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as well bark- as rock-lichens. But it is less easy to bring together on 
terms of equality the two remaining, large assemblages; and we gladly 
follow Naegeli and Hepp in keeping the corticoline Pyrenula separate 
from the saxicoline Verrucaria, as distinguishable, if by nothing else, by 
its undeniable inferiority. This inferiority is indeed, as already above 
suggested, of such a nature, as to involve even the fundamental question 
of class-affinity ; and in separating Verrucaria therefore from Pyrenula 
we are removing what with all their marked reduction and frequent 
obscurity of structure are still fully entitled to be called lichens, from 
what, at the best, deserve no higher name than the equivocal one of 
myco-lichens. Even as satisfactory a species as Pyrenula gemmata 
(Acrocordia, Koerb.) is so close, and the microscopical details scarcely 
embarrass the evidence, to Spheria mastoidea, Fr. (to which Fries him- 
self regarded his Verrucaria alba as ‘too near’) that Scherer is said by 
Hepp to have confused the two in his publications. The remark holds 
equally good of the central assemblage of the genus, with coloured 
spores (Pyrenula, Koerb.) if indeed here the fungic relationship does not 
become more evident. And when we reach the extremity of Pyrenila 
represented by P. punctiformis and P. rhyponta (Arthopyreniac, Koerb.) 
we have arrived where we touch Fungi, according to Fries; or enter 
among them, according to Wallroth (Naturgesch. d. Fiecht., 1, p. 150). 
Both of these were competent enquirers; and later investigations of the 
internal structure of the groups referred to, have done little, that I am 
aware of, to invalidate, in this regard, the earlier. 
Pyrenula, as here understood, may appear then to be distinguishable, 
in a measure, into smaller groups; but these assemblages, though passing 
in fact for genera with most recent writers, are far from satisfactorily 
defined. All internal structure of the apothecia, even that of the spores, 
fails at length to afford sufficient criteria. AZicrothelia, Koerb., in America 
at least, only adds the (typical) coloration to the spores of Arthopyrenia ; 
and its type (If. micula) might well appear, from this point of view, with 
difficulty separable even in species (Nyl. Pyr. p. 61) from a well-known 
form of the latter. Arthopyrenia seems better distinguishable from 
Acrocordia (the type of which was yet originally placed by Massalongo 
with the former, as it is now by Nylander) but the last exhibits finally, 
even in A. gemmata, a tendency to arthopyreniine modification which 
becomes distinct in the not rarely quadrilocular A. bifornis (Borr.!) and 
we lose at length all hold except on the paraphyses; these being undis- 
tinguishable in ordinary conditions of Pyrenwla (Arthopyrenia) puncti- 
formis, but yet sufficiently obvious in the v. fallax, Nyl. The colourless 
(or decolorate) spores of Acrocordia gemmata contrast, in like manner, 
sharply, with the coloured ones of Pyrenula, Koerb., but both offer only 
modifications (as shewn by the young spores of Pyrenula) of the same 
type; and P. hyalospora (Nyl.) might perhaps as well be considered a 
quadrilocular Acrocordia, as (with Nylander, who especially compares the 
