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; Il P l a t e CCCXLV.
MELOBESIA POLYMORPHA, z*k«.(sp.)
Ge n . Ch a r . Frond attached or free, either flattened, orbicular, sinuated or
irregularly lobed, or cylindrical and branched (never articulated),
coated with a calcareous deposit. Fructification; conical, sessüe ceramidia,
scattered over the surface of the frond, and containing a
tuft of transversely parted, oblong tetraspores.—Named from one of
the Sea-nymphs of Hesiod.
M e lo b e s i a polymorpha ; frond attached to rocks, thick, stony, encrusting,
or rising into short, clumsy branches, which are seldom much divided,
and often merely rudimentary ; ceramidia minute, depressed, extremely
numerous.
M e lo b e s i a polymorpha, Harv.Mau.cà. 2 .p. 108.
M i l l e p o r a polymorpha, Linn. Syst. Nat. 1285. Ellis and Soland. Zoop. 130.
N u l l i p o e a polymorpha, Jolinst. Brit. Lith. p. 238. t. 24. f. 1, 2, 3 (?), and
t. 25. f. 33. (in part.)
Spongites polymorpha, Kiitz. Sp. Alg. p. 699.
C o b a llium cretaceum lichenoides, Ellis, Cor. p. 7 6. t. 27. fig. d. D. (fide Jig.)
H a b . On littoral rocks all round the coast, extending beyond low-water
mark. Common.
Geogr. D is t e . (Probak^ -----„ x ,
De sc e . Frond at first appearing on the smface of rocks, pebbles, or shells, in the
form of little stony pimples, which gradually become confluent, so as to torm
an uneven crust resembling one of the crustaceous Lichens, and spreaibng
over indefinite spaces. This crust graduaUy grows thicker hy successive
thin coats of ceUular and calcareous substance formed and deposited on
the surface, and is very irregular in form ; sometimes continuing nearly flat,
sometimes rising into irregular stony knobs or lumpy masses, and sometimes
throwing up short, erect, scarcely divided branches. Ceramidia minute,
dot-like, sunk deeply in the outer layer of ceUs, extremely numerous and
often puncturing over the whole surface of fertile fronds as if they had been
closely marked with pin-holes. Colour variable according to the locality,
dark lurid purple near low-water mark, and passing into chalky-white as the
specimens grow nearer high-water maik. CeUs of which the frond is composed
about twice as long as their diameter. Substance stony.
To this form I refer most of the lumpy Nullipores, with thick
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