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 eu 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 the 
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 in 
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 
