56 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



smooth; flagellum naked. Outer maxillipeds rugose; inner lobe of the 

 ischium usually ending in a sharp tooth. 



Chelipeds subequal, naked or lightly pubescent. Merus rugose dorsal- 

 ly, more faintly so ventrally; armed on anterior margin with a rugose, 

 strongly projecting lobe, usually rounded at tip. Carpus covered with 

 flattened granules dorsally, faintly rugose to nearly smooth ventrally; 

 about two and a half times as long as wide ; armed on anterior margin 

 with three low, wide-set, spine-tipped teeth, a fourth rarely present ; 

 granules along posterior margin enlarged and roughened, forming a 

 low crest ending distally in a bifid spine, proximad to it another small 

 spine. Manus evenly granular dorsally and ventrally; flat and broad, 

 curved on outer margin which is unspined; a narrow band of short 

 pubescence on ventral surface along outer margin. Fingers broad, gran- 

 ular as in manus, meeting for their entire length or slightly gaping in 

 one cheliped ; gape with a short pubescence. 



Walking legs long and slender, lightly rugose dorsally, nearly smooth 

 ventrall}'. Merus with a fringe of plumose hair on anterior margin, all 

 segments with scattered plumose hairs and tufts of non-plumose setae; 

 anterior margin of merus of leg 1 with three to eight (usually three to 

 five) spines, of leg 2 with four to six, of leg 3 with one to seven (usu- 

 ally two to four) ; merus of leg 1 with two posterodistal spines, of leg 

 2 with one (rarely two), of leg 3 usually spineless, rarely with one spine. 



Measurements: Male holotype: length 9.5 mm (width not re- 

 corded). Paratypes: males, 3.8 to 10.4 mm; non-ovigerous females, 

 4.6 to 8.8 mm; ovigerous females, 4.1 to 8.7 mm. 



Color: Nearly all the material examined had lost its color in alco- 

 hol; a few specimens retain small red spots on the carapace. 



Ecology: Intertidal zone, under stones. Ovigerous females have been 

 collected in January, February, March, September, and October. 



Relationships: Petrolisthes nobilii is very closely related to P. 

 politus (Gray), 1831, of the western Atlantic; the two species may be 

 considered analogues. They resemble each other in having the carapace 

 broadest posteriorly, and in lacking an epibranchial spine. P. politus 

 has a smoother carapace ; it lacks the narrow line of pubescence on 

 the under side of the manus which is characteristic of P. nobilii] there 

 are three or four spines on the posterior margin of the carpus proximad 

 to the posterodistal spine; and the gape of the fingers is usually with- 

 out pubescence or is pubescent in one cheliped only. 



