34 



Raf. It is, however, more nearly allied to U. ridi- 

 hundus, of Say, and U. interncptics, of Raf.; the 

 umbones are not so broad as in the latter species, 

 and the posterior* margin descends much more 

 obliquely; none of the specimens which I found are 

 rayed; but some are nearly destitute'of the remark- 

 able ridge which resembles that of U. interrnptus. 

 No species has the lateral teeth more beautifully 

 granulated and striated. The anterior muscular 

 impression is very deep, and remarkable for pene- 

 trating under the cardinal tooth. 



Inhabits the Alabama river, near Claiborne, and is 

 rare. 



UNIOMASONI. 



Plate Y.—rig. 2. 



DESCRIPTION. 



Shell suborbicular; disks slightly flattened; umbones 

 broad, prominent, carinate behind; beaks slightly pro- 

 minent; umbonial slope straight and angulated; liga- 

 ment slope flattened, broad; epidermis olive, clouded 

 v/ith brown, polished; cardinal teeth prominent, com- 

 pressed, very oblique; within bluish white; cavity of 

 the umbo capacious. 



OBSERVATIONS. 



A small species, which is very distinct from any 

 hitherto described. I found it in the Savannah river, 

 at Augusta, in company with great numbers of U. 

 congarcmis, Lea, whh which, i)erhaps, it has more 



