88 OBSERVATIONS ON NAIADES, 



parvum et simplicem in loco dentis cardinalis habente ; dentihus lateralibiis, longts. 

 rectis, et valde imperfectis ; margaritd caruleo-alba et iridescente. 



Shell narrow-elliptical, transverse, compressed, inequilateral, rounded at both 

 ends; valves thin; beaks slightly prominent; cardinal tooth a simple, small tubercle 

 in both valves ; lateral teeth long, straight and very imperfect ; nacre bluish white 

 and iridescent. 



Hab. Ohio, T. G. Lea. 



My Cabinet. 



Cabinet of Dr Hildreth, Marietta, Ohio. 



Diam. 1-1, Length 1-7, Breadth 4-3 inches. 



Shell narrow-elliptical, transverse, rounded at both ends, compressed 

 from the beaks to the basal margin over the umbones, slightly arcuated 

 on the basal margin ; posterior margin much compressed, substance of 

 the shell thin; beaks minutely undulated, slightly prominent and 

 approaching the anterior margin ; ligament long and thick ; umbones 

 and inferior parts flattened ; umbonial slope rounded and elevated ; epi- 

 dermis very dark brown and wrinkled ; cardinal tooth formed of a 

 simple small tubercle in both valves, larger in the right valve : lateral 

 teeth straight, and so imperfect as to be divided, even in the left valve, 

 only near the posterior end ; anterior cicatrices distinct ; posterior cica- 

 trices confluent ; dorsal cicatrices situated under the plate between the 

 cardinal and lateral teeth ; cavity of the beaks wide and shallow. 



Nacre bluish white and iridescent. 



Remarks. — A single specimen of this extraordinary and highly inte- 

 resting shell came into my possession in 1827. The outline and teeth 

 presented such an anomaly, that I was induced when I published my 

 other memoirs on this family to lay it aside until I could better satisfy 

 myself in regard to it. It was a very old individual, and I feared the 

 peculiar characters it presented might have been produced by malfor- 

 mation and extreme age. After two or three years of unwearied at- 

 tempts, I fortunately procured from Mr T. H. Taylor of Louisville a 

 junior and an adult specimen, both exceedingly perfect, the latter of 

 which is here represented. This proteus family seems destined to perplex 

 the zoologist and to lead him into an inexplicable labyrinth. The pre- 



