PLANKTON OF THE GULF OF MAINE . 309 



too, it is a regular inhabitant of the whole continental shelf off Nova Scotia (Bigelow, 

 1917, and Huntsman, 1919), likewise over the Grand Banks of Newfoundland and 

 in the Gulf of St. Lawrence, where the Canadian fisheries expedition found it at 

 many localities and in large numbers (Huntsman, 1919). Generally speaking, the 

 Gulf of Maine is the most southerly important center of regular reproduction and 

 constant abundance for <S. elegans, as it is for various other boreal planktonic animals. 

 West and south of Cape Cod this chsetognath is less plentiful, less regular in its 

 occurrence, and more or less seasonal, ranging southward as far as Chesapeake Bay 

 in cold summers (e. g., 1916) but rare beyond Nantucket in warm (e. g., the year 

 1913), as I have elsewhere remarked (Bigelow, 1922, p 152). At Woods Hole it is 

 fairly plentiful from December to June, but decidedly rare or lacking entirely in 

 summer (Fish, 192.5, fig. 34). Probably it occurs farthest to the southward in 

 winter, but the limit to its distribution in that direction is not yet known for the 

 western Atlantic. 



It has been well established, both by our own records and by those of the Cana- 

 dian fisheries expedition of 1915 (Huntsman, 1919), that S. elegans (though not 

 dependent on the bottom at any stage of development) is a creature of coast and not 

 ocean waters. This, indeed, its occurrence in other seas would suggest. Broadly 

 speaking, the outer edge of the continental shelf is its offshore boundary west of 

 Cape Sable at all seasons, a fact illustrated by its rarity at our deep stations over the 

 continental slope 61 both in the cold months and in the warm. East of this, however, 

 Huntsman has shown that its outer limit fluctuates with the seasons, spreading out 

 to the eastward to cover the great oceanic triangle between the Nova Scotian and 

 Newfoundland Banks in spring, to contract again to the general contour of the con- 

 tinental edge as far as the tail of the Grand Banks (including the Laurentian Channel, 

 however) in midsummer. The high temperature, or high temperature combined 

 with high salinity, of the inner edge of the so-called Gulf Stream is an impassable 

 offshore barrier to it along the North American coast. 



Only a preliminary survey has yet been made of the collections of this species 

 gathered during the Gulf of Maine cruises; enough, however, to show that its range 

 covers the offshore parts of the gulf. We have seldom found it in any abundance 

 over the deep basin, however, as appears clearly from the accompanying chart 

 (fig. 86) showing the numbers of 8. elegans per square meter of sea area as calculated 

 from the catches of the vertical nets for the summer seasons of 1913, 1914, 1915, and 

 1916. Out of a total of about SO such hauls, only seven have yielded more than 50 S. 

 elegans per square meter anywhere in the gulf outside the general 100-meter contour, 

 and these seven stations were all located close to that contour line. With these few 

 exceptions, all our rich hauls of S. elegans have been in shallow water, either in the 

 coastal zone (in July, 1912, we found S. elegans in some numbers in Casco Bay) or on 

 the offshore banks. But the localization of the rich and poor catches show that not all 

 parts of the peripheral zone of the gulf offer an equally favorable habitat for S. elegans, 



•' None were taken at station 10220 in 1914, station 10352 in 1916, stations 20044 and 20129 in 1920, nor at any of the deep stations 

 on the slope west and south ot Cape Cod either in 1913 or in 1916, but a few were detected in the vertical haul from 500 meters off 

 Georges Bank, July, 1914 (station 10218). 



