188 



PALEOZOIC TIME. 



Among Trilobites, there were no Paradoxides, but large numbers 

 of species of Bathyurus, Dicettocephalus, Ag/wstus, Olenus, Conoco- 



Fig. 289, Orthis (Orthisina?) grandseva ; 290, Helicotoma uniangulata ; 291, Ophileta levata ; 

 292, Holopea dilucula; 293, 295, Orthoceras primigenium ; 294, 0. laqueatum ; 296, 297, Le- 

 perditia Anna; 298, several shells of the same, natural size. 



ryphe, etc., genera that began in the Primordial, and some also of 

 the genera Asaphus, Illcenus and others, which became prominent in 

 the succeeding period. Fig. 800 represents the pygidium, and 299, 



Figs. 299-302. 

 301 



W 



Figs. 299, 300. Bathyurus Saffordi ; 301, Bathyurellus nitidus ; 302, Amphion Barrandei. 



part of the cephalic shield of a Bathyurus ; Fig. 801, a species of 

 Bathyurellus ; 302, the pygidium of an Amphion. 



The Ostracoids, small Crustaceans that have the body concealed in- 

 side of a bivalve shell, in form somewhat like that of a clam, were 

 abundant. Fig. 298 represents several of one of the species ; and 

 296, a side view of the same, enlarged. In the existing seas, the 

 species are from a twentieth to a fourth of an inch in length ; while 

 many of those of the Silurian rocks are between a third and half an 

 inch. The shells are so abundant, in the shale of some localities, as 

 completely to cover the surfaces of the thin lamina?. 



Characteristic Species. 



1. Calciferous Epoch. 



Protozoans. — a. Sponges. Archceocyathus Minganensis B. occurs at the Min- 

 gan Islands, in the lower part of the Calciferous; also Triclwspongia sericea B. ; both 

 of these species appear to contain siliceous spicules. 



