even margin closed over the disk; soon cloven at one or
both ends, becoming triangular, quadrangular, or more irregular
in figure, and the margin expanding and disclosing
the disk, often so widely as to give to the lirella a close
resemblance to an irregular patellula, with sometimes a
prominent and crenulate, sometimes an obliterated margin.
Often, too, the lirellae become confluent, and the clusters
assume the appearance of imperfect tricce of a Gyrophora.
Their base is sunk in the crust, and even in the stone beneath.
It is not surprising that Acharius should, from the examination
of a single specimen, have placed this anomalous
production amongst the Lecidece. Its fructification, however,
in its most regular state, is that of an Opegrapha, and
indeed, very similar, although shorter, to the lirellae of
O. tesserata. The crust distinguishes the plant decidedly
from that species, and, when accurately examined, from
every other known Opegrapha.
It is surely better to regard the Graphides of Acharius,
as only a section of the genus Opegrapha, with which they
entirely agree in general appearance. The accessory margin
to the lirellae,more or less complete in different species,
is an unsatisfactory distinction, and the other characters
assigned by the great Swedish Lichenist are, if constant,
too minute for general use.—W. B.
2632. (Fig. 2.)
O P E G R A P H A tesserata.
Tessellated Opegrapha.
CRYPTOGAMIA Uchenes.
Gen. Char. Lirellae black, oblong or linear, with a
raised proper margin and a narrow disk.
Spec. Char. Crust tartareous, areolate, brownish
grey. Lirellae naked, prominent, short, obtuse,
simple or slightly divided, with a broad indexed
margin.
Syn. Opegrapha tesserata. DeCand. FI. Fr. v. 2.
313. Chev. Hist, des Hypox. 51. t. 11. f . 1.
O. petraea. Ach. Syn. 12.
S o decidedly is this species distinguished by its crust,
that no doubt can arise about it, although the specimen here
drawn is the only one that we have seen. It was gathered
by Mr. W. Robertson on Hoi wick Scar, by the Tees, in
Yorkshire. Acharius gives it as a native of Scotland. It
was first described in Flore Française, from specimens collected
by M. DeCandolle in the Alps; and it is well figured
in the Histoire Générale des Hypoxylons quoted above.
The crust forms patches of considerable extent, and is
said to be partially bordered with a black line when perfect.
It is of a structure not uncommon in various other genera
of Lichens, but not hitherto observed in any other Opegrapha
; being composed of granulations at first scattered
and convex, afterward crowded together and forming small
angular areolae, irregular in shape and size, the interstices
of which are barely visible to the naked eye. The general
surface is rather uneven, unpolished, of a brownish grey
with a tinge of red ; the internal substance white. Between
the areolae, and more rarely through their substance, arise
numerous, small, dull black lirellae, some solitary, some
crowded in little clusters. They are slightly prominent,