of the West Coast of North America. 401 



margin denticulate, sometimes spinous (a young specimen has 

 a row of six or seven spines). 



Surface of chelipeds covered with squamose ridges with a 

 crenulate edge, and thickly pubescent. The longitudinal 

 ridge on the carpus is formed of prominent oblique squamas, 

 and that of the manus of a row of longitudinal crenulate squa- 

 mose teeth, passing into a line of tubercles down the centre of 

 the dactylus, which has a beaded upper margin. Fingers 

 closely fitting, hooked at the tip. Chelipeds equal. 



Meros of ambulatory feet with a row of spines, hidden 

 among long setae, on the anterior border, and a spine at distal 

 end posteriorly on the second and third pairs ; a slender spine 

 at posterior distal end of propodus. Last three joints of these 

 feet with long hairs and traces of colour (blue and red) ; 

 meros pubescent. 



Mulege Bay, Gulf of California. 



PetroUsthes {Pisosoma) sinuimanus, nov. sp. 



Carapax almost orbicular, somewhat convex, punctate, be- 

 coming granular on the lateral margins ; front sinuous in three 

 low lobes, the centre one very small, the preorbitals very long 

 and low ; sulci enclosing the gastric and cardiac regions dis- 

 tinct in young specimens, which have the carapax smooth. 



Eyes very small ; external antennge very short, scarcely as 

 long as the carapax. 



Chelipeds equal, similar. Meros usually with a blunt lobe 

 at its anterior distal end ; carpus nearly twice as long as wide, 

 usually with a single blunt tooth in the centre of its anterior 

 margin ; manus and dactylus forming an obtuse triangle, outer 

 edge of manus and pollex serrated. 



Upper surface of the carpus and manus with three longitu- 

 dinal rolling ridges, divided by furrows equal to them in size, 

 the entire u]3per surface of meros, carpus, and manus deeply 

 punctate and granular; dactyli granular. Fingers hooked and 

 crossing at the tip. 



Ambulatory feet stout, punctate, the two anterior pairs with 

 the posterior distal end of tlie cai-jius produced backwards. 



Entire surface free from tomentosity or hairs, except two or 

 three stout hairs on the underside of the dactyli of the am- 

 bulatory feet. 



Length of carapax of largest specimen 5*5 millims., width 

 of ditto 5*5. 



Several specimens found under coral and stones at low 

 tide at La Paz and Port Escondido, Gulf of California. 



This species varies considerably : some few specimens are 

 without a trace of the lobe upon the meros or of tlic tooth upon 



