Two other wood rats (_N. albigula warreni_ and _N. micropus canescens_) occur at many of the same localities as _N. m. scopulorum_. The dens of _scopulorum_ almost always are situated among rocks, but the dens of _warreni_ and _canescens_ are in a variety of other situations as well as among rocks. Houses of sticks or cactus joints piled up around the base of a juniper (_Juniperus monosperma_), thicket of skunkbush (_Rhus trilobata_), clump of soapweed (_Yucca glauca_) or tree cactus (_Opuntia arborescens_) have been found to shelter only _N. a. warreni_ or _N. micropus canescens_. When these wood rats are associated with _scopulorum_ among the rocks, their dens can be recognized by the compact midden of innumerable cactus spines. The dens of _scopulorum_ have only a few loosely scattered spine areoles or none at all. I am grateful to the officials of the following institutions for permission to examine specimens from the collections under their care: Denver Museum of Natural History; Biological Survey Collection, U. S. Fish and Wildlife Service; American Museum of Natural History; Museum of Vertebrate Zoology, University of California; Museum of Zoology, University of Michigan. The drawings of the skulls were made by Victor Hogg. _Specimens examined._--Total 66, distributed as follows: #Colorado.# _Baca County_: "Furnace Canyon" [= Furnish Canyon], 1 (DMNH); Regnier, 4500 +- ft., 4 (2 DMNH, 2 KU); Two Buttes Reservoir, 4200 +- ft., 5 (3 DMNH, 2 KU). _Las Animas County_: Fisher Peak, "about 8000 ft." [6 mi. SE Trinidad], 1 (BSC); Long Canyon (near Martinsen), 1 (BSC); Mesa de Maya, 1 (MZ); 9 mi. W jct. Purgatory [= Purgatoire] & Chaquaqua [= Chacuaco] rivers ("Red Rock Canyon," collector's field notes), 1 (MVZ); Trinchera, 6 (5 DMNH, 1 AMNH); Trinidad, 5 (BSC); 20 mi. E Walsenburg, "Huerfano Co." [probably Las Animas County], 1 (DMNH). _Otero County_: 3 mi. NW Higbee, 4300 ft., 4 (KU). _Prowers County_: Two Buttes peak, 4600 & 4650 ft., 2 (KU). #New Mexico.# _Union County_: Clayton, 9 (BSC); 9 mi. NE Des Moines on the "Carramba River" [= Cimarron River], 1 (DMNH); Folsom, 6 (BSC); Raton Range (Oak Canyon), 8 (BSC); Sierra Grande, 9 (BSC). #Oklahoma.# _Cimarron County_: Tesequite Canyon, 1 (MZ). _Museum of Natural History, University of Kansas, Lawrence. Transmitted April 20, 1953._ 24-7674