444 MANUAL OF ZOOLOGY, 



dilia. The Gavial is distinguished by its elongated snout, at 

 the extremity of which the nostril is placed, and by the fact 

 that the teeth are pretty nearly equal in size and similar in 



Fig 174. — Skull of young Crocodilits biporcatits (after Van der HSven). 



form in the two jaws. In the true Crocodiles (fig. 174) the 

 fourth tooth in the lower jaw is larger than the others, and 

 forms a canine tooth, which is received into a notch excavated 

 in the side of the alveolar border of the upper jaw, so that it is 

 visible externally when the mouth is closed. In the Caimans 

 or Alligators the same tooth in the lower jaw forms a canine, 

 but it is received into a pit in the palatal surface of the upper 

 jaw, where it is entirely concealed when the mouth is shut. 

 The Crocodiles have the hind-legs bordered by a toothed 

 fringe, and the toes completely united by membrane. They 

 are essentially natives of fresh water, but sometimes frequent 

 the mouths of rivers. . They occur chiefly in Asia and Africa, 

 but species are found in some of the West Indian Islands. 

 The Alligators have the hind-legs simply rounded, and the feet 

 not completely webbed. They are essentially aquatic, and are 

 voracious animals, living upon fish or Mammals. The best- 

 known species are the Alligator of the Southern United States 

 i^A. Mississippiensis), the Caiman {A. palpebrosus) of Surinam 

 and Guiana, and the "Jacare" or Spectacled Alligator i^A. 

 sderops) of Brazil. The Gavial [Gavialis Gangeticus) is a 

 native of India, and is the smallest of the living Crocodiles, 

 attaining a length of about ten feet. 



True procoslian Crocodiles occur for the first time in the 

 Greensand (Cretaceous series) of North America. In Europe, 

 however, the earliest remains of procoelian Crocodiles are from 

 the Lower Tertiary rocks (Eocene). It is a curious fact that 

 in the Eocene rocks of the south-west of England, there occur 

 fossil remains of all the three living types of the Crocodilia — 

 namely, the Gavials, true Crocodiles, and Alligators ; though 

 at the present day these forms are all geographically restricted 

 ill their range, and are never associated together. 



