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Show 202 DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. [Feb. 28, very small details. The only inference I wash for the presentl to draw from this fact and its consequences is, that Prof. Fleischmann, too, is on his way to become an opponent of trituberculism. It would appear that the Allotheria, the Multituberculata mr k&xjiv, ought to have been a stumbling-block for the theory. But this is not the case; they have been simply pushed aside on account of being an aberrant order. Nevertheless, I shall refer to them later on. The dentition of Rodentia has as yet not much been dealt with in relation to the tritubercular theory. Scott was the first to touch upon the question, when describing the Plesiarctomys sciuroides, S. & 0 . , from the Uinta formation2, considered by him to be " one of the oldest, if not the very oldest known form of rodent." Owing to the importance which for this reason is attributed to the fossil, I must dwell upon the subject at some length. Scott has shown to his own satisfaction and to that of others that the superior molars of Plesiarctomys sciuroides " are plainly of the tritubercular pattern," and that " the inferior molars show the anterior triangle of three cusps with a talon behind, or what Cope has termed the tuberculo-sectorial molar." It might be questioned at once whether this specimen, the teeth of which are much worn according to the author's own assertion3 and according to what appears from the diagram i aud the figures ', is a proper object from which to draw such important inferences. I fail to see in its molars anything else than the usual Sciuromorphine type, which I agree with Scott in considering as a very old one. I have myself pointed this out twenty years ago in some fossils (Sciurus speetabilis) from the Eocene of Egerkingen u, which are rather older than the Uinta formation. The Uinta beds are considered by Zittel7 to be Lower Oliogocene, whilst the Bohnerz of Egerkingen has important relations with the oldest Eocene of Europe (Reims) and America (Puerco)s. On the other hand, this type is still in existence, and widely spread among living Sciuromorpha. I think that Scott is mistaken in what he considers to be the homologies, in the lower molars of Plesiarctomys, of the anterior triangle of Ungulates, Creodonts, and Lemuroids. This anterior triangle is formed, as clearly shown by unworn molars of most of the Sciuromorpha, by the antero-external and antero-internal cusp (the protoconid and metaconid according to Osborn's no- 1 See also W . B. Scott, " The Evolution of the Premolar Teeth in the Mammals" (Proc Ac. Nat. Sci. Philad. 1892, p. 410). 2 William B. Scott and Henry Fairfield Osborn, "The Mammalia of the Uinta Formation" (Trans. Amer. Philos. Soc. n. s. vol. xvi.pt iii. Aug. 20, 1889, pp. 476-478). 3 L. c. p. 477. 1 P. 476. 5 PI. xi. lc,l d. 0 Forsyth Major, " Nageriiberreste aus Bohnerzen Siiddeutschlands und der Schweiz." 7 ' Handbuch der Palaontologie, I. Palaozoologie,' IV. Band, 1892, p. 66. 8 L. Riitimeyer, "Die Eocane Saugethierwelt von Egerkingen," Abhandl. schweiz. palaont. Ges. xviii. 1891. |