96 



PUPILLIDAE 



nature. On the bluffs of the Mississippi and Ohio rivers, it is 

 often found beneath blocks of limestone. Singularly enough, 

 one of the favorite habitats is railway embankments, where it 

 may be found either in the cinders and debris of the sides of the 



embankment or among the 

 grass and weeds bordering 

 the roadbed. 



In the past, Gastrocopta 

 armifera has been placed in 

 several genera and will be 

 located under the names 

 Pupa and Bifidaria in some 

 older works. Three varie- 

 ties besides the typical have 

 been found in Illinois. 



Gastr ocopta armifera 

 armifera (Say). Fig. A. 

 The typical variety may be 

 known by its size and its 

 swollen whorls. The shell, 

 measuring over one-eighth 

 of an inch (4.0-4.5 mm.) in 

 height, has a large lamella 

 composed of the angular and 

 the parietal lamellae com- 

 bined, a large columellar la- 

 mella and two palatal folds, 

 the lower one being larger 

 than the upper one. The 

 shell of this variety has usually a third small palatal fold. 



Gastrocopta armifera similis (Sterki). Fig. B. This variety 

 differs from the typical principally in having a narrower and 

 more nearly cylindrical shell. The peristome is not continuous, 

 and the columellar lamella and the lower palatal fold are not so 

 heavy. This form is less widely distributed than the typical. 



Gastrocopta armifera affinis (Sterki). Fig. C. Shorter than 

 that of the typical form, the shell of affinis measures only about 

 one-eighth inch (3.5 mm.) in height. The peristome is not con- 

 tinuous. The merger of the angular and parietal lamellae is 

 more nearly complete and continuous. The columellar lamella 

 is thinner than in the typical armifera. 



