

SEA-FISHERIES LABORATORY. 



387 



DlNOFLAGELLATA. 



The monthly averages for Ceratium and Peridinium 

 throughout 1912 were as follows : — 



1912. 



Ceratium 

 tripos. 



Peridinium 

 spp. 



1912. 



Ceratium 

 tripos. 



Peridinium 

 spp. 



January 



February . . . 



3,977 

 1,211 



11,510 

 929 



13.342 

 1,014 



36 



62 







1,027 



1,283,389 



23,000 





1,318 



98 



2,669 



646 



5,157 



1,096 



1,367 



208 

 



August 



September... 

 October 

 November... 

 December ... 





33 





229 





176 







The maximum in both cases is in May, a month 

 earlier than in 1911. The numbers for Ceratium, tripos 

 were a little higher that year, but in 1912 Peridinium 

 reached far higher numbers. In 1911 the maximum was 

 only 38,000 (June 3rd), while in 1912 it was 8,650,000 

 (May 9th) — the greatest number of Peridinium, we have 

 ever recorded during these series of investigations. 

 Peridinium is to be regarded as an oceanic form, and this 

 exceptional abundance in 1912 agrees with other evidence 

 that that year our western coasts showed an unusually 

 large invasion of Atlantic organisms.* 



Noctiluca. 



We have remarked before (Part IY, p. 213) on the 

 exceptional occurrence of Noctiluca miharis in abundance 

 off the Isle of Man in the late summer of 1910, 

 and (Part V, p. 141) on its persistence in reduced 

 numbers in Manx waters during practically the whole 

 (10 months) of 1911. In 1912, again, this organism 

 was well represented throughout the year, the only month 



* See also Herdman and Riddell on the Plankton of the West Coast of 

 Scotland, elsewhere in this Report. 



