| 
| 
| 
| 
| 
| 
| 
) 
} 
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 raschw, not taken in the Gulf in 
the summer. A few TI. inermis were also taken on April 22, May 12, 
and May 13. But there were no 7. longicaudata, T. gregaria, or 
Meganyctiphanes in the hauls. 
The captures of 7’. raschiz being from the surface, it is easy to esgab- 
lish salinity and temperature: — the former ranges from 30.6% to 
31.7%, 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, 
raschw, 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, acold 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 7. raschii, absent in summer, abundant in early 
spring, is exactly the opposite of that of 7. inermis (abundant in 
summer, absent in winter and early spring), although both are north- 
erm species, finding their southern limit near Cape Cod. Possibly 
the seasonal influence of the St. Lawrence water may give the clue, 
_ 1. 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. 
‘Zimmer, C. Schizopoden. Nordisches Plankton, 1909, 6. 
*Kramp, P. L. Cons. Int. Expl. de la Mer. Bull. Trimestr. 1913, 3, p. 539, 
Schizopoda. 
