402 
BULLETIN OF THE BUREAU OF FISHERIES 
density of the eastern diatom center, reflected by the volumes of plankton, and 
more especially the rather large volumes along the 100-meter curve west of Nova 
Scotia contrasted with the barren water both over the basin to the west and close 
in to the neighboring coast on the east, point directly to a tonguelike drift of diatoms 
north ward toward the Bay of Fundy from the rich center of production off Cape 
Sable. 
The rich catches in the Eastern Channel (375 cubic centimeters at station 
20107) and off the southeast face of Georges Bank (290 cubic centimeters at station 
20109) similarly suggest another line of dispersal for the Cape Sable-Browns Bank 
diatoms toward the southwest, a thesis supported by the qualitative uniformity of 
the April catches in that region, illustrated by the following table: 
Diatoms 
Browns 
Bank, 
station 
20106; 
volume, 
690 cubic 
centi- 
meters 
Eastern 
Channel, 
station 
20107; 
volume, 
375 cubic 
centi- 
meters 
South- 
east 
slope of 
Georges 
Bank, 
station 
20109; 
volume, 
290 cubic 
centi- 
meters 
Chsetoceras laeiniosum 
x 
X 
x 
Chsetoceras debile 
x 
x 
x 
Chaetoceras atlanticum 
x 
x 
Chsetoceras decipiens 
x 
x 
x 
Chsetoceras diad'ema _ 
x 
X 
X 
Chsetoceras didymum 
x 
X 
X 
Chsetoceras convolutum 
X 
X 
Chsetoceras criophillum _ _ _ 
x 
x 
Thalassiosira gravida 
X 
x 
x 
Thalassiosira nordenskioldi 
X 
X 
Thalassiothrix nitschioides.. 
X 
X 
x 
Coscinodiscus 
x 
Rhizosolenia semispina _ 
x 
x 
x 
Lauderia glacialis_~ 
X 
x 
x 
Fragillaria sp 
x 
x 
Coscinosira _ 
x 
X 
If such a drift of diatoms from the Nova Scotian center was actually taking place 
at the time of our April cruise in 1920 it must have been strictly confined to the outer 
edge of Georges Bank, because the shallows to the northward (stations 20108, 20110, 
and 20111) supported a phytoplanktonic community not only much less abundant 
(15 to 120 cubic centimeters per haul), but one of rather a different type, in which 
the oceanic diatoms Chsetoceras decipiens, C. criophillum, C. atlanticum, G. densum, and 
Coscinodiscus were dominant, with the several species of Ceratium continuing as an 
important factor in April just as they had been in March. 
As long as the diatom flowerings continue at their peak, volumes of plankton as 
large as or larger than those noted on the chart (fig. 109) are to be expected all along 
the coast north and east of Cape Ann, on the one side of the gulf and over the banks 
west and southwest of Nova Scotia on the other (Browns Bank yielded one of our 
largest spring catches, as appears on the chart), locally, too, on Georges Bank (p. 385) ; 
and while the central part of the gulf is hardly less barren in April than in March, the 
spring flowering may be no less intensive there, once it is under full headway, than in 
the coastal zone. For example, diatoms were so plentiful in the western basin on 
