(178) 
the determination of species (compare Fr. L. E. p. 282) is especially diffi- 
cult; and the labour which has been given to this in Europe has yet to be 
attempted here. Estimates of European lichenographers of the present 
day differ indeed so widely as to the rank of the forms described, that it 
is hardly to be questioned that the confusion which Fries (Lich. Eur.) 
did so much, here as elsewhere, to remove, threatens now, with the 
increasing depreciation of other standards of judgment in view of a merely 
microscopical one, to return; and the species to become as uncertain as 
they were before Fries. The vast extent of our territory is less then in 
the way of an early determination of our Lecidee, than the paucity of 
enquirers, and the perplexities of the enquiry. Of the thirty species now 
known to me as North American, but two are properly or mainly calcare- 
ous; while the proportion of calcareous forms in the rupicoline groups 
of Europe is nearly one quarter of the whole number of forms: a fact 
which indicates sufficiently an interesting field for exploration. Another 
is, without doubt, afforded by the maritime rocks of California, the 
lichenose Flora of which has been so largely exhibited by Mr. H. N. 
Bolander; and yet another, and perhaps the most promising of any, by 
the alpine rocks of the Rocky Mountains. And there is no reason to 
suppose that the desultory studies of the very few lichenists who have 
collected in the ranges of the Appalachian chain, though this has yielded 
us almost all we know, hare exhausted its treasures. 
We find the true centre of Lecidea in the large group of lichens, 
inhabiting mostly granitic rocks, of which L. contigua, Fr., is the well- 
known type (ZLecidea, Koerb.). But the black hypothecium of this 
species passes gradually, in forms otherwise closely allied to it, into a. 
colourless (Lecidella, Koerb.) looking not seldom, and in other respects 
(especially in the little cluster typified by Z. arctica) towards Biatora. 
With the arctic cluster is most readily associable ZL. enteroleuca ; and the 
needle-shaped, bowed spermatia of the latter species relate it to the 
effigurate section (Psore sp., Thalledema, Auctt.) much as the same 
organs in Lecanora subfusca connect this with the effigurate section of 
Lecanora. With this sketch of the outlines of the genus, conceived strictly 
in the sense of Nylander, as respects that portion of his Lecidea to which 
the name is here confined, we proceed to indicate briefly such species as 
hare been added recently to our list. 
Of the first section (Thalledema) consisting of effigurate species, 
almost all calcareous, analogous to Sgwamaria in Lecanora, and to Psora 
in Biatora, though ditfering from the last in a much more evident tendency 
in the spores (a tendency not however quite unknown to the biatorine 
group) to pass into bilocular conditions, we possess only the long-ascer- 
tained L. candida (Web.) Ach., and ZL. vesicularis (Hoffm.) Ach., indicated 
as occurring in Arctic America by Hooker, and the former also by Th. 
Fries. LZ. vesicularis is only known to me, as an United States lichen, in 
specimens recently collected in the Uintah mountains, Utah (S. Watson) 
