58o 



The Class Ostracophori 



possesses being a number of parallel rods behind the head, 

 homologous with the lateral series of Birkenia. Lasianius is 

 therefore a specialized and degenerate representation of Bir- 



FiG. 365. — Lasianius problemaHcus Traquair. Upper Silurian. (After Traquair.) 



keiiia, differing somewhat as "the nearly naked Phanerosteon 

 differs from other Palmoniscida whose bodies are covered with 

 osseous scales." 



