Lagostomis, a genus of mammals of the chinchilla family, inhabiting the vast plains east of the Andes. There is but one species, L. tricho-dactylus, the viscacha or biscaho. The anterior feet are four-toed, with small falcular nails for digging; the posterior three-toed, with strong straight nails; ears and tail moderate. They dwell in burrows, which are near the surface, and so numerous that in many places it is dangerous to ride rapidly over the plains or pampas inhabited by them. Like the prairie dog of North America, this animal has companion burrowing owls, which sit at the mouth of the holes during the daytime; as in the case of the American rodent, it is not likely that the owl lives in the same hole, but it makes use of these burrows which it finds ready dug, driving out the viscacha, and perhaps occasionally making a meal on the unprotected young; from the absence of shrubs and trees on the great prairies and pampas, the owls, unable to burrow themselves, occupy the holes of the rodents as habitations and breeding places.

Lagostomus (L. trichodactylus).