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REVISION

OF THE

PELYCOSAURIA OF NORTH AMERICA

BY

E. C. CASE.

WASHINGTON, D. C.

PUBLISHED BY THE CARNEGrE INSTITUTION OF WASHINGTON

JULY, 1907.

CARNEGIE INSTITUTION OF WASHINGTON
Publication no. 55.

PRESS OF THE WILKENS-SHEIRY PRINTING CO.
WASHINGTON, D. C.

CONTENTS.

Page.

Introduction ................. 3

Historical review of the Pelycosauria ............ 5

Systematic revision of the suborder 17

Morphological revision of the suborder 77

Position and relations of the Pelycosauria ........... 157

Geological and geographical distribution . ........... 159

Bibliography ................. 162

Index 167

Description of plates 169

REVISION OF THE PELYCOSAURIA OF NORTH AMERICA.

INTRODUCTION.

The vertebrate fauna of the Permian beds of North America was made
known as early as 1877-78, and quickly attracted the attention of Professor
Cope, who, with his wonderful acumen, saw the importance of the fauna
lying so close to the beginnings of the reptilian line. From the first
discovery of Permian reptiles until his death he retained his interest in the
group, some of his latest papers having to do with the orders Cotylosanria
and Chelydosauria. Much of the material in the collections of Professor
Cope is in a very fragmentary condition, and none of it was carefully
prepared while in his possession. He contented himself with the descrip-
tion of new forms without detailed study or complete morphological discus-
sion, and yet he based upon this material many of his most brilliant
generalizations ; and it is more surprising that he should have seen so
much and built so well than that he described some genera and species
that will not stand and drew some conclusions that have proven incorrect.

From the discovery of Permian vertebrates in Texas until his death.
Cope sent parties into the field at iiTegular intervals, and the material
collected by them is now preserved in the American IMuseum of Natural
History in New York. These collections contain the types from Texas
described by Cope. A small collection made in Vermilion county, Illinois,
by Mr. William Gurley, and now in the Walker Museum of the University
of Chicago, contains the types from Illinois described by Cope. Another
small collection obtained from New Mexico by Professor Marsh is preserved
in the Museum of Yale University. The author made two collections
in Texas for the University of Chicago in 1895 and 1903 ; these are
preserved in the Walker Museum and contain the specimens upon which
was based the work of the late Doctor Baur and the author. In 1901
Dr. Ferdinand Broili, of IVIunich University, visited the Texas region,
accompanied by Mr. Charles Sternberg, and carried home many fine speci-
mens ; this, with a collection purchased by the IMunich University a few
years before from the veteran collector, Mr. Charles Sternberg, constitutes

4 INTRODUCTION.

the ouly other considerable collection of Permian vertebrates from the
United States.*

The fauna as represented in the various collections is very rich, con-
taining abundant representatives of the Pisces, Amphibia, and Reptilia.
The Reptilia is represented by two orders, the Cotylosauria and the Chely-
dosauria^ and the suborder Pelycosarcria. The present paper has to do with
the last of these only, but the author hopes to discuss the other forms in
future papers.

In 1904 the author received a grant from the Carnegie Institution
of Washington enabling him to complete the writing and illustration of
this monograph, which was already begun. To the authorities of the Insti-
tution are due his thanks for aid that permitted the work to take its present
form and scope. Much of the work was done at the American Aluseum, as
many of the types are preserved there, where every assistance was rendered
the author in the preparation of material and illustrations. For this and
for many valuable suggestions as to the form of the work and the interpre-
tation of specimens, the author desires to express his hearty thanks to Dr.
Henry Fairfield Osborn, the curator of the department of vertebrate pale-
ontology, and to Dr. W. D. Matthew of the same department.

The author is painfully aware that the following pages can lay no
claim to being an even approximately complete description of the Pelyco-
sauria ; much work, both of collection and description, remains to be done.
He has therefore refrained from much speculation, contenting himself with
the hope that he has placed the classification on a sound basis for progress
and has rendered the known material more available.

*During the summer of 1906 the author made a third collection in Texas, which will go to the Amer-
ican Museum in New York. I have just learned that there is a small collection from Texas in the Museum
of Comparative Zoology at Harvard University made by Mr. Chas. Sternberg.

HISTORICAL REVIEW OF THE PELYCOSAURIA.

The name Pelycosauria was first used by Cope in a description of
Clepsy drops natalis ; it was given to designate a new suborder of the Rhyn-
chocephalia^ based on the supposed absence of the quadrat o-ju gal arch and
the peculiar form of the ischium. He considered the suborder as superior
to and including the Theriodontia of Owen ; he says (44), p. 529 :

"The division Pelycosauria is established primarily on the genera Clepsydrops
and Dimctrodon^ but their cranial structure renders it highly probable that Edocyn-
odon^ Pariotichus, and Bolosaurus belong to it. It is also probable that the genera
Empedocles, Embolophorus and others determined from vertebrse belong to it, as the
latter are frequently accompanied by pelvic bones of the type of that of Dimetrodon.
All the genera known from teeth and crania, are of carnivorous habit, excepting
Bolosaurus and Diadedes ; they may be referred to a single family on this account,
which I call the Ckpsydropidcr. Bolosaurus will form the type of another family
characterized by the transverse position of the crowns of the teeth, under the name
Bolosaiiridcr. Prof Owen has named a group of Triassic and Permian reptiles the
Theriodontia^ characterized by the mannnal-like differentiation of the incisor and
canine teeth. The animals thus referred to by Prof Owen probably enter my sub-
order of Pelycosauria, although the structure of their pelvis remains to be ascer-
tained. If so, they correspond with my Clepsydropidcr, since Prof Owen does not
include herbivorous forms in his division. As it is plain that the herbivorous and
carnivorous forms belong to the same order, and probably suborder, it becomes neces-
sary- to subordinate the term Theriodontia to that of Pelycosauria. To another
division of reptiles from the South African Trias typified by the genus Pareiasaurus
Ow., he gives a special name, expressive of the deeply impressed surfaces of the centra
occupied by the remains of the chorda dorsalis. As this, or the perforate condition, is
characteristic of all the Pelycosauria, it is probable that it is present in Prof Owen's
Theriodontia also. It is also evident that since the dental characters of Pareiasaurus
do not serve to distinguish it as an order from the genera with distinct canine teeth,
this group must also be looked upon as a subdivision, perhaps of family value, of the
Pelycosauria or other parts of the Rhynchocephalous order."

It is evident that Cope here regards the Peiycosatiria as belonging in
the order Rhynchocephalia and his classification stands as follows :
Suborder: Pelycosauria.

Family Clepsydropidce : Clepsydrops, Dimetrodon, Ectocynodon,
Pariotichus , Embolophorus .

Titer iodo7ttia = Clepsy dropidce .
Family Bolosauridce : Bolosaurus, Evipedocles , Diadedes.
Family Pareiasaurida (?)

6 REVISION OF THE PELYCOSAURIA.

On November 7, 1878, Cope read a paper before tlie National Academy
of Science, whicli was reported in the American Naturalist of that year (40).
The taxonomic portion of this paper is as follows :

"The structure of the scapular and pelvic arches (of the Pelycosaurid) was stated
to be identical with that already described by Owen as belonging to ^y^ Ammwdontia.
Several important characters distinguish this group from the Pelycosauria^ but the two
together form an order, which Professor Cope would have, for the present at least, to
be retained as distinct from the Rhyiichocephalia. The characters of this order, with
its two suborders, were given as follows :

"Theromorpha Cope. Scapidar arch consisting at least of scapula, coracoid,
and epicoracoid, which are closely united. Pelvic arch consisting of the usual
three elements, which are united throughout, closing the obturator foramen (f pubo-
ischiatum) and acetabulum. Limbs with the phalanges as in the ambulatory
types. Quadrate bone proximally united by suture with the adjacent elements. No
quadrato-jugal arch.

'■'•Pelycosauria. Two or three sacral vertebrse ; centra notochordal; intercentra
usually present. Dentition full.

'■'■ Anotnodontia. Four or five sacral vertebrse ; centra not notochordal ; no inter-
centra. Dentition very imperfect or wanting.

"The Rhynchocephalia have no distal ischio-pubic symphysis, and apparently no
epicoracoid bone. They have an obturator foramen (foramen pubo-ischiatum) and a
quadrato-jugal arch.

"The order Theromorpha was regarded by Professor Cope as approximating the
Mammalia more closely than any other division of the Reptilia, and as probably the
ancestral group from which the latter was derived. This approximation is seen
in the scapular arch and the humerus, which nearly resemble those of the Monotre-
jnata, especially Echidna; and in the pelvic arch, which Owen has shown in the
Aitomodotitia to resemble that of the Mammals, and, as Professor Cope pointed out,
especially that of Echidna. The tarsus is also more mammalian than in an}- other
division of the reptiles. In the genus Dimetrodon the coracoid is smaller than the
epicoracoid, as in Monotremes. The pubis has the foramen for the internal femoral
artery."

The substance of the same paper was printed in 1880 (48) as a portion
of the "Second Contribution to the History of the Vertebrata of the Permian
Formation of Texas."

In these two papers was established the order Theromorpha.^ distinct
from the Rhynchocephalia., with the two suborders Pelycosauria and Anomo-
doiitia. Owen's Theriodo7itia was still included in the Pelycosauria., while
the Anomodontia was meant to include all other African forms.

It is of interest to insert here Owen's classification of the African forms
as it appears in the Catalogue of the Fossil Reptilia of South Africa in the
British Museum (117). (See next page.)

HISTORICAL REVIEW OF THE PELYCOSAURIA. 7

Order Dinosauria: Order Theriodontia: Order Anomodontia:

Section Tretospondylia. Section Binaralia. Family Cryptodontia.

Genus Tapinocephalus. Genera Lycosaurus, Genera Theriogna-

Family Serratidaiiia. Tigrisuchus. thzis , Kistecephalus .

Genera Pareisaurus, Family Mononaralia. ViMsX^y Endothiodontia.

Ajithodon. Genera Cynodracon , Cyno- Genera Etidothiodon .

suchus, Galesaurus, Nytho-
saiirus, Scalaposaurus,
Procolophon .
Family Tedinaralia.
Genera Gorgonops.

In his Second Contribution to the History of the Vertebrata of the
Permian Formation of Texas, p. 39, Cope discussed the relationship of the
Pelycosauria to the Mammalia and Batrachia more fully; he says:

"A not less remarkable characteristic of the Pelycosauria^ as represented by Clepsy-
drops and Dimetrodon, is their resemblance to the Batracliin in some important
respects. This is seen in the scapular and pelvic arches, which resemble very much
those of the Urodela^ and of such types as Eryops. The small coossified coracoid
only differs from that of Eryops in having two deep sinuses of its free border. The
general fonu of the pelvis is similar, but the ilium has a special and peculiar articular
face for the sacral diapophysis, which is wanting in Eryops. In the inferior arches,
the absence of obturator foramen, and general boat-like form, are the same in both;
but in the Pelycosauria the symphysis is not so deep, and the walls less massive.
But the resemblance of these arches to those of the Batrachia in question is greater
than to those of any order of reptiles.

"Another point of resemblance to the Batrachia is seen in the humerus. In my
previous essay on the Pelycosauria above cited, I defined six types of humerus as
occurring in the Texas Pennian. Two of these were described as wanting the fora-
men, while the others were stated to possess it; other differences between these types
exist, but they were not mentioned. Since then Gaudray has added a third form to
the fonner group, which he has ascribed to a reptile under the name of Euchiro-
saurus. I have detected this form in my Texas collections together with another,
which has no condyles at either extremity. Thus eight fonns of humerus are found
in this formation.

"That the type with the supracondylar foramen belongs to the Pelycosauria has
been satisfactorily shown by its presence in the skeleton of Clepsydrops tiatalis and
in Cynodraco major^ where Owen first identified it. I find the type without this
foramen frequently associated with the skeletons of Eryops and other Stegocephali.
There is no other element that can be regarded as the humerus of this type. It more-
over has distinct points of resemblance to the humerus of existing Batrachia., parallel
with similarity traceable in the femora of the e.xtinct and recent genera. There is
then every reason for believing that we have in the humerus oi Eryops aud its allies,
an element which approaches closely in its characters to that of the Pelycosaicria, and
hence to that of the Monotre))iata.

8 REVISION OF THE PELYCOSAURIA.

"There are some other peculiarities which constitute resemblances of the same
kind. The tooth-bearing elements of the roof of the mouth have batrachian character.
Such is the densely packed body of teeth seen in Dimetrodon ; and so are the teeth on
the vomer of Empedocles. There is also a possible existence of epiphyses, judging
from various specimens of humeri in my possession of both Pelycosanria and Stego-
cephaloiis forms.

"In spite of these approximations, the Pclycosaitria are distinctively reptilian in
their single occipital condyle, ossification of the basicranial cartilage and single vomer.

"Thus the reptiles and batrachia of the Permian period resembled each other and
the Mammalia more closely than do the corresponding existing fonns."

In the same j'car as the Second Contribution Cope described (50) a
"new division of the Pelycosaiiria^'' which he called the Cotylosauria and
which he evidentl}' regarded as of subordiual rank ; this suborder was
founded on the supposed presence of double occipital condyles, which was
later shown to be fallacious, the appearance being due to the loss of the
loosely articulated basisphenoid bone. In the suborder was placed the
family Diadedidce^ and to this family was ascribed a new genus, Helodedes^
described in the Second Contribution.

In 1881 (5) Cope gave a catalogue of the Reptilia of the Permian for-
mation in the United States in which all forms are placed in the suborder
Pelycosaiiria and no mention is made of the suborder Cotylosauria. The
list is as follows:

Suborder Pelycosauria. ClepsydropidcB — continued.

DiplocaulidcB: Theropleura uniformis Cope, Texas.

Diplocaulus salaviandroides Cope, 111. triangulata Cope, Texas.

ClepsydropidcB : obiusidens Cope, Texas.

Pariotichus brachiops Cope, Texas. Metarmosaurus fossaius Cope, Texas.

Ectocynodon ordinatus Cope, Texas. Embolophorous fritilliis Cope, Texas.

Archaobolus vellicatus Cope, Illinois. Lysorophus tricarinatus Cope, Illinois.

Clepsydrops colletti Cope, Illinois. Bolosauridcc:

vi7islovii Cope, Illinois. Bolosanrus striahis Cope, Texas.

pedunailatus Cope, 111. Diadedida:

naialis Cope, Texas. Diadedes sidcfopelicus Cope, Texas.

Dimetrodon i7idsivus Cope, Texas. phaseolinns Cope, Texas.

rediformis Cope, Texas. Empedodes alatus Cope, Texas.

biradicaius Cope, Texas. niolaris Cope, Texas.

gigas Cope, Texas. laiibuccatus Cope, Texas.

crudger Cope, Texas. Helodedes paridens Cope, Texas.

Theropleura retroversa Cope, Texas. isadi Cope, Texas.

It will be observed that in this catalogue the batrachian genus Dip-
locaulus is included among the reptiles ; it was speedily removed to its
proper place.

In 1882 (54) the genus Edaphosaurtis was described, and a new family
of the Pelycosauria, Edaphosauridce, was formed for its reception with the

HISTORICAL REVIEW OF THE PELYCOSAURIA. 9

genus Pantylus. In the same paper the validity of the suborder Cotylosauria
was questioned, as it already appeared that the double articular condyles
were the result of the accidental loss of the basioccipital. Cope says, p. 448 :
" I am still inclined to question whether the extraordinary characters of the cranio-
vertebral articulation which I have described, justify the separation of the Diadectida:
as a third suborder of the Theromorpka, which I have called the Cotylosauria, or
whether they are not due to the loss of a loosely articulated basioccipital bone."

In 1883 (56) Cope described a new species oi Parioticfnis, P. megalops,
and erected a new family Pariotichidce, to contain Pariotichtis, Pantylus, and
probably Ectocytwdon. In this same paper the Diadcdidcs were shown to
possess a basioccipital bone with a single occipital condjde, and the sub-
order Cotylosauria is not mentioned ; it had disappeared, as it was founded
on the supposed double occipital condjde; all Permian reptiles of the United
States were thus placed by Cope at that time in the Pelycosauria.

In 1S84 (60) appeared Cope's "Fifth Contribution to the History of the
Vertebrata of the Permian Formation"; the substance of the paper was also
published in the Proceedings of the American Association for the Advance-
ment of Science (62) in 1885. In these papers there is a further discussion
of the relationship of the Pelycosauria to the mammals.

" I. The relations and number of the bones of the posterior foot are those of the
Mammalia much more than those of the Reptilia.

"2. The relations of the astragalus and calcaneum to each other are as in the
Monotreme Platypus anatinus.

"3. The articulation of the fibula with both calcaneum and astragalus is as in
the Monotreme order of mammals.

"4. The separate articulation of the anterior part of the astragalus with the
tibia is as in the same order.

" 5. The presence of a facet for an articulation of a spur is as in the same order.

" 6. The posterior-exterior direction of the digits is as in the known species of
Monotremata.

"Thus the characters of the posterior foot of the Pelycosauria confirm the evi-
dences of Monotreme aflinity observed by Prof Owen and myself in the bones of the
legs, especially of the anterior leg. It remains a fact that with this resemblance in the
leg there is a general adherence to the reptilian type in the structure of the skull."

In 1885 (64) Cope published a paper in the American Naturalist in
which he derived all the reptiles with the possible exception of the Ichthy-
osaurs from the Theromorpha.

In 1886 (70) appeared his "Systematic Catalogue of the Species of
Vertebrata found in the beds of the Permian Epoch of North America."
The larger divisions stand as follows:

Order Theromorpha.

Suborder Pelycosauria.

Families ClepsydropidcE , Pariotichidce , Bolosauridcs , Diadectidce .

lO REVISION OF THE PELYCOSAURIA.

It is seen tliat there is no mention of the Cotylosauria.

In the same year (5) Baur published some obsen^ations on the rela-
tionship of the Pelycosauria and the mammals. He says:

" Cope betrachtet die Pelycosauria unter den Theroniorpha als die Ahneu der Sau-
o-ethiere. Ich glaube jedoch dass dieselben schon etwas zu stark specialisirt sind, um
diesen Anforderungeu eutsprecheu zu konnen.

"Dariiber aber kanu kein Zweifel sein, dass die Pelycosauria den Stammeltern
der Saugethiere sehr nahestehen. Beide sind vielleicht aus derselben Gruppe her\-or-
gegaugen, einer Gruppe, welche zwiscben den Batracbieni und Reptilien des Perm
in der mitte stehen wiirde, und welche ich Sauro-Mammalia uennen mochte, Folgen-
des Schema nioge den Zusanimeuhang ausdrucken:

THEROMOnPHA EUTHERIA CmONOTREMATa)

AUR0-MAMMAL1A

CARBONISCHE BATRftCHIER DEN EMBOLOMERI NAHESTEHENO.

In the following year, 1887, Baur published a diagram in different
papers (6 and 7) illustrating his views on the subject. This diagram is
given at the bottom of the next page.

Among the foreign writers on this group Seeley in 188S (120) gave the
following an-angement as his idea of the relationships of the Pelycosauria:

Subclass Anomodontia.

Orders Pareiasauria, Procolophonia, Dicynodoyitia , Gennetotheria, Pflycosaiuia,
Theriodontia , Cotylosauria, Placodontia .

Lydekker in his Paleontology gives the following (107):

Theromorous Branch.

Order Ano7nodontia.

Suborder Pareiasauria:

Family Pareiasaiiridce .
Suborder Theriodontia:

Families Tapinocephalida:, Gaksaiiridce , Clepsydropidts , Bolosauridtr,
Diadectidce.
Suborder Dicynodontia:

Family Dicyjiodontidee .
Suborder Procolophonia:

Family Procolophonidcs .

In 1889 (134) Zittel's Handbuch gives the follo\ving classification:

Order Theromorpha.
Suborders Anomodontia, Placodontia, Pareiasauria, Theriodontia {Pelycosauria').
Families Cynodontia {Clepsydropidd), Pariotichidce , Diadectida, Ettdothiodontida.

HISTORICAL REVIEW OF THE PELYCOSAURIA. II

In the same year Seeley (i2i) proposed the following arrangement:
Order Atiomodontia.

Suborders Pareiasauria, Procolophoyiia ,Dicynodontia ,Gennetotheria ,Pelycosauria (?),
Theriodontia, Coiylosaurta, Placodontia.

In 1890 was published Lydekker's Catalogue of the Fossil Reptiles of
the British Museum, Part IV (106), which has the following arrangement
of the forms most closely related to the Pelycosaiiria:

Theromorous Branch.
Order Atiomodontia.

Suborders Procolophonia, Dicytiodoniia, Theriodontia {Pelycosauria), including the
families Galesaurida , Tapinoccphalida: , Diadectidce, Clepsydropidce , Gorgo7iopsidcE .
Suborder Pariasauria .

Diagram accompanying Baut's paper in the Journal of Morphology, illustrating his views ot the phylogeny ot the reptiles.

In 1889 (74) Cope changed the name of the order from Theromorpha to
Theromora^ as the former was preoccupied. In the same paper he reestab-
lished the Cotylosatiria^ with a new description, as a suborder of the Thero-
mora, to include the families Pareiasauridis, PariotichidcB^ and Diadedidce.

12 REVISION OF THE PELYCOSAURIA.

In 1 891 {jj) appeared Cope's first "Syllabus of Lectures on Verte-
brate Paleontology" ; the classification is similar to that published in the
American Naturalist^ but the suborder Pelycosauria is omitted, and the
Theriodontia is used for a suborder including the families Clepsydropidcs^
Bolosauridce and Pariotichidce. The suborder Cotylosauria holds only the
families Pareiasajtrida; and Diadcctidce.

In 1892 (79), in a discussion of the cranial arches of the reptilia, the
Cotylosauria was raised to the rank of an order with the genera Chilonyx^
Pantylus^ Pariotichtis, and probably Parciasaiirus. The genera Diadcdes and
Empedocles are not mentioned, but are evidently meant to be included, as the
order is based on the completely roofed condition of the skull. The mem-
bers of this order are never again considered as part of the Pelycosauria and
so pass from farther consideration in this review. In this paper Cope
called the Thero^nora a "branch" opposed to the order Cotylosauria^ evi-
dently following Lydekker, with the two orders Tliei'iodontia and Anonio-
dontia. The first includes the African Theriodontia of Owen as well as
Cope's Pelycosauria of previous papers.

In the same year Seeley (122) gave a classification of the Permian
reptiles as follows:

Order I. Pareiasauridce . Suborder Procolophonia.

II. Theriodo7itia . Suborders Gennelotheria, Cotylosauria^ and
probably Pelycosauria .

III. Endothiodontia .

IV. Mesosauria.
V. Dicynodoyitia.

VI. Pleurodojitia.

In 1894 (80) Cope published a description of the Plesiosaurian skull,
in which the name Pelycosatiria was again used and ranked as an order
equivalent (?) to the Theriodontia and of equal rank with the Cotylosauria
and Theromora.

In a review of some of Seeley's paper in the same year Cope explained
(81) that his use of the term Theriodontia in the former paper was inad-
vertent and was meant to signify Pelycosauria ; that its use was due to the
fact "of the premature assumption by the English paleontologists that the
two names were s}'non3^mous."

In 1895 Seeley (123) placed the Theromora doubtfully in his new
order TherosucJiia^ with the Pelycosatiria and Cotylosauria as subgroups of
equal rank, the whole distinct from the Theriodontia.

In Bernard's Paleontologie (12) we find the following table:
Order TJieromorphes {Anomodonts sens lat.').

Suborders Cotylosaurie^is {Pareiasauriens), Procolophonie?ts , Tkeriodontes ,
including both the Clepsydropida and the Diadectidis, Dic}'nodontes {sens
slrici.), Appendice Theromorphes — Placodontes.

HISTORICAL REVIEW OF THE PELYCOSAURIA. 1 3

In the same year appeared Zittel's Grundziige der Paleontologie (135).
The scheme of classification is essentially the same as in the Handbuch.

In 1895 (98) Haeckel published his Systematische Phylogenie der
Wirbelthiere in which he gives the following classification:

Legion Therotnore (Theromorpha) .
Order Theriodontia.

Suborders Theriodontia, Pareosauria, Pelycosauria, Palalosauria .
Order Atiotnodontia.

Suborders Dicynodontia, Oudenodoniia.

The suborder Theriodoritia is divided into the families Cynodontia
{Binaralia)^ Cynodracontia ( Uninaralia\ Gorgonopsida ( Tedinaralid). The
first family contains the Clepsydropidce.

In 1897 Baur and Case (9) published a preliminary account of the skull
of Dimetrodon^ in which they showed that the Clcpsydropidce possessed the
two temporal arches of the Rhynchocephalia and that they must be placed
in that order ; they also showed that the Theromora could no longer be con-
sidered as a good group and that it should be dropped from the literature.

Cope replied to this paper in the same year (82) insisting on the reten-
tion of the order Thcromo7-a on other grounds than that of the presence of
\.\\& Pelycosanria (intending it now to include the pro-mammalian reptiles of
all regions), and admitting that the Pclycosauria probably belonged to the
Rhynchocephalia. Since that time the Pclycosauria have been regarded by
almost all authors as belonging in the Rhynchocephalia. Compare Broili's
classification below.

In 1898 (83), after Cope's death, appeared the second edition of his
"Syllabus of Lectures on Vertebrate Paleontology." In this the orders
Theromora, Pclycosauria., and Chelydosauria are ranked as equal ; the order
Pclycosauria contains the two families Bolosauridce and Clepsydropidcz.
The order Chelydosauria is new, and contains the genera Otocoelus and
Conodectes placed by Cope in the family Otoccelidcs and considered as ances-
tral to the turtles. In 1898 Smith-Woodward's "Outlines of Vertebrate
Paleontology" (127) placed the "so-called Pclycosauria'''' near the suborder
Proterosauria in the order Rhynchocephalia.

In the same year Gadow (90) made the Pelycosauria equal to the Theri-
odontia as an order in the subclass Theromorpha.

In 1899 appeared the completed paper by Baur and Case (10), in which
they reaffirm the views presented in the preliminar}^ paper.

In 1901 (91) Gadow's volume on the Reptiles and Amphibians in the
Cambridge Natural History series repeats the views of the first classification.

In 1902 (100) Hay, in his "Catalogue and Bibliography of the Verte-
brata of North America," makes the Pelycosauria an order of equal rank
with the Rhynchocephalia.

14

REVISION OF THE PELYCOSAURIA.

In the same year the translation of Zittel's Grundziige der Paleonto-
logie (136) presented the following classification:

Order Rhynchoccphalia .

Suborders Proterosauria, Pelycosauria , Rhynchocephalia vera.

In the same year von Huene (102) described a form, Ctenosaurus, from
the Triassic, which he places in his list next to the Theriodontia, but gives
only the family Clepsydropidce to indicate its position.

In the same year Osbom & McGregor presented their paper on the
divisions of the Reptilia (112). All the reptiles were divided into sub-
classes, the Diapsida and Synapsida. The Pelycosauria are placed with the
Mesosauria, Proganosauria^ etc., in the order Rhynchocephalia of the Diap-
sida.

In the next year, 1903, appeared Osbom's Memoir on the same subject
(113), in which the classification is elaborated as below with some minor
changes from the original paper.

Subclass Synapsida.

Subclass Diapsida.

Primarily with single or undivided temporal arches.

Primarily with double or divided temporal arches.

I. Cotylosatiria.

I. Diaptosauria (Superorder).

II. Anomodontia (Superorder) .

I. Proterosauria.

I. Theriodo7itia.

2. Pelycosauria.

Cy7iodo7itia.

3. Rhynchosauria.

Gomphodontia.

4. Procolophonia.

2. Dicynodontia.

5. Proganosauria.

3. Placodoiitia.

6. Chorislodera.

III. Testudhiata.

7 . Rhynchocephalia .

IV. Sauropterygia.

II. Phytosauria (including the Belodo7its

I. Nothosauria.

and A'eiosatirs).

2. Plesiosaicria.

III. Ichthyosauria.

IV. Crocodilia.

V. Dinosauria (Superorder).

I. Theropoda.

2. Cetiosauria.

3. Orthopoda.

VI. Squa77iaia (Superorder).

I. Lacertilia.

2. Mosasauria.

3 . Ophidia.

VII. Pterosauria.

Giving rise to the Mammals through some unknown

Giving rise to the Birds through some unknown type

ancestor of Anomodonts.

transitional between Proterosauria and Dino-

sauria.

HISTORICAL REVIEW OF THE PELYCOSAURIA. 15

In 1903 (iS) Broom published his classification of the Theriodonts
and related forms. Somewhat condensed, the scheme is as follows:
Rhynchocephaloid Orders. Theromorous Orders.

Order Procolophonia. Order Pareiasauria.

Family ProcolophonidcB. Family Pareiasaurida .

Genus Procolophonia. ParioHchidcs.

Order Pelycosauria. ■ Diadectida;.

Family Clepsydropidce . Order Therocephalia.

Genus Clepsydrops. Family ScylacosauridcE.

Dimetrodon . Aelurosauridcs .

Naosaurus. IclidosiichidcB.

E^nbolophorus . TitanosuchidcE .

? Gorgon opsida .
Order TJieriodo7iiia.

Familj' Lycosaurida.
GalesauridcE.
Gomphognathida .
Order Atio^nodontia .

Family Endothiodotitidts .
DicynodontidcE.
Lystrosauridce.
Cistecephaiida .

In 1904 (13) Broili, in his work on the Permian Reptiles and Stego-
cephalians from the Texas region, revives the order Theromora (using the
preoccupied name Theromorpha). His classification is as follows:

Order Rhynchocephalia.

Family Paterosaurid<B .
Genus Lysorophns.
Order Therotnorpha.

Suborder Coiylosauria Cope {Pareiasauria Owen).

Families Pareiasaurida; , Oiocalidcs, Diadectidcs, PariotichidcB.
Suborder Pelycosauria Cope {Theriodontia Seeley).
Families Clepsydropida, fBolosatiridce.

It will be obser\'ed that the genus Lysorophus commonly placed among
the Pelycosauria is the only one considered as belonging to the Rhyncho-
cephalia, and is placed in a new family. This family is considered as per-
haps the most primitive of all the reptiles.

Boulenger in 1904 (16) divided the reptiles into two great groups, the
Rcptilia Theromora, derived directly from the Labyrinthodojitia, and the
Reptilia Herpetomorpha, derived from the Microsauria. He places the
Pelycosauria as a side branch of the Rhynchocephalia, of ordinal rank.

SYSTEMATIC REVISION OF THE SUBORDER.

Order RHYNCHOCEPHALIA.
Suborder PELYCOSAURIA Cope.

Proc. Am. Phil. Soc, vol. xvii, 1878, p. 511. Also Pal. Bull. 29.

Original description : The Pelycosauria was first regarded by Cope as belonging
to the order Rhynchocephalia in a description of Clepsydrops natalis. "Of the general
affinities of this genus {Clepsydrops) it is only necessary now to state that my ref-
erence of it to the Rhynchocephalia is confirmed. It differs from the recent species
of the order in the absence of the quadrato-jugal arch and the remarkably developed
ischia. On this account I refer to Clepsydrops and its allies as a distinct suborder
under the name Pelycosauria.''''

For the description of the iscliium see the original description of the
genus Clepsydrops^ p. 37. The first of the characters mentioned in the
original description has been proved to be erroneous, but the second, with
characters of later discovery, shows that the Pelycosauria is unquestion-
ably entitled to subordinal rank or, if Osbora's classification be preferred, to
ordinal rank in the subclass Diaplosauria*

Revised description : Primitive Diapsidan reptiles, mostly adapted to land life,
but with some littoral and swimming forms. Carnivorous and predator}'. Skull low
and flattened to high and thin. Teeth simple with strong crenate cutting edges in
the most specialized forms. Incisors and anterior maxillary teeth becoming enlarged.
Vertebne notochordal. Intercentra present. Ribs two-headed. Neural spines much
elevated in the most specialized forms. Interclavicle T-shaped. Coracoid and pre-
coracoid separate from scapula until late in life. A rudimentary cleithrum present.
Humerus with entepicondylar foramen. Pelvis narrow and high ; the bones closely
united ; the two sides of the pelvis meeting in a deep median symphysis. Tarsus
with five elements in the distal row. Phalangeal forumla probabh- that characteristic
of the Diapsida. Manus 2, 3, 4, 5, 3, and pes 2, 3, 4, 5, 4.

The suborder Pelycosmiria is of special interest, as it illustrates perhaps
better than any other group known the stages in the advancing special-
ization of structure from a comparatively generalized skeleton to an
organization that was possibly the direct cause of extinction. The more
primitive forms of the family Poliosanridcs closely resemble the Protero-
sauria.

•students of this paper are requested by the author to read first the morphological description of
Dimetyodon incisivus, p. 95. This is the best-known form of the suborder and has been described as fully
as possible. In the description of other members of the group comparison has been made as uniformly as
possible with Dimetrodon incisivus, and the scheme of classificatiou will be best understood after a study
of the osteology of this typical form.

17

l8 REVISION OF THE PELYCOSAURIA.

The chief points of developmental evolution were :

(i) The gradual chauge of the form of the skull from a low, elongate type
with a flat top, to a very high thin type with a narrow top.

(2) The increase in the vertical curvature of the jaws with the development

of a toothless (diastemal) notch between the premaxillary and maxillary.

(3) The increase in size of the anterior incisors of both upper and lower jaws

and the increase in size of the anterior maxillary teeth. The appear-
ance of serrations on the cutting edges of the teeth.

(4) Increase in size of the external processes of the pterygoid.

(5) Increase in length of the neural spines until they became very long and

slender and finally developed transverse processes.*

Family POLIOSAURIDAE Fam. Nov.

Primitive Pelycosauria with low, flat, acuminate head, sometimes elongate. The
maxillary with straight tooth line. One or more teeth at the anterior end of the
premaxillary and dentary, and one or more teeth in the maxillary enlarged somewhat
above the others. Maxillary teeth not separated from the premaxillary teeth by a
toothless interval. Vertebral spines low and the neural arch free from the centrum
through life in some [PoHosautus). Abdominal scutes present. L,ong-bodied forms
with long tails ; probably aquatic.

Definitive characters :\

(i) Skull low and acuminate {Proterosaurian).

(2) Tooth line of maxillarj' straight or nearly so. Diastemal notch absent or

poorly developed.

(3) Neural spines short.

(4) Sacrum with two vertebrae.

Genus POLIOSAURUS Gen. Nov.J
Proc. Am. Phil. Soc, vol. xvii, 1878, p. 519. Also Pal. Bull., 29.

Type: Theropleiira uni/ormis Cope, No. 1148 Am. Mus. Nat. Hist., Cope, coll.;
from Texas.

Original description (taken from T. retrcwersd) : " Rhynchocephalian reptiles
with free neural arches, and a capitular costal articulation on the centrum ; the inter-
centrum probably, and the hyposphene certainly, wanting. This genus is similar to
Lysorophus in its free neural arch, but there is no capitular costal articulation on the
known vertebrae of that genus."

*Dr. Matthew has suggested that some readers may assume that this is meant to indicate stages of
phyletic evolution and not structural specialization of distinct genera. The Pelycosauria is as yet too inco-
herent a group for phyletic stages to be assumed; the points indicated are simply prominent stages in the
advance of the group to its overspecialization, indicated by different genera.

tUnder this head in the descriptions of the families, genera, and species, the most prominent charac-
ters will be grouped under numbers that correspond in each family, genus, and species, so that comparisons
can be instituted directly.

tThe type species, Thcropleura j-ciro-t'ersa, was founded on a single vertebra which is indistinguish-
able from vertebrae of the same region in Diopcus leptocephalus, so the latter becomes a synonym. As a
second specimen, Thcropleura iinifortnis, is distinct and well characterized, it must receive a new name,
Poliosaurus (iroXios, hoary, venerable), and become the type of the new family.

SYSTEMATIC REVISION OF THE SUBORDER. 19

For additional description of tlie genus by its author see tlie original
description of the skull of Poliosaurus uniformis^ below.

Revised description of the getms .•*

(r) No diastemal notch between maxillary and premaxillary. The series of
teeth uninterrupted.

(2) No well-defined canine in the maxillary ; several maxillary teeth in the

anterior third of the series larger than the others. Incisor teeth enlarged.

(3) Teeth with faint anterior and posterior cutting edges ; not crenate.

(4) Neural arch of vertebra free from centrum through life.

(5) Only slight diflference in the length of the bottom line of the vertebrae in

different jjarts of the column.

(6) Anterior dorsals without wide face for the intercentmm on the lower edge

of the anterior face of the centrum ; without sharp and deep median
keel. Posterior lumbars not greatly shortened and without a wide
extension of the inferior edges of the faces of the centra (compare
Elcabrosanrus baldicini, p. 28).

(7) Spines short.

(8) Spine of the axis low and broad.

(9) lyimb bones without well-developed articular faces.

(10) Character not shown.

(11) Abdominal scutes present.

(12) Tail probably long.

(13) A small, probably aquatic animal, not exceeding 700 mm. in length.

Cope's original description of the genus was based on comparison with

the genera Dimetrodon and Clepsydrops, but later studies of these forms

have shown that there is so much difference in different portions of the

vertebral column that the characters originall}^ used are valueless. The

first species of the geuus described was T. retroversa^ which turns out to

be the type of Diopeiis ; on the same page as the description of T. retro-

versa is the description of T. iiniformis^ which is now considered the type

of the genus under the new name Poliosaurus. The characters listed

above in the description are those which seem to involve the main lines of

development in all the genera of the Pelycosauria; as in all the genera

more detailed description and discussion will be found in the morphological

revision.

Pollosaurns uniformls Cope.

Proc. Am. Phil. Soc, vol. xvii, 187S, p. 519. Also Pal. Bull. 29.
Proc. Am. Phil. Soc, vol. xix, 1880, p. 40. Also Pal. Bull. 32.

Type: No. 11 48 Am. Mus. Nat. Hist., Cope, coll. The anterior portion of a
skull; thirteen vertebras, the first seven, beginning with the atlas, in connected series ;
limb bones and the fragments of the atlas ; from Texas.

Original description: It is described from "vertebrae of two individuals with
perhaps two others of smaller size. The dorsal centra are characterized by the absence

*The serial numbers are used for the same characters in all the genera irrespective of the families.

20 REVISION OF THE PELYCOSAURIA.

of lateral aud inferior edges, and the narrow reflected portion of the anterior border
for the capitular facet. The diapophyses are short, aud the tubercular faces are not
much extended. The zygapophysial surfaces are but moderately oblique. The sides
of the centrum are gently and uniformly concave, and the inferior middle line is
obtuse aud not prominent. The centra of the smaller specimens alluded to are a little
depressed and may pertain to another part of the column."

Aleasurements.

m, m.

( Antero-posterior 0.021 Expanse of anterior zygapophyses 0.019

Diameters of centrum -I Transverse 022 Width of neural canal 009

(^Vertical 021

In 1880 Cope added to this description an account of the skull :

"This species is about the size of one of the larger VaranidcB^ and about equal
to the Clepsydrops natalis. It is characterized by a long and acuminate head, with a
large lateral nostril on each side, well forwards, and approaching near the border of
the diastema. In the specimen the top of the head is crushed and the postorbital
portion is wanting. Anterior to the large lateral tooth there are nine teeth ; posterior
to it there are eighteen. The anterior cutting edge of the crown does not extend so
near the base as the posterior, and is best marked on the anterior teeth. In the crowns
preserved the edges are not serrate."

Measurements.

m. m.

Length of alveolar edge of mandible 0.120 Length of centrum of axis 0.018

from diastema to canine tooth 030 of centra of following five vertebrae... .071

of centrum of atlas 010 of ilium at acetabulum 040

"The lanciform shape of the skull with its consequent peculiarities distinguishes
this species from Clepsydrops natalis, and Dimetrodon incisivus. The canine tooth is
more posterior, the teeth more numerous, and the alveolar borders less curved than
in either of those species. The diastema is less excavated, and the muzzle less obtuse."

As mentioned in the original description, the species was described
from several sets of isolated vertebrae of different sizes ; of these only the
vertebrae w-ith skull, No. 1148 Am. Mus., are now certainly determinable.
As there is only a single species in the genus its characters are suflSciently
given in the description of the genus above.

Genus VARANOSAURUS Brolll.

Paleontographica, Bd. li, 1904, p. 71.

Type : Varanosaurus aciitirostris Broili.

The description of the genus is embodied in that of the single species

below.

Varanosaurus acutlrostrls Brolll.

Paleontographica, Bd. li, 1904, p. 71.

Type : A nearly perfect skeleton. The girdles and limbs not perfect. Preserved
in the Munich Museum. From Texas.

SYSTEMATIC REVISION OF THE SUBORDER. 21

Original description (translation of Broili's synopsis of the characters of the
species): " Skull elongate, sharply triangular. Orbits large, nearly circular, located
in the posterior half of the skull. Nares lateral, large, in the upper part of the over-
hanging snout. Parietal foramen present. A pair of good-sized lateral openings
posterior to the orbits and separated from them by a slender bridge of bone. Faint
sculpture of fine lines and pits on the middle of the skull roof The portion of the
skull posterior to the parietal foramen falling sharply downwards and backwards.

" The basispheuoid with a pair of lateral keel-like processes. Palatal vacuities
small, closed by the pterygoids, which bear a group of small teeth. Epipterygoid
strong.

" Teeth small, sharply conical with a large pulp cavity ; of nearly equal size
except in the anterior portion of the maxillary, where there are two of larger size in a
swollen region, 54 teeth in all (Pmx-j-Mx).

" Axis with the body concave ; strong spine ; horizontal zygapophyses and
strong diapophyses. Vertebrce deeply amphicoelous, smooth, the sides concave. Lower
side of the centrum with a well-developed keel. Neural arch with good-sized zyga-
pophyses with horizontal articular faces. Neural spines short and thin. Diapophyses
probably present on all presacral vertebrae as outstanding processes. Intercentra
between all vertebrae except the axis and atlas. Chevrons present.

" Ribs single-headed, directed outwards and backwards. Sacral ribs united with
the corresponding diapophyses, short and compressed.

" Scapula united with coracoid.

" Pelvis formed of united ilium, ischium, and pubis. Pubic foramen present.

" Humerus with entepicondylar foramen. Ulna with strong olecranon.

" Femur with well-developed trochanter. Tibia and fibula slender. Astragalus
and calcaneus strong. Metatarsals elongate. Phalanges short. Terminal phalanges
with claws. On the ventral side and the lower side of the limbs dermal ossifications
iu the form of elongate, slender rods."

Broili recognized in large part the relation of Varanosaiirus. He con-
sidered it as belonging to the Clepsydropidcs as opposed to the Cotylosauria.
He separated it from Naosaunis, Diinetrodon, and E^nbolophoriis by the
absence of elongate spines; from LysorJiopJius by numerous characters; from
Theropleura because the neural spines are coossified and short and because
Varanosaurus has single-headed ribs and intercentra ; from Archeobelus by
the indeterminate character of the last.

Broili was in error in assigning to Clepsydrops short spines and so not
separating Varanosa2ir7isirova.\X^ also in assigning to ThcropleuraXong spines.
He recognized the primitive position of Varanosaurus. He says, p. 81 :

"It is evident we have in the new genus Varauosaicrtts aciitirosfris the most
elongate and slender member of the Theromorpha yet known, and which resembles
in this respect certain of the Rhynchocephalia, especiall)- Proterosaitriis.''

Revised description : Ribs with rudimentary capitulum.

(i) No diastemal notch between maxillary and premaxillary.

(2) Two enlarged canines in maxillary. Incisor teeth large.

(3) Character not shown.

(4) Neural arch of vertebrae coossified with centra.

22 REVISION OF THE PELYCOSAURIA.

(5) Only a slight difference in the length of the bottom line of the vertebra

in different parts of column. Anterior dorsals without wide face for
the intercentnim.

(6) Character not shown.

(7) Spines short.

(8) Spine of axis low and broad.

(9) Limb bones without well-developed articular faces.

(10) Character not shown.

(11) Abdominal scutes present.

(12) Tail long.

(13) 600 to 800 mm. long.

It is evident that Varanosaurus closely resembles Poliosaurus; the sole
diflFerences ttat can be detected in a comparison of the specimen of Polio-
saurus with the description of Varanosaurus are the single-headed ribs,
tbe neural arches coossified witli the centra, and the elongate head. The
first of these characters is most interesting ; in the other members of the
Poliosauridcs, which Varanosaurus closely resembles, the ribs are dis-
tinctly dotible-headed throughout the presacral region ; indeed there is not
another member of the Pelycosauria in which the ribs are single-headed.
The elongate head of Varanosaurus is probably a good character distin-
guishing it from Poliosaurus, but the difference was not great; the head
of Poliosaurus was elongate, but probably rather wider and more flattened
than Varanosaurus.

Varanosaurus was almost equall}?^ close to the next genus Theropleiira.
It differs in the single-headed ribs and the less well-developed articular
condyles on the limb bones of the former. It agrees in the coossification
of the neural arches with the centra. The skull of Theropleura is very
fragmentary, but enough remains to show that it was quite elongate ; it
seems, however, to have been rather wider and more flattened than that of
Varanosaurus.

Recent statements made by Broili indicate that the ribs are not truly
single-headed, so the distinction between the three genera is not great ; see
morphological revision, p. 79.

Genus THEROPLEURA Cope.

Clepsydrops Cope. Proc. Am. Phil. Soc, vol. xxii, 1884, p. 30.
Diofeus Co'pe. Trans. Am. Phil. Soc, vol. xvii, 1S92, p. 11.

Type : An imperfect skull ; complete pelvis ; nearly complete vertebral column ;
both femora and tibise. No. 4155 Am. Mus. Nat. Hist., Cope, coll.; from the valley
of the Big Wichita river, Texas.

Original description : " The quadrate bones of both sides are distinctly displa}ed.
They are rather short, and articulate above b}' squamosal suture with the squamosal
bones, which overlap them posteriori}-. They narrow upwards, and are deeply
grooved on the anterior face below. Each edge of the groove is produced forwards ;

SYSTEMATIC REVISION OF THE SUBORDER. 23

the external for a considerable distance as an acuminate laminiform process, in the
usual position of the quadrato-jugal bone. The production of the internal edge is
shorter, and its extremity is vertically truncate. Its superior edge fits an incurvature
of the superior edge of the pterygoid bone, and its internal face is applied to the
external face of the latter.

" The pterygoid bone displays the subtriangular plate with dentigerous edges,
such as I have already described as present in the species of Dimetrodon. In this
species it is thinner and less massive than in any species of that genus yet known.
This specimen enables me to locate it more precisely than heretofore. The ptery-
goids were probably placed much as I have represented them to be, in the Evipedias
molaris Cope (Proc. Am. Phil. Soc, vol. xix, p. 56, plate v). They send inwards a
subtriangular plate from each side, which approach each other on the median line
without touching, and the adjacent edges are somewhat decurved. The posterior
edges are deeply concave on each side of the middle line, and, like the inferior edges,
are deutigerous. The process for the quadrate extends outwards and backwards, and
is thickened on its posterior edge, while its anterior edge which is continued from
the inferior edge of the posterior border, becomes very thin. The anterior production
for the ectopter}-goids e.xtends outwards and forwards, leaving the anterior edge of the
dentigerous plates as the concave posterior border of the large palatine foramina.
The anterior production of the internal edge of the plate becomes very thin, and is
broken in the specimen without showing the articulation for the palatine.

" The squamosal extends both above and below its anteriorly directed zygomatic
portion. The superior extremity shows squamosal suture for the parietal. * * *

" The premaxillary bones are distinct. The teeth of that bone and of the maxil-
lary are of unequal sizes.

" The axis has an expanded neural spine, and a diapophysis for rib articulation,
but no parapophysis or capitular fossa. The two latter features characterize all the
vertebrae which follow as far as the lumbar series.

"The column in the typical specimen is tolerably complete, with a break of
uncertain but probably uot great length in ^front of the sacrum, and the loss of the
distal part of the caudal series. Intercentra of rather small size are present through-
out the series anterior to the sacrum. * * * The bases of the neural spines are
compressed; they were probably not elongate as in Dimetrodon, though they are
unfortunately broken off, except that of the third cervico-dorsal vertebra. Here the
spine is short and truncate above and rather wide antero-posteriorly. As in Dime-
trodon there is no distinction between cervical and dorsal vertebrae.

"The pelvis is well preserved and has the characters already assigned to
C. natalis Cope. The ilium has a process or narrowed continuation with parallel
sides, directed backwards and upwards, and bearing a keel on the middle line on the
internal side. The ischia are much produced posteriorly, and are separated by a
notch on the middle line posteriorly.

" The head of the femur is expanded, including probably the homologue of the
great trochanter of the mammalia, and its articular face is crescentic, with obtuse
horns. There is a trochanter below it on the posterior edge of the shaft. The
condyles are inferior, and are separated by a deep groove above and a shallow one
below. The articular faces of the two condyles are continuous, forming an 00 -shaped
figure. The proximal extremity of the tibia is wider than the distal, and the articular
face is uninterrupted. That of the distal extremity is a transverse oval."

24 REVISION OF THE PELYCOSAURIA.

In 1892 Cope formed the genus Diopeus for the specimen previously
described as C. leptocephahis^ since he had discovered in it the presence of
two temporal arches.

"In Diopeus Cope the supratemporal region is elongate in the vertical direction,
and as elsewhere it overlaps the qnadrate at the distal extremity. Anteriorly it sends
forward a process probably for union with the postorbital bone, which is, however,
entirely free from the parietal and incloses a foramen with it, precisely as in Sphen-
odon. It further resembles the corresponding element in Sp/ienodoti in sending
upwards a branch for union with the parietal. There are in this genus two posterior
bars and two foramina, thus differing widely from the other Permian genera of this
or any other country- kuown to me. Whether it has a free parieto-quadrate arch I do
not know, but it is probable that the genus should be referred to the Rhynchocephalia
in the neighborhood of Palaeohatteria Credner. It differs from Sphenodon and
resembles closely the Theriodontia in the absence of an obturator foramen, and in the
character of its dentition. The zygomatic arch is not excavated below, but has a
straight outline to its junction with the jugal. The quadrate condyle is double like
that oi Sphenodon and the Clepsydropidce.''''

Revised description 0/ the genus :

(i) No well-defined diastemal space; the faint notch between niaxillar>' and
premaxillary filled with teeth.

(2) A single well-defined maxillary canine ; incisor teeth enlarged.

(3) Section of teeth at base quadrate.

(4) Neural arch coossified with centrum in adult.

(5) No great change in length of vertebrse in different parts of the column.

"As deep as long in all parts of column if measured at center." Poste-
rior lumbars not greatly shortened ; without wide intercentral face.

(6) Anterior dorsals without wide face on lower part of anterior face of cen-

trum for the intercentrum ; without median keel.

(7) Character not shown.

(8) Spine of axis not elevated and broad at top.

(9) Limb bones without well-developed articular faces.

(10) Character not shown.

(11) Abdominal ribs or scales absent ? (not observed).

(12) Tail long.

(13) Elongate, slender body, probably from 2 to 2.5 meters in length.

The specimen was originally described as belonging to the genus
Clepsy drops ; Cope, believing at the time that Clepsydrops had but a single
temporal arch and fenestra, compared it directly with the Theriodonts of
Africa ; when he determined that it had a double arch he removed it to a
new genus, Diopeus. The discovei^y that the Clepsydropidcp are all diap-
sidan removed the main distinction of Cope's classification, but other char-
acters, as listed above, justify the distinction of the genus.

SYSTEMATIC REVISION OF THE SUBORDER. 25

Theropleura retrovcrsa Cope.

Proc. Am. Phil. Soc, vol. xvii, 1878, p. 519. Also Pal. Bull. 29.

Type: Several isolated vertebrce. No. mi Am. Mus. Nat. Hist., Cope, coll.;
from Texas.

Original description : "Size medium, or rather larger than that of Clepsydrops
natalis. A number of small vertebrae may belong to a young individual, but I regard
as type a dorsal vertebra of an adult, where the suture of the neural arch is visible,
but adherent. The species is characterized by the wide posterior expansion of the
border of the articular face of the centrum, forming the capitular facet for the rib. It
approaches near to the diapopliysis, and descends to the basal fourth of the centrum.
There is an angular ridge passing backwards from the inferior border of the diapoph-
ysis to the border of the articular face. Below this angle and behind the capitular
costal face the centrum is deeply concave, the concavities of the opposite sides being
separated below on the median line by a narrow obtuse keel. The centrum is as
deep and long as wide.

Measurements.

m.

{Antero-posterior 0.025
Vertical 025
Transverse 025

"The small specimens agree with the large one in the strong longitudinal angle
connecting the diapophysis with the posterior border of the centrum, and in the wide
capitular articular surface."

The vertebrae described by Cope as belonging to this species are iden-
tified in form with tlie anterior caudals of the form later described by him
as Diopens leptocephahis, whicli shows the latter name to be a synonym.
For the revised description of the vertebrae, see p. 84. No. 1 754 Am. Mus.
Nat. Hist., Cope, coll., is a second specimen of this species.
Theropleura retroversa Cope.

Theropleura Iriang-ulala Cope. Proc. Am. Phil. Soc, vol. xvii, 1878, p. 520. Also Pal. Bull. 29.

Type: A single vertebra, in a lot of five or six. No. 1107 Am. Mus. Nat. Hist,
Cope, coll.; from Texas.

Original description of the synojiyni : "The superior part (of the vertebrae)
resembles that of the T. nniformis in lacking the angle posterior to the diapophysis
seen in the T. retroversa., and in the small extent of the capitular rib-facet. The
inferior part of the centrum diflfers in the presence of three longitudinal rib-like angles,
separated by two latero-inferior shallowly concave faces. The median rib is not very
prominent, is obtuse, and concave in profile. The articular faces are relatively rather
wider than in the vertebra; described as typical of the two species preceding (7". nni-
formis and T. retroversa) ; but in one vertebra the proportions are nearly the same.

"In the second vertebra mentioned the neural arch is entirely preser\-ed. The
diapophysis is at its base, and of small size ; the vertebra is from not behind the
median dorsal region. The neural spine is compressed and elevated, and with narrow,
truncate apex. The articular faces of the zygapophyses are nearly horizontal."

26 REVISION OF THE PELYCOSAURIA.

Measurements. „

m.

{Antero-posterior o.oiS
Transverse 017
Vertical 016

( Antero-posterior .023

Diameters of centrum No. 2 ■< Transverse 024

( Vertical 026

Expanse of anterior zygapophyses 020

Elevation of neural spine above zygapophyses 052

Fore and aft 016

Transverse 007

Diameter of same at summit \

This vertebra is a posterior lumbar of Theropleura retroversa. Thero-
pletira triangulata is therefore a synonym of Theropleura retroversa. For
the revised description of the vertebrae, see p. 84.
Theropleura retroversa Cope.

Clefsydrofs lej>tocephalus Cope. Proc. Am. Phil. Soc, vol. xxii, 1884, p. 30. Also Pal. Bull. 39.
Diofezis le^ptocefhalus Cope. Trans. Am. Phil. Soc, vol. xvii, 1892, p. 11.

Type : The imperfect skull ; the nearly complete vertebral column ; the complete
pelvis; both femora and tibia. No. 4155 Am. Mus. Nat. Hist., Cope, coll.; from Big
Wichita river, Texas.

Original description of the synonym : " While the vertebral centra of this species
are rather short, the bones of the head are very much attenuated, and the jaws are
long and slender. None of the four jaws is perfectly preserved, but the number of
the teeth in the maxillary bone may be approximately fixed at thirty in a continuous
series. One, and probably two of these, placed near the anterior part of the series,
are larger than the others. They are placed at the position of the corresponding large
maxillary teeth in Dimetrodon, but they do not display the dimensions seen in the
species of that genus. To strengthen the jaw at this point, a rib rises from the thick-
ened alveolar portion, and extends vertically on the inner side of the thin facial plate
of the bone. The facial plate is double, and each lamina, except at the rib, is not
thicker than wrapping paper.

"The premaxillary bones are robust, and are excavated postero-laterally for a
very large nostril on each side. The spine is long. The alveolar edge bears five
teeth, which are followed by a diastema. These diminish in size posteriorly, the first
one being the largest, and equaling the large maxillaiy teeth. The last two are quite
small, less than the usual maxillary teeth.

"The dentary bones are very slender, and the distal end is somewhat thickened
to support two teeth larger than the others. These are the third and fourth from the
extremity, and are not quite so large as the large teeth of the maxillary bone. The
remaining mandibular teeth are small, and are not so much compressed as in the spe-
cies of Dinietrodon. Many of them have only a posterior cutting edge, which is not
denticulate. The apices are strongly turned backward in the posterior part of the
series. The posterior part of the dentary bone rises and carries some of the teeth with it.

" The surface of the free edge of the internal plate of the pterygoid bone is
granular. The teeth on the posterior edge of the same are subconic, and in a
single series.

SYSTEMATIC REVISION OF THE SUBORDER.

27

"There are twenty-seven vertebrae in a continuous series from and including
the axis. All bear diapophyses, and all are rib bearing, except perhaps the last two,
where they are of reduced size. They are more or less opposite the neural canal as
far as the twenty-second centrum. On this vertebra the superior edge is on a level
with the floor of the canal, and posterior to this point the diapophyses rise from the
centrum. Two sacrals and ten caudals are preserved, and all have diapophyses and
neural spines. The centra in this species are rather short, being as deep as long
throughout the series, if measured at the middle. The edges are not undulate, as in
C. {Emholophorous) limbatus Cope. The intercentra are short and not extended
upwards on the sides as in that species."

Measurements.

Length of the quadrate bone 0.085

Width of condyle of quadrate bone (greatest)... .037
Length from condyle of internal anterior pro-
cess of do 032

Length from condyle of external anterior pro-
cess of do 097

Length of squamosal bone (vertical) 124

pterygoid from palatal foramen 116

Width of pterygoid at middle 090

Length of internal dentigerous edge of do 070

posterior dentigerous edge of do 051

maxillary bone posterior to canine

brace t8i

Thickness of maxillary bone at canine brace... .020

Depth of maxillary bone at nostril 016

Length of premaxillary bone (posterior apex

restored) 060

Width of premaxillary bone at third tooth 022

Diameter of large (first) premaxillary tooth 008

large maxillary tooth (canine) 009

small maxillary tooth 006

Length of crown of last maxillary tooth 009

twenty-seven continuous cervico-

dorsal vertebrae .855

two sacrals 065

ten caudals 260

Diameters centrum of axis:

Antero-posterior 034

Vertical posteriorly 031

Transverse posteriorly 030

Elevation of neural spine from centrum .071

neural arch from centrum 009

Width of postzygapophyses 030

Elevation of neural spine of fourth vertebra .05S

Diameters centrum sixteenth vertebra:

Antero-posterior 025

Vertical at end 035

Diameters end seventeenth centrum:

Vertical 034

Transverse 030

Expanse of postzygapophyses of seventeenth

vertebra 029

Diameters twentieth centrum:

Vertical at end 031

Antero-posterior 027

Diameters of twenty-ninth centrum:

Antero-posterior o

Transverse behind

Expanse of postzygapophyses of twenty-ninth

vertebra

Width of sacrum through fixed diapophyses

Diameters centrum twentieth caudal:

Antero-posterior

Vertical behind

Transverse behind

Expanse through diapophyses

Elevation of prezygapophyses (greatest)

Diameters of pelvis;

Antero-posterior (apex of pubis restored)--

Vertical through acetabulum

Antero-posterior diameter of ilium at acetabu-
lum

Depth of ischium at posterior edge of acetabu-
lum

Length of ischium from acetabulum

femur

Proximal diameter of femur:

.•Antero-posterior

Transverse (at middle)

Diameters shaft at middle:

Transverse

Antero-posterior

Diameters of distal end:

Transverse

Antero-posterior:

External condyle

Internal condyle

Length of tibia

Diameters of tibia:
Proximal:

Antero-posterior (middle)

Transverse

Median:

Antero-posterior

Distal:

Antero-posterior

Transverse

024
035

024
049

025

0265

0225

047

039

235
123

080
117
179

075
025

038
031

031
045
150

040
057

026
041

28 REVISION OF THE PELYCOSAURIA.

Tteropleura grandls sp. noT.

