TRIONYCID^E ; CHELONID^E. 551 



mandibles, from which habit it is sometimes designated as the 

 '* Snapping Turtle." It cannot be safely approached even by 

 Man. 



488. The two other families of this order are exclusively 

 aquatic ; coming on shore only to deposit their eggs, and doing 

 this stealthily by night. In the TRIONYCID^E, or River Tortoises, 

 however, the structure of the feet does not depart so widely from 

 the forms of the preceding families, as it does in the Turtles ; 

 for although the toes are connected by a web, and only three of 

 them are furnished with claws, they are still distinguishable. 

 Like the Emydse, these Tortoises are exclusively carnivorous ; 

 and they eat their food in the water. They subsist upon Fishes, 

 Reptiles, Birds, &c., at which they dart out from their hiding- 

 places, launching out their long necks and snapping at their 

 prey with great energy and rapidity. The edges of their man- 

 dibles are so sharp and firm, that they can readily bite off a 

 man's finger. The carapace has only a centre of bone, the cir- 

 cumference being cartilaginous ; and the plastron is not osseous 

 throughout. The skin, too, is destitute of scales. Hence these 

 animals are sometimes called Soft Tortoises. No species of this 

 family is European ; but almost every large river and lake, in 

 the warmer regions of the Old and New World, is inhabited by 

 them. They are particularly numerous in the Ganges ; where 

 they prey, with the Gavials, on the human bodies which are 

 always floating in that stream. The Marine Tortoises, CHELO- 

 NID^E, OT Turtles, are at once distinguished by the compressed and 

 paddle-like form of the feet ; of these, the anterior pair is most 

 developed ; and they are used as oars, or rather as aquatic 

 wings ; by means of which these animals can move through the 

 water in any direction, with considerable rapidity and address. 

 This conformation, however, renders their progression on land so 

 much the more difficult ; they can only shuffle along at a slow 

 rate and with laborious efforts ; and, from the flattened form of 

 their carapace, they are unable to recover their natural position, 

 when turned upon their backs upon a flat surface. The jaws of 

 the Turtles are robust ; and the upper mandible is received into 

 a groove in the lower, so that their grasp is very firm. Most 



