The AE-C spacecraft skimmed through the southern polar cusp over a wide range of magnetic local times (approx. =1030-1230 MLT) at approximately 71D invariant latitude during a large magnetic storm on May 16, 1975. The spacecraft was at a constant altitude of 283 km and was spinning at one revolution per 14.6 s. Low-energy electrons (0-500 eV) were measured with the photoelectron spectrometer experiment, electrons and protons with energies between 200 eV and 25 keV were measured with the low-energy electron experiment, and ionospheric temperatures with the cylindrical Langmuir probe experiment. The cusp was identified by the presence of intense fluxes of low-energy electrons and protons with Maxwellian energy spectra similar to those acquired by previous experiments at higher altitudes. The remarkable feature apparent from the AE-C observations reported here is the marked difference between the pitch angle distribution for th electrons and protons. The protons were observed to be flowing downward along the geomagnetic field lines in the cusp, whereas the pitch angles of the low-energy electrons behaved in a peculiar fashion. During three revolutions of the spacecraft, intense fluxes of low-energy electrons were observed at all pitch angles. High ionospheric electron temperatures (>3000/sup 0/K) were observed in the cusp, and the highest temperatures (approx. =4000/sup 0/K) occurred in the same region as the nearly 4..pi.. isotropic electron fluxes. These characteristics cannot be explained by field-aligned potential drops caused by double layers or anomalous resistivity. The absence of electron fluxes with higher energies (>1 keV) in this region would also eliminate various current-driven instabilities as the cause. We suggest that the low-energy electrons are scattered and that their pitch angles are isotropized by magnetic fluctuations associated with the Kelvin-Helmholtz instability caused by shear in the proton flow into the cusp.