Small rounded masses of Siderastrea radians are also 

 found here, along with the common rose coral Tdani- 

 cina areolata. These, together with 7avia jragum are 

 most resistant to the effects of sediment, fluctuating 

 temperature, and exposure to the atmosphere during 

 very low tides. 



Some of the shallow water corals may be found in 

 deeper water but few of the deeper water corals are able 

 to live in shallow water. In the intermediate depths there 

 is a good deal of intermingling. 



A curious effect of sediment is often to be found in 

 the fairly deep water behind the reef, where some of 

 the massive corals are able to live, but where sediment 

 is nevertheless present, and tends to settle on the upper 

 surface of the coral boulder. The uppermost horizontal 

 part of the surface is killed by the fine particles which 

 settle on it but the outer, more steeply sloping sides, 

 continue to grow so that the coral assumes a doughnut 

 shape 



Having collected the coral specimen from its particu- 

 lar kind of situation, there are several ways in which 

 it may be preserved. The color of the living colony can- 

 not be retained by any practical method, but the general 

 appearance of the live coral is kept by preserving it in 

 industrial ethyl alcohol of about 70% strength. If 

 placed in this immediately the polyps will contract but 

 they may be killed in an expanded condition if kept 

 in a dish of seawater in the dark for a while. When 

 fully expanded a cotton bag containing magnesium 

 sulphate is immersed in the water. The slowly dissolv- 

 ing crystals narcotise the polyps so that after a while 

 they do not contract even when placed in the alcohol 

 preservative. 



57 



