35 ° 
THE TANGANYIKA PROBLEM. 
it has been found by comparison that it is practically 
indistinguishable from the inferior Oolitic fossil known 
as Cerithium siibscalariforme. The above examples of 
the existence of a minute similarity between the shells of 
the halolimnic group and those of the Oolitic seas are 
sufficiently striking, but it should still further be pointed 
out that even the genus Ty phobia, of Tanganyika, is matched 
Chytra kirkii , upper, compared with a marine Jurassic onus/ ns, lower. 
by an Oolitic fossil genus Purpuroidia , from which it is 
very difficult, if not impossible, on conchological grounds, 
to distinguish it. From these comparisons it will be seen 
that we have numerous genera of gastropods belonging to 
the halolimnic series of Tanganyika, which are concho- 
logically indistinguishable from an equal number character- 
istic of the Oolite seas, and it will certainly be admitted 
that in this method of stating the fact we do not, in reality, 
do justice to the comparison at all, for it is unquestionably a 
