Systematics of Mice of the Subgenus Akodon (Rodentia: Cricetidae) in Southern South America, with the Description of a New Species Abstract Two species of yellow-nosed mice (genus Ako-don) occur in the forests and steppes of southern South America, but only one of these is currently named. Akodon xanthorhinus applies to the small-er, shorter-tailed species found over much of southern Chile and Argentina. A larger, longer-tailed form inhabits islands to the south, and this form is here described as new. Geographic vari-ation throughout the range of A. xanthorhinus is examined to assess the taxonomic position of the new form. Clinal variation does not account for the substantial differences of the new form: spec-imens of A. xanthorhinus from geographically in-termediate localities on Isla Grande de Tierra del Fuego are no more similar to the new form than are specimens from the mainland. The new form is therefore best considered a distinct species, Ako-don hershkovitzi. Introduction The akodont rodents are an endemic Neotrop-ical group that occupies a variety of habitats and presents an impressive array of morphologies fit-ting them to herbivorous, granivorous, omnivo-rous, or insectivorous diets. Trenchant differences among the various forms are lacking, however, and as a consequence, there is little agreement on the specific content of the tribe or even the genus (cf. Bianchi et al., 1971; Gardner & Patton, 1976; Reig, 1978). Conservative limits of the genus Ako-don Meyen, 1833, include the Akodon, Abrothrix, Thaptomys, Deltamys, Chroeomys, Hypsimys, and Chalcomys of various authors, totaling some 33 species (Honacki et al., 1 982). Many of these species are included within the subgenus Akodon, which reaches its greatest specific diversity in the central Andes. In southern South America, the subgenus Akodon currently includes the following taxa (from north to south): five subspecies of Akodon oliva-ceus (Waterhouse, 1837); three subspecies of A. iniscatus Thomas, 1919; monotypic A markhami Pine, 1973; A. xanthorhinus canescens (Water-house, 1837); monotypicA UanoiPine, 1976; and A. xanthorhinus xanthorhinus (Waterhouse, 1837). In early 1983, we collected mammals and birds in Magallanes, Chile. An Akodon we collected on a large island south of the Straits of Magellan, Isla Capitan Aracena, differed widely from related mice from Punta Arenas, currently referred to A. x. xanthorhinus. The new mouse weighed 50% more than comparable specimens from Punta Arenas, had an absolutely and relatively longer tail, and differed in details of its coloration. It therefore appeared to represent a new taxon. However, the taxonomy of mice of the subgenus Akodon from southern South America has not been compre-hensively reviewed since Osgood's "The Mam-mals of Chile" (1943). Recently described taxa (Pine, 1973, 1976) and other additional specimens from marginal localities, especially islands in the Cape Horn group, permit a more detailed revision of this group than was possible in Osgood's time. We therefore undertook an analysis of geographic variation among southern Akodon to determine (1) the application of available names and (2) the relationships of the new mouse to previously de-scribed taxa. Materials and Methods We examined a total of 470 specimens from the collections of the following institutions: American PATTERSON ET AL.: MICE OF SUBGENUS AKODON
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