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Show 1 9 0 4 .] LABYRMTHODONT SKULLS. 1 75 broad plates; while the vomers (vo.) bound the antero-posteriorly elongated posterior nares (ptn.) both behind and within. The only teeth observable are indicated by an impression of the middle part of the pterygoid region (fig. 5), where they occur chiefly in two close parallel rows, one on the outer edge of the pterygoid (pt.), the other on the maxilla (mx.). The teeth of each series are nearly uniform in size, but those of the pterygoid are somewhat larger than those of the maxilla. They are all cones with the usual thickened and folded walls. There are also traces of an irregular patch of minute teeth or tubercles still further back on the pterygoid. Three vertebral centra found in the same formation and locality as the skull are deeply-biconcave discs, not pierced by any foramen for the passage of a remnant of the notochord. One obliquely crushed specimen is shown of the natural size in PI. XII. fig. 8, and another imperfect specimen is similarly represented in fig. 9. The concavity at the end of the centrum is very slight near the outer rim and suddenly deepens towards the centre. It is difficult to determine the precise affinities of so fragmentary a Labyrinthodont skull, but if the vertebral centra are rightly ascribed to the same animal, it evidently represents one of the higher members of the Order. Though suggestive in some respects of Cricotios, as already mentioned, the new skull differs from that of Cope's genus in the thickening or depression of the middle part of the parietals, and in the very strong external sculpture. The associated vertebral centra also differ from those of Cricotus in being completed discs. Among other Labyrintho-donts, the specimen from Spitzbergen seems to approach most closely the skull of Trematosciurus*, with which it agrees in its general shape, external sculpture, dentition (so far as seen), and the relations of the quadrate bone. It is distinguished, however, by the peculiar disposition of the parietal bones. The new fossil thus represents a hitherto unknown genus, which may be named Aphaneramma and defined as follows :-Skull elongate-triangular, with the orbits widely separated and situated in its hinder half ; external bones strongly sculptured, and grooves for slime-canal deep. Parietal bones extending forwards between the orbits; frontals very long and narrow: both these elements excluded by the postfrontals and prefrontals from the orbital border. A single regular row of small teeth on the pterygoid parallel with the equally uniform row of teeth on the maxilla; clustered small teeth or tubercles further back on the pterygoid. Yertebral centra complete biconcave discs, not perforated. The type-specimen of the type-species, A. rostratum, is the imperfect skull now described. * H. Burmeister, ‘ Die Labyrinthodonten aus dem bunten Sandstein von Bern-bur0-,' pt. i. (1849). The minute posterior pterygoid teeth are seen in a specimen of Trematosaurus in the British Museum (no. R. 1733) and in one in Mr. W . E. Balston's collection. |
