142 
THE TANGANYIKA PROBLEM. 
are nevertheless highly remarkable from the fact that they 
are only found in Lake Tanganyika among the fresh 
waters of the African interior. To this category of 
animals belong the prawns, some crabs, the sponges, 
some protozoa, and a host of Cichlid fishes. Fishes of 
course are highly migratory forms, and, once established 
in fresh water, are sure to spread to a large extent 
through the rivers and lakes of the continental land-mass 
in which they happen to be ; still there is this peculiarity 
about the fishes which are at the present time en- 
countered in Tanganyika ; some of the cichlids, as Mr. 
Boulenger has shown, are primitive representatives of 
the group ; while, in Tanganyika, but not in Nyassa and 
the lakes to the south, there exists the ancient ganoid 
Polypterus, and several characinid fishes which although 
not restricted to Tanganyika, do nevertheless share the 
somewhat primitive characters which the other halolimnic 
animals undoubtedly possess. On account of this, I am 
inclined for the present to regard the African Polypteroids 
and at any rate the genera of Cichlidse peculiar to 
Tanganyika, as a piscine portion of the halolimnic group. 
The reasons for the incorporation of these fishes which 
are not wholly restricted to Tanganyika is again discussed 
further on, and, as thus defined, the halolimnic fauna 
of Tanganyika contains the following forms : — among the 
Teleostei fourteen genera of Cichlkke, Polypterus among 
the ganoids, seventeen genera of gastropods, possibly two 
Lainellibranchs, two crabs, two prawns, one gymnolaematus 
polyzoan, one medusa and some endemic protozoa. All 
these forms, with the exception of Polypterus, which is ob- 
viously an animal capable of migration, are the peculiar and 
characteristic feature of Lake Tanganyika, and it will be 
admitted that if the invertebrates of this halolimnic fauna 
