Geographic and Geologic Relations 407 



lation to the head, and so developed the 150 species of 

 Pomacentridae that cluster along the Mexican, Peruvian, 

 Chilian, and East Brazilian coast; that are continued across 

 to African shores, thence round S. Africa and Madagascar 

 on to India, the East Indian Archipelago and even to 

 Australia. Since probable types of the Pomacentridae like 

 Odonteus have been found in Upper Eocene to Miocene 

 rocks of Southern Europe the migration along the northern 

 sea edge of the American-African bridge may have been 

 effected in Mid-Eocene time. 



Possibly from one centre, but by no means unlikely 

 from several marine centres, members of the Pomacen- 

 tridae gradually evolved in body shape, in fin and spine 

 relation, but particularly in condensation and modification 

 of the cephalic bones and the teeth, as a food-diet that 

 contained calcified constituents was increasingly adopted. 

 So coastal genera of the Labridae arose as offshoots from 

 the Pomacentridae, whose remains are met with in rocks 

 of the Miocene-Pliocene and onward, while with gradual 

 breaking down of the Americo-African bridge and the 

 Afro-Indian bridge they more freely spread into increas- 

 ingly wider marine areas. 



As to the disappearance of the South Atlantic ( ?Ant- 

 arctlc) and the Afro-American bridges biologic and geologic 

 facts would suggest that such was effected during late 

 Oligocene or early Miocene times. For, as the studies of 

 Drummond, Scott Elliott, and especially Moore have re- 

 vealed, enormous "eurycolpic" (Moore) foldings of the 

 Central African region took place before or during Pliocene 

 times, and these resulted in extensive faults that must have 

 shaken a great part of the world during their formation. 

 Subsequently, over the entire altered area late Tertiary 

 strata of freshwater origin were laid down, that are still 

 being added to in the form of swamp, flood-plain or lake 

 deposits. Again along the eastern American coast, from 

 Trinidad to Argentina, depressions — either rather sudden 

 or In part steady — took place, so that the valleys of the 

 Amazon and Orinoco became arms of the sea. 



The Indo-Mascarene bridge seems to have been re- 

 moved about the same time as the above, for the subsequent 



