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. 
Planorbis. 
Planorbis. 
Limnaea. 
Limnaea. 
Isidora. 
Isidora. 
Physopsis. 
Aucy his. 
Ancy lus. 
Protaneylus. 
Miratesta. 
Ampullaria. 
Ampullaria. 
Lanistes. 
Vivipara. 
Vivipara. 
Cleopatra. 
Bit hy nia. 
(?) 
Melania. 
Melania. 
Unio. 
Spatha. 
Mutela. 
Aetheria. 
Corbieula. 
Batissa. 
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 
