  We report the first observation of the $\Xi_{c}(2930)^0$ charmed-strange
baryon with a significance greater than 5$\sigma$. The $\Xi_{c}(2930)^0$ is
found in its decay to $K^- \Lambda_{c}^+$ in $B^{-} \to K^{-} \Lambda_{c}^{+}
\bar{\Lambda}_{c}^{-}$ decays. The measured mass and width are $[2928.9 \pm
3.0(\rm stat.)^{+0.9}_{-12.0}(\rm syst.)]$ MeV/$c^{2}$ and $[19.5 \pm 8.4(\rm
stat.) ^{+5.9}_{-7.9}(\rm syst.)]$ MeV, respectively, and the product branching
fraction is ${\cal B}(B^{-} \to \Xi_{c}(2930)^0 \bar{\Lambda}_{c}^{-}) {\cal
B}(\Xi_{c}(2930)^0 \to K^- \Lambda_{c}^{+})=[1.73 \pm 0.45(\rm stat.) \pm
0.21(\rm syst.)]\times 10^{-4}$. We also measure ${\cal B}(B^{-} \to K^{-}
\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}) = [4.80 \pm 0.43(\rm stat.) \pm 0.60(\rm
syst.)] \times 10^{-4}$ with improved precision, and search for the
charmonium-like state $Y(4660)$ and its spin partner, $Y_{\eta}$, in the
$\Lambda_{c}^{+}\bar{\Lambda}_{c}^{-}$ invariant mass spectrum. No clear
signals of the $Y(4660)$ nor its spin partner are observed and the 90\%
credibility level (C.L.) upper limits on their production rates are determined.
These measurements are obtained from a sample of $(772\pm11)\times 10^{6}
B\bar{B}$ pairs collected at the $\Upsilon(4S)$ resonance by the Belle detector
at the KEKB asymmetric energy electron-positron collider.
