114 THE CHICAGO ACADEMY OF SCIENCES. 
the center of the shell, marked by rather coarse ridges; dorsal 
margin strongly arcuate, ventral border rounded, posterior mar- 
gin long, obtusely triangular, the umbonal slope rounded; an- 
terior margin rounded; surface shining, growth lines coarse, 
crowded; fine lines may be seen between the coarse ones when 
viewed with a lens; color varying from dark horn to yellowish 
brown, sometimes marked by large blotches of both colors on 
the shell and with a yellowish line bordering the ventral margin; 
ligament thin, dark brown; cardinal teeth very small, a single 
lamellar, elevated tooth, which forms a long, arched projection 
beneath the point of the beak in the right valve, and two ele- 
vated, curved, thin teeth in the left valve, one just beneath the 
beak and one midway between hinge margins; the hinge line in 
both valves is thickened and extends from the lateral to the 
cardinal teeth, rising to meet the latter; lateral teeth situated 
on either side of the cardinals in each valve, short, elevated, 
thick, curved, double in the right and single in the left valve; 
muscle scars and pallial line distinct, the latter crenulated; 
nacre bluish white, darker near the cavity of the beaks, which 
are deep. s 
Length, 11.00; height, 8.75; breadth, 7.00 mill. (12458). 
Animal: Not observed. 
Distribution: New York to Iowa, Wisconsin to Louisiana 
and New Mexico. 
Geological distribution: Pleistocene. 
Afabitat: Found in the smaller rivers and creeks, on a muddy 
bottom. 
Remarks; This species is easily known by its strongly tri- 
gonal outline and solid shell. It is distinguished from 
stamineum by its less distinctly marked umbones and more 
trigonal form; s¢réatinum is much more transverse and is very 
much more compressed, while the umbones are smaller, and 
the shell is smaller than stamineum generally. It does not 
seem to be a common shell, and is confined to the Desplaines 
River drainage and Lake Michigan. 
38. Sphzrium stamineum Conrad, pl. xxvii., fig. 1. 
Cyclas staminea ConraD, Amer. Jour. Sci. and Arts, Ist series, Vol. XXV., 
p. 342, pl. i., fig. 5, 1834. 
Cyclas fuscata RaFINESQUE, Prime, Proc. Bost. Soc. N. H., Vol. IV., 
p. 281, 1852. 
Cyclas bulbosa ANTHONY, PrRimg, l. c., p. 283, 1852. 
