FAUNA OF THE AFRICAN LAKES. 



557 



while two species belong to a widely flistributed and common 

 fresh-water genus [Potamonautes), the remaining three, though 

 members of the typical fresh-water group (Potamonidiie), 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 Brachyurans have as yet 

 been reported from Albert Nyanza, 



TctUe of Distribution of Bracliipira'\ . 



Niime of Species. 



Tan^an- Victoria »t 

 yika. Nyanza. 



Edward yV. Other parts of 



Nyanza. the world. 



Family Potamonidj*:. 

 Potamon (Potamonautes) 



in flatus 



„ orbitospinus 

 „ „ platynotus.. E 



„ „ sp. ? P 



Potamon (Geothelphusa) 



berardi 



„ „ eraini 



Potamon (Acanthothelphusa) 



" niloticus 



Platythelpbusa armata Gen. E 



maculata ... E 

 „ conculcata ... E 



4 genera and subgenera. .. 1 E, 1 P. 



11 species 4 E, IP. 



2 P. 



IP. 



IP. 



2 P. 1 E, 2 P. IP. 



IP 



Natal. 



Egypt, Abyssinia. 

 E.Africa, Abyssinia. 



Egypt, Abyssinia. 



2P 



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

 lakes in the list exhibits 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 pecuh'ar 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 that (with 

 the exception of Potamon (^Potamonautes) orbitospinus 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-watei"s of the Old World — may be considered as 

 the normal African group, and calls for little further remark. 

 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 unnamed forms included in the 



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

 Brachyurous Crustacea of the Third Tanganyika Expedition (70). 



