LOWER SILURIAN. 



199 



Among Radiates, there were now undoubted Corals (Figs. 317, 

 318), of the class of Polyps, as well as Grinoids (Figs. 324, 325), in- 

 creasing much the diversity and beauty of the flowers of the seas — 

 the only flowers of the Paleozoic world. There were, however, but 

 few Polyp-corals, compared with the number in later periods. Single 

 masses of the coral Columnaria alveolata H. (Fig. 318) occur in the 



Figs. 317-325. 



Radiates. — Fig. 317, Petraia corniculum ; 318 a, Columnaria alveolata ; 319, 320, Chsstetes lyco- 

 perdon ; 321 a, Graptolithus amplexicaulis ; 322, Palseaster matutina ; 323, Taeniaster spinosa ; 

 324, Lecanocrinus elegans ; 325, Pleurocystis filitextus. 



Black River limestone, weighing between two and three thousand 

 pounds. Cystids (Fig. 325) were the most characteristic kind of Cri- 

 noids. They belong in geological history eminently to this early era, 

 reaching in it their greatest expansion. The delicate plume-like 

 forms of life called Graptolites were common (Fig. 321). 



Brachiopods (Figs. 326-340), were yet the most abundant of 

 Mollusks, their shells outweighing and outnumbering those of all 

 other species. But with these there were large numbers of each of 

 the other classes, the Bryozoans, Pteropods, Lamellibranchs (Figs. 

 341-343), Gasteropods (Figs. 344-352) and Cephalopods. 



Multitudes of delicate corals, made by Bryozoans, occur in tho 

 limestone rocks. 



The Trenton species of Brachiopods were mostly of the Orthis 

 family (the genera Orthis, Orthisina, Leptcena, and Strophomena) ; and 

 with these there were species of the Lingula, Discina, and Bhyncko- 



