40 



Caroline L e e g a a r d. 



Table VI. Sue of the différent species. 



It appears tliat the chaiö-forming diatoms are small, for instance: 



Achnanthes taeniata 

 Chaetoceras debile 

 Melosira hyperborea 

 Navicula Granu 

 Skeletonema costatum. 



The occurrence of small forms in the brackish water of the Gulf of Finland agree 

 vvith that fact, that the small forms have a larger area relatively to the volume than 

 the big ones. Consequently they will easily keep themselves afloat in the brackish water. 



But not all the forms are small. Fragilaria cylindrus and Gonyaulax catenata for 

 instance exceed the size, which is noted in the „Nordisches Plankton", and other species 

 such as Thalassiosira baltica and Coscinodiscus lacustris show sometimes very large cells. 



But a long series of observations is required before it is possible to express any 

 decided opinion on this subject. 



XLVIII. 



