PLANKTON OF THE GULF OF MAINE 433 



factor in the diatom flora of the offshore waters of the gulf, whore 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 Aprd 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 it 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. 



Ch.se toceras 



The relationship which the diverse genus Chastoceras 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 Chretoceras 

 that precede the Thalassiosira swarms in spring (p. 421) are to be 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 

 Cli. criophilum and Ch. atlanticum, on the one hand, and the neritic forms Ch. 

 diadema, Ch. laciniosa, Ch. contortum, Ch. scolopendra, Ch. didymum, and Ch. 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. fnrcdlaturn, 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 Chretoceras species, barring Ch. 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 



