(19 ) 
Apothecia scutellaeformia, disco luteo-aurantiaco. Spore polari- 
biloculares [rarissime, in sp. exot., quadriloculares] incolores. Sper- 
matia ellipsoidea 1. oblonga; sterigmatibus multi-articulatis. Thallus 
foliaceus squamulosusve appressus, aut adscendens evernizformis, 
cartilagineo-membranaceus; plerumque flavicans. 
Ideally considered, the polar-bilocular spore may be said possibly to 
mediate between the brown type, and the less highly organized, colorless 
one: in nature however, the first is, on the whole, as distinct as either of 
the others; and the groups characterized by it are also curiously marked 
by external features of difference. We cannot but adopt the oldest name 
for the group now before us, which, as here limited, becomes exactly 
equivalent to Xanthoria, Stizenb.; and brings together the species repre- 
sented by Lichen parietinus, whether octosporous or polysporous (Xan- 
thoria, A, Th. Fr.) and those of which Lichen chrysophthalmus is taken 
for the type (Theloschistes, Th. Fr.). Widely as authors have differed 
with respect to its constituents, the genus, so taken, is, notwithstanding, 
in several respects, a natural one; distinguishable readily from the other 
members of the present family, and, by its typically subfoliaceous thallus, 
separable as well from Placodium, of the Lecanorei. It is indeed at once 
seen that the squamulose conditions of T. parietinus (from some of which 
conditions 7. candelarius widely differs only in its polysporous thekes) 
cannot be far separated from their foliaceous type; nor do the ascendant 
species (7. chrysophthalmus, the key to T. cymbaliferus (Eschw.) and T. 
villosus) diverge from this, other than were beforehand conceivable in a 
group so near to Usneei, and especially to Ramalina ; or other than (ex- 
actly) analogously to the ascendant varieties of Physcia speciosa and P. 
ciliaris : —but the case is possibly less clear as regards the relation of 
Placodium. There is yet no doubt that Placodium elegans, whatever 
resemblance may be found between its finest conditions and Theloschistes 
parietinus, is yet amember of another group; or that this other group 
is related to Theloschistes, precisely as Lecanora, as here taken, is related 
to Parmelia. 
Of the eight species, referable here, reckoned by Nylander (Syz.) the 
two foliaceous ones (7. parietinus, T. candelarius) are widely diffused, 
and belong at once to tropical and boreal, as well as austral latitudes : 
the remainder are natives of the warmer regions of the earth; only one 
(T. chrysophthalmus) extending far beyond them. But it is certainly 
probable that the number of species, as given, and generally received, is 
in fact too large. It would not indeed be practical to attempt to revive 
(except. excip.) the criticism of Wallroth (Naturgesch. 2, 333) and Meyer, 
1 This did not escape Norman; who, as he combined Placodium (DC.) Naeg. 
and Hepp, with his Theloschistes, consistently also reduced Lecanora (including 
Squamaria, DC.) to his Parmelia. (Con. p. 14. 
