FAUXA 01*' THE AFRIJAX LAKKS. 533 



latter lake 21 peculiar- genera occur, as compared with 2 in 

 Lake Victoria, 5 iu N\'asa, and a single genus in Lake Edward. 

 As concerns Tanganyika, the cas3 may be stated even more 

 forcibl}^ by pointing out that 41 genera in all are recognised 

 from the wliole continent, of which 21 belong exclusively to this 

 lake: in other words more than ha,lf the genera of Cichlidfe 

 known in Africa are confined within the limits of Tanganyika. 



It may be worth while to give a few more comparative figures 

 in the case of the three bigger lakes around which interest 

 principally centres. Li Nyasa 38 Cicldid fislies are found out 

 •of a total iish fauna of 63, which is 60 per cent, of the whole ; 

 in Victoria Nyanza 47 out of 86, wliich is some 54 per cent. ; in 

 Tangan3'ika 89 out of 146, or nearly 61 per cent, of the total. 

 Witli this remarkable total of 89 Cichlid fishes, Tanganyika, in 

 fact, estaHishes nnother record, possessing the richest Cichlid 

 fauna in the world. Next note how extremely large a proportion 

 of the endemic species ai-e Cicblidje. In Nyasa there occur 31 

 endemic Cichlid species out of a. total of 43 endemic species in 

 the lake, i. e. 72 per cent. ; in Victoria Nyanza 40 out of 60, or 

 ■66 per cent. ; in Tanganyika 84 out of 121, or 69 per cent. The 

 proportion of endemic genera belonging to this family is even 

 more extraordinary, for all the. genei-a which are endemic in 

 JSTyasa and in Lake Victoria are Cichlidte (the same is true of 

 the single endemic genus found in Edward Nyanza), and in 

 Tanganyika there are 21 out of 26 endemic genera, or 80 per 

 cent. Lastly, the number of endemic Cichlid forms as compared 

 with the total number of Cichlid forms known from the lakes in 

 question is a basis for further striking figures. Thus in Nyasa, 

 out of 38 species of Cichlidse, 31 are endemic, or 81 per cent.; in 

 Victoria Nyanza, out of 47 species, 40 are endemic, or 85 per 

 cent. ; in Tanganyika, out of 89 species, 84 are endemic, or over 

 94 per cent. 



From a consideration of all these figures it becomes very plain 

 that the large number of unique forms characteristic of Tan- 

 ganyika is especially due to a great development of the fishes of 

 this group, and that the same is true, though in lesser degree, for 

 iSr3'asa and Victoria Nyanza. 



The review of so largely represented a family must of necessity 

 be brief. The very characteristic genus Tilapia extends to 

 40 species in the list, but though some are peculiar to certain 

 lakes, there are no very striking features of distribution to be 

 noted. The genus Petrochromis appears to be mainly typical 

 of Tanganyika, for though an endemic form occurs in Nyasa and 

 there is a doubtful record from Lake Albert, it is not found in 

 Victoria N3fa,nza or any of the other lakes considered. The case 

 of Ha2)lochroinis is interesting as being, on the contrary, a genus 

 with a single widely distributed species recorded from Tan- 

 ganyika, Avhile it is better represented in all the other lakes 

 under review. Perhaps a more important — though unexpected — 

 feature is the existence of H. angustifrons and H. graueri in both 



