1910.] NATURAL SCIENCES OF PHILADELPHIA. 137 
b.—Columellar lamella running forward on the parietal wall in the 
position of an infraparietal lamella; inner end of the parietal 
lamella curving strongly toward the outer wall. 
WCC AOU Ao MOND: 22... s.cse.sececedoarece caheace B. ashmuni Sterki. 
Gee ONSEN AG GO. POU TANI, ..c.58.s6cc0 ss stcsae eeonnedee. B. a. minor Sterki. 
b'.—Columellar lamella normal in position, horizontal and con- 
spicuous in a front view. 
c.—Parietal barrier /-shaped, the inner end curving more or 
less towards the outer wall. 
d.—Basal fold well-developed, radial. 
B. cochisensis P. and F. 
d!.—Basal fold minute; angular lamella reduced. 
B. c. oligobasodon P. and F, 
d?,—Basal fold wanting; angular lamella reduced. 
B. prototypus Pils. 
c'.—Parietal lamella straight or bending slightly toward the 
columella at its inner end; shell small, rather slender. 
d.—Length 2, diam. 0.85 mm., or smaller; nearly cylindric. 
B. dalliana Sterki. 
d'.—Length 2 to 2.4, diam. 0.9; spire tapering more. 
B. bilamellata 8. and C.*° 
Bifidaria perversa Sterki. Fig. 29. 
Bifidaria perversa Sterki, Nautilus, XII, December, 1898, p. 90 (Nogales). 
Found in the Chiricahuas in the Valley of Turkey Creek below 
Paradise and in White Tail Canyon. Here- 
tofore known only from Nogales and the drift 
débris of the San Pedro River at Benson, 
Arizona. 
Bifidaria ashmuni Sterki. Fig. 30, a, b,c. 
Bifidaria ashmuni Sterki, Nautilus, XII, Sept., 
1898, p. 49 (Santa Rita Mountains, Arizona; 
Cook’s Peak and Dripping Springs, Organ Moun- 
tains, New Mexico). 
Bifidaria ashmuni form minor Sterki, t.c., Dec., 
1898, p. 92 (Nogales, Arizona). 
The typical form of B. ashmuni is nearly 
Fig. 29.—B. perversa, 
cylindric, tapering but slightly, composed of basal view, most of 
; the basal wall re- 
five strongly convex whorls. The last whorl imGvedh to show <the 
becomes straightened and slightly sinuous in sneer eee ae 
c : an colume ar 
basal vlew, and has a more or less conspicuous lainelie, 
oblique swelling or crest some distance behind 
the aperture. This crest is not always so strong, as shown in fig. 30 ¢ 
(a specimen from Page’s Ranch, Oak Creek, in central Arizona). The 
*® Bifidaria bilamellata Sterki and Clapp, Nautilus, XXII, pl. 8, fig. 7 (March, 
1909). Sterki, Nautilus, XXII, p. 126 (April, 1909). Yuma County, Arizona, 
