THE NATURAL HISTORY SURVEY. 119 
the hinge plate, and one placed near the ventral margin of the 
hinge plate; the dorsal tooth is nearly straight while the 
ventral tooth is very arcuate; in the right valve there is a 
single, large, arched tooth which extends from the center to 
the ventral border of the hinge plate, it is large at either end 
and small in the middle; lateral teeth double in the right and 
single in the left valve, rather small, elevated, pyramidal, 
slightly curved; hinge line rather solid; muscle scars indistinct; 
cavity of the beaks shallow; anterior bluish. 
Length, 11.00; height, 9.00; breadth, 5.50 mill. 
ef 9:50; 5 StaeeAOs oF 5:00) 
tt 95055 ee ea “K 4.75 | 
Animal: Not observed. Siphons said by Prime to be 
crimson. 
Distribution: New England west to Iowa, Canada south to 
Louisiana. 
Geological distribution: Pleistocene. 
ffabitat: Inthe large lakes, on a muddy bottom, in rather 
deep water. 
Remarks: Faébale has been found at but one locality thus 
far, but probably occurs anywhere along the shore of Lake 
Michigan. Its only locality, Miller’s, Ind., is at the extreme 
southern end of Lake Michigan. This interesting region is said 
by Prof. Garriott to be the most wind-»swept locality in the Chi- 
cago area. This fact accounts for the enormous quantity of sea 
wrack which lines the shore at this point and which is not to be 
found in such profusion anywhere else along the shore. This 
sea wrack has proven prolific collecting ground for molluscan 
life. : 
The present species is very variable, running from per- 
fectly smooth to coarsely striated and varying in color from 
yellow to black. It may always be known by its depressed 
umbones. 
42. Sphzrium occidentale Prime, pl. xxvii., fig. 10. 
Cyclas ovalis Prime, Proc. Bost. Soc. N. H., Vol. IV., p. 276, 1852 (Pre- 
occupied). 
Spherium occidentalis Prime, |. c., Vol. V., p. 122, 1855. 
Shell: Small, inflated, fragile, equilateral; umbones promi- 
nent but not much elevated, inflated, placed centrally, marked 
by very fine lines; dorsal and ventral margins rounded; anterior 
and posterior margins rounded; umbonal slopes rounded; sur- 
