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POLYGYRIDAE 



POLYGYRA MONODON (Rackett) 



The shell of the species Polygyra monodon is small. It rarely 

 exceeds five-sixteenths inch (8 mm.) in diameter and it some- 

 times measures only a little more than one-fourth inch (7 mm.). 

 The dome-shaped spire of monodon 

 has usually 6 closely coiled whorls. 

 The base of the shell appears flattened 

 when viewed from below, and a large 

 round umbilical opening is distinctly 

 present in this species. Just behind the 

 peristome, which is white and rather 

 thick, is a notable constriction of the 

 body whorl. The parietal wall has a 

 short well-marked plait, and the peri- 

 stome has no denticles on it. The 

 color of the shell is brown. 



No other shell in Illinois could 

 possibly be confused with a shell of 

 monodon, excepting perhaps that of 

 some specimens of Polygyra inflecta edentata, which is com- 

 pletely imperforate, whereas monodon is widely umbilicated. 



The animal of Polygyra monodon is yellowish brown; darker 

 on the head, eye peduncles and tentacles. The color varies in 

 intensity. 



This is one of the most abundant snails in Illinois and is 

 found in all suitable localities throughout the state. It is more 

 common in the northern than in the southern part of Illinois. 



The habitat of Polygyra monodon is in lowlands, usually on 

 the floodplains of rivers and creeks or the margins of lakes, in 

 woodlands of oak, hickory, elm and willow. The animal is some- 

 what gregarious; usually six to a dozen specimens are found 

 together under old logs and in forest debris. 



The author of this species, T. Rackett, was an English 

 zoologist who lived in the early part of the nineteenth century. 

 He described this species as Helix monodon in 1822. 



A wife, domestic, good and pure 

 Like snail, should keep within her door; 

 But not like snail with silver track, 

 Place all her wealth upon her back. 



— William Walsham How, Good Wives 



