OP CREATION. 65 



crescent-shaped buckler. It has been supposed by 

 Professor Agassiz that the singular shape of the head 

 served as a sort of defence to this animal in case of 

 attack ; and one can readily imagine that the soft sub- 

 stance of the orthoceratites, probably the largest and 

 most formidable of its enemies, would be injured by 

 any attempt to swallow so singular and knife-like an 

 animal as the one before us. 



Like many, and indeed most of the species belong- 

 ing to the Ganoid order of fishes, and common in 

 the older rocks, the bones of the head, and the scales 

 of this strange monster, were composed internally of 

 a comparatively soft bone, but each was coated with 

 a thick and solid plate of enamel, of extreme hard- 

 ness, and almost incapable of injury by any ordinary 

 amount of violence. The detached scales, the buckler- 

 head, and sometimes the complete outline of the ani- 

 mal, have thus been able to resist destruction, and 

 are found in sandy rocks, composed of such coarse 

 fragments that their accumulation would seem to 

 have been accompanied with violence sufficient to 

 have crushed to powder almost any remains of organ- 

 ized matter, and from which, indeed, we never obtain 

 any fragments of shells or other easily injured sub- 

 stances. The remains of this fish have been found 

 in Herefordshire and many parts of Wales, as well 

 as in Scotland, and lately also in Russia; but the ani- 

 mal was strictly confined to the period of the old red 

 sandstone, though it is not easy to guess what may 

 have been its habits, in what depth of water it pre- 

 ferred to live, or in what way it obtained its food. 



The Pterichthys (fig. 23) is even more strikingly 

 different from any existing species of animal than the 



