290 Dr. Hildreth oh fresh water Shells. 



hinge margin, elevated into a large wing, which is pinnated, 

 or folded ; forming an obtuse angle with the post dorsal mar- 

 gin ; basal margin, rounded ; anterior dorsal, arcuated ; an- 

 terior margin, truncate ; posterior, rounded ; epidermis, dark 

 brown, with a tinge of red below the beaks ; surface, wrink- 

 led ; slightly elevated ridges and furrows extending from the 

 beaks, to the anterior margin ; teeth, elevated, sulcated, and 

 radiating from the beaks ; cicatrices, smooth ; cavity, small 

 and angular ; naker, bluish white, and iridescent on the fore- 

 part, with a border of rich reddish brown, on the margin. 



Remarks. — I have several-specimens of this shell, in all of 

 which the wing is folded, in some, very beautifully — gener- 

 ally found in ripples, or rapid water, and rocky bottom. 



Genus Anodonta. 



Generic Character. 



Shell transverse, with three obsolete muscular impressions, 

 hinge simple ; destitute of teeth. 



No. 26 Anodonta Undulata. — Fig. 26. 



Shell very thin, not thicker than brown paper ; convex, 

 nearly oval ; epidermis greenish, or olivaceous, darker on 

 the umbo ; obscurely rayed and striated longitudinally ; rays 

 lighter than the general surface ; distantly waved transverse- 

 ly, waves appearing on the inside ; beaks prominent, acute, 

 approximate ; slightly decorticated, wax color beneath ; lig- 

 ament partly concealed ; hinge margin rectilinear ; anterior 

 dorsal margin compressed and angulated ; anterior margin 

 sub-truncated ; posterior margin rounded and projecting ; 

 basal margin ovally rounded ; surface glossy and polished : 

 destitute of cardinal or lateral teeth ; naker light cerulean, 

 tinged with violet ; cavity capacious ; basal and anterior 

 margins bordered with a broad line of rich brown. 



Length, 1.75; breadth, 3.00 ; diameter, 1.25. — Hab. Lit- 

 tle Muskingum. A very delicate and beautiful shell. 



The only specimen of univalve, is figured No. 27, and 

 was found in the Little Muskingum ; it is the largest I have 

 seen of that species, smaller ones being very common. — It 

 appears to belong to the genus Paludina, species Decisa ; 

 as described in American Conchology, plate 2. fig. 6. — It is 

 1.5 in length, and 1.00 in diameter. 



Closing Remarks. — In the above list of shells there are four 

 varieties, which I have not seen described, and have ventured to 



