mostly rather distant, but now and then clustered and confluent,
often as large, when fully grown, as mustard seed,
but very variable in size, as also in their figure, which is
sometimes regularly convex and hemispherical, but most
frequently more protuberant, and often irregular : occasionally,
too, their apex is flattened, occasionally singularly
mammillated. The surface of the shell is either black
and shining, or of a somewhat pruinose appearance, as if
covered by a slight pellicle from the crust, which now and
then rises, also, a little around the base. The orifice is
scarcely perceptible but in old tubercles, where it is either
a minute pore, or larger and often irregular. Nucleus
whitish, containing or composed of linear thecae, within
which Mr. Sowerby finds the “ sporae” united in pairs : in
drying it shrinks so as merely to line the interior of the
shell.
The large size of the tubercles distinguishes this from
all the other British Verrucarice that grow on bark, except
some states of V. nitida, a species with which it has little
else in common. One of the rock species, V. epipolcBa of
Acharius, has equally large tubercles, and is so similar that
it might be supposed a mere “ varietas loci;” yet its more
tartareous crust, with a powdery surface, and its rugose,
brownish, less variable tubercles afford perhaps constantly
distinctive marks. Under V. biformis we have remarked
how nearly that plant is allied to the present, and have endeavoured
to point out the differences. The South American
V. hymnothora of Acharius, Syn. Lick. p. 92, is so
like V. gemmata that we know not how to distinguish it;
we have, however, seen too little of that Lichen to affirm
confidently that it is the same.
We believe this to be the V. alba of Schrader; but, his
figure being such as to admit of some degree of doubt, we
prefer the later, but certain and generally adopted, name
given by Acharius.—W. B.