This paper describes 127 species, subspecies, and varieties of Radiolaria all of which are new and which came from two shale members of the Upper Eocene series, north and northeast of Mount Diablo, Middle California. Both these shales are typical radiolarites, very similar in lithologic character to the well-known Oceanic beds of Barbados Island. The lower of these two shale members, the Kellogg shale, has a thickness of about 130 feet and lies just below the Markley formation and, in the western portion of the area under consideration, forms the upper portion of a series of sands and shales which have been locally known as the “Nortonville” shales and which have been included in the upper portion of the Domengine formation by the senior writer (1926). The higher of the two members, the Sidney shale, has a thickness of about 700 feet and belongs to the Markley formation; it is a little more than 2000 feet above its base. A comparison of the radiolarian assemblages of the Kellogg shale with those of the Sidney shale shows a considerable difference. Sixty-three per cent of the Kellogg species have not been found in the Sidney shale, and a little more than 58 per cent of the Sidney shale species have not been found in the Kellogg shale. The paper gives a brief description of the stratigraphic relationships of the Tertiary formations in the area under consideration and discusses in considerable detail the lithology of the two shales and its probable significance. The writers’ conclusion is that these shales were deposited in fairly deep marine waters under tropical or semi-tropical conditions.