PLANKTON OF THE GULF OF MAINE 433 
factor in the diatom flora of the offshore waters of the gulf, where it can safely be 
credited with a coastal origin. 
Biddulphia is distinctly a spring species; in fact, we have never found it in the 
open gulf at any other season. At St. Andrews it occurs only irregularly and sparsely 
during the October-February period (McMurrich, 1917; Bailey, 1917), but Doctor 
McMurrich found it regularly, often in abundance, from February 26 until April 23, 
after which it is rare. Fritz (1921) likewise records an abundance of Biddulphia 
on April 20, but without naming the species concerned. The seasonal cycle is much 
the same for B. aurita in European seas, where Ostenfeld (1913, p. 500) describes it 
as living on the bottom for the greater part of the year, to invade the planktonic 
communities in great numbers during the spring months. 
Biddulphia mobilensis, a true planktonic form though neritic in nature, has 
been noted in September and October, 1915 (stations 10316 and 10327), and in 
March, 1921 (station 10505), always in small numbers. Like B. aurita, it is more 
abundant in the estuarine tributaries of the Bay of Fundy, where Bailey (1917) 
records if for various dates in January and February and again from August to 
October, and where he found it very abundant and locally dominant in August. 
Cliaetoceras 
The relationship which the diverse genus Chsetoceras bears to Thalassiosira 
during the spring flowerings of the latter, and the wide distribution of several of its 
members in the offshore and eastern coastal waters of our gulf at that time, have 
already been touched upon (p. 418). As a rule, the same species of Chsetoceras 
that precede the Thalassiosira swarms in spring (p. 421) are to he found in some 
numbers among the masses of the latter later in the season, even when Thalassiosira 
is most abundant. To enumerate them, station by station, would be repeating 
entire the lists given above (p. 423), for practically all the species of the genus defi- 
nitely known from the gulf have been found among the Thalassiosira plankton of 
April and May. Nor do the lists for the individual stations off the west and north 
coasts of the gulf for April (stations 20090 to 20096) differ seriously from the March 
lists (stations 20056 to 20062), Ch. decipiens being universal, with the oceanic species 
Oh. criophilum and Oh. atlanticum, on the one hand, and the neritic forms Ch. 
diadema, Oh. laciniosa, Ch. contortum, Oh. scolopendra, Ch. didymum, and Oh. sociale 
on the other, occurring often enough to show that though they may be overshad- 
owed by Thalassiosira all of them may be expected anywhere along this zone. Ch. 
debile shows decided augmentation in April, when it not only occurred at every 
coastwise station in 1920 but dominated the phytoplankton locally on Platts Bank 
on the 10th (station 20094). Ch. furcellatum, easily recognized by its peculiar 
spine-bearing spores, which was not found at all in March, appeared in numbers 
near Cape Ann, off Cape Cod, and in Massachusetts Bay on April 9, 18, and 20, 
1920 (stations 20090, 20116, 20117, and 20119). 
Practically the same association of Chsetoceras species, barring Oh. furcellatum, 
was likewise encountered off the west coast of Nova Scotia, on Browns Bank, and 
in the North Channel during April, 1920 (stations 20101 to 20106), and although 
