  Specific heat, magnetic susceptibility and electrical transport measurements
were performed at ambient pressure on high-quality single crystal specimens of
CeRhIn5 down to ultra-low temperatures. We report signatures of an anomaly
observed in all measured quantities consistent with a bulk phase transition to
a superconducting state at T_c=110 mK. Occurring far below the onset of
antiferromagnetism at T_N=3.8 K, this transition appears to involve a
significant portion of the available low-temperature density of electronic
states, exhibiting an entropy change in line with that found in other members
of the 115 family of superconductors tuned away from quantum criticality.
