196 



STEATIGRAPHICAL GEOLOGY 



Silurian and have many Devonian species : Murchisonia, Pleuroto- 

 maria, Euomphalus, Straparollus, Platyceras, Loxonema, Macro- 

 chilina, and Sellerophon. Besides these Cyclonema, Callonema, and 

 Eunema occur, but die out within the period. Scoliostoma and 

 Philoxene are Devonian only ; Naticopsis and Porcellia appear and 

 range upward. 



Among Cephalopoda the following continue : Orthoceras, 



Fig. 61. GROUP OF DEVONIAN FOSSILS. 



a. Bronteus granulatus. 



6. Bront. granulatus (pygidium). 



c. Calceola sandalina. 



d. Stringocephalus Burtini. 



e. Pleurotomaria aspera. 

 /. Clymenia striata. 



Cyrtoceras, Gyroceras, Poterioceras, Gomphoceras, and Trochoceras. 

 The last genus becomes extinct. The Ammonoidea make their 

 first appearance and are represented by Clymenia, Bactrites, and 

 the Goniatitidae, of which the following genera occur : Mimoceras, 

 Anarcestes, Agoniatites, Gephyroceras, Tornoceras, Mceneceras, Branco- 

 ceras, Beloceras, and Prolecanites. Clymenia is found only in the 

 Upper Devonian. 



Of Pisces, Pteraspis, Cephalaspis, Drepanaspis, Coccosteus, 

 Parexus, and Homosteus occur. 



