PLANKTON OF THE WOODS HOLE REGION 119 
(Witeschia seriata and Chetoceros decipiens) were fairly numerous 4t times but 
always played a minor rdle. 
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. Rhizosolenia 
alata, the first dominant species to appear in the 1922 swarm, occurred only as 
scattermg forms in 1923; while Nitzschia 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 Ditylium 
brightwelli is an example, did not appear at all. 
Te 
y 
5 . . e 
a =. a 
-o y 
a. Fe 5 eh es 
G.atlantious 
C.boreale 
Cecinctum 
C.coarctatmn 
C.contortum 
C.criophilum 
C.decipiezs 
Cedensun 
Codiadems 
C.didymun 
C.laciniosun 
C.lorenziamm 
Ceperuvianom 
Ceschuttii 
Cesociale 
C.teres 
C.willei 
Cospenove 
Fic. 22.—Distribution of Chetoceros in 1923 
The absence of Rhizosolenia 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— 
Chxtoceros 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, Rhizosolenia setigera, which has an extremely wide tem- 
perature range (fig. 16), apparently thrived with Nitzschia during the period. 
Nitzschia seriata is an Arctic oceanic species which often appears in large 
numbers off the Norwegian coasts. It is very variable in occurrence, being present 
