44 ON GENERA AND SPECIES, 
I must state that after much study of this arranges 
ment I have not been able sufficiently to understand it to 
make it practically useful. I do not clearly see what 
object the author gains by introducing sectional names not 
before used in the genus, more especially as these names 
(Cenopteris, Eupteris, Neuropteris, Doodya, Pleocnemia, &c.) 
are apparently not given as special sectional names, but 
used comparatively—that is, all the species under Cænop- 
teris, Eupteris, &c., are presumed to have venation similar 
to Ferns bearing those names. Therefore, in order to 
ascertain the venation of one Fern, it is first necessary to — — 
be acquainted with the venation of that with which it is _ 
put in comparison. As, for example, to know Dictymia, it 
is first necessary to be acquainted with the character of 
the venation of Doodia and Pleocnemia. Unfortunately 
too, the analogy in these two cases is far from obvious, the 
genera in both cases being in every respect of quite dif- 
ferent habits. I therefore see no good reason for making ` — 
such genera as Doodia and Plevenemia types for arranging — 
other genera by venation. 
With regard to his arrangement of Phegopteris and 
Aspidium, of which he enumerates in consecutive order 
299 species—thus viewing them as parts of a single genus 
—of these sixty-eight belong to the first part, Phegopteris ; 
the remainder to the second part, Aspidium. I do not 
consider it necessary to enter into further details, I will E 
only add that the sectional names are upon the same | 3 
principle as those of Polypodiwm, and that, in my opinion, ` 
. & simple generic name for groups of naturally allied ` 
species, would render their study much easier than the 
complicated comparative similitude with one another. 
Mettenius has also published a memoir on the genus, 
Asplenium and several other genera, Ge 
