1910.] NATURAL SCIENCES OF PHILADELPHIA. 99 



thin, corneous-brown. The surface is lusterless, sculptured with fine, 

 unequal wrinkle-stria?, and covered with a network of cuticular scales 

 or processes (readily removed by cleaning). There are 5h whorls. 

 the first one corneous and glossy, the first three convex; subsequent 

 whorls convex above, impressed above the lower suture; last whorl is 

 distinctly impressed above the projecting peripheral keel, the base 

 convex; in front it descends slightly or not at all to the aperture, and 

 is narrowly, rather deeply, guttered close behind the lip on the base. 

 The aperture is lunate, contracted by four teeth : a wide one within 

 the outer lip, two contiguous tubercles in the basal lip, and an oblique 

 straight parietal tooth. Parietal callus thin and transparent. 



Alt. 4.8, diam. 11.7 mm. 

 " 4.2, " 11.2 " 

 " 5. " 11 



" 5.5, " 12.2 " 



White Tail Canyon, on the northern side only, at Stations 10, 11, 16, 

 17, etc., in "slides" of igenous rock (rhyolite) ; type locality, Station 

 11, in a slide of angular rhyolite, coming down to the trail in the bed 

 of the canyon, with Sonorella micro. See map on p. 75. 



Genitalia are of the type usual in the fissidens group. The epi- 

 phallus and spermatheca are a little shorter, proportionately, than in 

 A. p. albicauda or emigrans. Measurements of the organs of three 

 individuals may be found in the table on p. 97. The mantle within 

 the last whorl is cream-white with a few inconspicuous gray dots; 

 collar pale slate-tinted. 



This species, of which several hundred specimens were taken, 

 inhabits suitable rock-slides over the whole northern side of White 

 Tail Canyon. At Station 11 it occurs close to the bottom of the 

 canyon, and only a short distance from where .4. fissidens is found on 

 the opposite side. The slopes of this side of the canyon are steep, 

 interrupted by cliffs, and the heights are difficult of access. At 

 Station 16 there are extensive rock slides sloping northward towards 

 the mesa, and perhaps 1,500 feet higher than Station 11. Here it 

 passes over the ridge and inhabits the opposite slope. While belonging 

 to the fissidens group, this species is very distinct by its sculpture of 

 cuticular scales, the strong carination, thin texture, etc. The young 

 shells form only a weak callous rib within the lip at resting periods. 



At all the stations there is considerable variation in size and, as in 

 all Chiricahua Ashmunellas, the height of the spire varies a good deal 

 among individuals of any colony. At Station 17 the shells average 



