GASTROCOPTA, NORTH AMERICA, WEST INDIES. 43 



Mexico; and from the Organ Mountains and Whiteoaks, Lin- 

 coln Co., N. M., on the east, to the vicinity of Jerome, Yava- 

 pai Co., Arizona, on the west. Chiefly in broken country and 

 foothills, but up to about 8000 ft. in some places. 



Bifidaria ashmuni STERKI, Nautilus, xii, Sept. 1898, p. 49 

 (Santa Rita Mts., Arizona, Ashmun; Cook's Peak and Drip- 

 ping Spring, Organ Mts., N. M., Cockerell). ASHMUN, Nau- 

 tilus, xiii, p. 14 (Santa Rita Mts., 20 miles from. Crittenden). 

 -PiLSBRY and FERRISS, Proc. A. N. S. Phila., 1906, p. 144; 

 1910, pp. 137-139, f. 30.-- Bifidaria ashmuni form minor 

 STERKI, Nautilus, xii, Dec. 1898, p. 92 (Nogales, Arizona). 

 PILSBRY and FERRISS, Proc. A. N. S. Phila., 1910, p. 139, f. 

 31. ASHMUN, Nautilus, xiii, p. 14. 



This species is readily known by the strong development 

 of the angulo-parietal lamella, the very deep immersion of 

 the lower palatal and basal folds, the anterior continuation 

 of the columellar lamella upon the parietal wall, alongside the 

 parietal lamella, and the long, gibbous neck of the last whorl. 



It is a common species within the limits given above, the 

 territory being well covered by over fifty lots in the museum 

 of the Academy, collected chiefly by Ashrnun, Ferriss and 

 the writer. 



The typical form of G. ashmuni is nearly cylindric, taper- 

 ing but slightly, composed of five strongly convex whorls. 

 The last whorl becomes straightened and slightly sinuous in 

 basal view, and has a more or less conspicuous oblique swell- 

 ing or crest some distance behind the aperture. This crest is 

 not always so strong, as shown in fig. 13 c (a specimen from 

 Page's Ranch, Oak Creek, in central Arizona), and sometimes 

 it varies from strong to wanting in the same lot. The peri- 

 stome is well expanded, continuous, and usually stands shortly 

 free from the whorl in front. The parietal lamella is sig- 

 moid, bending far to the right at its inner end. The angular 

 lamella, also sigmoid, runs from the peristome to the parietal 

 lamella, the two lamelke together forming a figure like the 

 letter X. The columellar lamella is broad and horizontal far 

 within, arising a half -whorl back (pi. 6, fig. 7), then sinuated 

 where the basal plica approaches it, as shown in pi. 6, fig. 6, 



