ÖPVERSIGT AP K. VETENSK.-AKAD. FÖRHANDLINGAR 1900, N:0 9. 1035 



Thalassiothrix lon^issimn Cl. & Grun. Sparingly at 13° — 

 27^ N. 43"— 34" E. {temj). 25,5; .m(. 38,8). — Arctic and ant- 

 arctic seas, whence it follows the currents to far distant regions. 



The above list contains 99 plankton-organisms noted from 

 the Red Sea, a number which doubtless will be multipled by a 

 more throughout exploration. In the following I denote by R 

 forms not found outside the Red Sea, by IP forms occurring in 

 the tropical parts of the Indian Ocean and the Pacific, by At 

 forms occurring in the tropical Atlantic and by A forms occurr- 

 ing in the temperate and northern Atlantic. 



Copepoda . . . 

 Ciliata . . . 



Number of 

 Species. 



37 



6 



Radiolaria . 



2 



Cystofiagellata 

 Silicoflagellata 



1 



1 



Dinoflagellatee 



19 



Murracytas . 

 Cyanophycese 

 Diatomaceae . 



1 



1 

 31 



R 



IP 



At 



A 



8 % 



92 % 



38 % 



13 



» 



100 » 



83 » 



17 



» 



50 » 



50 » 



50 



» 



100 » 



s 



100 



:> 



100 » 



— 



100 



» 



100 ;> 



80 3 



42 



» 



100 » 



100 » 







» 



100 » 



100 » 







3 ^ 



64 » 



29 » 



64 



We find thus that 8 % of the copepoda and 3 % of the 

 diatoms have not hiterto been found outside the Red Sea. 

 This depends doubtless on insufficient researches, as the basin 

 of the Red Sea is of such a recent origin that indigenous species 

 are highly improbable. This narrow sea, situated between two 

 very dry and hot countries is continually exposed to a strong 

 evaporation, by means of which the salinity increases and the 

 volume of the water decreases. Therefore, if the level should 

 remain, fresh supply of water from the Arabian Sea must come 

 in for covering the loss by evaporation, and with that water 

 doubtless plankton follows. One raay consequently expect to 

 find in the north a higher salinity than in the south, whick 



