quantum cellular automata (qca) are models of quantum computation of particular interest from the point of view of quantum simulation. quantum lattice gas automata (qlga - equivalently partitioned quantum cellular automata) represent an interesting subclass of qca. prior work on qca has investigated the relationship between these two classes of models. in the present paper we establish necessary and sufficient conditions for unbounded, finite quantum cellular automata (qca) (finitely many active cells in a quiescent background) to be quantum lattice gas automata. we define a local condition that classifies those qca that are qlga, and we show that there are qca that are not qlga.