Dr. Hildreth on fresh water Shells 289 



been but partial, I have no doubt, of being able to add a nun> 

 ber more to my collection. 



Alasmodonta. 



Generic Character. 



Shell, transverse, equivalve, inequilateral, free ; beaks, de- 

 corticated ; posterior muscular impression, compound 

 hinge, with prominent cardinal teeth in each valve, but with- 

 out lateral teeth. 



No. 24. Alasmodonta Uugosa. — Fig. 24. 



Length, 2.25 ; breadth, 4.10 ; diameter, 1.20. — Hab. Lit- 

 tle Muskingum. 



Shell, oblong oval, about equally broad, before and be- 

 hind ; beaks, very slightly elevated, wrinkled and decortica- 

 ted, wax color beneath ; ligament, external, and rather high- 

 er than the beaks ; anterior lunule, distinct, with a slightly 

 elevated ridge, extending from the beaks to the anterior ba- 

 sal margin; basal margin, a little shortened, or nearly strait, 

 the other margins rounded ; epidermis, ehesnut brown, with 

 a silky luster ; surface of the anterior part folded in a pinnate 

 form ; folds deeper and larger as they approach the anterior 

 basal margin ; curved upwards, and extending to the hinge, 

 indenting the edge, and appearing on the inside ; teeth large 

 and elevated, having in some specimens, a curved appear- 

 ance ; cicatrices, smooth ; cavity, small ; naker, pale flesh 

 colored in the center, pearly on the margin, with a nar- 

 row border of dark chocolate ; surface, glossy, with a rich 

 blue tinge, over the fimbriated portion of the shell. 



Remarks. — I have several specimens of this shell, young 

 and old — in some, the teeth are much deformed, but the 

 valves are equal and uniform. 



No. 25. Alasmodonta Complanata. — Pig. 25. 



Shell, ovately quadrangular ; hinge margin, elevated into 

 a large wing ; valves, connate ; ligament, concealed ; wing, 

 pinnate. 



Length, 4.75 ; breadth, 5.9 ; diameter, 1.75. — Hab. Duck 

 Creek. 



Shell, short behind ; disks, much flattened ; beaks, slight- 

 ly projecting ; ligament, between the valves ; anterior lunule, 

 much compressed, and folded across the traverse wrinkles -. 



Vol. XIV.— No. 2. 11 



