264 DR. W. A. CUNNINGTON ON THE BRACHYUHOUS [Mar. 5, 



considerably less than in perlatus, and the post-frontal crest does 

 not extend forward so far in the middle. The posteiior carpal 

 spine of the cheliped is also sharper and more prominent. Both 

 the male and female specimens show only a single transverse 

 furrow on the sternnm in front of the abdomen, while in the 

 specimens of allied species examined the males almost invariably 

 have two fuii'ows even in young individuals. 



From this description of the characters of these two ISTyasa Crabs, 

 it will be evident that my former contention is not without 

 foundation. These individuals agree to a considerable extent with 

 several species, and where they disagree with one they agree with 

 another, while, to my mind, they have not a single character 

 which satisfactorily distinguishes them from those forms to which 

 they are undoubtedly allied. In the present state of our know- 

 ledge, it would be futile to attempt to determine which species 

 should be eliminated, and Miss Rathbun has certainly taken the 

 right course in retaining most of the species hitherto described, 

 though it seems to have led her into some difficulties respecting 

 her key. Befi.ring in mind the facts which have been detailed at 

 some length above, I prefei", in a case like this, to leave the 

 specimens unnamed, and so at least avoid adding to the already 

 existing superfluity. 



Lake Tanganyika. 



POTAMON (POTAMONAUTES) PLATYNOTUS, Sp. n. (Plate XVII. 



figs. 1 & 3.) 



Description. — Carapace much flattened, antero-lateral margins 

 arcuated and denticulate, extending laterally slightly more than 

 an orbit's breadth beyond the external oi-bital angle. No definite 

 epibranchial tooth, but the end of the post-frontal crest forming 

 a distinct corner at that point. Regions and sutures on carapace 

 ill-defined, postero-laterally a few inconspicuous granular lidges. 

 Front rather deflexed, less than one-third the width of the cara- 

 pace, and with its anterior margin sinuated. Post-frontal crest 

 prominent, slightly arcuated, but sinuated laterally, extending 

 to margins ; branches of mesogasti'ic groove straight. Orbits, 

 eyes, and peduncles small. External orbital angle existing as a 

 short blunt spine. Ischium of external maxillipeds not showing 

 longitudinal furrow, though this may be faintly indicated in the 

 oldest specimens. Anterior portion of the sternum hairy in the 

 female, not hairy in the male. Chelipeds in both sexes subequal ; 

 merus trigonous, with a series of granules, and distally a stout 

 spine, on the anterior margin ; carpus with a prominent spine on 

 the inner margin and a slight process just behind it. Fingers 

 distally hollowed out, spoon-shape and meeting closely in a sharp 

 cutting-edge (Plate XVII. fig. 3) ; dactylus usually slightly 

 longer than the pollex. Teeth fairly uniform, of moderate size, 

 but the fingers of the larger chela gape a little and have proximally 

 a few larger flat crushing-teeth. Ambulatory legs of moderate 

 length, little compressed. Colour in life a uniform dull greenish 

 brown ; the dactyli of the chelipeds in the males usually black. 



