  We present a simple and efficient Finite-Difference Time-Domain (FDFD) scheme
for simulating dispersive (Lorentz-Debye) bianisotropic metasurfaces. This
scheme replaces the conventional FDTD update equations by augmented update
equations where the effect of the metasurface, positioned at a virtual node (or
node plane) in the Yee grid, is accounted for by judiciously selected auxiliary
polarization functions, based on the Generalized Sheet Transition Conditions
(GSTCs). This scheme is computationally -- time- and memory-wise -- more
efficient and easier to implement than a previously reported scheme for
dispersive metasurfaces. It is validated in three illustrative examples.
