408 
BULLETIN OF THE BUREAU OF FISHERIES 
part around the cape from the eastward. But if C. arctica occurs in the gulf chiefly 
as an immigrant from the north, as seems probable at present, its quantitative dis- 
tribution within the gulf in early spring does not parallel the distribution of tempera- 
ture, for at the time of the winter minimum the water is coldest next the western 
side of the gulf while arctica is most abundant in the eastern side. 
The actual proportions in which the several species of Ceratium occurred during 
the early spring of 1920 appears from the following list of actual counts of samples 
at representative localities : 
Relative numbers of species of Ceratium in samples, “Albatross” cruise, March 1 to 19, 1920 
Locality 
C. 
tripos 
C. 
lon- 
gipes 
Inter- 
medi- 
ates 
be- 
tween 
lon- 
gipes 
and 
arctica 
C. 
arctica 
c. 
fusus 
Massachusetts Bay, station 20050 - 
22 
1 
0 
1 
0 
Western Basin, station 20049 
25 
0 
1 
1 
0 
South center, station 20063 
49 
0 
6 
2 
2 
Eastern Basin, station 20054... 
12 
0 
1 
4 
1 
Off Mount Desert, station 20056 
9 
3 
0 
2 
0 
Southeast Basin, station 20064 
8 
2 
8 
3 
1 
Georges Bank: 
Northwest, station 20047 
20 
0 
0 
0 
0 
Southwest, station 20045 
22 
5 
5 
4 
1 
East, station 20065 
11 
1 
8 
2 
1 
Southeast, station 20068 
7 
9 
2 
2 
1 
Southeastern slope, station 20069 
5 
7 
X 
3 
0 
Eastern Channel, station 20071 
5 
8 
2 
5 
2 
Browns Bank, station 20072 
1 
6 
6 
9 
1 
Off southern Nova Scotia: 
Station 20074 
1 
6 
10 
7 
1 
Station 20077 
1 
2 
4 
15 
3 
With the advance of the season and hand in hand with the augmentation of 
diatoms, peridinians of all species so diminish in numbers that in 1920 they had 
practically disappeared from the two productive centers for diatoms in the two 
sides of the gulf by mid-April and were so scarce elsewhere that counts of the relative 
numbers of the several species of Ceratium are no longer significant. But 
when they reappear in the Massachusetts Bay region late in April or early in May in 
the western side of the gulf, and in the Nova Scotian waters in the eastern, following 
the eclipse of the diatom flowerings, a complete reversal has taken place in the 
relative importance of the two leading species, for we have found longipes far more 
numerous than tripos during the first week in May at every station where the genus 
as a whole was sufficiently abundant for counts to be of value, only excepting the 
southwestern edge of Georges Bank, where the two species were about equally 
numerous (station 20129, May 18, 1920). In fact, C. tripos is then practically non- 
existent within the gulf, or at best represented by occasional examples only. A 
slight recrudescence of C. arctica (or perhaps a fresh wave of immigration) apparently 
takes place during the first half of May, when occasional examples have been detected 
at most of our stations (except among the diatom swarms) ; and on the seventh of 
that month in 1915 C. arctica proved to be as abundant on German Bank (station 
10271) as C. longipes, its area of abundance coinciding with the location of the cold 
