PUPILLIDAE 95 



Gastrocoptas, when found in the field, are usually covered 

 with dirt and mucus, and the shells must be thoroughly washed 

 before the true characteristics of the dififerent species can be 

 seen, especially since identification is possible only through a 

 study of variation in the proportion and shape of the shells, and 

 in the manner of denticulation. In shells of the genus Gastro- 

 copta the peristome, or outer lip, is rounded, and most of the 

 shells of this genus, w^ith the single exception of the species 

 procera, are whitish in color and waxy in texture. 



Key to Species 



1. Shell whitish in color and waxy 2 



Shell brownish in color procera, p. 102 



2. Denticulations of aperture on both parietal wall and peri- 



stome, p. 96 3 



Denticulations of aperture on parietal wall orAy .cortic aria, p. 101 



3. Parietal denticulation very large, partly filling aperture; 



other denticulations placed directly on lip, p. 99 4 



Parietal denticulation small, tubercular; all other denticu- 

 lations placed on a callus or ridge bordering lip, p. 100 

 6 



4. Shell with 6 or 7 whorls armifera, p. 95 



Shell with 5 whorls, p. 97 5 



5. Shell ovate, diameter one-halt of height; outer lip with 1 large 



denticle contractu, p. 97 



Shell cylindroid, diameter one-fourth of height; outer lip with 

 2 denticles holzingeri, p. 99 



6. Shell conic, wide across body whorl; three-fifths as wide as 



high tappaniana, p. 101 



Shell cylindroid, narrow across body whorl; two-fifths as 

 wide as high pentodon, p. 100 



GASTROCOPTA ARMIFERA (Say) 



The species Gastrocopta arrnifera is one of the largest of 

 the pupoid snails having folds within the aperture. Measuring 

 about one-eighth inch (3.5-4.5 mm.) in height, the shell may be 

 recognized by its cylindrical shape, its 6 or 7 convex w^horls, 

 its white color, often resembling paraffin, and the arrangement 

 of the lamellae and folds in the aperture. 



This is one of the characteristic snails of the prairie region; 

 it occurs abundantly in almost every Illinois county. One of the 

 most versatile of all Illinois snails in its ability to adapt itself 

 to a wide variety of habitats, it appears to prefer those of a dry 



