4 P. T. CLEVE. PLANKTON, COI.LECTED BY THE SWEDISH EXPEDITION TO SPITZBEKGEN. 



II. StyliplailktOll (Sign S). The region of desmoplankton, wliich is subject to 

 variation in extent according to the seasons, is surrounded by an irregular band of water 

 containing styliplankton. In the west this plankton-type seeras always to occur in 

 mixture with desmoplankton, and such a mixture characterizes the Caribbean Sea, the 

 Antilles-current to the region of Bermuda. About the 40° breadth the styliplankton 

 becomes more differentiated and the region increases in breadth towards the European 

 and African coasts. It forms a narrow band west of Africa from Cape Verde to Canaries 

 and occupies the triangulär space between the Azores, the English Channel and Bermuda. 

 The extent of the region is subject to great variation according to the seasons. In the 

 summer it approaches towards the Färöe Channel (probably also towards Iceland) in a 

 raighty tongue, which sends branches through the English Channel into the German Ocean 

 and around Scotland into the North Sea. When the water enters the North Sea its salinity 

 becomes lowered by admixture of the continental coast-water and, consequently, the 

 plankton becomes also modified. Some of the species die away, others multiply, and 

 thus are originated in the North Sea two important derived styli-planktontypes, the 

 tripos-plankton in the north and the didymus-plankton in the south. I have distinguished 

 as a third type of North Sea plankton the hnlosphtera-plankton. This kind also originates 

 from the styliplankton by an considerable increase of the green alga Halosphivra viridis, 

 which seems to take place in the autumn around Färöe, from whence it desccnds to Scot- 

 land and enters the North Sea iinally reaching Skagerack. 



The styliplankton-water, which in the bcginning of the summer reaches the Färöe 

 Channel proceeds during the autumn towards Spitzbergen. 



The temperature of this water varies usually between 10° and 20° and the salinity 

 is about 35 p. m. 



The number of organisms constituting the styliplankton is very considerable and 

 the flora and fauna are subject to a great variability according to the breadth and the 

 season. Some species appear simultaneously at the African and South American coasts, 

 others occur in the whole region, others again scem to be limited to the eastern part. 

 I name among the more common and characteristic forms the following, marking with 

 e such forms, as occur in the eastern Atlantic. With s I denote forms, which as a 

 rule do not pass över the Färöe Channel, and with n forms which enter the northern 

 Atlantic. 



Änimals. Plants. 



Acartia Clausii {e n), Halosphcera viridis (??), 



Centropages typicus (n), Ceratium {trip. v.) aiirittim {e s), 



Clausocalatius arcuicornis (s), C. candelabrum (s), 



Corycceus rostratus {e s), C furca (e n), 

 Mecynocera Clausi (in the spring s), C lineatinn (n), 



Microsetella atlnntica (n), C. reticulatum (s), 



Oithona plumifera (s, n rarely), Dinophysis homunculus (s), 



O. similis (n), Diplopsalis lenticida (n), 



Onccea minuta (e ?*), Gonyaulax polygramma (n), 



Paracalanus pannis (n), Peridiniwn divergens (n), 



