MUSEUM OF COMPAEATIVE ZOOLOGY. 175 



moreover, are longer and narrower ; the anterior margin of the carpus is three- 

 toothed instead of five-toothed. The squames of the carpus and claw do not 

 tend to widen out into ridges or folds either on the upper or lower face, hut 

 preserve the form of close-set imhricated scales over the whole surface, includ- 

 ing the space between the longitudinal depressions of the carpus and along the 

 depressed line of the propodus. The form of the carpus approaches nearer 

 to that of P. armatus (Gibbes), but the present species may be readily dis- 

 tinguished from P. armatus by the prominent rugae of the carapace and the 

 squames of the chelipeds. From P. edwardsii (Sauss.) it is distinguished by its 

 longer chelipeds, by the ridges of the hinder part of the carapace extending 

 clear across the carapace without interruption, etc. The ridges of the frontal 

 lobes are much more strongly developed in P. agassizii than in any of the 

 allied species. 



Carapace 5X5 mm.; cheliped, 34 mm. 



One male, taken with Petrolisthes occidentalis Stimps. on the reef at Panama, 

 at low tide, March 12. 



Pachycheles panamensis, sp. nov. 



Carapace subcircular, of equal length and breadth ; upper surface flattened, 

 granulate, and setose, especially on the gastric and anterior part of the branchial 

 regions ; posterior portions of the branchial regions lightly rugose. Front broad, 

 produced to a rounded median lobe, lateral portions straight, inner orbital 

 angle rounded, not produced; outer orbital angle projecting as a triangular 

 tooth between the eye and the base of the antenna. Lateral border of the 

 carapace with a concavity behind the antenna ; the margin is slightly raised as 

 a rim which is lost in one of the branchial rugse before reaching the hind border 

 of the carapace ; hind border slightly concave. Chelipeds : unequal, the right 

 being the larger ; upper surface of the merus rugose and setose, under surface 

 smooth, internal distal angle produced as a denticulated tooth ; carpus short 

 and broad, upper surface tuberculous and setose, internal border armed with 

 a large tooth at the base, followed by one or two smaller teeth, lower sur- 

 face smooth and naked ; upper surface of the propodus furnished with small 

 tubercles which bear stiff bristles, inner margin rounded, not toothed, outer 

 margin granulated, lower surface convex, naked and polished near the centre 

 (where the surface is reticulated in the larger claw), squamoso-granular and 

 setose near the edges; fingers gaping, crossing at tips, toothless on both the 

 inner and outer margins (or at most slightly denticulated on the outer margin). 

 Ambulatory appendages setose. 



Length of carapace, 6.5 mm.; breadth, 7 mm.; breadth of frontal margin, 

 2 mm. 



Panama, March 12. 1 female ovig. 



Pachycheles rudis Stimps. is a larger species, with the posterior margin of the 

 carapace more concave (the concavity having almost the shape of a triangular 



