124 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



Contains five known species, from the east and west American 

 coasts. 



Remarks: Neopisosoma shares with Pachycheles three characters 

 which occur nowhere else in the family: the chelipeds are thick, robust, 

 and markedly differing in size (and bent in the normal manner at the 

 articulation of carpus and manus, not straight as in Orthochela) ; the 

 number of plates in the telson of the abdomen may vary within a single 

 species; and male pleopods are absent in some species. The principal 

 difference between the two genera lies in the structure of the side walls 

 of the carapace. In Pachycheles the chitinous material in the posterior 

 portion of the side wall is broken up into one or more separate pieces, 

 while in Neopisosorna these fragments are entirely lacking, leaving 

 membrane only. It may be that, when the species included in Pachy- 

 cheles are reviewed on a worldwide basis, Neopisosoma will prove to 

 be referable to it as a subgenus. 



Besides the three species treated in this report, Neopisosoma is 

 represented by two Caribbean forms previously included in Pisosoma: 

 these are Neopisosoma angustifrons (Benedict), 1901, and A^. cura- 

 caoense (Schmitt), 1924. 



The name of this genus is derived from the Greek v€o<i, new, and 

 Pisosoma. 



Key to the Eastern Pacific Species 



la. Chelipeds with flattened granules; carpus with crests; telson 



7-plated ; male pleopods present 2 



lb. Chelipeds with rounded, projecting granules; no crests on car- 

 pus ; telson 5-plated ; no male pleopods .... dohenyi 



2a. Carpus with 4-5 teeth occupying entire anterior margin ; its 

 surface with 3 distinct longitudinal crests, and a fourth along 

 posterior margin; manus of both chelipeds thickly covered with 

 long hairs hicapillatum 



2b. Carpus with 3 teeth occupying not more than proximal two- 

 thirds of anterior margin ; its surface with 3 low, often ob- 

 solescent crests; pubescence on manus of minor cheliped only 

 mexicanum 



Neopisosoma bicapillatum, new species 

 Plate 8; plate 30, fig. 3 

 Types: Holotype, male, U. S. National Museum Cat. No. 102409, 

 from reef north of Tagus Hill, Isla Albemarle, Galapagos Islands; 



