  In this work we study the effects of in-plane magnetic fields on thin films
of the Dirac Semimetal (DSM) \ce{Na2Bi} where one of the in-plane directions is
perpendicular to the $k$-separation between the two Weyl points for each spin
orientation. We show numerically that the states localized near the surface of
these thin films are related to the Fermi arc states in semi-infinite slabs.
Due to the anisotropy between the two in-plane directions, the application of a
magnetic field along these directions have differing effects. A field parallel
to the $k$ space separation between the Weyl points leads to a broadening of
the surface state band and a formation of an energy plateau, while a
perpendicular field shifts the energy where the hole and particle bands meet
upwards and sharpens the tips of the bands. We illustrate the effects of these
changes to the bandstructure by studying the transmission from a source segment
without a magnetic field to a drain segment with a field with the field and
interface at various in-plane directions.
