94 CORAL FORMATIONS. 
From the facts which came under our observation, both by direct 
examination and the collection of beach specimens, it was inferred 
that there were few species occurring in the open ocean that may not 
also grow in the larger lagoons and channels. The Nullipores forming 
the margin of many reefs may here be mentioned, (though not properly 
corals,) as requiring the surf. There are also several Millipores, some 
small Madrepores, Pocillopore, and small Astras that grow in the 
face of the breakers, where larger or weaker species would be dis- 
lodged or broken.* 
Within the inner channels, the presence of fresh water in the im- 
mediate vicinity is known to be fatal to many zoophytes. Yet the 
dilution may be at least one-half before all species are excluded. Upon 
the reefs enclosing the harbour of Rewa, (Viti Lebu,) where a large 
river three hundred 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 
Porites are most common. In many instances, the living Porites were 
seen standing six inches above low tide, where they were exposed to 
the sunshine and to rains; and associated with them in such exposed 
situations there were usually great numbers of Alcyonia and Xenie. 
Even in the impure waters adjoining the shores, these corals occur ; 
and the massive Porites in such places usually 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 than in the Pau- 
motus, 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 Alcyonide. 
The small lagoons, when shut out from the influx of the sea, are 
often rendered too salt for growing zoophytes, in consequence of eva- 
poration,—a condition of the lagoon of Enderby’s Island. 
* The author’s observations on the speczes of corals were not commenced till reaching 
the Feejees, where we were among the zvzer reefs. Previous to that time, this Depart- 
ment in Zoology was in the hands of Mr. J. P. Couthouy. 
