CLASS OF EEPTILES. 



363 



Eeptiles are divided into three orders : chelonian, saurian, 

 and ophidian. 



The chelonian (tortoise and turtle) have four limbs ; the 

 skin covered with large scales ; the mouth without teeth ; 



Fig. 364. The Agama ; a kind of Lizard. 



the jaws provided with a horny bill or covering ; the ribs 

 immovable, and in them we find the horny dorsal and ven- 

 tral plates called carapace and plastron, already described. 



Fig. 365. Crotalus, or Eattlesnake. 



The saurian or lizard-shaped reptiles, and the ophidians or 

 serpents, have the ribs and dorsal vertebrae moveable ; a scaly 

 skin ; and teeth. The two orders run into each other, but 

 it is generally agreed on to call those with limbs saurian, and 



