MARINE BIOLOGICAL STATION AT PORT ERIN. 43 



rapidly increased again, rising to 24-5 c.c. on the 25th. : the 

 average for eight hauls amounted to 12-7 c.c. The plankton 

 remained fairly abundant during the first three weeks of 

 October, but a decrease from 14-6 c.c. on the 18th to 5-2 c.c. 

 and 5-7 c.c. on the 23rd and 28th brought the average down 

 to 11-3 c.c. for nine hauls. 



The spring maximum was comparatively short and well 

 defined. Although the greatest amount was obtained on 

 May 4th, we may safely regard the period to have extended 

 over the fortnight — April 24th to May 7th. The collection 

 taken on April 20th contained 22-7 c.c. of plankton. On 

 May 12th 26-2 c.c. were taken. Five collections taken between 

 April 24th and May 7th contained an average of 69-6 c.c. each. 

 The summer maximum was much more limited in duration 

 than the spring one. The volume taken b}^ the coarse and 

 fine nets on June 11th amounted to 41 c.c. A few days before 

 and after that date the volume collected amounted to 20 c.c. 

 and 23 c.c. The autumn maximum occurred during the 

 later part of September. The combined sample taken on 

 September 25th contained 24-5 c.c. of plankton. This was 

 the greatest volume collected by the two nets between the 

 date of the summer maximum and the end of October. 



Biddulphia mobiliensis (fig. 6) was never completely absent 

 in any of the ten months. It was most abundant in March 

 with a total of 287,700 for eight hauls. After March the 

 numbers diminished rapidly, and only 50 were observed in the 

 whole of the August collections. The sinensis form also attained 

 its maximum in March, but was apparently absent in June, 

 July and August. Coscinodiscus concinnus arrived at its 

 maximum in April and the total for nine hauls was nearly 

 2 J- millions. The visitation was prolonged into June, but 

 none were observed in July and Augusl . Lauderia, Rhizosolenia 

 shrubsolii, and Chaelocems debile, decipiens, foes and sociale 

 were the most abundant diatoms in the spring maximum. 

 The four species of Chaetoceras mentioned were represented 



