DEVONIAN AGE. 



285 



called Clymenia. Fig. 562, Goniatites retrorsus ; Fig. 563, Clymenia SedgwicJcii. The 

 shell in Clymenia has the form of the Ammonites, but, unlike the Goniatites and Am- 

 monites, the siphuncle is ventral instead of dorsal; and the septa have no distinct 

 dorsal lobe on the medial line, as shown in Fig. 563 a. 



3. Articulates. — There were. a number of species of Trilobites, though fewer than 

 in the Silurian: the genera Phacops and Dalmanitas were common. Homalonotus had 

 European species; and one, H. armatus, had spines on the head, and two rows along 

 the back. This spinous feature appears to have reached its maximum in the Devonian 

 Aryes armatus (Fig. 564), and some species of Acidaspis. 



Figs. 564, 565. 



Crustaceans. — Fig. 564, Arges armatus; 565, Slate containing Cypridina serrato-s!;riata, natural 

 size ; 565 a. same, enlarged. 



Minute Ostracoids, referred to the genus Cypridina, abound in the Cypridina slate, 

 giving this name to the beds ; Fig. 565 represents a portion of the slate or shale, with 

 the shells of the C. serrato-striata on its surface, natural size, and 565 a, one of them 



Figs. 566, 567. 



Placoderms. — Fig. 566, Pterichthys Milleri (x %); 567, Coccosteus decipiens (x %.). 



oolarged. There were also other Ostracoids. The Prcearcturus gigas Woodward, from 

 the Old Red Sandstone of Herefordshire, is a gigantic Isopod crustacean; and Stylonu- 

 rus Scoticus Wd., another from the Old Red of Forfarshire. They must have been over 

 a foot long. 



