468 MR. J. E. S. MOOBE OK THE MOLLUSCS [Juiie 18, 



blocked again by fi high transverse dam running from east to 

 west, which is formed by the active volcanoes of the Mfumbiro 

 range. On the northern slopes of this range there are to be found 

 in places underlying the modern ashes and lava, which have been 

 piled upon them, old lake-deposits, and in these there are shells 

 specifically identical with those in Lake Kivu. Northward, these 

 old lake-deposits run under and become the floor of the Albert 

 Edward jSTyauza, and in this lake there are to be found among the 

 Mollusca the following gasteropodous forms : — 



Vivi2)ara. 



Mdania. 



Flanorhis. 



Limncea. 



Bytliinia. 



And to these there is here added one small shell which at first 

 sight I took to be a heavily-built Planorbis, but which is in reality 

 a modified Melania. The Albert Edward Nyanza is on the Nile 

 Avatershed, and the outlet of the lake appears as the Semliki river, 

 along the whole course of which there are old lake-deposits, con- 

 taining shells which are specifically identical with those living in the 

 Albert Edward Nyanza. The Semliki river flows into the Albert 

 Nyanza, and in this lake there appear the following gasteropodous. 

 molluscs : — 



Vivipara. 



Melania. 



Flanorhis. 



Limncea. 



Bytliinia. 



The planorbid-looking Melania of the Albert Edward Nyanza 

 is here wanting, but it is probably actually replaced by a keeled 

 melanoid. 



It is thus obvious that from Tanganyika throughout the long 

 series of lakes north of it, as far as the waters of the Upper Nile, 

 there are no traces whatever of the halolimnic fauna. And when 

 we turn from this series of lakes east and traverse the steppes of 

 Uganda to the Victoria Nyanza, we find that this lake also tells 

 the same story, the gasteropodous genera v>'hich have hitherto been 

 recorded in it being the following: — 



Vivvpura. Lanistes. 



Melania. AmpaUana. 



Flanorhis. Ancylus. 



Limtuea. Physojysis. 



Bytliinia. Isodora. 

 Cleopatra. 



Passing to the east of the A^ictoria Nyanza, the Tanganyika 



