In August three females were pregnant or lactating, or both. None of seven adult females taken in November was pregnant. Neotoma cinerea arizonae Merriam Bushy-tailed Wood Rat _Specimen_: Head of Prater Canyon, MV 7873/507. Another, in the Denver Museum, from Spruce Tree House, was reported by Finley (1958:270). _Neotoma cinerea_ prefers vertical crevices in high cliffs but occupies other areas. Neotoma mexicana inopinata Goldman Mexican Wood Rat _Specimens examined._--Total, 10: Headquarters, MV 7890/507 and probably 7861/507, 74421 MVZ; Spruce Tree Lodge, 6950 ft., 34802-34803; Spruce Tree House, 74419-74420 MVZ; Square Tower House, MV 7869/507; Cliff Palace, 74422 MVZ; Balcony House, MV 7868/507. The Mexican wood rat is the most common species of wood rat on the Mesa Verde. The two specimens from Spruce Tree Lodge obtained by R.B. Finley on September 2, 1949, are young individuals. Another species of the genus, the white-throated wood rat, _Neotoma albigula_, may occur within the Park, since three specimens (34757-34759) from the Mesa Verde were trapped on September 15, 1949, by R.B. Finley, approximately 4-1/2 miles south of the Park [6 mi. E, 17 mi. S Cortez, 5600 ft.--south of the area shown in Figure 2]. Finley (1958:450) stated that at that locality he trapped _Neotoma mexicana_ [No. 34801], that _N. albigula_ was perhaps more common there than _N. mexicana_, that dens of _N. albigula_ were more common than those of _N. mexicana_ under large rocks in the talus on the south slope of the Mesa, and that dens of _N. mexicana_ seemed to be more numerous in crevices of ledges in the bedrock and cliffs. Ondatra zibethicus osoyoosensis (Lord) Muskrat D. Watson (in letter of January 16, 1957) reported that he has seen muskrat tracks many times along the Mancos River. He also relates a report received from Chief Ranger Wade and D.A. Spencer who saw a muskrat, no doubt a wanderer, on the Knife Edge Road on a cold winter night. These men, both reliable observers, stopped and saw the muskrat at a distance of two feet, where it took shelter under a power shovel parked beside the road. Reports of dens seen along the Mancos River are available for 1944, 1945, 1946, and 1947. Microtus longicaudus mordax (Merriam) Long-tailed Vole _Specimens examined._--Total, 36: North end Mesa Verde National Park, 7000 ft., 76233-76237; entrance to Mesa Verde National Park, 5123-5126 in Denver Museum; Prater Canyon, 7600 ft., 76238-76244; Upper Well, Prater Canyon, 7575 ft., 69441; Morfield Canyon, 7600 ft., 76245-76259, 76261-76263; west bank Mancos River, northeast side Mesa Verde National Park, 76260.