114 TRIONYX. 
the latter from side to side was about six lines and a half; and from without inward 
it measures five lines. 
I have also had the opportunity of-inspecting a fragment of a costal plate of a 
Trionyx, about the size of that to which the specimens just described belonged, 
from the Cretaceous formation near Columbus, Mississippi, whence it was obtained 
by Dr. Spillman. The surface, however, is not so deeply pitted as in the costal 
fragments above described, nor are the ridges separating the pits so coarse. It 
probably indicates a different species. 
