FAUNA OF THE AFRICAN LAKES. 



541 



in Tanganyika. Quite a different conception now suggests itself, 

 in view of the recent description by Harnier (99, p. 50) of another 

 species belonging to this genus collected by the Siboga Expedition 

 in the Straits of Makassar. No one would have ventured to predict 

 that Moore's genus would be found to have a representative still 

 living in the sea, but the discovery shows that, as in the case of 

 Victorella, tlie Tanganyika species has affinities with a present- 

 day marine type and not problematical affinities with marine 

 Polyzoa of a past era. It may be pointed out that a further 

 instance of Afro-Indian associations is afforded by the finding of 

 this species of Arachnoidea in East Indian seas. 



A piece of negative evidence of some interest, but to which 

 perhaps no great importance need be attached, is the apparent 

 absence of Polyzoa from Lake Nyasa. It is admittedly a fact 

 that these organisms are small and inconspicuous, and little 

 likely to attract the attention of any but skilled naturalists ; 

 moreover, their distribution in the African lakes has in some 

 cases been merely deduced from a discovery of their sessile stato- 

 blasts. On the other hand, Nyasa has received a consideiable 

 amount of attention from a trained observer in the person of 

 Prof. Fiilleborn, and it is certainly strange that (so far as I am 

 aware) he collected no representativ es of this group from that 

 lake. 



Polyzoa are also unknown in Kivu, where Schubotz states he 

 was unable to discover them (156, p. xiv). This is less surprising 

 on account of the unusual salinity of the lake. 



MOLLUSCA. 



It is a task of exceptional difficulty to give an accurate account 

 of the molluscan famia of the big lakes. This is in a large 

 measure due to the work of the late J. R. Bourguignat, who 

 described a very large number of types, a considerable but varying 

 pi'oportion of which have not been accepted by other authorities. 

 Fi'om Tanganyika alone, Bourguignat described no less than 242 

 species *, and to this total must be added a number of species for 

 which other writers are responsible, yet in the opinion of some of 

 the principal specialists the number of different molluscan forms 

 living in that lake is very much smaller than the enormous total 

 which has been credited to it. 



The great interest attaching to certain Tanganyika molluscs 

 owiug to their remarkable marine-like appearance has already 

 been referred to, and on account of this, it is the moie to be 

 regretted that both genera and species have been unduly multi- 

 plied and that a generally accepted list of forms from this lake is 

 not available. In writing a paper such as this, it is necessary to 

 compile a definite list, and in doing so, I have followed more 



* Speaking geiierall}' it may be said that Bourguignat and his school, of which 

 Locard was the principal exponent, elevated species into groups, and varieties into 

 species. 



