  The symmetries of a free incompressible fluid span the Galilei group,
augmented with independent dilations of space and time. When the fluid is
compressible, the symmetry is enlarged to the expanded Schroedinger group,
which also involves, in addition, Schroedinger expansions. While incompressible
fluid dynamics can be derived as an appropriate non-relativistic limit of a
conformally-invariant relativistic theory, the recently discussed Conformal
Galilei group, obtained by contraction from the relativistic conformal group,
is not a symmetry. This is explained by the subtleties of the non-relativistic
limit.
