PLANKTON OF THE GULF OF MAINE 133 



to be expected anywhere in the gulf below 200 meters — witness the records from the 

 eastern basin and from the southeast deep. 



We have only two records for P. tarda, both over the continental slope off 

 Georges Bank in hauls from 750 to 100 meters, February 22 and March 12, 1920 

 (stations 20044 and 20069), which agrees with Sund's (1913) experience that this 

 species usually hves at a rather deeper level than P. multidentata, from which it is 

 separable by the low rostrum, hardly rising above the general dorsal outline, and by 

 its red color. We have not taken P. principis, but this species is recorded from south 

 of Marthas Vineyard by Sund (1913). 



Euphausiids 



We are indebted to Dr. H. J. Hansen, who identified the collections made dur- 

 ing the summer of 1912 and winter of 1912 and 1913, and to Dr. W. M. Tattersall, who 

 undertook the same task for the gatherings of 1914, 70 for abihty to include a chapter 

 on this economically important and faunistically instructive group of pelagic crus- 

 taceans. I have attempted the identifications of the euphausiids contained in 

 the tow nettings of our subsequent cruises by comparison with specimens named by 

 these two eminent speciahsts and by the aid of Zimmer's (1909) very clear keys 

 and descriptions; but while it is easy to name the adults of all the species occurring 

 regularly in the Gulf of Maine, by easily recognizable anatomical features, the larval 

 stages, occasionally abundant (p. 134), still await reference to their proper parentage. 



Knowledge of the occurrence of this group in the deep water outside the conti- 

 nental shelf abreast of the gulf, between the longitudes of 71 and 65°, is chiefly 

 based on the collections made by the Bureau of Fisheries' vessels in past years, 

 recently reported upon by Doctor Hansen (1915). 



Only a few species of euphausiids are yet known to occur within the gulf, nor 

 is it likely that the various oceanic members of the group will ever be found in its 

 inner parts except as stragglers; but these few (to be treated in detail below) are 

 among the most characteristic if not the most numerous members of its endemic 

 plankton. True, they seldom dominate the catch, or even form any considerable 

 part of it, except locally in the northeast corner of the gulf and near the mouth of the 

 Bay of Fundy, and when they swarm in other parts of the gulf it is only for brief 

 periods. But our tow nets have seldom failed to yield them in greater or less number, 

 except at times and localities when the catch as a whole has been of the scantiest. 

 Euphausiid shrimps are so important in the dietary of whales and of many fishes that 

 pursue them eagerly (and indeed one can well believe them dainty morsels) that they 

 are much more important economically than their small numbers, contrasted with 

 the hosts of copepods, might suggest. This subject is discussed in another chapter 

 (p. 97). 



The occasions on which we have made notably rich hauls of euphausiids within 

 the limits of the Gulf of Maine have been as follows: On Browns Bank, July 24, 

 1914 (station 10228), the haul at 60-0 meters yielded about 500 cubic centimeters of 

 small Thysanoessa, representing three species ( Thysancessa gregaria, Th. longicaudata, 



70 For tables of occurrence ot the several species in these years see Bigclow, 1914a, p. 411, and 1917, p. 282. 



