PLANKTON OP THE GULF OF MAINE 
437 
chusetts Bay and off the mouth of the Merrimac River, 63 and likewise out at sea, as 
exemplified by the western basin (p. 428). It seems that at this time of year Coscino- 
discus is decidedly more numerous near land and on the offshore banks than in the 
deeper parts of the gulf or over the bank west of Nova Scotia, for during the Halcyon 
cruise of December and January, 1920-1921, our largest catches of Coscinodiscus 
were made in the Massachusetts Bay region (stations 10488 and 10489) and off the 
Merrimac (station 10492), whereas only a scattering was taken in our January 
hauls at sea off Penobscot Bay or in the eastern side of the gulf (stations 10496 and 
10499 to 10502). Coscinodiscus was most numerous in the shallow waters over Georges 
and Browns Banks during the cruises of the Albatross in 1920 (stations 20066, 20072, 
20110, and 20111); but although this genus may reach its highest development in 
the gulf in or near comparatively shoal water, its abundance in the Western Basin 
at the end of February, 1920, and again a month later (station 20049, February 23, 
1920; station 20087, March 24, 1920), forbids the assumption that it is distinctively 
neritic. In fact, one of its commoner members — C. asteromphalus — has usually been 
described as oceanic in other seas. 
Coscinodiscus does not exhibit as definite a flowering period in the gulf as do 
Thalassiosira or the more plentiful species of Chsetoceras, nor does it ever rival the 
enormous numbers in which these latter genera so often appear there. None of our 
standard hauls has ever yielded more than a few cubic centimeters of Coscinodiscus, 
contrasted with hundreds of cubic centimeters of Thalassiosira and Chtetoceras during 
their period of greatest abundance (p. 399). 
In the open gulf we have made our richest catches of Coscinodiscus during mid- 
winter, in February, March, and April. In fact, this genus has occurred in almost 
every offshore haul between the end of December and the middle of April, and Fritz 
(1921) found it constantly throughout the winter and early spring at St. Andrews. 
Coscinodiscus has been detected only occasionally in the western half of the gulf 
generally or on the offshore banks during the late spring or early summer. Thus it 
was found at only 1 out of 14 stations (station 10266) between May 4 and 30 in 
1915, at 2 of the 12 June stations for that year, and not at all in the Massachusetts 
Bay region or off Cape Cod from May 4 to 17, 1920. If Coscinodiscus is not actually 
nonexistent in midsummer among the peridinian plankton of the basin of the 
gulf (likewise along the coastwise belt between Cape Ann and the Bay of Fundy) 
it is at least so overshadowed there by other more plentiful plant cells as to be 
overlooked easily. Fritz, too, records it as sometimes wanting and usually scarce 
at St. Andrews during June, July, and early August; but Coscinodiscus was a 
considerable element in the plankton near Lurcher Shoal, off Yarmouth, Nova 
Scotia, on August 12, 1914 (station 10245). Apparently this foreshadowed a wide- 
spread augmentation of it in the northeastern part of the gulf during the early autumn, 
for it occurred in considerable numbers at two stations off the eastern part of the 
Maine coast on September 11 and 15, 1915 (stations 10316 and 10317), again at these 
same localities on October 9 (stations 10327 and 10328), indicating that it is more 
63 At this locality we found Chsetoceras far more numerous than Coscinodiscus as early in the winter as Jan. 16 in the year 1913. 
