106 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



Petrolisthes brachycarpus Sivertsen 

 Plate 29, fig. 2 



Pctrolistes gracilis van brachycarpus Sivertsen, 1933, p. 8, pi. 3, 

 fig. 30 (type locality, Post Office Bay, Isla Floreana [Charles], 

 Galapagos Islands). Not Petrolisthes gracilis Stimpson. 



Previous records: Galapagos Islands. Post Office Bay, Isla 

 Charles: A. Wollebaek on Norwegian Zool. Exped. to the Galapa- 

 gos Islands 1925 (Sivertsen). 



Diagnosis: Carapace with low, enlarged, rough granules posterior 

 to cervical groove, nearly smooth anteriorly, regions distinct; no epi- 

 branchial spine; front broad, sinuously triangular to trilobate; carpus 

 one and a half to two times as long as wide, anterior margin with a 

 few enlarged granules or spinules, margins slightly converging distally; 

 manus swoolen on dorsal surface, outer margin with a sharp crest not 

 defined by a distinct groove; merus of walking legs unarmed. 



Description: Carapace covered with low, enlarged, rough gran- 

 ules posterior to cervical groove; hepatic, frontal, and gastric regions 

 nearly smooth; regions distinct. Front broad, sinuously triangular, 

 inner orbital angles produced, sometimes quite distinctly, giving front 

 a trilobate appearance ; median portion broad, produced, triangular with 

 rounded tip, and with a deep median groove. Outer orbital angle pro- 

 duced into a small sharp tooth. No epibranchial spine. Carapace cov- 

 ered with a short, sparse pubescence. 



First movable segment of antenna with a projecting lamellar lobe 

 on anterior margin ; second and third nearly smooth ; f lagellum naked 

 or with vestigial hairs visible only under magnification. Outer maxil- 

 lipeds lightly rugose. 



Merus of chelipeds lightly rugose, with a strongly projecting, ru- 

 gose, rounded lobe on anterior margin. Carpus one and a half to two 

 times as long as wide; anterior and posterior margins very slightly 

 converging distally; anterior margin with a few enlarged granules near 

 proximal end, produced into spinules in smaller specimens; a distinct 

 longitudinal crest about center of dorsal surface, and a second strongly, 

 obliquely rugose crest along posterior margin, ending distally in a small 

 incurving spine; between these crests a distinct, broad groove covered 

 with small rough granules; in addition, a faint crest sometimes pres- 

 ent near anterior margin ; surface with traces of pubescence. Manus 

 rather swollen, highest on inner side, sloping gradually to outer mar- 

 gin, latter bearing a distinct, sharp crest extending onto pollex ;• surface 



