THE NAUTILUS. 91 
figuration of the aperture with its lamell:e and folds, it stands 
nearest Bifid. Ashmuni. These two species represent a new type 
among the already very different groups of the genus. 
Bifidaria Dalliana n. s). 
Shell minute, ovate-turriculate, perforate-rimate, pale horn-col- 
ored, translucent ; apex somewhat obtuse; whorls 5, regularly in- 
creasing, convex, with the suture deeper between the upper than the 
lower whorls; the last whor! ascending at the aperture, compressed at 
the periphery, especially so toward the aperture, with a slight, shal- 
low crest-elevation, its base narrow except just behind the aperture, 
where there is a slight depression ; surface with very fine, crowded 
strive; aperture equaling a little over one-third of altitude, almost 
as wide as high, rounded below, with three almost equal angles 
above, margins approximate, somewhat extended upward and con- 
nected by a slight, straight callus, somewhat everted, especially 
below, without a thickened lip. Lamelle and folds: angular and 
parietal rather large, connected but distinct, the former ending at 
the margin; a nodule-like infraparietal; columellar rather large, 
lamellar, horizontally encircling the somewhat projecting columella ; 
basal transverse (radial) on the impressed part of the base, short 
lamellar, abrupt; parietal folds approximate, the superior rather 
short, the inferior longer, deeper in the throat, somewhat oblique. 
Alt. 1.6 to 1.8, diam. 0.8 to 0.9, apert. alt. 0.6 mm. 
Soft parts very light-colored. Jaw rather strongly arcuate, with 
rather fine, irregular, crowded, tubercular ribs projecting as irregu- 
lar denticulations on the cutting edge. Radula 0.48 mm. long, 
0.13 wide, with 72 transverse rows of 19 teeth, c: 4:5; the central 
narrow, with three short cuspids, the laterals bicuspid; margiials: 
one tricuspid, the others serrate—four to six-cuspid. 
Habitat—Nogales, Arizona, with the preceding species. 
Bifid. Dalliana stands near b. hordeacella Pilsbry, for the smallest 
forms of which it might be mistaken, and some of the smallest West 
Indian species of the genus. From hordeacella it is distinguished 
by its being less cylindrical, the presence of the infraparietal nodule, 
and the basal being lamellar, placed radially upon the impressed 
part of the base, and nearer the margin than is the basal of hordea- 
cellu. These differences appear to be trifling, but they are signifi- 
cant. Over thirty lots of B. hordeacella, from Key West, through 
Florida, Mississippi, Texas, New Mexico, Arizona, and from dif- 
