This chapter investigates how different taxa contribute to the 26-m.y. periodicity of extinction observed for marine animals from the middle Permian to Recent. Time series showing percent extinction at the genus level are presented for ten major taxonomic groups: foraminifera, corals, bryozoans, brachiopods, gastropods, bivalves, ammonoids, arthropods, echinoderms, and vertebrates. These groups, especially those with abundant fossil records, exhibit peaks of extinction at most points in the periodic sequence, indicating that periodicity is a property of the marine fauna as a whole and not produced by independent or idiosyncratic variations among a few taxa. Factor analyses of the time series...