98 REPTILIAN WATER TRESPASSERS. 



The contrast between the tooth of the Crocodile and 

 that of the tiger is very curious. In point of dimen- 

 sions they are about the same, but in their shape and 

 weight are very different : the tiger's tooth being solid, 

 heavy, and flattened, with a distinct knife-like edge on 

 the inner curve, while the Crocodile's tooth is hollow, 

 light, and rounded. 



These teeth are set in hollows in the jaw, and not 

 consolidated with the bones of the skull. Consequently, 

 they are easily removed, and, indeed, in dried skulls 

 the teeth are always liable to fall out, owing to the 

 shrinking of the soft material of the socket. It is 

 evident, therefore, that the number of teeth must 

 be extremely variable. In my collection there is a 

 skull of the great Gangetic Crocodile, or Gavial, a huge 

 reptile which sometimes attains the length of twenty- 

 five feet. It has a very long and narrow head. My 

 specimen belonged to a young animal, and the skull 

 measures only twenty-six inches in length ; yet, in the 

 middle, the diameter of the skull is only one inch and 

 three-quarters. Many of the teeth have fallen from the 

 sockets, but some still remain, so that their size and shape 

 can be understood. In the lower jaw there are twenty- 

 five teeth on each side, and in the upper jaw twenty- 

 nine, making a complement of one hundred and eight. 

 A figure of the African Crocodile is given in the 

 upper portion of Plate II. 



Another curious group of water-trespassers is to be 

 found in the marine and aquatic members of the 

 Tortoise tribe, some of which are vegetarians and others 

 carnivorous. 



