The 'Freshwater Algae of Africa. 581 



Genus TOLYPOTHRIX Kuetzin.;. 



I. Tolypothrix tenuis, Euetz., emend. Schmidt, Cyanophyceae Daniae, 

 Dot. Tidsskrift, xxii, 1898-99, p. 413. (Syn. : T. lanata (Desv.), 



Waitm.) 



Samples 52-55. 



(4) STIGONEMATACEAE. 



Genus STIGONEMA Agardh.* 

 1. Stigonema hormoides (Kuetz.), Boruet et Flahault, op. eit., ser. 7. 



v, 1887, p. 68. 



Sample 16 (rare). 



(5) RIVULAKIACEAE. 



Genus RIVULARIA (Roth) Agardh. 



1. Rivularia natans (Hedwig), Welw. ; Bornet et Flahault, op. cit., 

 ser. 7, iv, 1886, p. 369. (Syn. : Gloeotrichia natans (Hedw.), Rabenh.) 

 Sample 30 (young colonies attached to water-plants). 



Genus CALOTHRIX Agardh. 



1. Galothrix fusca (Kuetz.), Bornet et Flahault, op. cit., ser. 7, iii, 

 1886, p. 364. 



Samples 14 (on aquatics), 15 (on Phormidium valderianum). 



(Note. — Specimens of this genus that were not determinable also 

 occurred in samples 16, 29, and 29a.) 



Genus D1CHOTHRIX Zanardini. 



1. Dichothrix fusca, n. sp. (Fig. 38.) 



Filis in caespites penicillatos dense aggregatis, rupibus affixis (?), ad 

 750 /a longis, e basi angusta gradatim patescentibus ; filis et pseudo- 

 ramis fere rectis, raro paullo flexuosis; pseudoramis elongatis ad- 

 pressis, sed apicem versus divergentibus ; vaginis crassis, lamellosis, 

 apicem versus gradatim attenuatis, sed semper apertis, hyalinis vel 

 plus minus lutescentibus etiam luteo-fuscescentibus ; tnchomatibus 

 contentu dense granuloso et saepe brunneo, ad dissepimenta nou 

 constrictis, apicem versus gradatim attenuatis, sed non in pilum 

 productis, cellulis tarn longis quam latis vel brevioribus ; heterocystis 

 singulis vel raro binis, basilaribus, hemisphaericis. 



* Undeterminable specimens of this gentis were also present in sample 42, 



