“a 
. 
bn 
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THE NATURAL HISTORY SURVEY. 397 
The specimens from these localities are exceedingly variable 
as to size, shape, color, shape of beaks, etc. (vide Sterki). 
p. 127. 
48. Pisidium virginicum Gmelin (not Bourguignat). 
Large specimens of this species have been collected in 
Lilycash Creek. 
_Length, 7.50; height, 6.00; breadth, 4.50 mill. 
§ OO seaars 5.50; uf 4.50 *‘ 
S00 wee 7.00; ss d.00 
p. 128. 
49. Pisidium compressum Prime. 
This species has been found abundantly in Lilycash Creek 
and afew specimens in Lake Michigan, Dr. Sterki says that 
it varies very much in size, shape, prominence of beak, and in 
their ridges, striation, etc. 
p. 129. 
50. Pisidium politum Sterki, pl. xxxi, fig. 13. 
Dr. Sterki has very kindly forwarded figures of this spe- 
cies. He also remarks that the specimens from Joliet are the 
most beautiful ones he has thus far seen. 
The following species have been described or collected 
since the publication of Part I: 
152. Pisidium variabile Prime, pl. xxxi, fig. 19. 
Cyclas nitida MIGHELS, Linsley, Amer. Journ. Sci., Vol. XLVIII, p. 
276, 1845. 
Pisidium vartabile PRIME, Proc. Bost. Soc. N.H., Vol. IV, p. 163, 1851. ° 
Pisidium grande \WHITTEMORE, in litt., 1855. (vide Prime). 
Shell: Small, solid, inflated, inequilateral, oblique; um- 
bones very much elevated; full, very prominent, placed poste- 
riorly, smooth and polished to the naked eye but marked by 
fine lines when viewed with a lens; all margins rounded, the 
anterior being somewhat pointed or triangular and quite long, 
while the posterior is short and very broadly rounded; umbonal 
slopes rounded, the anterior subexcavated; surface shining, 
marked by rather heavy, regular growth lines; color varying 
from light yellow or straw to greenish or brownish, with azone 
of light or dark color near the ventral margin; in some speci- 
mens two zones are present, while in others the zone is hardly 
visible; ligament small and weak; cardinal teeth small, a sin- 
gle long, arched tooth in the right valve, and two more or less 
