112 



STROBILOPSIDAE 



This Strobilops snail is found generally distributed over 

 Illinois. Its habitat is in river valleys, on large river bluffs, in 

 woodland areas and less often in second growth woods and on 

 cut-over lands. Oak, elm, hickory, basswood, walnut and in 

 places pine are its natural cover. It has been found in all of the 

 state parks of Illinois, most often in second growth of oak and 

 hickory, and in the White Pines Forest State Park, Ogle County, 

 it has been found among pines. It is not common in floodplain 

 areas of Illinois. 



Strobilops labyrinthica virgo Pilsbry. A color form or albino 

 race of Strobilops labyrinthica^ virgo differs from the typical in 

 having a whitish or slightly greenish shell with white lip and 

 lamellae. In virgo the parietal lamellae emerge a little farther 

 than in the brown typical form, and the umbilicus is. often a 

 trifle smaller. The arrangement of the lamellae and folds is 

 about the same in both forms. The shell is usually somewhat 

 larger than that of labyrinthica labyrinthica and is more striking 

 in appearance. In Illinois, it has been seen from only four 

 counties: McHenry, Washington, Williamson and Saline. In 

 McHenry County it occurs with the brown typical form. It was 

 first discovered near Sebec, Maine. Its distribution extends from 

 Maine to Minnesota. 



Strobilops labyrinthica parietalis Pilsbry. In this variety or 

 form, the parietal lamellae penetrate more deeply into the shell 



aperture than in the typical variety, 



reaching as far back as two-thirds or, 



three-quarters of the last or body^l 



whorl. In other respects, this brown 



shell is similar to that of labyrinthica 



labyrinthica. 



In Illinois this variety has been 

 found in three counties only: Wash- 

 ington and Marion in the southern 

 part of the state, and La Salle in the | 

 northern part, where it is very rare. 

 The recently described variety parietalis may be found to be 

 more abundant in Illinois than the records indicate. Its distribu- 

 tion is said by Dr. Henry A. Pilsbry to be sporadic, the known 

 records being well scattered over the southeastern and southern 

 parts of the United States. Careful preparation of the shell is 

 needed for the determination of the variations of Strobilops. 



