222 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



Museum (see Remarks under the preceding species account) and were 

 seen by A. Milne Edwards and Bouvier. In a discussion of the first 

 maxillipeds of various porcellanids these authors referred to Pachy- 

 cheles rotondus (p. 293, footnote) ; the specimen which they evidently 

 studied, for it now lacks the mouthparts on the right-hand side, is an 

 example of Megalobrachium garthi. 



This species bears a superficial resemblance to Megalobrachium 

 sinuimanus (Lockington) because of the blunt tooth on the anterior 

 margin of the carpus. M. garthi may be readily distinguished by the 

 shallow pits covering the carapace, chelipeds, and walking legs, and espe- 

 cially by the five-plated telson. Lockington failed to distinguish be- 

 tween the two forms, and based the original description of M. sinui- 

 manus partly on specimens of M. garthi (see preceding account). 



Range: Isla Turner, Gulf of California, south to Puerto Utria, 

 Colombia; Islas Las Tres Marias, Mexico. Shore to 4 fathoms. 



Megalobrachium erosum (Glassell) 

 Plate 16, fig. 8 ; plate 40, fig. 2 



Pisosoma erosa Glassell, 1936, p. 289 (type locality, Bahia de la 



Magdalena, Baja California, Mexico). 

 Pisonella erosa, Glassell, 1938a, pp. 437, 442. 

 Megalobrachium erosa, Chace, 1942, p. 100. 



Previa us rec o rds : 

 Baja California. Bahia de la Magdalena: S. A. Glassell (Glassell 1936). 

 Gulf of California. N end IslaTiburon: S. A. Glassell (Glassell 1936). 



Diagnosis: Carapace heavily eroded, with strong, transverse ridges 

 across posterior portion and large shallow pits along lateral margins; 

 lateral margins rounded; front with three teeth separated by deep, 

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

 anterior margin with a broad, low, triangular tooth occupying proximal 

 third, surface with longitudinal rows of pits; manus with longitudinal 

 rows of pits; telson with seven plates. 



Description: Carapace about as broad as long, lateral margins 

 rounded ; surface heavily eroded, with punctae and strong, transverse 

 ridges across posterior regions, and large, shallow pits along lateral 

 margins ; anterior regions strongly marked ; surface naked or with 

 traces of pubescence. Front strongly projecting beyond eyes, rounded 

 or faintly trilobate in dorsal view, with a deep median groove ; tridentate 



