CICHLID FISHES OF LAKE VICTORIA. 159 



species, with a lai'ger mouth and more prominent lower jaw ; in 

 some species of this group the mouth is oblique, and in some the 

 outer teeth are strong and spaced. Finally, there are species 

 with a strongly projecting lower jaw, in some of which the cleft 

 of the mouth is nearly vertical. 



One species, R. ishmaeli, is of peculiar interest ; it is so like 

 H. cinereus that the types (12 specimens) include 6 examples of 

 the latter, but it differs in having much larger and more massive 

 pharyngeals, with the teeth large and blunt, whei'eas in H. cinereus 

 they are small and slender. I have described a similar pair of 

 species (//. tetrastigma and H.-placodon) from Nyassa. A remark- 

 able group of three species includes Haplocliromis sauvagei and 

 the monotypic genera Macroplexirodus and Hoplotilapia, which 

 scarcely differ from each other except for the considerable differ- 

 ences in dentition, and seem to illustrate Cope's paradoxical 

 view that a species may persist through several genera. It is 

 especially interesting to note that the normal markings are those 

 described above as characteristic of many Victoria species, but 

 that in addition all three are known to possess a " hicolor" form, 

 a sort of piebald, in which the dark pigment is concentrated into 

 a number of blotches and irregular ci'oss-bars which extend on to 

 the vertical fins. 



Another interesting example of the same species in different 

 genera is provided by Hcqylochromis annectens and Plaiytceniodus 

 degeni ; here the former shows a slight departure from the 

 normal Hci'plochromis dentition towards the Platijtceniodus type. 



The conclusion is that in Victoria most of the endemic 

 Cichlidfe have evolved in the lake from a t^'pe very similar to 

 Haplochromis cinereus, and that the primary evolution has been 

 in the size and shape of the mouth, and the number, structure, 

 and arrangement of the teeth, doubtless in adaptation to different 

 kinds of food and different methods of feeding. The facts seem 

 more in harmony Avith Gulick's theory of habitudinal segregation 

 than with the modern idea of evolution by accidental mutations. 

 The Cichlidee of Tanganj'ika and JSTyassa lead to the same 

 conclusion. 



In my paper on the Nyassa Oichlidse I called attention to two 

 striking examples of convei-gent evolution, Pseudotropheus and 

 Aulonocara of Nyassa, respectively showing a gi-eat resemblance 

 to Tropheus and Trematocara of Tanganyika. Lake Victoria 

 provides some more examples : Haploclirornis chilotes has the lips 

 thick and produced into lobes as in Lohochilotes of Tanganyika ; 

 M. ishmaeli has the pharyngeals massive and provided with large 

 blunt teeth as in H. placodon of Nyassa. Further, Haplochromis 

 ohliquidens and Macropleurodus bear a resemblance to Nyassa 

 genera in their dentition, the former to Heinitilap)ia, the latter 

 to Cliilotilapia. 



If the degree of differentiation be taken as a guide, one may 

 form the conclusion that the Cichlidte have inhabited Tanganyika 

 longer than Nyassa, and Nyassa longer than Victoria. 



