OF DIATOMS AND COPEPODA IN THE IRISH SEA. 197 
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 economie importance as a food-matter in the sea. 
Fra. 17.— Oithona helgolandica, from a photo-micrograph by A. Scott, 
ACARTIA. 
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. 
Fre. 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, 1919. The average of this species per haul throughout the ten years 
