XIV 
THE TANGANYIKA PROBLEM. 
CHAPTER XVII. 
GENERAL CONSIDERATION OF THE NATURE OF THE HAL0LIMN1C 
On some peculiarities of the fish-fauna in lake Tanganyika — Relation of some of the 
characteristic forms to both sides of the Atlantic — The character of the fishes 
of Tanganyika indicate that part of the fish fauna may have originated from a 
western sea — Peculiarities of the Congo fauna — The Congo depression pro- 
bably the remains of a former extension of the sea — The age and type of the 
Halolimnic fauna — Comparison of the hard parts of the Halolimnic animals 
with fossiliferous remains — The identity between the shells of the Halolimnic 
gastropods and a corresponding number of forms from the Jurassic seas — 
Details of this comparison — General consideration of the value of this com- 
parison — No valid geological objection to it — The number of corresponding 
points renders it improbable that the correspondence is a coincidence — The 
Halolimnic fauna would thus appear to be the remains of that of a Jurassic 
sea — The characters of the other Halolimnic animals in accord with this 
view — Recapitulation ■ 339 
