Mr. J. Ralfs on Spirulina and Coleochete. 309 
no determinate form, and by the naked eye cannot be distin- 
guished from Oscillatoria, to which indeed it is nearly allied, 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 striz ; but as I haye also been unable to per- 
ceive any granular matter, the apparent absence of striz 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, Kiitz. <‘‘ Stratum very lubricous, eruginose, sub- 
radiant ; filaments densely spiral, very slender, parallel, flexuose.”’ 
Kutz. Alg. xiv. no. 131!; Phycol. Gener. p. 183. 
On decaying alge 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 different colour, that it might be the Oscillatoria 
spiralis of Capt. Carmichael; but having communicated a speci- 
men to the Rey. M. J. Berkeley, he informed me of its real name, 
and sent me a specimen of Carmichael’s plant, which is a true 
Oseillatoria, 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 thei identity, although his specimens were 
gathered in fresh water, and I have always found mine in brack- 
ish pools. 
Prate X. fig. 1. Spirulina tenuissima. 
CoLtrocu£tTE, Bréb. 
Fronds minute, parasitic, green, disciform, appressed, composed 
