FAUNA OF THE AFRICAN LAKES. 557 



Avhile two species belong to a widely rlistributerl and common 

 fre.sh-watei' genus (Potamonautes), the remaining three, though 

 njembers of the typical fresh-water group (Potamonidje), con- 

 stitute a remarkable genus, which occurs only in Tanganyika. 

 All the forms from the other lakes under review belong to well- 

 known genera of the same family. No Brachy<n-ans have as yet 

 been reported from Albert Nyanza. 



Table of Distribution of Brachi/ii.raf. 



T>T c a ■ „ Tangan- Victoria ^r Edward t^- Othpi- 'mrte nf 



Family Potamonid^. 

 Potauioii (Potamonautes) 



infliitus ... P ... ... Natal. 



„ ,, orbitospinus ... ... E 



„ „ platynotus.. E 



„ sp.? ... P 



„ sp.? P 



Potamon (Geotlielplmsa) 



berardi . ... ... p Egypt, Abyssinia. 



" ,. " em'iii ^ • ••• -P ... P P E.Africa, Abyssinia. 



Potamon (Acanthothelphusa) 



■niloticus r. - T^ ^ ■■• Egypt, Abyssinia. 



Platytlielphusa armata Gen. E 



,, maculata ... E 



conculcata ... E 



4 genera and subgenera... IE, IP. 2 P. IP. i p. i p. 



11 species 4E, IP. 2 P. 1 E, 2 P. IP. 2 P. 



The table of distribution makes it clear that while each of the 

 lakes in the list exhil^its one or more representatives of the very 

 well-known genus Potamon with its sub-genera, these types are 

 associated in Tanganyika with three species of an interesting- 

 endemic genus. Both Nyasa and Tanganyika possess species of 

 Potamonautes which are peculiar to themselves, but it is in 

 Tanganyika alone among the big lakes that an endemic genus is 

 found. All the species enumerated appear to be confined to the 

 continent of Africa. 



Apart from the case of Tanganyika, it will be noted th.at (with, 

 the exception of Potamon {Potamonautes) orbitospimts from 

 Nyasa), the forms from the different lakes are by no means con- 

 fined to them, and indeed are often of wide distribution. This 

 whole series of types — types such as are known from all the 

 tropical fresh- waters of the Old World — may be considered as 

 the normal African group, and calls for little further remai'k. 

 In the paper already cited (70, p. 263) the present writer 

 expressed a conviction that the number of African species has 

 been unduly multiplied, and the imnamed foi-ms included in the 



t For further details concerning most of tbese forms, consult the Report on the 

 Brachyurous Crustacea of the Third Tanganyika Expedition (70). 



