524 
ZOOLOGY: A. a MAYER 
C. Montague Cooke, Jr. of Honolulu, kindly transported me in his 
automobile to eight of the larger streams and springs, between Palolo 
and Monanalua valleys, and these were all alkaline, ranging from 7.1 
to 8.12 PH.; the average being 7.34 PH. or 0.457 X 10-^. The higher 
alkalinity of the streams of Oahu may be due to the presence of elevated 
limestones, these being absent from Tutuila. Thus the surface waters 
draining off from Tutuila, and Oahu, being alkaline, cannot dissolve 
limestones by reason of their 'acidity,' and the Murray-Agassiz theory 
of solution of the shoreward parts of reef flats by fresh water is not 
supported. 
The openings in coral reefs opposite the mouths of streams are due 
to the fact that corals cannot survive and have never grown, in these 
places, due to silt and dilution in time of flood. This was proven at 
Tutuila by placing 26 specimens of 12 species of Acropora, Pavona, 
Psammocora, Porites, Pocillopora, Fungia, and Coeloseris, 150 feet from 
the mouth of Pago Pago brook in a place where the bottom is covered 
with fine brown volcanic mud and no corals are found. The salinity 
in this situation was observed to range between 31.38 to 25.48; that of the 
open sea about being 34.83. Yet the corals survived in this diluted water, 
for fifteen days, although the Acroporas did not expand. However 
all but one species were killed by the freshet due to the torrential shower 
of 4.3 inches on April 12, 1917, which reduced the salinity to 0.93, 
becoming only 9.25 at the end of 24 hours. All the corals died with the 
exception of 2 out of 3 specimens of massive Porites which withstood 
the dilution and silt but with apparent injury. This species of Porites 
Kves nearer to streams mouths and closer to the shore than does any 
other coral of Samoa. 
It is apparently uninjured by being placed for an hour in water of a 
constant temperature of 36° C, which would be fatal to all the Acropora, 
Pocillopora and dominant off-shore corals of the reefs. 
On the reef flats of both Murray Island, Australia, and Tutuila, 
Samoa, coral heads are most densely clustered in relatively quiet water 
about 150 to 200 feet shoreward from the region wherein the surges die 
out in ordinary weather. 
The greatest variety of species of corals are, however, found just 
where the surges die out in ordinary weather. 
In both Murray Island, Australia, and Tutuila, Samoa, four genera 
constitute over 90% of the coral heads of the reef flats. Thus : 
