34 KAAKK MUNSTER STRØM. M.-N. Kl. 



Sl(ïiir(islniiii p(ir(i(l(ß.\iiiii Mi^'i'k.n. 

 Me YEN in Nov. Act. p 777. 



I have mcntioncfl this common species here, on account of the many 

 confusions between it .iikI Sldut'astriuu i^racilr. It seems easy to separate 

 them for one who has only stiuhCd th( heiiihonic forms, hut the pelagic 

 forms with tlieii- whole range of varieties are a more difHcult matter. The 

 longer I have made observations on the two species, the more I am con- 

 vinced that there is no real specific separation between them in Nature. 

 Of course, all our classifications are more or less artificial, but these 

 species arc connected with so many intermediate forms, that it would 

 seem unlikely if the characters distinguishing them are sufficient for a 

 specific separation. 1 do not mean, that they should be regarded as a 

 single species at once ; that is in many cases a matter of convenience, but 

 I would emphasize that thorough studies should be made so that clear 

 definitions of the species could be obtained. As the matters are now, the 

 untrained observator will easily refer many of the pelagic forms to the 

 wrong species, and even the experienced may be in doubt in some cases. 



Staiirastriiui paradoxum var. ciiigiiliiin W. & G. S. West. 



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

 The Desmid was often frequent in the lakes, and appears to be a true 

 pelagic variety. 



Staiirastiiin proboscidcitiii Arch. 

 Archer : In Pritch. Infus. 



This species occurred in great quantities in Besvandet, and is one of 

 the very few, which does not occur in the British plankton. It is a true 

 limnetic form, which is much more frequent in the plankton than elsewhere. 

 It should be compared with the short-armed stout forms oï Staiirastrniit aiiatiiiiiiii. 



Stanrastriiiii pseiidopclagicimi W. & G. S. West. 

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



This species is very characteristic, but is rare in our plankton. It 

 seems to be scarce in the lakes in which it is observed. In spite of this 

 it is a true pelagic species, being restricted to the plankton only. 



StaurastTiiiii scxangularc Rabh. 



Rabenhorst: Kryptogamenflora Sachsen. 



Staiirastniiu scxangularc is a tycholimnetic form, being moi'e general 

 in the plankton than elsewhere. I have observed it in two collections in 

 none of which it was common. 



Stam-astniiii vcrticillatum Arch. 



Archer : in Quarterly Journ. Micr. Science. 



This species is a very rare one, and has essentially a western distribu- 

 tion. Indeed, it is only observed a very few times before. The Desmid 

 cocurred in the lake Tysselandsvandet in Western Norway. 



