18 ATOLLS. Ch. I. 



deep. Probably about half its area consists of sedi- 

 ment, and half of coral-reefs. The corals composing 

 these reefs have a very different aspect from those on 

 the outside : they are numerous in kind, and most 

 of them are thinly branched. Meandrina, however, 

 lives in the lagoon, and many great rounded masses 

 of this coral lie loose or almost loose on the bottom. 

 The other most common species are three closely 

 allied species of true Madrepora with thin branches ; 

 Seriatapora subulata ; two species of Porites l with 

 cylindrical branches, one of which forms circular clumps, 

 with only the exterior branches alive ; and lastly, a 

 coral something like an Explanaria, but with stars on 

 both surfaces, growing in thin, brittle, stony, foliaceous 

 expansions, especially in the deeper basins of the 

 lagoon. The reefs on which these corals grow are 

 very irregular in form, are full of cavities, and have 

 not a solid flat surface of dead rock, like that surround- 

 ing the lagoon ; nor can they be nearly so hard, for 

 the inhabitants by the aid of crowbars made a channel 

 of considerable length through . these reefs, in which a 

 schooner, built on the S.E. islet, was floated out. It is 

 a very interesting circumstance, pointed out to us by 

 Mr. Liesk, that this channel, although made less than 

 ten years before our visit, was then, as we saw, almost 

 choked up with living coral, so that fresh excavations 



1 This Porites has somewhat the habit of P. clavaria, but the 

 branches are not knobbed at their ends. When alive it is of a yellow- 

 colour, but after having been washed in fresh water and placed to dry, 

 a jet-black slimy substance exuded from the entire surface, so that the 

 specimen now appears as if it had been dipped in ink. 



