Anatomy, systematics, and zoogeography of 23 species of marine poeciloscleridan Demospongiae (Porifera) from the San Juan Archipelago, Washington, were studied from August 1958 through August 1961. A historical review of published references to Porifera and poriferologists of the Pacific northwest is presented. Relationships between ocean currents, as vectors of larval dispersion, and the known zoogeography of Pacific coast extant marine Porifera are discussed. The known sponge fauna of Washington at 48° N. latitude involves considerable overlap of boreal and temperate species and a moderate degree of endemism. Information on the biological associates of sponges is summarized. The Porifera studied are as follows: Acarnus erithacus De Laubenfels; Anthoarcuata graceae Bakus gen. n., sp. n.;Biemna rhadia De Laubenfels; Esperiopsis originalis De

Laubenfels; Hymedesanisochela rayae Bakus gen. n., sp. n.;Hymendectyon lyoni Bakusgen. n., sp. n.;Iophon pattersoni (Bowerbank); Lissodendoryx firma (Lambe); Lissodendoryx

aff. kyma De Laubenfels; Microciona microjoanna De Laubenfels; Mycale adhaerens(Lambe); Mycale hispida (Lambe); Mycale lingua (Bowerbank); Mycale psila (DeLaubenfels); Mycale richardsoni Bakus sp. n.;Myxilla incrustans (Esper); Ophlitaspongia pennata (Lambe); Plocamia karykina Dc Laubenfels; Plocamilla illgi Bakus sp. n.;Podotuberculum hoffmanni Bakus gen. n., sp. n.;Stelotrochota hartmani Bakus gen. n., sp. n.;Tedania gurjanovae Koltun; and Zygherpe hyaloderma De Laubenfels. An illustrated key to the local poeciloscleridan sponges is included.