Kützing’s definition is as follows : —
“ ïricliomata libera, basi vaginata, ex vagina longe prore-
pentia, vaginæ achroinaticæ tenerriniæ, simplices, utrimque
opertæ liberæ, nunquam coalitæ.”
Kützing makes a genus for tbe reception of the Oscillatoria
autumnalis Ag., of which Conf. decorticans of DiUw. is a
synonym. The genus is as follows : —
Phormidium.
“ Trichomata libera, basi vaginata, ex vagina prorepentia,
vaginæ achromaticæ, simplices (non lamellosæ), apertæ, latera-
liter in membranam plus minusve continuam coalitæ.”
I can offer no opinion on this genus, but I cannot perceive
in what the Conf. decorticans (Dilhvyn) differs generically
from other Oscillatorioe.
a. Filaments brittle.
1. Oscillatoria limosa Ag.
Plate L X X I . Fig. 2.
Char. Filaments hrittle, straight, large. Stratum rich dark
green, glossy, and gelatinous. Striæ strongly marked and
close.
O. limosa Harv. Hook. Br. Fl. p. 374. ; Harv. Manual,
p. 162. (Not of Orev. Flor. Edin. p. 303. ; or Hook.
Scot. Fl. part ii. p. 79.)
Stratum of a rich dark and æruginous green colour, sending
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 striæ 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 apparently
alluded to by Dillwyn In his description of Conferva
fontinalis, t. 64. ; but the figure is more like O nigra. In
drying it adheres closely to paper. From O. major it differs
in the much greater diameter of its filaments, and darker
colour. I t is therefore intermediate between these species.
2. Oscillatoria mucosa Hass.
Plate L X X I . Fig. 1.
Char. Stratum gelatinous, dark, æruginous green, glossy.
Filaments large. Striæ subdistant.
Hah. Floating in a pond like a little dusky cloud;
Stevenston : Rev. D. Landshorough.
This species agrees with the previous one in aUits characters,
save in the arrangement of the striæ. The filaments are of
the same diameter, of the same gelatinous habit, and present
the irregular and furrowed appearance when dried of O.
limosa ; the only difference between the tAvo species is in the
striæ, Avhich are twice as distant in this as in O. limosa.
The only specimen which I have seen of this species is
that sent me by the Rev. D. Landshorough. There can he
no doubt entertained of its distinctness.
3. Oscillatoria cinerea Hass.
Plate L X X . Fig. 4.
Char. Stratum o f a dull æruginous green colour. Filaments
large. Striæ close, very evident.
Hab. In a pond on Stanstead Common, Essex.
This is a fine and well-marked species. The diameter of
the filaments is equal to th a t of the two preceding Oscilla-
toriæ, but they are infinitely less mucous, and the stratum
when dried is not in the least glossy, neither do the filaments
collapse or become wrinkled in drying, but preserve the same
equal diameter in the dried as in the recent state. The
species, judging from Carmichael’s description, seems to
come near to the Oscillatoria littoralis of that observer.
R 4