A new ostracode assemblage, DFr6, characterizes the uppermost Frasnian rock sequences in western Canada. The assemblage or biozone contains elements of both the Frasnian and Famennian ostracode sequences and seems to be intermediate between both faunas, which in main aspects are strikingly different in composition. Similarities between the Devonian ostracodes of western Canada and their time-equivalent faunas of the Russian Platform and adjoining areas suggest the presence of a vast paleobiogeographic faunal province that is distinctly set apart from a "paleo-Tethyan" province whose ostracode representatives are found in central Europe and North Africa.The lower DFr6 subassemblage is contained in the Jean-Marie Member of the Redknife Formation, with the upper DFr6 ostracodes occurring in its upper member and in the Kakisa Formation. Both formations form prominent but lithologically similar carbonate sequences in the southwestern corner of the Northwest Territories and adjoining areas, causing problems in correlations, in particular in subsurface studies. Ostracodes of the upper DFr6 subzone were also recovered from the dolomites of the Winterburn Group of northern Alberta.