The Freshwater Algae of Africa. 577 



uneven edge, which is frequently obscured by the adhesion of numerous 

 foreign particles, and is generally verv wide, standing off considerably 

 from the mass of contained trichomes (Fig. 36, B and 1>) ; the brown 

 colour appears to become lost, as these older sheaths are hyaline. The 

 character of the trichomes will be sufficiently plain from the diagnosis 

 and the figures (Fig. 36, C, C"), without further description. The 

 individual close-fitting sheaths of the trichomes are sometimes plainly 

 visible. 



The only species of Schizothrix that at all approach this one in the 

 number of trichomes within the sheath are 8. mezicana, Gom., 

 8. fragilis, Gom., 8. rupicola, Tilden (Minnesota Algae, i, 1910, 

 p. 153, PI. VI, fig. 25), and 8. (Hypheothrix) calida, De Wildeman 

 (Algues Buitenzorg, 1900, p. 30, PI. XV, figs. 14), all of which are, 

 however, markedly distinct in other respects ; nor are the trichomes 

 nearly as numerous as in our species. 



(2) XOSTOCACEAE. 



Genus NOSTOC Vaucher. 



1. Nostoc hederulae, Menegh. ; Bornet et Flahault, Revis. d. Xostoc. 

 heterocyst., Ann. Sci. Nat,, Bot., Ser. 7, vii, 1888, p. 189. (Syn..: 

 .V. punctiforme (Kuetz.), Hariot). 



Samples 29. 29a, 33 (attached to Cladophora and other aquatic 

 plant s ) . 



2. Nostoc Unckia (Roth), Bornet et Flahault, op. cit., p. 192. 

 Sample 49 (?, no spores). 



3. Nostoc pruniforme (Linn.), Ag. ; Bornet et Flahault, op. cit 

 p. 215. 



Sample 40 (Victoria Falls !). 



Genus NODULARIA Mertens. 



1. Nodularia harveyana (Thwaites), Thuret; Bornet et Flahault, 

 op. cit., p. 243. 



Sample 26 (not very abundant among Spirogyra). 

 Recorded from Little Namaqualand by G. S. West. 



Genus ANABAENA Bory. 



1. Anabaena circinalis, Rabenh. ; Bornet et Flahault. op. cit., 

 p. 230. 



Sample 30 (?, in the mucilage of Riv niacin nutans, no spores). 



