  We have observed 26 interspecies Feshbach resonances at fields up to 2050 G
in ultracold $^6$Li+$^{23}$Na mixtures for different spin-state combinations.
Applying the asymptotic bound-state model to assign the resonances, we have
found that most resonances have d-wave character. This analysis serves as
guidance for a coupled-channel calculation, which uses modified interaction
potentials to describe the positions of the Feshbach resonances well within the
experimental uncertainty and to calculate their widths. The scattering length
derived from the improved interaction potentials is experimentally confirmed
and deviates from previously reported values in sign and magnitude. We give
prospects for $^7$Li+$^{23}$Na and predict broad Feshbach resonances suitable
for tuning.
