  High-resolution images of 7 newly identified BL Lac objects (among them one
BL Lac candidate) at z < 0.2 from the Einstein Slew Survey are presented for
the first time. In all cases we were able to resolve the host galaxy. Our
2-dimensional analysis of the host galaxies shows that all these BL Lac objects
are embedded in elliptical galaxies with an average M_R = -23.1 and r_e = 10
kpc. One BL Lac might have both a bulge and an underlying disk. These results
are similar to those obtained for the hosts of other BL Lac objects.
  We searched in our BL Lac objects for host galaxies, whose surface brightness
distribution does not follow a pure de Vaucouleurs law and determined the
statistical significance with numerical simulations. In two BL Lac objects (1ES
1255+244 and 1ES 1959+650) significant deviations were found.
  The environments of the BL Lac objects are highly interesting. In at least
two (perhaps three) cases we found evidence for interaction. All BL Lac objects
(except one) have at least 2 companions, some of which are bright, within a
projected distance of 60 kpc from the BL Lac. In two cases we found 5
companions within 50 kpc. This implies that gravitational interaction is
potentially important to the BL Lac phenomenon at least in these sources.
