266 DR. W. A. CUNNIKGTON ON THE BRACHYUROUS [Mar. 5, 



Occurrence. — Kasakalawe and Kituta Bay, both south end ot" 

 Tanganyika. Several specimens ; some females probably full- 

 grown, but the largest male apparently not so. The Crabs were 

 taken under boulders about high-water level. 



POTAMON (POTAMONAUTES) Sp. 



Under this heading, I place a single rather small male belonging 

 to the British Museum (Reg. No. 89.2.8.1), of which the only 

 particulars are : " Lake Tanganyika, E. 0, Hore (ex coll.)." This 

 specimen agrees with and differs from its near allies in very much 

 the same way as the unnamed forms from Nyasa, which are 

 dealt with above. Thus it finds its place near to the latter, with 

 which it agrees in showing only a single transverse furi-ow on the 

 sternum in front of the abdomen, although a male. It disagrees 

 with the Nyasa form, however, in being less inflated and in 

 showing the sculpturing more distinctly. Further, the antero- 

 lateral margins are more finely perlated, and the spine on the 

 merus of the chelipeds is longer and sharper. In this case also 

 the specimen differs little from several species, and appears to 

 have no satisfactory distinguishing characters of its own, so that 

 I again take the course least open to objection and leave it 

 nnnamed. 



Genus Platythelphusa A. Milne-Edwards. 



Platythelplmsa A. Milne-Edwards, Ann. Sci. Nat., Zool. 7^ ser., 

 t. iv. (1887) p. 146. 



Platytelphusa Hilgendorf, Deutsch-Ost-Afrika, Bd. iv. Lief. ix. 

 (1898) p. 21. 



Limnothelphusa Cunnington, Proc. Zool. Soc. 1899, p. 698. 



Limnotheljjhusa and Platythelphusa Moore, ' The Tanganyika 

 Problem' (London, 1903), pp. 280, 286. 



Platythelphusa and Limnothelphusa Rathbun, Nouv. Arch. 

 Mus. Hist. Nat. Paris, 4^ ser. vii. (1905) pp. 268, 269. 



There are a number of reasons which have led me to offer here 

 a new description of this genus established by A . Milne-Edwards in 

 1887. As I have stated elsewhere *, the account given of the type 

 species, P. armata, and particularly the figures of it, leave a good 

 deal to be desired. Miss Rathbun reproduces a photograph of 

 this same individual, and adds something to the description; but, 

 as a result of the Second and Third Tanganyika Expeditions, we 



very incomplete though it is, that his specimen should come into the group c, in 

 which the carapace extends laterallj' less than an orbit's breadth beyond the external 

 orbital ano-le. "While it may perhaps be doubted whether the distinction given 

 above under j and j' is of much weight, it will be evident that if the species 

 mroqoroensis were withdrawn from its false position, the new form platynotus 

 would then be distinguishable from amhigmis by the difference of the external 

 maxillipeds. It is not necessary to discuss here the position which mrogoroensis 

 should really occupy, the simpler course is taken of merely incorporating the new 

 species in the existing key. 



* Proc. Zool. Soc. 1899, p. 701. 



