Samuel Wendell Williston.

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the tribe or superorder Diaptosauria has a present use. Several
groups formerly placed under it are now relegated to other divisions.

14. ORDER RHYNCHOCEPHALIA

Terrestrial or littoral lizard-like reptiles of small or moderate size.
Palate primitive, with teeth on some or all the bones. Pectoral
girdle complete. Dorsal ribs holocephalous, articulating in inter-
central space and arch.

The three groups of reptiles here considered suborders are by
some authors given a family rank, by others ordinal. Except the
Hving Sphenodon, most of the genera are yet incompletely known.
The differences between them seem hardly greater than among the
Lacertilia with the inclusion of the Pythonomorpha.

A. Suborder rhynchosauria

Skull more or less depressed and broad, with a strong, decurved,
and edentulous beak, formed by the premaxillae. Temporal open-
ings relatively large, their boundaries as in the Sphenodontia. No
parietal foramen. Nares undivided. Palate with small interptery-
goidal opening. Dorsal intercentra absent or unknown. About
seven or eight cervicals and twenty- three presacrals; two sacrals.
A small pubo-ischiatic vacuity. Humerus without epicondylar
foramina.

A small group of terrestrial, perhaps in some cases subaquatic,
shore-dwelling and shell-eating reptiles from three to six feet in
length. The complete skull, tail, and mesopodials are known in
none. In Howesia a distinct intermedium tarsus is figured; if not an



2 8o



THE OSTEOLOGY OF THE REPTILES



error, it is the only known example among reptiles. The palatal
teeth are confined to the palatines in two or three rows, save in
Howesia, where they occur on the pterygoids only. However, the




Fig. 1 85. Skeleton of Rhynchosaurus (Rhynchocephalia). After Woodward.
Five sixteenths natural size.



THE SUBCLASS DIAPSIDA 281

anterior part of the skull of this genus is poorly known, and its im-
mediate relationships with the other genera are still in doubt.

Upper Triassic. Rhynchosaurus Owen, England. Hyperodapedon
Huxley, Scotland, India. Stenometopon Boulenger, Scotland.
Howesia Broom, South Africa.

B. Suborder SpheNodontia (Rhynchocephalia vera)

Upper temporal opening bounded by parietal, squamosal, post-
frontal, and postorbital. A single row of acrodont teeth on maxillae,
dentaries, and palatines. Premaxillae with a decurved beak, usually
with teeth. Frontals and parietals paired. No lacrimals. A parietal
foramen. Humerus with an entepicondylar foramen, sometimes
also with an ectepicondylar foramen. Pelvis with large pubo-ischiatic
vacuity. Carpus primitive. Twenty-three to twenty-five presacral
vertebrae, the neck with not more than eight. Parasternal ribs
present.

Two genera only, the living Sphenodon and the Jurassic Homoeo-
saurus, can be located with certainty in this suborder. Sphenodon
has long enjoyed the reputation of being the most primitive of living
reptiles, as evidenced by the persistent dorsal intercentra, deeply
amphicoelous vertebrae, and the single-headed ribs of primitive
type. So far as known Homceosaurus agrees closely, except that it
has no uncinate process on the ribs, a character in which Spheno-
don is almost unique among reptiles. Probably it has dorsal inter-
centra, but this remains to be determined. It has also no ectepi-
condylar foramen present in Sphenodon. Palacrodon and Opisthias
are known only from mandibles. The former, however, is said to
have teeth quite Hke those of Ardeosaurus which, according to
Nopcsa, is a near relative of Acrosaurus. Nor is the temporal region
of Ardeosaurus as well known as one could wish. Brachyrhinodon
has two temporal arches, but is poorly known otherwise. Of Eifelo-
saurus the skull is wholly unknown.

Middle and Upper Triassic. ? Eijelosaurus Jaekel, ? Polyspheno-
don Jaekel, Germany. Palacrodon Broom, South Africa. Brachy-
rhinodon Huene, Scotland.

Upper Jurassic. Homceosaurus, v. Meyer, Ardeosaurus v. Meyer,
Germany.^

MBut cf. page 268 above. According to C. L. Camp (1923), Ardeosaurus is
related to the geckos . — Ed.]



282



THE OSTEOLOGY OF THE REPTILES



Lowermost Cretaceous. Opisthias Gilmore, Wyoming.
Recent. Sphenodon Gray, New Zealand.




