598 



DR. W. A. CUNNINGTON ON THE 



(leal in the first instance with Moore's hypothesis that Tang;inyil<a 

 represents an old Jurassic sea. Tliis view, first put forward in a, 

 paper published in 1898 (131), was subsequently developed and 

 the evidence detailed at considerable length in " The Tanganyika 

 Problem," 1903, (137). Being thus a widely known theory, it is 

 only necessary to inquire how it accords with the facts which have 

 since come to light. From the botanical and geological, as well 

 as from the zoological side, more information is available than 

 wlien this hypothesis was pi'opounded, and it may at once be 

 said that recent discoveries do not favour the theor}^ As the 

 zoological evidence has been examined and discussed in the body 

 of this paper, it is only needful to summarise the conclusions. 



Moore's view rests in the main on his comparison of certain 

 marine fossil shells of the Jurassic period, with those of Gastero- 

 pods living in the lake at the present day — coupled with his 

 deductions as to the anatomy and relationships of the latter forms. 

 It has already been explained (p. 549) that, in the opinion of 

 leading experts, neither of these claims can be substantiated. If 

 the comparison with Jurassic fossils is held to be inadmissible, 

 the period of the supposed connection with the ocean remains in 

 doubt, but while Moore subse(iuently declared that he attached 

 no great weight to this comparison (138, p. G02). he still adhered 

 to his view that the so-called halolimnic animals were truly 

 marine or relict forms. As far as the molluscs are concerned, the 

 opinion of Pelseneer is in direct conflict with this view, for he 

 regards the halolimnic Gasteropods as emphatically fresh-water 

 types. 



In this connection it may well be asked — why are there no 

 thalassoid Ln.mellibranchs in Tanganyika ? Thei-e seems no 

 obvious explanation of the fact, yet surely some members of this 

 group would also exhibit a thalassoid appearance had they been 

 relict forms from the ocean. This itself is evidence which tells 

 against the view of a relict origin for the fauna. 



Nor do the other members of Moore's group of halolimnic 

 animals definitely support his contention. The medusa, once so 

 important, and admittedly a marine type, has lost most of its 

 significance. Not only are fresh-water medusae known to occur 

 more widely than was formerly supposed, but the Tanganyika 

 species has been found in the Niger and in Victoria Nyanza. 

 Tlie Decapod Crustacea — prawns and crabs — regarded in " The 

 Tanganyika Problem " as constituents of the halolimnic group, 

 have been shown to belong to typically fresh- water families. 

 Much stress was formerly laid upon the incrnsting gymnolsematous 

 Polyzoon Arachnoidea, but recent discoveries have modified its 

 importance. F^ince the genus is now actually living in Asiatic 

 seas, it can hardly be regarded as an ancient marine type 

 persisting only in Tanganyika, but must rather be looked upon as 

 a recent importation (cf. the analogous case of Victorella, p. 540). 

 Finally the sponges belong to the family Spongillidae, a charac- 

 teristically fresh-water assemblage. Thus, of the succession of 



