26 CORALS 



of a solitary imperforate coral. For this purpose the 

 English cup-coral, CcuyophyUia s}nithii, may be taken 

 (Figs. I, 2, 3, 4). 



The wall of the cup, which is approximateh' circular in 

 section, is called the " Theca," and passing radialh' inwards 



Fig. 2. — A group of four specimens of Carynphyllia smiihii and one specimen 

 (marked by a black ring) of Balanophyllia regia found at low water at Ilfracombe. 

 Nat. size. 



towards the centre of the cup are a number of vertical 

 partitions which are known as the " Septa." From the 

 centre of the bottom of the cup there rises up into the 

 cavity a spongy dome-shaped calcareous mass formed of 

 some ten to twenty thin twisted plates, called the " Colu- 

 mella." From the outer border of the columella a number 

 of vertical plates similar to the septa, but more sinuous in 



