One very striking and characteristic feature of the Santa Cruz fauna is the great abundance of marsupials which it contained and which resembled more or less those of modern Australia. There were no true Carnivora and their places were taken by a variety of carnivorous marsupials, some of which (_e.g._ _†Prothylacynus_) were as large as wolves and were closely similar to the so-called Tasmanian Wolf (_Thylacynus_). Another genus (_†Borhyæna_) had a short, bullet head, not unlike a small Puma in appearance and, besides, there were many smaller beasts of prey, in size like badgers and minks. Opossums were common and there were many very small herbivorous marsupials, which resembled, though perhaps but superficially, the Australian phalangers. At the present day South America contains no Insectivora, but in the Santa Cruz there was one family (†Necrolestidæ) of this order which bore considerable resemblance to the “golden moles” of South Africa. An extraordinary variety of rodents inhabited Patagonia in Santa Cruz times, all of them belonging to the Hystricomorpha, or porcupine suborder, and all referable to existing South American families. There were none of the northern forms of rodents, neither rats, mice, squirrels, marmots, hares, nor rabbits, but a very numerous assembly of tree-porcupines, cavies, chinchillas, coypus and the like. The genera, though closely allied to existing ones, are all extinct, and the animals were very generally smaller than their modern descendants. A few small monkeys of unmistakably Neotropical type have been found, but like other arboreal and forest-living animals, they are very rare among the fossils.