PLANKTON OF THE WOODS HOLE EEGION 
119 
(NitzscMa seriata and Chsetoceros decipiens) were fairly numerous 4t times but 
always played a minor role. 
As previously stated, unusual physical factors may cause great variation in the 
time when the maxima appear as well as in the constituent parts. Such was the 
case in the winter of 1923 (figs. 4 and 5, p. 100), when, after an unusually warm 
season, although quantitatively the winter diatom maximum was approximately 
the same as in the previous year, qualitatively it was very different. RMzosolenia 
alata, the first dominant species to appear in the 1922 swarm, occurred only as 
scattering forms in 1923; while NitzscMa seriata, a rather scanty form in 1922, out- 
numbered all others during the entire winter maximum by more than 1,000,000 : 1 
(fig. 11, p. 105). Certain other members of the 1922 maximum, of which Bitylium 
hrightwelli is an example, did not appear at all. 
a*atlimttena 
Ctdsetum 
Ctcoaretatom 
O«oontort;zn 
C^crlophilisa 
Ctdeelplens 
C«dladeBia 
Cdaolniosms 
Ctlorenzianom 
C <pcrnvl&mim 
C.sefaattll 
C«soclale 
C. teres 
C.villel 
0*sp.no7. 
Fig. 22.— Distribution of Chaetoccros in 1923 
The absence of RMzosolenia alata (excepting scattering forms) might have been 
caused by the extremely mild weather of the early winter. However, as it is a com- 
mon oceanic species there are many other factors which may have affected it. 
Certainly the unusual temperature influenced the neritic forms. During the short 
time when the temperature was normal in the early fall (fig. 11) many species — 
Chsetoceros didymum, Skeletonema, Leptocylindrus, etc. (figs. 21 and 22) — appeared 
and began their normal flowering season. When the unusual temperature condi- 
tions continued, however, they declined and remained as scattering forms or dis- 
appeared ; but one species, RMzosolenia setigera, which has an extremely wide tem- 
perature range (fig. 16), apparently thrived with Nitzschia during the period. 
NitzscMa seriata is an Arctic oceanic species which often appears in large 
numbers off the Norwegian coasts. It is very variable in occurrence, being present 
