Mus callosus Rengger, 1830 Cricetidae Don E. Wilson Russell A. Mittermeier Thomas E. Lacher, Jr PYL2 Rengger 1830 [769,1060,2562,2608] Mammalia Cricetidae Calomys Animalia Rodentia 238 517 Chordata species callosus    709.    Large Vesper Mouse    French: Calomys de Rengger/ German: GroRRe Vespermaus/ Spanish: Ratén laucha grande   Other common names: Big Laucha   Taxonomy. Mus callosus Rengger, 1830, “am Ufer des Paraguaystromes, ungefahr unter dem sieben und zwanzigsten Breitengrade.”Interpreted by P. Hershkovitz in 1962 as “opposite mouth of Rio Bermejo, Department of Villa del Pilar, Paraguay.” Restricted byJ. R. Contreras in 1992 to vicinity of Ciudad Pilar, Corrientes, Argentina. This species is monotypic.    Distribution.N & E Bolivia, extreme W Brazil (Mato Grosso State), Paraguay, and N Argentina.   Descriptive notes.Head-body 99-122 mm, tail 78-110 mm, ear 16-19 mm, hindfoot 21-23 mm; weight 30-52 g. The Large Vesper Mouseis medium-sized, with long and moderately lax pelage or short and appressed in wetter habitats. Upperparts of body are ocherous to tawny and often with fine mix of black or dark brown; rump and sides are generally paler; weakly defined ocherous lateral band is sometimes present; and venter is whitish to gray, sometimes washed with buff, with individual hairs dark gray at their bases. Eye-ring is defined by buffy hair, sometimes evident. Tail is bicolored, grayish brown above and whitish below. Ears are small, rounded and lightly haired; pale-colored post-auricular patches are present. Forefeet and hindfeet are white above, with whitish ungual tufts; hindfeet are narrow. Mammae count is 10-14. Diploid number of 2n = 50 is often assigned to the Large Vesper Mouse.   Habitat.Various habitats from Dry Chaco and semideciduous forests to grassy enclaves, secondary growth, old fields, and agriculture-dominated landscapes.   Food and Feeding.The Large Vesper Mouseis granivorous, frugivore, and insectivorous.   Breeding.Nests of the Large Vesper Mouseare generally aboveground in clumps of grass or in branches of dead trees. Nests built in laboratory were spherical, made of finely shredded, interwoven plant material; those in the field were simple depressions hollowed in the ground 10-15 cm deep. Gestation is 22 days; litters average 5 young.   Activity patterns.The Large Vesper Mouseis nocturnal, crepuscular, and terrestrial, although some individuals were also arboreal in captivity.   Movements, Home range and Social organization.Densities of the Large Vesper Mouseare 3—4 ind/ha; home ranges are 100-1000 m?.   Status and Conservation.Classified as Least Concern on The IUCN Red List.   Bibliography.Alho et al. (1986), Caceres et al. (2011), Carroll et al. (2005), Contreras (1992), Contreras et al. (2003), Dunnum, Vargas, Bernal, D’Elia et al. (2016), Henriques et al. (2000), Hershkovitz (1962), Justines & Johnson (1970), Hurtado de Catalfo & \Wainberg (1974), Mallmann et al. (2011), Massoia & Fornes (1965d), Mello (1981, 1984), Petter et al. (1967), Prado & Kloetzel (1995), Prado et al. (1998), Rodrigues & Ferro (1998), Salazar-Bravo (2015¢), SalazarBravo, Dragoo et al. (2002), de la Sancha (2014), Svartman & de Almeida (1992), Vaz-de-Lima et al. (1992), Vieira (1999). 3818814615 238 517