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In the Southern Hemisphere the reef-building Actinozoa do 

 not extend so far from the Equator. In the Southern Pacific 

 there are only a few reefs beyond the line of the tropic. 

 Houtman's Abrolhos, on the western shores of Australia, in 

 latitude 28° S., are of Coral formation. 



In the middle of the Pacific Ocean the distribution of the 

 reef-building Polyps extends oyer a zone of 56° of latitude in 

 width, which on the western coast of America is reduced to 

 16°, and on that of Africa to 12°, whilst on the shores of Asia 

 and Australia it extends over a diameter of 64°. 



This irregularity in the width of the Coral zone in different 

 parts of the ocean probably depends on the direction, force, and 

 temperature of the extra-tropical currents, like those of the 

 Galapagos Islands, which flow along the western shores of 

 both continents at the north, and at the south of the Equator, 

 and the inter-tropical currents found on their eastern shores; 

 the Coral zone appears to be contracted on the west shore, and 

 enlarged on the east. This irregular distribution of Coral reefs 

 may at first sight appear to form an exception to the general 

 law enxmciated by Dana ; but were all the physical conditions 

 fully understood under which the exceptions occur, it would 

 perhaps appear that the disposition of the warm and cold currents 

 of the ocean is the real cause of their distribution, and that the 

 exceptions, instead of breaking, in reahty proved the rule. 



Whilst the reef-building Actinozoa — Poritidoe, Astroeidce, 

 Gemmiporidoe, Madreporidoe, Meandrinidce — are limited to the 

 Coral seas, and are not found living at more than 100 feet 

 below the surface, other families of this class have a much 

 wider range. The CaryophyllidcB extend from the Equator to 

 the Arctic seas, and live at various depths, some species having 

 been found at more than 200 fathoms; the Alcyonaria, in like 

 manner, seem to prefer deep seas, Corallium having been found 

 at 120, and Gorgonia at nearly 200 fathoms; and M. Sars 

 dredged at Oxfjord Virgularia Finmarchica at a depth of 240 

 fathoms. Although depths equal to, or even exceeding these, 

 have yielded many species of Zoantharia, still in general the 

 members of this order are most abundant in seas of not more 



