186 THE CHICAGO ACADEMY OF SCIENCES. 



Subfamily Ariophantina-. 

 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; aperture lunate . .nitidus 



2. ShellS mill, in diameter, spire depressed; aperture trans- 



versely rounded arboreus 



B. Shell small, striated. 



1. Shell less than 3 mill, in diameter, umbilicus spreading, 



not deep minusculus 



70. Zonitoides nitidus Miiller, pi. xxviii, fig. 16. 



Helix nitida MULLER, Hist. Verm., Vol. II, p. 32, 1774. 

 Helix 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.) 

 6.25; " 5.50; " 3.00; " 1.50 " (12294.) 



6.00; " 5.00; " 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. 



Jaw: Similar to that of arboreus, 



Radula formula: V+l + i+H" ^(24 I 24); central 

 tooth with a base of attachment which is longer than wide; re- 

 flected portion tricuspid, the central cusp very long, the side 



