CAUSHS AFFEUTING THE GROWTH OF CORALS. 119 
III. LOCAL CAUSES INFLUENCING DISTRIBUTION. 
Coral making species generally require pure ocean water, 
and they especially abound in the broad inner channels among 
the reefs, within the large lagoons, and in the shallow waters 
outside of the breakers. It is therefore an assertion wide from 
the fact that only small corals grow in the lagoons and chan- 
nels, though true of lagoons and channels of small size, or of 
such parts of the larger channels as immediately adjoin the 
mouths of freshwater streams. 
There are undoubtedly species especially fitted for the open 
ocean; but as peculiar conveniences are required for the col- 
lection of zodphytes outside of the line of breakers, we have 
not the facts necessary for an exact list of such species. From 
the very abundant masses of Astrzeas, Mzandrinas, Porites, 
and Madrepores thrown up by the waves on the exposed reefs, 
it was evident that these genera were well represented in the 
outer seas. In the Paumotus, the single individuals of Porites 
lying upon the shores were at times six or eight feet in diam- 
eter. Around the Duke of York’s Island the bottom was ob- 
served to be covered with small branching and foliaceous 
Montipores, as delicate as any of the species in more protected 
waters. 
Species of the same genera grow in the face of the breakers, 
and some are identical with those that occur also in deeper wa- 
ters. Numerous Astras, Meeandrinas and Madrepores grow 
at the outer edge of the reefs where the waves come tumbling 
in with their full force. There are also many Millepores and 
some Porites and Pocillipores in the same places. But the 
weaker Montipores, excepting incrusting species, are found in 
stiller waters either deep or shallow. 
