  We show that the so-called hidden potential symmetries considered in a recent
paper [Gandarias M., Physica A, 2008, V.387, 2234-2242] are ordinary potential
symmetries that can be obtained using the method introduced by Bluman and
collaborators. In fact, these are simplest potential symmetries associated with
potential systems which are constructed with single conservation laws having no
constant characteristics. Furthermore we classify the conservation laws for
classes of porous medium equations and then using the corresponding conserved
(potential) systems we search for potential symmetries. This is the approach
one needs to adopt in order to determine the complete list of potential
symmetries. The provenance of potential symmetries is explained for the porous
medium equations by using potential equivalence transformations. Point and
potential equivalence transformations are also applied to deriving new results
on potential symmetries and corresponding invariant solutions from known ones.
In particular, in this way the potential systems, potential conservation laws
and potential symmetries of linearizable equations from the classes of
differential equations under consideration are exhaustively described. Infinite
series of infinite-dimensional algebras of potential symmetries are constructed
for such equations.
