EMYDLD.E. LXVH. 161 



/. XERO BATES, Ag. LAND TORTOISES. 



1. X. polyphemus, Daud. "GOPHER." L. 15. S. 

 States, N. to N. C.; burrows in the ground like a wood- 

 chuck. 



FAMILY LXVIL EMYDID^E. 



(T7te Pond Turtles.) 



Carapace ovate, broadest behind, the margin having a 

 tendency to flare outward, highest near the middle, 

 usually rather depressed, rarely strongly convex; plastron 

 covering the whole under surface, its plates twelve in 

 number; sometimes the anterior lobe (and rarely the 

 posterior also) movable on a transverse hinge, enabling 

 the animal to completely close the shell. Toes broadly 

 webbed in the aquatic species; scarcely webbed in the 

 others. Jaws never hooked and pointed, as in allied 

 families. They feed largely upon animals, but they 

 rarely catch active prey. They do not bite except under 

 much provocation. Species seventy or eighty, widely 

 distributed, inhabiting marshes, ponds, and the shores of 

 still streams; a few are strictly terrestrial. 

 * Carapace short, very high and strongly convex; plastron united 

 to the carapace by a more or less cartilaginous suture and 

 divided by a transverse hinge into two or more movable 

 pieces ; the anterior one, the smaller ; toes scarcely webbed ; 



terrestrial CISTUDO, 1. 



** Carapace somewhat elongated, considerably arched ; plastron 

 immovable ; toes short, with a small web ; feet more nearly 

 equal, and habits less aquatic than in the succeeding groups; 

 species of small size. 



a. Shell more or less carinatecl, without round spots; upper jaw 



deeply notched and arched downward. . CHELOPUS, 2. 



aa. Shell not carinated, black, usually with round, yellowish 



spots ; upper jaw slightly notched, its edges nearly straight. 



NANEMYS, 3. 



