PLANKTON OF THE GULF OF MAINE 



439 



Wherever Ditylium is endemic in European seas it occurs throughout the year, 

 though most commonly during the autumn and winter. McMurrich's and Fritz's 

 (1921) data, combined, show it more seasonal at St. Andrews, occurring only from 



Fig. 127.— Occurrence of the diatoms Ditylium and Thnlansiothriz mtschioides. O, locality records (or Ditylium; X. for 

 ThalauiMrix nilschioid's. February and March. 1920; 9. (or Th. nitnhioides, April, 1920; A. (or Th. nitschioidei, other 

 seasons and years. The hatched curve bounds the chie( area o( occurrence o( Th. nitschioidea in March 



mid-August until mid-December, with its maximum in October. In the open gulf 

 it has been recognized most often in December and January, when it occurred at 

 about 50 per cent of the Halcyon stations in 1920 and 1921 (stations 1048S, 104S9, 