Fig, 1 86, Skeleton of /fo>waoJtf«r«J (Rhynchocephalia). After Lortet.
Natural size.



THE SUBCLASS DIAPSIDA 283

C. Suborder Choristodera

Elongate, subaquatic reptiles, with a very slender face, terminal
undivided nares, with small teeth on all palatal bones. No parietal
foramen. Internal nares posterior. Teeth labyrinthine in structure.
Vertebrae shallowly amphicoelous without dorsal intercentra.
Twenty-six presacral, two or three sacral, and a long, flattened tail.
Dorsal ribs holocephalous, broad, and heavy. Parasternals stout.
Pelvis without pubo-ischiatic opening. Humerus with ectepicon-
dylar foramen. Mesopodials imperfectly known.

This small group of water reptiles, animals reaching a length of
eight feet, is of interest because of the retention of several primitive
characters, otherwise unknown in the Diapsida, especially the laby-
rinthine teeth and the absence of a pubo-ischiatic opening. The ar-
rangement of the bones of the temporal region is doubtful. The
legs are essentially terrestrial in structure, with but slight aquatic
adaptations, but the heavy flattened ribs and the elongate flat-
tened tail decisively indicate bottom-crawling aquatic habits. The
relationships between the known genera are very close.

Uppermost Cretaceous and Paleocene. Champsosaurus Cope
{Nothosaurops Leidy), North America. Simcedosaurus Gervais,
France, Belgium.

D. ? Suborder Thalattosauria

Marine reptiles with elongate face, posterior[ly placed external]
nares, sclerotic plates, and paddle-like extremities. Premaxillary,
anterior, mandibular, and pterygoidal teeth conical; those of the
prevomers, and posterior part of maxillae and mandibles low-
crowned. A parietal foramen. Vertebrae rather deeply biconcave;
intercentra unknown. Dorsal ribs holocephalous, articulating
chiefly with centra. Parasternal ribs slender. Humerus short, with-
out foramina.

These small reptiles of but three or four feet in length are still im-
perfectly known; nor is it quite certain that they have two temporal
openings. The upper opening occupies a peculiar position. The
limbs, so far as known, resemble those of the mosasaurs. The habits
of the thalattosaurs must have been similar to those of the mosa-
saurs; the dentition intermediate between that of the Mosasauridae
and that of the Globidentidae.



284 THE OSTEOLOGY OF THE REPTILES

Middle and Upper Triassic. Thalattosaurus Merriam, Necto-
saurus Merriam, California.

AA. SUPERORDER ARCHOSAURIA

Dorsal ribs attached exclusively to the arch, at least anteriorly, by
two articulations, the cervicals to arch and centrum. Usually an
antorbital vacuity. The quadra to jugal is well developed and usually
enters the border of the lateral temporal opening. No parietal fo-
ramen, tabulars, or [dermojsupraoccipitals, and doubtfully, [if] ever,
the interparietals. Teeth thecodont, confined to jaws, rarely absent.
Vertebrae never notochordal, nor the dorsal intercentra persistent.

15. ORDER PARASUCHIA

From small to rather large, crawling or leaping reptiles, character-
ized especially by the normal pelvis, absence of a secondary palate,
and a large antorbital opening. Body usually with dermal armor.
Roof bones of skull always paired; postfrontals present. Vertebrae
amphicoelous or platycoelous. Clavicles and interclavicle present,
the corocoid not elongate. Parasternal ribs generally present. Meso-
podials imperfectly known; phalanges not reduced.

The Parasuchia in the present sense were long united with the
Crocodilia as two suborders, the Parasuchia, sens, str., and the
Pseudosuchia or Aetosauria, but the marked differences in skull and
pelvis justify their ordinal separation. By some authors the three
suborders here recognized are each given ordinal rank. Sclerotic
plates are known in a single genus of Pseudosuchia.

A. Suborder Pseudosuchia

Typically a group of small, slender, climbing or leaping reptiles
with more or less elongated hind legs. The external and internal
nares are near the extremity of the more or less pointed skull; the
lateral orbits are large, as are also the antorbital openings. The epi-
podials are long, the clavicles and interclavicle slender.

None of the forms referred to this suborder is completely known,
and among the known forms there is a considerable diversity of
structure, some departing so widely, perhaps, that their location here
is provisional. Of the more typical, Sderomochlus has no dermal



THE SUBCLASS DIAPSIDA 285

armor, and Euparkeria alone has sclerotic plates ; the latter has been
accredited with an interparietal bone.

