The outer limits of propagation of ducted magnetospheric whistlers have been estimated by analysis of whistlers recorded at Byrd (longwire) station, Antarctica (L~7) during two 3-day periods of magnetic calm (July 2-4 and July 8-10, 1967). Path radii in an IGRF/Olson-Pfitzer geomagnetic field model were determined from the nose frequencies of observed whistlers. On the nightside, the path radii typically extended to about 5 RE geocentric distance. The dayside radii were generally larger; on 3 of the days they were observed in the 6-8 RE range in the afternoon sector and during periods of 1 or more hours in duration. It was also found that on most hours in the 6 days, the outer propagation limits were located within ΔR<0.3 RE of a plasmapause-type density falloff, usually on its inner side. From these results and earlier results on path radii, it is concluded that the distribution of ducted whistlers near 80 ¿W longitude tends to reflect the instantaneous distribution of disturbance processes such as perturbing substorm electric fields. The path limits tend to fall well within the plasmapause following disturbance onset, but move beyond it during the early stages of recovery and then approach coincidence with the larger plasmasphere limits during prolonged quiet periods.