Handbook of Paleontology 365 



suture lines. Trilobites had already begun to decline in 

 the Silurian and this decline is more marked in the De- 

 vonian. They are far from rare, however, but lack the 

 variety they previously had. There are new species of 

 Silurian genera, Phacops, Homalonotus (Dipleura) 

 Lichas, Odontocephalus etc. being among the common- 

 est genera. One of the largest and most striking forms 

 characteristic of the Devonian is the genus Terataspis. 

 Other crustaceans have had notable development in this 

 period, among them the phyllocarids abundant in the 

 Middle and Upper Devonian. Eurypterids attained 

 their greatest size during Devonian time, and some of 

 them were actually gigantic reaching lengths of six to 

 eight feet. Genera represented {Eurypterus, Stylonurus 

 and Pterygotus) are the same as in the Silurian. The 

 vertebrates are one of the most characteristic features 

 of the Devonian and because of the great development 

 of the fishes this period has been termed the "Age of 

 Fishes." Fishlike ostracoderms are present {Cephalaspis, 

 Pterichthys, Bothriolepis etc.). True fishes are pres- 

 ent in great variety. Sharks are represented by such 

 forms as Cladoselache. Lung fishes (Dipterus, Scau- 

 menacia) are an important element in this fauna; ar- 

 mored fishes or arthrodires are represented by such forms 

 as Coccosteus and Dinichthys. The ganoids (Holopty- 

 chius, Eusthenopteron) are the most advanced fishes of 

 the period. While the fish fauna is rich and varied and 

 each group has many representatives, the forms are 

 mostly very strange and curious and of a primitive char- 

 acter. Our modern bony fishes (teleosts) are entirely 

 absent. Amphibians, representing the lowest air-breath- 



