174 CHORDATA. 



The following two groups are included under the name of Hydro- 

 s a u r i a (large aquatic forms with teeth firmly implanted in the jaw, 

 feet-modified for swimming and strong or armoured skin). 



Order 4. Enaliosauria, with naked leathery skin, paddles, and 

 biconcave vertebrae (all from the Secondary period). Nothosaurus. 

 Plesiosaurus dolichodeirus. Ichthyosaurus communis. 



Order 5. Crocodilia, with a long tail, webbed feet, scales, and scutes. 

 Teeth in sockets, ventricle completely divided, longitudinal cloacal 

 aperture and solid grooved penis. Teleosaurus, Jurassic, amphicoelous 

 vertebrae. Steneosaurus, Jurassic and Cretaceous, vertebras opisthocoe- 

 lous. Procoelous vertebrae from the Cretaceous on : Alligator lucius 

 and Caiman in America, Crocodilus vulgaris in the Nile. Gavialis 

 gaugeticus. 



Order 6. Chelonia, with bony dorsal and ventral dermal shields ; 

 edentulous ; a urinary bladder and solid grooved penis. Chelone midas, 

 edible turtle. Trionyx. Cistudo (Emys) Europsea, Emys caspica. 

 Testudo Grseca, land tortoise. 



Order 7. Dinosauria. Fossil forms which possessed more than two 

 sacral vertebras, and were in many respects, especially as regards the 

 pelvis and hind limb, intermediate between Eeptiles and Birds. Igu- 

 anodon. Megalosaurus Bucklandi (Jurassic and Wealden). Also 

 Dicynodon in the Trias. 



