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 A/dbatross 
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,’ * 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 Beteus, 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 WVzka 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 
1Occas. Papers Calif. Acad. Sci., vil, pp. 1-262, pls. I-IV, 1900. 
