74: Notes on North American Crustacea. 



Found at Aspinwall, by Mr. Eowell, and in great abundance 

 at St. Thomas, by Riise. 



Specimens were taken at Panama by Messrs. Sternbergb 

 and Rowell, of a species wMcb is either identical with P- 

 armatusy or so closely allied that I have as yet been unable to 

 find the distinctive characters. . 



Petrolistheis politiis. 



Porcellana polita, Gtb.j ', Zool. misc. 14. GriflBtli's Cuv. Crust. 312. 



pi. XXV. f. i. 

 " magnijica, Gihhes ; loc. cit. 191. 



Barbadoes ; (Gill ;) St. Thomas ; (Riise.) 



Fetrolisthes marg^inatus, nov. sp. 



This species is allied to P. armatus, but the median lobe of the front 

 is smaller and more prominent, and the carpus shorter ; also there are 

 four teeth, equal in size and very sharp, on the anterior margin of the 

 carpus of the left cheliped. The surface of the carapax is smooth and 

 pubescent. The hands are granulated, and covered above with a very 

 short but dense pubescence ; — from the inner base of the finger to the 

 anterior angle of the carpus there extends a ridge of moderate promi- 

 nence. The anterior or front margin of the hand is regularly small- 

 tuberculated or crenulated, and the margin is conspicuous from the fact 

 that the tubercles are of lighter color than the rest of the hand ; — beneath 

 there are two rows of marginal granules. The meros-joint of the ambu- 

 latory feet is spinulose above, and 1-spined below, near extremity. 

 Color a deep purplish-crimson. Dimensions about the same as those of 

 P. armatus ; length of carapax about half an inch. 



Found at Barbadoes, by Mr. Gill. 



Petrolisthes gracilis, nov. sp. 



Carapax smooth, unarmed, and shaped as in P. rupicolus, but more 

 flattened, and with a less depressed front. Chelipeds long and slender ; 



