COMPLETE HAIG: EASTERN PACIFIC PORCELLANIDAE 123 



having a lightly pubescent carapace and chelipeds, and a trace of pu- 

 bescence in the gape of the fingers. These differences appear to be 

 constant, judging from the comparatively small series of the Atlantic 

 species available for examination. 



Remarks: The holotype of Pisosoma flagraciliata Glassell was 

 compared with two of the 12 syntypes of Petrolisthes htans. The two 

 nominal species proved to be identical, and Pisosorna flagraciliata be- 

 comes a synonym. 



With the removal of several species from Petrolisthes to other gen- 

 era, Petrolisthes hians and its close relative P. jugosus Streets become 

 the only New World Petrolisthes with five plates instead of seven in the 

 telson of the abdomen. It is not known whether any members of the 

 genus from other parts of the world have a five-plated telson. 



Range: Bahia de Santa Maria, Baja California; Guaymas, 

 Gulf of California, south to Bahia de Santa Elena, Ecuador; Isa- 

 bel, Tres Marias, and Revillagigedo Islands. Shore to about 4 fath- 

 oms; exceptionally to 18 fathoms. 



NEOPISOSOMA, new genus 

 Type species: Neopisosoma bicapillatu/n, new species. 



Carapace rounded or subquadrate, approximately as broad as or 

 a little broader than long. Side walls incomplete, ending at epibranchial 

 level or tapering off at this point with a narrow projection extending 

 to mesobranchial level, the posterior portion occupied by membrane 

 only. Front narrow, rounded and usually rather strongly produced in 

 dorsal view, trilobate or transversely sinuate in frontal view. Eyestalks 

 short and stout, retractile. 



Basal segment of antenna not produced forward to meet anterior 

 margin of carapace ; sometimes with a small inward projection. 



Basal segment of antennule broad, anterior face truncate, anterior 

 margin sinuate. 



Chelipeds large, thick, and robust, one distinctly larger than the 

 other ; carpus short and stout, about as broad as long ; manus and 

 fingers differing in form in the two chelipeds. 



Walking legs of moderate length, somewhat flattened ; propodus 

 with movable spinules on posterior margin ; dactylus ending in a simple 

 spine, with small movable accessory spinules on posterior margin. 



Telson of abdomen composed of either seven or five plates, Male 

 pleopods lacking in some species. 



