1879. | Brazilian Corals and Coral Reefs. 543 
sandy and muddy bottoms, as from the rocky surfaces which 
afford them a more secure foundation. Two or three additional 
forms have been found along the coast; but the soft nature of 
these corals does not permit of their entering into the structure of 
a reef, excepting as their minute spicules may be added to the cal- 
careous sand or mud, a very important element in the formation 
of coral reefs. 
We pass now from the corals proper to other organisms, that 
give rise to quite as durable a substance of the same chemical 
composition. These are among animals the Serpule and Barna- 
cles, and among plants the Nullipores. They grow abundantly on 
the shore, forming encrusting layers or thickened masses; but we 
have treated very fully of these forms on page 352 of this journal, 
in connection with the sandstone reefs. The thin encrusting 
nullipores, with nearly smooth or slightly mammillate surface, 
which cover so much of the Pernambuco reef, inhabit also many 
of the rocky shores, but are more abundant over several of the 
coral reefs that have reached too high a level for the growth of 
true corals, There is another common nullipore, composed of 
many intermingling and closely placed branches, which project 
outwards in all directions as numerous digitations. This form 
grows to an immense size at times, and is associated with the 
corals in reef-building. A coarsely jointed coralline forms large 
and dense clusters on the coast of Pernambuco, and its detached 
segments sometimes form quite a thick deposit, especially on the 
surfaces of reefs. 
The limestone-producing fauna and flora we have thus hastily 
reviewed, may not differ in their essential features from those of 
all the other coral regions in the world, but it has seemed best to 
treat of them as fully as we have, in order to show more clearly 
how few are the species of Brazilian corals, particularly those that- 
can aid materially in the building up of reefs. Up to this time 
but thirteen species of Madreporian corals, representing ten 
genera, have been found on or about the Brazilian reefs, and of 
these only three or four ever attain to any considerable size. 
Millepores have also contributed largely to the coral re : 
We have now to trace the gradual variation in coral growth as 
we proceed outward from the shore toward the reef grounds. 
_ Here is a rocky ledge, reaching to within about a fathom of the oe 
Surface at low tide. It is of small size, only a dozen feet each et 
