PLANKTON OF THE GULF OF MAINE 367 



tion (20129) just mentioned is our only record for it as far out at sea as the con- 

 tinental slope. 



A. Agassiz (1865) describes Pleurobrachia as abundant within Massachusetts 

 Bay in September. In October we have taken it off Cape Cod, off Penobscot Bay, 

 near Mount Desert Island, and off Machias, Me. (Bigelow, 1917, p. 304, stations 

 10323, 10327, 10328, and 10329), and in Massachusetts Bay and over the western 

 basin abreast of Cape Ann in November (Bigelow, 1914a, p. 403, and station 10401, 

 November 1, 1916). During the last days of December and first week in January 

 of the winter of 1920-21 (Halcyon stations 104SS, 10491, 10492, 10497, and 10501) 

 it occurred at the mouth of Massachusetts Bay, off Cape Cod, in Ipswich Bay, near 

 Mount Desert, and close to Yarmouth, Nova Scotia, our failure to find it at any of 

 our offshore stations on this last cruise suggesting that its area of distribution in the 

 gulf contracts to the coastal zone as winter advances. 



Thus, although Pleurobrachia does not depend on the bottom at any stage in 

 its development, it is more neritic than oceanic in the Gulf of Maine, just as it is 

 over the continental shelf south and west of Cape Cod (Bigelow, 1915, p. 320). 

 This is equally true of it in other seas as well, for although it ranges from the Antarctic 

 Ocean on the south to Spitzbergen on the north (it is not a regular inhabitant of 

 true polar water) and occurs in waters varying as widely in salinity as the Mediter- 

 ranean, on the one hand, and the inner parts of the Baltic, on the other (Kramp, 

 1913), it is chiefly confined to the general neighborhood of the land or of the coastal 

 banks and has seldom been taken on the high seas far from the coast (Mortensen, 

 1912, p. 73). 



The region of German Bank and the shoals west of Nova Scotia out to 

 the 100-meter contour generally are the chief and the only constant center of 

 abundance for Pleurobrachia within the limits of the Gulf of Maine. Whether in 

 March, April, May, June, August, September, or in January, we have invariably 

 found these ctenophores, either large or small, swarming there, except that on 

 August 14, 1912, when it abounded at one station (10030), only a few were taken 

 at another close at hand (10029). 



We have also seen it in great abundance about Grand Manan in August and 

 have found it numerous off Seguin Island both in August, 1912 (station 10040), 

 and in March (March 4, 1920, station 20058). Rich catches have also been made 

 in Massachusetts Bay in summer and autumn; likewise on April 20, 1920, when 

 Pleurobrachia monopolized the water to the exclusion of almost everything else at 

 a station (20118) in Cape Cod Bay, but when the swarm of these ctenophores was 

 limited to an area so narrow that few of them were taken that same day at a station 

 30 miles to the northward (station 20119), where they were replaced by a com- 

 paratively plentiful Calanus community. The waters over Browns Bank likewise 

 supported an abundance of Pleurobrachia in the spring of 1920, but we have not 

 found it there on our visits in June and July. 



Our records do not suggest that any definite ebb and flow takes place in the 

 numbers of Pleurobrachia existant in the Gulf from season to season. There may 

 be a general impoverishment in autumn and winter, but if this actually occurs the 

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