Geographic and Geologic Relations 405 



progressive evolutionary standpoint, are the most recent 

 and the most highly developed are the Jugulares, the 

 Anacanthini, and the Acanthopteri that typically show more 

 than 10 spines in the dorsal fin. None of these so far as 

 known date back further than the Tertiary period, and 

 mainly from Upper Eocene onward, except the late Creta- 

 ceous genus Prolates of the freshwater group Percidae. It 

 seems to be closely allied to and possibly ancestral to Lates 

 that is known from Upper Eocene on through higher strata 

 to living representatives. 



The preponderating number of these is marine. In 

 geographical distribution species may be said to occur in 

 nearly every tropical, subtropical and temperate sea, more 

 rarely in subarctic. The continuity of marine gulfs, seas, 

 and oceans would explain how such resulted. They in- 

 clude fishes which, in color, in shape, in special adaptation 

 to environment, often also in fin modifications, are strik- 

 ingly evolved. Further they can nearly all be shown to 

 have some fundamental primitive details that ally them 

 more or less clearly with simpler and in nearly all cases 

 freshwater fishes. This has been traced in earlier chapters. 



But the more primitive acanthopterous families are 

 largely, or in some instances wholly freshwater, and in their 

 present geographical distribution present many peculiar dis- 

 tributional features that call for explanation. We may 

 first refer in detail to the regions occupied by the Anaban- 

 tidae, Ophiocephalidae, and Osphromenidae, three nearly 

 related and wholly freshwater groups. The ten African 

 and four S. E. Asian species of the first are now separated 

 by many hundred miles, while between the eastern limit of 

 the African ones and the present coast line there is a wide 

 stretch of country. The three African and twenty-five 

 Asiatic species of Ophiocephalids occupy a reversed area 

 of territory that approximates in ratio to the number of 

 species. But a like East African zone is devoid of them. 

 The Osphromenidae occur in central and west-central Africa 

 where are three species, and in South East Asia where are 

 nineteen. Such distribution therefore suggests that in 

 earlier Tertiary times Africa and S. E. Asia were either 

 directly connected across what is now the Indian Ocean, 



