No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 99 



only seen two small crusts of about 4 mm. in diameter, growing 

 together with Lithoph. macrocarpum on Fucus vesiculosus. In habit 

 they resemble M. farinosa f. borealis. The cells, on the contrary, 

 are smaller than usual, 9 — 15 jj. long and 9— 11 /-Abroad, recalling 

 ill". Lejolisii, whereas the cortical cells are larger than usual in 

 the said species. I have seen no heterocysts. As to the concep- 

 tacles, they are partly of almost the same shape as those of M. 

 farinosa f. borealis, 225—300 //. in diameter, partly approaching 

 those of M. Lejolisii f. limitata. The orifice of the conceptacles 

 is not ciliated, but on this fact scarcely any stress can be laid. 

 Particulars are to be found under M. Lejolisii. The same is the 

 case with specimens from the coast of Norway growing on Chondrus 

 and Phyllophora together with Lithoth. membranaceum. The 

 conceptacles, however, are here in part smaller than in f. borealis, 

 while the crust resembles this form in habit. Also from the coast 

 of Sweden (Koster) there are some similar small specimens which 

 approach M. Lejolisii f. limitata in habit. Here, however, the 

 cells are longer than in the Danish and Norwegian ones mentioned 

 above ; thus in this respect they are corresponding with the typical 

 specimen ; heterocysts, on the other hand, have not been found. 

 The material I have in hand is very little, so that I can not yet 

 decide whether the specimens in question are perhaps only extreme 

 forms of M. Lejolisii, unquestionable specimens of which are found 

 on the same host plants. 



As to the f. callithamnioides admitted above, it appears to 

 me to be an unquestionable form of M. farinosa. In my opinion 

 it cannot be regarded as an independent species. In fact I have 

 seen specimens absolutely running into the typical form. It is 

 much varying and may be now slightly lacunose, now greatly so, 

 or composed of cell-rows subdichotomous or dichotomous-radiating. 

 I'have sometimes also seen typical M. farinosa scantily lacunose. 

 A corresponding state of things is found in M. minutula. The 

 same is the case particularly with young specimens of Lithoph. 

 zonale, but less emphatically. 1 ) The cells of f. callithamnioides 



a ) Cp. F o s 1 i e. Rem. Melob. Herb. Crouan p. 4. 



