Pep em de 
OF DIATOMS AND COPEPODA IN THE IRISH SEA. 191 
CALANUS. 
Calanus finmarchicus (Gunner) * is present throughout the year in the 
Irish Sea, and may be taken in small quantities at almost any time and in 
larger numbers on different occasions in different years. In 1907 it was 
fairly abundant (a few thousands in a haul) in April, and again at the end of 
July and the beginning of August, and in October. In 1908, on the other 
hand, the thousands per haul were not reached until later in the year, and 
the numbers remained relatively high from September to December (2,850 
on December 23rd). In 1909, in addition to occasional thousands in May, 
EA Calanus 
Jew "Fas. ' Mer ' Apr * Moy dane eum "Rag "Bap C Oct “Nov ^ Dec. 
Fia. 12.—Curves of Calanus for three years (1907-9) at Port Erin, showing 
successive waves of invasion, 2 or 8 in each summer, 
June, July, and October, we have evidence of an unusually large swarm that 
entered the bay on July 17th and 19th, when hauls estimated at 20,000 each 
were obtained. The average for these three years shows maxima in July 
and October (see fig. 12). 
In 1910 there were no very large hauls, and the thousands were only 
reached at the end of July and the beginning of August—perhaps the most 
usual time for swarms to appear in the bay. 
In 1911 the numbers in general were low, but two of the customary large 
swarms appeared in summer, one on July 4th and the other on July 18th. 
In 1912 the numbers were higher again, and thousands occurred on 
various dates from April to October. The very high record of 50,720 was 
obtained on May 17th, unusually early for such a large swarm. 
* [ use this older specific name as I am inclined to agree with Wolfenden, Esterly and 
others that the characters used in the attempt to separate “ finmarchicus” and “helgolandicus” 
as species are too slight and inconstant to be relied upon. 
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