186 THE CHICAGO ACADEMY OF SCIENCES. 
Subfamily Ariophantine. 
Genus ZONITOIDES Lehmann. 
Whorls rounded below, polished; aperture without callus; 
otherwise similar to Gastrodonta. 
KEY TO SPECIES OF ZONITOIDES. 
A. Shell large, polished, smooth. 
1. Shell 6-7 mill. in diameter,spire elevated; aperturelunate . .1z¢idus 
2. Shell5 mill.in diameter, spire depressed; aperture trans- 
versely roUndEeG, ;*)2 555. ote cs nctet ne eke eeamen '.,..arboreus 
B. Shell small, striated. 
1. Shell less than 3 mill. in diameter, umbilicus spreading, 
Hotideep.. fA Pipe De ade tenn Seale hehe Peas ae minusculus 
70. Zonitoides nitidus Miiller, pl. xxviii, fig. 16. 
Helix nitida MULLER, Hist. Verm., Vol. II, p. 32, 1774. 
Flelix hydrophila, INGALLS, Mss. 
Shell: Orbicularly depressed, thin, umbilicated; surface 
shining, covered with rather strong lines of growth; color 
smoky-horn; periphery rounded; sutures impressed; whorls 
five, convex, regularly increasing, except the last, which is 
very large in proportion, and obtusely angled on the periphery 
as it approaches the aperture; spire rather elevated, convex; 
aperture lunate, oblique; peristome simple, acute, the basal 
margin bow-shaped; terminations of aperture not approaching; 
umbilicus round, broad, deep, exhibiting the volutions to the 
apex; base of shell concave about the umbilicus, convex on 
the last whorl. 
Gr. diam., 6.00; lesser, 5.00; height, 4.00; umbilicus diam., 1.25 mill. (10224.) 
rf 6.25; “ 5,50; pee LIE af 1.50 “ (12294.) : 
6.003 5°" 08; #65 3,00; ¥ 1.25 “ (12224.) 
Animal; Blackish or grayish, otherwise similar to Z. ar- 
boreus Say. The heart is situated in a direct line with the in- 
ferior portion of the peristome, to the left of the umbilicus; 
pulsations regular, one hundred and one per minute when 
crawling on glass and one hundred and twenty-three to one 
hundred and thirty-eight when held in the hand; holding the 
shell in the hand seems to irritate or excite the animal, and 
cause the pulsations to increase. Length of foot when ex- | 
tended 9.00 mill., width 1.50 mill. 
Faw: Similar to that of arboreus. 
Radula formula: 149+4+4+4+19(24—1—24); central 
tooth with a base of attachment which is longer than wide; re- 
flected portion tricuspid, the central cusp very long, the side 
(ge koa) ea ee ees 
