286 THE TANGANYIKA PROBLEM. 



gascar and, through this island, the south of Africa itself, was perhaps at some 

 remote period connected in a tolerably close manner wjth India. The present 

 fauna of Madagascar, which shows marked Oriental affinities, bears this out ; and 

 from considerations of geological facts, particularly as regards the possession of a 

 common flora in Carboniferous times, Blanford, following Suess and Neumayr, is 

 inclined to regard the idea of a great continent, embracing Australia, India and 

 South Africa, as by no means improbable. The evidence for such a land-connec- 

 tion is not confined to beds of quite such ancient date, however, for both in 

 Jurassic and Cretaceous times the fauna of the two areas is distinctly suggestive of 

 the same continuity. If, then, we may imagine the ancestral Thelphnsa as living on 

 the shores of this early continent, in which the present Lake Tanganyika was 

 represented as a narrow bay or fiord, it is not unreasonable to suppose that while 

 Limnothelphusa, and perhaps Platythelphnsa, staying in the lake, retained most 

 nearly the ancestral characters, Hydrothelphusa and Parathelphusa, still largely 

 aquatic in habit, would resemble them more nearly than Thelphnsa, many species 

 of which spend most of their time upon land. 



PLATYTHELPHUSA ARMATA (FIG. II). 



The external characters of this remarkable crab have 

 been briefly described by Milne Edwards, " Annales des 

 Sciences Naturelles Zoologie," Tome III., p. 147, but as 

 he had no example of the male, and at the time was not 

 aware of the peculiar interest attaching to the Tanganyika 

 fauna in general, it is to be hoped that the animal will be 

 more studied in the near future, more especially so since the 

 peculiarly marine aspect of the crab at once struck Milne 

 Edwards himself. Thus he says : " This fresh-water crab 

 presents such a great resemblance to certain marine or 

 brackish species belonging to the Grapsides . . . that 

 we might be tempted to relate it to them but for the de- 

 velopment of the abdomen and the absence of meta- 

 morphosis." It is, however, obviously open to question 

 how far such marks of distinction should be allowed weight. 



LlMNOCARIDINA TANGANYIKA * (Fig. III). 



Description. — The rostrum (Figs- 1-2) is very long and slender, gently recurved, 

 varying from about I3 to twice the length of the carapace, and extending beyond 



* Caiman, " Proc. Zoo. Soc," 1899. 



