546 ZOOLOGY: L. R. GARY 
All of the coral reefs about Tutuila are fringing reefs, with the excep- 
tion of the large reef at Nueli (Blacks Bay on the charts), which appears 
to be changing from a fringing into a barrier reef. Along most of 
the north shore the reefs are restricted to the bays, or harbors, while 
on the south side of the island the reefs are continuous from bay to bay 
around many of the headlands. 
In Pago Pago harbor, which is bordered with coral reefs broken only 
where one of the numerous streams has its entrance, there exists all of 
the possible conditions of reef environment varying from those at the 
entrance of the harbor where the surf beats incessantly to those at its 
inner end where, even in severe storms, the water is only slightly agi- 
tated. Marked gradations in the salinity of the water and in the amount 
of sediment which it bears are also found at different points within this 
area so that the relationship of reef building organisms to these factors 
can be readily observed. 
Six species only of alcyonaria were found on the reefs at Tutuila. 
Of this number two occur so rarely that they are unimportant factors as 
reef builders. All six species belong to the Alcyonaceae. 
Two of the more abundant species contribute to reef formation only 
through the setting free of their spicules at the death of the colony. 
The others, Alcyoneum rigidum and A. confertum, form at the base of the 
colony a corallium-like mass of limestone composed of closely cemented 
spicules, upon which the living tissues are bourn. This rock is continu- 
ously added to as the colony grows outward and upward, the living 
tissues disintegrating about its base as expansion takes place. In this 
way heads composed of spicule rock are formed which extend to a height 
of 4 feet (up to low tide mark) above the general reef fiat, and which 
have a circumference as great as 20 feet. 
The distribution of the alcyonaria on the Pago Pago reefs depends on 
a number of factors. Very few specimens are found on the horizontal 
surfaces of the exposed reefs. On the nearly vertical faces of these reefs, 
however, Alcyonium rigidum often covers large areas forming a nearly 
continuous carpet. This species occurs on the faces and in the deeper 
holes of practically all of the reefs about Tutuila, but on the horizontal 
surfaces of only those reefs which while protected from heavy breakers, 
are traversed by strong currents which provide for good aeration, normal 
temperature of the water and against the silting up of the colonies. 
A. confertum, which is next in importance as a reef builder, is the most 
resistant of the four species and is consequently the most widely dis- 
tributed. 
A. glaucum requires much the same environmental conditions as A. 
