LAND AND FRESH WATER MOLLUSKS OF 

 ALASKA AND ADJOINING REGIONS 



BY WILLIAM HEALEY DALL 

 GENERAL DISCUSSION AND RESULTS 



THE first object of this work is to sum up the known mollus- 

 can fauna of the land and fresh waters of Alaska. This has 

 involved an examination, not only of the species obtained within 

 the political boundaries of Alaska, but also those of the adjacent 

 region to the west, east, and south. The result is that, for North 

 America north of latitude 49 North, the work includes a sum- 

 mary of our present knowledge of the mollusks, deduced in part 

 from the literature and in larger part from material actually 

 examined. To this is added a briefer examination of the mollusk 

 fauna of the adjacent parts of eastern Siberia which has to some 

 extent modified that of Alaska. As a whole the work may be 

 regarded as forming a synoptic manual of the boreal land and 

 fresh water mollusks of the western hemisphere. 



I. SUMMARY OF THE DISTRIBUTION OF FRESH WATER SPECIES 

 IN ALASKA AND ADJACENT REGIONS. 



It was thought best to tabulate the species of rivers and lakes 

 according to the drainage systems in which they are found. 

 Of course these systems are not geologically ancient, and it is 

 even probable that some existing species of the Mississippi 

 system were trapped by the changes of level which, according 

 to Gen. G. K. Warren, U.S.A., secured, for the Red River of 



ft) 



