2 I 8 
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 conchological 
characters, have appeared to be generically distinct. Thus 
we find already in the literature the names Ty phobia, 
Bathanalia , Limnotvochiis , Chytra , Paramelania , Bytho- 
cevas, Tanganyicia, Spekia, Nassopsis , Syrnolopsis , Stan- 
ley a, and Neothauma , while there is no doubt that the 
unique form, Melania admirabilis (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 
Cerit Jiium subscalariforme , 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. I\ Woodward, “ Proceedings of the Zoological Society,” 1857. 
