Boone, Crustacea, Cruises of "Eagle" and "Ara," 1921-28 209 



sharply etched reddish margins and tips; the chelae green with red- 

 dish lines; the finger-tips ocher yellow. According to Marcgrave de 

 Liebstad, who first recorded and figured the species from Brazil, it is 

 many colored, brown, blue, white, red, chelae whitish yellow at the 

 extremities. I am inclined to think that possibly some of the colors he 

 attributes to this species may really belong to species of Sesarma, 

 unless the young of A. pisonii, like that of Grapsus grapsus, have a 

 different coloration. This point is one worthy of the attention of 

 future field workers. 



Synonymy. — Aratv prinima Marcgrave de Liebstad, Hist. Rer. Nat, 

 Brasil, lib. 4, p. 185, and text figure. 



Sesarma pisonii Milne Edwards, Hist. Nat. Crust., vol. 2, p. 76, pi. 

 19, figs. 4 and 5, 1837. 



Aratus pisonii Milne Edwards, Ann. Sci. Nat., Ser. 3, Zool., vol. 20, 

 p. 187, 1853. — Rathbun, Rapport betreffende een vooloopig onder- 

 zoek naar den toestand van de visscherij en de Industrie van 

 zeeproducten in de Kolonie Curagao, vol. 1, p. 340, 1907; Bull. 

 U. S. Nat. Mus. 97, p. 323, pi. 96, 1918 ; Bijdragen tot de Dier- 

 kunde, Natura Artis Magistra te Amsterdam, Aflev. 23, p. 18, 

 1924. 



Subfamily : Plagusiinae. 



Genus: percnon Gistle. 

 Percnon gibbesi Milne Edwards. 



Plate 71. 



Name : Dedicated to Lewis R. Gibbes, an American carcinologist. 



Diagnostic characters : Carapace thin and ovate, disk-like, longer 

 than wide, with the tubercles of the dorsal surface flattened. Inner 

 surface of palm devoid of bristles. Meral joint of ambulatories of 

 moderate size, not very wide, as compared to the Pacific species. 



Type: The type came from the Antilles and is deposited in the 

 Paris Museum National d 'Historic Naturelle, 



Distribution: Subtropical and tropical shores of America, from 

 Lower California to Chile on the west ; from southern Florida, south- 

 ward in the Bahamas, Bermudas, and "West Indies to Brazil ; the east- 

 ern Atlantic from the Azores to the Cape of Good Hope. 



