40 



POLYGYRIDAE. 



Family POLYGYRIDAE 



To the family Polygyridae belong most of the large snaih 

 living in Illinois. The shell in the different species varies fron 

 one-fourth inch (5 mm.) to an inch and a half (40 mm.) ii 

 diameter and may be either globose or depressed. But in al 

 species the shell of the adult specimen has a reflected outer lip 

 Many species are provided with denticles or plications on thi 

 lip or parietal wall. 



The young and immature individuals of this family are 

 difficult to identify, because the lip or peristome in young speci- 





mens is not reflected, as it is in older individuals, and because 

 an umbilicus is present in the young of even those species in 

 which the shell of mature individuals is imperforate. Usually 

 it is safe to assume that immature specimens belong to the same 

 species as the adults with which they are found. 



The animals of the Polygyridae, though large, are completely 

 retractile within the shell. In color they vary from whitish or 

 cream to blackish or brownish. Usually the head, the long, 

 flexible eye peduncles and the short tentacles are of a darker 

 color than the rest of the body, and the underside of the foot 

 is usually of a lighter color. 



The body of the animal in some species of the family 

 Polygyridae is conspicuously granulated, and in all species 

 granules of varying sizes are present. The animal of nearly all 

 species of this family has a rather indistinct groove on each 

 side of the body extending from the edge of the shell to the 

 head. In most species the body of the animal is about twice 

 as long as the diameter of the shell. Polygyra palliata, a mem- 

 ber of this family, is pictured on this page. 



