The ? Canis Majoris stars are sharp-lined stars in the spectral-type range B0.5 to B2 which show radial-velocity and light changes in periods of the order of three to seven hours. The light amplitude is usually only a few hundredths of a magnitude; the radial-velocity amplitudes range from 5 km/sec to 150 km/sec. The 18 stars at present known to be ? Canis Majoris variables are listed in Table 33. The period which van Hoof (1962a) considers to be the fundamental period of pulsation is listed in column seven. This period is not necessarily identical with the dominant period of the radial-velocity or light variations.