M arch, r * 18SO
2632. (Fig. 1.)
O P E G R A P H A cerebrina.
Tumid-crusted Opegrapha.
R YP TOGAMIA Lichenes.
Gen. Char. Lirellce black, oblong or linear, with a
raised proper margin, and a narrow disk.
Spec. Char. Crust tartareous, continuous, very white.
Lirellae naked, prominent, short, obtuse, simple
or variously divided and deformed ; their margin
broad, inflexed, at length expanding and obliterated.
Syn. Opegrapha cerebrina. DeCand. FI. Fr. v. 2.
312. Ckev. Hist, des Hypox. 57. t. 12. ƒ 4.
Lecidea plocina. Ach. Lich. Univ. 155. Syn. 16.
C o m m u n ic a t e d long ago by the Rev. John Har-
riman, on calcareous stone, from the North of England.
It had previously been gathered by Mr. Dickson. Acha-
rius says his specimen was from England. Out of Britain
it appears to have been observed only by M. Ramond,who
found it in the Pyrenees.
Crust of inconsiderable but unequal thickness, of uncertain
extent and irregular outline, bordered more or less
perceptibly with black, without cracks, but frequently interrupted,
as if formed by the confluence of different small
pulvinulate patches, (an appearance owing perhaps to the
uneven surface of the stone,) pure white, unpolished, look-
ingas if powdery to the naked eye, but in reality solid, and
minutely pitted rather than wrinkled ; internally also white
and chalk-like. Lirellae without any accessory margin
from the crust, full black, sometimes polished, but perhaps
only from having been rubbed, not very numerous, mostly
in clusters but occasionally solitary ; at first oblong, or so
short as to be almost orbicular, with an inflexed, convex,