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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, 
without strie; 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.) 
Mf Bom 5 tp sey cL) rs eho os ernmay 2b warns 8 AU) 2455) 
: on o0s wt 408 ah tPO0 Ke Set Le (AO Bere) 
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 Zonitotdes arboreus, the pulsations 
regular, numbering eighty-seven to ninety beats per minute. 
Length of foot 5.00, width 1.00 mill. (Shell 5.75 mill. diameter.) 
Jaw: Arched, with a small median projection; anterior 
surface striated; ends bluntly rounded. 
Radula formula: 12+8+4+8-+ 12 (20—1—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 adternata. 
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.) 
