Large vesper mouse

The large vesper mouse ("Calomys callosus") is a South American rodent species of the family Cricetidae.
It is found in Argentina, Bolivia, Brazil and Paraguay.
Its karyotype has 2n = 50 and FN = 66. It was formerly synonymized with "C. expulsus", but the latter has 2n = 66 and FN = 68.
It is particularly notable as the vector of Bolivian hemorrhagic fever.