52 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



Description: Carapace naked or pubescent, covered with granules 

 and short, rough plications; about as broad in mid-branchial regions 

 as posteriorly. Front broadly, sinuously triangular, with a deep median 

 sulcus ; no supraocular spine. Outer orbital angle not produced. A single 

 epibranchial spine, occasionally obsolescent. 



First movable segment of antenna with a strongly projecting, lamel- 

 lar lobe, usually spine-tipped; second with a large projecting tubercle; 

 third nearly smooth; flagellum naked. Outer maxilHpeds rugose. 



Merus of chelipeds rugose, armed on anterior margin with a large 

 lobe, usually spine-tipped. Carpus two to two and a half times as long 

 as wide, naked or pubescent; covered with large granules tending to 

 form a median longitudinal crest, especially in young specimens; an- 

 terior margin armed with three low, wide-set, spine-tipped teeth, a 

 fourth occasionally present; posterior margin with a row of large 

 flattened granules, with one to four produced into spines, and ending 

 distally in a large bifid spine. Manus narrow, naked or pubescent, 

 covered with scattered granules similar to those of carpus; outer mar- 

 gin sometimes with a row of spines and a fringe of hairs, particularly 

 in young specimens. Gape of fingers with a short pubescence. 



Walking legs rugose; anterior margin of merus and carpus with 

 plumose hairs, all segments with long, non-plumose setae; anterior 

 margin of merus of leg 1 with two to five spines, of leg 2 with two to 

 six, of leg 3 with none or one to three; merus of legs 1 and 2 with one 

 or two posterodistal spines, one occasionally present on leg 3 also. 



Variations: Petrolisthes arrnatus is subject to considerable intra- 

 specific variation. Chace (1956, p. 20) concluded that recognition of 

 subspecies is not warranted, although some individuals in the west 

 American and west African populations differ markedly from typical 

 east American specimens. Examination of an extensive series during 

 preparation of the present report showed that variations within the Pa- 

 cific coast population cannot be correlated with geography. 



Material examined: See Table 11. 



Measurements: Males, 4.0 to 14.7 mm; non-ovigerous females, 4.0 

 to 10.9 mm; ovigerous females, 4.6 to 11.5 mm. 



Color: Carapace cream buff with regular designs of rich dark 

 brown. Eyes blackish brown. Antennule glaucous blue with bright 

 orange tips. Antenna orange. Chela cream buff, ridges dark garnet 

 brown. A distinct blue narrow band on inside of merus and a strong 

 greenish tinge on dorsal side of carpus, hand and fingers. Teeth in- 



