300 wklwitsch's African freshwater alg^e. 



Tliis genus must be placed iu the L>pigbyca; on account of the 

 structure of the sheath, which contains a sohtary trichome. The 

 comparative width of the sheath, its hyaline character with irregular 

 margin, along with the peculiar habit of the plant, characterize the 

 genus. The younger plants (consisting of short filaments of 12-20 

 cells) are endophytic, occurring between the lamella of the sheath 

 of PorpIu/rosip/io7}. As they increase in size they appear to break 

 through the outer lamellfe of the sheath of the host, and to closely 

 attach themselves to its outer surface by means of their own mucous 

 envelope, which is now considerably broader. 



5. OsciLLATORiA Vaucli. (1803). 



1. 0. LiMosA Ag. Dispos. Algar. Suec. 35 (1812) ; Gomont in 

 Ann. ScL Xat. 7e serie, Bot. xvi. 210-2, t. 6, f. 13 (1892). Crass, 

 trich. 9-5-15*5 fjL. 



Sierra Leone. Ad terram et parietes juxta fontes prope Free- 

 town ; Sept. 1853. No. 168. 



2. 0. TENUIS Ag. Ah/ar. Decas ii. 25 (1813); Gomont, Z.c. 220-1, 

 t. 7, f. 2-3 (1892). Crass, trich. 6-7-5 //. 



Ins. Principis. In staguantibus prope Bahia de S. Antonio, ad 

 limum subexsiccantem late caespitosa ; Sept. 1853. No. 169. 



Mossamedes. Cum Tohjpotriche limhata in stagnis profundis 

 prope Cavalheiros; Aug. 1859. No. 191. 



3. 0. ANiMALis Ag. in Flora, x. 632 (1827) ; Gomont, /. c. 227-9, 

 t. 7, f. 13 (1892). Crass, trich. 2-8-3 /x. 



Sierra Leone. Cum Phormidio Corio ad parietes humid, verti- 

 cals urbis Freetown freq. latissimis plagis atro-nitentibus parietes 

 obducens ; Sept. 1853. No. 167. 



4. 0. FORMOSA Bory, Diet. Class. d'Hist. Xat. xii. 474 (1827) ; 

 Gomont, /. c. 230-1, t. 7, f. 16 (1892). Crass, trich. 4-5-5 /x. 



Loanda. In limo humido urbis Loandte ; April 1858. No. 170. 



5. 0. Okeni Ag. in Flora, x. 633-4 (1827); Gomont, I.e. 232, 

 t. 7, f. 18 (1892). Crass, trich. 5-7-7 /x. 



Loanda. In fonte tepida, sulphate abundanti pr. S. Pedro freq. ; 

 July and Aug. 1854. No. 164. 



6. O. angustissima, sp. n. 0. strato expanso terugineo ; 

 trichomatibus angustissimis, laete arugineis, flexilibus, elongatis 

 et intricatis, apicibus non attenuatis nee capitatis, ad dissepimenta 

 non constricta; cellulis diametro l|^-2-plo longioribus, dissepimentis 

 indistinctis ; protoplasmate homogeneo. Crass, trich. 0-6 /x. 



Loanda. Cum 0. Okeni in fonte tepida, sulphate abundanti pr. 

 S. Pedro freq. ; July and Aug. 1854. No. 164. 



The specimens of this species are very fine ; it is a totally dis- 

 tinct plant from Phormidium. angustissimwn , though it is of the same 

 thickness. It possesses no sheath, and the trichomes are much 

 firmer and not so tortuose as those of the latter ; its cells also are 

 shorter and more indistinct. 



