Oscillatoria.] 



ALG.E CONFERVOIDE.E. 377 



filaments are rather thick, about a line in length, straight or variously 

 curved, of a greyish-green colour, and they radiate with great rapidity. 

 A portion of the stratum, not more than a line in diameter, placed on a 

 watch-glass, filled with water, overspread the whole area of the glass with 

 filaments in the course of a night." Carm. MSS. A fine species ; in 

 a dry state strongly resembling black satin. The striated stratum 

 affords an excellent " prima facie" character. 



18. O. Corium, Ag. (leathery Oscillatoria) ; stratum thick 

 subcoriaceous opaque dull-brownish streaked with pale-green, 

 filaments yellowish slender, striae indistinct distant. — Ag. Syst. 

 Alg. p. 64. Lyngb. Hydroph. Dan. p. 89. Grev. Fl, Edin. 

 p. 303. 



On the rocky bottoms of alpine rivulets; common.— Stratum thick, 

 tough, dull-brownish, occasionally streaked with pale-green, which, in 

 some varieties, is the prevailing colour, slightly glossy when dry; fila- 

 ments slender. In some situations it radiates fasciculately from its 

 whole upper surface; in others, it is found almost denuded of radii and 

 forming a compact leathery stratum. 



19. O. subfusca, Vauch. (brownish-green Oscillatoria); stra- 

 tum dull greyish-brown somewhat streaked with a green shade 

 soft void of tenacity, filaments very slender hyaline straight, 

 stria? inconspicuous. Lyngb. Hydroph. Dan. t. 26. Ag. Syst. 

 Alg. p. 69. 



Rocks and stones, in sub-alpine rivulets.— Stratum extensive, " soft, 

 slimy, void of tenacity, wrinkled, of a dusky-grey colour," (Carm.) 

 when dry greyish-brown, streaked with green towards the edges ; fila- 

 ments very slender, striae invisible. — Differs from the last chiefly in being 

 more gelatinous and fragile. 



20. O. violdcea, Johnston, (purple Oscillatoria); "mass 

 gelatinous dark purple, filaments very slender straight without 

 perceptible transverse stria? laid on a thin compact greenish 

 substratum." Johnst. Beriv. Flora, r. 2. p. 264. 



Rapid streams j near Berwick-upon-Tweed, Dr. Johnston, who con- 

 siders this the " Co///., mucosa confragosa, rivulis innasceos" of Dillenius. 



21. <). riijn'slris, Ag; (Rock Oscillatoria) ; stratum bUckish- 



green thick opaque extremely tough, filaments rigid straight 

 pale-green slender, striae not evident. Ag* Syst. Alg. p. 03. 

 Cm m. MSS. — o. ttnax, Carm, Huh. 



On the precipitous face of cascades ; Appin, dipt. CarmichaeL—" Stra- 

 tum extensive, Blimy, remarkably tough and elastic, black on the surface, 

 ash-coloured underneath, (when dry greenish-black] : ^to***/* pale- 

 green, Btraighl or variously curved, radiating, but not equally, in all 

 directions/' Carm. Af&R— • Differ* from o. tubfutem in habitat, colour, 

 Mud toughness of the .stratum ; which last peculiarity is sert character- 

 istic. When dry, it is difficult to separate the filaments on the table of 

 the ssicroscope. 



22. <>• spiralis, ('arm. (spiral Otctffatoria); stratum coriace- 

 ous greenish-black without lubricity, filaments spirally twisted 

 radiating in all directions, 



