468 CHELONIANS. 



SEVENTH FAMILY. TrionycJiida, (Gr. tg^s, treis, three ; "ovv^, 

 onux, nail.) 



SOFT-SHELLED OR RIVER TORTOISES. 



These Tortoises are distinguished by the complete absence of 

 scales from the body, the shell being covered with a soft skin. 

 The feet are broad, webbed, and move horizontally ; of the toes, 

 three on each foot are provided with nails or claws, whence the 

 term Trionyx, (see derivation above.) The form is that of a flat 

 orbicular disk, slightly elongated, with a long pointed head pro- 

 jecting upon a lengthened, slender neck. The structure of these 

 animals is well adapted to life and motion in the water. They 

 swim with great facility. In this process they are aided, not by 

 their flattened and webbed feet alone, but by the loose and flex- 

 ible skin of the body, forming a narrow flap or border around the 

 edges of the shell, and performing the office of a fin. The soft 

 carapace is generally dark colored, variegated with brown ; but 

 the plastron and all the under parts are pale, like the turbot. 

 The plastron is not entirely ossified in the Trionyx proper, and 

 is united to the carapace by cartilage. These Tortoises live 

 mostly on the muddy bottom of shallow waters, burying them- 

 selves in the soft mud, leaving only the head, or a small part of 

 it exposed. Sometimes they remain under water as long as half 

 an hour, without coming to the surface to take breath. They 

 are rarely seen on land, where, to them, locomotion is labored 

 and unsteady. They lay from a dozen to twenty or more eggs, 

 of a spherical form, having a thick but brittle shell, and about 

 the size of a musket ball. 



They feed upon fish, reptiles, and mollusks, especially Ana- 

 dontas and Paludinas, fragments of which have been found in 

 their intestines. Two genera represent this family. 



(1) Gymnopus, (Gr. naked-footed,) or PlatypeUes, (Gr. plains, 

 broad ; pelte, shield ;) (2) Cryptopus, (Gr. krupto, to hide ; pous, 

 foot,) or Aspidonect.es, (Gr. aspis, shield ; nectes, a swimmer,) 

 Agassiz. The type of the genus Gymnopus, or Platypeltes, is 

 the Trionyx fer ox, the species of this country earliest known to 

 foreign naturalists. The Tryonyx ferox, or P. ferox, (Lat. 

 fierce,) is found from Georgia to Western Louisiana. Though 

 fierce, it is not very large. Agassiz says the largest tortoise 

 which he ever saw or heard of belonging to this species, was one 

 foot and a half in length. As the generic name, Platypeltes, in- 

 dicates, the carapace is broad. The great breadth of the carti- 

 laginous circumference of the carapace, and the narrowness of 



