OF THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 307 



of this Society, it will be sufficient to relegate this portion of my 

 paper to an appendix, and briefly to state the impressions which 

 a careful examination of both sets of shells, the fossil and the 

 modern, have left upon my mind.* 



As a result of this detailed examination I find on con- 

 chological rn'ounds, that the evidence of an ancestral connection 

 between certain fossils of the Inferior Oolite of the Anglo- 

 Norman basin and the following halolimnic genera, viz., 

 Typhohia, Bathanalia, Limnotrochus, Ghytra, Paramelania, 

 Bythoceras, Tanganyicia, SpcJcia, and Nassopsis, is not nearly 

 so strong as I had anticipated from the inferences already 

 drawn and from what I had read in several publications. There 

 are two Jurassic genera, chiefly developed in the Lower 

 Oolites, viz., Amberleya and Purpurina, which have their 

 conchological analogues in Lake Tanganyika, and in some cases 

 the resemblance is very striking. But this is scarcely sufficient 

 to justify the assumption that the oceanic character of these 

 Tanganyika molluscs will more or less necessitate that the 

 Tanganyika region of to-day must have approximated in 

 character to an arm of the deep and open sea in ancient times,! 

 and the inference is in Jurassic times. Indeed some people, 

 I believe, have gone so far as to describe Tanganyika as an arm 

 of the Jurassic sea. On biological grounds alone this is not at 

 all probable ; because under any circumstances this would 

 have been a different zoological province from that occupied 

 by the Anglo-Norman basin in Jurassic times. 



It is further pointed out in the appendix, that, besides the 

 resemblance between Jurassic and Tanganyikan gasteropods 

 noted by Mr. Moore, there are other cases of what I have 

 regarded as mere mock resemblances ; but in order to appreciate 

 such cases it will be necessary to study the appendix closely, 

 which the majority of the members probably will not be 

 inclined to do. 



On the whole, taking the evidence of the Medusa, and the 

 other semi-marine forms, as well as that of the halolimnic 

 gasteropods themselves, a fairly good p)rimd facie case for the 

 originally marine origin of these exceptional organisms has 

 been made out ; nor do these curious gasteropods appear to be in 

 any degree of close relationship with their ordinary fresh-water 

 companions, although most of them undoubtedly bear traces of a 

 long probationary experience of life in fresh-water. This may 



* Appendix to Part 1. 



t Proceedings Royal Society^ 1898, p. 455. 



