Stygimys is an extinct mammal genus from the Upper Cretaceous and Paleocene of North America. It was a member of the extinct order Multituberculata within the suborder Cimolodonta, family Eucosmodontidae.The genus Stygimys ("Styx mouse") was named by R.E. Sloan and Leigh Van Valen in 1965. The name comes from the Styx (river of hell) from Greek mythology. The genus has also been known as Catopsalis (partly); Cimexomys (partly); Eucosmodon (partly); and Parectypodus (partly).