PLANKTON OF THE GULF OF MAINE 275 



It is interesting that SO per cent of the 10 records of occurrence within the off- 

 shore banks of a genus whose source is undoubtedly the oceanic basin outside the 

 continental edge should be for March and April, when the temperature is lowest, and 

 only two for the summer-autumn season (P. robusta, station 10100, August 13, 1913; 

 P. abdominalis, station 10246, August 12, 1914), whereas our summer stations alone 

 have yielded this genus outside the banks." However, with the possibility that a 

 rare species may be overlooked among the masses of Calanus and other of the more 

 plentiful copepods taken in the horizontal hauls, the few records do not show at 

 what season the genus as a whole (or any one of its several species) is most likely 

 to enter the Gulf of Maine. 



It is not likely that Pleuromamma succeeds in breeding in the gulf; but the 

 geographic distribution of the records indicates that individual specimens may be 

 long-lived there. No relation is apparent between the occurrences of Pleuromamma 

 in the gulf and high temperature, for its presence has been established there in 

 readings as low as 0.49 to 1.95° (station 20056), and the two midsummer records 

 may have been from water as cold as 4.22° and 7.58°, though, equally, the few speci- 

 mens involved may have been picked up by the open net near the surface in a much 

 higher temperature. 



Pleuromamma has not been taken on the surface in the Gulf of Maine, but 



none of the hauls producing it have been from deeper than 175 meters and all but 



three of them were as shoal as 100 meters, or shoaler, pointing to the strata above 



the latter level as the region which it usually inhabits in the gulf. At San Diego 



Esterly (1912) found both P. abdominalis and P. gracilis coming nearly or quite 



to the surface during the night and sinking to considerable depths by day, chiefly 



to deeper than 150 meters. Similar diurnal migrations, though not so deep, are 



to be expected of the few specimens unfortunate enough to stray into the Gulf 



of Maine. 



Pseudocalanus elongatus Boeck 48 



This is a northern species and one of the most widespread and abundant cope- 

 pods in the North Atlantic region and in the Arctic, where it is circumpolar. The 

 records of its distribution have recently been summarized by Farran (1910) and by 

 With (1915). On the European side its southern boundary seems to be the Black 

 Sea (Sars, 1903, p. 154), the Mediterranean, and the Gulf of Suez (Thompson and 

 Scott, 1903), which it would seem to have reached via the Suez Canal, not being 

 known from farther down the Red Sea or from the Indian Ocean. It is widespread, 

 probably universal, northward from Gibraltar to the North Sea, along the entire 

 length of the coast of Norway, and far up into the Baltic. It is recorded near the 

 New Siberian Islands, repeatedly and at many localities in the White Sea, about 

 Spitzbergen, off Jan Mayen, in the Norwegian and Greenland seas, about the Faroes, 

 Iceland, northward to Disko along West Greenland, from East Greenland, and 

 right across the North Atlantic from England to the Gulf of St. Lawrence. 



« None at stations 200M, 20045. 20058, 20009, 20077, 20100, February-April, 1920. 



11 According to With (1915) the P. minutus of Kr0yer was based on immatures of this species, which should therefore bear the 

 name minuttw; but until the change is generally accepted by students of the group (Willey's (1920, 1921) recent communications 

 still use efon^o(iM) it is as well to follow the more general usage in a paper not concerned with systematics. 



