Notes on Worth American Crustacea. Y5 



carpus narrow, about three times as long as broad, with its anterior and 

 posterior margins parallel, straight and smooth, the posterior margin 

 projecting and forming a sharp tooth at its outer extremity. Hands 

 smooth, microscopically granulated; fingers within or below hairy. 

 Ambulatory feet with the meros twice as long as broad, not dilated 

 towards its extremity, and smooth, without spines above. Color red- 

 dish. Length of the carapax, 0'44 ; breadth 0'41 inch. 



Taken at Guaymas, in the Gulf of California, by Capt. C. M. 

 P. Stone. 



Petrolisthes tridentatuis. 



Plate I. fig. 4. 



In this small species the carapax is smooth and unarmed. Front 

 much deflexed and tridentate ; with the median tooth or lobe triangu- 

 lar; margins smooth. The teeth of the front are most distinctly seen 

 in a front view. Feet nearly naked. Chelipeds obsoletely granuloso- 

 squamose ; carpus about twice as long as broad, with the anterior mar- 

 gin nearly straight, not toothed, and 'very slightly projecting at the 

 inner angle ; the posterior margin subsquamated, but not spinulated. 

 The carapax is generally minutely spotted with red, and streaked down 

 the middle with whitish. Chelipeds dark reddish. Ambulatory feet 

 annulated. Length of carapax, 0-20; breadth, 0-19 inch. 



Found at Barbadoes, by Gill, and at St. Thomas by Riise. 



Gray's short description of his P. affinis^ (for which no 

 locality is given,) applies in most respects to this species, and 

 may be the same. 



Pisosoma Riisei, nov. sp. 



Carapax rounded, smooth, and glabrous, faintly punctate and obso- 

 letely striated transversely. Front bi-marginate ; the upper margin or 

 crest straight; the lower margin projecting into a small triangular 

 tooth placed nearly in a vertical plane. The last three joints of the 

 ambulatory feet are hairy ; the meros-joint not dilated, and with smooth 



