314 Mr. K. I. Pocock on 



Opisthacanthus rugulosus^ sp. n. 



Colour of trunk, tail, and chelae a deep blackish green above, 

 a little paler below ; legs deep brown, paler distally ; coxal 

 areas brown, sometimes mottled, the maxillary processes of 

 first and second legs deeper tinted ; vesicle pale yellowish 

 brown. 



Allied to 0. validus, Thorell. 



Upper surface of trunk finely and closely granular through- 

 out ; the median eyes small, the space between them about 

 equal to or greater than a diameter ; the three lateral eyes 

 evenly spaced. Sterna smooth, polished, and finely punc- 

 tured throughout, the last obsoletely crested. 



Tail three and a half times the length of the carapace; the 

 lower side distinctly carinate, as in validus, the upperside 

 laterally more coarsely granular than in that species ; vesicle 

 compressed, granular below. 



Chelce more thickly and coarsely granular than in validus, 

 both hand and brachium being closely and distinctly granular 

 above ; so also are the crests on the upper and lower edges of 

 the inner surface of the hand more coarsely granular ; hand 

 thicker and more convex above, its width being very nearly 

 equal to the length of the keel along the hand-back ; the two 

 digits lobate in the adult. 



Legs punctured ; femora externally feebly granular ; tarsi 

 armed below with 4 inner and 3 outer spines, but there is no 

 spine on the lower angle. 



Genital operculum in male transversely oval, much wider 

 than long. 



Pectinal teeth 6. 



Length 72 millim., of carapace 9*3, of tail 33 ; width of 

 hand T'S ; length of keel of hand-back 8, of movable digit 9-3. 



Loc. Ishiromo, Nyasaland {8ir H. H. Johnston). 

 ^ Easily recognizable from 0. validus by its coarser granula- 

 tion, especially of the upper surface of the hand and brachium, 

 these areas being almost smooth in validus, with the hand 

 furnished with a reticulated pattern of smooth low ridges. In 

 validus, too, though the number of spines on the lower tarsi 

 is the same, there is one upon the inferior angle of this 

 segment. 



The African species of this genus may be recognized by 

 the following key : — 



a. Hand not so flat ; very -wide, the width exceeding 

 the length of the hand-back ; less of the carapace 

 showing below the lateral eyes; anterior crest 

 on humerus (upper arm) of pincers absent or 



