THE FAUNA OF THE GREAT AFRICAN LAKES. 641 



thus they are probably no older than the time of the separa- 

 tion of the species of Molluscs from one another, which now 

 possess their characters separately. 



On the whole then, the members of the Tanganyika 

 Molluscan group, which I have as yet examined, appear to 

 possess characters combining those of several living marine 

 genera, and thus the evidence as to their origin, which can 

 be deduced from the anatomy and characters of these 

 animals themselves, favours the view which I formed while 

 still on the shores of the lake, namely, that these forms have 

 survived as the representatives of an old contamination of 

 Lake Tanganyika with the sea, and this view is, as we have 

 seen, not negatived nor in reality, I believe, seriously con- 

 troverted by any of the objections which have hitherto 

 been raised against it. 



J. E. S. Moore. 



