82 OBSERVATIONS ON NAIADES, 



Remarks — This singularly formed Unio resembles in its exterior 

 an jinodonta, having a remarkably smooth epidermis and possessing 

 in some degree the exterior of the A. cataracta (Say). It is easily 

 distinguished from any described species. In some specimens the ar- 

 cuation of the basal margin is so great that it might almost be taken 

 for a malformation. 



Unio Glans. Plate VIII. fig. 12. 



Testa ovato-ellipticd, transversa, inaquilaterali, inflatd ; valvulis crassis ; denti- 

 bus cardinalibus subgrandibus et elevatis, lateralibus, laminatis rectisque ; marga- 

 ritd purpurea. 



Shell ovate-elliplical, transverse, inequilateral, inflated; valves thick ; cardinal 

 teeth rather large, elevated ; lateral teeth straight and laraelliform ; nacre purple. 



Hab. Ohio river, T. G. Lea. 



My Cabinet. 

 Cabinet of S. W. Conrad. 

 Diam. -7, Length -8, Breadth 1-3 inches. 



Shell ovate-elliptical, transverse, inflated ; substance of the shell 

 rather thick ; beaks somewhat prominent ; ligament small ; epidermis 

 black, or dark brown, and sometimes rayed ; cardinal teeth rather large 

 and elevated, in the left valve double and obliquely and deeply cleft, in 

 the right single, three sided, and pointed ; lateral teeth straight and lamel- 

 liform; anterior cicatrices distinct; posterior cicatrices confluent; dorsal 

 cicatrices in the centre of the cavity of the beaks ; cavity of the beaks 

 wide and subangulated ; nacre purple, except along the anterior and 

 basal margins. 



Remarks. — Although this small shell has no strikingly peculiar 

 character, it is nevertheless of a different species from any I have seen. 

 In form, it has more resemblance to U. zigzag (Nob.), than to any 

 other species, but differs altogether in the epidermis and nacre, being 

 generally destitute of rays, and having a purple nacre. 



