  We obtained K-band spectro-interferometric observations of the Miras R Cnc, X
Hya, W Vel, and RW Vel with a spectral resolution of 1500 using the VLTI/AMBER
instrument. We obtained concurrent JHKL photometry using the the Mk II
instrument at the SAAO. Our sources have wavelength-dependent visibility values
that are consistent with earlier low-resolution AMBER observations of S Ori and
with the predictions of dynamic model atmosphere series based on self-excited
pulsation models. The wavelength-dependent UD diameters show a minimum near the
near-continuum bandpass at 2.25 um. They increase by up to 30% toward the H2O
band at 2.0 um and by up to 70% at the CO bandheads. The dynamic model
atmosphere series show a consistent wavelength-dependence, and their parameters
such as the visual phase, effective temperature, and distances are consistent
with independent estimates. The closure phases have significantly
wavelength-dependent non-zero values indicating deviations from point symmetry.
For example, the R Cnc closure phase is 110 degr in the 2.0 um H2O band,
corresponding for instance to an additional unresolved spot contributing 3% of
the total flux at a separation of ~4 mas. Our observations are consistent with
the predictions of the latest dynamic model atmosphere series based on
self-excited pulsation models. The wavelength-dependent radius variations are
interpreted as the effect of molecular layers. The wavelength-dependent closure
phase values are indicative of deviations from point symmetry at all
wavelengths, thus a complex non-spherical stratification of the extended
atmosphere. In particular, the significant deviation from point symmetry in the
H2O band is interpreted as a signature on large scales of inhomogeneities or
clumps in the water vapor layer. The observed inhomogeneities might be caused
by pulsation- and shock-induced chaotic motion in the extended atmosphere.
