278 Mr. Barnes on the Genera Unio and Alasmodonia. 



probably arisen from the supposition that it belonged to the 

 genus Unio, as in its exterior it resennbles some varieties of 

 the U. purpureus. 



2. ALASMODONTA RUGOSA. — Fig. 21. Shell oblong- 

 oval, anteriour side with deep divergent folds. 



Hab. Wisconsan. Capt. Douglass. 

 Fox River. Mr. Schoolcraft. 

 Dr. Mitchill's Cabinet. My Collection. 

 Mr. Say's Collection. 

 Diam. 1.0 Length 2.0 Breadth 3.7 



Shell cblong-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 \n a. pinnate 

 form ; folds deeper above and somewhat obsolete below 

 the ridge, curved npward 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- 

 brous. 



Remarks. — 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 a 

 large wing ; valves connate ; ligament conceal- 

 ed. 



Hab. Fox River. Mr. Schoolcraft, 

 Wisconsan. Capt. Douglass. 



