Phyllotis chacoénsis J. A. Allen, 1901 Cricetidae Don E. Wilson Russell A. Mittermeier Thomas E. Lacher, Jr 4HCZW J. A. Allen 1901 [1876,2220,2442,2492] Mammalia Cricetidae Graomys Animalia Rodentia 241 520 Chordata species chacoensis    722.    Chaco Pericote    French: Pericote du Chaco/ German: Chaco-Neuweltfeldratte/ Spanish: Pericote del Chaco   Taxonomy. Phyllotis chacoénsis J. A. Allen, 1901, “Waikthlatingwayalwa, Chaco boreal [ Presidente Hayes],  Paraguay.”This enigmatic type locality corresponds to a disappeared mission founded by W. Grubb in the Paraguayan Chaco, about 80 km W Concepcion.   Eligmodontia griseoflavus centralisis treated as junior synonym of G. chacoensis, a proposition uncritically followed here. Nevertheless,it is important to note that this issue is not fully resolved because neither topotypes of G. chacoensisnor specimens from Paraguay have been included in recent comprehensive molecular and morphogeometrical assessments. Monotypic.    Distribution.SE Bolivia, NC Argentina, Paraguay, and extreme CS Brazil (Mato Grosso do Sul State).   Descriptive notes.Head-body 135 mm, tail 155 mm, ear 22 mm, hindfoot 27 mm; weight 75 g (all mean values from a large sample of adults). The Chaco Pericote is large and externally very similar to the Common Pericote (G. griseoflavus). Pelage is thick and soft; dorsum is yellowish brown to grayish drab, varied with black-tipped hairs; nose and top of head are more grayish; and venter is pure white. Ears are uniformly brown, thinly haired on both surfaces. Tail is much longer than head-body length, well-haired, and bicolored brown above and white below;it terminates in welldeveloped tuft. Dorsal surfaces of forefeet and hindfeet are white. Chromosomal complement is 2n = 41-42, FN = 44-46.   Habitat.Dense woodlands, gallery forests, and various marginal and ecotonal areas.   Food and Feeding.No information.   Breeding.Reproductive data from trapped Chaco Pericotes suggest that they breeds in autumn. An extensive study of a laboratory colony founded with individuals from southern Cordoba Province ( Argentina) retrieved several reproductive parameters. Average litters had 5 embyros (range 1-9). Females werre capable of producing 12 litters/year. Averaged gestation was 24 days (range 22-26). Combining rate oflitter production with averagelitter size, each female can produce an average of 64 young/ year; at least one female produced 49 young/year. Young opened their eyes at c.7 days old; weaning occured c.23 days after birth. Females became mature at ¢.3 months old. Males 90-120 days of age had large numbers of spermatozoa in epididymis. Maximum measured longevity was c.10 months.   Activity patterns.The Chaco Pericote is nocturnal and scansorial. All individuals recorded in woodlands in central Formosa Province ( Argentina) were caught in traps set on branches c.2 m aboveground.   Movements, Home range and Social organization.No information.   Status and Conservation.Not assessed on The [UCN Red List.   Bibliography.Allen (1901c), Anderson (1997), Braun & Patton (2015), Ferro & Martinez (2009), Hershkovitz (1962), Martinez & Di Cola (2011), Martinez & Gardenal (2016), Martinez et al. (2010), Pearson (1958), Theiler & Blanco (1996a, 1996b), Theiler & Gardenal (1994), Theiler et al. (1999), Thomas (1902c). 3818815062 241 520