  Differential production cross sections of K$^-$ and K$^+$ mesons have been
measured as function of the polar emission angle in Ni+Ni collisions at a beam
energy of 1.93 AGeV. In near-central collisions, the spectral shapes and the
widths of the rapidity distributions of K$^-$ and K$^+$ mesons are in agreement
with the assumption of isotropic emission. In non-central collisions, the K$^-$
and K$^+$ rapidity distributions are broader than expected for a single thermal
source. In this case, the polar angle distributions are strongly
forward-backward peaked and the nonisotropic contribution to the total yield is
about one third both for K$^+$ and K$^-$ mesons. The K$^-$/K$^+$ ratio is found
to be about 0.03 independent of the centrality of the reaction. This value is
significantly larger than predicted by microscopic transport calculations if
in-medium modifications of K mesons are neglected.
