An examination of Arctic grayling (Thymallus arcticus) collected on either side of the continental divide (Brooks Range) in Alaska revealed that lateral line scale counts were significantly higher on the North Slope than in the Yukon Basin to the south. An examination of geographic variation in this character within the North American range of the species suggested a division into three geographic areas: an area of uniformly low mean counts in the Bering Sea–North Slope of Alaska; an area of uniformly high counts in the remainder of Alaska and parts of the Yukon Territory and British Columbia; an area of variable mean counts in the Northwest Territories. Only two glacial refugia need be postulated to explain this pattern if it is assumed that populations in the first and last of these areas have a similar Mississippian origin and the high count populations a Beringian origin.

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