14 



THE TANGANYIKA PROBLEM. 



number of genera which are common to them both, and also 

 a number of genera which are peculiar to each. In the second 

 place, we find that the genera which are common to both 

 fresh-water areas are those which have been recorded in 

 innumerable places throughout the world. We should find 



TABLE I. 



Molluscan fauna of the Victoria Nyanza. 



Molluscan fauna of the fresh-waters of 

 Celebes. 



Comparison of the genera constituting the molluscan fauna of the Victoria Nyanza in 

 Central Africa and of the fresh-waters of the Island of Celebes. 



them in American fresh-waters, in the lakes of Polynesia, 

 and even in the pools and puddles of Japan. They are, in 

 fact, almost if not quite universal in their distribution 

 throughout the more permanent fresh-waters of the globe. 

 We have, then, in the two particular examples of fresh- water 

 faunas that have been chosen, two distinct types of animal 



