23 



border undulated ; epidermis brown ; nacre bluish. 

 Length | diam. f axis of the breadth. 



This species is rare and very distinct ; I have 

 found it at the rapids of the Ohio; breadth one inch 

 and an half. The cardinal tooth small and tuber- 

 cular ; lamellar tooth narrow and curved ; mus- 

 cular impressions slightly apparent; marginal 

 contour somewhat thickened, undulated, and 

 eroded. 



Third Sub-genus AXIMEDIA. 



Lamellar tooth slightly curved; axis nearly 

 medial ; valves almost equilateral. 



SPECIES VIII. Unio elliptica (Elliptio elliptica. ) 



Shell elliptical, angular posteriorly, thick, al- 

 most smooth ; epidermis chestnut brown ; nacre 

 pale violaceous ; cardinal tooth wrinkled, ob- 

 tuse ; lamellar tooth obtuse, thick. Length 

 diam. f axis T 7 F of the breadth. 



This shell is also rare, found near Louisville 

 and Maysville, K. Breadth about two inches >' 

 muscular impressions deep ; valves slightly ven- 

 tricose ; apices prominent, very obtuse. 



