April 13, 1841. 
William Yarrell, Esq., Vice-President, in the Chair. 
The following paper, on some new genera of Birds, by Hugh E. 
Strickland, Esq., was read. 
«Tt is not without some unwillingness that I venture to point 
out some new generic groups of birds, because I am of opinion that 
the process of naming and defining new genera has been in many 
cases carried too far already. The class of birds probably does not 
contain more than 6000 species, and these have already been dis- 
tributed into upwards of 1000 genera, and I think therefore there 
can be no doubt that systematic ornithologists are now fast approach- 
ing the point beyond which it will not be expedient to carry the 
subdivision of the older groups into new genera. For we must not 
lose sight of the fact, that expediency or practical convenience does 
form an element in the construction even of a natural system. In 
such a system the materials which constitute any group must be na- 
turally allied, and they must be placed in such order as will best 
show their natural affinities, and yet the number of nominal genera 
into which such a group is to be divided may be a question of mere 
expediency. For the species, which are the only rea/ ingredients in 
a family or subfamily, often pass from one form of structure to an- 
other without any hiatus, so that it becomes a mere matter of opinion 
whether the so-called genera into which they are to be classed shall 
be many or few. Nature draws no line by which the rank or ex- 
tent of genera can be determined. As a general rule, varieties of 
form are considered to constitute genera, and varieties of colour, 
species; but this criterion is far from infallible, for we very rarely 
find two species, however closely allied, possessing precisely the 
same form and proportions, so that if every difference of structure 
be held to be generic, we shall end in having as many genera as 
there are species. Take, for instance, the two very natural groups 
Corvus and Parus, as now restricted; it will be found on examina- 
tion that there are marked differences of both structure and habits 
which characterize almost every one of the species. It is plain then 
that we have in general no other guide in the definition of new ge- 
nera than a mere opinion as to the amount of structural variation 
which is considered to authorize their adoption, and I think there 
can be no doubt that in many of the genera recently established in 
ornithology, the standard has been reduced too low; in other words, 
these genera are based on diversities of structure of so little value as 
to be practically inconvenient. All genera profess to be of equal 
rank, and we should therefore aim at making them as nearly so as 
possible, and at the same time not inconveniently numerous. 
No. XCIX.—Procesepines or THE ZootoGicaL Society. 
