Rediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901) in the Mission 

 Mountains, Montana, with comments on Oreohelix elrodi (Pilsbry, 1900) 



ABSTRACT 



During summer 1997, extant populations of the endemic land snails Discus brunsoni and 

 Oreohelix alpina were rediscovered near the type localities in the Mission Mountains, Montana; 

 last known collections were made 33 and 48 years ago, respectively. D. brunsoni and Oreohelix 

 elrodi (also endemic to the Mission Mountains and nearby Swan Range) were previously reported 

 to be sympatric in subalpine limestone talus. Both species were found in 1997 in diorite talus; the 

 latter species also occupied argillite talus with little, if any, limestone present at any site. Live D. 

 brunsoni (n = 8) were found near the talus surface only on bare rock or foliose lichen on rock 

 during cool, wet conditions. Live Q, elrodi were found near the talus surface on rock (n = 9) or 

 organic litter accumulations (n = 55) during all conditions, although in reduced number during 

 warmer and drier weather. Above treeline, live O. alpina were found exclusively in exposed 

 locations under limestone talus, sometimes attached to rock surfaces (n = 7) but more often 

 present in organic detritus (n = 10). Lack of collections of D. brunsoni and O. alpina in recent 

 decades probably resulted from 1 ) extremely restricted distributions, 2) limited knowledge of 

 habitat requirements, and 3) scarcity of active collectors in the region. 

 Key words : Discus brunsoni , Oreohelix alpina , Oreohelix elrodi , Montana, distribution, ecology. 



