They contain a disk and a bulge, but little to no interstellar gas and no spiral arms.
They are nearly circular in profile, with no visible disk or central bulge.
They are uneven in distribution - neither circular, disklike, or elliptical - and contain no dominant central bulge.
They contain a bar of stellar material that extends out from the central bulge before trailing off into spiral arms.
They are elongated and elliptical, but have no visible disk or central bulge.