PLANKTON OP THE GULF OF MAINE 
269 
a month earlier in the season; probably more than in summer, though perhaps no 
more than in May. This parallels its seasonal periodicity off northern Europe, for it 
is usually most plentiful in the English Channel in autumn (Farran, 1910), with 
its plurimum falling in late summer and early autumn in the northeastern Atlantic 
up to Iceland (With, 1915). 
Another fact clearly brought out is that this species, like most other copepods, 
may be decidedly streaky in its distribution at times. For instance, when we made 
one of our richest catches of it (24,450 per square meter at station 10338) on October 
27, 1915, there were hardly one-sixth as many a few miles inshore (station 10339; 
about 4,040 per square meter). As a less striking example, there were respectively 
3,600 and 3,400 at two stations (10321 and 10324) at the mouth of Massachusetts 
Bay on September 29, but only 850 per square meter at a third station (10320). 
This makes it impossible to draw any but the most general conclusions from the 
numbers of specimens taken until a much larger body of information has been 
accumulated. 
I have purposely refrained from discussing seasonal periodicty for P. parvus on 
the offshore banks for want of sufficient data. Until something is known of its 
status there during the summer and autumn all that can be said is that it was slightly 
more plentiful on Browns Bank on June 29, 1915 (470 per square meter, station 
10296) than on March 13, 1920 (60 per square meter, station 20072), but both catches 
were so scanty and the difference between them so small that it is not significant. 
On the eastern part of Georges Bank it was not taken at all at two stations on March 
11, 1920 (stations 20065 and 20066), but was comparatively plentiful on April 16 and 
17 (3,400 per square meter at station 10310; 1,640 at station 10311). Off the south- 
western slope of the bank, on the contrary, it was much more numerous on February 
22 (5,000 and 3,000 per square meter, respectively, at stations 20044 and 20045) than 
on May 17 (only 400 per square meter at station 20129), contradictory observations 
from which no conclusions can be drawn. 
Vertical distribution . — With (1915) has described the species as usually near the 
surface in the northeastern Atlantic, and the majority of records of it in other seas 
have been from shoal towings. In the Gulf of Maine, however, it showed no ten- 
dency to congregate in the uppermost strata during the spring of 1920, for it was 
detected in a smaller percentage (10 per cent) of the surface hauls than of the vertical 
hauls, and only in small numbers at these few (table, p. 303). Little can be said of 
its vertical distribution in other months of the year because the copepods have not 
yet been listed from any of the surface hauls for 1915 or subsequently, and a record from 
a vertical haul merely locates the specimen somewhere between the top and the bottom 
of the water. It is probable, however, that most of the specimens collected by the 
Halcyon in 1920-1921 (table, p. 304) came from the general level at which the nets 
were working horizontally — that is, from depths varying from 20 to 240 meters. 
The average depth of all the vertical hauls which had more than the average 
number of P. parvus is 127 meters, and the four richest catches of all — that is, those 
with more than 20,000 P. parvus per square meter (stations 10332, 10333, 10336, and 
10338) — were, respectively, from 50-0, 80-0, 50-0, and 80-0 meters, locating the zone 
of chief abundance for the species as shoaler than 100 to 125 meters. 
