Recent observations show that extremely narrow emission lines are present in the spectrum of the terrestrial myriametric radiation, which on the basis of earlier observations has been characterized as nonthermal continuum radiation. The occurrence of these monochromatic emission is not predicted by previously published theories for the radiation. A linear instability, exciting low frequency electrostatic turbulence, is required by theories invoking a nonlinear coalescence to produce the radiation, but there are no conclusive observations associating low frequency electrostatic waves with the sources of myriametric radiation. In this study, the possibility that the radiation is produced by a nonlinear decay of electrostatic Bernstein waves with frequency near the upper hybrid frequency is considered. This mechanism can explain the narrow spectral lines, and does not require a linear instability at low frequencies.