  The low energy electronic spectra of rotationally faulted graphene bilayers
are studied using a long wavelength theory applicable to general commensurate
fault angles. Lattice commensuration requires low energy electronic coherence
across a fault and preempts massless Dirac behavior near the neutrality point.
Sublattice exchange symmetry distinguishes two families of commensurate faults
that have distinct low energy spectra which can be interpreted as
energy-renormalized forms of the spectra for the limiting Bernal and AA stacked
structures. Sublattice-symmetric faults are generically fully gapped systems
due to a pseudospin-orbit coupling appearing in their effective low energy
Hamiltonians.
