KONGL. SV. VET. AKADEMIENS HANDLINGAB. HAND. 34. N:o 2. 9 



During this period also the following, non-arctic, species appeared: 



Halosphcera viridis. Guinardia fiaccida. 



Biddulphia mobilensis. Lauderia anmdata. 



Eucampia zodiacus. Stephanopyxis turgida. 



All these species had probablv been swept down from the northern British coasts. 

 The following southern forms iticreased in abundance or reached their maximum 

 during the period VI.: 



Corycceus anglicus. Ulnzosolenia corpulenta. 



Euterpe acutifrons. R. robusta. 



Noctiluca niiliaris. 



On the other hand the following decreased: 



Acartia Clausii. Ckcetoceros curvisetus. 



Centropages typicus. C. densus. 



Paracalanus parvus. TJityluin Briglitwellii. 



Ceratium tripos. 



VII. St Vaast la Hogue in 1898—1899. 



The collecting of samples at this station commenced in June 1898, but became 

 interrupted in March 1899, so there is no complete series; still, the collection is of no 

 little interest. Also at this place the influence of arctic water is apparent at certain 

 times of the year, and if the plankton from St Vaast be compared with that from Plymouth 

 we note striking differences. As in the preceding cases we may consider the changes in 

 the nature of the plankton by periods. 



Period 1. June 4 th 1898. The prevailing plankton was the chceto -plankton, represented 

 by a great abundance of Ckcetoceros deeipiens. Plupocystis PoucJietii was also common. 

 As other boreal forms we note Centropages hamatus, Pseudocalanus elongatus, Temora 

 longieornis and Chaioceros teres. All these boreal forms had disappeared already by the 

 12th in the same month. Other species are of comparatively little importance and of 

 southern origin, as Ckcetoceros didymus, C. densus and Acartia Clausii. 



Period II. June 12 th to August 12 fh 18.98. The plankton consists chiefly of the 

 southern neritic species Rhizosolenia Shrubsolei and Guinardia fiaccida. Other southern 

 forms also occurred, but more or less sparingly, as: 



Cerataulina Bergonii. ( 'luetoceros Schuttii. 



Ckcetoceros danicus. Eucampia zodiacus. 



C. didymus. Rhizosolenia Stolterfothii. 



The only boreal form is Leptocylindrus danicus. Whether Ckcetoceros contorius 

 be of northern or southern origin is at present doubtful. 



Period III. Between September 6 th and October 6 th 1898. This period is remarkable 

 for the sterility of the water, Tintinnopsis ventricosa being the only species of any im- 

 portance. 



K Sv. Vet. Akad. Handl. Band 34. N:o 2. 2 



