ri 
taceus, uniformis, aut hypophlaeodes.” For a full account ot the 
synonymy of the genus, and for fuller historical observations, refei- 
ence may be had to the works of Tuckerman, Nylander and Alm- 
quist, to Koerber’s Systerna and Parerga, Th. M. Fries's Genera 
Heterolichenum , and Stitzenberger’s Beitrage. 
In Nylander’s definition of the genus the thalamium is said to be 
“ paraphysibus discretis nullis.” There are however a few species, 
especially the lecideoid ones, which present the appearance of reg¬ 
ular paraphyses ; and I have observed such even in A. radiata and 
in A. glaucescens. But in most cases the thalamium is pervaded by 
a confused tissue not differing, perhaps, from the hyphae of the hy- 
pophlaeoid thallus, as may be seen in A. punctiformis. The thallus, 
especially when well developed, often takes a deep blue color with 
iodine, and this may also be seen in the hypophlaeoid hyphae, after 
previous treatment with dilute sulphuric acid. The gonidia are 
mostly the concatenate ones of the Graph ideas {chroolepogonidia 
Nyl.) ; but in a number of species are the ordinary green gonidia 
(,haplogonidia Nyl.) ; for the latter Nyl. has proposed the distinc¬ 
tive name Allarthonia. According to Almquist, p. 7, both forms 
sometimes occur in the same species. 
The species of Arthonia have been largely increased by collectors 
in various parts of the world in recent times, among whom are 
specially to be mentioned Lindig for South America and Charles 
Wright for Cuba. The collections of the former have been deter¬ 
mined by Nylander. The Cuban Graphideae have been distributed. 
Among them are many new Arthonias, some of which have been 
named by Nylander, but they are as yet undescribed. The descrip 
tions I have attempted of some of them, being founded mostly on 
small specimens, must be regarded as imperfect; and I have not 
ventured to name these species, to which names have perhaps already 
been given by Dr. Muller, who has rendered an important service 
by the revision of the Lichens of Eschweiler and Fee. 
The synonymy of the European Arthonias is often conflicting, 
owing doubtless to some extent to the confusion of species in the 
early herbaria. The difference of opinion in regard to what shall 
constitute a species is great. These matters I do not undertake to 
decide. 
A list of the authorities consulted will be found succeeding this 
preface. I had the privilege several years ago of examining the Ar¬ 
thonias of the late Professor Tuckerman’s herbarium, which, how¬ 
ever, had not been thoroughly worked up by him. But I have not 
had the opportunity of consulting them again for the purposes of 
this work. 
The following pages are intended rather as a record than as a crit¬ 
ical revision and arrangement of the genus, which can only be at¬ 
tempted by one having access to the riches of the European herbaria, 
