52 ACTINOZOA. MADREPORARIA. 



patharia, in which the skeleton consists of an internal 

 horny rod ; these are also not found fossil ; (3) the 

 Madreporaria, including the well-known stony corals, in 

 which the skeleton is calcareous, these are very abundant 

 as fossils. 



SUB-ORDER. MADREPORARIA. 



There is a sclerodermic skeleton, consisting of carbo- 

 nate of lime, secreted by the ectoderm of the lower part 

 of the polyp. The entire skeleton is spoken of as the 

 corallum] it may be simple or compound, in the latter 

 case each individual is termed a corallite. 



In a typical simple coral, the skeleton has a more or 

 less conical form, the base of the cone is depressed and 

 termed the calyx, in it the polyp was placed. The wall 

 bounding the corallum is known as the theca (fig. 11 A, d) 

 sometimes there is outside this, another calcareous layer, 



FIG. 11. A. Diagram-section (horizontal) of a simple coral, a, colum- 

 ella; 6, primary septa; c, pali ; d, theca; e, dissepiments. 



B. Portion of a horizontal section of Cyathophyllum murchisoni, 

 Carboniferous Limestone, showing the septa composed of a thin 

 middle layer with a thicker layer on each side (magnified). 



the epitheca. The whole space enclosed by the theca is 

 termed the visceral chamber; this is divided up by 



