THE NATURAL HISTORY SURVEY, PW 
and pallial line faintly impressed; nacre bluish; cavity of the 
beaks shallow. . 
Length, 16.50; height, 11.75; breadth, 9.00 mill. (8513). 
“ 15.50; 12,00; © 9.00 “ (8513). 
“18.00; “ 18.00; ‘ 10.00 “ (12460). 
Animal: Not observed. 
Distribution: United States and Southern Canada. 
Geological distribution: Pleistocene. 
Hlabitat: In rivers and lakes, in soft mud. 
Remarks: The hinge teeth are arranged very peculiarly in. 
this species, the laterals being in a direct line with the cardi- 
nals, and not at right angles to them, as in the previous species. 
It is one of the largest of the genus and distinguished from the 
related species by its transversely oval outline, its peculiarly 
placed teeth, and its umbonal marking, which is intermediate 
between so/idu/um and stamineum. The umbones are also placed 
very near the center of the shell. The species does not seem 
common, although found in the southern, northern and western 
regions, under circumstances which should be conducive to 
their multiplication. 
40. Spherium striatinum Lamarck, pl. xxvii., fig. 2. 
Cyclas striatina Lam., An. sans Vert., Vol. V., p. 560, 1818. 
Cyclas edentula Say, New Harmony Dissem., p. 356, 1829. 
Cyclas albula PRiME, Proc. Bost. Soc. N. H., Vol. IV., p. 155, 1851. 
Cyclas tenuistriata PRIME, |. c., p. 156, 1851. 
Cyclas acuminata PRimE, 1. c., p. 158, 1851. 
Cyclas tnornata Prime, l.c., p. 159, 1851. 
Cyclas simplex Prime, l.c., p. 159, 1851. 
Cyclas modesta PRimE, 1|.c.. p. 159, 1851. 
Shell; Of medium size, not much inflated, solid, transversely 
elongated, very inequilateral; umbones depressed, full, placed 
anterior to the center of the shell, marked by numerous fine 
ridges, which are so fine in some specimens that the beaks 
appear smooth; dorsal margin arcuate; ventral margin rounded; 
posterior margin obtusely triangular; anterior margin broadly 
rounded; umbonal slope rounded, the posterior inclined to 
angular; surface shining, lines of growth coarse, but not so 
much so as in s/amineum; color greenish yellow, varying to dark 
horn in some specimens; ligament weak, dark horn colored; 
cardinal teeth small, those in the left valve unequal, one placed 
near the dorsal margin of the hinge plate, small, and extending 
diagonally toward the ventral margin, and one placed near the 
