ACT-More than 100 genera of fusulinids are distributed in the late Paleozoic geosynclines and adjacent marine shelves of Eurasia and the Western Hemisphere. Geographic distribution of these genera is uneven and forms the basis for recognizing 14 fusulinid faunal associations or subassociations which can be grouped into four faunal realms: Eurasian-Arctic realm (middle and late Carboniferous and earliest Permian), Midcontinent-Andean realm (Pennsylvanian and most of Permian), Middle Cordilleran realm (early Permian), and a Tethyan realm (middle and late Permian). Biogeographic separation of fusulinid faunas was remarkably complete at certain times during the Carboniferous and Permian Periods at which times only a few genera filtered between the faunal realms. Each fusulinid family has an evolutionary pattern that is quite distinct and independent from those of other families. A gradual concentration of endemic genera in the Tethyan realm and a gradual restriction of other genera to the Tethyan realm occurred during the Permian, few of these genera establishing wider geographic ranges at a later time. Particularly interesting are the dispersals of several genera of Schubertellidae and Ozawainellidae and Polydiexodina into southwestern North America during the Capitanian Age of the Guadalupian Epoch (late Permian). By the middle of late Permian time, nearly all fusulinids became extinct, except in the Eurasian Tethyan seas where advanced members of the Schubertellidae and Staffellidae formed a distinctive association in the youngest fusulinid fauna