OF FISHES FEOM LAKE TANGANYIKA. 29 



we know at present is that the watershed between these lakes is situated in their 

 common valley, and that the whole series of lakes, from Tanganyika in the south to the 

 Albert Edward in the north, appears to lie in one continuous valley-system, which owes 

 its origin to a single geological movement, that has affected, although it may be 

 at very different times, an immense area of ground, and reaches at the present time 

 actually to the shores of the Red Sea. 



The lakes which lie in these valleys immediately to the north of Tanganyika are 

 therefore of especial zoological interest, for it may be that in these isolated sheets of 

 water there exist animals analogous to those which constitute the Jurassic Halolimnic 

 fauna of Tanganyika itself. The similarity of the Halolimnic gastropods to those 

 of the Jurassic seas is, as I have insisted elsewhere, so complete and so remarkable 

 that no effort should be spared which may throw light on the real nature and origin 

 of these forms. 



The only geographical fact which is at present available is this, that there exists a 

 certain similarity in the fish-fauna of Tanganyika to that of the lower Nile, and it 

 may be that this is an indication that at some time the Nile watershed was further 

 south, and drained out of Tanganyika to the north, in which case Halolimnic animals 

 will without doubt be found among the lakes towards the north. All this is, however, 

 little more than mere conjecture, but it will help my present purpose if it renders 

 more apparent the extreme desirability of becoming better acquainted with the zoology 

 of the lakes in the Eift valleys immediately to the north of Tanganyika. 



The presence of a Halolimnic fauna in Lake Tanganyika, as something superadded 

 to the normal freshwater stock of the lake, is at present the central fact, and if the 

 expectations which the morphological characters of those Halolimnic animals already 

 known have raised should be fulfilled, we have something here which may completely 

 change our views respecting the past history of the continent, and provide morphology 

 with some most unique and valuable comparative material. 



EXPLANATION OF THE PLATES. 



PLATE I. 



Fig. 1. Lates microlepis, p. 6. 

 Fig. 2. Lamprologus fasciatus^ p. 7. 



- p. 7. 



PLATE II. 



Fig. 1. Lamfrologus furcifer, p. 9. 

 Fig. 2. Telmatochromis vittatus, p. 10. 

 VOL. XV. — PART I. No. 5. — Decemher, 1898. 



