  We report on molecular abundances and distributions in a starless dense core
L492. We have found that the abundances of carbon-chain molecules such as CCS,
C$_{3}$S, HC$_{3}$N, HC$_{5}$N, and HC$_{7}$N are comparable to those in
chemically young dark cloud cores called "carbon-chain--producing regions",
such as L1495B, L1521B, L1521E, and TMC-1. This is the first dark cloud core
with extremely rich in carbon-chain-molecules that is found outside the Taurus
region. In addition, the deuterium fractionation ratios of DNC/HNC and
DCO$^{+}$/HCO$^{+}$ are also comparable to those in carbon-chain--producing
regions, being significantly lower than those in the evolved prestellar cores
such as L1498 and L1544. On the other hand, the abundances of NH$_{3}$ and
N$_{2}$H$^{+}$ are systematically higher than those in carbon-chain--producing
regions. Our mapping observations reveal that the central hole of molecular
distributions, which were reported for CCS and C$^{34}$S in evolved prestellar
cores is not significant in L492, indicating that the depletion factor of
molecules is not very high. Furthermore, L492 is dynamically more evolved than
carbon-chain--producing regions, and the protostellar collapse has started like
L1498 and L1544. Therefore, it is likely that the chemical and dynamical
evolutionary stage of L492 is intermediate between carbon-chain--producing
regions (L1495B, L1521B, L1521E, and TMC-1) and evolved prestellar cores (L1498
and L1544).
