In the Pliocene of Texas, Nebraska and Idaho lived the American representatives of a genus (_†Stegodon_) which was a connecting link between the elephants and the †mastodons, and which was especially characteristic of the Pliocene of India. The tusks, which were confined to the upper jaw, had lost their enamel and the last molar, above and below, had five or six enamel ridges, but the crowns, which in the Asiatic species were buried in cement, had but a small amount of this material. Several species of _†Mastodon_ occur in the same beds, but only isolated teeth have been found. The †mastodons, in a broad sense of the term, have been divided into several genera and subgenera in accordance with different schemes; the simplest perhaps is to group into a second genus those species which had fully developed lower tusks. This four-tusked genus has received several names, of which _†Tetrabelodon_ is most commonly used in this country, but the term _†Gomphotherium_ is much older and, according to the law of priority, must therefore be employed. The lower Pliocene species of _†Gomphotherium_ had a pair of large lower tusks, of cylindrical shape, and both upper and lower tusks had longitudinal bands of enamel, and in order to support the weight of these great tusks the symphyseal, or chin, region of the lower jaw was greatly elongated; the molars had four cross-crests. [Illustration: FIG. 228.—Head of upper Miocene †mastodon (_†Gomphotherium productum_) showing the chisel-like lower tusks. Restored from a skull in the American Museum of Natural History.] In the upper Miocene is found another and more primitive stage of proboscidean development. In these species the grinding teeth were three-ridged; the upper tusks were quite short and curved downward, diverging somewhat from each other, and they had enamel bands. The lower tusks were still shorter and of depressed, flattened and somewhat chisel-like form and so worn as to show that they were regularly employed in cropping and browsing. The skull was low and broad and the symphysis of the lower jaw was greatly prolonged to carry the tusks. A very important fact concerning these early †mastodons is that they had the normal method of tooth-succession, permanent premolars forming beneath (in the lower jaw, above in the upper) the milk-teeth and pushing them out at maturity.