Type : Twenty-two or twenty-three disconnected vertebrae representing all parts
of the column. With the vertebrae are many fragments, among them an imperfect
ilium which probably belongs with them, as it is covered by the same kind of matrix.
Nos. 4130 and 4134 Am. Mus. Nat. Hist., Cope, coll.; from Texas.

Description : In general the form is the same as Theroplenra retroversa, but is
distinguished by its size, being nearly twice as large, and by the proportions of the
posterior vertebrae ; these are shorter when compared with the height and breadth
than vertebrae from the same region of the type species. The articular faces of the
centra are separated from the sides of the centra by a distinct ridge.

Genus ELCABROSAURUS noT.
Elcabrosaurus taldwinl sp. nov.

Type: A series of disconnected vertebrae. No. 2285 Am. Mus. Nat. Hist., Cope,
coll.; from El Cabre, New Mexico.

Description : This form is represented by a few imperfect ^•ertebrae only, but the
characters of the posterior lumbars are totally different from those of any other
members of the Poliosaiiridcr. The comparative table below best brings out the gen-
eric differences.

(i) Character not shown.

(2) Character not shown.

(3) Character not shown.

(4) Neural arch coossified with centrum.

(5) Posterior lumbars very much shortened and with wide facets on lower

half of articular faces of centrum.

(6) No wide iutercentral face on anterior face of centrum.

(7) Character not shown.

(8) Spine of axis elevated and strong (top broken off).

(9) Character not shown.

(10) Character not shown.

(11) Character not shown.

(12) Character not shown.

(13) Small, not exceeding i meter.

This species has been given the name of Mr. Baldwin, the collector of
most of the material from New Mexico in the Cope collection.

INCERTAE SEDIS.

Archaeobelus velUcatus Cope (plate 4).

"Species No. 4, " Cope. Proc. Am. Phil. Soc, vol. xvii, 1877, p. 56.

ArchcEobeliis vellkatiis Cope. Proc. Am. Phil. Soc, vol. xvii, p. 192. Also Pal. Bull. 26.

Type : A fragment of the right maxillary with the imperfect teeth in place.
Nos. 6524 and 6525 University of Chicago, Gurley, coll.; from Vermilion county, 111.

Original description 0/ genus : "The form (of the teeth) is conical, and the
surface is not grooved nor furnished with prominent ridges. The interior is hollow,
and the walls are composed of a few concentric layers without external enamel or

SYSTEMATIC REVISION OP THE SUBORDER. 29

cementiini. The solid base to which it is attached is shallow, presenting a smooth
surface on the opposite side, which is deeply impressed by a longitudinal groove at
one end."

Original description of species: "The crown is conic, subround in section, and
curved backward. There are no cutting edges, and the base is a little flattened in
front and behind. On each of the faces thus formed, there is an open, shallow groove,
sometimes obsolete. There are no other grooves or sculpture on the teeth. * * *
One of the specimens displays an extensive pulp cavity."

Measurements,

First specimen. Second specimen.

Diameter of base 0.004 i'^' 'ong 0.008 m. short 0.005 m.

Length of crown .010 m. .015 m.

There is so little of this specimen preserved that its exact determina-
tion is impossible. It belongs in the family Poliosaurida; because of the
straight tootli line of the maxillary, the lack of a diastemal notch and tlie
comparatively small size of the enlarged maxillary teeth. It is very
possible indeed that it belongs to the genus Poliosaurus. A small vertebra
in the collection No. 6578 University of Chicago, Gurley, coll., resembles
the vertebrae of Theroplciira except in its smaller size (fig. 4, plate 6). It
perhaps belongs with the jaw.

Pleurlstion brachycoelous Case (plate i. figs. 14 and 15).

Second Ann. Rpt. Dept. Geol. and Nat. Hist. Terr. Oklahoma, 1902-3, p. 67.

Type : Several isolated vertebrae mingled with vertebrae of Lysoroplnts tricari-
natus Cope. From near Orlando, Oklahoma Territory ; preserved in the Museum
of the University of Oklahoma.

Original description : The vertebrae "are chiefly characterized by the union of
the parapophyses and diapophyses in a broad wing-like transverse process, and by the
peculiarly broad and large neural canal. The centra are proportionately very broad
and the bottom line is devoid of sculpture and with no trace of a keel. The vertebrae
are deeply amphicoelous. The neural spine is low and the z}'gapophyses are relatively
large and with flat faces. In some the neural arch seems to be coossified with the
centrum and in others it is separated. The transverse process is broader above and
becomes narrower below, where it curves forward to touch the anterior edge of the
centrum. There is no evidence of the presence of an intercentrum."

Meastirements.

m.

Breadth across transverse processes 0.0095

Height from base of centrum to top of neural spine on

The position of this genus is uncertain ; it may prove to belong to
the same form as Bolosaurus^ which is as yet known only by the skull, but
its affinities seem rather with the Pelycosauria than with the Cotylosauria
(plate I, figs. 14 and 15). Specimens of this form occur in several large
lots of small bones and fragments from Texas in the American Museum
collections.

30 REVISION OF THE PELYCOSAURIA.

FOREIGN FORMS.
CalHbrachion gaudryl Boulc aod Gleng'eaud.

Bull, de la Soci^t^ d'Hist. Nat. d'Autun, t. xvi, 1893, p. i.

Type : A nearly complete skeleton. From the Permian beds of Autun, France.
Original description (Translated and condensed) :

The pterygoid has an external process which abuts against the lower jaw.

The lower edge of the maxillary is convex.

The incisor teeth are large. The anterior maxillary teeth are small and grow
larger in the anterior third of the maxillary, then smaller again to the pos-
terior end. The teeth are conical, sharp, and placed in the alveoli.

The lower jaws have a high coronoid process.

The vertebrse are platycoelous or slightly proccelous.

The cervicals are apparently strongly opisthocoelous.

The sides of the vertebral centra are concave.

No intercentrum is seen.

The notochordal canal is persistent.

The neural arch is free.

The diapophysis is not developed (in the lumbars) and the spines are low with
expanded distal ends.

The cervicals are elongate.

The number of cervicals and dorsals is not given. The sacrals are not seen.

There are about twenty presacrals.

The thoracic and lumbar vertebrae are remarkably long and sleuder.

The ribs are single-headed and attached directly to the centrum.

There are uo abdominal ribs or other armature. There are traces of structures
that may possibly be scales.

The coracoid and scapula seem to be loosely attached (the procoracoid is not
mentioned).

The clavicle is slender and enlarged at the distal end.

The interclavicle has an enlarged head and long posterior process.

The humerus has greatly expanded ends and a strong deltoid crest. The shaft
is slender in the middle. The distal end is at right angles to the proximal.

An epicondylar foramen is present.

The ilium alone is preserved, the surface finely sculptured. There is a single
impression for the attachment of the sacral ribs. The ilium is broader than
long, the acetabular cavity wide, but shallow. Both pubis and ischium are
lost, but they were probably loosely attached to each other.

The posterior limb has the same size as the anterior.

Meastirements.

Total length of specimen as it lies, about 462

Humerus 70

Length, lower jaw 70

Length, fourth digit of front foot 86

The tail is absent.

This specimen is placed by the authors in the Proganosauria {Prote-
rosauria). It differs from the Pelycosaiiria in three points, the elongate
cervicals, the opistliocoelous condition of the cervicals, and the single-headed

SYSTEMATIC REVISION OF THE SUBORDER. 3I

ribs. In other characters it is typically Pelycosauriau. The elongate
cervicals indicate relations with the Proterosanria^ but the structure is too
far advanced for that group. The bones of the girdles are well formed
and the limb bones have well-developed articular extremities. The single-
headed condition of the ribs may result from a rudimentary capitulum as
in Anonwsaurus.

Genus ANOMOSAURUS v. Huene.
Geol. u. Paleont. Abhdlg. Koken. N. F., vol. vi, 1902, Hft. i, p. 33.

Type : Several isolated vertebrae found with bones of Nothosaurus. From the
Lower Muschelkalk near Gogoliu and Naklo in Upper Silesia and from Snlzbad in
Upper Alsace ; from the Scliaumkalk (middle Muschelkalk) at Freiburg in Saxony ;
from the Upper Muschelkalk at Beyreuth, in Wiirtemberg and at Miihlhausen in
Thiiringia. Preserved in the Museum of the University' of Halle.

Original description : " Die Wirbel aus dem unteren IMuschelkalk von Gogolin
{Dadocrimiiss — Niveau, 3 m iiber dem Roth) sind den besser erhaltenen aus dem
sachischen Schaumkalk so ahnlich, dass ich nur letzterenaher schildere, aber auf
einige kleinere Unterscheide aufmerksam machen werde.

" Der Wirbelkorper ist etwas liinger oder auch gleich lang wie hoch. Die Gelenk-
facetten convergiren etwas nach unten und sind so tief amphicol, das die Hohlkegel
sich beiuahe beriihren. Der tiefste Punkt der letzteren liegt bedeutend unterhalb der
mediauen Liingsaxe. Bei den meisten Wirbelen ist der Riickenmarks canal sehr
hoch, aber schmal, bald oben und bald unten etwas weiter. Daher hat bei manchen
Wirbeln der obere Bogen unter der Diapophyse eiuer grossern Durchmesser als das
Centrum. Fiir den oberen Bogen characteristisch sind die langen, am Distalende ver-
dickten Querfortsatze. Der Dornfortsatz ist bei den meisten Wirbeln hoch und
schmal, seine Basis ist ein wenig nach hinten geriickt, bei einigen ist er jedoch kurz
und ziemlich dick; es handelt sich wohl um verscheidene Arten, zum Theil auch uur
verschiedene Abschnitte der Riickenwirbelsaule. Die Pra- und Postzygapophysen
sind massig schief bis ilach gestellt und sind kraftig ausgebildet. Bei einigen besitzen
die Prazygapophysen deutliche Langsrilleu und eine laterale Aufbiegung des seitlichen
Randes zur sicheren Fiihning des Charniers. In der Mitte hinter den Prazygapo-
physen befindet sich vor der Basis des Domfortsatzes eine dreieckige Grube. Unter
den Postzygapopli)-sen ist stets ein sehr starkes Hyposphen vorhanden, welches tief
herabreicht und nach unten sehr breit wird. Von hinten gesehen, ist es ein fast
gleichseitiges Dreieck mit der Spitze nach oben. Die Wirbel von Freyburg und
Querfurt aus dem Schaumkalk wechseln in einer gesammtehohe von 6-12 cm, die
grossern sind haufiger. Die Stiicke aus Gogolin sind nur 6-8 cm hoch. Bei beiden
sind die Querfortsatze hohl, wie man gelegentlich an Bruchflachen sieht. Der Quer-
fortsatz ist von imten her andeutungsweise doppelt verstrebt, am deutlichsten bei den
Stiicken aus Gogolin.

"Aus dem oberen ^Muschelkalk liegen mir 4 bedeutend grossere Wirbel vor. Die
ziemlich dicken Wirbelkorper sind etwas langer als hoch. Der Rand der Gelenkflachen
ist ziemlich stark nach den vSeiten umgeschlagen. Die Gelenkflachen selbst sind
tief amphicol, beide Hohlkegel beriihren sich in der Mitte und communiciren ver-
muthlich durch ein kleines Loch. Ueber dem Centrum baut sich der obere Bogen
sehr hoch auf. Die Grenze zwischen beiden ist als deutliche Naht erkennbar. Die
hintere Oeffuung des Neuralcanales ist bei einer Wirbellange von 3, 2 bis 3, 4 cm

32

REVISION OF THE PELYCOSAURIA.

etwa 2, 5 cm hoch und i, 5 cm breit. Der Wirbelkorper von Neckarvaihingen hat
hinten eine Breite von 3, 5 cm ; die Oberflache des Querfortsatzes ist aber von unten
an erst mit 7, 8 cm erreicht, und der Dornfortsatz misst weitere 6 cm, die gesammt
hohe betragt also 13, 5 cm. Bei einem der Wirbel von Bayreuth betriigt die I^ange
des Querfortsatzes 6, 5 cm. Der Querfortsatz ist oben flach, beginnt sehr dick und
breit mit einer nur angedeuteten zwei- oder dreifacben Verstrebung von unten (diese

Fig. I . — Sketch of a slab showing ventral surface of vertebrae of Anomosaurus.
After V. Huene.

Fig. 2. — A vertebra of Anomosaurus sp. from the Schaumkalk, middle (lower)
Muschelkalk, near Freiburg. X ^3. After v. Huene.

Fig. 3. — A vertebra of Anomosaurus from same locality as figure 2. X '3.
After V. Huene.

Figs. 4-13. — Various verlebree of Anomosaurus strunzi. From upper Muschelkalk, Bayreuth. 4-6 dorsals, 7-9 post-
dorsals or lumbars, 10-13 caudals. X /i- After v. Huene.

SYSTEMATIC REVISION OF THE SUBORDER. 33

ist bei 4 Wirbeln etwas verschieden), wird dann wieder diinner mit annahrend diei-
eckigem Quersclinitt, ain Distalende aber keulenformig dick. Der Processus spinosus,
der nur bei einem Wirbel vou Bayreuth und deiu von Neckarvaihingen erhalten ist,
ragt senkrecht uach oben, der eine ist am Distalende etwas verdickt. Beide lassen
auf der Riickseite des Dornfortsatzes eine schmale vorspringende Langsleiste erkennen,
wie sie sich bei Nothosaurus und Pareiasaurus findet. An der Wurzel des Dornfortsat-
zes und zwischen den Postzygapophysen liegt eine tiefe Hohlung mit ganz flachen
Boden. Die hinteren Zygapophysen stehen bei den verschiedenen Wirbeln in ver-
scliiedenem, doch nicht hohem Grade seitlich ab, wie es Hirer Lage im Skelet ent-
spricht, alle Steigen mehr oder weniger nach aussen an. In der Mitte unter ihnen
befindet sich ein aussergewohnlich kraftig ausgebildetes Hyposphen. Dieses springt
ebenso weit nach hinten vor wie die Postzygapophysen und hat deutlich nach oben
convergirende Gelenkflachen, wie es bei Zanclodon und verwandten Dinosauriern der
Trias bei den hinteren Riickenwirbeln der Fall ist. Die Prazygapophysen sind nicht
erhalten, aber aus der form der Postzygapophysen ist es unschwer, auf ihre Gestalt zu
schliessen."

The genus was referred to the Anomodontia in the original article.
Anomosaurus strunzl r. Huene.

Neuen Jahrb. fiir Min., Geol., u. Pal. Beilage Bd. xx, 1905, p. 321.

Type : Fragments of nine vertebrae in a block of stone and sixteen other verte-
brae which have been freed from the block. From the upper Muschelkalk at Laineck
near Ba)Teuth. Preserved in the private collection of Herr Chr. Stmnz, Bayreuth.

Original description: In the conclusion of his description of these vertebrae
V. Huene says : "Alle Wirbelkorper sind tief Amphic51 ; die lange der einzelnen
Wirbelkorper uimmt von vom nach hinten ab, steigt nur bei den Sacralwirbeln
nochmals um ein Weniges. An der Grenze von Riicken und Hals (die vordersten
erhaltene Wirbel) besteht unter dem Ouerfortsatz eine starke horizontale \'oragung ;
die Wirbelkorper sind hier und namentlich in der vordersten Brustregion mit einer
seitlichen Langskante versehen, welche an der hinteren Gelenkflache in ein kleines
Kuotchen iibergeht ; letzteres ist audi bei etwas weiter hinten gelgenem Wirbel noch
vorhanden, wo die .Seitenkante sclion fehlt ; diese Vorragung wird mit der Articu-
lation des Capitulum der Rippe zu thun haben (Parapophyse) in der Weise, dass das
Knotchen mit der Rippe des nachst folgenden hinteren Wirbels articulirt, d. h. das
Captulum wird auf der Grenze beider Wirbel sitzen und vielleicht liegt es nur am
Erhaltung zustand, dass am Vorderrand kein ahnliches Knotchen zu sehen ist. Der
obere Bogen ist sehr hoch gebaut und wird erst kurz vor dem sacrum niedriger. Die
Querfotsatze sind lang und werden in der hinteren Riickenregion abwarts gerichtet
und kiirzer, werden schliesslich diclit vor dem Sacrum kurz, dicke Stummel, die
auch namentlich an den Sacralwirbeln selbst sehr stark sind und mit Beginn des
Schwanzes ihren Ansatz hoher verlegen und kleiner werden. Ein starkes H}'posphen
ist vorhanden (nur an einem Wirbel dieses Individuums beobachtet). Die Facetten
der Zygapophysen stehen in der hinteren Ruckenregion, wo die Querfortsatze kurz
werden, scliief."

Revised description : Under this heading are grouped certain characters of the
vertebrae which are comparable to those of the American Pelycosaurs. The bottom
line of the lumbars is broadly rounded and slightly concave ; these are the vertebrae
that V. Huene regarded as cervicals or anterior dorsals. The upper half of the side

34 REVISION OF THE PELYCOSAURIA.

of the centrum is excavated by a deep longitudinal pit, which is strong on the anterior
of three vertebrse, but is absent on the third. The centrum is about as high as long.
The transverse processes rise from high up on the side of the neural arch and are
directed obliquely downwards ; their length is from 45 to 50 mm. These are the
vertebrse in block 1 1 1 of v. Huene's figure. Among the isolated vertebrae two show
longitudinal ridges on the side of the centrum Cv. H. (103) plate v, figs. 7-8) and
above the ridges the sides of the centrum are concave. The neurocentral suture is still
traceable. Another free vertebra (v. H., plate v, fig. 9) has a slight thickening of the
edge of the posterior face of the centrum. Still another (fig. 10) with a complete
neural spine has an even stronger thickening of this edge. The spine is strong but
thin transversely. The posterior zygapophyses are widely divergent and between
them there is a strong hyposphene. A sacral vertebra has very short and strong
transverse process with a rough articular face for the attachment of the ribs. Four
vertebrse (v. H., plate v, figs. 13-16) regarded by v. Huene as sacrals seem to be
anterior caudals. The ends of the ribs are broadly roimded into stumpy processes,
and the lower face is marked on either side of the median line by two deep pits, as in
the Pelycosaicria.

Measurements.

mm. mm.

Length of each of the three lumbars 35 Height of same from bottom of centrum to top

Length of vertebrae with ridges on side of cen- of spine no

trum 32 Height of spine of another above prezygapophy-

Diaraeter of anterior face of same : ses 60

Vertical 33 Length of the bottom line of a sacral 20

Horizontal 30 Diameter of anterior face of centrum of same :

Length of vertebra with complete neural spine.- 28 Vertical 30

Diameter of posterior face of same : Horizontal 30

Vertical 25 Length of each of three caudals 25

Horizontal 32

It is pretty certain that Anomosatirus is no true Pelycosaur, because
the vertebra are not notocliordal (with the exception of one specimen
mentioned by v. Huene) and because the PelycosauiHa do not have a hypo-
sphene. Occurring in the whole thickness of the Muschelkalk it is much
later than the Poltosanridcs, the only family with which it can be connected.
Many characters, as the elongate pit on the side of the centrum, and the
thickening of the posterior edge of the centrum marking the position of the
insertion of the head of the rib, and the nearly equal length of the vertebrse
throughout the column, indicate resemblances to the genus Naosatirus, but
there can be no true relationship. It is most probable that it is a persist-
ent form derived from the early Pelycosaurian stem and having much the
same history as Ctenosmirtis kozneni.

Stereorachls domlnans Gaudry.

Compt. Rendu Ac. Sc. Paris, t. 91, 1S80, p. 669.
Ann. and Mag. Nat. Hist. (5), vol. vii, 1S81, p. 69.

Type: An incomplete skeleton showing fragments of the skull, vertebral
column, shoulder girdle, and humerus; from near Igornay, France. Preserv-ed in
the Museum of the Jardin des Plantes, Paris.

SYSTEMATIC REVISION OF THE SUBORDER. 35

Original description (taken from the Ann. and Mag. Nat. Hist.): "M. Roche,
director of the Iron Works at Igornay, to whom we are already indebted for several
discoveries of curious fossils, has just found, in the Permian, a new genus of reptile,
which he has presented to the Museum of Paris. The Igornay animal is the most
perfect of those which have hitherto been met with in the Primary formations of
France. I propose to name it Stereorachis dominans.

" In Stereorachis the vertebrse present a striking contrast to those of the reptiles
of the same deposits. While in Actinodon and Enchyrosaiirus the centra are composed
of a median part, or hypocentrum, and two pleurocentra not soldered together, in
Stereorachis the centra are in a single piece, which adheres to the neural arch ; the
vertebral column has therefore acquired more solidity, which has led me to invent the
name Stereorachis. It must, however, be noted that the centra of the vertebrae were
still extremely hollow; their anterior and posterior faces were so concave that they
formed two cones united end to end ; I would not even assert that there was not a
perforation establishing the continuity of the notochord. This is a condition analo-
gous to that of many fishes.

"The new genus found by M. Roche presented another mark of superiority- over
the reptiles that lived with it. Its humerus had a neuro-arterial canal in the distal part.
I had already called attention, in Euchyrosaurns, to the rudiments of the arch, indicating
a tendency to the formation of this canal ; in Stereorachis the fonnation is completed.
When we find that, besides the neuro-arterial canal, the humerus had the epitrochlea
and its epicon widened as in those animals in which the supinator and pronator muscles,
the extensor and flexor muscles, are greatly developed, we are led to think that the old
quadruped of Igornay had arms more perfectionated than those of existing species.

" Stereorachis must have been a carnivorous animal of considerable size ; one of
its mandibles, although a little broken, measures 18 cm. The upper and lower jaws
are armed with conical teeth deeply immersed in the sockets ; their section is nearly
circular ; they are smooth externally, with a radiate structure in the interior ; the
front ones are stronger than the rest ; an inferior tooth has a crown 32 mm. high ; a
superior tooth, the point of which is unfortunately broken, must have been at least
40 mm. There is an entosternum which recalls that of the Labyrinthodonts ; it is
very broad in its anterior third and narrowed behind ; its length is 15 cm. Beside it
there is a large nearly quadrilateral bony plate, 14 cm. long and 5 cm. broad ; I
suppose this to be the homologue of the coracoid and scapula. There is also a cur\'ed
bone which I believe to be the homologue of the great bone in fishes regarded by
Mr. Kitchen Parker as a clavicle (epistemum of the Ganocephalus reptiles). I must
also notice long and arched ribs, formed by two pieces united end to end ; and hard,
brilliant, very fine, long, aciculate scales, as in Archegosaurus and Actinodon.

"In some respects Stereorachis shows afifinities with the Ganocephala and
Labyrinthodonts. In other respects it shows tendencies towards certain genera of the
Permian of Russia and the Trias of South Africa, upon which Professor Richard
Owen has made admirable investigations, and for which he has proposed the name
Theriodonts. Perhaps it still more nearly approaches some North American animals,
such as Enipedocles, Clepsydrops, and Dimetrodon^ ranged by Professor Cope in his group
Pelycosauria ; but at present I know no genus with which it could be identified."

A more complete description of this form appeared in 1883 (93) witli
figures. It was placed among the Stegocephali in Zittel's Handbuch, but
later was referred by Lydekker to the family Clepsydropidcs in the order

36 REVISION OF THE PELYCOSAURIA.

Thcriodontia. In the translation of Zittel's Grundziige it was referred to
the famil}^ Clcpsydropido' in the Pelycosauria ; it is now evident that it must
be transfen-ed to the family Poliosaurida; of the Pelycosauria.

The spines are short, there are abdominal ossicles, and the limb bones
have well-developed articular surfaces. From the size and appearance of
such bones as are preserved it is apparent that it belongs close to the genus
Theropleura.

Family CLEPSYDROPIDAE Cope.

Proc. Am. Phil. Soc, vol. xviii, 1878, p. 529. Also Pal. Bull. 29.

Original description: "The division Pelycosauria is established primarily on the
genera Clepsydrops and Dimetrodon, but their cranial structure renders it highly
probable that Ectocynodon, Pariotichus, and Bolosaurus belong to it. It is also prob-
able that the genera Empedocles^ Embolophorus^ and others detennined from vertebrae
belong to it, as the latter are frequently accompanied by pelvic bones of the t>'pe of
that of Dimetrodon. All the genera known from teeth and crania are of carnivorous
habit, excepting Bolosaurus and Diadectes ; they may be referred to a single family
on this account, which I call the Clepsydropidcr. Bolosaurus will form the type of
another famih- characterized by the transverse position of the crowns of the teeth,
imder the name of the Bolosauridce.^''

It is seen from this that the family was founded simply on the carniv-
orous character, but as it comprised forms now known to belong to other
families and orders, and as the carnivorous character is ordinal in value, it
becomes necessary to define the order from entirely different characters.

Redescription of family :

(i) Skull laterally compressed and facial region elevated.

(2) Tooth line of skull convex.

(3) Neural spines ver>' high.

(4) Sacrum with three vertebrae.

In 1882 (54), p. 450, the genus Edaphosaurjis was described and placed
in a distinct family, Edaphosauridce, "distinguished from the Clepsydropidce
by the presence of more than one series of teeth on parts of the jaws." The
family included Pantylus, Edaphosanrus^ and perhaps Helodectes.

In 1883 (56), p. 631, Pariotichns, Pantylus, and probably Ectocynodon
are referred to a new family, PariotichidcB , "which has the teeth like the
Edaphosauridce, but differs from it in the entire over-roofing of the temporal
fossae."

In 1888 (70) the family Edaphosauridcs was dropped and the genus
Edaphosaurus was included in the Clepsydropidce. This was the last change
made in the composition of the family which was considered to hold the
genera fLysorophus, A^'cheobolus, Clepsydrops, Dimetrodon, Naosatu-us,
Theropleura, Embolophorus, and Edaphosaurus.

SYSTEMATIC REVISION OF THE SUBORDER. 37

Subfamily CLEPSYDROPINAE nov.

(i) Vertebral spines simple.

(2) The bottom line of the anterior dorsals and posterior lumbars greatly

shortened.

(3) Cer\-icals larger than anterior dorsals.

(4) Crest of ilium turned to rear and prolonged.

Genus CLEPSYDROPS Cope.

Proc. Acad. Nat. Sc. Phila., 1875, p. 407.

Proc. Am. Phil. Soc, vol. xvii, 1878, pp. 509 and 529. Also Pal. Bull. 29.

Type: Clepsydrops collet ti, a series of disconnected vertebras. No. 6530 Univer-
sity of Chicago, Gurley, coll.; from Vermilion county, III. Homeotype(C «rt/rt/w): A
skull and large portion of the vertebral column, imperfect scapulae, pelvis, and humeri,
femora, tibia, fibula, and posterior foot and imperfect anterior foot. No. 41 10 Am.
Mus. Nat. Hist. , Cope, coll. ; from Texas. This number includes fragments of at
least two individuals, but it seems very probable that the skull belongs to the same
individual as the main portion of the spine, which consists of the vertebral column
from the fourth (or fifth) presacral to the middle of the tail, with the pelvis complete
and the femora of both sides in position with their heads in the acetabula. The
femur of the left side has been thrown up and backward until it points in a direction
almost diametrically opposite to the natural. The tibia and fibula are attached in
position to the distal end.

Original description of the type, tSj^: "They (the vertebrae) are deeply biconcave,
the articular cavities being funnel-shaped and continuous, thus perforating the entire
length of the centrum. In a dorsal vertebra the cavities communicate by a very
small orifice, while in the posterior the median contraction of the canal is less marked.
The posterior cavity is more gradually contracted than the anterior ; in the latter the
excavation is, in most of the vertebras, but slight (except beneath the floor of the
neural arch), until it falls rather abrviptly into the axial perforation. In an (?) anterior
dorsal it is as widely excavated at the border as the posterior funnel. Another pecu-
liarity is the absence of the processes of the centnim ; and a small capitular articula-
tion is seen sessile on the border of the cup of two of the dorsals.

"The axis* has a singular form, owing to the tubular perforation w'hich continues
the posterior excavation to the anterior face of the centrum. There are three articu-
lar faces, a larger subroimd inferior and two smaller superior, which border the neural
canal in front and below and are separated from each other and the inferior face by
the perforation in question. The anterior face slopes obliquely backwards and down-
wards, and is convex in transverse section. There is no facet for the free hypa-
pophysis of the odontoid, but it appears that the inferior articular face was applied
exclusively to the centrum of the atlas, as in Sphenodoii. But the axis differs from
that of the latter genus in the absence of a coossified odontoid process. Either that
element is entirely wanting or it consists of two pieces, interrupted in the middle
by the notochordal foramen, and in correspondence with superior articular facets.
There is no true h}papophysis of the axis, and the only indication of lateral processes
is a small articular facet on each side on the lower part of the rim of the posterior
funnel. These may have been related to rudimental cervical ribs. The neural arch
is broken off.

*This is the atlas with the intercentrum between it and the axis coossified with it. (PI. 7, figs. 9 and 10.)

38 REVISION OF THE PELYCOSAURIA.

"The dorsal vertebrjE have their sides somewhat contracted ; in one specimen the
inferior face is rounded; in another, which I suppose to belong to a different part of
the column, it is longitudinally acute. In this and another dorsal, where the parts
are exposed, the floor of the neural canal is interrupted by a deep fissure, which has
a triangular shape with apex downward when seeu in profile. This is due to the fact
that the opposite halves of the centrum are united by the circumferences of the artic-
ular cups, which have in profile an X-shape. The diapophysis does not project far
bej'ond the base of the neural arch and is compressed. The caudals are elongate, and
resemble, in the forms of the centrum and neural arch, those of LcElaps. The neural
spines are not preser\'ed, but if present were directed well backwards, bearing the
posterior zygapophyses, since the arch stands only on the anterior three-fifths of the
centrum. Chevron facets are not distinct, but two emarginations on the rim of the
posterior face of one of the vertebrae indicate their existence. In other centra even
these notches are wanting. The tail was evidently tapering. There is uo evidence
of the transverse fissures seen in Sphenodon and many Lacertilia, nor are there any
diapophyses on the caudal vertebrae preserved."

Original description of the iiomeotype, iSjS. Char. Gen.^ et ccBtera: "There is
no quadrato-jugal arch, but the zygomatic and postorbital arches are present. The
squamosal extremity of the z}-gomatic arch descends low on the quadrate as in turtles,
preventing mobility of the latter. The quadrate is not prominent in the specimen,
and appears to have been a thin bone, as in Ectocynodoii. The nostril is large and
latero-anterior. The symphysis of the mandible is short, and the premaxillary bones
appear to be distinct ; they are separated in the specimen by displacement, with the
indication that the junction was sutural. The teeth were of difterent sizes, and the
premaxillaries and canines are distinguished from the others by their proportions.
All are subround in section, with more or less defined anterior and posterior cutting
edges. The premaxillary teeth are larger anteriorly, diminish posteriorly, and are
separated by a notched diastema from the large canine. The succeeding teeth are of
medium proportions. The roots are sunk in deep alveoli. There is no surface
sculpture of the cranial bones, which is the character distinguishing the genus Ecto-
cynodon from Clepsydrops.

" The vertebrae have been described elsewhere, but important additions to our
knowledge can now be made. There are mostly small intercentra throughout the
dorsal and caudal series, in the latter prolonged into two processes below, constituting
the chevron bones. The transverse processes on the dorsal and lumbar vertebrae are
undivided, and on some of the dorsals, the ribs articulate with the centrum as well.
They are present on the anterior, but wanting on the posterior caudal vertebrae. In
adults the neural arch is coossified with the centrum, and on the lumbar and sacral
region the neural spines are greatly elevated, indicating the presence of a fin like
that of Basilisms. In one of the allied species the diapoph}ses of the three vertebrae
are vertically expanded for the attachment of the ilium, but the ceutra are not
coossified.

"The humerus in this genus is of remarkable character. Its proximal extremity
is expanded and regularl)' convex, with the articular surface at right angles to the
sides of the bone, and not developing a head. There is a strong deltoid ridge or tuber-
osity', not extending far from the head. The shaft is much contracted, and the distal
end is more expanded than the proximal. It is flattened and supports no condyle.

SYSTEMATIC REVISION OF THE SUBORDER. 39

Its outline is transverse at the middle and truncate at each lateral extremity. A. large
supracondj'lar foramen pierces the basal part of the distal expansion near the inner
border. The opposite edge is strongly grooved longitudinally, the groove being
bounded in front by a prominent crest, which sinks just proximal of the distal border.

"The ilium is a flat bone which contracts downwards and forwards to the pubis.
The latter is something like the ilium in form, widening in the opposite direction,
/. I?., downwards and forwards. Its fonn is something like that of the Crocodilia and
it is uncertain whether those of opposite sides unite below. The ischium is a remark-
able bone. It is greatly produced anteriorly and posteriorly to the acetabulum, in
forming with that of the opposite side, a keeled boat-shaped body, which at its
superior middle portion includes the inferior part of the acetabulum. In C. natalis
the anterior apex is below the middle line of the pubes near their anterior border.
In the same species there is an additional small element between the ilium aud pubis
on the superior side at their junction. The acetabulum is formed by the interrupted
junction of the three elements.

"The fenutr possesses no third trochanter, and the head and great trochanter are
not separated by a neck. The little trochanter is large, and the condyles are well
defined. The head of the tibia is expanded, and the fibula is well-developed at both
extremities. The phalanges are moderately elongate, and are depressed. The claws
are curved and compressed below."

On page 528 of the same article a table is given showing the charac-
ters of the humertis of Clepsydrops in contrast with those of other animals
of the same formation.

Despite the frequent use of the name Clepsydrops by Cope, his numer-
ous descriptions, and the labels in the collection, it is impossible to fix on
any characters used by him in the identification of specimens, beyond the
small size and the lack of condyles on the limbs. His frequent identifica-
tions of vertebrae as belonging to this genus are not jtistified by his descrip-
tions or direct comparisons. They are mostly D. incisivus.

Revised description of genus :

(i) Diastemal notch present, slight and filled with smaller teeth.

(2) Maxillary canine and incisor teeth enlarged.

(3) Teeth with cutting edge. Not crenate (?).

(4) Neural arch of vertebrae free in young, coossified in adult.

(5) Vertebrse with changing length in different parts of column (?).

(6) Anterior dorsals with the intercentral face on the anterior face of the

centrum and sharp keel.

(7) Spines vertical, slightly recurved in posterior lumbar region.

(8) Character not shown.

(9) Limb bones without well-developed articular faces.

(10) Humerus without prominent entepicondyle or ectepicondylar notch.

(11) Abdominal scutes absent (not observed).

(12) Tail very long and slender.

(13) I to 1.3 meters long.

40 REVISION OF THE PELYCOSAURIA.

C. coUettl Cope.

C. collelli Cope. Proc. Acad. Nat. Sc. Phila., 1875, p. 407.
Case, Jnl. Geol., vol. viii, 1900, p. 711.

Type : Isolated vertebrEe. Among others an atlas, an anterior dorsal, lumbars,
and caudals. No. 6530 University of Chicago, Gurley, coll.; from Vermilion county,
Illinois. Plate 7.

Original description: "There is a shallow fossa in the entering angle between the
superior and inferior articular facets of the front of the axis, and the centrum of the
same is obtusely keeled below. The border of the anterior face of the dorsal vertebree
with keeled centrum is undulate. The obtuse inferior face of another dorsal is rugu-
lose, and the edge of the face is not undulate. The inferior faces of the two caudals
are marked with fine parallel grooves, while in another caudal and the (?) sacrals the
same is smooth. There are some longitudinal ridges on the upper side of the larger
caudal."

Measurements.

m. m.

Length, centrum of axis 0.006 Width, centrum, rounded dorsal, behind o.oio

Width, centrum of axis at middle behind 008 Width, neural canal, behind 004

Depth, centrum of axis (oblique) 010 Length, centrum, larger caudal 014

Length, centrum of sharp-keeled dorsal 014 Width, centrum, larger caudal 008

Depth, centrum of sharp-keeled dorsal, behind.. .012 Depth, centrum, larger caudal 008

Width, centrum of sharp-keeled dorsal, behind-. .012 Length, smaller caudal 010

Length, centrum, rounded dorsal 012 Depth, centrum, smaller caudal 007

Depth, centrum, rounded dorsal, behind on Width, centrum, smaller caudal 007

The vertebra described by Cope a.s the axis is the atlas (plate 7, figs. 9
and 10) and the vertebra with an "obtuse inferior face" is a posterior
dorsal or lumbar (plate 7, figs. 1-8). Other specimens regarded by Cope as
belonging to the species are Nos. 6531 and 6578 University of Chicago.

These vertebrae might be part of the same animal referred to as Clep-
sydrops peduncnlafus, Dimetrodon obtusidens^ or Elcabrosaurus baldwini. It
is indeterminate.

Clepsydrops llmbatus Cope.

Proc. Am. Phil. See, vol. xvii, 1877, p. 193. Also Pal. Bull. 26, p. 196.

Type : Several isolated vertebrae. One showing the character described has
been sawn apart longitudinally and vertically. No. 4144 Am. Mus. Nat. Hist., Cope,
coll.; from Texas.

Original description : "As typical of the new species I select a vertebra, which
may be exactly compared with the corresponding one of C. colletii. The centrum is
about as wide as long, and its sides are ver}' concave, much more so than in C. col-
letii, and the rim-like borders of the articular extremities are connected by a straight
compressed hypophysial keel. The sides of the foramen cJwrdo' dorsalis are convex
in the longitudinal section, thus contracting the opening, as compared with the very
wide flare of the border of one of the extremities of the centrum. This flare receives
the wide recurved border of the opposite extremity of the adjoining centrum, forming
a kind of ball and socket articulation.

"This reflected surface forms a ridge with the funnel of the foramen at this
extremity of the vertebra. The concave extremity is produced downwards, so that

SYSTEMATIC REVISION OF THE SUBORDER. 4 1

the foramen is considerably above the middle point. The diapophysis and para-
pophysis are not distinct nor elongate, but are represented by a projecting ridge in
the superior part of the centrum, which is directed downwards and forwards toward
the rim of the articular face.

"Besides the great contraction of the centrum, its relatively shorter form distin-
guishes it from that of C. coUetii. It is also much larger than that species and the
C. peduiiculatiis, being the largest of the genus."

7)1 )n. mm.

Length of centrum 31 Transverse diameter of centrum 33

Vertical diameter of centrum 39 Width of neural canal 6

The single vertebra that can be identified as Cope's type is an anterior

dorsal of D. iiicisivus.

Clepsydrops pedunculatus Cope.

Cope, Proc. Am. Phil. Soc, vol. xvii, 1877, p. 62.
Case, Jnl. Geol., vol. viii, 1900, p. 713.

Type : A third cervical and an anterior caudal regarded by Cope as a dorsal.
No. 6534 University of Chicago, Gurley, coll.; from Vermilion county, Illinois (plate
7, figs. 14 and 15).

Original description : " Both differ from corresponding vertebrae of C. collet iia.-nA
C. lateralis [this is evidently a slip on the part of the describer ; there is no C. late-
ralis; C. vinslovii is evidently referred to, as it was the only other species of the genus
described at this date] in having elongate diapophyses for the attachment of the ribs.
These are present in the other species, but are either very short, or sessile. The third
cervical has a broad reverted anterior lip-like margin of the anterior articular face,
which resembles the corresponding part in C. lateralis (vinsloz'ii) in not being pro-
duced below. The median line is keeled, and there is a shallow longitudinal groove
on the upper part of the sides. The posterior articular face is regularly funnel-
shaped. The diapophyses are very stout, and are directed a little downwards and
strongly backwards. The articular faces are single, look downwards and outwards,
and are wide above, and narrow below. The base of the neural canal is deeply
incised, as in the other species.

Measurements.

m. m.

{Antero-posterior 0.015 Length of diapophysis above 0.009

Transverse 012s t^- ^ c j- . ■ (Vertical .008

,, . , ■' Diameter of diapophysis^ , . . .

Vertical 012 r r ^ [Antero-posterior... .005

"There is no recurved rim of the articular extremities, but the surface does not
pass regularly into the foramen chordse dorsalis, but by an abrupt descent at its
mouth. The sides of the centrum are concave, and the inferior portion forms a prom-
inent rounded rib."

Measurements.

m.

{Antero-posterior 0.016
Vertical 016
Transverse .015

In the description of the supposed dorsal attention is called to the long
and slender diapophysis ; it is evident that this is not a diapophysis, but

42 REVISION OF THE PELYCOSAURIA.

an anchylosed rib with tlie distal broken portion inclined forward, as is
characteristic of the anterior caudal ribs of the Rhynchocephalia.

This is an anterior caudal and is indeterminate.

Another specimen regarded by Cope as belonging to the species is

No. 6535 University of Chicago.

Clepsydrops vlnslovli Cope.

Cope, Proc. Am. Phil. Soc, vol. xvii, 1877, p. 61.
Case, Jnl. Geol,, igoo, vol. viii, p. 714.

Type : A single cervical with other vertebrce doubtfully associated. No. 6532
University of Chicago, Gurley, coll.; from Vermilion comity, Illinois (plate 7, figs.
16 and 17).

Original description : "The inferior median line is a keel; some distance above
it the sides of the centrum are full, rising in a longitudinal angle. There is no
constriction or fossa below the diapophysis as in C. collet ii. The latter is anterior in
position, is vertically compressed, and is curved forward for a short distance below.
The posterior articular face is regularly funnel-shaped from the margin ; the anterior
face has a broad recurved lip. This passes around the inferior margin, which is not
projected forwards as in C. colletii. The zygapophyses are well-developed and stand
close together. The neural spine is compressed, and the basal portion points some-
what forwards."

Aleasurements.

m. m.

Length of centrum o.oii Vertical diameter of diapophysis 0.006

Diameter of posterior articular face: Expanse of posterior zygapophysis 009

Vertical 009 Antero-posterior diameter of base of neural spine .005

Transverse 009 Transverse diameter of neural arch 006

These are the smallest vertebrae referred by Cope to this genus. They
might be the atlas and anterior cervicals of a small Clepsydrops natalis.
The species is indeterminate.

Another specimen referred to the same species by Cope is No. 6533
University of Chicago.

Clepsydrops natalU Cope.

Proc. Am. Phil. Soc, vol. xvii, 1878, pp. 509 and 529.

Type: This is the homeotype of the genus Clepsydrops. See description, p. 37.
No. 41 10 Am. Mus. Nat. Hist., Cope, coll.; from Texas.

Original description: "The muzzle of this species is compressed and descends
obtusely at the ends as Bolosajtnis striatits. The nostril and orbit are quite large.
The first premaxillary tooth is the largest and has a silky striation of the enamel ; its
crown is much less than that of the canine. The canine originates below a point a
short distance posterior to the nostril.

McasKrements.

m. m.

Length of skull posterior to base of quadrate. ..0.124 Length of crovifu of canine tooth 0.016

Diameter of nostril 019 Antero-posterior diameter of canine tooth 005

Depth of zygoma at orbit 012

SYSTEMATIC REVISION OF THE SUBORDER. 43

"The centra of the lumbar vertebrse are compressed, but not deeper than long,
nor acute on the median line below. The diapophyses are wide, and descend towards
the anterior articular border. The neural spines are compressed, and are very long.
Their apices are slender and are curved backwards. The faces of the zygapophyses
are oblique upwards and outwards. The caudal vertebrse have subround articular
extremities anteriorly, and become more compressed posteriorly. The diapophyses
are median on the former, and gradually become smaller to extinction. The zyga-
pophyses are strong, and the neural spines continue long for a considerable part of
the length of the entire series. The centrum is concave below the diapophyses, and
has a median inferior rib.

Measurements.

7)1. m.

Length of centrum, fourth from last lumbar ver- Depth of pelvis 0.080

tebra 0.018 Length of femur 120

Vertical diameter of do 017 Long diameter of proximal end 041

Transverse diameter of do 018 Length of tibia 085

Elevation of neural arch and spine of last lum- Transverse width of tibia 029

bar 087 Length of eleven caudal vertebrae 172

( Ilium 059 Length of fourth caudal vertebra 016

Antero-posterior extent of ■] Pubis 060 Length of eleventh caudal vertebra 014

Ischium 143 Transverse diameter of caudal 012

"This species differs from the C. vinsloviiin the more robust caudal vertebrse. It
is also considerably larger, agreeing in this respect with the C. peduncidatus. In the
latter the long transverse processes are decurved and narrowed at the extremities in a
manner not seen in any of the known vertebrse of C. natalis.''''

This specimen was covered with a very refractory matrix very nearly
the color of the bone, and only removed with great difficulty. The skull
was uncleaned when described by Cope, which accounts for his misconcep-
tion of its character. The other species of this genus are indeterminate ;
probably some of them are good, but they can not be distinguished from
this species or from each other. Until more material is collected this will
remain the only determinable species. The redescription of the species
is contained in the redescription of the genus.

Genus DIMETRODON Cope.

Proc. Am. Phil. Soc, vol. xvii, 1878, p. 512 and p. 529. Also Pal. Bull. 29.

Proc. Am. Phil. Soc, vol. xix, 1880, p. 42.

Am. Nat., vol. xx, 1886, p. 544.

Trans. Am. Phil. Soc, vol. xvi, 1888, p. 292.

Type: Dimetrodon incisivus. The imperfect skull, consisting of maxillaries
and premaxillaries. No. 4116 Am. Mus. Nat. Hist., Cope, coll. ; from Texas.

Original description : " Dentition as in Clepsydrops in the superior series.
Pubic bone not distinct from ischium. Humerus with trochlear condyles and a
defined proximal articular surface.

" The genus Dimetrodon embraces larger forms than the known species of Clep-
sydrops. It is probable that the species had the neural spines in the lumbar and
dorsal regions elevated in the same way. The humerus, while of the same general
character as that of Clepsydrops, differs remarkably in its more perfect articular

44 REVISION OF THE PELYCOSAURIA.

surfaces, indicating a terrestrial habit as distinguished from a probably aquatic one in
the former genus. The supracondylar foramen is present in this genus, and the prox-
imal articular surface winds obliquely round the expanded extremity of the bone.

"The separate jaws of D. incisiviis show well the character of the dental inser-
tions. A strong thickening of the inner wall of the maxillary bone is all that repre-
sents the palatine lamina. This enlargement does not extend to the level of the
external alveolar margin, which thus forms a parapet. The roots of the teeth are
long, and are contained in deep alveoli of the palatine thickening ; but the portion of
them which projects beyond the alveoli is adherent to the external parapet by the
side, and hence the teeth appear to be pleurodont. They are shed in after the absorp-
tion of the root in consequence of the presence of the crown of the successional tooth.
The process commences at the inner alveolar border, and extends inwards and
upwards, invading the palatine wall of the maxillary bone."

In 1880 (48) Cope added materially to his description of tlie genus
Dimetrbdon.

" In both specimens of D. indsivus^ portions of the palato-pteiygoid arch are
attached to the maxillary bone. One of these elements is an oval plate with a thick-
ening of its inferior side, so as to bevel the long border farthest from the maxillary
bone. The surface thus produced is thickly studded with small conical teeth irregu-
larly disposed.

"A second tooth-bearing element of the palate is adjacent to the last. It is a
massive plate, the ends of which are produced in opposite directions ; the one into a
massive shorter prominence ; the other longer and plate-like. Between these prolon-
gations, the inferior edge of the bone bears a single row of well-developed teeth. The
patch of small teeth first described, commences at the extremity from which the
longest process rises on the opposite side of the series of large teeth. This Z-shaped
bone is, from its massive character, generally preserved. * * *

"The posterior part of the skull of one of the specimens above mentioned displays
typical reptilian characters. The occipital condyle is not perforated, nor divided by
sutures. The exoccipital bones project well backwards. The lateral walls of the
brain case are massive as far forward as the exit of the fifth pair of nerves ; anterior
to this point they were thin or wanting. The basisphenoid carries two parallel
descending laminae, which bound a deep median fissure, and then unite anteriorly.
Posteriorly they abut on a descending process, which is followed by a lid-like element
which is applied to a circular fossa with a raised border near the occipital condyle.

"The articular face of the articular bone of the mandible consists of two parallel
cotyli, divided by a ridge of articular surface. This part of the jaw is much depressed,
as in Eryops. The large teeth of the lower jaw are at the anterior extremity.

"The neural spine of the axis is flat and elongate antero-posteriorly. From this
point the neural spines rise rapidly in elevation until on the dorsal region they are
many times as long as the diameters of the centra. The latter are not ver}' unequal
in their proportions in different parts of the column. Those from the posterior
regions are less compressed than the dorsals and cervicals. The dorsals are separated
by intercentra below, which are small in the D. incisivus, and larger in the D. gigas.
All the ribs are two-headed, commencing with the axis. All the cervical and dorsal
vertebrse have diapophyses with tubercular facets. The head of the rib is prolonged
downwards and forwards to the prominent border of the anterior articular face, against
which it abuts, but so far as yet observed without a corresponding facet. On the

SYSTEMATIC REVISION OF THE SUBORDER. 45

caudal vertebrae the two facets of the ribs are approxiinated and finally are not
distinguished. They are here coossified with the centra.

" VertebrcB. * * * The dentition of these animals was of the most formid-
able character, consisting of compressed, finely serrate teeth in the maxillary and
dentary bones mingled with huge conic tusks on the middle of the maxillary' and
anterior end of the dentar}-, and occupying the whole alveolar edge of the premax-
illary. The huge neural spines formed an elevated fin on the back. In a medium-
sized specimen of Dinietrodon incisivtis^ where the vertebral body is 35 mm. in length,
the elevation is 900 mm., or 201^ times as great. The apex of the spine in this
species is slender, and apparently was flexible."

In 1888 (70) appeared descriptions of the vertebrae and shoulder girdle.

'■'•Ribs. In this genus and in Naosaurus the sacral ribs are present as in Batrachia.
They are short, and vertically compressed, forming a wedge-like body.

'■'■ Sternum. * * * The anterior two-fifths of the bone is nearly square, and
slightly concave above, with three angles, one at each side and one anterior ; the rest
contracts posteriorly into a long, narrow, flattened shaft, which constitutes three-
fifths of the length. This portion is depressed so that the transverse section is lentic-
ular. The lateral edges are acute, and without articular facets of any kind. The
distal extremity is first grooved, and then fissured, each half tenninating in an obtusely
narrow apex which is applied to the other half The surface of this part of the
element is longitudinally grooved both above and below.

'■'■ Clavicles. The clavicles in the genus Dimctrodon are well-developed elements.
They consist of a vertical narrow and a horizontal expanded portion. The anterior
border of the bone is rounded ; the internal border is serrate or semidigitate. If the
latter unites with the episternum by suture it must be by a very open one. This
portion is more expanded than in the monotreme Mammalia ; while the episternum
is more produced posteriori)'."

This genus is represented by the largest ntimber of species and by the
largest number of individuals in both collections. It seems to have been
the most abundant animal of the Texas region.

Revised description :

(i) Large diastemal notch with few degenerate teeth or none.

(2) Maxillary canine and incisor teeth greatly enlarged.

(3) Teeth with crenate cutting edges.

(4) Neural arch very early coossified with centrum.

(5) Very marked change in length of bottom line of vertebne in different

parts of column. Posterior lumbars shortened, but without wide faces
on lower edge of articular faces of centra.

(6) Anterior dorsals with sharp narrow median keel and wide intercentral face

on lower edge of anterior face of centrum.

(7) Spines sharply recurved in posterior lumbar and sacral region.

(8) Spine of axis high and broad, reaching forward over atlas.

(9) Limb bones with well-marked articular surfaces.

(10) Humerus with well-developed entepicondyle and ectepicoudylar process.

(11) Abdominal ribs absent (not observed).

(12) Tail relatively short.

(13) Size varying in diflferent species, from about 1.2 to about 3 meters.

46 REVISION OF THE PELYCOSAURIA.

Dlmetrodon gig&s Cope.

Clefsydrops g^S'as Cope. Am. Nat., vol. xii, 1878, p. 327.
Proc. Am. Phil. See, vol. xvii, 1878, p. 515. Also Pal. Bull. 29.
Proc. Am. Phil. See, vol. xix, 1880, p. 43. Also Pal. Bull. 32.

Type : The head of a humerus, the pelvis, both femora, several dorsal, sacral
and caudal vertebrae, and two phalanges. No. 4006 Am. Mus. Nat. Hist., Cope, coll.;
from Texas.

Original description : "This animal is only represented in my collection so far
by a large part of the pelvis. This is of the same character as that of the C. natalis, but
differs in several details of fonn and is three times as large in linear measurements.
The portion anterior to the acetabulum is shorter than in the C. natalis, and relatively
deeper. The raised borders of the acetabulum unite, and form a thick obtuse hori-
zontal crest, which continues to the apex, which consists of a broadly expanded
shovel-like projection. This symphyseal portion is quite elongate, and carries on its
supero-anterior face an obtuse median keel. The opposed elements diverge above
the anterior part of the acetabulum. The latter is shallow, but entire ; its most
prominent borders are the anterior and postero-inferior."

Measurement s.

m. m.

Length from posterior border of acetabulum Total vertical diameter to superior border of

forward 0.200 acetabulum 0.155

Long diameter of acetabulum (right side) 100 Length of anterior symphysis 175

In 1880 Cope added to the description of D. gigas as follows :

"The peh-is of the D. gigas is in general like that of Clepsy drops natalis. The
elements are coossified, but the ischio-pubic symphysis is not so deep as in the
Batrachia of the same beds. The ilium is shortened, and its direction is at right
angles to the long axis of the inferior elements. The foramen of the internal femoral
arter}^ is distinct. The femur of the same individual of D. gigas has no head, but a
regular wide crescentic proximal articular surface. Below this on the posterior side
is the large trochanteric fossa, which is bounded by lateral ridges, which are at first
equal, but one soon exceeds the other in height, fonning a trochanteric ridge a little
above the middle of the shaft. The condyles are distinct from each other and are
flattened below. One of them bears a robust longitudinal crest above, which makes
it much larger than the other, and causes the groove that separates them above to
look outward or to the side which supports the trochanter.

" Three of the species may be distinguished as follows :

" Vertebral centra much compressed, acute below ; neural spines without processes D, incisivus,

" Vertebral centra less compressed, obtuse below : neural spines without processes ; larger... Z>. g-ig^as.

"Vertebral centra compressed, not acute below; neural spines with cross projections D-criici^er."

Revised description :

(i) Spines quadrangular, nearly square at base ; changing to rounded above ;
large, surface not striate.

(2) Third to sixth cervicals with axis through neural arch and middle of

centrum vertical.

(3) Intercentrum small in mid-dorsal and lumbar regions, without terminal

facet for capitulum of rib.

(4) Character not shown.

(5) Size, largest of genus. 2.5 to 3 meters in length.

SYSTEMATIC REVISION OF THE SUBORDER. 47

Dlmetrodon glg^anhomogenes sp. nov.

T}'pe : Two cervicals, eleven dorsals, six lunibars, five caudals, perfect right half

of pelvis. No. 112 University of Chicago ; from Coffee creek, Baylor county, Texas.

Description : This species is very near Dinietrodon gigas in size and character

of the vertebrae and pelvis. It differs from the other species in the shape of the

spines, the character of the keels on the cervical vertebrae, and the shape of the pelvis.

(i) Spines broad transversely at base ; becoming 00-sliaped above. A tendency

for the ends to be tuberculate.

(2) The third to the sixth cervical with axis through spine and middle of

centrum vertical.

(3) Intercentrum small in mid-dorsal and lumbar regions, without terminal

facet for capitulum of ribs.

(4) Character not shown.

(5) Size nearly as great as Dinietrodon gigas^ 2.6 meters at least.

D O o o

o o

(^00

CO C3 CD

Z30mm 630mm 850mm

Fig. 14. — Cross-section through the spines of various species of Dimetrodon, at approximately the same
level above the neural arch. The figures give the distance above the base. a. D. macrospondyluSt
No. 1019 University of Chicago. A lumbar, b. D. gigas, No. 1002 University of Chicago.
The ninth dorsal, c. D. incisivus. No. 1001 University of Chicago. The fourteenth vertebra.
d. D. giganhomogenes. No. 1 1 2 University of Chicago. An anterior dorsal.

Dlmetrodon Inclsirus Cope.
Am. Nat., vol. xii, 1878, p. 327.
Proc. Am. Phil. Soc, vol. xvii, 1878, p. 512, plate vi.

Type : An imperfect skull, consisting of maxillaries, premaxillaries, and frag-
ments of the preorbital portion of the skull. No. 41 16 Am. Mus. Nat. Hist., Cope,
coll.; from Texas.

Cotype : A vertebral column complete from axis to first caudal and a fragment
of the muzzle. Premaxillary and part of maxillary in position. No. 4008 Am. Mus.
Nat. Hist., Cope, coll.; from Little Wichita river, Archer county, Texas.

48 REVISION OF THE PELYCOSAURIA.

Original description: "This saurian is established on the nearly complete pre-
maxillary and maxillary bones of the right side with the left maxillary of the same
individual. Associated with these are portions of the postfrontal, frontal, and nasal
bones of the right side of perhaps the same individual, but, as the pieces are loose, this
relation can not be positively aflfimied. Portions of the maxillarj', premaxillary, and
other bones, with isolated teeth of numerous other individuals, are in my possession.

"The first-named specimens show that the mutual premaxillary and premaxillo-
maxillarj' sutures are distinct. There is a deep emargination of the border of the jaw
at the latter suture, and the maxillary alveolar border is gently convex downwards.
The nostril is large and is directed forwards as well as outwards. The premaxillary
spines are narrow. The form of the muzzle and jaws when in normal relation was
vertical and compressed in front. The premaxillary border of the jaw is rounded and
contracted behind the nostril ; the outline then expands backwards. There are but
two incisor teeth, of which the anterior is much larger than the second. Its root is
irregular in section, owing to the presence of one or more shallow longitudinal
grooves. The pulp cavity of some of the larger teeth is much contracted opposite
these grooves by the corresponding internal face, which is disproportionately convex.
The anterior two teeth of the maxillary bone are larger than those that follow, the
anterior exceeding even the first incisor. The other maxillaries are smaller and sub-
equal, excepting the last two, which are the smallest. Tlie crowns of the teeth are
lenticular in transverse section, the external side being much more convex than the
internal. The cutting edges are defined from the convexity of the latter by a shallow
groove at the base of each. The edge is not crenate as in Lt^laps and allied genera,
but presents much the same appearance owing to the presence of a transverse corru-
gation. There are 14 teeth and empty alveoli in the maxillary bone.

Measurements.

m. m.

