106 CALIFORNIA ACADEMY OF SCIENCES. 



Subtribe GALATHEIDEA. 



Rostrum present. Body flattened, the carapace divided by a lateral 

 (anomoural) line. Abdomen flattened, the sides of the segments generally 

 laterally produced. Tail-fin well developed. Pterygostomian regions free 

 from the epistome. External antennae four- jointed, the second and third 

 joints fused; acicle small or absent. First pair of pereopods chelate; the 

 last pair chelate, rudimentary, and folded in the branchial chamber. 



Legion PORCELLANINEA. 



Carapace broad, smooth. Antennules concealed. Antennae long and 

 generally furnished with a scale. Ischium of the maxillipeds broad and 

 flattened; merus broad, with a prominent inner lobe. Chelipeds large, 

 often flattened; first three pairs of ambulatory legs well developed; last 

 pair slender, inflexed. Abdomen loosely bent under the trunk. 



These crabs in the form of the carapace, the bend of 

 the abdomen, and in their flattened maxillipeds resem- 

 ble the true Brachyura; but these resemblances are not 

 indicative of true affinity for both groups had, in all 

 probability, an independent origin from Macrouran 

 ancestors. 



Genus Petrolisthes St. 



Carapace subovate, depressed, generally longer than wide. Front trian- 

 gular, entire or dentate, usually depressed, the margins more or less 

 undulated. Eyes of rather large size. First basal joint of the antennae 

 very short, not reaching the upper margin of the carapace; the second 

 joint is flattened and more or less cristate; flagellum long. Chelipeds 

 broad and flattened; the carpus elongated, with or without teeth on the 

 inner margin. The dactyls of the ambulatory legs are short and stout 

 and terminate in a single claw. 



l^ype. — P. violaceus (Guerin). 



