264 Mr, Barnes on the Genera Umo and Alasmodonta. 



Remarks. — This shell differs from the foregoing one, in its 

 outline, in its greater lengih,less breadth, and in being more tri- 

 angular. In tliat thelunules are not distinct; in this they are 

 strongly marked. The lateral teeth of the two differ in 

 length, thickness, direction and surface. Thisshell, if the 

 thickness only were observed, might be mistaken for a vari- 

 ety of the Crassus; but the teeth are totally different. 



16. Unio Purpureus. — Shell not very thick, ob- 

 liquely sub-truncate before; beaks depressed; epi- 

 dermis without rays, glossy; 



Unio Purpureus. Mr. Say. 

 Unio Purpurascens. M. Lamarck. 

 Unio Rarisulcata ? ^ 

 Unio Coarctata? ( 



Unio Rhombula ? )■ M. Lamarck. 

 Unio Carinifera ^ | 

 Unio Georgina ? J 

 American Conchology, Plate 3. Fig. 1. 

 Inhabits Lakes and Rivers eastward of the Alleghany 

 mountains. 



Cabinet of the Lyceum. My collection. 

 The varieties, which are exceedingly numerous, differ 

 very much from each other in the length of the diameter, 

 some measuring 13 lines, and some only 5. The length 

 and breadth are generally in the proportion's of 3 to 5. Mr. 

 Say's figure measures length 1*4, breadth 2-6, and many 

 specimens are twice as broad as they are long. 

 Diameter 1-3. Length 2 5. Breadth 4*5. 

 Inhabits Stony Creek, near Princeton, N. J. Mr. Sears. 



11 1-8 3-45 



Inhabits the Kayaderosseras. 



•75 ' 1-5 3-0 



Inhabits the Housatonick. 



Shell sub-oval, ovate-oblong, ovate—- rhomboidal, oblong- 

 ovate; thin, or not ren/ thick ; disks convex, convex-de- 

 pressed, or somewhat compressed ; before somewhat angu- 

 lated or rounded obliquely,- base rounded, straight, a little 

 shortened, depressed, sub-sinuate, or coarctate-sinuate; 

 beaks not prominent ; hinge margin elevated, compressed, 