Length of premaxillary axially, to middle of Length of diastema (chord) 0.032

maxillary suture 0.040 Depth of maxillary at third tooth no

Length of maxillary bone on alveolar edge from maxillary at antepenultimate tooth... .066

middle of premaxillary suture 230 Diameter of base of crown of first incisor tooth.. .015

Greatest width of the premaxillary 036 first maxillary tooth 018

Depth of face of premaxillary bone at nostril... .030 fourth maxillary tooth 009

"The portion of cranium above mentioned displays a number of peculiarities.
The orbit is lateral, and has a prominent and convex superciliary border. The zygo-
matic arch is so curved upward as to complete the orbit behind by the intervention
of a postorbital or postfrontal bone, which separates the malar and squamosal bones
from mutual contact. In front of this bone a portion of the frontal forms the super-
ciliary border, and in front of this, the prefrontal sends a wide process behind the
lachrymal to the orbit. This bone resembles a nasal bone in form, and extends
forward, and is decurved at the extremity. The width of the descending or malar
process of the postfrontal is such as to partially separate the orbit from the zygomatic
fossa. The superciliary surface is swollen, and is interrupted by a transverse groove
on the orbital part of the prefrontal. There is a vertical open groove on the malar
process of the postfrontal.

"Several large pelvic bones, corresponding with those which I have called ischia
in Clepsydrops natalis, are of a size appropriate to the present species. They include
both the ilia, ischia, aud pubes in one mass, forming a compressed boat-shaped body
with a prominent inferior keel.

SYSTEMATIC REVISION OP THE SUBORDER. 49

"The proraiueut character which distinguishes this species is the shortness of
the ischiatic symph}-sis. Its extent anterior to the acetabulum is only one-half of the
diameter of the latter, while it equals that diameter in the C. gigcis. It follows from
this, that the crest arising from the anterior border of the acetabulum is abruptly
decurved a little anterior to the latter, and descends to the inferior keel at a very steep
angle. At its point of decurvature is a prominent tuberosity. The front of the sym-
physis pubis presents an obtuse keel, which ternrinates short of the apex. The
inferior border of the acetabulum is not sharply deiined, except at its posterior portion."

Aleasuremcn/s.

m. m.

Total length 0.260 Total vertical diameter to superior border of

Length from posterior border of acetabulum acetabulum 0.135

forward 148 Length of anterior symphysis 085

Long diameter of acetabulum 095

In 1880 (48) Cope piiblislied a figtire of the vertebral column of Dime-
trodon incistvus, No. 4008 Am. Miis. Tlie description given was short
and formed part of tlie description of the genus quoted above, see p. 43.

Revised description :

(i) Spines lateralh' flattened at bottom, changing to rounded ; finally striate.

(2) Third to sixth cervicals with axis through neural arch and middle of

centrum nearly vertical.

(3) Intercentrum small in mid-dorsal and lumbar region, without capitular

facets at end.

(4) Lumbars with distinct keel.

(5) Size medium. From 1.6 to 2 meters.

The pelvis mentioned (No. 4165 Am. Mus.) as suitable in size to the
type skull is only one side and lacks the iliac crest. The peculiar short-
ness described is due to the fact that the distal portion of the ischium is
also broken away. An evidence of the haste in which the description was
written is seen in the fact that "anterior" is used instead of "posterior" in
the description of this ischium.

Dlmetrodon rectlformis Cope.

Am. Nat., vol. xii, 1878, p. 327.

Proc. Am. Phil. Soc, vol. xvii, 1878, p. 514.

Type: Several separate vertebrse. No. 1546 Am. Mus. Nat. Hist., Cope, coll.;
from Texas.

Original description : " Its size exceeds considerably that of the Oepsy drops
natalis equaling that of the C. ( ? Embolophoriis) limbatns Cope. * * *

" In Dimetrodon rectiformis, the depth of the centra does not exceed the length.
The margins of the articular faces are not twisted, and the articular faces of the zyga-
pophyses are horizontal. The opposite is the case in the C. limbatus. The spaces
for the intercentra are small ; they are large in C. limbatns. The vertebra described
as typical is a posterior dorsal. Here the diapophysis is nearly sessile, and below the
line connecting the zygapophyses. Its costal articular surface is narrowed downwards
and forwards, almost reaching the recun^ed border of the anterior face. The neural
spine is nmch elevated, and the sides of the centrum are concave. The inferior
articular borders are connected by an acute nearly horizontal edged keel."

50 REVISION OF THE PELYCOSAURIA.

Measurements,

m. m.

{Antero-posterior 0.031 Expanse of posterior zygapophyses 0.030
Transverse 034 Length of base of neural spine 025
Vertical 026

This is a synonym of Dinietrodoti incisivus.
Dimetrodon semiradicatus Cope.

Cope, Bull. U. S. Geol. and Geog. Survey Terr., vol. vi. Article 11, t88i, p. 80.

Type : An imperfect skull with the bones beautifully preserved and naturally
cleaned. Anterior end of skull and right niaxillar>-, orbital region, fragment of
pelvis, femur, and fragments. No. 4001 Am. Mus. Nat. Hist., Cope, coll. ; Big
Wichita river, Texas.

Original description : "A considerable part of the skull and some limb bones
represent this species. There are no vertebra: referable to the specimen, but the two
maxillary and premaxillary bones support nearly all the teeth in an excellent state of
preser\'ation. Continuity of the dental series is preserved by one maxillary bone or
the other, excepting just at the extremity, where there is a slight interruption on both
sides. On one of them it must be very slight.

" There are three teeth in each premaxillary bone. In the maxillary I count
seventeen, with the bare possibility of the necessity of adding one more. The first
premaxillar\' and third maxillary teeth are of nearly equal size and are much larger
than the others, the second premaxillary only approaching them. The section of the
base of the first premaxillary is subtrifoliate, there being one groove on the inner, and
two on the external face. The section of the middle of the crown is more than a
semicircle, with the base convex. The two angles are the sections of two ridges,
which are both presented posteriorly, the one on the inner, the other on the external
face of the crown. The crown of the second premaxillary has the same form, but the
base has only slight traces of the grooves. The third premaxillary is a diminutive
of the second.

" The crowns of the maxillarj' teeth differ from those of the premaxillaries in the
opposition of the cutting edges, which present anteriorly and posteriorly. The exter-
nal face is more convex than the internal. The crown of the large third tooth is not
expanded above the root but its antero-posterior diameter contracts regularly to the
apex. The crowns of the other teeth are wider at the base antero-posteriorly than the
root. They are slightly curved backwards, and their edges are more or less regularly
crenate.

" Several peculiarities distinguish this species from the D. incisivus, with which
it agrees in size. In the first place, the section of the root, at and below the base of
the crown of the third or large maxillary tooth and of the seventh tooth posterior to
it, is of the form of a figure co directed antero-posteriorly. This is due to the deep
grooving of the tooth on the opposite sides at this point ; the grooves not extending
on the crown. The grooves are deeper on the smaller teeth, giving it an almost
biradiculate character. In D. incisivus the sections of these teeth are subquadrate.

" In the second place, the section of the base of the first incisor differs from that
of D. incisivus, where it is subquadrate with two opposite shallow grooves. Next,
the nostril excavates the border of the maxillary bone; in D. incisivus, the nostril is
separated from that bone by the intervention of the nasal. In that species there are
but two premaxillary teeth; in D. semiradicatus there are three. ' * * *

SYSTEMATIC REVISION OF THE SUBORDER. 5 1

Aleasurcmenis.

f-. m.

Length of the dental series 0.252 Diameters of third maxillary at alveolar border:

premaxillary series (and bone) 049 Antero-posterior 0.020

diastema 024 Transverse 005

first premaxillary tooth from alveo- Diameters of third maxillary at base of crown:

lar border 057 Antero-posterior 018

Diameters of first premaxillary tooth at alveolar Transverse 015

border: Length of seventh maxillary from alveolus 026

Antero-posterior 022 Diameters of crown at base of cutting edge:

Transverse .015 Antero-posterior 012

Length of third maxillary from alveolar border .067 Transverse 009

" The approximation to a two-rooted condition in some of the teeth is a marked
peculiarity of this species. The median groove is most extensive on the smaller max-
illarj' tooth, extending into the base of the crown."

The figure co -shaped roots of the teeth described as characteristic of the
species occur in only two of the nearly complete series of teeth. An exam-
ination of the broken surface of the root of the large canine with a hand lens
shows that the walls have been broken and crushed in to take the figure co -
shape. In the natural condition the root liad only a slight depression on
either side, giving it a semiquadrangular outline.

The described excavation of the nasal bones by the nostril is an error,
the part considered by Cope as the end of the nasal in Dimetrodon incisivus
being the septo-maxillarj'. This has fallen out in Dimetrodon seniir'adicatns.

The shape of the root of the incisor teeth in the premaxillary would be
different if taken at any other place ; the base of the root is semiquadran-
gular as in Dimetrodon incisivus.

This is a synonym of Dimetrodon incisivus.
Dimetrodon dollovianus Cope.

Embolophorus dollovianus Cope.

Cope, Proc. Am. Phil. Soc, vol. xii, 1884, p. 43, plate i, figs. 4, 4a, and 4b.
Cope, Proc. Am. Assn. Adv. Sc. Phila., 18S4, p. 471. (Same plate as preceding.)
Case, Jnl. Geol., vol. xvi, 1903, p. i. 32 figs.

Type : A collection of fragments of a skeleton including parts of the skull, the
neural arch of the atlas, third and fourth cervicals, fragments of dorsals, an imperfect
sacrum, and astragalus. The third cervical with its attached intercentrum was
described as having the typical characters. No. 4064 Am. Mus. Nat. Hist, Cope,
coll.; from the Indian Territory.

Homeotype : A skull, nearly complete vertebral column, shoulder girdle, pelvis,
and fragments of limb bones. No. 1 14 University of Chicago. From Coffee creek,
a tributary of the Big Wichita river in Vernon county, Texas.

Original description : In 1884 Cope read two papers (60, 66) in which an
identical plate bore a figure labeled, a dorsal of a species of Embolophorus.
In one of these papers (60) appears the following description of this vertebra :

"The articulation of the ribs in Embolophorus. — The ribs of the Theromorpha
are two-headed. While the tubercular articulation has the usual position at the ex-
tremity of the diapophysis, the capitular is not distinctly, or is but partially indicated,
on the auterior edge of the centrum, in Clepsydrops and Dimetrodon. ln_Eiubolopho7-us,

52 REVISION OF THE PELYCOSAURIA.

as I showed in 1S69 [misprint for 1878], the capitular articulation is distinctly to
the intercentrum. A second and larger species of that genus, recently come to hand,
displays this character to a striking degree, since the intercentrum possesses on each
side a short process with a concave articular facet for the head of the ribs. From the
slight corresponding contact with the intercentrum seen in the Dimetrodon and other
genera, there can be little doubt that this is the true homology of the ribs in the order
Theromorpha. ' '

In 1888 (70) the specific name dolloviaims was applied to this species,
biit without further description.

Revised description :

(i) Spines square at base, rounded above, smooth.

(2) Third to sixth cervicals with axis through neural arch and middle of cen-

trum inclined strongly forward.

(3) Intercentrum of mid-dorsal and lumbar regions small and without tenni-

nal facets for capitulum of rib.

(4) Lumbars with sharp, low keel on mid line of centrum below, divided b}'

longitudinal groove.

(5) Size, that of/?, incisiviis^ 2 to 2.6 meters long.

The original description of the species was based on the observation
that the intercentrnm was large vnih. capitular faces and extended beyond
the edges of the centrum. Cope had not recognized this in the cervical
regions of his nncleaned specimens of D. incisiviis and others. As soon as
this character was made out it became evident that the animal belonged to
the genus Difucfrodon. The character of the anterior cervicals, however,
demanded that it be retained in a separate species. Other characters are
indicated in the morphological description below.

Dimetrodon macrospondylus Cope.

Clefsydrops macrospondylus Cope.

Proc. Am. Phil. Soc, vol. xxii, 1884, p. 35. Also Pal. Bull. 39.

Type: Twelve presacrals in series, three sacrals, and nine caudals. No. 4012
Am. Mus. Nat. Hist., Cope, coll. ; from Little Mountain, near Dundee, Archer county,
Texas.

Original description : " The individual by which the species is known, is repre-
sented by an axis vertebra, twelve continiious dorsal vertebrae ; nine other continuous
vertebrae, of which three are lumbar, two sacral, and four caudal ; also by a part of the
ilium, and by the greater part of the dentarj^ bone. All of these specimens were
found together, and possess an identical mineral appearance.

"That this reptile belongs to a distinct species from the C. leptocephalits is readily
determined by the form of the dorsal vertebrae. The centra are a little longer than
those of that species, but have a smaller vertical diameter. The latter is three-fifths of
the former, while in the C. leptocephahis the two dimensions are reversed, the depth
being a little in excess in corresponding parts of the column. The dentary bone, on
the contrary, is more robust than that of the C. leptocepJialus, and supports, probabl}-,
a small number of teeth.

SYSTEMATIC REVISION OF THE SUBORDER. 53

"The edges of the centra are not undulate or laterally flared. The centra are
strongly compressed, and in the anterior part of the column have an obtuse hypapo-
physial keel. The intercentra display equal width of the inferior surface ; and are
abruptly rounded at the extremities. The last one preserved is between the second
and third caudal centra. It is shorter and wider than the others, and does not display
any trace of a chevron bone. The diapophyses are opposite the neural canal on the
thirteen anterior vertebrae preserved. Each one sends a horizontal rib forwards to
the prezygapophysis, and another obliquely forwards and downwards which stops
short of the edge of the centrum. These ribs enclose a fossa in front of the diapo-
physis. Posteriorly the antero-inferior rib grows more robust, and evidently supports
part of the tuberculum of the rib. There is no facet for the capitulum till the ante-
penultimate vertebra of the anterior series is reached. Here on the penultimate the
anterior border is flattened into a facet, and on the last of the series, the facet marks
the summit of a distinct tuberosity, which is produced by the cutting away of the
border below it, to accommodate the intercentrum.

"The three lumbar vertebrae preserved are different from the dorsals in their
greater abbreviation. This character is not unknown in other species of Pelycosaiiria.
The centrum is contracted, but not compressed, at the middle. The diapophysis is
altogether on the centrum, and supports no rib-facet. Its antero-inferior buttress is
well developed, extending to the margin of the centrum, which is cut out below it for
the intercentrum. The sacrum is rather robust. Its two vertebra; are not coossified,
and support well-developed neural spines, and a large free diapophysis for the ilium.
The centra of the caudals, and their diapophj-ses and neural spines are well developed.
There is a fossa at the base of the spine on each side, in line with the zygapophysial
surfaces, equidistant between them.

"The fragment of the ilium is of appropriate size, and is quite robust. It displays
the fossa for the sacral diapophysis, and the acetabulum. The latter is remarkable for
the prominence of the tuberosity on the superior border, which exceeds that of any spe-
cies of Pelycosaiiria known to me. The section of the ilium through it is triangular.

" The dentary bone is accompanied by the splenial to the middle of the symphysis.
The latter is not very long. Its dentary portion turns upward. The ramus is quite
robust, differing from that of C. leptocephalus. It is broken off" a little anterior to the
tooth line, but the latter probably did not contain more than twenty-two teeth.
These have anterior and posterior cutting edges and are denticulate. The external
face of the dentary is excavated by shallow, undulating, branching grooves."

Measuremetits.

m. m.

Total length of vertebras preseri'ed 0.640 Diameters of a lumbar centrum, cont'd:

Diameters, centrum of a dorsal vertebra: Transverse at end 0.026

Antero-posterior 031 middle

Vertical behind diapophysis 019 Vertical behind arch

Transverse at end 021 at end

middle 0115 Length of sacrum

Diameters neural arch of same vertebra: Diameters of third caudal vertebra:

Length with zygapophyses 041 Antero-posterior

Width at prezygapophyses 022 Vertical at end

Diameters neural spine of the same vertebra: Transverse at end

Antero-posterior 0145 Antero-posterior diameter of acetabulum

Transverse behind 007 Transverse diameter of ilium at tuberosity

Diameters of intercentrum of do.: Length of dentary bone supporting twenty

Antero-posterior 0052 teeth

Transverse 023 Thickness at twentieth tooth

Diameters of a lumbar centrum: Depth ramus at second tooth

Antero-posterior 024 fifteenth tooth

023
022
029
055

024

023

022

0325

0265

044
0175
035
039

54 REVISION OF THE PELYCOSAURIA.

Revised description:

(i) Spines rectangular, oblong below, changing to rounded above, not striate,
smooth.

(2) Third to sixth cervical with axis through neural arch and middle of cen-

trum vertical.

(3) Intercentrum in mid-dorsal region larger and with ends enlarged forming

a capitular facet.

(4) Mid line of lower surface of lumbars with sharp, low keel.

(5) Size smaller. 1.2 to 1.6 meters.

Dimetrodon platycentrus sp. nov.

Type : A portion of the vertebral column, including part of axis and third cer-
vical, four posterior dorsals and two lumbars with fragments of long spines, and
fragments of amphibian bones. No. 4065 Am. Mus. Nat. Hist., Cope, coll. ; from
Deep river, Indian Territory.

Description :

(i) Spines similar to those of D. macrospondylus.

(2) Cervicals with axis through neural arch and middle centrum vertical.

(3) Intercentrum as in C. macrospondylus.

(4) Mid line of bottom of lumbar centra not keeled, but broad, flattened, and

rather rugose.

(5) Size almost that of C. macrospondylus.

This specimen is very close to C. macrospondylus in size and general
form, but the character of the bottom of the posterior dorsals and lumbars
is unmistakably different.

Dimetrodon obtusidens Cope.

Theropleura obtusidens Cope.

Proc. Am. Phil. Soc, vol. xix, 1880, p. 41.

Type: A mixed lot of bones containing many fragments. Several animals are
distinguishable from Pelycosaurian, Cotylosaurian, and Amphibian remains. The
parts described by Cope as typical are a mass of bones showing fragments of the two
lower jaws on one side and the badly crushed posterior portion of the skull on the
other, several vertebrse, two humeri, a femur, an imperfect scapula, and fragments of
spines. A third humerus in the lot is that of a Cotylosaurian, and there are numerous
indeterminate fragments of Amphibian bones. No. 4007 Am. Mus. Nat. Hist., Cope,
coll. ; from Texas.

Homeotype : There is no absolute certainty that the vertebrse and limb bones of
No. 4007 American Museum go together and with the fragments of the jaw, but Cope
considered and described them as so belonging and it seems probable that he was
correct. A second specimen. No. 4062 American Museum, labeled Theropleura by
Cope, and containing the basicranium and nearly complete vertebral column, has
vertebrse identical with No. 4007 American Museum. It is evident that Cope con-
sidered the two as the same, so the more perfect specimen is selected to complete
the description. No. 4062 Am. Mus. Nat. Hist., Cope, coll. ; from the mouth of Beaver
creek, a tributary of the Big Wichita river, Texas.

Original description of the type : "This species is represented by nearly all parts
of the skeleton, including jaws of both sides with teeth, numerous vertebrse, and

SYSTEMATIC REVISION OF THE SUBORDER. 55

bones of the limbs. Many of these pieces are preser\'ed in continuous masses, thus
greatly aiding in the identification of parts.

"Although the species is not larger than the Theropleiira retroversa^ the neural
arches are coossified with the centrum.

"The jaws are long and rather slender, and there is no such inequality in the
sizes of the maxillary teeth as in the genera Dimefrodon and Clepsydrops ; the canine
being scarcely larger than the others. The crowns are elliptical in section at the base,
with straight sides ; the sections of the crowns are lenticular, and the apices are not
very acute. The superficial coating is striate with fifteen or sixteen rather obtuse
ridges. The cutting edges are not very acute, nor are they denticulate. The number
of teeth in the dentarj' bone can not be precisely stated, but it is aboiit twenty-one.

" The mandibular articular face consists of two open parallel grooves, one shorter
than the other, extending obliquely to the long axis of the jaw. The palatal dentig-
erous bone is quite different from that of Dinietrodon. Its inferior face, instead of
being narrow, is rhombic. The ascending process arises from one of the terminal
angles of the rhomb, and the horizontal process continues from the opposite angle in
line with the inferior surface. The borders of the rhomb next to the ascending pro-
cess are dentigerous ; the one bears a single series of four large teeth ; and the adja-
cent angle and side bear numerous small teeth.

" The vertebrae have the elongated neural spines of the allied genera, and they are
simple. The centra have curved articular margins indicating the presence of inter-
centra, which are, however, not preserved. Traces of sutural articulation with the
neural arch remain. Many of the centra are much compressed and have a narrow,
sharp, median keel. In a few vertebrse, apparently from the posterior part of the col-
umn, an angular ridge extends posteriorly from the base of the diapophysis ; this is
apparent also on a caudal centrum. This point is characteristic of the T. relroversa,
but I do not find the large capitular facet of that species in the T. obtusidens. The
lateral ridges of the T. triangulcita are situated low dow-n on the centra. The diapo-
physes supporting the tubercular articulation are frequently elongate.

"The scapular and pelvic bones are of the usual type. The humeri belong to fonn
second of my Pal. Bull. No. 29. They have rather slender shafts, and much expanded
extremities. The proximal articular surface is well defined. The supracondylar
foramen and other points are as in the Pelycosaiiria generally. There were probably
distal condyles, but this is not absolutely certain."

Measiiremeyits,

m. m.

Length of mandibular series of teeth (nearly Length of another centrum on the same block -0.020

complete) on block o. 1 10 Diameters of humerus (separate) :

crown of mandibular tooth ooS Of head :

Antero-posterior diameter of mandibular tooth-- .004 Larger 065

Diameters of the articular extremities of a ver- Smaller 013

tebra on the same block : Of shaft 017

Vertical 021

Transverse 020

For description of the homeotype see the morphological description.

The spines and the character of the skull show that this animal was
far more advanced in development than the Poliosauridcv and was a true
member of the Clepsydropida;.

56

REVISION OF THE PELYCOSAURIA.

Revised description :

(i) Spines as in D. macrospoiidyliis^ but with very prominent and slender fore
and aft ridges at the base.

(2) Third to sixth cervicals with axis through neural arch and middle of cen-

trum vertical.

(3) Intercentrum of mid-dorsal and lumbar regions small and without promi-

nent terminal facets.

(4) Lumbars with keel on mid-line of centrum below.

(5) Size, small, i to 1.3 meters.

Dimetrodon navajovicus sp. nov.

Type : A well-preserved humerus in a large number of bones belonging to differ-
ent individuals under the general No. 2298 Am. Mus. Nat. Hist., Cope, coll., from
which are selected certain humeri, femora, and vertebrse for description. From El
Cabre, New Mexico.

Description :

(i) Spines unknown.

(2) Cervicals unknown.

(3) Intercentrum unknown.

(4) Character not shown.

(5) Size, small, i to 1.3 meters.

(6) Humerus with entepicond)-le
proportionately vev}- much longer than

/«= \ ^ ^^^^ \^ I in any other species of the genus. The

radial crest is separated from the proxi-
mal end by a considerable space.

Fig. 15. — Outline of the lower jaw of D. longiramus. No. 4091 Am. Mus. X Vi.

Fig. 16. — Outline of the scapula of the same. .<<'/, scapula, to, coracoid. /c, procoracoid. X Jj.

There is in the Cope collectiou a considerable quantity of material from
New Mexico, El Cabre and AiToyo de Agua, names that do not appear on
the maps. Among these, two Pelycosaurians are distingnishable, D. nava-
jovicus and Elcabrosatirus baldwini.

Tlie specimens consist of fragments only, and each, lot generally con-
tains the remains of several individuals. They were preserved by Cope in
small boxes and on the cover of one. No. 2299 Ameiican Museum, contain-
ing a characteristic humerus is written the name "navajovicus." I shall
adopt this name for the species, but another lot. No. 2298 American Mus-
eum, seemingly one individiral, and containing fragments from other parts
of the skeleton and in better state of preservation, is described as the type.

SYSTEMATIC REVISION OF THE SUBORDER.

57

Dimetrodon longiramus sp. nov. (Text figures 15 and 16.)

Cope. Name not published, but label found with a specimen.

Type: A lower jaw and scapulae with a few vertebrcC. No. 4091 Am. Mus. Nat.
Hist., Cope, coll.; from Texas.

Homeotype: No. 4136 Am. Mus. Nat. Hist., Cope, coll. A fragmeutaiy jaw,
from Texas.

Tlie name " longiramus" was found written by Cope on a label with the
fragmentary jaw, No. 4136. A closely similar jaw occurs witb a scapula
and a few vertebras labeled D. rectiformis. A lumbar vertebra, though evi-
dently belonging to Dimetrodon^ does not have the characters of the speci-
men regarded by Cope as D. rectiformis.

Description : The lower jaw is very long and slender and the posterior end resem-
bles that of D. incisiznis in form, but the upper and lower edges are not expanded as
in that species, so the jaw is not so high behind. The scapula is ver}- short and wide
compared with that of D. incisivus and the articular face for the humerus \-ery small.

FOREIGN FORM.
Ctenosaurus Koeneni v. Huene.

Geol. und Paleontolog. Abhdlg. Koken. N. F., Bd. vi,
Heft I, 1902, s. 38.

Type : A series of vertebrse with high spines
gradually widening distally; preser\'ed in a slab of
stone. From the upper part of the Buntersandstein,
east of Rheinhauseu near Gottingen. Preser\'ed in the
museum of the University of Gottingen.

Original description (adapted from a translation) :
"The specimens consist of several slabs carr>'ing a
poorly preserved series of vertebrae which have been
greatly compressed. One of these vertebrae with the
elongate spine attached measures 600 mm. in length.
The spines are so much compressed that the bases are
flat, though this may not have been the original condi-
tion ; the upper part of the spine is naturally flat and
the whole is bent and inclined to the rear. The verte-
brae are almost twice as long as high. The spine is
located over the middle of the neural arch, but the pos-
terior zygapophyses reach far back. v. Huene concludes that the animal is a last
survival of the family Clepsydropidcv which has persisted into the Trias.

"Derartige Wirbel weiss ich mit nichts besser zu vergleichen als mit den per-
mischen Clepsydropiden aus Texas und Bohmen. Der Umriss des Wirbelkorpers
erinnert am meisten an Naosauriis und Dimetrodon, der Bau des oberen Bogens an
diese und EmhoIopJwrits. Von diesen drien aber hat Dimetrodon die grosste Aehn-
lichkeit. Ob die Wirbelkorper ampicol sind wie bei den Clepsydropiden ist unmog-
licli zu erkennen. Audi die abnorm ausbilduug des Dornfortsatz ist bei Clepsydrop-
iden am ehesten zu erwarteu, ich brauche nur an Naosaurus und Dimetrodon zu
erinnern. Bei alledem halte ich es fiir mehr als wahrscheinlich, Clepsydropideii dass

Fig. \ 7. — Sketch of a slab showing ver-
tebrae of Ctenosaurus koeneni, from
the Middle Bunter near Gottingen.
X / s about. After v. Huene.

58 REVISION OF THE PELYCOSAURIA.

Ctenosaurus ein letzter Nachziigler der bisher nur aus dem Perm bekaniiten Familie
der Clepsydropiden ist. Ein solches Vorkommen ist zur Vervollstandigung der triassi-
schen Landfauna hochst interessant."

The position of the form is uncertain, occurring as it does, widely
removed, both geologically and geographically from other members of the
group. The evidence is very meager upon which to assert the persistence
of the suborder into a higher formation. It is probably a persistent member
of the Pelycosauria^ but may be a case of parallelism in some other group.
Subfamily NAOSAURINAE nov.

(i) Vertebral spines with lateral processes.

(2) Bottom line of anterior dorsal and posterior lumbars not greatly shortened.

(3) Cervicals smaller than anterior dorsals.

(4) Crest of ilium vertical and widely flared.

(5) Dorsal ribs with tuberculum reduced to a tuberosity on edge of rib.

Genus NAOSAURUS Cope.
Am. Nat., vol. xx, 1886, p. 544.
Am. Nat., vol. xii, 1878, p. 319.
Proc. Am. Phil. Soc, vol. xiv, 1878, p. 44.

Type: Naosaurus cruciger. A mixed lot of bones containing several imperfect
centra and several incomplete spines held in their natural position by the matrix.
No. 4003 Am. Mus. Nat. Hist, Cope, coll.; valley of the Little Wichita river, Texas.

Original description : The specimen was originally described as a species of
Dimetrodon in 1878 and 1880, see N. claviger. The original description of the
genus separating it from Dhnefrodon was as follows: "Spines not quite so elevated
as in the Dimetrodon incisivus ; but are more robust, and have transverse processes
or branches which resemble the yard-anns of a ship's mast."

Cope later described the skull of N. claviger as characteristic of the
genus Naosmiriis. He regarded it as at least veiy similar to that of Dime-
trodon^ for he remarks, '''' Naosaiints differs from Dimetrodon only in the
presence of transverse processes on the neural spines." The description
of the skull is given in the description of N. claviger below, but it is
a very curious fact that neither by I'elation of bones nor by any record
of number or label is there any considerable fragment of a skull unmistak-
abl}' connected with spines of Naosaurus^ either in the New York or the
Chicago collections. Two skulls are labeled by Cope as N. claviger and
N. cruciger^ but there is to-day no record of how he determined this rela-
tion. The skulls are so exactly like those of Dimetrodon and the vertebral
column varies so markedlj^ from that of Dimetrodon that the assignment of
these skulls to the genus seems at least worthy of resented judgment.
Should the skull of Naosaurus be shown to differ from that oi Dimetrodon,
the genus should be placed in a distinct family ; if the skulls are the same
the differences are hardly greater than those of very distinct genera.*

*Discoveries made during the summer of 1906, since this was written, seem to indicate that the skull of
Dimetrodon was totally different from that of Naosaurus. See the morphological description of A^aosaurus.

SYSTEMATIC REVISION OF THE SUBORDER. 59

Revised description :

(i) Large diastemal notch with few degenerate teeth or none. (?)

(2) Maxillar}' canine and incisor teeth greatly enlarged. (?)

(3) Teeth with crenate cutting edges. (?)

(4) Neural arch early coossified with centrum.

(5) Change in length of bottom line of vertebrae not marked.

(6) Anterior dorsals without keel or wide intercentral face. A process on

lateral edge of centrum marking position of capitulum of rib.

(7) Spines sharply recurved in posterior lumbar region so that the last long

spine overhangs the abruptly shortened spines of the sacrals and
caudals.
(9) Limb bones with well-marked articular faces.

(10) Humerus with well-developed entepicondyle and ectepicondylar process.

(11) Abdominal scutes present.

(12) Tail relatively short.

(13) Size, varying in different species. From 2 to 2.6 meters long.

Naosaurus clavlger Cope.

Am. Nat., vol. xx, 1886, p. 544.

Trans. Am. Phil. Soc, vol. xvi, 1888, pp. 287 and 293, plates 2 and 3.

Type: The type is doubtful as shown below. The original description was
made from a skull and vertebrae which are not connected to-day by reference or
number. I shall accept the series of vertebrae as the type specimen, as it is undoubt-
edly the series described by Cope, and the skull is now connected with it only by
inference.

1. A series of twenty-six vertebrae comprising a nearly complete vertebral
column to the first caudal, but not preserved in natural order and the spines imper-
fect; the pelvis and several ribs. No. 4002 Am. Mus. Nat. Hist., Cope, coll.; from
Coffee creek, a tributary- of the Big Wichita river, in Vernon count}', Texas.

2. The left half of a skull lacking the anterior end of the muzzle. (This skull
very possibly belongs with No. 4002.) No. 4036 Am. Mus. Nat. Hist., Cope, coll.;
from Texas.

Original description : This was furnished b)- a comparative table. See the
description of Naosaurus cruciger.

In 1888 Cope repeated this description of the genus in an account of
A^. claviger. He altered his analysis of the species of the genus somewhat,
as follows:

I. Neural spines distally cylindric :

Distal transverse processes represented by tuberosities A', cruciger.

II. Neural spines distally dilated and compressed :

Palatine teeth small, widely spaced N. clarnger.

Palatine teeth large, closely packed N. tnicrodus.

Revised description: See Naosaurus cruciger below.

As shown in the morphological description, the clavate distal end of
the spines is not a specific character, but a character of the cervical vertebrae
in all species.

6o REVISION OF THE PELYCOSAURIA.

Naosaurus cruciger Cope.

Dinu(rodon crttcigcy. Am. Nat., vol. xii, 1S78, p. 829.

Dimetrodon cruciger. Proc. Am. Phil. Soc, vol. xix, 1880, p. 44. Also Pal. Bull. 32.

Naosaurus cruciger. Am. Nat., vol. xx, 1886, p. 544.

Type: A mixed lot of bones containing several imperfect centra and several
incomplete spines preserved in natural position by the matrix. No. 4003 Am. Mus.
Nat. Hist., Cope, coll.; from the valley of the Little Wichita river, Texas.

The species was first regarded as a member of the genus Dimetrodon.

Original description : "In this species the spine sends off, a short distance above
the neural canal, a pair of opposite short branches, forming a cross. At various more
elevated positions there are given off tuberosities which alternate with each other.
They form on several consecutive spines oblique rows. The spines are broadly oval
in section, the long axis antero-posterior, and have a shallow groove on both the
anterior and posterior aspects. The centra are elongate as compared with their other
diameters, and are more compressed between the articular extremities, leaving a strong
inferior obtuse rib. Articular faces of zygapophyses oblique. Diapophyses short
and robust, with large costal faces, and standing below the prezygapophyses."

Mcasurcmoils.

7)1. m.

(Antero-posterior 0.043 Expanse of cruciform process 0.048
Vertical at end 02S

I Transverse at end 030

T^. . ■: ■ i. u f Antero-posterior. .030

Diameters of spine at base < ^ "^

(.Transverse 020

Elevation of posterior zygapophyses above cen- Diameters of spine at .090 m. / Antero-posterior. .016

trum 025

■{^

above base I Transverse 016

Elevationof cruciform process above centrum... .058 Length of several pieces of neural spines 140

Expanse of posterior zygapophyses 034

The description printed in 1880 is identical with the above.

In 1886 in a comparative table Cope established the name Naosaurus.

A full-sized individual is said to have the lowest yard-arm 260 mm.
wide and the whole spine a height of 500 mm., while the length of the
vertebral centrum is 60 mm. Naosaurus differs from Dimetrodon in the
transverse processes of the neural spines of the vertebrae. There are three
species which differ as follows :

Spines of vertebra2 cylindrical distally ; transverse processes replaced above by tuberosities... N. cruciger.
Spines of vertebrae expanded and compressed above. Palatine teeth large, forming a pave-
ment N. microdus (Edaf/iosaurus microdus Cope).

Palatine teeth much smaller and more widely placed N. claviger.

Revised description : The three species of A''(70jrrt//;v/-v are readily distinguished
by the character of the spines.

1. Spines with cross pieces above the first pair reduced to tuberosities N. cruciger.

2. Spines heavy and clumsy, with cross pieces commonly double and relatively long even to

the apex of the spine N. claviger.

3. Spines slender and elegant, cross pieces relatively long even to apex of spine -\'. microdus.

SYSTEMATIC REVISION OF THE SUBORDER. 6l

Naosaurus microdus Cope.

Edap/iosaurus microdus. Proc. Am. Phil. Soc, vol. xxii, 1884, p. 37.

Naosaurus microdus. Am. Nat., vol. xx, 1886, p. 544.

Naosaurus microdus. Trans. Am. Phil. Soc, vol. xvi, pp. 287 and 294.

Type: A number of fragmentary spines, a few vertebrse and two fragments of
the dentigerous plates of the pterj-goids. No. 4014 Am. Mus. Nat. Hist., Cope, coll.

Homeotype : A nearly perfect vertebral column from the third cervical to the
second or third caudal. The vertebrse were numbered as collected and are partly in
natural contact, so that their position is pretty certain, the spines are well preserved
and some ribs are present. No. 4060 Am. Mus. Nat. Hist., Cope, coll. ; from Beaver
creek. Big Wichita river, Texas. Collected by Jacob Boll in 1880.

lu tlie first description tlie animal was compared with Edaphosaiinis
pogonias.

Original description : " The grinding teeth of this species are about as numerous
as in the Edaphosaitrns pogonias., there being about seven in a transverse row on each
plate. They are, however, less closely placed than in the typical species and have
more conic crowns. They do not form a pavement, as they are separated by wider
interspaces.

"The centra are rather elongate and the foramen chordcc dorsalis is rather large.
No intercentra are preserved, and if present they must have been very small, as the
inferior rim of the centrum is not beveled to receive one. The neural spines have
transverse processes which begin near the base, and project at intervals from the sides-
The inferior ones are oval or subround in section ; those which succeed are more or
less compressed. Their extremities are enlarged fore and aft so as to be claviform in
outline, but are compressed except where they are thickened b}- lateral tuberosities.
These are rarely symmetrical, one being larger and situated high up, sometimes giv-
ing the apex an unsymmetrically bilobate fonn. Sometimes the}- project at right angles
to the terminal expansion. The shaft of the spine has a rather small medullary cavity,
and this issues by an open mouth at the apex without constriction. This peculiar
arrangement suggests a cartilaginous continuation of the spine which retains the nutri-
tive arterj' of the medullary cavity. The anterior face of the shaft is grooved from the
base for some distance upwards; the posterior face is plane and then rounded above."

Measureyncnls.

Diameters of inferior dental patch : m. Diameters of median dorsal : m.

Antero-post erior 0.043 Vertical :

Transverse 024 At end 0.032

Diameters of a posterior dorsal centrum : Behind arch .025

Antero-posterior 0335 Antero-posterior .0465

Vertical at end 027 Transverse:

Transverse at end 026 At end, at flare 037

middle 015 At middle 016

Measurements of piece of spine of same : Diameters of summit of spine :

Length 132 Antero-posterior 032

Diameters at base: Transverse 032

Antero-posterior 023

Transverse 019

In 1 886 the specimen was placed in tlie genus Naosaurus. See table
in description of A^. cruciger. In iSSS Cope published figures of the dental
plate of this species.

62 REVISION OF THE PELYCOSAURIA.

Revised description : See revised description of JV. cruciger.

N. microdus was first described by comparison witli Edaphosaiirus^ and
when the true position was recognized by Cope he attempted to retain the
character of the dentigerous pterygoid plate to distinguish it from N. clavi-
ger. The parts of the dentigerous plates of the two specimens were
fragmentary and are of little comparative value, as the teeth vary on the
pterygoid and palatine both in size and aiTangement. A comparison with
the preserved vertebras of the type, however, has made it evident that the
beautiful vertebral column of No. 4060 is the same species and permits a
more perfect description of the species.

FOREIGN FORM.
Naosaurus mirabilis Fritsch.
Fauna der Gaskohle, etc., vol. i, 1883, p. 29; vol. in, 1885, p. 121, fig. 309; vol. iv, p. 86, fig. 386.

Type: Vertebrse with imperfect spines. From Kuonova, Bohemia (pi. 28, fig. 2).

The specimen was first described as the anterior portion of the pectoral
fin of a fish. In the third volume, a figure of a vertebra was given and its
true position determined. In the fourth volt:me it is again figured and
described.

Original description: "* * * denn obzwar wit es niir mit einem fragment
zu thun haben, so hat der Domfortsatz doch mehr als die Zehufachs Hohe des Wirbel-
korpers. Der biconcave Wirbelkorper ist verdriicht und durch Druck und Bruck mn
45 Grad aus der Achse gedreht, wodurch sein Erkennen selir Erschwert wurde. Seine
lange betragt etwa 7 mm, der hohe 6 mm. Der Erhaltene Theil der neurapophyse ist
7 mm lang und da dies beim Vergleiche mit dem Amerikanischen exemplaren etwa
^ der Gesammtlange darstellt, so durft dieselbe 10 cm betragen haben.

" Die breite des Stammes betragt am Grunde 6 mm, am oberen Ende 4 mm.

"Von den unregelmassig entwickelten Seitendornen sind 5 Baar vorhanden iind
ihre L,ange varirt von 2-4 mm. Sie sind kurz koniscb, mit stumpfen Spitzen.

" An abgebrochenen Stellen sieht man dass der Dornfortsatz innerlich hohl war
denn er zeigt nur schwache Wande und der Innen raum ist mit eiuer weisen Masse
erfiillt.

"An der obern Halfte des Stammes verlauft eine erliabene Leiste, die etwa 1^
der breite desselben einnimmt, aber es ist schwer zu entscheiden, ob dies die vordere
oder hintere flache des Fortzatze war."

In 1895 Fritsch figured a vertebra and an incomplete spine of the same
species (plate 28, fig. 2). The only description accompanying the figure is
a statement of the length of the spine :

"Dieselben besitzen eine 13 fach lange des Wirbelkorpers und erreichen eine
lyange eines halben Meters."

The species is very close to if not identical with N. cruciger.

SYSTEMATIC REVISION OF THE SUBORDER. 63

INCERTAE SEDIS.

Bathygnathus borealis Leidy.

Jnl. Acad. Nat. Sc. Phila., (z) vol. 11, 1854, p. 327, plate 33.
Am. Jnl. Sc, (2) vol. xiv, 1855, p. 444.

Type : The left maxillary, incomplete above, but witli the alveolar edge preserved
from the maxillar}'-premaxillar>' suture to near the posterior end ; several teeth pre-
served entire. From the vicinity of New London, Prince Edward Island, Canada.
Preserved in the museum of the Philadelphia Academy of Science.

Leidy considered that the bone was the lower jaw instead of the upper;
this accounts for the name and for the terminology of his description.

Original description: " The specimen consists of the right dental bone consider-
ably broken, attached by its inner surface to a mass of matrix of red granular sand-
stone, with large, soft, angular, red chalk-like stones imbedded in it. The fossil has
seven large teeth protruding beyond the alveolar edge of the jaw ; and it is hard, brittle,
and cream-colored, and stands out in beautiful relief from its dark red matrix. The
jaw indicates a lacertian reptile, and in comparison with that of other known extinct
and recent genera is remarkable for its great depth in relation to its length.

"The depth of the dental bone below the contiguous pair of equal sized teeth
* * * is 4 inches, while its length in the perfect condition appears not to have
been more than 7^ inches; for in the specimen the middle part of the posterior
border is so thin and scale-like, that I am disposed to think it here came in contact
with the supra-angular and other neighboring bones.

" The outer side of the jaw is vertical and over the course of the alveolar parapet
is plane; but below this posteriorly and inferiorly above the base of the bone is
depressed into a moderately deep concavity. The upper or alveolar border forms a
convex line descending rapidly toward the chin. The base fonns an oblique line and
ascends anteriorly to the chin ; and it appears thick and rounded externally ; but on
the specimen it presents an abnipt border internally, as if the inner side of the bone
had been broken away, or as if the angular bone had articulated with it, much in
advance of the usual position in saurians.

" The external surface of the dental bone is everywhere marked by fine, reticular,
vascular grooves, and in the vicinity of the alveolar border it presents numerous
minute vasculo-neural foramina. There is no regular row of foramina visible in the
specimen, for the transmission of terminal branches of the inferior dental nerve, such
as exists in the Iguanas, Varanus, etc., but near the point of the chin there is a rela-
tively very large foramen, partially filled with matrix, which appears to correspond
with the internal mental foramen of the Iguana. [This is the nostril.] Just posterior
to this foramen there is a deep vascular groove, which in the perfect condition of the
specimen may have proceeded from another foramen.

"The teeth in their relation to the dental, are placed on the inner side, and rest
against the alveolar border, which rises in a parapet external to them. Whether the
parapet is supported between the teeth, as in Megalosaurus, I can not certainly
ascertain from the inner side of the jaw being so closely adherent to the matrix. The
dental bone is to be considered complete in its length in the specimen, is capable of
containing a series of 12 teeth posterior to and including that most anteriorly situated
in the fossil.

64 REVISION OF THE PELYCOSAURIA.

"As the teeth were worn away or broken off they were replaced by others pro-
duced at their inner side, as is indicated in the specimen by a young tooth, which is
situated internal to and is concealed by the largest mature tooth. The enameled
crowns of the fully protruded teeth are exserted at their base for several lines above
the alveolar border of the jaw. They are compressed, conical, and recurved, but com-
pared with those of Megalosaiirus they are not so broad, compressed, nor recurved,
and they are more convex externally and are less so internally. They resembled
much more in form those of the recent Monitor or/iatus, but are less convex internally.
The transverse section of the crowns of the teeth, except that of the first, is antero-
posteriorly elliptical, with the inner side less convex, and the extremities acute and
in most instances slightly incurved.

" The anterior and posterior acute margins of the crowns are minutely crenulated
and the crenulations commence just below the tip and descend as far as the enameled
base. In comparison with the teeth of Clepsysaitrus Pemtsylvaniciis^ those of the
fossil under examination are broader and more compressed, and except the first one
of the series, present an acute, crenulated margin anteriorly and posteriorly, whilst in
the fonner animal they are acute and creuulate only posteriorly. * * *

" From the extraordinarj' relative depth of the dental bone above described to its
length, and from its northern locality I have proposed for the carnivorous lacertian
to which it belonged the name Bathygnathits borealis.''^

The true position of this animal was recognized by v. Huene (103) and
independently by the author (34). It was either a large Dimetrodon or a
Naosaurus^ but it is impossible to say which. The Canadian geologists had
long recognized that the greater portion of eastern Nova Scotia and Prince
Edward Island was Permian and recorded the presence of the Triassic only
because of the presence of this animal, which was regarded by Leidy and
Cope as a Triassic Dinosaur. The recognition of its true position shows
that Triassic deposits do not occur in the region.

Tomicosaurus sp. Gen. nov. (Plate 27, figs. 8 and 9.)

Generic name on Cope's label.

Type : Six imperfect vertebrae and the anterior end of a lower jaw. No. 2212
Am. Mus. Nat. Hist., Cope, coll. ; from Texas.

The anterior end of the lower jaw is 35 mm. long and this appears to be about
one-half or one-third of the full length. The anterior end is swollen and there are
alveoli for three large teeth and one or two smaller ones. Posterior to the incisor
teeth are seven smaller teeth in sockets ; they are all recurved at the upper end and
are of about equal height. They are not crenate. The jaw is of small vertical height
and is rather thin. There is a deep groove on the inner side marking the position of
the splenial which is lost.

The vertebrae are crushed so that the form of the centra can not be made out.
Seen from above they show the peculiar character of v^ry wide expanse of both the
anterior and posterior zygapophyses, although the neural arch is not especially wide.
The neural spines seem to have been short. The length of nine vertebras is 42 mm.

It is impossible to locate this fonn. It may perhaps belong to the Bohsaiiridce,
but the general appearance indicates the Cotylosauria less than the Pelycosaiiria.

SYSTEMATIC REVISION OF THE SUBORDER.

65

Metamosaurus fossatus Cope (text-figures 18 and 19).
Proc. Am. Phil. Soc. vol. xvii, 1878, p. 516.

Type: Several vertebrae, one only perfect and showing characters. No. 401 1
Am. Mus. Nat. Hist., Cope, coll.; from Texas.

Original description : '■'■Char. Gen. — There are numerous vertebrse in the collec-
tion, from the median and anterior dorsal parts of the column, which differ from those
of Clcpsydrops and Epicordylits in their small antero-posterior diameter. That these
all belong to one species, or even one genus, is not probable, in view of the many
differences which they present. I select one of them whose characters are most
strongly marked, and designate it as above, without deciding, as yet, how many of
the others which agree with it in some respects, may hereafter be associated with it
as to species or genus.

"The centrum is a good deal shorter than wide, and like those of all the other
genera here described, is deeply biconcave. I have not yet ascertained whether it is
notochordal, owing to the state of the specimens. The diapophyses project just
,g ,g below the base of the neural arch, and are short and

with small tubercular facet. There is no capitular
facet. The facet for the intercentrum is excavated
at the anterior extremity of the base of the centrum
and is quite small. The neural canal is rather large.
The anterior zygapophyses have a peculiar form,
their articular faces being directed downwards and
outwards. This character, together with the form
of the centrum and intercentrum, distinguishes this
genus at once from those previously described.
,/o.,<„„. ia,e,ai "CZ/rtr. Specif.—'T\^^ posterior articular face is

1 a little deeper than wide, and has rather thick re-

"' curved margins. The sides are concave, and the

middle line below protuberant (in section), but not keeled. The intercentral fossa is
a transversely oval pit well defined all around, and not interrupting the contour of the
inferior margins of the articular faces.

Measttretnents.
Diameters of centrum: m. Diameters of centrum cont'd : m.

Antero-posterior 0.021 Vertical in front 0.024

Transverse behind 030 Width of intercentral fossa 010

Vertical behind 030 Expanse of posterior zygapophyses 025

" About the size of the Dimetrodon rediformis.''''

This vertebra is so far from unique in its general form and proportions
that it might be a posterior lumbar of two or three separate genera, but
the position of the anterior zygapophyses is unlike anything else in the
Permian collections. The vertebra is not crushed and the character of the
zygapophysial faces seems perfectly natural. There is no appearance of a
pathological condition.

Embolophorus fritillus Cope (plate 27, fig. 10).

Proc. Am. Phil. Soc, vol. xvii, 1878, p. 518.

Type : Two minute vertebrse in position aud complete with intercentrum and
ribs in position. No. 4010 Am. Mus. Nat. Hist, Cope, coll. ; from Texas.

F18 18— Vectebricol ll/e/amost

view No 401 I Am M

Fig 19 — Anienoi view of ihesa

66 REVISION OF THE PELYCOSAURIA.

Origitial description : " Generic character. The neural arch is coossified, and the
zygapophyses and diapophyses are well developed ; the latter not elongate, and
standing on the base of the neural arch. The centra are notochordal. The inter-
centra are narrowed and transversely extended. The ribs are two-headed ; the capit-
ulum is received into a fossa of the posterior border of the intercentrum in advance
of the vertebra which supports the diapophysis, to which the tuberculum is attached.

" Cfiar. spec. — Centra with circular section at all points, and contracted at the
middle. No carinae or grooves. The intercentra project beyond the edges of the
centra, giving the column the appearance of si:pporting annular ridges. Their lateral
angles extend upwards nearly to the base of the neural arch. The diapophyses are
short and are directed upwards and forwards ; their extremities are concave. The
zygapophyses are large and their articular faces nearly horizontal. The size of this
species is small, little exceeding that oi Bolosaurus striahts^

Measurements.

m. m.

Lengthof centrum with intercentrum attached-o. 0056 Expanse of the diapophyses 0.0080

Length of centrum 0040 heads of rib 0035

^. ^ , ^ (Vertical 0035 Elevation to summit of neural canal 0045

Diameters of centrum \ .-, ■ ^ ,

(Horizontal 0035

The original description is correct.

About the size of Lysorophus, the vertebrae are entirely different, lacking the
deep pit and carinae on the sides ; the articular faces are rounded out convexly, leaving
between them, when in position, a considerable space for the large intercentrum.
The neural arches are elongate antero-posteriorly and very low ; the spines are broken,
but were undoubtedly short. The articulation for the face of the rib on the inter-
centrum is peculiar. One side of the end is cut away leaving a step-like facet into
which the head of the rib fits. The ribs are double-headed with a strong tuberculum.

The position of this form is very uncertain ; it ma}' belong to the genus
Bolosaurus., of which the vertebrae are unknown, or it may be entirely new.
The two vertebrae described is the only specimen in the two collections.

Sphenacodon ferox Marsh.
Am. ]nl. Sc, vol. xv, 1878, p. 410.

Type : An imperfect lower jaw showing the anterior end. From El Cabre,
New Mexico. Preserved in the Museum of Yale University.

Original description : " The crowns (of the teeth) are much compressed, and have
sharp cutting edges, without crenulations. In the present species the carnivorous
teeth are crowded together, and the crowns are placed slightly oblique, and twisted.
The jaws were comparatively short and massive. The rami of the lower jaws were
apparently united by cartilage only, and the symphysis was short. The vertebrae are
deeply biconcave."

Measurements of the type of this species are as follows :

mm. mm.

Lengthof the dentary bone 150 Height above jaw of second lower tooth 15

Space occupied by the teeth 130 Depth of dentary bone at symphysis 26

Extent of four anterior caniniform teeth 25 Height of crown of compressed tooth 8

Extent of twenty compressed teeth 105 Transverse diameter 4

SYSTEMATIC REVISION OF THE SUBORDER. 67

A photograph of this specimen kindly sent me by Dr. Schuchert, the
Director of the Yale Musenm, shows that this is a typical Dimetrodon jaw.
The species is indeterminate. The other specimens described from the
same region by Marsh belong to the Diadectidcs and the Stegocephalia as
previously mentioned by Baur and Case.

Geosaurus (?) cynodus Gervais.

Zoologie et Paleontologie Centrales. Premifere Serie, Paris, 1867- '69, pp. 220-221, figs. 29, 30.

Type : The fragment of an upper jaw of the left side. From Moissey in France.
Preserved in the Museum of Besaufon.

This specimen was first described by Coquant (84) and later redescribed
and figured by Gervais.

Original description : "La piece est longue de 0.065 m. ; elle se compose d'un
fragment considerable du maxillaire gauche, portant une dent caniniforme suivie de
huit cuitres dents phis petites et decroissantes dont la premiere est a quelque distance
de celle qiu par sa grandeur et sa forme pent etre consid^r^e comnie une canine.
Les dents sont comprim^es, subcultri formes, tres-faiblement strides longitudinale-
ment, a bords anterieur et posterieur subtranchants, mais non denticul& en scie.

Cette de ces dents qui occupe la position
ant^rieure est aussi la plus grande et elle est
comparable a une canine, distante de la pre-
miere de celles qui suivent d'une longueur
de 0.0 10. Sa hauteur, audessus du bord du
maxillaire, est de 0.020, et sa longueur, a la
base, de 0.007. La plus grande des dents
qui la suivent n'a que o.oio de ftit. Les

Fig. 20.— Fragment of left maxillary of Giosaams dcntS plaCCCS aprCS Cclle-la VOUt en d^Crois-

cynodut. After Gervais. X }*. gj^^^. Q^ gg j-gj^j fort bieu coniptc de la

disposition des dents placees en arriere de la canine et de leur grandeur d^croissante
par I'iuspectiou de la contr^empreinte du meme morceau.

"On y voit, en avant de la canine, I'indice de quatre autres dents sub^gals entre
elles, dont la quatrieme, en comptant d'avant en arriere, est sensiblement ^cartee de
la canine elle-meme, corame Test d'ailleurs la premiere des dents de I'autre serie. Les
dents ^taient a pen pres, triangulaires a leur couronne, et leur forme ^tait assez peu
diSerente de celle des dents placees en arriere de la canine. Les quatres empreintes
de dents, celle de la canine et celles des huit dents qui suivent cette derniere, occupent
ensemble, une ligne courbe dont I'arc mesure 0.085."

The reference of the specimen to the Pelycosauria must remain very
doubtful until more of the animal is made known, but it is certain that it
has no relationship with the CrocodiHa, as pointed out by Baur and Case,
and that it resembles very closely the members of the family Poliosaurtdce.

Rliopalodon and Deuterosaurus.
These two genera have been assigned to various positions by different
authors, most placing them with the African forms, but Baur and Case (10)
and later v. Huene (103) placing them with the Pelycosauria. The imper-

68 REVISION OF THE PELYCOSAURIA.

fections of the specimens make it impossible to settle the matter and until
the discoveries of Amalitzky in northern Russia are published it seems
unprofitable to enter into a lengthy discussion. The crucial test of the con-
dition of the arches can not be applied because the region is not preserved
in either specimen. The points that have been cited by authors to show
their relations to the Pelycosauria; the enlarged maxillary and incisor teeth
with crenate edges ; the high facial region formed by the maxillary in
large part ; and the curved alveolar edge of the jaws, are all points that are
common to the Pelycosauria^ the ThcrocepJialia and the Theriodontia ; indeed,
the wide maxillary causing an elevation of the facial region is a necessary
accompaniment of the enlarged canines with their enormous roots.

Deuterosaurus has no enlarged external process on the pterygoid ;
Rhopalodon has such a process {vide v. Huene). The vertebrae of the two
are deeply amphicoelous but not perforate. Intercentra occur only in the
anterior portion of the vertebral column. They occur in connection with
Pareiasaunis^ which is found with Theriodont remains, Inostvanzevia annce
Amalitzky in the deposits of the North Dwina river ; Pareiasaurus^ even
the Pareias ail rides ^ are never found with the Pelycosauria.

All these points lead to the conclusion that they are nearer to the Theri-
odont than the Pelycosaurian stem. Von Huene's conclusion was that they
stood nearer to the Pelycosaurs than the Theriodonts, but were derived from
the beginning of the Pelycosaurian stem.

Family EDAPHOSAURIDAE Cope.

Proc. Am. Phil. Soc, vol. xx, 1882, p. 450. Also Pal. Bull. 35.
Proc. Am. Phil. Soc, vol. xx, 1883, p. 631. Also Pal. Bull. 36.

Type: The genus Edaphosaurus described below.

The family was first described as containing Pantylus and Edaphosaurus.

Original description: "The two genera may be placed in a separate family of the
Pelycosauria, to be called the Edaphosauridce. This family will be distinguished
from the Clepsydropidce by the presence of more than one series of teeth on parts of
the jaws."

In 1883 Cope added the structure of the temporal region to the descrip-
tion of the family.

'■'■Pariotichiis, Pantylus, and probably Ectocynodon must be referred to a special
family, the Pariotichidce, which has teeth like the Edaphosauridce, but differs in the
entire overroofing of the temporal fossae."

In 1888 (70) Cope listed the genus Edaphosaurus in the family Clepsy-
dropidcs^ abandoning the Edaphosauridcs.

SYSTEMATIC REVISION OF THE SUBORDER. 69

Revised description of the family: The structure of this family is so aberrant
that it can not be contrasted directly with the other families. So far as the characters
listed under serial numbers in the other families may be used they are as follows :

(i) Skull acuminate ; higher behind and becoming lower anteriorly.

(2) Tooth line straight.

(3) Neural spines (probably) low.

Aberrant Pelycosaurs, littoral or estuarine in habit; feeding upon moUusks and
crustaceans. Skull low, wide posteriorly and tapering to the anterior end. A large
superior temporal foramen and probably a smaller inferior one. Interparietal and
epiotic present. Incisor teeth approaching chisel-shape ; anterior maxillary teeth
broadly triangular and thin, with anterior and posterior cutting edges ; the posterior
maxillary teeth conical. Post-incisor teeth of the lower jaw all conical. On the
pterygoid and palatine and on the dentary large patches of stout crushing teeth.

Revised description of the genus : The serial numbers can not be used in the
description of the genus. As there is but a single genus and species in the family the
description of the family is characteristic of the smaller groups. See the morpho-
logical description.

Edaphosaurus pogonias Cope.

Proc. Am. Phil. Soc, vol. xx, 1882, p. 448. Also Pal. Bull. 35.
Trans. Am. Phil. Soc, vol. xvii, 1892, p. 15, plate 11, figs. 5 and 5a.

T\'pe : A nearly complete skull with the lower jaw of the left side and imperfect
axis. No. 4009 Am. Mus. Nat. Hist., Cope, coll.; from Texas.

Original description : '•'■Description of the genus. — Temporal fossse not over-
roofed; surfaces of cranial bones not sculptured. Mandibular and maxillar>' teeth
subequal. Posterior half of the mandibular ramus expanded inwards and supporting
numerous closely arranged teeth. Pterygoid, or perhaps an internal expansion of the
malar bones, supporting a dense body of teeth, corresponding to those of the lower
jaw. Teeth subconical.

" The single species of this genus in my possession shows the following characters
of systematic importance. An arch extends from the parietal plane posteriorly and
downwards to the external base of the quadrate. The specimen is not yet in a con-
dition to show how much of this is parietal, and how much squamosal or opisthotic.
The proximal half of the posterior part of this arch is a distinct element, perhaps a
transverse process of the supraoccipital. A distinct element connects the basioc-
cipital on each side of the quadrate. The articular extremity of the latter has a deep
antero-posterior concave emargination. There is a flat bone extending from it ante-
riorly which is apparently pter>-goid rather than quadrato-jugal. The tooth-bearing
portion terminates opposite the middle of the basisphenoid.

