MARINE BIOLOGICAL STATION AT PORT ERIN. 69 



addition to those from other parts of the Irish Sea. A 

 detailed account of the plankton results will be given, 

 as usual, by Mr. Scott and myself in the Lancashire 

 Sea-Fisheries Laboratory Report, to be published early 

 in 1913, but we may give here the following- preliminary 

 statement in regard to the variations of the year 1912. 

 There was a distinct Diatom maximum in April, largely 

 composed of Chaetoceras, which was represented by eight 

 species. Chaetoceras debile and C. sociale were the most 

 common Diatoms in the spring months. A collection 

 taken with the fine net in the Bay on April 29th 

 measured 29'5 c.c. It was practically a pure phyto- 

 plankton. Chaetoceras debile was represented by 

 36 millions and C. sociale by 44 millions. The other 

 Diatoms present were also in large numbers. Lauderia 

 borealis was represented by 12 millions, and Asterionella 

 japonica by 2 millions, and Thalassiosira nordenskioldii, 

 which was so abundant and persistent in the spring 

 of 1907 but comparatively scarce since, was represented 

 by 4 millions. The occurrence of Thalassiosira in 

 1912 appeared to be rather spasmodic. In some 

 collections chains of individuals were fairly numerous. 

 In others there were very few. Some days it appeared 

 to be common, on other days almost absent. The 

 Diatoms became scarcer in May, but there was a 

 distinct increase again towards the end of that month, 

 clue to the summer invasion of Rhizosolenia. In 

 previous years, R. semispina was the abundant species, 

 but in 1912 it proved to be comparatively rare. Its place 

 was taken by R. shrubsolei. A fine net collection, taken 

 in the Bay on 30th May, gave over 107 millions of 

 R. shrubsolei and nearly 2\ millions of R. sernispina 

 (see fig. 16). Diatoms were scarce in July and August, 

 but there was a marked autumn maximum during the last 



