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, Mo., 

 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, 



•' During June, 1915, Thalassiosira was detected at stations 102S1, 102S4, 10285, 10287, 10290; also bait a mile oft* Schoodic Head 

 oa the 3d, where it was extremely abundant, and oil the entrance of Petit Passage, Nova Scotia, on the 10th. 



