PROC. ENTOMOL. SOC. WASH. 87(2), 1985, pp. 381-386 THE EPHEMEROPTERA OF ALASKA' W. P. McCafferty Department of Entomology, Purdue University, West Lafayette, Indiana 47907. Abstract.— A synopsis of the Ephemeroptera known from Alaska is provided. New collections from the north slope of the Brooks Range are reported and include new records of the genus Heptagenia, Cinygmula subaequalis, and Ephemerella lacusths. Mayfly data concur with the generalized pattern of Arctic fauna being represented by relatively few, widespread species, and having a strong circumpolar component. More species are expected to be Holarctic or at least have sister species in the Palearctic than can now be accounted for on the basis of present systematic knowledge. Zoogeography suggests that the fauna was present in a glacial refugium and is now composed of low-vagility species expressed by widely disjunct continental distributions and more easily dispersed species expressed by more continuous widespread distributions. Ephemeroptera known from Yukon drainage systems contiguous with Alaska are also treated and should eventually be found in Alaska. The mayfly fauna of Alaska has been poorly known but of considerable recent interest because of the development and maintenance of a trans-Alaska pipeline corridor and its potential environmental impact. Freshwater ecological studies incorporating benthos (e.g., Watson et al., 1966; Nauman and Kemodle, 1974; Craig and McCart, 1975; Slack et al., 1977, 1979) have involved mainly the Brooks Range and Beaufort Sea drainage areas. Unfortunately, such studies have not provided much species-level information and therefore are of limited value for interpreting Alaskan mayfly faunistics. Southern Alaskan distributions were indicated by range maps for nine Ephem-eroptera genera by Allen and Brusca (1973). Edmunds et al. (1976) listed eight nominal species and at least seven other unidentified species among 12 genera reported from Alaska. Slack et al. (1977) added two genera to this in their study of the Dietrich River. Lehmkuhl (1979) reported one more nominal species and genus, and Harper and Harper (1981) reported an additional five nominal species and one genus from Umiat. Table 1 provides a taxonomic listing of the presently known mayfly fauna of Alaska and is based in part on the above references, beginning with Edmunds et al. (1976). A list of species that are very likely to be eventually found in Alaska can be generated on the basis of records from the adjacent Yukon Territory of Canada, particularly the Yukon River System-Pacific Drainage Basin, which is shared by Alaska and the Yukon. Records for this area are provided generally by Harper Purdue Experiment Station Journal No. 9905.