DEVONIAN ERA. 



07 



hard enamelled scales ; are frequently furnished with fin- 

 spines or external defences ; and are, many of them, of 

 forms so widely differing from those of existing seas, that 

 they have not unfrequently been mistaken for reptiles, for 

 crustaceans, or even for huge water -beetles ! And yet, 

 when closely examined, and their affinities made out, there 

 is nothing about them either abnormal or nondescript. 

 The more familiar forms are the ceplialaspis, or " buckler- 

 head," so called from the shield -like shape of the bony 

 head-plate, which consists of a single piece ; the ptericli- 

 tkys, or "wing-fish," having the body encased in a box- 

 like covering of bony plates, and furnished with two w T ing- 

 like appendages for swimming ; the coccosteus, or " berry - 



1, Cocccsteus; 2, Pierichthys ; 3, Cephalaspis. 



bone," similarly encased, and having the surface of the plates 

 covered with minute berry-like tubercles ; the ucantlwdians 

 (diplacanth, cheiracanth, &c.), having for the most part their 

 fins armed and supported by bony spines ; the dipterus, or 



