212 NORTH STAFFORDSHIRE COAL FOSSILS. 



stand up in front of the dorsal fins. Some of these are 

 smooth, as those of the dog-fish (Spinax Acanthias) : others 

 have the lateral edges of the spine serrated (as Myliobates) : 

 many of them are of a formidable character, and all of 

 them are calculated to enable their possessors to defend 

 themselves against the attacks of an assailant. 



The Placoids of the ancient Carboniferous seas must, 

 judging from the remains found, have attained a large 

 size. Like their modern representatives they too were 

 armed with spines which far exceeded in size those borne 

 by fishes of the present day. The teeth of these ancient 

 fishes were of a character no less formidable, some of them 

 being suitable for crushing and others for piercing and 

 cutting. Owing to the cartilaginous nature of the skeleton, 

 it is only teeth and fin-defences which are usually found 

 in a fossil state. The spines were placed upon the dorsal 

 margin of the fish to which the membrane of the fin was 

 attached. They present many varieties of form as well as 

 of surface ornament. One fish (Orthacanthus) had a long 

 cylindrical spine eighteen inches or more in length, its 

 under side armed with a double row of thorn-like barbs. 

 Others had large bony spines ribbed longitudinally (as 

 Ctenacanthus), or elegantly ornamented by lines arranged 

 in a sort of zig-zag fashion (as Gyracanthus). The ends of 

 many of these spines are frequently found rounded and 

 worn. The inference to be deduced from this is, that these 

 fishes frequented the more rocky parts of the sea, the ends 

 becoming worn by rubbing against the rocks.* 



At the present time many of these remains are enshrouded 

 in mystery. Our knowledge of the relationship of the spines 



* Quar. Jour. Geol. Soc., vol. ix., p. 281. 



