The genus Xanclomys, named by Rigby J.K. in 1980, is also known as Xancolomys. The identification is based on a single species, Xanclomys mcgrewi. Fossil remains were found in the Torrejonian (Paleocene)-age strata of the Swain Quarry in Wyoming (U.S.). Affinities are uncertain. There's perhaps a second, unnamed species.
References
Rigby (1980), Swain Quarry of the Fort Union Formation, Middle Paleocene (Torrejonian), Carbon County, Wyoming: geologic setting and mammalian fauna. Evolutionary Monographs, 3, vi+179pp.
Kielan-Jaworowska Z & Hurum JH (2001), "Phylogeny and Systematics of multituberculate mammals". Paleontology44, p. 389-429.
Much of this information has been derived from [1] MESOZOIC MAMMALS: Ptilodontoidea, an Internet directory.