AMPHIBIANS AND REPTILES. 219 
Family KINOSTERNID. 
The Musk ‘Turtles. 
Carapace rather long and narrow, outline usually rising gradu- 
ally from front to a point beyond center of shell, then abruptly 
descending, and bulk of body therefore thrown backward. Mar- 
gin of carapace turning downward and inward rather than out- 
ward. Plastron proportionately large, covered with horny plates, 
anterior pair coalescing into 1. Anterior and also sometimes pos- 
terior lobe of plastron, often movable upon fixed central portion. 
Shell covered with epidermal plates. Head pointed. Neck com- 
pletely retractile within shell, and bending by a sigmoid curve in 
a vertical plane. Eyes far forward. Jaws usually strong. Parie- 
tals prolonged downwards, forming a suture with pterygoids, or 
separated from latter by interposition of epipterygoid. No 
parieto-squamosal arch, squamosal widely separated from parie- 
tal. Pterygoids narrow in middle, in contact on median line. 
Temporal region not roofed over. Mandible with articulary con- 
cavities. Outer border of tympanic cavity deeply notched. 
Nuchal plate reduced to costiform processes underlying mar- 
ginals. A complete series of marginal bones connected with 
ribs. Dorsal vertebrze and ribs immovably united and expanded 
into bony plates forming carapace. Cervical vertebrae without 
or with mere indications of transverse processes, and centrum of 
last articulating with centrum of first dorsal. Caudal vertebra 
proceelous. Plastral bones 8, entoplastron absent, and epiplastra 
in contact with hyoplastra. Pubic and ischial symphyses in con- 
tact, separating 2 foramens, and pelvis not anchylosed to cara- 
pace and plastron. Digits with not more than 3 phalanges, which 
are furnished with condyles. Limbs slender, feet short, and 
claws 4 or 5. 
Small turtles mostly in tropical and temperate America. Two 
genera in our limits. 
Key to the genera. 
a. Carapace without traces of median keel in adult; head moderate; plastron 
with anterior and posterior lobes nearly equal in length, both freely 
movable and capable of closing shell; posterior lobe emarginate behind, 
its angles rounded. KINOSTERNON 
