A formalism is developed for the partial wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of $eta$ and $pi^0$ mesons. Different interpretations of a dip-bump structure of the $eta$ photoproduction cross sect
ion in the 1670 MeV region are presented and discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.
