The only known Mammals of Australia with rootless, ever-growing scalpriform incisors, in bodily size suitable for wielding those about to be described, are the Diprotodon , the Notherium , and the Phascolonus , all of which have become extinct. But the incisors of the known species of the above genera differ in shape from each other and, in a still more marked degree, from those of Sceparnodon ; nor do any such teeth from other and smaller Mammals match with the present Fossils. My first cognizance of this form of tooth was derived from casts, which were kindly transmitted to me in October, 1881, by Edward P. Ramsay, Esq., Curator of the Museum of Natural History, Sydney, New South Wales.