Mr. Barnes on the Genera Unio and Alasmodonta. 21l\ 



species. It most resembles the Unio Ventricosus; but is 

 less, thinner, " more flattened and even slightly concave on 

 the anterior slope, from the oblique carina to the angle at 

 the termination of the ligament." Mr.Say says the Ovatus is 

 not rayed, and our specimens accord with his description, 

 but M. Lamarck mentions a variety vi^ith rays from Lake 

 George. 



23. Unio Cariosus. — Shell ovate or oval, inflated, 

 not very thick, beaks somewhat prominent, cav- 

 ity moderate. 



Unio Cariosus. Mr. Say. 



Unio Cariosa. M. Lamarck. 



Inhabits Lakes and Rivers of N. America. 



My Collection. 



Diam. 1-6, Length 2-3, Breadth 8-7. 



American Conchology, plate 3, fig. 2. 



The dimensions and description of this shell vary so 

 much that it is difficult to find a sufficient number of perma- 

 nent characters by which it may be distinguished. It re- 

 sembles in this respect the Unio Purpureus; for of the 

 twelve characters mentioned by Mr. Say, and the six men- 

 tioned by M. Lamarck only four can be considered as in 

 any degree permanent ; and of these M. Lamarck has men- 

 tioned but one, and that is " injlated.^^ The colour, form and 

 size of the shell constantly vary. It is commonly broader 

 before, but often equally broad at both extremities ; and 

 somewhat pointed. It is never very thick ; often very tliin; 

 commonly a medium. Those from the Hudson are thin 

 and small, from the Raritan thicker and broad ; from the 

 western waters middle sized and of considerable thickness; 

 disks swelled, umbones elevated ; ligament exterior and el- 

 evated ; epidermis olive-brown or greenish, and commonly 

 radiated. Internal colour bluish white, reddish, rose, or 

 salmon j surface often warty. 



Variety (a) Cardinal teeth multipartite. 



Inhabits Lake Ontario. 



Mr. Bradhurst's Collection. 



