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 Thalassiothrix nitschioides. O, locality records for Ditylium; X, for 
Thalassiothrix nitschioides, February and March, 1920; ®, for Th. nitschioides, April, 1920; A, for Th. nitschioides, other 
seasons and years. The hatched curve bounds the chief area of occurrence of Th. nitschioides 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 10488, 10489, 
