(219) 
is, as @ whole, to be taken for an abnormal exhibition of what was, in 
inception, a compound type. 
Eschweiler (Syst. pp. 17, 19, fig. 28) was the first to indicate those 
peculiarities of spore-structure which have done so much to lighten the 
determination of Arthonie ; and his cited descriptions and figures of 
1824 (to be compared with the fuller account in his Lichens of Brazil) 
differ in no important respect from the latest definitions. It was long 
however before lichenists availed themselves of this invaluable clew ; and 
when the spores were at length studied, their general features of agree- 
ment in the several groups into which the natural genus had fallen apart, 
failed at first to incite a reunion of its members. Massalongo’s writings 
represent thus, here as elsewhere, the period of greatest discrimination or 
dismemberment; since which the tendency has been clearly the other way. 
This is evident in Koerber’s successive elaborations of the group, as in its 
treatment by Dr. Th. Fries. Stizenberger, finally (1862) leaves only 
Arthothelium apart from <Arthonia ; and even this distinction failed to 
find recognition in the Arthonia of Anzi (1860). 
The spore-type here, though more often peculiarly modified, when it 
stands sometimes in rather difficult relations to that of Opegrapha, reverts 
notwithstanding to, and, thus explained, is in fact the same with that 
generally expressed by Thelotrema, Heterothecium, and Graphis ; and its 
history is available therefore in the explication of those genera. Several 
interesting illustrations are afforded by Arthonie, of which the already 
cited A. cyrtodes, Tuck. (Obs. Lich. l. c. 6, p. 235, & in Wright Lich. Cub. 
n. 245-6) is one, that this type has really an extent not unlike that attrib- 
uted to it in the present treatise; and that the systematic value of the 
muriform modification of the plurilocular spore is by no means so great 
as has often been supposed. 
Chrysothriz, Mont. (Syll. p. 332. Cilicia noli-tangere, Mont.! in Ana., 
2, 2, p. 275, t. 16, f. 2) a byssaceous, tropical lichen, appearing to be prop- 
erly analogous to Cenogonium, is excluded here from Arthonia, Nyl. 
The contributions of Dr. Nylander to the illustration of Arthonia, so 
much exceed those of any other writer, that the genus, as here taken, 
may be said largely to rest on his determinations. ‘Jam 72 species,’ said 
this author, in 1861 (Lich. Scand. p. 257, n.) ‘hujus generis naturalis 
cognitas habeo ;’ and so considerably has the number been augmented in 
his recent publications, that it may be now reckoned at close on a hundred ; 
of which, as might be expected, the larger part (‘longe maximus nume- 
rus’) is tropical. Other estimates of European Arthonie shew however 
that the specific limits of even these are by no means yet agreed upon; 
and it cannot be doubted that the group, as a whole, whether we regard 
the probable number of so-called specific forms to be embraced in it, or 
their distribution, is still more than ordinarily uncertain. This is at any 
rate the case here, where these lichens have attracted as yet, except in a 
few districts, only casual attention. Fortunately, the writer of this con- 
