening of the dorsal, ventral, and lateral lobes,
especially the first two, and is therefore concomitant with the increasing com-
plication of the sutures, the closer coiling, and the greater involution of the
whorl in this order. We have already given the details sustaining this view
in our Genera of Fossil Cephalopods, and need only refer here to the cases of
Pinnacites (p. 311), in which the septa are double concaves on account of the
ridges formed by the large lateral saddles, and the family of the Primordia-
lidee (p. 316). ‘While still in the broad-whorled anarcestian stage, the septa
are nautiloidean or concave, but when the deep ventral”’ and dorsal? “ lobes and
large lateral saddles are formed, the septa become ammonitoid or convex along
the median line.” It becomes, therefore, necessary to look upon this differential
character as also attributable directly to the habits of the animal, and due to the
efforts of the Ammonoid to respond to the requirements of its surroundings,

The persistent ventral position of the siphon is a constant differential among
Ammonoids. Even the nostologic series of the Jura and Cretaceous, which
yielded so readily to physical changes, becoming uncoiled and departing in
many of their characters from the normal ancestral types, still retained the
ventral position of the siphon. Although there was considerable lateral varia-
tion in the position of this organ in some species, it remained, so far as known,
always external or ventral.

The size of the siphon becomes a matter of considerable importance in this
connection, and must be considered ag throwing some light on this obscure
point in the history of the Cephalopoda. The siphon was a far less important
organ among the later than among the earlier Nautiloidea. It was also smaller,
as may have been already gathered from what we have said above,’ in the adult

OP. Cley Dr 108; plac to. 4,
2 These two words should have been inserted, but were accidentally omitted. 8 Pages 12-17.

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52 GENESIS OF THE ARIETID.

or ephebolic stages of a Nautiloid, than in the young of the same individual.
The ancient primitive radicals like Piloceras and Endoceras had huge siphons, and
were macrosiphonulate, whereas in all the remaining forms it was quite small or
microsiphonulate. The siphon was also far less important and smaller among the
Ammonoidea as a whole than among Nautiloidea, since there were no macrosi-
phonulate forms in this order. It was also, as has been stated above, much larger
and more important in the typembryos, and in the earlier naepionic stage among
Ammonoids than subsequently in the growth of the same individuals.

This organ was also far less important, and smaller and less perfectly formed,
among the Belemnoids than among Ammonoids, and finally among the Sepioids
it became reduced to a mere rudiment, being distinguished with difficulty in the
internal shell.

We can therefore say, with some confidence, that the siphon became reduced
in size and importance during the progressive period of evolution or epacme
of each group of the Cephalopoda, and also followed a parallel course during
the development of the individual. When one reviews the various positions,
decreasing size, and lessening importance of the siphon in the various groups
of Cephalopoda, he becomes aware that these characteristics correlate with each
other, but they do not seem to be dependent upon any other character. They
are, however, correlative with higher specialization. Thus, in Nautilus, the posi-
tion of the siphon is variable ; in Ammonoids, a more highly specialized type, it
becomes more invariable, and always ventral in nealogic stages; in Belemnites
which remain straight, and in those more or less coiled, like Spirula, the siphon
is also constant, but on the ventral side of the shell. It seems, therefore, that
fixity of position is not dependent upon close coiling, but is purely a condition
of specialization, and is an accompaniment of the decrease in size and impor-
tance of the organ. The fixity and preservation of this differential character,
one of the most important in distinguishing the Ammonoids, could not have
been due to natural selection, since an organ invariably tending to become of
less importance in every order could neither have been, advantageous, nor have
offered a favorable lever for this law to work with.

Specialization has in all cases appeared to us to be due, not to natural selection,
but to physical selection, or the production of suitable modifications by the action
of forces which changed in a similar way large numbers of the same species,
perhaps nearly all the individuals in the same locality or same habitat, within
a comparatively limited period of time.

1 See in this connection the interesting researches of Dr. A. S. Packard, in the Memoirs of the National
Academy of Sciences (IV., Pt. I., p. 187 et seg.), in which this untiring investigator deduces similar conclu-
sions with regard to the action of physical surroundings upon cave animals. He also repeats after these new
and profound studies the assertion made in former publications, that natural selection does not appear to him
to be a cause of modification or of the preservation of variations, but the result of the action of other factors.

Dr. Packard’s own words are as follows: ‘* Such a phrase as ‘ natural selection,’ we repeat, does not to
our mind definitely bring before us the actual working causes of the evolution of these cave organisms, and
no one cause can apparently account for the result.’? The causes are ‘‘change in the environment,” ‘ dis-
use of certain organs,’’ “adaptation,’’ “isolation,” and ‘‘ heredity operating to secure for the future the
permanence of the newly originated forms as long as the physical conditions remain the same.”

“Natural selection, perhaps, expresses the total result of the working of these five factors, rather than

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ORIGIN OF DIFFERENTIALS. ays)

We do not intend to dispute entirely the action of natural selection and
the influence of the struggle for existence, but simply to deny the applicability
of the law to the more important modifications and series of modifications which
have occurred in the history of animals, taking the fossil Cephalopoda as a type.

We have in former papers conceded the preservation of differentials to the law
of natural selection, rather on account of the apparent logical necessity of thus
accounting for the invariability of minute differences, like the ventral position of
the siphon, the siphonal collar, the short funnel, the convexity of the septa and
ventral lobe of Ammonoids, and the divergence of the type from the common
stock of Nautiloids which these characteristics indicated, rather than from any
firm conviction derived from analytical study.

We think now that the changes in the surroundings acted upon the plastic
organism, inducing it to make efforts to accommodate itself to new conditions.
Effort, being a reaction from within upon a common organization, necessarily
produced similar series of modifications whenever the surroundings were not
changed so completely as to lead the phylum away from the original type on
lines of extreme divergence. Thus parallelisms occurred between the differen-
tials of the Nautiloidea and Ammonoidea, they were less apparent in Belemnoids,
which are more remote in habitat, and may be said to have been almost wholly
absent in Sepioids, which are still more remote in habitat, as pointed out above.
It passes without saying that the differentials are in many cases new modifica-
tions; and, if our position is true, they are adaptive characters, correlative in the
Nautiloids with their mixed habitat as swimmers and crawlers, in the Ammonoids
with their habitat as reptant forms, in the Belemnoids with their intermediate
habitat as leapers or bottom swimmers, and in the Sepioids with their habitat as
surface swimmers. The simple lobes and saddles, keelless abdomens, and ab-
dominal sinuses in the shells of the Nautiloids, the dendritic or deeper lobes
and saddles and keels and rostra of the Ammonoids, the straight internal shell
with its peculiar structures and the guard of Belemnoids, and also the degenerate
broad internal shell or pen of the Sepioids, are plainly of this nature. Effort
working alone upon a common organism could, of course, not produce such re-
sults. It is evident that it must have been assisted by the continuous action of
physical surroundings. The law, therefore, as referred to in the Preface,’ seems
to be, that, in so far as causes and habits are similar, they probably produce
representation or morphological equivalence between different series or forms
of the same type in the same habitat, and in so far as they are different, they
probably produce the differentials which distinguish series and groups from
each other.

being an efficient cause in itself, or at least constitutes the last term in a series of causes. Hence Lamarck-
ianism in a modern form, or, as we have termed it, Neolamarckianism, seems to us to be nearer the truth
than Darwinism proper or ‘natural selection.”

These words are so nearly our own views, and so valuable to us as confirmations of the theoretical
results given in the text of this memoir, that we regret not being able to quote still more largely from
this thoroughly scientific and philosophical writer.

1 Page vi. No. 18.

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54 GENESIS OF THE ARIETIDA.

I.

GENEALOGY.

GENERAL REMARKS.

HE Arietidx are divisible into three parts or stocks, the Psiloceran, the Pli-
catus, and the Levis Stocks. Each of the last two were probably derived
from different varieties of the single species Psi/. planorbe, or its geographical
affine in the province of the Mediterranean, Psi. caliphyllum' Psiloceras can
consequently be appropriately designated as the Radical Stock of the Arietide,
and, as stated above, this genus is also a surviving member of the radical stock
of the whole order of the Ammonoidea. It may also be considered as the first
branch of the Arietide.

The Plicatus Stock has four genera or series, Weehneroceras, Schlotheimia,
Caloceras, and Vermiceras. The first and second depart widely from the normal
Arietide, and they can be considered together, as if forming a second dis-
tinct branch. Caloceras and Vermiceras, especially the latter, are distinctly
arietian in aspect, and may be classed together in another or third branch
of the family tree.

The Levis Stock has five genera or series, Arnioceras, Coroniceras, Agassi-
ceras, Asteroceras, and Oxynoticeras. The first two are derivatives of the same
radical species, and can be closely associated as a fourth branch of the family.
Agassiceras and Asteroceras cannot be so closely associated with Oxynoticeras, on
account of the wider divergence of the adult characters of the last genus, but
they are apparently derivatives of the same radical species, and can therefore be
joined, forming a fifth branch. Oxynoticeras thus becomes separated from the
rest of the Arietide: as a sixth branch composed of one genus.

The Plicatus Stock can be followed from Psiloceras into a series of forms hav-
ing transitional characters, Weehneroceras, and ending in the production of the
peculiar series Schlotheimia, having characteristics widely divergent from those
of the normal forms of the Arietidse in their pilse, and in their single-channelled
keeless abdomens. The sutures retained the peculiar phylliform or psiloceran
character. In another direction, the same stock built up in part the normal Arie-
tide, producing by gradual modification the vermiceran series. Caloceras, though
truly arietian in aspect, was nevertheless much like Psiloceras, especially in its
sutures. The latter lost their complicated psiloceran characters in Vermiceras,
and became simpler in outline, or typically arietian.

The Levis Stock had no such complete transitions to Psiloceras, and began its
modifications at a later time in the Lower Lias, springing at once into the true

1 See Summary Plates xi. to xiv., which should be studied in connection with these ‘‘ General Remarks.’’

GENEALOGY. 55

arietian type in the form and sutures of Arnioceras, and from this the typical
genus of the family, Coroniceras, was evolved. The keel, double-channelled
abdomen, straight geniculated pile, and less complicated sutures of both genera,
are similar to those of Vermiceras in the Plicatus Stock.

This normal type was rapidly departed from in the next branch, in which
the highly aberrant compressed Ast. Collenoti appeared. This aberrant ten-
dency was still more decidedly brought out in the more rapid production of
similar, but more compressed and involute, forms in Oxynoticeras. In this, also,
the highest specialization was reached by the introduction of a new structure,
the hollow keel, as a nealogic and ephebolic characteristic.

The smooth variety of Psi/. planorbe, and its immediate congener, Psil. caliphyt-
um, were of course the most primitive forms which occurred in the Lias, and we
can treat the whole of the two stocks as a connected group arising in Central
Kurope from the smooth variety of planorbe, though, as a matter of fact, this is
probably artificial. The actual process of the evolution of the second branch, and
probably of Caloceras, as will be explained in Chapter III., took place in the
basin of the Northeastern Alps, and the forms found in Central Europe were
migrants. When arranged naturally the genera appear as in the Summary
Plates, as an assemblage of distinct and more or less divergent series.

We have considered each separate genetic series as a genus, because it was
necessary to do this, or else use a cumbersome trinomial or quadrinomial descrip-
tive nomenclature. Kvyen with the aid of binomials, we have not been able to
speak of any series under one name as a single species. Had this rule been
adopted, i.e. to treat each series as a single species, the opinions of paleontolo-
gists are not now in its favor, and probably no one would have followed us in
practice, however much disposed theoretically to praise our conservatism. Even
Quenstedt in his most recent work has proposed names for the different groups
of Arietide all ending in “ceras.” They are highly appropriate euphonically,
but for the most part are open violations of the law of priority in nomenclature
and not systematic in arrangement, though supported by observations and a
wealth of accurate illustrations which are of the highest importance to all stu-
dents of this branch of science.

We have tried to show, in the Introduction and in other parts of this essay,
that the metamorphoses of a normal individual in all its stages is a trustworthy
index of the morphogenesis of its group, and that a group of species tended to
have a cycle of forms corresponding to these metamorphoses. The unit of classifi-
cation is, therefore, not the species, but the genus; in other words, ut is the smallest natural
group which is genetically connected, and in which a more or less complete cycle of

forms or species may be traced. The genus may also be further defined as an
independent group of species, which must always be represented by a distinct
diverging line when represented graphically in a geological diagram or genea-
logical table. In such examples the genus becomes a series of forms, having a
distinct line of modifications traceable to the adult radicals, and more or less
present in the nealogic stages of their descendants. It has differential charac-
ters, but these may be, as in the case of Coroniceras with relation to Vermiceras,

56 GENESIS OF THE ARIETIDA.

much obscured by morphological equivalents, and in such series the closest study
of the structural gradations becomes the only sure guide.

As a rule, a series also runs through a gamut from the discoidal forms to the
involute, but not always, because there are series like Caloceras having no involute
forms,and no one species of Vermiceras or Arnioceras is more involute than another.
Nevertheless there is a decided development of the quadragonal whorl in Vermiceras,
which, as shown in the series of species in Coroniceras and Asteroceras, and during
the development of the individual in all normal forms of the Arietide, is usually
an intermediate stage to the future genesis of compressed and involute shells.

In such a system, also, certain radical forms which do not show the usual
morphogenetic cycle may occur, as was the case with Psiloceras before the more
involute forms of that genus’ were discovered in the Mediterranean province.
These may have a closely allied and inseparable series of varieties,” which
cannot be distributed into the different genera arising from them. In such
cases, the radical may be considered as an undeveloped series, and separated
as a distinct genus, though it consist of but one species with well marked varieties.

A species is a definite step, or gradation in the morphogenetic cycle of the
genus, and is distinguished by its form, amount of involution, sutural and other
adult and senile characters, and the more or less accelerated development of
the nealogic stages. In the descriptions, it will be noticed that the ephebolic
characters of the ancestral form, though it may be a closely allied species, are
nevertheless often accelerated in the nealogic stages, and the ephebolic stages
then acquire some peculiar distinctive differentials. The aberrant pathological
forms, and dwarfs of the same species, may often have more accelerated devel-
opment than the normal forms, and sometimes simulate distinct species. These,
as well as the normal varieties of species, have connections with other species
which can only be properly estimated with sufficient materials and accurate
study. After having secured the genealogy of a series, the species can be deter-
mined and separated, but until this is done, the work does not rest upon a secure
basis. The possession of a keel, or channels, or a line of tubercles, or increased
involution in the adult whorls, may distinguish one species from another in the
same series; but the same differences may make the shell appear to be identical
with a species occurring in another genus, and thus confuse the classification
unless the genesis of the characteristics has been traced.

The order adopted for illustrating the series in the Summary Plates is the
result of following out genetic lines, and therefore presents forms in their ap-
proximately natural relations, though necessarily having no reference to chronol-
ogy. The species are connected by lines indicating their natural affinities, and
show the relations of the series; but the title, Summary Plates, fully explains
the necessarily abbreviated and more or less artificial nature of the arrange-
ment. Comparison with Genealogical Table V. will serve to correct any erroneous
impressions which might arise from the study of these plates, in so far as the
species of Western Europe are concerned. Those from other localities, also
figured in the Summary Plates, will be found by reference to the descriptions.

1 Summ. PI. xi. fig. 11-13. + Summ, by si, fio, 15/25 Pl; xi fie,

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GENEALOGY. Sy

RADICAL STOCK.

Psiloceras caliphyllum, as supposed by Neumayr, may have been the radical
discoidal and smooth form from which Ps7. planorbe originated. It is a very close
ally of this species, differing only in the sutures, and these, like those of other mem-
bers of the genus in the Northeastern Alps, are phylliform, and have, as we have
said, a triassic aspect. Although we are disposed to share Neumayr’s opinion
that Psil. caliphyllum is the radical of all the Arietidse, we think, nevertheless,
that the evidence of the forms and sutures favors the theory that the Levis Stock
of the Central European province all sprang from Psi/. planorbe. The sutures of
the normal Arietidxe of Central Europe have less complicated margins than those
of Psiloceras and Caloceras of the same province; but these in turn are as a rule
less complex than those of the same genera in the Northeastern Alps, The
Arietidx, therefore, can be characterized as having degenerated in respect to
the sutural margins of the septa. The degeneration of the sutures in Ps¢loceras
planorbe and in Cal. laqueum and Verm. spiratissmum enables one to see that this
tendency was general even in the Plicatus Stock ; and it is probable’ that the
Plicatus Stock, with the exception of Vermiceras, all originated in the North-
eastern Alps from Psil. caliphyllum.

The degeneration of the sutures is due to an arrest of development followed
by the retention of nealogic characters, and is purely degenerative. This is,
however, accompanied by the evolution of a new character, an increase in the
depth and narrowness of the abdominal lobe, in the typical Arietide.

PLICATUS STOCK.
Weehneroceran Series.

The interesting forms discovered in the Mediterranean province, and de-
scribed by Wiihner in his “Unterer Lias,’? show that the closest affiliation
existed between Psiloceras and the schlotheimian group. The genus Weehne-

‘roceras,’ described farther on, contains species like Wehn. extracostatum, curvi-

ornatum, Panznert, ete., which are transitional between Schlotheimia and the true
plicated species of Psiloceras.

Schlotheimian Series.

In this series* the number of forms having the pile crossing the abdomen
with a peculiar forward bend, especially in Schiot. catenata, enable the observer
to see that a direct connection by transitional forms must have occurred between
this and Wehneroceras. The similarities are, however, not so close as to be
traceable in a series of connecting forms, and one is still left in doubt whether
the evolution of this series took place in an earlier formation than that of the
Planorbis bed, or in that bed itself. Suspecting that the nealogic stages of Schiot.

1 See Chapter IV. $ Samm. Pl. xi. fig. 7-10.
2 Mojsis. et Neum., Beitr., II., 1882. 4 Summ. PI. xi. fig. 3-6.

58 GENESIS OF THE ARIETIDAL.

catenata in varieties having the most discoidal forms and the pile crossing the
abdomen without a channel would throw some light on this problem, we begged
Professor Emerson to give us some specimens of this species from the Markolden-
dorf basin for examination. After making several preparations of those kindly
sent in reply to this request, the inner whorls and all stages up to the adult were
studied. The young to the diameter of 6-8 mm. resemble closely the older
nealogic stages of Wehn. curviornalum' and circacostatum, as figured by Wihner.?
The pile are slightly bent forward on the abdomen, are fold-like, as in Psiloceras,
and without the sharp bend and tongue-like forward projection which are the
primitive indications of a tendency to form a median ventral channel. This
tongzue-like projection is formed in the next stage, and the pile, which have in
the mean time become very sharply defined and prominent on the sides and
abdomen, also exhibit a slight flattening or decided depression, in most forms,
along the median line of the abdomen. It is evident from these facts that
Wiihner was right in considering the species of the waehneroceran series as tran-
sitions to Schlotheimia.

Caloceran Series.

This series is divisible into two subseries.

First Subsertes.--The direct connection of the plicated variety of Psil.
planorbe with Caloceras Johnston (torus, D’Orb.) has long been insisted upon by
Quenstedt, and in his collection the intermediate types are found. There is
(1) a plicatus with whorls slightly narrower dorso-abdominally than is usual in this
variety, and somewhat more prominent folds; then (2) one with the same form,
but still narrower dorso-abdominally, and for this reason with a blunter and
rounder abdomen; then (3)* a young one of this form precisely similar to the
Johnston. These show that Johnston’ is an offspring of the plicated p/lanorbis, in
which the more gibbous sides, narrower whorls, and rounder, broader abdomens
of the young of that form are retained throughout life.

From Johnstoni one can pass by gradations into Caloceras tortile* First, the
typical ¢ortile, with young until a late stage, having rounded abdomens and the
aspect of the narrower and smoother forms of Johnston. These become angular
on the abdomen at various ages, without producing a true keel. Secondly, those
which introduce a slight keel upon the elevated abdomen, but which subse-
quently disappears in the increasing angularity of the abdomen in the senile
stages. Thirdly, those which introduce a keel, then a squared or quadragonal
form of whorl, like that of Caloceras laqueum. Fourthly, those which are of very
large size, similar in all their stages, except in the angular abdomen, to the
stouter forms of Jo/nstoni, and like these becoming rounded in extreme old age.

The first variety grades into Cal. Lvasieum, which has rounded, gibbous
whorls in the young. This has a keel only at a very late stage, or may not

1 Summ. Pl, x1. fig. 7.

2 Unt. Lias, Mojsis. et Neum., Beitr., XII., Pl. xv., xvi.

3 The larger one (2) was fortunately a broken specimen, and showed precisely the same form as (3) in

the young.
4 Summ, Pl. xi. fig. 14; Pl. i. fig. 12-14.

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GENEALOGY. 59

have any, though, as in the keelless tortilis form, the abdomen may become
elevated, or very slightly subangular. Wright’s figure’ admirably illustrates
such an individual. The Sironotus variety figured by D’Orbigny has a more
compressed form and an earlier development of the keel.

Second Subseries. — Caloceras laqueum has many varieties. First, those which
develop the keel at a very late period of the growth, and grade into the third
variety of Cal. tortile. With these we find, as sub-varieties, some which, either
immediately before or at the time when the keel is developed, change by growth
the general form of the whorl. The abdomen may become elevated, as in the
first senile stage of some varieties of ¢ortile, or depressed, assuming the aspect of
carusense or spiratissimum. Secondly, those which develop a keel at a comparatively
early stage, and either retain the rounded sides, or become subquadragonal and
approximate in form and pilx to Ver. spiratissimum?

The senile whorl had metamorphoses, which produced an elevated or narrow
abdomen, similar to that of Cad. tortile at the same stage, though in some varieties
the sides were flatter, and there is a nearer approximation to the true trigonal
outlines of the old of Vermiceras.

The young of carusense*® repeated the characteristics of the intermediate forms,
but generally produced the keel at earlier periods. These are also lowest in
geological position, and pass into otuer varieties, occurring later geologically,
which are of much larger size. In all these larger specimens‘ the form is notice-
ably subquadragonal in the adult, and also has a keel, and sometimes faint
channels. There is a tendency in old age to produce a rounded whorl, with an
elevated angular abdomen in the clinologic stage, resembling the same part in
the old age of the prominently keeled varieties of tortie and nodotianum. In
the large variety of carusense we also find some forms which in their clinologic
stage have flattened and convergent sides, with a keel and slight channels. In
other words, there are some specimens which show a tendency in old age to
change the subquadragonal form of the adult, very much as in the genus Ver-
miceras. In this species, also, the sutures were observed in one case of extreme
age to lose the differentiated proportions of the adult, and partially retrograde,
becoming similar to those of Psiloceras.’ The: young and the adult of many
specimens of the raricostalum variety of earusense® are inseparable from the same
stages in the extreme of variety a of raricostatum,' with the exception perhaps of
slight differences in the marginal digitations.

The typical raricostatum,’ however, is not similar to Cul. Liasicum, being ex-
tremely broad transversely, and having a very immature gibbous whorl, which can
be called subquadragonal only in variety 4. In old age,’ even the broad whorl of
the typical variety diminished in transverse diameter, the abdomen became more
elevated, and the‘keel and pile obsolescent, until finally a fragment of the old
whorl cannot be distinguished from the same stage of Cal. tortie or nodotianum.””

1 Lias Amm., Pal. Soc., I. p. 316, pl. xvi. 2 Summ. Pl. xi. fig. 22.

8 Summ. Pl. xi. fig. 15. fore uoiged3,

6 Pl. ii. fig. 3, 8 a. 6 Pl. i. fig. 16. T Pl vie fig. 15.
Sha fig. 20 a: 9 Pl. i. fig. 24, 25.

10 Compare section of old nodotianum, pl. i. fig. 10, with section of old raricostatum, fig. 25.

SSeS

Sa

60 GENESIS OF THE ARIETIDZ.

Cal. nodotianum, as found at Semur, has two varieties. One of these resembles
the subquadragonal varieties of Cad. carusense until a late stage of development
with somewhat flattened sides, similar pile, keel, and faint channels. Afterwards
it assumed the more acute form of whorl characteristic of its own species. Cal.
sulcaum®* is transitional to Cal. Deffneri in its characters, but is not very closely
allied. The sutures of Deffneri and its young form as seen from the side
appear to justify the position given it as the extreme form of the caloceran
series. In the Mediterranean province Cal. Johnstow’ also occurs, and exhibits
transitional characters similar to those of the same species in Central Europe.
The pile are coarse, like those of the young in Psiloceras, and there is the same
tendency to an elevation of the abdomen, as in the same species in Central
Europe. Our remarks upon the subseries of this genus in the Northeastern
Alps are open to the objection that they were made upon the drawings of Neu-
mayr and Wiahner, but our inferences do not differ widely from those of either
of these writers, except in the names given to the genera and in the rejection of
the name Arietites. We shall sufficiently discuss the details of the subseries
occurring in the Northeastern Alps under the heading “ Caloceras,” in the chap-
ter on “ Descriptions of Genera and Species,” and shall find that these in part
exist also in Western Europe.

The first subseries in the Northeastern Alps contains the well known Cui.
Johustom. This seems to be the immediate radical of a small series, consisting of
Cal. hadroptychum, an unnamed form also figured by Wihner, and the giant Cal.
mgromonatum. The last has a keel, but no channels. ;

This subseries also includes Oa/. Liasicum, which is very close to Cal. Johnstoni,
Loki, and Seebachi, species having very immature keels, shallow channels, and
slightly depressed abdomens connecting Ziasiewm with Cul. Haueri of the next
subseries.

The second subseries includes forms like Cul. proaries, which shows in its
development how closely they are all connected with Psiloceras and the forms
of the first subseries. This is the representative of Cal. nodotianum of Central
Europe, and a close ally of this species, though the young are apparently more
immature at the same age in the development of the keel and form of whorl.
Cal. gonioplychum appears to connect this with the extraordinary series of Cal.
cycloides, Doetzkirchneri, Castagnola’, and abnormilobatum. This is peculiar to the
Mediterranean province, and shows that, like Psiloceras in the same region, Calo-
ceras probably had a complete cycle of forms, varying from the discoidal psiloce-
ratitic transitions with more or less elevated abdomens resembling Cal. Johnstoni
and tortile to Cal. abnormilobatum, having complicated sutures, more involute, com-
pressed whorls, and a narrowed umbilicus. This series, however, though it
evolved an elevated acute keel in the two highest species, did not have deep
channels in any species.

This subseries also contains Cal. daqueum, var. scylla, and Cal. prespiratissinum,
two forms that approximate to Vermiceras in their characteristics.

The third subseries arose apparently from Cal. Loki or Seebachi. The young

1 Summi. Pl. xi fig, 16. A Sumi. Pl. Si fig. 20121,

tts

GENEALOGY. 61

of its first member, Cal. Haueri, appears to indicate such a line of descent, though
of course this can only be considered a suggestion derived from Wihner’s figures.
Cal. perspiratus and supraspiratus are more or less decidedly channelled, and the
last inherits well defined keel and channels at an earlier stage than in Cal. Core-
gonense. Cal. ophioides is a very curious species, with an early development of the
keel and channels in some varieties, and a very late appearance of these in
other varieties, as shown by Wihner. This subseries appears in Central Europe
in a few keeled and channelled forms.’

The third subseries includes also Cad. laticarinatum, a varietal modification of
Cal. proaries according to Wahner, and this leads into several shells with much
depressed and very stout whorls, such as Cal. salinarium, centauroides, and Grunowt.
We consider Jaticarinatum as separable from proaries, because of the earlier or
accelerated development of the keel, and the broad and depressed abdomen.

There is also a subseries including only the curious Qal. Sebanum described by
Neumayr, which appears to be a form of Caloceras, possibly somewhat similar to
the equally remarkable Cal. daqueoides of Wiirtemburg.

This enumeration shows that the species of the Northeastern Alps, if arranged
in natural order, would probably form a greater number of subseries in that
province than in Central Europe, though for convenience’ sake we have here
placed them in the same number of subseries.

Vermiceran Series.

The young of Vernuceras spiratissimum,? before the quadragonal form is fully
developed, has a stage in which it approximates both in size and characteristics
so closely to some varieties of Cal. daquewn that separation is not natural. The
comparison of Fig. 17 and 18, Plate I., with Fig. 25, Summary Plate XI., shows
the tendency of this species to the production of varieties with channels like those
of Conybeart. The transition from spiratissimum to Conybeari has been recognized
by many paleontologists; in fact it is not possible to separate these species,
though the extreme forms of Conybeari have much stouter young, and usually
develop the channels and keel at a much earlier age.

Ver. Conybeari has the usual broad varieties, with late development of keel
and channels, as in Schlenbachi and the like, and also a form which acquires tuber-
cles, the Bonnardi form of D’Orbigny, and loses them again either in the adult or
during the first stage of senility. From this form the transition to ophioides,
D’Orb.,? which has the adult Conybeari form at a very early age, and also faint
tubercles, is natural and easy.

The old age metamorphoses of Ver. spiratissimum and Conybeari are quite dis-
tinct from those of Caloceras. ‘The sides showed an increasing tendency to con-
verge, the abdomen became narrower, the pila obsolescent, and the geniculx
disappeared. In very large specimens this tendency finally obliterated all traces

1 Summ. Pl. xi. fig. 14-16. 2 Pl. i. fig. 17; Summ. Pl. xi. fig. 23.
$ Pl: icfig. 2.1; Sumins Pl xi tig: Zo.

62 GENESIS OF THE ARIETID.

of the pil and of the channels, but often left the keel more prominent. The
whorl acquired the true flat-sided trigonal form, but never became rounded, so
far as yet observed.

LEVIS STOCK.
Arnioceran Series.

This series begins, when zodlogically considered, with Arn. miserabile, a form
very commonly in collections named Amm. planorbis or psilonotus, on account of its
close external resemblance to that species. It has, however, distinct sutures, and
acquires by growth a subacute abdomen. During the younger stages, while it is
still round on the abdomen, or in varieties with broad abdomens, it is, with the
exception of its smaller size, a close reproduction of the adult of Psil. planorbe,
var. deve. This grades into Arn. miserabile, var. cunciforme, which has a more
acute abdomen and curved and more perfect pile acquired at an earlier age,
and from this without a break the series passes into Arn. obtusiforme.*

Starting again from variety acutidorsale of miserabile, we can follow another
line of affinities. There are some forms of this variety which acquire in the
adult a keel with faint but abruptly terminating folds or pile, and these lead into
a variety of Arn. semicostatum.” ‘This species has many varieties, which grade
from an immature planorbis-like form® to those which are prominently keeled
and pilated even at a comparatively early age,’ and also into varieties which bave
deep channels on the abdomen.’ These last are inseparable from Arn. tardecres-
cens,’ and when they have numerous pilz they are inseparable from Arn. ceras.”
There are also varieties of Arn. semicostatum which fade into Hartmanni, and
this in turn grades into the still more compressed Bodleyi?? From Arn. Hart-
manni, also, we can pass into another compressed form, the true Amu. Saleuries
of Quenstedt.¥

Returning again to senucostalum, we find that one of its varieties is distin-
guished for remarkably raricostatus-like pila and alow keel. This when fol-
lowed out leads to Arn. kridioides.* This species in some of its varieties so closely
resembles Cal. raricostatum, that for a time it was thought to indicate the direct
descent of that species from semicostatum.

There are also some forms, usually identified as Anum. kridion in Germany,
which have remarkably broad whorls in the adult, and approximate to the true
kridion. These, however, never possess the tubercles of the true sridion, and
also have young which prolong the smooth stage and otherwise resemble the
young of the stouter forms of semcostatum.

2 Pleue tig. 4,0; Summ, Pl. xi io, 2,

* The apertures are also similar as figured by Quenstedt, Amm. Schwab. Jura, pl. xiii. fig. 27, by Du-
mortier,

ohn fig, 4 Pl. ii. fig. 8,9; Summ. Pl. xii. fig. 3.
* Pl. iu. fig, 10; Summ. Pl. xii. fig. 14. os iy 155 0,

"Plea. figs 11; Paranoia;

® Pl. il. fig. 19; Summ. Pl. xii. fig. 6, EL, Wet 20, 20 a,

aEl uote. 17; Summ, Pl xii. figs 5. ~ El ue fig. 25; Sutin, Pl, xii. fies 7.

18 Pl. Me tig, 20-27, “ Pl, i. fig. 28; Summ. Pl. xii. fig. 8.

GENEALOGY. 63

The only signs of old age observed in any specimens were the disappear-
ance of the genicule and pile, and increasing flatness and convergence of the
sides.

Coroniceran Series.

This series is composed of three subseries.

First Subseries. —The radical form is Cor. kridion, and this species shows direct
connection in many varieties with Arn. semicostatum. The similarities of form
and characteristics of the young of some varieties in both species indicate mutual
affinities, though the young of other forms of Aridion have a very different aspect.
Three specimens of Cor. kridion from Mohringen in the Museum of Stuttgardt,
named from their arnioceras-like forms Amm. Bodleyi, have the precise character-
istics of an immature /ridion, viz. divergent sides, an elevated abdomen and keel,
and tuberculated pile.* These grade into the typical Cor. kridion? having in the
extremely young stages whorls with gibbous, divergent sides, smooth at first,
but becoming more quickly pilated and tuberculated.

From these forms the transitions are complete to Cor. coronaries, which indeed
might be very properly considered as a variety of the same species, since it merely
exaggerates all the characteristics of rzdion. From this we can pass into the true
Cor. rotiforme,’ in which the adults differ greatly from kridion. The young * belong
to the typical variety, and are broader and flatter on the abdomen than in hrzdion,
and also have divergent sides and very heavy coarse tubercles. Senility is shown
only in specimens of exceedingly large size by the very gradual obsolescence of
the tubercles, pile, and channels, though we have not found any specimens, which
had become entirely smooth, or in which the channels had entirely disappeared.

The transition from Cor. rotiforme to Cor. lyra® is accomplished through a
variety, which is separable from the former only by a single character of no
special value. The superior lateral saddle is somewhat pointed and narrow,
instead of being cut into on the border by numerous marginal lobes, as in rod?-
forme. The varieties of lyra® which follow have, at an early age, a form similar.to
that of the adult rotiforme with a more or less elevated abdomen, slightly conver-
gent sides, and tuberculated pile. There is also a tendency to increase the
abdomino-dorsal diameter of the whorls, the pile becoming more closely set and
less prominent than in the first described variety.’ Senility® is indicated by
obsolescence of the tubercles and the decreasing width of the abdomen. No
specimens were observed in which the pile had disappeared, though in one
specimen they were reduced to broad curved folds, and the channels were almost
obsolete, the keel also having been reduced to a low broad ridge. This specimen
measured 440 mm., while one at Semur measuring 525 mm. had lost only the
tubercles, and the first senile or clinologic stage had but just been entered upon.

1 Tf Arn. kridioides had been found on the same level with the earliest form of Cor. kridion, it would
undoubtedly have to be considered a transitional form between semicostatum and that species; but since it is
not found there, perhaps the safest way is to indicate the descent from semicos/atum alone.

2 Pl. iii. fig. 3; Summ. Pl. xii. fig. 9.

8 Pl. iii. fig. 14-17. 4 P). iii. fig. 4-9 a. 5 Summ. Pl. xii. fig. 15.

6 Pl. iv. fig. 9-14. OP evs, Oy) Os 8 Pl; iv. fig. lo, 16.

64 GENESIS OF THE ARIETIDA,

From this species we may follow two lines of evolution, one into Cor. trigona-
tum,’ and one into Cor. Gimuendense” The former, trigonatum, can be distinguished
by its young whorls, which were stouter than is usual in the young of Wra, by
the increasing amount of the involution, which is no longer confined to the ab-

dominal region, but covers in the geniculx in some specimens, and by the earlier

period at which the pile become fold-like and the abdomen subangular.

For. Gmuendense is also distinguishable from dyra and from trigonatum by its
extremely flattened whorls in the young and adult, though it may otherwise
exactly resemble the young of the typical variety of (ra. The involution did
not increase by growth, but was confined to the abdominal area, and limited
laterally by the genicule. The senile changes were very distinct, and occurred
at earlier stages than in lyra; the abdomen® became narrower and the sides
convergent before the loss of the tubercles. Thus we can say with certainty,
that, in this species, degradational old age changes began to alter the form before
the other adult characteristics showed signs of obsolescence.

The Second Subseries of Coroniceras begins again with Cor. kridion. The con-
nection is made by a very remarkable form, Cor. Sauzeanum. The young in
some specimens are like the young of éridion, and then in the next older but still
immature stages* acquire the characteristics of the adults of kridion. The typical
Sauzeanum maintained until a late period of growth, and probably throughout
the ephebolic stages in some specimens, the broad abdomen and prominent tuber-
culated geniculz of the young, but the sides usually became slightly convergent.’
Variety Gaudryi,° for a greater or a less number of whorls repeated the typical
form of Sauzeanum. The geniculz in older stages were carried inwards, the
abdomen became slightly elevated and proportionately narrower, and the tuber-
cles almost obsolescent. A large whorl, over six centimeters in the abdomino-
dorsal diameter, was observed, in which these characteristics were not changed
otherwise than by the shallowing of the channels and the depression of the keel.

The transition forms from variety Gaudryi to Cor. bistilcatum™ are not perfectly
satisfactory. They are, however, nearly allied by the peculiarities of the abdo-
men and genicule in the young of dsulcatus, which are similar to those of the
young of variety Gaudryi until a late stage of growth. ‘Two specimens of large
size were observed. One had a diameter of 620 mm., the tubercles and channels
were almost obsolescent, the pila very thick and fold-like, but the genicule were
well developed and prominent, as in the adult. Another, 650 mm. in diameter,
had the abdomen much narrower proportionately, the tubercles had disappeared,
and the channels were almost obsolete, the keel being much reduced in size.
The former was 170 mm. in the abdomino-dorsal diameter of the last whorl, but
the latter reached the enormous size of 240 mm. in the same part. There was,
therefore, a difference of 70 mm. in the diameter of the last whorl, as compared
with the difference of only 30 mm. in the diameter of the entire shell.

1 Bh. vi. oo, 1,2; PL vi. figs 1; Summ. Pl. xu, fig? V5:

2 Pl. v. fig. 4-9; Summ, Pl. xii. fig. 14. ’ Pl. v. fig. 6, 8-9.

4 Pl. vi. fio. 0, 10; Samm. Pl. xit. fig..10. oO Vite. 0, 0) 12, Lo.

OOPL Vi tig id. as T Pl. vii. fig. 2-8; Summ. Pl. xii fig. 11.

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GENEALOGY. 65

The Third Subseries of Coroniceras begins with Oor. datum This species is
remarkable for retaining, until a late stage of growth, the characteristics of the
young of rotiforme, and for its exceptional form, the sides of the whorl being
exceedingly divergent, the pile fold-like and heavily tuberculated, the abdomen
gibbous and slightly elevated.

There is one variety of rotiforme with very stout and gibbous whorls in the
young, which cannot be distinguished from one variety of /atum until a late
stage of growth, except by the singleness of the pile. Single pile occur, how-
ever, in many specimens of all varieties of alum, so that this is not a distinction
of constant value. Cor. datum must, therefore, be considered a direct descendant
of rotiforme. From this species the transition to Cor,.Bucklandi? is accomplished
by numerous intermediate forms. These exchanged the form of datum in the
young for a sinemuriense-like stage, in which the abdomen became contracted
in breadth, the sides parallel, and the channels deep. This stage was retained
in some specimens for a long time, while in others it quickly gave place to
the huge pil, parallel but gibbous sides, transversely broad whorls, and flattened
abdomen of the adults of the typical Buckland.

In other forms, with similar young, the pile assumed during their adult stage
the usual aspect, with either only a trace of tubercles, or none. I have not been
able to follow the transitions of this, or the sinemuriense variety, into the stout form
of Buckland. There can be but little doubt, however, that the large form found
at Lyme Regis differs only in having had a more accelerated development ; i. e. in
skipping the double pile and large tubercles of the sinemuriense stage. It evi-
dently acquired, at a very early period in the young, large untuberculated pile,
and in old age was characterized by a very decided narrowing and rounding off
of the abdomen, obsolescence and bending forward of the pilex, disappearance of
the channels, and a broader and less elevated keel.

The evidence of transition from the sinemuriense variety to Cor. orbiculatum
rests upon similar grounds. The singleness and perfection of the pil are the
only differences which separate the young of orbiculatum from the young of such
forms as variety No. 5 of sinemuriense. In the adults, however, the narrowness
of the abdomen, flatness of the sides, and their convergence outwardly, are
marked differences in aspect, which were greatly increased by advancing age,
The abdomen in some very large specimens became almost obtusely angular, as
in Vermiceras, and the pile fold-like, much bent forwards, and the channels
obsolete.

Agassiceran Series.

This series obliges us to return once more to Psioceras planorbe. It has two
subseries. ,

First Subseries. —The young of Agas. levigatum® had a close resemblance to
the young of the compressed varieties of Cor. kridion, and to Cor. rotiforme in some
varieties, before the latter acquired tuberculated pile. But this likeness was

1 Pl. iii. fig. 19-23; Summ. Pl. xii. fig. 16. * Pl, in, fig. 18; Summe-Pl xii ho. 17.
8 Pl. viii. fig. 9-14; Summ. Pl. xiii, figs}

66 GENESIS OF THE ARIETIDA.

due to the stout whorls of the younger stages, and cannot be relied upon as at
all conclusive. The stout helmet-shaped whorl is a larval characteristic, derived
from the primitive ancestral Goniatitic form, Anarcestes. It is found in all the
Ammonitine at an early stage of growth, and may be retained in radical forms
until a late stage; and in this species it sensibly influenced the shape of adults.
The adults of many specimens of Agas. /evigatum' are closely parallel with
Psil. planorbe. Dwarted specimens sometimes have the form and smooth aspect
of planorbe, and even the apertures are similar, and Agas. levigatum, therefore,
must have been a direct descendant of Psil. planorbe.2 In var. d of devigatum the
depressed helmet-shaped whorl is exchanged in course of growth for the com-
pressed helmet-shaped, just as in planorbe. The young,’ unlike the adult of
planorbe, have short living chambers,‘ and the septa are quite distinct, and im
most specimens there is a raised siphonal ridge along the abdomen, though the
keel is not well developed, nor are the channels present. The misnaming of
varieties of levigatum as Amm. planorbe is also common in European collections.

The same peculiarities are present also in Agas. striaries. In some varieties
of this species there are perhaps still closer approximations to the general form
and aspect of the smooth forms of Psil. planorbe.

Agas. Scipionianum ® has two marked varieties, — one less involute, with spines
in the adult,’ and one more compressed, with smaller spines.’

Agas. nodosaries is apparently a compressed form, very similar to Scipiomanum.

Agas. Scipionis is a distinct species, having smooth and more involute whorls.”

The Coroniceran proportions and aspect of the sutures in Se/piomanum are well
marked, and would have led to the association of this species with that genus
if there had not also been similar sutures in Ast¢. obfuswm, showing that these pro-
portions are progressive characteristics of independent origin in each series.
The completeness of the gradations from the adults of Agas. striaries to the young
of this species also forbids this conclusion.

Asteroceran Series.

This series has two subseries.

First Subseries. —The more advanced varieties of Agas. lavigatum" have diver-
gent-sided whorls and fold-like pile, and a form™ similar to the tuberculated
young of Ast. obtuswum,” and still more like the untuberculated young of this
species.” In the accelerated development of the tuberculated variety of obtusum,"

iPr, vate 9, 12.

2 Compare the young of the last named, fig. 4, pl. i., with fig. 10, pl. viii.

8 Pl. viii. fig. 13.

4 Short living chambers are found in the young of Psil. planorbe, and therefore this characteristic is
really a confirmation of the assumed direct descent of Agas. levigatum from that species. Agas. levigatum is
an arrested development of Psil. planorbe, in so far as the living chambers and its small size are concerned.

5 Pl. ix. fig. 14, 15; Summ. PI. xiii. fig. 6. 6 Pl. x. fig. 11-13; Summ. Pl. xiii. fig. 7.
PDL Seriiek belo, 8 Pl. x. fig. 13, and pl. vii. fig. 15.

9 Summ. Pl. xiii. fig. 8. 10 P). viii. fig. 11.

1 Pi, viii. fig. 14. 2 Pl. viii. fig. 8.

18 Embryology of Cephalopods, pl. ti. fig. 11. 14 Pl, viii. fig. 4.

a

GENEALOGY. 67

the divergent-sided whorl is noticeable. This is often replaced by a parallel-sided
whorl on the fourth volution, and this in its turn is replaced by the convergent
sides of the fifth whorl? The divergent-sided whorl, with its tuberculated pile,
is skipped in the development of some specimens of obéwsum, and it is replaced on
the third whorl by the parallel-sided smooth whorl and pile of the later stage,
instead of on the fourth whorl, as described above.®

The broad abdomen and the correlative divergent-sided larval form of Ast.
obtusum are retained in the adults of some varieties,t but even in these the pile
are smooth and without genicule, and the whorls discoidal. Notwithstand-
ing this fact and the enormous size reached by some normal specimens before
manifesting old age, there are specimens in the closely allied Ast. stellare and
acecleratum which exhibit a remarkable tendency to assume retrogressive char-
acteristics, and to inherit them in their younger stages, while still becoming
more involute and holding the keel comparatively unchanged. These characters
induced me at first to estimate the whole series as geratologous, but this view
cannot be maintained. Most specimens lose the tubercles early, or do not have
them at all, the pila become mere folds, and bend forward, the keel being low
and broad and the channels shallow. There is so close a resemblance between
these ephebolic characteristics and the old age stages of the common English
form of Bucklandi at Lyme Regis, especially in the stout varieties of oblusum,
that collectors frequently call the old of Bucklandi by the name of Amm. obtusus.
Upon one oceasion I was myself completely deceived by the exposed portion of
a whorl, which, when finally cleared of its surrounding matrix, was readily iden-
tified as a senile specimen of typical Bucklandi. Nevertheless the characteristics
of Ast. obtusum, when compared with the radical Agas. striartes or levigatum, are not
geratologous, but nealogic. They have the same relation to the characteristics of
these radical forms that the fold-like pile and immature whorls of Cal. John-
ston’ have to those of its immediate radical, Psi. planorbe. Their real value as
radical characters is shown also by the fact, that in some full grown specimens of
oblusum tubercles appear, and in the ephebolic stages of Ast. Turnert of the next
subseries the typical arietian characters appear, namely, deep channels, well
defined keel, and quadragonal form. These therefore occur in the same succes-
sion as in other series of the Arietida, and during the growth of the individual
they appear in similar order.

Ast. acceleratum, the second and last of this subseries, occurs rarely, but is
found in several collections. It has young until a late period precisely identical
with the young of certain varieties of obtusum, and the adults of stellare. This
stage, which may last until the individuals are from 76 to 89 mm. in diameter,
is immediately followed by a stage in which the involution is increased, the sides
are flattened, the abdomen narrowed, and the pile obsolescent. In fact, during
its adult stage a form and characteristics are produced very similar to the stouter
varieties of Brooki, with which it was at first associated.

1 Pl. viii. fig. 6. 2 Pl, vai ae, 3

8 PJ, viii. fig. 8, does not show the inner whorls accurately enough, and a ecmparison of the figures is
necessary in order to give an accurate idea of the development.

4 Summ. PI. xiii. fig. 2, has parallel sides, but belongs to this gibbous whorled variety.

ban

68 GENESIS OF THE ARIETIDA.

Second Subseries. —Some specimens of Amm. stellare, Sow. have a young
stage during which the sides become more or less flattened and parallel. These
are intermediate between true odtusum and Turneri. The old of the stout va-
rieties of obtusum, and specimens of Twrneri in their first senile stage, have char-
acteristics similar to those of the adults of stel/are, and occasion confusion in the
identification of fragments. The extreme senile metamorphoses of Zwrneri, when
the whorl became smooth, the channels shallow, the sides convergent, and the
abdomen narrow, occurred, as in other species, at variable ages, sometimes in
shells only 102 mm. in diameter.

The differences between the adult of Twrneri and the adult of the next
species, As?. Brooki,? are well marked in most specimens, but the stoutest and
least involute forms of the latter are very closely allied to the former.. The adults
of the stouter variety of Brooki retained the channels, the keel remained promi-
nent, the sides remarkably flattened, and the pile in some specimens prominent
and like those of Turneri, but the whorls were generally more involute. The
young have very close resemblance to the adults of Turner’. The young? of
Ast. impendens had no very close resemblances to Turner at any stage. They
repeated the adult characteristics of the stouter variety of Brooki during the
nealogic stages, and in the adults exaggerated the normal tendency to conver-
gence of the sides, depression of the pile, and narrowing of the abdomen. The
adult of this variety approximated quite closely to the senile stage of sfellare.
The fine series of figures given by Wright in his “Lias Ammonites” shows
most completely the transitional forms of dmpendens, and are referred to below
in the description of Brooki. Ast. denotatum is simply a more involute form of
impendens.

The next species, Ast. Collenoti,s can be traced directly to the preceding
form, and, if my translation of the facts is correct, it is the geratologous offspring
of impendens or denotatum. The young? were similar to the young and adults of
ampendens, and also more remotely to the adults of sted/are, but the next or first
ephebolic stage was precisely similar in all respects, except the sutures, to the
first senile stages of tmpendens. In the adults of one variety this stage retained
distinct pil, though in other specimens the sides became smooth. The involu-
tion of the adult whorl was more considerable than in unpendens, and the shell
closer in this respect to denotatum.

The extreme variety of Collenoti had a similar form and development, but
was somewhat sharper on the abdomen, and the pilss were wholly confined to the
nealogic stages, the adult stage being similar in form and characteristics, except
in the sutures, to the extreme old age of impendens. Thus the characteristics
of the transient senile stages of Ast. obfuswm and other normal species were
similar to the permanent characters of the ephebolic and even nealogic stages
of degenerate or pathological species like Ast. acceleratum and Ast. Collenoti.

1 PTS aS, tee 2, Oe 2 Summ. Pl. xiii. fig. 4.
ole. tip, 6-9, * Pl. x. fig. 10; Summ, Pl, xiii, fig. 5.
5 Pl. ix. fig. 10-11 b.

nan

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j
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GENEALOGY. 69

Oxynoticeran Series.

The apparently wide divergence from the usual structure of the Arietide
presented by the hollow keel led me at first to classify this group as a distinct
family. The close affinities with the Arietidee shown by the young, however,
and the intermediate characters exhibited by the agassiceran series render such
a classification unnatural and undesirable.

The loss of the keel and flattening of the abdomen in the old has no parallel
in the normal forms of the Arietide, so far as known It must be remem-
bered, however, that this modification, together with its correlative decrease
in the lateral diameter of the whorl, is a fulfilment of the series of geratologous
transformations.

First Subseries. — There are two subseries; one, the oxynotum subseries, with
comparatively smooth shells, as in the less involute and stouter varieties of oayno-
tum, and one, the Greenoughi subseries, which has highly developed folds. Both
of these series progress in the amount of involution. The less involute Ozyn.
oxynotum, the somewhat more involute Ozyn. Simpsoni2 and the still more involute
Oxyn. Lymense of the first subseries are parallel with Ozyn. Greenoughi, Guibali, and
Lotharingum of the second subseries. According to most authors, we could legiti-
mately consider that the first three were only varieties of one species, though
very few would be willing to join the last three under one specific name. The
sutures of the adults of the oxynotum subseries are very close together, reminding
one of the approximate sutures in the oldest stages of the individual in other
genera. The pointed lobes and broad saddles, the short abdominal lobe and
long finger-like marginal lobes and saddles, remind us also of the senile pecu-
liarities of the sutures of Cor. trigonatum. The increase in number of auxiliary
lobes and saddles and the general aspect of the sutures are, however, upon the
whole additional complications, and therefore progressive characteristics.

Second Subseries. — The gradations are uninterrupted from Greenoughi® to
Lotharingum. The descriptions of the species show that the principal differences
consist in the increasing involution of successive species, and a correlatively
smoother and more compressed form of whorl.

-The young of ozynotum and Greenough’ resemble closely the young of Agas.
striaries. There are, however, no intermediate forms between the latter and
these two species which would enable one to verify this relation of the younger
stages. Whether Ozyn. orynotum or Agas. striaries gave rise to Oxyn. Greenoughi
cannot be decided at present, owing to this deficiency in the evidence; but that
both these forms came from the same common stock, and that this stock was
Agas. striaries, seem quite probable.

Oxyn. Guibali, the next species of this subseries, bridges the gap between
Greenoughi and Lotharingum. .The nealogic characters of Oxyn. Lotharingum also
show that this species must have been derived from Guibali. Lotharingum, like
Ast. Collenoti and other terminal forms of series which have marked geratologous
characters, is the smallest form of its own genetic line.

1 Pl. x. figs. 24 and 31. - Sumi Ply ke ae. Lie 8 Summ. PI. xiii. fig. 13.

70 GENESIS OF THE ARIETIDA.

Oxyn. Oppeli' is a remarkable form, apparently a direct descendant of Gree-
noughi, which alone survived in the Middle Lias.

Nore. —I have so far found but few specimens of the Arietide which could not be identified or properly
placed in some genetic series. ‘Two anomalies are in the Museum at Stuttgardt, and both were found in
the Angulatus bed. One is somewhat similar to the larger forms of Cal. carusense, and is labelled Amm.
bisulcatus. It has a very broad abdomen, the sides of the whorl divergent, the pile well developed, geniculee
prominent and straight. The keel is low and angular, and two sulcations on either side stretch to the
incurved edges of the abdomen and these edges form two ridges as prominent as the keel itself; the sutures
are similar to those of Vermiceras. It may be an extreme form of Caloceras, allied to Cal. Haueri, but is
apparently not allied to Jaticostatus, Quenst.

The other specimen is labelled Amm. nodosaries, Quenst. It resembles Agas. Scipionianum in the pile
and tubercles, the absence of channels, prominent keel, and helmet-shaped outline of the whorl in section.
The superior lateral saddles are narrow and deep, the superior lateral lobes also very narrow, long, bifid,
and deeply divided by a terminal marginal saddle. The inferior lateral saddles are deep, and occupy nearly
the entire breadth of the sides of the whorls, and have deep, rounded marginal saddles.

In the Museum of Amherst, Mass., there is also an enormous shell, which had reached the large size
of 600 mm. Though undoubtedly very old and much compressed, it had not yet suffered the loss of its
keel, which is plainly apparent, nor the pile, even on the extreme outer whorl. The three outer whorls
alone are preserved, the centre having been destroyed. The pile are about 20 mm. apart on the outer
whorl, and have depressed folds. They are more prominent and about 10 mm. apart on the second
inner whorl, and about 5 mm, apart on the innermost whorl. No genicule or tubercles were apparent,
but the specimen would require cleaning before this could be decisively stated. The pile were slightly bent
forward, and fold-like, as in Caloceras. On the umbilicus were two fossil shells, said to be Plagiostoma
gigantea, and the locality where it was found was Dorsetshire, England. The outer whorl was 110 mm. in
the abdomino-dorsal diameter, and the slow increase and evidently large number of whorls in the full
grown shell, as well as the rotund form of the sides of the whorls and the slight amount of involution and
extremely discoidal aspect, indicated a species of either Caloceras or Vermiceras.

7 Sumin. Pl, xiii. fig. 16,

ANAGENESIS. 71

ieee
GENESIS OF CHARACTERISTICS.

ANAGENESIS,’ OR THE GENESIS OF PROGRESSIVE CHARACTERISTICS.

HE introduction of the peculiar pile and single channelled abdomen in

Schlotheimia, which occurred in the earlier species, must be regarded

as a progressive complication, since it is not only a new characteristic, but it is

correlative with constant progress in the amount of involution, and with the

advent of species having more compressed, more involute and sub-acute whorls.

The weehneroceran series introduces the observer to Schlotheimia by its inter-
mediate modifications when one begins with the radical stock, Psiloceras.

Undoubtedly the steady increase of involution in successive species of the
psiloceran, wehneroceran, and schlotheimian series is, like the similar phenomena
of other series, to be regarded as progressive. This is clearly shown, both by
the steady increase of size in individuals throughout each series, and also by
the fact that these changes are in accord with the general progression of the
whole group.

The younger stages, as we have remarked above, were closer coiled during
the Mesozoic than in the Paleozoic, and the adult forms were more involute as
a rule in the Trias and Jura, than in the earlier geologic periods. The genesis
of this progressive character independently in each series may be seen by ex-
amining the different series in the four summary plates, and we need not allude
to it again in this chapter. It is also interesting to note, that the most exact
parallelisms in this respect are to be found between the series, which are
widely separated. Thus the extreme aberrant forms of the family, namely,
Schlotheimia, Weehneroceras, the radical Psiloceras, and the opposite extremes
of the group, Asteroceras and Oxynoticeras, all possessed highly involute
compressed whorls.

Neither of the first three had any species with quadragonal whorls; the shells
are all modifications of the helmet-shaped or secondary radical form. There is
an approximation to the subquadragonal in the most discoidal species, Sehdot.
catenata and some others, but this is not very noticeable, and the absence of
geniculs in the pile confirm this conclusion. These series, therefore, can be
placed in strong contrast with the more normal species of the caloceran series, in
which the quadragonal form of whorl and its correlated characters played a promi-
nent part. The acmic species of the progressive series of the Arietidae were
these pilated and tuberculated quadragonal whorls. In the development of the
individual, also, the quadragonal form and tubercles are the last characters added
by progressive growth, and were primarily of ephebolic origin.

1 Avd, upwards ; Téveous, descent by birth.

————

=,
bo

GENESIS OF THE ARIETIDZ.

Cal. Johnstom was at. first smooth, then ribbed, and the ribs had a peculiar
fold-like character, and they appeared in this succession in the young of all the
remaining series. The keel was added to these in the adult of Cad. tortile after
the pile were developed. The adult of Cal. daquewm had the keel, and added
also faint channels and in one variety the tubercles.’ If we are right in referring
Cal. Deffneri® to this series because of its sutures, then the terminal species of
Caloceras had a very highly accelerated development, producing the quadrago-
nal form, keel, channels, complete pile, and tubercles at nearly the same stage
of growth as in Ver. ophioides.

In the development of the young of Ver. Conybcari, the succession of charac-
ters was similar, — first a smooth whorl, then fold-like psiloceran pile, then keel,
then channels, then true pile, which often became tuberculated. In Ver. ophioides,
a tuberculated species with highly accelerated development, it is difficult to
determine whether the keel was developed before or after the channels, since
they appeared almost simultaneously.

In the varieties of Cal. laqueum, we found the forerunners of all the rounded,
quadragonal, keeled, channelled, and tuberculated forms of Vermiceras. The
variety which led into Ver. spiratissimum had no tubercles, and could be called
quadragonal, though it had only a slight keel and no channels, or at most
very faint bands of depression on either side of the keel. In Ver. spiratissimum,
these characteristics are fixed within narrower limits of variation, the keel, chan-
nels, and quadragonal form were invariably present in adults, but better defined
in some than in others, and no variety with tubercles has yet been discovered.
In Ver. Conybeari also the characteristics above mentioned were more invariable,
but here we found numerous adult individuals with tubercles on the pila, and
varieties which produced all these advanced characteristics, including the tu-
bercles in some cases, at a very much earlier age than in other species. Lastly,
Ver. ophioides is always tuberculated, channelled, and keeled in adults, though, as
shown by its young, evidently derived from those individuals of the tuberculated
variety of Conybeart which did not produce these same characteristics at so
early an age.

In the arnioceran series, the keel appeared in the young before the channels,
and also previous to the development of pile. This is the case in Arn. miserabile,
and in the derivative Arn. semicostatum. This is in strict accord with an indepen-
dent descent from the smooth Psiloceratites, but not with a supposed derivation
from any intermediate caloceran or plicated form of Psiloceras. The pile ap-
peared in the growth of an individual of Caloceras before the keel, — a condition
due to the fact that the young remained, as previously explained, very similar to
a plicated keelless Psiloceras during the earlier stages of development. The
channels were first apparent in the adults of certain varieties of Arn. semicostatum,
and in some other species of Arnioceras they became of specific value.

1 This progression was much fuller in the species of the Mediterranean province (see Summ. PI. xi.
fig. 17-19), showing the correlations of the development of the individual and evolution of forms in the
series better than in Central Europe,

+ Summ, Pl, x1. fig, 21.

ANAGENESIS. 13

There is a similar succession in the evolution of the varietal and specific
characteristics of the series. Thus, in Plate II., Fig. 10, 11, and 15 repre-
sent the extreme varieties of Arn. semicostatum, the former with immature pile
without channels, the second with well developed pile without channels, and
the third with well developed pil and distinct channels.!| The young of Arn.
tardecrescens, Fig. 19, shows that the derivation of this species was probably
from the unchannelled forms of Arn. semicostatum similar to Fig. 11. The
same is true of Arn. Bodleyi with reference to Hartmanni, as is shown by com.
paring the young of the former, Plate II. Fig. 23, with the adult of Hartmanni,
Fig. 17, which had very slight channels even in the adult, and this is still more
apparent in the involute flattened form of Fig. 24, in which the channels
were earlier developed. The close connection of all its characters, both of
young and full grown, with its immediate ancestor, forbids us imagining an
independent descent from a variety of any other species than MHartmanni, and
the evidence is strong that it had no descendants: beyond its own species.
The channelless variety of Arn. fulcaries, Fig. 26, gives similar evidence -of its
genetic connection with the channelless varieties of Arn. Hartmanni, or if this is
doubted, a more direct connection with Arn. semicostatum may be claimed ; but
certainly there is no evidence for any connection with the channelled varieties
of semicostatum or Hartmanni.

The pilz began with psiloceran-like immature folds, after the keel appeared
in the arnioceran varieties of Cor. kridion, and before the keel in the more acceler-
ated development of other varieties of the same species. In some forms the
pile were completed and became tuberculated before the channels appeared.’
This same confusion with regard to the time of the appearance of characteristics
with relation to each other is a peculiarity of highly accelerated species, as
before noted in Ver. ophioides.

Such observations are of importance, since they enable us to understand that
characteristics do not necessarily develop with invariable regularity. The usual
order of their succession may be in a measure changed, or even reversed, when
acceleration takes effect upon one character more than another. So far we have
found this occurred only in species where all the principal characters of the series
were undergoing exceptional acceleration.

The common form of the younger stages of all the Ammonitins during the
goniatitinula stage is shown in the plates.? The depressed goniatitic helmet shape
was succeeded in Psiloceras by a laterally flattened helmet shape. In Caloceras
the same form was succeeded for a very prolonged period, in species with flattened
abdomens, like Cad. carusense,* by a stage in which the abdomen became broader
and the sides slightly divergent. In Arn. ceras, as in Cal. carusense,> this often
occurred at a much earlier period, replacing entirely the psiloceran helmet

1 By accident these specimens were al] of different sizes. Thus they give false impressions. Although
fig. 15 is older and larger than the others here figured, my observations were made on specimens of similar
size and age.

4 Plems fip., 9:20.

8 Pl. i. fig. 4’a, for Psil. planorbe ; pl. vi. fig. 7, for Cor. Sauzeanum ; also in Embryology of Cephalopods.

oP i ie Tey de, el shat 2OF

10

74 GENESIS OF THE ARIETIDA.

shape, —a fact accordant with the more specialized structure and more acceler-
ated development of the species in this genus.

In Arnioceras' the goniatitic helmet shape was replaced by a purely psiloceran
helmet shape on the third whorl ; and this was retained throughout life in Arn.
miserabile,’ but lasted for a more limited period in Arn. semicostatum, and was then
followed by a flatter and broader abdomen, the sides becoming slightly divergent,
as in Arn. obtusiforme ;* and this condition was often maintained throughout the
adult stage.

The broad abdomen and divergent-sided whorl, which came out in only a few
species of Vermiceras and Arnioceras, and was not very strongly marked in them,
became in Coroniceras characteristic of the young at an early stage It is a
significant fact favoring our theory, that in the arnioceran-like forms of Cor,
kridion it did not replace the more compressed whorls of the arnioceran ancestor
until a late stage of growth. In other species of Coroniceras, however, the
broad abdomen and divergent-sided whorl replaced the laterally compressed,
helmet-shaped whorl inherited from Arnioceras, as in Cor. Jatum.’ All the species
of Coroniceras did not have this stage. It was in its turn more or less replaced,
in some of them, by the acceleration of other characters, as will be shown
farther on.

The law of succession in anagenesis, therefore, is, that progressive species in each sepa-
rate genetic series were the direct descendants of progressive varieties or forms. The facts
consequently are in strict accord with the theory of descent with modification, and with the
law of heredity, that lke tends to reproduce like.

Coroniceras was not derived from Arn. semicostatum directly, but indirectly,
through the more highly specialized forms of Arn. kridioides and Oor. kridion. It
was not the varieties of Cor. kridion with arnioceran characteristics most com-
pletely developed which led into Cor. rotiforme, but those with divergent-sided
and highly specialized pile, keel, and channels. So in Cor. rotiforme with refer-
ence to Cor. datum, and also in this last with reference to Oor. Bucklandi. These
are the purely progressive forms; and their connection with ancestral species
occurred through progressive varieties.

CATAGENESIS,’ OR THE GENESIS OF RETROGRESSIVE CHARACTERS.

Many large specimens of the species noted in the preceding remarks had
narrow abdomens, and the sides converged outwardly. Thus, in what is often
mistaken for the full grown adult stage of Caloceras an acute helmet shape
appeared, as in some varieties of Cul. Johnston’, tortile, Liasicum, and nodotianum.
This was certainly not, as usually stated by paleontologists, due to a retention of
the psiloceran form. It took place after the intermediate or progressive stages
in which the abdomen had become widened, more or less flattened, and the sides

1 Embry. Ceph., pl. ii. fig. 8, 9. 2 Pl. ii. fig, 4-7.
8 Compare above with semicostatum, pl. ii. fig. 10 and 15. © bl, iid 8:
© Pl iy fig,-22 4 tp), ivedigy 13 ple vie fig, 6; eo Pl ae figs 20;

7 Kara, downwards; Téveows, descent by birth.

> ae

CATAGENESIS. 75

gibbous ;' that is, after the quadragonal whorl had appeared in the development _

of the same individual.

We have also shown that in every series similar changes took place in the
geratologous species, and were accompanied by a correlative series of retrogres-
sive pathological changes in the keel, channels, pile, tubercles, and sutures. The
convergence of the sides is, therefore, a retrogressive character when it occurs
after the gibbous or quadragonal whorl has appeared either in the evolution of
the series or in the development of the individual. In Psiloceras a slight con-
vergence of the sides of the whorls was present, and was a primitive character
of the helmet-shaped whorl, and this occurred also in Arn. miserabile, and in the
nealogic stages of other forms of the Levis Stock. Such characters in the indi-
viduals of radical species occur before the quadragonal whorl is developed, and
in connection with primitive radical characteristics and forms which will not be
confounded with geratologous characteristics and a by any close observer, if
he have sufficient materials for study.

There is a true senile degeneration in the old age of some forms, which is
apparent in the marked convergence of the sides and sub-acute abdomen of the
old whorl, even in such discoidal species as the Psi. pleurolissum This, as a.de-
generative character, was reproduced at an earlier nealogic stage in the involute
species, as may be seen by comparing these figures with those of the involute
form Psi. mesogenos.? The same law holds also in Wehneroceras. In Schlo-
theimia it becomes apparent when we compare the old age of Schiot. catenata
having smooth abdomen and convergent smooth sides, with the sides and abdo-
men of Sch/ol. Boucaultiana which are similar in the nealogic and ephebolic stages.
Such characters are therefore retrogressive, and indicate decline in so far as the
forms of the whorls, the pile, and the channels are concerned, notwithstanding
the fact that they are often correlated with the progressive character of greater
involution, and appear in the nealogic stages of some (geratologous) species. It
will be observed that, in Cadoceras from the Mediterranean province,‘ the com-
pression of the whorl and other degenerative characteristics occurred without a
proportionate increase of involution, and that the same phenomena occurred also
in Coroniceras.°

The convergence of the sides was evidently a geratologous stage in Caloceras®
and Vermiceras, but in some species of Arnioceras a slight tendency of the sides
to become convergent in the adult stage was noticed. In Arn. semicostatum™ and
tardecrescens,° it occurred in the adult stage of varieties with well developed keels,
channels, and pil, but not so noticeably in the lower varieties of these species
with less accelerated development. In Arn. Bodleyi, where it was found in all
varieties,’ it is noticeable at an early stage, and in the still more highly accel-
erated development of the involute variety" it appeared very much earlier than

1 See also p. 59.
? Wihner., Unter. Lias Mojsis. et Neum., Beitr., IIT. pl. xxvi. fig. 4 a, b.

8 Wihner., fig. 3, same plate. 4 Summ. Pl. xi. fig. 17-19. 5 Summ. PI. xii. fig. 14, 15.
® Wiihner, in the work quoted, figures several species of this genus in their senile stages.
Pia. fig. 15. 8 Pl ii. fig. 19.

® Pl. ii. fig. 23. Pl. ii. fig. 24.

76 GENESIS OF THE ARIETIDA.

in any other species of this genus. Thus a high degree of specialization in the
development of keel, channels, and pils is correlative with decidedly retrogressive
changes.

In Coroniceras, the Bucklandi series exhibits very decided changes in both
the individuals and the species. The tubercles were first lost during the old age
of the individual, the sides became more convergent even in Bucklandi itself, the
abdomen narrower, the pile reduced to folds and bent like those of the adult of
Ast. oblusum, the channels shallow and finally almost obsolete, and the keel, even
though becoming apparently more prominent on account of the convergence of
the sides and obsolescence of the channels, was really not so sharp or well
defined.

Cor. orbiculatum exaggerates all these old age changes, becoming narrower on
the abdomen, with more convergent sides, and this convergency began even
in the ephebolic period in some examples. Similar changes occurred very late
in the life of individuals in the next subseries. Thus even the convergency of
the sides was not found in the adults of Cor. rotiforme in many specimens, and is
but slightly developed even in the extreme old age of some of this species, and in
its predecessor, Cor. kridion. 'This characteristic is, however, observable habitually
in the adults of Cor. ra. These lead into Cor. Gmuendense of the same series,
which had very convergent sides in the adult, and was often also destitute of
tubercles. The last were confined to the earlier stages of this species, and in old
age the changes were very marked and rapid. The extreme variety of Cor.
trigonatum inherited convergent sides, smooth and half obsolete pile, narrow
abdomen, shallow channels, and elevated keel, so early that we may say with
confidence they all appeared in the ephebolic period.

The old whorls of Cor. G'muendense and Cor. trigonatum™ have the sides of the
whorls convergent and a decidedly trigonal form. This form is correlated with
obsolescing pile and a marked though late decrease in the sutures. These
lose the characteristic prominence of the second lateral saddle, which is a pro-
gressive characteristic in this genus. All the lobes and saddles also become
broader and decrease in proportionate length, and finally in extreme age the
abdominal lobe is decidedly shortened? In the Museum of Comparative Zotlogy
there was also a much smaller specimen,’ in which the same stage of decline had
been reached at an earlier age. The law of succession was, therefore, quite differ-
ent from that which governed the inheritance of progressive forms. The most
retrogressive of the bucklandian varieties were those which were most closely
connected in every way with Cor. orbiculatum. The genetic connections also
between Cor. rotiforme and Cor. lyra were traceable only through those varieties of
rotiforme which had the most convergent sides and the most retrogressive pile,
tubercles, ete. This also holds for the connections between this last and Cor.
Gimuendense and Cor. trigonatum.

The law of succession in eatagenesis, therefore, ts that retrogresswve species in each
separate genetic serves are the direct descendants of retrogressive varieties or forms. The
facts consequently are in strict accord with the theory of descent with modification. The law

+P) ve fig. 8,95 pl vietig. 8; ply vit. fig, 1. ci iAp ih siten ae SOP ew odige 1, 2.

Sg

CATAGENESIS. 77
of heredity, that like tends to reproduce like, cannot be assumed with regard to the transmus-
sion of senile characters, since these were probably not directly transmitted from one species to
another. Nevertheless, the tendency to degeneration must have been inherited, of we can
Judge by the appearance of retrogressive characters at earlier stages in successive species.

In the three geratologous series, Asteroceras, Agassiceras, and Oxynoticeras,
we find the same laws of anagenesis and catagenesis. The psiloceran-like or
progressive species were the immediate progenitors or proximate radicals of
progressive varieties, species, and genera in the direct line of descent, but when
geratologous forms began to appear, and progression changed into retrogression,
there was a corresponding change in the radicals. Then the retrogressive forms
arose from varieties which were themselves also proportionately degenerate, and
had similar retrogressive and geratologous characters.

The progressive stage with divergent sides and broad abdomen, which
appeared in the young of Ast. ob/uswm and was found in some adults, was
suppressed, and was replaced by a modified quadragonal form in Ast. Turnert.
This in turn was replaced by the tendency to accelerate the development
of the trigonal convergent-sided whorl and its correlative retrogressive charac-
ters, the untuberculated pilx, low broad keel, and shallow channels, in Ast. Brook,
anpendens, and denotatum. The geratologous trigonal form appeared at an earlier
age in each successive species, until at last in As¢. Collenoti+ it took possession of
the earliest nealogic stages.

The retrogression of form in the series of species may often be compared
with parallel pathological series of individuals, which may be made within a
single species, _ Ast. stel/are® had dwarfed forms, much smaller than most of the
healthy adult specimens of its own species. These last, though so much larger,
ordinarily showed no signs of old age, while the dwarfs were completely changed
by senile metamorphoses. Much smaller but similarly dwarfed specimens oc-
curred in Ast, acceleratum, with even more compressed and prematurely aged
whorls. A remarkable series of these dwarfs, from which the two figures
referred to in the notes were drawn, is to be found in the Museum of Stutt-
gardt. The smallest of these completely geratologous specimens is not over
half the size of the largest, which itself is not of average size, as stated above.
The comparison of these dwarfs with the more involute varieties of Ast. Brooki
and the adult of Ast. Collenoti shows that they cannot have been connected by
direct inheritance. They were evolved independently of these geratologous
forms, and I am not calling upon the imagination to fill any blanks when I
speak of them as homoplastic morphological equivalents of As?. impendens and
Ast. Collenoti. It can hardly be doubted that the geratologous forms, when
found as dwarfed varieties within a species, are the products of the unfavorable
action of the surroundings, or, in other words, that they are more or less dis-
eased individuals. Their close parallelism in every respect with As?. Brooft,
impendens, and Collenoti shows that we can attribute with great probability the
origin of all such forms to similar pathological causes.

With regard to the agassiceran series, it may be remarked that the quad-

1 Plex. ig, 10-1; pl, x fgs 10; a Pls. tig, 1, 2. e Pl x. fig. 3:

78 GENESIS OF THE ARIETIDA.

ragonal form, or rather an immature representation of it, occasionally occurred
in some adult individuals of Agas. levigatum, in which the sides were flatter
than usual. In Agas. striaries the quadragonal form and the siphonal line or
keel were more decidedly expressed, as well as the tendency to elevate the abdo-
men. In Agas. Sciyronianum after the earlier nealogic stages were passed which
closely resembled the full grown of striaries, with the exception of the thicker
pilz and somewhat deeper umbilicus, the adult showed a quadragonal whorl
with a keeled abdomen and tuberculated pila. The old age had a smooth trigo-
nal whorl. In Agas. Scipionis,’ which is a naturally distinct form, the extreme
varieties had more involute whorls, smooth pile, and became trigonal and
smooth at an early stage.

Thus, at all stages of growth and decline, the correspondence or parallelism
between the individual and the morphogeny of the series is complete.

In the second subseries of Oxynoticeras we have found that there was one
species, Oxyn. Lotharingum, in which the whorl during the last senile stage became
completely rounded on the abdomen. ‘The sides became gibbous and narrower,
thus showing a slight tendency to revert to the primitive form of the less dis-
coidal Ayas. striaries and Psil. planorbe. These similarities were also greatly in-
creased by the appearance of senile folds similar to the primitive pilations of this
species and Psiloceras. The adults of the species of this subseries were also gera-
tologous, in so far as the forms were not only much compressed and trigonal, but
also smooth. The degeneration and the total loss of the hollow keel also oc-
curred in this oldest stage. We should not be at all surprised if species should
be found, and identified as belonging to this series, in which the hollow keel
was either not present at any stage, or was only slightly indicated during the
nealogic stages. hese adults would then correspond to the geratologous stage
of Oxyn. Lotharingum, in the same way that Ast. Collenoti corresponded to the
old of the normal forms of Ast. obtusum and _stellare.

If a tendency to the inheritance of retrogressive characters be granted,
and certainly their occurrence at earlier stages in successive species makes

this view seem highly probable, then the same law of replacement which pro- -

duced progression would now act upon successive organisms so as to produce
retrogression. The observed phenomena indicate the direct replacement. of
the characters of progressive ancestors by degenerate characters, which were
first observable in the old age of these ancestors themselves. If there had
been in most cases simply a mass of degenerate forms, without any defina-
ble evidences of successive gradations, as in the famous instance of the Magnon
examples of distorted Planorbide, it would be possible to say at once that
the parallelisms of the geratologous period, with retrogressive characters in
what we have called geratologous species of the same series, were purely homo-
plastic correspondences. On the contrary, the gradations are perfectly well
marked, as we have described them above and in the Introduction to this mono-
graph, and the replacement of progressive characters by the geratologous takes
place in strict accordance with the law of acceleration in heredity.

