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182
THE MARINE ALGÆ OF NEW ENGLAND.
Gloucester. The fronds form rose-colored crusts of considerable extent, and are so closely adherent that
they can scarcely be removed. The tetrasporic conceptacles are large, but very much flattened.
LITHOTHAMNION, Phil.
(From λιθος [lithos], a stone, and θ µνιον [sic] [thamnion], a bush.)
Fronds calcareous, thick, at first horizontally expanded, but afterwards producing
erect knobs or coralloid branches; otherwise as in Melobesia.
A genus comprising probably not more than twenty or twenty-five good species, most of which are
tropical. The larger and more solid forms inhabit deep water. In Lithothamnion the cortical portion is
markedly developed, and it not rarely happens that new lobes are produced which overlap the older
ones and form an imperforate layer over the older conceptacles, which are thus occluded before the
spores are ripe. In such cases sections show conceptacles which are apparently buried in the central
part of the frond.
L. POLYMORPHUM, (L.) Aresch. (Millepora polymorpha, L.; Sp. Alg.—Millepora
(Nullipora) informis, Lamarck.—Melobesia polymorpha, Harvey‚ Phyc. Brit., Pl.
345.)
Fronds thick and stony, purplish, becoming whitish, forming incrustations of
indefinite extent and occasionally rising in thick clumsy lobes, punctate throughout
with the very numerous, small, immersed conceptacles; antherozoids spherical, with
an appendage at one end (Bornet); tetraspores two-parted; cystocarps?
On rocks and stones in deep pools and below low-water mark.
Common from Nahant northward.
Not known with certainty south of Cape Cod, but very common northward, where it forms stony,
purplish incrustations on rocks. As usually seen, it adheres closely to the rocks, covering patches of
indefinite extent, and would be mistaken for a species of Melobesia. It is so hard and adherent that it is
mistaken by persons on the shore for a part of the rock itself. Although the determination of the present
species admits scarcely a doubt, the form usually found with us is smoother and less lobed than
European specimens of the same species. In the description given above the tetraspores are said to be
two-parted. This is true of all the American specimens examined, but it may be that what we have seen
were immature spores, which, when ripe, are four-parted.
L. FASCICULATUM, (Lamarck) Aresch. (Millepora fasciculata, Lamarck.—Melobesia
fasciculata, Harv., Phyc. Brit., Pl. 74.)
Fronds purple, stony, attached, afterwards becoming free, very irregular in outline,
densely branching, branches fastigiate, subcylindrical, apices generally depressed;
tetrasporic conceptacles densely covering the branches, flattened, hemispherical;
tetraspores two-parted.
On stones or in free globose tufts at low-water mark and in deep water.
Eastport, Maine; Europe.