SPIRULINA. 229 



ral feet in extent, firm, coriaceous, of a glossy black colour, void of lubri- 

 city. Filaments about half a line in length, twisted like a cork-screw, 

 radiating in all directions." Carm. 



4. O. nigro-viridis, Thw. ; stratum of a very dark olive- 

 green colour ; filaments delicate pale green, rigid, with ob- 

 tuse, curved apices ; striae inconspicuous, distant about half 

 the diameter of the filament ; endochrome very slightly gra- 

 nulose. Thw. in Harv. Phyc. Brit. t. ccli. A. 



In a brackish ditch at Shirehampton, Bristol, Mr. Tkwaites. Stratum 

 thick, dark olive-green, almost black, growing on mud and subsequently 

 floating. Filaments pale dull green, with distinctly curved apices. 



5. O. subuliformis, Thw. ; stratum of an intense aerugi- 

 nous green colour; filaments bright green, subuliform ; striae 

 inconspicuous, distant from one-half to three-quarters of a 

 diameter of the filament ; endochrome not evidently granu- 

 lose. Thw. in Harv. Phyc. Bril. t. ccli. B. 



With the preceding. Summer and autumn. Mr.Thwaites. Stratum 

 thin, appearing black in the water, but when taken out, of a beautiful deep 

 blue-green colour. 



6. O. insignia, Thw. ; stratum of a dark brown, almost 

 black colour; filaments brown, of considerable diameter, 

 their apices obtuse, slightly oblique and ciliated ; striae con- 

 spicuous, very close ; endochrome distinctly granulose. Thw. 

 in Harv. Phyc. Brit. t. ccli. C. 



With the preceding. November. Mr. Thwaites Stratum thin, spread- 

 ing over decaying vegetable matter. Filaments very large and rather 

 brittle. 



VII. SPIRULINA. Turp. [Plate 27, C.] 



Filaments lying in a mucous layer, rigid, simple, spirally 

 twisted, vividly oscillating. Tube continuous ; endochrome 

 green, more or less distinctly annulated. Name, a diminu- 

 tive of spira, a twist or curl. 



1. S. tenuissima, Kiitz. ; stratum very lubricous, aerugi- 

 nous, subradiant; filaments densely spiral, very slender, 

 parallel, flexuous. Harv. Phyc. Brit. t. cv. C. 



On decaying Algas, in a brackish pool, near Menai Bridge ; and I on sticks 

 in brackish pools, at Penman Pool, Dolgelly, Mr. Ralfs Aberdeen, Dr. 

 Dickie. Forms a gelatinous pellicle of a rich green colour. Filaments 

 very slender, vividly oscillating. 



