Opisthostoma ballorum Vermeulen, 1991  

[Jaap Vermeulen, 1994]

spire cylindrical. Apex slightly oblique. Whorl 3 1/2 - 3 7/8, convex; last whorl rounded. Constriction with a transverse palatalis. Tuba about half-way leaving a small gap between the tuba and the spire, with a slight, vertical depression at about 0.2 mm from the constriction and a swelling in between, rounded below. Radial ribs not sinuous, on the spire moderately spaced (4-6 ribs/0.5 mm on the penultimate whorl, 4 ribs/0.5 mm half-way of tuba). Spiral striation or very fine. Umbilicus up to 0.1 mm across, but often entirely covered by the tuba. Aperture tilted up to 90º with regard to the coiling axis (facing down), its upper margin usually widely below the level of the apex, circular to slightly angular. Peristome double, outer peristome touching the spire, moderately spreading beyond the inner but gradually widened towards the right side of the aperture and often partly covering apex; inner peristome widely projecting beyond the outer, forming a downwards curved tube of up to 2/3 of the length of the tuba, somewhat spreading, its outer surface with rather closely placed to moderately spaced radial ribs. Spire: height 0.8-1.0 mm and width 0.8-0.9 mm; index 1.0-1.3. Total width about 1 mm. Height and width aperture 0.35-0.40 mm.