Bathymetrical Distribution of Beef-huilding Corals. 69 



Antilles. A second occurs in the South Atlantic, outward 

 from the coast of Brazil. A third area, about the size of 

 Australia, extends through the Indian Ocean eastward from 

 Madagascar. A fourth lies just north of the Equator, in the 

 centre of the Pacific. The fifth, largest, and most important 

 in this connection, occupies an extent fully equal to that of 

 South America, and it lies on the eastern side of the Indian 

 Archipelago. Its extent is, in fact, nearly coterminous 

 with the principal area of coral reefs of the western part of 

 the Central Pacific. Over the whole of these areas the sea- 

 water, to a depth of 100 fathoms, has a temperature above 

 65° Fabr., and, indeed, over a large part the temperature 

 ranges to ten or more degrees above that at the depth 

 named. 



As plankton abounds under these conditions, and as the 

 sea-water has its normal salinity, is virtually free from 

 suspended terrigenous matter, and as it contains the usual 

 percentage of dissolved oxygen, there seems to be no valid 

 reason why reef-building corals should not thrive as well 

 there as in the bathymetrical zones which are nearer the 

 surface. It yet remains to be proved that they do not do so. 

 No one has yet advanced any evidence to the contrary. 



This being the case, it is obvious that some of the data 

 employed as arguments for, or against, either Darv/in's or 

 Murray's Theory, will need reconsideration before they can 

 be used again. 



