COMPLETE 



haig: eastern pacific porcellanidae 83 



Ecology: Petrolisthes tridentatus appears to be a strictly littoral 

 species, and has been taken only under stones. In the Pacific, ovigerous 

 females have been taken in January, February, March, May, October, 

 and December. 



Remarks: Petrolisthes tridentatus, originally described from the 

 western Atlantic, was first reported on the Pacific coast by Schmitt 

 (1935), who mentioned its occurrence at Isla Taboguilla, Panama. The 

 specimens on which this record was presumably based, three males and 

 nine females collected in 1904 by the Albatross, were examined by the 

 present writer. 



Haig (1957b) reported Pacific coast specimens taken by the Askoy 

 in Colombia and Panama, and also identified as this species a speci- 

 men from Ecuador referred by Nobili (1901b) to Petrolisthes gracilis 

 Stimpson. 



Boone (1931) listed seven specimens from Isla Taboguilla, Pan- 

 ama, as Petrolisthes erioinerus Stimpson. This material was re-exam- 

 ined by the present writer in the American Museum of Natural His- 

 tory; six of the specimens (including the one figured) proved to belong 

 to P. tridentatus, while the seventh is P. platyrnerus, described herein. 



Gray (1831) very briefly described Porcellana affinis from among 

 British Museum porcellanids without locality data. H. Milne Edwards 

 (1837) repeated Gray's description; White (1847) listed the species, 

 noting that Gray's specimens were three in number. Stimpson (1859, 

 p. 75) suggested that P. affinis might be the same as his Petrolisthes 

 tridentatus. According to Dr. Isabella Gordon, of whom the present 

 writer requested additional information on Porcellana affltiis, Gray's 

 three syntypes are still extant in the British Museum, but are dry and 

 in poor condition and unaccompanied by any data. Camera lucida 

 sketches provided by Dr. Gordon show that the front, orbits, chelipeds, 

 and walking legs agree very closely in form with those of Petrolisthes 

 tridentatus. However, without evidence that Gray's types came from 

 one of the American coasts, the two species cannot be proved to be 

 identical. 



Range: Bahia de Salinas, Costa Rica, south to Isla Puna, Ec- 

 uador. Also western Atlantic, throughout the Caribbean area. 



