This report is based upon a study of the Middle Cambrian fauna of the Cadiz formation in the Marble Mountains, San Bernardino County, California. The presence of this fauna at an apparently new locality was first noted by Dr. John H. Bradley, Jr.. in the course of reconnaissance work in 1932. An extensive collection was made in the spring of 1934 by Dr. Bradley and the author. Laboratory and library facilities for the preparation of the specimens secured were provided by the Los Angeles Museum, to which thanks are due. The author wishes to express his appreciation of the loan of several Walcott publications by Prof. A. J. Tieje, of the direction of the work by Dr. Bradley, and of valuable suggestions by Prof. B. F. Howell.