PALEONTOLOGY 



297 



visions of geological time some one cla.'^^s of animal.-^ was espe- 

 cially numerous in species, and was evidently the dominant 

 group of animals through that period. Tlie different ages are 

 therefore , spoken of in terms of the ])revailing life. Thus, the 

 "Silurian Age" is known as the age or era of invertebrates; 

 the " Devonian," as the age of fishes. In the same way we 

 have the "Reptihan Age," the "Mammalian Age," according 



