POLYGYRIDAE 47 



POLYGYRA INFLECTA (Say) 



The light brown shell of Polygyra inflecta is nearly one-half 

 inch (11 mm.) in diameter and is much wider than high. It has 

 an imperforate base. The surface of the shell is covered with 

 very short, hairlike projections 

 from the epidermis. In all but 

 one rare variety, shells of this 

 species found in Illinois are char- 

 acterized by 2 denticles on the 

 peristome and a single long plica- 

 tion on the parietal wall. 



The animal of this species is 

 dark bluish slate in color; the head, tentacles and eye peduncles 

 are blackish. The foot is very narrow. 



This Polygyra is confined largely to the southern part of 

 Illinois. No specimens have been seen north of Edgar County. 

 It is very abundant in the Wabash, Ohio and Mississippi valleys, 

 in the last as far north as Calhoun County, where it lives on 

 the limestone cliffs associated with Polygyra tridentata. It 

 appears to be gregarious, for in any location it nearly always 

 occurs in great numbers. 



Like the other species of the dentate polygyras, inflecta 

 is subject to great variation in the development or presence of 

 the denticles wnthin the aperture. The following variations 

 occur in Illinois. 



Polygyra inflecta inflecta (Say). The denticles on the peri- 

 stome of the typical form are rather widely separated, the space 

 between being much wider than the depth. The figure shows 

 a shell of this variety. 



Polygyra inflecta media Pilsbry. In this variety the lip 

 denticles are widely spaced as in inflecta inflecta, but are reduced 

 in size to mere swellings on the peristome. The parietal plication 

 is also smaller and less massive than in the typical inflecta. 



Polygyra inflecta edentata (Sampson). The variation known 

 as edentata occurs in only about 1 per cent of the specimens of 

 Polygyra inflecta examined from Illinois. Denticles on the 

 peristome are indistinct, their presence being indicated in a few 

 examples by only a very small swelling. This variation was first 

 noted in Arkansas, and no records of it have been seen from 

 states other than Arkansas, Illinois and Indiana. The Illinois 