"The occipital condyle is undivided, and the basisphenoid presents the usual two
divaricating protuberances to the basioccipital.

'■'■Description of the species: The facial plate of the os maxillare is sub vertical, so
that the orbit is lateral. The latter is rather small. The malar bone is narrow, and
is continuous with the dentigerous bone of the palate. The latter has a thickened
posterior edge, which commences below the anterior part of the orbit, and extends
posteriorly to the middle of the basisphenoid. Thence the border turns forwards. Its
anterior edge is below the anterior border of the orbit, and the general form is a longi-

70

REVISION OF THE PELYCOSAURIA.

tudinal oval. The maxillary teeth are somewhat weathered and obscured by a thin
layer of matrix. The posterior ones are compressed conic ; the premaxillaries are four
in number on one side, and are more nearly conic, and have incur\'ed apices. The
median premaxillary suture is, however, not clearly defined, so that the number of pre-
maxillaries remains uncertain. The center of the probable nostril measures one-third
the distance from the premaxillar}^ border to the anterior edge of the orbit. There are
eight rows of (?) pterygoid teeth at the posterior fourth of the series. The teeth are
subequal and obtuse, increasing a little anteriorly.

"The mandibular ramus is robust, and the external face slopes inwardly and down-
wards. The external border rises a little above a few of the posterior teeth, but it is
injured at the posterior of the coronoid process, so that its existence can not be ascer-'
tained. The border then descends and turns inwards to the articulation, which is
condyloid at its internal extremity. The inferior edge of the anterior part of the
ramus becomes a median ridge below the condyloid region, and terminates in a short,
compressed angular process. The symphysis is not coossified, and is convex down-
wards and forwards. The inferior part is subhorizontal, and forms the edge of a
transverse plate which is separated from the vertical part of the ramus by a deep
groove. The inner vertical face of the ramus is strongly convex, as is the corre-
sponding edge of the symphysial suture. The apices of the teeth are worn, but they
were probably conic, the posterior gradually smaller and more obtuse. The interior
face of packed teeth begins at the posterior two-fifths of the external series, and
expands inwards posteriorly. It contains six longitudinal rows opposite the ante-
penultimate dentary tooth.

"All the bony surfaces are smooth.

Measurements.

m. m.

Length of mandibular ramus (straight) 0.162 Width of extremity of o. quadratum 0.024

symphysis of ramus (straight) 038 occipital condyle 018

external dental series 077 Length of superior dental pavement 065

Width of ramus at dental pavement 040 Width o£ basisphenoid posteriorly 029

skull at ends of 00. quadrata 138

"The supposed axis vertebra is longer than wide, and the centrum is deeply exca-
vated posteriorly. Anteriorly it appears to have lost a piece — the centrum of the
atlas — which, while fitting it closely, was not coossified with it. There is a flat hori-
zontal convex ala in the place of a diapophysis, and an obtuse median hypapophysial
angle. The neural spine is compressed, except posteriorly, where it is transversely
expanded, tenninating above in a short obtusely acuminate apex. From this apex
an obtuse rib passes down the median Hue, and disappears above the neural arch,
where the spine is somewhat narrower. The postzygapophyses are well developed
and look downward."

Measurements of axis.

m. m.

Length of centrum below 0.020 Elevation of spine from postzygapophysis 0.038

Width, including diapophyses 035 Width of spine, posteriorly 020

In 1892 Cope gave a sTiort synopsis of the characters of the skull :

"In Edaphosauriis Cope, the skull is of a more depressed type than in the pre-
ceding genera. The postorbital is mainly preserved, and it is in contact with the
frontal (postfrontal) proximally, and sends out no bar posteriorly. There was appar-

SYSTEMATIC REVISION OF THE SUBORDER. 7 1

ently no supratemporal foramen, but a large infratemporal, which extends well upwards.
There is no parieto-quadrate arch. An element, perhaps supraoccipital, tenninates
in a free appressed apex on each side of the median posterior region. This may be
homologous with the small free bone described in Naosaiirus in nearly the same
position. The stapes is ver}' large, and is at least partially perforated near the
expanded proximal extremity. It is probably fully perforated as I have described it
in the Diopeus lepiocepkaliis."

Edaphosaurus mlcrodus Cope.

Proc. Am. Phil. Soc, vol. xxii, 18S4, p. 37. Also Pal. Bull. 39.

This is a synonym of Naosaurus microdus Cope, which see.

Table I. — Showing the Characters of the Suborder Pelycosauria.
Characters common to the primitive reptiles.

1. Vertebrae notochordal.

2. Intercentra present.

3. Interclavicle, claWcle and cleithrum present.

4. Entepicondylar foramen present.

5. Pelvis narrow.

6. Five elements in the distal row of the tarsus.

Characters common to the Diafsida.

1. Two lateral temporal fenestras.

2. Squamosal and prosquamosal separate, not closely united with the quadrate.

3. Opisthotic closely united with the exoccipital, but the suture distinct in some specimens.

4. Prevomers large and the vomers reduced.

5. Cranium short and the facial region elongate.

6. Axis with large free intercentra and neural arches.

7. Phalangeal formulae, probably, 2, 3, 4, 5, 3, in the pes and 2, 3, 4, 5, 4, in the manus.

Characters distinctive of the Pelycosauria.

1. Typical forms terrestrial.

2. Skull becoming laterally compressed and elevated in the facial region.

3. Anterior teeth, incisors and canines, becoming elongate and tusk-like, with sharp cutting edges, sometimes

even crenate.

4. Development of a toothless diastema.

5. External process of the pterygoid becoming very heavy and prominent.

6. Carpus and tarsus reaching a high stage of development. The individual bones well formed and closely

interlocking without a great deal of cartilage.

7. The bones of the pelvis united into a strong basin.

8. Tail becoming short and the spines becoming enormously elongated in the most specialized forms.

Table II. — Contrasting the Families of the Pelycosauria.

I. Poliosauridcs.

1. Skull low and acuminate (Proterosaurian).

2. Tooth line of the maxillary straight or nearly so. Diastemal notch absent or poorly developed.

3. Neural spines short.

4. Sacrum with two vertebrae.

II. ClefsydrofidcE.

1. Skull laterally compressed and the facial region elevated.

2. Tooth line of skull convex. Diastemal notch present.

3. Neural spines very high.

4. Sacrum with three vertebrae.

-2 REVISION OF THE PELYCOSAURIA.

Table II.— Contrasting the Families of the Pelycosaubi a— Continued.
II. Clepsydrofidcc — Continued.
Subfamilies.

I. Clepsydropi'niE.

t. Vertebral spines simple.

2. The bottom line of the anterior dorsal and posterior lumbar vertebrae greatly shortened.

3. Cervicals larger than anterior dorsals.

4. Crest of the ilium prolonged to the rear.

5. Dorsal ribs with tuberculum attached to prominent transverse process.
II. Naosaurincc.

1. Vertebral spines with lateral processes.

2. Bottom line of anterior and posterior dorsal and posterior lumbar vertebrae not greatly shortened.

3. Cervicals smaller than anterior dorsal.

4. Crest of the ilium vertical and expanded.

5. Dorsal vertebrae with tuberculum reduced to a tuberosity on the edge of the rib.
III. Edafhosauridce. (Possibly founded on a skull of Naosanrus.)

1. Skull acuminate, flat. Higher posteriorly.

2. Tooth line straight.

3. Neural spines (probably) low.

4. Character not shown.

Table III. — Contrasting the Characters of the Genera of the Poliosaurid.e.
I. Poliosaurus.

1. No diastemal notch between maxillary and premaxillary. The series of teeth uninterrupted.

2. No well-defined canine in the maxillary ; several maxillary teeth in the anterior third larger than the

others. Incisor teeth enlarged.

3. Teeth with faint anterior and posterior cutting edges ; not crenate.

4. Neural arches of the vertebrae free from the centrum through life.

5. Only slight difference in the length of the bottom line of the vertebrae in different parts of the column.

6. Anterior dorsals with wide face for the intercentrum on the lower edge of the anterior face of the centrum;

without sharp and deep median keel. Posterior lumbars not greatly shortened and without wide exten-
sion of the inferior edges of the faces of the centra.

7. Neural spines short.

8. Spine of the axis low and broad.

g. Limb bones without well-developed articular faces.

10. Character not shown.

11. Abdominal scutes present.

12. Tail long.

13. A small, probably aquatic animal, not exceeding 700 mm. in length.

II. Varanosaurus. (Ribs with rudimentary capitulum.)

1. No diastemal notch between maxillary and premaxillary.

2. Two enlarged canines in maxillary. Incisor teeth enlarged.

3. Character not shown.

4. Neural arch of vertebrae coossified with centra in adult.

5. Only a slight difference in the length of the bottom line of the vertebrae in different parts of the column.

Anterior dorsals with wide face on the anterior edge for the intercentrum.

6. Character not shown.

7. Spines short.

8. Spine of the axis low and broad.

9. Limb bones without well-developed articular faces.

10. Character not shown.

11. Abdominal scutes present.

12. Tail long.

13. 600 to 800 mm. long.

SYSTEMATIC REVISION OF THE SUBORDER. 73

Table III. — Contrasting the Characters of the Genera of the Poliosaurid.* — Continued.

III. Therofleura.

1. No well-defined diastema! space ; a faint notch between the maxillary and premaxillary, filled with teeth.

2. A single well-defined canine ; incisor teeth enlarged.

3. Section of tooth at base quadrate. Other characters not shown.

4. Neural arch coossified with the centrum in the adult.

5. No great difference in the length of the bottom line of the centra in different parts of the column ; but "as

deep as long if measured at the center" (Cope). Posterior lumbars not greatly shortened and without
wide face for intercentrum.

6. Anterior dorsals without wide face on the lower part of the anterior face of the centrum for the inter-

centrum ; without median keel.

7. Character not shown.

8. Spine of the axis not elevated ; broadened at the top.

9. Limb bones without well-developed articular faces.

10. Character not shown.

11. Abdominal scales or scutes absent (?). Not observed.

12. Tail long.

13. Elongate slender body, probably from 2 to 2.5 meters in length.

IV. Elcabrosaurus.

1. Character not shown.

2. Character not shown.

3. Character not shown.

4. Neural arch coossified with centrum.

5. Posterior lumbars very much shortened and with wide facets on the lower half of the articular faces of the

centrum.

6. No wide intercentral face on the anterior face of the centrum in the anterior dorsals.

7. Character not shown.

8. Spine of the axis elevated and strong.

9. Character not shown.

10. Character not shown.

11. Character not shown.

12. Character not shown.

13. Small, not exceeding i meter.

Table IV. — Contrasting the Characters of the Genera of the American Clepsydropid^e.

Cle^sydrofina.

I. Clefsydro-ps.

*i. Diastema! notch present, but small and filled with teeth of small size.

2. Canine and incisors enlarged.

3. Teeth with fore and aft cutting edges ; not crenate in all forms.

4. Neural arches free in the young ; coossified in the adult.

5. Vertebrae with changing length of the bottom line in different parts of the column ( ?).

6. Anterior dorsals with the intercentral face on the anterior face of the centrum and with sharp

keel.

7. Spines long, but probably nowhere near so elongate as in the genus Dimetrodon.

8. Character not shown.

9. Limb bones with well-developed articular condyles.

10. Humerus without prominent entepicondyle or ectepicondylar notch.

11. Abdominal scutes absent. (Not observed.)

12. Tail very long and slender.

13. From I to 1.3 meters long.

*The serial numbers are the same as those used for the genera of the other families so that the forms
may be contrasted directly.

74 REVISION OF THE PELYCOSAURIA.

Table IV. — Contrasting the Characters of the Genera of the American Clepsydropid.^ — Continued.

CUfsydrofinee — Continued.

II. Dimetrodon.

1. Large diastema! notch with few degenerate teeth or none.

2. Canine and incisors greatly enlarged.

3. Teeth with crenate cutting edges.

4. Neural arch very early coossified with the centrum.

5. Very marked change in the length of the bottom line of the centrum in different parts of the ver-

tebral column. Posterior lumbars shortened, but without wide faces on the lower edge of the
anterior face of the centrum.

6. Anterior dorsals with a sharp median keel and wide intercentral face on the lower edge of the

anterior face of the centrum.

7. Spines sharply recurved in posterior lumbar and sacral regions.

8. Spine of the axis high and broad, reaching forward over the axis,
g. Limb bones with well-marked articular surfaces.

10. Humerus with well-developed entepicondyle and ectepicondylar process sheltering an ectepicon-

dylar notch.

11. Abdominal ribs absent. (Not observed.)

12. Tail short and stumpy.

13. Size varying in the different species ; from about 1.2 to about 3 meters.

NaosaurinCE.

III. Naosaurus.

1. Large diastemal notch with few degenerate teeth or none. (?)

2. Canine and incisors greatly enlarged. (?)

3. Teeth with crenate cutting edges. (?)

4. Neural arch early coossified with centrum.

5. Change in length of the bottom line of the centrum in different parts of the column not marked.

6. Anterior dorsals without median keel or wide intercentral face. A process on the lateral edge

of the centrum marking the position of the capitulum of the rib.

7. Spines sharply recurved in the posterior lumbars so that the last long spine overhangs the

abruptly shortened spines of the sacrals and caudals.

8. Character not shown.

9. Limb bones with the articular face well marked.

10. Humerus with well-developed entepicondyle and ectepicondylar process sheltering an ectepicon-

dylar notch.

11. Abdominal scutes present.

12. Tail short and stumpy.

13. Size varying in different species. From 2 to 2.5 meters.

Table V. — Contrasting the Characters of the Different Species of the Genus Dimetrodon.

D. ffi^as.

1. Spines quadrangular, nearly square at base; changing to rounded above. Large, the surface not striate.

2. Third to the sixth cervical vertebrae with the axis through neural arch and the middle of the centrum ver-

tical.

3. Intercentra small in the mid-dorsal region ; without terminal facet for the capitulum of the rib.

4. Character not shown.

5. Size, largest of the genus. From 2.5 to 3 meters in length.

D. ffiganhomog^enes.

1. Spines broad transversely at base; becoming 00 -shaped above. A tendency for the ends of the spine

to become tuberculate.

2. The third to the sixth cervical vertebrae with the axis through the neural spine and the middle of the cen-

trum vertical.

3. Intercentrum in the mid-dorsal and lumbar regions small and without terminal facets for the capitulum

of the rib.

4. Character not shown.

5. Size nearly as great as that of D. gi^as, 2.6 meters at least.

SYSTEMATIC REVISION OF THE SUBORDER. 75

Table V. — Contrasting the Characters of the Different Species of the Genus Dimetrodon — Cont'd.

D. indsivus.

1. Spines laterally flattened at bottom, changing to rounded above ; finely striate.

2. Third to sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum

nearly vertical.

3. Intercentrum small in the mid-dorsal and lumbar regions ; without capitular facets at the end.

4. Lumbars with distinct keel.

5. Size medium. From 1.6 to 2 meters.

D. doUoi'iamcs.

1. Spines square at base, rounded above ; smooth.

2. Third to sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum

inclined strongly forward.

3. Intercentra in the mid-dorsal and lumbar regions small and without terminal facets for the capitulum of

the ribs.

4. Lumbars with low, sharp keel on the mid-line of centrum below, this keel divided by a shallow, longitu-

dinal groove.

5. Size that of D. incishnis. 2 to 2.6 meters.

D. macrosfondybis.

1. Spines rectangular, oblong below, changing to rounded above ; not striate, smooth.

2. Third to sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum

vertical.

3. Intercentra of the mid-dorsal and lumbar regions larger and with the ends enlarged to carry a facet for the

capitulum of the rib.

4. Mid-line of the lumbars with a sharp longitudinal keel.

5. Size smaller. 1.2 to 1.6 meters.

D. flatyce7Jtrits.

1. Spines similar to those of D. macrosfondylus .

2. Third to sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum

vertical.

3. Intercentra as D. macrosfondylus.

4. Mid-line of the lower surface of the centra of the lumbar vertebrae not keeled, but broad, flattened, and

rather rugose.

5. Size almost that of D. macrosfondyhis.

D. ohtiisidens.

1. Spines as in D. macrospondylus, but with very prominent and slender fore and aft ridges at the base.

2. Third to the sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum

vertical.

3. Intercentra of the mid-dorsal and lumbar regions small and without terminal facets for the capitulum of

the rib.

4. Lumbars with keel on the mid-line of centrum below.

5. Size, small, i to 1.3 meters.

D. navajoincus.

Most of the characters given above not recognizable. Size small, i to 1.3 meters.

Humerus with entepicondyle proportionately very much longer than in any other species of the genus. The
radial crest is separated from the proximal end by a considerable space.

D. lotigiramiis.
New species indicated by the slender proportions of the jaw and small articular face for the head of the
humerus in the scapula.

Table VI. — Contrasting the Characters of the Species of the Genus Naosaurus.
N. critciger.
Spines with the cross pieces above the first pair reduced to tuberosities.

N. claviger.
Spines heavy and clumsy, with cross pieces commonly double and relatively long even to the apex of the spine.

N. microdus.
Spines slender and elegant, cross pieces relatively long even to the apex of the spine.

MORPHOLOGICAL REVISION OF THE SUBORDER.

Family POLIOSAURIDAE Case (seep. i8).*

Genus POLIOSAURUS Case (see p. i8).

The discussion of the genus is contained in that of the single species.
Pollosaurus unlformls Cope (see p. 19).

Characteristic specimen, No. 1148, the type (plate i, figs. 1-8).

The original characters used by Cope have proven to be of little value, but the
ones listed in the redescription of the genus show that the animal occupied a most
important position in the order. As already shown by the author (29) Poliosaiirus is
probably the most primitive member of the group ; the nearest to the ancestral form.

Only the preorbital portion of the skull is preserved and it is so badly crushed
that its original form is not easily made out, but the nasals and frontals are broad
showing that the top was flattened acuminate. The orbits were large and lateral, and
the nares small and anterior in position. Cope described large teeth in the premax-
illary and in the anterior end of the dentary. The only evidence of them is a single
large, detached tooth which looks as if it had belonged in the anterior end of the
lower jaw. Cope also describes a diastema between the maxillary and premaxillary ;
of this there is no trace. From the anterior end of the series the teeth gradually
increase in size until near the middle and then as gradually decrease. The largest
are three times the size of those at the anterior and posterior ends.

The vertebrae regarded by Cope as belonging to the genus Poliosaiirus are all
characteristically shortened antero-posteriorly, so that the centra are nearly as wide as
long ; the articular faces of the centra are reverted on the sides and the arches are free
from the centra. The shape of the articular face on the centrum for the neural arch
slants gradually to the rear, growing deeper, and then rises almost vertically (see
plate I, figs. 6, 9, 11), leaving a deep triangular pit. The two faces are divided by
the neural canal which is much deeper in the middle than at either end, so that it is
also a deep triangular pit. Cope evidently used this character of a free neural arch
and the shape of the articular faces as decisive characters in determining the speci-
mens labeled by him, but they are indetenninate, as in young specimens of the genera
Dimetrodon and Clepsydrops the neural arch is frequently free, especially in the
caudals, and their articular faces have the same characters as in Poliosaiirus.

There are seven vertebrae in connected series and six more unattached, but evi-
dently belonging next to those preserved.

The atlas is illy preserved so that its form can not be made out; the neural arches
were free and have been lost. It is evident that the form of the atlas was much as in
Dimetrodon (see plate 16, figs. 5, 6). The remnants of an atlantal rib cling to the
sides of the centrum.

The axis is rather elongate, nearly twice as long as the atlas. The centrum has
no keel, but there is a sharp, slender ridge along the mid-line of the lower surface.
The anterior and posterior articular faces are only slightly reverted on the sides of the
centrum. The spine is short, elongate antero-posteriorly and proportionately very
heavy. The posterior zygapophyses are large, the anterior ones are very small,

*Page references after names refer to Systematic Revision. 77

78 REVISION OF THE PELYCOSAURIA.

but well formed. Between the lower edges of the axis and atlas is a small fragment
of bone that is probably the remains of an intercentrum. It is the only fragment of
an intercentrum preserved, though interceutra were present in all parts of the column.
In the vertebra posterior to the axis the bottom line becomes shortened and then
elongate again as in the ClepsydropidcB, but the change is very much less than in
that family. In the first seven vertebrse as the centrum becomes shorter the anterior
face is more and more reverted on the under surface, and the bottom line shows a
tendency to develop a low, rounded keel, but this never passes the incipient stage. In
the original description mention is made of " the narrow reflected portion of the
anterior border for the capitular facet," but there is no distinct facet and it is prob-
able that, as in the Clepsydropidce, the head of the rib articulated with the intercen-
trum in the anterior portion of the vertebral column. The spines of all are short and
broad antero-posteriorly ; the zygapophyses are well developed with nearly horizontal
faces. (In all of the first seven vertebrse the spines and neural arches have been
crushed down upon the centra, considerably reducing their apparent height.) The
transverse processes are inclined to the rear.

Ribs were present on all of the vertebrse. One belonging to the fourth or fifth
vertebra is nearly complete ; the capitulum and tuberculum are widely separated and
the distal end is widened.

The separate vertebrse are longer than the anterior seven, and the anterior artic-
ular face is not so much reflected on to the lower surface. Several show distinct facets
on the edge of the centrum for the head of the rib. To three or four of the posterior
vertebrse are attached masses of elongate, rod-like dermal scutes which probably cov-
ered the abdomen (plate i, fig. 7).

The single perfect limb bone preserved, a radius or fibula, shows that the ends
were devoid of well-developed articular surfaces. A single phalange is short and
stout.

Measurements.

mm. mm.

Length of skull from middle of orbit to anterior Length bottom line of :

end 140 8th vertebra 9

Length bottom line of : gth 10

Axis 15 loth 10

3d vertebra 13 nth 12

4th 12 12 th 12

5th 10 13th 13

6th 9 Length of rib, incomplete, attached to fourth or

7th 8 fifth vertebra 172

The animal with its long, low, acuminate head, straight tooth line, lack of
enlarged incisors, and limbs without condyles approaches in a general way to the
Proferosauria, but the larger teeth in the middle of the series, the method of their
implantation, the shape of the ilium, and the character of the vertebrae, all point in
the direction of the more specialized Pelycosaiiria. It is probably very close to the
ancestral form of the Pelycosauria, but is itself so far specialized as to preclude the
hope that in the Pelycosauria will be found any approach to the inception of the
reptilian stem.

There are in the American Museum of Natural History and the Uni-
versity of Chicago collections vertebrse that indicate the possible presence
of a larger species of Poliosaunis^ but they are too few and indeterminate
to warrant a description (plate i, figs. 19-12).

MORPHOLOGICAL REVISION OF THE SUBORDER. 79

Genus VARANOSAURUS Broili (seep. 20).
Varanosaurus acutirostris Broili. ( Paleontographica, Bd. Li, plates 10-12. This volume, plate 2.)

The description here given is a translation and condensation of the
original description by Broili of the single known specimen.

The form of the skull is an elongate triangle. The facial region is slender and
the edge of the skull roof is carried out over the side of the face anterior to orbits in
a sort of shelf Posterior to the orbits the parietal and superoccipital bend sharply
downward, forming an abrupt termination to the skull ; the parietals extend back-
ward somewhat in the median line and the posterior angles of the skull are rather
prominent, so that the region has a W-like profile.

The orbits are large and nearly circular. They lie in the posterior half of the
skull. The anterior nares lie near the anterior end of the snout and look directly
outwards. The parietal foramen is of good size and lies about opposite the posterior
end of the orbits.

The skull is marked by an obscure sculpture, on some bones, of fine punctse,
grooves, and ridges.

The premaxillaries send prominent processes backwards to unite with the nasals.
The prefrontals and lachr>-mals form a prominent ridge on the side of the face from
the upper anterior angle of the orbit.

The temporal region is unfortunately incomplete, the posterior and lower por-
tion being broken away. It shows the presence of one large opening separated by a
slender bridge from the orbit.

On the lower side of the skull the basisphenoid develops two strong lateral
processes which extend forward inclosing a triangular space. These processes pass
anteriorly into the pterygoids.

The inner branches of the pterygoids inclose a vacuity and are expanded into
thin plates; they are covered by a patch of small teeth. The otiter processes are
slender and pressed down on the basisphenoid, somewhat out of their natural position.

The columella (epipter^'goid) is perfectly preserved on one side and occupies the
usual position between pterj'goid and parietal.

The dentition is very characteristic. There are fift>'-four counted teeth in the
upper jaw, of which there are nine in the premaxillary, the anterior four being in the
position of incisors in the overhanging snout. The teeth are small, sharply conical in
form, of nearly equal diameter and large pulp cavity. In the first fourth of the max-
illary series are two teeth notably larger than the others, the posterior is the larger.
Between the large maxillary teeth and the large incisors the teeth are smaller.

The dentition of the lower jaw is unknown.

VertebrcE : There are thirty -six vertebrae preserved, of which twelve are con-
nected with the skull in direct series, three separate groups of three, six, and five,
with the two sacrals and eight caudals.

The atlas is unfortunately not made out.

The axis has an enlarged neural spine and a strong diapophysis directed back-
wards and outwards. The iutercentrum between axis and atlas is described as absent.

The remaining vertebras are smooth with concave sides and, especially in the
caudal region, have well-developed keels on the inner side of the centrum. They are
deeply amphicoelous (notochordal).

The neural arches are slender from side to side and have relatively large anterior
and posterior zygapophyses with horizontal articular faces. The neural spines are

8o REVISION OF THE PELYCOSAURIA.

slender and thin and are not elevated; on the side of the neural spines of the mid-
dorsals are paired rugose tuberosities, " knotchenartige Anschwellungen," which
Dr. Broili in correspondence likens to the process on the spines of Naosaiiriis. The
diapophyses occur on all vertebrae ; the outer end is about level with the upper end of
the intercentra. Intercentra occur between all vertebrae posterior to the axis ; they
are very strong and the lower surface is broad and smooth, presenting a marked con-
trast to the keels of the adjacent centra.

The sacral vertebrae resemble the nearest presacrals; the diapophyses are united
to the sacral ribs without suture.

The caiidah bear chevron bones, but none are preserved in sufficient perfection
to warrant description, though it seems probable that they lie with their anterior bor-
der on the lateral and lower edges of the posterior border of the preceding vertebrae
rather than to originate from intercentra.

^he^ presacral ribs were originally described as single-headed, but in response to
a request Dr. Broili has most kindly reexamined his specimen of I 'araiiosaiinis and
writes as follows : " Unter der Praezygapophyse entspringt eine ungemein kraftige —
dornahnliche — Diapophyse, welche (bei besonders guter Erhaltung) nach iinteii in
eine schmale, schwache Lamelle auslciKft.

" Der Rippenkopf, der nur in einem einzigen Stiicke gut zu erkennen ist, ist
demgemass ziemlich langsgestreckt. (Vergleisch S. 74 u. 75. [No. 14 in bibliog-
raphy.])

" Da, wie Sie sagen, die Ihnen bekanten Pelycosaurier, alle zweikopfige Rippen
besitzen, so entspricht viellicht die Leiste unter Diapophyse von Varanosaurus einem
nun mehr rudimentdren Capititlum der Rippe.

"Diese Leiste sowie auch die Rippe sind nur in einem Falle erhalten. (Fur die
Rippen bitte ich Tafel X, Fig. 2, hinter dem Buchstaben J. zu vergleichen.)

" Est diirfte daher die stellung von Varanosaurus unter den Pelycosaurier kin-
swegs deshalb eine so isolierte sein."

This seems to show that the capitulum, though small, is present and the ribs are
truly double-headed. The anterior of the two sacral ribs has a broad, shovel-like dis-
tal end, the second is inclined forward with its distal end underlying the first.

The shoulder girdle is too poorly preserved to show characters of value.

The pelvic girdle: The bones of the pelvis are closely united, the sutures are
closed. The shape of the pelvis is surprisingly like that of Dimetrodon.

The humerus is broken so that the two ends can not be placed together, but the
form was evidently close to that of Labidosaurus. The proximal half is proportion-
ately small, but the articular face is broad. There is a prominent deltoid crest. The
lower end shows a well-developed entepicondyle (die innere (Partie) sehr flach in
einem lappenformigen Fortsatz auslauft).

The. femur is represented by the distal and proximal ends, but the middle por-
tion is wanting, so that the true length can not be given. The proximal end has no
true head, but has a rough articular area which gradually contracts toward the other
side. The anterior face of the proximal end is deeply concave and there is a promi-
nent trochanter. The distal end is divided by a deep cleft into two parts, both bear
articular faces. The inner part is directed forwards and down for the tibia, the outer
part has two faces, one directed forwards and downwards for the fibula and the back-
wards and upwards for the tibia. The tibia and fbula are slender and elongate.

The calcaneus is flat, five-sided, and unites with the fibula -and astragalus. The
astragalus is more irregular in form than the calcaneus, but stronger and larger. The

MORPHOLOGICAL REVISION OF THE SUBORDER. 8l

remnants of the first and second digits show that the foot was fairly long with well-
developed digits and claws.

Dermal ossifications : Two or three fragments of dermal ossification remain to
show that the lower surface of the body was protected b}' slender, elongate rods of
bone. The only fragments preserved cling to the lower surface of the vertebral col-
umn and the lower surface of the humerus.

li/easu rements.

mm. mm.

Total length of the skull in the median line 145 Width of nares 5

Width of skull over the foramen magnum 45 Distance from posterior border of nares to an-

between orbits 20 terior border of the orbit 77

between external nares 10 Height of the skull over the foramen magnum,

Antero-posterior diameter of orbits 26 measured with the lower jaw 47

Width of orbits 29 Length of tibia 64

Antero-posterior diameter of nares 7 fibula 67

This animal very closely resembles Poliosanrus and was evidently
closely related to it both in structure and habits.

Genus THEROPLEURA Cope (see p. 22).

The discussion of the genus is largely contained in that of the first
species below. The animal was undoubtedly closely similar in form of body
to Varanosaurus and probably had the same habits. The form of both was
elongate and low ; the short legs permitted the bell}^ to drag on the ground
and the tail was long and slender. The chief difference in external appear-
ance was that the head of Varanosaurus was narrow and elongate, while that
of TJieropleiira.^ though long, was wider and flattened.

Theropleura retroversa Cope (see p. 25, plates 3-13).

Thero^pleura triangulata Cope, p. 25. Clefsydrofs leftoccphalus Cope, p. 26. Diofcus leptoce-
■phalus Cope, p. 26.

Characteristic specimens: No. 4155 American Museum, the type (Trans. Am.
Phil. Soc, vol. XVII, plate 2, fig. 8). No. 4026 Am. Mus. Nat. Hist, Cope, coll.,
femora. No. 1013 University of Chicago, fragments of a skull. No. 1014 University
of Chicago, left maxillaiy.

The skull is unfortunately poorly presers'cd ; the bones are clean and in good
condition, but many important ones are missing. Cope first recognized the double-
arched character of the skull in 1892 (78), but described only the temporal region (see
systematic revision, p. 26). In 1903 the author published a redescription of the skull,
showing the general form and proportions ; later studies have made it necessarj' to
alter somewhat the interpretation in the region of the temporal arches.

The skull was elongate and low, with a broad, flat top, more like the living
Varanus than Dimetrodon. The maxillary extended upward somewhat, but the
facial region was not elevated ; the frontals are as broad as the maxillar}' is high ; in
Dimetrodon the frontals are very narrow, not over a fourth or fifth as wide as the
maxillary is high.

^he premaxillary is similar to Dimetrodon ; there is a loug median process pro-
jecting backward to meet the nasals in the median line. The bones of the two sides
meet by a broad and strong sutural surface. There are five teeth ; the first two were
abruptly larger, the four posterior ones are small.

82

REVISION OF THE PELYCOSAURIA.

The maxillary has a thickened inferior edge accommodating the sockets of the
teeth and a thin superior portion as in Dimetrodon. The thin upper portion is not
so high, nor is the thickened lower edge so wide or deep, for the teeth were not so
large and the sockets are coixespondingly smaller. This is especially true in the
region of the enlarged maxillary, which has a socket not greatly larger than the rest.
The alveolar edge is straight. Anterior to the enlarged maxillary the thickened
margin plays out as the teeth become smaller. There are four small teeth anterior
to the enlarged maxillary and posterior to it nineteen can be counted, but a small
space is covered by a fragment of the lower jaw ; allowing five teeth to this space
there were twenty-four teeth posterior to the large maxillary. There are two large
maxillary teeth on the right side and a single one on the left. It is probable that this
genus had developed the same habit as the members of the Clepsydropido'^ of alternate
fuuctioual teeth; at least it had made the preliminary step in the process by the
development of two canines equal in size and abruptly larger than the others. There
is a distinct upward curvature of the jaw anterior to the large maxillary, indicating

Fig. 2 1 . — Restoration of skull of Theropleura relrooersa. About '4 nat. size.

the first step in the development of the diastemal notch, but it is very slight and
there is no interruption of the teeth, although they are smaller. The alveolar edge of
the maxillary is straight.

The nasals are represented by fragments only.

The frontals are represented by fragments and by a cast of the lower surface so
that nearly the perfect form can be made out. The cast shows the bones of the two
sides in nearly the coiTcct position with relation to one another. They formed a flat
shield-shaped area 146 mm. in length and 104 mm. in width.

The prefrontal is represented by a fragment only, but shows the same pit just
anterior to the orbit caused by the overarching of the roof of the skull that occurs in
Dimetrodon and l'aranosaiirns.

There is no trace of the lachrymal, j^^gnl, post/rontal, postorbital, or parietal.
The outlines of the orbit are unknown.

The base of the skull is lost, so there is no trace of the paroccipital, exoccipital,
basioccipital, or supraoccipital.

The quadrate is a thin vertical bone with paired condyles for the lower jaw.
The condyles are low and far apart ; they limit the jaw to a strictly vertical motion,
but could not have held it rigidly as in Dimetrodon. The upper, thin portion is bent
so that it is convex outwardly. The upper side of the inner condyle is flattened,
forming a shelf on which rest the quadrato-jugal (?) as in Dimetrodon., but there is no
trace of a foramen quadrat 11 m. The pterygoid articulates with the inner side of the
inner condyle as in Dimetrodon (plate 3, figs, i and 2).

MORPHOLOGICAL REVISION OF THE SUBORDER. 83

The condition of the arches is very uncertain. In Dinietrodon there are two
bones, the quadrato-jugal and prosquamosal overlying the posterior edge of the quad-
rate and the upper temporal vacuity is greatly reduced in size. In this specimen
there is a single bone overlapping the posterior edge of the quadrate and extending
forward to join the jugal (plate 3, figs, i and 4). This occupies the position of both
the quadrate and prosquamosal in Dinietrodon. A very careful search fails to reveal
any suture that would indicate a division of the bone ; there are several cracks in the
position of such a hypothetical suture, but they do not appear to be other than acci-
dental breaks. As the anterior end of this bone without doubt joined the jugal it
occupies the position of the prosquamosal in Dinietrodon, but as its posterior portion
overlaps the posterior edge of the quadrate it occupies the position of the quadrato-
jugal. It is hardly supposable that the two bones are united, however, for the animal
is undeniably far more primitive than Dinietrodon and the two bones should be
separate. There is the possibility that the quadrato-jugal was a thin, scale-like bone,
as indicated by its form in Dinietrodon, and has been lost, but the condition of the
bones gives little warrant for the assumption. The upper edge of the anterior portion
formed the lower edge of a large inferior temporal vacuity.

Above is a second bone, occupying the position of the squamosal in Sphenodon
and with a similar form. The upper end is divided into two parts ; the lower extends
forward, but its anterior end is broken and the connection can not be made out. The
upper and lower edges of this process are thin and show that they formed the edges
of the upper and lower temporal vacuities. According to this process the upper
vacuity was as large as the lower. The upper end of the bone has a distinct face
probably for the parietal bone.

Some light seems to be thrown on the condition of the temporal region by the
specimen of Varanosaiirus. It resembles the other Poliosaiiridce in so many respects
that it may safely be assumed that it was similar in the temporal region as well. The
postorbital region of \ 'aranosaitriis is preserved, but not the articular region ; there
was a great superior temporal vacuity and probabh- an inferior one as well. Broili
speaking of this region in correspondence says : "Ich kann jederseits riickwarts der
Augenhohlen je eine Offnung constatiren. Da die riickwartige Begrenzung derselben
fehlt, ist es immerhin noch moglich und sogar wahrscheinlich, dass noch eine 2te
Offnung vorhanden war; wurde aber dann nicht wie bei Dimetrodon oben sondem
an den Flanken des Schadels liegen."

It seems probable that the members of this more primitive family had two wide
temporal vacuities. If this be true, then the small superior temporal vacuity of the
long-spined forms is an additional evidence of the extreme specialization of the order.

On the lower surface of skull the basisphenoid and the pters-goids are preserved.

The stapes is a slender rod of bone with an expanded proximal end. The shaft
is slender and was quite elongate, but only the proximal portion is preserved. The
proximal end is divided into two unequal parts by a very deep groove. Just distal to
this groove the shaft is perforated by a foramen, which passes through somewhat
obliquely. This bone was regarded by Baur and Case as a possible rib (9), but this
seems to have been an error ; the finding of the elongate portion of the stapes in posi-
tion in the skull of Dinietrodon gigas and the proximal end of a stapes with its per-
foration in Edaphosauriis pogonias show that Cope was correct in his determination.
The form of the bone is shown in fig. 22. Cope compared this element directly with
the stapes of the Monotreme Mammalia and considered that its discover^' strengthened
considerably his idea that the Pelycosauria were the ancestors of the mammals.

84

REVISION OF THE PELYCOSAURIA.

The basispheiwid is quite similar to that of Dimetrodon^ but the anterior pro-
cess, the parasphenoidal portion, is much longer and heavier and extends well forward
in a straight line instead of being turned upward as a thin vertical plate. This is
one of the most primitive characters of the skull.

The pterygoids of both sides are preserved in part. The posterior half is present
on both sides. There was the same division of the bone into an anterior and pos-
terior and an external portion as in Dimetrodon. The anterior portion is largely
missing, but enough remains to show that it was flat
and covered with small teeth. The posterior portion
is nearly vertical, but inclined somewhat inward, and
the posterior end overlapped and articulated with the
inuer side of the inner condyle of the quadrate. The
external portion stood out at right angles to the other
part of the bone, but was far from vertical, slanting
backward at a large angle. The outer face of the ex-
ternal process abutting against the lower jaw is rugose,
but very thin; there are fifteen small teeth arranged
in sockets on the lower side. The development
of the external process of the pter3'goid from
this slanting condition with a thin external face
to the perfectly vertical position with the outer
face broad and rugose is one of the clearest
lines of development in the suborder.

There is no trace of the ectopterygoid.
The epipterygoid stands in the usual posi-
tion on the upper edge of the pterj-goid. It is
thin with an elongate base parallel to and rest-
ing on the upper edge of the pterygoid.
The lower jaws of both sides are represented by fragments, but these can not be
fitted together so as to give an accurate estimate of the length. The jaw was much
more slender than in Dimetrodon and of less width anteriorly, but was seemingly
quite high behind. The articular region was attached to the inner side instead of
being terminal in much the same way as in that genus, but the details can not be
made out. The anterior end was very slim, only 19 mm. high, the two sides united
in a long symphysis. The teeth are smaller than in the iipper jaw and more numer-
ous. The anterior end of the jaw is suddenly swollen and accommodates the sockets
of enlarged teeth. The first tooth is small, followed by three much larger ones,
after which the teeth are abruptly smaller. There are nineteen in the first third of
the jaw ; the total number can not be made out.

Vertebral cohivui (plate 13) : This consists of forty vertebrce which are in
connected series, except for a break just anterior to the two sacrals. The column as
preserved begins with the axis and ends with the ninth caudal ; the vertebrae are held
by a hard flinty scale of matrix and most are in the normal position ; but two or
three are turned through 90°. As indicated in the sj'stematic revision the vertebral
column differs from that of the Clepsydropida- in two points, the low neural spines
and the nearly uniform length of the vertebrse in all parts of the column.

Fig. 22. — Stapes of Thewpleura relroversa. X yi-
After Cope. a. Proximal end of same.

Fig. 23. — Lateral view of the basisphenoid of TherO'
pleura relroversa showing the large parasphenoid
rostrum. X I .

MORPHOLOGICAL REVISION OF THE SUBORDER. 85

Atlas : The centrum of the atlas is lost, but the neural arch of one side clings
to the under side of the skull ; it is very- similar to the neural arch of Dimetrodon
(plate 16, figs. 3 and 4).

Axis : The centrum of the axis is somewhat elongate and the bottom line fonns
a sharp ridge. The sides are concave and marked below the transverse process by
several longitudinal lines. Just below the transverse process of the left side is a good-
sized nutrient foramen. The transverse process springs from the neural arch and is
very short. The articular face is small and the distal end of the process is not free
from the side of the centrum. The spine is rather high, thin, and expanded antero-
posteriorly, with a wide superior edge. The anterior zygapophjses are small, but not
so disproportionately small as in the Clepsydropida;. Centrosphene and centantrum
(see morphological description of Dimetrodon incisiviis) are present, but small.

Third vertebra (counting the atlas as first) : The bottom line of centrum has
a distinct low keel, but the longitudinal lines on the sides are less definite. The dia-
pophysis is longer than in the axis and inclined more sharply to the rear. The lower
portion of the anterior face of the centrum is slightly cut out to accommodate an inter-
centrum. The spine is of nearly the same shape as in the axis. Several small two-
headed ribs, which probably belong to the anterior cer\icals, cling to the side of the skull.
Fourth to seventh vertebra" : In these the diapophjses grow gradually shorter and
stand out more nearly straight from the centrum. They do not originate, as in
Dimetrodon^ in three processes, one each from the anterior and posterior zygapophysis
and one from below, but rise directly from the neural arch below the line of the zyga-
pophyses. An inferior supporting ridge is present,
which at first inclines backward, but soon changes so
that on the fifth and sixth vertebrae it inclines forward
toward the anterior edge of the centrum. The bottom
line has now a distinct keel, but is formed by a gradual
contraction of the sides of the centrum (fig. 24) and
not by a sudden pinching in of the sides immediately
below the intercentrum as Dimetrodon (fig. 25).

Eighth to eleventh vertebra" : In these the bottom

Fig. 24. — Cross-section through middle of -,■ ... ,, .1 i • ^ -^ j j_i -j

. , . c T-L , line IS shorter than those anterior to it and the sides

a dorsal vertebra or / heropleura,

showing gradual contraction ot sides ^rc soiuewliat comprcsscd below the lutercentrum, but

below notochordal canal. ■; '4 . nothing like the Condition of Dimetrodon. The lower

Fig. 25.— Cross-section through middle of line is a broad rouuded keel with a median longitudinal

a dorsal vertebra of Dimetrodon. groovc that luakes it appear doublc ; the median groovc

showing the sudden pinching in of. ii..i -jjirii i j-j

L J L 1 .L . L J 1 1 IS narrowest at the middle of the centrum and widens

the sides below the notochordal canal

forming the narrow keel. toward cacli ciid. The sidcs of the vertcbrse are con-

cave so that the edges of the articular surfaces are very
prominent. This is true of all portions of the column posterior to the eighth vertebra.
The diapophyses stand out straight from the upper edge of the centrum and are ver}-
short ; the articular face looks directly out. The lower supporting ridge extends for-
ward toward the anterior edge of the centrum, but does not reach it in any of this
group of vertebrae. The change in position of the lower supporting ridge is peculiar
in that it is entirely independent of the diapophysis proper ; this shows little change
of form or position in the anterior two-thirds of the column. There are two or three

86 REVISION OF THE PELYCOSAURIA.

large ribs with widely divided capitulum and tuberculum ; the distal end is gone from
all, but enough remains to show that they were quite broad distally.

Twelfth to seventeenth vertebrcB : These are verj' similar to the preceding; the
centrosphene and centantra are larger than in the cervicals, but are still very small.
Between the seventeenth and eighteenth there is a small intercentrum, narrow antero-
posteriorly, with sharp ends not showing any face for the capitulum of the rib.

Eighteenth to twenty-first vertebm : The centrum of the eighteenth has a sharp
ridge on the mid-line below, but the median groove is lost. The diapophysis is short
and inclined a little backward so the articular face looks slightly backward as well as
outward. The diapophysis lies far forward almost directly beneath the anterior zj'ga-
pophysis and the lower ridge reaches quite to the anterior edge of the centrum and has
a flat articular surface on its edge showing that the capitulum and tuberculum of the
rib are fast approaching each other. On the twenty-first the lower ridge has entirely
disappeared as a ridge and the diapophysis is a short stub with its articular face look-
ing directly out.

Twenty-second to twenty-fifth vertebrce : On the twenty-third the rib is fused with
the centrum. It is very thin and slender at its proximal end, differing in this respect
ver}' markedly from the condition of Dinictrodon. From this point the ribs are traceable
to the sacrum, but are very small and almost rudimentary. On the twenty-fourth a
longitudinal ridge appears on the side of the centrum, on the succeeding one it is
stronger and remains until the twenty-ninth, where it is suddenly absent. The sud-
den appearance and short duration of this character is of great interest, as it was on
an isolated vertebra of this region that Cope founded the species Theropleitra trian-
gulata. The bottom line is a flattened keel.

Twenty-sixth to thirtieth vertebm : These vertebrae immediately preceding the
sacrals are slightly, but not greatly, shorter than the rest of the vertebrae. The bottom
line is very concave and the keel is reduced to a low obtuse ridge. The ribs are very
small, but it looks as if on the thirtieth there was a small opening between the capitulum
and tuberculum and the side of the centrum.

Thirty-first and thirty-second vertebrce : These are the sacrals. They are not con-
nected with the anterior series, but not more than one or two vertebrae, if that many,
are lost. The sacral ribs are large and strong and united solidly with the sides of the
centrum. The two vertebrae are firmly connected so that the posterior and anterior
zygapophyses of the first and second sacrals are greatly reduced and it seems as if the
neural arches of the two were even united by anchylosis.

Thirty-third to forty-first vertebrce : The nine caudals connect with the two
sacrals completing the posterior series. The thirty-third, first caudal, has a well-
developed rib still attached. The rib is nmcli larger than those of the lumbar series,
the capitulum and tuberculum are distinct, but close to each other, and the capitulum
is attached to the anterior edge of the centrum. The neural arch is quite high ; the
sides of the centrum are concave antero-posteriorly, but convex vertically. The
median line below is a blunt keel, but as the sides of the centrum are convex vertically,
there are lacking the deep pits on either side of the mid-line of the centrum below, so
characteristic of the caudals of the Clepsydropidce.

The second caudal has lost the rib and the faces for the caj^itulum and tubercu-
lum of the rib are shown. These are large flat facets not elevated on a process, with
their long axes at right angles and separated by a very narrow space. The face for
the tuberculum is on the upper edge of the centrum and the face for the capitulum is

MORPHOLOGICAL REVISION OF THE SUBORDER. 87

foniied by the reverted edge of the anterior articular face. This is the characteristic
feature upon which Cope founded T. retroversa.

In the third caudal the faces for the capitukim and tuberculum are as in the
second, but a strong ridge runs backward from the posterior edge of the capitular face
on the side of the centrum ; this ridge occurs only on the single vertebra and may be
only an unimportant variation.

'V^^i^ fourth to the seventh are similar to the preceding, the tubercular and capit-
ular faces are united, growing smaller.

The eighth shows the capitular face almost completely reduced, the rib is small
and projects horizontally.

The ninth has the rib reduced to a small process and the capitulum and tubercu-
lum are no longer distinguishable.

There are no chevrons or intercentra preserved in the caudal series, nor are the
lower edges of the centra cut out for the intercentrum unless this begins to appear on
the last caudal.

The shoulder girdle is not preserved.

The anterior limbs are not preserved.

Th^ pelvic girdle (plate 3, fig. 6) is nearly perfect; both sides are preserved. The
pelvis has been opened out on the ischio-pubic symphysis nearly flat, but the bones of
the two sides are hardly disturbed. The distal ends of the ischia and pubis are broken
away, but that is the only damage the pelvis has sustained.

The iliu)n has a strong crest which is turned sharply to the rear a short distance
above the acetabulum ; this portion is relatively narrow vertically ; its inner face shows
a deep semilunar impression di\-ided in its upper part by a sharp ridge for the attach-
ment of the sacral ribs. The ilium takes a large part in the acetabulum, sending
down a wide wedge-like portion that forms much of the cavity of the acetabulum and
divides the pubis and ischium except at the lower border of the acetabulum.

The ischium has a heavy end which forms a prominent postero-inferior edge for
the acetabulum. The distal portion extends far back and its upper edge, though not
thickened, is slightly incurved. The ischia of the two sides meet in a symphysis, but
the attachment was confined to the edges and did not extend to any considerable por-
tion of the inner side as in the Clepsydropidoe where the sides of the pelvis were more
nearly vertical. The suture line between the ischium and pubis is distinct and their
point of contact on the symphysial edge is marked by a notch ; the opposition of the
notches of the two sides left a small cartilage-filled space. This may be a feature of
youth.

Thepubis takes a relatively small part in the acetabulum. Its distal portion forms
a prominent border which unites with that of the ischium so that the lower edge of the
acetabulum is marked by a prominent ridge. The upper edge of the distal portion is
thickened into a strong ridge which extended to the distal end. The obturator fora-
men lies just below the anterior edge of the acetabulum and runs almost directly
upward and inward.

The posterior limbs are represented by the femora and tibia of both sides (plate
3, figs. 5, 7). The upper end of the femur is very wide so that the depression on the
posterior face is relatively much wider than in Dimetrodon; it ends sharply below.
The two sides of the cavity are marked by sharp ridges, but the radial process is rela-
tively small. From the lower end of the cavity a sharp ridge extends to the outer con-
dyle. This closely resembles the same ridge on the femur of Eryops, but starts anew

88 REVISION OF THE PELYCOSAURIA.

from the end of the cavity, while in Eryops it is a direct continuation of the radial
crest. The shaft is considerably contracted in the middle portion. The anterior face
of the distal end is flattened and even concave ; the posterior face has a very deep
groove separating the two condyles. The articular faces of the condyles look well
forward and are connected by a wide area, not separate as in Dimetrodon. The outer
condyle is longer than the inner.

The tibia is slightly curved and has a greatly enlarged proximal end, but the
articular face is not so nearly divided into two parts by a depression as in Dimetrodon.

Fig. 25 a. — Sketch restoration of Theropleura relroversa. About ^.

Length of maxillary (approximately)

from quadrate to maxillary, estimated

Total length of skull, estimated

Length of premaxillary

Antero-posterior diameter of :

Large maxillary tooth at base

Small maxillary tooth at base

Approximate length of column as preserved .

Length of the nine caudals

Bottom line of axis

Vertical diameter of axis just posterior to neu-
ral arch

Bottom line of :

8th, 22 mm.; vertical diameter as in axis . .

Measurements.

mm.

240

140

3S0

56

Bottom line of :

3th, 19 ram.; vertical diameter as in axis. .
23d, 20 mm.; vertical diameter as in axis. .
29th, 16 mm. ; vertical diameter as in axis. .
Height of spine of :

9.5 Axis above base of centrum

6.5 13th above lower edge of anterior face of

1 1 75 centrum

255 Length of nearly complete pelvic symphysis. .

30 ischium 140

across distal end of ilium 91

32 Width of acetabulum 85

Length of femur 18S

30 tibia 143

30

29.5

29

96

105
205

Theropleura grandls Case (see p. 28

and text-iig. 26).

Characteristic specimens : Nos.
4130 and 4134 American Museum.
The type, No. 4109 Am. Mus. Nat.
Hist., Cope, coll.: A lot of verte-
brae, including two presacrals, two
sacrals, and five caudals.

Nos. 4130 and 4134. Three
vertebrae are selected as character-
istic. The first, fig. 26, «, is either
the axis or the third cervical, the
centrum is elongate with a low,
sharp ridge on the median line below. The sides of the centrum are regularly convex
and marked by irregular longitudinal lines as in Diopeus relroversa. The transverse
process rises from high up on the side of the vertebra. The anterior articular face
has fairly well-developed centantra and a broad intercentral face below.

Fig. 26.— Three vertebrae of Theropleura grandis, Nos. 4130-4134
Am. Mus. Y. %. a. An anterior cervical, axis or third, b, A
mid-dorsal, c, A posterior lumbar.

MORPHOLOGICAL REVISION OF THE SUBORDER. 89

The second, fig. 26, b, from the mid-dorsal region, has a shorter centrum with the
bottom line broadly rounded, but not keeled, and concave antero-posteriorly, not
straight as in the forms with keels. The centrosphenes and centantra are present,
but small. The zygapophyses differ from those of the same region in Theropleiira
retroversa in being more oblique.

The t/iirci, fig. 26, r, a posterior lumbar, is ver>' short and proportionately broad ;
the sides are marked with longitudinal ridges as in Theropleiira retroversa. The
ribs are detached, leaving separate capitular and tubercular faces.

The ilium is similar to that of Theropleiira retroversa, but larger.

No. 4109. The two presacrals are of the form figured in Nos. 4130 and 4134,
but show a character that is hidden by the niatrix of that specimen. Instead of the
articular face of the centrum being reverted and passing gradually into the side of the
centrum, it is reverted, but separated from the side by a prominent narrow ridge
which extends all around the centrum, leaving a wide space for the intercentrum.

In the two sacrals the first has a wide recurved edge on the anterior face, but
the posterior fits against the anterior face of the second sacral verj' closely, leaving a
smaller interspace for a more narrow intercentrum than in Theropleiira retroversa.
The rib of the first sacral extends rapidly downward rather than out and has a broad
rugose distal end. The proximal end is free from the centrum, leaving an articular
space extending from the neural arch almost to the mid-line below and resembles
very closely the same face of Poliosaiiriis iiniforuiis (plate i, fig. 6). The anterior
edge of the proximal ends does not project beyond the anterior edge of the centrum
as in Dimetrodon gigas.

The anterior caiidals have a similar ridge separating the articular face and the
side of the centrum, but it is not so distinct as in the presacrals. The sides of the
caudals are concave antero-posteriorly and vertically so there is something of a keel
which is rather more sharp than in Theropleiira retroversa. The keel of one caudal
has a deep, narrow longitudinal groove dividing it into two parts. The caudal ribs
have the capitulum and tuberculum as in Theropleiira retroversa.

Genus Elcabrosaurus baldwinl Case (see p. 28).

Characteristic specimens : No. 2285 American Museum, the type (plate 4, figs. 1-5).

The axis is similar to that of Dimetrodon obtiisidens, with a narrow anterior
articular face and well-developed centantra. The bottom line has a sharp ridge
running to the posterior edge of the centrum.

An anterior dorsal has the bottom line narrow and sharp, approaching very
nearly to the condition of a true keel, but the sides of the centrum are gradually com-
pressed, not sharply pinched in, just below the intercentrum. The lower edge of the
anterior face is not bent back nor is there a wide face, showing that the intercentrum
was smaller than in Dimetrodon. The transverse process rises from high up on the
neural arch. Neither this vertebra nor the more posterior dorsal have the shortening
of the bottom line of the dorsals so characteristic of Dimetrodoti, but it is not certain
that the most anterior dorsals are present.

The more posterior dorsals have the centra relatively thin and high. The
bottom line is thin and sharp but concave antero-posteriorly. An intercentrum of
this region is thin antero-posteriorly and has no trace of faces for the heads of the ribs.

A lumbar is shorter with rounded bottom line. The sides are narrowed by a
deep pit on either side just below the transverse process. The transverse process

90

REVISION OF THE PELYCOSAURIA.

rises from high on the side of the neural arch ; it is short and projects almost straight
out. The side of the articular edge of the centrum is rounded as if for the beginning
of a capitular facet. The base of the neural arch is elongate antero-posteriorly,
between the zygapophyses.

The last tzvo lumbars are notably different from Dimetrodon and show the chief
distinguishing characters of the genus.

The centra are exceptionally short with deeply concave sides and bottom line.
The bottom line is wide and rounded. The portion of the face surrounding the
intercentrum is nearly circular, but on both the anterior and posterior faces there is a
wide extension of the face below the intercentrum fonning a flat face nearly as wide
as the portion above. These faces are not bent back as are the intercentral faces of
the anterior dorsals of Dimetrodon and seemingly fitted closely together leaving no
space for an intercentrum, which probably underlay the line of meeting of the two.

Measurements,

nun. mm.

Length bottom line of axis 23 Diameter of anterior face of centrum of same;

Diameter of anterior face of centrum of same: Vertical 24.5

Vertical 25 Horizontal 21

Horizontal 19 Length bottom line of second presacral 13

Length bottom line of : Diameter of anterior face of centrum of same:

Anterior dorsal (anterior face crushed) 22 Vertical 22

Posterior dorsal 21 Horizontal 21

Diameter of posterior face of centrum of same: Length bottom line of first presacral 11

Vertical 23 Diameter of anterior face of centrum of same :

Horizontal 17 Vertical 26

Length bottom line of a lumbar (?) 19 Horizontal 21

Family CLEPSYDROPIDAE Cope (see p. 36).

Subfamily CLEPSYDROPINAE Case (see p. 37)-

Genus CLEPSYDROPS Cope (seep. 37).

The single well-known and determinable species is Clepsydrops natalis.

The description of the genus is embodied in the discussion of that species

below.

Clepsydrops natalis Cope (see p. 42 and plates 4, 5, and 6).
Clepsydrops colletti Cope, partim, p. 40. Clepsydrops vinslovii, partim, p. 42.

Characteristic specimens: No. 4110 American Museum, the type. No. 41 11
Am. Mus. Nat. Hist, Cope, coll.: A pelvis with femur in position (plate 6). No. 2290
Am. Mus. Nat. Hist., Cope, coll.: A front foot lacking carpale i and metacarpale i.

The type specimen, No. 41 10 American Museum, has beeu repeatedly described
(Cope 44, Case 29) so far as the condition of the specimen permitted, but in the prep-
aration of this description the refractory matrix which previously obscured many points
has been completely removed ; for this reason previous descriptions are disregarded and
a complete redescription given.

The skull (plate 4, figs. 7, 8) was high and narrow; this appearance is empha-
sized by the crushing of the specimen from side to side in fossilization ; probably it
was not so high and narrow as in Dimetrodon incisivus. The condition of the speci-
men makes it impossible to trace all of the sutures in the skull, but it is evident that
the skull was closely similar to that of Ditnetrodon and that the bones were of the same
form and general relations. The posterior temporal region is badly crushed.

MORPHOLOGICAL REVISION OF THE SUBORDER. 9I

The end of the muzzle was abruptly rounded and high with the nostrils lateral,
but quite near the anterior edge. The tooth line of the maxillary is convex and there
is a slight diastemal notch between the maxillary and premaxillary. This is really
less well-developed than appears in the figure, where it is accentuated by the crushing
of the specimen ; it is most clearly indicated by the size of the teeth. The teeth are
similar to those of Diinetrodoii ; as in that genus there were two large maxillary
canine teeth which were alternately functional, for in each maxillary there is a large
tooth and an empty alveolus. On the right side there are fifteen teeth posterior to
the large canines, two canines, or rather one and an empty alveolus, and three or four
teeth preceding the canine, making twenty or twent3'-one in all. On the left side the
teeth are less perfectly preserved. The canine is abruptly larger tlian the others with
an elliptical section and sharp anterior and posterior cutting edges, but the edges are
not crenate. Posterior to the canine the teeth are gradually reduced in size until
the posterior ones are very small. There were four teeth in the premaxillary ; the
anterior three are larger than the posterior ones, but are not nearly so large as the
maxillary teeth immediately following the canine.

