Ulotrichacece 75 



The British genera are best arranged as follows : 



* Filaments thread-like, cells cylindrical with truncate 



apices. 

 t Filaments long and flexuose, attenuated towards 



base Ulothrix. 



ft Filaments short, attenuated at both base and apex Uronema. 

 ftt Filaments of variable length; transverse walls 



very thick; cells in pairs Binuclearia. 



** Filaments fragile, often moniliforin, cells with rounded 



apices. 



t Cells more or less cylindrical ; plants with a re- 

 semblance to a fragmented Ulothrix; with no 



prominent mucous coat Stichococcus. 



ft Cells cylindrical with hemispherical ends, or sub- 

 globose, often remote ; with a prominent mucous 

 envelope. 

 Cells cylindrical. 



| Cells equidistant, often in close contact. 



Cells large, short Hormospora. 



Cells minute, more elongate CloeotiJu. 



H Cells in pairs Geminella. 



( 'ells rounded Radio/Hum. 



The three genera Hormospora, Glceotila and Geminella are scarcely to be 

 distinguished from each other. Perhaps it would be better to unite them 

 under the name Geminella. 



Genus Ulothrix Klitz., 1833. [Hormiscia in the sense used 

 by Rabenhorst (1868), Hansgirg, and De Toni.] In this genus 

 the filaments are simple, not attenuated at the apex, but fre- 

 quently fixed at the base by a unicellular, simple or ramified 

 ' rhizoid.' The cells are commonly cylindrical or sometimes swollen, 

 and in the larger species the cell-wall is thick and evidently lamel- 

 lose. The chloroplast is parietal with one or many pyrenoids, and 

 varies much in its relative size. 



The genus Ulothrix was established by Ktitzing 1 for the species 

 U. zoimta two years before Fries' description of Hormiscia-. 

 Areschoug's 3 enlargement of the genus Hormiscia was based upon 

 erroneous conceptions, as he included in it species having no 

 affinity with each other. The original Hormiscia of Fries only 

 included two Algae previously known as "Conferva penicilliformis 

 Roth" and "Conferva Wormskioldii Flor. Dan." These Alga? are 

 commonly placed under the genus Urospora of Areschoug, but the 



1 Kiitzing in Flora, 1833, xvi, p. 517. 



2 Fries in Flora Scand. 1835, p. 327. 



3 Areschoug in Acta Beg. Soc. Sci. Upsala, ser. in, vol. vi, no. 2, p. 12. 



