488 Evolution and Distribution of Fishes 



furthermore were the two to flow in somewhat divergent 

 east and west directions, the conditions would be satisfied 

 geographically and geologically which would explain the 

 above distribution of Amia, Lepidosteus, and allies. 



Our present knowledge of the family Pachycormidae 

 would indicate that the more ancient genera like Euthynotus 

 and Pachyconmis from the Lias, originated in some rather 

 restricted land area of Central South Europe, and the 

 finding of the small freshwater Leptolepis as fossilized 

 food-remains, inside a specimen of the latter genus from 

 Normandy, is partial proof. But adoption of an anadro- 

 mus and later of a wholly marine habit, enabled them to 

 extend their range, until, from early Cretaceous time on- 

 ward they ranged from the seas of Russia westward to 

 the Niobrara seas of Kansas. So if we compare the 

 Amiidae, the Lepidosteidae, and the Pachycormidae, it 

 seems as if all three had a common and coeval central or 

 eastern European freshwater origin in Upper Liassic or 

 early Kimmeridgean times. Then the two former spread 

 westward into N. America by the N. Atlantis bridge, while 

 synchronously the pachycormids — becoming probably first 

 anadromous but later purely marine, travelled in parallel 

 advance with the amioids and allies toward N. America, 

 but along the southern shores of the N. Atlantis bridge. 

 The evolved descendants like Protosphyraena and Erisich- 

 the, that are found in Cretaceous beds from Kansas in the 

 West to Russian Kursk and to Lebanon in the east, would 

 indicate that a more or less continuous expanse of sea 

 existed alongside the N. Atlantis land at least to the last- 

 named locality. 



The above conclusions as to parallel continental and 

 oceanic migrational movements receive added confirmation 

 when comparison is made of the Engnathidae, Macrosem- 

 iidae, and Semionotidae — all of which were persistently 

 freshwater families — with the related Pycnodontidae. 

 For the latter resembled the Pachycormidae in beginning, 

 and In long remaining, as a freshwater family. But in later 

 evolution and distribution (p. 334) they became purely 

 marine. 