The posterior portion of the skull is badly crushed and only a few points can be
made out with certainty. They show that the previous description of this portion of
the skull by the writer was correct (29). On both sides of the skull the outline of
the anterior portion of the orbit can be traced and shows that it was large, nearly cir-
cular, and surrounded by a prominent rim as in Dimetrodon. A jugal can be traced
below. On the left side the fractured postorbital region shows the jugal connecting
with the prosquamosal (?) posteriorly and with the postorbital abo\-e, which though
broken and displaced can still be traced. The edges of a large inferior temporal vacuity
are distinct and the superior temporal vacuity was small. It is certain that the animal
had a diaptosaurian skull closely similar to, but more primitive than Dimetrodon.

The lower jaiv is ver>' similar to that of Dimetrodon incisiviis in form and pro-
portions, but the sutures can not be traced. The ramus was more slender and with a
longer symphysis in which the splenial takes large part. The posterior end is widened
and there is no coronoid process. The articular region is hidden. The teeth are
mostly hidden so the number can not be given, but on the left side there were three
large teeth at the end without a smaller one preceding them, as is common in the
genus Dimetrodon. The alveolar edge of the dentary is concave to correspond to the
convex edge of the maxillary.

The vertebral column : No vertebrae from the anterior portion of the column
have been identified. The dorsals are represented b}' several loose vertebrae from the
postdorsal region ; three connected vertebrae with ribs show the chief characters. The
centra are relatively elongate with the base of the spine elongate antero-posteriorly and
set well back over the posterior zygapophyses ; the faces of the zygapophyses are nearly
horizontal. The transverse processes are very slender and stand out straight from the
neural arch. The ribs are large and two-headed with a strong tuberculum and the
shaft nearly straight.

An anterior lumbar has the centrum and neural arch elongate antero-posteriorly;
the transverse process is slender and the lower supporting ridge runs forward to the
anterior edge of the centrum and joins the face for the capitulum of the rib.

Of the five vertebrae in connection with the pelvis and sacrum \\\^ first tivo have
the centra still rather long ; the bottom line is thinner and rounded, but not keeled.
The base of the neural spine is thin, but wide antero-posteriorly. The ribs are firmly

92 REVISION OF THE PELYCOSAURIA.

attached to the sides of the vertebra by capitulum and tuberculum as described in
the morphological description of Dimetrodon dollovianus, No. 112 University of
Chicago. They are roirnded, thin, and not very long.

The third presacral has the bottom line decidedly shorter and concave. The
lower edges of the articular faces of the centra are beveled, leaving wide spaces for the
intercentrum. This is the first of the vertebrae in which the neural spines are pre-
served. The neural arch is torn loose and displaced backward slightly, but the spine
is in nearly the natural position. The base of the spine is wide antero-posteriorl}', but
it rapidly narrows to a slender cylinder, tapering to the apex. It is naturally curved
to the rear. The capitulum and tuberculum of the rib are united and fused with the
sides of the centrum.

Theyf/ji/ and second presacrals are much shortened antero-posteriorly, the spines
resemble those of the third and are of nearly equal height. The ribs are small, with
the capitulum and tuberculum no longer distinct and closely fused to the side of the
vertebrae.

The sacrals : There are three sacrals. The spines of all and the neural arch of
the third are lost. The centra are largelj- hidden by the crests of the ilia which are in
position, but it is seen that the ribs of the first two are verj' strong.

The caitdals : The tail was very long and slender. There are seventeen caudals
connected with the sacrum and many others which have been arranged as nearly as
possible in position. It is evident that there are remnants of at least two tails in the
lot, so the exact length can not be given. The first ten caudals bear ribs which are
short but stout on the first and disappear on the tenth. All have the spines short and
weak. On the second is a displaced rib head which might be mistaken for a chevron,
but in common with the other members of the order the first few caudals have simple
intercentra and the chevrons begin more posteriorly.

Between the sixth and seventh the first chevron appears. It is represented by
the proximal end only, but it shows the presence of a long distal process divided
proximall}' by an elongate foramen as in Dimetrodon, No. 112 University of Chicago
(plate 21, fig. 9). The lower edges of the articular faces of the centra are cut away
to accommodate the wedge-like head of the intercentrum. By the thirteenth or four-
teenth caudal the vertebrae have become slender and elongate. The bottom line is
smooth, not marked with longitudinal lines as in some of the specimens from Illinois.
Chevrons are still present. Isolated vertebrae show the tail to have been continued to
very slender proportions.

Shoulder girdle: The imperfect scapulae of both sides are preserved seemingly
in natural position and possibly inclosing and hiding some of the anterior vertebrae.
The scapula of the left side is preserved from the distal end to the center of the artic-
ular face, that of the right side from the distal end nearly to the articular face. The
form is in general the same as Dimetrodon. The shaft is curved and is penetrated by
a foramen just distal to the articular face ; another foramen penetrates the bone just on
the scapular edge of the articular face. The articular face is deep, but is straighter
than in Dimetrodon in correlation with the simpler head of the humerus. The prox-
imal end of a scapula in the Chicago collection, No. 6540, probably belongs to this
species. On the anterior (dorsal) edge of both scapulae near the middle are fragments,
which are evidently the distal ends of the clavicles. On the right scapula a thin
splint of bone lies on the edge of the scapula and on the fragmentar)' end of the
clavicle. This is in exactly the position of a cleithrum. In some of the scapulae of

MORPHOLOGICAL REVISION OF THE SUBORDER. 93

Dimetrodon the anterior edge of the distal ends shows slight linear rugosities as if
there had been a loose squamous articulation with a small bone, an appearance which
suggests the possibility of a cleithrum (Nos. 4131 American Museum and looi
University of Chicago). The slender element described here seems after careful
study to be a distinct bone and not a splintered fragment ; if it is a distinct element
it is the cleithrum. The presence of a cleithrum in just such a rudimentary condition
is not surprising, but rather to be expected.

The fore limb: There are several humeri in the lot, but all are of the same
type. It is highly probable that they belong with the same species as the skull and
pelvis. The articular ends are simple, without head or condyles, and were evidently
covered with cartilage. Tlie proximal end is rounded in outline with no trace of an
articular face. The articular surface is widened next to the radial crest and is con-
tinued out upon it without interruption. The prominent radial crest leaves the main
part of the bone almost at right angles and the point of departure is marked on the
posterior side by a sharp ridge. The shaft is slender and subquadrate in section.
The entepicondyle is hardly larger than the ectepicondyle ; the entepicondylar fora-
men is narrow and elongate. On the anterior face of the distal end is a ridge which
extends to and widens the distal surface in the position of the condyle for the radius.

The radius and ulna are unknown unless a very thin fragment of a long bone
with an abruptly widened end represents the distal end of the radius.

The radiale has almost the same form as in D. incisivus ; it has a broad prox-
imal surface for the end of the ulna and two faces meeting at an angle below for the
centrale i and 2.

The uluare is thin and disk-like, with two articular faces on the inner side for
the intermedium and centrale i. In the specimen it is slightly turned in position,
showing the facets.

The iiitermediuni projects well beyond the proximal end of the radiale and
ulnare. It had the same form as in Dimetrodon incisivus^ but in the specimen it is
somewhat crushed.

The centrale i and 2 are rather different from the same bones in Dimetrodon.
Centrale i is rather more cuboid, and centrale 2 seemingly did not send a process
inward to articulate with the carpale 3.

Carpale 5 is absent, the others show nearly the same form and relation as in
D. incisivus.

The pelvis is nearly perfect ; the exact form of the acetabulum is hidden on both
sides by the heads of the femora which remain in the socket. The general form of
the pelvis is very similar to that of Dimetrodon incisivus., but the pubis and ischium
extended farther fore and aft, so that the symphysis is longer in proportion to the
height. The symphysis was quite deep and the two sides stood nearly vertical.

The iliimi has a high crest with a strong posterior prolongation. The inner
face of the crest can not be seen, but there was evidently a strong attachment to the
sacral ribs. The upper edge of the acetabulum is rather prominent over a relatively
deep cup.

The pubis has the upper edge thickened into a strong ridge. The obturator for-
amen is just below the anterior edge of the acetabulum. The bottom line is nearly
straight and the upper edge slants rapidly downward so that the anterior end is very
low and formed almost entirely by the thickened upper edge of the bone. The suture
between the pubis and ischium can not be traced.

94 REVISION OF THE PELYCOSAURIA.

The ischium has lost a small portion of the distal end. The upper edge slants
down and back and the lower edge slowly rises so the bone ends in a blunt point.

t\ve. femur is rather more elongate and slender than in Diopeiis. The posterior
depression of the proximal end is deep and the inner edge is developed more as a
tuberosit)' than a ridge. The shaft is rounded at the middle with a light rugose line
on the posterior face. The condyles lie on the posterior face looking backward more
than downward ; they are distinct, but not so clearly marked as in Dimetrodon.

The tibia is about three-fourths as long as the femur, the proximal end is
enlarged and the shaft is bent. The proximal face is divided by a groove as in Dime-
trodon^ but the division is not nearly so prominent nor is there a cnemial crest. The
distal end is broken.

The: fibula is a simple flattened shaft curved like the tibia. The distal end ter-
minates in two facets set at a large angle to each other.

The posterior foot : The tarsus of the left foot and the proximal ends of four
metacarpals. The careful cleaning of the specimen shows that the element described
by Cope as the fifth metatarsal is really an element of the tarsus. The tarsus is com-
plete and the bones lie in their proper places, but many of them have been slightly
moved in their places so that they no longer articulate accurately. There are eight
elements in the tarsus.

The fibulare (calcaneum) is twisted until it lies nearly at right angles to the
normal position and the faces normally applied to the tibiale are presented to the
front. The main portion of the bone is flat and disk-like. On the inner edge are the
faces for the tibiale; above the inner edge is beveled by a face for the fibula and
distally there is a face for the intermedium (cuboid).

The tibiale (astragalus) is roughly L-shaped, the two points on the inner side are
applied to the fibulare and the outer part terminates in a thickened roughened
surface. This lower part leaves the vertical portion more gently than in some others.
The two facets of the inner side applied to the two facets of the fibulare leave between
them a foramen through which a blood-vessel penetrated the foot. Below the tibiale
articulated with the centrale i (navicular), and by its lateral internal corner with the
intermedium + (cuboid).

There are two large bones in the second row of the tarsus, the centrale i and
the intermediiun +. The former is rather rectangular, longer than high and articu-
lates with the tibiale above, tarsals i and 2 below and the intermedium + below.

The intermedium + is a large bone evidently compounded of two or more origi-
nally distinct elements. It articulates with the tibiale and fibulare above and extends
distally to support the fourth metatarsal. From its position it seems that it is either
the intermedium + centrale 2 + tarsale iv or intermedium + centrale 2 ; in the latter
case it would be necessary to assume that the tarsale w has been lost and there is
nothing in the appearance of the foot to warrant such an assumption. The bone is
very long vertically and near the middle presents a sharp angle, as if two elements
had fused.

Tarsale i: This articulates by a broad face with the centrale i and sends a
strong process laterally from the distal end which widens the end to accommodate a
long and narrow facet for the head of the metatarsal 5.

Tarsale 11 and iii are small elements with large facets for the corresponding
metatarsals. From the dorsal side it is evident that tarsale i, 11, and iii articulate
proximally with the centrale i. On the ventral side tarsale 11 is not visible having
been crowded back by the crushing of the foot.

MORPHOLOGICAL REVISION OF THE SUBORDER.

95

Tarsale iv is not present as a distinct element, the fifth metatarsal articulates
with a broad facet on the intermedium + ; there is little doubt that the distal portion
of this represents tarsale iv.

Tarsale v is a small bone on the outer side of the intermedium and identified by
Cope as metatarsal 5. It carries a distinct saddle-shaped facet for the fifth metatarsal.

^h& phalanges are represented by the proximal ends only.

Fig. 26 a. — Sketch restoration of Clepsydrops nalalis. About J 5. Spines are restored except on the last
three lumbar vertebras.

Measitrements. — No. 4110.

Length of lower jaw

Width of anterior end of lower jaw

widest part of posterior end

Length of tooth line in upper jaw

large maxillary tooth

largest incisor

maxillary next posterior to the large
maxillary

three posterior dorsals

bottom line of anterior lumbar

bottom line of posterior lumbar ....

Length of first caudal 14

scapula, from distal end to center of

articular face 105

Width of distal end of scapula 30

Length of humerus 82

Width of proximal end of humerus 33

distal end of humerus 42

Length of pubo-ischiatic symphysis nearly com-
plete 126

Height from symphysis to top of iliac crest .... 89

Length of femur 121

The restoration of Clepsydrops na talis here given indicates the slender
proportions of the body and the very long tail. The spines are restored i>i
toto with the exception of the first three presacrals, which are preserved. It
is believed by the author that the spines on this form had not reached the
disproportionate length found in the genus Dimetrodon.

Genus DIMETRODON Cope (seep. 43).

Characteristic specimens: No. 41 16 Am. Mus.: The type, an incomplete skull.
No. 4008 Am. Mus.: Cotype, vertical column from axis to first caudal. No. 4040
Am. Mus.: A vertebral column with axis and several precaudals, sacrum and tail to
the ninth caudal. No. i University of Chicago : Pelvis, incomplete skull and
vertebral column, scaptilaand humerus, femur, tibia, and fibula. No. looi University
of Chicago : Nearly complete skull, anterior part of vertebral column, humeri, ulnse
bones, and front feet. No. 1003 University of Chicago : A complete front foot and
imperfect anterior limb bones.

96 REVISION OF THE PELYCOSAURIA.

The species Dimetrodott iticisivus is tlie most common in occurrence
and the best-known member of the Pelycosauria. The description and res-
toration of the genus is based largely on this species ; a few points as noted
below have been supplied from other species.

Details of the skull have been supplied from Dimetrodon gigas, No.
1002 University of Chicago. The shoulder-girdle is described almost
entirely from Dimetrodon dolloviaiius, No. 114 University of Chicago. The
posterior foot has been restored from that of Clepsydrops na talis, No. 4 no
Am. Mus. This is the only portion taken from another genus, but as the
fore foot of Clepsydrops, No. 2290 Am. Mus., closely resembles that of Dime-
trodon it is safe to assume a resemblance in the hind foot.

The skull : There are three skulls in the University of Chicago collection belong-
ing to the genus Dimetrodon. These supplement each other perfectly, one suppl3'ing
details lacking in the other.

No. I University of Chicago, D. vidsh'HS, is an imperfect skull found in a hard
joint-clay with the bones disarticulated and scattered, but free from any distortion.
It gives most clearly the characters of the basicranial region and the pterygoids, and
afforded an opportunity to make a cast of the brain cavity.

No. 1 00 1 University of Chicago, D. indsiviis, was preserved in a soft shale which
was easily washed from the bones with a soft sponge, permitting the finest details to
be made out. The bones were preserved in place, but badly broken and in places rotted
by g}'psum. It shows the temporal and quadrate regions and the relations of the
transverse, the structiire of the posterior portion of the top of the skull and the
lower jaws.

No. 1002 University of Chicago, D. gigas, was preserved in a compact red clay,
and the bones were covered with a hard scale of calcareous material, which was removed
with comparative ease, leaving the bones hard and perfect. This skull is unique in the
perfection of its preservation, the only portion missing being the temporal arches, in
part, of the left side and the median portion of the epipteiygoids. The skull lay on its
side, and all the bones are joined in their natural relations. The whole skull has been
crushed slightly from the sides, so that it appears more narrow than it really is. The
bones of the top of the skull have been slightly broken and the palate has been pushed
slightly downward, but on the whole the skull has been so little changed from its
natural condition in life that it is easily restored.

This specimen has made plain the general proportions of the skull and the bones
of the vomerine and ethmoidal region.

The quadrate, plate 11, figs. 1-4, is a thin plate of bone of considerable vertical
extent reaching nearly half the height of the posterior portion of the skull, but not
reaching such a great antero-posterior length as the same bone in Sphenodon. The
articular portion consists of two condyles elongate in the antero-posterior direction and
with their main axes converging slightly as they advance, so that all motion of the
jaws was rigidly limited to the vertical plane. The outer condyle is the more slender
and lies almost in the plane of the upper portion of the bone ; posteriorly it extends
beyond the main part of the bone as a prominent process, with its upper face flattened
into a sort of shelf to which is attached the lower end of the quadrato-jugal. The
inner condyle is stouter and is offset from the body of the bone. The posterior edge

MORPHOLOGICAL REVISION OF THE SUBORDER. 97

of the quadrate is rounded and gives attachment through its length to the quadrato-
jugal, but just above where the quadrato-jugal joins the upper surface of the inner
condyle the two are separated by a good-sized foramen, \h& foramen qiiadratiim. This
foramen serves as an important landmark in the skull ; it is not present in the Cotylo-
sauria; it is probably present in all the primitive Archosanria {^Diaptosaun'a, Osborn)
although it has been demonstrated only in the Pelycosaiiria and Rhyncocephalia vera;
it is present in the carnivoroits Dinosaurs, the Ichthyosaurs, and the Phyiosaiirs ; it is
absent in the Crocodilia, the Pterosaurs, and the Squamata.

The posterior end of the pter>'goid overlaps the quadrate on the inner side, the
lower edge extends back almost to the posterior limit of the bone and is attached to
the inner side of the inner condyle.

The quadrato-jugal occupies a relatively unimportant position in the skull. It
is a very thin plate of bone, with its lower end and posterior edge attached to the
quadrate, as described above. The upper end becomes very sharp and is wedged in
between the prosquamosal and squamosal and comes in contact with the parietal. It
is separated from any contact with the jugal by the descending process of the prosqua-
mosal, as described below, and in turn it separates the prosquamosal from the squa-
mosal, thus occupying a unique position among the reptiles. The position of the
quadrato-jugal is not anomalous, however, for if the upper end were withdrawn from
contact with the parietal by shortening, the prosquamosal and the squamosal would
come in contact, and a union of the two would produce the bone called squamosal or
squamosal + prosquamosal in Sphenodon.

The prosquamosal has the position usually assigned to the quadrato-jugal ; that
is, it connects the jugal and the quadrate. It would have been taken for the quadrato-
jugal in the present specimens if the presence of the foramen quadratum had not
indicated the true position of the quadrato-jugal. (The significance of the position of
the prosquamosal is discussed in the description of the temporal region below.) The
prosquamosal joins the jugal in about the middle of the inferior temporal arch, the
two bones narrowing somewhat as they approach, so the edges of the inferior arch are
concave both above and below. Posteriorly the prosquamosal widens, forming an
upper and lower process, and the bone becomes roughly T-shaped. The lower three-
quarters of the posterior edge join the quadrato-jugal, and the upper quarter joins the
anterior edge of the posterior process of the postorbital to form the posterior edge of
the superior temporal vacuity. The posterior edge of the prosquamosal passes under
the quadrato-jugal articulating with its lower surface, and finally articulates with the
edge of the quadrate near the quadrato-jugal. This is shown in specimen No. 1002
University of Chicago, and Nos. 4036 and 1826 Am. Mus.

The bones fonning the edges of the superior temporal vacuity are approximated,
so the vacuity is very small. In the crushed specimens the sides of the upper vacuity
are very close together and it seems that they must have been so in life. In No. looi
University of Chicago, the edges of the bones where they would meet are very thin,
and it is possible that they met over the vacuity, although there could have been no
true articulation even in this case. There is a strong rugosity of the lower ends of the
parietal which covers the vacuity, but this I am inclined to regard as pathological. In
specimen No. 1002 Universit}' of Chicago, Dimetrodon gigas, the vacuity is open, but
very small and narrow. In specimen No. 4036 Am. Mus., labeled by Cope Naosaurus
claviger, the vacuity is even smaller, not over 15 mm, long.

The parietal has a broadened horizontal upper portion which unites by strong
suture with the frontal, postorbital, and the parietal of the opposite side, but does not

98 REVISION OF THE PELYCOSAURIA.

join the postfrontal. The pineal foramen lies in about the middle of this horizontal
portion and completely posterior to the orbits. The descending portion of the bone
curves sharply outward and downward and joins the quadrato-jugal as described above.

The squamosal lies largely on the posterior and inner (toward the median line)
side of the parietal. Its lower end is widened and overhangs the distal end of the
paroccipital exactly as in Sphenodon, but in larger degree. The relations of the parie-
tal and squamosal are rather peculiar ; the squamosal forms the posterior side of the
parietal arch and reaches almost to the median line of the skull, thus fonning the
major portion of the posterior aspect of the upper part of the skull. In Sphenodon
the parietal forms the posterior part of the skull in the median line and does not pass
under the squamosal till about the middle of the parietal arch. This gives the squamo-
sal an appearance of greater prominence on the back of the Pelycosaurian skull, but
the bones have essentially the same relations in both forms.

The cranial region is formed by a single complex bone composed of the closely
coossified basioccipital, supraoccipital, exoccipital, paroccipital, and petrosal ; in none of
these specimens are there well-defined sutures separating these bones, so that the}' must
have united early in life. Plate 11, figs. 7 and 8, shows this region in No. i University
of Chicago, where it was found disarticulated and complete; the same region in the
other specimens has been somewhat crushed, but shows enough to make it evident that
they are of the same character as specimen 1. The following description is taken
from a previous paper discussing specimen i (Case 22) :

"The occipital region closely resembles that of Sphenodon. The condyle is
formed by the exoccipitals and basioccipital. The exoccipitals meet in the median
line above, excluding the supraoccipital from any part in the foramen magnum.
Laterally they join the expanded proximal ends of the opisthotics. The supraocci-
pital is a triangular plate inclined forward as it ascends and joining by the base of the
triangle the parietals above. Laterally it joins the opisthotics and inferiorly the
exoccipitals. The opisthotics are expanded proximally, joining the supraoccijsital
and exoccipitals. Distally they are elongated outwards, backwards, and downwards.
The lower edge of the proximal end is marked by a notch which, in union with simi-
lar notches in the basioccipital and petrosal form the fenestra ovalis. The opisthotics
remained free during life or until advanced age. This feature is found only in turtles,
Ichthyosaurs, and the young Sphenodon. It has been noticed in young lizards before
leaving the &gg.* The basioccipital fonns the lower portion of the condyle and lies
between the exoccipitals and opisthotics. The lower surface is trough-like for its
posterior half and supported a posterior extension of the basisphenoid. Laterally a
slight notch forms the inner wall of the fenestra ovalis. Anterior to the horizontal
trough-like portion the inferior surface rises sharply ; the angle thus formed is marked
by a large foramen of unknown function, perhaps the hypophysis passes into the
interior of the basioccipital, plate 11, fig. 8. The petrosals join the opisthotics, exoc-
cipitals, and the basioccipital, but the sutures are not distinguishable. The lower
part of the anterior edges was continued forward as long processes, the anterior-inferior
processes of Siebenrock.f These are partially destroyed in the specimen. A deep
notch in the anterior edge of the petrosals just above the origin of these processes,

* Siebenrock, F. : Das Skelet der Lacerta Simonyi Steind, und der Lacertiden familie uberhaupt ;
Sitzunberichten der kaiserl. Akademie der Wissenschaften in Wien. Mathm. Naturwiss. Classe., cm, Abth.
I, April, 1894.

tSiebenrock, F.: Zur Osteologie des Hatteria-Kopfes, ibid., Bd. cii, Abth. i, June, 1893.

MORPHOLOGICAL REVISION OF THE SUBORDER. 99

the iiicisura otosphenoidea Sieb., marks the point of exit from the brain cavity of the
fifth pair of nerves (trigeminus). The superior end of the anterior edge is separated
from the supraoccipital by a notch which is continued on the sides of the bone as a
shallow, short groove. The posterior edge contributes the last portion to the walls
of the fenestra ovalis.

"The basisphenoid remained free. The posterior edge is greatly thickened ver-
tically, and its lower edge stood well away from the basioccipital. The otic region
and the posterior edge of the basisphenoid were covered with a large mass of cartilage.
The lower surface of the basisphenoid is excavated by a deep pit, plate 11, fig. 2,
which opens on the posterior as well as the inferior surface of the bone and divides
the posterior into two parts. The upper edge of the posterior surface, forming the
base of the pit, was continued backward as a spout-like process articulating with the
lower surface of the basioccipital. The anterior edge is extended forward as a para-
sphenoid rostrum originating between the short and stout pterj^goid processes.

"The foramina penetrating these bones are remarkably similar in position to
those jDenetrating the same bones in Sp/ieiiodoii. The condylar foramen transmitting
the twelfth pair (hypoglossus) penetrates the exoccipital just anterior to the edge of
foramen magnum. Its outer end opens in a notch (the incisura vencr jiigularis Sieb.)
in the side of the exoccipital. A little below and further forward a second and much
smaller foramen opens in the same notch ; this may transmit either the ninth or tenth
pair of nerves or a minor blood-vessel. Passing forward the notch deepens and is very
soon converted into a foramen by the adjacent portion of the opisthotic. This is the
foramen vence jiigularis of Siebenrock and transmits the jugular vein and either the
ninth or tenth nerves or both of them. In Spheiiodon the foramen transmits not only
these but the twelfth pair as well, the nerv^es being separated from the vein by very
thin walls of bone and may be separated from each other or have a common canal.
The opening of the twelfth pair into the notch which forms the beginning of the
jugular foramen is then ver>' similar to the condition found in Sphenodon.

"The fenestra ovalis is a single opening leading by a very short canal directly
into the brain cavity, a character found in fishes and the amphibian Menopoma and
existing imperfectly in some recent reptilia, as the turtles. The same thing is
described by Cope as existing in another Permian reptile, from the same horizon as
the present specimen, but belonging to a separate family, the Diadectidce, and his
order Cotylosauria.

" The foramina for the seventh (facial) pair of nerves appear on the outer surface
of the petrosal just anterior to the fenestra ovalis. They are located relatively a little
further back than in Sphenodon. On the inner face of the same bone the foramina
appear at the side of the base of the brain cavity a little anterior to their external
opening. They are located just anterior to a slight ridge which defines the limits of
the tympanic cavity. In Sphenodon this is about the point of location of a foramen
common to the seventh and eighth nerves, which, however, almost immediately
divides, the posterior branch penetrating the inner wall of the tympanic cavity and
leading the auditory nerve to the inner ear.

" The foramen for the fifth (trigeminus) nerve is completed from the incisura
otosphenoidea by the membranous wall of the anterior portion of the brain case, as in
Sphenodon and many lizards.

" A cast of the brain cavity shows fairly well all parts posterior to the fifth pair
of nerves, and the hypophysis anterior to them. As is well known, the brain in the

REVISION OF THE PELYCOSAURIA.

reptilia does not fill the brain cavity, but is supported by a mass of connective tissue
carrying lymph and fat masses ; so a cast of the brain cavity does not give an exact
copy of the brain. However, many points can be brought out by such a cast.

" If the cast be held with the short terminal portion of the medulla horizontal,
the lower surface pitches downward at a sharp angle to a point anterior to the tympanic
region, and then ascends as sharply to the point of origin of the hypophysis. The
superior surface is horizontal and arched from side to side to a point over the
tympanic cavity and there turns upward at an angle of 45°. The angle thus pro-
duced is marked by a low, narrow ridge running across the cast and marking the

position on the brain of a narrow and elevated
cerebellum, fig. 27 cb^ such as occurs in Spheno-
don. This region was probably the seat of a large
amount of connective tissue, and it is probable that
the upper surface of the medulla descended at as
sharp an angle as the lower. This would make
still more marked the resemblance to Sphenodon
and to the cast figured by Cope. This sharp bend
of the medulla downward is not found in other
forms, though in the brain of Chelonia and some
Lacertilia a bend is apparent.

"The sides of the medulla show most pos-
teriorly the beginning of the twelfth nerves, figs.
27 and 28 (12), anterior to these the cast of the
jugular foramen, y«, and finally the large casts of
the tympanic cavity, Ty.

" Anterior to the tympanic casts a sharp con-
striction marks the ridge defining the limits of the
tympanic cavity, and then a sharp outswelling, the
point of exit of the trigeminus nerve (5). Near
where these leave the body of the cast a small
stub on each side marks the origin of the seventh
pair (7).

" The hypophysis is the most interesting
feature of the brain. Descending between the
anterior-inferior process of the petrosal and turning
posteriorly, it occupies a small notch in the pos-
terior edge of the upper surface of the basisphenoid
and then passes directly into the body of the basi-
occipital through the foramen mentioned. In the
Crocodilia a somewhat similar condition exists."
Some additional points have been made out from specimens looi and 1002,
University of Chicago. The distal ends of the paroccipitals rest on or close to the
upper edges of the quadrates and are overlapped by the squamosals. On the left side
of the cranial region of specimen 1002 the median portion of the stapes is preserved ;
it shows that the stapes was a slender rod extending from the foramen to the quadrate
just beneath the paroccipital. Unfortunately neither end is preserved. Cope speaks
of both a columella auris and a stapes, but there is no evidence of more than a single
bone in these specimens. The semicircular canals of both sides are fairly well pre-
served and show the presence of a large ampullar space (ampullenraum, Siebenrock)

Fig. 27. — A lateral view of cast of brain cavity
of D. inc/sivus, No. I University of Chi-
cago. X 1. eft, cerebellum ; 12, twelfth
aanial nerve; ju, cast of jugular for-
amen. Ty, cast of tympanic cavity ;
Hy, hypophysis; 5, 7, fifth and seventh
cranial nerves.

Fig. 28. — Ventral view of same. Lettering as
in fig. 27.

MORPHOLOGICAL REVISION OF THE SUBORDER. lOI

and well-developed semicircular canals. A displaced portion of the petrosal shows
the penetration of the canals into its body.

The jngal forms the lower half of the orbital rim. The orbital edge is widened
by the development of a strong, sharp ridge on the outer side of the bone so that the
socket is bordered on the lower side by a shelf of at least a centimeter in width.
The lower part of the bone is very thin and the edges are without thickening rugosi-
ties. On the inner side of the jugal a strong ridge extends obliquely downwards and
forwards from the orbit to the antero-inferior angle of the bone ; here it leaves the bone
and extends as a sessile process with a bifurcate end ; into the bifurcation of the end
articulates the upper end of the transverse, fig. 29. The articulation with the maxillary
is by a close interdigitating suture which locks the bones very closely together.

The bones of the top of the skull have
already been described from specimens Nos.
I and 1002 and the separate elements figiired,
but in the specimen No. looi the top of the
skull is preser\'ed on one side without dis-
tortion and the bones can be seen in their
natural relations, plate 10, figs, i and 2.

The postorbital consists of a flat ante-
rior portion and two posterior branches. One
of the posterior branches extends downwards
to join the jugal and fdrm the upper half of
29,-Innet view ot suborbital portion of skull ot the postcHor rim of the orbit ; it passes in-

a /nc«,«as, No. lOOl Umversity of Chicago. ^j^^ ^f ^j^^ j^^ j ^^^ 3^ fo„„3 ^^^^^ ^^^^^ ^f
Showing relations ol the transverse, pterygoid, , . , . ,

maxillary, and palatine. X >4. ^he Orbital rim than appears on the exterior.

The second, upper, posterior process passes
backward to join the prosquamosal and form the upper edge of the inferior temporal
vacuitj'. The anterior portion joins the postfrontal and parietal; its outer edge is
thickened and rugose and forms the posterior portion of the superorbital ridge.

The postfrontal is a quadrangular bone which articulates with postorbital and
frontal ; its outer edge carries forward the rugose superorbital ridge.

The roof of the orbit formed by the postorbital, postfrontal, frontal, and prefrontal
is rounded and vaulted so that its capacity is much increased inwardly. From the
inner edges of the lower side of the postorbital and prefrontal, ridges extend inward
in a curve, on the lower surfaces of the frontal aud postfrontal until they finally meet
on the median line of the skull completing a perfect semicircle. This truss-like ridge
surrounding the vaulted roof of the orbit adds greatly to the strength of the skull.

The lachrymal is not well shown in any of the specimens nor is there a lachrymal
foramen. In some of the specimens there is evidence of a faint suture on the anterior
edge of the orbit indicating the possible presence of a distinct bone, but it is impos-
sible to trace the suture out upon the facial portion of the skull. Howse and Swin-
nerton in their discussion of the development of Sphenodon say that there is no trace
of a lachrymal in that form. It may be very possible that it did not develop in the
Pelycosauria; certainly, if it did, it very early coalesced with the surrounding bones.

'Vhe frontal is an elongate bone lying horizontally in the skull ; near the pos-
terior end a process extends outward to the orbital rim forming the middle of the
edge. The union of the bones of the two sides gives a distinct cruciform arrangement
in the middle of the skuU roof. The articulations of the bone are best shown in
plate lo, fig. I.

REVISION OF THE PELYCOSAURIA.

The prefrontal forms the superior anterior angle of the orbit and extends forward
betvveeen the nasal and frontal above and the maxillary' and lachrymal (?) below.
The posterior portion of the bone is bent at right angles on the antero-posterior axis,
so that the upper portion of the bones is horizontal and the lower vertical. The
horizontal portion forms a part of the roof of the skull and the anterior part of the
superorbital ridge. On the vertical portion a strong ridge carries the superorbital ridge
forward on to the facial region.
Beneath the posterior end of this
ridge and just anterior to the orbit
is a deep pit. The presence of this
ridge and pit is one of the charac-
teristic features of the Pel5'cosaurian
skull.

The nasals are elongate bones
occupying the median line of the
skull and extending from a point
just anterior to the orbits to the
anterior nares in front.

The septo-maxillary : Ante-
rior to the nasal and forming the
posterior edge of the narial open-
ing is a singular bone, the septo-
maxillary, difficult of description,
but indicated in plates 17 and iS,
figs. I. Each bone is bent at right angles, so that
the lower half fonns the floor of the posterior half
of the nares and the upper half its posterior edge.
The two bones of the opposite side meet in the
median line. Of the vertical portion, the inner part
is only one-half so high as the outer, so that while
the outer part extends to the top of the nares, the
inner part reaches up only one-half the height. This
forms a dam across the posterior part of the nares,
so that the air in entering must first pass upward
and over the dam and then downward into the mouth.
On the outer side of the septo-maxillary a short pro-
cess at the posterior inferior angle of the nares
divides two foramina which pass between the septo-
maxillary and the maxillary to the interior of the skull,
problematical.

The premaxillaries are heavy rounded bones uniting in the median line by a
wide sutural area. The lower edge is thickened for the reception of the tooth sockets,
and the outer surface of the edge is marked by deep pits and rugosities. The suture
between the premaxillary and maxillary terminates below in the middle of the dias-
temal notch. Superiorly the premaxillaries send upward and backward long processes,
which pass between the nasals and form the upper portion of the nares. The premax-
illaries always carry large tusks and smaller teeth ; the tusks lie near the median line in
the fore part of the bone, but their number seems to be variable in the different species.
The maxillaries are peculiar in their great vertical extent, forming the greater
portion of the elevated facial region. The upper portion is remarkably thin, never

Fig. 30. — Secrion of skull of D. gigas.
No. 1002 University of Chicago,
opposite posterior end of palate. ^/,
palatine, //, slender vertical plates of
pterygoid, mv, maxillary.

Fig. 3 1 . — Cross-section of same skull through
diastemal notch, pmx, premaxil-
lary; px', prevomer : ft^ pterygoid;
», nasal.

Their function is entirely

MORPHOLOGICAL REVISION OF THE SUBORDER. 103

exceeding 2 mm., even in the largest specimen, while the edge of the bone carrying
the teeth may reach a thickness of 2 and 3 centimeters. The thinness of the upper
portion of the maxillary is shared by the adjacent bones, the nasals, prefontal, jugal,
and lachrymal, so that this part of the skull is almost always shattered in the processes
of fossilization and lost. The lower edge of the bone is very abruptly widened into
a thick dentigerous border (figs. 30 and 31 and plate 10, fig. 4), which is in strong
contrast to the weak upper portion of the facial region. The width of this border is
greatest opposite the enlarged canine near the anterior end of the maxillary and
decreases in width toward the posterior end of the bone as the teeth become smaller.
In the diastemal notch there seems to be no great wideuing of the edge, even in the
fonns where teeth are present in the notch. The posterior end of the bone articu-
lates with the jugal, as described above. The outer surface is marked on the lower
edge with pits and rugosities.

The teeth are lenticular in form, with distinct fore and aft cutting edges, which
are strongly serrate. The roots of the teeth are implanted in distinct sockets which
may reach a depth as great as the length of the tooth beyond the outer edge of the
bone (plate 14, fig. 8). The outer edge of the bone extends much farther down than
the inner, so that a good bit of the length of the tooth after it leaves the socket rests
against this edge. The root of the tooth is hollow and its inner end is open, so that
it is evident that the teeth were replaced by absorption of the root and continued
growth of new teeth. This process is seen in actual progress in several specimens.
One peculiarity of the deutition in the family Clepsydropidce is very striking. The
maxillary has always two alveoli for enlarged canine teeth, but in only one or two
specimens of the man)' preser\-ed are there two enlarged teeth present in the maxillary ;
in all the others there is one tooth functional and either an empty alveolus or a tooth
just beginning to appear from the socket. It seems that the two large canines of each
side were alternately functional, one growing to full size and function as the other fell
or was pushed out by the successional tooth. It is as often the anterior as the posterior
tooth which is lost, and the anterior is often present on one side of the jaw while
the posterior is present on the other side. Thus the animal was never deprived of its
powerful tusks for any considerable interval.

The number of the teeth seems to be variable in the different specimens, but
was never far from 20 in the maxillary and 28 in the lower jaw.

The trcvisi'erse is seen in specimens Nos. looi and 1002 University of Chicago.
On the inner side of the jugal, as described above and shown in fig. 30, a strong ridge
extends forward and receives into its bifurcated end the upper end of the transverse.
From this point the transverse extends straight downward on the anterior and outer
face of the outer process of the pter>'goid; its lower edge fuses with the pter>'goid so
that it is impossible to describe its lower limit exactly, but it does not extend very far
down on the pterygoid. The anterior edge of the transverse unites with the posterior
end of the maxillary, so that it is held firmly in its position.

The pte>y£-oid, as repeatedly described, has a distinct tripartite form, consisting
of an anterior horizontal portion, a medium vertical process, and a posterior portion
which joins the quadrate. The form of the bone is best shown in plate i i,figs. 5 and 6,
which are from specimen i University of Chicago.

The anterior plate is separated from the maxillary by the palatine and the trans-
verse. These bones join the pterygoid directly, so that there are no palatine vacuities
in the posterior part of the palate. The anterior processes come very close together
in the median line, but it is impossible to say whether they are united throughout
their length or not. It seems probable that there was a space between the posterior

I04

REVISION OF THE PELYCOSAURIA.

portions, but the anterior parts come close together. From the inner edges of the
anterior portions of the pteiygoids vertical plates extend upward in the skull, forming
a median septum in the lower part of the nasal region. Anteriorly these plates unite
and below they pass into the prevomers. The suture between the plates and prevomers
is visible anteriorly, but posteriorly it disappears (figs. 30 and 31, and plate 18, fig. i,
//). Similar vertical plates occur on the inner edge of the pterygoids of Protersiichiis
fergusi Broom. The median portions of the anterior processes were covered with
small teeth that were in part, at least, implanted in shallow sockets.

The median external process is a stout projection with a flat external face, which
formed a buttress for the lower jaw, such as occurs in the Crocodilia and in Sp/ieiiodon.
It stands much nearer the surface of the skull than in the forms mentioned, so that
its outer face is in almost the same plane as the side of the skull. The upper and
anterior portion of the external face of this process is certainly formed by the trans-
verse, and it is marked by a sculpture of fine lines. The lower edge of the process
is rounded, and carries a row of teeth in sockets. The number and size of these
teeth vary, and so seem to be of value in specific determination.

The posterior process is a broad plate standing nearly vertically in the skull, but
inclining inward somewhat at the top. At the point of departure from the median
process it is of less vertical extent and stouter, but as it passes back it becomes very
thin and plate-like. It joins the quadrate as described above, and from its upper
surface rises the epipterygoid.

The epipterygoid is the only bone that does not have a complete representation
in one of the three skulls. In No. 1002 the lower ends are still in contact with the
pter>'goid, but the upper part is lost. It seems that the bone articulated loosely with
the parietal by the intervention of cartilage, much as in Sphenodon. The form was
that of a slender flattened pillar.

The palatines are slender plates closely attached to both the maxillaries and
pterygoids. The attachment to the maxillary is very firm. A vertical expansion of
the bone is applied to the inner side of the alveolar edge, and from this springs the
horizontal plate. The bone reaches from the posterior end of the maxillary to a point
opposite the canine tooth. The anterior end forms the posterior edge of the posterior
nares.

The basispheiioid is best shown in plate 11, figs. 2 and 3. The posterior end is
swollen, and articulates with the basioccipital. There is evidence of the presence
of considerable cartilage in this region during life. On the lower surface there is a
deep pit, and near the anterior end two strong articular faces. The anterior end
terminates in a strong, median, vertical plate, the parasphenoidal rostrum.

The deep pit excavating the lower surface of the basisphenoid is, in all proba-
bility, the lower opening of the Eustachian tubes. In most reptilian forms the tubes
pass into the pharynx in the neighborhood of the basioccipital-basisphenoid suture
and anterior to the fenestra ovalis. In the Crocodilia and the aglossal batrachiaus they
have a common opening into the mouth. In the present fonn the tubes probably
penetrated the large mass of cartilage covering the otic region and the posterior end
of the basisphenoid and found a common opening in the deep pit described. It is
difficult to imagine the use of such an extensive cavity in the basisphenoid, but in
the Teleosauria an equally large cavity is found roofed over with bone. Anterior to
this pit two foramina penetrate the lower surface of the basisphenoid bone, and on its
upper surface a large foramen appears just posterior to the origin of the parasphenoid
rostrum. Through the pair on the lower surface the internal carotid arteries enter

MORPHOLOGICAL REVISION OF THE SUBORDER. I05

the bone, and through the upper they gain access to the brain cavity by way of the
pituitary fossa. On either side of the single foramen a pair of small foramina carry
branches of the internal carotid. All of these foramina are very similar in position
to the same ones in Spheiiodon.

The two articular faces near the anterior end are the basipterygoid processes.
There are no corresponding articular faces on the pterj-goid, and it is evident from the
specimen No. 1002, where the bones of the palatal surface of the skull are little dis-
turbed, that they did not articulate with the pterygoids on their inner side opposite
the external processes, as at first supposed, but much further back. It is probable
that there was a large mass of cartilage between the basipterygoid processes and the
pterygoid comparable to the meniscus pterygoideiis described by Howse and Swin-
nerton in the developing Sphenodon skull.

The parasphenoid : From between the basipterygoid process extends anteriorly
a vertical, compressed plate (plate 18, figs, i and 2, and plate 11, figs. 2 and 3), which
extends directly upward in the median line of the skull. The point of union of this
plate and the basisphenoid is marked on the upper edge by a deep notch. It has been
shown by Parker, Siebenrock, Howse and Swiunerton, and others, that the basi-
sphenoid of the adult reptiles is a compound bone, formed of the true cartilaginous
basisphenoid and a dermal ossification which is the parasphenoid of the amphibians.
In embry^onic, and even in early postembryonic life in Sphoiodon (according to Sieben-
rock), the suture between the two is traceable. In the forms with a cartilaginous
interorbital septum ( Crocodih'a, Lacertilm, and Chelonia) the cartilaginous presphenoid
is not ossified, and the parasphenoid extends as a slender stylifonn process from the
anterior end of the basisphenoid beneath the cartilaginous interorbital septum, and
supports in embryonic life the membranous floor of the pituitary' space. There is no
doubt that the anterior process of the basisphenoid in the Pelycosaiiria^ as in the
Lacertilia and Rhynchocephalia vera, is the remnant of the parasphenoid united to the
basisphenoid, and not the presphenoid, as first described by Baur and Case (10).

The ethmoid: Instead, howe\-er, of the parasphenoid process of the Pelycosauria
ending as a slender rod in the floor of the pituitary space, it extends upward as a
strong slender plate, and unites above with a second plate which is in contact with
the lower surface of the frontal bones. The suture between the parasphenoid and this
plate is closed, but its position is marked by a low ridge, showing the point of coossifi-
cation. The upper edge of the upper plate is planted finnly against the under side
of the frontals, and there seems to be ample evidence of a direct sutural union ; but
as the region is somewhat crushed, it is possible that the plate did not quite touch the
frontal in life, but was connected with it by cartilage, and that it has been forced into
close contact by the accidents of fossilization. However it may be, the relations of
the bone would not be altered. The anterior edge of the plate is irregular and very
thin, showing that it passed gradually into the cartilage of the interorbital septum in
front. The upper portion of the posterior edge is thin, but the posterior angle is
thickened and rounded. There is a deep notch between this angle and the para-
sphenoid below, and this notch marks the position of the escape of the second pair
of cranial nerves. There is no trace of either orbito- or alisphenoid ossification, as
remarked above.

There is no true median vomer.

The prevomers : The specimen No. 1002 is of especial value, as it preserves the
thin median plates of the skull. It clearly shows the presence of paired prevomers.
The prevomers (20) are rather stout rods of bones extending from the middle of the

Io6 REVISION OF THE PELYCOSAURIA.

premaxillaries backward and downward in a curve to a point opposite the end of the
palatine. Their form and relations are shown in plate i8, figs, i and 2, and plate
19, figs. 2 and 4. The curvature of the lower surface makes a vaulted roof to the
mouth in the anterior portion. In about the middle of their course they are free from
the bones on the sides, leaving a cavity which fonns the posterior nares; the sides of the
prevomers at this point are marked by a prominent rugosity of the edge. Superiorl)'
and posteriorly the prevomers join the vertical pterj-goid plates ; superiorly the upper
edges diverge and receive between them the united plates; posteriorly they shade
indefinitely into the plates, so that it is impossible to fix the exact limits of the bone.

The lower jaiv : In specimen No. looi the lower jaws are preserved almost per-
fectly ; the coronoid, which was a small splint bone, seems to be lost from both sides.
The posterior portion of the jaw becomes ver>' high b)- the development of the posterior
bones as vertical plates and from the inner side of this region the articular region
projects as an almost sessile process made up of various processes from the angular,
surangular, and prearticular (splenial) ; for this reason the posterior portion of the jaw
is almost always shattered in the ground and the more solid articular region is the
most commonly preserved. It was such an isolated mass which was interpreted by
Baur and Case as the articular region of the skull. Plate 9, figs. 1-4, shows the lower
jaws and the articular region in detail.

The articular is a flattened disk-like bone completely inclosed on all sides but
the superior. The upper surface bears two cotyli corresponding to the condyles of the
quadrate. On the under side of the articular the posterior ends of the prearticular
(splenial) and the angular meet in the median line and furnish the main support
of the articular region ; between the articular and angular is slipped the posterior end
of the surangular. This appears largely on the upper surface and fonns the inner
side of the pedicle supporting the articular and its main attachment to the main por-
tion of the jaw. On the outer side of the upper surface the prearticular appears and
the articular sends a process forward for a short distance between this bone and the
surangular. There is a deep pit extending backward and inward along the line of the
articular-surangular suture. From posterior edge of articular in specimen No. looi
a curious short curved process extends inward and upward (plate 11, figs. 9-1 1).

The main portion of the jaw is best understood from plate 9. The articular
pedicle is crushed down ; in the natural condition it stood out almost at right angles
from the jaw.

The surangular passes directly into a broad plate forming the posterior portion
of the upper half of the bone ; it rises rapidly as it passes forward to meet the rising
end of the dentary. There are impressions on the adjoining ends of these two bones
indicating the loss of the coronoid.

The angular forms the lower portion of the posterior half of the jaw. It is
rather wide and continues the lower edge of the jaw as far downward as the coronoid
carried the superior edge upward. It extends forward past the middle of the jaw,
forming a good portion of the outer surface of the jaw.

The prearticular extends forward between the angular and surangular till it
meets the splenial (presplenial of Baur).

The splenial is relatively narrow, covering the upper half of the inner face of the
jaw, but does not take part in the symphysis.

The dentary carries a variable number of teeth in the different species ; there are
always one or two enlarged tusks near the anterior end, corresponding to the incisor
tusks of the premaxillary above, but none that correspond to the canine tusks.

MORPHOLOGICAL REVISION OF THE SUBORDER.

107

^\\^ vertebral column (plate 13, fig. 2): The column contains twenty-seven pre-
sacrals, three sacrals (No. 4008 Am. Mus.), and at least nine caudals (No. 4040 Am. Mus.).

The atlas (Nos. i and looi University of Chicago) : Preceding the atlas is a
preatlantal intercentrum ; it is larger than the second, atlas-axis one, and has well-
developed tuberosities which carry faces for the head of the atlantal rib. The anterior
face is the larger, is concave vertically as well as transversely, and lodges the hemi-
spherical occipital condyle. The posterior face is convex vertically and fits against the
saddle-shaped lower portion of the anterior articular face of the atlas.

The centrum of the atlas is broad above antero-posteriorly and contracted below.
The shape of the face is best seen in plate 16, figs. 5 and 6. It is elongate, heart-
shaped, and partly divided into two parts by a compression near the middle ; the
lower part of the face is distinctly saddle-shaped. The foramen for the exit of the

inter i

Fig. 32. — First intercentrum, atlas, second intercentrum, and axis of D. incisivus. No. I
University of Chicago. r'«/c?/, preatlantal intercentrum, a/, atlas centrum ; inter 7.,
second intercentrum. X )i. ■ <', Anterior face of atlas.

Fig. 33. — First intercentrum, atlas, second intercentrum, and axis of D. incisivus, No. 1001
University of Chicago, /w^c;- /, preatlantal intercentrum ; «/, atlas centrum ; inter 2,
second intercentrum. •' Yz. a. Anterior face of atlas.

Fig. 34. — First intercentrum, atlas, second intercenlium, and axis of D. g/gas, No. 1002
University of Chicago, inter /, preatlantal intercentrum; a/, atlas centrum: inters,
second intercentrum. X K. o. Anterior face of atlas.

Fig. 35. — Axis of D. dollovianus, No. 1 14 University of Chicago. X 'i.

notochord is near the middle of the anterior face and is very
small as compared with the deep funnel for its entrance on the
posterior side. There is in the University of Chicago collection
an atlas firmly fused with the preatlantal intercentrum.

The neural arches of the atlas (No. lOoi University of
Chicago) are semicircular flattened elements entirely free from
the centrum. In the photograph, plate 15, fig. 2, they are placed as they lay on the
ground with reference to the other ^•ertebr^e (one has been turned over to show the oppo-
site side). On what is probably the outer surface there is a well-developed flattened
surface near the middle which seems to have articulated with the prezygapophyses of

io8

REVISION OF THE PELYCOSAURIA.

the axis. On the opposite, inner, side is a saddle-shaped articular face wider anteriorly
than posteriorly. Below this saddle face is a deep pit which communicates by a notch
on the anterior edge with a deep groove below the articular face on the outer side.

On the outer side of the lower end there is on some atlas arches preserved in the
American Museum a small smooth facet ; this may have marked the articulation with

the centrum. The arches were very loose in
their position and it has been an almost unan-
swerable puzzle to place them in any position
that would seem the correct one; they were
probably held free by a considerable mass of car-
tilage and ligament. (Plate i6, figs.'3 and 4.)

36 37 38

Fig. 36. — Thiid cervical of D. giganhomogenes, No. 1 12 University of Chicago. X }i.
Fig. 37.— Tfiird cervical of D. gigas, No. 1002 University of Chicago. X }i.
Fig. 38. — Third cervical of D. incisivus. No. 1001 University of Chicago. X yi.
Fig. 39. — Third cervical of D. dollovianus. No. 1 14 University of Chicago. X }i.

The second intercentrmn is smaller than the first, but has distinct processes and
facets for the head of the axial rib.

The axis (No. i and No. looi University of Chicago) has the centrum somewhat
elongate with the beginning of a keel on the median line below. The posterior face of
the centrum is lower than the anterior face, so that a line drawn through the middle
of the centrum antero-posteriorly would be inclined downward toward the rear. The
transverse process rises from the side of the neural arch and curves out and downward,
at the same time slanting to the rear. The process is not free from the centrum even
at its distal end, being bound to it by a strong ridge below. The posterior zygapo-
physes are large and well developed, but the anterior ones are very small with flat
horizontal articular faces (No. lOOi University of Chicago). The spine is ver>' wide

MORPHOLOGICAL REVISION OF THE SUBORDER. IO9

antero-posteriorly. The upper end has a large area for ligamentous attachment and the
front edge which extends out over the atlas has rugosities for the same purpose. On
the upper edge of the anterior articular face of the axis are a pair of concave facets lying
at the base of the anterior zygapophyses. On the upper edge of the posterior articular
face is a second pair of flattened facets which correspond to the anterior ones in posi-
tion. Similar but less well-developed facets appear on the succeeding vertebrse
throughout the presacral portion of the column. These facets seem to be different
from any described heretofore and, as they have evidently a somewhat similar function
to the zygosphene and zygantrum, they have been called by analogy centrosphene and
centantrum. These are evidently imperfect in function and development and are
variably developed in the different genera and species of the suborder Pelycosauria.

The third cervical vertebra (description of column to first caudal from No.
4008 Am. Mus.) : The centrum is shorter than that of the axis and has the bottom
line nearly straight along the edge of a well-developed keel. The posterior face is
lower than the anterior, preserving the drop in the neck. The transverse process is
short and inclined to the rear ; the outer end is free from the centrum and has a well-
developed facet for the tuberculum. The zygapophyses are nearly horizontal and the
neural spine is relatively short, but higher than that of the axis. The intercentrum
has facets for the capitulum of the rib on slight prominences.

In \h& fourth cen<ical vertebra the sides of the centrum begin to show the sharp
compression below the intercentrum which forms the narrow high keel in the dorsals.

In they?/?// cervical vertebra the compression of the sides of the centrum is very
marked and the keel very thin and high. The tranverse processes stand out nearly
straight and are short.

In the sixth cervical vertebra the centrum is greatly shortened on the bottom line
by the bending back of the anterior face to accommodate the intercentrum. The
sides are sharply contracted just below the intercentrum and the keel is nearly half as
high as the whole centrum. The centrum is higher than long on the bottom line.
(Length of the bottom line 23 mm. ; height of the centrum just posterior to the
neural arch 35 mm.)

The seventh to fourteenth vertebrse (anterior dorsals) are of the same form as the
sixth, but show a gradual decrease in the bending back of the anterior face below,
showing that the intercentrum is growing smaller. The keel on the bottom line
remains shorter than the height of the centrum and is very thin ; it extends up to just
below the notochordal canal. The anterior articular face has a very wide inferior pro-
cess for the intercentrum. The transverse process stands nearly straight out from the
upper edge of the centrum. It shows here the origin characteristic for all the genus ;
a ridge rises from the base of the anterior zygapophysis and runs posteriori}' ; a ridge
rises from the base of the posterior zygapophysis and runs anteriorly. These unite
and form the upper portion of the transverse process, the ridge continuing as the
anterior and posterior edges. Below a ridge rises from the side of the centrum and
forms the bottom of the process. The process is thus primarily triangular in section,
but the position of the lower edge is changeable. At first it extends from the trans-
verse process backward, in some forms reaching to the posterior edge of the centrum ;
in the dorsals it rises directly beneath the process and extends straight out; in the
posterior dorsals it swings forward until it touches the anterior edge of the centrum
and in the lumbers it gradually shortens and finally unites with the face for the capit-
ulum of the rib. The articular faces of the zygapophyses are very oblique, not hori-
zontal, and the spine rises vertically from directly over the center of the vertebra.

no REVISION OF THE PELYCOSAURIA.

The fifteenth verteln-a resembles the preceding. The inferior ridge here reaches
to the anterior edge of the centrum. The imperfect spine of a mid-dorsal, No. i
University of Chicago, is 872 mm. high.

The sixteenth to the eighteetith vertebra (posterior dorsals). The articular faces
of the centrum are more nearly circular than the preceding, the anterior face having
lost in large measure the wide inferior face for the intercentrum. The keel is still
apparent, but is not so thin, the sides of the centrum not being sharply contracted
immediately below the notochordal canal, but contracting gradually so that the section
of the vertebrae at the middle is rather a rounded wedge than a cylinder with narrow
ridge below (see figs. 24 and 25). On the eighteenth vertebra the inferior ridge sup-
porting the transverse process has extended so far forward as to join the anterior
articular face of the centrum. These vertebrae show a gradual elongation on the
bottom line. The perfect spine of a posterior dorsal of No. i is 863 mm. high.

On the nineteenth vertebra (first lumbar) the face for the capitulum of the rib
suddenly appears on the edge of the centrum. The sudden removal of the head of
the rib from a position between the centra and articulating by cartilage with the end
of the intercentrum to an articular face on the anterior edge of the centrum is a very
characteristic feature in the vertebral column. In one or two species there is a single
vertebra which shows an intermediate stage, but in most the change is as sudden as
the change of position of the capitulum in the Crocodilia. The vertebra which shows
this change has been rather arbitrarily assumed as the first lumbar ; there is reason to
believe that the first free rib was attached somewhat farther back.

The tzventieth resembles the nineteenth except that the face on the edge of the
centrum is larger. After the twentieth there is a break ; the next two are free from
the matrix and do not connect bj' a perfect fit with either the anterior or the posterior
series, but there is little doubt that the}' belong in the position assigned to them.

The twenty-first to the tzcenty-seventh are reckoned as posterior lumbars. The
centra gradually shorten on the bottom line luitil the posterior ones are much shorter
than high. The articular faces are nearly circular. The bottom line and the sides
are deeply concave ; a deep depression on either side of the median line below throws
the bottom line into prominence as a rounded ridge. The articular faces for the
capitulum and the tuberculum gradually approach each other until the}- unite in one
face and become much reduced in size. In the posterior dorsals the neural spines
begin to grow shorter and to curve to the rear and in the lumbars this continued until
on the posterior lumbars and the sacrals the spines are not over 100 mm. in height.
The spines rise from much farther back in the lumbars than in the dorsals so that the
axis of the spine is almost over the posterior z^-gapophj'ses ; this results in or accom-
panies the elongation of the anterior lumbars aud causes a much greater distance to
intervene between the pre- and postzygapophyses. Plate 12, fig. 10, shows three
posterior lumbars of No. i University of Chicago, giving an idea of the shape of the
centrum and the ribs.

The twenty-eighth and tiventy-ninth are the first two sacrals and terminate the
series in this specimen. The sacrals are best described from the next specimen.

No. 4040 Am. Mus. The anterior portion of the column is missing in this
specimen, but it is complete from the ninth presacral to the ninth caudal. The ninth
presacral (corresponding to the eighteenth vertebra of the preceding number) has a
face on the anterior edge of the centrum for the capitulum of the rib, so the lumbar
series begins one vertebra earlier.

MORPHOLOGICAL REVISION OF THE SUBORDER. Ill

The sacrals, the twenty-eighth to the thirtieth, are abruptly longer than the last
lumbars and are closely fitted one against the other, the lower edges being in close
contact and the intercentra reduced to small scales firmly coossified with the centra.
The transverse processes are reduced to faces only, and the ribs are strongly anchy-
losed to the sides of the centra. The head of the anterior rib projects forward beyond
the anterior end of the centrum forming a pair of faces which articulate with the
posterior edge of the last lumbar. This rib is larger than the others and the distal
end is turned downward, forming a broad vertical face which is applied to the inner
side of the ilium (plate 17, figs. 3 and 4). The two posterior ribs are smaller and do
not have the distal ends turned down to form a vertical face ; they were inclined
forward, and as shown in D. dollainamis seemed rather to support the anterior rib than
to support the ilium (plate 23, fig. i). The spines of the sacrals are much reduced in
height and strength ; the firm union of the centra and consequent immobility of the
sacrals has caused the partial atrophy of the zygapophyses so that between the sacrals
they are very small, even anchylosed, in some specimens.

