THE TANGANYIKA PROBLEM. 135 



Polypteridae, Lepidosirenidae, Characinidae, Cyprinidae, 

 Siluridae, Cyprinodontidae, Serranidae, Cichlidae and Masta- 

 cembelidae. Of these, the species occurring in Tanganyika 

 which represent the Polypteridae, Lepidosirenidae, Characi- 

 nidae and the Siluridae, are widely spread throughout the 

 fresh- waters of the African continent. But all the seven 

 species of the Cyprinidae, and the six species of Masca- 

 cembelidae, which occur in Tanganyika, are endemic forms. 

 The single species representing the Cyprinodontidae and 

 the Serranidae are the same, while among the 21 genera 

 and the 58 species of the Cichlidae, only one species, 

 Tilapia Burtoni, is found outside the confines of Tangan- 

 yika, this single species having made its way up the 

 Russisi river into Lake Kivu. It is, however, only among 

 the Cichilidae that endemic P'enera occur. 



The Cichlidae are found in the fresh-waters of the Old 

 and the New World, especially in the rivers of South 

 America, and we are further confronted by the extraordinary 

 fact that nearly half of the Old World species are confined 

 to the limits of Tanganyika itself, a circumstance which, 

 on the face of it, would almost at once suggest that in 

 Tanganyika we have the remains of the ancient point of 

 origin from the sea of this particular group of fishes. 

 Such a conception of the mode of origin of the Tanganyika 

 fish-fauna would fit in admirably with a number of other 

 facts relating to it. Thus, it was shown by Dr. Giinther 

 that the fish of the African fresh waters are related to each 

 other in such a manner as to suggest that they have spread 

 out from a centre to which Tanganyika would correspond ; 

 while more recently Mr. Boulenger, as the result of an 

 examination of the fishes which I obtained during the 

 Tanganyika expeditions, has confirmed this view, and 

 shown that the morphological attributes of the Tanganyika 



