ACTINOZOA. MADREPORARIA. 



57 



Columella absent. Tabulae extending across the central 

 part of the visceral chamber. Dissepiments form a peri- 

 pheral vesicular zone. Budding calicular. Silurian to 

 Devonian. 



Lithostrotion (fig. 13). Compound, massive or den- 

 droid. When massive the corallites are prismatic, when 

 dendroid they are cylindrical. Septa well developed, 

 alternately long and short. Columella styliform, laterally 

 compressed. Peripheral zone of dissepiments narrow. 

 Tabulae wide, occupying the centre of the visceral 



d w c t d 



FIG. 13. Lithostrotion basaltiforme, Carboniferous Limestone. A. Hori- 

 zontal section of a- single corallite, x 2. B. Vertical section, x 5; 

 c, columella ; t, tabulae ; d, dissepiments ; w. theca. 



chamber. Septal fossulae well marked. Carboniferous 

 Limestone. 



Omphyma. Simple, turbinate. Septa numerous, 

 alternately long and short, but extending only a short 

 distance into the visceral chamber, the central part being 

 occupied by the tabulae. The four primary septa are 

 placed in shallow fossulse. Peripheral zone of dissepiments 

 narrow. The theca gives off root-like processes. Bala to 

 Lower Ludlow. 



Zaphrentis. Simple, free, bilateral ; turbinate, coni- 

 cal or cylindrical, often curved; calyx deep. A well 



