340 bulletin: museum of comparative zoology. 



the mid depths off shore (Apstein, 1911). Sagitta hexaptcra, 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 pilcus and Beroe cucumis) or Arctic-boreal {Bolinopsis infundi- 

 hulum); while a true Arctic species, Mcrtcnsia 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 Michael 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 clcgans 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 norvcgica is more or less regular in 

 the deep hauls; Euhrohnia 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 



