1893.] DR. C. J. rOBSYTH MAJOB on illOCENE SQUlRli£LS, 193 



of the outer cusps. A siuiilar shape is showu by the outer cusps 

 of Sduroiiterus pearsoni, and by those of Pseudosciurus, which I 

 have long ago * described at length, in drawing the attention to 

 their various analogies with Ungulates. These analogies are so 

 deceiving, that the discoverer of Pseudoscmnis, having but isolated 

 teeth at his command, considered them to be from an Ungulate. 



Two lower molars of a Eodent from the Phosphorites of 

 Mouillac have been described by Nchlosser under the name of 

 I'Sciuroi.loii'-. He compares them with Pteromys, and suggests that 

 they are nearly related to, aiid perhaps identical with, the Oregon 

 Meniscomys '. 



In the British Museum are preserved several unpublished isolated 

 molars of a minute-sized Rodent from the Oligocene Bembridge 

 Limestone of the Isle of Wight, some of which, hkewise, can only 

 be approximated to Sciuropterus or a nearly related genus. Similar 

 remarks apply to a molar from the Swiss Eocene of Egerkingen, 

 lately published by Riitimeyer under the name of Ailumvus ', which, 

 however, is undoubtedly a lower molar of a Rodent, and agrees 

 most with those of the larger species of Sduroptenif<, although, as 

 stated above, it is somewhat intermediate bet\A"een Pteromys and 

 Sciuropterus. Ailuravus ha\ing relations to one of the species of 

 Plesiadapis (PI. yervaisii, Lem.), from the Lower Eocene of Reims \ 

 it results that Scinro^yternsAike Rodentia were very abundantly 

 represented and widely spread during the Tertiary. 



I shall hereafter point out more fully the resemblance between 

 two recent species of Sciuropteri, Sc. horsfieldi and 8c, 2>earsoui, 

 with the two Eocene genera Sciuroides and Pseudoscmnis. 



After this brief reference to fossils showing close analogy with 

 recent Flying-Squirrels, it remains for me to justify my arranging 

 these last in a distinct subfamily, the PteromyitKX. 



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, Griinth., and Pt. jjlicnomclus, 

 Griinth. — 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 

 Sciaroptems rolans, L. sp., which leans towards hypsodontism ; all 

 have in common an elegant sculpturing of the enamel, which gives 

 often a creuate appearance to the cusps or crests. But, apart from 

 this, almost every species possesses a pecidiar pattern of its molars. 



^ ' Nageriiberreste aus Bohnerzen Siiddeutschlands und der Scbweiz,' 1873. 



'■' M. Schlosser, -'Die Nager des europaischen Tertiars," I. c. pp. 91(73)- 

 93(75), pi. vu. (ii.) flgs. 3, 10. 



^ i.e. pp. 91, 146, 154. 



^ L. Riitimeyer, " Die Eocaae Saugethierwelt von Egerkingen " (Ziirich, 

 1891), pp. 94-98, pi. vii. figs. 18, 19. 



° Lemoiue, "Etude d' ensemble sur les dents des Mammiferes fossiles des 

 environs de Reims," Bull. Soc. Geol. France, t. xix. 1891, pi. x. flg. 65. 



Proc. Zool. Soc.~1893, No. XIII. 13 



