  The linear waves that propagate in a two fluid magnetised plasma allowing for
a non-gyrotropic perturbed ion pressure tensor are investigated. For
perpendicular propagation and perturbed fluid velocity a low frequency
(magnetosonic) and a high frequency (ion Bernstein) branch are identified and
discussed. For both branches a comparison is made with the results of a
truncated Vlasov treatment. For the low frequency branch we show that a
consistent expansion procedure allows us to recover the correct expression of
the Finite Larmor Radius corrections to the magnetosonic dispersion relation.
