EXTINCT ANIMALS 



shire and Herefordshire, also in Scotland. The 

 stone is quarried for road mending, and great 

 quantities of specimens have been found, though 

 no other fossils occur with these fish-heads. 

 It used to be imagined that this rock was the 

 deposit of a great fresh-water lake, but that is 

 not likely, since Pteraspis heads are found with 

 marine shells in the rocks of Galicia. The 

 curious thing is that although occasionally a 



Fig. 186. — Photograph from the original specimen of Cephalas- 

 pis lyelli, preserved in the Natural History Museum, one- 

 third the natural size, showing tlie saddler's-knife-shaped 

 head and the scale-bearing body. 



tail or body of Cephalaspis covered Avith scales 

 and provided with fins has been found attached 

 to a head-shield, as in Fig. 186, yet the body 

 or tail of Pteraspis remains unknown. The only 

 specimen showing any trace of the hinder 



2n8 



