80 



--. 



S. bacillaris Nag. (fig. 24 A) is an abundant species on damp earth, walls, 

 palings, etc. ; diam. of cells 2'7 3 - 8 p. S.flaccidus (Kiitz.) Gay (fig. 24 B) is 

 a larger species frequent on wet stones arid in rain-pools ; diam. of cells 

 7 10-5 /i. S. dissectus Gay (fig. 24 C) is a closely allied species to S.flaccidv*, 

 or perhaps only a form of it. S. variabilis West & G. S. West (fig. 24 D) 

 forms a thin green stratum on wet stones in the neighbourhood of waterfalls ; 

 the cells are very irregular in outward form and the chloroplast is often devoid 

 of a pyrenoid or may even possess two ; diameter of cells 3 6 p.. 



Genus Uronema Lagerh., 1887 1 . The filaments are simple, 

 relatively short, and destitute of a mucous coat; they consist of 

 cylindrical cells, the apical cell being acuminate and the basal cell 

 attenuate. The plants are fixed by a disc secreted by the basal 



cell. The chloroplast occupies a con- 

 siderable area of the cell- wall and is 

 parietal, containing two pyrenoids. The 

 cell-wall is firm and thin. 



The zoogonidia are produced singly 

 or in pairs from each cell; they possess 

 four cilia and a subapical pigment-spot. 

 Sometimes the zoogonidia are arrested 

 in their escape, the cilia are not de- 

 veloped, and an aplanospore is produced 

 by the acquirement of a strong cell- 

 wall. 



The only species is U.confervicolum Lagerh. 

 with filaments 4 6 p in diameter and cells 

 2 3 times longer than broad. It is an ex- 

 ceedingly rare plant, disti nguish ed from species 

 of Ulothrix by its short filaments, by the 

 attenuation of the apical and basal cells, by 

 the chloroplast, and by the firm cell-walls. I 

 have only met with it in abundance from the 

 Orkney and Shetland Is. 



I 'I 



U 

 c 



Fig. 25. A E, Binuclearia 

 tatrana Wittr., from Lewis, 

 Outer Hebrides ( x 440). 



The genus Rhaphidonema Lagerh. 

 (of which R. nivale is known from W. Yorks.) is a fungus. 



Genus Binuclearia Wittr., 1886 2 . The filaments are simple 

 and attached when young by a hapteron from the basal cell. The 

 cells are cylindrical with firm, distinctly lamellose cell-walls, the 

 transverse walls being unequal, a thin one and a very thick one 

 alternating. The cells thus appear to be arranged in pairs. The 



1 Lagerh. in Malpighia 1887, p. 518, t. xii, f. 110. 



2 Wittr. in Wittr. and Nordst. Alg. Exsic. 1886, no. 715. See also Schroder in 

 Forschungsberichte aus der biol. Station zu Plon, Teil vi, 1898, p. 1921. 



