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proper exciple not seldom blackens, to the immediately preceding genus, 
is not however enough to obscure for a moment the natural distinctness of 
the two groups. If Urceolaria be in fact a modification of the Lecanorine 
form of the Parmeliaceous apothecium, Thelotrema is as clearly an antici- 
pation of the Verrucariaceous; and though receding to dilated, and even 
scutellate conditions, these scarcely approach the perfection of the former, 
except as they depart from their own distinct centre. Imperfectly scu- 
telleform states of Thelotrema are sufficiently numerous, and afford in- 
teresting indications of what is now generally acknowledged as its proper 
affinity ; but the Verrucariaceous expression of the other line of diver- 
gence from 7. lepadinum—marked especially in Ascidium, Fée (called 
by Montagne a monocarpous Trypethelium) as well as in the closely akin 
T. depressum, Mont., and disappearing at length in immersed forms 
(Myriotrema, Fée, Leptotrema, Mont.) now curiously suggestive of Endo- 
carpon—is significant, and may well at first appear the more so. 
The weight of the evidence appears yet to sustain the conclusion of 
Eschweiler, that notwithstanding the presence of an inner hypothecial 
layer, the value of which this author perhaps understates in the present 
genus, as he ignores its existence in the Verrucariacei, and, still further, 
the imperfectness and inconstancy of the proper exciple (perithecium 
annulare, Eschw.) it is indeed this last, explained from the point of view 
of the now blackening lecanorine hypothecium (called by Eschweiler, in 
Urceolaria, perith. subcupulare, Syst. f. 12,17) and taken in connection 
with the structure of the thalamium, which determines, and as Lecano- 
reine, the position of Thelotrema. 
But this Thelotrematous modification of the hypothecium of Urceola- 
ria is often obscure, and at length obsolete; when the inner exciple, or 
accessory hypothecium, enclosed now in what appears a merely thalline 
receptacle (as in Leight. Brit. Ang. Lich. t. 12, f. 1, 2) may so simulate a 
really better exhibition of the Lecanoreine type than is predicable of the 
genus, that the whole structure shall appear at sight as referable to Gya- 
lecta as Thelotrema ; or, all excipular relation even of the thallus disap- 
pearing, may come at length (as in T. compunctum, T. Wightit, &c.) to 
constitute the apothecium. Such simple apothecia are readily taken (as 
by the present writer, in observations on T. simplex, Obs. Lich. 1. c. 6, 
p. 271) for exhibitions of the proper exciple, and have probably else- 
where been described as such (‘margo proprius’) by authors; but this 
proper exciple, the representative of the lecanorine hypothecium, must 
be said, from our present point of view, to be in fact wanting in such 
forms. 
The inner exciple, or veil, is itself, as has been remarked already, very 
often abortive, or obscure; but its place is taken, in numerous tropical 
species, by a remarkable crustaceous covering of the disk, saluted not 
seldom by the same name. This, which is well marked in 7. actinotum 
(Obs. Lich. 1. c. 5, p. 411) and 7. Wrightii (of the same memoir) appears, 
