Mr. J. Ralfs on Spirulina and Colcochsetc. 309 



no determinate form, and by the naked eye cannot be distin- 

 guished from Oscillatoria, to which indeed it is nearly alhed, as 

 its filaments are in like manner simple, oscillating and radiating. 

 Kiitzing describes them as inarticulate, and I have failed to de- 

 tect any joints or strise ; but as I have also been unable to per- 

 ceive any granular matter, the apparent absence of striae may pro- 

 bably depend upon the extreme fineness of the filaments. 



The close and regular spires formed by the filament are very 

 remarkable, and constitute, I believe, the only certain distinctive 

 mark between Spirulina and Oscillatoria. 



1. S. tenuissima, KUtz. "Stratum very lubricous, seruginose, sub- 

 radiant ; filaments densely spiral, very slender, parallel, flexuose." 

 Kutz. Alg. xiv. no. 131 ! ; Phycol. Gener. p. 183. 



On decaying algae in a brackish pool near the Menai Bridge, 

 Anglesea. On sticks in brackish pools at Penman Pool near Dol- 

 gelley. 



It forms at first a thin pellicle of a rich green colour, but in 

 an advanced state becomes somewhat skin-like and tinged with 

 brown ; filaments shortly radiate. 



Under the microscope the filaments are extremely slender, of 

 a pale bluish green colour, elongated, straight when free, equal, 

 not attenuated at the extremities, vividly oscillating. Spires very 

 close, like the volutions of some shells, broader than long. There 

 is no appearance of granular matter, and the filaments are so fine 

 that I cannot ascertain whether they are jointed. 



The oscillations of this plant are more vivid than those of any 

 species of Oscillatoria I have examined. 



When I first gathered this plant in 1841, I suspected, not- 

 withstanding its diff'erent colour, that it might be the Oscillatoria 

 spiralis of Capt. Carmichael ; but having communicated a speci- 

 men to the Rev. M. J. Berkeley, he informed me of its real name, 

 and sent me a specimen of CarmichaeFs plant, which is a true 

 Oscillatoria, and cannot belong to this genus, as the filaments, 

 in the dried state at least, though somewhat distorted, are not 

 regularly spiral. 



Through the kindness of Mr. Borrer I have been able to com- 

 pare our plant with the specimen in Kiitzing's ' Alg. Aq. Dul.,' 

 and am satisfied of their identity, although his specimens were 

 gathered in fresh water, and I have always found mine in brack- 

 ish pools. 



Plate X. fig. 1. Spirulina tenuissima. 



CoLEocH^TE, Breb. 

 Fronds minute, parasitic, green, disciform, appressed, composed 



