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



19 



to size, polar lobe, lateral lobes, and also vertical view. 

 I have here published two figures of original specimens. 

 (PI. 3 fig. 61—62). Mr. Itzigsohn says in his announce- 

 ment of the „Liste Desm." by De Brebisson (cfr. Botan. 

 Zeitung 1856) as follows: „Die aufgefiihrte M. itzigsohnii 

 Braun Mss. ist von mir unter den Namen M. neodamensis 

 A. Br. (Dec. LI und LII Nr. 508) in Rabenhorst's Algen 

 Sachsens &c 1856 vertheilt worden." But this is not quite 

 correct because M. neodamensis is a form of M. truncata, 

 but M. itzigsohnii is a form of M. decemdentata. The spe- 

 cimens distributed in Rabenhorst's exsicc. Nr. 508 do 

 not at all agree with the figure by Brebisson. 



M. truncata (Corda) Breb., the typical form: 

 West, Mngr. II pi. 42 f. 2 and 7; Borge, Sao Paolo pi. 5 

 f. 24; Stange, Micr.-formen fig. XVI: 1—2, XVII: 4—5. 

 The type considerably differs from M. decemdentata and 

 should on no account be confused with this species. M. 

 truncata is twice the size; the distance between the isthmus 

 and the basis of the polar lobe is nearly twice the length 

 of the polar lobe, but in M. decemdentata these distances 

 are of equal length. In M. decemdentata the lobules are 

 furnished with real spines (very constantly and characteris- 

 tically), which are longer, narrower and sharper than in M. 

 truncata, in which the ultimate lobules are often emarginate, 

 but not spinate. Moreover M. decemdentata is distinguished 

 by its polar lobe which has a straight (or nearly straight) 

 apex, with the angles suddenly drawn downwards and each 

 furnished with one distinct spine directed horizontally or 

 downwards. Polar lobes of an almost similar shape occur 

 also in certain forms of M. truncata especially in those belong- 

 ing to var. crenata or nearly related to this variety. The 

 difference which commonly has been pointed out as charac- 

 teristic is the size of the cells, but it exists only as long 

 as we compare the typical forms, because there are gigantic 

 forms of M. decemdentata with typical cell-form (cfr. Wolle, 

 Desm. U.S. pi. 33 f. 5—6 pag. 113; length - 83— 100 /t; 

 PI ay fair, Sydn. Desm. pag. 608: length = 88— 120 t u), as 



