16 



COPE 



Fig. 2. — Bothriolepis canadensis Whiteaves; bead and carapace, Iroin above, and bead from 

 below. From the De-vonie of New Brunswick. From Whlteaves. (Antiareha.) 



The Ostracophori are the oldest known Agnatha, and 

 the oldest Ostracophori have been found in the Siluric, in 

 the Salina of Pennsylvania and the Ludlow rocks of Eng- 

 land, which have produced Heterostraca. The Osteostraca 

 appear first in the Ludlow beds in England, and extend to 

 the Lower Devonic (Old Red Sandstone). They appear 

 first in America at the latter horizon in New Brunswick. 

 The Antiarcha commence in the Old Red, and continue 

 into the Chemung of the Lower Carbonic system. The 

 principal genus of the Heterostraca is the Pteraspis; of 

 the Osteostraca is the Cephalaspis; and of the Antiarcha 

 is the Pterichthys. (Fig. 2.) 



Subclass II.— CYCLIiE. 



Median diphycercal caudal fin ; brain case 



not segmented ; Saccocephala. 



The order Saccocephala is the only one known to per- 



