LACERTILIA AND CROCODILIA. 467 



Reptiles are a matter of considerable question. Upon the 

 whole, the oldest known Lacertilian would appear to be the 

 Protorosaurus of the Middle Permian Rocks; though good 

 authorities have placed this form in the Crocodilian group of 

 the Thecodontia. Protorosaurus attained a length of between 

 three and four feet, and differs from all existing Lizards in 

 having its teeth implanted in distinct sockets this being a 

 Crocodilian character. In other respects, the Permian reptile 

 approximates closely to the living Monitors ( Varanidce}, and its 

 slightly cupped vertebrae would lead to the belief that it was 

 aquatic in its habits. 



In rocks known, or supposed, to be of Triassic age, numerous 

 Lacertilian reptiles have been discovered, of which the most 

 important are Telerpeton, Hyperodapedon, and Rhynchosaurus, 

 of which the last is generally referred to the group of the 

 Anomodontia, to be subsequently spoken of. 



In the Jurassic period, the remains of Lacertilians are not 

 unknown, but call for little special notice. Several forms of 

 little importance have been described from the Middle Oolites. 

 In the fresh- water strata of the Purbeck series (Upper Oolites), 

 occur the remains which have been referred to the genera 

 Nuthetes, Macellodon, Saurillus, and Echinodon. These are, 

 perhaps, the first traces in the stratified series of remains, the 

 affinities of which to the typical Lacertidce cannot be disputed. 



In the Cretaceous Rocks, and almost exclusively confined to 

 strata of this age, occur the singular Lacertilians which form 

 the group of the " Mosasauroids." These remarkable Reptiles 

 were of gigantic size, Mosasaurus princeps being believed to 

 have attained the enormous length of not less than seventy- 

 five feet. The teeth of these reptiles are long, pyramidal, and 

 slightly curved ; but they are anchylosed to the jaw, and are 

 not sunk into distinct sockets as in the living Crocodiles. 

 From the shortness of the humerus, and the indications that 

 the vertebral column was unusually flexible, and that the tail 

 was laterally compressed, it was early conjectured that the 

 Mosasauroids were marine and aquatic in their habits. This 

 conjecture has been raised to the rank of a certainty by the 

 discovery that the fore and hind limbs of the Mosasauroids 

 were in the form of fin-like paddles, like those of the Ichthyo- 

 saur and Plesiosaur. There can, therefore, be no doubt that 

 Mosasaurus like the living Amblyrhynchus was aquatic in its 

 habits, and frequented the sea-shore, coming, in fact, only 

 occasionally to the land. Professor Marsh has also recently 

 shown that some species possess bony dermal scutes, thus 

 rendering their Lacertilian affinities somewhat dubious. 



