512 EXTINCT REPTILES OF THE LIZARD TYPE. 



taken merely to indicate the elongated form of these marine animals, 

 which had the anterior limbs expanded into fins like those of Chelo- 

 nians or Cetaceans. Mosasaurus in this country is found in the 



Fig. 145. Head of Mosasaurus. 



Upper Chalk ; it is best known from the Maestricht beds. The 

 genera recognised in the Niobrara group of North America are Platy- 

 carpus, Clidastes, Leiodon, Sironectes. 



The Dolickosauria is another well marked sub-order distin- 

 guished by having many vertebrae in the neck ; the intervertebral 

 articulation includes a zygosphene ; the limbs are small. The genera 

 Dolichosaurus and Saurospondylus are both from the Chalk. 



The HomoBosaurifi * is a group of Lizards with biconcave vertebrae 

 which ranges from the Trias to the Solenhofen Slates, and includes 

 Telerpeton ' 2 in the former, and Sapkceosaurus and Homceosaurus 3 in 

 the latter. 



Lacertilia. The typical Lizards are represented in the Tertiary 

 strata of Europe by Iguana and Lacerta ; and some fragments have 

 been referred to Scincus and to Anguis. 



PAL^EOSAURIA. Rhynchoce pit alia. This group, now almost ex- 

 tinct, has for its sole surviving representative the Hatteria of New 

 Zealand. This animal is often classed with the lizards, which it 

 resembles in form and size. It, however, has so many characters in 

 common with the older crocodilia and their allies, that it is conveniently 

 grouped with the Palseosauria rather than with the Cainosauria. Pro- 

 colophon, and many similar animals from Cape Colony regarded as 

 Triassic, may be placed in this group. Professor Huxley would place 

 here the British Triassic Hyperodapeton and Rhynchosaurus. Pro- 

 fessor Cope has referred many American genera to this type. 



Chelonia. Chelonians, so far as is known, retain the carapace 

 and plastron, more or less developed in all fossil forms. The 

 Chelonia have been divided into three principal groups first, Dema- 

 tochelyidae, in which the carapace is not developed, but represented by 

 a tesselated bony skeleton within the skin, such as is seen in the 



1 Huxley : " Anatomy of Vertebrates," 1871. 



2 Huxley : Q. J. G. S., vol. xxiii. 



3 Von Meyer : " Fauna der Vorwelt." 



