What is "zapus"

Zapus is a genus of North American jumping mice. It is the only genus whose members have the dental (tooth) formula: Zapus are the only extant mammals with a total of 18 teeth.

This genus was first separated from Old World jerboas by Coues in 1875. Members of this genus are very similar in appearance, all species having long tails, long hind feet and yellowish-brown pelage above and white below, the colors distinctly separated by a yellowish-orange lateral line.