The anterior caudals^ thirty-first to the thirty-ninth, are all of similar form and
the last is as perfect in form as the first, although it is only one-half the size. The
rapid reduction in size without any assumption of the cylindrical form characteristic
of long-tailed forms indicates the absence of a long tail, though chevrons of good size
occur; this is supported by the fact that in none of the numerous specimens of
Dimetrodon has any portion of a long tail been discovered. The centra of the caudals
are short with nearly circular faces ; the transverse processes are reduced so the ribs
are attached directly to the sides of the centra, but not anchylosed in the anterior ones.
The faces for the capitulum and tuberculum are separate in the anterior ones, but after
the fourth are united and on the ninth are ver}' small. On either side of the bottom
line the centrum is marked by a deep pit which throws the mid-line into a rounded
ridge ; it will be seen that the most posterior lumbars and the anterior caudals strongly
resemble each other. The intercentra of the anterior caudals are flat and wide antero-
posteriorly and underlie the point of contact of the two adjacent centra, but between
the fifth and sixth the lower edge of the faces of adjacent centra are cut away leaving
a wide triangular interspace to accommodate the head of the chevrons. The head of
the chevron fits in between the two vertebrae in such a manner that the long terminal
process is inclined sharply to the rear. Just below the head the chevron is pierced by
an elongate foramen. The ribs are short at best and on the ninth vertebra are reduced
to mere stubs.

The ribs are found on all vertebrae from the atlas to the ninth caudal. The
capitulum and tuberculum are well-developed and widely separated, even in the
atlantal pair, and only in the reduced ribs of the posterior lumbars and caudals do the
two unite. In the cer\-icals and anterior dorsal the capitulum articulates with a face
developed on a strong tuberosity on the lower side of the intercentnim ; Cope regarded
this as a characteristic feature of specific value, but it occurs in all members of the
genus. In the mid-dorsal region the head of the rib slips from the side of the inter-
centrum to the end, between the centra, and articulates with the intercentrum by a
cartilaginous connection ; the articular face disappears from the intercentrum in all
but D. macrospondylus, where there is a wide expansion of the ends of the inter-
centrum with a face for the rib even in the lumbar region.

At the eighteenth or nineteenth the capitulum of the ribs suddenly slips from its
position between the centra to the edge of the centrum where a face appears for it ;

112

REVISION OF THE PELYCOSAURIA.

the transverse process has greatly shortened in the posterior dorsals and lumbars, and
its terminal face is now nearly on a level with that for the head of the rib, the two
faces approach each other as the capitulum and tuberculum of the rib grow closer
together nntil they unite. (See figs. 51-53.)

The shoulder girdle is described largely from that of specimen No. 114 Univer-
sity of Chicago, D. dolloviamis, which closely resembles that of D. incisivus^ but is more
perfectly preserved. Scapula, coracoid, procoracoid, clavicle, interclavicle, and proba-
bly a rudimentary' cleithrum are present.

Fig. 40. — Diagram of shoulder girdle of D.
dollovianus. No. 1 1 4 University of Chi-
cago, d, clavicle ; J<co. procoracoid ;
CO, coracoid ; sc/>, scapula ; clt, cleith-
rum.

Fig. 41. — Inner surface of scapula of D. incisi-
BUS, No. 41 31 Am. Mus. sc/, scapula ;
CO, coracoid ; pre, procoracoid. X yi ■

The scapula is elongate with an ex-
panded distal end and narrow shaft; the
proximal end widens, the anterior portion
is thin and unites firml)' with the procora-
coid, though the suture remains traceable
through life. On the posterior edge the
bone is very heavy and forms the upper
half of the deep cotylus. Just above the
cotylus a foramen penetrates the bone and
opens into a deep semilunar cavity on the
inner side (fig. 41); just in front of the
cotylus a foramen penetrates between the
scapula and procoracoid and opens into the
same cavity on the inner side. This is the
homologue of the coracoid foramen of other
forms.

The procoracoid terminates anteriorly in a thin, straight edge, which shows signs
of having borne a heavy epicoracoidal cartilage.

The coracoid is a small bone, but it is very strong and forms the lower half of
the humeral cotylus. The coracoidal portion of the cotylus is set at an angle to the
scapular portion so that the whole face is twisted to accommodate the oblique articu-
lar face on the head of the humerus.

The cleithrum is doubtful, but a small bone in the Clepsydrops natalis can only
be interpreted as this element and some specimens of Ditnetrodon show an indefinite

MORPHOLOGICAL REVISION OF THE SUBORDER. II3

area of squamous suture which would just accommodate such a degenerate element as
is indicated by the specimen of Clepsydrops.

The clavicles are wide and thin anteriorly and taper to a point at the distal end ;
near the middle of the lower edge there is a slight rugose prominence. It is not
probable that the clavicles met on the lower side of the interclavicle, but they covered
the anterior end in large measure.

The interclavicle is very elongate. A separate specimen, No. 105 1 University of
Chicago, is nearly perfect ; it shows that the anterior end was thickened and enlarged ;
the lower surface is sharply rounded, so that it is almost hemispherical with the con-
vexity downward. The lower surface is quite rough with radial sculpture ; the upper,
inner, face is smooth. The edges of the anterior end are not complete, but enough
remains to show that there was no articular face for the clavicles and that they over-
lapped the anterior end nearly to the middle line. The posterior prolongation is
nearly flat, but the midline is thicker than the edges. The posterior end is marked
with rugose ridges. The total length of the specimen is 275 mm. (plate 15, fig. i).

The fore limb is described from specimen No. i University of Chicago, and the
fore foot from No. 1003 University of Chicago, both D. incisivus.

The humerus is without prominent condyles at the proximal end. The articular
face is a narrow, concave area winding obliquely across the laterally expanded proxi-
mal end from behind, forward, and inward. The radial crest is very prominent ; it
starts from the proximal extremity of the bone and grows to a prominent ridge which
stands at almost a right angle to the rest of the bone. Culminating in a strong tuber-
osity it extends downward, crossing the shaft obliquely and disappearing on the inner
edge of the entepicondyle and helping to complete the entepicondylar foramen (plate
14, fig. 3). The distal end is expanded at nearly a right angle to the proximal end.
The ulnar articular surface is rather saddle-shaped, and somewhat diagonally placed
on the outer extremity of the distal end. There is no anconeal pit on the posterior
face of the bone. The radial condyle is largely on the anterior face; it is a hemispheri-
cal prominence. The entepicondylar foramen is situated near the upper part of the
entepicondyle and is oval in outline. On the ectepicondyle a prominent, sharp pro-
cess defines an ectepicondylar notch.

The 7ilna is a slender bone, somewhat longer than the humerus, with a flattened
shaft. The shaft becomes gradually smaller toward the distal end and then expands
slightly again. The proximal end is excavated on its anterior face by a deep fossa
looking, in the natural position of the bone, upwards as well as forwards. This cavity
is divided by a low ridge into two facets, the larger looking forwards, and the smaller
and external one looking slightly outwards. The proximal extremity extends above
the articular face and forms the olecranon process. The outer side of the process has
a convex, rugose surface. The distal end is divided into two distinct articular faces
(plate 14, figs. 6 and 7).

The radius is curved and rather shorter than the ulna. The shaft is lenticular
in section with the edges becoming sharp and prominent toward the distal end. The
proximal end is expanded and the articular face for the humerus is deeply concave and
somewhat crescentic in outline. The distal end is less expanded and the single articu-
lar face is a shallow pit, oblong in outline.

Th& fore foot (No. 1003 University of Chicago): The length of the humerus with
which this foot was found is 210 mm., while that of No. i is 181 mm., so that it belongs
to a slightly larger animal. The carpus as preserved consists of eleven elements. The

114

REVISION OF THE PELYCOSAURIA.

radiate is a stout bone with a wide proximal face; the distal end is divided into two
articular faces which lie at an angle to each other. The iifnare is a thin disc-like bone,
much larger in size than the radiale. Between the two lies the intermediiun^ which
projects well beyond the proximal ends of the radiale and nlnare. Distal to the inter-
medium and ulnare lie two centrale ; the distal ends of these lie almost on a line with
the distal end of the radiale. On the ulnar side of the centrale 2 \s z. facet which, in
the specimen No. 1003, has nothing to articulate with it, but in specimen No. 1001,

where the foot bones are all present,
^\^ there is a thin disk-like sesamoid

which occupied this position. The
distal row consists of five bones.
The articulation of the different
bones is plain from fig. i, plate 16.
The itliiare has on the radial side
two articular facets which meet
facets on the vitermediiim and
centrale 2 ; the union of these four
faces leaves a foramen. The first
carpal projects prominently from
the side of the carpus and presents
a peculiar twisted surface which
pennitted a considerable range of
movement.

The phalanges are not pre-
ser\fed beyond the proximal half
A little more can be made out
from one or two other specimens,
No. 114 and No. looi University
of Chicago. The first digit had the largest of the metacarpals ; the second digit was
perhaps the longest. From data derived from incomplete specimens in the American
Museum the phalangeal formula seems pretty certainly to be the usual 2, 3, 4, 5, 4 of
the Rhynchocephalia.

The phalanges are relatively short, well-formed and with distinct articular sur-
faces. They indicate, as does the carpus, a strong, flexible foot, such as would be
possessed by a carnivorous, terrestrial animal. The terminal phalanges show that they
were cased in strong claws.

The posterior limb (No. i University of Chicago): ^ht femur is strong and hea\^-,
with well-developed articular surfaces. The proximal end is rounded anteriorly and
deeply excavated posteriorly so that it is crescentic in section. There is no distinct
head, the whole proximal end being rounded and thickened. There is a strong rugosity
near the outer part of the convex posterior surface. The shaft is roundly quadrate in
section. The distal end is divided by a deep groove into two strong condyles, both
bearing articular faces. The inner condyle is the shorter and extends inwards at a
small angle to the shaft ; its articular face is almost entirely on the posterior surface,
and looks more backwards than downwards. The outer condyle is longer than the
inner and is directed downwards. It bears two articular faces; one on the posterior
surface, looking almost directly backwards, is nearly square in outline ; the other is
apparently for the head of the fibula ; it is largely on the lower surface of the tuber-
osity and joins the posterior face by a narrow neck near its external side.

Fig. 41a. — Restoration of anterior foot of Dimetrodon. >; radiale;

?', intermedium ; u, ulnare ; Ci and ^2, centrale ; /, pisiform ;

'• ^. S- 4- S' carpals.
Fig. 4 1 4. — Restoration of posterior foot of Dimetrodon. f, flbulare ;

t, tibiale ; c, centrale ; i, intermedium ; /, 2, J, 4, ^, tarsals.

MORPHOLOGICAL REVISION OF THE SUBORDER. II5

The tibia is greatly enlarged proximally. The shaft is slender and curved and
the lower end is only moderately expanded. The cnemial crest is a strong ridge sepa-
rated from the body of the bone by a deep fossa opening on the outer side. The fossa
is continued into the upper side of the bone as a deep pit, which nearly divides the
articular face into two unequal halves ; these halves are again divided by a low troch-
lear ridge running fore and aft. The distal end is semicircular in outline, flattened
before and rounded behind. There is no indication of a division of the distal end into
articular facets.

The Jib It la has not been recognized in any specimen.

The posterior foot is not certainly known in the genus Dimetrodon. The foot of
the restoration is taken from the hind foot from New Mexico, which is assumed to
belong to D. navajovicus (plate 27); numerous isolated bones of larger animals show
that the foot must have been quite similar to that of the smaller species.

Restoration: In the restoration the only parts drawn without warrant
from actual specimens are the number of phalanges and the number of
caudal vertebrae. The ribs are not preserved in any collection, but thej^ were
observed in the ground in their natural position in the specimen No. looi
University of Chicago, but were so badly rotted by gypsum that they could
not be preserved. The posterior foot is restored from that of the genus
Clepsydrops. No trace of abdominal ribs has been found in any specimen
of the genus ; it seems fair to assume that they were absent. The height
of the spines, the slant to the rear, and the sudden shortening in the sacral
region are all repeatedly shown in the collections. The semiupright atti-
tude seems warranted by the shape and position of the humeral cotylus and
the acetabulum ; in no case can the humerus or femur be fitted into such a
position that the bell}' would touch the ground in walking. The legs were
far from straight and the animal must have stood in a crouching, semierect
position. The carnivorous dentition and strong claws both tell of a preda-
tory nature that must have demanded a swifter motion than could have been
attained by an animal which dragged its belly in progression. The tail was
probabl)'^ rather short ; in no specimen of the many referable to the genus
has a complete tail been found, but in none of these is there a vertebra of
the elongate, cylindrical shape characteristic of long tails. Moreover, such
vertebras of appropriate size are very scarce in beds prolific of other remains
of the genus ; the few found may well belong to the genus Theropleura.
The caudals preserved show a rapid diminution in size, so that vertebras as
well formed as the first caudals, but only half the size, occur in the tail of
Dimetrodon gigas. On the other hand, strong chevrons occur on the tail ;
these usually occur in forms with long and powerful tails, but they may
mean onl}' strength in a comparatively short tail.

The semiupright form, the short tail, the well-developed articulations
of the long bones, and the well-formed carpus and tarsus would indicate that
the members of this genus were true land forms. This idea is supported

Il6 REVISION OF THE PELYCOSAURIA.

by the abundant occurrence of the bones as water-worn fragments in beds
of limited extent mixed with pebbles and sand ; indicating that the bones
have been transported a considerable distance by strong currents, perhaps
of rivers, and laid down in eddies or on river bars or deltas. The occurrence
of the Illinois material in what seems pretty certainly a Permian river bar
in Carboniferous rocks would support this idea. Only very rarely do the
bones of this genus occur in the fine clays deposited in the deeper water.
In such cases the skeletons are much more nearly complete, indicating
that the body of the animal floated and perhaps journeyed far to its final
resting place.

In external form the animal must have been sufficiently bizarre, but
not more so than the living Phrynosoma or the Basiliscus of the West
Indies. The latter has a fringe of spines on the back which, though dermal
in origin, are nearly as high in proportion to the body as those of Dhnetro-
don and originate and terminate almost as abruptly. As mentioned in the
descriptions, all the high-spined forms of both subfamilies have, just above
the base of the spine, a region of rugose lines of swellings and above this a
sudden change in the form of the spine. It is altogether probable that the
rugosity marked the termination of the muscular attachments, and that the
upper portion of the spine was covered by a coating of skin which, though
probably tough, was relatively thin. The outlines of the spines could very
probably be easily traced through the thin covering. For the rest the body
was probably not unlike that of a smooth-bodied, finely scaled lizard with a
relatively large head, short body and semierect posture.

Haunting the banks of the streams or the upland, it probably lay in
wait and then made sudden, short, scuttling dashes upon its relatively slow-
moving prey, the Cotylosaurians, armored Chelydosaurians, and Amphib-
ians. That it attacked its own kind there is little doubt ; repeatedly the
spines are found with great exostoses, showing that they have been broken
and healed during life, evidences of sanguinary battles, perhaps in contests
for captured prey or for mates, or perhaps with the single notion of a can-
nibalistic meal.

Dlmetrodon glgas Cope (plates 17-21).

Characteristic specimens: No. 4006 Am. Mus.: The type. No. 1002 University of
Chicago: A large part of the vertebral column, the nearly perfect skull, the imperfect
vertebral column consisting of atlas, axis, third cervical, and another cer\'ical, probably
the fourth, eight connected dorsals and ten others, posterior dorsals and lumbars, two
sacrals, eighteen caudals, and the femur. No. 4034 Am. Mus. : Fragments containing
a perfect neural arch of atlas.

No. 1002 University of Chicago : The sktill of Dimetrodon gigas has been
largely described in the characterization of the genus, but certain features distinguish
it from the related species. The simple diastemal notch of Dimetrodon incisivus
becomes a sharp offset, for the premaxillary is greatly shortened, and its tooth line

MORPHOLOGICAL REVISION OF THE SUBORDER.

117

lies at a higher level than that of the maxillary. The change from one level to another
is accomplished abruptly, just anterior to the enlarged maxillar)- tooth. All the bones
of the skull are heavier, more clumsy, and are marked by rugosities and pittings more
strongly than in Dimetrodon incisivus.

The vertebral column : The inferior surface of the preatlautal intercentrum is
rough and the facets for the capitula of the ribs are not so well marked as in Dime-
trodon incisivus.

The atlas is similar to that of Dimetrodon incisivus, but is proportionatelj' broader
and shorter. The anterior face is nearly as broad as high. The opening for the
notochord on the posterior face is notably smaller than in Dimetrodon incisivus and
Dimetrodon obtusidens.

Fig. 42.— Axis of D. gigai. No. 4028 Am. Mus. X Vz.
Fig. 43. — Axis of D. %igas. No. 4147 Am. Mus. X Y^.
Fig. 44. — Spine of axis of D. gigas (?), Nos. 4054, 4055 Am. Mus.

X M.

Another atlas, No. 4034 Am. Mus., has the anterior face 38 mm. high and the
transverse diameter the same.

The neural arch is lost in this specimen, but in a very incomplete specimen of
this species, No. 4034 Am. Mus., the neural arch is preserved. It has the same form
as in Dimetrodon incisivus, but in common with the rest of the skeleton is stronger
and more rugose. The groove above the flat facet on the outer edge is almost con-
verted into a foramen (plate 21, fig. 8).

The secofid intercentrum is smaller than the first.

The axis has a broad and high spine, the apex is widened and thickened for
ligamentous attachment, and the anterior edge is rugose for the same purpose, but there
is no distinct face on the anterior edge as in Dimetrodon dollovianus (plate 21, fig. i).
There are several specimens of the axis in the two collections.

No. 1002 University of Chicago, fig. 34. Height of spine above center of neural
canal, 87 mm.

Il8 REVISION OF THE PELYCOSAURIA.

No. 4028 Am. Mus., fig. 42. Height of spine above center of neural canal,
105 mm.

No. 4147 Am. Mus., fig. 43 ; Nos. 4054 and 4055 Am. Mus., fig. 44. Height of
spine above center of neural canal, 104 mm. (This last is but a fragment among the
fragments of a very large and rugose skull ; it maj- perhaps be a specimen of Naosau-
riis claviger?^

The tltird cervical (fig. 38) is uncrushed and shows the form without distortion.
The anterior and posterior zygapophyses are well developed and their articular faces
are decidedly oblique with a very deep pit between them just above the origin of the
diapophysis on the side of the neural arch. The pits of the two sides narrow the base
of the neural spine just above the neural canal very decidedly. The anterior face of
the centrum is rendered rather oval in outline by the presence of the coossified inter-
centrum, but the articular part proper is nearly round. The posterior face is round
and with wide flaring edges which are hardly recur^-ed.

The intercentrum is so closely united with the centrum that hardly a trace of
the suture remains ; the anterior portion showing on the anterior face of the centrum
has an upper articular portion continuous with the articular face of the centrum
proper, and below this a wide rather rugose portion. On the two sides of the lower
part of the intercentrum the two faces for the capitula of the ribs are supported on
prominent processes. Below, the iutercentrum is continued into a sharp median keel
which is continuous with the median keel of the centrum. The latter is not over
1 mm. thick and reaches to one-third the height of the centrum. The transverse pro-
cess is very stout ; it starts relatively far back and descends to the lower fourth of the
centrum. The spine is very simple. The base is thickened and somewhat elliptical
with the anterior and posterior ridge somewhat drawn out to an edge. Near the
middle of its length the shaft contracts rapidly to a nearly circular slender rod. The
upper end tapers abruptly and shows no face or roughening for ligamentous attachment.

^\\^ fourth cervical closely resembles the first but for the more elevated spine. It
is not in contact with the others, so the position has been detennined by its characters.
Following this two or three vertebrae seem to be missing.

The dorsal vertebrer: There are eight dorsals in series and then ten which are
not attached, but are easily arranged from the matrix and form. The first of the
dorsals is evidently the first in number. The centrum is elongate vertically and
shortened antero-posteriorly. The lower edges of the anterior face are reverted some-
what on the sides of the centrum and there is a sharp median keel on the lower face
of the centrum, but this latter differs from Dimetrodon iitcisivtis^ No. 146 University of
Chicago, and Dimetrodon gigaiihomogeiies, No. 112 University of Chicago, in that it
joins the anterior and posterior edges of the centrum abruptly and does not gradually
round out before joining them. To the anterior face of the first dorsal is attached an
intercentrum which still shows a parapophysial facet.

The third dorsal has the neural arch and centrum ver}' high and short. The
keel, which forms a straight line from the anterior to the posterior edge of the cen-
trum, is not over i mm. wide in its thickest part, and maintains this thickness to one-
third the height of the centrum ; there it suddenly expands into a rounded barrel
surrounding the neural canal, as shown in fig. 45. The lower fourth of the anterior
face is narrowed and saddle-shaped for the articulation of the large intercentrum.
The diapophyses are rather more close to the body of the centrum than in No. iii
University of Chicago ; they extend almost straight downward without any inclination
to the rear, and the lower end reaches nearly to the lower fourth of the centrum.

MORPHOLOGICAL REVISION OF THE SUBORDER.

119

Fig. 45. — Cross-section through
third dorsal of D. gigas.
No. 1002 University o(
Chicago. X 1. Show-
ing sudden contraction of
sides of centrum below
notochordal canal.

The vertebras reckoned as the ninth dorsal, probably the fifteenth or sixteenth of

the series, is similar to the posterior dorsals of Di»ietrodoii incisiviis. The keel is still

narrow and sharp, but is less deep than in the anterior dorsal, being not over one-fifth

the vertical height of the centrum. The centrum is longer than high or wide and

the anterior and posterior faces have become rounded.

The spine of this vertebra is one of the first that is nearly
perfectly preserved. In comparison with the spines of the
other species the spines of Dimetrodon gigas do not exhibit
the swelling shortly above the base, and the point is marked
by a slight rugosity of coarse striations only. Just above the
rugosities the spines assume a quadrilateral or circular section,
which they maintain to the tip, not showing the peculiar flat-
tening of specimen No. 112 University of Chicago (fig. 14).
The diapophyses have become shortened and stand out from
the vertebra more than in the anterior portion of the series.
A rib attached to this vertebra has a rather short tuberculum
and long capitulum corresponding to the shortened diapophysis
of the vertebra (fig. 47).

The lumbar iiertebra- : The posterior ones of the separate
vertebrse show the capitular face on the edge of the centrum
characteristic of the lumbars. They are crushed too badly to
admit of accurate description, but all have the general form and proportions of the same
vertebrse in Dimetrodon incisiviis. The spines of the anterior ones are elongate and
have much the same shape as the dorsals, but the posterior ones are shorter and with
the base narrower and elongate antero-posteriorly. Near the middle the spine becomes
more quadrilateral. The spine rises from the posterior portion of the neural arch.

The sacrum (plate 17, figs. 3 and 4) is represented by the first two vertebrce which
are closely coossified and have the sacral ribs complete. The neural arches are badly
rotted and the spines are nearly gone, but enough remains to show that they are short
and slender compared with those of the dorsals and anterior lumbars. This sacrum
diflfers from that of Dimetrodon dol/onianns^ No. 114 Universit)- of Chicago, especially in
the form of the ribs, and resembles more closely that of Dimetrodon incisiz'us, No. 4008
Am. Mus. The centra are abruptly more elongate than the posterior lumbars and are
firmly attached to each other, but not coossified. The sides are concave, but there is
no keel on the median line of the lower side. The firm union of the two excludes
the intercentrum from between them, but it is present as a very thin and scale-like
element, coossified with the posterior of the two vertebrse, and in part underlying the
point of union of the two. The intercentrum between the posterior lumbar and the
first sacral is firmly united with the first sacral ; it is thin and small and projects for-
ward under the line of union of the two. The zygapophyses connecting the sacral
vertebrse are much reduced in size and are ver>' closely united.

The sacral ribs are supported on strong, short transverse processes rising from
the neural arch and centra and coossified with them. The sides of the arches are
swollen and expanded laterally in the position of the transverse processes to support
the ribs. The rib of the first vertebra is attached to the anterior end of the vertebra
in such a manner that the anterior half of the proximal end extends beyond the
anterior end of the centrum as an articular process which embraced the posterior edge of
the last lumbar. The ribs of the two sides form a pair of projections on the anterior

I20 REVISION OF THE PELYCOSAURIA.

face of the vertebra, best realized from plate 17, figs. 3 and 4. Seeley has figured the
same condition in Deiderosaurus. The middle portion of the rib is sharply contracted
and then widely expanded antero-posteriorly and decurved, forming a vertical face for
a strong attachment to the ilium. The outer surface of this part is concave and the
inner convex.

Fig. 46. — Lower view of same vertebra as shown in fig. 45.

Fig. 47. — Head of a dorsal rib from D. gigas. No. 1 002 University of Chicago. X 1 .

Fig. 48. — f^ght side of pelvis of D. gigas, No. 4006 Am. Mm. /«, pubis ; :V, ilium ; t'scfi, ischium. X /i.
The posterior end of the ilium is broken away.

There are eighteen caudal vertebrae, but none showing the elongate cylindrical
form that would indicate a long tail. Their general form is shown in plate 21, figs.
5, 6, 7. It does not differ materially from that of the caudals of Dimeh-odon incisivus.
The anterior caudals are very short antero-posteriorly and have nearly circular articu-
lar faces. The lower portion of the reverted edge is broader than the rest to accom-
modate the large intercentrum. The ribs rise from very low down on the side of the
centrum. In the mid-caudals the bottom line becomes very short, because the lower
half of the anterior and posterior faces are bent sharply toward the middle line (plate
21, fig. 6). When two adjacent vertebrae of this region are in position the beveling of
the lower edges forms a deep V-shaped notch, into which fits the proximal end of the
chevron, which has the same form as described in Dimetrodon gigauhonogenes, No.
112 University of Chicago (plate 21, fig. 9). In one vertebra of the middle region,
which is about half the size of the most anterior, the beveled portion of the lower edge
is nearly as great as the rest of the anterior and posterior faces. The rib is reduced to
a simple process from the side of the centrum.

In the most posterior vertebrae the centra are more elongate, all trace of rib has
disappeared and the chevron faces are smaller. Though the vertebrae are disconnected

MORPHOLOGICAL REVISION OF THE SUBORDER.

121

and some are lost, it is evident that the tail did not exceed one-third of the length of
the presacral vertebral column.

The shoulder girdle of Dimetrodon gigas is unknown.

The proximal half of the humerus is preserved in the type specimen, No. 4006
Am. Mus. It differs from Dimetrodon incisivus in the articular face, which involves
the whole of the proximal end, and the radial crest, which, while very strong, is not
long, beginning lower down on the head and not continuing so far distally. The
edges of the proximal end are quite rugose.

^ht pelvis (No. 4006 Am. Mus.) : The crest of the ilium is broken away so that
its exact form is not certain, but it projected to the rear, as in Dimetrodon incisivus.
Cope, in his description of the long axis of the ilium being at right angles to the long
axis of the ischium and pubis, did not recognize that the posterior end of the crest was

Fig. 49. — Anterior view of the same pelvis as shown in fig. 48. Showing the narrow and high pelvic cavity and

the deep symphysis, s.r, distal end of sacral rib; fii, pubis; il, ilium. X Yz.
Fig. 50.— Anterior view of the femur of D. gigas. No. 4006 Am. Mus. X /4 .

broken off. The face of the acetabulum is covered with matrix so that it is impossible
to locate just the parts taken by the several bones, but it is evident that the ilium
descended far down between the ischium and pubis. The edges of the acetabulum
are not more raised than in any other species. The anterior ends of the pudis are
broken away, so the full length is not known ; so far as preserved the edges of the
pubes of the two sides meet in a deep symphysis. The obturator foramen is located

REVISION OP THE PELYCOSAURIA.

just below the anterior edge of the acetabulum. The ischium is complete ; the upper
edge is slightly concave just posterior to the acetabulum, then rises to a slight rugose
prominence and falls suddenly to the distal end. The ischia of the two sides meet in
a deep symphysis, but this does not extend the full length of the bones, as the distal
ends are separated by a slight notch. The suture between the ischium and pubis is
not traceable. Viewed from either end the pelvis is seen to have been very narrow
and high, fig. 49.

'V:\tfemiir of Dimetrodoti gigas differs from that of Dimetrodmt incisivus in the
heavier outer condyle and the slightly curved shaft. In both the femora of this speci-
men the lower end has been crushed, so that the face on the outer condyle seems to
have been lost, and the groove between the condyles looks outward instead of forward.
Another specimen. No. 4024 Am. Mus., of the uncrushed distal end of the femur shows
that the groove between the condyles was not so definite as in Dimelrodon incisivus.

Measurements.— 'Ho. 1002 University of Chicago.

mm.

Total length of skull 455

Third cervical :

Elevation of spine above center of neural

canal 172

Length base of centrum including inter-
centrum 43

Anterior face ;

Vertical diameter 34

Horizontal diameter 36

Posterior face :

Vertical diameter 46

Horizontal diameter 46

Fourth cervical :

Length of bottom line 30

Posterior face ;

Vertical diameter 49

Horizontal diameter 46

First dorsal ;

Length, bottom line of centrum 31.5

Anterior face :

Vertical diameter 35

Horizontal diameter 37

Second dorsal :

Length, bottom line of centrum 29. 5

Posterior face ;

Horizontal diameter 41

Vertical diameter 49

Third dorsal :

Length, bottom line of centrum 25

Anterior face :

Vertical diameter 52.5

Horizontal diameter 37

Thickness of centrum :

Opposite notochordal canal 17

Just below notochordal canal 2.5

Fourth dorsal :

Length, bottom line of centrum 26.5

Anterior face :

Horizontal diameter 35

Vertical diameter 45

Fifth dorsal :

Length, bottom line of centrum 26

Sixth dorsal :

Length, bottom line of centrum 32

Anterior face :

Vertical diameter 42.5

Horizontal diameter 32

Seventh dorsal :

Length, bottom line of centrum 32

Posterior face :

Horizontal diameter 35

Vertical diameter 44

Eighth dorsal;
Imperfect.
Ninth dorsal ; mm.

Antero-posterior distance on bottom line

of centrum 34.5

Posterior face :

Vertical diameter, crushed 36

Horizontal diameter 38

Anterior face :

Vertical diameter 30

Horizontal diameter 38

Length of spine, incomplete 750

Probable length when complete. . 950 or 1000
Antero-posterior diameter of spine at base . 24. 5
Transverse diameter of spine at base .... 19
A lumbar vertebra :

One incomplete lumbar spine 540

Length, bottom line of centrum of a lum-
bar 36.5

Anterior face of same ;

Vertical diameter 45

Horizontal diameter 36.5

Sacral vertebrae ;

Length, bottom line of centrum of —

First vertebra 32

Second vertebra 34

Anterior face of centrum of first sacral :

Horizontal diameter 33

Vertical diameter 37

Posterior face of centrum of second sacral :

Horizontal diameter 38

Vertical diameter 29

An anterior caudal :

Length, bottom line 22

Anterior face :

Vertical diameter 36

Horizontal diameter 35

Posterior face :

Vertical diameter 35

Horizontal diameter 39

A median caudal :

Length, bottom line 22

Length at level of neural canal of same. . . 31
Anterior face :

Vertical diameter 27

Horizontal diameter 24

Posterior face :

Vertical diameter 28

Horizontal diameter 21

Length of femur 263

Width of head 77

Width, lower end loi

MORPHOLOGICAL REVISION OF THE SUBORDER. 123

Measurements. — No. 4006 American Museum.

7?ini. mm.

Length of fragment of humerus preserved Total length of pubo-ischiatic symphyses as

(about >^) 130 preserved 415

Width of proximal end 89 Total length of femur 250

Vertical diameter of acetabulum, right side ... 175 Transverse width of head 85

Other specimens of this species are: No. 4024 Am. Mus.: Caiidals,
vertebras, and the lower end of the femnr. No. 1327 Am. Mus.: An axis.
No. 4051 Am. Mus.: A femur, vertebrse, and fragments of spines. No. 4034
Am. Mus.: A few nearly perfect spines. No. 4050 Am. Mus.: A maxillary
and premaxillary.

Dimetrodon gig'anhomog'enes Case (seep. 47, plate 22).

Characteristic specimens : No. 112 University of Chicago : The type. No. 4043
Am. Mus. Nat. Hist., Cope, coll.: A few vertebrte with fragments of spines and a femur.

In the type the bones were covered by a thin scale, which was readily removed,
leaving them in most excellent condition and undistorted. They were undisturbed in
the ground, and numbered as collected, so that the relative position of the dorsals and
lumbars is certain. The first vertebra preserved is evidently the third of the series.
The atlas and axis are missing.

The t/ii/-d cervical carries a keel on the bottom line which joins the posterior
edge sharply. On the sides are two longitudinal ridges; the first starts from the
anterior edge of the centrum near the middle and rises backward to near the middle
of the centrum, where it disappears. This ridge does not appear on the third cervical
of Diii/etrodo/i o-i^as (No. looi UniversityofCliicago),but its absence may be due to the
crushed condition of the specimen. The second ridge is formed by the continuation
of the inferior supporting ridge of the transverse process to the posterior edge of the
centrum. Small centrosphenes and centantra are' present on the irpper edges of the
articular faces. The transverse process is rather more slender than in Dimetrodon
gigas and reaches nearly to the lower edge of the centrum. The base of the spine is
rather elliptical in form, and terminates in anterior and posterior edges. About one-
third up the length of the spine it becomes sharply rugose, and then suddenly contracts
to a nearly cylindrical form. The apex is swollen and marked by vertical rugosities
showing the attachment of a ligament. The processes on the intercentrum for the
head of the rib are well-developed and very prominent, with the articular faces looking
almost directly backward.

^\\& fourth cervical vertebra greatly resembles the third, except that the transverse
processes rnn more nearly straight down, not inclined to rear. The ridge on the side
of the centrum passing backward from the anterior face has disappeared. There is the
same inclination of the antero-posterior axis as in the third cer\-ical, so that the posterior
face is lower than the anterior. The spine is straight and has no rugosity at the tip.

A median dorsal has the bottom line sharply contracted below the intercentrum
to a keel not over i mm. thick and nearly one-third the height of the centrum. The
bottom line is straight, but the ends are widely flared so that the sides are sharply
concave. The centantra are present, but much smaller than in the cervicals. On the
anterior face the opening of the notochordal funnel is surrounded by a slightly
elevated ridge. The lower half of the anterior face is developed into a saddle-shaped
articular surface for the intercentrum. The transverse processes rise from the neural
arch above the neural canal and curve straight out and down, the lower end reaching
nearly to the lower edge of the centrum. The section of the transverse process is

124 REVISION OF THE PELYCOSAURIA.

triangular with the apex downward. Each edge is formed by a supporting ridge as
described in Dimetrodon incisivus. The lower ridge is ver>' thin, but reaches from the
suture between the neural arch and centrum well down on the centrum, fonning a
peculiar thin partition between the anterior and posterior portions of the upper part
of the vertebra.

The base of the spine is somewhat flattened. The antero-posterior diameter is
24 mm. and the transverse 14 mm. About 70 to 80 mm. up, the spine is somewhat
swollen and marked by rugose ridges ; at the swollen portion the spine becomes nearly
quadrangular, but with well-developed anterior and posterior grooves ; these continue
up the fore and aft faces of the spine (fig. 14). The median line of the lower portion
of the anterior groove is marked by a slender ridge from the swollen portion to the
upper edge of the neural canal. Above the swollen part, the spine rapidly flattens to
a rough figure 00 -shape, with the deeper groove on the posterior side. About the
middle of the spine this groove lessens in depth and becomes equal to or even less
than that of the anterior side. The apex seems to have been simple.

A posterior (the seventh) dorsal is longer, and the bottom line is sharp and thin,
but the keel is largely lost, for the sides of the centrum rise gradually to the noto-
chordal canal, instead of being sharply pinched in just beneath it. The anterior face
is nearly circular, with only a slight face below for the intercentnim. The centro-
sphenes and centantra are quite good-sized. The neural spine rises from far back, the
posterior edge lying almost directly over the posterior zygapophyses. The z)-gapo-
physes are far apart antero-posteriorly, with small and very oblique faces. The spine
is imperfect, but resembled closely that of the last dorsal preserved, the ninth, which
is shorter than in the anterior dorsal region and very thin transversely. Both the
anterior and posterior edges are thin and prominent at the base; 70 or 80 mm. up, the
spine is quadrangular, and then assumes the figure co -shape, but is more nearly round
than the anterior ones.

They?r5/ lutnbar closely resembles the posterior dorsals, except that the anterior
edge of the centrum is reverted and widened into a facet for the capitulum of the rib.
An intercentrum in position just touches the head of the rib (see the description of
the rib articulations below). The bottom line of the centrum is rounded and concave
antero-posteriorly ; all trace of the keel has disappeared.

The posterior liimbars are similar in most respects to the same vertebrae of
Dimetrodon mcisivus. The bottom line is concave antero-posteriorly, but is sharp
instead of rounded. The intercentrum is only slightly curved and rather wide antero-
posteriorly. It lies below the point of meeting of the two centra, and does not rise on
the sides of the centrum above the lower fourth, but touches the lower end of the
capitulum of the rib. This spine is weak at the base, but thickens at the upper end
to a somewhat clavate form.

The sacrals are not preserved.

There are five caiedals, inclosed in a hard matrix, and not in series. These show
a rapid decrease in size, with no tendency to a development of the elongate, cylindrical
form indicating a long tail. There are wide intercentral spaces with the chevron
bones in place. The chevrons are very wide at the top, with two facets on the
proximal end almost at right angles to each other. They are both concave from side
to side, to fit the corresponding portions of the vertebral centrum. If the length of
the chevron is held upright, the anterior face of the two is almost horizontal and the
posterior face looks nearly downward. If two adjacent vertebrae are placed in position,

MORPHOLOGICAL REVISION OF THE SUBORDER.

125

it is seen that in order to make the facets in the chevrons fit the centrum, the chevron
must be turned yet}' sharply to the rear. Just below the proximal end the chevron is
pierced bj' an elongate foramen (plate 2 1 , fig. 9).

The method of rib articulation: In the cervicals the head of the rib articulates
with a distinct process on the side of the intercentrum. The capitulum and tuber-
culum are widely separated; the ribs are short and not greatly curved. In the
anterior dorsal region the head passes in between the two adjacent centra and touches
the head of the intercentrum, but there is no articular face on the intercentrum, so it
is probable that the head of the rib was united to it by cartilage. The transverse
processes on the dorsals are short and grow shorter towards the rear, so that the
capitulum and tuberculum of the rib grow farther apart. In the posterior dorsals the

transverse process is ver>' short and stands out
• tab - — V^ ■''^^ almost straight from the neural arch ; the capitu-

lum and tuberculum are here farthest apart and
in a nearly vertical line. In the first lumbar the
head of the rib leaps suddenly from the notch
between the vertebrae and the end of the inter-
capi-i> — ''V^ centrum to the articular face which appears on
51 '^ b the edge of the centrum ; the head of the rib still

coptt

Fig. 51. — The head of a rib from the anterior lumbar region of D. giganhomogenes. No. 1 12 University of Chicago, cafit,

capitulum; tub, tuberculum; a, anterior view ; b, lateral view.
Fig. 52. — A mid-lumbar ot the same specimen as fig. 5 1 . a, lateral view ; b, anterior view. Showing both rib articulation

and intercentrum. itc, intercentrum ; (a fit, capitulum of rib ; tub, tuberculum of rib.
Fig. 53. — A posterior lumbar ot the same specimen as fig. 5 1 . a, lateral view ; b, anterior view. Lettering as in fig. 52.

projects somewhat beyond the anterior edge of the centrum and retains its cartilaginous
connection with the intercentn:m. In the posterior lumbars the change is progres-
sive, the transverse process shortens rapidly until it becomes a mere facet on the side
of the centrum and neural arch ; at the same time the facet on the edge of the centrum
enlarges. The capitulum and tuberculum enlarge, with the facets approaching each
other, until on the third or fourth presacral they unite into one, and the rib is reduced
to a sleuder process with a wide proximal end. At first the tuberculum and capitulum
lie at right angles to each other on the lumbars, and this continues until they are
fused. The space between the capitulum and the tuberculum is continued as a fora-
men as far back as the third or fourth presacral.

The right side of the pelvis is almost perfectly preserved (plate 21, figs. 9 and 10).
The three bones are united by close sutures. All the bones are very thin except the
region of the acetabulum and the upper edge of the pubis, which is rounded and
thickened. The S5'mphysis is very shallow, i. e., the bones of the two sides did not

126 REVISION OF THE PELYCOSAURIA.

meet for more than 3 mm. in the widest part between the ischia, and between the
pubes hardly more than i mm. The bones of the two sides are united through their
whole length. The upper part of the ilium is ver\' thin ; the anterior end is rounded,
but the posterior end extends backwards as a prominent process with a somewhat
thickened lower edge. The anterior and upper edges are thin and fluted with fine
grooves. The middle of the internal surface of the ilium is marked b}' deep and
wide pits and by prominent angles showing the attachment of sacral ribs. The
whole upper portion of the bone is bent so that the outer face is convex and the inner
concave above the acetabulum. The ilium fonns the upper third of the acetabulum ;
just above the edge of the cavity it is marked by a strong rugosity. On the posterior
edge the ilium meets the ischium in a low prominence. The anterior edge is marked
by a strong rugosity continuous with the one above the acetabulum. The ilio-pubic
suture passes through the middle of this rugosity. The ischium extends posterior to
the acetabulum, a distance greater than the antero-posterior width of the acetabulum,
100 to 80 mm. The posterior edge is rounded, not drawn to a point, so that the
posterior end was blunt and not acuminate. The acetabular border is very prominent,
making the cavity ver>' deep at this point. The lower edge is somewhat rounded,
but nearly straight, and the suture between the ischium and the pubis is marked by
a slight notch.

The pubis has a thickened upper edge, but the lower portion is abruptly thinned,
so that it is not over i or 2 mm. thick. The acetabular edge is raised, but not so
much as in the ilium and ischium. Anterior to the acetabulum, the edge of the pubis
is somewhat rugose, forming with the ilium a prominent rugosity. The foramen for
the internal femoral artery passes obliquely upward and backward from without inward,
and the internal opening is much larger than the outer.

The acetabulum is deep and imperforate. The general outline is triangular, with
the characteristic uotch on the posterior edge of the iliac portion. There is a promi-
nence at each angle on the different bones. These promiuences are not connected by
raised borders, but are separate, so that the edge of the acetabulum is flush with the
bones between the prominences.

Measurements. — No. 112 University of Chicago.

mm. mm.

Length, bottom line of third cervical, including Anterior face:

intercentrum 41 Horizontal diameter (measured ^/i) 32

Anterior face: Vertical diameter 38

Vertical diameter 34 Posterior face:

Horizontal diameter 41 Horizontal diameter 37

Vertical diameter 33

Length of spine of gth, nearly 500

Posterior face
Vertical diameter 46

Antero-posterior diameter, base of spine 24

Horizontal diameter 42 ~ '^ ,■ . ut-

^ Transverse diameter, base of spine 7

Height of spine above center of neural canal . 180 Length, bottom line of first lumbar 35

Length, bottom line of fourth cervical 39 Anterior face:

Anterior face: Horizontal diameter, distorted 31

Vertical diameter, undistorted 36 Vertical diameter 36

Horizontal diameter, undistorted 36 Posterior face:

Posterior face: Horizontal diameter, true 32

Vertical diameter 41 Vertical diameter, true 32

Horizontal diameter 43 Height of spine, twisted, complete 460

TT.„i,» „f ..„,•„„ .,K« •-„„.„_ „f ., „i 1 Length, bottom line of posterior lumbar, ap-

hleignt ot spine above center 01 neural canal. . 220 ■ t 1

Length, bottom line of an anterior dorsal .... 26
Anterior face

proximately 24

Anterior face:

, ,. ,. Horizontal diameter 33

Horizontal diameter, distorted 37 Vertical diameter 34

Vertical diameter, true 42 Posterior face:

Height of complete spine above center of neu- Horizontal diameter 30

ral canal 860 Vertical diameter 30

Length, bottom line of seventh posterior dor- Spine, incomplete 322

sal 35 complete, about 375

MORPHOLOGICAL REVISION OF THE SUBORDER. 1 27

Measurements. — No. 112 University of Chicago — Continued.
Dimensions of a chevron from an anterior caudal.

mm. mm.

Antero-posterior diameter of head 7.5 Distance from top of ilium down to edge of

Transverse diameter of head 22 ischium 195

Length, distal end missing 46 Length of ilium, antero-posterior 155

Total length, pubo-ischiatic symphysis 270 Greatest length of acetabular c vity 65

Dimetrodon Inclsivus Cope (plates 12-16 and 20).

Clefsydrofs limbatus Cope, p. 40. Ditnetrodon rectiformis Cope, p. 49. Dimetrodon semi-
radicatus Cope, p. 50.

Characteristic speciviens: No. 41 16: The type. No. 4008: Cotype. No. 4040
Am. Mus. Nat. Hist., Cope, coll. : The posterior portion of the vertebral column,
including the nine anterior caudals. No. i University of Chicago : An imperfect
skull, scapula, vertebral column, and humerus, femur, tibia, and fibula. No. looi
University of Chicago : Skull, lower jaws, imperfect vertebral column, shoulder
girdle, and fore limbs. No. 1003 University of Chicago: Imperfect fore limb with
complete tarsus. No. 4093 Am. Mus. : A pelvis. No. 4092 Am. Mus. : A pelvis,
sacral and caudal vertebrae, and four limb bones. No. 4089 Am. Mus. : A pelvis.
No. 4039 Am. Mus. : A pelvis, sacrals, and caudals, humerus and femur.

The main characters of the species have been given in the discussion of the
genus. Below are noted the points in which it differs from the related species.

The outer surface of the maxillary near the tooth line is very rugose and marked
with oblique grooves, which run downward and forward (plate 10, fig. 3). The lower
jaw is much stouter and relativeh* shorter than in some species — e. g., Dimetrodon
longiramiis.

The vertebrae of the cervical region are nearly upright, the neural arch lies
directly over the centrum and the axis of the spine is more nearly vertical ; in Dime-
trodon dollovianiis the neural arch has the appearance of having been pushed forward
so that the anterior cervacals are very oblique (fig. 54).

The intercentra of the anterior cervicals differ from those of other species in that
they are free from the succeeding centrum, in Dimetrodon gigas the suture between
the intercentrum and the lower portion of the articular face of the centrum is hardly
distinguishable. In the posterior cervical series the intercentra are free in all species.
The spines show a characteristic marking best shown in specimen No. lOOi Univer-
sity of Chicago. The spine of the fourteenth in series, a mid-dorsal, is described as
typical (plate 16, fig. 2). The base of the spine at the point of leaving the neural arch
is very thin and elongate antero-posteriorly. This shape continues upward some
distance (40 mm.) above the neural canal, and then there is a contraction to a nearly
round or slightly transverse oval section. The contraction is sudden and from both
anterior and posterior sides, so that it has the appearance of a knot or joint, which is
heightened by a sculpture of deep and sharp rugose grooves and ridges. This change
of shape, with its attendant rugosity, appears on all the spines at about the same
height. The upper portion of the spines has grooves on the anterior and posterior
side, but these are not deep and disappear half-way up. The upper fourth is very
irregular in section, which is partly due to pressure, bift not entirely; the most perfect
spines have a rounded oval section with low anterior and posterior edges taking the
place of the grooves of the lower half Throughout their length the spines are
marked by a fine sculpture of vertical lines, which become finer and more definite
toward the apex.

128 REVISION OF THE PELYCOSAURIA.

Specimen No. looi University of Chicago presents one difference from No.
4008 Am. Mus. that might be regarded as of specific value. In No. 4008 the spine
of the third cervical curves forward and lies close against the posterior edge of the axis
much as it does in Dimetrodon doUovianus, but in No. lOOi University of Chicago the
spine rises vertically from the centrum ; the base is wide antero-posteriorly, the front
edo-e very thin, and the posterior edge wider and grooved ; the sides are marked by
coarse striations. The spine contracts near the middle through a rugose swelling to
a smooth cylindrical shaft, which curves forward over the axis. The distal end of the
spine is marked by a distinct pit for ligamentous attachment (plate 15, fig. 2 and
text-fig. 37). The axis differs from that of No. i University of Chicago by having
the posterior edge of the spine not so broad and without the great cavity just above
the posterior zygapophysis. The bottom line has no well-defined keel, and the lower
edge of the posterior face is much lower than the edge of the anterior face.

These differences are so slight as to be possibly individual, or varietal, characters,
and are accepted as such until further evidence proves their specific value.

Measurements. — No. i University of Chicago.

mm. mm.

Total length of humerus 181 Greatest breadth

Greatest breadth :

Proximal end 42

T-i- .-1 .>„^ TIT Distal end 38

Poxlaiend'':':::::::::::::::::::::: 96 xotai length of femur .20

Breadth of proximal end 73

Diameter of shaft at center 24 jj^^^, ^^^ across condyles 69

Projection of deltoid ridge 35 Greatest diameter of shaft at center 36

Total length of ulna 202 ^^j^, ^^^^^^ ^j (j^,;^ j^^

Greatest breadth : Breadth, upper end from side to side 72

Distal end 37 Before back 51

Proximal end 55 Greatest diameter of shaft at center 21

Total length of radius 146 Greatest breadth at distal end 44

No. looi University of Chicago.

mm. mm.

Height of spine of the 14th vertebra from center Vertical height of spine of 3d cervical above

of neural canal 740 center of neural canal 144

Antero-posterior diameter of spine at base 27

Length, bottom line of centrum 29 thickness of spine at middle of base 6

Antero-posterior diameter of spine at base 5 Length, bottom line of centrum 25

No. 4008 American Museum.

mm. mm.

Length, bottom line of I2th, a dorsal 22 Width of keel on bottom line 13

Height of centrum posterior to neural arch ... . 30 Width of centrum at notochordal canal. ...... . 12

Width of anterior face of centrum at level of

Vertical diameter of anterior and posterior faces . 34

Width of keel on bottom line i

Width of centrum at notochordal canal 10

notochordal canal 25

Length, bottom line of last lumbar 15

Total length of centrum 28

Width of anterior face of centrum at level of Height of centrum posterior to neural arch 29

notochordal canal 24 Vertical diameter of anterior and posterior faces . 35

Length, bottom line of iSth, the first lumbar. . . 21 No keel present.

Total length of centrum 28 Width of centrum at notochordal canal 24

Height of centrum posterior to neural arch 25 Width of anterior face of centrum at level of

Vertical diameter of anterior and posterior faces . 30 notochordal canal 31

Dimetrodon dollovlanus Cope (p. 51; plates 23 and 24).

Emholofhorus dollovianus.

Characteristic specimens: No. 4064 Am. Mus.: The type. No. 114 University
of Chicago: A very complete specimen, including a skull lacking only the posterior
temporal region ; the lower jaws ; thirty-five vertebras, beginning with the atlas, from
the seventh presacral to the second caudal connected ; the shoulder girdle ; the fore
limb and incomplete fore foot ; the pelvis. From Coffee Creek, Vernon county,

MORPHOLOGICAL REVISION OF THE SUBORDER.

129

Texas. No. 4035 Am. Mus. Nat. Hist., Cope, coll. : Nine anterior vertebrse in con-
nection, beginning with the axis, and after a break six posterior dorsals in connection.
Spine nearly complete. No. 28 University of Chicago : A fragment of lower jaw.
From Coffee Creek, Vernon county, Texas. No. 4064 Am. Mus. Nat. Hist., Cope,
coll. : A fragment of the lower jaw shows that the bases of the teeth were decidedly
oval in section. This is different from other species where the teeth are rounded or
quadrate at base; it occurs in a second specimen, No. 28 University of Chicago. The
base of the large maxillary canine is quadrate in section, but nearer the middle it is
nearly hemispherical in section, the outer side being much more convex than the
inner. There are two teeth in the maxillary portion of the diastemal notch.

The character used by Cope to distinguish this species, the prominent intercen-
truni, is common to all species of the genus, but the forward inclination of the axis
and neural arch is a feature unique in the species. The more
posterior vertebrse of the type specimen are closely similar to
Dimetrodon incisivits. A posterior dorsal shows the low keel to
be divided by a shallow longitudinal groove. The spines of the
vertebrse are smooth. The astragalus is rough
and rugose, much stronger than any other
astragalus in the collections (plate 16, fig. 8).
No. 114 University of Chicago: The
skull is very similar in outline to that of
Dimetrodon incisivits. The section of the
teeth can not be made out, but there are three
teeth in the maxillar}- portion of the diaste-
mal notch. This seems to be a distinctive
character of the species ; in several specimens
of the genus there is a single tooth preceding
the enlarged maxillary-, but in others there is
none or a scar showing where a single tooth
has been lost, but never more than one. The
diastemal notch is nearly filled with teeth;
this is a primitive character and would indi-
cate that the species was perhaps the least specialized of the genus. In this skull both
large maxillary teeth are functional at the same time.

The vertebral column : The atlas is similar to Dimetrodon incisivus.
The axis has the centrum similar to Dimetrodon incisivus, but the posterior end
of the centrum is much lower than the anterior, so the whole vertebra slants down-
wards to the rear, and if the bottom line of the centrum is horizontal the spine slants
forward. The spine is proportionately much wider antero-posteriorly and extends
farther out over the atlas ; the upper end has a triangular facet for the ligament ; the
posterior edge, while wide, is not excavated by a deep groove as in Dimetrodon incisi-
vus ; the anterior edge has two small surfaces for ligamentous attachment.

The third cervical has the spine short and very slender; it curves sharply forward
and lies close to the posterior edge of the neural spine of the axis. The whole neural
arch stands far forward over the anterior part of the centrum, giving the vertebra the
characteristic inclined appearance as opposed to the vertical condition of the same
vertebra of Dimetrodon incisivus.

54

55

Fig. 54. — Lateral view of an anterior cervical o( D. dol-
lovlanus, No. 4064 Am. Mus. :< li.

Fig, 35. — Anterior view of the same vertebra as fig. 54.
X I. Showing the large intercentrum and
facets for the ribs, on which evidence Cope
referred this species to the genus Embolophorus.
itc, intercentrum.

I30

REVISION OF THE PELYCOSAURIA.

The vertebrae of the dorsal aud lumbar region are very similar to those of Dime-
trodon iucisiviis. Centrosphenes and centantra are present on all presacral vertebrse.
The neural arch is exceptionally high in the dorsals, so that the zygapophyses are
farther above the centra than in other species and are very oblique.

The seven posterior lumbars, the sacrals, and the first caudal are connected.
They show the sudden shortening of the centrum and increasing concavity of the
mid-line below in the lumbars and the sudden increase in length of the sacrals better
than any other specimen. As the vertebrte become shorter the sides of the centrum
are contracted by a deep pit just below the notochordal canal. The pit does not
extend to the lower edge, which remains rounded and without a trace of a keel. The
sides and bottom line become very concave, so the edges of the articular faces are pro-
portionately much wider flared than on the more anterior vertebrse. The capitulum
and tuberculum of the ribs unite and gradually grow smaller, until on the last lumbar
they are simple processes. The three sacrals are abruptly longer than the last lum-
bar, and the centrum is smoothly rounded, without the deep pits on the sides. The
centra fit closely together, and the intercentra are reduced to thin scales anchylosed to
the adjacent edges of the centra. The zygapophyses are atrophied and the spines are
small and weak.

The first sacral rib has a wide distal end, the posterior two are smaller. The
third is inclined sharply forward and rests against the second, rather as if it acted as a
support for the first than as supporting the ilium (plate 23, fig. i).
The caudals are as in Dimetrodon incisivHs.

The shoulder girdle: The elements of the shoulder girdle
of this species have been used in the restoration of Dimetro-
don incisivus. There are few points of difference between
the scapula and that of other species determinable from the
material at hand. The inner edge of the coracoid and procor-
acoid oi Dimefrodon incisivus is nearly straight and joins the
anterior edge by a sharp angle; the same edge in Dimetrodon
dollovianus seems to be more rounded and to join the anterior
edge in a gentle curve (plate 23, fig. 2).

The fore limb is represented by the humerus, the ulna,
and an imperfect foot. The ulna is more clumsy, with a
heavy proximal end, a more widely open articular cavitj', and
a less perfect olecranon process ; it is of the type of fig. 56.

The pelvic girdle : The pelvis is of the same form as
Dimetrodon incisivus. The ischium and pubis are separated
in the specimen (No. 114 University of Chicago) as if they
had not been so closely united as in Dimetrodon incisivus.
The hind limb is represented b)- the distal end of the femur and the proximal end
of the tibia only.

No. 4035 Am. Mus. This specimen evidently belongs to the same species as
No. 114 University of Chicago. It shows the fonn of the axis and third cervdcal
(plate 24, fig. i). The sixth vertebra is the first one to take on definitely the character
of the dorsals, the thin keel and shortened bottom line.

The spines of the anterior vertebrse are short, becoming very slender just above
the base; the spine of the seventh is abruptly higher than the others, and that of the
eighth even more so. The spines of all are imperfect, but are so slender at the ends
that it is evident that they are nearly complete. Only the lower portions are repre-

56

-Proximal end of an ulna

oi D. dollovianus. X "3,

Fig. 57. — Proximal end of an ulna

oi D. incisivus. X ^3.

MORPHOLOGICAL REVISION OF THE SUBORDER.

131

sented in the figure. A short distance above the base all the spines are marked by a
series of short parallel rugose lines, but there is no marked swelling.

The posterior series of six are posterior dorsals with longer centra and rounded
bottom line. The spines have begun to bend backward, approaching the sharp incli-
nation of the lumbar spines of other specimens. The fifth of the series has the bottom
line sharper, with a ridge divided longitudinally by a shallow median groove, making
it appear as a double ridge.

Measurements. — No. 114 University of Chicago.

Length of skull from anterior end to posterior

edge of orbit

Length, bottom line of axis

Height of spine from center of neural canal . .
Length, bottom line of —

3d cervical

4th

5th

6th

7th, ist dorsal

8th

Length, bottom line of —

2oth, ist lumbar 28.5

gth .
loth.
nth.
I2th.
13th.
14th.
15th .
i6th.
17th.
i8th.
19th.

38

38

32

29

29

25

27.5

24.5

32

31

32.5

34

35

36

37

33

30

2ISt .
22d. .
23d..
24th.
25th.
26th.
27th .
28th,
29th .
30th .

31st, 1st caudal 20.5

32d 18

33d 15

Length of scapula 33-40

Width, opposite humeral cotylus 12

Length of interclavicle 31-32

humerus 191

ilium, antero-posteriorly 150

ischio- pubic symphysis about 276

27
26
23
22
19
16

13
ist sacral 27

32.5
30

No. 4035 American Museum.

Length, bottom line of axis 34

Height of spine above neural canal, same .... 76
Length, bottom line of —

3d vertebra 32

4th vertebra 30

Height incomplete spine, same 160

Length, bottom line of 5th vertebra 26

Height incomplete spine, same 210

Length, bottom line of 6th vertebra 27

Height incomplete spine of same 200

Length, bottom line of 7th vertebra 25

Height incomplete spine, same 253

Length, bottom line of Sth vertebra 24

Height incomplete spine, same 350

Length, bottom line of gth vertebra 24

Height incomplete spine, same 450

Length, bottom line of ist posterior dorsal... 30

Height incomplete spine of ist posterior dorsal . 825

Dimetrodon macrospondylus Cope (p. 52, plates 25 and 26).

Clefsydro^s macrosfondylus.

