32 P. T. OLEVE, THE PLANKTON OF THE NORTH SEA, ENGLISH CHANNEL, ETC. 



Geographical and Seasonal Distribution of the plankton 

 organisms of the North Sea in 1899. 



A. Forms that, as a rule, are confined to tlie space above 

 the 50-metre plateau on tlie bottom. 



1. From January: Euterpe acutifrons (to February, but reappeared in November), 

 Tintinnopsis beroidea (to May, but reappeared in November), (C/uvtoceros curvisetus and 

 C. didymus in the Engl. Channel to March), Biddulphia mobilensis (to May, reappeared 

 in September). 



2. From February: Biddulphia avrita (to March), Rhizosolenia Stolterfothii (to 

 July, reappeared in November), Streptotheca thamesis (to March, reappeared in November). 



3. From March: Asterionella japonica (to May), Cerataulina Bergonii (to June 

 reappeared in November), Chcetoceros danicus (to May), Eucampia zodiacus (April, re- 

 appeared in September), Rhizosolenia setigera (to May). 



4. From April: Phwocystis Pouchetii (to June, also above the 200-metre plateau), 

 ( "/uctoceros densus (to September), Ditylum Brightwellii (reappeared in November), Guinardia 



flaccida (to July, reappeared in November), Rhizosolenia Shrubsolei (to July), Stephanopyxis 

 turgida (to May). 



5. From June: Podon polyphemoides. 



6. From July-August: Oikopleura dioica, Evadne spinifera Acartia bifilosa, Isias 

 clavipes, Cyttarocylis serratus, Tintinnopsis campanula, T. ventricosa, Noctiluca uiiliaris, 

 Lithodesmium undulatum, Rhizosolenia ealcar avis, Bacteriastrum varians. 



7. From November: Lahidocera Wollastonii, Rhizosolenia rolnista. 



B. Forms that, as a rule, are confined to the space above 



the 100-metre plateau. 



1. Spring-forms, or such as occur in April-May. 

 Southern forms: Northern forms: 



Ceratium tripos. Gonyaulax spinifera. 



Lauderia annulata. Peridinium depressum. 



P. ovatum. 

 Chcetoceros borealis. 

 var. Brightwellii. 

 C. decipiens. 



