HOPLOPHONEUS MENTALIS sp. nov. Type No. 12515, Princeton University Geological Museum, collecting locality 1015A1, left ramus of the lower jaw with the canine and third and fourth premolars in place (Fig. 1), secured by the 1920 South Dakota expedition from the uppermost levels of the Titanotherium beds (Chadron formation), two to two and one half feet below the thin local bed of white limestone at the contact between the Chadron and Brule formations (Oreodon beds), and two and a half to three feet above titanothere bones in place, in the valley of Indian Creek, near Taylor's ranch, west of Hart Table in Pennington County (locality shown in Fig. 2 of Plate 1 of the preceding paper, in about the center of the picture). So far as I am aware, this is the first Hoplophoneus to be described from the Titanotherium beds and is strikingly differentiated from all of the species of the overlying Oreodon beds by the extraordinary depth of the chin (as suggested in the specific name proposed), a character reminiscent of the great development of this structure in Hatcher's Eusmilus dakotensis from the Protoceras beds, to which the new form seems to be transitional. 1 Williston's measurements, Kansas Univ. Quarterly, Vol. III., No. 3, p. 72, 1895. 2 Specimens in the Princeton Geological Museum used by G. I. Adams, in defining these species. From the table of measurements it will readily be seen that Hoplophoneus mentalis is considerably smaller than the large H. occidentalis, approximating in size individuals of the insolens and robustus groups. A comparison with the specimens in the Princeton collection used by Adams in defining these two forms shows that, although the jaw depth back of the flange is the same in H. robustus and H. insolens as in the new form, the flange is absolutely larger in the latter and tapers less rapidly in width distally; both premolars are smaller, and in p4 the paraconid is disproportionately smaller, than in H. insolens (Princeton Univ. Geol. Mus. No. 11372) and is out of line with the other two cusps, toward the inner side of the jaw as in Eusmilus and hoplophonids in general, and has sharper cutting edges than in H. insolens; also the alveolus for mi is very much wider transversely, in front, than in the latter species. Between H. robustus and H. mentalis there is the same striking difference in the shape of the jaw flange, which is decidedly V-shaped in robustus, while in the new species it is U-shaped and of the Eusmilus type. The third premolar is as small as in robustus, but rakes backward a bit stronger and has a larger posterior cuspule. To the paraconid of p4 the same remarks are applicable as in the comparison with H. insolens. FOUNDED IN 1786 BY JOHN HYACINTH DE MAGELLAN, OF LONDON 1922 THE AMERICAN PHILOSOPHICAL SOCIETY HELD AT PHILADELPHIA, FOR PROMOTING USEFUL KNOWLEDGE ANNOUNCES THAT IN DECEMBER, 1922 IT WILL AWARD ITS MAGELLANIC GOLD MEDAL TO THE AUTHOR OF THE BEST DISCOVERY, OR MOST USEFUL INVENTION, RELATING TO NAVIGATION, ASTRONOMY, OR NATURAL PHILOSOPHY (MERK NATURAL HISTORY ONLY Excepted) UNDER THE FOLLOWING CONDITIONS : 1. The candidate shall, on or before November 1, 1922, deliver free of postage or other charges, his discovery, invention or improvement, addressed to the President of the American Philosophical Society, No. 104 South Fifth Street, Philadelphia, U. S. A., and shall distinguish his performance by some motto, device, or other signature. With his discovery, invention, or improvement, he shall also send a sealed letter containing the same motto, device, or other signature, and subscribed with the real name and place of residence of the author. 2. Persons of any nation, sect or denomination whatever, shall be admitted as candidates for this premium. 3. No discovery, invention or improvement shall be entitled to this premium which hath been already published, or for which the author hath been publicly rewarded elsewhere. 4. The candidate shall communicate his discovery, invention or improvement, either in the English, French, German, or Latin language. 5. A full account of the crowned subject shall be published by the Society, as soon as may be after the adjudication, either in a separate publication, or in the next succeeding volume of their Transactions, or in both. 6. The premium shall consist of an oval plate of solid standard gold of the value of ten guineas, suitably inscribed, with the seal of the Society annexed to the medal by a ribbon. All correspondence in relation hereto should be addressed TO THE SECRETARIES OF THE AMERICAN PHILOSOPHICAL SOCIETY No. 104 SOUTH FIFTH STREET PHILADELPHIA, U. S. A. |