52 Classification of the Family Cichlidee. 



The above data enable the origin and relationships of the 

 Cichlid fauna of Lake Tanganyika to be discussed. 



Ti/lochromis is found in the Congo and in West Africa, 

 and is represented in Tanganyika by a single species; it 

 is an isolated genus, whoso nearest relative is Piychocliromis 

 of Madagascar. Of the large African genus Tilapia only 

 the widely-distributed T. nilotica has reached Tanganyika, 

 ap|)arently through L. Kivu ; the endemic JS^eotilupiu has 

 the structure of T. nilotica and its allies, but ditiers in its 

 dentition, having all the teeth tricus|>id. 



A small group of endemic genera begins with Limnoiilapia, 

 which is nearly related to, but is in some respects more 

 generalized than Tilapia, and leads on the one hand to Loho- 

 chilotcs and on the other to Gephi/rochroinis, Sitnochromis, and 

 Tropheus ; in this group the Limnotilapia dentition (outer 

 teeth bicuspid, innei- tricuspid) undergoes various modifica- 

 tions ; Lohochifotes, teeth compressed, unicuspid ; Gephijro- 

 chromis, outer teeth conical ; Simochromis and lyopheus, 

 Hnterior outer teeth bicuspid, lateral conical. 



Another little group of endemic genera commences with 

 Ophthalmotilapia, which is closely related to Linuiolilapia, 

 but lias all tiie teeth tricuspid (or sometimes unicuspid), 

 small, and lixed. This genus has given rise to CyatJiopharynx^ 

 distinguished by the small scales and the form of the lower 

 ])liaryngeal, and to Cunniitytonia, Asprotilapia^ and Petro- 

 chrutnis, in which the tricuspid teeth are long, slender, and 

 movable. It is interesting . to note that the total number of 

 doisal rays is nearly the same in Petrochromis as in the 

 otlier genera, but that the spines have increased at the 

 expense of the soft rays ; this genus has a species in 

 \j. Nyassa, but there can be little doubt that it originated in 

 Tanganyika. 



The endemic Limnochromis, with conical teeth, does not 

 difttr very essentially from Limnotilapia in other characters. 

 Cypliotilaj'ia has one species from Tanganyika and another 

 from the Upper Congo ; if, as seems likely, this geims is 

 Livinochromis specialized, it probably originated in the lake. 

 The monotypic Boulenyerochromis is essentially a small- 

 scaled Limnotilapia, and l^erisnudus seems to diil'cr from it 

 only in the peculiar dentition. 



The seventeen genera mentioned above have the ])liaryngeal 

 a])ophysisformed by theparasjilu'iioid alone; iwoCLylochromi.s, 

 'J'llapia) are widely di.-^tiihuted genera, eaeh lejtresenled in 

 the lake by a single species; one endemic genus {^S'eotilapia) 

 is elosoly related to Tilapia ; the rest n)ay have originated iu 

 the lake from a single ancestral type, which Livinvtilapia 



