ORDOVICIAN PROETIDE TRILOBITE DIMEROPYGE, WITH A NEW SPECIES FROM NORTHWESTERN CANADA

Dimeropyge Opik, 1937, is a genus currently composed of at least 14 si milar Middle (predominantly) to possibly lowest Upper Ordovician speci es from Laurentia (13 species) and Baltica (one species). Possible Low er Ordovician specimens have been illustrated by Ross (1951). Dimeropy ge clintonensis Shaw, 1968, is redescribed, based upon additional mate rial of mature topotypes. A new species of Dimeropyge, D. speyeri, is proposed for material from the Esbataottine Formation in the Mackenzie Mountains, northwestern Canada, previously described as D. clintonens is. A phylogenetic analysis of 10 of the 14 species of this genus is p resented (the other species are less completely known, and are related to the analyzed species in a more traditional manner). Ontogenies fro m protaspid to holaspid stages are provided for D. clintonensis, D. sp eyeri, and D. virginiensis Whittington and Evitt, 1954. The larval sta ges of these species are very similar, supporting the close relationsh ip between species assigned to Dimeropyge.