THE DEVONIAN PERIOD 



365 



FIG. 377. A large trilo 

 bite (Dalmanites) of the 

 Devonian period. 



of complexity and diversification, as 



regards their internal structure. The 



early Paleozoic types had shells which 



were divided into chambers by a series 



of flat or saucer-shaped partitions. In 



some of the Devonian species these 



partitions became slightly folded at 



their edges, and the suture lines on the 



outside of the shell show corresponding 



lobes or angles. These simpler varie- 

 ties are called goniatites (Fig. 378). It 



will be interesting to compare them 



with the complex forms of later times. 

 Profusion of fishes. Of all the new 



developments among the Devonian 



animals, none is more important than 



the apparently sudden rise of the fishes. From meager 



beginnings in the previous periods they spread out into 



many different 

 types, and be- 

 came so abundant 

 that the Devonian 

 is sometimes 

 called the Age of 

 Fishes. Being 

 among the earliest 

 to make their ap- 

 pearance, it is but 

 natural that the 

 Devonian repre- 

 sentatives of the 

 class should have 

 been primitive in 

 their structure. 



FIG. 378. A coiled cephalopod (Goniatites) in which Lowest ' m the 

 the sutures are slightly folded. Scale are the Os- 



B. & B. GEOL. 21 



