Montana Field Guide

The shell is large for the genus, to 10.5 mm diameter, 4.5 mm in height, umbilicus to 3.5 mm diameter, shell depressed in profile with a low spire, to about 5 1/2 compressed whorls with a strongly (but not acutely) carinate periphery. Shell color is olive-brown, the basal surface tends to be a little lighter grayish-brown. There are no spiral bands, but the chitonous shell is wrinkled and weakly ribbed on the upper surface, the irregularities almost absent on the basal surface of adult shells. Dorsal surface of the animal is dark gray to blackish on the head and neck (Hendricks 2012; Burke 2013). Internal anatomy not described.

Active during cool and moist weather (Hendricks 1998), otherwise not described.

A combination of shell shape (flattened heliciform or flattened conic), shell dimensions, number of whorls, shell color (olive-brown and chitinous), the presence of radial striations on the shell, lack of reflected lip, and lack of teeth in the aperture distinguish this from all other Montana land snails (Hendricks 2003, 2012), including other Discus (which are smaller in diameter and more strongly ribbed).

Non-migratory; appears to make vertical movements through talus and boulder fields (Brunson 1956; Hendricks 1998).

Described originally as south-facing limestone talus (Berry 1955), but reexamination of the rock revealed the occupied slope to be predominately diorite with a minor amount of argillite. The slope lacks canopy cover, except at the margins where Douglas-fir and ponderosa pine occur, with scattered pockets of aspen, water birch, and mock orange (Hendricks 1998). This species appears to make vertical migrations through deep talus and boulder fields (Brunson 1956), making it all the more difficult to locate except under ideal moisture and temperature conditions.

Not described, but may feed on lichen attached to rock (Hendricks 1998).

Not described.

Although the occupied habitat is not particularly threatened by development or agriculture (logging and grazing), habitat requirements and food habits are poorly understood. Fire suppression efforts (especially use of fire retardants) and talus destabilization (trail maintenance, modification) could have negative impacts. Also, given the trail-side location, weed control efforts could negatively impact the population (Hendricks 2003).