22 CHELYDRID®. 
halfgrown, becoming gradually smoother with age. Vertebral 
shields much broader than long, at least three fourths the width of 
the costals. Plastron with angular lobes; bridge very narrow, 
somewhat variable in width, but never more than one tenth of the 
length of the plastron *; the hypoplastral bones enter for a much 
greater part in the formation of the bridge than the hyoplastra, the 
outer, digitate portion of which is scarcely expanded. A series of 
two or three inframarginals separates the marginals from the abdo- 
minal, the transverse diameter of which equals at least twice the 
LOE CEG 
+ 
Shell of Chelydra serpentina. 
longitudinal. Snout short and pointed; interorbital space narrow. 
Skin very warty; a pair of very small barbels on the chin. Tail 
nearly as long as, or longer than, the carapace in the young, two 
thirds or three fourths that length in the halfgrown and adult; a 
strong crest of large compressed tubercles along its upper surface ; 
a series of large divided scutes along its lower surface. 
* From what is known to be the case in Staurotypus, we may conclude that 
the specimens with broader bridge are females. 
