74 OBSERVATIONS ON NAIADES, 



parvis et imperfedis, lateralibus imperfedis et indivisis ; margaritd cmruleo-alba, 

 iridescente, et in natium cavo purpurea. 



Shell long-ovate, transverse, inequilateral, compressed and beautifully rayed ; 

 valves thin ; beaks scarcely prominent and retuse; cardinal teeth small and imper- 

 fect ; lateral teeth imperfect and divided ; nacre bluish white, iridescent and purple 

 in the cavity of the beaks. 



Hab. Ohio river, T. G. Lea. 



My Cabinet. 

 Cabinet of R. Peter, Pittsburgh. 

 Cabinet of Dr Hildreth, Marietta, Ohio. 

 Diam. -5, Length 1-1, Breadth 2-8 inches. 



Shell long-ovate, transverse, compressed; substance of the shell very 

 thin ; beaks scarcely prominent, and situated towards the anterior mar- 

 gin ; ligament linear ; epidermis slightly wrinkled, yellowish, with ob- 

 lique interrupted green rays, which enlarge posteriorly ; cardinal teeth 

 very imperfect; lateral teeth straight, very imperfect, (having little or 

 no longitudinal division, even in the left valve) enlarged at posterior 

 termination ; anterior cicatrices distinct ; posterior cicatrices confluent ; 

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

 of the beaks wide and very shallow ; nacre bluish white, iridescent, 

 purple in the cavity of the beaks. 



Remarks. — The specimen which is here described and figured, was 

 sent to me three or four years since, and has never ceased to excite in 

 me great interest and attention. The very imperfect state of the 

 teeth compelled me to doubt of the propriety of erecting it into a 

 new species, although the specimen^bore no appearance of a malforma- 

 tion in any other part, however different it was from other species of 

 the family I had seen. Two other specimens, one of which is young, 

 having recently come into my possession, prove to possess precisely the 

 same characters in every respect, and the only difficulty which now 

 stood in the way of giving it a place in our systems was to determine 

 its genus ! It appears to me, for the present, most proper to place it 

 with the Uniones. It cannot be placed with the Anodonta of Lam. for 

 he describes that genus as having "cardo linearis edentulus." It 

 would be equally difficult to class it with the Masmodonta of Say, for 



