1909. | OF THE THIRD TANGANYIKA EXPEDITION. 69 
Tanganyika, two in Nyasa, and two others in Victoria Nyanza. 
Of the genus Schizopera a single species (S. fimbriata) seems to 
be peculiar to Lake Nyasa; all the other seven species are 
found in Tanganyika, and of these only one (S. consimilis) is 
stated to occur also in one of the other lakes (Victoria Nyanza). 
The remarkable genus Jlyophilus, as above stated, is only re- 
presented by a single species from 'Tanganyika. Of the 20 species 
of the genus Cyclops, 17 have been stated to occur in Tanganyika. 
Two of these (C. lewckarti and C. neglectus) are common to 
all three lakes; three species (C. varicans, C. angustus, and 
C. agiloides) occur occasionally also in the other lakes, the 
first two in Nyasa, the last in Victoria Nyanza. The remaining 
12 species, on the other hand, seem to be endemic forms of 
Lake Tanganyika, Of the three species which have not yet been 
found in Tanganyika, one ((. emini) seems to be an endemic 
form of Victoria Nyanza; the second (C. albidus) is a widely 
distributed, almost cosmopolitan species, like C.. leuckarti; and the 
third (C’, dubius) is as yet only known from a solitary specimen 
found in Nyasa. The three species of the genus Hrgasiloides 
occur all in Tanganyika, and only one of them (C. brevimanus) is 
occasionally also found in Nyasa. In the latter lake, finally, a 
still undetermined species of the genus Hrgasilus occurs. 
Particular attention ought to be paid to the two remarkable 
genera, Schizopera and Jlyophilus. Both these genera must 
evidently be regarded as of marine origin, and the question thus 
arises, how we shall explain the occurrence of species of these 
genera in the purely freshwater lakes of Central Africa. The 
most obvious inference appears to be the belief, that these species 
are true “ relict” forms, that is to say, the remains of an ancient 
marine fauna prevailing here at a time when the lakes formed part 
of the Ocean; and indeed a supposition in favour of such a con- 
clusion was advanced some time ago by Mr. J. E. 8. Moore, 
who is of opinion that Lake Tanganyika might be the modified 
remains of part of an ancient Jurassic Sea, and that its fauna 
accordingly in some instances exhibits distinct traces of more 
primitive (marine) characters. Recent investigation of this lake 
tends, however, to disprove the supposition set forth by Mr. Moore 
about the fauna of Lake Tanganyika, and to show that it is on 
the contrary a highly specialised one, and does not exhibit any 
true relation to marine forms. Jam myself also of opinion that 
the theory of Mr. Moore about his so-called “ halolimnic ” (relict) 
forms can scarcely be supported. But, how are we to explain 
the presence in Lake Tanganyika of species of the two above- 
mentioned genera? I think that we need not regard these as 
true “relict” forms, although their marine origin seems to be 
indisputable. We have in this case recourse to another ex- 
planation, which may prove to be fully sufficient, namely, the 
accidental transport by the aid of migratory aquatic birds. 'The 
importance of such a transport for the distribution of small fresh- 
water animals-has long been recognised. It is indeed easily 
