Connection of Lake Tanganyika with the Sea. 457 



K 



Fig. 3. — Semidiagrammatic representation of the reproductive appai'atus in the 

 female of the so-called Lithoglyplius rufqfilosus. OY, Female genital gland. 

 FA, Opening of oviduct. GrR, Genital groove. K, Opening of brood pouch. 

 S, Ova contained in brood pouch. (E, Oesophagus. 



halolimnic fauna of Lake Tanganyika is entirely supported both by 

 the facts of distribution and by those of the morphology of the 

 individual halolimnic forms. Like the medusa, the halolimnic 

 gasteropods combine the characters of several modern marine types, 

 and so tliey cannot by any possibility be regarded as the forerunners 

 of the modern fresh- water stocks.* Consequently, the only way in 

 which their existence in Tanganyika can be accounted for is through 

 the supposition that this region was, as Thomson supposed, at some 

 time in open connexion either on the east, west, or north, with a deep 

 arm of the sea. 



Such a conception is, however, in the most uncompromising 

 conflict with the views respecting the permanence of the African 

 terrestrial conditions which, were advanced by Sir Roderic Murchison 

 in 185 2, f and which have been more recently and so ably advocated 

 by Dr. Gregory in 1896. J Nevertheless, the theory of the marine 



* It is certain from their anatomical characters that some of the halolimnic 

 molluscs (the Typhobias) originated from marine ancestors later than Cretaceous 

 times, for they possess the characters of genera such as S trombus and Pteroceras, 

 i.e., genera that are Post-cretaceous and marine. Of the latter of these genera 

 M. Fischer indeed remarks : " L'existence de ce genre a l'etat fossile parait 

 douteuse " (' Manuel de Conch vliologie et Paleontologie Conchy liologique,' 

 p. 671). 



f 'Roy. G-eogr. Soc. Journ.,' vol. 24, 1864, pp. clxxv — clxxviii. 



+ In his work, ' The Great Rift Valley,' p. 214, G-regory restates the geological 

 position as follows : — " That part of Murchison's theory, which affirms that Central 

 Africa has never been below the level of the sea, is still in harmony with the 

 known facts, for no deposits of marine origin have as yet been found in the 

 interior." 



