PLANKTON OF THE WOODS HOLE REGION 
117 
As the niimbers of Khizosolenia semispina diminished, in the late summer of 
1922, ChsBtoceros (fig. 19) increased, but lasted for only a short time. Another 
diatom {Corethron valdivise) then became very 
abundant and reached its maximum about Sep- 
tember 20 (fig. 10, p. 105). A rapid decline took 
place after this, followed by another Chaetoceros 
increase. In 1923 Corethron appeared on Sep- 
tember 21, reaching its maximum on November 3 
(fig. 11, p. 105). All available records for Coreth- 
ron show it to have its flowering season in the 
fall. In European waters Ostenfeld (1913) re- 
ports it to be most abundant in autumn. Ogilvie 
(1923) found it abundant on the south coast of 
Ireland in July, 1920, and in August and No- 
vember, 1921. Fritz (1921) records it from the 
Bay of Fundy in October, 1916, and in September 
and October, 1917. 
The winter maximum at Woods Hole consists 
usually of a greater variety of abundant species 
than that of the summer. In 1922 many species 
appeared suddenly about November 8. As the 
season progressed different forms predominated on different days, but all were 
usually abundant. At first Rhizosolenia alata f. genuina, a temperate oceanic 
V.3 
Fig. 19. — Occurrence of the more abundant spe- 
cies of Chsetoceros from May to December, 
1922. , Chxtoceros decipiens; — ... — , 
C. didt/murn: — . — , C. laciniosum; , 
C. schuttii: , C. sociale 
V.A. 
7.S 
FlQ. 20. — Occurrence of the more abundant species of Chaetoceros in surface collections of 1923. , Chxtoceros decipiens: 
, C. didymum; — ... — , C. laciniosum; — . — , C. schuttii; , C. sociale 
