  We point out the possibility of occurring instabilities in Laughlin liquids
of rotating dipolar fermions with zero thickness. Previously such a system was
predicted to be the Laughlin liquid for filling factors being greater and equal
to 1/7. However, from intra-Landau-level excitations of the liquid in the
single-mode approximation, the roton minima become negative and Laughlin
liquids are unstable for filling factors being less and equal to 1/7. We then
conclude that there are correlated Wigner crystals for filling factors being
less and equal to 1/7.
