Microplankton /rum the Finnish Waters during the Month of May 191%. 3 



content ourselves by comparing them with tlie plankton from better known regions and 



drawing our own conclusions as to the distribution and the conditions of lue of the 

 plankton dealt with hère. 



CHAPTEB T. 



THE SEPARATE SPEOIES AND TIIEIK DISTRIBUTION. 



With some few exceptions the différent species can be classified into three groups: 



Diatomaceae. 

 Peridiniales. 

 Ciliata. 



The groups will be discussed in the order mentioned abow, and afterwards some 

 remarks will be made on those species, which are to be grouped otherwise. Of course 

 the groups mentioned bave no equal systematic value; this basis of classification is rather 

 a practical one employed on this special plankton. 



Tlie species of the différent groups will be dealt with alphabetically. 



The material examined consisted of following species: 



Diatomaceae. 



A. Oceanic species. 



Achnanthes taeniata 

 Chaetoceras debile 



— Wighami 

 Coscinodiscus lacustris 



sp. 

 Fragilaria cylindrus 

 Leptocylindrus minimus 

 Melosira hyperborea 

 Navicula Granu 



— Vanhöffenii 

 Nitzschia longissima 

 Skeletonema costatum 

 Thalassiosira baltica 



B. Forms that live in brackish 'or 

 fresh water. Marine littoral forms. 



Amphiprora decussata 



Asterionella formosa 

 Cocconeis Placentula 

 Scutellum 

 Diatoma tenue 

 Melosira distans 



— granulata 

 Navicula cryptocephala 



gracilis 



major 



Placentula 



rhynchocephala 



viridula 

 Nitzschia Sigma f. elongata 



sp. 

 Rhabdonema arcuatum 

 Rhoicosphenia curvata 

 Stauroneis Heufleri 

 Synedra affinis 



— pulchella 



— radians 



N:o 5. 



