26G welwitsch's African freshwater algm. 



atrovireus solis luce et nidore cito nigrescens, latissimis rupium 

 plagas perpendiculares colore aterrimo tingens. 



This agrees in every particular with *S'. Myochrous, with the 

 exception that the filaments are never ocreate. From S.fujuratum 

 it differs in being of larger dimensions, and in having a relatively 

 thicker sheath. 



8. S. insigne, sp. n. S. rnpestris, spongioso CcX^spitosum, 

 pulviniilis elasticis, 4-6-5 mm. altis, violaceo-viridibus vel violaceo- 

 f nscescentibus ; filis crassis, in fasciculis arete adhrerentibus ; pseudo- 

 ramis solitariis vel raro gemiuatis, longis et flexuosis, filo primario 

 paullo angustioribus, apicibus subattenuatis ; vaginis crassis, achrois, 

 lamellosis, marginibus rectis vel irregularibus non ocreatis, srepe 

 coufluentibus ; trichomatibus pallide ferugineis, cellulis distinctis- 

 simis, quadratis vel diametro 1^-plo longioribus, nonnunquam 

 diametro duplo brevioribus et leviter torulosis, sajpe cylindricis et 

 diametro 3-4-plo longioribus ; heterocystis quadratis ; hormogoniis 

 brevibus, cellulis quadratis intcrdum diametro brevioribus, lamellis 

 interioribus vagina luteis vel aureis. Crass, fil. prim. 25-29 //. 

 (usque 33 //) ; crass, ram. 16-19 /^ ; crass, trich. 7'5-13*5 jx; long, 

 hormogon. 100-170 /x, lat. 15-19 ju 



Golungo Alto. Ad rupes madidas in umbrosis juxta rivum 

 Coango inter Sange et Undelle, nunc violaceo-viridis, nunc intensius 

 violacea; May 1856. No. 5. Etiam ad rupes rivul. Coango humect, 

 pulvinula livido-cinerea spongiosa formans; June 1856. No. 140. 



This plant is noticeable for the variability of its filaments, some 

 having parallel margins with long cells, others having firm irregular 

 margins with somewhat torulose trichomes, consisting of very short 

 transversely elliptic cells of irregular size. The latter filaments 

 much resemble the branches of a Stiijonema. The sheaths of this 

 plant are altogether remarkable, being quite colourless, and often 

 very irregular in the margin ; wherever they come in contact with 

 each other they appear to coalesce, and this coalescence gives rise 

 to a phenomenon {viz. the apparent inclusion of two parallel tri- 

 chomes in the same sheath) which, so far as we are aware, has not 

 been previously noticed in this genus. The branches are also most 

 peculiar, the majority being solitary, and given ofl" laterally from 

 one cell of the primary filament precisely as in Hapalosiphon. 

 Taking into consideration all these points, there are still un- 

 mistakable characters which place the plant in the genus Scytoncma. 



2. ToLYPOTHRix Kiitz. (1843). 

 After examining the three following species, we cannot agree 

 with Bornet and Flahault in separating the genera Hassallia and 

 Tuhjpothrix. The former is said to be distinguished from the latter 

 by its fragile filaments and its terrestrial habit. The three species 

 referred to are all terrestrial as described for Hassallia, but the 

 sheaths (especially that of T. crassa) are very firm, persistent, and 

 iiexile, agreeing with those of Tohjpothrix. Under which genus 

 ought these species to be placed ? The terrestrial habit points to 

 Hassallia, the flexile and non-fragile filaments to Tohjpothrix, It 

 appears to us that the only character left to separate the two sup- 



