1910.] NATURAL SCIENCES OF PHILADELPHIA. 143 
described from the State of Michoacan, Mexico, figured here for com- 
parison. In a long series of prototypus no specimen with even a 
vestigeal basal tooth was found. In view, therefore, of the very wide 
separation of the two forms geographically, it may be best to treat 
them as specifically diverse. 
Bifidaria dalliana Sterki. Fig. 36. 
Bifidaria dalliana Sterki, Nautilus, XII, p. 91, Dec., 1898. Pilsbry and 
Vanatta, Proc. A. N.S. Phila., 1900, p. 593, pl. 22, fig. 8. 
Chiricahua Mountains: Quartzite Peak near Fort Bowie; White 
Tail Canyon in several places (Ferriss and Pilsbry); Limestone Moun- 
tain and Shake Gulch (Ferriss). 
Other Arizona localities in collection A. N.S. P. are Nogales (type 
loc.), Santa Rita Mountains, Montezuma’s Well, Salt River near 
Tempe, Kirwagen’s ranch near Jerome; all collected by Mr. Ashmun. 
A B 
Fig. 36.—A. Bifidaria dalliana Sterki, front and obliquely basal views of a speci- 
men from White Tail Canyon below the junction of Indian Creek, Chiricahua 
Mountains. B, B. bilamellata S. and C, type. 
B. dalliana is related to B. cochisensis, but differs by being con- 
spicuously more slender, resembling B. p. hordeacella in shape, but it 
diverges more fundamentally by the parietal lamella, the inner end of 
which turns slightly toward the columella, while in B. ashmuni, cochis- 
ensis and perversa the inner end bends towards the outer wall. 
In the Chiricahuas the specimens are often longer than the types, 
one figured here measuring 2 mm. long, .85 wide. 
Bifidaria bilamellata Sterki and Clapp stands very close to B. dal- 
liana, but it differs by having a perceptibly more tapering spire, 
_ which is somewhat longer, and the columellar lamella has a vertical 
