  The surface Fermi arc states in $Z_2$ Weyl semimetals $A_3 Bi$ (A=Na, K, Rb)
are studied by employing a continuum low-energy effective model. It is shown
that the surface Fermi arc states can be classified with respect to the
ud-parity symmetry. Because of the symmetry, the arcs come in mirror symmetric
pairs. The effects of symmetry breaking terms on the structure of the Fermi
arcs are also studied. Among other results, we find at least two qualitatively
different types of the surface Fermi arcs. The arcs of the first type link
disconnected sheets of the bulk Fermi surface, while arcs of the second type
link different points of the same bulk Fermi surface sheet.
