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Show 1895.] SOUTH-AMERICAN MARSUPIAL. 873 The vacuity, judging from the spicules of bone which project into it from the nasals, and from its known development in the Ruminants, probably tends to ossify over as life advances, b u t- the specimen being old-evidently never entirely fills up. Interorbital space broad, smooth and rounded, with scarcely a trace of ridges, ledges, or postorbital processes; lambdoid ridges, however, fairly well developed. Lacrymal canal single, just on the rounded edge of the orbit. Zygomata slender, boldly expanded; malar as usual running back to form part of the glenoid fossa. Palate very imperfect, the anterior foramina reaching from between the third pair of incisors to halfway between the anterior and middle premolars; posterior vacuities extending from the large posterior premolar to behind the last molar, the bridge between their front limit and the back of the anterior foramina only 2*7 m m . across. Pterygoid processes slender and delicate, pointing backwards and inwards, their needle-like ends 1*6 m m . long. Bullae small, imperfect, transparent, formed as usual by the alisphenoids. Tympanic annular, but imperfect, only forming about three-fourths of a circle. Dentition. I. J- C.\; P. |; M . | x 2 = 46. Viewed as a whole, the teeth present a considerable resemblance to those of the Australian Dromicia (e. g. D. lepida, figured Cat. Mars. B. M . pi. xvi. figs. 2-5), especially in their relative proportions. Upper Jaw.-Incisors four in number; the first vertical, pointed, touching its fellow of the opposite side, but separated from i2, in fact very similar to its condition in Didelphys. 1_\ and i_3 flattened laterally, not pointed, but with a straight cutting-edge ; i4 separated from i3, smaller and rather more pointed *. Canines well-developed, as in average carnivorous Marsupials. Anterior and middle premolars small, narrow, two-rooted, sharply pointed, equal in size, the distance between them about equal to that behind the canine. Posterior premolar somewhat similar, but twice as large and rather thicker transversely, with one long main cusp, which stands up just higher than any cusp on the molars, and a small anterior secondary cusp, placed slightly internally. Molars low-crowned, with low rounded or scarcely pointed cusps, not unlike those of Petaurus or Dromicia; the two anterior square, quadricuspidate, although apparently2 there are only three roots to each tooth, the postero-internal cusp being placed on a sort of flange overhanging the palate and not supported by a root; third molar similar, but without the extra postero-internal cusp ; last molar minute, triangular, as small in cross-section as the last incisor. Lower Jaw.-Anterior incisor elongated, exactly as in typical 1 O n the left side (as shown in Plate L.) this tooth has been displaced and pressed against the front of the canine, but ou the right side, which appears to be normal, there is a small diastema. 2 It is at present impossible to be quite certain as to the number of roots each tooth possesses, as the teeth are so lirmly wedged in that without damaging the skull, as yet unique, they cannot be pulled out or their roots developed. |