THE NATURAL HISTORY SURVEY, 121 
shining; dorsal margin straight; ventral margin broadly rounded; 
posterior margin subtruncated; anterior margin rounded; um- 
bonal slopes rounded; surface smooth and shining, lines of 
growth very fine; color light yellowish, sometimes darker; liga- 
ment very thin, light brown; cardinal teeth small,a single, 
arched, elevated, lamellar tooth situated near the ventral mar- 
gin of the hinge plate in the right valve, and two elevated teeth 
in the left valve, of which the dorsal is situated near the center 
of the hinge plate, arched, lamellar, and the ventral is situated 
near the lower margin of the hinge plate, and is elevated, pyram- 
idal and solid; lateral teeth lamellar, straight, elevated, single 
in the left and double in the right valve; muscle scars very 
faint; cavity of the beaks shallow; nacre bluish white. 
Length, 12.50; height, 9.00; breadth, 7.00 mill. (9965). 
a 11.50; ae 8.00; Wi 6.00 ‘'~ (9965). 
Animal: White, greenish about the liver; mantle lobes 
very thin and transparent; siphons rather short, narrow, about 
equal in size, united only at base, pinkish in color; foot very 
long and narrow, white, capable of great extension, and extended 
through a cleft in the mantle near the anterior end of the ven- 
tral portion; ctenidia large, white, rounded, united above; labial 
palpi long and narrow, united at base, white. 
Distribution: New York west to Arkansas, Canada south 
to Alabama and Louisiana. 
Geological distribution: Pleistocene. 
Habitat: Found in rivers, ponds and lakes, in soft mud, 
either on the surface or buried to a considerable depth. 
Remarks: This is a distinct little shell, and can be con- 
founded with no other. It is acommon and abundant species, 
and may be seen on any pleasant day jerking its way over the 
muddy bottom of our rivers. Its transverse outline differs from 
that of any other species found in this area, and will at once 
distinguish it. The species is found in the northern and west- 
ern regions. 
44. Calyculina truncata Linsley, pl. xxvii., fig. 8. 
Cyclas calyculata DrapaRNaup, C. B. Apams, Amer. Jour. Sci. and Arts, 
2d series, Vol. XL., p. 277, 1841. 
Cyclas truncata Linstgy, Amer. Jour. Sci. and Arts., 3d series, Vol. VI., 
p. 234, fig. 3, 1848. 
Cyclas lenticula Gouin, Proc. Bost. Soc. N. H., Vol. III., p. 256, 1850. 
Cyclas pellucida Prime, Stimpson, Shells of New England, p. 16, 1851. 
