44 POLYGYRIDAE 



POLYGYRA DORFEUILLIANA (Lea) 



The shell of Polygyra dorfeuilliana is about one-fourth inch 

 (5-7 mm.) in diameter, has 6 whorls and a small but deep 

 umbilicus. The spire, which is flattened, has coarse, rather 



evenly spaced riblets, and the 

 roundly flattened base shows 

 1 V2. turns of the whorls. The 

 outer lip or peristome is thick- 

 ened, and the large, squarish, 

 U-shaped plication on the parie- 

 tal wall almost closes the aper- 

 ture. Just within the peristome 

 are two tubercles which still further constrict the aperture. 

 The shape of the plication on the parietal wall at once dis- 

 tinguishes this shell from any other found in Illinois. The color 

 is yellowish horn in living specimens, but this becomes whitish 

 when the shell is empty. 



The Polygyras have been divided into a number of subgroups 

 according to the shape of the aperture of the shell and the 

 position of the denticles within the aperture. The species 

 dorfeuilliana is the only Illinois member of a subgroup known 

 as typical Polygyra. All other members of this subgroup, which 

 is characterized by an elevated V- or U-shaped denticle across 

 the parietal wall, live in the southern part of the United States. 

 In Illinois, dorfeuilliana is known only from the upper part 

 of the relatively dry blufifs along the Mississippi River in Mon- 

 roe and Jackson counties where the forest is composed of oak 

 and elm, mixed with some pine, and where the underbrush is 

 very sparse. 



Polygyra dorfeuilliana was originally described from Ken- 

 tucky, opposite Cincinnati, Ohio. It is evident, however, that 

 this record is an error. The species has not been reported from 

 that locality within recent years, and a gap of more than 300 

 miles exists between the Illinois colonies and the Kentucky 

 locality from which it was originally described; dorfeuilliana 

 has not been seen from eastern or southeastern Illinois. Possibly 

 the Kentucky record is based upon specimens from another 

 locality, which had become mixed with Kentucky material. The 

 species dorfeuilliana is present in eastern Missouri; it undoubt- 

 edly crossed the Mississippi River to Illinois. 



