PLANKTON OF THE GULF OF MAINE 437 



chusetts Bay and off the month of the Merrimac River, 63 and likewise out at sea, as 

 exemplified by the western basin (p. 42S). It seems that at this time of year Cosci no- 

 discus is decidedly more numerous near land and on the offshore bunks 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 Chretoceras, 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 Chajtoceras during 

 their period of greatest abundance (p. 399). 



In the open guff 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 



« At this locality we found Chaetoceras far more numerous than Coscinodiscus as early in the winter as Jan. 16 in the year 1913. 



