256 OSCILLATORE^S. 



Hob. Ditches and ponds ; common. 



" Stratum extensive, blackish, with a shade of green; when 

 dry, blue black, very rapid in its growth and sending out 

 long vividly oscillating rays. Dillwyn's figure of Conferva 

 fontinalis answers to this species pretty correctly." Harv. 



20. OSCILLATORIA CONTEXTA Carm. 



Plate LXXI. Figs. 7. 4. 6. 



Char. Stratum glossy black, strongly striated. Filaments 

 somewhat thick, pale green. Stria? subdistant, evident. 



O. contexta Harv. Hook. Brit. Fl. p. 376.; Manual, p. 165. 



Hob. On moist ground. Appin: Capt. Carmichael. 

 Cheshunt : A. H. H. Sussex : Mr. Jenner. 



" Stratum of indefinite extent, three feet and upwards, 

 exceedingly thin, and peeling off in large flakes in dry 

 weather, of a deep but shining black colour, scored or striated 

 in all directions. These striae are caused by thick fasciculi of 

 filaments, shooting out either parallel to or across each other, 

 changing their course from time to time, and sending off la- 

 teral fasciculi. The 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 stra- 

 tum, not more than a line in diameter, placed in a watch-glass 

 filled with water, overspread the whole area of t\c glass with 

 filaments in the course of a night." Carm. MS. This is 

 a very distinct as well as fine species. The gloss of the stra- 

 tum is equal to that of satin, and the filaments are in calibre 

 not less than those of O. tennis, from which species it is dis- 

 tinguished chiefly by its colour. The filaments do not con- 

 tract in drying. 



21. OSCILLATORIA CARMICHAELI Hnss. 



Plate LXXI. Fig. 8. 

 ( 'liar. Stratum black, destitute of gloss, thin, brittle. Fila- 



