396 BULLETIN OF THE BUKEAU OF FISHERIES 



of the diatom genus Chastoceras as of the peridinian genus Ceratiuni (Bigelow 

 1914a, p. 405). 



In 1925 Cape Cod Bay was likewise the site of a rich flowering of Rhizosolenia 

 alata (p. 447) from the middle of December (appearing between the 10th and 15th) 

 through January. But while the Ipswich Bay diatoms may have been the precursors 

 of the vernal flowerings for the coastal belt Cape Ann-Cape Cod, marking the site 

 of their inception, this flowering of Rhizosolenia can hardly be so classed for Massa- 

 chusetts Bay, both because the waters in the western and central parts of the latter 

 contained almost no diatoms in January when Rhizosolenia was at its maximum in 

 Cape Cod Bay, and because when flowerings suddenly appeared off Plymouth to the 

 west and near Stellwagen Bank to the north during the last week in that February, 

 the plankton at the latter locality was dominated by Thalassiosira, with very few 

 Rhizosolenia detected in such of the towings for later dates as have yet been examined. 

 So far we have no other record of R. alata flowering richly in the Gulf of Maine in 

 winter; in this respect the shoal waters of Cape Cod Bay agree rather with the 

 Wood Hole region, where Fish (1925) has reported winter maxima of Rhizosolenia 

 for two different years. 



In summary, diatoms and peridinians alternate in dominating the phyto- 

 plankton of the gulf. The former, scarce in the offshore waters of the gulf during 

 late autumn and winter, flower in tremendous abundance during the spring, the 

 flowerings commencing in the coastal belt. Probably they always appear between 

 Cape Ann and Cape Elizabeth as early as the first week in March, perhaps earlier. 

 In early years the vernal flowerings appear in Massachusetts Bay by the last week of 

 February, perhaps not till the last week of March in late years, preceded (at least in 

 some years) by winter flowerings of Rhizosolenia in Cape Cod Bay. Eastward along 

 the coast from Cape Elizabeth to the Bay of Fundy diatoms swarm from early April on. 

 The diatom flowerings are of but brief duration in Massachusetts Bay, having passed 

 their climax in its southern side by the first week of April of 1925, and by the last 

 week of the month in the northern side of the bay in 1913; but the diatom maxima 

 endure till May to the northward of Cape Ann and to some extent throughout the 

 summer along the northern shore of the gulf. At St. Andrews the vernal flowerings 

 continue through May, followed by a period of scarcity in June. On the Nova 

 Scotia side diatoms swarm in April, but only for a brief period, reappearing in some 

 numbers in June (p. 389). Over the central deeps of the gulf the spring flowering 

 reaches its climax in May; and shortly after mid-June diatoms practically vanish 

 from the western basin, though in some summers diatoms are an element in the 

 plankton of the eastern part of the basin all summer. During some years, if not 

 annually, a secondary brief flowering of diatoms takes place in Massachusetts Bay 

 in late August or September, and at some time in late summer or early autumn 

 (the precise date varies from year to year) in the St. Andrews region and likewise in 

 the open Bay of Fundy. Diatoms probably play a more important role in estuarine 

 situations generally and close in to the shore than they do out at sea, but I can 

 offer little on this point, most of our towing having been done well out from the land. 



