INTRODUCTORY. 
In the summer of 1886 I published a key to the genera of mosses recog¬ 
nized in the Manual of Lesquereux and James. From the demand which 
has exhausted a large edition of that key, I have felt that the object of its 
publication was reasonably attained, that it really was helpful to students 
of mosses. Although much misgiving was felt as to its accuracy a con¬ 
siderable use of it has revealed but one serious omission, and neither time 
nor its users have indicated to the author how it could be materially im¬ 
proved. It is therefore reprinted here with the few alterations which have 
seemed desirable. 
But since there are no keys to the species even of the largest genera in the 
Manual, the novice, deserted after reaching the genus, is left almost as much 
bewildered as if he had not been led so far. I have therefore been induced 
to prepare keys to the species of all the genera. 
The only plea for such work is its anticipated usefulness. I hope that it 
will stimulate some to undertake the study and collection of mosses who 
have heretofore been deterred by their helplessness in the determination of 
them without more expensive aids than the amateur usually possesses. An 
earnest student equipped with patience, some skill in dissection, a compound 
microscope and the Manual, ought to be able with the additional assistance 
of these keys to determine the names of most of the mosses which he can col¬ 
lect. Those which remain uncertain he can refer to those who possess the 
illustrations and exsiccati which are often indispensable for identification. I 
shall be disappointed if these keys do not encourage more to enter upon the 
study of this exceedingly interesting group of plants, which, with the 
Hepaticas, are more neglected than any of which we now have accessible 
descriptions. 
In constructing these keys, I have thought it wise to make few changes 
in the nomenclature or in the rank of species. Of many in the Manual 
neither the present names nor the autonomy can be maintained. The 
changes I have made are, with one exception (Dicranum fuscescens), con¬ 
fined to the two genera which have been revised since the appearance of 
the Manual in 1884, viz., Sphagnum, by M. Jules Cardot, of Stenay, France, 
and Fissidens, by the author. M. Cardot is now engaged in a revision of 
Fontinalis and Dichelyma, and I regret that his results have not yet been 
published, that they might be included in the present keys. 
I have included in the keys all the new species known to me which have 
been published since the issue of the Manual and before 1890, when the 
relation of these could be ascertained from the descriptions and figures. 
