b P. T. CLEVE, THE PLANKTON OF THE NORTH SEA, ENGLISH CHANNEL, ETC. 



Eucampia zodiacus. Lauderia annulata. 



Guinardia Jiaccida. Rhizolenia Shrubsolei. 



Ditylum Brighhvellii. Stephanopyxis turgida. 



A t this season the euryhaline Centvopages hamatus, Acartia longiremis and A. 

 bijilosa reach their maximum. 



On the other hand, also tripos-plankton sets in having in its company Calanus 

 finmarchicus, Pseudocalanus elongatus, Evadne Nordmannii, Podon Leuckarti and Chcetoceros 

 Memalis. 



Period V. July — August. The tripos-plankton became now the prevailing kind, 

 but was intermingled with a certain amount of southern neritic plankton, for some time 

 also with Coscinodiscus concinnus. Rhizosolenia gracillima also appeared, but this species 

 was remarkably scarce in the year 1899. 



Characteristic species are Oikopleura dioica, Acartia Clausii, Paracalanus parvus, 

 Evadne spinifera and Sagitta. 



Period VI. From the end of August to the end of October. The tripos-plankton 

 continues to predominate. Oikopleura, Sagitta, Oithona similis and Paracalanus parvus 

 from the last period are still abundant. New are Centropages typicus, Podon intermedius 

 and Rhizosolenia Stolterfothii. Also Anomalocera Patersonii and Labidocera Wollastonii 

 were seen, but rarely. Limacina balea was for a short time visible, and then abund- 

 antly. Amphorella Steenstrupii occurred sparingly. The period VI is chiefly charac- 

 terized by the development of didy mus-plankton, containing Chcetoceros didymus, C. 

 curvisetus and C. Schiittii. The last named species appeared already at the end of June and 

 in the beginning of July, but for a short time only. It reappeared now abundantly. 



Period VII. November — December. The tripos-plankton (now containing Ceratium 

 bucephalum) and the didy mus-plankton continue as before, but the last named kind be- 

 came scarce or disappeared in December. Halosphcera appeared, but rarely, also Plecto- 

 phora arachnoides. The southern Ditylum Brighticellii, Eucampia zodiacus and Guinardia 

 Jiaccida, which were seen in the spring, reappear. 



The period VII. is characterized chietly by a number of arctic or boreal forms 

 most of which occurred sparingly. Such forms were the following: 



Biddulphia aurita. Coscinodiscus oculus iridis, 



Chwtoceros borealis. C. polychordus. 



C. constrictus. C. stellaris- 



C. debilis. Rhizosolenia setigera. 



C. diadema. Skeletonema costatum. 



C. laciniosus. Thalassiosira gelatinosa. 



C. scolopendra. T. Nordenskiöldii. 



C. teres. Thalassiothrix Frauenfeldii. 



