208 REPTILIA: TESTUDINATA, — XXX. 
Famity CXXII. EMYDIDAS. (Tue Ponp TurTLEs.) 
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. 
a, 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. . . . GRAPTEMYS, 310 (5); MALACLEMMYs, 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. . . . . . . . PseuprEmys, 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. . . . CHRyYsEMys, 313. 
dd. Carapace considerably arched; feet subequal, the toes narrowly 
webbed. . ... eee +» « . CLEmmys, 314, 
aa. Plastron with a movable tranawarge tiga | across its middle; a movable 
cartilaginous lateral suture uniting plastron with carapace. 
e. Body depressed; plastron emarginate behind; toes well webbed. 
Emypo1pEA, 315. 
ee. Body short and high; plastron rounded or truncate behind; toes 
scarcely webbed; not aquatic. . . . . TERRAPENE, 316. 
310 b. GRAPTEMYS Agassiz. (ypamros, engraved.) 
(Lower jaw with a spoon-shaped dilatation at tip.) 
a. Middle series of plates on carapace scarcely imbricated. 
608. G. geographicus (Le Sueur), Mar Turtiz. 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; 
