The five families reported below are small, each known through comparatively few species or genera. All save the Sabellariidae are represented by species rarely encountered even in large collections. The Paraonidae, Magelonidae, and Longosomidae, new family, and perhaps also the Ctenodrilidae have their affinities with the spioniform chaetopods. The occurrence of each of these is of particular interest because their presence has remained unknown from the areas where found. One species, Longosoma catalinensis
, new genus and species, is believed to represent a group for which a new family name is proposed. Twenty-six species of the Sabellariidae are discussed ; among them, four species and one subspecies are believed to be new.