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Pihylogeny
Acquired

Characteristic.

HYATT.

oui THS ONAN
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LIBRARIES _-
ite ae

- PHYLOGENY

o .,OF AN...

ACQUIRED CHARACTERISTIC.

BY ALPHEUS HYATT.

Extracted from Proceedings American Philosophical Society,

Vol. xxxii, No. 143.

PREFACE.

This memoir was first given as a short address before the American
Philosophical Society of Philadelphia, at the celebration of the one
hundred and fiftieth anniversary of the foundation of that illus-
trious body. A short preliminary abstract was subsequently pub-
lished in their Proceedings and in the American Naturalist for
October, 1893, with one diagrammatic plate. The statements
made in these two preliminary papers before all the facts were
brought together and correlated were true, in the main,” but
necessarily defective and have been put into more correct shape in

the following pages.

INTRODUCTION.

The nature of the evidence afforded by fossil shells is even at the
present time very little understood. They have been so often spoken

850

of slightingly, as a sort of jacket, an unimportant part, etc., that
all conclusions arrived at by their study alone are considered as
peculiarly lable to error.

A shell, to begin with, ranks as a primary, essential part arising
in an early stage of development from the shell gland common to
the embryos of all forms of Mollusca. Subsequently, by its mode
of growth it becomes a model of the external form, and at the
same time a mould of the outlines of the internal soft parts to an
extent which has not been fully appreciated. The shell is often,
also, a permanent record of the series of changes which the form
has undergone, from the time it first began to enclose the embryo
until the death of the soft parts, since it retains the young shell and
all the later stages of growth. Among Nautiloids and Ammonoids,
it also contains the calcareous tube or so-called siphuncle, which
exhibits remarkable and significant changes of structure and posi-
tion following upon the development of the animal. This siphuncle
connects the septa or horizontal partitions, which with their
sutures vary with the age of the animal constituting a third record
of changes and structural modifications.

All these parts, the shell proper, the siphuncle, the septa and the
sutures are in correlation with each other and together make an index
to the life history of the individual, which is unequaled in some
respects among other existing or extinct animals.

A single shell, either from a living or fossil form, may present
accurately the general history of the development of the young,
the stages of the adult and old age. ‘The results of heredity and of
the action of endemic or traumatic diseases may also be detected,
if one knows how to study and compare the remarkable and dis-
tinct series of metamorphoses displayed by this external or protec-
tive skeleton with those of congeneric forms. ‘This can be done
even when the young is not visible externally by breaking down or
dissecting a well-preserved fossil and thus following the history of
the shell backwards through all of its stages to the embryo.

The researches of Beecher, Schuchert and Clarke among Brachio-
poda have demonstrated that the shell and the internal brachial
armature of these forms possesses similar life histories to those here
described for the external and internal skeletons of the Cephalo-
poda. Jackson has demonstrated similar phenomena among Pele-
cypoda and Beecher among corals.

The vertebrate skeleton has long been considered a standard,

ool

and the evidence afforded by its fossil remains is very important
and convincing. The series made in the case of the horses found
by Marsh and Cope and those described by Gaudry are universally
quoted as the strongest proofs of evolution. This evidence is
considered complete, because naturalists understand and have
thoroughly studied the skeleton, and because it is internal and has
been assumed to be more invariable than the shell. All of these
arguments have their due weight, but there are no examples
of greater invariability than exist between the shells of the Nauti-
lus now existing and those of Barrandeoceras (Nautilus) of the
Cambrian, or the Triassic and Silurian Orthoceras, or of the
Prodissoconch stage in the young of Pelecypoda as demonstrated
by Jackson, or of the Protegulum among Brachiopoda as shown by
Beecher. The Prodissoconch and Protegulum are embryonic
shells that have persisted from the earhest horizons of geologic
time and are still to be found in living shells attached to their
apices.

The conclusions arrived at by the study of the vertebrate
skeleton are reliable, but they are neither more conclusive nor
important in theoretical meaning than any other series of equally
well-understood hard parts in any other branch of the animal
kingdom found as fossils when traced out in the same thorough
and careful manner.

How unreasonable it would seem to a student of fossil
Mammalia, if he were requested to do what it would be appropriate
to require from a student of the fossil Cephalopoda, viz., to
describe from the investigation of a single perfect fossil skeleton of
an adult, not only the characteristics of the skeleton at the
stage of growth at which the animal died, but the develop-
mental stages of this same skeleton, and in case it were the
remains of an old, outgrown animal, also, the retrograde metamor-
phoses through which it had passed during its last stages of decline.
It might require a life time to make out the stages of a single
species of mammal satisfactorily from the isolated specimens which
would be found and the attempt would be hopeless for all the
youngest stages of growth, wltile the bones were still cartilaginous.

This kind of evidence, however, is readily obtainable among
fossil Cephalopods with relation to the shell and other hard parts
as among living animals, and it can be obtained in good col-
lections everywhere, whether ‘‘in situ’’ or in museums. Thus it

dd2

is possible to study the relations of these fossil forms very minutely
and with a certainty of possessing a clue’ to their true relations,
which is rarely obtainable even among existing animals. For among
these we have only the embryos and young of contemporaneous
forms and necessarily lose all relations of succession in time, unless
the investigation embraces a prolonged series of experiments or is
more or less historical, and even then the facts cannot have a very
wide chronological range.

The class of Cephalopoda has two subclasses, ‘Tetrabranchiata
and Dibranchiata. These were established by Richard Owen as
orders—a purely technical difference, which does not change
in any way the value of the structural distinctions as given by this
eminent naturalist. The Tetrabranchiata are shell-covered ; and
they are represented by the modern Nautilus, the only existing
genus. The Dibranchiata are descendants of the former, but
enclosed the shell, and resorbed it in many forms, so that they
appear as naked animals. The cuttlefishes, squid, devil-fishes, etc.,
are existing types. In studying these types, the author has
been led to adopt a new method of characterizing the divisions,
and besides the old structural distinctions, which are still available,
to apply the correlations of habit and structure to the elucidation
of some of the ordinal characters.

The classification adopted is as follows:

Class Cephalopoda.
Subclass I, Tetrabranchiata.
Order, Nautiloidea.

oo) Amimonoidear
Subclass II, Dibranchiata.
Order, Belemnoidea.

“ ) sepioidea:

These four orders converge to one type by intermediate forms, by
embryology and development of the shells and internal hard parts,
by their morphology and by the possession of a similar embryonic
shell, the protoconch, or the cicatrix which is a remnant of the
aperture of this stage on the apex of the true shell or conch.

The class is composed of exclusively aquatic and marine animals,
and consequently they breathe with gills. The structures of the
orders mentioned coincide with the distinct habitats they respec-
tively occupy.

303

The animal of the Nautilus has a large mantle or fleshy sac
enclosing the internal organs, which can be opened around the
margin, or closed, at the will of the animal. Admitting the water
around the margin they fill their mantle cavity with fluid, and then
constricting the margin and compressing the mantle-sac, force it
out with violence through a fleshy pipe, which is exclusively used
for that purpose, and always situated on the ventral side. The reac-
tion of the stream is sufficiently powerful to drive the body of the
animal with varying degrees of swiftness backwards. ‘The fleshy
pipe is therefore an ambulatory pipe or hyponome ; and it is advan-
tageous to replace the old and confusing terms by this name.

The Dibranchiata change the external shell, which they inherit
from the Nautiloids, into an internal organ, and by suitable modif-
cations of shape and also taking advantage of the powerful hydrau-
lic apparatus, which they also inherit, and increasing its efficiency,
become exclusively swimmers.

The hyponome of the Nautilus causes a corresponding depres-
sion or sinus to occur in the aperture of the shell on the same side,
and its effect is also to be seen in the striz of growth on this side; so
that we know, from these indications in any fossil, what was the
comparative size of the pipe, and whether the animal was more or
less powerful as a swimmer.

Other indications, such as the openness or contracted form of
the various apertures of different genera, exhibit with equal clear-
ness what they could do in the way of crawling. The wide-open
apertures indicate powerful arms, capable of carrying and easily
balancing the large spire of the shell above ; the narrow contracted
aperture shows that the arms were small, and that the animal
could not so efficiently balance or carry the shell in an upright
position, and was therefore, according to the amount and style of
the contraction, more or less inefficient as a crawler.

In studying the different types of the Tetrabranchiata, we find
that there are two orders as first defined by Prof. Louis Agassiz—
the Nautiloidea and the Ammonoidea—and, further, that these divi-
sions coincide with differences in the outlines of the ambulatory
sinuses which indicate distinctions of habit general in the normal
forms of each order.

The extinct Nautiloidea had large ambulatory sinuses, and were
evidently capable, like the modern Nautilus, of rising to the sur-

oo4

face, and swimming with a jerky motion; though their open aper-
tures, as a rule, show their normal condition to have been reptant,
or bottom-crawling. The exceptional shells, which depart from
the typical form in the sinus and apertures, exhibit their peculiari-
ties in the adults, but not, as a rule, in the young, except in cases

May cyi4y
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Fig. 1.—Nautilus umbilicatus.

where direct inheritance has occasioned the exception, and these
are, in fact, the most conclusive proofs of the power of the habitat
to produce permanent changes in the apertures.

The orthoceratitic shells of this order are straight cones, with
internal septa dividing them into air-chambers, connected by a
tube passing through all the air-chambers, and Opening into the
body of the animal itself, which occupied a large terminal chamber,

30)

which however was a small part only of the whole length of the
cone. This is the simplest form: and others are, the bent or
arcuate, cyrtoceratitic; the loosely coiled, but with whorls not in
contact, gyroceratitic ; the closely coiled, with whorls in contact,
nautilian ; and the still more closely coiled or involute shells, the
involute nautilian, in which the outer whorls may simply overlap
the inner, or entirely conceal them by their excessive growth, as in
Nautilus pompttius.

The Ammonoidea in the earlier forms, the Goniatitinz of the Silu-
rian,* had apertures with well-marked ambulatory sinuses sufficient to
show that they must have had considerable powers of rising or leap-
ing in the water, if not swimming, like the Nautilus. In the later
forms of the same suborder and in the Ceratitine, Ammonitine and
Lytoceratinze the ambulatory sinus is absent; and in its place a
projecting crest or rostrum was developed indicating reduction in
size and disuse of the hyponome. This and the generally open
apertures enable us to see that they were more exclusively bottom-
crawlers than the Nautiloidea.

The most interesting of the facts in this order lies among the
exceptional shells, some of which must have been sedentary, and
could neither have crawled nor moved about with any ease ; but none
of these, so far as we know, seems to have exhibited a type of aper-
ture which indicated transition to an exclusively swimming habit.
These shells appear in our subsequent remarks among phylogerontic
and pathologic types.

The Belemnoidea of the Jura had a solid cylindrical body, called
the guard, attached to the cone-like internal shell, and partly
enclosing it. Aulacoceras of the Trias, as described by Branco, is
a transitional form with an imperfect guard, which frequently con-
tains fragments of other shells and foreign matter. This demon-
strates that this guard could only have been built by some external
flap or inclosing sac, independent of the true mantle. This false
mantle must have inclosed both the shell and the guard, and must
have been at the same time open, so as to admit the foreign mate-
rials which Branco found built into the substance of the guard.
One of the straight shells of the Silurian Nautiloidea, Orthocera-
tites truncatus, regularly breaks off the cone of its shell, and then
mends the mutilated apex with a plug. This plug, we are able to

* See Plate ii.

356

say, is the precise homologue, in position and in structure, of the
guard of the Belemnite.

Barrande endeavored to show this plug to have been secreted by
external organs, as he supposed—two arms stretching back from
the aperture like those of Argonauta, and reaching beyond the
broken apex. ‘The dorsal fold of Nautilus is, however, a secreting
organ stretching back over the shell; and, as the probable homo-
logue of the plug-secreting organ of the Orthoceratites and the
guard-building organ of the Belemnoidea, it enables us at once to
explain how the Belemnoidea arose from the Orthoceratites, and
why Aulacoceras had an imperfect mantle. This fold, which was
far larger among the ancient Orthoceratites, would have been
necessarily open on the ventral side, then more but not completely
closed in Aulacoceras, and finally completely closed in the later
Belemnoidea, and able to construct a guard as perfect as that which
they carry.

The solid guard of these animals, a compact cylindrical body
such as they were known to possess, could have been only a heavy
burden to a swimming animal. The Belemnoidea, therefore, were
not purely natatory; but for these and other reasons, which we
cannot here discuss, they were evidently ground-swimmers, prob-
ably boring into the mud for shelter, or as a means of concealing
themselves while lying in wait for their prey.

The old view, that the guard could have been in any sense a
‘guard ’’ against collisions with rocks, etc., in their wild leaps
backwards, is inadmissible for many reasons. The most obvious
are its position -as an internal organ, its solid structure, and its
weight. I think it more reasonable to suppose that it might
have increased the liability to injury from collisions. In tracing
the Belemnoidea to the Orthoceratites I have simply continued
the labors and carried out more fully the sagacious inferences of
Quenstedt and Von Ihering.

The modern Sepioidea are known to be almost exclusively swim-
mers; and the more ancient, normal, flattened forms, and their
descendants, the cuttle fishes, have very light, flattened, internal
shells, in which the striz of growth are remarkable for their for-
ward inflection on the dorsal aspect, due to the immense COE
tive iength of this side of the aperture.

The enclosure and suppression of the shell was predicted, with a
Sagacity which commands our highest admiration, by Lankester,

BIS

from studies of the embryo of Loligo ; and these facts carry out his
conclusions, substituting, however, the hood for the two mantle-
flaps which were_imagined by him as the organs which inclosed
the shell and formed the shell-sac.

Most paleontologists have considered the Sepioidea and Belem-
noidea as more closely allied; but they appear to us as two orders,
certainly as distinct as, and perhaps even more widely divergent
than, the Nautiloidea and Ammonoidea.

Among these two orders we recognize many exceptional forms—

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Fie. 2.—Argonauta sp. 2

such as the Spirula among Belemnoidea, and among Sepioidea the
octopods; and we think they all prove our position, that the
habitat so closely accords with the structural changes of the type
that its purely physical agency must be regarded as the efficient

308

and direct cause of the correlated changes of structure which dis-
tinguish the different orders and suborders, and often of the
exceptional genera and species.

We will mention but one of these exceptional cases, in some
respects the most pertinent—the existing Argonauta, or paper
nautilus (Fig. 2, p. 357). Here a thin shell secreted by the mantle,
by the edge of the mantle, and by the two pairs of long dorsal
arms, encloses completely the animal of the female alone, the male
being naked. As a sexual organ for the protection of the eggs; as
an adolescent and adult structure, originating at a late stage in the
life of the individual, and not in the shell gland of the embryo; and
in its microscopical structure—it is not a true shell, or similar to any
true shell among Cephalopoda. Still, in form and position, and
as built in part by the mantle, it is analogous to a true shell, and
has in part also the functions of a true external shell, and ought
therefore to support or refute the hypothesis maintained above. It
belongs to a swimming animal, and should therefore have the
hyponomic sinus in the aperture and striz of growth as in Nauti-
loidea; and these it certainly has. Compare the side view of
Nautilus umbilicatus (p. 354, Fig. 1), with the Argonauta and it will
be seen that the lines of growth agree in both and that both pos-
sess the hyponomic sinus on the outer side. One can appeal to
this example as a most convincing exception to prove the rule that
the shell is a true index of the most remarkable adaptive structures,
and, among the fossils, can give us exact information of important
similarities or differences in structure and habits.

The efforts of the Orthoceratite to adapt itself fully to the
requirements of a mixed habitat of swimming and crawling gave
rise to the Nautiloidea; the efforts of the same type to become
completely a littoral crawler evolved the Ammonoidea. The suc-
cessive forms of the Belemnoidea arose in the same way. But here
the ground-swimming habitat and complete fitness for that was the
object. The Sepioidea, on the other hand, represent the highest
aims as well as the highest attainments of the Cephalopods in their
evolution into surface-swimming and rapacious forms. We cannot
seriously imagine these changes to have resulted from intelligent
effort ; but we can with Lamarck and Cope picture them as due to
efforts on the part of the animal to take up new quarters in its en-
vironment and thus acquire habits and structures suitable to the

309

changed physical requirements of its surroundings and this position
is better supported by facts than any other hypothesis.

Confining the discussion to the Tetrabranchiata, which are the
most favorable for the present purposes, the next problem present-
ing itself is whether the two orders, Nautiloidea and Ammonoidea,
have had a common origin, or whether they bear internal evidence
of having sprung from different ancestors.

The embryo of all Ammonoidea, as shown by he author in his
Embryology of the Fossil Cephalopods of the Museum of Compara-
tive Zoblogy, and since confirmed by the more extensive researches
of Dr. Branco, is the little bag-like shell first discovered by Sae-
mann. ‘This is attached to the apex of the secondary shell. The
embryonic bag has been called the protoconch by Owen; and the
secondary or true shell, the conch,

There is no protoconch in most Nautiloidea, as first shown by
Saemann, then by Barrande, and subsequently by the author and
Branco; but where it ought to have been attached on the apex of
the conch, there isa scar, first demonstrated by Barrande. The view
brought forward by the author, that this scar indicated the former
existence of a protoconch in the Nautiloidea, has been opposed by
Barrande, Branco, and several authors, on the ground that the cica-
trix demonstrated the existence of a distinct embryonic form.
Therefore, according to Barrande, the Nautiloidea were not similar
to the Ammonoidea in their earliest stages of growth, and must
have been equally distinct in origin.

I have found the protoconch in several forms of Orthoceratites,
the figures being reproduced here, Figs. 3-7, and, further, it can
probably be found on the apex of all of the so-called perfect shells,
which have no scar or cicatrix. These, when described by De-
Koninck, were supposed by him, in his ‘‘ Calcaire carbonifere ”’
(Ann. du mus. roy. de Belgigue),to be fatal to this conclusion.
Having no scar, they could not possibly, according to DeKoninck,
have had a protoconch. When the so-called perfect apex is broken
off, the observer will probably find that this apex was the shriveled
remains of a protoconch which concealed the cicatrix underneath,
as in Fig. 4.

There is therefore no essential difference between the embryos of
the Ammonoidea and those of the Nautiloidea. ‘There are some of
minor importance which we cannot discuss here. These, however,
do not interfere with the facts of general agreement ; and there is

360

great ‘probability that the shell-covered forms of all kinds which
have the protoconch—namely, the ancient and modern Gastro-
poda, Tentaculites, and the ancient Pteropoda, and all the radical

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Fig. 3.—Aspect of the apex of the conch in Orth. unguis Phill., after the protoeconch has
been shed in the usual manner. 6b, conch or shell of the apex; ¢, cicatrix.

Fig. 4.—Aspect of the apex, after the protoconch has been aceidentally broken off, frae-
turing the outer shell, and exposing the cicatrix. 0c, as before.

Figs. 5-7.—Apex aud protoconeh of Orth. elegans Munst. from the front, side and above.
a, protoconch ; b, shell of apex.

Figs. 8, 9—Anotherindividual, said to be of the same species, less magnified. ab, as
before. The author has also, in Spy. cretafum, traced the strie of the outer shell on
the protoconech itself, showing the continuity of the shell over this part (a), and
completing the evidence that it must have been the shell which enclosed the em-
bryo, and could not have been a mere plug, as asserted by Barrande (Syst. si/.,
pl. 488). (See Figs. 10 and 11, p. 361).

361

forms of Cephalopoda—-had a common origin, probably in some
chamberless and septaless form similar to the protoconch.

Clarke has recently shown that a straight, Orthoceras-like shell
may have a complete egg-shaped protoconch like that of Bactrites.*
His form certainly has the characters of an Orthoceras, but the
protoconch is large and like that of the Ammonoidea. The shell
may be transitional from Orthoceras to Bactrites, but is probably
not a typical form of Orthoceras.

The young of the simplest and earliest of Ammonoidea, the Nau-
tilinidze, have in varieties of two species, as shown by Barrande, a
straight apex, like the adult shell of such forms as Bactrites + and

that described by Clarke. I have already claimed that this fact was

sufficient to prove the high probability of a common origin from a
straight shell like Orthoceras for both of the orders. Mmoceras
compressum, sp. Beyrich (Figs. 1-6, 20, Pl. ii), is a shell which
differs from all other Ammonoidea in an essential and highly impor-
tant character. The septa have no inner lobe. The V-shaped
annular lobe, which occurs in all the Ammonoidea except the Nau-
tilinidge, is also absent in this species. What is more to the point,
some species have the sutures of a true nautiloid, since they have

* “The Protoconch of Orthoceras,” Am. Geol., xii, Aug., 1893. See also Figs. 28, 29,
Pai
+ A straight form of Goniatitinee (see Figs. 30, 31, Pl. ii).

* Prof. Hall, in his Paleontology of New
York, described a young specimen of
Spyroceras (Orthoceras) crotalum, sp. Hall,
which he subsequently loaned me for fur-
ther study. Upon developing the speci-
men, I found the beautifully preserved
apex shown in Figs. 10-12. This shows
the shriveled protoconch with striations
passing on to its surface from the conch,
which are made somewhat more promi-
nent in the figures than in nature, in
order to demonstrate this connection.
The ananepionie substage is smooth and
distinctly marked off from the succeed-
ing, probably metanepionic substage, Fic. 10. Fic. 11.
which shows both longitudinal ridges and
transverse bands of growth. The metane-
pionic substage is marked off below by a more prominent band of growth, probably
indicating the aperture of this substage. The paranepionic substage below this
changes in the form of the cone and in the character of the ridges and bands of growth.
The absence of a hyponomic sinus in the young, of straight as well as of nautilian shells,
shows that they were not active swimmers in these earlier nepionic substages, and that
the hyponome was acquired or at any rate large and functionally active only at a com-
paratively late age of the ontogeny.

HHA
eee
Sst

Fies. 10-12, SPyROCERAS CROTALUM.

—————

362.

dorsal saddles in place of dorsal lobes, as in the sutures of their
nearest allies among the Nautilini and all of the remaining Ammo-
noidea. JAlimoceras ambigena Barr., of the Silurian (Figs. 7, 8,
Pl. 11), is a close ally of this Devonian species, and with AZzmoceras
(Gon.) “tuum (sp. Barr.) Hyatt (Figs. 40-42, Pl. viii), are the only
ammonoids which are not involute-nautilian in form. The whorls
are in contact ; but there is no impressed zone, and no sutural lobes
on the dorsum, as in true nautilian shells. On the contrary, they
are purely gyroceran forms, with rounded dorsum and sutural sad-
dles on this side in place of lobes. All of the Nautilinidz also have
the septa concave, as in the Nautiloidea, in place of the invariably
convex character of the septa in later Ammonoidea, as shown in
Pl. x. As doubts may disturb the mind as to whether JZ. compres-
sum is an ammonoid, we recommend a comparison of this shell
with the young of an undoubted species of Goniatitine, Agonza-
tites fecundus of Barrande, which is a miniature copy made by her-
edityax@iigs#o— 11 eR aa):

Bactrites is a perfectly straight form, similar to the members of
the Goniatitinze in all important characteristics, especially the siph-
uncle and septa, and it also has, like the young shell described by
Clarke and all the coiled Ammonoidea, a comparatively large proto-
conch, as demonstrated by Branco, whose figure has been repro-
duced on Pl. 2 of this paper. This same genus includes straight
cones like Bactrites (Orthoceras) pleurotomus Bar. (Syst. szl., Pl.
296), which are undeniably transitions to true Orthoceras in their
strie of growth and position of siphuncle. There is, therefore,
convincing evidence in the structures of these Silurian shells that
the Ammonoidea, with their distinct embryos, arose from the
orthoceran stock, and passed through a series of forms, in times,
perhaps, preceding the Silurian, which were parallel to those char-
acteristic of a number of genetic series among Nautiloidea, viz.,
straight, arcuate, gyroceran, and nautilian.

In Sezence (Vol. iii, No. 52, February, 1884, p. 127), an article
written by the author closed with the following words: ‘‘ The study
of the tetrabranchs teaches us that, when we first meet with relia-
ble records of their existence, they are already a highly organized
and very varied type, with many genera, and that there was a pro-
tozoic period ; and the tetrabranchs, like their successors, certainly
must have had ancestors which preceded and generated them in this
period, but of which we are at present necessarily ignorant. What-

363

ever the future may have in store for us we cannot now predict ; but
at present the search for the actual ancestral form, though necessary,
is nevertheless not hopeful. We can, however, rely upon the facts
of embryology, and predict without fear of failure that, when our
knowledge makes this prototypical form known, it will have a de-
cided resemblance in structure and in aspect to the earlier stages of
the shell as observed in the fossil cephalopods.’’

At the time this was written I had in my possession two fossils
which I had collected myself in the lowest Calciferous of Newfound-

Fig. 13.—Nautilus pompilius.
[Contributed by Henry Brooxs.]

land. I was aware that they presented peculiar and apparently sep-
tate siphuncles, but in the field had supposed this to be due to an
accident that not infrequently happens, viz., the intrusion of Ortho-
ceratites of small size into the open upper parts of the large siphun-
cles of the Endoceras. When an opportunity finally arose, through
Dr. C. S. Minot, Secretary of the Thompson Science Fund, to
illustrate and publish these forms, I found that this was not the
case, but that their siphuncles were truly septate and completely

364

closed to within a certain distance from the living chamber by a
series of partitions occurring at regular intervals. These forms I
shall describe under the name of Diphragmoceras in the Proceed-
engs of the Boston Society of Natural History, and I shall endeavor
to show that this genus is one of the distal ancestors of the Nautil-
oidea. This conclusion is based largely upon comparison with the
apical, metanepionic substage of development in the shell of the
modern Nautilus. The first septum of the shells has appended to
it a closed caecum or bag, the metanepionic representative of the
siphuncle, and the second septum is prolonged apically into a closed
tube, the end of which fits into this bag and usually lines it with a
second or internal layer. In some cases (Fig. 13, p. 363), probably
through the displacement of the second septum, this closed termi-
nation is carried forward and is then clearly seen to be a closed
tube extending into the siphuncle. The bottom of this tube, in
fact, forms a septum in the siphuncle, and the resemblance of this
early stage to the adult structures of Diphragmoceras becomes per-
fectly clear. Diphragmoceras had a closed tubular prolongation of
the base of the mantle like that of the metanepionic septa of Nauti-
lus and also more remotely similar to that which occurs in Endo-
ceratidzee. But it does not diminish in size towards the apex, hang-
ing like a cone in the middle of the siphuncle; nor does it, as in
that genus, also fill the siphuncle below its own extremity with a
continuous mass of calcareous matter having a cone in cone struct-
ure, nor has it any endosiphuncle. ‘The sheath fits the siphuncle
closely and rises step by step with the body, its end forming septa
across the siphuncle at the resting stages of this process correspond-
ing in number to those of the shell, but not corresponding in posi-
tion, each septum being situated just in the interval between two
septa, or opposite each air chamber of the conch. Thus the siphun-
cle becomes divided into air chambers like those of the surround-
ing shell, but these partitions are not pierced by any endosiphuncle,
as are the endocones formed by the sheath in the Endoceratidz and
the solid deposits and peculiar rosettes of the Actinoceratide.*

Dr. Charles E. Beecher has been fortunately able to lay hands
upon the primitive radical of all of the Brachiopoda through the
study of the early stages of the shell and has shown that the common
embryonic shell or pvotegu/um of recent and fossil Brachiopoda is
represented by one of the earliest occurring forms, Paterina. Dr.

*“ Genera of Fossil Cephalopods,” Proce. Bost. Soc. Nat. History, xxii, 188 , p22:

265

R. T. Jackson has accomplished the same result for the Pelecypoda
by following the same mode of analysis, and shown that Nucula was
the common form to which all bivalve shells can be traced. Among
corals, as shown by Beecher, there are satisfactory indications that
there is a common ancestral form of at least a large proportion of
that class, and the labors of Barrande, Mathews, Walcott and
Beecher are leading to similar conclusions for the Trilobites. The
theory of monogenesis, or origin of similar forms from one form,
is in other words now rapidly passing from the condition of a rea-
sonable inference from the facts cf development and evolution, in
which it has stood since the time of Von Baer, to that of a demon-
strated law of general application..

The individual coiled shell of every nautiloid may be said to
pass through the stages of the protoconch and point of the apex,
when it is nearly straight ;* then it becomes slightly curved or cyr-
toceran, and then through a more completely curved or gyroceran
stage, in which the first volution of the spiral is completed. After
this it continues the spiral, commonly revolving in the same plane
and becomes truly nautilian, the whorls on the outside touching the
exterior of the inner ones, and spreading so rapidly by growth as
to begin to envelop them, and in extreme cases, as in Vautilus
pompilius, completely covers them up.

The natural inference from these facts would be, that there was a
similar succession of forms in past times—the straight in the most
remote, the arcuate and the gyroceran in succeeding periods, and
the nautilian only in comparatively modern times. This would be
a perfectly clear and legitimate mental conception. The structural
relations of the adult shells appeared also to demand the same solu-
tion, as shown by the researches of Quenstedt, Bronn and Barrande,
and later of Gaudry. Barrande’s researches, however, demonstrated
that this idea could not be maintained, and that there were no such
serial relations in time, but that the whole series of forms from the
straight to the nautilian were present in the earliest period, and
occurred side by side in each Paleozoic formation.

This great author’s conclusions have had a curious effect upon

*Tt is to be noted in this connection that the earliest nepionic substages do not have
equal circular bands of growth, even in true Orthoceras, and are never quite symmetri-
cal on the dorsum and venter. In other words, the descriptive term, straight, is only
applicable in a general way. The youngest stages of the conch having dilferentiated

venter and dorsum and a compressed elliptical outline which is similar to that of the
radical ancestral form Diphragmoceras. See Figs. 10-12, p. 361.

SE Ee eEeeEEEEeEeEEeEeEeEEeeeeeeee

366

paleontologists. It has been hastily assumed by some, Barrande
himself leading in this respect, that the mental conception was
more than could be realized in nature; and that the imperfection
of the recorded succession was an obvious refutation of the doctrine
of evolution, and all pursuit of a solution unworthy of serious
attention.

Statistically, the logical picture coincides with the observed suc-
cession in time. The straight cones predominate in the Silurian
and earlier periods; while the loosely coiled are much less numer-
ous, and the close coiled and involute, though present, are also
rare. The close coiled, or nautilian shells, gain in numbers in the
Carboniferous, and the involute—meaning by this those that en-
velop more or less the inner and younger whorls—are much more
numerous than in the Silurian; while, in the later times of the
Jura, all disappear except the involute.

But suppose we reverse the course of nature and follow back the
diminishing number of nautilian and gyroceran shelis. We then
see, upon arriving at the Silurian, that the vanishing point of these
shells, although not traceable on account of the lost records of
Protozoic time, could not have been far distant, while the increas-
ing number and varied forms of the straight cones indicates for
them a more remote focus in time and consequently a more ancient
origin. ‘Thus we are able to see, that antecedent to the Silurian,
in the Protozo:c, there must have been a time when the straight
cones or their immediate ancestors predominated, to the exclusion
of the coiled and perhaps even of the arcuate types.

The involute shells of the earliest geological times were, there-
fore, probably evolved from the straight cones in regular succession ;
and we may, perhaps, hope to eventually get the evidence of this
succession in the fossils themselves. The exact counterpart of our
logical picture, as Barrande has truly stated, does not, however,
exist in the known geological records of later periods. Judged by
the cormmon classification, by the prevalent ideas about the affinities
of adult structures, and by the modes of occurrence of fossils in the
rocks, the forms seem to be without law or order in their succession,
and that eminent author’s objections to the theory of evolution
have never been fairly met and refuted by any modern writer.

But let us imagine, during the Paleozoic, a different condition of
affairs from what is now the general rule. Let us suppose such a
thing possible as the quick evolution of forms and structure, and

O67

that in these ancient periods, near their points of origin, animals
found the earth comparatively unoccupied, and were not only able,
but in fact forced, to migrate in every direction into different habi-
tats, and to make perpetual efforts to readjust their inherited struc-
tures to the new requirements demanded by these comparatively
unoccupied fields. Food and opportunity would have acted, in
such localities, as stimulants to new efforts for the attainment of
more perfect adaptation and for changes of structure useful to that
end. Wecan neither imagine the effort to change of habitat and
consequently change of habits, without their cause the primary
physical stimulant of change in the environment, nor the changes
of structure, except as results-of efforts on the part of the organ-
ism to meet the physical requirements of the surroundings. That
this process should end in the production of structures suited to the
environment is inevitable. With these factors at work, both without
and within the organism, the evolution of their structures obey a
physical law which acts amid a thousand disturbing forces perhaps,
but nevertheless must act with predominating force in one mean path
or direction, the resultant determined by the environment and the
inherited structures of the organism.

One can compare the changes taking place during the whole of
Paleozoic time with those known to have occurred in certain 1so-
lated cases in more recent times; such, for example, as that of
Steinheim, where a single species, finding itself in an unoccupied
field, proceeded with unexampled rapidity to fill it by the evolution
of new series and many species, all differing from each other, but
all referable, by intermediate varieties, to the original form—in this
example, a single species, the well-known Planorbis equiumbilica-
tus.*

The rapid evolution of the entire family of the Arietidz can also
be used to illustrate this point.. This family originates from one
ancestral species and yet the process is so rapid that eleven distinct
series and seven genera arise, culminate and disappear within the
limits of a single age of geologic history, the Lower Lias of Europe,
South America and North America.}

There are a number of other well-known cases, which could be
cited, illustrating the quick evolution of species in locations which

* “Genesis of Tertiary Species of Planorbis at Steinheim,’’ by Alpheus Hyatt, Memoirs
50 Year Anniv. Bost. Soc. Nat. Hist.

+ “‘Genesis of the Arietidz,’? by A. Hyatt, Smithson. Contrib. No. 678, Mem. Mus.

Comp. Zool.

368

were obviously free when they first entered them. If we admit
such possibilities, and then find similar phenomena in the Paleozoic
epoch, we shall no longer need our first picture, but can construct
a far more natural one.

The Nautiloidea will not then present themselves as a simple
chain of being, but as they really were—several distinct stocks or.
grand series, arising from a common stock or radical, and each of
these grand series divisible into many parallel lines of genetically
connected forms. In the Lower Silurian, some of these do not
have close-coiled forms at all; some of them have: but all, except
the most primitive series, which are composed wholly of straight or
arcuate forms, have some close-coiled species. These we can often
trace directly with the greatest exactness, both by their develop-
ment and by the gradations of the adult forms, to corresponding
species among the straight shells.

The series we have described above, from the straight Bactrites
to Goniatites, compares closely with any single genetic series of the
Nautiloidea, and shows that this last arose very suddenly in the
Protozoic, and evolved true nautilian shells in the Calciferous and
Quebec groups on the earliest fossiliferous level known positively to
contain the remains of Cephalopoda.

The genera of Ammonoidea evolved in the Silurian and Devonian
are structurally much more distinct from each other than any groups
of the same value (z. e., genera) in the succeeding formations, and ~
thus, in different but equally plain characters, teach us that they
also had a quicker evolution within those periods than in the later
formations. Either this was the case, or else the Ammonoidea were
created in full possession of an organization only attained by
similar parallel series of congeneric, close-coiled nautiloids, after
passing through all the intermediate transformations above described.

These comparisons bring out other curious results. Thus although
both are orders and taxonomically equal, we cannot compare the
whole of the Ammonoidea with the whole of the Nautiloidea, but
only with a more or less perfect single series of that order.

The radicals of the Nautiloidea, Diphragmoceras, Endoceras,
Orthoceras and Cyrtoceras, evolve through time as an organic
trunk giving off an indefinite number of small branches in Paleo-
zoic time, each branch complete in itself and composed of suc-
cessive species becoming more arcuate, coiled and closer coiled and
finally involute. In the Trias the trunk comes to an end, but a small

369

number of branches composed entirely of close-coiled forms con-
tinue the existence of the order.

The Ammonoids have similar straight radicals, but these are few
in number, dying out in the Devonian, leaving in that period a
number of branches of closely coiled and involute forms, the
Goniatitine. These immediately manifest a capacity for expansion
and become the radicals of other involute and more modified invo-
lute series which expand in the Trias and Jura, becoming less
numerous and degenerate in the Cretaceous and cease to exist with
that period or soon afterwards. The history of the Ammonoidea so
far as the succession of different forms is concerned is as a whole
like that of a single series of the Nautiloidea which can be traced
back to a primary straight radical and which has a complete history
of modifications, but which necessarily occupies much less space
chronologically, evolving and disappearing within perhaps the limits
of a single epoch of geologic time.

The trunk of the Nautiloidea is in other words a huge cone-like
trunk, clothed with branches but topped only by a few straggling
persistent survivors shooting up through time and reaching the
present surface with the tipofa single twig. The trunk of the Am-
monoidea is only a slender short branch, springing from the Nauti-
loid trunk, but spreading out and splitting up into many smaller
branches. Like a climbing vine of huge proportions it ascends
through geologic history, resting upon the level of each age or epoch
as upon a horizontal trellisand spreading into great masses of branches
at each of these resting places. It shows throughout its evolution
less power to resist the action of the surroundings both in the num-
ber and high specialization of the forms produced withevery change
in geologic history, but also in the more rapid and earlier disap-
pearance of each type, and finally in the total disappearance of the
entire order.

This comparison fully accords with the true picture of the genetic
relations. The remarkably sudden appearance and fully developed
structures of these earlier ammonoids finely illustrates the fan-like
character of the evolution of forms from centres of distribution, and
the quickness with which they must have spread and filled up the
unoccupied habitats.

The contemplation of the wonderful phenomena presented by
these series has finally led the author to the conclusion that the

370

phenomena of evolution in the Paleozoic were distinct from those of
later periods, having taken place with a rapidity paralleled only in
later times in unoccupied fields, like Steinheim.

The hypothesis of Wagner, that an unoccupied field is essential
for the evolution of new forms, gains immensely in importance, if
it is practicable to apply it to the explanation of the morphic phe-
nomena that have been observed. Every naturalist must see at once,
by his own special studies, that this is a reasonable explanation of
the rapid development of types in new formations and of the sud-
den appearance of so many of the different types of invertebrates in
the Paleozoic.

Newberry’s theory of cycles of sedimentation shows that the sud-
den appearance of types is inexplicable, except upon the supposition
that their ancestors retired with the sea between each period of de-
posit, and again returning after long intervals of absence made their
appearance for the first time in a given littoral fauna bearing
changed characteristics and different structures acquired by the
migrations of their own stock in unknown seas.

With this explanation and that of Wagner the facts that have
been observed fully coincide, and amply explain the phenomena,
both of sudden appearance in the first deposits of formations, and
subsequent quick development in the necessarily unoccupied
habitats. The researches of Barrande, Alexander Agassiz, Bigsby,
Gaudry and many others, show us that this must have been especially
true of the Paleozoic as compared with subsequent periods.

In order to make a logical and generalized picture of correspond-
ence between all the changes in the life of a nautilian close-coiled
shell and the life of its own group accord exactly with the facts, care
must be taken to limit it to groups quickly evolved, and these ex-
clusively Paleozoic. Among Nautiloidea there are no series trace-
able directly to arcuate forms after the expiration of the Carboni-
ferous. This is the common story, and we can see that the series
must have risen very rapidly during the Paleozoic, branching out
on every side from the common ascending trunk of the straight and
arcuate forms. The same is true of the Ammonoidea in the
Silurian, but only one short series, the Nautilinidz, arises from the
common trunk of straight cones. The close-coiled shells of this
one family became the stock form for the whole of the Ammonoidea.

The Nautiloidea of the Mesozoic are all nautilian forms, and
their genetic series do not present the rapid changes of form

sya

observed in the Paleozoic; they are all close coiled and have, as
observed by M. Barrande, small umbilical perforations. This same
statement applies also to the Ammonoidea; when near their point
of origin in the Silurian their forms are very quickly evolved, but
are much less quickly evolved after this period. The smaller gen-
etic groups in the Paleozoic are distinguished by differences between
the sutures, which are decided indications of structural distinctions.
Thus the groups of Clymeninne and Goniatitinze differ widely in
their sutures and position of siphuncle, and smaller groups have also
decided structural differences. In later times the families and, in
fact, the whole of the Ammonitine are more alike. There are
many genetic series in the Jura which can be distinguished by the
minor details of the ornaments and outlines of the sutures, the dif-
ferences being less structurally than in the Paleozoic. In other
words, the field of variation is structurally decidedly narrower in
the Mesozoic than in Paleozoic, whether we consider the Nautiloidea
or Ammonoidea.

I have observed the same phenomena repeated in each period
and in the mode of appearance of the genera and families in
lesser divisions of geologic time. Groups originate suddenly and
spread out with great rapidity and often, as in the Arietidz or the
Lower Lias, are traceable to an origin in one well-defined species
which occurs in close proximity to the whole group in the lowest
bed of the same formation. These facts and the acknowledged
sudden appearance of the greater part of all the distinct types of
Invertebrata and Vertebrata in the Paleozoic speak strongly for the
quicker evolution of forms in that time and indicate a general law
of evolution. This has, in former publications, been formulated
as follows: Zypes are evolved more quickly and there are greater
structural differences between genetic groups of the same stock while
still near the point of origin than appear subsequently. The varia-
tions or differences take place quickly in fundamental structural
characteristic, and even the embryos may become different when in
the earliest period of evolution, but subsequently only more superficial
structures become subject to great variations.

This law applies only to the epacme or rise and acme, not to the
paracme or decline of the same genetic groups or stocks. These
last will be shown further on to reverse this law of progressive evo-
lution.

The degraded uncoiled forms of the Nautiloidea and Ammonoi-

O62

dea, wherever they occur, whether in the Silurian or in the Creta-
ceous, invariably have coiled young, showing that they were the
offspring of coiled or nautilian shells, that is, of progressive forms
which have themselves been evolved from a series of straight arcu-
ate and gyroceran predecessors. ‘Their uncoiling is a truly retro-
gressive character, and this tendency is inherited in successive
forms in several series, and thus the whole structure is finally
affected, the whorl reduced in size, and the complication of the
sutures and shells at all stages of growth is degraded until, in the
development of the individual, only the close-coiled young remain
to testify to their exalted ancestry. In other words, the forms really
inherit degraded characteristics at such an early stage that it affects
their whole life except the earlier stages.*

If we examine any of the progressive series we find that charac-
teristic modifications or variations tend to appear first in the later
stages of growth and, asa rule, in adults, then in successive forms
of the same genetic series they tend to appear at earlier stages of
the ontogony and finally often disappear altogether or become
embryonic, and this is the case also with the degraded characteris-
tics. This is clearly shown in the illustrations given on Pls. ii, 111,
iv, especially in the history of the development of the sutures
among Ammonitine. The simpler sutures of the Nautilinidee of
the Silurian and Devonian have undivided ventral lobes and broad
lateral lobes. The more specialized forms of the same suborder in
the Devonian have the ventral lobes divided, prominent saddles are
also introduced, and the lateral sutures become more sinuous.
These characters, especially the division of the ventral lobes, occur
in these forms (as in Fig. 17, Pl. 2) in an early neanic substage,
having replaced the hereditary undivided ventral of the adults of
the Nautilinide and forced this characteristic back until it is
repeated only in the earlier or paranepionic sutures. In the Am-
monitine of the Trias and Jura this process is carried still farther.
The repetition of the undivided ventral of the Nautilinide is con-
fined to the earlier septa, which show sinuous lateral outlines (as in
Figs. 2, 3, Pl. 4) and these septa become immediately convex, the

* Several examples are given of such forms among Nautiloidea in the text and the
similar uncoiling of the gerontic or senile stage is shown in the ontogony of a number of
species in the plates, notably Eurystomites kelloggi (Pl. iv, Fig.1). Among Ammonitine
see young of Crioc. studeri (Pl. iii, Figs. 11, 12), Crioc. studeri, after Barrande (PI. ii, Fig.

40), Ancyloc. calloviense, after Barrande (PI. ii, Fig. 41), and Baculites, after Brown (Pl.
iii, Fig. 18).

first one alone being coricave, the divided ventral is introduced
earlier in'the ontogony and, finally, the division of the outlines by
digitations occurs in the earliest neanic substage, replacing the sim-
pler sinuous outlines of the preceding suborders.

In the evolution of a series heredity therefore acts according to a
definite law of replacement. Zhe ancestral characters are brought
anto contact with new adaptive characteristics, which are being con-
tinually introduced into the adult and adolescent stages of ontogeny,
and these eventually replace the former which are crowded back to
make room for them into earlier stages than those at which they first
appeared, and in many cases the latter are resorbed and disappear
during this process.

It is a fact, as shown by the writer and especially by Barrande
and Dr. Branco, that the embryonic shell has varied comparatively
little throughout time in the Ammonoidea, Nautiloidea, Belem-
noidea and Sepioidea. But these statements do not apply to the
earliest times in evolution of these types, when they branched off
from the common stock. The embryos of the Ammonoidea and
Nautiloidea become quite different from each other, the embryos of
the Belemnoids remained like those of the Ammonoids, almost
exactly similar to those of the Nautilinide as shown by Chalmas
and Branco, and finally in the Sepioidea, the protoconch or em-
bryonic shells changed more completely and soon disappeared.
Attention has been already called to this remarkable fact in the
‘ history of the evolution of these forms, that the separation of the
orders took place rapidly, and in the embryos as well as in the
adults near the origin of the orders, and that the comparative
invariability of the embryo was confined to the subsequent history
of these types after separation. There is also considerable ground
for the conclusion that the young, not the earliest stages of shell,
are more variable among the degraded types than among progres-
sive forms. The facts already stated with regard to the young of
Baculites and some crioceran forms show this.

This paper cannot be devoted to the discussion of the apparent
reasons for these changes, but we have been able to explain the
mode in which they take place. Zhe mode in each case ts the ear-
lier or accelerated development of ancestral characters, which as we
have said follow the same law, whether progressive and tending te
preserve the characters of the type, or retrogressive and tending to
destroy the characters of the type.

S74

Attention is given to the acceleration of development because it will
be used in this paper and also because in looking at the young in the
usual haphazard way, naturalists often do not find the strong marks
of affinity which the ordinary modes of studying lead them to
anticipate. The law of acceleration explains the disappearance of
important characteristics which often occur even in short and com-
paratively small series. It acts frequently within a small group like
the Arietidz, so that the later larval and adolescent stages are
unlike the same stages in very nearly related species in the same
family. Unless investigators are willing to take a small well-char-
acterized group and follow out all its transformations they cannot
hope even to understand the remarkable phenomena which are
shown more or less in the history of every complete genetic series.

Embryologists generally consider it essential to associate all
forms having similar embryos, and to place widely apart in classifica-
tion all forms having different embryos. Asa matter of experience
that is correct, but it does not apply to the earliest times in the
evolution of types and the surest guides of affinity are sometimes
the adult gradations of forms. These show that the Nautiloidea and
Ammonoidea with comparatively distinct embryos are nevertheless
more closely related than the Belemnoidea and Ammonoidea which
have precisely similar embryos, and Sepioidea and Belemnoidea
which have very distinct embryos must also be affiated.

The embryos of all these must have been precisely similar at
their origin, but they afterward became varied in the different
orders, and we cannot lay down any hard and fast rule by which
the embryo becomes an invariable criterion of affinity. We think
there is ample reason in the structures of these shells themselves to
account for the embryonic differences, and that it is possible to
reconcile them with the affinities indicated by the gradations
observed between the adults. These reasons which we have only
space to allude to here consist in tracing the gradations of adult
structures and in a series of correlations which are plainly apparent
between the adult structures, and the habits of the animals, and the
power which habits in conjunction with effort have to change the
adult structures, and then by the action of the law of acceleration
in heredity to change even the embryos, either quickly, when the
habits are widely changed, or more slowly when they vary but
slightly with the progress of time.

Evolution is apparently a mechanical process in which the action

305

of the habitat is the working agent of all the major changes; first
taking effect as a rule upon the adult stages, and then through
heredity upon the earlier stages in successive generations. Thus
in the open fields of the periods of their origin they expanded into
their different habitats, varying to accomplish this purpose with
great rapidity, but once in their appropriate habitat, inducements
to change or open fields became rarer and we get as a result com-
parative invariability. As time rolled on and the earth became
more crowded, the variability was reduced to less and less import-
ant structural changes, except in the retrogressive types. These
exceptions are our best proofs of the action of the habitat. The
changes in these retrograde forms are again remarkable for
the rapidity in which they take place, and some of these types, at
least, can be shown to have occupied free fields where they met
with new conditions, and to have changed their habits and struc-
tures rapidly to accord with these new conditions.

In 1843 Auguste Quenstedt began researches which ought long
ago to have led to this solution. He demonstrated by repeated ex-
amples, that among diseased types the most extensive changes of
form and structure might take place in a single species, and within
the narrowest limits of time and surface distribution. Quenstedt
was thus the first to show that in diseased forms the shell had the
inherent habit of reversing the process of growth and evolution, and
of becoming more and more uncoiled by successive retrograde
steps. Von Buch and Quenstedt, master and disciple, and the
author independently of either of these predecessors, in three suc-
cessive researches, have arrived at the identical conclusion, that
these uncoiled shells are truly distorted, or, as we may more
accurately express it, pathological forms. They are not, however,
rare or exceptional, as one might at first suppose, but occur in num-
bers and in every grade, from those that differ but lhttle from the
normal forms, to those that differ greatly; from those that are ex-
ceedingly confined in distribution, to those which lived through
greater lengths of time. SBut in all cases they exhibit degradation,
and are expiring types. The author has repeatedly traced series of
them, and studied their young, partly in Quenstedt’s own collec-
tion. In all cases they show us that great changes of form and
structure may take place suddenly ; and this lesson could have been
learned from Quenstedt’s work and example as well forty years since
as now.

346

When we attempt to understand these pathologic uncoiled series
and forms, which show by their close-coiled young that they were
descended from close-coiled shells, we find ourselves without com-
parisons or standards in the early life of the individual. ‘The laws
of geratology—that the old age of the individual shows degradation
in the same direction as, and with similar changes to those which
take place in successive species or groups of any affiliated series of
uncoiled and degraded forms—here come into use, and serve to ex-
plain the phenomena. This correspondence is shown in the uncoil-
ing of the whorls, loss of size, the succession in which the orna-
ments and parts are resorbed or lost, the approximations of the
septa, and position of the siphuncle. It is quite true, as first stated
by Quenstedt and also by D’Orbigny, that every shell, when out-
grown, shows its approaching death in the closer approximation of
the last sutures, the smoothness of the shell, the decrease in size,
etc.; but, in order to realize that these transformations mean the
same thing as those which take place in any series of truly retro-
gressive forms, we have to return to the types in which unfavorable
surroundings have produced distortions or effects akin to what
physicians would term pathological. .

This frequently happens in small series of Nautiloidea ; and, if
we confine ourselves to these, we can make very accurate com-
parisons: or, on the other hand, in the case of the Ammonoidea,
we may trace the death of an entire order, and show that it takes
place in accordance with the laws of geratology. Such series,
among the Nautiloidea, are abundant in the earlier formations ; but
they have not the general significance of the similar forms among
the Ammonoidea, and can be neglected in this article. There are
no known cases of degraded series of uncoiled forms among the
ammonoids of the earlier or Paleozoic periods ; they may have oc-
curred, but they must have been excessively rare.

In the Trias and early Jura, pathologic uncoiled forms are rare
among ammonoids, butin the Middle and Upper Jura they increase
largely ; and finally, in the Upper Cretaceous they outnumber the
normal involute shells, and the whole order ceases to exist. Neu-
mayer has shown, that a similar degradation occurs in all of the
normal ammonoids of the Cretaceous, and that their sutures are less
complicated than those of their immediate ancestors in the Jura.
This proves conclusively, that the degeneration was general, and
affected all forms of Ammonoidea at this time; since the uncoiled

forms are not confined to special localities, as in the Jura, but are
found in all faunas so far as known.

The facts show that some general physical cause acted simulta-
neously, or nearly so, over the whole of the known area of the
world during the Cretaceous period, and produced precisely similar
effects upon the whole type as had here and there been noticeable
only within limited localities and upon single species or small num-
bers of species during the previous periods. ‘This general cause,
whatever it may have been, affected the type so as to cause the suc-
cessive generations of the larger part of the shells to become dis-
torted, smaller and more cylindrical in their whorls, smoother and to
lose their impressed zones and their complicated foliated sutures.
In extreme cases they became again, with the exception of the
earliest stages which are usually broken off and lost, perfectly straight
cones, like the orthoceratitic radicals. So much alike are they, that
it is quite common for those who are not students of this group to
mistake the degraded Baculites for the radical Orthoceras. This
decrease in size, increasing smoothness, and uncoiling, is precisely
parallel with the similar transformations taking place during old age
in the normal involute shells of the Jura, which, when old enough,
also depart from the spiral, or tend to straighten out, and always
lose their ornaments, decrease in size, and so on.

The universal action of the surroundings, as we now know them,
is certainly not exclusively favorable to the continuance of life, and
may. be wholly more or less unfavorable. It certainly perpetually
excites the animal to new and more powerful exertions, and, like
perpetual friction, wears out its structures by the efforts which it
obliges it to make for the support of the structures in doing -work.
At first this leads to development, the supply being greater than the
demand ; but sooner or later, and with unvarying certainty, the de-
mand exceeds the powers of supply, and old age sets in, either pre-
maturely, or at the termination of the usual developmental periods.
The remarkable and at present unique example of the Ammonoidea
places us in a position where we can see the same process taking
place in the whole of a large group, with attendant phenomena
similar in every respect to those which we have observed in indi-
vidual shells of the same order.

In numbers of species and genera, and in the complication of the
internal structures and the production of the external ornaments on

318

the shells, the order reaches what appears to be the acme of evolu-
tion in the Jura; then retrogression begins, and, steadily gaining,
finally affects all forms of the type, and it becomes extinct. Smaller
series of the Ammonoidea and Nautiloidea go through the same pro-
cess within their more restricted time-limits, and in the same way,
but can be compared with the individual much more accurately and
closely. It is evident, then, that the comparison of the life of an
individual with that of its immediate series or group reaches a high
degree of exactitude, and that the observed phenomena of the life
of an individual should enable us to explain, in some measure, the
equivalent phenomena of the life of the group; and we are unavoid-
ably led to entertain the expectation that it does explain it.

The evidence is very strong that there is a limit to the progres=
sive complications which may take place in any type, beyond
which it can only proceed by reversing the process, and retrograd-
ing. At the same time, however, the evidence is equally strong
that there are such things as types which remain comparatively
simple, or do not progress to the same degree as others of their
own group. Among Nautiloidea and Ammonoidea these are the
radical or generator types. No case has yet been found of a highly
complicated, specialized type, with a long line of descendants tracea-
ble to it as the radical, except the progressive: and all our examples
of radicals are taken from lower, simpler forms; and these radical
types are longer-lived, more persistent and less changeable in time
than their descendants.

We find the radicals of the Nautiloidea living throughout the
Paleozoic, and perpetually evolving new types in all directions;
then this process ceases, and the primary radicals themselves die
out. But they leave shells, which are in that stage of progression
which I have called the nautilian. These, the more direct descend-
ants of the radicals, become secondary radicals and generate series
having more involute shells. These, in turn, as secondary radicals,
exhibit a greater chronological distribution than their descendant
involute forms. The same story may be told of the Ammonoidea,
but substituting at once the close-coiled shell (the secondary radicals)
for the primary radicals of the Nautiloidea, even as far back as the
Devonian. .

This is the essential element of difference between the life of the
whole order and that of the individual. One can accurately com-
pare the rise and fall of the individual and its cycle of transforma-

ot9

tions with that of any of the single series or branches of the same
stock which become highly specialized and then degenerate ; but,
when an attempt to go farther is made, similar difficulties arise to
those encountered in tracing the progress of types and orders. The
radical and persistent types are still present, and teach us that, as
long as they exist sufficiently unchanged, new types are a possibility.
I have traced a number of these in the two orders, and have
found that they change and became more complicated, and that
probably a purely persistent or entirely unprogressive type does not
exist among the fossil Cephalopoda.

The most celebrated example of unchanging persistency has been,
and is now supposed to be, the modern Nautilus. The similarities
of this shell to some of the Silurian coiled forms—which have
caused Barrande and others to suppose that it might be transferred
to the same fauna without creating confusion—belong to the cate-
gory known to the naturalist as representative. It is similar in
form, and even in structure, in the adults, but has young with en-
tirely distinct earlier stages of development, and belongs to dis-
tinct genetic series. The young of the existing Vautilus pompilius,
shown on PI. i, can be easily compared with those of their supposed
nearest congeneric shells, Barrandeoceras of the Silurian given on
Pl. v, Figs. 6-10.

Comparative invariability or persistency is common to all
radicals; and they force us to recognize the fact that the orders
could have produced new series, as long as they were present,
if it had not been for the direct unfavorable action of the physical
changes which took place, so far as we now know, over the
whole earth, Thus, in making comparisons between the life of
the individual and the life of the group, one cannot say that the
causes which produced old age and those which produced retrogres-
sive types were identical: it can only be said that they produced
simiar effects in changing the structures of the individual and of
the progressive types, and were therefore unfavorable to the farther
development and complication of these types. In their effects they
were certainly similar; but in themselves they might have been,
and probably were, quite different, agreeing only in belonging to that
class of causes usually described as pathological, or those whose
nature can be generally summed up as essentially unfavorable to the
progress, and even to the existence, of the organism.

In order to understand the meaning of these evidently degraded

380

structures, we must turn back to the first remarks upon the order.
The apertures and forms of the retrogressive shells all show that
they were exceptional, that they had neither well-developed arms
for crawling nor powerful hyponomes for swimming; that, in other
words, they could not have carried their spires in any of the ordi-
nary ways. Their habits, therefore, must have been more or less
sedentary; and like the sedentary Gastropoda, Fissurella, Patella,
etc,, as compared with the locomotive forms, they presented degen-
eration of the form and structure of their more complicated ances-
tors. Their habits did not require the progressive grades of struc-
ture, and they dispensed with or lost them; and in many cases this
took place very rapidly. This retrogression was in itself unfavor-
able to a prolonged existence ; and the phylogerontic nature of the
changes tells the same story, and one can attribute their extinction
to the unfavorable nature of their new habitats, and also call them

pathologic types without fear of misrepresenting their true relations

to other forms.

II. PRINCIPLES OF BIOPLASTOLOGY.

Relying upon the results of such researches as are described
above and especially upon those of Cope, Ryder and Packard, I
have in a former publication used the name Bioplastology to desig-
nate that branch of research which deals especially with the char-
acteristics of development and decline in the life of an individual
and endeavored to show that correlations exist between these and
the life history of the group to which the individual belongs. In
order to classify this branch of research properly it 1s necessary to
separate it from other allied modes of studying organic phenomena.*

/
AUXOLOGY OR BATHMOLOGY.+

Mr. Buckman and Bather, both well known for their original and
instructive researches on Paleozodlogy in England, have recently,
in a joint paper under the title of ‘‘The Terms of Auxology,’’f
criticised the nomenclature employed in my papers to designate the
stages of growth and decline in the individual. They have also

* The author has given a synopsis of the facts that seem to characterize the different
branches of research and their relations to Bioplastology in a paper entitled, ‘‘ Bioplas-
tology and the Related Branches of Biologic Research,’’ Proc. Bos. Soc. Nat. Hist., xxvi,
pp. 59-125 ; and a brief preliminary abstract appeared in Zool. Anzeiger, Nos. 426, 427, 1893.

+ Cope, Proceedings Phil. Soc., Phila., Dec., 1871, and Origin of the Fittest, p. viii, ete.
t Zool. Anz., Nos. 405, 406, 1892.

381

proposed in view of the correlations which have been shown to
exist between the transformations that occur in the stages of devel-
opment and decline in the individual and those that characterize
the evolution of the group to which it may belong, to designate the
study of these correlations by the new term ‘‘ Auxology,’’ This
term is open to the objection that it is derived from a=, meaning
simply progressive growth up to and including the adult stages, and,
although in common with others I have felt that it has claims to be
retained, there are good reasons why it should be restricted in
application, if adopted, to researches upon growth. I have placed
alternative terms at the head of this abstract, because one or the
other is likely soon to be adopted and I hardly feel competent to
arrive at a decision myself without further study of the facts.

Cope in his ‘‘ Method of Creation of Organic Forms,’’ used the
term Bathmism from Ba6yds, meaning a step or threshold, to
designate growth force, and it is therefore questionable whether
the term Bathmology should not be substituted for Auxology in
order to give uniformity to the nomenclature.

Dr. C. 5. Minot, who has given the first demonstration of the
fundamental law of growth, has shown that the common notions
with regard to the action of this force in organisms are erroneous.
His plotted curves of the actual additions in bulk to the body by
growth during equal intervals of time in guinea pigs show that
these increments are in steadily decreasing ratio to the increase of
weight of the animal from a very early age. He was so much
impressed by these facts that he characterized the whole life of the
individual as a process of senescence or growing old.

This law is applicable also to the growth of the body as measured
by the ratio of the increase of the shell in all its diameters and by the
distance apart of the septa with relation to the ratio of increase of the
transverse diameters of the volution. The great rapidity of the
growth starting from the apex of the conch is obvious and can be
observed in all the figures of the young given in this paper which
spread out suddenly in the building of this part of the skeleton.
The septa mark successive arrests in this process of construction,
and it can be readily seen that the first septa are wider apart in
proportion to the diameters of the volution in the nepionic (larval)
stagethan in the early part of the neanic (adolescent) stage and
that more uniformity in the distance apart occurs in the ephebic
(adult) stages until the last of the gerontic (senile) stage is reached.

DO2

Then the septa alter in this respect and finally in extreme parage-
rontic substage the approach of extinction is heralded by the close
approximation of several septa, as has already been stated above.
The greater number of these that show this change indicate that the
species possess great vital power and has a prolonged old age
changing slowly, and the small number show that senility is a more
rapid process. In the higher, more specialized Nautiloids and
Ammonoids there are usually only two or three approximate septa
in old age; in Endoceras, a radical type, there may be as many as
twenty-two which show degeneration in the rate of growth. There
are other phenomena of a similar character which might be noticed
in this connection, but must be deferred to future publications.

Naturalists have as a rule understood the differences between the
organic molecular increase that takes place within cells which is the
simplest form of growth, and that which follows this and builds up
the tissues of the body by the division of cells. Both of these pro-
cesses, although distinct from each other, result in additions to the
bulk of the whole body of the organism and come properly under
the head of growth. But while both are thus constructive so far as
the body is concerned, only one can be considered constructive or
anabolic while the other is essentially destructive or catabole SO 0 far
as the cell itself is concerned.

The function of nutrition and the nature of the organic structure
are the two essential factors of growth, and this term, z. ¢., growth,
also obviously applies to the morphology of metabolism, consisting of
intracellular increase, or anabolism, and cellular development, or
catabolism, and the phenomena resulting from the alternating
action of these in ontogeny. This at once shows that growth is not
simply progressive addition to the bulk of the body, since the mul-
tiplication of cells by fission is in itself catabolic or developmental
so far as the cells are concerned. Further than this the ultimate
results of catabolism are of the nature of reductions as is shown by
Minot’s law,* and also by Maupas’ observation} on the old age of
the agamic cycle in Infusoria and the results of late researches on
amitosis in cellular fission. These and the actual reduction of the
body taking place in extreme senility show that the term growth

* “Senescence and Rejuvenation,’’ Journ. Phys., xii, No. 2, 1891, and address on “ Cert.
Phen. of Growing Old,’’ Am. Assoc. Adv. of Sc.i, xxxix, Aug., 1890.

t ‘“‘ Recherches expérimentale sur la multiplication des Infusores ciliés,’’ Arch. de Zool.
experim. et gén., Sr. 2, vi, pp. 165-277, et ibid., vii, pp. 149-517.

383

covers decrease in bulk due to development and use as well as in-
crease.

When one passes beyond this and attempts to deal with the char-
acteristics of ontogeny or phylogeny he at once finds himself in the
presence of other forces, such as heredity and other processes,
namely, the acquisition of new characters and the renewal of the
powers of growth in nuclear substances by means of conjugation.

The manifestation of growth energy, in brief, arises from two
factors, or, at any rate, is always found associated with two, a living
organism and assimilation of nutritive matter, and is an obvious
result of their union.

GENESIOLOGY.

The term heredity has been used in two senses, one expressing
the results of the action of an unknown force which guides the
genesis of one organism from another and a second in which it
implies the force itself. Clearness of statement demands that some
other term than heredity should be used, and I have consequently
proposed to designate the study of the phenomena by the term
Genesiology, from Iveors, meaning that which is derived from
birth or descent, this force itself as genetic force, and the principle
of heredity thus becomes genism.

The continuity of the same element in the agamic division of
unicellular bodies, as in Protozoa, makes it comparatively easy to
explain the transmission of likeness, but this is growth of the onto-
genic cycle. Maupas shows this clearly and continually speaks of
the growth, full-grown virility, and senility of his generations of
unicellular, agamic protozoans. In fact they are obviously in a
disunited form the equivalent of the colony of protozoans, and
secondarily, although more remotely, the equivalent of the single
metazoan, or individual, which is essentially a cycle of agamic cells
reproducing by fission.

While this likeness of agamic daughter cells to the original agamic
mother cell which has disappeared in them may be considered a
manifestation of heredity, it is also a form of growth and readily
separable from the more complicated relations of organism pro-
duced by conjugation of two forms. When the transmission of
likeness is complicated with the effects of conjugation the difficul-
ties increase until finally, in the bodies of the Metazoa, they culmi-
nate in a problem of surpassing difficulty. Heredity is as plainly

do4

written in the life history of the Protozoan and in the growth of
cells, in the tissues in the budding of the Metazoa and partheno-
genesis as in these more complicated forms, but the phenomena of
transmission occurring after conjugation can be separated from
growth and considered upon entirely distinct lines.

The theories offered show this. Thus the corpuscular theories,
whether gemmules or biophors or pangenes are assumed, assert the
need of minute bodies for the transmission of characters, while on
the other hand the dynamic theories, maintained principally by
American authors, are more in accord with physical phenomena in
assuming that there is a transmission of molecular energy, and some
of these views support Hering’s theory of what may be called mne-
megenesis, namely, that heredity is a form of unconscious organic
memory, and this, from my point of view, is the only satisfactory
one yet brought forward.

Heredity is obviously manifested, for the most part, in the devel-
opmental results of growth and appears chiefly in the cytoplasmic
structures which Dr. Minot so clearly places before us as constantly
increasing with age while the comparative size of the nucleus which
represents the power of growth force decreases. Whether this be
granted or not, it can hardly be denied that, in describing the de-
velopment of organisms along ontogenetic and their evolution along
phylogenetic lines we are dealing with cycles of progression and
retrogression which are quite distinct from the growth of the body
as determined by the laws that govern its increase and reduction in
bulk, and that one cannot describe the study of both series of phe-
nomena under the same general term without danger of confusion.

Genism, in brief, is the transmission of likeness from one onto-
genic cycle to another of the same species. It appears to be due
to the same factors as the perpetuation and rejuvenescence of the
cycles themselves, namely the union of two distinct forms of the
same species or kind.

CTETOLOGY.*

Weismann and his supporters deny that ctetetic or acquired
characters are inheritable, but it is safe to make the assertion that
this will not be maintained by the students of Bioplastology.
Within the limits of my own experience in tracing the genetic
relations of varieties and species of fossils Cephalopods and other

* V7 4 ° °
Kzn76¢, something acquired.

385

groups through geologic time, although I have tried to analyze the
behavior of all kinds of characteristics, 1 have failed to find any
such distinctions. If Weismann’s theory is true, it ought to be
practicable to isolate in each type some class or classes of modifica-
tions that would be distinguished by the fact that they were not
inherited.

It is practicable to isolate inherited characters from new variations
_which have not become fixed in any phylum. It is also practicable
to point out characters which are transient in various ways appear-
ing in individuals but not in varieties, in species but not in genera,
and soon. When one has by this system of exclusion arrived at
the end of the list, he finds that there is no class of characteristics
which may be described as non-inheritable. The new variations of
any one horizon which can be isolated from inherited ones are not
distinguishable in any way from others which occurred previously.
Later in time these new variations in their turn become incorporated
with the younger stages of descendants. The transient characters
of the zodn also do not differ in any way from others that are
inherited in allied species, genera, etc. For example, the position
of the siphuncle is very variable in some species of Nautiloidea, in
others of the same order it is invariable within a certain range, and
finally, in other species and genera it is invariable. In the Ammon-
oidea, derived from the same common stock as the Nautiloidea, this
organ attains a fixed structure and is invariably ventral from the
Devonian to the end of the Cretaceous, although in number of
forms and genera the ammonoids far exceed the nautiloids. All
characteristics, even those observable in some groups only in old
age, are found in the adults of other groups, and finally in the
young of the descendants of these, according to the law of tachy-
genesis. Everything is inherited or is inheritable, so far as can be
judged by the behavior of characteristics. Cope has ably sustained
this opinion in all his writings and has called it the theory of
‘‘diplogenesis’’ in allusion to the essentially double nature of the
characteristics first ctetic and then genic.

It is probable that what has been called effort is the principal
internal agent of organic changes as first stated by Lamarck, and
subsequently rediscovered and first maintained by Cope and subse-
quently by others in this country. The modern school of dynam-
ical evolution, or the Neolamarckian school, which has adopted this

386

theory as a working hypothesis, regards effort as an internal energy,
capable of responding to external stimuli. They include under
this name both the purely mechanical or involuntary, as well as the
voluntary reactions of organisms, whether these are simply plasmic,
or cellular, or occur in the more highly differentiated form of nerv-
ous action.

The word ‘‘effort’’ has mental connections with conscious en-
deavor, and when we enlarge the definition so as to include purely
mechanical organic reactions, this obliges every one to make an
effort to rid himself of old habits of associating it with psychic
phenomena. It not only imperfectly explains what is meant, but it
does not of itself fully convey the idea of a force capable of mold-
ing the parts of the body into new forms, and cannot be used at all
for the characteristics which originate through its action.

No apology is therefore needed for the use of Entergogenism for
the popular term effort derived from ¢vtés, meaning within, and
goyov, Meaning work or energy. ‘This term does not interfere with
the name given to the general theory by Prof. Cope—kinetogenesis,
in allusion to its dynamical character as a theory of genesis—but is
supplementary to this more general title. It is also quite distinct
from his neurism or nerve force, and phrenism or thought force,
although both of these, if we rightly understand him, are certain
forms of entergogenism.

Dr. John A. Ryder * has discussed in one of his profound essays
the relations of the statical and dynamical phenomena of develop-
ment and evolution, using the terms ergogeny and ergogenetic for
all the modifications produced by organic energy, and he considers
kinetogenesis and statogenesis as divisions of the first named.
These instructive speculations and observations were written to
show that the changes of form produced by motion, and those mod-
ifications or conditions which may be properly considered as due to
the conditions of equilibrium, are often reached, as is claimed by
Ryder, as the result of Cope’s law of kinetogenesis and are consid-
ered by him as statogenetic. These are interesting in connection
with the above, and support the remarks made elsewhere with refer-
ence to the use of terms like ‘‘ avolution,’’ and are substantially in
agreement with the general views taken in this paper, although tak-
ing up a side of the mechanics of evolution not specifically dis-
cussed here.

* “ Energy as a Factor in Organic Evolution,” Proc. Amer. Philos. Soc., Phila., xx xi, 1893.

387

The part entergogenic energy or entergogenism has played in the
production of normal reactions, hypertrophy, etc., is well known,
and the fact that an organism cannot move or respond to external
stimuli without its aid needs no illustration. It seems equally plain
that modifications of structure and form follow as the results of
such repeated actions developing into habits, and this process neces-
sarily ends in the permanent establishment or fixing of these modi-
fications in varieties and species.

This theory accounts satisfactorily for the so-called mysterious
suitability of organic structures for the work they have to do.
Such a force, capable of producing changes of structure and sensi-
tive to the impinging action of external physical conditions, must
work in directions determined by these two factors, z. ¢., the struc-
tures already existent in the organism and the external forces them-
selves. It is obvious that these actions and reactions must, as has
been already stated above, produce habits and changes of structure
which are direct responses to the environment.

If one uses the Darwinian phraseology, one can say that the
variations thus produced are natural selections, and I have called
them in other publications physical selections, although it is likely
that the use of the word selection in any way may convey an erro-
neous idea of my meaning. Selection implies the choice of some
characters or tendencies out of a number of others, and in the
minds of most naturalists it also implies the survival of the fittest
chosen by the working of the struggle for existence in two direc-
tions, in one direction between contending organisms, and in the
other between the same organisms and their surroundings.
According to the opinions maintained in this paper, however, the
organism has no such power of choosing, in the evolution of its
characteristics. It is driven along certain paths and the influence
of the struggle for existence and survival of the fittest is, if it has
any influence at all, a perturbing force which has to be accounted
for but does not seriously affect characteristics until after they origi-
nate. Characteristics, therefore, are not evolved fortuitously and
in indefinite numbers for the animal to select out those that are
favorable and perpetuate only those, but according to the definite
law of variation of Lamarck and Cope.

The dynamical school does not reject the Darwinian doctrine, but
it uses this hypothesis in its proper applications as a secondary law
explanatory of certain phenomena of survival and perpetuation of

388

characteristics after they have originated through the action of this
law. .

According to my own view of the facts, often published else-
where, its use is unnecessary for the explanation of the quick evolu-
tion of series in the early periods of their evolution near the origin
of types, also for the elucidation of the pathologic phenomena in
the quick evolution of phylogerontic forms and series.

It can also not be applied to the explanation of experimental
results, as is admitted by all experimenters and most Darwinists,
in cases where modifications have been produced by the artificial
application of physical agencies, of which there are now so many
on record in both the animal and vegetable kingdoms.

It is plainly, as Dr. A. S. Packard has pointed out, a doctrine
derived from the study of the results of evolution and cannot be

_ applied to the more general and fundamental phenomena of the ori-

gin of types, the building up of series or the origin of character-
istics. My own experience leads substantially to the same opinion,
and I find its use unnecessary except for the explanation of the per-
petuation of some characteristics that occur during the acme of the
evolution of species. ‘The perpetuation of many characteristics
which are fundamental to the organism and species is necessarily
provided for by agencies which originated them and by heredity as
soon as they become fixed in the organism. I think there is good
ground for the statement that in many cases these are plainly not
advantageous.

Weismann and his supporters are necessarily Darwinians. No
one denies that ctetic characters arise through the action of the
surroundings. If these are perpetuated through heredity, evolution
is an undeniable corollary and it must follow the path defined by
the dynamical school. If, however, ctetic characteristics may origi-
nate at the bidding of the surroundings and persist in the succes-
sive members of the same genetic series only while the surroundings
are comparatively unchanged, or in other words sufficiently alike to
continue to force their reappearance, then it must be admitted that
the law of the survival of the fittest through the action of the strug-
gle for existence is probably a fundamental law of evolution in
organism.

In other words, the battle of the two contending theories is being
fought in the domains of ctetology and it is hoped that this paper.
may be a definite contribution to the Neolamarckian side of the con-

389

troversy. I cannot give further space here to theoretical discus-
sions of this sort and am obliged to refer any persons interested
to my other works, especially ‘‘ The Genesis of the Arietide’’ and
the ‘‘ Bioplastology, the related Branches of Research,’’* in which I
have more fully given my own views.

The exclusive Darwinians are, according to the views of the
Neolamarckians, as much out of the true path in one direction as
are the empiricists in the other in appealing exclusively, as they
ofien do, to the action of the surroundings in accounting for
observed modifications.

It is certainly not a very acute analysis of the facts which attrib-
utes to external causes exclusive power in producing modifications
in many cases as has been largely done by experimental zodlogists.
For example, Brauer and the author have both pointed out this de-
fect in the accepted explanations of the famous Schmankewitsch
experiments upon Artemia, and the same may be said of the ex-
planations of all experimenters who do not take into account the
internal reactions of the organisms themselves.

The physical forces of the surroundings must act through medium
of entergogenic movements, and this is shown clearly in the nature
of modifications produced which are extra growths, substitutions of
characteristics due to changes of functions, etc., or partial or abso-
lute obliteration of these due to the failure of genetic force to re-
peat characteristics in the presence of opposing influences and super-
imposed characteristics as in accelerated development.

Ctetology should also, however, include the study of the action
of physical forces.when they either actually do produce direct effects
upon organisms or may be assumed to act in this way. Changes in
light, food, heat and moisture may cause modifications that cannot
be included under the head of entergogenic reactions without dan-
ger or confusion.

Maupas gives exceedingly instructive examples of this class, and
quotes other authorities who have investigated these effects in Pro-
tozoa.

Beddard gives a number of examples of such modifications in
his Anzmal Coloration, and Semper has also discussed the same sub-
ject more extensively in his Watiirlichen Existenzbedingungen der
Thiere.+

* Smithsonian Contributions, No. 73, and Proc. Bost. Soc. Nat. Hist., xxvi.
+ Translation by Minot, Macmillan, 1892.

390

The use of the term entergogenesis makes it practicable to in-
dicate the essential distinction existing between the modifications
produced through the mediation of internal forces and those arising
as the direct results of the action of external forces by means of
the term ectergogenesis and ectergogenic.

These explanatory remarks serve to show that Ctetology is a
branch of research which needs to be isolated from researches upon
growth and Genesiology, since it is devoted to the study of the or1-
gin of acquired characteristics, and therefore necessarily considers
all of the internal reactions of the organisms in response to the ac-
tion of physical forces, as well as the more obscure reactions of
structures which are produced solely by (or supposed to be produced
by) the direct physical or chemical action of external physical
forces.

BIOPLASTOLOGY.

