344 



and there in patches over a surface of dead coral rock or 

 sand. In simiLar places about other regions species of 

 Porites are most common." Several species of corals grow 

 at the month of the Rio della Plata. 



Porites liniosa flourishes in muddy water and Astn^ea 

 bowerbnnki does not seem to mind mud or sediment, or even 

 muddy brackish water, growing on, and incrusting the 

 stones at the mouth of the Mangrove Creek, xlustralia, these 

 stones being covered with mud and slime, and washed over 

 twice in the twenty-four hours by muddy, brackish water. 

 (Tenison-Woods.) A common Red Sea coral, Stylophora 

 pistillata, is recorded by Milne Edwards and Haime from the 

 intensely salt and dense waters of the Dead Sea. 



The simple corals (Caryophyllia, etc.) are chiefly found on 

 muddy bottoms, often attached to a shell or other object 

 restinir on the mud. The bathvmetric distribution varies 

 from shallow water to a thousand fathoms or more. This 

 method of life corresponds well with what is known of the 

 Palgeozoic Tetracoralla, which commonly lived on a muddy 

 bottom, with their bases not infrequently showing signs of 

 attachment to shells or other foreign objects. The com- 

 pound corals build heads or stocks often of great size and 

 weio-ht. Thev are commonlv attached to stones, shells, or 

 to the rock bottom, and through rapid increase, by budding 

 or division, masses of great size may be formed over a small 

 object of support. Even on muddy bottoms a small object 

 of support may serve as the nucleus around which a coi-al 

 mass will grow, which, as it increases in size and weight, 

 will sink more or less deeply into the mud on which it i-ests. 



The typical compound or reef-corals are very restricted in 

 their bathymetrical distribution. They do not normally 

 occur below fifty fathoms, and the majority live in less than 

 twenty fathoms of, water. Very many, indeed, live so close 

 to the surface as to be exposed at the lowest tides. A 

 minimum annual temperature of twenty degrees Centigrade 

 marks the regions in which most reef-building corals occur, 

 though in a few cases colder regions are known to be 



