28 ME. G. A. BOULENGEE ON A COLLECTION 



That there are no Halolimnic representatives among the fishes which have hitherto 

 been obtained is no evidence that other fishes of a widely different and possibly of a 

 Halolimnic type may not in future be secured. On the other hand, the fact that the 

 Teleostean fishes now existing in Lake Tanganyika should not correspond with the 

 Molluscan section of the Halolimnic group is really what one would expect ; for, as I 

 have recently shown ', the facies of the Molluscan section of the Halolimnic group is 

 almost, if not quite, indistinguishable from that of the Jurassic seas. Except the 

 Herring-like Leptolepidce, few, if any, Teleostean fishes are represented in Jurassic beds, 

 and we should therefore expect the piscine accompaniments of the Halolimnic molluscs 

 to be entirely composed of Ganoids and the like. I found a species of Polgpterus, 

 which I took to be P. bichir, abundant on the southern shores of Lake Tanganyika, 

 and it is quite possible that some of the active carnivorous fishes which inhabit the 

 open water may be Ganoids too. What the fish is that so much surprised Glaive, 

 when he crossed the lake, by attacking the paddles of his boat, is quite unknown, but 

 I myself saw these same fishes attack the paddles of my own boat, not 20 miles from 

 the spot where Glaive described them, on the west coast of the lake. 



Judging, therefore, from the incomplete character of our knowledge of the fish- 

 fauna of Lake Tanganyika, and from the vast antiquity of the lake, as evidenced by 

 the Jurassic facies of its molluscan shells, it is only natural to expect that future 

 exploration may reveal, among these fishes, forms that are of the highest scientific 

 interest from a morphological point of view. 1 mean that Tanganyika and its 

 neighbourhood present one of those few localities where it is legitimate to expect that 

 we may discover many forms that in most places have become extinct. 



Our very slight acquaintance with the surface-forms existing in Nyassa and Tan- 

 ganyika, and the complete absence of all knowledge of the contents of the deep 

 waters of these lakes, unfortunately by no means exhausts the sum of our present 

 ignorance of these matters. We have no real knowledge of the extent of the 

 Halolimnic fauna, beyond the lake in which it was originally discovered. I have 

 shown only that this fauna is not present in Nyassa nor in Shirwa, nor yet even in the 

 little lake Kela, not more than 20 miles from the Tanganyika shore, and that it 

 is extremely probable that it does not extend to Mwero and Lake Bangweolo to 

 the west. But for anything that can actually be shown to the contrary, it may be 

 present in Lake Rukwa to the east, and in the Albert and Albert Edward Nyanzas 

 to the north, and it is perhaps almost to be expected that some representatives 

 of this stock should be found in Lake Kivu, which lies in the same great valley not 

 more than 50 miles to the north of Tanganyika. But what is the relation of this 

 lake, the effluent of which flows south into Tanganyika, to the Albert and Albert 

 Edward Nyanzas, with effluents flowing into the Nile, towards the north I All that 



1 " On the Hypothesis that Lake Tanganyika represents an old Jurassic Sea,'' Quart. Journ, Microsc, Sci. 

 ili. no. 162, June 1898. 



