CCELENTERATA. 



255 



>. Astrcea 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, 

 magnified. The cup-like depres- 

 sion at the top of a coral skeleton 

 is called calicle. 



FIG. 20T Fragment of Red Coral (Coral- 

 Hum rubrum), showing living cortex 

 and expanded Polyps. Mediterranean. 



