42 



DEVONIAN ERA. 



FIG. 22. 



FIG. 23. 



Cephalaspis Lyellii, as seen from above, and from the side. 



of its having been as weak in motion as 

 it is strong in structure. In the coccos- 

 teus, the outline of the body is of the 

 form of a short thick coffin, rounded, 

 covered with strong bony plates, and 

 terminating in a long tail, which 

 seems to have been the sole organ of 

 motion. While the tail establishes 

 this creature among the vertebrata and 

 the fishes, its teeth, chiselled, as it 

 were, out of the solid bone of the jaw, 

 like the nippers of a lobster, remind 

 us of the invertebrate part of cre- 

 ation. The pterichthys has also strong 

 bony plates over its body, arranged 

 much like those of a tortoise, and has 

 a long tail ; but its most remarkable 

 feature, and that which has suggested 

 its name, is a pair of narrow wing-like 

 appendages attached to the shoulders, 

 which the creature is supposed to have 

 erected for its defence when attacked 

 by an enemy. 



The group of ganoids seem to have 

 Pterichthys cornutus. been the police of their day, possess- 



