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Show 1901.] REPTILES PROM PATAGONIA. 173 septum, resembling that which in Chelys and Chelodina is formed by a downward process of the prefrontal joining the palatine. Of the mandible (Plate XVII.) only the dentary-splenial portion is preserved, with a fragment of the articulo-augular on each side. The two rami are firmly fused at the symphysis (fig. 1 a), which is gently rounded and not produced into a beak. The oral margin is impressed with a broad, rounded groove, which is bordered inside and outside by a rather acute edge. The limit of the horny sheath is indicated by a distinct constriction (s.) on each ramus, which extends across the deutary obliquely downwards and forwards. Scapula. Except the scapulae, all remains of the appendicular skeleton are too imperfect for description. The scapula of the right side (Plate XVIII. fig. 1) is nearly complete distally, while that of the left side is better preserved proxitnally. The bone is rather stout and laterally compressed, with a flattened outer face and an expanded proximal end. The latter portion closely resembles the proximal end of the scapula of M. platyceps in the British Museum. The tuberosity (t.) is remarkably prominent, while the contracted distal end is rounded. Carapace. The remains of the shell are very fragmentary, and parts only of the carapace can be recognized with certainty. The specimens are insufficient to determine the original degree of convexity of the armour, the pieces being not only too small but also probably a little distorted in fossilization. The trunk, however, seems to have been somewhat depressed. The bone of the carapace is thin, and its irregular outer face shows that it was completely covered with epidermal shields. The borders of the investing shields are marked on the carapace either by deep rounded grooves, or by differences in the elevation of the bone beneath adjoining shields. The largest fragment represents the left postero-lateral portion of the carapace, and indicates that there were no fontanelles between the costal and marginal bones. As preserved, its convexity is very slight, while its outer face exhibits irregularities which denote the borders of the last vertebral and costal aud three margiual shields. The edge of the row of marginal bones is excavated at intervals, so that the carapace is bordered by a series of large triangular prominences. The sutures between the component elements cannot be distinguished even on the inner face ; but this aspect of the fossil is interesting as showing the expanded upper end of the relatively small left ilium fused with a costal bone. Miolania is thus proved to have been Pleurodiran in the fixation of its pelvis. Caudal Sheath. The bony ring of a tail-sheath (Plate XVIII. fig. 2), originally discovered by M r . Santiago Both in 1897, is fractured at its |