118 OBSERVATIONS ON NAIADES, 



cicatrices situated on the under side of the cardinal teeth; cavity 

 of the beaks deep and angulated : nacre pearly white and iridescent. 



Remarks. — Among the numerous shells I have received within the 

 last five years from our western waters, I have obtained but three or 

 four of this interesting species. Its extreme rarity at first induced me 

 to doubt of the propriety of considering it a distinct species. It is 

 however, perfectly distinct from any described species and seems pe- 

 culiar in its yellow beaks and brown margin ; as well as in the beauti- 

 ful interrupted rays which pass over the umbones, leaving the ante- 

 rior and posterior slopes usually of a yellow colour. In form it 

 approaches the ebenus (Nobis), in colour it more nearly resembles 

 the unilatus (Barnes). A young individual of not more than three 

 growths presents such a shining and yellow epidermis as to resemble 

 very much a small Venus. 



Unio Subovatus. Plate XVIII. fig. 46 



&• 



Testa subovatd, transversa, inflatd ; valvulis crassis ; natihus prominentibus et 

 apicibus undulatis ; multis radiis viridibus; dentibus cardinalibus erectis et in 

 valvuid utrdque duplicibus, lateralibus laminatis brevibusque; margaritd albd. 



- Shell subovate, transverse, inflated ; valves thick ; beaks elevated and undulated 

 at the tip ; rays green and numerous ; cardinal teeth double in both valves and erect; 

 lateral teeth short and lamelliform; nacre white and very pearly. 



Hab. Ohio river, T. G. Lea. 



My Cabinet. 

 Cabinet of John Ronaldson. 

 Cabinet of the Academy of Natural Sciences. 

 Diam. 2-2, Length 3, Breadth 4-2 inches. 



Shell subovate, transverse, inequilateral, inflated ; substance of the 

 shell thick ; beaks elevated, incurved and undulated at the tips ; liga- 

 ment short and thick j epidermis yellowish with numerous green rays 



