Rattus Fischer, 1803 . Natl. Mus. Nat. Paris, 2:128.

TYPE SPECIES: Mus decumanus Pallas, 1778 (see Hollister, 1916b; = Mus norvégiens Berkenhout, 1769).

SYNONYMS: Acanthomys (Gray, 1867, not Lesson, 1842, or Tokuda, 1941), Christomys, Cironomys, Epimys, Geromys, Mollicomys; Octomys (Sody, 1941, not Thomas, 1922), Pullomys, Togomys .

COMMENTS: Rattus Frisch, 1775, is unavailable. Sody (1941) proposed the genera Christomys, Cironomys, Geromys, Mollicomys, Octomys, and Pullomys for various species we list in Rattus; all are nomina nuda. Togomys is based on R. exulans (Dieterlen, in Ansell, 1989a). Taxonomic changes altering the definition of Rattus as understood by Tate (1936), Ellerman (1941, 1949«, 1961), and Simpson (1945), were described and summarized by Misonne (1969), Musser (1981b), Musser and Newcomb (1983), Musser and Holden (1991), and Musser and Heaney (1992). Species we list here can be sorted into the following groups.

1. The norvegicus group. Rattus norvegicus, the type species of the genus, is divergent from Rattus rattus in morphology as well as electrophoretic and immunological traits (Chan, 1977; Chan et al., 1979; Baverstock et al., 1983«, c, 1986; Watts, in litt.)

2. The rattus group (adustus, argentiventer, baluensis, burrus, everetti, hoffmanni, koopmani, losea, lugens, mindorensis, mollicomulus, nitidus, osgoodi, palmarum, rattus, tanezumi, sikkimensis, simalurensis, tawitawiensis, tiomanicus, and turkestanicus). Morphology of these species generally reflects the conception of what is usually called subgenus Rattus (Musser and Holden, 1991). Whether or not this cluster, along with the norvegicus group, will eventually form the only contents of Rattus is a speculation that has to be assessed by systematic revision of the genus (Musser and Heaney, 1985, 1992; Musser and Holden, 1991). Comparative chromosomal data for many of these species were summarized by Musser and Holden (1991). Schwarz and Schwarz (1967) offered a most peculiar and idiosyncratic revision of the group.

3. Native Australian species (colletti, fuscipes, lutreolus, sordidus, tunneyi, and villosissimus), which were revised by Taylor and Horner (1973) and are reviewed by Watts and Aslin (1981); one {sordidus) also occurs in New Guinea. Results from biochemical and chromosomal studies indicated the species form a monophyletic cluster to the exclusion of either R. rattus or R. norvegicus (Baverstock et al., 19774, 1983«, 1986). Baverstock et al. (1983«) proposed a hypothesis of phylogenetic relationships based on cladistic analyses of electrophoretic, immunologic, and chromosomal data, and another proposed set of relationships assessed by isozyme elecrophoresis (Baverstock et al., 1986). Mahoney and Richardson (1988) cataloged taxonomic, distributional, and biological references. This group may also include the endemics from Timor {timorensis) and Flores (hainaldi). Furthermore, such endemic Nusa Tenggara (Lesser Sunda Isis) genera as Komodomys are morphologically similar to some members of the Australian Rattus.

4. Native New Guinea species {jobiensis, leucopus, mordax, novaeguineae, praetor, sanila, steini, and probably giluwensis), which are indigenous to New Guinea and adjacent archipelagos; one (leucopus) also occurs in NE Australia. All have been the subject of a systematic revision by Taylor et al. (1982, 1983). Known endemics of the Moluccas (elaphinus, feliceus, and probably morotaiensis) are also related to this group. Nature of the relationship among this group and members of Stenomys, members of the Australian cluster, and those genera of New Endemics native to the Philippine Isis (Musser and Heaney, 1992) remains to be resolved.

5. The xanthurus group (bontanus, foramineus, marmosurus, pelurus, and xanthurus), which occurs on Sulawesi and adjacent Peleng Isl, and may eventually be removed from Rattus (Musser and Holden, 1991).

Phylogenetic affinities of the remaining species listed below (annandalei, enganus, exulans, hoogerwerfi, macleari, montanus, nativitatis, ranjiniae, stoicus, and korinchi) are unresolved; some may eventually be excluded from the genus.