406 PROCEEDINGS OF THE ACADEMY OF [June 
Alt. 12.7, diam. 21.3 mm.; whorls 43. 
‘cc 9.9, ce ik7¢ < 
“ec 9, as 16 iz “ee 4;. 
There was a scalariform specimen among the bones. It measures 
13.3 mm. high, 16.6 wide. The normal height for a shell of this 
diameter should be about 9.5 mm. 
The Mineral Hill group, Twin Buttes and Tinaja Hills are much 
degraded outliers of the Sierrita Mountains. Only the Mineral 
Hill group has been worked for land snails, though all doubtless 
have Sonorellas—and very little else. 
The Mineral Hills are about 20 miles west of south from Tucson 
and about 7 miles north of the Sierritas.3 They stand at the summit 
of a long slope, rising about 1,000 feet in ten miles from San Xavier 
del Bac, on a mesa of perhaps 3,600 feet elevation. The xerophytic 
vegetation extends over the hills, mesquite, cat-claw, palo verde, 
ocotillo and sotol being the more conspicuous plants, to which may 
be added tree cacti on southern slopes, and on the mesa many opun- 
tias, cylindropuntias and a few barrel cacti and yuccas. The 
absence of Agave is peculiar. These hills are a favorite resort of 
rattlesnakes. I got also a coral snake. No mollusks whatever 
were found on Mineral Hill or Helmet Peak. San Xavier Hill is 
composed of white subcarboniferous limestone, like the hills south- 
eastward, except at the western end, which is whitish quartz, with a 
spur to the north of coarse pinkish-gray granite. There is a depres- 
sion in this end of the hill, between short, low cliffs of white quartz. 
The cliff towards the south has partly fallen in a tumble of huge 
blocks with some smaller stone between them. This talus is perhaps 
200 feet long to the last scattered blocks, and at the widest 40 feet 
wide; its lower end about 200 feet above the mesa. In it we found 
the Sonorella described above. ‘‘Bones”’ were abundant, but living 
snails extremely scarce, and confined to the deeper portions of the 
talus, between the piled-up quartz blocks. The entire range of this 
species is not much greater than the area occupied by a moderate- 
sized house. In this insignificant fastness it is making a last stand 
against extermination. 
We found no snails in a hill covered with granite boulders about ~ OY 
3 miles north of west from San Xavier Hill. It is possible, though 
unlikely, that some insignificant colony may exist there. 
8 While there we occupied a comfortable camp at the copper mine of Mr. 
L. D. Chilson, of Tucson, whose courtesy we would here acknowledge. 
