PLANKTON OF THE GULF OF MAINE 323 



dentata was much the more numerous of the two in the deep hauls in the eastern and 

 southeastern parts of the gulf (stations 10225, 10245, 10246, 10249), in the eastern 

 channel (station 10227)" (Bigelow, 1917, p. 295), and on the southern edge of 

 Georges Bank. 



Along the continental edge ahreast of the gulf, S. serratodentata has usually pre- 

 dominated over S. elegans at most of our stations irrespective of the season of the 

 year, or at least equaled the latter in numbers (stations 10218, 10219, 10220, 10233, 

 10260, 10261, 10295, 10349, 10351, 20044, 20077, and 20129). 



From New York southward &. serratodentata is the prevalent chsetognath right 

 in to the shore during warm summers such as that of 1913 (Bigelow, 1915), but in 

 cooler years, such as 1916, S. elegans is the dominant member of the pair over the 

 inner part of the shelf as far south as Delaware Bay and perhaps still farther, but 

 with S. serratodentata outnumbering it farther offshore, and along the continental 

 edge generally, as I have pointed out in a previous report (Bigelow, 1922, p. 152). 



The strong probability that S. serratodentata is not able to reproduce success- 

 fully in boreal water, though it not only grows to a larger size there than in higher 

 temperatures but attains sexual maturity, as evidenced by the large size of the repro- 

 ductive organs (Huntsman, 1919, p. 482), lends interest to the wide range of tem- 

 perature in which it occurs both in the Gulf of Maine and off southern Nova Scotia. 

 In the gulf its presence is definitely established in water as cold as 3.9° (station 

 10272, May 10, 1915) and 4.4° to 7.5° (stations 10281, 10282, and 10286, June 4, 10, 

 and 14, 1915), and the Canadian fisheries expedition likewise had it in 4° to 5°; but 

 most of the Gulf of Maine records (also the Canadian) have certainly been from 

 temperatures upwards of 7° to 8°, though there is no positive evidence of its presence 

 in the gulf in water warmer than 13.9° (station 10032, August 16, 1912; Bigelow, 

 1914, p. 122), most of the captures having been in subsurface hauls, or if at the surface 

 in regions of low surface temperature (stations 10030, 10229, and 10247). However 

 the occurrence of S. serratodentata elsewhere forbids the assumption that high tem- 

 peratures are per se unfavorable to it, for it has been taken in great abundance off 

 the continental edge in Gulf Stream temperatures (station 10070, surface 23.33°; 

 a few at stations 10071, 10073, and 10074 in temperatures of 24.44° and 23.9°), as 

 well as off southern Nova Scotia in 19.7° (Huntsman, 1919, Acadia station 44, 

 surface). 



Uncertainty as to the depth of the captures makes it impossible to establish 

 the precise salinity for the Gulf of Maine records of S. serratodentata except in the 

 following instances: 



Salinity, per mille 



Station 10025, closing net, 30 fathoms 32. 9 



Station 10027, closing net, 30 fathoms 33. 3 



Station 10030, surface 32. 7 



Station 10032, surface 32. 5 



Station 10229, surface 32. 01 



Station 10247, surface 32. 52 



It is not likely that it would be altogether barred from the surface by salinities 

 considerably lower than this, for Huntsman (1919) found it repeatedly in eastern 



