198 



PALEOZOIC TIME. 



same rock at Covington, Kentucky, the specimen being a small portion 

 of a frond; and the third (316 F), from near Cincinnati, is a section 

 of a stem resembling that of a Sigillarid or Lepidodendrid, the mark- 

 ings of the surface being the scars left by the fallen leaves. 



Fig. 316 B. 



Fig. 316 C 



Algx. — Fig. 316 B, Buthotrephis gracilis ; 316 C, B. succulosus. Land Plants. — 316 D, Psilo 

 phytum gracillimum ; 316 E, Sphenophyllum primsevum ; 316 F, Protostigma sigillarioides. 



2. Animals. 



1. Trenton Epoch. 



The seas of the Trenton period were densely populated with animal 

 life. Many of the beds are made of the shells, corals, and crinoids, 

 packed down in bulk ; and most of the less fossiliferous compact kinds 

 have probably the same origin, and differ only in that the shells and 

 other relics were pulverized by the action of the sea, and reduced to 

 a calcareous sand or mud before consolidation ; while others may be of 

 Rhizopod origin. 



The same four sub-kingdoms of invertebrate animal life were repre- 

 sented as in the preceding period, by marine species. All the grander 

 subdivisions of the Radiate and Molluscan sub-kingdoms had their 

 species. The Articulates were still confined to the inferior aquatic 

 classes of Worms and Crustaceans. 



