230 FISHES. 



Out of the 39 families or groups of freshwater fishes 

 15 are represented in the African region, t)r three more than 

 in the Indian region ; however of two of them, viz., the Ophio- 

 cephalidce and Mastacembelidce, a few species only have found 

 their way into Africa. On the other hand, the number of 

 species is much less, viz. 255, which is only two-tifths of that of 

 the known Indian species. The small degree of specialisation 

 and localisation is principally due to the greater uniformity of 

 the physical conditions of this continent, and to the almost 

 perfect continuity of the great river systems, wliich take their 

 origin from the lakes in its centre. This is best shown 

 by a comparison of the fauna of the Upper Nile with that 

 of the West African rivers. The number of species known 

 from the Upper Nile amounts to 56, and of these not 

 less than 25 are absolutely identical with West African 

 species. There is an uninterrupted continuity of the fish- 

 fauna from west to the north-east, and the species known to 

 be common to both extremities may be reasonably assumed 

 to inhabit also the great reservou^s of water in the centre of 

 the continent. A greater dissimilarity is noticeable between 

 the west and north-east fauna on the one hand, and that of 

 the Zambezi on the other ; the affinity between them is 

 merely generic ; and all the fishes hitherto collected in Lake 

 Nyassa have proved to be distinct from those of the Nile, and 

 even from those of other parts of the system of the Zambezi. 



Africa, unlike India, does not possess either alpine ranges 

 or outlying archipelagoes, the fresh waters of which would 

 swell the number of its indigenous species ; but at a future 

 time, when its fauna is better known than at ju-esent, it is 

 possible that the great difference in the number of species be- 

 tween this and the Indian regions may be somewhat lessened. 



The most numerously- represented families are the Silur- 

 oids, with 61 species; the Cyprinoids, with 52; the Mormy- 

 ridai, with 51; the Characinidte, with 35; and the Chromides, 



