We study magnetotransport in lateral two- dimensional superlattices with periods on the order of 100 nm. Pronounced low-field transport anomalies reflect the interplay of two characteristic lengths of the system, the cyclotron radius { R} and the period { a}. Measurements at very low temperatures reveal quantum oscillations, periodic in the magnetic field { B}, which are superimposed upon the commensurability anomalies in the magnetoresistance { p}. We show that the latter effect can be interpreted in terms of quantized periodic orbits which takes into account the chaotic nature of the classical phase space.