402 MB. J. B. B. MOOBB ON THE MOLLUSCS [June 18, 



This second list of molluscs, it will be seen, constitutes a scries 

 which we might and should expect to lind in any of the great lakes 

 ■with which naturalists are acquainted, in any of the tropical and 

 subtropical portions of the earth : and there is not the slightest 

 doubt that the specific forms which now represent these typical 

 freshwater genera of Gasteropods in Tanganyika are very closely 

 similar to the specific forms which represent the same genera, 

 well, let us say, in the lakes and rivers of the American continent. 



On my first expedition to the African interior I spent about 

 two months on Lake Nyasa and about a week on Lake Shirwa, 

 and during this journey I convinced myself that these two 

 southern representatives of the African equatorial freshwaters 

 contained nothing but the foilo.ving gasteropodous forms : — 



Ampullaria. lAmncea. 



Lanistes. Melania. 



l'liysopsis. Vivipara. 



1'lanorbis. Bythinia. 

 Isadora. 



Similar observations bad already been made by several careful 

 observers like Sir John Kirk, Mr. Crawshay, and others. On the 

 second Tanganyika expedition I again visited Lake Nyasa, this 

 time equipped with dredging- and collecting-gear of all sorts, 

 and 1 was consequently able to examine t he deep floor of the lake ; 

 but beyond an occasional Melania, generally dead, I found no life 

 on the vast mud plains which form the floor of the Nyasa Lake, 

 and which in some places are over a thousand feet below the level 

 of the sea. These plains were, so far as living things go, fresh- 

 water deserts. It will thus be seen that the work accomplished 

 in Lake Nyasa during the second Tanganyika expedition certainly 

 extended, but at the same time entirely confirmed, the conclusions 

 at which we had already arrived during the first. 



From a comparison of these lists, it will be seen that, so far 

 as the Gasteropods are concerned, the fauna of Nyasa and 

 Shirwa is represented, and indeed fully repeated, in Tanganyika ; 

 and judging from these observations themselves, and from what we 

 already knew of the freshwater fauna? in Africa, far to the south 

 and far to the north of the zoologically unexplored equatorial 

 regions, I felt justified in believing that the fauna of Nyasa and 

 Shirwa is the typical fauna of the freshwaters of Equatorial 

 Africa, of the whole of Africa for that matter ; and that in Lake 

 Tanganyika this typical African freshwater fauna has had something 

 added to it. At the time, this conclusion was vigorously opposed 

 during several discussions by Professor Gregory 1 , who, arguing 

 from what he believed to be the drift of geological observations 

 made at lhat time in the African interior, declared his conviction 

 that when the other great lakes, such as the Victoria Nyanza, the 

 Albert Nyanza, and Lake Rudolf, were explored, the peculiar 



1 Moore, J. E. S. : Proc. Roy Boo. vol. lxii. j>. 451. 



