a J 
Mr. Barnes on the Genera Unio and Alasmodonta. 267 
Diam. 1-4 Length 1-7 Breadth 3 
Shell about equally broad before ger behind, thick and 
very much swelled, the diameter being almost equal to the 
: length ; beaks broad round and somewhat elevated; poste- 
rior side very short ~ obtuse; anterior side wedge-shap- 
ed produced. Hinge margin nearly straight, and parall 
to the base; basal scale straight and slightly compressed 
in the middle; epidermis yellowish-green, rayed; surface 
wrinkled and striated transversely ; cardinal teeth elevated, 
pointed, sulcated; lateral teeth papillous; posterior cicatrix 
deep, and somewhat rayed with elevated lines; sabe ad 
the beaks moderate; naker pearly ahs: and iridescent; 
ternal surface papillous. abs 
Remarxs.—This shell is less than the Unio Siliquoideus, 
and also more rounded and gibbous, shorter behind an 
proportionally longer before than that species. The varie- 
ties of the two species approach each other, and are to be 
distinguished only by the teeth. 
B. TEETH OBLIQUE. 
** ** Cardinal teeth, broad, oblique, compressed. 
asmall size. 
20. Unio Venrricosus. Fig. 14. 6 large size. 
¢ the first variety. 
Shell large thick triangularly ovate, convex; um- 
bones large, round, prominent ; beaks recurved ; 
cavity capacious. 
Mya Radiata. Dillwyn’s Letter to Dr. Mitchill. 
Unio Cariosus.. Mr. Say’s Letter to the Author. 
Inhabits the Wisconsan. Mr. Schoolcraft. 
Mississippi, near Prairie du Chien, Capt. Douglass. 
Cabinets of the Lyceum and Dr. Mitchill. My Collec- 
tion. Mr. Say’s Collection, Philadelphia. 
Diam. 2.5 Length 3.5 Breadth 4.5. 
Shell with the anterior side very broad, sub-truncate ; 
posterior side rapidly narrowed, sub- “angulated ; disks very 
convex ; umbones large, round, elevated ; beaks recurved 
