THE NATURAL HISTORY SURVEY. 189 



in crevices of rotting wood, and under the bark of fallen, rot- 

 ten logs. 



Remarks: This is the most common of our small land 

 snails. When in progression the shell is carried on the back 

 at an angle of 45 degrees, tipping to the left side of the body, 

 and the head and neck are stretched far in advance of the aper- 

 ture of the shell. The eye-peduncles are always nervously 

 thrust about as though searching for danger, and the least 

 noise or jar will cause them to be drawn into the body. Arbo- 

 reus is infested by a curious parasite, Distoma appendiculata 

 Leidy,* which is sometimes found in considerable numbers. 

 Arboreus is more widely distributed than any other (excepting, 

 perhaps, Pyramidula alternatd) in this region, and there is prob- 

 ably not a single locality where it is not found. It loves com- 

 pany and is generally found by the dozen under the bark of 

 decaying trees or under chips of wood. 



SECTION PSEUDOHYALINA Morse. 



Surface of shell strongly striated. 

 72. Zonitoides minusculus Binney, pi. xxviii, fig. 12. 



Helix minusciila BINNEY, Bost. Journ. Nat. Hist., Vol. Ill, p. 435, pi. 



xxii, fig. 4, 1840. 



Helix minutilis MORELET, nee. FERUSSAC, Test. Nov., Vol. II, p. 1. 

 Helix apex ADAMS, Contr. Conch., p. 36. 



Helix lavelleana D'ORBIGNY, Moll. Cub., in text, p. 161, excl. pi. 1853. 

 Helix mauriniana D'ORBIGNY,!. c.,in pi. viii, figs. 20-22, excl. text. 1853. 

 Zonites minusculus var. alachuana DALL, Proc. U. S. Nat. Mus., p. 270, 



1885. (Variety.) 



Shell: Small, depressed, thin, umbilicated; surface shin- 

 ing, lines of growth strong; color white, periphery rounded; 

 sutures deeply impressed; whorls four, convex, slowly and regu- 

 larly increasing in size; spire almost flat, a trifle convex; aper- 

 ture very nearly circular, not expanded; peristome simple, 

 acute, the basal margin rounded; terminations of aperture not 

 approaching; umbilicus very large, deep, exhibiting all the vo- 

 lutions to the apex; columella with a thin, testaceous deposit; 

 base of shell convex (see Fig. 36). 



Greater diameter, 1.50; lesser, 1.30; height, 0.75 mill. (10235.) 

 2.50; " 2.10; " 0.75 " (12293.) 



Animal: With a narrow foot of medium length; eye-pe- 

 duncles not very long, cylindrical; color bluish-white; mucus 



*Proc. Phil. Acad., p. 202, 1877. 



