Summary of Conclusions Reached 523 



Miocene time. As in the case of marine migrants, and 

 owing to like constant agitation of water with resulting 

 high oxgenation of blood, the air-bladder inherited from 

 ganoid fish ancestors has become small or is even wholly 

 absorbed. 



The Siluridae, with derivative families Loricaridae and 

 Aspredinldae, that include fully 150 genera and 1200 spec- 

 ies are lake and river dwellers chiefly of subtropical and 

 tropical regions. But while the genus Arius in its early 

 Eocene and Oligocene history was also, some species grad- 

 ually migrated seaward, so that the modern species as well 

 as the genera Galeichthys and Felichthys are marine. The 

 same history attaches to the group Plotosidae of East Asia. 

 Genera of the aberrant families Loricaridae and Aspredin- 

 ldae inhabit like localities and show all stages of reduction 

 up to absorption of the air-bladder. The writer therefore 

 concludes from the evidence furnished by the above families 

 and derivatives from them, that all teleosts have evolved 

 from, and are descendants of, freshwater ganoid ancestors, 

 and so that the most primitive teleostean families — which 

 are also the families richest In species — are the existing 

 soft-finned ones. Amia Is regarded as one of the nearest 

 existing genera to the required ancestral form of some. 



From a different but related ancestor like Megahiriis 

 of Kimmeridgean age, Elops and Megalops seem to have 

 started and migrated seaward. But the young and even 

 adults still enter rivers freely. 



From forms intermediate between Eugnathidae and 

 Amiadae the Albulidae and Osteoglossidae arose, the latter 

 still keeping to swamps and lakes, the former marine. The 

 relations of Istieus, Alhiila, and Pterothrissus amongst Al- 

 bulidae; also of Dapedoglossus, Osteoglossuvi, and others 

 amongst Osteoglossidae, are traced geographically. 



The Notopteridae, Pantodontidae, Phractolaemidae, 

 and Hyodontldae, show interblended affinities with Osteo- 

 glossidae, and doubtless had common ancestral origin. Dis- 

 tribution of these over Gondwana land is traced. 



Thrissops, Chirocentrites, and Chirocentriis polyodon 

 of Sumatran freshwater strata, are all early forerunners 

 of the types that migrated seaward, and there originated 



