286 



PALEOZOIC TIME. 



4. Vertebrates. — In the Devonian rocks of Great Britain and Europe, large 

 numbers of species of fishes have been found. 



Among the Placoderms, which occur in the two lower divisions, there were two prom- 

 inent groups. Fig. 566, Pterichtkys Milleri Ag., represents one; and Fig. 567, Coccos- 

 teus decipiens Ag., represents the other. Also Fig. 568, Cephalaspis Lyellii Ag.; Figs. 

 Figs. 568 a, 568 b, scales of the same : a type sometimes referred to the Placoderms. 

 Of other Ganoids, there were, Fig. 569, a Holoptychius ; Fig. 569 a, scale, id. ; Fig. 570, 

 Dipt ems macrolepidotus, Sedgw. & Murch. 



Figs. 568-570. 



Ganoids. — Fig. 568, Cephalaspis Lyellii (X%); 568 a, b, scales, id.; 569, Holoptychius (XX)', 

 569a, scale, id. ; 570, Dipterus macrolepidotus (X Yz) ', 570 a, scale, id. 



Species of Pterichtkys, Diplopterus, Glyptolepis, Dendrodus, Platygnathus, etc. Holo- 

 ptychius (Fig. 569) belongs to the Upper Devonian only, and also to the early Carbonif- 

 erous. Pterichtkys (Asterolepis) Asmusi Ag., whose remains occur both in Russia and 

 Scotland, is supposed to have been twenty to thirty feet long. 



3. GENERAL OBSERVATIONS ON THE DEVONIAN AGE. 

 American Geography. — I. General features. — The Archaean area, 

 which had been enlarged on the north by successive additions from 

 emergence during the Silurian, continued expanding in the same direc- 

 tion, during the Devonian ; and, at its close, the State of New York 

 formed a part of the land. For, as seen on the map, p. 165, the rocks 

 which succeed one another reach less and less far northward, indicating 



