  Based on a sample of $(448.1\pm2.9)\times10^{6}$ $\psi(3686)$ events
collected with the BESIII detector at BEPCII, the decays of
$\psi(3686)\to{}K^{-}\Lambda\overline{\Xi}^{+} + c.c.$ with $\overline{\Xi}^+
\to \overline{\Lambda} \pi^+$, $\overline{\Lambda}\to \overline{p} \pi^+$ are
studied.Two excited hyperons, $\Xi(1690)^-$ and $\Xi(1820)^-$, are observed
with large significance ($ \gg 10 \sigma$) in the $K^{-}\Lambda$ invariant mass
distributions. A partial wave analysis is performed, and the spin-parities of
$\Xi(1690)^-$ and $\Xi(1820)^-$ are determined to be $\frac{1}{2}^{-}$ and
$\frac{3}{2}^{-}$, respectively. The masses, widths, and product branching
fractions of $\Xi(1690)^-$ and $\Xi(1820)^-$ are also measured.
