220 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



necessitate choosing a new name for the better known and more com- 

 mon species. 



Specimens from Isia Flamenco, Panama, identified by Nobili 

 (1901b) with the present species, were re-examined by the writer and 

 found to be Petrolisthcs leiuisi austrinus, a taxon proposed herein. With 

 the correction of Nobili's record (which was repeated by Rathbun, 

 1910, and by Glassell, 1937 and 1938a, with the provenance given as 

 Ecuador instead of Panama), the range of Megalobrachium sinuimanus 

 becomes restricted to the Gulf of California and outlying islands. 



Range: Gulf of California, from Isla Angel de la Guarda to Mazat- 

 lan ; Isla Isabel and Islas Las Tres Marias. Shore to 2^/2 fathoms. 



Megalobrachium garthi Haig 

 Plate 16, fig. 7; plate 39, fig. 4 



Pachycheles rotundas A. Milne Edwards and Bouvier, 1894, p. 291 

 (nomen nudum). 



Pachycheles rotondus, A. Milne Edwards and Bouvier, 1894, p. 293, 

 footnote. 



Megalobrachium garthi Haig, 1957a, p. 39, pi. 10, figs. 1-5 (type lo- 

 cality, Isla Turner S of Isla Tiburon, Gulf of California) ; 1957b, 

 p. 14. 



Previous records: 

 Gulf of California. Isla Turner S of Isla Tiburon: Velero III (Haig 

 1957a). Puerto Escondido or La Paz [as Petrolisthes (Pisosoma) 

 sinuimanus]: (Lockington 1878). 

 Mexico. Bahia Tangola-Tangola: (Haig 1957a). 

 Colombia. Bahia Humboldt: Askoy (Haig 1957b). 



Diagnosis: Carapace covered with very small, shallow pits; lateral 

 margins rounded ; front with three lobes separated by shallow, rounded 

 notches; carpus about one and a half times as long as wide, anterior 

 margin with a narrow, blunt tooth a little proximad of center, surface 

 with longitudinal crests; manus with longitudinal crests, defined by 

 broad grooves containing rows of deep pits; telson with five plates. 



Description: Carapace about as broad as long, very strongly con- 

 vex front to back and sharply deflexed anterior to gastric region ; lateral 

 margins rounded ; entire surface thickly covered with very small, shal- 

 low pits, visible only under magnification ; lateral margins roughly 

 granular; surface naked or with scattered plumose hairs. Front strongly 



