342 THE TANGANYIKA PROBLEM. 



continents, arose from a sea which, like the Atlantic, 

 originally occupied a position somewhere between the two. 



The fact that the consideration of the distribution of the 

 fish-fauna of Tanganyika points to this fauna having origi- 

 nated in a sea lying to the west of that lake, is extremely 

 interesting ; for we saw, when dealing with the geology of 

 these districts, that the distribution and character of the 

 aqueous deposits of the region of Tanganyika point to the 

 west as the only direction in which there seems any like- 

 lihood of there having been a former extension of the lake, 

 or a junction between it and a sea covering a part, or the 

 whole, of the unique Congo basin. 



A similar indication is afforded when we study the life 

 now found in the Congo. Thus, it is known, that one 

 of the remarkable sponge of Tanganyika, Potamolepis, 

 inhabits the lower reaches of the river. A certain number 

 of fishes are common to both waters, while the mollusc 

 Paramelania of Tanganyika is extremely similar in its 

 anatomy to the genus Tympanotamus, occurring low down 

 in the Congo, in its fresh-water, and also in the sea on 

 the west coast. 



We have also the fact that far up the Congo in its fresh- 

 water there occur red Algae, corresponding to the red 

 sea-weeds of the ocean. But by far the most interesting 

 fact yet brought to light about the Congo fauna, has resulted 

 from Mr. Boulenger's investigation of the fishes which 

 were collected in different parts of the river by the officials 

 of the Congo Free State. 



It was shown, as a result of this investigation, that the 

 Congo contains fifty-one species of the typical African 

 family, the Mormyridae. The Congo, in fact, repeating 

 with respect to this group the same peculiarities which 

 Tanganyika exhibits with respect to the Cichlidae. By far 



