CCELENTERATA. 



255 



Fig. ^2^b.^-Astr€Ba rotulosa. West Indies. 



The main kinds of reefs are fringing, where the reef is 

 close to the shore ; barrier, where there is a channel be- 



Fia. 206.— Cell of Madrepore Coral, 

 . magulfied. The cnp-Uke depres- 



siou at the top of a coral skeleton 



is called calicle. 



Fig. 20T ^Fragment of Red Coral (GoraU 



lium ntbrum), showing living cortex 

 and expanded Polyps. Mediterranean. 



