Microplankton /'nun the Finnish Waters during tke Month of May 1912. 39 



Melosira hyperborea Glenodinium bipes 



Navicula Granu Gonyaulax catenata 



Vanhöffenii 



Nitzschia longissima Didinium Gargantua 



Skeletonema costatum Laboea conica 



Thalassiosira baltica (= Coscinodiscus Lohmanniella öviformis 1 1910 Meunier, 



polyacanthus var. baltica 1880 Oleve pl. In, f. 20). 



and Grunow. p. 112). Mesodinium rubrum 



Tintinnopsis beroidea(V) 



Cocconeis Scutelhun tubulosa 

 Melosira granulata 



ßhabdonema arcuatum Radiosperma corbiferum 



Synedra affinis Xantbidium multispinosum (1910 Meu- 



pulchella nier, pl. 2.'3, f. 21): 



Some of tbese species are found in those parts of the ocean, which connect the 

 Arctic Ocean and the Baltic; but others have not been noted from the Connecting area. 

 These are: 



Àchnanthes taeniata Gonyaulax catenata 



Coscinodiscus lacustris 



Fragilaria cylindrus Tintinnopsis tubulosa 



Melosira hyperborea 



Navicula Granu Didinium Gargantua 



Vanhöffenii 



Nitzschia longissima Radiosperma corbiferum. 



Thalassiosira baltica 



As has been suggested by Jörgensen (1912, p. 10) thèse species must be looked 

 upon as relies from that time. when the Arctic Ocean was directly connected with the 

 Baltic. 



SIXE OF THE SPECIES. 



At first sight it looked as if many of the plankton-forms from the Finnish area had 

 very small dimensions. We shall compare the sizes of some of the species of the Fin- 

 nish material with the sizes, which are given in the „Nordisches Plankton" (table VI): 



N:o 



