240 CORAL AND ATOLLS 



45 fathoms. The actual details of the species, as given in the 

 paper, are as follows : " Stylopora, 1 species ; Favia, 1 species 

 at 45 fathoms ; Favonia, 1 species ; Leptoseris, 1 species ; 

 Fhyllastrcea, 1 species ; Psammmora, 1 species ; Montipora, 3 

 species, one in 44 fathoms ; Fhodarcea, 1 species ; Alveopora, 

 2 species." 



It is therefore safe to say that, in this part of the China 

 Sea at any rate, the species that we meet with at the surface 

 may live quite well at something over 40 fathoms. Nor 

 would I put this depth as the absolute limit of their range, 

 for the results of dredging are always somewhat uncertain, and 

 the experience of the difficulty of obtaining specimens from 

 beds that can be actually seen must make any one cautious of 

 assuming that negative results of dredgings mean necessarily 

 absence of coral growth. I have seen beautiful branches of 

 Stylopora come up on a fishing line from 12 fathoms, after I 

 had failed to bring up specimens with a far more elaborate 

 contrivance. 



The Keasons foe the Restricted Bathymetrical Range 

 OF Reef- BUILDING Corals. — Dana suggested the lowering of 

 the temperature of the water at greater depths, but the 

 temperature of depths far below the range of the reef-builders 

 is not sufficiently low to exclude coral growth ; and Dana 

 admitted that temperature could not account for the whole of 

 the phenomenon. 



It has been said that it is because the conditions for 

 forming calcareous skeletons are only present at comparatively 

 shallow limits ; and it is pointed out that deep-sea corals are 

 lightly calcified. There is, no doubt, some truth in this, but 

 30 or 40 fathoms would seem a narrow limit to set as the 

 maximum depth at which satisfactory calcareous skeletons 

 could be formed by the reef-building corals, when solitary 

 species, as Caryophyllia clavus, which I have taken in quanti- 

 ties from a cable at 380 fathoms, and which has been obtained 

 at much greater depths, possess a highly calcified corallum. 

 Again, it is possible that the Lithothamnionidce and Nulliporce 

 flourish, and build their skeletons, in great masses in depths far 



