FAUNA OF THK AFRICAN LAKES. 549 



family, they belong mainly to that of the Tiavidae. Tanganyika 

 is the only lake of those under i-eview which contains represen- 

 tatives of all the genera enumerated in the table of distribution. 

 — Victoria Nyanza, with a far smaller number of individual foi'ms 

 (28), can nevertheless show quite a comprehensive series of the 

 normal fresh-water types, each of the genera being represented. 

 The thalassoid genera and species are conspicuou.sly absent. — 

 Nyasa, with only slightly louer figures (24), does not difi'er very 

 markedly from Lake Victoria. The genera CleojKitra and Ancyhhs 

 are unrepresented, but the lake is lich in species of Lanistes and 

 Tiara, especially the latter, of which 9 forms (7 endemic) are 

 known. — Albert Nyanza and Edward Nyanza exhibit a progi'essive 

 I'eduotion in the number of species which they contain, but 

 otherwise possess no outstanding features. — Lake Kivu, finally, is 

 the extreme case, with a very reduced Gasteropod fauna. Of the 

 two species which are known from its waters, Tiara tibbeiculata 

 is the more widely distributed, it being in fact the only form 

 enumerated which has been found outside the continent of Africa. 



It was in the first degree the Gasteropoda which constituted 

 Moore's ai-gument for a halolimnic {i.e. I'elict) fauna living in 

 Tanganyika side by side with types which are common in tropical 

 fresh-waters. It is thus necessary to consider whether the balance 

 of evidence is still in favour of the views regarding these Mollusca 

 which Moore originally expressed. He held that the peculiar 

 forms in question were essentially primitive types, and after com- 

 parisons based on their anatomy he stated : — " It is difficult, or, 

 I may say, impossible, to view these exti'aordinary molluscs as 

 either the foi-erunners or the deiivatives of the fresh-water 

 molluscs which we find in the lakes and rivers all over the world 

 to-day. They are, however, readily intelligible if we regard them 

 as the forei'unners of several maiine grouj^s, such as the Strom- 

 bidte, the Naticas, and the early Ciriths, %o which I have referred " 

 (135, p. 466). 



These statements did not go by any means unchallenged, nor 

 did the astonishing suggestion of a resemblance between some 

 species and certain Jurassic fossil shells. Edgar Smith, in his 

 important paper on the Mollusca of Lake Tanganyika, pointed 

 out that Moore's conclusions were drawn from a stxidy of only 9 

 out of 23 so-called halolimnic genera, adding that it became 

 " mere conjecture " to suppose a relationship with marine forms 

 on account of the appearance of the shell (170, p. 78). As 

 an expei't conchologist, Smith dealt unfavourably too with the 

 supposed resemblances to Jurassic fossils. The matter was 

 approached from the geologist's standpoint by Hudleston, who 

 had made a speciality of Jurassic Mollusca (102). In a com- 

 prehensive paper on the origin of the halolimnic fauna of 

 Tanganyika, he failed to find evidence of a satisfactory chai'acter 

 in favour of Moore's views. In an appendix, Hudleston also 

 dealt seriatim with the comparisons between living and Jurassic 

 Gasteropods, only to reject likewise Mooi-e's conclusions. In a 



