762 



THE WONDERS OF GEOLOGY. Lect. VIII. 



the membrane which elsewhere surrounds them. From 

 the large size of the plate which covers the head, its 

 lamellar structure, and crescent -like form, terminating 

 in two horns or points, detached specimens were formerly 

 supposed to belong to trilobites or some other crusta- 

 ceans. The whole body is covered with scales, and 

 those of the head are highly ornamented with radiated 

 markings. The tail is a long pedicle supporting a fin.* 

 Numerous remains of these fishes have been found in the 



Lign. 172. — Cephalaspis Lyellii. 

 Lateral view, showing the produced dorsal lobe of the tail. 



Devonian strata of England, Scotland, and even Russia. 

 Mr. Miller states they are principally restricted to the 

 middle group, the cornstone and marls {ante, p. 752). 



Pterichthys.^ The fishes of this genus are distinguished 

 by two wing-like lateral appendages, which, like the spines 

 of the common Bull-head ( Cottus gobio), were weapons of 

 defence. The head and anterior part of the body are 

 covered with large angular tuberculated scutcheons. There 

 are two eyes, which are placed in front of the lateral spines. 

 Five or six species occur in the British strata ; all very 



* Medals of Creation, p. 645. 



f Winged-fish. Medals of Creation, p 



