154 MARIE V. LEBOUR. 
parable. Probably many of the more delicate forms are lost, but the 
relative seasonal abundance is well shown by the curve (Fig. 8) which 
shows June as the maximum month, thus agreeing with other observers. 
In this curve there is a depression in July which may be due to the 
fact that most of the samples were preserved in that month, rather 
than to the fact that the numbers are much less than in August. From 
September the curve falls and is very low until May, showing an almost 
complete absence of Peridiniales in the winter. Even if some of the 
individuals are lost the results show well the relative abundance of the 
species. Prorocentrum micans which is largely lost in the tow nettings is 
one of the few which has an autumn maximum, thus agreeing with the 
observations of other workers (Lohmann, 1908; Ostenfeld, 1913). 
Table 2 shows the average number of Peridiniales per cc. for each 
month. These numbers possibly do not show the real abundance of such 
large forms as Ceratiwm and the larger Peridinium species, which are 
often very common in the tow nettings when there are few in the water 
samples. 
The 5-fathom samples are found to be richer in specimens than the 
7-fathom samples. Usually they are more abundant at the surface than 
at 5 fathoms, but the species all occur in all the depths. It 1s well known 
that the Peridiniales form a large portion of the food of many of the 
plankton animals. Actinotrocha which sometimes occurs in the tow nets 
is a good instance of this, and the species which have just been swallowed 
can nearly always be identified. The following list shows the contents 
of five specimens taken June 25th, 1915 :— 
Specimen. ] 2 3 4 5 
Peridinium ovatum ; | i | 2a ee 
palhdum —. 3 — = = - 
> pellucidum . | = | 2 9 2 
) Sis. : : nae pee se Ik Me 
5 so. Juv. 3 - 
Pouchetia armata laa” ] 2 
Dinophysis acuminata. : gees) 
Other organisms | 5 
FLAGELLATA. 
‘““Nordisches Plankton,” Vol. 2. 
~ 
Pheocystis 1s certainly by far the most important of the flagellates, 
which interferes enormously with the catches by blocking up the tow nets 
in the early summer and entangles in its gelatinous covering many 
diatoms and Peridiniales. It also serves as food for many of the plankton 
