CHELONIAN KEPTILES. 397 



countenance. The strong bony scales forming their 

 coat of mail are frequently ridged, and those of 

 the tail are elevated into a deeply notched or saw- 

 like crest, which at the basal part is double. 



Frc. 331. CROCODILF. 



CHELOXIAN* REPTILES. 



The Chelonian Reptiles are distinguishable at the 

 first glance by the double buckler wherein their body 

 is enclosed, leaving only the head, neck, tail, and 

 four feet moveable. 



The upper buckler, named the carapax, or back- 

 plate, is formed by the ribs, eight pairs in number, 

 which are widened, united together, and solidly fixed 

 to the back-bone. The lower buckler, termed plas- 

 tron, or breast-plate, is formed of pieces that re- 

 present the sternum, nine in number. A framework, 



* XeAwi/rj, chelone, a tortoise. 



