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bulletin: museum of comparative zoology. 



likewise more diatoms at our other stations near land than in the 

 centre of the Gulf; but not enough to take the hauls out of the 

 Ceratium class. The diatom constituents of the Gulf Stations were 

 chiefly several small species of Chaetoceras, with occasional C. de- 

 cipiens, Rhizosolenia semispina and Nitschia serriata, etc. 



Peridinian plankton, in greater or less abundance, and composed 

 of different species at different localities, occupied the waters of the 

 Gulf of Maine (Stations 10057, 10086-10093, 10096, 10097, 10102, 

 10104) except at the few limited regions just mentioned; Nantucket 

 Shoals (Staton 10060), the continental shelf from abreast of Nantucket 

 to New York (Stations 10062, 10063, 10067, 10082, 10083, 10070) 

 (Fig. 82) . Unfortunately we have no data on the microplankton of the 

 Gulf Stream water at Station 10076, the bottle being broken in transit. 

 In the Gulf of Maine the prevalent organisms, of this plankton type, 

 were two species of Ceratium, tripos, and the form classed by Paulsen 

 (1904, 1908), as var. oceanica of C. longipes. (In my Report on the 

 cruise of 1912, these two species were treated together). Ceratium 

 longipes differs so noticeably from tripos in its curved apical horn and 

 serrate shell, that it is easy to count the respective numbers of the 

 two in plankton samples. And without delaying with the exact 

 counts, the result of the comparison was as follows : — 



On the whole, then, longipes was the more abundant of the two in 

 the Gulf, where it was taken at practically every station, though 

 notably absent at Station 10086, where it had been abundant a month 

 earlier (Station 10057). The table likewise suggests that the prepon- 

 derance of longipes was greater near shore than in the centre of the 

 Gulf, the only stations where tripos predominated being far from land. 



C. longipes occurred in the plankton on George's Bank, on Nan- 

 tucket Shoals, and over the continental shelf as a whole as far as 



