The western ringtail possum or ngwayir refers to a species of possum, Pseudocheirus occidentalis, found in a small area of Southwest Australia. They are a cat-sized marsupial with a stocky build, dark greyish-brown fur, pale underparts and a long prehensile tail with a whitish tip. Ngwayir forage at night through the upper canopy of trees, feeding on young leaves, flowers and fruit, especially in groves of the weeping peppermint Agonis flexuosa. Breeding occurs mainly during the winter, the single juvenile emerging from the pouch after about three months. The population has declined by more than 95% since British settlement, due to clearing of habitat, fire and the introduction of the red fox Vulpes vulpes, and is classified as Critically Endangered. The population in most areas has catastrophically declined or become locally extinct, but strongholds remain in the urbanised areas near Busselton and Albany. Taxonomy A description of the species was published in 1888 by Oldfield Thomas in a systematic review of specimens held at the British Museum of Natural History. The animal was first described as Pseudochirus occidentalis by Thomas, repeating an incorrect spelling of the genus, and currently recognised as Pseudocheirus occidentalis. The classification as subspecies Pseudocheirus peregrinus occidentalis allies the population to the ringtail P. peregrinus which is common in Eastern Australia. The original description of the western population was as a separate species, Pseudocheirus occidentalis, although it is also noted as a subspecies or member of a Pseudocheirus peregrinus species complex. Common names include the western ringtail possum, ngwayir, womp, woder, ngoor and ngoolangit. The names derived from the Noongar language were collated in an ethnographic survey of historical interviews, and included two names noted by John Gilbert and others at the Swan River Colony, King George Sound and elsewhere; the local names for this species are regionally distinct rather than dialectical variants. The common name assigned by Oldfield Thomas in his description of P. occidentalis was western ring-tailed phalanger. Description Western ringtails are largely-arboreal marsupials smaller than the size of a domestic cat, with stocky bodies, grasping feet and a strong, prehensile tail. The profile of the black back and rump slopes toward a prehensile tail that tapers to a fine white point. The species has a head and body length of 320–400 mm, a tail length of 300–400 mm, and a weight of 750 to 1350 g. Pseudocheirus occidentalis has dark grey-brown-black fur with light