+ Summ, Pl. xi. fig. 8:

'
{
|
|

A poco

ai wt iiss

CATAGENESIS 79

We can make our meaning plainer by comparing this cycle to an imaginary
cycle in the history of architecture. The buildings of primitive times would
necessarily be substantial, plain, and suitable to the limited wants of the people ;
then, as wealth increased, the architects would respond with showy structures,
having more ornamentation, and more complicated interiors. We will suppose
that they had begun to place most of their ornamentation in and upon the central
parts of the modern buildings, and, out of deference to inherited canons of taste,
had always, even in the most florid acme of their progress, adhered to this law,
leaving foundations primitive in style and uppermost portions always unadorned.
As time progressed, these structures would assume vast proportions, and would be
built in ever increasing numbers, until at last the nation, having outgrown its
strength, would begin to decline. The vast buildings would have to be aban-
doned, and smaller habitations would arise, in answer to the requirements of a
poorer population. The architects, faithful to their inherited canons, but forced
into simplicity, would gradually follow the decline, and record it in the structures
of the decadence. They would effect this, we will suppose, by reducing the
ornamentation from above downwards, thus gradually doing away with the cen-
tral band of ornamentation, and also by actually lessening the height and other-
wise contracting the bulk of the buildings. Primitive simplicity would thus be
restored, but strong traces would still be left in the style and construction of the
buildings of their having beea adapted, by a process of reduction, from a pre-
viously existing period of greater size and complexity in structure. It would
be possible to read in the style of the decadence, that all the buildings had
come from primitive forms through the medium of a progressive period, during
which the central stories had undergone the greatest modifications. This would
be traceable in many surviving peculiarities of the modes of laying the courses of
stone, the cutting and more elegant shaping of the interiors, etc. It would, how-
ever, be equally plain that the architecture of the upper stories had always been
more or less degenerate, and also that their degenerate forms had replaced the
progressive ornamentation and forms of the central parts of buildings during the
decadence of the nation.

This would quite accurately represent the reversion of the forms we have
been tracing, so far as the purely retrogressive series were concerned. We
can understand their structural degeneration and their positions as the latest
evolved forms of each series upon the same grounds, since they would neces-
sarily stand at the termini of the series. Their degenerate characters could not
be said, perhaps, to have been inheritable, any more than the architecture of the
buildings alluded to above, but a tendency to degeneration caused by the un-
favorable surroundings would have to be assumed. Lach generation in succes-
sion, acted upon by this tendency, like the successive buildings of the decadence,
would arrive earlier at a stage when senile characters would replace the progres-
sive characters of the adult period. The geratologous characters are, however,
in greater or less degree, reversions due to the loss of the progressive characters
of the adult; and this is equally true when the characters of geratologous species
are compared with those of the simple, generalized radical species from which

80 GENESIS OF THE ARIETID.

the group originated. That these reversions are the remnants of the earliest ac-
quired structures and physiological powers seems perfectly plain, in view of the
well known case of the return of childish structural peculiarities and memories in
man after his adult peculiarities and powers have been exhausted.

The peculiarities of series which, like Oxynoticeras, presented certain highly
progressive or novel characters in combination with retrogressive characters,
have been sufficiently described in these pages. It only remains to add, that
such types are not uncommon in the different families of the Ammonoids and
Nautiloids, and therefore they must not be considered as unique.’

DIFFERENTIAL CHARACTERISTICS.

The differential characteristics have already received a considerable share of
attention, but it still remains to review them in each series. The diagnosis
of each genus is necessarily deceptive, in so far as it gives false views of the
invariability of the differentials.

The psiloceran series presented an altogether peculiar helmet-shaped whorl,
with more decided congeners in the Trias than in the Lias. The involution
increased in successive species, and in correlation with this tendency the complhi-
cation of the sutures also became greater,

The marked differentials of Weehneroceras, which are transitional from the
plicated forms of Psiloceras to the series of Schlotheimia, the retention of
the psiloceran form and sutures, the geniculess pile, and the nascent channel
on the abdomen are so obvious, that they need only be mentioned and atten-
tion again be drawn to the very remarkable fact, that, as in Psiloceras, this
series departed from the discoidal radical, and exhibited increase of involution
in successive species.

Starting from Psil. planorbe, var. plicatum, as the radical discoidal progenitor of
the remainder of the Plicatus Stock of the Arietida, we find that the compressed
helmet-shaped whorl was exchanged in Cal. Johnston’ for a more gibbous rounded
whorl, but the discoidal character of the shell was maintained, and the pile did
not have genicule or tubercles except in the highest species. There was also a
tendency in Cul. Johnston’ towards a complication of the margins of the sutures
through the deepening of the lobes and saddles, which was especially noticeable
in Cul. nodolianun. This increase of complication took place especially in the
marginal lobes, and there is a backward trend of the auxiliary lobes and saddles,
which causes a close likeness between the tendency of the progression in this
genus and that of the involute forms of Psiloceras. In Caloceras, however, it

1 We can mention as similar cases the following: Subclymenia with its ventral lobe and ventral siphon,
a true Nautiloid of the Trigonoceratide; Pteronautilus among the Gonioceratide with its winged aperture;
Centroceras among the Hercoceratide with a deep V-shaped ventral lobe. Among Ammonoids there are
the genera Pinnacites and Celmceras with remarkable sutures among Nautilinide ; the Gonioclymenide
with ventral lobes instead of continuous saddles in the Clymenine; Beloceras with its extraordinary sutures,
and Medlicottia with its remarkable ventral lobe and first pair of saddles among the Prolecanitide ; and a

host of others.

|
|
|
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DIFFERENTIAL CHARACTERISTICS. 81

took place independently of increase in the breadth of the whorl by growth, or
of increase in the involution of the successive species.

The radical species of the laqueum subseries showed a completely arietian
form of whorl. This appears in Cad. daqueum as quadragonal in section, with a
keel, faint channels, and straight pile, tuberculated in one variety. This form
was perpetuated in Cui. carusense of the Upper Bucklandi bed; the keel and ribs
were, however, somewhat more highly developed in one variety of Cad. raricos-
tatum. The deep narrow abdominal lobe, also a peculiar arietian characteristic,
appeared in Cul. carusense, and was perpetuated in raricostatum; it was repro-
duced at a very early age in the last species, and in Cal. Deffnert. The peculiar-
ities of the straight or curved, fold-like, and crowded pile are differentials of
importance, which correlate with the other immature transitional characteristics
of this series. The series described in the chapter on Descriptions of Genera
and Species discovered in the Northeastern Alps shows that highly compressed
forms with acute abdomens occurred also in this genus. Cal. Custagnolai had
a tendency towards increase of involution, though this shell, and even the
extreme form abnormilobatum, must still be classed as discoidal.

In the radical species of Vermiceras, Ver. spiratissimum, the whorl became
quadragonal with flattened sides and abdomen, channels, and pile with arietian
genicule. These characteristics were maintained throughout the series, be-
coming more intense in Ver, Conybeari, and inherited at a very early nealogic
stage in Ver. ophioides. The shells remained discoidal, however, as in Caloceras,
even in the largest specimens. Looking back, we see that the radical species,
Cal. Johnstoni and laqueum, and Ver. spiralissimum, formed a series of proximate
radicals, in which there was a regular gradation in the intensity of expression of
the different characters after they were once introduced, culminating in the
quadragonal form and arietian sutures of spiratissimum. We could, therefore,
with perfect propriety associate these three forms in a distinct series, and they
would then be related by gradations parallel with those occurring in either Calo-
ceras or Vermiceras, though composed solely of radical species. This is possible
because of the discoidal forms of the species of the vermiceran branch of the
Plicatus Stock, all of which have numerous whorls, and retain the very long living
chambers, at least one volution in length, of the Psiloceran Stock.

The differentials of the Levis Stock had a more abrupt beginning, the transi-
tions from Psi]. planorbe to the first form, Arn. miserabile, or the lower varieties
of Arn. semicostatum, having been less complete, and the forms separated by a
certain interval of time. There was also a much quicker transition from the
helmet-shaped whorl to the quadragonal. This took place in the first species of
the first series, and this radical, whether the one or the other of the two men-
tioned, is keeled in adults. In Arn. semicostalum, also, the pile assumed in most
varieties the peculiar straight, trenchant aspect, and the prominent and square
geniculx, which are characteristic of this genus. In Arn. miserabile and semicos-
datum the keelless, smooth form of Ps?l. planorbe, var. deve, was retained so long in
the growth of some individuals that it became characteristic of some varieties, and

in other species of this series, though less important, it is always found as a
ll

.

,

82 GENESIS OF THE ARIETID™.

marked characteristic of the umbilicus. The sutures are also peculiar in the
simplicity of their marginal outlines and proportions, and these peculiarities
remain constant.

In the adult and young of some varieties of the radical species of the coroni-
ceran series, Qor. kridion, a form appeared having strongly divergent sides, lyre-
shaped tuberculated pila, sutures with deep abdominal lobes and prominent
inferior lateral saddles, while in the young of other varieties there was a nearer
approximation to the young of Arnioceras. In all the succeeding species of the
series except Cor. Sauzeanum, a direct descendant of kridion, this divergent-sided,
broad-abdomened whorl was found at an early nealogic stage, having the same
lyre-shaped pile, deep channels, and arietian sutures,

On looking back, we see that Arn. muiserabile, semicostatum, kridioides, and Cor.
kridion, may be considered as a series in which kridion was a terminal species with
an accelerated development in some varieties, and that from this last highly
specialized form arose, as we have stated above, the species of the highly pro-
gressive coroniceran series, the typical acmic series of the Arietidse. The arie-
tian differentials, the long abdominal lobe and prominent inferior lateral saddles,
and the combination of these with the quadragonal whorl, highly developed
keel, channels, and geniculated and tuberculated pil, were barely indicated in
the caloceran series, and appeared in perfection only in the higher species of
Vermiceras. Although they were generated with great rapidity in the arnioce-
ran series, yet they were present in full perfection and were comparatively
constant only in the species of the coroniceran series, which, as we have said,
were directly derived from Cor. kridion, a species in whose adults these characters
first appeared in their final arietian shape and proportions.

The remaining series, which can be properly called the geratologous genera
of the Levis Stock, form a distinct group composed of a central series and three
lateral series, offshoots from the common radicals, Agas. levigatum and striaries.
The necessary mode of arrangement places Asteroceras on the left, Agassiceras
in the centre, and Oxynoticeras' on the right. The structural characters: also
agree with such an arrangement. No progressive linear series can be formed
out of the radical species of these series, as in the genera mentioned above the
arrangement is necessarily radiatory like the spokes of a fan. The differentials
of the adult of the radical species Agas. devigatum were quite constant in the
species ; we refer to the discoidal smooth whorls and fold-like pile, the simple
but arietian sutures with their deep abdominal lobe and prominent inferior lateral
saddles. The shell also had fewer whorls and shorter living chambers than the
adult of Psiloceras planorbe. In Agas. striaries there is close similarity to daviga-
tum, but very distinct strie and a larger size. In Agas. Scipionianum, the prominent
keel, channelless abdomen, pila, and tubercles were abruptly introduced, and
were the principal differential characteristics which distinguished the series from
all others in the Arietidas. This abrupt introduction indicates the former exist-
ence of intermediate forms which remain to be discovered.

It may be that a true hollow keel may have appeared in Scipionianum, as is

1 Summ. PI. xiii. and xiv.

DIFFERENTIAL CHARACTERISTICS. 83

described by Quenstedt, though we failed in getting positive evidence of any-
thing more than a large solid keel. This, though distinct from the usual arietian
structure of this part, had not the black layer above the siphon which dis-
tinguishes the typical hollow keel of some species in Oxynoticeras.

In the well known species, Ast. obfuswm, the radical of the asteroceran series,
the keel was broad and low with shallow channels, and the pile were fold-like
with either small tubercles or none, and the sutures in adults were like those
of Coroniceras. The changes in course of growth from the divergent-sided to
the convergent-sided whorl were rapid in some varieties, though in others the
broad-abdomened and gibbous-sided whorl was retained even in adults: In Tur-
neri, keel, deep channels, and quadragonal whorls were correlated with peculiarly
flattened and broad sides. These species showed a tendency to specialization par-
allel with those of Coroniceras; nevertheless, in varieties of Turneri, and in the
succeeding forms Brook and Collenoli, the differentials, with the exception of the
keel and sutures, tended to become extinct in consequence of the prepotent
influence of heredity in the transmission of geratologous characters.

Parallel phenomena were also observed, as stated above, in individuals of
preceding series during old age, when the adult differentials disappeared, and also
in the adult stages of certain geratologous species of the progressive Coroniceran
series, Cor. corbiculatum, Gmuendense, and trigonatum, in which the quadragonal
form, tubercles, etc. were similarly affected.

In Oxyn. oxynotum, the differentials which enabled us to separate this from
Ast. impendens and Collenoti were the hollow keel and the sutures. The hollow
keel appeared, as has been shown, in Ozyn. oxynotum, but it was filled with layers
of shell, though in other species it was really hollow, and appeared during the
nealogic stages. The increase of involution was correlative with the steadily
increasing breadth and flatness of the sides, and an intensified trigonal outline.
Oxyn. Lymense* was more involute, more acute, and smoother even than ozynotum.
The differentials of the Greenoughi subseries were less important characters.
They consisted of a stouter form of whorl, which was more like that of Agas.
Scipiomanum, and fold-like pile. These are less pronounced in the higher
species, Oxyn. Guibali and Lotharingum, in consequence of the prepotency of
the geratologous tendencies shown in the more compressed, more inyolute, and
smoother whorls.

The genera of the Levis Stock had, as a rule, shorter living chambers, usually
less than one volution in length, and differed in this respect from the genera of
the vermiceran branch of the Plicatus Stock.

The important fact should be noted here, ¢hat in all individuals and series the
sutures were the last to yield to degeneration, and the characteristics of these are considered
by most authors as the pre-eminent differentials of the Arictide.

In estimating certain characters as differentials, we mean only those which
can be artificially separated and contrasted in different series of the same family,
and which may be therefore peculiar to some one series or genus. When amore
specialized series is contrasted with an ancestral radical species or series, then

1 Summ. PI. xiii. fig. 2. @ Simin, Pl. xii. fis, 12.

84 GENESIS OF THE ARIETIDA.

the equivalent or parallel characters are often differentials. Thus, the keel was
varietal in the lower species of Caloceras as compared with Psiloceras, and
became a differential in the higher forms. ‘The same held good for the quad-
ragonal form of Vermiceras, and its arietian sutures. A very instructive com-
parison may be made between the cretaceous angulatus-like forms of Hoplites,
and their approximately exact morphological equivalents in Schlotheimia, and
yet no one well acquainted with their development and genesis would hesitate
to use the channelled abdomen, pile, and form in both genera as true differen-
tials. These characteristics do not indicate affinity between these cretaceous
forms and Schlotheimia.

Vaeck, in his article upon the hollow keel of the Falciferi,! makes somewhat
similar statements, and gives details showing the presence or absence of this
peculiarity in different species of Harpoceras. Though not prepared to agree that
these forms really belong to the same genus, it has been evident to us for some
time that the hollowness of the keel was a characteristic which was homoplastic
in several distinct series, and it is not a mark of genetic affinity with Oxynoticeras,
unless accompanied by other characteristics showing that the descent of the
species possessing it was probably traceable to Oxynoticeras. Unless the nealogic
stages show traces of this ancestry, it is not in itself a differential characteristic
sufficient to bind the forms possessing it into the same genus.

The development of the keel, channels, and pile in Arnioceras shows that
they were new modifications in this series, as they were also in Caloceras. The
keel, after its appearance in varieties of Arn. miserabile, became of specific value in
semicostalum, and remained thereafter constant. The straight pile and peculiar
genicule were also first of varietal value in miserabile, and then approached spe-
cific importance in semicostatum, and became constant in other species. The
channels were variable in all the species in which they appeared, except one of
the most highly specialized, Arn. ceras. We have not, however, seen many spe-
cimens of this species, and it is not unlikely that this form may, upon further
research, prove to be as variable as the more generalized species.

1 Bemerk. u. d. héhlen Kiel d. Falcif., Jarhb. geol. Reichs., XXXVIL., 1888, p. 311.

i Siete

i

REMARKS. 85

Ly:

GEOLOGICAL AND FAUNAL RELATIONS.

REMARKS.

HE point of view in this chapter naturally rests upon the assumed existence

of a persistent series of discoidal shells which formed a continuous radical

stock for all the Ammonoidea, beginning in the Silurian and having their last

representative in Psiloceras of the Planorbis bed. This, as we have said above,

was closely allied to Gymnites of the Trias, and enables us to connect all the

Ammonitine of the Jura directly with the more ancient primary radicals of

the central trunk of the genealogical tree. The chronological distribution of this

trunk of forms must be actually represented by more or less broken lines, until

all the gaps now existing between the different systems or periods in the earth’s
history have been filled by the progress of discovery.

The surviving genus of the trunk stock, Psioceras, consists of a series of spe-
cies which we have called the Radical Stock of the Arietidse, which became in
the Lower Lias the generator of new series of peculiar modifications, spreading
out from Psi. caliphyllum or planorbe like the spokes of a fan, each genetic radius
being composed of a separate series of modifications or species. We have given
this classification above, and shown that the chronological distribution of the
species in each series is in accord with their positions ‘in the series; it now
remains to apply the same classification to the solution of the problems of choro-
logical distribution,

There are many more or less complete lists and monographs of local faunas
in the province of Central Europe, and extensive collections, which afford a solid
basis for comparison. The preliminary work of Prof. Jules Marcou,' in synchro-
nizing the minuter subdivisions of the Jura in Central Europe, was completed
by the more extensive application of the same principles by Oppel,” who visited,
studied, and synchronized the faunas of the different localities, and identified the
same beds in a large part of this province. The illustrated publications of Hauer,’
Neumayr,' Wiihner,> Geyer,’ and Herbich,’ have also thrown a strong light upon
the peculiarities of the faunas of the eastern part of Europe, particularly the
basin of the Northeastern Alps. All of these researches, and many others not
mentioned, have made still further advances in the classification of the chrono-
logical relations of the minuter subdivisions or beds practicable.

1 Roches des Jura, pp. 23, 162, 173, et seq.

2 Die Jura-Format. Eng. Frankr. u. d. siidwestl. Deutschl. Wiirtt. Jahresb., XII. - XIV., 1856.
3 Die Cephal. a. d. Lias d. nordostl. Alpen, Denksch. Akad. d. Wissensch., Wien, XI.

4 See note 2, page 86. 5 Mojsis. et Neum., Beitr., II. - VI.

6 Ceph. heirl. Schich, Abh. k. k. geol. Reichsans., XII.

7 Das Széklerland, Mitt. Jahrb. d. k. ungar. Anst., V., Pt. IT.

86 GENESIS OF THE ARIETIDA.

The principles of geographic distribution first announced by Marcou* have
been carried further by Neumayr,? who has defined the homozoic bands of life
in the faunas of what he has denominated the Mediterranean, Central European,
and Russian provinces.

Neumayr, in his article “Ueber climatische Zonen der Jura und Kreide-
zeit,”® describes the boundary between the Mediterranean and the Central Euro-
pean provinces. This line, as far as traced by him, begins at the east between
the Donetz and the Crimea, at about 47° north latitude, and runs thence to the
easterly end of the Carpathians; thence, north-northwest to the neighborhood of
Krakau; thence, southwest towards Vienna, and south of Briinn ; thence, west-
erly to the neighborhood of Lake Constance ; thence, west-southwest, and later
southwest through southeastern France; thence, across the Gulf of Lyons to
Spain, and across that country and Portugal to between 38° and 39° north lati-
tude on the Atlantic. This author regards the Mediterranean province south
of this line, and the Central European province north of it, as respectively parts
of two homozoic bands, which encircled the earth during the jurassic period.

The Central European province was defined by Neumayr, in a general way,
as including the British Islands, France, Germany, Bohemia, Moravia, and Poland,
north of the line described above, and perhaps the Dobrudscha region. The
Jura north of these countries was included in his Russian province, which con-
tained Central Russia, Petschora Land, Spitzbergen, Greenland, and perhaps
Vancouver's Island in North America. Neumayr quotes the works of various
authors upon the fossils found in South America, and concludes that the Jura in
Bolivia, Chili, the Argentine Republic, Columbia, and in Central America is
probably Mediterranean. He thinks also that the few fossils found in the United
states indicate the presence of a Central European fauna.

Waagen, in his “ Fauna of Kutch,” shows that India is a distinct basin, con-
taining forms of the Upper Jura found in the provinces of the Mediterranean
and Central Europe, besides numerous peculiar species. Steinmann is of the
same opinion with regard to the fauna of the Upper Jura which is found near
Caracoles in Bolivia.

We have examined a number of the latter collected by Alexander Agassiz
at this locality, also several species collected by him at the pass of Tilibichi in
Peru, as well as those mentioned in the chapter “ Descriptions of Genera and
Species ” of this work, and have read Gottsche’s “ Paleontology of the Argentine
Republic.” These and other sources of information show, we think, the same
history as in India; namely, that this region may be advantageously separated
as the South American province on account of the number of peculiar species it
contains. There are, over and above these, also a number of forms identical with
those of Central Europe and the Mediterranean. We have also seen the fossils
of the Upper Jura, found in California, through the kindness of Prof. Joseph

1 Roches des Jura, pp. 74-91, 230, ef seq.

2 Ueber Juraprov. Verh. k. k. geol. Reichsans., 1871, p. 54; Ueber unverm. auftret. Cephal., Jahrb.
geol. Reichsans., XXVIII., 1878; and Jurastud., Ibid., I., 1871, p. 524.

3 Denksch. Akad. Wien, 1883, XLVIL, and also Geog. Verbreit. d. Jurafor., Ibid., L., 1885.

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REMARKS. . 87

Leconte, and have collected some forms in California and other localities in the
United States. There are also a few species in the collections at San Francisco,
but these and the fossils collected at Vancouver’s Island, and described by Mr.
Whiteaves of the Canadian Survey, which we have also seen at Ottawa, show a
mixture of the species of the European province besides a number of peculiar
forms. Though not disposed to give any final opinion at present, the facts jus-
tify the suggestion that the North American assemblage of species has a distinct
facies of its own, and ought to be separated at least provisionally from the South
American and all European faunas as the province of North America.

The collections so far made in the Jura show that there is a prevalence of
the Arietids in the Lower Lias, and of the species of Perisphinctes in the Upper
Jura of the South American province, whereas these are less abundant in North
America. Whiteaves also shows a mixture of the species of the Cretaceous with
those of the Jura at Vancouver's Island, which, together with the peculiar
species found there, suggests a distinct basin for that locality as compared with
the Jura farther to the south and east in the United States. The fossils so far
found in the district of Atacamas, and at localities in the Argentine Republic,
show that a provisional separation should be made between this region and that
of northern Peru, and that two basins at least, if not more, exist in the Jura of
the South American province.

Both the physical features of the distribution of the deposits and the faunas
appear, therefore, to make it doubtful whether the terms Mediterranean, Cen-
tral Europe, and Russia can be assumed as appropriate names for the homozoic
bands of the jurassic period in America. It would be preferable to adopt for
these bands the nomenclature of Marcou. Thus, the Bande! Homozoique Cen-
trale of Marcou would become the Tropical Homozoic Band; the Bande Homo-
zoique Neutrale du Nord of Marcou would become the Temperate Homozoic
Band; and the Bande Homozoique Polaire du Nord of Marcou would become the
Polar Homozoic Band. These bands could then be subdivided into provinces
and basins according to the faunas, and the real facts of the distribution of
forms more clearly shown than by using the names of European regions for
that purpose.

Waagen, in his article “ Ueber die Zone des Amm. Sowerbyi,” has traced in a
general way, following out simply the physical features of the distribution of the
Jura, the following basins: I. South German Basin, consisting of Suabia, Fran-
conia in Bohemia, and southeastern Baden “und des Randen.” II. Helvetic
Basin, including Switzerland, departments of Doubs, Jura, and Ain, also Rhone,
Saone et Loire, Cote d’Or, Haute Sadne, Haut Rhin, and Bas Rhin, and the neigh-
boring deposits in the south of Baden. III. Mediterranean Basin, including the
departments of Lozére, Aveyron, Hérault, Gard, Ardéche, Dréme, Basses Alpes,
Var, and Bouches du Rhone, and suggests an Italian basin for the Southern Alps.
IV. Pyrenean Basin, including the departments of Lot, Charente, Charente
Inférieure, and perhaps Deux Sévres. V. Parisian Basin, including the depart-

1 The use of the word zone instead of band is likely to lead to confusion, on account of its employment
in geology for the synchronous faunas of the same beds, and we think it ought to be avoided.

88 . GENESIS OF THE ARIETIDA.

ments to the north, to which Waagen adds Dorsetshire and Wiltshire in southern
England. VI. North English Basin, from Gloucestershire to Yorkshire inclusive.
VII. North German Basin, including Hanover, Brunswick, and the neighbor-
hood of Magdeburg.

We have not needed to use these divisions precisely as laid down by Waagen,
but it is interesting to remark that they accord more or less completely with the
observations on the faunas here recorded. Our principal interest has been, of
course, in the central portion of each basin, and not in the more deficient records
of outlying localities. The South German basin is as it has been given by
Waagen. His Helvetic basin appears to be a natural division, with the exception
of the departments of Saone et Loire, the Cote d’Or, and the Rhone. The Cote
d@’Or has appeared to us to be the centre of a different basin, which extended in-
definitely through the departments to the westward, and also to the south until
it met the fauna in the valley of the Rhone described by Dumortier. Whether
such closely contiguous faunas as that of this valley and the Cote d’Or ought to
be designated by distinct names we cannot pretend to decide, but that they differ
materially from the point of view of the evolution of their faunas seems to us
highly probable.

The faunas of northeastern France and Luxemburg, though perhaps in a dis-
tinct basin from those of Westphalia, Hanover, etc., which are properly included
in the North German Basin, are all similar in so far as they contain similar resid-
ual faunas. The basin of the Rhone includes the departments mentioned as in
the Mediterranean basin by Waagen, with the exclusion of the southeastern part
of the department of Var, which, as shown by Dieulefait, belongs to the Italian
basin. We have not been able to study any collections from Wiltshire, but the
Dorsetshire fossils of the Lower Lias, though certainly presenting a very distinct
facies and association of forms from those of Waagen’s North English basin, have
not seemed to require separation into a different basin. The fossils do not resem-
ble those of any other fauna so closely as they do that of the rocks in the rest
of England to the northeast, and, though it may be natural to make this separa-
tion, we have not required it for the immediate purposes of this memoir, and have
consequently spoken of the entire region as the English basin.

The Lias in territories to the north, like Scotland and Sweden, is deficient in
Ammonitine, and Judd! remarks upon the estuarine character of the deposits.
At Dompau and Dishult in northwestern Sweden a few poorly preserved fossils
show the presence of the bucklandian fauna. It is possible that these deposits
may have a yet undiscovered fauna of Ammonitine distinct from more southern
localities ; but so far as one can see, the forms of the Swedish basin are not dis-
tinct from those of the faunas of North Germany.

Neumayr has already traced in a general way the origin of the fauna of
Central Europe to the Mediterranean province, and we think a still further
advance has been made practicable by the methods of constructing genetic series
as advocated in this monograph, and the discovery of definable cycles in the
genesis of forms. Though our conclusions have been reached under the dis-

1 Quart. Journ. Geol. Soc. London, 1873, XXIX. p. 98.

PSILOCERAS AND CALOCERAS. 89

advantages attending residence at a distance from the fields of research, the
results have appeared to be sufficiently novel and suggestive to warrant publica-
tion. The results reached have been just what one might have anticipated from
a prwri reasoning upon the basis of the theory of evolution and monogenesis,
but nevertheless have not been admitted without much hesitation, because of the
author's natural feeling that so great exactitude in statement with regard to the
relative age of faunas on the same horizon should be distrusted.

If our data have led us correctly, there are some basins in the Lower Lias
which were capable of evolving new forms. These we have called Aldainic?
Basins, because they were centres of origin for new series, and their faunas were
what we have called Autochthonous Faunas. Other basins were apparently
incapable of giving origin to new forms, or at any rate received all, or almost
all, the forms which occupied their territory by migration from the aldainic basins.
These we have called Analdainic or Residual Basins, and their faunas Residual
or Analdainic Faunas. The beginning of the Arietidee was in the Northeast-
ern Alps, and this, being the first autochthonous fauna, was older than all others,
Thence South Germany or Suabia was peopled by chorological migration, and
then the basin of the Céte d'Or. Thus a Zone of Autochthones, or an aldainic
band of basins, was formed running to the westward. North and south of this
zone all faunas seem to have been residual faunas.

The fauna of the Lower Lias in the basin of the Northeastern Alps was, how-
ever, not in the zone of autochthones after the deposition of the Angulatus bed.
This zone, just before the deposition of the Lower Bucklandi bed, had become
narrowed in its easterly extension, and confined to the faunas of South Germany
and the Cote d’Or.

PsILOCERAS AND CALOCERAS.

The discovery by Giimbel? of Psi/. planorboides in the triassic strata of the
Bavarian Alps having been confirmed by Winkler’ and the shell and sutures
figured, there can be no doubt that it is a true Psiloceras. As a result of our
researches upon cycles of form, we can, however, unhesitatingly assume that this
shell is too involute to be considered a radical of the Arietidse. It indicates, if
estimated according to the usual history of these cycles, that undiscovered species
of discoidal Psiloceratites must have existed in the Trias, as necessary antece-
dent or ancestral forms. Two forms have also been cited by Neumayr, in his
“Unterster Lias,” * as Agoc. planorboides and Afgoc. form. nov. from the Késsener
shales. These are from Wallegg, and appear to be the same as those previously
cited by Stur® as Amm. cf. longipontinus and later described by Wiihner.’ Wiih-
ner considers them both to be specimens of his Psi. Rahana, and writes that

1 ’AdSaivo, to make to grow. 2 Ober. Abth. d. Keupers, p. 410.

8 Zeits. deutsch. geol. Gesellsch., 1861, XIII. p. 489, pl. ix. fig. 3. _Neumayr also, Unterster Lias,
Abhand. geol. Reichsans., VII., figures this species in the Planorbis bed.

4 Abh. geol. Reichsans., Wien, VII. p. 44.

5 Fuhrer z. d. Excursion. d. deutsch. geol. Gesellsch., Wien, 1877, p. 148.
® Verhand. geol. Reichsans., 1886, p. 175.

12

90 GENESIS OF THE ARIETID A.

they were probably taken from loose rock not in place, and may have come
from a dark gray limestone in the horizon of Psil. caliphyllum or megastoma.
They cannot, therefore, be considered forerunners of the psiloceran forms of
the Planorbis bed.

Neumayr’s and Wiihner’s researches, quoted below in Table VI. and in the
chapter on “ Descriptions of Species,’ show that a wonderfully rich fauna of
Psiloceratites and Caloceratites existed in the region of the Northeastern Alps ;
but, so far as we know, there is nowhere any statement of the appearance in time
of the discoidal radical Psi. caliphyllum or planorbe before Caloceras in that prov-
ince, as there is in South Germany. The aspect of the fauna is older than that
of South Germany ; but though composed of an assemblage of radical forms of
Psiloceras, they occur side by side with Cal. Johnston and Schilot. catenata (subangu-
lare of Wiihner), and are equivalent to the fauna of the Caloceras bed of South
Germany, but not to the lowest Planorbis bed. Suess and Mojsisovics, in their
table of strata in the mountains of the Osterhornes,' Northeastern Alps, describe
a very thick Planorbis horizon, and in the uppermost bed they enumerate Psil.
planorbe, supposed to be the English form ; also Psi. Hagenowi and Cal. Johnstoni,
no fossils having been found in lower beds. Here again it is probably the
Caloceras bed, and not the lowest Planorbis bed, which contained the fossils
described.

In South Germany Psiloceras planorbe, the radical species of the Arietide, is
prevalent, as may be seen in collections, and in the works of all the geological
writers on this region, especially Quenstedt. Quenstedt notes what he calls the
Laqueum layer, and speaks of caloceran forms as having made their first appear-
ance somewhat later in the Planorbis horizon than Planorbis itself, and in the
“ Ammoniten der Schwabischen Jura” describes and figures a specimen, Planorbis,
var. /eve, from the Bone-bed, which is placed by most writers in the Rheetic.

In the neighborhood of Salin and Besan;on, Prof. Jules Marcou has shown
that there is a deficiency in the Planorbis horizon, and lately Louis Rollier,?
following in his footsteps, has confirmed these observations. Professor Mar-
cou, however, at Boisset, near Salins, found a true Planorbis bed containing
the typical species. W. A. Ooster, in the “Catalogue des Cephalopodes des
Alpes Suisses,’* enumerates many species; but unluckily the beds are not de-
fined. It is, however, evident that the collections in Switzerland which he
examined, and the authors he quotes, did not give any data contradictory to
Waagen’s conclusions, which we give below.

Waagen, in his “ Der Jura Franken, Schwaben und der Schweiz,” says that
outside of Suabia, whether going northeast or southwest, one finds nowhere the
typical development of the Lower Lias as it exists in Suabia; and it is especially
the lowest bed which is apt to be nearly everywhere starved out. This remark
and the table given by Waagen are very important, and coincide with the
results reached in this chapter.

1 Gebirgesg. d. Osterh., Jahrb. geol. Reichsan., XVIII., 1868, p. 195.
2 Form. Jurass. Soc. d’Kmulat. Porrentruy, 1883, p. 105.
8 Denksch. schw. Gesellsch. Naturwissen., X VIII., 1861.

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PSILOCERAS AND CALOCERAS. 91

M. Collenot’ mentions Amm. Johnstoni, tortilis, laqueum, and Burgundie as oc-
curring in the Planorbis horizon. The collections at Semur show that Planorbis
was small, and evidently already losing ground, whereas the fine suites of calo-
ceran fossils indicate at least that this series had suffered no loss by migration
when compared with the fauna of South Germany. This collection is also
arranged to show a bed similar to the Laqueum layer of Quenstedt, called by
Collenot the “zone of Amm. Laasicus,” which contains only caloceran forms, and
also Psil. longipontinum. Cal. laqgueum is smaller, and more like the German form
when found in company with Liasicus.? A few dwarfed forms of Psi. planorbe,
var. deve, have been found together at Saulieu, and at Beauregard there is a bed
with large forms of Cal. Johnstom and tortile, accompanied by a larger form of Cal.
Jaqueum than is usual in South Germany, and a small Psvd. planorbe, var. leve. The
latter is in Boucault’s collection, Museum of Comparative Zodlogy, but not rep-
resented at the time of my visit in the collections at the Museum of Semur. The
researches of M. F. Cuvier* are important in this connection. He states that a
separable Planorbis bed was found by him on the section of the railway between
Arcy-sur-Cure and Guillon, and immediately above this a bed characterized by
the presence of Cal. Lvasicum. Again, on page 177, he speaks of finding at
Gravelles, near Saulieu, a bed containing Psil. planorbe and Cal. laqueum or Bur-
gundie, and this agrees with Collenot’s observations.

Dumortier* states that Psi/. planorbe occurs everywhere in the Planorbis bed
of the basin of the Rhone in company with Cal. Johnstoni, though not an abun-
dant fossil, and from a fragment in his possession infers that the former may in
some cases have reached the great diameter of 220 mm. Quenstedt describes and
figures a specimen of Psi/. planorbe, var. leve, from Provence,’ which he names Amm.
psilonotus provincialis, Martin® designates the Planorbis bed in the region of the
Cote d'Or as the “zone of Amm. Burgundie” (our Cal. laqueum). He considers
that the beds of “lumachelle,” the Planorbis horizon, show evidences of having
been deposited during a period of violent currents, ete. This is an important
fact, since it indicates the littoral character of the deposits.

Terquem,’ in the department of Moselle, writes that Ammonites are generally
rarer and more often broken than Nautili in the Lower Lias, and enumerates
only six species. Chapuis and Dewalque state ® that in Luxemburg the Planor-
bis zone is not fossiliferous.?

1 Description Géologique de l’ Auxois, p. 209.

2 The remarks of M. Collenot on page 164 are very instructive, and confirm the impressions received
from the collections at Semur.

8 Notice Géologique, etce., Bull. Soc. de Semur, ser. 2, No. 8, 1886, pp. 170, 176.

4 Etude Paléontologique du Bassin du Rhone, p. 28, pl. i.

5 Amm. Schwab. Jura, pl. i. fig. 19.

6 Pal. Strat. de l’Infra-Lias de la Céte d’Or, Mém. Soc. Géol. de France, VII.

7 Infra-Lias Luxem., etce., Dept. Moselle, Mém. Soc. Géol. France, V. See also, for similar opinions,
Collenot, Deser. Géol. de ’Aux., p. 162, and Dumortier, Etudes Pal. Bass. du Rhone, I. p. 20, II. p. 97.

8 Descr. Foss. Terr. Secon. de Luxembourg.

9 The late researches of Schumacher, Steinmann, and Van Werveke, Erlaut. z. Geol. Uebersichtsk. d.
Westl. Deutsch-Lothringen, show that the Planorbis bed containing Psil. planorbe, var. plicatus, is found in

the region explored by them, though it is absent in the French part of Lothringen, as stated by Bleicher,
Bull. Soc. Géol. de France, ser. 8, XII., 1884, p. 445. In Deutsch-Lothringen it is one meter in thickness.

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92 GENESIS OF THE ARIETID.

In North Germany, according to Schlénbach,' the Planorbis horizon is pres-
ent; but Psil. planorte is largely, if not entirely, replaced by Cal. Johnstoni, and he
designates this layer as the “zone of Amm. Johnstom.” Braun’ gives similar
results for his work in the localities of northwestern Germany; and Emerson,
in his essay “ Die Liasmulde von Markoldendorf,” did not find Psiloceras in that
basin, though Johnstow was abundant, and of large size. Romer,’ the first ob-
server in North Germany, states that the Lower Lias is less developed in that
region than in South Germany, and enumerates only a few species. Schliiter, in
his “Schichten des Teutoburger Waldes bei Altenkirchen,” shows that a thick
Planorbis bed occurs in this locality, and Psi. planorbe is abundant, while Cad.
Johnstoni, which he considers to be identical with planorbis, var. plicata, and Amm.
luqueolus, is much less frequent.t He also gives Amm. angulatus as appearing in
the upper part of the same bed. There is unfortunately no record of the exact
beds in which the fossils occurred, and it is not certain, therefore, whether we are
here dealing with the Caloceras bed or a true Planorbis bed. Quenstedt also
describes and figures a specimen of Psil. planorbe, var. leve, from Quedlinburg.?

The paleozodlogical and geological data, therefore, appear to sustain the
conclusion, that Psiloceras and Caloceras, as a rule, arrived later in North Ger-
many and Luxemburg, the Cote d’Or, and the Basin of the Rhone, than in
South Germany.

In England the aspect of the fauna has greater similarity with the Cote d’Or
and South Germany, than with the North German and Luxemburg basins. The
Planorbis zone is well developed, and in the Bristol Museum the South German
varieties of Psil. planorbe and the English forms from Cotham® are found side
by side. This was also the richest collection in caloceran species which we saw
in England, though it was still far behind that at Semur. Rev. J. E. Cross, in
his “ Geology of Northwestern Lincolnshire,” claims that no true Planorbis bed
occurs, but in place of this a bed containing Amm. angulatus and Johnston, which
is probably the Caloceras bed. Wright’s section at Uphill railroad cutting shows
the bed containing “ angulatus and fragments of Laasicus,” called by him the
“ Angulatus bed,’ and at Binton, Warwickshire, there is a transition bed con-
taining only Zvasicus, included by him in the Planorbis zone.” In his sections of
the Planorbis horizon Psd. planorbe occurs earlier than any species of Caloceras at
the Uphill railroad cutting; at Binton, Warwickshire ; Street, Somerset ; and at
Brockeridge and Defford Commons. No mention, however, of Psiloceras in any
earlier bed occurs, and its appearance must therefore have been later, as a rule,

1 Ueber Eisen. d. Mittl. Lias, etce., Zeits. d. geol. Gesell., 1868, p. 498; Paleontogr., XIII.; and Die
Hannoverische Jura, p. 17.

2 Der untere Jura in nordwestliche Deutschland, 1871.

8 Verstein. norddeutsch. ool. Geb.

4 Zeits. deutsch. geol. Gesellsch., 1866, XVIII. p. 40.

5 Amm. Schwab. Jura, pl. i. fig. 17.

6 Stoddart, in his “ Notes on the Lower Lias of Bristol,” Geol. Mag., V., 1868, p. 139, shows that Amm.
Johnstoni oceurs in the section he described earlier than true planorbis, if one can judge from the names he
gave to the beds, since no lists of fossils were added. ‘The section given certainly indicates the existence of
a Caloceras, rather than a true Planorbis bed.

7 Wright, Lias Amm., pp. 11, 20.

WAHNEROCERAS AND SCHLOTHEIMIA. 93

than in South Germany. Tate and Blake! discuss the conditions of the deposi-
tion, and arrive at the conclusion, that “it seems probable that no portion of the
liassic beds was formed in very deep water, but that even the shales partook of
the nature of submerged mud flats.”

Psil. Hagenowi occurs in the Northeastern Alps, North Germany, Bohemia, and
Switzerland ; and in all these places the true Psi. planorbe, var. leve, is scarce.
This form is a degraded modification of planorbe which may have arisen inde-
pendently in each locality, and it indicates that this species probably lived under
unfavorable conditions in these regions. Caloceras was, however, strongly rep-
resented in the same basins. It formed an unbroken procession, so far as Cal.
Johustom was concerned, from the Northeastern Alps to England.

The facts, with certain exceptions, of which we shall take note farther on,
appear to indicate that Psiloceras was autochthonous in the Northeastern Alps.
It probably appeared as a radical or chronologic migrant from the Trias, and
gave rise to Caloceras in the Lias. Thence both series may have spread by
chorological migration into the basins of South Germany, the Cote d’Or, Switzer-
land, North Germany, and England. During these migrations they met with
favorable conditions in some localities, and unfavorable conditions in others;
hence the inequalities of representation. In both series, however, it is obvious
that it was the discoidal species which settled in the new territories to the west
of the Mediterranean province. It thus becomes evident that the more highly
specialized and more involute species were probably not the progenitors of any
of the derivative series that subsequently arose, —an inference agreeing exactly
with all our conclusions with regard to the radical nature of discoidal, as com-
pared with involute forms.

W #HNEROCERAS AND SCHLOTHEIMIA.

The exceptionally rich fauna of the Angulatus (Megastoma) bed given by
Wiihner’ contains, besides the distinctive Weehneroceran series, Schlot. angulata,
and other forms of the same series, as well as many of the involute Psilo-
ceratites and keeled Caloceratites, mentioned above. This assemblage shows
undoubtedly that a region so richly populated must have been exceptionally
favorable for the evolution of Weehneroceras, and possibly also the autochtho-
nous home of Schlotheimia. The announcement by Neumayr*® of Waagen’s
discovery of a true Schlot. angulata in the Rheetic beds near Parthenkirchen
in the Mediterranean province, should be mentioned in this connection. Suess
and Mojsisovics show that the Angulatus zone is very slightly developed
in the Osterhornes mountains, but it contains Psi. longipontinum, Cal. laqueum,
Schlot. angulata and Moreana, besides a possible Cor. kridion, identified as similar
to that figured by Dumortier in France. This assemblage, therefore, contains
the most important of the species found in other regions in the Caloceras bed,
as well as in the true Angulatus bed above.

1 Yorkshire Lias, p. 215. 2 Unter Lias, loc. cit., IV., 1886, p. 199.
8 Jahrb. geol. Reichsans., 1878, XXVIII. p. 64, and Abh. geol. Reichsans., VII. p. 44.

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94 GENESIS OF THE ARIETIDA.

The radical ferm Schlot. eatenata appeared in the Planorbis horizon, according
to the collection at Semur, and in this fauna the successive forms of the schlo-
theimian series succeed one another without a break in their gradations. Quen-
stedt’s work on “ Die Ammoniten des Schwabischen Jura” shows that in South
Germany the series may be complete in numbers of forms, and even more re-
markable in the size of specimens, and the whole series except Boucaultianus
appeared before the termination of the Angulatus fauna. There is also a speci-
men referred doubtfully even to the “ gelbe Sandstein” of the Rheetic beds near
Tiibingen, thus carrying the possible origin as far back as in the Northeastern
Alps. If, as we have supposed, Wekhn. subangulare is found in South Germany,
the evidence becomes still stronger that this was the probable centre for the
chorological distribution of the group in Central Europe.

Schiot. angulata and catenata are very numerous in North Germany; but there
is a notable tendency to the production of smaller specimens in the collections
we have seen. Schliiter, in his “ Schichten des Teutoburger Waldes bei Alten-
becken,’’' states that Amm. angulalus, Moreanus, and Charmassei occur there, but
that the latter is never so large as in South Germany.

Terquem, in his “ Province de Luxembourg et de Hettange,” ? mentions Amm.
anguiatus as occurring in abundance, and of good size, but no species like Char-
masse or Leigneletii. Chapuis and Dewalque give figures of Schlot. angulata, which
show that the species is similar to cadenatus in having discoidal whorls and
the pile crossing the abdomen. This species is evidently similar to that from
Markoldendorf, described by Emerson. Seebach, in his “ Hannoverische Jura,”
declares that in North Germany there has so far been found only the Amm. angu-
latus (equal to depressus, catenatus, and Moreanus), and denies the existence of
Charmasset. Brauns, in his “ Untere Jura im nordwestlichen Deutschlands,” cites
both angulalus and Charmasset.

The whole series, including radical, discoidal, and involute species, appear to
have come into the Northeastern Alps basin first, and to have reached in this
locality their highest development in discoidal forms. Thence they seem to
have spread somewhat later in time into the Angulatus horizon of the South
German basin, and migrated still later to the Cote d’Or and England. In the
first two basins they reached their highest development in involute forms, —
a fact which strengthens the impression that the series must have originated in
the Mediterranean province, since the involute forms are the descendants of the
discoidal forms. That they arrived in the Cote d’Or later than in South Ger-
many is shown by Tables I. and II., in which we find Charmassei appearing in the
Lower Bucklandi zone instead of the Angulatus zone, and by the presence of
two new and more highly modified species, D’ Orbigniana and Boucaultiana, which
have not been found in South Germany by any collector up to the present day.
These views are further sustained by the fact that the English fauna possesses
only a slender representation of the group, all the species being rare, and occur-
ring at about the same time as in the Cote d’Or, except Boucaultiana, which is

1 Page 42. 2? Mém. de la Société Géol. de France, V.
3 Descrip. Foss. Terr. Secon. de Luxembourg.

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VERMICERAS. 95

found somewhat earlier in the Upper Bucklandi bed. Neither Schlot. D’ Orbigni-
ana, nor any of the similar modifications so well exhibited in the collections at
Semur and in the Boucault collection of the Museum of Comparative Zodlogy,
are represented in this fauna.

VERMICERAS.

Vermiceras is represented in the Northeastern Alps by Ver. Conybeari, figured
by Hauer, and Ver. Hierlatzicum, Geyer, a dwarfed species. Amm. spiratissimum,
Hauer, occurs in company with Conybeari in the Lower Bucklandi bed at Enzes-
feld; but this is probably a species of Caloceras, similar to Cad. carusense, of the
large variety which occurs in the Bucklandi horizon in South Germany.

Suess and Mojsisovics do not give any species of this genus as occurring in
the Osterhornes mountains, and this is also the case in several other localities
where the formations are sufficiently well developed to lead one to expect that
the genus would be represented if at all common in this province, Cad. prespira-
tissimum, in the Angulatus bed of the Kammerkahr Alps and Adneth, as given by
Wiihner,' is the only example of a transitional form. Nevertheless the great
development of caloceran species in the Mediterranean fauna shows that a com-
plete series of transitional forms probably occurred in that province.

Giimbel does not mention Vermiceras, in his “‘ Geognostische Beschreibung der
Bayerischen Alpen,” as having been found in the Kammerkahr Alps, unless
indeed his Amm. spiratissimum is a true vermiceran form, or similar to Wihner’s
species of prespiralissimum, nor did he find any species of this series in the gray
limestones at Gastiitter Grabens. Herbich, in his “Széklerland,”? gives figures
and descriptions of Avict. multicostatus, with both young and adult similar to
and probably the same as his Ariet. Conybeart, all having been found near Also
Rakos in the Besanyer mountains. The radical species Ver. spiratissimum made
its appearance in South Germany earlier than elsewhere, if we can regard, as
seems to us correct in every way, transitional forms like that on Summ. Pl. XI.
Fig. 22, though named as belonging to Cal. daqueum, as really closer to Vermi-
ceras than to Caloceras. The principal transitions must have taken place in the
Caloceras bed of this basin, instead of in the Angulatus bed, as in the Mediter-
ranean province.

’ The basins of South Germany and the Cote d’Or are about equivalent in
the number of transitional forms, and it is as easy to trace the gradations from
Caloceras to Ver. spiratissimum in one locality as in the other. The extraordinary
evolution of the series .in the Cdte d’Or indicates that it must have met with
its most favorable home on the bucklandian horizon in this basin. Even on the
Tuberculatus horizon several new varieties were evolved, some of which, however,
like debilitatus, Rey., must be considered as degradational, and consequently in-
dicate the decadence of the genus in this later fauna.

According to Dumortier’s figures and descriptions, this genus is represented

1 Mojsis. et Neum., Beitr., V. p. 53.
* Mittheil. Jahrb. d. k. ungar. Geol. Anstalt., V., Part II.

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96 GENESIS OF THE ARIETIDA.

by very few forms in the basin of the Rhone, and Ver. spiratissomum appeared first
in the Lower Bucklandi bed.

In England the number of varieties or forms is not equal to either of the
three faunas above mentioned, but the transitional forms are present. Wright, in
his “Lias Ammonites,” gives a section at Red Car, and Amm. Conybeart is cited as
occurring in the lowest stratum of the Bucklandi zone. With regard to the Eng-
lish fauna, one can see, in spite of the large size and the multitude of speci-
mens, that the small number of distinct species and the entire want of autoch-
thonous species, or varieties, indicate a purely residual fauna composed of un-
modified forms. This basin is north of the zone in which autochthones arose
during the Lower Lias, and the basin of the Rhone lies south of this zone, and
both are residual faunas. Ver. Conybeari is mentioned by several authors as
occurring in North Germany and in Luxemburg, but, so far as we have seen,
other forms of this genus have not been cited, and Vermiceras appears to have
had but slight development in these basins

The facts, so far as now known, are opposed to the inference that this series
originated in the Northeastern Alps. On the contrary, it seems more likely
that it began in the Caloceras bed of South Germany with a variety of Cal.
Jaqueum, and subsequently appeared as Ver. prespiratissimum in the fauna of the
Angulatus zone in the Mediterranean province. The series, however, did not,
either at this time or on any subsequent horizon in this province, meet with
very favorable conditions for the evolution of new forms. It must be remarked,
also, that the variety of Conybeari figured by Hauer and by Herbich has a whorl
quite distinct from that which occurs most commonly in Central Europe. It is
more like the degenerate variety of Conybeari, which is usually called Bonnard,
though apparently of smaller size.

ARNIOCERAS.

There are quite a number of forms described by various authors as having
been found in the Mediterranean province, but they have all been found in hori-
zons above the Lower Bucklandi bed. This may be seen by our Table VI,
and also in the fact that Suess and Mojsisovics found no species of this genus in
the Osterhornes mountains, the beds above the Bucklandi zone being unfossil-
iferous, and Paul states, in his article “ Die Nérdliche Arva,’? that only one
species of this series was found in the Lias, and this occurred in the beds above
the Bucklandi zone.

My notes on the collections at Stuttgardt and Tiibingen do not show so rich
a fauna as in the Cote d’Or, nor do Quenstedt’s publications indicate so full a
development of the series as in that basin. Thus, though the series began in
the Angulatus zone, as shown in Fraas’s collection, it did not reach its acme of
development in the South German basin. The evolution of Arnioceras in the
fauna of the Cote d’Or is exhibited in the Semur collection, and in Boucault’s col-
lection of the Museum of Comparative Zéology. The large number of forms in

1 Jahrb. geol. Reichsans., XVIII., 1868, p. 233.

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CORONICERAS. : 97

the bucklandian horizon, and their early appearance in the Angulatus zone of
Cote d’Or, show that this was their most favorable home. We have identified
the earliest occurring Semur specimen with Arn. falcaries, but it had some tran-
sitional characters allying it with Arn. miserabile and also with Arn. semicostatum.
Arnioceras did not appear at all in the Angulatus zone, but in the Bucklandi
zone of the Rhone basin, if Dumortier’s work can be considered as authoritative
upon this question. This fauna also possesses specimens of much larger size than
any found elsewhere, and the series is quite as fully, though perhaps not so
richly, represented as in the basin of the Cote d’Or.

In England there are certainly fewer species and forms than in South Ger-
many or the Cote dOr, and they appear to have been wholly migrants, not
possessing the numerous varieties ohgervable in South Germany and at Semur.

Only one, or at most two, species of Arnioceras, called either obdiquecostatus of
Zeiten, or geometricus after Oppel, appear to have been found in North Germany.
Making all due allowances for negative evidence, this appears to indicate a very
slight representation of the genus. Schliiter gives, however, a lengthy descrip-
tion and figures of Aim. obliquecostalus as occurring in a bed between the Angu-
latus and the Bucklandi zone in the Teutoburger Wald, and his description and
figure show that this species may be in reality divisible into several, — one simi-
lar to Arn. oblusiforme, one to miserubile or semicostatum, and perhaps another with
more marked keel and channels. The forms are confined wholly to this stratum,
which may belong either to the Angulatus or the Bucklandi bed. The Luxem-
burg fauna was equally poor.

This genus, therefore, certainly does not have the aspect, as far as is now
known, of having originated in or near the basin of the Northeastern Alps. The
evidence is rather in favor of its having arisen from small planorbis-like forms,
occurring first either in the Céte d’Or or in the South German basins. At. pres-
ent the evidence is not determinative, though somewhat in favor of the former
basin. The series subsequently migrated to the Mediterranean province, making
its first appearance there in the Upper Bucklandi zone.

CoRONICERAS.

In company with the first arnioceran species at Semur is a doubtful form of
Cor. kridion, and later in the Scipionis bed a true Cor. kridion is found together
with a representative of Cor. rotiforme. Cor. datum also occurs in company with

these, but is the radical of another subseries of this genus. Oor. kridion is cited |

by Suess and Mojsisovics from the Osterhornes mountains as occurring in the
Angulatus zone, and this is ‘not a difficult species to identify. The Coroniceran
forms as cited by the same authors in the Bucklandi zone are represented only
by Cor. brsuleatum. Hauer’s work,’ however, shows that this is probably only a
local peculiarity, though the fauna is not so rich as that of either South Germany,
France, or England.

Dumortier, in his “ Etudes Paléontologiques du Basin du Rhone,” gives Cor.

1 Nordostlichen Alpen, Denk. Akad. Wien, XT.
13

98 GENESIS OF THE ARIETIDA.

kridion as occurring in the Angulatus beds, and figures a specimen.’ According
to Fraas’s collection, Cor. kridion certainly appeared in South Germany in the
Angulatus bed at Méhringen, and Quenstedt declares it to be a rare form in the
Bucklandi zone. Coroniceran forms are so numerous in the Bucklandi zone of
South Germany and France, that it becomes difficult to determine whether they
were more fully evolved in the one or the other of these basins.

Wright’s tables and lists show that the English fauna was by no means so
rich in numbers of species and varieties as either the French or South German ;
and this result, notwithstanding the great size and multitude of specimens found
in the various localities of that basin, confirms our experience in the study of
collections while in England.

The works of North German paleontologists show less thinning out of the
forms of this series in that direction than in any of the preceding genera. The
names bisulcatus, multicostalus, and the like, occur frequently. This suggests that
in bucklandian times the species of the Arietidse had become hardier and more
able to survive in the unfavorable localities to the northward, or else the sur-
roundings themselves had changed and become more favorable. There is one
fact, however, favoring the former as the most probable conclusion. The speci-
mens are neither very abundant, nor are they so large, nor so generally dis-
tributed in North Germany as in South Germany.

The radical of the third subseries of Corniceras, Cor. Sauzeanum, did not appear
earlier than the Upper Bucklandi bed in any fauna, not excepting that of the
Mediterranean province Chapuis and Dewalque show that Cor. Sauzeanum per-
sisted in the Luxemburg region, and that Cor. bisuleatum and mullicostatum were
also present ; but the number of forms found there are certainly very limited.
Schlénbach mentions the usual fauna of the Buckiandi zone in Brunswick, but
the species are not so numerous as in South Germany, and no note is made of
their abundance. The absence of the Tuberculatus bed, or its unfossiliferous
character when present, is noted by Schlénbach, and this indicates a decrease in
number of forms as compared with other regions. Brauns in “ Hannoverische
Jura,” and Emerson in “ Liasmulde von Markoldendorf,’ show that the coroni-
ceran series is represented, but is not remarkable for the number of species, and
in most. localities, so far as we can learn, the species of this series are not
abundant. Shliiter cites Cor. rofiforme and Cor. Gmuendense as occurring in the
Bucklandi zone of the Teutoburger Wald, and his descriptions support these
results. He alludes to other forms than these species, but does not enumerate
them.

The poverty of the later beds of the Lower Lias in North Germany, and the
constant recurrence of unfossiliferous strata, are characteristics similar to those
of the basin of the Northeastern Alps, and these facts indicate that similar un-
favorable conditions obtained there.

Dumortier’s work enables us to see, also, that in the Rhone basin on the
southern side of the Cote d’Or the fauna thinned out. Thus, though Cor. kridion

1 Pl Sv ig. 3, 4.
2 See Mojsisovics’s mention of the zone of Amm. Sauzei, Gebirgsgr. d. Osterhornes, p. 199.

AGASSICERAS. 99

appeared in the Angulatus zone, the number of species on the bucklandian hori-
zon was evidently more limited than in South Germany, Semur, or England.

The coroniceran series, therefore, seems to have arisen on the same level in
the Mediterranean province, in the South German basin, and probably in the
Céte d’Or. The radicals of the subseries, so far as known, do not follow the same
law. Cor. datum has not yet been mentioned or described as occurring in any
other basin than the Cote d’Or. Cor. Sauzeanum occurs, however, in northwest-
ern Germany, according to Braun, and in the South German, Cote d’Or, and
English basins in the Upper Bucklandian bed, though in the basin of the Rhone
and Mediterranean province it is not recorded with certainty from any level
earlier than the Tuberculatus beds.

It is possible that Cor. kridion may have originated in the Northeastern Alps,
but Neumayr and Wiihner have not yet found this species in their researches
among the fossils of the Angulatus zone, and no good figure has been published.
The early occurrence and large number of varieties and species in the collections
at Stuttgardt and Semur, and the numerous transitional varieties, also show that
Cor. kridion found its most favorable home either in the South German or the
Cote d’Or basin. The earlier occurrence of the radical of the third subseries,
Cor. latum, at Semur, indicates the Céte d’Or to have been the centre of distri-
bution for the Bucklandi subseries. The occurrence of Cor. Sauzeanum on the
same level in South Germany, Cote d’Or, and England shows, together with the
number and variety of the forms subsequently evolved, that the centre of dis-
tribution of the Bisulcatus subseries lay in one or the other of these basins.

This conclusion accords with the origin and distribution of the parent series,
Arnioceras, and derives additional support from this fact. It is evident also,
from these facts, that the Mediterranean province must be regarded .as having
been peopled with migrants from the province of Central Europe, so far as relates
to the subseries of this genus, and this makes it more likely that the radical spe-
cies of the whole series, Cor. kridion, also arose in this province. So far as known
its appearance in the Angulatus horizon of the Northeastern Alps is not sup-
ported by the presence of transitional forms, nor by the presence of Arnioceras in
the same horizon. The species, if a real éridion, certainly must be provisionally
regarded as a chorologic migrant from the west.

AGASSICERAS.

Agas. levigatum appeared in the Angulatus zone of the Semur collection, and
was represented by numerous specimens in this fauna. It is also attributed to
this horizon in the basin of the Rhone by Dumortier, and is well figured by him.
In South Germany Agas. levigatum did not appear until the Upper Bucklandi
bed. In England and North Germany it appeared associated with planicosta
above the Bucklandi horizon. This radical species, therefore, according to our
present knowledge, was a migrant in all of these basins, derived probably from
the Cote d’Or or the Rhone basin.

1 Etudes Pal., pl. xviii. fig. 5, 6.

100 GENESIS OF THE ARIETIDA.

Neumayr! includes what we consider the young of the radical species of
Agassiceras in his genus Cymbites, and states that he has not found them in
the basin of the Northeastern Alps. Geyer, in his “Cephalopoden Hierlatz-
Schichten bei Hallstadt,’ figures and describes under the name of Cymbites a
characteristic young form of Agas. lavigatum. Hauer’s drawings of Amm. abnormus,
in his “Unsymmetrische Ammoniten der Hierlatz-Schichten,” illustrate typical
shells belonging to the compressed variety of the same species, one of them
exhibiting the peculiar aperture, and another the gibbous young in the interior.
The radical species of the series, therefore, appeared in the Northeastern Alps
not earlier than the Upper Bucklandi beds, as in other faunas more or less
remote from the Cote d’Or.

In the next subseries we find that Agas. Scipionanus and Seipionis are char-
acteristic fossils of the Lower Bucklandi bed in the Cote d'Or and Rhone basins,
but in South Germany and England they appeared later, together with Agas. stria-
ries in the Upper Bucklandi bed, and in North Germany on the same horizon. So
far as known, no species of this subseries has been found in the Northeastern Alps.

This series, therefore, has the aspect of having first appeared and met with
a favorable home in the Cote d’Or or the basin of the Rhone, where its imme-
diate radicals are found.

ASTEROCERAS.

The asteroceran series is represented in the Northeastern Alps, though appar-
ently not by many forms. Hauer figures an Ast. obtusum, var. stellare, and we
have seen several specimens from this region, but the fauna evidently was not a
rich one as compared with those to the westward. According to Suess and
Mojsisovics, this species does not occur earlier than the Obtusus bed * in the strata
of the Osterhornes mountains, the Adnether-Schichten in which it appears being
placed by them above the Tuberculatus bed. According to our classification,
however, this curiously mixed fauna may have begun to receive migrants from
the west during the time of the lower bucklandian horizon.’

The first recorded appearance of Ast. obtusum occurred in the Upper Buck-
landi bed of South Germany, and in the similar formation of Luxemburg.

M. Collenot, in his table of the forms in the Cote d’Or, quotes only the usual
three names, Amm. oblusus, stellaris, and Brooki. Boucault’s collection in the
Museum of Comparative Zodlogy shows, however, that probably all the princi-
pal forms were present in the basin of the Cdte d’Or, and the type of Ast. Col-
lenoti was certainly found there. Dumortier shows in his work, that this species
was also present in the Rhone basin, but the series of forms in the genus was
not otherwise so complete as in the Céte d’Or. The finest series exists in the
collection at the Museum of Stuttgardt. This does not have Collenoti, though it

1 Ueber unvermit. auftret. Cephalopodentypen, pp. 63-65. Os, Cihes De 19 Os

8 The form cited by Wihner, Ariet. stellaformis, an ally of Ast. obtusum, var. quadragonatum, is cited as
having been found in the Megasoma or upper part of the Angulatus beds in the Kammerkahr Alps. This
is a doubtful matter, since only one specimen exists, and we have therefore allowed the text to stand
as written (Wahner, Mojsis. et Neum., Beitr., VI., pl. xxvi,, 1888). See also description of this variety,
Chapter V.

OXYNOTICERAS. 101

does possess Ast. acceleratum, a form found nowhere else except in the Cote d’Or.
Quenstedt’s collection at Tiibingen is very fine, and his descriptions and figures
indicate a full representation of species, though Codlenoti is not present.

Chapuis and Dewalque show that the Luxemburg rocks contain several differ-
ent forms of the genus, though they are not so numerous as in South Germany
or England. Schlénbach shows that there is an odfusus horizon in North Ger-
many containing the usual forms, but only fossiliferous in certain localities, and
Brauns publishes similar results in his work. This horizon according to Schliiter
does not appear to have been represented in the Teutoburger Wald, unless his
Gmuendense bed and the broken beds mentioned on page 48 of his work be con-
sidered the equivalent of all the beds between the Angulatus and Raricostatus
horizons.

The English fauna, according to Wright’s “ Lias Ammonites” and the collec-
tions examined by me, has all the principal forms, and often very large shells,
and there are also, as in the Cote d Or and Rhone basins, representatives of the
extreme modification of this genus, As?. Collenoti.

This series had, therefore, a more general development in all the basins we
have considered than any of the preceding series, but in spite of this there seems
to be a preponderance of forms in favor of England and France. The unusual
case of an early appearance of the radical species Ast. obfuswm in the Luxem-
burg region should have its ‘due weight, but the evidence of an equally early
occurrence in the South German basin shows that Ast. obtusum probably made
its appearance as an autochthone upon the level of the Upper Bucklandi bed in
the South German basin, and was thence distributed. It is probable that the
series subsequently met with more favorable conditions in the Cote d’Or and in
England than in any other basin.

>

OXYNOTICERAS.

Oxynoticeras oaynotum, the radical species of its peculiar series, appeared in
such profusion and with such excessively compressed and involute whorls in
the Northeastern Alps, South Germany, the Cote d’Or, and England, that one
seems to be dealing with contemporary migrants from some unknown fauna.
With regard to this conclusion, however, it may be well to be cautious. The
morphological gap is not so great as appears between an adult of a species like
Oxyn. oxynotum, and Agas. striaries or levigatum. This is indicated clearly by the
development of the individual in Ast. obfusum, oxynotum, and Agas. Scipioncanum,
as we have tried to show in the previous pages and in the descriptions of the
genera and species.! Ozyn. oxynotum was a species with a highly accelerated
development, and in such forms the departure from allied forms took place sud-
denly. In consequence of this abbreviated mode of evolution gaps were left in
the series which it is difficult to fill. The evidence with regard to the connec-
tion of Ast. Collenoti with Ast. obtusum and the young forms of Ozyn. oaynotum,

1 See young of Oxyn. oxynotum, pl. x. fig. 4, 5, and 14-17, and Summ. PI. xiii. fig. 9, 10, and compare
with Agas. levigatum, pl. viii. fig. 9, 10, and striaries, pl. ix. fig. 14, 15.

102 GENESIS OF THE ARIETIDA.

which convinced me of the derivation of that species from Agassiceras, was found
in 1875 in the Stuttgardt collection. The specimens of the last named species
had been selected by Professor Fraas out of several barrels of specimens of the
same species gathered in the same locality. I looked very carefully in all other
collections, handling hundreds of specimens, without finding any duplicates of
these forms.

Hauer has given, in his ‘‘ Norddstlichen Alpen,” ! an involute form, apparently
the same as Oxyn. Lymense, and figures of the young, which are, however, in part
distinct.’ Tis Amm. G'reenoughii is evidently a member of the same subseries, and
identical with the more involute forms of Amm. Giuibalianus of Reynés. This sub-
series is only sparsely represented in the Northeastern Alps, and its date of
appearance is not yet settled.

The collection at Semur has this species in the Birchii or Tuberculatus bed.
M. Collenot states that this bed in the Cote d’Or basin contains the same spe-
cies and is equivalent to the Tuberculatus, Obtusus, Oxynotus, and Raricostatus
beds of South Germany and England, and that it is not possible to separate the
faunas, as has been done elsewhere. The appearance of the usual forms of Oxyn.
oxynotum in great abundance in Southeastern France according to Dumortier, and
also of Oxyn. Simpsoni and Lymense, shows that the last named forms may have
made their first appearance in France. This is further substantiated by the fact
that Oxyn. Lymense, according to Wright, is found more abundantly in the South
of England than in the midland counties. The appearance of Oxyn. oxynotum
and Lymense in the basin of the Northeastern Alps can be accounted for by cho-
rological migration, in the same way that we have accounted for the presence of
Asteroceras and others in that basin. The radical species, oxynotum, is cited by
Schlénbach*® from only one locality in North Germany, and is not mentioned at
all by Dr. Brauns in his “ Unterer Jura nérdwestlichen Deutschland,” or by
Emerson. ’

The second subseries of this genus is completely represented in the fauna of
France. Three species only are found in England, none in South Germany, and
two in the Northeastern Alps. Apparently none have been found in North Ger-
many* or Luxemburg. The collections at Semur contain a nearly complete
series of forms, and Dumortier has added others occurring in the Rhone basin.
The home of the series, therefore, appears to have been in the Céte d’Or or
Rhone basin.

This is the only series of the Arietidae which overstepped the boundaries of
the Lower Lias. Other species have been reported by various authors as occur-
ring in the Middle Lias, especially the Jamesoni bed; but these were found asso-

1 Denkschrift. Acad. Wien, XI., pl. xiii. fig. 6, 7.

2 Fig. 6, 7, appear to us to belong to some species of the second or Greenoughi subseries.

8 Hisenst , etc., Zeitsch. deutsch. geolog. Gesellsch., XV., 1863, p. 502. Amm. affinis, however, de-
scribed in Paleontogr., XIII. p. 170, pl. xxviii. III. fig. 1, by the same author, is from Middle Lias, Greene,
Brunswick, which is very similar to if not identical with Oxyn. oxzynotum. We have not cited it in the
table, however, since it may prove to be more nearly connected with Oxyn. Oppeli than with oxynotum.

4 Schliiter describes Oxyn. Oppeli of the Middle Lias as occurring at Altenkirchen and Borlinghausen in
the Teutoburger Wald, and Schlonbach describes and figures the same from Amberg.

FAUNA OF SOUTH GERMANY AND THE COTE D’OR. 105

ciated with Cad. raricostatum, and therefore, according to our classification, are in
the Lower Lias. Oxyn. Oppeli and numismale survived-in the Middle Lias of
Germany, Oxyn. Oppeli alone in the basin of the Rhone, and Oayn. numismale
alone in England.

FaAuNA OF SoutH GERMANY. — TABLE I.

The notable facts brought out by this table are the following. The abundance
and concentration of schlotheimian forms in the Angulatus zone, and their early
appearance in the Rhetic. The completeness of the Caloceran series in the
lower horizons, and the poverty of the faunas existing between the Geometricus
or Upper Bucklandi beds and the Raricostatus bed in respect to these series, and
also in the vermiceran, arnioceran, and coroniceran series. The asteroceran series
reached a high stage of development as regards the number of forms, but is not
represented by the extreme modifications noticeable in the basin of the Rhone.
The oxynoticeran series is also present, and even passes into the Middle Lias, but
has not a full representation of species.

FAUNA OF THE COTE pD’OR. — Tassie II.

The Ammonites at Semur were named by M. Reynés, and these names have
come into circulation through publication by M. Collenot in his “ Description
Géologique de lAuxois,” and have also been quoted by Zittel and several other
authors. Reynés considers many well-marked varieties to be distinct species.
This is our principal disagreement with this author, and the following notes,
together with the descriptions of species and table, sufficiently explain other
differences of opinion.

Terquem’s figures of Hettangensis! show a keeled, broad caloceran form with
pile in the young, which belongs somewhere between Cul. daqueum and raricosta-
tum. ‘The specimens in the Museum at Semur, identified as Hetlangensis by
Reynés, do not agree with these figures. The specimens identified as Dedmast
belong to several species, and one of these is so exactly like Pirondi, as figured
by Reynés in his unpublished plates, that I have quoted this name as a synonym
for Johnston in the table.

With regard to the vermiceran series, we traced the relations as follows.
Beginning with spiratissimum, the forms appear to grade into Schlenbachi, which
represents Conybeari in the Scipionis bed, then into rotator, which is a close ally, if
not identical with Amm. caprotinus, D’Orb., and also with the spinous varieties of
Conybeart found in Germany. The simpler ribbed forms grade into conybearoides,
Rey., which is not very far removed from syratissimum, thence into true Conybeari,
and thence into Breom, which last is a stouter and more robust form. Breoni,
Rey., exactly agrees with typical Conybeari, and also with German forms of the
same name, whereas Conybeari, Rey., is equal to our Bonnardi. Bochardi, Rey., has
the form and characters of Conybeari during its earlier and adolescent stages, but

* Pal. Lias. de Luxem., ete., Mém. Géol. Soc. France, V., pl. xiii. fig. 1, a, b.

104 GENESIS OF THE ARIETIDA.

has no tubercles, The specimens are large shells, and afford fine examples of
the senile stages. Debililatus, Rey., is similar to our lowest transitional forms
of Conybeart. It may be a direct descendant of this from earlier times, or, more
likely, a degenerate form. This grades into Landrioti, Rey. (D’Orb.), which is
simply a more compressed form.

The occurrence of a form like Arn. falcaries in the Angulatus bed at Semur
shows that we may anticipate in the future the finding of the radical arnio-
ceran forms at this level or earlier. It is also very interesting to note that Arn.
Hartmanm, of the Birchii or Tuberculatus bed, is a morphological equivalent of
raricostatum, being, with the exception of the young, very similar to that species.

The more interesting facts shown by this table are as follows. The succession
of the forms in the schlotheimian series has remarkable regularity, according
very closely with their genetic relations. The caloceran series, though very com-
plete in the lower beds, is not so fully represented as in South Germany. Higher
up in the Birchii or Tuberculatus bed of Collenot, and probably upon the highest
level at about the time the Raricostatus bed of other basins was being deposited,
the series had an unusual number of forms. The vermiceran series has a most
extraordinary display of varieties, but apparently not quite so full a representa-
tion in the lowest beds as in South Germany. Arnioceras is more fully repre-
sented in the Bucklandi beds than in any other fauna, and has also many species
in the higher beds. The coroniceran series has a similar history, but is not more
fully represented than in South Germany. The agassiceran and asteroceran
series are also very fully represented, and have the most highly modified species ;
the absence of Brooki will therefore probably be supplied at no distant day.
The oxynoticeran series has also a complete history, and probably is nearer
perfection than is shown in the table, but it nevertheless seems to have had
no Middle Lias forms.

Fauna or THE Ruone Basin.— Taste III.

The basin of the Rhone is equally important with that of Semur, and we give
below a list of Dumortier’s species and their synonyms in the different horizons.
Dumortier mentions only Burgundice, and fragments of Johnstoni and planorbis, in
what he calls the Planorbis bed. This indicates the possible absence of the lower
beds of this horizon, since this is evidently the fauna of the Caloceras bed.

The Angulatus horizon has a fauna less rich in species than that of the Cote
d’Or, especially when one considers the large number of localities from which the
author’s collections were gathered. The list includes, besides the species given
in the table, Amm. bisulcatus, a very doubtful form. It may be a form of Cony-
beari, or similar to the peculiar sulcated form described in the note above on
page 70, but it is probably not a true Cor. brsuleatum.

There are no transitional beds mentioned between this and the bucklandian
horizon, and the beds are evidently not so fully presented, either geologically or
paleontologically, as in the basin of the Cote d’Or. The list is very meagre as
compared with that in the corresponding beds at Semur, but the presence of

FAUNA OF THE RHONE BASIN. 105

Scipiomanus indicates that the bucklandian horizon of this basin represents the
Lower Bucklandi beds of other basins.

Dumortier divided his zone of Amm. oazynotus into four beds, distinguished
by their faunas.

The “ Davidsoni bed” should have been called Striaries bed, since his Amu.
Davidsoni* is identical with Agas. striaries, The list of species does not enable
one to synchronize these beds with the Tuberculatus beds of Semur or other
basins, nor do they show that it is equivalent to any bed above the Upper
Bucklandi_ beds.

The Stellaris bed of Dumortier contains, besides the species mentioned in the
table, Amm. Locardi, a species of Deroceras, and Amm. Birch’, a form of Microde-
roceras ; both of these, therefore, belong to a family distinct from the Arietida.
The presence of Birchi, Boucaulliana, and obtusum show that this, and not the so
called Davidsoni bed, is the equivalent of the bed immediately above the Upper
Bucklandi beds at Semur. This result confirms our opinion that the David-
soni bed of Dumortier should be called the Upper Bucklandi bed.

Dumortier’s Planicosta bed contains Cluniacensis,”? which is identical with Asé.
Collenoti; and this seems to settle the geological position of this important species.
Amn. jejunus® seems to be an abnormal or diseased Arn. miserabile; Pellati is
a young form of Cal. raricostatum ; and armentalis,t if one can trust the aspect of
the inner umbilical pilx, is a diseased form of Cad. raricostatum. It appears from
the figure to be similar to the deformed Ann. longidomus ceger of Quenstedt,’ and
other similar pathological forms, in which the keel and channels have been super-
seded during growth by pilx crossing the abdomen.

Viticola (Plate XX XI. Fig. 9-13) is the same as the Johnstonian variety of
Cal. raricostatum ; Hdmundi (Plate XX XIX.) is the equivalent of the young of Cad.
nodolianum ; tardecrescens (Plate XX XI. Fig. 8, 4) may be related to Arn. falearies.
The umbilicus, sutures, and general aspect of the last indicate that it is a form
of Arnioceras. Oosteri (Plate XXX. Fig. 2-4) is a keeled and channelled form of
Arnioceras, with distorted pile.

Amm. plancosta, subplanicosta, and Pauli are all varieties of our Der. planicosta,
and belong to a family distinct from the Arietide.

The three upper beds of Dumortier are apparently the equivalents of the
Birchii or Tuberculatus beds in the table of the Cote d’Or basin.

