surrounded by closed- and open-canopy forest (Brunson 1956), but the rock types comprising the 

 talus inhabited by the snails are infrequently mentioned m published reports. Berry (1955) and 

 Frest and Johannes (1995) identified the talus as limestone; both Elrod (1901, 1902, 1903a) and 

 Brunson (1956) failed to mention rock composition. I did not detect limestone at the three sites 

 where I found one or both species. D. brunsoni was found exclusively in talus predominantly of 

 diorite boulders. O. elrodi was found at this site as well as in smaller-sized talus of argillite (Table 

 1). D. brunsoni may be more of a habitat specialist than previously appreciated, associating with 

 only a subset of available rock types. 



The biology and ecological requirements of Discus brunsoni and Oreohelix elrodi remain 

 largely unknown, so explanations for patterns of presence or absence near the surface of talus 

 slopes are speculative. O. elrodi was more abundant (4-6 fold during my searches) than D. 

 brunsoni near the surface of talus in wet and cool conditions, and a few individuals could be still 

 be found when it was warmer and drier. Several factors could contribute to this pattern. First, 

 absolute population size of O. elrodi at Site 1 may be greater than that of D. brunsoni . Ratios of 

 each species near the talus surface could be representative for all depths in talus. Second, I found 

 significant differences between the two species in substrate use. Some D. brunsoni were found on 

 foliose lichen (tentatively identified as Arctoparmelia subcentrifuga ) growing on the diorite, but 

 otherwise were on bare rock. In contrast, O. elrodi were most often found on organic litter and 

 vegetation. Preference by O. elrodi for organic litter may keep them nearer the surface of talus 

 slopes where litter accumulations are larger and apparently more numerous. Third, larger shell 

 size of O. elrodi might reduce its rate of desiccation by decreasing the surface area/volume ratio 

 (see Goodfriend 1986), allowing larger individuals to remain nearer the drier talus surface for 



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