THE NATURAL HISTORY SURVEY. 123 
angulate posteriorly; surface shining, lines of growth very faint; 
color varying from bright yellow to greenish horn, sometimes 
very dark horn; ligament as usual; cardinal teeth very small, 
a single, long, elevated, lamellar, arched tooth in the right valve, 
which has a large pyramidal projection near the anterior end 
giving the hinge the appearance of a double tooth, and two 
teeth in the left valve, one near the ventral margin of the hinge 
plate, elevated, pyramidal, and one near the dorsal border, 
lamellar, depressed, curved, extending diagonally toward the 
ventral border; lateral teeth long, lamellar, elevated, slightly 
curved, one in the left valve and two in the right; muscle scars 
faint; cavity of the beaks deep; nacre bluish white, darker near 
the postero-ventral portion, lighter in yellowish specimens 
Length, 6.00; height, 5.00; breadth, 3.00 mili. (12465). 
EI STOP ty SAO i 20 (12465). 
Animal: Not observed. 
Distribution: New England west to Michigan, Canada 
south to Kentucky. 
Geological distribution: Pleistocene. 
Habitat: Same as S. truncata. 
Remarks: A species at once distinguished by its rhombic- 
orbicular outline and inflated beaks and shell. It is the smallest 
Sphertum found in this area, and is wider in proportion to its 
length than any other species. It does not seem to be very 
common, and, like the last species, is confined to the south- 
western part of the western region. 
46. Calyculina partumeia Say, pl. xxvii., fig. 6. 
Cyclas partumeia Say, Journ. Phil. Acad., Vol. II., p. 380, 1822. 
Cyclas cornea, var. 2, Lam., An. sans Vert., Vol. V., p. 558, 1818. 
Cyclas orbicularia Barratt, Amer. Journ. Sci. and Arts, Vol. XLVIII., 
p. 276, 1845. 
Cyclas mirabilis PriME, Proc. Bost. Soc. N. H., Vol. IV., p. 157, 1851. 
Cyclas cerulea Prime, |. c., p. 161, 1851. 
Cyclas eburnea ANTHONY, I. c., p. 279, 1852. 
Shell: Of good size, inflated, fragile, very nearly equi- 
lateral, pellucid; umbones elevated, inflated, of good size, placed 
near the center of the shell, calyculate, very finely marked by 
growth lines; dorsal margin slightly arched, ventral rounded; 
anterior margin broadly rounded, posterior roundly truncated; 
umbonal slopes rounded; surface shining, polished, marked by 
very fine growth lines; color greenish horn or yellowish, with 
frequently a broad zone of dark purple on the ventral border; 
