TRANSACTIONS OF SECTION D. 601 



3. A liemarkable Example oj Milllerian Mimicry among African 

 Butterflies. By Professor E. B. Poulton, F.R.S. 



■i. Melanism in Yorkshire Lepidoptera. By G. T. Porritt. 

 See Reports, p. 316. 



5. Report on the Influence of Salt and other Solutions on the 

 Development of the Frog. — See Reports, p. 327. 



6, Halolimnic Faunas and the Tanganyika Problem. 



(a) By J. E. S. Moore. 



The author dealt, firstly, with the characters of freshwater faunas in general. 

 It was pointed out how the existing conceptions of the origin of freshwater 

 faunas had arisen. Attention was also drawn to the fact that many freshwater 

 organisms had no near relations in the sea at the present time, this fact leading 

 to the supposition that the freshwater faunas must have been derived from the 

 sea at a somewhat remote period. 



The author drew attention to the fact that many freshwater organisms were 

 very widely distributed over the land surfaces of the world. It had been sought 

 to explain this by the conception that such freshwater organisms were capable of 

 great migration. 



The difficulties of such a conception were next considered, and a number of 

 other facts in relation to the character of freshwater faunas studied in relation to 

 the probability that the sea is getting Salter in the course of time. 



It was pointed out that slow physical changes were capable of producing great 

 changes in animals subjected to them, and the author suggested that this change 

 in the nature of the sea might have been concerned in the production and 

 separation of marine and freshwater faunas. 



Whatever the actual cause of the separation, the general freshwater fauna 

 of the globe had features of antiquity about it. It was convenient to regard 

 this general freshwater fauna as the primary freshwater fauna. 



To this primary fauna it was found that in many places— as, for instance, in 

 the Caspian Sea— there were added numbers of animals which had from their 

 structure obviously been derived from the sea, and were quite independent in 

 origin from the freshwater fauna of the land in which they occurred. 

 It was to these faunas that he had applied the name of halolimnic. 

 He drew especial attention to the misunderstanding which had arisen through 

 Mr. Edgar Smith's incorrect use of the term thalassoid. This term could only be 

 applied to animals which were like, but not related to, marine forms. Halolimnic, 

 on the other hand, meant marine in origin. If a fauna was thalassoid it was not 

 halolimnic, and vice versa. 



The author congratulated Mr. Cunnington on the many additions he had 

 recently made to our knowledge of the fauna of the great African lakes, pointing 

 out that the present time seemed in every way suited to a renewed discussion of 

 the Tanganyika problem. 



Having reviewed the fauna of the lake as we now know it, the author pointed 

 out that the Tanganyika problem consisted of questions as to the nature and origin 

 of the number of animals which were peculiar to that lake. 



Regarding this it appeared that only three suppositions could be made : — 



1. That the peculiarities in the Tanganyika fauna were due to modifications of 

 the general A&ican freshwater fauna. 



