378 INDIAN CYPRINID£. Sarcoborine. 
the Perilamps and Leucises are, on the other hand, clearly enough confined to 
Sarcoborine ; but there is a group still required to fill up the space between 
the Opsarions and the Apalopterine in order to complete the Sarcoborine, and 
unite that group with the aberrant circle. Whether the American genus 
Amia, or the genus Sudis, Cuv., or Erythrinus, Gronov. which all natu- 
ralists suppose to present near relations to Cyprinide@, may, one or all, be 
destined to fill up this blank, is a question regarding which, without those 
genera before me, I cannot venture an opinion. -Amia, I may remark, is said 
to be without cecal appendages to the stomach, a circumstance which 
ought to place it with the Cyprins, rather than with the Clupeide. 
It may be necessary to explain in this place why I have given the two 
principal groups of Cyprinide the rank of sub-families, rather than that 
of mere genera. A genus appears to have been intended as the lowest deno- 
mination ef a perfect group; and, indeed, is still so regarded that no smaller 
groups are supposed to be comprised within it, although where the species 
are numerous they may be conveniently separated into artificial sections, or 
sub-genera. Should such sections be further augmented, so as to become ne- 
cessary to separate them still farther, it is obvious that this can only be done 
by augmenting the value of the higher group, by raising it to the rank of a 
family, or sub-family, when the sub-genus would naturally become a genus. 
This is what I have done; and though a species may be so isolated, as to form 
a distinct family of itself, by means of the numerous links that would be 
requisite to connect it with the nearest known forms being lost, or undis- — 
covered, yet this is so unlikely now to be the case in zoology, that we may 
regard the number of genera as the safest rule for determining the value of 
groups; and as genera are understood to be the lowest denomination of perfect 
groups, and sub-genera mere artificial sections of genera, we can have no 
uncertainty in the nomenclature of groups; though I am aware that for want 
of a little reflection on this subject, the distinction between genus and sub- 
genus is often confounded, or ill understood. 
