COMPLETE 



haig: eastern pacific porcellanidae 57 



The new species is also close to Petrolisthes armatus (Gibbes) ; the 

 two occupy much of the same range. P. nobilii is most easily distin- 

 guished by the following characters: carapace triangular and broadest 

 posteriorly, instead of being nearly as wide across the midbranchial 

 regions as posteriorly; front somewhat narrower and more triangular; 

 manus broader, its outer margin more strongly curved; a narrow band 

 of short pubescence on ventral surface of manus along its outer mar- 

 gin, this pubescence lacking in P. armatus; a single spine on posterior 

 margin of carpus proximad to the double posterodistal spine, while in 

 P. armatus the number of these spines is variable, but usually two or 

 three. 



Remarks: Nobili (1897) reported a specimen of Petrolisthes politus 

 (Gray) from "Panama"; by this he probably meant Panama City, in 

 which case the specimen was undoubtedly P. nobilii. Apparently 

 Nobili's record was the source of Rathbun's (1910) listing of "Pan- 

 ama" for P. politus in her checklist of Pacific coast crabs occurring 

 from Panama to Isla Chiloe. 



Boone (1931) reported Petrolisthes armatus (Gibbes) from several 

 western Panamanian localities. This material was examined by the 

 writer in the American Museum of Natural History; a portion of it 

 proved to be P. nobilii. 



This new species is named in honor of Giuseppe Nobili, in recogni- 

 tion of his contributions to west American carcinology. 



Range: Cabeza Ballena, mouth of the Gulf of California, south to 

 Punta Brava, Bahia de Santa Elena, Ecuador; Isla Isabel off the 

 Mexican coast. 



Petrolisthes robsonae Glassell 



Plate 18, fig. 2 



Petrolisthes armatus, Hildebrand, 1939, p. 23. Not P. armatus 



(Gibbes), 

 Petrolisthes robsonae Glassell, 1945, p. 227, text-fig. 3 (type locality, 



Miraflores Locks, Panama Canal, Canal Zone). Haig, 1957b, p. 



10. 



Previous records: Panama. Miraflores Locks, Panama Canal, Canal 

 Zone: S. F. Hildebrand (Hildebrand) ; Elinor D. Robson (Glassell). 

 Bellavista, Panama City: Askoy (Haig). 



Diagnosis: Carapace finely rugose; a single small epibranchial 

 spine; front sinuously triangular; carpus a little over twice as long as 



