COMPLETE HAIG : EASTERN PACIFIC PORCELLANIDAE 179 



Basal segment of antennule large, laterally expanded, with two to 

 four broad lobes on anterior margin and often tuberculate on anterior 

 face. 



Chelipeds large, flattened, subequal; carpus longer than broad, its 

 anterior margin armed with a strongly projecting, angular lobe; fingers 

 long and slender. 



Walking legs of moderate length, somewhat flattened ; merus often 

 greatly expanded, its anterior margin crested ; movable spinules on pos- 

 terior margin of propodus greatly reduced in number or absent, at 

 most one or two at articulation with dactylus; dactylus very short, end- 

 ing in a simple spine, posterior accessory movable spinules greatly re- 

 duced in size or entirely absent. 



Telson of abdomen composed of five plates. 



Contains three species, all eastern Pacific south-temperate. 



Remarks: The three species for which this genus is proposed have 

 several characters in common which set them apart from Petrolisthes. 

 These include the slight forward projection of the basal antennal seg- 

 ment, which slightly excludes the movable segments from the orbit; the 

 form of the basal segment of the antennule (text-fig. 6) ; the very short 

 dactylus of the walking legs, with posterior movable spinules absent or 

 greatly reduced in size; and the five-plated telson of the abdomen. 



The name is derived from the Greek aAAo?, other, different, and 

 Petrolisthes. 



Key to the Species 



la. Carapace covered with granules and tubercles, front with five 

 lobes; lobe on proximal half of anterior margin of carpus join- 

 ing distal half of margin at nearly a right angle . . spinifrons 



lb. Carapace smooth, front with three lobes; lobe on proximal half 

 of anterior margin of carpus joining distal half of margin in a 

 broad curve 2 



2a. Orbital margin nearly straight ; carpus of walking legs with a 

 sharp anterior crest angulosus 



2b. Orbital margin rounded, concave ; carpus of walking legs with- 

 out an anterior crest punctatus 



