on closer examination, a satisfactory specific distinction.
As the tubercles within the crust enlarge, a smooth roundish
wart rises above each, not much unlike, except in size,
to those of Lichen ceuthocarpus, t. 2372. When the apex of
the tubercle begins to emerge, a bluish cloud is often observable
around it, caused by the black shell under the filmy
surface of the crust. At length the tubercle is completely
denuded, but not much raised above the crust, which sometimes
forms a little socket around its base. It is now of a
full polished black, and shows at the centre a minute, circular,
or occasionally irregular, pore, through which the
pale nucleus is often perceptible.—W. B.
