  Fragment mass distributions from fission of excited compound nucleus
$^{178}$Pt have been deduced from the measured fragment velocities. The
$^{178}$Pt nucleus was created at the JAEA tandem facility in a complete fusion
reaction $^{36}$Ar + $^{142}$Nd, at beam energies of 155, 170 and 180 MeV. The
data are indicative of a mixture of the mass-asymmetric and mass-symmetric
fission modes associated with higher and lower total kinetic energies of the
fragments, respectively. The measured fragment yields are dominated by
asymmetric mass splits, with the symmetric mode contributing at the level of
$\approx1/3$. This constitutes the first observation of a multimodal fission in
the sub-lead region. Most probable experimental fragment-mass split of the
asymmetric mode, $A_{L}/A_{H}\approx 79/99$, is well reproduced by nuclear
density functional theory using the UNEDF1-HFB and D1S potentials. The
symmetric mode is associated by theory with very elongated fission fragments,
which is consistent with the observed total kinetic energy/fragment mass
correlation.
