PREFACE. 
The genus Arthonia (the name said by the author to be derived 
from the Greek Artho , (aspergo) to sprinkle, “propter thallum 
apotheciis minutis quasi adspersum,” was established by Acharius 
in Schrader’s Neuer Journal f. d. Hot. 1806, accompanied by a 
table representing tolerably well, according to Krempelhuber, four 
species and one variety; but as F6e observes, (Ess. p. xxxi) the 
Greek word equivalent to aspergo is ardo , and the proper spelling of 
the name would have been Ardonia. The species as interpreted by 
him were described in his Lichenographia Universalis and Synopsis 
Lichenum , the genus being thus defined: “ Receptaculum univer¬ 
sale [thallus], crustaceum plano-expansum adnatum uniforme. Par- 
tiale [apothecia] innato-sessile subtrotundo-difforme immarginatum 
(atrum) membrana subcartilaginea tectum, parenchymate solido 
similari.” Some of his Arthonias, however, do not belong to the 
genus, while other lichens now comprised in it, including the pale- 
truited species, were referred to other genera, especially Graphis 
and Opegrapha. Fries, in his Lichenographia Europcea ref or mat a, 
did not accept the genus, but described several species belonging to 
it under Coniocarpon and Coniangium. The spore characters were 
first indicated by Eschweiler as follows: “ Asci [thekes] ovato- 
pyriformes, thecas [spores] foventes 3 vel 5 subcylindricas annulatas, 
annulis 1-15.” (Syst. p. 17, andf. 20.) F6e did not have a clear 
conception of the genus, regarding it in the Suppl. as an empirical 
one, and his figures of spores referred to Arthonia are mostly, if not 
all, those of species of Graphis , as are many of his Arthonias; but 
he retains Coniocarpon DC. for Arthonias with colored fruit, (equiv¬ 
alent to Spiloma Ach.) Succeeding writers of the ante-microscopic 
period followed Acharius. The genus, as here understood, was defi¬ 
nitely established by Nylander in his Synopsis Arthoniarum , 1856, 
who has been followed by most subsequent writers, though some 
retain Art hot helium Mass, for the species with muriform spores, and 
Coniangium Fr. for those with 2 locular spores. The genus is de 
fined by Tuckerman, Genera, p. 217, as follows: “Apothecia ro- 
tundata oblongave, margin q accessorio thallode nunc instructa, pro- 
.prio destituta, plus minus aggregata 1. dein in pseudostroma difforme 
1. rotundatum 1. stellatum confluentia. Sporae (in thecis plerumque 
abbreviates pyriformibus) oblongo-ovoideae, (nymphaeformes) 1. ob- 
longae 1. rarissime fusiformes, 2-4-pluriloculares, demum et muri- 
formi-multiloculares, fuscescentes 1 . decolores. Spermatia oblonga 
1 . bacillaria, 1 . acicularia; sterigmatibus simplicibus. Thallus crus. 
