49 



OBSERVATIONS. 



I formerly supposed this shell a variety of myti- 

 loides, but the differences are so constant in a great 

 number of specimens, that it may be useful to intro- 

 duce it to conchologists by the name which Rafinesque 

 has bestowed upon it. It differs from mytiloides in 

 not being oblique, in being about as long as it is high, 

 in having the beaks distant from the anterior margin, 

 and never in any stage of growth having the poste- 

 rior side prolonged obliquely downwards. 



Inhabits the Ohio and its tributaries. The speci- 

 men figured belongs to the cabinet of Mr. Feather- 

 stonhaugh, and is from Cumberland river, Tennessee. 

 It connects U. mytiloides with 77. imdatus. 



UNIO NIGER. 



Plate XXVI. 



DESCRIPTION. 



Shell elliptical; with age, subovate, or subtriangu- 

 lar; thick and ponderous; disks somewhat flattened; 

 posterior lunule with short, oblique, vermicular raised 

 lines; posterior side compressed, cuneiform; umbo 

 broad, flattened, summit obtusely rounded; umbonial 

 slope angulated; epidermis reddish-brown, frequently 

 rayed; within purple or salmon colour; cardinal teeth 

 direct, prominent; lateral teeth thick, distant from 

 the cardinal teeth; posterior muscular impression 

 slightly impressed; cavity of the beak shallow. 



G 