The notable facts brought out by this table are as follows. There is a
regularity in the distribution of the schlotheimian series similar to that in the
Cote d’Or basin. Caloceras is not so fully represented in the lower beds, and is
equally deficient in the Bucklandi zone. It is represented by a full list of species
in the highest beds, with the exception of xodotianum, which is absent. Cul.
carusense, however, is more fully represented, and Cal. raricostatum has a greater
number of varieties than in any other fauna. The arnioceran series is not so
fully represented in the Bucklandi zone, but it is notably richer in forms in the
highest beds than in any other fauna. Coroniceras is well represented in the

1 Pl. xxi. fig. 1-4. 2 Pl. xxv. fig. 8-10. S° Pl Sexi, fos 0-6.
+ Plea hee 1; 2. 5 Die Amm. d. Schwab. Jura, pl. vi. fig. 3.
14

106 GENESIS OF THE ARIETIDA.

lowest beds and in the Bucklandi zone, but is deficient above. Asteroceras is
probably more fully represented than is shown in the table, since the extremes
of the series have been found, and, the fauna being near to that of the Cote
dOr, there are grounds for anticipating the discovery of intermediate forms.
Agassiceras is complete in its lower forms, but Scipion’s has not yet been found.
The oxynoticeran series is not only quite complete, but has also a middle lias
representative. As regards Schlotheimia, Caloceras, Vermiceras, Arnioceras, and
Asteroceras, this fauna impresses one as containing the most highly modified
derivatives, and as being possibly a residual fauna representing an acme of choro-
logical migration and varietal modification so far as these genera are concerned.
Possibly Oxynoticeras will also have to be included in this category, and then the
parallel with the English fauna north of what we have called the zone of
the autochthones would be complete.

Fauna or EnGianp.— Tasie LV.

In this table the same regularity of succession is found in the schlotheimian
series as in the Cote d’Or and Rhone basins. Caloceras is again deficient in the
Bucklandi zone, as in the Rhone basin, but is quite fully represented and has an
extraordinary new form in the Raricostatus bed, Cal. aplanatum. There is also a
curious parallelism with the Rhone fauna in the arnioceran series, which, as in
that basin, has the extraordinary form of Arn, Macdonelli of the Raricostatus bed.
Besides the general absence of radical species, except of course the generally
distributed psiloceran and caloceran radicals, there is in this fauna a very impor-
tant fact to be noted, similar to that observed in the fauna of the Rhone. The
extreme modifications in the highest formations are very generally present, —
more so than in any other fauna. Thus, besides Cu/. aplanatum and Arn. Mac-
donelli there are doubtful forms of Cor. bisuleatum in the Oxynotus zone. As?.
Collenoti, Ast. denotatum, and the extraordinary series of var. sagillarius of Ast.
obtusum, are also present. The Oxynotum subseries is complete, and the second
or Guibalianus subseries alone is imperfectly represented.

The English fauna is therefore a residual fauna, not only because of the
absence of radicals, but because it presents a chronological and biological acme in
the evolution of the most highly modified and most recent forms of the different
series, thus clearly indicating chronologically and biologically its more recent
derivation by chorological migration from the older, though apparently contem-
poraneous, faunas of the autochthonous zone.

Fauna OF THE Province or CentTRAL Evrorre.— Taser V.

This table has already been amply explained, with the exception of certain
general facts. The independent origin of the schlotheimian and psiloceran series
is in strong contrast with the Northeastern Alps fauna, which as tabulated in
Table VI. shows that Psiloceras and Schlotheimia are connected by means of
intermediate weehneroceran forms. Schlotheimia and Caloceras are character-

FAUNA OF THE PROVINCE OF CENTRAL EUROPE. 107

istic of the Planorbis zone; they were immediately succeeded in the Angulatus
zone by a full presentation of schlotheimian, caloceran, and vermiceran species,
that is, of the entire Plicatus Stock. This stock then entered upon a period of
decadence, slight in the Lower Bucklandi, but more marked in the Upper Buck-
landi bed. Arnioceras attained its greatest development in the Upper Bucklandi
zone and was more persistent in the higher beds than Coroniceras. This last
attained its fullest expansion earlier in the Lower Bucklandi beds, and declined
rapidly in the Upper Bucklandi, and disappeared altogether in the Obtusus bed.
This decline is shown by the geratologous characteristics of the species in the
Upper Bucklandi beds, rather than by a less number of forms. Thus Cor. orbicu-
latum, Gmuendense, trigonatum, and the muilticostatus variety of bisulcatum, are all
degenerate species as compared with the forms of the Lower Bucklandi_ bed.
They have more convergent-sided whorls, and these are usually developed at an
earlier age.

Agassiceras also reached its acme in the Lower Bucklandi bed, but is more
persistent, and has some forms in the higher formations. Asteroceras is the only
series which attained its acme in the Obtusus zone, and then declined in the
Oxynotus zone. The oxynoticeran series reached its maximum in the Oxynotus
zone, and, though surviving the changes which attended migration into iniddle
liassic habitats, became extinct in that formation.

The schlotheimian series is a highly modified series, composed of involute
derivatives, and ceased to exist in the Obtusus bed, but there are a few
dwarfed forms in the Oxynotus bed. Caloceras persisted in the highest beds,
whereas its highly modified derivative series, Vermiceras, is shorter lived, and
less fully represented in the highest beds. Arnioceras is parallel with Calo-
ceras, and is the radical series from which the more highly modified and
shorter lived Coroniceras originated. Agassiceras, the radical of the remaining
series, persisted from the Angulatus to the Oxynotus bed, whereas the deriva-
tive Asteroceras and Oxynoticeras were both shorter lived. These series, even
when thus minutely followed out, accord with the law of persistence in radical
stocks, as expressed above, on page 26.1 Psiloceras itself is not persistent, and
is an apparent exception. It is the last of a long line of paleozoic secondary
radicals which survived in the Lower Lias. It can be compared with the
upper part of a stem which has reached the point of growth at which it splits
into many branches. Psiloceras was in like manner resolved into derivative
forms, the arietian radicals Caloceras, Arnioceras, and Agassiceras.

We have already noted and discussed the rise and progress of each series:
first, the radical stage, or epacme; second, the acme; third, the final decline, or
paracme, caused by the prevalence of geratologous forms. The result. of such a
serial history, when the series are considered together as one family found within
certain specified beds, is shown in this table. There is a precise parallelism
between the history of the whole and of any one series. The Planorbis and

1 Tf, as we have inferred above, on page 24, the channelled and keeled species of Caloceras are transi-
tional to Hildoceras Walcoti and other radical forms of the Carinifera, this opinion acquires additional
strength, since Caloceras would then become the tertiary radical for the whole of the Carinifera of the Jura.

108 GENESIS OF THE ARIETIDA.

Angulatus zones contain principally radical species and their immediate deriva-
tives. The Bucklandi zone is characterized, with some exceptions occurring only
in the Upper Bucklandi bed, by the presence of truly progressive forms. The
highest beds, the Obtusus and Oxynotus zones, are almost exclusively the homes
of more or less degenerate and geratologous forms.

Extraordinary and unforeseen correlations, such as these, between chrono-
logical distribution and a biological classification founded upon the life history of
the individual, cannot be accidental. We have already shown, in preceding chap-
ters, that our classification of series is natural, and capable of verification by means
of the cycles which are found to be present in the history of the individual and of
the group. The process of verification does not, however, end with this, since
approximately exact agreements may be found between the paleozodlogical and
geological records wherever both classes of facts exist and have been minutely
studied.

There is even some evidence that cycles may be traced in the so-called con-
temporaneous faunas of the same horizon. Thus, what we have said about the
analdainic faunas of England and the basin of the Rhone indicates this possibility.
These faunas show an extraordinary evolution of the geratologous forms of the
geratologous series; the aldainic basins show, on the contrary, in so far as the
Cote d’Or and South Germany are concerned, an extraordinary assemblage of
the progressive forms of the Arietidw, whereas the originating or aldainic centre
of the family in the Northeastern Alps has a fauna in which the radical series
are enormously developed. Zs would seem almost evidence enough that there are
cycles in the chorological migration, as well as in the chronological evolution of forms. The
whole might be represented as a complex of vortices, in which the result is apt to
be a cycle, whether the spiral lines of evolution form small vortices upon the same
or nearly the same horizons, or whether the picture is the blending of all these
into one great spiral, or a series of more or less parallel and blended spirals
ascending through geologic time.

Fauna oF THE PROVINCE OF THE MEDITERRANEAN. — TaBLeE VI.

It was intended to omit this table, as well as those of the North German
basin, Italy, Corsica, Spain, ete., the species of which have not yet been fully
described and illustrated, since it is not practicable in such researches to accom-
plish much unless aided by very full information. Lists of names from which
these faunas might have been made up are rarely of much use, since authors
differ essentially in the identification of species, and therefore we have not
considered it safe to venture upon tabulating them. The publication of Wihner’s
and Neumayr’s researches, however, induced the author to attempt to give a
tabular view of the Mediterranean province. It has not been found practicable
to carry out the system of connecting the forms by lines representing genetic
bonds, except in so far as they have been published by the authors named above,
and the usual connecting lines have therefore been omitted in series occurring
above the Lower Bucklandi bed, and in all the genera of the Levis Stock.

FAUNA OF THE PROVINCE OF THE MEDITERRANEAN. 109

The mixed faunas of the Adneth and Hierlatz beds, and of the gray lias
limestones and Fleckenmergel, have been described by. Giimbel,' by Dionys
Stur,? and by Geyer,’ with very interesting remarks upon the similar faunas
elsewhere. The first author regards the faunas of the Adneth and Hierlatz
limestones as having species representing not only the various faunas of the
Lower Lias, but also the faunas of the Middle and even Upper Lias. Oppel con-
sidered the Hierlatz beds as the equivalent of the Obtusus, Oxynotus, and Rari-
costatus beds. Geyer, who has examined this locality in detail, thinks, if it is
compared with any single fauna, that we should have to select that of the Oxy-
notus bed. He however calls attention to the occurrence of As?. obtusum and
Cal. raricostatum in the same horizon, thus demonstrating the mixed character of
the fauna. Stur regards it as possible that the different beds of the Lower
Lias may, by further investigation, be defined in the Adneth and Hierlatz beds.
This conclusion, however, rests upon theoretical considerations, and not upon
actual observations, and this author observes, “‘ dass in den Alpen einzelne arten
der Lias fauna héher oder tiefer hinauf und herabreichen als in den ausser-
alpinischen Schichten beobachtet wurde, ... und .. . wihrend der Liaszeit
innerhalb der Alpengebiets eine weniger streng geschiedene und minder man-
nichfaltige Gliederung wirklich vorhanden ist.” ®

Both Stur and Giimbel distinguish only three faunas in the Lower Lias of
the Kammerkahr Alps: 1. A yellowish limestone with a species similar to
Johnston. 2. An intensely red limestone with Amm. spiratissimus of Hauer, Li-
asicus of Hauer, Haueri, Kridion, Ceras, Bodleyi, Mierlatzicus, Grunowt, bisulcatus, oxy-
notus, euceras, Charmasset, acutiangulatus, Doetzkirchnert, Hermanni, Kammerkahrensis,
Partschi, cylindricus, Lipoldi, Foetterli, Petersi, but in which, however, a true
Bucklandi bed was not distinguishable according to Giimbel. 38. Above this,
thinner layers with Amm. raricostatus, zithus, densinodus, and a form similar
to stellaris. Giimbel states that the Adneth or dark red limestones, the Hier-
latz, and the gray limestones of Gastatter Grabens are equivalent to one
another, and that each contains a mixture of species from Lower, Middle, and
Upper Lias.

Suess and Mojsisovics® distinguish a Planorbis, an Angulatus, a Bucklandi,
a Tuberculatus, and an Obtusus bed in the Osterhornes mountains, but
consider the Angulatus bed as the equivalent of the Enzesfeld limestones,
and the Obtusus bed as the equivalent of the Adneth limestones. The fauna
found by them did not, however, so far as published, appear to justify this
conclusion.

Wiihner’ gives a clear statement of the facts in his “ Heteropischen Differ-
enzirung des alpinen Lias.” He quotes Stur® as having distinguished two beds at
Enzesfeld, the yellow limestones of the Angulatus zone underlying the true red
limestones of the Adneth or Rotiformis horizon. The various localities of the

1 Geogn. Beschreib. d. bayer. Alpen, pp. 428-482. 2 Geol. d. Steirmark.
3 Ceph. Hierlatz-Schichten. 4 Neues Jahrb. 1862, p. 60.
6 Geol. d. Steirmark, p. 433. © Op. cit., p. 195.

7 Verhandl. k. k. geol. Reichsans., p. 168.
8 See Stur, Lias Hirt. u. Enzesf. Jahrb. geol. Reichs., 1851, pt. 3, pp. 19, 24.

110 GENESIS OF THE ARIETIDA.

Mediterranean province are summarized by Wiihner in this very satisfactory
paper, and one sees that the lowest beds are apt to be well defined, but that
after passing through the Angulatus zone definition becomes more difficult, so
that even this author, for whom as an acute discriminator of species we have a
great respect, seems not to have been able to define the separate beds in either
the Adneth or the Hierlatz limestones.

Herbich makes a valuable contribution to this problem in his Széklerland,
in which he describes several species of the Arietide, including an Asteroceras
like stellaris of Hauer, equivalent to our obtusum, var. stellare, and Atgoc. Althii,
which appears to be a true Microceras allied to Micr. planicosta, together with a
number of species of the Lytoceratidse, all occurring in a bed not over three
meters thick, and he denies that any distinct beds can be defined! Geyer,
in the work above quoted, gives a detailed argument for the probable
admixture of faunas, and comes to the conclusion that Oppel’s scheme of
zones is not applicable to the Northeastern Alps so completely as it is to the
formations of Central Europe. Favre, in his “Terrains Liassiques et Keupe-
riens de la Savoie,’ gives a list of localities in which mixtures of different
faunas have been announced by various authors, and Geyer adds several other
localities.

Favre considers that the species in such localities, among which he includes
the Northeastern Alps, must have been protected from the geological changes
which produced new forms and modifications in other localities, and adds that
we must seek the causes of admixture in the continuation of sediments of the
same nature, and in the configuration of the surface. His idea was, that the per-
sistent species continued to exist in closed basins, where they were secure from
the action of the causes that destroyed the faunas to which they originally
belonged in other localities. This explanation has a reasonable sound, but it
appears to us inadequate. We regard the species quoted as migrants from pre-
viously existing faunas, which, having found favorable homes in these localities,
became the radicals of new series upon new horizons; or else they were survivors
of the geratologous forms of faunas upon the same horizon, which, having found
favorable conditions in these new localities, persisted perhaps somewhat longer
than the parent series. We have not found adequate evidence of closed areas,
except perhaps between the western extension of the Mediterranean province as
a whole, and that of Central Europe. The basins of the Lower Lias were evi-
dently not, as a rule, so completely closed as to keep out migrants from other
basins and provinces, since all the evidence tends to prove the constancy and
uninterrupted migration of species throughout the faunas of Central Europe and
the Mediterranean province.

Whatever hypothesis is maintained, there seems to be no possible way of
accounting for the finding of a species in a truly anachronic position ; that is to
say, in a bed which belongs to an earlier horizon than that in which it has been
proved to have originated. A specimen of Coroniceras Bucklandi in the Planor-
bis bed, or even in the lower part of the Angulatus bed, would introduce great

1 Page 108.

FAUNA OF THE PROVINCE OF THE MEDITERRANEAN. 1i1

confusion into any stratigraphical or genetic classification. We have not yet
been able to find any such case!

Examples of mixed faunas such as have been quoted above are not so exten-
sively mixed as has been claimed. The Hierlatz and Adneth limestones are,
for example, mixtures only of the faunas of the beds above the Angulatus bed;
the examples given of so-called psiloceran forms as occurring in them are due
to mistakes in identification, since these forms are species or young of species of
Arnioceras or Agassiceras, and the species cited as belonging to the Middle and
Upper Lias are either radical forms or else morphological equivalents, like all
the so-called anachronic forms which we have yet studied. A paper by W. B.
Clarke is very instructive in this connection, since he found in the Rheetic a true
Arcestes, showing conclusively how favorable this region must have been for the
preservation of ancient forms. He also was able to make out and describe the
Planorbis and Angulatus horizons, with a full list of species already described by
Wiihner and others, and, above this, the Hierlatz horizon.

The facts appear also to accord perfectly with the theory of autochthonous
faunas. Ifthe Northeastern Alps were the seat of origin for the major portion of
the radical forms of Arietides, we should naturally expect to find in this province
the geological and zovlogical relations which are shown in Table VI.; namely,
a clear definition of the lower formations and faunas throughout the Planorbis
and Angulatus horizons, and an extraordinary number of radical species and
their immediate allies, these also having in the sutures a more ancient or triassic
aspect than in Central Europe. An analdainic fauna made up of modified forms
arising by migration from other faunas would necessarily be shown either in the
admixture of forms above these horizons in case the sediments were similar and
continuous, or else in the non-appearance of new radical or progressive forms if
the sediments were more varied and more distinctly separable, as in England
and in the basin of the Rhone.

While the Mediterranean province was an analdainic fauna so far as the Arie-
tide were concerned during the deposition of the upper beds of the Lower Lias,
subsequent to the deposition of the Angulatus beds, this was by no means the
case with other groups, such as the Lytoceratide. On the contrary, as has been
already announced by Neumayr, this province was the autochthonous home of
this family, and Neumayr’s opinion is strongly sustained by the remarkable series
of species described from the Northeastern Alps by Geyer, Hauer, and others, and
an especially fine series by Herbich from Siebenburgen. . The Lytoceratide are
by no means absent from the faunas of the Lower Lias in Central Europe, though
generally quoted as being found in the Middle and Upper Lias. Thus Amu.
Driani, Dumortier, and Amm. Salisburgense and Amm. ailus of the same author, are
apparently members of this family, found in the Oxynotus bed of the basin of the

* Barrande, with all his knowledge and close study of the fossil Cephalopoda, has not been able to prove
a single example. Those he has given are readily explained as morphological equivalents, and we have
found by the investigation of Bohemian specimens that the Nautili of the present time are entirely different
from paleozoic forms. As soon as the nepionic and nealogic stages are studied and compared, they are

found to be distinct. This is also true of his Gon. (our Celeceras) prematurum.
* Geol. Verhiilt. d. Geg. nordw. vy. Achen-See.

112 GENESIS OF THE ARIETIDA.

Rhone. The last two are closely comparable in aspect with species figured by
Hauer from the Adneth limestones.’ In the same way, we should be disposed
to regard the Mediterranean province as the autochthonous home of some genera
of the Middle Lias, which appear here in association with the Arietide.

The Arietide afford an excellent standard, since their genera and species
have been found, with rare exceptions, only in the Lower Lias; and, so far as
our knowledge now goes, the series of forms and cycles have a very complete
and satisfactory aspect, indicating a history of progress and decline within the
limits of that group of strata in the faunas of Central Europe.

In the Mediterranean faunas, however, so far as known, only the rise of the
group is recorded in the sediments and fossil remains, and its acme and decline
are not clearly indicated. We have been accustomed to look upon the fauna of
the Hierlatz beds as composed for the most part of degraded dwarfs, whose pecu-
harities or modifications were due to the unfavorable action of the surroundings
upon migrants from other contemporaneous faunas of the Lower Lias. This
seems to be the only theory which can account for the prevalent smaller size
and more or less degraded aspect of many of the shells, when compared with
their nearest allies in other locations.

SUMMARY.

The facts cited above, though far from complete, show that the series of the
Radical and Plicatus Stocks, with the exception of the vermiceran series, were
probably evolved in the Mediterranean province. The series of the Levis Stock
had however a different history, since they probably arose in the basins of Cen-
tral Europe. We therefore venture to differ in part from the eminent geologist
and paleontologist Neumayr, who regards, if we properly understand his views,
the Northeastern Alps as the aldainic home of the whole of the Arietide.

The sutures of all the Mediterranean forms of Psiloceras and Caloceras are, as
figured by Wihner, more complicated, or, as we should say, more triassic than
those commonly found in Central Europe; but we occasionally find a variety of
Psil. planorbe, like that figured by Quenstedt? and by Wright,’ in which there is
a close approximation to the outlines common in the Mediterranean province.
After having written the above, we were extremely gratified to find precisely the
same results with regard to the relation of caliphyllum and planorbe, but more fully
and exactly stated by Neumayr, in his “ Unterster Lias” (p. 25). His conclu-
sion, that planorbe is consequently a derivative of Psil. caliphyllum, and is char-
acteristic of Central Kurope, while the latter species is equally characteristic of
the Mediterranean province, is sustained by the fact that the sutures of caliphyl-

1 The peculiarities of the senile whorls are similar to those of Oxynoticeras Lotharingum, and will lead
to much confusion until the sutures and the young are fully known. It is quite possible that our own con-
clusion may be wrong in this respect, but the sutures of Salisburgensis and altus, Hauer, are Lytoceran, and
the aspect of these compressed shells is very similar to that of those found in France, whose sutures are
however unknown. The young are known only in Driani, which resembles some of the forms described
by Herbich.

2 Amm. d. Schwab. Jura, pl. i. fig. 19. 8 Lias Amm., pl. xiv. fig. 1,

te

SUMMARY. 113

Jum become simpler with advancing age, and more like those of planorbe, and by
the scarcity of the latter, which, though found by Wihner," is declared to be rare.
One of Wihner’s specimens was transitional to Hagenowi in its sutures, and this
indicates that the province of the Northeastern Alps was the autochthonous
home of caliphyllum, planorbe, and Hagenowi, and adds greatly to the probabilities
in favor of Neumayr’s hypothesis. In Cal. Liasicum, Johnstoni, and nodotianum it
is common to find varieties varying in the sutures between the Mediterranean
and Central European extremes of modification, the latter being of course the
most numerous in their own province and rare in the Northeastern Alps. The
sutures of Liusieum,? tortilis, and nodotianus,s when contrasted with Quenstedt’s,
Wright's, and our own figures, give a good idea of the extent of variation, which
is quite as great as in Psi. planorbe, if not greater.

Undoubtedly these facts, and the nearer approximation in aspect and sutures
of the Mediterranean forms of Psiloceras to Gymnites of the Trias, the genus we
have always regarded as the probable ancestor of the former, are strongly in
favor of Neumayr’s opinion that the forms of the European province arose by
chorological migration from the apparently more ancient fauna of the Mediter-
ranean province. The richer evolution of triassi¢ forms in the Mediterranean
province, as described and illustrated by Mojsisovics, can also be brought forward
in favor of this view. Nevertheless, it is not right to yield entirely to the fasci-
nations of this opinion until there is positive proof that Psil. planorbe or caliphyllum
occurred earlier in this province than in Central Europe.

With regard to the origin of Caloceras from this province, the facts are still
stronger in favor of Neumayr’s view, but Vermiceras appears to have arisen in
South Germany.

With regard to the origin of Wehneroceras and Schlotheimia, it seems prob-
able from the zovlogical evidence that they also arose in the Mediterranean prov-
ince. The evidence is, however, geologically incomplete, since it is probable
that Schiot. catenala occurred quite as early in South Germany. Weebhneroceras,
the series of connecting forms uniting Schlotheimia and Psiloceras in this same
province, is not yet proved to be of as ancient origin as Schlotheimia itself, and
this introduces an anachronism which requires additional facts for its explanation.

Mosch ® has decided that the Lias to the west of the head-waters of the Rhine
contains species peculiar to the Central European province. W. A. Ooster’s
descriptions and figures of species confirm this conclusion, since he does not men-
tion any novel species, though he describes twenty-one forms, representing more
or less all the genera of the Arietide.®

Zittel’ remarks that there is great resemblance between the Upper Lias in
Provence and Lombardy. Mojsisovics,’ in quoting these observations, says that

1 Verh. k. k. geol. Reichsans., 1886, p. 169.

2-D'Orb., Terr. Jurass., I. pl. xlviii. 8 Ibid, pl. xin. 4 Ibid., pl. xlvii.

5 D. Jura Alpen d. Ost-Schweiz, 1872, p. 1.

® Cat. des Ceph. des Alpes Suisses, Denk. schweiz. Gesellsch. Naturwis., XVIII., 1861; see also Studer,
Geol. d. Schweiz, II. p. 231, for similar views.

7 Central-Appenn., Geogn. pal. Beitr., Beneke, II. p. 174.

8 Dolomit Riffe Siid-Tyr. und Venet., p. 26.

15

114 GENESIS OF THE ARIETIDA.

they raise the question whether the Mediterranean forms of the Swiss Alpine
Jura may not have come by the way of southern France into the western Alpine
region.

The very interesting and instructive essay of M. Dieulefait on the “Zone a
Avicula contorta et Infra Lias dans le Sud-est de la France”! shows that in Prov-
ence a southern and northern basin may be clearly separated. The southern or
Mediterranean basin comprises a range of deposits reaching from the neighbor-
hood of Toulon and Brignolles to Draguignan, Grasse, and Nice. The basin of
the north and northwest, or of the Durance, encloses the valley of that river and
the neighborhood of Castellane and Digne in the department of Basses Alpes.
The basin of the Mediterranean possesses a series of beds identified as belonging
to the zone of Avicula contorta, but there are no Ammonitinee, and all the beds
above these in the Lower Lias are absent. In the basin of the Durance, how-
ever, a very complete series of lower lias beds, including a Planorbis and Angu-
latus bed, has been described. M. Dieulefait has here traced the limits of the
Mediterranean province at a very important, and for our theory an essential
locality. He has shown that the sharp division between the Mediterranean
faunas and those of Central Europe, which, according to our conclusions, ought to
exist along the boundaries between the basin of Italy and of the Rhone, can be
actually traced in the field.

Dumortier’s extensive observations in the valley of the Rhone and Collenot’s
at Semur show the sudden spreading out by migration of forms of Psiloceras and
Schlotheimia from South Germany into the Cote d’Or at about the same time,
and a somewhat later appearance of these radicals in the Rhone and North Ger-
man basins, and possibly still later in England. It seems more likely also, from
the two tables given above, that the species of Schlotheimia, Psiloceras, Caloceras,
and perhaps Vermiceras, were migrants from the Cote d’Or basin to the Rhone,
than that the reverse should have taken place. Coroniceras also thins out in
this direction, whereas the genera having their acme in the upper horizons of the
Lower Lias, viz. Asteroceras, Agassiceras, and Oxynoticeras, are more abundantly
represented, perhaps, than in the Cote d’Or. All the information obtainable
with regard to the faunas of the Lower Lias in Switzerland indicates a general
thinning out in numbers of species and varieties in that basin which, like the
basin of the Rhone, lies to the south of the autochthonous zone.

Kmerson’s collection from Markoidendorf now at Amherst, Mass., and others
we have seen, show that the fauna of North Germany was probably derived from
South Germany, and this accords with Seebach’s conclusion, that a connection
existed between the Hanoverian and South German faunas during the time of the
deposition of the Lower Jura.? There is considerable doubt whether the English
species of Psiloceras and Caloceras came by the way of the Cote d’Or, or found
this locality by independent migration. The former opinion is supported by the
general fact that the English fauna does not contain an autochthonous series, nor
does any radical species appear earlier in this basin than in those of the conti-
nent; it is therefore probably a residual fauna, peopled by chorological migration.

1 Ann. des Sci. Géol., I. 1869, p. 473, pl. v. 2 Hannoverische Jura, p. 70.

ea

SUMMARY. 115

The prevalence of the geratologous forms of the different series in the highest
beds of the Lower Lias indicates that this fauna, like those of the Swiss and
Rhone basins, is also a residual fauna, but lying north instead of south of the
zone of the autochthones. The only definite information with regard to the Lias
faunas of the higher northern latitudes, which I have been able to lay hands on, is
the “I Sueriges Aldre Mesozoische Bildungen,” by B. Lundgren. Cor. Bucklandi
and bisuleatum are mentioned, and Cor. Sauzeanum,® Agas. Scipionianum, Agas. stri-
aries, and Arn. falearies are figured.’ These indicate the presence of the Buck-
landi beds in northwestern Sweden, but the fossils were in bad condition and not
abundant in the number of species. Lundgren mentions, also, that these beds are
underlaid by an unfossiliferous bed, which he thinks is probably the equivalent of
the Planorbis and Angulatus beds of Central Europe. M. Hebert has, in his inter-
esting paper, “L’Age des Grés 4 Combustible d’Helsinborg et d’Hoganas,” ® given
proofs of the presence of the existence of the Planorbis and Angulatus beds in
southern Sweden, but they contain no specimens of Ammonitine.

It is well known that the Lias does not exist in Central Russia, and A. Pav-
low, in his article on “Russie, Esquisse Géologique,’™ gives an account of the
deposits of the Jurassic, but mentions the Lias as occurring only in the Crimea
and perhaps the Caucasus, and refers these to the fauna of the Mediterranean
province, and not to Central Europe. Savi E. G. Meneghini, “Geologia della
Toscana,” gives several lists of fossils from many distinct localities, among which
are a number of the Arietidex. Von Rath® quotes a list of fossils from Mene-
ghini containing many Arietide, and he states that there are a number of new
forms; but lists of names and descriptions of species are unfortunately not
usually of value in such work as we are striving to do. Taramelli, in his mono-
graph, “ Del Lias nelle Provincie Venete,”® describes and figures several species
of Ammonitine, His Amm. Gubalianus is a true Oxyn. Guibali of considerable size,
300 mm. in diameter, and too involute for a specimen of Greenoughi. Arietites
rotiformis is a young form of Cor. Gmuendense, or some such compressed shell; it
is assuredly not rotiformis if his figure is correct. Ar. oblusus is a true oblusum.
Ar. stellaris is the adolescent form of Ast. sfellare. All of these have the facies of
the Northeastern Alps, except perhaps @uwibali, which is new to us as occurring in
the Mediterranean province.

Sacco states, in his “ Lias della Valle Sturio di Cuneo,” ” that all the beds of
the Lower Lias are present, and gives lists of fossils, including a supposed Psi.
planorbe, several species of Schlotheimia, Ver. Conybeari, and a doubtful Cor. kridion,
and Cor. Bucklundi and bisuleatum are said to be of good size and abundant near
Pouriac. In “Lias Inferiore ad Arieti,” by C. de Stefani, it is distinctly stated,
according to Geyer, that the Lower Lias of Italy is divisible into only two parts;
one which is similar to the Angulatus horizon, and yet contains the fauna of

1 Sueriges Geologiska Undersékning, ch. xlvii., Mollusk. 2 Pi. ii. fig. 5-7.
Ble ialie eos ie ag. O: 5 Pl. ii. fig. 8.
6 Ann. Sci. Géol., I., 1869. 7 Annu, Géol. Universel, IT., 1886, p. 302.

§ **Geogn.-mineralo. Fragm. a. Italien,’’ Zeitsch. deutsch. geol. Gesellsch., XX., 1868, p. 320.
® Atti dell’ Instituto Veneto, ser. 5, V., 1880, Appendix.
10 Boll. del R. Comitato Geol. d’ Italia, XVII., 1886, p. 15.

116 GENESIS OF THE ARIETID.

Spezia, and another higher horizon, which is supposed to be the equivalent of the
Bucklandi horizon. This last is said to contain Cephalopods representing all the
later faunas of the Lower Lias, and some species are quoted as being referable to
the Middle Lias,

Canavari, in his ‘‘ Fauna der unteren Lias von Spezia,” so frequently quoted
above, states that the fossils occur in a single zone, which does not admit of sub-
division, though it was carefully investigated, layer by layer, by Cocchi. He
states also, that it is unquestionably the lowest of the lower lias sediments in
Italy, and comprises all the horizons except those of Planorbis and Oxynotus.
He considers that the fossils have closer affinities with those of the Mediterranean
province than with those of Central Europe, a fact which seems to be established.
The species of the Lytoceratide and of Amaltheus, ete. which are supposed
to be anachronic and to indicate a fauna derived from the Middle and Upper
Lias, appear to us to be found in their appropriate positions, like those of the
Northeastern Alps. They may be either the radicals of the similar forms which
oceur in the Middle and Upper Lias of the Central European faunas, or morpho-
logical equivalents, or pathological specimens.! This is also Canavari’s opinion
with relation to some forms, since he expressly states that the agoceran species, }
| as he calls them, are the immediate forerunners of Microderoceras. The fauna
i of the Rhone basin is almost exclusively composed of species having a Central
European aspect. There are, it is true, some slight indications, in the presence
of three species of Lytoceratidee in this basin, that the migrants may have come
this way on their march into Central Europe, but there are no supporting facts
with which we are acquainted. The absence of the Planorbis horizon, or at any
rate its sporadic appearance in Italy, and the absence of Ammonitine in this
horizon of southern Provence, are very serious difficulties in the path of a sup-
posed southern track of migration.

The evidence, so far as known, seems therefore strongly in favor of the view,
that during the time of Planorbis and Caloceras, and perhaps earlier in the
Angulatus horizons, the stream of migration flowed south and westerly from the
Northeastern Alps into Italy, while another from the same basin directed itself
westerly along the then existing coast lines into the basins of South Germany |
and the Cote d’Or, and the species were distributed thence into the basins to
the north and south of these two, in the province of Central Europe. In South
Germany and the Cote d’Or the conditions became favorable during the time of
the Angulatus horizon for the evolution of Vermiceras among the descendants of
the Plicatus Stock, and for the origin of Coroniceras, Arnioceras, and Agassiceras
of the Levis Stock. Asteroceras arose later in these same faunas in the Upper
Bucklandi beds, and Oxynoticeras probably even still later, though here the
series is evidently older than the date of its first appearance. The migrations of
i these genera spread the forms to the east into the faunas of the Northeastern

1 The figures of Amaltheus given by Canavari in his last work, “‘ Fauna del Lias inf. della Spezia,
R. Comit. Geol. d’ Italia,” III., Pt. II. pl. vi. are certainly startlingly similar to Amaltheus, but such
resemblances in forms of widely distinct series are not uncommon. See the pathological case figured on
Plate X. Fig. 19 of this memoir, and others quoted in the descriptions of the species.

i eae

SUMMARY. Ly

Alps, and thence they passed southerly into the Italian basin. Migrants also
passed in all other directions into the residual basins to the north and south
of the basins of the Céte d’Or and South Germany, in the province of Central
Europe.

While these faunas in the Northeastern Alps and Italy became analdainic
faunas so far as the Arietidee were concerned, they were aldainic faunas for some
other groups, like the Lytoceratide, and also very likely for the Liparoceratida,
Deroceratid, and possibly other families. These mixed faunas, which have been
deemed such sources of confusion, are in reality the most instructive, and will
enable us to trace both chronological and chorological migrations with greater
security, if the views here advanced are correct.

Table V. shows that there are but two examples of what Neumayr calls cryp-
togenous types in Central Europe, species appearing suddenly without apparent
ancestors, Schiot. catenata and Psil. planorbe, var. leve. Schiot. catenata, however,
cannot be called an unquestionable cryptogenous form in the Northeastern Alps.
It is in that basin connected by intermediate forms, as stated above, with Psilo-
ceras, and it is therefore probable that in course of time the geological evidences
which are now confusing will be brought into accord with the paleozodlogy.
Psil. planorbe is a radical derived from Psil. caliphyllum, or else from pre-existing
triassic ancestors, and the absence of a complete series connecting it or Psi.
caliphyllum with Gymnites of the Trias is evidently due to the absence of an
equally complete series of formations. That the intermediate species might have
been deep-sea forms, and therefore not represented in the rocky strata now
exposed, as supposed by Neumayr, is an admissible explanation. Newberry’s
hypothesis! of the retirement of the sea is, however, equally supposable, and has
the additional recommendation of explaining the absence both of intermediate
forms and of the sediments. Newberry thinks that the presence of intermediate
links in paleozodlogic history, and their absence from localities so far explored,
are explicable on the supposition that the chain of the rocky deposits is incom-
plete in those localities, and that the sea had retired from them carrying with it
the threads of life. The missing links of the record were then evolved in other
places, but not brought back by the return of the ocean to its former shores.
This seems to us more in accord with what is already known of the merely frag-
mentary aspect of the geologic record in any one region, the occasional discov-
ery of the absent leaves of the record in other places, and the want of absolute
synchronism between the strata of Europe and those of America.

That Psil. planorbe was a littoral form, as well as its congeners, can hardly be
doubtful, since, besides the facts quoted above, they are found associated in the
same series of layers with bones of saurians and even remains of insects in Eng-
land. The remarks of Martin and other authors, quoted above, upon the charac-
teristics of the lumachelle in the Céte d’Or, and the broken aspect of the shells
of Ammonoids compared with those of swimmers like the Nautiloids, as stated
by Terquem, in the department of Moselle, the opinions of Tate and Blake, and

1 Circles of Deposition in American Sedementary Rocks, Proc. Am. Ass. Ady. Sci., XXII., 1878,
pp. 185, 189.

118 GENESIS OF THE ARIETIDA.

the great abundance in which Ammonoids occur as contrasted with Nautiloids,
are all in favor of the conclusion that they were structurally rostrated, creeping
animals, which necessarily followed the shore lines in their migrations. Fraas
takes the view that the Suabian Lower Lias was as a whole, when compared
with the synchronous strata to the west and north, a deep-sea formation, and
cites the absence of sandstones and coarse deposits, the small Lamellibranchs,
and Brachiopoda. It is very evident, however, that whatever the bathymetrical
differences of the South German basin, and however far removed from the
ancient shores now represented by the Black Forest and the Vosges, the sur-
roundings were not sufficiently distinct to make any marked differences in the
Arietidee of this basin.

We have noted above the occurrence in Peru of Cal. Ortoni, a form having
close resemblance to a species of the Northeastern Alps, and the apparent iden-
tity of other species with those of Central Europe, the forms found at Vancouver's
Island and in California, etc., show that on this continent the faunas possessed a
mixed character. The paucity of the development both geologically and paleon-
tologically of the Lower Lias is in accord with the similar deficiency of this stage
in the analdainic basins of northern Europe, India, and Italy. There is another
fact in this connection, which strikes us as very remarkable, — the absence of any
absolutely new types of Ammonitine. So far as explorations have gone, not a
single species indicates the evolution of any widely distinct family or genus from
those found in Europe. Thus, although not able to produce any satisfactory evi-
dence that all the faunas throughout the world during the lower lias age were
more or less analdainic faunas derived from the zone of the autochthones of the
Arietidxe in Europe, the evidence is sufficient to make such an opinion worthy of
the attention of students of geology and paleontology.

The view expressed by Neumayr, that the Cephalopoda are exceptional
in respect to the rapidity with which their modifications probably took place,
seems to us erroneous. ‘here is no greater aspect of pliability in this than
in other types, when accurately classified. When, however, we assemble
within the same family species of the Lytoceratinse and Ammonitins, or in
the same genus forms of entirely distinct stocks without sufficient reference
to their genetic history, then of course a belief in the polygenesis of the
progressive series,’ and in an exceptional tendency to modification, becomes
essential in order to explain the heterogeneous aspect of the groups. We think,
however, that even the most variable families of Cephalopoda are not, as a
rule, any more variable than the Unionidae, Ostreadse, or Hippuritidee, among
Lamellibranchs, or the Planorbidew, Vermetide, etc., among Gasteropoda, and
many other groups that might be mentioned.

The expansion of the whole series of forms of Psiloceras, Schlotheimia, and
Weehneroceras in the Northeastern Alps, and the apparent rapidity of chorologi-
cal migrations and changes and introduction of new series, the equally sudden

1 We desire to call attention here to the fact that we have admitted the polygenetic derivation of retro-

gressive types like Baculites, etc.; but this in no manner commits us to the doctrine of polygenesis for any
of the progressive types. So far as we know, these are monogenetic in mode of origin.

| res

SUMMARY. 119

expansion of the Arietidee in the Bucklandi zone of Central Europe, the rapidity
with which the forms of the still later beds must have come into being in order
to be presented in a body, as in the Tuberculatus beds of the Cote d’Or, and the
limited thickness of the beds, are all against the supposition that it required vast
periods of time for a species to become modified and give rise to series of distinct
forms. Hither the species of the Arietidas had time enough during the deposi-
tion of the Planorbis, Angulatus, and Bucklandi beds of the Lower Lias to spread
themselves over the entire area of modern Europe, and generate from one form
all the series described above, or else the same species and genera had invariably
distinct centres of origin in the different basins. One might support the latter
view and favor polygenesis even in this extreme sense with considerable show
of reason, if there were not such a mass of evidence in favor of migration, some of
which we have given above. If there were space, we could add examples from
the researches of various well known zodlogists upon the migrations and modi-
fication of species in modern times, both along the coasts and over the land. The
more striking examples are, however, quite well known, and hardly need to be
dwelt upon.

120 GENESIS OF THE ARIETIDA.

|
i

V. |

DESCRIPTIONS OF GENERA AND SPECIES OF ARIETIDZ}

RADICAL STOCK.
FIRST, OR PSILOCERAN BRANCH.

PSILOCERAS.

HELL smooth, plicated or with fold-like pile in some subseries. The abdo-
men is rounded, or with smooth median zone, never channelled or keeled.
Whorl in section is compressed, helmet-shaped. The sutures are similar in pro-
portions and outlines to those of Caloceras. This is shown in the broad abdomi-
i nal lobe and large siphonal saddle, the equality in length and size of the abdomi- if
nal and lateral lobes and saddles, their leaf-shaped marginal digitations, and the
number and inclination posteriorly of the auxiliary lobes and saddles.
i The living chamber is one, or more than one, volution in length, and is shorter
i in the young than in the adult stages.” Senility is indicated by increasing con-

vergence of the sides, and the loss of plications,® but a subacute abdomen, such as
appears in the old whorl of Wehneroceras, is never present. The completeness |
and accuracy of Wihner’s illustrations and descriptions, which enable one to study 4

all the stages of growth in some species, has tempted us to suggest the existence
of three subseries in this genus. (1.) The first contains smooth shells, typical
helmet-shaped whorl, and an old age in which a subacute whorl is not yet re-
corded in any species. (2.) The second contains plicated shells exactly similar
in form, but the folds numerous and regular, and in some species figured by
Wihner these cross the abdomen with a forward bend. They are, however, not
true pile, and, so far as we know, they do not become depressed along the median
zone as in Weehneroceras. (3.) The third contains shells having psiloceran forms
but flattened sides, and often plicated as in the second subseries, though the
Psil. Hagenowii is smooth. We regard this subseries as of doubtful utility, but do
not know how to dispose at present of the forms it contains.

1 Throughout this chapter there is no attempt to give a complete synonymy of any one species.
The references given under each name are only those which were considered essential to settle the applica-
tion of the specific name and the range of the forms to which it was applied in this memoir. The localities
given are those of specimens in the collections of the Museum of Comparative Zodlogy.

2 Quenstedt, Amm. Schwab. Jura, pl. i. fig. 6, shows a nealogic stage in which this chamber is not quite r
half a volution in length. Wiihner takes note of this, (Unter. Lias d. nordést. Alpen, Mojsis. et Neum.,
Beitr., 1V., 1886, p. 135,) and states that in one example of Psil. planorbe from Wiirtemburg observed by him
the living chamber was only two thirds of a volution in length, and suggests the same opinion with regard
to the shorter living chambers of the young.

5 Quenstedt figures what may be a fragment of an old specimen of Psil. planorbe, Amm. Schwab. Jura,
pl. iii. fig. 1, and Wiahner has figured several old specimens in Unter. Lias, Mojsis. et Neum., Beitr.

Ata etm

FIRST, OR PSILOCERAN BRANCH. 121

First AND SECOND SUBSERIES.

Psiloceras planorbe, Hyarr.

Var. leve.
Plate I. Fig. 1-4. Summ. Pl. XI. Fig. 13 Pl. XII. Fig. 1.

Amm. planorbis, Sow., Min. Conch., V. p. 69, pl. ececxlviii.

AEgoc. planorbis, Wrigur, Lias Amm., p. 308, pl. xiv. fig. 1-4.

Amm. psilonotus levis, QuENStT., Die Ceph., p. 73, pl. iii. fig. 13; Amm. Schwab. Jura, pl. i. fig. 1-7.
Amm. Sampsoni, Porty., Rep. Geol. Londonderry, ete., p. 188, pl. xxix. a, fig. 13.

Psil. planorbe, Hyarr, Bull. Mus. Comp. Zool., I. No. 5, p. 73.

Localities. — Whitby, Watchet, Montloy, Semur, Rudern, Nellingen, Balingen, Neuffen.1

This remarkable form is a somewhat flattened discoidal and perfectly smooth
shell in its typical adult form. The young are often plicated.

Var. plicatum.

Plate I, Fig. 5,6. Summ. Pl. XI, Fig. 2.

Amm. psilonotus plicatus, QuensT., Amm. Schwab. Jura, pl. i. fig. 1-14 (mot fig. 8, 18).

This shell differs from variety /eve merely in having immature pile or folds in
the neologic and ephebolic stages. There is therefore the most gradual and
hardly perceptible gradation from the preceding variety to this form. The septa
of both are exceedingly variable. The marginal digitations may be either very
shallow, as in the Arietidee generally, or they may be foliaceous and complicated, as
in the radical series. The lobes and saddles may also vary exceedingly in size
and proportions; some species have deep and narrow saddles with long broad
lobes, as in the radical series, while others, more like the typical Arietidx, have
shallower, broader saddles, and shorter, more pointed lobes. In the collection at
Semur there are forms from Saulieu identical with the South German, which
when compared with raricostatum and Johnston’, show closer approximations than
any specimens seen elsewhere.

The Bristol collection contains undistorted specimens of this species from
Cotham, and in Dr. Wright’s collection from Whitby the plhcatus variety is labelled
Am. erugatus, Bean. The connection with the flattened Watchet specimens of
planorbis, Sow., can be clearly made out by the large tablet in the British Museum,
containing about one hundred and fifty specimens. Of these, perhaps ninety
exhibit folds like those of plicutus and erugatus. The largest on this slab is from
60 to 80.5 mm. in diameter. These large specimens are not equivalent to Cad.
Johnston’, as Oppel supposed, but to piicatus. Hrugatus seems to be a dwarfed form
with the folds often developed very strongly in the young,’ and the shell has fine
stris of growth, as in Agas. striaries, Plate IX. Fig. 14, 15. In the Museum of
Comparative Zodlogy the series is complete from /eve to var. plicatum, as figured
by Quenstedt in “ Der Jura,” and in another direction to the var. of planorbe from
Semur? This is a slightly plicated form, having the sides of the whorls broader

1 These localities also include var. plicatum. 8 See Pl. i. fig. 5, 6.
2 Amm. erugatus Bean has only the young plicated, resembling in this respect var. eve. It is however
always a small form or dwarf.

16

122 GENESIS OF THE ARIETIDA.

than usual, and the involution slightly increased, a modification. which is also
sometimes present, though less marked, in erugatus.

Wihner found what he claims to be Psi. planorbe at Pfonsjoch in the Pla-
norbis bed. ‘These were small specimens, measuring 15-40 mm. in diameter, and
one of them is said to be similar to Hagenowi In the same work he figures
the following discoidal shells of the smooth subseries: Psi/. polycyclum and cali-
phyllum, Plate XV., and Psil. pleurolissum.2,Neumayr, in the Unterster Lias,?
gives Psil. planorboiles, a more involute, smooth species of this series. Planorboides
appears to lead into two much more involute and compressed species figured by
Wiihner in the same work, Psi. Atanatense and mesogenost Both of these are
devoid of true pils, and possess only senile fold-like pilations.®

SECOND SUBSERIES.
Psiloceras longipontinum, WAuner.

Amm. longipontinus, Opp., Pal. Mittheil., p. 129, pl. xli.
Psil. longipontinus, WAuNER, Unt. Lias, Mojsis. et. Neum., Beitr., IV. p. 196.
4igoc. Clausi, Nnum., Unterst. Lias, Abh. k. k, geol. Reichsans., VII. pl. iii.

The original of this species in the Museum of Stuttgardt has considerable like-
ness to Psi/. planorbe, var. plicatum. Oppel seems to have considered it one of the
schlotheimian series.’ The open umbilicus, straight folds in place of true pile,
keelless abdomen, and helmet-shaped form of whorl, show it to be a member of
the psiloceran series. The sutures,’ as figured by Oppel, exhibit the strong psilo-
ceran affinities of the species. In his specimen the last whorl has become smooth
on one side, and the pile nearly obsolete on the other, thus indicating the
approach of senility, though the shell is but 95 mm. in diameter. The pile begin
to obsolesce posterior to the last septum. The living chamber is nearly one volu-
tion in length, though still incomplete. An empty cast in the Semur Museum
from Ruffy undoubtedly belongs to this species; it is 155 mmi.in diameter, and the
last whorl is smooth, showing its great age. There are specimens in the collec-
tion at Munich labelled Amm. Roberti, Hauer, locality Filder, and Amm. Oceduensis,

1 Unter. Lias, Mojsis. et Neum., Beitr., IV. p. 186. me Meats (SEES oj ze oe ah

8 Abhandl. geol. Reichsans., VII. pl. iv. 4 Op. cit., III. pl. xxvi.

> We have figured only the most involute of this smooth series on Summ. Pl. xi. fig. 13.

° The closeness of the parallellism between some of the forms of Psiloceras and some species
of the Lytoceratide is such as will be likely to cause considerable confusion unless great care is taken
in studying the species. Comparison of such forms as Amm. Petersi, Hauer, Ceph. nordost. Alpen,
pl. xxi. fig. 1-3, Lyt. Petersi, Herb., Széklerland, pl. xx., Lyt. 2 Driani, sp. Dumort., Etudes Pal. du Basin du
Rhone, and Lytoc. (Amm.) Roberti, Hauer, Capric. oesterr. Alpen, pl. iii., will show that without close
study of the sutures and young no separation can be made with certainty. In fact, in identifying Driani
in the absence of figures of the sutures as a form of Lytoceras, we have been led by the geological position
and size, which accord better with Lytoceras than with a species of Psiloceras. It is possible that in doing
this we are illustrating these remarks in a forcible manner.

See also in this connection the forms of Rhacophyllites and Phylloceras figured by Canavari in his
‘Fauna des unteren Lias von Spezia,’’ pl. ii.

* The sutures figured by Portlock, as well as the form of the section (b) of his Amm. Sampsoni (fig. 13 c,
not fig. 13 a), suggest longipontinus, and may indicate the presence of this form, or transitional varieties, in
the English basin.

ret ee sehr

eee mn

FIRST, OR PSILOCERAN BRANCH. 123

Despl. d. Champ., locality Blumenstein am Thuner See. One of the specimens
from Filder shows the exact aspect and markings of Psi. planorbe, but has the
form of longipontinum. Though it is somewhat difficult to judge from a figure,
nevertheless, Ay. Claust, Neumayr, very closely resembles Psi. longipontinum,
and we have considered it to be a variety of this species with somewhat stouter
whorls than the normal form. It is also a large aged specimen, and according to
Neumayr came from Wiirtemburg.

Quenstedt referred this species, in his “ Ammoniten des Schwabischen Jura,”
to Cal. laqueum. is comparisons were evidently made with the old whorl of
laqueum, and, as this has no keel, and is smooth or with obsolescent pile, it is of
course very like the adult stages of Psi. longipontinum. Nevertheless, both the
young and adult stages of daqueum are easily distinguished from the same stages
of longipontinm. Quenstedt’s figure shows the length of the living chamber to
have exceeded one volution.

Tate and Blake’s citation of this species from the Angulatus bed? is likely to
mislead. Their species is, as figured, a diseased Caloceras, or poorly drawn
species of Schlotheimia with pile crossing the abdomen, but certainly not, as
named by them, dongipontinus.

Species of the second subseries figured by Neumayr in the work quoted
above are as follows. Psil. eryptogonium, Plate VI., is discoidal. Psdl. majus and
Gernense, Plate V., are slightly more involute shells. Wiihner, in Volume IV. of
the work above quoted, figures Ps?/, sublaqueum, Plates XV., XVI., Psil. crebri-
cinctum, Plates XVI., XVIIL, Psi. pachydiscus and polyphyllum, Plate XVII, all
discoidal shells. This subseries and the preceding agree closely with the western
European forms except in the involute species. Wihner also figures, in Vol-
ume III. of the same work, Psi. Berchta and aphanoptychum, Plate XXIII,
which are discoidal, and Psi/. pleuronotum, Plate XXV., calcimontanum, Plate
XXIV., and Aummerkarense, Plates XXIV., XXV., which are more involute and
compressed.”

THIRD SUBSERIES.
Psiloceras Hagenowi, Winner.

Amm. Hagenowi, Dunx., Paleontogr., I. pl. xiii. fig. 22, pl. xvii. fig. 2.

Amm. Hagenowi. Trr@. et Prrr., Lias Inf. de Est de la France, Mém. Soc. Géol., VIII. pl. i. fig. 3, 4.
Amm. Hagenowi, Quenst., Amm. Schwab. Jura, pl. i. fig. 18.

Psil. Hagenowi, WAHNER, Unt. Lias, Mojsis. et Neum., Beitr., IV. p. 196.

The form of this shell approximates to that of Psi. planorbe, var. leve, but the
sutures are more widely distinct, and degenerate in outline. Ih Terquem and
Piette’s figure they resemble quite closely the sutures of Popanoceras Kingianum
and antiquum, Goniatitinee of the Dyas. The lobes of that figured by Quenstedt
are not so coarsely dentate, and approximate more closely to the sutures of Psi.

1 Yorkshire Lias, p. 273, pl. v. fig. 4.
2 On Summary Pl. xi., outline figures have been given of the principal forms, aphanopiychum, fig. 11,
and Aammerkarense, fig. 12.

124 GENESIS OF THE ARIETIDZ.

planorbe. The saddles sometimes have entire margins, as in some Ceratitinee of
the Trias. Neumayr’s Hagenowi, in his “Unterster Lias Nordalpen,”* is not a
true Hagenowi, if the sutures are correctly drawn. Such facts and the remark
of Wiihner quoted above (page 113) show that Hagenowi is probably a dwarted
deformation of Psil. planorbe, which is likely to occur in any locality, and has an
independent existence as a race or species only in certain basins where it is
abundant. It seems to indicate, wherever it appears, that Ps¢/. planorbe has there
been subject to unfavorable conditions.

Neumayr in the work above quoted, Plate IV. Fig. 1, gives a Psil. (A/goc.)
Naumann, a good-sized species with numerous folds, compressed slightly conver-
gent sides, and a rounded smooth abdomen, exactly the form and characters of his
Hagenowi, except that it is more decidedly plicated. The smaller Psi/. ( Aigoc.)
erebrispirale, \bid., Plate V. Fig. 4, is probably the young of this shell. The sutures
have complicated margins, as in pther shells of this province, and are not similar
to those of Hagenowi. We place it here until its exact affinities can be settled
by the study of a series, or of the young.

Aigoceras Struckmanni? Vbid., Plate VI. Fig. 5, as remarked by this distinguished
authority, is a unique survival of triassic forms. It resembles the flat-sided
whorls in Tirolites, and even certain earlier forms, like Popanoceras. It may be
provisionally associated with this series until the sutures are known, since the
shell is smooth, and similar to that of Psé/. planorbe. This series should be care-
fully studied with ample materials. It may be that confusion exists between
some forms now supposed to be true Psil. Hagenowi and some triassic forms
still surviving in the Lias. Canavari, in his “Fauna del Lias Inferiore di Spe-
zia,” 1888, Plate VII., has figured a series of what appear to be true Tropites.
These are very close congeneric forms of this triassic genus, and in our opinion
should be referred to Tropites itself? This gives greater force to the suggestion
made above.

Canavari, in his “ Fauna des unteren Lias von Spezia,” gives some interesting
forms of this genus. Psil. (dfgoc.), Plate XIX. Fig. 2, 4, 5, is a plicated form
similar to pleuronotum. Psil. pleuronotum, Plate XIX. Fig. 3, may possibly be the
same as Psil. caleimontanum, as stated by Wahner, but it is a dwarf, like most of
the species from this locality. Pesil. (Aigoc.) Portisi, Plate XIX. Fig. 6, appears
to bear a similar relation to Psil. mesogenos, Wéabner, however, considers it iden-
tical with the young of his Psi. Kammerkurense.

1 Abhandl. geol. Reichsans. Wien, VII. pl. ii.-

2 Wihner’s Psil, Struckmanni, Unt. Lias, Mojsis. et Neum., Beitr., IV. p. 196.

3 The survival of characteristic triassic forms in the Jura shows that the connections between these
two systems are closer than has been supposed, and gives support to opinions advocated in the chapter on
Geological and Faunal Relations, and adds another group to the three already noted, Psiloceras, Lytoceras,
and Phylloceras. These facts demonstrate that no insuperable barrier arrested the migration of forms and
the continuity of the faunas in time. See remarks on Tropites in note to page 154.

4 Paleontogr., XXIX., and also Mem. del, Car. Geol. d’ Italia, III., 1888.

eee

SECOND, OR SCHLOTHEIMIAN BRANCH. 125

TMAGOCERAS.

Tmaegoceras latesulcatum, Hyarr.

Amm. latesulcatus, HAvER, Ceph. d. Lias, d. Nordéstl. Alpen, pl. ix. fig. 1-3.

This extraordinary form, found in the red limestones of Adneth, has a combi-
nation of characteristics altogether distinct from that-of any other species. The
form of the whorl, its smooth shell, and the discoidal mode of growth, are purely
psiloceran. The sutures are, however, arietian, and more like those of Caloceras
than typical Psiloceras or those of any other genus. We are not aware of its
having been found elsewhere than in the Mediterranean province. Hauer
appears to think that its affinities may lie with the Arietidx, and that is also our
opinion, but until the young have been studied it cannot be classified.

Tmaegoceras levis, Hyarr.
Ariet. Levis, GEYER, Ceph. v. Hierlatz b. Hallstadt, pl. iii. fig. 10.

This is a smooth, keeled, and channelled discoidal form like the preceding,
but dwarfish, like other species of this locality.

PLICATUS STOCK.
SECOND, OR SCHLOTHEIMIAN BRANCH.

The living chamber is of uncertain length, though Quenstedt gives it in his
«¢ Ammoniten des Schwiabischen Jura” as possibly a volution in length in Schlo-
theimia. The shell is involute in some forms. The whorl is flattened laterally,
and in old age became subacute. A smooth median zone or channel was formed
on the abdomen by the suppression of the piles, which were continuous across the
abdomen in the preceding nealogic or ephebolic stages. There are no geniculs,
though the pile are very completely developed. The forward bend is necessarily
gradual, the whorl never having a sufficiently quadragonal form for the forma-
tion of abrupt bends or genicule on the edges of the abdomen. The sutures
resemble those of Psiloceras and Caloceras.

W A HNEROCERAS.?

The adult has a smooth median zone along the abdomen. The pilm, so far as the
young are known, cross the abdomen during the earlier nealogic stages, and this
character is retained throughout the adult stages in some species. The smooth zone
is really an incipient channel, formed subsequently by the resorption of the pile.
This process may take place either in the later nealogic, ephebolic, or senile stage,
according to the species. In old age the pile tend to degenerate into folds, and

1 Tunyos, a furrow.
2 Dedicated to Dr. Frantz Wahner, as a token of respect for his remarkably accurate and instructive
researches upon the Arietidae.

126 GENESIS OF THE ARIETIDA.

become wider apart, the abdomen narrower, and the whorl consequently much
compressed and subacute. No proper quadragonal whorl is formed during the
growth, and therefore the senile outline of a section of the whorl is not trigonal,
as in the senile stages of shells of other branches having a flattened abdomen
and a keel in the ephebolic stages, All the species have true pile, though these
are not prominent, and the earlier nealogic stages resemble adult specimens of
the second subseries of Psiloceras, in which the folds are well developed and
cross the abdomen. We cannot distinguish either this genus or Schlotheimia,
or Caloceras, from Psiloceras by means of the sutures. Psil. sublaqueum, Wiih.,
and other species of Psiloceras having plications which cross the abdomen until
a late stage of growth, are not distinguishable until they are nearly full grown
from some discoidal forms of this series.

Waehneroceras subangulare, Hyarr.
Amm. subangulare, OrprEL, Paleontolog, Mittheill., p. 130.

We have referred the species to this genus entirely upon the information
derived from notes made before Waeehneroceras was separated. It will be seen,
however, that no species of Schlotheimia has young which remain similar to
Psiloceras for such a prolonged stage as in Weehneroceras,

One of the types of Amm. subangularis, Oppel, from Kalthenthal, in the collec-
tion at Munich, has a form similar to that of Ps. planorbe, and pilations which
cross the abdomen. The young is also a pure planorbe until over 14 mm. in
diameter. Another specimen from Filder, which we have referred also to this
species, has curved and close-set pila, and the form and smooth abdomen of
planorbe (not channelled at all) until over 26 mm. in diameter; then the pilee
begin to cross the abdomen. ‘This last specimen was named Amm. planorbis by
Oppel. There are also specimens from Hammerkhar, formerly referred by us to
subangulare, which may be distinct. They certainly possess characters which were
noted by us as intermediate between this form and true angulala, and one of
them has a very peculiar old whorl, and may be a caloceran form.!

Waehneroceras tenerum, Hyartr.

4igoc. tenerum, Neum., Unterst. Lias, Abh. k. k. geol. Reichsans., VII. pl. iii. fig. 4, 5.
Psil. tenerum, Wiu., Unt. Lias, Mojsis. et Neum., Beitr., 1V. p. 198.

This form, described by Neumayr as occurring in the Northeastern Alps and
also in Central Europe, at first seemed to us identical with Wah. subangulare.
Neumayr remarks that, though the young are so similar, the adults are separable,
and we have upon his authority held it to be distinct. He also looks upon. this
species as very closely allied to Psiloceras, and to be a transition form from the
latter to Schlot. angulata.

Species of this series have been figured by Wihner in Volume III. of his
“Unteren Lias” as follows: Woh. Paltar, Plate XXL, and Rahana, Plate XXII;

' Proc. Bost. Soc. Nat. Hist., XVII., 1874, p. 18.

| apis aoa Ss

"nl asco Sai sent a

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4
)

SECOND, OR SCHLOTHEIMIAN BRANCH. 127

and in Volume II. he figures Wek. extracostatum, Plates XIV., XVI., and Panznert,
Plates XV., XXI. The figure of eatracostatum shows an old whorl which is acute,
but not involute. Among discoidal shells, Wek. circacostalum, Plates XV., XV1.,
curvornalum, Plate XVI., and haploptychum, Plate XVII., show that the whorls of
their earlier nealogic and adult stages are without channels. Wek. anisophyllum,
Plate XIX. Fig. 1 a, shows a very old stage with subacute trigonal whorl, and
pile replaced by folds. Woh. megastoma, Plate XVIII. Fig. 2, 3, shows ear-
lier nealogic stages with pile continuous across the abdomen in the adult and
senile stages. Woh. euplychum, Plates XVIII., XX., stenoptychum, Plate XX.,
latimontanum, Plate XX., and diploptychum, Plate XXL., also belong to this ge-
nus. The last two are senile specimens, with subacute outer whorls, and all
the above are discoidal shells exhibiting transitions from Psiloceras to Schlo-
theimia.

There are, however, involute forms in this series also figured by Wihner in the
same work, but in Volume IV. These are Wek. Guidow, Plate XXVI. Fig. 3 a, b
(not Fig. 7), and Woh. Emmrichi, Plate XXVI.' We
doubt whether either of these involute forms can
be regarded as transitional to Schlotheimia, as sup-
posed by Wiihner.

The results of our work upon the nealogic
stages and their meaning in Schlot. catenata, and all ped of
other species, show that series arose only from dis- Rye. 20-22. — Views from in front,
coidal shells, and probably never originated from Dadsiae ates Willie std he te
the compressed and involute forms. These are involution of this species. The charac-
themselves invariably discoidal and less compressed Ghee spent De ee ss

° genus are also noticeable in these
in their own young, showing them in every case figures?
to have been derived from shells having depressed abdomens and discoidal
whorls.

Canavari, in his “ Unteren Lias von Spezia,” ® describes and figures dwarfs or
the young of Wek. (Aigoc.) Emmrichi under the name of Guidoni. Wiihner thinks
that Canavari’s forms (Plate XVIII. Fig. 14, 15) are referable to his Guddon’, and
Fig. 16 to be identical with his Kmmrichi. The last is to us a very remarkable
form, since it possesses continuous lateral and abdominal constrictions.

SCHLOTHEIMIA.

The form varies in this genus from discoidal to involute, but the umbilici are
never entirely covered in. The whorls are usually flattened more or less on the
sides, and the abdomen depressed. In the nealogic stages this form is common,

1 We have given outline figures of Wah. curviornatum, Summ. Pl. xi. fig. 7, haploptychum, fig. 8, toxo-
phorum, fig. 9, and Emmrichi, fig. 10.

2 This figure, according to Wahner, is poorly drawn, the last volution too narrow, the umbilicus too
open. It, however, exhibits the general aspect of involute forms in this series, and we have retained it
with that purpose in view.

8 Paleontogr., XXIX., and Mem. del. Carta Geol. d’ Italia, III, 1888.

128 GENESIS OF THE ARIETIDA.

but in the adults of involute species the whorl is necessarily more compressed.
The compressed stage occurs very early in the most involute species, the flatten-
ing of the sides and the depressed abdomen being omitted. A distinct median
channel is formed on the abdomen in all species except some varieties of Schiot.
catenata. The pile cross the abdomen in the earlier nealogic stages, but this
peculiarity is rarely retained in adults except in catenata. The channel is formed
by the suppression of the pile along the median zone of the abdomen, and is
sometimes, especially in the young, supplemented by the bending inwards of the
shell, This channel is converted into a smooth zone in old age by the degen-
eration and disappearance of the geniculw, and the tendency of the abdomen to
become narrower elevates this zone and makes the whorl subacute. Involution
so far as known does not decrease in old age, and while it is easy to separate the
senile stages of involute species from the senile stages of any species of Waeh-
neroceras, it is not practicable to distinguish those of the discoidal species until
the ephebolic stages are studied. The specimens figured by Quenstedt* show
that, in extremely aged specimens, the abdomen becomes in some cases
rounded, and it is instructive to compare Fig. 10m, Plate IIL, with the aged
Psiloceras, Fig. 1m, in order to see how complete the reversion occasioned by
senility may sometimes become.

The sutures are not distinguishable from those of Weehneroceras. They are
perhaps less like. those of Caloceras than those of that genus. The superior
lateral lobes also are usually not so long and narrow, nor the superior lateral
saddles so large and deep, nor the auxiliaries so much inclined posteriorly.
The sutures are similar, both during the nealogic and senile stages, to those
of Weehneroceras, and the differences, if any can be detected, occur only in
the adult stages.

Wihner’s plates? are so complete, that one can study the history of the devel-
opment of each form, and the relations of the species in their nealogic stages.
The young of the more involute species, like Schdot. ventricosa and marmorea, are
similar to the later nealogic stages of less modified and more discoidal forms, like
Schlot. donar, and are also similar to the adult stages of still more modified species,
like Sehiot. angulata. These facts confirm the opinions we have advanced in the
description above, and in other parts of this memoir.’

1 Amm. d. Schwab. Jura, pl. iii. and iv.

2 Mojsis. eb Neum., Beitr., IV., 1886.

2 We have several times referred in this memoir to extraordinary parallelisms. But we know of none
more remarkable than those figured by Canavari in his ‘‘ Fauna der Unteren Lias von Spezia.” We refer
to the genus Ectocentrites of Wihner, in which the young as described by Canavari are similar to Lytoceras,
while the later nealogic and adult stages have the pile: and abdominal channel of Schlotheimia.

SECOND, OR SCHLOTHEIMIAN BRANCH. 129

First SUBSERIES.

Schlotheimia catenata, Winner.
Summ. Pl. XI. Fig. 3.

Amm. catenatus, Sow., De la Beche, Traité de Géol., p. 407, fig. 67.

Amm. catenatus, D’OrB., Terr. Jurass. Ceph., p. 301, pl. xciv.

4igoc. catenatus, Wrieut, Lias Amm., p. 320, pl. xix. fig. 5-7 ; pl. xvii. fig. 3-6.
Schlot, catenata, WAn., Unt. Lias, Mojsis. et Neum., Beitr., [V., 1886, p. 196.

Aigoc. subangulare, Wiu., Unt. Lias, Mojsis. et Neum., Beitr., [V., 1886, p. 162.
Amm. angulatus thalassicus, QueNst., Amm. Schwab. Jura, pl. ii. fig. 9 (not fig. 4, 5).
Amm. angulatus psilonotus, QuENST., Ibid., pl. ii. fig. 10, 11.

Amm. angulatus hircinus, QuENST., Ibid., pl. ii. fig. 12.

Amm. angulatus oblongus, QUENST., Ibid., pl. ii. fig. 6.

Agoc. angulatus, Neum., Unterst. Lias, Abhandl. geol. Reichsans., WII. p. 38, pl. ii. fig. 5.
ZEigoc. subangulare, Nuum., Ibid., p. 33.

Localities. — Chevigny near Semur, Balingen, Diebrook near Ravensburg, Miihlhausen, Coppenbriigge
in Westphalia, Hildesheim, Markoldendorf.

In the collection of the Museum of Stuttgardt from the Planorbis bed there
is a specimen of this species, which is more discoidal than Sehlot. angulata, and
more like Weehneroceras in its aspect than any other members of this series, and
the same facts are observable in Quenstedt’s collection. In the collection at
Semur there are three specimens from the Planorbis bed correctly named cadenatus.
They are not large, and one specimen at the diameter of 52 mm. shows signs of
old age in its obsolescing pila and smooth abdomen. We have also examined
D’Orbigny’s types and confirmed these comparisons. Neumayr compares his
specimen from the Planorbis bed of Pfonsjoch with the North German species of
angulatus, which is a true catenatus, and in Professor Emerson’s collection from
Markoldendorf, now at Amherst, Mass., all specimens of this species agree very
closely with catenalus as figured by Quenstedt. The pile cross the abdomen with
a forward bend, but in one precisely the peculiarities of Quenstedt’s Fig. 12
are exhibited, the pile being straight as they cross the abdomen. <Amm. ang.
oblongus, Quenst., may be a large variety; the whorl as figured resembles that of
catenala.

Schlotheimia striatissima, Hyarr.

Amm. angulatus striatissimus, Quenst., Amm. Schwab. Jura, pl. iii. fig. 2.
Amm. angulatus striatus, QuENsT., Ibid., pl. iii. fig. 8-5.

Locality. —Semur.

Two specimens of this species in the Museum of Comparative Zodlogy and
Quenstedt’s descriptions and figures show that it is a discoidal shell like cadenaéa,
but the abdomen is narrower, the whorl more compressed, and the pile more
numerous and finer than in that species. They remind one in this respect of the
second subseries, but unfortunately there are no transitional modifications by
which to follow out the connection, if it existed, with these dwarfed forms of the

Oxynotus bed. The mould of the young specimen supposed by Quenstedt to
17

spre

130 GENESIS OF THE ARIETID&.

have probably come from the “ gelbesandstein” of the Trias, near Tiibingen,
belongs to this species, and it contains also other discoidal varieties, as well as the
extraordinary compressed but still discoidal form of striatissimus, Quenst.

Schlotheimia colubrata, Hyarr.

Amm. colubratus, Zivy., Verst. Wiirt., pl. iii. fig. 1.
Amm. Moreanus, D’Ors., Terr. Jurass. Ceph., pl. xciii. |
Amm. Moreanus, Haver, Ceph. Nordéstl. Alpen, pl. xv. fig. 1, 2 (not fig. 3, 4).
4igoc. Moreanus, Wricut, Lias Amm., p. 822, pl. xvii. fig. 1, 2.

Amm. angulatus Thalassicus, Quenst., Amm., Schwab. Jura, pl. ii. fig. 4, 5 (not fig. 9).

Localities. — Deyrolay, Hanoyer.

In the Semur collection there is a specimen named Moreanus from the lower
part of the same zone with Jzusieus, and it may be said to agree with D’Orbigny’s
figure." This is a variety identical with colubratus, Ziet., growing to a larger size
than catenata, At the diameter of 168 mm. in this specimen, the pils crossed the |
abdomen, showing that old age had set in. That this is sometimes a nealogic
feature retained throughout life is shown by another specimen, which at the diam-
eter of 21 mm. has the pile continued across the abdomen. |

Schlotheimia angulata, Zrrret.

Summ. Pl. XI. Fig. 4.

Amm. angulatus, ScuLotT., Die Petrefactenkunde, p. 70.

Amm. angulatus depressus, QueNst., Amm. Schwab. Jura, pl. ii. fig. 1, pl. iii. fig. 9.

Amm. angulatus costatus, QuENST., Ibid., pl. ii. fig, 8.

Aigoc. angulatus, Wricut, Lias Amm., pl. xiv. fig. 5, 6.

Schlot. angulata, ZirreL, Handb. d. Paleont., I. p. 456, fig. 637. \

Schlot. angulata, WAnNER, Unter, Lias, Mojsis. et Neum., Beitr., IV., 1886, p. 163, pl. xix. fig. 1-3, pl xx,
fig. 1-6.

Localities. —Muhlhausen, Hildesheim, Lyme Regis.

The young appear to be smooth for about one and a half whorls, then lateral
tubercles appear. These spread upon the sides into folds, which on the early
part of the fourth or last of the third whorl rapidly become true depressed pila,
and then begin to be continued across the abdomen with a very decided forward
bend at the geniculx, and form an acute angle on the abdomen. The depression
which obliterates the angle of intersection of the pile on the abdomen and forms
the smooth zone begins on the last half of the fourth whorl.

On the early part of the fourth whorl the abdominal lobe is somewhat deeper
than the superior laterals, and these again very much deeper than the inferior
laterals. The saddles are broad and shallow, the superior laterals being a trifle
shallower than the inferior laterals. On the first quarter of the fifth volution
the bases of the superior and inferior lateral saddles and the tops of the supe-
rior lateral lobes have become trifid, or unequally divided, whilst those of the ?
inferior lateral lobes and auxiliary saddles are equally divided. The abdom- |
inal lobes are shorter than the superior laterals, though the saddles maintain

1 The original at the Jardin des Plantes is a fragment, and D’Orbigny’s figure is in large part a resto-
ration, especially with regard to the internal whorls.

SECOND, OR SCHLOTHEIMIAN BRANCH. ul

their old proportions. In the full adult condition the characteristics of the
sutures differ considerably from those of the typical Arietide, and approximate
to those of Psiloceras.

The seventh whorl increases in size with great rapidity, the abdomen be-
coming narrower, the channel shallower, the pile more depressed, losing their
prominent somewhat abrupt genicular bend, and on the abdomen becoming
depressed to a level with the siphonal line. The involution of this whorl is
about two fifths, and that of the ninth a trifle over one half. The peculiar flatten-
ing of the sides and form of the adult whorl, and the amount of involution, are
close approximations to the adult characteristics of Amm. Charmassei, but the
septa are different and the young more robust; the pils are developed earlier
and more rapidly, and the abdominal channel also. In some specimens, however,
these last are not noticeable until quite a late period, the pile being continuous
across the abdomen, as in Der. planicostum, even on the sixth volution.

In the collections at the Stuttgardt Museum are several very fine specimens
of the old age of this species, and it is easy to distinguish it from Charmassei by
the narrowness of the whorls and its more open umbilicus and discoidal aspect.
One of the largest of these measures 495 mm., the last whorl 17 mm.; another
measures 515 mm., and the last whorl 18.5 mm.

In the Museum at Stuttgardt, in the centre of a crushed specimen of the true
angulata from Kirchheim, the young was very clearly exposed. This had very

smooth and round, though rather stout whorls. The pile appeared on the sides |

as faint folds, which are straight at first, then curve, reach the abdomen, and
finally cross it with a forward inflection. These become very prominent and
decided before the channel is formed, which finally cuts through the pile. This
variation, however, is considerable, since in the adult of this specimen the channel
is only partially developed, the pile being only about half cut through, though
the specimen is about two and one fourth inches in diameter. There is here a
close likeness to some of the trias forms, but not to the true planorbe, which the
young does not resemble closely. They resemble Weehneroceras very closely.
The same relations were observed in young specimens in Professor Quenstedt’s
collection, and in the Museum of Comparative Zodlogy.

It often occurs, also, that after the channel is developed, and the shell is
quite large, the pile again cross the abdomen, but this is not so frequent as
has been supposed. They oftener remain separate until old age.

The original of Amm. angulatus, Sow., which we saw in the British Museum, is

only a malformed communis."

1 See also Wright, Lias Amm, p. 478.

182 GENESIS OF THE ARIETIDAL.

Schlotheimia Charmassei, Wiuvyer.
Summ. Pl. XI. Fig. 5.

Amm. Charmassei, D’OrB., Terr. Jurass, Ceph., p. 296, pl. xci. (not pl. xcii.).
Amm. angulatus compressus, QuENST., Amm. Schwab. Jura, pl. ii. fig. 2.

Amm. angulatus compressus gigas, QUENST., Ibid., pl. iv. fig. 2.

Schlot. Charmassei, Wiu., Unt. Lias, Mojsis. et Neum., Beitr., IV. p. 196.
4igoc. Charmassei, Wriaut, Lias Amm., p. 823, pl. xx. fig. 1-3.

Localities. —Semur, Lyme Regis, Tiibingen,

Besides the characteristics mentioned in the description of angulata the follow-
ing may be added. On the sixth volution, the extremely gibbous form of the
young begins to change. The whorl increases more rapidly, the abdomen is
narrower, and the pile as in preceding species, with this exception. On this
volution, or perhaps on the fifth, they become bifurcated, or else have interme-
diate short pile interspersed between the longer ones. The sutures have remark-
ably large abdominal lobes, shallower than the superior laterals, but with much

more ragged outlines. The siphonal saddle is extraordinary in this respect. It _

is very large, and marked with several lateral minor lobes and saddles. The
remaining lobes and saddles are more complicated than in angulata.

