OSCILLATORIA. 257 



ments slender, straight, brittle. Striae subdistant, scarcely 

 perceptible. 



O. nigra Carmichael, MS. 



This species differs only from the following in the absence 

 of gloss on the filaments ; a difference which is, in all pro- 

 bability, of specific importance. 



22. OSCILLATORIA TEREBRIFORMIS Ag. 



Plate LXXIL Fig. 4. 



Char. Stratum terrestrial, bluish black, glossy. Filaments 

 slender, straight, brittle. Striae scarcely evident. 



O. terebriformis Ag. 



Hob. Marshy places, Aberdeen, Nov. 1839 : Dr. Dickie. 

 Sussex : Mr. Jenner. Notting Hill : A. H. H, 



A very abundant species. 



23. OSCILLATORIA DECORTICANS Grev. 

 Plate LXXI. Fig. 10. 



Char. " Stratum smooth, glaucous green, membranaceous. 



Filaments very slender, curved, pale bluish green. Striae 



distant." Harv. 

 Grev. Flora Edin. p. 304. C. decorticans Dillw. t. 26. ; 



Harv. Manual, 164. 

 fi corticola. Stratum blackish green. See PL LXXI. fig. 4. 



O. corticola Carm. MS. 

 Hob. Damp walls, rotten timber, often on pumps, &c. 



Common. /3 "on the trunk of an old sycamore where 



the rain water trickled down : " Capt. Carmichael. 



Stratum membranaceous, not very gelatinous, peeling off in 

 large flakes, and imperfectly adhering to paper ; filaments very 

 minute. I strongly suspect that the O. contexta of Carmi- 

 chael is identical with Greville's O. decorticans, the /3 variety 

 is altogether different, 



8 



