  A modified version of the bilocal particle is presented in terms of complex
space time. Unusual constraint structure of the model is studied, and a new
concept of the physical equivalence is proposed in accordance with Dirac's
conjecture. It is found that in the quantum theory the physical state
conditions are compatible with existence of eigenstates of momentum only when
the dimension of space time is four. An example of scattering amplitude is
calculated.
