Search Field Guide
Advanced Search
MT Gov Logo
Montana Field Guide

Montana Field Guides

Idaho Forestsnail - Allogona ptychophora
Other Names:  Helix townsendiana, Helix ptychophora, Mesodon ptychophorus, Polygyra townsendiana, Polygyra ptycghophora.

Native Species

Global Rank: G5
State Rank: S5

Agency Status

External Links

General Description
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.

Diagnostic Characteristics
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.

Species Range
Montana Range


Range Comments
British Columbia to Oregon through western Montana (Burke 2013). In Montana, reported from six counties west of the Continental Divide and abutting Idaho: Lake, Lincoln, Mineral, Missoula, Ravalli, Sanders. Elevation range is 777 to 1747 m (2550 to 5730 ft). Can be locally abundant; 164 reported were at one site in Missoula County in October (Hendricks 2012).

Observations in Montana Natural Heritage Program Database
Number of Observations: 99

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Predicted Distribution in Montana
Predicted distribution model for Idaho Forestsnail (Allogona ptychophora). Records were spatially unique and had a locational uncertainty of ≤ 400 meters.  Hotter colors indicate areas that are predicted to have more suitable habitat for the species.  Black dots are positive data used to build the model.  Gray dots are locations where a survey capable of detecting the species has been performed.  Landownership, a shaded relief map, and county lines are included for reference.  Details of the modeling effort, a description of the environmental layers used, and a more thorough interpretation of model outputs can be found in the report Land Mollusk Surveys and Predicted Distribution Models on USFS Northern Region Lands: 2007.

Predicted Distribution Map

More model output for this species
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).

  • Literature Cited AboveLegend:   View Online Publication
    • Burke, T. E. 2013. Land snails and slugs of the Pacific Northwest. Corvallis, OR: Oregon State University Press. 344 p.
    • Carney, W.P. 1966. Mortality and apertural orientation in Allogona ptychophora during winter hibernation in Montana. The Nautilus 79:134-136.
    • Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.
    • Pilsbry, H.A. 1940. Land Mollusca of North America (north of Mexico), Volume 1 Part 2. Monograph of the Academy of Natural Sciences of Philadelphia Monograph Number 3(1): 574-994.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Elrod, M.J. 1902. Daphnia pond, a study in environment. University of Montana Bulletin #16, Biological Series 5: 230-233.
    • Forsyth, R.G. 2004. Land snails of British Columbia. Royal British Columbia Museum: Victoria, British Columbia, Canada. 188 pp.
    • Frest, T.J. and E.J. Johannes. 2001. An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Science 36(2):1-51.
    • Hendricks, P. 2005. Surveys for animal species of concern in northwest Montana. Section 4: Terrestrial mollusk surveys in northwestern Montana; and section 5: Plum Creek owl and mollusk surveys. Unpublished report to the Montana Department of Fish, Wildlife & Parks, Montana Natural Heritage Program, Helena, Montana, May 2005. 53 p.
    • Illich, P.M. 1966. The dispersion and activity of the terrestrial gastropod, Allogona ptychophora (A. D. Brown), in relation to its microhabitat. Master’s Thesis, University of Montana, Missoula, MT. 88 pp.
    • Smith, A.G. 1943. Mollusks of the Clearwater Mountains, Idaho. Proceedings of the California Academy of Sciences, fourth series, 23:537-554.
    • Stabins, H. 2004. Forest owl and invertebrate monitoring report for northwestern Montana Plum Creek managed landscapes for 2003 and 2004. Plum Creek.
    • Vanatta, E.G. 1914. Montana shells. Proceedings of the Academy of Natural Sciences of Philadelphia 66:367-371.
  • Web Search Engines for Articles on "Idaho Forestsnail"
  • Additional Sources of Information Related to "Snails / Slugs"
Login Logout
Citation for data on this website:
Idaho Forestsnail — Allogona ptychophora.  Montana Field Guide.  .  Retrieved on , from