On the sixth volution, the form of the whorl changes more than in angulata.
The involution of this whorl equals one half of the side of the sixth, whereas in
angulata the envelopment does not equal this until it reaches the ninth volution.
The involution at the same age in this species, i. e. on the ninth whorl, covers
full two thirds of the side of the eighth whorl. ‘There is a form in Professor
Fraas’s collection from Méhringen answering to the young of Charmassei, as fig-
ured by D’Orbigny, Plate XCI., and another from Filder, which is precisely inter-
mediate in its characteristics between this and the smoother, flatter variety figured
on Plate XCII. The oldest specimens in the possession of the Museum of Stutt-
gardt measured 53 mm., and the last whorl 23 mm. Schlot. angulala parts with its
pile and grows smooth much earlier apparently than Charmassei. Possibly this
occurs at about the same age, but the superior size of Charmassec makes it seem
older when the senile characteristics begin to appear.

Schlotheimia Leigneletii, Winner.

Amm. Leigneletii, D’Ors., Terr. Jurass. Ceph., p. 298, pl. xcii.
Schlot. Leignelelii, Wku., Unt. Lias, Mojsis. et Neum., Beitr., IV. p. 197.
Amm. compressus (pars), QUENST.

Localities. —St. Thibault, Semur, Vaihingen, Stuttgardt, Behla.

The same class of facts divides this species from Charmasset that we used
above to show the differences between the latter and angulata; namely, that the
young differ as well as the old in some specimens.

The differences are very great between the fifth whorl of Leigneletii, and the
same age in Charmassei. The tubercles are more prominent on the edge of the
abdomen, the pilze more depressed on the sides, and their terminations tubercular
on the edge of the abdomen, which, instead of being a broad, rounded space, is a

SECOND, OR SCHLOTHEIMIAN BRANCH. 133

flattened zone. The reduction of the abdomen of course occurs in all species of
this group, but in other species, except Boucaultiana, it is found only during the
senile stage.

Amm. angulatus compressus of Quenstedt may also in part belong to Charmassei,
since two specimens from the Stuttgardt Museum of this name apparently belong
to this species only. ‘The envelopment in one of these specimens covers about
two thirds of the sides of the eighth whorl, and about the same age the pile
again cross the narrow abdomen, obliterating the median depression or smooth
zone, and introducing a series of crenulations instead. This is a return to the
young condition, and indicates the first degradational or clinologie stage. It is
not intended by this to deny that there are no young which closely approximate
to the young of Charmassei. On the contrary, some specimens are apparently
identical in all respects, except the greater flatness of the whorls and the earlier
period at which involution appears, and the two species are connected by numer-
ous transitional forms.

Schlotheimia Boucaultiana, Wiunerr.
Summ. Pl. XI. Fig. 6.

Amm. Boucaultianus, D’Orx., Terr. Jurass. Ceph., p. 294, ples
Schlot. Boucaultiana, WAn., Unt. Lias, Mojsis. et Neum., Beitr., IV. p. 196.
4iigoc. Boucaultiana, Wricur, Lias Amm., p. 327, pl. xviii. fig. 1-4.

Locality. — Semur.

This remarkable species differs from Le/gneletii in about the same manner that
the latter differs from Charmassei, in other words, it is more involute than Leigne-
dei at the same age; i.e. on about the seventh or eighth whorl at least three
fourths of the sides are hidden. The pilx are not so coarse as in that species,
and the abdominal channel is obliterated at an earlier age and is succeeded by
crenulations caused by the pila. The sutures differ considerably. The specimen
examined was one of D’Orbigny’s types. The same transitional forms which lead
into Leigneletii also lead into other more compressed and more involute forms
which are transitional to the true Boucaulliana. They differ from Leigneletti: only
in the suppression of the tuberculated pile, and a general tendency toward obso-
lescence of the pile. on the sides.

Schlotheimia D’Orbignyana, Hyarr.

Amm. Charmassei (pars), D’OrB., Terr. Jurass. Ceph., pl. xcii. (not pl. xci.)

Locality. — Semur.

This species has depressed pile and resembles'closely Boucaulliana, but is not
so involute. It is in fact, as described by D’Orbigny, an extreme modification of
Charmassei, with excessively compressed whorls, and acquiring in the clinologic
stage a subacute abdomen. It resembles more closely Schlot. ventricosa of Wahner
than it does any other species, but it is even more compressed and more like
Charmassei in the adult stage than that species. D’Orbigny’s figure is that of an
old shell; the adults are less acute and more like Oharmassei or Leigneletii.

a

ee

134 GENESIS OF THE ARIETID.

The forms figured by Wiihner in his “Unteren Lias”* may be divided into
three subseries. It was not practicable to determine whether these series were
artificial or natural, though many figures of the young were given by Wihner.

The first series can be distinguished by the finer pila and somewhat com-
pressed whorls. They are as follows. Schlot. catenaia, Wih., and angulata, in the
Planorbis bed. The following, though still discoidal, are slightly more involute
forms, if one can say this after comparison with Neumayr’s figure of angulatum
from Pfonsjoch? They are Schlot. montana, Wiah., Plates XIX., XX., Donar, Plates
XIX., XXL, eatranodosa, Plate XX., pachygaster, Plate XXI, and marmorea, Plate
XXIL, and all occur in the Megastoma and Marmorea beds.

The second or coarsely pilated series have more gibbous forms in the young
and much deeper channels, or, in other words, the piles have more prominent ter-
minations on the abdomen. The discoidal forms are as follows. Schiot. ind., Plate
XVUI. Fig. 4, which has in an exaggerated condition the characteristics of the
subseries, and may be a pathological specimen, fawrina, Plate XIX. Fig. 5, angu-
lata, var. ind., Plate XX. Fig. 5. All three of these were found in the Megastoma
and Marmorea beds, but were followed by two young forms occurring, according
to Wihner, in the Rotiformis beds. These are Sehlot. scolioptycha and posttaurina,
Plate XXIII, and appear to have been the young of species, which may have
been more involute in the adults.

The third subseries has young with even stouter whorls than in the second
subseries, though not otherwise separable. Schiot. trapezoidale, the first species,
occurred, according to Wihner, in the Marmorea bed, and was succeeded by
ventricosa, Plate XXIII., and an undetermined form, Plate XXII. Fig. 12, both
in the Rotiformis bed.

Canavari in “ Unteren Lias von Spezia” describes dwarfs or young of Schist.
(Aigoc.) trapezoidale, Plate XVIL. Fig. 8, 9, and ventricosum, Plate XVII. Fig. 10,
which seem to be identical with forms described by Wiihner ; also Schiot. (-Aigoc.)
catenatum, Fig. 1, comptum, Fig. 3-5, Collegnoi, Fig. 6, all of which are very closely
allied, and may be either young or dwarfs of Schiot. Charmassei, or the more invo-

lute varieties of Schlot. angulata.

Srconp SUBSERIES.

The abdominal channel is narrower and deeper proportionally than in the
first subseries, and is a true furrow, in place of being a smooth zone or mere
depression formed between the interrupted pils, as in Weehneroceras and in the
first subseries of Schlotheimia. The shells known are finely pilated, and the
furrow is similar to what it is in the young of some species of the first subseries.°
The species have been found only above the Bucklandi zone, and are all, so far

as known, dwarfs.

1 Mojsis. et Neum., Beitr., [V., 1886. 2 Abh. k. k. geol. Reichsans., VII., pl. ii. fig. 5.
8 See Schlot. trapezoidale, Wih., Mojsis.-et Neum., Beitr., IV. pl. xxiii. fig. 2c, and others on the same

plate. ;

i — einem

ST atten

SECOND, OR SCHLOTHEIMIAN BRANCH. E39

Schlotheimia rotunda, Hyarv.

Amm. lacunatus rotundus, QuENsT., Amm. Schwab. Jura, p. 167, pl. xxii. fig. 5, 6.

This shell is more discoidal than any others described below. The whorls are
also stouter as arule. The pilz on the umbilical shoulders are coarser and are
tuberculated according to Quenstedt’s figures and descriptions. Amm. lacunoides,
Quenst.," may be the young of this or an allied species. It occurs so far as
now known only in South Germany.

Schlotheimia lacunata, Hyarrv.
Am. lacunatus, BuckMAN, Murch. Geol. Cheltenh., 2d ed., p. 105, pl. ii. fig. 4, 5.
Amm. lacunatus, Quenst., Amm. Schwab. Jura, p. 167, pl. xxii. fig. 1-4.
Amm. lacunatus, Dum., Etud. Pal. d. Bas. d. Rhone, p. 120, pl. xxi. fig. 18-20.
Amm. lacunatus, Wrigut, Lias Amm., p. 330, pl. lvi. fig. 16-18.
Amm. deletum, CANAVARI, Lias v. Spezia, Paleontogr., X XIX. pl. xviii. fig. 18.
Amm, sp. ind. efr. lacunata, CANAVARI, Fauna del Lias, Mem. del. Carta Geol. d’ Italia, II., 1888.

Localities. —St. Thibault, Semur.

The pile are not coarse or tuberculated at the umbilical shoulders. The
whorl is also more compressed and the involution greater than in Schiot. rotunda,
covering about two thirds of the side. The young according to the figures given
are also not smooth to so late a stage as in that species. The description of the
originals in the Geology of Cheltenham in a measure makes up for the figures.
The latter belong to a discoidal species, the former gives the usual combination
of an involute shell, narrow abdomen, flattened sides, and half-concealed whorls.
An important statement is also added, that the “ribs” cross the abdomen in the
young. The latter indicates the possibility of a direct derivation of the second
subseries from Schiot. catenata, and also serves to confirm the identification of
Wright's species with this, since Wright mentions the same characteristics.

Schlotheimia Geyeri, Hyarr.
Schlot. lacunaius, Geyxr, Liasis. Cephal. v. Hierlatz b. Hallstadt, p. 259, pl. iii. fig. 22, 23.

This species has fine but sparsely distributed pile at the umbilical shoulders
which speedily divide into two or more finer pile. The abruptness of the divis-
ion gives the umbilical pile a resemblance to those of Schlot. Quenstedti in Geyer’s
figures, but there are no tubercles, and the involution covers about four fifths of
the side, and the whorls are considerably compressed.

Schlotheimia angustisulcata, Guyer.
Schlot. angustisulcata, GEYER, Liasis. Ceph. Hierlatz b. Hallstadt, p- 256, pl. iil. fig. 24, 25.

The pile are finer, the whorls more compressed, the involution quite as exten-
sive as in the preceding. The sutures which are figured in this species, if they
can be correctly given in so small a figure, are quite distinct from those of the
similar involute forms of Schlotheimia.

1 Amm. Schwab., p. 162, pl. xxi. fig. 24, 25.

136 GENESIS OF THE ARIETIDA.

Schlotheimia Speziana, Canavart.

Zigoc. Spezianum, Canav., Unt. Lias v. Spezia, p. 166, pl. xviii. fig. 12.
Schlot. Spezianum, Canav., Fauna del Lias, Mem. del. Carta Geol. @ Italia, III., 1888.
This form is more compressed, has different pilations, and a remarkabl
P ? )
narrow channel. It is also as involute as any other species of this subseries, and
appears in the drawing to exceed all other forms in this respect.

THIRD, OR VERMICERAN BRANCH.

The living chamber is in most species attenuated, cylindrical, at least a volu-
tion in length, and sometimes over one and a half volutions. The shell in the
majority of forms is discoidal, and the area of envelopment almost invariably
limited to the abdomen. During the senile stages, the whorl tends to acquire
smooth, rounded, and convergent sides, and frequently loses the keel and channels,
thus completely reverting to the smooth cylindrical form of the young. The
sutures in each separate series tend to increase in the depth and breadth of the
second lateral saddles in the higher species, and there is a backward trend of the
auxiliary lobes and saddles which is strongly marked in some forms. In Vermi-
ceras the sutures become more decidedly arietian, the abdominal lobe is deeper
and narrower, the lateral lobes are broader and less dendritic, and the auxiliary
lobes and saddles are not as a rule inclined posteriorly.

CALOCERAS.

The shells are extremely discoidal, with numerous almost cylindrical whorls
which often retain the nealogic form throughout life. The pile are curved, and
they usually have an immature fold-like character, in keeping with the arrested
development of the form in the adult whorls. They also do not have well de-
fined genicule, and in some species they may be straight, and even tuberculated.
The sutures usually have longer and narrower lobes, deeper saddles, and more
complicated margins than in Psiloceras. They are, however, hardly distinguish-
able generically from those of some species of that genus, which occur in the
Northeastern Alps, and in some species also they approximate to those of
Vermiceras. The range of form and characteristics is very great, as might be

imagined, in a group which is transitional from Psiloceras to the true Arietide.

First SUBSERIES.

The whorls are rounded and gibbous, the keel when present not prominent ;
the channels absent or appearing merely as smooth, inflected zones; the pile
fold-like, and without genicule or tubercules. The sutures are very variable,
some having more complicated margins, as in the Psiloceratites of the North-
eastern Alps, and others approximating more nearly to the simplicity of Psi/.
planorbe of Central Europe. The abdominal lobe, however, as in Psiloceras, is
not usually deeper than the superior laterals,

THIRD, OR VERMICERAN BRANCH. LOT

Caloceras Johnstoni, Hyarr.

Amm. Johnstoni, Sow., Min. Conch., p. 464, pl. eccexlix,

Amm. torus, D’OrB., Pal. Francaise Ceph., p. 212, pl. liii.

Amm. psilonotus plicatus, Qurenst., Amm. Schwab. Jura, pl. i. fig. 12, 13.

Amm. Johnstoni, QuENs’., Ibid., pl. i. fig. 20. :

4ligoc. Johnstoni, Wricut, Lias Amm,, pl. xix. fig, 3, 4.

4Aigoc. Belcheri, Wricut, Ibid., pl. xix. fig. 1, 2 (not pl. xv. fig. 7-9).

Aigoc. Johnstoni, Neum., Unterst. Lias, Abhandl. geol. Reichsans. Wien, VII. pleut fig: 2:

igoc. torus, Neum., Ibid., pl. iii. fig. 38.

4igoc. Johnstoni, WAu., Unt. Lias, Mojsis. et Neum., Beitr., IV. pl. xvi. fig. 6-9.
Localities. — Wiesloch near Heidelberg, Bristol, Cheltenham.

This form differs from plunorbe in the outline of the whorl, which is much
narrower, more rotund and gibbous laterally, and in the greater prominence of
the pilee.

A specimen in the Museum of Stuttgardt measuring 120 mm., labelled fortilis,
Nirtingen, has a living chamber still incomplete, though nearly one volution in
length. Abdomen is slightly more elevated than in typical adult torus and the
sides more inclined, as is usual in old age of this species. Otherwise the form
and pilx, especially in the umbilicus, are the same.

Sutures of adult are similar, as far as seen, to those of Psiloceras, and in old
age the lobes and saddles decrease in size, becoming simpler in outline. Quen-
stedt’s specimen, figured in“ Ammoniten des Schwibischen Jura,” Plate I. Fig. 20,
is 110 mm. in diameter and shows the effects of senility in the compressed whorl.
His Figure 13 shows the living chamber to have been at least one volution in
length. The typical forms of this series are found in the Northeastern Alps, but
the distribution is general, as has been already noted by Neumayr.

In the collection of the Sorbonne at Paris there is one specimen from Beaure-
gard precisely similar to that figured by D’Orbigny, except that the whorls are
much larger and stouter. In the collection at Munich there are specimens from
Pfonsjoch, Kander in Bresgau, and Lyme Regis, exhibiting the typical form of
Johnstoni until they reach the diameter of 145 mm.

Var. Beauregardiense.

Amm. Beauregardiensis, COLLENOT.

This form from Beauregard in the collection at Semur is 185 mm. in diameter,
and has whorls increasing more rapidly in size than in the typical Johnstoni, but
otherwise does not differ from that species.

Caloceras tortile, Hyarr.
Plate I. Fig. 12-14. Summ. Pl. XI. Fig. 14.
Amm. tortilis, D’Or., Terr. Jurass. Ceph., p. 201, pl. xlix.
Amm. raricostatus, DunK., Paleontogr., I. ploxin. Ag. 17.
Aigoceras intermedium, Wriaut, Lias Amm., pl. xv. fig. 5, 6 (not fig. 3, 4).
Amm. laqueus (pars), Quenst., Amm. Schwab. Jura, p. 19, pl. i. fig. 15, 16 (mot fig. 14, nor p. 18, fig. 4).
Localities. —Semur, Rinteln, Quedlinburg.

This species is very generally misinterpreted by German and English paleon-

tologists. The young have exactly the same broad, gibbous whorl as the young
18

138 : GENESIS OF THE ARIETIDA.

of the keelless Johnston’, but gradually become elevated a little on the abdomen,
and at the same time acquire a faint keel. Subsequently the abdomen becomes
more elevated, and slight channel-like inflections appear on either side. At the
diameter of 98 mm. this occurred in one specimen from Beauregard in the collec-
tion at Semur. At the diameter of 195 mm. in other specimens from Beauregard,
the faint channels had disappeared, the pile: were nearly obsolete, and the keel
not so distinct. The marginal digitations of the lobes and saddles were also
deeper and much changed. At the diameter of 270 mm. senile changes were far
advanced in the only specimen of this size yet studied. The abdomen had
become rounded and keelless, and the pile so nearly obsolescent as to be barely
distinguishable.

A specimen from Beauregard in the collection of the Sorbonne, under the
name of Anum. laqueolus, Schlénbach, must have been when complete about 200 mm.
in diameter. The outer whorl of this shell resembles a typical ¢ortile, with
depressed abdomen and keel. The abdomen at earlier stages in the same speci-
men is rounded. Laqueolus, Schlonbach, is not of this species, but belongs to
Cal. Liasicum.

In some specimens the abdomen changes from rounded and rather flattened
in the young to a more angular outline in older stages, but does not acquire a
keel. This occurs'in D’Orbigny’s original at the Ecole des Mines, and in speci-
mens labelled fortilis from Chalandry, in the collection of the Sorbonne, at sizes
varying from 22 to 55 mm. _ It is probable that a well defined keel never made
its appearance even in the adults in some of these specimens.

Var. raricostatoides.

There are two specimens in Quenstedt’s collection from Quedlinburg, three
in the Museum of Comparative Zodlogy, and others at Semur, all found in
association with Planorbis. 'These seem to be identical with the forms described
by Dunker in the “ Paleontographica” as Amm. raricostatus.

A part of the specimens identified by Oppel as Johnstom in the Munich col-
lection appear to belong to Cul. tortile. One specimen especially is a rather
compressed form, from Waldenburg, with a slight keel developed at a late stage
of growth, and at the same time there is a change of form in the whorl, which
approximates to the parallel-sided, flattened-abdomened, carusense-like varieties
of Cal. Nodotianum ; the pile also begin to wear a more advanced aspect.

The torus-like variety is finely represented in the Bristol Museum by speci-
mens from Cotham, and a form which appeared to be the same was reported as
coming from the Bucklandi bed at Ashley Down. This has somewhat. stouter
whorls than the earlier forms at the same age, and shows the same tendency
to become stouter and larger manifested in the later occurring species of other
progressive series. The young have the usual development of forti/e, in some
instances producing a decided keel, and in others merely a slightly more com-
pressed form in the adult or old, the abdomen remaining keelless. They have
straight pile, and look remotely like raricostatus in form, but the young have

ag its

THIRD, OR VERMICERAN BRANCH. 139

the usual stout smooth whorl of the young of Johnstoni. Quenstedt places them
with /aqueus, but this, we think, is a mistake, arising from not giving proper
weight to the characteristics of the nealogic stages.

The presence of this form in the North German basin is worthy of remark,
since it is a degraded variety. The transitional keelless varieties uniting this
species and Johnstom would have been considered distinct under the name tortie,
while the keeled forms would have been separated and designated as a distinct
species, but for the fact that similar variations are also represented within two
other species, Cal. Liasicum and Nodotianum. It is evident from this, that the
keel in Caloceras has not become an hereditary character, but is a morphological
equivalent in varieties of different species.

Caloceras Liasicum.

Amm. Liasicus, D’OrB , Pal. Fran. Ceph., I. pl. xlviii.

Amm. Liasicus, HAvER, Ceph. Lias Nordostl. Alpen, pl. iii. fig. 1-3.

Amm. sironotus, Qumnst., Handb. Pet., p. 482, pl. xxxvii. fig. 1; and Die Amm. Schwab. Jura, p. 23, pl. i.
fig. 21.

Amm. laqueolus, ScuLON., Paleontogr., XIII. pl. xxvi. fig. 1.

Aiyoc. laqueolus, Wricut, Lias Amm., p. 315.

4éyoc, Liasicum, Wrieut, Ibid., pl. xv. fig. 1, 2; pl. xvi. fig. 1, 2.

Aigoc. tortile, Wrieut, Ibid., pl. xv. fig. 10, 12.

Ariet. Liasicus, WAu., Unt. Lias, Mojsis. et Neum., Beitr., VI., 1887, pl. xx. fig. 1-5.

Localities. — Semur, Bristol.

A large specimen in the Tiibingen collection, about 100 mm. in diameter,
shows by comparison with D’Orbigny’s figure that sdronotus, Quenst., is prob-
ably identical. One specimen at Semur retained very gibbous sides and broad
abdomen to a diameter of 175 mm., and then formed an elevated abdomen with-
out acquiring a true keel as figured by D’Orbigny. Another shell had reached
the diameter of 260 mm., but no true keel was formed, though old age began to
show its approach in the obsolescence of the pile. In D’Orbigny’s collection
these very broad forms stand side by side with the narrow one figured by him,
which is identical with sironotus, Quenst. D’Orbigny’s original has the keel as
well developed at a diameter of 100 mm. as the broad variety at a diameter of
250 mm. A comparison of the young with the young of fortile showed that they
are closely allied by their development. No constant distinction exists, except
that Liasicum is usually a stouter shell, and has about the same relation to ¢ortile
that the stouter forms of carusense in the Upper Bucklandi bed have to those of
the same name in lower beds. Wihner’s work upon this species gives figures of
the young, and exhibits a close alliance with Ca/. Johnstoni. The keel appears
in his Figure 3b, in a small but probably full-grown specimen, but no channels
are noted in his figures or description.

The extraordinary series of forms discovered by Neumayr and Wihner in
the Northeastern Alps enable us to give the following list of species, arranged
in subseries.

140 GENESIS OF THE ARIETIDZ.

Cal. (Aigoe.) Johnston, as figured by Wihner, Mojsis. et Neum., Beitr., IV.,
Plate XVI. Fig. 6-9, and Neumayr, Unterster Lias, Plate IIL, show that the
typical coarsely pilated form of the Central European province exists also in
the Northeastern Alps, but has probably a more limited number of descend-
ants in that fauna. A not infrequent but very interesting variation in this
species is the /orus variety, also present in the Northeastern Alps, Neum., Ibid.,
Plate III., and Wihner, op. ci/., Plate XVI. Fig. 6. It is distinguished by a
marked tendency to sudden increase in the size of the whorl by growth at a
late nealogic stage. The next gradation in the subseries, as exhibited in the
Northeastern Alps, is a species having a still quicker increase in bulk, as de-
scribed by Wihner, Cal. (goc.) hadroptychum, \bid., Plate XVII. Fig. 1-3.
The increase in the whorl takes place quite early, and the coarse fold-like
pile and rather broad whorls indicate the next step in gradation to be, as
pointed out by Wihner, the unnamed form figured on his Plate XVII., which
leads, as also pointed out by the keen eyes of this author, into the remark-
able Cul. (Atgoc.) mgromontanum given on Plate XXIV. The affinity is better
shown by the young figured on Plate XXV. Fig. 2, which is very similar to
the adult of the preceding species. This species has a distinct but broad keel
in the adult, and slightly compressed whorls similar to those of Oa. proaries, and
is a good example of morphological equivalence. Cal. Liasicum, as described and
figured by Wiahner,’ evidently has compressed whorls, and is more closely allied
to Cal. Johnstoni in all varieties than the same species in Central Europe.

Cal. (Ariet.) Loki* has close relations to Liasicus of the Northeastern Alps,
as pointed out by Wihner, and Cad. (Ariet.) Seebachi® is also an allied species.

SECOND SUBSERIES.

The whorl is subquadragonal in the adult. An obtuse keel is always present.
Very shallow channels are developed, and the pile are prominent, straight, and
in some species have slight genicule like those of Vermiceras.

The sutures, with the exception of Cal. laqueum,’ have an abdominal lobe
deeper than the superior laterals, but the superior and inferior lateral lobes
are of nearly equal size and length, the superior lateral saddles broader, but of
about the same depth as the inferior laterals, and the marginal lobes and saddles
similar to those of Psid. planorbe.

The young are similar to Qal. Johnston. The clinologic period has a sub-
acute abdomen, but this becomes rounded in the last part of the senile stage.
The lobes in this stage return to their younger or psiloceran proportions, the
abdominal lobe becoming shallower and broader, the lateral lobes narrower and
shorter, and the lateral saddles broader and shallower in proportion.

1 Mojsis. et Neum., Beitr., VI. pl. xx. + lbids, Vv... pl. XVil. e dbids; Vi Dl. xoc

4 Cal. laqueum seems to have an abdominal lobe shorter than the inferior lateral lobes, and in some
specimens the sutures are similar to those of the first subseries. In other specimens they resemble more
closely those of Psil. planorbe, and in still others they become similar to the sutures of Vermiceras.

THIRD, OR VERMICERAN BRANCH. 141

Caloceras laqueum, Hyarr.

Summ. Pl. XI. Fig. 22.

Amm. laqueus, Qurnst., Amm. Schwab. Jura, pl. xviii. fig. 4; pl. i. fig. 14 (not fig. 15, 16).
Amm. intermedium, Porti., Geol. Londonderry, p. 186, fig. 17.

4igoceras intermedium, Wriaut, Lias Amm., p. 314, pl. xv. fig. 3, 4 (not fig. 5, 6)

igoceras Belcheri, Wriaut, Ibid., p. 313, pl. xv. fig. 7-9 (not plo eke NO do),

Ariet. Scylla, Win., Unt. Lias, Mojsis. et Neum., Beitr., VI. 1887, plexes lio: 758;

Amm. Scylla (pars), Reyné&s, plates.

The youngest specimen I have yet seen of this species was 26 mm. in
diameter. The abdomen, however, was smooth, with no indications of the
immature keel of the adult, the sides exceedingly gibbous. The pile evidently
began early, and were closely crowded and slightly curved forwards.

In one specimen the pile were very slightly developed in the adult; in
another, at a corresponding size, they were already disappearing, and upon the
next or senile whorl they were almost obsolete. The keel probably becomes
very slight at this time, and the likeness to its own young must then have
been remarkably close.’ This specimen was 53 mm. in diameter.

The similarity of the adult of this species to the young of Ver. spiratissimum
is unmistakable. A specimen from Bebenhausen, in Quenstedt’s collection, shows
that the sutures are intermediate between those of Cal. Johnston’ and those-ot
Ver. spiratissimum. The young of a specimen from Oestringen in Fraas’s collec-
tion, Stuttgardt Museum, when about 26 mm. in diameter, has the exact form
and characters of Quenstedt’s figure, but no signs of a keel, though this appears
soon afterwards. A fine series in the Semur Museum shows that the keel may
not yet have arisen in a specimen at the diameter of 45mm. The whorl also
at the time of the appearance of the keel may have either a broad, depressed
abdomen, as in the varieties which approximate to the young of Ver. spiratissi-
mum and carusense, or this part may be elevated, as in Cal. tortile.

The young, however, are like the young of Cul. Johnston’. The sutures also
vary in the same way, some specimens having sutures like those of Johnston, and
others approximate to those of carusense and spiratissinum. Old age in all these
was marked by narrowing of the abdomen, loss of the keel, etc., which probably
precedes a rounding off of the same region, though this extreme effect of senility
was not observed. ‘The pile often cross the abdomen in the young, but not
in the adult. In one specimen, however, which had the senile angularity of
the abdomen well marked at the diameter of 73 mm., the pile again crossed
the abdomen, and then faded out almost entirely. Another specimen, even at
the extreme diameter of 105 mm., retained a keel, as in the adult.

igoc. Beicheri, Wright, from the Angulatus bed, may be an example of this
species. It exhibits the squared or quadragonal form of this series, and is not,
as figured, at all similar to any species of the first subseries. oe. intermedium,
Wright, from the lower part of the Angulatus bed, probably also belongs to

* Quenstedt figures and describes, in his Amm. Schwab. Jura, one old specimen a trifle larger than that
described above, which confirms this supposition as to the senile degradation of the keel, and it has no pile
on the last whorl. The living chamber is still incomplete, though as long as the last volution.

142 GENESIS OF THE ARIETIDA,

this species. The abdominal view is not similar, not being flat enough on the
abdomen, but the lateral view has the straight perfect pile of this subseries.

The Amm. Burgundice, Martin, as identified at Semur, is identical with this
species. It is, however, smaller than those from Saulieu, which are associated
with Psil. planorbe, and is placed in the same bed as Liasicum. Wiihner’s figures
and description of Arie. Scylla,' Reynés, seem to agree closely with the descrip-
tions and figures of this species, The aspect of the umbilical or young whorls
in Wahner’s figures shows that Sceyl/a, Wih., is certainly not identical with
the Johnstoni-like variety of Cal. raricostatum, though it very closely resembles
that form.

Caloceras carusense.

Plate I. Fig. 15, 16. Plate II. 1-3a. Summ. Pl. XI. Fig. 15.

Amm. carusensis, D’Oxs., Terr. Jurass, Ceph., pl. Ixxxiv. fig. 3-6.
a

Amm. Arietis, Zint., Verst. Wiirt., p. 3, pl. ii. fig. 4 (not fig. 2, 3).

Amm. spiratissimum, Hauer, Ceph. Lias Nordéstl. Alpen, pl. iii. fig. 1-3.?

Amm. latisulcatus longicella, Quenst., Amm. Schwab. Jura, pl. xii. fig. 5 (not fig. 1-4, 6).
Amm. laqueus (pars), QUENST.

Amm. Scylla (pars), Reynks, plates.

Localities. — Lyme Regis, Semur, St. Thibault, Balingen, Willershausen in Hanover, Luxemburg.

The characteristic of this species as given by D’Orbigny, the crossing of
the abdomen by the pile, is not an important peculiarity, since it 1s com-
mon in the young of caloceran forms. The young of the normal variety is,
however, identical with D’Orbigny’s figure. It acquires the keel when the
shell is about 25 mm. in diameter, and is at this stage very similar to one
variety of Cal. laquewm. The sides in the later stage and adults become more
flattened, and the abdomino-dorsal diameter of the whorl increases proportion-
ally. One variety in the Museum of Comparative Zodlogy has much stouter
more quadragonal whorls than this, with flattened sides and abdomen, though
the pile are never very prominent or perfectly geniculated.

The abdominal lobe is long, and much deeper than the superior laterals.
This is owing largely to the non-development of the superior laterals, which
remain short and broad. The superior lateral lobes are shallow and broad, the
inferior laterals narrow, and not usually long in proportion. The most character-
istic parts of the sutures are the first auxiliary saddles; these are remarkably
large, and often tongue-shaped. The auxiliaries do not, therefore, incline back-
wards, at least in adults. The marginal lobes and saddles, and the margins of
the superior and inferior lateral saddles and lobes, are simple, and like those
of Psil. planorbe.

This variety retains the keel until a very late age, even after the shell
becomes perfectly smooth. The form at this time is precisely similar to that
of the old of the stouter variety of Cal. Nodotianum or tortile ; subsequently, how-
ever, the whorl becomes round, as in Plate Il. Fig. 1-3a. This stout variety

1 Mojsis. et Neum., Beitr., VI. pl. xxv.
2 The specimen in Oppel’s collection enabled me to quote this as.a synonym.

sie els ents is RSS sine STE is 8

THIRD, OR VERMICERAN BRANCH. 1438

is sometimes identified with Amm. Liasicus in Germany, but that species has a
form more like Johustoni, a larger keel, and entirely distinct sutures.

A specimen from Aldingen, in the Museum of Stuttgardt, shows an entirely
smooth senile whorl, precisely similar in form to that described above in the
collection of the Museum of Comparative Zodlogy, though it is not half the size,
the diameter being 103 mm. Another from Vaihingen had a living chamber still
incomplete, though nearly one and a half volutions in length. On the latter
part of the eighth volution in this specimen the sides began to become flatter
and convergent, and on the ninth and tenth volutions the form was subtrigonal,
the channels absent, the pile still prominent though obsolescing, and the keel
reduced to a raised line; diameter, 163 mm. Another, of nearly the same size
as Hauer’s figure of Amm. spiralissimum, agreed closely, the sutures also being
identical. The form of the whorl is, however, slightly more flattened laterally.
It belongs to the large variety of carusense, and is found, according to Hauer,
with Conybeari, roliformis, and bisulcalus, in the “ gelben kossener Schichten of
Enzesfeld.’ A specimen from Elwangen, labelled Amm. torus, in the Geo-
metricus zone, exhibits all the characteristics of the large specimen described
above. It has larger and stouter whorls and pilx than the specimens described
from the Lower Bucklandi beds, though the sutures and other characteristics
are similar. A specimen of this variety from Aalen also occurs in Professor
Quenstedt’s collection at Tiibingen, with larger and more prominent pile than
usual.

The young and old stages of this species at Semur and elsewhere are usually
identified either as torus, or tortilis, or Johnstoni, because of the resemblances of
the stages of development and senility in the different species of this series.

Caloceras longidomum, Hyarr.

Amm. longidomus, QueNstT., Amm. Schwab. Jura, p. 50, pl. vi. fig. 1, 2.
Amm. longidomus eger, QuENsT., Ibid., pl. vi. fig. 3.

This species, as described and figured by Quenstedt, cannot be classified
with certainty. Not having seen specimens unquestionably referable to the
species, we cannot positively decide as to its true affinity. It is, according to
Quenstedt’s description, a more immature or primitive form than spzratissimum,
since he alludes emphatically to the resemblances between the young and
Psiloceras. He also states that the young are closely allied to the young of
spiratissimum. This evidence seems to conflict, but the sutures, their backward
inclination, and the fact that the abdominal lobe, though longer than the supe-
rior laterals, is only slightly longer, the not very prominent and curved pile of
Quenstedt’s figure, the broad keel and slight channels, and the somewhat com-
pressed form of the older whorls, are all characteristics similar to those of caru-
sense. It may be a variety of carusense larger than the French, and becoming
senile more slowly. The curved pile are not like dagueum, and the cylindrical
whorl and tendency of the pil to cross the abdomen in the young also suggest
connection with carusense.

144 GENESIS OF THE ARIETIDA.

Caloceras Nodotianum, Hvyarr.

Plate I. Fig. 7-11 a. Summ. Pl. XI. Fig. 16.

Amm. Nodotianus, D’Orx., Terr. Jurass. Ceph., p. 198, pl. xlvii.

Locality. — Semur.

I have never seen the original, but the species as identified in D’Or-
bigny’s collection and at the Museum of Semur, and also in Boucault’s collection
named after D’Orbigny’s types, has not a close resemblance to Oppel’s type of
Nodotianum. This last is probably its morphological equivalent in the genus
Arnioceras, since it has smooth young, and is otherwise similar to Arnioceras.
A specimen in the Museum of Comparative Zovlogy, said to be from Semur,
has a stouter form and straighter pile than any specimen I have seen else-
where. It has in these characters and in general aspect resemblances with
forms like Cal. proaries, var. latecarinalum, but the abdomen differs in not being
so much flattened.

The fine suite of specimens in the Museum at Semur shows that this species
has several varieties. One resembles. the variety of Cal. tortile from Walden-
burg. Another, at 128 mm. diameter, has the sides inclined and the abdomen
narrow, but not yet entirely acute. Another, even at the small diameter of
57 mm., has an abdomen acute, as is represented in D‘Orbigny’s figure. The
septal digitations of this species are not so complicated as in Zvasicum or the
torus variety of Johnston. The examination of the specimens in the Museum
at Semur shows them to have been derived from Cul. carusense. The shells
found in the Tuberculatus bed resemble the adults of this species until a late
stage of growth. Plate I. Fig. 11, represents the full-grown adult, and Fig. 11
a section of the last whorl with its broad abdomen; Fig. 7, a larger specimen ;
Fig. 9, 10, the approach of old age in a fragment of a still larger specimen.
In the section the abdomen is shown growing narrower on the last whorl.

Caloceras raricostatum, Hyarr.

Var. A.
Plate VI. Fig. 15.

Amm. raricostutus, D’Orx., Terr. Jurass. Ceph., p. 212, pl. liv. fig. 1, 2 (fig. 3, var. By:

Amm. raricostatus, QuENsT., Amm. Schwab. Jura, pl. xxiii. fig. 22, 23; pl. xxiv. fig. 4-10 (other figs., var. B).
Ariet, raricostatus, Wricut, Lias Amm., pl. vii. fig. 2-6 (pl. xxvi. fig. 5-14, var. B).

Ophioceras Johnstoni, Hyarr, Bull. Mus. Comp. Zool., I., No. 5, p. 75.

Localities. — Lyme Regis, Somerset, St. Thibault, Semur, Salins, Balingen, Boll, Willershausen in
Hanover.

The pile apparently begin abruptly, but they are really preceded by de-
pressed folds hardly perceptible to the naked eye. The pile are very closely
set at first, but begin to be more widely separated on the fifth or sixth whorl.
On the third or fourth whorl there are over forty, while on the eighth whorl
there are not over thirty. No other changes take place in them or in the

THIRD, OR VERMICERAN BRANCH. 145

form of the whorl until about the sixth whorl. During this volution the
abdominal region is raised to a slightly greater prominence, and the siphonal
ridge appears.

A large specimen from Semur shows pile, which are obtuse, but prominent
and bent forward. These characteristics belong to the adult stage, and are
preserved without change throughout the tenth whorl. On the ninth and tenth
volutions the pil are very numerous, being respectively forty-one and _ thirty-
eight in number, and the young of this shell must have had a larger number
of pilx than any specimens described above. On the second and third quarters
of the eleventh volution the pila became more and more depressed, and finally
disappeared. The twelfth whorl was rounded and smooth, like that of the young,
and therefore a good illustration of the nostologic stage.

There is not usually much variation in the sutures of this species. The
abdominal lobe is considerably longer than the superior lateral lobes, and the
inferior laterals may be of about the same length, or not more than half as
long. ‘The superior lateral lobes are broad at the summits and serrated, the
inferior lateral lobes are very small in some specimens, owing to the small size
of the first auxiliary saddles. The two larger saddles may be of equal depth,
or the inferior laterals somewhat the deeper; the superior laterals are, however,
very broad in proportion to their depth, and the inferior laterals much narrower,
occasionally even club-shaped. These proportions are apparent at an early
age, and were observed upon the latter part of the third whorl before the
development of the marginal lobes.

Var. B.
Plate I. Fig. 24, 25 a

Amm. raricostatus, Z1Ev., Verst. Wiirt., p. 18, pl. xiii, fig. 4.

Amm. raricostatus, QuENST., Amm. Schwab. Jura, pl. xxiii. fig. 8-21, 24-31; pl. xxiv. fig. 1-8 (other figs.,
var. A).

Amm. raricostatus, Haver, Ceph. Lias Nordostl. Alpen, pl. xvi. fig. 10-12.

Ariet. raricostatus, Wrieut, Lias Amm., pl. xxvi. fig. 5-14 (pl. vii. fig. 2-6, var. A).

Ophioc. raricostatus, Hyarr, Bull. Mus. Comp. Zodl., I., No. 5, p- 75.

The true pile begin upon the third whorl. There are about forty on the
third and fourth whorls, decreasing to about twenty-five on the fifth whorl,
and on the seventh whorl there are only about twenty pile, the last of which
already begin to exhibit symptoms of senile degradation. On the eighth whorl
the pile are degraded to mere blunt folds, The remainder of this whorl could
not be observed, but a fragment of the first quarter of the ninth shows that
these blunted folds are still more depressed, being merely lateral ridges. The
whorl at this time has an elevated abdomen, and the keel has disappeared.
The form is similar to the old age of the stout variety of Cal. tortile.

The distinctions between this and the preceding variety are to be sought
in the sutures, the development of the pile, and the size of the adult shell.
The young are precisely like the young of Cal. carusense, Amm. arictis, Ziet.,
but on the fifth volution the whorl spreads out more laterally, and the pilae

19

146 GENESIS OF THE ARIETID.

become more prominent as well as more widely separated and fewer in number
than on the fifth whorl of this species or of Cal. Johnstoni.*

The large form of Oal. carusense exhibits no sign of senility on the beginning
of the ninth whorl, thus attaining a much larger size in its adult condition than
the typical raricostatus, which often exhibits signs of senile decay upon the latter
part of the seventh whorl.

The abdominal lobe is somewhat longer than the superior laterals, and the
inferior laterals shorter than, or about equal to, the superior laterals. The
superior lateral saddles are very broad in proportion to their depth, as are also
the inferior laterals, the latter being either equal to or rather deeper than the
former. The first auxiliary saddles are, as usual, very variable in size and
form, but when compared with the inferior laterals they are very much more
prominent than in the adult of Cai. carusense. This seems to be the only marked
difference between the sutures of these two species, and it is probably not very
important.

The true raricostatus from the Raricostatus bed, is rarely misnamed in collec-
tions, but there are other forms of distinct species occurring earlier which are
frequently misnamed raricostalum. The peculiar variety of ¢ortile from Quedlin-
burg is one of these, but it has smooth and gibbous young whorls like the
young of Johnstoni. Cal. suleatum, with coarse but sparse pile, from Semur,
is another example. Some varieties of carusense afford other examples, but
raricostalus is frequently almost inseparable from the young of carusense until
the specimens are over 51 mm. in diameter.

The adult of variety A of true raricostatum is almost precisely like carusense
in those varieties which have very closely set pile in the young, as in Plate I.
Fig. 16. Cal. raricostatum, var. A, therefore, seems to have arisen through an
arrested development of carusense, and then subsequently to have given rise to
the peculiar flattened typical whorls of variety B.

Caloceras aplanatum, Hyarr.

Ariet. tardecrescens, BLAKE, Yorkshire Lias, p. 285, pl. v. fig. 5 a, b.

Locality. —- Whitby.

This species is represented by a specimen which we were at a loss to
dispose of until we read Blake’s description, and saw the figure. The latter is
poor, but with the description it suffices, if one has a specimen in hand. The
whorl in the young has a completely caloceran form and pile, which are similar
to the young of Cal. raricostatum. It is in fact a much compressed, keeled, chan-
nelled form of caloceras similar to Nodotianum.- It occurs in Blake’s Jamesoni bed
of the Middle Lias, but is doubtless to be accounted for in the Raricostatus
bed of Wright, which is included in Blake’s Jamesoni bed. It is discoidal, and
the pile on the outer whorl have become depressed and curved. Specimens
in the British Museum from Robin Hood’s Bay have been named Conybeart by

1 Plate I. Fig. 25 a represents an abdominal view of the adult.

te me — ilar

5 mabe

THIRD, OR VERMICERAN BRANCH. 147

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Fig. 23, 24. Views from the side and abdomen of Cal. aplanatum.

Bean, and were said to have been found in the Lower Lias. Their young, seen
from the side and only in the umbilicus, have the peculiar pile and general
aspect of raricostatus, with similar rotund sides and fine closely set pile.

Cal. (Ariet.) prespiratissinum, Wih.,* has distinctly caloceran sutures and pile
without genicule. It develops a keel at an early stage, and has a subquadragonal
whorl in the adult with slight channels. It is a close morphological equivalent
of the Vermiceran-like variety of Cal. daqueum of Central Europe, if not identical
with it, and is certainly, as stated by Wihner, transitional to Ver. spiratissimum.

Wiihner’s figures prove that Cal. proaries is a form with late development of a
keel, the exact equivalent of Cal. Nodotianum in the Central European province.
Wiihner’s full series of young and adults,* and Neumayr’s senile specimen figured
in Unterster Lias,? show that the young of Cal. proaries (Plate XXX. Fig. 7) resem-
ble very closely the adult stages of Psi. sublaqueum, Wah. (Plate XXX. Fig. 4),
Cal. Johnstoni (Plate XVI.), and Cal. (Psil.) orthoptychim, Wah. (Plate XXVII.
Fig. 2), and the unnamed form figured on Plate XXVIL Fig. 3. Cal. (Psil.)
gomoptychum, Wih.,* has the same compressed whorls as in the more advanced
stages of proaries, and appears to be intermediate between that species and Cul.
cycloides. The sutures agree with those of proaries. We venture to differ from
Wiihner, who associates this species more closely with Cai. Sebanum of the Pla-
norbis bed. The apparently intermediate aspect and characteristics seem to
have been inherited at an earlier stage than in proaries, but not quite so early
as in cycloides, if one can use figures for arriving at such conclusions. Cai. (Ariet.)

1 Mojsis. et Neum., Beitr., V. pl. xxi. 2 Tbid., IV, pl. xxviii-xxx.
8 Abhandl. geol. Reichsans.,, VIE. pl. xxviii. 4 Mojsis. et Neum., Beitr., IV. pl. xxvii.

148 GENESIS OF THE ARIETID.

cycloides, Wiih.,' is a slightly more compressed form, which may be transitional
between the last and the next species, Cal. (Ariet.) Doetzkirchneri. This last is
figured by Neumayr2 Wiihner’s figures of the young of this species show the
rounded sides, slight keel, and pile similar to those which proaries has at later
stages in some specimens, and even in adult stages in others. Cal. (Ariet.) Cas-
tagnolai, figured by Wiihner,’ shows in its very compressed whorls, narrower
umbilici, and sharp prominent keel, which are well developed at an early stage,
when the shell is about 15 mm. in diameter, that the cycle of normal modifications
is approaching completion. Cal. ( Ariet.) abnormilobatum* gives us the final grada-
tion. This is a shell having still more compressed whorls, narrower umbilici, due
to the more involute whorls, and a more attenuated keel.

This keel and that of Castagnolai leads to the suspicion that it may be hollow,
but Wihner is too keen an observer, as shown in his complete descriptions, to have
let such an obvious peculiarity pass unnoticed. His remarks also show that he
knows how to distinguish between the morphological equivalence of this species
with Oxynoticeras and its true genetic affinities, as demonstrated by the nea-
logic stages and their similarities to the later stages and adults of Castagnolai and
cycloides. Wihner’s descriptions, which we did not consult until we had written
the above, are sustained by our experience so far as the serial relations and affini-
ties of Doetzkirchnert, cycloides, Castagnolat, and abnormilobatum are concerned.”

THIRD SUBSERIES.

This subseries contains species which have better defined channels and more
prominent keels in the adults than is common in the second series, and during
the clinologic stage these are still retained. The whorl in other words becomes
rounded only in the nostologic stages, and probably very rarely attains this ex-
treme of modification. The clinologic stage has also slightly flattened and
inclined sides.

Caloceras sulcatum, Hyarr.
Plate I. Fig. 19, 20. Summ. Pl. XI. Fig. 20.
Amm. Conybeari, Zint., Verst. Wiirt., pp. 3, 35, pl. ii. fig. 4?

Amm. Nodotianus, Haurr, Ceph. Lias Nordostl. Alpen, pl. vi. fig. 4?
Amm. kridion, Quenst., Amm. Schwab. Jura, pl. ii. fig. 7 (not fig. 5, 6).

Locality. — Semur.

This species is precisely similar to Hauer’s figure, except that the sutures are
more distinctly caloceran, having the line of auxiliaries inclined backwards. Our
specimens are also somewhat stouter, the abdomen broader, the channels deeper,
the geniculze more prominent, but the pile and general aspect of the shell are
exactly similar.

1 Mojsis. et Neum., Beitr., V. pl. xxii., xxiii.

2 Abhandl. geol. Reichsans., VII. pl. v. fig. 1.

3 Mojsis. et Neum., Beitr., V. pl. xxii., xxiii. 4 Tbid., pl. xxviii. fig. 4-7.

5 We have given outline figures on Summ. Pl. xi. of Cal. cycloides, fig. 17, Castagnolai, fig. 18, and
abnormilobatum, fig. 19. ‘

il teeersineer- ltetae

THIRD, OR VERMICERAN BRANCH. 149

One specimen in the Museum of Comparative Zodlogy has somewhat deeper
channels than is usual in this species, but is otherwise quite similar to the raricos-
tatus-like variety (Plate I. Fig. 19, 20). Quenstedt identifies this variety with
Arn. kridioides (kridion) in his “ Ammoniten der Schwabischen Jura,” but from
this species it differs essentially, if we are right in our selection of the form to
which the name Amm. kridion, Oppel, has been applied. Undoubtedly there is a
close resemblance between this species and raricostatum, on the one hand, and Arn.
kridioides on the other. The young and the channels separate it from the former,
and the great breadth of the whorls, channels, caloceran pile, and sutures, from
the latter. The raricostatus-like form of the whorl and pile, and absence of
tubercles, distinguish it from what we consider to be the true fridion. Zieten’s
figure of a specimen from Kalthenthal, near Stuttgardt, has exactly the aspect
of this species, and though the abdomen looks somewhat broader in Zieten’s sec-
tion the pile have no tubercles. It is more like this species than any form of
kridion or kridioides, if the figure is accurate.

Caloceras laqueoides, Hyarr.
Amm. sinemuriense, FRAAS.

In this specimen, now in the collection of the Museum at Stuttgardt, found,
according to Fraas, in the Angulatus bed, there is a most singular mingling
of the characteristics of dagueum with the peculiar pile of Coroniceras Buckland,
var. sinemuriense. :

The young and adult whorls are smaller and more numerous than those of
sinemuriense, and like those of daqueum. The abdomen, however, has narrow
channels, and many of the pile in the adult have large tubercles somewhat
thrown back, which give them the aspect of the undivided pile of senemuriense.
Between these there are usually two or more of the linear pil of one variety of
laqueum, and the tubercles when covered by the shell do not extend into spines,
but remain mere tubercles.

In old age or on the. last whorl of this specimen, which may perhaps be
prematurely old, the intermediate pilx alone are found, the stout tuberculated
simuriense-like pile having become obsolescent. At this time the form and
characteristics of the whorl are precisely as in daqgueum, except the channels;
these still remain very much shallower. Upon the whole, therefore, it is prob-
able that this may be a distinct species. Together with others, it shows that
Caloceras may have forms which are the morphological equivalents of the tuber-
culated, keeled, and channelled progressive forms of Vermiceras, Coroniceras,
and Asteroceras.

150 GENESIS OF THE ARIETIDA.

Caloceras ? Deffneri.
Summ. Pl. XI. Fig. 21.
Amm. Deffneri, Opr., Mittheilungen, II. p. 181, pl. xl.
Locality, — Stuttgardt.

This species has whorls at first sight apparently identical in form with those
of the typical Conybeart.

The young have prominent pile and geniculz on what seems to be the first
quarter of the fourth whorl, and the genicula become tuberculated in the adult,
without, however, exhibiting the angular forward bend of Conybeari. :

The abdominal lobe is extremely broad, its lateral branches at first extending
over the channel ridges on either side, and then diminishing to two pointed minor
lobes. The siphonal saddle is very large. The superior lateral lobes are very
narrow, profusely branching, a trifle longer than the abdominal lobe, and very
much longer than the inferior laterals. These and the auxiliary lobes are often
inclined posteriorly, as in Caloceras. The inferior lateral saddles are about as
deep as the superior laterals, and have deeply cut margins, as in that genus. The
first auxiliary, however, is often of considerable size, and then the inclined aspect
of the inner margin is destroyed. The superior lateral saddles are penetrated by
a very peculiar and remarkable marginal lobe, which divides them into two
portions, the inner shorter than the outer half. The proportions of the lobes and
saddles, and this last peculiarity, show, besides the form, a closer repetition of
the characteristics of Conybeari than could have been anticipated from the gen-
eral aspect of the shells.

The channels are shallow, but have lateral ridges, and the keel is well formed
and prominent, as in Conybeari. The series of this species in the Museum
at Stuttgardt illustrates the different ages at which senile characteristics may
begin to appear. The last specimen described above was only 175 mm. in
diameter. Another specimen, however, reached the size of 380 mm., and yet
only the last volution and a half exhibited senile degradation. The first senile
half-volution had obsolescing pilze and tubercles, while the last half-volution was
entirely smooth. The channels and keel remained almost unchanged, as in the
adult. Not even a fragment of a living chamber was present. Oppel’s original
is in the Museum at Stuttgardt. The eighth and ninth whorls of this speci-
men are senile, the tubercles have disappeared, the sides are more convergent,
and the abdomen more elevated than in the adult; the keel and channels, how-
ever, were retained even after the pile disappeared, though they had become
shallower.

The sutures indicate affinity with the Caloceran series, but our knowledge of
the early stages is incomplete, and this opinion is consequently uncertain.

Neumayr in his “ Unterster Lias” figures a large specimen of Cul. (:Arvet.)
Huueri, and gives a section. These show that the nealogic stages of this species
are first similar to Johnston, then as the keel appears resemble Cul. Loki and the
like, and finally take on the narrow channels of the adult. The closely set, bent,

<P emmmme

THIRD, OR VERMICERAN BRANCH. 1k

immature-looking pile are also characteristic and persistent in this subseries.
The sutures are distinctly caloceran. Our own notes made in the Museum at
Munich give the same results as regards this important species. Neumayr
clearly points them out as transitional, while calling the species an Arietites. It
is evident that we differ mostly in the limits which are ascribed to genera.
Cal. (Ariet.) Loki, Wih.,' and Cad. (Ariet.) Seebachi, figured on Plate XX., indicate,
when compared with Cal. (Ariet.) Hauert, Wah., that Hauert must have been con-
nected with Johnston’ through some such flat-sided shells as the former. The
Cul. (Ariet.) Haueri of Wihner, as figured on Plate XIX. and especially on Plate
XVIL, shows acceleration in the earlier development of the keel and channels.
The specimen on Plate XVI. Fig. 3, though about the size of the specimen fig-
ured on Plate XVII., has very shallow channels, and an immature keel, which
contrast markedly with the deep channels and perfect keel of the former. Cad.
(Ariet.) coregonense, Wih.,’ is figured so fully that, as in Cal. Haueri, one can see
that the keel and channels were developed at different stages of growth, in some
much earlier than in others, and that old age began also in some cases much
earlier than in others. Cal. (Ariel.) ophioides,? Wih. (not D’Orbigny’s species,
which is a true Vermiceran species with constant channels, tuberculated pile,
etc.), has also varieties in which channels are very late in appearing, and others
in which they appear early. Oud. (Arict.) perspiratus, Wih.,* a stout form of whorl,
but the age at which channels appear is not given. Cul. (-Ariet.) supraspiratus ,
Wih.,° has the channels developed at an early age as compared with other
species.

Caloceras Newberryi,’ Hyart.
Locality. — Peru.

Two very interesting specimens of this species have been placed in my hands
for identification and description through the kindness of Prof. J. S. Newberry.
They are reported as having been collected near, but not at, the Cerro de Parco
mines in Peru. The largest is 128 mm. in diameter; abdomino-dorsal breadth
of last whorl, 24 mm.; transverse diameter, 20 mm.; next inner whorl, 20 by
16.5 mm. It resembles the form of Cal. Nodotianum in the aspect of the sec-
tion when restored, and in the number, close proximity, and linear appearance
of the pilations. They are also similar in being slightly and evenly curved.
The keel is low and broad, the channels shallow and more distinct than in the
figure, but the abdomen similar to that of the section, Fig? 9, Plate Lo The
outer whorl of the older stages and all the inner whorls are compressed, as
in the typical forms of Nodotianum. The distinct keel and shallow channels
appear late in the life of the shell, as is usual in that species. The living
chamber is incomplete, but over one volution in length. The species more
closely resembles Cui. proaries, Neum., than any other form of the fauna of the
Northeastern Alps, but differs in having flatter sides in all the whorls, an earlier

1 Mojsis. et Neum., Beitr., V. pl. xvii. 2 Tbid., VI. pl. xxi-xxvi.
8 Tbid., pl. xxv. fig. 4-6. 4 Tbhi¢., pl. xx. 5 Ibid., pl. xx. fig. 6-9.
® This species has been referred to previously in these pages as if identical with Cal, Nodotianum.

GENESIS OF THE ARIETIDA.

Dy

Ws

ssh ZY

\
(

VY VS}

\ WKS

oss”

Fig. 25, 26. Views from the side and in section of Cal. Newberryi showing incomplete living chamber and
outlines of whorls.

Fic. 27. View of suture made up from the last suture in Fig. 28 and the study of others. The abdomen
is projected, to show depth and narrowness of abdominal lobe.

26

development of keel and channels, narrower abdomen in the whorls of the adult,
and in being, like the species of Central Europe, considerably smaller. The
largest specimen had just begun to pass into the first senile stage. The internal
or young whorls have pilx similar to those of the young of Cul. raricostatum and
Cat. carusense. The sutures are similar to those of the normal species of Central
Europe, having broader lobes and saddles than is customary in the basin of the
Northeastern Alps. This agrees with other characteristics, which are essentially
similar to species from the European province. The second and smaller speci-
men, which is 80.5 mm. in diameter, has similar but straighter pile. The
abdomen is broader and more depressed, and the channels better defined, but
how much: of this is due to pressure cannot be stated. Both specimens have
been distorted by pressure. The first has been affected in such a way that it is
easy to restore the normal form, whereas in the second case it is not easy to
separate the results of pressure from the true characters.

—— oer ae eee = eee .

YZ

SO

WAAC

LLLLDYPL)) MN

Fra. 28, 29. Views from the side and in front of Cal. Ortoni, showing geratologous changes of the pile in the clinologic stage and the slight constrictions in the umbilicus due to
the greater or less permanence of apertures, or imperfect resorption of these apertures. — Fra. 80. Section taken along the broken line marked in Fig. 28.

De ee a

1S)

THIRD, OR VERMICERAN BRANCH. 15

Caloceras Ortoni, Hyarr.

Caloceras Ortoni, Hyatt, Proc. Bost. Soc. Nat. Hist., XVII, p. 867.

Locality. —Tingo, near Chacapoyas, Northern Peru.

The shell is fully preserved in the only specimen found. This form resembles
Cal. salinarium of the Northeastern Alps more than any other species. There are
the same closely crowded fold-like bent pile without genicule, similar narrow
channels with depressed lateral ridges and sunken keel, and similar gibbous form
of whorl, flattened abdomen, and discoidal aspect. The young were studied in
section. The earlier stages are excessively broad and smooth for three whorls.
Coarse tubercular folds appear on the latter part of the third or first quarter of the
fourth volution, near the abdomen. These gradually lengthen, but remain very
broad folds separated by wide depressions during the entire fourth whorl. There
are about twenty pile on this whorl including the tubercles, thirty-five on the
fifth, and perhaps fifty-eight on the sixth,

Occasionally a pilation is wanting, indicating the former presence of a more or
less constricted aperture, but these, though numerous, are not at regular intervals.
Occasionally pilations are doubled, but these are not shown in the figure.

On the seventh whorl there are about eighty pile, and on the latter part of
this volution they begin to lose their prominence, and on the latter part of the
eighth they suddenly degenerate into coarse crowded striations. These changes
are accompanied by a very slight elevation of the abdomen, broadening and
shallowing of the channels, while the keel appears to be more prominent.

The young whorls are similar to those of Cal. Liasicum. The keel appears as
a low, broad ridge on the first quarter of the sixth volution, but the channels
were not present, in the section examined, until first quarter of seventh volution.
They are at this time very shallow and narrow, and the keel is also depressed and
not very broad, but on the eighth volution both these parts become more fully
developed. Effort was made by removing the shell to see the sutures, but not
with success. The auxiliary portions of the sutures are inclined posteriorly, but
otherwise nothing was satisfactorily ascertained.

Cul. (Ariet. proaries var.) latecarinatum, Wibner,’ is the geographical equiv-
alent of the broad, depressed-whorled varieties of Cal. Lnasicum of the Middle
European province. Wiihner considers that Loki may be the nearest affine
to Cal. Liasicum, taking as his guide Reynés’s figure of the latter. This means
only the compressed varieties of this species, which we have noted in the first
subseries. The extreme depressed whorls of Jatecarinatum are closely similar
to the next form of the subseries Ca/. (_Aviet.) salinarium, figured on Plate XVIIL.,
and this is very likely, as supposed by Wahner, an old specimen of salinarius,
though described by Giimbel as Amm. euceras. Cal. (Ariet.) centauroides, Wih.,
exhibits very stout whorls in the young, and acquires the deep channels and
well developed keel at a late stage of growth, and these continue to be better

1 Mojsis. et Neum., Beitr., V. pl. xvi. = Tbid., Viepl: xxiv.

20

154 GENESIS OF THE ARIETID.

defined, though the first old age stage is shown to have begun by the flatness and
inclination of the sides in the section given by Wiihner on Plate XXIV. Fig. 7 e.
Cal. (Ariet.) Grunowi (Hauer), Wiih ,* resembles closely centauroides, but is evi-
dently even less advanced, since the development of the keel is less marked, and it
is doubtful if it ever have channels. The two species mentioned above, centau-
roides and Grunowi, as described by Wiihner in their younger stages, have sutures
which differ from the similar forms described by Canavari in his Fauna of the
Lias, so often quoted above. The sutures are unquestionably arietian, having
deep narrow abdominal lobes and lateral sutures like those common in Caloceras.
The sutures, form, and characteristics of Aegoc. centauroides, Canavari, figured on
Plate V., ally it closely with the species figured on Plate VII. as Acgoc. Listeri?

The extraordinary species figured by Neumayr, Cul. (digoc.) Sebanum, Pied.
is supposed by him to be a species with young, like those of the schlotheimian
series. It is apparently, if the figures are accurate, a keeled caloceran form, with
prominent angular genicule in the young, and we entirely agree with Wihner
that it cannot be allied to Schlotheimia. Such a shell might be traced either to .
Cal. tortile, or almost any species of Caloceras having an immature keel and well
defined pila. The characteristics suggest a subseries of which the tuberculated
Cal. laqueoides of the Angulatus bed of Wiirtemburg would be also a member.

Geyer, in his “Lias. Ceph. d. Hierlatz b. Hallstadt,” gives three species of
small size, Cal. (Arietites) sp. indet. aff. Nodotianus, D'Orb., Plate TIT. Fig. 16 ; Cul.
(Ariet.) doricus, Plate IIL. Fig. 3; and Oal. ( Ariet.) raricostalus. This is a fauna
mostly composed of dwarfed forms of species, which there lived under unfavorable
conditions, as did those of Spezia in the south.

Canavari, in his Unteren Lias v. Spezia, gives Cad. ( Ariel.) Corregonense, Fig.
12-15, which seems tobe the young of a stout variety of Johnstoni ; Cal. (Arict.)
retroversicostatus, which may be young of Cad. salinarium described by Wihbner from
the Northeastern Alps; Cul. (Afgoc.) helicoideum, Plate V. Fig. 7, tortwosus, Fig. 8,
and carusense, Fig. 10, all belonging apparently to the same species, most likely
young or dwarfs of the last named ;* and Cad. ( Arve.) raricostatum, Fig. 9, 1s prob-
ably the young of some Caloceran species, since the drawing does not have the
aspect of raricostatum.

VERMICERAS.

In this genus we find several characteristics which were merely specific or
varietal in Caloceras, becoming established as an integral part of the growth, and
furnishing good generic characteristics.

1 Mojsis. et Neum., Beitr., VI. pl. xxv. fig. 2, 3.

2 The species accompanying this one, figured on the same plate as Tropites ultratriasicus, Arielites Cam-
pigliensis, ligusticus, and discretus, are all apparently true Tropites with tubereulated and coronate whorls in
the earlier nealogic stage, and acquiring a keel and pilee while still retaining the coronate depressed form of
their triassic radical, Tropites subbullatus, The sutures as figured are similar to those of the adult of
Tropites Jokeyli, as given by Hauer, Ceph. d. Hilst. Schich., Denks, Akad. Wien, IX., 1855, pl. iv.

8 Unterst. Lias, Abhandl. geol. Reichsans., VII. pl. iv. fig. 2-4.

4 Referred by Canavari to the young of proaries in Mem. della Carta Geol. d’ Italia.

THIRD, OR VERMICERAN BRANCH. 155

The young whorls for a very limited stage are smooth, then the rounded
abdomen and immature pile of Caloceras appear. The keel is introduced after
this stage, and we have for a stage of greater or less duration, according to the
species, a resemblance to somé varieties of Caloceras laqueum.

The adults are characterized by quadragonal forms and flattened, keeled, and
channelled abdomens. The pile are straight, with distinct genicule bending
forwards. In one variety of Verm. Conybeari the genicule are tuberculated, in
other examples they are smooth.

The sutures have arietian proportions in the adults, though they retain the
immature proportions of the young until a late period of growth, and often even
in the adult stage. The abdominal lobe is longer than the superior laterals, and
the superior lateral saddles shallower than the inferior laterals; the auxiliary
saddles and lobes may occasionally have a backward trend in the young, but this
is not found in adults.

The old stage retains the keel, and has smooth, somewhat flattened and con-
vergent sides. This is very distinct from the similar stages of Caloceras, in which
the keel is lost and the whorl becomes rounded. The extreme form assumed in
old age, when contrasted with the adult whorl, can be best described as trigonal.
It is, however, still similar to the senile stages of Caloceras before the keel is lost,
and the sides are more gibbous than in the trigonal senile whorls of the more
highly developed species of Coroniceras. The sutures degenerate, the abdominal
lobe becomes shorter. Our observations on the geratologous period in this
genus were not so satisfactory as in some others, senile specimens being of rarer
occurrence. Quenstedt, in his “ Amm. Schwab. Jura,” Plate VIL, figures under
the names of brevdorsalis and brevidorsalis macer several fragments of large shells,
which are probably examples of senile metamorphoses belonging to this genus,
but we are not able to designate the probable species. Although the last whorls
are represented as perfectly smooth in these figures and the sides convergent,
and the abdomen considerably narrowed, the keel and channels are still persistent.
The whorl in the oldest specimen had become so excessively altered by senile
degradation that it was smooth and helmet-shaped, as in Psiloceras, and the
channels obsolescent, though a low broad keel still remained.

There is also in the British Museum a fossil, 1010 mm. in diameter, labelled,
“Zone of A. planorbis and Pent. tuberculatus, Newbold Quarries, Rugby, Warwick-
shire.” This has the outer whorls compressed and smooth, as in Psi. planorbe, but
with a keel and obsolescent channels preserved on part of the last volution. We
identified this as an aged specimen of Verm. Conybeari, but eminent paleontologists
in England have expressed their opinion that it might be a specimen of planorbe.
We are much indebted to Mr. Henry Woodward, of the British Museum, for a
large drawing of this fossil, but unfortunately this is not sufficient to settle the
questions involved. We have had no opportunity for re-examination, and should
have considered our former opinion as probably erroneous but for other evidence.
According to Wright, Pentacrinus tuberculatus is not found below the Angulatus
bed in England. We have also seen in the rock at Lyme Regis sections of old
whorls of Conybeari closely resembling this, and also a still more advanced stage,

156 GENESIS OF THE ARIETIDA:

in which the channels were entirely obsolete, the keel being almost completely
merged in the surface, or represented only by a raised sub-angular line on the
sub-acute abdomen.

These specimens are among the few rare examples of species in this family
which have entered upon what we have called the nostologic stage on account of
the resemblances to ancestral forms which make their appearance in consequence
of senile degeneration of the differential characters of the preceding adult stages.
It is to be anticipated that in very exceptional cases of extreme senility, the
reversion to the form and characteristics of Psi. planorbe may have been com-
pleted by the entire loss of the keel at the termination of the nostologic stage,
but we have not yet seen such a case in Vermiceras, or any other keeled and
channelled genus of the normal Arietide.

Vermiceras spiratissimum, Hyarr.
Plate I. Fig. 17,18. Summ. Pl. XI. Fig. 23.

Amm. spiratissimus, QuENsT., Handb. d. Petrefact., p. 355, pl. xxvii. fig. 9; Amm. Schwab. Jura, pl. xii.
fig. 7-10; pl. xiii. fig. 1, 2, 6.

Discoceras spiratissimus, Hyarr, Bull. Mus. Comp. Zool., I., No. 5, p. 77.

Amm. arietis, Zimr., Verst. Wiirt., p. 3, pl. ii. fig. 2, 3 (not fig. 41).

Amm. Conybeari, Ziev., Ibid., p. 35, pl. xxvi. fig. 2.

Amma. latisulcatus, Quenst., Amm. Schwab. Jura, pl. xii. fig. 1-4 (not fig. 5, 6).

Localities. —Whitby, Semur, Filder, Stuttgardt, Balingen, Vaihingen, Nellingen, Metzingen, Hohenheim.

var. A. The pile begin early upon the third whorl, the shell during the first
two whorls being smooth. The pil are about twenty in number on the third or
fourth whorl, and increase to from thirty-two to thirty-four on the sixth whorl,
and forty-five to fifty on the eighth. The aspect of the shell, until the keel be-
comes well defined, is precisely like that of the adult of Cal. laqueum. At earlier
periods the development is the same as in that species; the keel, however, is always
developed earlier. The whorls assume the flattened sides and abdomen on the
fourth whorl, and this continues in some specimens throughout the fifth. The
channels become deeper upon the last quarter of the fifth whorl or the first
quarter of the sixth; but while these remain without well defined lateral ridges,
the shell continues immature. When, however, the ridges appear, the abdomen
and the pile gradually acquire their adult characteristics.

The variety figured on Plate I. Fig. 18, might be called the dwarfed or rari-
costatus variety of this species. The pile are between fifteen and nineteen in
number on the third whorl, and only about twenty-two on the fourth, increasing
again to twenty-six on the fifth. The young, however, are like those of typical
spratissimum.

Senile characters made their appearance in one specimen upon the ninth
whorl. A fragment of the fourth quarter of this whorl, in one specimen, exhib-
ited unmistakable signs of advanced senility. The pile are only ridges, destitute
of genicule and slightly bent forwards. The whorl is broader near the dorsum,
and the sides converge. The keel and channels remain apparently unchanged.

i This seems to be identical with carusense, judging from the type in Oppel’s collection.

THIRD, OR VERMICERAN BRANCH. 157

The sutures have reverted to larval outlines. On the eighth whorl the lobes are
all of equal length; the superior lateral saddles, however, are deeper than the
inferior laterals, and the first auxiliary saddles not more than half as deep as the
inferior laterals.

The abdominal lobe and the larger saddles are much shallower in proportion
to their breadth in this species than in Conybeari. The rate of increase in the
bulk of the whorl by growth is also less than in Conybeari, and the umbilicus
shallower. The longest living chamber was observed in a specimen in the Museum
of Stuttgardt from Vaihingen; it was full one and a half volutions in length,
and not complete. Quenstedt’ figures a senile specimen with a living chamber,
the aperture preserved, which is a trifle over one and a half volutions in length.
The aperture is remarkable for having no lateral sulcations, and no abdominal
rostrum. It would be instructive to compare this with the aperture of an adult
or young specimen, since it suggests degeneration in the rostrum, and, if this be
true, is another characteristic occurring through senile metamorphosis which is
analogous to the younger stages.

The Museum of Comparative Zodlogy received in exchange from the Museum
of Stuttgardt a young specimen of this species labelled “ Amma. daqueus, Quenst.,
Lias, and found with Amm. psionotus at Nellingen.”? The genicule had already
begun to be developed, and the presence of a subquadragonal form of whorl, as
well as the keel and immature channels, at such an early age, shows that this
must have been a vermiceran and not a caloceran species.*

A specimen from the Arietenkalk in the Museum of Tiibingen, and belonging
either to this or to Cad. longidomus, has a rupture in the shell at an early age, and
is distorted. The distortion of the spiral is slight, but the pile cross the abdomen,
which has no keel. On the first part of the exposed whorl they are more or less
alternate, but subsequently quite regular, and on the latter part of this whorl a
keel-like ridge appears below, though not high enough to interrupt the pile.
The diameter of this specimen is about 39 mm.

Vermiceras Conybeari, Hyarr.
Summ. Pl. XI. Fig. 24.
Amm. Conybeari, Sow., Min. Conch., I. p. 70, pl. cxxxi.

ve sh D’Ors., Terr. Jurass. Ceph., p. 202, pl. 1.
te . Quenst., Amm. Schwab. Jura, pl. xv. fig. 1.
us: + Hauer, Ceph. d. Nordostl. Alpen, p. 16, pl. ii. fig. 1-6.

Discoc. Conybeari, L. AGAssiz, Bull. Mus. Comp. Zodl., I. No. 5, p. 77.
Ariet. Conybeari, Wrieut, Lias Amm., pl. ii. fig. 1-3.
Amm. obliquecostatus, Zimv., Verst. Wiirt., p. 20, pl. xv. fig. 1.
Amm. Bonnardi, D’Ors., Terr. Jurass. Ceph , p. 196, pl. Ixiv.
Ariet. Bonnardi, Wricut, Lias Amm., p. 196, pl. xi. fig. 1-3.
Ariet. Conybeari, Hersion, Széklerland, Mitth. Jahrb. ungar. geol. Anst., V. pt. 2, pl. xx. n.
Ariet, multicostatus, Herpicn, Széklerland, Ibid., pl. xx. a, xx. B.
Localities. —Lyme Regis, Semur, Salins, Mohringen, Vaihingen, Balingen, Waltzing in Luxemburg, Adnet.

The young of this species is smooth throughout the first volution. On the sec-
ond whorl scattered folds appear, which develop into true pile on the third whorl.

1 Amm. Schwab. Jura, pl. xiii. fig. 6. 2 See Plate I. Fig. 17.
® A similar form is figured by Quenst., Amm. Schwab. Jura, pl. vi. fig. 3, as 4mm. longidomus ceger.

158 GENESIS OF THE ARIETIDA.

These at first have the depressed aspect of the adult pilee in Caloceras, and the
rotundity of the abdomen increases the resemblance to this genus. On the first
quarter of the fourth whorl the abdomen grows broader, flatter, and the pile
acquire immature geniculea. The channels make their appearance upon the
second quarter of the fourth whorl, and the bent genicule of the adult become
apparent also, though very obscure. When the lateral ridges of the sulcations
are developed on the fifth whorl, the shell becomes similar to Ver. spiratissimum ;
and finally, as the suleations deepen and broaden, and the genicule become more
salient and bend more forward, the adult characteristics of the species are fully
brought out.

The young as compared with the young of spiralissimum present considerable
differences. They are broader in proportion and increase faster in bulk, Thus
they form an umbilicus deeper and with fewer volutions within a given diameter
than in smratissinum. Five volutions of spératissimum have about the same diam-
eter as four or four and a half of Conybeari. There are about twenty-five pile on
the third whorl, thirty-six on the fifth or sixth whorl, and forty on the seventh
whorl.

The channels are deeper and broader, the lateral ridges and keel sharper and
narrower, the sides more deeply furrowed, the pila more salient, and the whorl

arrower from side to side in proportion to the breadth of the channel area, and
narrower also in proportion to the dorso-abdominal diameter than in spiratissimum.

The sutures also differ considerably. The abdominal lobe in some specimens
is one half deeper than the superior laterals; the inferior lateral saddles are
deeper than the superior laterals, and the inferior lateral lobes shorter than the
superior laterals ; the auxiliary lobes and saddles continue the inclined line formed
by the apices of the lobes. This anterior inclination is subject to variations in
the adults of varieties. In the young the lobes and saddles are nearer to the same
level, and approximate to the outlines of the sutures in spiralissmum. In Pro-
fessor Fraas’s collection there are two specimens, one in which the superior and
inferior lateral lobes are about equal, and one in which the inferior laterals are
a little the longer ; these are both full grown.

A specimen in the Museum of Stuttgardt has a living chamber nearly one
and a half volutions in length, and still incomplete.

One specimen in the Museum of Comparative Zodlogy completes nine and
one half. whorls without exhibiting any senile characteristics. The largest speci-
men yet recorded is now in the collection of the British Museum ; this measured,
according to Wright, about 460 mm. in diameter. The one figured by Wright, in
“TLias Amm.,” was 340 mm. in diameter, and old age had begun to show its effect
slightly upon the last whorl. A specimen from Lyme Regis, in the collection of
the Museum of Comparative Zoilogy, is associated upon the same. slab with
Birchii. The largest specimen in the Stuttgardt Museum was 365 mm. in diameter,
and had not yet begun to exhibit very decided senile characteristics.

In the collection at Tiibingen is a specimen, perhaps the same figured by
Quenstedt, Plate XV. Fig. 1, with undoubted spines on the casts of the genicule.
The original of Sowerby’s figure is 455 mm. in diameter, and had begun to lose

THIRD, OR VERMICERAN BRANCH. 159

the pile, but the specimen shows distinctly that the form of the adult is more
compressed than in spiratissimum, with more convergent sides, and it has tuber-
cules. It is precisely similar to the original of D’Orbigny’s Bonnardi in the Ecole
des Mines. Ver. Bonnardi is figured by Wright as occurring in the Turneri bed,
and a much more discoidal form is regarded by him as the true Conybeari and
figured as such. The great flatness of the whorls and aspect of the whole shell
in this figure are probably the effect of age. The sutures figured have senile pro-
portions, the abdominal lobe being of about the same length as the superior lat-
erals. The specimens figured by Hauer from the Northeastern Alps, and by
Herbich from Siebenburgen, have more convergent sides and less angular ge-
nicule than is common in Central Europe. The variety from Luxemburg is very
like the more discoidal varieties in England.

