6 ARKIV FÖR BOTANIK. BAND 14. N:0 9. 



Diploneis Smithii and Mastogloia elliptica have been found 

 in new, very large varieties. The fossil, arctic forms of 

 Hyalodiscus stelliger and of Bhabdonema arcuaium are conside- 

 rably larger than the same species in the LitorinaSea, or 

 now living at the West coast of Sweden. Together with Rhah- 

 donema minutum, we have the gigantic Rh. Oestrupii in the 

 same association. 



By the richer flora, by the occurrence of many species 

 lacking in deposits from the Litorina-eipoGh, by the absence 

 of some characteristic »Litorina^> -iorms and, finally, by the 

 often luxuriant development of the species, it does not generally 

 offer any difficulties to distinguish associations of fossil, 

 marine diatoms, deposited in the Finland of to-day during 

 an early-quaternary transgression of the Arctic Sea, from the 

 flora, imported at a later period by the waters of the Lito- 

 rma-Sea. 



As to the systematic arrangement I have followed, for 

 the naviculoid forms, Cleve's S^'nopsis, and for the rest 

 Schütt's monography in »Die Natürlichen Pflanzenfamilien» 

 by Engler & Prantl, part I, 16, p. 55—57, with the alter- 

 ations, proposed by 0strup in Danske Diatoméer. 



The geographical distribution of the species and varieties 

 being of great importance for the elucidation of the geological 

 conditions under which the diatoraaceous strata have been 

 deposited, I have endeavoured to give an account of the 

 habitat and the area of each form. The datas used have 

 been furnished, as to the Naviculoid forms, by Cleve's 

 Synopsis, completed with statements, given in the later papers 

 by Mr 0strüp. As to the remaining Pennatae and the Cen- 

 tricae, my data are, no doubt, very incomplete, since I have 

 been prevented from lack of time to gather all the notices 

 scattered in numerous papers on the subject. As far as the 

 pelagic forms are concerned, however, the treatise given by 

 Mr Gran in »Nordisches Plankton» III, p. 19, has been con- 

 sulted. I have also noticed the indications given in the 

 various works by Cleve, Grunow ard 0strüp, mentioned 

 above. 



