The Radiolaria described in this paper came from two areas in southern California, the Palos Verdes Hills and the Newport area. Most of these deposits consist of organic shales referred to as the Monterey shale. In the Palos Verdes Hills the deposits are about 2500 feet thick and have been divided into five lithologic members. Three are named (beginning at the base) the Altamira shale, the Valmonte diatomite, and the Malaga mudstone. Radiolaria were abundant in the latter two members. Most of the Newport area samples studied contain a very large proportion of species common to the Valmonte member of the Palos Verdes Hills. The writers conclude that the shales containing the Radiolaria of the Palos Verdes Hills and Newport area were laid down under conditions not greatly dissimilar to those existing in the adjacent Catalina Channel under open sea conditions; and that at least the upper portion of the Malaga mudstone is almost certainly bathyal, although possibly other portions were deposited under shallower water conditions. Ninety-one species, all of them new, are herein described.