6 r. T. CLEVE. rLAXKTON, COLLECTED BY THE SWEDLSII EXPEIHTION TO SPITZBEKGEN. 



The temjjerature varies usually betweeri about 5° in the winter and 14° in the sum- 

 iner, and the salinity is about 34 p. ra., but these iigurcs are subject to great variations 

 according to relative abuiidance of oceanic or coast-water that enters in the cornposition 

 of the triposplankton-water. 



The triposplankton is chiefiy constituted by cilioflagellates and entomostraca, the 

 diatoms being almost absent. As stated above the animals are to a great extent of the 

 same species as in the didyinusplankton, which is easily explained as both types are 

 derived from styliplankton. 



Among the organisms we note the following: 



Animals. Flants. 



(Sac/itta bipunctata), Ceratium furca, 



{Acartia Clausii), C. fusus, 



Anomalocera Patersonii, C. tripos, 



Calanus finmarchicus, C trip. v. macroceros, 



{Centropages typicus), ' Peridinium divergens. 



{Oithona similis), 



{Paracalanus pannis), 



Pseudo calanus elongatus, 



Temora longicornis, 



Evadne Nordmannii, 



E. spinifera, 



Podon intermedius. 



Many of the species of the styliplankton also enter into the triposplankton, as 

 Acanthometron quadrifolium. Plectophora arachnoides, probably originally belonging to 

 the cha^toplankton and abnndant around Scotland, enters also frequently into the tripos- 

 plankton. 



III. CliaetoplanktOll (Sign C). This planktontype occurs in the western and 

 northern parts of the Atlantic only and during the spring. From March to June or July 

 it can be traced from about the 40° Lat. and 70° Long. to the Newfoundland Banks and 

 to the south of Iceland, from whence it turns across the Färöe Channel and enters the 

 North Sea, replacing its triposplankton, and reaches the coasts of Scandinavia. It dis- 

 appears iii the sumraer, becoming replaced by styliplankton, but rules in July and August 

 around Spitzbergen. When the water with the cha^toplankton touches the coasts, especially 

 of Iceland, it sweeps away the neritic plankton therc and spreads it along the coasts of Scot- 

 land and Scandinavia, where it enters into the fjords. Thus many species of northern origin 

 may remain during the summer cmprisoned in the fjords, especially in their deeper water. 



The temperature of the chajtoplankton- water varies usually between 5° and 9° and 

 the salinity is about 35 p. m. 



The organisms of the chajtoplankton are chiefiy diatoms, especially Chcetoceros deci- 

 piens and Ch. constrictus. C. borealis and C. criophilus occur both in chteto- and tricho- 

 plankton so that it is difficult to decide whether they belong to one or the other type. 



