16 PLA>iKTON-TYPES. NORTHERN NERITIC PLANKTON. STYLI-PLANKTON 



Limits 

 Lat. N. 



C. polychordus 72°— 50^ 



C. radiatus 74°— 20° 



Nitzschia delicatissima 65° — 57° 



Skeletonema costatum 63° — 37° 



Thalassiosira gelatino.sa 69° — 50° 



Thalassiothrix Franenfeldii 63°— 21° 



II. Styli-plankton. This kind constitutes the plankton of the 

 water with 35 p. m. salinity, or the » Gulf-stream water » of the 

 hydrographers. The range of distribution of this kind is West of 

 S. Africa, or the Benguela current, the Gulf of Guinea, the Cape 

 Verde region and the space between the Canaries, the Azores and 

 the mouth of the English Channel. From March to May this area 

 expands westwards, across the whole Atlantic, betw^een 40° and 50° 

 N., so it seems as if the water containing this kind of plankton 

 ascended from deeper layers to the surface. Many of the species of 

 the Styli-plankton also occur more or less intermingled with Desmo- 

 plankton in the western Atlantic, so that the Styli-plankton surrounds 

 the region of the Sargasso Sea in the form of an irregular ring. 



The water between 40° and 50° N., containing Styli-plankton 

 advances northwards towards Iceland and the Faroe Channel and 

 finally moves towards Spitzbergen. During the summer, especially 

 in August, the water between 40° and 50° N., that contains Styli- 

 plankton, becomes covered by a sheet of water containing Desmo- 

 plankton. This is particularly the case in the western regions, along 

 the American coast and above the Newfoundland Banks. Some 

 specimens of the Desmo-plankton, more or less intermingled with the 

 Styli-plankton, drift, tow^ards Iceland and the Faroe Channel, but in 

 November the water with Desmo-plankton disappears from the area 

 between 40° and 50° N., and then a number of Styli-plankton forms 

 reappear, more or less intermingled with Tricho-plankton. 



The Styli-plankton is very rich in species. I give the fol- 

 lowing list of the more important ones: 



