Amphitherium Prevostii. Stonesfield Slate.

These observations are made to prepare the reader to appreciate more justly the interest felt by every geologist in the discovery in the Stonesfield slate of no less than seven specimens of lower jaws of mammiferous quadrupeds, belonging to three different species and to two distinct genera, for which the names of Amphitherium and Phascolotherium have been adopted. When Cuvier was first shown one of these fossils in 1818, he pronounced it to belong to a small ferine mammal, with a jaw much resembling that of an opossum, but differing from all known ferine genera, in the great number of the molar teeth, of which it had at least ten in a row. Since that period, a much more perfect specimen of the same fossil, obtained by Dr. Buckland (see [fig. 286.]), has been examined by Mr. Owen, who finds that the jaw contained on the whole twelve molar teeth, with the socket of a small canine, and three small incisors, which are in situ, altogether amounting to sixteen teeth on each side of the lower jaw.

Fig. 287.

Amphitherium Broderipii. Natural size. Stonesfield Slate.

The only question which could be raised respecting the nature of these fossils was, whether they belonged to a mammifer, a reptile, or a fish. Now on this head the osteologist observes that each of the seven half jaws is composed of but one single piece, and not of two or more separate bones, as in fishes and most reptiles, or of two bones, united by a suture, as in some few species belonging to those classes. The condyle, moreover (b, [fig. 286.]), or articular surface, by which the lower jaw unites with the upper, is convex in the Stonesfield specimens, and not concave as in fishes and reptiles. The coronoid process (a, [fig. 286.]) is well developed, whereas it is wanting or very small, in the inferior classes of vertebrata. Lastly, the molar teeth in the Amphitherium and Phascolotherium have complicated crowns, and two roots (see d, [fig. 286.]), instead of being simple and with single fangs.[269-A]