  Although some 20--30,000 supernova remnants (SNRs) are expected to exist in
the Milky Way, only about 230 are presently known. This implies that most SNRs
are ``missing''. Recently, we proposed that small ($\simlt 1^\circ$), faint,
high-velocity features seen in large-scale 21-cm line surveys of atomic
hydrogen ({\sc Hi}) in the Galactic plane could be examples of such {\it
missing} old SNRs. Here we report on high-resolution \schi observations of one
such candidate, FVW 190.2+1.1, which is revealed to be a rapidly expanding
($\sim 80$ \kms) shell. The parameters of this shell seem only consistent with
FVW 190.2+1.1 being the remnant of a SN explosion that occurred in the
outermost fringes of the Galaxy some $\sim 3\times 10^5$ yr ago. This shell is
not seen in any other wave band suggesting that it represents the oldest type
of SNR, that which is essentially invisible except via its \schi line emission.
FVW 190.2+1.1 is one of a hundred "forbidden-velocity wings" (FVWs) recently
identified in the Galactic plane, and our discovery suggests that many of these
are likely to be among the oldest SNRs. We discuss the possible link between
FVWs and fast-moving atomic clouds in the Galaxy.