With the inclusion of the doubtful forms there are but few con-
stant characters to distinguish the group from the Rhynchocephaha ;
typically, however, the absence of palatal teeth, and the attachment
of the dorsal ribs are decisive. As a whole, however, the group is one
of wide genetic possibiHties and [may] have had a close genealogical
relationship with all the other members of the Archosauria, and
especially the Saurischia. Nearly every known genus has been ac-
credited with family rank.

Family Aetosauridae. Twenty-five presacrals; two sacrals. Hu-
merus a Httle longer than radius and ulna; hind legs a half longer
than the front. Dorsal scutes transversely elongate, covering the
whole back; abdomen with small plates.

Triassic. Aetosaurus Fraas, Dyoplax Fraas, Germany. Stegomus
Marsh, Connecticut.

Family Ornithosuchidae. Scapula slender, coracoid short and
broad. Legs very slender, the epipodials a Httle longer than the
propodials. Two rows of dermal plates, each longer than broad.

Euparkeria is accredited with an interparietal, the only member
of the group.

Triassic. Ornithosuchus Newton, ? Erpetosuchus Newton, Eng-
land. Euparkeria Broom, Sphenosuchus Haughton, South Africa.

Family Scleromochlidae. Premaxillae united. Twenty-one
presacrals, three sacrals. Scapulae slender, coracoid long. Pubes
long and slender, expanded at extremity; calcaneum with tuberosity;
feet as long as tibia, the epipodials longer than propodials. Slender
parasternal ribs. No dermal armor.

Triassic. Scleromochlus Woodward, England.

B. Suborder Pelycosimia

Large, heavily built, terrestrial or marsh reptiles. External and
internal nares near extremity of triangular skull. Antorbital open-
ings large, the orbits relatively small. Upper temporal opening not
depressed below level of [parietals]. Palatines approximated or con-



286 THE OSTEOLOGY OF THE REPTILES

tiguous, without respiratory canal. Teeth compressed, curved, and
sharply pointed. Legs short and rather stout.

This group, proposed as a separate order, is based almost exclu-
sively upon Erythrosuchus. In the structure of the skull it is some-
what intermediate between the Pseudosuchia and the Phytosauria.

Triassic. Erythrosuchus Broom, South Africa. ? Scaponyx Wood-
ward, South America.

c. SUBORDER Phytosauria

Large, crawling, subaquatic reptiles, reaching a length of twenty
or more feet, especially characterized by the elongate face, com-
posed chiefly of the premaxillae, the posterior nares, and the deep
respiratory canal, formed by the underarching of the palatines.
Skull rugose, the lateral, temporal, and antorbital openings large,
the supratemporal opening small and more or less depressed below
the plane of the parietals. Tip of premaxillae decurved, with two
or three very long, cylindrical teeth on each. Teeth either cyhn-
drical throughout, or the posterior ones more or less flattened and
separated. Neck, body, and tail covered with four or more rows of
strong dermal bones; the pectoral region and abdomen with smaller,
bony scutes. Tail long and flattened, compressed. Feet probably
webbed. Vertebrae platycoelous ; two sacrals.

Family Phytosauridae. Ilium with postacetabular process;
pubis not dilated at extremity.

Triassic. Phytosaurus Jaeger, Mystriosuchus Fraas, Mesorhinus
Jaekel, Germany. Parasuchus Lydekker, India. Paleorhinus WiUis-
ton, Angistorhinus Mehl, Lophoprosopus Mehl, Rocky Mts. Rutiodon
Emmons (Rhytidodon) , CaroUna, New York, Connecticut.

Family Stagonolepidae. A supracoracoid foramen. Ilium with-
out postacetabular process; pubes dilated at extremity.
Triassic. Stagonolepis Huxley, England.

[D. Suborder Desmatosuchia]

[Large, long-tailed reptiles reaching a length of perhaps sixteen
feet, especially characterized by the probably secondary absence of
the upper temporal opening. Cervical and anterior dorsal bony
plates bearing long horn-Uke outgrowths. Skull with large antorbital



THE SUBCLASS DIAPSIDA 287

opening and dorsal anterior nares, snout not greatly produced.
Teeth thecodont. Distinguished from the Phytosauria especially by
the absence of the upper temporal opening, which may have been
secondarily lost as in the caimans. Von Huene refers Desmato-
suchus to the Phytosauria.

