COMPLETE HAIG : EASTERN PACIFIC PORCELLANIDAE 49 



posterior margin rugose, some of the rugae produced into spines. Manus 

 granular, with a longitudinal crest of larger, flattened granules extend- 

 ing from base of dactylus; surface pubescent, more distinctly so to the 

 outside of this crest ; outer margin with a row of large, well-spaced gran- 

 ules, sometimes developed into spinules; outer margin often with a 

 fringe of hairs. Dactylus with a row of large flattened granules con- 

 tinuing the row on manus; gape of fingers with a short pubescence. 



Walking legs rugose; anterior margin of merus and carpus with a 

 fringe of plumose hairs, all segments with long tufts of non-plumose 

 setae; anterior margin of merus of leg 1 with five to seven spines, of 

 leg 2 with four to seven, of leg 3 with four to seven; merus of legs 1 

 and 2 with one or two posterodistal spines. 



Material examined: See Table 10. 



AIeasure?nents: Males, 2.9 to 11.9 mm; non-ovigerous females, 2.4 

 to 6.8 mm; ovigerous females, 3.0 to 12.5 mm. Stimpson (1859) gave 

 the length as about }4 inch (13 mm). 



Color: In specimens preserved for only a few years in alcohol, the 

 ground color is yellow, overlaid on the carapace with dark red spots 

 and broken marblings. All granules on the chelipeds are dark red, and 

 the same color appears on the walking legs in the form of small 

 spots on the merus and broad stripes on the carpus and propodus. The 

 outer maxillipeds and the ventral surface of the manus and fingers are 

 also dark red. Traces of this coloration remain, particularly on the gran- 

 ules of the chelipeds, in many specimens which have been a long time in 

 preservative. 



Ecology: Petrolisthes marg^lnatus commonly inhabits interstices of 

 Pocillopora coral, in depths to about 6 fathoms. Much less frequently 

 it occurs under stones in the intertidal zone, or on hard substrates in 

 depths not exceeding about 4 fathoms; it was once dredged by the 

 Velero III from a coral bottom at 22 fathoms, a depth that must be con- 

 sidered exceptional. It was once taken by Hancock Foundation col- 

 lectors from sponge dredged in 1-4 fathoms. 



Ovigerous females have been taken in October and in every month 

 from December through May. 



Relationships: On the Pacific coast, Petrolisthes marginatus has 

 its closest affinities with P. hirtispinosus Lockington, which like it has 

 a crest formed of enlarged granules on the dorsal surface of the manus. 

 P. marginatus differs mainly in the shorter carpus, (average) smaller 

 number of carpal teeth, and lack of a strong supraocular spine. P. 



