BRANNER: THE STONE REEFS OF BRAZIL. 269 
On the sandstone reefs four species of corals were obtained, Porites 
verrilli, Porites branneri, Favia gravida, and Millepora aleicornis. Al- 
though two of these, Porites verrilli and Favia gravida, are very common, 
growing abundantly on every reef visited, the corals at no place form 
any considerable part of the stone reefs, but exist only in small, isolated 
masses. The other two species are not at all abundant, Porites branneri 
being obtained only on the Rio Grande do Norte reef, and Millepora 
шешу only at Pernambuco. 
The outer edge of the sandstone reefs slopes gradually toward the sea, 
and is everywhere cut up by the waves, forming pools and caverns that 
are lined with encrusting anemones, ascidians, etc. It would seem 
that these sheltered pools, continually washed as they are by the 
fresh water of the outside of the reef, ought to afford splendid locations 
for the growth of these corals. On the contrary, they do not grow here 
at all, but are found chiefly on the inner edge of the reef, even in places 
where the coral heads are nearly covered by the silt and sand that is 
washed by the river currents against the inside of the reefs. Small 
masses of coral are scattered over the top of the reefs in the shallow pools 
that are always full of water, but the largest heads are always found 
along the extreme inner edge. The abundant growths of encrusting 
anemones and barnacles on the exposed portions of the sandstone afford 
à considerable protection from the never-ceasing pounding of the waves, 
but the corals scattered in small, isolated masses are of little or no im- 
portance in the formation or preservation of these wonderful sandstone 
reefs, 
-Porites verrilli is by far the hardiest and most abundant coral on this 
part of the coast, and thrives wherever there is a suitable ledge of rock 
Upon which to grow. It forms remarkably round, even, perfect heads, 
never attaining a greater size than a foot in diameter on the sandstone 
reefs, and usually only a few inches. It was found commonly on all the 
reefs visited, and its hardiness is well shown by the apparent ease with 
which it adapts itself to all sorts of unfavorable conditions, growing high 
пр on the reef, sometimes entirely exposed at low tide, and sometimes 
buried in the mud on the inside of the reef. The rock of this species is 
remarkably solid and firm, and is much thicker and more lasting than 
that of any other species. 
Growing with Porites verrilli, though not so common, is Favia gravida. 
These two species form nine tenths of all the coral life on the sand- 
stone reefs, and follow each other in distribution, although Favia gravida 
is not so hardy, and does not thrive so well in the muddy water along the 
