A new species of the New Guinea endemic murine genus Coccymys is described, based on a small sample from Mt. Dayman and Mt. Simpson in the Maneau Range at the far eastern end of the Owen Stanley Ranges of eastern Papua New Guinea, and two specimens from the western portion of the Owen Stanleys, one from Smith's Gap near Mt. St. Mary, the other from Bulldog Road in the Wau area. Coccymys kirrhos, n. sp., is a vicariant relative of C. shawmayeri, which occurs in the Central Cordillera of Papua New Guinea extending from Mt. St. Mary in the east to the Telefomin region in the west. Coccymys shawmayeri in turn is the eastern montane vicariant of the western New Guinea C. ruemmleri, so far recorded only from the Snow Mountains in western New Guinea (Papua Province of Indonesia) and the eastern end of the Star Mountains over the border in the western section of Papua New Guinea. Coccymys ruemmleri and C. shawmayeri are regionally sympatric in western Papua New Guinea where the former is apparently restricted to high altitudes on the Star Mountains and the latter occurs at lower altitudes in the highlands bounding the Telefomin Valley. The ranges of C. shawmayeri and C. kirrhos, n. sp., overlap at the western section of the Owen Stanley Ranges, and both species have been caught at Bulldog Road, but in different years. This linearly distributed trio of species has been found only in the montane forests and alpine grasslands of the Central Cordillera—there are no records from mountains on Vogelkop Peninsula and the Huon Peninsula, nor from any of the north coast ranges. The new species is described within the context of rediagnosing the genus Coccymys, and documenting morphometric and geographic limits of C. ruemmleri and C. shawmayeri based on most specimens stored in collections of museums. This material consists primarily of museum study skins and accompanying skulls, some fluid-preserved specimens, skeletal fragments from modern samples of owl pellets, and Holocene and Late Pleistocene fossils (for C. ruemmleri only). All species of Coccymys are nocturnal and scansorial; stomach contents from samples of C. shawmayeri indicate the diet consists of seeds, fruit, and arthropods.

The taxon albidens is represented by six modern examples collected at 2800 m and 3225 m in 1938 from the northern slopes of the Snow Mountains of western New Guinea, and three Late Pleistocene fossils obtained from the same region. The species was initially described as a Melomys (Tate, 1951); later an alliance with Coccymys was suggested (Flannery, 1990; Menzies, 1990; Musser and Carleton, 1993), but restudy of anatomical traits (derived solely from stuffed skins with accompaning skulls) reveals a degree of morphological divergence not only from species in Coccymys but from any other “Old Endemic” New Guinea murine. A new genus, Brassomys, sampled by only six modern specimens and three Late Pleistocene fossils, is proposed to embrace albidens.