POLYGYRIDAE 41 



Genus POLYGYRA Say 



All members of the family Polygyridae found in Illinois 

 belong to the genus Polygyra, which is not found outside of 

 North America and certain islands of the West Indies. Charac- 

 teristics of the genus are those described for the family Poly- 

 gyridae. The figure on page 40 pictures an Illinois species, 

 Polygyra palliata (Say). 



The genus Polygyra contains the largest species of land 

 snails inhabiting Illinois and also the largest number of species 

 of any genus found within the state. The conspicuous size and 

 color of the shells make them objects easily seen and eagerly 

 sought by collectors. 



Key to Species and Varieties 



1. Base of shell with umbilical opening; sometimes opening 



partially obscured by reflected lip, p. 60 2 



Base of shell without umbilical opening; umbilicus com- 

 pletely closed by a callus, p. 54 17 



2. Aperture or parietal wall of shell with denticles, p. 44 3 



Aperture or parietal wall of shell without denticles, p. 48. ... 13 



3. D.enticles in aperture only on parietal wall, p. 56 4 



Denticles in aperture only on outer lip, or on both parietal 



wall and outer lip, p. 44 8 



4. Shell ^ to 1 inch in diameter; large umbilical opening 



partly covered by widely spreading lower lip; denticle 



on parietal wall short and narrow thyroiduSy p. 56 



Shell 3'2 inch or less in diameter; umbilicus wide, often not 

 partly concealed by lower lip; denticle on parietal wall 

 small, tubercular, p. 60 5 



5. Umbilicus not at all concealed by lower lip 



tr'tdentata unidentata^ p. 45 



Umbilicus partly concealed by lower lip, p. 61 6 



6. Umbilical opening small, a mere slit, almost entirely covered 



by reflected lower lip fraterna jraterna^ p. 61 



Umbilical opening distinct, only partly covered by reflected 

 lower lip, p. 60 7 



7. Denticle long; umbilicus round, partly obscured by lower 



lip Jraterna cava, p. 61 



Denticle short; umbilicus only very slightly obscured by 

 lower lip monodon, p. 60 



8. Denticles in aperture only on outer lip 



tr'tdentata bidentata, p. 45 



Denticles in aperture on both outer lip and parietal wall, 

 p. 44 ; 9 



