136 BULLETIN 97, UNITED STATES NATIONAL MUSEUM. 



ward at base, then abruptly recurved toward thumb leaving a high, 

 narrow gape. 



Dactyls of first three legs slightly curved, of last leg straight, with 

 posterior or lower edge convex; all are longer than their propodi. 

 First leg slender, reaching end of propodus of second; second with 

 merus expanded below, reaches end of propodus of third; third 

 much the stoutest, the lower edge of merus and of carpus-propodus 

 much dilated; fourth leg slender, reaching end of merus of third; 

 all margins sharp. 



Variations. In the small male, palm less high than in adult male, 

 thumb of normal shape, triangular, as long as high, less deflexed, 

 dactylus about as wide, moderately curved, when closed, making an 

 insignificant gape. 



Measurements. Male, holotype, length of carapace 5.5, width of 

 same 12.8 mm. 



Specimens examined. San Matias Bay, eastern Patagonia; Hass- 

 ler Exped. ; 1 male holotype, reproducing right cheliped (5741, 

 M. C. Z.) ; 1 young, paratype (-19248, U.S.N.M.). 



Affinity. Belated to P. cristata in the sharp dorsal crest and to 

 P. monodactyla in the spinelike thumb. 



PINNIXA MONODACTYLA (Say). 



Pinnotheres monodactylum SAY, Journ. Acad. Nat. Sci. Philadelphia, vol. 1, 

 1818, p. 454 (type-locality, American; type probably not extant; said 

 to be in "Richmond Museum"). 



Diagnosis. Thumb reduced to spinif orm angle of propodus ; dac- 

 tylus strongly curved to meet thumb. Carapace narrow, If times 

 as wide as long. 



Description of male. Carapace subelliptical, narrowing each side 

 to middle of lateral edge, which is rounded, a tubercle each side 

 marking situation of antero-lateral angles. Surface punctate. Or- 

 bits suborbicular. Antennae subequal to width of front. 



Chela oblong, somewhat quadrate; palm concave and ciliated at 

 middle, a spiniform angle instead of a thumb, with a tooth at its 

 base and another at base "of dactylus larger. Dactylus abruptly in- 

 curved at base, rectilinear toward tip, with an angle at interior mid- 

 dle, tip acute, attaining tip of spiniform angle or thumb. 



First, second, and fourth pairs of legs subequal, second rather the 

 largest; third pair largest of all, and, as also the fourth pair, with 

 somewhat dilated carpus-propodus. 



Abdomen with a few larger punctae, terminal joint rounded at 

 tip. (After Say.) 



Measurements. Male, length 0.3 inch (7.6 mm.), width 0.5 inch 

 (12.7 mm.) 



Range. Probably Atlantic coast of the Southern States. Not 

 seen since the type was taken. 



