  The neutrino oscillation data find a good approximation in the so-called
tri-bimaximal pattern. Recently a paper appeared showing that also the
bimaximal pattern, which is already ruled out by the measurements, could be a
very good starting point in order to describe the lepton mixing. In this paper
I review both the flavour structures and then I present an explicit flavour
model based on the discrete group S4, in which the PMNS mixing matrix is of the
bimaximal form in first approximation and after it receives corrections which
bring it in agreement with the data. The resulting spectrum of light neutrinos
shows a moderate normal hierarchy and is compatible, within large ambiguities,
with the constraints from leptogenesis as an explanation of the baryon
asymmetry in the Universe.
