12 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



6a. Chelipeds thick, robust, one distinctly larger than the other; 

 side walls of carapace incomplete, the portion posterior to 

 epibranchial or mesobranchial area occupied by membrane 

 only Neopisosoma 



6b. Chelipeds subequal, usually not robust ; side walls of carapace 



entire 7 



7a. Basal segment of antennule not laterally expanded ; basal seg- 

 ment of antenna either not produced inward, or with a distinct 

 inward projection forming a partial suborbital margin ; front 

 triangular or trilobate, usually rather prominent ; telson almost 

 invariably 7-plated. Petrolisthes 



7b. Basal segment of antennule laterally expanded ; basal segment 

 of antenna strongly produced inward and, with the outer side 

 of basal antennular segment, forming a complete or nearly 

 complete suborbital margin ; front tridentate or distinctly trilo- 

 bate; telson 5-plated 8 



8a. Front tridentate, strongly produced beyond eyes; basal segment 

 of antenna not at all produced forward ; anterior margin of 

 carpus with narrow spines Liopetrolisthes 



8b. Front trilobate, two supplementary lobes sometimes present; 



basal segment of antenna produced forward and in contact 



with outer orbital angle, narrowly excluding movable segments 



from orbit ; anterior margin of carpus with a broad lobe. 



A liopetrolisthes 



9a. Dactylus of walking legs ending in two or more large, strong, 

 fixed spines; carapace markedly broader than long; front 

 nearly transverse in dorsal view Polyonyx 



9b. Dactylus of walking legs ending in a single spine, usually with 



accessory movable spinules on posterior margin 10 



10a. Movable segments of antenna minute and flagellum rudi- 

 mentary, their total length less than or scarcely exceeding 

 width of eye; carapace about 1^ times as long as broad; 

 front strongly tridentate in dorsal view. . . Minyocerus 



10b. Movable segments of antenna normal 11 



11a. Front prominent, strongly tridentate or trilobate in dorsal 



view 12 



lib. Front deflexed, appearing rounded or faintly trilobate in dorsal 



view 13 



