The western ringtail possum or Ngwayir is a possum found in a small area of Western Australia, regarded as a subspecies (Pseudocheirus peregrinus occidentalis) of the common ringtail possum, or as a separate species. It is a small animal with dark greyish-brown fur without any rufous tinge, pale underparts and a long prehensile tail with a pale tip. It is nocturnal and mainly arboreal, feeding on buds, leaves, flowers and fruit. It breeds mainly in the winter, the single juvenile emerging from the pouch after about three months. Its population seems to be declining, probably due to habitat loss and the introduction of alien species, and the International Union for Conservation of Nature has rated it as "endangered".