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MANUAL OF ZOOLOGY. 



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 

 (A. Mississippiensis), the Caiman (A . palpebrosus) of Surinam 

 and Guiana, and the " Jacare " or Spectacled Alligator (A. 

 sclerops) of Brazil. The Ga vials inhabit fresh waters, and appear 

 to be exclusively confined to the Ganges and other large rivers 

 of India. The Gangetic form (Gavialis Gangeticus], in spite of 

 its numerous pointed teeth, is not so highly carnivorous as the 

 true Crocodiles. 



Fig. 204. Skull of young Crocodiles biporcatiis (after Van cler Hoven). 



True proccelian Crocodiles occur for the first time in the 

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

 however, the earliest remains of proccelian 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 

 in their range, and are never associated together. 



Stib-order 2. Amphicoelia. The Amphiccelian Crocodiles, 

 with biconcave vertebrae, are entirely extinct. They have but 

 a limited geological range, extending only from the Lias to 

 the Chalk inclusive, and being therefore strictly Mesozoic.* 

 The biconcave vertebrae show a decided approach to the 



* If the so-called "Thecodont" Reptiles, such as Thecodontosaurits 

 and Belodon, belong to this sub-order, then the Amphicoelian Crocodilia 

 date from the age of the Triassic rocks ; as is also the case if Stagonolepis 

 be included here. 



