BIGELOW: OCEANOGRAPHY OF MASSACHUSETTS BAY. 413 



on the surface between Cape Ann and Boon Island, during the last 

 half of April and continued more or less abundant until the middle of 

 May. To my surprise the great majority of specimens in these hauls 

 proved to be a species, Thysanoessa raschii, not taken in the Gulf in 

 the summer. A few 2\ inermis were also taken on April 22, May 12, 

 and May 13. But there were no T. longicaudata, T. gregaria, or 

 Meganyctiphanes in the hauls. 



The captures of T. raschii being from the surface, it is easy to estab- 

 lish salinity and temperature-. — the former ranges from 30.6% o to 

 31.7%c, the latter from 40.7° to 46.7°. Thus the species was living in 

 extremely uniform water, with a combination of physical characters, 

 low temperature coupled with low salinity, not paralleled anywhere 

 in the Gulf, at any depth, in summer. 



There is nothing surprising in the occurrence of any of these euphau- 

 siids in our Gulf, considering their distribution elsewhere. ^ In fact 

 all might have been expected there. Thus Meganyctiphanes is 

 widely distributed in Boreal waters near land. Thysanoessa inermis, 

 raschii, and longicaudata, though cold water species, all extend as far 

 south as the northern part of the North Sea ^; inermis to Vineyard 

 Sound (Rathbun, Loc. cit.). Nematoscelis megalops is a wide ranging 

 oceanic species. Thysanoessa gregaria, according to Zimmer, {Loc. 

 cit., p. 21) is a southern form of very wide distribution in the warmer 

 parts of the Atlantic. Its appearance in the Gulf of Maine is caused 

 by the Gulf Stream water, which is its oceanic constituent. But the 

 details of the occurrence of these various species in the Gulf are 

 less easily understood. For example, it was surprising to find Thy- 

 sanoessa longicaudata and T. gregaria, a cold water and warm water 

 species, side by side, instead of finding the latter side by side with 

 other warm water organisms, e. g. Salpa and Physophora (Bull. 

 M. C. Z., 1914, 58, p. 103). Equally hard to explain is the fact that 

 the occurrence of T. raschii, absent in summer, abundant in early 

 spring, is exactly the opposite of that of T. inermis (abundant in 

 summer, absent in winter and early spring), although both are north- 

 ern species, finding their southern limit near Cape Cod. Possibly 

 the seasonal influence of the St. Lawrence water may give the clue, 

 T. raschii being rather the more northern of the two species ; but this 

 seems hardly likely, inasmuch as both are widely distributed in the 

 Arctic Ocean. Other possible factors are salinity and food supply. 



1 Zimmer, C. Scliizopoden. Nordisches Plankton, 1909, 6. 



2 Kramp, P. L. Cons. Int. Expl. de la Mer. Bull. Trimestr. 1913, 3. p. 5.39, 

 Schizopoda. 



