2741
VERRUCARIA polysticta.
Many-dotted Verrucaria.
CR YPTOGAMIA 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. Scales minute, tartareous, very thin,
crowded, angular, even, whitish, upon a thick
black continuous substratum. Tubercles minute,
immersed, at length slightly emerging, flattish
above; Shell black throughout; pore obsolete.
H i t h e r t o , to the best of our knowledge, undescribed,
but not uncommon on walls, whether of brick or flint, growing
chiefly, but not exclusively, on the mortar. It occurs
also occasionally on sand-stone, and on large flints on the
downs of Sussex.
Thallus in irregular patches, often two or three inches
or more in length, composed of a black substratum varying
in thickness, but scarcely exceeding a quarter of a line,
and innumerable, minute, and extremely thin, tartareous,
superficial scales, generally so crowded as to form an even
surface of little angular areolae, separated by very narrow
cracks, in which, as well as at the edges of the patch, the
black substratum is visible. These areolae are sometimes
slightly convex, sometimes rather concave from their edges
being a little raised, but more generally perfectly flat;
their surface unpolished, ash-coloured, or even white, but
frequently with a tinge of brown, unchanged by moisture
in dried specimens, but in the recent Lichen of a dull green
when wet; the colour of their internal substance, when
they are thick enough to admit of its investigation, is pale
green; that of the substratum, which appears of rather a
loose texture, is dull black. Within this black substance