DR. LINDSAY ON WEST-GREENLAND LICHENS. 353 
Thalline areole frequently pulviniform, unaffected by potash. Most variable in its 
sporidia, which are frequently simple in the young state, and muriform in the old, 
their outline and size varying correspondingly. The young sporidia are sometimes 
colourless or pale olive; oval or ellipsoid, straight or suberescentie; granular, or contain- 
ing a single, large, eccentric nucleus or endospore; or their contents resemble those of 
the sporidia of many Lecanore (e. g. the tartarea group) in consisting of a mass of nuclei- 
form oil-globules and granular matter (sometimes they maintain this condition to 
maturity, but are then to be considered abortive); gradually acquiring the deeper olive or 
brown colour ofthe normal sporidia. As the normal sporidium is developed, its protoplasm 
becomes divided transversely into a varying number of loculi. The septa or division- 
spaces are either straight across, in which case the loculi are equal in size or nearly so; 
or they are variously oblique, giving rise to great irregularities in the size and form of the 
loculi. At first 3 transverse septa, equivalent to 4 loculi, were common in one form of the 
plant; while in another there were, at a later stage, the colour being dark brown, 7 to 10 
such septa. Longitudinal division of the loculi sooner or later occurs as a general rule. 
At first it affects only one or a few loculi, and is subcentral ; that is, there is a subcen- 
tral division longitudinally of the transverse loculi. But as age advances, this longitudi- 
nal division becomes much more general, and it goes on till a muriform structure results— 
that is, till the loculi are converted into a series of subcubical or subspherical cellules or 
corpuscles, as in the sporidia of L. grenlandica and .L. geminata. In the old state the 
sporidium becomes broken up, as in grenlandica, into irregular masses of these sub- 
cubical corpuscles, which are of a dark brown colour. This brown colour of the mature 
and old sporidia is sometimes so deep as to obscure the contained loculi and their subdi- 
visions. In the middle stages of development, when the transverse septa are distinct, the 
sporidia are frequently broadly ellipsoid or oblong-oval, straight, slightly curved, or 
. plano-convex. Sometimes there is a bulging of the epispore opposite to each loeule. In 
the old state (the muriform condition) the form is much more irregular and variable, 
resembling in this respect the sporidia of Urceolaria scruposa. Thus they are obovate, 
pyriform, or oblong, with irregular bulgings of the epispore. Linear-oblong forms, with 
7—10 transverse septa, sometimes resemble, save as to colour, the sporidia of Graphis. 
With such a variety of shape, there must be corresponding differences in size. These 
differences, as well as other variable characters of the plant, are illustrated by the follow- 
ing chief forms, under which it occurs in Greenland :— 
(1.) Growing on the under or shady side of stones. Areolæ, as usual, lead-coloured, or 
ash-grey, sometimes slightly white-pruinose, and as flat and brown as in L. fusco-atra, with 
which it is apt to be confounded. The sporidia, however, at once distinguish. it. Apo- 
thecia flat and simple, though frequently or generally convex or subspherical, often 
deformed in age. Sporidia sometimes girt with a broad, hyaline margin, as Hog 
nata ; oval or oblong-oval and simple, or oblong, with a central constriction, and muriform; 
‘0009’ long and :00045” broad. Colour from deep olive-green to dark brown, in oldish 
or mature apothecia. ig 
(2.) Thallus consisting of the ordinary lead-grey, discrete areole. Sporidia very large, 
VOL. XXVII. 3B 
