Reptilia. 205 



DIFFERENCES BETWEEN A SNAKE AND A "GLASS 



SNAKE." 

 SNAKE. GLASS SNAKE. 



No lids ........ Eyes Movable lids 



Dilatable Mouth Not dilatable 



Extensible Tongue . . '. . . Not extensible 



Invisible externally Ear Visible externally 



Broad plates Ventral scales Small 



Short, strong Tail Long, brittle 



Absent Lateral groove Present 



THE TURTLES. 



General Characters of Turtles. In turtles the relatively 

 short and broad body is inclosed between two bony shields, 

 the dorsal one being called the carapace, and the ventral, 

 the plastron. The carapace is made up of (i) the widened 

 spines of the thoracic vertebrae, (2) the ribs, which have 

 widened and grown together, and (3) a series of. marginal 

 plates. There is no breastbone, but the plastron is made 

 of a set of bony plates. Both carapace and plastron are 

 covered by a set of horny, epidermal scales which do not 

 coincide with the underlying bony plates. The "tortoise 

 shell " of commerce is made of the epidermal plates of the 

 big sea turtle known as the hawkbill turtle. 



There are no teeth, but instead the jaws are horny. The 

 neck and tail are the only movable parts of the spinal 

 column, and these, with the legs, can be withdrawn so as 

 to be protected by the shell. In the boxshell turtle there 

 is a hinge in the plastron to make the protection more 

 complete by closing the shell. The sea turtles have pad- 

 dles, while the land turtles have feet, with more or less 

 distinct toes. Some of the sea turtles weigh as high as a 

 thousand pounds. The green turtles, so valued for soup, 

 are caught in the West Indies at night, when they come 



