256 O S C IL L A T O R EÆ .
Hah. Ditches and ponds; common.
“ Stratum extensive, blackish, with a shade of green; when
dry, blue black, very rapid in its growth and sending out
long vividly oscillating rays. Dillwyn’s figure of Conferva
fontinalis answers to this species pretty correctly.” Harv.
20. Oscillatoria contexta Carm.
Plate L X X I . Figs. 7.4. 6.
Char. Stratum glossij black, strongly striated. Filaments
somewhat thick, pale green. Striæ subdistant, evident.
O. contexta Harv. Hook. Brit. F l. p. 376.; Manual, p. 165.
Hab. On moist ground. Appin: Capt. Carmichael.
Cheshunt : A . H . H. Sussex : Mr. Jenner.
“ Stratum of Indefinite extent, three feet and upwards,
exceedingly tliin, and peeling olf in large fiakes in dry
weather, of a deep but shining black colour, scored or striated
in all directions. These striæ are caused by thick fasciculi of
filaments, shooting out either parallel to or across each other,
changing their course from time to time, and sending off la-
terarfasciculi. The filaments are rather thick, about a line in
length, straight, or variously curved, of a greyish green colour,
and they radiate with great rapidity. A portion of the stratum,
not more than a line in diameter, placed in a watch-glass
filled with Avater, overspread the whole area of the glass with
filaments in the course of a night.”— Carm. M S . This is
a very distinct as well as fine species. The gloss of the stratum
is equal to that of satin, and the filaments are in calibre
not less than those of O. tenuis, from which species it is distinguished
chiefly by its colour. The filaments do not contract
in drying.
21. Oscillatoria Carmichaeli Hass.
Plate L X X I . Fig. 8.
Char. Stratum black, destitute o f gloss, thin, brittle. Filan
m
O S C IL L A T O R IA . 257
ments slender, straight, brittle. Striæ subdistant, scarcely
perceptible.
O. nigra Carmichael, MS.
This species differs only from the following in the absence
o gloss on the filaments ; a difference which is, in all probability,
of specific importance.
22. O sc il la to r ia t e r e b r ifo rm is Ag.
Plate L X X I I . Fig. 4.
Char. Stratum terrestrial, bluish black, glossy. Filaments
slender, straight, brittle. Striæ scarcely evident.
O. terebriformis Ag.
Hab. Marshy places, Aberdeen, Nov. 1839 Dickie.
Sussex: Mr. Jenner. Netting H ill: A. H. H.
A very abundant species.
23. Osc il la to r ia decorticans Grev.
Plate L X X I . Fig. lo.
Ghar. “ Stratum smooth, glaucous green, membranaceous.
Filaments very slender, curved, pale bluish green. Striæ
distant.”— Harv.
Grev. Flora Fdin. p. 304. C. decorticans Dillw. t. 26. •
Harv. Manual, 164.
fl wrricoZa. — Stratum blackish green. See PI. L X X I . f i g . 4 .
O. corticola Carm. MS.
Hab. Damp walls, rotten timber, often on pumps, &c.
Common. fl “ on the trunk of an old sycamore where
the rain water trickled down : ” Capt. Carmichael.
Stratum membranaceous, not very gelatinous, peeling off In '
large fiakes, and imperfectly adhering to paper; filaments very
minute. I strongly suspect tha t the O. contexta of Carmichael
IS identical with Greville’s O. decorticans, the /3 variety
IS altogether different.