 As in all oryzomyines, the squamosal bone lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity, but "Lundomys" is unusual in that the squamosal and the tegmen tympani usually overlap when viewed from the side.In the mandible, the angular and coronoid processes are less well-developed than in "Holochilus".The capsular process of the lower incisor, a slight raising of the mandibular bone at the back end of the incisor, near the coronoid process, is small.