52 James D. Dana, Esq., on the Structure, 



Again, the same genera occur in the shallow waters of the 

 reef inside of the breakers. Astrseas, Meandrinas, and Po- 

 cilloporas are not uncommon, though requiring pure waters. 

 There are also Madreporas, some growing even in impure 

 waters. One species was the only coral observed in the 

 lagoon of Honden Island (Paumotus), all others having dis- 

 appeared, owing to its imperfect connection with the sea. 

 Upon the reefs inclosing the harbour of Eewa (Viti Lebu), 

 where a large river, 300 yards wide, empties, which during 

 freshets enables vessels at anchor two and a-half miles off 

 its mouth to dip up fresh water alongside, there is a single 

 porous species of Madrepora (M. cribripora) growing here 

 and there in patches over a surface of dead coral rock or 

 sand. In similar places about other regions, species of Po- 

 ntes are most common. In many instances, the living Porites 

 are seen standing six inches above low tide, where they were 

 exposed to sunshine and to rains ; and associated with them 

 in such exposed situations, there were usually great numbers 

 of Alcyonia and Xenise. Porites also occur in the impure 

 waters adjoining the shores ; and the massive species in 

 such places, commonly spread out into flat disks, the top 

 dying from the deposition of sediment upon it. 



The exposure of six inches above low tide, where the tide 

 is six feet, as in the Feejees, is of much shorter duration 

 i;han in the Paumotus, where the tide is less than half this 

 amount ; and consequently the height of growing coral, as 

 compared with low-tide level, varies with the height of the 

 tides. The powers of endurance in some coral zoophytes 

 cannot surprise us, for it is well known that these animals 

 are often very tenacious of life. The hardier species belong 

 mostly to the genera Porites and Pocillopora, besides the 

 family Alcyonidae. 



The small lagoons, when shut out from the influx of the 

 sea, are often rendered too salt for growing zoophytes, in 

 consequence of evaporation, — a condition of the lagoon of 

 Enderby's Island. 



Coral zoophytes sometimes suffer injury from being near 

 large fleshy Alcyonia, whose crowded, drooping branches 

 lying over against them, destroy the polyps, and mar the 

 growing mass. But Serpulas and certain species of bar- 



