OCR Text |
Show 1900.] FOSSIL MARSCPIAL FROM TASMANIA. 785 and on the other hand agreeing with the majority of recent ones, iu which it is variable and only feebly developed \ The coronoid process is that of the right side (fig. 8). It is a remarkably thin plate, in comparison with the general solidity of the other bones, with the anterior and upper margin but little thickened. In comparison with that of other marsupials it is of considerable breadth; there is no concavity on the lower half of the outer surface such as is present in most forms. The form of the posterior curved margin, where it is passing backwards and downwards towards the condyle, may be taken as indicating that the latter was placed fairly high up as regards the angle of the jaw. Limb-bones. These are represented by a fairly complete left and a broken right femur ; a left tibia broken distally, and a right tibia also broken ; a left fibula broken distally and a right more perfect one. N o part of the anterior limb or of the foot is preserved. The Femur (text-fig. 1, and figs. 10, 11, PL L.).-The left femur (figs. 10, 11, PL L.) is entire except for the upper end of the trochanter, which evidently rose slightly beyond the head. Its total length is 107 mm., and when compared with the corresponding bone of a Trichosurus, which is of about equal length, it is at once seen to be remarkable on account of its massiveness. The shaft is straight without any anterior curve, and the posterior surface is flattened. A line passing along the long axis practically cuts through the tip of the great trochanter, the head being turned considerably inwards. Tbe lesser trochanter is characterized by the strong development of the tuberosity at its upper end ; while the ridge, which is continued downwards from tbe great trochanter, has a marked tuberosity at its low-er end similar to that which is present in Phascolomys. At its ventral distal extremity the shaft swells out, the lateral surface of the outer side being turned, so that it becomes visible in ventral view as in the femurs of Phascolomys and Phascolarctos. There is also a distinct depression beneath the inner condyle, which is present but not so strongly developed in Phascolarctos. The condyles are of interest because, whilst iu marsupials it is characteristic to find the outer larger (in Macropodidae and Phalangeridae notably so) than the inner, the reverse condition obtains here, and the inner one is slightly larger than the outer- a point of structure in which the fossil apparently differs from all other Marsupialia. On the anterior face at the condylar end there is a broad surface with only a slight development of groove, the latter being less marked even than in Phalangers and Dasyures, in which there is a broad, distinctly concave surface with distinct margins. What 1 H. F. Osborne, " Mesozoic Marsupialia," Journ, Acad. Nat. Sci. Philadelphia, vol. ix. 2, 1888, p. 262, |