28 



It certainly approaches U. niger, Raf.; the young of 

 the latter resembling it so much, as to lead to the 

 inference that they may be varieties of one species, 

 occasioned by difference of locality. Specimens from 

 Augusta resemble the niger more than those from the 

 Congaree river; and in Flint river, Georgia, is a va- 

 riety of the latter, differing only from the congarceus 

 in being rather larger and more ponderous. 



UNIO MASONI. 



Plate XII.— Fig. 2. 



DESCRIPTION. 



Shell suboval, thin; umbones broad, inflated, disks 

 slightly flattened near the umbonial slope; beaks dis- 

 tant from the anterior margin; ligament margin ele- 

 vated; umbonial slope angulated; epidermis oliva- 

 ceous, polished, wrinkled inferiorly; summits decor- 

 ticated; within white, cardinal teeth oblique, rather 

 thick. 



SYNONYME. 



U. masoni, Nob. New fresh water shells, p. 34. pi. 5. fig. 2. 

 Cab. A. N. S. No. 2100. 



OBSERVATIONS. 



Inhabits Savannah river, at Augusta. When the 

 description was originally published, I had seen only 



