290 AMERICAN JOURNAL 



slightly attached to the penultimate whorl ; umbilical channel 

 rather wide, rimate, and bordered by a carina, to which the 

 longitudinal ribs extend and join. 



The above interesting species we consider the type of a 

 new genus. It may be called an operculoid Vertigo, as it re- 

 sembles that genus very closely. The spire of two specimens 

 we received is obtuse, but the large majority are acute at the 

 apex, which has the appearance of shells that become decol- 

 lated, two or three whorls being much smaller than the rest. 

 The operculum is membranaceous, circular, consisting of 

 about 5 volutions, nucleus central. "We defer giving generic 

 characters, until more species are obtained, but would propose 

 the generic name "P^/_2)o^V/ea." 



7. Pterocyclos ? PARVA, Pease. 



Descri-ption. — T. turbinata, solida, fusco-rufescens, longitu- 

 dinaliter tenuissime striata, apice acuto, late umbilicata ; anfr. 

 4, ultimo ad peripheriam angulato et costato, basi bicostato, 

 spira unicostata, costis rugosis ; perist. continuo, anfr. penul- 

 timo vix adnato ; apertura rotundato ovata. 



Dimensions. — Alt. 2|, diam. 3| mill. 



Shell turbinate, depressly conical, solid; spire acute, amber- 

 color or brownish-red, longitudinally finely striated ; whorls 

 4, angulate and ribbed at the periphery, a single rib encircling 

 the spire and two on the base of the shell ; ribs wrinkled or 

 granulose ; whorls of the spire angulate ; lip simple, continu- 

 ous, attached slightly to the penultimate whorl; aperture 

 nearly circular, angulate posteriorly; umbilicus open, com- 

 prising about one-fourth of the diameter of the shell. 



We have placed this species provisionally under genus 

 Pterocyclos, for reason of the peculiar shape of its operculum. 

 It may, however, form the type of a new sub-genus. The 

 operculum is horny, and may be described as a hollow screw. 

 The outer end is blunt and slighly indented, the thread on 

 the outside makes three revolutions; at the lower or oj^en 

 end the edge is expanded, forming a thin disc. The interior 

 is smooth, the course of the outer threads being defined by 

 fine strias. The operculum is embedded and held by the disc 

 at the lower end, also by the threads and a muscle which fills 

 the interior cavity, so that it is very difficult to detach safely. 

 If macerated, the operculum is likely to fall to pieces. It is 

 possible that Cycl. apise (Reel.) and strigattis (Gld.) collected 

 by the American Exploring Expedition at the Samoas, may 

 prove to belong to the same genus as the above, although 

 M. Recluz's description of the operculum does not agree with 

 ours. 



