NORTH AMERICAN USNEACEAE. 141 
ORIGINAL DESCRIPTIONS. 
The original descriptions are always given, and have in 
all cases been copied from the original work. It seems 
desirable, considering their varied sources, to bring them here 
under one cover. 
FIGURES. 
The references refer to the plates which accompanied the 
original descriptions. If no plate was published with the 
original description to the earliest figure following the pub- 
lication of the name. Of the Linnean species the Dillenian 
plate is always cited in brackets, as they were invariably re- 
ferred to by Linneus, and represent his conception. 
The present work is illustrated with half-tones of the type 
specimens, if found still preserved in herbaria. All the 
plates heretofore published in connection with my former 
articles are again reproduced with the kind permission of the 
editors of the Bulletin of the Torrey Botanical Club, Botani- 
cal Gazette, Mycologia, Prof. Bruce Fink, and M. Bonnier 
of the Sorbonne, Paris. 
KEYS. 
The keys, it is hoped, will be valuable, augmented as they 
are by the classification, and the diagnoses for each species 
_ and variety. Even the best and most logical keys are to the 
author’s mind, however, never as satisfactory as_ brief 
italicized diagnoses, which have been based as far as possible 
on external features. 
DESCRIPTIONS. 
The descriptions have been compiled to allow comparison. 
The plants of a genus are always treated under definite cap- 
tions, 2. ¢., thallus, cortex, lacinia or primary and secondary 
branches, fibrils, apothecia, spores, ete. 
DISTRIBUTION. 
As I have already stated the distribution in North America 
of the species of this family follow to a marked degree the 
