378 Evolution and Distribution of Fishes 



Until much more is known about fossil forms, one can 

 only speak in the most general way as to the above centre 

 of origin. But when we note that the living Percopsidae 

 and Aphredoderidae, as well as several fossil Eocene genera 

 of the latter are or were inhabitants of N. W. America; 

 that the Centrarchidae — which are an advance on the 

 second — consist of 9 genera and 24 species that also are 

 N. American, except for Kuhlia that occurs in fresh and 

 brakish waters of rivers from Central Africa to N. Aus- 

 tralia; that of living Percidae there are 12-14 genera with 

 about 90 species, of which 9 genera and 76 species are N. 

 American, while 3 decidedly evolved genera and 10 or 11 

 species extend from N. America to W. Europe thence to 

 N. Asia and Australia, strong grounds are furnished for 

 accepting N. W. America as the primitive centre of evolu- 

 tion for the primitive Acanthopterygii. 



Again in the Aphredoderidae, the Centrarchidae, and 

 the Percidae, community of structure and descent is sug- 

 gested with the Percopsidae, in that muciferous canals are 

 developed in some genera of all four great groups, while 

 other structural features show close affinities throughout. 

 Finally not a few of those which have travelled furthest 

 from the N. American continent show a more evolved 

 structure than do the most specialized of those that still 

 exist there. 



In a succeeding chapter various details of structure that 

 bear on the geographical distribution will be presented. But 

 here one may appropriately refer further to some points 

 of special geographic interest. To treat first of the Cen- 

 trarchidae that seem perfectly to unite the Aphredoderidae 

 with the Percidae, these are all N. American except Kuhlia. 

 Except for one or two, nearly all are centred east of the 

 Rocky Mountains (Fig. 66). This might indicate that they 

 mainly evolved after the later extensive upheaval of these 

 mountains. But the remarkable distribution of the six 

 known species of Kuhlia would indicate that during early 

 Tertiary times a few Centrarchids had passed down to S. 

 America, and then migrated over Koken's South Atlantis. 

 For thus alone does it appear possible and likely to people 

 regions that include S. and E. Africa, the Mascarene 



