598 DR. W. A. CUNNINGTON ON THE 



deal in the first instance with Moore's hypothesis tliat Tanganyika 

 represents an ohl Jurassic sea. This view, first put forward iu 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 liave 

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

 as from the zoological side, more information is available tha.n 

 when this hypothesis was propounded, and it may a,t once be 

 said that recent discoveries do not favour the theory. As the 

 zoological evidence has been exa.mined and discussed in the body 

 of this pa,per, 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 tlie lake at the presei:it day — coupled with his 

 deductions as to the ana,tomy and relationships of the latter forms. 

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

 leading expei'ts, 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 subsequently declared that he attached 

 no great weight to this comparison (138, p. 602). he still adhered 

 to his view tha,t the so-called halolimnic animals were truly 

 mai'ine or relict forms. As far as the molluscs axe concerned, the 

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

 rega.rds the halolimnic Gasteropods as emphatically fresh-water 

 types. 



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

 thalassoid Lamellibranchs in Tanganyika? There seems no 

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

 group would also exhibit a thalassoid appearance haxl they been 

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

 a.gainst 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 

 impoi^tant, and admittedly a marine type, has lost most of its 

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

 more widely than was formerly supposed, but the Tanganyika 

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

 The 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 incrusting gymnolaematous 

 Polyzoon Arachnoidea, but recent discoveries have modified its 

 importance. Since the genus is now actually living in Asiatic 

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

 ])ersisting 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 



