Diagnosis. Slightly curved posteriorly. Height ca. 35% of length. Outer surface sculptured by weak irregular, radial, low lines, sometimes coalescing, ca. 70 (close to aperture). Foramen shorter than half shell height.
Description. Shell size ca. 4 mm; high-conical, slightly arched posteriorly; height ca. 35% of length. White, translucent. Protoconch lost. Foramen terminal, oval, width 41% of length; turned dorsally; 2% of aperture area; edges rather irregular. Teleoconch widening towards aperture; total shell angle ca. 110°. Sculpture almost smooth, except for weak sculpture of irregular radial lines, ca. 70 close to aperture, arranged in mosaic of coalescing, divergent lines; mosaic crowded towards apex, retaining the same number of radial lines from dorsal to ventral; lines surrounded by smooth interspaces as wide as lines. Aperture slightly concave, elliptical, width 74% of length; edges irregular. Inner surface smooth, glossy. Septum slightly curved (concavity posterior), ca. 1/2 of shell height; about as high as wide, ventral edge straight, with ca. 30% of aperture width; narrowing up to posterior edge of foramen, forming posterior, ventral floor of foramen .
Measurements (in mm). Holotype: 3.8 by 1.3.

The generic attribution of P. volcano is based on the loss of the protoconch, and by the rounded shape of the fissure (following definition by Farfante 1947). An attribution to the genus Fissurisepta Seguenza, 1862 to P. volcano is not plausible because it is lower, more curved backwards at the apex, the foramen is wider and more elongated, and the sculpture is not so developed.
The low shell profile and the weak shell sculpture distinguish this species from any other congeneric species in the Atlantic, which have stronger radial ribs or threads. The species differs from P. sportella Watson, 1883, in lacking radial pits or ribs, and by the shorter septum.

Type locality. Brazil. Espirito Santo; off Itaunas, continental slope of Abrolhos. 18°59*S 37°48'W, 607 620
Distribution. Only known from type locality.
Habitat. Sandy bottoms, 607 620 m (dead specimen).