106 bulletin: museum of compakative 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 ovum, 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). Clione 

 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, i. 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 



