Opinions from P. D. Gingerich 1991
- 'Cardiolophus belongs to Isectolophidae'
- 'Cardiolophus radinskyi belongs to Cardiolophus'
- 'Eohippus is a subjective synonym of Hyracotherium'
- 'Eohippus pernix is recombined as Hyracotherium pernix'
- 'Eohippus pernix is a subjective synonym of Hyracotherium vasacciense' according to Kitts 1956
- 'Eohippus pernix belongs to Eohippus' according to Hay 1930
- 'Eohippus resartus is a subjective synonym of Hyracotherium cristatum'
- 'Eohippus resartus is a subjective synonym of Hyracotherium angustidens' according to Kitts 1956
- 'Eohippus validus is a subjective synonym of Hyracotherium vasacciense'
- 'Eohippus validus is a subjective synonym of Hyracotherium vasacciense' according to Matthew 1899
- 'Eohippus validus is a subjective synonym of Hyracotherium vasacciense' according to Trouessart 1898
- 'Eohippus venticolus is recombined as Hyracotherium venticolum'
- 'Homogalax aureus belongs to Homogalax'
- 'Homogalax planeticus belongs to Homogalax' according to Gingerich 1980
- 'Homogalax planeticus is a subjective synonym of Cardiolophus radinskyi'
- 'Hyrachyus singularis is a subjective synonym of Hyracotherium vasacciense'
- 'Hyracotherium aemulor belongs to Hyracotherium'
- 'Hyracotherium craspedotum belongs to Hyracotherium'
- 'Hyracotherium cristatum belongs to Hyracotherium'
- 'Hyracotherium cristatum is a subjective synonym of Hyracotherium angustidens' according to Kitts 1956
- 'Hyracotherium sulcatus is a subjective synonym of Hyracotherium index'
- 'Orohippus angustidens is a subjective synonym of Hyracotherium index'
- 'Orohippus cuspidatus is a subjective synonym of Hyracotherium index'
- 'Orotherium cristonense is a subjective synonym of Hyracotherium vasacciense'
- 'Orotherium cristonense is a subjective synonym of Hyracotherium angustidens' according to Kitts 1956
- 'Orotherium index is recombined as Hyracotherium index'
- 'Orotherium loevii is a subjective synonym of Hyracotherium index'
- 'Pliolophus is a subjective synonym of Hyracotherium'
- 'Protorohippus is a subjective synonym of Hyracotherium'
- 'Systemodon primaevus is a subjective synonym of Homogalax protapirinus'
- 'Systemodon protapirinum is recombined as Homogalax protapirinus'
- 'Systemodon semihians is recombined as Cardiolophus semihians'