THE NATURAL HISTORY SURVEY. 211 



are as much developed on the base as on the upper surface; 

 color uniform dark horn, paler in some specimens; periphery 

 rounded; sutures very deeply impressed; apex large, smooth, 

 withput striae; whorls four, regularly increasing, the last in- 

 flated; spire a little elevated and convex; aperture nearly cir- 

 cular; peristome sharp, simple, the terminations approaching 

 each other but not connected by a callus; columella rounded; 

 umbilicus widely open, spreading, exhibiting all the volutions 

 to the apex; base slightly rounded. 



Gr. diam., 5.75; lesser, 5.00; height, 2.50; umbilicus diam., 1.50 mill. (10229.) 

 " 5.50; " 5.00; " 2.75; " " 2.00 " (10228.) 



" 5.00; " 4.50; " 2.50; " " 1.50 " (10227.) 



Animal: With a rather short foot, truncated before and 

 rounded behind, the margins having the same wide border and 

 groove as in the other species of the genus; tentacles short, 

 thick, blunt; eye-peduncles long, cylindrical, not much taper- 

 ing, the eyes on large swellings at their tips; color blackish or 

 dusky bluish above, dirty white beneath, including all of the 

 foot. Heart situated as in Zonitoides arboreus, the pulsations 

 regular, numbering eighty-seven to ninety beats per minute. 

 Length of foot 5.00, width r.oo mill. (Shell 5.75 mill, diameter.) 



Jaw: Arched, with a small median projection; anterior 

 surface striated; ends bluntly rounded. 



Radula formula: V+l+i+f +V (20 I 20); central tooth 

 with a base of attachment a little longer than wide, not much 

 expanded at the outer lower corners; reflection tricuspid, the 

 central cusp long and narrow, the side cusps very short and 

 thick; lateral teeth similar to central but bicuspid, the inner 

 cusp long and narrow, reaching below the base of attachment 

 and the outer cusp very short; marginals variable in form, all 

 bicuspid, the inner cusp long and pointed and the outer cusp 

 short, the base of attachment becoming very broad. All cusps 

 have well-developed cutting points. There are about 100 

 rows of teeth. 



The radula and jaw do not differ materially from those of 

 alternata (Fig. 48), excepting that the bases of attachment are 

 more square and not so much produced as in alternata. 



Genitalia: See generic description. 



Distribution: "Ontario to Winnipeg, Manitoba, Montana 

 and Vancouver Islands, south to New Mexico and Arizona. 

 Kern River Region, California. (Pilsbry.) Northern China, 

 Kamchatka and Alaska. (Randolph.) 



