546 



DR. W. A. CUNNINGTON ON THE 



Of tlie smaller lakes, Albert Nyanza has 4 endemics out of a total 

 of 13, Edward Nyanza 1 out of 10, while Kivu only contains two 

 species, neither of which is endemic. In other words, more than 

 90 percent, of the forms in Tanganyika are only known from that 

 lake, while Victoria Nyanza has 39 per cent, of endemic species 

 and Nyasa some 41 per cent. 



In the next place it must be emphasised once more that the 

 greater number of the endemic species of Tanganyika are types 

 which have been described as thalassoid — 58 out of 76 belonging 

 to that category. Thus there are more than three times as many 

 thalassoid as non-thalassoid endemic species, actually some 76 per 

 cent, having this characteristic appearance. Even when the non- 

 endemic forms are added to swell the total, the shells having this 

 marine aspect outnumber the normal series by more than two to 

 one, there being respectively 58 and 26 species. 



The figures which refer to the genera are even more arresting 

 than those which have been dealt with. Tanganyika alone con- 

 tains one or more representatives of each of the 35 genera named 

 in the table. The number of genera represented in Lake Victoria 

 sinks to 11, but it is significant that this is due to the absence 

 from that lake of the large total of 24 genera which are peculiar 

 to Tanganyika. Of this total of 24, 23 are regarded as thalassoid, 

 the single exception being the genus Neothauma, as already 

 mentioned. Apart from these endemic genera, both Tanganyika 

 and Victoria contain species belonging to the same 11 genera — 

 those of the "normal African fresh-water fauna" to adopt 

 Moore's term. It is interesting to observe that while 28 species 

 of these less specialised genera (including 11 endemics) occur in 

 Victoria Nyanza, 25 (including 17 endemics) are found in Tan- 

 ganyika. Lake Nyasa with 9 of these ordinary fresh-water 

 genera comes next, and the other lakes follow with still smaller 

 numbers. No endemic genera are to be observed outside Tangan- 

 yika. It is thus clear that over and above the representatives of 

 certain well-known fresh-water genera, thei-e is, in Tanganyika, 

 a whole series of unique Gasteropods which are not represented 

 elsewhere. 



It may not be unprofitable to institute a comparison with the 

 group of the fishes, in which alone so large a number of endemic 

 genera is known. Tanganyika contains 25 endemic genera of 

 fishes, as compared with 24 endemic genera of Gasteropods, but 

 whereas with the fishes there are in addition 29 non-endemic 

 genera represented, there are only 11 non- endemic genera of 

 Gasteropods. Again, among the fishes there are a few endemic 

 genera found in the remaining lakes, while this is not the case 

 with the Gasteropods. The comparison serves to show that while 

 the actual numbers both of genera and species are less in the 

 group now under discussion than in that of the fishes, it affords 

 quite as conspicuous an instance of the peculiar characters of the 

 Tanganyika fauna. 



The table of distribution already furnished now calls for more 



