24 R- Gronblad, New Desmids. 



always in the middle of the vertical view („a vertice") found 

 a distinct but flat tumidity. Vide PI. 2 fig. 1 and 2! 

 Various forms observed by me agreed with the following 

 figures: f. evoluta Turn., E.-Ind. pi. 23 f. 1; Ducellier, 

 Desm. Suiss. II pag. 136 pi. 3 f. 1 and 3; Stan ge, Micrast.- 

 Formen fig. IX: 4—5, 7, 10. In a sample from Russian 

 Karelia was found a mass of M. rotata of various forms, 

 but without exception possessing a polar lobe which stands 

 high above the lateral lobes. Cfr. Wo lie, Desm. U. S. pi. 

 34 f. 1—3. Another sample, also from Russian Karelia, 

 contained various forms of M. rotata, which all had a strong 

 resemblance to M. quadridentata (Nords t.) G r 6 n b 1. (cfr. 

 Desm. Keur. page 35—36); Wittr. & Nordst. exsicc. N:o 

 371; Borge, Sao Paolo pi. 5 f. 33. But I do not think 

 there is any reason for uniting my forms with M. quadri- 

 dentata, which is an easily distinguished gigantic tropical 

 species. (Cfr. Wittr. & Nordst. exsicc. fasc. 21 p. 35. 

 „length 335—360//"; I have myself measured 372/*.) - l ) 

 Both the typical M. rotata and this Karelian form are very 

 variable and between these there are many intermediate 

 forms. The features of this characteristic form are: a polar 

 lobe which stands more or less high above the lateral lobes; 

 the margins of the ultimate lobules are very variable but 

 commonly broadly 2— 4-dentate as in M. quadridentata; and 

 finally, the perhaps most important of peculiarities viz. the 

 upper and the lower lateral lobes are of equal breadth, 

 each of them being subdivided into 4 ultimate lobules (as 

 in M. quadridentata), whereas in the typical M. rotata the 

 upper lateral lobe is always broader than the lower. I now 

 think it will be best to place our form as a „forma pseudo- 

 quadridentata, nova f." of M. rotata with the following- 

 diagnosis: 



Semicellulae trilobae, lobo polari prominenti, lobulis 

 ultjmis acute bidentatis; lobis lateralibus inferioribus superiori- 

 busque aequilatis bis dichotomis segmentis ultimis truncatis 



M Vide our PI l Pig. 14 14'. 



