1901.] 01" THE GREAT AEEICAN LAKES. 469; 



espedition crossed the Man Plateau and again descended into the 

 lesser and more eastern series of faulted valleys in which Lakes 

 Baringo, Naivasha, Itudolf, and several minor pools and marshes 

 occur. The fauna of Lake Baringo had already been examined by 

 Dr. Gregory, and the molluscan fauna in this and the minor lakes 

 which occur in the same district are similar in kind to those which 

 are to be found in the Victoria ]^fyanza itself. So also with respect 

 to the larger lakes Stephanie and EudolF, which lie to the nortli, 

 we have now the evidence of various exploi'ers which makes it 

 quite certain that nothing of the nature of the remarkable halo- 

 limnic Gasteropods occurs in either of them. 



To sum up, all the evidence which has recently been collected 

 with respect to the following lakes — Shirwa, Nyasa, Eukwa, Ban- 

 gweolo, Moero, Tanganyika, Kivu, the Albert Edward Nyanza, the 

 Albert Nyanza, the Victoria JSTyanza, Lake Baringo, and Lake 

 Kudolf — declares in the most emphatic manner that the halolimnic 

 Gasteropods, and, indeed, the whole halolimnic fauna, is found no- 

 where beyond the confines of Lake Tanganyika itself, nor have the 

 prolonged and tedious examinations which I have made among the 

 numerous old lake-deposits, like those which occur at a considerable 

 elevation north and west of IS^yasa, all about Lake Kivu, on the 

 plains between Kivu and the Allaert Edward J^yanza, in the Semliki 

 Valley, and in the neighbourhood of the Albert Nyanza, revealed 

 any traces whatever of the past existence of these forms. On the 

 other hand, a very superficial examination of the old lake-beds 

 which have bean at one time part of Tanganyika itself, like those 

 ■\\ hich occur near the outlet of the lake, at Masswa on the west coast 

 and beyond its northern extremities, is all that is needed to 

 demonstrate theformer presenceof theseforms in abundance in such 

 districts. I think therefore that I am now justified in putting it 

 forward as a demonstrated conclusion, that the halolimnic fauna 

 neither is, nor ever has bsen, present in nuy of the districts sur- 

 rounding the numerous and widely separated lakes which I have 

 just named. The recently accumulated facts regarding the dis- 

 tribution of the African freshwater mollusca show that there is in 

 the lakes which now exist, and has been in those lakes and rivers 

 which have long since vanished, a fauna similar to that which now 

 generally survives ; and thus the evidence which the facts of 

 distribution reveal is iu no way opposed to the view that the 

 halolimnic fauna is something exotic which has been added to 

 the ordinary freshwater fauna iu the case of Tanganyika. It 

 offers no support Avhatever to the view that the halolimnic fauna 

 is the relic of an old freshwater stock. On the other hand, the 

 facts directly militate against this view, with the cumulative force 

 of negative ap])earauces. They are in no way opposed to our accept- 

 ance of the clue which is afforded as to the nature and origin of 

 the halolimnic fauna by the similarity of the halolimnic shells; 

 to those which occur in the Jurassic Seas. On the other haud^ 

 they are exactly in accord with such a view. 



