494 PROCEEDINGS OF THE ACADEMY OF [Juiie, 



Black Mountain is a rather remote and isolated outlier of the 

 Tucson Range, which has here its southeastern terminus. It is a 

 long, straight, level-topped ridge, divided by a deep gap into a 

 longer and a shorter mountain. The slopes are everywhere very 

 steep, covered with black basalt, like Tumamoc Hill at Tucson. 

 Slides of this rock occupy a large part of the slopes. Between the 

 slides, which are, of course, barren of vegetation, there is some desert 

 verdure. Ocotillo, mesquite, cat-claw, palo verde, etc., are typical 

 plants, and giant cacti grow on the south side. No agave or sotol 

 were seen. The Sonorellas are found rather deep in the slides. 

 They probably inhabit the whole northern slope, but we worked 

 only a couple of hours, on the north side of the east end, close under 

 the summit. Some hazard attends the hunt in these slides, which 

 axe s® steep that the heavy rock starts to move on small provocation. 

 Black Mountain, like the rest of the Tucson Range, is very dry. 

 It stands on a plain much lower than the Mineral Hill group and 

 higher than Tucson. The station where Sonorella was collected 

 we would roughly estimate as 3,200 or 3,300 feet above the sea. 

 Sonorella eremita n. sp. PI. VIII, figs. 7 to 7e. 



The shell is globose-depressed, umbilicate (the width of umbilicus 

 contained about 6^ times in the diameter of shell), more solid than 

 other species of the same region, glossy, pinkish buff, fading to nearly 

 white around the umbilicus, and having a chestnut-brown shoulder 

 band, without noticeable light borders. The embryonic shell, of 

 about 1| whorls, has strongly developed sculpture of the hachitana 

 type. The initial half-whorl has some radial ripples or wrinkles; 

 then there appears a series of long, protractive threads on the outer 

 two-thirds, meeting shorter forwardly ascending threads on the 

 inner third; the intervals occupied by short radial impressions. 

 The threads are subject to more or less interruption, particularly 

 on the greatest convexity of the whorl. The later whorls are marked 

 with very fine, unequal growth-lines. 



The spire is very low, conoidal. Whorls 4|, moderately convex, 

 the last slowly descending in front. The oblique aperture is rounded, 

 but slightly wider than high. Peristome slightly expanded above, 

 the outer and basal margins expanding more, slightly thickened, 

 the margins converging, connected by a very thin parietal film. 



Alt. 11.9, diam. 19.3 mm.; umbilicus 3 mm. 



West end of San Xavier Hill, Mineral Hill group, about 20 miles' 

 S. S. W. of Tucson, Pima Go., Arizona. Types No. 112,161, A. N. 

 S. P., collected by Pilsbry and Daniels, 1910. Topotypes in col- 

 lections of Ferriss and Daniels. 



