Twinleaf, Jeffersonia diphylla

A subspecies of the Midland shooting star, Dodecatheon meadia jeffersoni

Giant Ground Sloth, Megalonyx jeffersonii

Jefferson Mammoth, Mammuthus jeffersonii (sometimes demoted to the sub-species, Mammuthus columbi jeffersoni).

An early mammal, Baioconodon jeffersoni

The earliest known squirrel, Douglassia jeffersoni

Traversodont (an early cynodont), Boreogomphodon jeffersoni

Jefferson salamander, Ambystoma jeffersonianum 

Blue Ridge Seal salamander, Desmognathus jeffersoni

A subspecies of the American badger, Taxidea taxus jeffersoni

A crawfish, Orconectes jeffersoni

Two parastitic ‘worms’, Rhipodocotyle jeffersoni and Pararhipidocotyle jeffersoni 

Jefferson’s short-nosed scorpion fly, Brachypanorpa jeffersoni  (endangered) 

A jumping spider, Dendryphantes jeffersoni

A bryozoan (coral-like creature), Floridinella jeffersoni

A jellyfish relative, Dicodonium jeffersoni

A fungus, Triphragmiopsis jeffersoniae

Part of this list was reprinted, with permission, from A Passion for Nature:  Thomas Jefferson and Natural History by Keith Thomson