106 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Of the three components, Arctic, Boreal, and Temperate Atlantic, 
into which the northern pelagic communities can be divided according 
to Hjort (Murray and Hjort, 1912, p. 637), the plankton of the Gulf 
belongs distinctively to the Boreal, for only a single species distinc- 
tively characteristic of polar waters, Calanus hyperboreus, was detected 
in 1912. Thus the ctenophore Mertensia ovwm, was, conspicuously 
absent, though it is known from Massachusetts Bay (A. Agassiz, 1865) 
and is recorded from the Bay of Fundy by Fewkes, (1888). The polar 
pteropod Limacina helicina was likewise wanting, whereas its boreal 
relative L. balea was taken at several stations, in some abundance. 
Nor did we detect the Arctic prawn, Hymenodora glacialis, a species 
lacking in boreal as well as in tropical waters. On the other hand 
Calanus finmarchicus, the most characteristic animal of all in the Gulf, 
is the most important member of the Boreal, as opposed to the polar 
plankton, in the Norwegian Sea and in the North Sea; and it is the 
commonest copepod off San Diego, California (Esterly, 1905, p. 126). 
Euthemisto, Meganyctiphanes norvegica, and Euchaeta norvegica are 
all characteristic of the Norwegian Sea, and of the southern edge of 
the Newfoundland Banks (Murray and Hjort, 1912, p. 108). Clone 
limacina, too, is by no means a sure indication of polar water, for 
though it is abundant in the Labrador Current off the east coast of 
Newfoundland, and has been taken off the west coast of Greenland, 
near Spitzbergen, and at other Arctic stations, it is not associated 
with polar water in the Norwegian Sea, (Murray and Hjort, 1912, 
p. 107) but, on the contrary, is found in Atlantic water there, and 
south of Iceland. To judge, however, from its great abundance in 
high latitudes and comparative scarcity in our Gulf, it appears to 
reach its maximum development in a lower temperature than that 
of the Gulf of Maine in summer. And neither is Eukrohnia hamata 
purely Arctic, for it occurs in the mesoplankton at lower latitudes; 
as for example in the Bay of Biscay, where Fowler, (1905) found it 
in one haul from fifty fathoms, 2. e., at about the same depth as our 
one record, and in many hauls from greater depths. And there is no 
more reason to assume a polar origin for the Gulf of Maine speci- 
mens than there is for the Biscayan ones. 
Most of the important Medusae and ctenophores, for example 
Aurelia, Cyanea, Melicertum, Bolinopsis septentrionalis, are regular 
inhabitants of the Norwegian Sea, and of the northern part of the 
North Sea. Staurophora is known from Helgoland; while Pleuro- 
brachia pileus and Beroe cucumis are apparently cosmopolitan. To- 
mopteris helgolandica is known from the North Sea, the coast of 
