  A sixth-order quadrupole boson Hamiltonian is used to describe 26 states
$0^+$ and 67 states $2^+$ which have been recently identified in $^{168}Er$.
Two closed expressions are alternatively used for energy levels. One
corresponds to a semi-classical approach while the other one represents the
exact eigenvalue of the model Hamiltonian. The semi-classical expression
involves four parameters, while the exact eigenvalue is determined by five
parameters. In each of the two descriptions a least square fit procedure is
adopted.
  Both expressions provide a surprisingly good agreement with the experimental
data.
