E. Engblom, P. E. Lingdell, A. N. Nilsson & E. Savolainen 1993: The Genus Metretopus (Ephemeroptera, Siphlonuridae) in Fennoscandia - Identification, Faunistics and Natural-History. - Entomologica Fennica 4: 213-222.
Morphological characters are presented for the separation of nymphs and winged stages of Metretopus alter Bengtsson, 1930, from those of M. borealis (Eaten, 1871) based on Fennoscandian material. The known records of both species in Finland and Sweden are mapped, and a recent record of M. alter from Norway is given. Habitat preferences and phenological data of both species are presented. The documented wide distribution of M. alter in Fennoscandia indicates that it previously has been confused with M. borealis.