110 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.24 



The specific name, from the Greek TrAarvs, broad, and [i-qpoi, thigh, 

 refers to the broad, inflated merus of walking leg 3. 



Range: Known only from the two localities listed above, Port 

 Parker, Costa Rica, and Isla Taboguilla, Panama. 



Petrolisthes crenulatus Lockington 

 Plate 23, fig. 4 



Petrolisthes crenulatus Lockington, 1878, pp. 395, 398 (type locality. 

 Puerto Escondido, Gulf of California). Glassell, 1936, p. 286; 

 1937, p. 80; 1938a, p. 444. 



Previous records: Gulf of California. Puerto Escondido: (Lock- 

 ington) ; S. A. Glassell (Glassell 1936, 1937). Off Arena Bank: W. 

 Beebe on Xaca (Glassell 1937). 



Diagnosis: Carapace plicate, rather rough and granular along lat- 

 eral margins, anterior regions and grooves strongly accentuated ; no 

 epibranchial spine; front trilobate; carpus about one and a half times 

 as long as wide, covered with long hairs, proximal half of anterior 

 margin with three or four blunt, wide-set teeth ; manus not swollen, 

 without a heavy crest on outer margin; merus of walking legs unarmed. 



Description: Carapace covered with short plications, becoming 

 rough and granular on lateral margins; protogastric and hepatic lobes, 

 and the grooves defining them, strongly accentuated and elevated above 

 frontal region, the latter strongly deflexed. Front trilobate, median lobe 

 broadly triangular and projecting only slightly beyond lateral lobes. 

 Outer orbital angle produced into a very small tooth. No epibranchial 

 spine. Frontal and posterolateral regions bearing long plumose hairs, 

 indistinct in young specimens. 



First and second movable segments of antenna somewhat roughened 

 by granules ; third nearly smooth ; flagellum naked. Outer maxillipeds 

 faintly rugose. 



Merus of chelipeds smooth, armed on anterior margin with a low, 

 finely granular lobe ; covered with long plumose hairs. Carpus about 

 one and a half (1.4 to 1.7) times as long as wide, with three or four 

 blunt, wide-set teeth on proximal half of anterior margin, proximal 

 tooth usually smallest ; surface covered with granules, rough and pro- 

 jecting along posterior margin ; a median longitudinal crest of raised 

 granules, it and posterior crest defined by a broad groove; groove and 

 dorsal crest usually obscured by the long, plumose hairs covering the 



