Such planes are readily
found in the diagrams of ITA83 as planes parallel to
just one axis and projected as dashed lines, e.g.xxz
in P4bm and (Nos. 100 and 113). In particular,
Table 3 is exactly in conformity with the
distinction shown between Ek and En planes. See,
for instance, the dashed and dot-dashed lines for R3m
and R3c (Nos. 160 and 161).