554 MANUAL OF ZOOLOGY. 



latter are ground down in advanced age. Unlike any other 

 Saurian, Hatteria is devoid of any copulatory organ. 



DISTRIBUTION OF LACERTILIA IN TIME. It is hardly pos- 

 sible, with our present knowledge, to speak very positively as 

 to the exact range of the Lacertilia in time. This uncertainty 

 arises from two causes, firstly, that there is some doubt as to 

 the exact age of some deposits which have yielded Lacertilian 

 remains; and secondly, that the affinities of some extinct 

 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 

 five or six feet, and differs from all existing Lizards in having 

 its teeth implanted in distinct sockets this being a Croco- 

 dilian character. In other respects, the Permian reptile ap- 

 proximates closely to the living Monitors ( Varanid&\ and its 

 slightly cupped vertebrae would lead to the belief that it was 

 aquatic in its habits. Both pairs of limbs were present, both 

 pentadactylous, and constructed on the type of the limbs of 

 the typical Lizards. 



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

 Lacertilian reptiles have been discovered, of which the most 

 important are Telerpeton, Hyperodapedon, and Rhynchosaurus^ 

 of which the last is sometimes 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 Lacertida cannot be disputed. 



In the Cretaceous rocks occur the singular Lacertilians 

 which form the group of the " Mosasauroids." These remark- 

 able Reptiles were of gigantic size, Mosasaurus pri?iceps being 

 believed to have attained the enormous length of not less than 

 seventy-five feet. The teeth of these reptiles are long, conical, 

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

 are not sunk into distinct sockets as in the living Crocodiles. 

 The vertebrae are proccelous. From the shortness of the hu- 

 merus, and the indications that the vertebral column was un- 

 usually flexible, and that the tail was laterally compressed, it 

 was early conjectured that the Mosasauroids were marine and 



