A family of matrix languages (or two-dimensional languages) is called an abstract family of matrices (AFM) if it is closed under the six operations of union, (column) catenation, Kleene closure. ε-free homomorphism, inverse homomorphism, and intersection with regular matrix languages. This paper shows that the class of sets accepted by nondeterministic two-dimensional on-line tessellation acceptors is an AFM, but the class of sets accepted by deterministic two-dimensional on-line tessellation acceptors is not an AFM.