246 OSCILLATORE^. 



Kiitzing's definition is as follows : — 



*' Trichomata libera, basi vaginata, ex vagina longe prore- 

 pentla, vaglnje achromaticje tenerrimte, simplices. utrimque 

 opertas llberae, nunquam coalltfe." 



Kiitzing makes a genus for the reception of the Oscillatoria 

 autumnalis Ag., of which Conf. decorticans of Dillw. Is a 

 synonym. The genus is as follows : — 



Phormidium. 



*' Trichomata libera, basi vaginata, ex vagina prorepentia, 

 vaginae achromaticae, sunplices (non lameUosaj), apertai, latera- 

 liter in membranam plus minus ve continuam coalitaB." 



I can offer no opinion on this genus, but I cannot perceive 

 in what the Conf. decorticans (Dillwyn) differs generlcally 

 from other Oscillatorice. 



a. Filaments brittle. 



1. Oscillatoria limosa Ag. 



Plate LXXI. Fig. 2. 



Char. Filaments brittle, straight, large. Stratum 7'ich dark 

 green, glossy, and gelatinous. Strl» strongly marked and 

 close. 

 O. limosa Harv. Hook. Br. Fl. p. 374. ; Harv. Manual, 

 p. 162. (Not of Grev. Flor. Edln. p. 303. ; or Hook. 

 Scot. Fl. part ii. p. 79.) 



Stratum of a rich dark and jeruginous green colour, send- 

 ing out from its edges long radii equally or in bundles ; It is 

 also glossy, even in the dried state. Filaments when recent 

 of equal diameter, but in the dried condition they are seen to 

 be variously twisted and furrowed, and the striae to be much 

 less conspicuous. The furrowing and consequent irregularity 

 of diameter of the filaments in dried specimens, affords not 

 unfrequently a distinguishing character between nearly allied 

 species. Mr. Harvey remarks that this fine species Is ap- 

 parently alluded to by Dillwyn in his description of Conferva 



