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into several natural divisions with differences of about the value that 
are often taken for genera, and if you are to subdivide the Acronyctas 
into genera, then those divisions which I have called respectively 
Viminia, Cuspidia, and Bisulcia are the three primary divisions.” 
That surely is clear enough as to the biological values of Dr. 
Chapman’s subdivisions. As to the convenience, Dr. Chapman 
further writes: “‘Secondarily, if your genus Cusfdia is so large that 
it would be convenient to subdivide it, characters are easily found to 
do so. This could not be done so definitely in Vzmenza, which is 
very homogeneous.” It will be observed here that the subdivisions 
are based on characters, not on “ opinion.” 
But in practice our systematists have grouped their species, quite 
as much as a matter of convenience, as a matter of indicating re- 
lationships. Although, from the biological point of view, this idea 
of genera appears to us an exceedingly absurd one, except so far as 
grouping for convenience has resulted in the subdivision of an unwieldy 
genus into its natural sub-genera ; yet, as uz fait accompli, it has to 
be reckoned with, and in considering it we may grant that the 
groupings of species dy name are matters of convenience, and that the 
name soon carries with it, or expresses, the idea of the relationships 
existing among the groups themselves. Dr. Chapman says, with 
regard to these genera of convenience, “ You may, as you find con- 
venient, make the whole of the Acronyctids into a genus, 7. e. 
Acronycta may be your genus. My three main divisions may be your 
genera; or you may further subdivide Cwsfzdia—all according to 
convenience, not because the differences are greater or less (zz “tz, 
December 22nd, 1895). 
This states fairly the position of ‘genera of convenience,” 
although it seems to me to be rather more at the expense of what we 
may term “natural genera,” or natural groupings, than I should be 
inclined to allow. For if Cuspidia and Viminia are, as the Doctor 
states, “two primary divisions,” with differences of about the value 
that are often taken for genera, I would maintain that these are 
absolutely the genera ; that their union is unnatural so far as it gives 
us a tribal division with a generic appellation, and that their further 
subdivision must be trenching on specific characters. As a point of 
criticism of the Doctor’s statement, however, I would suggest that it 
appears to me that the subdivisions set up in Cusf7d7a are almost as 
important biologically, and present as important differences as the 
differences existing between Vmrnéa and these various subdivisions. 
That being so, and since each of the British species included in the 
various subdivisions of Cusf7dia, itself forms one of a very natural 
group of species distributed over the palaearctic and nearctic regions, 
I am inclined to look upon these subdivisions in the light of natural 
and well-defined genera. 
It will be seen from my remarks that I agree largely with 
Wollaston, who writes: “ With respect to their immediate associates, 
genera cannot be isolated and distinct, but must of necessity merge 
