  Different sequences of ellipsoids are represented on the ellipticity-rotation
plane. The rotation parameter is defined as the ratio of kinetic energy related
to the mean tangential equatorial velocity component to kinetic energy related
to tangential equatorial component velocity dispersion and residual motions.
Systems with isotropic stress tensor are considered as adjoint configurations
to their counterparts with anisotropic stress tensor, different angular
momentum, and equal remaining parameters. Both nonequilibrium figures and
figures elongated by imaginary rotation are represented on the
ellipticity-rotation plane. An application is made to a reduced sample of
elliptical galaxies. The position on the ellipticity-rotation plane of both
sample objects and related adjoint configurations with isotropic stress tensor
is inferred from existing observations within the SAURON project. With a single
exception, slow rotators are characterized by low ellipticities, low anisotropy
parameters, and low rotation parameters, while the contrary holds for fast
rotators. A possible interpretation of slow rotators as nonrotating at all and
elongated due to negative anisotropy parameters, is exploited. Finally, the
elliptical side of the Hubble sequence is interpreted as a sequence of
equilibrium (adjoint) configurations where the ellipticity is an increasing
function of the rotation parameter, slow rotators correspond to early classes
and fast rotators to late classes. In this view, boundaries are rotationally
distorted regardless of angular momentum and stress tensor, where rotation has
to be intended as due to additional kinetic energy of tangential equatorial
velocity components, with respect to spherical configurations with isotropic
stress tensor.
