V E R R U C A R I A concinna.
Neat Verrucaria.
CRYPTOGAMIA Lichenes.
Gen. Char. Tubercles of a different substance from
the thallus, simple, convex, not expanding, but
furnished with a central pore, and inclosing a
somewhat gelatinous nucleus.
Spec. Char. Crust determinate, very thin, tartareous,
continuous, even, grey, somewhat pruinose. Tubercles
of a middle size, prominent, hemispherical,
umbilicate, black.
F o u n d on limestone rocks on the Durham shore of the
Tees, near Eglistone. The late Mr. Robson, who appears
t&have first discovered the species, sent it from the same
county, and the late Sir T. Gage from Killarney. It occurs
also, but rarely, on chalk on the Sussex Downs.
The extremely thin crust forms roundish patches, an inch
or two in diameter, mostly circumscribed by a narrow black
line. Its surface is continuous, or, very rarely, marked with
a few irregular cracks, no otherwise uneven than as it follows
the inequalities of the stone, unpolished, and looking
as if slightly powdery. Under a good magnifier it appears
pitted all over with extremely minute blackish dots. Its
usual colour, when wet, is a smoky brownish grey, varying
in tint; in some specimens the same when dry, in others
of a dark lead or mouse colour. Occasionally, however,
the external hue is the same as that of the internal substance,
almost white with a very faint tinge of green when
wet. Tubercles numerous, regularly scattered in general,
but some of them sometimes confluent, about as large as
poppy-seed, hemispherical or rather more prominent, of a
full black, usually more or less polished : their base sunk
in a very slight degree in the stone beneath the crust; the
crust sometimes rising a little around, and in some instances