POTSDAM PERIOD. 193 



Articulates. — Crustaceans : Trilobites. — Over forty American species of 

 Trilobites of the Calciferous epoch have been described. They belong to the 

 following genera : — Dicellocephalus, Bathyurus, Arionellus, Menocephalus, Cono- 

 cephalus, Amphion, Agnostus, Cheirurus, and Asaphus. They are for the most 

 part the same that characterize the Potsdam, but the genus Paradoxides is 

 wanting, Dicellocephalus and Bathyurus are more numerous in species, and 

 Agnostus, Cheirurus, and Asaphus are new additions to the tribe. Asaphus 

 and Cheirurus have their fuller development later in the Silurian. 



Fig. 261 represents the Bathyurus Saffordi B., a common species ; a, the gla- 

 bella, b, the pygidium. Some of the other species are Agnostus Americanus B. 



Fig. 261. 



Bathyurus Saffordi. 



(Fig. 259 A represents a foreign species of this genus), A. Canadensis, Dicelloce- 

 phalus magnificus B., a species eight or nine inches long, Arionellus cylindricus 

 B., Bathyurus capax B., Cheirurus Apollo B., Asaphus illsenoides B., all of which 

 occur in the Quebec group, which has afforded in all thirty-six species of Trilo- 

 bites. Phillipsburgh, C.E., and the Mingan Islands have afforded other species 

 of the genera Bathyurus, Amphion, Asaphus, and Menocephalus. 



Ostracoids. — Besides Trilobites, there are the earliest of the bivalve Crusta- 

 ceans, — very small species having the body enclosed in a bivalve shell somewhat 

 like a clam-shell, whence the name Ostracoid. Fig. 260, Leperditia Anna, from 

 St. Ann's, Canada, side-view ; 260 a, same, in profile ; 260 b, a group of the same 

 in the rock, natural size. 



3. Species of Wide Range. 



The following species continue from the Potsdam epoch into the Calciferous : 

 —Lingula acuminata, Ophileta compacta, Archeocyathus Minganensis. 



According to the latest investigations, the Calciferous and Chazy epochs are 

 wholly distinct in life. The Orthoceras laqueatum (fig. 258), referred to the 

 Calciferous, is suspected to be exclusively a Chazy species ; the specimen from 

 which it was described as Calciferous was of uncertain locality. 



2. European. 

 The Primordial life of Europe was quite similar to that of Ame- 

 rica. The rocks contain sea-weeds (Fucoids) allied to Palaeophycus. 

 The lower sandstones are penetrated by the burrows of sea-worms 

 (Scolithus). Graptolites occur in Sweden in the upper slates ; and 

 the shells of Lingulee are in so great numbers as to give the name 



H 



