238 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ing the general features of other calcareous reefs, being by turns hard 
and flat, cavernous, shelly and fragile, and filled with pools of water 
containing seaweeds and a few small corals. The part nearer the igneous 
rocks is the more solid; further from the shore it becomes more cavern- 
ous, the most fragile places being where the reef has its greatest width. 
It is highest along the outside, where it is covered by the dark and 
brownish polyps, seaweeds, and other calcareous growths. ‘The pools 
in this reef have in them a few small corals, Siderastraca and Favia, 
the specimens of the latter genus being the finest I have seen on 
the Brazilian coast. The specimens of Siderastraca are small, none 
being found larger than a man’s head. It is probable that many of 
the corals have been removed from this reef for the purpose of making 
lime. 
To the oceanward of the southeastern corner of the island where the 
fringing reef ends, the rocks are rough and are washed high up by the 
waves, which break here with full force. Wherever the water breaks 
over the top of one of the high rocks at this corner of the island and 
runs down the inside surface, this inside is covered by calcareous terraced 
rings which grow along the sides and over the surface parallel to each 
other like broken contour lines. These rings contain little pools of 
water one above another, and this water is continually renewed by the 
splashing of the waves and by spray from the ocean. These little bands 
are about three centimetres in thickness, are from eight to thirteen cen- 
timetres high, and are surmounted by rows of barnacles. 
The outer side of the rocks along the northeast part of the island 
appears to be crusted over by dark-brown corallines. Near the middle 
of the east side of the island there is a large pool among the higher 
rocks of the shore, the water of which is continually renewed by the 
waves ; this pool contains a few fish, corals, etc. — all quite beyond tide 
level. It is only by leaping that the waves reach this height, but the 
island standing so well out at sea receives the full force of the waves, 
and they are thrown by the huge blocks of rock at the base of the bluff 
high into the air, and are thus carried as spray or as waves high up the 
sides of the rugged cliff. 
Near this large pool and supplied in the same way are two other 
pools, one a little above and emptying into the other. The two are 
about the same size, being about twelve metres in length by one to two 
metres in width, and a metre or more in depth. These higher pools 
contain excellent exhibitions of the wearing or dissolving power of the 
sea-urchins upon rocks. The sides of the rocks are almost completely 
