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332
At first sight, A. praeruptarum may be taken for A. fuscata, but the
absence of C-reaction and the pale lower surface brings this species
nearer to the rufescens-group. The irregularly thickened areolae,
the scarce, irregular apothecia, the texture of the upper cortex and
the habitat are the most striking characteristics in this species.
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3. Acarospora complanata H. Magn. n. Sp.
Thallus plus minus orbicularis, ambitu subradiatus, centroversus
areolatus, obscure castaneus vel nigro-fuseus, hypochlorito caleico
rubescens, areolis planis, uniformibus laevibusque, arcte adnatis.
Apothecia minutissima, punctiformia, singula vel pauca, discus
planus, thallo subaequatus.
Thallus continuous, forming areas up to at least 6.5 cm. in diam.,
invading and destroying other erustaceous lichens, 0.4—0.6 mm.
thick, areolate, quite smooth, of a very dark reddish brown colour,
in the circumference indistinctly lobate, thinner and somewhat
shining. Marginal areolae about 1 mm, broad and up to 2 mm.
long, partly concave, paler brown than the central areolae, which
are 0.5—0.8 mm. in diam., of uniform size and separated by thin,
distinct, regular cracks, plane, largely affixed to the substratum,
unaltered by KOH but coloured distinetly reddish with CaClOs.
Cortex 30—50 u thick, white, with 8 w dark brown upper stratum
and a thin 4—6 u broad amorphous layer. Hyphae more or less
perpendicular, leplodermatous, in water with distinct lumina, 3—4 u
in diam., more or less round or irregular in shape. Gonidia 7—13 u
in diam., yellowish green, in a 120—70 u thick, dense, unbroken
stratum with even surface. Medulla 400—170 « thick, quite un-
transparent on account of immense masses of white dense-lying
grains, in KOH not, in HCl at least partly dissolving, revealing the
partly perpendicularly directed or slightly intricate, 2.5—4 u thick,
very pachydermatous hyphae with irregular outlines, Air-spaces
abundant, medulla sometimes almost arachnoid. Marginal cortex
lighter or darker brown, lower one pale brown or absent. Areolae
largely affixed,
Apothecia partly abundant but very inconspicuous, very small,
punctiform, 0.1—0.2 mm. in diam., immersed, disc concolorous with
the thallus or slightly darker, blackish, round, plane, lying in the
thalline level.
No excipulum observed. Hypothecium 35—100 u high, cup-like,
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