35° 



THE TANGANYIKA PROBLEM. 



it has been found by comparison that it is practically- 

 indistinguishable from the inferior Oolitic fossil known 

 as Cerithium sub scalar if or me. 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 Typkobia, of Tanganyika, is matched 



Chytra kirkii, upper, compared with a marine Jurassic onitstus, 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 



