Part of lower jaw of Didelphis Azaræ; recent, Brazil. Natural size.

Fig. 291. End view seen from behind, showing the inflection of the angle of the jaw, c. d.

Fig. 292. Side view of same.

The only question, therefore, which could fairly admit of controversy was limited to this point, whether the fossil mammalia found in the lower oolite of Oxfordshire ought to be referred to the marsupial quadrupeds, or to the ordinary placental series. Cuvier had long ago pointed out a peculiarity in the form of the angular process (c, [figs. 291.] and [292.]) of the lower jaw, as a character of the genus Didelphys; and Mr. Owen has since established its generality in the entire marsupial series. In all these pouched quadrupeds, this process is turned inwards, as at c d, [fig. 291.] in the Brazilian opossum, whereas in the placental series, as at c, [figs. 290.] and [289.] there is an almost entire absence of such inflection. The Tupaia Tana of Sumatra has been selected by my friend Mr. Waterhouse, for this illustration, because that small insectivorous quadruped bears a great resemblance to those of the Stonesfield Amphitherium. By clearing away the matrix from the specimen of Amphitherium Prevostii above represented ([fig. 286.]), Mr. Owen ascertained that the angular process (c) bent inwards in a slighter degree than in any of the known marsupialia; in short, the inflection does not exceed that of the mole or hedgehog. This fact turns the scale in favour of its affinities to the placental insectivora. Nevertheless, the Amphitherium offers some points of approximation in its osteology to the marsupials, especially to the Myrmecobius, a small insectivorous quadruped of Australia, which has nine molars on each side of the lower jaw, besides a canine and three incisors.[269-B]

Another species of Amphitherium has been found at Stonesfield ([fig. 287.] [p. 268.]), which differs from the former ([fig. 286.]) principally in being larger.

Fig. 293.

Phascolotherium Bucklandi, Owen.