442 BULLETIN OF THE BUREAU OF FISHERIES 



from July 26 to August 8, 1912; on German Bank, near Mount Desert Island, and 

 off Penobscot Bay from August 12 to 14, 1913 (stations 10095, 10099, and 10101); 

 and again off Penobscot Bay on August. 14, 1914 (station 10250). Fritz (1921) 

 found it throughout September and during the first week of October at St. Andrews ; 

 Bailey (1917) likewise lists it from the Bay of Fundy for September 18; but occa- 

 sional specimens in the tow in Massachusetts Bay on October 1, 1915 (station 10322) 

 constitute our only autumnal record for it in other parts of the gulf. N. seriala 

 has not been detected in winter either at St. Andrews or in the open gulf, nor in the 

 eastern channel, on Georges Bank, or over the continental slope at any season. 



The seasonal fluctuations of N. seriata are essentially the same in the Gulf of 

 Maine as in the English Channel, where it attains its maximum abundance in August 

 (Ostenfeld, 1913); but it is described as most plentiful in spring in the northern 

 part of the North Sea and over the northeastern Atlantic generally. Hence, if 

 Ostenfeld's (1913, p. 415) suggestion that this species includes two biologic races — 

 a northern, with maximum in spring, and a more southern, with maximum in 

 August — be well founded, the Gulf of Maine N. seriata belongs to the latter. How- 

 ever this may be, N. seriata is one of the several diatoms that are summer forms in 

 the gulf but which Fish (1925) found to be characteristic of the winter flora at 

 Woods Hole (p. 423). 



This species is of minor importance in the gulf, where it occurs only sparingly 

 even at the time of its greatest abundance, and never, so far as known, in swarms 

 such as have been recorded in European waters. Several other neritic species of the 

 genus have been reported from the estuarine waters at St. Andrews and St. Marys 

 Bay (Fritz, 1921; Bailey and Mackay, 1921), but they are not likely to be found 

 out in the open sea in the gulf except as strays. 



Rhizosolenia 



The species of this genus that appears most frequently in the towings in the 

 inner parts of the Gulf of Maine is the variety semispina of Rh. hebetata (Gran 1908. 

 p. 55, fig. 671b), a form which fortunately is very easily recognized. In March Rh. 

 semispina is widely distributed in the coastal belt from Cape Cod to Penobscot Bay 

 on the western side of the gulf (stations 20058 to 20061 and 20088 in 1920; 10505 

 and 10506 in 1921), and in the shoal water along western Nova Scotia out to the 

 Eastern Channel (stations 20072, 20078, 20079, and 20084) in the eastern; likewise 

 over the outer part of the shelf off Shelburne (stations 20075 to 20077). As a rule 

 Rhizosolenia has proved wanting among the sparse Coscinodiscus-Ceratium plank- 

 ton that occupies all the central and deeper parts of the gulf during that month, but as 

 a notable exception to this rule it dominated the diatom community of the western 

 basin on March 5, 1921 (station 10510). A few Rh. semispina were also noted near 

 the northern edge of Georges Bank on March 11, 1920 (station 20064), and over the 

 slope to the southward on February 22 (station 20044). In April of that year 

 Rhizosolenia semispina occurred at nearly all the stations in the gulf proper 

 (stations 20089 to 20098, 20100 to 20107, 20109, 20112, and 20114 to 20117), domi- 

 nating the plankton in the Western Basin on the 18th (station 20115). It was like- 

 wise recorded over the continental slope southeast of Georges Bank on the 16th 



