268 ¥IRST PRINCIPLES OF NATURAL CLASSIFICATION. 
more definite than her species; and it must conse- 
quently follow, that, as they are of different ranks, 
there must be some prevalent number of these ranks. 
(327.) Upon this abstruse question little has been 
said or written, although all naturalists have long been 
accustomed to use different names to denote the relative 
value of their divisions. Mr. MacLeay, looking to annu- 
lose animals alone, in speaking of the rank of the genus 
Scarabeus, seems to think that there are eight different 
descriptions of circular groups ; but this opinion is the 
result, as he himself premises, more of conjecture than 
of analysis. It is, nevertheless, much nearer the truth 
than could have been supposed; for if he had been 
aware that sub-genera are likewise circular, the number 
would have been nine. Now, this is precisely the very 
highest number of circular groups, differing in value 
: each from the other, that can be traced in ornithology; 
and in the typical divisions of the order Lepidoptera 
among insects. This fact, in both instances, rests not 
upon theoretical supposition, but upon demonstrative 
analysis. We mean not to assert that there can be 
no divisions of sub-genera, which may not, in them- 
selves, be circular ; because it seems to be a law of 
nature to carry this principle into her lowest assem- 
blages ; but hitherto we have not clearly detected any 
sub-genus of this description. Should the divisions of 
sub-genera, in such cases, really be, in themselves, dis- 
tinct circles, they may be detected, probably, in the 
family of Carabide Sw., composed of the Carabide and 
Harpalide of authors. 
(328.) The animal kingdom, then, may be pre- 
sumed to contain nine different ranks or gradations of 
circular groups, commencing with the highest, and ter- 
minating with the lowest assemblages. These groups 
have received the following names, which at once indi- 
cate their relative value: —1. Kingdom; 2. Sub- 
kingdom ; 3. Class; 4. Order; 5. Tribe; 6. Family ; 
7. Sub-family ; 8. Genus ; 9. Sub-genus. This latter 
is the lowest description of circular group hitherto de- 
