OF DIATOMS AND COPEPODA IN THE IRISH SEA. 189 
The actual detailed numbers are of no importance except as indications 
of the relative abundance of the species. It is clear that Oithona and 
Pseudocalanus (in 1909) far outnumber the others. Acartia shows a notable 
increase in 1910. 
The Copepoda as a whole are a summer and autumn group, all the crests 
of their annual curves being found between May and October. Figure 11 
shows curves of occurrence of the five most abundant of the above-named 
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Mar. Apr. May 
June July Aug. Sept. Oct. Nov. Dec. 
Fia. 11.—Curves of five most abundant Copepoda at Port Erin in 1912. 
species for the year 1912, which may be regarded as typical. Curves of 
Calanus are shown separately in figure 12. The remaining one of our six 
selected species, Calanus finmarchicus, although much the largest individually 
and probably one of the most important from the fisheries point of view, only 
occasionally occurs in very large quantities in the Irish Sea, and its total 
numbers in a year are much below those of the other species, as the following 
table shows. 
LINN. JOURN.—BOTANY, VOL. XLIV. 
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