The polychaetous annelids of California are named with 650 species in 283 genera, 5 subgenera and 56 families. Twenty-four new species or subspecies, three new genera, two new names and eight new combinations are given. In all 549 species or 84%, are believed to have their known geographic distribution limited to California or the northeastern Pacific Ocean, and about 101 others, of more cosmopolitan character, are known also from other oceans.