Characteristic Specimens : No. 4012 Am. Mus. : The type. No. loi 9 University
of Chicago : Vertebrae of the posterior dorsal and lumbar region with the intercentrum
and spines almost perfectly preserved. Nos. 4054 and 4055 Am. Mus. : Axis and
several other vertebrse.

Nos. 4054 and 4055 Am. Mus.: The axis (figs. 58 and 59) has the usual elongate
centrum, with a low, sharp ridge on the bottom line. The anterior face is nearly cir-
cular, with a very prominent edge surrounding the notochordal funnel. On the upper
edge are relatively large and deep centantra. The posterior face is circular and sur-
rounded by a wide, flat border not recurved onto the side of the centrum. The spine
is short and relatively stout. The posterior edge is grooved, but not deeply excavated
as in Dimetrodon incisiviis. The upper end has an irregular face for ligamentous
attachment, and there is a distinct face for the middle of the anterior edge.

132

REVISION OF THE PELYCOSAURIA.

No. 4012 Am. Mus. : The first cervical preserved, the third (?) (described by Cope
as the axis) has the same upright form as Dimetrodon incisivus. The centrum is rather
higher than wide, so the articular faces are narrowed.

The next two and a half vertebra are connected and belong in the anterior dor-
sal series ; they have the same form as vertebrce of the same region in Dimetrodon
incisivus ; the lower edges of the centra are recurved to accommodate the intercentrum
and rib, but not nearly so much as in Dimetrodon incisivus and Dimetrodon dollo-
2>ianus, because the intercentra have already assumed the characteristic form of the
species and the ends project beyond the edges of the centra with distinct tenninal
facets for the capitulum of the rib. These vertebras do not connect with the series

which follows, which begins with a half
vertebra and contains nine whole ones of
the posterior dorsal and lumbar regions.
The anterior ones have a low keel on the
mid-line of the centrum, but by the fifth of
the series the bottom line is rounded ; on
the same vertebrse is the first evidence of
a broadening of the edge of the anterior
articular face to form the facet for the
capitulum of the rib. The advent of this
face is much more gradual than in Dime-
trodon incisivus, where it appears without
warning. On the sixth and seventh the
face is plain and the lower supporting ridge
of the transverse process extends forward
almost to the capitular face ; on the ninth
of the series the two facets have com-
pletely fused. Intercentra are present
and show the characteristic form of the
species ; the best view is from below. The
intercentra are of nearly equal width in
the whole series ; slightly concave on the mid-line, but projecting beyond the edges
of the centra and the ends enlarged and flattened to accommodate the face for the
capitulum of the rib.

After this series are three lumbars, two free and one attached to the sacrum ;
they have the shortened, wider form of the posterior lumbars of Dimetrodon incisivus.
The ribs are fused to the sides of the centra, but the capitula project forward beyond
the edge of the anterior articular face and into the intercentral space in a manner not
seen in Dimetrodon incisivus. In these the intercentra have lost the wide-ended form
and underlie the centra as in other species of the same genus.

The sacrals are of the same form as Dimetrodon incisivus. Between the last
sacral and the first caudal is a very narrow intercentrum, but between the first and
second caudals the intercentrum is much wider.

No. 1019 University of Chicago (plates 25 and 26) : The series consists of three
connected posterior dorsals, a broken and disconnected vertebra, and then five more in
connection. The anterior four have the spines attached, but in the posterior ones the
neural arches are broken and the spines are arranged by their characters. The only
spine perfect to the tip is one of the lumbars. All of the spines are somewhat twisted
and bent, but this seems to be due rather to the accidents of fossilization than to any
natural condition.

Fig. 58. — Axis of D. macrosponJylus, Nos. 4054, 4055
Am. Mus. cs, centrosphene. X - i. Anterior view.
Fig. 59. — Lateral view of the vertebra shovra in fig. 58.

MORPHOLOGICAL REVISION OF THE SUBORDER. 1 33

The centra have the usual elongate fonn of this portion of the column ; the
dorsals have the last traces of a keel, so the bottom line of the centrum is straight, but
the lumbars have no keel, and the bottom line is concave. The transverse processes
are all lost, but they originated high up on the side of the centrum and the neural
arch. The intercentra have the characteristic fonn of the species and the rib-head
articulated in the triangle between the upper portions of the centra and the end of the
intercentra. Several rib-heads are preserved in this position.

The lumbars are distinguished by the presence of the capitular facet on the side
of the anterior articular edge. Between the last dorsal and the first centrum with a
well-developed capitular face there is one with a somewhat imperfect face. The heads
of several ribs are preserved in position in the lumbar series, showing that they touched
the end of the intercentrum in the first lumbars as well as the capitular face on the
edge of the centrum.

The spines are very characteristic in appearance. The bases of the dorsal spines
are somewhat longer antero-posteriorly than transversely, but a few centimeters from
the base a notable swelling gives the spine a quadrangular section. The sides of this
swelling are marked by ridges and grooves, giving it a roughly fluted appearance.
Above this the spine becomes rounded and then oval (see fig. 14). A deep groove on
the posterior face persists nearly to the summit, while a similar one on the anterior
face disappears at about half the height of the spine. The apices of the spines are
very slender ; in those most nearly complete they are not over 2 or 3 mm. in width.

In the lumbars the bases of the spines are much more elongate antero-posteriorl}-.
They do not swell to quadrangular shape, but pass directly to a rounded section,
though there is a short region marked by rugose ridges in the position of the swelling.
In one of the posterior lumbars the spine is complete and shows that the tip end was
slightly enlarged and roughened.

Measurements.
Nos. 4054 and 4055 American Museum.

mm. min.

Length, bottom line of centrum 27 Height of spine above neural canal 64

No. 4012 American Museum.

Length, bottom line of — Length, bottom line of —

An anterior dorsal 18 5th presacral 19

I2th presacral (probably the i6th vertebra) 24 4th " 16

nth " 24 3d " 16

loth " 24 2d " 13

9th " 23 ist " 12

8th " 23 ist sacral 26

7th " 22 2d " 24

6th " 20 3d " 22.5

No. 1019 University of Chicago.

mm. mm.

Length, bottom line of a lumbar 32 Dorsals, continued:

Anterior face ; Anterior face :

,^ . ^ , J. , c. Honzontal diameter 27

Horizontal diameter 26 Vertical diameter 33

Vertical diameter 29 Transverse diameter, base of spine 19

Transverse diameter of centrum at middle 14 Antero-posterior diameter base of spine... 14

Vertical diameter of centrum just posterior to Transverse diameter, 5 cm. above base 18.5

arch 22 Antero-posterior diameter, 5 cm. above

Posterior face, vertical diameter 29.5 base 17

Length, bottom line of posterior dorsals and Length of incomplete dorsal spine of same

four lumbars, each 31 vertebra, probably 100 mm. short 873

Dorsals: Length of second incomplete dorsal spine. 800

Length, bottom line 28 Length, complete lumbar spine 675

134

REVISION OF THE PELYCOSAURIA.
Dimetrodon plalycentrus sp. Case (p. 54).

Characteristic specimen : No. 4065 Am. Mus. The type.

This species is very similar to Dimetrodon viacrospondylus, but the bottom line
of the centrum of the posterior dorsals and anterior lumbars, instead of being drawn
to a keel, is broad and rounded and even flattened. This is more apparent on the
posterior portion of the column, so that on the second lumbar vertebra the bottom of
the centrum is nearly flat transversely and is marked by rugosities which have a
distinct tendency to a radial arrangement. The bottom line is concave antero-
posteriorly, and the edges of the centra are very prominent. The articular surfaces
are reflected on the sides of the centrum and are beveled on the lower edge, leaving a
large space for the intercentrum.

Measurements.

mm. 7?im.

Length, bottom line of— Length, bottom line of —

2d lumbar 21 Penultimate dorsal 25

ist lumbar 23 Antepenultimate dorsal 26

Last dorsal 23

Dimetrodon obtusidens Cope (p. 54, plate 25).

Therofleura obtusideyis Cope.

Characteristic specimens : No. 4007 Am. Mus. : The t>pe. No. 4062 Am. Mus.
Nat. Hist. Cope, coll. : Homeotype. The basicraniuni and a series of twenty-one or
twenty-two vertebrse, not all in series; numerous fragments of spines. From the
mouth of Beaver Creek, a tributary of the Big Wichita river, Texas. No. 1060
University of Chicago : A single axis ; from Texas. No. 2152 Am. Mus. Nat. Hist.,
Cope, coll. : A humerus ; from Texas.

The type specimen consists of a number of mixed bones. The jaws originally
described by Cope are the two lower jaws, and on the other side of the mass is seen
the posterior face of the skull, with the ele\-ated postorbital region of a typical Dime-
trodon. The "palatal dentigerous bone" described by Cope is part of the pterygoid,
but it is not at all certain that it belongs with the skull, as it seems too small. The
"rhombic" form described by Cope is due to the fact that the pterj'goid approaches
in form that oi t\\& Poliosauridcc ; the external process of the pterygoid does not stand
upright at right angles to the main portion, but lies at a low angle to it, so that the
external process of the pterygoid and the palatal portion fonn the rhombic area. The
external face of the external process is very narrow, and on the lower edge there are
but three teeth in sockets ; the patch of small teeth begins at the inner edge of the
process, instead of after an inter\'al as in Dimetrodon incisiz'us.

With the specimen are three humeri, one of which belongs to some member of
the DiadedidcB ; the other two probably belong with the skull, as they are of the same
size. They are of the same general form as Dimetrodon incisivus, but the radial pro-
cess begins much farther down on the side of the bone and is separated from the head
by a considerable interval. A scapula is also preserved in the mixture of bones, which
has the same form as Dimetrodon incisivns.

The vertebral column is represented by several vertebrae probably belonging with
the skull. By direct comparison the vertebral column. No. 1838 Am. Mus., is seen to
belong to the same species and is described as Dimetrodon obtusidens.

No. 4062 : The base of the skull is nearly complete, lacking only the distal ends
of the paroccipitals and a fragment just over the foramen magnum. The occipital

MORPHOLOGICAL REVISION Q OF THE SUBORDER.

135

condyle is flattened and is marked by a pit for the termination of the notochord ; its
section is triangular and the articular face is continued on to the lower surface. The
exoccipital and supraoccipital both take part in the formation of the condyle. The
exoccipital forms the sides of the foramen magnum and meets above it, shutting out
the supraoccipital. The lower surface of the basicranium is the same as in Dinietro-
don incisivus.

The axis: The best-preserved axis is No. 1060 Universit}- of Chicago (plate 25,
fig. 6). In the present specimen the spine is lost, but the centrum shows the usual
elongate form, the well-developed centantra and the wide face for the intercentrum on
the lower half of the anterior articular face. The transverse process rises from well
below the level of the anterior zygapophyses instead of on a level with them, as in
Di>netrodo)i incisivus.

The third vertebra is verj' similar to
the axis, but with a narrow spine ; the
transverse process is longer and inclines
rather more to the rear, the face for the
rib looking backward as well as down-
ward. There is a deep pit at the base of
the spine on either side.
The fourth vertebra resembles the second, but the sides
of the centra are pinched in below the notochordal canal, so
that there is the beginning of the narrowing of the bottom
line to form a keel ; this is most prominent in the anterior half
of the centrum.

The fifth vertebra is joined to the second, but is com-
pletely reversed in position in the specimen ; it has been placed
in the correct position in the figure. This vertebra shows the
typical characters of the posterior cervicals and anterior dorsals.
The centrum is shortened on the bottom line by the bending
back of the inferior edge of the anterior face, and the sides are
sharply pinched in just below the notochordal canal, forming
a high and thin keel. The anterior face of the centrum has
well-developed centantra and a wide face for the intercentrum.
The transverse process stands well out from the side of the
centrum.

The sixth to the thiiHeenth are not connected, but have
been placed in position from their characters. The first three
are of similar fonn ; they are imperfect, but all show the sharp keel and shortened
bottom line. The transverse process stands well out, almost horizontally, from the
side of the centrum.

The ninth has lost the lower half of the centrum, but preserves the neural arch
and the base of the spine. The anterior face of the centrum is rounded, having largely
lost the face for the intercentrum, but the centantra are still evident. The neural arch
is high and the faces of the zygapophyses are quite oblique, but not so much so as in
Dimctrodon doUavianiis. The transverse process is short and stands out horizontally
from the side of the neural arch. The base of the spine presents ver>' clearl)- some of
the characters of the species. It is smooth below, but a short distance up becomes
slightly rugose ; below the rugosity the spine is thin, but wide antero-posteriorh-, and

Fig. 60. — Left humerus ot D.
oblusidens, No. 2152
Am. Mus. en/, ent-
epicondylar foramen.

Fig. 61. — Posterior surface of
tire skull of D. oblusU
dens. No. 4062 Am.
Mus. X %.

136 REVISION OF THE PELYCOSAURIA.

the fore-and-aft edges are drawn out into very thin and prominent ridges ; above the
rugosity the section of the spine is rounded with grooves on the anterior and posterior
surfaces, and its surface is smooth as in Dimetrodon tnacrospondyliis.

The tenth vertebra shows a slight decrease in the sharpness of the keel; the
anterior end of the keel is rather rouuded and the posterior end is double, having a
slight narrow groove dividing it longitudinally.

The eleventh and tivelfth vertebra- are longer and the keel below is less strong ;
the sides of the centra are regularly convex, the sudden narrowing just below the
notochordal canal so characteristic of the dorsals having disappeared. The anterior
face is nearly as round as the posterior, due to the loss of the face for the intercentrum
on the lower edge. Looking at the vertebra from above it is seen that four strong
ridges run from the base of the spine, one to the base of each of the zj'gapophyses ;
this is true of the same region of all the species of the genus, but in none is it so
apparent as in this specimen.

The thirteenth to the sixteenth are connected. These are rather longer than the
anterior dorsals, and the bottom line has a very low keel. The ends of the centra are
rather abruptly flared, so that the vertebtje are concave from end to end on both sides
and the bottom line. The inferior supporting ridge of the transverse process curves
gradually forward in these vertebrse; by the sixteenth it reaches nearly to the anterior
edge of the centrum.

The seventeenth to the tiventieth are imperfect, but show the gradual elongation
forward of the inferior supporting ridge of the transverse process and its growth in
height; in the twentieth it is nearly as high as the transverse process itself The
elevation of this ridge is accompanied by the development of a pit both behind it and
above it. On the nineteenth the ridge has reached the anterior edge of the centrum,
and on the twentieth the face for the capitulum appears on the edge of the centrum.
The centra grow more elongate and the keel becomes lower, but does not disappear.
Between the eighteenth to the twentieth there is a small intercentrum with sharp
ends, lacking an articular face, as in Dimetrodon iiicisivus.

The twenty-first to the tiventy-third vertebra; : The first of these is imperfect and
may be the posterior half of vertebra twenty. On the twenty-second the ridge from
the transverse process just touches, but does not join, the capitular face. On the
twenty-third the two are rmited.

There are two anterior caudals in the box with these vertebrae, but they seem
entirely too large to belong to the specimen.

No. 1060 University of Chicago : The axis. The upper portion of the spine is
broken away, but the lower part shows that it was enlarged, having much the same
form as No. 114 University of Chicago. The centrum is relatively much more elon-
gate than in Dimetrodon incisivics. The lower surface is marked b}- a sharp but very
low ridge, which does not reach to the anterior and posterior edges of the centrum.
The under side of the two anterior zygapophyses is concave, so that as they meet they
form an arch over the neural canal and extend well anterior to the edge of the cen-
trum ; at the base of the z3'gapoph}'ses are well-developed centantra. The diapophj'ses
slant backward, but are not at any point free from the centrum, and do not extend
below its middle. The anterior face of the centrum has a well-developed face for the
intercentrum, occupying nearly one-third of the height of the face. The posterior
face is circular.

MORPHOLOGICAL REVISION OF THE SUBORDER. 1 37

Measurements. — No. 4062 American Museum.

inni .

Diameter occipital condyle : Length, bottom line of —

Horizontal 15 6th cervical 16.5

Vertical n nth, a dorsal ig

I2th, " 20

13th, " 16.5

14th, " 20

15th, " 20

Width across occipital plate 52

Length, bottom line of — •

Axis 21

3d cervical 22 i6th,

4th " 22 17th, " 21

5'h " 21 18th, " 20

Height of centrum posterior to neural arch. .. . 17.5 23d, a lumbar 17

No. 2152 American Museum.

mm. mm.

Length of humerus 147 Width, distal end 57

No. 1060 University of Chicago.

mm. mm.

Anterior face of centrum : Posterior face of centrum :

Vertical diameter 12 Vertical diameter 11

Horizontal diameter 10 Horizontal diameter 12

Length, bottom line of centrum, 17 mm.

Other Specimens of tliis species are Nos. 1015 and 1017 Am. Mus., and
180 University of Chicago.

Dlmetrodon navajovicus Case (p. 56, plate 27).

Characteristic specimens : No. 2299 Am. Mus.: The type. No. 2288 Am. Mus.
Nat. Hist, Cope, coll. ; from New Mexico. No. 2285 Am. Mus. Nat. Hist., Cope, coll. :
Collective number covering many lots, but mostly this species ; from New Mexico.
No. 1034 University of Chicago. No. 1046 University of Chicago.

There is no fragment of the skull preserved.

The humerus., described from No. 2285, is most easily recognizable in this species ;
it is of the general form of Dimetrodoii incisivus with well-developed articular surfaces,
but the proportions are notably different. The head is broad, with the usual oblique
face, but the face does not extend to the radial border as in Dimetrodoii incisivus.
The radial crest joins the proximal portion of the bone at an obtuse angle, and the
line of union is marked on the posterior side by a sharp ridge. The crest is ver>' short,
beginning low down on the distal end and looking rather like a wide process than a
ridge ; it terminates in a broadened apex with a smooth surface for ligamentous attach-
ment. The upper end is separated from the articular face by a wide concave inter\-al.
The shaft is more slender compared to the ends than in other species. The lower
end has well-developed radial and ulnar faces. The entepicondyle is very long,
extending so far inward that a line drawn straight down from the eutepicondylar fora-
men would divide the distal end of the bone into two nearly equal halves. In other
species there is not more than a third or fourth of the distal end inside of such a line.

No. 2299: The femur has a wide proximal end, with a deep depression on the
posterior face, with a prominent process on the inner side. The lower end has stout
and well-developed condyles separated on the posterior side by a deep groove, but the
articular faces lie so much on the posterior face that they are not separated by the
distal notch.

138

REVISION OF THE PELYCOSAURIA.

The vertebrce preserved are all of one type. They are short and high with the
lower end broad and marked by a wide groove with sharp edges, so the vertebra has
the appearance of being double keeled ; this is very different from the double keel
described in Dimctrodon dollovianiis, for there it is a sharp narrow keel and the groove
dividing it is verj' narrow. No vertebrae of this t}'pe have been found with any other
species of Divieirodon ; they are much closer to the kind found in Theropleura^ and
might well belong to such an animal, having become accidentally associated with the
typical Dimetrodon humeri. On the other hand, no vertebrae of the type of Dime-
trodon occur in the abundant material from New Mexico, and it seems probable that
the vertebrae must belong with the humeri. As we do not know the humerus of
Thcropleura^ and as it is not certain that these vertebrae had high spines, it is, of
course, possible that D. iiavajoviciis may turn out to belong close to Theroplenra.

There are several fragments of small skulls which may be shown later to belong
here, as Archeobelus vellicatiis, or two small maxillaiy fragments, Nos. 1013 and 1014
Universit}- of Chicago, from Texas.

The humerus is 92 mm. long ; the proximal end 46 mm. wide, and the distal
end 70 mm. wide.

The front foot : A. small front foot. No. 2290 Am. Mus., from New IMexico (plate
5, fig. 6), may possibly belong to this species. It resembles in almost every particular
the front foot of D. iudsiz'us, No. 1003 University of Chicago. This foot was described
by Cope (70) (plate 3, fig. 6) as posterior, but this mistake was largely due to the fact
that the radiale and ceutrale were separated from the rest of the foot and were not
recognized by him in the uncleaned material.

Subfamily NAOSAURINAE Case (p. 58).
Genus NAOSAURUS Cope.

There is no certain evidence of the skull of A^iosaurus ; according to Cope's
determinations the skull is not distinguishable from that of Dimctrodon^ but, as
explained above (p. 58), the identifications can not now be confirmed either hy the
specimens or records. (See note on p. 145.)

The axis and atlas are unknown. The
cervical vertebrae show a most remarkable dif-
ference from those of Dimetrodon] from the
fifth or sixth they decrease in size forward and
the spines are at the same time enlarged. In
Naosaurus claviger the section of the base of
the spine of the anterior cervicals is greater
than the centrum. In both Naosaurus microdus
and Naosaurus claviger the distal ends of the
neural spines of the cer\'icals are clavate, and
this was probably true of A'', cruciger as well.
The details of the column are given in the
description of N. microdus. The bending of
the spines to the rear, which begins in the
anterior dorsal region, and becomes so acute in the presacral region, is most remarkable
and was at first attributed to accident, but as it occurs so regularly and in three dis-
tinct specimens, all that show this portion of the column, it may be accepted as natural.
Beyond a few anterior caudals the tail is unknown.
The clavicle^ No. 4037 Am. Mus., is bent at nearly a right angle in the middle-

MORPHOLOGICAL REVISION OF THE SUBORDER. 1 39

A cleithruin occurs in No. 4060 Am. Mus. ; as suggested by the occurrence in
C. natalis^ it is a slender, almost rudimentary element, articulating with the end of
clavicle and upper (anterior) edge of the scapula.

The scapula, No. 4146 Am. Mus., is larger than, but very similar to, Di)iietrodoii
incisiviis. (Plate 30, fig. 2.)

The humerus is of the form of Dimetrodon gigas; it is proportionately longer and
more rugose. (Plate 31, fig. 2.)

The anterior portion of the limb and the foot are unknown.

^\\.t pelvis is described in the discussion of Naosaiirus claviger.

Abdominal ribs : In preparing the specimen of N. claviger for mounting. Dr.
Matthew found traces of abdominal ribs, showing their presence in this animal.

The posterior limb is unknown. Many isolated limb bones may belong to this
genus, but they can not be definitely determined.

There are several enormous tern:inal phalanges with the spines, which indicate
that the feet were armed with powerful claws ; this animal probably greatly exceeded
the genus Dimetrodon in the development of the claws. (Plate 30, fig. 3.)

Naosaurus claviger Cope (p. 59; plates 28, 29, and 35).

Characteristic specimens: No. 4002 Am. Mus. : The type. No. 4036 Am. Mus.
Nat. Hist., Cope, coll. : The posterior half of a skull. No. 4015 Am. Mus. Nat. Hist.,
Cope, coll. : A vertebral column with cervicals and dorsals in fair condition, but the
spines incomplete and several others in a refractor}' concretionary matrix. No. 4103
Am. Mus. Nat. Hist., Cope, coll.: An interclavicle and scapulae. No. 4146 Am. Mus.
Nat. Hist., Cope, coll.: A scapula of the left side.

The skull : In 1888 (70) Cope published a pretty full description of this species,
evidently founded on specimens No. 4036 and No. 4002 Am. Mus. This description
is accompanied by figures of the spines and the interclavicle.

"The skull (No. 4036 Am. Mus.) : One of the best-preserved specimens of N.
claviger includes a skull, but the extremity of the muzzle is unfortunately wanting.
The median line rises forwards so that the convexity of the top of the muzzle is higher
than the posterior parts of the skull, whose profile descends rapidly. This throws
the orbit far back and gives the animal a peculiar appearance.

"The orbit is nearly round, the superciliary border being arched. Anterior to it
is a large antorbital fossa bounded by a longitudinal ridge above. Above the ridge
is a longitudinal groove, which is separated from that of the opposite side by a narrow
ridge only. The quadrate boue is large and laminiform, and is truucate above, having
a good deal the shape of the same bone in a fish. The parietal buttress is produced
downwards and backwards, and is in contact with the superior third of its posterior
border. Beneath and within it is a narrow opisthotic. The pterj-goid is large, and
is distally vertically compressed. Anteriorly it becomes flattened so that it is hori-
zontal, and is studded with small conical teeth rather distantly placed. * * * *

" Vertebra; (No. 4002 Am. Mus.): A large series of these are preserved, and they
show many interesting characters. The intercentra are not distinct in the anterior
part of the column, are separated posteriorly and in the sacrum. The centra are com-
pressed and have an acute inferior keel. The neural spines are moderately compressed
below the first transverse process; above this point they are antero-posteriorly oval in
section. The distal half is compressed. They expand to a point below the apex,
where the anterior edge extends obliquely backwards to the summit. A short corre-
sponding oblique edge truncates the posterior superior angle. The medullar}' cavity

I40 REVISION OF THE PELYCOSAURIA.

of the spine is not closed at the apex. On several of the vertebrae the lowest transverse
process is double, but the sides of the same vertebrae differ from each other in this
respect in some instances.

"The two sacral vertebrae are not coossified, and the zygapophyses are well
developed and distinct, as are the intercentra. The latter are flat, and but little
developed in the upward direction. The neural spines are rather elevated and slender.
They are compressed without cross-processes, and the apex of the spine has small
tubercles.

^'■Ribs : The ribs are long and well curved, and are moderately compressed on
their proximal half, and cylindric for their distal. The head is well distinguished
from the tubercle, as in the manner of a mammal. That is, the tubercular surface is
sessile on the convexity of the rib, and pedunculate. In this respect these ribs differ
from the usual form of two-headed reptilian ribs. The head is so long on the anterior
dorsal vertebrae, as to articulate with the posterior edge of the vertebra in front of
the one with which its tubercle articulates. It becomes shorter on the posterior part
of the column, articulating with the edge of the rib which supports the tubercle. On
the caudal series the head is retracted so as to be close to the tubercular articulation,
which is the most extensive, and which is deeply notched on one of its faces. This
gives the appearance of a three-headed rib in this genus and in Dimetrodou. * * *

Measurements.

No. I. (Skull.) m- No. 3. (Vertebras.)

Depth of muzzle at sixth tooth from last 0.172 Diameters centrum dorsal vertebra : m.

Length of skull posterior to same tooth 232 Antero-posterior 0.039

Diameters of orbit : Transverse 034

Antero-posterior 057 Vertical 035

Vertical 056 Expanse prezygapophyses do 041

Vertical depth from line of eyebrow to end of Diapophyses do 082

quadrate 200 Elevation of neural spine to first process 024

Width of condyles of quadrate 050 Transverse diameter of process 025

Diameters of crown of sixth tooth : Diameters of neural spine at process ;

Vertical 028 Antero-posterior 030

Antero-posterior 014 Transverse • .028

Transverse...... ■• '■■".■■',■•,''■'■,■ „^, Length of the two sacral vertebrae 084

Thickness of maxillary bone at sixth tooth 022 t^, . r

No. 2. (Vertebra probably of No. i.)
Diameters of dorsal neural arch, with zygapo-

Elevation of —

Neural canal of do 010

spine of do 084

physes : r ^u t

Antero-posterior 064 ^^"8'^ °*~ , . , , ,,„

Transverse (posterior) 036 R>b on outside of curve 260

Head of rib 045

Diameters of neural spine near base

Antero-posterior o33

Transverse 027

Transverse diameter of rib just beyond tubercle .017
Antero-posterior do 020

In 1892 Cope gave a further description of the temporal region of the skull
accompanied by a restoration. "The orbit is in the posterior part of the skull, and
the nnizzle is greatly elevated and compressed. The zygomatic (quadrato-jugal) is
greatly decurved posteriorly, and the supratemporal is accordingly decurved also.
The postfroutal is a narrow bone, wider than long, and it has connection with the
frontal, parietal and postorbital only. The postorbital is an L-shaped structure, of
which the shorter limb is inferior, extending to the jngal, while the longer limb is
posterior, extending to the supratemporal, in contact with the parietal. It encloses
no foramen with the latter; but it encloses a larger foramen with the jugal, zygomatic
and supratemporal at the other boundaries. This is the infratemporal foramen of

MORPHOLOGICAL REVISION OF THE SUBORDER.

141

Baur. Posterior to the parietal is a small transverse element, which appears to be
merely adherent to the former. Its determination is not easy at present. The supra-
temporal is elongate vertically, and narrow antero-posteriorl}'. Beneath and towards
the middle line of the skull is a part of another bone, which may be the paroccipital or
even the exoccipital. The pineal foramen is distinct. No parieto-quadrate arch."

This description is erroneous in making the statement that there is
no superior temporal vacuit3^ The bones of the temporal region have an
arrangement similar to that of Dimetrodon^ and the superior vacuity is even
smaller in proportion. Other than a somewhat greater rugosity no charac-
ters can be made out that will distinguish this skull from that of Dimetrodon.

The vertebral column is in general similar to that of Naosaurits uiicrodiis and
the vertebrae have the same modifications in the different parts of the column, but they
are larger and more clumsy; this is especially true of the spines. They have the same
form and origin from the centra, the same swelling out just below the first pair of
processes and the same slight groove on the fore-and-aft faces disappearing about half-
way up, but they are slightly rounder in section and much heavier; the processes are
nodular and often double or bifid. Specimen No. 4002 shows several cases of fracture
and healing of the spines during life. In neither specimen showing the vertebral
column is there any cousiderable number of vertebrae in connected series, but most of

them can be placed in nearly the proper
position by direct comparison with
Naosaurus microdus. There are twenty-
five presacrals in all.

ths-cervicals: In neither specimen
is the atlas or axis preserved. No. 4002
has four connected cer\'icals, probably
the third to the seventh, with only the
lower parts of the spines ; No. 4015 has
three connected cer\acals, probably the
fourth to the sixth, with the spines
nearly complete, figure 62. Both of
these show the same decrease in the
size of the centnim toward the anterior
end and accompanying increase in the
size of the neural spines.

TheyfrjY and smallest of the series
in No. 4002 Am. Mus. is probably the
third. The centrum is longer than
high and the sides are marked by a
deep elongate pit, which extends to the
anterior edge of the centrum ; the upper
edge of the pit is formed by a prominent
_.,._, . •,,,,,. M AMr^ ridge, which reaches to the base of the

rig. 63. — 1 hree antenor cervicals ol A", c/ouiger. No. 'lUID °

Am. Mus. ^%. Showing the small centra and trausvcrsc proccss. The anterior artic-

large spines and the inclination of the neck. ular face is Small and narrow. The

142 REVISION OF THE PELYCOSAURIA.

transverse process is short with a verj' small articular face. The base of the spine is
thin and elongate antero-posteriorly ; it stands well forward so that the posterior
zygapophyses stand over the middle of the centrum.

The second oi No. 4002 Am. Mus. (^the first of the three in No. 4015 Am. Mus.)
is the fourth cervical. The centrum is larger than the first; the pit on the side is
shorter; the transverse process is heavy, but very short, almost rudimentary'. The
neural arch is high and the zygapophyses stand far above the centrum with rather
oblique faces. The base of the spine in No. 4015 is nearly as large as the centrum.
The lowest processes are long and decurved. The top of the spine is growing large,
but the upper end is broken away, so the exact form is unknown. The whole spine
is inclined forward, but as the centra were placed obliquely, rising rapidly in the neck,
they were more nearly vertical than appears at first sight.

The thirds No. 4002 Am. Mus. (=the second No. 4015 Am. Mus.), is the fifth
cervical. The pit on the side of the centrum is less elongate; the transverse process is
short and stauds out almost straight from the vertebra. In No. 4015 the anterior edges
of the centrum show the irregular projection forming a face for the head of the rib. The
neural arch is high and the base of the spine larger than the centrum ; the first pair
of processes extends out 53 mm. from the side of the spine, two-fifths longer than the
centrum itself The top of the spine is enlarged as in the fourth cervical, but is
incomplete.

The fourth of No. 4002 Am. Mus. (=the third No. 4015 Am. Mus.) is the sixth
cervical. The pit on the side of the centrum is smaller, the angulation of the anterior
edge fonning a face for the rib-head is stronger; between the third and fourth there is
a wide and flat intercentrum, with its upper side divided into faces for the adjacent
vertebrse. The conesponding vertebrae of No. 4015 has an incomplete spine, with
the end swollen and appearing to be flattening into a clavate form.

They?/?// No. 4002 is the seventh cei-vical; it has the centrum rounded on the
bottom line, with the pits of the anterior vertebrae reduced to slight depressions. The
tranverse process rises from high up on the neural arch, just below the base of the
anterior zygapophysis, and extends almost straight out. The edge of the anterior face
of the centrum is bent back in a sharp angulation for the head of the rib. There are
well-developed centantra on the upper edge. The base of the spine is very large and
the first processes are longer than the centrum.

The eighth and ninth (?) vertebrae, first dorsals. It seems probable that the two
vertebrae described by Cope as typical of the species (plate 26, fig. i) belong next in
the series. They are the last with clavate apices and are probably the first dorsals.
The spines of the other dorsals are roughly rounded or clubbed at the end.

In the dorsals begins the backward curve that terminates so sharply in the
posterior lumbars (plate 29). The succession of vertebrae posterior to the ninth is
rather problematical, but they have been arranged in order by characters corresponding
to the vertebrae of the column of ^V. microdus. The anterior ones show the peculiar
forward inclination of the transverse process from the base of the anterior z}'gapophyses
characteristic of the genus. Four connected vertebrae from specimen No. 1348, field
number. Am. Mus., show the two posterior dorsals and the first two lumbars with ribs
attached. The head of the rib in the dorsals is between the centra, evidently touching
the end of the intercentrum and engaging the angular process on the edge of the
centrum. The tuberculuni, reduced to a rugosity, touches the end of the short transverse

MORPHOLOGICAL REVISION OF THE SUBORDER.

143

Fig. 64. — The two postenor dorsal and two anterior lumbars ot A^. claciger,
No. 4015 Am. Mus '3 Showing the condition ot the tuber-

culum ot the nb and the sudden change in position of the capitulum.

process ; the ribs curve strongly backward and outward and then down. A portion
of the nearly complete dorsal rib has been left ofi" in the drawing in order to reveal the
condition of the posterior ones. The first lumbar rib has the head suddenly shortened

so that it extends but a short
distance between the vertebrae
and articulates largely with the
capitular face on the edge of the
centrum. In the second lumbar
the transverse process is very
short, hardly more than a face
on the neural arch ; the tubercu-
lum is changed from a rugosity
on the rib to a facet which artic-
ulates strongly with the face
for the ueural arch. The capit-
ulum is much reduced in size
and articulates with the face on
the edge of the centrum alone.
The two separate sacrals are probably the first and second. Their centra are
nearly the same length as the last lumbars. The sacrum was strong, but the vertebrae
were not so firmly united as in the genus Dimetrodon. The lower edges of the centra
are beveled, showing that they were separated by an intercentnim instead of being
fused or closely pressed together with the intercentrum anchylosed below the point of
contact. The zygapophyses between the first and second sacrals are not over one-third
as large as the anterior zj'gapophj'ses of the first sacral and are poorly formed, showing
the degeneration due to the immobilitj' of the
sacrum. The ribs are strong and closely united
with the vertebrae. The capitulum of the first
sacral rib projects slighth' beyond the anterior
edge of the centrum to articulate with the pos-
terior border of the last lumbar. The rib is in-
clined sharply down and the distal end is flattened
into a vertical plate to articulate with the inner
surface of the ilium. The second rib is similar
to the first, but rather smaller. The whole dis-
tance across the sacrum is small, showing that
the pelvis was narrow as in Diinctrodoii. The
spines are very short and thin, but wide antero-
posteriorly.

No caudals are preser\'ed.
The shoulder girdle : This is known only
from isolated bones of different specimens.

No. 4146 Am. Mus. : This is a very large
scapula of the left side ; the distal end and part of
the anterior edges are broken. It is ver>' similar
in general form to that of Dimetrodon^ but is
nearly one-third larger than Dimetrodon dolloznanus.

Fig. 65. — Ribs of Naosaurus. a. An
anterior dorsal of N. microdus.
No. 4109 Am. Mus. All
others more posterior dorsal
ribsot N. claviger. No. 4002
Am. Mus. All > '4.

The anterior edge of the coracoid

and procoracoid was nearly straight. The coracoid suture is persistent, but the

144

REVISION OF THE PELYCOSAURIA.

procoracoid-scapiilar suture is hardly traceable. The coracoid foramen and the one
on the shaft are both present and in the same position as in Dimetrodon; they open
into a similar crescentic cavity on the inner side. Another specimen, No. 4138 Am.
Mus., has the distal end complete, but lacks the anterior portion.

The clavicle is unknown (see Naosaitriis microdits No. 4060 Am. Mus.).

The interclavicle is represented by a nearly perfect specimen, No. 4103 Am. Mus.,
preserved with two imperfect scapulae. This specimen was described by Cope as
belonging to the genus Dimetrodon, and his description is quoted in the discussion
of that genus. The shape is very similar to that of the intercentrum of Dimetrodon,
but the scapulse accompanying it show that it belongs to the genus Naosaiinis. It is
larger and stronger than the interclavicle of Dimetrodon.

Tl^&fore limb is unknown.

Fig. 65a. — Alternative restoration of Edaphosaums [Naosaurus). Compare plate 35. The animal is here represented
with the skull ot Edaphosaurus instead ot a skull modeled on that of Dimetrodon. X about }4-

The pelvis is represented by the badly broken and imperfect right half and the
nearly perfect left half (plate 31, fig. i). The only parts lacking are a distal border
of the ischium, which is attached to the fragment of the right side, and the distal end
of the pubis.

The ilium takes a large part in the acetabulum, but the sutures are not clearly
traceable. The crest rises almost vertically abo^•e the acetabulum and is widely flared
at the distal end. There are no distinct facets on the inner side for the sacral ribs, but
a series of strong rugose lines.

The ischium expands toward the distal end, so that the termination is high and
wide, verj' different from the ischium of Dimetrodon.

MORPHOLOGICAL REVISION OF THE SUBORDER. 145

"^he^ pubis has lost the distal end, so that its exact length can not be given, but
it was evidently fully as long as the ischium. The obturator foramen is large and
oval in outline and lies under the middle of the acetabulum very close to the posterior
end of the pubis.

The posterior limb is unknown.

Naosaurits daviger was a short, stump)- animal with a round barrel and a large
head. The head was proportionateh- quite large and the tail was almost rudimentary
in its abbreviation. The limbs were short and robust, and the supporting pelvic and
pectoral girdles were proportionately heavy. The attitude when at rest must have
been with the belly on the ground, but when walking the limbs were probably
straightened enough to swing the belly just free. In studying the proportions one is
constantly reminded of the body of a particularly sturdy hog with strong limbs; the
motion in walking must have been singularl}- like that of a hog, a waddling gait with
the head held low. Compare plate 35. This restoration by the American Museum
gives a good idea of the form of the animal. The anterior cervicals are restored from
Di)iietrodon and are, in my opinion, wrong; the anterior cervicals were probably
smaller with low spines. The skull is modeled from D. gigas^ and is wrong if, as
suggested in the note below, the true skull is that of Edapliosaiiriis. The tail seems to
me to be rather too long.

Measurements. — No. 4002 American Museum.

mm. mm.

Length, bottom line of centrum of vertebrae: Length, bottom line of centrum of vertebrae :

ist (3d cervical) 26 igth 38

2d 29 20th, about 41

3d 27 2ist (broken)

4th (broken) 29 22d 36

5th 34 23d 36

6th 37 24th 33

7th 36 25th (ist sacral) 25

8th (broken) 37 Total length of same 38

9th 42 Length, bottom line of centrum of 26th vertebra-. 31

loth (broken) 42 Total length of same 42

nth 41 Length of spine of —

I2th 44 6th vertebra (8th from atlas, broken) about 475

13th 44 7th vertebra 485

14th 48 18th vertebra (7th presacral) 465

15th 43 2ist vertebra (4th presacral) 235

i6th 43 Length of imperfect symphysis 237

17th 39 Antero-posterior diameter of acetabulum 75

i8th 39

No. 4015 American Museum.

Length, bottom lineof ist vertebra (4th cervical).- 25 Height of incomplete spine of same 178

Height of incomplete spine of same 108 Length, bottom line of 3d vertebra (6th cervical).. 28

Length, bottom lineof 2d vertebra (5th cervical).. 28 Height of incomplete spine of same 205

No. 4146 American Museum.

Greatest length of incomplete scapula 335 Probable total length across curve 350

Greatest diameter of humeral cotylus 80 mm.

Note. — During the past summer (1906) the author conducted an expedition into the Permian beds of Texas,
and a specimen discovered suggests a rather diiierent interpretation of the position of NaosaurKS. In a bed
of sandstone which had never before yielded fossils there were found several spines of A\ microdus and
several fragments of a skull ; notably, the typical plate with crushing teeth from the upper or lower jaw of
Edaphosaurus. From the occurrence of the specimen in a sandstone otherwise barren and far from any
other remains the association seems certain, though the fragments of the skull were loose in the wash just
below spines which were partly in position. It will be remembered that the type specimen of Naosaurus

146 REVISION OF THE PELYCOSAURIA.

microdus has such a plate associated with the other bones and is the single other specimen of Naosaurus
which has any portion of the skull associated with it. It was originally called Edaphosaurus microdus by
Cope. If this association is a true one, as seems certain, the name Naosaurus must be given up, as it is
preoccupied by Edaphosaurus and the subfamily Naosaurince of this paper will disappear and the members
will be placed in the family Edap/iosauridic.
Family : Edafhosauridcc.

E. fogonias, E. microdus, E. crucigcr, E. ckiviger.

It may seem that there is undue hesitancy in uniting the two genera on the evidence cited, but to any
one familiar with the occurrence of bones in the Texas beds the possibility of accidental association is so
evident that the greatest conservatism seems the best course. The original specimen of E. microdus is a
mass of broken bones collected from the surface and there is no history of the specimen preserved; the
evidence rests almost entirely on the last one (bearing the Field Number loi Coll. of E. C. C). To me it
seems extremely probable that the two genera must be united.

This materially alters our conception of the character of Edaphosaurus {Naosaurus). We recognize
that the long-spined forms were specializing toward a diet of shell-fish and crustaceans, perhaps even toward
a herbivorous diet ( Edaphosaurus), as well as toward a purely carnivorous diet and predatory nature
(Dimetrodon). The suggested relationships with Placodus are somewhat strengthened, as the long-spined
Cteuosaurus occurring so close to Placodus may have had a dentition similar to that of Edaphosaurus
(Naosaurus).

Naosaurus cruciger Cope (page 60).

Characteristic specimens: No. 4003 Am. Mus. : The type. No. 4004 Am. Mus.
Nat. Hist., Cope, coll. : A skull labeled by Cope N. criiciger. No. 4080 Am. Mus.
Nat. Hist., Cope, coll.: A collection of mixed and broken spines and vertebrse closely
similar to tlie type in appearance and matrix. No. 4004 : The skull labeled by Cope
as belonging to N. claviger is imcleaued, but presents no recognizable differences from
the skull of Dimetrodon.

No. 4003 : No considerable portion of the type specimen can be put together,
so little can be made out of its general fonn. The isolated vertebral centra strongly
resemble those of N. microdus., but the fragments of spines show that above the first
pair the transverse processes were not developed beyond simple nodular rugosities,
never extending more than 10 mm. from the spine. The first pair is not over 20 mm.
long, no longer than the spine is thick at their point of origin. The processes alter-
nate above the first pair, as described by Cope, but the oblique arrangement on several
adjacent vertebrae mentioned by him does not hold.

One spine shows a large medullary cavit}' near the base. This does not occur
in the other species, but its presence or absence may be due in large measure to the
accidents of fossilization.

No. 4072 : In 1888 Cope published a figure of a spine which he called N. criiciger.,
but it is very different from the type, resembling A'', microdus much more closely.

Naosaurus microdus Cope (page 60; plates 28 and 32).

Edaphosaurus microdus Cope, page 61.

Characteristic specimens: No. 4014 Am. Mxis. : The t)'pe (plate 32). No. 4060
Am. IMus. : Homeot}'pe : A nearly perfect vertebral column from the third (?) cervical
to the second or third caudal, twenty-nine vertebrae in all. It is probable that two or
three posterior lumbars are lost. The specimen was exceptionally carefull)' collected
for the time and the methods then prevailing. The vertebrae were numbered as taken
up and a small sketch accompanied the specimen showing their position when found.
This, and the fact that man}- of the vertebrae are in connection, makes it possible to
give a nearly complete description of the column. From Paint Creek, Hardeman
county, Texas. No. 4037 Am. Mus. Nat. Hist, Cope, coll. : A clavicle, vertebral
spines, humerus, and terminal phalange ; from Texas.

MORPHOLOGICAL REVISION OF THE SUBORDER. 147

No. 4014 : The type is represented by a fragment of the pterygoid showing teeth
(which is indeterminate, for the teeth on the pter^'goid var\' in size in different parts)
and by fragments of the spines and vertebrse. Direct comparison of the fragments
with like parts of No. 4060 show that that specimen belongs to the same species. The
type is so imperfect that the following description is taken entirely from No. 4060.

The figure of the vertebral column (plate 32) very probably shows the natural
curvature, for many of the vertebrae are in connection and on mounting the specimen
for photographing they fell into the curves naturally. The position of the cervicals
is taken from JV. claviger^ No. 4015 Am. Mus. The spines begin in the anterior dorsal
region to be inclined to the rear and in the lumbar region show a sharp bending
backwards. This is -increased until the posterior lumbar spines are bent so sharply
back that they lie nearly parallel to the vertebral column and overarch the shortened
spines of the sacral and the anterior caudal vertebrte. That this peculiar character is
not due to accidental bending or crushing is evident, from i. The gradual appearance
of the curvature of the spines; 2. The fact that the spines show no evidence of
crushing or fracture ; 3. The fact that the same curvature occurs in two other
specimens of A''. daz'ige)\ No. 4002 Am. Mus. and No. 4015 Am. Mus.

The vertebrae are described in detail below.

They?;-^/ vertebra is represented by the centrum and a short portion of the spine ;
it may perhaps be the axis, but it seems more probable that both axis and atlas are miss-
ing, and that this is the third cervical. The centrum is flattened vertically with a
prominent ridge on the side from the base of the transverse process to the posterior
edge of the centrum. The anterior zygapophyses are very strong. The spine is weak,
and the end not clavate.

The vertebra reckoned as the fourth cervical is voxy imperfect ; about half the
spine is preserved, showing a beginning of a distal expansion.

^\i^ fifth is represented by the centrum only.

The sixth has the spine broken, but the distal end is broadly clavate with the
bases of broken processes near the apex. The sides of the clavate apex are marked
with shallow grooves, which indicate the course of nutrient vessels under a covering
of skin. The first pair of processes on the spine is far up, nearly half-way to the apex.
The centrum is elongate without any keel on the bottom line.

The seventh has a considerable portion of the spine attached to the centrum ; the
first pair of processes is nearer to the centrum than on the fifth, but is still far above it.
The upper portion of the spine is separated from the lower by a small break, but only
a very short piece is lost. The apex is flattened and broader than the fifth. The cen-
trum shows no sign of shortening nor is there any keel. The transverse process rises
from the side of the neural arch just below the anterior zygapophysis.

The eighth cervical has lost the lower part of the centrum, but the zygapophyses
are well developed. The transverse process rises from just below the anterior zyga-
pophysis and extends straight out. The spine is complete. The base is somewhat
swollen just above the neural arch and slightly rugose; at the level of the first pair of
processes it is slightly thicker antero-posteriorly than transversely ; above the first
processes the section becomes oval with a groove on the anterior and posterior sides,
which extends half-way up the spine. There are five pairs of processes on the spine ;
the first pair curves out and downward and the ends are slightly expanded and rugose.
The second pair are opposite each other like the first, but above the pairs are slightly
displaced ; at the apex there is one odd process. The apex of the spine is clavate, but

148 REVISION OF THE PELYCOSAURIA.

inclined somewhat to the rear. The first pair of processes is only a short distance
above the centrum ; through the mid-dorsal region the first pair rise at this level, but
in the posterior dorsal and lumbar regions they rise from farther and farther up on
the spine.

The ninth vertebra : The centrum is elongate with nearly round articular faces
and wide notochordal funnel. The anterior face does not have a wide intercentral
face below, but on the middle of each side the edge is widened by a sharp angulation,
marking the point where the rib-head passes between the centra to articulate with the
intercentrum. The sides of the centra are pinched in somewhat below the noto-
chordal canal, constricting the lower portion into a broad obtuse ridge, which, how-
ever, in no wise resembles the sharp, thin keel of the cervicals and anterior dorsals of
Dimetrodon. The neurocentral suture is closed, but still clearly visible. The trans-
verse process rises far up on the neural arch, almost directly below the anterior zyga-
pophysis. The anterior zygapophyses have nearly horizontal faces, but they look a
little in as well as up. The posterior zygapoph)ses rise from high up on the spine,
well above the line of the anterior zygapophyses. This is a very distinctive character
through the whole column. The spine shows the same characters as that of the
seventh vertebra ; there are four pairs of processes and then four on one side and three
on the other. The lower pair stood straight out from the spine, but are broken away.
The apex of the spine is clavate and bent to the rear, but it is not so wide as on the
seventh.

The tenth vertebra {first dorsal) has the same form as the eighth. The centrum
is broken and the posterior end lost. The transverse process springs from the base of
the anterior zygapophj^sis as much as from the neural arch ; a strong supporting pro-
cess extends from the base down toward the centrum. This origin of the transverse
process seems to be peculiar to the genus ; it occurs in none of the ClepsydropincB
or the Thcropleuridcc. The spine is as in the seventh and eighth vertebrae ; the pro-
cesses of the first pair are opposite, the others alternate ; there are eight on each side.
The apex of the spine is still clavate, but ver}- much narrower than in the preceding
vertebra ; the top is marked bj' a shallow but well-defined circular pit.

The eleventJi resembles the preceding one very closely. The anterior face of the
centrum is broken, but the edge of the posterior face shows the expansion of the edge
of the side marking the position of the capitulum of the rib. The transverse process
is located well up on the base of the anterior zygapophysis with a strong supporting
ridge below reaching well down onto the centrum. The first pair of processes is per-
fectly preser\-ed ; they stand out almost straight from the side of the spine and the
ends are expanded into rugose knobs. The apex of the spine is thin, but hardly
expanded antero-posteriorly ; the processes above the first pair are much shorter, but
are not reduced in size as they go up the spine, so that one process near the top is
longer and stronger than any below except the first pair.

The tivelfth has the centrum broken, but the transverse process of the left side is
perfectly preser\'ed. This stands so far forward and is so thoroughly incorporated with
the anterior zygapophysis that it is impossible to say whether the transverse process
stands out from the anterior zygapophysis or the anterior zygapophysis from the trans-
verse process. The supporting ridge below runs down to the centrum, but does not
fuse with it, being separated from it by a sharp notch at the lower end. The trans-
verse process runs straight out or even slants a little forward, so that it lies almost

MORPHOLOGICAL REVISION OF THE SUBORDER. 1 49

entirely anterior to the spine. The first pair of processes stands out straight from the
spine. The one on the left side has two small processes given off from its base ; above
there are ten processes on each side. The apex of the spine is sharp and nearly cir-
cular ; the top is marked by a shallow pit.

The thirteenth has a complete centrum and more than one-half of the spine. The
centrum is elongate and the articular ends are round ; the edges are not reverted
except at the angulation on the middle of the edge where the capitulum of the rib
enters. The sides of the centrum are contracted below the notochordal canal by an
elongate depression which does not reach the ends ; this contracts the bottom line
into a blunt keel with a longitudinal depression on the mid-line. The transverse pro-
cess is very strong with a wide articular face for the tuberculum of the rib. The
whole process is inclined forward so that nearly the whole of the process is anterior to
the centrum. The spine is notably bent to the rear.

T\i& fourteenth anAJifteenth are very similar to the thirteenth.

The sixteenth has the depression on the side of the centrum below the noto-
chordal canal smaller and more shallow, so that the keel is less apparent, but there is
still a longitudinal depression on the mid-line. An attached iutercentruin is small
and slender without anterior articular faces or expanded ends ; evidently the capitulum
of the rib found its main articulation against the edges of the adjacent centra. The
spine is bent well back and somewhat curved, the apex is slender with a shallow pit.
This is the last perfect spine.

The seventeenth is similar to the sixteenth ; the spine is as long as the complete
spine of the eleventh. The faces for the capitulum on the centrum are very strong.

The eighteenth and nineteenth are similar to the sixteenth. On the last the
transverse processes are no longer inclined forward, but stand out straight from the
side of the neural arch.

The tzventieth has the spine very sharply bent backward. A small intercentrum
lies between the nineteenth and twentieth.

In the tiventy-first the inferior supporting process of the transverse process is
very weak.

The twenty-second is represented by a fragmentary' spine and neural arch.

On the twenty-third (first lumbar ?) the expansion of the sides of the centra for
the capitulum of the ribs is no longer present.

On the tioenty-fourth the transverse process is very short and a face suddenly
appears on the anterior edge of the centrum for the capitulum of the rib.

The tu'enty-Jifth is similar to the twenty-third, the spine is bent back in a half
circle overlying the sacrals and caudals. The imperfect spine measures 478 mm.

The tzventy-sixth has a very short spine not more than 10 mm. long; if this spine
or the spines of the succeeding vertebrae were longer they would come in contact with
the overhanging spine of the twenty-fourth.

T\xtjirst sacral has a short spiue with a strong rib and carries a wide distal face
for the ilium. The rib rises from the neural arch alone, instead of from the centrum,
in part.

The ribs: There are several nearly complete ribs preserved; one from the
cervical region is distinctly two-headed, the tuberculum and capitulum being widely
separated. In the dorsals the rib has a distinct head and then rises sharply so that
the shaft rests against the end of the transverse process and the tuberculum is repre-

I50

REVISION OF THE PELYCOSAURIA.

sented by a mere tuberosity on the edge of the rib ; the rib then curves sharply down-
ward again. The distal ends of the ribs are slightly expanded and round in section.
In the lumbar region the capitulum suddenly leaps to the edge of the centrum and
the tubercular tuberosity becomes a face in the same plane as the capitulum. The
two are closely united with the centrum and soon fuse together. The ribs were short
and slender and stood out nearly straight from the sides of the vertebrae.

Fig. 65*.— Anterior surface of the clavicle of the left side of N. microdus. </, articular face for the cleithium.
Fig. 65c.— Scapula and imperfect coracoid of the left side of N. microdus. co, coracoid; scp, scapula. X Yi-
Fig. 65</.— Itmer view of the left side of the left half of the pelvis, ilium, and pubis of N. microdus. il, ilium;
fu, pubis. X Yi-

The clavicle has a rounded anterior end marked by deep, radiating rugosities.
The posterior end is narrowed and carries strong rugosities marking the attachment
of the cleithrum. At the middle the bone is bent at an angle of 45° and then tapers
to a point. It differs from the clavicle of Dimetrodon in the corrugation of the
anterior edge and the sharp bend ; in Dimetrodon it is nearly straight.

The fore limb is known by the humerus only, No. 4037 Am. Mus. It has the
general form of Dimetrodon incisivus. The articular face is oblique, but on the outer
edge of the proximal end is a second small face, probably marking the attachment of
a ligament. The bone is heavier than in Dimetrodon incisivus and the edges of the
articular face are marked with rugosities. Just opposite the inner edge on the posterior
face is a prominent nodular rugosity. The radial crest is strong and prominent, but
beo-ins rather low on the proximal end. The distal end is similar to that of Dime-
trodon incisivus, but is stronger and roughened by rugosities around the articular faces.
On the lower corner of the entepicondyle is a distinct face surrounded by prominent
rugosities for the attachment of a ligament.

There is a single enonnous ungual phalange with this specimen, three or four
times as large as any occurring with the genus Dimetrodon, even D. gigas, indicating
enormously powerful claws on the feet.

MORPHOLOGICAL REVISION OF THE SUBORDER. 151

The pelvis is represented by both ilia, parts of the pubes and a fragment of the
ischium.

The iliitm has the same form as that q{ N. claviger ; the upper end is flared and
marked by radiating rugose ridges at the extremity. The pubis and ischium are so
incompletely preserved that they can not be perfectly characterized, but in general
they have the same form as N. claviger.

The Iiind li»ib is unknown.

Aleasurements.

No. 4060 American Museum. mm. mm.

Seventh cervical : Length, spine of 15th vertebra 812

Heightof spine above posterior zygapophyses 412 Length, bottom hne o: ■

Antero-posterior diameter of spine : ^^'J' vertebra 43

At first processes 18 17th vertebra 43

Atapex 38 iSthvertebra 45

-■■"hth vertebra : 19 h vertebra 39

T ^u c . 20th vertebra 40

Length of centrum 34 21st vertebra lo

Height of spine from bottom of centrum ...';20 a »u

I, ,,„>aKro Tfi^-ct ^^.-cU- vertebra 34

23d vertebra 29

Ninth vertebra (first dorsal):

Length of spine from bottom of centrum. . . 57S 24th vertebra 2^

Eleventh vertebra (dorsal): Vertical diameter of ilium. !....'..!!.".'.!!!."." .'.' 140

Length of spine from bottom of centrum. . . 707 Total length of clavicle 158

Length, bottom line of centrum of— Total length of scapula (exclusive of coracoid). . 165

13th %'ertebra 39 No. 4037 American Museum.

15th vertebra 40 Length of humerus 217

EDAPHOSAURIDAE Cope.
Edaphosaurus pogonlas Cope (plate 34).

Characteristic specimen. No. 4009 Am. Mus. The tA'pe.

This specimen is unique, nothing identifiable with it occurring in either the
New York or the Chicago collections. The depressed form of the skull and the sug-
gestion of the axis that the vertebrae were low and broad indicates affinities with the
Cotylosaiiria, but the temporal region with its enormous superior temporal vacuity
and almost certain inferior vacuity indicates affinities with the Pelycosanria. As the
condition of the temporal arches is of more fundamental importance than that of the
shape of the skull and the vertebrse the animal is referred tentatively to the Pelycosauria
in the family Edaphosaitridcv. Its habits of life must have been ver>' similar to those
of Placodiis^i and if future discoveries should show that it really possessed a single
temporal vacuity, or that the inferior vacuity was decadent, the kinship of Edapho-
smirns with Placodiis as an ancestral form would be strongly suggested.

The skull is roundly triangular and flattened above ; the temporal region is ele-
vated and the upper surface descends in an almost straight line to the anterior end.
The external nares are small and nearly terminal, but open laterally. The orbits are
of moderate size and look nearly straight outwards. The dentition is verj' peculiar,
varying from chisel-shaped incisors to thin, triangular cutting teeth in the anterior
portion of the maxillary and conical teeth in its posterior portion.

The pre»iaxillary is short and relatively broad, but with a long posterior prolon-
gation in the median line which extends back to join the nasals. There are four

152

REVISION OF THE PELYCOSAURIA.

teeth in each premaxillary which are badly worn, but were apparently furnished with
a strong terminal cutting edge, something like that of the modern rodents or the
ancient Placodus. The teeth projected slightly forward from the edge of the jaw.
The posterior edge of the bone forms the anterior edge of the nares.

The viaxillary is a broad plate extending upward somewhat obliquely and unit-
ing with the nasals above and the premaxillary anteriorly. The anterior edge forms
the posterior edge of the nares and the posterior end lies below the middle of the eye-
socket. There are fourteen teeth in the bone ; the anterior five are thin triangular
plates that had originally well-developed anterior and posterior cutting edges, but

these have been largely destroyed by decay.
The posterior nine teeth are conical. All
the teeth are in sockets and rest against
the outer edge of the bone which descends
lower than the inner.

The nasals are broad, flat plates, em-
bracing the premaxillaries anteriorly and
extending between thefrontals posteriorly.
T\\Q froiitals are very broad and flat ;
they meet the parietals posteriorly in a
wide suture and form the major portion
of the upper edge of the orbit.

