396 
BULLETIN OF THE BUREAU OF FISHERIES 
of the diatom genus Chastoceras as of the peridinian genus Ceratium (Bigelow 
1914a, p. 405). 
In 1925 Cape Cod Bay was hkewise the site of a rich flowering of Rhizosolenia 
alata (p. 447) from the middle of December (appearing between the 10th and 15th) 
through January. Butwhile 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. (data 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. 
