20 



PLANKTON-TYPES. DIDYMUS-PLANKTON. DESMO-l'LAXKTON. 



Limit;- 



Chaetoceros curvisetus ... 11° N. 



C. danicus 21°N. 



C. densus 12°N. 



C. didymus 20°N. 



C. Schiitii 35°N. 



Ditylum Brightwellii 23° N. 



Eucampia zodiacus 34°N. 



Guinardia flaccida 16°N. 



Lauderia annulata 21°(7)N. 



Lithodesmium undulatum 40° N. 



Rhizosolenia calcar avis ... 5° N. 



R. gracillima 4° S. 



R. setigera 7°N. 



R. Shrubsolei 18°N. 



R. Stolterfothii 10° N. 



Stephanopyxis turgida .. 5° S. 



Streptotheca thamesis ... 45° N. 



Some of these species go very far to the soiilh, even to the 

 Gulf of Guinea. They enter the plankton above the 200 metre plateau, 

 west of the European Continent, and arrive in the spring and the 

 summer through the English Channel into the south part of the 

 North Sea. The same kind of plankton also moves west of the 

 British Islands towards Scotland. There are some few Baltic forms 

 among these species. 



111. Desmo-plankton. This kind is the prevailing one in the 

 whole of the tropical Atlantic, in the southern hemisphere between 

 Africa and S. America and in the Etjuatorial Current. The average 

 space it occupied in the northern hemisphere was to the left of a 

 line drawn from Cape Verde to the Newfoundland Banks, but the 

 extension of this area was very different at different seasons. In the 

 winter the northern limit was at about 35° N., but in May it had 

 advanced beyond 40°, nearly to 45° N. In November the limit had 

 retired below 40° N., but the region had moved eastwards, so that 

 Desmo-plankton was found in November 1898 off the Canaries and 

 Gibraltar. 



