528 RADIATES: POLYPS. 



The Sub-Order of Stauracea has the coral simple or 

 compound by budding, and the septa apparently in multi- 

 ples of four. All the species are fossil. It contains Stau- 

 ridae, Cyathophyllidae, Cyathoxonidae, and Cystiphyllidae. 



Wherever circumstances have favored their growth, 

 Coral Reefs and Islands abound in all the hot regions. 

 When a reef is near the shore, it is called a Fringing 

 Reef; when at a distance, a Barrier Reef; and when it 

 surrounds a body of water, an Atoll or Coral Island. 

 The body of water thus surrounded is called a Lagoon. 

 Coral Reefs are in all stages of formation, from those 

 which have just begun to form to those which have grown 

 to the surface of the water, and, having received the de- 

 bris thrown upon them by the waves, have become dry 

 land,* and even the home of man. There are scores of 

 islands in the Pacific which are thus made up of the skele- 

 tons of coral polyps ; and the islands which skirt the coast 

 of Florida the Keys are a reef which has reached 

 and risen above the surface here and there. According 

 to Agassiz, a large part of Florida itself is composed of 

 old coral reefs. There are reefs in the Pacific which are 

 several hundred miles long, and one on the northeast 

 coast of Australia is a thousand miles in length. The 

 reef-forming corals are mainly Astraeas, Mseandrinas, Po- 

 rites, and Madrepores. The frailer corals, those of the 

 Order Alcyonaria, such as the Gorgonias and their allies, 

 adorn the reef as it approaches the . surface of the water, 

 but contribute little to its growth. Only an inch or less 

 of the surface of a growing coral mass is alive, death 

 going on below, growth above. 



The reef corals are essentially of the same composition 

 as limestone or marble, being composed of ninety to 

 ninety-six per cent of carbonate of lime ; the other parts 

 are organic matter, phosphates, fluorides, magnesia, silica, 

 and oxide of iron. 



