1910.] NATURAL SCIENCES OF PHILADELPHIA. 141 
fold is very small. The upper margin of the peristome is adnate 
for some distance. In this form, or race, if such it proves to be, 
B. ashmumi cochisensis makes its nearest approach to B. dalliana and 
to the following race. 
Possibly Dr. Sterki at the time of his original description had 
cochisensis before him, together with typical ashmuni, since he mentions 
‘specimens from the Santa Rita Mountains. We have examined a 
lot collected by Mr. Ashmun at that place and find them all to be 
.cochisensis. The terms of Sterki’s original description apply only 
to the form herein defined as ashmuni, for he mentions the crest 
Fig. 33.—Bijidaria cochisensis P. and F. Santa Rita Mountains, Arizona. 
“forming a projecting angle at the base” and the columellar lamella 
“ascending to the body-whorl between the parietal and columella.’ 
Careful examination of a series of several thousand examples, supplying 
data for the present account, has shown no intergrading forms between 
ashmuni and cochisensis, yet careful cleaning of the aperture is neces- 
sary for their discrimination. 
Bifidaria cochisensis oligobasodon n. subsp. Fig. 34, a, b, c. 
The shell is externally similar to B. cochisensis, but differs by the 
reduction of all the teeth. The parietal barrier is simplified (fig. 34 b), 
and the basal fold is reduced to a minute tubercle or a mere vestige, 
-or in a few apparently mature shells it seems to be wholly lost. Parietal 
margin adnate. 
