788 P. T. CLEVE, SOME ATLANTIC PLANKTON-ORGANISMS. 



the American coast dips below the warmer Atlantic and spreads 

 towards the Azores and the European coasts. In November the 

 surface-water from the sumraer gets driven away or rather 

 raixed with the underlying strata and then the west-atlantic 

 plankton comes to the surface. Most of the species of the tricho- 

 plankton do not multiply in the water with so high a salin- 

 ity as about 35 p.m. They die sooner or later, but with 

 the exception of Chcetoceros decipiens, which increases and gets 

 conveyed as cAte^o-plankton over the Wywille ridge into the 

 northern Atlantic and finally to Spitzbergen. 



This hypothesis receives considerable corroboration, if the 

 seasonal distribution of other species from West Atlantic habitat 

 be considered. 



Thalassiothrix longissima Cl. & Grün, in 1898. 



March. East of Jan Mayen (71° N. 1° 30' W.). Färöe 

 Channel. — At 23° N'. IT W. (rare). — From the Azores to 

 the English Channel (more or less abundant) and thence along 

 48'— 49° N. to 33° W. — Davis Strait — S. of Newfoundland 

 banks from 43° N. 45° W. to 40° N. 71° W. 



April. N. of Jan Mayen (74°— 75° N. 5°— 9° W.). Along 

 58° N. from 4° to 28° W. — Between 40°— 50° N., 7°—70° W. 

 From the Azores to the English Channel — S. of Cape Farewell. 



May. N. of Iceland, from 70° N. 15° W. to 77° N. 2° 30' W. 



— From the Färöes to Greenland, along 57° — 59° N. — Between 

 49'— 47^ N. 22^—32° W. — Davis Strait. — From 42° N. 47° 

 W. to 40° N. 68° W. 



June. Iceland to S. of the Färöes (63° N. 13° W. to 60° 

 N. 9° W.). — Den marks Sound (65°— 66° N. 29°^-31° W.). — 

 SE. of Greenland (56° N. 33° W.) to Cape Farewell (abundant). 



— At 41° N. 58° W. 



July. Abundant at 65° N. 5° W., rare in the Färöe Chan- 

 nel. — The Irminger Sea, from 60° N. 17° W. to 58° N. 44° W. 



August. S. of Iceland. The Färöes. The Azores. Davis 

 Strait. Everywhere rare. 



