THE DEVONIAN PERIOD 



583 



had cutting edges that closed shears-like, much like the mandibles 

 of a turtle. The front part of the body was encased in heavy 

 plates. Related types of less formidable aspect were also known. 

 The sharks left abundant relics in the form of teeth and fin spines, 

 some of the latter reaching a foot in length. In both classes, the 

 devices of warfare make up nearly the whole record, and this 

 doubtless correctly implies the state of affairs of the vertebrate 

 kingdom. 



\M 



f r -m nil 



Fig. 418. Macropetalicthys sullivanti Newb., plates on the head of a charac- 

 teristic Onondagan fish. 



Corals were affected adversely by the increased turbidity of 

 the waters, but continued in diminished importance, especially in 

 the western part of the interior. Crinoids were abundant locally, 

 for certain beds of limestone are composed largely of their remains. 

 Most of the genera were the same as those of the Onondaga epoch, 

 but there were some new ones foreshadowing the remarkable 

 development of the crinoids in the Mississippian period. The 

 climax of the brachiopods was somewhere about this time. In- 



