Abstract

Species of Atrypoidea have the potential of being biostratigraphically useful for the Upper Silurian strata of Arctic Canada. Critical to any biostratigraphic scheme is the relationship between A. phoca (Salter, 1852) and A. scheii (Holtedahl, 1914) since there is disagreement as to whether these species are synonymous, or distinct and stratigraphically separate species. Detailed morphological analysis of topotype A. scheii from Goose Fiord, Ellesmere Island shows that it falls within the range of morphological variation displayed by topotype A. phoca from Cape Riley, Devon Island. Consequently, A. scheii is maintained as a synonym of A. phoca.Other new species that may prove to be biostratigraphically useful include Atrypoidea gigantus n.sp. from an unnamed formation at Goose Fiord and A. netserki n.sp. from member C of the Read Bay Formation on Beechey Island. Atrypoidea gigantus, the largest species of Atrypoidea so far reported from Arctic Canada, is closely related to Atrypoidea foxi (Jones, 1974). Atrypoidea netserki is morphologically closest to A. phoca.Although the Atrypoidea sequences in the Ludlovian and Pridolian strata of Arctic Canada are now better known it is still difficult to delineate exact evolutionary trends, possibly because the various species have a facies- as well as a time-controlled distribution.

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