208 REITILIA : TF:STUDINATA. — XXX. 



Family CXXII. EMYDID^. (Thk Ponp Turtles.) 



Caraj)ac-e oviito, broadu.**! iR-liintl, tlu> mar<iin havinji^ a U-ndi'iicy 

 to Hare outward. lii;:;lu'st lu-ar tlu' middle and usually not stroiij^ly 

 conve.\ ; j)lastron loviriii;: the whole under suriaee, its plates twelve 

 in number; sometimes the anterior lobe (and rarely the ])osterior 

 also) movable on a transverse hin^e, enaldin^ tin- animal to eom- 

 pletely elose the shell. Toes broadly webbi-d in the aijuatie sjieeies; 

 scarcely webbed in the others. The pond turtles feed lar^'ely upon 

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

 bite except under ranch jjrovocation. Species about 80, widely dis- 

 tribute<l, inhabitinj; marshes, ponds, and the shores of still streams ; 

 a few are strictly terrestrial. 



a. Plastron without hinge, immovably joined to carapace. 



b. 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. . . . Graptkmys, .110 ('<); Malacurmmys, 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 Pskl'dkmys, 312. 



bb. 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. . . . Chryskmys, 313. 



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



webbed Clkmmvs. 314. 



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

 cartilaginous lateral suture uniting i)lastron with carapace. 



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



Kmydoipka, 315. 



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



scarcely webbed ; not aquatic Tekkai-exk, 316. 



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

 (I^wer jaw with a spoon-shaped dilatation at tip.) 

 o. Middle series of plates on carapace scarcely imbricated. 



608. Q. geographicus (Le Sueur). Map Turtlk. Dark 

 olive brown with greenish and yellow streaks and reticulations, 

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

 yellowish; caraj)ace strongly notched behind and usually decidedly 

 keeled. Miss. Valley, K. to N. Y., common \V. 



aa. Middle series of dorsal plates distinctly imbricated. 

 Co;). G. pseudogeographicuB (Molbr.). Similar but grayer, 

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