Triassic. Desmatosuchus Case, Texas.]

16. ORDER CROCODILIAN

[Loricata]

Internal nares carried far back in the mouth by the union of the
maxillae and palatines, and in the later forms the pterygoids also.
Premaxillae never much elongate, the external nares terminal. Ace-
tabulum formed by ilium and ischium only, the so-called pubes
(Pprepubes) excluded and not meeting in a median symphysis.
Phalanges of fourth and fifth digits reduced; calcaneum elongate.
Two sacral vertebrae.

The Crocodilia are at once distinguished from all other reptiles by
the structure of the palate and pelvis. There is not a very great di-
versity of structure among the known forms. All are lizard-like in
form, with a long, flattened tail, very predaceous, with conical the-
codont teeth, and more or less water-loving in habit. In size they
vary from less than one foot to about fifty feet in length. The verte-
brae were platycoelous in all till about the beginning of the Lower
Cretaceous; procoelous in all since the early part of the Eocene.
Some have a relatively broad skull ; others a more or less elongated
face, sometimes very slender, as in the ancient teleosaurs and the
modern gavials. In such forms the nasals do not reach the external
nares, and the splenials meet in a symphysis. The upper temporal
openings in the modern forms are smaller, very small in the broad-
faced types. In the early types the arch between the orbit and lateral
temporal opening was covered immediately by the skin; since
Wealden times the bar is more cylindrical and more deeply placed.
The amphibious crocodiles have a strong dermal, osseous armor
along the back and tail, sometimes also on the under side. Both the
carpus and tarsus are peculiarly modified, suggesting, v. Huene
thinks, a primitive, more upright- walking gait.

^ [For recent morphological and taxonomic treatment of the Crocodilia, see numerous
papers by C. C. Mook, 1921-, Bulletin, Amer. Mus. Nat. Hist. — Ed.]



288 THE OSTEOLOGY OF THE REPTn.ES

A. Suborder Eusuchia

An antorbital opening primitively present but lost in many an-
cient and all modern forms. Mandible with an external vacuity
posteriorly. Nine cervical vertebrae, twenty-three or twenty-four
presacrals. No sclerotic plates in orbits. Body with dermal bones.
Feet partly webbed, clawed, not paddle-like.

Until within recent years, and still by some authors, the Eusuchia.
comprised only those crocodiUans with procoelous vertebrae, am-
phicoelian forms comprised in the suborder Mesosuchia. It is now
known that the change in the form of the vertebrae was a relatively
unimportant one and may have occurred in different lines of descent.

Family Teleosauridae. Vertebrae platycoelous. Internal nares
large, situated at posterior end of palatines. Face very long and
slender. An antorbital opening sometimes present. Postorbital bar
not modified. Upper temporal opening large. A nearly complete
dermal armor. Front feet much smaller than hind. From two to
ten feet in length.

Jurassic. Pelagosaurus Bronn, Teleosaurus Geoffroy, Teleido-
saurus Deslongchamps, Suchodus Lydekker, Aeolodon Meyer, Cro-
codilemus Jourdan, Gnathosaurus Miinster, Europe. Steneosaurus
Geoffroy, Europe, Madagascar.

Cretaceous. ? Teleorhinus Osborn, Wyoming.

Family Pholidosauridae. Vertebrae platycoelous. Internal
nares opening in palatines and pterygoids. Face long; the nasals
reach to the premaxillae. Upper temporal opening smaller than
orbits. Postorbital bar modified. Front legs larger than in the
Teleosauridae. Dorsal and ventral armor present.

Upper Jura and Lowermost Cretaceous. PhoUdosaurus Meyer
(Macrorhynchus) , Pterosuchus Owen, Europe.

Family Atoposauridae. Vertebrae platycoelous. Posterior nares
not reaching pterygoids. Head short, broad. Upper temporal open-
ings much smaller than orbits. Dermal armor composed of two rows
of quadrilateral plates, probably extending on tail. Probably no ven-
tral scutes. Tail long. Small reptiles from eight to sixteen inches in
length.



THE SUBCLASS DIAPSIDA 289

Upper Jurassic. Atoposaurus Meyer, Alligator ellus Jourdan,
Alligatorium Lortet, Germany.

