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Show 178 DR. A. S. WOODWARD ON EXTINCT [Mar. 5, show that this element overlapped the maxilla to a considerable extent. The maxilla itself (mx.) is relatively large, and best preserved on the right side. It is stout and curves inwards in front. It articulates not only with the pterygoid behind by the intervention of the transverse bone, but also with the palatine by a broad articular palatal process which extends inwards from its middle. It likewise articulates directly with the prefrontal in an extensive suture. It shows 14 or 15 large shallow sockets for the implantation of teeth (fig. 1 l>); and one dental crown preserved at the hinder end of the left maxilla is very slender and recurved. The fragmentary remains of the mandible show it to have been of the usual slender ophidian type, with a very loose articulation between the dentary (d.) and articulo-angular region (ag.); and the dentary exhibits a series of large shallow tooth-sockets like those of the maxilla. Behind the skull there are remains of a long series of typical ophidian vertebrae, which do not present any features worthy of special note. The neural arches are shown to have borne delicate low spines, though nearly all of these have been broken away and are only represented by their bases in the fossil (Plate X X . fig. 2, n.). The ribs (r.) are very stout. Erom this description it is evident that the Patagonian fossil in question represents a typical member of the order Ophidia. As shown, however, by the conformation of the occiput and the relatively small size of the quadrate, it belongs to one of the more generalized types. Its closest allies may therefore be sought among the Boidae and Ilysiidae, which still constitute so large and characteristic a part of the Ophidian fauna of South America. The skull bears much general resemblance to that of a Boa constrictor, but is readily distinguished from the latter by its non-projecting supratemporal and relatively small quadrate. It is similarly distinguished from the skull of all the other Boidae \ In precisely this character, on the other hand, the fossil skull agrees with that of the existing Ilysiidae ; and its occipital region is almost identical with that of the South American genus Ilysia2. The resemblance to the latter, indeed, is so close that, although the coronoid region of the mandible is not observable in the fossil, there need be little hesitation in referring the extinct type n ow described to the family ilysiidae. It differs from the existing genera of the family in its more numerous marginal teeth and relatively smaller palatine teeth; in its elevated sagittal crest; and in the presence of well-developed neural spines on the vertebrae. It also differs from the South American Ilysia, though agreeing with the Javan Cylindrophis, in the possession of a small postfrontal bone. It may, in fact, be regarded as a comparatively gigantic forerunner of the Ilysiidae, analogous to Glyptodon among the Armadillos and Phororhachos among the Cariamas. 1 G. A. Boulenger, Catalogue of the Snakes in the British Museum (Natural History), vol. i. (1893). ? G. A. Boulenger, torn. cit. (1893), p. 132, fig. 8. |