COMPLETE HAIG: EASTERN PACIFIC PORCELLANIDAE 109 



ending distally in a small incurving spine, between these crests a dis- 

 tinct broad groove; surface covered with scattered large rounded gran- 

 ules or small tubercles; margins subparallel or very slightly converging 

 distally, anterior margin unarmed ; surface with traces of pubescence. 

 Manus rather swollen, highest on inner side, sloping gradually to outer 

 margin, latter bearing a distinct sharp crest extending onto pollex, this 

 crest defined by a strong groove near outer margin ; surface with scat- 

 tered small granules, a row of about eight larger rounded granules or 

 small tubercles forming an even longitudinal row at about center; sur- 

 face with traces of pubescence, thicker and a little longer along outer 

 margin and extending onto ventral surface, there forming a short pile 

 in a narrow band along margin. Fingers finely granular; gape with a 

 thick pubescence produced on proximal half of fingers into a short 

 tuft. Ventral surface of all segments smooth. 



Walking legs short, granular, covered with plumose and non-plu- 

 mose hairs; merus not armed with spines, that of leg 3 inflated, nearly 

 as broad as long. 



Abdomen smooth, covered with a short, thick pubescence. 



Measurements: Holotype male: length 5.2 mm, width 5.2 mm. 

 Paratypes: males, 2.5 to 4.3 mm; non-ovigerous females, 4.3 and 4.5 

 mm; ovigerous females, 3.5 to 4.9 mm. 



Color: All traces of color had disappeared in the examined ma- 

 terial. 



Ecology: All the known material, consisting of 14 specimens from 

 two stations, was collected in the littoral under stones. Included were 

 ovigerous females taken at Port Parker, Costa Rica, in February. 



Relationships: Petrolisthes platymerus is most closely related to 

 P. schmitti Glassell and P. brachycarpus Sivertsen. All are small spe- 

 cies with pubescent carapace, sinuously triangular to trilobate front, 

 manus with dorsal surface swollen and outer margin crested, and gape 

 of fingers with a thick tuft of pubescence. P. platymerus differs from 

 the other two in having the entire carapace rough and uneven, and 

 the merus of walking leg 3 short and broad. It is somewhat less closely 

 related to P. holotrichus Nobili, which has a nearly smooth carapace, 

 no swelling or outer crest on the manus, and no tuft in the gape of the 

 fingers, and is tomentose over its entire surface. 



Remarks: One of the specimens from Isia Taboguilla, Panama, 

 reported by Boone (1931) as Petrolisthes eriomerus Stimpson, proved 

 to belong to this species. 



