76 PROCEEDINGS OF THE ACADEMY OF [Feb., 
noticeably expanded, basal margin somewhat more so; columellar 
margin rather broadly dilated and brought forward. The parietal 
callus is short, thin and transparent. 
Alt. 7.2, diam. 14.5 mm.; aperture 7.5 mm. wide, 7 high. Whorls 
44, 
Distribution: North side of White Tail Canyon, in slides of igneous 
rock (rhyolite), at Stations 10, 11,15, 16,17. Type locality, Station 10. 
See map on p. 75. 
This is the smallest Sonorella yet known from the Chiricahuas. It 
is allied to S. virilis by the genitalia and the indistinct sculpture 
pattern on the embryonic whorls, but differs by its diminutive size, 
thin shell, comparatively narrower umbilicus and the absence of 
distinct white borders along the brown band. 
S. micra occupies the north side of White Tail Canyon to the exclu- 
sion of S. virilis leucura, which lives on the opposite or south side. 
It lives in “slides” of angular, dark purplish-gray rock (rhyolite), 
together with Ashmunella lepiderma, and can be found only deep in 
the rocks, where they rest on the earth below. ‘The slopes are mainly 
toward the south and west, hence exposed to the direct sun, rarely 
shaded to any extent by the small trees. The snails are found from 
the bottom of the canyon (Station 11) to perhaps 6,800 feet (Station 
16), where they occur over the crest of the ridge, in an extensive slide 
sloping northward. The type locality, Station 10, is below the great 
cliffs along Indian Creek. The lower stations are easily accessible, 
but the higher call for arduous climbing and, from the nature of their 
haunts, the work of quarrying the snails out is severe. We secured 
but few living specimens, but many dead shells, more or less fresh, 
show the species to be remarkably constant. Besides a slight varia- 
tion in elevation of the spire, no variation in form is noticeable. 
Measurements of two lots follow: 
Digm/in mm... 125 ile toed. 1355) Wola Sie 14.25 
Sato LO). cuz. osc, i 0 0 1 2, fe 4 
Station L7isc.c00 0 1 0 4 4 10 4 
Diam. in mm........ 14.5 14:75 ALD 15:25 
Station 10.422" 4 7 7 1 
Stationely fic eH ik oF 2 0 
On the southern side of the canyon we found a few dead specimens 
among limestone rocks about 20 feet above the bed of the canyon, 
below the junction of Indian Creek. They}agree fully with those 
from the north side of the canyon. 
