  The water-Cherenkov tanks of the Pierre Auger Observatory can detect
particles at all zenith angles and are therefore well-suited for the study of
inclined and horizontal air showers (60 - 90 degrees). Such showers are
characterised by a dominance of the muonic component at ground, and by a very
elongated and asymmetrical footprint which can even exhibit a lobular structure
due to the bending action of the geomagnetic field. Dedicated algorithms for
the selection and reconstruction of such events, as well as the corresponding
acceptance calculation, have been set up on basis of muon maps obtained from
shower simulations.
