PLANKTON OF THE GULF OF MAINE 



327 



Inasmuch as the planktonic communities of the deeper levels of the Atlantic 

 never penetrate the gulf in toto ( p. 67), it can hardly be questioned that such examples 

 of S. maxima as appear there come via the northeastern route in the band of cold 

 mixed water along the edge of the continent, not from the much greater depths which 

 they inhabit off the slope. Very likely the chief source of supply for this species in 

 the Gulf of Maine is the deep oceanic triangle between the Nova Scotian and New- 

 foundland Banks, where the Canadian fisheries expedition found S. maxima in great 

 abundance in a haul from 200 meters on the 1st of June, 1915 (Huntsman, 1919, 

 p. 429). In short, it is as a distinctively northern visitor and as such alone that 

 S. maxima reaches the Gulf of Maine, but our experience so far has been that but few 

 individuals find their way in through the eastern channel, which is the only line of 

 ingress sufficiently deep to be normally open to it. 



S. maxima is an extraordinarily voracious animal and as such must occupy an 

 important position in the natural economy of the plankton of the deepest waters of 

 the gulf if it ever enters the latter in any abundance. 



Sagitta lyra Krohn 



This chffitognath is as distinctly a summer visitor as is its larger relative, 

 S. maxima, a winter one to the inner parts of the Gulf of Maine, where it has been 

 detected on six occasions in three distinct years — all in July and August. These 

 records are as strictly confined to the deep trough as are those of S. maxima (p. 325) , 

 and whether within or without the gulf the depths of capture are about the same as 

 for that species. 



S. lyra occurs side by side with S. maxima over the continental slope in late winter 

 and early spring as well as in summer. 



Being a summer visitor to the gulf, S. lyra occurs there in rather higher tem- 

 peratures than does S. maxima. About 6° is the lowest in which our records estab- 

 lish its presence, and the upper temperature limit for the captures so far made 

 within the gulf is at least as warm as 8.17° (station 10031). Our records for it over 



