Plectostoma retrovertens (Tomlin, 1938)

Tomlin (1938) original descriptions on Opisthostoma retrovertens – “Shell dextral, regularly conical until the last whorl, which mounts one side of the cone until in the adult the upper margin of the peristome is exactly level with the apex of the shell; number of whorls six, apex rather blunt; aperture almost circular, facing backwards vertically in a position the reverse of a normal aperture; peristome duplex; there is no spiral sculpture, but the whorls other than the smooth protoconch have prominent, but the whorls other than the smooth protoconch have prominent, thin, rather distant, retractive axial costulations; the protoconch consists apparently of one whorl, and the costulations though few on the second whorl are distinctly traceable; suture deep; umbilicus oval in shape and rather deep, not covered by the deviating whorl. The specimens are all dead and no operculum is obtainable.”