Mr. Barnes on the Genera Unto and Alasmodonta, 267 



Diam. 1-4 Length 1*7 Breadth 3-2. 



Shell about equally broad before and 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 and obtuse; anterior side wedge-shap- 

 ed produced. Hinge margin nearly straight, and parallel 

 to the base ; basal margin 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 line'?; cavity of 

 the beaks moderate; naker pearly white and iridescent; in- 

 ternal surface papillous. 



Remarks. — This shell is less than the Unio Siliquoideus, 

 and also more rounded and gibbous, shorter behind and 

 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. 



i a small size. 

 20. Unio VENXRicosus.Fig. 14. < 6 large size. 



( c the first variety. 

 Shell large thick triangularly ovate, convex ; um- 

 bones large, round, prominent ; beaks recurved ; 

 cavity capacious. 



Mya Radiata, Dillwi/nh 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 antefior side very broad, sub-truncate; 

 posterior side rapidly narrowed, sub-angulated ; disks very 

 convex; umbones large, round, elevated; beaks recurved 



