636 SCIENCE PROGRESS. 



that of Tanganyika/ Lastly, they cannot conceivably have 

 originated in Tanganyika through the effect of environment, 

 since this would have affected the whole of the fauna and 

 not simply have superadded new genera to a list which 

 in other respects is so strikingly similar to that found in 

 Nyassa. 



There remain then three hypotheses, two of which if 

 they are not still actually tenable must receive some further 

 consideration here. The first of these seeks to explain the 

 existence of the unique group of organisms found in Tan- 

 ganyika, by supposing them to be the persistent remains of 

 an extinct fresh water fauna, and this view has been said to 

 have a certain amount of palseontological support. Some of 

 the original shells brought home from Tanganyika have for 

 several years been regarded by many geologists, notably by 

 White - and Tausch,^ as being probably related to certain 

 Cretaceous brackish or fresh-water fossils of America and 

 Southern Europe, the so-called Faramellanias of Tanganyika 

 being compared to the Pyrguliferas of Cretaceous times. 

 The possibility of such a comparison has naturally led the 

 way to the view that the enigmatical Tanganyika animals 

 may not in reality have resulted from the marine con- 

 tamination of the lake, but be the survivals of a prehistoric 

 fresh-water stock, which once upon a time existed wide- 

 spread in Africa and in Europe and America also. But 

 although there is the most remarkable similarity between 

 the Faramellanias of Tanganyika and the fossil Pyrguliferas, 

 it must, I take it, be confessed that the determination of a 

 real identity between fossil and living shells of this sort is 

 hazardous in the extreme. For example, if the singular 

 Lymnotrochus of Tanganyika had become fossilised in 

 ancient beds, it would almost certainly have been classed 

 along with the true Trochi, although in reality it is nothing 

 of the kind. On these slender grounds, of a similarity 



^ I have discussed the evidence bearing upon the relative antiquity of 

 the lakes in a paper in the Joutnal of the Royal Geographical Society now 

 in the press. 



- Proc. 0/ U. S. A^at. Mus., S. 98, Washington, 1883. 



^ Sitzungsber, d. Kais. akad. d. Wissensch., Bd. xc., i, p. 57. 



