Periods (top panel) and associated pulsation amplitudes (bottom panel) of the periodic variables (other than purely eclipsing binaries) as a function of their V′ magnitude. Multiple periods of the same object are connected with solid lines. The color of each marker indicates the group to which the star belongs: red for group 1 (SPB), green and cyan for group 2 (new class, see text), blue for group 3 (δ Sct), magenta for group 4 (γ Dor) and black for either red giants or periodic variables fainter than V′ = 15.5 mag, unless clearly belonging to one of groups 1 to 4 (see text).