  The spatial variation of the local density of states in optimally doped
Bi$_{2}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+\delta}$ (superconducting transition
temperature is 34 K) is studied by scanning tunneling spectroscopy at 4.2 K in
zero magnetic field. Two-dimensional density-of-states modulation aligned with
the Cu-O-Cu bond with a periodicity of about five lattice constants is
observed. It is found that this modulation accompanies the appearance of a new
energy gap of approximately 10 meV, whose gap edge peak is spatially modulated
in intensity. This gap coexists with the superconducting gap, the value of
which ranges from 10 meV to 60 meV.
