456 BULLETIN OF THE BUREAU OF FISHERIES 



(1913) points out, but before it can be used in this way for American waters a far 

 clearer insight must be gained into its hydrographic and geographic relationships. 

 In fact, it is still an open question whether Th. longissima is oceanic or neritic in the 

 western Atlantic, or as indifferent to the proximity of coasts or shallows as it is on 

 the European side. 



Thalassiothrix nitschioides, although one of the most characteristically neritic 

 of all pelagic diatoms, has occurred far more often in our tow nettings than has its 

 relative, Th. longissima. Fritz (1921) found Th. nitschioides at St. Andrews through- 

 out the year except between October 15 and December 13, and the numbers counted 

 were usually so small that its absence from the hauls made during that period is 

 perhaps not significant. Probably it occurs irregularly the year round in similar 

 situations all along the coast line of the gulf, and its presence or absence and its rela- 

 tive abundance out at sea may depend more on the currents sweeping it out from 

 these sources of supply around the coast line than on local flowerings. 



It seems that few drift out to sea during the -winter, for it was detected at only 

 one station — off the mouth of the Merrimac River (station 10492) — during the mid- 

 winter cruise of the Halcyon in 1920 and 1921, and not at all in our tows off Gloucester 

 from November, 1912, to February, 1913. But we had it off the western part of 

 Georges Bank on February 22, 1920 (station 20045), and during that March it was 

 found at four stations in the coastal belt between Cape Cod and the Bay of Fundy; 

 also in the Eastern Channel, on the southeastern slope of Georges Bank, and at two 

 stations off Shelburne, Nova Scotia (stations 20056, 20058, 20059, 20064, 20066, 

 20068, 20071, 20075, 20076, 200S4, and 200SS; fig. 127). Th. nitschioides attains 

 its widest distribution in the gulf in April, during which month in 1920 it not only 

 occurred more regularly in the coastal belt than in March (in fact, at almost every 

 inshore station where diatoms of any sort were plentiful), and off Nova Scotia out to 

 the southeastern slope of Georges Bank, but likewise at four localities in the central 

 basin of the gulf (stations 20089 to 20093; 20095 to 20098; 20100, 20102 to 20107, 

 20109, 20114, and 20117). 



Our records suggest that Th. nitschioides practically disappears again from the 

 offshore parts of the gulf after the end of April, for it was detected at only one station 

 off Cape Elizabeth (10277) during the May cruise of the Grampus in 1915, not at all 

 at the 10 stations occupied by the Albatross on the western side of the gulf and on 

 Georges Bank from May 4 to 17, 1920 (stations 20120 to 20129). We have not found 

 it at sea in the gulf during the summer and only once during the autumn, viz, off 

 Penobscot Bay on October 9, 1915 (station 10329). 



Th. nitschioides follows much the same seasonal cycle in north European waters, 

 where it flowers mo3t abundantly from February until April, according to locality, 

 diminishing in abundance during May, and with its annual minimum in August. 

 It is far less important as a member of the plankton in the Gulf of Maine, where we 

 have never found it abundant, than it is in the North Sea region, where it occurs at 

 all times of the year (Ostenfeld, 1913, p. 409), very generally over the entire area, 

 and at times in great numbers. 



The occurrence of Th. nitschioides so far offshore off Nova Scotia and over the 

 southeastern slope of Georges Bank, contrasted with our failure to find it in any of 



