98 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
Looking into the statistics for the individual more impor- 
tant genera of Diatoms, we find that the numbers of Biddulphia 
were very much higher this spring than we have ever seen them 
before in the 12 years of this intensive work, and reached a 
maximum of 1,389,000 in one haul on April 18th. The in- 
teresting form Brddulphia sinensis was very variable in 
character this year, and showed again figures such as we gave 
in the Report for 1912. 
Chaetoceras was as usual very abundant, with a high 
monthly average of nearly 22 millions in May. As an example 
of the way in which a single form may on occasions become 
dominant and almost monopolise the plankton, we find that 
in the haul of May 21st, out of about 58 millions of Chaetoceras 
over 51 millions belonged to the one species C. debile. Rhizo- 
solena usually attains its maximum in June, but this year it 
was in May, fully a month earlier than it has ever been before 
in our experience. The great crest of the Chaetoceras curve, 
extending from the middle of April to late in May, covers the 
maxima of five out of the remaining six selected genera. 
Guinardia has the only maximum that is outside the Chaetoceras 
curve. 
In a survey of the monthly averages of the seven 
more important genera of Diatoms we find that Biddulphia 
and Coscinodiscus reach their spring maxima in April, while 
the other five, Chaetoceras, Rhizosolema, Thalasstoswa, Lauderia, 
Guinardia, have the maxima in May. 
Amongst those Copepoda which are of greatest importance 
in connection with the food of fishes, we find that Calanus 
finmarchicus, which seems to be associated with the local 
mackerel fishery, attained its greatest numbers in July this: 
year, but remained in fair abundance up to the middle of 
September. Temora longicornis, which we found in 1917 to be > 
definitely related to the summer herring fishery off the Isle of 
Man, showed in 1918 a perfectly regular curve of monthly 
