NORTH AMERICAN BATRACIIIA AND REPTILIA. 
53 
b. Eyes superior, rather close together; alveolar plate 
narrow; a small pointed projection at symphysis 
of jaws; no scales between the costal and marginal 
rows Ohelydra. 
Genus Chelydra, Schw. 
103. O. serpentina, Linn. Common Snapping Turtle. Head 
rough, covered with soft skin; tail with two rows of large scales 
beneath; ridges of carapace disappearing with age; jaws moder- 
ately hooked. Throughout the United States, except Pacific 
sub-region. 
Genus Macrochelys, Gray. 
101. M. lacertina, Schw. Alligator Snapper. * Head very 
large, covered with smooth, symmetrical plates; tail with many 
small, imbricate scales beneath; carapace strongly tri-carinate; 
the keels not disappearing with age; jaws strongly hooked. 
South of Missouri river, in tributaries to the Mississippi and 
Gulf of Mexico; north to Wisconsin.* Rare. 
Family CIHOSTERNIUMC. 
Head pointed in front; eyes situated far forward; lower jaw 
terminating in a sharp point; limbs slender; feet short. 
a. Plastron small, narrow behind, with eleven scales; 
front and hind portions very little, if at all, mov- 
able on middle Aromochelys. 
b. Plastron larger; front and hind portions broad and 
rounded, freely movable on middle part (except 
often in old specimens); scales 8 to 11. Alveolar 
plate flat and rather broad Cinosternum. 
Genus Aromochelys, Gray. 
105. A. odoratus , Latr. Musk Turtle. Ho point at sym- 
physis of upper jaw; the end of lower curved somewhat upward 
and outward; scales of carapace not imbricated in adult; shell 
dusky, clouded, sometimes spotted; two yellow stripes, one 
above, the other below the eye, extending along the neck. Aus- 
troriparian and Eastern sub-regions. 
106. A. carinatus , Gray. Little Musk Turtle. A point or 
chisel edge at symphysis of upper jaw; scales of keel somewhat 
*Fide Dr. P. R. Hoy. 
