  It is argued that exotic mesons consisting of two quarks and two antiquarks
are not ruled out in quantum chromodynamics with a large number $N$ of colors,
as generally thought. They can come in two varieties: short-lived tetraquarks
with decay rates proportional to $N$, which would be unobservable if $N$ were
sufficiently large, and long-lived tetraquarks with decay rates proportional to
1/N. The $f_0(500)$ and $f_0(980)$ may be examples of these two varieties of
exotic mesons.
