Irregularities in Side-Feeding Patterns, Energies, and Multipolarities in theEr154Yrast Cascade to Spin 36

States of ${}_{}{}^{154}{}_{}{}^{}\mathrm{Er}$ were studied by means of the (${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$4n$) and (${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$,$4n$) reactions. Beginning with a 40-nsec isomeric state [$J^{\pi }=({10}^{-},{11}^{-})$], an intensely populated unusual cascade of $\Delta J=2\mathrm{}$ and $\Delta J=1\mathrm{}$ transitions was established up to spin (35,36) and 12.5 MeV excitation. On an $E$ vs $I(I+1\mathrm{})\mathrm{}$ plot the yrast levels form a series of straight-line segments with side feeding occurring primarily at the ends of segments. A second cascade of even-spin, even-parity levels from the ground state to $J^{\pi }={18}^{+}$ (quasi-ground-state band) does not exhibit these properties.