PLANKTON OF THE GULF OF MAINE 455 



western side of the gulf during April, 1920, nor did Fritz find it at Si. Andrews at 

 any time during the spring or until the end of August. But it occurred sparingly 

 at two of our April stations in the northeast corner of the gulf and off the Nova 

 Scotian coast (stations 20101 and 20103), likewise locally off Georges Bank (station 

 20109), in the basin (stations 20114 and 2011.')), and off Cape Cod (station 2011G) 

 during that month in 1920. We have twice made rich catches of Thalassiothrix 

 between Cape Elizabeth and Penobscot Bay in May (station 10277, May 13, and 

 station 10280, May 31. 1915). It likewise dominated the diatom plankton on the 

 western end of Georges Bank and southeast of Nantucket Shoals on July 23, 1916 

 (stations 10347, 1034S, and 10354), but we have not found it elsewhere in the open 

 gulf during June, July, or the first half of August, though Fritz (1921) records it at 

 St. Andrews on August 28. 



Th. longissima was present in small numbers off Penobscot Bay on September 

 15, 1915 (station 10317), and irregularly at St. Andrews during that month in 1917, 

 according to Fritz. It flowers abundant!}- in the Bay of Fundy and along the coast 

 of Maine in October, for Fritz counted over half a million in her standard haul at 

 St. Andrews on October 6, 1917. It was abundant near Mount Desert Island on 

 October 9, 1915 (station 1032S), and a corresponding augmentation of this species 

 extended southward at least as far as Cape Ami during the last 10 days of that 

 month (stations 10329 and 10330). 



Fritz found few Th. longissima at St. Andrews after the middle of October and 

 none in January or February. Neither have we found it anywhere in the open gulf 

 during the winter. McMurrich (1917) describes it as present in great numbers at 

 St. Andrews on February 26, 1915. 



On the whole these data suggest two maxima for Th. longissima — one late in the 

 spring and the other in October, 7 ' paralleling its seasonal histor}* in the North Sea 

 region, where its chief flowering time is May, though it may also occur in great 

 quantities around Scotland in August and November (Ostenfeld, 1913, p. 408). 

 At Woods Hole Fish (1925) found it regularl}- in late winter and spring but only 

 occasionally at other seasons. The flowerings of Thalassiothrix observed by Mc- 

 Murrich in February and March show that its seasonal cycle is less regular than 

 that of Thalassiosira, Biddulphia, etc. 



Th. longissima is usually a minor element in the phytoplankton of the inner parts 

 of the gulf, where its flowerings are not only local but brief in duration. But it was 

 extremely plentiful on the western end of Georges Bank on July 23, 1916, at the 

 stations just mentioned, where with fewer Rhizosolenia styliformis it formed a very 

 rich and monotonous diatom community (fig. 124), and when its center of abundance 

 extended over a considerable area, out to the continental slope on the south and to 

 Nantucket Shoals on the west. 



We have never seen this flowering of Thalassiothrix rivaled within the gulf, 

 and a single occurrence of this sort does not necessarily establish Georges Bank as a 

 major center of production for it. This species is so large and so easily recognized 

 that it may finally prove of great value for the study of ocean currents, as Ostenfeld 



,! Probably the "Thalassema" mentioned by Bailey (1917, p. 107) as dominating some of the October gatherings in Passama- 

 quoddy Bay were actually Thalassiothrix longistima. 



