The arrangement of this book is that of the author's Genera 

 Lichenum., 1872; and the few variations from this will, it is 

 hoped, explain themselves. The plants described are, in great 

 part, sufficiently well settled; and the new things appear to 

 demand an at least provisional place : though the author would 

 have preferred to keep the most of these last back, with Horace, 

 nonum in annum. And this not merely from hesitation as to 

 the novelty or the rank of the lichens referred to, but because 

 he entertains strongly the opinion that the science of Lichens 

 whether as regards morphology or system has by no means 

 kept pace, since Fries's day, with the diagnostic enumeration 

 of new forms called arbitrarily species ; and he is sorry to have 

 possibly added to the number of these constructions. Agreeably 

 to the wishes of the friends who have urged an early publication, 

 this part of the work, comprising the more conspicuous lichens, 

 is printed first. 



Amherst, Mass., 

 1 Nov., 1881. 



