Montana Field Guide

A very small shell, to about 2.4 mm diameter but more typically to 2.1 mm, 1.3 mm in height, flattened heliciform with a slightly elevated spire, with barely 4 whorls. Shell is translucent yellowish brown to darker brown, with a series of relatively tall cuticular riblets more or less regularly spaced and with very fine radial and spiral striae between. The aperture is crescent-shaped, obliquely wider than tall, lip not thickened, periphery rounded, umbilicus about 1/4 the shell diameter (Hendricks 2012, Burke 2013).

The spots are very small, yellowish brown shells (less than 3.0 mm diameter) with 4.0 to 4.25 whorls, which separates them from other species. Species of Pristiloma are more tightly coiled with more whorls, slightly larger in diameter with a narrow to absent umbilicus, and lack riblets. Punctum minutissimum is flatter in profile (lower conic) with a wider umbillicus than P. randolphi though similar in diameter, P. californicum is similar in shape to P. randolphi but larger with more solid riblets, Paralaoma caputspinulae is larger still (to > 2.0 mm diameter) with rather high cuticular riblets visible under magnification but with a flatter profile like P. californicum.

Near moisture, including streamside riparian zones; often disturbed sites. Tree canopy species include Douglas-fir. Found under woody debris and rocks, in leaf litter and duff (Hendricks 2012). Habitat in Montana is poorly understood.