Boone, Crustacea, Cruise of "Alva," 1931 53 



Remarks : On the Samoan specimen, which is about one or two 

 moults larger than the other nine specimens, the five transverse 

 ridges of the precervical region of the carapace are replaced by a 

 series of interrupted rugae, formed of small squamae-like arcs, 

 with the convex margin anterior and fringed with fine setae. 



References : Golathea latirostris, Dana, J., U. S. Explor. Exped. 

 Crust., vol. XIII, pt. 1, 1852, p. 480 ; Atlas, 1855, pi. 30, fig. 8.— 

 Benedict, J. E., Proc. U. S. Nat. Mus., vol. XXVI, 1903, p. 302. 



Family: PORCELLANIDAE 



Genus: PETROLISTHES Stimpson 



Petrolisthes armatus (Gibbes) 



Discussion: For full description and figure of this species, 

 consult Bulletin of the Vanderbilt Marine Museum, vol. Ill, 1930, 

 p. 73, pi. 19. 



Material examined : Forty-two specimens, taken on the reef 

 at Apia, Samoa, September 5, 1931. One male specimen. Falcon 

 Island, Palm Islands, Queensland, October 7, 1931. 



Distribution: This species is practically tropicopolitan in 

 the tidal zone of the Indo-Pacific and of the west coast of America 

 from Lower California to Peru, including the Galapagos Archi- 

 pelago. It is also found throughout the West Indian region and 

 eastward in the tropic Atlantic on the west coast of Africa. 



The Samoan specimens show quite interesting degrees of va- 

 riation among the forty-two specimens. The majority have the 

 carpus of typical length and armed with three teeth on the anterior 

 margin, but five specimens have the carpus of normal length armed 

 with three teeth on one side, but with four equally developed teeth 

 on the carpus of the opposite cheliped. One specimen has the 

 carpus greatly foreshortened, less than half the normal length, 

 but armed with three teeth. Five specimens have the anterior mar- 

 gin of one carpal joint armed with coarse serrations, slightly 

 smaller than the three teeth, among which these serrations are 

 interspersed. There is also considerable variation in the degree 

 of corrugations or rugae on the carpus and legs. This varies from 

 normal to a few excessively rough surfaces on a few individuals, to 

 some that are almost entirely smooth. One such specimen also has 

 the hepatic tooth mJssing on one side, but present on the opposite 

 side. 



