First Record of the Land Snail <i>Pristiloma idahoense</i> (Gastropoda: Pristilomatidae) for Montana

Abstract

The land snail Pristiloma idahoense (Pilsbry, 1902) is reported from Montana for the first time. Five live individuals were found under downed wood beneath a mature coniferous forest canopy at 1670 m elevation in the Big Creek drainage of the Bitterroot Mountains, Ravalli County, Montana. This location extends the known range approximately 75 km east and over the crest of the Bitterroot Mountains from the nearest sites in Idaho County, Idaho and supports the hypothesis that the terrestrial mollusc fauna of Montana west of the continental divide has been strongly influenced by a molluscan radiation, which developed in a northern Idaho Pleistocene refuge. The probable route of dispersal for P. idahoense between the Bitterroot Mountains of Montana and the adjacent Lochsa River drainage of Idaho was over the lower mountains to the north in the Lolo Pass area.