PLANKTON OF THE GULF OF MAINE 
181 
Time 
Surface 
hauls 
Vertical 
hauls 
March _ _ 
Per cent. 
14. 5 
11 
3 
Per cent 
G 
5 
4 
April.. . . 
May 
In several instances the greater percentage on the surface was the result of a 
definite concentration there, proved by the capture of hundreds of specimens in the 
surface net at several stations where A. longiremis was so scarce deeper down that 
the vertical net missed it altogether — for instance, off the Isles of Shoals on March 
5 (station 20061); off the northern edge of Georges Bank, March 11 (station 20063); 
on its eastern edge and southern slope, April 16 (stations 20108 and 20109); and, 
notably, on March 23, off Yarmouth, Nova Scotia (station 20083), where the richest 
surface catch of all was made (711 specimens) . At a rather larger number of localities 
the yield of the vertical nets was considerable, where few or none were taken on the 
surface, as shown in the following table: 
Locality 
Date 
Hour 
Station 
Number 
per 
square 
meter in 
vertical 
hauls 
Number 
taken in 
surface 
hauls 
Near Mount Desert 
Apr. 12,1920 
Apr. 15,1920 
Apr. 16,1920 
Apr. 17,1920 
Apr. 18, 1920 
May 16,1920 
May 17,1920 
1 p. m 
10 p. m . 
1 a. m 
20099 
280 
0 
Northern Channel 
20105 
1,300 
53 
Browns Bank _ _ 
20106 
240 
2 
Deep water north of Georges Bank _ 
7 a. m 
20112 
863 
0 
Western basin 
4 a. m 
20115 
800 
0 
Off Cape Cod . 
11 p. m 
8 a. m 
20125 
470 
0 
Southwest part of basin 
20127 
1, 437 
27 
The most that can be said from this is that at times A. longiremis tends to gather 
at the surface, both in spring and in midsummer, but that on other occasions it keeps 
at least a few fathoms down. The hauls here listed give no evidence of diurnal 
migrations, for the richer surface catches 'were more often between 9 a. m. and 5 p. m. 
than at night, and, on the other hand, several of the hauls in which it most predomi- 
nated in deeper levels were between sunset and sunrise. 
A. longiremis has been found over a very wide range of salinity, being common 
in water as brackish as 6.72 per mille in the Baltic and as salt as 35.32 per mille in 
the English Channel. In the Gulf of Maine it occurs well within these limits. It is 
likewise eurythermal over a wide range of temperature, being present in the gulf 
indifferently in water as warm as 16° and as cold as 0.3° to 2°. The physical limits 
within which it reproduces locally have not been determined, but the presence of 
juveniles in August (p. 177) proves that reproduction takes place successfully in summer 
temperatures, probably upwards of 10 to 12°. 
Acartia tonsa Dana 
This species was originally described from Port Jackson, Australia, and was 
reported by Giesbrecht (1892) from the west coast of South America, and from the 
Malayan Archipelago by Cleve (1901). On the one side of the North American 
