PLANKTON OF THE GULF OF MAINE 
459 
coast, according to Gran (1902, p. 17), Phseocystis reaches its maximum after the 
diatoms have passed their apex of abundance, with a monotonous Phseocystis plank- 
ton succeeding them for a very short period. Apparently it bears much the same 
temporal relationship to the vernal diatom flowerings in Massachusetts Bay, but 
in the western basin farther offshore it seems that Phseocystis precedes instead of 
succeeds the greatest seasonal abundance of diatoms. 
The records of the International Committee point to May as the month in which 
Phseocystis is at its maximum in the North Sea — that is, about the same season as 
in the Gulf of Maine. Judging from the general geographic distribution of Phseocys- 
tis, the latter is probably its most southerly center of abundance in the western side 
of the North Atlantic, but the optima of temperature and salinity for this alga can 
not be established for American waters until more records are available. It may, 
however, be of interest to note that the Gulf of Maine collections (being from water 
of 3 to 4.5°) have been well within the temperature limits of Ph. pouchetii in European 
waters. But the salinity in which we have found it (31.43 to 32.45 per mille) is far 
less than the mean of the European records, which is given by Ostenfeld (1910) as 
about 34.8 per mille for pouchetii and as 34.89 per mille for globosa, though the former 
also occurs at the mouth of the Baltic in waters less saline than those of the Gulf of 
Maine. 
HALOSPHSERA 
The unicellular pelagic alga Halosphsera viridis Schmidt 73 has been found at many 
of our stations, sometimes in considerable numbers, though it is not sufficiently 
prominent in the Gulf of Maine to have received a local vernacular name as it has 
in the Mediterranean (Steuer, 1910, p. 2). Halosphsera was first detected in the 
gulf in 1915, when it was widely distributed over the eastern basin of the gulf in 
May (stations 10269, 10270, 10271, 10272, and 10273), though nowhere abundant, 
and occurred locally off Mount Desert in June (stations 10284 and 10286) ; also at one 
station (10310) in August. It was likewise found across the whole breadth of the 
continental shelf south of Nova Scotia in June (stations 10291, 10293, 10294, and 
10296), and off Shelburne in September (station 10313); likewise on German Bank 
on September 2 of that year (station 10310) and in the Massachusetts Bay region 
early and late in October (stations 10322, 10336, and 10337). During the spring 
cruises of the Albatross in 1920 Halosphsera was detected at some thirty stations in 
the gulf widely distributed both in time and space (stations 20044, 20045, 20048, 
20054, 20057, 20064, 20067, 20069, 20070, 20072, 20073, 20074 to 20076, 20078 to 
20080, 20086, 20097, 20098, 20100, 20105, 20112, 20120, 20123, 20124, 20126, and 
20129). These records, combined, suggest that Halosphsera attains its maximum in 
the gulf late in the spring, practically disappearing again in midsummer, 74 though it 
has been described as plentiful at that season in the colder waters about Cape Breton, 
Nova Scotia (Wright, 1907). Doctor McMurrich found Halosphsera in late spring 
and early summer (April 17 to July 6) at St. Andrews, which corresponds to the 
May-June maximum in the open Gulf of Maine. 
73 Identification according to Lemmermann, 1908, p. 21. 
74 Our failure to find Halosphsera previous to 1915 was probably due to the fact that most of our stations in previous years were 
in late July and August when Halosphsera is rare in the Gulf of Maine. 
