Diplacodon progressum Peterson is not referable to the genus Diplacodon Marsh and is assigned the new generic name Pseudodiplacodon. Diplacodon is regarded as a nomen dubium, but may be a senior synonym of Eotitanotherium, a genus that is clearly distinct from Pseudodiplacodon. Only the type species of Pseudodiplacodon is accepted as valid, although there is one large individual belonging to this genus that could potentially represent a second species. Recognition of a second species is regarded as inappropriate, however, in the absence of additional specimens or distinct character differences.