Var. planaries.
Amm. planaries, Fraas, MS.
Amm. Bonnardi, OppEL, not D’ Orbigny.

Locality. —Semur,

The specimen in the Museum of Comparative Zodlogy on the ninth whorl
had an abdominal lobe one half longer than the superior lateral lobes, and
inferior lateral saddles one haif deeper than the superior laterals. The in-
ferior lateral lobes, however, are somewhat longer than the superior laterals,
and the first and second auxiliaries, which show plainly on the sides, are still
longer than these. Thus the sutures appear to incline rapidly towards the
umbilicus, as in Caloceras, but this is a delusion due to the peculiar proportions
of the auxiliary saddles. The outlines of the superior lateral saddles are covered
by the involution of the whorl, instead of being in part exposed, as in Conybeari,
in which last, also; these saddles are apparently broader. The superior lateral
saddles are divided by a single marginal lobe.

The pile begin to show senile characteristics on the first quarter of the tenth
whorl, and on the second quarter of the same whorl the abdomen has suffered a
diminution in breadth. Throughout the remainder of the volution there is no
change in the abdomen, but the pile become obsolescent near its termination.
The external aspect of the adult is similar to Conybeari.

Only one specimen of this variety occurred in Professor Fraas’s collection ; it
is placed with Bucklandi, but its position with relation to that species was consid-
ered uncertain. Professor Fraas considers it a new species under the name of
Amm. planaries, and the sutures differ greatly from those of the specimen described
above, though in the form it is more like it than either of them is like Congbeari.
On the last volution of this specimen the pilee are almost obsolete, the keel more
prominent, the channels considerably shallower than in the adult. The form of
the whorl changes somewhat and the sides tend to converge, and the abdomen is
narrower, but these changes are very slight, and due entirely to the obsolescence
of the pile.

This form was at first identified with Bonnardi, D’Orb., but the examination of

160 GENESIS OF THE ARIETIDA.

the original at the Ecole des Mines showed the young of the true Bonnardi to be
tuberculated, which is not the case with the young of planaries. This fact was
apparently not observed by Oppel, who considered planaries to be identical with
the typical Bonnard. It is possible that Conybeart, as figured by Hauer, may
belong to this variety.

Vermiceras ophioides, Hyarr.

Plate I. Fig. 21-23. Summ. Pl. XI. Fig. 25.
Discoceras ophioides, Hyatt, Bull. Mus. Comp. Zool., I., No. 5, p. 76.
Amm. ophioides, D’OrB., Terr. Jurassique, p. 241, pl. lxiv.

Locality. —Semur.

The young is smooth for one volution and a half. On the third quarter of
the second, scattered folds begin, developing into true pile on the first quarter
of the third whorl. During the first half of this whorl, after the keel is devel-
oped, the rounded sides of the shell show that the form of the whorl, as well
as the immature pile, resemble Cal. laqueum.

The abdominal sulcations are well defined on the last quarter of the third
whorl, and from their well marked character on the early part of this quarter it
may be inferred that they begin on the third quarter, where, however, they were
not directly observed. For the same reasons, also, I should infer that there are
well defined lateral ridges to the sulcations almost immediately after their first
appearance on this same third quarter. The very rapid appearance of these
’ characteristics probably prevents a repetition, or only permits a very partial
one, of the adult characteristics of any of the species intermediate between Calo-
ceras Johnstoni and Ver. Conybeart. In the course of the growth through the second
quarter, the sides of the whorls remain rounded and the pile more or less imma-
ture, as in the adults of /agueum and Johnstom. On the third quarter of this whorl,
and simultaneously with the channels, the peculiar genicule and squared or
quadragonal whorl appear, and we find also distinct lateral ridges to the channels,
a well defined keel, and what seem to be minute tubercles, but are really only
very angular genicule.

From this period these characteristics, which render a fragment of the adult
whorl identical in its aspect with the adult of Conybeari, are increased and
strengthened, but not otherwise changed by growth.

The sutures, however, though observed in only one specimen, differ somewhat.
The lobes and saddles are more pointed and have smoother outlines than in Ver.
Conybeari. It is a species which illustrates admirably the law of acceleration in
heredity.

Canavari,in his work on the Lias of Spezia, figures under the name of Ver.
(Ariet.) spiratissimum, Plate XX. Fig. 2, a very interesting dwarf, with exceedingly
narrow channels and linear sunken keel. This is probably distinct, and the name
supraspiratas subsequently given by this author, in his republication of this paper
in the third volume of the “ Memorie della Carta Geologica d’ Italia,” to the same

FOURTH, OR CORONICERAN BRANCH. 161

species does not appear to indicate the exact affinities. Ver. (Ariet.) Conybeari,
Plate XX. Fig. 6, Ver. (Ariet.) doricus, Figs. 8-10, and abjectus, Fig. 11, all seem
to be the young of some species of Vermiceras, in which keel and pile are
developed early, possibly some form of Conybeari.

LEVIS STOCK.

The living chambers may be cylindrical, or they may be broadened out and
considerably modified by the growth of the whorl, but the length is invariably
under one volution, and often does not exceed one half of a volution. There
seems to be no necessary correlation between the shape of the chamber and its
length; the most attenuated and cylindrical whorls have not invariably the
longest living chambers, nor the broadest whorls invariably the shortest living
chambers. It is however true, in a very general way, that the longest living
chambers, as a rule, occur in the Plicatus Stock among the species which have
the most attenuated or cylindrical whorls.

None of the shells of the Levis Stock are directly or indirectly traceable
to any known form of Psi. planorbe, var. plicatum. Their gradations and radical
forms, nevertheless, do indicate derivation from planorbe, var. leve, and we must
therefore consider the keels, channels, pila, and sutures which are similar in
the two stocks as having originated independently in each stock, or, in other
words, as homoplastic, and not homogenous characters.

The higher species of each series tend to become involute, and to elongate
the abdomino-dorsal diameter of the whorl.

The sutures are almost purely arietian in proportions and outlines, the
auxiliaries are rarely or never inclined posteriorly, the marginal digitations are
less complicated, and the’ saddles broader and less dendritic than in the Plicatus
Stock.

FOURTH, OR CORONICERAN BRANCH.

The shells are discoidal, and involution is limited to the area of the abdo-
men. During senile degeneration the shell is apt to acquire flattened smooth
sides and a narrow abdomen, but never loses the keel, nor becomes rounded on
the abdomen, nor decreases in the amount of involution. Flattened sides and
narrow abdomens may also appear in the adults of species with accelerated
development of progressive characters.

ARNIOCERAS.

The members of this genus may be recognized by the smoothness and thin,
discoidal psiloceran form of the first three or four whorls. The keel appears as
an angular ridge, which develops later into a true keel. There are lateral folds
in the young, which develop later into pile. The true pile appear after the
keel, and then in some specimens well defined channels arise.

21

_
a
]
q
)
q
i

162 GENESIS OF THE ARIETIDA.

The form in adults is discoidal, but the whorl is quadragonal. The adult
shell is discoidal ; no involute forms have been found. The pile are prominent,
thin, sharp, straight, and smooth;’ the genicule very abrupt, and on a level
with the abdomen.

The sutures have immature margins, but an arietian aspect. The siphonal
saddles are large and pointed; the abdominal lobe may be either equal to or
much shorter than the superior lateral lobes. The latter are remarkably large
and long, and the inferior lateral lobes short. This gives an elevated aspect to
this portion of the suture. The superior lateral saddles are more distinctly bifid
in this genus than in any other, owing to the absence, as a usual thing, of the
accompanying marginal lobes of large size. The sutural margins are generally
smooth or simply serrated, instead of more or less foliaceous.

The living chambers may be from one half to one volution in length.

Aged specimens are very rare, though the species are well represented by
individuals. Indications of the approach of senility have been seen im some
specimens, and the geratologous metamorphoses were probably similar to those
of Vermiceras. Such a giant, however, as Amm. Arnouldi, Dum., figured in the
“ ftudes Pal. Bassin du Rhone,” Plate VI, which was 274 mm. in diameter, is
not described or figured as affected by senile metamorphoses, and the huge
Amm. geometricus, Dum., Plate XXX., which was 162, mm. in diameter, had a

similar history.
First SUBSERIES.

Arnioceras miserabile, Hyarr.

Plate Il. Fig. 4-7. Summ. Pl. XII. Fig. 2.

Var. acutidorsale.

Plate II. Fig. 4-6.

Psil. acutidorsale, Hyarr, Bull. Mus. Comp. Zool., I., No. 5, p. 73.

Amm. miserabile, Quenst., Amm. Schwab. Jura, pl. xiii. fig. 27-380.

Ariet. nodotianus, Wrieut, Lias Amm., pl. xxxvii. fig. 4, p. 300.

Amm. Macdonelli, Porti., Geol. Rep. Londonderry, p. 184, pl. xxix. A, fig. 12.

Locality. — Semur.

The lobes and saddles of one specimen in the Museum colléction from
Semur are shallow and broad; the inferior lateral saddles, however, taper to a
blunt point. The superior lateral saddles are divided by marginal lobes more
deeply than the inferior laterals, which are only serrated. The auxiliary lobes
are smooth, the superior laterals deeply serrated.

The shell is smooth for the first four and three quarters volutions. Very
obscure folds then begin to appear near the umbilical shoulders, and on the
second quarter of the fifth whorl reach half-way across the side. These still
remain, however, more prominent near the umbilicus, and are less prominent
near the abdomen, which, with the exception of the keel, is perfectly smooth.

1 The American species Arn. Nevadanum has tubercles, but it is not yet unquestionably settled that

this is an arnioceran form,
2 See Arn. Macdonelli, page 164.

FOURTH, OR CORONICERAN BRANCH. 163

In other young specimens, the acuteness of the abdomen begins upon the latter
part of the third or first part of the fourth whorl, and the strie of growth are
regular and well marked. Previous to this the abdomen is rounded, as in
Psil. planorbe.

The smoothness of the sides of the whorls, the immature folds, and the flat
discoidal aspect of the young, make the shell very like planorbe, var. leve, and
in the next stage the folds give an aspect somewhat similar to the plicatus
variety of planorbe. The prolonged smooth stage of the young, before it
takes on the folds, has no correspondence with any form of Caloceras, and
indicates direct derivation from planorbe, var. deve. In the typical specimens
of Arn. miserabile, var. acutidorsale, the folds are sometimes not apparent upon
the cast, even upon the fifth whorl, but in one specimen a careful exami-
nation showed that the original shell must have had faintly marked folds,
which stretched entirely across the side and had the usual abrupt terminations.
Quenstedt* figures this variety. The aperture is shown in his Fig. 27 to have
been similar to that of planorbe, having a well marked rostrum, broad lateral
sinuses, and a constriction. It is by no means certain, as Quenstedt states in
the same work on page 104, that Wright’s figure of the young of semicostatum,
Plate I. Fig. 7 of his “ Lias Ammonites,’ is a specimen of this species; it is
quite as likely that Wright was correct. Professor Quenstedt’s specimens at
Tiibingen are for the most part young from the Oelschiefer, but a large one?
was nearly, if not quite, full grown. The keel in this appeared as a sharp
ridge at an early age, and maintained the same character in adults.

The abdomen does not broaden out as in adult of acutidorsale, but per-
sists mM maintaining its angular character throughout life. The pile began
quite early, but never appeared to get beyond the fold-like stage. Some-
times, however, they bend forwards and may cross the abdomen, and then the
abdominal ridge forming the keel is crenulated? The variety occurs in South
Germany, especially in the Oelschiefer of Quenstedt.

A form doubtfully referred to this variety was collected by Professor Orton
at Ipishguaniina in Northern Peru.*

Var. cuneiforme.
Plate II. Fig. 7.

Arnioceras cuneiforme, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 78.

Abdomen acute, as in variety acutidorsale ; sides regularly convex; pilx
depressed, most prominent in the centre, and sloping gradually to either side.

The abdominal lobe is somewhat longer than the two lateral lobes, which
are of about equal length. Superior lateral lobes and saddles are pointed, the
inferior lateral lobes and saddles mere serrations.

1 Amm. Schwab. Jura, pl. xiii. fig. 27-30. 2 No. 7742 of his collection, locality unknown.

8 This does not indicate any affinity with other genera; it is a sporadic and purely pathological modifi-
cation, as it is also in the young of Oxyn. Oxynotum, and many other forms in which the young shells are

often affected by similar abdominal crenulations.
4 Proc. Bost. Soc. Nat. Hist., XVII., 1875, p. 367.

ee

———

164 GENESIS OF THE ARIETID.

The superior lateral lobes are slightly serrated, and the superior lateral
saddles have the generic division; but otherwise the lobes and saddles are
apt to be entire. These characteristics were observed in one specimen on the
fifth whorl.

The general aspect of the shell is like that of the young of Psi. planorbe ;
the pile, however, are.not merely broad prominent folds as in that species,
but distinct immature pile, similar to those of other species of Arnioceras, and
the form is quite distinct, besides being obscurely keeled. Some shells have
straight pile and gibbous whorls, and others have bent pile and flatter whorls.

Arnioceras Macdonelli, Hyrarr.

Amm. Macdonelli, Portiock, Geol. Rep. Londonderry, p. 134, pl. xxix. a, fig. 12.
Ariet. Macdonelli, Tarn and Buaxn, Yorkshire Lias, p. 290, pl. v. fig. 8 a-b.
Ariet. nodotianus, Wrieur, Lias Amm., p. 300, pl. xxxvii. fig. 4.

Wright's reproduction of Portlock’s figure and Portlock’s own figures show
that this is a most remarkable modification of mserabile, occurring in the Rari-
costatus bed, or what he first called the base of the Jamesoni bed. It is
evidently an aged specimen, a very rare occurrence in this genus, and is con-
sequently smooth. The young, however, have pile, and these and the section

given by Portlock, the absence of channels, and compressed whorls, show it to
be closely allied to nuserabile, var. aculidorsale.

Arnioceras obtusiforme, Hyarr.
Plate Il. Fig. 8-9a. Summ. PI, XII. Fig. 3.

Amm. obliquecostatus, BRAuNS, Der Untere Jura, pl. i. fig. 38-5.
Asteroceras obtusum (pars), Hyarr, Bull. Mus. Comp. Zool., I., No. 5, p. 79.

Locality. —Semur.

This species has the pils so closely resembling the curved depressed pile
of Ast. obtusum, that it was formerly referred to that species. The young,
however, are precisely similar to the young of Arnioceras, much too flat
laterally for obfusum, and the pile never begin with tubercles or heavy folds,
as in that species. The keel is depressed, and the channels are very. shallow or
absent.

Var. A.

The pile are developed abruptly on the last quarter of the third whorl.

The curved pil resemble those of the typical form of miserabile, var. cuneiforme.

Var. B.

The pilz are developed gradually, beginning with minute, regular folds on
the first quarter of the third whorl, and they continue in the adult to resemble
those of miserabile, var. cuneiforme, although the genicule become more promi-
nent and make a nearer approach to those of Arn. semicostatum. The abdomen is
narrow, the keel well defined, and in two specimens channels were faintly shown. |
The whorls of varieties A and B are both more compressed than in variety C.

FOURTH, OR CORONICERAN BRANCH. 165

Var. C;

The whorls are stouter than in variety B, and acquire on the first quarter
of the fourth whorl, or later, a close resemblance to those of semécostatum. The
inferior lateral saddles are considerably deeper than the superior laterals, the
inferior lateral lobes considerably shorter than the superior laterals, and pointed.
The sutures were observed upon the latter part of the fifth whorl.

SECOND SUBSERIES.

Arnioceras semicostatum, Hyarr.
Plate Il. Fig. 10-16. Summ. Pl. XII. Fig. 4.

Amm. semicostatus, Simpson, Amm. of Yorkshire Lias, p. 51.1
Ariet. semicostatus, Wrieut, Lias Amm., pl. i. fig. 7 (not fig. 4, 5, 8).
Arn. semicostatum, Hyarr, Bull. Mus. Comp. Zodl., I., No. 5, p. 74.

Localities. — Whitby, Semur, Basle, Spezia.

Var. A.

Plate II. Fig. 10, 16.

During the first four and three quarters or five volutions, the shell closely
resembles Arn. miserabile, var. acutidorsale. After this the pile appear. They are
at first broad and depressed, but possess the sharp definition of true pile, and
terminate abruptly on the edge of the abdomen. The abdomen is rounded, and
the keel a distinct though depressed ridge. Its time of appearance could not be
determined, but it was plainly apparent on the second or third quarter of the
fifth whorl, and previous to this the aspect of the abdomen was precisely that of
nuserabile, var. acutidorsale.

Var. B.

Plate II. Fig. 11-14.

In this variety the young resemble veryclosely the adults of Arn. miserabile,
var. acutidorsale. The pile make their appearance earlier than in variety A, but,
while becoming more numerous, often retain their fold-like aspect, and terminate
abruptly near the abdomen. The keel appears about the same time as the pile,
and may be either with or without slight channels. In some specimens the
whorls become stouter than usual in the adult, and the genicule prominent. In
one specimen they are inclined posteriorly.

In the Museum of Stuttgardt there are three specimens of this variety, one
from Behla and one from Muhlfingen (No. 4688), both in the Geometricus or
Upper Bucklandi bed. Another from Filder was found in the Angulatus bed.

1 This name does not appear in the first edition of Morris’s Catalogue, 1848, but is found in the second
edition, 1854, as Amm. semicostatum, Y. & B., Geol. Yorkshire, p. 257. This is an erroneous reference, since
no such species was described in that work. In the Museum of Yorkshire is a specimen with this name, and
it was described by Simpson in his Monograph of the Ammonites of the Yorkshire Lias, which was not cited
in Mr. Morris’s first edition, though published in 1843. .

166 GENESIS OF THE ARIETIDA.

Var. C.

The adults are remarkable for their prominent straight keels. The channels
when present are very shallow. ‘'he young remain smooth for a longer time
than in other varieties. The pile: appear between the first quarter of the fourth
and first quarter of the fifth whorl.

While smooth throughout the first three or four whorls, it is identical with
the adults of miserabile, var. acutidorsale, but the sutures are more immature, The
pilze develop quickly, and are similar to those of variety B. In fact, the young
can be distinguished only by the larger size, quicker growth, and smaller num-
ber of the pila. Associated with these are specimens with compressed whorls,

perhaps males.
Var. D.

Plate Il. Fig. 15, 15 a

This has a narrow abdomen, and the pilz are more prominent near the dor-
sum. They appear on the fourth quarter of the third, or on the first half of the
fourth whorl, earlier than in some specimens of variety B, and are more slowly
developed. Some of the young are very like the adult of Arn. miserabile, var.
cuneiforme. The pile bend forward when they first appear, or soon after, as in
this variety, although subsequently becoming straight, like those of the adults of
variety A. The abdomen is sharp, as in miserabile, var. acutidorsale ; the keel does
not appear until the pile begin to acquire their prominent, straight adult char-
acteristics. The sutures have serrated outlines.

The abdominal lobe (Plate II. Fig. 15 a) may be equal to the superior lateral
lobes, or one fourth shorter, and the siphonal saddle is remarkably large. The
superior lateral saddles are divided symmetrically, and are equal in depth to the
inferior laterals, The superior lateral lobes are very broad, and about one half
longer than the inferior laterals. These characteristics were observed on the
third quarter of the fifth volution of a specimen from Semur. In specimens from
Whitby, on the second quarter of the same volution the sutures are similar in all
respects, but the superior lateral lobes are at first equal to the abdominal lobe
in successive sutures, and then slightly longer. At still earlier stages, when the
marginal lobes first appear, the abdominal lobe is usually of the same depth as
the superior laterals, or shallower (Plate II. Fig. 15 a). One specimen from Semur
had sutures maintaining these immature proportions even on the latter part of
the fifth whorl.

There are several specimens from Spezia in Bronn’s collection, Museum of
Comparative Zodlogy, labelled by Capelini Amm. subarietinus, Menegh. These seem
to belong to this species, but are so compressed that it is difficult to make sure of
the identification. The young are smooth until a very late stage, as is usual in
semicostatum, and the pile and form are also similar. They are in the yellow
clayey shale, and described as from Coregna near Spezia.

FOURTH, OR CORONICERAN BRANCH. 167

Arnioceras Hartmanni, Hyarr.
Plate Il. Fig. 17, 18. Plate III. Fig.1, 1a. Summ. Pl. XII. Fig. 5.

Amm. Harimanni, Oppr, Der Jura, p. 79; Wiirt. Jahresh., XII. p. 199.
Amm. geometricus, OpPEL (pars), Ibid.

Arn. kridiforme, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 74.
Amm. kridion, D’OrB., Terr, Jurass. Ceph., p. 205, pl. li. 3

Amm. falcaries (pars), QuENST., Amm. Schwab. Jura, pl. xiii. fig. 21.
Amm. robustus (pars), QUENST., Ibid., fig. 22.

Localities. — Whitby, Lyme Regis, Semur, Bonnert, Suabia, Gmiind, Adnet.

This species has more compressed adult whorls than any variety of Arn. semi-
costatum, and, although the pile are similar, they begin to appear at an earlier
age and are developed more gradually. The abdomen is also in many speci-
mens, though not in all, distinctly channelled, and the keel prominent.

In one’specimen the superior lateral lobes are nearly as long as the abdominal
lobe on the sixth whorl, and on the sdme whorl in another they were two fifths
shorter. The inferior lateral saddles are deeper than the superior laterals, and
the inferior lateral lobes very short.

A specimen in the Museum of Stuttgardt, collected by Prof. Fraas, is from
Arietenkalk, Hechingen (No. 5026 of that collection); another, from Gmiind,
was found in the Geometricus bed, and is labelled Amm. Nodotianus, D’Orb. Two
others, from Behla, are labelled Amm. falcaries, Quenst.; these belong to his
sparsely ribbed variety, which is just intermediate between Arn. Hartmanni, and
some varieties of Arn. semicostatum.

A specimen of falcaries, Quenstedt, figured by him,’ is described as partly
unrolled. Examination of the broken end, however, shows that a calcareous
worm tube has occasioned the distortion by having been built upon the abdomen
of the growing shell. This is a common occurrence, and was observed in several
specimens at Semur. There are others, however, in which this distortion, as in
other species of Ammoniting, takes place without the presence of any foreign
body between the whorls. Such examples have been named Crioceras Eryon and
Mandubwis by Reynés. These and other cases show the kind of error likely to
occur from the use of such names as Crioceras, Gyroceras, ete.

The flattened sides and general aspect of Quenstedt’s figure of falcaries ro-
bustus? agrees apparently more nearly with this species than any other known
to me. This species is the one commonly named Amm. geometricus, Oppel, in
the collections in Germany, and seems to have been in part confused with that
species by Oppel.

1 Der Jura, pl. viii. fig. 6. 2 Amm., Schwab. Jura.

168 GENESIS OF THE ARIETIDZ.

Arnioceras tardecrescens, Hyarr.
Plate Il. Fig. 19, 21-22. Summ. Pl. XII. Fig. 6.

Amm. tardecrescens, Hyarr, Bull. Mus. Comp. Zodl., I., No. 5, p. 74.
Amm. tardecrescens, HAvER, Ceph. Lias Nordéstl. Alpen, p. 20, pl. iii.
Amm. falcaries (pars), Quens'., Der Jura, pl. vii. fig. 7 (not fig. 6).
Amm. falcaries densicosta, Quunsr., Amm. Schwab. Jura, pl. xiii. fig. 7.

Localities. — Yorkshire, Semur, Durrenburg.

The pile appear on the fourth whorl at variable times. There are fewer
whorls, and they are wider from the abdomen to the dorsum and have generally
rounder sides, than in Arn. Hartman.

The abdominal lobe is equal to or somewhat longer than the superior laterals ;
the inferior lateral saddles are shallower than the superior laterals, and the inferior
lateral lobes are much shorter, sometimes a third less, than the superior laterals
on the last quarter of the sixth volution. On the third quarter of the same
whorl in the same specimen from Semur, the abdominal lobe was one half shorter
than the superior laterals. The siphonal saddle was very large, and the superior
lateral lobes very long and broad, with straight sides, the inferior lateral lobes two
fifths shorter than the superior laterals. The first auxiliary saddles are visible
on the sides. The marginal lobes are still hardly more than mere serrations,
except along the bases of the saddles. The superior lateral lobes have very
broad and minutely serrated summits.

A specimen in the Museum of Stuttgardt had curious characteristics. The
sutures are undoubtedly arnioceran, the keel very prominent, and the channels
shallow. The form of the whorls and the pile, however, are similar to those of
Conybeari. Another specimen from Boihingen is precisely similar, but the pile
terminate abruptly at the genicule somewhat below the edges of the channels,
instead of being continued upwards and forwards, as in the former and in Cony-
beari. Neither of these shows the young whorls well enough to enable one to
identify them accurately either with Arn. Hartmann’ or Arn. tardecrescens, but
they are undoubtedly arnioceran forms. Both are referred to the Geometricus
zone.

The original of Quenstedt’s figure in Der Jura, from Pforen, Baden, named
Amm. falcaries, has the. narrow sulcated keeled abdomen, rounded sides, and
pile of this species. There is also from Achdorf in Baden a specimen about
26 mm. in diameter, which just begins to show the pile.’ The figure by
Quenstedt? shows a form in which the young is smooth for a considerable num-
ber of whorls.

1 This may be the specimen figured in Amm. Schwab. Jura, pl. xiii. fig. 18, as Amm. falcaries levis-
simus.

2 Amm. Schwab, Jura, pl. xiii. fig. 7.

FOURTH, OR CORONICERAN BRANCH. 169

Arnioceras ceras, L. Acassiz.
Plate Il. Fig. 20, 20a.

Arnioceras ceras, L. Acassiz, Bull. Mus. Comp. Zodl., I., No. 5, p. 74.

Amm. ceratitoides, QuENst., Amm. Schwab, Jura, pl. xiii. fig. 10 (not fig. 8, 9, 11).
Amm. Turneri, Quenst., Ibid., pl. xix. fig. 6-8 (not fig. 5-9).

Amm. ceras, HAvrr, Ceph. Lias Nordéstl. Alpen, p. 25, pl. vi. fig: 4-6.

Localities. —Semur, Whitby, Lyme Regis.

This species approximates to the aspect of Coroniceras, and also imitates
closely the general form and characteristics of some varieties of Ast. Turneri.
Both in England and Germany, when the interior of the umbilicus or the smooth
compressed younger whorls are not preserved, even the most acute observers are
apt to consider the adult whorl as belonging to Turneri. Some of Quenstedt’s
figures, especially Fig. 8, Plate XIII., may be either ceras or some allied species
of Armoceras. The keel is prominent, the channels are broader and deeper than
usual, the genicule are prominent and slightly bent forward, the sides, however,
flat and slightly convergent, and the pile straight and smooth, as usual in this
genus. ‘The pile begin upon the third quarter of the fourth whorl.

The superior lateral lobes are somewhat longer than the abdominal lobe. The
inferior lateral saddles are one fourth deeper than the superior laterals, the infe-
rior lateral lobes one half shorter than the superior laterals on the latter half of
the sixth volution.

A specimen in the Museum of Stuttgardt, locality uncertain, is referred to the
Geometricus zone. Two young specimens from the Bucklandi zone, labelled
Buckland (No. 2756), in Quenstedt’s collection, also probably belong to this
species. The young are smooth, and the form differs from that of typical
ceras only in being a trifle stouter. The channels, perhaps, also appear at quite
an early period, but this sometimes occurs in specimens of the typical form.
There is also a large specimen from Jettenburg.

What appeared to be very close allies of this species were collected by Pro-
fessor Orton at Ipishguaniina, in Northern Peru.

Arnioceras Bodleyi, Hyarr.

Plate II. Fig. 23-24a. Summ. Pl. XII. Fig. 7%.
Amm. Bodleyi, Bruck., Murch. Geol. Cheltenh., pl. ii. fig:
Amm. ceratitoides, QuENSt., Die Ceph., pl. xix. fig. 13 ; Amm. Schwab. Jura, pl. xiii. fig. 8, 9, 11.
Amm. geometricus, OpreL (pars), Der Jura, Wiirt. Jahreshf., XI. p. 199.
Ariet. semicostatum, Wriaut, Lias Amm., pl. i. fig. 4, 5, 8 (mot fig. 7).
Arn. falearies, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 74.
Ariet. difformis, BuAxn, Yorkshire Lias, p. 289, pl. vi. fig. 3 a, b.

Localities. — Whitby, Bonnert, Semur, Raidwangen, Basle, Salins.

There are three varieties in this species; one, variety A, figured on Plate II.
Fig. 23, has stout, thick whorls; the second, variety B, has flattened whorls; and
the third, variety C, figured on Plate II. Fig. 24, has flattened whorls like those
of the second variety, but they are somewhat wider on the sides.

1 Proe. Bost. Soc. Nat. Hist., 1875, XVII: p. 366,

99

ca

170 GENESIS OF THE ARIETIDZ.

Varieties B and C, from Semur, showed tubercular-like folds on the latter
part of the first, and part of the second whorl, which were continued on the um-
bilical border of the succeeding whorls, gradually developing into true pile on the
third whorl.

For a short interval in the specimen of variety A the shell is smooth again,
and in that of variety C the folds still remain apparent, but so depressed that
they were made out with difficulty. On the first quarter of the third whorl in
one specimen of variety B, and the third quarter of a specimen of variety C, the
folds reappear on the umbilical border, but develop so gradually that lateral pile
are not produced until the latter part of the first quarter of the fourth whorl.
Several other specimens of these same varieties, however, from the same locality,
did not show the psiloceran folds in the young, or differ from those of variety A.

A fragment from Ramert in the Museum of Stuttgardt is the true ceraliloides
of Quenstedt, which differs from ceras in having a more prominent, narrower
abdomen and shallower channels.

A specimen of the stout variety from Cheltenham, named Bodleyi, Bruck., has
well preserved young which show this species to be closely allied to ceras. The
thinner variety described above has the young much compressed, and similar to
the adult of the Cheltenham specimen. On the other hand, the young of the
Cheltenham specimen is precisely like the adult of Arn. Hartmanni. Oppel’s de-
scription shows that he identified the compressed variety as the Bodley: of Bruck.,
and the stout varieties as Amm. geometricus.

Arnioceras falcaries, Hyarr.
Plate Il. Fig. 25-27.

Amm. falcaries, Quenst., Der Jura, p. 70, pl. vii. fig. 6 (not fig. 7).
Amm. falcaries, QuENST., Amm. Schwab. Jura, pl. xiii. fig. 12-14.
Arnioceras incipiens, Hyatt, Bull. Mus. Comp. Zool. I., No. 5, p. 74.
Amm. acuticarinatus, Simps., Museum at Whitby?
Amm. Youngi, Simps., Mon. Ammn., p. 46?

Localities. —Semur, Robin Hood’s Bay, Balingen.

The sides are convex, the whorls compressed, and the abdomen obtusely
angular, keel prominent. ‘The pile begin with a line of tubercles, which appear
on the first half of the fourth whorl, preceding the true pilze by about one fourth
of a whorl. The pile are not strongly developed upon the umbilical shoulders
of the whorls, which in many specimens are almost, smooth.

Variety A, figured on Plate II. Fig. 25, 26, has prominent genicule and
keel without channels, but some specimens leading to the next variety have less
prominent genicule.

Variety B has less prominent pile and keel. The channels, though mere
linear depressions, begin to appear in some specimens.

Variety C, figured on Plate H. Fig. 27, has even less prominent pilx, but a
keel with distinct narrow channels, and in some specimens the pile were devel-
oped abruptly, not being preceded by the usual line of tubercles.

1 The ? in these cases is due to the fact that I was not permitted to examine the originals in the
Museum at Whitby.

— ne

FOURTH, OR CORONICERAN BRANCH. 171

The shell of variety A is smooth for three or three and a half volutions; the
tubercles begin to spread entirely across the sides on the first quarter of the
fifth whorl, and about this time the geniculee have become prominent. The chan-
nels are not present in any of these specimens, but more or less faintly marked
narrow depressed zones may be observed on either side of the keel. This variety
leads directly into the next, in which the depressed zones become channels. The
geniculs differ in aspect from those of variety A, because they abut against the
well defined lateral ridges of the channels.

Variety B has the pile developed at about the same period as in variety A,
but the channels appear in the young, and on the second quarter of the fifth
volution they are quite distinct.

There is one specimen of variety A in which the pile are slightly inclined
posteriorly, and the genicula more prominent than in any other specimen. A
very slight sinking of the abdomen in this specimen would produce a form of
variety C, which is found at Robin Hood’s Bay in England, and which has a
keeled, channelled, and flattened abdomen. The single suture which was exposed
in this specimen possessed remarkably pointed and serrated superior and inferior
lateral saddles, and very broad, rounded, but serrated superior lateral lobes. The
auxiliary saddles and lobes were pointed and serrated. There was a very large
siphonal saddle, and all of the larger lobes and saddles appeared of about the
same depth and length.

One specimen of this species from Balingen was received in exchange from
the Museum of Stuttgardt, under the name of Nodolianus. Two specimens in
Quenstedt’s collection belonged undoubtedly to this species, variety A. One
from Lias, a, Pforen, named Amm. falcaries (No. 4428), and one from Géppingen
(No. 11182), were in the Arietenkalk. The last was 63 mm. in diameter and
a typical form of variety A; the pile are, however, inclined posteriorly, while in
the other they are pointed forwards. In the specimen from Pforen the pile begin
abruptly near the abdominal side unpreceded by tubercles. Other specimens,
especially the original of his figure, Plate VI. Fig. 6, also from Pforen, show
that Hartmanni and this species have intermediate varieties.

Several forms are found in the Semur collection under the name of Hettan-
gensis, Rey., one of which has smooth young, with fine pilations and an adult
whorl having close resemblances to this species and also to Arn. miserabile, var.
acutedorsale.

TuirD SUBSERIES.

Arnioceras kridioides, Hyarr.
Plate II. Fig. 28. Summ. Pl. XII. Fig. 8.

Ophioceras kridioides, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 75.
Amm. kridion, Quenst., Der Jura, pl. vii. fig. 8, Amm, Schwab. Jura, pl. xi. fig. 5, 6 (not fig. 7).
Amm. Bucklandi carinaries, Quenst., Amm. Schwab. Jura, pl. xi. fig. 3.

Localities. — Basle, Semur.

This species approximates in aspect to Cal. raricostatum, and was on this
account at first erroneously referred to that species. The shell is, however,

172 GENESIS OF THE ARIETIDA.

smooth, as in Arnioceras, on the first three whorls, the pile being acquired only
on the last quarter of the third or first quarter of the fourth volution. They are
only about twenty-five in number on the fourth whorl, and gradually decrease in
number on subsequent whorls.

The sutures on the second quarter of the sixth whorl show close affinity for
Arn. semicostatum. This resemblance ceases in a great measure after the beginning
of the fifth volution, when the pile assume an aspect similar to those of Cul, rari-
costatum. ‘The resemblance is due to the fact that the pile remain undeveloped ;
if they become more prominent, the shell would be more like semicostatum. The
keel is also not so well developed as in semicostatum, and on this account resem-
bles that of a species of Caloceras. The abdominal lobe at this time is slightly
longer than the superior laterals, and these are about one half longer than the
inferior laterals. The superior lateral saddles are broad, shallow, and deeply
divided by only one marginal lobe. The inferior lateral saddles are tongue-
shaped, and slightly deeper than the superior laterals. The lobes and saddles
are serrated, and the first auxiliary saddle is very small. There are four speci-
mens in the Museum of Stuttgardt which entirely confirm these observations.
They are from Behla, and labelled Amm. kridion, Quenst. One is more com-
pressed than the other, and closely approximates to Arn. semicostatum; in fact,
the young shell is quite as smooth as the gibbous variety of that species, and
with the exception of the abdomen, keel, and sutures it is identical with it.

The original of Quenstedt’s description from Bebenhausen, the type in Sua-
bia, bears out these remarks in every particular; but in his “‘ Ammoniten des
Schwibischen Jura,” Figure 7 has channels and a form not identical with others
of this species, all of which are similar to the young of Cor. kridion during the
adult stage.

Arnioceras? Nevadanum,! Hyarr.

Amm. Nevadanus, GAs, Am. Journ. Conch, Philad., V., 1869, p. 6, pl. iii. fig. 1; IV. pl. xvi.

This interesting form was found near Volcano, in Nevada, and probably
belongs to the Lower Lias. The young as figured by Gabb is smooth, and
the late stage at which the pila were introduced, their linear, straight aspect,
and crowded arrangement throughout the young whorls, are unquestionably
arnioceran. The sutures also, as figured in Volume IV. Plate XVI., have the
characteristic outlines of this genus. Nevertheless, the older whorls have the
form and proportions of Ver. Conybeari, and are also tuberculated, the abdomen
being keeled and channelled. The abdomen has, however, much broader chan-
nels than any specimens of Vermiceras yet observed. The character of this part
is evidently not unlike that of the specimen in the Stuttgardt Museum described
in note to page 70 as occurring in the Angulatus bed and yet having channels

1 The species associated with this by Gabb, under the name of Amm. Colfaxi (Am. Journ. Conch.,
1869, V. p. 7, pl. iv. fig. 2, IV. pl. xvi.), and reported as found in the Lias on the western slope of the
Sierra Nevada near Colfax, was in poor condition, and was consequently so badly represented in the figure
as to be indeterminable.

FOURTH, OR CORONICERAN BRANCH. 173

with entire lateral ridges, which occupy nearly the whole breadth of the abdomen.
Gabb’s figures are a little at variance with his description on this point, and may
have been taken from different whorls; one in Volume V. has narrow channels,
while the section in Volume IV. Plate XVI. has broad channels. The section,
description, and sutures show lateral distortion. If it were not for this and the
possible errors of the figures, we should be positive that iti was a tuberculated
arnioceran form.

Arnioceras Humboldti, Hyarr.

Locality. — Humboldt County, Nevada.

This species is closely allied to Arn. tardecrescens, from which, however, it differs
in the sutures and proportions of the whorls, those of the latter being broader in
proportion to their breadth. This species also probably reached a larger average
size and had a thicker shell. It differs
from Arn. Bodleyi in the same charac-
ters, and the sides are less divergent
outwardly than in that species, and not
so flat. The great thickness of the
shell reminds one of Arn. Hartmann,
but the whorls increase faster by
growth in the abdomino-dorsal diame-
ter, and it has a smaller number of
whorls at the same age. The figures
are close to the natural size, and give
accurately the proportions of the fos-
sil. The actual diameter of the frag- 1 Fie. 32.
ment represented in Figure 31 is 48.5
mm., and the keel is a trifle more prominent than it appears in the drawing.
The pile were much abraded and are truthfully portrayed in this figure, but
when entire they possessed the usual sharpness of the genus Arnioceras.

The transverse section represented in Figure 32 is in part a restoration, and
has been slightly reduced in the cut. The extreme breadth of the side and keel
is 19.5 mm. The sutures are given with sufficient accuracy in Fig. 33, but the
median lobe which divides the superior lateral saddles has been overlooked, and
the abdominal lobe has not been indicated. The latter has the usual arnioceran
proportions, being somewhat shorter than the superior laterals. The marginal
lobe dividing the superior lateral saddles is unusually broad, and in fact the
broad massive aspect of the two lateral saddles is a marked characteristic of
these sutures.

In the collection of the Mining Bureau at San Francisco is a specimen
of Arnioceras, which, judging from a hasty sketch, resembles this species. It
was labelled as coming from Inyo County, California, but we were not able to
verify the locality. It is, however, quite certain that species of the Lower
Lias have been found in the West in the regions occupied by the exposures of
the Jura.

174 GENESIS OF THE ARIETIDAL.

Geyer, in his “ Ceph. Hierlatz b. Hallstadt,” gives figures and descriptions of
the following species of this genus. Arn. (Psil.) abnorme and Suessi ;* Arn. ( Avie.)
semilevis, Plate III. Fig. 7, a channelled form like Arn. ceras ; Arn. (Ariet.) ambiguus,
and (Ariet.) of Quenstedt, Plate III. Fig. 14; the last is probably the same as
Arn. cuneiforme, and probably the same as his undetermined species of Amphiceras
figured on Plate II. Fig. 30. Hauer, in his “ Ceph. Lias Nordéstl. Alpen,” gives
figures and descriptions of Arn. (Amm.) difformis, which may be the same as
semilevis, Geyer, though channels and keel are both figured as preceding the pilee
in his Plate VII. Fig. 12. His young specimen, Plate VII. Fig. 9, named Amm.
multicostalus, is probably also a species of Arnioceras; but the larger specimen,
Plate VII. Fig. 7, 8, is a coroniceran form. All of these were from Hierlatz.

CORONICERAS.

The young are stouter than in Caloceras or Arnioceras, and smooth for a
shorter period, and the stage following this usually has tuberculated pile and a
whorl with more or less divergent sides. The abdomen in the adult is keeled and
channelled, the sides parallel or slightly convergent, the piles being prominent and
heavily tuberculated. In the old, the tubercles are lost, the channels obsolete,
the keel very prominent, the abdomen very narrow, and the outline of the whorl
in section trigonal.

The abdominal lobe in adults is deep and narrow, the superior lateral saddles
are generally shallower than the inferior laterals, and the first auxiliary lobes and
saddles are of comparatively small size. The great length of the abdominal lobe,
the shallowness of the superior lateral saddles, the small size of the first auxiliary
saddles, and the shortness and comparatively small size of their corresponding
superior and inferior lateral lobes, give great prominence to the inferior lateral
saddles. The outlines of the sutures are also much complicated, the marginal
lobes being broader and longer than is usual in this family. In old age the
abdominal lobe becomes shorter, often only slightly exceeding the superior
laterals in length. Degeneration also takes place in other lobes and saddles,
especially on the margins. The oldest sutures are, therefore, simpler than those
of the adult.

The first subseries has heavily tuberculated pile, and the whorl is very
gibbous near the umbilical shoulder.

The second subseries has the tubercular and inner portions of the pile more
nearly equal in prominence, the whorls are not usually so stout or numerous, and
the abdomen has a flatter outline.

The third subseries is apt to have young with broader abdomens than in the
first two, and the pila are frequently divided in the nealogic stages, Massive
whorls and pile are characteristic of the first senile stage in the larger shells.

1 Amm. Suessi, Hauer, Unsym. Amm. Hierlatz-Schichter, Sitz. Akad. Wien, 1854, XIII. pl. i. fig. 1-6,
and the figures of Geyer, show that this species has not, as supposed by Rolle, Sitz. Akad. Wien, 1857,
XXVL., and by Stur, Geol. d. Steirmark, any close affinity with Hagenowi from the Bone bed of the Wald-
hauser Hohe near Tiibingen.

ert

FOURTH, OR CORONICERAN BRANCH. 17

First SuBSERIES.

Coroniceras kridion, Hyarr.
4
| Plate Ill. Fig. 2, 3. Summ. Pl. XII. Fig. 9.
Amm. kridion, Ziev., Verst. Wiirt., pl. ili. fig. 2.
Amm. kridion, HAvUER, Ceph. Nordostl. Alpen, pl. iii. fig? 4-6.

Localities. — Semur, Stuttgardt, Balingen.

|

!

The pile were already visible on the first part of the third whorl, but when

| they began could not be ascertained. On the first quarter of the third whorl

the flattened abdomen of the younger volutions became more elevated, and the

keel was introduced. The keel continued to increase in prominence thereafter,

but the channels, which are faintly visible on the fourth whorl, only broaden out,

and do not sensibly increase in depth, after they reach the last part of the fifth

volution.

The form acquired on the third or fourth whorl is carried throughout life, the
sides curving evenly from the dorsum to the abdomen; the abdomen is elevated,
the pile are either overhanging or slightly tuberculated on the latter part of
the third whorl, but very soon the curvature becomes equal and the tubercula- |
tions disappear, though the genicule sometimes remain very prominent even on |
casts. There are three specimens of this species in the Museum of Stuttgardt,
| the exact position of which, with relation to Bucklandi, is considered uncertain
by Professor Fraas. The young in all these specimens are smooth, and precisely
| similar to the young of the specimens from the Angulatus bed, from which the
adults, however, differ slightly. The tubercular processes on the casts, as in all
other specimens of this species, are blunt, and covered smoothly by the shell, not t
protruding into spines. The specimens in the Bucklandi bed have longer,
stouter whorls, with different sutures, but these differences are not sufficient to
separate them; they are probably closely allied direct descendants.

Oppel claimed to have had the original of Zieten’s description, and, according
to him, it is a species like Conybeari, which is found with and under Bucklandi. |
The above is the only species answering to this description and agreeing with i
Zieten’s figure in having tuberculated pile, slightly divergent sides, a raised
abdomen, and prominent keel. There are no channels in Zieten’s figure, but his
specimen was young, and even in the full-grown fridion they are very shallow.

} Two adults and three young specimens from Mohringen, labelled Bodleyi (No.

3977), are in the Museum of Stuttgardt, from the Angulatus zone. The casts

appear to be identical with Amm. Caprotinis D’Orb., but the apparent tubercles |
were merely covered smoothly by the shell, and not continued out into points.
Besides these specimens there is a fossil from Filder (No. 8978), which is precisely
; like Zieten’s figure,! and confirms these identifications.

Though there is close approximation in the characteristics of the young in
most forms, there are sometimes differences. The young of the normal forms

sinh Rint

1 Zieten’s original T was not able to see ; it could not be found in the Museum at Munich during

TH Vaait.

176 GENESIS OF THE ARIETIDA.

often have broad and gibbous whorls, like the young of sinemurtense, and the pile
and sutures are also sometimes quite similar to those of that species.

A specimen of this species occurs in the Scipionis bed of the collection at
Semur, in company with the Amm. Hehli of Reynés, from some representatives of
which it cannot be distinguished.

Coroniceras coronaries, Hyarr.
Amm. coronaries, QuENst., Der Jura, p. 68, pl. vii. fig. 5; Amm. Schwab. Jura, pl. xvi.

Quenstedt’s original is a very large cast, 470 mm. in diameter, and has about
thirteen whorls, with the young showing in the centre. It differs from variety A
of rotiforme in persistently maintaining throughout life the breadth and elevation
of the abdomen, together with the keel, channels, and ridges.

The adult, though much larger, is similar to kridion in its heavy overhanging
pile, divergent sides, and broad, elevated abdomen. The young with its large
pile and prominent genicule is similar to the young of some varieties of rotiforme.
There is a broad space on either side of the abdomen, which even in Quenstedt’s
large specimen is not covered by the succeeding whorl, a character also present,
though not invariable, in the adults of rotiforme and kridion. Quenstedt’s figure
shows the undiminished dorso-abdominal diameter of the last whorl, and the effects
of senile degeneration in the pila ; these last, having lost the genicule, thus be-
come reduced to massive bent folds. The form has been changed somewhat,
but nevertheless the keel, channels, and even the lateral ridges, are persistent.

The sutures, though evidently senile, still have an abdominal lobe longer than
the superior laterals,’ but the marginal lobes and saddles have degenerated more
markedly.

Coroniceras rotiforme, Hyarr.

Plate III. Fig. 4-17b.

Amm. rotiforme, Sow., Min. Conch., V. p. 76, pl. ccccliii.

Amm. rotiforme, Zinv., Verst. Wiirt., p. 35, pl. xxvi. fig. 1.

Amm. rotiforme, D’Ors., Terr. Jurass. Ceph., p. 293, pl. Ixxxix. fig. 1-3.

Amm. rotiforme, Hauer, Ceph. Nordéstl. Alpen, pl. i. fig. 1, 2; pl. ii. fig. 7-9.

Amm. rotiforme, Quenst., Amm. Schwab. Jura, pl. xv. ‘

Ariet. rotiforme, Wricut, Lias Amm., p. 278, pl. v. fig. 1-4; pl. vil. fig. 1 (not pl. ix. fig. 1-8).

Localities. —Semur, Stuttgardt, Vaihingen, Balingen.

Var. A.
Plate ILI. Fig. 4, 10, 14-16.

This has smooth young during one or more, but rarely throughout two
volutions. Large, coarse approximated tubercles then appeared, and rapidly
developed into folds, which became more widely separated on the first quarter of
the third whorl, and acquired the aspect of the adult pile of Cor. kridion. The
keel appeared on the third quarter of the third whorl, but remained a mere
ridge, until the advent of the channels about one volution later, when it became

1 In the adult stage the abdominal lobe was undoubtedly much longer in proportion.

aspen i,

FOURTH, OR CORONICERAN BRANCH. 177

more prominent. Upon either the latter part of the fourth, or first quarter of
the fifth volution, the whorl attained its adult characteristics.

During the first volution the increase laterally had been very great, forming
a deep umbilicus; subsequently the tubercles and folds were added to the width
of the abdomen of the earlier whorls, giving a general resemblance to Cor. datum.
The young whorls of specimens in which the tubercles appeared later on the
third whorl were usually rounder, and exhibited, when seen from the side, only a
very remote resemblance to Cor. datum. These passed suddenly, so fast did the
tubercles grow to be folds and then true pilx, into the stage in which they re-
sembled Cor. kridion. After this stage, the preponderance of the abdominal
region is not so marked, though it may be maintained throughout the fourth
volution. Quenstedt’s young specimen, with a living chamber one volution in
length,’ exhibited a broad abdomen on the fourth whorl.

The genicule are at first not tuberculated, but sharp and angular, as in some
varieties of Cor. kridion. The abdomen, however, does not usually become sufli-
ciently prominent in the earlier stages of growth to bear comparison with that
region in kridion. After this period the umbilical shoulders are developed more
proportionally, and finally on the fifth volution the whorl becomes broader dor-
sally than near the abdomen. The dorsal curves of the pile become more
prominent, and sink or are contracted to form the tubercular genicule. These
subsequently bend forward in some specimens, ascending the abdomen. This
last character may occur earlier, on the third whorl, or, on the other hand, be
omitted altogether, even in adults.

This description of the stages of development may be curiously altered by a
malformation of the abdomen. The pilw, Plate III. Fig. 7, 11,? are continued
across, cutting up the abdomen into a series of waves entirely obliterating the
keel and channels.

This variety has young which differ considerably from one another in the
relative breadth of the abdomen, some being excessively broad and flat during
the young whorls, and others, especially the microceran forms, have much nar-
rower whorls. The number of the pile also differs, these parts being more
widely separated in the broad, flat young than in others.

In the majority of adult specimens, the superior lateral saddles are deeply
divided by two marginal lobes, and spread out laterally beyond, or on the ge-
nicule. One specimen, however, from Semur, though not differing in other
respects, has superior lateral saddles so long and narrow that the superior lateral
lobes occupy the genicular line. The abdominal lobe extends beyond the supe-
rior laterals by about one third, and the superior lateral saddles are of about
the same depth as the inferior laterals, though much broader.

Var. B.
This variety is founded on two specimens, which maintained a broad ab-
domen and the immature, thick, unshapely pile of the young until a late

1 Figured in Amm. Schwab. Jura, pl. xv. fig. 9.
2 Vig. 7 represents the abdomen erroneously, the forward donna of the pile where they meet on
the abdomen being flattened out in the specimen.

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178 GENESIS OF THE ARIETIDA.

stage of growth. The lobes and saddles also remained immature, and the
pile were in some instances divided. They resemble Cor, /atum in the rounded
outline of the superior and inferior lateral saddles, but are unquestionably roti-
formian in the equal height of the saddles, and in the prolonged and slender
marginal lobes.

Van. C.

Plate III. Fig. 17.

This is not the Amm. caprotinus of D’Orbigny, as I supposed in my first review
of this species, but a local variety of Cor. rotiforme found at Semur. The tubercles
are very distinct and prominent, and the pile are thicker and more decidedly
depressed as they approach the tubercles than in variety B. Wright's figure
of Sowerby’s original,’ and his other figures, show affinity with this variety ;
but it is not practicable to identify them with other varieties as they are here
described.

During the first senile stage, on the second quarter of the tenth whorl, the
keel and channels may be even more elevated than in the adult, but smooth
zones appear on either side of the channel ridges. The genicule, whose tuber-
culated bends are also lower on the sides than in the adult, do not terminate,
as in that stage, close to the channel ridges, but on the outer edges of the
smooth intervening zones.

The abdominal lobe at this period is only one fourth longer than the superior
laterals, and the inferior laterals are about one tenth shorter than these last.
There is evidently a tendency, as in other cases of senility, to return to the
immature proportions of the young.

In the next senile stage the pile began to lose their prominence and their
tubercles, and on the last quarter of the tenth whorl the latter had entirely dis-
appeared. The abdomen also became more prominent on account of these
changes, and marked alteration in the outline of the whorl occurred still later in
the more advanced stages of degeneration. The flattening and convergence of
the sides, however, really began with the advent of the smooth zones, and this
was the beginning of the metamorphoses which in later stages materially altered
the outline of the whorl. The keel became more prominent on account of the
greater shallowness of the channels, though these still retained their lateral
ridges. A slight increase in the breadth of the sides at this stage would have
produced a whorl in all respects like Cor. orbiculatum.

Several collections were closely examined for this purpose, but they did not
contain many young specimens. We found it difficult to trace the likeness of the
young roliforme to the adult of sridion, on account of the much greater gibbosity
of the whorls in the ordinary forms of that species.

A sufficient number of specimens of rotiforme, however, always show all the
intermediate stages between the extremely thick /aum-like young (Plate LI.
Fig. 15) of one variety and a variety in which the young are difficult to sep-
arate from the adult of sridion by their forms and external characteristics. The

1 Lias Amm., pl. v. fig. 1-8.

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FOURTH, OR CORONICERAN BRANCH. i¢9

sutures of the nearly adult sridion are, however, often quite distinct from those of
a rotiforme of the same size, but whether this difference is invariable or not, I
am unable to say.

The largest specimen in the Museum of Stuttgardt is 470 mm. in diameter.
On the latter part of the whorl the pile are nearly obsolescent, with no genicule,
thus reverting exactly to the condition of those of Cal. Johnstoni, var. torus. The
sides were rounded, channels very shallow, but the keel still prominent. There
is also a fragment of a very old specimen figured by Quenstedt.!

His Fig. 5, together with his Fig. 9, quoted above, show that the living
chambers of the nealogic stages probably exceeded one volution in length, but
we have not been able to ascertain what they were in adults.

Coroniceras lyra, Hyarr.
Plate IV. Fig. 1-17. Plate V. Fig. 1-3a. Summ. Pl. XII. Fig. 13.

Coroniceras lyra, Hyatt, Bull. Mus. Comp. Zool., I., No. 5, p. 78.

Amm. multicostatus brevidorsalis, QueNsT., Amm. Schwab. Jura, pl. vi. fig. 4-6; pl. vii. fig. 1-6.
Amm. multicostatus, WAvEeR, Ceph. Lias d. Nordéstl. Alpen, pl. vii. fig. 7, 8 (not fig. 9, 10).
Arietites bisulcatus, Wricut, Lias Amm., pl. iii., iv.

Localities. —Semur, Aalen, Filder, Gmiind, Boll, Tiibingen.

Var. A.

Plate IV. Fig. 1, 8, 12-14.

This is similar to Cor. rotiforme. The bases of the superior lateral saddles are
very narrow on the sixth or seventh whorl. The bases of the superior lateral
lobes are proportionally broad, and on the same line with the geniculz, instead
of on the side, as in other varieties. The superior lateral saddles are pointed,
but on the eighth whorl they become broader, and are subdivided by three mar-
ginal lobes. ‘The abdominal lobe is longer than the superior laterals by about
one third, and the inferior lateral saddles exceed in depth the superior laterals by
about one fourth.

Var. B.

Plate IV. Fig. 2-5.

This has young with the same rapid lateral increase and deep pit-like um-
bilicus during the first whorl which was previously observed in Cor. rotiforme.
The lateral increase is, however, less marked on the second whorl, and_ the
abdomen begins to become more prominent and rounder. The pile began as
folds, probably on the second or third quarter of this volution, and the angular
ridge, which is to become the keel, appeared on the last quarter of this or the
first quarter of the third volution. The pila never overhang, nor does the abdo-
men acquire greater breadth than the dorsum, as in the young of Cor. kridion and
Cor. rotiforme. This stage is skipped entirely, and it is replaced by a stage
having the same proportions and pile as in the more advanced stages of Cor.
rotiforme. The abdomen on the third whorl becomes flatter, the keel plainer, and

1 Ami. Schwab. Jura, pl. xv. fig. 2.

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180 GENESIS OF THE ARIETID.

the channels are indicated by faint depressions. Upon the third quarter of this
whorl continuous channel ridges appeared, flanked by tuberculated geniculse
bending forwards upon the abdomen. ‘The flatness of the abdomen is due to the
rise of the geniculw upon the sides, which occurred previous to the appearance
of the tubercles. The tuberculated genicule began to fall below the level of the
abdomen upon the last quarter of the fourth whorl, and the abdomen became in
consequence more elevated. The whorl acquired rapidly the flattened sides and
peculiar aspect of the adult, and the transformation was completed on the third
quarter of the fifth volution. Thus in the earlier stages there is a smooth ele-
vated abdomen, which becomes flattened in the next stage, and then elevated
again, but in the last stage it is furnished with keel, channels, and genicul.

The sutures on the last part of the third whorl have an abdominal lobe one
third longer than the superior laterals, but the superior and inferior lateral sad-
dles are of equal depth. These proportions are still unchanged on the first half
of the fifth whorl in some specimens, whereas in others, on the last half of the
same whorl, the difference between the lobes and saddles is about one fifth, and
on the second quarter of the sixth volution the proportion becomes one third.
Before the close of the fourth volution the lobes become more complicated and
broader at the top, and the marginal saddles more numerous and leaf-like, as in
the adult of their own species; the inferior lateral saddles are also deeply cut by
two marginal lobes into three marginal saddles. The similar tripartite division
of the superior lateral saddles and superior lateral lobes becomes at the same
time very marked. The saddles also broaden out at their bases, and upon the
sixth volution spread over the genicula. This broadening of the bases of the
saddles, and the position occupied by the bases of the superior lateral lobes in
consequence of this, are characteristics of some value in the species. They also
show that the external characteristics of the shell develop contemporaneously
with the sutures, and arrive together at their adult development upon the latter
part of the fifth whorl. The abdominal lobe extends beyond the superior lat-
erals by about one third of its own length, and the inferior lateral saddles are
deeper than the superior laterals in the same proportion, The abdominal lobe of
the last suture of the third volution is one third longer than the superior lateral
lobes, but the two larger saddles are of equal depth. Quenstedt describes and
figures all specimens from Suabia as having an abdominal lobe shorter than the
superior laterals, and the superior lateral lobes pointed. This character was found
in the nealogic and adult stages. The figures of the very aged forms which he
calls Amm. brevidorsalis, Plate VII., would have had comparatively short ab-
dominal lobes, to whatever species they might have belonged.’ Quenstedt com-
plains of Wright for not paying attention to his distinctions, but we think
Wright’s figures of multicostatus show that he was right. ‘The English specimens
had long abdominal lobes, and, like French and German shells described above,
are undoubtedly identical with those figured by Quenstedt. in every other

1 For example, the huge Cor. Bucklandi, Amm. Schwab. Jura, pl. ix. fig. 1, and coronaries, pl. xvi.,
of Quenstedt. Compare also the gradual decline in length of the abdominal lobe of an aged Cor. trigona-
tum, Plate VII. of this monograph.

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FOURTH, OR CORONICERAN BRANCH. oul

respect. A subsequent re-examination and remeasurement of all specimens in
the Museum of Comparative Zotlogy has shown that the average length of the
abdominal lobe for nealogic and adult shells is considerably over one third longer
than the superior laterals. The sutures also vary from the comparatively simple
margins, with solid looking and very slightly indented saddles, to the extreme
forms figured in our plates and by Quenstedt.

Var. C.

Plate IV. Fig. 9-11, 15, 16.

In this variety the channels are slower in reaching their full development, and
the pile are not so prominent, but are more numerous and conform more closely
to the shape of the whorl. The whorl is altogether flatter, and increases some-
what faster by growth than in variety B. The channels are hardly perceptible
on the fourth volution, and in consequence of the smaller size and want of prom-
inence in the geniculx, the abdomen has at the same time more prominence than
in variety B. These characteristics are more or less variable. Thus individual
specimens may resemble variety A in some characters, or variety B in others.
In a specimen of variety C, Plate IV. Fig. 15, 16, senile characters begin to be
apparent upon the second quarter of the ninth whorl. The pile are still slightly
tuberculated, the abdomen though much narrowed is still comparatively broad.
In a specimen of variety B, at same time the abdomen had become narrow, the
pila had lost not only the tubercles, but also the genicule, being in their second
stage of obsolescence. A specimén in the Museum of Stuttgardt, from Gép-
pingen, measuring 440 mm. in diameter, showed more pronounced senility. ‘The
sides were exceedingly convergent, the pila obsolescing, the abdomen elevated,
though the channels and keel were not much changed. In another of the same
diameter the channels were obsolete, the keel a low broad ridge, the pilee reduced
to broad lateral folds, and the sides very convergent. In the large specimens
figured by Quenstedt,' if the figures are accurate, the keel, channels, and lateral
ridges are persistent.

In the Museum at Semur is a fine suite of specimens named Vereigetorix,
Reynés. These specimens did not show senile decline as early as is usual in this
species. One at the diameter of 525 mm. still retained the pile and the chan-
nels, though the abdomen had become much elevated. This specimen was dis-
torted by lateral pressure, so that the transverse dorsal diameter was shorter than
the abdominal.

Wright’s figure? seems to be identical with this species, and the more com-
pressed specimen figured on Plate IV. seems to be intermediate between my Cor.
lyra and Cor. Gmuendense. do not remember having seen any such forms myself,
nor are any English specimens mentioned in my notes.

1 Amm. Schwib. Jura, pl. vii. 2 Lias Amm., pl. iii.

182 GENESIS OF THE ARIETIDA.

Coroniceras trigonatum, Hyarr.
Plate VI. Fig. 3. Plate VIL. Fig.1. Summ. Pl. XIL. Fig, 15.

Aster. trigonatum, Hyatt, Bull. Mus, Comp. Zodl., I., No. 5, p. 79.
Amm. Brooki, Zunr., Verst. Wiirt., p. 26, pl. xxvii. fig. 2.

Amm. Brooki (Riesenbrooki), Quenst., Der Jura, p. 68.

Amm. Crossi, QuENST., Amm. Schwiib. Jura, pl. xiv. fig. 6.

Amm. nudaries, QUENST., Ibid., fig. 5 ?

Locality. — Aalen.

Great size is a characteristic of this species. One specimen was 380 mm. in
diameter, and another measured 503 mm. Quenstedt describes one from En-
dingen 700 mm. in diameter.

The young were seen only from the side, but the following characters could
be made out, even from this point of view. The form of the whorl in trans-
verse section at an early stage is evidently quadragonal, since during the first
four or five whorls the sides are flat and the pile tuberculated, as in Cor. lyra.
After this the dorsum increases more rapidly, and the whorl gradually assumes
the trigonal form. The tubercles and genicule become atrophied, the pile
are merely lateral folds, and the channels very shallow by the time the shell
reaches the second quarter of the sixth or seventh volution. On the eighth
volution the channels are represented only by smooth inflected zones on either
side of the keel.

The sutures on the latter part of the sixth or seventh whorl have abdominal
lobes, which are one half longer than the superior laterals, the inferior lateral
saddles one half deeper than the superior laterals. The lobes and saddles are all
exceedingly broad, and the outlines very complicated. After this period the
sutures degenerate, the abdominal lobe decreases in length, and the lobes and
saddles, though they retain their complicated marginal inflections, become pro-
portionally broader.

A fine suite of specimens in the Museum of Stuttgardt, from the Geometricus
bed, show that the species is very similar to Cor. lyra (multicostatus of German
authors). The whorl, however, has a broader dorsum, and is larger, and the
volutions are less numerous. There are also fewer and stouter pile at the same
age than in Cor. ra. There are two varieties included under this name. One
is a smaller form, with premature development of senile whorls, etc., and has
broader whorls; the other is the normal form, having slower development of the
adult and senile characters, and this alone has been figured.

The more involute shells of this species are the Amm. Riesenbrooki of Quenstedt,
and the less involute are the normal Amm. Brooki of most German authors.

Wright’ describes the Stuttgardt and Tiibingen specimens, but considers
them identical with Cor. Gmuendense and his Arietites Cross’, —a mistake arising
from not having observed the differences in the umbilicus due to the number
and shape of the whorls, which are less numerous and stouter than in Gmuen-
dense. Quenstedt appears to have been led into a similar error, possibly through

1 Lias Amm., p. 284.

FOURTH, OR CORONICERAN BRANCH. 183

Wright’s visit to his collection. Quenstedt’s huge specimen, 700 mm. in diam-
eter, noted above, is described’ as having the pile: obsolescent near the termina-
tion of the last volution, and the keel as showing but little above the almost
obsolete channels. This, therefore, is an extreme example of senile degeneration
in the clinologic stage, but it has not yet reached the nostologic stage.

Coroniceras Gmuendense, Hyarr.
Plate V. Fig. 4-9. Plate VI. Fig. 1, 2. Summ. Pl. XII. Fig. 14.

Amm. Gmuendense, OrpeL, Der Jurafor., Wiirt. Jahreshf., XII. p. 200.
Amm. Brooki, Zrev., Verst. Wiirt., pl. xxvii. fig. 2.

Aster. tenue, Hyatt, Bull. Mus. Comp. Zodl., I. No. 5, p. 79.

Ariet. Crossi, Wrigut, Lias Amm., p. 283, pl. x. fig. 1, 2.

Localities. — Semur, Gmiind, Gdppingen, Aalen, Aargau.

The adults of this species are readily distinguishable from Cor. lyra by the
smaller size of the whorls, the characteristics of the sutures, the extreme narrow-
ness of the abdomen as compared with the dorsum, and the broad, shallow chan-
nels. The keel is more prominent also than in Cor. lyra, and the pile end very
abruptly with geniculz or pseudo tubercles. This peculiarity is observable on
the latter part of the sixth whorl, and the bending forward of the geniculs, as
they rise on the narrow abdomen, is hardly observable on the cast until after the
completion of the seventh whorl. On the eighth volution the genicule become
less prominent on the cast, and the depressed genicule and pile: form a single
arch slightly interrupted by the tubercular aspect of the former. These charac-
teristics are not altered when the shell is present, but have about the same ex-
pression as upon the cast. The genicule on the seventh whorl, in one specimen
examined, are prominent, and their forward bend plainly observable, though
without tubercles.

The abdominal lobe is broad and deep (Plate V. Fig. 5). The superior lateral
saddles and lobes are nearly obsolete, the inferior lateral lobes and the first aux-
iliary saddles are but slightly developed. On this account the inferior lateral
saddles, which are of about the usual size, acquire remarkable prominence.
We have already noticed, in variety C of Cor. rotiforme, a tendency towards the
suppression of the superior lateral saddles, and here it is actually carried out.
The marginal lobes and saddles of the superior laterals, however, remain on one
specimen from Aargau, but on one from Semur only the inner of the three sad-
dles is of noticeable size. These characteristics are present in the adults of this
species, and consequently are not due to old age.

On the latter part of the eighth whorl the pile lose their tubercles, (Plate V.
Fig. 5,) and the genicule become almost obsolete, being reduced to curved con-
tinuations of the depressed arched pilx&, which are most prominent at the um-
bilical shoulders. The channels continue to be very well defined, though much
shallower, (Plate V. Figs. 8, 9,) and channel ridges are preserved until the first
quarter of the tenth whorl. On the second quarter of this whorl the pile are

1 Amm. Schwib. Jura, p. 115.

184 GENESIS OF THE ARIETIDA.

straight, prominent dorsally, but obsolete on the edge of the abdomen. The
channel ridges have also disappeared, and the channels are only indicated on
either side of the keel. The keel, however, is persistent.

The abdominal lobe on the latter part of the ninth volution is somewhat
more than one half longer than the superior laterals, and the inferior laterals
one half longer than the superior lateral lobes. This is a senile tendency to
return to larval proportions, since the proportional adult difference in length of
the abdominal lobe is at least three fifths.

A specimen in the Geometricus bed, from Nurtingen, labelled nodosaries, in
the Museum of Stuttgardt, exhibits the characteristics of this species. Quen-
stedt’s original of nodosuries shows that the identification of such specimens with
his nodosaries is not correct. It is very often regarded as the young of Cor. tri-
gonatum, but is far too much compressed, and whorls too small, though otherwise
quite similar.

Wright's figure of an old specimen of this species under the name of Ariet.
Crossi leaves little room for doubt that it occurs in England with the same
peculiar form as in Germany. Wright does not mention that there are any
varieties.

SECOND SUBSERIES.

Coroniceras Sauzeanum, Hyarr.
Plate VI. Fig. 4-14. Plate VIII. Fig. 1-3. Summ. Pl. XII. Fig. 10.
Amm. Sauzeanus, D’Ors., Terr. Jurass. Ceph., p. 304, pl. xev. fig. 4, 5.
Amm. spinaries, Quenst., Der Jura, pl. vii. fig. 4; Amm. Schwab. Jura, pl. ii. fig’ 8-14 (fig. 15-17?).

Localities. — Whitby, Leicestershire, Semur, Salins, Gmiind.

D’Orbigny’s original specimen, (Plate VI. Fig. 12, 13,) with which this iden-
tification was made, is smooth probably throughout the first four whorls. The
centre was obscured, and the exact number of whorls was estimated. The abdo-
men is flat, with a very obscure siphonal ridge on the fifth whorl. The pile are
terminated by a tubercle, which is elevated so that it stands on a level with or
above the abdominal continuation of the pile. These nearly meet, and in some
specimens actually do cross the siphonal ridge, giving the shell a microceran
aspect.

The further development of these peculiarities would lead to a form in which
the keel would become more distinct, but would be guarded by very shallow
channels, and in which also the pilw, gracefully curving as in this specimen,
would terminate in a tubercle standing out prominently on the edge of a flat-
tened abdomen. Such a form, of which the young is shown in Fig. 10, 11,
occurs in the same locality, and it is evidently an older individual of this
species.

The sutures of this specimen are visible on the third quarter of the sixth
whorl. The abdominal lobe is shallower -and broader than in variety Gaudryi,
and the inferior lateral saddles also broader proportionately. The sutures are
more like those of the young of variety A, Cor. bisnicatum. The edges of the

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FOURTH, OR CORONICERAN BRANCH. 185

lobes and saddles are, however, serrated, not deeply divided by the marginal
lobes, as in the last named species. The abdominal lobe is one half longer than
the superior laterals, and the inferior lateral saddles exceed the superior laterals
in the same proportion.

A fine suite of these specimens exists in the Museum of Stuttgardt, showing
the variations described above. Some are very decidedly ‘planicostan in aspect,
but not more so than other specimens of Coroniceras, in which the keel becomes
entirely suppressed, and the abdomen is crossed by the pilx. Young specimens
from Behla pass through stages which repeat exactly the characteristics of Cor.
kridion when considerably older and perhaps full grown. One of these is labelled
capraries, Fraas, planicostan variety ; another lot of three specimens is named
Danulicus, on account of their thick whorls and pile. A large specimen from
Gmiind, on the last part of the last whorl, has all the characteristics of the stout
English specimens of var. Gaudryi, Reynés. There is also a fragment of a much
older shell, the dorso-abdominal diameter of the whorl being 60 mm., which has
similar characters. The channels are, however, very broad and shallow, and the
keel also low and broad.

Since the above and the description of var. Gaudryi were written, I have
found in the collection of the Museum of Comparative Zodlogy English speci-
mens of this species exhibiting the young. In these, for one or two volutions,
the whorls are smooth, then obscure tubercles or swellings begin to appear upon
the sides, which elongate into folds on the third whorl, and become distinct pile
on the latter part of this whorl or the first quarter of the fourth. The external
resemblance to the young of Cal. Johnston’ is complete in the pilx, the com-
pressed or embryonic form of the whorl, and the absence of a keel; the sutures,
however, do not appear to be similar. Even on the early portions of the third
whorl the abdominal lobe is quite long, the superior and inferior lateral lobes
exceedingly short, and the corresponding saddles of equal depth. From this
time the complication consists in the crenulation, or rather serration, of the mar-
gins, and the slow increase of depth in the superior lateral saddles; the other
saddles and lobes remain about what they were at first with regard to their
proportions. The keel is perceptible as a slightly raised siphonal line on the first
quarter of the fifth whorl or last of the fourth. In the first of this stage, the
abdomen, pile, and form of the whorls are similar to those of the adult of Cor.
kvidion. On the fifth volution, however, the abdomen becomes flatter, the ge-
nicular band of the pilze more abrupt, and finally tuberculated, and the hitherto
divergent or gibbous sides flatter and slightly convergent.

The young figured by Quenstedt’ are questionable. They are more com-
pletely pilated than is usual in the species, and the form of the whorl is quite
different. We doubt the correctness of the identification.

1 Amm. Schwib. Jura, pl. xi. fig. 15-17.

24

186 GENESIS OF THE ARIETIDA.

Var. Gaudryi.
Plate VI. Fig. 14. Plate VIII. Figs. 1-3.

Cor. multicostatum, Hyatt, Bull. Mus, Comp. Zodl., I., No. 5, p. 78.
Amm. Gaudryi, Reynts, Plates.
Ariet. Sauzeanus, Wriaut, Lias Amm., Pal. Soc., pl. viii. fig. 1-6.

On the sixth volution this shell has slightly convergent sides, a thick, low
keel with shallow broad channels. The pil are tuberculated, and the geniculse
bending forward break up the channel ridges into a series of waves. They also
pass over the umbilical shoulder on the dorsal side, but are not so prominent
there. The very rapid increase in size of the whorl renders the umbilicus about
half an inch deep at the end of the sixth volution. On third quarter of the fifth
whorl the channels are very faint, the genicule where they ascend upon the
abdomen are less prominent, and tubercles much higher up on the edge of the
abdomen. If the pila were less prominent and devoid of abdominal extensions,
this stage would precisely represent the usual form of var. Sawzeanum.

On the fifth and sixth whorls the abdominal lobe is about two fifths longer
than the superior laterals, and the inferior lateral saddles exceed the superior
laterals in the same proportion.

The German specimens are precisely like the English. One in Quenstedt’s
collection from Betzenrieth bei Géppingen is identical with the English specimen
of the same age. Wright’s figures all belong to var. Gaudryz, and exhibit a well
defined keel and convergent sides at an early age.

Coroniceras bisuleatum, Hyarr.
Plate VII. Fig. 2-10. Summ, PI. XII. Fig. 11.

Amm. bisulcatus, Brue., Encycl. Meth., I. p. 39, pl. xiii,

Amm. bisulcatus, D’Orz., Terr. Jurass. Ceph., p. 187, pl. xliii.

Cor. bisulcatum, Hyarr, Bull. Mus. Comp. Zodol., I, No. 5, p. 77.

Ariet. rotiformis, Wrieu'r, Lias Amm., p. 278, pl. ix. (not pl. v., vii.).

Amm. multicostatus, Sow., V. p. 76, pl. ecccliv.

Amm. multicostatus, HAvgR, Ceph. Nordostl. Alpen, pl. i. fig. 3, 4.

Ariet. subnodosus, Wricut, Lias Amm., p. 288, pl. vi. fig. 2, 3.

Amm. resurgens? Dum., Etudes Pal. Bassin du Rhone, pt. 2, pl. xxiii. fig. 3-6.
Amm. milticostatus, Zret., Verst. Wiirt., pl. xxvi. fig. 3.

Localities. —Lyme Regis, Semur, Hechingen, Balingen.

There are four specimens of this species, two from Semur, one from Hech-
ingen, and one from Balingen, which differ in a significant manner. Both of those
from Semur have a somewhat closer resemblance to the full grown Cor. Sauzea-
num than the German specimens;. they differ, however, in some respects. On
one, the pile are visible on the last quarter of the sixth whorl, and show on the
cast distinct traces of tubercles, and the genicule terminate before they reach
the channel ridges, which are continuous and entire. In the other specimen, the
pile are visible on the first quarter of the seventh whorl, do not show on the cast
distinct traces of tubercles, and the genicule pass over the channel ridges as in
Sauzeanum. In both German specimens the channel ridges have a crenulated

FOURTH, OR CORONICERAN BRANCH. 187

outline, and the pile are similar. As a whole these four specimens differ from
Cor. Sauzeanum, var. Gaudryi, in having a shallower umbilicus and a somewhat
greater number of whorls in proportion to the size of the shell. One specimen
from Semur is intermediate in characters between the German specimens, and
the true Sauzeanum, var. Gaudryi. The Semur specimens also differ in the depth
and groove-like aspect of the channels, and the almost sunken aspect of the keel
on the casts. The prominence of the genicule reminds one of the fifth whorl of
Sauzeanum, var. Gaudryi.

Both specimens from Semur have similar sutures. The ventral lobe is deep,
the superior lateral saddles and lobes very shallow and broad, the inferior lateral
saddles very prominent, and the inferior lateral lobes obtuse. The marginal lobes —
are more evenly distributed than in the German variety.. The sutures on the
seventh whorl have an abdominal lobe from one half to two fifths longer than
the superior lateral lobes, and the inferior lateral saddles exceed the superior
laterals in the same proportion.. Both in fact approximate to Cor. Sauzeanum, var.
Gaudryi, by their sutures. In the German specimens the lobes and saddles show
about the same general proportions, though the inferior lateral saddles are much
broader, and the inferior lateral lobes deeper, and acute instead of obtuse. There
is a large specimen in Professor Quenstedt’s collection from Bodelshausen -
(No. 10673), which is similar to these, but unfortunately the name of this was
not noted.

