ao 
38 THE NAUTILUS. 
would be an interesting task of Paleontology, to detect a fossil form, 
or forms, from which the recent ones are derived. 
So far, it has not been possible to examine the soft parts and thus 
complete our knowledge and description of the species; but it is to 
be expected that the necessary fresh, if possible living specimens will 
be found, and I hereby would invite the active collectors of the 
north-western States to look specially for this Pupa, in order not 
only to make a complete examination, but also to know more about 
its geographical distribution, and possible variations. 
Description. 
Shell narrowly perforated, turrited-cylindrical, vitreous (or whit- 
ish), very minutely striate, shining; apex rather pointed ; whorls 5, 
regularly increasing, well rounded, especially the upper ones, the last 
somewhat narrowed and a little ascending towards the aperture, 
compressed at the base but not carinated, at some distance from the 
outer margin provided with an oblique, rather prominent, acute 
crest corresponding in direction to the lines of growth, extending 
from the base to the suture, formed by a whitish callosity ; behind the 
crest the whorl is flattened, and corresponding to the lower palatal 
lamella, impressed; aperture lateral, scarcely oblique, relatively 
small, inverted subovate, with a slight sinus at the upper part of 
the outer wall, margins approximated; peristome moderately re- 
flected ; lamellee 6; one parietal, rather long, very high, in its 
middle part curved outward, towards the aperture bifurcated, the 
outer branch reaching the parietal wall; one columellar, longitu- 
dinal, rather high, its upper end turning in nearly a right angle 
towards the aperture, but not reaching the margin ; basal exactly at 
the base, short, high, dentiform ; 3 in the outer wall, viz.: the lower 
palatal long ending in the callus, highest at about its middle; the 
upper short, rather high on the callous ; above the upper one supra- 
palatal, quite small, dentiform, nearer the margin. 
Length 1:7 mill., diam. 0°8 mill. (‘068 x ‘032 inches). 
As already stated, our species ranges beside P. armifera and P. 
contracta Say, standing nearer the latter. Yet it is different from 
this species by the shape of the aperture, the wanting callous* con- 
necting the margins on the body whorl, by the longer crest behind 
the aperture, which in contracta disappears in about the middle of 
* In many specimens of P. contracta so strongly developed, that the peri- 
stome is rendered continuous. 
