CARBONIFEROUS AGE. 



301 



Under Vertebrates, there were only Fishes and Reptiles. The 

 Fishes were either Ganoids or Selachians ; and the latter embraced 

 large numbers of the Cestraciont kind, having great bony plates in 

 the mouth, for mastication. Fig. 600 represents, natural size, one 

 from a large species, of the genus Cochliodus, from Illinois. The posi- 



Figs. 600, 600 A. 



Teeth of Cestraciont Sharks. — Fig. 600, Cochliodus nobilis ; 6^0 A, C. coatortus (x %)• 



tion in the mouth is shown in Fig. 600 A, representing, one third 

 the natural size, the jaw of a foreign species. The teeth of other 

 sharks, called Hybodonts, are shown in Figs. 601 to 603. These also 



Teeth of Sharks. — Fig. 601, Carcharopsis Wortheni ; 602, Cladodus spinosus ; 603, Orodus mam- 



millaris. 



were numerous. Large fin-spines of some of the Sharks have been 

 found in the rocks, one of them eight inches long. 



The class of Reptiles is represented by Amphibians, the earliest 

 kind known. The relics are tracks. A reduced view of a slab from 

 near Pottsville, Pennsylvania, is shown in Fig. 604. There is a suc- 

 cession of six steps, along a surface little over five feet long : each 

 step is a double one, as the hind-feet trod nearly in the impressions 