The keel is quite prominent at the earliest period observed on the first
quarter of the fourth whorl, but the channels are hardly discernible. At this
period the channel ridges are not developed, and the tuberculated genicule are
high upon the sides. When the channel ridges are distinguishable on the fifth
volution, they are continuous. The keel loses its prominence after the channels
deepen upon the latter part of the fifth, and the early part of the sixth whorl.
The pile in the young are more numerous than in the adult. ©

The largest specimen from Semur measured 348 mm. in diameter, and had
about eight and a half volutions. The pile retained all their adult peculiarities
and original sharpness, and the quadragonal form of the whorl was also un-
changed. The channels were, however, broader and shallower than in the adult.
The approximation of this form in aspect and characteristics to its morphological
equivalent, Cor. lyra, is so close, that only the most careful study can show them
to have been distinct. ‘The young of these two species are quite different at all
stages, and can generally be readily separated.

This species has always the broad abdomen of Sauzeanum and its spinous
tubercles, and the young are not so stout as in Cor. lyra. In the succeeding
stages the young of dra rapidly changes from divergent to. parallel sided, and
then to a convergent sided whorl, whereas in this species the development is
much slower. The later stages (Plate VII. Fig. 8) are similar in form to lyra
when quite small (Plate IV. Fig. 9). The genicule usually cut up the channel
ridges into waves, and, though not invariable in the species, this occurs so gen-
erally as to be a useful distinction, and is evidently of genetic importance in the
series. The resemblances of the young to the adult of Aridion and the young of

188 GENESIS OF THE ARIETIDA.

rotiforme may be observed by comparing the figures on Plates VII. and III., but
from these it may be distinguished by the flatness of the abdomen, the elevated
geniculee, and the much earlier development of the channels.

At Semur there are several varieties of this species. One was 620 mm. in
diameter, the last whorl about 170 mm. in diameter from abdomen to dorsum.
The abdomen was quite narrow on the last whorl, but the tubercles were still
traceable, or rather the genicula were very thick and prominent, resembling
tuberculations. Another specimen 650 mm. in diameter, has a last whorl 240 mm. |
in diameter, and the abdomen much narrower, about 110 mm. in breadth,
the dorsum being fully 160 mm. in breadth. The keel in this more advanced _ . |
| ‘senile stage is considerably reduced in size, and the channels are almost obso-
lete ; the tubercles are nearly obsolescent, but the genicule still rise above the
edge of the abdomen. ‘This peculiarity of the pile shows that the Sauzeanus
form is persistent, and it enables the observer to distinguish the differences
between a member of this series and all others.

Wright’s figure’ of a specimen from Semur, named by him Arietiles rotiformis,
looks like the full grown adults of the more discoidal variety of this species, but
his reference of it to the Lower Bucklandi bed is probably incorrect. Dumor-
tier’ declares that a species identical with disudcatus, D’Orb., but with channels
not so deep, is found in several localities in the Angulatus bed in the basin of
| the Rhone. Unfortunately, no figures accompany his description, and figures
of young and adult would be necessary to support this opinion. Cor. kridion
and Verm. Conybeari are very like disulcatum in the adults, but are quite distinct
at earlier stages.

We think perhaps the more involute and broad whorled variety of this species
should be recognized as distinct. It is the Amm. resurgens of Dumortier, and the
subnodosus of Wright. Wright was mistaken in placing his specimen with Amal-
theus, it being an undeniable Arietian, probably occurring not later than the
| Obtusus bed, and perhaps as early as the Upper Bucklandi bed. In the Museum
of Comparative Zodlogy there is also a magnificent specimen from Lyme Regis,
measuring 375mm. This is a perfect cast of one side, showing the same char-
acters as in the small specimens figured by Dumortier, and the one figured by
Zieten as multicostatus. These characters persist even at that advanced stage,
without any signs of senility, and the pile, tubercles, genicule, and form of
whorl remain unchanged.

The examination of Sowerby’s original has induced us to join Oppel in sup- |
pressing the name of multicostatus. Sowerby’s fossil is precisely similar to the
adults of the common French variety of this species.

a.

1 Lias Amm., pl. ix. ij
2 Htudes Pal. du Bassin du Rhone, pt. 1, p. 115, and pt. 2, p. 115. 5
8 Lias Amm., pl. vi. fig. 2, 3. [

FOURTH, OR CORONICERAN BRANCH. 189

Coroniceras Hungaricum, Hyarr.

Amm. Hungaricus, HavER, Ceph. Lias Nordéstl. Alpen, pl. iv.

The figure of this species possesses the exact form and characteristic of the
bisulcatus series. It has similar unshapely genicule thrown out beyond the
edges of the abdomen, giving the whorl a peculiar angular and squared aspect ;
the genicule also interrupt the channel ridges, and the keel, though well de-
veloped, is almost counter-sunken in the deep channels. The pile are very
straight in Hungaricum, and have no tubercles; the form is also somewhat more
compressed than in disudcatus. The sides also are perfectly flat and parallel, and
the depressed abdomen and nearly equally flattened dorsum are of the same
breadth, the whorl in section being a parallelogram with the sides about one
fifth longer than the transverse diameter. The specimen figured by Hauer was
135 mm. in diameter, and consequently the complete shell must have reached a
much larger size, since his specimens exhibit no signs of the approach of senility.

THIRD SUBSERIES.

Coroniceras latum, Hyarr.
Plate III. Fig. 19-23a. Summ. Pl. XII. Fig. 16.
Coroniceras latum, Hyatt, Bull. Mus. Comp. Zool., I., No. 5, p. 77.
Amm. Bucklandi pinguis, Quenst., Amm. Schwab. Jura, pl. ix. fig. 3?

Locality. —Semur.

Many of the young of this species, Plate III. Fig. 22, 23, have large tubercles
early on the second whorl, and on the third these become elongated into tuber-
cular folds. On the fourth, or on the latter part of the third volution, the inter-
vals between them increase, and they become true pile. In other specimens,
Plate III. Fig. 19, the pila are acquired as in rotiforme, Plate III. Fig. 5, and there
is also in many specimens, Plate HI. Fig. 22, a close resemblance to the adult of
Cor. kridion, Plate II. Fig. 3. The keel appears on the first quarter of the fourth
whorl, but at the latest stage observed on the second quarter of the fifth volu-
tion of a cast the keel was still very thin, sharp, and but slightly elevated. The
channels, however, though very shallow and broad, had acquired lateral ridges.
On the second whorl the breadth of the abdomen is very much increased by the
development of tubercles, the sides becoming exceedingly divergent in some
specimens, and the abdomen gibbous. On the fourth whorl the central area
begins to become depressed, Plate ILI. Fig. 23, but the abdomen on either side
retains its remarkable gibbosity. In correlation with this and with the narrow
dorsum, the abdomen is never entirely covered by the succeeding whorls, but has
an exposed border on both sides. On one specimen, Plate III. Fig. 22, 23, both
the pila and genicule are double; in others, the pilz are single and the genic-
ulze are double; on another, the duplication of the geniculze ceases on the third
quarter of the fourth whorl, with the exception of one single genicula on the last
quarter, which is double. One cast of the second variety was very much broader

SS

190 GENESIS OF THE ARIETIDA.

than any other observed, and the genicule were hardly yet perceptible on the

second quarter of the fourth volution. Another cast, though nearly as broad as

the last, is somewhat flattened on either side of the keel; it has prominent and

immature tubercles, though the pile and genicule are still imperceptible, and the '

channels still undeveloped on the latter part of the fourth volution. These two

specimens show the retention of nealogic form and characters. When specimens

, develop more rapidly, the great breadth of the abdomen’ begins to decrease, and '

true pile replace the tubercular folds on the fourth whorl.

The sutures in this species are peculiar in respect to the great breadth of the

lobes and saddles in comparison with their length or depth, the regularity and é

small size of the marginal lobes, and the rotundity of the marginal saddles even

in the oldest stage examined, on the second quarter of the fifth whorl. At this

| time the superior lateral saddles are not so deep as the inferior laterals, but in

1 the latter part of the fourth whorl they are about even (Plate Ill. Fig. 23a). The

1 abdominal lobe exceeds the superior laterals by less than one third, and the

inferior lateral lobes exceed the superior laterals in the same proportion. At the |

earliest period examined, the first quarter of the fourth whorl, the abdominal lobe

is only about one fourth longer than the superior laterals, and the inferior lateral

saddles, instead of being deeper, are about one third shallower than the superior |
)
|

laterals.

A splendid series of this species from the Bucklandi bed at Semur gives very
remarkable variations. The young have all the variations above described, and
1 in addition the following : —

i 1. Forms which at a comparatively early age have an abdomen and tubercles
like the adult of var. Gaudryi of Cor. Sauzeanum.

2. Three specimens with young, having the typical broad abdomen of datum,
but speedily changed by growth so as to resemble the young of Cor, orbiculatum.

3. One specimen has sides flattened, pile numerous and single, approximat-
1 ing to the adult Bucklandi in aspect. ;
| 4. Another has single pile in the young and double in the adult, just the
1 reverse of all other specimens yet observed.

5. Another has the double pilx in the young, but the sides are gibbous in-
stead of being flat or divergent, and it then speedily acquires convergent sides,
becoming similar to Cor. rotiforme. The abdomino-dorsal diameter is less than
usual, and the increase in size more gradual than in the typical form of Cor.
latuin.

‘These variations and resemblances all seem to be expressions of transient
tendencies, except those which approximate to Cor. kridion and rotiforme. The
agreement of the young forms as shown above, and of Fig. 15 and 21, Plate IIL,
the similarity of the sutures of the young of rotiforme, Plate III. Fig. 10 a, and

he: aes

1 of datum, Fig. 23 a, show that the differences between these forms are not. great,
and consist mostly in the excessive development of the broad-abdomened whorl
in some varieties of Cor. datum. All the specimens I have seen are also of small
size, and seem to be the young of some yet unknown adult form similar to Cor.
Buckland. The sutures of Quenstedt’s Amm. Bucklandi pinguis agree remarkably

FOURTH, OR CORONICERAN BRANCH. Heald

well with those of datum, and lead us to hope that this may prove to be the adult.
Certainly it is very distinct from the true Bucklandi, and the characteristics, so
far as shown, are such as one might expect in the first senile stages of Cor. latum.

Coroniceras Bucklandi, Hyarr.

Plate III. Fig. 18. Summ. Pl. XII. Fig. 17.

‘
Amm. Bucklandi, Sow., Min. Conch., II. p. 69, pl. exxx.
Amm. Bucklandi, Zint., Verst. Wiirt., pl. xxvii. fig. 1.
Amm. Bucklandi, Puwux., Geol..York., p. 1, pl. xiv. fig. 13.
Ariet. Bucklandi, Wrieur, Lias. Amm., p. 269, pl. i. fig. 1-3.
Amm. Bucklandi, Quensr., Amm, Schwab. Jura, pl. ix. fig. 1 (mot fig. 2, 3).
Amm. Bucklandi costaries, QuENS’T., Ibid., pl. xi. fig. 1.
Amm. solarium, QuENST., Ibid , pl. viii. fig. 1-3,
Amm. sinemuriensis, D’OrB., Terr. Jurass. Ceph., p. 303, pl. xev. fig. 1.
Amm. sinemuriensis, Quenst., Amm, Schwib. Jura, pl. xi. fig. 18-20.
Cor. sinemuriense, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 78.
Localities. — Lyme Regis, Semur, Basle, Aargau, Scheppenstadt, Schaichhof, Balingen, Tiibingen.
|
| Var. sinemuriense.
4 Plate III. Fig. 18.
| : :
This has young which closely resembles the young of Cor. datum. The breadth

of the abdomen, divergent sides, immature folds, and tubercles are quite similar.
| The folds also begin with large tubercles on the first part of the second whorl.
On the third quarter of the third whorl the true pile begin. After this the
abdomen no longer increases so fast in breadth, and finally, upon the latter part
of this volution, or the beginning of the fourth, this region is hardly wider than
a the dorsum, and the sides flattened. On the first or second quarter of the fourth
whorl the pile become duplicate or triplicate, and the broad, thin, abdominally
projecting tubercles characteristic of this species arise. These peculiar pile and
tubercles occur, in some specimens, intercalated with single pilee and tuberculated
genicule bending forward upon the abdomen. The keel on the third quarter of
the third whorl was well developed, and must have appeared considerably earlier.
The channels were but slightly developed on the first quarter of the fourth whorl,
though they have well defined ridges, and probably began later than the keel,
somewhere perhaps upon the last half of the third volution; but this could not be
ascertained with certainty. One specimen from Semur had but two divided pile
upon the third whorl; after this they remained single to the fifth volution, the
last observed. D’Orbigny’s figure of Amm. sinemuriensis was taken from a young
individual of about five and a half whorls, in which the pile are all divided. This
is as exceptional in the species as are the specimens without any divided pilex.

The superior lateral saddles are much narrower than the inferior laterals.
The abdominal lobe is about one half longer than the superior laterals.

A fine specimen of this species from Semur, Plate HI. Fig. 18, retains the
peculiar characteristics of sizemuriense for five and a half volutions, with a similar
rate of increase, and slightly divergent or flattened sides, These sides become
then more rounded, the pile single, parting with their tubercles; and on the |
eighth volution, or perhaps. sooner, the whorl assumes all the characteristics of i

te

192 GENESIS OF THE ARIETIDA.

the adult of Oor. Bucklandi of German authors. The pile are more widely sep-
arated, about six less on the eighth whorl than on the seventh; they are thick,
solid, untuberculated, and the geniculx bend abruptly and squarely forward on a
level with or a trifle above the channel ridges, interrupting them with very slight
elevations. The abdomen is flattened, but more or less rounding between the
genicule, and its breadth is a trifle less than the dorsum, instead of being slightly
broader, as in the young during the first five or six volutions. The channels sink
into the abdomen, and the keel hardly shows above the lateral ridges.

The sutures on the third quarter of the eighth whorl in this specimen have
an abdominal lobe about two fifths longer than the superior laterals, and the
inferior lateral saddles are also two fifths deeper than the superior laterals.

A finely preserved specimen from Schaichhof agrees precisely in all its charac-
teristics with the above, but on the first quarter of the tenth volution the inferior
lateral saddles are about one third longer than the superior laterals. A specimen
from Semur on the latter part of the tenth volution had an abdominal lobe
about one third longer than the superior laterals. A slight rounding off of the
abdomen, greater prominence of the keel, and shallowing of the channels, indi-
cate the approach of old age in this specimen, whereas, at a corresponding age,
the Schaichhof specimen still had the angular geniculx and flattened abdomen of
the adult.

The largest specimen of the sinemuriense variety, as shown by the young, was
found in the Stuttgardt Museum. It measured about 610 mm. in diameter. There
were some indications of old age, but the form of the whorl and the pilz held
their own wonderfully. There was also in the same Museum a specimen in which
the pilze had genicule on a level with the abdomen, and therefore very promi-
nent, the channels excessively shallow, and keel broad and low; it was 375 mm.
in diameter, and the channels had probably been deeper at earlier stages.

Of the specimens figured by Quenstedt in his “ Ammoniten des Schwiibischen
Jura,” Bucklandi, Plate XI. Fig. 1,seems to belong to what we call true Buckland,
as well as most of the figures of young on Plate X. The specimens figured as
Amm. sinemuriensis, on Plate XI. Fig. 18-20, are doubtless the young of our Cor.
Bueklandi, var. sinemuriense. These forms are not rare, but the adults must be
rare, or they would not have escaped Quenstedt’s attention.

Var. Bucklandi.

The stout English variety of Bucklandi' is a form with much larger and fewer
whorls than Bucklandi, var. sinemuriense. The adult whorls are similar in their
general characteristics, but the young in the stout English variety has very
much larger whorls, with thick, sparse, single pile, like the German specimen
in the Stuttgardt Museum described above and the young forms figured by
Quenstedt.

The Amm. solarium of Quenstedt is founded upon large, senile specimens, as

is shown by the fragments figured. Their sutures, the huge fold-like, smooth -

1 Wright, Lias. Amm., pl. i. fig. 1-3. 2 Amm. Schwiib. Jura, pl. viii.

FOURTH, OR CORONICERAN BRANCH. 193

pila, and shallow channels, show this plainly. They probably belong to the
typical variety of Cor. Buckland, though the evidence must be considered incom-
plete until the adults and young are known.

Coroniceras orbiculatum, Hyarr.

Coroniceras orbiculatum, Hyatt, Bull. Mus. Comp. Zodl., L., No. 5, p. 78.

Amm. Bucklandi macer, Quenst., Amm. Schwib. Jura, pl. ix. fig. 2 (not fig. 1, 3); pl. x. fig. 5.
Amm. Bucklandi costosus, QuENS?., Ibid., pl. x. fig. 1, 2.

Amm. Bucklandi, QuENST., Ibid., pl. xi. fig. 2 (not fig. 1).

Amm. oblongaries, QuENST., Ibid., pl. xiv. fig. 4.

Localities. — Semur, Scheppenstadt, Balingen.

The breadth and crowded aspect of the pilex in the Scheppenstadt specimen
on the fourth and fifth whorl, and the narrowness of the sides, resemble the
characteristics of the same age in Cor. Bucklandi, var. sinemuriense, more than any
other species of the same genus. The young whorls are much too small in all
their dimensions, and the volutions too numerous for Cor. Buckland. The adult,
with its prominent tubercles and with the dorsal broader than the abdominal
region, shows a remarkable resemblance to Cor. rotiforme.

The last sutures on the ninth whorl have an even, rounded outline, due to
the small size and regularity of the marginal lobes and the roundness of the mar-
ginal saddles, which are similar to those of Cor. datum on the fifth volution. The
abdominal lobe is about one half longer than the superior laterals, the inferior
lateral saddles exceed the superior laterals by about two fifths. The saddles and
lobes, however, are broad and comparatively short in Cor. datum and in the young
of other forms of Coroniceras. One specimen which is identical with this in the
septal outlines shows the abdominal lobe on the eighth whorl to be one third
longer than the superior laterals, and the superior lateral saddles are not quite
one third longer than the inferior laterals.

One of the casts from Balingen measuring 288 mm. in diameter had about
ten volutions. The increase in the transverse diameter of the whorl is more uni-
form and gradual than in Cor. Bucklandi, var. sinemuriense. On the latter part of
the ninth whorl the pile show the approach of old age in the loss of their tuber-
cles. The genicule also descend farther upon the sides, and are less abruptly
joined to the abdomen, which therefore is more rounded and prominent than in
the adult. The channels have become shallower, and finally lose their lateral
ridges upon the latter half of the tenth whorl. The keel is still of considerable
size, and thus acquires somewhat greater prominence than in the preceding
stages. The breadth of the abdomen measured across the geniculx is 6 mm. less
than the breadth of the dorsum when measured through the umbilical shoulders
on the second quarter of the tenth whorl, and 13 mm. less than on the fourth
quarter of the same volution.

The abdominal lobes were not visible on the last quarter of the ninth whorl,
but the inferior lateral saddles were one sixth deeper than the superior laterals.
On the second quarter of the tenth whorl the abdominal lobe was one half

25

194 GENESIS OF THE ARIETIDA.

longer than the superior laterals, and the inferior lateral saddles were one third
deeper than the superior laterals,

The young are generally identified with the young of dzsu/eatum in France
and Germany. They resemble this species very closely, but have more diver-
gent sides, whorls much stouter, and do not have the smooth period so fully
shown in the young. They equally closely resemble in worn specimens the
untuberculated variety of Verm. Conybeari, and are often, especially in large speci-
mens, mistaken for Conybeart when the tubercles are either slightly developed or
obscured, All of these resemblances, however, are merely transient, and not of
the same value as the precise agreement of the younger and older stages in this
species and in Bucklandi ; it is in fact a more highly specialized bucklandian form,
with better defined channels and smaller and finer pile. ‘The resemblances in
the aspect of the young to Cor. datum are not sufficient to unite the species.

Canavari, in his Unterer Lias v. Spezia,’ describes and figures Cor. (Arvet.)
sinemuriense, Pl. XX. Fig. 1, which may be the young of that species. Cor.
(Ariet.) Monticillense, Fig. 3, 4, and rotiforme, Fig. 12, may be both the young of
the last named, or of some other allied species. Ariet. mudlicostatus does not
resemble, so far as the lateral view given in Fig. 7 allows one to see, any
species that we know.

FIFTH, OR AGASSICERAN BRANCH.

The shells are discoidal only in the radical species and lower members of the
same genetic series; in the more specialized and higher forms of the same se-
ries the involution may exceed that of the shells of any series previously de-
scribed, except Schlotheimia. Thus, in shells in which the genicule are absent,
the whorl may pass inwards beyond the area of the abdomen, and embrace the
sides. The umbilicus, however, so far as observed, has never been entirely
covered in. Degeneration of the form of the whorl, i. e. flattening and conver-
gence of the sides, narrowing of the abdomen, and the advent of fold-like pile,
may take place at an early nealogic stage in some species, and may be character-
istic of entire series. The keel is, however, retained even in extreme old age.
The keel takes on a distinct aspect in one series of this branch, Agassiceras, and
is transitional to the true hollow keel of Oxynoticeras.?

AGASSICERAS,

The characteristics which distinguish this genus are principally due to the
exceedingly immature aspect of the lower forms, the shortness of the living
chambers, and the development in the higher species of tuberculated pile in
association with highly convergent sides and angular keeled abdomens without
channels. The young of the radical species, Agas. levigalum, are remarkable for

1 Paleontogr., XXIX.
2 Quenstedt considers it to be a true hollow keel, See below, in the description of Agas. Scipionianum.

ne

= een

FIFTH, OR AGASSICERAN BRANCH. 195

the prolonged existence of the goniatitic proportions, which are generally con-
fined to nzpionic stages of growth in other Ammonitinw. They are also very
similar in some of the nealogic and adult stages, both in form and characteristics,
if we except the sutures, to Psiloceras The sutures acquire the deep arietian
abdominal lobe quite early in life. The sutures of the higher species, Agass?-
ceras Scipionianum, are very similar to those of Coroniceras. The affinities of
Agas. levigatum and Ast. obtusum, and also those with Psiloceras, have been fully
discussed elsewhere.” In the clinologic stage the abdomen becomes more acute,
and the sides smooth. Neumayr has lately redescribed this genus in part
under the name of Cymbites.’

Agassiceras levigatum, Hyarr.
Plate VIII. Fig. 9-14. Summ. PI. XIII. Fig. 1.

Amm. levigatus, Sow., Min. Conch., pl. 570, fig. 3.

Amm. levigatus, Orr., Die Juraf., p. 81.

Amm. abnorme, Haver, Unsymm. Amm. Ilierl.-Schich., Sitz, Akad. Wien, XIII. pl. i. fig. 11-17.
Cymbites globosus, Geyer, Ceph. Hierl.-Schich., pl. iii. fig. 26.

Localities. — Lyme Regis, Semur,

This species has an exceedingly immature or nepionic form. It seems
frequently to complete its growth in five whorls. The aperture has a simple
pointed rostrum, the lateral edges slightly flaring, with a broad shallow constric-
tion, Pl. VIII. Fig. 12, very similar to the aperture of Oppel’s type of Amm. pla-
norbis The living chamber is about one half a volution in length.

Var. A, Plate VII. Fig. 11. This is smooth during four volutions, and the
pilze, if present, are developed only on the last whorl. The whorls are more
compressed than in other varieties, and the umbilicus not so deep.

Var. B, Plate VIII. Fig. 9, is smooth only during the first three or three
and a half whorls, and then has immature folds like those of var. plicalum of
Psil. planorbe. The younger whorls are wider than in other varieties, and the
umbilicus deeper.

Var. C has the pila much more distinct, but the period at which they appear
is the same as in the preceding variety. The pile are apt to cross the abdomen,
forming slight ridges. This, like all other characteristics, is found more or less
also in other varieties.

Var. D, Plate VIII. Fig. 10-12, is founded on the presence of a faintly
defined siphonal ridge. This includes members of other varieties, regardless of
the time at which the pile are developed, their greater or less prominence, and

1A paper by E. Haug, “ Ueber Polymorphidae,”’ Neu. Jahrb. Mineral., 1887, II. p. 92, gives an in-
teresting account of this genus, in which he substantially agrees with our descriptions, but insists upon the
keelless character of the whorls, If we are correct, this is an adventitious character common enough in
dwarfed forms, or arrested development in some individuals or in the varieties of the same species, but a
variable within the species, and not a generic character.

2 See pages 65, 66.

3 Jahrb. Geol. Reichsans., XX VITI., 1878, p. 64, note.

4 We have studied Oppel’s type of this species, and found that Oppel’s figure gives the lateral curves
of the aperture in an exaggerated form, and the constriction too deep. The real aperture is therefore more
like that of /evigatum than it appears to be in his figure. :

196 GENESIS OF THE ARIETIDZ.

the breadth or thinness of the whorls. Some of these have stouter adult whorls
than usual. If the slight siphonal ridge were absent, there would be a closer
resemblance in form to Psi/. planorbe, var. erugatum. The young have at first
deep umbilici, due to the abrupt umbilical shoulders, Plate VIII. Fig. 10, 13, 14, i
common to the Goniatitinula and early nzepionic stages of the Arietide. This
stage is succeeded by flatter whorls and less abrupt umbilical shoulders, which
last in some cases throughout the first three whorls, but the fourth whorl is apt
to increase fast enough to be somewhat broader than the third. The aspect of
the umbilicus when the fourth whorl is completed is thus altered in such speci-
mens from deep to shallow, just as it changes at much earlier stages in other
species after the earlier goniatitic proportions are outgrown. In some specimens
this change takes place much earlier, The pile are introduced generally after
the second stage of growth, and but very rarely before the reduction in the
comparative breadth of the whorl begins. The sutures are also immature on
the fourth whorl, but the abdominal lobe is considerably deeper than the superior
i laterals, as among true Arietidz, The other lobes are pointed, and the saddles
serrated.

The Museum at Semur and the Museum of Comparative Zodlogy afford
ample material for tracing the connections between this species and Agas. striaries.
Quenstedt, in “ Ammoniten des Schwibischen Jura,” p. 106, has also noted the
affinities of this species and striaries. According to Oppel, it appears in the bed
immediately above the Bucklandi bed, and in the Museum of Stuttgardt is a
specimen in the Geometricus bed from Degerloch. In England, however, it is
usually found associated with Deroceras planicosta in the Obtusus zone, and at
Semur with Schiot, angulata, and above this in the Geometricus bed. The speci-
mens described and figured by Hauer and Geyer from the Hierlatz fauna seem
to be unquestionable, since no other species with which we are acquainted has
the peculiarities of this form.

Agassiceras striaries, Hyarr.

Plate IX. Fig. 14, 15. Summ. Pl. XIII, Fig. 6.

Amm. striaries, Quenst., Der Jura, p. (0; pl. vill, figs b,
Amm. striaries, Quenst., Amm. Schwiib. Jura, p. 105, pl. xiii. fig. 24-26.
Psiloceras planilaterale, Hyarr, Bull. Mus. Comp. Zool., I., No. 5, p. 73.

Locality, — Semur.

Sides of the whorls in adult specimens may be either flattened or decidedly
gibbous, and also either plicated or smooth. Abdomen is very broad, depressed,
convex, smooth or very slightly ridged by lines of growth. The position of the
siphon is often indicated by a ridge. The young are smooth for the first three
whorls, the plications begin to appear on the fourth whorl. These observations t
were made upon five specimens in the Museum of Comparative Zodlogy, which
had been labelled Amm. planorbis by M. Boucault; but they differ from that spe-
cies in the smaller size and greater proportional bulk of the whorls, the breadth
and depressed convex form of the abdomen, and the presence of a siphonal ridge.

FIFTH, OR AGASSICERAN BRANCH. 197

Several specimens of this species in the Stuttgardt Museum, Upper Bucklandi
bed, from Balingen, showed living chambers, as pointed out to me by Professor
Fraas, always much shorter than in planorbe, and the sutures distinct. The
peculiar folds appearing on some shells, and the form and aspect of the whorls,
like those of the nealogic stages of Scipionianus, show that their affinities are in
the direction of this species. The examination of the originals of Quenstedt’s
descriptions from Pforen fully sustained the above, and a fine suite of the same
species at Semur, in the corresponding horizon, exhibited several forms transi-
tional to the young of Seinonianus.

Professor Misch, in the Museum of the Polythenic at Ziirich, showed me
several specimens of striaries, in which the keel was so faint as to be hardly per-
ceptible, and the striations no better marked than in Psiloveras. These were
named psilonotus, and were found at Salins associated with typical striaries. The
apertures are also similar to those of Psi. planorbe.

Agassiceras Scipionianum, Hyarr.
Plate VII. Fig. 11-15. Plate X. Fig. 11-13. Summ. Pl. XIII. Fig. 7%.

Amm. Scipionianus, D’Ors., Terr. Jurass. Ceph., p. 207, pl. li. fig. 7, 8.
Amm. Scipionianus, Quenst., Amm. Schwiib. Jura, pl. xiv. fig. 1-3 (not pl. xvil.).
Ariet. Scipionianus, Wricut, Lias Amm., p. 289, pl. xiii. fig. 1-3; pl. xix. fig. 8-10.

Localities. — Whitby, Semur, Arton in Luxemburg, Gmiind.

This species varies exceedingly. Some of the young show a crenulated keel,
and they may also be either smooth or pilated on the sides. The abdomens are
keeled, and occasionally, though very slightly, channelled. The form of the
whorl in the young may be either very gibbous, Plate VU. Fig. 11, 12, or com-
paratively compressed. The pil also vary from comparatively thin and depressed
to prominent and well defined, with or without tubercles; they may also be very
numerous or few in number, and be very distinct, or thick, awkward-looking
folds. It has been commonly supposed that the true affinities of this fossil were
with the margaritatus group, but its development is altogether peculiar, and its
sutures are distinctly arietian. There are two varieties of this species with dis-
tinct nealogic stages but similar adults; one, as described above, very gibbous
and heavily pilated,’ and another more compressed at all stages, and approxi-
mating to Agas. nodosaries.” The latter may be identical with Agas. nodosaries,
or it may be distinct; the materials at hand are not sufficient to determine this
question.

In old age the tubercles are suppressed, the sides become flatter and more
convergent, the genicula bend less abruptly and curve slightly forward, the
channels disappear, but the keel remains very prominent and sharp. The clino-
logic stage just before the pile become obsolete is very similar.to the adult of
Ast. Collenoti, but the shell is not so involute.

The young of this species has the gibbous volutions so characteristic of devi-
gatum and striaries. The sides are at first divergent, but they become nearly

i-Plate vii fig. 11,125 ple x. fig, 21, tz. 2 Plate x. fig. 13; pl. vii. fig. 15

198 GENESIS OF THE ARIETID.

parallel on the latter part of the second whorl; the dorsum also broadens, and
the umbilical shoulders become more abrupt. On the third volution the sides are
parallel, the dorsum and abdomen of the same breadth, and the latter elevated
into an obtuse ridge. ‘This ridge on the fourth whorl becomes a true keel, un-
accompanied by channels, though there are traces of their formation. The in-
crease of the abdomino-dorsal diameter of the whorl after this period speedily
elevates the abdomen, and proportionally decreases the transverse diameter of
the shell on the latter part of the fourth volution, destroying even the faint
traces of the channels mentioned above. On the fifth volution the sides become
slightly convergent, and this convergence increases very slowly on the sixth
volution.

Thick and widely separated folds appear on the early part of the third whorl,
but rapidly grow into true pile. The genicule may become tuberculated on the
fifth volution, or they may remain permanently without tubercles; there is, how-
ever, great variation with regard to their prominence and number.

The duration of the different stages of growth also varies; in some specimens
the abdomen remains flattened through the keel-forming stage until the first
quarter of the fifth volution is reached. In one specimen the pile are reversed
in position, bending posteriorly, but subsequently begin slowly to change to a
natural position on the fifth volution. A number of the specimens from Semur
have the pile but very slightly or not at all developed. None of them seem to
reach beyond four and a half volutions, and their small size may possibly be due
to the same cause as the absence of the pile.

On the early part of the fourth volution the abdominal lobe is considerably
longer than the superior lateral lobes, which in turn are shorter than the infe-
rior laterals. The inferior lateral saddles are slightly deeper than the superior
laterals. On the latter part of the same volution the abdominal lobe has in-
creased in length, and the superior lateral saddles are shallower; the inferior
lateral saddles become deeper proportionally, and the lateral lobes are nearly
equal in length, the inferior laterals still remaining, however, slightly the long-
est. The marginal lobes are very minute, and remain so, the sutures having a
comparatively even outline for that reason. In some specimens the lengthen-
ing of the abdominal lobe continues until the superior lateral saddles are almost
obliterated ; in others, the lobes and saddles may remain with about the same
proportions as in the stage of development last described.

There are two specimens in the Stuttgardt Museum, from the Geometricus
bed, but they do not show the young, or give any better clue to the true devel-
opment. There are also three in the Stuttgardt Museum, from the Pentacrinus
bed near Krumenacher, which appear to be the young of this species, or of
Scipionis. One of them, with the shell present, shows all the peculiar marks of
Agus. striaries, while another, a cast, is so broad on the abdomen, and the fold-
like pile are so prominent, that it looks remotely like the young of Cor. Sauze-
anum. The three are identified as young of Cor. Sauzeanum, but the young of
this last is very distinct in the sutures and other characteristics. A specimen in
the collection at Semur, from the same horizon, under the name of Amm. lavi-

eg spot nm eetenneneeneanttineren

FIFTH, OR AGASSICERAN BRANCH. 199

gatus, maintains the aspect of sériaries until a late period of growth, and then
develops the keel and form of Seipionianus ; and there is also another fossil, which
is exactly similar to the later, but still immature, stages of Scipiomanus.

The keel may, perhaps, have a hollow above the siphon, such as Quenstedt
describes in his “ Ammoniten des Schwibischen Jura,” Plate XIV. Fig. 1, but
the inner or nacreous layer does not form a partition between the interior of the
shell and the interior of the keel, nor does the black layer occur above this par-
tition, as in Oxyn. oxynotum and others, which have true hollow keels. In the
specimens examined, the keel was elevated, as in Quenstedt’s figure, but the
siphon laid directly against the shell layers, which filled the interior of the keel,
and there was no black layer.

Agassiceras nodosaries, Hyarr.

Amm. nodosaries, QuEenst., Der Jura, p. 78, pl. viii. fig. 8; Amm. Schwib. Jura, I. pl. xvii. fig. 1-3.

Locality. — Bempflingen.

The specimen of this species in the Museum of Comparative Zodlogy is less
compressed than those figured by Quenstedt, but it shows that nodosaries is prob-
ably quite distinct from Seipronianus. The whorls are more compressed than in
the latter, but the tubercles and pile are retained until a much later age. These
same distinctions are, of course, still more marked when the species is compared
with Seipionis. The exact horizon was not marked on our specimen. The
cast measured 160 mm., and the outer whorl 60 mm., the same whorl at the
beginning being somewhat less than 30 mm.; the greatest transverse diameter
of the same was about 30 mm., and the least about 20 mm. Our specimen is,
therefore, a trifle larger than the inner whorl of the fragment figured by Quen-
stedt. in “ Ammoniten des Schwiibischen Jura,” Plate XVII. Fig. 1, at the point
marked “k.” It is also of about the same diameter as his abdominal view of
the same whorl marked “q.’ The keel is also in the same condition, being
coated with matrix, the genicule are bent and run nearly to the keel, there are
no channels, and on the younger part of this whorl the keel is well preserved and
prominent. Quenstedt’s specimens were found in the Tuberculatus bed. It is
not unlikely that the compressed variety of Agas. Scipionianum described above
ought to be transferred to this species, but we have not been able to gather
sufficient evidence to settle this question.

Agassiceras Scipionis, Hyarr.
Plate IX. Fig. 12,13. Summ. Pl. XIII. Fig. 8.

Amm. Scipionis, Rrynis, Plates. e
Amm. Scipionianus olifex, Quenst., Amm. Schwib. Jura, pl. xvii. fig. 7-10 (not pl. xv.).

Locality. — Semur.

The shell of this species is smooth at an early age, and quite similar to the
old stages of Scipionianus in form and characteristics, but it is more involute.
Quenstedt’s figures and descriptions of his Seipionianus ohfex appear to apply to

200 GENESIS OF THE ARIETIDA.

this species. His specimen as figured is, however, younger, and consequently
less involute, the pile are without tubercles, and the general aspect similar. His
shell was, according to his figure, notably more involute than Sepiomanus, and
this agrees also with a specimen in the Museum of Comparative Zodlogy. This
last is larger than that figured by Quenstedt, and, though comparatively senile
and quite smooth on the outer whorl, is more involute than any specimen of
Scipionanus and has a more compressed and more acute whorl. My notes taken
at the Museum at Semur say, “ the Scipionis of Reynés is only a less involute form
of Scipionianus,” but it is probable that the specimen observed at Semur may have
been exceptional, and either extremely old or a pathological example.

Geyer, in his Liass. Ceph. Hierlatz b. Hallstadt, mentions Cymbies globosus,

Plate ILL. Fic. 26, a young form of Agas. levigatum, as cited above, and also an’
8 ,ay g uh AY ’ ;

briet. indet., Plate IIT. Fig. 18, which, if not a specimen of Agas, Scipionanum, is a
very close ally. These are small shells, as is usual in that locality.

The Afgoc. Cocchi, Canav., Unter. Lias v. Spezia, Plate XIX. Fig. 11, may be
a young specimen of NSeipionianum, but we cannot venture to refer it to this
=o) ih ?
genus.

ASTEROCERAS.

The form of the whorl is noticeably less discoidal than in the preceding series,
except in Ast. obtusum. The abdomen in adults is usually narrower, the sides are
flatter and more convergent, as well as broader, than is usual in Coroniceras. The
involution is not limited to the abdomen, and the whorls tend to grow inwards,
covering more or less of the sides. The pile are fold-like, bending forward on
to the abdomen, and in most species smooth and without genicule. The young
have very stout gibbous whorls with divergent sides, which become more and
more convergent in the nealogic stages, and remain so throughout life. The keel
is constant in all the young and adult specimens, but the channels are often very
shallow, and sometimes absent.

The sutures have a deep abdominal lobe, but the lateral lobes are apt to be
short and pointed, and the saddles broad. They are similar to those of Coroni-
ceras, but the marginal lobes are rarely so long as in that genus. In old age the
abdominal lobe and the lateral lobes and saddles are of about the same length,
but become broader proportionally, the inferior lateral saddles become shallower,
and this occurs also in many dwarf forms, which of course are prematurely
degraded. These senile changes are more marked than in Coroniceras, though
the old age is not otherwise noticeably different. The genus with relation to
other genera of the Arietide is notably geratologous, or in other words the shells
exhibit characteristics similar to those of the senile stages of Coroniceras, and these
characteristics may be reproduced in the adult, and even in the nealogic stages.
Each species and individual, however, also has a senile stage in which decline is
manifested unmistakably, and during this stage the whorl becomes still more

tna Seca

FIFTH, OR AGASSICERAN BRANCH. 201

convergent, more involute, and smoother, and the sutures more degenerate, but
the keel, so far as observed, though it may become much depressed, never wholly
disappears. Probably this does occur in extremely aged specimens, in what we
have called the nostologic stage, but such extreme examples have not yet been
seen by the author.

First SuBSERIES.

Asteroceras obtusum, Hyarr.
Plate VIII. Fig. 4-8. Plate IX. Fig. 1. Summ. Pl. XIII. Fig. 2.

Amm. obtusus, Sow., Min. Conch., II. p. 151, pl. elxvii.

Amm. obtusus, D’Orp., Terr. Jurass. Ceph., p. 191, pl. xliv.

Amm. obtusus, Quenst., Amm, Schwiib. Jura, p. 141, pl. xix. fig. 2, 3.

Ast. obtusus, Hyatt, Bull. Mus. Comp. Zodl., I., No. 4, p. 79.

Ariet. obtusus, Wricut, Lias Amm., p. 293, pl. xxi. fig. 1-5.

Amm. Smithi, Sow., Min. Conch., IV. p. 148, pl. eccevi.

Amm. Smithi, Quenst., Amm. Schwib. Jura, p. 140, pl. xix. fig. 1.

Amm. Turneri, Z1eT., Verst. Wiirt., p. 15, pl. ii. fig. 5.

Amm. Turneri, Quenst., Amm. Schwib. Jura, p. 143, pl. xix. fig. 10-13.

Amm. stellaris, HavER, Ceph. Lias Nordéstl. Alpen, pl. v. fig. 1-3.

Aigoc. sagittarium, Tare et Buaxn, Yorkshire Lias, pl. vii. fig. 2.

Aigoc. sagittarium, Wrient, Lias Amm., p. 355, pl. lii. fig. 1-5 ; pl. Isii. a, fig. 1-6.

4igoc. Slatteri, Wriaut, Lias Amm,, p. 374, pl. 1. fig. 1-5 (not fig. 6-8).

Amm. capricostatus, QuENST., Amm. Schwiib. Jura, pl. xix. fig. 14, 15.

Localities. —Lyme Regis, Whitby, Robin Hood’s Bay, Boll, Balingen, Bempflingen, Salins, Besancon,

Adnet.

Var. sagittarium.

A specimen from Bempflingen has pile, which cross the abdomen. Speci-
mens in Quenstedt’s collection from the same locality show this peculiar deforma-
tion, to which he calls attention,’ and compares them with sagitlarium, but does
not seem sure of the identification, since in another place (p. 252) he appears to
admit Wright’s association of sagittarium with Jumesoni. Blake states that his
types came from the lower part of the Oxynotus bed, that is, from the Obtusus
bed of other authors. This fact, and the obvious agreement of the sutures and
piles with capricostatus, Quenst., and the Turneri deformation common in South
Germany, and their differences when compared narrowly with Jameson, leave
but little doubt that Wright was in error in thinking this form occurred in the
Jameson’ bed, or was identical with Jamesoni. The specimens figured represent
quite completely what is perhaps the most remarkable degradational series of
the Lias. The resemblance of one of Wright’s figures, Plate LIT. Fig. 1, 2, to
the forms of Wehneroceras, especially Wehn. latimontanum,? is a remarkably
good example of morphological equivalence.’ Others among these deformed
specimens, both in England and Germany, resemble AMicroceras planicosta in the

1 Amm. Schwab. Jura, p. 145,

2 Unter. Lias, Mojsis. et Neum., Beitr., II. pl. xx.

8 A very remarkable example of morphological equivalence caused by a wound is figured by Neumayr
in his ‘‘ Stiimme des Thierreichs,’’/1889, p. 82. The shell of a keeled and channelled species has been
broken on the abdomen, and beyond the wound the characteristics have changed so as to resemble those of

Schlotheimia.

26

202 GENESIS OF THE ARIETID.

) depressed form of the whorl, and the coarse pile: which cross the abdomen have
a similar broad, flattened aspect. The siphonal saddle, according to Wright's
figures, Plate LXII. A, seems to have suffered considerable alteration from what
it is in the typical form of obtusum. The lobes and saddles of the Bempflingen
specimens have the regular differences of one half to one third in the lobes, and
the abdomen is unusually broad.

There is a specimen of variety D, from Lyme Regis, in which for a short
space the keel has been pressed inward and the sides ruptured. While on the
recovery from this injury the abdomen retained a flattened aspect, it is about as
broad as that of some forms of sagitéarium, and otherwise similar. Narrow folds
and furrows are noticeable crossing the abdomen, which correspond to similar
small folds and furrows on the sides. The effect of the rupture is otherwise
noticeable in the temporary absence of the pile and the greater intervals be-
tween the next two pairs of sutures. This example shows that there may be
a tendency to vary in the direction of Microceras, which is produced in some
specimens by disease, and in others by wounds. Such characteristics were not
observed in the later stages of diseased specimens. They probably disappeared
in course of growth, just as the similar characteristics of the young of Cor.
Sauzeanum were suppressed in the adult stages.

The forms of this species may be divided into several varieties, according to
the adult characteristics, and the slower or quicker development of the keel,
| channels, and form.

Var. B.

This has flattened sides, pile not very prominent, but running nearly to the

base of the keel, and the channels are very narrow as well as shallow.

Var. C.

This is the normal Zurneri of Zieten, and has the pile reaching nearly to the
base of the keel in the nealogic stages, and perhaps in the adult. In all other
characteristics, even in the prominence of the pile, it agrees with variety D.

Var. D.
Plate IX. Fig. 1.
This is the typical form, and has well rounded, gibbous sides, prominent pile,

broad abdomen, broad shallow channels, and a depressed keel.

Van. EB.

Plate VIII. Fig. 4-8.

| This is similar, but has deeper channels and a keel more prominent, narrower
i and more convergent sides in the adult, showing some resemblance to Asé. ;
i Turneri, Hauer’s specimen of Amm. stellaris figured in “ Nordéstlichen Alpen”
belongs to this variety, and is not identical with the true stedlare.

The pile may be gradually introduced by a series of plain folds, or by tuber-
cular folds, Plate VIII. Fig. 4, 5. The whorl is smooth in specimens having the

FIFTH, OR AGASSICERAN BRANCH. 203

first mode of development for two and a quarter volutions. The increase is
gradual, so that well defined pile are not produced until the last of the third or
first quarter of the fourth whorl. An English specimen of variety A has large
tubercles on the second quarter of the third whorl. These continue at long
intervals, only about two to a quarter of a whorl. The true pile do not begin
to appear until the third quarter of the fourth volution. “Even then these are
exceedingly oblique and fold-like, and, though they soon assume the aspect of
true pile, retain their obliquity until the second quarter of the fifth volution.
Another English specimen shows acceleration by developing similar tubercles
on the last quarter of the second volution, and also by the development of per-
fect straight pils on the second quarter of the fourth volution. A third speci-
men of variety E, from Lyme Regis, has tubercles beginning on the last quarter
of the second whorl, and perfect pile on the last part of the first quarter of the

fourth volution.
Var. Smithi.

The British Museum possesses a card with several young specimens of the
variety Simiti, which at first appear to be identical with the full grown devgatum
or striartes. They have short living chambers, becoming more or less contracted
at, the apertures, and fold-like pilz with striations. They have not, however, the
peculiar form of the young of /evgatum, Plate VILL Fig. 10, 13, nor similar
sutural digitations, and the living chamber is about three fourths of a volution in
length. It’ is interesting to note here the fact, that acceleration in the develop-
ment of the tubercles and pile occurs in variety E, which has more involute
shells than other varieties.

Ast. obtusum has characteristic sutures, and the number of specimens usually
exhibiting these parts were also favorable for testing the diagnostic value of the
proportions of the lobes and saddles in the definition of the species. We have
made large numbers of measurements, of which the following are selections.
The fractions express the differences between the abdominal and superior lateral
lobes, or the inferior and superior lateral saddles. The abdominal lobe and infe-
rior lateral saddles being always longer, the fraction expresses at the same time
the proportionate lengths in equal divisions of these two.

A specimen of variety B, from Robin Hood’s Bay, has three sutures on the
third and two on the fourth quarter of the fifth volution, with a difference of
only two fifths between lobes and saddles, and one septum on the third quar-
ter, in which the lobes are equal, the saddles remaining unchanged. One from
Teuchsloch bei Bempflingen has lobes varying from one fifth to one third, and
saddles from one sixth to two thirds. A specimen of variety C, from Boll, has
these proportions in none of its sutures, but either two fifths or one half between
the lobes, and one fifth or one third between the saddles. Comparisons were
made upon sutures of the same age in each case. Another specimen of this
variety from Boll, having similar gibbous sides, has similar proportions between
the lobes and saddles, with exception of the eighth suture, in which the difference

204 GENESIS OF THE ARIETIDA.

of the lobes is only two fifths, and that between the cells only one fourth. This
shows that the proportions in stouter specimens from Boll are not due to the
greater prominence of the pile and gibbosity of the sides, nor is there any marked
deviation from the usual rounded outline of either lobes or saddles. A specimen
of variety D, from Lyme Regis, has sutures with lobes differing one half with
great uniformity, but saddles differing one half to one third or one fourth, irre-
spective of this constancy between the lobes. A specimen from Lyme Regis
shows that there is no correlation between these proportions and the variations
in outline of the inferior lateral saddles. Thus, in the Lyme Regis specimens,
No. 1 has the inferior lateral saddles flattened and rounded; No. 2, pyramidal,
with two marginal saddles forming a club-shaped expansion at the top; No. 4,
straight sides and slightly concave base ; No. 5, like No. 1 again; and No. 7, like
No. 4.

The sutures of the first specimen described from Bempflingen as having the
microceran pile, have the usual proportions of others. A specimen from Lyme
Regis has lobes differing from one half to three fifths, the saddles, however,
with remarkable constancy, remaining about one half, as far as measured. The
wounded specimen described above had lobes and saddles, varying from one.
half to the excessive difference of five sevenths, and the extremes of difference
were not the nearest to the fractured portion of the shell, but some sutures
removed from the fracture. A small specimen from Whitby, on the third quar-
ter of the fourth volution, showed lobes differing from one half to three fifths,
and saddles from nearly equal to one third, A somewhat larger specimen from
Lyme Regis had lobes differing three fourths, and the saddles three fourths and
two thirds on the first quarter of the sixth volution. On the right side of a speci-
men from Lyme Regis a rare distortion occurs. The first auxiliary lobes are
obsolete, or at any rate only represented by a marginal lobe, and the first and
second auxiliary saddles form a solid bank.

By combining all of these observations, it becomes possible to trace a series of
modifications. There is evidently (1) a very immature form or variety, in which
a microceran aspect is assumed through pathological causes; (2) a variety in
which a low keel, very shallow narrow channels, flat sides, and depressed pile are
developed much more quickly than in this malformed variety ; (3) a variety in
which the development of pile, channels, and keel is still more accelerated, and
combined with more gibbous sides and more prominent pile in adults; (4) a
variety in which development of the pile is accelerated, accompanied by the
advent of broader and deeper channels, and a more prominent keel in the later
_ stages. The specimens from Salins and Besangon are dwarfs, having resem-
blances to Zurneri, Ziet.

FIFTH, OR AGASSICERAN BRANCH. 205

7

Siren

WU

CONT)

Fie. 34. Fie. 35.

Var. quadragonatum, Hyarr.
Localities. — Lyme Regis, Semur.

A form in the Museum of Comparative Zodlogy, represented in Figures 34,
35, closely resembles the stout variety of obfuswm, but exaggerates the char-
acters of that form and of variety B. Though young, it has a more subquad-
ragonal whorl than is usual in the adults of od/usum, var. B, a flatter abdomen
and broader channels, and quite distinct pile, with a tendency to the formation
of tuberculated genicule, though actual tubercles are not present. The diameter
is 53 mm. ‘The outer whorl is 20 mm. on the sides, and the transverse diameter
the same. The sides are about parallel, the abdomen flat, distinct, sub-angular,
and genicule are present.. The abdominal part of the pile do not bend forward,
but pass on to the abdomen and interrupt the channel ridges. The ridges are
well marked, though not so prominent as in Twrneri.

It is evidently a modified form of odtusum, in which the pile by a very slight
increase in the geniculs would become tuberculated. Dumortier, in his “ Etudes
Pal. Bassin du Rhone,” describes a specimen of obdfusum having eight or nine
irregular nodes upon the young whorls until 20 mm. in diameter, and gives these
as characteristic of the young of his specimens. They probably belonged to this
variety, in which the young are more strongly marked in this way than is usual
in other varieties of obfusum."

There is a large specimen in the Museum of Comparative Zodlogy, from Lyme
Regis, 500 mm. in diameter. Though considerably altered by pressure, the last
whorl has the aspect of var. guadragonatum, and the normal form is comparatively
slightly altered on the third qnarter of this volution. It is here only 115 mm. in
abdomino-dorsal diameter, which is considerably less than would occur in any

equally large specimen of other varieties. There are pseudo tubercles on the

outer whorl, but these may in large part be due to distortion of the pile by

VI. pl. xxv., to Asteroceras
ue to clinologic degeneration in some species, which may, however,
The umbilical whorls are heavily though sparsely tuberculated, and
See also page 100, note 3, above.

1 The similarity of Arietites stelleformis, as figured by Wahner, Unter. Lias,
may be simply a case of parallelism, d
belong to an entirely different genus.
the outer whorls are, in our opinion, those of an old shell.

206 GENESIS OF THE ARIETID.

pressure. The keel is low and broad, as in odtuswm, though prominent enough
to show above the lateral ridges when seen from the side. D’Orbigny’s figure of
obtusum is correct, and gives this variety as it occurs at Semur, the abdomen
| sometimes being wider than the dorsum, instead of being narrower than or
i about equal to the dorsum, as in all other varieties.

| There is a normal specimen of this species in the Museum at Stuttgardt, col-
lected in the Upper Bucklandi bed ‘at Géppingen. The majority of specimens,
however, belong to the Obtusus bed just above this.

Confusion, as remarked above, is not infrequently occasioned by the resem-
blances of the senile stages in Cor. Bucklandi to the adults of obtusum and Brooki.
Sometimes even old specimens of Cor. trigonatum and G'muendense are mistaken
by paleontolongists of experience and reputation for ob/usum, especially if the
inner whorls are concealed. The larger and older specimens of od/uswm are apt
to acquire the more abrupt umbilical shoulders which are characteristic of the
| young and adult of Ast. stedlure.

Asteroceras stellare, Uyarr.
Plate IX. Fig. 2, 3. Plate X. Fig. 1, 2-

Amami. stellaris, Sow., Min. Conch., I. p. 211, pl. xciii.

Anm. stellaris, Z1utT., Verst. Wiirt., p. 15, pl. ii. fig. 5

Amm. Brooki, Quenst., Amm. Schwab. Jura, p. 116, pl. xv. fig. 2, 3 (not pl. xx., xxi).
Ariet. Brooki, Wricut, Lias Amm., p. 295, pl. xxii. fig. 1-6.

Amm. obtusus suevicus, QuENST., Amm, Schwab. Jura, pl. xx. fig. 1.

Localities. —Semur, Lyme Regis, Gmiind, Tiibingen.

The nealogic stages are similar to the older ephebolic stages of var. E of Ast.
obtusum. In point of fact, the two forms run into each other by intermediate
varieties, and can be separated only by artificial lines. The young in one
i specimen from Whitby exhibited on the first quarter of the fifth volution
channels as deep, keel as prominent, and an abdomen considerably narrower
than those of the most highly modified forms of Ast#. obtusum, var. E, on the last
quarter of the sixth whorl, over a whorl and a half later. In a specimen from
Lyme Regis the development is parallel with that of od¢usum, var. 1K, until the
first quarter of the sixth whorl, then the sides became flattened, the pile de-
pressed, and the abdomen narrowed to the area of the channel ee

Sowerby’s types, figured by Wright, are young specimens, and exhibit very
completely the fact that the young may develop the characteristics of the species
at a comparatively early stage, and are more highly modified as a rule than the
adults of obfusum in any variety.

The sutures on the sixth volution of a specimen from Gmiind had lobes differ-
ing two thirds and saddles one half; and on last quarter of same, the lobes differed
three fourths and saddles two thirds. In an older specimen from Semur, on the
second quarter of the seventh whorl degeneration had already begun, the lobes
differing only one fifth to one sixth, and saddles about two fifths. This and the
fold-like character of the pile and trigonal form showed that old age had fully
begun on this whorl. There are two specimens of sfe//are in the Museum of Com-

FIFTH, OR AGASSICERAN BRANCH. 207

parative Zodlogy, which are so similar to Ast. Turneri that they differ in only one
characteristic, namely, the shallowness of the umbilicus, due to the gradual
curvature of the sides. In Ast. Turner the breadth of the dorsum, and the con-
sequent abruptness of the umbilical shoulders, is a marked peculiarity, even at
an early nealogic stage. These specimens were in the nealogic stage; if older,
they would probably also have shown a less amount of involution than in Ast.
Turnert. This last species becomes generally, though not invariably, larger in
five volutions than the former in the course of five and a half. Specimens of
stellare also approximate very closely to As¢. aeceleratum ; they differ, however, in
the less involution of the whorls, and in other correlative characteristics.

Depressed tubercles similar to those of the young of ob/usum appeared, in the
only specimen in which they could be detected, on the last quarter of the second
whorl, and true pile on the third quarter of the third whorl, earlier by one
volution than in var. E of oddusum. Thus even in this unimportant character
acceleration appears to have taken place as it had in other characters.

There is one specimen of this species in the Museum of Stuttgardt, from the
Geometricus bed of Géppingen, though it is more common in the Obtusus bed.
The largest specimen in this Museum reached a diameter of 450 mm. (PI. X.
Fig. 1, 2). The last whorl was perfectly smooth, the abdomen had become sub-
acute, and the channels obsolescent, resembling those of the adults of Ast.
Collenott.

Asteroceras acceleratum, Hyarr.
Plate IX. Fig. 4. Plate X. Fig. 3.
Locality. — Semur.

The involution covers two fifths of the sides on the sixth whorl, and one half
of the second quarter of the eighth, whereas in Ast. stedlare the extreme limit of
involution is one third. The whorl is similar to that of this species, but is much
broader abdomino-dorsally. The umbilical shoulders are large and abrupt, the
dorsum much broader than the abdomen, the latter being but little wider than
the area of the channels. The latter are very broad and shallow, with smooth
but depressed lateral ridges. The keel is well marked, but depressed as in
obtusum. The abdomen is therefore quite different from that of either Brooki
or Turners.

The young are similar to s/ed/are until a late nealogic stage, and differ only in
the greater involution of the whorls in later stages, and in the earlier develop-
ment of the senile folds and trigonal form. The umbilicus could be observed in
only one specimen. In this the pile: began with coarse folds on the last quarter
of the second whorl, which developed into true pile on the first quarter of the
fifth whorl.

The largest specimen from Semur measured 202 mm., and had completed the
seventh, and part of the eighth volution. The breadth of the first quarter of
the eighth whorl measured on the sides was 77 mm. There is a specimen in
the Museum of Stuttgardt, labelled Amm. stellaris, found at. Gbppingen in the

208 GENESIS OF THE ARIETID.

Geometricus bed, and one, broken across, from the Obtusus bed at Balingen.
The last (Pl. X. Fig. 3) shows the young with shallower channels and flattened
sides, somewhat similar to Ast. obfusum at an older period! The sides of the
young, however, are flatter and broader than I have yet seen in any variety of
stellare, and more like those of an aged Cor. trigonatum. The characteristics of
the nealogic stages and of the adult are evidently geratologous. This spe-
cimen is 258 mm. in diameter, The whorl of the adult is smooth, and of same
shape as the senile stage of Ast. obtusum, and the sutures also agree exactly with
those of the old of that species. Comparing it with a specimen of Zurneri from
Endigen of about the same size, it is seen that the latter has a much broader
abdomen, deeper channels, more trenchant keel, and keeps its pile and form
intact until a much later age, than Ast. acceleratum, and it does not increase in
size so fast, is not so involute, and grows much larger. There are also several
very fine specimens from Endigen, which enable us to connect acceleratum with
stellare without the aid of the similar varieties from Semur or Gmiind, and they
are regarded as so connected by Professor Fraas, who has labelled them Amm.
obtusus. There is a series of five perfect specimens belonging to the Stuttgardt
Museum, sufficient to convince the most sceptical. Nevertheless, it differs in the
form of the young and in the adult from either s/ellare or obtusum, being both
more involute and more accelerated in its mode of development. It is, as a rule,
identified with Brook, and it bears the same relation to obluswm that Ast. ampendens
bears to Turner.

SECOND SUBSERIES.

Asteroceras Turneri, Hyarr.
Plate IX. Fig. 8,9. Summ. Pl. XIII. Fig. 3.

Amm. Turneri, Sow., Min. Conch., V. p. 75, pl. cecclii.

Aster. stellare, Hyarr, Bull. Mus. Comp. Zodl., I., No. V. p. 80.

Amm. compressaries, Qumnst., Amm. Schwiib. Jura, p. 126, pl. xvii. fig. 4-6.
Amm. cf. obtusus, QuENSsT., Ibid., p. 148, pl. xix. fig. 9. :
Amm. undaries, Qumnst., Ibid., p. 148, pl. xx. fig. 2-6.

Amm. Turneri, Quenst., Ibid., p. 142, pl. xix. fig. 5 (not fig, O-o).
Arietites Turneri, Wricur, Lias Amm., p. 292, pl. xii. fig. 1-6,

Localities. — Lyme Regis, Gloucester, Semur.

The amount of involution on the third quarter of the sixth whorl is two fifths
of the side. The abdomen is broader, the channels more deeply sunken and
broader, and the keel thinner and less immature in its aspect, than in Ast. stellare
or Ast. acceleratum. The sides also are flatter, and the dorsum is but very slightly
broader than the abdomen. The umbilical shoulders are abrupt, but the umbili-
cus is hardly so deep as in acceleratwm, the lateral increase of the shoulders by
growth being considerably less than in that species, though greater than in typical
varieties of oblusum. The pilse are thinner, more numerous, and do not have the

? This figure is erroneous in one important particular. The youngest part of the abdomen visible

in the figure, as seen from the front, is much flattened, whereas in the specimen it was but slightly more
depressed than in the older part of the same whorl, represented as trigonal immediately below.

FIFTH, OR AGASSICERAN BRANCH. 209

fold-like character common in those species. They are more acute and about
equally prominent near the dorsum, and also on the edge of the abdomen, and
often interrupt the channel ridges. The earliest period examined was the third
quarter of the fifth whorl. One specimen, from Lyme Regis, had a much nar-
rower channel area than in obfusum of the same age, and the pile reached nearly
to the base of the keel; in another, from Gloucester, the channels were better
developed, but extremely narrow. This species even on the fifth volution had a
better developed keel, deeper and more distinctly marked channels, and flatter
sides, than any variety of As/. obtusum, stellare, or acceleratum.

One specimen from Semur on the second quarter of the sixth whorl had

lobes differing from two fifths to three fifths, and saddles from two fifths to.

one half.

Senile characteristics begin to appear on the latter part of the seventh whorl.
The pile diminish to large folds on the second quarter of the eighth whorl, and
subsequently disappear altogether. The channels also increase in breadth and
diminish in depth. The keel acquires greater prominence in the clinologic
stage on account of the shallowness of the channels, but finally becomes
depressed. The largest specimen measured had about eight whorls, and the
diameter was 327 mm.

A fine series of this species is in the Museum of Stuttgardt. These shells
became smooth at variable ages. One from Balingen, about 113 mm. in diam-
eter, had become entirely smooth; another from Endigen nearly half a whorl
older had still very prominent pile. The peculiar form of the whorl, the deep
channels and flat sides, hold constantly, however, in these, as well as in a young
specimen from Balingen, labelled Amu. obtusus, which also belongs to this species,
This last is beautifully preserved, and may be compared with obéuswm of the same
age and perfection.

The forms identified by Oppel in the Museum at Munich as Amn. Turnert
precisely accord with the above.

The adult specimens of one variety of Turneri and a large variety of Arn.
ceras, found together in the Planicosta bed at Lyme Regis, are quite similar, and
have led to confusion in names, though the young are distinct, and the pile of
Arnioceras are not bent or curved as in Ast. Turneri. The same error has been
also repeated by Quenstedt in his identification of Amm. cf. obtusus,' a variety
of ceras from Ofterdingen, with the English. form of this species as figured by
Wright, i. e. with the young as shown in Wright’s plate.

Another source of confusion lies in the resemblances of fragments of the
more discoidal variety of this species, when of considerable size, to Ver, Cony-
bear’. One fragment of an outer whorl from Lyme Regis in the Museum of
Comparative Zoilogy is very similar to a Conybeari of the same size. It has pile
not quite so straight, the genicule form an even curve with the pile, and the
abdomino-dorsal diameter is greater in proportion than is common in that species.
The abdomen is precisely similar in its keel and channels.

1 Amm, Schwib. Jura, pl. xix. fig. 6-8 (not fig. 5).

27

210 GENESIS OF THE ARIETID.

Asteroceras Brooki, Hyarr.
Plate IX. Fig. 5-7. Summ. Pl. XIII, Fig. 4.

Amm. Brooki, Sow., Min. Conch., II. p. 203, pl. exc.
Amm. Brooki, Quenst., Amm. Schwib. Jura, pl. xx. fig. 11, 12; pl. xxi. fig. 1 (not pl. xv.).
Ariet. Brooki, Wricut, Lias Amm., p. 280, pl. vi. fig. 4, 5.

Localities. — Lyme Regis, Bempflingen ?

The pilz are very close together and well defined on the first quarter of the
third volution. On the last quarter of the sixth volution, peculiar genicule are
formed by the abrupt bending of the straight pila, which contrast forcibly with
the more gradual curves of these parts in Ast. Turneri. On the first quarter of
the sixth whorl these are even better marked, owing to the depression of the
abdominal parts and greater distance of the genicule from the channel ridges.
There are, however, specimens in both species which do not differ in their pile
at any stage, and are precisely intermediate in all characteristics (Plate IX.
Fig. 5-7). The channels are perfectly well defined, and the lateral ridges are
entire. The channels broaden out rapidly on the latter part of the fifth whorl,
but do not increase perceptibly in depth, and have probably already reached
their full adult development.

The differences between the young of this species and the young of Ast. Tur-
neri are considerable. The young of the latter throughout the fifth volution had
a whorl with a dorso-abdominal diameter but very little longer than the trans-
verse, while at a still later stage and in the adult the dorso-abdominal diameter
is two sevenths longer than the transverse. This last is about the proportion of
the same diameter upon the first quarter of the fifth whorl in the young of As¢.
Brooki. The sides begin to be convergent at a much earlier age in Brook, and
the resemblance to the old of Turneri becomes very close. The amount of invo-
lution is also one half on the latter part of the fifth whorl and the early part of
the sixth volution, while in 7Zurneri of the same age it is only one fourth, — about
the same as in the young of Brook.

The pils retain their distinctness and the channels increase in depth and
breadth by growth, while the abdomen remains throughout much narrower than
in Ast. Turners. The increase of the dorso-abdominal diameter of the whorl by
growth is more rapid in proportion to the transverse than in Turneri. The old
shell even on the first half of the eighth whorl envelops more than half of the
preceding whorl. ‘This contrasts very decidedly with Zurnert, which at the same
age is less involute, and the transverse diameter of the whorl near the dorsum is
but little shorter than the sides, the breadth of the abdomen being only about
two fifths less than that of the sides. In this species the dorsal diameter is nearly
a third less than the breadth of the sides, and the breadth of the abdomen is two
thirds less.

The largest specimen measured had seven and a half guar and the diam-
eter was 241 mm.

In the Museum of Stuttgardt from the Obtusus bed theres is one specimen of
this species labelled Amm. Turnert, Sow., Pleinsbach, No. 4187.

FIFTH, OR AGASSICERAN BRANCH. Zit

Asteroceras impendens, Hyarr.
Plate X. Fig. 6-9.
Ariet, impendens, Wricut, Lias Amm., p. 302, pl. xxii. a, fig. 1-5.
Ariet. Collenoti, Ibid., p. 304, pl. xxii. a, fig. 6~9; pl. xxii. x, fig. 1-3.
Amm. Fowleri, Buckm., Murch. Geol. Cheltenh., pl xii fis. 7:

Amm. impendens, Quenst., Amm.:Schwib. Jura, p. 151, pl. xx. fig. 7-10.
Ariet. impendens, BLaxe, Yorkshire Lias, pl. vi. fig. 7.

Localities. — Semur, Lyme Regis.

This species differs from Brooki in the greater amount of the involution, the
smaller size, the earlier age at which the same form of whorl is passed through,
and the earlier age at which degeneration begins.

In Wright’s “ Lias Ammonites” the figures of Brookt, impendens, and Collenoti
show in the clearest manner what are the proper limits of the species. The fig-
ure of Brooki, on Plate VI. Fig. 4, is taken from the less involute form, which
retains its pile until a late stage of growth; that of Collenoti on Plate XXII. B
is an old and very large individual of impendens, which approximates to Brooki, but
has the usual difference in the amount of involution and begins to show degen-
eration of the pilx also earlier than is common in Brooki,; that of Collenoti on
Plate XXII. A, Fig. 6-8, is a yet more accelerated form, growing old and losing
pile, etc. earlier than in the specimen shown on Plate XXII B. The figure of
impendens itself is still more accelerated than the specimen figured on Plate
XXII. A, Fig. 6-8, and has also somewhat stouter whorls. The young figured
on Plate XXII. A, Fig. 4, is similar to the adult of the true Ast. Brooki, having
the same form, pile, and involution until a late nealogic stage.

All of these forms have the broad abdomen, the peculiar channels, and the
young like Brooki, and are quite distinct from the true As¢. Collenoti. They are
undoubtedly transitional forms connecting the two species. Those who wish may
join them, but, as we have previously said, all the series and about all the species
of the Arietidx are closely connected by intermediate forms and modifications,
and, to be really consistent, we must then also include the entire family under
a single specific name. We doubt if any paleontologist would secure serious
support if he attempted to do this.

Asteroceras denotatum, Hyarr.

Amm. denotaius, Srmps., Foss. Yorkshire Lias, p. 76.
Ariet. denotatus, Wrieut, Lias Amm., pl. vi. fig. 1 (Collenots in the text, p. 804).
Amm. tenellus, Simps., Foss. Yorkshire Lias, p. 97?

This species has been universally placed either with Brooki or Collenoti. It is,
however, quite distinct from either of these forms. If one compares the figure
of denotatus by Wright with the young of impendens figured by the same author on
Plate XXII. A, Fig. 4, and that of the young of the same species by Quenstedt,
Amm. Schwiib. Jura, Plate XX. Fig. 8, it will be seen that denotatus stands just
between tmpendens and Collenoti. The young of impendens is much less involute,
and shows the same stout whorl as in the adult, a form which is in strong con-

212 GENESIS OF THE ARIETIDA.

trast with the greater involution and flatness of the shell of denotutus. On the
other hand, denolatus as figured by Wright, when compared with the accurate
figure of adult Codlenoti by D’Orbigny and of the young by Dumortier, shows that
the latter is a form which is smooth, acute, and geratologous to an extreme
degree at a much earlier age than either denotatus or wmnpendens.

Asteroceras Collenoti, Hyarr.

Plate IX. Fig. 10-11 b. Plate X. Fig. 10. Summ. PI. XIII. Fig. 5.

Amm. Collenoti, D’OrB., Terr. Jurass., I. p. 395, pl. xev.

Aster. Collenotit, Hyatt, Bull. Mus. Comp. Zool., I., No. 5, p. 80.

Amm. Cluniacensis, DumMort, Etud. Pal. Bassin du Rhone, p. 148, pl. xxv. fig. 8-10.
Aigoc. Slatteri, Wrieur, Lias Amm., p. 374, pl. 1. fig. 6-8 (not fig. 1-5).

Localities. — St. Thibault, Semur.

D’Orbigny’s two original specimens now in the Museum of Comparative
Zovlogy show that his figures are faithful. The pile in a specimen from St.
Thibault, figured on Plate IX. Fig. 10-11 of this memoir, arise as lateral folds on
the last quarter of the second volution, and become fully developed on the third
whorl. On the first quarter of the third whorl, the keel appears, and on the second
quarter the channels, but these are at first only linear depressions. At this stage
the involution is about one third. On the second quarter of the fourth whorl, the
channels are still shallow, but have depressed, lateral, entire ridges, the pile being
prominent near the dorsum and disappearing on the edge of the abdomen before
reaching the channel ridges. The involution is now about one half. The transi-
tion from the rounded whorl of the early nealogic stage to the acute form char-
acteristic of the species takes place with extraordinary rapidity during the first
quarter of the third volution. The usual intermediate stage, common in other
species having a quadragonal or stout whorl with more or less depressed abdomen
and flattened parallel sides, is entirely omitted. During the fourth whorl the
smooth inflected zones, which represent the channels in this species, become -
developed, and the pile are better defined. On the first quarter of the fifth
volution the elevation and sharpness of the abdomen increase, but no obvious
changes occur in other characters; the involution of the whorl exceeds one half
of the side of the preceding whorl. At this stage and immediately preceding
it the resemblance to the adult of denotatus is extremely close, except of course
as regards the difference of size and the superior sharpness of the abdomen. On
the last part of fifth volution degenerative changes begin, the pile rapidly disap-
pear, and the channel zones become less distinct.’

In D’Orbigny’s other specimen, from Champlony near Semur, the pil are
equally obsolescent on the last part of the third whorl, and on the first quarter
of the fourth they are represented but faintly on the sides.

In another specimen, figured on Plate X. Fig. 10,7 from the same locality, the
pile are entirely absent, being represented only by lines of shell growth, or
hardly perceptible folds, even on the first part of the fifth volution. On the

1 Figured by D’Orbigny, Terr. Jurass., pl. xev. fig. 6, 7.
2 Also figured by the same author on pl. xev. fig. 8.

FIFTH, OR AGASSICERAN BRANCH. 213

second quarter of the fifth whorl in the St. Thibault specimen, the channel ridges
are still raised lines marking the angular junctions of the sides and smooth
channel areas. On the last part of the same whorl in the third specimen just
mentioned, and in fact on the second quarter, even this angularity has almost
wholly disappeared, the channels being obsolete, the keel therefore additionally
prominent. The involution of the last part of the fifth whorl covers three fourths
of the sides of the preceding whorl, exclusive of the channel area and the keel,
which would somewhat increase this amount.

Oppel refers this species to the young of Guibalianus, our Oxyn. Greenoughi, in
which, however, he was probably mistaken. The specimens in our possession
show that this species has not been correctly quoted as coming from any other
localities than Cdte d’Or, the basin of the Rhone, and perhaps Mierlatz. .

Sutures of the first specimen described above on the third quarter of the
fourth whorl had lobes differing from one third to one half, and saddles about
one third; and the third specimen on the first quarter of the fifth whorl had
lobes differing one third and saddles a trifle less. The outlines of the suture are
similar to those of Coroniceras and Asteroceras. Three saddles are to be seen
upon the side, the inferior laterals being deeper than the superior laterals, as in
other species, but the first auxiliaries are unusually large, nearly as deep as the
inferior laterals, and very broad. The abdominal lobe, as stated, is from one half
to one third longer than the superior laterals, and the superior lateral saddles
about one third shorter than the inferior laterals. There is therefore no ground
for the reference of this species to the genus Amaltheus, as has been supposed by
some authors. According to Oppel this species is found in the Tuberculatus bed,
and though Oppel probably never saw a true Col/enoti, this statement is approxi-
mately correct. Dumortier’s specimens of Collenoti (Cluniacensis) were found in
his Planicosta bed immediately above the Oxynotus bed, and all of his beds
above the Bucklandi and Davidsoni (Striaries) beds are equivalents of the Birechii
or Tuberculatus zone at Semur. D’Orbigny’s originals were reported as coming
from the Gryphea arcuta beds, but this was evidently considered to be doubtful
by Oppel, even before Dumortier found his specimens.

The extraordinary series figured and described by Wright from the Oxynotus
bed, under the name of Slatteri, are widely distinct. The figures of the shell and
sutures we have quoted above are certainly taken from a species which is very
closely allied with the true OCollenoti. It is assuredly an Arietian, with affinities
allying it to obtuswm, and comes nearer to Collenoti than any other species in
respect to involution, smoothness, form of whorl, and abdomen. The other mem-
bers of Slatteri as figured are probably diseased specimens of ob/usum.

The keel of this species was examined very carefully to determine whether
it was solid or hollow, and it was found to be solid.

A dwarf form of Ast. (Aviet.) stellare is figured by Geyer in his “ Lias. Ceph.
d. Hierlatz b. Hallstadt,” and his Ast. (Oxyn.) Collenoti is certainly very similar to,
if not identical with, the French form of that name. Asteroceras ( Arvet.) stelleeforme,
Wih., Mojsis. et Neum., Beitr., VL, Plate XX VI, seems to be a species of this

214 GENESIS OF THE ARIETIDA,

group occurring in the Kammerkahr Alps. The young being heavily tuber-
culated and the pile inclined towards the apex, the umbilicus reminds one of
Ast. oblusum, var. quadragonatum. Vf it should prove identical when the young are
examined, it would be interesting as showing the early occurrence of this species.’

SIXTH, OR OXYNOTICERAN BRANCH.

OXYNOTICERAS.

This genus was formerly considered by the author as a distinct family * from
the Arietide. The similarity of the adult sutures, their mode of development,
and the affinities of Oxynoticeras with Agassiceras, which it has been possible to
trace more fully since the publication of Dumortier’s “ Etudes Pal. du Bassin du
Rhone,” show that the genus belongs properly to the Arietid, notwithstanding
the hollow keel. ‘The earlier nealogic stages have the psiloceran form, and the
later nealogic stages have the form and characteristics of Agass. striaries, while
the adult sutures are unquestionably arietian.

Baron Schwartz, to whom we are indebted for being made aware of the im-
portance of the hollow character of the keel among the Ammonitine, was at the
time of our visit at Tiibingen searching for specimens of Oxyn. oaynotum in which
the structure of the keel could be studied. Several specimens were subsequently
found by the author in the collections at Stuttgardt and Semur, which showed
the essentially hollow interior of the keel in oxynotum, and also in Greenoughi,
Guibali, and Lotharingum. The late stage of growth at which it appears, and the
early senile stage in which it completely disappears, are very marked in Guibali,
and especially in Lotharingum.

