This comment is intended to complete the picture of dispersion curves for surface polaritons for $n$-InSb with ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}}_{0}$ parallel to the surface and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}\ensuremath{\parallel}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}}_{0}$ as given by Wallis, Brion, Burstein, and Hartstein by including the dispersion curves for "degenerate" surface modes. The corresponding decay constants and electric field ratios have also been plotted.