144 BULLETIN 97, UNITED STATES NATIONAL MUSEUM. 



length, third a little wider, its merus over twice as wide as long; 

 fourth leg shortest, reaching end of carpus of third. 



Abdomen strongly narrowing distally for its first segment, then 

 moderately tapering to the penultimate segment, which is constricted 

 at middle; last segment rounded at tip. 



Description of female. Much larger than male. Carapace and 

 abdomen soft and yielding; carapace more uneven, less deflexed pos- 

 teriorly and without an antero-lateral marginal line. Median groove 

 on gastric region very deep. 



Chelipeds smaller than in male; palm narrower, its sides nearly 

 parallel; fingers longer, less deflexed. not gaping, sharp-pointed, 

 tips crossing ; thumb without a terminal notch, but instead a shallow 

 lobe at middle of prehensile margin ; edge of dactylus feebly sinuous. 



Legs more alike than in male; first leg reaching to middle of dac- 

 tylus of second ; fourth leg reaching beyond end of carpus of third ; 

 merus of third leg about twice as long as wide. 



Variations. In some males the antero-lateral angle is vertically 

 compressed and correspondingly thin, forming a laterally projecting 

 lobe. 



Color. In life, grayish-white (Cooper). Specimens in formalin 

 from Doctor Fraser are as f ollows : General color of females orange- 

 rufous with patches of scarlet on the gastric regions. Eggs orange- 

 chrome. Male, orange-rufous, or dirty greenish-white with orange- 

 rufous spots on carapace and a few of the same on chelipeds and 

 legs. 1 female from Taylor Bay was entirely white in life. 



Measurements. Male (174G8), length of carapace 7.6, width of 

 same 13 mm. Female (174G8), length of carapace 15.2, width of same 

 22.8 mm. 



Habitat. Commensal in clams and according to Holmes, in the 

 cloaca of a large holothurian, Liosoma arenata \arenicold\ Stimpson 

 (now Molpadia arenicola). I think that Holmes's specimen may be 

 P. barnharti. 



Range. From Prince of Wales Island, Alaska, to Humboldt Bay, 

 California. San Pedro, California (Holmes). 



Material examined. 



Cordova Bay, Prince of Wales Island, Alaska ; taken in pairs from 

 gill chambers of giant clams; June 16, 1897; steamer Albatross; 

 7 males, 5 females (4 ovig.) (21792). 



Beaver Harbor, British Columbia ; in shells of Schizothaerus nut- 

 tallii; July 12, 1888; steamer Albatross; 7 males, 9 females (7 ovig.) 

 (17468). 



Departure Bay, British Columbia; in Schizothaerus nuttallii; 

 1908; Geological Survey of Canada; 1 male, 1 female (40398). 



Denman Island, British Columbia; from clams; May 12. 1914; 

 steamer Albatross; 6 males, 8 females (6 ovig.) (48426). 



