158 ON THE NAIADES, 



Anodonta incerta, Plate VI. fig. 16. 



Testa lato-ellipticd, postice subangulatd, inflatd, margine dorsali subrectd ; val- 

 vulis tenuissimis ; epidermide subviride, obsolete radiatu ; natibus complanatis et 

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



Shell wide-elliptical, 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 

 rounded; 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. cutarada 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 



