1 92 1. No. 4. THE PHYÏOPLA.NKTON OF SOME NORWEGIAN LAKES. 35 



Genus Dcsjuidiutii Ac. 1824. 



Dcsniidittiu aptogoiiiiiii Breb. 

 De Brébisson : Alg. Falaise. 



The Desmid was present in a single collection from the Figgenelven 

 river, and it occurred in considerable quantities. The species is a ben- 

 thonic form, and probably only the currents have forced it away from its 

 natural growing-places. 



D('siiii(//iiiii Psnidostirptoiicnia W. & G. S. West. 



W. & G. S. West : Freshw. Algæ Ceylon. 

 This species was originally described from Ceylon and is one of the 

 more noteworthv of the genus. It has later been reported on from the 

 British freshwater plankton, and except in the Tropics it seems to be a 

 true limnetic form. Its occurrence in the Jaeder plankton is very noteworthy, 

 as this district is undoubtedly the richest in Norway with regard to fresh- 

 water Algæ. 



PI. I, Fig. I. 



Genus Sphccrozosnia Corda 1835. 

 Sphœrozosnia vcrtchi'atu)n Ralfs. 



Ralfs: Brit. Desm. 

 The Desmid is not unfrequent in the Norwegian lakes, and sometimes 

 it ma}- be found in quantities. I have never observed Splnvrozosma Aiihcrt- 

 imiiim from any Norwegian lake, our principal plankton form seems to be 

 Spliœrozosum vcrtcbratmn. 



Genus Spo)idylosiuui Breb. 



Spondylosium plamini (Wolle) W. & G. S. West. 



W. & G. S. West: Periodicity Brit. Freshw. Phytopl. 

 Spondylosium planum is one of the most frequent constituents of our 

 freshwater plankton. It is a true limnetic form, being one of the leading 

 forms of the Caledonian phytoplankton. It has very little common with 

 Spondylosium piilchntm, though it was recorded as a variety of that species 

 until a few years ago. 

 PI. I. Fig 8. 



Genus Hyalothcca Ehrbg. i 841. 



Hyalothcca ncglccta RAcm. 



Raciborski : in Flora vol. Ixxxi. 



The Desmid is a very rare one, but is more general in the plankton 

 than elsewhere. It is by no means so common in the pelagic region as 

 the benthonic species Hyalothcca mucosa and Hyalothcca dissilicns, but I 

 think it is a real limnetic species. 



