X PREFACE. 



opportunity may enter into the consideration of the synonymy 

 and tlie nomenclature-controversy. 



The lichens described are. the more common forms occur- 

 ring in the United States, those with which tlie collector is 

 likely to come in contact. At the close is given a fairly 

 complete list of the lichens found in the United States ; this 

 will prove helpful to those who wish to make exchanges. 

 The artificial key is especially intended for the use of those 

 who are not in possession of a compound microscope. 



I take this opportunity to express my grateful obligations 

 to Dr. N. L. Britton and Prof. Lucian M. Underwood, of 

 Columbia University, who placed at my disposal the Univer- 

 sity collection of lichens. I am also greatly indebted to my 

 wife, who has kindly given aid in correcting the manuscript 

 and in reading the proof. 



Albert Schneider. 



Chicago, January, 1898. 



