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Show 1901.] REPTILES FROM PATAGONIA. 177 which is exposed between the opisthotic, parietal, and the bone at the upper end of the quadrate. The fragment is doubtless the highest point of the anterior otic bone, of which the upper part is otherwise completely buried by the surrounding elements. The parietals (pa.) occupy nearly half the entire length of the cranium, curve downwards to form the side walls, are much compressed in their anterior two-thirds, and rise into a conspicuous sagittal crest. They are flattened in the middle line at their anterior end, and are not pierced by a pineal foramen. Each of the frontals (fr.) is nearly three times as long as broad, and slightly widest at its truncated anterior end. There is no supraorbital boue ; but posteriorly and anteriorly the outer border of the frontal is slightly notched for the accommodation of the postfrontal and prefrontal respectively. The postfrontal (pt.f.) seems to have partly bounded the comparatively small orbit (orb.) behind ; but this bar is broken away on both sides. The prefrontal (pr.f.), best preserved on the left (fig. 1 a), is flattened and triangular in shape, almost equilateral ; it is only slightly in contact with the postero-lateral angle of the nasal bone. The nasals (na.) are also flattened and triangular in shape, but antero-posteriorly elongated and with a somewhat coucave outer side which bounds the relatively large narial opening (nar.). They are widest at their articulation with the frontals. They are incomplete in front, and the premaxillae . are unfortunately not shown. The greater part of the palate is obscured by matrix or broken away, but some features at the postero-lateral angles of the cranium and in the facial region are well shown. As observed especially on the left side (fig. 1), a long and narrow plate of bone (s.t.) forms the postero-superior boundary of the parietal and otic region, and seems to constitute the articulation for the quadrate. This is doubtless the element commonly named supratemporal in Snakes, Lizards, and Mosasaurs. The quadrate (qu.) is evidently short and broad, but is only imperfectly shown in section on the left side. Its remains (PI. X X . fig. 1 c) are not readily interpreted ; but the upper end of the bone seems to be displaced outwards and incomplete in the fossil, while the more expanded lower end shows the large notch which usually forms a loose articulation for the pterygoid in Snakes. At first sight, it might be supposed that the quadrate was of the same form as that of the Mosasaurs, with a deep posterior notch for the auditory meatus; but closer study seems to make this interpretation impossible. At the side of the cranium, below the supratemporal and parietal, the upper border of a large prootic (pr.o.) is exposed; while between this bone and the orbit the downwardly curved portion of the parietal forms a sharp longitudinal lateral ridge (v.). There are no traces of temporal arcades. The short pterygoids (pt.) are partly exposed, and a portion of the palatine below the orbit on the left side bears traces of two comparatively minute teeth. There are distinct remains of an ectopterygoid or transverse bone (ec.) on each side between the pterygoid and maxilla ; and a fragment on the left side seems to |