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bulletin: museum of comparative zoology. 



10267, 10268, 10275, and 10277, where none were detected) was one 

 or other variety of C. longipcs (Paulsen, 1908); C. tripos occurring 

 at three stations only, as illustrated by the following table: — 



Ceratium longipes was still the prevalent species in June, C. tripos 

 being no more abundant than the month before. But by September 

 C. tripos was as abundant as C. longipes, or outnumbered it, every- 

 where, except locally near the coast of Maine, (Stations 10317, 10318); 

 and it greatly predominated over C. longipes off Gape Cod and in 

 Massachusetts Bay in October (Stations 10330, 10336, 10337, 10338). 



Ceratium arctica, like other typical northern species, was far more 

 numerous in the Gulf in May than we have ever found it there in 

 summer. But though it was most common where Gabot Gurrent 

 water was most in evidence (Station 10271), it occurred in small 

 numbers at most of our other stations as well. 



In June Ceratium arctica was limited to the extreme northeast corner 

 of the Gulf (Stations 10283, 11284, 10286, Petit Passage), and to the 

 waters off Shelburne. In September and October it was not detected 

 at all. 



According to J0rgensen (1911) the presence of C. arctica is a sure 

 index of polar water. But while this is true for European waters, 

 off our coast an almost equally cold habitat exists in the Gulf of St. 

 Lawrence; and though Herdman, Thompson, and Scott (1898) did 

 not detect C. arctica there, its presence in the Gabot Gurrent off 

 southern Nova Scotia suggests that it reaches the Gulf of Maine by 

 that route, not from the Banks of Newfoundland, as J0rgensen sup- 

 poses. 



The genus Peridinium almost always occurs in the Geratium 



