318 J. E. S. MOORE. 



known I have not thouglit it necessary that I should give 

 figures of them here. 



Besides the above marine types the halolimnic fauna 

 contains two forms, Syrnolopsis and Turbonella terebri- 

 formis, which, although they do not resemble any known 

 Jurassic shells, nevertheless exemplify in a remarkable 

 manner the marine affinities of the halolimnic mollusca as a 

 whole; for the shell of the first of these species is practically 

 undistinguishable from that of the genus Syrnola, a form 

 found in the tropical seas, the second from that of the genus 

 Terebra. 



It is thus apparent that with the exception of Ty phobia,^ 

 and possibly of Bythoceras, all the halolimnic genera now 

 living in Lake Tanganyika arc generically identical with 

 Jurassic forms, while two of these, Paramelania and Nas- 

 sopsis, contain forms which are specifically indistinguishable 

 from their corresponding Jurassic types. 



Curious and startling as the foregoing comparison undoubt- 

 edly appears, I might still have had some hesitation in 

 bringing it forward as evidence of the origin of the halo- 

 limnic fauna, had not the three authors, White, Tausch, and 

 Oppenheim, practically forced my hand by attempting the 

 comparison of which I have spoken between the living halo- 

 limnic and the old cretaceous fresh-water stocks. Whatever 

 may be the real value of evidence which is based upon shell 

 structure alone (and this certainly becomes more and more 

 questionable as time goes on), it will have been rendered 

 clear that the amount of this kind of evidence favouring the 

 similarity of the halolimnic and old cretaceous fresh-water 

 stocks is utterly insignificant beside that which can be pro- 

 duced in favour of the similarity of the halolimnic and old 

 marine Jurassic forms. 



So far as I am concerned, therefore, this paper will have 



* The genus Typhobia, as I have shown, is, however, closely related to 

 Bathanalia, and there is very little doubt that it simply represents a modifi- 

 cation of the former form. It may be that the genus Typhobia in reality 

 represents the Jurassic form Purpuroidea. 



