XXXV1il as W. A. Lewis on 
into one of two categories; either they are in universal employ 
themselves, or, at all events, they prevent any other name having 
the title of universal employ. I took the period of thirty years 
for the prescriptive right. The date 1842 is thirty years 
exactly from the date (1872) when this limitation was proposed, 
and both plans are thus made to come to the same thing. If a 
name found in a publication since 1842 be the name given as 
the true name in all publications, it is in universal employ. 
Good; it cannot be disturbed. But if in any publication since 
1842 a name is given as the true name, then it follows that no 
other name is in universal employ. ‘Therefore, the names 
which (in the phrase of a great French entomologist) ‘ usage 
has consecrated” are effectually preserved by both methods. 
On the other hand, where xo usage has “consecrated” the 
names, our principle does not intervene. ‘Thus both plans are 
applicable or inapplicable together. 
Suppose a question arises as to the true name of any species. 
The choice at present lies among all the names in all the books 
there are. Henceforward, it will lie only among names which 
since 1842 have been treated as the true names ; and we have 
the difficulty confined within reasonable limits. It does not 
become impossible to find cases of sickness, but the plague is 
stayed. There could be no difficulty in agreeing what work is 
the true starting-point in the case of each Order ; and operations 
in synonymy would soon fall into mere routine. 
Here then, as I submit, we find a point where the ground 
of “universal employ” and the ground of logical deduction 
are conterminous,—at which we can unite the suffrages of 
two schools of doctrine; and it is so fenced around by a 
principle, that “the man of science” can occupy it to his 
advantage. 
Having defined the proposal in a few words, I have to say 
something more about it. 
There is a natural indisposition to make a sweeping limitation 
which may seem to serve out hard measure to the good de- 
scriptions, while it aims only at protecting us from the bad. 
It may be said by some who are far from unfriendly to the 
movement, “Suppose an unmistakably ‘ prior’ name is dis- 
covered to-morrow in an ancient work, will you not consent to 
its being brought up to supersede names in use?” ‘That is a 
question which deserves an answer; and it shall have the best 
which I can give. 
There is no such thing as a category of plain cases ; nor can 
there be one law for dealing with plain cases and another for 
obseure cases. Directly you admit of such a difference, see 
what you open the door to. Who is to decide what is a plain 
case, and what an obscure one? When one writer proposes to 
pass by an old name on the ground that it is not a plain case, 
another may insist in bringing it forward on the ground that 
