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bulletin: museum of comparative zoology. 



skioldi, and Chaetoceras debile were restricted to a narrow coastal zone 

 (Fig. 99). 1 



Diatoms diminished still more during the summer, till by September 

 there was no longer any pure diatom plankton at any of the stations; 

 while even mixed plankton was limited to a narrow belt from off 

 Penobscot Bay, to the mouth of the Bay of Fundy (Fig. 100), and to 



Fig. 99. — Microplankton types, June 1915. 

 5, Diatom 



3, Ceratium 



4, Mixed diatom and Ceratium 

 , oflFshore limit to Thalassiosira 



the mouth of Massachusetts Bay where Skelatonema was the pre- 

 dominant genus. Thalassiosira had practically vanished, except 

 for an occasional example at one Station (10317), its place being 

 taken off the coast of Maine by various species of Chaetoceras and 

 Rhizosolenia. 



In the Gulf the seasonal history of Ceratium is the reverse of that 



I Thalassiosira was taken at Stations 10275, 10276. 10277, 10278, 10281, 10284, 10285, 

 102S7, 10302, 10303, 10317. 



