Small mammals of the mid-Araguaia River in central Brazil, with the description of a new species of climbing rat Author Rocha, Rita G. Author Ferreira, Eduardo Author Costa, Barbara M. A. Author Martins, Iracy C. M. Author Leite, Yuri L. R. Author Costa, Leonora P. Author Fonseca, Carlos text Zootaxa 2011 2789 1 34 journal article 10.5281/zenodo.206170 6fa16a5a-560e-432f-ad9e-f93e8bd3e90d 1175-5326 206170 Hylaeamys megacephalus (Fischer) Identification. The genus “ Oryzomys ” was recently revised and divided into ten new genera, including the megacephalus species group, which was assigned to the new genus Hylaeamys (Weksler et al. 2006) . Hylaeamys megacephalus is a medium-sized species with large ears and long feet. Dorsal pelage ranges from gray-brown to brown, the fur is gray-based and in some adults small light gray fur patches are visible on the dorsum. Juveniles have completely dark gray dorsal pelages. Ventral pelage is white with well-defined lateral lines. The tail length is approximately the same as the head-body length. Front and hind feet are white dorsally and the claws are covered by long ungual hairs. Females have four pairs of mammae. Craniodental characters ( Fig. 6 ) closely agree with descriptions by Musser et al. (1998) and Weksler (2006). The rostrum is moderately long and zygomatic notches are moderately deep. The interorbital region is almost hourglass shaped with squared dorso-lateral margins. The lacrimal bone is in contact mainly with the maxilla. The incisive foramen is teardrop shaped and short not reaching the anterior margin of molar rows. It has pattern 2 of carotid circulation ( sensu Voss 1988 ) in which the stapedial foramen and posterior opening of alisphenoid canal are large, and the squamosal-alisphenoid groove and sphenofrontal foramen are absent. The labial accessory root of M1 is absent. The flexi of M1 and M2 do not interpenetrate and the mesoflexus of M2 is a single internal fossette. The hypoflexus of M3 is present. FIGURE 6. Dorsal, ventral and lateral views of skull and mandible of Hylaeamys megacephalus (female, UFES 1327). Measurements (n = 29): HB = 92–125, T = 88–127, HF = 22–29, E = 20–25, W = 23–59. Distribution. This species occurs in Trinidad and Tobago , Venezuela , Guianas, Paraguay and northern and central Brazil throughout eastern Amazonia and Cerrado biomes ( Musser & Carleton 2005 ). Natural history. Hylaeamys megacephalus was well distributed throughout the study area. Thirty-eight individuals ( 29 adults and nine juveniles) were captured both in pitfalls (n = 17) and Sherman traps (n = 21). All seventeen adult males caught had scrotal testes. Two females were lactating in June and September 2007 , and two were pregnant in June and November 2008 . The number of embryos varied from three to four. Vouchers (n = 32: 21ɗ 11Ψ): UFES 1308–1333 , 1424 –1429.