26 R. Gronblad, New Desmids. 



M. denticulata includes not only such forms as have 

 the ultimate lobules rounded, but also many denticulate 

 forms, which have been described by various authors. Such 

 forms are intermediate between this species and M. thoma- 

 siana and, in my opinion, they would with the same right 

 or perhaps better be placed in M. thomasiana. The way 

 that these two species are now defined seems to me quite 

 artificial. But to refer all forms with denticulated margins 

 to M. thomasiana so that M. denticulata would include only 

 not-denticulated forms, would perhaps be a more natural 

 arrangement. — (But on the other hand two closely allied 

 forms viz. M. dent. v. intermedia and M. dent, forma Him, 

 would then be referred to different species!) 



var. intermedia Nordst.; Wittr. & Nordst. exsicc. 

 N:o 370; Borge, Sao Paolo pi. 8 f. 11. This form already 

 considerably differs from the typical one with its denticulate 

 margins and the more numerous and more prominent pro- 

 tuberances. The denticulate margins resemble M. thomasiana 

 (inclus. var. notata), but in that species the ultimate lobules 

 are slenderer with longer denticulations. On the other hand 

 this form resembles M. verrucosa, in which the protuberances 

 are also numerous, but less prominent, and the marginal 

 denticulations are less developed and irregular. All these 

 forms posses a slight but very characteristic feature, viz. 

 the ultimate lobules are narrowed outwards with conspicu- 

 ously convex sides and it seems as if the two denticulations 

 on each lobule were a little convergent. The var. inter- 

 media possesses a broader polar lobe with a less retuse 

 apex than the type. — PI. 2 fig. 3. 



Old semicells of M. denticulata sometimes become 

 coarsely granulate and rough, whereas the younger ones 

 can be quite smooth or delicately punctate. Such a form 

 has been figured by Petkoff (Period. Spisan. 1 59, 1899 

 pi. 4 f. 69) erroneously as „M. rotata". 



M. denticulata f. Hirn (Desm. Finl. pi. 1 f. 22) is inter- 

 mediate between the type and var. intermedia but should 

 be referred to the former on account of the smooth margins. 



