The Articles illustrations are from Sefve 1910, Sefve 1912, and Boule et Thévenin 1920.

According to Alberdi (1993) the synonyms for
Hippidion principale are (among others): Onohippidion compressidens and Hippidium bonaerense;

Hippidion devillei: Hippidium bolivianum, Onohippidion peruanum, Parahipparion burmeisteri

ALBERDI M.T.A. 1993. Review of the genus Hippidion Owen, 1869 (Mammalia: Peridssodactyla) from the Pleistocene of South America. Zoological Journal of the Linnean Society, 108: 1-22.