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



21 



have the margins of the ultimate lobules rounded or retuse 

 (not bidentate) and so, without spines, it is considered by 

 most authors. Again, Ralfs described M. crenata: lateral 

 lobes are sometimes entire, but more usually crenate, oc- 

 casionally having a few inconspicuous teeth", and he also 

 figured it as such (1. c. pi. 10 fig. 4b). Also Delponte 

 (Desm. subalp. pi. 5 f. 17—18) figured M. crenata furnished 

 with acute spines at the margins. But Delponte added 

 to his form a mark of interrogation, and in fact the 

 margins much more resemble M. truncata from which is is 

 distinguished only by its higher polar lobe. I have never 

 seen such a form. 



Like West I have very seldom seen M. crenata. But 

 many transitional forms occur. M. truncata seems to be 

 much more variable in Finland than in England, so, that 

 one may frequently find forms which just as well could 

 be regarded as belonging to both species. Therefore 1 

 would prefer to unite these forms in one species as M. 

 truncata type and var. crenata (Breb.) Reinsch. 



The typical M. truncata is figured by West (Mngr. II 

 pi. 42 f. 2 and 7); Stange (Micr.-formen, fig. XVI: 1—2, 

 XVII: 4—5); and also the typical cell-form by Borge (Sao 

 Paolo pi. 5 f. 24). A slightly different form is M. neoda- 

 mensis Braun in Rabenhorst, Exsicc. N:o 508), which 

 neither with regard to shape, nor to size, can be distinguished 

 from e. g. some of the forms figured by West (Mngr. II 

 pi. 42 f. 3 and pi. 45 f. 5). 



Hab. The type is common in all parts. PI. 1 fig. 

 4—5, 8, 11; — the var. crenata is exceedingly rare; only in 

 Gov. Archangel. — PI. 1 fig. 7. 



var. quadrata Bulnheim (in Hedwigia 1859 pi. 2 

 f. 2); Rabenh. exsicc. N:o 1224! This variety consists of 

 a group of forms, which very constantly and characteris- 

 tically differ from all other forms (-- also from v. crenata —). 

 The most important and distinguishable characters are: the 

 very thick habit (also „a vertice"), the closed and less deep 

 incisions, the highly arched polar lobe (as in M. crenata) 



