Geographic and Geologic Relations 409 



thence, as well as later, into Africa and India. The Indian 

 genus Etropius in its lobed crowded teeth, many dorsal 

 fin-spines, and other characters, seems to be one of the most 

 specialized genera, as it is furthest removed from ances- 

 tral beginnings of the entire family. 



As has been advocated by Branner( and Steinman) the 

 Antilles belonged during later Cretaceous days to a wide 

 continental mass that was again connected with the North 

 East American continent and its extensive lake system. 

 Evolving in the latter region, and widely prevalent in the 

 freshwaters of it, were the two large and closely related 

 families of the Percidae and Centrarchidae. The former 

 of these seems to be the oldest Acanthopterous family of 

 which we have sufficient and exact record. For several 

 species of Mioplosiis have been described by Cope from 

 Lower Eocene or Green River shales, while numerous speci- 

 mens of Prolates from the Mountain or Upper Cretaceous 

 beds of France indicate that already the Percidae occupied 

 a wide area of the northern hemisphere. But even these 

 in constructive structure are anticipated, and led up to, as 

 already explained, by the Percopsidae and Aphredoderidae, 

 the two genera of the former of which we would regard 

 as sole remaining representatives of ancestral Acanthop- 

 terygii, which though unknown in the fossil state, probably 

 traced back in origin to the Mid-Cretaceous period. 



Here it is worth emphasizing that while the Old World 

 or Eastern Hemisphere region was evidently shaken to its 

 core by seismic and volcanic action, and had most of its 

 teleostean genera obliterated during the late Cretaceous 

 and early Eocene periods, the North American and largely 

 also the northern half of the South American region were 

 less convulsed, and retained more direct continuity in their 

 organic life. So while the Percidae sent freshwater deriva- 

 tive types southward that evolved the primitive or fresh- 

 water Serranidae, and the Cichlidae, that both spread over 

 South America and in turn reached Africa, the Centrar- 

 chidae evolved wholly in North America as descendants 

 from evolving Percopsidae and Aphredoderidae, or from 

 primitive Percidae of the continent. The Percidae on the 

 other hand — taking advantage of the wide North Atlantis 



