are at first flat, or nearly so, and regularly orbicular, with
a narrow margin, scarcely rising above the disk, occasionally
discoverable; but they soon become very convex, often
nearly hemispherical, losing all appearance of a margin,
and are not unfrequently irregular in shape and confluent
: their internal substance is greyish.
It requires a practised eye to distinguish this species from
other obscure Lichens which usually grow on rails; but its
structure is found, upon examination, to be peculiar. It has
a near affinity to Leaded uliginosa, Engl. Bot. t. 1466.
—W. B.
