  We establish the presence of topologically protected edge states on the (001)
surface of HgS in the zinc-blende structure using density-functional electronic
structure calculations. The Dirac point of the edge state cone is very close to
the bulk valence band maximum. The Dirac cone is extremely anisotropic with a
very large electron velocity along one diagonal of the surface elementary cell
x' and a nearly flat dispersion in the perpendicular direction y'. The strong
anisotropy originates from a broken fourfold rotoinversion symmetry at the
surface.
