The Spine-finned Teleostei 377 



and I spine with 8 soft rays in each one of the ventrals. In 

 all of these also the salmonid adipose dorsal fin still persists. 



In the living species of Aphredoderus (Fig. 61) there 

 are 3 spines and 11-12 soft rays in the dorsal fin, 2 spines 

 and 6 rays in the anal, i spine and 8 rays in the ventrals. 

 But here the adipose fin if originally present, has now 

 failed to develop. From the last to such genera of the 

 Centrarchidae and Percidae as are shown in Figures 62, 

 61,1 64 and 6^, the transitions are beautiful and gradual, 

 up to such evolved and specialized types as the Yellow 

 Perch, {Perca flavescens) of the Eastern States andAm- 

 blopletes as well as many related forms. 



We can now pursue study of the evolution and distribu- 

 tion of the Acanthopterygii as a whole. Prolates heberti 

 from the Upper Cretaceous strata of Mont Aime, in France, 

 seems to be the oldest known type. But simultaneously, 

 so far as can be determined at present, various genera of 

 the nearly related Berycidae had also appeared in marine 

 strata. We can explain the evolutionary continuity of the 

 Berycidae with the earlier types of freshwater Aphredoderi- 

 dae, but there seems no good means for explaining the ap- 

 pearance of the Berycidae except from such a freshwater 

 source. 



As to the possible centre of such origin, all present data 

 point to the extensive lake-regions of Western America. 

 For though the sea extended over considerable parts of 

 eastern and southern North America in Cretaceous-Eocene 

 times, a large lake or lakes persisted more or less in the 

 central-western part, up even into northern Canada. In 

 truth to understand the probable origin of the rich fresh- 

 water fish-fauna that Leidy, Cope and more recent workers 

 have described, we must suppose the previous existence near 

 there of abundant progenitors in large lakes. 



We accept it then as most consonant with all known 

 facts, that by Mid Cretaceous time the freshwater Centrar- 

 chidae and Percidae, also the marine Berycidae, had already 

 diverged ecologically into two distinct environal areas, and 

 were starting evolution of the varied genera that now make 

 up each of the three families. 



