PREFACE Crustaceans were collected by several members of the Harriman Expedition, particularly by Professor Trevor Kincaid, Professor W. B. Ritter, and Dr. Wesley R. Coe. After the return of the Expedition these specimens were arranged by groups and sent to specialists for study. The Decapods have been elaborated by Miss Mary J. Rathbun, who has included in her investigation the extensive collections from the Pacific coast already in the United States National Museum, so that her paper may be regarded as a comprehensive revision of the group for the west coast of North America from California to Arctic Alaska. The Isopods have been treated by Miss Harriet Richardson, the Amphipods by Dr. S. J. HoImes, tlie Pycnogonids by Dr. Leon J. CoIe. The chapter headings are from the facile pens of Mrs. Louise M. Keeler and Mr. F. A. Walpole- the Amphipods by Mr. Ialpole, the others by Mrs. Keeler. C. HART MERRIAM, opportunities for studying the Pacific fauna, as the material is in some cases remarkably abundant. So rich in crabs and shrimps were some parts of the sea bottom explored by the Albatross that only a portion of each dredge haul was preserved for study, many a peck or quart of these animals being thrown over- board by the ships naturalists. Our knowledge of the Decapod fauna of the Northwest is, for the most part, of recent growth. More than two fifths of the species enumerated below have been described within the last twelve years, while during that time our acquaintance with thc species known to Brandt, Stimpson, Lockington, and other pioneers in this field has been greatly extended. In rgoo Dr. S. J. Holmes published a very useful Synopsis of California Stalk-Eyed Crustacea, with descriptions of genera and species, and it has been thought unnecessary to repeat citations for the species which he gives. An effort has been made to figure all the little-known species. In addition to the general collection of Decapods made by Dr. William E. Ritter of the Harriman Expedition, those obtained by Dr. W. R. Coe and Professor Trevor Kincaid have been placed at my service. One new species, a Beieus, is notable as the first AIpheid reported from as high a latitude as Sitka. A remarkable case of dimorphism is here recorded for the first time the cosmopolitan species Processa canalicuafa Leach, more commonly known by the later name Nika edulis Risso, is found to possess in certain cases two chelate feet of the first pair instead of the characteristic asymmetrical disposition of a chelate foot on one side and a simple one on the other.