CONTENTS. 
xiii 
CHAPTER XII. 
THE CRUSTACEA OF LAKE TANGANYIKA. 
The crabs — Platythelphusa and Limnothelphusa — The prawns 
PARE 
• 279 
CHAPTER XIII. 
THE NEW TANGANYIKA POLYZOAN. 
Arachnoidia ray la>ikesteri ........... 295 
CHAPTER XIV. 
THE TANGANYIKA MEDUSA. 
General structure of this organism — Its apparent life history .... 298 
CHAPTER XV. 
THE SPONGES AND PROTOZOA OF LAKE TANGANYIKA. 
Spongilla moorei- — Affinities of Spongilla moorei — Spongilla tanganyikce — Affinities 
of Spongilla tanganyikce — Potamolepis welteneri — Livingstone’s scum . . 309 
CHAPTER XVI. 
GENERAL CONSIDERATION OF THE NATURE OF THE HALOLIMNIC 
FAUNA. 
Recapitulation of certain matters discussed in earlier pages — The geo- 
graphical isolation of the Halolimnic group — Its coexistence with the 
normal African fresh-water fauna — The distinctive character of the Tan- 
ganyika fishes — The general characters of the components of the normal 
Tanganyika fauna — These are not structurally intermediate between those of 
the general African fresh-water fauna and the Halolimnic group — The Halo- 
limnic gastropods cannot be regarded as derivitives from any recognised 
fresh-water types — Similar reasoning applies to the Tanganyika jelly-fish — 
Impossibility of regarding the marine characters of the Halolimnic group as 
having been brought about through convergence — Impossibility of regarding 
the Halolimnic group as the relic of an old fresh-water stock — The presence 
of the Halolimnic animals necessitates the supposition of a former extension 
of the sea into Central Africa, and thereby throws light into the geological 
history of the continent 3 2 5 
