The Soft-finned Teleostei 371 



show the completed change. Fourth: where all of the 

 above three changes are observed to be proceeding coinci- 

 dently, the fishes showing such are often passing, or have 

 passed in some genera from a freshwater to a marine 

 habitat. 



Special reference need not be made here to anatomical 

 details that have contributed to some of the above changes, 

 as these are dealt with later. But it should be added, that 

 while these changes are broadly and fairly minutely applic- 

 able throughout, they are indicative rather than absolute. 



A review of the observations set forth in this chapter 

 causes the writer to accept that from preexisting leptolepid 

 or amioid stock of Cretaceous or early Eocene age, most of 

 the existing genera and species of malacopterous teleostean 

 fishes are descended. The most active and extensive area 

 of evolution evidently was the great system of freshwater 

 lakes that once covered a large part of the N. American 

 continent, though this need not preclude the former exist- 

 ence of other and even large lakes which may have been 

 located over that part of North Atlantis that now is sub- 

 merged beneath the Atlantic. There is ample and ever- 

 increasing evidence also, that great stretches of freshwater 

 existed along the eastern part of South America, and that 

 these were populated by an abundant fish fauna. See for 

 this the author's work "Fishes the Source of Petroleum" 

 (p.p. 286-288). An acceptance of the primitively fresh- 

 water origin of these malacopterous fishes, and of the later 

 migration of some derivative groups into the sea, furnishes 

 the important Key to their present-day structure, aflinities, 

 ecology, taxonomy, and distribution. 



