336 
THE TANGANYIKA PROBLEM. 
series which bore the slightest resemblance to any of the 
halolimnic forms. 
Finally, Tausch, by the extensive comparisons which he 
made, has unconsciously shown that the single original com- 
parison between Pyrgulifera and Paramelania is itself radi- 
cally untenable. He found that some forms of the so-called 
Pyrgulifera were more or less indistinguishable from the 
genus Alelanopsis, and, as he expressly states, he could 
arrange an insensibly graduated series of shells stretching 
from the typical Pyrgulifera , on the one hand, to the 
typical Alelanopsis on the other. The shell varieties of 
Pyrgulifera are thus indistinguishable from the shell 
varieties of Alelanopsis. But the animal Alelanopsis bears 
no sort of relationship whatever to the animal Paramelania , 
and this is a fact of which Tausch was not aware. 
The idea that the halolimnic fauna is the remnant of a 
cretaceous fresh- water stock is thus seen to be based on a 
single and also on an erroneous comparison, and it is con- 
sequently absolutely incapable of further development in 
any way. 
We find, then, that all the hypotheses which we have as 
yet considered, and which from time to time have been 
advanced to account for the presence and character of the 
halolimnic group — namely, the direct metamorphosis of a 
normal fresh-water stock, convergence of certain members of 
a fresh-water stock, special creation and hetrogenesis, 
operating among a fresh-water stock, and finally the per- 
sistence of an extinct fresh-water stock, although they may 
be all quite intelligible, and even possible, in other cases, 
are each quite inapplicable to the actual facts of the special 
problem presented by the presence of the halolimnic group 
in Tanganyika as it now exists. Without invoking special 
creation and hetrogenesis, we cannot explain the exist- 
