Dr. Hildreth on fresh water Shells. 281 



Tersely from the beaks to the base; basal margin rounded 

 behind, compressed in the middle, angulated slightly before ; 

 epidermis horn color or light chesnut ; surface finely wrin- 

 kled and glabrous ; cardinal teeth deeply sulcated and ere- 

 nated ; lateral teeth, two in each valve ; muscular impres- 

 sions deep and posterior one rough ; naker pearly white and 

 iridescent. Variety B. is smaller than the other, and of a 

 rich pink, or deep flesh color on the inside ; both varieties 

 will stand erect, on the posterior side, and are neat, hand- 

 some shells. 



No. 8. Unio Verrucoscus Purpureus. — Fig. 8. 



Shell nearly circular, sub-truncate before, irregularly tu- 

 berculated ; tubercles transversely compressed ; inside purple. 



Length, 3.5; breadth, 3.6; diameter, 1.9 ; (larger than 

 the figure.) — Hab. Muskingum. 



Shell very thick ; rounded behind, sub-truncate before ; 

 beaks elevated, ligament deeply inserted ; hinge margin near- 

 ly strait, compressed, alated ; basal margin rounded ; epider- 

 mis light brown, surface of the anterior part studded with 

 transversely compressed tubercles ; cardinal teeth very deep- 

 ly sulcated, broadband crenated cavity of the beaks very 

 deep, compressed and directed backwards ; posterior mus,- 

 cular impression very rough, anterior one compound ; naker 

 bluish purple, and iridescent. 



No. 9. Unio Verrucosus Albus. — Fig. 9. 

 The exterior of this shell is much like that of No. 8 ; its 

 form is sub-triangular, and angulated before ; surface waved 

 transversely, tubercles round and standing on the tops of the 

 waves ; cardinal teeth much smaller, and posterior cicatrix 

 deeper ; naker pearly white, and iridescent on the fore part ; 

 it is a most beautiful shell. — Hab. Muskingum. 



No. 10. Unio Nodosus. — Fig. 10. 



Shell sub-quadrangular, emarginate before, knotted, ridg- 

 ed, corrugated, lateral tooth terminating abruptly. 



Length, 2.725; breadth, 3.25 ; diameter, 1.7. — Hab. Duck 

 Creek. 



Shell thick, short and obtusely rounded behind ; beaks el- 

 evated, and approximate ; with the ligament passing be- 

 tween them ; anterior lunule compressed, alated ; hinge 

 margin strait; anterior dorsal, rounded; anterior margin, 



Vol. XIV.— No. 2. 10 



