THE DEVONIAN PERIOD 



589 



interpreted as placoderm fishes, later as jawless fishes, and now as 

 a distinct class between the arthropods and the vertebrates. 1 

 Their chief interest lies in their suggestion that the vertebrates 

 sprang -from the arthropods. The ostracoderms bear external 



Fig. 420. Restoration of Cephalaspis, seen from the side. (After Patten.) 



Fig. 421. Reconstruction of the head and trunk of Tremataspis, seen from 

 above. Natural size. (After Patten.) 



resemblances, in the head and trunk, to trilobites and king-crabs, 

 while some of them have caudal fins and fish-like bodies. Because 

 of their fish-like features and the presence of bone cells in the dermal 



1 W. Patten, On the Origin of Vertebrates, with special reference to the 

 structure of the Ostracoderms. International Zool. Cong., Berlin, 1901. On 

 the Appendages of Tremataspis, Am. Nat., XXXVII, 1903, p. 223. On the 

 Structure of the Pteraspida and Cephalaspidce, Am. Nat., XXXVII, 1903, p. 

 827. New Facts concerning Bothriolepis, Biol. Bull. No. 2, 1904, p. 113. 



