OF DIATOMS AND COPEPODA IN THE IRISH SEA. 



119 



haul over the ten years, viz., 8171 (see table, p. 190). Although this is a 

 small species (fig. 17), still from its very great abundance it must be of 

 considerable economic importance as a food-matter in the sea. 



Pig. 17. — Oiihona helyolandica, from a photo-micrograph by A. Scott. 



AcAKTIA. 



Acartia clausi, Giesbr., is a summer species widely distributed over the 

 North Atlantic, and present in greatest abundance in the Irish Sea from May 

 to October (inclusive), and having a maximum generally in June, with 

 another slighter rise in autumn, September or October. 



Fig. 18. — Acartia clausi, from a photo-micrograph by A. Scott. 



The following are some of Our highest records : — 59,490 on June 27th, 

 1912 ; 59,360 on August 24th, 1911 ; 52,200 on May 20th, 1912 : 50,100 

 on June 2nd, 1913 ; 44,000 on September 29th, 1913 ; and 41,950 on June 

 17th, 1912. The average of this species per haul throughout the ten years 



