_Measurements._--Three males and 3 females from the Blue Mountains average, respectively: total length 233, 234; length of tail 138, 139; hind foot 31.8, 31.8; ear 16, 16; weight 29, 33 grams. _Distribution._--The Blue Mountains of southeastern Washington. =Erethizon dorsatum= (Linnaeus) Porcupine _Description._--The porcupine is one of the largest rodents found in Washington, being exceeded in size only by the beaver. Its body is heavy and stocky, its legs short, its tail long and thick and its eyes small. It is best known for the modified hairs, or quills, of its tail and dorsal area. These vary in greatest diameter from one-sixteenth to three-sixteenths of an inch and from three-quarters of an inch to five inches in length. They are ivory-white with black tips. In addition to quills, the porcupine possesses wooly, black underfur and long, banded guard hair. The bands of the guard hairs are black and yellow, varying in width. Commonly they are of a single color, black, yellow or brown. Porcupines range over virtually all wooded parts of North America north of Mexico, in and above the Transition Life-zone. The Canadian porcupines have been studied by Anderson and Rand (1943A) and intergradation between the eastern _dorsatum_ and the western _epixanthum_ has been shown. The porcupines are commonly considered to be forest animals. However, they are rather rare in the denser coniferous forests. In the more open areas on the Cascade Mountains, especially on the eastern slopes, they are not uncommon. They are rather common in the coniferous forests of northeastern Washington and the Blue Mountains. They seem to be rather common also in desert areas at the southern edge of the Columbian Plateau. The huge incisors of the porcupine are adapted to feeding on bark. They do feed on bark to a certain extent in Washington, but it is my observation that more herbs and bushes are eaten than bark. In areas where porcupines are common, trees are commonly girdled, usually close to the top. Trees girdled in this manner in the Kettle River Mountains included western larch, ponderosa pine, and grand fir. The tops of some trees were killed. The ordinary walking gait of the porcupine is a slow deliberate walk in which he appears to waddle somewhat. They can increase their speed to a slow trot. They are slow, deliberate climbers, ascending and descending trees with head upward. They are able also to climb rocks and cliffs, sometimes being seen on the tops of large boulders. Despite their large size, porcupines are not commonly seen. They are mainly nocturnal and, in the daytime, find concealment high in the branches of some conifer or a cave between the rocks in a talus slide.