180 University of California Publications in Zoology [Vol, 23 



Remarks. — This species can always be distinguished by the short, stout carpus; 

 by the fact that the merus joint of the ambulatory legs is not hairy and attains 

 the greatest width, or dilation near the distal end, particularly in the third pair 

 of legs. Baker states ' ' the ' flat-crab ' is common under stones between tides. ' ' 



Biological Survey of San Francisco Bay. — This littoral species was 

 only taken twice, one specimen among the rocks at Sausalito and four 

 others in rocky places along the Richmond shore, north of the 

 Standard Oil pier. Those from the latter locality are very small, 

 juvenile specimens. Petrolisthes cinctipes is doubtless of more com- 

 mon occurrence than the above records, based on a very limited num- 

 ber of shore stations, seem to show, for Stimpson reported, "It is 

 abundant in some parts of San Francisco Bay." 



Petrolisthes eriomerus Stimpson 



Plate 32, figure 2 



Petrolisthes eriomerus Stimpson, Ann. Lye. Nat. Hist. N. Y., 10, 119, 1871; 

 Holmes, Occas. Papers Calif. Acad. Sci., 7, 108, pi. 1, fig. 15, 1900. 



Pig. 114. Petrolisthes eriomerus, cheliped (after Holmes). 



Characters. — Carpus of ehelipeds about twice as long as wide, anterior and 

 posterior margins parallel, upper surface with irregularly scattered small and tiny 

 tubercles; lobe at inner angle, if present at all, never prominent and not inter- 

 fering with parallelism of margins. Carapace finely striated over entire surface, 

 except in cardiac region; anterior branchial and gastric regions with small, irregu- 

 larly placed tubercles, which scatteringly follow the areolations. Merus of ambu- 

 latory legs hairy. 



Dimensions. — Largest of several specimens collected at Half Moon Bay, May 11, 

 1913, measured: length of carapace 10 mm., width 10.5 mm., length of carpus of 

 cheliped 8 mm., width 3 mm. 



Type Locality. — Mendocino, California. 



Distribution. — Prom British Columbia to Lower California. 



Bemarks.— Differs from P. cinctipes in that the ehelipeds are longer and 

 smoother with narrower parallel-sided carpus, and in having hairy, less dilated 

 merus joints of the ambulatory legs (Holmes). 



