The other divisions of the genus are represented by the Vulpine Phalanger, an animal with long loose fur, which inhabits New South Wales, Western Australia, and North Australia; by Cook’s Phalanger, of New South Wales and Van Diemen’s Land. The genus Perameles, the Bandicoots, has species in Van Diemen’s Land, Australia, New Guinea, and in the Arru Islands, and the genus Petaurus has a corresponding distribution. The Didelphidæ are found in the United States, California, Mexico, Peru, Guiana, Brazil, Paraguay, Banda Oriental, and Chili; and Brazil is the country where they abound the most in species and individuals, the number diminishing to the north and south. The Marsupials have a great ancestry, and some of them lived when the continents and oceans of the earth were in very different relative positions to those they now occupy. Indeed, it is most probable that the fossil remains of the most ancient mammal belong to this order. There is a small double-fanged molar tooth of a mammal which was found by Plieninger, in 1847, contained in a jumble of shells and of the remains of reptiles and fishes in strata beneath the Lias formation of Diegerloch, near Stuttgart. It and another which was discovered close by, by the same professor, belonged to animals which were dead when this topmost stratum of the Trias, immediately beneath the Lias, was being formed. They are Triassic in age, therefore, and they somewhat resemble the back teeth of a fossil which was found subsequently in the Purbeck strata of England, and which evidently belonged to a Marsupial more or less resembling the existing Kangaroo-Rats or Potoroos, of the genus Hypsiprymnus. Later on, Professor W. Boyd Dawkins, F.R.S., discovered a small tooth belonging to the same extinct genus as that which included Plieninger’s fossil, namely, Microlestes; and its resemblance to one of Hypsiprymnus is even greater. Its position was high up in the Trias of Watchet in Somersetshire. Mr. Charles Moore, of Bath, had previously found many specimens of teeth of the same family in a fissure, down which they had been washed by the Triassic sea. A lower jaw of a small Mammal was found in the Trias of North America by Emmons; and it has on one side three incisors, one long canine, then a diastema, three premolars, and seven molars with three points. It is therefore one of the Myrmecobius group.