SEA-FISHERIES LABORATORY. 177 



December. The Diatoms taken by themselves form the 

 usual double-crested curve with a greater maximum in May, 

 a minimum in August and a second lower maximum in 

 November. The monthly average for Diatoms in May was 

 about 5 millions, and in November 400,000. The largest 

 single catch of Diatoms was 16,669,000 on May 9th. These 

 numbers for the vernal maximum in May are much lower 

 than in the previous year when (May, 1918) the average for 

 the month was 26-J millions, and the largest single catch was 

 over 73 millions (May 21st). 



It may be useful to state here that the distance traversed 

 in each of our 15 minutes hauls is as nearly as possible half-a- 

 mile, and we estimate our usual rate of towing to be about 

 2 miles per hour. 



The Dinoflagellate maximum was in July when the 

 monthly average was 130,404. It had risen from about 8,000 

 in January and fell to about 4,000 in September, with a second 

 rise to 10,000 in November. The largest single haul of Dino- 

 nagellates was 318,200, on July 28th, mainly composed of 

 Ceratium tripos. The largest haul of Peridinium was 55,200 on 

 July 21st. 



The highest monthly average for the Copepoda (both in 

 the adult condition and as Nauplii) was in June (100,354 

 adults, and 37,425 Nauplii) though the largest individual 

 catch was in July (126,563 on July 31st). These times are 

 unusually early for Copepoda. Last year the highest monthly 

 average was in August, and the largest single catch in 

 September. This year (1919) we had the unusual phenomenon 

 of the Diatoms being still abundant (in the millions per haul) 

 at the time of the Copepod maximum. Moreover, it is excep- 

 tional to have the maximum of the Dinoflagcllatrs later than 

 that of the Copepoda. 



Taking our usual seven dominant genera of Diatoms more 

 in detail, we find from the monthly averages I hat two of them 



N 