The separation of Auxology or Bathmology, Genesiology and
Ctetology show also that the study of the correlations of ontogeny
and phylogeny to be distinct from either of these, and this branch
of research can be designated by the term Bioplastology from
Bios, life, and /IAactés, meaning molded or formed.*

To sum up in a few words the rather ambitious aims of this com-
paratively new recruit in the army of investigation, it aspires to
show that the phenomena of individual life are parallel with those
of its own phylum and that both follow the same law of morpho-

* Bioplasm, bioplast, bioplastic have already been used by Beale and others for the liv-
ing cell and its contents, but the term ‘‘ Bioplastology ’’ has not been used, nor have the
names proposed by Beale been generally adopted. If they were, Bioplasmology would
cover the requirements of students of such phenomena, and there is already in use Plas-
mology with about the same meaning, and Histology for the descriptive side of the study
of cellular structures.

Biogeny has been used in extra scientific literature by Fiske with the same meaning as
Bioplastology, and Haeckel has named the law of embryonic and ancestral correlation
the law of biogenesis, but there is a strong objection to both of these. Biogenesis is the
name given to the theory of the origin or genesis of life from life in contradistinction
to the assumption of spontaneous generation or abiogenesis and has a well-established
place in scientific literature. Therefore, while the law of correlation of the stages of
development and those of the evolution of the phylum may, if one chooses, be called a
law of biogenesis, it is more accurate to consider it a law of correlation in Bioplastology,
or better still, the law of palingenesis or regular repetition of ancestral characters which
very nearly expresses what the discoverer, Louis Agassiz, saw and described. The fact
that Agassiz was wrong in his theory, not believing in evolution and not recognizing
the meaning of his law in this sense, does not absolve those who profit by his labors from
recognizing his discovery of the facts and his obviously full acquaintance with the law
and:its applications to the explanation of the relations of organisms. It is Agassiz’ law,
not Haeckel’s.

O91

genesis, that not only can one indicate the past history of groups
from the study of the young, and obviously the present or existing
progression or retrogression of the type by means of the adult char-
acters of any one organism, but that it is also possible to prophecy
what is to happen in the future history of the type from the study
of the corresponding paraplastic phenomena in the development of
the individual.

Whether these claims are well founded or not the nomenclature
to be employed is a matter of importance and should be accurate,
appropriate and convenient for those who are interested in this

work.
ONTOGENY. TABLE I,
CONDITIONS. STAGES. STAGES, SUBSTAGES SUBSTAGES.
Embryonic. 1. Embryonic. Several.* No popular names.
evga Ananepionic.
2. Nepionic. { etanepionie.
Anaplasis. ( wee Paranepionic.
Ce Ananeanic.
(": 3. Neanic. { Metaneanic,
eee Paraneanic,
me Anephebic.
Metaplasis. {0 4, Ephebic. { Metephebic.
nares Parephebic.
Senile Anagerontic.
Paraplasis. ! or 5. Gerontic. { Metagerontc,
Old. Paragerontic.

Recent researches have, in my opinion, clearly demonstrated that
all the stages of development like the embryonic will have to be sub-
divided in studying rmany groups. These subdivisions are also rela-
tively important and their differences are often well defined.

The ovum and the extreme degraded substage of the senile period
represent the widest departures structurally and physiologically
from the adult, one being at the commencement and the other the
termination of ontogenesis. Departing from the ephebic stage
in either direction towards these extremes one finds the same law.
Contiguous substages of development, when considered in sequence,
differ less from each other and from the adult the nearer they are to the
éphebic stage, and they differ, on the other hand, more from the adult
and from each other in structure and form the nearer they are to the

* These stages were enumerated and more or less described under the names of Prot-
embryo, Mesembryo, Metembryo, Neoembryo, Typembryo in my paper on ‘“* Values in

Classification,” etc., and to these Jackson ndded Phylembryo in his Phylogeny of the Pele-
cypoda, p. 289.

392

two extremes of the ontogeny. ‘This is an evident corollary from
the phenomena of the ontogenetic cycle and need not be dwelt
upon here.

The terminology of the different departments of research which
come properly under the head of bioplastology is recognized at
present only in the case of embryology, but it is obvious to the
student of epembryonic development that similar terms for the
study of other stages and periods will in course of time be needed,
and in fact the old terms—nealogy, ephebology, and geratology—
are cited in that sense in the Century Dictionary, and may introduce
some confusion. It is not now necessary to discuss this question,
but only to draw attention to the facts. I therefore pass on to the
consideration of the term epembryonic.

Among fossil nautiloids it is rarely practicable, on account of
the frequent destruction of the protoconch, to find an embryonic
stage. My last work on Carboniferous cephalopods contains descrip-
tions of the entire ontogeny of a number of species, with the
exception of the embryonic stages. In such cases the fact that the
embryology is wholly omitted can be pointed out by the use of the
term ‘‘epembryonic stages,’’ and this has already been found use-
ful above. *It only remains to add that the same prefix is also useful
in designating the exclusion of other stages—thus one can speak
also of the ‘‘epinepionic’’ or ‘‘epineanic’”’ stages in this same
way without danger of confusion with any other term.*

It is often possible to employ a more specific and characteristic
designation than epembryonic. Thus among shell-bearing forms
one can distinguish between the embryonic shell and the true shell ;
for example, the protegulum and tegulum of Brachiopoda as defined
by Beecher, the prodissoconch and the dissoconch of Pelecypoda as
defined by Jackson, the periconch and conch of Scaphopoda, the
protoconch and conch of Cephalopoda. In all of these forms it is
practicable to speak of tegular, dissoconchial, or conchial stages or
periods, meaning thereby all of the epembryonic stages of these
types. | :

Haeckel, in his Morphologie der Organismen, sketched the physi-
ology of ontogeny and phylogeny and gave the general correlations
of the two series of phenomena, together with an appropriate

* Postembryonic is in use for the young stages among embryologists, and is equivalent

to the term nepionic, but it is not consistent with the other terms of bioplastology, and
is a hybrid.

393

nomenclature which has been here adopted, with some necessary
changes.

The dynamical relations of three great phases of evolution in the
phylum were designated by Haeckel * as the efacme, including the
rise of the type from its origin, the acme, meaning the period of its
greatest expansion in members and forms, and the paracme, or de-
cline towards extinction, and these phenomena were correlated with
the similar physiological phenomena of the ontogeny, and these
appear in the table of phyletic terms given below.

Previous to this, in the same volume (p. 76), Haeckel gives his
classification of the development of the individual under three
headings: ‘‘Anaplasis oder Aufbildung (evolutio),’’ meaning
thereby to include the physiological phenomena of all of the stages
developed in the four earlier stages of the individual. This is cer-
tainly a useful term for the entire series of transformations from the
fertilization of the ovum until the progressive stages are all passed
through. It does not express nor can it be used for cases of retro-
gression in which degenerative characters are introduced at such an
early age that progression is hmited to the embryonic, or to that
stage and a part or the whole of the nepionic stage.. There are
also some examples among parasites in which progression seems to
have been reduced so much that one can say it is practically elim-
inated from all stages succeeding some of the earliest embryonic.
For such forms as these the proper term would ‘be Paraplasis, from
mapa Tidoow, meaning to change the form for the worse, to deform.
Thus the stages of such forms could be collectively spoken of as
paraplastic with relation to the ontogeny of others of their own type
or allied types, whereas they could not be described as anaplastic.

The explanatory word ‘‘evolutio ’’ is here used by Haeckel ina
confined and erroneous sense. Evolution really means continuity
in time invariably accompanied by change, but whether the modi-
fication be progressive or retrogressive, or a combination of pro-
gression and retrogression, is immaterial. It is obviously better not
to use these terms for ontogenic phenomena. ‘There are sufficient

terms in ‘‘development,’’ ‘‘ differentiation of characteristics,’
‘‘rise,’’ and one has always a slight mental reservation in employ-
ing this word for the growth and development of an individual or
isolated zoon.

* Morphologie der Organismen, Vol. ii, pp. 820-366.

394

‘* Metaplasis oder Umbildung (transvolutio)’’ is used by the same
eminent authority for the adult period in a general sense, and it
appears to the writer to have useful function as a descriptive term
especially, since it is uniform with anaplasis and paraplasis. ‘Thus
one can describe the metaplastic phenomena or characteristics of
the ephebic stage in any form as metaplasis, and also speak of the
general meaning of metaplasis without referring to that stage of
ontogeny in any special form. The use of ‘‘transvolutio’’ is
obviously objectionable, since it introduces confusion and conflicts
with the proper definition of ‘‘evolutio’’ or evolution as given
above.

‘* Cataplasis oder Riickbildung (involutio),’’ used by Haeckel for
the senile stage, is open to the objection that there is no correspond-
ing Greek word, and also that zatazidoow, the only Greek verb to
which this term can be referred, means to spread over or plaster.
Paraplasis, derived from zapa zidcow, meaning to change the form
for the worse or deform, is an obviously preferable designation.
Thus the paraplasis or paraplastic phenomena of all the periods of
development or only of the paragerontic substage in ontogeny may
be spoken of and correctly described under this term.

The use of ‘‘involutio’’ as a descriptive term is objectionable,
not only on the grounds given above, but because ‘‘ involution ”’
and ‘‘volution’’ are both in common use as descriptive terms for
the peculiarities of the whorls of Gasteropoda and Cephalopoda.
Any modification of evolution is objectionable because it is mislead-
ing. For example, the word ‘‘avolution,’’ supposed to mean
things that do not evolve or have not been evolved, represents an
unnatural condition. One can, of course, conceive of matter in a
state of more or less stable equilibrium, but there are other words
than ‘‘avolution’’ in habitual use to express this conception. It
is also to be regretted that it has been applied by several eminent
writers to ontogeny, and is probably fairly established in this appli-
cation. The growth and development of the tissues is in a general
way evolution, as much so as that of a colony of Protozoa. But it
is also obvious that the product of the development: by division of
a single autotemnon, which forms a cycle, or when held together so
as to form a colony, and the product of the division of an ovum in
Metazoa held together more compactly so as to build up an individ-
ual or zoon, are not the same as the product of the evolution of an
ancestor into a phylum through successive independent forms or

395

ontogenic cycles. One cannot accurately speak of the ‘‘ growth”’
of a phylum, nor ought the word ‘‘ development’”’ to be used for
the phylum. Development should be restricted to the zo6n or
individual or its morphic equivalent among Protozoa, since it
expresses more clearly the differences that exist between ontogeny
and phylogeny than their similarities, and for the same reason it is
advantageous to use evolution for the phylum alone in the sense in
which it is commonly employed. The necessity of subdividing the
embryonic stage is admitted, and in all probability this really
includes several stages with their own substages, but the discussion
of this problem must be left to the future.

The paragerontic stage is in no sense ‘“‘atavistic’’ or ‘‘ rever-
sionary,’’ as it is defined by Buckman and Bather. Reversions are
the returns or recurrence of ancestral characteristics in genetically
connected organisms which have been for a time latent in inter-
mediate forms. Ido not think that we can include in this category
purely morphic characteristics which habitually recur in the same
individual as the result of paraplasis, or which occur in the paracme
of a type more or less invariably. In the individual the resem-
blance of the smooth round shell of the whorl of the paragerontic
ammonoid after it has lost the progressive characteristic of the
ephebic stage cannot be considered as a reversion. It is simply an-
alogy of form, not structural similarity of characteristics. A better
known and more easily understood case is the resemblance of the
lower jaw of the infant before it has acquired teeth and_ that
of the extremely old human subject in which these parts have been
lost and the alveoli and upper parts of the bony mandible have dis-
appeared through resorption. ‘The forms are alike, but no one
would venture to consider the infant’s cartilaginous jaw and that of
the old man as similar in structure.

The best example of similar phenomena in the phylum known to
me is the close resemblance of form between the straight Baculites
of the Cretaceous or Jura and Orthoceras of the Paleozoic, which
has been described above, and is figured further on. One occurs
in the paracme and the other in the early epacme of the group of
chambered shells. They are widely distinct in their structural
characteristics, and these differences are greater in the young than
at any subsequent stage of their ontogeny, Baculites having a close-
coiled shell in the nepionic stage, and Orthoceras is straight from
the earliest stage. The return of a similar form in Baculites in the

396

epinepionic periods of development in obedience to the law of the
cycle does not carry the structure back with it to a repetition of the
orthoceran siphuncle and sutures.

The structure of an individual during its development might be
represented graphically by an irregular spiral of one incomplete
revolution which describes a curve, continually increasing its dis-
tance from the point of departure until the meridian of the ephebic
stage is reached, and then beginning to return. Sucha curve would
always as a spiral rise more or less vertically, and consequently,
even if it completed the revolution, must terminate in space. It
might, perhaps, reach nearly to the same imaginary vertical plane,
but never to any point approximate to that of its departure. Structure
separates the extremes of life as widely as possible, and does not
permit us to regard them as approximate, nor can one regard old
age, however complete its return in external form, as a reversion.

One of the most noteworthy contributions of bioplastology is
that it gives proper values to this class of analogies and shows them
to be constantly recurring in the individual and in the phylum in
obedience to well-ascertained laws of morphogenesis.

The different stages have been described by Dr. Beecher among
Brachiopoda, Dr. Jackson among Pelecypoda, and the author
among Cephalopoda; and Buckman and Bather and also Blake * in
England, and Wiirtenberger in Germany have admitted their exist-
ence, and the last redescribed them. Wiirtenberger has admirably
described the phenomena of bioplastology as they occur among
Ammonitine, and correctly interpreted the iaw of tachygenesis and
its action in these forms, but failed to quote either Prof. Cope or
the author. This omission was not so remarkable as the fact that
Neumayr and some other investigators, after they had received the
printed records of the work done in the same direction in this
country, continued to quote Wiirtenberger as the sole discoverer of
these phenomena and of the law of tachygenesis. Wiirtenberger’s
work was apparently independent, and it has higher value on that
account, but it needs rectification from a historical point of view.

Buckman and Bather propose to use the prefix ‘‘ phyl’’ for forms
occurring in the phylum which represent in their adult characters
stages in the evolution of the phylum corresponding with those in
the development of the ontogeny, and give an instructive table in

*“ Evolution and Classification of Cephalopoda,”’ Proc. Geol. Assoc. Lond., Vol. xii, pp.
276-295, 1892.

O97

which Haeckel’s physiologic terms are placed side by side with
those proposed for the morphic phenomena. In following out the
same ideas the following table has been constructed, which differs
from theirs in the use of nepionic, as stated above, and also in the
use of phylanaplasis, phylometaplasis and phyloparaplasis as corre-
spondents of the similar ontogenetic terms :

SUMMARY, TaBLeE II.

ONTOGENY. PHYLOGENY.
Embryonie. Phylembryonic.
Anaplasis < Nepionic. Phylanaplasis 1 Phylonepionic. \ Epacme.
Neanic. Phyloneanic.
Metaplasis Ephebic. Phylometaplasis { Phylephebic. \ Acme.
Paraplasis { Gerontic. Phyloparaplasis Phylogerontic. \ Paracme.

Buckman and Bather gave the following appropriate example from
Beecher’s and my own researches :

‘Thus we would say that the Productidze attained their paracme
in the Permian, when they were represented by the phylogerontic
Strophalosia and Aulosteges; that the characters of the neanic and
ephebic stages of Coroniceras trigonatum are phylocatabatic’’ (here
phylanagerontic). While granting the need of using this distinc-
tive prefix for the periods of evolution in the phylum one is likely
to become confused unless he fully understands the use of the word
‘‘ phylum’’ as applicable to all grades of genetic series. Thus, in
ordinary acceptation of the term, a phylum may be the entire class
or any subdivision of it, even a single genus, provided the forms
can be shown to be genetically connected. It has been employed
in this way several times in this text after the names, species, genus,
family, etc., the ammonoidal phylum or ordinal phylum, phylum of
the Goniatitinze or subordinal phylum, family phylum, and even a
phylum of varieties and individuals.

Ahisas, (ONaelniay,

Phylum expresses genetic connection, cycle the totality of the
phenomena, whether morphic or physiologic, which are exhibited by
ontogeny or phylogeny. ‘Thus, one can describe the cycle of the
phylum in its rise and decline, the epacme, acme and paracme as
purely dynamical phenomena exhibited by the increase in numbers
of forms, etc., or the cycle of the ontogeny as shown by the in-

a ee eee eee

398

creasing complexity of the development and its decline, the ana-
plasis, metaplasis and paraplasis of the individual; or one may
describe the cycle as exhibited by the embryonic, nepionic, neanic,
ephebic and gerontic stages, or the cycle of the phylogeny as exhib-
ited by the corresponding phylostages * of evolution designated by
their appropriate prefix ‘‘ phyl.’’

There appears to be real need of two terms under the head of
cycle, one for ontogeny and the other for phylogeny. It is proposed
to use in this way ontocycle or ontocyclon for the ontogeny, mean-
ing the cycle of the individual, and phylocycle or phylocyclon for
that of the phylum. ‘This will make it practicable to use the terms
monocyclon or monocyclic, polycyclon or polycyclic, etc., to de-
scribe the number of cycles observed. Thus the ammonoids are
polycyclic, the Arietidz are decacyclic, the genus Coroniceras is an
incomplete monocycle.

It is not necessary to defend these terms before students of bio-
plastology ; they will be tested, and, if convenient, adopted. For
the benefit of others it may be mentioned that the cycle is of all
degrees of development in ontogeny. Thus, Insecta are apt to stop
at the ephebic stage and in many other animals there is a similar
limitation. On the other hand, there may be the most unexpected
development of the cycle. Thus, Podocoryne starting from the hy-
droid stage passes through a permanent colonial stage built up by
budding which gives rise by secondary buds to independent medusz.
The life of an independent medusoid bud ends with a paragerontic
substage in which the veil is destroyed, the bell is partially re-
sorbed and turned back together with the tentacles, and the pro-
boscis is left naked and projecting. In this condition the old of
Podocoryne is similar to the hydroid with which the colony began.
This gerontic transformation has been observed by Dujardin in
Cladonema and Syncoryne, by Hincks in Podocoryne and Syn-
coryne, and by Gosse in Turris.

Man is not completely ontocyclic, but makes a close approach to
this in the loss of the hair, teeth and proportions and shape of the
body; and certainly in some parts, as in the mandible described
above, there is sometimes a completed cycle.

* This word is a fearful hybrid, and I beg pardon of my classical friends in advance of
their merited wrath.

7 Dujardin, Ann. Sci. Nat., Series 3, Vol. iv, pp. 257-281, 1815; Hincks, British Hydroid
Zoophytes, Vol. i, p. XxXviii, 1868.

Oo a ee ne es

399

What the limits of the ontocycle may be has not yet been ascer-
tained, but so far as the facts are known it would appear to be coin-
cident with the limits of agamic reproduction, or, in other words,
with the limits of the growth of one autotemnon or of one ovum
after cojugation by fission, and includes all agamic generations pro-
duced by division or by budding.

The act of self-fission is similar whether it takes place for a cer-
tain cycle among Protozoa or Metazoa under purely organic condi-
tions or follows upon the conjugation of two zoéns, and is due to
the rejuvenation caused by the union of the nuclear elements of
their bodies as among Protozoa, or the more differentiated genera-
tive cells of the Metazoa. Under all conditions the cells divide in
obedience to the laws of growth, and whether the resulting daugh-
ter cells remain fastened together forming colonies as in Protozoa
or masses of tissue as in Metazoa, or whether they separate and
become distinct autotemnons or distinct zodns the action is the
same.

The product of this autotemnic function in single cells has, as
shown by the researches of Maupas, a cycle of transformations
which are like those of an individual among Metazoa, although
they may reach in some forms over six hundred so-called genera-
tions and therefore include thousands of distinct protozoans. It is
obvious to the student of bioplastology in reading Maupas’ re-
searches * that this cycle among Protozoa Ciliata is the equivalent
of the cycle of the individual among Metazoa. Although he uses
the word individual for the autotemnon he does not speak of the
successive forms as generations but as partitions, ‘‘ bipartitions’’
being his usual term, showing clearly that he recognizes these are
not generations like those of distinct successive zoOns in Metazoa.

Maupas’ researches show, as in fact he himself states, that there
is a cycle of partitions produced from one autotemnon after conju-
gation, when isolated and allowed to propagate by fission without
the renewed stimulus of conjugation with others of different broods.
The earlier successive partitions are incapable or at any rate do not
show any desire to conjugate with their fellows. Each of his cul-
tures of isolated autotemnons passed through these youthful or
anaplastic stages, and then a series of metaplastic partitions was
developed in which the micronuclei became more numerous and

* “Recherches expérimentales multiplication des infusoires ciliés,” Archiv. de zool.
expér. et géir., Sér. 2, Vol. vi, pp. 165-277 ; ibid., Vol. vii, pp. 149-517.

400

conjugation with other broods took place whenever it was permitted
by the experimenter.

In the generations immediately succeeding these, degenerative
changes, both structural and physiological, took place in the parti-
tions which were distinctly paraplastic, although the cultures were
maintained under conditions which precluded the supposition that
these changes could have resulted from unfavorable, abnormal sur-
roundings. ‘The successive partitions then ‘had gerontic transforma-
tions, lost their micronuclei, became much reduced in size and
unable to conjugate with others with the usual normal results, and
finally the external buccal apparatus was affected, reduced, or oblit-
erated, and so on. These changes were termed senile by Maupas,
who explains the entire phenomena as a cycle comparable with that
of the individual among Metazoa.

One is, of course, at this incipient stage of bioplastology, con-
fused by many apparently inexplicable phenomena. When, how-
ever, one contemplates the confusion of the most eminent authori-
ties with regard to the relations of the autotemnon among Protozoa
and Metazoa, shown by the use of the same term for the autotem-
non, the individual, and the zoon, and also the prevalent confusion
with relation to the morphology of forms designated as colonies—
some regarding the whole product of one egg as an individual and
others considering each bud or independent zooid as properly des-
ignated by that term and defining the colony as an aggregate of
more or less connected individuals—it is surprising that there
should not be more difficulties in the path of this new branch of
research.

Those who try to find the cycle of metamorphoses in their own
special branches of research will be often disappointed and probably
deny that it exists at all. Thus, in my own case, I for some time
could not find any evidence of its existence among certain cephalo-
pods, notably those having a primitive organization like Endoceras
and Orthoceras; but I have since seen well-marked senile stages in
these shells. Undoubtedly there is as great distinction between
the paraplastic and anaplastic periods, and between phyloparaplasis
and phylanaplasis everywhere, as there is between the correlations
of the corresponding periods at the extremes of the ontogeny and
phylogeny.

Paraplasis essentially differs from anaplasis, as has been described
above in treating of relations of analogy between the gerontic and

401

the nepionic stages. The earlier characteristics of the ontogeny
are, as the author has striven to explain in several publications,
essentially distinct, being in large part in most animals and in some
cases almost wholly genetic. In considering the simplest manifes-
tations of the cycle, palingenesis accompanied always by tachygen-
esis must be taken into account, and also cenogenesis in groups like
Lepidoptera, Hymenoptera, most Echinodermata, many Vermes,
where a supposed ancient and regular palingenetic record is assumed
to have been disturbed by ctetic characters acquired by the larve.*

The gerontic characters, on the other hand, and all paraplastic,
as well as their corresponding phyloparaplastic characters belong to
the category of analogies in so far as they are purely morphic
resemblances or equivalents. This is clearly shown in the physiology
of all the parts and organs in the anaplastic and paraplastic periods,
the former being full of hereditary and perhaps, also, acquired
power, and the latter more or less weakened and reduced or worn
out by the exercise of those powers and the constant wear and tear
of the surroundings.

Retrogressive reductions in every form, although often indicating
and accompanying a high degree of specialization, partake more or
less of the same nature when considered with reference to their
morphic and accompanying functional attributes, and one cannot
study such bioplastic phenomena as if they were of the same nature
and subject to exactly the same laws as progressive genetic and
ctetic characters. As I have pointed out above, and in several
other publications, there are all degrees of completeness in the
evolution of the cycle, and it is dependent upon a variety of causes
whether occurring in the ontogeny or phylogeny. If it were con-
stant and invariable and independent of the surroundings in the

* Such examples are, correctly speaking, not disarrangements of palingenesis, although
so translated by Haeckel, if I rightly understand his ideas of a confused record. Ceno-
genism does occur in such examples in obedience to the same law that governs palin-
genesis, but it occurs through the introduction of ctetic characters during the larval
instead of in the neanic or ephebic stages, and the crowding back of these upon the
nepionic and embryonic stages. The use of terms indicating that nature has confused
or destroyed its own ontogenic records of the transmission of characters in certain cases
assumes (1) that these are exceptional cases, (2) that cenogenesis is not the normal mode
of transmission in certain types in which it occurs, (3) that both of these modes of trans-
mission are not affected by tachygenesis, all of these implications being erroneous
according to the opinions expressed above. One can assume a disturbance or perturba-
tion, or decided change of mode according to law, but ‘“‘ destruction,’’ ‘‘ confusion,” or
‘« falsification’ are subjective terms inapplicable to the objective character of the phe-

nomena to which they are applied, appropriate in metaphysics, perhaps, but entirely
out of place in natural science.

402

phylum, it would not be so closely parallel to the ontogenic cycle,
which we know to be subject to great variations in accordance with
the surroundings of the individual or species.

The standard of reference in bioplastology is the ontogenic
cycle, and this should be studied first in every group. Without
a full knowledge of this, the morphology of the group cannot be
properly translated, nor can the forms be taxonomically treated
with reference to their natural relations. This branch of research
aims to complete Von Baer’s law and Louis Agassiz’s great discov-
ery of the correlations of palingenesis and phylogenesis, and it,
therefore, asserts an equal utility for the metamorphoses of the
nepionic, neanic, ephebic, and gerontic stages, provided these be
applied in each group according to the ontogenetic development of
the cycle in the zoodn and its phylogenetic evolution in the same

group.
III. ONTOGENETIC STAGES.

My own researches have led me to the conviction that subdivis-
ion of the developmental phenomena of the nepionic, neanic. and
ephebic stages are necessary, and for obvious reasons I shall take
my illustrations wholly from the shell-covered Cephalopoda.

Those who do not believe that there was a protoconch in nauti-
loids will have to reconstruct this part of the nomenclature in ac-
cordance with their own views. Having been reproached by Prof.
Blake in his address before the Geologists’ Association in 1892 in
London for holding to this opinion, it is only necessary for me to
point again to the new evidence with regard to the existence of the
protoconch given in the Introduction to this memoir.

Granting, therefore, that the conch begins with the nepionic
stage, the first part of this period is the ananepionic substage. This
substage is more or less similar in all the nautiloids on account of
the existence of the cicatrix on the point of the apex of the conch and
the surrounding comparatively smooth area which is, as a rule, ellip-
tical, the apex being in most forms of Nautiloidea, when seen from the
side, like a broad cup, and in section a laterally compressed ellipse,
the vertical or ventro-dorsal diameter being the longest.

This substage is frequently figured in the plates of this memoir,
and has been well shown in figures of several species, in the Gene-
sis of the Arietide, pp. 10, 11, and in Wautilus pompilius in Fossil

403

Cephalopods of the Museum of Comparative Zodlogy, ‘* Embryol-
ogy,’’ Vol. ii, Pl. ii, Fig. 1, and in a number of figures of Bar-
rande in his Systéme Stlurien, Pls. 487, 488, a few of which were
drawn and given to Barrande by the author. I first described this
substage among the nautiloids under the descriptive name of the
‘‘asiphonula,’’ but have since substituted the term, Protosipho-
nula. Among ammonoids this substage has been forced back into
the embryonic stage and has practically disappeared from the conch,
probably through the action of tachygenesis. The tendency of
the embryo to build a solid calcareous protoconch of imbricated
structure may be attributed to the earlier inheritance of the char-
acteristics of the calcareous, apical conch of its nautiloid ancestor.

This explanation has been supposed by Prof. Blake to show that
the protoconch of ammonoids was necessarily identical with the
apex of the shell or early part of the ananepionic substage, proto-
siphonula, of nautiloids. It would have such a meaning, perhaps,
if there were a cicatrix on the protoconch of ammonoids and if
there were not more or less rugose lumps, supposed to be the rem-
nants of protoconchs, covering up the cicatrices of the apices of
the conch in some nautiloids as figured above on page 360 of the
Introduction. These facts must be reinvestigated by the opponents
of this view, and it lies with them to prove that the latter are not
the remnants of shriveled, horny protoconchs, and that the cicatrix
was not a passageway from the embryo into the shell or at any rate
an aperture through which the animal of the protosiphonula com-
municated with the protoconch, before one can consider the facts
in a different light or admit any other hypothetical explanation.

It will be seen below that I have altered my view in so far as the
primary origin and nature of the cecum is concerned. Barrande
imagined that my view necessarily implied the passage of the em-
bryo bodily out of the protoconch into the conch, but this was a
mistake arising probably from inadequate statements. The young,
when it had passed by growth out of the protoconch, or as the an-
terior parts of the embryo grew out of the protoconch into this
position, began to build the shell, and finally at the end of the pro-
tosiphonula stage rested in the apex, which was then aseptate and
was the first living chamber. The structure of the apex in Endo-
ceras, Piloceras and Actinoceras indicates large and direct, open,
tubular connection between the protoconch and the animal when
in this first chamber through which the endosiphuncle in the

404

generalized nautiloids, Endosiphonoidea, opened into the proto-
conch.

The tubular opening of the apex in Endoceras, Piloceras and
Actinoceras and other genera having a marked endosiphuncle, is
not closed by the czecum of the siphuncle as was formerly supposed.
It is, on the contrary, directly continuous with the endosiphuncle,
as was first pointed out by Foord in his Catalogue of British Cepha-
lopoda. ‘This is an attenuated, central, more or less irregular tube
or axis formed by the extension of the points of successive endo-
cones or sheaths. It is more or less interrupted by pseudosepta,
and is a separate and distinct part occupying the axis of the large
siphuncle. This organ is continuous with some corresponding part
in the embryo which existed in the protoconch. On the other
hand, the true siphuncle, including the czecum of the first air cham-
ber, is a secondary organ formed by the funnels of the septa. The
living apical chamber was, as said above, a shallow cup, and its
limit in the living animal was probably as indicated by Henry
Brooks in the drawings given on Pl. i of this paper. At any rate,
his conclusions with regard to the probable situation of the aperture
of this stage seem to me to be sustained by observation.

The next substage is indicated by the presence of the czecum ly-
ing within the apex, and this is formed by the funnel of the first
septum and in association with the first septum is universal among
Cephalopoda, with the exception of some sepioids, so far as the in-
ternal structures are concerned. It has been descriptively named
the ceecosiphonula. ‘This may be considered as a part of the meta-
nepionic substage in nautiloids, but among ammonoids and belem-
noids it is forced back according to the law of tachygenesis into
the calcareous apex of the ancestral shell, being consolidated with
and disappearing in the aperture of the calcareous protoconch.
The limit of the living chamber which rested upon this first septum
has been determined in existing form of Wautilus pompilius by Mr.
Brooks and is shown in his drawings on PI. i.

In a general way it may be also said that the external character-
istics of this age are characteristic of the entire order of Nauti-
loidea.

Among Nautiloidea the shell of this substage grows less rapidly
in all its diameters and may either remain smooth and approxi-
mately retain the earlier form, becoming, however, more compressed,

or it may become more rapidly altered to a depressed ellipse. That

405

is to say, one with the transverse axis longer than the dorso-ventral
and is apt to be ornamented with coarse ridges, whether the shell
is subsequently smooth or remains ridged. The septum succeeding
the first septum among nautiloids and also belonging to the meta-
nepionic substage has a large siphuncle compared with the ventro-
dorsal axis, and this has been called the ‘‘ macrosiphonula.’’ The
remarkable observations of Henry Brooks have amply sustained
these statements made in previous publications, as may be seen in
diagram Fig. 11, Pl. i.

The macrosiphonula brings before the observer certain internal
characteristics which, although much altered, appear to have been
derived from the earliest ancestors of the nautiloids, Diphragmo-
ceras. The metanepionic substage is therefore in part in all forms
very primitive, in spite of the fact that in highly accelerated nau-
tian shells it is very much modified and also that some of its
external characteristics are derived from the more recent ancestors
of its own ordinal or subordinal phylum.

The paranepionic substage begins with the third septum and its
accompanying living chamber and, so far as I know, it does not
carry any external characteristics derived from a very remote
ancestry but usually in nautilian shells points very definitely to
some known or unknown gyroceran ancestor. This is broadly
shown in the fact that in the greater number of the more generalized
forms of nautilian shells the three parts of the nepionic stage occur
before the whorls touch. The external characteristics and form of
the metanepionic and paranepionic substage have been largely
derived from the immediate ancestors of the species. They often
have their corresponding phyletic forms within their own genetic
group or family, whereas the characteristics of the ananepionic
substage are, in large part at least, derived from remote ancestors.

Thus by the aid of direct observation it is not difficult to see
that the substages of development in ontogeny are the bearers of
distal ancestral characters in tnverse proportion and of proximal
ancestral characters in direct proportion to their removal in time
and posttion from the protoconch or last embryonic substage. It is
already generally admitted that this law is true of the embryonic
stages themselves with reference to the protembryo, although most
observers would hardly dare state this in the same positive terms as
here employed because they are confused by what they call abbre-
viated development. They have not traced the systematic regu-

406

larity with which the law of tachygenesis works in producing the
replacement of hereditary characters in every series of forms, and
do not trust or know how to use this law.

The paranepionic substage is consequently among Nautiloids as
among Ammonoids of longer duration than either of the preceding
substages and of more variable limits. The siphuncle has acquired
its ephebic aspect and characters, but it is very often in a different
position from that which it subsequently assumes, as it is in Vaw-
tilus pompilius and other forms figured in this memoir. I have
hitherto considered that it included the latter part of the cyrtoceran
volution, but it now seems more natural to hmit it to that portion
of the whorl which assumes the gyroceran curve or, in other words,
turns sharply away from the straighter cone of the preceding sub-
stages on its return curve towards the apex. ‘This is well shown in
Mr. Brooks’ drawings and also in the other forms of nautilian
shells, especially those of -Barrandeoceras tyrannum and Sacheri
of the Silurian. At or near the end of the paranepionic substage
in Vautilus umbilicatus and pompilius there is in almost every shell
amore or less sharply defined constriction which marks a perma-
nent aperture. The limits of both substages are subject to varia-
tions that will be noticed in the succeeding descriptions, but it
suffices here to note the fact that the upper limits of the paranepionic
substage are in a general way definable by the limits of the gyro-
ceran form in close-coiled nautilian shells. That is to say, this
substage, as a general rule, approaches its end and neanic charac-
teristics begin to appear at or near the completion of the first volu-
tion, when growth brings the whorl in contact with the apex or
dorsal side of the conch. Tachygenic forms are often notable
exceptions to this definition and introduce modifications that have
to be studied in each separate series.

The transformations that distinguish the subdivisions of the
neanic stage are very well marked in some forms and less distinctly
in others, but I have constantly found the need of defining two
stages. Ananeanic is a suitable term for the first substage, which is
usually well marked in nautilian* shells by the first appearance of

*In my Genera of Fossil Cephalopods nautilian forms have been defined as those having
the whorls in such clese contact that the dorsum of the enveloping or later formed whorl
is modified, either flattened or bent inwardly along the area of contact, and has what is
called an “impressed zone.’’ There are, however, some shells that are difficult to classify.
These have the yolutions in contact but do not have an impressed zone. Most of them

are transitional between gyroceran and nautilian forms and may be placed in either
eategory.

407
the impressed zone. This is the name I have given to the area on
the dorsum affected by the contact of the dorsum of the growing
whorl with the venter of the already formed whorl of the next inner
volution. This is either flat, gibbous, or indented in accordance
with the form of the venter of the whorl it touches or envelopes,
but it is usually indented more or less deeply.

There is a notable exception to this rule when in highly tachy-
genic shells the zone of impression is inherited and the dorsum
becomes furrowed before the first whorl bends. ‘This is one of the
most complete demonstrations of the probable inheritance of
acquired characters that I know, and an excellent illustration of
the law of tachygenesis. It occurs in some groups of nautilian
shells of the Carboniferous and also in the Jura, Cretaceous and
Tertiary, as well as in the existing species of Nautilus early in the
nepionic substage, as may be seen in the drawings of Henry Brooks
GRE):

In tracing out the distinct phyla to which different nautilian forms
belong, it can be shown that the impressed zone is invariably con-
sequent upon close coiling, never appearing in ancestral forms in
the nepionic stage unless through this agency. Asa rule, it comes
in the ontogeny after this stage, usually in the ananeanic substage
of more generalized and less closely coiled shells, but when one
ascends in the same genetic series to the more specialized nautilian
involved shells this purely acquired character becomes, through the
action of tachygenesis, forced back, appearing as a rule in the
nepionic stage before the whorls touch. It is therefore in these
forms entirely independent of the mechanical cause, the pressure of
one whorl upon another, which first originated it. One need only
to add that this configuration of the dorsum is never found in adults
of any ancient and normally uncoiled shells, so far as I know, nor
so far as they have been figured. I have so far found only one form
—Cranoceras of the Devonian—in which there is apparently a
slight dorsal impression, which may have arisen independently of
close coiling.

There are apparent exceptions to this rule in some of the ex-
tremely close-coiled forms of nautilian shells of the Calciferous and
Quebec faunas (some of which are figured in the plates of this
raemoir), but in these the first whorl bends so abruptly and enlarges
with such extreme rapidity that the inflection of the dorsal side
before the whorls touch can be attributed to mechanical effects of

408

three factors, viz., rapid spreading of the whorl, the abrupt curva-
ture and contact or close proximity of the paranepionic stage to the
apical part of the conch. Even, however, if this conclusion be
doubted and if, in a few forms of extremely specialized nautilian
shells of these early periods of geologic history, it can be asserted
that the impressed zone has really become inheritable ; the position
assumed in this paper, that the impressed zone is mechanically gen-
erated in the later stages of growth and becomes an inheritable
characteristic only in forms with accelerated development, is posi-
tively strengthened. The whole argument being based upon mor-
phology, it makes no essential difference how early the impressed
zone appears or in what form it appears, provided the shells in
which it is characteristic of the first volution before contact are the
descendants of those in which this character is transient and
obviously due to the moulding during growth of one volution over
the next inner volution. ;

My experience, however, in writing this paper has led me to dis-
tinguish two kinds of impressed zones; that which occurs on the
free dorsal sides of the young and that which occurs as the direct
result of contact. I propose therefore to call the former the dorsal
Jurrow and the latter the contact furrow.

The ananeanic substage among Carboniferous cephalopods is not
only marked by the beginning of the contact furrow but also, as a
rule, by the introduction of correlative changes in the form of the
whorl. ‘Thus the tetragonal whorl, with an outline similar to that
of an inverted trapezoid in section, and consequently an obvious
repetition of the ephebic whorl of Temnocheilus, and with sutures
also like those of the adults of that genus, appears at this stage in
Carboniferous cephalopods of several different genera, showing their
immediate descent from Devonian Temnocheili.

The first appearance of the dorsal lobe in the sutures is correlated
with closer coiling and is apt to make its first appearance in primi-
tive nautilian shells at this stage in the contact furrow. This lobe
however, occurs also before the whorls touch in a number of forms,
notably Barrandeoceras of the Silurian, and in one of these, Bar-
randeoceras Sternbergt, it occurs in the ephebic stage, although
this is a gyroceran form and no contact furrow is formed. There
is also another smaller lobe which appears in the centre of this,
the annular lobe. These are not strictly correlative with the
impressed zone, since a dorsal lobe appears in some cyrtoceran

409

shells which do not have an impressed zone at any stage in Bar-
randeoceras while the dorsum is still convex, and in MVaut-
Jus aratus it and the annular lobe is found beginning, in the third
septum, and similar observations have been made on a few other
species in the descriptive part of this memoir. ‘The characteris-
tics of the ananeanic substage of JV. pompilius show how distinct
this substage is in existing nautilus from the preceding and suc-
ceeding substages. The longitudinal ridges disappear during this
substage, and the broad transverse bands of growth become in con-
sequence for a time more prominent. The uniform brown of the
paranepionic may begin to be striped on the sides in the latter part
of the same substage, but this is often delayed until the ananeanic
substage and always become more definite at this time.

- In the metaneanic substage the shell becomes smooth, the brown
striping extends on to the venter, and the markings become more
distinct and more widely separated. ‘The whorl which, during the
preceding substage, had lost the subtrigonal outline of the para-
nepionic and become kidney-shaped in outline, with a deep im-
pressed zone, now acquires a deeper impressed zone and slightly
flattened sides and venter, thus forming lateral zones, as in Vautelus
umbticatus, and repeating at this stage the form of whorl character-
istics of that species. During the paraneanic substage the deposits
of porcellanus matter in the umbilical zone begin but do not
become a very marked characteristic.

In the ephebic stage these deposits on either side increase and
the whorl spreads inwardly closing the umbilici, the whorl in the
meantime losing its flattened venter, which again becomes rounded.
The metephebic substage begins when the umbilical perforations
become obliterated by the ingrowth of the umbilical zones.

The parephebic substage is definable externally only by the ces-
sation of the coloration. This may be due either to the fact that
senility is not marked by any peculiar structural changes, as hap-
pens often in other highly involute species of Nautiloids and even
in many Ammonoids with smooth shells, or because no very large
old specimens have been collected.

These remarks do not represent fairly all the ontogenic changes
in existing Nautili, which will be treated in another essay, but they
suffice for the purposes of this paper and serve, with other facts
cited, to show the applications of the nomenclature used in the
following pages.

410

In general terms transition to the ephebic stage takes place in
the paraneanic substage or near its termination, and characteristics
derived from the ephebic stages of immediate ancestors in the same
phylum, such as the trapezoidal whorl of Temnocheilus mentioned
above, are completely replaced by characteristics peculiar to the
genus and species. While there are often marked distinctions be-
tween this and the ananeanic substage, the differences are much
less obvious between this and the ephebic stage except in those shells
in which this period has degenerate characteristics. In these phylo-
gerontic forms marked distinctions are likely to make their appear-
ance owing to the disappearance of hereditary external ornaments
and markings which have been present until near the end of the
neanic stage.

The ephebic stage has not been so fully studied among the nauti-
loids or ammonoids, and in both of these orders it might be
considered questionable whether any subdivisions were essential.
But I have found it convenient to subdivide this stage in some of
the descriptions given in this memoir, and since this stage is much
prolonged in some forms of Ammonitinz, especially those with
numerous whorls like the shells of Caloceras, Vermiceras and the
like, it is probable that when its characteristics have received more
attention subdivisions will be found to be as necessary as in other
stages. ‘[he gerontic stage has been described above and is neces-
sarily illustrated in the text which follows, and the subdivision of
this stage into two or more according to the species is convenient
in order to distinguish the well-marked substages of decline.

The limits of the earlier epembryonic stages are somewhat more
difficult to define among Ammonoidea than Nautiloidea, because the
shells of the former are the bearers of a larger number of heredi-
tary characters, and being more highly specialized descendants of
the latter, the history of these stages is more complicated by the
intrusion of new modifications through the action of the law of
tachygenesis.

The protoconch, with a large aperture connecting with the open-
ing of the conch, is plainly seen in the figures of AZimoceras com-
pressus and others on Pl. 11, of this paper, and also in Sandberger’s
figures of species of Goniatitine on the same plate. This is very
distinct from the aspect of the apex of the conch in Nautiloidea.
In that order the neck of the protoconch must have been at least
as narrow from side to side as the scar on the outer surface of the

411

apex, and at least as long ventro-dorsally as the same. In other
words, the aperture of the protoconch in Nautiloidea was narrow
and elongated vertically, while that of the Ammonoidea in all hay-
ing cylindrical, straight or loosely coiled young shells, was an open
tube, as happens in Clarke’s Orthoceran form, in Bactrites and in a
‘number of Goniatitinze as shown in the figures.

In most groups of Goniatitinz and the other suborders of Am-
monoidea which, asa rule, have invariably closely-coiled first whorls,
the effect of contact is to produce immediately a deep, contact fur-
row and an almost entire obliteration of the umbilical perforation
between the neck of the protoconch and the nepionic volution.
Two funnel-shaped openings are left on either side, as shown in fig-
ures on Pl. ii, and these represent the more complete perforation
present in all Nautiloidea and in the earliest forms of Goniatitinze
among Ammonoidea. ‘The probable position of the aperture of
the protoconch has been indicated in Embryology of Fossil Cephalo-
pods, p. 110, and in Pl. iv, Fig. 1, and this information, gathered
from sections, agrees well with the figure given by Dr. Brown of the
supposed aperture of Baculites which is reproduced in outline, Fig.
Cy), Nelealiges

The growth of this form out of the protoconch, as in Bactrites,
must have been quite different from that of the true Nautiloidea.
Nevertheless it is obvious that as the animal grew outside of the
limits of the protoconchial aperture, it began to build the shell of
the apex of the conch and the first living chamber. This was the
ananepionic substage and it in part more or less resembled in some
of its essential characteristics and for a short time, the aseptate,
apical living chamber of the Nautiloid, but this resemblance must
have been transient and much accelerated.

After or during the building of this external skeletal ibe it
became practicable for the animal to lift itself, or, more properly
speaking, to progress by growth out of the protoconch, and the
next step can be seen in Branco’s Fig. 10, Pl. iii, and the details in
my Fig. 7, Pl. iii, both of which, and others also given, show that
the bottom of the czecum occupied the aperture of the protoconch
and is formed, as in Nautiloids, of the closed funnel of the first
septum. It is therefore inherited earlier, according to the law of
tachygenesis, since the first septum and the czecum occupy the same
position with relation to the protoconch as the scar or cicatrix in

* Proc. Acad. Sci. Phil., 1892, Pl. ix, Figs. 5 and 10, 11.

412

the apex of the shell in Nautiloidea. This and the fact that the
protoconch is calcareous are in favor of the opinion that the charac-
teristics of the ananepionic substage of the ancestral nautiloids ap-
peared in combination with the protoconchial stage in ammonoids.
Thus the first septum and ceecum in this order is the floor of the
first living chamber of the apex of the conch and is one substage
earlier in this order than in nautiloids, and should be called anane-
plonic.

- The figures, so far as the shell is concerned, also seem to demon-
strate that the czecum at this substage probably represents some em-
bryonic structure. This is Zittel’s explanation of the origin of the
siphuncle, it being as stated by him obviously traceable to the
czcum, and this in turn being probably formed out of a part of the
body or the shrunken mantle of the embryo, since it lies in the
Ammonoidea directly in the aperture of the protoconch.

While, however, this organ fills the diameter of the apex in the
median plane, it is narrower laterally, and one feels that this sup-
position is open to certain objections that will be discussed more
fully in a paper now in preparation on the Endoceratide. It may
be mentioned here, however, that in these ancient forms of the
Nautiloidea the opening from the siphuncle into the protoconchial
shell is closed in a different way from what it is in the normal
Nautiloidea, and in the protosiphonula the endosiphuncle communi-
cated with the protoconchial shell, passing through the bottom of
the ceeccum and apex. The elements of the walls of the siphuncle
surrounding the endosiphuncle in these forms are, however, similar
to what they are in the Nautiloids of less primitive organization,
and it becomes probable that the caecum was formed in the meta-
nepionic substage in Nautiloidea as a secondary epembryonic organ,
and that this has been crowded out of the metanepionic into the
ananepionic in Ammonoids. In other words, like some other char-
acters it was acquired in the epembryonic stages of Diphragmo-
ceras and like these has been inherited earlier in descendants.

One naturally, if disposed to adopt the theories of genesiology
as a working hypothesis, looks for the largest representation of an-
cestral characters in the earliest and most generalized forms. Thus
the Goniatitine of the Silurian, which belong in all except the
terminal members of series like Pinnacites and Celceras to this
category, one ought to find the transitions to Bactrites, or, failing
these, indications in the young of the less specialized forms of the

413

Silurian of their immediate derivation from Nautiloid ancestors.
This is precisely what actually occurred and in the Nautiloidea such
evidence is easily obtained as has already been stated above in the
pages of the Introduction and other publications.

It also follows, if the theories advanced by the author are true,
that the Nautilinide among Goniatitinz, as ancestors of the Am-
monoidea, and especially the genus Mimoceras as the centre of
derivation, should also show more prolonged retention of nautiloid
characters in their ontogeny than is usual in their supposed descend-
ants. The researches of Sandberger, Barrande, Branco and the
author show this to be a fact. The figures of Pl. 11 copied from
Barrande and Branco exhibit this in AZimoceras compressum, am-
bigena and the whole of the Nautilinide of the Silurian, and the
essential distinctive characteristic of this family is the nautiloid
form of the septa and lateral sutures. The shells of this genus also
do not possess a contact furrow, as noted above, and have no an-
nular lobes on the dorsum.

The first suture of AZimoceras compressum, Figs. 3, 4, Pl. 11, and
in some other allied species of the Devonian is bent into a slight
lobe on the venter, which is a purely nautiloid character, and not
to be confounded with the ammonoidal lobe in the same situation
in the third suture that follows this. This is shown by the occur-
rence of similar lobes in the Endoceratidz and some cyrtoceran
forms of Nautiloidea and in figures of sutures of autilus deslong-
champseanus and clementinus of the Cretaceous, also copied from
Branco, which have similar first and second sutures. ‘The aselate
first septum is in JZ. compressum, followed on the second septum by
a broad, almost imperceptible saddle, also considered aselate by
Branco, but which is obviously a transition to the latisellate, or
broad-saddle type of suture in the more specialized forms. The
limits of the ananepionic substage in this form, which, as said
above, is directly transitional to Bactrites, is therefore that part of
the whorl which is represented by these two septa and the living
chamber in which the animal rested while constructing the second
one.

The characters of these two septa, however, are not repeated in
the closer-coiled forms of the Nautilinidee and Primordialide. In
these the repetition of the outline of the second suture may be
entirely omitted, the shell passing immediately in the second sep-
tum to the repetition of the peculiar undivided ventral of the

~— a

414

Nautilinidz, obliterating the primitive characteristics of the second
septum and substituting the more advanced characteristics of the
Nautilinide as is plainly demonstrated in Fig. 16, Pl. ii, of Azar-
cestes (Goniatites) Zateseptatus and in the Primordialide in Gephuro-
ceras (Goniat) serratum, Fig. 17 of same plate. In the Ammoni-
tinze and Lytoceratine, and probably in the Ceratitinz, as in most
of the Goniatitine, this substage is obviously hmited to the first
septum and the corresponding living chamber. The limits of this
living chamber in one form may possibly be indicated by the trans-
verse imbricated line between the third and fourth septa in my
Fig. 1, Pl. iv, of Embryology of Fosstl Cephalopods. ‘This line
seems to demonstrate an arrest of growth at this time in the calca-
reous deposits corresponding to that indicated in Fig. 11 of the
same plate which is probably due to a former aperture.

The metanepionic substage must obviously begin with the advent
of the characteristics of the tubular microsiphuncle and the ventral
lobe in sutures, whether this occurs in the second or third septum
or later.

It is limited in duration to the repetition of the characteristics
of the Nautilinidz in certain of the Goniatitinz. Thus that family
of the Silurian and Devonian is phylo-metanepionic, or corresponds
in the phylum in its ephebic characters to the metanepionic sub-
stage of its descendants. ‘The closely allied family of the Primor-
dialidze, for example, as shown in Fig. 17, Pl. ii, has several septa
with this character appearing in the metanepionic substage, the
construction of the divided ventral lobe so characteristic of all
normal forms of Ammonoidea not taking place until the shell is
nearly or about 3 mm. in diameter in one species, according to
Branco’s figures, and still later in some other species.

In the Ceratitinee of the Trias this substage is in many species,

as shown by Branco’s drawings, prolonged through several septa

and there are decided indications that it is subdivisible into two
parts, one characterized by the purely nautilinian ventral lobe and
lateral sutures with only one broad lobe, and asecond older portion
having the undivided ventral lobes and lateral sutures of other rad-
ical forms among Goniatitine, ex. Prolecanites.

In Zrachyceras Munsteri the eighth suture, according to Branco,
is still undivided or nautilinian, and Tropites, according to the
same author’s figures, has this substage still more prolonged. In
Megaphyllites, Pinnacoceras, etc., all more highly specialized forms

=u ee ee ee ee ee eee

—e

415

of the Trias, it is apparently shorter in duration than in the gener-
alized and less complex organization of Tirolites if one can judge
by the simple characters of the ephebic stage.

In the Jura and Cretaceous, among the Ammonitine and Lyto-
ceratine, typical Ammonoids with more highly specialized struc-
tures than any Triassic shells, the primitive characters of this sub-
stage are, as one can read in Branco’s drawings and to a less extent
in mine, still more limited in extent, being confined as a rule to a
few sutures or to one, and finally, in many forms they are obliter-
ated altogether. That is to say, the divided ventral lobe encroaches
upon and finally obliterates the intermediate stage so that the meta-
nepionic substage, which begins with the third septum and micro-
siphon, is wholly changed in the aspect of the sutures. In other
words, the undivided ventral lobe of the Nautilinide has been re-
placed in this substage by the divided ventral of the Primordialide
which appears in the suture of the second septum.

This is also, like the preceding, an excellent example of what is
meant by the law of tachygenesis, the earlier inheritance through
the crowding back and replacement of distal by proximal genetic
characteristics.

Fig. 3, Pl. iv, shows the prolonged duration of the nautilinian
characteristics in this substage in second, third and fourth septa of
Vermiceras (Arietites) spiratisstmun of the Lower Lias, the decided
change to a divided ventral and two lateral lobes not coming in
until the seventh suture.

Fig. 7, Pl. iii, shows the section of Deroceras planicosta of the
Lower Lias and the delayed approximation of the siphuncle to the
ventral side. Fig. 7 shows the primitive structure of this organ in
the earlier substages, and the figures from Branco show the duration
of characteristics to be in correlation with these primitive charac-
teristics. .

Fig. 7, Pl. iii, shows the structure of the siphuncle in the meta-
nepionic substage. The transitional aspect of the second septum
can be observed in Figs. 6 and 7 of the same plate. Thisisa
direct reference, as I shall show in another paper, to the similar
structure of the ephebic siphuncle, and also the swollen aspect of
the early stages of the siphuncle in the Endoceratide, although in
some species of this family as many as six funnels may take part in
the construction of the swollen apical end of this organ. ‘These
facts are also in direct correlation with the more specialized and

416

complicated structure of Ammonoidea. They show that these
forms do not retain the tendency to form a cecum with double
walls as in Nautiloidea, and such an example as that figured in
Nautilus pompilius, in which a misplaced second septum necessarily
shows a long tubular czecum like that of the living chamber of
Diphragmoceras, probably does not occur. In other words, one of
the most persistent of the nepionic characteristics of Nautiloidea
does not exist in the more specialized shells of Ammonoidea so far
as known.

It is obvious from the preceding that the paranepionic substage
begins in most forms of this order with the first appearance of the
divided ventral lobe, or what I have called the siphonal saddle and
it is limited in extent by the duration of the simple entire goniatitic
outlines of the sutures which accompany all the substages of the
nepionic stage in all the suborders of Ammonitinz, except, of
course, the stock in which they originated, the Goniatitine.

In the Ceratitine, Ammonitine and Lytoceratinz it is gener-
ally true that this occurs, and the ananeanic substage begins with
subdivision of the lobes and saddles into minor lobes and saddles or
digitations, and this is often also accompanied by the advent of a
minute siphonal lobe in the apex of the siphonal saddle. It is
not essential here to discuss the limits of the neanic stage and its sub-
stages. They vary so much with the condition of development and
the position of each species in its own series or genus and of each
series or genus in its own group, that it is impracticable to define
them except in very comprehensive terms.

Thus one may say the limit of the neanic stage is reached when
the specific characteristics begin to appear in normal progressive
forms. But there are exceptions to this in some highly tachygenic
species, as in Oxynoticeras oxynotum, for example, and many others
in which certain characteristics are carried back to earlier substages.
Still, as a rule, this definition does good service if the occurrence
of exceptions are constantly anticipated.

The limits of the substages can be obtained in some species of
each series, and are quite distinct in the external characteristics of
the form of the whorl and of the ornamentation. The sutures of
the ananeanic substage are different from those of the metaneanic
since they are much simpler and less completely digitated, but
there is, as a rule, but slight, if any, differences between the sutures
of the metaneanic and paraneanic or ephebic sutures. These

417

substages have been described, although not defined according to the
nomenclature used in these pages, by Wiirtenburger in his essay re-
ferred to above; by S. S. Buckman in his extensive and monumental
work published by the Paleontographical Society in their volume
for 1891 on the ‘‘ Ammonites of the Odlite,’’ and by the author in
the Genesis of the Arietide.

The gerontic stage has also been fully described and separated
into two subdivisions by Mr. Buckman and the author, and is easily
distinguished from the ephebic by the external characters, and as
stated above the septa become more or less approximated in the
paragerontic substage and there is often slight but perceptible de-
generation in the sutures.

All_of the remarks made above apply Hel enough in a general
sense to the progressive series of the Ammonoidea, but although
we know the younger stages of only a few species of the retrogres-
sive species, there are indications that they will require modifica-
tions to be true also for the phylogerontic forms.

Thus Choristoceras (of) Hensel, as figured by Branco,* has appar-
ently a considerable number of sutures having the undivided ven-
tral lobe. These are less in number than in some progressive forms
like Zropites subullatus, figured on the same plate, but unluckily
the immediate ancestors of this species: are unknown and exact
comparisons cannot be made.

The young of the uncoiled forms of the Ammonoidea show
however, in all their characters that the early inheritance of
gerontic tendencies interferes with and delays the development of
the progressive, more complicated structures of the forms from
which they must have been derived. This is admirably shown in
the drawings of Dr. Brown, some of which are reproduced on
lite aig

Fig. 13 shows a.complete young shell which isin the neanic stage
of growth. Fig. 17 isa restored side view of the protoconchial stage
and ananepionic substage with aperture. Fig. 16 gives front view of
the first volution in the paranepionic substage which begins at the
fourth septum, and Fig. 18 side view at the sixth septum. Fig. 1,
Pl. iv, shows the sutures for the same age.

Figs. 14-16 show the gradual diminution of the area of the con-
tact furrow and the decrease in lateral diameters of the volution

* Op. cit., Paleonlogr., xxvi, Pl. v.

418

while the shell is still in the nepionic stage and as it approaches the
point of departure from the spiral and the subsequent loss of the
contact furrow. Dr. Brown records that the spacing of the septa
increases after the deposition of the twelfth septum, and that these
partitions are more widely separated. This correlates with a cor-
responding increase in the lateral diameters and together indi-
cate an increased rate of growth. Nevertheless there is no quicken-
ing in the processes of development nor any resumption of pro-
gressive characters. The shell becomes a compressed ellipse in
section, loses the contact furrow, and the straightened cone does
not acquire the digitate sutures and pass into the neanic stage of the
Ammonitine until after it has departed from the spiral.*

It is clear from this and other examples taken from later stages of
growth that these are tachygenetic forms so far as the early inherit-
ance of gerontic characters is concerned. Correlating with this,
or in consequence of this, the inheritance of progressive characters
in the sutures is delayed, and these parts change more slowly in
these phyloparaplastic shells than in the phylometaplastic forms of
the same order. ‘The internal structures and the shell itself also, as
previously stated, never attains even in the stage of ephebic devel-
opment characteristics comparable to those of phylometaplastic
species. ;

It follows upen the preceding remarks that the characters of these

stages have different duration in different members of the same
genetic series, being more prolonged in the more primitive and
shortened up through the action of tachygenesis in the more special-
ized shells of the same series. It is also obvious that the limits of
each substage must be defined differently according to the position
of the animal in time and in the evolution of its own special series.
There are theoretically no exceptions to this law in its broadest
acceptation, but in its practical applications this is not the case.
Thus the protoconchial stage is so nearly invariable in each order
that it is characteristic of all Nautiloidea and all Ammonoidea, having
peculiar characters in each of these orders, but this comparative in-
variability is less apparent in the characters of the ananepionic,
metanepionic and paranepionic substages, and especially in the
neanic stage, which are not as constant. The tendency to change
* Having received specimens of these precious fossils through the kindness of Dr.

Brown, I am able to confirm his observations, although I have not yet had proper oppor-
tunity to go over all the material and study every detail of the development.

419

along certain lines of modification in accordance with definite gen-
etic laws becomes, in other words, more apparent in the later than
in the earlier substages of the ontogeny.*

In order to give a clear and comprehensible example of the gen-
eral application of these laws I have quoted below several pages
from Buckman’s interesting and instructive paper on ‘‘Some Laws
of Heredity and their Application to Man.” f

How THE TRANSMISSION OF VARIATION WOULD AFFECT THE ORIGIN
OF SPECIES.

‘Tt is not difficult to understand the origin of species if the sur-
mises that I have submitted, concerning the transmission of devel-
opmental variation, arecorrect. The greater and greater elaboration
of any particular features in, say, an adult male, as functional mod-
ification necessitated by environment, are transmitted to the male
sex alone, and appear earlier and earlier in that sex. The greater
and greater elaboration of these features results in the course of
time in the formation of a marked and distinguishing character
in the male sex; and this character being transmitted in accord-
ance with the law of earlier inheritance ultimately appears early in
life in the male. Then the character tends to appear in the female
sex also, though why it does so is not clear. Bysuch process, how-
ever, there arise both males and females which possess characters
different to those which their ancestors possessed.

«« By the time that this character, influenced by the law of earlier
inheritance, appears at an age early enough to be transferred to the
female, the male has probably either further elaborated this charac-
ter—which further elaboration 1s at first transmitted to the males only
—or he has elaborated something else so much that it seems likea new: »
character which is transmitted in the same way. In course of time
this further elaboration, or this new character as the case may be, is
transmitted also to the females; and so it becomes plain how,
merely by the gradual transmission of developmental variations,
both sexes of what may be called an incipient species, beginning
with a slight variation in one sex alone, are able to diverge wider
and wider from the original stock.

‘The same laws of transmission would of course hold good if

* The application of this law, however, to the gerontic substages demands a longer dis-

cussion than can be given here, and must be deferred to future publications.
t Proc. Cotteswold Natur. Field Club, Vol. x, Pt. iii, pp. 258-322, 1891-1892,

420

the developmental variation arose in the female in response to
changes of environment; while if both sexes were exposed to the
same changes of environment necessitating the same functional
modifications to be acquired to bring them into better adaptation
with their surroundings, it is reasonable to conclude that the result
would be the production of a greater difference in a shorter space
of time.

‘‘Thus it is clear that the gradual accumulation of slight devel-
opmental variations transmitted in accordance with the law of ear-
lier inheritance would be sufficient to cause the origin of various
species ; and at the same' time there can be little doubt that this
cause has also been assisted by both Natural and Sexual Selection in
the production of diverse species from one original stock.. I am
inclined to think that developmental variation has been more im-
portant in the origin of species than has abnormal, or as Darwin
calls it, ‘spontaneous,’ variation. The transmission of such ab-
normal variations as supernumerary digits seems to be so much more
_ uncertain than the transmission of developmental variation, while
practically speaking the origin of Ammonite species seems to be
almost entirely attributable to developmental variation.

‘¢ Specialized structures like the long neck of the giraffe and the
proboscis of the elephant, to take familiar instances, are, in my
opinion, developmental variations. They did not arise, in the first
place, in certain members of the pregiraffian or preélephantine
species. as abnormal or ‘spontaneous’ variations which gave their
possessors such great superiority over their fellows in the struggle
for existence that those possessors survived by the law of Natural
Selection. These features began imperceptibly—the neck and the
nose grew more in proportion to other features during the lives of

the individuals on account of the habits of the animals, and they

may be compared in this respect to the enlarging skull of civilized
Man. ,

‘As the features of the adult become in course of time the fea-
tures of the adolescent by the law of earlier inheritance, the elon-
gation of nose and neck would become exaggerated from one
generation to another. I do not see any reason to suppose, at any
rate at first, that the giraffan or elephantine ancestors were the
favored individuals of the community, and that the other members
died out because they did not possess elongated necks or noses.
I do not suppose that all the members of the species possessed

bai g
a

421

these features in the same degree, but I do imagine that a gradu-
ally increasing elongation was more or less common to all the mem-
bers of the pregiraffian or preélephantine species as a result of
their habits.

‘To take the case of the giraffe alone, for the sake of clearness
—it is hardly necessary to suppose occasional droughts during
which those members of the community with the longest necks
would survive, while others starved because they were not able
to reach such high branches as their longer-necked fellows. An
extra inch or so of neck could not make so much difference as this.*

“‘T do not say that the giraffe or its ancestors have not had the
best of it when there was a struggle for existence, and that natural
selection has not played its part; the fact of the giraffe’s existence
is proof enough that it was better adapted to its environment than
some of its competitors; and the longer the neck grew doubtless
the greater superiority the animal would possess.

** As to the short-necked forms which would connect the present
giraffe with the stock from which it originally came, their dying out
is not difficult to explain. The law of earlier inheritance allows us
to imagine a small beginning becoming more accentuated in all
members of a species as time goes on, and as the shorter-necked
forms were really the parents of the longer-necked forms, the dis-
appearance of the former would be due, as the lawyers say of a
lease, to effluxion of time.

“« Arising from and coéxisting with developmental variation there
seems to be another factor important in differentiating species, and
this is the time when the offspring is produced.

‘Offspring produced early and offspring produced late in the life
of a parent shewing considerable developmental changes between
early and late maturity, or between early maturity and. senility,
would in all probability differ to a certain extent. It is, I think,
reasonable to suppose that if there were, say, a decline of vigor
after a certain period of the parent’s life, the offspring produced
after this time would be more likely not only to be somewhat less
vigorous altogether, but would probably exhibit declining vigor at
an earlier age than those produced before any decline of vigor
set in.

*¢The adults would have the best of it in a drought on account of their larger size.

Therefore if there were a long-necked ‘sport’ among the young pregirattes it would
have no chance against the adults unless its neck were of a preternatural length.”

422

‘‘ This seems to be a reasonable deduction from what is observed
in phylogenetic series of Ammonites, where from the same stock
arise one series which continues to progress, another series which
retrogrades, though both lived together and were presumably sub-
ject to the same environment.

‘¢ More marked still wouid be the effects if from any cause there
arose a difference among members of a species as to the time in their
lives when offspring were produced. There is the case in Man—
the professional classes defer marriage till late in life, agricultural
laborers marry very early.

‘‘' These surmises illustrate what may be supposed to be accom-
plished in the differentiation of species by the transmission of de-
velopmental variations in accordance with the law of earlier inher-
itance. Further consideration will shew that, if some members of
a species acquire, on account of environment, habits necessitating
the increased use of one part, and other members acquire other
habits with different results, and so on, there would, in course of
time, arise from one original stock two or more species very differ-
ent from each other or to the parent form—simply because their
small initial differences had been constantly increased by the action
of the law of earlier inheritance.”’

IV. DESCRIPTIVE TERMS.*

Before attempting to enter upon the deseriptive part of this essay
it is essential to define, as briefly as possible, the meaning of the
terms which are constantly employed in the descriptions of the
different forms. The term ‘‘coil’’ has been applied solely to the
whole shell, while ‘‘ whorl’’ and ‘‘ volution’’ have been used when
in the singular or when numbered only for a particular whorl or
volution. Thus the first whorl or first volution is the first completed
revolution of the shell, and so on. I have also been obliged to use
volution for parts of a single whorl in describing substages.

In describing the aperture I have used the terms ‘‘crest’’ for pro-
jecting parts and ‘‘sinus’’ for inflections of the outline to distin-
guish them from the saddles and lobes of the sutures. The ventral
sinus of the aperture and lines of growth is here called the ‘‘ hypo-
nomic sinus,’’ it being due to the large size of the hyponome or

*Special students of Cephalopoda will, it is thought, be grateful for this chapter.

Other classes of readers, if there be one who gets so far and has the courage to go farther,
can skip and refer to it in connection with the descriptions which follow.

Cee

423

motor organ usually called ‘‘ fleshy funnel ’’ in the modern nautilus,
as has been explained above.

It is useless to discuss the terms ‘‘ ventral ’’ and ‘‘ dorsal.’’ There
can be no debate on their application, unless it is based upon new
anatomical information. The fact is obvious, so far as now known,
that in Mautilus pompilius, and all other Nautiloids, the outer side
of the whorl is ventral and the inner side is dorsal. Whenever,
even in straight shells, Orthoceras, etc., the lines of growth can be
seen, the ventral side is indicated by the ‘‘hyponomic sinus,’’ and
in nautilian or coiled shells it is invariably on the outer side.

The term ‘‘ depressed ’’ is used for the flattening of the whorls,
which affects the abdomen and dorsum and acts at right angles to
the transverse diameter of the coil; ‘‘ compressed ’’ for the similar
effect on the sides, which acts in the plane of the transverse diame-
ters and at right angles to the plane of coiling. When the sides,
lateral zone, or faces are inclined inwardly towards the umbilici, the
term ‘‘divergent’’ is applied, and when they incline outwardly
towards the abdomen the term ‘‘ convergent ’’ has been used.

The adoption of these terms has been found to give clearer ideas
of the development and true importance to the different characters
of the volutions. The term ‘‘sides’’ is used in a general way, and
distinguishes the whole of the lateral aspect of the whorl at any
stage. ‘The ‘‘lateral zones’’ and lateral faces, etc., as will be seen
in the descriptions, are developed as modifications out of the sides
of the young and immature whorls. ‘The outer angles occurring on
either side in the young or in the biangular forms are in the text
named “lateral angles,’’ being really on the sides of the whorl and
distinct from the angles arising later in the life of the individual,
and later in the evolution of the group. ‘The junction of the * lat-
eral faces’’ and abdomen are the ‘‘ abdominal angles,’’ and those
of the ‘‘lateral faces’’ and inner faces of the mature whorls
are called the ‘‘umbilical shoulders,’’ and the inner surfaces
are the ‘‘umbilical zones.’’ All of these parts are developed in
succession and in various combinations, from a round or elliptical
form of whorl, having the vertical or ventro-dorsal diameter longer
than the transverse, both in the individual and in the evolution of
the group.

The venter is the area between the outer angles, whether they be
the ‘‘lateral’’ or ‘‘abdominal’’ angles, on the outer part of the
whorl, and the ‘‘dorsum’’ is the corresponding part on the inner

424

part of the same, between the ‘‘ lateral amgles’’ or the ‘‘ umbilical
shoulders.’’ The ‘‘ zone of impression,’’ or ‘; impressed zone,’’ is
the area on the dorsum, which is concave, and lies between the
‘umbilical zones.”” The impressed zone may appear indepen-
dently as a ‘‘dorsal furrow,’’ or, after contact, as a ‘‘ contact fur-
row.’ The ‘‘ zone of inclusion’’ or ‘included zone ’’ is the cov-
ered area corresponding to this on the.venter. The term ‘‘ zones
of involution’’ or ‘‘area of involution’’ can be used for both of
these when the whorls are not separated or it is desired to speak of
the two together. ‘The “lines of involution ’’ are the outer bound-
aries of the ‘‘zone of impression ’’ on the dorsum, and the ‘‘lines
of inclusion ’’ the corresponding lines on the venter.

The terms ‘‘ involved ’’ and ‘‘involution’’ should be limited to
whorls having a ‘‘ zone of impression ’’ or ‘‘ impressed zone,’’ that
is, to ‘‘nautilian’’ shells. ‘* Coiled’’ can be applied to all shells
that have the gyroceran curve and even to shells with the whorls
in contact. Nevertheless these sometimes have closer affinity with
nautilian shells of a given series than with the gyroceran shells of
the same series.

Whorls with only two surfaces and angles are ‘‘digonal ;’’ three
surfaces and angles ‘‘trigonal;’’ four surfaces and angles ‘é tetra-
gonal,’’? and when the abdomen is much broader than any other
side ‘‘ trapezoidal ;’’ five surfaces and angles ‘‘ pentagonal ;’’ six
surfaces and angles ‘‘ hexagonal ;’’ seven surfaces and angles ‘‘ hep-
tagonal ;’’ eight surfaces and angles ‘‘ octagonal ; nine surfaces and
angles ‘‘enneagonal ;’’ ten surfaces and angles ‘‘ decagonal.”’

The outlines on the Diagram Plate, opposite, page 425, will be
found to explain these terms more fully. :

EXPLANATION OF DIAGRAM PLATE.

Diagram A.—Section of compressed elliptical whorl with primi-
tive regions indicated, ananepionic substage of nautilian shells and
ephebic stage of many primitive orthoceran and cyrtoceran forms.

Diagram B’.—Section of depressed elliptical whorl occurring
older in the ontogeny or correspondingly later in the phylogeny
than A.

Diagram B”,—Section of a reniform whorl with a contact fur-
row. ‘This may be evolved from B’ by the growth and involution

Proceedings Amer. Philos, Soc,

Diagram Plate (Hyatt).

eS KNIN

Vol. XXXII, No. 14a,

425

of the whorl,* and may be an intermediate stage leading into a
whorl like that shown in H, or it may acquire lateral angles as in
C, thus passing into.G, or A may pass directly into H.

Diagram C.—Section of a digonal whorl with primitive regions
and lateral angles, 1. g., occurring in the ephebic stage of ortho-
ceran and cyrtoceran forms and in the young of nautilian forms,
Edaphoceras.

Diagram D.—Section of a trigonal whorl with gibbous venter,
lateral angles, 1. g., and projecting dorsal angle, p. d. g., ex. Tri-
gonoceras.

Diagram F&.—Section of a trigonal, shield-shaped whorl, with
concave venter, lateral angles, 1. g., and projecting dorsal angles,
p. d. g. Either D or E may evolve into a tetragonal whorl by the >
appearance of a lateral zone on the outer part of the sides and the
rounding off and disappearance of the dorsal angle, ex. Trigono-
ceras.

Diagram F.—Section of a tetragonal whorl with gibbous venter
and dorsum and lateral zones, 1. z. This may be developed from
i con trom C:

The morphic distribution of these forms is as follows: A, B and
C may be Orthoceran, Cyrtoceran or Gyroceran, but are more gen-
erally Orthoceran; D may be Orthoceran, but is usually Cyrto-
ceran and Gyroceran; E and F are almost exclusively Gyroceran.
All of the remaining outlines belong to Nautilian forms.

Diagram G.—Section of a tetragonal, trapezoidal whorl with a
contact furrow nearly as broad as the dorsum, the sides flat and
well defined. ‘This may be evolved from C or B” in development
of Nautilian forms. ‘The abdominal angle, a. g., in this form is
derived from the lateral angle of forms like C. Sides, s., are still
undivided, ex. Temnocheilus.

Diagram H,—Section of a hexagonal whorl with lateral zones,
l. z., developed between the abdominal shoulders or angles, a. g.,
and the umbilical shoulders, u. s., and umbilical zones, u. z., devel-
oped between the latter and the lines of involution, l. in. The
contact furrow remains primitive or undivided. ‘This may be

* This same diagram can also be used to represent the paragerontic substage of the de-
generation. A reniform whorl may result in the gerontie stage from such an ephebie
whorl as is represented in H, J, K, or P. Qshowsanintermediate stage between P anda
reniform paragerontic whorl. No confusion need result from this double use of the same
outline, since it does not imply identity of structure, but simply the identity of form at
the extremes of the ontocycle in the individual and of the phylocyele in the group.

426

developed from G or B, or from C, with an intermediate transforma-
tion like G, or from B, with an intermediary like B’, and F may give
rise to a similar modification when close coiled. A number of Pale-
ozoic forms have this outline, ex. Metacoceras.

Diagram TI.—Section of an octagonal whorl derived from H by
the building out of the venter and the formation of a central ven-
tral zone, c. v. z., two lateral ventral angles, |. v. g., and two lat-
eral ventral zones, 1 _v- z., ex: Tainoceras.

Diagram 7.—Section of a decagonal whorl derived from I by the
subdivision of the impressed zone (contact furrow) and the forma-
tion of a central dorsal face, c. d. f., and two lateral dorsal faces,
l. d. f., ex. some species of Tainoceras and Ccelonautilus.

In their gerontic substages the whorl of G, H, I and J become
more or less rounded and show a tendency to return more or less
completely to the outline of B”.

Diagram K.—Section of an octagonal, truncated, cuneiform
whorl, usually derived from a whorl similar to H by the convergence
of the lateral zones and the subdivision of the impressed zone,
c. d. f., central dorsal face, 1. d. f., lateral dorsal faces.

Diagram L.—Section of a gerontic whorl derived from K. By
farther degeneration the dorsal angles may disappear and the whorl
assume approximately the reniform outline of B.

Diagram M.—Section of a heptagonal, cuneiform, anagerontic
whorl derived from K. ‘The acute ventral angle, v. g., is formed
by the convergence of the lateral zones and the disappearance of
the abdominal angles. ‘The dotted lines represent the similar trans-
formation which subsequently takes place in the same form on the
dorsum by the convergence of the lateral dorsal faces. The whorl
then becomes a hexagonal cuneiform. This outline has been repre-
sented with rounded umbilical shoulders, but these have to be con-
sidered as equivalent to two angles, and they are often more or less
angular.

Diagram £.—Section of a metagerontic whorl of K or M; sim-
ilar forms may also result from the paragerontic degeneration of Q,
ex. Stroboceras sulcifer, sp. De Koninck.

Diagram NV.—Section of a paragerontic whorl of L. The dotted
line represents the obliteration of the zone of impression which
may take place in very old whorls in this substage or in the aper-
tures of the ephebic stages of phyloparagerontic species.

427

Diagram O.—Section of an octagonal, truncated, cuneiform
whorl with a concave abdomen in which a gibbous, central, dorsal
face is formed and the lateral dorsal faces are excessively narrow.
This may be derived from E by involution and the formation of
umbilical shoulders and umbilical zones, ex. Apheleceras, Subcly-
menia.

Diagram P.—Section of a highly complicated fluted whorl with
concave abdomen. ‘The venter has become subdivided into a fluted
central ventral zone, c. v. z., and two fluted lateral ventral zones,
l. v. z., these having become. incorporated with the lateral aspect,
and the intermediate lateral ventral angles, |. v. g., form the bor-
ders of what is usually considered as the sides of the whorl.

