Opisthostoma banki Maassen, 2002

Maassen (2002) original descriptions on Opisthostoma banki – “Shell sinistroid, white, slightly translucent, large for the genus; spire more or less cylindrical. Whorls approximately 3 1/3 (tuba not included); top whorls distinctly oblique, moderately elevated. The penultimate whorl widest, convex with the suture impressed. Constriction distinct, abrupt. Tuba consisting of approximately ¾ whorl, touching the body whorls over its entire length, bulging and rather abruptly narrowed towards the contriction, approximately circular in section. Shell with smooth top whorls; the following ones with rather wide, thin and sharp, distinct radial ribs, which are widely spaced on the penultimate whorl (5 ribs/0.5 mm). Ribs crossed by a distinct spiral striation. Umbilicus closed. Aperture tilted 14-45° with regard to the coiling axis. Its upper margin just below the level of the apex; apertural teeth absent. Peristome double. Outer peristome spreading beyond the inner one, but gradually narrowed towards the right side of the aperture where is it absent. Inner peristomw distinctly protruding beyond the outer one, somewhat spreading at the right side of the aperture spreading over the widest whorl of the spire as well as the whorl above. Constriction with a transversal lamella at the palatal side and a distinct parietalis, which continues approximately up to the sharp inner curve of the tuba.”