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 — Thecodontosaurus and Palaosaurus, 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 vertebrae, 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 Teleosaurus ; but they are chiefly remarkable for the depth of 

 the spinal canal at the middle of each vertebrae, 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 vertebrae 

 of the Bhi/nchosaurus 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 Dinosaurs. 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 Bhi/tichosaurus, 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 Thecodontosaurus and Palaosaurus " are, that in their 

 thecodont type of dentition, biconcave vertebrae, double-jointed ribs, and proportionate 

 size of the bones of the extremities, they are nearly allied to the Teleosaurus ; 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.^) 



1 'Report on British Fossil Reptiles,' in Report of the Eleventh Meeting of the Brit. Assoc, p. 153, 

 1842. 



2 Ibid., pp. 153-155. 



