Plectostoma mirabile (Smith, 1893)
“The long upcurved spines which form a single series around the whorls are almost straight upon the upper volutions, but upon the last, which is detached for some distance from the penultimate and is twisted backward and upward, they are much curved towards the umbilicus. They are pellucid and semitubular. The most striking feature of this wonderful species is the great development o£ the last lamella behind the aperture, where it forms a sort of ear-shaped shield.” (E. A. Smith, 1894)
“Kükenthal hat diese wunderbare Form in etwa einem Dutzend Exemplaren vom Baramflufs mitgebracht; sie entsprechen vollständig der Smith’schen Abbildung und Beschreibung. Etwa zwei Drittel sind gefarbt, ein Drittel bei tadelloser Erhaltung farblos und durchsichtig.” (Kobelt, 1897)
“The very elongated ribs and sinuately twisted last whorl identify this beautiful little species. It is slightly larger (Height 4.3 mm) and has more highly developed ribs than O. concinnum.” (Solem, 1964)
E.A. Smith (1894) original descriptions on Opisthostoma mirabile – “Testa dextrorsa, conica, anguste et profunde umbilicata, rufescens vel pallida; anfractus 7, convexi, primi duo laeves, caeteri lamellis tenuissimis pellucidis, remotis, spinis elongatis fere rectis sursum directis, instructis, ornati; spinarum series in anfr. ultimo valde curvata; lamella ultima pone aperturam maxima, scutiformis; apertura retrorsa, circularis; peristoma tenue, leviter expansum.”
Kobelt (1902) descriptions on Opisthostoma (Geothauma) mirabile – “Schale rechtsgewunden, eng und tief genabelt, kegelförmig, rötlich oder blass; 7 gewölbte Windungen, die 2 apikalen glatt, die folgenden mit feinen, durchsichtigen, weitläufigen Lamellen, die in gerade, nach oben gerichtete Stacheln ausgezogen sind, die Stachelreihe auf der letzten Windung ist sehr gekrümrat; letzte Lamelle hinter der Mündung sehr gi'oss, schildförmig; Mündung rückwärts gerichtet, kreisrund; Mundrand dünn, leicht ausgebreitet.”
By Vermeulen (1994)
"Spire conical with flat to concave sides. Apex not oblique. Whorls 5 3/8 - 7 1/2, convex; last whorl rounded or slightly angular. Constriction with a parietalis, a longitudinal and a transverse palatalis, a columellaris which continues as a ridge-shaped transverse basalis. Tuba gradually narrowed towards the constriction, (slightly) angular below. Radial ribs with a deeply trough-shaped projection half-way, abrading to a scar with a deep, semi-circular loop (projection of those close to tuba slightly double-channeled, abrading to a scar with a single deep loop when the shell is observed in front view); those on the spire moderately to widely spaced (2-4 ribs/0.5 mm on the penultimate whorl); those on the tuba widely spaced (2 ribs/0.5 mm half-way the tuba), below with a distinctly curved projection. Spiral striation absent. Umbilicus open, 0.20-0.30 mm across. Aperture tilted up to 30 degree with regard to the coiling axis, circular to elliptic. Peristome double; outer peristome widely spreading beyond the inner but abruptly narrowed towards, and absent along the right side of the aperture, with a very large wing along the upper side; inner peristome distinctly protruding from the outer, spreading. Spire: height 1.8-3.1 mm; width 1.3-1.9 mm; index 1.4-1.6. Total width 2.6-3.9 mm. Height aperture 0.5-0.7 mm; width 0.6-0.9mm"
Opisthostoma mirabile – “Alt. 4 mm, diam. maj. 5 mm, min. 2.5 mm. Apertura cum perist. 1.5 mm lata.” (E. A. Smith, 1894); Opisthostoma (Geothauma) mirabile – “H. 4, Durchm. 5 : 2.5 mm.” (Kobelt, 1902)
Type locality – “Gomanton Hill, N. Borneo” (E. A. Smith, 1894)