Cimolomys
Scientific classification

Kingdom: Animalia
Therapsida
Class: Mammalia
Order: Multituberculata
Family: Cimolomyidae
Genus: Cimolomys
Species
  C. clarki
  C. gracilis
  C. milliensis
  C. trochuus

Ref.

Cimolomys is a mammal genus from the Upper Cretaceous of North America. It was a member of the extinct order of Multituberculata.
For those of a technical inclination, it's within the Suborder of Cimolodonta, and the family Cimolomyidae.

Genus: Cimolomys Marsh OC, 1889
Aka: Allacodon (partly); Meniscoessus (partly); Ptilodus ( partly); Selenacodon (partly)
Reference: Marsh (1889), Discovery of Cretaceous Mammalia. Am. J. Sci, 3, xxxviii: p.177-180.

Species: Cimolomys clarki Sahni, 1972
Place: Texas & Wyoming
Country: USA
Age: Campanian-Maastrichtian, Upper Cretaceous
Remarks: Possibly also New Jersey. Probably weighed about the same as a malnourished rat, 300g.
Reference:

Species: Cimolomys gracilis Marsh OC, 1889
Aka: Cimolomys digona Marsh, 1889; Meniscoessus brevis; Ptilodus gracilus Osborn HF, 1893; Selenacodon brevis Marsh, 1889
Place: Montana, South Dakota, Wyoming & Sasakatchewan
Country: USA & Canada
Age: Maastrichtian, Upper Cretaceous
Remarks: A rat-sized 415g.
Reference: Marsh (1889), Discovery of Cretaceous Mammalia. Part II. Am. J. Sci. (3) 18, p.81-92.

Species: Cimolomys milliensis Eaton JG, 1993a
Place: Mill Creek, Utah
Country: USA
Age: Campanian, Upper Cretaceous
Remarks:
Reference:

Species: Cimolomys trochuus Lillegraven JA, 1969
Place:
Continent: North America
Age: Maastrichtian, Upper Cretaceous
Remarks: The holotype is in the collection of the University of Alberta.
Reference:

Page reference: Kielan-Jaworowska Z & Hurum JH (2001), Phylogeny and Systematics of multituberculate mammals. Paleontology 44, p.389-429.

(This information has been derived from [1] MESOZOIC MAMMALS; 'basal' Cimolodonta, Cimolomyidae, Boffiidae and Kogaionidae, an internet directory. As that's my webpage, there are no issues of copyright. Trevor Dykes)