16 



ZONITIDAE 



EUCONULUS CHERSINUS (Say) 



The glassy, yellowish-white shell of Euconulus chersinus 

 has at least one more whorl, 6-6^, than that of Euconulus 

 fulvus, and the whorls are more closely coiled. The body whorl 

 of the mature shell is usually rounded and not angulate as in 

 fulvus. However, all immature shells of the genus are distinctly 

 angulate on the periphery. 



Euconulus chersinus, especially the typical form, is abundant 

 in hilly regions bordering the large Illinois rivers. Occasionally 

 it is found in isolated woodlands containing oak, cherry, hickory 

 or ironwood. Of the two species, fulvus and chersinus, the latter 

 is the more abundant and more generally distributed through- 

 out Illinois. 



Euconulus chersinus chersinus (Say). The height of the 

 typical chersinus shell, shown in the figures below, is as great 



as or greater than the diameter; each dimension is about one- 

 eighth inch (2.8-3.0 mm.). The spire is higher than that of 

 fulvus. 



Euconulus chersinus polygyratus (Pilsbry). Although the 

 shell of this race is about the same size as that of the typical 

 form and has the same number of 

 whorls, the spire is less elevated, be- 

 cause the whorls are narrower and 

 more tightly coiled. In chersinus pol- 

 ygyratus, the periphery is higher on 

 the body whorl, causing the aperture to 

 be narrower and higher than in cher- 

 sinus chersinus. 



Known records indicate that cher- 

 sinus polygyratus in Illinois is confined to the northern part, 

 Cook and Henry counties being probably the southern limit. 



