  We present a family of spin ladder models which admit exact solution for the
ground state and exhibit non-Haldane spin liquid properties as predicted
recently by Nersesyan and Tsvelik [Phys. Rev. Lett. v.78, 3939 (1997)], and
study their excitation spectrum using a simple variational ansatz. The
elementary excitation is neither a magnon nor a spinon, but a pair of
propagating triplet or singlet solitons connecting two spontaneously dimerized
ground states. Second-order phase transitions separate this phase from the
Haldane phase and the rung-dimer phase.