The lateral zones lying between the abdominal shoulders, a. g.,
and the umbilical shoulders, u. s., have become subdivided into
two lateral faces, the outer one, |. f., is a broad flute, and the inner
one is subdivided into three lateral facets, 1. t., two of them, the
outer and inner facets, fluted, and one of them, the central one,
shghtly gibbous and ridged.

The contact furrow has a central dorsal facet, c. d. t., two lateral
dorsal facets, 1. d. t., and two lateral dorsal faces, 1. d. f., the angle
between |. d. t. andc. d. t. is the tertiary dorsal angle, t. d. g., but
is not lettered, and the angle between 1. d. f. and 1. d. t. is the dor-
sal face angle and is also not lettered in this diagram, but these are
lettered in Diagram Q. The facets are introduced by the subdivis-
ion of the central dorsal face, which is at first flat, as in L.

The secondary lateral angle, s. l. g., is developed between the
flute of the lateral face, 1. f., and the outer facet of the inner lateral
face that extends from s. I’ ¢: to u.s.~- The lateral facets formed
out of the surface of this face are three in number, marked l. t.,
and the angles between these are the tertiary lateral angles, but are
not lettered. The angles on the central gibbous lateral facet are
due to longitudinal striz.

Diagram Q.—Section of a gerontic whorl of P. The flutings
and other ornaments have been obliterated, but the impressed zone
retains its peculiar characteristics. The more advanced parageron-
tic substage would approximate to Diagram N, but with more de-
pressed venter. Coloceras is a phyloparagerontic form, having an
almost reniform whorl in the neanic and ephebic stages.

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429

These diagrams and examples (with the exception of A, B and
C) were taken from Carboniferous forms published in the Fourth
Annual Report of the Geological Survey of Texas, 1892, but they
are applicable to all of the Nautiloidea, provided certain distinc-
tions be made. The outline expands by growth from an ananepionic
stage, in this case having the approximate outline of A, and may
develop into B and C, with decided lateral angles, but in the ephe-
bic stage may sometimes return to the form of Edaphoceras, C.
Species of other groups may pass through B’ and, becoming invo-
lute, take on the outline of B”, and then, if the shell progresses
still more, it may tend towards forms of H.

It must, however, be noticed that fossils of such species occurring
in the earliest geologic period have not, as a rule, even approxi-
mately well-defined angles, and these being deficient, the zones are
not apt to be well differentiated. One can readily see that these
shells, even though they may be involute from an early stage, have
not the more highly specialized characteristics of the whorl found
in some of the Devonian fossils. The latter, in their turn, take
rank as a whole below the still more progressive and highly orna-
mented nautilian shells of the Carboniferous which represent the
acme of the order.

The paracme of the order begins in the Trias, and retrogression
is plainly manifested in the steady decline of the external ornaments
and less angulation of the whorl. ‘The universal absence of all of
the third and fourth orders of modifications of the whorl is one of
the marked features of this decline, beginning with the Trias and
becoming universal in the Jura and other subsequent periods.

The nomenclature of the sutures needs no special description,
except with reference to the ‘‘annular lobe.’’ This is a small
indentation in the sutures, occurring either in the centre of a dorsal
saddle or a dorsal lobe. It is pointed or V-shaped. In some forms
it may arise before a dorsal lobe is formed in the middle of a primi-
tive but persistent dorsal saddle, or it may arise subsequently in the
centre of a broad dorsal lobe. Its development has not been fully
described. It is often accompanied by an internal pointed caecum
called the ‘‘annular cone,’’ and both are probably connected with
the development of the ‘‘ annular muscle.”’

It has been usual to measure the distance of the siphuncle and
describe its position, with more or less circumlocution, as ventral,
dorsal, central, etc., but in these descriptions the following terms

430

have been employed, which are best explained by the following
diagram, Fig. 14.

Ventran and dorsan
express only the posi-
Promioventran. tion of the shell, this
Extracentroventran alone being superfi-
cial. By using these
terms and others, a
Intracentroventran considerable degree of
accuracy can be ob-
tained, and others can
also be employed if
Dorsocentren essentially based on
the same siysitem:
‘Thus; for exam pile;
Centrodorsan proximo-ventran ex-
Extracentrodorsan Presses the position of
the siphuncle in No-
thoceras and Bathmo-
Subdorsan ceras, where this organ
is so close to the shell
that its own wall is in
ee part absent and in
part much modified. Subventran is applicable only to those forms:
in which the wall of the siphuncle is not altered or modified
through contact with the shell, although it may lie quite closely
against it. The other terms sufficiently explain themselves, except
the use of ‘‘ extra’’ and ‘‘intra.’’ It is not meant to confine these
terms to the two where it is used in the diagram. It is obvious
that these prefixes may be employed wherever they are needed.
Thus one can say ‘‘intraventrocentren’’ for a location between
centren and ventrocentren positions.

It would not be proper, however, to use these prefixes on either
side of centren for the reason that the comparisons are all made
from the centre towards the dorsum, on the one hand, and towards
the venter on the other. Thus everything on the dorsal side of this °
point is not inside of the centre but dorsad of this point or axis,
and everything on the ventral side is not outside of the same axis
but ventrad of it. I have also used Wilder’s term, mesal, for the
plane of the siphon, instead of median.

Subventran

Centroventran

Ventrocentren

Centren

Intracentrodorsan

Propiodorsan

431

These terms and others of the new descriptive nomenclature, of
which only very few will be used in these pages, because I think it
will be essential to discuss them further before applying them to the
descriptions of cephalopodan shells, have been gradually introduced
in consequence of the labors of Wilder and Gage, in this country,
and are in a fair way of being adopted in Europe through the
effort of Franz Eilhard Schulze and others.*

Terms like ventran, ventrad, ventral, dorsan, dorsad, dorsal, cen-
tren and centran, and so on, strike one at first as awkward and bar-
barous, but their utility becomes apparent, as in the case of the
siphuncle cited above, as soon as one begins to use them, and they
can be made to have an exact meaning which it is not practicable
to gain otherwise without the repetition in every description of the
same explanatory text.

The shells of Nautiloidea and Ammonoidea are divided by trans-
verse partitions or septa into what are called ‘‘ air chambers,’’ and
the intersections or lines made by the edges of these when they
strike against the inner surfaces of the shell of the whorl are called
the sutures. Fig. 15 shows the edges of these septa as they would
appear in lVautilus umbilicatus (Fig. 1, p. 345) if the shell there
figured had been fossilized, the air chambers filled with infiltrations
and the outer walls of the last whorl destroyed except in the umbil-
icus. The outer empty chamber beyond the suture of the last
septum is the cast of the living chamber. The sinuous edge of
this is the impression left by the edge of the aperture on the right
side. This being a cast artificially made, is somewhat more perfect
than natural casts of the interiors of such forms in the rocks and
the spreading abutments of the septa against the inner wall are
broad bands. Usually, in fossils, the upper extremely thin parts of
these bands have disappeared, leaving only a line below correspond-
ing to the lower parts of the bands in this figure and more nearly
representing the thickness of the internal part of the calcareous
septum.

* See Wilder, Science, ii, 1831; Wilder and Gage, Anatomical Technology, 1882, and other
papers. Also Schulze, Biologisches Centralblatt, xiii, Nos. 1, 2, 1898; Hyatt, ibid., Nos. 15,
16; and again, Schulze, Verh. d. Anat. Geselicch., Versam. Gottingen, 1893, p. 104; and
reprint of same, Deutsche Zool. Gesell., GOttingen, 1893, p. 6.

432

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;
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Fic. 15.—Nautilus wmbilicatus.

V. DESCRIPTIONS.

In treating of the history of the impressed zone it has become
essential to describe a number of new genera and also new species.
The old names—Gyoceras, Lituites, Nautilus, etc.—convey en-
tirely false ideas of affinity and would serve to confuse the student

| of these fossils, since the new names ignore these groups. Thus it
| is not at all in contradiction of the nomenclature if I state that the
close-coiled Zarphyceras prematurum of the earlier Quebec faunas
is the last of its phylum and has no descendants in the Upper
Silurian or later; but if I call it Nautilus, and say that Vawufelus

See

433

prematurum had no descendants, even a tyro would begin to won-
der why it bore the same generic title as the existing species.

The limits of time and space have not enabled me to follow out
each genetic series in this paper, but it will be readily recognized
by naturalists that shells having such very different forms in their
younger stages must have belonged to different phyla. I have,
however, tried in the introduction and in the parts treating of
the history of the impressed zone to discuss the facts and arrange
them in more intelligible form than is practicable in the following
descriptions.

The families into which genera have been assembled are entirely
provisional since more information with regard to the genealogy of
the forms is needed before any satisfactory results can be reached
in defining these larger groups.

NAUTILOIDEA.

‘TARPHYCERATIDA.

This family includes shells which had elliptical whorls with gyro-
ceran mode of growth or subquadragonal whorls with nautilian
mode of coiling, the venter narrower than the dorsum in most
forms. The shells comparatively smooth, the sutures with ventral
saddles or only slight lobes, shallow, broad lateral lobes and either
saddles or faint lobes on the venter of free whorls. ‘The siphuncle
is ventrad of the centre.

The genera are as follows: Tarphyceras, Aphetoceras, Delto-
ceras, Pycnoceras, found exclusively in the Quebec faunas older
than the Chazy; Eurystomites and Barrandeoceras,* found in both
the Quebec faunas and the Lower Silurian ; Planctoceras and Falcili-
tuites, found only in the Lower Silurian.

Tarphyceras,} n. g.

This genus has heretofore been confounded with Eurystomites by
Schroder, the species being found together and resembling each
other in general aspect. It differs, however, from that genus in
having a more discoidal form, more numerous and more slowly
growing whorls, in length of living chamber, in form, aperture,
and other characters.

*In my Genera of Foss. Ceph. I included this genus under the title of Nautilide.

t Tapgbs, close.

4S4

The young become almost as close coiled during the paranepionic
substage as in Trocholites, differing in this respect from those of
Eurystomites. The dorsal furrow appears in some species, perhaps
in all, in the paranepionic substage. ‘This might be considered as
due to the quick growth and contiguity of the whorls, the dorsum
of the paranepionic substage being brought close to the dorsum
of the preceding metanepionic and ananepionic substages of the
first whorl. ‘This extraordinary condition of the first whorl obtains
also in Trocholites and will be discussed more fully under the head-
ing of Zarphyceras prematurum and Trocholites. I do not intend,
here or elsewhere, as has been stated in other parts of this paper, to
express a positive opinion that the dorsal furrow in any of these
nautilian forms was originated in the nepionic stage by the mechan-
ical stress of the metanepionic dorsum even in these very closely
coiled shells. The evidence that this may have been the cause is
not satisfactory, nor is there any positive evidence of an entirely
satisfactory character that the dorsal furrow was genetic.

The siphuncle is centren in the ananepionic substage, but becomes
quickly propioventran and continues near the venter for a more or
less prolonged period, shifting slowly towards the center. In
Eurystomites this shifting usually takes place later, or does not
occur at all, and the siphuncle is larger.

The septa are less convex usually than in Eurystomites and, as a
rule, more numerous in each volution.

The sutures have well-marked lateral lobes and have broad sad-
dles on the venter. This ventral saddle may be rounded or straight
or have a slight shallow depression or lobe in the median line. The
sutures, as they approach the lines of involution, are usually more
inclined forwards towards the umbilicus than in Eurystomites.

The whorl in section has a flattened venter and frequently slightly
flattened zones on the sides, so that there is often a decided approxi-
mation to the quadragonal form.

The living chamber is somewhat over one-half of a volution in
length. The aperture is like that of Trocholites, with a deep, broad
hyponomic sinus encroaching upon the lateral zones, these last being
bordered by broad crests, with slight sinuses at the lines of involu-
tion. There appears to have been a slight crest on the dorsum.
The lines of growth are parallel with the borders of the aperture.

The shell usually has strong striz of growth externally, but no
costations ; there are only the broad, slight ridges following the

435

lines of growth, which are more or less sporadic in shells of this
group. ‘These primitive coste are probably due to the imperfect
resorption of the more or less expanded borders of the apertures
occurring in some shells but not in others during the progressive
stages of development but common in all shells in the gerontic
stage.

The shell is very thick on the venter, somewhat thinner, but still
thick on the sides and dorsum.

The type is Zarphyceras prematurum.

The species of this genus are as follows: *

Larphyceras Aucotnt, Hyatt, Newfoundland.
oe prematurum, Hyatt, Newfoundland.
iy frarnswortht (sp. Billings, pars.), Phillipsburg. f
i Champlainense, sp. Whitfield, Fort Cassin.
a Seeleyz, sp. Whitfield, Fort Cassin.
te extensum, Wyatt, Newfoundland.

es MacDonald, n. s., near Lexington, Va.

This last species has a form and suture like that of Champlain-
ense, but the siphuncle is nearer the venter and the young have
flatter and more divergent sides and broader abdomen in the neanic
stage.

TARPHYCERAS AUCOINI, N. S.

ioc, Port au Bort:

Pl. iv, Figs. 17-22.

The ananepionic substage seen in the somewhat rough casts is
given in Figs. 20-22, Pl. iv, from the side and front. These figures

* Nautilus calciferous of Billings (Pal. Foss., i, p. 258) is probably a species of this genus
surviving in the later forms of the Quebec at Port au Choix. The small siphuncle and
its position appears to indicate this, but I have no specimens of this species and haye
not seen any at Ottawa.

} This species has two or more very distinct species. The one referred to above has an
elliptical or oval whorl in the ephebic stage, the dorsum a little broader than the venter,
There is a contact furrow in the neanic and ephebie stages. The sutures have ventral
saddles, with probably slight dorsal lobes in the zone of involution, and a free living
chamber over one-half of a volution in Jength. The siphuncle is subyentran in the
ananeanic substage, becoming propioventran in the paraneanie and yentrocentren in
the metephebic substage. The diameter of the largest specimen, somewhat compressed,
was 140 mm. by 146 mm.; the estimated longest diameter of this through the free living
chamber was about 160 mm,

The type of Farnsworthi is a very distinct specics and belongs to another genus and is
cited below under the heading of Aphetoceras.

436

show the apex to be blunt and rounded, but this rotundity may be
exaggerated in this part which had to be in part restored.

The umbilical perforation is present, but it is very small. The
whorl grows very rapidly in all of its diameters and the bending of
the shell in the paranepionic substage is very abrupt, bringing the
continuation of this substage, the dorsum, in contact with the dor-
sum of the metanepionic and ananepionic parts of the first volu-
tion.

In correlation with this, as in Trocholites, a distinct dorsal fur-
row appears as the shell bends in the first part of the paranepionic
substage. The coiling is so close that the slightest variation in the
same direction would obliterate the umbilical) perforation. The
growing mantle while building the shell might have been influ-
enced by the proximity of the metanepionic dorsum and the small
diameter of the curve. The dorsal furrow here, as in Trocho-
lites, although occurring in the paranepionic substage before the
whorls touch, is perhaps due to the close contiguity of the whorls
and the rapid ingrowth of the primitive umbilical zones. ‘This
process is still apparent in the first part of the second whorl, a sec-
tion of which is given immediately above the apex in Fig. 20.
This is the first of the ananeanic substage, and the siphuncle shifts
from its previously subventran position to propioventran. In the
metaneanic substage, in the latter half of the second volution, the
elongation of the ventro-dorsal diameters is faster, and the ten-
dency to develop lateral zones by the flattening of the sides becomes
marked. The sections of the whorls in the upper half of Fig. 20
are slightly distorted by compression, the lower half is in proper pro-
portion. The aspect of the section is better given in the more
enlarged Fig. 21, and the decrease in lateral diameters in proportion
to the ventro-dorsal is a marked characteristic and continues in the
ephebic stage.

In some specimens this change is not so marked and the flatten-
ing of the sides develops later.

In the later stages the siphuncle is slightly nearer the center as in
Fig. 19.

Fig. 17 gives the full-grown ephebic stage, and is very close to
the original. The section Fig. tg shows how closely this species
resembles Zarphyceras Champlainense, differing only in the greater
rotundity of the venter and in the position of the siphuncle and in

437

the possession of very slight folds or nascent costations, which ap-
pear in some casts, as in the side view Fig. 17.

These specimens occurred in a dolomitic limestone, on a hill to
the west of the inside beach of Port au Port, in the calciferous of
Murray and Howley.

‘TARPHYCERAS PREMATURUM, D. S.

Loc., Port au Port, Newfoundland.

Pl, iv, Figs. 12-16.

This species is apt to be confounded with Yarphyceras Aucoini,
but the whorls increase faster by growth and are much larger at the

same age.

_ Fig. 14 shows in part the nepionic whorl of this species and the
ananeanic substage. The section of the ananeanic whorl above the
ananepionic apex is restored, and is probably made too angular and
the abdomen too broad. The other parts of the figure are accurate.
The side view in Fig. 15 gives the same showing the prominence
of the early nepionic substages and the first of the paranepionic.
Fig. 16 shows the paranepionic and earlier substages from the
front. These figures give satisfactorily the differences between the
young of this species and Yarphyceras Aucotnt.

The presence of a very narrow umbilical perforation is plainly
evident in this specimen and this is similar to that of Aucotne.
The metanepionic dorsum is distinctly separated from the parane-
pionic dorsum, here shown in outline on the inner edge of the sep-
tum, by a narrow, smooth space which curves around between them,
but in consequence of its ventral curvature as it crossed between
them it cannot be seen in a side view. This perforation or bend is
larger and wider than in Acorn, and the involution or ingrowth
of the nascent umbilical shoulders is less than in Awcoruz. It is
consequently doubtful whether the abruptness of the curvature and
the ingrowth of the umbilical shoulders fully accounts for the pres-
ence of the dorsal furrow in the dorsum of this specimen. The
condition of the specimen is not wholly satisfactory, otherwise a
more definite opinion could probably be given. The inner or dor-
sal surface of the ananepionic and metanepienic substages has been
more or less eroded and it is not practicable to say, as in Aucofnz,
that they might have influenced the formatiou of the outline of the
opposing dorsum of the paranepionic whorl as it was bent around
the umbilical perforation.

The shell in its later stages, as shown in Figs. 12 and 13, resem-

438

bled closely Aucoinz, but the abdomen becomes more prominent
and the contact furrow is deeper and broader in consequence of
this and the breadth of the venter.

The siphuncle in the paranepionic substage is subventran, becom-
ing propioventran in the ananeanic as seen in section above in
Fig. 14, and extracentroventran in the septum seen below in Fig.
12. The position alters slightly in the succeeding stages.

The living chamber is obviously over one-half of a volution in
length and is shown in an incomplete fragmentary condition in the
outline on the farther side of Fig. 12; the form in section of the
Same Specimen partly restored is given in Pig. 135-2 live ie
depth of the dorsal lobes in the sutures is shown upon the venter
of the exposed whorl in the upper part of the section which is still
covered by the dorsal layer and the remnants of the septa.

‘TARPHYCERAS EXTENSUM.
Loc., Port au Choix, Newfoundland.

This fossil resembles Zarphyceras Seeleyz, but has a shorter living
chamber and the living chamber and part of septate whorl are free
in gerontic stage. The contact furrow increases in depth with the
ephebic stage and then decreases with the approach of the gerontic
stage. The ventro-dorsal diameter slightly decreases, as is shown
in Fig. 1, Pl. vi, in the paragerontic substage, when the whorl is
almost straightened out, and at the same time the impressed zone
is found to be wholly lost, as shown in the section, Fig. 2.

In section 4 the inner whorl represents a section of the
ephebic stage and the outer whorl is the gerontic stage. The
uppermost, with siphuncle nearer the venter and reduced impressed
zone, is the anagerontic, and Fig. 2 is the paragerontic sub-
stage. The whorls are apparently smooth. ‘The septa are not very
concave. ‘The sutures have ventral saddles, dorsal lobes and slight
lateral lobes. In the anagerontic substage they are nearly straight
on the sides and decidedly inclined forwards.

TARPHYCERAS CHAMPLAINENSE.
NAUTILUS CHAMPLAINENSE, Whitfield, (Bull. Am. Mus., New
MorlkeaViolbnesmiestt..3) Pl ar):
Loc., Fort Cassin, Lake Champlain.
Ploiv, Bieste4—ne
The nepionic stage of this species, as in others of this group, has

439

a very small umbilical perforation, the bending of the paranepionic
stage taking place with great abruptness. When seen laterally
(Fig. 4, Pl. iv) the umbilicus shows a much larger perforation than
exists internally. This is due to the curvature of the perforation
and its-decrease in diameter internally. Starting from either side,
it is an unsymmetrical cone with a pear-shaped base, which de-
creases internally and bends in a bow-like curve as it crosses
between the dorsan surfaces of the meta- and paranepionic sub-
stages. ‘The external orifices are usually owing to the fact that the
matrix is difficult to clean out, apparently broader than they really
are. The actual diameter is about 1 mm., diminishing to .5 mm.
atetme center. In section, however, it may be seen, as in Fig. 9,
to have a minute perforation between the metanepionic dorsum at
the center below and the paranepionic dorsum just above this. The
outline of the section (Fig. 10) probably passed not far from the
apex in this specimen, probably through the metanepionic substage,
judging from the outline of the section (Fig. 9, and the enlarged out-
line, Fig. 1£), which shows transitional characteristics from the
dorsoventrally elongated oval of the whorl of the ananepionic sub-
stage common to most Nautiloids and the transverse oval of the
earlier paranepionic also found at this substage in a large number. of
nautilian shells. This outline, Fig. 11, is similar to that of the
shells of Vautz/us pompilius at the same age.

The paranepionic substage of Fig. g has also an outline simi-
lar to that of Vautilus pompitius at the same age, being kid-
ney-shaped, with a broad but well-defined dorsal furrow. The
presence of this dorsal furrow, although the whorls do not touch,
appears at first to justify the opinion that this is a case in which
inheritance may be assumed. ‘The paranepionic dorsum is, how-
ever, very closely approximated to the dorsum of the metane-
pionic substage, and it seems possible that this proximity modified
the shape of the secreting edge of the dorsal side of the mantle
and caused the corresponding impression shown in the shell. At
any rate, it is not safe to assume that this represents any hereditary
tendency. The exceedingly quick growth from the apex to the
paranepionic and the sudden curvature of the early paranepionic
whorls might have produced this also, as pointed out in other
similar cases. In making another specimen of this species (Fig. 4,
Pl. iv) I was fortunate enough to crack the fossil so as to expose the
entire length of the cast of the umbilical perforation. I found this

440

to be, as stated above, a bow-shaped, dark, smooth filling, as shown
in Fig. 5 and more enlarged in Figs. 6 and 7. Fig. 8 is an ideal
restoration of a side view of the nepionic stage, and gives the loca-
tion of sections shown in Figs. 6 and 7. By the aid of Fig. 7 one
can see that the furrow which appears in the dorsum of the
paranepionic substage is first found just as the whorl makes the
sharp turn to form the umbilical perforation. This shows also that
its origin may be purely meclianical. The hard wall of the dorsum
of the metanepionic was only about .5 mm. distant from the grow-
ing pliable edge of the paranepionic as it made the turn, and this
pliable border may have been built to conform to the shape of the
internal metanepionic dorsum. This becomes possible when one
takes into consideration the rapid growth of the whorl in its lateral
and ventro-dorsal diameters at this stage. The increase of the
former broadening out the volution causes the involution of the
apex on the sides when this is reached, and rapid increase of the
ventro-dorsal diameters forces the building shell to make this sud-
den turn, owing to the more rapid building out of the ventral side.

Immediately after passing this point of greatest pressure, as shown
in Fig. 6, the zone produced by it begins to decrease in depth and
increase in width, but it does not disappear altogether, because the
growing shell immediately strikes the dorsal side of the metane-
pionic and ananepionic substages and the true contact furrow
appears. This is shown in the truncation of the dorsal corner of
the outline in Fig. 8 when it strikes the apex. The centre of Fig. 5
is approximately the same as Fig. 6.

A Trocholites-like outline is assumed in the neanic stage (shown
in Fig. 5 in section of second whorl below center) and in the ephe-
bic stage the whorl is apt to become slightly flattened on the venter.
The outer whorl of section, Fig. 5, is flattened in this way and
represents the anephebic condition of the living chamber.

This shell is smooth until the ananeanic substage, as in Fig. 4,
and then becomes costated. ‘These costz are infrequent, low,
broad elevations which become less distinct with the incoming of
the anephebic substage and are very often absent in the later ephe-
bic substages, beginning however again in the gerontic stage, but
are never so constant or prominent as in the earlier stages.

The siphuncle of the metanepionic whorl, if the mark in the
centre of the enlarged outline (Fig. 11, Pl. iv) really represents
this organ or its general location, is centren. ‘This, however, is a

441

mere spot, so that this must be regarded as doubtful. In the later
paranepionic it is unquestionably propioventran or subventran. In
the neanic stage it approximates to and attains an extracentroven-
tran position, which it retains throughout life. The position in the
gerontic stage was, however, not observed.

Having had an opportunity for close study of Whitfield’s origi-
nals and also the fine collection of Mr. Walcott (now in U. S. Na-
tional Museum), from same locality, there is but little doubt that
- the-specific name is correct.

TARPHYCERAS (?) CONVOLVENS.

DISCOCERAS CONVOLVENS, Angelin et Lindst. (Aragm. Si/., xvi, Fig.
Bre not sels x, ise 5).

This form has the sutures and similar position of siphuncle and
last part of outer whorl free and the lines of growth similar to other
species of this genus, as figured on Pl. xvi of Angelin and Lind-
strom. The figure in section on Pl. x, Fig. 5, is doubted, because
the whorls appear to be closer coiled and the dorso-ventral diame-
ters increase faster than in other specimens figured.

Lvurystomites.

This genus was first described by Schréder,* who saw that the
Nautilus Kelloggt of Whitfield was generically distinct from his
genus Estonioceras. He also included in the same genus WVautilus
Champlainensis, but this, with See/eyz and similar discoidal forms,
are here placed in the genus Tarphyceras.

The siphuncle is subventran in the nepionic and ananeanic sub-
stages, becoming extracentroventran in all the later stages of devel-
opment, or it may remain nearer the venter. The rate of growth
of the shell is more rapid than in Tarphyceras and there are fewer
whorls in the same diameter. The ventro-dorsal diameters are
consequently longer in proportion than in Tarphyceras. The whorl
may be rounded until a late stage of development, but usually
acquires a more or less flattened venter and primitive lateral zones
and ill-defined umbilical zones like those of some species of Tar-
phyceras. The lateral zones are apt to be more convergent and
the abdomen narrower.

*1Op Gib. Pau Abh. Dames et Kayser, V, p. 26.

442

The umbilical perforation is large and the impressed zone is a
contact furrow not generated until the whorls come in contact.

The contact furrow is deeper and the amount of involution
slightly greater in the ephebic stage than is usual in Tarphyceras.
It has been supposed, from the large specimen described by Whit-
field, that this shell was close coiled and involute throughout life.
There is, however, one large specimen (Fig. 4, Pl. v) in the Wal-
cott collection, U. S. National Museum, which has the entire living
chamber and part of the septate whorl free. The living chamber
is very variable in length. It is shorter than in Tarphyceras in the
adult of Hurystomites Kelloggit, and in the aged specimen referred
to above it was very long. The aperture, as figured by Whitfield,
has lateral crests which are most prominent opposite the centres of
the lateral zones, receding into sinuses on the umbilical zones.

The sutures may remain throughout life almost straight, with the
shightest of lateral lobes and ventral saddles, or they may become
quite sinuous, with well-defined lateral lobes and the ventral saddles
entire or divided by median lobes. A distinct dorsal lobe makes
its appearance in the contact furrow when this is formed and on
the gerontic volution this furrow persists as an impressed zone
although entirely freed from contact with the inner whorl (Fig. 5,
Pl. v). It diminishes slowly in depth and breadth, but its per-
sistence on the dorsum of this very long free gerontic stage shows
that it has acquired a strong hold upon the organization of this
specimen. Having no other specimens it cannot be said that this
persistence is common to all individuals of the species.

EURYSTOMITES KELLOGGI.
NauTiLus KeLioce!, Whitf., of. cit. (Bull. Am. Mus., N. Y., i,
INO Sob xxx: not Pigxexxa shies sana)
EurystomitEes KeEtiocci (?), Schréder, op. cit. (Pal. Abh. Dames
et Kayser, v, hft. 4, p. 26).
Pl. v, Figs. 4, 5.

The figures of Whitfield give an excellent general representation
of this species.. The young are, however, slightly costated in the
neanic stage and there are at least two distinct forms placed by
Whitfield under this name.

445

EURYSTOMITES ROTUNDUS.
NauTILus Ketiocet, Whitf., op. cit. (Bull. Am. Mus., New York,
ie exocxd eeSer4euG +) NOt Elia xxx):

Loc., Fort Cassin.

Pl. v, Figs. 21-25. ‘

This species increases more rapidly in the growth of the ventro-
dorsal diameters than in Ae//ogez and retains the siphuncle near the
venter for a longer time during the growth. ‘This may be due,
however, to the differences in the size, and not a matter of age,
since in large whorls it assumes a similar position to that of Ae//oggz.
Fig. 21, Pl. v, gives a view of the first two whorls from the side,
partly restored from the study of the section, and the dotted lines
explain the position of the last section (Fig. 25, Pl. v) of the
centre of first volution.

This figure shows the metanepionic above and paranepionic be-
low, just before the paranepionic comes in contact with the apex.
This was the last section taken. Fig. 22 shows the first section,
secured through the inner dorsal part of the metanepionic substage,
ance bigs) 23,..24, 21. v, show the successive sections connecting
this with Fig. 25, and thus demonstrating the large size of the
umbilical perforation and the correlative rotundity of the dorsi of
the meta- and paranepionic substages.

EURYSTOMITES GIBBOSUM, Nn. g. )
Loc., Port au Port Choix, Schooner Island, Newfoundland.

I mention this new species here without giving figures, because it
is important in the consideration of the relations of the dorsal lobe
and impressed zone and it is so peculiar that it can be easily recog-
mized:

The general aspect is like that of Aurystomites Kellogg’, but the
septa are more deeply concave than in any species of these faunas
and the lateral sutures run forward on the sides as in Tarphyceras.
The outlines of the whorls in section at all epinepionic stages is like
that of the last whorl of the specimen of (Vautilus Kelloget, here
Lurystomites rotundus, as figured by Whitfield on Pl. xxxi, Fig. 4,
and in section the whorls at all stages are ovals similar to the meta-
nepionic substage of Lurystomites rotundus (Fig. 25, Pl. v), but
the abdomen is rounder. No lateral zones or umbilical zones are
differentiated, but there is a faint approximation to the digonal
form probably in the early neanic substages. The sides are only

slightly convex and slope evenly and divergently outwards and con-
sequently appear flattened in some specimens.

The envelopment covers the abdomen, which last is prominently
convex.

The length of the sub-V-shaped dorsal lobe in the sutures is
greater than in any species I have yet seen, and this is very instruc-
tive. Occurring as it does in a shell which is not very involute,
and with a contact furrow but little exceeding the ordinary
dimensions, it shows that the depth of the dorsal lobe in the
sutures is not only correlated with the extent and depth of the
contact furrow but also largely dependent upon the concavity of the
septa. In other words, if this species had had septa of ordinary
concavity the dorsal lobes in the sutures would not have been so
deep and sub-V-shaped as they are. The sutures have also broad
lateral lobes running well forward to sharp saddles at the lines of
involution. There are broad saddles at the abdominal angles and
shallow ventral lobes or straight sutures across the venter. The
siphuncle becomes intracentroventran in the ephebic stage and is
very large, as it is in Eurystomites Kellogg. ‘The whorls come in
contact in the ananeanic substage. ‘The shell grows quite large,
but, so far as I have seen, none have any part of the last whorl free.

EURYSTOMITES VIRGINIANA.
NauTILUS KELLOGGI(?) (pars), Whitf. (not figured).
Loc., near Lexington, Va., and Fort Cassin.

This shell had more cylindrical whorls and more numerous and
straighter sutures at all stages than in Ke//oget. The siphuncle is
nearer the venter, and in the type-specimen, which is over 90 mm.
in diameter (in collection U.S. National Museum), it is still almost
subventran at the entrance into the living chamber. This last is
less than one-half of a volution in length. ‘The whorl is almost
circular in this specimen at all stages observed, including the neanic
stage, and the involution is very slight; the dorsal lobe correlates
with this, being correspondingly shallow and narrow. ‘The sutures
otherwise resemble those of Ke//oggz, but are straighter, and the
three specimens from Virginia do not show the ventral lobes that
often occur in Kelloggt.

There is a young specimen in the American Museum under the
name of Kellogg?, from Fort Cassin, that appears to belong to this
species, having similar sutures, form of whorl and involution.

445

EURYSTOMITES UNDATUM.
NavuTILus uNDaTus, Hall (Pat. New York, i, p. 52, Pl. xiii and
Kay O25) = =.

Loc., Poland, Herkimer county, N. Y., Black River Limestone.

ebve PIgSs W128).

This species has much broader whorls in the young than in
Eurystomites of the Quebec faunas. ‘The position and size of the
siphuncle, the large umbilical perforations and the sutures and the
flattened abdomen of the adult stage and comparison with the
heavily costated forms like Déscoceras antiquisstmum and others
show that this shell is probably a member of the genus Eurysto-
mites.

The nepionic stage has a very large umbilical perforation and in
correlation with this the whorl has a rounded dorsum at this age.
The metanepionic substage has. a broadly elliptical form and sub-
ventran siplhuncle ; the paranepionic, on account of the rapid trans-
verse growth, has a subdigonal whorl, as shown in Fig. 2, Pl. v.
The shell does not increase so fast transversely in the neanic stage
and the whorl becomes rounder, a slight contact furrow appearing
when the whorls come in contact, and the living chamber at this
age is less than one-half of a volution in length. Light costations
also appear in this substage, but the nepionic whorl is smooth with
the exception of strong lines of growth. ‘The abdomen becomes
flattened in the paraneanic substage, and the sutures show slight,
ventral lobes and very slight lateral lobes.

The siphuncle is propioventran in the paranepionic substage and
neanic stage. ‘The costations become stronger in the paraneanic
substage but are reflected on casts only to a very slight extent.

The young are, however, quite variable, and the figures, Pl. v,
give probably an extreme form so far as the retention of the broad
subdigonal form is concerned. In other varieties or species, for I
think there are several species usually placed under this name, the
sides and venter become slightly flattened in the metaneanic sub-
stage, or even before this. In the specimen figured this change
had not yet taken place, although the shell was in the metaneanic
substage.

The aperture in this specimen flared out laterally, but is removed
imnthersection Wigs 2, Pll v.

Slight, foldlike costa are better developed in the ephebic stage,

446

and, although always present, they are only occasionally developed
into decided costations even in full-grown specimens.

The shell grows quite large, but so far as I have seen none have
any part of the last whorl free. The largest shells often have com-
pressed whorls, with abdomens much narrower and flat, and sides
much flatter than in the earlier stages.

Planctoceras.

This group was first described by Remelé under the name of
fEgoceras and subsequently under that of Tragoceras, but both of
these being preoccupied, Schréder proposed that of Planctoceras.*

Schroder considers it to be a subgenus, and that the only dis-
tinction between this and Fstonioceras lies in the fact that it was
probably not close coiled at any stage.

As Estonioceras is here limited, however, the sutures are differ-
ent and have ventral and dorsal saddles with lateral lobes, as in
Falcilituites. The young and all stages so far as seen have also
compressed elliptical instead of depressed whorls. ‘That is to say,
they are probabiy never digonal, and do not resemble those of
Estonioceras at any stage, unless in the very earliest or nepionic
stage which is not known: ‘The whorls, as shown by Schroder in
his fine figures, have the dorsum and venter somewhat depressed
and very nearly equal and distinct from the side in the young. In
other words, there is a faint tendency to form a quadragonal whorl.
Later, probably in the ephebic stage, the dorsum may exceed the
venter in breadth, and in the gerontic stage the whorl becomes al-
most circular,

The lines of growth are similar to those of Falcilituites, z. e.,
they have broad ventral sinuses and a broad latero-dorsal crests.

The volutions are attenuated and the living chambers very long.

The siphuncle is small and about twice its own diameter removed
from the venter, or, in my nomenclature, is extracentroventran in
the neanic and ephebic stages as measured on Schréder’s figures.

The only species referred to this genusin Europe is the Plancteceras
(Orthoceratites) fa/ca/um, sp. Schlot., which, judging from the fig-
ures of Dewitz, Schréder, Quenstedt and Ejichwald, probably in-
cludes several quite distinct species. Planctoceras Quenstedi (Lit.,
falcatus, Quenst.), for example, has distinct sutures and outline

* Dames et Kayser, Pal. Abh., v, hft. 4, 1891, p. 41.

447

from the species figured either by Dewitz or Schréder. In fact, the
figures show that there are very likely three species under this one
name. :

This genus is described here partly because it is an excellent illus-
tration of the correlation of the dorsal and ventral saddles with
elliptical compressed whorls and gibbous abdomens and gibbous
dorsal sides such as occur in many cyrtoceran and gyroceran forms,
and also because of its resemblance to Aphetoceras.

A phetoceras,* n. g.

The shells of this genus are remarkable, for their resemblances,
until a late stage of growth, to the cyrtoceran genus, Melonoceras,
from which they differ in having open apertures, and in this case
they would probably compare more closely in these stages with
Oonoceras. These shells are, however, coiled with an even gyro-
ceran curvature that does not bring the whorls in contact at any
stage.

The form of the whorl in section is compressed elliptical or ovi-
form, the venter narrower than the dorsum. ‘This outline is com-
mon to all of the epembryonic stages as far as known. ‘The nepi-
onic substage has, however, not been seen as yet.

There is no impressed zone at any stage.

The whorl probably deviates from the spiral in the paragerontic
substage, but this has not been observed, unless Marnsworthi is a
true member of this generic phylum.

The shell is invariably smooth so far as kno-yn.

The sutures have very nearly the same form throughout the epem-
bryonic stages, so far as known, having dorsal and ventral saddles
and broad lateral lobes in correlation with gyroceran characters of
the coil.

The siphuncle is subventran or propioventran and probably does
not vary much from these positions in any species.

This genus is separable from Planctoceras by the gyroceran mode
of coiling, by the form of the whorl in section, by the length of
the living chamber and position of the siphuncle.

APHETOCERAS AMERICANUM, 0. s. (Pl. vi, Figs. 5-8, > 34).
Loc., Port au Choix, Newfoundland.

This shell has an open gyroceran coil and, so far as could be

*Ayetds, free.

448

seen, it was not in contact at any stage, but the earlier and proba-
bly nepionic whorl was not seen.

The whorls increase slowly by growth, especially in the transverse
diameters ; the ventro-dorsal growth is somewhat more rapid, but
not sufficiently so to close up the volutions. In the gerontic stage
the living chamber begins to depart slightly from the preceding
curve of growth, as shown in the drawing (Fig. 5, Pl. vi).

The shell is probably smooth.

The whorls in section are compressed, the dorsum wider than the
venter, and the dorso-ventral diameter much larger than the trans-
verse, especially in the ephebic and gerontic stages. The abdomen
becomes more or less flattened in the last two stages, but is rounded
in the neanic stage. The dorsum remains rounded and gibbous
throughout all the stages so far as known.

The sutures have ventral and dorsal saddles and broad lateral
lobes in the neanic stage and probably also in the later nepionic
stage. After the abdomen becomes flattened, slight ventral lobes
are developed in the sutures of the ephebic and gerontic stages.

The siphuncle is large, propioventran in all the stages observed.

APHETOCERAS BOREALE, n. Ss. (Pl. v, Figs. 15-17, > ).
Loc., Schooner Island (on southeast side), Newfoundland.

This resembles Aphetoceras Americanum, at the same age, in
sutures and form, but the siphuncle is slightly nearer to the venter
and the coiling is obviously distinct and the abdomen has not the
well-marked, flattened aspect of the former.

It is doubtful, of course, whether the whorl actually does form a
coil in the specimens collected ; but, if it does, the inner whorls
were probably more loosely coiled than in Aphetoceras Americanum,
since the curvature of this fragment is larger than in any correspond-
ing part of Americanum.

APHETOCERAS FARNSWORTHI.
LITUITES FARNSwoRTHI, Bill. (fars.) (Geol. Surv. Canada, Pal. i,
De Qiks INE, BAL) ;

Loc., Phillipsburg.

This species probably belongs to a distinct genus, and is cited
here provisionally under this name because it may be merely a
highly degenerate species of Aphetoceras. It is also coiled in the
neanic stage, but apparently the whorls are not in very close con-
tact. There are certainly two species, and probably three, usually

449

included under this name. One is separated above as Zurphyceras
Farnsworthi and the other below as Aphetoceras attenuatum. The
type is that figured by Billings, and this had the living chamber
free and deviating strongly from the spiral. It was 91 mm. long
on the dorsal surface and more than one-half of a volution in
length when this measurement was applied to the coil of the preced-
ing whorls. The siphuncle in the ephebic stage was propioventran
and the septa much closer together than is usual in this genus.

APHETOCERAS ATTENUATUM.
LiTUITES FaRNSWORTHI, Bill. ( pars.) (op. ci¢., p. 21).
Loc., Phillipsburg.

This species is founded upon the specimen described by Billings
on p. 2t of his Paleozoic Fossils as having first two whorls in con-
tact and making a coil an inch across. ‘These whorls are, however,
not in contact on his specimen, if my drawing of this is correct.
The specimen is of nearly the same size as the type of Aphetoceras
Larnsworthi, bat one and a quarter volutions are free, so as to
leave a gap of 8 mm. before the completion of the first quarter of
the septate part of the eccentric volution, and at the end of the
same this gap has increased to 13 mm., and in the next quarter, at
the end of the living chamber, it is 25 mm. ‘The departure of the
free whorl of Aarnusworthi increases, as shown in Billings’ drawing,
in less than one-half of a volution to 40 mm.

The septate part of the eccentric volution in this specimen is
58 mm. long, the living chamber is 88 mm. long. ‘The former
would occupy about three-fourths of a volution if it followed a reg-
ular open spiral curve, and the latter would be about one-half of a
volution, estimated in the same way.

The septa are similar to those of Murnsworthi. The fragment of
the siphuncle observable in the neanic stage changes in the length
of 1o mm. from nearly subventran to propioventran.

Deltocerus,* n. g.

The shells of this group resemble those of Aphetoceras, but are
just one grade more complicated. The whorls are similar in section,
but grow more rapidly in the ventro-dorsal diameters, the siphuncles
in some species are very large and ventral. The sutures are simi-

*Agdtos, ascroll.

450

lar to those of Aphetoceras, but the whorls are in contact either in
the earlier epembryonic stages or throughout the ephebic stage. A
departure from the spiral regularly takes place in the gerontic stage
or earlier ; sometimes the entire ephebic stage is free.

No impressed zone has been found at any stage, although a slight
flattening of the dorsum was observed in one species.

This group is represented by several species in the Newfoundland
basin of the Quebec fauna, but it is only necessary here to describe
one.

DELTOCERAS PLANUM, DN. Ss.
Loc., Port au Choix, on north side, Newfoundland.

This fossil is apparently very close to Barrandeoceras natator,
but it increases more rapidly in the dorso-ventral diameters and
has a larger siphuncle, and this is closer to the venter and it differs
also in the greater compression of the form.

In the neanic stage it agrees more closely with zatator in aspect,
but the siphuncle issubventran. In the ephebic stage and anage-
rontic substage it becomes propioventran and increases in size until
it becomes 7 mm. in diameter ventro-dorsally where it enters the
living chamber. The transverse diameter was not measurable, but
it is undoubtedly less than this in correlation with the compressed
character of the volution. ‘The ventro-dorsal diameter of the last
whorl through the living chamber is 53 mm., the transverse
only about 28 mm. to 30 mm., the whole diameter of the coil
at this place being 163 mm.

The incomplete living chamber is over one-quarter of a volution
and has departed slightly from the closer spiral of the ephebic stage.
This departure is very gradual at first until the gerontic stage begins,
and then becomes more apparent and widens more rapidly. The
whorls are in absolute contact only in theneanic stage. The venter
appears to be rounded at all stages of growth.

Barrandecceras.

This genus was described in my Genera of Fossil Cephalopods to
include shells having large umbilical perforations, compressed
slightly costated or smooth whorls. ‘The venter usually narrower
than the dorsum, the whorls barely in contact or with very slight
contact furrow, siphuncle near but above centre, septa deeply con-

451

cave, sutures having usually ventral and dorsal saddles and lateral
lobes. This last statement is true of all the forms having the gyro-
ceran mode of coiling, but not of those which have the closer nau-
tilian form. In these there is a slight dorsal lobe and a different
form of the paranepionic whorl which may eventually lead to their
generic separation.

The type is Barrandeoceras (Naut.) natator, sp. Billings.

BARRANDEOCERAS MINGANENSE.
Loc., Mingan Islands.

There is a specimen from the Chazy limestone of the Mingan
Islands in the collection of the Museum of the Geological Survey
at Ottawa which has very similar characters to those of Larrandeo-
ceras natator, but is distinct in some of its characters. The living
chamber is short and, if complete, about a quarter of a volution in
length. It is free and in section is compressed oval, the abdomen
broader than the dorsum, but the centro-dorsal diameter is longer
than the transverse.

iiiecesipnunclesis; nearer the centre, being ventrocentren., Lhe
neanic, or perhaps an ephebic stage has slight annulations or raised
lines of growth, judging from the marks on the section. This is
labeled as coming from the white limestone of Large Island.

There is no impressed zone at any stage observed. ‘The ephebic
stages have a whorl similar to that of Bavrandeoceras convolvans in.
the neanic stage, but the abdomen is broader.

BARRANDEOCERAS CONVOLVANS.
LITUITES CONVOLVANS, Hall (Pal. cf New Vork, i, p. 53, Pl. xiii,
Pigs 2):

Loc., Watertown, N. Y.

The specimen figured by Hall has in the ephebic stage sutures.
with slight dorsal lobes. This, however, may have been a mistake
in drawing or an abnormal individual variation. A specimen in
the Museum of Comparative Zodlogy from the same locality, ex-
hibiting the form of the whorl and the sutures of the ephebic stage,
does not have such lobes.

The characteristics otherwise are so close to Hall’s description,
and figure that, in spite of this and the supposition that the siphun-
cle was ventral, I have referred this and a suite of sections of the
same to his species.

The whorls are variable in the coiling, and in some specimens
are plainly not in contact at any stage. In others the neanic volu-

452

tion is in contact, but this is so shght that no contact furrow is
formed. ‘The whorls are mostly gyroceran in the character of the
coil becoming excentric in the ephebic stage.

The section is a much compressed oval, the ventro dorsal diam-
eter much longer than the transverse, the abdomen narrowly rounded
and dorsum broader, but also gibbous. The neanic stage has a more
rounded outline in section.

The shell is smooth.

The sutures have ventral and dorsal saddles with broad lateral
lobes in the neanic and ephebic stages.

The siphuncle varies from centroventren to intracentroventran in
the neanic and ephebic stages.

BARRANDEOCERAS NATATOR.

NAUTILUS NATATOR, Bill. (Can. Wat. iv, No. 6, 1859).

BARRANDEOCERAS NATATOR, Hyatt (Gen. Foss. Ceph., p. 299).
Loc., Mingan Islands.

This species has volutions compressed oval in section, the dorsum
somewhat broader than the venter ; siphuncle is extracentroventran,
even in the neanic stage; septa deeply concave; sutures with dor-
sal and ventral saddles and the lateral lobes as in other species of
this genus.

The volutions are in contact, but no contact furrow was formed
at any age. ‘The contact takes place as in the young of Lsfonzo-
ceras perforatum, Fig. 9, Pl. vii, on the venter of the paranepi-
onic volution.

The volution in the neanic stage, dorso-ventral diameter 13 mm.,
has a much narrower venter in proportion to the dorsum than in
the adult. The venter was rounded at all stages and also the dor-
sum. ‘The ananeanic and nepionic stage were not present in the
original specimen in the Museum at Ottawa, but in following out
the same lines it is easily ascertained that the umbilical perforation
must have been enormous, at least 15-17 mm. indiameter. The
living chamber was somewhat over one-fourth of a volution in
length. The whole diameter was about 108 mm. _ It was reported
as having been found in the Chazy lmestone.

BARRANDEOCERAS STERNBERGI.
NAUTILUS STERNBERGI, Barr. (Sys¢. Svd., Pl. xxxvi, XxXxvi1).
Loc., Bohemia. PI. xiv, Figs. 2-5.

This species has, as is usual in transitional species with gyroceran

453

mode of coiling, very variable aspects, owing to the closer coiling
of some specimens than of others.

There is no impressed zone in most specimens at any stage,
although there is a slight flattening of the dorsal side and an
obvious although very slight modification of the dorsum, which
takes place in the most closely coiled shells.

The whorl in section is closely similar to that of za¢ator and the
siphuncle similarly situated. The sutures are similar, with the
exception of a faint dorsal lobe that appears in this species.

The whorls do not touch in some specimens at all (Pl. xiv, Fig.
2); in others they may touch in the neanic and ephebic stages. In
some they may become excentric in the gerontic stage, and in
others this may occur earlier in the ephebic stage. Very likely
there is more than one species included under the name, but it is
obvious that they are transitional to Barrandeoceras Sachert.

BARRANDEOCERAS SACHERI.
NAUMIEUS SACHERD, -Bbarrande’ CSysz7. S77, Pl xxxix). Plo vy, Fic:
II-14.

Loc., Bohemia.

The large umbilical perforation is shown and the almost straight
form of the ana- and metanepionic substages. The paranepionic
substage has sutures with dorsal lobe (Fig. 13) and form with flat-
tened dorsum (Fig. 14), precisely like that of the close-coiled forms
of Sternbergt in the ephebic stage. In L. Sacheri, however, the
coiling is not variable and a contact furrow is invariably formed
after contact, which takes place always as in Fig. 11, at the apex.

The sutures in the ana- and metanepionic substages have ventral
and dorsal saddles and form in section with similar position of
siphuncle to Larrandeoceras natator of the Chazy and resemble
Sternbergt only in the paranepionic substage. In the neanic stage,
after the impressed zone is generated, the whorls become more
compressed and this resemblance is less noticeable.

BARRANDEOCERAS TYRANNUM.

NAUTILUS TYRANNUS, Barr. (Sys¢. Sv7., Pl. xxxvili). Pl. v, Fig. 6-10.
Loc., Bohemia.

This species is similar to Sacherz, but has a smaller umbilical per-
foration and is somewhat closer coiled, the contact furrow appear-
ing sooner and the Sternberg? stage of the paranepionic is consid-
erably shortened. Its first appearance in the outline of the aperture
is shown in Fig. 6 in the paranepionic substage.

454

Figs. 6-9, Pl. v, show the side and front views of two speci-
mens, the smaller in the metanepionic and part of the paranepionic
substages and the other older. These are magnified to show
the ananepionic substages, and Figs. 6, 8, and 10 show the cicatrices
on the apices of both of these. The longitudinal striz shown on
these are necessarily exaggerated, these markings being perceptible
with difficulty under a magnifier. It is interesting to compare
these with the young of the existing Nautilus on PI. i, and it is also
obvious that if found without their older stages in any locality they
would certainly be described as cyrtoceran forms.

BARRANDEOCERAS (?) ELRODI.
GYROCERAS ELRODI, White (Zleventh Ann. Rep. Geol. Indiana,
Oh SEOs Iek vocals hier 1)

Loc., Hartsville, Ind.

This species has an oval outline in the full-grown and senile stage
figured by White, with siphuncle slightly above centre by descrip-
tion, but slightly below centre in the figure. The living chamber is
not quite one-half of a volution in length, but it is very large, and
this, together with one-half of the last volution, are free. The
younger whorls are closely coiled, but not more than two and a
half, if so many, are in contact; the remainder of the third and
first quarter of the fourth are free and the last part excentric. Dr.
White describes them as rounded outline in section, giving the
impression that there was no impressed zone.

The rate of growth in the ventro-dorsal diameters is rapid, and
consequently the living chamber on the last of the third and first
of the fourth volution is very large, especially in the ventro-dorsal
diameters.

The form and sutures are similar to those of Barrandeoceras
Sternbergt, and the species, if it is a member of this genus, is inter-
esting on account of its appearance in the Niagara group, the close
coiling of the young, and the length of the free whorl.

Pycnoceras,* n. g.

This genus has shells similar to those of Aphetoceras in the
nepionic stage, with siphuncle subventran, similar form in section
and similar sutures, with ventral and dorsal saddles and shallow
lateral lobes. ‘This may be seen by comparing figures of Apheto-

* Tluzvos, Close.

455

ceras (Pl. vi, Fig. 5) with the figure of the young of Pycnoceras
apertum (Pl. v, Fig. 18). The nepionic stage has rounded dorsum
and more rounded venter than appears in the Fig. 19, Pl. vi, be-
cause of the presence of a thick band of shell on the venter, con-
sisting of its own shell which is not present on the sides and also
of the corresponding part of the shell of the dorsum of the next
older whorl that has been broken away. A slight contact furrow
is present at the beginning of the ananeanic substage when the whorls
come in contact at the point indicated in Fig. 18 by the end of the
outline of the restored apex. This zone is further shown by the
band of shell left on the venter from the dorsum of the next older
whorl, which was the neanic volution. Upon this, also, there are
remnants of the septa of this stage, showing that this zone was
immediately accompanied by the advent of dorsal lobes in the
sutures. These replaced the dorsal saddles of the nepionic stage.

In the ephebic stage the siphuncle assumed a propioextraventran
position and retained this until the gerontic stage.

The form of the whorl remains quite similar, the ventro-dorsal
diameters being longer than the transverse, but the venter becomes
broader in proportion than the dorsum in neanic and ephebic
stages.

In the gerontic stage the living chamber and part of the septate
last whorl alone are free in some species, in others the age at which
the whorl becomes free varies greatly. |

The type of the genus is the young specimen, Fig. 18, which
shows that the young are distinct from those of Tarphyceras, being
much less closely coiled and having distinct form of whorl and
large umbilical perforation.

There are several undescribed species of this genus in the fauna
of Newfoundland.

PYCNOCERAS APERTUM, n. Ss. Pl. v, Figs. 18-20.
Loc., Port au Port, Newfoundland.

This single specimen was found in the dolomitic limestone or
calciferous in company with the closer coiled young of Tarphyceras.

The nepionic stage is prolonged and _ has the oval form of whorl
and sutures of the adults of the cyrtoceran genus, Melonoceras, and
of the nepionic and neanic stages of the gyroceran form, Apheto-
ceras, its nearest affine, which occurs, however, later in the fauna
of the Quebec group.

456

The characteristics have already been given in the generic de-
scriptions and the presence of the contact furrow in the neanic
stage noticed. It only remains to call attention to the fact that
this and the dorsal lobes of the sutures are generated together as the
whorls come in contact.

PYCNOCERAS CALCIFERIFORME, DN. Ss.
Loc., Port au Choix and Schooner Island, Newfoundland and
Phillipsburg, Canada.

This species is sufficiently abundant at Port au Choix, and seems
at first identical with calczferus of Port au Choix, but the latter
is probably a species of Tarphyceras, having the small siphuncle of
that group.

The shell reaches a considerable size, 128 mm. in the entire
diameter. This specimen has a living chamber somewhat over one-
half of a volution in length, and a similar living chamber occurs in
a younger specimen longer than in Eurystomites.

The whorl in section is an oval with evenly rounded sides, no
umbilical shoulders, and the abdomen broader than the dorsum, but
in the neanic stage, and perhaps in the early part of the ephebic
stage, the sides are evenly rounded and very gibbous, and the venter
may be narrower than the dorsum, measuring through the thickest
inner part of the whorl ventrad of the impressed zone.

The siphuncle is very large, measuring just before entering the
living chamber about 7 mm., and is propioventran in position, but
less than its own diameter distant from the venter. It has a sub-
ventran position in the ananeanic substage, the earliest age observed.
Billings described the siphuncle in Zurphyceras calciferus as small
at the diameter for the whole shell of three inches, and the septa as
numbering about twelve to the inch along the venter at the diame-
ter of three inches. At this diameter in calczferiforme the septa
are six or eight to the inch, and the siphuncle is about 5 mm. in
diameter.

The contact furrow is very slight at all stages. ‘The septa are
deeply concave, approximating to those of EAurystomites gibbosus,
but owing to the slight amount of involution the dorsai lobes are shal-
low ; thus showing the dependence of this character upon the amount
of involution, as well as the concavity of the septa. There are
broad ventral saddles with almost straight suture or slight lobes,
broad lateral lobes trending forwards to narrow saddles at the lines
of involution.

457

The shell is smooth except from strong striz of growth, and oc-
casional folds as in other species of this group, the casts are all per-
fectly smooth.. A specimen from Phillipsburg has identical
form and position of siphuncle, and is in collection of Museum of
Comp. Zodlogy.

Falcilituttes.

This genus set apart by Remelé, the type selected being Letuctes
Dechent equal to Discoceras subcostatum Ang. et Lindstrom.* This
species has a very close-coiled whorl in the nepionic stage, the um-
bilical perforation not being figured at all by Angelin and Lind-
strom, a fact of essential importance when comparing this type with
Estonioceras, ‘The coiled volutions are three in number according
to their figures, but the centre may be erroneously drawn.

The shell has a decidedly quadragonal whorl hke that of some
species of Schroederoceras, and the abdomen is even slightly con-
cave along the median portion? The lines of growth are strongly
marked and have a different aspect from those of Estonioceras.
The hyponomic sinus is deeper and broader and apparently the
lateral lines rise towards the dorsum in crests, but these really join
across the dorsum, forming one huge broad, dorsal crest. In other
words, if figured correctly, the aperture on the free volution must
have had a very deep hyponomic sinus and huge projecting dorso-
lateral crests undivided by any dorsalsinus asin Estonioceras. ‘The
closely coiled volutions may have had lines of growth with dorsal
sinuses, but if so these disappeared on the free part of the whorls.
These volutions may also have had a contact furrow, but it must
have been slight, since it entirely disappears on the early part of the
free volution in both of the European species mentioned below,

The sutures have also ventral saddles with deep lateral lobes.
Dorsal sutures are not given.

The siphuncle is much smaller than in Estonioceras and is nearer
the,centre, being but little above this point or centroventren. This
organ is ellipochoanoidal according to Angelin and Lindstrom
figures which are very clear and apparently exact.

There are only two species as yet described, Fulcilituttes Decheni

*T have not been able to obtain from any library in this vicinity Remelé’s principal
works, but there is no doubt that he selected Discoceras subcostatum, as described by

Angelin and Lindstrom. His papers were published in the Festsch. 50 jahr. Jubelyf. a.
Forstakad, Eberswalde, and the Untersuch. w. d. versteinerngsf. Diluvial., ete.

458

Remelé, sp. Ang. et Lindstrom, and Fucilituites 2 Muellauert, sp.
Dewitz. This last has the ventral saddles and approximately quad-
ragonal form of this genus. ‘The sutures also have dorsal saddles
and the siphuncle is small and centren. ‘There is a slight contact
furrow in the coiled volutions, which is still retained, but shows to a
less degree in the free part of the whorl as figured by Dewitz, and
the dorsal part of the aperture is flat, not concave. ‘The living
chamber was evidently entirely free in these two species when full
grown, since in the figures by Angelin and Lindstrom and by
Dewitz this is shown. ‘The umbilical perforation in MJzuellauert is
so much larger than in Dechenz that I refer this species to this genus
with considerable doubt. The close-coiled volutions are only two
in number.

Trochotiide.

This group was formerly included by the author under the family
name of Tainoceratidze, but was separated in Carboniferous Cepha-
lopods Fourth Ann. Rep. Geol. Surv. Texas, and is here placed
under its proper title. ‘The shells are smooth, or with heavy trans-
verse ridges, which are really primitive costations, but are never
very prominent. The whorls are nephritic or depressed sub-
quadragonal or trapezoidal, the venter generally broader than the
dorsum, and the form is usually nautilian. The sutures as a rule
have broad and slight ventral lobes and lateral lobes.

The siphuncle is dorsad of the centre. The genera are as follows:
Litoceras and Trocholitoceras confined to the Quebec faunas,
Schroederoceras and Trocholites found in both the Quebec faunas
and the Lower Silurian.

Schroederoceras.

This genus has been described by Schroeder and others as Dis-
coceras, and as having close affinity with Trocholites.

The affinity with Discoceras is apparently close, but when one
considers the heavily costated shells of that genus and the younger
stages of the conch, it becomes obvious that the species having such
distinct characters and different modes of development cannot be
associated according to the mode of research adopted here.

There are some species like Schroederoceras Eatont and Eich-
wald, which approximate in the number and form of the whorls to

459

Trocholites, but this is not sustained by closer approximation in the
early stages. The nepionic stage has whorls which depart more
widely from the-trocholitean form of the same age than the later
stages of growth.

The umbilical perforation is large, the whorls are few in number
and increase less rapidly by growth and change more in form than
in Trocholites, the sutures are more sinuous, the siphuncle is not
so close to the dorsum, the apertures narrower in transverse and
longer proportionately in ventro-dorsal diameters and have deeper
narrower hyponomic sinuses, the living chambers are much shorter,
varying, so far as known, from less than one-fourth of a volution to
somewhat more than one-half of a volution, and the size is very
much greater at the same age in all dimensions and there are fewer
whorls.

The resemblances consist in the surface ornamentation, which,
although much coarser, is similar to that of Trocholites.

But even here the deep V-shaped dorsal sinus found in some
species is quite distinct. The aspect of the neanic stage before the
whorl acquires the flattened abdomen and sides is similar, but this
likeness becomes of less importance when the younger nepionic
stage is considered. The ananepionic substage may possibly have
very fine straight transverse striations, which are not usually visible,
but it is apparently smooth as seen in my specimens and in the
figures given by others.* ‘The metanepionic stage has strong trans-
verse bands of growth with finer strize on the surface of the bands.
The borders of the bands are prominent and crenulated, the crenu-
lation being due to short longitudinal depression and intermediate
folds that occupy the edges of the bands and are discontinuous be-
tween them.

The costations also begin to appear in this substage, and these
are in some species apparent as obscure folds on the casts. These
are distinct from the bands of growth being less numerous on the
surface and more widely separated. ‘The crenulations disappear
subsequently probably before the completion of the second whorl,
but there are often a few continuous longitudinal raised lines per-
ceptible on the centre of the venter and near the umbilical shoulders.
The cyrtoceran form is retained longer in the nepionic stage than
in Trocholites and the change to the gyroceran curve that brings

* See Schroeder’s figure of Schroederoceras ( Troch.) Damesi, Pal. Abh. v, Pl. xxviii, Fig. 2a.

460

the whorl finally into contact is more gradual, so that the umbilical
perforation is larger and the contact occurs in the usual way on the
ventral side of the ananepionic substage, instead of on the dorsal
side of the metanepionic substage, as in Trocholites.

The whorl has short ventro-dorsal and longer transverse diameters,
or broad whorls like many species of Trocholites, but is hke a broad
whorled typical. nautilian form from the earliest stage and has not
the kidney-shaped outline so common in sections, especially of the
younger stages of the shell in Trocholites.

The modifications of this outline through the flattening of the
abdomen and lessening of the gibbosity of the sides occurs doubtless
at different stages in different species, but in Schroederoceras angu-
latum and Saemanni it is fully developed only in adults.

The contact furrow is well marked in the young and continues in
some species to be a well-defined depression throughout life, becom-
ing, however, somewhat less marked in the free part of the whorl or
gerontic stage. In some species it is very faintly marked ap-
parently before this stage is reached. It seems to be dependent
upon the closeness of the coiling and involution, which is as a rule
very slight at all stages in the ontogeny and all stages in the
phylogeny. It is consequently somewhat remarkable that this zone
should persist upon the dorsum of the shell so long after the whorl
becomes free of pressure on that side in the gerontic stage.

The siphuncle does not apparently, so far as is seen, materially
change the position it has at the end of the first whorl. It may, as
in Saemanni, become slightly more removed from the dorsum, but
in angulatum it is very close to the dorsum, even in the ephebic
stage. The walls of this organ are thick, and it is often preserved
in the middle of loosely crystalline calcareous deposits under condi-
tions which are not usually considered favorable for the preserva-
tion of siphuncles.

SCHROEDEROCERAS ANGULATUM.
LITUITES ANGULATUM Saem. (fa@dentogr., ii1, Pl. xxi, Fig. ta-6; not
c-@).

Loc., Brevig, Norway.

The original of the Z7¢. angulatus of Saemann (Fig. 1a—6) isin the |
Mus. of Comp. Zodlogy. It has a subquadragonal whorl in the
ephebic stage with a flattened and slightly concave abdomen. ‘The
shape in cross section is peculiar and quite different from that in
Fig. 1¢@. The abdomen on the living chamber is slightly elevated

461

the flat zone being narrower than the transverse diameters imme-
diately internal to this. This may be due to compression, since on
the septate portion the lateral curve from the abdomen to the um-
bilical shoulders show the somewhat flattened aspect given in
Saemann’s figure. The umbilical shoulders are rounded. The
abdomen not so broad as the dorsum, that is not so broad as the
transverse diameter through the umbilical shoulders.

The cast shows faint broad fold-like costations bending apically
_ which were more prominent on the shell, as is shown by other speci-
mens from the same locality. Saemann’s figure is correct in outline
and proportions, but it is incorrect in that it does not give the
sutures which are apparent on the original, and it also brings the
cast of the whorls in close contact, whereas these are separated by
the thick dorsal and ventral shell layers. The whole surface of the
cast is also erroneously given, since it is marked by obscure costa-
tions, which must have been more prominent upon the exterior of
the shell. ‘These are more prominent in the young than upon the
full-grown whorls. The sutures have well-marked ventral and dor-
sal lobes and lateral lobes with saddles at the abdominal angles and
umbilical shoulders. The sutures are numerous and close together
as in most species of this group and in Trocholites.

The siphuncle is nearer the dorsum than that given in Fig. te.

The apex is smaller than in the original of Figs. 1c and 1a, and
the umbilical perforation smaller and the rate of increase by growth
less, so that the species is smaller than Saemannz.

The living chamber in azgu/latus is free as figured by Saemann on
aiewouter part only. Imo the orginal of Pigs 1c=7 itis free for
nearly the entire length.

The prominent costz of the true Desc. antiguissimum are not
present in this shell nor in its allies, and the differences in formare
supplemented by the close coiling of the living chamber in anzzquzs-
StmUM.

Saemann’s original is 91 mm. in diameter, and has somewhat
more than three and ahalfvolutions. ‘The living chamber measured
along the median lateral line is 53 mm. in length from aperture to
suture. ‘The transverse diameter of the septal floor is 26.5 mm.,
the dorso-ventral diameter in median plane is 20.5, both without the
shell. The aperture is narrower in proportion to the ventro-dorsal
diameter, owing to the flaring of the lips and the slight constriction.
Only one-half is preserved and it is slightly distorted ; it may bea

462

little too narrow in the figure on account of the necessary restora-
tion, and the ventral sinus is somewhat too narrow and too deep
owing to a mistake of the artist. ‘The impressed zone continues on
the free part of the living chamber, but becomes distinctly shallower
and is almost obliterated in the dorsal outline of the aperture.

SCHROEDEROCERAS SAEMANNI.
LITUITES ANGULATUS Saem. (Pa/eon., iii, Pl. xxi, Fig. 1c-d, not Fig.
1a—b).
Loc., Brevig, Norway.

The two specimens used by Saemann, one for his section Fig. 1d,
and other for the siphuncle, Fig. 1c, are both in the collection of
the Mus. Comp. Zodlogy and cannot be considered identical with
Lituites angulatus (Figs. 1a—6).

The characteristic differences have been noted under description
of that species. The abdomen of the ephebic stage is flat and
slightly convex, broader than the dorsum, and the sides are slightly
flattened in the full grown as in the Saemann’s Fig. 1¢@, which was
taken from the exposed last septum or floor of a living chamber in
the metephebic substage on the last quarter of the third volution, a
substage preceding that in which the whorl became free, which I
have considered as the parephebic substage. The sides incline in-
wards and the umbilical shoulders are hardly perceptible.

There is an impressed zone broader and deeper than in Schroedero-
ceras angulatum. ‘The sutures are similar, but have a broader ven-
tral, dorsal and lateral lobes. The saddles on the abdominal
angles and those at the lines of involution are also narrower.

The siphuncle is propiodorsan on the first quarter of the fourth
volution, as figured by Saemann. It is nearer the dorsum in the
younger whorl, being less than its own diameter distant from that
side on the early part of the third quarter of the second whorl.

The sides are gibbous and the abdomen rounded throughout the
earlier whorls until the beginning of the third whorl in the anephebic
substage.

The ventrodorsal diameters increase by growth more rapidly than
in angulatum, and the whole shell is consequently larger at corre-
sponding stages of development.

The living chamber is longer as well as in every way larger on
the third whorl in the anephebic substage before the free part of the
whorl is reached, than it is in amgudatum at a later age in the early
part of the parephebic substage as figured by Saemann. In this

463

specimen, the original of Fig. 1d, it is about 75 mm. in length along
the median lateral line from suture to aperture. The transverse
diameter of the septal floor of this given by Saemann in Fig. 1d is
29 mm., the ventro-dorsal diameter in the median plane being
24 mm..

The aperture at this stage spreads laterally, slightly flaring but
without any preceding constriction. ‘The hyponomic sinus of the
aperture was not preserved, but judging from the lines of growth in
both species it was broader and perhaps shallower than in angu-
Jatum. Inthe larger specimen, the original of Fig. 1c, the living
chamber was measured along the umbilicus, it being incomplete.
The whole diameter of this shell, consisting of nearly four and three-
fourths volutions, when complete was over 112 mm.

The length of the living chamber measured along the inner part
on the umbilical line, corresponding to the line of involution, was
about 75 mm. As estimated by measurements corresponding to
this along the median lateral line to a point opposite the termina-
tion of the inner line of measurement, this living chamber was cer-
tainly over 100 mm. in length. The transverse diameter of
the venter of this living chamber at 35 mm. beyond (orad) the
septal floor was 34 mm. without the shell. ‘The shell would increase
this to between 2 and 4 mm., according to the place of measure-
ment, whether between or on the ridges. ‘There are well-marked
narrow ridges or costs at more or less irregular intervals on this
shell with coarse lines of growth between them. ‘These ridges are
not perceptibly reflected on the cast of the interior as in angulatum,
even in the young stages of one specimen, but in another they are
faintly shown on the cast of the side of part of the third whorl.

I have been entirely unable to find the usual marks on the ex-
terior of the siphuncle of this species, or any other similar form
which usually accompanies the short funnels of ellipochoanoidal
forms, but Holms and Schroeder’s statements are specific, and they
have had better opportunities for their studies, so that I merely
suggest a doubt with regard to the structure of such siphuncles as ap-
pear in this species and which have usually been described as an-
nulated. ‘The contact furrow is well marked in the neanic stage
and in ephebic and metaphebic substages, but in the paraphebic
stage it is perceptibly lessened and shows a decided tendency to
disappear on the free whorl. The dorsum was distorted near the
apertural end so that the exact amount of this dirninution could not

464

be seen, but it was clear that the impressed zone had become nar-
rower and shallower. ‘The termination of the living chamber being
also absent, it could not be ascertained whether it finally disappeared
or not on the dorsal rim of the aperture.

SCHROEDEROCERAS TUBULATUM, n.s. PI. vii, Figs. 1-3, and PI. xiv,
Figs. 6-12, >#4.

Loc., Brevig, Norway.

This species was included by Saemann under the head of angu-
fatum, but it has much broader whorls, increases more slowly in
size and the free part of the whorl is longer, not only the living
chamber but a considerable portion of the septate whorl being free.

A cast of the latter part of the first or first part of the second
whorl is costated, and the narrowness of the side shows that the
young whorl was not so broad ventro-dorsally as in amgulatus at the
same stage.

One specimen shows the living chamber in the ephebic stage be-
fore the uncoiling begins. ‘This is of about the same age as that
figured by Saemann in his angulatus, Section 1d. The ventro-
dorsal diameter of the septal floor of this is 26 mm., and the trans-
verse about 32 mm. ‘The venter was the broadest part at this stage
as it is in the early ephebic stage of angulatum. ‘The umbilical
shoulders do not exist even in the rounded form that they take on
in the adult of angu/atus and in the ephebic and gerontic whorls of
Saemanm. ‘The sides incline or diverge outwardly more decidedly
and are flatter than in Saemanni at the same stage.

The shell has coarse lines of growth upon this living chamber at
more or less irregular intervals, with finer lines between them, and
at still rarer and less regular intervals there are the usual narrow
ridges which are the remains of the costz of earlier stages. The
ventral sinus is broader and deeper than in angulatus or Saemanni
at the same stage, and there is a deep sinus in the impressed zone
on the dorsum with a shallow subacute V shape.

The type of the species is the specimen showing the extended last
whorl figured in this paper, Pl. vu, Fig. 1.

According to my estimate this specimen must have had at least
five complete whorls. The diameter of the coiled part was proba-
bly about 118 mm., and this is estimated to contain nearly five
volutions, the length of the free part was over 115 mm. measured
along the median lateral line, along the dorsal line of this mould
of the outer whorl it could be measured more readily as 105 mm.

405

The incomplete living chamber occupied 75 mm. of this free part
as measured above the median lateral line from the broken edge to
the imperfect remnant of the septal floor.

The transverse diameter of the termination of the third whorl
was 15 mm. without the shell, the breadth of the side 10 mm., the
ventro-dorsal diameter in the mesal plane, as estimated, was of
about the same length. The transverse diameter about the middle
of the last quarter of the fourth whorl was 22 mm., the ventro-
dorsal in the mesal plane was 17 mm. both without the shell.

The shape of the living chamber must have been greatly altered
near its termination. ‘The fragment of mould of one side and part
of the dorsum preserved shows that the impressed zone had become
narrowed and disappeared completely. The dorsum remained
slightly flattened, but this flattening given in the restored section,
ige3) Pie vil, is probably greater than 1f was in the fossil. “Whe
lines of growth on the dorsum of the first part of the free hving
chamber have such a faint sinus that they would ordinarily be de-
scribed as straight, the lateral crests are much reduced, the ventral
sinus was not visible, but it also probably became reduced or
shallower. The transverse diameters were also much reduced, and
aspect of the aperture changes so that the ventro-dorsal diameter is _
much longer than the transverse. The outline given may be de-
fective in making this diameter somewhat too long and the abdomen
not quite flat enough, but certainly there is an entire change in the
proportions of the whorl and an approximation to this reconstructed
outline.

The sutures do not differ materially, if at all from these of
Saemanni so tar as could be seen. They are visible on the third
whorl and had the usual curvatures. The two last on the fifth whorl
were visible on the dorsum and partly on the side. These had a
deep dorsal lobe, with saddles and lateral lobe as in Saemannz, and
were very interesting, since they showed that the dorsal sutures had
not been immediately affected by separation of the whorls. The
last suture is given in Fig. 1, on Pl. vii.

The zone of impression is fainter, but still perceptible in the dor-
sum of the first part of the living chamber, but has entirely disap-
peared on the latter part of the same. It is more strongly marked
on the dorsum of the third and early part of the fourth whorls than
on the latter part of the fourth, but it is broad and still quite dis-

466

tinct just before the whorl becomes free on the last quarter of the
fifth volution (Fig. 2).

The nepionic stage of this species is given in Figs. 6-7, Pl. xiv.
The advent of the hyponomic sinus can be seen in the lines of
growth of the metanepionic substage in the front view, Fig. 6. The
umbilical perforation is larger than it appears to be in the side view,
Fig. 7, because it 1s in part overlapped by the inward growth of
the umbilical zones of the paranepionic volution. |

The lines of growth are entire and very fine lines on the anane-
pionic and metanepionic substages, and there are no longitudinal
ridges. The sides are convergent and rounded, and the abdomen
is rounded and narrower than the dorsum in these substages. At
the beginning of the paranepionic the abdomen becomes suddenly
flattened, the sides also tending to become flatter and the whorl
spreads laterally very fast, the venter becoming wider than the
dorsum. Slight crenulations also appear, and in consequence of
these faint longitudinal lines may be seen with a magnifier.

Regularly spaced transverse lines are first noticeable in the
paranepionic forming the forward edges of broad laminz on the
surface and having finer lines of growth between them, as in Fig. 10,
JE, Sane

The septa in this substage are deeply concave and have broad
ventral saddles divided by narrow V-shaped central ventral lobes,
as in Fig. 10, Pl. xiv. There are shallow lateral lobes and dorsal
lobes in the contact furrow.

The siphuncle is propiodorsan in this substage as givenin Fig. g,
but was not seen in earlier ages. It is slightly nearer the dorsum in
the succeeding stages of development of this specimen. __

A distinct dorsal furrow appears in this shell in the early part of
‘the paranepionic and deepens until replaced and enlarged by the
contact furrow. Contact takes place upon the area of the scar, but
not on the dorsal side of this area. I was not able to define the ex-
act line of contact because the apex had been slightly fractured in
making the preparation, but it was quite clear that contact did not
occur upon the dorsum of the ana- nor metanepionic substages as it
does in Trocholites. The involution is greater and the contact
furrow deeper in the ananepionic substage, where it begins, than
at any subsequent substage, as shown in Fig. 8, Pl. xiv.

In the meta- and paraneanic substages the more prominent lines
of growth described above on the edges of the broad bands become

467

subcostal in aspect, but are somewhat exaggerated in Fig. 11. In
the ephebic stages these subcostz are less prominent and do not
have any corresponding ridges on the cast, which is smooth. ‘The
venter is also less elevated, the ventro-dorsal being less in proportion
to the transverse diameters and the whorl assumes the broad de-
pressed outline in section of this species.

