PLANKTON OF THE GULF OF MAINE 
465 
Elizabeth (station 10319) was chiefly C. serrata (Brandt, 1906, Taf. 39, figs. 4 and 6). 
McMurrich (1917) records C. ehrenbergi and two species of Tintinopsis — T. cam- 
panula, and T. ventricosa — from St. Andrews, while his unpublished plankton lists 
note Cyttarocylis denticulata and C. subulata. 
According to Brandt (1910) the limits of C. denticulata in the North Sea area 
are chiefly determined by temperature, its upper optimum being about 12°. In a 
general way this is true also of the Gulf of Maine and of Nova Scotian waters, for 
it is more numerous in the cold Nova Scotian current than in the higher temperatures 
of the gulf, but the data are not sufficiently extensive to show whether its distribu- 
tion within the gulf reflects the slight regional differences in temperature that prevail 
tiiero 
OTHER UNICELLULAR ORGANISMS 
The reader must not assume that the foregoing notes exhaust the major groups 
of unicellular organisms in the Gulf of Maine. On the contrary, such important 
divisions as the coccolithophorias, the silicoflagellates, and the infurosia (apart from 
the tintinnids) have not been mentioned at all, not because they do not occur but 
because they have not been detected so far in our offshore hauls, or only on the 
rarest occasions. Infusoria, in particular, may be expected to prove of considerable 
ecologic importance when tow-net catches, preserved by methods suitable for these 
minute and very delicate organisms, are intensively studied. Such, at least, is the 
case in June in the Gulf of St. Lawrence, where the infusorian genera Mesodinium 
and Laboea occur in abundance, as they do also in the waters off Halifax in May. 
(Gran, 1919, p. 493.) The silicoflagellate genus Distephanus occurs at times in some 
numbers at St. Andrews. (McMurrich, 1917, p. 4.) 
We have not detected Notiluca in any of the Gulf of Maine towings, though 
its wide distribution in general and its seasonal abundance in the Irish Sea and 
coastal regions of the North Sea region in particular, where it is one of the most 
frequent sources of phosphorescence (Ostenfeld, 1910; Herdman, Scott, and Dakin, 
1910), point to its presence in the gulf as probable. 
Globigerina is likewise to be expected in the gulf as an occasional immigrant 
from the ocean waters of the open Atlantic, but is never likely to prove of anj^ im- 
portance in the Gulf of Maine plankton. 
NOTES ON THE BIOLOGY OF THE PHYTOPLANKTON 
Perhaps no phenomenon in the natural economy of the gulf so arrests attention 
(certainly none is so spectacular) as the sudden appearance of enormous numbers 
of diatoms in early spring, and their equally sudden disappearance from most of its 
area after a brief flowering period. As precisely this same phenomenon takes 
place in north European waters, where biologists have long occupied themselves 
with the marine plankton, no wonder the possible factors, hydrographic and seasonal, 
or the physiology of the diatoms themselves, which first permit and then estop 
their almost inconceivably rapid multiplication and finally even prohibit their fur- 
ther existence, have been the subject of much study and discussion. Nevertheless, 
as Herdman (1920, p. 817) has recently declared, the factors governing this phenom- 
enon still remain imperfectly understood. 
