292 



HISTORICAL GEOLOGY. 



time, nine-tenths of all fishes are Teleosts, but in Devo- 

 nian times all the fishes were Ganoids and sharks, espe- 

 cially the former,, though differing in species and genera 

 from Ganoids and sharks of the present day. But we 

 must give some figures of these strange Devonian fishes 

 before discussing their affinities any further. 



Description of Some Devonian Fishes. The Ceph- 

 alaspis (head-shield, Fig. 208) was a small fish, of very 



FKI 208. 



Fiu. 209. 



FIGS. 208, 209. Devonian fishes Placoderms : 208. Cephalaspis Lyelli. (After Nich- 

 olson.) 209. Pterichthys cornutus. (After Nicholson.) 



curious shape, with mouth beneath the head-shield. The 

 Pterichthys (winged fish, Fig. 209) was so completely in- 

 cased in bony plates that it must have swum mainly by 

 means of its wing-like anterior fins. The mouth was also 

 beneath. The Coccosteus (berry-bone, Fig. 210) was cov- 

 ered with bony plates in front parts, but the tail was 

 usable for locomotion. The Dinichthys (Fig. 211) was a 



