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THE TANGANYIKA PROBLEM. 
ganyika, and in the concluding summaries, attention has 
been expressly drawn to the fact, that it appears probable 
that the African ganoids, and certain other portions of the 
Tanganyika fish-fauna are in reality the now more or less 
scattered piscine portion of the halolimnic fauna. And in 
this connection I have emphasised the very remarkable 
fact that, notwithstanding the opportunities which always 
exist for fishes to migrate throughout the fresh waters of a 
continent, actually about half the species of Cichilidte 
belonging to the Old World are restricted to the confines of 
Lake Tanganyika even down to the present day. In the 
succeeding chapters the Tanganyika problem has been 
considered in the light of all the evidence which is now 
available. It has been shown in the first place that the 
halolimnic fauna cannot now be regarded in any other light 
than as something wholly distinct in origin from the general 
fresh-water fauna of Africa, and that it is also equally 
impossible to regard it as anything but the relic of some 
ancient sea. In conclusion, the possible mode of origin of 
this marine fauna has been considered together with the 
value and the significance of the remarkable correspondence 
which subsists between the shells of the halolimnic gastro- 
pods and the remains of those found in the deposits of the 
old Jurassic seas. 
