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Show 78 MR. R. LYDEKKER ON A SIRENIAN JAW [Feb. 2, unsolved problem of the evolution of the Sirenian order, and that was accordingly worthy of being brought under the notice of this Society. Before proceeding to the description of the specimen a few words are necessary as to the Sirenian remains hitherto recorded from the Venetian Tertiaries. Some years ago the late Baron Zigno1 described and figured a certain number of Sirenian remains from the Miocene of Belluno, in the north of Venice, which were referred to four species, under the names of Halitherium bellunense, 3. angustifrons, H. curvidens, and //. veronense. At a later period these four species were reduced by Professor Lepsius2, of Darmstadt, to two ; II. bellunense being transferred to Metaxytherium, while //. angustifrons and H. curvidens were merged in H. veronense. Since to my mind the distinction between Metaxytherium and Halitherium is not of sufficient importance to be regarded as a generic one, we may, so far as this information goes, reckon the Venetian Sirenians as indicating two species of Halitherium, under the names of H. bellunense and H. veronense. Vicenza, where the specimen under consideration was obtained, is situated, I need hardly say, in the south-western half of the Province of Venice, a little north of the parallel connecting Verona and the city of Venice. In spite, however, of its distance from Belluno, it is most probable that the mammaliferous beds of both localities are of the same horizon; in which case those of Belluno should be reckoned as Upper Oligocene. Of the Sirenians from Venetia the types of Halitherium bellunense and H. veronense exhibit the cheek-teeth in a good state of preservation. In the latter species 3 the upper premolars are very small teeth, with nearly cylindrical crowns. On the other hand, the upper molars are relatively large teeth, with oblong crowns, carrying two transverse ridges, with fore-and-aft talons. The anterior talon in these teeth is very large and prominent, while the posterior one is considerably smaller. Their first transverse ridge is more nearly continuous than the second. "When somewhat worn, as is the case with those of the type specimen, these transverse ridges show nearly straight bands of dentine, and not the distinct trefoils observable in the molars of Halitherium schinzi from the Oligocene of Hessen- Darmstadt. A distinct tubercle occurs in the inner half of the median transverse valley of these teeth. In Baron Zigno's figures there is no indication of what I shall allude to as a masked sele-nodont structure in these molars. Coming now to the consideration of the specimen forming the subject of this communication, of which a representation of the teeth is given herewith (see fig. 1, p. 79), it may be observed, in the first place, that it is a fragment of the left maxilla of a very young mammal of comparatively large size. It shows part of the palatal surface, the 1 Mem. E. 1st. Veneto, vol. xviii. pp. 438-449, pis. xiv.-xviii. (1875); see also Zigno, op. cit. vol. xxi. pp. 291-298, pi. iv. (1880). 2 Abhandl. mittelrhein. geol. Vereins, vol. i. pp. 1-179, pis. i.-x. (1881-82) • see also Capellini, M e m . E. Accad. 1st. Bologna, ser. 4, vol. vii. pp. 39-53 (1886)! 3 Zigno, op. cit. vol. xviii. pi. xviii. |