Plectostoma pulchellum (Godwin-Austen, 1890)
Dem O. (G.) grandispinosum ähnlich, aber mit kürzeren Stacheln.” (Kobelt, 1902)
“The specimens from Barit Mountain have a thicker and less conical spire than typical examples; but as they agree in every detail of sculpture, I think it advisable to regard them at present in the light of a variety rather than as a distinct species.” (E.A. Smith, 1894)
Godwin-Austen (1890) original descriptions on Opisthostoma pulchella – “Shell pyramidal, thin, narrowly perforate; sculpture, wavy costulation on a smooth surface; upon the lower whorls this forms the base of sharp, thin, white cirque-like bands standing at right angles to the whorl; on the penultimate and antepenultimate these in the centre are produced into short spines, they are generally found worn off at an early stage of growth: colour ochraceous with a golden tinge, nearly white on the free portion of the whorl; spire conical; apex papillate; suture much impressed, whorls 7 up to the constricted portion, whence the latter part is free and curved outwards from the axis and upwards; aperture circular; peristome double, very thin, much expanded, particularly the outer margin.”
Sowerby (1896) original descriptions on syntype Opisthostoma linterae – “Testa ovato-conica, elata, rufescens vel alba, anguste perforata; spira leviter convexa; anfractus 7, convexi, apicales laeves, caeteri lamellis numerosis tenuissimis pellucidis undulatis in medio plus minusve productis instructi; anfractus ultimus versus aperturam valde contortus, retrorsus et solutus, lamellis antice productis, cristam basalem formans; apertura circularis; peristoma leviter reflexum, extus lamella tenuis, expansa, antice et postice producta marginata.
Kobelt (1902) descriptions on Opisthostoma (Geothauma) linterae – “Schale eng durchbohrt, ei-kegelförmig, rötlich oder weiss; Gewinde leicht gewölbt; 7 gewölbte Windungen, die obersten glatt, die folgenden mit dünnen, welligen, in der Mitte vorgezogenen Lamellen, letzte vorn sehr verdreht, zurückgewendet, abgelöst, Lamelle vorn vorgezogen, unten eine Kante bildend; Mündung kreisrund; Mundrand leicht zurückgeschlagen, mit breitöm, dünnem, ausgebreitetem, oben und unten vorgezogenem Saum.”
Kobelt (1902) descriptions on Opisthostoma (Geothauma) pulchellum – “Schale eng durchbohrt, kegelförmig, dünn, mit welligen Rippen, die auf den unteren Windungen häufig abgebrochene Stacheln tragen, gold-ockerfarben; Apex zitzenförmig; Naht sehr eingedrückt; 7 Windungen, letzte eingeschnürt, dann abgelöst, nach aussen und oben gekrümmt, mit grösseren, lamellenartigen Stacheln; Mündung kreisrund; Mundrand doppelt, sehr dünn, sehr ausgebreitet, besonders rechts.”
By Vermeulen (1994)
"Spire conical with flat to concave sides. Apex slightly oblique or not. Whorls 5 3/4- 6 7/8, convex; last whorl rounded. Constriction with a parietalis, a longitudinal and a transverse palatalis, a distinct columellaris which continues as a ridge-shaped transverse basalis or not. Tuba gradually to rather abruptly narrowed towards the constriction, rounded below. Radial ribs on the spire rather closely placed to widely spaced (1-7 ribs/0.5 mm on the penultimate whorl), sinuous, often with a shallowly concave projection half-way, abrading to a (slightly) sinuous scar, those on the tuba moderately to widely spaced (2-3 ribs /0.5 mm half-way), below with a shallowly concave projection, abrading to a not or slightly sinuous scar. Spiral striation absent. Umbilicus open, 0.15-0.25 mm across. Aperture tilted up to 30 degree with regard to the coiling axis, circular. Peristome double; outer peristome (widely) spreading beyond the inner, but rather abruptly narrowed towards, and absent along the right side of the aperture, with a distinct, widely rounded to obtuse wing along the upper side, and usually a similar but less conspicuous wing along the lower side; inner peristome hardly to distinctly protruding from the outer, spreading. Spire: height 2.4-3.5 mm; width 1.6-2.2 mm; index 1.4-1.6. Total width 3.0-4.0 mm; Height and width aperture 0.7-1.0 mm"
Opisthostoma linterae – “Alt. 4, diam. maj. 4, min. 2.” (Sowerby, 1896); Opisthostoma (Geothauma) pulchellum – “2.3, Durchm. 2.2 mm.” (Kobelt, 1902); Opisthostoma (Geothauma) linterae – “H. 4, Durchm. 4 : 2 mm.” (Kobelt, 1902)
Shell height – 2.3 mm; Shell width – 2.2 mm.
Type locality – “Baram district, Borneo” leg. C. Hose (Godwin-Austen, 1890)
Other localities – “Mulu, Tampasang, and Barit Mountain” leg. A. Everett (E.A. Smith, 1894)
Lower Tutoh Valley, Sarawak, Malaysia.