STROBILOPSIDAE 



111 



Genus STROBILOPS Pilsbry 



The only genus of the family Strobilopsidae found in Illinois 

 is Strobilops. In early works on land snails, this genus is found 

 under the name Strobila. The change in nomenclature was 

 made because the name Strobila had already been used. Most 

 species of the genus Strobilops are found in Illinois. 



Key to Species 



1. Parietal lamella broadened and slightly reflected near emerg- 



ing end aenea, p. 1 14 



Parietal lamella not broadened and not reflected near emerg- 

 ing end, pp. Ill, 113 2 



2. Parietal and infraparietal lamellae emerging from aperture. 



labyrinthica, p. Ill 



Only parietal lamella emerging from aperture. . . .affinis, p. 113 



STROBILOPS LABYRINTHICA (Say) 



The commonest Strobilops in Illinois, and the first one to be 

 discovered and named by an American scientist, is labyrinthica. 

 The shell is less than one-eighth inch (2.30 mm.) in diameter 

 and about one-sixteenth inch (1.75 mm.) in height. The umbili- 

 cus is small. 



Strobilops labyrinthica labyrinthica (Say). In the typical 

 form, two of the lamellae, the parietal and the infraparietal, 



are visible from the front or base of the aperture, but the third, 

 or interparietal, lying between these two, cannot be seen until 

 the shell is broken open. The parts of these lamellae that 

 emerge from the aperture are smooth, but within the chestnut- 

 brown shell they are sawlike on the edge. The lamellae extend 

 only half a turn within the whorl. Four of the 5 or 6 basal 

 folds show through the base of the shell. These form a curving 

 series toward the aperture. 



