OP THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 335 



Part III. — Conclusions. 



1. The zoological aspect. 



2. The palaeontological evidence. 



3. The argument from geology. 



To a certain extent the probable conclusions have already 

 been indicated in Parts I and II of this communication, but a 

 brief summary at the final stage may be of use. On the whole 

 we have three main factors to guide us in the investigation, 

 and these we will take in the order above indicated. 



The zoological aspect of the question. — This is mainly studied 

 by means of conchological comparison, and it will be seen on 

 referring to Part I, and more particularly to the Appendix, 

 that, in my opinion, the resemblance between the Tanganyika 

 shells and those of our British Inferior Oolite is not suthciently 

 close to warrant any theory as to the derivation of the former 

 from the latter. But, on the other hand, there is the malaco- 

 logical evidence derived from the study of the anatomy of the 

 existing mollusc, which reveals a peculiar archaic character, 

 and also a singular blending of attributes usually held to be 

 distinct. Such peculiarities, whilst pointing to the exceptional 

 character of this assemblage of gasteropods, fail altogether to 

 establish any connection with the Inferior Oolite of the Anglo- 

 Xorman basin. Yet the very existence of a group of halo- 

 limnic gasteropods limited to Tanganyika, is in itself a proof 

 that there is something remarkable about these molluscs, and 

 such a view is further conlirmed by anatomical investigation. 

 Hence these gasteropods may, in some way, have had a remote 

 marine origin, although that need not have been Jurassic. 



It has always seemed to me that the most hopeful line of 

 research is to be sought in the waters of the Congo basin, and 

 particularly in Lakes Bangweolo and !Mwero. If the halolimnic 

 gasteropods had their origin in the vast inland seas of this 

 immense system, as they existed formerly, there should be 

 some trace of tlieni in the lakes of the Upper Congo, This, 

 Mr. Moore informs us, is unfortunately not the case, although 

 in Lake Mwero a genus closely approaching the Neothauma of 

 Lake Tanganyika has been found. I am rather inclined to 

 consider that the zoological evidence points to a local and 

 restricted origin for these Tanganyika sliells, and if we accept 

 the theory of their special marine derivation, whether Jurassic 

 or more recent, it must always be with a certain degree of 

 doubt. 



The 2^(^il<^ontologiccd evidence. — Since the hypothesis of a 