SCHROEDEROCERAS RAROSPIRA.
CLYMENIA RAROSPIRA (pars) Eichw. (Leth. Rossica, Pl. 1, Fig. 1a—é,
ieee not big. 2za—h, nor Kig. 6¢@, 4, ¢*).

This species has the aspect of Schroederoceras Saemanni on the
latter part of the second and third whorl, but the early part of the
same whorl in section is rounded and without a zone of impression.
The whorls increase faster by growth in the ventro-dorsal diameters
than in Saemanni. If Eichwald’s figures can be relied upon the
species are distinct. The distribution of the prominent strize of the
neanic stage is instructive. They occupy all of the first whorl ex-
cept the apical part and are lost upon the last half of the second
whorl, persisting somewhat longer than in Saemanni or angulatum.
The siphuncle is depicted as very large, and according to the figure
is nearer the dorsum in the first and second whorl than it is in the
same age in Saemannt. ‘The faster increase in dorso-ventral
diameters makes the adult somewhat larger in diameter of the coil
at the same age.

The fact that the last volution is not free at the end shows proba-
bly that the specimen figured had not reached the gerontic stage of
degeneration. It is of course to be expected that some species of
Schroederoceras never become uncoiled, and this may be one of
these. Eichwald’s Fig. 14 also shows that the impressed zone is
deeper on the second whorl in the anephebic stage than it is sub-
sequently on the third whorl in the parephebic when a tendency
towards uncoiling begins to show itself in this way. ‘The sutures.
as shown in Figs. 3a, 4, ¢, are like those of Saemanni.

SCHROEDEROCERAS TERES.

Lit. TERES, Eichw. (S¢/. zn Esthland, p. 105).

Lir. TERES, Dewitz (Schrif. physical-okonon. Gesel/,, Konigsberg,
Solel yeti 4):

Pim GERES) Schroeder (@é7d., xxii, Plo ii, Fig. 2).

Discoc. TERES, Schroeder (zézd., xxili, p. 96).

*See Trocholitoceras Eichwaldi.

468

Lit. TERES, Holm (7a Adh., Dames et Kayser, 111, hit: 1 Pia
Fig. 5-8).
Loc., Kandel, Esthland.

The smooth whorl has in section an abdomen somewhat broader
than the dorsum as figured by Dewitz and the siphuncle closer to
the dorsum than in Odini. The living chamber is free and the
aperture like that of a@zgulatum. ‘The impressed zone is continued
to the edge of the aperture. It suffers, however, a certain obvious
diminution and the dorsal edge of the aperture is merely flattened
instead of being concave as is the dorsum at the beginning of the
living chamber. This peculiarity is described by Schroder, who
gives the best figures.

Holms’ figures of the young have been copied in outline on
Pl. vi, Fig. 21-27. These sections show how closely the young
resemble those of Schroederoceras Eatoni,and if correctly identified
and drawn indicate considerable variation in the form of the
young and the relations of the umbilical perforation. In Fig.
21, it is between the ananepionic and paranepionic ; in Fig. 22, it is
situated as in Trocholites, viz., carried more on to the metanepionic
substage, and is differently shaped.

The young (Figs. 23-27) give a rare opportunity for the study of
the nepionicstage. The ananepionic substage (Figs. 26-27) is like that
of Hafoni, and one sees the peculiar shape of the apex and the great
comparative depth of the apical chamber. The first septum and
czcum of course belongs to the later metanepionic substage, but
the whorl itself is ananepionic, and this a broad elliptical section as
seen in the front view of Fig. 26. The dorsum broader than the
venter and rounded. The shape is here decidedly cyrtoceran.
The first septum and czecum is seen in this view and the siphuncle
is subventran. In the metanepionic it changes as in other forms
towards the centre. ‘This is shown by its becoming extracentroven-.,
tran in the third septum, which belongs to the later age of the para-
nepionic substage. At the angle of the turn a faint, but plainly
marked dorsal furrow appears. The point at which this im-
pression occurs is like that of similar forms of early faunas, and
the shape of the whorls show a very rapid increase of the lateral
diameters and the usual approximation to the kidney-shaped whorl
which characterizes rapidly growing shells of Nautiloids at similar
substages. It seems probable, therefore, that this may have been

469

produced by the mechanical effect of the proximity of the stiff wall
of the metanepionic substage. It would be extremely instructive to
make a number of such preparations and study comparatively the
amount and variability of this characteristic with relation to the
size of the umbilical perforation, its position, etc.

SCHROEDEROCERAS ? BANDONIS.

SCHROEDEROCERAS ? BANDONIS, Rem. (Unter. verstein. Diluviat-
iwaschecoe, 1, Pl. ii, Fig. 4).

SCHROEDEROCERAS ODINI, Vern. (Geol. Russta, Pal., ii, Pl. xxv,
Fig. 8).

This entirely smooth shell has rounded whorls, the ventro-dorsal
diameters in adults longer than the transverse. ‘There are deeply
sinuous sutures with slight ventral lobes on the abdomen in the
neanic stage, and these are replaced by flattened saddles (if cor-
rectly figured) in the ephebic whorl. It is obviously, if the charac-
ters are correctly depicted, quite distinct from Schroed. teres.
These species agree in general aspect, but not in the form of whorl
of the coiled stages of growth, and differ also in the sutures and in
position of siphuncle and in the shape of the free whorl.

In Odini there is no impressed zone on the free whorl, and
probably this was very slight in the neanic stage, as shown by
Verneuil’s Fig. 8¢.

SCHROEDEROCERAS DENCKELMANNI.
iu CORNUARIENIS, De Vern: (Pas, Russia, Pl. xxv, Fig. 7):
Lit. DENCKELMANNI, Rem. ;
DIscocERAS DENCKELMANNI, Rem. (Zeztsch. deutsch. geol. Gesell.,
XXXvllil, 1886, p. 468).

This is a completely smooth shell with rounded and more
numerous whorls at the same size than in Schroederoceras angulatum
and a less deeply marked impressed zone.

SCHROEDEROCERAS DAMESI.
MROCHOLIMES) DaAwesI, Schroeder (“Ceph. d. Untersil.,” ad:
Abh., Dames et Kayser, v, Pl. xxviii, Fig. 2).

This shell was erroneously referred to Trocholites by Schréder,
if his figure is correct. The young has the large umbilical perfora-
tion, the large whorls and rapid increase by growth, as well as the
characteristic surface markings of this genus. The last whorl has

470

also the form common in the neanic stage of species like Schroe-
deroceras angulatum and especially Scemanni, which it very closely
resembles. It is obviously an immature shell of some species of
this genus.

SCHROEDEROCERAS EATONI.

Liruires Eatoni, Whitf. (Bull. Am. Mus., New York, 1, No. 8,
BY xxviii (2), Pigs 5s—jret. Bl xxx Pigsi1; motliicass)s
Discoceras Eatoni, Schroder (‘‘ Sil. Ceph.,’’ Pal. Abh., Dames

et Kayser, v, p. 22). Pl: wi, Pigs. 28-35, and Plo wines
7-8.
Loc., Fort Cassin, Lake Champlain.

Having had the original of this species, lam able to state that the
apex or nepionic stage is closely similar to that of Holms’ figures of
Schroederoceras (Lit.) teres. The single specimen, Fig. 35, Pl. vi,
that showed this section has a large apical or air chamber very deep
and cap-shaped in outline, with abrupt ventral side, exactly as in
Helms’ figures, the second chamber being proportionately some-
what less in depth. The umbilical perforation is, however, much
larger, as may be seen in this section, and in Fig. 31, Pl. vi.

The septa continue throughout the first and larger part of the
second whorl, that is during the nepionic and neanic stages, to be
proportionately wider apart on the venter and nearer together on
the dorsum until the decrease by growth in the ventro-dorsal
diameters in the anephebic stage makes them more equal on the
first quarter of the third whorl where they begin to assume the
usual depths. The siphuncle begins subventran in the first chamber,
inclining centrally in its passage through the first and succeeding
septa until near the end of the first whorl, when it becomes centren.
It is in other words nearer the venter than the centre during the
cyrtoceran or nepionic stage and becomes centren in the ananeanic
substage, as in the figure from Whitfield’s specimen and in other
figures, Pl. vi.

The sutures have the usual broad ventral saddles and lateral lobes
in the nepionic stage and probably dorsal saddles, but these last
were not distinctly seen.

The siphuncle in the metaneanic and paraneanic substages trends
slowly towards the dorsum until the third quarter of the second
whorl is reached, and after that the approximation proceeds more

ee Te

471

rapidly until it reaches the centrodorsan position in the anephebic
substage at the beginning of the third whorl.

The ventro-dorsal diameters also slowly decrease by growth cor-
relatively with this movement, along the mesal plane and proceed
with equal steps, correlative with changes in the septa, and relative
dimensions and shapes of the air chambers and the shifting of the
siphuncle towards the dorsum to the first quarter of the third whorl
where they take on the adult proportions and aspect.

These facts are admirably wellshown in the figures of Schroedero-
ceras (Lit.) teres by Holm, reproduced here if allowance is made
for the more cyrtoceran or less involute form of /Hafonz, which
has a larger umbilical perforation. The third septum in both
forms, however, comes internally to the same point, the end of the
cyrtoceran stage, when the whorl makes a sudden bend and assumes
the gyroceran curvature that brings it at the end of the first whorl
against apex of the conch. In Figs. 21 and 22, from Holm, this
bend is more abrupt and more like that of Trocholites than in this
species. The dorsal side of the last quarter of the first whorl
actually strikes and lies upon the dorsal side of the first air cham-
ber, whereas in this species the contact takes place farther towards
the apex. In ¢erves also, according to Holm’s figures, the approxi-
mation of the siphuncle towards the dorsum takes place more
rapidly and probably earlier than in Hatonz. Holm found no signs
of a cicatrix on the apex of feres, but no shell is represented in his
figures and he describes the whorls as so very closely approximated
that there was but one shell wall. The young shell is very thin,
and probably this explains the difficulty of separating the whorls.
At any rate, the absence of the cicatrix is not established by his
observations. I think he must have overlooked the shell wall, this
not being absent in any other forms that I have examined.

Fig. 34, Pl. vi, gives the aspect of an accidental section, the
location of which is shown by the line through Fig. 35, taken from
the center of Whitfield’s original of this species. The sections
passed subdorsan to the shell, cutting across the two first septa of
the metanepionic substage. The peculiar aspect of this part of the
section is due to the continuity of the lateral shell lines on either
side with those of the paranepionic whorl which is given in section
of volution immediately under this. The convex line dividing the
metanepionic from the paranepionic volution, the projecting third
septum. The reverse, the splinter from which this section was

472

taken, is given in Fig. 31, Pl. vi. The core of the umbilical per-
foration was exposed, the metanepionic volution is smaller and
younger, the paranepionic section is older and is shown to be con-
vex on the gyroceran turn or curve around the core. The state of
the section left this observation open to some doubt owing te the
fact that it was slightly clipped on one side, exposing an older part
of the same whorl. On wearing this same section down a shade
farther the beginning of a dorsal furrow became apparent, and
iS) SiVEMUIMNN LIES. 32, 32.

It is, however, obvious that the dorsal furrow is very slight and it
occurs in the usual place on the paranepionic dorsum ; the rotundity
and form of the metanepionic whorl was perfectly well defined: ‘The
umbilical perforation in this fossil was very small, and the occurence
of a dorsal furrow at the place designated in the drawing could be
accounted for as due to the contiguity of the dorsum of the grow-
ing whorl of the paranepionic to that of the stiff wall of the
metanepionic substage.

The position of the siphuncle in the apex could not be deter-
mined, but its place in the other whorls was plainly seen and
_ agrees closely enough with the positions determined by Whitfield
in the young of afonz, with which also the characters of the
sutures of the older whorls agreed in this specimen.

The contact furrow is deeper relatively in the neanic stage
than it is subsequently, when one takes into accourit the form of
the whorl and the relative extent of the sides covered by involu-
tion. It is, however, very well marked in all stages, and its disap-
pearance upon the latter part of the last whorl, as has been shown
in Whitfield’s figures and those given in this paper, is a significant
and instructive fact that has been discussed in other parts of this
essay. The aperture of Fig. 7, Pl. vii, was removable, and this
being taken off the last vestige of the impressed zone is seen on
the dorsal side of the free whorl in the front view of the same
specimen, Fig. 8. The portion removed is so short that it is pos-
sible it may represent the rim of the aperture itself.

The sutures of the anephebic stages differ considerably from
those of the adult, being straighter and more like those of Trocho-
lites, and it may be questioned whether this should not be called
the paraneanic substage on account of its close resemblances to
Trocholites.

In the full-grown shell of the parephebic and gerontic age, as

Vv ee ee ee eee

473

shown in Whitfield’s figure, Pl. xxxii, and in my figure, the oldest
sutures are more sinuous than those of an earlier stage just under
the free part of-the living chamber, as given in my copy of his
figure, with sutures drawn in from the original chambers (Fig. 28,
Pl. vi). They have normally in the ephebic stage ventral and
dorsal lobes, with lateral lobes and saddles at the abdominal angles
and umbilical shoulders.

The length of the living chamber in a full-grown specimen is
over one-half a volution, and the latter part is free, as given by
Wimtheld and. in my Fig. 7, Pl. vu.

SCHROEDEROCERAS CASINENSIS.
LituiTEs EaTonli, var. CaAsINENsIS. Whitf. (Bulet. Am. Mus.,
NEWRVOnG ine NO oo lely sexx). 9 llvin Migs. 26-25, amd) i
vil, Bigs. 4-6,
Loc., Fort Cassin, Lake Champlain.

This is a distinct species, the sutures being straighter in the
ephebic stage than in true Hatonz, the venter and sides are more
decidedly flattened, and the relative proportions of the last whorl
at the same age different.* The ventro-dorsal and transverse
diameters are about equal, whereas in Ha¢oni the transverse is con-
siderably longer than the ventro-dorsal in the mesal plane. The
amount of involution in Lafond and the depth of the contact furrow
in the ephebic stage is also greater.

Whitfield’s figure is given on Pl. vi, Fig. 36, with some emen-
dations taken from the original specimen. ‘This shows that the
ephebic stage had not a free living chamber, and that shown in my
Migee ele vii, represents the gerontic. stage) “ine front view,
Fig. 5, shows the deeper contact furrow and the dorsal lobes in
the dorsum of the metephebic substage and the slight but imper-
ceptible change which takes place in the broader, shallower zone of
the early part of the gerontic living chamber below. ‘The free
part of this chamber is at first concave just beyond the broken end
of the metephebic whorl, then flattened, and finally convex on the
dorsum, as shown in Figs. 5 and 6.

The length of this living chamber was nearly three-fourths of a
volution, beginning somewhat beyond the broken part given in

* Whitfield himself thought this was probably a distinct species, as shown by his
remarks on page 382.

474

Figs. 4and 5. ‘Thesiphuncle is very large and propiodorsan in the
ephebic and gerontic stage.

Litoceras.

This genus was described in Genera of Fossil Cephalopods, page
259.

The siphuncle is very large and is dorsad or below the centre in
adults, but is ventrad in Zztoceras Whiteavsi in the neanic and ear-
lier stages, and is very likely ventrad in the young at some stage in
all species, as it is in those of Schroederoceras that have been
studied. The young are slightly costated also and the adults
smooth, as in other genera of similar groups. The umbilical per-
foration is of good size, and in the nepionic stage the shell is cyr-
toceran and similar to the shells of Schroederoceras of the same
group, but with much broader whorls and deeper umbilici. These
differences are maintained in the later stages of growth, the whorls
being much larger, broader and have in the ephebic stage similar
abdomens and convex, divergent sides without umbilical shoulders,
resembling the neanic stages of species of Schroederoceras.

The increase by growth in the lateral diameters of the whorl is
rapid, as in the young of Schroederoceras and other allied genera,
but it continues longer, and even the adults may have very broad
whorls, so that these adults resemble in form the neanic stage of
Schroederoceras.

The aperture is less compressed than in the full-grown shells of
Schroederoceras, and resemble those of the anephebic stage of that
genus, but are not flaring or trumpet shaped, as in Trocholites.
In fact, there has been a slight turning in of the edges in all the
specimens observed, but this, however, may be due to compression.
The hyponomic sinus is smaller and shallower than in the ephebic
aperture of Schroederoceras. .

The contact furrow is broader and deeper than in Schroed-
eroceras and the involution more marked on account of the rotund-
ity and breadth of the abdomen, which is covered in.

The end of the whorl, even in full-grown shells, is not free, and
in this respect also the species resemble the neanic stage in
Schroederoceras. The living chambers are, so far as observed,
longer than in Schroederoceras and shorter than in Trocholites.

The sutures have deep dorsal lobes, saddles on the lines of

475

involution and broad lateral lobes, and the invariable ventral lobe
of Schroederoceras is replaced by a saddle or nearly straight suture.

The type of this genus, when it was first described, were the
specimens in Geological Museum at Ottawa identified as Vawtzlus
versutus of Billings, but these appear here as Litoceras Whiteavst,
since there is every reason for supposing that they are not the
species described by Billings under the name of versutus.

LITOCERAS WHITEAVSI.
NAUT. VERSUTUM (?) (ars), Bill. (Geol. Can., Pal. Foss., i, p.

258).
Loc., Point Rich and Gargamelle Cove, Newfoundland.

Having examined the so-called originals of this species, so far as
they exist in the Geological Survey Museum at Ottawa, I have
found that none of them came from Billings’ locality, Bonne Bay,
and none of them agree with Billings’ description. Billings’
species had ten septa to the inch; this species has the sutures about
one-quarter of an inch apart, a difference showing essential dis-
tinction.

The young on the second whorl has the siphuncle ventrocentren
and are slightly costated. These costz disappear before the end
of this whorl and the surface is marked only by the lines of growth.
The siphuncle also shifts gradually, becoming centrodorsan, but
in the adult it does not approximate to the dorsum, remaining
nearer the centre than the dorsum. The abdomen is very broad in
the later stages, and in the adult the diameter through the abdomi-
nal angles is longer than the ventro-dorsal diameter.

The sides are divergent; that is, slope inwardly. They are
rounded and have no umbilical shoulders, the dorsum being coex-
tensive with the contact furrow which covers the abdomen com-
pletely. ‘The sutures are sinuous, having well-marked ventral
saddles, lateral lobes and probably dorsal lobes, aithough the latter
were not seen. ‘The specimens from which this description was
taken were collected at Gargamelle Cove, near Billings’ locality,
and probably belong to this species, as it is identified by the Geo-
logical Survey of Canada. The form of the whorl is not so broad
laterally, the chamber of habitation is less than one-half of a volu-
tion in length and smaller in every way than in Lz¢oceras insolens.

A section of the whorl is more like that of zsoZens in the ephe-

476

bic stage than in the specimens in the museum at Ottawa, but the
sides are rounder at the stages of growth observed.

The siphuncle is similarly situated and somewhat smaller than in
insolens,

The diameter of the largest and most perfect specimen was about
150 mm. ‘The transverse diameter of the fourth whorl at the
whole diameter of 75 mm. was 42 mm., and the ventro-dorsal 25
mm. The diameter of the siphuncle at this stage was 4 mm.
The diameter of this organ increased slightly to the living cham-
ber, but probably did not exceed 6 or 7 mm. On the last quarter
(probably of the fourth whorl), just before the living chamber was
reached, the siphuncle was found to be misplaced, as is not uncom-
mon in species from this locality. This organ has very thick walls
and often maintains its form and proportions when unsupported by
the septa, although thrown out of place by the movements in the
matrix, as happened in this case. It is thrown over to the left and
arches towards the venter rising above the centre. The specimen
being excavated, however, it was found to be in its usual place,
a few septa younger than the point at which it appeared. The
entrance into the living chamber was not, however, satisfactorily
observed, the septum being broken by compression, although the
entrance seemed to be in the usual place, between the centre and
the dorsum. The septa were about 6 mm. apart as measured on
this siphuncle.

The shell was very thick near the aperture, which was similar to
that of zzsolens, but appeared to have a narrower hyponomic sinus
than in that species. The way in which the lateral crests run for-
wards to the lines of involution indicate that there was a crest on
the dorsum also, but this could not be observed.

LITOCERES INSOLENS (?).

NAUTILUS INSOLENS (?) Bill. (Pa/. Foss., i, p. 258). Pl. vi, Figs.
Q-II, nat. size.

Loc., Gargamelle Cove, W. Coast Newfoundland.

This species is so similar in dimensions and characteristics to the
one described by Billings and was found so near his locality that
I have ventured to apply the same name, although he does not dis-
tinctly state whether the siphuncle was dorsad or ventrad of the
centre.

The types were not to be found in the museum at Ottawa during
my visit to that museum several years ago.

The young of this species increases in the transverse diameters with
great rapidity. The ananepionic stage, Figs. 9, 10, Pl. vi, has the
usual straight, fine striz and the metanepionic and succeeding sub-
stages throughout the first, and a part of the second whorls have
the costations which are common at the same age in other shells of
this family. The umbilical perforation is of considerable size; the
whorls change from the rounded, cyrtoceran form of the anane-
pionic substage, which apparently has the ventro-dorsal longer
than the transverse diameters, very rapidly as the gyroceran stage
approaches on the latter part of the first half of the first whorl or
the metanepionic substage. In the paranepionic on the last half
of the first whorl and before the whorls touch, the whorl is like the
metanepionic volution as shown in section in Fig. 11, Pl. vi, trigo-
nal, the venter broader than the dorsum, and the angles are rounded.
In the ananeanic substage, after the completion of the first whorl,
the wherl becomes digonal, with a contact furrow. Near the end
of the first whorl, in the paranepionic substage, the ventro-dorsal
diameter was 3 mm., roughly measured ; the transverse through the
abdominal angles were approximately 6 mm.; half of a volution
beyond this, in the ananeanic substage, the transverse had become
10 Or 11 mm., and the ventro-dorsal about 6 mm. ; less than one-half
volution later in the paraneanic the transverse had become 16 mm.
and the ventro-dorsal about 7 mm. ; somewhat more than one-half
volution later, in the anephebic substage, the whorl had become
changed to kidney shaped in section, and the septum at the base of
the living chamber was exposed. ‘The transverse diameter was
29 mm., the ventro-dorsal 12 mm., both taken without the shell.

Fig. 11, Pl. vi, shows a sectional view of the metanepionic,
neanic and ephebic volutions. ‘The diameters through the umbili-
cal zone, parallel with the mesal plane, were equal or about the
same, roughly measured, as the ventro-dorsal diameters.

The anaphebic sutures of the septum at the base of the living
chamber in the specimen figured has a well-marked median saddle,
narrower than in a full-grown shell, and on either side of this were
faintly marked ventral lobes. These last were continued on the
sides, rising steeply to the umbilical zones, where they culminated
in broad saddles. ‘These descended abruptly in the contact fur-
row, forming a broad, deep, dorsal lobe. ‘These sutures are quite

distinct from those of full-grown shells. The siphuncle was propio-
dorsan, being a shade less than its own diameter removed from
that surface, its diameter being 3 mm.

The whorl is still kidney shaped in section in this substage, with
rounded lateral zones, elevated rounded abdomen and rounded
abdominal angles, but there is an evident tendency to broaden on
the sides and to form steep, horizontal umbilical zones. ‘These
parts, being developed out of a digonal whorl, have the usual primi-
tive form of the kidney-shaped whorl, but the slightest flattening
of the lateral zones would convert the section into a quadragonal
outline. There is a deep wide contact furrow at this age, and the
involution completely covers the abdomen of the next inner whorl
to the abdominal angles, the umbilical zones actually bulging
inwards, and encroaching somewhat on the umbilici, comparing
closely with the younger stages of Zvocholitoceras Walcotti, Fig.
12, Jee wae

The living chamber of this specimen, Fig. 9, although incom-
plete, was nearly one-half of a volution in length at the end of the
third volution. About one-quarter of a volution from the septal
floor it measured in transverse diameter 33 mm. and the ventro-
dorsal 15 mm., showing that the rate of growth in the transverse
diameter had begun to lessen considerably. The depth of the
umbilicus measured from the umbilical shoulders was 15 mm. at
about the end of the last half of the third whorl. The shell was
very thick on the venter even at this age.

During subsequent growth the sides are apt to become broader and
flatter, but the transverse diameters always exceed considerably the
ventro-dorsal. The fossils are all apt to be more or less distorted
by pressure, so that it is difficult to draw the line between this species
and Litoceras Whiteavesi, except in the young. In these the whorl
is of greater breadth and the siphuncle nearer to the dorsum than
the last mentioned.

As the sides become better defined the sutures change. The
ventral saddle disappears in a broad lobe or almost straight suture,
slight saddles appear at the rounded abdominal angles and the
broad lateral lobes ascending to the lines of involution and the blunt
saddles, as in the young, on the primitive and rounded umbilical
zones are all better defined. The broad deep dorsal lobe also re-
mains as in the young in the contact furrow.

The whorl was not free at the aperture in any specimens observed.

(ie,

The diameter of the largest specimens was estimated at 177 mm.;
the imperfect living chamber in this was somewhat less than one-half
of a volution in length. ‘The transverse diameter ot the septal floor
of this chamber was, estimating by half measurement, more than
74 mm., the ventro-dorsal about 50 mm. The siphuncle from
which the measures were taken may not have been in the centre in
this specimen, so the measurements of the transverse diameter may
be faulty. The living chamber in this and the next specimen de-
scribed reached well into the first half of the fifth volution, as esti-
mated by careful comparison with the young specimen above de-
scribed and figured.

The most perfect fossil of this species was 140 mm. in diameter.
The living chamber showing lines of what appeared to be the
rugged edge of an aperture was just one-half of a volution in length.
The suture of the septal floor was similar to that described above.
The transverse diameter at the septal floor was about 60 mm., the
diameter through the side about 31 mm. The transverse diameter
midway in this chamber became nearly 74 mm., and the diameter
through the side 40 mm.

Near the aperture the ventro-dorsal diameters continued to in-
crease and the transverse decreased, or in other words the aperture
was not so broad as the middle of the chamber which was slightly
expanded. ‘The shell was enormously thick on the venter, showing
age, it was near the middle about 2 mm. in thickness, and near this
aperture 6.5 mm. in thickness. The lines of growth indicated a very
large, broad and deep hyponomic sinus and broad lateral crests, but
these were not distinctly seen.

The siphuncle, in the specimen 177 mm. in diameter, reached
the large size of 11 mm. at the septal floor, and less than one-half of
a volution younger was 6.5 mm. in diameter. ‘The septa were only
6 to 6.5 and 7 mm. apart as measured on the siphuncle at this age
near the living chamber. ‘They were nearer together than in adults
at this gerontic stage as is usual in outgrown specimens. ‘The last
two sutures of the smaller fossil described as 140 mm. in diameter
were 7 mm. distant, which is probably the average distance of a
full-grown shell, judging also by the remains of an isolated siphuncle
in the collection belonging to this species.

LITOCERAS BIANGULATUM, N. S.
Loc., Pt. Rich., Newfoundland.

This shell appears in the collection at Ottawa under the name of

480

LVautilus versutus. The sides, however, until a late stage are
angular, forming a truly digonal whorl with broad rotund abdomen.

The ventral saddle is more plainly marked and more prominent,
and the whorls more numerous at the same age. ‘There are saddles
at the abdominal angles and lateral lobes; the dorsal sutures were not
seen. The contact furrow is about the same as in Litoceras Whit-
cavest. Itis simply a species retaining the digonal, neanic whorl
until a late stage, probably throughout life.

LITOCERAS ? HERCULES.
NavutTiLus HERCULES, Bill. (ep. Geol. Surv. Can., 1856, p. 306).
Koc.s Charleton Pt, Anticosti.

This smooth shell found in the Lower Silurian of Anticosti has
the digonal form of whorl similar to that of Lztoceras biangulatum
and the young of Léteceras insolens. It is, however, a very much
larger and more rapidly growing shell. The sutures have ventral
median saddles, and on either side ventral lobes as in the young of
znsolens. ‘(he abdominal angles have saddles and there are well-
marked lateral lobes rising to slight saddles at the lines of involu-
tion. The diameter of Billings’ specimen was 6% inches with
incomplete hving chamber.

Trocholitoceras, n. &.

This genus has been framed to include forms which are essentially
similar to Trocholites, but have the siphuncle ventrad of the centre
in the earlier substages of development.

The forms stand in development and adult characters between
Litoceras and Trocholites.

Type is Trocholitoceras Walcott.

TROCHOLITOCERAS WaLcoTTI. PI. vi, Figs. 12-20.
Loc., Fort Cassin.

The series of sections drawn in Figs. 14-19, Pl. vi, gives the his-
tory of the development of the shell and siphuncle in this interesting
species. The first sectional cut (Fig. 14, Pl. vi) shows the round
ananepionic volution, the umbilical perforation and below this the
paranepionic volution with the siphuncle ventro-centren, and the
outline beginning to broaden. and approximating to the kidney-
shape, above the round ananepionic section is the ananeanic whorl
with the siphuncle centrodorsen, It will be observed that this section

481

cuts at right angles to the long axis of the narrow pear-shaped
umbilical perforation and that there is a faint but well-defined dor-
sal furrow in the dorsum of the paranepionic volution. In Fig.
15 a somewhat older section is shown and the siphuncle of the
metanepionic substage is propioventran. ‘The umbilical perforation
is narrower in consequence of the approximation to the dorsum of
the parenepionic whorl and the dorsal furrow is well-defined at
this bend, and broader and deeper than it is beyond this in
ig. 1.

The birth of the dorsal furrow is shown in Fig. 16, since one
can see here the distinct outlines of the metanepionic volution
broadening out internally, and the dorsal side of this remaining
stiff and rounded while the plastic dorsal side of the growing
paranepionic volution was bent into a dorsal furrow while being
built around this abrupt bend. In Fig. 17 the section has passed
inside of the paranepionic whorl, and the aspect begins to be
confused by the fact that it cuts across the septa and shell. This
and Figs. 18 and 1g are similarly confused, and are of value only for
tracing the positions of the siphuncle. This organ obviously begins
in a subventran position, becomes propioventran in the metane-
pionic and paranepionic, centrodorsan in the ananeanic after the
completion of the first volution, and finally subdorsan in the meta-
neanic substage on the third volution. This position is retained
throughout life, as is shown in the section, Fig 13, Pl. vi.

The innermost volution shown in the side view of the same speci-
men (Fig. 12) is the last quarter of the third and first quarter of the
fourth volutions. The smooth, still kidney-shaped whorl of the last
quarter of the third volution in Fig. 13 shows the paraneanic sub-
stage. The third sectional outline of a whorl below the central
rounded ananepionic tip gives this age, and the third sectional
outline of a whorl above the same ananepionic centre gives the sec-
tion across the first quarter of the fourth whorl, which is the an-
ephebic stage, and has a very distinct outline. Owing to the de-
crease in the rate of growth of the lateral diameters, the sides and
abdomen have become contracted and the kidney shape of the
earlier ages has been exchanged for a helmet shape in outline.*

The living chamber in this specimen occupies at least the greater
part of one-half of a volution, but its exact length could not be ascer-

* This section is unluckily in a position which is the reverse of that of Fig. 12.

482

tained. The aperture was not very plainly discernible, but was ap-
proximately as given in the figure.

The ephebic stage has raised lines or bands of growth straighter
on the sides than in the gerontic stage, which has evidently begun
on the last whorl. This has moderately heavy ridges which are re-
flected on the cast of the living chamber.

It is separable from Schroederoceras Hatoni by the broad whorls
of the young and the near approximation of the siphuncle to the
dorsum in the neanic stage.

TROCHOLITOCERAS (?) EICHWALDI.
CLYMENIA RAROSPIRA, Eichw. (Leth. Rossica, Pl. 1, Fig. 2, a, b, c,
aMnGO,\d,D5 Cy Oma lntTps asp acces

The descriptions and figures of Eichwald show conclusively that
this is widely different from Schroederoceras rarospira and is nearer
to true Trocholites. The form of the whorls in the young, the slow
rate of increase in the dorso-ventral diameters, the rotundity of the
sides and abdomen in the young and even in the full-grown whorls,
the small diameter and close approximation of the siphuncle to the
dorsum, make this shell very like a species of Trocholites.

On the other hand, the sutures are more sinuous, having deeper
ventral and lateral lobes than are common in that genus. ‘The
living chambers are less than one-fourth of a volution in length, with
the lateral crests of the aperture most prominent about the centre of
the lateral aspect.

The question of affinity can of course only be definitely settled
after the development of the siphuncle in the apex of the conch has
been studied. The appearance of the umbilicus, as shown in Fig 6
of Eichwald, is similar to that of other species of this genus, but this
of course may be due to erroneous draughting.

Trocholites.

This genus has been fully described and correctly defined by
Schréder,* and the following description is largely taken from his
work and adapted to the needs of this work. The shell of the ne-
pionic stage, as first shown by Holm,} is so closely coiled that no
umbilical perforation is externally visible. Observations of two
young specimens of T. described below have, however, shown the

* “Unters. ub. sil. Ceph.,’’ Pal. Abt., Dames et Kayser. N. F. (current Vol. v), heft 4.
7 ‘‘Sil. Ceph.,”’ Pal. Abh., Dames et Kayser, iii, Pl. vy, Figs. 9, 10 and 11.

483

existence of lateral depressions or open nepionic umbilici, and the
usual umbilical perforation is present, although rendered very small
by the closeness of the coiling. .-

The first air chamber observed in two specimens is unusually
deep and broadens laterally by growth with extreme rapidity. I
have not been able to expose a complete apex so as to see the cica-
trix, but have seen the outline of the umbilical perforation at the
centre. The siphuncle is closed at the end, but not perceptibly
swollen into a pouch as in most Nautiloids. It is not close to the
dorsum in the first chamber, but the cecal end is centren as shown
in the section of the ananepionic substage (Fig. 24, Pl. iv).

It clings closely to the dorsal side as in the young of éwternastriata,
as shown in Fig. 25, which represents a truncated apical chamber and
the paranepionic substage of the first whorl. Holm and Schréder’s
observations have shown that it is ellipochoanoidal or has in other
words short funnels and a porous wall between contiguous septa.
Schréder’s observations apply to the full-grown shell and Holm’s to
the young.* |

The extremely rapid expansion of the whorls ceases before the
first whorl is completed, but it gives to the nepionic shell, when seen
from the venter, the aspect so common in Ammonoids during what
is usually called the goniatic stage. So far as now known to me,
no other Nautiloid possesses this peculiarity to such a remarkable
degmeen the nepionic Stage, Pig? 39) Pl. va.

The mode of growth of the siphuncle is independent of the close
coiling, since it has the same history in Zrocholites tnternastriata,
with a large umbilical perforation, as in true Trocholites of later
times, with a more minute perforation.

The septa as in most nautiloids are much wider apart, at first
gradually decreasing until the end of the first whorl or thereabouts,
as shown in Holm’s figures, when they assume the normal distance
and are less deeply convex. The sutures exhibit corresponding
differences, having large ventral saddles, deep lateral lobes and
probably, although these were not clearly seen, dorsal saddles in
these earlier stages.

The lines of growth are much straighter in the nepionic stage
than subsequently. The hyponomic sinus is so broad and shallow
that it is hardly observable on the third quarter of the first whorl

* Holm’s observations and mine are similar and I have reproduced his figure in Pl. iy
of this paper.

484

and the lines are almost straight on the sides. The lines of growth
alone are visible. There are no prominent bands marking perma-
nent apertures, nor are the characteristic coste of Trocholites
visible, nor any longitudinal ridges in my specimens. Growth
lines show that in the nepionic stage not only the form and sutures
were distinct but also the aperture. The apertures are trumpet-
like in the ephebic stage and have a moderate hyponomic sinus
with broad lateral crests, increasing in prominence towards the
dorsum. Whether there are sinuses in the contact furrow has not
been determined, but one infers their presence because the lines of
growth incline apically just before reaching the lines of involution.
The form of the whorl continues rounded in all species of this
genus, although in some there is a distinct tendency towards angu-
lation of the sides.

The contact furrow appears very early in consequence of the
close coiling of the whorl. This zone is not deep, but it is well
marked and may extend nearly to the abdominal angles in some
species and it remains throughout life. So faras known no specimen
has been found with even a part of the last whorl free. The form
of the whorl in section is consequently nephritic, except in some
species having flatter sides and more pronounced abdominal angles
than usual.

In one species only, Z. czrcularis, is there any tendency to forma
pentagonal whorl and this was not only very obscure but observed
only in one specimen, the type form. The whorl is therefore very
primitive.

The length of the living chamber is given as usually about three-
quarters of a volution by Schréder, but some of his species have it
less than one-half of a volution. Z. Reme/ecand ZT. ammonius have
one invariably somewhat less than one-half of a volution in length.
It is obvious that in this genus it varies between these limits.

TROCHOLITES INTERNASTRIATA.
LITUITES INTERNASTRIATA Whitf. Fort Cassin Foss. (Bul/. Am.
Mus., New York, i, No. 8, Pl. xxix, Figs. 5-8). Pore (@ascuae
This species, of which I have studied the originals, has young of
cyrtoceran form, with a good-sized umbilical perforation, as in
Schroederoceras and Litoceras. The siphuncle is centren in
what is probably the second septum, and it has not the prolonga-
tion beyond this septum, as figured by Whitfield. It inclines

485

rapidly towards the dorsum, attaining a fixed position in the fifth
septum, if I am right in estimating the first septum drawn by Whit-
field as the second.*

It is much larger in the nepionic stages, contracting as it nears
the sixth, and becoming a narrow tube in the seventh septum.
Subsequently it again increases by growth as the shell grows larger,
so that it has the usual large diameter common in this group. If
the trend of the siphuncle towards the apex from the dorsum to
the centre is followed out it can be seen that the ceecum must have
been situated somewhat on the ventral side in the apical chamber.

The rapidity with which the siphuncle becomes propiodorsan,
attaining this position in the metanepionic substage or as the first
whorl bends to assume the gyroceran curve, shows affinity appar-
ently for Trocholites, but the position in the second septum and
the size of the siphuncle and the sutures of later stages are not in
favor of this view. The form of the whorl is very similar to that
of Schroederoceras Ezchwaldi, but from this it is separated by the
sutures, which in the ephebic stage on the fourth whorl have slight
saddles instead of lobes on the venter and the siphuncle is not so
close to the dorsum and is larger. The suture of the earlier stages
are straight and are trocholitean in aspect, with well-marked dorsal
lobes, as is also the form and ornamentation of the young whorls,
which are slightly costated.

There is a well-marked contact furrow, and I did not find the
tendency of the last whorl to become free, as described by Whit-
field, the contact furrow being well defined at the termination of
the whorls in the original of Fig. 5, Pl. xxix, of his work.

The slower growth and distinct form of the apex, which is more
cylindrical and not cap shaped, and the development of the
siphuncle, separates it from the young of Schroederoceras Eatont,
and also that of Schroederoceras teres and Trochottoceras Walcotte.

Although the position of the siphuncle at an early stage is not
yet known in species of Litoceras, this species is obviously dis-
tinct because of the narrowness of the whorls, which resemble
those of Hazon in outline. Besides the ventral saddles, the sutures
of the fourth volution have well-marked lateral lobes and dorsal
lobes in the contact furrow. The whorl remains throughout
life in transverse section depressed, elliptical, as in Trocholites,

*T am not satisfied with this correction. The aspect of the first chamber is more nat-
ural in Whitfield’s drawing than in mine.

486

and the markings resemble those of that genus, as does also the
development of the siphuncle. The larger size of the umbilical
perforation is interesting, but this alone does not warrant generic
separation.

TROcHOLITES CANADENSIS, Pl. iv,. Figs. 23. and. 24, and Ele
Figs. 39 and 4o. j
Loc., Falls of Montmorency, near Quebec.

The four specimens representing this species came from the
Bronn collection. They are similar to 7. ammonius in form, but
differ in being broader proportionately in the transverse diameters
of the whorls and have deeper umbilici. The whorls are rounded,
there being no tendency to angularity, either of the sides or abdo-
men, and in these specimens the size is small. ‘There are fold-like
coste from an early neanic stage and the living chamber may be
considerably over one-half of a volution in length. ‘The exterior
is marked by longitudinal lines along the venter and often on the
sides, but these have none of the regularity and prominence observ-
able in Conrad’s figure, and that figure shows no costations which
are more prominent and fold-like in this than in Z. ammonius or
any other described species of Trocholites.

The extremely broad aspect in section of the ananepionic volu-
tion is given in Fig. 24, asseen from the front. The umbilical
perforation between this and the larger paranepionic volution is
very narrow. In Fig. 23 looking through the transparent para-
nepionic volution one sees the umbilical perforation and the meta-
nepionic volution as it is turning or revolving around the core
of the perforation. The outlines in both of these views belong to
different ages and are, consequently, quite distinct. The upper
section of a whorl in Fig. 24 is the ananepionic substage; the upper
section in Fig. 23 is a visual section of the metanepionic whorl just
before it changes by growth into the paranepionic, which is seen
below in same figure, and this last in turn is younger than the
lower section in Fig. 24, which is a later age of the same substage.
Taking these in regular order, it is seen that the ananepionic has a
rounded dorsum and almost digonal whorl on account of its very
rapid transverse growth; that this, as it becomes older, acquires a
concave dorsum in the metanepionic of Fig. 23. Then, as the
whole revolves while growing, at a later age but part of this same
substage, after the shell has passed this bend and is freer to grow on

487

the dorsal side, the centre of the dorsum again begins to round
out, but traces of the primitive dorsal furrow remain in the de-
pressions on either side of the central, gibbous dorsal face formed
by this outgrowth, as in Fig. 24.

This gibbous face is immediately suppressed when the whorls
come into contact, and its transient appearance can only be
accounted for as due to the genetic tendency of the paranepionic
whorl to resume the gibbous metanepionic form of dorsum as soon
as the pressure resulting from the abrupt curve is slightly relieved.”

TTROCHOLITES AMMONIUS, Hall.

This species, of which the collection of the Museum of Compara-
tive Zodlogy possesses a very large number, collected by Mr. C. D.
Walcott, has a very peculiar, rough, fretted surface, and only very few
specimens show longitudinal lines such as are described and figured
in Z. planorbiformis by Conrad. ‘This surface is due to the minute
crenulations or waves in the outlines of the projecting edges of the
laminz of growth. When these are wide enough apart one can
distinguish crenulated transverse lines; when too close they inter-
fere and the regularity and continuity of the lines are broken into
a multitude of more or less discontinuous, short lines. Sometimes
a network of lines is formed by the regularitv of the intersection
of the crests of the crenulations in successive laminge. This cuticu-
lar ornamentation is so easily destroyed that it is often present only
on parts of the same specimen.

' Longitudinal lines may be seen through it, but, as stated by Hall
and observed by the writer, these are rarely present in the New
York specimens. They do, however, sometimes exist all over the
abdomen and sides, and are well defined in specimens in which the
cuticular corrugations are absent.

The lines of growth are extrernely crowded, and what are called
the costee occur at wider intervals and more irregularly. They are
probably the traces of former apertures. ‘These are more promi-
nent in some specimens than in others, but never seem to have the
aspect of true fold-like costations.

The lines of growth form deep, broad sinuses on the venter ;
rise into lateral crests on the sides, sinking towards the lines of
involution, and forming a sinus in the contact furrow. ‘These are

* This opinion would be more convincing, if it were not for the fact, that in Cranoceras
similar transformations occur in an adult cyrioceran form of the Devonian.

488

parallel to the outlines of the apertures, but these-last not infre-
quently have shallow, broad constrictions and slightly projecting or
trumpet-like lips in full-grown whorls.

The specimens of Z. ammonuzs from the same locality may vary
from very broad-whorled forms to those with much narrower almost
cylindrical whorls, the former being slightly deeper umbilici and
the latter being shallower, as in Z. cérvculares. The venter and
sides are, however, almost invariably projecting and rounded,
unless angulated by compression, whereas in czrcu/arts there is a
distinct tendency towards truncation or flattening of the abdomen
and sides. ;

The sutures in the ephebic stage may be nearly straight, but there
are in most specimens broad ventral lobes, saddles at the apdomi-
nal angles, lateral lobes and saddles on the umbilical zones and
lobes in the contact furrow. These inflections are, however, always
slight, and the sutures give the impression of being almost straight
in most specimens.

The contact furrow is distinct but not deep in the ephebic stage
and continues to be present in the aperture of the whorl, which is
never free.

TROCHOLITES INCONGRUUS, Ang. et Lindst.

CLyM. INCONGRUA, Eichw. (Leth Rossica., Pl. 1, Fig. 7).

CLYM. INCONGRUA, Schroder (Ceph. d. Untersil., Pal. Abh., Dames
et Kayser, iv, eit 4 abl up ig. 2=4).

TROCHOLITES INCONGRUUS, Ang. et Lindst. (/7agm. Sil., Pl. ix,
Figs. 15-18).

This species is beautifully figured by Angelin and Lindstrom and
the living chamber and the lines of growth and sutures fully given.
It is obviously a smaller species than 7. ammonius, with deeper um-
bilical whorls much broader proportionately, abdomen very broad,
but sides rounded as shown by Schréder.

TROCHOLITES HOSPES.
PALEONAUTILUS HOSPES, Remelé (Zeztsch. deutsch. geol. Gesell,
AKRAM MO oMe wes eilew ee) 1).
TROCH. HOSPES, Schroder (Ceph. d. Untersil., Pal. Abh., Dames
et Kaysern) ve heit4, Pla, Figs):
This species, supposed by Remelé to be distinct generically from
Trocholites, is merely, as shown by Schréder, a species of Trocho-

489

lites, with very broad whorls quite similar to those of his Z. con-
tractus.

TTROCHOLITES DEPRESSUS.

CLYMENIA DEPRESSA, Eichw. (Leth. Ross., Pl. 1, Fig. 5).

TROCH. DEPRESSUS, Schréder (Ceph. @. Untersil., Pal. Abt., Dames
Selayseiny, leite4> lel, Higa):

TROCHOLITES MACROSTOMA, Schréder (Ceph. d. Untersil., Put. Adt.,
Dames et Kayser, v, helt4, Pl.1, Fig. 1):

TROCH. CONTRACTUS, Schréder (zd¢¢., Pl. i, Fig. 2).

Excessively broad whorls and deep umbilici but no lateral zones.
Living chamber about one-half volution in length according to
Schréder’s drawings. Schréder also describes the following species :

Min@en.ORBIS, ochroder Cvzd., Pl. 1, Pig. 23).
ae MACROMPHALUS, schroder @éz7., Pl 1, Fig. 5).
ee SORAVIENSIS: Schroder (zézd., Pl. 1, Figs 1).

TROCH. REMELEI, Schréder (zézd., p. 18), was described as 7. zn-
congruus by Ang. et Lindst. (frag. Sz/., Pl. ix, Figs. 15-18), and this
has a living chamber not quite one-half a volution in length. His
Troch. damest (thid., Pl. v, Fig. 2) shows sculpturing and form of
the young which appears to place it in the genus Schroederoceras
rather than in Trocholites and it has been referred to that genus.

Trocholites circularis, Mill. et Dyer, of the Cincinnati group of
the Hudson river, is probably a distinct species. The type is inthe
Museum of Comparative Zodlogy. This has an aperture like that
of Z. ammonius and length of living chamber as in that species
about one-half of a volution. The whorls are not so stout as in
ammonius, the sides being slightly compressed, the abdomen nar-
rower than the dorsum.

TROCHOLITES DYERI, N. sp.

This is a form in the Dyer collection from the Cincinnati group,
having a form of whorl broader and quite like that of Z. ammonius,
but with a longer living chamber and distinct aperture.

The living chamber is considerably over one-half of a volution
in length and the lateral and ventral edges of the aperture are flar-
ing like the mouth of a trumpet. This gives extraordinary promi-
nence to these parts and especially to the hyponomic sinus. The
umbilici were not seen, but are probably deeper than in Z. ammo-

490

nius or circular?és and the involution of the whorl, although not
distinctly seen, is also apparently greater.

Trocholitus minusculus, Mill. et Dyer, is a small species having
such extraordinary sutures that one suspects some distortion, never-
theless there is no proof of any action that would have brought
this to pass. The form, except the size, is like that of Z. ammontus.
The incomplete living chamber is somewhat less than one-half of a
volution in length. The sutures have flexures like those of the
lines of growth in other forms, z. ¢., they form a deep, broad sinus
on the venter, rise into prominent saddles on the sides which inter-
nally sink towards the lines of involution, probably forming a
lobe in the contact furrow. These outlines are unique among the
species of Trocholites. The shell is shown on part of another
specimen, and the hyponomic sinus in the lines of growth on the
venter is narrower than the ventral lobe of the sutures.

T. planorbiformis, sp. Hall, may be distinct from Z: ammonius,
since the name has been adopted by Hall, who has studied the type,
and this may be the same as Z. planorbiformis, Conrad.

TROCHOLITES BLAKEI.
TROCHOLITES PLANORBIFORMIS, Blake (British Ceth., Pl. xxix,
BIg.v@)):

This species, considered by Blake as identical with A/anorbifor-
mis Conrad, is obviously a distinct form. It has deep ventral lobes
in the sutures and costee which are figured on either side of the ab-
domen. No longitudinal ridges are described, although the surface
was studied and the transverse markings were plainly seen.

Blake states that this isidentical with Letuztes hibernicus, Salter,*
but the latter is a ribbed species with part of the whorls free and
does not even belong to the same family. There are probably sev-
eral species confused under this one name.

It occurs in the Bala beds at Llandovery.

TROCHOLITES ANGUIFORMIS.

NauTiLus (TROCH.) ANGUIFORMIS, Blake (Brit. Ceph., Pl. xxviii,
Big 2.

_ This is also a.true member of this genus.

-* Murchison’s Siluria, p. 220, Fig. 3.

491

TTROCHOLITES SCOTICUS.
NauTiLus (Trocu.) scoricus, Blake (Brz¢. Ceph., Pl. xxix, Fig. 6,
Pl. xxviii; a4).
Blake’s figures show sutures, but he states that none are discern-
ible. The aperture and form of whorl and striz indicate that this
is a species of Trccholites.

Hercoceratide.

In ‘‘ Carboniferous Cephalopods,’’ second paper, fourth Annual
Report Geol. Survey of Texas, | separated the Tainoceratide, includ-
ing the Temnocheilus, Metacoceras and Tainoceras from the Her-
coceratidz, but further study leads me to think that this is not
advisable considering the approximation in form and characters of
the two sets of genera and have reunited them here under the old
name.

In genera of fossil Cephalopods I regarded J?¢yssoceras (Cyrt.)
alienum, sp. Barrande, as the arcuate radical type of this family.
It has a single row of large, lateral tubercles, sutures nearly straight,
whorl in section depressed, elliptical and siphuncle ventral, and it
has no dorsal furrow. The genera properly included under this
family name are as follows: :

Ptyssoceras, Trochoceras, Hercoceras, Anomaloceras, Lower
Silurian; Centroceras, Devonian; ‘Temnocheilus, Devonian to
Dyas (Permian); Metacoceras, Tainoceras, Carboniferous and
Dyas; Foordiceras,* Dyas.

I have also provisionally placed Coelogasteroceras in this family
on account of the general resemblances of the form of the nepionic
stage, the smooth shell and the hollow ventral zone in the abdomen.

Ptenoceras,f Nn. g.

Under this name I propose to place all those forms formerly in-
cluded under the name of Hercoceras in my Genera of Fossil
Cephalopods, whether turbinate or coi.ing in the same plane, which
have no impressed zone at any stage. The whorls are open, or
barely in contact, and are rounded in the early stages and subquad-
ragonal later in life. The apertures are similar to those of Herco-

* All these genera are mentioned or redescribed below as far as needed for the pur-
poses of this paper except Foordiceras and Tainoceras, which have been described 1n
“Carboniferous Cephalopods,”’ quoted above.

tI]z7yv0s, winged.

ea ee et

492

ceras, but are more widely open and often have spreading lips to the
lateral sinuses as in Pfenoceras (Gyr.) alatum, Barrande, Pl. xliv.

These forms are interesting because of their obviously close
genetic affinity with Hercoceras, and yet the entire absence of an
impressed zone at any stage in consequence of the loose mode of the
coiling.

Ptenoceras flexum, sp. Barrande, Pl. xliv, and Ptenoceras
tardum should also be included in this genus, and probably Bar-
rande’s Zrochoceras nodosum, Pl. xxv, but his other forms described
under this name belong to widely different genera. _

Flercoceras.

This genus described by Barrande (Systeme Stlurien, 11, Text 1,
p- 152) should be limited to such species as those placed under this
name by this author. I formerly included also under this name cer-
tain gyroceran and trochoceran forms. These are separated here,
but so far as regards their near affinity, I still hold the opinion that
they belong to the same family group, and are genetically connected.
Hercoceras includes only nautilian forms, having a small umbilical
perforation, the impressed zone being present only after the whorls
come incontact. They have peculiar contracted apertures, figured
by Barrande, depressed whorls broader on the venter than on the
dorsum, often with large spines or nodes, siphuncle subventran,
and are often trochoceran in their mode of growth.

The section of Hercoceras mirum, the type of this genus, given in
Figs. 13, Pl. viii, shows the small comma-shaped umbilical perfora-
tion, deep apical chamber and septa of the nepionic stage. The
czecum is very small and is packed away inthe ventral angle of this
chamber under the septum. The siphuncle is phenomenally small
in this genus in the nepionic substages, but increases subsequently
to a respectable size. ‘This and the absence of longitudinal ridges
on the exterior of all of this genus and its allies has a genetic sig-
nificance which is not yet understood.

The young are sometimes in contact only in the neanic stage, and
in the same species this may vary so that the whorls remain in con-
tact throughout the ephebic stage, the last whorl with the living
chamber being free as in Hercoceras (Gyroc.) nudum, sp. Barrande.
flercoceras (Troch.) transtens, sp. Barrande, Pl. xxx, is a species of
this genus, and it seems to me quite possible that Barrande’s

493

Gyroceras minusculum (Pl. xxx) may also prove to be related to
species of this genus.

The young of- these forms are all closely coiled and have con-
tact furrows when the volutions are in contact, and these are
also retained more or less in the gerontic stages.

The section is at first rounded, then broadens out to a digonal
form, which in some species may remain more or less digonal or
become quadragonal.

The young of Hercoceras has the subquadragonal form in some
species like that of the adults of Trochoceras.

Flercoceras (Adelphoc) secundum, sp. Barrande, is a _ giant
form of this genus, with the impressed zone retained in the gerontic
stage.

HERCOCERAS IRREGULARIS.
HERCOCERAS MIRUM, vay. IRREGULARIS, Barrande (Pl. xliii). Pl.
vill, Figs. 14-15.

This is a distinct species having different and less closely coiled
young than the typical Mercoceras mirum, and is transitional be-
tween Hercoceras and Ptenoceras. The nepionic stage given in
Figs. 14-15, Pl. viii, shows that the metanepionic whorl is a de-
pressed ellipse, the paranepionic volution is more rounded, the
ventro-dorsal slightly longer than the transverse diameter, and the
neanic whorl may be subquadragonal, or pass from this directly
to the digonal form of the ephebic stage.

The exterior of the nepionic and neanic volutions have very
coarse, transverse ridges without any longitudinal markings.

The czcum is large in the: apex. It is not correctly given in
igenns, and issventrocentren! In another specimen at a some-
what younger age, it was very large compared with the diameter of
the ananepionic volution and centren. In this also it remained in
the mesal plane in later ages, although shifting to propioextraven-
tran position.

The umbilical perforation is small and comma-shaped, and
although it seems impracticable that the paranepionic whorl should
succeed in growing around the apex without enveloping it, this
really occurs, and no impressed zone is formed in the ananeanic
substage. The volutions come in contact later, and a faint con-
tact furrow appears in the metaneanic substage, which becomes
deeper in the ephebic stage as figured by Barrande.

be. 4B eee Ee. §-§_ Lae. Wa a ee eee. C8 Se, 2 oe. ee eee

494

There is obviously a great variation in the coiling of the shells of
this transitional species as is shown by Barrande’s figures. One shell
has no contact furrow at a very late substage of development. It
is possible, however, that there are several species included under
this name. ;

A slight impressed zone or flattened dorsum is retained in the
gerontic stage. Considering the slight coiling of the shells, this
fact is important.

Anomatloceras.

This genus was described in Genera of Fossil Cephalopods, p. 283,
and includes nautilian forms having close-coiled young with a small
umbilical perforation. The whorls are depressed oval, kidney-
shaped or digonal with a deep impressed zone. The sutures are
almost straight, or with slight ventral and lateral lobes.

The siphuncle is subventran, and in the type is always laterad of
the mesal plane.

ANOMALOCERAS ANOMALUM.
NAUTILUS ANOMALUS, Barr. (Pl. xxxiv). Pl. vil, Figs. 16-20.
Loc., Bohemia.

This species possesses very closely coiled whorls, and is of great
interest in connection with the history of the impressed zone, as is
demonstrated by the sections given on Pl. vii. These sec-
tions began with Fig, 16, which passed through the larger end of.
the comma-shaped umbilical perforation. The paranepionic sec-
tion just below the centre is distorted slightly by the obliquity of
the direction of the cut, and has a septum crossing it just below the
siphuncle, and this organ is excentric and not so near the venter as
in the later stages. The section of a volution above the perforation
is also paranepionic, but older, and shows rapid expansion in lateral
diameters and a tendency to assume the nephritic outline, and has
in correlation with this a very slight dorsal furrow. The lateral
asymmetry of this whorl is probably in part due to a slight obliquity
of the section. The siphuncle is subventran as in all later stages:
The metaneanic substage appears in the second outline of a volu-
tion below the perforation, and this has a digonal nephritic form.

This becomes trapezoidal and more rounded in the sections of
the outer ephebic volutions above and below those described above,
and in the full-grown specimens of some shells may become a much

495

depressed oval, as shown in Barrande’s figures. Fig. 17 gives a
cut farther in towards the narrower part of the umbilical perforation
and shows the paranepionic substage younger than in Fig. 16, and
with more depressed and approximately digonal outline. Above
this the paranepionic whorl is older than in Fig. 16, and with a
more decided impressed zone and broader transverse diameter ap-
proximating to the nephritic shape.

In Fig. 18 the cut has passed beyond the perforation and shows
the paranepionic volution above when it first touches the dorsum of
the metanepionic or ananepionic substage below. ‘The latter is
distorted because the cut goes through the inner or dorsal side of the
curve of the metanepionic and ananepionic substages. The oval in
the centre is apparently due to a cut through the fundus of the first
septum, which must be deeply concave. In Fig. 19 the cut has
approached nearer the ventral side of the apical chamber and is
apparently wholly within this and shows the increase in depth of
the impressed zone as the ananeanic substage begins and also the
decidedly nephritic outline which this at once assumes. ‘This also
shows that the digonal outline of the volution below the centre
belongs to the neanic stage. In Fig. 20 the cut has passed close to
the outer side of the ananepionic substage and as in the centre it does
not intersect any septum it is probably wholly within the apical
chamber. This chamber must be very deep, as it is in Hercoceras
and some other forms. The broader shaded outline of the ananep-
ionic substage is the shell which is cut obliquely by the section.
The sections of the ananeanic whorl above and the metaneanic
below intersect a number of septa and show the passage to the
farther side of the umbilical perforation from that with which the
series began in Fig: 16.

Zemnochetlus.

This genus is very similar in its general aspect to Hercoceras and
Anomaloceras, but it has distinct young and this shows that it has
been directly evolved from a cyrtoceran form and not from either of
these nautilian genera.

The form known as Gyroceras proximum, sp. Barrande, Pl. ciil,
has the tuberculations on the lateral angles, a trapezoidal whorl,
the siphuncle subventran and sutures and impressed zone as in this
genus, but until it is better known it is not practicable to decide
whether it belongs to this genus or to Hercoceras.

i: ~~

. rien Wii, GS” Sain Bie, ee aoe, ee Wee By wads Feet)

ie, We

= Se ea ee.

2 ee eS

496

I have also examined another young specimen of a different spe-
cies of this genus which has a much larger umbilical perforation,
but is otherwise quite similar in the characteristics of the nepionic
stage. The contact furrow begins in this specimen with a very
slight impression late in the neanic stage and the tubercles appear
earlier than in Zemnocheilus subtuberculatus.

TEMNOCHEILUS SUBTUBERCULATUS.

NAUTILUS SUBTUBERCULATUS, Sandb. (Vers?¢. ass., Pl. xii, Fig. 3).
Rive pines. 27. ands23.

The umbilical perforation is large and open (Fig. 27, Pl. x).
The nepionic stage has the first apical chamber very deep. The
first suture has the usual ventral saddle and lateral lobes, but on
the dorsal side there is a well-defined dorsal saddle. The apical
chamber and the inner parts from the second to the fifth are coated
with calc spar, while the centre is filled with iron pyrite.

The second suture has a dorsal lobe in place of a saddle and this
persists in later stages. In the paranepionic substage a digonal
whorl is developed and the lateral saddles appear dividing the late-
ral lobes from ventral lobes that replace the ventral saddles of the
metanepionic substage. Contact takes place in the metaneanic or
paraneanic substage after the digonal whorl has been replaced by a
trapezoidal outline.

The form of the whorl soon after contact is shown in Fig. 28 and
this has the adult outline with the exception that the contact furrow
and the tubercles have not yet made their appearance.

This description was taken from a specimen in coll. Museum of
Comparative Zodlogy, from the lower Devonian of Wissenbach.

Metacoceras.

This genus, which has been described in my Genera of Fossil
Cephalopods (p. 268), and subsequently redescribed in ‘‘ Carbonif-
erous Cephalopods,”’ Second Annual Report of Texas, 1890, and
Fourth Annual Report of Texas, 1592, is of no special value in this
connection except as an illustration of a number of genera of the
same genetic stock as Temnocheilus, which have more or lesss
similar characteristics in the young. ‘They all have large umbilical
perforations and a similar history in the development of the im-
pressed zone.

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497

Figs. 16-19 give the adult and general aspect, and Fig. 32,
Pl. x, shows the beginning of the contact furrow. This begins
only after contact with the apex and in strict correlation with the
rounded immature form of the metanepionic and the temnocheilan
or tetragonal trapezoidal form assumed by the paranepionic volu-
tion. ‘The sutures have ventral and dorsal saddles throughout the
metanepionic, but in the paranepionic become straighter on the
venter or with a faint lobe, and a similar change takes place in the
dorsal sutures. The dorsal lobe is more easily perceptible after
contact and becomes deeper with the increase in depth and breadth
of the contact furrow and seems to be correlated in development
with that modification, although it appears before this furrow is
formed.

Tainoceras.

This genus has similar young to those of Metacoceras and proba-
bly has a similar history.

Centroceras.

This genus, described in Genera of Fossil Cephalopods, possesses
a typically quadragonal whorl in the adult stage of the less involute
forms, but has a digonal whorl in the nepionic stage, and this
becomes similar to that of ‘Temnocheilus, that is trapezoidal in out-
line and furnished with tubercles in the neanic stage. The
contact furrow is faintly marked in some forms like Centroceras
(Cyrt.) tetragonum, sp. Vern.,* but it is a mere narrow band on the
dorsum.

It is obvious in this genus that the impressed zone exists only in
the later stages and after the whorls come into contact. Hall
describes a slight impressed zone in Centroceras (Discites) ammonis,
sp. Hally and shows the living chamber complete and nearly one-
half of a volution in length.

It is likely that Hall’s Gyroceras Stebost may prove to belong to
genus Centroceras (Gyroceras) Ohioense, sp. Meek,§ is a very large
shell of the Corniferous fauna of Ohio which has the form of whorl
and single outer row of tubercles of this genus.

* Trans. Geol. Soc. London, vi, Pl. xxx.
TP JAG, ING Von Ay SOyolG, Tis tht, Jel, Oey
# MCh, IAL, xray

@ Pal. of Ohio, i, p. 230, Pl. xxii.

EE ——<— So —- FS e e

498

Coclogasteroceras.

This genus was described in my ‘‘ Carboniferous Cephalopods,”’
second paper, fourth Ann. Rep. Geol. Texas.

Coelogasteroceras canaliculatum of the Carboniferous has an
umbilical perforation of considerable size, but the history of the
impressed zone is similar to that of Anomaloceras. One section
was obtained shown in Fig. 33, Pl. x. This cut across the meta-
nepionic as it was changing in form on its passage into the para-
nepionic substage and shows the dorsum becoming flattened and an
outline transitional to the full nephritic outline of the paranepionic,
which is drawn below at a plane which passed through this substage
just before the apex was reached. In making this section, the apex
was seen and passed through by grinding.

The size and shape of the umbilical perforation in this species
does not justify the assumption that the dorsal furrow could have
resulted from the abrupt bending of the volution at the gyroceran
bend. The curvature of the first whorl is gradual; the expansion of
the volution laterally and ventro-dorsally is not remarkable. ‘The
diameter of the umbilical perforation was four millimetres in one
specimen and in the section figured it was somewhat less at the same
points. ‘The increase by growth was also approximately the same
in both of these fossils.

Unfortunately the absence of a dorsal furrow on the dorsum of
the metanepionic substage was not demonstrable with unquestion-
able certainty in either of these specimens, but it seemed to be
entire and gibbous in both as given in the figure.

The shell is apparently smooth in the nepionic stage, although
this may have been in part due to the condition of preservation.
It is obvious that there are no lateral furrows or ridges as in Colo-
ceras at any stage. Faint transverse folds were observed in the
neanic stage of one specimen, and the abdomen and lateral zones
become flattened at the same time. A hollow, central, ventral zone
appears in the anephebic substage and _ persists throughout the
ephebic stage.

The sutures are nearly straight in the nepionic, and then acquire
a slight ventral lobe in the neanic stage ; this deepens in correlation
with the ventral hollow zone in the ephebic stage, and the lateral
lobes and saddles on the umbilical shoulders also become more
marked in this stage.

499

The siphuncle is propioventran in the paranepionic and very large ;
in subsequent stages it is somewhat nearer the centre and continues
to be large.

Discoceratide.

This family includes some genera formerly associated under the
Tainoceratide and others not heretofore noticed in my classifica-
tion.

Although it is a provisional and heterogeneous group in some
respects, the genera are alike in being more or less heavily ribbed,
and im having open apertures so far as known. This association
also brings together forms having a tendency to develop into more
or less turbinate coils.

The genera are as follows: Peismoceras, Systrophoceras, Trocho-
ceras, Mitroceras, Lower Silurian; Plectoceras and Discoceras,
Quebec faunas to Upper Silurian.

Plectoceras.

This genus was described in Genera of Fossil Cephalopods, page
268, by the author to include the costated forms similar to Disco-
ceras, but having the siphuncle ventrad of the centre.

The type was Plectoceras (Vaut.) Jason, sp. Billings. The mode
of coiling may be quite close and regular, with perhaps a slight
impressed zone or flattened dorsum, or the coil may be open, and
sometimes it is very irregular. In several specimens of /ason the
first whorls may touch, the ephebic volution may be open and
free and yet the extremity of the living chamber again come in
contact. ‘The umbilical perforation is large and the impressed zone
is absent until the whorls come into contact and it is invariably
absent in gerontic whorls.

The species are as follows :

PLECTOCERAS JASON, sp. Billings (Canadian Wat., iv, p. 164).

Type in Museum of Geological Survey at Ottawa. It occurs in
the Calciferous of the Mingan Islands and there are similar forms
in the same horizon in Newfoundland.

PLECTOCERAS OBSCURUM, 0. S.

This species occurs in the Black River fauna in New York and is
quite commonly mistaken for the young of ZLurystomites undatius,

500

but it has an open gyroceran spiral, the siphuncle is nearer the
venter and the costz are more highly developed and more promi-
nent, and have a distinct character from those of that species.

PLECTOCERAS BICKMOREANUS, sp. Whitfield (Bull. Am. Mus., New
Norks):

This species of the Niagara fauna has an open gyroceran whorl,
and in the gerontic stage the last whorl is free and in some speci-
mens completely straightened out and lituitean in aspect.

IOS VOGA US Ne (2

Under this name I propose to separate such costated forrns as
those described by Barrande as Trochoceras, but which differ from
true Trochoceras and Discoceras in the development of the form,
outline of the apertures, position of the siphuncle and so on.

Peismoceras (Troch.) angulatum, optatum, placidum, disjunctum,
sp. Barrande and others agree in having plain rims to the apertures
without deep sinuses, except, of course, the ventral sinus.

The siphuncles are ventrad of the centre, the whorls oval in sec-
tion, the volutions are barely in contact or open, the apices are
very large and the umbilical perforations excessively open and
large, and there is no impressed zone at any stage.

Dscoceras.

The type of this genus was described and figured by Eichwald
under the name of Clymenia antiquissima, but was subsequently
considered as a distinct genus by Barrande.+

The genus has been subsequently recognized by Schréder and
Remelé, but it has by both these authors been used for the smooth
forms, having a quadragonal section to the whorl and dorsal
siphuncle, as well as for the costated shells.

The neanic stage of all the smooth shells of allied species having
the siphuncle dorsal and, therefore, formerly included under the
same name, has decided costations with the same aspect and con-
tour as in the adult of Desc. antiguissimum. Similar species
having costations throughout life cannot be included in the same
genus with those that have them only in the neanic and earlier

*Iletopa, a cable.
7Syst. Sil. de la Boheme, ii, p. 177.

501

stages of growth. The large number and great variety of form of
these smooth species, while still maintaining this difference of the
later stages of growth, shows that this separation indicates a natural
distinction, and I have therefore placed all under the generic name
of Schroederoceras, to commemorate that author’s distinguished
services in this field of inquiry.

DISCOCERAS ANTIQUISSIMUM.
CLYMENIA ANTIQUISSIMA, Eichw. (Urwelt Russ/., ii, Pl. iii, Figs.

BO 17):

This is a peculiar species represented in the collection in the
Museum of Comparative Zodlogy by a specimen from Porsgrund,
in Norway. It is heavily costated, as in the figure given by Eich-
wald, and these costations are deeply impressed upon the cast
throughout the earlier stages and in the ephebic stage. They
degenerate only in the gerontic stage.

The abdomen is broader than the dorsum and the sides convex
and evenly rounded. ‘The costs are very prominent and sharply
defined, as in the original figure. ‘The sutures, as far as these could
be seen, appeared to be similar, ‘The size was also similar and the
last whorl in close contact, as in Eichwald’s figure of this species.

The specimen described had reached the anagerontic stage, the
coste having disappeared, or, at any rate, ceased to be reflected on
the cast near the end of the last whorl, whereas in all previous
stages, except probably the earliest nepionic, they are almost
equally prominent on both the cast and the shell.

The siphuncle is subdorsan at all the stages observed from what
appeared to be the second to the third and fourth whorls. It is
quite large, especially on the second whorl.

The neanic whorl is digonal and heavily costated. The ephebic
and gerontic whorls are depressed ovals, the abdomens broader
than the dorsi. The section of the gerontic volution had ventro-
dorsal diameters 25 mm. and transverse 35 mm., without the shell.
The whole diameter of this specimen was about 110 mm.

DISCOCERAS GRAFTONENSE.

LiTuITES GRAFTONENSIS, M. et W. (Proc. Acad. Philadelphia,
1870).

LITUITES GRAFTONENSIS, M. et W. (Geo/. 7//., iil, V1).

502

LITUITES MULTICOSTATUS, Whitfield ( Geol. Wisconsin, Pl. xx, Fig. 7).
TROCHOLITES MULTICOSTATUS, Whiteaves (Geol. Canada, Pal. Foss.,
1, Pt a el ava ee ioaey) one avai eeliioS. a2 12

This interesting species of the Niagara fauna is given here in
order to show the young neanic stage which was preserved in relief
attached to the centre of a mould of the older whorls, Figs. 22, 23,
Pl. viii. The close connection of Discoceras and Trocholites is
demonstrated by thisdrawing. In fact, if separated at this age, the
young would have to be placed in that genus. Fig. 21 shows the
cast of a perfect mould of another specimen of the same species
which has reached the ephebic stage.

Whether this had a dorsal furrow in the umbilical perforation
could not be determined. The perforation is certainly very small.
Whiteaves’ figure shows that the siphuncle is subdorsan in the
ephebic stage as it is in the neanic stage described above.

Systrophoceras,* n. g.

This genus includes the remarkable series of costated trochoceran
and gyroceran forms described by Barrande in his Systeme Szlurien,
which have the whorls either very slightly in contact, or not touch-
ing at any stage, and are devoid of an impressed zone.

Systrophoceras (Troch.) arietinum, rapax and pingue, sp. Barrande,
have a depressed subtrigonal or subkidney-shaped outline to the
whorl with the siphuncle dorsad of the centre, and in many charac-
ters are distinct from the others cited below under the name of
Peismoceras. These species may have been close-coiled in their
younger stages.

Trochoceras.

Barrande described this genus in 1848, and in the same publi-
cation later gave a list of the species { in which the characteristic
form, Zvrochoceras Davidsont, was mentioned first, and this con-
sequently is his type. Hall described the same genus under the
same name, but without knowledge of Barrande’s work in the
Paleontology of New York,§ but his types are both quite distinct,
and do not belong to any genus yet described from Bohemia.

* SWotpogos, rolled up.

+ Haidinger’s Berichte, iii, p. 266, 1847.
{ Ibid., iv, 1848.

2 Vol. ii, 1852, p. 336.

503

Thus, although both Barrande and Hall have courteously ac-
knowledged each other, and have mutually joined names as au-
thority for this genus calling it Trochoceras, Barrande and Hall,
the Trochoceras of the former is not the same as that of the latter,
and the name of one or the other or both must be dropped.

I have therefore retained Trochoceras Barrande, and propose for
Hall’s remarkable forms, Zrochoceras Gebhardt and turbinatum,
the new name of Mitroceras* with Mitroceras (Zroch.) Gebhard,
sp. Hall, Pl. Ixxvii and lxxvua as the type.

It must not be supposed that all forms of Nautiloids having the
turbinate spiral are devoid of impressed zones. There are some
species that do have this characteristic, but it is invariably slight,
and occupies necessarily a position on the sides rather than on the
dorsum of the whorls.

Lituitide.

Recent investigations have shown that this group, instead of in-
cluding about all of the unrolled, shell-covered Cephalopoda of the
Paleozoic, must be limited to certain well-defined homogeneous
series with peculiar characteristics.

My observations lead me to think that Lituites is a degenerate
form of Cyclolituites, a view similar to that of Holm and Schréder,
who regard this genus as the radical of the Lituitide corresponding
to the younger stages of true Lituites.

The genera included in this family form a degenerating series
which may have evolved from Cyclolituites, or some form that this
most closely represents, becoming specialized by reduction of the
spiral and simplification or loss of correlative characters during
growth of the whorl, lessening curvature of the annuli and lines of
growth and in the outlines of the apertures, until finally, in the ex-
treme forms of Rhynchorthoceras, the whole shell is straight or
orthoceran, except during the earliest stage, the nepionic, and in
that it is not a perfect coil.

This process takes place through the disappearance in the earlier
stages of the progressive characters of Cyclolituites and the gradual
replacement of these by characteristics that first appear in the
paragerontic stages of such species as Ang. precurrens. ‘That is to
say, Rhynchorthoceras has from a comparatively early stage the ven-

* From Mizpa, agirdle, but also used for ‘‘ turban,” in which sense it is here quoted.

504
tral and dorsal crests and lateral sinuses in its lines of growth that
are first observable in the degenerative stages of the ontogeny o
allied and more complicated shells (Aug. precurrens), it includes
in other words some species at least that are purely phylopara-
gerontic.

No genus of this family, except Cyclolituites, has an impressed
zone, the transverse section being round or more usually a com-
pressed oval ellipse. The most obvious external characteristic,
which fails of being distinctive only in some species of Angeli-
noceras, and in them in the ephebic stage only, is the forward cur-
vature of the lines of growth and costze on the sides and the promi-
nent paired ventrolateral crests and corresponding lateral sinuses.

The shell varies from that of Cyclolituites with whorls touching
until a late ephebic stage, only a part of the hiving chamber being
free, through forms like Lituites with a portion of the camerated
whorl and the whole of the living chamber free and straight, to
Rhynchorthoceran forms which have uncoiled whorls.

The apertures vary, but possess in Lituites, Ancistroceras and
Cyclolituites, prominent ventro-lateral crests and deep ventral
sinuses.

The siphuncle is large and subcentral, central or just above the
centre and in the young approximates to the dorsum. It is, so far
as known, ellipochoanoidal and microchoanitic, z. e., composed of
short funnels that are directed towards the apex and having porous
walls between the funnels and the next septum.

All of these forms known to me occur in the Orthoceran and
Varginatus limestones of Northern Europe and Niagara limestones
and Quebec faunas in this country. They seem to be absent from
more southern faunas of the same stages.

Foord doubts the appearance of true Lituites in the rocks of Great
Britain, and I think he could have positively denied their appearance
there since Zz¢. 2bex., sp. Sowerby, certainly has none of the usual
characteristics of any of this family.

Trochoceras speciosum, Blake** has most extraordinary costz
turned forwards as in the Lituitidz, but the siphuncle is ventral
and the description is inadequate, and at variance with the figure
so that one cannot arrive at any definite conclusion.

* Brit. Ceph., Pl. xiv, Figs. 12-16.

505

Cycloliturtes.

