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original locality. It is best compared with P. flabellosa ; from which it 
differs in its regularly radiant, much darker thallus, almost obsolete hypo- 
thallus, etc. Traces of the hypothallus are distinctly observable how- 
ever, in the plant before us, under the microscope; as in all the species 
of the present group, including Lecothecium asperellum, Th. Fr. The 
medullary layer is far better defined in P. Petersii than in the squamu- 
lose forms of Lecothecium ; and is moreover modified in a marked way, 
(precisely as in P. centrifugwin, Nyl. Syn. t. 2, f. 11) contrasting espe- 
cially with what we find in P. lurida. But if the latter, Collemaceous as 
it is, approaches too closely to unquestionable Pannarie to be readily 
separated from them, the present may be said to be, in like manner, 
associable with P. flabellosa, and through that with P. tryptophylla.— 
The spores of the little group we have been examining sufficiently shew 
that Pannaria, if not advancing beyond the unilocular grade in its best- 
developed forms, shows an evident isis in the direction of such advance, 
in its inferior members. And there is also some evidence, once more in 
the present group (Lecothecium radiosum, Anz., € Koerb. Parerg., sub 
Wilmsia, p. 406) but by no means confined to it, that Pannaria offers 
really a decolorate exhibition of the modifications of the brown spore; 
and Belongs therefore, not to the series in which Lecanora follows Par- 
melia, but rather to that which includes at once Unibilicaria, Solorina, 
and the equally decolorate Collemei. From this point of view it cannot 
of course surprise us should lichens otherwise sufficiently Pannarieine, 
be found to exhibit the highest, or muriform modification of the coloured 
spore. And it is certainly no more surprising than that this should be 
the case in Collema, as understood by Nylander.——P. byssina (Hoffm. 
sub Collemate. Koerb. Purerg. p. 410. Leptogium, Zw. ers. n. 174! 
Nyl. Syn. 1, p. 120). On the earth, Illinois (E. Hall). Massachusetts, 
at the tops of walls (H. Willey). Thallus of minute, imbricated or 
somewhat ascendant, ash-coloured or whitish squamules; reduced in 
most of the Massachusetts specimens to mealy granules; with the aspect 
now of P. brunnea, and now of P. nebulosa (Hoffm.) Nyl.; composed (as 
cluso. Spore octone, ellipsoidee simplices 1. rarius biloculares, dein magis 
oblonge sporoblasto variabili, incolores, longit. 0,011-0,023™™-, crassit. 0,005-— 
0,006™- Lecidea, Tuckerm. in litt., et in Nyl. Syn. 1, p. 93. Pterygium, Nyl. 
l.c. Lime-rocks, Alabama, T. M. Peters. The finally blackened apothecia of 
this and the other me:nbers of the present group, growing upon rocks, are by no 
means carbonaceous, or properly lecideine. In the excellent specimens before me 
of Lecothecium asperellum, Th. Fr. (e herb. auet.) and in LP. flabellosa, it is easy to 
see that the young fruit is pale, and in no respect typically diverse from that of 
pseudo-biatorine states of other Pannariw; aud I observe young apothecia of pre- 
cisely the same character in P. nigra, which occurs moreover, as noted above, and 
also by Nylander (Lich. Scand.) with brown fruit. And there can scarcely be a 
doubt that further enquiry would shew that the other forms agree in this respect 
also with these. 