Family GoNioPHOLiDAE. Vertebrae platycoelous. Internal nares
bounded by pterygoids and palatines. Face rather broad, not long.
Postorbital bar subdermal. A dorsal armor of two or more rows of
plates.

Lowermost Cretaceous. GoniophoUs Owen, Europe, North and
South America. Nannosuchus Owen, Theriosuchus Owen, Machimo-
saurus Meyer, Bernissartia DoUo, Europe.

Upper Cretaceous. Coelosuchus Williston, TeleorUnus Osborn,
Wyoming. Notosuchus Woodward, Cynodontosuchus Woodward,
South America.

Family Dyrosauridae. Vertebrae platycoelous; internal nares
between palatines and pterygoids. Face very slender. Postorbital
bar subdermal. From fifteen to eighteen feet in length.

Lower Eocene. Dyrosaurus Pomel, Africa.

Family Hylaeochampsidae. Vertebrae probably procoelous.
Internal nares surrounded by pterygoids. Palate with large foramen
between ectopterygoid and maxillae. Skull short, broad.

Wealden Cretaceous. Hylceochampsa Owen, ?Heterosuchus Seeley,
England.

Family Gavialidae. Vertebrae procoelous. Posterior nares sur-
rounded by pterygoids. Face very slender. Postorbital bar sub-
dermal. Upper temporal openings large. Nasals remote from nares.
Dorsal but no ventral scutes. From ten to fifty feet in length.

Pleistocene, Recent. Gavialis Oppel, Rhamphosuchus Owen,
Paleosuchus Falconer and Cautley, India.

Family Tomistomidae. Vertebrae procoelous. Posterior nares
surrounded by pterygoids. Face less elongated, gradually merging
into cranium. Postorbital bar subdermal. Nasals extend into nares.
Sometimes an antorbital opening. From six to forty or more feet in
length.

Upper Cretaceous. Thoracosaurus Leidy, Holops Cope, United
States.

Eocene. [Tomistoma, Europe, Africa.] Eosuchus DoUo, Belgium.

Plioeene. Tomistoma (?) [Gavialosiichus], Florida.



290 THE OSTEOLOGY OF THE REPTILES

Pleistocene. Tomistoma, Hungary.
Recent. Tomistoma, Borneo.

Tertiary. Leptorhamphus Ameghino, Oxydontosaurus Ameghino,
Argentina.

Family Crocodilidae.^ Vertebrae procoelous. Posterior nares
surrounded by pterygoids, single or divided. Upper temporal open-
ings small. Postorbital bar subdermal. Face never slender. Teeth
stout, anisodont. Dorsal plates in two or more rows, the ventral
armor present or absent. The nasals usually reach the external nares.
From four or five to more than forty feet in length.

Uppermost Cretaceous. Deinosuchus Holland, Bottosaurus Leidy
[Agassiz], Brachychampsa Gilmore, Leidyosuchus Lambe, ? Polydectes
Cope, North America. Crocodilus Laurenti, Italy.

Eocene. Crocodilus Laurenti, Diplocynodon Pomel, Europe, North
America. Limnosaurus Marsh, North America.

Oligocene. Caimanoidea Mehl, South Dakota.

Miocene. ^'' Crocodilus'^ [?], [Alligator], North America.

Pleistocene. Crocodilus Laurenti, Europe, India, Africa, North
America. [Alligator, North America.]

[Recent. Crocodilus, Osteolaemus, Osteoblepharon, Alligator, Cai-
man, Jacare.]

Incertae Sedis. Lower Jurassic. Notochampsa Broom, South
Africa.

B. Suborder Thalattosuchia

Marine crocodiles, without bony armor, and with Hmbs more or
less modified as paddles, without claws. Vertebrae platycoelous.
Face more or less elongated. Nares at posterior end of palatines.
Prefrontals large, protuberant. Supratemporal openings large.
Bones of skull smooth. Orbits with sclerotic plates. No antorbital
or mandibular openings. Seven cervical, twenty-five presacral,
vertebrae. Tail long, with distal fin-like dilatation.

1 [Willis ton here includes the genera Alligator and Caiman under the CrocodUidae,
and places Tomistoma in a separate family, but Mook {op. cit.) has shown that Alli-
gator, Caiman, and Jacare are more distinct from Crocodilus and its allies {Osteolae-
mus, Osteoblepharon) than is Tomistoma. — Ed.]



