560 



HISTORICAL GEOLOGY. 



LIFE. 



Plants supposed to be related to the Equiseta occur in tlie Lower Hel- 

 derberg sandstone of Michigan; the species is Annularia Romingeri of 

 Lesquereux. Another species from the same region is the Psilophyton cor- 

 nutum Lesq. 



The beds abound in animal fossils, the number of species even exceeding 

 those of the Niagara group. Species of the BeceptacuUtes group occur of 

 large size. Crinoids were rather numerous, and some of them, like Melo- 

 crinus nohilissimus, were remarkable for their size and beauty. Two Gystoids 

 of the period are shown in Figs. 805, 806 ; the stems of each were fitted for 



Bbaohiopods. — Fig. 807, StrophoneDa radiata ; 808, a, RhynchoneUa veBtricosa ; 809, a, Pentamerus galeatus ; 

 810, a, P. pseudo-galeatus ; 811, Eatonia singularis ; 812, Meristelia sulcata ; 818, Orthis varica ; 814, Spirifer 

 macropleurus ; 815, Meristelia laevis. 807, 808, Hall ; the others. Meek. 



anchoring in the mud of the sea bottom. The last of reported Gh'aptolites 

 occurs in the rocks. Polyp-corals were not largely represented; Favosites 

 Helderbergice appears to have been the most common kind. Hydroid Corals 

 and Bryozoans were numerous. Tentaculites were common, and one kind, 

 T. elongatus, from the Shaly limestone, was three inches in length. 



Some of the common Brachiopods are represented in Pigs. 807 to 815. 

 Among them Pigs. 809, 809 a, are of Pentamerus galeatus, of the Lower 



