Fusulinacean faunas in Upper Paleozoic lithological sequences containing volcanic rocks in the western Canadian Cordillera form two assemblages based on geographic association of genera. One assemblage, in Permian strata, is dominated by genera of the family Schwagerinidae and occupies belts in the eastern and western parts of the western Cordillera. This assemblage is associated with brachiopods, bryozoans, horn corals, and crinoids and is in limestones interbedded with clastic rocks and volcanic rocks of variable composition. The other Permian assemblage is dominated by genera of the family Verbeekinidae and occupies a central belt where it occurs with crinoid detritus and algae in thick, regionally extensive limestones associated with cherts, basalt, and ultramafic rocks. The less-well documented Pennsylvanian fusulinaceans appear to occupy similar belts. Because fossils of both assemblages are at least in part time equivalent, their distribution may well be due to differing local environments. In addition, or alternatively, this diversity may be brought about by major crustal movements juxtaposing originally isolated biogeographic provinces.