202 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
seen that these reefs are a long way out from the shore. In order to 
spend a second day on them it was necessary to anchor our boat and 
remain there over night. When the tide was high, except that the sea 
was not very rough, to all appearances we might have been anchored in 
the middle of the ocean. 
The water was a little short of two metres deep on the higher parts 
of the reef at high tide ; judging by the posts planted on the reef, I take 
it that the tides here rise about three metres, 
These reefs are traversed by irregular channels from one to ten 
metres deeper than the top of the reef, and varying in width from three 
or four metres to half a kilometre or more. The whale-fishers of the 
Barra de Caravellas have planted here and there along these channels 
tall poles to serve as guides in sailing across the reefs when the water 
is shallow on top of the rocks, and to mark anchoring places for their 
boats at night. a 
When the tide is ebbing the first visible signs of the reef are muddy- 
looking splotches in the water; these get browner and yellower as the 
water gets shallower, until the rocks begin to appear at the surface. 
When the reef is quite uncovered it has a deep yellow color, — between 
lemon and orange. The water itself looks yellow and muddy over the 
reefs, but this is deceptive, for it is perfectly clear, — at least it was so 
during my visit. 
The Lixa reef is the flattest and smoothest I have seen on the coast 
of Brazil. Except on the edges, where it is always more or less ragged, 
it has the appearance of being 
one solid compact mass of coral 
rock built up to an even level. 
The view over its surface at low 
tide reminds one of a great prairie 
covered with short dead grass, the 
sky line unbroken save here and 
there by a few black points, — 
blocks of the reef rock broken 
Fic. 100. Profile of the edge of Lixa 
coral reef. 
out by fishermen in search of squid or fish. 
The top of the reef is dead so far as the corals are concerned. Only 
two forms were found alive in the shallow pools on the surface, — Porites 
and Favia, — and these are all small and apparently stunted. Other 
polyps are also abundant, but the patches are small and the species few. 
Living corals are found only along the edges and over the bottom of 
the channels that cut the reef, and in the isolated patches that rise 
