THE MOLLUSCA OF MUSCATINE COUNTY. 9 



Liberty, in Muscatine County, is a form which approaches very 

 near to the typical reflexa of Say. Average measurements of 

 some of the different forms are as follows : 



Length. Greatest Diameter. . Length of Aperture, 



mm. mm. mm. 



37 12 18 



37 13 17 



37 12 15 



32 9 13 



27 10 13 



One variety is slender, wrinkled, and very light color, whilst 

 most of the others are dark, rather tumid, and scarcel} 7 wrin- 

 kled. Variety zebra (Tryon) has in some specimens well- 

 marked, alternating dark and light lines or bands parallel to 

 the margin of the outer lip ; but it shades off into varieties 

 without light lines. The short form was very abundant two 

 years ago in Brigg's Slash, on Muscatine Island. TLe epider- 

 mis was either eaten or eroded from the spire of nearly all of 

 this variety. 



L, desidiosa, SAY. Abundant along muddy margins of ponds. 

 Light horn color ; slight umbilical opening. Length of shell, 

 14 ; of aperture, 8 mm. 



L. pallida, ADAMS. Was very abundant about three years ago 

 in a small pond in Muscatine, but seems now to be extinct in 

 this region. Length of shell, 11.5 ; of aperture, 6.5 mm. 

 Epidermis is dark, or black ; but this may be some substance 

 foreign to the shell. Shell bluish white in the aperture. It 

 is probable that L. humilis (Say) is found here, inasmuch as 

 it is reported by Mr. W. A. Marsh, from Aledo, 111., only 

 eighteen miles from Muscatine ; and we have small Limnece 

 that do not seem to fall under desidiosa or pallida. 



PHYSA. 



P, gyrina, SAY. It is very difficult to say whether this species is 

 abundant or not, or whether it really exists here. We have 

 plenty of Physce; but just what they all are, it seems nobod} 7 " 

 knows. As far west as Des Moines, the relative length of 

 aperture and shell accords better with Say's description of 

 the species than shells found here. The largest Physa that I 