This generic name was given by Remelé, who has done more
than any other one author to clear up the relations of the different
forms of Lituitide. The species mentioned by him was Cyclolituztes
applanatus, and to this Holm added a new form, Cyclolituites lyn-
ceus. is drawings show that Le/uctes Lynnensis, Kjerulf,* is a spe-
cies of this genus. The drawing made by Barrande of this last is
defective in representing the umbilical perforation as too large.
Kjerulf’s drawing gives this much smaller. It also gives the lines
of growth as bending apically on the first volution and first half of
the second volution. They then change to the peculiar forward
bend of the Lituidz, and without doubt the aperture changes at
this time also to the outline of the adult, so that this is the an-
ephebic substage. ‘The hyponomic sinus is narrow and deep, and
the crests on the abdominal angles, at first blunt in the anephebic
stage, become more prominent in the ephebic stage. ‘The sides
have lateral sinuses and probably the dorsum is occupied by a crest.
Only the last ‘quarter of the outer volution is tree. Schroder
doubts whether this is a distinct genus, thinking that it may prove
to be the young of true Lituites.

CYCLOLITUITES AMERICANUS.
Loc., Gargamelle Cove, Newfoundland.

This species has a quadragonal whorl with somewhat flattened
lateral zones. ‘The abdomen is also depressed, but with a slightly
gibbous central zone and linear ventral channels on either side, the
abdominal angles appearing, in consequence, as lateral ventral
ridges. ‘The lines of growth show that the usual hyponomic sinus
was present in the aperture, with sharp, narrow crests on the
abdominal angles and broad lateral sinuses on the sides. The lines
of growth on the venter are crossed by a secondary system due to
the impression of the dorsal lines of an outer whorl, which has
been broken off in this specimen. ‘These show that the aperture
has a prominent median dorsal crest and that the coiling was close,
as in other species of this genus.

The sutures seen through the thin shell are nearly straight at
first, then in the ephebic stage become flexed with very slight
lateral lobes and ventral saddles. There are probably slight flex-

* Vivies t Christiania, p. 14, 1865.

5C6

ures or lobes to correspond with the ventral channels, but these
were very indistinct through the shell.

The siphuncle is of medium size and ventro-centren in the
middle of the volution actually seen, and at its termination in what
seemed to be the septal floor it was centren.

The original specimen is a nearly completed whorl, 36 or 37 mm.
in diameter, and if prolonged and restored to a point opposite the
dorsal marks described above it must have been, when complete,
about 74 or 75 mm. in diameter.

The dark blue color of the last septum of the fragment described
indicated that it might have been the floor of the living chamber,
and if so, that living chamber must have been over three-quarters
of a volution in length. Every observer, however, knows that this
inference is open to great doubt because of the frequent invasion
of the matrix into septal chambers through accidental breaks in the
shells. Pseudo-septa were observed in this specimen. So far as
could be seen the involution simply covered the abdomen, and the
contact furrow, although not perceptible on the first part of the
whorl described, was evidently present later. This is very inter-
esting, because this furrow is not persistent upon the uncoiled
whorls in any species or form of Lituites yet described and seems
to have no hold at all upon the organization.

Lituttes.

This generic name has been applied to the majority of forms that
have the last part of the last whorl or the living chamber free.
This general application of the name is so erroneous that it hardly
needs discussion. It is, as stated above in this paper, a common
tendency of the growth of the whorls in degenerative shells of the
Nautiloids throughout the Paleozoic and of the similar forms of
Ammonoids during each geologic period, and also a common ten-
dency of the extreme senile or paragerontic substage in the ontogeny
of all shells of both orders whenever they attain the extreme limits
of their existence. Later authors, especially Remelé, No6tling,
Dewitz and Holm, have recognized this fact in some way, either
directly or by limiting the generic application of the name Lituites,
or by separating the genera Ancistroceras, etc., from Lituites.
Remelé was the first to demonstrate the divisibility of the Lituitidz
into different genera, Boll’s previous effort in this direction being
unsystematic and subsequently repudiated by himself.

507

Notling* shows conclusively that there are two groups usually
included in Lituites that differ in their lines of growth and aper-
tures, etc. The true Lituites have, according to Notling, four
principal sinuses, deep ventral and dorsal and_ shallow lateral
sinuses. Schréder has criticised this statement, making out five
sinuses and five crests in the apertures and lines of growth. Not-
ling’s} statement is substantially the same so far as the larger sinuses
and crests are concerned, but Schréder pointed out that the dorsal
sinus was subdivided by acentral crest into two smaller sinuses.
The correct way of describing the sinus of the inner side, judging
by the growth and development, is to regard it as the dorsal sinus,
and the dividing crest and minor sinuses being developed later as
minor or subsidiary dorsal crest and sinuses.

Holm? has confirmed this view and, with the fine materials at his
command, has figured the dorsal sinus spreading at the base and
divided by a slight reéntrant crest, which is also reflected in the
lines of growth on that side of the living chamber, while the ven-
tral sinus is deeper and narrower and undivided. ‘These facts
increase the differences of the aperture between Lituites and Ancis-
troceras, and at the same time the slight median crest in the aper-
ture and lines of growth on the dorsum of Lituites makes the
affinity with Cycloceras and Ancistroceras clearer than it would
otherwise be. ‘The crest and sinuses are also very much more pro-
nounced in Lituites, and the enrolled portion of the whorl is con-
tinued longer and is more closely coiled, the whorls being in con-
tact for between three and four volutions. Holm’s figures of Zzv.
fituus show that on the early part of the straight whorl the lines of
growth are entirely different from the later parts of the same whorl.
The outlines have a slight, shallow dorsal sinus, the median dorsal
crest not having yet been developed. ‘The same peculiarity is
observable in Notling’s figure on a part of the shell preserved and
show the lines of growth at about the same stage of growth, and
also upon Lossen’s figure of the same species. There are also
decisive costations on the coiled whorls, which are similar in both
of these figures. These in the younger substages are bent apically
towards the venter and forwards towards the dorsum, and have not
the more complex curves of the older stage.

* “ Beitr. z. Kennt. d. Ceph. a. Silurg. d. Prov. Ost-Preussen,’’ Jahrb. d. k. Preuss. Geol.
Landesanst. wu. Bergak., 1883, p. 126 ef seq., and Zeitsch. Deutsch. Geol. Gesell., 1882.

+ ‘‘Untersuch. u. Sil. Ceph.,’’ Pal. Abt., Dames et Keyser, v, heft iv, p. 44.

TAftryck. Geol. Foren. Stockholm Forhandl., xiii, 1891.

508

It is plain that the coiled young represents the nepionic and
neanic stages and that the aperture must have differed essentially
in these stages and perhaps may have been open or else more like
that of Cyclolituites.

Notling also demonstrates in his paper in the Zeztschrift that the
earlier stages had compressed whorls, the abdomen broader than
the dorsum, and also that the siphuncle was nearer the dorsum in the
youngest stage observed, and gradually departed from this towards
the centre, becoming dorsocentren in the ephebic or outstretched
whorl. In old age it again changes its position and tends towards
the dorsal side. N6tling has also shown that the siphuncle was
ellipochoanoidal, consisting of short funnels and the usual porous
sheaths, or that which corresponds to this part in the siphuncles of
other forms. The structure of the siphuncle in the younger stages
was, however, not described or figured. A list of the species ac-
cording to Notling is as follows: Z. “tuus, De Montfort; ZL. per-
fectus, Wahlenberg; to this Holm added, Z. Zornguistz, Holm,
and gave very instructive figures of the two species already known.
L. discors, Holm, has a broad dorsal crest in the lines of growth
and aperture and is here referred to Ancistroceras, and LZ. afpla-
natus Remelé.

Angelinoceras, n. g.

There are several species usually referred to Lituites which can
neither be included in this genus nor in Ancistroceras or Holmiceras.
These have open coils in the young, and the usual lituitean out-
stretched free whorl in the ephebic and gerontic stages. The only
species known to me are those described by Angelin and Lindstrom
in their Fragmenta Silurica. The lines of growth, and the annuli,
during the neanic stage, have curves similar to those of Cyclolituites
in A. /atus, viz., with deep ventral sinuses, crests at the abdomi-
nal angles, deep Jateral sinuses near the dorsum and dorsal crests.
These curves change in the ephebic whorl, becoming less sinuous,
but, beyond the fact that they differ very much from those of
Ancistroceras or Lituites, they cannot be defined with accuracy from
the figures given.

The increase by growth is more rapid than in Lituites and less
rapid than in Ancistroceras, in 4. Zafus and in A. anguinus it 1s
very slow throughout life. The ephebic whorl is extended with the
usual lituitean curve and closely reseinbles in aspect, but not in the

509

lines of growth, Molmiceras precurrens, sp. Holm. In A. an-
guinum, however, it remains attenuated. The coiled portion of
the shell has about three whorls coiled, and their attenuated propor-
tions and compressed form approximates more closely to those of
Lituites than to those of Ancistroceras. The close coiling in Ang.
sp. zzdet. (as figured by Angelin) of the nepionic stage shows also
more affinity for Lituites than for Ancistroceras. The figures of
Lit. lituus given by the same authors show also essential differences
from those of the true Zz¢. “fuws, as figured by Lossen and Notling.
The coiled whorls are not in contact, not so compressed, free from
the large fold-like costations of that species and have the character-
istic lines of growth bending forward and with prominent ventro-
lateral crests near the apex of the whorl if correctly figured. ‘Taken
altogether, the characteristics of the species of this genus show a
series of forms standing apparently between Lituites and Ancistro-
ceras.
Ancistroceras.

The name of Strombolituites was substituted by Remelé.* Boll
had originally used the name Ancistroceras in connection with 4.
undulatum, the species which must be considered the type of the
genus, but had subsequently abondoned its use,+ and this and his
insufficient diagnosis was supposed by Remelé to justify the sup-
pression of hisname. Boll’s type, however, being a good species
and a distinct genus, his name must stand in spite of his own desire
to suppress it and his defective description. Ndétling has also dem-
onstrated that wsdu/atum has a closed spiral for one and one-half
whorls (said by him to be about two whorls). This is compressed
elliptical in the nepionic, and becomes more or less quadragonal
near the end of the spiral, assuming very quickly the circular form
after this. |

Remelé’s paper deals also with Lituites and he really divides the
group of Lituitidse into three genera, since he endeavors to limit
the name of Ancistroceras to the forms which he subsequently
described as Rhynchorthoceras.

The genus Ancistroceras differs from Lituites, according to
Notling, in having only three sinuses, a ventral and two lateral
sinuses in the lines of growth and aperture, the dorsum being oc-
cupied by a broad low crest. Schréder, in the paper quoted above,

* Zeitsch. geol. Gesells., 1881, Pl. elxxxvii, ‘‘Strombolituites,” ete.
ft Arch, d. Verds. Freunde d. Naturg. Mecklenburg, xi.

510

asserts that lines of growth in Lituites and Ancistroceras are similar
and certainly this appears to be in part true. There are distinct
inflections indicating the probable presence of five crests and five
sinuses as this author states. These are perfectly well shown in Avec.
Torelli, as figured by Remelé, and in his Anc. (Stromb.) Bolts.
But in all of these there are other characters not found in Lituites
or in other genera of this family which separate these fossils as a
distinct group in my opinion of generic value.

While the lines of growth are similar, they show that differences
must have existed in the form of the crests and sinuses on the dorsal
side of the aperture corresponding to the slight development of the
median minor crest and paired minor sinuses on the dorsal side.
In fact when one describes the curves of the dorsal lines of growth
as indicating a dorsal crest in place of a lobe, he is coming nearer
to the actual aspect than when he correctly classifies the outlines as
a broad sinus subdivided by a minor crest and secondary sinuses.
In other words, the great dorsal sinus of Lituites has reached the
disappearance point in this genus during the ephebic stage but has
not entirely vanished except perhaps in some species. It, also, as
is well known, is a much larger, broader form, spreading out rapidly
in the outstretched or free part of the whorl. It is also plain that
the enrolled part or young shell of Ancistroceras has fewer and less
closely coiled whorls than in Lituites. Thus 4. Zoredi, as figured
by Remelé, has only one to one-half volutions enrolled and these
do not touch although closely approximate. In fact the young of
Ancistroceras are only coiled during the nepionic stage, and perhaps
ananeanic substage, and the figures show much larger, stouter whorls
even at the apex than im lLituites. The figures of Nemelemon
A. Torelli and of Notling of A. wndulatum are very careful studies,
and exhibit the changes in development of the lines and annuli.
These have in the neanic stage subacute, narrow crests, lateral
sinuses rising to prominent ventro-lateral crests and between these
on the venter is a deep, broad median sinus, thus resembling those
of Cyclolituites. The paraneanic substage is present on the early
part of the outstretched whorl in Zore/i and undulatum.

The siphuncle is also much larger in this genus than in Lituites.
The study of the pseudo-septa by Holm led him to observe the
siphuncle in 4. uudulatum and Torelli and his description is as
follows :* ‘* Der siphonen scheint mir wenigstens auf der einen oder

* Paleontol. Abh., Dames u. Kayser, iii, hft. i, ‘“ Organiz. Silur. Ceph.,’’ 1885, Pl. xxi.

511

der anderen Seite, keine eigene, festere, verkalkte Hulle gehabt zu
haben,’’ If the siphuncle were holochoanoidal, it would have as
thick and might have thicker walls than the septa themselves.

A list of the species is as follows, as given by Notling: A. wnxdu-
latum, Boll.; Zoreli’, Rem.; Barrandez, DeWitz.; Bol, Rem. To
these Notling has also added Cvy¢. Odinz, Eichwald (Lethea Ros-
stca, Pl. xxvi, Fig. 14a—-6), and he thinks this may be identical
with wrzdulatum. |

Ancistroceras (?) Dyeri, n. s., is a large fragment quite different
from any European species, having the sutures with slight broad
ventral lobes, slight saddles at the abdominal angles, lateral lobes,
saddles at the umbilical shoulders, and apparently narrow dorsal
lobes.

The fragment is that of a rapidly enlarging arcuate whorl, sub-
quadragonal in section, the lateral zones slightly convergent out-
wards, the dorsum broader than the venter.

The siphuncle is ventrocentren.

The lines of growth seen on the living chamber had the charac-
teristic ventral sinus, slight crests on the abdominal angles, shght
lateral sinuses, broad low crests on the umbilical shoulders and in-
ternally faint minor dorsal sinuses apparently rising to an equally
faint median dorsal saddle.

It has characteristics which appear to be intermediate between
Ancistroceras and Rhyncorthoceras. ‘This fossil is from the Niag-
ara Group near Chicago, Ill., Dyer collection, Mus. of Comp.
Zoology, and is worth describing in this connection, although until
it can be studied in the young and figured it is hardly safe to refer
it to this genus. It has been named Cyrtoceras amplicorne, Hall,
and closely resembles that species, but the section is more decidedly
quadragonal, the sides and venter flatter and the transverse diame-
ter broader. |

Rhyncorthoceras.

The designation Rhyncoceras has also been used by Remelé and
others, but Rhyncorthoceras was used first, and should be exclusively
employed. Rhyncoceras is not an equivalent, and there cannot be
two names for one genus.

Remelé’s description of this genus is perfectly clear and satis-
factory. It is in my opinion another grade in morphic degenera-
tion of the Lituitide, and is directly in line with and supplementary

512

to the modifications of Lituitesand Ancistroceras. It is completely
uncoiled in the young, and the tip or apex has not even the open
coiling of Ancistroceras, but is really an open or cyrtoceran curve.

The annuli of the shell are also simpler in curvature and accord-
ing to Remelé they have low broad dorsal and ventral crests and
corresponding low broad lateral lobes. These phylogerontic curves
appear to be acquired in the early ephebic stages, and therefore ap-
pear earlier in the ontogeny than in Ancistroceras.

The siphuncle is large and may be either dorso-centren, or about
centren, and in 2. Beyrichea is said by Remelé to be nearer to the
venter than to the dorsum or ventrocentren.

The list of species given by Remelé* is as follows: R. Beyrvichia,
Zaddachi, Oelandicum, damest, tenuistriatum.

Rhynchorthoceras (?) dubium. In the Dyer collection, Museum
Comparative Zodlogy, there is a fragment that shows this genus
probably occurs in the Niagara group of Indiana, but the younger
stages are wanting and it cannot be surely placed here until these
are known. The first part of the free volution has the usual bands
‘of growth with hyponomic sinus, these lines inclining orad and
without inflections or with hardly perceptible lateral sinuses to the
dorsum where they unite in low, broad saddles. :

There are also three inconspicuous low, broad costz on this part
of the shell. ‘The form is a slightly compressed ellipse, the siphun-
cle large, ventrocentren, the sutures have ventral and dorsal sad-
dles and lateral lobes. The growth bands lose their inclination in
the older part of this volution, becoming straighter on the sides
and the hypomic sinus almost disappears. This last characteristic
seems to place these fossils in this genus.

Flolmiceras, Ni. g.

Lituites precurrens sp., Holm, has open, discoidal whoris, like
those of Angelinoceras latum, and closely resembles this species in
form and proportions, both of the enrolled and outstretched whorls,
but the lines of growth and annulations are very distinct. It has
the four major sinuses in the lines of growth, as in Lituites, but the
median dorsal crest is absent. The aspect shows the presence of
another genus in this family and the sutures are also different from
those of Lituites, having distinct ventral and dorsal lobes in the
ephebic stage, with low, broad, almost straight, lateral saddles.

* Zeitsch. Deutsch. Geol. Gesell., xxxiy, 1882.

513

The figure by Holm, p. 763, shows conclusively that the sutures
in the nepionic stage are straight, Trocholites like, and quite dis-
tinct from those of the later stages. The narrow annuli cross the
whorl during the ephebic stage or first part of the free whorl, with
the true Ancistroceran curves, namely, with shallow ventral sinus
between two low, narrow ventro-lateral crests, broad, shallow lat-
eral sinuses and a very slight but perceptible dorsal sinus not
divided by a crest, as in Lituites.

These change in the gerontic stage, the ventral and dorsal sin-
uses being replaced by low, broad crests, the lateral sinuses alone
remaining. This stage repeats exactly the degenerate characters of
the curves in the lines of growth of the ephebic stage of Rhyncortho-
ceras and show, together with other facts, that we are dealing with
a degenerating series. The siphuncle is dorsad of the centre in
the ephebic stage, but it is nearer the centre than in Lituites.

This genus does not seem to stand in the line of modifications
leading from Lituites to Ancistroceras, nor in that leading from
Lituites to Rhyncorthoceras.

Ophidioceratide.

The apertures and costated whorls of Ophidioceras have been
supposed by several authors to show that it belonged in the family of
the Lituitide. The apertures are, however, distinct, having only
three large sinuses and a corresponding number of crests and the
costations and lines of growth have not the peculiar forward bend-
ing lateral curves of the Lituitide. ‘The ornamentation of the
younger stages and the form of the nepionic stage is so widely dif-
ferent that no close comparisons can be made with the young of
Cyclolituites, the closest coiled form of the Lituitide.

This genus was formerly supposed by the author to belong in the
same group with Ascoceras and Glossoceras, which had similar aper-
tures, but recent investigations have shown that these genera are
widely separated in structure.

Ophidioceras.

This genus, fully described by Barrande, becomes very interest-
ing in the history of the impressed zone on account of its highly
ornamented and costated whorls and the peculiar, excentric charac-
ter of the free whorl and the aperture with deep, narrow hypono-

514

mic sinus, lateral crests and dorsal crests bending inwards and con-
tracting the opening. It is also of interest in this connection as
showing how narrow and comma-shaped the umbilical perforation
may be without affecting the form of the dorsum, and especially
with regard to the history of the degeneration of the impressed
zone on the dorsum of the free whorl and living chamber.

Ophidioceras.

OPHIDIOCERAS RUDENS.
OPHIDIOCERAS BARRANDE (Sys¢. Sz/., Pl. xlv); Pl. viii, Figs. 29-35.
Loc. Bohemia.

This species has a flattened comma-shaped umbilical perforation
and, although the increase in size is rapid, it is not excessive in
the lateral diameters as compared with the ventro-dorsal from the
ananepionic substage to the paranepionic. ‘The result is a volution
which curves evenly about the core of the perforation and preserves
the rounded dorsum and the general aspect of the section without
great modification throughout the nepionic stage. ‘The cicatrix is
well-marked, as,shown in Fig. 30, and the ananepionic substage
has an elongated ventro-dorsal and short transverse diameter.

In the metanepionic substage the whorl becomes broader on the
venter than on the dorsum, and in the paranepionic the dorsum
spreads, becoming broader, but does not quite equal the venter in
breadth. In the ananeanic substage the longitudinal ridges become
more prominent and more easily observable and the costations also
appear.

The contact furrow begins as soon as contact is complete and is
at once deep and definitely defined, as a hollow fitting over the
ananepionic tip, and it completely covers in this substage. The
contact takes place on the dorsal side of the ananepionic substage
and the furrow is deeper at this point in proportion to the whorls
than it is at any subsequent age. ;

There were two specimens showing the nepionic stages of this
species under observation, the one drawn and this one. Both
exhibit the peculiar globular form of the apex, and the well-defined
ana- and metanepionic substages, which can be quite closely com-
pared with those of WVautilus pompilius, and they have similar con-
strictions to the first two constrictions depicted in Henry Brook’s
drawings on Pl. i of this paper.

515

The dorsum of the whorl becomes at the same time broader and
the whorl alters in shape to an approximately kidney-shaped outline
with the ventro-dorsal, shorter than the transverse diameter. After
this age the increase of growth proceeds more slowly. Inthe meta-
neanic substage, the coste and longitudinal ridges become well
developed, but the venter remains rounded and the lines of growth
show a deep, broad hyponomic sinus and lateral crests, and the
aperture at this stage must have been very distinct from that of the
next substage.

In the paraneanic substage the central ventral zone appears at first
as a broad band, in low relief, arising obviously from the elevated
edges of the narrow hyponomic sinus, which begins to appear at
this age. In the anephebic stage, at the beginning of the third
volution, this acquires its specific prominence and characters. ‘The
metephebic stage is introduced by the subsequent moulding of the
dorsum over this broad carination which modifies the outline of the
contact furrow in section, and gives it the peculiar central dorsal
face and narrow lateral dorsal faces as peculiar to this genus as are
the ventral modifications which give rise to them.*

The sutures do not seem to be much modified after the nepionic
stage is passed by. The czecum, if a spot observed on the broken
apex of one specimen is correctly translated, is subventran or nearly
so in the first or metanepionic septum and the siphuncle is about
the same position relatively or propioventran in the paranepionic
substage as observed in two specimens and given in one of these,
Fig. 30, Pl. viii, and then changes slowly to centroventran in the
anephebic substage. The living chamber is very long, being, if the
excentric free part were applied to the coil, almost one volution in
length. It is, as has been described by Barrande, present in small
(young?) shells, but I doubt its existence, as well as that of the pecu-
liar ophidioceran aperture, before the substage in which the ventral
zone appears.

The free whorl in this genus is specially interesting, because even
in large shells the impressed zone is preserved on the dorsum in a
very significant way. It-is well known that most of the shells, if
not all of this genus, have the lituitean bend, that is to say, the free
living chamber, after it becomes free and excentric, bends suddenly
ventrally, as in Fig. 27, Pl. viii, making the last part of the living

* This is usually called a keel or carina, but it is a modification of a different kind and
sometimes has keels upon its borders.

516

chamber straight on the dorsum and producing a slight curvature
in reverse of the spiral on the venter. In Ophidioceras this is
accompanied by the outgrowth of a transverse dorsal spur which
divides this region into two distinct parts, as shown in the same
figure. ‘The inner part of the living chamber, Figs. 32, 35, has the
central dorsal face and lateral dorsal faces derived from the closely
coiled whorls. These parts and the whole zone disappear as they
approach the dorsal spur, Figs. 32, 34. On the outer side of this spur
the impressed zone reappears, but it is the primitive form of this
which reappears and is perpetuated, the dorsal faces of the ephebic
impressed zone are not reconstructed, Figs. 32, 33. The spur is not
a prolonged costation ; it occurs indifferently between two costations
or as the continuation of a costation, and is obviously independent
in its origin and construction.

These facts show that there is some constantly recurring peculi-
arity in the growth of these shells which causes the outgrowth of the
dorsal spur, and this outgrowth temporarily interrupts the construc-
tion of the impressed zone. Notwithstanding this interruption, the
latter has even in the largest shells made such an impression on the
organism or become so fixed in the organization that, as soon as
the outgrowth stops, the impressed zone reappears. ‘The spur
either directly obliterates the ephebic characters of this zone, the
dorsal faces, or else fills the space which transitional characters
would have occupied, so that when the zone comes in beyond the
spur it is evenly rounded as in the neanic stage. It is, however,
shallower and nearer the aperture it, in part or almost entirely, dis-
appears. The spur always occurs as a divide between the excentric
spiral and the reversed curve which begins beyond it, and has
some obvious connection with this change in the mode of building
the shell, as is shown in Fig. 29, Pl. viii.

The sutures occupying the nepionic whorl are six in number and
very wide apart from the first to the fourth.* The fifth and sixth
show approximation and the seventh is about the normal distance.
The growth of the shell in the nepionic substages and in the ana-
neanic substage, to which the fourth, fifth and sixth sutures belong,
must have been very much more rapid than subsequently. They

*The great size and depth of the apical air chamber is very remarkable. It is
not satisfactorily settled in my mind that there is not at least one septum nearer the apex
than that which is here counted as the first, but even in well-preserved specimens this
has not been observed.

517

have ventral and dorsal saddles until the contact furrow is formed,
and then probably a ventral lobe is always generated.

Barrande’s figure of this species, P]. xlv, Fig. 21, gives similar
observations upon a different specimen. When the median ventral
zone appears, the broad ventral saddle becomes narrowed to the
width of this zone and the lateral lobes are proportionately broad-
ened out.

OPHIDIOCERAS TENER.

OPHIDIOCERAS TENER, Barrande (Syst. Sc?7., Pl. xlv); Pl. vii, Figs.
24 and 25.
Loc., Bohemia.

The specimen of this species, Figs. 24 and 25, gives the peculiar
and very large ananepionic substage of this species, and in the side
view the two marked constrictions indicating the same changes of
form as are described in Offhidioceras rudens, but subsequently
there is a marked bulging of the sides, in what has been termed in
other forms the metanepionic substage, beyond the second constric-
tion. If the first septum occurs where it is figured, the metane-
pionic substage must be placed in the Ophidioceran forms later
than in other forms like Vautilus pompilius, which have the first sep-
tum nearer to the apex, and the ananepionic substage must be con-
sidered as greatly prolonged. Although the specimen had a perfect
surface on the side depicted of the nepionic stage, it is possible
that there may have been other septa* between this and the apex,
but of so fragile a nature that they were not preserved. The
surface of this cast is iron pyrite. ‘There are also six septa occupy-
ing the nepionic stage of this specimen.

There was a minute circular mark on the apex, indicating the
position of the czcum to be propioventran, but this was not abso-
lutely certain. In the second septum the siphuncle was extracen-
troventran and in the neanic stage it attained a centroventran
position. ‘The subsequent stages observed were similar to those of
Ophidioceras rudens except that the peculiar flattened ventral zone
of thisspecies was introduced later than in that species, as described
and figured by Barrande.

The primitive rounded outline of the impressed zone was main-
tained ionger in this species than in Ophidioceras rudens.

* See Ophid. tessellatum.

518

OPHIDIOCERAS TESSALLATUM.
OPHIDIOCERAS TESSALLATUM, Barrande (Sys¢. Sz/., Pl. xlv); Pl. viii,
Figs. 26-28.
Loc., Bohemia.

The specimen, Fig. 28, Pl. vili, showed the metanepionic sub-
stage with the usual two septa and long apical chamber, but internal
to the first septum there was on the venter internal dark lines, indi-
cating a subventran siphuncle. ‘This was cut off by another dark
line which may possibly have been the fragmentary remains of a
septum. Nevertheless there was no positive proof of this and the
question must still be left open. The usual circular mark occurs,
indicating the ccecal termination on the worn apex in a subventran
position. In the second septum the siphuncle is extracentroven-
tran.

The formation of the ventral zone began earlier in this species
than in Ophidioceras rudens. ‘The flattening of the abdomen began
even in the paranepionic substage and in the ananeanic substage
the formation of the zone was well advanced. The development of
the costze seemed also to be accelerated in some specimens.

Fig. 27, Pl. viii, shows the contact furrow as it first appears when
crossing the apex. Fig. 27 shows that the umbilical perforation is
larger in this species than the others described here, since the first
whorl does not meet the ananepionic substage on the dorsal side
but strikes it on the surface of the apex, ventrad of the centre.
The contact furrow is consequently not at first so deep as in other
species, unless this characteristic is variable.

Rutoceratide.

This family consists of a number of genera which are interesting
in connection with the history of the impressed zone only in so far
as they show that this peculiarity is correlated with close coiling, or,
in other words, is due to contact.

Thus, Zitteloceras, Halloceras, Rutoceras, Kophinoceras and Stro-
phiceras as a rule do not have the whorls in contact and do not
have an impressed zone. The shell in most of these is a rough
imbricated structure with ridges or nodes arising from the greater
or less permanency of the frilled projections of the apertures.
These genera, found in the Silurian and Devonian, were described
in my Genera of Fossil Cephalopods, p. 284, and associated

519

with others of the Silurian Adelphoceras and Triplooceras, which
also had rows of large nodes but were true nautilian shells and had
contact furrows. -

The genus, Coelogasteroceras (Solenoceras), described in my
** Carboniferous Cephalopods,’’ second paper, p. 447, was there
removed from the Rutoceratidz and placed with Coloceras under
the name of Coloceratidz, an error corrected in this paper.

I also included in this family the Triassic genus Phloioceras,
having nautilian shells and a deep impressed zone, with Phlovoceras '
(Waut.) gemmatum, sp. Mojsisovics, as the type and also with
Pleuronautilus, of Mojsisovics.

Iam strongly inclined to the opinion that the resemblances of
these Triassic shells to Rutoceras are superficial, but having no
‘specimens at my command I cannot make comparisons.

A delphoceras.

This genus was described by Barrande in his Systéme Szlurien,
and Adelphoceras Lohemicum the type, is a large shell with a
highly contracted dumbbell-shaped aperture set in the dorso-ventral
diameter or vertically. The outline in section is depressed kidney
shaped, with a shallow impressed zone, which is probably not
present before the whorls come in contact, or at any rate is very
slight at a late stage of growth, according to Barrande’s figures.

This species has a large subventran siphuncle and there are three
rows of tubercles on either side, and it is obviously closely related
to Triplooceras, but is remote from Hercoceras, as is demonstrated
by the aperture form ornaments and lines of growth.*

Triplooceras.

This genus, described in Genera of Fossil Cephalopods, is
obviously closely related to Adelphoceras, having three rows of
tubercles on either side, but the form is more highly developed,
being a depressed oval and the coiling closer with a deeper contact
- zone and. the ornaments disappear much earlier on the shell. It is
obviously a grade more progressive than Adelphoceras, but in the
same genetic group.

Besides Zreplooceras (Naut.) inspiratum, sp. Barrande, PI.
*‘46r,’’ there is Z7zplooceras (Troch.) reliquum, sp. Barrande, Pl.

* Barrande’s Adelphoceras secundum is here referred to Hereoceras.
p

520

‘¢493,’’ which has also the characteristic form and markings of
this genus. ‘This last has no contact furrow, according to Barrande’s
Fig. 7, even in a late neanic substage, although there isa distinct
contact furrow in the ephebic stage according to his figure of the
full-grown shell.

Melonoceratide.

Under this title, in Genera of Fossil Cephalopods, 1 included
a number of genera having special interest in this connection. The
impressed zone is not present in Melonoceras, which is an arcuate
form, and in most species of Oonoceras.

Cranoceras, containing the only apparently arcuate form possess-
ing a dorsal furrow, belongs to this family and appears to be allied
to the more closely coiled nautilian forms Nedyceras. All of these
forms have subtrigonal whorls, with siphuncle ventrad of the centre.
The resemblance of Estonioceras and Remeléceras have led me to
place them also under the same family name.

E-stonioceras.

This genus was described by N6tling,* and separated from
Lituites, which it only remotely resembles in having some of the
volutions free.

Schréder has more fully described the genusy than any other
author, and given all the European species with great care, but has,
in my opinion, included in it some forms with quadragonal whorls
and siphuncles in different positions which should be separated as
Remelé has done under the name of Facilituites.

Estonioceras has a nepionic stage with a large umbilical perfora-
tion hke that of other species of the same phylum. The apex
itself, the ananepionic substage, is remarkably large and grows with
extreme rapidity in its transverse diameters, showing the tendency
to form a broad, digonal whorl, and is cap-shaped when seen from
the side as in Trocholites and Ophidioceras and very large in all its
diameters. The sutures of the meta- and paranepionic substages
throughout the greater part of the first whorl, as seen in the speci-
men Fig. 13, Pl. vii, and in Schréder’s figure of apex of stonieceras
amperfectum, Pl. iv, Fig. 5, a—b, reproduced here on PI. vii, Figs. 20

* Op. cil., Jahrb. d. kénig.-preus. geol. Landesan. u. Bergak., 1882.
+ ‘‘Ueber Sil. Ceph.,’”’ Pal. Abh., Dames et Kayser, v, hft. 4.

0 ee oe

521

and 21, have saddies on the venter with perhaps very slight ventral
lobes on either side of this, saddles at the lateral angles and faint
dorsal saddles. _ Schréder. also describes the same substages in
Estonioceras perforatum and the sutures of the first whorl, but his
descriptive nomenclature is not clear and the text is consequently
not perfectly intelligible. Apparently the first whorl has broad
ventral saddles and nearly straight dorsal sutures with sometimes
very slight dorsal saddles. He states very distinctly, however, when
the whorls touch, at or near the end of the first whorl, that a decided
change takes place, the dorsal sutures acquiring well-marked dorsal
lobes. He also clearly states that in the uncoiled volutions this
dorsal lobe, although it persists, loses in height and breadth.

In his descriptions of Letuctes Mucllaurét, of Dewitz, he makes
these statements clearer by saying that the dorsal and ventral sad-
dles possessed by the adult of this species are similar to the sutures
of the young species of Estoniceras perforatum and tmperfectum,
which have sutures with ventral and dorsal saddles as figured by
him only on the venter of Estoniceras imperfectum. There is also
a shallow lobe developed in the middle of the dorsai saddle in
Listoniceras perforatum, which persists even in the gerontic stage.
After the lateral angles disappear in the ephebic stage, the saddles
and lobes are less prominent and become almost straight in the
more rounded volutions of the gerontic stage, but the approximate
return of the same outlines as are found in the paranepionic substage
is plainly visible, Figs. 17 and 18, PI. vil.

The lines of growth show a broad hyponomic sinus and lateral
crests which increase in prominence towards the dorsum, but
directly in the centre of that side there is a crest and on either side
of this shallow dorsal sinuses. ‘There is, however, a dorsal sinus
which persists in the gerontic stage in the lines of growth of a
specimen figured by Schréder of Lstontoceras heros.*

The aperture is wide in the ephebic stage, but evidently contracts
with the whorl in extreme age, as shown in Schréder’s figure of
Listonioceras tmperfectum, Pl. iu, Fig. 2, b, and in the figures of
Eistonioceras biangulatum in this paper, Pl. vii, and sometimes the
ventro-dorsal diameter may become longer than the transverse in
the paragerontic substage. This is, in part, a return to the early
proportions, since Schréder describes the apex of his /s/onioceras

* Op. cit. Pl. v.

——————

a <~ - ieee

522

pervforatum as having an apical chamber in which the breadth but
little exceeds the ventro-dorsal diameter and doubtless at the apex
itself in the ananepionic substage, as in most Nautiloids, the ventro-
dorsal diameter exceeds the transverse.

The coiling is so loose that the umbilical perforation is of very
large diameter, and the impressed zone, generated only after con-
tact, is very slight even on the second whorl and does not persist |
after the whorls separate. The dorsum is, however, affected toa
limited extent on the free whorl in some species as shown in
Schroéder’s admirable figures. These figures give one great satisfac-
tion, their accuracy, size and detail being full of information.

The whorls touch during the neanic stage only in some species,
Estontoceras ariense, but in others they may continue in contact
probably throughout the ephebic or a large part of that stage,
Liston. perforatum and imperfectum.

The lateral angles become rounded in the ephebic stage, but there
is no tendency to form lateral zones or to flatten the abdomen as in
Falcilituites. The whorls simply become rounded, depressed ovals
and in the paragerontic stage the length of the transverse diame-
ters decrease.

The siphuncle is fully described by Schréder in Zstontoceras im-
perfectum, and it is plainly ellipochoanoidal in the ephebic stage.
What it may be in the young has not been determined. The fun-
nels are very short and the connecting walls thin and long. The
position is subventran in the young, tending more towards the
centre and becoming extracentroventran in some species with the
advance of age. In the paranepionic substage it may again return
to a position nearer the venter.

The species described by Schréder are as follows :

LE stontoceras perforatum, Schroder; Estonioceras (Lit.) lamellosum,
sp. His. Descoceras lamellosum as figured by Angelin et Lindstrom
seems quite distinct with closer coiled whorls and deeper impressed |
zone, too deep in fact for a species of this genus, whereas Hisin-
ger’s figure in the Lethea suecica is a true Estonioceras. Never-
theless Schréder asserts that both figures were made from the same
‘individual.’”’ stonioceras (Lit.) heros, sp. Remelé; ariense, sp.
Schmidt; (Le#.) cmperfectum, sp. Quenstedt.

LE stonioceras muellauert and Schréder’s E'stonioceras decheni have
been referred to the genus Falcilituites of Remelé in this paper.

523

ESTONIOCERAS PERFORATUM, Schréder (of. cc¢., Pl. xxvi); Pl. vii,
Figs. 9-12.

Loc., Reval.

The specimen, Fig. 10, Pl. vil, shows the dorsum of the parane-
pionic volution with the shell of the dorsum preserved. ‘The dorsal
crest and dorsal sinuses of the lines of growth and in part the
sutures are visible. After this was drawn a part of the shell was
removed, exposing the dorsal sutures which are given in Fig. 12,
Pl. vii. ‘These show the presence of a dorsal lobe as described
above with faint saddles, the remains of the younger dorsal saddle,
on either side of this. The ventral sutures have saddles at this
stage as may be seen by the outline of the whorl, but these were not
seen, although the ventral lobes on either side are plainly visible in
the side view of the paranepionic volution in Fig. 11. In the
metaneanic substage the dorsal lobe broadens and deepens in corre-
lation with the widening and deepening of the contact furrow, and
the lateral lobes appear then almost like saddles on the sides as in
Fig. 11 above in the outline of the only septum visible at this age in
this specimen. ‘They are, however, still really slight aborad inflec-
tions or lobes. ‘There is no true annular lobe at any stage.

Fig. 9, Pl. vii, reproduced from Schréder’s figures of /sfonzo-
ceras perforatum, shows that in this species in at least some varieties
the neanic stage probably does not acquire a contact furrow until it
strikes the metanepionic substage.

The specimen figured is in collection of Mus. Comp. Zodlogy.

E;|STONIOCERAS BIANGULATUM, n. sp. PI. vil, Figs. 13-19.
ioc), Breslau.

The figures of this species show the large umbilical perforation
and digonal whorl of the paranepionic substage and neanic stages
seen from the side in the centre of Fig. 13, Pl. vii, and then from
the front with part of the outer whorl between the broken lines and
also the terminal part of the free whorl removed in Fig. 15. The
portion removed belongs to the ephebic stage, which in this species
has a digonal section. The lateral anglesdo not show rounding and
the lateral diameters continue to increase steadily and rapidly until
the anagerontic substage begins as the whorl becomes free. ‘Then a
decisive decrease is noticeable in both of these characteristics. In
this specimen the transverse diameter through the middle of the
free volution without the shell, Fig. 17 and 18, was 42 mm., the

524

ventro-dorsal .30 mm. at the termination of the same, the fragment
of the living chamber also devoid of shell was transversely about
4o mm., while the dorso-ventral had increased to 32 mm. This
and the point of view of Fig. 18 gives the aspect of a more con-
siderable diminution in the lateral diameters than actually took
place. ‘The sectional view of this end shows true proportions in
Fig. sco7 PL yvaie .

The section, Fig. 15, gives the neanic whorl at the inner break in
the side view, Fig. 13, and this shows how very small and slight the
zone of involution is in this species. It broadens slightly with age,
but immediately disappears in the free part of the whorl, as it does
also in most species of this genus.

The lines of growth are given on the dors n of the metagerontic
substage in Fig. 17, and these do not diffe. materially from those
of the nepionic stage in Zstonioceras perforatum. The lines of
growth could not be observed on the dorsum of the earlier stages
of growth, but it is probable that in the stages in which the whorls
are in contact that the dorsal crest is narrow and occupies the area
of the impressed zone.

The sutures in the paranepionic substage have ventral saddles
with very slight ventral lobes on either side, saddles at the lateral
angles and apparently lateral lobes. ‘Three sutures of this substage
were followed on the dorsum to the centre and no central inflec-
tions could be seen. This was somewhere about the sixth or
eighth septum, as nearly as could be ascertained, and the suture
formed a very shallow lobe across the dorsum, but this would
ordinarily be described as straight. These, in other words, are
closely similar and of about the same age as the complete dorsal
sutures of Hstonioceras imperfectum given in Fig. 21, Pl. vii, and
probably about the same age as the dorsal sutures of Astonioceras
perforatum given in Fig. 12, Pl. vii. In the ephebic stage broad
lobes appear on the venter, reaching to the saddles at the lateral
angles. The septum, Fig. 15a@, Pl. vii, given to show the contact
furrow, also shows that a faint narrow dorsal lobe coextensive
with this furrow is produced by contact. In the paragerontic
substage, as shown on the last three sutures of Fig. 18, the broad
ventral lobe is replaced by faint saddles with very faintly marked
lobes on either side and the saddles of the lateral angles in conse-
quence of the rounding of these angles have become lateral saddles.
The lateral lobes appear only very faintly or are absent on the

525

under side or dorsum. The dorsal lobe is not, however, affected
to the same extent by senile degeneration, and persists, although
narrower in proportion in the centre of the suture, as may be seen
mobs. 17) Pl. vii.

The siphuncle is propioventran in all the stages observed from
the ephebic to the anagerontic.

Remeléceras,* n. g.

This genus, known at present only by one species, is closely allied
as regards aspect and the late appearance of a contact furrow to
Estonioceras. It differs in having a much deeper furrow, a nephri-
tic instead of a digonal or depressed elliptical form of whorl and in
the dorsal sutures and apparently also in the extraordinary form of
annular muscle.

REMELECERAS IMPRESSUM. PI. viii, Figs. 1-8.

Loc. (?)

This extraordinary form is described and figured in this
memoir on account of its interesting connection with the history of
the impressed zone, notwithstanding the absence of any informa-
Monmitnercearad to the locality. The side view, Fig. 1, Pl. visi,
shows the sutures, which are similar to those of Estonioceras, and
the impression of what appears to be the annular muscle at the base
of the living chamber is very distinct. ‘This may be seen on the
dorsal side, Fig. 3, where the lower line has a deeper and broader
depression in the cast reaching across the contact furrow. These
two lines of depression depart from each other widely on the ven-
tral side, Fig. 2, the outer one forming a broad saddle. They of
course correspond to raised ridges on the inner surface of the shell
of the living chamber and may have been due to abnormal action
in the secretions along the upper and lower borders of the annular
muscle.

The depth of the contact furrow in the full-grown shell near the
end of the incomplete living chamber was somewhat greater than is
given in Fig. 4, but only a shade deeper, and is also slightly
deeper than this beyond the base of this living chamber on the
septate part of the volution. In younger stages, shown successively
in Figs. 5-7, with their accompanying sections, Figs. 6-8, this
furrow diminishes in depth and breadth and almost disappears

* Dedicated to Remelé, well known for his original observations on fossil Cephalopods

a —-

526

on the third fragment. This shows that it did not begin to exist

in this shell until late in the neanic stage and the younger nepionic
stage must have been similar to that of Estonioceras.

It is also interesting and suggestive to note that the depth and
development of the dorsal lobe correlates exactly with the depth
and breadth of the contact furrow. ‘The lateral asymmetry in the
dorsal lobes of the sutures is another fact to be noted in this speci-
men.

The central whorls existed in this specimen, but were completely
concealed by the matrix. A section was made of these, but they
exhibited no structures.

The siphuncle was not visible.

This cast reminds the observer more closely of Astonzoceras (?)
Jamellosum, as figured by Angelin and J.indstrom, than any other
form, but according to Schréder this last is a true estonioceran form
with only a shght contact furrow.

Nedyceras.

This genus was described by the author in Genera of Fossil
Cephalopods, p. 281. It includes a large number of species with
subtrigonal whorls, the dorsum much broader than the venter,
which is elevated and usually subangular. The siphuncle is sub-
ventran and quite large.

The sutures have ventral saddles, lateral lobes and the dorsum
may have a slight lobe or be nearly straight. The genus is of inter-
est in this connection because, although completely coiled and the
whorls in contact in several forms and although the whorl approxi-
mates to the’ nephritic outline, it never has an impressed zone.
This is easily accounted for when one examines the figure of Vedy-
ceras , vestusium, Barrande, Pl. “35. This shell) showsmaiens
although close-coiled, the rate of growth is slow and the umbilical
perforation very large, so that there is no pressure of one whorl
upon another. |

The genus has a number of forms in the Devonian, which also
show similar peculiarities whether they are similar or more open in
their coiling than vestustum, or have the turbinate mode of growth,
which last is not unusual.

The shells are all smooth.

527

Cranoceras.

This genus was described in Genera of Fossil Cephalopods,
p. 281, for a series of cyrtoceran forms having in the Silurian rep-
resentatives like Cvanoceras (Cyrt.) hospitale, sp. Barrande, Pl.
pause wezum Ply “Tan. and Surnus bl. 483) and “4847.

The whorls are subtrigonal with the dorsum, much wider than the
venter, which is apt to be elevated and subangulated. ‘The young,
until they are quite large, are compressed elliptical in section, with
the ventro-dorsal diameter longer than the transverse, then expand-
ing more rapidly they become more depressed and take on the
subtrigonal outline, the dorsum broader than the venter, which in
some species changes subsequently into the nephritic with a slight
impressed zone, Fig. 43, Pl. vii.

The sutures have ventral saddles, slight lateral lobes and slight
broad dorsal lobes, but in some species may be approximately
straight and in the young stages are of this character in most forms.
Considering the size of the shells the septa are remarkably close
and numerous, and only slightly concave.

The siphuncle is propioventran and apt to be filled with radia-
ting deposits. ‘The Silurian forms do not have the nephritic out-
line and also have no impressed zone at any stage, judging from the
large shell of Cranocerus turnus, which, although it has a nautilian-
like form in the large fragment described by Barrande, probably
did not coil very closely.

The Devonian forms are, however, more interesting in connec-
tion with the history of the impressed zone. These can be included
under the names of Cranoceras (Cyrt.) depressum and Cranoceras
(Cyrt.) lineatum.

In the Museum of Comparative Zodlogy, in the Schulze collec-
tion from Pelm near Gerolstein, in the Eifel, there is a specimen of
Cranoceras lineatum 159 mm. in length along the median lateral line,
transverse diameter of smaller end 45 mm,, abdominodorsal 41 mm.,
and diameters of larger end 109 mm. and 85 mm. ‘This is evi-
dently a quick-growing and very large specimen, but showing no
signs of having been coiled. It has, however, near the larger end
on the incurved dorsal side a very faint impressed zone given in
inenouthine, Hise 42 ble vines traced= from the specimen. |; some
specimens do not exhibit this depression, but most of this species
do have similar depressions and some of these are so nearly straight

0 a

2 ——

528

and the angle of growth so convergent that it becomes difficult,
perhaps impossible, to attribute the existence of this zone to con-
tact and pressure of a coiled whorl, unless it was acquired by inher-
itance through some unknown closely coiled forms.

None of these specimens have the double impressed zone figured
in Cranoceras ( Cyrtoceras) depressum, by D’ Archiac et De Verneuil,*
but I have studied some fragments of this species showing the same
peculiarity. The two latero-dorsal impressions or faces and the
central gibbous dorsal face give an outline similar to that of the
young of the Zrocholtes canadense, given in Fig. 24, Pl. iv, of this
paper. ‘The history of the appearance of this modification ia this
large adult whorl, arising as it does from the direct modification
of the younger rounded dorsum} without being preceded by the for-
mation of an impressed zone is, however, entirely distinct from
that which occurs in the paranepionic substage of Trocholites. In
several genera of Carboniferous nautiloids (ex. Asymptoceras,
Apheleceras) similar faces appear on the dorsum, but the central,
gibbous dorsal face is fitted into the hollow flute or ventral zone of
the next inner whorl and is obviously a result of close-coiling and
adaptation of the plastic dorsum of the growing external volutions
to the ventral modifications of the inner volution.

In Solenocheilus of the Carboniferous, however, the whorl has a
rounded venter and yet notwithstanding this a gibbous dorsal face
and dorso-lateral concave faces or furrows are formed independently.
In Cranoceras depressum the origin of the gibbous dorsal face and
latero-dorsal faces or furrows appears also, so far as the facts go, to
have been entirely independent of any correlation with the ventral
surface, which is rounded and gibbous. ‘These characteristics do
not seem to have had a mechanical origin in any of the shells, so
far examined, which have the dorsal side free or comparatively free
from contact.

A very large and remarkable specimen in the Schulze collection,
Mus. of Comp. Zodlogy, shows a very short living chamber, which
has an aperture very broad transversely and with a nephritic out-
line and apparently very broad and well-marked impressed zone.
This species is not a variety of Zxeatum, but a distinct species pre-
cisely similar to D’Archiae and De Verneuil’s figures of Phragmoce-
ras subventricosum, but the siphuncle is ventral.

* Geol. Trans. London, 2d ser., vi, Pl. xxix.
+ This is also figured by Roemer, Harzgeb. Paleontogr., iii, Pl. vi, in a young specimen.

It is questionable, however, even in this form, whether there was
anything more than a flattened dorsal side on the septate part of
the whorl, since this is the aspect of the perfect side, the left side of
this specimen, the right dorsal side and part of centre being crushed
in by pressure. A second specimen of smaller size shows the pecu-
liar dorsal aspect of Cranoceras depressum, but so faintly that the
gibbous face and flutings are hardly perceptible.

I have been, of course, struck by the resemblance of these shells
to the young of the nautilian forms of the Mesozoic, but there is
still closer resemblance in the general aspect of species of Urano-
ceras and the closely set septa of the species of Cranoceras, and
their contracted apertures show that it is not safe to consider them
as radical forms.

They resemble the young of some species of the Nephritidze, but
this family has a peculiar ornamentation in young shells and isa
closed generic series having apparently its own slender radical
forms in the Devonian and possibly even its own arcuate radicals
in this period.

Nephritide.

This family name is given to cover a series of genera having
heavily ridged shells in the young, and for the most part in adults,
with whorls having considerable resemblance in general outline and
sutures to the true Nautilidz, with which I formerly associated
them.

Sphyradoceras, described in my Genera of Fossil Cephalopods,
page 298, contains the remote radicals of the group and this genus
has arcuate and trochoceran forms. ‘They are of value in this con-
nection only in so far as they show that the impressed zone, as a
rule, is not present when shells are not in close contact.

Uranoceras has a number of large stout shells with solid, nautilian-
looking whorls which are, however, never, so far as I have seen, in
sufficiently close contact to produce a contact furrow. These forms
are interesting, however, because the dorsum is always slightly
flattened and has the aspect common to the nepionic stage of
nautilian shells, so that one continually expects to find a specimen
with a dorsal furrow. I have, however, not yet found an example
of this kind, although the whorls are often so close as to touch
each other. The type is Uranoceras (Cyrt.?) uranum, sp. Barrande,
in the Silurian, but most of the species occur in the Devonian.

—s

i ——

530

My references, in Genera of Fossil Cephalopods, to some Car-
boniferous nautiloids as probably members of this genus were
erroneous. Barrandeoceras has been referred to above as belonging
to the Tarphyceratide.

Pselioceras, mentioned also in my Genera of Fossil Cephalo-
pods, as another member of this family, may possibly be a genus
of Rineceratidz, but it does not belong here.

The family of the true Nautilidz have been properly limited
farther on to Mesozoic genera.

Rhadinoceras,* n. g.

The species here noticed under this name were formerly included
in the genus Nephriticeras. They have compressed elliptical or
almost rounded whorls, growing more slowly than in Nephriticeras,
have the impressed zone only in the later stages of growth and are
transitional between gyroceran forms and Nephriticeras.

RHADINOCERAS CORNULUM.
NAUTILUS ‘CORNULUS; sla ay, Vi ov. ei ty, El sey

Hall’s figure shows the nepionic and neanic stages of this shell,
and there is a slight contact furrow.

The form of the whorl in section is almost circular, not changing
much throughout the nepionic stage.

The sutures are similar to those of Nephriticeras, with shght
ventral and dorsal lobes and rather narrow lateral lobes.

The siphuncle, according to Hall, is dorsad of the centre.

The shell has only fine strize and fine longitudinal ridges.

Having studied the original of this species in Prof. Hall’s collec-
tions, I can confirm his observation and state that this is obviously
a close-coiled nautilian form with a slight contact furrow produced
after the whorls come into contact in the ananeanic substage, but
not existing previously.

The umbilical perforation was very large, and young shells show
that Rhadinoceras contains transitional forms between Nephriti-

ceras and some cyrtoceran ancestor. In other words, these two

genera were not derived from any coiled nautilian form of the
Devonian or Silurian, but are progressive modifications of some
closely allied arcuate form. This conclusion is sustained also by
the existence of a peculiar cyrtoceran form associated with these

x "Padives, slender.

a ee

531

which may be a survivor of the ancestral genus of this group. I
allude to the peculiar arcuate species described by Hall from the
Goniatites limestone of Manlius, N. Y., under the name of Cyréo-
ceras liratum. Wall recognized the affinity of this shell, in the
ornamentation and form to species here described as included in
Rhadinoceras, and it can be easily observed that the young of
Rhadinoceras cornulum directly repeats the characters of his Cyrfo-
ceras liratum.

RHADINOCERAS HYATTI.

NGmiuSpavATID, lal (Pa7. Vv. We, v, Pt. 11, Plo cxxvi).

This species, so far as figured by Hall and so far as known to me
from the observation of Prof. Hall’s collection, is even less closely
coiled than ARhadinoceras cornulum.

The early stages figured by Hall show no dorsal furrow and the
form is similar to that of cornulum, but it is a depressed ellipse in
_the nepionic stage, increasing more rapidly by growth in its trans-
verse diameters than in cornudum. ‘The affinity of this species with
the nepionic stage of Nephriticeras is indicated not only by the form
of the whorl, which is identical, but by the presence of coarser
longitudinal ridges, and by the sutures.

Whether the whorls of this species were ever in close contact is
doubtful, on account of the absence of more complete specimens and
the want of a contact furrow on the fragments, so far as known to
me.

But the single fragment figured by Hall, and examined by me,
was not old enough to settle this question, and I am inclined to the
opinion that it will be found to be a true nautilian shell.

Nephriticeras.

This genus, described by the author in Genera of Cossil Ceph-
alopods, p. 300, formerly included the transitional species separated
above under the name of Rhadinoceras.

These shells are all unquestionably nautilian:

The early part of the nepionic, probably metanepionic substage, is
similar in transverse section and ornaments to the full-grown shells
of Rhadinoceras, but the paranepionic volution becomes speedily
depressed and subtrigonal, the dorsum broad and much flattened,
the abdomen elevated and narrower than the dorsum.

The siphuncle is dorsad of the centre.

532

The sutures have ventral and dorsal lobes and lateral lobes in the
ephebic stage, but in the earlier stage there are ventral saddles.

NEPHRITICERAS LIRATUM.
NAUTILUS LIRATUS, sp. Hall (Pal. WV. Y., v. Pt. 11, Pl. Tyaiancie
Ix)

This species in the metanepionic substage is distinctly annulated
and also has broad longitudinal ridges, as shown in Hall’s figures
on Pl. lx. These ridges disappear together with the annulations on
the abdomen of the paranepionic volution, but persist longer on the
dorsum, and in some specimens they are very large flutes on the
sides even in the neanic, as is shown in Hall’s Fig. 3, Pl. lvii.

In the neanic stage the form of the volution changes from sub-
trigonal to a broad depressed oval.

No impressed zone has been observed, but this may be due to the
age of the shells so far observed, none of which as figured, nor so far
as I have seen, exceeded one volution.

NEPHRITICERAS JUVENIS.
NAUTILUS LIRATUS, var. JUVENIS, Hall (eZ, WV. Y., v, Pt ny Blin
ENE S32155 10):

This shell, described as a variety of “vatus by Hall, is obviously
distinct. The form changes more rapidly than in “raf¢ws and, in
the fragment of the nepionic volution figured by Hall, it may also
be seen that the longitudinal ridges are much smaller than in Zva-
tus, more like those of the young of Wephriticeras bucinum. It dif-
fers from the last in having no impressed zone at the same age.

It is highly probable than an impressed zone appeared in a later
stage than has yet been described.

NEPHRITICERAS SUBLIRATUM.
NAUTILUS SUBLIRATUM, sp. Hall (Pal. W.' Y., v, Pt. ii, Pl. lvii).

This species has similar changes of form to those of Zratum, but
it is altogether a broader whorled species and acquires the nephritic
outline at an earlier stage of growth, and probably has in perfect
specimens a smaller umbilical perforation. |

There are no longitudinal ridges on the ventral side in the orig-
inal specimen, which was in the neanic stage of development, but
these are large and persistent on the dorsum as in WVephriticeras
firatum. In Hall’s figures the sutures have been confused with the

533

lines of growth and the dorsal sutures are not correctly given. The
dorsal lobes exactly coincide with the impressed zone in Fig. 6 of
his plate. ‘This figure shows the last part of the paranepionic volu-
tion in section below and the ananeanic with the impressed zone
above this. The smoothness of the impressed zone in Hall’s Fig. 6
of this species shows that the longitudinal ridges were obliterated
as they are in other forms by the pressure of the growing whorl,
and that this zone is probably due to contact and did not occur on
the free side of the volution in the umbilical perforation. I use
the general term ‘‘impressed zone,’’ because, although my notes
and Hall’s observations and the figures all seem to warrant the
statement that this zone in this species is a contact furrow, I have
not been able to revise and confirm these observations.

NEPHRITICERAS BUCINUM.
Mawes BUCINUS, Hlall (Paz, 7. Y., v, Pt. 1,.Pl. Ix).

The paranepionic volution is shown in Hall’s Fig. 1, Pl. lx, with
a convex dorsum, and in Pl. cvii, Figs. 2 and 3, it is again shown
with the siphuncle dorsad of the centre and the outline distinctly
subtrigonal. ‘These figures indicate great variability in the time
at which the impressed zone appears, since the section in PI. cvii is
very much larger than that of about the same age of Fig. 2, Pl. Ix.
One is disposed to think that these are perhaps different species.
Fig. 2 of Pl. lx gives in front view a section of the paranepionic
volution with a distinct but narrow impressed zone marked on the
dorsum. This whorl hasa nephritic outline and is very different
from the subtrigonal outline of a whorl with convex dorsum referred
to above, which belongs to an obviously later stage of growth in a
larger species.

Having examined these specimens in Prof. Hall’s collection some
years since, I find in my notes the statement that ‘‘ no depression
(meaning the dorsal furrow) occurs in the centre of any of these
shells until the whorls touch, which they do at a late stage of
growth.’’ ‘The form changes from a depressed oval in the metane-
pionic to nephritic more rapidly than in Nephriticeras subliratum
and the transverse diameters increase faster. The longitudinal
ridges are smaller and less prominent than in Wephriticeras iratum.

The sutures in the young have ventral and dorsal saddles and
only in later stages these are replaced on the dorsum and venter by

534

bread, shallow lobes, but in some specimens the sutures are nearly
straight or may retain slight saddles on the venter.
The siphuncle is extracentrodorsan.

NEPHRITICERAS CAVUM.
NAumInUSKCAuUsnCho/. Vs Vauy,. Pt. 115 Plo evi):

The fragment of the neanic stage, figured by Hall, has the
nephritic whorl and similar sutures to the full grown of Wephritice-
ras bucinum, but the dorsal lobes are deeper perhaps and more
V-shaped. The septa are different in being much more widely sep-
arated, but are otherwise similar to those of the later stages in
Nephriticeras bucinum. I find in my notes that the impressed
zone occurs after the dorsal lobes are formed and at an earlier stage
than in ducenum.

Siphuncle is unknown.

NEPHRITICERAS ACREUM.
NAUTILUS ACR&US, Hall (Pal. WV. Y., v, Suppl., Pl. cix).

The fragment of the neanic stage, figured by Hall, shows the
nephritic outline impressed zone and ridges similar to those of the
older stages of Wephriticeras bucinum occurring at an earlier stage
than they do in Wephriticeras cavum.*

NEPHRITICERAS MAGISTER.
NAUTILUS MAGISTER, Hall (Pal. WV. Y., v, Pls. lxii, cvii, cviil).

The large fossils of this species which I have examined have not
afforded me any information with regard to the young, but the
nephritic form of the whorl, the impressed zone and large beaded
siphuncle dorsad of the centre show that the species belongs in the
same genus with LVephriticeras bucinum.

This species may have either slight ventral lobes or saddles on
the venter.

NEPHRITICERAS MAXIMUM.
NavTILUs MAxIMuS, Hall (Pad. WV. Y., v, Pt. ii, Pls. Ixxiii, xxiv).

This is like Wephriticeras magister, known only through large
fossils, but the young of the specimen figured by Hall on PI. Ixxiii

*T regret very much that in finishing this paper I have had no opportunity to revisit
Prof. Hall’s collection and study again his old and new materials. It is not improbable
that his fine series of Nephriticeran species may show that the impressed zone was pres-
ent asa dorsal furrow in the paranepionic substage of some of the more inyolute and
tachygenic shells.

ee CU

535

has, according to my notes, and when seen from the side, a general
resemblance to Wephriticeras oriens.

The sutures and position of the siphuncle and form of whorl
places it in this genus.

NEPHRITICERAS ORIENS.
NAUEILUS ORIENS, Hall (Pav. V., v, Pt. 1, Pl lx, and Suppl,
Ble cv).

This species is obviously closely allied to Wephriticeras magtster
and maximum. ‘The shell shows coarse longitudinal ridges and stri-
ations of growth as in other species of this genus, and the sutures
and position and structure of siphuncle also justify its associations
with these species in the same genus.

NEPHRITICERAS INELEGANS.
GYROCERAS (NAUT.) INELEGANS, Meek (Pad. Ohio, 1, Pl. xxi).

This form is closely allied to magzster and is probably a species
of this genus.

Ludoceratide.

This family was described in my Genera of Fossil Cephalo-
pods, and again in ‘‘ Carboniferous Cephalopods,’’ Fourth Annual
heop. Geol. Surv. Texas, p. A465.

The genera are of interest in this paper because of the absence
of the impressed zone in the more generalized open-whorled Eda-
phoceras, its appearance as a contact furrow in Endolobus and its
appearance as a dorsal furrow in Potoceras dubium. I have placed
this last form in this family with much reservation. The young
have characteristics similar to those of Hudolobus Avonensis, but
the development is more advanced and decidedly tachygenic.

The absence of a dorsal furrow in the nepionic whorl of so highly
specialized and so involute a shell as Ephippioceras is upon the
whole rather remarkable and requires confirmation with a better
preparation than the one at my command. The highly digonal
form of the young has induced me to transfer this genus from the
Apsidoceratide, under which it appeared in my Gevera of Fossil
Cephalopods, to this family.

Ledaphoceras.

This genus was first described by the author in Genera of Fos-
stl Cephalopods,* the type being a large Carboniferous species

* Proc. Bost. Soc. Nat. Hist., xxii, 1888, p. 288,

—

536

eight inches in diameter described by Meek and Worthen* and
fully figured. by them.» These figures reproduced on —PEy vue
Fig. 22-24, show the generic differences of this species and the
forms on the same plate, which are good examples of the genus
Estonioceras. Edaphoceras differs in having non-involute whorls
without an impressed zone and a more completely digonal outline
in transverse section of the full-grown volution.

The sutures have ventral lobes, saddles at the lateral angles and
dorsal lobes with slight median saddles if the figure is correct.

The siphuncle is centren in the adult.

Notwithstanding the close resemblance of the type species to
Listonioceras ariense as figured by Schroder, I doubt whether this
Carboniferous type has direct genetic connection with Estonioceras
of the Silurian. Until the young,are known it will be impracti-
cable to settle this question, but at present the close-coiled shells
of Edaphoceras niotense, as described by Meek and Worthen, and
of Edaphoceras (Vaut.) hesperis, Eichwald,+ both with siphuncles.
nearly or exactly centren and neither having an impressed zone
and the peculiar form described by Foordt as Solenocheilus cale-
donicus which is similar but has a slight impressed zone, all point
to a separate phylum from that of Estonioceras.

I do not, however, wish to imply that they did not arise from the
same common origin, possibly some form of Eudoceras, but simply

that Edaphoceras does not appear to be a direct descendant of

Estonioceras.
Lindolobus.

This. genus was first described in Genera of Fossil Cephalopods,
and subsequently in the Second and Fourth Ann. Rept. Geol. Surv.
Of LeExas.

Unluckily I have never been able to study the young of the type
Endolobus spectabilis of Meek and it may be that none of the spe-
cies referred to this genus really belong to it.

EXNDOLOBUS AVONENSIS.
NAUTILUS AVONENSIS, Dawson (Geol. of Acadia, p. 311). PI. viii,
Figs. 36-39.
Loc., Joggins, Nova Scotia.
The ananepionic stage of this species, Fig. 38, Pl. vili, has a tri-
gonal shape and the cicatrix, although necessarily exaggerated in

(C20, (Of JMB 7, Jel, saise,
+} Leth Rossica, Pl. xlv, Fig. 7.
t Cat. Foss. Ceph., ii, p. 172, Fig. 30.

q
:

537

the figure, is approximately given. This form is like that of the
arcuate forms of genus Tripteroceras in their ephebic stage. The
shell was smooth. A paranepionic septum is shown below and in
the specimen (Figs. 36-37) a still younger septum was developed
after this drawing was made. ‘These have ventral saddles, very
faint lateral lobes, and minute shallow dorsal lobes, resembling in
shape those of the older stages.

As shown in these drawings, the dorsum of the nepionic stage,
which ends with the section just below the apex, is rounded and
the impressed zone is a contact furrow beginning in the ananeanic
substage only after the whorls touch. ‘This zone deepens rapidly,
but is never very broad or deep.

The side view shows‘the cyrtoceran form of the metanepionic
substage and the large size of the umbilical perforation, which is
given by a dotted line.

The siphuncle is nearly subventran in the paranepionic substage,
but it does not increase proportionately in size and becomes cen-
troventran in the neanic septum as shown above the apex, and
ventrocentren in the ephebic stage.

The lateral angles are more acute and the form more perfectly
digonal in the neanic and early ephebic stage than in the paranepi-
onic or gerontic stages.

The specimen figured is in Museum of Comparative Zodlogy.

A young specimen of this species from Windsor, N. S., in the
Museum at Ottawa, shows the living chamber of the early ephebic
stage or paraneanic substage at the end of the second whorl. ‘This
is not quite one-half of a volution in length and has a deep, rather
narrow hyponomic sinus with large median lateral crests and deep
sinuses near the lines of involution.

Lophoceras.

This genus, described in Fourth Annual Report Geological Sur-
vey of Texas, has a very slight impressed zone in some species and
it is clearly dependent upon the contact of the whorls.

Potoceras.*

POTOCERAS DUBIUM, n. sp. Pl. x, Figs. 15—22.
WocsG):
The nepionic stage is shown enlarged in Figs. 16-18, Pl. x, and

* I]étog, drinking.

538

this is in a general way very similar to that of Azdolobus avonense
during the ana- and metanepionic substage, but in the paranepionic
a dorsal furrow appears which is not present in Endolobus at the
same early age. The longitudinal ridges appear also in this sub-
stage, the previous substages being smooth. ‘The umbilical perfo-
ration, Fig. 15, shows the very abrupt bend which takes place at
the end of the metanepionic substage just before the dorsal furrow
appears. This furrow is broad and well defined and cannot be
said to be correlative with a nephritic outline. The section of the
whorl at this age, Fig. 17, still retains in some measure the tri-
gonal outline of the ana- and metanepionic substages. It has be-
come temnocheilan or trapezoidal through the great broadening of
the abdomen, but if no furrow were present it would have to be
described as a modified subtrigonal (see Fig. 17 which gives the
form correctly). It is in no sense nephritic, although obviously
transitional and standing between the preceding digonal and suc-
ceeding nephritic outline shown in the ananeanic substage. ‘This
substage occupies the last quarter of the first whorl. ‘The broaden-
ing out of the furrow, which also increases in depth, although the
curvature remains constant, can be observed in this same substage
while the volution is still free, also the advent of a purely nephritic
outline and a minute annular lobe in the middle of the dorsal lobe.
The siphuncle shifts somewhat nearer the centre.

Contact takes place on the ventral side of the ananepionic volu-
tion, but the apical end is not free. ‘The dorsal sutures in conse-
quence of the annular lobe have a much spread-out or flattened V
shape like those of Exdolobus avonensis at a later stage and in the
contact furrow (see Fig. 37, Pl. viii).

The form of the adult also resembles that species. The sutures
have ventral saddles, lateral lobes and dorsal lobes in the ephebic
stage and the outline is nephritic. ‘The annular lobe does not in-
crease much in size with advancing age and seems to disappear in
this stage. Although the locality of this specimen is unknown, the
probable age is Devonian.

Fearing to trust my own conclusions in this instance, and having
one valve of a Brachiopod which was detached from the specimen
described above, I sent the latter to Mr. Charles Schuchert in the
National Museum, Washington, for determination. This gentle-
man very kindly gave me the benefit of his great special knowledge
of this group and returned it to me with some other specimens of a

539

species of Martinia from the Iberger Kalk, Upper Devonian of Grund,
Germany, with which he considered the species to be closely related.

Liphippioceras.

EPHIPPIOCERAS FERRATUM, Hyatt.
NAUTILUS FERRATUM, Owen (Geol. Kentucky, ui, Pl. x, Fig. 2).
Figs. 23-26, Pl. x, enlarged 5 diameters.

The nepionic stage is given in Fig. 23, from the side showing the
lateral longitudinal ridges of the paranepionic and part of the meta-
nepionic substage. These ridges are more acute on the venter and
wider apart and blunter on the sides. The form in section of the
metanepionic is digonal, and that of the paranepionic substage has
amore elevated venter and flatter dorsum. ‘There was no dorsal
furrow in the paranepionic substage, so far as could be ascertained,
but the condition of the specimen left this fact open to doubt.

It is interesting to note that the form and characters of the young
of this very aberrant form seem to indicate affinity with the Eudo-
ceratide. |

The peculiar ridge-like mesal division of the septa, which corre-
late with the prominent ventral and dorsal saddles of this genus, are .
not present in the nepionic stage. ‘The imperfect condition of this
fossil did not enable me to make detailed observations upon the
young farther than in the stage figured.

Trigonoceratide.

This family includes the close-coiled nautihan forms Coelonau-
tilus, Stroboceras, Apheleceras, Subclymenia and Diorugoceras.
The young of all of these genera, except possibly Diorugoceras,
which I have not seen and which is also very involute, have a simi-
lar history. They are rounded in the nepionic stage and have an
impressed zone only late in life, if they have it at all. Usually the
form is similar to that given in Figs. 29 and 30, Pl. x, of Apheleceras
mutabile (sp. D’Orb.), Hyatt.

This species shows in the young that the genus has been but
recently derived from an arcuate type. The apex in the ananepi-
onic and part of the metanepionic substage is free and the whorls
barely touch at first. ‘he corrugated shell of the nepionic and
neanic stages show also the same primitive characters and the resem-
blances of these younger stages to the loosely coiled gyroceran form

=". tea a.
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—— == aris

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hull

540

of Trigonoceras are closely parallel. Ifthe adults were not known
they would be referred necessarily to that genus.

The group is of importance in the history of the impressed zone
since it shows in its most specialized and highly involute members
that a contact furrow may appear even in a form of whorl that has
naturally a gibbous dorsum and concave abdomen.

Fig. 2, Pl. xu, of Drorugoceras (Vaut.) planidorsatum (sp. Port-
lock), Hyatt shows the peculiar character of the contact furrow in
these forms when it occurs.

It is probable that the early neanic stage has a gibbous dorsum
fitting into the hollow abdomen and that the involution is acquired
rapidly in the later substages of the neanic stage, but not having
seen specimens of the young I cannot state this as a fact.

Triboloceratide.

The figures of Zhoracoceras puzosianum of Pl. ix show a shell
which in form isa slightly depressed oval and both in this respect
and in the fluted ornamentation approximates to the nepionic stage
of Zhoracoceras canaliculatum and other subspinous forms of the
same genus. ‘This last species has aiso a similar form, and by com-

- paring this with the young of the loosely coiled, gyroceran forms

on the same plate, Figs. 14 and 15 of Triboloceras, it will be seen
how closely they resemble them. Triboloceras in turn grades into
the nautilian form of the same family, Vestinautilus Kontnckz,
Figs. 5-13. The figures show the development of this form
through a nepionic stage which is at first similar to Z. puzostanum,

- then becomes similar in ornamentation to Z. canaliculatum and

then passing into the neanic stage these primitive characters are
replaced by the peculiar acquired ornamentation and whorls having
the hollow, central, ventral and lateral ventral zones of this family
and smooth, gibbous, umbilical zones with broad, fluted, lateral
faces. The subspinous ornamentation persists in this form on the
ridges throughout the ephebic stage. In the gerontic stage these
progressive characters disappear and with them the fluted faces and
zones also tend to extinction and in the paragerontic stage do actu-
ally give way to a rounded form without salient angles. This last
is not figured, but the tendencies towards extinction of the orna-
ments, etc., may be seen in the anagerontic substage delineated in
Figs. 5 and 6.

541

Vestinautilus Konincki leads into such forms as Vestinautilus pin-
guts, Figs. 16-19, which has the ridged characters, etc., confined
to the nepionic Stage, which is somewhat abbreviated. The sub-
spinous characteristics are also crowded back and replaced earlier
by gerontic modifications similar to those which occur only in the
senile stage of V. Koninckt. ‘Thus these degenerative changes are
shown to occur in what is properly the parephebic substage of V.
pinguis. Yhe history of the impressed zone accords with that of
the other characters and may be seen in the figures to have been
introduced as an acquired character dependent upon close coiling.
It is not present in Triboloceras nor in the nepionic or ananeanic
substages of the nautilian forms. It appears only after contact, and
in other words is a contact furrow and its characteristics are deter-
mined wholly by the moulding of the dorsum on the peculiar ven-
tral surfaces which are encountered during growth.

COLOCERAS GLOBATUM.
WaGminwsS cLoBpatus, De Koninck (Cale, Carxbon.; Pl.-xxxi)):

Plax, Pigs. 1-14.

The development of this species was partially described in my
‘* Carboniferous Cephalopods,’’ second paper, Fourth Ann. Rept.
Geol. Surv. Texas, p. 447-451, but no figures were given and the
genus Coloceras was then erroneously referred to the same genetic
series as Coelogasteroceras. More extended study of both of these
forms has shown me that the latter belongs to a distinct series.
Coloceras globatum has the peculiar lateral flutes and characteristics
of the Triboloceratide in the nepionic and neanic stages, and the
hollow ventral zone of the paranepionic substage, which led me to
suppose that it belonged to the same genetic series as Coelogastero-
ceras, may be accounted for equally well when C. g/obatum is referred
to the Triboloceratide. Figs. 5 and 6, Pl. ix, of Vestinautilus Kon-
zuckt show that the broad, hollow, ventral zone of the ephebic,
stage becomes narrow and the abdomen is gibbous on either side of
it in the anagerontic substage of this form.

The similarity of the ventral hollow zone of the young of C.
globatum may be accounted for, if it is supposed to be an accele-
rated phylogerontic character. ‘The only difficulty in the way of
this assumption is the preéxistence of the lateral flutes in the neanic
stage. I have, however, frequently seen similar examples of the
unequal acceleration of characters and this is probably another of

542

this class. At any rate the ornamentation, form and lateral flutes
all plainly point to the same genetic stock as Koninickioceras,
whereas in Coelogasteroceras* there are no lateral flutes or faces and
a very distinct and more primitive shell, especially in the nepionic
stage, as may be seen in the section, Fig. 33 of Pl. x.

The figures of Coloceras globatum on Pl. x give the history of
the dorsal furrow. ‘They show also that considerable variation .
exists in the form of the ananepionic substage and it may be that
Figs. 1o-12 belong to a different species from those that show a
flatter and more trigonal outline in the early stages. The umbilical
perforation, however, remains about the same in all the specimens.
This is of good size and there is no abrupt curve at the beginning
of the paranepionic substage which would account for the genesis
of the nepionic furrow in the dorsum of the specimen in Figs.
to-12, which is perfect in its proportions and markings. In the
specimens given, 1 and 2 and 7, there is a more abrupt curve
at this point and more sudden appearance of this zone, but the pas-
sage of the form into the nephritic outline is gradual even in these
specimens. ‘The first suture in Fig. ro obviously belongs to the
first living chamber of the metanepionic substage, while the second
and third are paranepionic, although the second is still within the
limits of the metanepionic volution, z. ¢., built in that part before
the dorsal furrow appeared. ‘The third suture is indented by the
furrow. ‘The ananepionic substage is at first smooth except for
horizontal and inconspicuous growth strize, then becomes longitudi-
nally ridged, Fig. 7.

The changes of form in this substage, which can be divided into
three parts, are well marked in these drawings. ‘There is first the
age of the cicatrix with a form which is a very elongated trigonal
and quite distinct in every way from the next; then the age in
which the broad trigonal form appears, but the surface of the shell
is still smooth, and lastly the digonal, longitudinally ridged age
passing into the metanepionic and often bounded by a slight con-
striction. ‘The metanepionic, Fig. 6, has an elliptical form with
longitudinal ridges intersected by the edges of the growth bands.
In this the digonal outline tends to disappear, although sometimes
it is maintained more or less by the early appearance of the promi-
nent, broad lateral ridge. This ridge, however, usually appears.
later, as shown in section, Fig. 3, and is characteristic of the snecies.

