Measurements of the heat capacity of a single crystal of ErRh//4B//4 have been made in the temperature range of 0. 4 K to 1. 5 K. This temperature range includes the temperature for the superconducting to ferromagnetic transition. The measurements include data taken on both heating and cooling of the sample. The transition as measured with the heat capacity is hysteretic in temperature and has a sharp maximum in both the heating and cooling cycles which occurs at the same temperature as the occurrence and disappearance of the satellite lines observed in the neutron scattering.