4 RATHBUN 



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 ship's 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 the 

 species known to Brandt, Stimpson, Lockington, and other pio- 

 neers in this field has been greatly extended. 



In 1900 Dr. S. J. Holmes published a very useful 'Synopsis 

 of California Stalk-Eyed Crustacea,' 1 with descriptions of genera 

 and species, and it has been thought unnecessary to repeat cita- 

 tions 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 Betaus, is notable as the first Alpheid 

 reported from as high a latitude as Sitka. 



A remarkable case of dimorphism is here recorded for the first 

 time : the cosmopolitan species Processa canaliculata 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. 



General features. The Decapod fauna of the North Pacific is 

 rich in individuals, if not in species or in variations of form. 



In the mass of material examined (about 50,000 specimens) 

 certain types were found to be largely in excess, namely, the Pan- 

 dalid, Hippolytid, and Crangonid shrimps, the Pagurids or hermit- 

 crabs, the Maioids or true spider-crabs, and the Lithodids or 

 Anomuran spider-crabs. 



In point of numbers the Pandalids take the lead. The most 



1 Occas. Papers Calif. Acad. Sci., vn, pp. 1-262, pis. i-iv, 1900. 



