OWEN.—CLASSIFICATION OF REPTILIA. 81 
the slight indication of the sacral vertebre; the non-confluence of the caudal 
hzmapophyses with each other, are all “ plesicsauroid.” In the size and number 
of abdominal ribs and sternum may perhaps be discerned a first step in that series 
of development of the hemapophyses of the trunk, which reaches its maximum in 
the plastron of the Chelonia. The connexion of the clavicle with the scapula is 
common to the Chelonia with the Plesiosauri; the expansion of the coracoids— 
extreme in Plesiosauri—is greater in Chelonia than in Crocodilia ; but is still 
greater in some Lacertia. The form and proportions of the pubis and ischium, as 
compared with the ilium, in the pelvic arch of the Plesiosauri, find their nearest 
approach in the pelvis of marine Chelonia; and no other existing reptile now 
offers so near, although it be so remote, a resemblance to the structure of the pad- 
dles of the Plesiosaur. Both Nothosaurus and Pistosaurus had many neck-vertebra, 
and the transition from these to the dorsal series was effected, as in Plesiosaurus, 
by the ascent of the rib-surface from the centrum to the neurapophysis ; but the 
surface, when divided between the two elements, projected further outwards than 
in most Plesiosauri. In both Nothosaurus and Pistosaurus the pelvic vertebra 
developes a combined process (par- and di-apophysis). but of relatively larger, 
vertically longer size, standing well out, and from near the fore part of the side 
of the vertebra. This process with the coalesced riblet indicates a stronger ilium, 
and a firmer base of attachment of the hind limb to the trunk than in Plesiosaurus. 
Both this structure and the greater length of the bones of the fore-arm and leg 
show that the Muschelkalk predecessors of the liassic Plesiosauri were better 
organized for occasional progression on dry land. The Sauropterygii extend from 
the Trias to the chalk inclusive. 
Order V.— Anomodontia (avoyos, lawless, odous, tooth).—This order is represent= 
ed by three families, all the species of which are extinct, and appear to have been 
restricted to the triassic period. Teeth wanting, or confluent with tusk-shaped 
premaxillaries, or confined to a single pair in the upper jaw, which bave the form 
and proportions of canine tusks. A foramen parietale and two nostrils, tympanic 
pedicle fixed. Vertebre biconcave; pleurapophysis of the trunk long and curved 
the anterior ones with bifurcate heads; a sacrum of four or five vertebrae forming 
with broad iliac and pubic bones, a large pelvis. Limbs ambulatory.—Family 
Dicynodontia. A long ever-growing tusk in each maxillary bone; premaxillaries 
connate, and forming with the lower jaw a beak-shaped mouth, probably sheathed 
with horn. This includes two genera—Dicynodon and Ptychognathus——all the 
known species of which are founded on fossils from rocks of probably triassic age 
in South Africa. Family Cryptodontia. Upper as well as lower jaw edentulous, 
The genus Oudenodon closely conforms to the dicynodont type, and the species are 
from the same rocks and localities -—-Family (inathodontia. Two curved tusk- 
shaped bodies holding the place of the premaxillaries, and consisting of confluent, 
dentinal and osseous substance, descending in front of the symphysis mandibulze 
These bodies are homologous with the pair of confluent premaxillary teeth and 
bones in the existing New Zealand amphiccelian lizard Rhynchocephalus; they are 
analogous to the tusks in the Dicynodonts, and must have served a similar purpose 
jn the extinct reptiles of the New Red (Trias) Sandstone of Shropshire (Rhyncho- 
saurus), in which alone this structure, with an otherwise edentulous beak-shaped 
Vou. V. G 
