We present a new generic type of pattern generated by bounding walls on the interface between miscible liquids in a horizontally vibrated cell. The pattern is observed in laboratory experiments and numerical simulations below and above the frozen-wave instability threshold. At the threshold, a competition develops between the new "fish-spine" pattern and frozen waves, while above the threshold these two kinds of patterns may coexist in spatially separated domains. We propose a theoretical model for the formation mechanism of the fish-spine pattern and its spreading along the interface.