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Show 1893.] DR. C. J. EORSYTH MAJOR ON MIOCENE SQUIRRELS. 193 of the outer cusps. A similar shape is shown by the outer cusps of Sciuropterus pearsoni, and by those of Pseudosciurus, which I have long ago1 described at length, in drawing the attention to their various analogies with Ungulates. These analogies are so deceiving, that the discoverer of Pseudosciurus, having but isolated teeth at his command, considered them to be from an Ungulate. Two lower molars of a Rodent from the Phosphorites of Mouillac have been described by Schlosser under the name of Sciurodon2. H e compares them with Pteromys, and suggests that they are nearly related to, and perhaps identical with, the Oregon Meniscomys 3. In the British M u s e u m are preserved several unpublished isolated molars of a minute-sized Rodent from the Oligocene Bembridge Limestone of the Isle of Wight, some of which, likewise, can only be approximated to Sciurop>terus or a nearly related genus. Similar remarks apply to a molar from the Swiss Eocene of Egerkingen, lately published by Rutimeyer under the name of Ailuravus4, which, however, is undoubtedly a lower molar of a Rodent, and agrees most with those of the larger species of Sciuropterus, although, as stated above, it is somewhat intermediate between Pteromys and Sciuropterus. Ailuravus having relations to one of the species of Plesiadapis (PI. gervaisii, Lem.), from the Lower Eocene of Reims 3, it results that Sciuropterus-like Rodentia were very abundantly represented and widely spread cluriug the Tertiary. I shall hereafter point out more fully the resemblance between two recent species of Sciuropteri, Sc. horsfieldi and Sc, pearsoni, with the two Eocene genera Sciuroides and Pseudosciurus. After this brief reference to fossils showing close analogy with recent Elying-Squirrels, it remains for m e to justify m y arranging these last in a distinct subfamily, the Pteromyince. Taking the genus Pteromys in a restricted sense, it is a very homogeneous one, in its dentition as well as in the characters of the skull. The Sciuropteri, on the contrary-with which I propose to unite Pteromys tephromelas, Giinth., and Pt. phceomelas, Giinth.-show on closer examination such a variety in the shape of their molars, that, if found in a fossil condition, they would without hesitation have been assigned to four or five genera. All of them are more or less brachydont, with the exception of Sciuropterus volans, L. sp., which leans towards hypsodontism; all have in common an elegant sculpturing of the enamel, which gives often a crenate appearance to the cusps or crests. But, apart from this, almost every species possesses a peculiar pattern of its molars. 1 ' Nageriiberreste aus Bohnerzen Siiddeutschlands und der Schweiz,' 1873. 2 M . Schlosser, "Die Nager des europaischen Tertiars," I.e. pp. 91(73)- 93(75), pi. vii. (ii.) figs. 3, 10. 3 i.e. pp. 91, 146, 154. * L. Ruthneyer, " Die Eocane Saugethierwelt von Egerkingen" (Zurich, 1891), pp. 94-98, pi. vii. figs. 18, 19. 5 Lemoine, "Etude d'ensemble sur les dents des Mammiferes fossilea des environs de Reims," Bull. Soc. Geol. France, t. xix. 1891, pi. x. fig. 65. PROC. ZOOL. Soc-1893, No. XIII. 13 |