Opisthoporus birostris (Pfeiffer, 1854)
“The tube behind the aperture is not curved backwards, as in the last species, but forwards, and a second tube is formed by an inflected sinuation of the lip.” (Reeve, 1864)
Pfeiffer (1854) original descriptions on Cyclostoma birostre (Cyclotus) – “C. testa umbilicata, depressa, subdiscoidea, solidula, irregulariter striata, fulvo-lutea, fascia peripherica castanea et superne strigis latis angulatis ornate; spira plana, vertice subtili, vix prominulo; anfract. Fere 5 convexiusculis, rapide accrescentibus, ultimo terete, subtus obsolete maculato, antice soluto et tubulo antrorsum curvato munito; umbilico lato, anfractus omnes latiores et convexiores monstrante quam superne; aperture diagonali, circulari; perist. duplice, interno brevi, recto, externo expanso et inflexo, superne in rostrum apertum, anfractum ultimum tangentem, producto. Operc. Album, arctispirum, extus concavum.”
Reeve (1864) descriptions on Pterocyclos birostris – “Shell very broadly openly umbilicated, discoid, fulvous, banded and sharply wave-streaked with chestnut, whorls rounded, ring-striated throughout, last whorl rather uncoiled, furnished with an incurved tube behind the aperture; aperture circular, lip concavely inflected, tubularly sinuated at the upper part.”
Martens (1867) descriptions on Opisthophorus birostris – “Testa discoidea, latissime umbilicata, perpendiculariter striatula, fulvolutea, fascia peripherica maculosa et superne strigis fulminates rufocastaneis picta; apex pallidus, vix prominens: anfr. 4½. convexiusculi, sutura profunda discreti, ultimus antice solutus, teres et prope solutionem tubulo antrorsum curvo aperto umnitus; aperture diagonalis, circularis; peristoma duplex, externum subtus et extus fornicatim prolongatum, superne in canaliculum apertum anfractui penultimo appropinquantem excurrens. Operculum crassum, extus concavum. spiris oblique striatulis, centro fusco, margine excavato.”
Kobelt (1902) descriptions on Cyclotus (Opisthophorus) birostris – “Schale sehr weit genabelt, scheibenförmig, gestreift, braungelb mit einer kastanienbraunen Fleckenbinde in der Mitte, oben braun gestriemt; Apex blass, kaum vorspringend; Naht tief; 4½, ziemlich gewölbte Windungen, letzte vorn abgelöst, stielrund, mit offener, nach vorn gerichteter Nahtröhre; Mündung diagonal, kreisrund; Mundrand doppelt, äusserer unten und rechts vorgezogen, oben in ein der vorletzten Windung genähertes Kanälchen auslaufend. Deckel dick, aussen konkav, Mitte braun, Windungen schräg gestreift, Rand rinnenförmig.”
Cyclostoma birostre (Cyclotus) – “Diam. maj. 26, min. 19, alt. 7 mill.” (Pfeiffer, 1854); Opisthophorus birostris – “Diam. maj. 23½, min. 18, alt. 10: apert. lat. = long. 9 Mill. excluso canaliculo.” (Martens, 1867)
Type locality – “Sarawak, Borneo” (Pfeiffer, 1854)
Other localities – “Sarawak an der Nordwestküste von Borneo.” (Martens, 1867); “Niah N.P., Sarawak, Malaysia” (Vermeulen, 2003); “Gunung Mulu N.P., Sarawak, Malaysia” (Vermeulen, 2003)