176 UNI VALVE 8HELLS 



Very common at the Falls of the Ohio River. It 

 is probably the largest species of this genus in the 

 United States, and may be readily distinguished from 

 its congeners by its broad groove. 



2. M. *elevata. Shell gradually attenuating to 

 the apex, slightly and irregularly wrinkled, oliva- 

 ceous ; suture not deeply impressed ; volutions nine 

 or ten, with several more or less elevated revolving 

 lines, of which one being more conspicuous gives the 

 shell a carinated appearance ; aperture oblique, 

 equalling the length of the second, third, and fourth 

 volutions conjunctly. 



Length one inch. 



Breadth two-fifths. 



Inhabits Ohio River. 



Distinct from our other species, by the elevated re- 

 volving lines. 



3. M. *conica. Shell conic, rapidly attenuating 

 to an acute apex, very slightly wrinkled, olivaceous ; 

 suture not deeply impressed ; volutions seven or 

 eight ; aperture oblique, equalling the length of the 

 second, third, and fourth whirls conjunctly. 



Var. a. With from one to three, revolving, rufus 

 or blackish lines. 



Length nearly 3-5 inch. 



Of the aperture 1-4 inch. 



Inhabits Ohio River. 



May be readily distinguished from M* virgvmca 