*T have provisionally referred Coelogasteroceras to the family of the Hercoceratide.

543

The dorsum becomes flattened in the latter part of the metane-
pionic substage and other transitions to the nephritic outline are
obvious in the gradual spreading out of the transverse diameters.

The dorsal furrow appears as described above sometimes when
the bend is abrupt and sometimes when it is gradual; in other
words, it is obviously not correlated with the size or shape of the
umbilical perforation nor dependent upon the curvature of the
volution. It appears always in the same place at or about the third
suture and when the nephritic outline is assumed at the beginning
of the paranepionic substage. But it will be observed in section
Fig. 4, that the outline, which has been very carefully drawn, is
not remarkable for being very broad in proportion, nor does the
study of this specimen give any grounds for supposing that the dor-
sal furrow could be considered a necessary condition of the. mode
of growth. The curvature is about the same during the remainder
of the first volution, but the zone broadens with growth and devel-
opment of the nephritic outline, as may be seen in Figs. 2, 11, 13,
14 and Sec. 3. This zone has longitudinal ridges, but these are
much finer than those of the sides and abdomen.

The neanic stage begins when the longitudinal ridges and cen-
taleezone! disappear on the venter. Phe ridges persist on) the
dorsal side, but disappear in what is probably the paraneanic sub-
stage, leaving the heavy lateral ridge and its accompanying flutes.
The neanic stage is therefore phyloanagerontic.

The ephebic stage is perfectly smooth and phyloparagerontic in
aspect.

The action of tachygenesis upon degenerative characters is thus
clearly apparent throughout the neanic and ephebic stages in this
interesting species. ‘This fact is entirely in accord with the princi-
ples of Bioplastology as explained above with regard to the action
of this law upon retrogressive characters.*

Rineceratide.

The figures of Pl. ix show that this family has characteristics
closely resembling the arcuate forms of Thoracoceras which are
repeated in the ananepionic substage. Rineceras, however, never
has a hollow ventral central zone but remains gibbous on the abdo-
men throughout life.

This characteristic also serves to distinguish the nautilian mem-

* See pp. 873, 415, 417.

—=—

544

bers of the same family when compared with the closely allied
forms of the Triboloceratidz, all of which have a hollow central
ventral zone at some stage.

Lispoceras sulciferum, Fig. 24, shows the nepionic stage and
ananeanic substage with form and characteristics approximately
repeating those of Rineceras, and these resemblances are consider-
ably closer than the figures would lead one to suppose. I did not
notice until too late to replace them that these figures were not so
complete as I had thought them to be.

The greatest development of the impressed zone in this family
occurs in the compressed lenticular form of Phacoceras, Figs. 26,
27, and although Fig. 27 is not entirely satisfactory in the young,
as given by DeKoninck, it seems to demonstrate together with his
description that the nepionic stage had a section which would place
it either in this family or in some other with fluted whorls and a
gibbous abdomen. None of these genera have any species so far
known which have a dorsal furrow, the impressed zone being
strictly a contact furrow as in the Triboloceratide.

The genus Pselioceras of the Dyas is perhaps a member of this
family, but I have strong doubts whether it does not belong to an
independent family phylum in spite of the general similarity to other
genera of Rineceratidz. It is of some interest here because the
umbilical perforation is very large, and it adds one more illustration
to the many already noticed of shells having primitive forms and
primitive modes of coiling in the young, which have the impress 2
zone only in the shape of a contact furrow. ‘There is a slight con-
tact furrow generated after the whorls touch in Psehoceras chhioneum,
sp. Waagen.

Thrincoceras.

I mention this genus of the Rineceratidz especially because I
wish to correct here a curious mistake that has inadvertently oc-
curred in my drawing of Zhrincoceras kentuckiense, p. 432, Hourth
Annual Report of the Geological Survey of Texas. ‘The section
Fig. 13 shows a furrow on the free dorsum of the nepionic volution.
A careful reéxamination shows that this does not exist. There isa
mark due to erosion which occurs at the point previously examined,
but this is not present on other parts of the same volution.

The history of the impressed zone in this species does not differ
from that of the same character in other genera of the same family

545

of which the best known form is Desectoceras (LVaut.) discors, sp.
McCoy. All species have large umbilical perforations, the nepi-
onic stage has no dorsal furrow and there is only a contact furrow
generated in later stages.

Koninckiocerauide. .

The genera Koninckioceras and Domatoceras have been exam-
ined and these have no impressed zone until after contact.

Solenccheihde.

In Aipoceras, the arcuate form of this family, there is no impressed
zone, and in Oncodoceras, some of which last are gyroceran, no
impressed zone has been observed. In Asymptoceras, although
the forms are all close coiled, this zone is only faintly indicated in
some species, and when it is better definea it occurs late in the
ontogeny, and then only as a contact furrow. The same remarks
apply also to species of Solenocheilus. In the description of Cran-
oceras this genus was referred to as comparable with Cranoceras
depressum in the peculiar configuration of the dorsum.

There are however, differences which show that this resemblance
is not very close or significant. In Solenochetlus Springeri, for ex-
ample, the gibbous dorsum and latero-dorsal flutes and heavy ridges
on the umbilical shoulders appear before the contact furrow, but
‘this comes into existence as soon as the whorls touch and modifies
the dorsum in proportion to the amount of involution. The latero+
dorsal flutes also are dependant upon the extent and size of the
ridges or keels on umbilical shoulders and are not as in Cranoceras
primitive inflections of the dorsal surface.

Incerta Sedes.

The new genera Peripetoceras of the (Permian) Dyas and Syrin-
goceras of the Trias together with Mojsisovics genus Pleuronautilus
of the Trias have been given together here as a matter of conve-
nience, although it is by no means certain that they belong to the
same family.

9, - *k
PCKIPELOCET AS. Ny Si.
This genus has been instituted for a single species described
below, which cannot be placed with any other species.

Ilepizet7s, clasped around.

546

PERIPETOCERAS FRIESLEBENI, Geinitz (Leonh. et Bronn, /ahzé.,
19415 PS xa, Pier) ais sto Plexi

Loc., Tunstall Hill, England, Dyas.

This shell has a metanepionic substage with a subangular abdo-
men and siphuncle propiodorsan. The umbilical perforation is
small and a dorsal furrow appears in the paranepionic substage.
The apex, as shown in Fig. 1, Pl. xi, is narrow and compressed ;
the metanepionic, Figs. 2 and 3, broadens on the dorsum but
remains rounded; the dorsal furrow at its first appearance, just
beyond the gyroceran bend in the paranepionic, is deeper, as shown
in Fig. 3, than it is subsequently when opposite the largest diam-
eter of the umbilical perforation, Fig. 2, and the whorl changes at
the same time from digonal to trapezoidal or temnocheilan-like.
The siphuncle, however, remains propiodorsan.

The neanic substage has a nephritic outlne and in the ephebic
stage the volution becomes subquadrate with a flattened abdomen.

The living chamber is somewhat over one-fourth of a volution in
length, with broad, shallow, hyponomic sinus, broad, low, lateral
crests and sinuses on the umbilical zones.

The siphuncle continues to be propiodorsan in position.

The sutures have broad, ventral and dorsal lobes and lateral
lobes. There are annular lobes in older stages according to
Geinitz. I could find none in the early ephebic stage of the single
specimen from Tunstall Hill, which showed a perfect septum, but
they may be present in later-substages.

Syringoceras,* Nn. g.

This genus has been framed for Triassic species like the type,
Syringoceras granulosostriatus, which have a tubular, nepionic volu-
tion with the siphuncle subventran. The early nepionic shell is
also ornamented with very closely set transverse ridges, but it has
no longitudinal ridges until a comparatively late stage. This nepi-
onic ornamentation is like that of the genus Hercoceras at the same
age. The impressed zone is present only after contact and is not deep.

The genus includes the group of Wawtilus Barrandet of Mojsiso-
vics, the equivalent of Wautilus linearis, Laube, and S. (LVaut.)
evolutum, sp. Mojsisovics.

Syringoceras (Maut.) granulosostriatus and linearis, stated by

yy =
mUOlYS, a tube.

DAT

Mojsisovics to be the same as Acts Munst, have been figured on
Pl. xi, Figs. 4-8, to show that the impressed zone is present only
after contact in these Triassic species, which have good-sized um-
bilical perforations and a cylindrical first whorl.

Pleuronautilus.

This genus was described by Mojsisovics to include a number of
costated nautilian shells of the Trias, having in one section of this
genus shells with the nepionic stage marked by transverse bands
and in the species copied from Mojsisovics, Pl. xii, Fig. 3, the um-
bilical perforation is very large.

In correlation with this the apex is free and the generic char-
acters appear late in the neanic stage.

This shell appears at first to be an extraordinary exception to
the rule that generalized forms, with large umbilical perforations,
slow growth of the dorso-ventral diameters and more or less cylin-
drical first volutions, always have a gibbous dorsum in the nepionic
stage. Mojsisovics’ figure, copied here, Pl. xii, Figs. 4 and 5, and
in his description, has a dorsal furrow in the paranepionic substage.
In order to confirm or refute such an important observation I wrote
a letter of inquiry to Dr. Edmund Mojsisovics von Mojsvar and
have received in return the following courteous reply, which shows
clearly that the species cannot be quoted as exceptional in the
opinion of this eminent authority. I quote below both my trans-
lation and the original letter : |

Die Impression auf der intern: Seite des (auf Taf. iv, Fig. 3,
meiner Hallstatter Cephalopoden) zu Péeuronautilis superbus
gestellten Fragmenten kann nicht durch eine Verdriickung
erklart werden, sondern nun als eine thatsadchlich der Schale
sukommende Ejigenschaft betrachtet werden. Ich halte es
aber jetzt fiir wahrscheinlich, dass dieses Fragment trotz seiner
grossen Uebereinstimmung mit dem ersten Umgange von Plewro-
nautilus superbus nicht zu dieser Art, sondern zu einer andern neuen
Art gestellt und nicht als erster Umgang betrachtet werden darf.
Ich neige vielmehr jetzt der Ansicht zu, dass die Impression auf der
concaven Seite von weggebrochenen innern Umgangen herriihren
diirfte.”’

‘‘‘The impression upon the inner side of the fragment (PI. iv,
Fig. 3 @) of my Hallstatter Cephalopods), referred to Pleuronautilus
superbus, cannot be explained as due to compression, but must be

i
ni

SS S465 SS SS SS

i
ti
i

548

regarded as an actual characteristic belonging to the shell. I now,
however, consider it probable that this fragment, in spite of its
great similarity to the first volution of Plewronautilus superbus,
should not be placed with this species, nor regarded as a first
whorl, but as another new species. I incline much more at present
to the view that the impression (the author’s dorsal furrow) upon
the concave side might have originated from a whorl now broken
away.”’

Nautihde.

Without attempting at present to limit the chronologic distribu-
tion of this family, it is necessary in this connection to make some
remarks with reference to my observations on the general affinities
of the genera described in this paper, which are all Mesozoic.

Digonioceras is obviously the most primitive type yet found in
the Mesozoic, and the most primitive or most generalized species is
Digonioceras excavatum, as figured by D’Orbigny. The broad first
whorl of this species is persistent in adults and so also is the slight
amount of the involution and the discoidal character of the coil.
The digonal and approximately nephritic outline of the young in
the paranepionic is succeeded by a subtrigonal outline in the adult.

This is substantially paralleled by the development of the species
of Cenoceras, Cymatoceras, Eutrephoceras and Nautilus.

All of these are apt in their nepionic substages to bring out the
nephritic, and in the paranepionic the subtrigonal form of whorl
with a broad dorsum, converging lateral zones and more or less
subacute or elevated venter. This occurs even when the nephritic
outline or some other is assumed in the later stages.

There is, therefore, in all of these genera some direct reference
to the form of the ephebic stage of Digonioceras.

This fact is of great importance in connection with the assump-
tion made in this memoir, that after the Trias the survivors of the
Nautiloids are all nautilian shells and bear the marks of their descent
from close-coiled ancestors and are not directly connectible with
straight or arcuate types as the nautilian shells of the Paleozoic
often are.

Digonioceras, n. g.

Digonioceras excavatum, was described in my Genera of Fossil
Cephalopods, as a member of the genus Endolobus surviving in the

o49

Jura, but the observations on the young given in this paper show
that these forms are not so closely related as I then supposed.

The species differ from any species of Endolobus in the form of
the young and in having the annular lobe and dorsal furrow devel-
oped earlier and in not having any large nodular tubercles. The
form of the whorl in section is, however, similiar in adults of Digo-
nioceras and also the aperture. The umbilical perforation is larger
than usual in other allied genera of the same period and the invo-
lution is apt to be less in the older substages, leaving the umbilici
open.

D’Orbigny’s figure copied on PI. xi, Figs. 13, 14, shows that a
dorsal furrow was present in the paranepionic substage* and there
is a similar furrow at the same age in Digondtoceras rotundum, the
type of this genus.

DIGONIOCERAS, sp. (?)

iihesspecies: from Balingen, Middle Lias, Bigs. 19=21, Pl. xi,
shows a form similar to Dugonioceras excavatum. ‘The metanepi-
onic outline in this has no dorsal furrow, as shown in the corrected
section, Fig. 21, but the suture has an annular lobe. The dorsal
furrow begins on the dorsum at the second septum of this fragment,
which was probably the fourth or fifth of the complete shell.

DIGONIOCERAS ROTUNDUM, DN. s.

This has affinities with excavatus, but the large fine young speci-
men, Figs. 6-11, Pl. xii, show that the shell was specifically distinct.
It is obviously from the Oolite, but the locality is not known.
Figs. 6 and 7 show the neanic stage and Fig. 8 the nepionic. ‘The
involution is not greater than it is in D. excavatim and the form
is very similar in the paranepionic. ‘The whorl, however, is really
nephritic in the ananeanic substage, and has already assumed an
outline in section quite distinct from that of Dzgonioceras exca-
vatum. Vhis last-named species retains throughout life, if cor-
rectly figured by D’Orbigny, the same form as the paranepionic
volution of D. rotundum shown in Fig. 8. The outer whorl in
Fig. 7 should be a little broader in proportion and more com-
pletely nephritic. There is a slight trace or linear depression
near the median line on the abdomen, but this may be an individual
character, and not important to the diagnosis of the species.

* This species, at first referred to the Lias, was subsequently in this author’s Prodrome
placed in the Inferior Oolite.

\
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——

=>:
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500

Cenoceras.

This genus was described in my Genera of Fossil Cephalopods to
include a number of the Nautili of the Trias and Jura which should
be separated. I propose now to limit the genus to those forms
which, like Cenoceras intermedium, as figured by D’Orbigny, have
trigonal ananepionic substages with subquadragonal metanepionic
volutions and a dorsal furrow in the nepionic stage. The ephebic
stage is also more or less quadragonal, with the dorso-ventral longer
than the transverse diameters and the lateral zones convergent.
The umbilical shoulders are prominent and the umbilical zones
broad and at right angles to the plane of the coil. The sutures
have ventral and dorsal saddles only in the first and second septa.
The annular lobe and dorsal lobe are apt to develop very early, in
some species certainly in the third septum. ‘The siphuncle is near
the centre in the first septum and subsequently varies from dorsad
to ventrad of centre, but is never near either-the venter or the dor-
sum. ‘The ornamentation has both longitudinal ridges and trans-
verse bands, but the former may or may not be present in adults.

CENOCERAS INTERMEDIUM.
NAUTILUS INTERMEDIUS, Sow. (?) (Jin. Conch., Pl. 125).
NAUTILUS INTERMEDIUS, D’Orb. (Zerr. Jurass., Pl. 27).
Loc., Balingen, Middle Lias.
Lelbeo Si, NEWS, Ti ato,

I feel considerable doubt whether Figs. 17 and 18 are really the
young of C. zztermedius and the name is taken solely on D’Orbigny’s
authority. It has, however, a peculiar compressed form and obvi-
ously a large umbilical perforation in the ananepionic and a sub-
quadrate outline in the metanepionic, with siphuncle ventrocentren
as in most specimens of this species. ‘The ana- and metanepionic
substages have no dorsal furrow.

Figs. 15 and 16 show the paranepionic and ananeanic substage of
a specimen with the siphuncle dorsocentren, evidently an unusual
position, since several other specimens of nearly the same age have
it ventrocentren and in adults it is still nearer the venter. The
whorl is tetragonal in the paranepionic, with well-marked ventral,
lateral and dorsal lobes in the sutures and annular lobes. The dor-
sal furrow is also well developed and the umbilical perforation,
restored with a dotted line in Fig. 15, must have been quite large.

551

There seems to have been no close bending of this whorl sufficient
to cause the formation of a dorsal furrow in this shell.

The ananeanic volution given in section, Fig. 16, is too rounded,
the lateral zones in this specimen are quite flat and convergent as
in adults, and the abdomen is also flattened. ‘The zone of contact
is marked bya shaded space in Fig. 16 and is deep and well
marked off from the dorsal furrow above in the same figure.

CENOCERAS LINEATUM.
NAUTILUS LINEATUS, Sow. (AZim. Conch., Pl. 141).
NAUMLUS EINEATUS, D’Orb.<(7e77. Jurass:, Pl. xxxi).
oe. Bayeux, Ini. Oolite:
Pl. xi, Figs. 22-27 and 28-31.

The ananepionic and metanepionic substages and part of the
paranepionic are shown in Figs. 24-27, and also the cicatrix and
general form and shell ornaments, which last are continued in the
adults of several species of this genus.

The umbilical perforation is small and comma-like, contact tak-
ing place on the dorsum of the ananepionic volution. A well-
developed dorsal furrow is present in the paranepionic but not in
Me wmMetanepiomic, as shown in’ Figs. 26, 22> and 23, There are
annular lobes in the nepionic stage, but these disappear in the para-
neanic substage.

Figs. 28-31 are so similar to the early stage of this species that I
have referred them to it, although this was identified by Quenstedt
as WVautilus aratus, Schlot.

CENOCERAS ARATUM.
NAUTILUS ARATUS, Schlot.
ioc. suapia, Middle lias.

i hios: 22=35

The specimen shown in Figs. 32-35 was figured first in my Z7-
bryology of Fossil Cephalopods, is one of Saemann’s originals and
although quite perfect in some respects has no shell.

It is a cast in iron of the interior and shows the characteristics
figured very distinctly. The early beginning of the annular lobe
in the third suture and that of the dorsal furrow in the metanepi-
onic between the third and fourth sutures is very interesting in view
of the fact that this shell had a comparatively large umbilical per-

552

foration and the curvature of the first whorl is so uniform that its
early origin cannot reasonably be attributed to that asacause. The
furrow deepens immediately and affects the outline of the fourth
suture. A slight dorsal lobe appears in the suture of the third
septum at the sarne time with the annular lobe, and is better
given in Fig. 33 than in Fig. 34. The flattening of the dorsum
is apparent in the second suture, and, so far as I could see after
repeated observations, my former figure in Limdryology of Cephalo-
pods was erroneous in placing an annular lobe in this suture. ‘This
species shows highly accelerated development in all of its charac-
teristics and this acceleration is obviously genetic and independent
of the size of the umbilical perforation, which is very large con-_
sidering the fact that it is a Jurassic species.

I have also examined another less perfect specimen of this species
having a considerable part of the shell preserved, but the first and
second apical chambers were lost. The external shell of the um-
bilical zones had longitudinal ridges as well as external parts of the
lateral zones and the venter in the paranepionic substage. ‘The
form of the whorl in section near the ends of the paranepionic sub-
stage remains about the same, except that the venter becomes
slightly broader and flatter. The umbilical perforation is not quite
so large and the gyroceran bend is more abrupt in this specimen,
but otherwise it is exactly similar to the first described specimen.
It is in Museum of Boston Society of Natural History.

CENOCERAS CLAUSUM.

NAUTILUs CLAusus, D’ Orb. (Lerr. Jurass., Pl. xxxiii).
oes, st. Vigor, near Bayeux int, Oolite:
JONG Suis LORS Siti

This species has a small umbilical perforation. ‘The form and
general aspect are very similar to those of other compressed shells
of this genus, but the shell in the paranepionic substage has peculi-
arly well-marked and broad growth bands with interrupted longitu-
dinal ridges. ‘The ana- and metanepionic volutions are shown in
Figs. 13-15 and have a rounded dorsum, the dorsal furrow appears
in the paranepionic at the gyroceran bend and deepens rapidly as
the shell grows around the perforation, ‘The amount of involution
is probably about the same as in Cenoceras granulosus, which it also
resembles in general aspect as well as in ornamentation.

503

CENOCERAS GRANULOSUM.
NAUTILUS GRANULOSUS, D’Orb. (Zerr. Jurass., Pl. xxxv).

Loc., Chatillon, France, Oxfordian.

Pisa Pies: 26—-30,-and Mie. a1) Pl) xt.

In this species, which is well characterized by its compressed
form and tubercular ornamentation, the compressed form is present
even in the nepionic stage. Figs. 37 and 38 show that the umbil-
ical perforation is of medium size. Contact takes place on or near
the dorsal edge of the cicatrix on the apex, as shown in Fig. 31,
Pl. xii. The citatrix is plainly visible in several specimens of this
species and it is also obvious that in none of them does the dorsal
furrow appear until after the gyroceran bend begins. ‘The dorsum
of the metanepionic substage remains rounded and gibbous until
the bending begins and then it becomes flattened and immediately
hollow, showing the commencement of the dorsal furrow as in
Figs. 36 and 37, and this continues to deepen and broaden through-
out the paranepionic, as is shown in Figs. 38 and 39. ;

Cymatoceras.

This genus, described in Genera of Fossil Cephalopods, had for its
type Cymatoceras (Vaut.) pseudoelegans, sp. D’Orb., which is found
in the Necomian together with Cymatoceras neocomiense. Both of
these have costz which pass entirely across the venter. Inthe type
species these appear very late in the ontogeny in the ephelhic stage,
whereas in zeocomiense and other species the costations appear
earlier in the ananeanic substage. ‘The sutures have sight ventral
lobes or saddles with deep lateral and dorsal lobes. ‘There are
annular lobes at a very early age in some species.

CYMATOCERAS ELEGANS (?). |
NAUTILUS ELEGANS (?) Sow. (JZin. Conch., Pl. cxvi).
NAUTILUS ELEGANS (?) D’Orb. (Zerr. Jurass., Pl. xix).
Woe) exas.) Cretaceous.
Pl. xii, Figs. 16—21.

This species is represented by a number of specimens of the
young, but these do not break apart well and have to be cut and
viewed, as a rule, in sections.

The large size of the apical chamber is noticeable, and the great
distance apart of the first sutures indicates the rapid growth of the

Sie Sao

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Sere

Do4

young shell. This fact is very interesting since here we also find a
high degree of acceleration in other characters. Thus the dorsal
furrow appears in the ananepionic substage at a considerable dis-
tance from the gyroceran bend and continues after this, as shown in
Fig. 20, along the dorsum and is continuous with that of the para-
nepionic.

The costations appear in the neanic stage.

CYMATOCERAS DESLONCHAMPSIANUM.

NautiLus DESLONCHAMPSIANUS, D’Orb. (Zerr. Jurass., Pl. xx).
Loc., Rouen, France, Cretaceous.
Pl. xii, Figs. 22-27.

_ This species, which is represented by several good specimens of
the young, has very nearly the same ontogeny as Cymatoceras
elegans, except, of course, in the specific characteristics and the
position of the siphuncle. ‘This last is propiodorsan in the meta-
nepionic instead of being propioventran as in C. elegans (2). The
sutures of the early epembryonic stages differ from those figured by
Branco for the same species, but this may be owing to the fact that
we have really observed different species. The dorsal furrow
appears as in Cymatoceras elegans in the metanepionic at the second
septum, as in Fig. 24, and is continued in the paranepionic sub-
stage.

CYMATOCERAS SIMPLEX (?).
NAUTILUS SIMPLEX, Sow. (A@in. Conch., Pl. 122).

Loc., England, Cretaceous.

Bie ip 23.

This single specimen differs somewhat from the specimens of
Cymatoceras deslonchampsianus and may be more distinct in the
adult, but I do not feel sure of the fact that it is a different species.

It has been figured in this connection because it shows that the
dorsal furrow is present in this shell both in the metanepionic and
paranepionic substages.

CYMATOCERAS RADIATUM.
NAUTILUS RADIATUS, Sow. (Min. Conch., Pl. 356).
NAUTILUS RADIATUS, D’ Orb. ( Zerr. Jurass., Pl. xiv).
Loc., Rouen, Cretaceous.
Pl. x11, igs.s2ocandeso,vand Pl xii, Mies ands:

The ananeanic substage is shown in outline in centre of Fig. 30,

505

Reed and imktie: 1, Plexi which is the reverse of that on Hie.
30, but enlarged two diameters. ‘The presence of an annular lobe
is noted as it appeared in the specimen, but this part was covered
by remnants of the nacreous layer and it was not positively defined.
The dorsal furrow began between the first and second septum and
is faintly shaded in Fig. 1, Pl. xiii. The dorsal sutures were cov-
preduexcemtedsmadrds: repkesenteds) dle side view, Ply xiit) Hie 2F
shows these sutures, So far as seen, the last two in this figure being
themirst: twoxot Pig. 29, Pl. xi.

The broad costz of the genus made their appearance in the ana-
neanic substage at the same time that the septa approximate and
the zone of contact is formed.

It will be observed that the costz are broader at first than they
are in later age even in this figure, showing that growth was more
rapid at first as in the development of the septa.

Lutrephoceras,* n. g.

This genus includes these forms like the type Lw/rephoceras
Dekayt, which have globose ananepionic substages, increasing subse-
quently with great rapidity in all their diameters. The ana- and
metanepionic substages are highly tachygenic and these shells have
very small, and often hardly perceptible and much flattened, um-
bilical perforations. ‘The siphuncles are subdorsan from the apex
through the nepionic stage in some species, in others this position
is not maintained, but the siphuncle is generally in later stages
near the dorsum and in the ephebic stages it is dorsad of the
Gentine:

The nepionic stage has longitudinal ridges and transverse bands,
the former disappearing in adults which are smooth.

The form of the whorl in section is nephritic from an early age
and changes but little throughout life.

The sutures are almost straight, having but slight ventral lobes,
broad ventro-lateral saddles, lobes on the umbilical zones and deep
lobes in the zone of impression. There are no annular lobes at
any stage of development.

“Evtpegys, clasping around.

—*
AO

“ua-= ate

506

EUTREPHOCERAS, Dekayi.

NautiLus, Dekayi. Morton (Synop. Org. Rem., Pl. viii, Fig. 4).

Loc., Dakotah, Cretaceous.

Plain iiessn— Sel exivs Pie 1

The ananepionic substage in this species is very obtuse and al-
most saucer shaped, the whorl increases so rapidly in all its diame-
ters. ‘The cicatrix is present on one specimen and is a double
depression with a dividing ridge on the cast of the apical chamber.
There is a peculiar plate of nacreous matter which may be the
equivalent of a similar plate which fills in the apex of the shell in

Tautilus pompilius or it may be simply a remnant of the apical
deposit which has this peculiar form. However this may be, the
czcum is seen through it in one specimen, and in another it can
be seen in the same position, although the plate is not visible, the
apex being more completely covered by the external shell.

It seems clear that the dark spots observed in these two speci-
mens were due to the presence of the cecum filled bya dark,
sparry deposit and showing through the nacreous layer.* If so
this organ is close against the venter of the apical chamber. I was
not able to see the youngest septa, but there are evidently very few
of them and the one shown in Fig. 4 is probably either the third
or fourth septum.

The metanepionic substage is not so smooth as the ananepionic,
and although it is difficult to observe without making a section, I
am quite sure that there is a faint dorsal furrow present before the
gyroceran bend begins. ‘The longitudinal ridges and the trans-
verse bands with the usual crenulated edges begin to be observable
in this substage.

The bend which begins the paranepionic substage is very abrupt
and almost at right angles to the dorsum of the metanepionic sub-
stage and has a deep dorsal furrow. ‘The umbilical perforation is
consequently so small and arcuate that it is very difficult to observe.
In Fig. 6 the lateral angle of the shell and of the first septum that
is built upon the dorsum of the apex has been cut off and shows the
opening of the umbilical perforation in part, but has a misleading
outline since it is just the reverse in shape of the true internal per-
foration. It, however, shows that there is a perforation as does
also Fig. 4. This shell must grow in these younger substages with

*It can be observed in the apex of Nautilus pompilius through the thin shell of the
ananepionic substage.

557

great rapidity upon the venter in order to swing that part around
the very sharp curve made by the gyroceran bend.

The paranepionic substage has well-marked longitudinal ridges
and transverse bands of growth given in Fig. 6. ‘The latter part
of the paranepionic in this species, if this be properly limited by
ieeans Of tue ornamentation, 1s close coiled). Bhat is -tov say, it
touches dorsum of the ananepionic and envelops it, the involution
being almost complete from the very beginning.

The umbilical perforation is, however, not completely closed nor
is it subsequently closed by extra growths of shell as in Mautlus
pompilius. (he area of the umbilical zones is marked off at an
early age by the smoothness of the shell, the longitudinal ridges
being absent on these parts. In some specimens the shell mark-
ings are much stronger than in others, but in all they seem to grow
more decided until near the end of the metaneanic substage.

The meta- and paranepionic substages have an elevated subangu-
lar abdomen not shown in any of the figures, the outline of the
section of the whorl is in reality in these early substages depressed
subtrigonal similar to the young whorl of Cymatoceras, but less
acute, and to that of Mautelus pompitus, but more pronounced than
in that species on account of the subangularity of the venter; the
venter of Vautilus pompitius being more rounded in the paranepi-
onic substage.

The ananeanic and metaneanic are blended and probably not
separable, but the paraneanic can be distinguished. The former
has the siphuncle tending more towards the centre, although in
some specimens this alteration is not so great as in others. ‘The
transverse bands become broader and their edges have tubercular-
like short ridges on a secondary band, which are sometimes well
marked off on their apical borders from the sunken younger parts
of the same bands of growth. ‘These ridges are always continuous
from band to band and over the sunken parts of each band. In
the paraneanic substage, as shown in Figs. 7 and 8, these ornaments
begin to diminish and finally die out. In Fig. 8 this substage is
limited by the retention on one side of a partial constriction or
permanent aperture, which, however, is not present in all shells.

In the anephebic stage, also shown in Figs. 7 and 8, orad of the
constriction, the shell is very nearly as smooth as it is in the full
grown. The form of the whorl remains about the same. The
siphuncle has become dorso-centren in position in this shell, in

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others it may still remain nearer the dorsum, but in most shells it
shifts its position somewhat.

In the metephebic stage the shell appears to have been smooth
and the whorl is apparently somewhat more depressed or more
absolutely nephritic in outline. ‘This distinction is due to the
larger size and greater proportionate increase in lateral growth.
The dorsal sutures in this substage and probably throughout the
ephebic and possibly earlier have not only the broad dorsal lobes
in the contact furrow, but narrow and very shallow lobes, which
cannot be described as annular lobes, although they resemble these
as they appear in the neanic stage of ndolobus avonensis, Fig. 38,
Pl. viii. They are, however, much shallower. In the centre of
these, in the only specimen perfect enough to show this, there were
minute linguiform saddles as given in Fig. 1, Pl. xiv. The sutures
have to be in perfect condition to observe such markings and this
may account for the absence of similar markings upon other nauti-
loids. The siphuncle may be either ventrocentren, centren or
dorsocentren, but it is more commonly dorsocentren.

EUTREPHOCERAS, sp. (?)

Pl xii ehiee 3.

Koc. + France; Cretaceous.

This shell is referred to here because it shows clearly the pres-
ence of a faint dorsal furrow in the metanepionic substage opposite
a corresponding furrow in the paranepionic. ‘The cast of the per-
foration was preserved in this specimen and it was extremely flat
and comma shaped. ‘The whorls are coiling towards the observer
so that there can be no doubt that the section of the central volu-
tion is metaneplonic.

EUTREPHOCERAS FAXOENSE, 0. S.
Loc., Faxoe, Denmark, Cretaceous.
Pl. xi, Figs. 9—12.

This species differs from Lutrephoceras Dekayi in the extreme
subdorsan position and smaller size of the siphuncle in the nepionic
stage, has larger umbilical openings and is also apparently a smaller
form. Otherwise it is very close in sutures and form to this spe-
cies. The umbilical cast is preserved on one side in Fig. g, and
shows the involution to have been considerably less than in &. De-
kayt. ‘The development is, however, so similar otherwise that no

559

special description is necessary. It must be noted, however, that
the shell was absent, so that no comparison of the ornamentation
could be made.

EUTREPHOCERAS IMPERIALIS.
NAUTILUS IMPERIALIS, Sow. (A@iz. Conch., Pl. xiii, Figs. 13-16).

Loc., Isle of Sheppy and Isle of Wight, Tertiary.

Pl. xiii, Figs. 14-16.

In this interesting Tertiary species the siphuncle is subdorsan
even in the apical chamber, as is shown in Fig. 14, and it clings to
this position throughout the nepionic stage. ‘The form does not
seem to differ materially from that of Eutrephoceras Dekayt. The
umbilical perforation is of about the same form and size, that is to
say, it is as small as is practicable to afford room for the shell to
turn and has a depressed comma shape. ‘The external umbilici are
more open than in &. Dekayz and smaller than in &. Faxoense.
The ornamentation is quite distinct. In the nepionic stage there
are longitudinal ridges and transverse bands, but these are never so
prominent as in Vekayz. In what I suppose is the neanic stage
these still persist, but are so fine that their intersecting lines, with
minute depression in the checker-board-like spaces between them,
give a punctate aspect to the surface when viewed with a cross
hight. |

The specimens from the Isle of Sheppy, supposed to be identical
with this species, shows the presence of a dorsal furrow in the
opposed dorsi of the meta- and paranepionic volutions, Fig. 16,
and the very small size of the perforation.

This species has an annular lobe which has no connection with
the. subdorsan siphuncle. I could not find any traces of these in
the older sutures. The sutures resembled those of Lutrephoceras
Dekayt except that I could not find any signs of the linguze-form
dorsal saddles in the centre of the dorsal lobes.

Nautilis.

Before beginning the brief notice of this genus, which I propose
to give, I desire to return thanks to Henry Brooks, whose observa-
tions and drawings have contributed so largely to the interest of
this paper. ‘These are also noticed in connection with the figures
themselves. Iam also deeply indebted to Dr. Charles E. Beecher,
of New Haven, who has loaned me a series of beautiful prepara-

560

tions, making a complete series of all of the substages of develop-
ment in JVautzlus pompilius and more or less of other species, and
also to Dr. R. T. Jackson, for similar material. I hope to use this
material more extensively and effectually in the future. In this
paper full justice cannot be done to the work of Dr. Beecher or
Mr. Brooks.

This generic name, heretofore supposed to include nearly all
of the coiled or nautilian forms of Nautiloidea and still used by
some conservative paleontologists in this way, is really not applica-
‘ble to any forms except the living species of nautiloids and possi-
bly some shells inthe Tertiary. Even these last cannot be satisfac-
torily referred to the genus Nautilus until their nepionic substages
have been worked out.

The genus Eutrephoceras is a near ally but still distinct in most
of its characteristics. The broad outline of all of the epinepionic
stages of growth, the general position of the siphuncle, dorsad of
the centre, and the distinct sutures of Eutrephoceras separate the
species. [he minute umbilical perforations and closer coiling of
the younger substages of the conch in Eutrephoceras show also that
it-is the terminal group of some other genetic series than that to
which Nautilus probably belongs.

The genus Cymatoceras of the Cretaceous differs in the broad
costations as well as in the outline of the nepionic whorl. The
sutures of this genus are more like those of Nautilus than the
sutures of Eutrephoceras.

The genus Nautilus is obviously still more remote from Cenoce-
ras of the Jura in the sutures of all stages and form of the ananepi-
onic and succeeding nepionic substages, although in the outline of
the ephebic whorl and position of the siphuncle there is close
approximation. If one excepts the comparison of the ananepionic
substage, which is obviously similar to that of Hudrephoceras Dekayt,
being only more compressed, the nepionic stage and the ananeanic
substage are very close in aspect to those of Digonioceras, although
the succeeding substages become quite distinct.

I cannot in this memoir give full descriptions of the substages of
development which I hope to treat fully in the future. It will suf-
fice to refer to the accurate drawings of Mr. Brooks, given on PI. 1,
and to notice the fact that young shells and preparations now in
my possession of Wautilus umbilicatus, pompilius and macromphalus
show no variations in their characteristics worth noticing here. It

561

is essential, however, to call attention to the statement made else-
where, that the dorsal furrow begins in VVauttlis umbilicatus,
pompilius and macromphalus in the metanepionic or at any rate be-
fore the gyroceran bend begins.

The ornamentation is similar to that of the young of most other
genera of the Mesozoic during the nepionic stage, but the young
of Nautilus do not repeat the broad costze of the epinepionic stages
of Cymatoceras. ‘The shell of Wautelis pompilius becomes smooth
in the ananeanic substage which begins when contact occurs.

The color of the ana- and metanepionic substages are pearly,
the outer layer of shell being thin and colorless in these substages.
A uniform brown spreads over the exterior in the paranepionic
substage. This tends to break up into transverse bands in the ana-
neanic at the same time that the ornaments begin to disappear.

This breaking up into bands is due to a decided fading out of
the coloration which may sometimes seriously affect the stripes
themselves. In the metaneanic, sometimes after the coloration has
for a brief space been reduced, the bright, broad, brown stripes of
the adult appear upon a white ground.

The form of the outline of the whorl changes in the ananeanic,
the sides and venter becoming flattened and being less involute,
the whorl repeats approximately the ephebic whorl of Mautlus um-
bilicatus. ‘To speak more accurately, it would at this time be iden-
tical with any species that might have an ephebic form exactly
intermediate between Wautilus umbilicatus and pompilius, since the
involution of the latter is at all stages somewhat greater than that
of the former species at the same age. In the paranepionic the animal
begins to deposit calcareous matter along the lines of involution in
the umbilical zones and thus spreads more towards the centre and
increases the involution. ‘This process really begins with the meta-
neanic and is often marked bya permanent constriction beyond which
the transverse lines of growth become coarser than they are in the
ananeanic substage.

In the anephebic substage, the closing of the umbilici by the
spreading inwards of the calcarous deposits of the umbilical zones
begins and is carried out fully in the metephebic substage, the
umbilici being completely covered up and obliterated. In the
parephebic substage the brown coloration disappears, leaving the
surface white. No degenerative modifications other than this loss

SES SO ee

562

of color and occasional approximation of two last septa have been
observed in any shells that have come under my observation, and,
therefore, I have thought this change probably belonged to the
later ephebic and not to the true gerontic stage.

These facts show clearly that in this genus the least involute of
existing species, WVautilus umbilicatus, is the most primitive and
has characteristics repeated more or less in the young of the more
involute Vautilus pompilius. This observation is of great import-
ance in this paper, since it confirms the opinion that genetic groups
of Nautiloids and Ammonoids are series of parallel morphic modifi-
cations, in the evolution of which the shells progressed from less
closely coiled and less involute to more closely coiled and more
involute shells.

Dr. Beecher has called my attention in his preparation of Vawzz-
lus macromphalus to a very important fact in connection with the
bioplastology of the Nautiloids, viz., that there are indications in
the ontogeny of this species of degenerative changes which have also
taken a parallel course to those observed in other genera and families ;
in other words, that it is more closely coiled and more involute in
the nepionic stage than later in life.

The nepionic stage of this species differs in form from that of
Nautilus pompilius, but the most marked distinction les in the
abrupt bending of the shell in building the gyroceran curve. This
consists partly in the formation of thick extensions of the shell
along the lines of involution. These are similar to the testaceous
umbilical extensions occurring in the same situation in LVaz¢zlus
umbtlicatus, but begin later in the ontogeny of that species, and
also similar to those occurring in the young of JV. pompifius earlier
than in wmbzlicatus, but later than in the ontogeny of macrompha-
lus. All of these facts and also the form of the young of macrom-
phalus can only be accounted for by assuming that it is probably a
descendant of Vautilus pompilius, which exhibits an accelerated
development of earlier nepionic substages and then in the ephebic
stage becomes less involute.

I shall try to put these propositions in future papers into convinc-
ing form with illustrations, but it is easy to verify them with any
good specimen of LV. macromphalus since the internal whorls are
visible in every case.

These observations confirm in the most unexpected manner the
generalization deduced from fossil shells, that in progressive series,

563

evolution is towards closer coiling of the shell and in retrogressive
series the direction of evolution is towards uncoiling.

Aturide.

In my second paper on ‘‘ Carboniferous Cephalopods,’’ Geological
Survey of Texas, Fourth Annual Report, p. 389, | pointed out the
fact that the genera Enclimatoceras of the Mesozoic, Hercoglossa
of the Cretaceous and Aturia of the Tertiary formed a distinct
group by themselves. |

These genera have ventral saddles, deep lateral lobes and lateral
saddles of so highly specialized outlines that the sutures resemble
those of some of the Clymeninz. ‘The forms are compressed and
as a rule deeply involute. Unfortunately I have been unable to
get the ananepionic substages of Enclimatoceras or Hercoglossa.

It is, however, fortunate that the involute character of the young
in these genera and close coiling of adults in the entire group
makes it highly probable that the young when investigated will not
be likely to contradict the conclusions obtained from the study of
Aturia.

Through the kindness of the Directors of the National Museum
and Geological Survey and Dr. W. H. Dall and Mr. T. W. Stan-
ton, I received a number of sections of EAxchmatoceras Ulrichi,
from Prairie Creek, Wilcox county, Alabama, and Zell county,
Texas, Tertiary, but not one of these had a centre perfect enough
to be of any use.

Aturia.

This genus, first described by Bronn, has long been admitted and
is easily recognized by the aid of the peculiar sutures and siphuncle.

ArturIA Morrissi, Michellotii.

Loc., Baldasseres, Tertiary.

PE xu, Pigs. 17—To.

The ananepionic substage in this species is very globose and the
growth of the apex is certainly very rapid in all its diameters. This
rapid increase is, however, not sustained in the transverse diame-
ters of the metanepionic and succeeding stages. The gyroceran
bend is so abrupt and the coiling is so close at the end of the meta-
nepionic, that | have not yet succeeded in seeing and studying the
dorsum of this substage. The opening of the umbilical perforation

564

can be seen in Fig. rg, which is enlarged six diameters, as a black
spot at the junction of the sutures and is visible only under a mag-
nifier in the original. The other figures are also enlarged six di-
ameters.

Fig. 19 also shows the first three sutures and the highly acceler-
ated development of the first suture which takes on immediately
the peculiar lobes and saddles of the generic group to which this
species belongs, and also the great depth of the apical chamber.

ATURIA ZIZAC, Bronn.
oc; Daxbrance. Wertiany:
Jel, Sabi JANSSy BO:

‘Figs. 20 and 21 give front and side views of the nepionic and
half of the neanic stages enlarged about ten times with the first four
sutures.

This species has a globose apex similar to that of Morrissi and
the umbilical perforation is also minute. ‘This and the closeness
of the coiling is shown and the subdorsan siphuncle are shown in
Fig. 22. Ihave restored the dorsal shell of the ananepionic sub-
stage in this specimen. ‘The extraordinary depth of the apical
chamber, the lobate character of the suture of the first septum, and
the highly tachygenic (accelerated) development of all of the char-
acters of the apex are noticeable in this species as in Aturia Mor-
USSU. ,

Scaphites.

The phylogerontic forms known by this name are of interest in
this paper because of the invariably excentric retroversal character
of the living chamber and their obviously intermediate station be-
tween the more uncoiled phylogerontic genera and such phyloge-
rontic genera as Sphaeroceras and the like which are closer ap-
proximations to normal shells and are consequently persistently in-
volute at all stages of development.

The figures of this genus, in consequence of ee retroversal bend
of the living chamber, do not usually give any data, and although
the literature is so abundant I was forced to make what observa-
tions I could in finishing up this paper upon the materials immedi-
ately in hand. In one fine large specimen of Scaphites from
Mingusville, Mont., Coll. Bost. Soc. Nat. History, I was able to
excavate the dorsum and found the impressed zone retained even

565

upon the edge of the aperture or rather in the base of the dorsal
crest. The aperture had the usual shelf-like constriction figured
by Meek and on the dorsal side were two narrow sinuses and a
median dorsal crest, the length of which could not be determined.

Mr. Stanton, in his ‘‘ Colorado Formation,’’* shows a similar re-
tention of the impressed zone in Scaphites ventricosus.

The gerontic whorl is quite free for some distance, and although
the impressed zone sensibly diminishes in depth and_ breadth
towards the aperture it is not obliterated. These two species have
comparatively short living chambers, which are free only for a part
of their length, and one would naturally expect that the very deep
contact furrow of the ephebic and anagerontic substage would per-
sist. The conditions are quite different from those that occur in
shells with more extended gerontic stages, lke Scaphites larve-
jormis, Meek and Hayden, and in these the paragerontic substage
may perhaps have no impressed zone.

I have, however, examined a considerable number of scaphitoid
sheils from European localities and some of these gave positive
information of the persistence of the impressed zone in the lower,
inner border of the aperture, although, as in Scaphites nodosus, it
was sometimes hardly perceptible in the outline of this part.

Flelicancylde.

This family name serves the purpose of temporarily uniting all
phylogerontic species of the Cretaceous in America which have
three rows of tubercles on either side. The characteristics are
given below under the generic title ‘*‘ Helicancylus.”’

Ffelicancylus, Gabb.t

It is probable that genetic connection as shown by the ornamen-
tation existed between cretacic shells of normal involute form like
Acanthoceras Rémondi of the nodose variety figured by Gabb as
having three rows of tubercles and his Crvoceras /atus.t This last
also has three rows of spines and single costze, but has an open coil
without an impressed zone. ‘There are similar marks of affinity in
the species described by the same author as Welicancylus eguicosta-
Zus, which has also three rows of nodes. The last, however, has the

* Bull. U. S. Geol. Survey, Pls. xliv and xly.
Leal, (Heithee, Me LBS oxtail, CHael jot, JA, soy
ilbids iyPl. xv, Hig, 2.

566

composite mode of development described below in Nostoceras and
Emperoceras with a gerontic stage which is a close approximation to
Hamulina and Ptychoceras,* and affords evidence that this genus is
a phylogerontic form in which the gerontic retroversal last volution
replaces the helicoceran. ‘These and other forms appear at any
rate to give an approximate solution of the difficult problem of the
derivation of such form as Hamites, Hamulina, Ptychoceras and
Baculites, and also Turrillites and Helicoceras.

The helicoid spiral appears sandwiched between a phylogerontic
nepionic stage in Nostoceras and Emperoceras and a true onto-
genetic, gerontic living chamber with a retroversal curvature. ‘This
ontogeny shows this spiral to be a special, probably pathologic adap-
tive mode of development peculiar to the ephebic stage of some of
the phylogerontic series, but not necessarily having any correspond-
ing feature in the gerontic stages of any large number of normal
formed Ammonitine.

This explanation is in accord with the fact that all normal Am-
monoids and Nautiloids revolve in the same plane even in the
gerontic stage, and enables one to explain the most puzzling of the
degenerative forms. ‘Thus there may be, asin Macroscaphites [vaniz,
shells with retroversal gerontic stages derived directly from normal
Ammonitine. Some helicoceran forms are also derived directly
from similar normal forms, the most wonderful example being
the series discovered and accurately described many years since by
Quenstedt, who traced helicoceran and crioceran, and even bacu-
lites-like shells all back to their proper origin in Cosmoceras (Amm.)
bifurcatum of the Jura. Neumayr is constantly alluded to as the
person who discovered this important biological fact, whereas the
credit is due to Quenstedt, who showed that all such forms in the
Jura were probably pathologic derivatives of normal forms. I
have examined a considerable number of the species of Turrillites
and Helicoceras from European localities, and although the apices
of some of these were small enough to have shown at least the be-
ginning of an excentric nepionic or neanic stage, if any had existed
I did not succeed in finding any indications of the presence of such
forms in the young. It is, however, very strange that the youngest
stages are invariably absent even in large series of specimens of the
same species, and this suggests that the youngest stage was especially
liable to destruction, and might not have been like a normal formed

* See remarks on Ptychoceras.

567

involute Ammonoid, 7. ¢., it might have been excentric or helicoid.
So far as known, however, all European series approximate to normal
forms in the young. Here and there also there are diseased indi-
viduals, as in the so-called Zurrilites Boblayet (Arietide) and Turril-
ites Valdani and Coynart figured by D’Orbigny, and other isolated
examples of unsymmetrical shells having helicoid tendencies in the
ephebic and even younger stages. It is also fully demonstrated by
specimens and drawings that many Turrilites and _ helicoceran
forms do not have a retroversal living chamber in the gerontic
stages as in.the scaphitoid and ancyloceran-like series traceable to
various genera. This may be due to the incompleteness of the
specimens heretofore collected and the perishability of the excentric
gerontic volution when present. ‘This hardly accounts for those
species having contracted living chambers and apertures, the presence
of which are almost conclusive in favor of the opinion that they
could not have had retroversal gerontic living chambers.

These facts and the tendency of the terminal gerontic volution to
return to the mode of revolution in the same plane and to resume
the lost bilateral symmetry of the whorl in Emperoceras and Nos-
toceras show plainly that the helicoid spiral is acquired, adaptive
pathologic tendency that may come in anywhere as an intermediate
stage in the ontogeny or phylogeny of any degenerative species or
series, and is not strictly speaking a normal phylogerontic charac-
teristic.

Another interesting result of the discovery of Helicancylus by
Gabb is that Hamulina, Hamites, and probably also the allied
Ptychoceras can be definitely characterized as phylogerontic forms
of phylogerontic series. The author has previously claimed, with
Quenstedt, that this was the only way to account for the Hamites,
Ptychoceran and Baculites-like modifications of European forms.
American forms with helicoid tendencies, like Helicancylus, having
gerontic stages which differ from true Ptychoceras only in the close-
ness with which the gerontic retroversal bend is made, afford posi-
tive evidence in the same direction.

It should be noted in this connection that these remarks do not
necessarily imply that Ptychoceras has not a distinct mode of de-
velopment, an ontogeny of its own and also its own peculiar
genetic series as may be seen in the remarks on that genus.

I have had an opportunity to study the gerontic stage of a species
of Helicancylus in the Whitney Coll., Mus. of Comp. Zodlogy,

568

which may be new. The gerontic stage is the same as that of
F1. equicostatum, and is closely bent and like Ptychoceras, although
there is no gerontic contact furrow. The costz are large, single.
and tuberculated, not alternately entire and tuberculated as in
Gabb’s species.

Nostoceratide.

This is probably a more or less artificial group, but it serves the
present purpose of showing the common characteristics of several
groups of phylogerontic species. I have united under this name all
such distorted forms of the Cretaceous in this country with unsym-
metrical spirals in the ephebic stages, more or less prominent cost
and two rows of tubercles on the abdomen. The earliest stages are
too little known for any general description to be given, the
gerontic stages often have a retroversal living chamber and are
tuberculated.

The genera are Nostoceras, Didymoceras, Emperoceras, Exitelo-
ceras.

Quenstedt was the first to call attention to the persistency of
styles of ornamentation in series of degenerative shells and to point
out that these were indications of affinity that could not be lightly
laid aside. A considerable proportion of the phylogerontic species
of the Cretaceous in this country have only two rows of tubercles
with costations bifurcated at the bases of these tubercles, but I have
not been able to find any corresponding ornamented normal form
which might be considered their phylogerontic radical.

Flelicoceras Stevensoni (Whitfield) is represented among the
specimens sent me from Yale Museum by a fine specimen and the
youngest part of this specimen indicates a change in the spiral,
but the young was not sufficiently defined to enable me to place the
species in its proper genus.

I have before mea fragment of a whorl very similar to Stevensoni
in costze and tubercles, but of larger size than is usual in that
species, and yet this has an irregular contact furrow on the upper
side. ‘The irregularity of this furrow may be due to age and the
species may have been a true turrilites-ke form when younger, or
it may indicate that the separation of shells with the helicoceran
mode of growth into different genera from true turrilites-like shells
with a contact furrow is artificialand not advisable. This fragment

P| ee ee et a i i ln

569

reported as found at Colorado City Mineral Springs, and is in
Museum of Comparative Zodlogy.

fTelicoceras uimbilicatum, Meek, Snvertebrate Paleontology, Pl.
xxli, Fig. 5, is probably a close ally of Stevensont, but my informa-
tion is not satisfactory.

fTeteroceras Conradi, as figured by Whiteaves in AZesozorc Fossils,
i, Pt. 11, Pl. xii, and supposed to be identical with Ammonocerattes
Conradi of Morton is also a form that is not sufficiently well-known
to be referred to its proper genus. The costze have no tubercles
and resemble those of the young of Wostoceras Stantoni and helicinum.
There is also obviously a retroversal gerontic volution shown by
Whiteaves in his Fig. 3, and there is apparently no contact furrow,
the mode of growth being helicoceran and not turrilitean.

It may be useful in connection with these descriptions of phylo-
gerontic forms to note the fact that there are some series of true
ancyloceran forms in this country having shells revolving in sym-
metrical spirals in the same plane, and not having helicoidal ephebic
stages. ‘They are similar to most of the European series, and it is
not advisable to name them till proper comparisons can be made.

Ancyloceras percostatum and Rémondi, Gabb, described in
Paleontology of California, are good examples of species having this
kind of spiral.

Lindigia.

This genus Karstens,* with Zzxaigza helicocerotdes as the type, has
(in this small species) linear, untuberculated coste, a helicoceran
spiral in the ephebic stage, and comparatively a very large and long
retroversal gerontic volution.

fleteroceras Conrad of Whiteaves may be a species of this genus
occurring in North America, but Lindigia has peculiar ventral
crests in the coste of the anagerontic substage that are quite dis-
tinct from those figured by Whiteaves in his species.

LFTelicoceras stmplicostatum of Whitfield resembles this species, but
it may nevertheless be the parephebic substage of some other tuber-
culated species which has lost its ephebic tubercles.

NVostoceras,+ n. g.
The species of this genus have a close-coiled unsymmetrical shell
during the ephebic stage and are true turrilites. There are two

* Geol. de la Colombie, Venezuela, ete., Pl. i, 1856.
T Nootos, areturn.

See Sr! coe, Ve

ph he ae

510

rows of ventral tubercles, which become more or less deflected
during development towards the lower side (whether this be the
left or right side) of the whorls. There is a contact furrow which
is maintained as long as the whorls are sufficiently close coiled and
then disappears on the free gerontic volution. This volution 1s
excentric and then recurved as in all retroversal living chambers.
The nepionic stage is not yet known, but it is obviously quite
different from that of the more loosely coiled helicoceran spirals of
the genus Emperoceras.

This genus has the two rows of ventral tubercles and general
aspect of the shells of Ptychoceras and Emperoceras, described in
this paper and these characters contrast decidedly with those of the
Helicancylus phylum.

The nepionic and perhaps earlier neanic substages are not known,
but there are indications in some specimens of JVostoceras helicinum
that in the early neanic substages the whorl is not a normal ammo-
noidal spiral, but an open, whorled, irregular shell of some kind.
The specimens I have in hand also show that in both species,
Nostoceras Stantont and Vostoceras helicinum, the last neanic or
earliest ephebic substage has no contact furrow and has single costz
without tubercles. The ephebic stage has tubercles asa rule, and
more or less bifurcated costz, but both may be absent in some shells.
The gerontic volution is apt to have tubercles even when they are
absent in the ephebic stage.

This genus is of interest in connection with the history of the
impressed zone because here, as in other allied forms, this charac-
teristic enters upon a new phase of its history. The nepionic stage
being. unknown, one cannot state positively that it has a close-coiled
shell and a contact furrow, but since this has now been found in so
many uncoiled forms, it is legitimate to infer that it was present.
In such shells the contact furrow which arises after the degeneration
and loss of the nepionic contact furrow is obviously distinct,
occupying the side and not the dorsum of the whorl.

The type is Wostoceras Stantoni, U.S. National Museum; Loc.,
Chatfield, Novarro county, Texas.

NOSTOCERAS STANTONI.
Loc., Chatfield, Novarro county, Texas.
This species has several varieties.

Var. retrorsus.
This variety has from five to six complete turrilites-like whorls

571

before the retroversal gerontic stage begins. The apex does not
exhibit any indications that the species had an excentric young
stage even at the’small diameter of 5 mm. in one specimen. ‘There
appear to be no tubercles on the earliest whorls examined, probably
the neanic stage. ‘Two irregular rows of tubercles are introduced in
the ephebic stage with alternating untuberculated coste. The
tuberculated costz are sometimes bifurcated, and sometimes single.
The costz are closely set, subacute ridges, with concave flutes
between them both, arching apically, the flutings broader than the
costal ridges, but the surface is otherwise smooth.

aiheshersht of the coil) is over 4o mm. in the largest specimen:
through the ephebic whorls, although the apex isimperfect. In two
other specimens this length is much less, although the number of
the whorls is about the same. The diameter of this specimen
through the parephebic whorl is 34 mm. The height (transverse
diameter) of the parephebic substage is 19 mm., the ventro-dorsal
diameter about 13 mm. The diameter of the umbilical opening
must have been less than 12 mm.

The costz are wider apart in the last of the ephebic stage, or par-
ephebic substage, and I expected to find that they died out altogether
for a certain space, but there was no evidence of this. They, how-
ever, appear to be slightly more prominent on the gerontic volution
than on the parephebic substage.

The contact furrow begins early, being present on the smallest
whorl examined. ‘There is therefore no positive indications that
this species had uncoiled or excentric young as in Emperoceras.

In the anagerontic substage the whorl bends downwards or orally
in two dextral specimens, and in the metagerontic acquires larger
tubercles and coarser coste, sometimes bifurcated, and bends
upwards towards the base of the ephebic volution, forming the
retroversal living chamber. ‘The last part of this, or the parage-
rontic substage, is nearly or quite straight, the bifurcations disappear,
leaving the costz straight, and the tubercles also gradually disap-
pear. The latest senile substage is also nearly if not quite bilaterally
symmetrical and strongly contrasts in this respect with all the stages
preceding the metagerontic substage. The return to the symmet-
rical form of whorl really begins in the metagerontic substage. The
living chamber has an aperture in one specimen. ‘This is straight
across the venter, has slight crests on the sides, and is straight or
with very slight crest on the dorsum.

572

Mr. Stanton has kindly examined the numerous specimens in the
National Museum, and estimates that the retroversal chamber in
this variety is generally the sixth or seventh volution and also
remarks that one specimen is nearly double the size of the largest
one mentioned above, and that there are but few that are smaller.
The three specimens I have of this variety are dextral, but there are
others in the National Museum which are sinistral.

Var. prematurum.

This variety has more closely set costee and smaller tubercles and
the gerontic stage begins earlier, there being, if my estimate is
correct, only three or four closely coiled whorls. The last volution
is well preserved in the only specimen of this variety that I have
and this shows clearly an open aperture, almost straight across the
venter, with slight crests on the sides and equally obscure crest on
the dorsum. It is, in other words, precisely similar to the aperture
of variety retvorsum. ‘The specimen here described is sinistral, and
is the only one obviously belonging to this variety in the collection
of the National Museum.

Var. aberrans.

This variety may have three, four or five closely coiled whorls
and considerable variation in the tuberculations, etc., but when the
gerontic stage begins, the aspect is distinct. The anagerontic
substage does not bend so abruptly as in vetrorsum or prematurum
it is more oblique to the axis of the spire and the retroversal meta-
gerontic substage, if it be superadded in this variety, would be more
oblique than in var. prematurum. One specimen is dextral and the
other is sinistral.

Remarks.

This species was discovered by Mr. Stanton in the Ripley beds,
where it is associated, as stated by the same gentleman, with a
number of other phylogerontic species, such as two species of
Ptychoceras, Zurrilites splendens, Shum., Wostoceras (Lurr.) heh-
cinum, Shum., Felicoceras navarroensis, Shum., and a variety of
other typical Ripley species. Mr. Stanton also informs me that out
of 26 specimens in the National Museum, 16 are dextral and 10 are
sinistral.

5¢3

NOSTOCERAS HELICINUM.
HETEROCERAS HELICINUM, Shumard.*
Loc., Chatfield, Novarro county, Texas.

At the diameter of 8 mm. in one of the two specimens before me,
there are indications that the young was more loosely coiled, and
perhaps more or less excentric in comparison with the later closer-
coiled stages. The contact furrow was also obviously absent in
these earlier substages. In the other specimen, at diameter of about
9mm., there are similar indications. Nevertheless, I was by no
means sure of what these changes indicated, whether a helicoceran,
scaphetoid or hamites-like shell. All that can be said is that they
show irregularities in the growth of the young not present in the
turrillitean volutions of the ephebic stage.

The young, probably in the anephebic substage, has single coste,
each tuberculated on either side of the venter. ‘These become more
or less irregularly bifurcated, and with intermediate entire costa with-
out tubercles, usually one, sometimes two, in each interspace in the
metephebic substage. ‘The whole is a flat turbinated coil of not
more than four or five whorls with prominent tubercles and costa-
tions.

In the anagerontic substage the volution abandons the spiral, the
contact furrow disappearing immediately, and the shell grows down-
wards and outwards,:as in the anagerontic substage of /Vostoceras
Stantont, var. aberrans.

The single tuberculated costz of the young are similar to those
of the later stages of Ancyloceras Jennyt, Whitf., Pal. Black Hills,
and some of the helicoceran forms found elsewhere ; but the young
shells were obviously quite different, being more closely coiled and
stouter, shells. Specimen in Coll. U. S. Nat. Mus., No. 21103.

Didymoceras,} n. g.

There are aseries of forms having loose helicoid spirals, two
rows of more or less irregular ventral tubercles and irregularly
bifurcated coste, which also have, or appear to have, a gerontic
stage with a retroversal volution, as in Nostoceras. ‘These are all
larger shells and are separable by the helicoceran mode of growth
in the ephebic stage.

* Received through the kindness of Mr. T. W. Stanton, who identified the species.
t4Ovpog, double.

DT4

Beside the type form, Didymcoerus nebrascense, in the Yale Uni-
versity Museum, there are several closely allied species, as follows:
Didymoceras (Het.) cochleatum and tortum, Meek, JLnvertebrate
Paleontology, Pl. xxi.

Some of the species described by Whitfield and others from the
Black Hills have similar ornamentation and helicoceran whorls, and
probably belong to the same series, if not this genus. I refer to
Heteroceras Newtont, Exploration of the Black Fitlls, Pl. xv, and
its possible gerontic stage, Ancyloceras tricostatus, Fig. 7 of same
plate. With regard to this form I have, however, doubts arising
from its close resemblance to JVostoceras helicinum, and these make
it necessary to study the young before it can be definitively referred
to the same genus with WVebrascense.

DIDYMOCERAS NEBRASCENSE.
HETEROCERAS NEBRASCENSE, Meek (/nvert. Foss., Pl. xxii, Fig. 1).
Heteroceras, Whitf. (Pal. Black Hills, Pl. xv, Fig. 6).

Loc., Near Buffalo Gap, S. Dakota.

PE xiv, Figs:

The young of this species is unknown, but the younger stages of
the closely allied cochleatum show that it did not have a contact
furrow—at least in the early ephebic substage. The metephebic
substage has more or less irregular, obscure tubercles and rather
fine, closely set costze, occasionally bifurcated at the tuberculations.
These disappear in the parephebic substage. The geronic volution
is retroversal as in Nostoceras. The cost increase in size and
prominence in the anagerontic substage, and also become tubercu-
lated and bifurcated. During the metagerontic snbstage these
characters are more developed, and the volution makes a retroversal
bend. All of the ornaments are lost, however, in the paragerontic
substage, the coste depressed and finally disappear except on the
venter, and the whorl becomes again bilaterally symmetrical. The
costee and lines of growth bend slightly forwards across the venter,
then backwards into sinuses on the inner parts of either side and
form symmetrical crests across the dorsum. The aperture is pre-:
served in this specimen and shows the same outline.

Mr. T. W. Stanton* in discussing a collection of fossils from Fort
Pierre shales, near Boulder, Colo., described substantially the
same remarkable characteristics in this species and in fortum, and

* Proc. Colorado Scien. Soc., ii, Pt. iii, 1887.

579

was the first to state that most of our Western forms of Heteroceras
probably had similar irregularities in the development of the last
volution. ;
E-mperoceras,* ni. g.
The young are hamites-like, so far as known in the neanic stage
and become helicoceran in the ephebic stage. _It is not positively
known that they have an extended gerontic stage.

EMPEROCERAS BEECHERI.
Loc., Near Buffalo Gap, S. Dakota.

This species has, in the earliest substage, observed probably the
metaneanic straight volution with straight coste, having each two
minute tubercles on the venter, and no intermediate untuberculated
and single costze. The section is compressed oval, the dorsum
broader than the venter. The siphuncle is certainly in the mesal
plane between the rows of ventral tubercles in this substage. The
sutures are simple and appear to be symmetrical, or more nearly so
than in the succeeding substages.

The paraneanic is introduced when the hamites-like first bend of
this specimen is made, and is terminated by a permanent constric-
tion in the elbow of the second bend in both specimens of this
species. Bifurcated coste appear and intermediate untuberculated
coste in this substage.

The next arm, probably the anephebic substage, is bent more or
less downwards, but the curvature is distinct from that of the met-
ephebic stage, and the form of volution in section is still a depressed
oval, although much more gibbous on the upper than on the lower
side. ‘The section is that of a compressed ellipse, the ventrodorsal
diameters increasing faster than the transverse.

The intermediate single coste running uninterruptedly across the
venter are more numerous in this substage, occurring from one to
three between each bifurcated and tuberculated costation. The
bifurcations are not always well marked, but they are more distinct
than those given in the drawings, and here and there a costation
may be single and have tubercles. ‘This volution begins to twist in
the metephebic substage, and the asymmetrical helicoceran form is
fully developed in the flattening of the lower side and the increas-
ing gibbosity of the upper side, whether this be right or left, and
the tubercles are correspondingly deflected. The siphuncle has

”
* Epznpos, deformed,

ee a

So
———

ee ee
I

wae
p> — > —~

ie y- eo

ile) 26 Sane

576

shifted less, and consequently the upper row of tubercles is brought
over the trace made by this organ in the cast of the interior.
Great irregularity appears in this substage, the costee may be bifur-
cated at the tubercles and between them, or they may run across
the venter and be bifurcated at the base of the tubercle of the oppo-
site side. ‘This ornamentation is similar to the fragment figured by
Gabb in Paleontology of California as Ammonites Cooperi, Vol. 1,
Pisaig

The dorsal crests formed by costze occupy the somewhat flattened
dorsum of the early part of the paraneanic substage, but when the
twisting begins these dorsal crests begin te be unsymmetrical also.
In other words, the lines of growth and costz assume the usual
direction and aspect of turbinate shells, whether Gasteropoda or
Cephalopoda.

The spiral is quite irregular in the anephebic substage, but is
more regular in the metephebic and parephebic substages. In the
parephebic substage the tubercles disappear in this specimen.

There is a decided contraction of the transverse diameter of the
spiral in this substage.

The absence of the tubercles on this substage is similar to the
change that takes place in /Vostoceras nebrascense at the same age
and enables one to classify all the substages satisfactorily.

Li xtteloceras,* n. g.

After a careful survey of the forms referred to this genus, it
has become evident that there is a series having the following char-
acteristics and quite separable from the full-grown stages of any
other genus referred to the Nostoceratidze. They are, however,
not so easily separated from the young of Nostoceras if my obser-
vations are correct, since the single coste with two lines of tuber-
cles are found in the young of that genus and of Emperoceras.
This, however, is entirely in accord with the system advocated in
this and other publications and is in my opinion another argument
in favor of distinguishing the group by another name.

The series of forms figured by Meek in his /nzvertebrate Paleon-
tology, P|. xxi, have a single costz with two rows of tubercles, each
costation being tuberculated. The ephebic stage is helicoceran
and the gerontic stage probably has the retroversal living chamber..

E=tzyhos, becoming extinct.

5t7

The species are as follows: Lxiteloceras (Heteroceras) Cheyen-
mense and angulatum. LE xiteloceras (Ancyloceras) uncum, Meek,
Invertebrate Paleontology, Pl. xxi, is probably a fragment of the
gerontic stage of one of these.

Exiteloceras (Ancyloceras) Jennyi, Whitfield, Paleontology of the
Black Hills, P\. xvi, has also similar ornamentation, but the costze
differ somewhat. This form, if the drawing is correct, has a ten-
dency to asymmetry and when older was probably helicoidal.

Ancyloceras lineatus, Gabb, Paleontology of California, has also
similar costz, form and tubercles, but this may be a fragment of
Ptychoceras.

I have also before me two fragments, one 20 mm. in transverse
diameter by 19 mm. ventro-dorsally, the other 17 mm. transversely
by zo mm. ventro-dorsally, which have precisely the coste and
tubercles of Hxiteloceras angulatum, as figured by Meek, namely,
very prominent, subacute single coste reaching completely round
the whorl, each one having two tubercles on the venter with a slight
depression on the prominent costation between them. ‘They are
fragments of helicoceran whorls and the aspect is altogether dis-
tinet from that of any form in other genera. Loc., Hlm Fork,
Dallas county, Texas. Mamites Fremonti, Marcou, Geology of
North America, p. 36, Pl. i, Fig. 3, is probably a gerontic stage of
some species of this group. The anagerontic substage in his figure
has single coste without tubercles, but the metagerontic substage
has the retroversal bend and every third costation has two ventral
tubercles. All costze are single and prominent.

Exiteloceras (Helicoceras) pariense, White, U. S. Geol. Survey
Vgeroo Merid., Wheeler, Pt: 1, Laz, Pie xix, Migs 2. 1s another
species of this series which shows by the twist in the costations that
it is probably in older stages helicoidal.

Ptychoceratide.

I use this family name here provisionally and only in order to
make clearer the essential distinctions that seem to exist between
the series represented by the genera, Sciponoceras, Ptychoceras and
Diptychoceras and other series of genera described in this paper.

The young, so far as known, have slight, smooth shells in the
neanic stage, the ephebic stage has the lines of growth and cost
inclined forwards in passing over the sides and venter and probably

a NENT et, SNR cially VE

CERN) tests BE

578

corresponding apertures like those of Baculites, but with less prom-
inent rostra or ventral crests. As the gerontic stage begins the
aperture changes in outline and the shell bends with a sharp curve
and forms a gerontic perforation, which is long and narrow. A
gerontic dorsal furrow appears in this bend and beyond it a gerontic
contact furrow also appears. In Sciponoceras the gerontic stage
has not been fully observed and in Diptychoceras these gerontic
characters begin to appear in the ephebic stage.

The family characters are therefore simply the straight mode of
growth and the changes in the aperture and also probably the ten-
dency observed in all species of Ptychoceras to lose the rostrum in
old age. This can be seen in the backward or aborad inclination
of the coste on the gerontic arm as compared with the forward
curves of the same in the ephebic stage on the opposite parts of the
first arm.

Sciponoceras.**

This form apparently completes the series of which Ptychoceras
and Diptychoceras are obviously members. In comparing these
two last and in studying their development and comparing them
also with the young of Emperoceras I was struck by the peculiar
form of rostrum or low, broad, ventral crest indicated by the lines
of growth in the ephebic stage and the irregularities of the constric-
tions indicating apertures especially at the gerontic bends. The
apertures of the ephebic stage may have had considerable resem-
blances to the apertures of species of Baculites in the ephebic stage,
but when old age approaches the modifications attending the ten-
dency to bend in Ptychoceras are entirely distinct and the apertures
altogether different.

These facts are nicely shown in D’Orbigny’s figures of the type
of this genus, Sceponoceras (Baculites) baculoides, Terrains Crétacés,
Pl. cxxxviii. This shell at first appears to represent the ephebic
and younger stages of a species of Ptychoceras, but on more closely
examining the drawing, if this be correct, it can be seen that it
is an outgrown or aged specimen having a gerontic stage of its own.
This is indicated by the partial disappearance of the costz near the
terminal aperture, which is also just beginning to make the first
gerontic bend and has an entirely different outline from the con-
strictions figured below on the cast of the same specimens.

* Suinwy, a staff.

579

The extremely attenuated and much elongated cone of this spe-
cies is also altogether different from that of Ptychoceras.

Another very interesting line of investigation is suggested also
by these studies. ‘The resemblances of this shell and the full-grown
and senile stages of Baculites are indications either of affinity or
very close morphic parallelism. JI am personally inclined towards
the latter opinion since Baculites itself seems to me to be a com-
posite of the extreme phylogerontic forms of several different
genetic series.

Ptychoceras.

This genus is interesting here on account of its relations to the
gerontic stage of Helicancylus and also because of the presence of
a secondary development of the impressed zone, which appears
during the gerontic stage of the ontogeny of most of the species
now referred to this genus. This last character and the close
angular bending of the straight limbs of the whorl, separate the
species wherever they occur. It is very likely that eventually this
and Baculites will be split into distinct series and shown to belong
to a number of different genera, but just now, with the exception
of Sciponoceras, this is not desirable.

The American fossils I have seen all have the two rows of ventral
tubercles and are not similar to the Helicancylus phylum in their
ornamentation. ‘They are much more like the young of Amperoce-
ras Beecheri in the singleness and tuberculation of each one of the
coste.

PTYCHOCERAS CRASSUM, Whitfield.
oc Near Boulder, Colo,, Cretaceous:
Pl. xiv, Figs. 18-21.

Fragments of this species kindly loaned me by Mr. T. W. Stan-
ton and identified by him show the following significant facts in
the history of the impressed zone. ‘The ephebic stage, which is I
think the latter part of the straight arm with closely set tubercu-
lated costze inclined orally, is of the usual rounded form in section.
The venter between the two rows of ventral tubercles is narrower
than the dorsum, which is somewhat flattened but still entirely gib-
bous, the ventro-dorsal and transverse diameters are nearly equal
near the bend. As the bend is made a decided enlargement of the
ventro-dorsal diameters occurs and the cost after this become more

580

widely separated and are inclined apically and the sides flatter.
This difference in the inclination of the ribs shows that the slight
crest in the lines of growth and probably apertures of the ephebic
stage have been lost in the gerontic stage.

The dorsum as the bend is made becomes flattened and when
this is completed it is a distinct furrow which cannot be called a
dorsal furrow or a contact furrow. ‘The true dorsal furrow, if it
occurred at all in this form, must have been between the protoconch
and the apex, the true contact furrow probably did occur in the
nepionic stage which has not yet been seen.

This furrow then which occurs in the bend before the contact of
the gerontic volution or arm takes place is probably a gerontic
dorsal furrow. ‘The lines of growth in this furrow are bent for-
wards into a slight but well-defined crest in two of the specimens
examined and the costations were wholly absent. The umbilical
perforation which occurs here is not very small and it occurs be-
tween two straight volutions and is the reverse morphically of the
nepionic perforations; thus it also is a gerontic perforation and
not an umbilical perforation, a degenerative and not a progressive
character. The length of this perforation was 4 mm. more or less
in three specimens; the vertical diameter was very much less but
was not measurable.

Just before contact takes place one costation crosses the dorsum
with a forward bend or crest in two specimens. Close to it, but
at the contact, in another specimen, there occurs a costation which
is the reverse of this, having a sinus which marks the beginning of
the gerontic contact furrow. This furrow in the only fragment
showing the dorsum in older parts of the gerontic stage obliterates
the coste. The lines of growth were nowhere visible in this con-
tact furrow, so that, whether this side had crests or sinuses in the
apertures, could not be observed.

PTYCHOCERAS TEXANUM, Shum.*
Loc., Chatfield, Texas.

Three fragments of this species, sent like others through the kind-
ness of Mr. T. W. Stanton, show peculiarities with reference to the
gerontic contact furrow and gerontic dorsal furrow, resembling
essentially those described for Ptychoceras crassum, but in this

*Identified by Mr. T. W. Stanton. See Shum., Proc. Bost. Soc. Nat. Hist., viii, p. 190.

581

small fossil the gerontic umbilical perforation is much larger and
wider in proportion.

One in fact begins to find the same difficulties in the application
of the purely mechanical theory of the origin of the gerontic dorsal
furrow here that was mentioned in accounting for the origin of the
dorsal furrow in the nepionic stages of the close-coiled Nautiloids.
My opportunities and materials do not permit me to discuss the
subject intelligently but merely to note the facts.

One fragment of a volution or an arm, apparently of this species
and identical in every way with the other two of the same lot in
ornamentation and form, has, however, a gibbous dorsum.
~ It is either not a Ptychoceras or it is the paragerontic substage of
this species after it has passed the age in which the gerontic con-
tact furrow is present, or else, as I have suspected from the exami-
nation of other species, any species of Ptychoceras may have modi-
fications that would place it in the genus Hamulina, z. ¢., some
specimens may not be closely appressed in the gerontic stage and
may not have the gerontic contact furrow.

Diptychoceras.*

The single species described by Gabb as Diptychoceras levis is of
interest in this connection as a further modification of Ptychoceras.

It has in its ephebic stage a straight arm occupying the same
position with relation to the younger or first straight arm as that of
the gerontic arm of Ptychoceras. That this is the ephebic stage is
shown not only by the presence beyond it of the third straight arm,
but also by the presence on the second arm of cost that incline
orally in passing on to the venter.

The gerontic characteristics of Ptychoceras are therefore only in
part, not as a whole, carried back into the ephebic stage of Dipty-
choceras. ‘The gerontic stage or third arm in the ontogeny of the
shells of this species is similar to that of Ptychoceras and this has
its own gerontic characters.- The tendency to the peculiar mode
of growth first found in the gerontic stage of Ptychoceras, the
closely appressed retroversal straight limb is, however, inherited in
the ephebic stage of Diptychoceras.

