AMPHIBIANS AND REPTILES. 203 
aa. Limbs not in form of paddles, capable of movement at wrist and ankle- 
joint; land and pond turtles. 
c. Carapace leathery, its margin flexible; no dermal plates; toes 5-5, 
claws 3-3; head small; snout pointed; body very flat. TRIONYCHID# 
cc. Carapace firm, ossified; dermal plates present; claws mostly 5-4. 
d. Fingers and toes spreading, not closely bound together, and 
more than I joint free. 
e. Tail very long and strong, crested with tubercles; plastron 
narrow and small, cross-shaped, and with 9g plates beside 
bridge; head large; body highest in front. CHELYDRIDA 
ee. Tail short, not crested; plastron broad. 
f. Lower jaw ending in long sharp point; carapace highest 
behind middle, and its edge not flaring outward; plastron 
with g or I1 plates. KINOSTERNIDA 
ff. Lower jaw without long point at symphysis; carapace 
highest about middle, and its edge flaring outward; 
plastron with 12 dermal plates. EMYDIDA 
Family DERMOCHELY D&. 
The Leather Turtles. 
Carapace with several longitudinal ridges with deep grooves 
between, completely osseous, and 7 in number in adult. Plastron 
incompletely osseous and with 5 keels. Body highest in front, 
and widest just before bridge. Head short, high and very 
broad behind. Upper jaw with 2 pits and 2 tooth-like pro- 
jections. No enlarged alveolar surface, jaws simply sharp-edged. 
E,xoskeleton consisting of mosaic-like juxtaposed plates. Skull 
without descending processes to parietals. Vertebre and ribs 
free, separated from bony exoskeleton. Plastral elements 8. No 
entoplastron. Body covered with a smooth leathery skin. Head 
covered with small shields. Limbs paddle-shaped, clawless, and 
digits of fore limb much elongated. Hind limbs much exposed. 
Phalanges without condyles. 
One genus, with a single species, widely distributed in warm 
seas, and among the largest of turtles. 
