8 P. T. CLEVE. THE PLANKTON OF THE NORTH SEA, THE ENGLISH OHANNEL, AND THE SKAGERAK. 



The Evadne Nordmannii, E. sjnnifera, Fodon intermedius and P. Leuckarti abundant 

 ill tlie preceding periods, have now disappeared. 



The soxitherii iieritic plankton. As characterizing the plankton above the 50 inetre 

 plateau we note now Coscinodiscus concinnus and Biddidphia mobilensis, bnt also a 

 considerable number of other species, most of whicii have been foiind from the English 

 Channel to Sivagen. Among these species we note the following: 



Animals. 



Proto pedata, in the E. Channel in August, at Skagen in November. 



Acartia bifilosa. 



Corycceus anglicus. 



Euterpe acutifrons, at Plymouth and Helder in September, from the E. Channel to Skagen 



in November. 

 Temora longicornis. 



Sagitta bipimctata, vevj common above the whole 50 inetre plateau. 

 Tintinnopsis campanula, from the English Channel to Skagen. 



Plants. 



Bellerochea malleus, 



Chcetoceros ana st om osans. 



Ditylum Brightwellii, abundant from the E. Channel to Skagen. 



Guinardia flaccida. 



Lithodesmium undulatum, observed from the end of September onwards. 



Rhizosolenia robusta, from the English Channel to the mouth of the Schelde. 



R. Stolterfothii, from the E. Channel to Skagen, where it appeared in the first few days of October. 



Streptotheca Thamesis, from the E. Channel to 55° N. 5° 30 E. 



The Skagerak in 1898. 



The seasonal changes in the plankton will be examined for certain periods with 

 reference to the prevailing plankton-types. 



Period I. January — Felbriiary. 



The prevailing plankton is tripos-plankton, but is partly mixed with remnants of southern 

 neritic plankton, which disappear, and more or less rarely so with forras which belong to 

 the northern neritic plankton and increase in frequency in the next period. 



Besides the most commom dinofiagellates of the tripos type, we note some more 

 remarkable species such as Halosphcera, which was more or less common in the whole of the 

 Skagerak, and Arachnactis albida, not formerly found in the Skagerak. The last-named species 

 was seen during the last few days of January and the first few days of February both in the open 

 Skagerak and along the coast from Vinga to Måseskär. This pelagic actinia is known from 



