  We present a programme of spectroscopic observations of galaxies in a sample
of optically-selected clusters taken from the catalogue of Couch et al (1991).
Previous ROSAT observations of these clusters have shown them to have lower
X-ray luminosities, given their optical richness, than might be expected on the
basis of local samples. In the present paper we extend this work by determining
velocity dispersions of a subsample of the clusters. We confirm the dynamical
reality of all but one of the original sample, and find velocity dispersions
comparable with present-day clusters of equivalent comoving space density.
Thus, in the context of the $L_X-\sigma$ relation for present-day clusters,
there is evidence for a higher velocity dispersion at fixed X-ray luminosity.
  A key question is whether the high velocity dispersions are indicative of the
gravitational potential. If they are, the X-ray luminosities measured in Bower
et al., 1994 (Paper I), would then imply an implausibly low efficiency of X-ray
generation. Alternatively, the discrepancy could be explained if the clusters
were systems of lower virial temperature, in which the apparent velocity
dispersion is inflated by an infalling, unrelaxed halo. This might result
either from an increase with redshift in the infall rate for clusters, or from
the preferential selection of clusters embedded in filaments oriented along the
line of sight. Since clusters with similar properties can be found in local
optically selected catalogues, we suggest that the latter explanation is more
likely.
