1910.] NATURAL SCIENCES OF PHILADELPHIA. 73 
and they probably never persist in the adult stage. All immature 
specimens taken by us in November, from diam. 10 mm. on, have 
a strong callous rib within the lip-edge. 
Adult stage-—There are 44 whorls in small, 42 in large individuals 
of the type lot, slowly increasing at first, the last whorl seen from above 
about twice as wide as the penultimate. The lip is blunt with rusty edge, 
but not thickened within. The outer margin is slightly expanded, the 
basal a trifle more so; parietal callus rather thick at the edge, straight. 
The umbilicus contained about 5.2 times in the total diameter. Alt. 
11.8, diam. 23.5 mm.; aperture 10 x 11.3 mm. 
Distribution: Southern side of White Tail Canyon, Chiricahua 
Mountains, Stations 1, 2, 3, 4, 5, 9, 12, 14. Type locality, Station 
No. 14. Also in Jhu Canyon. See map, fig. 6, p. 75. 
This is the only Sonorella on the southern side of White Tail Canyon, 
living on steep slopes varying from northeast to north or northwest. 
It occurs (in November) rather deep under rocks, and excepting on 
the more arid slopes and ridges, colonies may be found where suitable 
shelter occurs throughout the length of the canyon, generally rather 
high on the slopes, but in at least one case only about 20 feet above 
the bed of the canyon. The more favorable slopes, such as those 
Stations 5,14, 15 are situated on, are wooded with pinyon below, 
oak and a few long-leaf pine above. The ridges and slopes with 
southern or eastern exposure are barren or nearly so. The rock is 
limestone, mostly with covering of earth and fine stone, and there are 
no rock slides. Stations 1, 2, 4, and 9 are decidedly more arid and 
barren than 5 and 14, Station 5 being near the bottom of a deep narrow 
ravine, densely wooded, while Station 14 is on a steep shady northern 
slope. The lots taken show that the shells respond to more favorable 
conditions by reaching a larger size, as seen in the table of measurements. 
The shells from Station 5 have the spire somewhat more depressed 
than any other lot. Those from near Jim Artels’ old camp, near head 
of White Tail not far from Station 1, are the smallest. 
The table following shows the shells from high on the ridge (Stations 
1 and 4) to be in the main smaller than those from the mid-slope; but 
this ridge becomes very dry above, with less shade, while the slope 
lower down is well shaded on northwest exposures (caused by the 
lateral washes and ravines, running northward), the northeast exposures 
being for the most part barren. The size of individuals in the colonies 
collected appear, therefore, to be related to the amount of shade and 
moisture. 
