24 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
covered with algse. On the windward side is a very interesting reef, made up chiefly 
of masses of dead coral on the shore side; these masses were always well covered on 
the outside with small crustaceans and univalve mollusks, and by breaking the masses 
and pulling them apart, which could usually be done quite easily with the hands, 
many other species were found hidden or lurking in the interstices or in burrows of 
their own making. Several species of fishes were thus obtained, including some that 
are new. 
This part of the Porto Rican coast was particularly rich in mollusks, a number 
of species being obtained here that were not seen elsewhere. One interesting bivalve, 
Oytherea dione, seems to be not uncommon here, though it is said not to occur at any 
other place about Porto Rico. 
CHARACTERISTICS OF THE AQUATIC FAUNA OF PORTO RICO. 
Certain interesting peculiarities of the aquatic fauna of Porto Rico are directly 
traceable to the physical characteristics of the shores and environing waters. The 
shallow, submerged bank from which the island rises borders it very narrowly, and all 
sides soon drop off into great depths. The 100-fathom line is close to the shore, par- 
ticularly on the north and south sides. On the north a depth of 3,000 fathoms is 
soon found, and a little farther out is the “Brownson Deep,” with its great depth of 
4,561 fathoms. On the Caribbean side also the platform is narrow, a depth of 2,500 
fathoms being soon reached. On the east and west ends the platform is continuous in 
each direction and the depths are frequently less, though by no means inconsiderable, 
as 700 fathoms has been found at the east and 660 fathoms in Mona Passage. Not only 
is the border of shallow water about the island very narrow but there are scarcely 
any banks or shoals. Probably the only ones are in Mona Passage and these are of 
uncertain depth and location. With the exception of San Juan, Guanica, and Jobos 
harbors on Porto Rico, and Ensenada Honda on Culebra Island, the entire coast is 
exposed, not only to frequent storms but to the strength of the trade winds, and for 
a part at least of every year, or even of every day, there is a heavy surf which beats 
against the rocky shores or swashes back and forth incessantly on the sandy beaches, 
holding detached objects, rocks, sticks, or animals at its mercy. 
That this rigorous environment has produced certain modifications of form and 
habit which enable the animals to resist or circumvent the force of the sea is perfectly 
evident from an examination of the species of any group. The crustaceans, perhaps, 
have been most interestingly modified, the adaptation taking the direction of an 
unusual development of hooks and spines upon the legs which enable them to hold on 
to corals, algae, or other objects; and the fauna on the exposed coast is remarkable for 
the great number of species possessing such characters and the almost entire absence of 
species not so modified. Some species also simulate bits of alga, or actually have algae 
growing on their backs, so that when clinging to a mass of coral they are practically 
indistinguishable. Often have we examined small masses of dead coral and, deciding 
that it contained nothing, would be on the point of throwing it away, when a small 
portion of the mass would begin to move and we would discover it to be a small 
algse-covered crustacean. Other species of crustaceans maintain themselves by living 
in the interstices among the rocks or coral, or burrowing into them. 
The most characteristic feature of the molluscous fauna was the great preponder- 
ance of those species which, such as gasteropoda, can cling to rocks, or which either 
