OBSERVATIONS. 



I obtained numerous specimens at the Falls of the Ohio, 

 on the rocky flats which are exposed in a low state of the 

 water. Its elongated form is somewhat similar to that 

 of the rectus, Lam. ; but it is much thinner, more widely 

 rounded before, and more compressed, particularly anteri- 

 orly. Its teeth distinguish it from any other species hith- 

 erto described. Old shells are very much decorticated 

 and eroded ; and in some individuals, the impressed line 

 on the lateral tooth is hardly perceptible : still it cannot 

 for one moment be mistaken for an Alasmodonta, as the 

 habit is quite different. Mr. Lesueur has presented me 

 with a specimen found in the Wabash. 



REFERENCE TO THE PLATE. 



The two views present the inner and exterior pages of the shell. 

 PLATE VL 



