182 THE CHICAGO ACADEMY OF SCIENCES. 



when viewed from the aperture. As in Z. arboreus the head 

 and neck are carried far in advance of the shell, when in mo- 

 tion. This is also a common species, although not as numer- 

 ous in individuals as Z.'arboreus. It seems to occupy about the 

 same localities as that species. 



SECTION GLYPHYALINIA Martens, 1892. 



68. Vitrea indentata Say, pi. xxviii, fig. 11. 



Helix indentata SAY, Journ. Phil. Acad., Vol. II, p. 372, 1822. 

 Hyalinia subrupicola DALL, Bull. U. S. Geol. and Geogr. Surv. of Terr., 



Vol. Ill, p. 163, 1879. 

 Zonites indentatus var. untbilicatus SINGLEY, British Naturalist, April, 



1893, p. 81. 



Shell: Small, depressed, thin, pellucid, subperforated, fre- 

 quently almost imperforate; surface shining, polished, covered 

 with strong, impressed striae which are equidistant, the spaces 

 on the last whorl being much wider than the striae; color, yel- 

 lowish or dark horn; periphery rounded; sutures impressed; 

 whorls four and one-half, rapidly increasing, the outer whorl rap- 



FIG. 38. 

 Jaw of VITREA INDENTATA Say. (Original.) 



idly enlarging as it approaches the aperture; spire flat, a little 

 convex; aperture large, transversely oval; peristome simple, 

 thin, acute, the lower portion extending clear to the umbilicus; 

 umbilicus not perforated, but the region is strongly indented; 

 base of shell convex ( Fig. 36).* 



Greater diameter, 5.00; lesser, 4.50; height, 2.50 mill. (10221.) 

 5.00; " 4.50; " 2.75 " (10222.) 



Animal: Similar to Z. arboreus and V. hammonis; black- 

 ish above, lighter below and on the sides; foot 9 mill, long, 

 2 mill, wide, shell 5 mill., greater diameter. Heart as in the 

 other species of the genus, pulsations regular, 160-162 beats 

 per minute. When the animal is emerging from the shell the 

 heart almost stops beating. 



Jaw : Long, narrow, somewhat bow-shaped, ends bluntly 

 pointed; upper margin rounded, lower margin with a broad, 

 median projection (Fig. 38). 



*These figures are introduced to enable the student to perceive the differences between 

 these minute shells. 



