  Lenticular galaxies with M_B < -21.5 are almost exclusively unbarred, whereas
both barred and unbarred objects occur at fainter luminosity levels. This
effect is observed both for objects classified in blue light, and for those
that were classified in the infrared. This result suggests that the most
luminous (massive) S0 galaxies find it difficult to form bars. As a result the
mean luminosity of unbarred lenticular galaxies in both B and IR light is
observed to be ~0.4 mag brighter than than that of barred lenticulars. A small
contribution to the observed luminosity difference that is found between SA0
and SB0 galaxies may also be due to the fact that there is an asymmetry between
the effects of small classification errors on SA0 and SB0 galaxies. An E galaxy
might be misclassified as an S0, or an S0 as an E. However, an E will never be
misclassified an SB0, nor will an SB0 ever be called an E. This asymmetry is
important because elliptical (E) galaxies are typically twice as luminous as
lenticular (S0) galaxies. The present results suggest that the evolution of
luminous lenticular galaxies may be closely linked to that of elliptical
galaxies, whereas fainter lenticulars might be more closely associated with
ram-pressure stripped spiral galaxies. Finally it is pointed out that fine
details of the galaxy formation process might account for some of the
differences between the classifications of the same galaxy by individual
competent morphologists.
