264 Mr. Barnes on the Genera Unio and Alasmodonta. 
MARKS This shell differs from the foregoing one, in its 
outline ] th.less breadth and) mn being more tri- 
Seale. In that the lunules are not distinct; in this they are 
strongly marked. The lateral teeth of the two differ in 
Jengih, thickness, direction and surface. This shell, if the 
thickness only were observed, might be mistaken for a vari- 
ety of the Crassus; but the teeth are totally different. 
16. Unio Purrureus.—Shell not very thick, ob- 
liquely sub-truncate before; beaks depressed; epi- 
dermis without rays, glossy; 
_ ' Unio Purpureus. Mr. Sa 
Unio Purpurascens. WM. 5 
\ 
Unio Rhombula? t M. Lamarck. 
Unio roe ? es 
Unio Georg 
Americano ecoitneeds Plate 3. Fi 
ig. | 
ee ae Lakes and Rivers eastward of the Alleghany 
ee 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 proportions of 3 to 5, Mr. 
Say’s figure measures length 1°4, breadth 26, and many 
specimens are twice as broad as they are long. 
Diameter 1°3. Length 2-5. Breadth 4°5. 
Inhabits Stony Creek, near eevee ts. J. Mr. Sears: 
1°8 
Inhabits the Kayaderosseras. 
' 15 3:0 
Inhabits the Housatonick. 
Shell sub-oval, ovate-oblong, ovate—rhomboidal, oblong- 
ovate; thin, or not very thick ; disks convex, convex x-de- 
pressed, or somewhat compressed ; before somewhat angi 
lated or rounded obliquely ; ms rounded, straight, a little 
shortened, depresse ssed, sub-sinuate, or coarctate-sinuate ; 
beaks not prominent; hinge eins elevated, compressed, 
