CHAPTEE X. 



TURTLES AND TORTOISES. 



(Ghelonia.) 



S has been stated in a previous chapter, naturalists 

 place all the existing forms of turtles and tortoises 

 in an order, Chelonia, il constituting one of the groups 

 of the Class Reptilia. There are upward of 250 

 species of them known, the majority of which are fresh-water 

 types, being most numerous in tropical and sub-tropical regions, 

 where the country is well watered by ponds, rivers, lakes, and 

 marshes. Taken as an assemblage of vertebrated animals, the 

 existing forms are a well-circumscribed group, and are not rep- 

 resented by any true aberrant species. It is with the Batrachia 

 only that they can claim any affinity, as is shown by their struc- 

 ture. From all other existing reptiles they are clearly distin- 

 guished by the hard osseous shell that incases their bodies, 

 divided as it is into an upper or domed portion called the cara- 

 pace, and a ventral or Hat part, termed the plastron. Further on 

 I shall describe these structures a little more in detail. 



Chelonians have the skin of the head, neck, legs, and tail, either 

 covered with scales or tubercles, or else soft and smooth, as in 

 our soft-shelled turtles. Sometimes an osseous nucleus occurs in 

 the scales or tubercles, such as we find in Heloderma or on the 

 back of our crocodiles. 



Peculiarities of the greatest interest to the anatomist mark 

 the skeleton and other structures of these animals. A short tail 

 is always possessed by them, and this in some species may be 

 more or less elongate. Without exception, the entire order is 

 toothless, the margins of the jaws being armed with a horny 

 sheath, with cultrate edges, corresponding to the same structure 

 as we find it in hard-beaked birds, as, for example, a parrot. 



In the United States we have the Ghelonia represented by up- 

 ward of fifty species, and many subspecies. There are among 

 these the more lowly organized, paddle-footed, great marine 

 turtles, such as the Loggerhead, the Green Turtle, and the 

 Hawk's-bill. Many of these live to be of great age, and grow to 

 immense proportions, in some cases coming to weigh as much as 

 1,200 pounds, at the same time attaining a length of eight or nine 



