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Show 1893.] DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. 203 menclature)l more or less transversely united, together with Osborn's paraconid ~, and include between them what I have called the anterior transverse valley. Owing to the much-worn condition and partly too, perhaps, to the feeble development of this anterior part-as found in some recent Sciuri and in Arctomys-the anterior valley has vanished in the fossil molars, though I think that some traces of it are still visible in the first and third molar of Scott's figures :), so that, in order to find out the typical triangle, Scott has encroached on what trituberculism declares to be a late addition to the inferior molars, for he considers, as it were, the postero-internal cusp, Osborn's eatoconid, of the " heel" to be the postero-internal part of the typical triangle. What he calls the talon behind, is but the median cusp (hypoconulid) of Osborn's talon. This hypoconulid is in fact the real " talon," viz. that part which is so generally well developed on the posterior side of third lower molars, but which in many Sciuromorpha can be distinctly made out in the anterior molars too, as well as in milk-teeth of Lepus and Myolagus, and both in milk-teeth and permanent molars of Lagodus and Titanomys''. The conclusions to be drawn from the foregoing analysis are, I a m glad to state, the very same at which Scott has arrived, as they tend to show, even more unmistakably, " that the Rodents are to be derived from the same generalized group of primitive placental Mammals, the Bunotheria, to which we refer the origin of the Ungulates, Creodonts, and Lemuroids "'. In respect to what Scott considers plainly to be "the tritubercular pattern" of superior molars, it cannot be denied that there appear three principal cusps, two external and one internal one, in the upper molars of Plesiarctomys sciuroides ; but there are other parts to be seen, even in these much-worn molars, and I have already pointed out that it is dangerous to draw7 inferences from worn teeth. Very similar remarks apply to two papers by Schlosser 6, in which this author endeavours to refer the molars of Rodentia to trituberculism. I therefore refrain from discussing them at length, and I wish only to remark upon the second of the papers quoted. Schlosser asserts in the most positive manner, what at first sight appears to be a startling fact, that Plesiadapis and Protoadapis, from the Lower Eocene of Reims, are Rodentia. Plesiadapis had previously been 1 Cf, e. y., H. F. Osborn and J. L. Wortman, "Fossil Mammals of the Wahsatch and Wind River Beds." Collection of 1891. L. c. p. 86, figs. 1 & 2. 2 Ib. 3 L. c. p. 476, and pi. xi. fig. 1 d. 4 See also the inferior molars of "Plesiadapis" in Lemoine, "Etude d'en-semble sur les dents des Mammiferes fossiles des environs de Reims " (Bull. Soc Geol. de France, trois. serie, t. xix. Mai 1891, pi. x. fig. 65 e), and of Dcctica-dapis, ibid. pi. xi. fig. 146 e, 146 ss. * Scott, /. c. p. 478. 6 M a x Schlosser, "Die Differenzirung des Saugethiergebisses" (Biol. Centra-blatt, Band x. Nos. 8 & 9, Erlangen, 1 & 15 June 1890, pp. 250, 251).- Id, " Ueber die systematische Stellung der Gattungen Plesiadapis, Protoadapis, Pleuraspido-therium und Orthaspidothcrium" (Neues Jahrb. f. Mineralogie. Geologie und Palaontologie, Jahrgang 1892, Band ii. pp. 239. 240). |