Mice of the Akodon boliviensis Size Class (Sigmodontinae, Cricetidae), with the Description of Two New Species from Brazil Abstract Two species of Brazilian sigmodontine mice de-scribed as new are Akodon lindberghi, known from less than a hectare plot of cerrado near Brasilia, DF, and Akodon sanctipaulensis, from the marsh-es at the eastern base of the Serra do Mar in south-eastern Sao Paulo. Survival status of the first is discussed. Both species are included in the Akodon boliviensis size class, an assemblage of the 13 smallest species nearest the typical form of the genus. The larger species of Akodon, all in the A. mollis size class, are listed with taxonomic notes. The phyletic relationship between species within and between the size classes has not been deter-mined. The provisional arrangement is for con-venience of characterization of the two new species within a difficult, undefined genus. Other taxa of the akodont group used for reference are also dis-cussed. Plectomys paludicola, a nomen nudum mentioned in the literature, is the same as Akodon lindberghi. mals of the region during the last decade failed to reveal the presence of this savannah species out-side the narrowly restricted plot of an otherwise extensive suitable habitat (fig. 1 ). A third species of Akodon, from open, marshy fields on the eastern base of the Serra do Mar in southeastern Sao Paulo State, collected in 196 1 by A. M. Olalla, also appears to be distinctive, and is described as new. This is the first of a planned series of taxonomic and biogeographic papers on the small mammals of the Atlantic forest region of southeastern Brazil and the cerrado of central Brazil. Cooperative fieldwork with the Museu Nacional and the Uni-versidadede Brasilia was carried out in 1986, 1987, and 1988. It is expected that continued collabo-ration between the Brazilian scientific institutions and the Field Museum of Natural History will result in a thorough inventory of the small mam-mals of the highlands and fragmented remains of the coastal forest of Brazil. Introduction Material A collection of small mammals made during July and August 1986, in the cerrado region of Brasilia, Distrito Federal (fig. 1), includes two species of the sigmodontine genus Akodon. One, the wide-ranging Akodon cursor Lund, is repre-sented by four specimens. The second, heretofore undescribed, is represented by seven specimens captured in a small segment of wet valley-side open grassland, or cerrado campo limpo. Intensive trapping and ecological studies of the small mam-Specimens examined of the tribe Akodontini in the collections of the Field Museum of Natural History (fmnh) represent nearly all species of all tribal genera except Blarinomys and Juscetinomys. They, together with others of the tribe, were stud-ied in the Museu Nacional, Rio de Janeiro, and the British Museum (Natural History), London. The last eight figures in the text (figs. 15-22) illustrate all cranial, dental and morphometric ter-minologies used here. Reference will be made to HERSHKOVITZ: NEW SPECIES OF AKODON
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