278 Mr. Barnes on the Genera Unio and Alasmodonta. 
probably arisen from the supposition that it belonged to the 
genus Unio, as in its exterior it resembles some varieties of 
the U. purpureus. 
2. ALASMODONTA RUGOSA.—Fig. 21. Shell oblong- 
oval, anteriour side with deep divergent folds. 
Hab. Wisconsan. Capt. Douglass. 
ox River. Mr. Schoolcraft. 
Dr. Mitchill’s Cabinet. My Collection. 
Mr. Say’s Collection. . ; 
Diam. 1.0 ngth 2. Breadth 3.7 
Shell oblong-oval, about equally broad before and be- 
hind; beaks slightly elevated, wrinkled and decorticated, 
exhibiting a wax colour beneath ; ligament external and as 
high as the beaks ; anteriour lunule distinct with a slightly 
elevated ridge extending from the beaks to the ant. basal 
margin; basal margin a little shortened; the other margins 
regularly rounded; epidermis chesnut brown, with a silky 
lustre ; surface of the anteriour part folded in a pinnate 
form; folds deeper above and somewhat obsolete below 
the ridge, curved upward and extending to the hinge and 
anteriour margins, indenting the edge and visible on the 
interiour. Teeth large and elevated with a fold behind ; 
cicatrices smooth ; cavity small; naker pale flesh coloured 
in the center, pearly white on the margin with a narrow 
border of dark chocolate colour; surface smooth and gla- 
rous 
Remarxs.—This is a very beautiful shell, and unlike any 
of its congeners. In the one figured, the left valve is slight- 
ly compressed, the right a little gibbous and the base crook- 
ed, which may perhaps be accidental. 
3. ALASMODONTA CompLaNata. Fig. 22. Shell ovate- 
ly quadrangular, hinge margin elevated into @ 
pris wing ; valves connate ; ligament conceal- 
ed. 
Hab. Fox River. Mr. Schoolcraft. 
Wisconsan, Capt. Douglass. 
