PLANKTON OF THE WOODS HOLE REGION iy) 
As the numbers of Rhizosolenia semispina diminished in the late summer of 
1922, Chetoceros (fig. 19) increased, but lasted for only a short time. Another 
diatom (Corethron valdivie) then became very i 
abundant and reached its maximum about Sep- # 8 
tember 20 (fig. 10, p. 105). A rapid decline took z 
place after this, followed by another Cheetoceros 
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 3. 
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 
Treland 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. We 
The winter maximum at Woods Hole consists Fic. 19.—Occurrence of the more abundant spe- 
usually of a greater variety of abundant species: 968 of Chetoc’tos from ai aan 
than that of the summer. In 1922 many species © didymum; —.—, ©. laciniosum; ——, 
appeared suddenly about November 8. As the ©?) ~-— @ sociale 
season progressed different forms predominated on different days, but all were 
usually abundant. At first Rhizosolenia alata f. genuina, a temperate oceanic 
Sepeo 
Oote 
Nove 
Dece 
VeSe 
Br Sect cree ant Ng) Le oy eZ) inns nies 
KOS SSL IRnNG EPS EPRE ease va el nen bass maM Glzen TUR: ean SE 
VeAe 
Ae 
Sa 
VeSe 
Ne 
Fia. 20.—Occurrence of the more abundant species of Cheetoceros in surface collections of 1923. ----.-, , Chetoceros decipiens; 
—, C. didymum; —eeo—, C. laciniosum; —»—, C. schuitlii; —-—=, C. sociale 
