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Show 704 DR. C. I. FORSYTH MAJOR ON THE [June 1, Brachyuromys, and even less than in some of the Rhlzornns (especially with regard to the lower molars). In the shape of the outer wall of the infraorbital canal, Siphneus shows closer agreement with Tachyoryctes (especially with T. splendens) than with Cricetus, tbe lower portion of the outer wall advancing more forward. There is likewise more similarity than with Cricetus in the form of tbe canal itself, which in Tachyoryctes and Siphneus is broader in its upper part than in the first-named genus, whereas (apparently as a consequence of the broadening of the skull) in both the inferior, narrower part appears considerably shortened vertically. In this respect Tachyoryctes is somewhat intermediate between Cricetus and Siphneus. The malar bone of Siphneus is stronger than in Cricetus; in S. armandi it is as strongly developed and reaches nearer to the lachrymal than in Tachyoryctes. As regards the flattening and inclination of tbe occiput, there are different gradations in this respect in the genera under consideration (Spalax, Siphneus, Rhizomys, Tachyoryctes); one end of the series is occupied by Spalax, the other by Tachyoryctes. In the latter the inclination is scarcely more than in Cricetus frumentarlus; in old individuals scarcely less than in young Spalax. For the rest the skull of Siphneus is transformed to be used as a shovel and drill in a similar way as in Spralax. The Molars of Brachyuromys as compared with those of other Muriclce and of Mammalia generallg. A few introductory remarks are indispensable. In Didelphyidae and many Insectivora there are on the outer side of the upper and on the inner side of the lower molars three very conspicuous cusps. These are considered by Winge' to be the oldest, most primitive parts of the Mammalian molar. They are the same which Osborn in upper molars has called parastyle, mesostyle, metastyle 2; in Winge's plates 3 they are designated from before backwards by 1, 2, 3. The middle one is supposed to be the oldest of the three, so that according to Winge's view the protocone is something toto ccelo different from Cope's and Osborn's protocone ; this last, 6 in Winge's figures, is according to the latter author one of the latest additions to the tooth. If we review the more primitive Ungulates and the Ancylopoda, we find equally three outer cusps in the superior molars; but it may be seen at once-and in this I think I am in agreement with Winge-that they are not homologous in the different groups. 1 H. Winge, " O m Pattedyrenes Tandskifte, isrer med Hensyn til Tajndernes Former." Vidensk. Meddel. Naturh. Foren. i. Kjobenhavn, 1882, p. 15, pl. iii. 2 See e.g. H. F. Osborn, "The Rise of the Mammalia in North America," Address, Boston, 1893. p. 35 (text-figure of Anchithcrium). H. F. Osborn and 0. Earle, "Fossil Mammals of the Puerco Beds," Ann. Mus. Nat. Hist. vol. vii. Art. i., New York, 1895, p. 44, fig. 14. 3 L. c. pl. iii. H. Winge, " Jordfundne og nulevende Pungdyr (Marsupialia) fra Lagoa Santa, Minas Geraes, Brasilien. Med Udsigt over Pungdyrenes Slaegtskab" ("E Musco Lundii"), Kjobenhavn, 1893, pl. ii. figs. 2a, 2b, 8 b, 10. |