Acta Societatis pro Fauna et Flora Fennica, 49, N:o 7. 27 



M. denticulata in Wittr. & Nordst. exsicc. N:o 1454a 

 is a form of var. intermedia, intermediate between this and 

 M. thomasiana v. notata, (whereas M. denticulata in Wittr. 

 & Nordst. exsicc. N:o 552 is nothing but a reduced form 

 of M. thomasiana. 



Very closely allied to M. denticulata v. intermedia is M. 

 verrucosa B i s s. If in a fluid under a covering glass these 

 two forms of Micrasterias scarcely can be distinguished from 

 each other; only the margins of the former are more 

 conspicuously denticulated than in the latter. But if the objects 

 are studied without a covering glass in very little fluid, 

 all the protuberances become quite conspicuous, and under 

 a high magnification one is able to perceive even the 

 characteristic granulations of M. verrucosa. Perhaps M. ver- 

 rucosa should be classed as a variety of M. denticulata, but 

 on the other hand the granulations are such a characteristic 

 feature as the elongated protuberances in M. thomasiana 

 — that I did not think it necessary to unite them. 



M. thomasiana Arch. This species also varies consider- 

 ably the most reduced forms being very closely allied to the 

 var. intermedia-group of M. denticulata. Jacobsen made 

 of it (1875) a „f. thomasiana 1 ' of M. denticulata. But this 

 was not a good arrangement and has not been adopted by 

 other algologists. 



I have not seen any specimens from Finland either of 

 typical var. notata N d t., or of var. subnotata West. A 

 form with 4 small subapical notches on the polar lobe will 

 be figured here. — PI. 2 fig. 8—9. 



Genus Cosmarium Corda. 



C. cedercreutzii, nova spec. Cellulae subparvae medio 

 sinu anguste lineari non profunde constrictae. Semicellulae 

 subrectangulares ad apices versus paullum angustatae, late- 

 ribus convergentibus 4-undulatis, apice truncato recto 4- 



