10 Acta Societatis pro Fauna et Flora fennica. VIII, n. 2. 



Epithemia turgida var. Westerman- Coscinodiscus balticus Grun. 



nil Kiitz. C. lacustris Grun. 



E. gibba (Ehb.) Kiitz. Campylodiscus Clypeus Ehb. 



Bhabdonema arcuatum (Ag.) Kiitz. C. echineis Ehb. 



E. minutum Kutz. Surirella striatula Turp. 



Grammatophora oceanica Ehb." Actinocyclus crassus (W. Sm.) Ralfs. 



Melosira Borreri Grun. Diploneis didyma Ehb. 



Hyalodiscus scoticus (Kiitz.) Grun. i>. interrupta Kiitz. 

 Coscinodiscus asterompkalus (Ehb.) Grun. 



The occurrence of Rhabdonema arcuatum, Coscinodiscus 

 asteromphalus, Hyalodiscus scoticus and some other, rarer forms, 

 not enumerated here, prove that the water, in which these de- 

 posits were formed, was more salt than it is in our time. 



The diatomaceous vegetation of the larger lakes is in ge- 

 neral tolerably uniform. On the surface the following forms are 

 found in abundance: 



Tabellaria fenestrata Kiitz. Asterionella formosa Hassal. 



Melosira granulata Ralfs. Stephanodiscus Astrcea (Ehb.) Grim. 



Fragilaria capucina Desm. Cyclotella comta v. radiosa. 



In the lake Lojo (in the vicinity of Abo) as well as in a 

 lake in northern Savolaks the interesting Synedra Crotonensis 

 Edw. was found. This species occurs in a similar manner in the 

 lake Erie in Northern America, in the lake of Genevra, in the 

 northern Italian lakes and in the lake Malaren in Sweden. 



The stones on the bottom of the lakes are often coated by 

 a velvet-like stratum of Gomphonema geminatum C. Ag. As is well 

 known, several ,,relicta" forms of crustaceans are found in the 

 large lakes of Sweden and Finland, indicating a connection bet- 

 ween the arctic sea and the Baltic during the glacial epoch. I 

 have not been able to find any such „relicta" forms among the 

 diatoms in the gatherings which I have examined. The diatoms 

 of Ladoga are all fresh-water forms. Mr Grunow mentions in his 

 monograph of Grammatophora *) Gr. oceanica var. minor as oc- 

 curring in Ladoga, but this may be an error. 



*) Bot. Ccntralbl. 1881. 



