distichous

In examining the form, and inquiring into the habits of this species; we cannot but observe a slight approach to Tamias, and a more distant one to Spermophilus. Its ears are placed farther back than in the Squirrels generally, its tail is only sub-distichous, and withal it often digs its own burrow, and lives indiscriminately in the ground and on trees. In all these particulars it appears, in connexion with the Downy Squirrel, (Sc. lanuginosus,) to form a connecting link between Sciurus and Tamias.

1846, John James Audubon, John Bachman, The Viviparous Quadrupeds of North America, page 131