PLANKTON OF THE GULF OF MAINE 449 



neritic in other seas and usually confined to the neighborhood of the coast. In 

 north European waters it has its maximum in spring but has been found flowering 

 in autumn as well at many localities. 



Thalassiosira M 



The spring flowerings of Thalassiosira (fig. 129) are perhaps the most notable 

 event in the phvtoplanktonic cycle of the coastal belt of the Gulf of Maine. In 1920 

 these commenced first in the coastal belt between Cape Elizabeth and Cape Ann, 

 probably during the last week of February, and they progressed so rapidly that by 

 March 5 (stations 20059 and 20060) a tow of a few minutes clogged the nets with 

 brownish masses of Thalassiosira nordenskioldi (Th. gravida only occasion all)' appears 

 in these catches, and Th. decipiens still more rarely), with smaller amounts of CJiseto- 

 ceras criophilum, Oh. decipiens, Ch. didymum, Ch. diadema, Ch. atlanticum, Ch. lacinio- 

 sum, Ch. debile, Rhizosolenia semispina, Eh. setigera, Thalassiothrix nitschioides, 

 Coscinodiscus, and Lauderia glacialis. Thalassiosira also commenced to flower at ■ 

 about this same date in the Massachusetts Bay region in 1925, when it was not 

 detected in Cape Cod Bay in December or January, but was extremely abundant 

 near Stellwagen Bank on February 24, in Cape Cod Bay and near the tip of Cape Cod 

 during the first week of April, and still plentiful in the northern side of Massachusetts 

 Bay during the last week of the month. 



Thalassiosira is a characteristically neritic genus, and at first its flowerings are 

 closely confined to the immediate vicinity of the land. Thus it was overshadowed 

 by Chnetoceras 22 miles out at sea on March 5, 1920 (station 20061), though dia- 

 toms were in as great volume there as close inshore, with practically the same list 

 of species plus the more oceanic Chsetoceras atlanticum but lacking the neritic Thalas- 

 siothrix nitschioides. m During the first week of March in 1920, Jeffreys Ledge marked 

 roughly the offshore boundary for the flowerings of Thalassiosira in the western side 

 of the gulf; in fact, it did not spread out over the western basin until some time 

 between March 24 and April 18 in that spring. 



Thalassiosira may be expected to commence multiplying one or two weeks later 

 in the season in Massachusetts Bay than it does just north of Cape Ann, for only 

 occasional specimens were noted off Gloucester on March 1 and at the head of Massa- 

 chusetts Bay on the 5th in 1920; fl7 but it was extremely abundant at both these 

 localities from April 6 to 9 (stations 20089 and 20090). 



In the northern side of the gulf the first flowerings of Thalassiosira hardly 

 spread beyond Cape Elizabeth, it being only sparsely represented near Seguin 

 Island on March 4, 1920 (station 20057), though other diatoms were moderately 

 abundant there (p. 425), and it was not found at all off Mount Desert Island the day 

 before (station 20056). On April 10 (station 20096), however, it dominated a 

 moderately abundant assemblage of diatoms at the first of these localities, evidence 



» For records of Thalassiosira during the spring of 1913 see Bigelow, 1914a. It has since been recognized at station 10260in August, 

 1914; stations 10275 to 10278, 10280, 10281, 10285, 10287, 10290, 10301, 10302, 10322, 10328, 10329 and off Schoodic Head on June 3 and 

 PetitPassageonJunel0,1915; stations 20050, 2005S to 20061, 20072, 20088 to 20107, 20109, 20114 to 20117, and 20122 in 1920: and stations 

 10505 to 10507 in 1921. 



M Halospbasra was likewise detected at this station (p. 459). 



,; At this station (20002) no peridinians were detected and but few diatoms, chiefly Th. nordenskioldi with occasional cells of 

 Chxtoceras decipiens, Ch. atlanticum, Ch. criophilum, and Laudiria glacialis. 



