ANIMALS. 237 
to the squamate or Lacertine division of the order, the teeth being implanted in 
sockets, either loosely or confluent with the bony walls of the cavity; these I have 
termed the ‘Thecodont’ Lacertians.”” 
The following genera—TZhecodontosaurus and Paleosaurus, which have been esta- 
blished on some teeth and jaws (found along with several other bones in the Magnesian 
conglomerate near Bristol), belong to this group. 
The vertebree, associated with the teeth and jaws of these Thecodont Lacertians, “are 
biconcave, with the middle of the body more constricted, and terminal articular cavities 
rather deeper than in Ze/eosaurus; but they are chiefly remarkable for the depth of 
the spinal canal at the middle of each vertebra, where it sinks into the substance of 
the centrum; thus the canal is wider, vertically, at the middle than at the two ends of 
the vertebra: an analogous structure, but less marked, obtains in the dorsal vertebre 
of the Rhynchosaurus from the new Red Sandstone of Shropshire.” 
“ Besides deviating from existing lizards in the thecodont dentition and biconcave 
vertebrae, the ancient Saurians of the Magnesian conglomerate also differed in having 
some of their ribs articulated by a head and tubercle to two surfaces of the vertebra, 
as at the anterior part of the chest in Crocodiles and Dimosaurs. The shaft of the rib 
was traversed, as in the Ichthyosaur and Rhynchosaur, by a deep longitudinal groove. 
Some fragmentary bones indicate obscurely that the pectoral arch deviated from the 
Crocodilian and approached the Lacertian or Enaliosaurian type in the presence of a 
clavicle, and in the breadth and complicated form of the coracoid. ‘The humerus 
appears to have been little more than half the length of the femur, and to have been, 
like that of the Rhynchosaurus, unusually expanded at the two extremities. 
“The tibia, fibula, and metatarsal bones manifest, like the femur, the fitness of the 
thecodont Saurians for progression on land. ‘The ungual phalanges are sub-com- 
pressed; curved downwards, pointed, and impressed on each side with the usual curved 
canal.” | 
The general conclusions which may be drawn from the knowledge at present 
possessed of the osteology of Zhecodontosawrus and Pale@osaurus “are, that in their 
thecodont type of dentition, biconcave vertebre, double-jomted ribs, and proportionate 
size of the bones of the extremities, they are nearly allied to the Zé/eosaurus ; but that 
they combine a Lacertian form of tooth, and structure of the pectoral and probably 
pelvic arch with these Crocodilian characters, having distinctive modifications, as the 
moniliform spinal canal, in which, however, the almost contemporary Rhynchosaur 
participates.” (Owen.”) 
‘ Report on British lossil Reptiles,’ in Report of the Eleventh Meeting of the Brit. Assoc., p. 153, 
1842. 
2 Tbid., pp. 153-155. 
