334 THE TANGANYIKA PROBLEM. 



halolimnic fauna owes its origin to convergence seems, if 

 possible, more hopelessly untenable than the idea that it 

 has been directly metamorphosed out of an ordinary fresh- 

 water fauna, with which conception, of course, it is very 

 analogous. 



We are thus inexorably driven, by the evidence, to the 

 conclusion that the halolimnic fauna is not only an assem- 

 blage of organisms which is distinct en masse from the 

 normal fresh-water fauna of the great African lakes, but 

 also that this group is distinct in origin from these. 



Can it, however, be viewed as not so much a relic fauna 

 of the ocean, but as a persistent remnant of a type of fresh- 

 water fauna which belonged to a departed era, and was 

 once widespread over the African, and possibly other 

 continental, land-masses ? 



This is a view which, at first sight, may appear to have 

 some semblance of support. Thus it is known that, in f.he 

 upper cretaceous fresh-water beds of Southern Europe and 

 North America, there occur the remains of fresh-water 

 faunas containing shells, which are not like those occurring 

 generally in the fresh waters of to-day. And it was pointed 

 out by the geologist White in America, and Tausch iri 

 Europe, that there occurs among these beds the very 

 variable genus Pyrgulifera, some of the polymorphs of 

 which appear to correspond with Smith's not too repre- 

 sentative figure of the original Paramelania of Tanganyika. 



From this very flimsy ground, Dr. Gregory advanced the 

 view that the whole halolimnic fauna of Tanganyika might 

 correspond to these cretaceous fresh-water stocks, and that 

 it was a remnant of them. However, to give any semblance 

 of probability to this view, two things are necessary. It 

 must be shown that the fresh-water fauna of the type 

 occurring in the upper cretaceous beds of Southern Europe 



