Boone, Crustacea, Cruises of "Eagle" and "Ara," 1921-28 73 



The fifth legs are characteristically small, with the merus and 



carpus elongated, slender, subequal, the propodus scarcely half the 



length of the carpus and with the dactyl forming a small weak chela, 



which is enveloped in a brush of outstanding setae. 



Synonymy. — Pisosoma angustifrons Benedict, Bull. U. S. Fish. 



Comm., vol. 20, part 2, p. 135, pi. 3, fig. 6, 1901.— Schmitt, 



Bijdragen tot de Dierkunde, Natura artis magistra te Amsterdam, 



Afl. 23, p. 74, 1924. 



Genus: PETROLISTHES Stimpson. 

 Petrolisthes airmatus (Gibbes). 



Plate 19. 



Diagnostic chabacters: Carpus of chelipeds armed with three 

 teeth on anterior margin ; merus of first and second ambulatories with 

 one subdistal spine on the posterior lateral margin ; no such spine on 

 the merus of the third ambulatory leg. Lateral margins of carapace 

 terminating anteriorly in a sharp distal (or hepatic) spine. 



Type : The type material was from Florida and was originally de- 

 posited in the Boston Society of Natural History and Charleston 

 Museum, S. C 



Distribution: The entire "West Indian region; the Indo-Pacific 

 region, and on the West American coast from Lower California to 

 Peru, including the Galapagos Islands. 



Material examined: One, Cape Cruz, Cuba, 3 fms., February 11, 

 1924, by the "Ara." One, Pigeon Key, Fla., April 17, 1923. 



Technical description : Carapace nearly as long as wide, moder- 

 ately convex; surface covered with flattish, broken, transverse rugae, 

 which are more prominent on the lateral branchial regions. Rostrum 

 broadly triangular, with a distinct but shallow median depression; 

 frontal margin slightly sinuate and finely crenulated; the superior 

 orbital margin is unbroken. The lateral margins are carina-like and 

 terminate sharply in a sharp postorbital spine. The hepatic sinus is 

 shallow but distinct. The anterolateral or postorbital angle is almost 

 right-angled. There are a pair of wide, transverse ridges slightly 

 separated from each other by the median groove, which, taken to- 

 gether, form a prominent postrostral transverse groove across the 

 anterior gastric region. The abdomen is composed of six segments, of 

 which the anterior three are dorsally visible, the remaining segments 

 being loosely flexed under the body. The first segment is but little 



