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. 

 7.00; " 5.50; " 4.50 " 

 8.50; " 7.00; " 5.50 " 



p. 128. 



49. Pisidium compressum Prime. 



This species has been found abundantly in Lilycash Creek 

 and a few 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, pi. 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, pi. xxxi, fig. 19. 



Cyclas nitida MIGHELS, Linsley, Amer. Journ. Sci., Vol. XLVIII, p. 



276, 1845. . 



Pisidium variabile 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 a zone 

 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 



