BRANNER: THE STONE REEFS OF BRAZIL. 269 



On the sandstone reefs four species of corals were obtaineil, Porites 

 verrilU, Poritea hranneri, Favia gravida, and Millepora alcicornis. Al- 

 though two of these, Porites verrilU 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 hranneri 

 being obtained only on the Rio Grande do Norte reef, and Millepora 

 alcicornis only at Pernambuco. 



The outer edge of the sandstone reefs slopes gradually toward the sea, 

 and is evei*ywhere 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 

 a 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 verrilU 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 appai'ent ease with 

 which it adapts itself to all sorts of unfavorable conditions, growing high 

 up 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 verrilU, though not so common, is Favia ijrari<la. 

 These two species form nine tenths of all the coral life on the sand- 

 stone reefs, and follow each other in distrilnition, although Favia gravida 

 is not so hardy, and duos not thrive so well in the muddv water along the 



