228 N'otes on North American Crustacea. 



The single species upon which the genus above described is 

 established, seems to belong to the Corystoidea rather than to 

 any other tribe of Brachyua, notwithstanding the small deve- 

 lopment of the antennae, which are no larger than in many 

 Maioids or Cancroids. The tribe named is by no means well 

 constituted, and, as far as understood, it seems to rest upon 

 general rather than particular characters. And, though our 

 genus ap^Droximates to none of those hitherto referred to this 

 tribe, yet in general habit, want of a distinct rostrum, epistome 

 covered by the narrow outer maxillipeds, compressed posterior 

 feet, etc., it shows so many of the characters found in different 

 genera of Corystoids, that we have not hesitated to arrange it 

 here. 



Pliosonia parTifrons, nov. sp. 



PI. V. f. 6. 

 Carapax convex, pubescent ; median regions well separated from the 

 hepatic and branchial ones. Upper surface armed with erect blunt 

 spines, as follows ; four large and seven small ones on the gastric region, 

 the large ones on its posterior part ; one on the cardiac, and one on the 

 intestinal region, curved forward ; two on the inner part of the bran- 

 chial, and two longer ones on the anterior part of its lateral margin ; 

 three small ones on the hepatic region. There is also a spine on the 

 middle of the pterygostomian ridge. The facial region occupies less 

 than one-third the width of the carapax. Distance between the bases 

 of the chelipeds about one-half the widm of the carapax. First pair of 

 ambulatory feet in the male about one and one-half times the length of 

 the carapax. Color brownish or buflf. Length of the carapax in a 

 male, 0.61 ; breadth, excluding spines, 0.53 ; in a female, length, 0.81 ; 

 breadth, 0.7 inch. 



It was found in great abundance at Cape St. Lucas, by Mr. 



Xantus. 



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