1915.] NATURAL SCIENCES OF PHILADELPHIA. 395 
fading to white around the umbilicus and on both sides of the chestnut- 
brown shoulder band. 
The surface is glossy, lightly marked with growth lines, and 
under a strong lens showing impressed spiral lines on the upper 
surface of the last whorl (lacking, however, in many individuals). 
Initial 4 whorl radially rippled, granulation then beginning, the last 
2 whorl having close protractively spiral threads, the intervals densely 
wrinkled radially. Spire very low conic. Whorls 42, the last 
descending in front. The aperture is rounded oval; peristome 
narrowly expanding, inconspicuously brown-edged, slightly thickened 
within, the margins converging, joined by a thin, brownish-edged 
parietal callus. 
Alt. 14, diam. 23 mm.; umbilicus 2.6 mm.; aperture 12 x 13 mm. 
Genitalia (Pl. XII, figs. 1-3, 5, 5a).—The penis is small and slender, 
at the base enclosed in a short but thick sheath. Penis-papilla 
cylindric, more than half the length of penis, tapering distally to a 
blunt or a somewhat pointed end. Retractor muscle inserted on 
the epiphallus near its base. Epiphallus as long as the penis or 
somewhat longer, terminating in a minute, bud-like flagellum. Lower 
part of the vas deferens large, its diameter equal to or exceeding that 
of the epiphallus. Vagina usually about twice the length of the 
penis. 
Santa Rita Mountains, the type from Station 5, Walnut Branch 
of Agua Caliente Canyon, at about 6,000 feet, with S. santaritana 
and S. clappi, type No. 112,164, A. N.S. P., collected by Ferriss, 
Daniels and Pilsbry, 1910. Also taken at Station 3, ‘Soldier Can- 
yon,” at about 4,500 feet, and in Madera Canyon at Stations 7, 8 
and 15. 
This fine species, named for Dr. Bryant Walker, is not uncommon, 
though less generally distributed than S. santaritana. In the type 
locality it lives with S. santaritana and S. clappi, sometimes all under 
the same rock, sometimes in separate rock piles. The smallest 
specimens, Station 5, measure 20 mm. in diameter; the largest, 
Station 15, 24.3 mm. 
Station 3 is in a small canyon running in north of the mouth of 
Agua Caliente, opening to the mesa between two high granite crags. 
The rock is a coarse granite, and shells are not numerous. A single 
giant cactus growing here is further east than we have seen the 
species elsewhere. 
Many specimens have been dissected. The slender, short penis, 
with a short, thick basal sheath, and the enlarged free vas deferens 
