LOWER HELDERBERG PERIOD. 



253 



II. Life. 



This period was prolific in species, beyond even the Niagara or 

 Trenton : over 300 have been named and described. Among them 

 there are the same families and genera as in the preceding periods, 

 but with some marks of progress in new forms, and with a range 

 of species almost completely distinct. Yet it has been noted as a 

 striking fact that very many of the species of the Niagara period 

 have their closely-related or representative species in the Lower 

 Helderberg. 



1. Plants. Figs. 417, 418. 



Limestone strata seldom contain remains of 

 plants ; and, accordingly, little is known of the 

 botany of the Lower Helderberg period. 



2. Animals. 

 Many Corals and Crinoids occur in the beds, 

 and some of the latter are of remarkable size 

 and beauty, — as the Mariacrinus nobilissimus, 

 and other species of the same genus. The last 

 of the Hali/sites, or Chain-coral, existed in this 

 period, and a few species of Cystids (figs. 417, 418). 

 Brachiopods still take the lead in numbers of all 

 other kinds of life. In the Water-lime one 

 layer is full of the little Tentaculites ornatus (figs. 

 431, 432). Among the Trilobites the Dalmania 

 pleuroptyx (fig. 244 C) is a common form. 

 Quite a different form of Crustacean appears for 

 the first time in these rocks. It is represented 

 in the Eurypterus remipes Dekay (fig. 433). Un- 

 like Trilobites, it has large jointed arms, and a 

 body which resembles that of the Sapphirina 

 and Caligus groups of modern Crustaceans. (Figs. 175, 176 repre- 

 sent the female and male of a Sapphirina from our own seas. See 

 page 151.) 



Characteristic Species. 



1. Radiates. — (a.) Polyps. — Among Corals there are species of Zaphrentis, 

 Favosites, Stromatopora, Halysites, Syringopora, Chsetetes. (b.) Echinoderms. — 

 Group of Cystideans : Fig. 417, Apiocysiis Gebhardi, found in the Lower Pen- 

 tamerus ; fig. 418, Anomalocystis, a remarkable species from the same rock.' In 

 the group of Crinideans there are species of the genera Mariacrinus, Platycrinus, 

 Edrioerinus, Aspidocrinus, etc. 



Cystideans. — Fig. 417, 

 Apiocystis; 418, Anoma- 

 locystis. 