THE SUBCLASS DIAPSIDA 29 1

Family Metriokhynchidae.

Upper Jurassic. Dacosaurus Quenstedt, Geosaurus Cuvier,
Europe. Metriorhynchus Quenstedt, Europe, Patagonia.

Lowermost Cretaceous. Neustosaurus Raspail, ? Enaliosuchus
Dollo, Europe.

[DINOSAURIA]

17. ORDER SAURISCHIA

More or less upright-walking reptiles. The normal pubes and
ischia meet in a ventral symphysis, the acetabulum perforated. No
predentary or rostral bones. One or more antorbital openings. No
dermal bones.

A. Suborder Theropoda

Carnivorous or secondarily herbivorous in habit. More or less
bipedal in gait, the hind feet more or less digitigrade, the front legs
more or less reduced. Pubes meeting in a long ventral symphysis,
with a distal dilatation.

Family Plateosauridae. Teeth less compressed, not recurved
and somewhat thickened, their anterior and posterior borders den-
ticulated. Anterior vertebrae platycoelous; twenty- three presacrals,
three sacrals. Front legs a little longer than the femora, preaxonic,
their phalangeal formula 2, 3, 4, 5, (?), the first claw large. Hind
feet more mesaxonic, the first and fifth toes reduced. Feet digiti-
grade or semiplantigrade. Astragalus without ascending process.

Upper Triassic. Plateosaurus Meyer, Gressylosaurus Riitimeyer,
Pachysaurus Huene, Teratosaurus Meyer, Europe. Euskelosaurus
Huxley, Gryponyx Broom, South Africa.

This, the most primitive family of the Theropoda, is thought by
some to have an ancestral relationship with the Sauropoda. The
characters drawn chiefly from Plateosaurus may not and probably do
not apply to all the genera listed in the family. The reptiles were
clearly bipedal in gait, though of rather heavy build. Jaekel thinks
that the hind feet were purely plantigrade, but this was improbable
since the mesaxonic structure distinctly indicates the elevation of
the ankle from the ground. Plateosaurus attained a length of about
fifteen feet.



292



THE OSTEOLOGY OF THE REPTILES



Family Anchisatjridae. Smaller and more slender theropods.
Vertebrae amphicoelous. Teeth compressed, more or less recurved.
Astragalus without ascending process.

Upper Triassic. Anchisaurus Marsh, Megadactylus Hitchcock,
Ammosaurus Marsh, Connecticut Valley. Thecodontosaurus Riley
and Stutchbury, England, Africa, AustraHa. Massospondylus Owen,
South Africa. Zanclodon Plieninger, Sellosaurus Huene, Europe.

[No MS. was found for (i) the Coelurosauria, containing several
families and numerous genera of light-limbed saurischian dinosaurs,
including the Ornithomimidae, (2) the Megalosauria group of the




Fig. 187. Skeleton of Gorfoj^wrwj (Saurischia). After Lam be. One thirty-sixth natural size.

Jurassic, and (3) the Deinodont group of the Cretaceous. For group
I see papers by Osborn 191 7 {Bulletin, Amer. Mus. Nat. Hist., vol.
XLiii), von Huene 192 1 {Acta Zodlogica, Bd. II) ; for groups 2 and 3
see Matthew and Brown, 1922 {Bulletin, Amer. Mus. Nat. Hist.,
vol. XLVi). — Ed.]

B. SUBORDER SAUROPODA (OPISTHOCOELIA, CETIOSAURIA)

Quadrupedal, semiplantigrade, herbivorous dinosaurs, with long
neck and tail and small skull. Postfrontal sometimes present. Teeth
subcylindrical, with a thickened, spoon-shaped crown, in a single row,
and more or less restricted to anterior part of jaws, the premaxUlae
with teeth; no predentary. No coronoid process to mandible. The
anterior, sometimes all, presacral vertebrae opisthocoelous, with a
more or less developed hyposphene-hjrpantrum articulation, and with
hollow, lateral cavities in centra. Four or five sacrals, twenty-six or



THE SUBCLASS DIAPSIDA 293

twenty-seven presacrals. The pubes are massive and meet in a large
ventral symphysis. Carpals and tarsals reduced, feet preaxial. Limb
bones cancellous in structure. From about fifteen to about ninety


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