MONTANA SHELLS. 



Montana Shells. 



NATURE STUDY LESSON. 

 Morton John Elrod. 



The state of Montana is not very productive of conchological speci- 

 mens. The conditions are all against shell growth. The rivers are 

 rapid, the water quite soft, and food in the rivers scarce. The large 

 lakes, as Flathead lake, contain clear, cold water. They are usually 

 deep, with rock bottoms, and surrounded by mountains with steep slopes. 

 The marshy, stagnant parts of the lakes are usually small. The mount- 

 ain sides in summer become dry and parched, except in protected por- 

 tions and along streams. Great stretches of plain are without moisture 

 for a portion of the summer, drying up almost every living thing that can- 

 not move to the water-courses. The days are hot, the nights cool. In this 

 mountainous state, where very little soil is lower than 3,000 feet above 

 the sea, the air is dry and evaporation 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 a few rivers. Even 

 such ponds usually become dry each summer. 



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 be- 

 came 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 mountain lakes, or larger lakes, which are mere ex- 

 pansions of rivers. Such isolation must have caused the separation of 

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

 ment. 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. There is very little doubt but that the isolated lakes in 

 Montana and the northwest will produce intei-esting variations. But the 

 sparsely settled country and the small number of collectors make the 

 work of collecting and studying very slow. 



The lack of lime in the waters of the state in considerable quantity 

 Is another element contributing to the paucity of shell life. Specimens 

 taken from water invariably have thin or frail shells. Some are ex- 

 ceedingly delicate. The land forms, although not numerous in species, 

 have thicker and heavier shells, affording much better protection. One 

 species of slug, without a shell has been taken, but in small numbers. 



In considering the above conditons it is apparent that collecting liv- 

 ing shells is confined largely to the rainy season, i. e., the spring and early 



