2i8 THE TANGANYIKA PROBLEM. 



and as their identification is sufficiently easy, it is un- 

 necessary to enter here into a description of their 

 specific representatives. It only remains to remark that, 

 as is generally the case with the great African lakes, 

 the normal fresh water molluscs found in Tanganyika 

 are in a specific sense distinct from the representa- 

 tives of the same genera occurring in the neigh- 

 bouring lakes. But besides these well-known forms, the 

 lake also contains no fewer than 14 individual gastro- 

 podean types which, when judged by their conch ological 

 characters, have appeared to be generically distinct. Thus 

 we find already in the literature the names Typhobia, 

 Bathanalia, Limnotroc/ms, Ckytra, Paramelania, BytJw- 

 ceras, Tanganyicia, Spekia, Nassopsis, Syrnolopsis, Stan- 

 leya, and Neothmima, while there is no doubt that the 

 unique form, Alelania admiradz/ts (Fig. 1) should be 

 added to this list, for it is not only peculiar to the lake but 

 conchologically indistinguishable from the form known as 

 Cerithium subscalarifornte, which occurs as a fossil in some 

 of the marine Jurassic beds. In dealing with the molluscan 

 section of the fauna of Lake Tanganyika we are thus 

 confronted with a unique assemblage of molluscan forms 

 all the members of which, so far as is at present known, 

 are wholly restricted to the confines of the lake. Our 

 first knowledge of the existence of this singular group 

 in the lake dates back in its origin to some of the 

 earliest explorations in the African interior. It was, 

 in fact, Speke, during Burton's celebrated expedition to 

 Tanganyika, who originally picked up the shells of some of 

 the above types on the beach, and two of these particular 

 specimens, after finding their way into the British Museum, 

 were described by S. P. Woodward * under the titles of 



* S. P. Woodward, " Proceedings of the Zoological Society," 1857. 



