PLANKTON OF THE GULF OF MAINE 
453 
abundant during the first days of May, 1913, that the streaks in which it occurred 
were dense enough to discolor the water, the proportion of living cells and chains 
rapidly diminished and dead debris increased after the 1st of May. 
In 1915 Thalassiosira, like most other diatoms, had likewise entirely disappeared 
from the banks off western Nova Scotia by May 7 to 10 (stations 10271 and 10272), 
where our tows for the spring of 1920 proved it plentiful in April, though it may 
persist until later close in to the coasts. It is also probable that it vanished by 
May from the parts of Georges Bank where it flowers in April, none having been 
found on the western end on May 16 and 17 in 1920 (stations 20127 to 20129), nor 
in any of our summer tows on the bank. 
As the spring draws to a close the range of Thalassiosira continues to contract, 
until by the middle of June it is confined to the immediate vicinity of the land from 
Cape Elizabeth on the west to the northern shores of Nova Scotia on the east 69 ; 
but notwithstanding this shrinkage in the area occupied by it, it continues flowering 
actively along the northern shore of the gulf. Thus we made almost pure catches of 
Thalassiosira nordenskioldi and Th. gravida and in great abundance near Mount 
Desert Island, off Penobscot Bay, and off Casco Bay on May 10 to 13 in 1915 (stations 
10275 to 10277), and again off Schoodic Head, a few miles east of Mount Desert 
Island, on June 3. It was also fairly plentiful off the mouth of Penobscot Bay on 
June 14 (station 10287), and in 1912 Th. gravida was a considerable element in the 
plankton at two stations between Casco Bay and Penobscot Bay as late in the 
season as July 26 to August 2 (stations 10016 and 10022). 
In 1915 it was not uncommon near Mount Desert Island and off Machias, Me., 
as late as July 15 and 19 (stations 10301 and 10302), while Bailey (1917, p. 98) 
records it from Eastport on July 29 and locally along the shores of the Bay of Fundy 
during the first half of August. 
Thalassiosira was not detected at any station outside the 100-meter contour in 
the northern and eastern deeps of the gulf in August, 1913, 1914, or 1915, but in 
1912 we found it at two stations and in some numbers in the Eastern Basin as late 
as the 14th of that month (stations 10027 and 10028). Evidently its summer status 
varies from year to year in this part of the gulf. This is also the case at St. Andrews 
and probably in all estuarine situations generally along the coast line east of Mount 
Desert Island. Thus Doctor McMurrich’s notes give it as dominant only until 
about June 8 at St. Andrews in 1916 and scattering until July 6, but in 1917, when 
Fritz (1921, p. 53) found its flowering culminating early in May, with “the enormous 
total of 8,750,000 frustules” in her tow on the 1st, it persisted in moderate numbers 
throughout June. She noted a second maximum (1,760,000 in the tow) on July 3, 
and while only small numbers of Thalassiosira were taken after that date, the genus 
persisted, among more numerous diatoms of other genera, right through the late 
summer and early autumn until October 24, which was her latest date for it. Thus 
there is a marked contrast between the seasonal periodicity of Thalassiosira at St. 
Andrews on the one side of the gulf and in Massachusetts Bay in the other, where, 
99 During June, 1915, Thalassiosira was detected at stations 10281, 10284, 10285, 10287, 10290; also half a mile oil Schoodic Head 
on the 3d, where it was extremely abundant, and off the entrance of Petit Passage, Nova Scotia, on the 10th. 
8951—28 30 
