The slender Oldfield mouse (Thomasomys gracilis) is a species of rodent in the family Cricetidae. It is found in Ecuador and Peru.
References
Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. pp. 894–1531 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.