GLASS-SPONGE COLONIES OF THE DEVONIAN 



33 



Enough however has been given to indicate the degree of mor- 

 phologic specialization displayed by these ^hexactinellids in the 



Fig. 14 



Fig. is 



Fig. 16 



Fig. 17 



Fig. 18 



Fig. 19 



Fig. 14. — The incipient annulated or Ceratodictya stage. 



Fig. 15. — The annulated stage combined with an extreme expression of the 

 prismatic form (Rhabdosispongia) . 



Figs. 16, 17. — Phases of the Ceratodictya stage, Hydnocerina (16), showing 

 departure from the type. 



Figs. 18, 19. — Expressions of two of these phases (Rhabdosispongia and Hydno- 

 ceras) from the Frasnian formation of France. 



Devonian, a condition which must have required ages of time to 

 work out. The Devonian sponge colonies must therefore have had 

 a vast ancestry. 



