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 with 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 Thelphusa 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 Platythelph usa, staying in the lake, retained most 
nearly the ancestral characters, Hydrothelphusa and Parathe/p/iusa, still largely 
aquatic in habit, would resemble them more nearly than Thelphusa, many species 
of which spend most of their time upon land. 
PLATYTHELPH USA 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. 
Limnocaridina Tanganyika:* (Fig. III). 
Description . — The rostrum (Figs- 1-2) is very long and slender, gently recurved, 
varying from about ij to twice the length of the carapace, and extending beyond 
* Caiman, “ Proc. Zoo. Soc.,” 1899. 
