Plectostoma fraternum (Smith, 1905)
Smith (1905)'s description
"Testa dextrorsa, pyramidalis, anguste umbilicata, rufescens; anfractus 6 1/2, regulariter lente accrescentes, perconvexi, lamellis paucis, tenuibus, obliquis, in medio anfractuum in spinas productis, instructi, ultimus pone constrictus, dein descendens et subito ascendens atque retroversus, antice solutus, infra spinis excavatis cristatus; apertura subcircularis; peristoma obliquum, duplex, album, margine interno expanso, tubaeformi, externo tenuissimo, aliquanto dilatato. Diam. max 2.75 mm.; alt. 2.25."
Vermeulen (1994)'s description
"Spire conical with slightly convex sides. Apex slightly oblique. Whorls 5 5/8- 6 1/8, convex; last whorl rounded or slightly angular. Constriction with a parietalis, a longitudinal and a transverse palatalis, a columellaris. Tuba gradually narrowed towards the constriction, rounded below. Radial ribs widely spaced (1-2 ribs/0.5 mm on the penultimate whorl, 1 rib/0.5 mm half-way the tuba), with a deeply trough-shaped projection half-way, abrading to a scar with a deep, semi-circular loop (projection of those close to the tuba double-channeled either with both channels equally deep or with the upper channel much deeper than lower, abrading to a scar with single deep loop when the shell is observed in front view); those on the tuba below with a slightly curved projection. Spiral striation, inconspicuous. Umbilicus open, 0.20 mm across. Aperture hardly tilted with regard to the coiling axis, circular. Peristome distant from the spire, double; outer peristome spreading beyond the inner all around, though gradually somewhat narrowed along the right side of the aperture, somewhat widened along the upper side; inner peristome hardly protruding from the outer, spreading. Spire; height 2.1-2.4 mm; width 1.5-1.6 mm; index 1.4-1.5. Total width 2.8-3.0 mm. Height and width aperture 0.6-0.8 mm."