brown, and occasionally to a dull flesh-colour. Their margin
is elevated, thickish, uneven, flexuose, but disappears on the
application of moisture by the swelling of the disk, which,
when dry, is flat and considerably depressed, thin, and of
nearly the same hue internally as superficially.
In the structure of the thallus this Lichen differs but
little from L . scabrosa, t. 1878, which, when growing on a
compact substance, is found to begin in the same manner
with a film and minute granulations : but the powder which
soon covers the surface is, in that species, of a paler and
more yellow hue, and the structure of its patellulae is different.
L . aeruginosa is more nearly allied, perhaps, to
L . quadricolor, t. 1158. Indeed it must be admitted that
these two recede more in general appearance than in any
essential character ; yet it would scarcely be justifiable to
regard them as but one species. In L . aeruginosa the granulations
of the thallus are smaller, more crowded and confluent,
and of a greener hue, and the powder they produce
is much more copious and of a dark verdigris-green, whilst
that in L . quadricolor is not much darker than the granules.
The patellulae also are smaller in L . aeruginosa, their margin,
perhaps, more elevated, and their colour not altogether
so variable. From another nearly allied species,
L . Lightfootii, t. 1451, it differs in most of these and in some
additional particulars.—W . B.