longer periods than D. brunsoni and small O. elrodi . The four live O. ehodi found on 10 June in 

 warm and dry conditions were 18-21 mm diameter and estivating at that time. Fourth, D. 

 brunsoni may tend to be nocturnal or crepuscular and make vertical migrations to the talus surface 

 during periods of activity (Brunson 1956). Timing of my searches would not have detected this. 

 ACKNOWLEDGMENTS 



Field work was generously supported by a Canon Exploration Grant administered by The 

 Nature Conservancy and Canon U.S.A., Inc. I benefited greatly from conversations with T. J. 

 Frest and especially R. B. Brunson, whose knowledge and documentation of the snails of the 

 Mission Mountains were enthusiastically shared whenever requested. J. S. Marks and L. M. 

 Hendricks participated in the hunt for Discus brunsoni ; T. Gignoux identified the rocks at the D_, 

 brunsoni site. T. Shreve visited the type locality of Oreohelix alpina with me. An earlier draft of 

 the manuscript benefited greatly from the comments of two anonymous reviewers. This paper is 

 dedicated to the memory of the late J. R. Reichel of the Montana Natural Heritage Program, who 

 supported my efforts even before this project was conceived. 

 LITERATURE CITED 

 Alden, W. C. 1953. Physiography and glacial geology of western Montana and adjacent regions. 



U. S. Geological Survey Professional Paper 23 1 . 200 pp. 

 Ausden, M. 1996. Invertebrates. Pp. 139-177 In Ecological census techniques, a handbook (W. 



J. Sutherland, ed.). Cambridge University Press, Cambridge. 

 Berry, S. S. 1955. An important new land-snail from the Mission Range, Montana. Bulletin, 



Southern California Academy of Sciences 54:17-19. 

 Brunson, R. B. 1956. The mystery of Discus brunsoni . The Nautilus 70:16-21. 



12 



