133 
The species of Py/aisie//a also are so closely related to Hypnum 
(Raphidostzgium) cylindricarpum Muell. that Jaeger (St. Gall. Nat. 
Gesell..1876—77: 304) calls the latter a Py/aisia. Hypnum cylindri- 
carpum, notwithstanding, is not a unique species in this respect, 
but is very closely related to several other species, notably 4. 
microcarpum Muell. Entodon is also more closely allied to Plagio- 
thecium than to any of the other Isotheciaceae. 
All the species of Jsothecium itself excepting, perhaps, Z. 
myurum are so closely related to Brachythecium and other genera 
of the Brachytheciaceae that there is no reason whatever for putting 
them in another family. These conclusions were arrived at inde- 
pendently, but a comparison with Lindberg’s Musci Scandinavici 
will show that this is essentially his idea of the relations of the 
species, although he combines the genera to an extent not likely to 
be approved by succeeding workers. 
These facts have led to the conclusion that, in the Hypnaceae 
at least, Lindberg's general classification must be conceded to be 
much more natural than that of Schimper. In order to present 
the result of two years' labor in a form available for immediate 
use, the generally accepted classification has necessarily been fol- 
lowed in part, but care has been taken to arrange the species in 
genera in a way that will not require any change in order to con- 
form to the general principles of Lindberg's classification. 
A great deal of attention has been given to ascertaining the 
habitat and distribution of the species, as data of this kind have 
proved of the greatest value in deducing those general principles 
of biology which represent the highest achievements of science 
and to which the systematist, the physiologist, and the morpholo- 
gist alike contribute. 
In this connection it is worthy of remark that very few col- 
lectors give sufficient data on their labels. It is to be hoped that 
the collectors of the future will record the exact habitat of each 
collection and tíme at which the collection was made as well as 
locality and year. Had these data been given with each specimen 
studied in the preparation of this revision, the work would have 
been much simplified and its value greatly enhanced. The aim of 
the work has been to:render intelligible the species already de- 
