2 PROCEEDINGS OF THE NATIONAL MUSEUM vol.84 



forms from a single or few ancestors, which suddenly gained access 

 to a vast, deep, unoccupied lake provided with innumerable ecological 

 niches, has happened elsewhere, though to a lesser extent. The bar- 

 bine cyprinids of Lake Lanao, the cottoids of Lake Baikal, and 

 Orestias in Lake Titicaca are examples in point. 



In lakes that give free access to the surrounding fauna, the various 

 ecological niches are normally filled by fishes of diverse groups. 

 Where access has been limited, and these niches have been filled 

 through the recent modifi ation of one or a few closely related forms, 

 a rather peculiar situation arises. Certain of the evolved species 

 develop unusual modifications, body forms, and physiognomies, very 

 unlike those exhibited by members of the particular group elsewhere. 

 Among the Tanganyika cichlids the Asijro-iiV^ Asprotilapia and 

 Eiianfiopvs, the Anthki^-like Cyatho pharynx^ and the blenny-Iike 

 T elmatochromis are examples. In Lake Lanao (see Herre, 1924 and 

 1933), certain species of cyprinids {Mandibular ca resinus, Spratelli- 

 cyjyris palata, Pun this tras) have developed very peculiar characters 

 and physiognomies, although all the Lanao species have probably 

 evolved rather recently from a single ancestral Puntius. These pe- 

 culiarly adapted or modified lake genera present numerous difficulties 

 to the taxonomist. While they probably are (in Tanganyika and 

 Lanao at least) younger than most of the genera outside the lake, 

 they oft€n far surpass the latter in the extent of their anatomical 

 modifications. Such matters make it difficult or impossible to re- 

 flect the true lines of phylogeny in any general scheme based purely 

 on the degree of morphological difference observed in the existing 

 forms. 



Another peculiarity in these autochthonous lake faunas, in part 

 inseparable from the great divergence among closely related forms 

 discussed above, should be mentioned. In the evident "hurry"' of 

 evolving forms to fit ecological niches, it frequently happens that 

 the change in minor characters of anatomy or color, or characters 

 usually found to be of only specific value, has fallen behind the 

 change in more striking features, usually taken to be of generic sig- 

 nificance. To me this indicates rather clearly that these "generic" 

 characters are phylogenetically young. Regan (1922, pp. 158-159) 

 has noted some peculiar minor characters that run through series of 

 genera and species of the African lakes and often enable one to 

 tell at a glance from which lake a certain species comes. To the 

 instances he cites may be added the tendency of many of the Vic- 

 toria cichlids to retain a few light-centered ocelli on the posterior 

 part of the soft anal fin. These ocelli are seldom seen in the Nyasa 

 or Tanganyika species, or, if present, they are usually in a different 

 position. 



