  The density of states of a 2D d-wave superconductor in the vortex state with
applied magnetic field $\bf H$ in the plane is shown to exhibit fourfold
oscillations as a function of the angle of the field with respect to the
crystal axes. We find further that the frequency dependence of the density of
states and the temperature dependence of transport coefficients obey different
power laws, thus leading to different magnetic scaling functions, for field in
the nodal and anti-nodal direction. We discuss the consequences of this
anisotropy for measurements of the specific heat.
