THE NAUTILUS. 17 



During a visit to the Philadelphia Academy of Sciences some 

 time ago, Mr. Pilsbry called the writer's attention to the fact that 

 heterostropha had a smooth shell, while gyrina and some others had a 

 shell with impressed spiral lines. Following up this suggestion a 

 large number of Physa? have been examined, with the result that in- 

 stead of there being two species in northern Illinois, there are at 

 least four species and one variety. 



The following notes have been made from fully adult specimens, 

 and the figures are outline drawings of photographs, and are there- 

 fore accurate. 



Key to Northern Illinois Physcs. 



A. Shell smooth, broad, spire short. heterostropha. 



B. Shell with impressed spiral lines. 



a. Shell rather broad, ovate, spire short, acute ; aperture wide 



and spreading ; whorl 4|-5 ; shell thinner than b and c ; 

 peristome callus bordered by red. sayii. 



b. Shell elongated or cylindrical, narrow, spire generally long ; 



apertur every narrow ; whorl 5-6 ; peristome callus 

 bordered by red. gyrina. 



c. Shell broad, inclining to be shouldered ; spire sharply conic ; 



aperture roundly oval ; whorls 4^-5 ; peristome callus 

 white without red border. Integra. 



Physa heterostropha Say. Fig. 1. 



Limnce heterostropha Say, Nicb. Encycl., Amer. ed., pi. 1, fig. 

 6, 1817. Physa fontana Haldeman, Mon. pt. 2, p. 3 of cover; 

 Physa, p. 26, 1841. 



Shell polished, subovate ; whorls 4-4^; spire _£v 



moderately elevated, acute, the whorls slightly jC \ ffl\ 



convex ; color varying from light horn to If \A j jijfjD 

 greenish ; sculpture consisting only of fine I \\/ 

 growth lines; sutures impressed, margined by V y 

 a white line which is frequently bordered by p IG j 



a dark chestnut line ; protoconch consisting of 



one whorl, which is smooth, and varies from porcelain-white to rather 

 dark horn color; aperture rather large, oval, occupying from two-thirds 

 to three-quarters of the length of the entire shell ; peristome thin, 

 acute, thickened on the inside by a whitish or bluish callus, which is 

 bordered on the inside with red; columella almost straight, with a 

 whitish callus which is sometimes lined with red. 



