THE NAUTILUS. 87 



soil is lower than 3000 feet above the sea, the air is dry and evapo- 

 ration rapid. A passing rain-cloud may leave considerable moisture, 

 but it is soon taken up by the parched earth or evaporated if left on 

 the surface. Stagnant ponds with decaying vegetation are few and 

 confined to the vicinity of the few rivers. Even such ponds usually 

 become dry each summer. 



No doubt the western mountain region will produce some excellent 

 material for study of variation through isolation, when collections 

 have been made more extensively. Most of the valleys were former 

 lake beds of greater or less extent. As these lakes have been 

 drained, they left swamps in which rhinoceroses, camels, three-toed 

 horses, elephants, titanotheriums, and other beasts have become 

 mired, their remains being buried for long ages. These swamps have 

 dried up, and the waters have become more widely separated, now 

 occurring as deep mountainous lakes, or larger lakes, which are mere 

 expansions of rivers. Such isolation must have caused the separation 

 of shells of a species which naturally would take different lines of 

 development. Accompanying this gradual separation of waters we 

 might expect a region of moisture on the land adjacent to the lakes, 

 giving suitable environment to the land snails. 



As a result of the above conditions, we may expect great variations 

 in adjacent regions, where the barriers may be sufficient to cut off all 

 communication between the regions. Such variations have been 

 illustrated in part by Hemphill's suite of Patulas (Pyramidula), in 

 the Lichtenthaler collection at the Illinois Wesleyan University. 

 This has also been shown by collections made in the Sandwich Isl- 

 ands. There is very little doubt but that the isolated lakes in Mon- 

 tana and the northwest will produce interesting variations. But the 

 sparsely-settled country and the small number of collectors makes the 

 work of collecting and studying very slow. This may be better un- 

 derstood by a practical application. The State of Montana has an 

 area of 14G,000 square miles. So far as the writer is able to discover, 

 he is the only resident of the State who has collected fresh-water and 

 land shells, and this has been done at odd moments while prosecuting 

 other lines of work. 



The accompanying list is not large. Five species is the maximum 

 taken in one day. Those taken from mountain sides represent much 

 toil for a few scattered specimens. The list, incomplete as it must 

 be, represents the specimens collected at intervals during the past 



