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any of six South American species of rodents that superficially resemble a chinchilla but are more ratlike in body form. Chinchilla rats have short limbs, large eyes, and large, rounded ears. The forefeet have four digits, the hind feet five, and the hairless soles are padded and covered with tiny tubercles that provide traction on bark or rocks. Abrocoma species have small claws, but claws are large and curved in Cuscomys; the second digits of both genera are hollowed out underneath. Stiff hairs, possibly used as grooming combs, project over the middle three toes. Abrocoma species are medium-sized rodents weighing up to 350 grams (12.3 ounces) with a body 17 to 23 cm (6.7 to 9.1 inches) long and a densely haired tail of 6 to 18 cm. Cuscomys is larger, weighing 910 grams, with a body length of 35 cm and a long, furred, two-coloured tail (26 cm). Chinchilla rats' long, soft, dense fur ranges from silvery to brownish gray on the upperparts with white, gray, or brownish underparts.