A 2-dimensional mixture theory is developed for wave propagation in a laminated medium in which every layer is made of a fiber reinforced composite material with the angle of reinforcement alternating from layer to layer. The developed theory contains as special cases the 2-dimensional mixture theory for a laminated medium made of isotropic layers, as well as the equivalent modulus theories for bi-directionally and unidirectionally fiber reinforced composites. The developed mixture theory is applied to the problem of a semi-infinite crack in the composite which is under dynamic loading. The induced fracture mode of the crack is of mixed type and contains both Mode I and Mode II types of opening. A numerical method of solution is applied to the four coupled mixture equations of motion in the average displacements and results are given for the dynamic stress fields in the composite.