Description of a new species of Akodon (Rodentia : Sigmodontinae) from southern Brazil

Cranial and external morphology of 54 specimens of rodents of the genus Ako don from southern Brazil was analyzed. The sample included 27 individuals w ith a karyotype of 2n = 44 and 13 with 2n = 46 and 14 nonkaryotyped animals . Principal components analysis separated individuals with 2n = 44 from tho se with 2n = 46. Individuals with 2n = 44 were distinguished from those wit h 2n = 46 by narrow and elongated molars, ectolophid present, narrow intero rbital breadth, reduced tegmen tympani, and distal baculum with the central and lateral digit approximately equal in size and proportions, not enlarge d in the extremity. Discriminant functions analyses including 6 A. sanctipa ulensis individuals and holotypes of A. serrensis and A. s. leucogula resul ted in 3 distinct groups. The 2n = 46 individuals were related to A. serren sis, but those with 2n = 44 were not assignable to any described species fo r Akodon. We describe and propose the recognition of a new species for the genus.