Opisthostoma castor van Benthem Jutting, 1952  

Description by van Benthem Jutting (1952)

"shell obliquely low-cylindrical, somewhat less cylindrical than the following species O. pollux n.sp. Greyish-brown. First whorl smooth, following ones ornamented with fine, white transverse ribs, somewhat coarser than in the following species, close-set in the earlier whorls, but wider apart one the last one. No spiral sculpture. Whorls 4, convex. The top whorls almost in one plane, slightly oblique. the two large last whorls convexs, although somewhat more compressed than in O. pollux. Suture deep. Last whorl directed upwards, adnate, not deviated in transverse direction. It ends midway up the height of the preceding whorl. Umbilicus open, but not wide. Aperture round, directed to the sky, horizontal or a little oblique. Peristome continuous, circular to rounded-triangular, duplex. Operculum unknown."