GLASS-SPONGE COLONIES OF THE DEVONIAN 



31 



ontogeny. In a progressed species the preliminary phases may be 

 reduced by acceleration and even suppression but they are usually 

 determinable; that is, a species of Hydnoceras (cf. H. WalcoUi 



Fig. I 



Fig. 2 



Fig. 3 



Fig. 4 



Fig. s 



Fig. 6 



Fig. 7 



Figs. 1-3. — The typical or radicle form as expressed by (i) Cyathodictya and 

 (2, 3) Dicyospongia. 



Fig. 4. — The development of the Prismodictya faces. 



Figs. 5-7. — The Prismodictya type with inception of Hydnoceras tufts. 



Clarke) will show over its initial surface, first the smooth and then 

 the prismatic and tufted development, and even in its mature 

 and final expression, decided development of the concentric rings. 



