392 
BULLETIN OF THE BUREAU OF FISHERIES 
(chiefly Skeletonema and Khizosolenia alata; pp. 448 and 447), whereas hauls at several 
stations farther out in the bay or off exposed stretches of the coast line 27 were domi- 
nated by the peridinian genus Ceratium (p. 407), as the open gulf as a whole usually 
is in summer. 
We also found the water in Casco Bay, near the Harpswell biological laboratory, 
so cloudy with diatoms and Peridinium with bright red chromatophores on July 27, 
1912, that its transparency was only about 4 meters. Two days later, however, a 
tow at the same location yielded hardly a diatom and very little phytoplankton of 
any kind, its place being taken by a fair representation of copepods, small medusae, 
and many ophiuran larvae. 
Tows for the years 1912, 1914, and 1915 proved diatoms a major element in the 
phytoplankton in the neighborhood of Mount Desert Island in August; locally 
swarming (p. 431). Fritz (1921) also found this to be the case in the St. Andrews 
region. She also records an abundant July plankton of diatoms in the more open 
waters of the Bay of Fundy. Our few August tows in the Grand Manan Channel 
have yielded chiefly diatoms, though the phytoplanktonic community as a whole 
has been extremely sparse there. Diatoms have likewise shared with the peridinians 
the domination of our summer tows in the northeastern corner of the gulf off the 
mouth of the Bay of Fundy, and we have found this condition on German Bank and 
off Lurcher Shoal during each August when we have visited that region, while there 
were a few diatoms as far offshore as Browns Bank on July 24, 1914, among the 
more abundant peridinians that characterized the phytoplanktonic community there. 
Cape Sable, however, seems to mark the eastern boundary for diatoms as an appre- 
ciable factor in the plankton during the latter half of the summer. 
Diatoms were a much more important factor in the plankton of the gulf in the 
ummer of 1912 than at that season in 1913, 1914, or 1915. During that July and 
August they occurred in great abundance all along the coast from Seguin Island 
(situated a few miles east of Casco Bay) as far eastward as the mouth of the Grand 
Manan Channel, and were plentiful enough over the whole northeastern corner of the 
gulf, mingled with the peridinians, to give a distinctive aspect to the catches, instead 
of being limited to the narrow confines just outlined as the usual bounds to their 
summer flowerings. More interesting than the unusual abundance of diatoms which 
characterized that summer is the fact that this was mostly due to a species ( Asterion - 
ella japonica) which has not been found in the offshore waters of the gulf since that 
time (p. 432). The genera Thalassiosira and Chsetoceras likewise were more wide- 
spread and numerous in the eastern side of the basin then than we have since found 
them at that season, reflecting an unusually late continuance of their vernal flowerings 
(Bigelow, 1914, p. 132). 
This much stress has been laid on the midsummer status of diatoms in the Gulf 
of Maine because of the very important role which this group of microscopic plants 
plays in the economy of the sea earlier in the season; but when all is said, diatom 
plankton occupies only a small part of the area of the open gulf during the warm 
months, as contrasted with the much more extensive area which then supports a 
typical peridinian plankton dominated by the genus Ceratium. 
” Stations 10630, 10631, 10632, 10636, 10838, 10640, and 10641. 
