ARKIV FÖR BOTANIK. BAND 14. N:0 9. 



Plagiogramma Gregorianum 



Grev. 

 Grammoiofhora arcuata Ehb. 

 G. marina v. macilenta W. Sm. 

 G. hyalina n. sp. 

 Rhabdonema arcuatum (Ag.) 



KÜTZ. 



R. minutum Kütz. 

 Hyalodiscus stelliger Bail. 

 H. scoticus (Kütz.) Grun. 

 Melosira Borr er i Grün. 



Paralia sulcata Heib. 

 Biddulphia aurita (Lyngb.) 



Bréb. 

 Podosira glacialis Grun. 

 Coscinodiscus asteromphalus 



(Ehb.) Grun. 

 C. curvatidus Grun. 

 C. subbvlliens Jörg. 

 C. {lacustris var.?) septentrio- 



nalis Grun. 



Moreover, a number of forms clearly illustrate the arctic 

 origine, though usually present only in a few, scattered or 

 isolated specimens. These species may have been introduced 

 with the arctic water, either scantily represented from the 

 beginning, or later on decimated on account of not having 

 found the conditions necessary for further development. 

 Such are: 



Colonels aemula (A. S.). 

 Navicula directa W. Sm. 

 N . kariana Grun. 

 N. gelida Grun. 

 N. distans (W. Sm.). 

 N. glacialis Cl. 

 N. glacialis var. septentrionalis 

 Cl. 



Ampliora polaris 0str. 

 Achnanthes polaris 0str. 

 A. septentrionalis 0str. 

 Synedra kamtschatica Grun. 

 Grammatophora arctica Cl. 

 Sceptroneis gemmata Grun. 

 Coscinodiscus hyalinus Grun. 

 C. subtilis var. glacialis Grun. 



There is, on the whole, a great resemblance between this 

 formation and the flora of the Arctic Sea, enumerated in the 

 respective works by Cleve, Grunow and 0strup. 



If we now compare tliese old, arctic deposits with the 

 saltwaterflora, that immigrated to the northern Baltic from 

 the south during the Litorina-epoch, we find that the fol- 

 lowing species occur abundantly in both: 



Rhoicosphenia curvata. 

 Cocconeis Scutellum. 

 Nitzschia Sigma. 



Synedra af finis. 

 Rhabdonema arcuatum. 

 Rh. minutum. 



