500 Evolution and Distribution of Fishes 



feeders over muddy beds. Their remains therefore occur 

 in continental freshwater deposits, alongside plant remains, 

 freshwater molluscs, or freshwater eurypterids and crusta- 

 ceans. 



Fourth: Though from evidence yielded by plant and by 

 invertebrate remains, a S. Atlantis and also a Gondwana 

 continent existed in the Siluro-Devonian time, fishes do not 

 seem to have reached either of these continents from N. 

 Atlantis till close of the "Old Red" or during earlier Car- 

 boniferous time. Then through some fundamental changes 

 in the configuration and relations of these continents, con- 

 nection was established with north and south Africa, also 

 at least with part of India and the eastern part of Australia, 

 thence onward to antarctic lands (p. 136). From all of 

 these regions freshwater fishes have been secured. 



Fifth: During late Devonian or early Carbonifer- 

 ous times derivative species from primitive freshwater 

 elasmobranchs — rarely from other groups of fishes — be- 

 came either anadromous in habit or ultimately marine, and 

 spread abundantly — so far as present knowledge helps us — 

 along the shores, bays and shallower seas that surrounded 

 the N. Atlantis continent, from W. Russia to Canadian, 

 Wisconsin and lowan shores. But in the early Permian 

 period some widespread and highly destructive agency or 

 agencies so operated as to obliterate these largely or wholly; 

 and not till Jurassic times did a reinvasion of the sea by 

 more specialized elasmobranchs, and such ganoids as the 

 specializing pycnodonts, take place. 



Sixth: When such connection, as is indicated under the 

 fourth caption, had been made all of the primitive mailed 

 fishes had already been obliterated, and only taper, fairly 

 lithe, and scale-covered types persisted. But during mid 

 or late Triassic times these migrated along far-reaching 

 inter-continental freshwater channels of travel, so that they 

 entered S. Africa, India and even Australia. Therefore 

 alike over N. Atlantis and S. Atlantis-Gondwana, Actin- 

 opterygians like Acrolepis, Coccolepis, Atherstonia and 

 Myriolepis, were represented by related species of each of 

 these genera, or by genera of near afl'inity with each other. 



