  We present high angular resolution observations of HC$_3$N J=5--4 line and 7
mm continumm emission from the extreme carbon star CIT 6. We find that the 7 mm
continuum emission is unresolved and has a flux consistent with black-body
thermal radiation from the central star. The HC$_3$N J=5--4 line emission
originates from an asymmetric and clumpy expanding envelope comprising two
separate shells of HC$_3$N J=5--4 emission: (i) a faint outer shell that is
nearly spherical which has a radius of 8\arcsec; and (ii) a thick and
incomplete inner shell that resembles a one-arm spiral starting at or close to
the central star and extending out to a radius of about 5\arcsec. Our
observations therefore suggest that the mass loss from CIT 6 is strongly
modulated with time and highly anisotropic. Furthermore, a comparison between
the data and our excitation modelling results suggests an unusually high
abundance of HC$_3$N in its envelope. We discuss the possibility that the
envelope might be shaped by the presence of a previously suggested possible
binary companion. The abundance of HC$_3$N may be enhanced in spiral shocks
produced by the interaction between the circumstellar envelope of CIT 6 and its
companion star.
