WELWITSCIl'S AFRICAN FRESHWATER ALGM. 267 



posed genera is the fragility of the sheaths, which in itself is 

 certainly an insufficient generic distinction. 



1. T. crassa, sp. u. T. terrestris, strato crasso spongioso 

 nigricante vel atro-viride ; filis crassis flexuosis, dense intertextis ; 

 pseudo-ramispaucis, remotis, brevibus et suberectis; vaginis crassis, 

 firmissimis, valde lamellosis (lamellis inaiqualibus in crassitudine), 

 non ocrearis, sordido-luteis ; trichomatibus aerugineis, cellulis sub- 

 quadratis vel diametro duplo longioribus ; heterocystis solitariis, 

 quadrato-oblongis vel subquadratis. Crass, fil. 25-27 /x ; crass, 

 trich. 11-5-14-5 /x. 



Pungo Andongo. Ad dextr. flum. Cuanza locis palnstribus inter 

 Lythraceas, etc. prbpe Candumba; March 1857. No. 11. 



2. T. phyllophila, sp.n. T. strato dense intricato, olivaceo- 

 viridis vel nigro-viridis ; fills circiter 1 mm. altis, irregulariter 

 pseudo-ramis ; pseudo-ramis brevibus, filo primario subparallelis ; 

 vaginis crassis, achrois, firmis et persistentibus, non ocreatis ; 

 trichomatibus subparallelis, olivaceo-viridibus ; cellulis diametro 

 1-1^-plo longioribus, nonuuuquam diametro brevioribus (plerumque 

 in ramis parvis et ad apices filorum primariorum est) ; heterocystis 

 solitariis, ad basin pseudo-ramorum vel inter eos, subquadratis, 

 oblongis vel subhemisphatricis. Crass, fil. 12-5-18 /x; crass, trich. 

 8-5-10 [J.; long, heterocyst. 8-5-13 /x. 



Goluugo Alto. Ad folia viva lUiwrea; (Alsodeiic) spec, e Viola- 

 cearum familia, in sylvis deusis de Alto Queta ; Dec. 1855. 



The nearest species to this is T. hijssoidea (Hass. Brit. Frcshw. 

 Ahj. i. 233-4 ; ii. t. Ixvii. f. 5), from which it differs in its much 

 thicker colourless sheath, which is not fragile, and in the usually 

 longer cells. 



8. T. arenophila, sp. n. T. terrestris, strato compacto tenue 

 submcmbranaceo fulvo ; filis brevibus, dense intricatis, flexuoso- 

 contortis et apicem versus atteuuatis ; pseudo-ramis rarissimis 

 brevibus et subappressis ; vaginis crassis, firmis et lamellosis, 

 fiavis vel ilavo-brunneis, marginibus glabris, non ocreatis ; tricho- 

 matibus terugineis ; cellulis diametro l:^-2^-plo longioribus, proto- 

 plasmate granuloso ; heterocystis solitariis, rectangulari-oblongis, 

 diametro circiter li-plo longioribus. Crass, fil. 14-5-15 /x ; crass. 

 trich. 5-5 /x. 



Pungo Andongo. Ad terram arenoso-huraosam in editissimis rupi- 

 bus Pedra Cazella, cum Schhotriche delicatissuna ; Jan. 1857. No. 151. 



4. T. LiMBATA Thur. in Born. & Flab, in Ann. Set. Nat. 7e serie, 

 Bot. v. 124 (1887). A smaller form with yellowish brown sheaths, 

 which are often somewhat rough on the exterior. Crass, fil., 9-5- 

 10 ji ; crass, trich. 5'5-7 /x. 



Mossamedes. Cum Oscillatoria tenui in umbrosis muscosis ad 

 ripam fiuminis Bero prope Cavalheiros ; Aug. 1859. No. 191. 



XVIII. NOSTOCE^. 



1. NosTOc Vauch. (1803). 

 1. N. repandum, sp. n. Thallis irregulariter expansis et 

 laciniatis, circiter 15 cm. latis, buUato-gyrosis, fere coriaceo- 



