1 92 1. No. 4. THE PHYTOPLANKTON OF SOME NORWEGIAN LAKES. 3 1 



soiiicii'liat inflated, occasionally very slig/ifly loidulatcd , sides coircex and angled, 

 thus making four angles on each seniicell, the outer two of them being 

 furnished 'with spines. Spines stout and rather long, up to 7 8 of the length, 

 generally only slightly diverging. — Vertical vieiv elliptic, each pole furnished 

 with a spine. 



Cell-wall smooth, chloroplast a.xilc. — Cells often surrounded with gela- 

 tinous eircelopment. 



Occurrence : As plankton in lakes. 



Length without spines: 21 — 2i,j 11, -with spines: 24 — ^2,) n, breadth 

 'without spines: 2i,j — 22,j a, 'with spines: jj — 60 u, length (f spines: iS — 

 20 f(, breadth of isthmus. 9 — 10 u, thickness 11 — 12 a. 



This variety occurred in the mountain lake Besvandet in considerable 

 quantities. — In dimensions it agrees well with the form which Messrs. West 

 regard as the type, but the whole appearence is very different. — Arthro- 

 desmus Incus possesses a great range of variation. This variety must be 

 regarded as an adaptional form to the pelagic life. Its characters are rela- 

 tively constant, and I have never seen an^' . intermediate forms between 

 this variety and any other of that species, so that there are good reasons 

 for regarding the form is a separate species, Arthrodesnuts Huitfeldtii sp. nov. 

 As far as I can see, it is a true pelagic variet}-, and I think it likely, that 

 the form should be found bv some other explorers, in other parts of the 

 Caledonian plankton area. 



I ha\-e named the variety in honour of the well-known limnologist 

 H. Hl'itfeldt-Kaas Esqr. 

 PI. I, Fig's 6-7. 



Arthrodesmus quiriferus W. & G. S. West. 

 W. & G. S. West : Scott. Freshw. Plankton. 



This species, which is exclusively confined to the plankton, was rare 

 in a single lake. — The cells were twisted at their isthmus as in the forms 

 described by Messrs. West. This Alga is a very characteristic feature of 

 the Caledonian plankton, but nevertheless it is one of the more uncommon 

 plankton Desmids one can observe, at least in Norway. 



Genus Staurastrum Me vex em. Ralfs 1845. 



Staurastrum anatimtm Cooke & Wills. 

 CooKE 6: Wills: in Grevillea 1880. 



This species is a frequent and characteristic Desmid in our freshwater 

 plankton. — It is no exclusive plankton species, but surely it is a true 

 pelagic form. — The occurrence of Staurastrum anatinum in the benthos 

 is rare, I have hitherto never found it in Norway. There are numerous 

 varieties, and I have found a new one in the Norwegian freshwater 

 plankton, 'oiz. 



