206 VERTEBRATA. 



not take place in the heart itself as in other reptiles. The lungs 

 are confined to the thorax. As in the tortoises, the anal cleft is 

 longitudinal. 



This order contains the alligator (Alligator lucius), the Gan- 

 getic crocodile ( Gavialis gangeticus), and the crocodile [of the 

 .Nile] (Crocodilus vulgaris). " Cayman " and " Jacare " are the 

 names of certain Alligatoridas given by savages and imposed on 

 science. 



Of the two extinct families, Teleosauridce have amphicoelous , 

 and Stenosauridae opisthocoelous vertebrae. 



There are about twenty-three recent species, all confined to fresh 

 water. Some of the extinct forms were marine. The remains of 

 crocodiles and alligators are found in the Tertiary deposits of 

 England. 



Teleosauridce. Mecistops. Gavialis. 



*Teleosaurus Crocodiius (Croco- *Leptorhynchus. 



dile). 



Stenosaurida. Alligatorida. 



*Stenosaurus. Gavialida. Alligator (Alligator). 



' 



Tomistoma = Rhyn- - 



,-,7.7.7 , ' Jacare. 



Crocodihda. chosuchus. 



Osteolaetnus. 



*Froterosaurus. 



Order IV. ICPITHYOPTEKYGIA. 



ICHTHYOSAURIA. 



Limbs paddle-like, furnished with marginal ossicles ; the digits 

 not more than five, but with numerous phalanges. Neck very 

 short. No sacrum nor sternum. Body fish-like. 



The jaws were produced ; the nostrils were placed close to the 

 large orbits ; the teeth were lodged in grooves, not in distinct 

 sockets, and were numerous and powerful. The vertebrae were 

 amphicoelous. A vertical caudal fin is supposed to have been 

 present. 



If we except Eosaurus (from the Coal-measures of North 

 America), one genus only is known, the species of which abounded 

 during the Mesozoic period, and it is believed were very voracious. 

 They were supposed to be marine, corning occasionally to the 

 shore. Coprolites are said to be their droppings. 



* Ichthyosaurus. 



