54 



BULLETIN OF THE BUREAU OF FISHERIES 



Ever since the early eighties it has been known (from many collecting trips 

 carried on by the vessels of the United States Bureau of Fisheries from the laboratory 

 at Woods Hole) that the inner edge of the tropical water, carrying with it an extra- 

 ordinarily rich and diversified tropical plankton, lies only a few miles south of the 

 100-fathom contour off Marthas Vineyard in summer, just as is the case farther west 

 and south. Hence, although actual records of the pelagic fauna and flora at this 

 same relative position farther east have been very scanty up to within the last few 

 years, there was no reason to doubt that a tropical community occupied the same 

 relative position along the slope off Georges Bank; while the deep-sea explorations of 

 the National and Michael Sars, of the Canadian fisheries expedition of 1915, and of 

 the international ice patrol (Fries, 1922), have shown that the same assemblage of 

 warm-water planktonic animals and plants characterizes the inner (northern) edge 

 of the Gulf Stream to and beyond the southern corner of the Grand Banks of New- 

 foundland. It was therefore to be expected that any lines we might run seaward 

 as far, say, as the 1,000-meter contour, would bring us into warm water, where our 

 tow nets would yield a tropical plankton instead of the boreal community charac- 

 teristic of the Gulf of Maine to the north. And so it has proved, as the follow- 

 ing brief notes on our offshore hauls will illustrate. 



On July 10, 1913, for instance, we saw fragments of gulfweed on the surface 

 near Nantucket Lightship, and the neighborhood of the stream was made evident 

 over the 150-meter contour to the south (station 10061) by "the presence of Salpae, 

 Phronima, and the amphipod genus Vibilia, though the bulk of the plankton still con- 

 sisted of Calanus Jinmarchicus, with such other boreal forms as Euchseta norvegica, 

 Euthemisto, and Sagitta elegans " (Bigelow, 1915, p. 268) . We had a similar experience 

 over the 1,000-meter contour, some 70 miles farther east, about a week later in the 

 season the following year (station 10218), when we found the water of the high tem- 

 perature 27 characteristic of the inner edge of the Gulf Stream, more properly the 

 tropical water (p. 52), with a typically tropical plankton including Salpa fusiformis 

 and its relative genus, Doliolum; the tropical amphipod genera, Phronima, Vibilia, 

 and Oxycephalus; the copepods Rhincalanus and Sapphirina; the chastognaths Sagitta 

 enflata, S. kexaptera, and Pterosagitta draco; with the 11 species of tropical pteropods 

 and 19 species of tropical medusas and siphonophores listed below, and gulfweed 

 (Sargassum) floating on the surface, as I have elsewhere noted (Bigelow, 1917, 

 p. 245). 



Tropical pteropods and ccelenlerates taken over the continental slope off Georges Bank, July 21, 1914, 



station 10218 



Species 



Mollusks: 



Limacina rangii, d'Orb 



Creseis conica, Eschscholtz 



Creseis acicula, Rang 



Hyalocylis striata, Rang 



Cuvierina columnella. Rang — 



Diacria trispinosa, Lesueur 



Cavolina longirostris, Lesueur.. 



Cavolina uncinata, Rang 



Peraclc reticulata, d'Orb 



Corolla calceola, Verrill. 



Firoloida desmarestia, Lesueur. 

 Pleurobranchea tarda, Verrill. . 



Medusae: 



Stomotoca ptcrophylla 



Toxorchis kellneri.. 



Laodicea cruciata 



60-0 

 meters 



X 

 X 

 X 



300-0 

 meters 



1 

 2 



X 

 X 

 X 



400-0 

 meters 



1 

 1 

 1 

 1 

 2 

 1 

 1 



Species 



Medusa; — Continued. 



Rhopalouema lunemrium. 



Rhopalonema velatum 



Liriope scutigera 



Liriope tetraphylla ... 



Aglaura hemistoma. 



Nausithbe punctata - 



Siphonophores: 



Hippopodius hippopus 



Diphyes spiralis 



Diphyes appendiculata 



Diphyes bojani 



Diphyopsis dispar.. 



Diphyopsis mitra 



Agalma elegans.. 



Anthophysa formosa 



Physalia physalis 



60-0 

 meters 



X 

 X 



X 

 X 



X 

 X 

 X 

 X 

 X 



300-0 

 meters 



X 

 X 



x 



X 



x 



X 



x 

 x 



400-0 

 meters 



" Temperature 17.7° and salinity 36.04 per mille at 40 meters; 20.48° at the surface. 



