340 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the mid depths off shore (Apstein, 1911). Sagitta hexaptera, taken in 
the Gulf in 1912 but not in 1913, is oceanic, very widely distributed. — 
The Salpae are, of course, all visitors from the Gulf Stream, as are 
such coelenterates as Physalia, Agalma elegans, and Physophora — 
hydrostatica. 
The ctenophores of the Gulf are either cosmopolitan forms (Pleuro- 
brachia pileus and Beroe cucumis) or Arctic-boreal (Bolinopsis infundi- 
bulum); while a true Arctic species, Mertensia ovum, has been recorded 
rarely (A. Agassiz, 1865, Fewkes, 1888) and the only oceanic Medusa, 
Aglantha digitale, is widely distributed over the North Atlantic. 
In short, the more important members of the Gulf plankton are of 
three types, 1, Arctic-boreal; 2, Gulf Stream; 3, Arctic; of which the 
first greatly outnumbers the other two in number of species and in 
number of individuals. 
I have already pointed out (1914a, p. 107) that the summer plank- 
ton of the Gulf of Maine resembles that of the Norwegian Sea and 
the North Sea; a parallel which can be drawn even more closely with 
the collections made during the winter of 1912-1913 (1914b), and the 
summer of 1913. 
And it is not only in its individual components that the plankton 
corresponds to the other side of the North Atlantic, but in their method 
of association; for example Dr. D. Damas informs me that the 
plankton assemblages found in the Gulf in 1912 (1914a) correspond 
almost exactly to many of the hauls taken by the MicHaE. Sars off 
the coast of Norway. And Dr. Otto Pettersen writes calling attention 
to the similarity of the Grampus plankton to that of the Skagerrak. 
The parallel does not extend to the Norwegian Sea and North Sea as a 
whole, but only to the southern part of the former and northern part of 
the latter, where Arctic-boreal plankton, temperate neritic species, and 
warm water species carried around the northern end of Scotland by the 
sweep of the Atlantic Current, meet. There, as in the Gulf, Calanus 
finmarchicus is perhaps the most important member of the plankton 
being found locally in vast shoals (Farran, 1911, p. 38), and Pseudo-— 
calanus in great numbers. Sagitta elegans is taken in almost every 
haul; Limacina balea is locally abundant; Anomalocera pattersoni is 
taken more or less regularly on the surface, though seldom in great 
numbers; Aglantha digitale is frequently, Pleurobrachia irregularly 
recorded (Kramp, 1913a), Euchaeta norvegica is more or less regular in 
the deep hauls; Eukrohnia hamata, Calanus hypoboreus, and Metridia 
longa are both visitors from the north, as are the several northern 
species of Thysanoessa, and Meganyctiphanes norvegica. And all the 
