37 



This species may be found abundantly in the Fox, 

 Vermillion, and Illinois rivers. The variations of this 

 «pecie&, or rather of the shells, within the limits of 

 the county, are very considerable, and due, I have no 

 ■doubt, to the position they occupy, the tempei-ature, 

 food, chemical elements of the water, etc. Thus, in 

 some specimens from one locality, the whirls are round- 

 ed, and have from one to two bands, and are of a 

 dark horn color. From another locality, the whirls 

 are eleven, and the color very light, resembling F. 

 pallidum^ Lea. I refer to mature shells ; in the young 

 shells, the differences are not so marked. 



PI.EUROCKKA L.KWISI1, Lea. 



Sulcate, somewhat thin, conical, elevated ; spire 

 -much elevated, with indistinct suture ; whirls eleven, 

 flattened, covered with sulcations, of which there are 

 four to five on the body, which is angulate on the 

 periphery. Horn color or dark brown, banded or 

 without bands, white or purple within. 



This species is found in the same localities as the 

 preceding one. Having both from the same stations 

 that had evidently grown up together, and finding the 

 difference in the characters of the two shells well 

 maintained and constant, in both the young and adult 

 shell, I am satisfied that they are distinct. P. Zewisii 

 is a much broader shell at the base ; more pyramidal 

 in shape ; has sulcations ; and is of more solid texture 

 than P. Suhulare. Of the soft parts of the two, I 

 •cannot speak as yet. Nor is it essential at this time, 

 .as we base our species upon the characters of the 