The young of Oxyn. Greenough’ and G'wibali are very similar in several varieties
to those of Agas. striaries, and in oxynotum they are almost identical with this spe-
cies? The young of Lotharingwn, however, have more accelerated development,
and skip these striaries-like forms, beginning at a very early stage to resemble
the adult of Greenough.

These facts appear to justify the conclusion that the first appearance of the
hollow keel occurred in a genus whose origin is traceable by developmental char-
acteristics to the arietian species Agus. striaries, and whatever its subsequent
value, whether characteristic of families or common to larger groups, it must be
here considered as of generic importance, and certainly not sufficient to outweigh
other characters, which bind the oxynoticeran series to their associates among
the Arietide: of the Lower Lias.*

Oxyn. Greenoughi is in every way very nearly allied to oaynotum, and some vari-
eties, especially among the German forms in the Museum of Stuttgardt, have
more acute abdomens than the true Greenoughi, approximating very closely to the

1 See notes on pages 100 and 205. 2 Proc. Bost. Soc. Nat. Hist., XVII. p. 280, 1874.

3 See description of Oxyn. orynotum.
4 Tf, as supposed by Quenstedt, a hollow keel also existed in Agassiceras, this argument is much
strengthened, since this genus is in our view more decidedly arietian in its characteristics than Oxynoticeras.

SIXTH, OR OXYNOTICERAN BRANCH. 215

stouter varieties of oxynotum. On the other hand, the duration of the s¢riaries-
like stage in Greenoughi, the sutures of the adult, which are simpler or more
arietian in outline than in oxynotum, and the essentially hollow keel, seem to indi-
cate an independent origin directly from Agas. striaries. The specimen of Gree-
nought in the Museum of Stuttgardt, in which the hollow keel was observed, had
the outer shell of the keel remarkably thick, but the interior evidently hollow,
while in the French specimens at Semur the shell of the keel was of usual thick-
ness. The former may possibly indicate a transition to oxynotwn.

Oxyn. Giubali, however, by the resemblances of the young to the adult of
Greenough, and by the younger period at which the adult characteristics of. the
species are inherited, is apparently a direct derivative from Greenough. The same
reasons would also apply to Lotharingum, in which the young lose the sfriaries-like
stage almost entirely, and repeat only the adult form and characteristics of Gree-
nough. These characteristics, the continual decrease in the duration of the adult
stages, and the earlier period at which the senile stage of decline makes its ap-
pearance in each successive species, indicate that these three species belong to a
distinct subseries from oxynotum. The earliest representatives are found in the
Tuberculatus bed at Semur, and in the Oxynotus bed of Dumortier in the basin of
the Rhone. The different species seem, therefore, to form two subseries; one
consisting of oxynotum and its allies, and another composed of Greenoughi, with
Guibali and Lotharingum and their allies, but all on the same geological horizons.

First SUBSERIES.

Oxynoticeras oxynotum, Hyarr.
Plate X. Fig. 4, 5, 14-22, 27. Summ. Pl. XIII. Fig. 9, 10.

Amm. orynotus, QuENsT., Petrefactkunde, XCVIIL., pl. v. fig. 11; Amm. Schwiib. Jura, pl. xxii. fig. 28-49.
Amaltheus oxynotus, Wriegut, Lias Amm., pl. xlvi. fig. 4-6.
Amm. oxynotus, Dum., Etud. Pal. Bassin du Rhone, pl. xxxiii. fig. 2, 3, 5 (not fis; 2).

Localities. — Lyme Regis, Cheltenham, Stonehouse, Gloucester, Hanover, Pliensbach, Balingen, Salins.

The young are at first smooth, and in this early stage resemble closely Psilo-
ceras. They may continue to retain this smoothness and the rotundity of the
abdomen until the specimen is 12 mm. in diameter, as figured on Plate X. Fig. 17.
Their sides then become flatter, and slight folds and striations appear. The re-
semblance to Agas. striaries is so decided in some young specimens, that, if found
independently, no one would hesitate to place them in the same genus as closely
allied species. This same resemblance also necessarily includes a close likeness
in the young to Psil. planorbe. The sutures are also similar to those of Agas.
striaries, as may be seen in collections at Stuttgardt, where there is a very fine
series of exceptional varieties collected by Professor Fraas.

The keel appears much later in the striaries-like forms figured on Plate X.
Fig. 4, 5, than in the normal forms figured on Plate X. Fig. 16-18, but in all
varieties the arietian characteristics of the sutures are apparent. The keel on
its first appearance seems to be solid, though I could not, as in the case of

SS ae

ssescepeacmnaais ies

crear

216 GENESIS OF THE ARIETID.

Oxyn. Lotharingum, determine this with absolute precision. If this could have
been unquestionably settled, the evidence of descent from sériaries would have
acquired additional probability.

There is also an interesting variety which resembles the young of Amaltheus
margariatus, having even the crenulated abdomen, as figured on Plate X. Fig. 19.
This leads into a variety having a blunter and deeply crenulated abdomen, as in
Phylloceras Boblayi, and also resembling it in form, though distinct in the sutures
(Plate X. Fig. 20). The involution, however, is irregular, decreasing with age,
instead of preserving the normal amount of increase, though the specimens did
not exceed an inch in diameter. These and Quenstedt’s observation and figures,
especially in his “ Ammoniten des Schwibischen Jura,” show that all cren-
ulated specimens in this group are probably pathological, and also in most cases
dwarfish."

The typical form, figured on Plate X. Fig. 18, prevails in the majority of
specimens, and the resemblance of these to the young of striwries is very much
obscured by the early development of the compressed adult form, the sharp keel,
and characteristic sutures of the species.

The structure of the keel in one specimen at Semur was plainly visible (Plate
X. Fig. 27). The external shell enveloped the cavity of the keel and the internal
nacreous layer formed a convex floor, but the space between these two, instead of
being hollow as in Oxyn. Greenough, was filled by layers of shell. These were
thickest at the centre and gradually diminished to either side. Their attenuated
lateral extensions formed a third layer between the outer shell and the nacreous
lining, but how far this extended upon the sides was not ascertained. The dark-
colored layer, which was considered an essential characteristic of a fully de-
veloped hollow keel by Baron Schwartz, is also present, lying just above the
nacreous lining and a little on one. side.

Besides these forms, there is at Semur, identified as a form of Lotharingus by
Reynés, a variety of this species which attains the large size of 393 mm. Even
at this size the characteristic form of the adult is maintained, though the involu-
tion is perceptibly less, the unbilicus being quite open. Oxyn. oxynotum is the
only species of the group which attains as large size in its normal variety without
losing the keel, and therefore I think the specimen belongs to this species. The
examination of old and young forms at Semur enables us to state, that in extreme
old age, when the shell is about 335 mm.in diameter, the form sometimes changes.
The keel becomes very broad, a depressed zone makes its appearance on the sides
near the umbilicus, and the involution becomes so much less that I have com-
pared the aspect of the umbilicus to that of Amm. Romam.

The examination of specimens of oxynotum in the Kcole des Mines at Paris
showed a very thin external layer of shell near the abdomen, a thicker internal

1 The small specimens figured by Canavarion Plate VI. of the work so often quoted above, as Amaltheus
margaritatus and acteonoides, and Ariet. (Oxynoticeras) Castagnolai, are probably all related to these peculiar
pathological forms, and are, notwithstanding their close imitation of the characteristics of Amaltheus, really

only morphological equivalents. Canavari has himself referred Castagnolai to Oxynoticeras, and this is
evidently an entirely distinct species from that figured by Wahner as Castagnolai, which in our opinion is a

species of Caloceras.

SIXTH, OR OXYNOTICERAN BRANCH. 217

layer, which formed the partition above the keel, and above this again a succes-
sion of finer layers; but these did not fill up the interior of the keel completely.
A hollow portion or zone filled in the fossil with pyrites, occupied the outer
half of the interior of the keel. My notes and sketches make no mention of any
dark layer in these specimens.

Oxynoticeras Simpsoni, Hyarr.
Summ. Pl. XIII. Fig. 11.
Amm. Simpsoni, Simps., Amm. York. Lias, p. 37.

Amaltheus Simpsoni, Wrieut, Lias Amm., p. 892, pl. xlvil. fig. 4-7.
Amm. oxynotus (pars), Dum., Etud. Pal. Bassin du Rhone, pl. xxxiii. fig. 1, 4? (mot fig. 2, 3, 5).

Locality. — Whitby.

This species is quite different in form, sutures, and the amount of involution,
and it is better to hold it as distinct than to confuse it with oxynotum.

It is admirably figured by Wright. The shell is considerably more tumid, the
whorl thicker and stouter than in oxynofum, and this peculiarity is observable even
in the young. The amount of involution is greater, and consequently the um-
bilicus is smaller, than in that species. The margins of the sutures are much
simpler, especially as regards the auxiliary lobes and saddles than in oxynotum.
It is intermediate in all its characteristics between oaynotum and Lymense, and this
is an additional reason for separating it from the former.

If we are right, either this species or a form transitional to it is found in the
basin of the Rhone.

Oxynoticeras Lymense, Hyarr.
Summ. Pl. XIII. Fig. 12.
Amaltheus Lymensis, Wriaut, Lias Amm., pl. xlvi. fig. 1-3; pl. xlvii. fig. 1-3; pl. xlviii. fig. 1, 2.

Amm. Semanni, Dum., Etud. Pal. Bassin du Rhone, p. 154, pl. xl., xliii.
Amm. oxynotus, Havrr, Ceph. Norddstl. Alpen, pl. xiii. fig. 8, 4, 8, 9 (mot fig. 6, 7).

Locality. — Lyme Regis.

This is merely a more involute form of Oxyn. oxynotum, which deserves a sep-
arate name on this account, but is closely related to that species.

Oxynoticeras numismale, Hyarr.

Amm. oxynotus numismalis, Quenst., Amm. Schwab. Jura, p. 289, pl. xxxvii. fig, 1-8, 6, 7 (not fig. 4, 5).
Amailtheus Wiltshirei, Wricur, Lias Amm., pl. xlviii. fig. 3.
Locality. — Boll.

This species has, according to Quenstedt’s figures, young similar to the adults
of oxynotum, and the adult has a hollow keel. This is lost in old age, the whorl
becoming rounded as in Lotharingun. It seems to be an extremely geratologous
form of the first subseries surviving in the Middle Lias. The sutures are oxynoti-
ceran in outline, and confirm this view of the affinities of the species.

Quenstedt considers it identical with Ozyn. Oppeli, which is, however, a stouter

form at the same stages of growth. He also erroneously identifies it with Ozyn.
28

ee

218 GENESIS OF THE ARIETID.

Lymense as described by Wright. The senile stages separate it from the last,
though it is probably closely allied, and might be considered a variety if occurring
in the same bed. Wright’s Wiltshire’, which seems to be identical, was found in
the Henleyi bed of the Middle Lias.

SECOND SUBSERIES.

Oxynoticeras Greenoughi, Hyarr.
Plate X. Fig. 30. Summ. Pl. XIII. Fig. 13.

Amm. Greenoughi, Sow., Min, Conch., II. p. 71, pl. exxxil.

Amm. Greenoughi, Hauer, Ceph. Nordéstl. Alpen, p. 46, pl. xii.
Amm. oxynotus, Haumr, Thid., pl. xiii. fig. 6, 7 (not fig. 3, 4, 8, 9).
Amaltheus Greenough, Wrieur, Lias Ammonites, p. 384, pl. xliv.
Amaltheus Guibalianus, Wrreut, Ibid., p. 385, pl. xlv.

Amm. Guilbalianus, D’Orz., Terr. Jurass. Ceph., p. 259, pl. xxiii.
Amm, Guibalianus, Rryniis, Plates (pars).

Amm. Guibali, Reyniis, Ibid.

The examination of German specimens led to the conclusion that this species
was closely allied to oaynotum in development and in sutures, and the splendid
suite of this species at Semur enabled us to solve all difficulties.

Here also we were able to compare it with specimens of the true Collenoti,
D’Orb., the originals of which are in the Museum of Comparative Zodlogy, and
they have not the slightest claim to be considered identical. Oppel was probably
led astray by what he supposed to be the types in D’Orbigny’s collection.

Reynés has divided this species into three forms, not very readily distinguish-
able by their adult characteristics, but quite distinct when their development
and old age are studied. His principal observations on Lotharingus, Guibali, and
Greenoughi were made in the Museum at Semur. We however refer his Guba
to Greenough, because of their close resemblance in development and old age, and,
in order to avoid the use of a new name, distinguish the next species, his G'u-
baliunus, as Guibali. This also is justified by the types in the Semur collection, in
several of which these names are interchanged. The true Gudbalianus, D’Orb., as
may be seen by comparison of the original specimen and the Semur collection,
has more abrupt umbilical shoulders, a more open umbilicus, less involute whorls,
and retains the keel and typical form of the whorls until a later stage of growth
than any of the group except oxynotum.

The shell sometimes attains the size of 235 mm. before any marked change of
form is observable, and in one specimen reached the size of 410 mm. before the
keel disappeared. Finally, however, the keel begins to disappear, and eventually
all traces of it vanish in the rounded abdomen. The form, however, seldom
changes as completely as in Guibali. The length of the ribs, whether they are
all long or alternately long and short, is a characteristic of great variability, and
is of no use in distinguishing the species.

There are, so far as we have seen, no representatives of this subseries in the
South German basin, and this observation is sustained by Quenstedt’s “ Ammo-
niten des Schwiibischen Jura,’ which does not contain a single undoubted form

SIXTH, OR OXYNOTICERAN BRANCH. 219

of this subseries. Quenstedt’s Amm. Guibahanus is not a true Greenoughi, and is
properly referred by him to the radians group. An error is also shown by the
use of this name for a species of the Middle Lias, since Guibalianus does not
occur above the Lower Lias.

The species as figured by Wright is a large shell, about 475 mm. in diameter,
which has already lost the keel and pilw, the abdomen being rounded. The
internal whorls of the original are heavily pilated, but the last whorl and a half
are smooth. Sowerby’s figure is taken from a very large and aged specimen, and
the pilations shown in the umbilicus indicate a shell with heavier folds at the same
age than exist in either Hauer’s or Wright’s figures. Wright’s descriptions, how-
ever, coincide with Sowerby’s figure, and the old of Sowerby’s shell has a com-
pletely elliptical aged whorl. The size at which senility affects the shells, and
the general characters and aspect of these figures, are the same as in Greenoughi.
The young forms figured by Hauer may possibly be the young of this species;
they seem to be too heavily pilated for the young of oxynotum.

Oxynoticeras Guibali, Hyarr.
Pl. X. Fig. 28, 29, 31. Summ. Pl. XIII. Fig. 14.

Amm. victoris, Dum., Etudes Pal. Bass. du Rhone, II. p. 136, pl. xxxi., xlii.
Amm, Guibali, Reyn¥s, Plates (pars).
Amm. Guibalianus, Reynés, Ibid.

Locality. — Lyme Regis?

The keel of this species may begin to disappear in some specimens even at the
size of 100 mm. In one specimen of the Semur collection this is accompanied by
a singular and marked lateral deflection of the hollow keel, and at the size of
170 to 180 mm. it had wholly disappeared, and the outer whorl had a very broad
and gibbous abdomen; the sides, however, remained convergent and rounded.

There is a specimen of this species from Lyme Regis in the Museum of Com-
parative Zodlogy, which was found associated in the same slab with Cal. carusense
and raricostatum. The diameter of this specimen is 145 mm. The keel is not
present on the cast, as is usual in this species, but it had probably been present
in the perfect shell, and evidently not impaired by age; the whorl and invo-
lution of the sides were also not altered from the adult condition. A section
showing the inner whorls had been formed by fracture, and the outlines of these,
the hollow keel, and the amount of involution of the whorls, are the same as in
Oxyn. Guibali.

Amm. victoris, Dum., is evidently closely allied to Greenough, but, as figured
by Dumortier, presents very peculiar sutures. It attains a large size before
losing the keel, though one was seen by Dumortier which at a diameter of
456 mm. had no keel. It may prove to be a form which is transitional between
Greenough and this species.

Ra aT

SST SE ENCES RES

ee

somernnainmion es

220 GENESIS OF THE ARIETID.

Oxynoticeras Buvigneri, Hyarr

Amm. Buvigneri, D’OrB., Terr. Jurass. Ceph., pl. Ixxiv.
Amm., Buvigneri, Dum., Etudes Pal. Bass. du Rhone, p. 147, pl. xxxiv.

The original is not correctly figured by D’Orbigny. The specimen is altered
by compression, and this distortion is represented in his figure as natural; it has
one side more compressed than the other, and this side has been selected in his
figure as characteristic of both sides. The abdomen of the original also possesses
a keel, which is not shown in the figure. The figure is, however, near enough
to that given by Dumortier to enable one to identify it as the same, and the fact
that it has a keel is an important point in this connection. It is much more
involute than any species of the Gcenoughi subseries except Lotharingum, but
from this last it can be distinguished by the much larger size attained before
the keel is lost. Dumortier’s specimen reached the diameter of 126 mm., and
D’Orbigny’s that of 184 mm., without perceptible marks of senile degeneration.
We regard this difference as an uncertain characteristic, but have no means of,
verifying the connection with Lotharingum.

Oxynoticeras Lotharingum, Hyarr.
Plate X. Fig. 23-26. Summ. Pl. XIII. Fig. 15.

Amm. Lotharingus, Reynés, Plates.

In this species at the size of 100 mm. the keel had almost disappeared, and
the pile in several instances crossed the abdomen, The abdomen had become
rounded, but the involution had not perceptibly decreased. The umbilicus is
smaller in the adult, the whorls stouter in proportion than in the preceding spe-
cies, and the characteristic form and aspect of Greenoughi are found only in the
young. The younger stages had a solid keel, the hollow keel occurring only
at later stages of growth and in adults, and it suffered from degeneration and
finally disappeared in the senile stage. ‘his is one of the most interesting ex-
amples yet discovered of the similarities of the old and young stages in the same
individual. The resemblances which usually exist between the old and young
shell are also present, and the absence of the hollow keel in extreme old age
shows how seriously the organization may degenerate after the adult period,
even with regard to the most important structural differentiations,

Oxynoticeras Aballoense, Hyarr.:

Amm, Aballoense, Dum., Etudes Pal. Bass. du Rhone, p. 141, pl. xxvii. fig. 1, 2; pl. xxviii. fig. 1; pl. xxxviii.
fig. 1-3; pl. xl. fig. 1.

This species as described and figured by Dumortier seems to be quite different
from Greenoughi, and yet the stouter specimens of that species certainly approxi-
mate to it quite closely. We have not the means at hand of finding by com-
parison whether the principal characteristics cited by Dumortier, namely, the
deep umbilicus and abrupt shoulders of the whorls on the edge of the umbilici,

SIXTH, OR OXYNOTICERAN BRANCH. 221

are present also in Greenoughi, and therefore retain the separate appellation given
by him, There is also a possible relationship with the Oxyn. Oppeli of the Middle
Lias, which makes it desirable to keep it separate, for the present at least, from
Guibalianum. If it is a distinct species, or even a distinct variety, of Greenoughi, it
may be the immediate ancestor of Oppel.

Oxynoticeras Oppeli, Scutén.
Summ. Pl, XIII. Fig. 16.
Oxynoticeras Oppeli, ScHLON., Zeit. deutsch. Gesells., XV. p. 515.
Amm. Oppeli, Scui6n., Paleontogr., XIII. p. 161, pl. xxvi. fig. 4, 5.

Amm. Oppeli, Dum., Etudes Pal. Bass. du Rhone, p. 125, pi. xxxv., xxxvi.
Amm. oxynotus numismalis, QueNs’., Amm. Schwiib. Jura, p. 298, pl. xxxvii., fig. 4, 5 (not fig. 1-3, 6, 7).

The peculiar stout form of this species at the same age distinguishes it readily
from the Middle Lias congener of the same name described and figured by
Quenstedt.! The stout form of the young, gibbous sides, and the blunted abdo-
men, show that it may have been a member of a subseries in which Aballoense
was the first representative in the Lower Lias. The figure by Dumortier exhib-
its a prominent keel even at the diameter of 165 mm. Schlénbach’s specimens
did not completely lose the keel until over 500 mm. in diameter.

Geyer in his Liass. Ceph. Hierlatz b. Hallstadt gives Oxyn. oaynotum, Guibali-
anum, and a form allied to the latter under the name of Oayn. of. Collenoti ; also
two undetermined species and a distorted form, named Ozyn. Janus. These are
all small and dwarfish, except the first, which, however, cannot be called large,
the largest individual measured by Geyer having been found to be only 74 mm.
in diameter.

1 Amm. Schwiib. Jura, pl. xxxvii. fig. 1-3, 6, 7.

i

INDEX.

Aalen, 143, 179, 182, 188.
Aargau, 183, 191.
Acanthoceras, 23, 33.
angulicostatum, 33.
mammillare, 23.
Acceleration, Law of, ix, x, 2, 19, 28, 40-45, 47, 78.
Achdorf, 168,
Acme, x, 21, 107, 112,
Acmic forms, 23, 28, 71.
radicals, 23.

Adnet, or Adneth, 109, 111, 112, 125, 157, 167, 201.

Adnether-Schichten, 100.

Advantageous differences, 50.

Hgoceras Althii, Herb., 110.
angulatum, Neum., 129, 134.
angulatus, Wright, 130.
Belcheri, Wright, 137, 141.
Boucaultiana, Wright, 133.
Buonarotti, Mojs., 7.

* catenatum, 134.
catenatus, Wright, 129.
centauroides, Can., 154.
Charmassei, Wright, 132.
Clausi, Neum., 122, 123.
Cocchi, Can., 200.
crebrispirale, Neum., 124.
heterogeneum, Wright, 41.
intermedium, Wright, 137, 141.
Johnstoni, Neum., 137.
Johnstoni, Wah., 137.
laqueolus, Wright, 159.
Liasicum, Wright, 139.
teri, Can., 154.

Moreanus, Wright, 130.
Naumanni, Neum., 124.
planorbis, Wright, 121.
planorboides, Giim., 89.
planorboides, Neum., 89.
Portisi, Can., 124.
sagittarium, Tate & Blake, 201.
sagittarium, Wright, 201.
Slatteri, Wright, 201, 212, 213.
Spezianum, Can., 136.
striatum, Wright, 41.
Struckmanni, Neum., 124.
subangulare, Neum., 129.
subangulare, Wah., 129.
tenerum, Neum., 126.

ZEgoceras tortile, Wright, 139.
torus, Neum., 137.
trapezoidale, Can., 134.
Agassiceran Series, 65.
Branch, 194,
Agassiceras, 30, 40, 54, 77, 82, 99, 100, 102, 106, 107,
111, 114, 116, 194, 214.
Agassiceras levigatum, 25, 65, 66, 67, 78, 99, 100
101, 194, 195, 197, 200, 208.
nodosaries, 66, 197, 199.
Scipionianum, 66, 77, 78, 82, 83, 100, 101, 195,
197, 199, 200.
Scipionis, 66, 78, 100, 115, 119, 199.
striaries, 66, 67, 78, 82, 100, 101, 105, 115, 121,
196, 197, 198, 203, 214, 215, 216.
Agassiz, Alexander, vii, 86.
Prof. Louis, vii.
Agoniatites, 25, 26.
Ain, 87.
Aldainic Basins, 89, 117, 118.
Aldingen, 143.
Also Rakos, 95.
Amaltheide, 50.
Amaltheus, 48, 116 note, 188, 213.
Amaltheus acteonoides, 216 note.
Greenoughi, Wright, 218,
Guibalianus, Wright, 218.
Hawskerense, 24, 188.
Lymensis, Wright, 217.
margaritatus, 216, 216 note.
oxynotus, Wright, 215.
Simpsoni, Simps., 217.
Wiltshirei, Wright, 217, 218.
Ambulatory pipe or hyponome, 29.
America, 87, 117.
Amherst, 114, 129.
Ammonitine, 2, 3, 5, 7, 18, 16, 18-36, 39, 42, 48, 51,
66, 85, 88, 91, 103, 114, 116, 118, 167, 195.
Ammonites, diseased forms, 82.
Ammonites Aballoense, Dum., 220.
abnormis, Hauer, 100, 195.
acutiangulatus, 109.
acuticarinatus, Simps., 170.
affinis, 102 note.
altus, Dum., 111, 112 note.
angulatus, 92, 94.
angulatus, Quenst., 150.
angulatus, Schlot., 130,

’

224

Ammonites angulatus, Sow., 131.
angulatus compressus, Quenst., 132, 133.
angulatus compressus gigas, 132.
angulatus costatus, Quenst., 130.
angulatus depressus, Quenst., 130.
angulatus hircinus, Quenst., 129.
angulatus psilonotus, Quenst., 129.
angulatus oblongus, Quenst., 129,
angulatus striatissimus, Quenst., 129.
angulatus striatus, Quenst., 129.
angulatus Thalassicus, Quenst., 129, 130.
annulatus, 42.
Arnouldi, Dum., 162.
arietis, Ziet., 142, 145, 156.
Beauregardiense, Coll., 137.
Birchi, 105.
bisulcatum, Brug., 186.
bisulcatus, 104, 109, 143, 186.
bisulcatus, D’Orb., 186, 188.
Bochardi, Rey., 103.
Bodleyi, 63, 109.
Bodleyi, Bruck., 169, 170, 175.
Bonnardi, Opp., 159.
Bonnardi, D’Orb.7 157.
Boucaultiana, D’Orb., 133.
3reoni, Rey., 103.
brevidorsalis, 180.
Brooki, 182.
Brooki, Coll., 100.

Brooki (Riesenbrooki), Quenst., 182, 206,

210.
Brooki, Wright, 206.
Brooki, Ziet., 182, 183.
Bucklandi, 190.
Bucklandi, Phill., 191.
Bucklandi, Quenst., 191.
Bucklandi, Sow., 191.
Bucklandi, Wright, 191.
Bucklandi, Ziet., 191.
Bucklandi carinaries, Quenst , 171.
Bucklandi costaries, Quenst., 191.
Bucklandi costosus, Quenst., 193.
Bucklandi macer, Quenst., 193.
Bucklandi pinguis, Quenst,, 189, 190.
Burgundiz, Coll., 91.
Burgundic, Martin, 142.
Buvigneri, D’Orb., 220.
Buvigneri, Dum., 220.
capraries, 185.
capricostatus, Quenst., 201.
caprotinus, 178.
caprotinus, D’Orb., 103, 175, 178.
carusensis, D’Orb., 142.
catenatus, D’Orb., 129.
catenatus, Sow., 129.
ceras, Hauer, 169.
ceras, Quenst., 109, 170.
ceratitoides, Quenst., 169, 170.
Charmassei, 109, 130.
Charmassei, D’Orb., 132, 133.

INDEX.

Ammonites Cluniacensis, Dum., 212, 213.
Colfaxi, Gabb., 172.
Collenoti, D’Orb., 212.
colubratus, Ziet., 130.
communis, 131.
compressaries, Quenst., 208.
compressus, Quenst., 1382, 133.
Conybeari, D’Orb., 157.
Conybeari, Hauer, 143, 157, 160.
Conybeari, Quenst., 157.
Conybeari, Sow., 157.
Conybeari, Wright, 95.
Conybeari, Ziet,, 148, 156.
cordatus, 32.
coronaries, Quenst., 176.
Crossi, Quenst., 182.
cylindricus, 109.
Danubicus, 185.
Davidsoni, 105,
debilitatus, Rey., 104.
Delmasi, Rey., 103.
denotatus, Simps., 211.
Deffneri, Opp., 150.
Deffneri, Wright, 211.
difformis, Hauer, 174.
deletum, Can., 135.
densinodus, 109,
Doetzkirchneri, 109.
Driani, Dum., 111, 112 note.
erugatus, Bean, 121.
euceras, 109, 153.
falearies, Quenst., 62, 167, 168, 170, 171.
falcaries robustus, 167.
falcaries densicosta, Quenst., 168.
desiderata, 68.
Foetterli, 109.
Fowleri, Buck., 211.
Gaudryi, Rey., 186.
geometricus, 167.
geometricus, Dum., 162.
geometricus, Opp., 97, 167, 169, 170.
Gmuendensis, Opp., 183.
Greenoughi, 102.
Greenoughi, Hauer, 218.
Greenoughi, Sow., 218.
Greenoughi, Wright, 218.
Grunowi, 109.
Guibali, Rey., 218, 219.
Guibalianus, 102, 115, 213, 219.
Guibalianus, D’Orb., 218.
Guibalianus, Opp., 213.
Guibalianus, Quenst., 219.
Guibalianus, Rey., 218, 219.
Hagenowi, Dunk., 128.
Hagenowi, Quenst., 123.
Hagenowi, Terq., 123.
Hartmanni, Opp., 167.
Haueri, 109.
Hehli, Rey., 176.
Hermanni, 109.

Ammonites hircicornis, 5 note.
Hierlatzicus, 109.
Hungaricus, Hauer, 189.
impendens, Blake, 211.
impendens, Quenst., 211.
intermedium, Portl., 141.
jejunus, 105.

Johnstoni, 91, 92.

Johnstoni, Coll., 91.
Johnstoni, Quenst., 137.
Johnstoni, Sow., 137.
Kammerkahrensis, 109.
kridion, 62, 71, 109, 149, 172.
kridion, D’Orb., 148, 167, 171
kridion, Hauer, 175.

kridion, Ziet., 175.
lacunatus, Buckman, 135.
lacunatus, Quenst., 135.
lacunatus, Dum., 135.
lacunatus, Wright, 135.
lacunatus rotundus, Quenst., 135.
lacunoides, Quenst., 135.
levigatus, 198.

levigatus, Opp., 195.
levigatus, Sow., 195.
laqueolus, 92.

laqueolus, Schl6n., 138, 139.
laqueus, Coll., 91.

laqueus, 157.

laqueus, Quenst., 137, 141, 142, 157.

laticostatus, Quenst., 70 note.
latisuleatus, Hauer, 124.
latisuleatus, Quenst., 156.
latisulcatus longicella, Quenst., 142.
Leigneletti, Wih., 132.
leiostraca, Mojsis., 6.

Liasicus, 91, 143.

Liasicus, D’Orb., 139.
Liasicus, Hauer, 109, 139.
Lipoldi, 109.

Locardi, 105.

longidomus, 105.

longidomus, Quenst., 143.
longidomus eger, Quenst., 105, 143.
longipontinus, 89.
longipontinus, Oppel, 122.

ef. longipontinus, Stur, 89.
longipontinus, Wih., 122.
Lotharingus, Rey., 220.
Macdonelli, Portl., 162, 164.
mandubius, Rey., 167.
microstomus impresse, 32.
miserabile, Quenst., 162.
Moreanus, D’Orb., 130.
Moreanus, Hauer, 130.
Mullanus, Meek, 31.
multicostatum, Ziet., 186.
multicostatus, 174, 179.
multicostatus, Hauer, 179, 186.
multicostatus, Sow., 186.

INDEX. 220

29

Ammonites multicostatus brevidorsalis, Quenst., 179.
Nevadanus, Gabb., 172.
nodosaries, Quenst., 70 note, 184, 192, 199.
Nodotianus, 171.

Nodotianus, D’Orb., 144, 167.
Nodotianus, Hauer, 148.
nudaries, Quenst., 182.
Oeduensis, Despl. d. Champ., 122.
obliquecostatus, Brauns, 164.
obliquecostatus, Opp., 97.
obliquecostatus, Ziet., 157.
oblongaries, Quenst., 193.
obtusus, Coll., 100.
obtusus, D’Orb., 201, 206.
obtusus, Hauer, 67, 100.
cf. obtusus, Quenst., 201, 208, 209.
obtusus, Sow., 201, 208, 209.
obtusus suevicus, Quenst., 206.
ophioides, D’Orb., 160.
Oppeli, Dum., 221.
Oppeli, Schlén., 221.
oxynotus, 105, 109.
oxynotus, Dum., 215, 217.
oxynotus, Hauer, 217, 218.
oxynotus, Quenst, 215.
oxynotus numismalis, Quenst., 217, 221.
Partschi, 109.
Pauli, 105.
Petersi, 109.
planaries, 159.
planaries, Fraas, 159.
planicosta, 99, 105.
planorbis, 55, 62, 66, 126, 195, 196.
planorbis, Fraas, 159.
planorbis, Opp., 195.
planorbis, Sow., 121.
psilonotus, 62, 137, 159.
psilonotus levis, Quenst., 121, 137.
psilonotus plicatus, Quenst., 121, 135.
psilonotus provincialis, 91.
raricostatus, 109, 138.
raricostatus, D’Orb., 144.
raricostatus, Dunk., 137.
raricostatus, Hauer, 145.
raricostatus, Quenst., 144, 145.
raricostatus, Wright, 145.
raricostatus, Ziet., 145.
refractus, 32. ;
resurgens, Dum., 186, 188.
Riesenbrooki, Quenst., 182.

- Roberti, Hauer, 122.
robustus, Quenst., 167.
Romani, Auct., 216.
rotiforme, D’Orb., 176.
rotiforme, Hauer, 143, 176.
rotiforme, Quenst., 176.
rotiforme, Sow., 176.
rotiforme, Ziet., 176, 186.
Semanni, Dum., 217.
Salisburgensis, 111, 112 note.

Ammonites Sampsoni, Portl., 121, 122 note.
Sauzeanus, D’Orb., 184.
Scipionianus, D’Orb., 197.
Scipionianus, Quenst., 197.
Scipionianus olifex, Quenst., 199.
Scipionis, Rey., 199.

Scylla, Rey., 141, 142.
semicostatus, Simp., 165.
semicostatus, Y. & B., 165 note.
Simpsoni, Wright, 217.
sinemuriensis, D’Orb., 191.
sinemuriensis, Fraas, 149.
sinemuriensis, Queust., 191, 192.
sironotus, Quenst., 139.
Smithi, Quenst., 201.
Smithi, Sow., 201.
solarium, Quenst., 191, 192.
spinaries, Quenst., 184.
spiratissimus, Hauer, 109, 141, 142, 143.
spiratissimus, Quenst., 156.
stellaris, 109, 202.
stellaris, Coll., 100.
stellaris, Hauer, 201, 202.
stellaris, Sow., 68, 206.
stellaris, Ziet., 206.
striaries, Quenst., 196.
subangularis, Opp., 126.
subarietinus, Menegh., 166.
subplanicosta, 105.
Suessi, Hauer, 174.
tenellus, Simps., 211.
tortilis, Coll., 91,137.
tortilis, D’Orb., 137.
torus, D’Orb., 137, 1438.
trachyostraca, Mojsis., 3, 6.
Turneri, Opp., 208, 209.
Turneri, Quenst., 169, 201, 208.
Turneri, Sow., 208, 210.
Turneri, Ziet., 201, 202, 204.
(Scaphites) umbilicus, 34,
undaries, Quenst., 208.
victoris, Dum., 219. _
vertebralis, Sow., 32.
Youngi, Simps., 170.
zithus, 109.
Ammonoids, ix, 2, 3, 5, 9-19, 22, 25, 26, 31, 85-87, 39,

44, 48-54, 80, 85, 117, 118.

Anachronic species, 110, 111 note.

Analdainic Basins, 89.

Faunas, 89, 111, 117, 118.

Analogies, 25.

Analogy, mimetic, 27.

Anarcestes, 1-4, 15, 17, 18, 22, 66.

Anarcestes fecundus, 1.
subnautilinus, 2.

Anaplasis, x, 20, 30.

Anaplastic mode of development, 38, 39.

Anaplastology, 21.

Anagenesis, Laws of, 71, 74, 76, 77.

Ancyloceras, 29, 32.

INDEX.

Androgynoceras hybridum, 41.
Henleyi, 41.

Annular muscle, 50.

Angulatus Zone and Bed, 89, 92, 98, 95-98, 101, 108,
104, 106-111, 114-116, 119, 128, 141, 149, 154,
155, 165, 172, 1:5, 158:

Angustisellati, 3, 17.

Arcestes, 5, 111.

Arcestes priscus, Waag., 4 note.

Arcestineg, 3, 4, 5, 7, 48.

Arcy sur Cure, 91.

Ardéche, 87.

Argonauta, 26.

Argentine Republic, 87.

Avietenkalk, 157, 167, 171, 187.

Arietids, xi, 5, 6, 7, 22, 24 note, 25, 80, 88, 34-37,
54-57, 67, 69, 83, 87, 89, 91, 98, 101, 105, 108,
110-118, 117-119, 121, 124, 180, 186, 156, 178,
184, 196, 200, 211, 214.

Arietide, Genera of, 85, 87, 102, 105, 108, 110, 112.

Arietites, 22, 60, 151.

Arietites abjectus, 161.

ambiguus, 174.

bisuleatum, 186.

bisuleatus, Wright, 179.

Bonnardi, Wright, 157.

Brooki, Wright, 206, 210.

Bucklandi, 188,

Campigliensis, 154 note.

Castagnolai, Can., 216 note.

Collenoti, Wright, 211.

Conybeari, 95, 166, 167.

Conybeari, Herbich, 95, 157.

Conybeari, Wright, 157.

Crossi, 182, 184.

Crossi, Wright, 188.

denotatus, Wright, 211.

difformis, Blake, 169.

discretus, 154 note.

dorsicus, 161.

impendens, Quenst., 211.

impendens, Wright, 211.

levis, Geyer, 125.

Liasicus, Wih., 139.

ligusticus, 154 note.

Macdonelli, Tate & Blake, 164,

multicostatus, 95, 194.

multicostatus, Herbich, 95, 157.

Nodotianus, Wright, 162, 164.

obtusus, 115, 151.

obtusus, Wright, 201.

raricostatus, Wright, 144, 145,

rotiformis, 115, 188.

rotiformis, Wright, 176, 186, 188, 197.

Sauzeanus, Wright, 186.

Scipionianus, Wright, 197.

Seylla, Rey., 142.

Seylla, Wah., 141, 142.

semicostatus, Wright, 165, 169.

semilevis, 174.

INDEX.

Arietites spiratissimus, 160.
stelleformis, Wih., 100 note, 205 note, 218.
stellaris, 115.
stellaris, Gey., 213.
subnodosus, Ziet., 186.
supraspiratus, 160.
tardecrescens, Blake, 146.
Turneri, Wright, 208.

Arnioceran Series, 62, 104, 106.

Arnioceras, 40, 41, 54, 56, 73-75, 82, 84, 91, 96, 97,
104-107, 111, 116, 144, 161, 164, 169, 171, 174,
209.

Arnioceras (Psil.) abnorme, 174.

(Ariet.) ambiguus, 174.

Bodleyi, 62, 73, 75, 169, 173.

cuneiforme, 163, 174.

ceras, L. Agassiz, 25, 62, 738, 84, 169, 170,
209.

difformis, 174.

falcaries, 90, 97, 104, 105, 115, 168, 170, 171.

Hartmaini,- 62, 73, 104, 167, 168,170, 171,
173.

Humboldti, 173.

incipiens, 169, 170.

kridiforme, 167.

kridioides, 62, 74, 149, 171.

Macdonelli, 106, 164.

miserabile, 25, 62, 72, 74, 75, 81, 82, 84, 97,
105, 162, 163, 164, 165.

miserabile, var. acutidorsale, 163, 165, 166, 171.

miserabile, var. cuneiforme, 164, 166.

Nevadanum, 172.

obtusiforme, 62, 74, 97, 164.

semicostatum, 25, 41, 62, 63, 72-75, 81, 84, 97,
163; 164165167; 172.

(Ariet.) semilevis, 174.

(Psil.) Suessi, 174.

tardecrescens, 21, 62, 73, 168, 173.

Arton, 197.

Ascoceratites, 36.

Asellati, 2, 16, 18.

Ashley Down, 138.

Asiphonophora, 15, 16.

Asiphonula, 10, 16, 18, 49.

Aspidoceras, 22, 23, 33, 42.

Aspidoceras Edwardsianus, 23.

perarmatum, 23.
Rupellense, 23.
Aspidoceras Stock, 42.

Asteroceran Series, 66, 103.
Asteroceras, 30, 34, 48, 54, 71, 77, 100, 102, 106, 107, |
110, 114, 116, 149, 200, 213.
Asteroceras acceleratum, 67, 68, 77, 101, 207, 208, 209.
angulicostatum, 34, 48, 56, 71, 77.
Brooki, 67, 68, 77, 83, 97, 206, 207, 208, 210,
2LE,

Collenoti, 21, 37, 40, 47, 55, 68, 69, 77, 78, 83,
100, 101, 105, 106, 197, 207, 211-218, 218.
denotatum, 65, 68, 77, 106, 211, 212.

impendens, 68, 77, 88, 208, 211, 212.

227
Asteroceras obtusum, 33, 48, 66-68, 76, 77, 88, 100,
101, 106, 109, 110, 164, 195, 200, 201, 203,
206, 209.
obtusum, var. quadragonatum, 205, 213.
obtusum, var. sagittarium, 106, 201.
obtusum, var. Smithi, 203.
stellare, 67, 68, 76, 77, 115, 202, 206, 209, 213.
stelleforme, 213.
tenellus, 183.
trigonatum, 182.
Turneri, 21, 25, 67, 68, 77, 169, 202, 205, 207-
210:
Atacamas, 87.
Atlantic, 86.
Aturia, 25, 26.
Autochthones, Zone of, xi, 89, 96, 106, 114, 118.
Autochthonous Faunas, 89, 111, 113.
Aveyron, 87.
Avicula contorta, 114.

Baculites, 1, 20, 28-32, 387, 43, 46, 47.
Bactrites, 1, 2, 38, 18, 14.
Baden, 87, 168.
Balatonites, 7,
Balfour, 8, 40 note, 46.
Balingen, 121, 129, 142, 144, 156, 157, 170, 175, 176,
186, 191, 198, 197, 201, 207, 208, 209, 215.

Band of Aldainic Basins, 89.
Bande Homozoique Centrale, 87.

Homozoique du Nord, 87.

Homozoique Polaire, 87.
Barrande, vii, 1, 2, 14, 84, 49, 111 note.
Basins, Analdainic, 89; residual, 89; closed, 110.
Basle, 169, 171, 191.
Bas Rhin, 87.
Basses Alpes, 87, 114.
Batrachia, 28.
Bean, 147.
Beauregard, 91, 137, 138.
Bebenhausen, 141, 171.
Behla, 182, 165, 167, 185, 171, 172:
Belemnites, 52.
Belemnoids, 9, 10, 26, 48, 53.
Beloceras, 80 note.
Bempflingen, 199, 201, 202, 204, 208, 210.
Beneckia, 3.
Besancon, 90, 201, 204.
Besanyer Mts., 95.
Betzenrieth bei Goppingen, 186,
Beyrich, 1, 4.
Binton, 92.
Black Forest, 118.
Blake, 93, 117, 128, 146, 201.
Blastula (mesembryo), 8.
Blastrea, 8.
Blumenstein am Thuner See, 123.
Bochard, viii.
Bodelshausen, 187.
Bohemia, 86, 87, 93.

92, 29.

aay oe

228 INDEX.

Boihingen, 168.

Bolivia, 86.

Boll, 144, 179, 201, 208, 204, 215.
Bone bed, 90.

Bonnert, 157, 167, 169.

Boisset, 90.

Zoueault, 7, 91, 95, 100, 144, 196.
Bouches du Rhone, 87.
Brachiopoda, 118.

Branco, 1, 2, 7, 8, 14, 17, 18, 21.
Brauer, 9 note, 45.

Braun, 92, 94, 98, 99, 101, 102.
Bréon, viii.

Bresgau, 137.

Brignolles, 114.

Bristol Mus., 92, 121, 187, 138, 139.
British Islands, 86.

Museum, 121, 131, 146, 155, 158, 203.
Brockeridge and Defford Commons, 92.
Bronn, 7, 166.

Brooks, W. K., 10, 15.
Brunn, 86.

3runswick, 88, 98.

3ucklandi Zone, 96, 97, 98, 104, 105, 106, 108, 109,
116, 119, 134, 138, 169, 190, 196, 213.
Buckman, 135,

Cadoceras, 23.

Cecophora, 16.

Czecosiphonula, 11, 14, 16, 17, 49.

Cxeum, siphonal, 9, 18, 14, 19.

California, 86, 87, 118, 173.

Caloceras, 22, 24, 33, 40, 54-56, 58, 60, 61, 70 note, 72-
75, 80, 81, 84, 89, 90, 92, 938, 95, 105-107, 112-
114,°116, 120, 123, 125, 136, 139, 149, 150, 154,
155, 158-160, 163, 172, 174.

Caloceras abnormilobatum, 60, 81.

(Ariet.) abnormilobatum, 148.

aplanatum, 106, 146.

Armentalis, 105.

Burgundie, 91.

carusense, 33, 59, 60, 70 note, 73, 80, 81, 98,
105, 142, 143, 144, 146, 152, 154.

Castagnolai, 60, 81.

(Ariet.) Castagnolai, Wih., 148.

centauroides, 61.

(Arviet.) centauroides, Wih., 153, 154.

Coregonense, 61.

(Ariet.) Coregonense, Wih. 15, 24, 151, 154.

cycloides, 60, 147.

(Ariet.) cycloides, Wiih., 148.

Deffneri, 60, 72, 81, 150.

(Ariet.) doricus, 154.

Deetzkirchneri, 160.

(Ariet.) Doetzkirchneri, Neum , 148.

Edmundi, 105.

gonioptychum, 60.

(Psil.) gonioptychum, Wah., 147.

Grunowi, 61,

Caloceras (Ariet.) Grunowi (Hauer), Wah., 154.
hadroptychum, 60.
(Z&goc.) hadroptychum, 140.
Haueri, 60, 61, 70 note, 151.
(Aviet.) Haueri, 150, 151.
(Ariet.) Haueri, Wiih., 151.
(digoc.) helicoideum, 154.
Johnstoni, 58, 60, 67, 72, 74, 75, 80, 81, 90-93,
113, 121, 125, 136, 139-141, 145-147, 150,
154, 155, 160, 179, 185.
(Agoc.) Johnstoni, 58, 60, 140, 141.
laqueoides, 61, 149, 154.
laqueum, 25, 57-61, 72, 80, 81, 91, 98, 95, 103,
123, 140-144, 147, 149, 155, 156, 160.
laticarinatum, 61.
Liasicum, 58, 59, 60, 74, 91, 118, 138, 189, 140,
142, 144, 153.
Loki, 60, 150.
(Ariet.) Loki, Wih., 140, 151, 153.
longidomum, 143, 157.
nigromontanum, 60.
(Megoc.) nigromantanum, 140.
Newberryi, 151.
Nodotianum, 59, 60, 74, 80, 105, 113, 181, 138,
139, 142-144, 147, 151.
ophioides, 61.
(Ariet.) ophioides, Wah., 151.
(Psil.) orthoptychum, Wah., 147.
Ortoni, 118, 153.
preespiratissimum, 60, 95.
(Ariet.) praespiratissimum, Wiih., 147.
perspiratus, 61.
(Ariet.) perspiratus, Wah., 151.
proaries, 60, 61, 140, 144, 147, 148.
proaries, Neum., 151.
(Ariet.) proaries, Wih., 148, 153.
raricostatum, 33, 59, 62, 81, 103, 105, 109, 142,
144, 146, 152, 171.
(Ariet.) raricostatum, 149, 152, 154.
(Ariet.) retroversicostatus, 154.
salinarinm, 61, 153, 154.
(Ariet ) salinarium, 154.
Sebanum, 61, 147.
(goc.) Sebanum, Pich., 154.
(Ariet.) Seebachi, 140, 151.
suleatum, 6v, 146, 148.
(Ariet.) supraspiratus, Wih., 151.
tardecrescens, 105.
tortile, 25, 55, 59, 72, 74, 91, 118, 187, 188, 142,
144, 145, 154.
(goc.) tortuosus, 154,
Caloceras Bed, 90, 92, 93, 96, 1
Series, 58, 108, 150.
Campodea, 45.
Canadian Survey, 87.
Canavari, 116, 124, 127, 184, 185, 154, 160, 194.
Capelini, 166. :
Caraccoles, 86.
Carinifera, 24, 107.
Carnites, 3.

Sent.

oe NN

INDEX. 229

Carpathians, 86.

Castellane, 114.

Catagenesis, Law of Succession in, 74, 76.

Cataplasis, x, 20.

Cataplastic forms, 32.

mode of development, 38, 39.

Cataplastology, 21.

Caucasus, 115.

Celeceras, 80 note, 111 note.

Celtites, 7.

Central America, 86.

Europe, xi, 55, 57, 60, 61, 85-88, 94, 96, 99,
106, 110-119, 126, 186, 140, 147, 152, 153,
159.

Russia, 86, 115.

Centroceras, 25, 26.

Cephalophora, 14.

Cephalopoda, 8, 10, 16, 19, 25, 26, 38, 39, 45, 47, 49, 51,

53, 116, 118.

Ceratites, 22 note.

Ceratites Sturi, 22.

Ceratitine, 3, 6, 7, 28, 30, 48, 124.

Cerro de Parco, 151.

Chacapoyas, 153.

Chalandry, 138.

Champlony, 212.

Chapuis, 91, 94, 95, 101.

Characteristics, differentials, ix, 19, 22, 53, 80.
replacement of, in heredity, ix, 44, 74, 78.
supposed to be advantageous, 50.
genesis of, 71.
irregular development of, 73.
genesis of retrogressive, 74.

Charente, 87.

Charente Inférieure, 87.

Cheltenham, 135, 137, 170, 215.

Chevigny, 129.

Chili, 86.

Chippeway Point, 31.

Choristoceras, 28, 30.

Chorological distribution, 85, 108.

Chronological distribution, 85.

Cicatrix, 9.

Clarke, 111.

Classification, remarks upon, vil.
unit of, 55.

Clinoceras, 167.

Clinologic stage, 20, 46, 133, 136, 140, 141, 155, 164,

180, 183, 184, 188, 195, 197, 200, 201.

Closed Basins, 110.

Clydonautilus, 25.

Clymenine, 3, 7, 25, 26, 49, 80 note.

Cocchi, 116.

Cochloceras, 28, 30.

Coeloceras, 42, 95.

Cceloceras Pettos, 23, 24, 42.

Coleoptera, 9 note, 45.

Colfax, 172. a

Collar of siphon, 17, 44.

Collenot, vi, 90, 91, 100, 101, 104, 114.

Columbia, 86.

Conch, 9, 13, 15)

Cope, viii, 16 note, 2, 27, 28, 42, 48, 46, 47.

Coppenbriigge, 129.

Coregna, 166.

Coroniceran Branch, 161, 175, 183.

Series, 63, 66, 83, 97, 98, 99, 104.

Coroniceras, 22, 30, 33, 84, 48, 52, 54, 55, 56, 64, 65,
74, 75, 76, 83, 84, 97, 98, 105, 107, 114, 116, 149,
155, 169, 173, 185, 198, 195, 200, 213.

Coroniceras bisulcatum, 25, 64, 94, 97, 98, 104, 106,

107, 184, 186, 194.

Bucklandi, 38 note, 65, 67, 74, 76, 110, 115, 149,
159, 175, 190, 191, 192, 193, 206.

coronaries, 63, 176.

Gmuendense, 33, 64, 76, 83, 98, 107, 115, 181,
182, 183, 206.

Hungaricum, 189.

kridion, 41, 62-65, 73, 74, 76, 82, 93, 97-99,
171, 172, 175-179, 185, 188-190.

latum, 65, 74, 97, 99, 177, 178, 189, 190, 191,
193, 194.

lyra, 63, 76, 179, 181, 182, 183, 187.

(Ariet.) Monticellense, 194.

multicostatum, 98, 186.

orbiculatum, 65, 75, 76, 83, 107, 178, 190,
193.

rotiforme, 21, 31, 63, 65, 74, 76, 78, 97, 98, 176,
178, 179, 188, 188-190, 193.

sinemuriense, 191.

(Ariet.) sinemuriense, 194.

Sauzeanum, 64, 81, 82, 98, 99, 107, 115, 184-
186, 187, 190, 198, 202.

Sauzeanum, var. Gaudryi, 64, 186, 187, 190.

trigonatum, 338, 33 note, 64, 76, 83, 182, 184,
206, 208.

Corsica, 108.

Cosmoceras, 23, 26, 29.

Cosmoceras bifurcatum, 29, 31.

latum, 177.

Taylori, 23.

Costidiscus, 23.

Céte d’Or, xi, 87-89, 91-102, 104-106, 108, 114, 116--

119, 213.

Cotham, 92, 121, 138.

Cretaceous, 29, 33, 34, 37, 87.

Crimea, 86, 115.

Crioceras, 29, 34, 47.

Crioceras Eryon, 167.

Mandubius, Rey., 167.

Cross, 92.

Cryptogenous Types, 117.

Cuvier, 91.

Cyclolobus, 5, 6.

Cyclolobus Oldhami, 4, 5.

Cycle in evolution and development, 20, 38, 78, 112.

Cycles in history of individuals and groups, 108.

in chronological migration, 108.

in chronological evolution of forms, 108.
Cymbites, 100, 195.

230 INDEX.

Cymbites globosus, Geyer, 195, 200, 202.
Cyrtocerina, 12, 13.
Cyrtoceras, 25.
Cyrtoceras indomitum, Bar., 34.
Logani, Bar., 34.
rebelle, Bar., 34.

Dactyloceras, 23, 42.

Dactyloide, 23.

Darwin, 27.

Davidsoni Bed, 105, 213.

Definition of genus, 55.
of species, 56.

Degerloch, 196.

Degeneration, acceleration in, x.
of sutures, 57.
tendency to inheritance, 77.
law of replacement, 78.
sutures persistent in, 83.

Dentalium, 10, 15, 16.

Desmoceras, 24, 105.

Deroceras armatum, 23.
Dudressieri, 23, 42.
planicosta, 99, 105, 131, 196.

Deroceratidee, 117.

Development, three phases of, x, 37.
acceleration in, ix.
anaplastic mode of, 38, 39.
cataplastic mode of, 38.
metaplastic mode of, 38.

Dewalque, 91, 101.

Deyrolay, 130.

Diebrook, 129.

Dieulefait, 88, 114.

Differences, advantageous, 50.

Differential characteristics, ix, 19, 22, 53, 80.

Differentials, origin of, 48.
morphological, viii, ix.

Digue, 114.
Diptera, 45, 47.
Dinarites, 22.

Dorsetshire, 88.

Déshult, 88.

Doubs, 87.

Draguignan, 114.

Dréme, 87.

Dumortier, 88, 91, 93, 95, 97-99, 102, 104, 105, 111,
114, 135, 188, 205, 212-214, 219-221.
Dunker, 123, 138.

Durance, 114.

Durrenburg, 168.

Dwarfs, 77, 112, 184, 204, 216.

Kcole des Mines, 138, 159, 160, 216.
Effort, Law of, ix, 53.
Elwangen, 143.
Emerson, viii, 58, 92, 94, 98, 102, 114, 119, 129.
Endigen, 208, 209.
Endoceras, 13, 15, 35 note, 52.
Endoceratide, 11, 12, 13, 16, 19, 20, 48.
Endocones (sheaths), 12, 13.
Endosiphon, 12, 13.
England, 64, 88, 92, 93, 96, 97, 99, 100-108, 106, 108,
111, 114, 117, 155, 159, 169, 170, 171, 184, 196.
Enzesfeld, 95, 109, 143.
Epacme, x, 21, 52.
Epacmic radicals, 28.
Ephebolic, 12, 18, 19, 20, 87, 75, 206.
Equivalence, Morphological, viii, 21, 22, 25, i428;
29, 30, 56.
Organic, viii.
Equivalent species, 22.
Equivalents, Morphological, viii.
Organic, vill.
Etheridge, viii.
Europe, 117, 118, 119.
European Province, 118, 152.
Evolution by cycles (vortices), 108.
Law of Types in, 16 note.
of geratologous forms, 31, 36, 47.
requirements of a theory of, 38.
Exact parallelism, 27.
Existence, struggle for, 27, 38, 53. .

Dinarites Mahomedanus, 22.

Diploplacula, 8.

Discoceras, 36.

Discoceras Conybeari, 157.
ophioides, 160.
spiratissimum, 155.

Distoma, 47.

Distribution, Chorologic, 85, 103.
Chronologie, 85.
Geographic, 86,

Dobrudscha, 86.

Dohrn, 30.

Dompan, 88.

Donetz, 86,

Donar, 134.

DOrbigny, 7, 81, 88, 86, 87, 58, 59, 61, 104, 129, 130,

132, 188, 187, 188, 189, 142, 144, 161, 159, 178,
184, 191, 206, 212, 213, 218, 220.

Falciferi, 84.
Fauna of Central Europe, 106.
Cote d’Or, 103.
England, 106.
Kutch, 86.
Province of the Mediterranean, 108.
Rhone Basin, 104.
South Germany, 103.

Faunas, Analdainic, 89, 111, 117, 118.
Autochthonous, 89, 111, 113.
Residual, xi, 89, 106, 114, 116.
Mixed, 109-111.
of the Lias, 154.

Favre, 110.

Filder, 122, 123, 126, 182, 156, 165, 175, 179.

Fischer, ix, 7.

|

a

nce, catenin

i

ON, ae

INDEX. 231

Fleckenmergel, 109.
Fossil Cephalopods, viii, 2, 51.
France, 86, 88, 93, 97, 98, 101, 102.
Southern, 114.
Fraas, vii, 7, 33, 96, 98, 102, 118, 132, 141, 149, 158,
159, 167, 185, 197, 215.
Franconia, 87.
Funnels of siphon, 13.

Gabb, 172, 173.
Gard, 87, 88.
Gastatter Grabens, 95, 109.
Gasteropoda, 8, 15, 28, 118.
Gandry, vii.
Gelbesandstein, 94.
Genealogy of a series, 56.
Genesis of Progressive Characteristics, 71.
Retrogressive Characteristics, 74.
Genus, definition of, 55.
Geographic Separation, 27.
Distribution, 86.
Geometricus Bed, 143, 165, 167, 168, 169, 182, 196,
197, 198, 207, 208.
Geratology, ix, 20.
Geratologous Forms, law of evolution of, 31, 36, 46.
Geratologous Radicals, 28.
Germany, 62, 86, 103, 143, 167, 169, 201.
Geryonea, 45.
Geyer, 85, 95, 100, 109, 110, 111, 115, 135, 154, 173,
174, 196, 200, 218, 221.
Gloucester, 208, 209.
Gloucestershire, 88, 215.
Glyphioceras diadema, 22 note, 24.
Gmiind, 167, 179, 183-185, 197, 206, 208.
Gomphoceras Belloti, Bar., 34.
Goniaclymenide, 80.
Goniatitine, 1-4, 7, 10, 11, 14, 17-19, 25, 28, 30, 39,
44, 48, 49, 123.
Goniatites, 25, 49.
Goniatites atratus, 2, 18.
Listeri, 2.
prematurum, 111 note.
Goniatitinula, 17, 196.
Gonioceratide, 80.
Goppingen, 171, 181, 182, 183, 186, 206, 207.
Gottsche, 86.
Grasse, 114.
Gravelles, 91.
Greenland, 86.
Griesbach, 4.
Gryphea arcuata Beds, 213.
Guibalianus Subseries, 106.
Guillon, 91.
Gulf of Lyons, 86.
Giimbel, 49, 89, 95, 109, 153.
Gymunites, 5, 6, 22, 85, 118, 117.
Gymnites Credneri, 6.
fecundus, 2.
Humboldti, 6.

Gymuites incultus, 6.
Palmai, 6.
Gyroceras, 25, 29, 167.

Habit, effects of, x, 26, 27, 29, 30, 47, 49-51, 53.
Heckel, 6, 18, 20, 21, 22, 38.
Halorites, 6.

Halorites decrescens, 6.
Ramsaueti, 6.
semiglobosus, 6.
semiplicatus, 6.

Hall, 34, 35.

Halstadt, 213.

Hamites, 29, 38, 47.

Hammerkhar, 126.

Hanover, 88, 130.

Hanoverian Fauna, 114, 215.

Haploceras, 24, 84

Harpoceras, 84.

Harpoceras Sowerbyi, 24.

Hauer, 28, 85, 95, 97, 100, 102, 109-112, 125, 148,

148, 159, 196.

Haug, 195 note.

Haute Sadne, 87.

Haut Rhin, 87.

Hébert, viii.

Hechingen, 167, 186.

Helictites, 28.

Helvetic Basin, 87, 88.

Henleyi Bed, 218.

Henslow, Origin of Floral Structures, 50 note.

Herault, 81, 87.

Herbich, 55, 85,95, 96, 110, 111, 159.

Hercoceratide, 80.

Heredity, Law of, ix, 73, 74, 77.

Heterology, 10 note, 27.

Hierlatz, 109, 110, 111, 196, 213.

Hierlatz Bed, 109, 111, 112, 213.

Hildesheim, 129, 130.

Hildoceras Walcoti, 24, 107.

Hippuritidae, 118.

Hohenheim, 156.

Holm, 13, 35.

Holeodiscus, 23.

Hollow keel, 55, 214, 215.

Holochoanoidal Funnel, 12.

Homogeny, 10 and note, 27.

Homology, 10 note, 27.

Homoplasy, 10 and note, 27.

Homozoic Bands, 87

Hoplites, 33, 84.

Hoplites Bruguierianus, 23, 26.
Cornuelianus, 23.
Royerianus, 23.

Humboldt Co., 178,

Hungarites, 3.

Hydra, 45.

Hyponome, 29, 49.

Hymenoptera, 9 note, 44.

aon INDEX.

India, 27, 86, 118.

Inexact parallelism, 27,

Insecta, 9 note.

Inyo Co, 173.

Jpishguaniina, 153, 169.

Italy, xi, 108, 114, 116, 117, 118.
Italian Basin, 87, 88, 114, 117, 119.

Jackson, 8 note.

Jamesoni Bed, 102, 146, 164, 201.
Jettenburg, 169.

Judd, 88.

Kalthenthal, 126, 149.
Kammerkahr Alps, 95, 109, 214.
Kandar, 137.

Keel persistent in old age, 34, 194.
in Agassiceras, 194, 214 note.
‘hollow, 214, 215.

Kirchheim, 131.

Kossener Shales, 89.

Krakau, 86.

Krumenacher, 198.

Kutch, 27, 86.

Lake Constance, 86.

Lallierianus, 42.

Lamarck, 43, 46.

Lamellibranchs, 51, 118.

Landrioti, Rey., 104.

Langley, vii.

Lankester, 8, 10 note.

Larve, Goniatitinula, 17.
Thysanuriform, 9 note.

Latisellati, 3, 17, 19.

Laqueum Layer, 90, 91.

Law of Acceleration, ix, x, 2, 19, 28, 40-45, 47, 48.
Evolution of Types, 16 note.
Heredity, ix, 73, 74, 77.
Morphogenesis, viii.

Succession in Anagenesis, 71, 74, 76, 77.
ie ‘6 ~—- Catagenesis 74, 76.
Variation, x.

Lecanites, 3.

Leconte, 87.

Leicestershire, 184.

Lepidoptera, 9 note.

Lepisma, 45.

Levis Stock, 25, 54, 57, 62, 75, 81, 82, $3, 108, 112,

116,161.

Liparoceras Bechei, 41.
Henleyi, 41.

Liparoceratide, 117.

Lituites, 26, 29, 35, 47.

Living Chamber, 9.

Lobites, 28, 30.

Lombardy, 113.

Longobardites, 3.

Lot, 87.

Lower Bucklandi Bed, 89, 94, 96, 100, 105, 107, 108,
143.

Lozére, 87.

Lubbock, 45.

Luxemburg, 88, 91, 92, 96, 97, 100, 101, 102, 142, 157,
159, 197.

Luxemburg Basin, 92.

Lyme Regis, 65, 67, 130, 132, 137, 142, 144, 155, 157,
158, 167, 169, 186, 188, 191, 195, 201-204, 206,
208-211, 215, 217, 219.

Lytoceras, 33, 44.

Lytoceras Driani, 122 note.

immane, 5. ;

Petersi, 122 note.

Roberti, 122 note.
Lytoceratidee, 110, 111, 116, 117, 122 noite.
Lytocerating, 3-9, 18, 27, 29, 30, 82, 48, 116, 118.

Macrocephalites, 23.

Macrocephalites macrocephalum, 23.

Macrosiphonophora, 15, 16.

Macrosiphonula, 12, 13.

Magdeburg, 88.

Magnon, 29, 31, 78.

Magnosellaride, 18.

Mammalia, 46.

Marcou, viii, 7, 85, 86, 87, 90.

Markoldendorf, 58, 94, 114, 129.

Marmorea Beds, 128, 184.

Marsupialia, 47.

Martin, 91, 117.

Mediterranean Faunas, 112.

Mediterranean Province, 56, 57, 60, 75, 86, 87, 88, 98,
94-99, 108, 110-116, 125.

Medlicottia, 80.

Meek, 381.

Meekoceras, 3.

Megaphzyllites, 4.

Megastoma Bed, 93, 134.

Meneghini, 115.

Meroblastic, 18.

Mesembryo (blastula), 8.

Mesozoa, 8.

Mesozoic Radicals, 22.

Metamorphology, 18, 21.

Metaplasis, x, 20.

Metaplastic mode of development, 35, 39.

Metaplastology, 21.

Metazoa, 8.

Metembryo, 8.

Metzingen, 156.

Microceras, 110, 202.

Microceras planicosta, 110, 201.

Microderoceras, 105, 116.

Microsiphon, 18, 19.

Microsiphonula, 12, 17, 18.

Mimetic Analogy, 27.

INDEX. 200

Mimoceras, 1, 2, 3.

Mimoceras compressum, 1.

Mining Bureau, 173.

Minot, 46.

Mixed Faunas, 109-111, 116, 117.

Mohringen, 4, 5, 63, es 192, 157,176.

Mosch, vii, 84, 113, 197

Mojsisovics, 3, 4, 6, 7, 22, 90, 93, 95, 96, 97, 100, 109,
113, 140.

Mollusea, 10.

Monophyllites, 4, 5.

Monophyllites Suessi, 5.

Monoplacula, 8.

Monoplast (ovum), 8.

Montloy, 121.

Moravia, 86.

Morphoceras, 23.

Morphogenesis, Law of, viii.

Morphological Difference, ix.

Differentials, viii.
Equivalence, viii, 21, 22, 25, 27, 28, 29, 30, 56.

Morphology, Law of, viii.

Moselle, 91, 117.

Miihlfingen, 165.

Muhlhausen, 129, 130.

Munich, 122, 126, 137, 188, 151, 209.

Munier Chalmas, viii, 14, 49.

Muscle, Annular, 50

Museum at Bristol, 92, 139.

Museum of Comparative Zodlogy, vii, 13, 76, 91, 95, 96,
121, 129, 181, 188, 142-144, 149, 157, 158, 159,
166, 169, 181, 185, 186, 188, 196, 199, 200, 205,
206,. 209, 219,919:

Museum at Munich, 209.

Museum at Ottawa, 87.

Museum at Semur, 91, 103, 122, 141, 144, 162, 181,
196, 200.

Museum at Stuttgart, 63, 77, 96, 99, 100-102, 122.
129, 181-183, 187, 141, 143, 149, 150, 157, 158,
165, 167-169, 171, 175, 179, 181, 185, 186, 199,
196,197, 198, 205, 207, 209, 210, 214, 915,

Museum at Tiibingen, 157.

Museum at Ziirich, 197.

lon)

Neepionic stage, 9, 11, 12, 18, 25, 111 note, 195, 196.

Natural Selection, 28, 38, 43, 50, 53

Nautili, 91, 111 note.

Nautilini, 2, 25.

Nautiloids, ix, 2, 8,9, 11, 12, 14-16,
87, 89, 48-58, 80, 117, 118

Nautilus, 12, 29, 49-5:

Nealogic, 12, 18-20, a 25, 139, 140, 150, 195, 206.

Nealogic Stages, 75, 111 note, 127, 128, 197, 206, 208,
212.

Nellingen, 121, 156, 157.

Neoembryo, 8.

Neo-Lamarckian School, 43.

Neuffen, 121.

96, 28, 29, 34+

Neumayr, 5, 6, 21, 29, 32 note, 33, 42, 56, 60, 61, 85,
OG, 654 89,00; 108,011, 119. 1 io 14752118;
122, 123, 126, 129, 184, 187, 189, 140, 147, 150
151.

Nevada, 172, 173.

Newberry, 117, 151.

Newbold Quarries, 155.

Nice, 114.

Norites, 3, 4.

North America, 86, 87.

Northeastern Alps, xi, 55-
94-102, 106, 108, 110-11

39, 140, 151-153, 159,

North English Basin, 88.

North Europe, 118.

North German Basin, 88, 92, 93, 102, 108, 139.

North Germany, 92, 93, 94, 96, 97, 98, 99, 100, 101, 102,
108, 114, 129.

North Peru, 157, 163, 169.

Northwest Germany, 92.

Nostologic Stages, 20, 28, 32, 87, 46, 51, 183.

Nurtingen, 137, 182.

57, 60, 61, 81, 85, 89, 90,
3, 116-118, 126, 150, 137,
£02

Obtusus Bed, 107, 109, 188, 196, 202, 206, 207, 208,
210;

Oelschiefer, 163.

Oestringen, 141.

Ofterdingen, 209.

Olcostephanus, 28, 33.

Olcostephanus Gravesianus, 23.

Ontogeny, x.

Ooster, 90, 113.

Ophidioceras, 36, 47.

Ophioceras Jobnstoni, 144.

kridioides, 171.

raricostatum, 145.

Oppel, 85, 97, 109, 110, 121, 122, 126, 138, 144, 149,
150, 159, 160, 167, 175, 188, 196, 209, 213, 218.
Oppelia hecticus, 24.
steraspis, 51.
Organic Equivalence, viii.
Origin of Differentials, 48.

Floral Structures, 50 note.

Variations, according to Weissman, 43.
Orthoceras, 1, 13, 26, 34, 87, 39, 46.
Orthoceras crotalum, Hall, 35 note.

docens, Bar., 34.

fusiforme, Hall, 35 note.

politum, 11.

truncatum, 11.

unguis, 11.

Orthoceratide, 12, 13, 20, 25, 35, 86, 48, 49.
Orton, 168, 169.

Osterhornes Mts., 90, 93, 95, 96, 97, 100, 109,
Ostreade, 118.

Ovum (monoplast), 8.

Owen, Richard, 8.

| Oxynoticeran Branch, 214, 215.

Series, 40; 69, 104, 106, 107.

30

234

Oxynoticeras, 30, 33, 34, 47, 48, 54, 5D, (15. ( 7, 18;
80, 82, 83, 84, 101, 106, 107, 108, 109, 114, 116,
148, 214.

Oxynoticeras Aballoense, 220.

Buvigneri, 220.
Castagnolai, 216.
Collenoti, Geyer, 213.
Greenoughi, 69, 213, 214, 216, 218.
zuibali, 69, 83, 115, 214, 215, 218, 219.
Guibalianum, 218.
Janus, 221.
Lotharingum, 34, 51, 69, 78, 83, 112 note, 214,
216,218) 220,
Lymense, 69, 83, 102, 217, 218.
numismale, 103, 217.
Oppeli, 69, 70, 102 note, 103, 217, 221.
oxynotum, 21, 40, 46, 69, 83, 101, 102, 199, 214,
215,216, 218, 221,
Simpsoni, 69, 102, 217
Oxynotum Subseries, 106.
Oxynotus Bed, 107, 109, 111, 129, 201, 2138, 215.
Zone, 106, 107, 116.

Pachydiscus, 23.
Packard, 3, 43, 47, 52.
Paracme, x, 21, 107, 112.
Parisian Basin, 87.
Parallel Character of Differentials, 84.
Parallel Series, 27.
Parallelism, 22, 25, 27, 28, 48, 50, 53, 109.
Parthenkirchen, 93.
Pathological Species, 30.
Pavlow, 115.
Pelecypoda, 8.
Peltoceras athleta, 22, 42.
Pentacrinus Bed, 198.
Pentacrinus tuberculatus, 153, 155,
Perisphinctes, 24, 87.
Perisphinetes aberrans, 33.
Defranci, 24.
Peru, 86, 87, 115, 118, 151, 153, 169.
Petschora Land, 86.
Pettos Stock, 23.
Pfonsjoch, 122, 129, 134, 137.
Pforen, 168, 171, 197.
Phragmoceras perversum, 34.
Phylembryo, 8, note.
Phylloceras, 27, 122 note.
soblayi, 216.
Phymatoceras enervatum, 24.
Physical Selections, ix, 52.
Physical Surroundings, action of, x, 52 note, 53.
Physiological Equivalent, x.
Pictet, 33.
Pictetia, 24.
Piette, 123.
Piloceras, 12, 13, 52.
Pinnacites, 51, 80.
Placenticeras, 31, 32.

INDEX.

Placenticeras placenta, Meek, 31.

Planicosta Bed, 105, 209, 213.

Planorbide, 29, 30, 31, 78, 118.

Planorbis Bed, 57, 85, 90, 91, 92, 94, 104, 110, 114,

115, 116, 122, 129, 184, 197.

Planorbis Zone, 29, 90, 91, 92, 94, 104, 107, 108, 116.

Planulati, 42.

Plicatifera, 24, 42.

Plicatus Stock, 25, 54, 55, 57,

124 E22, 128;

Pliensbach, 210, 215.

Polar Homozoic Band, 87.

Poland, 86.

Polygenesis, 118.

Polyphylletic Origin of Forms, 31.

Popanoceras, 4, 5, 24.

Popanoceras antiquum, 4, 5, 23.
Kingianum, 5, 1238, 124.

Portlock, 164.

Portugal, 86.

80, 81, 88, 107, 112, 116,

Pouriac, 115.
Pourtalés, 121.
Primary Radicals, 3, 22.
Primitive Radicals, 3, 16, 52.
Primordialide, 51.
Prodissoconch, 8, note.
Progressive Characteristics, Genesis of, 71.
Progressive Forms, Morphogical Equivalence in, 21,
99
Progressive Series, 25.
Prolecanites, 3, 4, 5.
Prolecanitide, 4.
Pronorites, 4.
Protection, effect of, 47.
Protembryo, 8.
Protoconch, 1, 8, 11, 18, 14, 49.
Protozoa, 8.
Provence, 91, 118, 114, 116.
Psiloceran Branch, 120.
Psiloceran or Radical Stock, 54, 57, 71, 80, 81, 107.
Psiloceras, 5-7, 18, 22, 28, 34, 35, 52, 54, 56-60, 71-
73, 75, 78, 80, 84, 85, 89, 90, 92, 93, 101, 102,
113, 114, 117, 118, 120, 125-128, 131, 186, 137,
155, 195, 197, 215.
Psiloceras acutidorsale, 162.
aphanoptychum, 123.
Atanatense, 122.
Berchta, 123.
caleimontanum, 123, 124.
caliphyllum, 54, 55, 57, 85, 90, 112, 117, 122.
crebricinctum, 123.
(goc.) crebrispirale, 124.
(Megoc.) Portisi, 124.
cryptogonium, 123.
Hagenowi, Wih., 90. 93, 120, 123, 124, 174 note.
Kammerkarense, 123, 124.
longipontinum, Wih., 91, 98, 122,
majus, 1238.
mesogenos, 21, 75, 124.
megastoma, 96.

123.

INDEX.

Psiloceras Naumanni, 124.
(Aigoc.) Naumanni, 124.
pachydiscus, 123.
planilaterale, 196.
planorbe, 6, 22, 25, 37, 39, 41, 54-56, 58, 62, 65-
67, 78, 80-82, 85, 90-98, 112, 118, 115, 117,
121-124, 126, 136, 140, 142. 155, 156, 161,
163, 164, 195-197, 215.
planorboides, 89, 122.
pleurolissum, 75, 122.
pleuronotum, 123, 124.
polycyclum, 122.
polyphyllum, 123.
Rahana, 89.
sublaqueum, 123.
sublaqueum, Wah., 126, 147.
tenerum, Wih., 126.
Psiloceratites, 6, 72, 85, 89, 90, 93, 136.
Pteronautilus, 80.
Pteropoda, 8, 10, 16.
Ptychites, 5, 6.
Ptychoceras, 29.
Pulchellia, 23.

Pyrenean Basin, 87.

Quadragonal Whorl, 56, 77, 78.

Quedlinburg, 92, 137, 138, 146.

Quenstedtioceras, 23, 28, :

Quenstedt, vii, 1, 29, 32, 33, 87, 55, 58, 62, 83, 90, 91,
92, 93, 96, 98, 101, 105, 112, 118, 121, 123, 125,
128, 129, 131, 135, 187, 138, 189, 141, 143, 149,
155, 157, 158, 163, 167, 168, 169, 171, 177, 179,
180, 181, 182, 183,184, 185, 186, 187, 190, 192,
196, 197, 199, 200, 201, 209, 211, 216, 217, 218,
219, 221,

Radical Stock, 22, 24, 57, 85, 107, 112, 120.
Radicals, Acmic, 23.
Geratologous, 28.
Mesozoic, 22.
Primary, 3.
Primitive, 3, 16.
Retrogressive Forms, 28.
Secondary, 3, 22, 71.
Theory of, 21, 28.
Transitional, 3.
Raidwangen, 169.
Ramert, 170.
Raricostatus Bed, 103, 104, 106, 109, 146.
Red Car, 96.
Reineckia, 23.
Replacement of characteristics, law of, 44; in anagene-
sis, 74; in catagenesis, 78.
Residual Basins, 89.
Faunas, xi, 89, 106, 114, 116.
Retrogressive Characters, genesis of, 74; tendency to
inheritance of, 78.
Retrogressive Forms, morphological equivalence in,
28, 30.

