208 RBPTILIA: TESTUDINATA. — XXX. 



Family CXXII. BMYDIDJE. (The Pond Tuktles.) 



Carapace ovate, broadest behind, the margin having a tendency 

 to flare outward, highest near the middle and usually not 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 com- 

 pletely close the shell. Toes broadly webbed in the aquatic species ; 

 scarcely webbed in the others. The pond turtles feed largely upon 

 animals, but they rarely catch active prey. Most of them will not 

 bite except under much provocation. Species about 80, widely dis- 

 tributed, inhabiting marshes, ponds, and the shores of still streams ; 

 a few are strictly terrestrial. 



M. Plastron without hinge, immovably joined to carapace. 



6. Alveolar surface of jaws broad ; carapace depressed ; toes short, broadly 



webbed. 



c. Alveolar surface of jaws smooth, a deep groove in front; upper jaw 



not notched in front; head covered with soft skin; carapace more or 



less keeled. . . . Graptbmys, 310 (6); Malaclbmmys, 311. 



cc. Alveolar surface of upper jaw divided by a longitudinal ridge parallel 



to margin ; upper jaw notched in front; head with thin hard skin ; 



carapace scarcely keeled Psehdkmys, 312. 



hb. Alveolar surface of jaws narrow. 



d. Carapace depressed (never keeled) ; toes strong, broadly webbed, the 



hind feet largest; alveolar groove of jaws well marked, except in 



front; upper jaw notched in front. . . . Chrtsemys, 313. 



dd. Carapace considerably arched; feet subequal, the toes narrowly 



webbed Clemmys, 311. 



aa. Plastron with a movable transverse hinge across its middle; a movable 

 cartilaginous lateral suture uniting plastron with carapace. 

 e. Body depressed ; plastron emarginate behind ; toes well webbed. 



Emtdoidba, 315. 



«e. Body short and high ; plastron rounded or truncate behind ; toes 



scarcely webbed ; not aquatic Tebeapeme, 316. 



310 b. GRAPTEMYS Agassiz. {ypmrros, engraved.) 

 (Lower jaw with a spoon-shaped dilatation at tip.) 

 a. Middle series of plates on carapace scarcely imbricated. 



608. G. geographicuB (Le Sueur). Map Turtle. Dark 

 olive brown with greenish and yellow streaks and reticulations, 

 especially distinct on neck, legs, and edges of carapace ; plastron 

 yellowish ; carapace strongly notched behind and usually decidedly 

 keeled. Miss. Valley, E. to N. Y., common W. 



aa. Middle series of dorsal plates distinctly imbricated. 



609. G. pseudogeographicus (Holbr.). Similar but grayer, 

 the markings on the shell paler, less distinct and in larger pattern ; 



