Wikipedia
Cimolodon is a genus of mammal from the Upper Cretaceous of North America. It was a member of the extinct order of Multituberculata within the suborder Cimolodonta and possibly the family Cimolodontidae.
The genus Cimolodon was named by Othniel Charles Marsh in 1889. It is also known as Allacodon (partly); Cimolomys (partly); Halodon (Marsh 1889); Nanomys ("small mouse") (Marsh 1889); nomyops (Marsh 1892); Ptilodus (partly). While some Cimolomys material has indeed been referred to Cimolodon, that doesn't necessarily mean that the whole genus or a particular species has. It could well be that one-time Cimolodon fossils have subsequently also been referred to Cimolomys as well.
"Cimolodon seems to be more closely related to the Paracimexomys group than are other ptilodontoideans," (Kielan-Jaworowska & Hurum, 2001, p. 404). Odd as it may sound, the placement of this genus within Cimolodontidae is tentative. Its tooth enamel is gigantoprismatic, while its possible relatives favor a microprismatic style (p. 418 ibid.).