84 OBSERVATIONS ON NAIADES, 



and imperfect specimen of this shell when I described the donadfor- 

 mis, and I presumed it to be merely a variety of that shell. Subse- 

 quently, my attention being draw^n particularly to it, I procured some 

 of all the different growths, and among them the beautiful specimen 

 now figured, which is the only one I have seen of a pink colour. On 

 an examination of these, I could no longer doubt of its being distinct ; 

 but some doubts have arisen in my mind whether the donadformis 

 may not be a variety of the U. zigzag (Nob.). The specimen des- 

 cribed as donadformis is a very fine and perfect one, and if it be a true 

 species is the only one I have seen. Among the numerous specimens 

 of zigzag which I have examined, none have had those perfect and 

 beautifully pointed beaks of the donadformis; should future specimens 

 fully establish the donadformis, its natural place will be between the 

 zigzag and the present described species. These observations it is 

 hoped will draw the attention of conchologists to this species, with 

 the expectation of being able, by examining many specimens, to decide 

 upon the question. 



Unio Ebenus. Plate IX. fig. 14. 



Testa subellipticd, oblique recurvd, inaquilaterali, ventricosd ; valvulis o'assis ; 

 natibus prorrdnentibus et subterminalibus ; epidermide nigro-fuscd, sed post nates 

 luted; dentibus cardinalibus magnis, lateralibus magnis curvisque; margaritd 

 alba. 



Shell subelliplical, obliquely recurved, inequilateral, ventricose ; valves thick ; 

 beaks elevated and nearly terminal ; epidermis blackish brown, behind the beaks 

 yellow ; cardinal teeth large ; lateral teeth large and curved ; nacre pearly white. 



Hab. Ohio river, T. G. Lea. 



My Cabinet. 



Cabinet of Professor Vanuxem. 



Cabinet of P. H. Nicklin. 



Diam. 1-1, Length 1-5, Breadth 1-6 inches. 



Shell subelliptical, obliquely recurved, inequilateral, very ventricose ; 



