392 Evolution and Distribution of Fishes 



Indian Isles, i is peculiar to the Caroline Islands, and 3 

 surround Tahiti. 



If a short review be now made of the six related families 

 Percidae, Centrarchidae, Cichlidae, Pomacentridae, Labri- 

 dae and Scaridae, it can be said that the two first are almost 

 wholly N. American and purely freshwater, a few species 

 only of the first having spread out across the Behring sea 

 area into N. Asia and then into Europe. From species in- 

 habiting the S.W. States or Northern Mexico, the Cichlidae 

 branched off into rivers and lakes of S. America, as a tropi- 

 cal freshwater group that steadily migrated eastward across 

 swamps and rivers of the S. Atlantis bridge into Africa, 

 where they abundantly multiplied, and are now represented 

 in nearly all the lakes, rivers and extensive swamps of the 

 central continental area. Outliers from these passed north- 

 eastward along the Indo-Mascarene bridge till they reached 

 Madagascar, India and Ceylon. 



The Pomacentridae, diverging from centrarchid or 

 percid ancestry, gradually acquired a brakish and later a 

 marine coastal habitat, along the southern or south-eastern 

 States region, and about a time when sea-connection existed 

 between the Gulf and the Pacific. Thus arose the western 

 and the eastern pomacentrid representatives, probably in 

 early Eocene time. Evolving species and genera moved 

 eastward along the southern coastal edges of the S. Atlantis 

 continent, that was effecting, along its inland freshwaters, 

 the simultaneous advance of the Cichlidae. By late Eocene 

 or Oligocene days the Cichlidae in freshwaters, and the 

 Pomacentridae along the coasts, had reached Indian fresh 

 and saltwaters respectively. But while the land-freshwater 

 environal conditions surrounding the Cichlidae retarded 

 further eastward progress, the highly favorable shore and 

 coral-reef environment, with rich and varied associated 

 life, stimulated the origin of those abundant marine species 

 of Pomacentridae that now occur over the Easter Archi- 

 pelago from N. Australia to S. Japan. 



Ancestors of the Labridae, and in turn of the Scaridae, 

 branching off, the former from the Pomacentridae, the 

 latter from the Labridae, followed the main lines of migra- 

 tion already pursued by the Pomacentridae, except that a 



