Necromys is a genus of South American sigmodontine rodents allied to Akodon.

[2] Small rodents in South America were studied by the British zoologist Oldfield Thomas, curator at the Natural History Museum, London who erected the genus Bolomys in 1916.

[3] Members of the genus Necromys are spread out over a wide area of Central and South America.

[2] In 1987, the Argentine zoologist Osvaldo Reig listed the characteristics that distinguished the genus Bolomys from Akodon as; the braincase is broad and deep; the occipital region is short; the rostrum is fairly short; the rostrum tapers forwards when viewed from the side; the occiput is short and truncated; the zygomatic plate is broad, with the front edge straight or slightly concave; the upper incisors are orthodont or proodont; the molars are mesodont, broad and robust; the upper molars have transverse loops; and the lower molars have the lingual cusps slightly in front of the labial cusps.

[3] There is very little variation in the karyotype of Necromys, where 2n=34 is the rule, with N. lactens and N. lasiurus having diploid numbers of 2n=36.