Opinions from W. D. Matthew and R. A. Stirton 1930
- 'Equus (Protohippus) perditus is recombined as Protohippus perditus'
- 'Equus cumminsii is recombined as Plesippus cumminsii'
- 'Equus eurystylus is recombined as Hipparion eurystyle'
- 'Equus eurystylus is recombined as Hipparion eurystyle' according to Hay 1930
- 'Equus minutus is replaced by Hipparion phlegon' according to Matthew 1925
- 'Equus minutus is replaced by Hipparion phlegon'
- 'Equus minutus is replaced by Hipparion phlegon' according to Hay 1930
- 'Equus phlegon is recombined as Hipparion phlegon'
- 'Equus phlegon is recombined as Hipparion phlegon' according to Matthew 1926
- 'Equus phlegon is recombined as Hipparion phlegon' according to Matthew 1925
- 'Hipparion minor is a subjective synonym of Hipparion sellardsi'
- 'Hipparion occidentale belongs to Hipparion'
- 'Hipparion sellardsi belongs to Hipparion'
- 'Hippidium interpolatum is recombined as Pliohippus interpolatus'
- 'Hippotherium montezumae is recombined as Hipparion montezuma'
- 'Hippotherium sinclairi is recombined as Hipparion sinclairi'
- 'Hippotherium sinclairi is recombined as Hipparion sinclairi'
- 'Merychippus mirabilis is recombined as Pliohippus mirabilis'
- 'Neohipparion is a subjective synonym of Hipparion'
- 'Neohipparion whitneyi is recombined as Hipparion whitneyi'
- 'Neohipparion whitneyi is recombined as Hipparion whitneyi' according to Hay 1930
- 'Pliauchenia (Megatylopus) gigas is recombined as Paracamelus gigas'
- 'Pliohippus belongs to Equidae'
- 'Pliohippus fairbanksi is a nomen dubium'
- 'Pliohippus pernix belongs to Pliohippus'
- 'Pliohippus proversus is recombined as Plesippus proversus'
- 'Pliohippus proversus is recombined as Plesippus proversus'
- 'Pliohippus robustus belongs to Pliohippus'
- 'Protohippus (Calippus) belongs to Protohippus'
- 'Protohippus ansae belongs to Protohippus'
- 'Protohippus coalingensis is a nomen dubium'
- 'Protohippus lenticularis is recombined as Hipparion lenticulare'
- 'Protohippus lenticularis is recombined as Hipparion lenticulare' according to Hay 1930
- 'Protohippus pachyops is recombined as Pliohippus pachyops'
- 'Protohippus placidus is recombined as Protohippus (Calippus) placidus'