56 ACTINOZOA. MADREPORARIA. 



together. Dissepiments fairly abundant. Lias to Upper 

 Greensand. 



Holocystis. Compound, massive, convex ; calyces 

 polygonal. Columella small, styliform. Corallites united 

 by their walls or by costae. The four primary septa are 

 much better developed than the others. Tabula3 present. 

 Lower Greensand. 



Thecosmilia. Compound, branching or rarely almost 

 massive. Multiplication by fission. Margin of calyces 

 irregular. Columella rudimentary or absent. Septa, 

 strong, dentate, and more or less exsert. Dissepiments 

 abundant. Epitheca thick and folded, but often not 

 preserved. Lias to Corallian. 



Section II. Rugosa. 



The corallum is compact and imperforate, and gene- 

 rally bilaterally symmetrical. The septa are usually in 

 multiples of four, there being four primary septa. In 

 most cases the septa are of two sizes, the longer alternating 

 with the shorter. Dissepiments are abundant and tabulae 

 are often present. One or more septal fossulae usually 

 occur. There is no coenenchyma. 



Cyathophyllum. Simple or compound ; branching 

 or massive. Septa numerous, of two sizes, alternating, 

 the longer giving rise to a false columella. Tabulae small, 

 occupying the central part only of the visceral chamber. 

 Dissepiments form an extensive peripheral zone of vesi- 

 cular tissue. Bala to Carboniferous Limestone. 



Acervularia. Compound, massive ; corallites with 

 two walls, the outer polygonal, frequently hexagonal, the 

 inner circular. Septa well developed, reaching the centre. 