The prefrontals form the upper an-
terior corner of the orbit.

The lachrymals are short bones,
rounded anteriorly and extending back
on the floor of the orbit to the anterior
third of the lower edge.

The parietals are flat anteriorly with

a good-sized parietal foramen, but the

posterior portion is somewhat convex.

The bones of the two sides meet in a

,auru.poson,a, ^jj , ^ dcpressiou, SO that the crown of

Fig. 67. — Diagram of the lower surtace ol the same, both ° , ,, . . ,

the skull IS arched antero-postenorly and
depressed in the mid-line. The outer
edge is concave and forms the upper
^"' border of the superior temporal vacuity.
From the posterior outer corner a process

Fig. 66. — Diagram of the upper surface of the skull of Edapho
sauTUS pogonias.

xyi.

pmx. premaxillary; mx. maxillary; na. nasal;
/. lachrymal; pr.f. prefrontal; //■. frontal; fo.f.
postfrontal; fo.o. postorbital; ju.
parietal ; sq. squamosal ; qj? quadrato-jugal ;

q. quadrate; /s</ .' prosquamosal ; pi. palatine; i i i

ft. pterygoid;/;., prevomers ; Ss. basisphenoid ; CUrVCS gently OUtward and downward tO
bo. basioccipital ; sip. stapes; f.oc. paroccipital ; UuitC with the SquamOSal.
cvo. exoccipital ; ?i*. interparietal ; c/o. epiolic. TllC interparietal: BetWCCU the

parietals posteriorly is a small diamond-shaped bone which extends downwards beyond
the parietals and separates the pair of bones below.

The postfrontal is represented by a fragment of bone between the frontal and
parietal whose posterior edge forms the anterior edge of the superior temporal vacuity :
the lower edge is missing.

The postorbital and jugal are not distinct.

The quadrate resemljles that of the other Pelycosauria ; the upper portion is thin
and plate-like and the lower end carries two large condyles, the outer somewhat more

MORPHOLOGICAL REVISION OF THE SUBORDER. 1 53

posterior than the inner. The long axis of the condyles is inclined somewhat inward.
The outer condyle is extended backward, as in Diiiietrodon, forming a sort of shelf on
which rests the lower end of the quadrato-jngal.

The qtiadrato-jiigal and prosquamosal occupy the same relative positions as in
Diutetrodon. The first rests against the posterior edge of the quadrate and o\'erlies
the posterior edge of the prosquamosal. There are indications that a quadrate foramen
was present, but it is closed in the specimen, perhaps by pressure. Superiorly, the
quadrato-jugal passes below the lower ends of the squamosal and a second bone, the
epiotic (?). The anterior end of the prosquamosal is broken away, but it reaches up
as far as the upper edge of the quadrate, touching the lower end of the squamosal.

The squamosal is a thin and slender element convex in curvature, which joins
the parietal above and the quadrato-jugal and the prosquamosal below. At its lower
end a wide process started forward toward the postorbital, but this is broken so that
its anterior connections can not be made out. The process evidently is a portion of a
bridge across the temporal vacuity ; Cope considered that there was but one such
bridge and that the animal had a single temporal arch, but the condition of the speci-
men makes probable the possibility of the presence of a second arch below.

"XT^^T^^^^^T^vTW

68 69

Fig. 68. — Diagram of the lateral surface of the skull of Edaphosaurus pogonias.
Fig. 69. — Diagram of (he posterior surface of the same.
Lettering as in figs. 66 and 67.

Epiotic {?) : Below the parietal and interparietal and above the posterior wall of
the cranial cavity is a pair of slender bones that curve outward and downward ; lying
next to the lower edge of the squamosal they extend outward and downward until
they touch the upper ends of the quadrato-jugal. These bones are in the exact posi-
tion of the epiotics, and there is little doubt that they are homologous with the same
bones in the Cotylosauria and Stegocephalia. Thej^ do not occur in the other families
of the suborder.

The posterior surface of the cranium is formed by a single mass of bone, the
sutures between the basioccipital, supraoccipital, exoccipitals^ and the paroccipitals are
not distinguishable. The plate is partly obscured in the specimen by the cnishing
which has forced the parietals with the interparietal and the epiotics down over it as
far as the foramen magnum. The paroccipital processes extend outward nearly to the
quadrate. The occipital condyle is relatively broad and oval in outline with no pit
marking the position of the anterior end of the notochord.

The basispheiioid has the same form as in Dinteirodoii, but is relatively longer.
There is a strong parasphenoid process, well-developed articular faces for the ptery-
goids and a large pit on the lower surface.

154

REVISION OF THE PELYCOSAURIA.

The stapes: On either side of the basisphenoid is a short, wide bone, which
occupies the position of a stapes. The inner end is smaller, but terminates in a flat
surface ; just below the extremity the bone is pierced by a foramen.

The palate is well preserved on one side. There is a great median vacuity fonn-
ing the posterior nares, but there are no palatal vacuities. The sutures between
the pterygoids, palatines and prevomers can not be made out.

The prevomers are thin plates
connecting anteriorly and laterally
with the premaxillaries and anter-
iorly with each other; more pos-
teriorly they are cut out on the
median line, so that when the two
were in position there was an elon-
gate heart-shaped vacuity in the
Fig. 70.— Diagram of the upper surface of the lower jaw of £(/apAo- median line. At the anterior end,
saums pogonias. whcre the two bones meet, there are

four conical teeth on each bone; the posterior is the larger.

The pterygoids articulate with the basisphenoid in the mid-line and send a strong
process backward, which articulates with the inner side of the lower end of the quad-
rate. There is no descending external process forming a buttress for the lower jaw,
as in the other Pelycosauria. The line of union with the palatine can not be made out.
Covering a large portion of the pterygoid and the palatine is an oval plate studded
thickly with stumpy conical teeth irregulary arranged. On the inner edge there are
some teeth of smaller size. Most of the teeth are injured by decay, but it can be seen
that the ends were very blunt, resembling the pharyngeal teeth of Labriis. The plate
bearing the teeth is very heavy and extends backwards, underlying the anterior half
of the temporal region.

The lower jaxv of the left side is nearly perfectly pre-
served. The sutures between the separate bones can not
be made out. The anterior symphysis is very strong and
was formed by the splenial as well as the dentary. There
are twenty counted teeth and alveoli and there were per-
haps three or four more at the posterior end. The anterior
teeth are similar to the premaxillary teeth above, but there
are none corresponding to the triangular teeth of the an-
terior portion of the maxillary — all are conical, growing
smaller towards the posterior end. The alveolar edge is
somewhat elevated. In the posterior half of the jaw is a
dentigerous plate corresponding in size and shape to the
pterygoid plate above and studded with the same kind of
teeth. It is probably supported largely by the dentary, but
the splenial may also take part. The articular region has
two cotyli corresponding to the condyles of the quadrate above. There are no open-
ings on the outer side of the jaw aud none can be made out on the inner side.

The axis has a short centrum with elongate pits on either side as in Naosaiirits.
The transverse processes rise from the neural arch and the upper edge of the centrum;

-Axis of Edaphosaums
pogonias.

MORPHOLOGICAL REVISION OF THE SUBORDER.

155

the posterior edge is continued as a long ridge on the side of the centrum to the
posterior edge. The anterior face is elongate vertically, but it has been cnished so

that the form is ob-
scured. The spine is
low, but it was very
heavy, curving forward

Fig. 72. — Diagram of ihe palatal surface of Placodus.

After V. Huene.
Fig 73. — Diagram of the posterior surface of the skull of

Placodus. After v. Huene.

Lettering as in figs. 66 and 67.

Placodus.

Skull low and broad.

A single temporal vacuity.

Incisor teeth chisel-shaped; projecting forward from

the skull.
Maxillary teeth fiat and adapted to crushing or

grinding.
Posterior nares a single opening formed by the pre-

vomers and premaxillaries.
Palatine teeth few and large.
Teeth of the lower jaw reduced to the incisors and

crushing teeth.
Pterygoid without external process.
Interparietal and epiotic present.
Occurring in the Triassic.

over the anterior face;

the posterior zygapo-

physes are large, but

the anterior ones are

small. The posterior edge of the spine is

very wide, extending out over the sides of

the centrum. For measurements see the

original description, page 69.

Position and relatiotiships : It is most
unfortunate that the vertebras and limb of
this fonn are not known. The evidence of
the skull shows that it has little in com-
mon with the rest of the Pelycosauria. The
probable similarity of habits to Placodus has
been pointed out above, and a comparison
of the skulls shows many points of resem-
blance. These are best shown in a com-
parative table.

Edaphosaurus.

Skull low and broad.

Probably two temporal vacuities.

The same.

Maxillary teeth thin and sectorial.

Posterior nares a single opening formed by the pre-

vomers.
Palatine teeth numerous and smaller.
Lower jaw with teeth on the border as well as the

crushing teeth.
Pterygoid without external process.
Interparietal and epiotic present.
Occurring in the Permian.

There is not sufficient evidence to warrant any conclusion that there
is an actual relationsiiip between Edaphosaurus and Placodus., but the simi-
larity of the two is certainly very suggestive. If Placodus is a true Synap-
sidan form, related to the Anomodonts, as held by many authors, it could
have no connection, genetically, with. Edaphosaurus, but it must have passed
in any case through a similar stage of evolution in the growth of the pala-
tine and dentary crushing teeth and the loss of the teeth on the edges of the

1^6 REVISION OF THE PELYCOSAURIA.

maxillary and the deutary. Two things are wortliy of note in the study of
the relations of the two. i. It is not proven that Edapliosaiirus had two
temporal vacuities, though I believe it to have been the case. 2. The new
genus of v. Huene, Anoniosatinis^ which he believes to be a Pelycosaurian,
and which is certainlj'^ very closely related to the suborder, comes from not
only the same horizon, but even from the same locality as Placodus (103),
and some of the described vertebras at least may belong to it. Should this
turn out to be true it may be that future discoveries mil also show that
Edaphosaurus occupies an ancestral position to the Placodontia.

POSITION AND RELATIONS OF THE PELYCOSAURIA.

The Pelycosmiria constitutes a highly specialized and short-lived branch
from the beginning of the Rhynchocephalian stem. Its history is a most
striking example of rapid evolution to extreme specialization from very
primitive and generalized conditions — illustrating the fact that high special-
ization of individual parts may arise as modifications of structures that are
in general on a very low plane of development as well as of structures that
have reached a very high plane of development. Extreme specialization may
occur at the beginning of a phylum as well as in the more advanced stages.

The most primitive of the suborder, the Poliosanridcs^ are not far from
the Proferosaitria and Proganosaiiria; perhaps rather more primitive, because
of the persistent notochordal condition of the centra, but revealing no more
of the origin of the reptiles. The Pelycosanria in general differ from the
Proterosauria in the higher degree of ossification, especially of the pelvis
and pectoral girdles, and from the Proganosmtria in the lack of adaptation
to water life. The Therocephalia of South Africa approach the Pelycosaurs
in many particulars of structure, but the fundamental difference in the
temporal arches prevents any assumption of genetic relationship.

The most striking feature of the group is, of course, the enormous
neural spines, but the specialization of the group is shown in other points
not to be overlooked. The form of the alveolar edge of the upper and lower
jaws ; the secondary closing of the superior temporal vacuity ; the method
of rib attachment ; the enormous claws ; these are departures from the normal
fully as great as the condition of the neural spines. The use of the spines is
the first consideration presented in the study of the animals and it seems
impossible to assign to them any utilitarian value. The animals were
fiercel}' caraivorous, developing enormous tusks, perhaps in correlation with
the developing armor of the Amphibia^ Cotylosauria^ and Chelydosauria
which formed their prey. Easily masters of their world, they may have
developed the spines as a mere exuberance of growth from some possible
utilitarian beginning, but finally they served no more useful purpose than
the plates of Stegosaunis or the spines of the modern PInynosoma or Basi-
liscus. It is perhaps an illustration of Beecher's law that the development
of spines and excrescences accompanies the approaching extinction of a
group.

There is no doubt that the Pelycosauria existed beyond the limits of
North America, as evidenced by the Naosaurus of the Permian of Bohemia.
The forms described by v. Huene are not true Pelycosaurs, but it is very
possible that they are forms derived from the beginning of the Pelycosaurian

158

REVISION OF THE PELYCOSAURIA.

Stem, whicli persisted into tlie Triassic of Europe when they died out at the
end of the Permian in North America. Moreover it must be remembered
that the Triassic of North America is yet far from completely explored and
specimens similar to those of the Muschelkalk maj^ yet turn up on this
continent.

The ideas expressed as to the relationship of the Pelycosauria may be
pictured by the following diagram :

VNCHOcaeHALIA

PROGANOSAURI/

PROTEROSAUR

AN0M0SAURU9(?)

CTENOSAURUS

NAOSAURUS

PRIMITIVE RHYNCHOCEPHALIA

The sudden change in the direction of the line beyond Clepsydrops
indicates the beginning of the extreme specialization.

With the fuller knowledge of the anatomy of the Pelycosauria it seems
hardly necessary to mention the unfortunate generalization of Cope in which
he placed the Pelycosauria in an ancestral relationship to the mammals.
This idea gained little credence, but the name Theromora, suggested by it,
has had an unfortunate and confusing effect upon the sj^stems of classification.

Jaekel has recently (136) made the suggestion that the spines on the
back of the ClepsydropidcB\i^x& free from the skin, and that when the animal
detected danger it threw the body into curves, causing the spines to stand out
in different directions and present a spiny front to all comers. This seems
but one more fanciful suggestion for the use of the spines. There is no
necessity for the assumption that the spines were free from the body, and,
as shown in the text above, p. 147, they were in all probability covered by a
thin but tough layer of skin. The ligament that bound the spines together
would be elastic and would not interfere with the bending of the body in a
vertical plane ; the vertebrae do not have zygosphene and zj^gantrum as
stated by Jaekel, and there was very little possibility of lateral movement,
certainly none of a partial rotation of the vertebrae on the notochordal axis,
as would be necessary if the spines were to point outward as indicated in
Jaekel's sketch. Moreover, the spinal column of the animal was short and
it could not be thrown into sinuous curves as supposed by Jaekel.

GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION.

In North America Pelycosaurian remains have been found in north
central Texas, Baylor, Archer, Wilbarger, and Vernon counties, and the
adjacent portions of the Indian Territory^ ; New Mexico; northeastern
Oklahoma ; Cowley county, Kansas ; Vermilion county, Illinois, and the
vicinity of New London, Prince Edward Island, in Canada. The remains
of Pelycosaurs always occur mingled with remains of an abundant fauna
composed of fishes, amphibians, and other orders of reptiles. The faunas
of the different regions show slight but well-marked differences which
indicate that there was some difference of distribution in the Permian
animals of the continent.

Beyond the limits of North America Pelycosaurs occur in Bohemia,
Naosmirus^ and less certainly in central Germany, Ctenosaurtis and Anomo-
saiinis; and in France, Callibrachion and Stereorachis. Pelycosanria do
not occur in Africa, and it is improbable that they occur in the Russian
deposits.

There is no locality in which Pelycosaurs occur with Theriodonts,
Therocephalians, or Anomodonts. The Theriodontia and Therocephalia are
found only in Africa and Russia ; the Pelycosanria only in North America
and Central Europe.

Cotylosaurians occur in North America, Russia, and South Africa, but
the families are different. The Panotic/iidcs are not represented outside of
North America and the Cotylosaurians are represented on this continent, if
at all, by a single genus and species, Labidosaurus hatnattis Cope; this
animal resembles in general form the Pariotichida; and may well turn out
to be closer to that family than to the Pareiasaiwido'.

Stegocephalians of closely related form occur in North America, South
Africa, Russia, and India. Their wider distribution is explainable on the
basis of their greater antiquity, and the same reason perhaps applies to the
wide extension of the Cotylosauria.

The character of the distribution is certainly suggestive of a possible
separation of a North American-European land-mass from an African-Asiatic
land-mass in the time when the Stegocephalians were predominant and the
Cotylosauria were just beginning their great radiation. By the time the
specialized Pelycosanria^ Theriodontia^ and Therocephalia began their develop-
ment the masses were so far distinct that the groups did not mingle. This
is further supported by the development in the North American mass of the

'59

l6o REVISION OF THE PELYCOSAURIA.

specialized Chelydosauria direct from the Cotylosaurm, an order wliicli has
not been recognized in Europe, and the specialized family Edaphosauridcs
with its suggestion of ancestral relations to the Placodontia.

After the Permian time, in early Triassic, Anomodonts appear in Africa,
India, and Scotland, and Williston reports their possible occurrence in the
Triassic of Wyoming (132). (Cope's Dtcynodon rosmarits from the Trias of
Pennsylvania is iuore probably a Dinosaur fragment.) Pareiasaiirida; are
mingled in the Triassic of Central Europe with Pelycosaurian remains,
Sclerosaiirns armatus with Ctenosaurus and Anomosajiriis. This evidence
is too feeble to be more than suggestive, but taken for what it is worth it
indicates the possible closer union of the two great masses in Triassic than
Permian time.

The geological range of the Pelycosauria in North America is seemingly
through the Permian and dying out before the Triassic, but our knowledge
of the age of the beds in which the remains occur is far from perfect. In
the southwest portion of the United States, where the bones occur in the
greatest abundance, they are found in the so-called "Red Beds," which have
been the cause of much controversy relative to their exact position. It is
not within the scope of this work to discuss the age of the beds in which
the Pelycosauria occur, nor have the facts brought out in this study aided
greatly to clear np the matter ; that will be helped only when a more nearly
perfect list of the faunal constituents is known. Recent writei's, with the
single exception of Adams, assign to the Red Beds a position distinctly
above the Carboniferous.

The fossil beds in the vicinity of Danville, Vermilion county, Illinois,
occur in a very limited area surrounded by rocks of the upper Carboniferous.
It has been suggested, with considerable reason, that this deposit is the
remnant of an old river bar deposited during Permian time between walls of
Carboniferous rock.

The Red Beds of Texas are directly traceable into the Red Beds of the
Indian Territory to the north, and are identifiable with the deposits that
surround the Wichita Mountains and the Arbuckle Hills. These regions
have recently been studied by Taff (126), who calls the Red Beds of the
Arbuckle Hills "Permian (?)," and also calls them "Rocks of very late
Pennsylvanian or early Permian age," which have been deposited across
the western end of the Arbuckle uplift. "Thej- lie in a nearly flat position
across the eroded edges of several thousand feet of the Pennsylvanian, all
of the Mississippian, Devonian, Silurian, and a large part of the Ordovician
rocks. These older formations were sharply folded and eroded prior to the
deposition of the ' Red Beds.' " Concerning the region around the Wichita

GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION. l6l

Mountains, lie says the Red Beds surround the mountains, lying nearly
horizontal, but having local but variable dips away from the mountains,
which were the old Permian land areas.

Adams (1-3) obser\'ed in the northwestern part of the Indian Territory
and in Eastern Oklahoma that the red color transgressed the strata diagon-
ally from the Pennsylvanian into the Permian. He saw no indication of
unconformability between the Pennsylvanian and the Permian, or between
other stratigraphic horizons. According to Taff: "If there is no uncon-
formity at the base of the 'Red Beds' north of the Canadian River, and if
Dr. Adams' observations concerning the color of the strata are correct, the
stratigraphic unconformity of the 'Red Beds' across the Arbuckle uplift is
local, though the uplift was profound and the erosion great from the begin-
ning of the uplift through a large part of the 'Red Beds' time."

The Red Beds of northeastern Oklahoma are considered as definitely
Permian by Gould (95); the determination rests upon the evidence of
invertebrates as well as on the vertebrates, which are very similar to those
of the Illinois region.

The bones from Cowley county, Kansas, are few in number and were
found below the surface in sinking a well. From the evidence of related
invertebrates these fossils were referred by Adams to the Garrison formation
which he places (3) just above the Cottonwood limestone. It includes in
its lower portion the Cottonwood shales as defined by Prosser, and regarded
by him as the uppermost series of the Upper Coal-measures, and in its
upper portion the Neosho formation, which Prosser regards as the lowermost
of the Permian. Haworth also places the Cottonwood limestone, on strati-
graphic evidence, at the top of the Upper Coal-measures.

The rocks of Prince Edward Island and the adjacent portion of the
mainland of Nova Scotia have been regarded by the Canadian geologists,
without exception, as Permian. The discover^' oi BathygnatJnis boreal is and
its reference to a Dinosaur of Triassic age by Cope and Leidy compelled
the assumption of a small region of Triassic deposits, but the determination
of its true position shows that the whole region is Permian.

No trace of the Pelycosauria has been found in North America above the
Permian ; they seemingly became extinct at the end of that time, but it is
not beyond the bounds of possibility that remains may be found in the
Triassic similar to the Cienosaunis and Anomosanrus from the Triassic of
Europe.

BIBLIOGRAPHY.

The following list of papers includes only those that refer to the Pely-
cosauria as defined in the preceding pages ; only those which contain some
additional or important matter are admitted; those in which the name is
merely mentioned have been excluded. Broili in his large paper on the
Texas fauna, No. 14 below, has given a very admirable and nearly perfect
list of all the important papers on Permian Reptiles. Hay in his Bibliog-
raphy of the Fossil Vertebrata of North America (100) has given a nearly
perfect chronological list of the papers containing descriptions or mention
of the Pelycosmiria up to the time of publication, 1900 ; minor papers of later
date are included in the list below :

1. Adams, G. I. The Carboniferous and Permian age of the Red Beds of eastern Oklahoma from strati-

graphic evidence. Am. Jnl. Sc, 4th, vol. 12, 1901, pp. 383-386.

2. . Stratigraphic relations of the Red Beds to the Carboniferous and Permian in northern Texas.

Bull. Geol. Soc. Am., vol. 14, 1903, pp. 191-200. Also abst. Science, new series, vol. 16, 1902,
p. 1029.

3. , GiRTY, G. H., and White, D. H. Stratigraphy and paleontology of the Upper Carboniferous rocks

of the Kansas section. Bull. No. 211, U. S. Geol. Survey, 1903, p. 72.

4. Baur, G. Zur Morphologic des Carpus u. Tarsus der Reptilien. Zoolog. Anzeig., vol. viii, 1885, pp.

631-638.

5. . Ueber die Kanale im Humerus der Amnioten. Morph. Jahrb.. vol. xii, 1S86, pp. 299-305.

6. . Ueber die Abstammung der Amnioten Wirbelthiere. Biolog. Centralb., vol. vii, 1887, pp. 481-

493. Also Sitzb. der Gesell. f. Morph. u. Physiol. Munchen, 18S7. pp. 44-61.

7. . On the phylogenetic arrangement of the Sauropsida. Jnl. Morph., vol. i, 1887, pp. 93-104.

8. . Archegosaurus. Am. Nat., vol. xxxi, 1897, pp. 975-980.

g. and Case, E. C. On the morphology of the skull of the Pelycosauria and the origin of the mammals.

Preliminary Communication. Anat. Anzeig., Bd. 13, Nos. 4-5, 1897, pp. iog-120. Also Science,
N. s., vol. 5, No. 119, 1897, pp. 592-594.

10. . The history of the Pelycosauria, with a description of the genus Dimetrodon Cope.

Trans. Am. Phil. Soc, n. s., vol. xx, 1899, pp. 1-58.

11. Bede, J. W. The age of the Kansas-Oklahoma Red Beds. Am. Geol., 1901, pp. 46-47.

12. Bernard, Felix. Elements de Paleontologie. Paris, 1895.

13. Broili, Ferd. Pelj'Cosaurierreste von Texas. Zeitsch. deutsch. geolog. Gesell., Bd. 56, Hft. 3, 1904,

pp. 268-274.

14. . Permische Stegocephalen und Reptilien aus Texas. Paleontographica, Bd. li, 1904, pp. 1-120.

15. . Stammreptilien. Anat. Anzeig., Bd. xxv. No. 23, 1904, pp. 577-587.

16. BouLENGER, G. A. On the characters and affinities of the Triassic reptile Telerpeton elginense. Proc.

Zool. Soc. London, vol. i, 1904, pp. 470-481.

17. BouLE, M., and Glangeaud, P. Le Callibrachion gaudryi, nouveau reptile fossile du Permien d'Autun.

Bull. Soc. d'Hist. Nat. d'Autun, t. 16, 1893, pp. 1-17.

18. Broom, R. On the classification of the Theriodonts and their allies. Rept. S. Af. Assn. Ad. Sc, 1903.
ig. . On She structure of the palate in Dicynodon and its allies. Trans. South African Philos.

Soc, vol. II, igoi, pp. 169-176.

20. . On the mammalian and reptilian vomerine bones. Proc. Linn. Soc. N. S. Wales, vol. 27,

1903, pp. 545-560.

21. . Descriptions of the paleontological material collected by the members of the Geological Survey of

Cape Colony. On a new reptile ( Proterosuchus fergusi ) from the Karroo Beds of Tarkastad,
South Africa. Ann. South Afric. Mus., vol. 4, 1903, pp. 159-163.

22. Case, E. C. On the foramina perforating the cranial region of a Permian reptile (Dimetrodon) and on

a cast of its brain cavity. Am. Jnl. Sc, 4th, vol. 16, No. 3, 1897, pp. 321-326. Also abst. Science,
N. s., vol. 5, No. 119, 1897, p. 594.

162

BIBLIOGRAPHY. 1 63

23. Case, E. C. The significance of certain changes in the temporal region of the primitive Reptilia.

Am. Nat., vol. 32, i8g8, pp. 69-74.

24. . The vertebrates from the Permian bone bed of Vermilion county, Illinois. Jnl. Geol., vol. viii,

igoo, pp. 698-729.

25. . Paleontological notes. Jnl. Geol., vol. x. No. 3, 1902, pp. 256-261.

26. . On some vertebrate fossils from the Permian Beds of Oklahoma. Second Ann. Rpt. Dept. Geol.

and Nat. Hist. Terr. Oklahoma, 1902-3, pp. 62-68.

27. . New or little known Vertebrates from the Permian of Texas. Jnl. Geol., vol. xi, No. 4, 1903, pp.

394-403.

28. . The osteology of Embolophorus doUovianus Cope, with an attempted restoration. Jnl. Geol.,

vol. XVI, No. I, 1903, pp. 1-28.

29. . The structure and relationships of the American Pelycosauria. Am. Nat., vol. 37, 1903, pp.

85-102.

30. . A remarkably preserved specimen of a Pelycosaur collected during the last summer in Texas.

Science, n. s. , vol. ig, 1904, p. 253.

31. . The osteology of the skull of the Pelycosaurian genus Dimetrodon. Jnl. Geol., vol. xii. No. 4,

1904, pp. 304-311.

32. . On the structure of the fore-foot of Dimetrodon. Jnl. Geol., vol. xii. No. 4, 1904, pp. 312-315.

33. . The morphology of the skull of the Pelycosaurian genus Dimetrodon. Trans. Am. Phil. Soc,

N. s., vol. XXI, pt. I, 1905, pp. 6-29.

34. . Bathygnathus borealis Leidy, and the Permian of Prince Edward Island. Science, N. s., vol.

XXII, 1905, p. 52.

35. . On the skull of Edaphosaurus pogonias Cope. Bull. Am. Mus. Nat. Hist., vol. xxii, art. 11, pp. 19-26.

36. Cope, E. D. On the fossil remains of Reptilia and fishes from Illinois. Proc. Phil. Acad. Nat. Sc, 1875,

pp. 404-411. Reprinted in Ann. Mag. Nat. Hist., 4th, vol. xvii, 1875, pp. 178-1S4.

37. - — ■■ On the vertebrate bone bed in eastern Illinois. Proc. Am. Phil. Soc, vol. xvii, 1877, PP- 52-63.

38. . Descriptions of extinct Vertebrata from the Permian and Triassic formations of the United States.

Proc. Am. Phil. Soc, vol. xvii, 1877, pp. 182-193. Also Pal. Bull. 26.

39. . Recent paleontological discoveries. Am. Nat., 1877, p. 757.

40. . The Theromorphous Reptilia. Am. Nat., 1878, pp. 829-830.

41. . A new fauna. Am. Nat., 1S78, pp. 327-328.

42. . Clepsydrops in Texas. Am. Nat., 1878, p. 57.

43. . Prof. Marsh on Permian reptiles. Am. Nat., 1878, pp. 406-407.

44. . Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proc.

Am. Phil. Soc, vol. xvii, 1878, pp. 505-530. Also Pal. Bull. 29.

45. . The homology of the chevron bones. Am. Nat., 1878, p. 3ig.

46. . Gaudry on Permian Vertebrata. Am. Nat., 1879, p. 333.

47. . The relations of the horizons of extinct Vertebrata of Europe and America. Bull. U. S. Geol.

and Geog. Survey of the Terrs., vol. v, 1879, pp. 33-54. Published 1880.

48. . Second contribution to the history of the Vertebrata of the Permian formation of Texas. Proc.

Am. Phil. Soc, vol. xix, 1880, pp. 38-58. Also Pal. Bull. 32.

49. . The structure of the Permian Ganocephala. Am. Nat., 1880, pp. 383, 384.

50. . The skull of Empedocles. Am. Nat., 1880, p. 304.

51. . Catalogue of the Vertebrata of the Permian formation of the United States. Am. Nat., 1881,

pp. 162-164.

52. . The Permian formation of New Mexico. Am. Nat., 1881, pp. 1020, 1021.

53. . Art. II. On some new Batrachia and Reptilia from the Permian beds of Texas. Bull. U. S.

Geol. and Geog. Survey of the Terrs., vol. vi, 1881, pp. 79-82.

54. . Third contribution to the history of the Vertebrata of the Permian formation of Texas. Proc.

Am. Phil. Soc, vol. xx, 1882, pp. 447-461. Also Pal. Bull. 35.

55. . Permian Vertebrata. Am. Nat., 1882, p. 925.

56. . Fourth contribution to the history of the Vertebrata of the Permian formation of Texas. Proc.

Am. Phil. Soc, vol. xx, 1883, pp. 628-636. Also Pal. Bull. 36.

57. . Permian reptiles and fishes. Proc. Acad. Nat. Sc. Phila., 1883, p. 69.

58. . On the Saurians of the Permian epoch. Science, iv, 18S4, p. 340. Abst. of a paper before

the A. A. A. S., 1884.

59. . Note on the phylogeny of the Vertebrata. Am. Nat., 1884, pp. 1255-1257.

164 REVISION OF THE PELYCOSAURIA.

60. Cope, E. D. Fifth contribution to the knowledge of the Permian formation of Texas and the Indian

Territory. Proc. Am. Phil. Soc, vol. xxii, 1884, pp. 28-47.

61. . The structure of the columella auris in Clepsydrops leptocephalus. Am. Nat., vol. xvin, 1884,

p. 1253.

62. . On the structure of the brain and auditory apparatus of a Theromorphous reptile of the Per-
mian epoch. Proc. Am. Phil. Soc, vol. xxiii, 1885, pp. 234-238. Also Proc. A. A. A. S., 34th
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63. . The structure of the columella auris in the Pelycosauria. Mems. Nat. Acad. Sc, vol. iii, 1885,

PP- 93-95-

64. . On the evolution of the Vertebrata progressive and retrogressive. Am. Nat., 1885, pp. 140-148,

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65. . The genealogy of the Vertebrata as learned from paleontology. Trans. Vassar Bros. Inst., vol.

Ill, 1885, pp. 60-80. Same as the preceding.

66. . The relations between the Theromorphous reptiles and the monotreme Mammalia. Proc. A. A.

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67. . The long-spined Theromorpha of the Permian epoch. Am. Nat., vol. xx, 1886, pp. 544, 545.

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70. . Systematic catalogue of the species of Vertebrata found in the beds of the Permian epoch in

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72. . On the shoulder girdle and extremities of Eryops. Trans. Am. Phil. Soc, vol. xvi, 1888,

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73. . Pineal eye in the extinct vertebrates. Am. Nat., vol. xxii, 1888, pp. 914-917.

74. . Synopsis of the families of the Vertebrata. Am. Nat., vol. xxiii, 1889, pp. 849-877.

75. . The mechanical causes of the development of the hard parts of the Mammalia. Jnl. Morph.,

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76. . Review of the catalogue of fossil Reptilia and Batrachia (Amphibia) in the British Museum.

Pts. II, III, IV. Am. Nat., vol. xxv, 1891, pp. 644-646.

77. . Syllabus of lectures on geology and paleontology. Phila., 1891, pp. 1-90.

78. . The homologies of the cranial arches of the Reptilia. Am. Nat., vol. xxvi, 1892, pp. 407-408.

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80. . On the structure of the skull in the Plesiosaurian Reptilia and on two new species from the

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81. . Seeley on the fossil reptiles. 11. Pareiasaurus ; vi. The Anomodontia and their allies : Further

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114. . Reclassification of the Reptilia. Am. Nat., vol. xxxviii, 1904, pp. 93-115.

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117. Owen, Richard. Descriptive and illustrative catalogue of the fossil Reptilia of South Africa, in the

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1892, pp. 311-370.

123. . Same. Pt. ix. Sec. i. On the Therosuchia. Phil. Trans. Roy. Soc, vol. 185, 1895, p. 1007.

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No. I, 1897, pp. 53-56.

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pp. 120-122.

131. . The temporal arches of the Reptilia. Biol. Bull., vol. vii, 1904, pp. 175-192.

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1904, pp. 668-697.

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from the American System of Dentistry.

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Leipzig, 1887-1890. (See pages 554-572.)

135. . Grundziige der Paleontologie. 1S95.

136. . Text-book of Paleontology (Translated by Chas. Eastman). Vol. 11, 1902, p. 169.

137. Jaekel, O. Ueber die Bedeutung der Wirbelstacheln der Naosauriden. Sonderabdruck aus dem Mai

ProtokoU der deutschen geologischen Gesellschaft, Jahrg. 1905, pp. 192-194, 2 figs.

138. Beasley, W. H. Naosaurus, a fossil wonder. Sc. American, vol. xcvi, No. 18, 1907, p. 368.

139. Beede, J. W. Invertebrate paleontology of the Upper Permian beds of Oklahoma and the Panhandle

of Texas. The Kansas Univ. Sc. Bull., vol. iv, No. 3, 1907.

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Washington, 1905.

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Am. Mus. Nat. Hist., vol. xxiii, Art. xiv., pp. 265-270.

INDEX.

PAGE.

Anamosaurus 32

strunzi 33

Archaeobelus vellicatus 28

Bathygnathus borealis 63

Callibrachion gaudryi 30

Clepsydropidae 36, go

Clepsydropiuae 37, 90

Clepsydrops yj, 9°

colletti 40, 90

gigas 46, 116

leptocephalus 26, 81

limbatus 40, 127

macrospondylus 52, 131

natalis 42, 90

pedunculatus 41

vinslovii 42, 90

Ctenosaurus koeneni 57

Deuterosaurus 67

Dimetrodon 43, 95

cruciger 60

dollovianus 51, 128

giganhomogenes 47, 123

gigas 46, 116

incisivus 47, 127

longiramus 57

macrospondylus 52, 131

navajovicus 56, 137

obtusidens 54, 134

platycentrus 54

rectiformis 49, 127

PAGE.

Dimetrodon semiradicatus 50, 127

Diopeus leptocephalus 26, 81

Edaphosauridae 69, 151

microdus 61, 146

pogonias 69, 151

Elcabrosaurus baldwini 28, 8g

Embolophorus dollovianus 51, 126

fritillus 65

Geosaurus cynodus 67

Metamosaurus fossatus 65

Naosaurinae 58, 138

Naosaurus 58, 138

claviger 59, 139

cruciger 60, 146

microdus 61, 146

mirabilis 62

Pleuristion brachyccelous 29

Poliosauridae i8, 77

Poliosaurus 18, 77

uniformis 19, 77

Rhopalodon 67

Sphenacodon ferox 66

Stereorachis dominans 34

Theropleura 22, 81

grandis 22, 88

obtusidens 54, 134

retroversa 25, 81

triangulata 25, 81

Tomicosaurus 64

Varanosaurus acutirostris 79

167

DESCRIPTION OF PLATES.

Lettering for all the Plates.

ang, angular.
a?t, articular.
bo, basioccipital.
bs, basisphenoid.
c I , centrale i.
c 2, centrale 2.
cl, clavicle.
cleit, cleithrum.
CO, coracoid.
dent, dentary.
epici, epiclavicle.
epiot, epiotic.
epipt, epipterj-goid.
eth, ethmoid.
/, frontal.
fe, femur.
fib, fibulare.
//, ilium.

intcl, interclavicle.
inter, interceutrum .
intp, interparietal.
iiitm, intermedium.
isch, ischium.
/. jugal.
/, lachrymal.
»ix, maxillary.
n, nasal.
orb, orbit.
/, parietal.
p f, pineal foramen.
pas, parasphenoid.
prf, prefrontal.
pnix, premaxillary.
pii, posterior nares.
po, paroccipital.
proc, procoracoid.

psq, prosquamosal.

pt, pterygoid.

pub, pubis.

q, quadrate.

q f, quadrate foramen.

qj, quadrato-jugal.

r, radiale.

s, sesamoid.

sq, squamosal.

st, stapes.

sni, septo-maxillary.

sura, surangular.

sp, splenial.

scap, scapula.

/, tibia.

lib, tibiale.

H, ulnare.

Plate i.
Fig. I. Left side of skull of /'t)//£i«7«;7« ««//;)rwM, No. 4143 Am. Mus. Nat. Hist. X i.

2. First eight vertebrae of same, left side. X i.

3. First eight vertebrae of same, lower surface. X i.

4. Side view of a sacral of same showing facet for rib. X i-

5. Lower view of same vertebra. X i.

6. Upper surface of a lumbar of same showing facets for attachment of neural

arch. X I.

7. Lateral view of a lumbar of same showing rod-like abdominal scales. X i.

8. A limb bone of same. X i.

9. Upper view of a vertebra of a large species of Poliosaurus, showing shape of

articular surface for neural arch. X i.

10. Side view of same. X i.

11. Upper view of a smaller vertebra of Poliosaurus. X 2.

12. Side view of same. X 2.

13. Side view of dorsal vertebrae of /"i^/w^w/v^ with neural arches. X i.

14. l^dX&raXv'iQVj oi a. vert&hra. o{ Pleuristioii brachyaelous. X 3-

15. Anterior view of same. X 3.

Plate 2.
Fig. I. 'Right side oi s^wW oi l'ara?iosaiirus aciiiirostris. X i.

2. Upper view of same. X i-

3. Posterior limb of same. X i.

4. Posterior lumbar vertebrae of same. X i.

All figures copied from Broili.

i6g

lyo REVISION OF THE PELYCOSAURIA.

Plate 3.

Thcroplei<?a reiroversa.

Fig. I. Quadrate and quadrato-jugal (?) of right side. X >^.

2. Posterior view of same. X J^.

3. Anterior end of lower jaw. X J^.

4. Articular region of left side with pterygoid. X Y^.

5. Femur and tibia. X y^.

6. Outer view of pelvis crushed flat. X Yi.

7. Posterior view of femur. X Y^-

Plate 4.

Fig. I. Lateral view of an anterior vertebra, axis ?, oi Elcabrosaurus baldwini, No. 2285
Am. Mus. Nat. Hist. X i.

2. Lateral view of a dorsal of same. X i.

3. Lateral view of a lumbar of same. X i-

4. Lateral view of a posterior lumbar of same. X i.

5. Anterior of same. X i.

6. Archeobelus vellicalus Cope. X 2.

7. Skull of Clepsydrops natalis Cope, from the right side. No. 4110 Am. Mus. Nat.

Hist. X I.

8. Skull of same from left side showing the postorbital region. X i.

Plate 5-

Fig. I. Lumbars and anterior half of tail, Clepsydrops natalis^ No. 41 10 Am. Mus.
Nat. Hist. X I.

2. Caudals from middle portion of tail, same. X i.

3. Caudals from posterior portion of tail, same. X i.

4. Upper surface of posterior foot, same. X i.

5. Lower surface of same. X i.

6. Upper surface of anterior foot of a small Dimctrodon, possibly D. navajoviais,

from New Mexico, No. 2290 Am. Mus. Nat. Hist. X i.

7. Femur of Clepsydrops natalis, from Illinois, No. 6548 Univ. of Chicago. X i.

8. Vertebrae of a small 77/rro/>/«/ra, from Illinois, No. 6578 Univ. of Chicago. X i.

9. Ilium of a small Clepsydrops (?), from Illinois, No. 6556 Univ. of Chicago. X i.
10. Ilium of a small Clepsydrops (?), from Illinois, No. 6557 Univ. of Chicago. X i.

Plate 6.
Clepsydrops ftalalts Cope, No. 4110 Am. Mus. Nat. Hist. All figures X i.

Fig. i. Humerus.

2. Scapula with clavicle and cleithrum (?).

3. Left half of pelvis with femur, tibia, and fibula; limb thrown up and back.

4. A posterior dorsal.

5. First lumbar.

6. Three anterior dorsals.

description of plates. 171

Plate 7.

Fig. I . Type of Clepsydrops coUetii, lumbar vertebra, lateral view, No. 6530 University of
Chicago. X i>^.

2. Same, anterior view. X i^.

3. Same, posterior view. X i/^.

4. Clepsydrops sp., caudal vertebra from side. No. 6534 Univ. of Chicago. X Y^.

5. Same, from below. X i^.

6. C7(f/>5)'^;-ti/5f(?//f///, dorsal vertebra from below. No. 6534 Univ. of Chicago. X i.

7. Same, posterior view. X i.

8. Same, anterior view. X i.

9. Clepsydrops sp., atlas, anterior view. No, 6529 University of Chicago. X i}4-

10. Same, lateral view. X i)^.

11. C/<?/>5)'a';v/>5 sp., lumbar vertebra, lateral view, No. 6534 Univ. of Chicago. X i.

12. Same, anterior view. X i.

13. Clepsydrops s^., dorsal vertebra, No. 6534 University of Chicago. X i.

14. Clepsydrops pedimciilatus, posterior lumbar vertebra, posterior view. No. 6534

University of Chicago. X 1%.

15. Same, lateral view. X !%■

16. C&/!>5)'a'/(7/!>5r7«5/,?i'//, axis, lateral view, No. 6532 University of Chicago. X 1%.

17. Same, posterior view. X 1Y2.

18. Clepsydrops s^., humerus. No. 6545 University of Chicago. X i.

19. Same, humerus turned 90°. X i.

Plate 8.

Fig. I. Photograph of right side of skull oi Dimetrodon incisiz'us, No. looi University
of Chicago. X ^ ,..
2. Explanatory figure of same.

Plate 9

Fig. I. Lower jaw Dimetrodon t?icisivus. No. 1001 University of Chicago, inner view of
left ramus. X Yij-

2. Explanatory figure of fig. i.

3. hower ja.w Bimelrodon inelsh'us, No. looi University of Chicago. Outer view

of right ramus. X 7/,^.

4. Explanatory figure of fig. 3.

Plate 10.

Fig. I. Top of skull, Z'/;«<'/r£7a'()« ?«r«/j7M, No. looi University of Chicago. X about ^.

2. Explanatory figure of same.

3. Outer view of maxillary of Z'/wif/^W^w tncislvus, "No. 1016 University of Chicago.

4. Inner view of maxillary of Dimetrodoti incishms. No. 78 University of Chicago.

172

REVISION OF THE PELYCOSAURIA.

Plate ii.

Fig. I . Inner view of quadrate of Dimeirodon incisivus, No. looi University of Chicago,
showing method of attachment of pterygoid and the foramen quadratum. X i.

2. Lower view of the basisphenoid of Dhnetrodon incisivus, No. i University of

Chicago. X yi.

3. Lateral view of same. X }^.

4. Quadrate of same. X yi.

5. Inferior view of pterygoid of same. X ^.

6. Lateral view of pterygoid of same. X yi.

7. Superior view of basicranium of same. X %.

8. Lower view of same. X %.

9. Upper view of articular region of lower jaw of same. X yi .

10. Lower view of same. X )4 ■

11. Lateral view of same. X %.

Plate 12.
K\\ Dhnefrodo7t incisivus, No. i University of Chicago. X J^.

Fig. I. Lateral view of atlas and axis.

2. Anterior view of same.

3. Posterior view of same.

4. Anterior view of an anterior dorsal of same.

5. Lateral view of same.

6. Anterior view of a more posterior dorsal.

7. Lateral view of same.

8. Anterior view of same.

9. Lateral view of a lumbar.

10. Lateral view of three posterior lumbars of same.

1 1 . Anterior view of the first of the same three lumbars.

12. Inferior view of same.

Plate 13.

Fig. I. Vertebral column of 77/r;(;/>/ir?^ya 7r/;oi'f;-5a, No. 4155 Am. Mus. Nat. Hist. X %.
la. Caudal series of same specimen shown in figure i which in the specimen con-
nects with the sacrals. X }4.

2. Vertebral column of Dimeirodon incisivus, No. 4008 Am. Mus. Nat. Hist. X %.

3. Posterior portion of vertebral column of Dimclrodofi incisirits, No. 4040 Am.

Mus. Nat. Hist., from the last lumbar to the ninth caudal. X }4 .

Plate 14.

Fig. i. Femur of Z)/w^'/^^fi^t'«?M««V?<5, No. I University of Chicago, posterior view. X }4.

2. Same, anterior view. X J^.

3. Humerus, same. X }4-

4. Tibia, same. X ]4.

5. Top view of tibia. X }4.

6. Ulna of same, anterior view. X >^.

7. Ulna of same, inner view. X }4.

8. A fragment of the maxillary Dimetrodoyi sp., showing the depth of the tooth

sockets; No. 1018 University of Chicago. X about yi.

9. A fragment of the maxillary of Di^ncirodon ijicisivus showing the size of the

canine; No. 78 University of Chicago. X about >^.

DESCRIPTION OF PLATES. 1 73

Plate 15.

Fig. I. A clavicle of right side, probably Dimetrodon, No. 1080 University of
Chicago. X ^,5.

2. Anterior cervical vertebrae of Dimctrodon incisivus, No. looi University of

Chicago, a, the preatlantal intercentrum ; b, the atlas ; c, the second inter-
centrum ; d, the axis. The neural arches are in the position in which they
were found, but one is reversed to show the opposite side. X V^.

3. United ilium and pubis of a small specimen of Dimctrodon incisivus, No. 181

University of Chicago. X about %.

4. Interclavicle of Z'/wt'/''Wt>« sp., No. 1051 University of Chicago. X ^5.

5. Scapula of left side of Dimctrodon incisivus, No. looi University of

Chicago. X Vg.
5a. Fragment of right scapula of same, showing the depth of the humeral cotylus.

Plate 16.

Fig. I. Lower side of the forefoot of Dimctrodon incisivus, No. 1003 University of
Chicago. X I.

2. Fragment of the spine of the fourteenth vertebra of Dimctrodon incisivus,

No. looi University of Chicago, showing the finely striate surface. X i.

3. Outer side of neural arch of Dimctrodon incisivus, No. 1002 University of

Chicago. X I.

4. Inner side of same. X i.

5. Anterior view, face of atlas of Dimctrodon incisivus. No. 1566 Am. Mus. Nat.

Hist. X I.

6. Posterior view of same. X i.

7. Tibiale (astragalus) of Dimctrodon incisivus. No. 4025 Am. Mus. Nat Hist. X i .

8. Tibiale (astragalus) of Dimctrodon dollovianus. No. 1836 Am. Mus. Nat.

Hist. X I.

9. Tibiale (astragalus) of (?) No. 2278 Am. Mus. Nat. Hist. X i.
10. Tibiale (astragalus) of (?) No. 4130-4 Am. Mus. Nat. Hist. X i.

Plate 17.

Fig. I. Skull oi Dimctrodon gigas. No. 1002 University of Chicago. X nearly Yi.

2. Explanatory figure of same.

3. Lower view of the first two sacrals of same. X Y^.

4. Anterior view of same. X Yt

Plate 18.
Fig. I. Skull of Dimctrodon gigas, No. 1002 University of Chicago, with the bones of the
left side of the face removed, showing the ethmoid, prevomers, etc. Slightly
larger than fig. i, plate 17.
2. Explanatory figure of same.

Plate 19.
Restoration of skull of Dimctrodon gigas. No. 1002 University of Chicago.
All figures X about %.
Fig. I. Lateral view.

2. Lower view.

3. Posterior view.

4. Median section.

174 REVISION OF THE PELYCOSAURIA.

Plate 20.

Restoration of Dimetrodon incisivus. X about Yt .

Plate 21.

Fig. I. First intercentrum, atlas; second intercentrum, axis, and third cervical of
Dimetrodon gigas, No. 1002 University of Chicago, inter i , preatlantal inter-
centrum. a/, atlas ; /«/<?/- ^, second intercentrum. X Y2.

2. Femur of same. X >^.

3. Two anterior dorsals of same. X ^i .

4. Anterior view of an anterior dorsal of same. X Yi .

5. 6, and 7. Three caudals of same. X Y-

8. Neural arch of atlas oi Di?nctrodon gigas, No. 4034 Am. Mus. Nat. Hist. X i.

9. Lateral view of an anterior caudal of Dimetrodon gigan/iomogenes, No. 112

University of Chicago, c, Anterior view of chevron of same. X ^3.

Plate 22.
Dimetrodon gigan/iomogenes, No. 112 University of Chicago.

Fig. I. Fourth cervical, anterior view. X Y-

2. Anterior dorsal, anterior view. X Y-

3. A posterior dorsal, anterior view. X Y-

4. A posterior dorsal, near end of series, anterior view. X Y-

5. An anterior lumbar, anterior view. X Y-

6. A posterior lumbar, anterior view. X Y-

7. Same as figure 2, posterior view. X Y-

8. Same as figure I, posterior view. X Y-

g. Outer surface of left half of pelvis. X Yi,-
10. Inner surface of same. X ^^j-

Plate 23.

Fig. I. Sucrnm of Dimetrodon do//ot>iaHus, "No. 114 University of Chicago. X i.

2. Scapula, coracoid and procoracoid with clavicle of same. X nearly Yi-

3. Right side of skull of Dimetrodo7i ineisivus, No. 4001 Am. Mus. Nat. Hist.

X y^. 'X:y^&oi Dimetrodon semi radieatus.

Plate 24.
Fig. I. The anterior cervicals and posterior dorsals of Dimetrodoti dollovianus, No. 4035
Am. Mus. Nat. Hist. X Y--
2. A dorsal vertebra and nearly complete spine of Dimetrodon gigatihomogenes ,
No. 112 University of Chicago. X ^S.

Plate 25.

Fig. I. Vertebral column of Dimetrodon macrospondylus. No. 4012 Am. Mus. Nat.
Hist. X Y^-

2. Vertebral column of Dimetrodon obtusidens. No. 4062 Am. Mus. Nat. Hist. X Yi.

3. Lower view of dorsal vertebrae of Dimetrodon viacrospondylns. No. 4012 Am.

Mus. Nat. Hist. To show shape of intercentra. X J^.

4. Lumbar vertebrae of Dimetrodon macrosporidylus, No. 1019 University of

Chicago. X i.

5. Inferior view of same vertebrae. X i.

6. A-x.is of Dimetrodon obtusidens, 'No. 1060 University of Chicago. X i.

DESCRIPTION OF PLATES. 175

Plate 26.

Fig. I. Dorsal and lumbar vertebrae of Dimetrodofi macrospondyhis, showing nearly
perfect spines ; No. 1019 University of Chicago. X Yi.

Plate 27.

Fig. I. Proximal end, femur, Dimctrodon navajovicus, No. 2285 Am. Mus. Nat. Hist.
X I.

2. Humerus of same. X i.

3. Lower side of lumbar vertebra of same. X i.

4. Lateral view of same vertebra. X i.

5. Two posterior dorsals or lumbars of same. X i.

6. Fibulare oi Dimctrodon tHcisiviis, No. 2275 Am. Mus. Nat. Hist. X i.

7. Tihia.\& oi Dimeirodon navajovicus^ No. 2285 Am. Mus. Nat. Hist. X i.

8. Upper view of vertebrae (?) Tomicosaurus sp.. No. 2212 Am. Mus. Nat.

Hist. X I.

9. Inner side of anterior end of jaw of same, type. No. 4110 Am. Mus. Nat.

Hist. X I.

10. Lateral view of vertebrae of Embolophonis fritillus, No. 4010 Am. Mus. Nat.

Hist. X 2.

11. K iy^icaX ca.\xAa.\ oi Dimctrodon. X about J^.

12. A typical caudal of Dimctrodon. X about ^2 ■

13. A typical caudal of Dimctrodon, anterior view, spine complete. X about yi,.

14. Lateral view of an anterior dorsal of Thcroplaira. X about Y^.

Plate 28.

Fig. I. The posterior cervicals or anterior dorsals of Naosaurus claviger. No. 4002 Am.
Mus. Nat. Hist. X }i.

2. Naosaurus mi rabifis a.{ier 'Pr'xtsch. X about Ji .

3. Anterior view of eighth vertebra of Naosaurus microdus. No. 4060 Am. Mus.

Nat. Hist. X Yi-

Plate 29.

Fig. i. Posterior lumbar and sacral region of Naosaurus claviger. No. 4002 Am. Mus.
Nat. Hist. X 1/3.
2. A dorsal spine o{ Naosaurus microdus (?), No. 4072 Am. Mus. Nat. Hist. X f'z.

Plate 30.

Fig. i. Upper surface of interclavicle oi Naosaurus claviger (?), No. 4103 Am. Mus.
Nat. Hist. X 14.

2. Scapula of right side of Naosaurus claviger (?), No. 4146 Am. Mus. Nat. Hist.

.yf/, scapula; f(7, coracoid; /r, procoracoid. X >2.

3. Ungual phalanx of Naosaurus. X I.

Plate 31.

Fig. I. Outer side of right half of pelvis of Naosaurus claviger, No. 4002 Am. Mus.
Nat. Hist. //, ilium; pu, pubis; iscli, ischium. X Y-
2. Knmeras of Naosaurus claviger. No. 4037 Am. Mus. Nat. Hist. X Y-

Pl.\te 32.
Vertebral colximn of Naosaurus fnicrodus, No. 4060 Am. Mus. Nat. Hist. X ^.

176 REVISION OF THE PELYCOSAURIA.

Plate 33.
Ends of various limb bones showing form ; see text-figures.

P'iG. I . Proximal end of humerus oi Dimclrodon hic/sivits, No. 1044 University of Chicago.

2. Proximal end of humerus of Dimctrodon obtusidcns, No. 1045 University of

Chicago.

3. Proximal end of humerus of Dimctrodon navajovicus. No. 1037 University of

Chicago.

4. Proximal end of humerus oi Naosaiirus, No. 1038 University of Chicago.

5. Proximal end of humerus of Dimclrodon jiavajoviciis, No. 1046 University of

Chicago.

6. Proximal end of humerus of Dimclrodon sp., No. 1039 University of Chicago.

7. Distal end of humerus oi JVaosaurus, No. 34 University of Chicago.

8. Distal end of humerus (?) Tlicroplciira, No. 1043 University of Chicago.

9. Distal end of humerus oi Dimetrodon incisivus, No. 1031 University of Chicago.

10. Distal end of humerus oi Dimclrodon sp., No. 1209 University of Chicago.

1 1 . Distal end of humerus oi Dimctrodon obtusidcns, No. 1028 University of Chicago.

12. Distal end of humerus oi Dimctrodon navajovicus , No. 1030 University of Chicago.

13. Proximal end of femur of (?).

14. Proximal end of femur of C/cpsj'drops, No. 1033 University of Chicago.

15. Proximal end of femur oi Dimctrodon sp., No. 1050 University of Chicago.

Plate 34.

Edaphosanrns pogonias. All figures X Yi.

Fig. I. The upper surface of the skull.
2. The lower surface of the skull.

Plate 35.

Naosaurns clavigcr Cope, mounted skeleton in the Cope Collection of the American

Museum of Natural History, presented by Morris K. Jesup. X about yi.
The skeleton was mounted by Mr. Adam Hermann, with the assistance of Dr. W. D.

Matthew, under the direction of Professor H. F. Osborn.
The backbone belongs to a single individual and constitutes the type; the skull, the

shoulder and pelvic girdles, limbs, and feet represent an assemblage of several

individuals.
The lighter areas represent the restorations in plaster, most of which are based upon

actual knowledge.

(See note under morphological description oi Naosaimcs claviger.')

PELYCOSAURIA

Figs. 1 to 8. Poljosaurus unifotmis. Figs. 9 to 13. Poliosaurus sp. Figs. 14 and 15. Pleuristion brachycoelus.

PELYCOSAURIA

Vatanosaurus acutirostris, after Broili.

PELYCOSAURIA

TTieropleura retroversa.

PELYOOSAURIA

Figs. I to 5. Elcabrosaurus baldwini. Fig. 6. Atcheobelus vellicatus. Figs. 7 and 8. Clepsydrops nalalis.

PELYOOSAURIA

ics. 1 to 5, Clepsydrops nat.li

PELYCOSAURIA

Clepsydrops natalis.

PELYCOSAURIA

Various Clepsydrops vertebrae from Illinois.

PELYCOSAURIA

Dimetiodon incisivus.

PELYCOSAURIA

Dimetrodon incisivus.

PELYCOSAURIA

Dimetiodon iocisivus.

PELYCOSAURIA

Dimetrodon incisivus.

PELYCOSAURIA

Dimelrodon incisivus.

u:ui

PELYCOS*URIA

Figs. 1 and la, Theropkura reliovecsa. F.gi. 2 .od 3, Dimeliodon ii

PELYCOSAURIA

Figs. 1 to 7, Dimetrodon incisivus. Figs. 8 and 9, Dimetiodon sp.

PELYCOSAURIA

Figs. I and 4, Dimetrodon sp. Figs. 2, 3, and 5, Dimetiodon incisivus.

PELYCOSAURIA

Figs. I lo 7, Dimetrodon incislvus. Fig. 8, Dimetiodon dollovianus. Figs. 9 and 10, Unidentified astragali

PELYCOSAURIA

Dimetiodon gigas.

PELYCOSAURIA

Dimetiodon gigas.

PELYOOSAURIA

Restoration of skull of Dimetrodon gigas.

PELYCOSAURIA

PELYCOSAURIA

Figs. I to 8, Oimetiodon gigas. Fig. 9, Dimebodon giganhomogenes.

PELYCOSAURIA

Dimetrodon giganhomogenes.

PELYCOSAURIA

Figs. 1 and 2, Dimetrodon dollovianus. Fig. 3. Dimetrodon incisivus.

PELYOOSAURIA

Fig. I. Dimctiodon dollovanus. Fig. 2, Dimctrodon giganhomogenei

m

PELYOOSAURIA

3, 4, and 5. Dimeliodon msciospondylu!. Figs. 2 and 6. Dimctiodon oblusidei

PELYOOSAURIA

Dimetrodon macrospondylus.

PELYCOSAURIA

Figs. I to 5 and 7, Dimetrodon navajovicus. Figs. 8 and 9, Tomicosaunis.

Fig. 6. Dimeliodon incisivus. Fig. 10, Embolophoius fritillu

Figs. II to 14, Dimetrodon sp.

PELYCOSAURIA

Fig. I, Naosaums claviget. Fig. 2, Naosauius mirabilis. Fig. 3, Naosautus miciodus.

PELYCOSAURIA

Fig. I, Naosaurus claviger. Fig. 2, Naosaurus miciodus.

PELYOOSAURIA

Naosaurus claviger (?)

PELYCOSAURIA

Naosaurus claviger.

PELrCOSAURI*

PELYCOSAURIA

Various limb bones.

PELYCOSAURIA

PELYCOSAURIA

Date Due

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