Montana Field Guide

A large shell, to 24 mm in diameter and 15 mm in height, heliciform with up to 5 3/4 whorls. Shell is opaque and covered with a light brown chitinous layer (periostracum) that is never “hairy” and becomes worn away with age; shell also with fine incremental striae lighter in color and wrinkle-like axial riblets extending to the undersurface. Very fine wavy spiral striae present throughout the shell. The last whorl is slightly contracted behind the aperture lip, which is reflected, white, and slightly thickened near the base with a slightly bulging callus; aperture is oval, not rounded, the base partly obscuring the umbilicus, which is deep but very narrow (Hendricks 2012, Burke 2013). Internal anatomy is described by Pilsbry (1940).

Subspecies present in Montana is A. p. ptychophora.

Mature individuals differ from other species in Montana by a combination of shape and medium to large size, absence of spiral bands, presence of a flared or reflected lip around the aperture, umbilicus partially covered by aperture lip, and lack of any teeth, the last which separates Allogona from Cryptomastix.

Mesic mixed conifer forest, often near water such as stream-side riparian, and seeps, but sometimes well away from surface water. Canopy species include western redcedar, western hemlock, Engelmann spruce, Douglas-fir, grand fir, western larch, ponderosa pine, lodgepole pine, black cottonwood, aspen and paper birch; secondary canopy includes alder, willow, dogwood, and mountain maple. Found most often under woody debris or rocks in leaf litter and duff, sometimes on the surface and in the open (Hendricks 2012).

The winter survival of hibernating individuals is related to the orientation of the shell; those with the aperture pointed up rather than against the ground have a reduced probability of mortality for unknown reasons (Carney 1966).