Field and museum studies of the wood rats of Colorado have revealed the existence of an unnamed subspecies of Neotoma mexicana in eastern Colorado south of the Arkansas River. The characters of the new subspecies are most distinctive in the northeastern part of its range near Two Buttes and Higbee. It differs in cranial characters from N. m. fallax and N. m. inopinata and averages slightly larger, but cannot be distinguished by coloration of the pelage. This heretofore undescribed subspecies may