Hesperomys was introduced by
George Robert Waterhouse in 1839 for the American rodents with cusps arranged in two series. The name combines the Greek ἑσπερος "west" and μυς "mouse". He considered it possible that species of
Hesperomys would be found in the Old World, but did not doubt that the Americas were their chief abode. He included as species
Mus bimaculatus (=
Calomys laucha),
Mus griseo-flavus (=
Graomys griseoflavus),
Mus Darwinii (=
Phyllotis darwini),
Mus zanthopygus (=
Phyllotis xanthopygus),
Mus galapagoensis (=
Aegialomys galapagoensis),
Symidon hispidum (=
Sigmodon hispidus),
Mus leucopus (=
Peromyscus leucopus), and the
woodrats (
Neotoma). In following years, authors like
Johann Andreas Wagner and
Spencer Fullerton Baird expanded the genus to include additional American species, such as those placed now in
Scapteromys,
Oxymycterus,
Abrothrix, and
Peromyscus. In 1874,
Elliott Coues designated
Mus bimaculatus Waterhouse as the
type species of
Hesperomys. In 1888,
Herluf Winge used
Hesperomys in a sense similar to modern
Calomys (but confusingly placed species related to what is now known as
Oryzomys in
Calomys), but in the same year
Oldfield Thomas argued that
Hesperomys could not be separated from the
hamsters (
Cricetus). In 1896, however, he united it with
Eligmodontia instead, where it remained until he reinstated it for modern
Calomys in 1916. He did not use
Calomys (introduced by Waterhouse in 1837 for
Mus bimaculatus), because he thought it to be
preoccupied by an earlier name
Callomys d'Orbigny and Geoffroy, 1830. In 1962,
Philip Hershkovitz noted that the
International Code of Zoological Nomenclature mandates that a name cannot be considered preoccupied even when it differs by only one letter from another, so
Callomys cannot invalidate
Calomys. As
Calomys Waterhouse, 1837, and
Hesperomys Waterhouse, 1839, both had
Mus bimaculatus as their type species, the two are
objective synonyms and the older name,
Calomys, prevails; since then,
Hesperomys has no longer been in use as a valid name. ==References==