PLANKTON OF THE GULF OF MAINE 
441 
waters as a whole (Ostenfeld, 1913), but its rarity or absence in the inner parts of 
the Gulf of Maine contrasts sharply with its status in European coastal waters, 
such as the English Channel and the North Sea generally, where it is one of the 
most dominant of diatoms. This difference in its distribution in the two sides of 
the North Atlantic can not be explained until its life history is better known for 
American waters, but it is at least suggestive that Guinardia flowers chiefly at a 
time of year when the Gulf of Maine offers the least favorable environment for the 
multiplication of diatoms of any sort. 
Lauderia 
The brief dominance of Lauderia glacialis off the coast of Maine in the very 
scanty pelagic flora of early March (stations 20056 and 20058) prior to the flowering 
of Thalassiosira has already been mentioned (p. 421), as has its occurrence near Cape 
Ann and in Massachusetts Bay at that same season (stations 20060 to 20062). 
In the western side of the gulf the flowering of Lauderia probably reaches its cul- 
mination by the end of March, at the latest, for it was not detected at any of the 
April stations west of Mount Desert in 1920. It is later in appearing in the eastern 
side of the gulf, for while none were detected at our several stations off western 
Nova Scotia on March 23, 1920, it was present there and out to the eastern chan- 
nel and the southeast face of Georges Bank by April 15 and 16 (stations 20101, 
20107, and 20109), accompanying the early flowerings of Chsetoceras and Thalas- 
siosira, though nowhere abundant. 
Thus Lauderia appears just prior to the rich vernal flowerings of Thalassiosira 
and Chsetoceras, reaches its maximum while these two genera are still in a state of 
active multiplication, and diminishes or vanishes after the brief period of a few 
weeks while they are still swarming. We have occasionally found Lauderia among 
other diatoms in May (station 10285 in 1915), but it is not recorded for later sum- 
mer or autumn. Neither McMurrich (1917), Bailey (1917), nor Fritz (1921) have 
detected it at St. Andrews or in the Bay of Fundy. L. glacialis (fig. 117; Gran, 
1908, p. 23, fig. 23) is the basis of all our records for the genus. 
NitscMa 
Nitschia seriata, like Skeletonema costatum (p. 448), is a summer species in the 
Gulf of Maine, where it has not been detected during the spring months. Our 
earliest seasonal record of it is for June 10, when it was represented by occasional 
examples among the more abundant Chsetoceras and other genera off Petit Passage, 
Nova Scotia, in 1915. Fritz (1921) found it constantly at St. Andrews from July 
3 onward throughout the summer; Bailey (1917) records it from the Bay of Fundy 
in August; and it has appeared with comparative regularity in our July and August 
tow nettings in those parts of the gulf where diatom plankton persists so late in the 
season, more especially in the coastal belt between Cape Elizabeth and Nova Scotia. 
For example, N. seriata was present in fair quantity on Jeffreys Bank off Penobscot 
Bay, as well as close in to the land nearby (stations 10016 to 10021 and 10025), 
