268 DR. W. A. CUNNINGTON ON THE BRAOHYUROUS [Mar. 5, 



alteration. In the restatement which follows, the subgenera are 

 omitted, as they are not aifected, and care has been taken to 

 retain the oi'iginal form as far as possible. 



tSubfamily Potabionin.^. 



e. Ocular ijeduncles large, not tapering towards distal extremity. 

 f. A stout triangular process descends from the external 



angle of the front Platythelphusa. 



f . No process descending from the external angle of the 

 front. 



g. Front not armed with sjiines or spiuules Potamon^. 



g'. Front armed with spiuules Hydrothelphusa. 



e'. Ocular peduncles small, tapering towards distal extremity. Eeimetopus. 



Since there are now three species included in the genus Flaty- 

 theljjJitisa, it may be well to furnish a ke}^ to them, although they 

 are much more distinct and well defined than is the case with 

 many species of Potcmionautes. 



Key to the Species of Platythelphusa. 



a. Carapace extending laterally more than an orbit's breadth beyond 

 the external orbital angle ; front less than one-third width of 



carapace armata. 



a'. Carapace extending laterally less than an orbit's breadth beyond 



the external orbital angle ; front more than one-third width of 



carapace. 



b. Carapace moderatelj^ convex; carpus of cheliped without spines 



on outer margin ; ambulatory legs of moderate length, anterior 



margin of the merus without spines maculata. 



b'. Carapace exti-emely flattened ; carpus of cheliped bearing spines 

 on outer margin ; ambulator3' legs long, anterior margin 

 of the merus produced distallj^ into two spines conctiJcata . 



Platythelphusa armata A. Milne-Edwards. (Text-figure 84.) 



Platythelphusa armata A. Milne-Edwards, Ann. Sci. Nat., 

 Zool. 7' ser., iv. (1887) p. 147. 



Platytelphusa armata Hilgendorf, Deutsch-Ost-Afrika, Bd. iv. 

 Lief. ix. (1898) p. 22. 



Platythelpjhusa armata Moore, ' The Tanganyika Problem ' 

 (London, 1903), p. 286. 



Platythelphusa armata Rathbun, Nouv. Arch. Mus. Hist. Nat. 

 Paris, 4'= ser., vii. (1905) p. 269. 



Desa^iptioti. — Carapace moderately convex, extending laterally 

 more than an orbit's breadth beyond the external orbital angle. 

 The antero- lateral margins differ little in length from the postero- 

 lateral, with which they are almost directly continuous. Number 

 of spines on antero-lateral margin extremely variable, usually 

 four or five, in addition to the spine at the external orbital angle. 

 Regions and sutures fairly well marked. The postero-lateral 

 regions exhibit a series of small slightly oblique granular ridges. 



