Plectostoma shelfordi (Smith, 1905)
“Remarkable on account of the way in which the last whorl is curved up the spire, so that the upper edge of the peristome is shghtly above the apex. Under the microscope the surface is seen to be minutely spirally striated.” (E. A. Smith, 1905)
E. A. Smith (1905) original descriptions on Opisthostoma shelfordi – “Testa destrorsa, minima, conica, rufescens; anfractus 5 convexi, primus Iaevis, caeteri liris obliquis, tenuibus, arcuatis, instructi, ultimus primo peculiariter contractus et contortus, deinde arcuatim retrorsus, usque ad apicem spirae ascendens, lamellis fortioribus omatus; apertura circularis; peristoma duplex, pallidum, margine interno anguste expanso, externo angusto, spirae contiguo.”
By Vermeulen (1994)
"Spire conical with flat wides, Apex not oblique. Whorls 4 3/4 - 5, moderately convex; last whorl rounded to slightly angular at the periphery. Constriction with a transverse palatalis (only checked through the shell wall). Tuba touching the spire over its entire length, close to the constriction with a sharply outlined, distinct swelling, on top with a deep semi-circular furrow opening to the lower side if the shell is observed in front view; tuba rounded below. Radial ribs not sinuous, on the spire rather closely placed (4-5 ribs/ 0.5 mm on the penultimate whorl), slightly crested towards the upper margin of the whorls and there attached to the surface of the previous whorls; those on the tuba moderately spaced 3 ribs/0.5 mm half-way), without a vrest as above. Spiral striation present. Umbilicus open, 0.30 mm across. Aperture hardly tilted with regard to the coiling axis its upper margin widely above the level of the apex, about circular or slightly angular. Peristome touching the spire, double; outer peristome spreading beyond the inner, but rather abruptly narrowed towards, and absent or narrow along the right and lower side of the aperture, with a distinct, rounded wing along the lower left side and a similar, less conspicuous wing along the upper right side; inner peristome protruding from the outer, spreading, with some spreading lamellae on its outer surface. Spire:height 1.5-1.7 mm; width 1.1-1.3 mm; index 1.3-1.4. Total width 1.5-1.7 mm. Height and width aperture 0.5 mm."
Opisthostoma shelfordi – “Long. 2, diam. 1.6 mm.” (E. A. Smith, 1905)
Type locality – “Picsing, Upper Sadong, Sarawak” leg. S. Beddome (E. A. Smith, 1905)