114 TRIONYX. 



tlie latter from side to side was about six lines and a half ; and from without mward 

 it measures five lines. 



I ha-\'e also had the opportunity of inspecting a fragment of a costal plate of a 

 Trw)ujx, 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 aboA'c described, nor are the ridges separating the pits so coarse. It 

 probably indicates a different species. , 



