50 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



cessacii (A. Milne Edwards) and P. monodi Chace from west Africa, 

 and P. amoenus (Guerin) from eastern America, are closely related 

 Atlantic forms. 



Remarks: Petrolisthes marginatus was first reported from the Pa- 

 cific coast by Nobili (1901b), on the basis of material collected by 

 Enrico Festa at Isla Flamenco, Panama, and Bahia de Santa Elena, 

 Ecuador. Subsequent study has shown it to be one of the most widely 

 distributed and abundant west American species. In the Atlantic it is 

 known from but few records. Pacific and Atlantic populations have not 

 been critically compared, but the comparatively few Atlantic specimens 

 seen by the writer do not appear to differ from Pacific examples. 



As earlier noted by the writer (Haig, 1956a, pp. 26-27), Galapagos 

 Islands specimens identified by Boone (1932) as Petrolisthes gala- 

 thinus (Bosc) are actually P. marginatus, as probably is the record by 

 Hult (1938) of P. galathinus from the Galapagos. The presence of P. 

 marginatus in the Galapagos Islands has been amply confirmed, while 

 there are no substantiated records of P. galathinus from that area. 



Although very common south of the Gulf of California, P. margi- 

 natus does not appear to be well established in the Gulf, where it is 

 largely replaced by P. hirtispinosus. 



Range: Bahia de Guaymas, Gulf of California, south to Bahia 

 de Santa Elena, Ecuador; Clipperton, Isabel, Tres Marias, Revillagi- 

 gedo, and Galapagos Islands. Shore to about 6 fathoms; exceptionally 

 to 22 fathoms. Also known in the Atlantic from the eastern Caribbean 

 area. 



Petrolisthes armatus (Gibbes) 



Plate 19, fig. 2 



Restricted synonymy: 



Porcellana armata Gibbes, 1850, p. 190 (type locality, Florida). Not 



P. armata Dana, 1852, p. 426. 

 Porcellana gundlachii Guerin, 1855, pi. 2, fig. 6 (type locality, Cuba). 

 Petrolisthes armatus, Stimpson, 1858, p. 227; 1859, p. 73. Streets, 



1871b, p. 240. Lockington, 1878, pp. 396, 399. Bouvier, 1895, p. 



8. Ortmann, 1897, p. 280. Rathbun, 1910, pp. 558, 599, pi. 41, fig. 

 3. Boone, 1931, p. 151, text-fig. 6 (part) ; 1932, p. 35, text-fig. 



9. Glassell, 1938a, p. 444. Steinbeck and Ricketts, 1941, p. 456. 

 Holthuis, 1954a, p. 15; 1954b, p. 161. Bott, 1955, p. 52. Garth 

 and Haig, 1956, p. 4. Haig, 1957b, p. 9. Not Hildebrand, 1939, 

 p. 23. 