It would be interesting to follow out the history of the impressed
zone in the gerontic stages of shells of this species, but I have no

*Gabb, Pal. Cal., ii, p. 148.

582

materials. Gabb states that both the second and third arms en-
velop more or less the preceding, and they must therefore have
contact furrows in both stages.

VI. SUMMARY.

The importance of the impressed zone can be made apparent
better by discussing the correlative facts of the morphology than by
any other means.

When one considers the mode of growth of the young of any
one of the straight or primitive arcuate forms of Nautiloids, the
prominent fact is the bilateral symmetry of the cone and the
asymmetry of the ventral and dorsal sides as in Spyvoceras (?) cro-
talum, Figs. 1o-12, p. 361, and the young of other forms, p. 360.
It is obvious from these drawings and other observations that this
asymmetry is due to the more rapid growth of the ventral as con-
trasted with the dorsal side. This is shown by the greater breadth
of the bands of growth and the intervals between the sutures that
are greater on that side. Subsequently in the ontogeny of the
straight forms, in Endoceras, Orthoceras, the growth becomes
more nearly equal and in many forms is practically equal and the
shell is built out in nearly straight lines. The angles of the curves
made by the dorsal and ventral sides near the apex are on this
account entirely distinct from each other, the venter departing
from the end of the cicatrix at a much wider angle than the dor-
sum, which is much less inclined and soon tends to assume an
almost straight line.

The two sides, venter and dorsum, tend therefore to become less
divergent after the nepionic stage is passed, but they nevertheless
continue as long as the cone increases in the ventro-dorsal diame-
ters to grow in more or less divergent directions during the neanie
and ephebic stages except in the living chambers of certain species.
In these the diameters become shortened towards the aperture and
the sides converge more or less either in the lateral or ventro-dor-
sal diameters or in all diameters. This occurs in some species
only in the gerontic stage, but in others it may occur at any stage
after the nepionic.

In all shell-covered cephalopods, so far as known, the nepionic
shells have open apertures and all four sides are continually diverg-
ent in these younger substages of development. The asymmetry of

vo ee =

583

the apex of the conch in all arcuate and coiled forms is also very
strongly marked and there is an obvious correlation between the
close coiling of the young, the size of the umbilical perforation and
the rate of increase of the outer or ventral side. Thus in shells
with large umbilical perforations, the first whorl increased slowly and
was more nearly equal on the ventral and dorsal sides than in those
with small perforations in which the outer sides or ventral increased
much faster than the inner. ‘This is shown by the lines of growth
whenever they are observable and by the distance apart of the sutures,
both of these being much more widely separated on the venter than
on the dorsum, and also by the extremely long and gibbous outline
of the venter as compared with that of the dorsum.

One can readily illustrate this by drawing a circle with lines radi-
ating from the centre and then roughly projecting upon this back-
ground the figure of any of the species given, allowing the centre
of the radii to coincide with the centre of the umbilical perforation.
It can then be easily seen, that as the whorl grows, if the umbilical
perforation be small, the outer side has necessarily in keeping pace
with the inner to describe a much larger arc in proportion than it
does when the umbilical perforation is larger. This necessarily
follows because the two sides, starting froma given place in the
plot of the radii, are more nearly parallel in proportion as the per-
foration is larger. ‘Thus in shells with small perforations the increase
of the ventro-dorsal diameters of the body is often much in excess
of all other diameters and this preponderance in highly involute
shells may be continued until near the end of the gerontic stage.
The proportional increase in breadth of the growth bands of the
venter as compared with those of the dorsum is a corollary of
this proposition, or in other words the bands on the outer convex
side necessarily have quicker growth than those of the dorsum,
being built out farther in the same periods of time.

The ananepionic substage, as a rule, has the lines of growth
straight or with ventral crests broader in the median line than at
any other part, but in the metanepionic or early paranepionic
at latest the hyponomic sinus is introduced. While the bands of
growth still remain broader on the venter in spite of this depres-
sion on that side, there is after this stage a constant lagging
behind of the central ventral surface due to the presence of the
hyponome.

Among Ammonoidea this is not the case except in the more gen-

—.
—

=H SSS

ote se ne

584

eralized Goniatitine.* The higher Goniatitinze and almost all
shells of the remaining suborders of this order have a rostrum on the
venter. Shelis having this peculiar structure, due to the absence of a
hyponome, continue to increase or broaden out the bands of growth
after the rostrum is introduced into the ontogeny, producing often
long-pointed or palmate growths. This is certainly independent of
the spiral mode of growth and has no effect upon it, since the ros-
trum is very well developed in forms like Baculites, having phylo-
gerontic straight whorl, and it may be entirely absent in the geron-
tic stage of Ptychoceras and in forms with lateral lappets to the
apertures as in some Scaphites and other genera which are more
closely coiled.

Taking into consideration all of such facts there still remains a
certain obvious and necessary relation between the ratios of growth
of the bands on the outer and inner sides of a coiled shell which
has been described above, and which is a mechanical necessity of
growth in a spiral.

It is also true, as a rule, that the lateral diameters increase faster
in shells with small umbilical perforations than in those with large
open centres. But this seems to be merely a function of the quicker
growth and general accompaniment of the early age of such types and
to have direct exceptions that do not enable us to bring it under any
uniform law. ‘Thus Estoniocerasis a type with Jarge umbilical per-
forations and slow-growing ventral bands of deposition, but the
lateral diameters increase fast as in the young of some forms like
Li stontoceras imperfectum, Figs. 20 and 21, Pl. vii.

In nearly all shells there is a noticeable tendency to decrease the
lateral diameters in the later nepionic and neanic stages, and is
obviously due to Minot’s law of growth, which is noticed in the In-

troduction, p. 381.

Among Nautiloids it is observed in Trocholites as a generic
character occurring in the neanic stage and is in these species and
in the nepionic stage of Ammonoidea an absolute decrease so well
marked that in the former the apex and in the latter the protoconch
are not covered and can be seen beyond the outer volution, this
being the usual aspect in a ventral view of a Goniatite or the young
of Ammonitine.

A similar decrease occurs in other forms of Nautiloids than

* See Introduction, p. 355.

585

Trocholites,* but is usually less and occurs later and more slowly
and it is not an absolute decrease. That is to say the outer whorl
never falls off somuch in the ratio growth as to become actually
smaller than the inner volution in any of its diameters until the
gerontic stage. In this stage the falling off in the rate of increase
by growth may and sometimes does accomplish this result on the
last part of the outer whorl.

A description of the parallelism of different genetic series and
the constant and often repeated tendency that these exhibit to
evolve a series of similar forms has been given in the Introduction.
This tendency produces straight, arcuate, loosely coiled and close
coiled, and finally involute shells in each group, however distinct
they may be in structure.

The tendency to bend towards the side opposite the hyponome is
almost universal in all shell-covered Cephalopods. There are a
few arcuate species that bend towards the hyponome like Barrande’s
Cyrtoceras nitidum, but many even of his group of the so-called
“‘ endogastrica’’ have, like his Cyrt. Murchisonia and Cyrt. neutrum,
the hyponome and therefore the true venter on the outer or convex
cides binere: 1s only one genetic series \or) genus, as a whole;
that appears to contradict this statement. All of the species of the
true Phragmoceras except one, 2. perversum, Barrande, bend
towards the ventral side and about all have the siphuncle and also, of
course, the azygos sinus of the hyponome in the aperture and the
corresponding sinuses in lines of growth on the same side. ‘The
shells of this genus are much compressed and the apertures are very
much elongated and present a unique aspect. ‘They are contracted
along the central parts and the hyponome or motor organ is
removed as far as possible from that part of the aperture which
must have given opportunity for the external extension of the arms.
This fact, however, is counterbalanced by the aperture of P. perver-
sum, this being an extreme case of differentiation and removal as
widely.as possible of the hyponomic and brachial sinuses of the
apertures and yet the shell is bent towards the dorsum and the
siphuncle is ventral. Many species of Gomphoceras (Acleistoceras)
are bent ventrally, whereas others with similar apertures and charac-
teristics are bent dorsally. So far, therefore, as the characters of
the apertures go, it is not possible to state that the bending is inva-

*This peculiarity has led some authors to suppose that Trocholites had a protoconeh
like that of the Ammonoidea.

= RSS LS

a a er tt ee

pa fa a a Sn he Oa

p+ - eo

ie Se Ago swe

586

riably towards the dorsum, but that this is the general tendency of
arcuate forms is obvious.

When it comes to the evolution of coiled forms the problem is
different. Among these last, including also the loosely coiled or
gyroceran, there is so far as known no exception to the rule that all
such shells are bent dorsally from the earliest substages of the
conch.

I have assumed in other papers that coiling among Gasteropoda
could be accounted for by the unequal growth caused by the weight
of the shell when carried above the foot and the facts appear to
justify this conclusion in so far as that class is concerned. The
presence of the hyponome on the ventral side in Cephalopoda
would of itself account for the tipping of the shell towards the
opposite or dorsal side both when the animal was crawling and
swimming. ‘This would leave the ventral edge of the mantle free
to deposit calcareous matter undisturbed by pressure, whereas the
dorsal edge would be more subject to disturbance and to shocks
from compression which might interfere with the work of excretion.
It is reasonable to suggest such a mechanical explanation both for
the general tendency to bending and coiling and also for the dorsal
direction.

If it were possible to account for the exceptions observed, as in
the tendency of Phragmoceras towards the venter, by means of
exceptional habits or structures, this suggestion would have more
force, but unfortunately this cannot be done, at least at present. It
is obvious, however, that there is some directive cause which acts
upon every genetic series in greater or less proportion, giving to
each evolving series the same tendency to produce in succession
the straight, arcuate,* and then the coiled forms in different de-
grees of intensity and that most of these have coiled in a dorsal
direction away from the hyponome or organ of locomotion.

The position of the siphuncle with reference to the mode of
coiling need not be discussed, since it obviously has no general
relations, except that it is always, except in turbinate forms, Tro-
choceras, Turrilites, etc., and in abnormal forms, like some species

* Even in large and some small species and specimens of Baculites there is an arcuate
tendency. D’Orbigny figures this in B. incurvatus, Terr. Crétac., Pl. exxxix, and Mr.
Stanton has put together a very large specimen of Baculites in Nat. Mus. having a curve
like Cyrtoceras. This is some five feet long, straight or nearly so in the younger part

and arcuate in the older stage.
This specimen is from the Ripley Formation, Texas.

587

of Psiloceras and one of Anomaloceras and in pathologic indi-
viduals, always in or approximate to the mesal plane. ‘There 1s,
however, a fact to be noted. In the Endoceratide and Actino-
ceratide it is always in direct connection with the cicatrix. In
other forms not having an endosiphuncle* this connection is
not strictly maintained, and while it is often situated over the area
of the cicatrix, it may be, as in Eutrophoceras Dekayt, near the shell
but not over the cicatrix, or as in Hercoceras, Fig. 13, Pl. vill, at
some distance from the apex. ‘There is upon the whole, however,
a distinct tendency towards location in the mesal plane and centren
or ventrad of the centre, those having a subdorsan siphuncle like
some species of Eutrephoceras and Aturia being exceptional. In
most forms, even those having siphuncle subdorsan in the second
septum, it is nearer the venter in the first septum; marked ex-
amples of this are the Lutrephoceras Dekayi of the Cretacic, Fig.
Zeeeexaiinancdeseverall Species) on schroederoceras, or else it tends
towards the centre, as in Zrocholites canadensis, Figs. 39 and 40,
Pl. v. It is also to be observed that in the adults of most forms
of Nautiloids the siphuncle is centren or ventrad of the centre, that
is on the same side with the hyponome. This tendency is more
general among arcuate and coiled Nautiloidea than among straight
forms, which as a rule have the siphuncle centren,} and finally in
the Ammonoidea the subventran position is universal.

Whatever may be the cause of the general tendency of each
genetic series to evolve along parallel lines of modification so far as
the tendency towards coiling is concerned, it is obvious that it is
not dependent upon time, climate or any special differences of
structure. ‘The bending takes place in every series even in the
Piloceras with a huge siphuncle filled with calcareous matter and
there is no positive proof that they may not have had coiled forms
which belong to the same genetic series although none have been
found. Arcuate and coiled shells are also found in every period,
and under every condition of climate so far as geographic distribu-
tion is concerned.

It has been assumed in the Introduction that differences of habit

could be used to account for these general tendencies producing

* See Introduction, p. 412.

+The exceptions to this rule are very interesting. They include the radical type Di-
phragmoceras, the Endoceratide and the remarkable genus Bathmoceras. All of these
haye the siphuncle in most examples ventrad of the centre and in many of them it is
subventran,

2 Sc SSS See

Yee Gree;

—— << _ ———- =o entnong

ae
aac

Sane

088

parallelisms in the evolution of different and diverging genetic
series. ‘Thus the Belemonoids and Sepoids, both preéminently
swimming types* and with organizations obviously derived from an
Orthoceran radical, have straight internal shells.

There is an obvious correlation between coiling of the shell and
the habit of crawling. Thus all univalve crawling mollusca have
this general tendency. Among Gasteropoda, this is well known
and those shells which degenerate and tend to loose the spiral
mode of growth and become irregularly straightened out in these
older stages of growth, are forms which become attached or lead sed-
entary lives, z. e., Vermetus attached late in life and Magilus buried
in coral. The most significant case, however, is that of Fissurella,
which has a coiled shell in the nepionic stage and becomes similar
to Patella, a depressed, straight cone in the neanic and ephebic
stages, the habitat being like that of Patella and the approximate
forms of Haliotis and others, comparatively sedentary upon littoral
rock ledges. |

A habit of crawling could be considered as sufficiently general in
application and sufficiently persistent in an organization like that
of the Nautiloids and Ammonoids, which are covered by shell and
possess only the hyponome as a motor organ to affect entire orders
and continue constant through time and geologic changes in the
majority of forms.

With such a habit the tendency to become more exclusively
crawling and to depend upon that mode of life, might, as has been
explained in the introduction, produce in each series the same ten-
dency, but it seems impracticable, so far as my experience goes, to
find any other cause sufficiently general and likely to be undis-
turbed by geologic and climatic changes.

It is certainly not inherent in the organism to coil up. If the con-
verse be assumed one must account for the continuance and persist-
ence of the absolutely straight Orthoceras from the earliest times
to the Trias and why these were unaltered and did not become
arcuate or coiled as a whole. Inherent tendencies must, if the
term has any meaning at all, work out their own evolution to some
degree. They must sensibly affect the organization in all series
having a common embryo unless held back or kept in abeyance by
interfering causes. It is difficult to imagine any interfering cause
acting so constantly through long geologic periods that it could

* See Introduction, p. 356.

589

hold in abeyance the inherent tendency to become coiled in the
genus Orthoceras. This is more obvious when one considers that
this trunk form is perpetually giving rise to branches that show the
tendency to coil up. In assuming that habit is the cause as deter-
mined by the law explained in the Introduction, p. 367, the greatest
difficulty seems to disappear. As long as the shells could maintain
themselves in the station they have been forced into, or had chosen,
just so long would they maintain the form suitable for their habits
or surroundings and they would change only in proportion as they
changed their stations. Thus the main line might continue as long
as it existed to hold the same form while its branches seeking new
habitats and novel modes of life would change in directions deter-
mined by those. Whatever the causes may be, the fact 1s obvious,
that the tendency towards becoming arcuate and coiled is general
in the descendants of straight shells and not confined to any special
series or time.

That it is an acquired character seems also to be a reasonable
conclusion. An acquired character is one that is introduced into
the life of the individual and is not present in the embryo before
the tissues become differentiated into germ plasm and somato
plasm. It is impossible to disprove or prove that a characteristic
is acquired or genetic unless it can be followed back to its origin.
Until this is done one cannot assert positively that it was not
potentially existent in the embryo and became apparent at the
proper time in the ontogeny in accordance with genetic law.

The law of acceleration can be true only upon condition that
there are such things as acquired characteristics introduced in
epembryonic stages. The examples given above in support of this
law are all instances of acquired characters introduced late in the
ontogeny and gradually forced back to younger and younger stages
in successive generations, or species, or genera. ‘This law is based
upon the assumption that such characteristics exist and it is also
supposed to show the mode in which they are inherited.

It is not necessary for me here to deal with any of these facts,
except the tendency towards coiling among shell-covered Cephalo-
pods. ‘This tendency is manifested in the conch alone of the Nau-
tiloidea, that is, in the epembryonic stages, and we can follow it as
described above, both in the phylogeny and ontogeny, progressing
with equal steps. That is to say, the more generalized of each
genetic series show in their ontogeny that they were derived from

a aa a ca

SS ane Geer)

590

the more loosely coiled, and the more specialized show that they
were derived from forms which were tightly coiled. In other words,
the tendency to closer and closer coiling gains in the organization
of the different genetic series, and is manifested more intensely in
the young of more specialized forms and makes them coil more
quickly and closer. In general, it is also easily seen that after the
trunk forms die out in the Trias, as explained in the Introduction,
page 370, and it is not possible for any new genetic series to be given
off from these, this tendency has greater force. In the Juraand Cre-
taceous the shells are exclusively nautilian, and even the nautilian
shells with very large perforations, common even in the Triassic,
have entirely disappeared.

In the shells shown on Pl. xi-xiii there is not one that has a
really large umbilical perforation and a free cyrtoceran apex, such
as is seen in so many of the Silurian, Devonian, Carboniferous,
and even in some Triassic shells. All of these transitional forms
disappear with the trunk forms, and the same fact is true of the
Ammonoidea. ‘The transitional forms disappear in the Devonian at
the same time with Bactrites, the radical straight form of this
order. With regard to special series, it becomes more difficult to
show agreement between chronology and bioplastology on account
of the deficiencies in the records of collected forms and the gen-
eral tendency of radical species to persist and be found either on —
exactly the same level with their descendants or even to outlive
them and be present in later faunas.

In studying the coiling of nautilian shells one is struck by the
fact that the ana- and the metanepionic substages are comparatively
straight. They are not really straight, as has been explained above,
but their comparatively straight aspect, in contrast with the suc-
ceeding stages of development, is noticeable.

At the end of the metanepionic substage the curvature is apt to
be suddenly altered, bending more rapidly inward. This is what I
have called the gyroceran bend, because it is the first indication
that the shell is a true nautilan form. If one compares the length
of the ana- and metanepionic substages in the different plates begin-
ning with Pl. iv and ending with Pl. xiii, it will be seen that there
is a notable decrease in the comparative length of these two sub-
stages when the umbilical perforations become very small, and the
same is true of the species of the Calciferous and Silurian, which
have small umbilical perforations, as shown on PI. iv—vi.

591

In many shells with very large perforations the curvature is often
uniform, and there is no sudden alteration in the direction of coil-
ing of the first whorl, as in several Carboniferous forms and the
remarkable shell Plewnautilus superbus, Pl. xii. The same is true
of the coiling of all gyroceran forms in their ephebic and earlier
stages. The coiling is more uniform than that of more special-
ized and more closely coiled shells. This, and the presence of
smaller umbilical perforations in the same genetic series, is easily
accounted for if we admit that the tendency to become closer
coiled is genetic, and that in accordance with the law of tachy-
genesis it affects the growth of the young earlier in the more spe-
cialized and later-occurring forms, thus shortening up the ana- and
metanepionic substages.

The elliptical outline in section, the universal rotundity of the
dorsum in the ana- and metanepionic substages and the sutures,
serve to reinforce the assumption that these substages derive their
characteristics, so far as form is concerned, frorn arcuate or straight
ancestors. ‘This is in general the adult characters of most species
of groups having orthoceran or cyrtoceran forms, and in none,
except Cranoceras of the Devonian, has any signs of a dorsal fur-
row been found. ‘The ornamentation of these substages, and usu-
ally the paranepionic, in part or as a whole, also points distinctly
to some straight or arcuate ancestor. The ananepionic substage is
universally smooth or with only a few longitudinal ridges, but the
metanepionic varies more. The form and markings in Vestinautilus,
Pl. ix, point distinctly to a similarly ornamented arcuate ancestor,
and the gradual shortening up of the younger substages is also
shown by the figures on this plate and the explanations.

The outline of the first volution changes abruptly at or imme-
diately after the beginning of the gyroceran bend, that is, at the
beginning of the paranepionic substage in most nautilian shells.
The dorsum is apt to become flatter in species having large umbili-
cal perforations, and in those with small perforations, this tendency
is intensified and the dorsum is apt to become concave, the dorsal
furrow making its appearance. ‘The sutures of the ana- and meta-
nepionic substages are apt to have ventral and dorsal saddles,
whereas a dorsal lobe very often appears in the paranepionic, ex.,
Barrandeoceras. ‘This dorsal lobe is still more plainly marked when
the dorsal furrow is present in the paranepionic volution.

The flattening or broadening out of the dorsum, which occurs in

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592

a great many forms in the paranepionic, is paralleled by the similar
tendencies occurring in shells that have the whorls contiguous.
This is the first effect of contact, and the formation of a lobe in
the sutures also very commonly accompanies slight contacts. Nev-
ertheless, dorsal lobes in the sutures and the flattening of the dorsal
side may occur in cyrtoceran and gyroceran coils of species that
appear to be transitional, from more primitive uncoiled to the close
coiled nautilian forms, as in Barrandeoceras Sternbergi, Pl. xiv,
and other examples, such as Aphetoceras boreale, Pl. v.

These characteristics obviously exist under different conditions
on the free whorls of primitive shells and the similar whorls of
the young of nautilian shells than they do on whorls which are in
contact. In order to make these distinctions clear, I have named
the dorsal hollow zone that appears before or independently of con-
tact, the dorsal furrow, and that which occurs after that, the contact
Jurrow, both being considered part of the same feature, the com-
pressed zone.

Before proceeding further it is necessary to study the origin and
history of the impressed zone, and to define it more clearly than
has been done in the preceding pages.

In the first place, as already stated, it does not exist in any of the
trunk or radical forms, except Cranoceras. Its first appearance, so
far as the morphology is concerned, is in nautilian forms after
contact, and this occurs constantly in different genetic series. In
fact the definition of a nautilian shell is based upon the possession
of a contact furrow.

If we regard any genetic series by itself we can often see that the
impressed zone is purely a contact furrow. Thus, in the Estonio-
ceras, it is absent in the umbilical perforation on the dorsum of the
nepionic stage and it is slight and present only in the contact stages,
being soon lost upon the free part, or gerontic stage of the coil. In
other species of some other groups the same thing occurs either com-
pletely or partially: Eurystomites, Pl. v; Tarphyceras, Pl. vi;
Schroederoceras, Pl. vii, and so on.

In transitional species with large umbilical perforations, the dor-
sal furrow is not present in any specimen, although many have
been examined and recorded. In the major number of nautilan
forms, in the Silurian, Devonian and Carboniferous and quite
a number of Triassic species, the umbilical perforations are large
and there are no dorsal furrows. In many of these species the

<<.)

593

looseness of the coiling is shown by the free apex and the slight
development and late incoming of the contact furrow.

It is, of course; as has been stated above, practically impossible
in many series to get sufficient evidence to establish the agreement
of chronology with bioplastology. But there are here and there
series that show such an agreement, and give approximately com-
plete and positive evidence in favor of the descent of nautilian from
arcuate forms. But even if this agreement occurred in a smaller
mumiber of Series than it actually does, the evidence from the
morphology alone would be sufficient. It is not possible to explain
why the apex of the transitional forms with large umbilical perfora-
tions is so often free, or the existence of the larger umbilical
perforations themselves, or, in fact, any of the peculiarities of the
nepionic stage, which resemble those of radical forms, except on
the assumption that they have been derived from these same straight
or arcuate radicals through direct genetic connection. Thus,
although the chronological record may coincide with the bioplas-
tology only in a few series, these few become positive evidence of
the highest value, that confirms the inferences drawn from the testi-
mony of the bioplastology and outweighs any amount of negative
evidence derived from the incompleteness of the record.

With these remarks, we can now pass on to the consideration of
the history of the impressed zone, and its mode of origin and
apparent history in different series.

There are a number of orthoceran and arcuate forms that may be
cited as the radicals of the Tarphyceratide.

These, like the history of the transitions into Aphetoceras, are
almost complete, since in this last genus the curvature in the young,
until a late stage, is so slight that one is not absolutely certain
whether to consider that such a fragment as is figured on PI. y,
Figs. 15-17, is really a part of a gyroceran shell or a fragment of a
cyrtoceran form that never coils. The position of the siphuncle,
section of the whorl and sutures make the young of these forms
genetically identical with the adults of such forms as Aphetoceras
Americanum, and on the other hand the full-grown characters and
large gyroceran coils, are closer in some species than in others and
the genus passes by insensible gradations into the more closely
coiled nautilian genus, Pycnoceras.

This last has the large umbilical perforation and almost cylindrical

Sw ee

594.

first whorl, slight contact furrow of an ordinary transitional form, but
otherwise the nepionic stage resembles the adults of Aphetoceras in
its section and position of siphuncle and sutures.

The gap between Pycnoceras and the next member of this series,
Tarphyceras, is wide and one or more genera are needed to fill up
the interval.

In all of the genera mentioned above, except Tarphyceras, there
is no dorsal furrow, the zone of impression is produced by contact,
and the umbilical perforations are large.

In Tarphyceras, however, although in form, sutures and position
of siphuncle the genus is closely allied to Aphetoceras, the young
are altogether distinct.

As depicted on Pl. iv, the young have very small umbilical perfo-
rations, the whorls broaden out by growth rapidly, and after a short,
straight or only slightly curved apical part is built in the ana- and
metanepionic substages, the broadening volution makes a sudden
and very abrupt gyroceran bend towards the apex. ‘This is very
sudden and the umbilical perforation is flat or comma-shaped.

It might of course be shown, if other intermediate shells were
found, that the mechanical effects of this sudden bending did not
produce the dorsal furrow, but that this is an adequate mechanical
cause can reasonably be claimed by those who oppose the view that
it is due to heredity.

It has already been shown that the outer side or venter tends to
grow faster than the inner, and if this reaches a point in its ratio of
growth that far exceeds that of the inner side, it is obvious that it must
act upon that side as a force that bends or tends to make it more
arcuate in proportion to this excess of growth or rapidity of increase.
The outer side being free would be apt to retain its genetic
form, and the inner side or dorsum would be greatly influenced or
moulded by the pressure to which it was subjected. Thus it can be
assumed that in case of a sudden bending, asin Tarphyceras, the
venter would maintain its rounded outline and forcing the dorsum
inward as it grew would tend to make it assume the arcuate form or
bend inwards in a crease or dorsal furrow in the paranepionic volu-
tion conforming more or less with the shape of the dorsum of the
metanepionic volution. |

There are some reasons why this explanation is not wholly satis-
factory. In the first place, if this be the case, why did not the
whorl of the paranepionic completely close the umbilical perfora-

595

tion and plaster the dorsal shell layers against the dorsum of the
metanepionic substage? This is partly answered by the fact that
the tendency to shell building on that side would prevent this until
a small umbilical perforation was formed and also by the fact that
in many shells the whorl of the paranepionic actually does plaster
itself on to the dorsum of the metanepionic and the umbilical per-
foration is reduced to a very small aperture. It is, however, abso-
lutely essential to call in the aid of heredity, otherwise the tendency
to shell building in the dorsum of the nepionic stage cannot be
considered sufficient to prevent the entire obliteration of the umbil-
ical perforation. The shell on the dorsum of the older stages is in
great measure absent in most nautilian shells, but there is no such
difference in gyroceran or cyrtoceran forms or in loose coiled gyro-
ceran form with the whorls touching, nor yet in nautilian form with
very faint contact furrows. ‘The tendency to build thick shell on
the dorsum of the nepionic whorl, while still free, is therefore one
that can only have been derived from shells having free dorsal sides
and this tendency is obviously strong enough to stiffen that side
and prevent the entire closing of the umbilical perforation.

In the second place there are a number of Cretaceous, Tertiary
and recent Nautiloids having accelerated development of the dorsal
furrow, and in these the furrow appears on both sides of the com-
ma-shaped umbilical perforations. It is perfectly plain in these
that no bending of the whorl could account for the result and that
it is in no sense due to a moulding of one whorl upon another.
The outlines of the dorsum of the paranepionic substage in these
species does not coincide with those opposed to it; they are the
reverse of each other.

Nevertheless it is practicable, as has been said above, to appeal
to the curvature of the paranepionic volution at the gyroceran bend
as a possible mechanical cause for the incoming of the dorsal furrow
on the distal part of the curve so long as the curve is sufficiently
abrupt to produce it, or so long as the absence of ancestral forms
does not enable us to trace the origin of this character back to a
contact furrow and account for its presence in the earlier stages of
species like those of the genus Tarphyceras by the action of the law
of acceleration.

I have consequently thought it safer for the sake of argument to
concede that the dorsal furrow of Tarphyceras was perhaps present

Ear SSeS

— fi

O96

in the paranepionic because of mechanical and not through genetic
causes.

In the Trocholitidz the straight and arcuate forms are not yet
known nor are the nautilian forms quite satisfactory.

The dorsal side of Lztoceras insolens, which has a comparatively
large umbilical perforation, has not yet been studied in the parane-
pionic substage, and although it seems very likely that it is gibbous
and without a dorsal furrow, this cannot be stated positively. In
Trocholitoceras and Trocholites, the umbilical perforations are very
small and have dorsal furrows on the paranepionic after the gyroce-
ran bend has been passed by.

The same argument can be framed for their appearance that was
used for the Tarphyceratidz, viz., that the weight of evidence is
in favor of the mechanical generation of the dorsal furrow in the
paranepionic. ‘There is also one fact possibly of some importance
in this connection. In the specimen of TZvrocholites canadensts,
in section Figs. 39 and 4o, Pl. vi, it can be seen that the inner part
of the dorsal furrow, where it first appears, is a single, broad fur-
row. As it becomes more distant from the gyroceran bend, how-
ever, it becomes divided into two smaller furrows by the rising of
a central gibbous face.

It might be assumed that the development of this central gibbous
face was due to heredity, this being the expression of a tendency to
return to the rounded dorsum of radical types as soon as the pres-
sure due to the abrupt bending was removed.

Precisely similar furrows and a median gibbous face occur, how-
ever, on the dorsum of Cranoceras. The curvature of this form and all
of its characteristics indicate that the bending of the cone could not
have been the mechanical agent which caused a single dorsal furrow
and the appearance of the two dorsal furrows and the central gib-
bous face complicates the problem and seems to make it insoluble
on a purely mechanical basis. I have called this a gibbous face,
but in reality it is not a ‘‘face’’ at all in the sense in which that
term is here used. It is a modification of the primitive rounded
dorsum and is really a ‘‘zone’’ or secondary modification. In
Trocholites it arises as a modification of the dorsal furrow, and is
therefore a true ‘‘ face.”’ It is possible that with advance of knowl-

edge this distinction may be more important than it seems now, and
may enable us to explain the exceptional characteristics of Cranoceras.

Before it could be safely assumed that mechanical causes gener-

597

ated the single or double dorsal furrows of Zrocholites canadensis,
or that heredity influenced the appearance of both, it would be
necessary to find more forms of the same genetic series and study
their history.

In some species of the genus Schroederoceras, the dorsal fur-
row appears as in Trocholites. ‘The umbilical perforation is larger
but still small in all of these, so that it can hardly be assumed that
the bend is too gradual to have caused the dorsal furrow to arise in
the paranepionic.

The gerontic stage of the species of this family, in fossils well
enough preserved to be observed, has an impressed zone which is
very short-lived in some species when the last whorl is free. The
entire obliteration of this zone takes place in Schroederoceras Eatont
in one specimen, Pl. vi, Figs. 28-35, and in another it is present
for a longer time after the volution becomes free, although evidently
much reduced, Figs. 7 and 8, Pl. vii. In Schroederoceras casinense,
Pls. vi and vil, similar obliteration can be observed.

The zone, however, persists long enough in these forms and
others to demonstrate the important fact that it has a deep hold
upon the organism. If this were not the case it could not exist in
substages of senile degeneration. Its persistency is somewhat less
in the species cited than rmany others, ex. Aurystomites Kelloggz,
Pl. v, but it is sufficient to show that its continued existence in the
ontogeny is not wholly limited by the continuance of close coiling
and contact. That it is more or less dependent upon coiling with
involution is obvious because it entirely disappears in some species
in the older substages of the gerontic stage when these are free.

The Tarphyceratidze and Trocholitide having so closely involute
shells in the young are confined, with the exception of Trocholites,
to the earliest or Calciferous faunas.

The next forms that one meets, having the impressed zone, occur
in the Devonian. ‘There are so far as known no shells having an
impressed zone in the form of a dorsal furrow between the Hudson
River group and the Devonian group, although there are many having
the contact furrow.

The Devonian genus Cranoceras, referred to several times above,
consists of two species with very large shells, and, so far as can be
seen, purely arcuate forms, is the only case of a cyrtoceran form
with a dorsal furrow that I have been able to find. The zone in
this shape appears on the free inner or dorsal side and is obviously a

598

dorsal furrow similar to that which appears on the dorsum of the
nepionic stage. The section of this whorl is nephritic. The ap-
pearance of the dorsal furrow is very often in the young and in later
stages of growth correlated with the appearance of a nephritic out-
line in the whorl. ‘This happens so often that I at first supposed it
was a general law of association the two appearing together. It is
true, that in a number of forms, the nephritic form appears in asso-
ciation with the dorsal furrow, but in quite a number of others the
outline is not nephritic, and yet a dorsal furrow arises as will be
noted farther on.

The large size and gradual curvature of the cone in this genus
makes it unlikely that the existence of the dorsal furrow is due to
contact or to any mechanical effect of coiling. The dorsal furrow
in these is either due to inheritance from other species, or is acquired
in their later or ephebic stage.

The genus may be degenerate and may have arisen from coiled
forms and the dorsal furrow and nephritic outline may have been
derived from thissource. Against this is the fact that the shells are
of large size and the septa are closely approximate. Both of these
characters are common in primitive Paleozoic shellsand uncommon
in degenerate phylogerontic series. The study of the fossils them-
selves does not seem to support this view of their affinities since it
is difficult to point to any preéxisting coiled form from which they
could have been derived. If it is assumed that they are primitive
arcuate forms descended from other arcuate forms or straighter
cones, it is easy to trace them back into the Silurian and point out
their probable ancestors, in closely allied species which do not have
a dorsal furrow.

The problem here assumes a very interesting character due to the
fact that the Silurian forms of Cranoceras, C. furnus, and others
have trigonal whorls and sutures which are in every way identical
with the young of several nautilian shells of the same period and
are evidently their ancestral radicals. These arcuate species, how-
ever, do not have dorsal furrows, and it seems, therefore, highly
probable that here is a case of acquired characteristic coming in very
late in the ontogeny of the ephebic stage, accompanied bya nephritic
outline.

Contact furrows arise from close coiling in fossils like Wedyceras
vetustum having similar subtrigonal whorls, but no examples are

599

known in these groups of the appearance of a dorsal furrow in the
young.

Anomaloceras anomalum is a remarkable Silurian fossil, on
account of the habitual excentric position of the siphuncle, but this
is always near the venter and in this species the form of the shell
and character of the sutures show that the genus belongs in the
same genetic group with Hercoceras.

In Hercoceras the evidence is very complete that the impressed
zone originated as a contact furrow. In all the gyroceran forms of
the allied genus, Ptenoceras, there is nothing of the sort. In the
loosely coiled forms like Hercoceras irregularis, Pl. viii, Figs. 14
and 15, there is no dorsal furrowin the nepionic stage. Even in the
closely allied Hercoceras mirum, although the last has a small um-
bilical perforation, there was no dorsal furrow in the single specimen
examined and figured (PI. vii, Figs. rr and12). So far it is obvious
that close coiling does not of itself even with a favorable form of
whorl necessarily bring about the genesis of a dorsal furrow.

If the sudden bending of a broad whorl was necessarily followed
by the formation of a dorsal furrow it would certainly have been
produced in Hercoceras mirum. A single exception in such cases
becomes a very significant positive fact against this assumption, and
that exception appears to occur in thisspecies. ‘The terminal mem-
ber morphically of this series is Anomaloceras, and in the single
species of this genus known, there is a dorsal furrow as shown in
Figs. 16-20, Pl. viii. ‘The umbilical perforation was small in this
shell, and of course it can be claimed that the furrow in the para-
nepionic was produced by mechanical pressure, and not inherited
from forms like Hercoceras, in which it first arose as a contact
furrow.

Potoceras dubtum, which has been figured on Pl. x, Figs. 15-22,
has unfortunately no recorded locality, but as noted in the description
there were indications that it was a Devonian fossil. At any rate,
whatever its age, the characteristics were plain and the presence of a
dorsal furrow in the paranepionic easily established.

The length of the ana- and metanepionic substages were decidedly
Paleozoic, and so also was the large umbilical perforation. It is
more difficult here to account for the genesis of the dorsal furrow
upon the mechanical hypothesis than in Anomaloceras on account
of the large umbilical perforation and the slow growth of the apex.
Nevertheless it can be reasonably claimed that the abruptness of

me ee

600

the gyroceran bend in this shell is sufficient to account for the dor-
sal furrow in the nephritic outline of the paranepionic substage.

In the preceding remarks I have dealt solely with those genetic
series and forms in which the dorsal furrow appears, but there are
many in which there is no sign of any furrow.

As has been said above, all of the straight and arcuate forms and
the gyroceran shells, in none of which has either a dorsal or a con-
tact furrow been found, except in Cranoceras. Passing these by,
one comes to the nautilian shells which are transitional between the
gyroceran and nautilian having the whorls in closer connection than
in the gyroceran and a slight contact furrow. ‘These, so far as
known, have other correlative characters. The umbilical perfora-
tions are large and open, the apex of the conch is often free, the
contact taking place on the venter of the ana- or metanepionic sub-
stage or later, and the whorls are subsequently never involute, or in
other words, they are discoidal shells.

In these shells I have in Paleozoic time found no exception to the
rule, that the dorsum of the nepionic stage is convex, and there is
no dorsal furrow, a furrow being formed only after contact, and in
later stages of development. One of the best examples of these
series is that of Barrandeoceras. Barrandeoceras Sternbergi contains,
as has been stated in the descriptions, two distinct forms, one Bar-
randeoceras Sternberg?, Pl. xiv, Fig. 3, has the whorls approximate,
and in the other they are not in contact. The purely gyroceran
character of these shells is apparent in the loosely uncoiled
young as well as in the later stages. They are also valuable
in showing that the flattening of the dorsum and a dorsal lobe may
arise as in Pl. xiv, Fig. 5, independently of contact, and this and
the form of the ephebic stage is precisely similar to that of the para-
nepionic volution of Barrandeoceras tyrannum. In this last and in
Barrandeoceras Sacheri and Bohemicum, there is no dorsal furrow,
but these ephebic characters of Sternberg? are repeated and a contact
furrow is produced after the whorls touch.

Estonioceras is another series in which nearly all degrees of coil-
ing can be studied, and here also the absence of a dorsal furrow in
the nepionic stage isa marked characteristic. The contact furrow is
maintained as long as the whorls are held together, showing pro-
gressive growth, but this rapidly disappears in the gerontic stage, as
shown by the figures given on Pl. v and vii.

Remeléceras impressum is also a good example of the generation of

ee _

601

a contact zone in the later stages of development given on Pl. viii,
Figs. 1-8.

Another belonging to the same category is Eurystomites, of which
the species are described and figured on Pl. v. This genus has also
its corresponding gyroceran forms in Barrandeoceras convolvans de-
scribed in the text and the resemblance of these to the young of
true species of Eurystomites is very close.

The series of the Tainoceratide are interesting in this connection,
because in the earliest species of Temnocheilus itself, which occur in
the Devonian, there is no dorsal furrow, and only a contact furrow
as isshown in Figs. 27 and 28, Pl. x. The umbilical perforation is not
large, and in succeeding species in the Carboniferous, although
there are several genera, there are none having the dorsal furrow.

Metacoccras cavatiformtis, Fig. 16-19, p. 496, and Pl. x, Fig. 32,
are good examples of this group.

Among the most remarkable of the Silurian series in which no
dorsal furrow was present is that of the highly ornamented and
modified genus Ophidioceras. The elaborate ornamentation of the
shell and the costz, combined with a peculiar hollow ventral zone
bordered by ridges, the free living chamber and aperture with
lateral and dorsal crests show this type to be very peculiar and
highly specialized. The small size and shape of the umbilical per-
foration shows also very close coiling. One would suppose this
amply sufficient in a quick-growing whorl like that of Ophidioceras
to force the premature development of a dorsal furrow, but there is
not the least sign of one in either of the three species examined and
figured on Pl. viii. In this group a very interesting fact is notice-
able in the gerontic stage. The impressed zone is persistent on the
free dorsum until it meets a projecting spur which coincides with
the more or less abrupt htuitean bend on the venter. On the other
side of this spur, it has, however, such a hold upon the organization
that it is not obliterated by the building of the spur, but is resumed
again on the oral side, and continues to the edge of the aperture.
In this last stage, however, the impressions made by the sharp ridges
on the borders of the median ventral zone are obliterated, and when
near the aperture the zone becomes narrower and shallower and
finally disappears.

Endolobus (Pl. viii, Figs. 36-39) is another example of the
absence of a dorsal furrow in a good-sized umbilical perforation and
the presence of a contact furrow in the older stages.

aes) Vee T

602

The mechanical moulding of the dorsum upon the venter of the
next inner whorl is shown of course in all of these examples, but it
can be still better illustrated by such forms as Ophidioceras, just de-
scribed, and Apheleceras mutabile (Pl. x, Figs. 29-31) and Dzorugo-
ceras planidorsatum (Pl. xii, Figs. 1, 2). These and many other
examples besides those figured serve to demonstrate that in every
shell, so far as known, the configuration of the dorsum is absolutely
dependent upon the shape of the venter, the former being invariably
a reverse or mould of the latter. The same is also truce im the
earlier stages of the contact furrow in those species that strike and en-
velop the apex of the conch.

The number of series which have close-coiled shells, but in which
the impressed zone is purely a contact furrow, is in the Carboniferous
even larger than in the Devonian, but it will suffice to refer to two
extreme examples. Ephippioceras, which is a highly specialized
species with peculiar sutures and septa and very involute, appears to
belong in this category, and also Phacoceras, ‘These forms are in
part figured on PI. ix.

Similar transitional shells with good-sized or large umbilical per-
forations are also present in the Trias, and are illustrated in
Syringoceras granulosostriatum and linearis, Pl. xi. There are
several other species in the Trias that belong in the same category,
but it is not always easy to get preparations that will establish the
fact that the dorsal furrow is absent.

The disappearance of the straight and arcuate types in this period
together with the transitional nautilian shells has been remarked
above, and in the course of the following pages this fact will be
noticeable. In dealing with those types in the Carboniferous that
possess a dorsal furrow, one is struck by their small number and
their decisive testimony in favor of the assumption that the dorsal
furrow is inherited.

The phylogerontic character of Coloceras globatum is evident
from the figure of the ananeanic stage on Pl. x, and the comparison
that may be made with the senile whorls of Vest/nautelus koninckt.
It then becomes obvious that Coloceras belongs to the same genetic
series as Vestinautilus, but that it inherits degenerative characters
at an early stage. It is in other words a degenerate form with a
highly accelerated development of the gerontic or degenerate
characters of other species of the same series. Of course this ac-
celeration affects both the ornamentation or ridges as well as the

603

form. It is to be anticipated of course in species of this kind that
other characters will also show acceleration. Accordingly one finds
as shown in several figures that in Co/. globatum a dorsal furrow
is to be found in the paranepionic substage.

The umbilical perforation is of good size in this species, the
curvature is often gradual and uniform, the ana- and metanepionic
volution increases slowly in size, and there is apparently no
mechanical agency in any of these characteristics that would have
caused or led up to the appearance of the dorsal furrow in the para-
nepionic substage. Another point is obvious in this species. It is
a descendant of a special series which probably arose from Zhora-
ceras Puzonianum and canalculatum, or some species of more an-
cient origin combining the characters of these two. ‘This series
then obviously passed through the distinct phases of gyroceran and
nautilian evolution and acquired a contact zone, which in the highly
specialized phylogerontic Coloceras became by the law of tachy-
genesis a dorsal furrow inherited in the paranepionic.

The facts in my opinion cannot be accounted for on any other
hypothesis.

It is hardly doubtful when other involute and highly specialized
shells have been fully investigated that many more examples of the
accelerated inheritance of the impressed zone will be found.

Wiannoceras Lrieslebem (Pl. xi) is) the only ‘species: imsthe
Dyas that I have been able to investigate, and this has a dorsal
furrow and a small umbilical perforation. Its congeneric forms are
also unknown, and its evidence is consequently not of much value,
except in so far as it shows the occurrence of this class of forms in
this period.

I was not able to obtain shells having small umbilical perforations
and suitable for examination in the Trias, and have to leave that
period a blank record except in so far as noted above.

The close-coiled shells of the Jura are, however, sufficiently
abundant and the evidence very interesting.

In the first place, as noticed elsewhere, there are no arcuate radi-
cals in existence. They have all disappeared in the Trias, and with
them went also the transitional forms of all kinds, the gyroceran
and even the primitive nautilian with very large umbilical perfora-
tions. Under these circumstances one should expect to find a
decided change in the behavior of characteristics.

If the impressed zone was maintained and perpetuated by mechani-

604

cal means, by the abrupt curvature of the whorl at the gyroceran
bend, and had not through time or constant repetition become
fixed in the organism and genetic, one ought to find in some species
of the Jura having larger umbilical perforations than others, that a
dorsal furrow was absent, or else variable and often very slightly de-
veloped.

Suppose, on the other hand, without paying any attention to the
manner of the origin of the impressed zone, except in so far as the
facts show that it appeared late in the life of primitive species
and is an acquired character, one asserts that time and fixation in
nautilian shells has made it hereditary.

It is then of no consequence whether a given shell of the Jura has
a large or small umbilical perforation. Being a highly specialized
nautilian shell and apparently without other than strictly nautilian
progenitors, it follows from the law of tachygenesis, that the im-
pressed zone ought to be represented by a dorsal furrow in the para-
nepionic substage, or earlier in every species. ‘The mechanically
generated contact furrow of transitional nautilian shells occurs in
the ana- and metaneanic substages, rarely later, consequently if
the dorsal furrow arose out of this through the law of tachygenesis
it should appear in the preceding stages of the ontogeny before the
whorls touch in every shell of the Jura.

It is of course possible that exceptions to this rigorous logical de-
duction might have occurred in diseased young individuals, or in
species directly traceable to arcuate forms in the Trias, but so far
no such shells have been found.

In looking at the apices of the species of Digonioceras and of
Cenoceras, considerable difference is noticeable in the sizes of the
umbilical perforation. For example those of Digonioceras excava-
fum, Pl. xi, and Digonioceras, sp. (2), Pl. xii, Figs. 6-11, are com-
paratively quite large. But in these the dorsal furrow appears at the
same age as in Cenoceras intermedium and others having very much
smaller perforations and more rapid increase of the metanepionic
substage. In other words, the rapid increase of the ventro-dorsal
diameters and other diameters and the sudden bending of the shell
and the abrupt gyroceran curve of Cenoceras intermedium and Line-
atum and clausum have no effect whatever upon the genesis of the
dorsal furrow. As if to make this conclusion still more secure,
Cenoceras aratus, the single species in the Jura, which does present
a slight acceleration in the development of the dorsal furrow, has

605

an umbilical perforation which is of medium size and has also
slower growth of the metanepionic and paranepionic substage than
most of the shells of this period. ‘This species, figured on Pl. xi,
Figs. 32 and 33, has so large a perforation and so gradual an in-
crease in bulk of the nepionic, that it affords no basis for a belief
in mechanical causes. If it had been found that the dorsal furrow
occurred a little later or not at all in this specimen then there
might have been some grounds for the supposition that genism had
had no influence upon the perpetuation of the impressed zone.
But when one finds in place of retardation a slight acceleration in
the development of the dorsal furrow the facts certainly appear to
be very strong in favor of the ordinary theory of diplogenesis and
tachygenesis.

The same argument applies with greater force to the Nautiloidea
found in the Cretacic. ‘These being more remote than Jurassic
species from any primitive nautilian forms, they ought to exhibit
the action of tachygenesis in the earlier appearance of the dorsal
furrow at least in a considerable number of the species.

From the remarks already made above and from the figures
given, especially on Pls. xii and xiii of this work, it may be seen
that so far no specimen has been found in this period which did
not show the presence of a dorsal furrow on the metanepionic volu-
tion, a substage earlier than most of the species of the Jura. This
fact has alreadv been used in other connections, especially in the
discussion upon the relations of the dorsum to the venter in nau-
tihan shells. It is very positive evidence against the supposition,
that the configuration of the dorsum of the metanepionic substage
has any effect upon the outline of the dorsum of the paranepionic
even in cases where they are brought close together on the opposite
sides of even the narrowest of umbilical perforations. Provided it
did not touch it is obvious that the dorsal side of the paranepionic
substage in Cretacic shells was free to assume any shape.*

In following the same theoretical line into the Tertiaries, the
evidence is less satisfactory; only one species was found, Autrepho-
ceras tmperias, which gave any evidence. ‘This had the dorsal
furrow in the metanepionic substage. The Aturidz, however,

*Tt will be easily seen that this argument could also be applied to the case of Trocho-
lites canadensis, but in the absence of positive evidence in the genetie series of the
Tarphyceratide I have thought it best not to assume that such use could be made of the
parallel facts observed in Mesozoic shells.

606

showed the highest degree of tachygenetic development in all the
structural characters of progressive evolution among Nautiloids.
That is to say, the size of the apical chamber, the immediate
assumption of a highly matured outline in the first suture which
has the aturian generic lobes and ventral saddles, the subdorsan
siphuncle, the minute umbilical perforation and the rapid increase
of all the diameters of the apex in the nepionic stage and the
almost complete involution of the apex and first whorl in neanic
stage, all indicated a high degree of acceleration. It is therefore
probable that in this family a correspondingly early inheritance of
the dorsal furrow will also occur, unless there is some interference
arising from the highly tachygenic development of the character-
istics cited above in the metanepionic substage that may have re-
placed it or rendered it very obscure. Sections ought to have been
made to establish this fact, but I could not obtain materials for this
purpose in the limited time at my disposal.

The existence of the dorsal furrow has been observed in the
metanepionic substages of the three existing species of Nautilus
that are the most important, viz.: the least involute autzlus um-
bilicatus, the most involute Wautilus pompilius and the degenerate
shell of Wautilus macromphalus. It might of course be expected
that some of the less involute shells of the Cretaceous, Tertiary or
Present, if any such be found, would resemble the Jurassic shells in
having a dorsal furrow in the paranepionic. I expected this might
occur in Vautilus umbtlicatus, but so far as I could see the dorsal
furrow appeared in this shell quite as early as in Vaurilus pompilius
or macromphalus.

I here take the opportunity to refer to the structure of the shell
of the dorsal side among Nautiloidea.

The shell of course in all forms with free whorls is as complete
on the dorsal as it is on the ventral side. It is also complete on
the dorsum in the nepionic stage of all nautilian species. An
additional layer called by various names, but known in the modern
Nautilus as the black or dark-colored layer, makes its appearance
after contact and lies between the exteriors of the shells of the
venter and dorsum in each whorl.

I have never been able to detect the homologue of this layer
among fossils probably because it is necessary to look for it in sec-
tions under the microscope.

As regards the behavior of the shell in the impressed zone after

607

contact it is obvious in all fossils, as it is in the Nautilus, that the
outer porcellanous layer is apt to disappear in the contact furrow
and that this disappearance is due to contact seems almost beyond
question, especially in Schroederoceras and other shells that have
free whorls in the gerontic stages.

In Paleozoic shells, like Hurystomites Kellogg¢, Schroederoceras, °

Estonioceras and many others the loss of the excretory function is
only temporary, since the free volution is protected on the dorsum
by a thick shell as soon as it begins to depart from the spiral. In
all of these that I have observed, the contact area has not been
large, but in Axnomaloceras anomalum, Trocholitoceras Walcott,
Lindolobus avonensis, ‘Varphyceras and others in which the contact
is closer and the furrow broader, the outer porcellanous layer does
not pass on to the dorsum.

Pompeckj* states that the mantle border of aut:lus pompilius on
the venter and sides has triple folds and two furrows, which indi-
cate that these parts of the rim of the border secreted the outer
porcellanous layer which protects the body of the animal on the
outer exposed sides. On the dorsum the continuation of this
border is entire and not furnished with folds or furrows for secre-
tion of the porcellanous layer which is also absent on that side.

The aperture is not built out on the dorsal side in any involute
Nautiloid that I have been able to examine.

I have not yet been able to find in any of the involute shells
observed to have this peculiarity and in which the suppression of
the dorsal layer was more complete, that the last volution became

free and that the deposition of dorsal shell layers was resumed in.

the gerontic stage. The evidence at present from this accords
with that to be obtained from coiling, namely, that shells having a
certain degree of closeness of contact or involution do not as a rule
have a free volution in the gerontic stage. That the aperture
might have become free and still be protected by adequate shell
layers on the dorsum in the gerontic stage remains to be deter-
mined. ‘That this must have been very rare, if it ever occurred, is
shown by the fact that no shell has been observed in the Paleozoic
and none have been seen in the Mesozoic, Tertiaries or recent
Nautiloids, having such a gerontic stage at the apertural end of an
involute whorl.

In recent Nautilus it is especially noticeable, as stated above,

* Amm. mit Anormal. Wohnkammer,”’ p. 259.

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608

that gerontic degeneration is slight and does not affect the amount
of involution nor the size of the whorl. ‘This may be due to the
rarity of shells that have reached an advanced age or to the brittle-
ness of the senile volution, but against this there is sufficient evi-
dence.

Thus, in many Mesozoic fossils and in recent Nautili, shells are
often found with the last two or three septa approximating and this
is plainly a mark of the failure of the powers of growth and shows
in most examples of large size that the animal has probably reached.
the extreme limits of its existence.

One fact is of great interest in this connection. Extreme cases
of degenerative series are rare among Nautiloidea. The Lituitide
stand alone as the only complete series that can be compared with
several that are found among Ammonoidea. The Discoceratide
have also some turbinate genera that can be closely compared with
the helicoidal spirals of a number of Ammonitinz. All such forms
and others that may be supposed from their characteristics to exhibit
similar characteristics, disappear with the Paleozoic and all, so far
as I know, before the Carboniferous period. ‘There are phyloge-
rontic species like Coloceras globatum in the Carboniferous, but no
uncoiled phylogerontic forms.

In Mesozoic, Tertiary and Cenozoic times, the uniformity of the
type is conspicuous, and while it is plainly degenerating from the
Carboniferous to the present, this process is not accompanied by
the evolution of uncoiled series. ‘The degeneration takes place as
stated above in ornamentation of the shell and in the number and
variety of the series and forms evolved, but not in the coiling,
which is really progressive, nor yet in the sutures, since Aturia is
certainly one of the most if not the most highly accelerated and
specialized of the whole order.

These facts all bear directly upon the history of the impressed
zone, since in all uncoiled whorls the primitive contact furrow tends
to disappear and the outer dorsal porcellanous layer is restored to
its full development on that side.

-In Paleozoic time as well as in later times no involute shell has
yet been observed with a free gerontic volution, that is to say, when
the area of involution reached beyond the limits of the venter and
the area covered extended inwardly on to the sides of the next
inner whorls, the gerontic stage also remained involute, or, if
decreasing in its ventro-dorsal diameters, this decrease never seemed

609

to reach the extreme point of degeneracy, so as to allow the aper-
ture to become again free and complete on all sides.

This is, of course, negative evidence and it may be, as in Ammon-
oids, that the dorsal edge of the mantle never loses in any series
when restored to freedom the power to resume the shell-secreting
structures and function on the dorsal side. It can be readily seen
that as the whorl became gradually loosened from the inner whorl
the mantle border would extend the secreting furrows inwards from
both sides, or, more correctly speaking, perhaps, the non-secreting
edge of the dorsal border would be contracted and finally disappear.
There is no antecedent improbability that this might not take place
in any involute nautilian shell at a sufficiently degenerative substage
of itsontogeny. The remarkable fact, however, remains that it does
not take place so far as I know, although I have constantly been on
the watch for some such examples.

Ammonoidea.

It is not necessary to give any extended notices of observations
on special groups in this order. I have already described the
absence of the impressed zone in the ordinal radicals Bactrites and
im) most of the Nautilinide on pp. 361, 362, 411, 413 and the
figures and explanations of Pl. ii, and Figs. 40-42, Pl. viii, of
Mimoceras lituum. The more specialized genera of the Goniati-
tinee have the impressed zone, but it is strictly a contact furrow and
appears as shown in figures of Agonzatites fecundus, one of the Nau-
tilinidz, sometimes very late in the ontogeny. In other still more
highly specialized species the loose coiling of the young, figured by
Sandberger in several species of Gephuroceras, Alanticoceras lati-
dorsale of the Devonian and by the author in Glyphtoceras crenis-
tria and atratus of the Carboniferous* indicates, that this zone is
either absent on the ananepionic dorsum, or, if present, must occur
as a slight dorsal furrow due to tachygenesis. The larger number
of the Goniatitinze, as shown by Branco and the author, have, how-
ever, such closely coiled nepionic stages that, as in all Ceratitine,
Lytoceratine and Ammonitine, so far as known, the umbilical per-
foration is closed along the mesal line as shown in Fig. 3, PI. iii,
and is represented only by funnel-like lateral prolongations, which
do not appear to have an open connection with each other.

* Embryology of Fossil Cephalopods, P|, iii.

610

The impressed zone is among most of the Ammonoidea therefore
essentially a contact furrow, and the tendency to close coiling has
been accelerated to so great an extent that contact takes place
between the permanent protoconch and the ananepionic substage and
a contact furrow is thus produced earlier than in any known Nauti-
loid. The position of the first septum in the aperture of the pro-
toconch shows that. contact must have taken place before it was
deposited as the floor of the ananepionic living chamber, z. ¢., at
the very beginning of the building of the apex of the conch.

It is also obvious that this high degree of acceleration in devel-
opment was attained in the Devonian, as a permanent hereditary
character of the whole order since the Nautilinidz are the only
representatives of the Goniatitinze in the Silurian and disappear in
the Devonian. There are also but very few species with open um-
bilical perforations in the Devonian, outside of the Nautilinide,
and so few in the Carboniferous, that Branco denies the correctness
of my figures of the two species above mentioned. That open um-
bilical perforations should occur sporadically in the young of some
Carboniferous species of Goniatitinze is of course to be expected,
and that Branco should not have found any simply demonstrates
the rarity of their occurrence.

The history of the impressed zone among Ammonoidea is par-
allel with that of the Nautiloidea in regard to the shell layers
on the dorsum. ‘These are complete in Bactrites and all of the
Nautilinidz which do not have a contact furrow and incomplete in
all Ammonoids that do have this furrow, the outer layer reaching
only to the lines of involution. This is shown in Fig. 3, PI. iui,
and it is observable in this that the shell of the apex of the conch
appears to end at the outer edges of the umbilical perforations, but
this observation needs revision or confirmation. ‘There is a third
layer between the dorsal and ventral walls of the shell correspond-
ing to the organic black layer of Nautilus and it is often calcareous
and well preserved in some fossils.* ;

The extraordinary variety of degenerative series among Ammon-
oidea and their connection with the history of the impressed zone
is of great importance in this paper.

The duration of the habit of close coiling and involution in the
majority of shells from the Devonian to the Cretaceous is the most

* There is the same tendency to calcification here as in the case of the protoconch as
compared with the membranous protoconch of Nautiloids.

Sake

611

noticeable and one of the most persistent characteristics of the
general morphology of the order.

Nevertheless, in every example of uncoiled phylogerontic shells
the impressed zone tends to become less and to disappear, obeying
the same law as among the Nautiloids. There is, however, a dif-
ference in its behavior, which is at first rather confusing. Involute
shells may have free gerontic volutions and in these the zone does
not appear to have, as a rule, so deep a hold upon the organization
of the Ammoncoids that it does upon many of the Nautiloids.
For example, in deeply involute Scaphitoid shells there may be free
living chambers in the gerontic stage and the zone diminishes
greatly, almost disappearing on the edge of the aperture. In crio-
ceran and baculites-like forms, however, it does not appear to per-
sist to any marked extent upon the dorsum beyond the cessation of
contact in the young whorl.

There are no examples in the history of its retrogression which
can be compared with the persistency exhibited in a number of
Nautiloids. For example, in Aurystomites Kelloggz, Ophidioceras
and others the impressed zone, although it may not be present in
the nepionic stage before contact, and very shallow after contact,
nevertheless persists in the gerontic stage. Although showing a
tendency to disappear and finally vanishing at the aperture, the pro-
cess is slow, and it has obviously made a strong impression upon
the organism.

What has previously been said of the degenerative characteristics
and degenerative series of the Nautiloidea may be of some assist-
ance in clearing up this apparent anomaly. The phylogerontic
transformations of the Lituitidze, as stated above, are the only ones
among Nautiloids that can be compared with any of the completely
uncoiled retrogressive series of Ammonoids. Although in the
Lituitidz the impressed zone is a mere contact furrow of slight
extent and obviously transient development, nevertheless they serve
as a comparative standard to show how much more complete the
degenerative changes are among the Ammonoids than among Nauti-
loids. If the observer studies any species of Ammonoid in the
gerontic stage the same morphic law becomes apparent. As I have
tried to show in Genesis of the Arietide,* the greater specialization
and more complex ephebic development of the ontogeny in Am-

* Pp. 28-37.

612

monitinge is attended by a correspondingly intensified series of
degenerative changes in the gerontic stage.

Considering the nature and extent of these retrogressive changes
in both ontogeny and phylogeny, one ceases to be astonished that
the impressed zone disappears quickly in any individual and begins
to wonder at the conservative power of genism which preserves the
close coil of the nepionic stage as a definite record of the derivation
of such straightened out shells as Baculites. I have tried to account
for this by supposing that the young of even these degenerate forms
had similar habits as those of their ancestors, or were specially pro-
tected. The former supposition may be the true one, since it is
entirely in accord with the facts that the tendency to degeneration
should not necessarily take effect upon the development of the
earlier stages, but the latter can hardly be true.

The retrogressive forms have usually slenderer shells than the nor-
mal forms, and there is no evidence that they possessed any special
pouches or contrivances for the protection of the young.

It is interesting in this connection to notice the results of an ex-
tended research made by Dr. F. J. Pompeckj upon these extra-
ordinary Ammonitine. His observations include about all of the
more remarkable distorted fossils of this kind from the Carboniferous
to the Cretaceous, especially those which have contracted apertures
and exhibit connections with normal forms. Dr. Pompeckj arrives
at the conclusion that the living chambers having such peculiarities
are one and all to be classed as senile characteristics.

His conclusions are as follows :

‘‘y. Die Bildung ‘anormaler’ Wohnkammern ist nicht mit
Resorptionserscheinungen verbunden; Resorptionserscheinungen
sind an den Ammonitenschalen iiberhaupt nicht nachzuweisen.

‘‘2, Ein Ammonit mit ‘anormaler’ Wohnkammer ist fast aus-
nahmlos als vollkommen ausgewachsen zu betrachten.

‘€3. Der ‘anormalen’ Wohnkammer gehen weniger veranderte
Wohnkammern voraus und schliesslich in den Jugendstadien solche,
die in vollkommen regelmassiger Spirale gewachsen sind; man
darf daher bei der Beschreibung von Ammoniten nicht eigentlich
von einer anormalen Wohnkammer sprechen, sondern von einer
anormalen letzen Wohnkammer des ausgewachsenen Individuums.

““4. Die ‘anormalen’ Wohnkammern der Ammoniten sind
nicht auf sexuelle Unterschiede zuriickzufiihren.

‘¢5. Die ‘anormalen’ Wohnkammern und die mit denselben

eS ie

613

zusammenhangenden Formveranderungen des Ammonitentieres sind
als senile Charaktere aufzufassen.’’

I am not prepared to adopt without more extended study the first
of Dr. Pompeckj’s results. Although he has presented very strong
evidence, it is difficult to believe that in all cases when the aper-
ture is contracted and the whorl or living chamber is excentric that
this is never resorbed, because these so often occur in very small
shells. These small shells are apparently of the same species with
larger ones having similar chambers, and I have certainly considered
them as individuals which had inherited the degenerative tendency
to excentricity in their early stages. Dwarfs certainly occur having
prematurely degenerative characters of this kind, and it may be that
Dr. Pompeckj is right in his generalization, and that all such occur-
rences can be regarded in the same way.

Dr. Pompeckj does not deny that, when change of habit might
be such as to favor the inheritance of gerontic characters, that they
become genetic and that degenerative series might have been thus
built up. If this occur at all the appearance of gerontic characters
must take place according to the law of tachygenesis and in conse-
quence of this appear earlier in the ontogeny of descendants of the
same series. ‘The shells in every degenerate series, therefore, ought
to show this earlier inheritance in proportion to their degeneracy
and to their place in the evolution of the series. In other words
some at least of the more degenerate species would necessarily
exhibit phylogerontic characters in their neanic stage and should
be classified not as dwarfs but as young shells.

Through the kindness of Dr. C. E. Beecher my attention has
been drawn toa species which is of importance in this connection
and this has been loaned me by Prof. O. C. Marsh, Director of
Yale University Museum. ‘This extraordinary helicoidal shell,
Eimperoceras Beechert, is exceptional in so far as it exhibits, in a
magnified and unmistakable way, the action of tachygenesis upon
gerontic characteristics.

The neanic stage has a single, straight, baculites-like cone which
turns in the same plane, building out the peculiar form known as
Hamites. This, after making the hamitean bend, deviates from
the plane of growth of the neanic stage and becomes a loose but
regular spiral which has generally heretofore been described as
Helicoceras.

614

In Nostoceras similar phenomena are observable but, in this tur-
rilites-like, closer coiled spiral, the young shells are quite different
and it is not certain that they are irregular and similar to Hamites.
The species of this genus and of Emperoceras and Didymoceras
show that the spiral coiled stage is an ephebic stage, not a true
gerontic stage of the ontogeny, because passing beyond this the
gerontic stage appears taking on the usual retroversal form. ‘The
ephebic whorl departs from the spiral in this stage, again becoming
excentric, and then builds back towards itself and towards the
spiral, forming the peculiar crook found more or less in the parage-
rontic substage of the so-cailed Hamites, Ancyloceras, Scaphites.

Thus one gets in these two genera a demonstration that the tur-
rilites and helicoceran modes of building the shell are acquired
characteristics of the ephebic stage of the ontogeny interpolated
between gerontic and neanic stages which have the usual charac-
ters of these stages in the ontogeny of degenerate forms.

These forms are also interesting in connection with the history
of the impressed zone, because if they have close-coiled young, like
those of the crioceran and baculites-like shell already studied,
which is highly probable, they must have had a contact furrow in
the nepionic stage and then lost it in the neanic stage. The gene-
sis of another contact furrow in the still later stages of Nostoceras
and similar turrilites-like spirals, is therefore secondary and phylo-
gerontic, and is not strictly speaking a progressive characteristic.
This furrow is also situated on the lateral aspect and not on the
dorsum as in symmetrical shells.

The phylogerontic renewal of the impressed zone is also in Pty-
choceras, a generic character, as pointed out to me by Mr. T. W.
Stanton, to whose courtesy and the kind permission of Mr. C. D.
Walcott, Director of the Geological Survey, and Mr. Goode, Direc-
tor of the National Museum, I owe the fine materials described
above. :

The return of close coiling in gerontic stages of this species is a
remarkable phenomenon. ‘There is a gerontic umbilical perfora-
tion formed by the sudden bending of the gerontic living chamber
which is elongated and not usually very small, but the gerontic
bend is often very abrupt. The inner side at the bend is occupied
by a gerontic dorsal furrow which reminds the observer of the dor-
sal furrow in the paranepionic substage of the coiled young of
Nautiloids. As in the young of Trocholites and Tarphyceras the

615

dorsum of the gerontic volution is brought into contact with the
dorsum of the next younger volution and a contact furrow results,
which so far as I know occurs in all the species properly referred to
this genus, although very slight in some of them.

The significance of the facts brought out by the study of degenera-
tive series has been fully discussed elsewhere, and need not be
noticed again.

The facts and arguments brought forward seem to justify the fol-
lowing conclusions :

1. The impressed zone is primitively a contact furrow, an ac-
quired characteristic of the dorsum of the whorls of nautilian shells
having large umbilical perforations, which appeared either in the ana-
neanic or metaneanic substages, and rarely later in their ontogeny.
There is abundant positive evidence that in these primitive forms
this furrow is a purely mechanical result of the nautilian mode of
growth, not appearing in the ontogeny before contact and either
partially or entirely disappearing on the free gerontic volution.

2. The impressed zone does occur independently of contact on
the free dorsum of the paranepionic substage as a dorsal furrow in
some close-coiled, highly tachygenic, nautilian shells in the Quebec
group and in the Devonian.

3. While there is no positive proof that the dorsal furrow origi-
nated through heredity in the paranepionic substages of these nauti-
loids of precarboniferous age, there is also no satisfactory evidence
that it originated in the young of such species as have this character
through purely mechanical agencies.

4. There is positive evidence that the similar dorsal furrow which
also appears at the same age in the young shells of Coloceras glo-
batum and perhaps Coelogasteroceras canaliculatum among Carbon-
iferous nautiloids can be explained only when it is considered as a
transmitted, tachygenetic characteristic.

5. This fourth conclusion is supported by the presence of a similar
dorsal furrow in the paranepionic substage of the young shells of all
of the nautiloids of the Jura, so far as observed.

6. The fourth and fifth conclusions are rendered still more proba-
ble by the presence of the dorsal furrow at an earlier age, the meta-
nepionic substage, in all of the nautiloids so far as observed, from
the beginning of the Cretaceous, through the Tertiaries to and in-
cluding the living species of the genus Nautilus. Its presence on
this cyrtoceran volution in Cretacic shells can be explained only

616

when it is considered as a transmitted, tachygenetic characteristic
derived from ancestral, nautilian shells of the Jura, which have the
same characteristic at a later age, z. e., in the paranepionic substage.

7. The first conclusion is also sustained by the parallel phylogeny
of the impressed zone in the ancestral forms of the Ammonoidea,
the Nautilinide and especially in Mimoceras, the radical genus of
this family.

8. The fourth, fifth and sixth conclusions are also supported by the
presence of a contact furrow on the dorsum of the earliest age of
the conch in the specialized and highly tachygenic forms of the
Goniatitinee of the Devonian and of all of the remaining Ammonoids
to the end of the Cretaceous.

g. These cumulative results favor the theory of tachygenesis and
diplogenesis, and are opposed to the Weissmannian hypothesis of
the subdivision of the body into two essentially distinct kinds of
plasm, the germplasm, which receives and transmits acquired char-
acteristics, and the somataplasm, which, while it is capable of ac-
quiring modifications, either does not or cannot transmit them to
descendants.

le ili he ee Se
= " , a
se
OT SESE — Py,
LOSER SSIR SES

617

EXPLANATION OF PLATES.

RVAT Ee

Illustrations of nepionic stage and ananeanic substage in Wautelus pompilius
from preparations made by Henry Brooks and drawn under his direction. They
are all enlarged to show the details of the surface ornamentation and changes of
form.

Fig. 1. The paranepionic aperture and earlier nepionic substages seen from
the front, this preparation having been obtained by breaking down the full-
grown shell. The septum which appears here necessarily belongs to a later time
and shows the position of the siphuncle and its large size in the floor of a living
chamber older than is represented in this igure, but in the same substage. The
actual living chamber of this age was therefore deeper than is represented here at
the beginning of the paranepionic substage. The subtriangular outline of the sec-
tion of the shell is supposed to represent and probably does approximately repre-
sent the aperture. It is noticeable also that the dorsal furrow is well developed,
although the shell has not yet completed the gyroceran curve.

Fig. 2. Side view of the same showing the apex. The ananepionic substage
is not distinctly visible, but the constrictions showing apertures of the metane-
plonic substages are delineated.* This figure is especially intended to exhibit
the changes that take place in the ornamentation of the shell.

Fig. 3. The ananepionic and metanepionic substages in another preparation
seen from the front. The ananepionic is the elongated disk of the apex and scar in
the centre of this. The metanepionic includes the shell outside of this to the
outer constriction.

The details in this have not been completely drawn, but the transverse lines of
growth are shown upon the shaded side of the drawing.

Fig. 4. Same from the ventral side, showing especially the latter part of the
metanepionic substage and the deep constriction that in some specimens marks
the termination of this substage. The lines of growth show no trace of a hypo-
nomic sinus in this or any other preparation at this age.

Fig. 5. The same substages of the nepionic stage seen from the front in another
preparation. The details of the transverse striation are not fully given in this
drawing and this makes the ananepionic substage appear more gibbous than it
really is. This impression is corrected by Fig. 6.

Fig. 6. View of the same from the venter, very carefully finished in all its
details, The limits of the ananepionic substage and the aperture of the first part
of the metanepionic substage are more plainly marked in this specimen than is
usual.

* These drawings and others jn this paper will appear to most observers to be upside
down. They are really right side up and the conventional mode of representing these
shells followed hitherto in all works is unnatural, It is full time that these forms should
be pictured, as are all others in scientific and popular works, as they stand in nature.
The greatest objection to this is the inconvenience of comparison with illustrations
hitherto published, but this cannot be avoided, and must be endured for the sake of
progress,

Proceedings Amer, Philos. Soc.

IG:

ven EA

SSE
SSE

Plate I ( Hyatt oF

618

Fig. 7. Side view of the apex of the conch in another preparation showing the
same substages and a part of the paranepionic substage.

Fig. 8. Diagram of the exterior of the ananepionic substage. This also shows
the position of caecum and septum of the first living chamber of the metanepionic
in the interior, and supposed outlines of aperture of ananepionic substage, In
the ananepionic substage the apex of the conch is empty and this diagram there-
fore gives the erroneous impression that the czecum and first septum belongs to
this substage, whereas it is obviously a part of the metanepionic substage.

Fig. 9. Front view of the same showing outline of aperture of ananepionic
substage and also the position and size of the primitive siphuncle or czecum first
septum of the metanepionic substage.*

Fig. 10. Diagram of same and exterior of first living chamber of the metane-
pionic substage showing change of position towards the venter of the siphuncle in
the septum of the second living chamber of same substage.

Fig. 11. Front view of the same with siphuncle of the same.

Fig. 12. Side view of the exterior of two first substages and supposed aperture,
with the siphuncle and first septum of the paranepionic substage. The siphun-
cle, it will be observed, changes again towards the centre between these two
septa.

Fig. 13. Front view of the same showing approximate outline of aperture
taken from actual outline of shell in section at the constriction terminating
the metanepionic substage. This shows the nephritic character in the volution
and exhibits also the dorsal furrow beginning to form at this early age before
the gyroceran curve begins. This drawing is placed so that the observer can
compare the outlines of the shell at this substage with that of the later age of
the paranepionic substage in Fig. 1. In the latter the siphuncle has assumed the
permanent position of the ephebic stage below the centre.

* Figs, 9-11 should have been reversed to accord with the side views and with the other
figures.

Vol. XXXII, No. 143,

Proceedings Amer. Philos. Soc.

Plate ll (fiat).

619

Brare ir

Figs. 1-6. Mimeceras (Goniatites) compressum, after Branco, Paleontogra-
phica, xxvii, Pl. viii, much enlarged, to show the loose mode of coiling, absence
of impressed zone, primitive nautiloid sutures of the young until a late stage, and
protoconch joining the conch without any constriction on the sides or abdomen,
but with a slight constriction on the dorsum, showing tendency to coil, these
being typical ammonitoid characteristics. Fig. 6, 1 and 2 and & represent the
first, second, and older septum, the septa of the later stages are shown with ven-
tral siphonal lobe in Fig. 5. Fig. 20 is the same species after Sandberger.

Figs. 7 and 8. Mzmoceras (Gonzatites) ambigena, after Barrande, Systeme
Stlurien, Pl. iii, Fig. 22,and Pl. xii, Fig. 7, showing the absence of an impressed
zone at a late stage, probably the ephebic stage of development.

Figs. 9-11. Agoniatites (Goniatites) fecundus, after Barrande (zdzd.), Pl. x,
Figs. 13-15, showing the absence of the impressed zone until a late stage; Fig.
II is nearly natural size, and this shows, when compared with others of Bar-
rande’s figures of this species, which have the impressed zone in adults (Bar-
rande, Pl. vii, Figs. 1o and 11), that this characteristic comes at a much earlier
stage in some specimens, and is originated by close coiling, as it is in Agonzatites
Vanuxen, but at an earlier stage than in 4. fecundus.

Figs. 12 and 13. Agoniatites (?) (Gontatites) crebriseptus, after Barrande
(zézd.), Pl. vii, Figs. 1 and 2, reduced one-third, showing how similar to some
nautiloids the adults of this genus may be, both in form and sutures,* with the
exception of the ventral siphonal lobe, which alone enables one to place them
among Ammonoids.

Figs. 14 and 15. dAgoniatites fecundus, after Barrande (zdzd.), Pl. xi, Figs. 2
and 4, enlarged to show the variation of the coiling of two varieties in the pro-
toconchial and nepionic stages. These are both included under one name by
Barrande.

Fig. 16. -Avarcestes (Goniatites) lateseptatus, after Branco, of. ci¢., xxvil,
Pl. vi, enlarged, showing the immature ventral sutures of this with the primitive
undivided siphonal lobe beginning in the second septum of the metanepionic
substage. This continues substantially the same in aspect throughout life in the
genera Mimoceras, Anarcestes, Agoniatites and Pinnacites, all Silurian forms of
Goniatitinee.

