  Certain limits of the duality between M-theory on ${T^5/Z_2}$ and IIB on K3
are analyzed in Matrix theory. The correspondence between M-theory five-branes
and ALE backgrounds is realized as three dimensional mirror symmetry.
Non-critical strings dual to open membranes are explicitly described as gauge
theory excitations. We also comment on Type IIA on K3 and the appearance of
gauge symmetry enhancement at special points in the moduli space.
