46 ON THE NAIADES, 



Anodonta incerta. Plate VI. fig. 16. 



Testa lato-cllipticd, postice subangiilatd, inflatci, margine dorsali subrcctd ; val- 

 vulis tenuissimis ; epidermidc suhviridc, obsolete radiatu ; natibus complanatis et . 

 minute undulatis; cicatricibus vix cernendis ; margaritdcceruleo-albu et iridescente. 



Shell wide-elliptica!, subangular behind, inflated, nearly straight on the dorsal mar- 

 gin ; valves very thin ; epidermis greenish with obsolete rays, beaks flattened and 

 minutely undulated ; cicatrices scarcely perceptible ; nacre bluish white and iridescent. 



Hab. Ohio River near Cincinnati. T. G. Lea. 



My Cabinet. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Cabinet of Professor Vanuxem. 

 Cabinet of P. H. Nicklin. 

 Diam. 1-2, Length 1-5, Breadth 3-2 inches. 



Shell wide-elliptical, subangular behind, inequilateral, inflated, dor- 

 sal margin nearly straight, rounded before ; substance of the shell very 

 thin; epidermis very smooth, green and olive green with obsolete 

 rays, three being more distinct on the posterior part of each valve ; lig- 

 ament long and thin; beaks flattened, minutely undulated near the 

 tip which terminates with a minute point from which an indistinct 

 line runs towards the posterior margin ; cicatrices scarcely perceptible ; 

 cavity of the beaks scarcely perceptible ; cavity of the disk deep and 

 I'ounded ; nacre bluish white and iridescent. 



Remarks. — Among the earliest shells I procured from the Ohio, 

 many years since, were several specimens of this fragile Anodonta. 

 The difficulty of separating the species of a genus with so few tangible 

 characters induced me to lay this aside with some other species until 

 more leisure would permit a thorough examination. It perhaps most * 

 closely resembles the A. catarada of Say, but differs from it peculiarly 

 in the flatness of the beaks. It is generally more inflated, particu- 

 larly near the umbonial slope. It resembles the A. Ferussaciana (nobis), 

 the description of which see. The young differ from the old in being 

 much compressed and in having rays only on the posterior part of the 

 shell, where the three on each valve are distinctly visible — they are 



