INTRODUCTION 



The Mission Mountains of northwestern Montana are recognized as an area of significant 

 snail endemicity in the Interior Columbia River Basin (Frest and Johannes 1995). The mountains 

 extend about 80 km north to south and 19 km east to west, rising abruptly from a base at 1036 m 

 in the Swan and Flathead valleys to a crest of nearly 3018 m. The range is composed of 

 Precambrian Belt rocks (mostly limestone and argillite) that were deeply dissected by alpine 

 glaciers during the Pleistocene (Alden 1953). The Mission Mountains still support small cirque 

 glaciers and permanent ice patches. The portion of the mountain range within Lake County 

 contains the type localities for three narrowly endemic terrestrial snail species, none of which has 

 yet been documented at more than two sites. 



Oreohelix errodi (Pilsbry, 1900) was discovered in 1899 in talus slopes between 1067- 

 1524 m above the north side of McDonald Lake (Pilsbry 1900, Elrod 1903a), where it was most 

 common, and also found rarely along the south side of the lake. The amphitheater around 

 McDonald Lake remains the only known locality for this species in the Mission Mountains, but it 

 has been found more recently above Lion Creek in the nearby Swan Range (Fairbanks 1984). 

 Oreohelix alpina (Elrod, 1901) was first found in 1900 on ASinyaleamin Mountains (Elrod 1901, 

 1902, 1903b) and again later that year on the west ridge of McDonald Peak; both localities were 

 above treeline between 2377-2743 m and remam the only sites where this species has been 

 located. Discus brunsoni Berry, 1955 was first encountered (a single shell) in 1948 in talus slopes 

 above the north side of McDonald Lake at an estimated elevation of 1067 m, with additional 

 material collected there in 1950 (Berry 1955, Brunson 1956). The type locality remains the only 

 known site for D. brunsoni . Interestingly, this talus slope is also the type locality for O. elrodi, 



