CIti K'O] (ILIA 



273 



in length, are referred to the Oebiosaurus hmyus. The latter 

 must have been the most gigantic whale-like of Crocodilian^. 



Sub-Order 3. — PEOCCELIA* 



The best and most readily recognizable characters by which 

 the existing Croeodilians are grouped in appropriate genera 

 are derived from modifications of the dental system. 



In the caimans (genus Alligator) the teeth vary in number 

 from {|5^ to ||jj|| ; the fourth tooth of the lower jaw or canine, 

 is received into a cavity of the palatal surface of the upper jaw, 

 where it is concealed when the mouth is shut ; in old indi- 

 viduals the upper jaw is perforated \>y these 

 large inferior canines, and the fossae are con- 

 verted into foramina. 



In the true crocodiles (genus Crocodilus) 

 the first tooth in the lower jaw perforates the 

 palatal process of the intermaxillary bone 

 when the mouth is closed ; the fourth tooth 

 in the lower jaw is received into a notch exca- 

 vated in the side of the alveolar border of the 

 upper jaw, and is visible externally when the 

 mouth is closed. 



In the two preceding genera the alveolar 

 borders of the jaws have an uneven or wavy 

 contour, and the teeth are of unequal size. 



In the gavials (genus Gavicdis) the teeth 

 are nearly equal in size and similar in form 

 in both jaws, and the first as well as the Teeth of the Gavial. 

 fourth tooth in the lower jaw passes into a groove in the 

 margin of the upper jaw, when the mouth is closed. 



The number of teeth is always greater in the gavials than 

 in the crocodiles or alligators. The first five pairs of teeth 



* Pros, front ; koilox, hollow; vertebra with tlio cup at the fore part and the 

 ill behind. 



