Abstract
The present distributions of stonefly genera in North America, their occurrence as endemics, or as shared with the Far East, Europe and South America, are considered in conjunction with geological history. It is concluded that the Plecoptera of North America have four sources of origin.There was an ancient eastern fauna shared with Europe before the formation of the North Atlantic Ocean. A second group moved in from the west during the formation of the western mountains. After formation of the isthmus one genus moved northward from South America. After the Pleistocene period several species migrated from the Bering Strait region, possibly from an Alaskan refugium. Some of these have clearly moved eastward, but a few may have moved westward.

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