Mr. Barnes on the Genera Unio and Alasmodonta, 269 



hent, the rays fewer, and the polish .less brilliant. It ap- 

 proaches the Unio Cariosus. 



■ Inhabits the Delaware at New Hope. Mr. J. Scars. 

 My Collection. 



Remarks, — With the most respectful deference to the 

 two distinguished Naturalists whose names are mentioned 

 above, I have ventured to differ from them both, as they do 

 from each other. I think a slight examination of our (/ab- 

 inets would convince either of them that this shell requires 

 a separate designation. Two bivalves -can scarcely be 

 more unlike than this and the Unio Radiata of Lamarck; and 

 the recent discovery, of the variety C, in our own waters, 

 which produce thousands of the Unio Cariosus, seems con- 

 clusive as to that. This variety it will be observed has 

 precisely the same diameter and length as the shell from the 

 Wisconsan, and the difference in the teeth may be acciden- 

 tal. There is the same necessity for distinguishing these 

 as any others. They are totally unlike. 



C outline 

 21. Unio Siliquoideus. Fig. 15. < of the 



I shell. 

 Shell long-ovate, sub-cylindrical, thick, regularly 

 rounded, rayed, beaks slightly elevated, cavity 

 small ; inside white. 



Inhabits the Wisconsan. Capt. Douglass. 



Dr. MitchiU's Cabinet. My Collection. 



Diam. 1-3— 1-6 Length 1-8--2-1 Breadth 3-3— 3-8. 



Shell elongated transversely, disks swelled ; beaks about 

 one fourth from the posterior extremity ; hinge margin 

 straight ; basal margin convex depressed ; anterior margin 

 rounded ; posterior sub-angulated ; epidermis yellowish ol- 

 ive rayed with distant dark green narrow lines ; surface 

 deeply wrinkled, and somewhat imbricated ; striae dark 

 and lamellar on the anterior slope ; smooth and bright on 

 the centre of the disks ; cardinal teeth elevated crest-like 

 compressed, and very oblique ; in some specimens nearly 

 parallel to the edge of the shell ; lateral teeth long and 



