OF DIATOMS AND COPEPODA IN THE IRISH SEA. 



Ill 



The actual detailed numbers are of no importance except as indications 

 of the relative abundance of the species. It is clear that Oithona and 

 PseudocaJanus (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 



30.000 



20,000 



10000 



*— ■ r**=—' c t- -1--- 1 1 1 1 1 — 



Mar. Apr. May June July Aug 1 . Sept. Oct. Nov. Dec. 



Pig. 11. — Curves of five most abundant Copepoda at Port Erin in 1912. 



species for the ) r ear 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 veiy 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. ZOOLOGY, VOL. XXXIV. 9 



