324 CLASS xv. 



Saurii. 



Tliecodontosaurus RILEY and STUTCHBURY. Differs from the exist- 

 ing lizards in the dentition, being neither according to the acrodont 

 form (anchylosed to the summit of alveolar ridge), nor the pleuro- 

 dont (anchylosed to the outer wall of alveolar groove), but im- 

 planted in sockets either loosely or confluent with the bony wall of 

 the cavity. Teeth conical, rather slender, compressed, acute, ante- 

 rior and posterior edges finely serrated. Pulp cavity remains open 

 in base of crown. Lacertine form of pectoral and probably of pelvic 

 arch combined with crocodilian characters of vertebrae and ribs. 

 Vertebrae biconcave. 



Sp. Tkecodontosaurus antiquus BIL. and STUTCH. Oldest division of the New 

 Bed sandstone. 



Palceosaurus RIL. and STUTCH. Same locality. Teeth compara- 

 tively much broader than in the preceding. 



Rhynchosaurus OWEN. Cranial structure lacertine, jaws with 

 chelonian and ornithic modifications. Vertebrae biconcave. New 

 Red sandstone. OWEN Rep. Br. Assoc. 1841, pp. 145 153. Trans, 

 of the Cambridge Phil. Soc. 1842, Tom. vn. Pt. 3, p. 335, PL 5, 6. 



In the three last genera, from the oldest division of the New Red sand- 

 stone, containing the most ancient of lacertine animals, the spinal canal is 

 moniliform, sinking into the middle part of the centrum of the vertebrae. 



Dicynodon OWEN. Jaws like the last but with mammalian 

 canine teeth. Vertebrae slightly biconcave. From sandstone rock 

 at the south-eastern extremity of Africa, Journal of the Geol. Soc. 

 i. 1845, pp. 318322. 



Cladyodon OWEN. Teeth compressed, anterior and posterior 

 edges serrate ; in their breadth, as compared with their length, they 

 are intermediate between Thecodontosaurus and Palceosaurus pla- 

 tyodon, thus approaching the form of Megalosaurus. 



Sp. Cladyodon Lloydii OWEN. Teeth alone known. Same locality as 

 Thecodontosaurus. 



Protorosaurus MEYER. Thecodont type of dentition, long and 

 thin. Feet resemble those of the Monitors. 



Sp. Protorosaurus Speneri, from the cupriferous schist of Thuringia ; Cuv. 

 i. foss. v. i, pp. 300 306. 



Mosasaurus CONYB. Acrodont type of dentition. Teeth smooth 

 palatine (pterygoid) teeth. Vertebrae concavo-convex. Locomc 

 tive extremities unknown. 





