jW. Barnes on the Genera Unio and Alasmodonta. 265 



carinate or depressed; epidermis has generally a silky lustre- 

 surface with smaller wrinkles placed between larger ones 

 or with transverse elevated distant furrows, or smooth; car- 

 dinal teeth small, or not very large, sulcated or striated ; 

 naker livid, cerulean, green, purple, red, violet, white, with 

 various shades and mixtures of these colors; no cavity under 

 the beaks. 



Remarks. — The terms of the foregoing general description 

 are taken from Mr. Say^s and from the six species of JH La- 

 marck mentioned above. This is a very common shell, of a reg- 

 ular and uniform appearance, without prominence of parts, 

 or strongly marked characters ; which perhaps induced M. 

 Lamarck to say " it is nothing remarkable."* Amidst a va- 

 riety almost infinite, like that of the human countenance, 

 there is still a characteristic identity of this species, which 

 can scarcely be mistaken by an experienced observer. One 

 variety of the Radiatus from the Saratoga Lake approaches 

 nearest to this species, but the least appearance of rays for- 

 bids its association. 



* * * Cardinal teeth small, direct.. 

 17. Unio Radiatus. — Shell broad-ovate, thin, fine- 

 ly striated, glossy rayed, within bluish white, or 

 tinged with red. 



Unio Ochraceous. Mr. Say. 



Mya Radiata. Mr. Dillwyn. 



Unio Radiata. M. Lamarck. 



American Conchology, plate 2, fig. 8. 



Inhabits lakes and rivers of North-America. 



Cabinet of the Lyceum. My collection. 

 Diam. -6— -9 Length 1-2— 1-5 Breadth 2-0— 2-5. 



Shell with the anterior side broad, thin and fragile, disks 

 in old specimens somewhat convex; in youug, depressed; 

 beaks slightly elevated and approximate; ligament eleva- 

 ted ; hinge margin elevated, compressed, carinate ; basal 

 margin commonly a little depressed, and sometimes arcua- 

 ted ; anterior margin narrow; posterior broad; anterior 

 dorsal sub-truncate; epidermis greenish yellow or olive- 

 brown, rayed with dark green, and very finely striated trans 



*See Aa. Sans Vertebres, Vol. VI. p. 74. U. Georgina. 



Vol. VI.— No. 2. 34 



