  For a constant density of spinless fermions in strongly disordered two
dimensional clusters, the energy level spacing between the ground state and the
first excitation is studied for increasing system sizes. The average indicates
a smooth opening of the gap when the Coulomb energy to Fermi energy ratio $r_s$
increases from 0 to 3, while the distribution exhibits a sharp
Poisson-Wigner-like transition at $r_s \approx 1$. The results are related to
the transition from Mott to Efros-Shklovskii hopping conductivity recently
observed at a similar ratio $r_s$.
