Vesper mouse

Vesper mice are rodents belonging to a genus "Calomys". They are widely distributed in South America. Some species are notable as the vectors of Argentinian hemorrhagic fever and Bolivian hemorrhagic fever.
The genus was originally named "Hesperomys", but was changed to "Calomys" since 1962.
History.
"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.