M a t e c m m : .
I
A m -
4-,
P l a t e CCXXXIX.
RIVULAEIA ATRA, B o th .
G e n . C h a e . Frond globose or lobed, fleshy, firm, composed of continuous
radiating filaments, annulated within, each springing from a spherical
globule. R it u l a e ia {Roth),—so named by Roth, in allusion to the
fluviatile habit of some of the first-discovered species.
R iv u l a r ia tttra ; fronds minute, scattered, globose, or hemispherical, firm,
smooth, glossy black-green; filaments dark green, densely packed.
Rivülae ia atra. Moth, Cat. Bot. vol. iii. p. 340. Ag. Syn. p. 130. Ag. Syst.
p. 34. F .B o t .t .\1 9 3 . Harv. in Hook. Br. vol, ii. p. 393. Harv.
in Made. Fl. Hib. part 3. p. 335. Harv. Man. p. 152,
E uaotis atra, Kiitz. Fhyc. Gen. p. 241.
L in o k ia atra, Lyngb. Hyd. Ban. p. 195. t. 65.
L in ck ia hemispherica, Sdmm. Enam. vol. ii. p. 114.
T k em e l la hemispherica, Linn. Sysi. Nat. vol. ii. p. 714. Huds. Fl. Aug.
p. 565. Lightf. p. 900. With. vol. iv. p. 81.
Chætophora atra, Ag. Bisp. p. 43.
H a b . On rooks and stones, and on Corallines and other Algæ, between
tide marks. Perennial ? At all seasons. Very abundant.
Geogk. D is t e . Shores of Europe.
D e sc e . Fronds one or two lines in diameter, hemispherical when attached to
flat surfaces, globose wben growing on filiform Algæ, very hard, of an exceedingly
firm, compact substance, and dark colour. Filaments subulate,
attenuated, connected together in branching, subdichotomous series, filled
with dark-green endochrome, which is annularly divided in the upper part,
and coheres in oblong masses in the lower. Each filament springs from a
transparent globule (or connecting cell).
A very common plant on all rocky shores, growing either on
the rocks, or on the smaller Algæ, especially on Cladophora
rupestris and CoraUina ojjicinatis. It forms small, hard wartlike
balls or hemispheres, rarely as large as tbe seed of Sweet-
Pea {Lathyrus odoratus), and sometimes completely covers the
plant to which it attaches itself.
Carmichael describes an allied species, B. applanata, said to
differ from B. atra in being flatter and thinner in substance, and
growing in similar localities. This I have never seen.