Opinions from J. Leidy 1869
- 'Agriochoerus belongs to Agriochoeridae'
- 'Anchippus belongs to Anchitheridae'
- 'Anchitheridae belongs to Solidungula'
- 'Anchitherium belongs to Anchitheridae'
- 'Anchitherium (Hypohippus) was reranked as Hypohippus and belongs to Anchitheridae'
- 'Anchitherium (Hypohippus) affinis is recombined as Hypohippus affinis'
- 'Anchitherium (Parahippus) was reranked as Parahippus and belongs to Anchitheridae'
- 'Anchitherium (Parahippus) cognatus is recombined as Parahippus cognatus'
- 'Anoplonassa forcipata belongs to Anoplonassa'
- 'Balaena palaeatlantica is recombined as Protobalaena palaeatlantica'
- 'Balaena prisca is recombined as Eschrichtius priscus'
- 'Balaenoptera pusilla is recombined as Eschrichtius pusillus'
- 'Canis indianensis belongs to Canis'
- 'Catodon vetus belongs to Catodon'
- 'Cetophis heteroclitus belongs to Cetophis'
- 'Colophonodon holmesii is recombined as Squalodon holmesii'
- 'Cynorca proterva is recombined as Squalodon protervus'
- 'Delphinapterus gabbii is recombined as Tretosphys gabbii'
- 'Delphinapterus lacertosus is recombined as Tretosphys lacertosus'
- 'Delphinapterus ruschenbergeri is recombined as Tretosphys ruschenbergeri'
- 'Delphinus calvertensis is recombined as Lophocetus calvertensis'
- 'Delphinus conradi is recombined as Priscodelphinus conradi'
- 'Delphinus occiduus belongs to Delphinus'
- 'Dorudon serratus belongs to Dorudon'
- 'Equus (Protohippus) was reranked as Protohippus and belongs to Equidae'
- 'Eschrichtius cephalus belongs to Eschrichtius'
- 'Eschrichtius leptocentrus belongs to Eschrichtius'
- 'Hemicaulodon effodiens belongs to Hemicaulodon'
- 'Hipparion affine belongs to Hipparion'
- 'Hipparion gratum belongs to Hipparion'
- 'Homocamelus belongs to Camelidae'
- 'Homocamelus caninus belongs to Homocamelus'
- 'Hoplocetus obesus belongs to Hoplocetus'
- 'Ixacanthus coelospondylus belongs to Ixacanthus'
- 'Macrophoca atlantica is recombined as Squalodon atlanticus'
- 'Manatus antiquus is recombined as Ischyrotherium antiquus'
- 'Megaptera expansa is recombined as Eschrichtius expansus'
- 'Ontocetus emmonsi belongs to Ontocetus'
- 'Oreodontidae belongs to Ruminantia'
- 'Orycterocetus crocodilinus is a subjective synonym of Orycterocetus cornutidens'
- 'Orycterocetus quadratidens belongs to Orycterocetus'
- 'Phoca debilis is recombined as Squalodon debilis'
- 'Phoca modesta belongs to Phoca'
- 'Phoca wymani belongs to Phoca'
- 'Phocageneus venustus belongs to Phocageneus'
- 'Phocodon holmesii belongs to Phocodon' according to Agassiz 1850
- 'Phocodon holmesii is an objective synonym of Squalodon pygmaeus'
- 'Physeter antiquus is replaced by Catodon vetus'
- 'Priscodelphinus acutidens belongs to Priscodelphinus'
- 'Priscodelphinus atropius belongs to Priscodelphinus'
- 'Priscodelphinus grandaevus is recombined as Tretosphys grandaevus'
- 'Priscodelphinus harlani belongs to Priscodelphinus'
- 'Priscodelphinus spinosus belongs to Priscodelphinus'
- 'Priscodelphinus stenus belongs to Priscodelphinus'
- 'Protobalaena belongs to Balaenidae'
- 'Protohippus placidus belongs to Protohippus'
- 'Rhabdosteus latiradix belongs to Rhabdosteus'
- 'Saurocetus gibbesii belongs to Saurocetus'
- 'Squalodon mento is recombined as Delphinodon mento'
- 'Squalodon pelagius belongs to Squalodon'
- 'Squalodon wymanii is recombined as Delphinodon wymani'
- 'Stenorhynchus vetus is recombined as Lobodon vetus'
- 'Stylemys belongs to Chelonia'
- 'Tretosphys uraeus belongs to Tretosphys'
- 'Trichechus virginianus belongs to Trichechus' according to Dekay 1842
- 'Zarhachis flagellator belongs to Zarhachis'
- 'Zarhachis tysonii belongs to Zarhachis'
- 'Zarhachis velox belongs to Zarhachis'
- 'Zeuglodon cetoides is recombined as Basilosaurus cetoides'
- 'Zeuglodon pygmaeus is recombined as Squalodon pygmaeus'