On the arid plateaus of the north-west, the guanaco and vicuna are still to be found, though less frequently, together with a smaller species of viscacha (Lagidium cuvieri).
The Peruvian chinchilla (C, brevicaudata) is larger, with relatively shorter ears and tail; while still larger species constitute the genus Lagidium, ranging from the Andes to Patagonia, and distinguished by having four in place of five front-toes, more pointed ears, and a somewhat differently formed skull.
In Chinchilla the fore-feet have five and the hind four digits, the tail is long and bushy, and the auditory bullae are enormous, appearing on the top of the skull; Lagidium has four digits in both foreand hind-feet, and Lagostomus three only in the hindfeet, while the auditory bullae are much smaller (see Chinchilla and Viscacha).