230

Reynés, 102, 103, 153, 167, 176, 181, 185, 200.

Rhabdoceras, 28, 30.

Rhacophyllites, 122 note.

Rhetic, 28, 90, 103, 111.

Rhine, 113, 114.

Rhone, 87, 88, 91, 96, 98-101, 103, 106, 108, 111, 112,
188. .

Rhone Basin, 92, 96, 97, 102, 104, 106, 108, 111, 114—
1G; 213; 217.

Rinteln, 137.

Robin Hood’s Bay, 146, 170, 171, 201, 203.

Rollier, 90.

Romer, 92.

Rostrum, 29, 49.

Lotiformis Zone, 109, 134, 189.

Rudern, 121.

Ruffy, 122.

Rugby, 155.

Ruminantia, 27.

Russia, 87.

Russian Province, 86.

Ryder, viii, 43.

Salins, 90, 144, 157, 169, 184, 197, 201, 204, 214.

Sageceras, 4.

Sandberger, Guido, vii, 2, 14, 18.

San Francisco, 87, 173.

Sannionites, 13, 48.

Sadne et Loire, 87, 88.

Saulieu, 91, 121, 142.

Scaphites, 31, 32, 47.

Scaphites umbilicus, 34.

ventricosus, 32.

Scaphopoda, 10, 16.

Schaichhof, 191, 192.

Scheppenstadt, 191, 193.

Schlonbach, 92, 98, 101, 102.

Schloenbachia tricarinatus, 24.

Westphalicus, 24.

Schlotheimia, 5, 6, 7, 40, 44, 54, 58, 71, 73, 75, 80, 84,
93, 106, 107, 118, 114, 115, 118, 128, 125-127,
134, 185, 154, 157, 194, 201 note.

Schlotheimia angulata, 93, 94, 126, 128, 129, 182, 134,

196. :
angulata, Wah., 180, 184.
angulata, Zittel, 130.
angulicostata, Gey., 155.
angustisulcata, Gey., 135.
Boucaultiana, 94.

Boucaultiana, Wih., 21, 75, 183.
catenata, 7, 25, 40, 57, 71, 78,
div, 127,128, 13, 134/185;
catenata, Wah., 25, 58, 129, 134.

colubrata, 130.

comptum, 134.

Charmassei, 41, 94, 133, 134.
Charmassei, D’Orb., 182.
Charmassei, Wiih., 182.
donar, 128, 134.

75, 90, 94, 113,

236 INDEX.

a6

Schlotheimia D’Orbigniana, 94, 95, 133.
extranodosa, 154.
Geyeri, 135.
lacunata, 135.
Jacunatus, Gey., 135.
Leigneletii, 94.
Leigneletii, Wih., 132, 133.
marmorea, 134.
montana, Wih., 184.
Moreana, 93, 128.
pachygaster, 134.
posttaurina, 134.
Quenstedti, Gey., 185.
rotunda, 135.
scolioptycha, 134.
striatissima, 129.
Speziana, Can., 136.
trapezoidale, 134.
taurina, 134.
ventricosa, 128, 133, 134.

Schlotheimian Series, 57, 105, 106, 122.

Schliiter, 92, 94, 97, 98, 101.

Schwartz, 2, 14, 216.

Scipionis Bed, 108, 176.

Scotland, 88.

Secondary Radical, 3, 22, 71.

Seebach, 94, 114.

Selection, physical, ix, 52.

Semper, 8, 30.

Semur, 60, 91-93, 95-99, 102-105, 114, 121, 122, 129,
130, 132, 133, 135, 137-189, 141-146, 148, 156,
157, 159, 160, 162, 164, 166-169, 171, 175-179,
183, 184, 186-193, 195-198, 206, 208, 209, 211,
O12, 2iG, 210.

Senile Degeneration, 75.

Senility in Orthoceratites, 34, 35.

in Goniatitinee, 35.
less marked in ancient forms, 35.
in the individual described by D'Orbigny, 36.

Separation, Geographical, 27.

Sepioids, 18, 26, 48, 53.

Septum, 9.

Shaler, 46.

Sheaths of the Siphon (Endocones), 12.

Siebenburgen, 111, 159.

Silesites, 24.

Silphologie, 9 note.

Siphon, structure of, 11, 15.

collar of, 17.

changes in, during growth, 34.

funnels of, 13.

position of, 51, 52.

importance in ancient groups, Dl, oes

Siphonal cecum, 9, 13, 14, 19.

Solenhofen, 51.

Somerset, 92, 144.

Sorbonne, 137, 138.

South America, 86, 87.

Southeastern France, 102.

South England, ©8.

Southern Alps, 87.
South German Basin, 87, 94, 96, 97, 99, 101, 114, 118,
218.
South Germany, 88-102, 104, 107, 108, 113, 114, 116,
117, 121, 185,163,
Sowerby, 68, 121, 158, 178, 188, 206, 219.
Spain, 86, 108.
Specialization, causes of, 52.
Species, definition of, 56.
Spezia, 116, 154, 166.
Spitzbergen, 5 note, 86.
Spheeroceras, 23, 32.
Spheroceras refractum, 82, 47.
Spinifera, 23, 24, 42.
Spirula, 26, 52.
Stages of Growth and Decline, 14.
Stephani, 115.
Steinheim, 29, 30.
Steinmann, 86.
Stellaris Bed, 105, 109.
Stephanoceras bullatum, 32.
coronatum, 23.
Gervilli, 32.
microstomum, 82.
nodosum, 23.
platystomum, 82.
refractum, 32, 47.
Stephanoceras, Genetic Relations of, 32.
Stephanoceratide, 28.
Stonehouse, 215.
Street, 92.
Striaries Bed, 105, 203.
Struggle for Existence, 27, 38, 50, 53.
St. Thibault, 1382, 185, 142, 144, 212, 213.
Stur, 89, 109.
Stuttgardt, 182, 156, 158, 176, 182.
Suabia, 87, 89, 90, 118, 167, 180.
Subclymenia, 25, 26, 80.
Subnodosus, 188.
Suess, 90, 93, 95, 96, 97, 100, 109, 115.
Surroundings, action of, x, 52 note, 53.
Sutures, origin of digitations of, 50.
degeneration of, 57. :
persistence in degeneration, 83.
Sweden, 88, 115.
Swedish Basin, 88.
Swiss Alps, 114.
Switzerland, 87, 90, 93, 114.
Széklerland, 95, 110.

Tenia, 45, 47.

Taramelli, 115.

Tate,.95, 117, 123.

Temperate Homozoic Band, 87,
Tentaculites, 10.

Tertiary Radicals, 19, 22, 23, 107.
Terqueum, 91, 94, 103, 117, 128.
Teuchsloch, 203.

Teutoberger Wald, 97, 98, 101.

a

INDEX. Zot

Theory of Morphological Equivalence, viii, 21, 28.
Theory of Radicals, 21, 28.
Three Modes of Development, 37.
Thysanura, 45.
Thysanuriform larve, 9 note.
Tilibichi, 86.
Tingo, 153.
Tirolites, 24, 124.
Toulon, 114.
Tmegoceras, 125.
Tmegoceras latesulcatum, 125.
levis, 125.
Transitional Radicals, 3.
Trachyceras aon, 22 note.
Trigonoceratidee, 80.
Trocholites, 35.
Tropical Homozoic Band, 87.
Tropites, 22 note, 24.
Tropites Campigliensis, 154 note.
discretus, 154 note.
Jokeyli, 154 note.
ligusticus, 154 note.
subbullatus, 154 note.
ultratriasicus, 157 note.
Tuberculatus Bed, 102, 104, 105, 119, 144, 199, 213,
215.
Tuberculatus Horizon, 95, 98, 99, 100, 213.
Tiibingen, 94, 96, 101, 130, 132, 189, 143, 152, 158,
163, 179, 182, 191, 206, 214.
Tubularia, 45.
Turneri Bed, 159.
Turrilites, 28, 33.
Turrilites Boblayi, 31,
Coynarti, 31.
Valdani, 31.
Typembryo, 8, 14, 18, 49, 52.
Types, Cryptogenous, 117. -
Law of Evolution in, 16 note.
Tyrolites, 22 note.

Uhlig, 33 note.

Unionide, 118.

Unit of Classification, 55.

United States, 86, 87.

Uphill, 92.

Upper Bucklandi Bed, 81, 95, 98-101, 108, 105, 107,
108, 139, 165, 188, 197, 206.

Vaeck, 84.
Vaihingen, 152, 143, 156, 157, 176.
Vancouver’s Island, 86, 87, 118.
Variation, 87, 89.
Law of, x.
Origin of, 48. See also Cope and Differentials.
Veliger, 8, 14, 18.
Vermetide, 118.
Vermiceran Branch, 136,
Series, 61, 112.

Vermiceras, 33, 34, 48, 54-57, 59, 60, 65, 70 note, 72,
74, 75, 81, 82, 84, 95, 96, 106, 107, 1138, 114, 116,
136, 140, 146, 149, 151, 154, 156, 161, 162, 172.

Vermiceras Bonnardi, 158.

Bonnardi, Wright, 159.

Carusense, 141.

Conybeari, 21, 25, 61, 72, $1, 95,,96,.115, 150,
155, 157, 159, 160, 161, 166, 168, 172, 175,
188, 194, 209.

Hierlatzicum, 95.

ophioides, 72, 73, 81, 87, 156, 160.

spiratissimum, 57, 59, 61, 72, 81, 95, 96, 141,
147, 158, 159, 160.

prespiratissimum, 96.

Vienna, 86.

Von Buch, 29, 32, 49.

Von Jhering, 10.

Von Rath, 115.

Voleano, 172.

Vortices in Evolution, 108.

Vosges, 118.

Waagen, 4, 21, 27, 28, 33 note, 50 note, 51, 87, 88, 90.

Weehneroceran Series, 57, 58, 79, 93.

Wehneroceras, 7, 54, 57, 71, 80, 98, 118, 118, 120, 125-
127, 129, 181, 1384.

Weehneroceras anisophyllum, 127.

circacostatum, 58, 127.
curviornatum, 57, 58, 127.
diploptychum, 127.
extracostatum, 57, 127.
euptychum, 127.
Emmrichi, 21, 127.
(ZEgoc.) Emmrichi, 127.
Guidoni, 127.
latimontanum, 127, 201.
megastoma, 122, 127.
Paltar, 126.

Panzneri, 57, 127.
tenerum, 126.
stenoptychum, 127.
subangulare, 126,

Wihner, 6, 24, 57, 58, 60, 61, 85, 89, 90, 98, 95, 99,
108-113, 120, 122-124, 126-128, 184, 189, 140, 142,
147, 148, 1538, 154, 213.

Waldenburg, 188, 141, 144.

Wallegg, 89.

Waltzing, 157.

Warwickshire, 92, 155.

Watchet, 121, 157.

Westphalia, 88.

Western Alps, 114.

Western Europe, 56, 60.

Weissmann, 43, 44, 47, 49.

Wellershausen, 142, 144.

Whitby, 121, 146, 156, 166, 167, 169, 184, 197, 201, 204.

Whiteaves, 87.

Whitney, viii. ©

Wiesloch, 137.

i
Ht
i
i
i

238 INDEX.

Wiltshire, 88.

Winkler, 89.

Woodward, 155.

Wright, viii, 41, 59, 68, 92, 96, 98, 101, 102, 112, 113,
121, 135, 146, 155, 158, 159, 163, 164, 178, 180-
184, 186, 188, 201, 206, 209, 211, 213, 217-219.

Wiirtemburg, 123, 154.

Wiirtenberger, 2, 21, 24, 41, 42, 43, 61.

Xenodiscus, 8 note.

York, Museum of, viii.
Yorkshire, 88, 168.

Zeiten, 97, 149, 175, 188, 202, 204.
Zittel, vii, 4,7, 21, 82 note, 108, 113.
Zone of Amm. Burgundie, 91.
Amm. Liasicus, 91.
Autocthones, 89, 96, 106, 114, 118.
(See also Tables I.-V.)
Ziirich, 34, 197.

TABLE I.—Genealogy of the Arietide in the Basin of South Germany, after Quenstedt, Fraas, Oppel, and their Collections.

NOTE. —— Q. — Quenstedt, and O. = Oppel.

Middle Lias.

Oxyn. numismale
pe). Ves (pars) Q.
|

Qxyn. Oppeli
= oxyn. numismale (pars) Q.

Raricostatenbank,

or
Raricostatusbett.

Cal. raricostatum
as «

Oxynotenlager,

———— | —-—*-—- | —-

Schl. lacunata

or | Same
Oxynotusbett. Schl. rotunda Oxyn. oxynotum
l ms l
Ast. stellare
| | Ast. naar = obtusus suevicus Q. |
= “ ,
Turnerithone, | : | u
nai - sii: y, | | Ast. Brooki “Ast. obtusum |
= ey i = Turneri (pars) Same
| y | =capricostatus — 1
f Ast. Turneri = obtusus (pars)
| | = nudaries Q. = Smithi Q. |
| | a Scipionis : |
= Scipionianus
| | Same olifex Q. |
Zwischenlager, i
lagi 1 a, B, | | Same PO fet Ast. Turneri = Agas. nodosaries |
. s = compressaries = 7
Tuberculatusbett. { | = Turneri (pars) Q. = Turneri (pars) |
= obtusus (pars) Q.
( | , |
| fn. tardecrescens Arn. Bodleyi ipioni
| =] falearies (pars) = ceratitoides (pars) Q. — ase ee 4
| | =| densicosta Q. = geometricus O. - ie ee
Cor. bisuleatum Ast. acceleratum
| | =multicostatum Sow. Cor. trigonatum |
iid ok den. ‘ J : (not Quenst.) =nudaries
a i Ss : = sonra O cag a — — — mei a = Crossi Q. (not Wright) Ast. stellare Agas. striaries -_ - -
— “— Bucklandi | ig | ~~ not D’Orb. i | = on @ Arpad ais Bs "iia
: | Cor. Gmuen¢|2nse
l | | Cor. Sauzeanum «| O. ;
| Arn. kridioides = spinaries Q. \ Ast. obtusum = — — — — — — — — Same
| | | = kridion (pars) Cor. orbiculatum = "
| = Buck. carinaries Q. = Bucklandi (pars)
| | | | = sis macer
4 | | ; | Arn. ceras { | = : sone ia
— — —Cal. carusense Cal. sulceatum = ceratitoides (pars) Q. Mee ia |
| = latisul. longicella Q. | | |
Cor. lyra Cor. Bucklandi
Same | | | Same ticostatus : es (pars)

Arietenlager,

or
Bucklandibett.
= Lower Bucklandi
bed.

—

Schl. Charmassei
= ang. compressus gigas.
(pars) Q.

Angulatenbank,
or
Angulatusbett.

Schl. Leigneletii
=angl. compressus (pars) Q.

Schl. Charmassei
= angl. ow pipes (pars) Q.

Schl. angulata

4 = angl. depressus (pars) Q.

Schl. colubrata
= angl. Thalassicus (pars) Q.

Schl. catenata

|
Schl. striatissimus
es “

= striatus (pars) Q.

Cal. longidomus Q.

Cal. Deffneri
ae “ ‘6y

= planaries, Fraas

Verm. Conybeari
. oc

= Q |

Same |
= latisuleatus Q.

Arn. Hartmanni
= falcaries
=robustus Q.

= mul

“ previdorsalis

_——aee(OOr, coronaries
= “ Q.

ae «“
= sinemuriensis
= solarium Q.

Cor. rotiforme————_—_—<Cor. latum
ee «

= Buck. pinguis? Q.

costaries (pars)

Agas. levigatum
= striaries (pars) Q.

Cal. carusense
= laqueus (pars) Q.

Cal. laqueoides

Fraas

Verm. spiratissimum,
_— “

|
|
|
|
|

—— Arn, semicostatumi—— = —— Se
a “

—Cor. kridion
= kridion Ziet.
(not Quenst.)

Upper part of this is
the Laqueus or Cal-
oceras bed.

Psilonotenbank,

or
Planorbisbett.

;

= angl. Thalassicus (pars) Q.

Sclil. catenata
= ang. psilonotus
= “ hireinus Q.

Psil. longiy

= laqueus

Bonebed.

Gelbe sandstein.

i

Schl. striatissimus
= striatus (pars) Q.

yontinum
« i:
“ 0;
Ul

Gi Johnstoni

=i. plicatus (pars) Q.

=silonot.

Cal. Liassicum
=sironotus Q.

Cal. tortile
= laqueus (pars) Q.

Cal. laqueum

Verm. spiratissimum?

(pars) Q.

= laqueus (pars) Q.

P; planorbe var. plicatum
“ “ i;

NM

“

Psil. planorbe var. leve
= psilonot. EQ:

TABLE II.—Genealogy of the Arietide in the Basin of the Cote d'Or, after Collenot and the Collections at Semur, and Boucault’s Collection

NOTE. —— R. — Réynes, and Coll. — Collenott.

in Museum of Comparative Zodlogy.

{
'
Cal. nodotianum Cal. raricostatum Same? Ast. Collenoti
A (young.)
| i :
Birchii | | Verm. Conybearim—=Verm. Conybeari Same Same Cor. bisulcatum, SMe Sees Oxyn. Lotharingum
Le or ie a | var. planaries = Bréoni D’Orb. et R. sa =
uberculatus bed. “ Bonnardi O. = Bochardi = tenuarius R. ‘
U per ey of the —all the beds of the | = debilitatus Ast. Brooki ste
wer Lias. Lower Lias above Schl. lacunata | | = Landrioti R. Oxyn. nei =
the Upper Buck- | - = (pars) R.
landi bed. | Schl. Boucaulti- | | Ast. acceleratum Ast. Turneri = Guibalianus (pars)
ana | R.
| |
Oxyn. i
| | | Ast. stellare Ast. obtusum ; hag eee ee
| 3 | = pg 2 var. quadragonatum Same Same = Guibali (pars) R.
-
| | | [ ‘i Cor. bisulcatum | |
var. like Sauzeanum |
| | | | : : Cor. Gmuendense |
| | | = Isis R.
. Schl. Leigneleti Same sis |
| | | | Var. Bonnardi ———= Verm. Conybeari jaoeeoArn. Hartmanni Cor. Sauzeanum
Bucklandi bed = Conybeari R. = Conybearoides R. = manubrius R. = nodosus D’Orb. Cor. lyra Agas. striaries
ae andi | | | | ‘ = Crioceras Eryon R. = Gaudryi R. = Vercingetorix : |
= Upper Bucklandi b 4 ul : ,
sppe ; and named in part also = Terquemi R. |
| | | | Arnioceras in all forms as compressaries |
including Arn. mise- Quenst. Cor. rotiforme Same Agas. levigatum |
| | | | rabile and Arn. kridioi- = Dall Ere R - = Petri R.
| " des. (See Table V.) |
Same Same , : |
Bucklandi Zone. 4 | | |
| | | | |
I l
| | | | Cor. Bucklandi
oe = sinemuriense D’Orb.
| | | | —=Verm. ophioides i = Ausoniensis R.
u
| 7 usaaies | | Cor. rotiforme=——<Cor. latum
Scipionis bed. Schl. D’Orbigniana ‘ = Hehli (pars) R. |
= Lower Bucklandi 7 | | | | iMiesae Verm. Conybeari
bed. —-—- -—|- —- —- —- — — — — — Cal. carusense Verm. spiratissimum = Bouvillei
| = Scylla R. = Hettangensis =Rotator Cor. kridion Cor. coronaries Agas. Scipionianum—=——A gas. Scipioni
= Delmasi R. = Schlenbachii =Hehli (pars) R. = Hehli (pars) R. g Pp gas. Scipionis
| = Collenoti R.
|
[ , one cette
, > T
Cal. sulcatum
me Schl. Charmassei Schl. angulata Cal. Johnstoni Cal. carusense Verm. spiratissimum ——Verm. Conybeari
Angulatus Zone. { Angulatus bed. c | = Delmasi (pars) = Delmasi (pars) R. = Hettangensis (pars) (young.) Arn. falcaries — — — — — — — Cor. kridion? Agas. levigatum
Schl. striatissimum = Pirondii R. = Delmasi (pars) R- = Hettangensis (pars) R.
(bed not known.)
L |
( ‘
Schl. colubrata Psil. longiponti- Cal. Liasicum | |
Cal. lagueum

Liasicus bed.
= Caloceras bed.

num

Planorbis Zone. <

Pianorbis bed.

~~’

Cal. Johnst

Cal. laqueum

Cal. tortile

Schl. catenata
|

Psil. planorbe, var. plicat:

= Beauregardiense Coll.

= Burgundiz Mart.

Psil. planorbe, var. lev

1 ' ' f] ; ‘
: TABLE ITII.— Genealogy of the Arietide in the Basin of the Rhone, after Dumortier.
, e
: NOTE. D. = Dumortier. F
Middle Lias. Oxyn. Oppeli?
: = Oppeli D.
Cal. raricostatum
= Pellati Arn. Macdonelli
= armentalis = nodotianus D.
= viticola Cal. carusense
= vellicatus D. = Edmundi D. : Amm. tardecrescens D. .
of this formation is
Planicosta bed. \ Arnioceras (sp.?) not determinable.
= Raricostatus bed. = Oosteri D.
Ast. Collenoti
: = Cluniacensis D.
i Arn. miserabile
[ = Jejunus D.
f
T
Oxyn. Buvigneri
| = Buvigneri D.
i { Oxyn. Guibali
{ ce Oxyn. Lymense = victoris D.
! | = Saemanni D.
| Ver. Conybeari
| Oxynotus bed. ‘ Same. = Bonnardi? Arn. Bodleyi?
= re bed. D’Orb. & D.
4 : Oxyn. Simpsoni Oxyn. Aballoense
i = Oxynotum (pars) = ie D
a DB,
] Oxynotus Zone. {
i Oxyn. Oxynotum
i = Oxynotum (pars) D.
:
t
Same. Cal. raricostatum ! |
{ mas es D. : Oxyn. Guibalianum?
i | Cal. carusense i Arn. Bodleyi is as ray
; Ss is bed. ‘ = Landrioti D. = geometricus D. |
{ pa oe and Tu- 7” m ue ane | | Ast. stellare Seer De neh S ene s
berculatus beds. = . | é - = ne D. |
Ast. obtusum é |
| = oe,
| |
| | | ;
Schl. lacunata Cor. bisulcatum |
= lacunatus D. | | | = resurgens D. — — — —dAgas. striaries
_ = Davidsoni Same |
| | ie) Cor. bisulcatum : : = Berardi (pars) D.
Davi i bed : ie = multicostatum D. a
avidsoni bed. | | Same? Ver. Conybeari Arn. kridioides? 1 Cor. kridion Agas. levigatum
(Striaries bed). =“D. =debilitatus Rey. = Patti D. Cor. bisulcatum = Sauzeanus D. = Berardi (pars) D. |
= Upper Bucklandi | | | = Falsani (pars) D.
bed. = wie ace D. : |
| |
Arn. semicostatum Cor. Sa |
| | | = Hartmsoni Dy: = “« (pars) D.
2 |
" | Laas !
( ) | / Cor. Gmuendense
| | Arn. Bodleyi ee Es dD. |
| Ver. Conybeari? = geometricus D.
| | = ‘Ee Cor. lyra Cor. ——— Agas. striaries - - - Agas. Scipionianum |
= di Sa Chirmasees = a eS SS SS | Arnioceras (sp.?) = aureus = bisulcatus D. = Davidsoni ne * YD.
mote eee te «“ ~, | = Apnonldi D. = bisuleatas D. (pl. 2, not pl. 3) aoe |
: | (Arn. Hartmanni?) ? : (pl. 3, not pl. 2)
| — — Ver. spiratissimum? | | | |
= “ 2); Saree ; [ee Or. rotiforme Se ee af eae et an
| — ah es «9 D,
5 -
( ‘) |
| Unknown form 2
| = bisulcates (pars) D.
| ‘
Rettman, pie) ee eb aL, Sy cane ke Wake ae al accel | j- -—- — — — — — — Cor. kridion Agas. levigatum
Angulatus Zone. ; = Angulatus bed. = angulatus D. ; : ee << D), : = PP ey
|
epics |
L |
|
Cal. Johnstoni=——Psil. planorbe Jal. laqueus? | | 1 See Part II, p..174.
= “« — = AAD; = Burgundie D. : * ee ‘ ‘ : r
| | | 2 This is a form mentioned in Part I., p. 115, probably a species of
Liasicus bed Coroniceras, allied to Cor. kridion or rotiforme.
Planorbis Zone. 4 — Caloceras bed. r | : | | 3 The species of the Arnioceran series are arranged in line accord-
pega oe a em |G se Se: a RL es Nee tae nr, a Eeieea ny) 7 nar oem ing to the beds in which they occur. It was not\possible to trace the
genealogy accurately.
| \

TABLE IV. — Genealogy

of the Arietida in the Basin of England, after Wright and

W. = Wright, and B. — Blake.

various Collections.

Middle Lias.

Oxyn. memismale
= Amal. Wiltshirei
WwW.

Raricostatus Zone.
= “ bed.

Cal. aplanatum
= Ariet. tardecrescens
B.

Arn. Macdonelli

“c

Cal. raricostatum 1 = Amm.
Ww

= Ariet.

Cal. carusense

Portl.

= Ariet. nodotianus W.

Oxyn. Guibalii
|

Ast. Collenoti
= Megoc. Slatteri

es yas Leash Care ae | (pars) W.
Oxyn. Lymense
| | Ast. denotatum 2am. “~ W py so : er.
: Schl. = Arietta : ; = Amal,“ * 4
~ mg { <— "a w | | Same? ? = “* Collenoti Ast. obtusum Oxyn. Simpsoni |
a 2 (pars) W. = Arigtaete =Amal. “ W.
| | | : = Agoc. sagittarium
Ast. impendens = Slatteri Oxyn. oxynotum Amal. Guibalianum
| | | = cae : (pars) W. AMAL, ; ' Ww.
= “* Collenoti 1
| | (pars) W. | 1
| 1
f : Ast. stellare 1
| | = Ariet. “ W. te. uk ole oe
Obtusus Zone. | | | Same Same? |
= “ bed. Ast. obtusum- Agas. levigatum — — — — —
| | | a hipts W: Amn. Sow
= Amm. Smithi Sow. |
|
|
| |
Ast. Brooki
| | | = Ariet W: |
beter es ad | | Ver. Conybeari Same |
‘Tile ia oa ‘ = Ariet. Bonardi W. = geometricus W. Ast. Turneri Ast. ObtUSUM) nel
gi
| | = Ariet. “‘ |
L | | | | |
r ] |
Arn. Bodleyi Cor. bisuleatum Cor. Gmuendense | ee
| | | = Ariet. difformis B. = Ariet. subnodosus = Ariet. Crossi W. cc. “ie eo oe ee ee ionamin
= “ semicostatum (posit. uncertain) W. = Ariet. =
| 1 (pars) W.
Arn. Hartmanni
Upper | ; | | |
Bucklandi Zone. 4 Schl. Boucaultiana Arn. Ceras
4 “ bed. 3 “ Ww. | ,
Arn. tardecrescens l
| |
Arn. semicostatum———_«-Arn. falcaries Cor. Sauzeanum :
| | = Ariet.2 “ (pars) W. = Ariets 6 |
{ | | | |
r | | !
| | Cor. lyra
| —— -—| = Ariet. bisuleatus W. |
| Cor. Bucklandi
| =Ariet. “ W
|
Lower | | Cor. rotiforme Cor. Bucklandi |
Bucklandi Zone. 4 Schl. Charmassei Ver. Conybeari | = Ariet. “ (pars)W. = Ariet. sinemuriense
= “ bed. | == Aigoe. “= | == Aliens. ** OW, | B. |
|
| | 7 | |
| Ver. spiratissimum j—- -—- — a a ae ee eee |
[ (position uncertain)
| |
f sate |
Ariet. Conybeari B.
Schl. angulata | | H .
= Higoc. “ Cal. laqueum 4
| | i
on ao Schl. colubrata | '
as ved. 4 = &goc. morianum W. Cal. liasicum
a, ane “4 aa zone = JEgoc. laqueolus W. | i
oe | Schl. catenata
= goc. “ W. Same Same ————Cal. Jaqueum |
: 4 == /Egoc. intermedium (pars)
= * Belcheri (pars) W. |
= Amm. intermedium Portl. |
|
Cal. Johnstoni Cal. tortile | .
= Hgoc. “ = Zgoc. intermedium | 1 May also occur in Oxynotus Zone, according to Wright.

Planorbis Zone. y,
= bed.

= Belcheri (pars) ad

Psil. planorbe var. lev
“ac Ww

= ZEgoc.
= Amm.

| (pars) W.

4 Sow.
erugatus Bean.

Psil. planorbe var. plicatum
= Amm. Johnstoni (Authors).

| 2 See Wright’s Plates, pl. 6, figs. 2 and 3.

3 The lines connecting the species of Arnioceras indicate

genetic bonds only in a very general way. The true succes-

sion of the forms is not given in this part of this table.

TABLE V.— Genealogy of the Arietide in the Province of Central

Europe.

Henleyi bed.

Oxyn. numismale

Same

Bes

Ibex bed.

MIDDLE LIAS.

Jamesoni bed.

Oxyn. Oppeli

Vai ta eee Pe

Same

LOWER LIAS.

nN

E

J)

Cal. aplanatum
Raricostatus bed. | Arn. jejunum Same? Arn. Oésteri Ast. Collenoti
2] : P Arn. Macdonelli '
m Same Same Same
= 4 Oxyn. | BR
a Ast. denotatum Oxyn. Lymense és
wm Schl. Same Same Same Same? xyn. Buvigneri
Re} a Cayenne He rotunda Same Same Oxyn. Simpsoni
1 Oxyn. Guibali Oxyn. Aballoense
- =| J Oxyn. oxynotum
Ps 5 4 L | | Oxyn. Greenoughi
of | f
tk | { | Cal. raricos- a Pape
< 4 Same tatum
= Ceepey Hae. 4 Same | Same Ast. impendens——_——Same Same Same Same
oO i
= 4 { 3 |
<
oa f Same
Tuberculatus bed. J Same | | Same Same Same Same Agas. nodosaries
Ast. Brooki Ast. Turneri ———=Same Same
: | | |
[ f ge.
Schl. Boucaultiana | Arn. Bodleyi
| Schl. lacunata | ;
a : Cor, trigonatum Cor. Gmuendense
= Dae meer iandi Schl. Leigneleti —- ——| | Same Same | I Cor. orbicu- Ast. stellare==Ast. accele-
es oe Cal. Nodotianum Same Cor. lyra latum ! Ast. quadrago- ratum
- Geometricus bed. Gute l l arin
S Same |
nD | Same | Ast. obtusum Same
<
BE 4 : 1
Bucklandi Zone. Cor. Bucklandi |
io
O | Cor. rotifor Cor. latum |
i | Same=——=Verm. ophioides —_| ; ‘
so Lower Bucklandi | Agas. stri—Agas. Scipionianum—'
- bed. | | Arn. tarde- Arn. ceras Arn. Hartmanni dioides Cor, bisul- ---Cor. Sauze-===Same Cor. coronaries
rs) Same Same Cal. Deffneri crescens |
< Same | Cal. tortile? Same Same | |
(England) Cal. longi- | |
| domum | Same Arn. obtusiforme Same \ al Rte Teal i a, la
L L | | | :
if ve | |
Schl. Leigneleti | | | |
| Cal. laqueoides | | |
Pe Schl. Charmassei | Cal. sulcatum —_— Cor. kridion
-~ | Angulatus Zone. + Angulatus bed. | | i . | | |
= | Cal. car Cal. laq Verm. spiratissi--—- Verm. Conybeari Arn. miserabile ? ------- Arn. semicos
Bee Schl. angulata —_—_— | | tatum
5 ; Same — — —
a Schl. colubrata |
|
= | a !
=a Cal. Liassicum |
~ Caloceras bed. Same Psil. longipon- Same Same Cal. laqueum - -- Verm. spiratissimum? Psil. Hagenowi
Mee he tinum |
a 4
ae | |
Z
- Schl. catenata Cal. John Cal. tortile | |
a : stoni |
o 3 ; |
= Planorbis bed. Z
|
3 . )
= ba
2S Same ——= Psil. planorbe, var. plicatum Psiloceras planorbe, var. leve
q
—

Bone bed.

Psiloceras planorbe, var. leve

(So. German basin)

_—.

TRIAS.

{

(
|
Rhetic Zone. 4
L

Gelbesandstein.

a Sey ee

Schl. striatissima (questionable)
(So. German Basin).

1 This occurs, according to Quenstedt, in
the Lower Bucklandi bed.

ty

- TABLE VI.— Genealogy of the Arietide® in the Mediterranean Province, after Hauer, Neumayr, Wahner, Mojsisovics, Herbich, Giimbel, Geyer, and Rothpletz.

; Arn. Bodleyi? Hy. ~
. Amm. “ Giimb.
Arn. falcaries? Hy.
Amm. “ Giimb.
Arn. ceras Hy.
Amm., “ Hauer a
Arn. tardecrescens Hy. Y
Amm. Hauer
Arn. semileve i. eenae P ‘“ t
: Amm. “ auer or. Gmuendense’? Hy.
ees ‘ f Ar. “Geyer Ar. uh Rothp. Ast. Collenoti Hy.
ey Amm. difformis (pars) Hauer Oxy. “ Geyer
eckenmerge., 4 % Oxy. Janus Geyer
= Upper Bucklandi to Arn. Suessi Hy. Amm. “ Hauer
Raricostatus bed. Sch. angustisulcata Geyer Cal. suleatum Hy. Psil. “ Geyer Cor. young
Amm. Nodotianus Hauer Amm. “ Hauer Ar. sp. ind. Geyer Oxy. Greenoughi Hy.
: pl. iii. fig. 15. Ast. Brooki? Hy. Amm. “ Hauer
Sch. Geyeri Hy. Cal. carusense Hy. Cor. Hungaricum Hy. Ar. r Rothp.
Amm. Liasicus Hauer Arn. abnorme Hy. Amm. e Hauer Oxy. Guibalianum Geyer
Sch. lacunata Geyer Pail. hig Geyer Amm. oxynotus (pars) Hauer
Cal. doricus Hy. Ast. stellare Hy.
Ar. “Geyer Arn. cuneiforme Hy. Cor. bisulcatum? Hy. Ar. “Geyer Oxy. Lymense Hy.
Ar. Quenstedi Geyer Amm. < Giimb. Amm. oxynotus (pars) Hauer
Sch. tenuicostata Hy. Cal. Haueri Hy. dwarf Verm. Hierlatzicum Hy. Ar. ambiguus af
ea eA Herb Ar. sp. ind. Geyer pl. iii. Amm. « Hauer. Ar. ampliceres 4
f fig. 16 Ar. © Geyer. ’ Cor. Bucklandi Hy. Agas. levigatum Hy. Ast. obtusum Hy. Oxy. oxynotum Hy.
Tme. leve Hy. Cal. Haueri? Hy. var. sinemuriense? Amm.abnormis Hauer Amm. stellaris Hauer Oxy. x Geyer
=Ar. Geyer Amm. “ Giim. Arn. miserabile? Hy. Amm. Bucklandi Giimb. Cym. globosus Geyer
Sch. Charmassei Hy. Amm. euceras ‘ Amm. “ Giimb. Amm. levigatus Giimb.
== Am: 1/* Hauer
[ Sch. posttaurina Sch. aff. ventricosa Wih.
Wih.
Cor. bisulcatum Hy.
Amm. multicostatus Hauer
Enzesfelder-Kalk, Sch. colubrata Hy. Cal. suleatum Hy. Verm. Conybeari Hy. .
Rotiformis bed, 4 i i x : Amm. Nodotianus Hauer Amm. a Hauer Cor. rotiforme Hy.
PST oa ce Risk lanth bod: Amm. moreanus Sch. scolioptycha Sch. ventricosa Wih. ‘I'me. latesulcatum Hy. Cal. ophioides Hy. | Amm. Hauer
Hauer Wah. = Amm. ee Hauer Ar. ee Wih. Cal. salinarium Hy Cal. carusense Hy.
| Amm. “ Hauer Amm. spiratissimus Hauer Cal. laqueum var. Scylla Hy.
Amm. Liasicus Hauer Ar. . tt Wih. Cor. kridion Hy.
| 2 Amm. “ Hauer
|
Weh. Emmrichi Wah. sp.? |
Weh. Guidoni big d: | $ Ast. stelleforme Hy.
- Ar. 4 Wah
Sch. marmorea Weh. diploptychum “ “ |
- Wah. Sch. trapezoidale Cal. abnormilobatum Hy.
Wah. Weeh. latimontanum “ “ | Ar. ss Wah.
| ] Cor. kridion? Hy.
Weh. stenoptychum “ “ | Amm. “ Mojsis.
Sch. pachygaster | Cal. Grunowi Hy.
Wah. Weh.euptychum “ “ | Cal. Castagnolai Hy. Ar. Ke Wah. .
| eee en AT. € Wah.
| eh. anisophyllum “ “ Cal. supraspiratum Hy.
nl tobe el i | I Psil. Kammerkarense Wih. | Ar. ae Wah. Cal. centauroides Hy.
= Angulatus and : 4 Weh. haploptychum “ “ | l Cal. Deetzkirchneri Hy. Ar. na Wah.
Caloceras beds. | [ Cal. nigromontanum Hy. Cal. perspiratum Hy. = Aw fs ah. FO
Weh.curviornatum “ “ Pgil.calcimontanum ‘“ | => Aes ef ah. Ar. Wah. I Cal. prespiratissimum Hy.
: ! Cal. cycloides Hy. Ar. 2 Wih.
. Sch. angulata Wah. Weh. circacostatum “ “ Psil. pleuronotum . | unnamed Cal. fig. 5, pl. xvii. Cal. Coregonense Hy. =Ar. “ Wah. Cal. latecarinatum Hy.
Sch. extranodosa var. undetermined.} i Wah. Ar. “ Wa I Ar. " Wah.
Wah. Weh. Panzeri « —« Pgil. aphanoptychum “ | Cal. Seebachi Hy. I Cal. gonioptychum Hy.
wi ee . Ar. bid Wah. Cal. Haueri = = Ar. td Wih. |
eh. Frigga « « Psil. Berchta i il. ah. Cal. Hadroptychum Hy. Ar. ul eum.
Sch. Donar Wah. Sch. taurina Wah. | . | | Pal reese. ae ie —" wih. Cal. tone Hy. | Cal. ae i Hy.
Psil. crebricinctum Wih. Psil. Atanatense “ Ar. « Wah. = Ar “* Newum,
; | Weh. Rahana “ & Psil. polyphyllum “ 1
Sch. montana Wah. | Psil pleurolissum “ Cal. Johnstoni Hy. Cal. Liasicum Hy. Cal. orthoptychum Hy.
| Weh. Paltar «+ Psil. pachydiscus «“ — Psil. sublaqueum Wah. ‘ | Ng, “O Wah. Ar. ey ah. = An. e Wih.
| Psil. polyeyclum “
|
| |
Sch. angulat?® —e — Psil. Gernense Wah. Cal. Johnstoni Hy. Cal. Sebanum Hy.
Eg. iP Neum. Eg. « Neum.
Peil. planorboides Wah 1 This variety is figured in Mojsis. et Neum., Beitr., IV. pl. xx. fig. 5, and
Sch. catenata Wah. Psil. majus Wah. = Eg. “ pet is, we think, a distinct species.
Planorbis bed. 4 = Mg. angulatum (pars) Neum.
= Hg. subangulare Neum. et Wah. 2 List of Wehneroceras was so long that I could not use customary nomen-
l Psil. ecryptogonium Wih. Psil. Hagenowi Wah. clature, and have referred each species to the describer of the species instead of
=e i Neum. Amm. “ Dunk. the describer of the genus
Psil. planorbe Hyatt 8 .
=e. -Neum;
Psil. caliphyllum Wah
L = &g. # Neum.

EXPLANATION OF PLATES.

ALL specimens not otherwise described are in the collection of the Museum of
Comparative Zodlogy, and all not mentioned as “casts” have the shell present, either
in part or as a whole. Paul Roetter drew the figures in outline by measurement; the
author redrew all the specimens using these outlines, but testing the accuracy of the
measurements before they were finally placed on stone. The outlines in the Summary
Plates were sketched by the author, and redrawn by Miss Pierson. Unless otherwise
specified, the figures’ are approximately of natural size, although the process of reducing
by photography from the enlarged drawings has introduced some slight deviations from

the measured diameters of the originals.

PLATE I.

Psil. planorbe. Fig. 1, cast with incomplete living chamber, showing folds at an early
stage of growth. Fig. 2, suture much enlarged. Loc. Whitby. Fig. 3, 4, cast with similar
folds in the young, but smooth in the adult. Fig. 4a, young of Fig. 4 enlarged. Loc. Neuffen.
Fig. 5, 6, cast of the more involute variety, loc. Balingen, The specimen has distorted sutures,
showing the broad abdominal lobe and the large median saddle on one side, but is otherwise
normally formed.

Cal. Nodotianum. Fig. 7,} specimen reduced to less than one half, showing incomplete
living chamber. Fig. 8, sutures enlarged. Fig. 9, a fragment of a cast showing sutures and.
part of living chamber. Fig. 10, section of four whorls. Fig. 11, acast. Fig. 11a, section of
last whorl. Loc. Semur.

Cal. tortile. Fig. 12, specimen with portion of living chamber. Tig. 13, same, portions
of the two outer whorls removed, showing their rounder outlines. Fig. 14, suture of same,
enlarged. Joc. Semur.

Cal. carusense.? Fig. 15, cast of the younger stages, broken out of the interior of an
adult specimen, loc. Balingen. Fig. 16, cast, loc. St. Thibault.

Verm. spiratissimum. Fig. 17, cast, living chamber incomplete, loc. Nellingen. Fig. 18,
specimen with distinct channels, developed at an early age, loc. Semur. :

Cal. sulcatum. Fig. 19, specimen with incomplete living chamber, showing the smooth
young in the centre. Fig. 20, suture of the same, enlarged. Loc. Semur.

Verm. ophioides. Fig. 21, cast of a broken specimen, showing the well developed chan-
nels and keel in the young, and the early appearance of the pile. Figs. 22, 23, sutures of this
and an older specimen, enlarged. Loc. Semur.

Cal. raricostatum. Fig. 24, specimen, showing the senile metamorphoses. Fig. 25,
section of last two whorls, showing the corresponding change of form for comparison with
Fig. 25a, the adult of the same variety.’ Loc. Balingen.

1 This figure is not numbered. 2 See Plate II. Fig. 1.
8 See Plate VI. Fig. 15, for the Johnstoni-like variety.

GENESIS OF THE ARIETIDAE, PLATE |.

ROETTER & HYATT, DEL. HELIOGRAPH, HART & VON ARX, N.Y,

PLATE II.

Cal. carusense.! Fig. 1, specimen reduced to one third, showing incomplete living cham-
ber and old age. Tig. 2, the same broken so as to show sections of the old whorls and the
depressed abdomen of the adult stage. Fig. 3, enlarged adult sutures, also shown on Fig. 1.
Fig. 3a, same, but very old, also shown on Fig. 1. Loe. Semur,

Arn. miserabile. Fig. 4, large smooth specimen, with sutures and incomplete living
chamber. Fig. 5, cast with sharp abdomen and gibbous sides, living chamber incomplete.
Fig. 6, enlarged sutures of the same. Fig. 7, var. cuneiforme, with incomplete living chamber.
Loe. Semur.

Arn, obtusiforme. Fig. 8, section of a cast, showing form of internal whorls. Fig. 9,
specimen with incomplete living chamber. Fig. 9a, enlarged sutures of fig. 9. Loc. Semur.

Arn. semicostatum. Fig. 10, variety with incomplete living chamber, the young remain-
ing smooth until a late period of growth and ribs immature, loc. Semur. Fig. 11, cast, with
ribs earlier developed than in Fig. 10, and slightly more prominent. Fig. 12, young from
same blocks of limestone. Fig. 13a, sutures from other young specimens on the same block,
of different ages, all natural size. Loc. Whitby. Fig. 14, cast with folds in the extreme young
stage and true pile beginning afterwards; otherwise the form is perfectly normal, loc. Basle.
Fig. 15, normal variety with deep channels. Fig. 15a, suture of the same, enlarged. Fig. 16,
specimen with incomplete living chamber, channels developed at an earlier age than in normal
variety, and abdomen broader and flatter in proportion than is usual in the species at any age.
Loc. Semur.

Arn. Hartmanni.? Fig. 17, cast, loc. Bonnert. Fig. 18, suture of the same, enlarged.

Arn. tardecrescens. Fig. 19, cast of a young specimen with incomplete living chamber.
Fig. 19a, enlarged suture. Loc. Yorkshire.

Arn. ceras. Fig. 20 and 20a, specimen with incomplete living chamber, a very broad
abdomen, and deep channels, loc. Semur.

Arn. tardecrescens. Fig. 21 and 22, sutures of a specimen of a normal form (abdomen
narrower than the last), at the diameters of 63 mm. and 83 mm. Loc. Semur.

Arn. Bodleyi. Fig. 23, broken specimen, showing planorbis-like folds on the young shell,
with living chamber incomplete. Fig. 24, more involute variety with similar fold in the young
and incomplete living chamber. Fig. 24a, suture of the same, enlarged. Loe. Semur.

Arn. falearies. Fig. 25, young with slight tubercles on the genicule. The last quarter is
part of the living chamber. Fig. 26, larger specimen, ribs not tuberculated or arising from
tubercles as in the above, and keel very prominent. Fig. 27, cast with deep channels and abdo-
men very narrow. Loc. Semur.

Arn. kridioides. Fig. 28, specimen showing the smooth young, the early period at which
the pile begin, and the similarity of the umbilicus to that of a normal species of Arnioceras.
Loe. Basle.

1 See Plate I. Fig. 15, 16. 2 See Pl. Til. Fig. 1, 1a.

GENESIS OF THE ARIETIDAE.

PLATE Il.

oe Nf woe
- tf ar el

Sa!

E ATT, DEL.
ROETTER & HYATT, HELIOGRAPH, HART & VON ARX, N. ¥

PLATE III.

Arn. Hartmanni.' Fig. 1,1, cast. Fig. 1 shows the thick shell lying on the keel of

the cast. Loc. Lyme Regis.

Cor. kridion. Fig.2, young. Fig. 2a, outline of young suture of Fig. 2, enlarged. Fig. 3,
cast. The last volution in this represents the living chamber. Loc. Balingen.

Cor. rotiforme, var. A. Fig. 4-4a, young smooth stage and suture. Fig. 5, 6, 8, 8a—10,
10a, older stages of same. Fig. 7, 11-13, pathological cases with pile crossing the abdomen.
Loc. Semur. Fig. 14, 15, 15a, 16, kridion-like variety of this species. (Fig. 14, loc. Stuttgardt ;
Fig. 15, 16, loc. Balingen.) Fig. 17, 17 a, variety with discoidal form and large tubercles, figure
reduced to about two thirds, loc. Semur. Fig. 17 b, sutures.

Cor. Bucklandi, var. sinemuriense. Fig. 18, figure reduced to less than one half, show-
ing the divided pile of the young (sinemuriense stage), and the solid Bucklandian pile of the
adult, loc. Semur.

Cor. latum. Fig. 19, young with narrow abdomen. Fig. 22, older stages of same variety,
showing affinities for Cor. rotiforme and Bucklandi. Fig. 20, section of young of variety with
broader abdomen. Fig. 21, 23, 23a, older stages and suture of same. Loc. Semur.?

1 See Plate II. Fig. 17.
2 These specimens all appear to be in the nealogic stages of development.

GENESIS OF THE ARIETIDAE, PLATE Ill.

ROETTER & HYATT, DEL, HELIOGRAPH, HART & VON ARX, N.Y.

PLATE IV.

Cor. lyra.! Fig. 1, young of variety with broad abdomen and closely arranged pile.
Fig. 2, young of var. B, with narrower abdomen and rounded sides. Fig. 3, older stage of same
variety. Fig. 4, 5, nearly full-grown stage of same variety. Loc. Semur. Fig. 6, 7, full-grown
stage of variety with narrower abdomen, flattened sides, and closely arranged pile, figure
reduced to about one half, loc. Filder. Fig. 8, young of same variety as Fig. 1, but transitional
to var. B. Fig. 9-11, young of var. C. Fig. 11a, suture of same. Fig. 12-14, young of variety
like Fig. 1, 1 a, and Fig. 8, but with narrower abdomen and more flattened sides. Loe. Semur.
Fig. 15, 16, cld specimen of var. C, with very convergent sides, and tubercles considerably
reduced, diameter 250 mm., loc. Gmiind. Tig. 17, sutures on the inner side (dorsum),? loc.
Semur. 4

1 See Plate V. Fig. 1-3. 2 All the specimens figured were casts.

{

|

PLATE IV.

HELIOGRAPH, HART & VON ARX, N.Y.

GENESIS OF THE ARIETIDAE,

ROETTER & HYATT, DEL.

|
|
|
|

PLATE V.

Cor. lyra.’ Fig. 1-3, half-grown shell of same variety as Fig. 6, 7, Plate IV., showing how
narrow the abdomen is in some specimens before the shell was full grown. Fig. 3a, suture,
slightly older than that delineated on Fig. 2, showing the changes which had taken place. Loc.
Semur.

Cor. Gmuendense.’ Fig. 4, half-grown specimen, exhibiting variety with discoidal form
and compressed whorls, figure reduced to less than one half. Fig. 5, full-grown specimen of
same variety with marks of approaching old age upon the last whorl, figure reduced to less than
one half. Loc. Semur. Fig. 6, specimen in which the wider abdomen and young proportion of
Fig. 4 were maintained until a much later stage than in Fig. 4 or 5, figure reduced to about one
half. Fig. 7, umbilicus of Fig. 6, about natural size, to show the smoothness of the young
whorls, Loc. Aargau. Fig. 8, 9, same variety as Fig. 5, but showing the effects of senile

decline in the convergence of the sides, degeneration of the pile and tubercles, diameter
205 mm., loc. Semur.

' See Plate IV. 2 See Plate VI.

GENESIS OF THE ARIETIDAE. PEALE ¥.

ROETTER & HYATT, DEL, HELIOGRAPH, HART & VON ARX, N.Y,

PLATE VI.

Cor. Gmuendense. Fig. 1, 2, figures reduced to about one third, taken from a specimen
which exhibited compressed whorls and convergent sides at an older stage than in the specimens
figured on Plate V. Old age is apparent also in the two closely approximated sutures of outer
whorl. Loc. Aalen.

Cor. trigonatum.’ Fig. 3, large variety, having stouter and more numerous whorls, and
arriving at the same stage of senile decline later than in the smaller variety described in the
text, figure reduced to about one third. Loe. Aalen.

Cor. Sauzeanum.? Fig. 4, young, loc. Whitby. Fig. 5, another older specimen, loc.
Semur. Fig. 6, another specimen, broken across, showing embryo, and having keel just begin-
ning to be perceptible on the outer whorl. Fig. 7, centre of same section enlarged, showing
young whorls. Fig. 8, specimen like Fig. 12, in having no keel on the outer whorl. Fig. 9,
variety in which both tubercles and keel appear at an earlier stage. Loc. Whitby. Fig. 10, 11,
same variety, showing stouter form of young and earlier developed keel. Fig. 12, 13, D’Or-
bigny’s type, showing the prolonged duration of the smooth stage, and absence of the keel.
Fig. 14, adult of var. Gaudryi. Loc. Semur.

Cal. raricostatum.’ Fig. 15, Johnstoni-like variety, loc. Balingen.

1 See also Plate VII. Fig. 1, for side view. 2 See Plate VIII. Fig. 1-3.
3 See Plate I. Fig. 24, 25.

| Hi
|
GENESIS OF THE ARIETIDAE. PLATE VI. |
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ROETTER & HYATT, DEL. ih

HELIOGRAPH, HART & VON ARK, N. Y.

liaise iaataaaes ee inns

PLATE VII.

Cor. trigonatum. Fig. 1, old specimen of the stout variety, showing adult suture and the
closer approximation and degenerative changes in lobes and saddles in old age, figure reduced to
about one third. Loc. Aalen,}

Cor. bisulcatum. Fig. 2-4, young. Fig. 5, 6, young with earlier developed and more
prominent pile. The coarse heavy pile of the last figure are remarkable, and the young has
also a broader abdomen and a form like an older stage of Cor. latum. Fig. 7 shows the decrease
in breadth of the abdomen with age, which is also seen in Fig. 6. Fig. 8, older stage, with
suture. Fig. 9, 10, nearly full-grown stage of same variety. Loc. Semur.

Agas. Scipionianum.? Fig. 11, 12, young of gibbous variety. Fig. 13, 14, young, show-
ing development of pile from folds. Fig. 13a, 14 a, enlarged sutures also indicated upon
corresponding figures, Fig. 15, front view of same specimen as that of Plate X. Fig. 13.
Loc. Semur.

1 See, for ventral view of same, Plate VI. Fig. 3.
? See Plate X. Fig. 11-13. Summ. Pl. XIIL BIB, fs

PEATE. Vi.

HELIOGRAPH, HART & VON ARX, N. Y.

GENESIS OF THE ARIETIDAE,

ROETTER & HYATT, DEL,

PLATE VIII.

Cor. Sauzeanum.! Fig. 1-3, var. Gaudryi, older and younger whorls of the same speci-
men, loc. Leicestershire. Fig. 3a, dorsum showing sutures.

Aster. obtusum.? Fig. 4, 5, young of var. H, showing large tubercles and broad abdo-
men. Fig. 6-8, older stage of same specimen. Loc. Lyme Regis.

Agas. levigatum. Fig. 9, side view of var. B, with living chamber. Fig. 10, var, D, sec-
tion showing the extremely broad young and secondary helmet-shape of the later whorls, which
are like those of Psiloceras except of course in the keel (the outline of the centre is uncer-
tain except as regards the breadth). Fig. 11, var. A, showing the absence ofa keel. Fig. 12,
var. D, showing outline of aperture and living chamber, loc. Semur. Fig. 13, very stout young,
showing the goniatitic form, and striations like those of Agas. striaries. Fig. 14, section of

variety from Lyme Regis.?

1 See Plate VI. Fig. 4-14. 2 See Plate IX. Fig. 1.
3 All these figures are enlarged about two diameters, except Fig. 9 and 12, which are about natural size.

GENESIS OF THE ARIETIDAE. PLATE Vin,

ROETTER & HYATT, DEL. HELIOGRAPH, HART & VON ARX, N, Y.

2 ms e ist . ee ss seca Mier ere pices = soe st

PLATE IX.

Aster. obtusum.! Tig. 1, var. D, loc. Lyme Regis.

Aster. stellare. Fig. 2, 3, figures reduced to about two thirds, loc. Tiibingen.

Aster. acceleratuin.? Fig. 4 shows variety having the nearest approximation to Aster.
stellare. The section is similar to that of Fig. 9, but is more involute. Loc. Semur.

Aster. Brooki. Fig. 5, 6, stout-whorled, broad-abdomened variety, approximating to
Turneri, but with broader sides at the same age. Fig. 7, older stage of the same variety.
Figures reduced to about two thirds. Loc. Lyme Regis.

Aster. Turneri. Fig. 8, 9, old specimen, figures reduced to about two thirds, loc. Semur.

Aster. Collenoti.® Fig. 10, young, showing compressed form and acute abdomen.
Fig. 10 a, b, the same more enlarged, but the figures fall short in depicting the acuteness of the
abdomen, and by improper shading show a keel which has no existence. Fig. 11, young and
older stage; the young are again too rounded, the outer whorl is however approximately accu-
rate. Fig. 11a, b, centre of same more enlarged, showing the involute form of even this early
stage, but the front view is not sufficiently compressed. Loc. Semur.

Agas. Scipionis. Fig. 12, 13, lateral and sectional view of young, loc. Semur.

Agas. striaries. Tig, 14, 15, variety with flattened sides and broad abdomen, loc. Semur.

1 See Plate VIII. Fig. 4, 8.

2 The umbilical shoulders are not made abrupt enough in this figure, and the umbilicus is shallow as in Aster.
stellare, instead of being deep as in this species. See Plate X. Fig. 3,

8 See Plate X. Fig. 10.

GENESIS OF THE ARIETIDAE. PLATE IX.

ROETTER & HYATT, DEL. HELIOGRAPH, HART & VON ARX, N, ¥.

PLATE X.

Aster. stellare.1 Fig. 1, 2, drawn from a sketch of a specimen in the Museum of Stutt-
gardt, 450 mm. in diameter, showing extreme modifications in old age, loc. Géppingen.

Aster. acceleratum. Fig. 3, drawn from sketch of specimen in Museum of Stuttgardt,
258 mm. in diameter, showing premature senility, loc. Balingen.

Oxyn. oxynotum. Fig. 4, 5, young of striaries-like variety, magnified twelve times, loc.
Balingen.

Ast.impendens. Fig. 6, young magnified four diameters. Fig. 7, abdominal view of
same, showing the early age at which the convergent sides, deep channels, and prominent keel
are developed. Fig. 8, 9, older stage of same specimens. Loc, Semur.

Aster. Collenoti2 Fig. 10, full-grown specimen, natural size, showing ribbed young, loc.
Champlony, near Semur.

Agass. Scipionianum.’ Fig. 11, 12, var. spinaries of Quenstedt, loc. Gmiind. Fig. 13,
older specimen of same variety, with more compressed whorls and less prominent tubercles, loc.
Semur.

Oxyn. oxynotum. Fig. 14, abdominal view of young with part of whorl removed, mag-
nified three diameters. Fig. 15, same specimen when whole. Loc. Balingen. Fig. 16, young
with prominent pile and keel, loc. Gloucester. Fig. 17, young in the Museum of Stuttgardt,
showing absence of the keel until a late stage of growth, and exhibiting similarity to the
adult of Agass. levigatum and striaries. Fig. 17 a, suture of same enlarged. Fig. 18, ordinary
aspect of the young. Fig. 19, pathological case with crenulated abdomen, like the margaritatus
forms. Fig. 20, young of a variety, with folds on the abdomen. Loc. Balingen. Fig. 21, 22,
adult, loc, Salins.

Oxyn. Lotharingum. Fig. 23-26, showing solid keel in young, hollow keel in adult,
and partly obsolescent keel in old age of specimen in Museum at Semur.

Oxyn: oxynotum. Fig. 27, showing hollow keel filled with layers of shell in specimen at
Museum of Semur.

Oxyn. Guibali. Fig. 28, 29, 31, drawn from sketch of specimen in the Museum of Semur,
showing solid keel in young, hollow keel in adult, and absence of keel in old age.

Oxyn. Greenoughi. Fig. 30, enlarged perfect specimen of hollow keel in adult, loc.
Stuttgardt.

1 See Plate IX. Fig. 2, 3. 2 See Plate IX. Fig. 10, 11.
3 See Plate VII. Fig. 11-15.

PLATE X.

GENESIS OF THE ARIETIDAE.

HELIOGRAPH, HART & VON ARX, N. Y.

ROETTER & HYATT, DEL.

eee ne ee nee een ee ene ene enn eee enSD NIECE NUNDSNUNmONEOINEO i RI is a =—

SUMMARY PLATE XI.

This and the following two Plates, XII. and XIII., have been prepared from various sources,
as well as from specimens already figured in the preceding plates, in order to illustrate the
association of forms in all the series described in this Memoir. The sequence in each series is
accurate, with certain exceptions, where it has been found necessary to alter to some extent the
exact order of the species. These alterations have been noted below, and most of the forms
necessarily omitted in this summary may be traced by comparing the plates with Table IV.,
“ Genealogy of the Arietidz in the Province of Central Europe.” ‘The species of the Medi-
terranean Province figured in these plates, and not mentioned in that table, have been more
or less noted or described in the chapter on “Descriptions of Genera and Species,” and are
Fig. 7-13 and Fig. 17-19 on Plate XI., and Fig. 10 on Plate XIII. The remainder all occur in
the Jurassic Province of Central Europe.

The connecting bars designate affinity, and show the genesis of the forms. No attention
has been paid to the geological horizons, but representative forms, or, as they have been called in
the text, morphological equivalents, have been placed on the same, or nearly the same, horizon-
tal lines in the three plates. ‘This has brought out very completely the curious discordance
which occurs in the normal progressive series in the centre of the Arietide, as given on the
right of Plate XI. and the whole of Plate XII. in the genera Caloceras, Vermiceras, Arnioceras,
and Coroniceras. heir quadragonal whorls, and deep channels and keels in adults, and the
absence of involute forms, are in marked contrast with Schlotheimia, Weehneroceras, and the more
involute forms of Psiloceras, on the left of Plate XI., and the geratologous series at the other
extreme of the group, Asteroceras, Agassiceras, and Oxynoticeras, as illustrated on Plate XIII.

Psil. planorbe, var. leve, Fig. 1; var. plicata, Fig, 2.

Psil. aphanoptychum (sp. Wah.), Fig. 11.

Psil. Kammerkarense (sp. Wih.), Fig. 12, shows the more involute and plicated form.

Psil. mesogenos (sp. Wih.), Fig. 13, is an involute shell really belonging to the true
Levis stock, and therefore somewhat out of place at the top of the direct descendants of var.
plicatus, but it is placed there for comparison with its morphological equivalents in other series.

Weeh. curviornatum (sp. Wih.), Fig. 7, has the pile on the abdomen, a trifle too strongly
shaded; but this form is undoubtedly distinct from Schlot. angulata.

Weh. haploptychum (sp. Wih.), Fig. 8, is one of the typical forms of this genus, and
the contrast between this and Schlot. angulata is well shown,

Weh. toxophorum (sp. Wih.), Fig. 9, is a degenerate shell, having compressed whorls,
and pile crossing the abdomen, as in the proximate radical Weh. curviornatum. It is, however,
more involute.

Weh. Emmerichi (sp. Wah.), Fig. 10, shows a notably involute shell, with degenerate
pile and compressed whorls.

Schlot. catenata, Fig. 3, gives the tongue-shaped connections between the pile on the
abdomen, but they are somewhat too strongly shaded.

Schlot. angulata, Fig. 4, is evidently a transition to the next species,

Schlot. Charmassei, Fig. 5. The whorl is more involute, but the degenerate characters
of compression in the whorls and-shallowing of the abdominal channel begin to appear.

Schlot. Boucaultiana, Fig. 6. The involution has attained its maximum, and the degen-
eration of the pile and channel is well marked.

Cal. tortile, Fig. 14. The young in the centre of the umbilicus shows the close relationship
to Psil. planorbe, var. plicata, below.

Cal. carusense, lig. 15, has similar smooth young to that of-tortile below, and has no
keel in the nealogic stage.

Cal. Nodotianum, Fig. 16, is very similar to carusense, but with more compressed whorls
and better developed pile.

Cal. cycloides (sp. Wih.), Fig. 17, shows compressed degenerate whorls.

Cal. Castagnolai (sp. Wih.), Fig. 18, is more degenerate than the last, but slightly
more involute.

Cal. abnormilobatum (sp. Wah.), Fig. 19, is a dwarfish and more degenerate form than
Castagnolai, but has more involute whorls.

Cal. suleatum, Hyatt, Fig. 20, shows smooth young, as in Fig. 15, and the growth of the
pile from tubercles on the edge of the abdomen in the young.

_ _Cal. Deffneri, Fig. 21, has the pile and tubercles too heavy, but it shows that the young
is similar to that of Cad. sulcatum below, and that the pile have no abdominal extensions.

Cal. laqueum, Fig. 22, is an extreme form of this species, which approximates very closely
to a true spiratissimum, differing however in the sutures and in the age at which the keel
appeared. This figure is therefore placed to the right, and under Verm. spiratissimum. The
less specialized varieties of this species, which would have stood between Cad. tortile and Cal.
carusense, have not been figured.

_. Verm. spiratissimum, Fig. 23, shows typical form, with keel developed early, and but
slight channels. :

Verm. Conybeari, Fig. 24, shows normal untuberculated variety, with stout whorls and
deep channels.

Verm. ophioides, Fig. 25, exhibits the tuberculated pile and concentrated development
of this species, as shown in the early age at which the tubercles appeared.

nen

Ee reeks

SUMMARY PLATE XI.

ERS & PRINTERS, BOSTON.

Lux Co., ENGRAV

BA a

SENET TEES TET

SUMMARY PLATE XII.

Psil. planorbe, var. leve. Fig. 1 shows the dwarfed, but very common form of this
variety, which is evidently a close ally of the next, Arn. miserabile.

Arn. miserabile. Fig. 2 represents the acute but keelless variety of this species.

Arn. obtusiforme, Fig. 3, is not very similar to miserabile, but the evidence of gradations
places it in this relation.

Arn. semicostatum, Fig. 4. The figure represents the nearly full-grown shell, but it may
be easily seen that, if the keel were absent, the smooth whorls of the young would closely resem-
ble the adult whorls of Psil. planorbe, var. leve.

Arn. Hartmanni, Fig. 5, exhibits young and adult characters like those of the preceding.

Arn. tardecrescens, Fig. 6, belongs to another subseries of forms than that in which it
is placed, but it serves to show that quadragonal whorled shells with channelled abdomens
existed in this genus.

Arn. Bodleyi, Fig. 7, shows a slightly degenerate compressed whorl, and is the terminal
form of the subseries containing Hartmann.

Arn. kridioides. Fig. 8 gives a view of the transition between Arnioceras and the lowest
species of Coroniceras. The smooth young straight pile and divergent sides of the adult whorl
are clearly shown.

Cor. kridion. Fig. 9 shows that the tuberculated pile, smooth young, and form of whorl
are exactly intermediate between Arn. kridioides and Cor, Sauzeanum.

Cor. Sauzeanum. Fig. 10 shows the later nealogic and ephebolic stages, having the
peculiar divergent sides, flattened abdomen, and prominent tubercles of a typical coroniceran
form. The young, however, still retain the smooth aspect, indicating derivation from Arnioceras.

Cor. bisulcatum. Fig. 11 shows the very deep channels and peculiar flat abdomen of this
species.

Cor. rotiforme. Fig. 12 represents a form similar to Cor. coronuries.’

Cor. Lyra, Fig. 13. This is as a rule much gmaller than rotiforme. ‘The sides are more
convergent, and the whorls more compressed and less numerous than in that species.

Cor. Gmuendense, Fig. 14, shows degeneration in the compressed whorls of the adult as
compared with Lyra.

Cor. trigonatum, Fig. 15, exhibits still more clearly than in Gmuendense the effects of the
premature development of old age characters. The early stage at which they appear is repre-
sented in the widening of the spaces between the pil. This shell was inferior in size only to
rotiforme, and much larger than Gmuendense.

Cor. latum, Fig. 16. This is the extreme form of this genus, and has in proportion to
its age and size more divergent sides and a broader abdomen than any other. It may be, as
described in the text, the young of a yet undiscovered adult, but is not the young of the next
form, Bucklandi.

Cor. Bucklandi, Fig. 17, shows the very stout bulky form of this species, its pile, and
the divided pile of the early stages of the sinemuriense variety. This species is not inferior to
rotiforme in size.

1 The size of the plates did not permit the use of larger specimens, and therefore these figures do not properly
represent the comparative size of the different species in the genus Coroniceras.

T= SES TPR P33 eee een
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SUMMARY

BOSTON.

ENGRAVERS & PRINTERS,

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SUMMARY PLATE XIII.

Agas. levigatum. Fig. 1 shows the more compressed variety of this species.

Ast. obtusum. Fig. 2 shows the stouter variety with well marked channels (a little too
deeply shaded), with stout gibbous whorls and broad abdomen. ‘This has young almost identical
with the adults of the stout varieties of Agas. levigatum.

Ast. Turneri. Tig. 3 shows typical variety, with flattened sides and deep channels. It is
notably more involute than obtuswm.

Ast. Brooki. Fig. 4 shows an extreme involute variety of this species, with very conver-
gent sides and narrow abdomen. The channels are almost obliterated, and the keel very
prominent,

Ast. Collenoti. Fig. 5 gives a view of this remarkable dwarfed form, in which degenera-
tion of the pil and the channels and convergence of the sides have produced morphological
equivalence with Oxyn. oxynotum and Guibali. The amount of the involution is, however,
greater than in any preceding species of the same series.

Agas. striaries. Fig. 6 gives a view of the adult, with a decided keel.

Agas. Scipionianum. Fig. 7 shows the stouter, heavily tuberculated variety, which has
young almost identical with the stouter varieties of Agas. striaries.

Agas. Scipionis. Fig. 8 shows an aged specimen in the Museum of Comparative
Zodlogy, with extremely involute whorls, but keel still prominent. The degeneration of the
adult as regards the pile and form can, however, be inferred from this figure. The old of
Scipionianum at the same age is much less changed, and does not exhibit increased involution
of the whorls.

Oxyn. oxynotum, Fig. 9,10. The first figure shows the young of a variety in which at
an early stage there is close likeness to the young of Agas. striaries, and the adults of Agas.
levigatum.

Oxyn. Simpsoni. Fig. 11 shows the stouter form and slightly greater involution of the
whorls in this species when compared with omynotum.

Oxyn. Lymense. Fig. 12 shows the greater involution of whorls as compared with any
preceding form of the same subseries, and the very acute degenerate whorl.

Oxyn. Greenoughi. Fig. 13 shows the stout form of the whorls better defined, and pilee
of this subseries as compared with the oxynotum subseries.

Oxyn. Guibali. Fig. 14 shows more involute whorls than in Greenoughi.

Oxyn. Lotharingum. Fig. 15 shows the smaller size of this species, and the degener-
ation of the pile. The involution of the whorls is, however, greater than in any preceding
species.

Oxyn. Oppeli. Fig. 16 shows the extremely involute form of the Middle Lias. The stout
whorls indicate that no great amount of degeneration had taken place. It may have been a
direct descendant of Greenoughi.

LUX Co., ENGRAVERS & PRINTERS, BOSTON

eS VV EA. Soli,

SUMMARY PLATE XIV.

The three preceding plates do not illustrate the biological relations of the Aietidee as a whole
with sufficient clearness, and this plate has been added for the purpose of supplying the defi-
ciency. ‘he series of Psiloceras has been placed in what may be deemed its true position, be-
tween the Plicatus stock and the Levis stock; otherwise, the arrangement is the same. The
resemblances of the morphological equivalents in each series can be readily seen by following
the forms along horizontal lines from left to right. The independence of the origin of these
representative forms can be studied by following up the series in vertical lines, which represent
descent. ‘To a large extent, also, the more obvious differential characters which distinguish each
series become appreciable by the same process.

Psil. planorbe, var. leve, Fig. 1; var. plicata, Fig. 2.

Schlot. catenata, Fig. 3, is the radical of this series.

Schlot. angulata, Fig. 24, is evidently a transition to the next species. The artist has
exchanged Fig. 4 with Fig. 24.

Schlot. Charmassei, Fig. 5. ‘The whorl is more involute, but the degenerate characters
of compression in the whorls and shallowing of the abdominal channel begin to appear.

Schlot. Boucaultiana, Fig. 6. The involution has attained its maximum, and the degen-
eration of the piles and channel is well marked.

Weeh. curviornatum (sp. Wiih.), Fig. 7, is undoubtedly distinct from Schlot. angulata, and
is one of the radicals of this series.

Weeh. haploptychum (sp. Wih.), Fig. 28. The artist has exchanged Fig. 8 with Fig. 28.

Weeh. toxophorum (sp. Wah.), Fig. 9, is a degenerate shell, having compressed whorls,
and pile crossing the abdomen, as in the proximate radical Wah. curviornatum. It is, however,
more involute.

Weeh. Emmerichi (sp. Wih.), Fig. 10, shows a notably involute shell, with degenerate
pile and compressed whorls.

Cal. tortile, Fig. 11, is the radical of this series.

Cal. carusense, Fig. 12, has similar young to that of tortile below.

Cal. Nodotianum, Fig. 13, is very similar to carwsense, but with more compressed whorls
and better developed pile.

Cal. cycloides (sp. Wiih.), Fig. 14, shows compressed degenerate whorls.

Cal. Castagnolai (sp. Wiih.), Fig. 15, is more degenerate than the last, but slightly
more involute.

Cal. abnormilobatum (sp. Wih.), Fig. 16, is a dwarfish and more degenerate form than
Castagnolai, but has more involute whorls,

Cal. laqueum, Fig. 17, is an extreme form of this species, which approximates very closely to
a true spiratissimum. This figure is therefore placed to the right, and under Verm. spiratissimum.

Verm. spiratissimum, Fig. 18, shows typical form, with but slight channels.

Verm. Conybeari, Fig. 19, shows normal untuberculated variety, with stout whorls and
deep channels.

Verm. ophioides, Fig. 20, exhibits the tuberculated pile of this species.

Psil. aphanoptychum (sp. Wih.), Fig. 21, is one of the Plicatus stock of Psiloceras.

Psil. Kammerkarense (sp. Wih.), Fig. 22, shows the more involute and plicated form of
this subseries.

Psil. mesogenos (sp. Wiih.), Fig. 23, is an involute shell belonging to the true Levis stock."

Arn. semicostatum, Fig. 4. The figure represents the nearly full-grown shell; but if
the keel were absent, the smooth whorls of, the young would closely resemble the adult whorls
of Psil. planorbe, var. leve. The artist has exchanged Fig. 4 with Fig. 24.

Arn. Hartmanni, Fig. 25, exhibits young and adult characters like those of the preceding.

Arn. tardecrescens, Fig. 26, belongs to another subseries of forms than that in which it
is placed, but it serves to, show that quadragonal whorled shells with channelled abdomens
existed in this genus.

1 Two subseries ought to have been shown here, but in trying to reduce the size of the plate the forms have
been placed in the same line. A similar liberty has been taken with the subseries of Caloceras and Arnioceras, but
this does not interfere with the truthful presentation of the general zoological relations of the forms.

SUMMARY PLATE XIV. (continued).

Arn. Bodleyi, Fig. 27, shows a slightly degenerate compressed whorl, and is the terminal
form of the subseries containing Hartmanni.

Arn. kridioides. Fig. 28 gives a view of the transition between Arnioceras and the lowest
species of Coroniceras. ‘The smooth young straight pile and divergent sides of the adult whorl
are clearly shown. ‘he artist has exchanged Fig. 8 with Fig. 28.

Cor. Sauzeanum. Fig. 29 shows the later nealogic and ephebolic stages, having the
peculiar divergent sides, flattened abdomen, and prominent tubercles of a typical coroniceran
form. The young, however, still retain the smooth aspect, indicating derivation from Arnioceras.

Cor. rotiforme. Fig. 30 represents a form similar to Cor, coronaries.

Cor. Lyra, Fig. 31. This is as a rule much smaller than rotiforme. The sides are more
convergent, and the whorls more compressed and less numerous than in that species.

Cor. trigonatum, Fig. 32, exhibits the effects of the premature development of old age
characters. Fig. 1 on the extreme right shows the dwarfed form of Psil. planorbe, var. leve,
from which both the arnioceran as well as the agassiceran series may have been derived in
Central Europe.

Agas. levigatum. Fig. 33 shows the more compressed variety of this species.

Agas. striaries, Fig. 34. The striations were too fine to be represented.

Ast. obtusum. Fig. 2 shows the stouter variety with well marked channels with stout
gibbous whorls and broad abdomen. This has young almost identical with the adults of the stout
varieties of Agas. levigatum.

Ast. Turneri. Fig. 36 shows typical variety, with flattened sides and deep channels, It is
notably more involute than obtuswm.

Ast. Brooki. Fig. 37 shows an extreme involute variety of this species, with very conver-
gent sides and narrow abdomen. The channels are almost obliterated, and the keel very
prominent.

Ast. Collenoti. Vig. 38 gives a view of this remarkable dwarfed form, in which degenera-
tion of the pile and the channels and convergence of the sides have produced morphological
equivalence with Oxyn. owynotum and Guibali. The amount of the involution is greater than in
any preceding species of the same series.

Agas. Scipionianum. Fig. 39 shows the stouter, heavily tuberculated variety, which has
young almost identical with the stouter varieties of Agas. striaries.

Agas. Scipionis. Fig. 40 shows an aged specimen in the Museum of Comparative
Zodlogy, with extremely involute whorls, but keel still prominent, The degeneration of the
adult as regards the piles and form can, however, be inferred from this figure. The old of
Scipionianum at the same age is much less changed, and does not exhibit increased involution
of the whorls.

Oxyn. oxynotum, Fig. 41, 42. The first figure shows the young of a variety in which at
an early stage there is close likeness to the young of Agas. striaries, and the adults of Agas.
levigatum.

Oxyn. Simpsoni. Fig. 43 shows the stouter form and slightly greater involution of the
whorls in this species wheu compared with omynotum.

Oxyn. Lymense. Fig. 44 shows the greater involution of whorls as compared with any
preceding form of the same subseries, and the very acute degenerate whorl.

Oxyn. Greenoughi. Fig. 45 shows the stout form of the whorls better defined, and pile
of this subseries as compared with the oxynotwm subseries.

Oxyn. Lotharingum. Fig. 46 shows the smaller size of this species, and the degeneration
of the pile. The involution of the whorls is, however, greater than in any preceding species.’

Oxyn. Oppeli. Fig. 47 shows the extremely involute form of the Middle Lias. The stout
whorls indicate that no great amount of degeneration had taken place. It may have been a
direct descendant of Greenoughi.

1 The extreme old age of this form is marked by decrease in the amount of involution of the whorl, and also by
the loss of the prominent hollow keel.

RS & PRINTERS, BOSTON

Lux Co., ENGRAVE

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