PLANKTON OF THE GULF OF MAINE 407 



How closely the foregoing data, obtained in European waters, would apply to 

 the Gulf of Maine is 3*et to be determined, but judging from Peck's results and from 

 the large volumes of phytoplankton which we have ourselves obtained, there is 

 no reason to suppose that its fecundity is lower than that of the North Sea or even 

 than the still more prolific waters of the West Baltic. When such numbers as I have 

 listed as examples are expanded from the trifling bulk of a cubic meter of water to 

 cover the 36,000 square-mile area of the Gulf of Maine north of its offshore banks, 

 and to a stratum at least 20 meters thick, they become too vast for the human mind 

 to envisage. Peridinians never approach the diatoms in actual numbers so far as is 

 known. For example, the largest count recorded by Gran (1915) in the North Sea 

 (May 9, 1912) was 3,740 per liter for Ceratium longipes, a species with an April to 

 June maximum, and hence to be expected in relatively large numbers at that par- 

 ticular season. 



PERIDINIANS 



The peridinian communities of the Gulf of Maine, like those of the North Sea, 

 consist chiefly of one or other of two species (longipes and tripos) of the genus 

 Ceratium, 37 with smaller numbers of C. fusvs and at times C. arctica The two 

 predominant species alternate in dominance with the season of the year. 



CEEATItTM 



Judging from winter data for Massachusetts Bay (Bigelow, 1914a) and from 

 our December and January stations of 1920-1921, C. tripos predominates every- 

 where in the gulf throughout the winter, though C. longipes likewise occurs in small 

 numbers in most of the winter catches. Tripos was still the predominant member 

 of the pair at every station in the western, central, and northern parts of the gulf 

 and on Georges Bank as a whole during early March, 1920, except n the flowering 

 centers for diatoms (p. 383 ; fig. 104), where so few Ceratium occurred that the relative 

 numbers of the two species are not significant. C. longipes or intermediates between 

 it and C. arctica, such as are reported by Paulsen (1908), occurred side by side with 

 C. tripos at most of the March stations. Off the southeastern slope of Georges 

 Bank longipes was at least as numerous as tripos, outnumbered it in the Eastern 

 Channel, on Browns Bank, and over the slope farther east, and was the only member 

 of the pair detected in tows made in the Northern Channel and over the shelf abreast 

 of southern Nova Scotia, from March 17 to 20 (stations 20073 to 20076 and 20078). 



Ceratium arctica, interesting because its occurrence is associated with low tem- 

 peratures (J0rgensen, 1911), was likewise very generally distributed over the gulf 

 in March, 1920, occurring only in very small numbers in the western half, but rela- 

 tively more abundant in the Eastern Basin (though subordinate to tripos there) ; 

 predominant, or at least as numerous as either C. longipes or C. tripos, at our 

 several stations from Browns Bank to Cape Sable and off Shelburne; and more 

 abundant, absolutely as well as relatively, in the eastern side of the gulf than in the 

 western. The distribution of C. arctica at this season suggests an intrusion on its 



" Identifications of peridinians follow Paulsen (1908) strictly. Being concerned here only with questions of distribution and 

 relative abundance, not with systematica or genetic relationships, Paulsen's view that C. longipes and C. arctica arc distinct (not 

 varieties of one species as Meunier (1910) maintains) is accepted without comment. 



