Geographic AND Geologic Relations 415 



genera that still Include living species is as follows : Arms 

 is known from freshwater strata of Mid-Eocene to Mid- 

 Oligocene age, and extends from Brazil to England and 

 Germany. Amiiiriis is recorded from Lower Miocene rocks 

 of Western Canada, and is now abundant from Massachus- 

 sets south to Texas and even Guatemala. Clarias, Hetero- 

 hranchiis, and Silurus are found as Pliocene fossils in the 

 Siwalik hills of India, but the first of these still exists from 

 Senegal and the Nile eastward through Syria and Siam to 

 Java, Borneo, and the Philippines. The second nearly 

 duplicates Clarias, while Silurus extends from the Rhine 

 eastward through Afghanistan to Formosa, Cochin China 

 and the East Indian Archipelago. Macrodes and Rita, 

 also fossil in the lower Pliocene of the Siwalik Hills, is 

 represented now by one species from Asia Minor, and fully 

 twenty from India and the East Indian Archipelago. 



Such facts furnish collective proof that the Siluridae 

 must have had wide distribution, by some fairly continuous 

 landways, from America to the East Indian Archipelago, 

 and this not later than Oligocene time. Finally it should 

 be again emphasized that the Loricaridae and Aspredinidae 

 are clearly highly specialized offshoots from more simple 

 Siluridae, that are now wholly confined to rivers — often 

 to mountain streams — of Central and S. America. It seems 

 by no means unlikely that these have reached the high alti- 

 tudes where they at present live, not by skilful and vigorous 

 leaps over rapids and cataracts as do salmon now, but that 

 they originally existed at much lower levels, and when 

 steady or sudden elevation of Andean and other mountain 

 ranges took place, up to the point of attaining their highest 

 positions, ancestors of these families participated in the 

 general uplift, and yet survived. For C. Darwin {260: 

 232), A. Agassiz {261) and many others since have shown 

 that relatively recent but steady elevation of the Andes 

 has gone on through thousands of feet. 



The gradual reduction in size, and ultimate disappear- 

 ance of scales, among species of such genera as Schizopy- 

 gopsis, Gymnocypris, Mola, Paraphoxinus, and Nemachilus, 

 in the succeeding family Cyprlnidae, might well indicate 

 that the now scaleless Siluridae developed from one or 



