PLANKTON OF THE GULF OF MAINE 
417 
20129), it is probable that a considerable production of Peridinium takes place 
during that month. Doctor McMurrich likewise notes Peridinium as appearing in 
May at St. Andrews, and occurring in some numbers from June until September, 
while Willey (1913) describes it as sometimes abundant there in July and August. 
Specific identification of the several members of this genus which occur in our 
tow nettings must await a specialist, but I may note that P. depressum 44 was the 
species chiefly responsible for the May maximu m in the eastern half of the gulf in 
1915, whereas most of the specimens so far identified in the rich catches from the 
other side of the gulf in the same month of 1920, especially station 20127, were P. 
crassipes. Inasmuch as the few Peridinium so far named from the summer and 
autumn catches likewise belong to P. crassipes, it is probable that that species 
occurs in the gulf throughout the year. P. pallidum is also recorded from the center 
of the gulf (Bigelow, 1915, p. 334, station 10090). The only species so far identified, 
in the estuarine waters off St. Andrews is P. divergens, typically a neritic form (Willey 
1913; McMurrich, 1917). 
The genus Dinophysis has been noted often enough in a preliminary examina- 
tion of the catches to show that it may be expected anywhere in the gulf in summer, 
at which season its presence has been established in the central basin, off Lurcher 
Shoal, in the northeast corner of the gulf, in the coastal belt between Cape Elizabeth 
and Penobscot Bay, on the northwest part of Georges Bank, and off Shelburne, 
Nova Scotia; but only occasional specimens have been noticed among the Ceratium. 
Until its presence in the hauls has been fully listed, discussion of its seasonal and 
regional distribution would be idle; but its absence or at least rarity in the spring 
hauls for the years 1913, 1915, and 1920 suggests that it is at its lowest ebb at that 
season. Most of our records for Dinophysis are based on D. norvegica, a species 
widely distributed in northern waters (Paulsen, 1908). D. homunculus, native to 
warm seas and a valuable index for warm currents because it is easy to recognize, 
has not been found within the gulf although a lookout has been kept for it, but was 
noted south of Marthas Vineyard on October 1 , 1915 (station 10332). 
No doubt the plankton of the gulf will finally be found to include many if not 
most of the naked peridinians known from other seas. 45 So far, however, I can 
only record the presence of considerable numbers of an unidentified gymnodinid 
among the scanty plankton of the Eastern Basin on March 3, 1920 (station 20055). 
DIATOMS 
It is probable that with sufficient search all the diatom species that are pelagic 
in northern seas would be found in the Gulf of Maine at one season or another, but 
few species or groups of species, and fewer genera, are ever sufficiently abundant 
there to dominate the plankton . 48 
The following remarks apply chiefly to the open gulf. Quite different associations 
of diatoms are to be expected in its estuarine tributaries, especially a rich representa- 
tion of brackish-water species that have been practically nonexistent at our Grampus. 
Albatross, and Halcyon stations. No study has yet been made of the plankton of 
14 Identifications follow Paulsen (1908). 
** For descriptions of these, see Knfoid and Swezy’s (1921) monograph and beautiful illustrations. 
48 On the identifications of the diatoms see p. 382. 