Figs. 17-19. Gephuroceras (Goniatites) serratum, after Branco, of. cz¢., Xxvil,
Pl. vi, enlarged, showing sutures of Devonian Goniatitinze with accelerated devel-
opment. The mimoceran undivided siphonal lobe is here shown in the metane-
pionic substage, 2-4 septa, but in the paranepionic, where the coil is 3 mm. in
diameter, the siphonal saddle arises in the centre of this lobe as a new character
acquired in the later stages of growth.

Figs. 20-25. These give the protoconch and young of various species of
Goniatitinze of the Devonian after Sandberger, Fahrbuch ad. Nass. Verein, 1851,

* Mimoceras ( Goniatites) litwus is a still larger form, also figured by Barrande, which has
no impressed zone and isvery similar to many nautiloids which have similar compressed

elliptical whorl and subventran siphuncles. His figure is reproduced here in reduced
outline, Figs. 40, 41, Pl. viii.

620

Pl. iii. They are somewhat enlarged and show the loose coiling of several genera
in the nepionic stages of development during this period of their evolution. Sub-
sequently the coiling becomes closer, as has been demonstrated by Branco. Fig.
20, Mimoceras compressum; Fig. 21, Anarcestes subnautilinus ; Fig. 22, Agonia- .
tites bicanaliculatus, var. gracilis; Fig. 23, Gephuroceras planorbe; Fig. 24,
calculiforme, and Fig. 25, sublamellosum ; Fig. 26, Manticoceras latidorsale,
and Fig. 27, Glyphioceras diadema.

Figs. 28 and 29. Protoconch of Orthoceras, after Clarke, 4m. Geol., xii,
August, 1893.

Figs. 30 and 31. Protoconch of Bactrites, after Branco.

Vol. XXXII, No. 143,

Proceedings Amer. Philos. Soc.

Tate Te ( Hyatt ).

621

IAL wns JOULE

Figs. 1-7. Deroceras (Amm.) planicosta, Hyatt, Embryology Ceph. Bull.
Mus. Comp. Zoblogy, iii, No. 5, Pls. i and ii.

Fig. 1, side view of nepionic and neanic stages, X 80 diameters. Fig. 2, sec-
tion of another specimen, x 21.5 diameters; B,protoconch. Fig. 3, centre of same,
enlarged to show the umbilical perforation (U) as it occurs in Ammonitinz and most
of the Goniatitinze. Fig. 4, protoconch and first volution with ananepionic first sep-
tum; x, probably sutures of the first septum on the dorsum seen through the whorl ;
xX 80.* Fig. 5, side view of protoconch, ananepionic first septum I e, aud meta-
nepionic septa, 2 e, 3 e; D, shell; B, naked cast of interior of protoconch; y, coni-
cal appendage of caecum seen through the whorl. Fig. 6, section of same speci-
men exposing interior of the protoconch (y), the conical czecal prolongation, and
the fundus of the caecum and the first two septa, S, being the neck of the small
siphuncie at the third septum, which is broken off. Fig. 7, thin section of cecum
and part of conch with four septa, showing formation of caecum by the first septum
I e, the composition of the czecal prolongation y, the neck of the cecum formed
by the second septum 2 e, the siphon begun by the third septum and continued
by the fourth, both of which have funnels directed apically as in Nautiloids; S/,
organic deposit in the interior; S/’, inner layer; S//’, wall of siphuncle; X 317
diameters.

Fig. 8. Deroceras (4¢goc.) planicosta, Branco, Faleontographica, xxvii, Pl. x,
showing protoconch from a different point of view and less magnified. Fig. 9,
same, with first to fourth sutures showing.

Fig. 10. Pleuroceras (Amaltheus) spinatum, Branco (262d.), Pl. xiii, enlarged,
showing the interior of the protoconch; the septa of first whorl are cut exposing
the cecum. The septa are all convex and strictly ammonitoidal except the
first, which is concave, as in Nautiloids and the adults of Mimoceras, Anar-
cestes and Agoniatites among Ammonoids of the Silurian period.

Figs. 11 and 12. Crzoceras Studert, Branco (z67d.), Pl. xiii, enlarged, showing
the coiled young of this uncoiled degenerate form. +

Figs. 13-18. Baculites compressus, Brown, Proc. Acad. Sct. Phila., 1891, p. 1593
1892, p. 136, Pl. ix. Fig. 13, enlarged young shell in the neanic stage, showing
the lines of growth, aperture and rostrum on the ventralside. Fig. 14, front view
of shell in the paranepionic substage; the siphuncle is not subventran. Fig. 15,
front view with the two metanepionic and four paranepionic sutures, those witha
siphonal lobe divided by a siphonal saddle being paranepionic inage. Figs. 16
and 17, front and side views, with restoration of the ananepionic substage. Fig.
18, side view of Fig. 15.

Figs. 19-21. Apex from the front and side and sutures of Maztzlus Clemen-
tinus, after Branco, op. ct¢., xxvii, Pl. ix.

Fig. 22. Sutures of Mautilus deslongchampsianus, after Branco, (2bzd.),
1 abe

* This figure has no number.
+ See also for similar forms Pl. xi, Figs. 40, 41,

Sb 2 2a re eae ie on

‘eee
Pe

ee «lh 2 wos
ae ae

—

Cak

f
mj

622

Prare LV:

Fig. 1 Bacudites compressus, enlarged sutures after Brown, see PI. iii.*

Fig. 2. Deroceras (Aegoceras) planicosta, enlarged sutures after Branco,
Faleontographica, xxvi, Pl. x. These show the ananepionic suture I, the metane-
pionic or goniatitic sutures 2-4, and the paranepionic with divided siphonal lobe
at the diameter of I mm. and 2 mm., and the next septum, the 7, here given, is
transitional to the first neanic septum, the 8 of this series, which shows the begin-
ning of ammonitic digitations in saddles and lobes and a divided dorsal lobe.
By comparing this with the sutures of Pl. ii, Fig, 16, Avarcestes lateseptatus, and
Gephuroceras serratum, Pl. ii, Fig. 17, it will be seen that the ephebic ventral
lobes and smooth sutures of the Goniatitinze, represented in Gephuroceras, are
limited to the paranepionic in Deroceras. The goniatitic ventral lobe in other
words is replaced in the ananeanic of Deroceras, representing the Ammonitinz,
by the digitate lobes and saddles of that suborder.

Fig. 3. Vermiceras (Arietites) spiratissimum, enlarged sutures, after Branco,
(zbzd.), Pl. ix, showing also acceleration of development through the replacement
of the ephebic characters of the Goniatitinee by those of the Ammonitine in the
ananeanic substage.

Fig. 4-11. Zarphyceras Champlainense, (sp. Whitfield), Hyatt; Loc., Fort
Cassin; U. S. N. Mus., Walcott Coll. Fig. 4, side view slightly enlarged, show-
ing involution and small unbilical perforation ; the crack indicates the direction
of the section given in Fig. 5. Fig. 6 gives general section and the centre is of
about the same age as Fig. 6. Fig. 7 is younger and shows beginning of the
dorsal furrow narrower and deeper than in Fig. 6. Fig. 5 shows that it is
probably due to the mechanical effects of the sudden bending shown in Fig. 7.
Fig. 8, ideal section showing location of sections Figs. 6 and 7. Fig. 9, section of
another specimen, natural size, showing a younger stage at the centre. Fig. 1o,
side view of same specimen. Fig. 11, enlarged section of metanepionic centre of
Fig. 9, showing outline like that of Mautzlus pompilius at the same age.

Fig. 12-16. Y7arphyceras prematurum, Hyatt, Quebec Group; Loc., Port au
Port, Newfoundland. Fig. 12, side view of fragmentary specimen, natural size,
giving part of livingchamber. Fig. 13, front viewof same. Figs. 14 and 15, front
and side view of nepionic and part of neanic stage slightly enlarged; Fig. 16, front
view of nepionic whorl of same (X 2) showing a dorsal furrow and the abrupt
bending of the whorl. The narrowness of the umbilical shoulders is not natural,
being probably in part due to the obliquity of the septum and partly to erosion of
the outline at this point.

Figs. 17-22. Tarphyceras Aucoini, Hyatt, Quebec Group; Loc., Port au Port,
Newfoundland. Fig. 17, side view, natural size, of ephebic stage; Fig. 18, part
of neanic whorl to show sutures. Fig. 19, section of ephebic whorls, natural size,
of another specimen. Fig. 20, section, natural size, of another specimen, the upper
whorls a little depressed by pressure; Fig. 21, the nepionic stage enlarged (four
diameters) to show more accurate outline and the dorsal furrow and sudden bend-
ing of whorl and narrow umbilical perforation. Fig. 22, side view of same. The
apex in all of these specimens was too much eroded to show the cicatrix.

*This figure is not numbered.

Proceedings Amer. Philos. Soc. Vol. XXXII No. 143,

Plate IV ( Hyatt).

623

Figs. 23 and 24. Zrocholites canadensis, Hyatt; Loc., Falls of Montmo-
rency (?); Coll. Mus. Comp. Zodlogy, Bronn Coll.

Fig. 23. Much enlarged. ‘The siphuncle shows through the transparent venter
of the nepionic volution and it passes from subdorsan in the paranepionic below
to centren in the metanepionic above. The umbilical perforation appears beyond
the siphuncle and has a well-developed dorsal furrow, can also be seen; Fig. 24
shows the gibbous outgrowth of the dorsum in the umbilical perforation at some
distance from the gyroceran bend.

Fig. 25. Zrocholites (Lituttes) internastriata (sp. Whitfield), Hyatt. This
was drawn from the centre of his original specimen, Bz//. Am. Mus. Nat. Hist.
LV. Y., Pl. xxix, Fig. 6, enlarged to show the centren position of the siphuncle in
the first septum and its gradual approach to the dorsum in the paranepionic whorl
as in 7. canadensis. This also shows a much larger umbilical perforation than
is found in Caxadensis or ammonius or the species figured by Holm.

Fig. 26. Zrocholitessp.? after Holm, /ad. Abh. Dames et Kayser, iii, Pl. v,
Fig. 11, to show the probable beginning of the siphuncle to be nearer the centre
than is described by him. His Fig. 9 of Zrocholites incongruus shows also a
small umbilical perforation and the siphuncle subdorsan, but its tip or caecum is
directed towards the centre of the apical chamber.

624
PLATE Vi

Figs. I and 2. Lurystomites undatus (sp. Hall), Hyatt; Black River, Poland,
Herkimer Co., N. Y.; Mus. Comp. Zodlogy, Walcott Coll. Natural size, show-
ing large umbilical perforation and absence of dorsal furrow. A contact furrow

ht cl

is formed when the whorls come in contact in neanic stage. Siphuncle is too
small and too near the venter in both inner whorls. (Fig. 3 is blank on this
plate.)

Figs. 21-25. Eurystomites rotundus, Hyatt, Quebec Group; Fort Cassin, U.S.
N. Mus., Walcott Coll. Enlargedslightly. Fig. 3, partly diagrammatic side view
: | showing direction of section. Fig. 4,section. Fig. 5, section of nepionic somewhat

! nearer to that indicated in Fig. 3. Fig. 6 is about on that line and Fig. 7 is on
the further side of it in the umbilical perforation. This series shows the large

rf umbilical perforation and absence of impressed zone, until the whorls come into
: contact in the neanic stage.

ti Figs. 4 and 5. Lurystomites (Naut.) Kelloggi (sp. Whitfield), Schréder;
: Loc., Fort Cassin, Quebec Group; Walcott Coll. U.S. Nat. Mus. Fig. 4, reduced
i one-third, showing the cast with the partly exfoliated rough shell in the gerontic
¢ stage and the restored gerontic free whorl which is in outline. The matrix was
i preserved so as to give the dorsal outline of this restored volution but not the
y sides or the venter. Fig. 5, section of the termination of the gerontic whorl.

f This is ideal so far as the sides and venter are concerned and may be too long
ventrodorsally, but the dorsum is correct and shows the much narrowed but still
persistent impressed zone.

: Fig. 6-10. Barrandeoceras (Naut.) tyrannum (sp. Barrande), Hyatt; Loc.,
4 Lochkov, Bohemia; Schary Coll. Mus. Comp. Zodlogy.

_ Fig. 6, front view of part of the nepionic volution showing the cicatrix ana-,
"I meta- and part of paranepionic substages, the constriction next to the cicatrix and
4 the one just beyond this belongs to the ananepionic substage; the second is
i

i) also seen in Fig. 7 a, the next constrictions seen in both of these figures
‘i belong to the metanepionic substage. There is apparently no hyponomic
ni sinus in these two substages and its absence indicates the limits of the
| metanepionic substage. It is not plainly visible on this specimen until near the
cracked line, which is really the septum of the living chamber. Fig. 7, side view,
shell was not on the living chamber, but has been restored from other specimens.
Suture is about as indicated with ventral and dorsal saddles and broad shallow
lateral lobes. Figs. 6and 7 are x 4 diameters. Fig. 7a, an enlarged side view of
apex of Fig. 7 to show true aspect of this part. Figs. 8,9 and 10, similar views
of another specimen showing identity of cicatrix and youngest substages in both
shells. The markings are so delicate that they are easily obliterated and are
necessarily much coarser in these drawings than in nature. Fig Io is enlarged
about four diameters.

Figs. 11-14. Barrandeoceras Sacheri (sp. Barrande) Hyatt; Loc., V. ch.
Pridoli, Bohemia; Schary Coll., Mus. Comp. Zoélogy. Fig. 11 shows the large
umbilical p2rforation, the sudden bending of the whorl at the end of the metane-
pionic substage ; this occurs also in Fig. 7 and Fig. 9. Fig. 12,frontofsame. Fig.

—— =

Proceedings Amer. Philos. Soc.

Vol. XXXII, No. 143.

625

13 shows the dorsal side of Fig. 11 on the paranepionic whorl inside of umbilical
perforation and just before the apex is reached. This has sutures with dorsal
lobes and is flattened as is shown in section of the same, Fig. 14; this flattening
also occurs in the paranepionic whorl of Fig 6.

Figs. 15-17. Aphetoceras boreale, Hyatt, Quebec Group; Loc., Schooner’s
Island, Newfoundland. Fig. 15, side view, and Figs. 16 and 17, sections all one-
third reduced, showing form and absence of impressed zone. For other species of
this genus see Pl. vi.

Figs. 18-20. Pycnoceras apertum, Hyatt, Quebec Group; Loc., Port au Port,
Newfoundland. Fig. 18, side view, reduced one third, with apex restored. Fig.
19, view of venter of same encrusted with dorsal shell of older volution, the
remainder of this volution having been destroyed by erosion. ‘This shell shows
the contact furrow and the dorsal lobes in the sutures of older stages. Fig. 20,
view of the part of the nepionic whorl of Fig. 18, enlarged 2 diameters, showing
the absence of dorsal furrow and the form of the metanepionic and paranepionic
substages of this species. ‘The remnants of the dorsal shell described above are
omitted in this figure and in Fig. 18.

626

IDEN, WE

Figs. 1-4. Tarphyceras extensum, Quebec Group; Loc., Port au Choix, New-
foundland. Reduced one-third. Fig. 1, lateral view, showing position of siphuncle,
septa in section and free volution. Fig. 2, section of living chamber at the ter-
mination restored by observation of the more perfect parts of the same volution.
Dorsum appeared to have no impressed zone in this obviously the gerontic stage.
Fig. 4, section of two ephekic whorls in fart restored, showing impressed
zone and general form. Fig. 3, section of younger whorl, restoration in part.
Dimensions are incorrect in these sections, but the form is correct.

Figs. 5-8. Aphetoceras Americanum, Quebec Group; Loc., Port au Choix,
Newfoundland. Reduced one-third. Fig. 5, side view showing gyroceran mode
of growth, suture with ventral lobe and younger sutures with ventral and dorsal
saddles. Fig. 7, section of the outer whorl. Figs. 7, 8, sections taken at the
two contiguous breaks in the outer and next inner whorls. Dimensions of these
sections are not correct, but form is properly represented,

Figs. 9-11. Litoceras insolens (?) (sp. Bill.), Hyatt, Quebec Group; Loc.,
Gargamelle Cove, Newfoundland. Fig. 9, side view of young specimens, very
nearly natural size. Fig. 10, interior whorls enlarged to show large umbilical
perforation, costations of metanepionic, paranepionic and ananeanic substages,
and the loose coiling of the ananeanic substage. Fig. 11, section of nepionic,
ananeanic and anephebic volutions showing the absence of impressed zones in
the nepionic and changes of form in older whorls. Compare this with the young
of Trocholiioceras Walcottz.

Figs. 12-20. Trocholitoceras Walcottt, Quebec Group; Fort Cassin; U. S.
Nat. Museum, Walcott Coll. Fig. 12, side view of type specimen natural
size. Fig. 13, section of same. Fig. 14, section of centre of same enlarged to
show the largest diameter of the umbilical perforation and the ananepionic sub-
stage and paranepionic with impressed zone. Fig. 20 gives location of this section
and all the rest are taken between the two bisecting lines of this figure. Figs, 15—
19, successive sections gradually passing out of the umbilical perforation and
showing the position of the siphuncle and increasing depth of the impressed zone
after contact These sections also show that the impressed zone occurs after the
gyroceran bend in the beginning of the paranepionic substage, and is apparently
a result of the great increase in transverse diameters, nephritic form of whorl
andabrupt bending. Fig. 20, location of sections, ideal. The shape of the ana-
nepionic volution in Fig. 13 is more accurate than in Fig. 14 or 15.

Figs. 21-27. Schroederoceras teres (sp. Eichw.), after Holm, P2/. Abh. Dames
e¢ Kayser, iii, Pl. v. Figs. 21 and 22 show the subventral czecum in apical
chamber and shifting of position to dorsad of centre in the ananeanic substage.
Compare with Schroederoceras Latoni, Fig. 35. Figs. 23-27, ananepionic,
metanepionic substages, the septa belong wholly to the metanepionic. There is
no dorsal furrow in this shell until the third septum is reached and by comparing
this with sections, Figs. 21 and 22, it is seen that this indicates ether the begin-
ning, Fig. 21, or the completion of the gyroceran bend, Fig. 22, although Holm’s
Fig. 25 would lead to the supposition that the bending had not yet begun.

Figs. 28-35. Schroederoceras Eatoni, sp. Whitf., Hyatt, Quebec Group; Loc.,

ed seman. Ye
1

Adkk \ \ \

a co

Proceedings Amer. Philos. Soc.

Vol. XXXII, No. 143,

eae: Val Fhyate)).

627

Fort Cassin; Coll. U.S. N. Mus. and Am. Mus., N. Y. Fig. 28, side view of
original (slightly changed), from Whitfield, Bz/Z. Am. Mus., Pl. xxxii, Fig. I.
Fig. 29, section of gerontic living chamber at the end. Fig. 30,section of ephebic
whorl just above free end of living chamber. These two show the presence of a
well-developed contact zone in the ephebic stage and its complete disappearance
on the free gerontic volution. Fig. 31, shows a section of a specimen which ex-
hibits the umbilical perforation with a core of the matrix; this cut passed inside
of the line drawn through Fig. 35 and represents the metanepionic above the
core and below it the paranepionic volution, the neanic being the next section
of a volution above the metanepionic. Figs, 32 and 33, younger ages of the
nepionic and older ages of the paranepionic volutions. Fig. 34, section along the
line indicated in Fig. 35. Fig. 35, drawing enlarged from Whitfield’s original
PI. xxxviii, Fig.7. Umbilical perforation may be somewhat larger proportionally
than in nature.

Figs. 36-38. Schroederoceras casinense, Quebec Group; Loc., Fort Cassin;
Coll. Am. Mus. N. Y. Fig. 36, side view (somewhat changed), from Whitfield,
op. ctt., Pl. xxxii, Fig. 2. Fig. 37, section of outer whorl of same near the line
of broken shell on the living chamber of Fig. 36. Fig. 38, shows sutures on
the venter of same specimen.

Figs. 39 and 40. Zrocholites canadense ; Loc., Falls of Montmorency, Bronn;
Coll. Mus. Comp. Zoology. Fig. 39 gives section. Compare with that of Z7o-
cholttoceras Walcottt, Fig. 40 shows the centre of this; the lower volution is
the nepionic and this shows how much wider this is than the older neanic yolu-
tion above.

|
|

628

PrAnE Nob

Figs. 1-3. Schroederoceras tubulatum, Hyatt, pars Lit. angulatus, Saem.;
Coll. Mus. Comp. Zodél., Loc., Brevig, Norway. Reduced one-third. Fig. 1, side
view of the fragment; the free whorl is restored as shown in this figure. The
suture and form of the restoration was taken from the well-preserved dorsum and
cast of the interior of the right side of the free whorl. The umbilical perfora-
tion is probably incorrect. The aperture follows the lines of growth, but is very
likely incorrect and the ventro-dorsal diameter may be too long. Fig. 2, section,
the outer volution being restored as regards the venter and right side; the dorsum
and left side are accurate. Fig. 3, restored outline of living chamber at termina-
tion showing the obliteration of the impressed zone. See also Figs. 6-12, PI. xiy.

Figs. 4-6. Schroederoceras casinense, Quebec Group; Loc., Fort Cassin; U. S.
Nat. Museum, Coll. Walcott. Natural size. Fig. 4, side view showing living
chamber aperture. Fig. 5, dorsum of living chamber with aperture and ephebic
volution. This shows contact zone in the ephebic stage and its disappearance
upon the free volution ; the whorl was broken away and removed at xx. Fig. 6
showing dorsal crest of the aperture and replacement of impressed zone by a gib-
bous surface just beyond the shaded area in Fig. 5. See also PI. vi.

Figs. 7 and 8. Schroederoceras Eatoni (sp. Whitf.), Hyatt, Quebec Group ;
Loc., Fort Cassin; U. S. N. Mus., Coll. Walcott. Naturalsize. Fig. 7, side view
showing lines of growth, sutures, and aperture. Fig. 8, front of same with ventral
sutures and rim of aperture removed showing the remnants of impressed zone.
See also Pl. vi.

Figs. 9-12. Estontoceras perforatum, Schroder, Silurian, Fig. 9, side view
after Schréder, Pal. Abh. Dames et Kayser, v, Pl. xxvi, Fig. 1 a, reduced one-
third, showing free nepionic and free gerontic volutions with lines of growth.
Figs. 10 and 11, Loc., Reval, Mus. Comp. Zodél., Bronn Coll., showing parane-
pionic whorl with lines of growth on the dorsum and absence of dorsal furrow
and lateral sutures, reduced one-third. Fig. 12, three sutures of upper part of
dorsum of the paranepionic substage of Figs. 1o and 11, the shell removed and
the whorl enlarged.

Figs. 13-19. “Lstonioceras biangulatum, Silurian ; Loc., Breslau; Mus. Comp.
Zool., Kranz Coll. Figs. 13 and 14, reduced one-third the abdomen of Fig. 13, is
distorted by pressure.* Fig. 15, venter of paranepionic and section of neanic
below with beginning of impressed zone (this is more accurately given in Fig.
15, a); above is ephebic whorl, but this and sutures are distorted by perspective.
This view is taken from the interior of Fig, 13 with parts between fractures re-
moved. Fig. 16, venter of ephebic stage, showing sutures with ventral lobes not
saddles as on outer volution of Fig. 15. Fig. 17, dorsum of free gerontic volution
showing lines of growth with dorsal crests, sutures with dorsal lobes ; depression in
cast perhaps annular muscle, which disappears on the sides; there are faint marks
on the venter as if the upper edge of this may have risen into a saddle on that side
as in Fig. 1, Pl. viii, of Remeléceras. The impressed zone disappears early on this
volution. Fig. 18, venter of the same, showing change in sutures and return of

* The apex of this was not clearly seen and it may be free.

tt eg

Philos. Soc.

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629

saddles in the last three sutures of the paragerentic substage. Fig. 19, sectional
view of terminal end of Figs. 17 and 18, showing dorsum slightly broader and
flaiter than venter.

Figs. 20and 21. Lstontoceras imperfectum, after Schroder, of. czt., Pl. xxvii,
Fig. 5 a, b, showing young enlarged with subventran siphuncle, etc., and no im-
pressed zone.

Figs. 22-24. Edaphoceras ( Tenmoch) niotense, Met. W. Geol, Lll., v, Pi. xix,
Fig. 3, much reduced in size. Fig. 23, the dorsum is more convex than the
venier.

630

Re Are Wort.

Figs. 1-8.* Remeléceras impressum; no locality: Coll. Mus. Comp. Zodlogy.
Natural size. Fig. 1,side view showing sutures and annular muscle in base of
living chamber. Fig. 2, ventral side of fragment of same specimen. Fig. 3, dor-
sal side of same fragment with impressions of annular muscles on cast. Fig. 4,
section of end of living chamber showing the decrease of the impressed zone in
the anagerontic substage. Fig. 5, dorsal view of the second and younger frag-
ment of same. Fig. 6, section of older end of same showing depth of impressed
zone in the ephebic stage. Fig. 7, still younger fragment of same, showing the
dorsal sutures of a late neanic or anephebic substage. Fig. 8, section.

Figs. 9-13. Hercoceras mirum, Barrande. Figs. 9-12, slightly enlarged,
Koneprusy. Fig. 13, natural size, Hlubocerpy, Mus. of Comp. Zodlogy, Schary
Coll. Figs. 9 and Io, side view and front of the ananeanic substage showing first
beginning of contact furrow and the trochoceran form of the young which is more
marked than in the adult. Figs. 11 and 12, side view and front of paranepionic
substage of the same specimen showing the absence of the dorsal furrow just be-
fore the apex is reached.

Figs. 14and 15. Hercoceras irregularis (sp. Barrande), Hyatt; Loc., Bohemia;
Mus. Comp. Zodél. Fig. 14, side view of meta- and paranepionic volution, show-
ing the peculiar costz without longitudinal ridges of this genus. Fig. 15 shows
the form in section of the meta- and paranepionic whorl and the absence of the
contact furrow in correlation with the rounded form of whorl. The czecum is not
correct; this organ is large and ventrocentran in this specimen.

Figs. 16-20. Avomaloceras anomalum (sp. Barrande), Hyatt; Mus, Comp.
Zodlogy, Schary Coll. Slightly enlarged. Fig. 16, section passing through umbil-
ical perforation which is filled with a peculiar dense shell-like deposit, not found
so far in other forms, and also cutting the meta- and paranepionic substages. The
neanic stage with a deep impressed zone and the two sections of the outer whorl
which are in the ephebic stage. The siphuncle appears to be nearer the centre
in the metanepionic substage in this and in Fig. 17 than in the later stages.
There is a dorsal furrow at the usual place beginning beyond the gyroceran curve
in the paranepionic substage in correlation with the nephritic outline ofthis sub-
stage. Fig. 17, view of a section of the metanepionic and paranepionic substages
of same cutting deeper into the umbilical perforation which is becoming nar-
rower. Fig. 18, a still deeper cut which has passed through the apex of the
conch and shows the first contact of the whorls. Fig. 19 shows the beginning
of the contact zone, the paranepionic section having passed into the ananeanic and
below the rounded ananepionic has replaced the metanepionic volution. Fig. 20,a
still deeper cut, showing the shell of the ananepionic substage becoming broader
through the approach of the section to the exterior of the ananepionic apex. A
shade farther and the ananeanic and metaneanic sections would blend into one
long figure and the ananepionic would disappear.

Figs. 21-23. Discoceras Graftonense (sp. Meek and Worthen), Hyatt; Loc.,
Waukesha, Wis., Niagara Group; Mus. Comp. Zoélogy, Day Coll. Natural size.

* Fig. 1 has no number on the plate.

XXXIl, No. 143,

Vol

L=SSVVV\Ty
IVA
Vi :

Selce ASS ‘ :

631

Fig. 21, side view of a cast of a mould of this species. Fig. 22, a similar speci-
men, but with nepionic stage and the beginning of the ananeanic substage in
relief preserved in the centre, showing small umbilical perforation, subdorsan
siphuncle (see also Fig. 23 for front view of same) and sutures. The sutures
have slight ventral lobes in the ananeanic, but are almost if not quite straight on
the venter of the paranepionic substage (shown in Fig. 23). The first suture
was not visible in this specimen.

Fig. 24 and 25. Ophidioceras tener, Barrande; Mus. Comp. Zoélogy, Schary
Coll.; Loc., Bohemia. X 3 diameters. Fig. 24, front view of section of neanic
and ephebic volutions, the nepionic in relief in the centre. The outline of the
ananepionic substage is given, but the cicatrix was unluckily destroyed by the
incautious use of acid in cleaning it. The position of the siphuncle is nearer the
venter than in older stages. Fig. 25, side view somewhat larger to show the con-
strictions on the nepionic whorl and the great comparative size of the apical
chamber and the first suture and constriction,

Figs. 26-28. Ophidioceras tessellatum, Barrande; Mus. Comp. Zodlogy, Schary
Coll. Fig. 26, X 3, to show dorsal outline of paranepionic volution without a
dorsal furrow and ananeanic dorsum just below this with the beginning of con-
tact furrow made by envelopment of the apex. Figs. 27 and 28, x 4 diameters,
to show similar characters to those of O. ¢ezer, and, the matrix filling the umbili-
cal perforation having been retained, this specimen shows also just how the
paranepionic volution strikes the apex. The absence of an impressed zone is
also noted in the paranepionic and position of siphuncle.

Figs. 29-35. Ophidioceras rudens, Barrande; Loc., Bohemia; Mus. Comp.
Zodlogy, Schary Coll. Fig. 29, natural size; Figs. 30 and 31, x 4 diameters;
Figs. 32-35, natural size; Fig. 29, side view showing general form of this species
and of the genus; Figs. 32-35 show the history of the contact furrow on free
whorl with gibbous median dorsal face and lateral dorsal furrows or faces as in
section 35, and also as on all of the close-coiled whorls. In the centre is the area
of the spur, shown in section Fig. 34, and in the lower part is the modified con-
tact furrow growing slightly narrower and shallower towards the aperture. Sec-
tion of this part is given in Fig. 33; Figs. 30 and 31, side and front views of
nepionic stage of another specimen showing cicatrix, form of ananepionic sub-
stage, which is a compressed almost quadragonal ellipse, metanepionic with
venter broader than dorsum and paranepionic with dorsum broadening out more
but stiil narrower than venter.

Figs. 36-39. Exdolobus avonensts (sp. Dawson), Hyatt; Carboniferous; Loc.,
Joggins, Nova Scotia; Coll. L. Agassiz. Natural size. Fig. 36, side and front
views showing the ana- and metanepionic substages in the centre (see also Fig.
38, enlarged view, showing form more accurately and cicatrix). The ananeanic
substage coming in when the apex is reached and the absence of the impressed
zone until after this contact is shown above the apex in Fig. 37. Below this is
seen the dorsal sutures and deep impressed zone produced by contact (shown also
in Fig. 39, more enlarged).

Figs. 40-42. Mimoceras (Gontatites) lituum, after Barrande, of. czé., Pl. x,
showing the young and probably the adult of this form without any impressed
zone and its similarity to some species of Nautiloidea, reduced one-third.

632

Fig. 43. Cranoceras (Cyrt.) lineatum (sp. De Verneuil), Hyatt; Devonian,
Pelm near Gerolstein; Mus. Comp. Zodlogy, Schultze Coll. Fig. 43, outline to
show the impressed zone which seems to appear in this cyrtoceran form in corre-
lation with the nephritic outline independently of contact.

PLATE IX.

Figs. 1 and 2. 7horacoceras (Cyrt.) puzosianum after De Koninck, Calc.
Carbon. P|. xxxiil, Figs. lo and 11, toshow in an adult of arcuate form the same or-
namentation and form that are also present in the young of the more highly
ornamented species like Zhoracoceras canaliculatum and the young of many
nautilian forms. See Figs. 11-13 of Vestenautilus Koninckt.

Figs. 3 and 4. Thoracoceras (Cyrt.) canaliculatum, after De Koninck, zdzd.,
Pl. xxxiil, Fig. 9, to show the spinous character of the ornamentation produced by
prominent lines of growth in crossing over the longitudinal ridges ; also for com-
parison with the young of Triboloceras, Vestinautilus, Rineceras, etc. _

Figs. 5-13. Vestinautilus (Naut.) Kontncki (sp. De Koninck), Hyatt; Figs.
5-8, after De Koninck, z6zd., Pl. xxx, Fig. 1; Figs. 11-13, Hyatt, 27d.
Ceph., Pl. 4; Figs. 9 and 10 original. This series shows ontogeny of this spe-
cies. Figs. 9 and 10, nepionic stage and ananeanic substage. Figs. 11-13, ana-
and metanepionic with rounded whorl and cyrtoceran form and ornaments like
T. puzosianum ; the roughened spinous ornaments come in later in the parane-
pionic substage. The limit of the paranepionic is shown in Fig. 9, the ananeanic
begins in last half of the first volution when the inner longitudinal ridges cease
on the sides. Compare abdomen with ephebic stage of Triboloceras, Fig. 15.
The ephebic stage begins near the end of the first half of the second volution
when the gibbous face and the lateral dorsal flutes or faces begin to appear in the
zone of involution asin Fig. 7. The anagerontic substage is shown in the loss
of the ornaments in Figs. 5 and 6, and also in the diminution of the hollow cen-
tral ventral zone and tendency of the abdomen to become rounded.

Figs. 14 and 15. 77zboloceras (Gyroc.) intermedium, after De Koninck,
tb2d.5 Pl xxx, Hig. 4:

Figs. 16-19. Vestinautilus (Naut.) pinguts, after De Koninck, 7dza., Pl.
xxx, Fig. 6 a-c, and Fig. 7 a,b. Figs. 18 and 19 show the anephebic substage
with spinous ornaments, the loss of these in the succeeding part of the ephebic
stage and the replacement of the ventral hollow zone, which is present in the
nepionic stage of this species, by a gibbous face like that of the gerontic stage of
Konincki. Figs. 16 and 17 show the parephebic substage and anagerontic
substage, the latter occurring through loss of the lateral fluted faces as in Fig. 5,
of Konincki. In the succeeding gerontic substages the whorl loses its angularity.

Figs. 20 and 21. Rineceras (Gyroc) tessellatum, after De Koninck, 262d,
Pi exxocit, Higa. 5e:

Figs. 24 and 25. Léspoceras (Naut.) sulciferum, after De Koninck, 262a.,
Pieexxi,, Niger, b,

Figs. 26 and 27. Phacoceras (Naut.) oxystomum, after De Koninck, zdzd.,
BP xvid) Hig 3°

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Proceedings Amer. Philos. Soc.

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Plate XN (

633

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Figs. 1-14. Coloceras (Naut.) globatum (sp. De Koninck), Hyatt; Loc., Visé,
Belgium, Carboniferous ; Coll. De Koninck, Mus. Comp. Zodlogy.

Fig. 1. Side view of nepionic and neanic volution, natural size. Fig. 2, same
enlarged in front view and ends of volutions restored; compare neanic volution
with the gerontic volution of Vestinaucilus pinguts, Pl. ix, Fig. 17; it will be
seen that this genus resembles the latter in the lateral fluted faces, but has rounded
sides, such as have been described as appearing in the paragerontic substage of
that species ; Fig. 2 also shows the impressed zone well-developed in the parane-
pionic substage. Figs 3-6, sections of meta- and paranepionic substage of Fig.
Io, showing development of outline and correlation of impressed zone with
nephritic form. The ananeanic substage begins immediately after this on the
latter half of the still uncoiled first volution and then the longitudinal ridges dis-
appear on the abdomen and also the crease or hollow central ventral zone, the
section becomes in the metaneanic similar to that of the upper volution in Fig. 2.
Fig. 7, enlarged oblique view of apex of same, showing the ana- and metanepionic
substages and the beginning of the impressed zone in a shaded crescent near the
base of the figure. Fig. 8, view of venter of another specimen ananepionic and
a pait of metanepionic showing the beginning of the hyponomic sinus in the
bands of growth. Fig. 9, end view of same with cicatrix. Figs. 10-12, views of
another specimen showing the first three sutures, impressed zone and ventral
hollow zone of the paranepionic substage. Fig. 13, shows the impressed zone
of the ananeanic substage and the beginning of the true impressed zone after con-
tact in the shaded crescent-like depression from which the apex has been removed.
Fig. 14, another specimen of same age with the pseudo-impressed zone and the
apex (ananepionic substage) in place. In all sections the venter is the lower side.

Figs. 15-22. fvtoceras dubium. Fig. 15, side view slightly enlarged showing
shape of umbilical perforation and abrupt bending of the paranepionic substage
when the zone begins. Fig. 16, front view of ana-, meta- and paranepionic sub-
stages and neanic volution in part. Figs. 17 and 18, enlarged views of same
without the neanic volution. Fig. 19, enlarged view of details of bands of growth
and longitudinal ridges taken from same. Figs. 20 and 21, views of ephebic vol-
ution, natural size. The history of the impressed zone is parallel with that
of Coloceras except that it comes in only after the abrupt bending of the first
whorl, and the form and character of the ana- and metanepionic substages
differ. Fig. 22, view of the ananepionic substage showing the flattened aspect of
apex. Figs. 22 and 9g (the latter described above) are, however, more distinct
than the specimens.

Figs. 23-26. Ephippioceras (Naut.) ferratum (sp. Owen), Hyatt; Loc., Ed-
mondson Co., Ky., Carboniferous; Mus. Comp Zodlogy. Enlarged four diameters.
Fig. 23, side of fragment of paranepionic substage, showing also umbilical per-
foration, apex restored and fragment of cast of ananeanic substage with parts of
two sutures. Fig. 26, venter of same. The longitudinal ridges are wider apart
and broader at their crests on the sides than on the central parts of the venter as
shown in Fig. 23. Figs. 24 and 25 show sections of both ends of the fragment
covered by shell in Fig. 23.

Figs. 27 and 28. Zemnochetlus (Naut.) subtuberculatum (sp. Sandberger),
Hyatt; Loc , Wissenbach; Coll. Mus Comp. Zodlogy; Devonian.

i
| Fig. 27, side view of ana-, meta- and paranepionic and perhaps beginning of
| ananeanic substages before the whorls touch. It will be observed that the apex
is not enveloped even in this closely coiled form and that the dorsal furrow is not
il present at the end of the volution, Fig 27, which is given in the section Fig. 28.
| Figs. 29-31. Apheleceras (Naut.) mutadile (sp. D’Orb.), Hyatt; Loc., Car-
I boniferous; after D’Orbigny, fel. Universelle, Pl. |xxxvill, Figs. 1, 2 and 4.
| Show the free apex and moulding of the dorsum to fit the hollow venter of this
species. Fig. 31 shows the surface of the shell of earlier substages.
Fig. 32. Metacoceras cavatiformis (same specimen as Figs. 16-19, p. 496 of
this paper) showing the beginning of the impressed zone at contact with the apex.

| Fig. 33. Celogasteroceras canaliculatum, Hyatt; Loc., Edmondson Co., Ky.;
Hi Mus. Comp. Zoél.; Carboniferous. A section across the meta- and paranepionic
volution showing the large umbilical perforation, comparatively slow increase in
size of the first whorl and p-esence of a dozsal furrow in the paranepionic sub-
ii stage.

Proceedings Amer. Philos. Sec. Vol. XXXH, No. 143.

(X25

ZZ yy jl

Plate XI ( Hyait).

635
PWT Eel:

Figs. 1-3. Peripetoceras (Naut.) Frieslebent (sp. Geinitz); Loc., Tunstall
Hill, England; Mus. Comp. Zoél.; Dyas. Natural size. Fig. 1 shows the
section through the apex of the conch, the ananeanic volution below and a
later age of the neanic stage above. Fig. 2, the cut has passed through. the um-
bilical perforation, the metanepionic above this and the paranepionic below ;
above the metanepionic is the paraneanic or anephebic substage. Fig. 3, the
cut has approached the farther side of the umbilical perforation and shows an
older age of the metanepionic and a younger age of the paranepionic with a deeper
and better defined dorsal furrow than in Fig. 2.

Figs. 4-8. Syringoceras (Naut.) granulosostriatus, after Mojsisovic’s AZedtt.
Triaspr., Pl. \xxxii, Figs. 7 and 9, Trias. Figs. 4 and 5, nepionic stage enlarged.
Fig. 8, more enlarged view of apex, with a cicatrix. Figs. 6 and 7, paranepionic
and ananeanic substage with longitudinal striations and beginning of impressed
zone after contact.

Figs. 9-12. Syringoceras (Naut.) Linearis, after Laube; Fauna St. Cassian
Denksch, Akad. Wien, 1869, Pl. xxxvi, Trias. Fig. 12, natural size. Figs. 9-11,
enlarged. Fig. 10, to show more accurately shape of apex. All show nepionic
stage and development same as in granlosostriatus.

Figs. 13 and 14. Digonioceras (Naut:) excavatum, after D’Orbigny, Zerr.
Furass., Pl. xxx, Lias. These show the nepionic stage with an impressed zone
existing before contact, also the annular lobe.

Figs. 15 and 16. Cenoceras (Naut.) intermedium (sp. Sow.), Balingen, De
Koninck Coll. Mus. Comp. Zo61.; Middle Lias. Slightly enlarged. These show the
large umbilical perforation and sutures, the paranepionic and ananeanic substages.
The dorsal furrow is present only in the paranepionic substage and the beginning
of the contact furrow is shown also in the shaded area on the dorsum of Fig. 16.

Figs. 17 and 18. Cenoceras (Naut.) intermedius (2) (sp. Sow.), after Bar-
rande and Hyatt, Sys¢. SzZ., Pl. cccclxxxix, Fig. 7; D’Orbigny Coll. Jarden des
Plantes; Middle Lias. These show the ana- and metanepionic substages with
cicatrix and sutures, but no impressed zone.

Figs. 19-21. Digonioceras sp. ? (similar to excavatus), Balingen; De Koninck
Coll., Mus. Comp. Zodl.; Middle Lias. Natural size. Fig. 19 shows sutures,
etc., of paranepionic substage. Fig. 20 gives outline of same from dorsum with
the dorsal furrow in the paraneptonic, the upper outline of this figure is incorrect
since the dorsal furrow begins immediately below this. Fig. 21 gives this out-
line correctly, it being the last of the ananepionic substage at the second suture;
in Fig. 21, the venter is placed uppermost for comparison’ with Fig. 20.

Figs. 22-27. Cenoceras lineatum (sp. Sow.), Bayeux; Coll. Duval, Mus.
Comp. Zodlogy ; Inferior Ool. Fig. 22, natural size, showing umbilical per-
foration, metanepionic substage below perforation and paranepionic above this,
the neanic stage being below the metanepionic volution. The dorsal furrow
is well developed in the paranepionic substage. Fig. 23, the reverse of the two
upper sections of Fig. 22.

Figs. 24 and 25, views of another specimen, showing the nepionic stage, en-
larged 3 diameters, showing the position of the siphuncle ventrad of centre and

636

dorsal furrow in paranepionic substage. The sutures, of course, belong to the
neanicstage. Fig. 25 shows the minute umbilical perforation and the close coiling
of the whorl. Figs. 26 and 27, apex of same, enlarged 3 diameters and giving
ornamentation of shell and cicatrix. The dorsal furrow begins at the first or
gyroceran bend in the paranepionic substage.

Figs. 28-31. Cenoceras lineatum (?), Oolite (Naut.) aratus of Quenstedt’s
Coll., Tiibingen, from sketches in my notes, showing the nepionic stage with
dorsal furrow as in /izeatus.

Figs. 32-35. Cenoceras (Naut.) aratus, Saemann’s original specimen; Mus,
Comp. Zodlogy; Middle Lias; Suabia. Figs. 32 and 33, enlarged 2 diam-
eters, Showing markings on the cast, form of nepionic stage, large umbilical per-
foration and sutures. The shell probably had longitudinal ridges and bands of
growth on the dorsum as well ason the venter. Figs. 34 and 35, copied from
Embryology Ceph., Hyatt, Pl. iv, much enlarged and corrected to show ana- and
metanepionic substages and annular lobe, which begins in the third suture. The
dorsal furrow begins between the third and fourth sutures, the last being the
oldest in Fig. 35. The curvature is uniform, gradual, and there is apparently no
mechanical cause for its early appearance in this shell.

Figs. 36-39. Cenxoceras (Naut.) granulosus (sp. D’Orb.), Chatillon; Coll.
Boucault, Oxfordian; Coll. Mus. Comp. Zod]. Slightly enlarged. Figs. 36 and
37, showing extraordinary quick growth of the dorso-ventral diameters in ana-
and metanepionic substages and beginning of paranepionic with dorsal furrow
in what is probably the fourth septum. Figs. 38 and 39, similar views of another
older specimen in paranepionic substage. See also Pl. xii, Fig. 31.

Fig. 40. Crioceras (?) Studert, Ooster, after Barrande, Callovian, much en-
larged, to show the close-coiled first volution.

Fig. 41. Azcyloceras (?) calloviense, after Barrande, Callovian, much enlarged,
to show the close-coiled young.

: +

4 *

i 19 ay
in, i

Vol. XXXII, No. 143.

Fath

Plate XII ( Hlyatt).

Proceedings Amer. Philos. Soc.

Fe a ee

637

IB Aa SOL

Figs. 1 and 2, Dzorugoceras (Naut.) planidorsatum, after Portlock, Geol.
Rep. Londonderry, etc., Pl. xxxv, Fig. 1; Carboniferous. Fig. 1, side view, re-
duced considerably. Fig. 2, section of outer whorl showing how completely the
contact furrow is moulded to the form of the whorl.

Figs. 3-5. Pleuronautilus superbus, after Mojsisovics, Das Gebirge um Hall-
staat, i, Pl. xvii, Trias. Fig. 3, reduced one-third, showing the striated nepionic
stage, the very large umbilical peiforation, free ananepionic substage, also the
close-coiled stages. Figs. 4 and 5, lateral, dorsal views of the fragment of what
is probably another species reduced one-third, showing an impressed zone as
described and figured by Mojsisovics.*

Figs. 6-11. Digonioceras rotundum, Oolite; Coll. Mus. Comp. Zodlogy; no
locality.

Figs. 6 and 7, side and front views of nepionic stage and ananeanic substage,
natural size, showing especially the large, pear-shaped umbilical perforation and
the amount of involution which covers only about one half of the side. The
outer part of Fig. 6 still has remnants of the dorsal shell of the enveloping neanic
and ephebic whorl and parts of four septa clinging to it. Two older sutures in -
the paranepionic volution and two younger in the metanepionic volution are also
shown and first to the third are seen in Fig. 7, which also shows the narrow ana-
and metanepionic substages. Fig 8, the same broken down, showing the apical
chamber and czeum enlarged in Fig. 9. Fig. 10, section of ananepionic substage
at first septum. Fig. 11, section of metanepionic passing apicad of second septum
and showing early beginning of impressed zone, both have the venter down-
wards, :

Fig. 12. Cenoceras (Naut.) clausum, after Barrande and Hyatt, Syst. S7Z.,
Pl. cccclxxxix ; D’Orb. Coll. Jardin des Plantes; Oolite; somewhat enlarged,
shows the well-defined impressed zone in the paranepionic substage and the first
three sutures.

Figs. 13-15. Cenoceras (Naut.) clausum (?), St. Vigor le Grand near Bayeux,
Bronn Coll. Mus. Comp. Zoél.; Lower Oolite. Fig. 13, somewhat enlarged,
showing the shape of umbilical perforation and ana-, meta- and part of parane-
pionic substages. The amount of involution is shown by the dark line. Fig. 14,
front view of same, natural size. Fig. 15, enlarged to show shape of ananepionic
substage at first septum, the venter down.

Figs. 16-21. Cymatoceras (Naut.) (sp. ?), Texas. Fig. 16, side view of ne-
pionic stage, and ananeanic substage with sutures enlarged two diameters. The
approximation of the fourth and fifth sutures appeared in several specimens of the
young of this species. ‘The third and fourth sutures are too close together in this
drawing and the spaces between the fifth, sixth, seventh and eighth, somewhat too
wide. The spaces between these last are not so wide as that between the third
and fourth in the original, this space being also slightly less than that between the
second and third. Fig. 17, section of apex and ananeanic substage enlarged two
diameters with the deep zone of contact. Figs. 18 and 19, the appearance of the

* See p. 547, above.

638

apex as the grinding plane passed inwards. Fig. 20, same showing the metane-
pionic and paranepionic, both with dorsal furrows opposed to each other. Fig.
21, section of ana- and paranepionic volutions. This cut passed in the plane of
the first septum, truncating the fundus of this and then obliquely across the suture
line of the fourth septum. The second suture has a well-defined annular lobe and
cone.

Figs. 22-27. Cymatoceras (Naut.) deslongchampsianum (sp. D’Orb.); Rouen;
Coll. Boucault and Bronn; Mus. Comp. Zo61; Cretaceous. Figs. 22 and 23, side
and front views, natural size, nepionic stage and ananeanic substage (this shell
has faint longitudinal ridges and transverse bands on the casts not shown in any
drawings) the sutures and small umbilical perforations are shown. Fig. 24
shows metanepionic outline at second septum and paranepionic between the fifth
and sixth septum of the same specimen, both with dorsal furrows. Fig. 25, the
reverse of the same specimen. Figs. 24 and 26, part of cast of chambers in the
dorsal furrow of Fig. 24, showing the annular lobes. Fig. 27, another specimen
showing ananepionic substage at the first septum with a dorsal furrow, and para-
nepionic also with dorsal furrow between fifth and sixth septa.

Fig. 28. Cymatoceras ( Naut.) simplex (?); Yeoville, England; Coll, De Kon-
inck, Mus. Comp. Zodél.; Cretaceous ; showing the nepionic volution and part of
the neanic stage. The slight subangular, umbilical shoulders which begin to
appear in the anephebic substage. The longitudinal ridges and transverse bands
are absent on this cast, but this may be due to the state of preservation.

Figs. 29 and 30. Cymatoceras (Naut.) radiatum (sp. Sow.); Rouen; Boucault
Coll., Mus. Comp. Zodél.; Craie Chlorite. Natural size. Fig. 29, side view show-
ing the fourth and subsequent sutures with the broad bands and constrictions
beginning in the ananeanic substage. In this the eighth and ninth sutures show
closer approximation than any of the preceding. Fig. 30 shows the same with
the ananepionic substage at the first septum and the paranepionic at the fifth.
The dorsal furrow begins immediately between the first and second septum in
the metanepionic substage as is shown by the cast of umbilical perforation and
by Pigs 1.0R Lai.

Fig. 31. Cenoceras granulosus, showing the ana- and metanepionic substages
with fragment of the dorsal shell and septa of the ananeanic whorl clinging to the
venter indicating the amount of involution and the depth of the contact zone.

4
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Vol. XXXII

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Proceed

639

PLATE XIII.

Figs. I and 2. Cymatoceras ( Naut.) radiatum, showing the reverse of Fig. 30,
Pl. 12, enlarged to 2 diameters. The beginning of the dorsal furrow is indi-
cated by the shaded area reaching from near the first septum to the edge of the
lower or fifth septum.

Fig. 2, side view of same, showing that the dorsal furrow began on the dorsum
of the metanepionic substage between the first and second septa and in advance
of the gyroceran bend.

Fig. 3. Eutrephoceras (sp. ?); Loc., France; Duval Coll., Mus. Comp. Zodl. ;
Cretaceous; natural size; showing the dorsal furrow in the meta- and paranepi-
onic substages and section of the ananeanic stage below.

Figs. 4-8. Eutrephoceras De Kayt, Dakotah, Cretaceous, preparations by
Henry Brooks. Fig. 4, enlarged 6 diameters, and Fig. 5 same, enlarged 4 diam-
eters, view of ana-, meta- and part of paranepionic substages. The citatrix is a
double depression and the ananepionic outline is given just beyond this. There is
a plate of the nacreous layer ventrad of this and partly covering it, with a shaded
area. This spot is evidently the apex of the czecum seen through the nacre. The
two first substages are very short and smooth, but the dorsal furrow is present
although exceedingly shallow before the bending begins in the later metanepionic.
The umbilical perforation is present, as shown in Fig. 4, but is very small and
elongated, comma-like in shape. Fig. 6, enlarged 4 diameters, shows the perfo-
ration in an older stage, but it is not correctly given. It is exposed by shaving
off the angle of the last septum and the perforation is consequently actually the
_ reverse of what it is in the centre of the umbilicus. This preparation, however,
does show accurately the contact of the paranepionic dorsum with the dorsal side
of the ananepionic substage and how close the coiling is. Figs. 7 and 8, side and
front view enlarged 2 diameters of the meta- and paranepionic substages, the
ornamentation becoming less in the latter which is terminated by a permanent
constriction in this specimen, and also the anephebic substage in which the longi-
tudinal ridges disappear and bands of growth assume the fine unbroken outlines
of the adult. Fig. 7 is erroneous in making too great difference between the
ventral lines of growth in the young parts of the whorl. The hyponomic sinus
really appears about the middle of the paranepionic substage.

‘Figs. 9-12. Lutrephoceras Faxoense, Faxoe, Denmark; Krantz Coll., Mus.
Comp. Zodlogy; Cretaceous. Fig. 9, front view, natural size, showing the cast of
the umbilicus continuous with the very small umbilical perforation of the young.
Fig. 10, side view of the same specimen. Fig. 11, young with first septum delin-
ealed. Fig. 12, front view of same, showing the aspect of the apex and the um-
bilical perforation, the dorsal furrow apparently beginning as in Letrephoceras
De Kayz. Both of these are enlarged 4 diameters.

Figs. 13-16. Eutrephoceras (Naut.) impertalis (sp. Sow.); Isle of Sheppy
and Isle of Wight; Mus. Comp. Zodlogy; Tertiary. Fig. 13, front view of inner
whorls enlarged 2 diameters. Fig. 14, fragment of nepionic or neanic stages,
showing the minute umbilical perforation, the absolutely subdorsan position of
siphuncle in these early substages. This specimen has a double first septum.
Fig. 15, front of specimen from Isle of Sheppy, showing similar position of

— —*

i
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640

siphuncle at about the same age. Fig. 16, another specimen from same locality,
showing the dorsal furrow in both metanepionic and paranepionic substages.
Both the last are enlarged 2 diameters.

Figs. 17-19. Aturia Morisst Michellottt ; Raldasseres, Mus. Comp. Zodlogy ;
Tertiary. Figs. 17 and 18, front and side views of the nepionic and neanic stages
enlarged 6 diameters. Fig. 19, nepionic stage, showing the umbilical perfora-
tion, seen from the exterior as a small black spot.

Figs. 20-22. Aturza 2izac, Sow.; Mus. Comp. Zodlogy; Tertiary. Figs. 20
and 21, side or front view of specimen from Dax, Bronn Coll., enlarged ten times,
showing apical character, siphuncle, first septum with deep lobes and caecum.
Fig. 22, side view of fragment of another specimen with umbilical perforation,
ananepionic substage in section and siphuncle.

PLATE XIV.
Fig. 1. Lutrephoceras De Kayt. Reduced one-third. Two dorsal sutures,

- showing the linguze form, minute, median saddles.

Figs. 2-5. Barrandeoceras Sternbergt (sp. Barrande); Schary Coll., Mus.
Comp. Zoédl. Reduced one-third. Fig. 2, from Lochkov, variety in which
whorls do not touch at all. Fig. 5, section of one, same locality, in which whorls
barely touch, showing that it has no contact furrow. Figs. 3 and 4, specimen in
which whorls touch in ephebic stage, but become free at the base of the living
chamber. This has throughout a flattened dorsum, but no contact furrow. The
appearance of a furrow in Fig. 4 is due to compression. These figures show also
the narrow dorsal lobes of the sutures.

Figs. 6-12. Schroederoceras tubulatum,n.s. Reduced one-third. Coll. Mus.
Comp. Zo6l.; Loc., Brevig, Norway; Silurian. Figs. 6 and 7, nepionic stage.
Figs. 8-12, ana- and metaneanic substages.

Figs. 13 and 14. Dzdymoceras nebrascense (sp. Meek). Reduced one-third.
Loc., near Buffalo Gap, So. Dakota; Coll., Yale University Museum ; Cretaceous.
Views of the parephebic substage and gerontic stage.

Figs. 15-17. Emperoceras Beechert. Reduced one-third. Loc., near Buffalo
Gap, So. Dakota; Yale University Museum; Cretaceous. Fig. 17 shows the
earlier stages with Hamites-like whorls from above. Fig. 16 shows the similar
apex of Fig. 15 corresponding in age to part of Fig. 17. Fig. 15, side view of
Fig. 16, giving the ephebic stage with its tubercles and bifurcated costee and the
parephebic substage with single costze and no tubercles.

Figs. 18-21. Ptychoceras crassum ; Whitfield Coll., U.S. National Museum;
Loc., Boulder, Col.; Cretaceous. Fig. 18, side view of ephebic and gerontic
limbs, with gerontic umbilical perforation, reduced one-third. Fig. 19, section of
same, natural size, showing the gerontic contact furrow. Fig. 20, view of dorsum
of gerontic limb, in and just orad of gerontic umbilical perforation, natural size ;
shows the gerontic dorsal furrow, with dorsal crests in lines of growth and one
costation and below the contact furrow. Fig. 21, section of the upper end of
Fig. 20, showing the gerontic dorsal furrow.

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INDEX TO PHYLOGENY OF AN ACQUIRED

Abiogenesis, 390

Acanthoceras Rémondi,
565

Acceleration, law of, 373,
374

Acleistoceras, 585
Acme, 393, 397
Acquired characters, 407
Actinoceras, 403, 404
Adelphoceras, 519
secundum, 493, 519
bohemicum, 519
fegoceras, 446
Agassiz, Alex., 370
Louis, 353, 390, 402
Agoniatites fecundus, 362,
609
Aipoceras, 545
Anagerontic, 391

Anaplasis, 391, 393, 397,

398
Ananeanic, 3g1, 406, 407,
408
Ananepionic, 391, 405,
4II, 412, 414, 418, 436,
468, 583
Anarcestes, 414
Ancistroceras, 509
Bolli, 510
undulatum, 510, 511
Dyer. su
Ancyloceras calloviense,
372, O14

Jennyi, 573, 577
lineatus, 577

PROC. AMER. PHILOS. SOC. XxxII. 143. 4c.

641

Ancyloceras percostatum,
569
tricostatus, 574
uncum, 577
Anephebic, 391
Angelinoceras, 457, 458,
508
anguinum, 508
latum, 508, 512
Annular lobe, 361, 408,
429
Annular cone, 429
Annular muscle, 429

Ammonitine, 355, 371,
372, 415, 416
Ammonites bifurcatum,
566

Ammonoceratites Con-
radi, 569
Ammonoidea, 352, 358,

359, 361, 368, 370, 371,
373, 374, 376, 378, 385,
410, 413, 416, 417, 418,
431
Anomaloceras, 494
anomalum, 494, 599,
607
Apertures, 353
Apheleceras, 528, 539
mutabile, 539, 602
Aphetoceras, 433, 447,593,
594
americanum, 447, 593
attenuatum, 449
boreale, 448, 592

CHARACTERISTIC.

Aphetoceras Farnsworthi,
448

Apsidoceratidze, 535
Argonauta, 356, 357, 358
NTEtIG2e 67.097 1374
Artemia, 389
Ascoceras, 513
Asiphonula, 403
Asymptoceras, 528, 545
Aturia, 563

Morrissi, 564

Zizac, 504
Aulacoceras, 355, 356
Autotemnon, 399
Auxology, 380, 381, 390
Avolution, 394 _

Bactrites, 361, 362,
412, 413, 5090, 609
Baculitess 9725 .379.0oc7,
395, 411, 417, 477,
566, 579, 612
baculoides, 578

368,

Barrande, 356, 359, 365,
366, 369, 371, 372, 413,
513

Barrandeoceras, 351, 379,

408, 409, 433, 450,

454, 600
bohemicum, 600
convolvans, 451, 601
Minganense, 451
natator, 452

Sacheri, 453, 600

PRINTED AUGUST 20, 1894.

Ps.

Barrandeoceras Stern -
Niel, sels}, — AKO),
592, 600
tyrannum, 406, 453,
600
Bather, 380, 395, 396, 397
Bathmology, 380, 390
Beale, 390
Beddard, 389
Beecher, 350, 364, 365,
392, 396, 397, 613
Belemnoidea, 352, 356,
357, 358, 373, 374
Biogenesis, law of, 390
Bioplastology, 380, 384,
39°
Blake, 396, 402, 403
Brachiopoda, 350, 392
Branco, 355, 359, 373,
411, 413, 414, 415, 417,
609, 610
Brooks, 404, 405, 406, 407
Buckman, 380, 395, 396,
397, 417, 419

Ceecosiphonula, 464
Czecum, 404, 411, 412
Caeleceras, 412
Caloceras, 410
Cataplasis, 394
Cenoceras, 548, 550, 560,
604
aratum, 551, 604
clausum, 552, 604
granulosum, 553
intermedium. 550, 604
lineatum, 551, 604
Cenogenesis, 401
Centroceras, 497
tetragonum, 497
ammonis, 497
ohioense, 497
Cephalopoda, 392
Ceratitinee, 414, 416
Choristoceras, 417
Cicatrix, 403, 411
Clarke, 350, 361, 421
Cladonema, 398

, Clymenine, 371, 563

642

Clymenia antiquissima,
500, 501
depressa, 489
incongrua, 488
rarospira, 467, 484
Coelogasteroceras, 408,
519
canaliculatum, 498
Coloceras globatum, 541,
602, 603
Conch, 359, 392
Contact furrow, 408
COIS, AIO, AES, B80, san
385, 386, 387, 396
Coroniceras, 398
trigonatum, 397
Cosmoceras'bifurcatum,

566, 596, 600
Cranoceras, 4¢9, 520, 527,
545

depressum, 527, 545
hospitale, 527
lineatum, 527
nigrum, 527
turnum, 527, 598
,Ctetology, 384, 388, 389,
292
Crioceras latum, 565
studeri, 372
Cycle, 397, 398
Cyclolituites, 503, 505
Americanus, 505
applanatus, 505
lynceus, 505
Cymatoceras, 548, 553,
560
Deslonchampsianum,
554
elegans, 553
radiatum, 554
simplex, 554
Cyrtoceras amplicorne,
511
depressum, 527
hospitale, 527
lineatum, 527
liratum, 531
Murchisonia, 585
neutrum, 585
nigrum, 527

Cyrtoceras nitidum, 585
tetragonum, 497
turnus, 527
uranum, 529

Dall, 563
Darwinian doctrine, 387
Deltoceras, 433, 449
planum, 450
Deroceras planicosta, 415
Descriptive terms, 422
Dewitz, 506
Dibranchiata, 352, 353
Didymoceras, 568, 573,
614
cochleatum, 574
nebrascense, 574
tortum, 574
Digonioceras, 548, 549,
560, 604
excavatum, 548, 604
rotundum, 549
Diorugoceras planidor-
satum, 540, 602
Diphragmoceras, 363, 368,
405, 412, 416
Diptychoceras, 578, 581
loevis, 581
Diplogenesis, 385, 616
Discites ammonis, 497
Discitoceras discors, 545
Discoceras, 458, 500
antiquissimumn, 445,
461, 501
convolvens, 441
Denckelmanni, 469
Eatoni, 470
Graftonense, 501
teres, 467
subcostatum, 457
Dissoconch, 392
Domatoceras, 545
Dorsal furrow, 408
lobe, 408

Echinodermata, 401

Ectergogenesis, 390

Edaphoceras, 429, 535
hesperis, 536
niotense, 536

Effort, 385, 386
Embryonic, 391, 397, 398
Emperoceras, 566, 568,
570, 575, 578, 614
Beecheri, 575, 579,
613
Enclimatoceras, 563
Ulrichi, 563
Endoceras, 363, 368, 400,
403, 404, 582
Endoceratide, 412, 415
Endolobus, 536, 601
avonensis, 536, 607
“spectabilis, 536
Endosiphonoidea, 404
Entergogenesis, 386, 387,
89°
Epacme, 393, 397
Epembryonic, 392, 410
Ephebic, 381, 391, 397,
398, 409, 410, 417, 445,
473
Ephebology, 392
Ephippioceras, 602
Epinepionic, 392
Epineanic, 392
Ergogeny, 386
Estonioceras, 446,
520, 536, 607
ariense, 522, 536
biangulatum, 521, 523
decheni, 522
heros, 522
imperfectum,
521, 524, 584
lamellosum, 522, 526
perforatum, 521, 523,

457,

520,

524
Eudoceratide, 535
Eurystomites, 433, 434,

441, 456, 592, 601
Kelloggi, 372, 442,

597, 607
gibbosum, 443, 456
rotundus, 443
undatum, 445
Virginiana, 444

Eutrephoceras, 548, 555,

558, 560, 587, 605

Dekayl, 556, 560, 587

643

Eutrephoceras
558

imperialis, 559, 605

Evolution, law of, 367,

371

Exiteloceras, 568
pariense, 577
angulatum, 577
Cheyennense, 577
Jennyi, 577
uncum, 577

faxoense,

Falcilituites, 433, 446, 457,
520, 522
Decheni, 457
Muellaueri, 458
Fissurella, 380, 588
Foord, 404
Funnels, 404

Genesiology, 383, 390, 412
Gephuroceras, 414
Geratology, 392
Gerontic ssi sou, 307,
398, 410, 417, 419, 472
Glossoceras, 513
Glyphioceras atratus, 609
crenistria, 609
Gomphoceras, 585
Goniatites, 368
Goniatitinze, 355, 361, 369,
BY/it, Anko}, Wain, Aiea, cet,
414, 416, 584, 609, 6i0,
616
Growth, law of, 381
Gyroceras, 432
Elrodi, 454
inelegans, 535
minusculum, 493
nudum, 492
ohioense, 497
proximum, 495
Stebos, 497

Habitat, action of, 375

Haeckel, 390, 392, 393,
397

Hall, 361

Halloceras, 518

Hamites, 566, 613, 614
Fremonti, 577
Hamulina, 566
Helicancylus, 565, 570
eequicostatus, 565
Helicoceras, 566, 613
navarroensis, 572
pariense, 577
simplicostatum, 569
Stevensoni, 568
umbilicatum, 569
Hercoceratidz, 491
Hercoceras, 492, 599
irregularis, 493, 599
mirum, 492, 493, 599
nudum, 492

secundum, 493
transum, 492
Hercoglossa, 563
Hering, 384
Heteroceras, 574
angulatum, 577
Cheyennense, 577
Conradi, 569
helecinum, 573
nebrascense, 574
Newtoni, 574
Holm, 463, 468, 471,
599, 579
Holmiceras, 512

preecurrens, 509
Hymenoptera, 401
Hyponome, 353

Impressed zone, 407, 408

Jackson, 350, 365,
396

Kinetogenesis, 386
Koninckioceratidae, 545
Kophinoceras, 518

Lamarck, 358, 387
Lepidoptera, 401
Lindigia, 569
helicoceroides, 569
Lispoceras sulciferum, 544
Litoceras, 474, 485
biangulatum, 476

Litoceras hercules, 480
insolens, 475, 476, 596
Whiteavsi, 474

Lituites, 432, 506, 520
angulatum, 460, 462
applanatus, 508
Bickmoreanus, 500
cornuarietis, 469
convalvans, 457
Decheni, 457
Denckelmanni, 469
discors, 508
Eatoni, 470, 473
Farnsworthi, 448, 449
Graftonensis, 501
heros, 522
hibernicus, 490
internastriata, 484
lamellosum, 522
lituus, 508
Lynnensis, 505
Muellaueri, 458, 521,

522
multicostatus, 502
perfectus, 508
teres, 467, 468
torniquisti, 508
Lophoceras, 537
Lytoceratinz, 355, 414,
415, 416

Macrosiphonula, 405
Macroscaphites Ivani, 566
Magilus, 588
Manticoceras latidorsale,
609
Maupas,
399, 400
Megaphyllites, 414
Melonoceras, 447, 520
Mesal, 430 .

382, 383, 389,

Metacoceras, 496
cavatiformis, 601

Metagerontic, 391

Metaneanic, 391, 445

Metanepionic, 391, 405,
414, 418, 466

Metaplasis, 391, 394, 397,
398

Metazoa, 394, 399

644

Metephebic, 391, 409
Microsiphuncle, 414
Mimoceras, 413, 609, 616

ambigena, 362

compressum, 361, 362,

Anh, 428s)

lituum, 362, 609
Minot, 363, 381, 382, 384
Mitroceras, 503
Mnemegenesis, 384
Monogenesis, 365

Nannoceras
603
Nautilinidz, 361, 370,
372, 373, 413, 414, 415,
609, 610, 616
Nautiloidea, 352, 359, 368,
369, 370, 371, 373, 379,
378, 385, 404, 410, 418,
615
Nautilus, 351, 352, 353,
379, 407, 432, 548,
559, 606, 610
aciS, 547
acreeus, 534
anomalus, 494

Frieslebeni,

aratus, 409, 551
avonensis, 536
Barrandei, 546
bucinus, 533
Calciferus, 435
cavus, 534
Champlainense, 438,
441
clausus, 552
cornulus, 530
Dekayi, 556
Deslonchampsianus,
413, 554
discors, 545
elegans, 553
evolutum, 546
gemmatus, 519
globatum, 541
granulosus, 553
granulosostriatus, 546
Hercules, 480
hesperis, 536

Nautilus Hyatti, 531
imperialis, 559
inelegans, 535
intermedius, 550
insolens, 476
inspiratum, 519
Jason, 499
Kelloggi,

443, 444
linearis, 546
lineatus, 551
liratus, 532

441, 442,

liratus, var. juvenis,
532

macromphalus, 560,
561, 607

magister, 534
maximus, 534
oriens, 535
planidorsatus, 540
pompilius, 355, 363,
365, 379, 402, 404,
406, 409, 416, 422,
439, 514, 560, 561,
607
prematurum, 433
radiatus, 554
rotator, 452
Sacheri, 453
scoticus, 491
simplex, 554
Sternbergi, 452
subliratum, 532
subtuberculatus, 496
tyrannus, 433
umbilicatus, 354, 358,
406, 409, 431, 560,
561, 606
undatus, 445
versutus, 475
Nealogy, 392
Neanic, 381, 391, 397, 398,
406, 418, 472
Nedyceras, 520, 526
vetustum, 526, 598
Neolamarckian, 385, 388,
389
Nepionic, 382; “3oi)mg3G7.5
398, 402, 407, 416, 470
Neumayr, 396, 566

Neurism, 386

Newberry, 370°

Nephriticeras, 531
acrzeum, 5534
bucinum, 533
cavum, 534
inelegans, 535
juvenis, 532
hratum, 532
magister, 534
maximum, 534
oriens, 535
subliratum, 532

NoOtiing, 506, 520

Nostoceras, 566, 568, 569
helicinum, 569, 570,

573) 574) O14

Stantoni, 569, 570
tricostatus, 574

- Oncodoceras, 545
Ontogenetic stages, 402
Ontogeny, law in rela-
HOnmow3sOL, 407, 410
Oonoceras, 447, 520
Ophidioceras, 513, 514,
530, 601, 602
rudens, 514
tener, 517
tessellatum, 518
Origin of species, 419
Orthoceras, 351, 361, 368,
377, 400, 582
elegans, 360
unguis, 360
Owen, Richard, 352, 359
Oxynoticeras oxynotum,
416

Packard, 380, 388
Paleonautilus hospes, 488
Palingenesis, law of, 390,

4o1

Paracme, 393, 395, 397,
429

Paragerontic, 382, 391,
395

Paraplasis, 391, 393, 394,
395, 397, 398, 400

645

Paranepionic, 391, 405,
406, 416, 418, 445, 466
471, 472, 477

Paraneanic, 39I, 409, 445,
472
Parephebic, 409, 472
Patella, 380, 588
Paterina, 364
Peismoceras, 500
angulatum, 500
disjunctum, 500
opatatum, 500
placidum, 500
Pelecypoday) 3507 18355,
392, 396
Periconch, 392
Peripetoceras, 545
Frieslebeni, 546
Postembryonic, 392
Phloioceras, 519
gemmatum, 51g
Phragmoceras, 586
perversum, 585
subventricosum, 528
Phrenism, 386
Phylanaplasis, 397
Phylembryonic, 397
Phylogenesis, 397, 401
Phylogerontic, 397, 410
Phyloneanic, 397
Phylometanepionic, 414
Phylometaplasis, 397
Phylonepionic, 397
Phyloparaplasis, 397
Phylephebic, 397
Phylostages, 398
Physical. selections, 387
Piloceras, 403, 404
Pinnacites, 412
Planctoceras, 433, 446
Quenstedi, 446
Planorbis
tus, 367
Plasmology, 390

oequiumbilica-

Plectoceras, 499
Bickmoreanus, 500
Jason, 499
obscurum, 499

Pleuronautilus, 547
superbus, 547, 591

Podocoryne, 398
Pompeckj, 607, 612, 613
Potoceras, 537

dubium, 537, 599
Prodissoconch, 351, 392
Prolecanites, 414
Primordialidz, 413, 414,

415
Protegulum, 351, 364, 392
Protoconch, 359, 373, 402,
410, 412

Protosiphonula, 403
Protozoa, 394, 399
Pselioceras, 530, 544

ophioneum, 544
Ptenoceras, 491

alatum, 492

flexum, 492

tardum, 492
Pteropoda, 360
Ptychoceras,’ 566, ‘570,

579

crassum, 579, 580

Texanum, 580
Pycnoceras, 433, 454, 593,

594
apertum, 455

calciferiforme, 456

Quenstedt, 356, 365, 375,
376, 446, 566, 568

Radical types, 378, 379
Remelé, 446, 457, 458, 506,
509, 511, 522
Remeléceras, 520, 522
Beyrichia, 512
damesi, 512
impressum, 522, 600
Oelandicum, 512
tenuistriatum, 512
Zaddachi, 512
Replacement, law of, 373
Rhadinoceras, 530
Hyatti, 531
cornulum, 530
Rhyncorthoceras, 511
dubium, 512
Rineceratida, 543

Rutoceras, 518
Ryder, 380, 386

Scaphites, 564, 614
larvee formis, 565
ventricosus, 565
Scaphopoda, 392
Schuchert, 350
Schroder, 433, 442, 446,
463, 468, 520
Schroederoceras, 458, 474,
475, 592, 597, 607
angulatum, 460, 462
Bandonis, 469
Casinense, 473, 597
Damesi, 469
Denckelmanni, 469
Eatoni, 468, 470, 484,
485, 597
Eichwaldi, 485
Odini, 469
rarospira, 467
Saemanni, 463, 467
tOGES #407, eA Ona
485
tubulatum, 464
Sciponoceras, 578
baculoides, 578
eploidea, 352, 356, 357;
373, 374,
Siphuncle, positions of, 430
Solenoceras, 519
Solenocheilus, 528, 545
caledonicus, 536
Springeri, 545
Sphyradoceras, 529
Spirula, 357
Spyroceras crotalum, 360,
361, 582
Stanton, 563, 565, 572,573,
574, 579, 580, 614
Statogenesis, 386
Strombolituites, 509
Bolli, 510
Strophiceras, 518
Surroundings, action of,
377
Syncoryne, 398

646

Syringoceras, 546
evolutum, 546
granulosostriatus,

546, 602
linearis, 546, 602

Systrophoceras, 502
arietinum, 502
pingue, 502
yapax, 502

Table, descriptive terms,
428
Ontogeny, 391, 397
Phylogeny, 397
Tachygenesis, 401, 403,
404, 406, 407, 411, 415,
418, 616
‘Tainoceras, 497
Tainoceratide, 458, 491
Tarphyceras, 433, 441,
442, 456, 592, 594
595, 607, 614
aucoini, 435, 437
calciferus, 456
Champlainense, 435,
436, 438
convolvens, 441
extensum, 435, 438
Farnsworthi, 435, 449
Mac Donaldi, 435
prematurum, 432,434,
435, 437
Seeleyi, 435
Tegulum, 392
Temnocheilus, 408, 494,
OOK
subtuberculatus, 496
Thoracoceras, canalicula-
tum, 540, 603
puzosianum, 540, 603
Thrincoceras, 544
Kentuckiense, 544

‘Trachyceras munsteri,

AEs
Triboloceratidz, 540
‘Triplooceras, 519

inspiratum, 519
regulum, 519

Trochoceras, 502
angulatum, 500
Davidsoni, 502
disjunctum, 500
Gebhardi, 503
Opatum, 500
placidum, 500
regulum, 519
speciosum, 504
transiens, 492
turbinatum, 503

Tropites subullatus, 417

Trocholites, 434, 436, 458,

460, 466, 471, 472,
484, 517, 520, 584,
585, 596, 614
ammonius, 484, 487
anguiformis, 490
arietinum, 502
Blakei, 490
Canadense, 486, 527,
587, 596, 605
circularis, 484, 489
contractus, 489
Damesi, 469, 489
depressus, 489
dyeri, 489
hospes, 488
incongruus, 488
internastriata, 484
macromphalus, 489
macrostoma, 489
minusculus, 490
multicostatus, 502
orbis, 489
pingue, 502
planorbiformis, 490
rapax, 502
Remelei, 484, 489
_scoticus, 491
soraviensis, 489
Trocholitoceras, 458, 478,
480, 596
Eichwaldi, 484
Walcotti, 476, 480,
485, 607

Turrilites, 566
Boblayei, 567
Coynarti, 567

Turrilites splendens, 572
Valdani, 567

Uranoceras, 529
uranum, 529

Variations, develop-
mental, 420
spontaneous, 420

647

Variations, transmission
of, 419
Vermiceras, 410
Spiratissimum, 415
Vermetus, 588
Vestinautilus Konincki,
540, 602
pinguis, 541
Von Baer, 365, 402
Jhering, 356

Wagner, 370

Walcott, 365, 442, 614
Weismann, 384, 385, 388
Whitfield, 472, 476
Wiirtenberger, 396, 417

Zitteloceras, 518
Zoon, 399

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