158 THE CHICAGO ACADEMY OF SCIENCES. 



Genitalia: "The penis sac is short, stout, cylindrical, re- 

 ceiving the vas deferens and retractor muscle at its summit; 

 the genital bladder is small, elongated, bluntly tapering at its 

 apex, on a short, narrow duct; the oviduct is greatly convo- 

 luted." (W. G. Binney, 1. c.) 



Distribution: Canada to Minnesota, south to St. Simons 

 Islands, Georgia, and Texas. (Pilsbry.) 



Geological distribution: Pleistocene; Loess. 



Habitat: Found under rotten logs and pieces of wood in 

 forests where there is more or less moisture, particularly near 

 the edge of the woods. On rainy days or just after a rain, it 

 may be seen crawling over the ground, on tree trunks, etc. 



Remarks: Thyroides is distinguished from all others of the 

 group by its open umbilicus, thin, spreading peristome and 

 wide aperture. The parietal tooth is frequently wanting, and 

 a variety of the bucculenta form is imperf orate. In habits the 

 animal varies, some specimens being shy in captivity and re- 

 quiring a great amount of persuasion to induce them to crawl 

 over the hand or on a table; other individuals are bold and 

 will readily crawl over the extended hand, and will even allow 

 themselves to be picked up by the shell without withdrawing 

 into it. It is found in all parts of the area. 



58. Polygyra clausa Say, pi. xxix, fig. 4. 



Helix clausa SAY, Journ. Phil. Acad., Vol. II, p. 154, 1821. 



Helix ingallsiana SHUTTLEWORTH, Fischer's Notitiae, Vol. II, pi. iii, 

 fig. 5. 



Shell: Semi-globose, varying from thin to rather solid, 

 umbilicated; surface with very numerous crowded, oblique, 

 rib-like lines of growth, crossed by numerous fine spiral lines; 

 the nuclear whorl is smooth; color yellowish to greenish-horn; 

 periphery broadly rounded, sutures deeply impressed; whorls 

 five to five and one-half, rounded, convex, rather closely and 

 regularly increasing, the last a little spreading; spire varying 

 from somewhat depressed to elevated and sub-conical; aperture 

 diagonally lunate, expanded above, narrowed below, the colu- 

 mella a trifle dilated; peristome contracted behind the narrowly 

 reflected portion, which is white and rounded in old specimens; 

 the terminations widely separated and connected by a very thin 

 callus; umbilicus of good size, partly covered by the reflected 

 columellar portion of the peristome; base of shell rounded. 



Greater diameter, 17.00; lesser, 15.00; height, 10.50; mill. (11910.) 

 18.00; " 15.00; " 12.00; " (12406.) 



