158 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



largest individual catch was 101-7 c.c. on May 17th. The 

 monthly average catch rises from 3-8 c.c. in January, through 

 9-8 c.c. in April, to 45-3 c.c. in May, and then falls to 31-6 in 

 June, 12-2 c.c. in August, 19-6 c.c. in September (due to the 

 Copepod maximum) down to the winter minimum 24 c.c. in 

 December. The Diatoms taken by themselves form the usual 

 double crested curve with a greater maximum in May, a 

 summer minimum in August, a second lower maximum in 

 September and the winter minimum in December. The 

 monthly average for May was over 21 millions (much greater 

 than in 1919) and in September nearly 1J millions. The 

 largest single catch of Diatoms was 66,168,350 on May 24th. 

 These numbers are more like those of 1918 than of 1919, when 

 the Diatom catches were unusually small. 



The Dinoflagellate maximum was in June, when the 

 monthly average was 184,000. It had risen from about 5,000 

 in January, and fell to a minimum of 1,463 in October. There 

 was no marked second rise. The largest single haul of Dino- 

 flagellates was 617,900 on June 3rd, mainly composed of 

 Ceratium tripos, but the largest haul of Peridinium (152,000) 

 was also on the same date — much earlier than in 1919. 



The highest monthly average for the Copepoda (both 

 Nauplii and adults) was in September (74,328 adults and 

 86,956 Nauplii) — much later than last year — and the largest 

 individual catch was 192,510 on September 27th. The monthly 

 maxima are this year in their normal order — Diatoms first, 

 then Dinoflagellates and lastly Copepoda. The great spring 

 increase in Diatoms was late in appearing, but once it did 

 appear was in abundance. 



Ta,king our usual seven dominant genera of Diatoms in 

 detail we find from the monthly averages that, as last year, 

 Biddulphia and Coscinodiscus have their spring maxima in 

 March, while Rhizosolenia is earlier than usual with its maximum 

 in May along with Chaetoceras, Thalassiosira and Lauder ia. 



