Third Discontinuity in the Yrast Levels ofEr158

Discrete yrast transitions from states with spins up to $I=38\mathrm{}$ have been observed in ${}_{}{}^{158}{}_{}{}^{}\mathrm{Er}$ via the reaction ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}({}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}, 4n\gamma )$. In addition to the pronounced backbend at $I=14\mathrm{}$ and the upbend at $I=28\mathrm{}$ previously known, the start of a third yrast discontinuity at $I=38\mathrm{}$ is indicated. Candidates for the $I=40\mathrm{}$ state are suggested and possible causes of the yrast discontinuity are discussed.