984 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
This lst of occurrences shows several points of 
interest. First, that Ceratiwm tripos is in the sea off 
Port Erin the whole year round—in every month the 
average haul runs to hundreds, and in most of them to 
thousands. Secondly, there is a well marked maximum 
in June and July, the highest figures being 33,350 in 
June and 69,000 in July; and although the numbers are 
less at the beginning and end of the year, they never get 
very low. It is difficult to speak of a ‘‘ winter minimum ”’ 
when such numbers occur as 2,040 on December 5dth; 
1,560, 1,840 and 1,400 on December 19th, 24th and 27th 
respectively; 650 on January 13th ; 1,240 on February 
Ist; and 1,050 on March 26th. Ceratium tripos is 
‘ 
usually regarded as an ‘“‘ oceanic’’ species, but if that 
term implies an organism which is brought in by 
currents from the open sea and cannot continue to live 
and reproduce in our coastal waters, the above figures, 
showing relatively large numbers per haul at all times 
of the year, are difficult to reconcile with such an idea. 
We prefer to regard Ceratiwm tripos as a cosmopolitan 
form capable of living both in the ocean and on the 
coast. For such forms inhabiting practically all parts 
of the sea the term ‘‘ 
panthalassic’’ may be employed. 
On the other hand, Peridinium seems to be a much 
more typically oceanic species. It is absent during half 
the year, appears suddenly early in April (250 on 
April 4th, 1,000 on April 8th, 18,200 on April 15th), 
reaches its maximum in May (20,750 on May 26th, 
20,500 on June 14th), and then diminishes to odd 
hundreds in the beginning of October, after which there 
are only rare occurrences of a few individuals. It is 
natural to regard Peridiniwm as an invasion from the 
North Atlantic, reaching its climax in May and then 
dying out. 
