272 bulletin: museum of comparative zoology. 



at high tide. This mass of rock is shaped Uke a pyramid, fifteen feet 

 broud at the base, much honeycombed out by the waves. -^ At another 

 part near by I found an extensive area of Porites rock nearly two feet 

 above the level of low tide. 



Porites verrilli is at Maceio, as at every other place where we collected, 

 the most abundant coral, and is by far the most important structural 

 coral of the reef. It grows everywhere, even on the sand-covered inner 

 edges of the reef, where no other coral can live except Favia conferta. 

 Notwithstanding the abundance of this species, it grows only in small 

 isolated heads, and in no place could I find large masses of Porites 

 growing in such a way as to form any considerable addition to the reef. 

 At one time it must have grown in huge heads all over the reef, for the 

 older portions are nearly solid Porites rock, which can readily be seen 

 wherever the reef has been excavated for lime. So while the greater 

 part of the reef has been built up by this species in former times, for 

 some reason it has been crowded out of the growing part of the reef, and 

 is now scattered everywhere in small isolated masses with Favia con- 

 ferta. This coral forms extremely solid and lasting rock, thougli it is 

 not so dense and durable as that of the Millepores, nor so hard and 

 tough as the rock of the Orhicella aperta. 



Porites hranneri was found in only one place, growing in small heads, 

 and appears to be rare here as elsewhere. 



Favia gravida is scattered all over the reef with Porites verrilli in small 

 heads which form no thick layers of coral rock. Its distribution on this 

 coral reef agrees exactly with what was already* observed on the sand- 

 stone reefs. 



Millepora alcicornis and Millepora hraziliensis were found in great 

 numbers, and the former was, next to Porites verrilli, the most important 

 sliuctural coral obtained, forming with the Porites the greater part of 

 the old reef. Millepora alcicornis lives on the extreme outer edge of 

 the reef in the heavy breakers where few other corals grow. In these 

 exposed places it thrives, growing either in huge erect clusters on sub- 

 merged bases of rock, or in overhanging masses many feet in extent on 

 the extreme outer edge of the main reef. In these the corals grow either 

 outward horizontally or downward from the under surface of these over- 

 hanging ledges. In these single clusters all variations from the bluntly 

 lobed to the slenderly pointed or fenestrated forms, until recently known 

 as distinct varieties, were found, showing clearly that these are all sim- 

 ply different phases of this highly variable species. Much of these 



1 This i8 an uptilted block that has been undermined by the waves. See pages 

 100 and 161 of this report. — J. C. B. 



