102 ANTHOZOA 



The solitary corals (i.e. the corals which do not form 

 reefs) are found in almost all latitudes, but live mainly in 

 rather deep water, the larger number occurring between 

 depths of 50 and 1000 fathoms ; some few (e.g. Garyophyl- 

 lia) live in quite shallow water, whilst others inhabit the 

 depths between 1000 and 2900 fathoms. The species of 

 solitary corals have a wide distribution, being apparently 

 but little affected by conditions of temperature and depth. 

 It might therefore be expected that they would also have 

 a long range in time ; this however is not the case, for 

 existing species extend but a short way back into the 

 geological record, and not a single living form is found 

 fossil in the English Cainozoic formations ; about a third 

 of the living genera, however, are represented in Cainozoic 

 rocks, and a few (e.g. Caryophyllia, Parasmilia, Trocho- 

 cyathus) occur in Mesozoic formations, but none range into 

 the Palaeozoic. 



The distribution of the reef-building corals, unlike that 

 of the solitary forms, is limited by both depth and tempera- 

 ture. Thus they are found only in shallow water, not 

 usually extending lower than 20 or .30 fathoms, and only 

 where the temperature of the ocean is not less than 65°F.; 

 they flourish only in water warmer than this. Like the 

 solitary corals, the reef-building genera of the present day 

 have but a very limited geological range, only a very few 

 extending back so far as the Mesozoic period. 



Corals, with possibly one or two exceptions, can only 

 exist in salt water; but Madrepora cribripora is said 

 to inhabit nearly fresh water. Clear water is likewise 

 generally necessary, but one species, Porites limosa, thrives 

 in muddy situations. In geological times, and especially 

 in the Palaeozoic and Mesozoic periods, the reef-building 

 corals had a much wider geographical range than they have 



