SILURIAN ANIMALS. 



319 



Fig. 363. 



IKE 



» , ilillii llSiill^ 



Fig. 367. 



Figs. 363-367.— Silurian Cephalopods: 363. Orthoceras medullare (after Meek). 364. Ormoceras 

 tenuifilum, showing chambers and siphuncle (after Hall). 365. Orthoceras vertebrale (after 

 Hall). 366. Orthoceras rmilticameratum (after Hall). 367. Orthoceras Duseri (after Hall). 



to the straight. The gradual change from the straight through the 

 open-coiled to the close-coiled may be traced. Barrande gives 1,622 

 species of Cephalopods in the Silurian. . . 



